A process for preparing acrylic acid or methacrylic acid comprises

The present invention relates to a process for preparing acrylic acid and methacrylic acid.
Acrylic acid is a major basic chemical product. Owing to its very reactive double bond and the acid function, it is particularly useful as a monomer for preparing polymers. The bulk of acrylic acid monomer production is esterified prior to polymerization, for example to make adhesives, dispersions or coatings. Just a fraction of acrylic acid monomer production is polymerized directly, for example to make superabsorbents. Whereas, in general, the direct polymerization of acrylic acid requires high purity monomer, acrylic acid purity requirements are not so high if the acrylic acid is esterified before it is polymerized.
It is common knowledge that acrylic acid can be produced by heterogeneously catalyzed gas phase, oxidation of propene with molecular oxygen over solid catalysts at from 200 to 400xc2x0 C. in two stages via acrolein (cf eg. DE-A-1 962 431, DE-A-2 943 707, DE-C-1 205 502, DE-A-195 08 558, EP-A-0 257 565, EP-A-0 253 409, DE-A-2 251 364, EP-A-0 117 146, GB-B-1 450 986 and EP-A-0 293 224). The catalysts used are oxidic multicomponent catalysts based, for example, on oxides of the elements molybdenum, bismuth and iron (in stage 1) or molybdenum and vanadium (in stage 2).
DE-C-2 136 396 discloses removing the acrylic acid from the reaction gases obtained by catalytic gas phase oxidation of propene or acrolein by countercurrent absorption with a mixture of 75% by weight of diphenyl ether and 25% by weight of biphenyl. DE-A-2 449 780 describes cooling the hot reaction gas by partial evaporation of the solvent in a direct condenser (quench apparatus) prior to the countercurrent absorption. The problem here is, as with further process steps, the production of solids in the apparatus, reducing plant availability. According to DE-A-4 308 087, this production of solids can be reduced by adding a polar solvent such as dimethyl phthalate in an amount of from 0.1 to 25% by weight to the relatively a polar solvent mixture of diphenyl ether and biphenyl.
In addition to the above-described absorption of the reaction product comprising acrylic acid into a high boiling solvent mixture, other known processes envisage a total condensation of acrylic acid and of the water of reaction formed in the course of the catalytic oxidation. This gives rise to an aqueous acrylic acid solution which can be further worked up via distillation with an azeotrope (cf DE-C-3 429 391, JP-A-1 124 766, JP-A-7 118 766, JP-A-7 118 966-R, JP-A-7 118 968-R and JP-A-7 241 885) or via an extraction process (cf DE-A-2 164 767, JP-A-5 81 40-039, JP-A-4 80 91 013). In EP-A-0 551 111, the mixture of acrylic acid and by-products produced by means of catalytic gas phase oxidation is contacted with water in an absorption tower and the resulting aqueous solution is distilled in the presence of a solvent that forms an azeotrope with polar low boilers such as water or acetic acid. DE-C-2 323 328 describes removing acrylic acid from an acidified, aqueous butanol/acrylic acid esterification waste liquor by extraction with a specific mixture of organic solvents.
The processes described above have the disadvantage of employing for the extraction or absorption an organic solvent which has to be removed again in a further operation, such as a rectification, under high thermal stress. This may cause the acrylic acid to polymerize.
JP-A-7 082 210 describes a process for purifying an acrylic acid comprising acetic acid, propionic acid, acrolein and furfural as well as acrylic acid. This process comprises adding water and then crystallizing under reduced pressure to obtain a purity of 99.6% for the acrylic acid crystals after removal and washing. Japanese Patent 45-32417 discloses a process wherein an aqueous acrylic or methacrylic acid solution additionally comprising acetic acid and propionic acid is extracted with heptane or toluene before water is removed from the extract by distillation. In the next step, the remaining extract is cooled down to xe2x88x9220 to xe2x88x9280xc2x0 C. to bring about a crystallization of acrylic acid or methacrylic acid. The crystals are removed, and the mother liquor is recycled into the extraction process. According to this patent, it is necessary to use an organic solvent or extractant, since the solution otherwise solidifies on cooling without forming crystals. This process is disadvantageous in that, as well as requiring the addition of an organic solvent, a distillation has to be carried out to remove water. Canadian Patent 790 625 relates to a further purification process for crude acrylic acid by fractional crystallization. In this process, if propionic acid is the main impurity in the crude acrylic acid, the temperature is not reduced below the peritectic temperature of the acrylic acid/propionic acid system, whereas it is not reduced below the eutectic temperature of the acrylic acid/acetic acid system when acetic acid is the main impurity. The acrylic acid used for crystallization in this process is prepared by conventional processes, for example by gas phase oxidation of propene or acrolein, and then subjected to a prepurification by conventional known processes, for example extraction. The crystallization of acrylic acid is said to be preferably carried out in the substantial absence of water.
EP-A-0 616 998 describes a process for purifying acrylic acid by a combination of dynamic and static crystallization of a prepurified acrylic acid, for example an acrylic acid which has been prepurified by distillation.
Common to the processes described in the above documents is that they require a (pre)purification of the acrylic acid prior to crystallization. Since the prepurification generally utilizes organic solvents which have to be subsequently separated off again under high thermal stress, there is always the risk of the acrylic acid undergoing premature polymerization.
EP-A-0 002 612, which relates to a process for purifying acrylic acid in aqueous solution by fractional crystallization, discloses the addition of salts to the acrylic acid solution so as to break up the water/acrylic acid eutectic system which exists at an acrylic acid content of 63% by volume.
EP-A-0 675 100 describes a process for preparing xcex1,xcex2-unsaturated C3-C6-carboxylic acids, eg. methacrylic acid, by oxidative dehydrogenation of the corresponding saturated C3-C6-carboxylic acid, followed by melt crystallization with subsequent fractional distillation or followed by fractional distillation with subsequent melt crystallization.
It is an object of the present invention to provide a process for obtaining acrylic acid or methacrylic acid in high purity without complex operations.
We have found that this object is achieved, surprisingly, by a process whereby acrylic acid or methacrylic acid from a gaseous product mixture which has been subjected to a condensation can be crystallized directly from the solution formed in the condensation. More particularly, the process found requires no further purifying step and no addition of assistants.
The present invention accordingly provides a process for preparing acrylic acid or meth-acrylic acid, which comprises
(a) preparing a gaseous product mixture having essentially the composition of a reaction mixture of the catalytic gas phase oxidation of C3-/C4-alkanes, -alkenes, -alkanols and/or -alkanals and/or precursors thereof to form acrylic acid or methacrylic acid,
(b) condensing said gaseous product mixture,
(c) crystallizing acrylic acid or methacrylic acid from the solution obtained in step (b), and
(d) removing the resulting crystals from the mother liquor.
In a preferred embodiment, at least a portion of the mother liquor is recycled into step (c) (step (e)). Further preferred embodiments of the invention will be apparent from the description which follows, the subclaims, the drawing and the Example.
In the process of the present invention, acrylic acid or methacrylic acid is crystallized directly and unmediatedly without further intermediary or purifying steps and without addition of assistants from the solution which is formed in the course of the condensation of the product mixture. This product mixture has essentially the composition of a reaction product formed in a catalytic gas phase oxidation process to form the acid.
The sole figure illustrates a preferred embodiment of carrying out the process of the present invention.
Step (a)
Step (a) produces a gaseous product mixture which essentially has the composition of a reaction mixture of the catalytic gas phase oxidation of C3- or C4-alkanes, -alkenes, -alkanols and/or -alkanals and/or precursors thereof to form acrylic acid or methacrylic acid. It is particularly advantageous for the gaseous product mixture to be prepared by catalytic gas phase oxidation of propene, acrolein, tert-butanol, isobutene, isobutane, isobutyraldehyde, methacrolein, isobutyric acid or methyl tert-butyl ether. Suitable starting compounds include all precursors of the aforementioned compounds from which the actual C3/C4 starting compound is formed as an intermediate during the gas phase oxidation. Examples which may be mentioned here are methyl tert-butyl ether and isobutyric acid for the production of methacrylic acid.
A particularly advantageous source of the gaseous product mixture to be used in the process of the present invention is the catalytic gas phase conversion of propene and/or acrolein into acrylic acid using molecular oxygen according to known processes, especially as described in the above-cited references. This gas phase reaction is preferably carried out at from 200 to 450xc2x0 C. with or without superatmospheric pressure. The heterogeneous catalysts used are preferably oxidic multicomponent catalysts based on the oxides of molybdenum, bismuth and iron in stage 1 (oxidation of propene to acrolein) and the oxides of molybdenum and vanadium in stage 2 (oxidation of acrolein to acrylic acid). When propane is used as a starting material, it can be converted into a propenelpropane mixture by: catalytic oxydehydrogenation as described, for example, in Catalysis Today 24 (1995), 307-313, or U.S. Pat. No. 5,510,558; by homogeneous oxydehydrogenation, as described for example, in CN-A-1 105 352; or by catalytic dehydrogenation as described, for example, in EP-A-0 253 409, EP-A-0 293 224, DE-A-195 08 558 or EP-A-0 117 146. When a propene/propane mixture is used, propane acts as diluent. Further suitable propenelpropane mixtures are refinery propene (70% of propene and 30% of propane) or cracker propene (95% of propene and 5% of propane). In principle, propene/propane mixtures such as those mentioned above can be oxidized with oxygen or air or a mixture of oxygen and nitrogen of any composition to acrolein and acrylic acid.
The conversion of propene into acrylic acid is strongly exothermic. The reaction gas, which as well as the starting materials and the products advantageously includes an inert diluent gas, for example recycle gas (see below), atmospheric nitrogen, one or more saturated C1-C6-hydrocarbons, especially methane and/or propane, and/or water vapor, can therefore absorb only a small fraction of the heat of reaction. Although the type of reactor used is not subject to any restriction per se, it is common to use tube bundle heat exchangers packed with the oxidation catalyst, since with this type of apparatus the predominant fraction of the heat of reaction can be removed to the cooled tube walls by convection and radiation.
The catalytic gas phase oxidation process produces not pure acrylic acid, but a gaseous mixture which, as well as acrylic acid, may essentially include as secondary components unconverted acrolein and/or propene, water vapor, carbon monoxide, carbon dioxide, aitrogen, propane, oxygen, acetic acid, propionic acid, formaldehyde, further aldehydes and maleic anhydride. The reaction product mixture customarily comprises (each percentage based on the total reaction mixture) from 1 to 30% by weight of acrylic acid, from 0.05 to 1% by weight of propene and from 0.05 to 1% by weight of acrolein, from 0.05 to 10% by weight of oxygen, from 0.05 to 2% by weight of acetic acid, from 0.01 to 2% by weight of propionic acid, from 0.05 to 1% by weight of formaldehyde, from 0.05 to 2% by weight of aldehydes, from 0.01 to 0.5% by weight of maleic anhydride and from 20 to 98% by weight, preferably from 50 to 98% by weight, of inert diluent gases. The inert diluent gases present include, in particular, saturated C1-C6-hydrocarbons, such as from 0 to 90% by weight of methane and/or propane, and also from 1 to 30% by weight of water vapor, from 0.05 to 15% by weight of carbon oxides and from 0 to 90% by weight of nitrogen, each percentage being based on 100% by weight of diluent gas.
Methacrylic acid can be prepared similarly to acrylic acid by catalytic gas phase reaction of C4 starting compounds with molecular oxygen. A particularly advantageous way to obtain methacrylic acid is, for example, by catalytic gas phase oxidation of isobutene, isobutane, tert-butanol, isobutyraldehyde, methacrolein or methyl tert-butyl ether. The catalysts used are again transition metal mixed oxide catalysts (eg. Mo, V, W and/or Fe). Particularly suitable processes for producing methacrylic acid are those which are based on methacrolein, especially when the methacrolein is produced by gas phase catalytic oxidation of tert-butanol, isobutane or isobutene or by reaction of formaldehyde with propionaldehyde as described in EP-B-0 092 097 or EP-B-0 058 927. It is thus possible to prepare methacrylic acid in two stages by (1) condensation of propionaldehyde with formaldehyde (in the presence of a secondary amine as catalyst) to form methacrylic acid and (2) subsequent oxidation of the meth-acrolein to methacrylic acid.
