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31 year old woman | Doral, FL, USA | Seeking men 25-40 within 50 miles of Miami, FL
Loving life!
I love to be around friends and family. I like to meet new people and have fun. I don't really like to be bored. I usually am doing something, even when I'm watching TV. Traveling, art, exploring, and Bikram yoga are some of my favorite things. I spent most of my time teaching, studying for my Masters, hanging out with friends, at the beach, and doing yoga. I love to laugh and have fun. I am pretty easygoing and usually up for anything.I like to go out and have a good time. I enjoy going out and dancing but also love to just go out and chill. I am looking for someone with a positive attitude to make me laugh, who also is easy to talk to.
Book club , Camping , Coffee and conversation , Dining out , Hobbies and crafts , Movies/Videos , Museums and art , Music and concerts , Exploring new areas , Performing arts , Playing sports , Religion/Spiritual , Shopping/Antiques , Travel/Sightseeing , Wine tasting
Aerobics, Cycling, Dancing, Inline skating, Running, Soccer, Swimming, Tennis / Racquet sports, VolleyBall, Walking / Hiking, Yoga
I exercise 5 or more times per week.
Don't display my sign
I have Cats
I like Dogs
I LOVE LOVE LOVE pretty much anywhere in Europe. I also like to visit friends and family across the country. I enjoy Downtown Miami and exploring the artistic parts of Miami.
I mostly enjoy anything that s funny. I love to laugh! Sometimes it's also fun to watch movies and listen to things that make you think. My favorite food is definitely sushi, I think I could eat it everyday and never get sick of it!
I love art and travel. I also like to go out and check out new resturants and bars.I like to be outdoors enjoying the beautiful Florida weather. While I like to be busy sometimes it's nice to just hang out.I am pretty much up for anything.
'Live What You Love'
Z{{Cta}} {{#if HasMoreInfo}} ?{{CtaSecondary}} {{/if}}
|What she is looking for
|5'6" (167cms)
|5'9" (175cms) to 6'7" (200cms)
|Body type:
|About average
|Slender, About average, Athletic and toned, A few extra pounds
|No preference
|No preference
|Social Drinker
|Social Drinker
|Education / Teacher / Professor
|No preference
|$35,001 to $50,000
|$35,001 to $50,000
|Never Married
|Never Married
|Have kids:
|Wants kids:
|White / Caucasian
|No preference
|Christian / Other
|Christian / Other
|Bachelors degree
|Bachelors degree
I am currently working on my Masters in Reading...teaching reading that is, I can read just fine :-).


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To make reservations by phone, call 1-800-331-3131 in the USA and Canada (or any of our worldwide reservation telephone numbers).
NEWLY-RENOVATED! Residence Inn Hartford Rocky Hill hotel has completed a full renovation! Located off I-91, we're the only Marriott in Rocky Hill and offer redesigned suites with full kitchens and 50% more space than traditional hotel rooms. We're just 10 min. from Hartford Convention Center and nearby Foxwood Casino and CT Science Center, making us the ideal choice for business trips and family vacations. As a TripAdvisor Certificate of Excellence Winner with pet-friendly accommodations, we're a top choice among Rocky Hill hotels. Guests rave about our free perks including daily hot breakfast, property-wide WiFi and even grocery delivery to help stock the fridge. Our new Residence Inn Mix features free light fare and local brews, is a great way to relax and mingle with colleagues (Mon-Wed). The Residence Inn Hartford hotel is great for families or extended stays as our indoor pool, outdoor SportCourt and BBQ area make it feel like home. Stay with us and you'll see why we stand out among Rocky Hill hotels.
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Indian food is typically served with naan, a flatbread that some people refer to as "pizza if it didn't have all those gross toppings." Try a slice with this Groupon.
$12 for $25 Worth of Indian and Mediterranean Cuisine
The menu features dozens of authentic dishes from all regions of India, such as prawns in mango curry ($14.50), sauce-simmered chicken with garbanzo beans ($12.50), and classic royal biryani with lamb ($13.50).
Qazi's Indian Curry House & Mediterranean Cuisine
At Quazi's Indian Curry House & Mediterranean Cuisine, each bowl of curry or platter of tandoori-baked meat comes with a side of history. The gregarious owners are happy to share the evolution of Indian cuisine with guests, even pinpointing the origin of certain recipes all the way back to 300 BC. The menu itself divulges some of these stories, citing the region of origin for some dishes and telling the tale of how biryani rice felt that time mangos left it for a hot dish of curry.
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473 North 36th Street
Seattle, WA 98103
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518 Bainbridge Road Saint Charles MO 63301
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Free Health Clinic, Memphis, TN
CNS Healthcare
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1203 Peabody Ave, Memphis, TN 38104
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2192 Central Ave, Memphis, TN 38104
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1660 Bonnie Ln Ste 105, Cordova, TN 38016
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6963 US Highway 70, Memphis, TN 38133
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NHL Players Association
NHL lockout 2012: Gary Bettman, Donald Fehr trade barbs as deadline approachesComment
NHL Commissioner Gary Bettman stuck to his vow that players will be locked out come Saturday at midnight EDT if a new CBA isn't hammered out before then, and he has the unanimous support of his owners to impose yet another lockout.
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I am 16 and struggling with anorexia and depression for over 4 years now. Every day is a struggle but I'm on my road to recovery! (:
Amaro It's brittany biiitch (;
- 19
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babyfattbutt @roadtorecovery. You sound like me 8 years ago. 3y
fluoresecnt It's been more than 2 years.... 9mon
lauren.marshall_ @instagram inactive 1mon
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Discover a selection of top forums brawl sale on the internet. Come to share your passion on forums brawl sale and meet other fans of brawl sale. Then, why don't you create your own forum of brawl sale ?
Free forum : A PG rated forum to share stories about the animals we love, as well as horses for sale, stallions at stud, training advice.
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Dα♦ is a Mario Kart Wii Competitive Team and Nintendo Gaming Community with the theme of our members showing a tribute to females, the female lifestyle, and femininity. . . no matter their gender.
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My Account X
Windham Weaponry HBC Centerfire Rifle
Key Features
16" Chrome-Lined Heavy Profile Barrel
A2 Flash Suppressor
6-Position Adjustable Buttstock
Windage & Elevation Adjustable Sights
30-Round Magazine Included
Availability: Sold Out
- To buy online and deliver to a Gander Mountain store or an Independent Firearms Dealer, simply add this item to your cart. Click here for additional details.
- You must be at least 18 years old to purchase this item. State and local laws may vary.
- Additional discounts do not apply.
- details & specs
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- accessories
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- reviews
details & specsback to top
Product DescriptionFrom the onset, Windham Weaponry has had one goal: to build the finest AR type rifles in the country. All of their rifles are built with 4150 Chrome Moly Vanadium steel barrels which are chrome-lined for long wear and ease of maintenance and 7075 T6 aircraft aluminum receivers with a durable black hard coat anodize finish. Their MPC is available in a modified version designed to be compliant with state regulations in New York, New Jersey, Connecticut, and Massachusetts. The MPC utilizes a gas-impingement system that's housed in an M4-A4 flattop upper receiver with a detachable carry handle. The rifle's bolt is made of Carpenter 158 Steel and its 16" heavy profile barrel has an A2 flash suppressor and a 1 in 9" right-hand twist. Other notable features include: a 6-position buttstock, windage and elevation adjustable sights, M4 double heat shield handguards, and an A2 black plastic grip. Each rifle ships with a hard plastic carrying case, a web sling, and one 30-round magazine and carries a lifetime warranty.
product reviewsback to top
REVIEW SNAPSHOT®by PowerReviews
Best Uses
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Reviewed by 3 customers
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Comments about Windham Weaponry HBC Centerfire Rifle:
Outstanding Weapon. Buy it now.
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Best Uses
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Comments about Windham Weaponry HBC Centerfire Rifle:
This rifle is a tack driver. It will shoot any ammo dead on. With hand loads it is beyond outstanding. Shot 8 out of 10 in a half inch group with the other 2 within 3/4 inch of the 8
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Best Uses
Comments about Windham Weaponry HBC Centerfire Rifle:
The best built A/R on the market today. The HBC is the choice of true pros. Buy 1 and you will not buy any other brand.
