IL45375A - Hydrogen fluoride catalysed alkylation process - Google Patents

Description

iBt» o una «ηικι Β Hydrogen fluoride catalysed alkylation proeess UOP Inc.

C. 43416 This Invention relates to a process for producing an alkylation reaction product from lsobutana and a C3-C3 olefin using hydrogen fluoride alkylatlon catalyst. This invention also relates to an improved alkylatlon process for providing hydrocarbon motor fuel components.

Alkylatlon of lsoparafflnlc hydrocarbons such aa lsobutana, laopentane and the like, with oleflnic hydrocarbons such as propylene, butylenes, aoylenes, and with olefin-acting compounds such as CJ-CJ alkyl halides, using hydrogen fluoride aa a catalyst, is well known as a commercially Important method for producing gasoline boiling range hydrocarbons. The C5-C10 hydrocarbons normally produced by the laoparaffin-olefin alkylatlon reaction are termed "alkylate." Alkylate is particularly ueeful as a motor fuel blending stock because of its high motor and research octane ratings. It can be used to Improve the overall octane rating of gasoline pools to comply with the requirements of modern automobile motors. High octane alkylate fuel components are particularly important in producing motor fuel of sufficient quality when it is desired not to employ alkyl lead compounds In the ootor fuel to aaet octane requirements. A continuing goal in the alkylatIon art ia to provide a hydrogen fluoride catalysed alkylatlon process more economical than conventional alkylatlon processes and capable of providing an alkylate product having ootor and research octane ratings higher than ia possible using conventional processes.

Generally, commercial leopara fin-olefln alkylatlon processes enploy Isobutane as the leoparaf in reactant and utilise propylene, butylenea, amylenes, or mixtures thereof, as the olefin-acting agent. The isobutane and olefin are typically contacted with hydrogen fluoride catalyst in an alkylatlon reactor and mixed to form an eaulaion or alkylatlon reaction mixture. After the alkylatlon reaction between the isobutane and olefin is substantially complete, the reaction mixture of hydrocarbons and catalyst is withdrawn from the reactor and settled in order to separate immiscible hydrocarbon and catalyst phases. The hydrogen fluoride catalyst phase thua separated Is recycled to the reactor for further catalytic use. The hydrocarbon phase produced by the settling operation is further processed, normally by fractionation, to recover the alkylate product and to separate unconsumed Isobutane for further use in the alkylatlon reactor by recycling from the fractionation step.

It has been found necessary to maintain the reactor temperature, relative amounts of catalyst and hydrocarbons charged, catalyst strength, and other processing conditions within narrow ranges in order to provide a high quality alkylate product. A molar ratio of isobutane to olefin in the hydrocarbon feed to the alkylatlon reactor of about 10:1 or more is one condition essential to the production of high octane alkylate In hydrogen fluoride catalysed alkylatIon. The aolar ratio of lsobutane to olefin in the hydrocarbon feed to an alkylatlon reactor is conventionally termed the "external" lsobutane/olefin mole ratio. The external iao-butane/olefln mole ratio is to be differentiated from the molar ratio of lsobutane to olefin In the alkylatlon reaction mixture formed within the alkylatlon reactor, which is conventionally termed the "internal" Isoparaffin/olefin mole ratio. In alkylatlon processes using hydrogen fluoride catalyst, the quality of the alkylate product is substantially improved by increasing the external lsobutane/olefin mole ratio but is not Improved by increasing the Internal lsobutane/olefin mole ratio. That is, only the ratio of lsobutane to olefin In the hydrocarbon feed to the alkylatlon reactor is Important in providing a high octane product in hydrogen fluoride operations, not the concentration of lsobutane In the reaction mixture within the alkylatlon reactor. The opposite is true In sulfuric acid alkylatlon, wherein the quality of the alkylate product is improved by an increased Internal lsobutane/olefin mole ratio, i.e., a higher concentration of lsobutane in the reaction mixture within the alkylatlon reactor. In hydrogen fluoride catalysed alkylatlon processes, it has been found desirable to employ as high an isobutane/olefln mole ratio as is economically possible In the hydrocarbon feed to the reactor, since the quality of the alkylate product le thereby Improved. This improvement le exemplified by the increased octane rating of the alkylate product when a higher external lsobutane/olefin mole ratio la utlllaod. Thus, In conventional operations a very considerable amount of laobotane la naceeaar-ily eased unreacted through the reactor and oust be recycled to the reactor after fractionation of the hydrocarbon phase produced In the settler. This fractionation of the settled hydrocarbon phase la performed to separate the excess, unea ted laobotane from the higher boiling alkylate product* Large amounts of iaobutane must accordingly be passed, unre-aetad, through an alkylatIon reactor and aettler and separated from the alkylate product by fractionation In a conventional hydrogen fluoride alkylatlon operation. This required fractionation atep neeeaaltatea the uae of fractionation equipment of large capacity with high energy consimption in order to vaporise the iaobutane to separate it from the heavier alkylate. Prior art has attempted to alleviate the problem cauaed by the large iaobutane requirement by, for example, circulating an emulelon (alkylatlon reaction mixture) of hydrogen fluoride catalyst, iaobutane and reaction products continuously through the alkylatlon reactor In an attempt to utilise the Iaobutane contained in the reaction mixture to provide a portion of the exceae lsobutane needed. This method of increasing the lsobutane/olefin mole ratio had been found useful in sulfuric acid catalysed alkylatlon processes, since the quality of the alkylate product Is Increased, in sulfuric acid operations, when the Internal lsobutane/olefin mole ratio is Increased by raising the lsoparaffin concentration In the reaction mixture within the alkylatlon reactor. In this early type of hydrogen fluoride alkylatlon operation, emulsion was w f i o the reactor again along with fresh olefin and fresh and recycled lsoparaffln. A modification of the emulsion circulation system was effected by passing the reaction mixture emulsion of hydrogen fluoride catalyst, lsoparaffln and reaction products from a first alk letion sone into a second alkylation zone, where the emulsion was contacted with a fresh olefinic feed and further alk latlon occurred. These early attempts to provide a high internal lsoparaffin/olefin mole ratio in the alkylatlon reactor by processing schemes analogous to those used In sulfuric acid alkylatlon failed to provide any increase in the quality of the alkylate product in hydrogen fluoride catalysed processes, and have generally been abandoned in commercial operations. It has been found that the quality of the alkylate product in hydrogen fluoride catalysed alkylatlon Is improved only when the external iso-butane/olefln mole ratio is increased, and that the quality of the product is not Improved by Increasing the Internal isobutane/olefin mole ratio. The conditions necessary for successful operation of a hydrogen fluoride catalysed alkylatlon process have thus been found not to be analogous, In this respect, to the conditions required for successful operation of a sulfuric acid alkylatlon process. Significant expense and difficulty are, therefore, still encountered In commercial hydrogen fluoride catalysed operations in attempting to provide the required external isobutane/olefin mole ratio In the hydrocarbon feed to the alkylatlon reactor. The required, high external isobutane/olefin mole ratio used in conventional operations necessitates throughput, separation and recycle of excessive amounts of isobutane In the conven- tloi l alkylation system. This problem is substantially alleviated by the process of the present invention.

