Proportionation of olefins

Abstract

A PROCESS FOR PRODUCING INTERMEDIATE MOLECULAR WEIGHT OLEFINS FROM MIXTURES OF HIGHER AND LOWER MOLECULAR WEIGHT OLEFINS BY PROPORTIONATING A MIXTURE OF SAID HIGHER AND LOWER MOLECULAR WWEIGHT OLEFINS OVER A MOLYBDENUM OXIDE, TUNGSTEN OXIDE, OR MIXED MOLYBDENUM OXIDE-TUNGSTEN OXIDE CATALYST AT 150*C. TO 220*C., RECOVERING THE PRODUCT WHICH INCLUDES A MAJOR CONSTITUENT INTERMEDIATE MOLECULAR WEIGHT OLEFINS NOT PRESENT IN THE FEED, SEPARATING THE MIXTURE TO PRODUCE AN INTERMEDIATE MOLECULAR WEIGHT OLEFIN PRODUCT AND A MIXTURE OF HIGHER AND LOWER MOLECULAR WEIGHT OLEFINS WHICH ARE RECYCLED TO THE PROPORTIONATION STAGE IN MIXTURE WITH ADDITIONAL HIGHER AND LOWER MOLECULAR WEIGHT OLEFINS IN DISCLOSED. CABON MONOXIDE MAY BE PASSED THROUGH THE PROPORTIONATION REACTOR WITH THE MIXED OLEFIN FEED STOCK.

Claims

Jan. 11, 1972 F. w. STEFFGEN PRoPoRTIoNA-HON oF oLEFINs Filed April l, 1969 c; c; c; 556e 5. (5m/14PM E] Wwf/54km# ,wrom/EK United States Patent O 3,634,538 PROPORTIONATEON OF OLEFINS Frederick W. Stetlgen, Laguna Beach, Calif., assigner to Atlantic Richfield Company, Philadelphia, Pa. Continuation-impart of application Ser. No. 537,270, Mar. 25, 1966. This application Apr. 1, 1969, Ser. Int. Cl. C07c 3/6'2 U.S. Cl. 260--683 D 8 Claims ABSTRACT F THE DISCLOSURE A process for producing intermediate molecular weight olefins from mixtures of higher and lower molecular weight olefins lby proportionating a mixture of said higher and lower molecular weight oletins over a molybdenum oxide, tungsten oxide, or mixed molybdenum oxide-tungsten oxide catalyst at 150 C. to 220 C., recovering the product which includes a major constituent intermediate molecular weight olelins not present in the feed, separating the mixture to produce an intermediate molecular weight olen product and a mixture of higher and lower molecular weight olefiins which are recycled to the proportionation stage in mixture with additional higher and lower molecular weight oleiins is disclosed. Carbon monoxide may be passed through the proportionation reactor with the mixed oleiiu feed stock. `CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application Ser. No. 537,270, filed Mar. 25, 1966, now abandoned. BACKGROUND OF THE INVENTION Field of the invention This invention is concerned With a method for producing olelins and, more particularly, to a method for producing one or more olelins having a predetermined chain length by proportionation of a mixture of linear olelins of greater and less molecular weight than the desired olens. More specifically, this invention relates to the preferential formation of olens of a molecular weight equal to or nearly equal to the overall average molecular weight of the olefins from which they are prepared. Molybdenum oxide, tungsten oxide and mixtures of these oxides which have been pretreated with a reducing agent are used as the catalysts. Carbon monoxide may be passed through the proportionation reaction zone with the mixture of linear oletins. Description of the prior art The disproportionation of oleins has been described by Chenicek, U.S. Pat. 2,614,137, has been described as a reaction in which polymers, prepared by a previous polymerization step, having molecular weights above and below the polymer desired are comingled and reacted at selected conditions in the presence of certain catalytic agents to effect an averaging of molecular weights of the polymers charged. It is proposed that the mechanism of this reaction is essentially a combination of substantially simultaneous reactions including hydrogen transfer, cracking and polymerization which yields a product containing hydrocarbon compounds varying in molecular weight over the entire range existing between the extremes in molecular weights of the polymers subjected to the reaction, and including saturated compounds formed by virtue of the hydrogen transfer reactions during the process. Monomeric oleiins, up to 30 percent by weight of the polymers, are charged into the reactor to provide a component which will average with the low polymers, i.e., copolym- Patented Jan. 11, 1972 erized therewith, to form a copolymer of the ultimately desired molecular weight. This highly complex reaction occurs at relatively high temperatures, preferably between 300 C. and 400 C., over silica-containing catalysts which are known to catalytically promote cracking, depolymerization, dehydrogenation, hydrogen transfer, e-tc. Another type of reaction, also known as a disproportionation reaction, is described by Banks, U.S. Pat. 3,261,879 and by Sherk, U.