Provided is a high density multimodal polyethylene, having a shear ratio (SR) of 18 or more and a HLMI of 15 g/10 mins or less comprising at least 20% by weight of a high molecular weight fraction, which high molecular weight fraction has:

The present invention is concerned with high density multimodal polyethylenes, methods for their production and uses thereof. In particular the invention relates to high density multimodal polyethylenes having especially superior stress-crack resistance. These polyethylenes can be used in polyethylene pipes to increase their stress-crack resistance making them suitable for use in no-sand pipe installation.
Polyolefins such as polyethylenes which have high molecular weight generally have improved mechanical properties over their lower molecular weight counterparts. However, high molecular weight polyolefins can be difficult to process and can be costly to produce. Polyolefins having a multimodal molecular weight distribution (MWD) are desirable because they can combine the advantageous mechanical properties of high molecular weight fraction with the improved processing properties of one or more lower molecular weight fractions.
For many high density polyethylene (HDPE) applications, polyethylene with enhanced toughness, strength and environmental stress cracking resistance (ESCR) is important. These enhanced properties are more readily attainable with high molecular weight (HMW) polyethylene. However, as the molecular weight of the polymer increases, the processibility of the resin decreases. By providing a polymer with a broad or bimodal MWD, the desired properties that are characteristic of high molecular weight resin are retained while processibility, particularly extrudibility, is improved.
There are several methods for the production of multimodal or broad molecular weight distribution resins: melt blending, reactor in series configuration, or single reactor with dual site catalysts. Use of a dual site catalyst for the production of a bimodal resin in a single reactor is also known.
Chromium catalysts for use in polyolefin production tend to broaden the molecular weight distribution and can in some cases produce bimodal molecular weight distribution but usually the low molecular part of these resins contains a substantial amount of the co-monomer. Whilst a broadened molecular weight distribution provides acceptable processing properties, a bimodal molecular weight distribution can provide excellent properties.
Ziegler-Natta catalysts are known to be capable of producing bimodal polyethylene using two reactors in series. Typically, in a first reactor, a low molecular weight homopolymer is formed by reaction between hydrogen and ethylene in the presence of the Ziegler-Natta catalyst. It is essential that excess hydrogen be used in this process and, as a result, it is necessary to remove all the hydrogen from the first reactor before the products are passed to the second reactor. In the second reactor, a copolymer of ethylene and hexene is made so as to produce a high molecular weight polyethylene.
Metallocene catalysts are also known in the production of polyolefins. For example, EP-A-0619325 describes a process for preparing polyolefins such as polyethylenes having a multimodal or at least bimodal molecular weight distribution. In this process, a catalyst system which includes at least two metallocenes is employed. The metallocenes used are, for example, a bis(cyclopentadienyl) zirconium dichloride and an ethylene-bis(indenyl) zirconium dichloride. By using the two different metallocene catalysts in the same reactor, a molecular weight distribution is obtained, which is at least bimodal.
Polyethylene resins are known for the production of pipes. Pipe resins require high resistance against slow crack growth as well as resistance to rapid crack propagation yielding impact toughness. However, there is a need to improve in the performance of currently available pipe resins.
Methods are known for producing an improved pipe resin by employing specific catalysts belonging to the general types discussed above, to produce a high molecular weight linear low density polyethylene fraction having a narrow MWD.
However, it is still necessary to produce a polyethylene that can be used in a pipe to increase the stress-crack resistance of the pipe sufficiently to render it suitable for use in no-sand pipe installation. Pipes for no-sand pipe installation require especially high stress-crack resistance, since their surfaces are not shielded from abrasive rock and earth surfaces by a layer of sand, but instead are directly in contact with the rock and/or earth.
It is known to use conventional cross-linked polyethylene for no-sand installable pipes. However, cross-linked polyethylene is very expensive (considerably more expensive than non-crosslinked PE). In addition, large diameter pipes formed from cross-linked PE are not available and it is not possible to join such pipes by butt-fusion. These characteristics of cross-linked polyethylene are discussed in xe2x80x9cThe creep behaviour of polyethylene under the influence of local stress concentrationsxe2x80x9d, 3R international 34, volume 10-11, 1995, pages 573-579. In this document, cross-linked polyethylene (PE-X) having a full notch creep test value of 5100 hrs is disclosed (FIG. 12). Problems in welding PE-X are discussed in xe2x80x9cLong term durability of welds involving cross-linked and non cross-linked polyethylenexe2x80x9d 3R international 37, volume 10-11, 1995, pages 694-699.
It is also known to provide a protective layer around conventional non-crosslinked PE to render it suitable for use in no-sand installation pipes. This also increases the cost considerably and has the disadvantage that the outer layer needs to be peeled off for welding, making installation laborious and expensive. The characteristics and problems associated with these materials are discussed in detail in the published newsletter of Werner Strumann GmbH and Co., October 1997, pages 1-3.
U.S. Pat. No. 5,405,901 discloses the production of polyethylene blends in gas phase using two reactors for the production of films. A low density resin is produced in the first reactor and a high density resin is produced in the second reactor. There is no disclosure of the production of a polyethylene blend having properties required by pipes, in particular pipes having stress crack resistance.
U.S. Pat. No. 5,284,613 discloses the production of bimodal molecular weight polyethylene resins containing two fractions of different molecular weight for the production of blown films exhibiting improved machine direction/transverse direction tear balance. Again, there is no disclosure of the production of polyethylene pipe resins, in particular having improved stress-crack resistance.
EP-A-0533154 discloses the production of ethylene polymer blends of a virgin or recycled low molecular weight ethylene polymer produced from a chromium-based catalyst and a high molecular weight ethylene polymer produced from a titanium-based catalyst. It is disclosed that the blends may be used for bottle, film, pipe and/or drum applications. However, the resins disclosed therein do not exhibit superior stress-crack resistance required by the art.
U.S. Pat. No. 4,547,551 discloses the production of ethylene polymer blends of high molecular weight and low molecular weight ethylene polymer, with the resins being useful for the manufacture of film or in blow moulding techniques, the production of pipes, and wire coating. There is no disclosure of the provision of pipe resins having enhanced stress crack resistance.
It is an object of the present invention to overcome the problems of the above prior art and to provide a polyethylene suitable for use in a pipe that can be laid in a no-sand installation method. Accordingly, the present invention provides a high density multimodal polyethylene, having a shear ratio (SR) of 18 or more and comprising at least 20% by weight of a high molecular weight fraction, which high molecular weight fraction has:
(a) a density (xcfx81) of 0.930 g/cm3 or less; and
(b) a high load melt index (HLMI) of 0.30 g/10 mins or less.
The present invention further provides a method for the production of a high density multimodal polyethylene as defined above, which method comprises mixing a high molecular weight polyethylene fraction as defined above with one or more lower molecular weight fractions.
Further provided is a polyethylene pipe comprising a high density multimodal polyethylene as defined above. The invention also provides a polyethylene pipe comprising a high density multimodal polyethylene having a high molecular weight fraction, which high molecular weight fraction has a density (xcfx81) and a high load melt index (HLMI), which satisfy the following relationship:
xcfx81xc3x97HLMIxe2x89xa60.37
wherein the units of density are g/cm3 and the units of HLMI are g/10 mins, and the density is 0.930 g/cm3 or less.
Further provided is a method of pipe installation comprising forming a hole or trench for receiving a pipe and installing a polyethylene pipe as defined above in the hole or trench. The invention also provides a method of re-lining a pipe comprising installing a polyethylene pipe as defined above in an existing pipe.
Additionally, the present invention provides use of a high density multimodal polyethylene comprising a high molecular weight fraction, which high molecular weight fraction has a density (xcfx81) and a high load melt index (HLMI), which satisfy the following relationship:
xcfx81xc3x97HLMIxe2x89xa60.37
wherein the units of density are g/cm3 and the units of HLMI are g/10 mins, wherein the high density multimodal polyethylene comprises at least 20% by weight of the high molecular weight fraction and the density (xcfx81) is 0.930 g/cm3 or less and the high load melt index (HLMI) is 0.40 g/10 mins or less, in a polyethylene article to provide the article with resistance to stress-cracking.
By virtue of the careful control of the density, the HLMI and the SR value of the high molecular weight fraction of multimodal polyethylene, polyethylene can be produced which has stress crack resistance superior to known polyethylene. The superior mechanical properties of the present polyethylene enable it to be used in pipes for no-sand installation.
In conventional pipe installation, a sand bed is employed on which the polyethylene pipe sits, which sand bed protects the surface of the polyethylene pipe from the destructive mechanical forces applied to it by, for example, sharp rocks and stones in the surrounding earth. The use of sand requires an extra installation step and, when transportation and purchase costs for the sand are considered, the total cost of using sand amounts to approximately 10% of the total installation cost. Therefore, a further advantage of the present polyethylene and pipes is that they can afford a 10% reduction in pipe installation costs, whilst still providing superior mechanical properties.