The prior art has attempted to utilise plural alkyletion reactors for a variety of reasons, but never in order to obtain a higher isoparaffin/olefin mole ratio in the feed to the alkyla-tlon reactor in the manner taught by the present Invention. For example, D. S. Patent 2,256,880 teaches the use of several reactors and settlere in a procesa for sulfuric acid catalysed alkyla-tion of laoparaffln with olefins. The settled hydrocarbon phases recovered from each reactor settler system are subjected to flash distillation between succeeding stages In order to separate lso-paraffln vapor from the higher boiling aIkyletion reaction product, which remains liquid in the flash separation. The vaporised ieo-paraffln Is subsequently condensed and recycled. A portion of the liquid alkylation reaction product may be passed to a succeeding stage, but at least a portion of the liquid remaining after flash distillation between stages Is passed directly to fractionation in order to recover the product. Avoidance of accumulation of alkylation reaction products in the reactors and the use of extremely low lsoparaffin/olefln mole ratios within the alkylation reaction sone are also taught In the above cited patent, contrary to the procedures utilised in the process of the present invention using hydrogen fluoride catalyst. U. S. Patent 2,820,073 also teaches the use of plural alkylation reactors and settlers In lsoparaffin-olefin alkylation, but utilises fractionators between each succeeding stage in order to separate unreacted lsoparaffin in a settled hydrocarbon phase from the alkylation reaction product in the settled hydrocarbon phase. The lsoparaffin thus separated is recovered as a vapor, condensed, and passed to a succeeding stage. The reaction product is recovered. D. S. Patent 3,007,983 teaches the use of two reactors and settlers In laopara ln-olefln alkylatlon. The settled hydrocarbon phase recovered from each stage is subjected to flash distillation to separate the ieoparaffln, as a vapor, from the higher boiling alkylatlon reaction product, which remains liquid. The ieoparaffln vapor Is condensed and passed to a succeeding stage. The alkylatlon reaction product is recovered as a liquid. The teachings of the last mentioned patent are directed prloarlly to autorefrlgeratlon in sul furlc acid alkylatlon. U. S. Patent 3,236,912 teaches the alkylatlon of isobutane vlth propylene and butyanes in one reactor-settler system to produce one alkylatlon reaction product and the alkylatlon of ethylene with isobutane in a second reactor'settler system to produce a second alkylatlon reaction product. The ethylene reactaat is passed through the first reactor-settler system in admixture with propylene, butylenes and Isobutane, but is not reacted in the first system. When it is desired to recover the first and second alkylatlon reaction products in admixture, the settled hydrocarbon phase, containing unreactad ethylene. Is recovered from the first reactor-eettler system and passed directly to the second reactor-settler system, where the ethylene In the settled hydrocarbon phase is reacted with isobutane. It may be possible to pass ethylene through the first reactor-settler system without alkylatlon reaction of the ethylene, since ethylene cannot be reacted with an ieoparaffln to form an alkylatlon reaction product using hydrogen fluoride catalyst or sulfuric acid catalyst. Obviously, if the ethylene could react to form alkylate under conventional, propylene or butylenes alkylatlon conditions, ethylene would react In the flrat reactor-settler systea. When ethylene la contacted with hydrogen fluoride catalyst at propylene-butyl-enes alkylatlon conditions, It oras stable ethyl fluoride, which Is inert to alkylatlon reaction.

* * SUMMARY OF THE INVENTION * * It is an object of the present invention to provide a process for alkylating lsobutane with C3-C5 olefins utilising hydrogen fluoride alkylatlon catalyst.