As with the production of acrylic acid, the product is not pure methacrolein, but a gaseous mixture which, as well as methacrylic acid, may essentially include as secondary components unconverted methacrolein and/or water vapor, carbon monoxide, carbon dioxide, nitrogen, oxygen, acetic acid, propionic acid, further aldehydes and maleic anhydride. The process of the present invention is used especially when the reaction mixture comprises from 0.02 to 2% by weight of methacrylic acid, based on the total reaction mixture, and otherwise essentially the same corresponding constituents as with the production of acrylic acid.
Step (b)
Step (b) subjects the reaction product of step (a) to a condensation, particularly to a partial or total condensation, to obtain a solution. The condensation can be effected in one or more stages according to customary processes, and the type of condensation is not subject to any special restriction. The condensation is advantageously carried out in a direct condenser where previously produced condensate is contacted with the hot gaseous reaction product. Suitable apparatuses for the condensation are in particular spray scrubbers, Venturi scrubbers, bubble columns or apparatuses having betrickled surfaces.
The mixture obtained by partial or total condensation of the reaction product of step (a) preferably comprises from 60 to 99.5% by weight of acrylic or methacrylic acid, from 0.1 to 40% by weight of water, and also from 0.1 to 15% by weight of impurities, especially, each percentage being based on 100% by weight of condensate, from 0.01 to 5% weight of acrolein or methacrolein, from 0.05 to 5% by weight of acetic acid, from 0.01 to 5% by weight of propionic acid, from 0.01 to 5% by weight of formaldehyde, from 0.01 to 5% by weight of further aldehydes and from 0.01 to 5% by weight of maleic acid. It is particularly preferable for the condensation to afford a mixture comprising from 93 to 98% by weight of acrylic or methacrylic acid, from 1 to 5% by weight of water, and also from 0.5 to 5% by weight of impurities, especially, each percentage being based on 100% by weight of condensate, from 0.01 to 3% by weight of acrolein or methacrolein, from 0.1 to 3% by weight of acetic acid, from 0.01 to 3% by weight of propionic acid, from 0.01 to 3% by weight of formaldehyde, from 0.01 to 3% by weight of further aldehydes and from 0.01 to 3% by weight of maleic acid.
Step (c)
Step (c) crystallizes the solution obtained in step (b), which comprises acrylic acid or methacrylic acid. Thus, the solution obtained in the condensation step is fed directly to the crystallization step. No solvent is added, especially no organic solvent. The crystallization process used is not subject to any restriction. The crystallization can be carried out continuously or batchwise, in one or more stages. The crystallization is preferably carried out in a single stage. In another preferred embodiment of the invention, the crystallization is carried out as a fractional crystallization. In the art of fractional crystallization it is customary to term all stages which produce a crystallizate which is purer than acrylic or methacrylic acid solution feed purifying stages and all other stages stripping stages. Multi-stage fractional crystallization processes are advantageously operated according to the countercurrent principle whereby the crystallizate is separated from the mother liquor in each stage and fed to the particular stage having the next higher degree of purity, while the crystallization residue is fed to the particular stage having the next lower degree of purity.
The temperature of the solution during the crystallization is advantageously within the range from xe2x88x9225xc2x0 C. to +14xc2x0 C., especially within the range from 12xc2x0 C. to xe2x88x925xc2x0 C. The solids content in the crystallizer is advantageously within the range from 0 to 80 g of solids/100 g, preferably within the range from 15 to 35 g of solids/100 g.
In an advantageous embodiment of the invention, the crystallizing is effected by cooling apparatus walls or by evaporating the solution under reduced pressure. In the case of the crystallizing by cooling, the heat is removed via scrape coolers connected to a stirred tank or to a vessel without stirrer. The circulation of the crystal suspension is ensured in this case by means of a pump. Alternatively, it is possible to remove the heat via the walls of a stirred tank having a close-clearance stirrer. A further preferred embodiment of cooling crystallization involves the use of cooling disc crystallizers as manufactured for example by Gouda (Netherlands). In a further suitable variant for crystallization by cooling, the heat is removed via conventional heat transferors (preferably tube bundle or plate heat transferors). These apparatuses, unlike scraped-surface coolers, stirred tanks having close-clearance stirrers or cooling disc crystallizers, have no means for avoiding crystal layers on the heat-transferring surfaces. If, in operation, a state is reached where the heat transfer resistance has become too high due to crystal layer formation, the operation is switched over to a second apparatus. During operation of the second apparatus, the first apparatus is regenerated (preferably by melting off the crystal layer or by flushing the apparatus through with unsaturated solution). If heat transfer resistance becomes too high in the second apparatus, operation is switched back again to the first apparatus, etc. This variant can also be operated with more than two apparatuses in alternation. In addition, the crystallization can be effected by conventional evaporation of the solution under reduced pressure. In a further advantageous embodiment of the invention, a crystallization takes place in apparatuses in which the crystals grow on cooled surfaces within the crystallization apparatus, ie. are immobilized in the apparatus (eg. layer crystallization process of Sulzer Chemtech (Switzerland) or static crystallization process of BEFS PROKEM (France)).
Step (d)
Step (d) separates the acrylic or methacrylic acid crystals obtained in step (c) from the mother liquor. For a layer crystallization or a static crystallization, the separation of the crystals from the mother liquor can take place in the crystallization apparatus itself, since the crystals are immobilized in the apparatus and the mother liquor can be removed from the apparatus by letting it flow out. The crystals are removed from the crystallization apparatus by melting the crystals and then letting the melt flow out. For a suspension crystallization, any known solid-liquid separation is suitable. In a preferred embodiment of the invention, the crystals are separated from the mother liquor by filtration and/or centrifugation. Advantageously, the filtration or centrifugation is preceded by a (pre)thickening of the suspension, for example by means of one or more hydrocyclones. Centrifugation can be carried out in any known centrifuge which works batchwise or continuously. It is very advantageous to use push air centrifuges which can be operated in one or more stages. Also suitable are screw sieve centrifuges or screw discharge centrifuges (decanters). A filtration is advantageously effected by means of press filters which can be operated batchwise or continuously, with or without stirrer or by means of belt filters. In general, filtration can be effected under superatmospheric pressure or under reduced pressure.
The solid-liquid separation may be accompanied and/or followed by further process steps for increasing the purity of the crystals or of the crystal cake. In a particularly advantageous embodiment of the invention, the separation of the crystals from the mother liquor is followed by a single- or multiple-stage washing and/or sweating of the crystals or of the crystal cake. In washing, the quantity of wash liquor is suitably within the range from 0 to 500 g of wash liquor/100 g of crystallizate, preferably within the range from 30 to 200 g of wash liquor/100 g of crystallizate. The wash liquor used is not subject to any restriction. It is advantageous, however, to wash with pure product, ie. with an acrylic or methacrylic acid liquid whose purity is greater than that of the crystal cake to be washed. A wash with water is also possible. The wash can take place in customary apparatus for the purpose. It is advantageous to use wash columns in which the removal of the mother liquor and the washing take place in one and the same apparatus, centrifuges, which can be operated in one or more stages, or press filters or belt filters. The washing can be carried out on centrifuges or belt filters in one or more stages. The wash liquor can be passed in countercurrent to the crystal cake.
Sweating describes a local melting-off of impure regions. The sweat quantity is advantageously within the range from 0 to 100 g of molten-off crystallizate/100 g of crystallizate prior to sweating, preferably within the range from 5 to 35 g of molten-off crystazizate/100 g of crystallizate. It is particularly preferable to carry out the sweating on centrifuges or belt filters. A combined wash and sweat in one apparatus can also be suitable.
The acrylic acid crystals and methacrylic acid crystals after the solid-liquid separation and any further washing and/or sweating constitute the purified acid obtained from the process. The purity of the crystals obtained is generally within the range from 97 to 99.99% by weight of acrylic acid or methacrylic acid, especially within the range from 98.5 to 99.9% by weight of acrylic acid or methacrylic acid. The crystals prepared by the process of the present invention include only very minimal amounts of impurities, such as acetic acid, maleic acid or aldehydes.
If desired, the purified acid can be esterified by known methods or further purified by known methods. In an advantageous embodiment of the invention, step (d) is followed by step (e) explained below.
Step (e)
Step (e) recycles the mother liquor which remains after the crystals have been separated off, at least partly directly into the crystallization step (c). The proportion of recycled mother liquor is within the range from 0 to 100% by weight, preferably within the range from 20 to 80% by weight.
The figure illustrates a preferred embodiment of the process of the present invention. The line 2 and compressor 3 supply air to the synthesis reactors 4 and 5. In addition, reactor 4 is supplied via line 9 with recycled gas which has been compressed by compressor 6 and which consists essentially of nitrogen, carbon oxides and unconverted starting materials, together with propene or isobutene from line 1. The synthesis reactor 4 is where the first stage of the two-stage gas phase oxidation, namely the oxidation of propene or isobutene to the corresponding acrolein, takes place. The acrolein is then oxidized to the corresponding acid in synthesis reactor 5. This gives rise to a gaseous product mixture which, as well as the acid, comprises impurities mentioned above. This gaseous product mixture is fed via line 7 to the condenser 8, where it is cooled down and condensed to a solution. The uncondensed portion of the product mixture is removed via line 9, with a portion being recycled as recycled gas, as described above, into reactor 4, while the other portion, preferably 50% of the total stream of line 9, is removed from the plant as a waste gas via line 10. The solution formed in the condenser 8 is fed via line 11 to the crystallizer 12, where the crystallization is carried out. The mother liquor of the crystallization is fed together with the crystallizate via line 13 to a suitable apparatus 14 for solid-liquid separation, the crystallizate being removed via line and the mother liquor via line 16. In a preferred embodiment, at least some of the mother liquor is reintroduced via line 17 into the crystallization step (in line 11 and crystallizer 12). Thus, the purified crude acid is removed via line 15.
The process of the present invention has the advantage over existing processes that, after condensation of the product mixture produced in the gas phase oxidation, the solution formed in the condensation yields a very high quality crude acid directly by crystallization. When using a crystallization having more than one purification stage, it is possible to produce a pure acid directly, without a prepurification having to be carried out in departure from the above-cited references, Canadian Patent 790 625, JP-A-7 082 210 and EP-A-0 616 998.
It is a further important advantage of the process of the present invention that the process is carried out at a relatively low temperature, ie. that the main stream of acrylic acid or methacrylic acid is removed directly as product via condensation and crystallization. Since, in contradistinction to the prior art, no assistant is added and thus no high thermal stress (especially in the case of high acid contents) is needed to remove this assistant, polymerization problems and the use of process stabilizers as in the prior art are minimized. In addition, fouling is avoided or reduced as well as a result. It is surprising that it is possible to crystallize acrylic acid solutions or methacrylic acid solutions obtained by gas phase oxidation and condensation directly and that the products obtained have very high purity. It is particularly surprising that this is possible with aqueous condensates.

