EP0863860A1

EP0863860A1 - Isoparaffin/olefin alkylation process using rare-earth exchanged faujasite catalysts

Info

Publication number: EP0863860A1
Application number: EP96930549A
Authority: EP
Inventors: John Scott Buchanan; Tracy Jau-Hua Huang
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1995-11-22
Filing date: 1996-08-13
Publication date: 1998-09-16
Also published as: AU6954996A; AU708623B2; EP0863860A4; WO1997020787A1; CA2231445A1

Abstract

An isoparaffin olefin alkylation process conducted in the presence of RE USY or RE USX is disclosed. Catalysts useful have a particle size range from 50 to 150 microns and an attrition index of less than 10 and preferably less than 5. The alkylate product is useful, inter alia, as an octane enhancer for gasoline.

Description

ISOPARAFFIN/OLEFIN ALKYLATION PROCESS USING RARE-EARTH EXCHANGED FAUJASITE CATALYSTS

The instant invention relates to an isoparaffin-olefin alkylation process which is carried out in the presence of a rare-earth exchanged faujasite such as ultra-stable Y- zeolite (RE-USY) , or ultra-stable X-zeolite (RE-USX) . Catalysts useful are those typically used in FCC applications, having a particle size range from 50 to 150 microns and an attrition index of less than 10 preferably less than 5. The alkylate product is useful, inter alia, as an octane enhancer for gasoline. As a result of curtailing the use of tetraethyl lead as an octane-improving additive for gasoline, the octane number specification of all grades of gasoline has increased as well as the production of unleaded gasoline. Isoparaffin-olefin alkylation is a key route to the production of highly branched paraffin octane enhancers which are to be blended into gasoline.

Alkylation involves the addition of an alkyl group to an organic molecule. Thus, an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Industrially, alkylation often involves the reaction of C₂-C_b olefins with isobutane in the presence of an acidic catalyst. Alkylates are valuable blending components for the manufacture of premium gasolines due to their high octane ratings. In the past, alkylation processes have included the use of hydrofluoric acid or sulfuric acid as catalysts under controlled temperature conditions. Low temperatures are utilized in the sulfuric acid process to minimize the undesirable side reaction of olefin polymerization and the acid strength is generally maintained at 88-94 percent by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature-sensitive and the acid is easily recovered and purified. The typical types of alkylation currently used to produce high octane gasoline blending component, that is, the hydrofluoric acid and sulfuric acid alkylation processes, have inherent drawbacks including environmental concerns, acid consumption and disposal of corrosive materials. With the increasing demands for octane and the increasing environmental concerns, it has been desirable to develop an alkylation process based on a solid catalyst system. The catalyst of the present invention offers a refiner a more environmentally acceptable alkylation process than the currently used hydrofluoric and sulfuric acid alkylation processes.

Crystalline metallosilicates, zeolites, and molecular sieves generally have been widely investigated for use in the catalysis of isoparaffin-olefin alkylation. For example, U.S. Pat. No. 3,251,902 describes the use of a fixed bed of ion-exchanged crystalline aluminosilicate having a reduced number of available acid sites for the liquid phase alkylation of C₄-C₂₀ branched-chain paraffins with C₂-C₁₂ olefins. The patent further discloses that the C₄-C₂₀ branched-chain paraffin should be allowed to substantially saturate the crystalline aluminosilicate before the olefin is introduced to the alkylation reactor. U.S. Pat. No. 3,450,644 discloses a method for regenerating a zeolite catalyst used in hydrocarbon conversion processes involving carbonium ion intermediates.

U.S. Pat. No. 3,549,557 describes the alkylation of isobutane with C₂-Cj olefins using certain crystalline aluminosilicate zeolite catalysts in a fixed, moving or fluidized bed system, the olefin being preferably injected at various points in the reactor.

U.S. Pat. No. 3,644,565 discloses the alkylation of a paraffin with an olefin in the presence of a catalyst comprising a Group VIII noble metal present on a crystalline aluminosilicate zeolite, the catalyst having been pretreated with hydrogen to promote selectivity. U.S. Pat. No. 3,647,916 describes an isoparaffin- olefin alkylation process featuring the use of an ion- exchanged crystalline aluminosilicate, isoparaffin/olefin mole ratios below 3:1 and regeneration of the catalyst. In this patent, particle sizes are limited to less than 40 microns and are prepared by ball milling. In the instant invention, particle sizes range from 50 to 150 microns.