The multimodal polyethylene of the present invention can be bimodal, trimodal or may have a larger number of fractions. The high molecular weight fraction can itself be multimodal, e.g. bimodal or trimodal. Thus, the high molecular weight fraction may include all of the fractions of the polyethylene except the lowest molecular weight fraction, or may include only the highest molecular weight fraction. Preferably the high molecular weight fraction is monomodal.
The high molecular weight fraction should have a density of 0.930 g/cm3 or less, an HLMI of 0.4 g/10 mins or less more preferably 0.3 g/10 mins or less and have an SR value of 18 or more. The HLMI is the high load melt index and is measured according to the procedures of ASTM D 1238 using a load of 21.6 kg at a temperature of 190xc2x0 C. Other related parameters include the MI-5 and MI-2, which are equivalent to the HLMI, except loads of 5 kg and 2.16 kg are used respectively. The SR value is a ratio of the HLMI and the MI-5 (SR-5). The HLMI of the high molecular weight fraction (HMWF) is preferably 0.30 g/10 mins or less and most preferably 0.25 g/10 mins or less. The density of the HMWF is preferably 0.928 g/cm3 or less, more preferably 0.925 g/cm3 or less and most preferably 0.923 g/cm3 or less. The SR value of the final polyethylene is 18 or more. Preferably the SR value of the polyethylene is 20 or more and most preferably from 25 to 35.
The proportion by weight of the HMWF is 20% or more relative to the total weight of polyethylene. Preferably the proportion of the HMWF is 45% or more, and may be 55% or more or 60% or more if required. The most preferred content is 45%-55%.
Typically the final polyethylene comprising both the HMWF and lower molecular weight fractions has a density of 0.955 g/cm3 or less, preferably 0.945 g/cm3 or less. Preferably the final polyethylene density is from 0.930-0.955 g/cm3.
The HLMI of the final polyethylene comprising both the HMWF and lower molecular weight fractions is 30 g/10 mins or less, typically 15 g/10 mins or less, and preferably from 5-10 g/10 mins.
The stress crack resistance of the polyethylene of the present invention can be graded with reference to the full notch creep test (FNCT) and/or the notch pipe test (NPT). It is preferred that the polyethylene of the present invention has a value of 2000 hrs or more, preferably 4000 hrs or more and most preferably 5000 hrs or more in a FNCT. In a further preferred embodiment the present polyethylene has a value of 5000 hrs or more, preferably 7000 hrs or more and most preferably 10000 hrs or more in a NPT. Generally, the lower the density and the HLMI of the high molecular weight fraction of the present polyethylenes, the more resilient these polyethylenes are in the FNCT and the NPT. In addition, the greater the proportion of the HMWF, the higher the FNCT and NPT times of the polyethylene will be.
The full notch creep test (FNCT) is used mainly in Europe by resin producers for development purposes. Depending on the selected test conditions, the rupture time can be strongly reduced, such that information can be obtained on highly resistant materials in a short time. The test equipment is simple, being the usual set-up for a tensile creep test. In the test, a sample is immersed in water or a specified surfactant solution at 80xc2x0 C. or 95xc2x0 C. A constant load is applied to the sample (a small barxe2x80x9410xc3x9710xc3x97100 mm) and the sample is notched on four sides perpendicularly to the stress direction. The time to rupture is recorded as a function of the applied stress. The test method has been standardised in Japan (JIS K 6774). With reference to the present invention, the conditions applied were:
a 10xc3x9710xc3x97100 mm bar sample notched on four sides with a razor blade to a depth of 1.6 mm was immersed in a solution of 2% by weight Arkopal(copyright) N-100 (Hoechst commercial product) at 95xc2x0 C. (xc2x10.5xc2x0 C.) and a constant stress load of 4.0 MPa applied based on the initial remaining cross section at the place where the notches were introduced.
The notch pipe test (NPT) was developed by British Gas and has been standardised as EN 33479. It is applicable to pipes with a wall thickness of 5 mm or more or a diameter of 63 mm or more. The pipe is mechanically notched and pressure tested at 80xc2x0 C. A hoop stress of 4.0 MPa is applied for PE 80 and of 4.6 MPa for PE 100 (based on the unnotched pipe). Four notches are machined at 90xc2x0 on the circumference of the pipe. The depth must be 20xc2x12% of the minimum wall thickness. The test conditions followed for the production of the present results were strictly according to the EN 33479. The pressure test method was carried out in accordance with ISO 1167.
The polyethylene of the present invention can be PE 100 or PE 80 and can be chemically or physically blended. A PE 100 is defined as a polyethylene which, when formed into a pipe and subjected to an internal pipe resistance test (measured according to ISO 1167) at 20xc2x0 C., has a stress of 10 MPa or greater when the internal pipe resistance test curve is extrapolated to 50 yrs. A PE 80 is defined in the same way, except it has a stress of between 8 and 10 MPa when the internal pipe resistance test curve is extrapolated to 50 yrs. The nature of the blending of the HMWF with the lower molecular weight fractions (LMWF) is not specifically limited by the choice of PE 100 or PE 80.
The polyethylene of the present invention is produced by a method which comprises mixing the high molecular weight polyethylene fraction with one or more lower molecular weight fractions. In one embodiment, the high molecular weight fraction is produced separately from the one or more lower molecular weight fractions, and said high and lower molecular weight fractions are then mixed together in a physical blending process. Alternatively, the high molecular weight fraction is produced in the presence of the one or more lower molecular weight fractions, or the one or more lower molecular weight fractions are produced in the presence of the high molecular weight fraction, such that said high and lower molecular weight fractions are mixed together in a chemical blending process.
In the case of chemical blending to form a bimodal polyethylene, the high (first) and low (second) molecular weight polyethylene fractions can be made in two serially connected reactors, or three serially connected reactors for making a polyethylene resin having a trimodal molecular weight distribution, in which a third polyethylene is chemically blended with the first and second polyethylenes. In an alternative arrangement, the first and second polyethylenes may be chemically blended as foresaid, and then physically blended with a third polyethylene to produce a trimodal molecular weight distribution. In further alternative arrangements, the polyethylene resin has a bimodal molecular weight distribution and is produced by physically blending the first and second polyethylenes together or alternatively the polyethylene resin has a trimodal molecular weight distribution and is produced by physically blending together the first, second and third polyethylenes. Alternatively, a trimodal PE may be produced in three reactors in series.
Exemplary processes and conditions for producing the multimodal polyethylene of the present invention will now be discussed. The methods for producing the present polyethylene are not particularly limited, provided that the density and HLMI of the HMWF are controlled within the limits discussed above, and the SR value of the final polyethylene is 18 or above. These values can be controlled by making appropriate alterations to the production conditions according to known standard procedures. However, in a preferred embodiment, the polyethylene of the present invention is formed by polymerising ethylene monomer in the presence of a catalyst. When producing the HMWF of the polyethylene, an alpha olefin co-monomer having from 3-10 carbon atoms, such as butene or hexene, is preferably also present. The HMWF and the LMWF can be produced in parallel reactors and then blended together (physical blending) or can be produced together in the same reactor, or in two or more reactors in series (chemical blending). The catalyst employed is preferably a metallocene, but chromium based catalysts and Ziegler-Natta catalysts can also be used.
A particularly preferred method for producing the present polyethylene comprises:
(i) contacting ethylene monomer and a co-monomer comprising an alpha-olefin having from 3 to 10 carbon atoms with a first catalyst system in a first reactor under first polymerisation conditions to produce a product comprising a first polyethylene having a first molecular weight and a first density and the first catalyst system comprising (a) a metallocene catalyst selected from one of components A or B, component A comprising a bis tetrahydroindenyl compound of the general formula (IndH4)2Rxe2x80x3MQ2 in which each Ind is the same or different and is indenyl or substituted indenyl, Rxe2x80x3 is a bridge which comprises a C1 -C20 alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine or amine radical, which bridge is substituted or unsubstituted, M is a Group IVB transition metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen and component B comprising a metallocene catalyst of general formula Rxe2x80x3(CpRm)(Cpxe2x80x2Rxe2x80x2n)MQ2, wherein Cp is a cyclopentadienyl moiety, Cpxe2x80x2 is a substituted or unsubstituted fluorenyl ring; each R is independently hydrogen or hydrocarbyl having 1 to 20 carbon atoms in which 0 m 4; each Rxe2x80x2 is independently hydrocarbyl having 1 to 20 carbon atoms in which 0 n 8; Rxe2x80x3, M and Q are each as defined above, the metallocene component B having a centroid-M-centroid angle in the range 105xc2x0 to 125xc2x0; and (b) a co-catalyst which activates the catalyst component;
(ii) providing a second polyethylene having a second lower molecular weight and higher density than the first polyethylene; and
(iii) mixing together the first and second polyethylenes to form a polyethylene resin having a multimodal molecular weight distribution.
