Isobutane/butene Alkylation Catalyzed By Metal Modified X Zeolites

With the upgrading of domestic gasoline standards,the demand for alkylates has increased,and with the improvement of national environmental protection policies,higher requirements have been put forward for the green,safe,and low-energy operation of alkylation processes.Currently,the traditional liquid acid technology mainly applied in industry has the disadvantages of environmental and safty issues.Therefore,the development of a green,efficient and environment-friendly solid acid catalyst is the promosing approach to solve the above practical problems.Because zeolite have a variety of pore structure,acidity and excellent hydrothermal properties,non-corrosive and little environmental hazard,they are expected to replace liquid acid catalysts.This thesis mainly focused on the X zeolite modified with metal cations as soild acid catalysts for C₄ alkylation in order to prolong the lifetime of zeolite catalysts and reduce the effect of carbon deposition on the selectivity of target products.It provides scientific basis and experience for the development of new and efficient X-type zeolite catalysts for the alkylation industry.In this study,a series of rare-earth modified X-type zeolite catalysts were prepared by using NaX zeolite as raw material,adjusting the amount of rare earth introduced through the exchange and calcination times of rare earth lanthanum.Comparing the structure and acidity of different rare earth modified X zeolite catalysts,it was found that as the number of La³⁺exchanges increased,the Br?nsted acid sites of the zeolites increased and the Lewis acid sites decreased,but the rare earths were introduced too much,the total acid density decreased.Combined with the alkylation performance of five rare earth modified zeolite catalysts,the initial yield of C₈ products of 2LaC+3LaC was found to be the highest,which was 66.71%,and the initial conversion rate of butene was 89.94%.It is shown that the strong Br?nsted acid content on the catalyst is an important factor affecting the alkylation performance.In order to prolong the lifetime of the rare earth modified zeolite catalysts further,based the mechanism of the solid acid catalyzed alkylation reaction,it is believed that the concentration of butene at the active site of the catalyst will affect the ratio of alkylation and oligomerization reactions,so that the copper was introduced into the rare earth modified X-type zeolite to prepare the bimetallic modified catalysts.The results show that the bimetallic?RE and Cu?modified zeolite catalysts have a longer lifetime,significantly improved the selectivity of the C₈ products,and the longest lifetime of CuLaX can reach 15 h.Combined with the characterization of the catalysts and the effect of copper valence on catalytic performance,the advantages of introducing copper ions were reflected in two aspects,one side the introduction of copper ions increases the concentration of strong Br?nsted acid sites,accelerates the transfer rate of hydrogen negative ions in the reaction,and reduces the occurrence of side reactions;and the other side the Cu⁺can interact with acid sites competitively adsorb butene to reduce the butene concentration at the active site,inhibit the side reactions such as oligomerization,and prolong the lifetime of the catalyst.