Abstract
The fundamental study of catalytic conversion of Methylcyclohexane (MCH) was made to produce high octane-value isoparaffins such as dimethylpentanes via dimethylcyclopentanes which are isomerization products of MCH. After decationizing faujasite to various levels, it was used as the carrier for rhodium catalysts. The content of rhodium in the catalysts was fixed at 3wt%. Major reaction products were classified into 4 groups: 1) dimethylcyclopentanes, 2) dimethylpentanes, 3) methylhexanes and 4) C1-C6 hydrocarbons.
The effect of percent ion exchange of the carrier on catalytic activity and selectivity were investigated and the results are shown in Fig. 2. The yield of dimethyl pentanes exhibited a maximum when 34% of Na+ was replaced by H+. The time course of reaction on this catalyst, Rh(3wt%)/HNaY-34, was measured by changing the time factor W/F, (weight of catalyst)/(feed rate of MCH). The results shown in Fig. 3 show that dimethylpentanes were formed by ring-opening of dimethylcyclopentanes rather than by isomerization of methylhexanes which gave only dimethylcyclopentanes as primary products as shown in Fig. 4. The product pattern of dimethylpentanes could be interpreted by the selective bond breaking of the bisecondary carbon atoms of dimethylcyclopentanes as in the case of the ring-opening of dimethylcyclopentanes on a Rh/C catalyst observed by Bragin et al.3)
The poisoning of the acidic site by Na2CO3 and that of metallic Rh site by thiophene were studied. These poisoning effects on the product distribution of ringopening and ring-isomerization are shown in Tables 1 and 2, respectively. It was shown from these results that ring-opening of MCH occurred on the metallic site to give 2- and 3-methylhexanes as major products and n-heptane as a minor indicated that the bisecondary carbon bonds of MCH were selectively split on the Rh sites. The results given in Table 2 showed that the rate of ring-isomerization of MCH taking place on the acidic site was enhanced by the presence of Rh sites. Especially the formation of 1, 1-dimethylcyclopentane required co-existence of acidic and metallic sites. Hydrocracking products of MCH on Rh/HNaY and Rh/SiO2 catalysts shown in Table 3 were similar and they consisted mainly of methane and hexanes. The hydrocracking reaction required only the metallic site. All these reaction routes are speculated schematically in Fig. 5.