In the above method, the first polyethylene may be monomodal or bimodal, the second polyethylene may have a monomodal molecular weight distribution and may have been produced using a metallocene catalyst, a Ziegler-Natta catalyst or a chromium-oxide based catalyst. Alternatively, the second polyethylene may have a bimodal molecular weight distribution and has been produced using one or two of those different catalyst systems. The first and second polyethylenes may be mixed together with a third polyethylene to provide a trimodal molecular weight distribution in the resultant polyethylene resin. The third polyethylene may be produced using a metallocene catalyst, a Ziegler-Natta catalyst or a chromium-oxide based catalyst.
When the metallocene catalyst is catalyst A, each bis tetrahydroindenyl compound may be substituted in the same way or differently from one another at one or more positions in the cyclopentadienyl ring, the cyclohexenyl ring and the ethylene bridge. Each substituent group may be independently chosen from those of formula XRv in which X is chosen from group IVA, oxygen and nitrogen and each R is the same or different and chosen from hydrogen or hydrocarbyl of from 1 to 20 carbon atoms and v+1 is the valence of X. X is preferably C. If the cyclopentadienyl ring is substituted, its substituent groups must not be so bulky as to affect co-ordination of the olefin monomer to the metal M. Substituents on the cyclopentadienyl ring preferably have R as hydrogen or CH3. More preferably, at least one and most preferably both cyclopentadienyl rings are unsubstituted.
In a particularly preferred embodiment, both indenyls are unsubstituted.
Rxe2x80x3 is preferably a methylene or ethylene bridge which is substituted or unsubstituted.
The metal M is preferably zirconium, hafnium or titanium, most preferably zirconium. Each Q is the same or different and may be a hydrocarbyl or hydrocarboxy radical having 1-20 carbon atoms or a halogen. Suitable hydrocarbyls include aryl, alkyl, alkenyl, alkylaryl or aryl alkyl. Each Q is preferably halogen. Ethylene bis(4,5,6,7-tetrahydro- 1 -indenyl) zirconium dichloride is a particularly preferred bis tetrahydroindenyl compound used in the present invention.
The metallocene catalyst component A used in the present invention can be prepared by any known method. A preferred preparation method is described in J. Org. Chem. 288, 63-67 (1985).
When the metallocene catalyst is catalyst B, decreasing the centroid-M-centroid angle in Zr-based metallocenes of catalyst B tends to increase both the long chain branching and the co-monomer incorporation of the metallocene catalyst when used for the production of polyolefins. The metallocene catalysts B of the present invention have a very open structure which permits the facile incorporation of co-monomer with larger substituents such as hexene in polyolefin production. In this way, PE with densities around 0.9 or lower may be produced at a commercially acceptable polymerisation temperature in a slurry process. The production of PE with such low densities has hitherto not been possible with Cr-based and closed structure Cent-Zr-Cent ( greater than 125xc2x0) metallocenes in a loop slurry process. Lower co-monomer concentrations need be used in the process thereby reducing the likelihood of reactor fouling and avoiding excessive use of expensive co-monomer.
Preferably Cp is a substituent cyclopentadienyl in which each R is independently XR*3 in which X is C or Si and each R* is independently H or hydrocarbyl having 1 to 20 carbon atoms. More preferably the cyclopentadienyl is substituted with Ph2CH, Me3C, Me3Si, Me, Me and Me3C,Me and SiMe3, Me and Ph, or Me and CH3xe2x80x94CHxe2x80x94CH3.
Preferably, each Rxe2x80x3 is independently YRxe2x80x2xe2x80x33 in which Y is C or Si and each Rxe2x80x2xe2x80x3 is independently H or hydrocarbyl having 1 to 20 carbon atoms.
The structural bridge Rxe2x80x3 is generally an alkylene radical having 1 to 20 carbon atoms, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, preferably Mexe2x80x94Cxe2x80x94Me, Phxe2x80x94Cxe2x80x94Ph,xe2x80x94CH2xe2x80x94, Etxe2x80x94Cxe2x80x94Et, Mexe2x80x94Sixe2x80x94Me, Phxe2x80x94Sixe2x80x94Ph or Etxe2x80x94Sixe2x80x94Et.
The metal M is preferably Zr or Hf and each Q is preferably C1.
In order to maximise co-monomer incorporation, it is preferred that the centroid-M-centroid angle is no more than 119xc2x0.
The co-catalyst which activates the metallocene catalyst component can be any co-catalyst known for this purpose such as an aluminium-containing co-catalyst or a boron-containing co-catalyst. The aluminium-containing co-catalyst may comprise an alumoxane, an alkyl aluminium and/or a Lewis acid.
The alumoxanes used in the process of the present invention are well known and preferably comprise oligomeric linear and/or cyclic alkyl alumoxanes represented by the formula:
for oligomeric, linear alumoxanes and
for oligomeric, cyclic alumoxane,
wherein n is 1-40, preferably 10-20, m is 3-40, preferably 3-20 and R is a C1-C8 alkyl group and preferably methyl.
Generally, in the preparation of alumoxanes from, for example, aluminium trimethyl and water, a mixture of linear and cyclic compounds is obtained.
Suitable boron-containing co-catalysts may comprise a triphenylcarbenium boronate such as tetrakis-pentafluorophenyl-borato-triphenylcarbenium as described in EP-A-0427696, or those of the general formula [Lxe2x80x2xe2x80x94H]+[B Ar1 Ar2 X3 X4]xe2x80x94 as described in EP-A-0277004 (page 6, line 30 to page 7, line 7).
The metallocene catalyst system may be employed in a solution polymerisation process, which is homogeneous, or a slurry process, which is heterogeneous. In a solution process, typical solvents include hydrocarbons with 4 to 7 carbon atoms such as heptane, toluene or cyclohexane. In a slurry process it is necessary to immobilise the catalyst system on an inert support, particularly a porous solid support such as talc, inorganic oxides and resinous support materials such as polyolefin. Preferably, the support material is an inorganic oxide in if its finally divided form.
Suitable inorganic oxide materials which are desirably employed in accordance with this invention include Group 2a, 3a, 4a or 4b metal oxides such as silica, alumina and mixtures thereof. Other inorganic oxides that may be employed either alone or in combination with the silica, or alumina are magnesia, titania, zirconia, and the like. Other suitable support materials, however, can be employed, for example, finely divided functionalised polyolefins such as finely divided polyethylene. Preferably, the support is a silica having a surface area comprised between 200 and 900 m2/g and a pore volume comprised between 0.5 and 4 ml/g.
The amount of alumoxane and metallocenes usefully employed in the preparation of the solid support catalyst can vary over a wide range. Preferably the aluminium to transition metal mole ratio is in the range between 1:1 and 100: 1, preferably in the range 5:1 and 50:1.
The order of addition of the metallocenes and alumoxane to the support material can vary. In accordance with a preferred embodiment of the present invention alumoxane dissolved in a suitable inert hydrocarbon solvent is added to the support material slurried in the same or other suitable hydrocarbon liquid and thereafter a mixture of the metallocene catalyst component is added to the slurry.
Preferred solvents include mineral oils and the various hydrocarbons which are liquid at reaction temperature and which do not react with the individual ingredients. Illustrative, examples of the useful solvents include the alkanes such as pentane, iso-pentane, hexane, heptane, octane and nonane; cycloalkanes such as cyclopentane and cyclohexane; and aromatics such as benzene, toluene, ethylbenzene and diethylbenzene.
Preferably the support material is slurried in toluene and the metallocene and alumoxane are dissolved in toluene prior to addition to the support material.
Where the reaction is perfonned in a slurry using, for example, isobutane, a reaction temperature in the range 70xc2x0 C. to 110xc2x0 C. may be used. Where the reaction is performed in solution, by selection of a suitable solvent a reaction temperature in the range 150xc2x0 C. to 300xc2x0 C. may be used. The reaction may also be performed in the gas phase using a suitably supported catalyst.
In accordance with the invention, ethylene and the alpha-olefinic co-monomer are supplied to the reactor containing the metallocene catalyst. Typical co-monomers include hexene, butene, octene or methylpentene, preferably hexene. Hydrogen may be additionally supplied to the first reaction zone. Because the metallocene catalyst component used in the present invention exhibits good co-monomer response as well as good hydrogen response, substantially all of the co-monomer is consumed in the first reactor in this embodiment. This produces high molecular weight polyethylene copolymer having a monomodal molecular weight distribution.
The temperature of the reactor may be in the range of from 70xc2x0 C. to 110xc2x0 C., preferably from 70xc2x0 C. to 100xc2x0 C.


A container for disks having a central opening includes a case having hingedly connected lid, spine, and base portions, a pedestal projecting forwardly from a panel portion of the base for holding one of the disks, and a hinge structure projecting forwardly from the base for pivotally supporting one or more trays holding additional disks. The hinge structure includes a spaced pair of posts, each post having a spaced pair of leaf members and a reinforcing bridge connecting inwardly facing tips of the leaf members, for snap engagement with pairs of inwardly facing stub journals that are formed on the trays. The case has a closed position with the lid and base portions snaped together, each having a compact recessed overhanging lip formation opposite the spine portion for facilitating opening of the case.

The present invention relates to optical data disks such as compact disks (CDs) and video disks (DVDs) that have central circular locating openings, and more particularly to devices for protectively enclosing such disks for storage of same.
