Hydrodecyclization of Methylcyclopentane and Benzene in the Presence of a Reforming Catalyst* Koichiro Iijima**, Shin'ichi Shimizu**, Tsuneyoshi Furukawa** and Nobuichiro Yoshida** Summary: Hydrodecyclization reaction of methylcyclopentane (MCP) and benzene was studied under the conditions close to commercial reforming pro- cesses, and in the presence of a platinum-alumina reforming catalyst poisoned by coke and/or thiophene or activated by chloride. Decyclization reaction of MCP takes place competitively on two different kinds of active site. One of them is highly active, but is easily poisoned by small amount of thiophene added to the feed or moderate amount of coke deposited on the catalyst, while the other one is relatively less active, but is little affected by those poisons. The former would be on the surface of plati- num, and the latter is perhaps acid sites of the alumina carrier. The rate of hydrodecyclization of MCP-including small amount of hydro- cracking-, which was catalyzed by each site mentioned above was nearly of first order with respect to the partial pressure of MCP. And the rate of isomerization of MCP to six-membered ring compounds was also observed to be of first order with respect to the partial pressure of MCP. From the experiment of chloride activation, it seems that decyclization reaction of MCP can take place on. relatively weak acid sites, while isomeriza- tion to six-membered ring takes place only on relatively strong acid sites. According to the kinetic discussion on hydrodecyclization of MCP and benzene, it is concluded that the rate constant of cyclization of n-hexane to MCP is higher than that of n-hexane to six-membered ring, and the rate constant of MCP to six-membered ring is much higher than that of n-hexane to MCP, under the conditions close to commercial reforming processes, using the catalyst moderately poisoned by coke and sulfur compounds. presence of metalic oxide catalyst such as Introduction chromium oxide and molybdenum oxide. The reactions occurring in reforming pro- Work of Kasanski and Liberman4) also cesses involve isomerization, dehydrogena- showed that in the presence of a platinized tion, dehydrocyclization, hydrocracking and charcoal catalyst, dehydrocyclization of par- desulfurization reactions. Among these re- affins occurs most readily on the platinum actions, dehydrocyclization is one of the most surface. effective reactions to yield high octane num- On the other hand, Haensel5) suggested ber reformate1). that hydrodecyclization of methylcyclopen- On the dehydrocyclization reaction, par- tane (MCP), reverse reaction of the dehy- ticular investigations have been done by drocyclization, proceeds in accordance with Twigg2), Herrington and Rideal3). They carbonium ion mechanism. According to suggested that paraffinic hydrocarbons are this mechanism, such hydrodecyclization can converted directly to six-membered ring be promoted on the acid sites of the catalyst. compounds, or converted to five-membered In the present paper, kinetic data are ring compounds and isomerized subsequently presented for hydrodecyclization of MCP to six-membered ring compounds in the and benzene in the presence of a fresh or 1.5% coked platinum-alumina reforming * Received November 20 , 1962. ** Daikyo Oil Co ., Ltd., Research Laboratories, 1 catalyst. Effects of sulfur compound and Daikyo-cho, Yokkaichi, Mie. chloride in the feed stock are also discussed. Volume 5-March 1963 2 lIijima, Simizu, Furukawa and Yoshida: Hydrodecyclization of Methyl- Fig. 1 Schematic diagram of equipment Apparatus and Procedure lyzed by means of a Perkin-Elmer 154 B gaschromatograph unit. Each component of The bench scale unit used in conducting the mixture was measured by peak area and this investigation is shown in Fig. 1. The corrected by relative response which had reactor consisted of a stainless steel tube been obtained by preparatory experiments. 25mm inside diameter and 100cm long with Yield of the reaction products was calculated a coaxial thermowell in electrically heated neglecting the components having seven or furnaces. The upper section of the reactor more carbon atoms and standing upon no contained stainless steel rods preheat section loss base. while the space below was filled with catalyst. Twenty cubic centimeters of fresh platinum- Results and Discussion alumina reforming catalyst or the same volume of 1.5% coked catalyst-comes from Reaction of Methylcyclopentane the same lot of the fresh catalyst and it will Major reactions of methylcyclopentane be called simply coked catalyst hereafter- (MCP) in the presence of hydrogen over were used for comparison. Both catalysts platinum-alumina catalys may be conveni- were dryed in a nitrogen atmosphere and ently classified into isomerization(six-mem- reduced by hydrogen before use. bered ring formation), hydrodecyclization Source of materials is as follows. (C6 paraffins formation)and hydrocracking Methylcyclopentane; (C1～C5 paraffins formation). Neglecting Phillips Petroleum Co., >99% pure. the reaction intermediates such as carbonium Benzene; ions and