`S. Pat. 3,296,330. This disproportionation reaction, however, is approximately the converse of the previously disclosed proportionation reaction in that a single molecular weight olefin constitutes the feed to the process while a plurality of higher and lower molecular weight olefins comprises the effluent from the process. Similarly, a group of intermediate .molecular weight olefins may constitute the feed to the Sherk process for thereby producing a spectrum of olefins including olefins with higher molecular weight and lower molecular Weight than any oleiins contained in the feed stock. This process, then, consists essentially of converting an oleiin stream of narrow range intermediate molecular Weight olefins to an olefin stream of broad range higher and lower molecular weight oleiins. The Sherk and Banks processes are carried out over a cobalt oxide-molybdenum oxide catalyst suppoited on alumina. The catalyst is pretreated with an oxidizing agent and mild pretreatment with a reducing agent such as carbon monoxide or hydrogen can be tolerated, although such pretreatment reduces the disproportionation activity of the catalyst. As will ybe pointed out more specilically hereinafter, my invention is distinguished from the prior art inventions in that by proportionation I mean a reaction which converts linear oletins into all possible carbon numbers of CH2n linear oleins without changing the total number of molecules present in the reaction mixture. At equilibrium, the reaction mixture has a unimodal distribution of molar concentrations versus molecular weigh't with a maximum molar concentration at or near the average molecular weight of the feed mixture. In the proportionation reaction oleliins having carbon numbers higher and lower than the feed average decline. All possible linear CH2n isomers are found but no carbon-carbon chain branching is produced during the proportionation reaction. It is, accordingly, a principal object of my invention to provide a method for producing intermediate molecular weight olel'ins in high yield from a mixture of higher and lower molecular weight oleiins by proportionation. SUMMARY OF THE INVENTION In the present invention, a mixture of oleiins is prepared from olens of a higher molecular weight and oletins of a lower molecular weight, with little or no olefin content in a molecular Weight intermediate said higher and lower molecular weights. The mixture may desirably -contain carbon monoxide to maintain the catalyst activity. The mixture, with or Without carbon monoxide, is then contacted at from about C. to about 220 C. with a catalyst which consists essentially of molybdenum oxide, tungsten oxide, or mixtures of these oxides, supported on a non-cracking support, alumina being the preferred support. This catalyst is pretreated with a reducing agent such as carbon monoxide or hydrogen to maximize proportionation efficiency. A mixture of olens is recovered from the contacting step which includes, in addition to the higher and lower molecular weight oleiins, intermediate molecular Weight olens which, depending upon the nature of the feed stocks, etc. preferably comprises a major portion of the recovered mixture. By major portion, I mean that either the total of the intermediate oletns, in mole percent, exceeds the total of olens in either the higher molecular weight range or the lower molecular weight range, or the mole percent of the intermediate olefin produced in maximum yield exceeds the mole percent of any other smgle molecular weight olefin, in the preferred operating embodiment. The intermediate molecular Weight olens are removed as the desired product and the higher and lower molecular Weight olens are mixed with additional feed to produce the desired ratio and recycled to the proportionation zone. A principal object of the invention` then, is to provide a proportionation process.y for producing intermediate molecular weight oleiins from a mixture of higher and lower Imolecular weight oleins. A more specific object of the invention is to provide a proportionation reaction in which a mixture of higher and lower molecular weight olens and carbon monoxide are proportionated over a molybdenum oxide, tungsten oxide, or a mixed oxide, catalyst to produce a major portion of oleiins having an average molecular weight intermediate the higher and lower molecular weight olefins. Another specific object of the invention is to provide a proportionation process for preparing an intermediate molecular weight olefin from a mixture of higher and lower molecular weight oleiins, said intermediate molecular weight oleiins being present in the highest molecular yield. As will be apparent from the specification which follows, these are exemplary of the objects of this invention and are not limiting thereof. BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 of the drawing illustrate the relative molar concentrations of the feeds and effluents of the most closely related prior art process of which I am aware. FIGS. 3, 4 land 5 represent the feed and eluent molar concentrations of three examples of the present proportionation process. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a means by which a variety of linear olens can be converted into more useful or valuable linear homologs. For example, waste olens produced in refining or other processes as excess material can be converted into oleiins of greater economic value. Refining processes produce oleiins such as ethylene and propylene in large volume, and there is a constant need to find profitable uses for these materials. There are also a number of higher oleiins, i.e., in the C14 and above range, produced in wax cracking and like processes which generally have low commercial value. Using the process of this invention, it is possible to combine a wax cracking operation in which oleiins with little rvalue are combined with such olens as ethylene, propylene and butene to produce oleiins having an intermediate number of carbon atoms which are of greater commercial worth. For example, olens having a relatively high chain length can be combined with those of a lower chain length to produce oleiins in the range useful for preparation of detergent alkylates, that is, in the C-C16 range. For example, a linear @23H46 olefin and ethylene can be proportionated to produce linear C12H24 oleiins which are valuable in detergent alkylate production. Those materials recovered from the proportionation reaction efliuent which fall outside of the desired molecular Weight range can be recycled with more of the mixed feed reactant oleiins having the appropriate size to produce more useful olefins after proportionation. The straight chain oleiins produced by the process of this invention can be used in producing oxo-products such as aldehydes and alcohols wherein straight chain oleiins of a given molecular weight are often needed as starting materials. Olefins available in cracked gasoline can be extracted from the gasoline and proportionated with lighter oleins or heavier oleiius from another source to produce oleiins falling within a more useful average molecular weight range. Also, 4 cracked gasoline itself could be passed over the catalyst of this invention in the presence of a lighter or a heavier olefin feed to produce olens having a more desirable molecular weight for use as chemical raw materials. In carrying out the process of the present inventlon, linear feed oleiins having a discontinuous molecular weight distribution, i.e., having unequal molecular weights, are proportionated, that is, olens having a molecular weight equivalent to the average molecular weight of the feed oleiins are produced, by passing the feed oleiins into contact with a transition metal oxide catalyst which has been pretreated with a reducing agent. The metal component of the transition metal oxide should be molybdenum or tungsten. The metal oxide, afer treatment with the reducing agent, exists in either the oxide or carbonyl form or a mixture of the two. The pretreatment of the metal oxide is performed by heating it in the presence of a reducing agent, preferably carbon monoxide. The pretreatment of the metal oxide catalyst should be performed at temperatures above about 200 C. and preferably at temperatures of from about 400 C. to about 600 C. It is theorized that a semi-carbonyl-type compound, perhaps a dicarbonyl, is formed in the carbon monoxide pretreatment. In any event, the metal oxide is at least partially reduced during the pretreatment. The catalyst of the present invention can be best used if placed on a non-cracking support material such as alumina or silica. Use of a cracking support, such as silicaalumina combined, leads to complex side reactions. The Weight percent of metal oxide to support material may vary over a wide range but it is more practical to use it in amounts of l to 40 percent by Weight of the support material. After the catalyst has been properly prepared, feed olens having a discontinuous molecular Weight distribution are passed thereover at a temperature of C. to 220 C. The resulting reaction produces a mixture of olefins, at least a portion of which are olens having a molecular weight equal to the average molecular Weight of the mixed oleiinic starting materials. The preferred catalysts for the present invention consist essentially of carbon monoxide pretreated molybdenum trioxide, tungsten trioxide and mixtures of tungsten oxide and/or molybdenum oxide with other transition metal oxides such as cobalt oxide. The proportionation catalyst tends to deactivate with time but its life appears to 4be extended by conducting the proportionation reaction in the presence of the reducing gas used in the pretreatment of the catalyst, i.e., carbon monoxide. When the catalyst activity has deteriorated beyond a desirable limit, it can be regenerated by heating in the presence of an oxygen-containing gas to burn off deposits and then again pretreated with the reducing agent, preferably carbon monoxide, in the manner described above. The catalyst of this invention may be prepared by rst preparing a solution