Process for alkylation of aromatic compounds using a catalyst

Abstract: Catalyst for the alkylation of aromatic compounds consisting of a zeolite Y modified by treatment with a phosphorous compound.

Description: The present invention relates to an improved procedure for the alkylation of aromatic compounds with C₂-C₅ olefins, a procedure which uses a catalyst obtained by impregnating a zeolite Y with a solution of a phosphorus compound. At present most processes for the production of cumene use a catalytic system composed of phosphoric acid on infusorial earth or kieselguhr catalysts of the same type - suitably modified - are used in the production of oligomers of propylene. The main advantages of this catalytic system lie in the low production costs and high selectivity towards cumene; on the other hand the acidity and impossibility of regeneration cause problems of corrosion in the plants and - above all - for disposal of the exhausted catalyst. Another catalytic system composed of aluminium trichloride and hydrochloric acid in slurry is at present used on an industrial scale, but also this has problems relating to the high corrosivity of the system and difficulties in separating this from the reaction mixture. To overcome the above draw-backs different kinds of processes have been proposed, using as a heterogeneous catalyst, a zeolite, possibly modified following suitable treatment and/or by the addition of rare earth. U.S. Patents 4393262, 3755483 and 4291185 describe the use of a zeolite of the HZSM 12 type in the synthesis of cumene. U.S. Patent 3251897 describes the alkylation of aromatic hydrocarbons in the presence of zeolites of the Y and X types and specifically of zeolites wherein the cations are rare earth and/or hydrogen. U.S. Patent 3631120 describes an alkylation process of benzene with zeolites with a ratio Si/Al of 4.0 to 4.9 in acid form. These systems are characterized by their regenerability by means of thermal treatment, by operating in a heterogeneous phase and by being easily processed and transportable. Among all known systems for the alkylation reaction of benzene to cumene, which generally differ by their different activities and selectivity, the most promising from an industrial point of view is undoubtedly the system based on the type-Y zeolite. This catalytic system is characterized by a good activity - it can in fact operate at temperatures ranging from 150 to 180°C - and good selectivity towards cumene. The possibility of operating at low temperatures is a very important factor for this type of reaction, because, in these catalysts, one of the causes of deactivation is the polymerization of the olefin and subsequent cyclization forming aromatics with large dimensions which cannot migrate out of the microporous structure present in the zeolite crystal (Venuto et Al., J. Catalysis 5, 384-493, 1966; IEC 190-192, Sept. 1967). In addition there is also the effect of the formation of carbon due to dehydrogenating cracking reactions also favoured at higher temperatures. With respect to the type-Y zeolite, this, however, is characterized by a sensitive reduction in the selectivity along with the increase in the conversion of the benzene. The advantage of a selectivity which remains high, even at high conversions of benzene, lies in the possiblity of operating even with low feeding molar ratios Benzene/Olefin and consequently reducing some of the costs related to recycling the converted benzene. Zeolite Y, on the other hand, is able to convert polyalkylated products into cumene owing to its acid properties which cause the transalkylation reaction; to do this it is preferable to use a second reactor where a mixture of polyalkylates (mainly diisopropylbenzene, in the synthesis of cumene) and benzene are fed under specific conditions. This naturally leads to higher investment and plant management costs connected not only to the cost of the second reactor but also to the necessary separation of the polyalkylates from the heavier products. It is not possible to recycle the polyalkyates in the same reactor where the alkylation is carried out because the transalkylation reaction generally takes place under different conditions than those present in the primary reactor (higher temperatures). Attempts have been made to improve the performance of zeolite Y by an exchange with rare earth (U.S. Patent 32518971) or by means of deposition treatment of carbon which produces a 1% increase in the selectivity to cumene (U.S. Patent 4.798.816). These, however, have not succeeded in completely eliminating the above draw-backs. It is known that zeolites of the ZSM 5 type can be treated with phosphorus compounds (U.S. Patent 4.128.592) to obtain modified catalytic forms with an improved selectivity; e.g. in alkylation reactions of toluene with ethylene, this improvement can be seen by a high increase of the selectivity to the paraposition (Journal of Catalysis 89, 267-273, 1984 ). Furthermore, EP-A-0 252 761 discloses a cracking catalyst which comprises a phosphorus-treated ultrastable Y-type crystalline zeolite and a non-zeolitic inorganic oxide matrix. US-A-4,970,183 discloses a hydrocarbon oil catalytic cracking catalyst composition comprising a particulate mixture of 95 to 50 % by weight of a non-phosphorus