IMPROVED PROCESS FOR THE ALKYLATION OF OLEFINS WITH PARAFFINS

Abstract: A process for the alkylation of at least one olefin with at least one paraffin in the presence of an alkylation catalyst to produce alkylates wherein the at least one olefin is alkylated with at least one paraffin in the presence of a slurry of catalyst particles. A portion of the catalyst particles is removed during the reaction, and active catalyst particles are added to the slurry. The process of the present invention is particularly applicable to the alkylation of butenes with isobutane to produce alkylates.

Description: IMPROVED PROCESS FOR THE ALKYLATION OF OLEFINS WITH PARAFFINS This invention relates to the alkylation of olefins with paraffins to produce alkylates such as high octane automotive fuels. More particularly, this invention relates to the alkylation of olefins with paraffins in the presence of a catalyst slurry. The term "slurry", as used herein, means that the catalyst is provided as a suspension of solid particles in the reaction medium. Many plants which are used for the alkylation of olefins with paraffins to produce desired alkylates use catalysts such a sulfuric acid or hydrogen fluoride (HF) . The use of such catalysts, however, presents a high corrosion risk. Such catalysts are also highly toxic and present difficulties in the disposal of spent catalyst. Such catalysts may pose danger to humans and to the environment in the case of accidental release. It has also been known to use zeolite catalysts in such alkylation reactions. Zeolites which have been employed include zeolite X, zeolite Y, mordenite, and other zeolites. The acidit of such catalysts may be controlled by means of ions of rare earth atoms (La, Ce, etc.) or of Group II metals (Ba, Ca, etc.) which replace the Na ions orginally present in the zeolite Na ions may also be exchanged with H^ ions as well. Upon calcination of NH 4 containing zeolites, NH- is released and acidic H sites are generated in the zeolite structure. An example of a typical alkylation reaction is one in whi (n-butenes) are alkylated with isobutane. When n-butenes are contacted with isobutane in the presence of an acidic catalyst, such as a zeolite catalyst, secondary and primary butyl carbocations are formed. The secondary butyl carbocation may react with isobutane to form 2,2,3-tri-methylpentane, and the primary butyl carbocation may react with isobutane to form 2,2-dimethylhexane. Secondary reactions may also take place, which result in t dimerization of olefins via the secondary or primary carbocatio For example, the secondary butyl carbocation may react with 2-butene to form, for example, 3,4-dimethyl-2-hexene. The dimerization product, which is also an olefin, can further reac with carbocations and produce C- 2 and higher olefins. Such olefins may form polymers which lead to deactivation of the catalyst. If the reaction is carried out in the presence of hydrogen, a large fraction of the olefins formed will be converted to saturated hydrocarbons. A large excess of isobuta is required in many cases in order to obtain a product comprise mostly of desired alkylate(s). The alkylation reaction is dominant when the catalyst is fresh. Gradually, olefin dimerization and trimerization become preponderant and the isobutane is no longer reacted. In a fixe bed operation or in a stirred reactor with suspended catalyst, the olefin dimerization becomes the main reaction after 6 to 12 hours on stream. In accordance with an aspect of the present invention, the is provided a process for the alkylation of at least one olefin with at least one paraffin to produce at least one alkylate. T process comprises alkylating the at least one olefin with the at least one paraffin in a reaction zone in the presence of a slurr of alkylation catalyst particles. A portion of the alkylation catalyst particles are removed from the reaction zone, and acti catalyst particles are added to the reaction zone. Preferably, the amount of active catalyst particles as that are added to the reaction zone is the same as the amount of catalyst particles removed from the reaction zone. The active catalyst particles may be fresh catalyst particles, or regenerated catalyst particles which were removed from the slurry and regenerated as hereinafter described. In accordance with one embodiment, the removal of a portion of the catalyst particles from the reaction zone comprises passing the catalyst particles from the reaction zone to a catalyst recovery zone to effect separation of the catalyst particles from a portion of the slurry, and passing the catalyst particles to a catalyst regeneration zone to effect regeneration of the catalyst particles. The regenerated, or reactivated, catalyst particles may then be returned to the slurry of catalyst particles in the reaction zone. In accordance with one embodiment, a portion of the catalys particles are continuously removed from the reaction zone, and active catalyst particles are continuously