Method for purifying acrylic acid and methacrylic acid

Abstract: (a) preparing a gaseous product mixture having essentially the composition of a reaction mixture of the catalytic gas phase oxidation of C3-/C4-alkanes, -alkenes, -alkanols and/or -alkanals and/or precursors thereof to form acrylic acid or methacrylic acid, characterized by

Abstract: (b) condensing said product mixture,


Solid surface material is prepared from an extrudable composite material comprising a matrix of at least one acrylic resin and a filler dispersed in the matrix, said acrylic resin comprising an acrylic epoxy-ftmctional copolymer as a matrix resin crosslinked with a straight or branched chain aliphatic carboxylic acid or anhydride of such acid.

This invention is directed to producing thin sheets of extrudable acrylic compositions for solid surface applications having desired physical properties. More particularly, the invention is directed to improving the heat resistance of such materials.
Artificial (or synthetic) marble can be considered as a general designation for various types of materials used as building products, such as bathroom vanity tops, sinks, shower stalls and kitchen counter tops, for example; furniture; sanitary use; lining materials; and stationary small articles. Artificial marbles encompass cultured marble, onyx and solid surface materials typically comprising some kind of resin matrix and either with or without a filler present in the resin matrix. Solid surface materials are typically filled resin materials. Corian(copyright), sold by E. I. du Pont de Nemours and Company, Wilmington, Del., (DuPont), is a solid surface material comprising an acrylic matrix filled with alumina trihydrate (ATH).
While the prior art discloses many polymeric compositions containing fillers for various purposes, the solid surface market is non-differentiated with respect to heat resistance, and the problem of improving heat resistance has not been adequately addressed. Such compositions are not readily extrudable to form thin sheet material.
In accordance with this invention there is provided solid surface material having improved heat resistance. The solid surface material comprises a crosslinked acrylic composite as a matrix and at least one filler dispersed in the matrix. In a preferred embodiment the matrix is selected from an epoxy functional copolymer such as poly (methyl methacrylate/glycidol methacrylate) and a diacid as the crosslinking agent. The filler is calcium carbonate or another filler commonly disclosed in the art. The compositions of this invention are readily extrudable to form thin sheet material which has high heat resistance.
This invention comprises acrylic composites that can be extruded into thin sheets, which are thermoformable , have high heat resistance and resistance to staining. Acrylic resins useful in the present invention are not specially limited as long as they include a cross-linkable component and can be formed into an acrylic solid surface material. Examples of useful acrylic resins include various kinds of conventional acrylic monomers, acrylic oligomers, vinyl monomers for copolymerization other than acrylic monomers, or oligomers. As the acrylic monomer, (meth)acrylic ester is preferred. Examples of (meth)acrylic ester include methyl (meth)acrylic ester, ethyl(meth)acrylic ester, butyl (meth)acrylic ester, 2-ethylhexyl (meth)acrylic ester, and benzyl (meth)acrylic ester. The acrylic resin has an epoxy functionality provided by copolymerization of the acrylic component with from about 8 to 35% by weight of glycidyl methacrylate, preferably from 10 to 20% by weight of glycidyl methacrylate, based on the weight of the acrylic resin.
The acrylic polymer matrix is crosslinked using a straight or branched chain, aliphatic dicarboxylic acid such as adipic, pimelic,suberic, azelaic, sebacic, undecanoic, and 1,12-dodecandioic acid in an amount from about 7 to 15% by weight of the acrylic polymer. Also useful are anhydrides of the acids such as decanedicarboxylic acid anhydride.
The ingredients are mixed at a low temperature to prevent cross linking, for example on a roll mill at temperatures from 75xc2x0 to 140xc2x0 C., extruded and thereafter cross linked at temperatures of 170xc2x0 to 210xc2x0 C. As just described cross linking can be accomplished by heating the reactants to a temperature above about 170xc2x0 C. or by the addition of a small amount of a catalyst to speed up the reaction such as dibutyltin dilaurate or methyltriphenylphosphonium bromide in amounts from 0.05 to 1% by weight of the total mixture. Fillers useful in the present invention include, for example, calcium carbonate, barium sulfate, aluminum oxide, magnesium hydroxide, kaolin, or decorative agents, as a list that is not exhaustive and not intended to limit the invention. Fillers can be present in effective amounts from as low as about 20% by weight to about 75% by weight. Preferably, amounts from 30 to 60% by weight are used.
It is known to include in solid surface materials other additives such as pigments, dyes, flame retardant agents, parting agents, fluidizing agents, viscosity control agents, curing agents, antioxidants, toughening agents and color inhibitors. Additives to provide simulated granite are disclosed in U.S. Pat. No. 4,085,246.
Solid surface materials of this invention can be prepared by a continuous extrusion process using a multi-feeder twin-screw extruder equipped with vacuum and a sheet die of proper dimensions. The extruded sheets can be directly transferred either onto a double belt press or into an oven for curing. Light pressure may be needed for maintaining sheet gauge or profile during curing. The resulting solid surface material is thermoformable, i.e. reshapeable under controlled conditions of temperature and force which is useful in building product applications.
Heat Resistance Test Method
Heat resistance is determined by a xe2x80x9chot block testxe2x80x9d. A metal block (a 800 g stainless steel cylinder of 2 inches (5.08 cm) diameter and 1xe2x85x9e inches (4.76 cm) height is heated with and internal cartridge heater and its temperature is controlled by a temperature controller. In the Examples below thin samples (thickness less than xc2xc inch (0.6 cm) are laminated onto xc2xe inch (1.9 cm) particle boards before the test. The metal block, which is heated to and maintained at a desired temperature (xc2x12xc2x0 C.), is placed on a sample surface for 5 minutes. The sample surface is then inspected for any visible (qualitative) change with an unaided eye. If a tested surface with a subtle surface change can still be refinished to the original look using light sanding, the sample is considered xe2x80x9cPassxe2x80x9d at the test temperature.

Solid surface materials prepared from extrudable acrylic composites


Non-hydrogenative endothermic catalytic cracking of hydrocarbon, particularly petroleum, fractions at relatively low pressures and high temperatures in a system where the endothermic heat required for cracking is supplied by catalyst as the heat transfer medium, which catalyst has been heated by burning coke deposited on the catalyst during cracking; and wherein a decomposable compound of platinum, palladium, ruthenium, iridium, osmium, rhodium or rhenium, is introduced into contact with the cracking catalyst during said process.

