MXPA02008554A - Process for producing polypropylene from c3. - Google Patents

Abstract

A process for producing polymers from C2 C4 olefins selectively produced from a catalytically cracked or thermally cracked naphtha stream is disclosed herein. A mixture of the naphtha stream and a stream of steam is fed into a reaction zone where it is contacted with a catalyst containing from about 10 to 50 wt. % of a crystalline zeolite having an average pore diameter less than about 0.7 nanometers at reaction conditions that include temperatures from about 500 C to 650 C and a hydrocarbon partial pressure from about 10 to 40 psia.

Description

PROCESS TO PRODUCE POLYPROPYLENE FROM OLEFINS C. PRODUCED SELECTIVELY IN A FLUID CATALYTIC DEBUGGING PROCESS FROM A FEED OF NAFTA / WATER VAPOR Field of the Invention The present invention relates to a process for producing polypropylene from C3 olefins produced selectively from a stream of catalytically disintegrated or thermally disintegrated naphtha. Background of the Invention m ^ The need for low emission fuels has 15 created an increased demand for light olefins in synthesis processes of alkylation, oligomerization, MTBE, and ETBE. In addition, a low cost supply of light olefins, particularly propylene, continues in demand to serve as a feedstock for the production of polyolefins, particularly polypropylene. The fixed bed processes for dehydrogenation of light paraffins have recently attracted renewed interest to increase olefin production. However, these types of processes typically require relatively large capital investments and high operating costs. It is therefore advantageous to increase the production of olefins using processes that they require relatively small capital investment. It would be particularly advantageous to increase the production of olefins in catalytic disintegration (cracking) processes. A problem inherent in producing olefin products using FCC units is that the process depends on a specific catalyst balance to maximize the production of light olefins while also achieving high conversion of the feed components of 650 ° F + (340 ° C +) . In addition, even if a specific catalyst balance can be maintained to maximize overall olefin production, olefin selectivity is generally low due to undesirable side reactions, such as disintegration, isomerization, aromatization and hydrogen transfer reactions. Light saturated gases produced from undesirable side reactions result in increased costs to recover desirable light olefins. Therefore, it is desirable to maximize the production of olefins in a process that allows a greater degree of control over the selectivity to C2-C4 olefins. SUMMARY OF THE INVENTION An embodiment of the present invention is a process for producing polypropylene comprising the steps of (a) feeding steam and a stream of naphtha containing less than about 40% by weight of paraffins and between about 15 and about 70% by weight of olefins within a reaction zone; (b) contacting the naphtha feed with a catalyst comprising a crystalline zeolite having an average pore diameter of less than about 0.7 nm at conditions including a trature of about 500 to 650 CC, a partial pressure of hydrocarbons of 10 to 40 psia, a residence time of hydrocarbons of 1 to 10 seconds, and a weight ratio of catalyst to feed of about 4 to about 10, where no more than about 20% by weight of • paraffins are converted to olefins, where the polypropylene comprises at least about 90 mol% of the total C3 products; and (c) separating propylene from C3 products and polymerizing propylene to form polypropylene. In a preferred embodiment of the present invention, the crystalline zeolite is selected from the ZSM series. In another preferred embodiment of the present invention the catalyst is a ZSM-5 type catalyst. In yet another preferred embodiment of the present invention, the feedstock contains from about 5 to 35% by weight of paraffins, and of about 20 20 to 70% by weight of olefins. In still another preferred embodiment of the present invention the reaction zone is operated at a trature of about 525 to about 600 ° C. Detailed Description of the Invention 25 Feeds that are adequate to produce the relatively high yields of C2, C3, and C4 olefins are streams that boil in the range of naphtha and contain less than about 40% by weight, preferably from about 5 to about 35% by weight, more preferably from about 10 to about 30% by weight, and most preferably from about 10 to 25% by weight of paraffins, and from about 15% by weight, preferably from about 20% by weight to about 70% by weight of olefins. The food can also contain nafteños and aromatics. Naphtha boiling range streams are typically those having a boiling range of about 65 to about 430 ° F (18-225 ° C), preferably from about 65 to about 300 CF (18-150 ° C) ). The naphtha feed may be a thermally disintegrated or catalytically disintegrated naphtha derived from any suitable source. Naphtha streams can be derived from the fluid catalytic disintegration (FCC) of gas oils and residues or from delayed or fluid coking of waste. Preferably, the naphtha streams used in the present invention derive from the fluid catalytic disintegration of gas oils and residues because these naphthas are typically rich in olefins and / or diolefins and relatively light in paraffins. The process of the present invention is carried out in a process unit comprising a reaction zone, a separation zone, a catalyst regeneration zone, and a fractionation zone. The naphtha feed is fed into the reaction zone as a mixture of naphtha and steam, where it makes contact with a hot, regenerated catalyst source. The hot catalyst vaporizes and disintegrates the feed at a temperature of about 500 to 650 ° C, preferably about 525 to 600 ° C. The decay reaction deposits coke in the catalyst, thereby deactivating the catalyst. The disintegrated products are separated from the coked catalyst and sent to a fractionator. The coked catalyst is passed through the separation zone where the volatiles are separated from the catalyst particles with a separation medium such as steam. The separation can be carried out under low stringency conditions to retain a larger fraction of the hydrocarbons adsorbed for energy balance. The separated catalyst is then passed to the regeneration zone where it is regenerated by burning at least a portion of the coke in the catalyst in the presence of a gas containing oxygen, preferably air. Decooking restores catalyst activity and simultaneously warms the enter catalyst 650 and 750 ° C. The hot regenerated catalyst is then recycled to the reaction zone to react with fresh naphtha feed. Chimney gas formed by burning coke in the regenerator can be treated for particle removal and for carbon monoxide conversion. The products disintegrated from the reaction zone are sent to a fractionation zone where several products are recovered, particularly a C3 fraction, a C4 fraction rich in olefins, and a C5 fraction rich in olefins. The amount of steam co-fed with the naphtha feed will typically be in the range of about 10 to 250 mole%, preferably about 25 to 150 mole% steam to naphtha. Although attempts have been made to increase conversions to light olefins in the process unit itself In the FCC, the present invention uses its own distinctive process unit, as previously described, and receives naphtha from a suitable source in the refinery. The reaction zone is ^^ operates at process