Data disks such as compact disks and video disks typically have large amounts of digitally stored information that is optically readable through a transparent bottom layer of the disk by a movable head during rotation of the disk. The information is arranged in one or more tracks that are covered by a thin.protective top layer of the disk that can have labeling applied thereto such as by silkscreening. Normal handling of the disk can result in scratching of the bottom layer, resulting in loss of data by interference with the optical path such as by loss of focus and/or lateral image displacement. Also, data can be lost by scratching of the protective layer which is typically very thin, on the order of 20 microns, resulting in removal of information from a vapor deposited metal layer that is only about 0.1 micron thick. Protective containers for the disks in common use have a central pedestal for supportively gripping the disc by engaging the central opening without contacting either side of the disk within data-containing regions thereof. Such containers may have a ledge for contacting portions of an outer perimeter of the disk for stabilizing the disk against tipping on the pedestal. The disk is loaded into the container by lowering it onto the pedestal while gripping opposite perimeter portions, engagement with the pedestal being typically effected by simultaneous finger pressure against the disk proximate the central opening. Removal of the disk is similarly effected by finger pressure against the pedestal, and simultaneous lifting at the perimeter portions.
One class of containers, known as xe2x80x9cjewel boxesxe2x80x9d have a clear plastic body and a pivotally connected clear plastic lid, an insert member fitting within the body and being formed with the various disk-contacting surfaces and associated members. Another class of containers has the body and lid integrally formed and pivotally joined along opposite edges of a narrow, generally rectangular spine member, with disk-supporting structure integrally formed in the body, such containers referred to as xe2x80x9cDVD.boxesxe2x80x9d being somewhat oversize as compared with the jewel boxes. These boxes have an important advantage of being less expensive to provide than jewel boxes.
It is also known to provide disk containers with an interior partition for storage and access of a pair of disks. In a typical configuration, such containers include a partition portion having disk retainers on opposite sides and a pair of transparent lids that are pivotally connected at respective opposite sides along opposite end edges of the partition portion. Unfortunately, the dual-disk storage boxes of the prior art are excessively expensive to provide in that they are significantly more complex and tooling costs must be amortized over much smaller quantities of production. There are also containers for three disks, wherein one disk is supported in a fixed position relative to the container body, and a pair of disks are supported on opposite sides of a hinged tray. One such example is configured as a DVD box, with the tray having a hinged connection to the spine member. A particular disadvantage of this arrangement is that the tray slides laterally relative to the body as the lid is opened because the spine member pivots relative to the body as the lid is opened. This sliding movement is objectionable in that damage to one or more disks can occur by scratching. A further objection is that the sliding movement produces vibration and jarring which has a tendency to dislodge disks out of engagement with supporting structure, with a consequent likelihood of being dropped as the container is opened. Compounding this problem is the fact that the one-piece DVD box configuration typically has snap-together structure for holding such boxes closed, and opening of those cases is somewhat difficult because there is little room for finger depressions that are gripped during opening of the boxes, particularly in view of extra space required inside the boxes for clearing the trays, the DVD box configuration having somewhat restrictive standard outside dimensions. The shallow finger depressions of the prior art are also an impediment to automated loading of disks into the containers in that they are particularly difficult to grip for opening by machines.
Another problem associated with multiple disk storage containers is that separate tooling and parts inventory are required for containers holding each number of disks, and a container for a particular number of disks cannot ordinarily be converted for holding a greater number of disks.
Thus there is a need for a protective disk container that has an integrally formed enclosure, that can be inexpensively converted for multiple disk storage, and that otherwise overcomes the disadvantages of the prior art.
The present invention meets this need by providing a molded disk container that accommodates multiple disk trays without subjecting the trays or disks held in the container to sliding contact during opening and closing of the container. In one aspect of the invention, a disk container includes a case having base, lid, and spine portions, the base portion including a base panel portion, a forwardly projecting base pedestal for retaining a first disk, and a hinge structure connected to the base portion for engaging and pivotably supporting a tray holding a second disk, the hinge structure projecting forwardly from the base portion and hinged connections of the base and lid portions to the spine portion being spaced sufficiently to allow the closed condition of the case with the first disk being retained on the base pedestal and the tray engaging the hinge structure while holding the second disk. The container can be in combination with the tray, the tray including a tray panel portion and a tray pedestal projecting from a first side thereof for retaining the second disk. Preferably the tray has a first spacer structure on the first side of the tray panel portion for preventing contact between the case and the second disk when the case is in the closed condition and the tray is engaging the hinge structure. The tray pedestal can be double sided for supporting a third disk on a second side of the tray panel portion, a second spacer structure on the second side of the tray panel portion preventing contact between the case and the third disk when the case is in the closed condition thereof. Preferably the case has a shroud formation for preventing contact between the tray and the first disk.
Preferably the hinge structure is configured for receiving plural counterparts of the tray. Also, the container can be in combination with at least two of the trays. The container can be assembled with three of the trays pivotally engaging the hinge structure.
The base portion of the case can include a shroud formation for protecting an edge portion of the disk, with a pair of finger depressions formed therein on opposite sides of the pedestal for permitting the disk to be gripped by a user""s fingers when the disk is engaging the pedestal.
The lid portion of the case can include a lid panel portion, with side wall portions of the case in combination with the spine portion forming an enclosure in a releasably held closed condition of the case, a side wall portion opposite the spine portion being inwardly displaced from perimeter extremities of the base and lid panel portions in the closed condition to form respective lips in the base and lid portions for facilitating opening of the case, the lips being hook-shaped in cross-section and projecting toward each other for further facilitating opening of the case. The side wall portions can be formed on each of the base and lid portions, respective lip extremities of the side wall portions being in overlapping relation in the closed condition of the case. The respective portions of the lip extremities are preferably formed on corresponding inwardly displaced side wall portions opposite the spine portion, with mating registration tabs on the side wall portions within the inwardly displaced side wall portions.


A method for fracturing subterranean formations surrounding oil and gas wells using a fracturing fluid consisting of a foam constituted by a liquid phase and a gaseous phase. The liquid phase has a foam forming substance dissolved therein. The foam forming substance is preferably a surfactant such as a non-ionic hydrofluoroether surfactant. The liquid phase is preferably CO2 and the gaseous phase N2.

The present invention relates to the field of fracturing subterranean formations around oil and gas wells. In particular, the present invention relates to an improvement in fracturing using liquid CO2 as a fracturing medium.
Hydraulic fracturing has been widely used for stimulating the production of crude oil and natural gas from wells completed in reservoirs of low permeability. Methods employed normally require the injection of a fracturing fluid containing suspended propping agents into a well at a rate sufficient to open a fracture in the exposed formation. Continued pumping of fluid into the well at a high rate extends the fracture and leads to the build up of a bed of propping agent particles between the fracture walls. These particles prevent complete closure of the fracture as the fluid subsequently leaks off into the adjacent formations and results in a permeable channel extending from the well bore into the formations. The conductivity of this channel depends upon the fracture dimensions, the size of the propping agent particles, the particle spacing and the confining pressures.
The fluids used in hydraulic fracturing operations must have fluid loss values sufficiently low to permit build up and maintenance of the required pressures at reasonable injection rates. This normally requires that such fluids either have adequate viscosities or other fluid loss control properties which will reduce leak-off from the fracture into the pores of the formation.
Fracturing of low permeability reservoirs has always presented the problem of fluid compatibility with the formation core and formation fluids, particularly in gas wells. For example, many formations contain clays which swell when contacted by aqueous fluids causing restricted permeability, and it is not uncommon to see reduced flow through has well cores tested with various oils.
Another problem encountered in fracturing operations is the difficulty of total recovery of the fracturing fluid. Fluids left in the reservoir rock as immobile residual fluids impede the flow of reservoir gas or fluids to the extent that the benefit of fracturing is decreased or eliminated. Attempting the removal of the fracturing fluid may require a large amount of energy and time, sometimes not completely recovering all the products due to formation characteristics. Consequently the reduction or elimination of the problem of fluid recovery and residue removal is highly desired.
In attempting to overcome fluid loss problems, gelled fluids prepared with water, diesel, methyl alcohol, solvents and similar low viscosity liquids have been useful. Such fluids have apparent viscosities high enough to support the proppant materials without settling and also high enough to prevent excessive leak-off during injection. The gelling agents also promote laminar flow under conditions where turbulent flow would otherwise take place and hence in some cases, the pressure losses due to fluid friction may be lower than those obtained with low viscosity-base fluids containing no additives. Certain water-soluble, poly-acrylamides, oil soluble poly-isobutylene and other polymers which have little effect on viscosity when used in low concentration can be added to the ungelled fluid to achieve good friction reduction.
In attempting to overcome the problem of fluid compatibility when aqueous fracturing fluids are used, chemical additives have been used such as salt or chemicals for pH control. Salts such as NaCl, KCl or CaCl2 have been widely used in aqueous systems to reduce potential damage when fracturing water sensitive formations. Where hydrocarbons are used, light products such as yelled condensate have seen a wide decree of success, but are restricted in use due to the nature of certain low permeability reservoirs.