This invention relates to catalytic cracking of hydrocarbons. It more particularly refers to improvements in the endothermic catalytic cracking of petroleum fractions and alternating exothermic catalyst regeneration.
Endothermic catalytic cracking of hydrocarbons, particularly petroleum fractions, to lower molecular weight desirable products is well known. This process is practiced industrially in a cycling mode wherein hydrocarbon feedstock is contacted with hot, active, solid particulate catalyst without added hydrogen at rather low pressures of up to about 50 psig and temperatures sufficient to support the desired cracking. As the hydrocarbon feed is cracked to lower molecular weight, more valuable and desirable products, "coke" is deposited on the catalyst particles. The coked catalyst is disengaged from the hydrocarbon products, which are then resolved and separated into appropriate components. The coked catalyst particles, now cooled from the endothermic cracking and disengaged from the hydrocarbon products, are then contacted with an oxygen containing gas whereupon coke is burned off the particles to regenerate their catalytic activity. During regeneration, the catalyst particles absorb the major portion of the heat generated by the combustion of coke, i.e. they are "reflexively" heated, with consequent increase of catalyst temperature. The heated, regenerated catalyst particles are then contacted with additional hydrocarbon feed and the cycle repeats itself.
A flue gas comprising carbon oxides is produced during regeneration. In conventional operation this flue gas contains substantial quantities of carbon monoxide. The carbon monoxide is either vented to the atmosphere with the rest of the flue gas or is in some way burned to carbon dioxide, in an incinerator or a CO boiler or the like.
It has recently become desirable to decrease the content of carbon monoxide in the regenerator flue gas for at least two reasons. In the first place, CO combustion is extremely exothermic and in view of the increasing cost of energy, burning CO in the regenerator increases the heat efficiency of the reflexive endothermic catalytic cracking system. In the second place, since carbon monoxide is an air pollutant, more and more stringent controls are being placed upon its venting into the environment. It is therefore clearly desirable to provide means for burning carbon monoxide within a reflexive hydrocarbon catalytic cracking system. This has been attempted in the past and is being attempted at present by means of increasing the temperature and air input to the regenerator so as to support thermal combustion of carbon monoxide in the regenerator. This technique has been difficult to commercialize and to operate successfully in a smooth, steady state manner.
In the past attempts have been made, in fact it has sometimes been commercial practice, to employ special catalysts for this process which contain a cracking component and a component for catalyzing the oxidation of carbon monoxide. The CO oxidation components used in the past have been metals of the transition element group and/or of the iron group. In particular, manganese, cobalt and especially chromium have been used for this purpose.
Two major variants for endothermically cracking hydrocarbons are fluid catalytic cracking (FCC) and moving bed catalytic cracking. In both of these processes as commercially practiced, the feed hydrocarbon and the catalyst are passed through a "reactor"; are disengaged; the catalyst is regenerated with cocurrent and/or countercurrent air; and the regenerated reflexively heated catalyst recontacted with more feed to start the cycle again. These two processes differ substantially in the size of the catalyst particles utilized in each and also in the engineering of materials contact and transfer which is at least partially a function of the catalyst size.
In fluid catalytic cracking (FCC), the catalyst is a fine powder of about 10 to 200 microns, preferably about 70 micron, size. This fine powder is generally propelled upwardly through a riser reaction zone suspended in and thoroughly mixed with hydrocarbon feed. The coked catalyst particles are separated from the cracked hydrocarbon products, and after purging are transferred into the regenerator where coke is burned to reactivate the catalyst. Regenerated catalyst generally flows downward from the regenerator to the base of the riser.
One typical example of industrially practiced moving bed hydrocarbon catalytic cracking is known as thermofor catalytic cracking (TCC). In this process the catalyst is in the shape of beads or pellets having an average particle size of about 1/64 to 1/4 inch, preferably about 1/8 inch. Active, hot catalyst beads progress downwardly cocurrent with a hydrocarbon charge stock through a cracking reaction zone. In this zone hydrocarbon feed is endothermically cracked to lower molecular weight hydrocarbons while coke is deposited on the catalyst. At the lower end of the reaction zone the hydrocarbon products are separated from the coked catalyst, and recovered. The coked catalyst is then passed downwardly to a regeneration zone, into which air is fed such that part of the air passes upwardly countercurrent to the coked catalyst and part of the air passes downwardly cocurrent with partially regenerated catalyst. Two flue gases comprising carbon oxides are produced. Regenerated catalyst is disengaged from the flue gas and is then lifted, pneumatically or mechanically, back up to the top of the reaction zone.
The catalysts used in endothermic catalytic nonhydrogenative cracking are to be distinguished from catalysts used in exothermic catalytic hydrocracking. Operating conditions also to be distinguished. While the catalytic cracking processes to which this invention is directed operate at low pressures near atmospheric and in the absence of added hydrogen, hydrocracking is operated with added hydrogen at high pressures of up to about 1000 to 3000 psig. Further, non-hydrogenative catalytic cracking is a reflexive process with catalyst cycling between cracking and regeneration (coke burn off) over a very short period of time, seconds or minutes. In hydrocracking, on the other hand, the catalyst remains in cracking service for an extended period of time, months, between regeneration (coke burn off). Another important difference is in the product. Nonhydrogenative catalytic cracking produces a highly unsaturated product with substantial quantities of olefins and aromatics, and a high octane gasoline fraction. Hydrocracking, in contrast produces an essentially olefin-free product with a relatively low octane gasoline.
This invention is not directed to hydrocracking nor is it within the scope of this invention to use hydrocracking catalysts in the process hereof. Hydrocracking catalysts have an acidic cracking component, which may be a crystalline aluminosilicate zeolite, amorphous silica alumina, clays or the like, and a very strong hydrogenation/dehydrogenation component. Strong hydrogenation/dehydrogenation components are illustrated by metals such as molybdenum, chromium and vanadium, and group VIII metals such as cobalt, nickel and palladium. These are used in relatively large proportion, certainly large enough to support heavy hydrogenation of the charge stock under the conditions of hydrocracking. To the contrary, strong hydrogenation/dehydrogenation metals are neither required nor desired as components of non-hydrogenative catalytic cracking. In fact, it is usual for some metals, such as nickel and vanadium, to deposit out on the catalyst from the charge stock during non-hydrogenative cracking. These are considered to be catalyst poisons in this process and therefore to be avoided or at least minimized. Their detrimental effect in nonhydrogenative catalytic cracking is to increase the coke and light gas, including hydrogen, produced in the cracking reaction and therefore to reduce the yield of desired liquid products, particularly gasoline.
FIG. 1 and the sectional element thereof shown in FIG. 2 are representative of a commercial fluid catalytic cracking unit. Referring now to FIG. 1, a hydrocarbon feed 2 such as a gas oil boiling from about 600.degree. F. up to 1000.degree. F. is passed after preheating thereof to the bottom portion of riser 4 for admixture with hot regenerated catalyst introduced by standpipe 6 provided with flow control valve 8. A suspension of catalyst in hydrocarbon vapors at a temperature of at least about 950.degree. F. but more usually at least 1000.degree. F. is thus formed in the lower portion of riser 4 for flow upwardly therethrough under hydrocarbon conversion conditions. The suspension initially formed in the riser may be retained during flow through the riser for a hydrocarbon residence time in the range of 1 to 10 seconds.