containing matrix and 5 to 50 % by weight of a Y-faujasite containing phosphorus. EP-A-0 397 183 relates to catalytically active zeolites and specifically to phosphorus/zeolite Y compositions, active for the conversion of hydrocarbons. FR-A-2 285 176 discloses the use of small pore ZSM zeolites impregnated with P for alkylation among a variety of other reactions. These documents, however, do not completely eliminate the prior art drawbacks. The Applicant has now found that using a catalyst obtained by treating type-Y zeolites with phosphorus compounds, a considerable improvement in the selectivity in the formation of desired alkylated products starting from aromatic substrates (particularly in the preparation of cumene starting from benzene) is produced, and this selectivity is barely or not at all influenced by an increase in the conversion of the aromatic substrate. Moreover the use of these catalytic forms leads to a reduced formation of polyalkylated products with a consequent decrease in the relative costs of their treatment, as previously specified. The present invention consequently relates to an improved process for the alkylation, with C₂-C₅ olefins, of aromatic compounds, carried out in the presence of a catalyst composed of a type-Y zeolite impregnated with a solution of a phosphorus compound. The catalyst is obtained, by impregnation of the particular zeolite with a solution, which may or may not be aqueous, of a phosphorus compound and subsequent drying/calcination of the material thus obtained. The final catalyst obtained is particularly active in alkylation reactions of benzene with C₂-C₅ olefins and, particularly, in the alkylation of benzene with propylene. Y zeolites suitable for the purpose are normally available on the market or synthesized using the known methods. Before treatment, the zeolite, which may or may not be in acid form, can be calcinated in the presence of water vapour for a period of 1 to 24 hours at a temperature ranging from 400 to 700°C. The impregnation treatment is carried out by putting the zeolite in contact with solutions, which may or may not be aqueous, containing phosphorus compounds and subjecting the material thus obtained to conventional drying and/or calcination. The final quantity of phosphorus present on the catalyst will range from 0.1% to 25% by weight, and preferably from 0.1% to 8% by weight of phosphorus. Different phosphorus compounds may be used for the impregnation treatment. Suitable compounds may therefore be represented by derivatives containing one or more of the following groups: PX₃, RPX₂, R₂PX, R₃P, X₃PO, (XO)₃PO, (XO)₃P, R₃P=O, R₃P=S, RPO₂, PPS₂, RP(O)(OX)₂, RP(SX)₂, ROP(OX)₂, RSP(SX)₂, (RS)₂PSP(SR₂), (RO)₂POP(OR)₂, (RO)₂POP(OR)₂ wherein R is C₁-C₁₀ alkyl or C₆-C₃₀ aryl, and X is hydrogen, ammonium R or a halogen such as chlorine, bromine, fluorine and iodine. These compounds also include RPH₂ primary phosphines, R₂PH secondary, and R₃P tertiary phosphines; R₃PS tertiary phosphinic sulphides; RP(O)(OX)₂ primary and R₂P(O)OX secondary phosphinic acids; the corresponding sulphurate derivatives such as RP(S)(SX)₂ and R₂P(S)SX; the esters of phosphonic acids such as (RO)₂P(O)H, (RO)₂P(O)R, (RO)P(O)R₂; R₂POX phosphinous acids; their phosphite and ester derivatives. The corresponding derivatives containing sulphur may also be used, such as, for example, (RS)₂P(S)H, (RS)₂P(S)R, (RS)P(S)R₂, R₂PSX, (RS)P(SX)₂, (RS)₂PSX, (RS)₃P, (RA)(PR₂) and(RS)₂PR. Among the above compounds those of phosphoric acid, polyphosphoric acid, mixtures of polyphosphoric acids, acid and non-acid ammonium phosphates, primary, secondary and tertiary phosphines, are particulary preferred. The treatment which produces the modified zeolite, i.e. impregnation and reaction of the Y zeolite with the solution of the phosphorus compound, can be carried out on the zeolite in powder form, whether in acid form or in the form of ammonium salt. When the treatment is carried out on zeolite in powder, before being used in the reaction, the treated zeolite should be mixed with suitable binders; for this purpose silicon, aluminium, zirconium, magnesium oxides or natural clay oxides can be used or combinations of the above. After mixing, a paste is obtained which is fed to an extruder or other machines for the desired moulding. The products of the moulding operations are then calcined at a temperature ranging from 300 to 700°C. If the treatment is carried out on zeolitic catalysts which have already been formed, the treated zeolite is subjected to thermal treatment at temperatures ranging from 150 to 700°C; preferably from 400 to 700°C. The alkylation reaction may be carried out in continuous, semi-continuous or batch-wise, but preferably in continuous. The reaction is carried out at a temperature ranging from 100 to 300°C, preferably from 110 to 200°C, at a pressure of 1.013 to 5.065 MPa (10 to 50 atms), preferably from 3.039 to 4.052 MPa (30 to 40 atms) and with a feeding rate aromatic + olefin of 0.2 to 200 h⁻¹ but preferably from 0.5 to 10 h⁻¹; the alkylation reaction is preferably carried out in a flow reactor. The reaction may be carried out in a gaseous phase, liquid phase and mixed phase; it is preferably however to operate in a liquid phase, in that this makes it possible to minimize the formation