added to the slurry. In another embodiment, a portion of the catalyst particles is periodically removed from the reaction zone, and active catalyst particles are added periodically to the slurry. As part of the catalyst regeneration process, the catalyst is recovered from the slurry in a catalyst recovery zone. Catalyst recovery may be accomplished through any one of various means known in the art, such as through the use of decanters, hydroclonββ, filters, centrifuges, etc. The catalyst may be recovered as a more concentrated slurry than as found in the reaction zone, or as a paste or a wet solid. Once the catalyst is recovered, it is passed to a catalyst regeneration zone, wher regeneration of the catalyst takes place by means known in the art. In accordance with one embodiment, the catalyst may be a zeolite catalyst. Zeolite catalysts which may be employed include, but are not limited to, Zeolite Y, ZSM-5, Zeolite-Beta Zeolite X, zeolite Omega, mordenite, and chabazite. In accordance with another embodiment, the catalyst may be an acidic clay. Examples of acidic clays include natural clays such as mo tmorillonite, kaolin, Fuller's earth, bentonite, sepiolite, hectorite, and illite, which are acid washed. In accordance with a further embodiment, the catalyst may in the form of particles of acidic compounds, such as, for example, HF, BF-, F_C-SO_H, which are impregnated in porous supports of adequate particle size. In accordance with another embodiment, the catalyst particles have a particle size of from about 0.1 micron to abou 4 mm, preferably of from about 1 micron to about 200 microns, most preferably of from about 10 microns to about 100 microns. The alkylation reaction may take place in a stirred reactor a loop reactor, or other well-mixed reactor. The reaction zone, in one embodiment, may include at least two reaction stages, which may be in the form of reactors in series. When two or mor reactors are employed, each of the reactors may be of the same type, or the reactors may be of different types. Also, there is a continuous flow of catalyst from the first toward the last reactor of the series. By employing more than one reaction stage, each reactor will contain catalyst of a relatively narrow distribution of residence times, which thus will have a well-defined level of activity. As an alternative, the volume of a well-stirred slurry reactor can be divided into two or more compartments through which the reaction mixture flows in series, in order to simulate a plug flow reactor. By removing a portion of the catalyst particles, and replacing the removed catalyst with fresh or regenerated catalyst, one can maintain a constant activity and selectivity i the reactor system. Various flow configurations may be employed in the alkylation process, depending upon the activity and life of the catalyst, and other conditions controlling the economics of the process. In one alternative, each reaction stage; i.e., each reacto or compartment of a reactor, is provided with means to remove from and to introduce catalyst to the reactor or compartment, independent of the flow of the reagents and products. Catalyst removal and addition can be done while the reactor is on-line. In another alternative, catalyst may be removed from one o more reactors. Fresh catalyst is introduced into the same or a different reactor than the one from which used catalyst was withdrawn. Fresh catalyst can then be introduced into one or more reactors upstream or downstream from the reactors from whi used catalyst is withdrawn. In yet another alternative, catalyst may flow with the effluent from one compartment or reactor to the next, but may also be withdrawn from a given reactor or compartment or the effluent and be recirculated to one or more reactors or compartments upstream of the reactor or compartment from which the catalyst was recovered. In a further embodiment, catalyst flows with the effluent from one compartment or reactor to the next until the catalyst reaches the last of the compartments or reactors with respect t the movement of the reactants. A portion of the catalyst particles are withdrawn from the compartment or reactor, and is passed aβ hereinabove described to the catalyst recovery zone, and then to the catalyst regeneration zone. The regenerated catalyst is re-introduced into the system upstream from the las of the series of compartments or reactors. It is to be understood, however, that the scope of the present invention is not to be limited to any particular type of reactor, or to any type of catalyst addition, withdrawal, and/or regeneration scheme. When the reaction zone includes at least two reaction stages, all of the paraffin requirements are introduced into the first stage. All of the olefin may also be introduced into the first stage, or a portion of the olefin may be introduced into each reaction stage. Alkylation reactions which may be employed include the alkylation of olefins with isoparaffins, such as, for example, the