U.S. Pat. No. 3,655,813 discloses a process for alkylating C₄-C₅ isoparaffins with C₃-C₈ olefins using a crystalline aluminosilicate zeolite catalyst wherein a halide adjuvant is employed in the alkylation reactor. The isoparaffin and olefin are introduced into the alkylation reactor at specified concentrations and catalyst is continuously regenerated outside the alkylation reactor. U.S. Pat. No. 3,893,942 describes an isoparaffin- olefin alkylation process employing, as catalyst, a Group VIII metal-containing zeolite which is periodically hydrogenated with hydrogen in the gas phase to reactivate the catalyst when it has become partially deactivated. U.S. Pat. No. 3,236,671 discloses the use, in alkylation, of crystalline aluminosilicate zeolites having silica to alumina mole ratios above 3 and also discloses the use of various metals exchanged and/or impregnated on such zeolites. U.S. Pat. No. 3,706,814 discloses another zeolite catalyzed isoparaffin-olefin alkylation process and further provides for the addition of C₅+ paraffins such as Udex raffinate or C₅+ olefins to the alkylation reactor feed and the use of specific reactant proportions, halide adjuvants, etc. U.S. Pat. No. 3,624,173 discloses the use, in isoparaffin-olefin alkylation, of zeolite catalysts containing gadolinium.

U.S. Pat. No. 3,738,977 discloses alkylation of paraffins with ethylene employing a zeolite catalyst which possesses a Group VIII metal component, the catalyst having been pretreated with hydrogen. U.S. Pat. No. 3,865,894 describes the alkylation of C,-C₉ monoolefin employing a substantially anhydrous acidic zeolite, for example acidic zeolite Y (zeolite HY) , and a halide adjuvant. U.S. Pat. No. 3,917,738 describes a process for alkylating an isoparaffin with an olefin using a solid, particulate catalyst capable of absorbing the olefin. The isoparaffin and the olefin are admixed to form a reactant stream in contact with catalyst particles at the upstream end of an adsorption zone after which the reactants are passed concurrently with the catalyst so that a controlled amount of olefin is adsorbed onto the catalyst before the combination of reactants and catalyst is introduced into an alkylation zone. This controlled olefin adsorption is said to prevent polymerization of the olefin during alkylation. U.S. Pat. No. 4,377,721 describes an isoparaffin- olefin alkylation process utilizing, as catalyst, ZSM-20, preferably HZSM-20 or rare earth cation-exchanged ZSM-20. This catalyst may be in the form of a finely divided powder, but specific size limitations are not given. Furthermore, attrition indices (heretofore discussed primarily in regard to FCC catalyst applications) are not mentioned.

U.S. Pat. No. 4,384,161 describes a process of alkylating isoparaffins with olefins to provide alkylate employing as catalyst a large pore zeolite capable of absorbing 2, 2,4-trimethylpentane, e.g., ZSM-4, ZSM-20, ZSM- 3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y and the rare earth metal-containing forms thereof, and a Lewis acid such as boron trifluoride, antimony pentafluoride or aluminum trichloride. The use of a large pore zeolite in combination with a Lewis acid in accordance with this patent is reported to greatly increase the activity and selectivity of the zeolite thereby effecting alkylation with high olefin space velocity and low isoparaffin/olefin ratio. U.S. Pat. Nos, 4,992,615; 5,012,033; and 5,073,665 describe an isoparaffin-olefin alkylation process utilizing, as a catalyst, a zeolite designated as MCM-22. U.S. Pat. Nos. 5,258,569 and 5,254,792 disclose isoparaffin olefin alkylation processes which utilize MCM-36 and MCM-49 respectively, as catalysts.

U.S. Pat. No. 5,292,981 describes a process for isoparaffin-olefin alkylation in which a slurry of zeolite particles and a feed of liquid reactants comprising isoparaffins and olefins is circulated in a reactor. The isoparaffin/olefin ratio is less than 100/1 in the slurry. A first portion of the slurry is recycled to provide a ratio of at least 500/1. A second portion of the slurry is passed to a separating means wherein alkylate product is separated from the zeolite.