of tars and carbon by-products and lengthen the catalyst life by the washing action which the presence of the liquid phase guarantees with respect to a gaseous phase. The feeding molar ratio between aromatic compound and olefin can vary from 2/1 to 30/1, it is preferable to operate within a range of 4/1 to 10/1. Within this range of molar ratios the polyalkylation reaction and polymerization of the olefin are minimized allowing a greater duration period between two subsequent regenerations of the catalyst. The above catalyst is also active in transalkylation processes of polyalkylates carried out in the presence of benzene and above all in the transalkylation of diisopropylbenzene (DIPB) which are by-products of the alkylation of benzene with propylene. The regeneration of the catalyst can be carried out by thermal treatment with gases containing oxygen (such as air) with a suitable temperature profile and maximum temperature of 500 to 700°C to burn the carbon residues deposited inside the zeolitic structure of the catalyst, without damaging the structure itself. EXAMPLE 1 Y zeolite extrudates are used in acid form and having the following characteristics: SiO₂/Al₂O₃: 5.9 Molar (in the zeolitic structure) BINDER: clay; content: 25% of the zeolite powder PELLET DIAMETER: 1.5 mm 10 g of the above zeolite are put in contact with 50 ml of an aqueous solution containing 0.37 g of H₃PO₄ (0.1 g as P). The system is left to rest for 5 hours with occasional stirring and the water is subsequently slowly evaporated to dryness. The solid is thermally treated at 150°C for 2 h and subsequently at 500°C for a further 2 h. The product obtained contains a phosphorus percentage, equal to 1% by weight (calculated as P). X-ray analysis showed that the zeolite structure had not been modified. 4.65 g of the catalyst thus prepared are put in a cylindrical reactor having a length of 15 cm and diameter of 1.5 cm diluted with at least 1 volume of quartz chips having a low surface area. A thermowell is placed along the main axis of the reactor with a thermocouple which slides along said axis to measure the temperature in the catalytic bed. A mixture of benzene and propylene prepared by directly weighing the single compounds to obtain the required molar ratio benzene/propylene, is fed to the reactor. The mixture is kept in a pressure tank at 2.026 MPa (20 atms) and sent to the reactor by means of a volumetric pump. The reactor is situated inside a thermostat-regulated chamber at the test temperature which shows a maximum ΔT of 0.1°C; the maximum ΔT existing along the main axis of the reactor during each test is 1°C. A valve is situated at the outlet of the reactor to keep the pressure at the indicated test value and is followed by a condenser where the reaction products are collected while the uncondensable products are measured with a volume meter and continuously analyzed. In Table I below the tests at different benzene conversions obtained by variation of the contact time within the indicated range of WHSV. As can be seen, the Table shows the conversion values of benzene and propylene and the selectivity to cumene (CUM), to diisopropylbenzenes (DIPB) with the distribution of isomers and to triisopropylbenzenes (TIPB). When the catalyst used in the tests is discharged, after 120 hours of reaction, the percentage of phosphorus present is equal to 1%. EXAMPLE 2 (comparative) Zeolite Y without modification was used in the same experimental apparatus as Example 1 and exactly under the same conditions. The aim is to compare the results with those obtained in Example 1, approximately within the same conversion range of benzene where the influence of the transalkylation reactions of benzene to the final selectivity value to cumene is reduced to the minimum. The drop in selectivity to cumene between tests 1 and 4 in Table 2 is about double compared to the data shown in Table 1 and all the selectivity values to cumene can be found 1.5 points below the selectivity values shown in Table 1 in the same conversion range. The TIPB and DIPB fractions are higher with respect to the values of Example 1 which confirms that in this reaction the selectivity to cumene is mainly influenced by these compounds. EXAMPLE 3 The experimental apparatus and catalyst are the same as those used in Example 1 as are all the reaction conditions except for the temperature which was modified as shown in Table 3. At a temperature of 170°C the selectivity value to cumene was definitely influenced by the transalkylation reactions and in fact the values shown in Table 3, in the same conversion range of benzene, are higher than those of Examples 1 and 2. The selectivity values to cumene are quite constant within the whole conversion range up to the maximum conversion value of propylene. The distribution of the DIPB isomers is basically similar to that of Examples 1 and 2 and near the equilibrium value. EXAMPLE 4 (comparative) The Y zeolite without modification was tested under the same conditions as used in Example 3 and the values found are shown in Table 4. The selectivity to cumene is at least 1 point % lower than the data of Example 3 due, as can be seen, to the formation of 20% more of DIPB and a double quantity of TIPB. Also in this series of tests at T=170°C the distribution