Process for the preparation of mono alkyl aromatic compounds

Abstract: Process for the mono alkylation of a hydrocarbon substrate containing aromatic hydrocarbon compounds comprising contacting the aromatic substrate with an alkylating agent consisting of a mixture of olefinic compounds and polyalkylated aromatic compounds in presence of a fluorinated sulphonic acid.

Description: The present invention relates to a process for the preparation of mono alkyl aromatic compounds. Benzene and other aromatic hydrocarbons are readily alkylated with olefins using a catalyst comprising a fluorinated sulphonic acid being supported on polar porous contact material. US patent No. 5,959,169 discloses a process to remove aromatic hydrocarbons from a hydrocarbon mixture by selective alkylation of the noxious unsubstituted aromatic compounds with an olefinic alkylating agent in the presence of a catalyst consisting of a fluorinated alkyl sulphonic acid on a silica containing support material. An alkylation process for production of iso-propyl benzene, cumene, from benzene is disclosed in patent No. AU-B - 491,575, where the feed is alkylated with propylene and n-butene in the presence of a liquid catalyst. This catalyst is a complex of AlCl 3 , HCl, benzene and di-isopropyl benzene or di-sec-butyl benzene. The spent catalyst is discarded. The product is this single component, cumene. Another process for cumene production is described in the patent applications EP- A - 537 389 and EP-A-538 518. The feed is benzene, which is alkylated with propylene or propylalcohol over a catalyst. This is disclosed in the two applications as a Zeolite EU-1 catalyst and a Zeolite Beta catalyst, respectively. The formed by-products, propylene and di-isopropyl benzene, are separated from the process stream and recirculated to the process, where di-isopropyl benzene undergoes trans-alkylation with benzene to form isopropyl benzene, while the product, cumene, must be separated from the rest of the process stream. A catalyst for transformation of hydrocarbons is disclosed in US patent Nos. 4,613,723 and 4,547,474. The transformation can be isomerisation of C 4 - C 30 , such as straight chain paraffins, branched chain paraffins, cyclo-paraffins, naphthenes or alkyl aromatic compounds. The catalyst is a C 4 - C 18 perfluorinated alkanesulphonic acid having bond to Lewis acid metal fluoride, where the metal can be selected from the metals in the group II to VI, preferably antimony, tantalum or niobium. The catalyst is supported by fluorinated alumina or silica and the difficult preparation of the catalyst is further described in US patent No. 4,547,474. In a mono-alkylation process in a mixed stream of hydrocarbons containing aromatic compounds it is desirable to achieve high conversion with maximum selectivity to mono alkylated products. However, the alkylation reaction produces not only the desired mono alkylated product, but also products in which two or more alkyl groups are introduced. This problem is particularly important under conditions with high conversion of the aromatic feedstock. It has been observed that fluorinated sulphonic acids including trifluoromethanesulphonic acid supported on a polar porous support material are capable of catalysing trans-alkylation reactions in which the poly-alkylated aromatic by-products are reacted with non-alkylated aromatic compounds to produce mono-alkylated aromatic compounds. In accordance with the above finding, this invention is a process for the mono-alkylation of aromatic hydrocarbon compounds in a hydrocarbon substrate comprising contacting the hydrocarbon substrate with an alkylating agent consisting of a mixture of olefinic compounds and poly-alkylated aromatic compounds in presence of a catalyst consisting of trifluoromethanesulphonic acid as the catalytic active material supported on a polar support material. The process according to the invention is in particular useful in the removal of benzene from reformat gasoline. With the tightening specifications on benzene content of gasoline it is desirable to convert benzene to less noxious alkyl derivatives such as ethyl or isopropyl benzene. These compounds have high octane numbers and alkylation of benzene to these compounds increases the octane value of the product. Poly-alkylated benzenes being employed in the inventive process as alkylating agent such as tri-isopropyl benzene or triethyl benzene boil at temperatures being outside the range of compounds to be desirable to include into gasoline. In the following examples the invention will be disclosed in more detail. EXAMPLES Comparison Example 1 A stream of C6 distillate cut from reformat containing 30% benzene was alkylated with an alkylating agent consisting of solely propene. The alkylation reaction was carried out in a 100 ml reactor filled with silica gel on loaded with 10 g of trifluoromethanesulphonic acid catalyst. The reactor was submerged in a bath for temperature control. The reaction was performed at 80°C with total feed flow of 2.5 g/min. using various molar olefin/benzene ratios. The results are shown in Table 1. The results indicate high conversion rate of benzene with a low selectivity to isopropyl benzene, when using propen as the sole alkylating agent in the reaction. Alkylation of benzene with propene at 80°C Propene/benzene molar ratio 1:1 2:1 3:1 Benzene conversion, % 52 72 92 Composition of aromatics in product: Benzene, %wt 33 15 3 Isopropyl benzene, %wt 25 15 4 Di- and poly-isopropyl benzenes, %wt 42 70 93 Example 2 Alkylation of benzene in presence of poly-alkylated benzene and propen alkylating agent according to a specific embodiment of the invention. The same reactor as above was used but in this Example 20 g trifluoromethanesulphonic acid supported on silica gel was used as catalyst. A feed containing the same C6 cut of reformat as disclosed above but mixed with di- or tri-isopropyl benzene and propene was reacted at the below summarized conditions. The results are shown in Table 2. Alkylation of benzene with propene and di- and tri-isopropyl benzene Temperature, °C 80 110 80 110 Propene/benzene molar ratio 1:2 1:2 1:2 1:2 Benzene conversion, % 35 44 39 41 Feed Propene, %wt 5.2 3.6 4.6 4.6 Benzene, %wt 23 23 22 22 Isopropyl benzene, %wt 0 0 0 0 Di-isopropyl benzene, %wt 0 0 21 21 Tri-isopropyl benzene, %wt 17 21 0 0 Residual hydrocarbons balance balance balance balance Product Propene, %wt 0 0 0 0 Benzene, %wt 15 13 14 13 Isopropyl benzene, %wt 7 9 8 11 Di-isopropyl benzene, %wt 6 11 19 18 Tri-isopropyl benzene, %wt 15 12 6 4 Residual hydrocarbons balance balance balance balance As apparent from the above results, there is a significant conversion of the poly-alkylated benzene in the feed and an increased productivity of isopropyl benzene. Poly-alkylated aromatic compounds can be recycled to the reactor to react with benzene in a trans-alkylation reaction to form the desired mono alkylbenzene product.

Claims: Process for the mono-alkylation of aromatic hydrocarbon compounds in a hydrocarbon substrate comprising contacting the hydrocarbon substrate with an alkylating agent consisting of a mixture of olefinic compounds and poly-alkylated aromatic compounds in presence of a catalyst consisting of trifluoromethanesulphonic acid as the catalytic active material supported on a polar support material. Processes according to claim 1, wherein the hydrocarbon substrate is reformat gasoline. Process according to claim 1, wherein the polyalkylated aromatic compounds comprise tri-isopropyl benzene and/or triethyl benzene.

Inventors: HOMMELTOFT SVEN IVAR, LAURENTS KARSTEN, HOMMELTOFT, SVEN IVAR, LAURENTS, KARSTEN
Applicants: TOPSOE HALDOR AS, HALDOR TOPSOE A/S
Application year: 2001
Main classification: C07C2
IPC codes: C07B61, C07C15, C10G29, C07C2, C10G35