It is another object of the present invention to provide a hydrogen fluoride catalysed alkylatlon proesse which produces an alkylate product having superior quality and superior utility as a motor fuel blending component.

It is a further object of the present invention to provide an economical method for Increasing the external leoparaffln/ olefin mole ratio In a hydrogen fluoride catalysed isoparaffin-ole- ln alkylatlon process.

It is a further object of the present Invention to provide a hydrogen fluoride catalysed leopara fin-olefin alkylatlon process which has a reduced requirement for fractionation to separate the alkylate product from unreacted leoparaffln which is to be recycled to the alkylatlon reactor.

In an embodiment the present invention relates to a process for producing an alkylatlon reaction product from an leoparaffln and a ono-olefln selected from propylene, butylenes end aalenes, which comprises the steps of: admixing a first portion of the mono-olefln with the leoparaffln and contacting the resulting first hydrocarbon mixture with a flrat hydrogen fluoride alkylatlon catalyst phase In a first alkylatlon reaction sone at hydrogen fluoride alkylation conditions to form a first alklation reaction mixture; reaovlng the first alkylation reaction mixture from the first alkylatlon reaction cone, settling the first reaction mixture to provide a first settled hydrocarbon phase and the first hydrogen fluoride catalyst phase, and recycling the first catalyst phase to the first alkylation reaction sone; admixing a second portion of the mono-olefln with at least a portion of the first settled hydrocarbons phase and contacting the resulting second hydrocarbon mixture with a second hydrogen fluoride catalyst phase in a second alkylation reaction sone at hydrogen fluoride alkylation conditions to form a second alkylation reaction mixture; reaovlng the second alkylation reaction mixture from the second alkylation reaction zone, settling the second reaction mixture to provide a second settled hydrocarbons phase and the second hydrogen fluoride catalyst phase and recycling the second catalyst phase to the second alkylation reaction sone; and, fractionating the second settled hydrocarbons phase to provide a higher boiling product stream and a lower boiling lsoparaffin stream, recycling the isoparaffln stream to the first alkylation reaction sone and recovering the alkylation reaction product from the product stream.

Among the more important advantages of the process of this invention, relative to prior art alkylation operations, are the advantages which derive from a substantial reduction in the overall excess amount of isobutane required in relation to the amount of olefin reactant utilised in the operation. By passing all of the isobutane but only a portion of the olefin, in admixture, into a first alkylation reactor, a substantially smaller amount of isobutane is required in the first hydrogen fluoride catalyzed alkylation reaction in order to provide an adequate external volar excess of laobutaae relative to the aaount of oa la uti-llaad. Tha settled hydrocarbon phaaa recovered fro* the first settler la then admixed with a second portion of the olefin feed to fore a second hydrocarbon reactor feed,which Is charged to a second alk letIon reactor and contacted with a second hydrogen fluoride catalyst phase, whereby the earns relatively small aaount of laobutana Is utilised to provide the desired external molar excess of laobutaae in both the first and second hydrocarbon feeds to the respective alkylatlon reactors. The aettled hydrocarbon phase recovered frost the second settler is then fractionated to separate and recycle uareacted laobutana to the first reactor and to recover the desired alkylatlon reaction product. Tha aaount of laobutana which must ba thus separated by fractionation and recycled la substantially less than that found In conventional hydrogen fluoride catalysed laobutane-olefIn alkylatlon processes employing the same external laobutane/olefln sole ratio. Alternatively, a conventional aaount of laobutaae aey be explored In the feed to the first alkylatlon reactor, giving a higher octane alkylate product than la obtained In conventional alkylatlon operations. By the method of tha preaent invention, unre-acted iaopara ln contained in all the aettled hydrocarbon phaaa recovered from the first reactor-settler system la admixed with a second portion of the oleflnic feed stock to provide a high external laobutane/olefln mole ratio In the hydrocarbon feed to the second alkylatlon reactor. This second hydrocarbon feed la then contacted with a second hydrogen fluoride catalyst phase In the second reactor. When the second portion of the oleflnic feed la admixed with the first aettled hydrocarbon phase externally to the second reactor and the resulting mixture of oleflnic feed stock and settled hydrocarbon phase is then charged to the second reactor, the effective, external isoparaffin/olefin nole ratio is substantially increased, providing higher quality alkylate product from the second reactor. Conversely, the prior art methods, in which lsobutane is employed in admixture with hydrogen fluoride catalyst as a feed to plural alleyletion tones, fail to provide lsobutane which acts to produce a high external isoparaffin/olefin mole ratio in the reactor feed, resulting in a low quality alkylate product.

Turther objects, embodiments and advantages of the present invention will be apparent to those skilled in the art from the following description of the drawing and detailed description of the invention.

* * DESCRIPTION OF THE DRAWING * * The attached drawing Is a schematic illustration of a preferred embodiment of the process of the present Invention. In the particular embodiment set forth, the alkylatable hydrocarbon is lsobutane and the oleflnlc feed stock is a mixture of propylene and butylenea. The scope of the present invention is not limited to the embodiment shown, and various other suitable reactants and embodiments will be obvious to those skilled In the art from the description hereinafter provided.