conditions that will maximize the selectivity of olefins (particularly propylene) C2 to C4 with conversion 15 relatively high C5 + olefins. Catalysts suitable for use in the practice of the present invention are those which comprise a crystalline zeolite having an average pore diameter of less than about 0.7 nanometer (nm), said zeolite ^^ Crystalline comprising from about 10 to about 50% 20 by weight of the total fluidized catalyst composition. It is preferred that the crystalline zeolite be selected from the family of medium pore size crystalline aluminosilicates (< 0.7 nm), otherwise known as zeolites. Of particular interest are medium pore zeolites with a silica ratio 25 to alumina of less than about 75: 1, preferably less than about 50: 1, and more preferably even less than about 40: 1, although some embodiments may have silica to alumina ratios greater than 40: 1. The pore diameter, also known as the effective pore diameter, is measured using standard adsorption techniques and hydrocarbon compounds of known minimum kinetic diameters. See Breck, Zeolite Molecular Sieves, 1974 and Anderson et. al., J. Catalysis 58, 114 (1979), both of which are incorporated herein by reference. The medium pore size zeolites that can be used in the practice of the present invention are described in "Atlas of Zeolite Structure Types", editors. H. Meier and D. H. Olson, Butterworth-Heineman, Third Edition, 1992, which is incorporated herein by reference. Medium pore size zeolites generally have a pore size of about 5 to about 7A and include for example, structure type zeolites MFI, MFS, MEL, MTW, EUO, MTT, HEU, FER, and TON (IUPAC Zeolite Nomenclature Commission). Non-limiting examples of such medium pore size zeolites include ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, silicalite, and silicalite 2. The most preferred is ZSM-5, which is described in US Pat. Nos. 3,702,886 and 3,770,614. The ZSM-11 is described in the patent US 3,709,979; the ZSM-12 in the patent US 3,832,449; ZSM-21 and ZSM-38 in US Patent 3,948,758; ZSM-23 in US Patent 4,076,842; and the ZSM-35 in US Patent 4,016,245. All of the above patents are incorporated herein by reference. Other suitable medium pore size zeolites include silicon and aluminum phosphates (SAPO), such as SAPO-4 and SAPO-11 which is described in US Patent 4,440,871; chromosilicates; gallium silicates; iron silicates; aluminum phosphates (ALPO), such as ALPO-11 described in US patent 4,310,440; titanium aluminosilicates (TASO), such as TASO-45 described in EP-A 229,295; boro silicates, described in US Pat. No. 4,254,297; titanium aluminophosphates (TAPO), such as TAPO-11 described in US Patent 4,500,651; and iron aluminosilicates. Medium pore zeolites may include "crystal blends" which are believed to be the result of faults occurring within the crystal or crystalline area during the synthesis of zeolites. Examples of crystalline mixtures of ZSM-5 and ZSM-11 are disclosed in US Patent 4,229,424 which is incorporated herein by reference. The crystalline mixtures are in themselves medium pore size zeolites and should not be confused with physical mixtures of zeolites in which crystals other than crystallites of different zeolites are physically present in the same catalyst compound or hydrothermal reaction mixtures. The catalysts of the present invention are held together with a component of inorganic oxide matrix material. The inorganic oxide matrix component agglutinates the catalyst components together such that the catalyst product is sufficiently hard to survive collisions between particles and with the reactor wall. The inorganic oxide matrix can be made from an inorganic oxide sol which is dried to "bind" the catalyst components together. Preferably, the inorganic oxide matrix ^^ is not catalytically active and will comprise oxides of silicon and aluminum. It is also preferred that the separated alumina phases are incorporated into the inorganic oxide matrix. Species Aluminum oxyhydroxide-α-alumina, boehmite, diaspore, and transition aluminas such as α-alumina, β-alumina, α-alumina, d-alumina, e-alumina, α-alumina, and p-alumina can be used . Preferably, the alumina species are an aluminum trihydroxide such as gibbsite, bayerite, nordstranditium, or doyelite. The matrix material may also contain phosphorus or aluminum phosphate. Preferred process conditions include temperatures of from about 500 to about 650 ° C, preferably from about 500 to 600 ° C; partial pressures of 0 hydrocarbons of about 10 to 40 psia (70-280 kPa), preferably about 20 to 35 psia (140-245 kPa); and a catalyst to naphtha (w / w) ratio of from about 3 to 12, preferably from about 4 to 10, where the catalyst weight is the total weight of the catalyst compound. Of preference, the residence time of naphtha in the zone of reaction is less than about 10 seconds, for example about 1 to 10 seconds. The reaction conditions will be such that at least about 60% by weight of the C5 + olefins in the naphtha stream are converted to C4- products and less than about 25% by weight, preferably less than about 20% by weight. of the paraffins are converted to C4- products, and that the propylene comprises at least about 90 mol%, preferably more than about 95 mol% of the total C3 reaction products with the weight ratio of propylene / total C2 products greater than around 3.5. Preferably, the ethylene comprises at least about 90 mol% of the C2 products, with the weight ratio of propylene: ethylene being greater than about 4, and that the C5 + product of "full range" is improved in octanes of both engine and research in relation to the supply of naphtha. It is within the scope of this invention to pre-coke the catalysts before introducing the feed to further improve the selectivity to propylene. It is also within the scope of this invention to feed an effective amount of single ring aromatics to the reaction zone to improve the selectivity of propylene against ethylene. The aromatics can be from an external source such as a reforming unit or they can consist of heavy naphtha recycle product from the current process. The following examples are presented for purposes illustrative only and should not be taken as limiting the present invention in any way. Examples 1-13 The following examples illustrate the criticality of the process operating conditions for maintaining purity of chemical grade propylene with samples of disintegrated naphtha on ZCAT-40 (a catalyst containing ZSM-5) that has been vaporized with water 1500 ° F (815 ° C) for 16 hours to simulate a commercial balance. The comparison of Examples 1 and 2 10 shows that increasing the catalyst / hydrocarbon ratio improves the conversion of propylene, but sacrifices the propylene purity. The comparison of Examples 3 and 4 and 5 and 6 shows • that reducing partial pressure of hydrocarbons significantly improves the purity of propylene without compromising the conversion 15 of propylene. The comparison of Examples 7 and 8 and 9 and 10 shows that increasing the temperature improves both propylene conversion and purity. Comparison of Examples 11 and 12 shows that decreasing the residence time of the catalyst ^^ improves the conversion and purity of propylene. Example 13 20 shows an example where both high propylene conversion and purity are obtained at a reactor temperature and catalyst / hydrocarbon ratio that can be achieved using a conventional FCC reactor / regenerator design for the second stage.