Low density vases such as CO2 or N2 have been used in attempting to overcome the problem of removing the fracturing (load) liquid. The low density cases are added to the load fluid at a calculated ratio which promotes back flow subsequent to fracturing. This back flow of load fluids is usually due to reservoir pressure alone without mechanical aid from the surface because of the reduction of hydrostatic head caused by gasifying the liquid.
Moreover, low density liquefied gases have themselves been used as fracturing fluids. Reference is made to Canadian Patents 687,938 and 745,453 to Peterson who discloses a method and apparatus for fracturing underground earth formations using liquid CO2. Peterson recognized the advantages of liquid CO2 as a means to avoid time consuming and expensive procedures involved in the recovery of more conventional fracturing fluids. Peterson however does not disclose the use of entrained proppants in conjunction with liquid CO2. The combination of a liquid CO2 fracturing fluid and propping agents has been described by Bullen in Canadian Patent 932,655 wherein there is described a method of entraining proppants in a gelled fluid, typically a gelled methanol, which is mixed with liquid carbon dioxide and injected into low permeability formations. The liquid carbon dioxide is allowed to volatilize and bleed off and the residual liquid, primarily methyl alcohol, is in part dissolved by formation hydrocarbons and allowed to return to the surface as vapor. The balance, however, is recovered as a liquid using known recovery techniques. It has, however, been demonstrated that the need to use a galled carrier fluid has resulted in the negation of some of the fluid recovery advantages attendant upon the sole use of liquefied gas fracturing fluids.
Subsequent disclosures have been concerned primarily with the development of more advantageous gelled fluids to entrain proppants for subsequent or simultaneous blending with the liquefied carbon dioxide fracturing fluid. Reference is made to Canadian Patents 1,000,483 (reissued as Canadian Patent 1,034,363), 1,043,091, 1,197,977, 1,241,826 and 1,242,389 in this regard. Each of these patents teaches the nature and composition of gelled or ungelled carrier fluids, typically methanol or water based, which, when blended with liquid CO2 produce a two-phase liquid system which allegedly is useful in attempting to overcome the problems of leak-off and fluid compatibility with formation fluids while at the same time beings capable of transporting increased concentrations of proppant material into the fracture zones.
Treatments have also been designed utilizing, combinations of fluids with nitrogen or carbon dioxide and even binary foams where nitrogen and liquid carbon dioxide are combined into an aqueous or water-based fracturing fluid. Reference is made in this regard to U.S. Pat. No. 5,069,283 issued on Dec. 3, 1991 to the Western Company of North America. The addition of nitrogen and/or liquid carbon dioxide provides a non-combustible gas that aids in the recovery of the treatment fluids. These gasified fluids also reduce the amount of potentially damaging aqueous fluid pumped into the formation. Despite this, this method nevertheless requires the incorporation of a thickening agent into an aqueous fluid to provide sufficient viscosity to entrain adequate proppants and to prevent leak-off. Although these gasified fluids reduce the amount of potentially damaging gelled and/or cross-linked load fluid pumped into the formation, the risk of contamination by significant residual liquid fractions remain high.
From the foregoing, it will be readily appreciated that the use of liquid CO2 as a fracturing agent is known. It is further known to use other liquids having propping agents entrained therein for blending with the liquefied gas fracturing fluid. The propping agents are subsequently deposited in the liquid or foam-formed fractures for the purpose of maintaining flow passages upon rebound of the fracture zone. It is further known that proppant materials can be introduced into a liquid carbon dioxide system if a chemically gelled or cross-linked liquid, usually alcohol or water-based, is mixed with the CO2 to impart sufficient viscosity to the mixture to support proppant particles and to control leak-off in the fracture. So-called xe2x80x9cbinaryxe2x80x9d systems incorporating additional quantities of nitrogen in a thickened aqueous substrate are known. All of these practices lead to residual chemicals and gel precipitates left in the fracture proppant pack that can impair production of the well.
In Canadian Patent 1,134,258, it has been recognized that proppant materials can be introduced directly into a liquid carbon dioxide stream using little or no other viscosifying liquid components while still transporting significant quantities (up to 800 kg/m3 and more in some situations) of proppant material into the fracture zones. This has been achieved by pressurizing and cooling the proppants to substantially the storage pressure and temperature of the liquefied CO2 prior to blending of the trio for injection down the well bore.
This method, based as it is on the injection of pure or virtually pure CON, enjoys the obvious advantage of lessening the impact of the treatment fluid on the formation. A gas as mentioned in this application describes any substance that at atmospheric conditions exists in the vapour phase of that substance. Liquid CO2, and gases such as nitrogen, air, exhaust gas, natural as and inert gases, are all relatively inert to the formation being stimulated and therefore no damage is done to the formation due to injection since it is believed that CO2 and the other aforementioned gases do not change the relative permeability of the reservoir rock. The liquid CO2 fracturing medium converts to a gaseous state after being subjected to formation temperatures and pressures to eliminate associated fluid pore blockage in the formation and to promote complete fluid recovery on flow back. Moreover, no residual chemicals or gel precipitates are left behind to impair fracture conductivity.
Moreover, as demonstrated in U.S. Pat. No. 5,558,160, significant advantages can be obtained from combining gases, in particular N2, with liquid CO2. In particular, liquid CO2/N2 treatment pressures at equivalent volumetric rates.
The applicant has now discovered that significant viscosity increases in a liquid CO2 fracturing fluid system can be obtained by introducing a foamer or surfactant into the liquid CO2, and then bubbling N2 into the CO2. This results in a viscous foam with N2(g) as the internal phase. CO2(l) as the external phase, and the foamer or surfactant as the interface between the phases.
The object of the present invention is to provide a method of fracturing subterranean formations surrounding oil and gas wells comprising injecting into said wells a liquid CO2 fracturing fluid With higher viscosity than currently available.
A further object of the present invention is to provide a method of fracturing subterranean formations surrounding oil and gas wells using a fracturing fluid comprising foam of N2(g) in CO2(l) in which a foam forming substance has been dissolved.
A further object of the present invention is to provide a method of fracturing subterranean formations surrounding oil and gas wells using a liquid CO2 fracturing fluid capable of creating a wide fracture.
A further object of the present invention is to provide method of fracturing subterranean formations surrounding oil and gas wells using a liquid CO2 fracturing fluid capable of transporting a large proppant load.
A further object of the present invention is to provide a method of fracturing subterranean formations surrounding oil and gas wells using a liquid CO2 fracturing fluid capable of controlled leak off into a formation.
In a broad aspect, then, the present invention relates to a method of fracturing subterranean formations surrounding oil and gas wells using a foam constituted by a liquid phase and a gaseous phase, said liquid phase hog a non-functional, nonionic fluorochemical stabilizer dissolved therein.
In furtherance of the present invention, a foam forming substance that is soluble in liquid or supercritical CO2 is added to CO2 in modest volume (about 1-30, preferably 2-20 more preferably about 10 L/m3). Nitrogen is then bubbled into the liquid, to create a foam useful in the method of the present invention. The proportion of gaseous phase in the liquefied CO2 is from about 1 to 75 weight %.
The foam forming substance useful in the method of the present invention is a fluorochemical stabilizer comprising a nonionic, fluorinated hydrocarbon that may be linear, branched, or cyclic, and optionally may contain one or more additional catenary heteroatoms, such as nitrogen or oxygen. The stabilize may be selected from the group consisting of fully- and partially-fluorinated alkanes, amines, ethers, and aromatic compounds. Preferably, the fluorochemical stabilizer is non-functional, i.e. lacking functional groups that are polymerizable, reactive toward acids, bases, oxidizing agents, reducing agents or nucleophiles. Preferably, the number of fluorine atoms exceeds the number of hydrogen atoms in the fluorochemical stabilizer. To be non-flammable, the relationship between the number of fluorine, hydrogen, and carbon atoms can preferably be related in that the number of fluorine atoms is equal to or exceeds the sum of the number of number of hydrogen atoms and carbon-carbon bonds:
# F atomsxe2x89xa7(# H atoms+# Cxe2x80x94C bonds).
One class of compounds useful as fluorochemical stabilizers comprises perfluorocarbons in which all carbon-bound hydrogen is replaced by fluorine atoms. Such compounds are known to be inert and exhibit high thermal stability. Such perfluorinated compounds may include perfluoroalkanes, perfluoroamines and, perfluoroethers, which may be linear or branched, and cyclic or acyclic. Examples of perfluorinated compounds include perfluoroalkanes having the general formula CnF2n+2, perfluoroethers and polyethers having the general formula CnF2n+2Om and perfluoroamines having the general formula CnF2n+3N, where n is an integer of 3 to 20 and m is 1 to 5.