containing the metal component of the catalyst, i.e., in the case of molybdenum oxide an ammonium molybdate solution may be used. The support material is impregnated with the transition metal catalyst compound containing solution and then dried at an elevated temperature (about 400 C. or greater) to implant the metal in its oxide form upon the support material. The metal oxide and support material are then heated in the presence of carbon monoxide at ternperatures of at least 200 C. and preferably 400 C. or higher, and then cooled. The carbon monoxide pretreatment of the metal oxide catalyst probably converts at least part of the metal oxide to a carbonyl derivative, possibly an oxycarbonyl or carbonyl itself. The carbon monoxide pretreatment is conducted at temperatures at which metal hexacarbonyls are unstable, and thus it is known that the catalyst does no take the form of a hexacarbonyl as might otherwise be expected. The carbon monoxide pretreatment apparently provides a stable carbonyl intermediate. The effect carbon monoxide pretreatment has upon the metal oxides is not fully understood. Alumina in its activated form has provided to be the most suitable support material for the metal oxide catalyst of this invention. Other high surface area support materials such as silica can be used, however. The instant proportionation reaction proceeds more efciently in the vapor phase; however, reaction in the vapor phase is not essential as liquid phase proportionation can also be accomplished. Because the proportionation reaction is reversible, it is desirable to have sufficient contact time between the olens and the catalyst to allow equilibrium conditions to be established or approximate equilibrium conditions. When equilibrium conditions are reached, the product distribution resulting from the present process approximates a unimodal curve having somewhat higher molar concentrations in the region of the average molecular weight. As suggested earlier, the olens suitable for use are linear olefns and include olens having chain lengths of from C2 up to at least C25, however, in theory there is no limitation on the size of the olens which may be used. Tests indicate that the location of the double bond does not restrict the activity of the olen since the double bond is quickly isomerized to other positions in the molecule over the catalysts used for proportionation. The following examples are provided to illustrate further the nature of this invention and how it can be practiced, however, it should be understood that the invention is not restricted to these examples. EXAMPLE I A molybdenum trioxide-on-alumina catalyst was prepared by impregnating 50 gms. of tabular alumina sold under the trade name Harshaw AL 1404 with an aqueous impregnating solution containing 20 milliliters of deionized water and 6 gms. of ammonium molybdate. The ammonium molybdate impregnated alumina was dried with mixing and stirring to assure that all liquid would be absorbed on the alumina. The drying was effected at 100 C. unt-il the material appeared thoroughly dry. It was then put in a muffle furnace and dried min. at 200 C. after which the furnace was reset to 500 C. and heated for about 16 hours\at this temperature. The catalyst was purged with nitrogen to remove adsorbed oxygen. The molybdenum oxide-on-alumina was then treated with carbon monoxide for about 3 hours at a temperature of 550 C. with carbon monoxide being passed into contact with the catalyst at the rate of 6 liters of carbon monoxide per hour. Eflluent from the catalyst bed was passed through a U-tube containing Ascarite and it was determined that carbon doxide is released during the carbon monoxide pretreatment which indicates that the carbon monoixed acts as a reducing agent. After the carbon monoxide pretreatment was completed, the catalyst was cooled in the presence of carbon monoxide. EXAMPLE II A catalyst was prepared in the same manner as described in Example I except that 5.85 gms. of ammonium meta-tungstate instead of ammonium molybdate -was used with 20 milliliters of deionized water. -In both Examples I and II, after calcination in air, a catalyst was obtained having approximately 10 weight percent of molybdenum trioxide and tungsten trioxide, respectively. EXAMPLE III A 40 ml. volume of catalyst comprising 3.5 weight percent cobalt oxide and 12.5 Weight percent molybdenum trioxide-on-alumina was pre-carbon monoxide treated in the manner described in Example I except the carbon monoxide pretreatment was performed for about 1/2 hour in a reaction chamber. A mixture of 0.6 liter per hour of carbon monoxide, 3.0 liters per hour of ethylene, and 3.0 liters per hour of butene-l was passed over the catalyst at atmospheric pressure at times and temperatures as indicated in Table 1 below. The effluent was recovered and analyzed at various times during the' reaction with the results being shown under GC Analysis in Table l. TAB LE l A B c Accumulated on stream time, hr. :m.in 0:30 1:40 2:25 Temp., C 151 20 253 GC analysis (CO-free basis) mole percent 23. 