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Are you Denis McMaster?Claim your profile
Publications (7)28.3 Total impact
- Biophysical Journal 01/2012; 102(3):325a. DOI:10.1016/j.bpj.2011.11.1781 · 3.83 Impact Factor
Article: Interactions of Key Charged Residues Contributing to Selective Block of Neuronal Sodium Channels by mu-Conotoxin KIIIA[Show abstract] [Hide abstract]
ABSTRACT: Voltage-gated sodium channels are important in initiating and propagating nerve impulses in various tissues, including cardiac muscle, skeletal muscle, the brain, and the peripheral nerves. Hyperexcitability of these channels leads to such disorders as cardiac arrhythmias (Na(v)1.5), myotonias (Na(v)1.4), epilepsies (Na(v)1.2), and pain (Na(v)1.7). Thus, there is strong motivation to identify isoform-specific blockers and the molecular determinants underlying their selectivity among these channels. μ-Conotoxin KIIIA blocks rNa(v)1.2 (IC(50), 5 nM), rNa(v)1.4 (37 nM), and hNa(v)1.7 (97 nM), expressed in mammalian cells, with high affinity and a maximal block at saturating concentrations of 90 to 95%. Mutations of charged residues on both the toxin and channel modulate the maximal block and/or affinity of KIIIA. Two toxin substitutions, K7A and R10A, modulate the maximal block (52-70%). KIIIA-H12A and R14A were the only derivatives tested that altered Na(v) isoform specificity. KIIIA-R14A showed the highest affinity for Na(v)1.7, a channel involved in pain signaling. Wild-type KIIIA has a 2-fold higher affinity for Na(v)1.4 than for Na(v)1.7, which can be attributed to a missing outer vestibule charge in domain III of Na(v)1.7. Reciprocal mutations Na(v)1.4 D1241I and Na(v)1.7 I1410D remove the affinity differences between these two channels for wild-type KIIIA without affecting their affinities for KIIIA-R14A. KIIIA is the first μ-conotoxin to show enhanced activity as pH is lowered, apparently resulting from titration of the free N terminus. Removal of this free amino group reduced the pH sensitivity by 10-fold. Recognition of these molecular determinants of KIIIA block may facilitate further development of subtype-specific, sodium channel blockers to treat hyperexcitability disorders.Molecular pharmacology 06/2011; 80(4):573-84. DOI:10.1124/mol.111.073460 · 4.12 Impact Factor
Article: Orientation of mu-Conotoxin PIIIA in a Sodium Channel Vestibule, Based on Voltage Dependence of Its Binding[Show abstract] [Hide abstract]
ABSTRACT: Mutant cycle analysis has been used in previous studies to constrain possible docking orientations for various toxins. As an independent test of the bound orientation of μ-conotoxin PIIIA, a selectively targeted sodium channel pore blocker, we determined the contributions to binding voltage dependence of specific residues on the surface of the toxin. A change in the "apparent valence" (zδ) of the block, which is associated with a change of a specific toxin charge, reflects a change in the charge movement within the transmembrane electric field as the toxin binds. Toxin derivatives with charge-conserving mutations (R12K, R14K, and K17R) showed zδ values similar to those of wild type (0.61 ± 0.01, mean ± S.E.M.). Charge-changing mutations produced a range of responses. Neutralizing substitutions for Arg14 and Lys17 showed the largest reductions in zδ values, to 0.18 ± 0.06 and 0.20 ± 0.06, respectively, whereas unit charge-changing substitutions for Arg12, Ser13, and Arg20 gave intermediate values (0.24 ± 0.07, 0.33 ± 0.04, and 0.32 ± 0.05), which suggests that each of these residues contributes to the dependence of binding on the transmembrane voltage. Two mutations, R2A and G6K, yielded no significant change in zδ. These observations suggest that the toxin binds with Arg2 and Gly6 facing the extracellular solution, and Arg14 and Lys17 positioned most deeply in the pore. In this study, we used molecular dynamics to simulate toxin docking and performed Poisson-Boltzmann calculations to estimate the changes in local electrostatic potential when individual charges were substituted on the toxin's surface. Consideration of two limiting possibilities suggests that most of the charge movement associated with toxin binding reflects sodium redistribution within the narrow part of the pore.Molecular pharmacology 04/2011; 80(2):219-27. DOI:10.1124/mol.111.071779 · 4.12 Impact Factor
Article: Individual Residues of μ-Conotoxin PIIIA Appear to Show Distinct Electrostatic Interactions with Ions in the Conduction Pathway of Sodium ChannelsBiophysical Journal 02/2011; 100(3). DOI:10.1016/j.bpj.2010.12.291 · 3.83 Impact Factor
Article: Multiple, Distributed Interactions of μ-Conotoxin PIIIA Associated with Broad Targeting among Voltage-Gated Sodium Channels[Show abstract] [Hide abstract]
ABSTRACT: The first μ-conotoxin studied, μCTX GIIIA, preferentially blocked voltage-gated skeletal muscle sodium channels, Na(v)1.4, while μCTX PIIIA was the first to show significant blocking action against neuronal voltage-gated sodium channels. PIIIA shares >60% sequence identity with the well-studied GIIIA, and both toxins preferentially block the skeletal muscle sodium channel isoform. Two important features of blocking by wild-type GIIIA are the toxin's high binding affinity and the completeness of block of a single channel by a bound toxin molecule. With GIIIA, neutral replacement of the critical residue, Arg-13, allows a residual single-channel current (∼30% of the unblocked, unitary amplitude) when the mutant toxin is bound to the channel and reduces the binding affinity of the toxin for Na(v)1.4 (∼100-fold) [Becker, S., et al. (1992) Biochemistry 31, 8229-8238]. The homologous residue in PIIIA, Arg-14, is also essential for completeness of block but less important in the toxin's binding affinity (∼55% residual current and ∼11-fold decrease in affinity when substituted with alanine or glutamine). The weakened dominance of this key arginine in PIIIA is also seen in the fact that there is not just one (R13 in GIIIA) but three basic residues (R12, R14, and K17) for which individual neutral replacement enables a substantial residual current through the bound channel. We suggest that, despite a high degree of sequence conservation between GIIIA and PIIIA, the weaker dependence of PIIIA's action on its key arginine and the presence of a nonconserved histidine near the C-terminus may contribute to the greater promiscuity of its interactions with different sodium channel isoforms.Biochemistry 12/2010; 50(1):116-24. DOI:10.1021/bi101316y · 3.19 Impact Factor
Article: Isolation and characterization of a high affinity peptide inhibitor of ClC-2 chloride channels.[Show abstract] [Hide abstract]
ABSTRACT: The ClC protein family includes voltage-gated chloride channels and chloride/proton exchangers. In eukaryotes, ClC proteins regulate membrane potential of excitable cells, contribute to epithelial transport, and aid in lysosomal acidification. Although structure/function studies of ClC proteins have been aided greatly by the available crystal structures of a bacterial ClC chloride/proton exchanger, the availability of useful pharmacological tools, such as peptide toxin inhibitors, has lagged far behind that of their cation channel counterparts. Here we report the isolation, from Leiurus quinquestriatus hebraeus venom, of a peptide toxin inhibitor of the ClC-2 chloride channel. This toxin, GaTx2, inhibits ClC-2 channels with a voltage-dependent apparent K(D) of approximately 20 pm, making it the highest affinity inhibitor of any chloride channel. GaTx2 slows ClC-2 activation by increasing the latency to first opening by nearly 8-fold but is unable to inhibit open channels, suggesting that this toxin inhibits channel activation gating. Finally, GaTx2 specifically inhibits ClC-2 channels, showing no inhibitory effect on a battery of other major classes of chloride channels and voltage-gated potassium channels. GaTx2 is the first peptide toxin inhibitor of any ClC protein. The high affinity and specificity displayed by this toxin will make it a very powerful pharmacological tool to probe ClC-2 structure/function.Journal of Biological Chemistry 08/2009; 284(38):26051-62. DOI:10.1074/jbc.M109.031724 · 4.60 Impact Factor
Article: State-dependent inhibition of cystic fibrosis transmembrane conductance regulator chloride channels by a novel peptide toxin[Show abstract] [Hide abstract]
ABSTRACT: Peptide toxins from animal venom have been used for many years for the identification and study of cation-permeable ion channels. However, no peptide toxins have been identified that interact with known anion-selective channels, including cystic fibrosis transmembrane conductance regulator (CFTR), the protein defective in cystic fibrosis and a member of the ABC transporter superfamily. Here, we describe the identification and initial characterization of a novel 3.7-kDa peptide toxin, GaTx1, which is a potent and reversible inhibitor of CFTR, acting from the cytoplasmic side of the membrane. Thus, GaTx1 is the first peptide toxin identified that inhibits a chloride channel of known molecular identity. GaTx1 exhibited high specificity, showing no effect on a panel of nine transport proteins, including Cl(-) and K(+) channels, and ABC transporters. GaTx1-mediated inhibition of CFTR channel activity is strongly state-dependent; both potency and efficacy are reduced under conditions of elevated [ATP], suggesting that GaTx1 may function as a non-competitive inhibitor of ATP-dependent channel gating. This tool will allow the application of new quantitative approaches to study CFTR structure and function, particularly with respect to the conformational changes that underlie transitions between open and closed states.Journal of Biological Chemistry 01/2008; 282(52):37545-55. DOI:10.1074/jbc.M708079200 · 4.60 Impact Factor
Top Journals
The University of Calgary
Calgary, Alberta, Canada
- • Department of Physiology and Pharmacology
- • Department of Biochemistry and Molecular Biology


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She made it from Mooloolaba almost to Albany in Western Australia, but a broken rudder destroyed Margaret Williams attempt to be the first female solo unassisted circumnavigator of Australia. Four months later, she is getting prepared to do it all again
Margaret Williams
Carolyn Tucker (Sunshine Coast Daily) reported Friday that after Margaret's dream of making maritime history was dashed by gale force winds and treacherous seas, Sunshine Coast GP Margaret Williams is gearing up for another go.