Referring to the drawing, a conventional olefin alkyla-tlon feed stock is charged continuously through conduit 1 at a rate of about 300 moles/hour propylene and 300 moles/hour butylenea along with smaller amounts of other hydrocarbons, conventionally present in a commercial ole in feed stock but not necessary for operation of the process, including 120 moles/hour lsobutane, 35 moles/hour n-butane and 70 moles/hour propane. The continu and 3. The two portions of oleflnlc feed stock are passed Into conduits 2 and 3, respectively, each at the rate of 150 moles/hour propylene, 150 moles/hour butylenes, 60 moles/hour Isobutane, 17.5 moles hour n-butane and 35 moles/hour propane. Conventional, externally derived, makeup Isobutane is passed into the process via conduit 4, charged Into conduit 2 and admixed vlth the portion of the olefin feed stock therein. The nakaup Isobutane stream is passed through conduit 4 at a rate of 500 nolee/hour of Isobutane, along with conventional amounts of unnecessary, non-reactive hydrocarbons including about 15 nolee/hour n-butane and about 10 moles/hour propane. The admixed makeup Isobutane and portion of olefin feed continue through conduit 2. Recycled isobutane from conduit 24 is passed into conduit 2 and admixed with the contents thereof. The recycle isobutane is passed into conduit 2 at the rate of 3550 moles/hour isobutane, along with some other non-reactive hydrocarbon recycle resulting from imprecise fractionation, including 525 moles/hour n-butane and 225 moles/hour propane. The total hydrocarbon charge to reactor 5 thus includes 150 moles/hour propylene, 150 moles/hour butylenes, 4110 moles/ hour isobutane, with non-reactive hydrocarbons including 270 moles/hour propane and 557.5 moles/hour n-butane. The external isobutane/olefin mole ratio in the feed to reactor 5 is thus 13.7. The combined feed is passed through conduit 2 Into reactor 5 and admixed with conventional hydrogen fluoride alkyla-tlon catalyst to form a reaction mixture. The hydrogen fluoride alkylatlon catalyst Is charged to reactor 5 through conduit 0. The catalyst contains about 85 weight percent acid, less than 1 weight percent water, with the remainder made up of conventional organic diluent. Hydrogen fluoride alkylatlon conditions aalatelned la reactor 5 Include a taaperature of about 90-100°?. aad a preasure auf lclaat to aalatala hydrocarbons and eatalyat n the liquid phase. A catalyst/hydrocarbon voloaa ratio of a-bout 1:1 to about 2:1 la utilised. Boat generated a tha alkyla-tlon reaction la withdrawn by the uae of Indirect heat exchange In reactor 5. Cooling water la charged through conduit 6 Into reactor 5 and paaaad la Indirect heat exchange with the reaction alxture. Uaed cooling water la withdrawn via conduit 7. After a contact tlate of about 0.1 odnuta to about 5 ainutee, reaction alxture In reactor 3 la withdrawn aad paaaad through conduit 8 Into aettler 9. The reaction alxture la allowed to stand without agitation n aettler 9, whereby the hydrogen fluoride eatalyat forae a heavier phase and the hydrocarbon coaponenta of the reaction alxture fora a lighter settled hydrocarbon phase. The eatalyat phase la withdrawn froa the bottoa of aettler 9 through conduit 10 aad paaaed back to reactor 5 for further catalytic use. Regeneration of the eatalyat uaed la reactor 5 aay be accomplished by paaelag a allp atreaa of eatalyat froa conduit 10 to conventional regeneration oaana. Referring again to aettler 9, the flrat aettled hydrocarbon phase feraed therein la withdrawn froa the top of aettler 9 via conduit 11, paaaed Into conduit 3, and coa-alngled with the remaining portion of olefin feed therein. The flrat aettled hydrocarbon phese paaaed through conduit 11 includes approximately 3800 nolee/hour lsob tona, substantially no olefins, S57.S aoles/hour n-butane, 280 ao ea hour propane and 300 coles/ hour of alkylate. The combined hydrocarbon charge to reactor 12 from conduit 3 lncludec about 3860 aolea/hour laobutane, 150 solas/ hour propylene, 150 aolea hour butylenea, 575 aolea hour n-butane, 315 raolea hour propane and 300 aolea hour alkylate. The external laobutane/olefln sole ratio of the hydrocarbon charge to reactor 12 la thus about 13:1. The reaction conditions employed in reactor 12 are similar to those employed in reactor 5, I.e., a temperature of about 90-100°F. , add/hydrocarbon volume ratio of about ltl to about 2:1 and a pressure sufficient to maintain the reaction mixture components In the liquid phase. Hydrogen fluoride catalyst containing about 85 weight percent acid, less than about 1 weight percent water, with the remainder made up of organic diluent, is charged to reactor 12 through conduit 19 and Intimately admixed with the hydrocarbon feed from conduit 3 to form a second reaction mixture. Cooling water is charged through conduit 13 and paeaed in indirect heat exchange with the reaction mixture In reactor 12. Used cooling water Is withdrawn through conduit 14. After a contact time of a-bout 0.1 minute to about 5 minutes, the reaction mixture Is withdrawn from reactor 12 and passed through conduit IS into reaction soaker 16. The reaction mixture of catalyst, reac-tanta and reaction products la maintained in reaction soaker 16 for a contact time of about 10 minutes at a temperature and pressure substantially the same as employed in reactor 12. The reaction mixture Is then withdrawn and passed through conduit 17 into settler 18. The reaction mixture Is allowed to stand without agitation in settler 18 to facilitate separation of the catalyst and hydrocarbons into separate phases. The heavier catalyst phase is withdrawn from the bottom of settler 18 through conduit 19 and recycled to reactor 12 for further catalytic use aa described. A portion of the catalyst in conduit 19 may be passed to a conventional regeneration operation if desired. The second settled hydrocarbon phase Is withdrawn from settler 18 and passed through conduit 20 into isobutane stripper 21 at the rate of about 325 moles/hour propane, 3550 no lee /hour Isobutane, 575 moles /hour n-butane and 600 moles/hour alkylate (C^- hydrocarbons) . In isobutane stripper 21, the second settled hydrocarbon phase la fractionated to separate a lighter recycle isobutane stream and a heavier, product alkylate stream. The conventional fractionation operation performed in isobutane stripper 21 may utilize conventional ancillary equipment, not shown, such as trays, rebelling means, re fluxing means, etc. , all known In the art. Alkylate product is removed as a bottoms product from Isobutane stripper 21 through conduit 22, passed out of the operation, and recovered for motor fuel or other desired uses at the rate of 600 moles /hour. Normal butane, a by-product of the process in the embodiment shown. Is withdrawn as a side cut through conduit 23 at the rate of 50 moles /hour. Conventional recycle Isobutane is withdrawn as a side cut on a higher tray in isobutane stripper 21 through conduit 24. The recycle isobutane stream is passed out of Isobutane stripper 21 through conduit 24 at the rate of 3320 moles /hour isobutane, 500 moles/hour n-butane and 225 moles/hour propane. The recycle isobutane stream in conduit 24 is passed into conduit 2 as described above. An overhead stream is withdrawn from isobutane stripper 21 and passed through conduit 25 into conventional depropanlser 26. The overhead stream is passed trou ieostripper 21 at the rate of 100 moles /hour propane, 230 moles /hour Isobutane and 25 moles /hour n-butane. In depropanlser 26, the feed from conduit 25 la fractionated to separate propane from isobutane and n-butane. The isobutane and n-butane are withdrawn, at the rate of 230 moles/hour Isobutane and 25 moles /hour n-butane, as a bottoms product and lsobutane etraan. Propane, admixed with eons hydrogen fluoride, la withdrawn overhead through conduit 28, at the rate of 100 aolee/ hour propane, and passed through conduit 28 into conduit 29 In admixture with hydrogen fluoride from conduit 36. The mixture of propane and hydrogen fluoride In conduit 29 is passed Into condenser 30 and condensed to liquefy the propane and acid. The liquefied propane and hydrogen fluoride are then passed through conduit 31 Into settler 32. Most of the hydrogen fluoride passed into settler 32 settles out as a heavy phaae of relatively pure acid and is withdrawn through conduit 33. This relatively concentrated acid nay be passed back Into the recycle catalyst streaas in conduit 10 and condvlt 19 by conventional means not shown. The liquefied propane phase in settler 32 is withdrawn and passed through conduit 34 into hydrogen fluoride stripper 35, wherein the propane Is fractionated to separate out any remaining acid. The acid is withdrawn overhead through conduit 36, passed back into conduit 29, and treated as described above. The propane Is withdrawn as a by-product fron the bottom of hydrogen fluoride stripper 35 through conduit 37 at the rate of 100 moleshour.