0 24. 1 31. 7 50. 5 4l. 8 33. 2 4. 6 4. 5 5. 3 12.6 16. l 16. 5 Trans C4Hg-2 6. 5 8. 6 9. 7 QsHio-l- 2. 8 l 4. 9 3. 6 The result-s of these tests show that during time period A 50 mole percent propylene was produced from the ethylene-butene feed stream, but that as time passed the percentage conversion decreased gradually, indicating some deactivation of the catalyst. EXAMPLE IV An olefin feed containing molar proportions of 60% ethylene, 20% hexene-l and 20% octene-l =Was passed over 40 mls. (39.1 gms.) of a catalyst prepared in the manner described in 'Example I with the eilluent having the composition shown in Table 2. EXAMPLE V An ole-iin feed comprising 50 mole percent ethylene and 50 mole percent butene-1 Was passed over 40 mls. (14.8 gms.) of a catalyst prepared in the same manner as described in Example I except silica was used as the support material instead of alumina. As the results shown in Table 2 indicate, silica does not appear to be as effective as a support as is alumina. EXAMPLES VI AND VII An olefin feed comprising molar ratios in one instance 2/3 ethylene and 1/3 octene-l and in the second instance 1/3 ethylene and 2/3 octene-l were passed into contact with 40 mls. (39.1 gms.) of the catalyst of Example I with results las shown in Table 2 being obtained. Equilibrium product composition was not established in VII as closely as in VI. EXAMPLE VIII A 10 weight percent cobalt oxide-on-alumina catalyst sold under the trade name Girdler T302 was heated in the presence of oxygen to about 500 C. and was pretreated with carbon monoxide in the same manner as described in Example I. Feed olens comprising 50 mole percent ethylene and 50 mole percent butene were then passed over 40 mls. (46.2 gms.) of the catalyst. As the results shown in Table 2 indicate, no proportionation of the feed olens was detected. EXAMPLE IX EXAMPLE X A molybdenum oxide-on-alumina catalyst was initially prepared in the manner described in Example I but was pretreated with hydrogen as a reducing agent instead of carbon monoxide. The hydrogen pretreatment was performed at about 550 C. for about 15 minutes. Water was produced during the pretreatment process indicating that reduction took place during the reaction. After the hydrogen pretreatment, the catalyst was cooled in the presence of hydrogen. 40 mls. (39.5 gms.) of the resulting catalyst was then used in the proportionation reaction in which 50 mole percent of ethylene and 50 mole Without desiring to be bound by the following suggested explanation, it is postulated that the reaction involved, the proportionation reaction of this invention, comprises both 'isomerization and proportionation, the latter believed percent of butene-l were passed thereover. No carbon to constitute a substantially simultaneous reaction of two monoxide was used during the proportionation in this olens of differing molecular weight with the catalyst reaction. As the results shown in Table 2, indicate, some followed by exchange of olefin molecule moieties between proportionation of the olefins was accomplished. the two olens and separation from the ca1t1a1yst. Sinlxlze the exact nature of the catalyst is not known, owever, t e EXAMPLES XI AND XII reaction mechanism of the olens with the catalyst is not Molybdenum oxide-on-alumina (Example XI) and e0mp1ete1y understood tungsten OXlCle-O-alurnina (EXaInPle XH) eatalysts, Pre- As previously indicated, however, the present invention pared in the manner described in Examples I and II, recomprises more than simply the discovery 0f a unique sPeetlVely, Were 'used ln Proportionatlon reactions in Whlell reaction mechanism. Indeed, the present invention conetllylene and butene-l Were Used as the different feed stitutes a particular sequence of operations involving the olens. The effectiveness 0f the Catalyst Was determined catalyst and utilizing the reaction mechanism, whether at different time intervals, as the results tabulated in the mechanism is as proposed or not Table 3 illustrate, and b0tl1 the molybdenum and tung' The specic steps of this invention are: first, preparing sten eatalysts retain their activity OWer at least a 3 l'lOllr a feed mixture consisting essentially of higher molecular period. Weight oleiins and lower molecular Weight oleiins, with The tOtal feed ln EXarnPle XI Was 224-09 nllllllnoles carbon monoxide if desired. Olens in an intermediate and the total Product Was 218-90 InlllirnOleS- Thus, 977 range between the higher and lower molecular weights Percentofthe feed,in moles, was recovered in unmodified are effectively absent, Le., are absent or substantiauy 0r PrOPOrtOHated f0rIn- Reference t0 Table 2 sllOWs that absent. Second, the mixture is reacted at the specified in EXarnPle V 98-95 Percent 