Pt/SAPO-11催化剂上正十四烷临氢异构化: Ⅰ 反应条件对催化性能及稳定性的影响

Hydroisomerization of n-tetradecane over a Pt/SAPO-11 catalyst with 0.6% metal loading was carried out in a fixedbed downflow reactor system. Reaction parameters such as temperature, pressure and WHSV, as well as the H2/CH molar ratio were varied in order to investigate the catalytic behavior, and thus to obtain the optimum reaction conditions. The catalytic performance was influenced by those reaction variables. It was shown that reaction temperature has the greatest impact on the hydroisomerization of n-tetradecane. The conversion of n-tetradecane increases up to 95% with increasing reaction temperature up to 340℃, while the isomerization selectivity lowers to about 87%. Increasing reaction pressure up to 3.0MPa has a negative effect on hydroconversion of n-tetradecane, but has little impact on the isomerization selectivity. With increasing WHSV, the n-tetradecane conversion decreases accordingly, but the isomerization selectivity increases a few units. The influence of H2/CH ratio on the catalytic performance presented a more complicated picture, and its effect was found to be relevant with other reaction parameters. At low reaction temperatures with conversion level less than 92%, nearly the same trends, sharp change of conversion and small change of selectivity, were observed as that of changing WHSV. However, at higher reaction temperatures with conversion level of above 95%, the H2/CH rise favors the isomerization selectivity, while the conversion decreases a little. Catalytic stability was found to be largely influenced by both reaction pressure and the H2/CH ratio. Fast deactivation was observed at atmospheric pressure, and stable catalytic performance was realized under high pressures above 0.5MPa. It should be point out that a critical minimal H2/CH ratio should be used in order to maintain the stable catalytic performance under higher pressures. It was also found that the ratio should be increased when the hydroisomerization was carried out at higher reaction temperatures. These results were in good agreement with our previous findings for the hydroisomerization of n-heptane over 0.4% Pt/SAPO-11 catalyst. The conclusion could be drawn from the obtained data that the reaction parameters interact with each other, which indicates that variation of one parameter needs the adjusting of others in order to gain a maximum isomerization yield. Moreover, the optimum reaction parameters are obtained for an optimal performance of hydroisomerization n-tetradecane: temperature 300℃～330℃, pressure 0.5MPa～2.0MPa, WHSV < 10h－1 and H2/CH 1.1～8.7. Under these conditions, excellent selectivity and stability of the catalyst were observed at low pressure and H2/CH ratio. High selectivity to i-C14 above 90% could be maintained even with conversion up to 95%.