Margaret's first attempt to circumnavigate Australia solo, non-stop and unassisted ended abruptly last December when she slammed into 50 knot winds and 40 foot waves off the coast of West Australia.
Unable to steer with a broken rudder she admitted it was game over and her 12-metre sloop Against All Odds limped into harbour.
Against All Odds
But undeterred by memories of terrifying electrical storms, faulty equipment, fears of piracy, sleep deprivation and sea sickness, Margaret said the time was now right for a second try.
'I know – people keep saying 'you're a sucker for punishment',' she laughed.
Her boat is back in the water for the first time since she aborted record attempt, with a new rudder, and a new mainsail on the way.
When the final glitches are ironed out in the next week or two, Margaret will be ready to launch again.
'I'll hopefully take off from Albany or Fremantle this time and I think the ideal time to go is April-May,' she said.
'There is less likelihood of storms in the southern ocean and I can get that leg out of the way first.
'Of course I'd love to start from home on the Sunshine Coast again but it would be much higher risk, so I will probably be sailing up the east coast in late May or early June.'
Once again the voyage will be largely self-funded although a mainsail being provided by Colin Quin Sailmakers at Pacific Paradise is a bonus.
Colin said he had never met Margaret but agreed to make her a new sail after receiving a call from her mother.
'She said Margie's stuck over there in Albany, is there any way you can help?' he said.
'We're only a small business and we're fairly new to the area but we know Margie is well known and well liked and we were happy to give her a hand.'
Margaret said she learned a lot from her first attempt where she had early problems with electrical equipment and her radar, forcing her to stay awake during the night.
This time there would be no chance of a repeat.
'I won't to go until I'm happy with everything.'
Once again Margaret is aiming to complete the 6700 nautical mile journey in about 80 days and her preparations and progress can be tracked at www.solosailoz.com.au - but don't try it until closer to the date – it's only history at the moment…..
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text: Charter Schools State School Board Gives Final Approval To New Charter Schools By Dave DeWitt • Mar 7, 2013 Dave DeWitt / WUNC The State Board of Education has given final approval to 23 charter schools to open this fall. Last year, 63 applicants began the process of applying to start a charter school, with an eye toward opening this fall. Twenty-five made it to this final round. How Charter Schools Are Changing Public Education By Frank Stasio & Alex Granados • Mar 6, 2013 Listen Listening... / 31:31 A panel of experts discuss how charter schools are changing public education Seventy new charter schools have applied to become part of North Carolina's growing population of alternative public schools. For the longest time, the number of charter schools in the state was capped at 100, but lawmakers changed that back in 2011. New Charter Schools Approved By Dave DeWitt • Mar 1, 2012 Nine new charter schools have been approved by the State Board of Education. They were fast-tracked after the legislature eliminated the cap on charter schools last summer.Dave DeWitt: All nine schools were eventually approved by the State Board of Education, after some discussion. Many of the questions raised came from State Treasurer Janet Cowell, who wondered, among other things, about the future bond ratings for school districts that lose students to charters.But in the end, the separate votes on each school were mostly unanimous. Lawmakers Lift Cap on Charter Schools By Jessica Jones • Jun 10, 2011 Lawmakers have overwhelmingly approved a measure that would lift the cap on charter schools in the state. The legislation is the result of nearly two months of negotiations between Democrats and Republicans. Democrat Joe Hackney is the House Minority Leader. Joe Hackney: "Many of us rebelled at many of the provisions of what I'll call the long version bill of earlier in the session. So for many on our side this bill comes as a relief." Charter School Bill Closer to Governor's Desk By Jessica Jones • Apr 8, 2011 A bill that would lift the current limit of one hundred charter schools in North Carolina has tentatively passed the state House.The bill would allow the addition of up to fifty charter schools every year. It has been the subject of hours of debate, discussion and even compromise in committees. But lawmakers were still wrangling over the bill on the House floor yesterday. House Majority Leader Paul Stam told the body he was growing impatient. Charter School Bill Passes Senate By Jessica Jones • Feb 24, 2011 State senators have tentatively approved a bill that would eliminate North Carolina's current cap on charter schools. The schools receive public money, but they function independently of local districts. Right now only one hundred charters are allowed to operate in the state at any given time. Democrats introduced a number of amendments on the Senate floor they said would help more at-risk children attend charters. But they were outvoted by the Republican majority. Democrat Gladys Robinson is from Greensboro: Charter School Bill Would Lift Cap By Jessica Jones • Feb 14, 2011 Listen Listening... / 3:32 A bill in the state Senate would abolish the current limit of one hundred on charter schools in North Carolina. For years, advocates of charter schools have pressed legislators to pass a law that would allow more charters to operate in North Carolina. The schools receive public money, but they function independently of local districts. Right now only one hundred of them are allowed to operate at any given time in the state. But the new Republican-controlled legislature is likely to eliminate that limit completely. And that would make some charter school advocates very happy. Changing Charter Schools By Dave DeWitt • Feb 7, 2011 The State Legislature is making good on its promise to change laws that govern charter schools. But some public school advocates say the current bill is too far-reaching. Pages« first ‹ previous 1 2 3


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Douglas Edward Gray
Douglas Edward Gray
Douglas Edward Gray of Frisco, Texas, formerly of Jacksboro, Texas, was born on July 30, 1942, in Denison, Texas. He passed away on Saturday January 11, 2014, in Plano, Texas. He was 71 years old.
Douglas married Theda Cantrell on September 1, 1962, in Jacksboro. He was a member of the First United Methodist Church and retired from Primexx Operating after 37 years.
He is preceded in death by his parents and infant daughter, Shelly Dawn Gray and a grandson, Caleb Christopher Heskett.
Survivors include: wife, Theda Gray of Frisco; daughters, Krista Gray of Lewisville and Keri and husband Chris Heskett of Sanger and their daughters Madison and Peyton;
a very special aunt Dorothy Martin of Jacksboro; and many other extended family members and friends.
If so desired memorials may be made to the First United Methodist Church of Jacksboro or the American Cancer Society, www.cancer.org
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text:
A new report has highlighted the risks involved for children who practice gymnastics. Arthritis and broken bones are just two areas of concern.
X-rays of 12-16 year old athletes in America were looked at and the study revealed they were enduring joint injuries that were capable of affecting them later in life.
The report was presented at the annual meeting of the Radiological Society of North America, where scientists explained that the gymnasts involved in the study portrayed a "broad constellation of recent injuries" to their knuckles and wrists as well as signs of early necrosis - otherwise known as the "death" of bones.
Jerry Dwek who led the research at the University of California, San Diego said, "We were surprised to be looking at injuries every step down the hand all the way from the radius to the small bones in the wrist and on to the ends of the finger bones at the knuckles. These types of injuries are likely to develop into early osteoarthritis."
Research in the past has already indicated that gymnastics is as risky as contact sports. Of 10,000 children doing gymnastics every year, 52 will have an injury, compared with 75 youth rugby players.
Doctors are concerned that children have a lot of pressure put on them to do well from parents, which could contribute to injuries. Sammy Margo, a chartered physiotherapist from northwest London, said, "Twenty years ago, 1 per cent of my patients were children. Now it's more like 20 per cent. I do see many children suffering gymnastics injuries. I'm also seeing something I never saw 20 years ago — children with lower-back problems. Some parents are pushing their children into intensive training."
The scans of the children revealed evidence of necrosis, chronic stress injuries and cartilage tears around a number of joints and bones. Dr Dwek feels more research is required, "It is possible that by changing the way that practice routines are performed, we might be able to limit stress on the joints and on delicate growing bones," he commented.
Matthew Greenwood, performance and technical director for British Gymnastics, said,
Performance and technical director for British Gymnastics, Matthew Greenwood said,"We have become more aware of the importance of fitness and safety in recent years, and we are careful not to risk long-term injury by over training."
Changes being introduced to tackle the problem include foam mats and low-impact trampolines. In addition, the minimum age required to compete will rise from 16 to 17 next year.


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Brandy Ho's Hunan Food
Brandy Ho's Hunan Food
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Phone: (415)788-7527
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Co-founder and former CEO Roland Dyroff will become a member of the supervisory board, the company said Friday.
The job cuts, affecting mostly nontechnical personnel, were spurred by slower spending in the computing industry, the company said. The management change was part of a shift to focus from technology matters to business matters.