0f the feed steek Was 25 temperature with the catalyst, which has been preactivated, ICCOVefeCl ill unchanged 01 PrOPOrtlOlla'ted ferm and ln and, third, recovering a mixture of oleiins which includes Example VII 93.7 percent of the feed was recovered either not only remnants of the higher and lower molecular unchanged or proportionated. This iS eXtreInly signllleallt weight olens but a major portion of intermediate molecusince it shows that the reaction is true proportionation 1mweight 01ens The total m0131- quamities of the reaction and not a cracking reaction, which Would result olefns in the mixture are substantially equal to the molar in an increase in the number of moles in the eiuent as quantity 0f olehs in the feed, The term major portion Compared With the feed and that it 1S IlOt a pOlylIlellZalOn as used herein means, depending upon the number 0f reaction since this would result in a reduced molar olefin species falling within the intermediate range, i.e., quantity in the eluent. The Consistency 0f resultS ill this the width of the intermediate olen range, and the relative area, Only seine 0f Whlell are reported, Shows that this 35 molar quantities of the feed stocks, that either the molecuis not a combined polymerization-cracking reaction Since lar sum of all olens in the intermediate range exceeds an identity and the quantity of reduction from polymerithe molecular sum of the olens in either the higher zation and of increase from cracking would be only comolecular weight range or the lower molecular weight incidental and, therefore, not repeatable. range or, in the alternative, that the olefin species present TABLE 2 Example- IV v VI VII VIII IX X Catalyst Composit.ion. v 10% M003 10% M903 10% MoOs 10% M003 10% C0203 16% CrzOs 10% M003 90% A1203 90% S1202 90% A1203 90% A1203 90% A1203 85% A1203 90% A1203 Pretreatiug, reducing agent CO GO CO CO C0 CO Hz Run temp.. o 178 176 176 Feed comp.,mole percent: Total product, millimoles Product comp., mole percent: TABLE 3 Example XI XII Catalyst composition 10% Moos-90% AlzOs 10% WGs-90% A1203. Catalyst, Wt./vo1 39.1 g./40.0 ml .5 g./40.0 ml. Run temp., 0-..-. 78 0. 'Feed composition 50 mole percent ethylene, 50 mole percent ethylene, mole percent butcned. 50 mole percent butene-l. Feed rate, moles/hr 0 21 0.21. Time on stream,a hrs 1 1-2 b 2. 5 3 1 1-2 b 2 3 Product composition in mole percent Ethylene. 19. 6 19. 4 19.9 20. 7 18. 1 18. 6 20. 2 18. 5 Propene 58. 7 59. 5 58. 1 68. 1 56. 6 56. 8 55. 9 58. 1 1 and 2-bute 20. 1 19. 4 20. 3 19, 6 7. 2 21.7 21. 2 20. 1 1 and 2-butenes- 1. 5 1. 5 1.6 1. 5 2. 5 2. 3 2. 1 1. 9 1,2 and B-hexenes 0. 1 0.2 0.1 0. 1 0.6 0. 7 0.6 0.4 On stream catalyst agefater pretreating with CO and cooling to run temperature. b A compositegas sample was collected over a 1 hour period. in the greatest quantity in the intermediate molecular weight range exceeds in molar concentration the quantity of any single molecular weight olefin in either the higher molecular weight range or the lower molecular weight range. This invention may be practiced in an equivalent but less efficient form by producing only a substantial quantity of intermediate molecular weight olefins by, for example, operating the reaction zone such that equilibrium is not closely approached and recycling very large quantities of the higher and lower molecular weight feed stock. To better understand the present invention and to distinguish it from the inventions of the prior art, reference is made, first, to FIGS. 1 and 2 which illustrate the process described lby Sherk in the aforementioned patent. In this prior art process, the feed initially comprised a single olefin, propylene. The efiiuent, on the other hand, included substantial quantities of C2 and C., olefins, ethylene and butylene. Lesser amounts of pentene, hexene, and heptene were also produced. In a second disproportion stage, the prior art teaches a feed consisting of a major portion of C5 olefin, significant portions of C3, C7, C3, C9, and C13 olefins with a trace of C11 olefin. Interestingly, about one-third of the C5 olefin is converted to a C., olefin but the Cq-Cw olefins remain unchanged and the C3 olefin is actually decreased. The nature and purpose of this reaction is not clear except that it does produce a lower molecular weight olefin. `Contrary to the prior art, reference now being made to FIG. 3, my invention contemplates feeding a mixture of olefins, Feed A and Feed B in FIG. 3, of higher and lower molecular weight, C2 and C4 to a proportionation zone to produce an efiiuent of intermediate molecular Weight, C3, in which the olefin species of this intermediate molecular weight exceeds in quantity the efiiuent of the original feed olefin species. According to my invention, the intermediate molecular Weight olefin is removed as the product and the higher and the lower molecular weight remnants of the feed in the effluent