alkylation of butenes with isobutane to produce alkylates such as tri-methylpentane and dimethylhexane, in particular, 2,2,3-trimethylpentane and 2,2-dimethylhexane. It is to be understood, however, that the scope of the present invention is not to be limited to the above-mentioned alkylation reactions. The alkylation process of the present invention may be carried out at a temperature of from about -50°C to about +150°C preferably from about +20°C to about +100°C, and at a pressure o from about 1 atm to about 100 atm, preferably from about 20 atm to about 50 atm. The alkylation process may also be carried out at an WHSV of from about 0.1 hr. " to about 10 hr. " , preferably from about 1 hr. " to about 5 hr. " . The invention will now be described with respect to the drawings, wherein: Figure 1 is a schematic of a first embodiment of the process of the present invention wherein the alkylation reaction takes place in a single reactor; Figure 2 is a schematic of a second embodiment of the present invention wherein the alkylation reaction takes place in a plurality of stages and catalyst is removed from each stage; and Figure 3 is a schematic of a third embodiment of the process of the present invention wherein the alkylation reaction takes place in a plurality of stages, the catalyst flows with the effluent from one reactor to the next, and is removed from a given reactor and is recirculated to one or more reactors upstream from the reactor from which the catalyst was recovered. Referring now to the drawings, in accordance with an embodiment of the present invention, as shown in Figure 1, a f of olefin in line 10 and paraffin in line 11 is passed to reac 12, which contains finely divided catalyst particles as hereinabove described, which become suspended as a slurry in t reaction medium. In reactor 12, the olefin is alkylated with paraffin in the presence of the slurried catalyst under alkylation conditions such as those hereinabove described to f a desired alkylate product. The alkylate product is withdrawn from reactor 12 through line 19. A portion of the slurried catalyst and the reaction mediu is withdrawn from reactor 12 through line 13 and passed to catalyst recovery zone 14. In catalyst recovery zone 14, the catalyst is separated from the reaction medium by means known the art. The reaction medium is withdrawn from catalyst recov zone through line 15 and returned to reactor 12. The catalyst, which may be in the form of a more concentrated slurry, a past or a wet solid, is withdrawn from catalyst recovery zone 14 through line 17 and passed to catalyst regeneration zone 16. I catalyst regeneration zone 16, the catalyst is regenerated by a catalyst regeneration means known in the art. After the cataly has been regenerated, or reactivated, it is withdrawn from catalyst regeneration zone 16 through line 18, and is returned reactor 12, wherein the catalyst returns to the catalyst slurry In accordance with another embodiment, shown in Figure 2, paraffin in line 21, and olefin from line 20 and passed to line 23, are fed to first stage alkylation reactor 22. Reactor 22 contains catalyst particles which become suspended in the reaction medium as a slurry. Effluent is withdrawn from reacto 22 through line 31 and passed to second stage reactor 30. A portion of the catalyst and reaction medium is withdrawn from reactor 22 through line 25 and passed to catalyst recovery zone 24. The catalyst is separated from the reaction medium and is withdrawn from catalyst recovery zone 24 through line 26 and passed to catalyst regeneration zone 28. The reaction medium i withdrawn from catalyst recovery zone 24 through line 27 and returned to reactor 22. A portion of the olefin in line 20 is passed to line 33, an fed to second stage reactor 30. The olefin is alkylated with an paraffin which may be contained in the effluent from line 31 which enters reactor 30. Reactor 30 contains catalyst particles which become suspended as a slurry of particles in the reaction medium. The olefin is alkylated with paraffin in the presence o the slurried catalyst under alkylation conditions. Effluent is withdrawn from the second stage reactor through line 37. A portion of the catalyst and reaction medium is withdrawn from reactor 30 through line 32, and passed to catalyst recovery zone 34. Reaction medium is separated from the catalyst in catalyst recovery zone 34, passed through line 35, and returned to reacto 30. Catalyst is withdrawn from recovery zone 34 through line 45 and passed to regeneration zone 28. Effluent in line 37 is passed to third stage reactor 38, wherein the effluent, containing paraffins and alkylate, is contacted with olefin from line 39 which was passed to line 39 from line 20. Third stage reactor 38 also contains finely divided catalyst particles which are suspended in the resulting reaction medium as a slurry of catalyst particles. Alkylate product is withdrawn from third stage reactor 38 through line 44. A portion of the catalyst