The hydrocarbon vapor-catalyst suspension formed in the riser reactor is passed upwardly through riser 4 under hydrocarbon conversion conditions of at least 900.degree. F. and more usually at least 1000.degree. F. before discharge into one or more cyclonic separation zones about the riser discharge, represented by cyclone separator 14. There may be a plurality of such cyclone separator combinations comprising first and second cyclonic separation means attached to or spaced apart from the riser discharge for separating catalyst particles from hydrocarbon vapors. Separated hydrocarbon vapors are passed from separator 14 to a plenum chamber 16 for withdrawal therefrom by conduit 18. These hydrocarbon vapors together with gasiform material separated by stripping gas as defined below are passed by conduit 18 to fractionation equipment not shown. Catalyst separated from hydrocarbon vapors in the cyclonic separation means is passed by diplegs represented by dipleg 20 to a dense fluid bed of separated catalyst 22 retained about an upper portion of riser conversion zone 4. Catalyst bed 22 is maintained as a downwardly moving fluid bed of catalyst countercurrent to rising gasiform material. The catalyst passes downwardly through a stripping zone 24 immediately therebelow and counter-current to rising stripping gas introduced to a lower portion thereof by conduit 26. Baffles 28 are provided in the stripping zone to improve the stripping operation.
The catalyst is maintained in stripping zone 24 for a period of time sufficient to effect a higher temperature desorption of feed deposited compounds which are then carried overhead by the stripping gas. The stripping gas with desorbed hydrocarbons pass through one or more cyclonic separating means 32 wherein entrained catalyst fines are separated and returned to the catalyst bed 22 by dipleg 34. The hydrocarbon conversion zone comprising riser 4 may terminate in an upper enlarged portion of the catalyst collecting vessel with the commonly known bird cage discharge device or an open end "T" connection may be fastened to the riser discharge which is not directly connected to the cyclonic catalyst separation means. The cyclonic separation means may be spaced apart from the riser discharge so that an initial catalyst separation is effected by a change in velocity and direction of the discharged suspension so that vapors less encumbered with catalyst fines may then pass through one or more cyclonic separation means before passing to a product separation step. In any of these arrangements, gasiform materials comprising stripping gas hydrocarbon vapors and desorbed sulfur compounds are passed from the cyclonic separation means represented by separator 32 to a plenum chamber 16 for removal with hydrocarbon products of the cracking operation by conduit 18. Gasiform material comprising hydrocarbon vapors is passed by conduit 18 to a product fractionation step not shown. Hot stripped catalyst at an elevated temperature is withdrawn from a lower portion of the stripping zone by conduit 36 for transfer to a fluid bed of catalyst being regenerated in a catalyst regeneration zone. Flow control valve 38 is provided in transfer conduit 36.
This type of catalyst regeneration operation is referred to as a swirl type of catalyst regeneration due to the fact that the catalyst bed tends to rotate or circumferentially circulate about the vessel's vertical axis and this motion is promoted by the tangential spent catalyst inlet to the circulating catalyst bed. Thus, the tangentially introduced catalyst at an elevated temperature is further mixed with hot regenerated catalyst or catalyst undergoing regeneration at an elevated temperature and is caused to move in a circular or swirl pattern about the regenerator's vertical axis as it also moves generally downward to a catalyst withdrawal funnel 40 (sometimes called the "bathtub") adjacent the regeneration gas distributor grid. In this catalyst regeneration environment, it has been found that the regeneration gases comprising flue gas products of carbonaceous material combustion tend to move generally vertically upwardly through the generally horizontally moving circulating catalyst to cyclone separators positioned above the bed of catalyst in any given vertical segment. As shown by FIG. 2, the catalyst tangentially introduced to the regenerator by conduit 36 causes the catalyst to circulate in a clockwise direction in this specific embodiment. As the bed of catalyst continues its circular motion some catalyst particles move from an upper portion of the mass of catalyst particles suspended in regeneration gas downwardly therethrough to a catalyst withdrawal funnel 40 in a segment of the vessel adjacent to the catalyst inlet segment. In the regeneration zone 42 housing a mass of the circulating suspended catalyst particles 44 in upflowing oxygen containing regeneration gas introduced to the lower portion thereof by conduit distributor means 46, the density of the mass of suspended catalyst particles may be varied by the volume of regeneration gas used in any given segment or segments of the distributor grid. Generally speaking, the circulating suspended mass of catalyst particles 44 undergoing regeneration with oxygen containing gas to remove carbonaceous deposits by burning will be retained as a suspended mass of swirling catalyst particles varying in density in the direction of catalyst flow and a much less dense phase of suspended catalyst particles 48 will exist thereabove to an upper portion of the regeneration zone. Under carefully selected relatively low regeneration gas velocity conditions, a rather distinct line of demarcation may be made to exist between a dense fluid bed of suspended catalyst particles and a more dispersed suspended phase (dilute phase) of catalyst thereabove. However, as the regeneration gas velocity conditions are increased there is less of a demarcation line and the suspended catalyst passes through regions of catalyst particle density generally less than about 30 lbs. per cu. ft. A lower catalyst bed density of at least 20 lb/cu. ft. is preferred.
A segmented regeneration gas distributor grid 50 positioned in the lower cross-sectional area of the regeneration vessel 42 is provided as shown in FIG. 1 and is adapted to control the flow of regeneration gas passed to any given vertical segment of the catalyst bed thereabove. In this arrangement, it has been found that even with the generally horizontally circulating mass of catalyst, the flow of regeneration gas is generally vertically upwardly through the mass of catalyst particles so that regeneration gas introduced to the catalyst bed by any given grid segment or portion thereof may be controlled by grid openings made available and the air flow rate thereto. Thus, oxygen containing combustion gases after contact with catalyst in the regeneration zone are separated from entrained catalyst particles by the cyclonic means provided and vertically spaced thereabove. The cyclone combinations diagrammatically represented in FIG. 1 are intended to correspond to that represented in FIG. 2. Catalyst particles separated from the flue gases passing through the cyclones are turned to the mass of catalyst therebelow by the plurality of provided catalyst diplegs.
As mentioned above, regenerated catalyst withdrawn by funnel 40 is conveyed by standpipe 6 to the hydrocarbon conversion riser 4.
The regenerator system shown in FIGS. 1 and 2 is usually designed for producing a flue gas that contains a substantial concentration of carbon monoxide along with carbon dioxide. In fact, a typical CO.sub.2 /CO ratio is about 1.2.
As noted above, there has recently been a marked increase in the desire to reduce carbon monoxide emissions from the regenerator of a reflexive non-hydrogenative catalytic cracking process. Prior proposed solutions, of increasing the temperature of the regenerator sufficient to thermally burn CO, or of incorporating chromium or iron with the cracking catalyst to support catalytic CO combustion, have not accomplished a sufficient reduction in CO emissions or, when this reduction has approached sufficiency, it has been at the expense of a great detriment to the operation and product distribution of the cracking reaction side of the process. In addition to the fact that increased production of coke on the cracking side throws this entire reflexive system into heat imbalance, the increased production of light gas unduly strains the capacity of the compressors and the entire gas plant, that is the series of separation operation in which the C.sub.4.sup.- gasiform part of the product is resolved into its component parts.
It is therefore an important object of this invention to provide a novel means of reducing carbon monoxide emissions from a reflexive, non-hydrogenative catalytic cracking process.
It is another object of this invention to provide a novel catalyst for such a process.
It is another object of this invention to provide an improved process for the fluid catalytic cracking of gas oils in the absence of added hydrogen.
Other and additional objects of this invention will become apparent from a consideration of this entire specification including the claims hereof.
Various references which have been uncovered may bear upon the subject matter of this application. The following list is not suggested to be exhaustive or all inclusive. It does, however, identify those presently known references which, in the opinion of counsel, seem to bear upon this subject matter:
U.S. Pat. No. 3,660,310; Kluksdahl
U.S. Pat. No. 3,788,977; Dolbear
U.S. Pat. No. 3,364,136; Chen et al
U.S. Pat. No. 2,436,927; Kassel
U.S. Pat. No. 3,226,339; Frilette et al