Certain conventional equipment and operations necessary for the operation of the embodiment described in the foregoing have been omitted fron the drawing and description thereof, e.g., pumps, valves, rebollers, etc. The use and placement of such conventional items will be obvious to those skilled in the art. The foregoing description illustrates sons of the advantages of the present invention when embodied in a hydrogen fluoride catalysed isoparaffin-olefin alkylation process. For example, the hydrocarbons are charged to reactor 5 and reactor 12 at high external lsobutane/olefln mole ratios of about 13:1, necessary in order to produce alkylate of sufficient quality. Tet fractionation requlresents In isobutane stripper 21 need only be sufficient to separate isobutane equivalent to an overall isobutane/olefln mole ratio of less than 7:1. The alkylate produced is of a quality equal or superior to alkylate produced in conventional alkylation processes using a conventional 12:1 external isobutane/ olefin mole ratio, while the fractionation requirements are substantially reduced, with attendant savings In capital and utllltes costs. By contrast, alkylate produced in a conventional hydrogen fluoride catalysed alkylation process using an overall Isobutane/ olefin mole ratio of 7:1 would be low in quality and lack utility as a blending stock to upgrade low gasoline pool components to the desired octane level.

* * DETAILED DESCRIPTION 07 THE INVENTION * * The hydrogen fluoride catalysed alkylation process of the present Invention may be applied to the alkylation of isobutane, isopentane or similar isoparaf ins. The preferred isoparaffins are Isobutane and isopentane, particularly isobutane. A mixture of two or more isoparaffins may also be employed, if desired. Conventional isobutane alkylation feed stocks are suitable for use In the present process. Such conventional makeup isobutane feed stocks may contain some non-reactive hydrocarbons such as normal paraffins. For example, a conventional commercial isobutane alkylation feed stock generally isobutane, 4 weight percent n-butane and 1 weight percent propane.