are recycled. Similarly, in FIG. 4, a single lower molecular weight feed, C2, Feed A, is mixed with higher molecular weight feeds, Feed B and Feed C, C6 and C3, to produce an effiuent in which an intermediate molecular weight olefin, C3, exceeds in quantity the molar amount of C2, C6, and lC8 remaining in the effluent mixture and in which the sum of the intermediate molecular weight olefins, C3, C4, and C5, constitutes at least a substantial portion of the efiiuent and preferably a major portion thereof. The intermediate olefins are removed as the product and the remaining higher and lower molecular weight feed olefins y are recycled. As previously pointed out, at equilibrium the reaction mixture has -a unimodal distribution of molar concentrations versus molecular weight with the maximum molar concentration at or near the average molecular Weight of the feed mixture. This is illustrated in FIG. 5 wherein it is desired to produce a C3 olefin from a mixture of C2 and C3 olefins. An equal molar mixture of Feed A and Feed B, ethylene and octene would produce an effiuent having a major proportion of C5 olefin; however, as illustrated in FIG. 5, the distribution favors intermediate molecular weight olefins near the weighted average molecular weight of the feed mixture. Itis possible, therefore, to shift the process to produce the desired intermediate molecular weight olefin by varying the relative molar inputs of the higher and lower molecular weight olefin feeds. In the present invention, the desired intermediate weight molecular olefin product is Vremoved and the higher and lower molecular weight olefins remaining from the feed are recycled with makeup feed to produce therefore only such limitations should be imposed as are indicated in the appended claims. I claim: 1. A proportionation process, in which a feed mixture of linear olefins of higher and lower molecular weights, intermediate molecular weight olefins being substantially absent, having a bimodal distribution of molar concentrations versus molecular Weight is converted to a product mixture of linear olefins having a unimodal distribution of molar concentrations versus molecular weight with a maximum molar concentration near the average molecular weight of the feed mixture, for producing intermediate molecular weight olefins from higher and lower molecular weight olefins which comprises the steps of: contacting said feed mixture consisting essentially of higher molecular weight olefins and lower molecular weight olefins, at a temperature of from about C. to about 220 C. with a non-cracking catalyst consisting essentially of oxides of molybdenum, tungsten, mixtures thereof, or mixtures of said oxides with cobalt oxide, said catalyst having been pretreated with a reducing agent; recovering an eftiuent mixture of olefins including at least a substantial portion of olefins of molecular weight intermediate the molecular weights of the olefins in the feed mixture, the total mola-r quantities of efiiuent olefins being substantially equal to the total molar quantities of feed olefins; separating said effluent mixture into a product stream.- comprising the intermediate molecular weight olefins and into one or more recycle streams comprising higher and lower molecular weight olefins; passing at least one recycle stream to the reaction zone, and recovering said intermediate molecular weight olefins as product. 2. The proportionation process defined in claim 1 wherein the catalyst is supported on alumina. 3. The proportionation process defined in claim 2 wherein the recycle stream comprises `both higher and lower molecular Weight olefins and is passed with added feed into contact with said catalyst. 4. The proportionation process of claim 3 wherein the intermediate molecular weight olefins comprise a major portion of the efiiuent olefin mixture. 5. The proportionation process of claim 4 wherein the feed mixture includes carbon monoxide. 6. The proportionation process of claim 4 comprising the further step of controlling the ratio of higher molecular weight olefins to lower molecular weight olefins in the feed mixture for thereby controlling the molecular weight of the intermediate molecular weight olefins produced therefrom. 7. The proportionation process of claim 1 wherein the source of higher molecular weight olefin feed is cracked gasoline. 8. The proportionation process of claim 7 wherein the lower molecular weight olefin feed is ethylene. References Cited UNITED STATES PATENTS 2,196,363 4/1940 Robertson 260-683 3,094,481 6/ 1963 Butler et al. 208-89 3,429,804 2/ 1969 Sze et al. 260-674 2,614,137 10/ 1952 Chenicek 260-683 3,261,879 7/ 1966 Banks 260-683 3,296,330 1/1967 Sherk 260'-683 3,526,676 9/1970 Turner et al. 260-683 DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER, JR., Assistant Examiner U.`S. Cl. X.R. 260-671 R

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