U.S. Pat. No. 5,366,948 discloses a process of the preparation of a catalyst intended for catalytic cracking purposes. It may be prepared with an attrition index of less than 10 and is prepared by spray drying. It is generally in the form of a fine powder of 10-200 microns. The instant invention is concerned with a process for the alkylation of isoparaffins with olefin molecules in the presence of a composite catalyst. The catalyst comprises a rare-earth exchanged faujasite such as an ultra stable X- zeolite(RE-USX) or ultra-stable Y-zeolite(RE-USY) . The most suitable catalyst for use in the instant invention is a fluidizable catalyst in the particle size range of 50-150 microns, having an attrition index of less than 10 and preferably of less than 5. A low attrition index for a catalyst indicates low loss of catalyst over a cycle of operation. The sodium content of the FCC catalyst is preferably less than 1.0 wt% and more preferably less than 0.5 wt%. The degree of rare earth exchange in the zeolite component is preferably higher than 30% and more preferably high than 60%. Such catalysts have traditionally been used in applications involving fluid catalytic cracking (FCC) units. The high quality alkylate produced in the instant invention may be used as octane blending stock for gasoline manufacturing. In FCC operations catalysts comprising RE-USY or RE- USX provide gasoline products with improved octane number. They also produce lower amounts of coke than catalysts which do not comprise rare-earth faujasites. The amount of rare-earth exchange in the catalyst is inversely proportional to the amount of coke make. Similar benefits may also be obtained if these catalysts are employed in the alkylation of isoparaffins with olefins.

The alkylation of isobutane with light olefins is important in the manufacture of high octane gasoline blending stocks. Alkylation typically comprises 10-15 % of the gasoline pool. It has high RON and MON, is low in sulfur content, contains no olefins or aromatics, demonstrates excellent stability and is clean burning.

Feed Feedstocks useful in the present alkylation process include at least one isoparaffin and at least one olefin. The isoparaffin reactant used in the present alkylation process may be one possessing up to 20 carbon atoms and preferably has from 4 to 8 carbon atoms. Representative examples of such isoparaffins include isobutane, isopentane, 3-methylhexane, 2-methylhexane, 2,3- dimethylbutane and 2 , 4-dimethylhexane.

The olefin component of the feedstock includes at least one olefin having from 2 to 12 carbon atoms. Representative examples of such olefins include butene-2, isobutylene, butene-1, propylene, ethylene, pentene, hexene, octene, and heptene merely to name a few. The preferred olefins include the C_A olefins, for example, butene-1, butene-2, isobutylene, or a mixture of one or more of these C„ olefins, with butene-2 being the most preferred. Suitable feedstocks for the process of the present invention are described in U.S. Pat. No. 3,862,258 to Huang et al. at column 3, lines 44-56, the disclosure of which is incorporated by reference. Hydrocarbon streams containing a mixture of paraffins and olefins such as FCC butane/butene stock may also be employed. The isoparaffin/olefin weight ratio in the feed may range from 1:1 to over 100:1. Although the ratio in the reactor of above 100 is desirable, a ratio of over 500:1 in the reactor is more desirable and a ratio of over 1000:1 is most desirable. A high isoparaffin/olefin ratio may be achieved by recycle of part of the reactor effluent or by back-mixing of the reactor content. Alkylation Catalyst Catalysts suitable for use in the instant invention comprise rare-earth exchanged USY(RE-USY) zeolites described in U.S. Pat. No. 3,293,192 and rare-earth exchanged USX (RE-USX) zeolites. The catalyst particles range in size from 50-150 microns. The degree of rare- earth exchange in the zeolite component is preferably higher than 30 wt% and more preferably higher than 60 wt%. Rare-earth ion exchange is performed by conventional techniques in the instant invention. The zeolites are exchanged with at least one rare-earth cation, such as cations of lanthanum or cerium. Mixtures of rare-earth cations may also be used. The catalyst of this invention must be at least partially dehydrated, preferably by spray- drying. The rare-earth metals may be added by ion-exchange either before or after spray-drying. A calcined catalyst possesses a greater attrition resistance than does fresh catalyst. This further dehydration can be accomplished by heating the catalyst to a temperature in the range of from 200°C to 595°C, in an atmosphere such as air, nitrogen, etc. and at atmospheric, subatmospheric, or superatmospheric pressure for a period of from between about 30 minutes to about 48 hours. The catalyst, of this invention, being of small particle size (50-150 microns) is in the form of a spray-dried powder.

