Alkylation process

Abstract: Improved process for the supported liquid phase alkylation of an aliphatic hydrocarbon feedstock in the presence of a fluorinated sulphonic acid catalyst with an olefinic alkylating agent in a reactor containing a fixed bed of particular polar contact material, wherein a reaction zone with the fluorinated sulphonic acid catalyst is moveable established by absorbing the acid catalyst within a confined area of the contact material and passing a process stream of the aliphatic hydrocarbon feedstock and the olefinic alkylating agent through the reactor and the reaction zone, and withdrawing an alkylated product stream from the reactor, wherein the improvement comprises introduction of the fluorinated sulphonic acid alkylation catalyst into the reactor dissolved in a hydrocarbon solvent comprises C₃-C₉ hydrocarbons and adsorption of the acid catalyst in the solution of the hydrocarbon solvent on the contact material at inlet end of the reactor.

Description: The present invention relates to improvements in the supported liquid phase alkylation of aliphatic hydrocarbons in the presence of a fluorinated sulphonic acid catalyst. Acid catalyzed alkylation of aliphatic hydrocarbons with olefinic hydrocarbons is a well known process for the preparation of high octane gasoline products. In the past, alkylation of hydrocarbons has been accomplished in liquid phase by mixing paraffins and olefins in the presence of a strong acid catalyst and stirring the mixture until the alkylation reaction was completed. Presently, the acid catalysts usually employed in the industrial alkylation of aliphatic hydrocarbons are concentrated sulphuric acid or anhydrous hydrofluoric acid, which strength may be increased by addition of a Lewis acid, such as BF 3 or SbF 5 . Further alkylation catalysts are fluorinated sulphonic acids, as disclosed in U.S. Patent Nos. 5,220,095 and 5,245,100. In the process of US Patent Nos. 5,220,095 and 5,245,100 utilizing fluorinated sulphonic acid alkylation catalysts, a reaction zone is established on solid contact material having the fluorinated sulphonic acid catalyst adsorbed within a confined area of the contact material. In the reaction zone, the process stream is converted under alkylating conditions to a product stream of alkylated hydrocarbons by catalysis of the fluorinated sulphonic acid adsorbed on the contact material. During the alkylation reaction, the reaction zone moves continuously from the inlet towards the outlet end of the alkylation reactor by interaction with the process stream flowing through and reacting in the zone. In the process of U.S. Patent No. 5,245,100, the acid catalyst being adsorbed on the contact material passes by interaction with the process stream sequentially through a first and second reactor. The catalyst is recycled to the first reactor after having passed through leaves the second reactor. In an industrial alkylation reactor being operated under the above conditions, the cross sectional diameter of the reaction zone will typically be larger than the length of the reaction zone. It is, therefore, necessary to introduce the acid catalyst consistently on the top of the contact material, during transference of the catalyst between the reactor in order to prevent maldistribution, when the reaction zone passes through the reactor as mentioned above. Maldistribution on top of the reactor will result in distortion of the reaction zone during passage of the process stream through the reactor and movement of the reaction zone. It has now been observed that distribution of the catalyst on top of an alkylation reaction can be improved, when introducing the catalyst dissolved homogeneously in a solvent. It has futher been observed that fluorinated sulphonic acid catalysts are soluble in a solvent of C 3 -C 9 hydrocarbons. Based on the above observations, the invention provides an improved process for supported liquid phase alkylation of an aliphatic hydrocarbon feedstock in the presence of a fluorinated sulphonic acid catalyst with an olefinic alkylating agent in at least two reactors containing a fixed bed of a particulate polar contact material, wherein a