particles and reaction medium are withdrawn from third stage reactor 38 through line 41 and are passed to catalyst recovery zone 40. The reaction medium is separated from the catalyst, is withdrawn from catalyst recovery zone 40 through line 42, and returned to third stage reactor 38. Catalyst is withdrawn from recovery zone 40 through line 46, and passed to regeneration zone 28. Catalyst which has been regenerated in catalyst regeneration zone 28 is returned to first stage reactor 22 through line 29, to second stage reactor 30 through line 36, and to third stage reactor 38 through line 43. In each of reactors 22, 30, and 3 the returned catalyst again becomes part of the catalyst slurr In accordance with yet another embodiment, as shown in Figure 3, olefin in line 40 is passed to line 53, and along wi paraffin in line 51, is passed to first stage reactor 52, whic contains finely divided catalyst particles which are suspended the reaction medium as a slurry. The olefin and paraffins are reacted in reactor 52 under alkylation conditions. The effluen as well as the slurried catalyst particles, is withdrawn from reactor 52 through line 55 and passed to second stage reactor 5 Olefin from line 50 also enters reactor 54 through line 56. Reactor 54 is operated under alkylation conditions, and an effluent, which also contains the slurried catalyst, is withdra from reactor 54 through line 57. The effluent is then passed t third stage reactor 60. Olefin from line 50 is passed to line 59, and enters reactor 60 as well. The catalyst particles in reactor 60 are suspended as a slurry of catalyst particles in t reaction medium. Reactor 60 is operated under alkylation conditions, and a desired alkylate product is recovered through line 71. A portion of the catalyst and the reaction medium is withdrawn from reactor 60 through line 61 and passed to catalys recovery zone 62. In catalyst recovery zone 62, the catalyst i separated from the reaction medium. The reaction medium is withdrawn from catalyst recovery zone 62 through line 63 and returned to reactor 60. The catalyst is withdrawn from catalys recovery zone 62 through line 65 and is passed to catalyst regeneration zone 64. Regenerated catalyst is then passed through line 67 to first stage reactor 52, or through line 69 t second stage reactor 54. In each of reactors 52 and 54, the regenerated catalyst again becomes part of the catalyst slurry. The invention will now be described with respect to the following examples; however, the scope of the present invention is not to be limited thereby. Example 1 (Comparative) An acidic Y zeolite shaped as extrudates of approximately 1 mm diameter and 6 mm long was heated in a furnace under constant air sweep and held at 232°C for 12 hours. The catalyst was removed from the furnace and allowed to cool in a dessicator. A 18 gram portion of this catalyst was loaded into a 3/4" diameter, stainless steel reactor equipped with a 1/4" pre-heat tube and a 1/8" thermowell, facilitating a travelling thermocouple. The test unit included a feed tank, containing a pressurize solution of 95% isobutane and 5% trans-2-butene, sitting on a digital balance with O.lg sensitivity. The feed was delivered to the reactor by a piston metering pump. The reactor was located in a thermostated, mechanically stirred oil bath. Reactor pressure was controlled by a diaphragm-dome regulator. Reactor effluent samples were taken from a high pressure sampling port with a locking pressure syringe and analyzed by GC using a 60 meter OV-1 capillary column. The results in Table 1 were obtained under the following conditions: Average reactor temperature = 135°C, reactor pressure = 520 psig, WHSV = 2.4 hr "1 . Table 1 Example 2 - Alkylation of Butenes with Isobutane in the Presence of a Catalyst Slurry A pre-mixed feed consisting of 96% isobutane and 4% mixed 2-butenes was delivered to a 300 ml stirred autoclave, which w swept with dry nitrogen prior to addition of the feed and preheated to a temperature of 121°C, by a piston metering pump. The autoclave was equipped with an internal thermowell, a slur drain valve, a feed charging bomb, and dual exit lines fitted with sintered metal filters (1 micron openings) to prevent catalyst from leaving the autoclave. Pressure is controlled b dome back pressure regulator. Reactor effluent samples are ta from a high pressure sampling port with a locking syringe and analyzed by gas chromatography. 