It is desired to incorporate the catalytically active catalyst zeolite with another material, i.e., a binder, which is resistant to the temperatures and other conditions employed in the isoparaffin alkylation process of this invention. Binder materials are usually added to the zeolite in a slurry. The entire catalyst is then spray dried. Suitable binder materials include active and inactive materials such as clays, silica and/or metal oxides such as alumina. These can be either naturally occurring or provided in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Use of a binder material in conjunction with the catalytically active crystalline material, i.e., combined therewith, which itself is catalytically active may change the conversion and/or selectivity of the catalyst. Inactive materials suitably serve as diluents to control the amount of conversion so that products can be obtained economically and in a controlled fashion without having to employ other means for controlling the rate of reaction. These materials can be incorporated into naturally occurring clays, e.g., bentonite and kaolin, to improve the crush strength of the catalyst under commercial operating conditions. Good crush strength is an advantageous attribute for commercial use since it prevents or delays breaking down of the catalyst into fines.

Naturally occurring clays which can be composited with the present catalyst crystals include the montmorillonite and kaolin family, which families include the subbentonites, and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite, or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification. Binders useful for compositing with catalyst crystals also include inorganic oxides, notably alumina.

The alumina binder may undergo a phase transformation during calcination, whereby the water solubility of the alumina is decreased. The hydroxyl content of the alumina may be decreased by calcination. In particular, calcination may transform the pseudoboehmite form of alumina into gamma-alumina. Apart from or in addition to the foregoing binder materials, the present catalyst crystals can be composited with an inorganic oxide matrix such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica- beryllia, silica-titania as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia, silica-magnesia-zirconia, etc.

The relative proportions of finely divided catalyst crystals and inorganic oxide matrix can vary widely with the catalyst crystals content ranging from 1 to 95 percent by weight and more usually, in the range of 2 to 80 weight percent of the composite.

Since the catalyst of the instant invention is employed as small fluidized particles as is that typically used in FCC applications, it is subject to attrition. Catalyst attrition can cause serious losses in any fluidized application, whether it is an FCCU or an alkylation unit. The amount of attrition that occurs over time with a catalyst depends on whether or not the catalyst is fresh or has been treated. It is also dependent upon the severity of the operating conditions employed.

Catalysts that have been calcined have approximately the same attrition resistance as equilibrium catalysts or those that have been steamed. All three have greater attrition resistance than fresh catalyst. The ability to quickly determine the attrition resistance of the catalyst in the unit permits a timely change to a more attrition-resistant catalyst in order to decrease losses, along with eliminating particle emissions, fines in the slurry oil, and wear in power-recovery trains. The preferred method of determining attrition resistance is the jet-cup method, as discussed in the article "Method speeds FCC catalyst attrition resistance determinations," Oil and Gas Journal. April 16, 1990, vol. 88, p. 38. This method eliminates the need for particle size measurement or accurate sampling procedures. Attrition resistance determinations are thus made more quickly. The jet-cup method provides data for an attrition index, WD, which is the gradient (or slope) of a plot of cumulative weight percent catalyst fines v. time in hours. The jet-cup test apparatus confines most of the catalyst sample to a small cup, into which a high velocity air flow is introduced.

The air agitates the catalyst sample, causing attrition of the particles as they collide with the wall of the jet cup.

The attrition index for the jet-cup test is the Davision Index, DI. The index expresses the jet-cup data as:

DI={[(c/m x 100) + H - G]/100 -G} X 100 where: c = weight percent catalyst fines collected m - weight of the initial sample

G= weight of particles less than 20 microns in the sample before the test

H = wt% of particles less than 20 microns left in the sample after the test

A low DI value indicates a good attrition-resistant catalyst. Operating Conditions -

The operating temperature of the alkylation process herein can extend over a fairly broad range, e.g., from 0°C. to 400°C, and is preferably within the range of from 50°C, to 200^QC. The practical upper operating temperature will often be dictated by the need to avoid an undue occurrence of undesirable side reactions. The pressures employed in the present process can extend over a considerably wide range, from atmospheric pressure to 13790 kPa (2000 psig) . The mole ratio of hydrogen to olefin in the feed is controlled to be less than or equal to 0.2:1.0, preferably 0.15:1.0.

The amount of catalyst used in the present alkylation process can be varied over relatively wide limits. In general, the amount of catalyst as measured by the weight hourly space velocity (WHSV) based on olefin can range from 0.01 to 5 hr^"1. It will, of course, be realized by those skilled in the art that the amount of catalyst selected for a particular reaction will be determined by several variables including the reactants involved as well as the nature of the catalyst and the operating conditions employed.

As discussed in the feed section, the mole ratio of total isoparaffin to total olefin alkylating agent in the combined hydrocarbon feed can be from 1:1 to 1000:1 and is preferably in the range of over 500:1 and most preferably over 1000:1.