of DIPB isomers is more or less similar to the data of the previous examples and consequently the treatment carried out on the catalyst in Example 3 evidently does not induce p-selectivity in this reaction. EXAMPLE 5 10 g of the zeolite having the characteristics of Example 1 are put in contact with 50 ml of an aqueous solution containing NH₄H₂PO₄ in quantities of 0.3 total grams expressed as phosphorus. The system is then treated as described in Example 1. The catalyst thus obtained contains 3% of P and on XRD analysis showed no modification in the zeolitic structure. It gave a selectivity to cumene of 88.5% at a 9.6% conversion of benzene, under the same conditions as Example 1. Under the same conditions as Example 3 the selectivity to cumene was 93.1% at an 11.9% conversion of benzene. EXAMPLE 6 Using the same zeolite as Example 1 a preparation is carried out as described in Example 1 but after drying the system, the solid thus obtained is thermally treated at 200°C for 2h. Analysis showed the same characteristics of the material obtained with the procedure indicated in Example 1. The catalyst thus obtained was tested under the same conditions as Example 1 showing a selectivity to cumene of 88.5% at a 9.7% conversion of benzene. The same material under the conditions of Example 3 gave a selectivity to cumene of 92.5% at an 11.5% conversion in benzene. EXAMPLE 7 A Y zeolite is used in ammonium form in powder having the following characteristics: Si₂O₃/Al₂O₃ = 5.9 10 g of this zeolite are put in contact with 50 ml of an agueous solution containing 0.74 g of 85% H₃PO₄ (0.2 g as P). The system is kept under mechanical stirring at room temperature for 10h. The excess water is subsequently evaporated slowly. The solid thus obtained is thermally treated at 150°C for 2 h and subsequently at 550°C for a further 4h. The product obtained contains 2% by weight of phosphorus. X-ray analysis shoved that the zeolitic structure had not undergone modification. The material thus obtained is charged in an 0.5 l autoclave in a quantity of 2 g and with a quantity of benzene equal to 200 ml (200 cc). The quantity of propylene necessary to have the molar ratio indicated in Table 5 is subsequently charged. The tests with different conversions of benzene are carried out keeping the system under reaction conditions for different times. As can be seen from the results of tests 1, 2 and 3 even with very low molar ratios of benzene and propylene, the selectivity to cumene maintains good values. In the group of tests with higher feeding ratios (C6/C3 = 7.6) the effect of the transalkylation reaction on an increase in the conversion in benzene is evident; the data at higher conversion can be compared to the values obtained in Example 3.

Claims: Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins consisting in carrying out the reaction in the presence of a catalyst, characterized in that the catalyst is a type-Y zeolite impregnated with a solution of a phosphorus compound, obtainable by impregnation of a Y-zeolite with a solution of a phosphorus compound and subsequent drying and/or calcination of the so obtained product, said catalyst containing from 0.1 to 25 % by weight of phosphorus. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to claim 1, characterized in that the reaction is carried out at a temperature ranging of from 100°C to 300°C. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to claim 2 characterized in that the reaction is carried out at a temperature ranging from 110 to 200°C. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to any of the Claims, characterized in that the reaction is carried out at a pressure of 1.013 to 5.065 MPa (10 to 50 atms.) Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to Claim 4 characterized in that the reaction is carried out at a pressure of 3.039 to 4.052 MPa (30 to 40 ats.) Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to any of the previous Claims, characterized in that the reaction is carried out at a feeding rate WHSV aromatic + olefin of 0.2 to 200 h⁻¹. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to Claim 6 characterized in that the reaction is carried out at a feeding rate aromatic + olefin WHSV of 0.5 to 10 h⁻¹. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to any of the previous Claims, characterized in that the feeding molar ratio between aromatic compound and olefins varies from 2/1 to 30/1. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to Claim 8, characterized in that the feeding molar ratio between aromatic compound and olefins ranges from 4/1 to 10/1. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins according to any of the previous Claims, characterized in that the aromatic compound is benzene and the olefin is propylene. Procedure for the alkylation of aromatic compounds with C₂-C₅ olefins, according to any of the previous Claims, characterized in that it is carried out in a flow reactor.

Inventors: ARRIGONI VIRGINIO, CAVANI FABRIZIO, GIROTTI GIANNI, TERZONI GIUSEPPE, ARRIGONI, VIRGINIO, CAVANI, FABRIZIO, GIROTTI, GIANNI, TERZONI, GIUSEPPE
Applicants: MINI RICERCA SCIENT TECNOLOG, MINISTERO DELL' UNIVERSITA' E DELLA RICERCA SCIENTIFICA E TECNOLOGICA
Application year: 1992
Main classification: B01J29
IPC codes: B01J29, C07C2, C07C6