Useful perfluorinated liquids typically contain from 3 to 20 carbon atoms and may optionally contain one or more catenary heteroatoms, such as divalent oxygen or trivalent nitrogen atoms. The term xe2x80x9cperfluorinated liquidxe2x80x9d as used herein includes organic compounds in which all (or essentially all) of the hydrogen atoms are replaced with fluorine atoms. Representative perfluorinated liquids include cyclic and non-cyclic perfluoroalkanes, perfluoroamines, perfluoroethers, perfluorocycloamines, and any mixtures thereof. Specific representative perfluorinated liquids include the following: perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluoromethylcyclohexane, perfluorotributyl amine, perfluorotriamyl amine, perfluoro-N-methylmorpholine, perfluoro-N-ethylmorpholine, perfluoroisopropyl morpholine, perfluoro-N-methyl pyrrolidine, perfluoro-1,2-bis(trifluoromethyl)hexafluorocyclobutane, perfluoro-2-butyltetrahydrofuran, perfluorotriethylamine, perfluorodibutyl ether, and mixtures of these and other perfluorinated liquids.
Commercially available perfluorinated liquids that can be used in this invention include: FLUORINERT FC-43(trademark)-Electronic Fluid, FLUORINERT FC-72(trademark) Electronic Fluid, FLUORINERT FC-77(trademark) Electronic Fluid, FLUORINERT FC-48(trademark) Electronic Fluid, FLUORINERT FC-87(trademark) Electronic Fluid, Performance Fluid PF-5060(trademark), Performance Fluid PF-5070(trademark), and Performance Fluid PF-5052(trademark). Some of these liquids are described in FLUORINERT(trademark) Electronic Fluids, product bulletin 98-0211-6086(212)NPI, issued February, 1991, available from 3M Co., St. Paul. Minn. Other commercially available perfluorinated liquids that are considered useful in the present invention include perfluorinated liquids sold as GALDEN(trademark) LS fluids available from Montedison Inc., Italy, KRYTOX(trademark) fluids available from DuPont and FLUTEC(trademark) PP fluids available from BNFL Fluorochemicals Ltd.
Perfluorinated compounds are known and can be made by techniques such as direct fluorination, electrochemical fluorination, addition polymerization of fluorine-containing monomers and the oxidative polymerization of fluorine containing monomers. See, for example, Chemistry of Organic Fluorine Compounds II, M. Hudlicky and A. Pavlath, Eds., ACS Monograph 187, American Chemical Society, Washington, D.C., 1995, pp. 95-120.
It is preferred that the fluorochemical stabilizer contains aliphatic hydrogen atoms. Perfluorinated compounds, since they lack chlorine atoms, are not ozone-depleting agents, but these compounds may exhibit a global warming potential (GWP) due to their long atmospheric lifetimes. It is preferred that the fluorochemical stabilizer contains at least one aliphatic hydrogen atom in the molecule. These compounds generally are very thermally and chemically stable, yet are much more environmentally acceptable in that they degrade in the atmosphere and thus have a low global warming potential, in addition to a zero ozone depletion potential.
Partially fluorinated liquids, containing one or more aliphatic or aromatic hydrogen atoms, may be employed in the fluid compositions of the invention. Such liquids, like the above perfluorinated counterparts, typically contain from 3 to 20 carbon atoms and may optionally contain one or more catenary heteroatoms, such as divalent oxygen or trivalent nitrogen atoms. Useful partially fluorinated liquids include cyclic and non-cyclic fluorinated alkanes, amines, ethers, cycloamines, and any, mixture or mixtures thereof. Preferably, the number of fluorine atoms exceeds the number of hydrogen atoms and more preferably the number of fluorine atoms is equal to or exceeds the sum of the number of combined hydrogen atoms and carbon-carbon bonds. Although not preferred, due to environmental concerns, the partially fluorinated liquids optionally may contain one or more chlorine atoms provided that where such chlorine atoms are present there are at least two hydrogen atoms on the geminal or adjacent carbon atom(s).
One class of partially fluorinated liquids useful as fluorochemical stabilizers are hydrofluorocarbons: i.e. compounds having only carbon, hydrogen and fluorine, and optionally catenary divalent oxygen and/or trivalent nitrogen. Such compounds are nonionic, may be linear or branched, cyclic or acyclic. Such compounds are of the formula CnFmH2n+2xe2x88x92m, where n is from about 3 to 20 inclusive, m is at least one, and where one or more non-adjacent xe2x80x94CF2xe2x80x94 groups may be replaced with catenary oxygen or trivalent nitrogen atoms. Preferably the number of fluorine atoms is equal to or greater than the number of hydrogen atoms, and more preferably the number of fluorine atoms is equal to or exceeds the sum of the combined number of hydrogen atoms and carbon-carbon bonds of fluorine atoms.
Another useful class of partially fluorinated liquids includes fluoroalkyl-substituted aromatic compounds such as hexafluoroxylene.
A preferred class of hydrofluorocarbon liquids particularly useful to form the stable fluid composition of the invention comprises fluorinated ethers of the general formula:
(R1xe2x80x94O)nxe2x80x94R2xe2x80x83xe2x80x83(I)
where, in reference to Formula I, n is a number from 1 to 3 inclusive and R1 and R2 are the same or are different from one another and are selected from the group consisting of alkyl, aryl, and alkylaryl groups and their derivatives. At least one of R1 and R2 contains at least one fluorine atom, and at least one of R1 and R2 contains at least one hydrogen atom, R1 and R2 may also be linear, branched, cyclic or acyclic and optionally, one or both of R1 and R2 may contain one or more catenary heteroatoms, such as trivalent nitrogen or divalent oxygen. Preferably the number of fluorine atoms is equal to or greater than the number of hydrogen atoms, and more preferably the number of fluorine atoms is equal to or exceeds the sum of the number of combined number of hydrogen atoms and carbon-carbon bonds. Although not preferred, due to environmental concerns, R1 or R2 or both of them optionally may contain one or more chlorine atoms provided that where such chlorine atoms are present there are at least two hydrogen atoms on the R1 or R2 group on which they are present.
More preferably, the fluid compositions of the present invention are prepared with fluorinated ethers of the formula:
Rfxe2x80x94Oxe2x80x94Rxe2x80x83xe2x80x83(II)
where, in reference to Formula II above, Rf and R are as defined for R1 and R2 of Formula I, except that Rf contains at least one fluorine atom, and R contains no fluorine atoms. More preferably, R is an acyclic branched or straight chain alkyl group, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, i-butyl, or t-butyl, and Rf is preferably a fluorinated derivative of a cyclic or acyclic, branched or straight chain alkyl group having from 3 to about 14 carbon atoms, such as n-C4F9xe2x80x94, i-C4F9xe2x80x94, i-C3F7, (n-C3F7)CFxe2x80x94 or cyclo-C6F11xe2x80x94. Rf may optionally contain one or more catenary heteroatoms, such as trivalent nitrogen or divalent oxygen atoms.
In a preferred embodiment, R1 and R2, or Rf and R, are chosen so that the compound has at least three carbon atoms, and the total number of hydrogen atoms in the compound is at most equal to the number of fluorine atoms. In the most preferred embodiment. R1 and R2 or Rf and R are chosen so that the compound has at least three carbon atoms, and more preferably number of fluorine atoms is equal to or exceeds the sum of the number of combined hydrogen atoms and carbon-carbon bonds.
Representative hydrofluoroether compounds described by Formulas I and II include the following:
wherein cyclic structures designated with an interior xe2x80x9cFxe2x80x9d are perfluorinated.
Preferred segregated hydrofluoroethers include C3F7OCH3, (CF3)2CFOCH3, C4F9OCH3, (CF3)2CFCF2OCH3, (CF3)2CFCF2OC2H5, (CF3)3COCH3, CH3O(CF2)4OCH3, and CH3O(CF2)6OCH3, C3F7OC2H5, C4F9OC2H5, c-C7F13OCH3, c-C7F13OC2H5, C7F15OCH3, C7F15OC2H5, C10F21OCH3, and C10F21OC2H5. By xe2x80x9csegregatedxe2x80x9d it is meant that hydrogen atom(s) and fluorine atom(s) are not found on adjacent carbon atoms. Blends of one or more fluorinated ethers are also considered useful in practice of the invention.
A number of synthetic routes to hydrofluoroethers are known. These methods may be broadly divided into two groups; methods of fluorinating an ether compound, and methods where the ether linkage is formed within a compound by reaction with a fluorine-containing precursor. The former methods include: (1) direct fluorination of an ether compound; and (2) electrochemical fluorination of an ether compound. The latter methods include: (3) the addition reaction of an alcohol to a fluorinated olefin; (4) alkylation of a partially fluorinated alcohol; and (5) non-catalytic alkylation of a fluorinated carbonyl compound with a suitable alkylating agent. Japanese Patent No. JP 6-293686 provides a partial summary description of these varied methods.