SuSE, which believes the German Linux market is ahead of the U.S. market, laid off 30 U.S. employees in February. --Stephen Shankland, Special to ZDNet News


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A process for the production of propylene, the process including: fractionating a hydrocarbon stream comprising n-butenes, isobutylene, and paraffins into at least two fractions including a light C4 fraction comprising isobutylene and a heavy C4 fraction comprising n-butenes and paraffins; contacting at least a portion of the heavy C4 fraction with a metathesis catalyst to form a metathesis product comprising ethylene, propylene, C4+ olefins, and paraffins; fractionating the metathesis product into at least four fractions including an ethylene fraction, a propylene fraction, a C4 fraction comprising C4 olefins and paraffins, and a C5+ fraction; cracking the light C4 fraction and the C5+ fraction to produce a cracking product comprising ethylene, propylene, and heavier hydrocarbons; and fractionating the cracking product into at least two fractions including a light fraction comprising propylene and a fraction comprising C5 to C6 hydrocarbons.
1. A process for the production of propylene, the process comprising:
fractionating a hydrocarbon stream comprising n-butenes, isobutylene, and paraffins into at least two fractions including a light C4 fraction comprising isobutylene and a heavy C4 fraction comprising n-butenes and paraffins;
contacting at least a portion of the heavy C4 fraction with a metathesis catalyst to form a metathesis product comprising ethylene, propylene, C4+ olefins, and paraffins;
fractionating the metathesis product into at least four fractions including an ethylene fraction, a propylene fraction, a C4 fraction comprising C4 olefins and paraffins, and a C5+ fraction;
cracking the light C4 fraction and the C5+ fraction to produce a cracking product comprising ethylene, propylene, and heavier hydrocarbons; and
fractionating the cracking product into at least two fractions including a light fraction comprising propylene and a fraction comprising C5 to C6 hydrocarbons.
2. The process of
3. The process of
4. The process of
5. The process of
6. The process of
7. The process of
8. The process of
9. The process of
10. The process of
11. The process of
contacting at least one of the mixed-C4 stream and the heavy C4 fraction with the isomerization catalyst to convert at least a portion of the 1-butene to 2-butene.
12. The process of
recycling at least a portion of the ethylene recovered from fractionating the metathesis product to the contacting;
recycling ethylene recovered from the cracking product to the contacting; and
feeding a hydrocarbon stream containing ethylene to the contacting.
13. The process of
14. The process of
15. The process of
16. The process of
17. The process of
18. The process of
19. The process of
20. The process of
This application, pursuant to 35 U.S.C. �119(e), claims priority to U.S. Provisional Application Ser. No. 61/088,221, filed Aug. 12, 2008, which is incorporated by reference in its entirety.
1. Field of the Disclosure
Embodiments disclosed herein relate generally to the processing of a C3 to C6 hydrocarbon cut from a cracking process, such as steam or fluid catalytic cracking, primarily for conversion of C4 olefins to propylene via metathesis.
2. Background
In typical olefin plants, such as illustrated in U.S. Pat. No. 7,223,895, there is a front-end demethanizer for the removal of methane and hydrogen followed by a deethanizer for the removal of ethane, ethylene and C2 acetylene. The bottoms from this deethanizer tower consist of a mixture of compounds ranging in carbon number from C3 to C6. This mixture may be separated into different carbon numbers, typically by fractionation.
The C3 cut, primarily propylene, is removed as product and is ultimately used for the production of polypropylene or for chemical synthesis such as propylene oxide, cumene, or acrylonitrile. The methyl acetylene and propadiene (MAPD) impurities must be removed either by fractionation or hydrogenation. Hydrogenation is preferred since some of these highly unsaturated C3 compounds end up as propylene thereby increasing the yield.
The C4 cut, consisting of C4 acetylenes, butadiene, iso- and normal butenes, and iso- and normal butane can be processed in many ways. A typical steam cracker C4 cut contains the following components in weight %:
Typically, the butadiene and C4 acetylenes are removed first. This can be accomplished by either hydrogenation or extraction. The product from butadiene and C4 acetylene removal is designated Raffinate I. If extraction is employed, the remaining 1-butene and 2-butene remain essentially in the same ratio as that of the initial feedstock. If hydrogenation is employed, the initial product from butadiene hydrogenation is 1-butene. Subsequently, hydroisomerization occurs within the same reaction system changing the 1-butene to 2-butene. The extent of this reaction depends upon catalyst and reaction conditions within the hydrogenation system. However, it is common practice to limit the extent of hydroisomerization in order to avoid "over hydrogenation" and the production of butanes from butenes. This would represent a loss of butene feedstock for downstream operations. The butenes remaining in the mixture consist of normal olefins (1-butene, 2-butene) and iso-olefins (isobutylene). The balance of the mixture consists of both iso- and normal-butanes from the original feed plus what was produced in the hydrogenation steps and any small quantity of unconverted or unrecovered butadiene.
A Raffinate I stream can be further processed in many ways. A Raffinate II stream is by definition a stream following isobutylene removal. Isobutylene can be removed in a number of ways. It can be removed via fractionation. In fractionation isobutane will be removed along with the isobutylene. In addition, some fraction of the 1-butene will be lost as well. The resultant Raffinate II will contain primarily normal olefins and paraffins and minimal isoolefins and isoparaffins. Isobutylene can also be removed via reaction. Reactions include: reaction with methanol to form MTBE, reaction with water to form tertiary butyl alcohol, or reaction with itself to form a C8 gasoline component. In all reaction cases, the paraffins are not removed, and thus the mixture will contain both normal and iso-paraffins. The paraffin content and composition of the Raffinate II impacts downstream processing options.
The butenes have many uses. One such use is for the production of propylene via metathesis. Another is for the production of ethylene and hexene via metathesis. Conventional metathesis involves the reaction of normal butenes (both 1-butene and 2-butene) with ethylene (principally the reaction of 2-butene with ethylene to form propylene). These reactions occur in the presence of a group VIA or VIIA metal oxide catalyst, either supported or unsupported. The paraffin components of the reaction feed are essentially inert and do not react, and are typically removed from the process via a purge stream in the separation system that follows the metathesis reactor. Typical catalysts for metathesis are tungsten oxide supported on silica or rhenium oxide supported on alumina. Examples of catalysts suitable for the metathesis of olefins are described in U.S. Pat. No. 6,683,019, for example. Isobutylene (isobutene) may be removed from the feedstock prior to the metathesis reaction step. The reaction of isobutylene with ethylene is non-productive and reaction with itself and/or other C4's is limited in the presence of excess ethylene. Non-productive reactions essentially occupy catalyst sites but produce no product. If allowed to remain in the feed to the metathesis unit, the concentration of this non-reactive species would build up creating capacity limitations. The reaction of 1-butene with ethylene is also non-productive. However, it is common to employ a double bond isomerization catalyst within the metathesis reactor to shift 1-butene to 2-butene and allow for continued reaction. Typical double bond isomerization catalysts include basic metal oxides (Group IIA), either supported or unsupported. Magnesium oxide and calcium oxide are examples of such double bond isomerization catalysts that may be physically admixed with the metathesis catalyst. No equivalent co-catalyst exists for the skeletal isomerization of isobutylene to normal butene. In the case of a conventional metathesis system employing both a metathesis catalyst and a co-mixed double bond isomerization catalyst, the butadiene must be removed to a level of less than 500 ppm to avoid rapid fouling of the double bond isomerization catalyst. The metathesis catalyst itself can tolerate butadiene levels up to 10,000 ppm.
In some cases, an isobutylene removal step is employed prior to metathesis. Options include reacting it with methanol to produce methyl tertiary butyl ether (MTBE) or separating the isobutylene from the butenes by fractionation. U.S. Pat. No. 6,358,482 discloses the removal of isobutylene from the C4 mixture prior to metathesis. This scheme is further reflected in U.S. Pat. Nos. 6,075,173 and 5,898,091. U.S. Pat. No. 6,580,009 discloses a process for the production of propylene and hexene from a limited ethylene fraction. For molar ratios of ethylene to butenes (expressed as n-butenes) from 0.05 to 0.60, the inventors utilize a Raffinate II stream as the C4 feedstock.
The typical metathesis process takes the Raffinate I feedstock and removes the majority of the isobutylene via fractionation, as described above to form a Raffinate II. In this step, the isobutene is removed as well plus some quantities of normal butenes, dependent upon the fractionation conditions. The Raffinate II is then admixed with ethylene, passed through guard beds to remove poisons, vaporized and preheated and fed to the metathesis reactors. The operating conditions are typically 300� C. and 20 to 30 bar pressure. The reactor effluent following heat recovery is then separated in a fractionation system. First the ethylene is recovered overhead in a first tower and recycled to the reactor system. The tower bottoms are then sent to a second tower where the propylene is recovered overhead. A side draw is taken containing the majority of the unconverted C4 components and recycled to the reactor. The tower bottoms containing the C5 and heavier products plus C4 olefins and paraffins are sent to purge. The purge rate is typically fixed to contain sufficient C4 paraffins to avoid their buildup in the reactor recycle stream. In some cases, a third tower is employed on the tower bottoms stream to separate the C4 components overhead and the C5 and heavier components as a bottoms stream.
U.S. Pat. No. 6,271,430 discloses a two-step process for the production of propylene. The first step consists of reacting 1-butene and 2-butene in a raffinate II stream in an auto-metathesis reaction to form propylene and 2-pentene. The products are then separated in the second step. The third step reacts specifically the 2-pentene with ethylene to form propylene and 1-butene. This process utilizes the isobutylene free raffinate II stream. The pentenes recycled and reacted with ethylene are normal pentenes (2-pentene).