A device receives void configuration information that identifies a set of rules for generating void information based on printed circuit board (PCB) design information, and receives, based on receiving the void configuration information, the PCB design information that identifies via information of a PCB. The device compares, based on receiving the PCB design information, the set of rules, associated with the void configuration information, and the via information associated with the PCB design information, and generates the void information based on comparing the set of rules, associated with the void configuration information, and the via information associated with the PCB design information. The void information includes a set of parameters associated with a set of voids to be included in the PCB. The device performs an action based on generating the void information.

Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of tools for designing electronic systems such as integrated circuits, printed circuit boards, and the like. The tools work together in a design flow that chip designers use to design and analyze entire semiconductor chips. Since a modern semiconductor chip can have billions of components, EDA tools are essential for their design.

Printed circuit board void information generation using parameter-based rule sets


An intravascular stent includes an eluting sheath fabricated from a mesh for controlled release of therapeutic drugs and for delivery of the therapeutic drugs in localized drug therapy in a blood vessel. The eluting sheath is attached to at least a portion of an outside surface area of the stent structure and is fabricated from a mesh designed to neck down in response to a radially outward directed force resulting in the uniform expansion of the stent. The eluting sheath can be loaded with at least one therapeutic drug for the release thereof at a treatment site to facilitate repair of a damaged vessel. The stent has a high degree of flexibility in the longitudinal direction, yet has adequate vessel wall coverage and radial strength sufficient to hold open an artery or other body lumen.