Olefins which are suitable for use in the process of the present invention include C3-C5 olefins. Mixtures of two or more olefin compounds may also be employed in the present process with good results. For example, conventional olefin feed stocks used in commercial olefin alkylatlon operations contain mixtures of propylene and butylenes, butylenes and amylenes, or propylene, butylenes end amylenes. The benefits of the present process may be obtained using such feed stocks as veil as when using a single olefin. A conventional C3-C5 olefin alkylatlon feed stock, which is particularly preferred for use In this process, may be derived from petroleum refining operations such as catalytic cracking and may therefore contain substantial amounts of saturated hydrocarbons, lighter and heavier olefins, etc.

The hydrogen fluoride catalysts employed in the present process are well known in the art. Generally, hydrogen fluoride alkylatlon catalyst contains about 75 weight percent or more of titratable acid, about 5 weight percent or less water, with the remainder being organic diluent. Such a alkylatlon catalyst is suitable for use in both the first and second alkylatlon steps In the present process. A particularly preferred catalyst for use In both alkylatlon steps contains about 85 weight percent acid and less than 1 weight percent water, the remainder being organic diluent.

Numerous alkylatlon reaction cones suitable for use in the process of this Invention are known in the art. For example, but not by way of limitation, the types of alkylatlon reactors described in United States Patents 3,456,033, 3,469,949 and 3,501,536 may suitably be employed for both alkylatlon reactors In the present process. Alkylatlon conditions associated with the particular alkylatlon reactors described In the above-listed patents or in connection with other suitable conventional alkylatlon reactors may be used in conjunction with the descrlp- Hydrogen fluoride alkylatlon conditions suitable for use in an embodiment of the present process include a temperature of about 0°F. to about 200° ., a pressure sufficient to maintain the reactants and the hydrogen fluoride catalyst in the liquid phase, and a contact time between the hydrocarbons and catalyat of about 0.1 minute to about 30 minutes. In a preferred embodiment utilising a hydrogen fluoride alkylatlon catalyst containing about 85 weight percent acid, a catalyst/hydrocarbon volume ratio of about 1:1 to about 5:1 is preferred, and a temperature of about 50°F. to about 150°F. is preferably employed in the alkylatlon reaction sones.

In a particularly preferred embodiment, the reaction mixture of hydrogen fluoride catalyst, reactants and reaction products formed in the alkylatlon reactor Is passed through a reaction soaker. In the description of the preferred embodiments herein provided, It is Intended that both the alkylatlon reactor and a reaction soaker, if one la utilised, are Included within the scope of the term "alkylatlon reaction xone." Suitable reaction soakers are well known In the art. For example, the reaction soakers described In United States Patents 3,560,587 and 3,607,970 may suitably be employed In the present process. Such reaction soakers are conventionally vessels equipped with perforated trays, baffle sections, or the like, to maintain an alkylatlon reaction mixture in the form of a fairly homogeneous mixture, or emulsion, for a predetermined length of time. The alkylatlon reaction mixture of catalyst and hydrocarbons Is maintained in the reaction soaker for a time which depends on the composition of the reaction mixture. A reaction soaker residence time of about 1 minute to about 30 minutes la preferred. The temperature and pressure maintained in the reaction soaker are the sane as the temperature and pressure maintained in the associated alkylation reactor.

Means for settling the reaction mixture effluent from the alkylation reaction zone in order to separate a settled hydrocarbon phase and a hydrogen fluoride catalyst phase are well known in the alkylation art. Generally, the effluent alkylation reaction mixture recovered from an alkylation reactor or soaker comprises a mixture of unreacted isoparaffin, alkylation reaction products, hydrogen fluoride catalyst and catalyst-soluble organic materials, possibly with small amounts of light hydrocarbons, etc. When this alkylation reaction mixture is allowed to stand unstirred, I.e., settled, the alkylation reaction products, isoparafflns and light hydrocarbons form a lighter settled hydrocarbon phase. The hydrogen fluoride catalyst and catalyst-soluble hydrocarbons form a separate phase. The settled hydrocarbon phase is then simply mechanically separated from the catalyst phase. The temperature and pressure maintained during such a settling operation are substantially the same as those described above in connection with hydrogen fluoride alkylation conditions employed in a reactor. The hydrocarbons and the catalyst are maintained in the liquid phase during the settling separation operation.

Some means for withdrawing heat from the alkylation zone is necessary for optimum operation of the process. A variety of means for accomplishing the heat withdrawal are well known. For example, in one embodiment the heat generated in the alkylation reaction may be withdrawn directly from the alkylation reactor by indirect heat exchange between cooling water and the reaction mixture in the reactor.