Isobutylene removal from the C4 stream can also be accomplished by employing a combined catalytic distillation hydroisomerization deisobutyleneizer system to both remove the isobutylene and recover n-butenes at high efficiency by isomerizing the 1-butene to 2-butene with known isomerization catalysts and thus increasing the volatility difference. This technology combines conventional fractionation for isobutylene removal with hydroisomerization within a catalytic distillation tower. In U.S. Pat. No. 5,087,780 to Arganbright, 2-butene is hydroisomerized to 1-butene as the fractionation occurs. This allows greater than equilibrium amounts of 1-butene to be formed as the mixture is separated. Similarly, 1-butene can be hydroisomerized to 2-butene in a catalytic distillation tower. In separating a C4 stream containing isobutylene, 1-butene, and 2-butene (plus paraffins), it is difficult to separate isobutylene from 1-butene since their boiling points are very close. By employing simultaneous hydroisomerization of the 1-butene to 2-butene with fractionation of isobutylene, isobutylene can be separated from the normal butenes at high efficiency.
The metathesis reaction described above is equimolar, i.e., one mole of ethylene reacts with 1 mole of 2-butene to produce 2 moles of propylene. However, commercially, in many cases, the quantity of ethylene available is limited with respect to the quantity of butenes available. In addition, the ethylene is an expensive feedstock and it is desired to limit the quantities of ethylene used. As the ratio of ethylene to butenes is decreased, there is a greater tendency for the butenes to react with themselves which reduces the overall selectivity to propylene.
The metathesis catalysts and the double bond isomerization catalysts are quite sensitive to poisons. Poisons include water, CO2, oxygenates (such as MTBE), sulfur compounds, nitrogen compounds, and heavy metals. It is common practice to employ guard beds upstream of the metathesis reaction system to insure the removal of these poisons. It does not matter if these guard beds are directly before the metathesis reaction system or further upstream as long as the poisons are removed and no new poisons are subsequently introduced.
Metathesis reactions are very sensitive to the location of the olefin double bond and the stereo-structure of the individual molecules. During the reaction, the double bond on each pair of olefins adsorb on the surface and exchange double bond positions with the carbon groups on either sides of the double bonds. Metathesis reactions can be classified as productive, half productive or non-productive. As described above, non-productive reactions result in essentially no reaction taking place. When the double bonds shift with metathesis reaction, the new molecules are the same as the originally adsorbed molecules thus no productive reaction occurs. This is typical for reactions between symmetric olefins or reactions between ethylene and alpha olefins. If fully productive reactions occur, new products are generated no matter which orientation the molecules occupy the sites. The reaction between ethylene and 2-butene to form two propylene molecules is a fully productive reaction. Half productive reactions are sterically inhibited. If the pair of olefins adsorb in one orientation (typically the cis position with respect to the attached R groups), when the double bonds shift, new products are formed. Alternately if they adsorb in a different steric configuration (the trans position), when the bonds shift, the identical olefins are formed and thus no new products are formed. The various metathesis reactions proceed at different rates (a fully productive reaction is usually faster than a half productive reaction). Table 2 summarizes the reactions between ethylene and various butenes and the reactions between the butenes themselves.
The reactions listed in Table 2 represent the base reaction with ethylene (reaction 1, 4 and 5) as well as the reactions between the various C4 olefins. It is especially important to make a distinction between the selectivity to propylene from total C4 olefins (including isobutylene) and the selectivity to propylene from the normal C4 olefins involved in the reaction. The reaction of isobutylene with 2-butene (reaction 6) produces propylene and a branched C5 molecule. For this reaction, propylene is produced at 50 molar % selectivity from total C4's (similar to reaction 2) but at a 100 molar % selectivity from the normal C4 (2-butene). For the purposes of definitions, conventional metathesis is defined as the reaction of the C4 olefin stream with ethylene. However, the C4 stream can also react in the absence of ethylene as a feedstock. This reaction is called auto or self metathesis. In this case, reactions 2, 3, 6, and 7 are the only possible reactions and will occur at rates dependent upon the feedstock composition.
In conventional metathesis, the focus is to maximize reaction 1 to produce propylene. This will maximize the selectivity to propylene. As such, excess ethylene is used to reduce the extent of the reactions of butenes with themselves (reactions 2, 3, 6, and 7). The theoretical ratio is 1/1 molar or 0.5 weight ratio of ethylene to n-butenes but it is common in conventional metathesis to employ significantly greater ratios, typically, 1.3 or larger molar ratio to minimize reactions 2, 3, 6 and 7. Under conditions of excess ethylene, and due to the fact that both isobutylene and 1-butene do not react with ethylene (see reactions 4 and 5), two process sequences are employed. First, the isobutylene is removed prior to metathesis. If isobutylene is not removed, it will build up as the n-butenes are recycled to achieve high yield. Second, 1-butene is isomerized to 2-butene by including a double bond isomerization catalyst such as magnesium oxide admixed with the metathesis catalyst. Note that this catalyst will not cause skeletal isomerization (isobutylene to normal butylenes) but only shift the double bond from the 1 position to the 2 position for the normal butenes. Thus by operating with excess ethylene, eliminating isobutylene from the metathesis feed prior to reaction, and employing a double bond isomerization catalyst, reaction 1 is maximized. Note, however, that by removing the isobutylene, potential production of propylene or other products is lost.
When there is limited or no fresh ethylene (or excess butylenes for the ethylene available), there are currently two options available for propylene production. In these cases, the first option will first remove the isobutylene and then process the normal butenes with whatever ethylene is available. The entire n-butenes-only mixture is subjected to metathesis with the available ethylene. Ultimately, if there is no fresh ethylene available, the C4's react with themselves (auto metathesis). Under low ethylene conditions, reactions 2, 3, 6 and 7 will occur, all leading to a lower propylene selectivity (50% or lower versus 100% for reaction 1). The lower selectivity results in lower propylene production. Note that reactions 6 and 7 will be minimized as a result of the removal of isobutylene (to low levels but not necessarily zero). Alternately, the molar flows of ethylene and butenes can be matched by limiting the flow of butenes to produce conditions where there is a high selectivity of the normal butenes to propylene via reaction 1. By limiting the flow of n-butenes to match ethylene, the production of propylene is limited by the reduced butenes flow.
Pentenes and some hexenes are formed to some extent in the conventional metathesis case with low ethylene via reactions 2 and 3. The volume of these components will depend upon the ethylene/n-butenes ratio with a lower ratio producing more C5 and C6 components. In the conventional prior art case where isobutylene is removed before any metathesis, these C5 and C6 olefins are normal olefins since no skeletal isomerization occurs. It is possible to recycle these olefins back to the metathesis step where, for example, the reaction with ethylene and 2-pentene will occur yielding propylene and 1-butene. The 1-butene is recovered and recycled. Note however, with limited ethylene, reaction 1 can occur only to the limit of the ethylene availability. Ultimately these non-selective byproducts, pentenes and hexenes, must be purged from the system.
U.S. Pat. No. 6,777,582 discloses a process for the auto-metathesis of olefins to produce propylene and hexene. Therein, auto-metathesis of a mixed normal butenes feed in the presence of a metathesis catalyst operates without any ethylene in the feed mix to the metathesis reactor. Some fraction of the 2-butene feed may be isomerized to 1-butene and the 1-butene formed plus the 1-butene in the feed react rapidly with the 2-butene to form propylene and 2-pentene. The feed to the reactor also includes the recycle of the 2-pentene formed in the reactor with unreacted butenes to simultaneously form additional propylene and hexene. The 3-hexene formed in the reaction may be isomerized to 1-hexene.
In U.S. Pat. No. 6,727,396, ethylene and hexene-1 are produced from butene-1 by metathesis of butene-1 and isomerization of the hexene-3 produced therein to hexene-1. The initial starting material is a mixed butene stream wherein butene-1 is isomerized to butene-2 with isobutylene being separated therefrom, followed by isomerization of butene-2 to butene-1, with the butene-1 being the feed to the metathesis.
In U.S. Pat. No. 7,214,841, the C4 cut from a hydrocarbon cracking process is first subjected to auto-metathesis prior to any isobutylene removal and without any ethylene addition, favoring the reactions which produce propylene and pentenes. The ethylene and propylene produced are then removed leaving a stream of the C.sub.4's and heavier components. The C.sub.5 and heavier components are then removed leaving a mixture of 1-butene, 2-butene, isobutylene, and iso- and normal butanes. The isobutylene is next removed preferably by a catalytic distillation hydroisomerization de-isobutyleneizer. The isobutylene-free C4 stream is then mixed with the product ethylene removed from the auto-metathesis product together with any fresh external ethylene needed and subjected to conventional metathesis producing additional propylene.