The fluorinated ethers (alkoxy-substituted perfluorocompounds) suitable for use in the method of the invention can be prepared by alkylation of perfluorinated alkoxides prepared by the reaction of the corresponding perfluorinated acyl fluoride or perfluorinated ketone with an anhydrous alkali metal fluoride (e.a., potassium fluoride or cesium fluoride) or anhydrous silver fluoride in an anhydrous polar, aprotic solvent. (See, e.g., the preparative methods described in French Patent Publication No. 2,287,432, German Patent Publication No. 1,294,949, and U.S. Pat. No. 5,750,797 (Flynn et al.). Alternatively, a fluorinated tertiary alcohol can be allowed to react with a base, e.g., potassium hydroxide or sodium hydride, to produce a perfluorinated tertiary alkoxide which can then be alkylated by reaction with alkylating agent.
Suitable alkylating agents for use in the preparation include dialkyl sulfates (e.g., dimethyl sulfate), alkyl halides (e.g., methyl iodide), alkyl p-toluenesulfonates (e.g., ethyl p-toluenesulfonate), alkyl perfluoroalkanesulfonates (e.g., methyl perfluoromethanesulfonate), and the like. Suitable polar, aprotic solvents include acyclic ethers such as diethyl ether, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether; carboxylic acid esters such as methyl formate, ethyl formate, methyl acetate, diethyl carbonate, propylene carbonate, and ethylene carbonate; alkyl nitriles such as acetonitrile; alkyl amides such as N,N-dimethylformamide. N,N-dimethylformamide, and N-methylpyrrolidone; alkyl sulfoxides such as dimethyl sulfoxide; alkyl sulfones such as dimethylsulfone, tetramethylene sulfone, and other sulfolanes; oxazolidones such as N-methyl-2-oxazolidone; and mixtures thereof.
As yet another alternative, the fluorinated ethers may be prepared by reacting a fluorinated carbonyl compound, such as a ketone or acid fluoride, with an alkylating agent in the presence of a Lewis acid catalyst as described in U.S. Ser. No. 09/042,819 filed Mar. 17, 1998 (Lamanna et al.).
Other useful hydrofluoroethers are the omega-hydrofluoroalkyl ethers described in U.S. Pat. No. 5,658,962 (Moore et al.), which can be described by the general structure shown in Formula III:
Xxe2x80x94Rfxe2x80x2xe2x80x94(Oxe2x80x94Rfxe2x80x3)yxe2x80x94Oxe2x80x94Rxe2x80x3xe2x80x94Hxe2x80x83xe2x80x83(Formula III)
wherein:
X is either F or H;
Rfxe2x80x2 is a divalent perfluorinated organic radical having from 1 to about 12 carbon atoms;
Rfxe2x80x3 is a divalent perfluorinated organic radical having from 1 to about 6 carbon atoms;
Rxe2x80x3 is a divalent organic radical having from 1 to 6 carbon atoms, and preferably, Rxe2x80x3 is perfluorinated; and
y is an integer from 0 to 4.
Representative compounds described by Formula III which are suitable for use in the processes of the invention include the following compounds:
The omega-hydrofluoroalkyl ethers described by Formula III can be prepared by decarboxylation of the corresponding precursor fluoroalkyl ether carboxylic acids and salts thereof or, preferably, the saponifiable alkyl esters thereof, as described in U.S. Pat. No. 5,658,962.
Alternatively, the omega-hydrofluoroalkyl ethers can be prepared by reduction of the corresponding omega-chlorofluoroalkyl ethers (for example, those omega-chlorofluoroalkyl ethers described in U.S. Pat. No. 5,785,950 and U.S. Pat. No. 5,403,575 (Flynn et al.), which is also described in U.S. Pat. No. 5,658,962.
The fluorochemical stabilizer should be soluble in the liquid or supercritical CO2 from at least 0.01 weight percent to completely miscible. Preferably the fluorochemical stabilizer should be soluble in the liquid or supercritical CO2 from at least 0.05 weight percent. The solubility of the stabilizer in CO2 may be determined by charging a pressure vessel having a sight glass with liquid or supercritical CO2, and adding a known amount of stabilizer and known amount of carbon dioxide. Generally, the fluorinated stabilizer of the present invention produce clear solutions (or microemulsions) and no interface between separate phases is observed. Less soluble materials will form a hazy solution or two separate phases will develop, and an interface between phases may be observed.
The fluorochemical stabilizer is generally, used at concentrations from about 0.01 volume percent up to about 10 volume percent. Preferably, the stabilizer is used at concentrations from about 0.02 volume percent up to about 5 volume percent. For most applications due to cost considerations, the stabilizers are used in the minimum amounts necessary to produce a stable fracturing fluid.
The preferred foam forming substances are hydrofluoroethers, such as 3M HFE-7100 methoxy-nonafluorobutane, or 3M HFE-7200 ethoxy-nonafluorobutane.
3M HFE-7100 (C4F9OCH3) consists of two inseparable isomers with essentially identical properties. These are (CF3)2CFCF2OCH3 and CF3CF2CF2CF2OCH3.
3M HFE-7200 (C4F9OC2H5)consists of two inseparable isomers with essentially identical properties. These are (CF3)CFCF2OC2H5 and CF3CF2CF2CF2OC2H5.
Each of these hydrofluoroethers is soluble in CO2(l), but neither has heretofore been used in a well fracturing fluid as a foam forming substance in CO2(l).
Efficacy of these hydrofluoroethers as foamers may be demonstrated by the following examples:

Foamed nitrogen in liquid CO2 for fracturing


A water pump low pressure cutoff switch comprising a cylindrical housing incorporating an upper water chamber and a lower dry chamber. The water chamber is connected to a water line adjacent the pump, and is formed by a movable circular plate having a sealing means and a centered bypass button post on its top surface. The bottom surface of the movable plate has a pair of cylindrical electrical contacts with flat faces. A fixed plate creating the dry chamber has matching aligned electrical contacts which move apart to break the circuit when a calibrated compression coil spring affixed between the plates expands when a predetermined lower water pressure is met.

1. Field of the Invention
The present invention relates generally to water pumps. More specifically, the invention is a low pressure cutoff switch for water pumps.
2. Description of the Related Art
The related art of interest describes various cutoff switches, but none discloses the present invention. There is a need for automatically terminating the operation of a water pump undergoing low pressure to prevent a possible fire and electrical damage to the water pump. The device is simple in construction, and thus economically low in cost to produce. The related art is discussed in the order of perceived relevance to the present invention.
U.S. Pat. No. 4,180,374 issued on Dec. 25, 1979, to Elliott R. Bristow describes a well pump protection system including a timing device, a first ball check valve, a second check valve, and a third pressure pop-off or gate valve. The first valve utilizes a ball acting on a spring supporting a piston with its shaft supporting a bridge contact plate contacting two separated contacts from an overhead position in a separate conduit. The second check valve utilizes a flat valve and a light spring to lower the bridge contact plate to break contact with the two separated contacts positioned above the contact plate. The first and second valves are distinguishable for confining their contacts in separate housings.
U.S. Pat. No. 5,672,049 issued on Sep. 30, 1997, to Ugo Ciurlo describes an electromechanical device inserted in a water pipe by a union for the protection of a pump in waterworks in the absence of water comprising a branch from an outlet of a pump to a cavity partially delimited by a membrane, a moving rod element or piston in a casing pushed by a spring toward the membrane and capable of yielding under limited water pressure to act on the membrane and moving electrical contacts, and interacting with fixed contacts of a pump supply circuit to enable the pump to be switched on, and off in the absence of pressure acting on the membrane. The device is distinguishable for requiring a piston.
U.S. Pat. No. 2,554,266 issued on May 22, 1951, to Jacob L. Pauly describes a pressure actuated switch for use with oxygen demand regulators comprising a cylindrical housing containing a coil compression spring around a vertical sleeve containing a piston having an upper contact pin for contacting a U-shaped leaf spring having a first movable contact bead contacting a second fixed contact bead located on a vertical electric coupling leaving the housing, and air ports on its bottom abutment plate. The piston has an upper adjustment nut above an external coil compression spring held by a cross pin traversing an elongated slot. A round mounting flange has a water influent port externally threaded for connection to a pipe. A water chamber is formed between the mounting flange having an upper abutment plate and a lower resilient bottom diaphragm. When pressure is applied to the chamber, the contacts are engaged. A fall in pressure within the chamber will permit the spring on the piston to return the piston to its neutral or normal position permitting the contacts of the leaf spring and the stationary contact of the upper coupling to disengage to break the electrical circuit. The device operates between 6 to 25 psi water pressure for oxygen demand regulators. The device is distinguishable for requiring a piston and a spring clamp.
U.S. Pat. No. 3,139,493 issued on Jun. 30, 1964, to Irving W. Krieger, Sr. et al describes a pressure switch with a low pressure cut-out comprising a square housing attached to a threaded water outlet and containing a contact block, a frame assembly, and a vertical rod within a coil spring resting on an actuating lever extending outside the housing. A flexible diaphragm is located between the housing and the water outlet pipe connected to a base of a flat spring member. The device is distinguishable for requiring a contact block, an adjustable coil spring, a flat spring member, and an actuating lever.
