Dealkylation of coal liquid under CO-steam atmosphere, II. Model reactions using alkylbenzenes on supported nickel catalysts

Abstract Dealkylation of alkyl aromatics is a fundamental reaction in the upgrading of coal liquid produced by the usual hydrogenative liquefaction of coal. To develop a catalyst for the studied reaction, we performed the catalytic dealkylation of toluene and of ethylbenzene as model compounds by using a CO/steam mixture under atmospheric pressure at 380–620°C in a conventional flow system with a fixed bed of catalyst. Some runs with H2 and H2/steam in place of CO/steam were also perfomed. Both toluene and ethylbenzene are practically inert under CO/steam even at 500°C. Among the various catalysts examined, MgO-supported nickel catalyst was found to be effective for demethylation of toluene. On this catalyst a benzene yield of greater than 30% is obtained from the reaction of toluene at 500°C. The striking feature of the MgO-supported nickel catalyst is the depression of coke formation even at 500°C. The size of the Ni particles in the MgO-supported catalyst is estimated by XRD to be smaller than 10 A. Serious coke formation occurs on silica-supported and alumina-supported nickel catalysts of which activities are usually higher than that of MgO-supported catalyst. The addition of K2CO3 to these two catalysts partly depresses coke formation and enhances their catalytic activities. This K2CO3 addition effect is primarily due to the fact that potassium increases the dispersion of Ni on the catalyst carrier. The extent of the coke formation is considered to be strongly dependent upon the size of Ni particles. CO/steam mixture is found to be superior to H2 as a reducing agent, and is especially effective on the MgO-supported nickel catalyst. The supported nickel catalysts facilitate dealkylation of ethylbenzene to give benzene yield of 21.2% and toluene yield of 11.6% at 380°C without serious coke formation.