olefins, the reaction paths can be Wako Pure Chem. Ind., JIS special illustrated as a reaction scheme in Fig.2. grade. Thiophene; Wako Pure Chem. Ind. 1,2-Dichloropropane; Tokyo Kasei Kogyo Co., E.P. grade. Hydrogen; Tokai Gas Chem. Co., >99.5% pure. Fig. 2 Reaction scheme Methylcyclopentane, thiophene and 1,2- As shown in Fig.2, k, k1 and k2 represent dichloropropane were used as received. the rate constant of consumption of MCP, Benzene was treated with chromatographic the rate constant of six-membered ring grade silica-gel before use. Hydrogen was compounds(benzene and cyclohexane)for- passed through a de-oxygen reactor to con- mation reaction from MCP, and the rate vert trace amounts of oxygen to water, and constant of C6 paraffins and C1～C5 paraffins then dried over alumina. formation by hydrodecyclization plus hydro- Analysis cracking reaction from MCP, respectively. Reactor effluent mixture was directly ana- Typical distribution of products and rate Bulletin of The Japan Petroleum Institute cyclopentane and Benzene in the Presence of a Reforming Catalyst 3 Table 1 Reaction of MCP: Distribution of products and rate constants under various reaction conditions Pressure 17 atm abs., Hydrogen/MCP 10 moles/mole . constants under various reaction conditions to MCP consumed by hydrodecyclization plus are shown in Table 1. Rate constants k hydrocracking is nearly constant, either in Table 1 were calculated assuming the fresh or coked catalyst was used. Therefore, following conditions; first order reaction both reactions mentioned above may also be with respect to the partial pressure of MCP, considered to be of first order with respect plug flow in the reactor, no reverse reactions to the partial pressure of MCP, since and no change in contact time due to volume hydrodecyclization and hydrocracking of change originated in the reactions. Methyl- six-membered ring compounds formed by cyclopentene which is dehydrogenated prod- isomerization of MCP hardly occurred. In- uct of MCP was assessed as a feed material. In relatively low conversion range-up to approximately 50% conversion-, either fresh or coked catalyst was used, values of k were recognized to be constant at the same temperature. So, within the above limit, it may be accounted for that the rate of con- sumption of MCP is nearly of first order with respect to the partial pressure of MCP. Fig.3and Fig.4show mole% yield of C1～C5, paraffins, C6 paraffins, and benzene plus cyclohexane against conversion of MCP, in the presence of fresh or coked catalyst respectively. From these figures it is shown that in the low conversion range-up to approximately 50%-, the ratio of MCP Fig. 3 Selectivity of the reaction of MCP consumed by six-membered ring formation over fresh catalyst Volume 5-March 1963 4 Iijima, Shimizu, Furukawa and Yoshida: Hydrodecyclization of Methyl- fresh or coked catalyst, until a steady state about thiophene poisoning had been estab- lished in each case. Rate constants k, k1 and k2 in the experi- ment of thiophene addition are shown in Table 2. In the presence of fresh catalyst, very small amounts of thiophene addition into the feed MCP caused rapid decrease in k2, but when 0.078 mole% (equivalent to 0.03 weight % of sulfur) or more thiophene was added, k2 approached a constant value. On the other hand, in the presence of coked catalyst, there were little change in k2 even with relatively large amounts of thiophene addition. As shown in Table 2, there are Fig. 4 Selectivity of the reaction of MCP substantial differences in iso-hexane to n- over 1.5% coked catalyst hexane ratios between those with and with- feasibility of such reactions of six-membered out thiophene addition and also between both ring compounds will be discussed in the later catalysts. section of this paper. It is well known that sulfur compounds It should be noted that in the same reaction impair platinum catalysts, and coke deposit- conditions, there are only slight differences ed on the catalysts also covers platinum in the values of kl between fresh and coked surface predominantly6) and it causes de- catalyst, while k2 of fresh catalyst were crease in activity of platinum. It seems that markedly larger than that of coked catalyst. the hydrodecyclization and the hydrocracking reactions promoted on the platinum surface, Apparent activation energy of either six- membered ring formation reaction or hydro- according to the mechanism suggested by decyclization plus hydrocracking reaction Kasanski and Liberman4), gave high value was 30～35 kcal/mole, in the presence of of rate constant k2, in the presence of fresh either fresh or coked catalyst. catalyst and in the absence of thiophene. On the other hand, the data in Table 2 Effects of Thiophene Addition on the Re- show that hydrodecyclization plus hydro- action of MCP cracking reactions are still retained con- In order to investigate the effects of sulfur siderably even under the conditions that compounds on the reaction of MCP, thio- considerable amount of thiophene was added phene was added into the feed MCP in and 1.5% coked catalyst was used.