U.S. Pat. No. 3,637,326 issued on Jan. 25, 1972, to Winston C. Dowell describes a manual control for a pressure-responsive switch of a submersible motor and a pump comprising a manual control for a pressure-responsive switch that activates a pump without regard to the level of liquid in the tank or sump may be below a predetermined value. The device is distinguishable for requiring manual control of a submersible motor and pump.
U.S. Pat. No. 1,169,305 issued on Jan. 25, 1916, to Walter V. Turner describes an electric pump governor comprising a piston, a cut-in and a cut-out valve piston with each having a cut-in and cut-out position, communication through which fluid is admitted to the control piston being established when the cut-in valve piston is in its cut-out position and the cut-out valve in its cut-in position. The device is distinguishable for requiring three pistons.
U.S. Pat. No. 2,765,743 issued on Oct. 9, 1956, to William H. Hollinshead describes a manual switch control for controlling the circuit of a pump having a resilient impeller. The device is arranged so that when the suction line of the water pump is broken or draws air rather than water, the circuit to the motor will open and the motor will stop with a manual on/off lever in a square casing containing also a pair of fixed contact points and a movable pair of contact points on a plate moved by the lever to break the electrical contact by separation of the contact points. The device is distinguishable for its manual control.
U.S. Pat. No. 2,990,780 issued on Jul. 4, 1961, to Kenneth G. Kreuter describes a water valve for a well pump inserted in the water pipe line comprising upper and lower chambers separated by a wall having a valve element closing the wall opening via a spring on the valve element""s shaft. A cam on a rotatable shaft which traverses the pipe acts a stop. The device is distinguishable for its non-electrical control.
U.S. Pat. No. 3,106,894 issued on Oct. 15, 1963, to Odd F. Johnsen describes a pressure operated reduction valve for water supply systems comprising a double acting valve with a primary valve and a secondary valve arranged in parallel and operated by the pressure in a pressure bell. A diaphragm located between the pressure medium in the pressure bell and a chamber kept at water outlet pressure controls the regulating valve. A part of the diaphragm forms the valve seat of the secondary. The valve body is combined with the valve body of the primary valve. A range switch is controlled by the pressure in the pressure bell, and will work in a range determined by the working pressure setting at any time, which pressure in turn controls the regulating valve. The system is distinguishable for requiring a range switch.
U.S. Pat. No. 3,140,819 issued on Jul. 14, 1964, to Joseph E. Coyle describes a vacuum cut-off switch for detecting large leaks in a vacuum system and responding by cutting off the current flow to the vacuum pump motor. The device is distinguishable for its mechanism being responsive to a large leak in a vacuum system.
U.S. Pat. No. 3,141,475 issued on Jul. 21, 1964, and U.S. Pat. No. 3,150,684 to Paul A. Guinard et al. describes a regulating valve for a motorpump controlled by a pressure responsive switch.
U.S. Pat. No. 3,271,971 issued on Sep. 13, 1966, to Erik H. Jensen et al. describes low pressure cut-outs for refrigerant compressors.
U.S. Pat. No. 3,274,940 issued on Sep. 27, 1966, to Robert A. Cottrell describes a pressure control system for the prevention of gas locks for a well pump and for pumps continuing to pump when the well is dry.
U.S. Pat. No. 3,295,450 issued on Jan. 3, 1967, to Siegfried Schoenwald et al. describes an electrical control device system for individual water pump installations comprising a control device connected to a pressure-responsive switch for electrically controlling the pump, and comprises a control member responsive to the quantity and velocity of the water passing through the control device for controlling the pressure switch in response to the flow rate.
U.S. Pat. No. 3,318,247 issued on May 9, 1967, to Clyde E. Yost describes an automatic pump control switching device for oil wells and gasoline engines comprising a spring loaded ball and valve system adjustable by screw-thread means. A solenoid valve system is also connected and dependent on the ball and valve system.
U.S. Pat. No. 3,551,620 issued on Dec. 29, 1970, to Jimmie N. Hoover describes a flow, no-flow device which differentiates between gas and liquid flow therethrough. A movable element similar to a valve element and a valve seat remains in the open position for liquids, but closes for gas flow. A switch associated with the movable element interrupts the current flow to a pump motor in a well bore.
U.S. Pat. No. 3,683,137 issued on Aug. 8, 1972, to Marshall A Stiltner describes a pressure switch diaphragm assembly with clamping diaphragm sealing means comprising the actuation of the pressure switch by a pressure responsive diaphragm.
U.S. Pat. No. 3,694,105 issued on Sep. 26, 1972, to Thomas B. Martin describes a system of valves used with a constant-speed pump comprising an adjustable pump by-pass valve and a discharge valve which inactivates the pump motor when discharge pressure exceeds a maximum or falls below a minimum.
U.S. Pat. No. 3,794,789 issued on Feb. 26, 1974, to Johnnie J. Bynum describes a pressure sensitive control for a pump regulator comprising a water pressure switch sensitive to a given lower pressure level below a preset low pressure for disconnecting the electrical circuit.
U.S. Pat. No. 4,200,775 issued on Apr. 29, 1980, to Michael Bodnar describes a pressure responsive switch with a low pressure cutoff comprising a diaphragm exposed to a pressure source and operating a combination of levers to open and close a switch at predetermined pressure values. An element ia provided between the diaphragm and the switch operating means to open the contacts.
U.S. Pat. No. 4,215,254 issued on Jul. 29, 1980, to Nobuyuki Ohki describes a pressure switch with a resiliently mounted contact.
U.S. Pat. No. 5,197,859 issued on Mar. 30, 1993, to Elliot J. Siff describes a well pump system having a sensing device for detecting a parameter correlated to the rate of flow into and out of the pressure tank.
U.S. Pat. No. 5,198,631 issued on Mar. 30, 1993, and U.S. Pat. No. 5,524,333 issued on Jun. 11, 1996, to Ronald L. Hogue et al. describes a pressure responsive control device and method of assembling the device, respectively. The pressure sensitive device has a housing made up of a plurality of housing members, a diaphragm, a bistable snap-disc, a switch, and an actuator.
U.S. Pat. No. 5,725,359 issued on Mar. 10, 1998, to Paul A. Dongo et al. describes a pool pump controller which includes a pneumatic pressure sensor having at least one port disposed to react to negative pressure within a pool""s pump intake chamber. The sensor input port, which includes a check valve, is connected to a pump control through a pneumatic tube. The pump control switch combines a diaphragm switch and an opto-interrupter to provide control of the pump motor in a watery environment.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a water pump low pressure cutoff switch solving the aforementioned problems is desired.
The present invention is directed to a low pressure cut-off electric switch for water pumps for home or commercial use with pools, wells, and spa pumps to prevent damage to the pump and motor, and to eliminate fire damage. The electric switch automatically cuts off electrical power to a water pump when the influent water pressure drops below approximately 6 to 8 p.s.i, thereby preventing possible fire and/or damage to the pump. The invention incorporates a by-pass feature for manually overriding the switch. The electric switch comprises a cylindrical metal housing with two electrical wires entering at the bottom to connect to separate contacts protruding at a certain spacing in a first fixed mounting plate. A movable second metal plate holds two contacts at the same certain spacing, and mounts a 6-8 pound compression spring based on the first plate. A rubber diaphragm abuts the second plate to seal water in the upper chamber from entering between the plates. A bypass button in the form of a rod is centered in the second plate and diaphragm and extends to an aperture in the housing and is sealed with a second rubber seal. The bypass button serves to temporarily test the electrical connection by pushing the contacts together. Also, the by-pass button closes the contacts to prime the water pump when the water pressure is between 6-8 psi.
A water inlet and outlet pipe is positioned on the side of the housing between the second metal plate and the top of the housing. At normal water pressure in the switch, the contacts are joined to conduct line current. But when the water pressure in the upper water chamber drops below 6-8 psi, the compression spring pushes the second plate upward to separate the contacts to cut off the electrical circuit to the water pump.
Accordingly, it is a principal object of the invention to provide an automatic low pressure cut-off switch to prevent a water pump from operating when a low water pressure is detected.
It is another object of the invention to provide a cylindrical, automatic, low pressure cut-off switch housing having a lower dry chamber having a first pair of electrical contacts supported by a fixed first plate for contacting an upper matching second pair of electrical contacts.
It is a further object of the invention to provide an automatic low pressure cut-off switch having a water containing chamber defined by a housing and a diaphragm, the diaphragm abutting a movable plate having switch contacts, a compression spring biasing the movable plate away from a fixed plate bearing switch contacts, in which water pressure in the water containing chamber overcomes the bias of the compression spring to close the switch contacts, but in which the compression spring forces the switch contacts to an open position when water pressure falls below a predetermined limit defined by the spring constant.
Yet another object of the invention is to provide an automatic low pressure cut-off switch having a second pair of contacts aligned with the first pair of contacts and a centered spring attached to the movable plate and the fixed plate.
Still another object of the invention is to provide an automatic low pressure cut-off switch with a post centered on the movable plate extending outside and acting as a bypass button for temporarily testing the electrical connection.
It is an object of the invention to provide improved elements and arrangements thereof for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.