This invention relates to vascular repair devices, and in particular intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency thereof. Stents are particularly useful in the treatment of atherosclerotic stenosis in arteries and blood vessels. More particularly, the invention concerns an intravascular device having a prefabricated, patterned mesh stent cover that helps to prevent the formation and release of embolic debris in the body lumen and is capable of eluting therapeutic drugs with uniform and controlled drug distribution at the treatment site while providing the intravascular device with a uniform patterned biocompatible and/or hemocompatible surface.
An intravascular interventional device such as a stent is particularly useful in the treatment and repair of blood vessels after a stenosis has been treated by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means, to help improve the results of the procedure and reduce the possibility of restenosis. Stents also can be used to provide primary compression to a stenosis in cases in which no initial PTCA or PTA procedure is performed. While stents are most often used in the procedures mentioned above, they also can be implanted in any body lumen or vessel such as the urethra, esophagus and bile duct and the like.
In typical PTCA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the aorta. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient's vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressure to press the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient's vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty. In angioplasty procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. Stents are generally cylindrically shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as coronary artery. Stents are usually delivered in a compressed condition to the target location and then are deployed into an expanded condition to support the vessel and help maintain it in an open position. The stent is usually crimped tightly onto a delivery catheter and transported in its delivery diameter through the patient's vasculature. The stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of the delivery catheter, which expands the compressed stent to a larger diameter to be left in place within the artery at the target location. The stent also may be of the self-expanding type formed from, for example, shape memory metals or super-elastic nickeltitanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen.
Since it is often useful to provide localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the stent, it is also desirable to provide stents with a biocompatible and/or hemocompatible surface coating of a polymeric material with the capability of being loaded with therapeutic agents, to function together with the intravascular devices for placement and release of the therapeutic drugs at a specific intravascular site. Drugs can also be loaded on a stent without using a polymer coat, for example, by chemical linkage. Drug-eluting stent devices have shown great promise in treating coronary artery disease, specifically in terms of reopening and restoring blood flow in arteries stenosed by atherosclerosis. Restenosis rates after using drug-eluting stents during percutaneous intervention are significantly lower compared to bare metal stenting and balloon angioplasty.
The above-described, non-surgical interventional procedures, when successful, avoid the necessity for major surgical operations. However, a danger which is always present during these procedures is the potential for particles of the atherosclerotic plaque, which can be extremely friable, breaking away from the arterial wall. For example, during deployment of a stent, the metal struts of the stent can possibly cut into the stenosis and shear off pieces of plaque which become embolic debris that will travel downstream and lodge somewhere in the patient's vascular system. When any of the above-described procedures are performed in the carotid arteries, the release of emboli into the circulatory system should be avoided. For example, debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, possibly resulting in a stroke. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages. Embolization in other vasculature may induce possible acute myocardial infraction when a procedure is performed on the coronary arteries and gangrene when performed in peripheral arteries, such as the arms and legs. In addition, current design and fabrication methods for drug-eluting stent devices are not optimal. Accordingly, various limitations exist with respect to such current design and fabrication methods for drug-eluting stents.
While stents are helpful in holding open otherwise blocked or occluded vessels, the stent does have an open structure which may include struts and spines which cooperatively provide the scaffolding necessary to maintain the vessel open at the site of treatment. Due to the open nature of the stent structure, there is a possibility that growth material can pass through the openings between the struts and extend into the inner lumen of the stent structure. For example, excessive cell or tissue growth (intimal hyperplasia) can cause partial restenosis to develop over time, which is detrimental to the patient. The tissue or cell growth can extend into the tubular opening created by the stent and can block or otherwise reocclude the opening and can possibly cause abnormal blood flow through the stent which can cause formation of thrombi that are detrimental to the patient's health.
Prior art devices have been created to help reduce the passage of such growth through the wall of the deployed stent, including a stent covering which surrounds the open stent. In this manner, the gaps between the stent struts can be covered to prevent material, such as plaque, from prolapsing between the struts. Coverings have included a variety of materials such as ePTFE, autologous vein grafts, pericardium and fibrin. The covering should be sufficiently flexible and expandable to allow the stent to deploy from its collapsed or compressed position to a fully expanded position.
Covered stents also help prevent the struts from cutting into the plaque of the stenosis which helps reduce the possibility of forming embolic debris that can be released into the blood stream, as described above. Moreover, in the event that any embolic debris may be created from the expansion of the stent, the covering could trap the embolic particles against the arterial wall, thus preventing the particles from being released into the bloodstream.
Some prior art covered stents are difficult to manufacture due to the flexibility of the covering and the requirement that the covering be capable of expansion when the stent is deployed within the patient's vasculature. For these reasons, the material used to form the covering may be subjected to intricate processing to obtain the desired flexibility for the covering and to attach the covering to the stent. A covering which does not expand normally can cause the stent to misalign within the body vessel and can cause an non-uniform deployment of the stent. Moreover, some coverings are made from a sheet of material which is rolled into a cylindrical shape by creating a longitudinal seam which runs along the length of the covering and then the covering is attached to the stent. Such coverings can be more susceptible to tearing, especially at the seam, when the stent is expanded.
Some prior art stents that are covered may have a tendency to shorten when expanded and the covered material also shortens, providing an undesirable result. As the stent and the covered material are expanded into contact with an artery or vessel wall, the shortening movement may scrape along the artery wall and cause injury or dislodge plaque material which may embolize. Further, as these prior art covered stents shorten upon expansion, the cover material shortens past the stent struts at the stent ends, leaving a covered stent with exposed stent struts, and not fully covered upon expansion.
Moreover, the addition of drug elution to the stent adds a whole new set of engineering challenges. Current design and fabrication methods for drug-eluting stent devices are not optimal. One limitation, for example, is that current drug eluting stent designs employ spray techniques in which a mixture of the drug in a polymer and/or solvent solution is spray coated on the entire stent surface with a primer, drug, and topcoat layers being used to control release kinetics. This approach tends to cause cracking in the drug-coating layer, since the layer also undergoes stretching during stent expansion, and a considerable amount of the drug is washed out into the blood stream, and only a fraction gets into the tissue/artery. Further, the amount of the drug that can be loaded on the stent is limited by mechanical properties of the coating, since a higher drug content in the polymer makes the coating more brittle and causes cracking thereto. Therefore, loading a higher drug dose requires coating with more polymer on the device. Moreover, the spray techniques require large spaces to avoid webbing and pooling. Special equipment for crimping the drug-eluting stent on the balloon and to securely attach the stent on the balloon is also needed in accordance with current fabrication methods. Often spray coatings may be damaged during the crimping processes. Stents designed for acute deliverability may not make the optimal elution vehicles.
What has been needed and heretofore unavailable is a novel design that decouples the two major functional characteristics of the drug-eluting stent device, namely the purely mechanical stent structure and the local drug-eluting component. Current devices are constrained by their design construct which necessitates optimizing both factors—mechanical stent expansion and drug-elution kinetics simultaneously. Thus, it would be desirable to have a stent structure that is optimally designed for expansion (i.e., allowable stress/strain, scaffolding, radial strength, etc.) independent of the drug-eluting component, and the drug-eluting component designed for local drug release independent of mechanical factors associated with stent expansion. The present invention meets these and other needs.

This patent is subject to a terminal disclaimer.

Drug-eluting stent cover and method of use


Provided are a monolithic microwave integrated circuit device and a method for forming the same. The method includes: forming an sub-collector layer, a collector layer, a base layer, an emitter layer, and an emitter cap layer on a Heterojunction Bipolar Transistor (HBT) region and a PIN diode region of a substrate; forming an emitter pattern and an emitter cap pattern in the HBT region and exposing the base layer by patterning the emitter layer and the emitter cap layer; and forming an intrinsic region by doping a portion of the collector layer of the PIN diode region with a first type impurity, the PIN diode region being spaced apart from the HBT region.

The present invention disclosed herein relates to a monolithic microwave integrated circuit device and more particularly to, a monolithic microwave integrated circuit device including a hetrojunction bipolar transistor (HBT) and a method for forming the same.
Due to the development of wireless communication service, a portable wireless communication device has been extensively used. A wireless communication device requires a power amplifier of various frequencies and outputs, which includes a mobile phone for voice and video communication, a smart phone with a wireless communication function such as Wi-Fi or Bluetooth besides a mobile phone feature, and a Portable Media Player (PMP) or a notebook computer with a wireless communication function.
A bipolar transistor may be used as an ultrahigh frequency semiconductor device in an ultrahigh-speed broadband communication network. Recently, researches for realizing a faster ultrahigh-speed operation by reducing a parasite component of the above device have been being made. Especially, the HBT may be used as a basic device of a power transistor and a power amplifier. For manufacturing a value-added integrated circuit, a Monolithic Microwave Integrated Circuit (MMIC) technology is used, where passive devices such as a capacitor, a resistor, an inductor in addition to the HBT (i.e., an active device) are integrated into the same chip.
Due to the development of various forms of wireless communication technologies, a wireless terminal needs to support various wireless communication standards. When a power amplifier fit for each wireless communication function is used, a high frequency switch is required to distribute input signals of diverse frequencies into each power amplifier.

Monolithic microwave integrated circuit device and method of forming the same

Electronics and Telecommunications Research Institute


An apparatus and a method for performing hitless switching between optical transmission lines such as optical fiber circuits are provided. An optical switch or optical switching network having input terminals and output terminals for selecting optical signals inputted to the input terminals to the output terminals with a selection ratio which can be varied continuously is used. An optical signal converter for generating an optical signal of light which does not interfere with another optical signal is attached to the optical switch. Further, a signal loop interconnecting one of the output terminals of the switch and the input of the optical signal converter is provided. When hitless switching between two optical transmission lines is performed, the same information signal is first inputted to the two transmission lines on the transmission side, then the optical signal from the two lines are transmitted to one of the output terminal (aimed output terminal) of the switch and another output terminal connected to the signal loop. The phase difference between the optical signals is detected and adjusted, and the optical switch is controlled so that the optical signal to be selected at the aimed output terminal is varied to the signal passing through the signal loop.

