Propene, supercritical, alkylation

A continuous procedure for the alkylation of mesitylene and anisole with supercritical propene, or propan-2-ol in supercritical carbon dioxide, with a heterogeneous polysiloxane-supported solid acid Deloxan catalyst has been reported giving 100% selectivity for monoalkylation of mesitylene with 50% conversion at 250 °C and 150 bar by propan-2-ol in supercritical carbon dioxide. p-Toluenesulfonic acid monohydrate has been demonstrated as an efficient catalyst for the clean alkylation of aromatics using activated alkyl halides, alkenes or tosylates under mild conditions. Cyclohexene, for example, reacts with toluene to give 100% cyclohexyltoluenes (o m p-29 18 53) under these circumstances. 

Fig. 4.8-10 compares the durability results of the 2-methyl-propene and 2-methyl-propane reaction in the gas phase, liquid phase and supercritical phase. Very high initial activity, with yields of alkylate (2,2,4,-trimethylpen-tane) as high as 70%, was observed in the liquid phase reaction (50 °C, 35 bar). However, the activity decreased rapidly, and no activity was observed when the accumulated feed amount of olefin reached 20 mmol/g-cat. Similarly, rapid catalyst deactivation was observed in the gas phase reaction. Alkylate yield dropped to near zero at an accumulated alkene feed of 20 mmol/g-cat. For the supercritical-phase reaction, the catalyst deactivation was suppressed by the SCF. Even when the accumulated alkene feed reached 35 mmol/g-cat (after 5.6 h), the alkylate yield was still higher than 10%. Although the yield of alkylate decreased with time-on-stream, 2-methyl-propene conversion was almost 100%. If the reaction was carried out in the liquid phase at conditions (125 °C, 50 bar) only slightly different from those of the SCF reaction, the deactivation behavior was similar to that of the gas phase reaction. 

Poliakoff et al. introduced the supercritical phase to the Friedel-Crafts alkylation reaction by using SCCO2 or by making propene, one of the reactants, the supercritical fluid [56]. This heterogeneous supercritical phase reaction was conducted continuously and the selectivity was very high if a solid acid Deloxan catalyst was utilized. 

Alkylation of benzene with propene to cumene on H-BEA zeolites in supercritical conditions was a good example to prolong the catalyst lifetime (290-310°C, 5.7 MPa) [193]. 

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