Another use of the C4 olefin stream is as a feedstock to an olefin cracking process, where the olefins are reacted with themselves over a zeolitic catalyst to produce a mixture comprising ethylene, propylene, and aromatics (such as benzene). Similar to the metathesis process, the paraffins are inert in this cracking process and must be removed from the process via a purge stream. U.S. Pat. No. 6,307,117 and U.S. Patent Application Publication No. 20050080307 both describe such a process. A mixture of typically C4 to C6 olefins as well as paraffins is vaporized and fed to a reactor filled with a crystalline zeolitic catalyst and operating at a temperature between 450 and 600� C. and a pressure between 10 and 70 psia. The reactor effluent is first sent to a compression step. The cracking reactor system operates at relatively low pressure to avoid fouling of the catalyst in the cracking reactor. In order to reduce the energy costs due to refrigeration in the subsequent separation system, the pressure is typically increased to pressures on the order of 12 to 25 barg. This allows the subsequent fractionating towers to utilize cooling water instead of refrigeration in the overhead condensation step. The compression effluent is then sent to a separation system where the ethylene and propylene are recovered along with an aromatics stream. The ethylene and propylene is recovered overhead in a first tower. Unlike metathesis, these products contain sufficient quantities of ethane and propane that additional purification of this stream is necessary. This can be accomplished by additional fractionation or by utilizing the recovery system of an adjacent facility such as an olefins plant. The tower bottoms contains C4, C5 and C6+ paraffins and aromatics. This is sent to a second tower. The overhead is a C4/C5 stream and the highly aromatic C6+ stream is the bottoms product. The unconverted C4 and C5 products are typically recycled. The cracking process can handle both iso and normal olefins with equivalent efficiency. There is no need to remove isobutylene for example from the feed to maximize propylene production.
As described above, there is considerable interest in the processing of C4, C5, and heavier olefin streams to produce lighter olefins, such as propylene. Accordingly, there exists a significant need for processes that may result in the production of high purity propylene from such olefin-containing streams at low cost and low energy.
In one aspect, embodiments disclosed herein relate to a process for the production of propylene, the process including: fractionating a hydrocarbon stream comprising n-butenes, isobutylene, and paraffins into at least two fractions including a light C4 fraction comprising isobutylene and a heavy C4 fraction comprising n-butenes and paraffins; contacting at least a portion of the heavy C4 fraction with a metathesis catalyst to form a metathesis product comprising ethylene, propylene, C4+ olefins, and paraffins; fractionating the metathesis product into at least four fractions including an ethylene fraction, a propylene fraction, a C4 fraction comprising C4 olefins and paraffins, and a C5+ fraction; cracking the light C4 fraction and the C5+ fraction to produce a cracking product comprising ethylene, propylene, and heavier hydrocarbons; and fractionating the cracking product into at least two fractions including a light fraction comprising propylene and a fraction comprising C5 to C6 hydrocarbons.
In another aspect, embodiments disclosed herein relate to a process for the production of propylene, the process including: contacting a mixed-C4 stream comprising n-butenes, isobutylene, and paraffins with a metathesis catalyst whereby auto-metathesis occurs including the reaction of isobutylene with n-butenes to form an auto-metathesis product comprising ethylene, propylene, and heavier olefins including unreacted isobutylene and paraffins; fractionating the auto-metathesis product into at least four fractions including an ethylene fraction, a propylene fraction, a C5+ fraction, and a C4 fraction containing n-butenes, isobutylene, and paraffins; fractionating the C4 fraction into at least two fractions including a light C4 fraction comprising isobutylene and a heavy C4 fraction comprising n-butenes and paraffins; contacting at least a portion of the heavy C4 fraction and ethylene with a metathesis catalyst to form a metathesis product comprising ethylene, propylene, C4+ olefins, and paraffins; feeding the metathesis product to the fractionating the auto-metathesis product; cracking the C5+ fraction to produce a cracking product comprising ethylene, propylene, and heavier hydrocarbons; and fractionating the cracking product into at least two fractions including a light fraction comprising propylene and a fraction comprising C5 to C6 hydrocarbons.
Other aspects and advantages will be apparent from the following description and the appended claims.
In one aspect, embodiments herein relate to the processing of a C4 to C6 hydrocarbons to form lighter olefins, such as ethylene and propylene. In another aspect, embodiments disclosed herein relate to the conversion of C4 to C6 olefins to ethylene and propylene via an integrated metathesis and cracking process. More specifically, embodiments disclosed herein relate to fractionation of a mixed C4 stream to form a light C4 fraction including isobutylene and a heavy C4 fraction including 2-butene, metathesis of 2-butenes in the heavy C4 fraction, and the subsequent cracking of a combined stream including the light C4 fraction and C5+ metathesis products to produce propylene at high yields.
In another aspect, embodiments disclosed herein relate to the auto-metathesis of the C4 feedstock without ethylene to form a reaction effluent comprising ethylene, propylene, unreacted C4 olefins, C4 paraffins and C5/C6 normal and iso-olefins. In some embodiments, isobutylene is not removed from the feedstock to that auto-metathesis reaction. The reactor effluent is first fractionated to recover light ethylene and propylene products. The remaining effluent is subjected to continued fractionation to recover a C4 product overhead and a C5 and heavier stream. The C4 overhead stream is fractionated to create a light C4 fraction comprising isobutylene and isobutene, and a heavy C4 stream comprising mostly normal butenes and normal butane. The heavy C4 stream is admixed with ethylene and subjected to metathesis. The products of this metathesis reaction are mixed with the products of the first auto-metathesis reaction and go to the common separation system. Some or all of the C5 and heavier stream is fed to the cracking reactor along with some or all of the overhead from the C4 fractionation tower. The effluent from the cracking reactor contains ethylene, propylene, and aromatics.
In other embodiments, the light gases from the cracking reaction may be sent to the separation zone of the metathesis reaction system. In this manner the ethylene produced in the cracking reaction section may be used to provide additional ethylene for the metathesis reaction, and reduce or minimize the required feed ethylene.
The mixed C4 feed to processes disclosed herein may include C3 to C6+ hydrocarbons, including C4, C4 to C5, and C4 to C6 cracker effluents, such as from a steam cracker or a fluid catalytic cracking (FCC) unit. Other refinery hydrocarbon streams containing a mixture of C4 olefins may also be used. When C3, C5 and/or C6 components are present in the feed, the stream may be pre-fractionated to result in a primary C4 cut, a C4 to C5 cut, or a C4 to C6 cut.
C4 components contained in the feed stream may include n-butane, isobutane, isobutene, 1-butene, 2-butene, and butadiene. In some embodiments, the mixed C4 feed is pretreated to provide a 1-butene feed for the metathesis reaction. For example, when butadiene is present in the C4 feed, the butadiene may be removed via hydrogenation or extraction. In other embodiments, the mixed butenes feed following or in conjunction with butadiene hydrogenation may be subjected to hydroisomerization conditions to convert 1-butene to 2-butene, with isobutylene being separated from a 2-butene stream by fractionation. The 2-butene stream may then be isomerized back to 1-butene in a subsequent step for use as feed to the metathesis portion of the processes disclosed herein.
The 1-butene may then be contacted with a metathesis catalyst to convert at least a portion of the 1-butene to ethylene, propylene, and C5 to C6 metathesis products. In some embodiments, the 1-butene may be subject to auto-metathesis, and in other embodiments may be subject to conventional metathesis, where ethylene is co-fed with the 1-butene to the metathesis reactor.
The metathesis reactor may operate at a pressure between 2 and 40 atmospheres in some embodiments, and between 5 and 15 atmospheres in other embodiments. The metathesis reactor may be operated such that the reaction temperature is within the range from about 50� C. to about 600� C.; within the range from about 200� C. to about 450� C. in other embodiments; and from about 250� C. to about 400� C. in yet other embodiments. The metathesis reaction may be performed at a weight hourly space velocity (WHSV) in the range from about 3 to about 200 in some embodiments, and from about 6 to about 40 in other embodiments.
The reaction may be carried out by contacting the olefin(s) with the metathesis catalyst in the liquid phase or the gas phase depending on structure and molecular weight of the olefin(s). If the reaction is carried out in the liquid phase, solvents or diluents for the reaction can be used. Aliphatic saturated hydrocarbons, e.g., pentanes, hexanes, cyclohexanes, dodecanes and aromatic hydrocarbons such as benzene and toluene are suitable. If the reaction is carried out in the gaseous phase, diluents such as saturated aliphatic hydrocarbons, for example, methane, ethane, and/or substantially inert gases, such as nitrogen and argon, may be present. For high product yield, the reaction may be conducted in the absence of significant amounts of deactivating materials such as water and oxygen.
The contact time needed to obtain a desirable yield of metathesis reaction products depends upon several factors such as the activity of the catalyst, temperature, pressure, and the structure of the olefin(s) to be metathesized. Length of time during which the olefin(s) are contacted with catalyst can conveniently vary between 0.1 seconds and 4 hours, preferably from about 0.5 sec to about 0.5 hrs. The metathesis reaction may be conducted batch-wise or continuously with fixed catalyst beds, slurried catalyst, fluidized beds, or by using any other conventional contacting techniques.