1. Field of the Invention
This invention relates to a hitless switching apparatus and method for optical transmission lines in an optical network.
2. Description of the Related Art
In an optical network which includes a plurality of nodes and optical transmission lines formed from optical fibers or the like for interconnecting the nodes, it is sometimes desired to switch a route along which a signal is transmitted without interrupting transmission of a signal between two nodes. Switching is desired, for example, when it is tried, after the signal transmission route is switched to a bypass route due to the occurrence of trouble in a certain optical transmission line or node, to switch the signal transmission line back to the original route after recovery from the trouble, or when another route must be used to transmit a signal in order to perform construction or maintenance of the equipment. Here, to switch the signal transmission route to a different optical fiber accommodated in the same optical fiber cable is included within switching the signal transmission route to another route. Since switching of an optical transmission generally takes place independently of communication between users in a network, a countermeasure must be taken upon switching to prevent the switching from causing an obstacle to regular communication of the users. In particular, hitless switching must be achieved so that an error of even one bit is not produced. In this instance, since a transmission route before switching and another transmission route after switching generally present different propagation delay amounts, switching that absorbs the difference between the propagation delay amounts must be realized. Since the difference in propagation delay time between the routes is quite large compared with the time per signal bit, mere switching between transmission lines using an optical switch cannot realize hitless switching. Even for switching to a different optical fiber in the same optical fiber cable, since the transmission rate is as high as 1 Gbit/second or more, the phase of the signal cannot be identical between the optical fibers and it is necessary to compensate for the difference in propagation delay time.
A hitless switching system suitable for use with an optical network is disclosed, for example, in Japanese Patent Laid-Open Application No. 80636/91 (JP, A, 3-80636) or No. 56925/92 (JP, A, 4-56925). FIG. 1 shows the construction of the hitless switching system disclosed in the former application. An optical fiber cable 103 accommodates n optical fibers 104.sub.a to 104.sub.n for signal transmission constituting n/2 pairs of bidirectional transmission lines, and a single spare optical fiber 108. The optical fibers 104.sub.1 to 104.sub.n for signal transmission are removably connected at one end side thereof to output ports of optical dividers 105.sub.1 to 105.sub.n by way of connectors 109, respectively. The input ports of the optical dividers 105.sub.1 to 105.sub.n are connected to optical signal transmitters 101.sub.1 to 101.sub.n by way of linear polarizers 107.sub.1 to 107.sub.n, respectively. Meanwhile, the other ends of the optical fibers 104.sub.1 to 104.sub.n are removably connected to the input ports of optical combiners 106.sub.1 to 106.sub.n by way of connectors 109, respectively. The output ports of the optical combiners 106.sub.1 to 106.sub.n are connected to optical signal receivers 102.sub.1 to 102.sub.n, respectively. The spare optical fiber 108 has a pair of connectors 109 attached to the opposite ends thereof and has a polarization orthogonal rotator 110 and an optical path length adjuster 111 interposed therein. Each of the connectors 109 can be connected arbitrarily to one of the optical dividers 105.sub.1 to 105.sub.n and one of the optical combiners 106.sub.1 to 106.sub.n. Further, an optical path controller 112 which can be connected arbitrarily to two of the optical combiners by way of connectors 109 is provided. The controller 112 measures the polarization directions of and the difference in time between two optical signals inputted to the optical combiners to control the polarization orthogonal rotator 110 and the optical path length adjuster 111.
In order to switch the transmission route from a first optical fiber for signal transmission to a second optical fiber for signal transmission, the spare optical fiber 108 is first connected to the free ports of an optical divider 105.sub.n and an optical combiner 106.sub.n to which the first optical fiber is connected to set a bypass route by the spare optical fiber 108. Then, the optical divider 105.sub.n and the polarization orthogonal rotator 110 are operated so that a signal light beam in the first optical fiber 104.sub.n and another signal light beam in the spare optical fiber 108 may be linearly polarized perpendicularly to each other, and the signal light beams are introduced into both of the optical fibers 104.sub.n and 108. Thereafter, the optical path length adjuster 111 is adjusted so that the signals passing in the two optical fibers 104.sub.n and 108 do not have a difference between arriving times, and then, the optical combiner 106.sub.n is switched to the spare optical fiber 108 side to set the signal transmission route to the spare optical fiber 104.sub.n 108. Then, the first optical fiber is removed from the optical divider 105.sub.n and the optical combiner 106.sub.n ; instead, a second optical fiber is connected to the optical divider 105.sub.n and the optical combiner 106.sub.n. Thereafter, a similar procedure is followed to switch the transmission route for an optical signal from the spare optical fiber 108 to the second optical fiber, thereby realizing hitless switching from the first optical fiber 104.sub.n to a second optical fiber.
Separately, FIG. 2 shows the construction of the hitless switching system disclosed in Japanese Patent Laid-Open Application No. 56925/92. The system is constructed so that an optical transmitter 121 and an optical receiver 123 are interconnected by way of a pair of optical fibers 122 and 125 provided in parallel to each other. While the optical fiber 122 has an ordinary construction, the other optical fiber 125 has an optical path length adjuster 127 and a polarization controller 128 interposed therein. An optical switch 124 of the 1.times.2 construction for inputting signal light at an arbitrary branching ratio into the optical fibers 122 and 125 is provided on the optical transmitter 121 side. An optical coupler 126 for combining signal light inputted thereto from the two optical fibers 122 and 125 is provided on the optical receiver 123 side. Also hitless switching by the system is performed by adjusting the polarization conditions of the two optical fibers 122 and 125 so that they may be orthogonal to each other and by varying the branching ratio of the optical switch 124 while adjusting the propagation time of signal light in the other optical fiber 125 by means of the optical path length adjuster 127.
With the conventional hitless switching systems described above, however, In order to prevent possible interference between signal light beams from two optical transmission lines when the signal light beams are combined, the polarization directions of the two signal light beams to be combined must be adjusted so as to be orthogonal to each other. Accordingly, optical transmission lines by which a polarization condition is maintained must be used; as well, a polarization controller must necessarily be inserted in at least one of the two optical transmission lines. Further, in order to compensate for the propagation delay time, an optical path length adjuster must necessarily be inserted in at least one of the two optical transmission lines. In other words, the conventional hitless switching systems disadvantageous in that a special optical transmission line must be used, which complicates the entire system.

Hitless switching apparatus and method for optical network


A bulging apparatus has a heating station, a tube expanding station, a preforming station, and a main forming station. A straight tube as a workpiece is gripped by first holding mechanisms or second holding mechanisms, and delivered between the stations as the first holding mechanisms or second holding mechanisms are displaced. During a preforming process and a main holding process, both the first holding mechanisms and second holding mechanisms can be lifted and lowered vertically and can be moved horizontally.

Bulging processes have been employed to produce hollow formed bodies which are long and whose cross-sectional shapes and dimensions perpendicular to the longitudinal direction thereof differ from position to position (see, for example, Patent Document 1). As described in Patent Documents 2, 3, bulging apparatus for performing bulging processes have a single compressing mechanism that is combined with interchangeable dies. The bulging apparatus have a plurality of dies each interchangeable with another die suitable for a shape to be formed.
A bulging process using a straight tube as a blank workpiece will specifically be described below. First, the straight tube is gripped and placed in a die. Then, a fluid under pressure (generally water under high pressure) is supplied into the straight tube.
Therefore, the straight tube has its inner circumferential wall pressed by the fluid under pressure, and is expanded diametrically outwardly. As the straight tube is placed in the die, the expanded portion of the straight tube is finally stopped by the die. Therefore, the straight tube is formed into a shape corresponding to the cavity of the die. This process is also referred to as a tube expanding process.
Then, the die is removed from the compressing mechanism, and another die is mounted in the compressing mechanism for performing a next forming process. At this time, the die used in the tube expanding process is retracted from the compressing mechanism, and the die to be used in the forming process is moved to the compressing mechanism.
The expanded straight tube is transferred to the die, and then compressed to a predetermined shape by the compressing mechanism. A final formed product is now obtained.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-96118
Patent Document 2: Japanese Laid-Open Patent Publication No. 10-156429
Patent Document 3: Japanese Laid-Open Patent Publication No. 2001-150048