reaction zone with the fluorinated sulphonic acid catalyst is moveable established by adsorbing the acid catalyst within a confined area of the contact material and passing a process stream of the aliphatic hydrocarbon feedstock and the olefinic alkylating agent through the reactor and the reaction zone, and withdrawing an alkylated product stream from the reactor, wherein the improvement comprises steps of mixing and dissolving the fluorinated sulphonic acid alkylation catalyst in a hydrocarbon the solvent comprising C 3 -C 9 hydrocarbons; and introducing the fluorinated sulphonic acid alkylation catalyst into the subsequent reactor dissolved in the hydrocarbon solvent and adsorbing the acid catalyst in the solution of the hydrocarbon solvent on the contact material at inlet end of the reactor. Preferred solvents for obtaining a homogeneous acid catalyst solution comprise C 3 -C 5 hydrocarbons. The above process is useful in an alkylation process being performed in at least two reactors connected in series. Thereby, the acid catalyst leaving a first reactor is introduced on top of a subsequent reactor as previously described in U.S. Patent No. 5,245,100, which by reference is incorporated herein. When performing the alkylation process in two or more reactors, a mixing unit between the outlet of the first reactor and the inlet of a subsequent reactor is arranged. In the unit, the acid catalyst is mixed and dissolved with the hydrocarbon solvent. The solvent is, preferably, a process stream leaving the first reactor, in order to prevent transfer of a separate acid phase to the inlet of the second reactor. The above features and advantages of the invention will further be illustrated in the following Examples by reference to the drawings, in which the sole Figure shows a reactor system with two alkylation reactors connected via a mixing unit. Example 1 The reaction system used in this and the following Examples is shown in the Figure. Alkylation of paraffins with olefins was carried out by passing a feed stream of 5% by weight 2-butene in isobutane at a mass flux of 1000 g/cm 2 · h and at a temperature of 0-80°C through a first alkylation reactor (4) and an effluent stream leaving the first reactor to a mixing unit (8) being connected to the outlet end of the first reactor. Reactor (4) and (10) had a total length of 6 m, each with a diameter (i.d.) of 1/4". The volume of mixing unit (8) was 40 ml. The reactors were loaded with each 100 ml of silica (Merck 100) contact material. At the inlet of reactor (4), 6 ml of trifluoromethanesulphonic acid alkylation catalyst were applied on the contact material at the beginning of the process. After passage through the mixing unit (8), the effluent stream was introduced into the second reactor (10), from which a product stream of alkylated product (12) was withdrawn and analyzed. Comparison Example A A feed stream as specified in Example 1 was treated by a process similar to that of Example 1, except that the effluent stream leaving the first reactor was directly passed to the second reactor without passage through the mixing unit. Further process conditions and results obtained by the above Example 1 and Comparison Example A are summarized in the following Table 1 and Table 2, respectively. Example 2 A feed stream of 7.5% by weight propene in isobutane was passed through the reaction system as described in Example 1 at a mass flux of 1000 g/cm 2 · h and a temperature between 0-40°C. Comparison Example B The feed stream of Example 2 was passed through a reaction system as described above, except that the effluent stream from the first reactor was directly passed to the second reactor without passage through the mixing unit. The process conditions and results obtained by Example 2 and Comparison Example B are summarized in the following Table 3 and Table 4, respectively. Temp. 0 10 20 30 40 60 80 C5 3.52 3.14 3.49 3.91 8.04 9.00 21.30 C6 2.04 2.19 2.55 2.95 5.50 8.59 11.50 C7 2.76 3.16 3.93 4.74 7.46 10.67 10.40 C8 83.85 83.31 79.95 74.51 65.94 57.87 43.49 C9 2.15 2.12 2.79 3.82 5.19 6.95 6.76 C10+ 5.68 6.08 7.29 10.08 7.88 6.92 6.55 RON (Calc.) 98 97 95 93 90 86 87 MON (Calc.) 94 94 92 90 