The activity of silica-alumina catalyst in the isomerization of m-xylene was measured at the temperatures of 290°C, 320°C, 380°C, and 430°C in the liquid phase under a pressure of 300 kg/cm2. The observed activities were considerably higher than those in vapor-phase reactions, moreover even after 20 days practically no decline in the activity was observed except for the measurements at 430°C. This superior ability of the catalyst in the liquid phase can be ascribed to the cleaning effect of the liquid reactant: in the liquid-phase reaction the high-boiling by-product, which, in vapor-phase reactions, diminishes the activity because of its strong adsorptivity on the surface sites, is successively dissolved in the reactant; therefore, more surface sites are constantly available for the isomerization. This interpretation was substantiated by the following results: 1) when the reaction was operated in the liquid phase, about eighteen times as much high-boiling by-product was obtained as in the vapor phase; 2) the activity in the liquid-phase reaction was much higher than that in the vapor phase; 3) the decreased activity caused by the interruption of the flow was regenerable when the flow was resumed; 4) the addition of the high-boiling by-product to the reactant m-xylene resulted in a considerable decrease in the activity. In addition, the identification of the components in the high-boiling by-products was carried out by means of mass and NMR spectroscopic studies.

No abstract

The liquid-phase isomerization of m-xylene was studied over a silica-alumina catalyst under pressure on the additions of 2% of 8 higher-boiling compounds and 20–50% of benzene to reactant m-xylene. The catalyst activity in the isomerization was not greatly affected by hexamethylbenzene, naphthalene, α-methylnaphthalene, diphenyl, or s-dibenzyl. On the other hand, the activity was greatly lowered by 1,6-dimethylnaphthalene, diphenylmethane, and anthracene. Moreover, a very rapid exchange reaction occurred between an aromatic ring of diphenylmethane and a reactant xylene molecule, while the content of the isomerization product decreased linearly with an increase in the amount of benzene. From these results, the chemisorption states of xylene were discussed as follows. Most xylene molecules may be deduced to be chemisorbed on acid sites by those benzene rings. On the other hand, the fact that diphenylmethane inhibits the isomerization implies the existence of such a chemisorption state of xylene as a methylbenzylcarbonium ion, which may be an intermediate in the disproportionation reaction of xylene. The acid sites available for the chemisorption of diphenylmethane and for the disproportionation were speculated to be common and to have both acidic characters, protonic and Lewis.

Conversion of synthesis gas to light olefins was carried out in a two-stage system consisting * determined by X-ray fluoresence spectrometry * To whom correspondence should be addressed.