Table 1 Table 1 (continued) , = CH? C2H4 C2H6 The above examples (1,2,7 and 8) show that CJ / CJ > 4 and CJ / CJ >;3 . 5 can be achieved by selection of suitable reactor conditions. Examples 14-17 The disintegration of olefins and paraffins contained in the naphtha streams (ie, catalytic naphtha, coker naphtha) on small or medium pore zeolites such as ZSM-5 can produce significant amounts of ethylene and propylene. The selectivity to ethylene or propylene and the selectivity of propylene to propane varies as a function of the catalyst and the operating conditions. It has been found that the conversion of propylene can be increased by co-feeding water vapor together with catalytic naphtha to the reactor. The catalyst can be ZSM-5 or other small or medium pore zeolites. Table 2 below illustrates the increase in propylene conversion when 5% by weight of steam is co-fed with a catalytic naphtha containing 38.8% by weight of olefins. Although propylene conversion increased, the purity of the • Propylene decreased. Thus, other operating conditions may need to be adjusted to maintain the propylene selectivity sought. 25 Table 2 Table 2 (continued) The light olefins resulting from the preferred process can be used as feeds for processes such as oligomerization, polymerization, co-polymerization, terpolymerization, and related processes (hereinafter called "polymerization") to form macromolecules. Such light olefins can be polymerized both alone and in combination with other species, according to the polymerization methods known in the art. In some cases it may be desirable to separate, concentrate, purify, improve, or otherwise process the light olefins prior to polymerization. Propylene and ethylene are preferred polymerization feeds. Polypropylene and polyethylene are products of preferred polymerizations made therefrom.

