超临界条件对改善催化剂失活状况的研究

STUDY ON SLOWING DOWN CATALYST DEACTIVATION UNDER SUPERCRITICAL CONDITIONS

苯/乙烯烷基化制乙苯反应为一典型的催化反应过程。在较小的苯/乙烯比的条件下,不论气相法还是液相法反应,催化剂的失活速率都比较快。由于超临界流体具有良好的溶解性能和扩散性能,因而当反应处于超临界态下进行时催化剂的失活状况将得到明显的改善。探讨了超临界条件下催化剂失活减缓的原因。

Benzene alkylation with ethylene is a typical catalytic reaction. When the reaction is carried out in gas phase or liquid phase, obvious catalyst deactivation is observed. This paper aims at slowing down the rate of catalyst deactivation of benzene alkylation reaction based on some special properties of supercritical fluid (higher solubility than gases and higher diffusibility than liquids). The results indicate that when the reaction conditions are above the critical points of the mixed reactants, the coke precursors which directly deactivate catalyst can be removed by dissolving themselves into the products from the reactor, leading to a longer catalyst lifetime. If the coke precursors have already turned into coke, the supercritical fluids are not able to dissolve the coke on the catalyst and to restore the activity of the deactivated catalyst becomes very difficult. Very high reaction temperature is not allowed since the catalyst deactivates rather rapidly even under supercritical conditions when the reaction temperature is above 300℃.