The settled hydrocarbon phase recovered from the first settling operation Is combined with a second portion of the olefin feed In order to provide the hydrocarbon charge to the second alkylatlon reactor. Thus, the first settled hydrocarbon phase Is utilised to provide a high external lsobutane/olefln mole ratio In the feed to the second alkylatlon reactor. The hydrocarbon feed formed from the first settled hydrocarbon phaee and the second portion of oleflnlc reactant Is then charged to the second alkylatlon reactor and contacted with a second hydrogen fluoride alkylatlon catalyst therein. It is contemplated that sufficient Isobutane is charged to the first alkylatlon reactor that no further extraneous isobutane need be added to the admixed second portion of oleflnlc feed and first settled hydrocarbon phase prior to charging this hydrocarbon admixture to the second alkylatlon reactor. The same general alkylatlon conditions are used In the second alkylatlon step as are used in the first alkylatlon step. Although a reaction soaker may be utilised in connection with both the first and the second alkylatlon reactors, in a preferred embodiment a reaction soaker is employed only In connection with the second alkylatlon reactor. The temperature and pressure used in the reaction soaker are the same as those employed In the associated reactor. After completion of the reaction of all olefins charged to the second alkylatlon reaction sone, the resulting reaction mixture Is settled by any suitable, conventional method to provide a second settled hydrocarbon phase and to recover the second hydrogen fluoride catalyst phase for recycle to the second alkylatlon reaction cone. The second settled hydrocarbon phase Is recovered from the second settling operation and is passed to a conventional isobutane stripping tractIon*tion operation, whereby the heavier alkylate product la separated from the lower boiling, unconsuaed lsobutsne and free any hydrogen fluoride which ny be present In the aeeond settled hydrocarbon phase. Any suitable method utilised In the prior art to fractionate the settled hydrocarbon phase recovered free a settler nay be eaployed to separate the higher boiling alkylate product froa the lover boiling leobutane recycle ntreaa.

The elhyletlon reaction product produced in the preferred eabodlaent of the present procees will generally comprise C7-C9 saturated hydrocarbons resulting from the alk letion reactions of Isobutane with the olefins In both the first and second alky etion sonea. The prlaary components of the product include, for exaaple, dlaethylpentanea and trinethylpentanea. It la well known that •ore highly branched hydrocarbons generally possess superior properties as wotor fuel. The present Invention is directed, in part, to providing notor fuel alkylate containing a higher ratio of more highly branched hydrocarbons» audi as trie*th Ipentsnes, to less branched hydrocarbons, such aa dinethylhexnss. This benefit Is obtained by the use. In the present process, of high external leo-btttane/olefin mole ratios In both alky1s ion reactlone, unattainable In prior art process on a generally econoaicsl or operative basis. Thus, It is apparent that the present invention provides a novel process for producing s superior notor fuel alkylate product by a aethod nore economical and convenient than haa been available in prior art hydrogen fluoride catalysed alklatlon proeeaaea.

In general, the benefits and advantages of the present process ere provided when at least two different portions of the olefin esctent feed stock and st least two different hydrogen fluoride catalysts in at least two different alk letIon zones are employed. One suitable modification of the present process Is to divide the olefin feed stock Into a plurality of portions, e.g., three or more. The total laobutane feed and a first portion of the olefin feed stock are admixed and than contacted with a first hydrogen fluoride catalyst in a first alkylatlon zone, the catalyst and hydrocarbons are settled and separated, and the first settled hydrocarbon phase and a second portion of the olefin feed stock are admixed and then contacted with a second hydrogen fluoride catalyst in a second alkylatlon cone. The second settled hydrocarbon phase recovered by settling the resulting mixture s admixed with a third portion of the olefin feed stock and the resulting hydrocarbon mixture Is contacted with a third hydrogen fluoride catalyst In a third alkylatlon cone, etc., without addition of further leobutane between stages. The settled hydrocarbon phase recovered from the last alkylatlon zone in the series Is fractionated to recover the alkylatlon reaction product and separate unreacted leobutane for recycle to the first alkylatlon zone. Such a modification Is within the scope of the present invention.

Where It is desired to employ two alkylatlon zones and to divide the olefin feed stock Into tvo portions, as In the preferred embodiment, It Is preferred that the two portions of ole-flnlc feed be such that neither portion contains less than about 10 volume percent of the total amount of olefin used In the process. For example, In a continuous operation, the first portion of olefin may be fed to the first alkylatlon zone at a rate of 10 moles/hour along with an amount of leobutane sufficient to provide the desired molar excess thereof in the first reactor at hydrogen fluoride alk latlon conditions. The second portion of olefin is preferably admixed with the first settled hydrocarbon phase to be charged to the second alkylatlon reaction zone at a rate of at least about 1 mole/hour and not more than about 100 moles/hour. Preferably the two portions of olefin feed stock do not vary in the relative amounts of olefin they contain by more than about 1:5 to about 5:1, by volume. Best results are achieved in a two-reactor system, as described In the preferred embodiments, when the two portions of olefin feed stock contain roughly equal amounts of the oleflnic feed stock. In this way, the amount of lsobutane needed to provide a high external iso-butane/olefin mole ratio in the hydrocarbon feed to each alkylatlon reactor is kept to a minimum, while the highest quality alkylate product possible can thereby be obtained from both the first and the second reactors.