88 85 85 Temp. 0 10 20 25 30 C6 1.830 1.476 3.311 4.151 4.673 C7 2.378 2.375 4.602 5.608 6.240 C8 90.085 89.126 82.049 79.690 77.349 C9 1.487 1.733 2.734 3.436 3.712 C10+ 4.221 5.291 7.304 7.115 8.025 RON (Calc.) 98 98 95 94 93 MON (Calc.) 95 95 93 91 91 Temp. 0 10 20 30 40 C6 4.456 3.624 10.624 5.060 6.440 C7 25.736 30.790 37.117 37.453 38.236 C8 47.056 43.197 36.535 40.417 39.103 C9 10.313 10.379 8.261 9.007 8.764 C10+ 12.384 11.959 7.411 8.019 7.398 RON (Cal.) 90 90 88 88 87 MON (Cal.) 89 88 86 86 85 Temp. 0 10 20 25 C6 7.261 8.411 8.807 9.702 C7 27.552 32.294 35.829 37.490 C8 40.769 40.609 38.543 38.658 C9 10.791 9.079 7.939 7.109 C10+ 13.611 9.578 8.843 6.993 RON (Calc.) 90 91 90 89 MON (Calc.) 88 88 88 87 Example 3 A feed stream of 20% (w/w) propylene and 80% (w/w) isobutane was reacted by a process and in a reaction system as described in Example 1 above. Prior to introduction into the first reactor, the feed stream was diluted with part of the product stream being withdrawn from the second reactor and recycled from the outlet of the reactor to the inlet of the first reactor. The olefin concentration at inlet of the first reactor was, thereby, adjusted to 2,0% (w/w) at a total hydrocarbon mass flux through the reaction system of 4200 g/cm 2 h. At the above process conditions, pressure drop in the reactors was between 10 and 12 bar. The composition of the product stream was as follows: C 5 19.8% (w/w) C 6 11.3% (w/w) C 5 24.2% (w/w) C 5 19.5% (w/w) C 5 11.7% (w/w) RON (estimated) 87 MON (estimated) 87 Comparison Example C In a process and reaction system as described above in Example 3, isobutane was alkylated with propylene except that the system was not provided with a mixing unit between the reactors. The effluent from the first reactor was directly passed to the second reactor. As a result, the pressure drop in the reactors increased to 27-34 bar. The composition of the product stream obtained in this Example was similar to that of Example 3. As apparent from the above Examples and results, dissolution of the acid alkylation catalyst prior to introduction into the alkylation reactor results in a much decreased pressure drop. At the same time, product composition of alkylated product obtained in the inventive process is substantially unchanged when compared to a process without dissolution of the alkylation catalyst prior to introduction into the reaction system.

Claims: Process for the supported liquid phase alkylation of an aliphatic hydrocarbon feedstock in the presence of a fluorinated sulphonic acid catalyst with an olefinic alkylating agent in at least two reactors containing a fixed bed of particulate polar contact material, wherein a reaction zone with the fluorinated sulphonic acid catalyst is moveably established by adsorbing the acid catalyst within a confined area of the contact material and passing a process stream of the aliphatic hydrocarbon feedstock and the olefinic alkylating agent through the reactor and the reaction zone, and withdrawing an alkylated product stream from the reactors comprising the steps of: mixing and dissolving the fluorinated sulphonic acid alkylation catalyst in a hydrocarbon solvent between outlet of the first reactor and inlet of a subsequent reactor, the solvent comprising C 3 -C 9 hydrocarbons; and introducing the fluorinated sulphonic acid alkylation catalyst into the subsequent reactor dissolved in the hydrocarbon solvent and adsorbing the acid catalyst in the solution of the hydrocarbon solvent on the contact material at inlet end of the reactor. The process of claim 1, wherein the hydrocarbon solvent comprises C 3 -C 5 hydrocarbons. The process of claim 1, wherein the hydrocarbon solvent is a process stream being withdrawn from the reactor. The process according to anyone of the preceding claims, wherein the acid catalyst is withdrawn from a first alkylation reactor and introduced into a second reactor dissolved in at least a part of the process stream from the first reactor.

Inventors: HOMMELTOFT SVEN IVAR, HOMMELTOFT, SVEN IVAR
Applicants: TOPSOE HALDOR AS, HALDOR TOPSOE A/S
Application year: 1995
Main classification: C07C2
IPC codes: C07C2, C07C9, C07B61, B01J31