The catalyst contained within the metathesis reactor may be any known metathesis catalyst, including oxides of Group VIA and Group VIIA metals on supports. Catalyst supports can be of any type and could include alumina, silica, mixtures thereof, zirconia, and zeolites. In addition to the metathesis catalyst, the catalyst contained in the metathesis reactor may include a double bond isomerization catalyst such as magnesium oxide or calcium oxide. In some embodiments, the catalyst may include a promoter to reduce acidity; for example, an alkali metal (sodium, potassium or lithium), cesium, a rare earth, etc.
The effluent from the metathesis reactor may be sent to a separation system to separate the metathesis effluent into carbon number groups by technology well known in the art. For example, the products of the separation system may include an ethylene stream, a propylene stream, a C4 stream, and a C5+ stream. The propylene stream may be recovered as a product stream, which may also undergo further purification steps to obtain a high purity propylene product. The C4 stream may be recycled back to the metathesis reactor or a pre-treatment stage, such as isomerization or fractionation. The ethylene stream may be recovered as a product stream or may be recycled back to the metathesis reactor for use as an ethylene feedstock for the conventional metathesis reaction.
The C5+ fraction recovered from separation of the metathesis reactor effluent may be combined with isobutene, such as contained in a light C4 fraction resulting from pre-separation of a mixed C4 cut, and fed to a cracking unit to produce additional ethylene and propylene. In some embodiments, additional C5 and/or C6 fractions, such as resulting from pre-fractionation of a C4-C6 cut to result in the metathesis butene feed, may also be fed to the cracking unit. In the cracking unit, the mixed feed may be heated to a temperature in the range of 150� C. to about 1000� C., sufficient to crack the C4 to C6 hydrocarbons to form ethylene and propylene, among other products. The cracking may be performed using thermal cracking, steam cracking, catalytic cracking, or a combination thereof. In some embodiments, the cracking is catalytic and is performed in the presence of a crystalline zeolitic catalyst.
The cracking reactor may operate at a pressure between 1 and 20 atmospheres in some embodiments, and between 2 and 110 atmospheres in other embodiments. The cracking reactor may be operated such that the reaction temperature is within the range from about 150� C. to about 1000� C.; within the range from about 300� C. to about 800� C. in other embodiments; and from about 450� C. to about 600� C. in yet other embodiments. The cracking reaction may be performed in the presence of a crystalline zeolitic catalyst in some embodiments, ZSM-5 zeolitic catalyst in other embodiments, and in the presence of a ZSM-5 zeolitic catalyst with a Si/Al ratio of greater than 50 in some embodiments, and a Si/Al ratio of greater than 200 in yet other embodiments.
Effluent from the cracking reactor may be sent to a separation system to separate the metathesis effluent into carbon number groups by technology well known in the art. For example, products from the cracking unit may include ethylene, propylene, C4s, C5s, C6s, as well as various aromatics. Ethylene may be recovered from the separation system as a product or may be recycled to the metathesis reactor as an ethylene feedstock for the conventional metathesis reaction. Propylene may be recovered as a product stream, which may also undergo further purification steps along with the metathesis propylene stream to obtain a high purity propylene product. The C4 stream may be recycled back to the metathesis reactor, a pre-treatment stage upstream of the metathesis reactor, or to the cracking unit. Similarly, the C5 and C6 fractions may be recycled to pre-fractionation, to the metathesis unit, or to the cracking unit.
Integration of metathesis and cracking, as described above, may result in additional yield of propylene as compared to cracking or metathesis alone. For example, processes according to embodiments disclosed herein may yield 10% or more additional propylene as compared to metathesis alone; an additional 15% propylene in other embodiments; and an additional 20% propylene in yet other embodiments, as compared to metathesis alone. Alternatively, the integration of metathesis and cracking may result in a similar amount of propylene production while using a reduced amount of ethylene feedstock.
In some embodiments, both auto-metathesis and conventional metathesis may be performed. For example, an initial auto-metathesis step may be purposely utilized, where isobutylene may be reacted with the normal butenes, and isobutylene conversions can reach 50 or 60%. The products from the reaction of isobutylene with 1-butene may include ethylene and 2-methyl 2-pentene while the products with 2-butene may include propylene and 2-methyl 2-butene. These auto-metathesis reactions may be used in combination with a second conventional metathesis reaction system and a modified fractionation/isobutylene removal sequence to result in a desired production of ethylene and propylene from the entire butenes stream.
In some embodiments, an olefin feed to a conventional metathesis reactor may include essentially pure normal butenes. This can be any mixture of 1-butene and 2-butene and may also contain C4 paraffins as a feed diluent. In some embodiments, the isobutene content, based on a combined amount of olefins in the feed mixture; may be less than 10%; less than 5% in other embodiments; less than 2% in other embodiments; and less than 1% in yet other embodiments.
In other embodiments, isobutene separation specifications in the pre-fractionation stage may be relaxed, thus allowing some flexibility for ethylene feed to the metathesis reactor. For example, feeding some isobutene, such as up to an isobutene concentration in the mixed C4 feed of about 15%, to the metathesis reactor will allow the reduction in the overall energy costs as the fractionation requirements are reduced. This flexibility may advantageously allow for lower capital costs, due to the relaxed separation requirements, as well as the potential for the integrated metathesis-cracking process according to embodiments disclosed herein to operate with low or no net ethylene consumption. In some embodiments, a ratio of ethylene to butenes in a conventional metathesis reactor feed may range from about 0.1 to about 2.5. In other embodiments, a ratio of ethylene to butenes in a conventional metathesis reactor feed may range from about 0.8 to about 2.0; and from about 1.5 to about 2.0 in yet other embodiments.
Referring now to
The heavy C4 fraction may be recovered as a bottoms fraction via flow line 16 and fed to metathesis reactor 18. When used, ethylene may be co-fed to reactor 18 via flow lines 20 and/or 22. Metathesis reactor 18 may contain one or more beds 24 of a conventional metathesis or an auto-metathesis catalyst, with or without isomerization functionality, suitable for converting at least a portion of the linear butenes in the heavy C4 fraction, with or without co-fed ethylene, to ethylene and propylene.
Effluent from metathesis reactor 18 may be fed via flow line 26 to a separation system 28, which may include, for example, distillation apparatus for separating the effluent into carbon number groups. As illustrated, separation system 28 may fractionate the metathesis product into at least four fractions, including an ethylene-containing fraction recovered vial flow line 30, a propylene-containing fraction recovered via flow line 32, a C4 fraction recovered via flow line 34, and a C5+ fraction recovered via flow line 36. The C5 fraction 36 may contain C4 components in addition to C5 and heavier components.
A portion of the C2 fraction recovered via flow line 30 may be purged from the system via flow line 38. The purge from line 38 is utilized primarily to purge trace components that may exist in the ethylene stream, including but not limited to hydrogen, methane, and/or ethane. If desired, at least a portion of the ethylene recovered via flow line 30 may be recycled as ethylene feed via flow line 22 to metathesis reactor 18.
The C4 fraction recovered via flow line 34 may be recycled to metathesis reactor 18 via flow line 40. In some embodiments, at least a portion of the C4 fraction may be recycled to fractionator 12 via flow line 41. In some embodiments, at least a portion of the C4 fraction may be purged, if necessary, via flow line 42. The purge via line 42 may serve to purge C4 paraffins from the system that could otherwise build up to substantial levels as the recycle is increased to allow for high overall conversion of the C4 olefins. Typically, stream 34 may contain between 30 and 60% paraffins as a result of the recycle buildup of paraffins within the system.
Although not illustrated, the C4 fraction recovered via flow line 34 may alternatively be fed to a downstream cracking unit, as described below.
The light C4 fraction, including isobutylene, in flow line 14 and the C5+ fraction recovered via flow line 36 may be fed to a cracking unit 44. Additionally, additional C5 and/or C6 components, such as from a pre-fractionation of a C4 to C6 cut (not shown), may be fed via flow line 46 to cracking unit 44. In cracking unit 44, the hydrocarbons are subjected to elevated temperatures, as described above, to crack the hydrocarbons to form propylene and ethylene, among other components.
Effluent from cracking unit 44 may be fed via flow line 48 to a separation system 50, which may include, for example, distillation apparatus for separating the effluent into carbon number groups. Separation system 50 may fractionate the cracking product into at least two fractions, such as a lights fraction including propylene, and a heavy fraction including C5 and C6 hydrocarbons, for example. As illustrated, separation system 50 may fractionate the cracking product into at least three fractions, including an ethylene-containing fraction recovered vial flow line 52, a propylene-containing fraction recovered via flow line 54, and a C4+ fraction recovered via flow line 56. If necessary, the C4+ fraction may be further separated into a C4 fraction, a C5 to C6 fraction, and an aromatics fraction. A portion of the C4+ fraction may be recycled to fractionator 12. Alternatively, a portion of the C4+ fraction, such as C5 to C6 hydrocarbons, may be recycled to the cracking unit via flow line 60; in some embodiments, a portion of the C4+ fraction, such as aromatics, may be purged via flow line 62.