The alkylation process of the present invention can be carried out as a batch-type, semi-continuous or continuous operation utilizing a fixed bed reactor, moving bed reactor ebullating bed, slurry reactor or fluidized bed reactor. The catalyst after use, is conducted to a regeneration zone where coke is removed, e.g., by burning in an oxygen- containing atmosphere (such as air) at elevated temperature or by extracting with a solvent, after which the regenerated catalyst is recycled to the conversion zone for further contact with the organic reactants. Particular process configurations and variations may be accrued at by substituting the present catalyst for the catalyst as described in U.S. Pat. Nos. 4,992,615; 5,012,033; and 5,073,665. Examples

Alkylation Testing Procedure

All the commercial catalysts used in these examples were evaluated in isobutane/butene-2 alkylation conducted in a slurry reactor using the following procedure: Prior to the testing, catalysts were crushed to <149 (<100 mesh) and pretreated at 400°C for 3 hours in dry air. Each of the catalysts tested is typically used in FCC cracking operations. Then 10-40 grams of catalyst was placed in a 300 cc stainless steel stirred autoclave and the reactor was filled with 200 ml of isobutane. The slurry was stirred at 1900 rpm and heated to 120°C. The pressure was kept at 2965 kPa (430 psig) . After the desired temperature was reached, butene-2 was continuously fed into the reactor at a butene weight hourly space velocity of 0.1 (based on zeolite component) until an external isobutane/butene-2 mole ratio of 21:1 was reached. At the end of the run, the total reactor content (hydrocarbons) was discharged through a 2 micron filter under a N₂ flow into a metal bomb which was kept at -73°C. It was then weathered to ambient temperature and pressure. Liquid and gas products were analyzed gas chromatographically. Each material balance was based on the recovered liquid and gas samples. Example 1 A commercial catalyst (CTX-40, manufactured by W.R. Grace) containing approximately 25% REY and a matrix (binder) is called Catalyst A. 40 grams of Catalyst A was tested in isobutane/butene-2 alkylation using the above procedure. The olefin conversion, C + alkylate yield (g C₅+ produced per g of olefin converted) , and C_b+ alkylate distribution are given in the Table. Example 2

A commercial catalyst, containing 30% REY, 4% rare earth oxide, 0.36% Na and a binder, is called Catalyst B.

33 grams of Catalyst B was tested in isobutane/butene-2 alkylation using the above procedure. The results are listed in the Table.

Example 3

10 grams of Catalyst B was used in the same testing as in Example 2 except that the butene WHSV was increased to 0.33 (based on zeolite) . The results are shown in the

Table.

Example 4

A commercial catalyst, containing 35% RE-USY, 2.5% rare earth oxide, -0.2% Na and a binder, is called Catalyst C. 33 grams of Catalyst C was tested in isobutane/butene-2 alkylation using the above procedure. The results are summarized in the Table.

Conclusion from Examples 1-4

Clearly, all the commercial catalysts tested above showed good olefin conversion and high C₅+ alkylate yield.

The high C+ alkylate yield indicated that all the catalysts are effective for isobutane/butene alkylation.

The high trimethylpentanes (TMP) content in C₈ reflected a high octane quality, due to its branched nature. In addition, RE USY (Catalyst C) was more active than REY

(Catalysts A and B) as evidenced by the higher butene conversion.

Table Isobutane/Butcne-2 Alkylation over Small Particle Catalysts of Low Attrition Index

(120°C,2965 kPa (430 psig) and IO = 21/1)

Claims

1. An isoparaffin-olefin alkylation process which comprises reacting isoparaffin and olefin under alkylation conditions in the presence of a catalyst which comprises a faujasite, wherein at least 30 percent of the active sites of the faujasite have been exchanged with a cation or cations selected from the rare-earth metals to provide an alkylate product.

2. The process of claim 1, wherein the catalyst is employed as particles which range in size from 50 to 150 microns.

3. The process of claim 2, wherein the particles possess an attrition index of no greater than 10.

4. The process of claim 2, wherein the catalyst particles form a spray-dried powder.

5. The process of claim 1, wherein at least 60% of the active sites of the faujasite have been exchanged with a cation or cations selected from the rare-earth metals.

6. The process of claim 3, wherein the catalyst particles have an attrition index of no greater than 5.

7. The process of claim 1, wherein the faujasite is either RE-USY or RE-USX.

8. The process of claim 1, wherein the catalyst comprises no more than 1.0 wt% sodium.

9. The process of claim 1, wherein the catalyst further comprises a binder.