11.6 grams of finely ground acidic Zeolite Y, prepared and treated as described in Example 1, were also charged to the autoclave and slurried in the reaction mixture. Reaction conditions were as follows: Average reactor pressure: 490 psig Reactor temperature: 121°C WHSV = 4.65 hr. "1 The results of this reaction are listed in Table 2 below. Table 2 Hours on Stream 6.5 11 Feed from start of run (g/g cat) 30.2 51.2 Butenes Conversion 99.5 56.9 Selectivity, C g + 90.3 76.3 Example 3 The reaction hereinabove described in Example 2 was carrie out with a fresh batch of catalyst for 10 hours. After the catalyst was on stream for 10 hours, 47.Og feed/g catalyst had been used. Approximately 30% of the catalyst slurry was then removed via the slurry drain valve and replaced with an equal amount of freshly activated catalyst, which was dispersed in isobutane, and delivered to the autoclave through the feed bomb. Effluent samples were drawn and analyzed after the feed was restarted at the previous rate and the system temperature and pressure returned to set points. After an additional six hours, at a total of 74.Ig feed/g catalyst, butene conversion was 94.2% and the selectivity to C 5 product was 90.7%. Replacing of approximately one-third of the catalyst inventory was repeated approximately every 10 hours of operation. In this manner, the performance of the reactor was maintained constant at the level hereinabove indicated. Advantages of the present invention include the provision o a finely dispersed catalyst slurry, which results in a uniform reaction and thermal loading of the reactor volume. The process of the present invention also provides for the reduction or elimination of so-called "hot spots" in the reactor, and enables one to remove catalyst from and introduce fresh catalyst to the reactor without interrupting the reaction. This enables the reduction of catalyst inventory as compared with a fixed bed reactor, and enables one to maintain reactor productivity and product selectivity at a desired level by keeping catalyst in the reactor which has adequate distribution of activities. In addition, when one employs catalyst particles having a size as hereinabove described, a rapid exchange between reagents and products is favored, and the rate of catalyst deactivation is reduced- It is to be understood, however, that the scope of the present invention is not to be limited to the specific embodiments described above. The invention may be practiced other than as particularly described and still be within the scope of the accompanying claims.

Claims: WHAT IS CLAIMED IS: 1. A process for the alkylation of at least one olefin a least one paraffin to produce at least one alkylate, comprising: alkylating said at least one olefin with said at least one paraffin in a reaction zone in the presence of a slurry of alkylation catalyst particles; removing a portion of said catalyst particles from said reaction zone; and adding active catalyst particles to said reaction zone. 2. The process of Claim 1 whereion said removing of a portion of said catalyst particles from said reaction zone comprises: passing said portion of said catalyst particles from said reaction zone to a catalyst recovery zone to effect separation o said portion of catalyst particles from a portion of said slurry and passing said portion of catalyst particles to a catalyst regeneration zone to effect regeneration of said portion of catalyst particles. 3. The process of Claim 2, and further comprising: passing said regenerated catalyst particles to said slurry in said reaction zone. 4. The process of Claim 1 wherein said reaction zone includes at least two reaction stages. 5. The process of Claim 4 wherein said at least one olefi is introduced into each of said at least two reaction stages of said reaction zone. 6. The process of Claim 4 wherein a portion of said catalyst particles is removed from each of said at least two reaction stages of said reaction zone. 7. The process of Claim 4 wherein said portion of catalys particles is removed from the last reaction stage, with respect to the movement of reactants, of said at least two reaction stages of said reaction zone. 8. The process of Claim 1 wherein a portion of said catalyst particles is continuously removed from said reaction zone, and active catalyst particles are continuously added to said slurry. 9. The process of Claim 1 wherein a portion of said catalyst particles is periodically removed from said reaction zone, and active catalyst particles are periodically added to said slurry. 10. The process of Claim 1 wherein said at least one paraffin is an isoparaffin. 11. The process of Claim 10 wherein said isoparaffin is isobutane. 12. The process of Claim 11 wherein said at least one olefin is a butene. 13. The process of Claim 12 wherein said at least one alkylate is selected from the group consisting of trimethylpentanes and dimethylhexanes. 14. The process of Claim 1 wherein the catalyst is a zeolite catalyst. 15. The process of Claim 1 wherein said catalyst has a particle size of from about 0.1 micron to about 4 mm. 16. The process of Claim 15 wherein said catalyst has a particle size of from about 1 micron to about 200 microns. 17. The process of Claim 16 wherein said catalyst has a particle size of from about 10 microns to about 100 microns.

Inventors: SUCIU GEORGE D, WESTNER ANDREW, SUCIU, GEORGE, D., WESTNER, ANDREW
Applicants: LUMMUS CREST INC, ABB LUMMUS CREST INC.
Application year: 1992
Main classification: C07C9
IPC codes: C07B61, C07C2, C07C9, C10G35