In some embodiments, the ethylene-containing stream 52 may be to the metathesis reaction system for reaction with the C4 olefins in metathesis reactor 18. In other embodiments the propylene in stream 54 may be admixed with the propylene in stream 32 to form propylene product. In further embodiments, the separation system 50 may produce a mixed ethylene/propylene stream instead of separate streams 52 and 54.
The mixed ethylene/propylene stream could then be admixed with the metathesis reactor effluent 26 to utilize the common ethylene and propylene fractionation systems within separation system 28 and thus reduce capital and utility costs.
Referring now to
Following the auto-metathesis reaction, effluent from the auto-metathesis reactor 72 may be fed via flow line 76 along with conventional metathesis effluent recovered from reactor 18 via flow line 26 to separation unit 28, producing carbon number fractions as described with respect to
In separation system 28, the C4 fraction contains unreacted C4 olefins and any C4 paraffins found in the mixed feed 70. The composition has been considerably altered due to the reaction of the olefins in the auto-metathesis reactor 72. This stream is sent fractionator 12. In fractionator 12, the C4 stream is separated into a light C4 fraction, recovered via line 14 and containing unreacted isobutylene, isobutene and some fraction of normal butenes and normal butane, and a heavy C4 fraction recovered via line 16 and containing primarily normal butenes and normal butane. Stream 77 can allow for the purge of the paraffins from the metathesis system. The heavy C4 fraction from fractionator 12 is directed to metathesis reactor 18 via line 16. This stream may be admixed with ethylene via line 20 or line 22. Note that since a large fraction of the C4 olefins have reacted in auto-metathesis reactor 72, a considerably reduced amount of ethylene is required to be added via lines 20 or 22 to maintain an equivalent ethylene/butenes ratio for the metathesis reactor 18.
The C5 fraction recovered from separation unit 28 will contain pentenes and hexenes (both iso and normal). This fraction may be fed to the cracking reactor 44 via line 36, as described for
As described for
In some embodiments, there may be additional fresh mixed C4 feed introduced to the system at fractionator 12, such as via flow line 78, as opposed to all of the C4 feed entering the system via line 70. It would be characteristic of this stream to contain high concentrations of paraffins that would thus be purged via line 77 prior to entering the reactor 18 and separation system 28.
In some embodiments, C5 and heavier components may be allowed to remain with the mixed C4 fraction fed to fractionator 12. Isopentenes formed in the auto-metathesis step could be subsequently reacted with ethylene in the conventional metathesis reactor. Isobutylene would be re-formed by reaction with feed ethylene and/or product propylene. Note, however, that to the extent that the normal pentenes are allowed to pass to the conventional metathesis, they react to form propylene and normal butenes which is a desirable reaction. At this point, there is a mixture of n-butenes, isobutylene, and both iso and normal butanes and some C5 and heavier material.
In some embodiments, such as illustrated in
The following examples illustrate the unique and unexpected advantages of integrating the metathesis reactor systems and the cracking reactor systems. The integration may reduce the utilities for the cracking reactor system by reactively separating the C4 paraffins from the C4 olefins. Further the integration may allow for similar or greater amounts of propylene to be produced from a mixed C4 stream with similar or lesser amounts of valuable ethylene feedstock.
The following examples are derived from modeling techniques. Although the work has been performed, the Inventors do not present these examples in the past tense to comply with applicable rules.
For each of the simulation studies, the olefin feed is 100 kg/h. Mixed butenes feed compositions include 15% isobutene mixed with n-butenes, and n-butane is not included in the feed simulated. For the cracking simulations, isobutene is used as the C4 iso-olefin, 2-methyl 2-butene is used as the model feed for the iso-pentene, 2-methyl 2-pentene is used as the model feed for the iso-hexene and 1-hexene is used as the model feed for n-C6 feed.
For simulation of the cracker, a conversion reactor is used. The product distribution for the olefin cracking is obtained from "Cracking of pentenes to C2-C4 light olefins over zeolites and zeotypes: Role of topology and acid site strength and concentration," Bortnovsky et al., Applied Catalysis A: General, 287, 2005, 203-213. A typical product distribution for the cracking reaction using ZSM-5 as the catalyst is shown in Table 3. The example provided is for the cracking of 2-methyl 2-butene. Table 3 also provides the corresponding reaction stoichiometry that would be used in the conversion reactor simulating the cracker.
A conventional metathesis process is simulated. Isobutene 400 in the C4 feed 402 is removed via separator 404 before the feed is sent to the conventional metathesis reactor 406. Ethylene 408 is fed to metathesis reactor 406 at a rate to maintain an ethylene to n-butene molar ratio at the inlet to the conventional metathesis reactor 406 at 1.8 (38.5 kg/h ethylene feed). An overall C4 utilization of 96% and an overall C2 utilization of 94% are used to simulate the metathesis reactor effluent 410, which is subsequently separated into C2s 412, C3s 414, C4s 416, and C5+ 418, with C2 and C4 purge and recycle streams 420, 422, 424, and 426. The details and results of the simulation are given in Table 4. The propylene produced is 112.4 kg/h, resulting solely from the conventional metathesis of butenes and ethylene.
A process similar to that illustrated in
Example 1 indicates that an additional 14% of propylene may be produced over the conventional metathesis process of Comparative Example 1. The integrated process, including cracking and metathesis, allows for additional processing of the isobutylene and C5/C6 products produced in the conventional metathesis to produce additional propylene, resulting in reduced purge of C5/C6 materials from the process. The cracker additionally produces a small quantity of aromatics (1.7 kg/h).
Example 2 also simulates a process similar to that illustrated in
Example 2 indicates that an additional 11% of propylene may be produced over the conventional metathesis process of Comparative Example 1. As compared to the flow scheme of Example 1, there is a 3% decrease in propylene production rate when the cracker recycle is sent back to the cracker.
The process configuration for this Example is the same as for Example 1 with the following differences. The ethylene to n-butene ratio is maintained at 1.0, as compared to 1.8 in Example 1, and about 50% of the isobutene in the mixed C4 feed is allowed to pass through fractionator 12 to conventional metathesis reactor 18. These feed changes relax the specifications on the deisobutanizer upstream of the metathesis reactor. Additionally, isobutene is half as productive as ethylene in propylene production by metathesis, where the resulting branched C5 olefin (2-methyl 2-butene) may be sent to cracker 44 via flow line 36 to produce additional light olefins. The details and results of the simulation are given in Table 7. The propylene produced is 117.1 kg/h, resulting from conventional metathesis and cracking.
The process conditions of Example 3 result in a slight decrease in propylene production as compared to Examples 1 and 2. However, it is important to recognize the added benefit of decreased ethylene consumption and less stringent C4 separations.
The process configuration for this Example is the same as for Example 1 with the following differences. The ethylene to n-butene ratio at the entrance of the conventional metathesis reactor 18 is adjusted so that there is no net ethylene consumption in the process, i.e., the amount of ethylene fed to the conventional metathesis reactor is the same as the ethylene produced in the cracker. Additionally, as in Example 3, about 50% of the isobutene in the raffinate is allowed to pass through to the conventional metathesis reactor 18. The details and results of the simulation are given in Table 8. The propylene produced is 83.3 kg/h, resulting from conventional metathesis and cracking.
While Example 4 results in a lower propylene production, Example 4 provides the advantage of operating without the need for an ethylene feed stream and with less stringent isobutylene separation specifications. Examples 3 and 4 illustrate the flexibility of processes according to embodiments disclosed herein to accommodate varied feed requirements suitable for both integrated and non-integrated refiners.
Simulations are performed for a stand-alone cracker, similar to that illustrated in
The feed to cracker 500 is fed via flow line 502, where effluent 504 is calculated as described above. The resulting effluent 504 is then separated to produce a C2/C3 fraction 506, a C4-C6 fraction 508, and an aromatics fraction 510. A portion of the C4-C6 fraction may be purged via flow line 512. The results of the simulations of the above feeds a-d are given in Table 9.
The results show that the propylene production rates from the different olefins are very similar. A significant difference in each of the cracker cases is that the cracker recycle rates are substantial. In each of cases a-d, the cracker recycle rate is about 3.9 times the feed flow rate. In contrast, the recycle rates for processes according to embodiments disclosed herein, such as shown by Examples 1-4 show cracker recycle rates of 8-52 kg/h, ranging from 2-13% the recycle of Comparative Examples 2a-2d.
A process similar to that illustrated in
As described above, embodiments disclosed herein provide for the integrated metathesis and cracking of C4-C6 feeds. Integration of the cracker into the metathesis process clearly shows a propylene yield advantage. Other advantages have also been recognized utilizing process variations, where the flexibility of the processes disclosed herein may provide significant cost advantages for refiners having a limited ethylene supply. Additionally, processes according to embodiments disclosed herein may allow for the production of high purity propylene from C4 olefins at low cost and low energy consumption.
While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.
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