EXAMPLE In order to demonstrate the benefits and advantages of the present invention in contrast to prior art alkylatlon methods, two runs, one using the method of the present invention and the other using a conventional alkylatlon procedure, were performed. The olefin feed stock employed in both runs contained 48 weight percent propylene, 10.4 weight percent butene-1, 26 weight percent butene-2 and 15.6 weight percent isobut lene. lsobutane was employed as the isoparaffln feed stock. In Run 1, the method of the present invention, using two stages of alkylatlon, was utilized, and in Run 2, the conventional, single-stage method was utilized. In both Run 1 and Run 2 the same temperature, pressure and catalysts were utilized. The hydrogen fluoride catalyst utilised contained 89 weight percent hydrogen fluoride, 10 weight percent organic diluent and 1 weight percent water. The temperature utilised for the alkylatlon reactions was about 99°?. The pressure employed was sufficient to maintain the re-actants and catalyst as liquids. In each run the hydrocarbon feed and catalyst were continuously charged to a conventional, bench-scale alkylatlon reactor at a catalyst/hydrocarbon weight ratio of about 1.5:1, and a 10 minute residence time In the alkylatlon reactor was maintained in each run. In Run 1, using the method of the present invention, the olefin feed stock was split into two portions. The total lsoparaf ln feed stock and a first portion of the olefin feed stock were admixed and the resulting hydrocarbon feed was charged to a conventional alkylatlon reactor and contacted with hydrogen fluoride catalyst therein at the above described conditions to form a first reaction mixture. After the specified residence time, the first reaction mixture was withdrawn and conventionally settled to separate a first settled hydrocarbon phase from a settled catalyst phase. The resulting first settled hydrocarbon phase and the second portion of the olefin feed stock were contlnuouely charged to a conventional alkylatlon reactor and contacted with hydrogen fluoride catalyst therein at the above described alkylatlon conditions to form a second reaction, mixture. No additional iso-butane was added to the second reaction mixture, the lsobutane contained in the first settled hydrocarbon phase being the sole supply of lsobutane in the second reaction mixture. After the specified residence time, the second reaction mixture was withdrawn and conventionally settled to separate a second settled hydrocarbon phase from a settled catalyst phase. The second settled hydrocarbon phase was recovered, fractionated to separate out C5 and heavier hydrocarbons and the Cj+ hydrocarbons were recovered as the alkylate product of Run 1. The alkylate product of Run 1 was analysed and the results are set forth in the Table. In Run 2, using a conventional one-stage alkylatlon procedure, the whole olefin feed stock was continuously charged to 4 conventional alkylatlon reactor at a rate equal to the combined feed rate of the first and second portions of olefin feed stock In Run 1. In Run 2, the total Isobutane feed stock was continuously charged to the alkylatlon reactor at the same rate as was used in Run 1. The olefin feed stock and Isobutane feed stock were admixed and the resulting hydrocarbon mixture was charged to the alkylatlon reactor and contacted therein with hydrogen fluoride catalyst at the above-described alkylatlon conditions to form a reaction mixture. After the 10 minute residence time, the reaction mixture was withdrawn from the reactor and conventionally settled to separate a settled catalyst phase from a settled hydrocarbon phase. The settled hydrocarbon phase was recovered, fractionated to separate out C5 and heavier hydrocarbons, and the C«j+ hydrocarbons were recovered as the alkylate produet of Run 2. The alkylate product of Run 2 was analysed and the results are set forth in the Table.

TABLE; Alkylate Product Analysis Ran I Ran II Cg Hydrocarbons, vt. Z 61.5 56.1 Co+ Hydrocarbons, wt. Z 6.1 9.6 Triosthylpentanes, wt. % 56.3 50.4 Dinethylhe anas, wt. Z 5.15 5.8 Research Octane Number (Clear) 95.2 94.5 Motor Octane Number (Clear) 92.4 92.1 * * * Referring to the Table, it la apparent that the process of the present invention Ohm 1) provided a superior alkylate prod-cut relative to conventional alkylatlon procedures (Run 2). Yet, no additional lsobutane was employed In Run 1 and the required fractionation to separate the Cj+ alkylate hydrocarbons was iden-tlcal in Run 1 and Run 2. The figures shown in the Table deeon-strate that the process of the present Invention produces an alkylate product havinn higher octane ratings with reduced aaounts of undesirable heavy ends (Co+ hydrocarbons).

Claims (4)

1. A process for producing an alkyletIon reaction product from an isoparaffln and a mono-olefin selected fron propylene, butylenes, and anlenes which comprises the steps of: (a) admixing a first portion of said nono-olefin with said isoparaffln and contacting the resulting first hydrocarbon mixture Tflth a first hydrogen fluoride alk latlon catalyst phase in a first alkylatlon reaction zone at hydrogen fluoride alkylatlon conditions to form a first alkylatlon reaction mixture; (b) removing said first alkylatlon reaction mixture from said first alkylatlon reaction sons, settling said first reaction mixture to provide a first settled hydrocarbons phase and said first hydrogen fluoride catalyst phase, and recycling said first catalyst phase to said first alkylatlon reaction zone; (c) admixing a second portion of said mono-olefin with at least a portion of said first settled hydrocarbons phase and contacting the resulting second hydrocarbon mixture with a second hydrogen fluoride catalyst phase In a second alkylatlon reaction tone at hydrogen fluoride alkylatlon conditions to form a second alkylatlon reaction mixture; (d) removing said second alkylatlon reaction mixture from said second alkylatlon reaction zone, settling said second reaction mixture to provide a second settled hydrocarbons phase and said second hydrogen fluoride catalyst phase, and recycling said second catalyst phase to said second alkylatlon reaction zone; and, (e) fractionating said second settled hydrocarbons phase to provide a higher boiling product stream and a lower boiling isoparaffin stream, recycling seid iaoparaffln stream to said first alkylatlon reaction sone and recovering said alkylatlon reaction product from said product stream.

2. The process of Claim 1 wherein said Isoparaffin is lsobutane.

3. The process of Claim 1 wherein said mono-olefln is selected from butene-1, butene-2 and isobutylene.

4. The process of Claim 1 wherein said first portion of said mono-olefln comprises from about 10 mole percent to a-bout 1000 mole percent of said second portion of said mono-olefln.