Claims (1)

1. CLAIMS 1. A process for producing polypropylene comprising the steps of: (a) feeding steam and a naphtha feed containing less than about 40% by weight of paraffins and between about 15 and 70% by weight of olefins within an area of reactor; (b) contacting the naphtha feed with a catalyst comprising from 10 to 50% by weight of a crystalline zeolite having an average pore diameter of less than about 0.7 nm at conditions including a temperature of about 500 to 650 ° C , a hydrocarbon partial pressure of 10 to 40 psia, a hydrocarbon residence time of 1 to 10 seconds, and a weight ratio of catalyst to feed of about 4 to 10, where no more than about 20% by weight of paraffins are converted to olefins, where the polypropylene comprises at least about 90 mol% of the total C3 products; and (c) separating propylene from C3 products and polymerizing propylene to form polypropylene. 2. The process of claim 1, wherein the amount of steam fed into the reaction zone with the naphtha feedstock is about 1 to 50 mol%. 3. The process of claim 1, wherein the zeolite crystalline is selected from the ZSM series. 4. The process of claim 3, wherein the crystalline zeolite is ZSM-5. The process of claim 4, wherein the reaction temperature is from about 500 to about 600 ° C. The process of claim 5, wherein at least about 60% by weight of the C5 + olefins in the feed are converted to C4- products and less than about 25% by weight. 10 weight of paraffins are converted to C4- products. The process of claim 1, wherein the propylene comprises at least 95 mol% of the C3 products ^^ total. 8. The process of claim 7, wherein the weight ratio of propylene to C2- products is greater than about 3.5. 9. The process of claim 8, wherein the amount of steam fed into the reaction zone with the ^^ Naphtha feed material is around 2 to 20% 20 molar. The process of claim 1, wherein said naphtha feed contains from about 5 to about 35% by weight of paraffins. 11. A process to produce polypropylene by buying the steps of: (a) feeding steam and a naphtha feed containing less than about 40% by weight of paraffins and between about 15 and 70% by weight of olefins within a reactor zone; (b) contacting the naphtha feed with a catalyst comprising a crystalline zeolite having an average pore diameter of less than about 0.7 nm at conditions including a temperature of about 500 to 650 ° C, a partial hydrocarbon pressure of 10 at 40 psia, a hydrocarbon residence time of 1 to 10 seconds, and a weight ratio of catalyst to feed of about 4 to 10, where no more than about 20% by weight of paraffins are converted to olefins, where the polypropylene comprises at least about 90 mol% of the total C3 products; and (c) separating propylene from C3 products and polymerizing propylene to form polypropylene. The process of claim 10, wherein the propylene comprises at least 95 mol% of the total C3 products. The process of claim 10, wherein the amount of steam fed into the reaction zone with the naphtha feedstock is about 1 to 50 mol%. The process of claim 10, wherein the crystalline zeolite is selected from the ZSM series. 15. The process of claim 13, wherein the crystalline zeolite is ZSM-5. 16. The process of claim 14, wherein the reaction temperature is from about 500 to about 600 ° C. The process of claim 15, wherein at least about 60% by weight of the C5 + olefins in the feed are converted to C4- products and less than about 25% by weight of the paraffins are converted to C4- products. 18. The process of claim 16, where the weight ratio of propylene to C2- products is greater than about 3.5. 19. The process of claim 17, wherein the amount of steam fed into the reaction zone with the naphtha feedstock is about 2 to 20 mol%. The process of claim 11, wherein said naphtha feed contains from about 5 to about 35% by weight of paraffins. • 02 < 8 S5 -20-Summary Disclosed herein is a process for producing polymers from C2-C4 olefins produced selectively from a stream of catalytically disintegrated or thermally disintegrated naphtha. A mixture of the naphtha stream and a stream of water vapor is fed to a reaction zone where it is contacted with a catalyst containing from about 10 to 50% by weight of a crystalline zeolite having an average pore diameter less than about 0.7 nanometers under reaction conditions including temperatures ranging from about 500 to 650 ° C and a partial pressure of hydrocarbons of about 10 to 40 psia.