The Study Of Acetylene Selective Hydrogenation Activity On Cu/SiO₂ Catalyst

Ethylene is mainly produced by steam cracking of naphtha. This cracking process also produces impurities e. g. acetylene that causes an irreversible damage of the catalysts used in downstream processes of the steam cracker (for example Ziegler-Natta catalysts in the polymerization of ethylene). So the acetylene content has to be reduced to concentrations lower than 1 ppm to avoid this damage. The selective hydrogenation of acetylene is one process to remove traces of acetylene from steam cracker cuts during the production of ethylene. Current disadvantages of commercially used Pd-Ag/Al2O3 catalyst are relative short cycle time (fast deactivation) caused by green oil formation and deposition of coke. Therefore a targeted improvement of the hydrogenation catalyst (especially non-noble metal catalyst) is one possibility to increase the ethylene selectivity.Non-noble metal copper was usually added into Pd based catalyst as promoter to increase the ethylene selectivity during the process of acetylene hydrogenation. In 2000, professor Cui Zuolin of Qingdao university of science and technology used nano copper particles as catalyst to catalysis the polymerization of acetylene, they prepared a series of different shapes of carbon nanofibers. Our previous work is that using the polymerization of acetylene on copper removed traces of acetylene in industrial ethylene, and got good result. This thesis research work is that we prepared a certainty load of copper catalyst Cu/SiO2, and investigated the hydrogenation activity of acetylene and the selectivity of ethylene using this catalyst with different treatment, processing conditions as follows:acetylene processing and no processing. The experimental results show that:the initial ethylene selectivity using catalyst dealt with acetylene is better than untreated; the treated catalyst has no activity of ethylene hydrogenation, untreated has. The possible reason is that:when acetylene contacts with the metal copper, it can form a special kind of active phase, and this active phase has strong adsorption for acetylene, but weak adsorption for ethylene, so the treated catalyst has higher selectivity, and no ethylene hydrogenation; when the untreated catalyst catalysis the reaction of acetylene hydrogenation, there is a process of formation of the active phase, so the ethylene selectivity also rose slowly; when catalysis the reaction of ethylene hydrogenation, the metal copper has some certainty of activity, and higher temperature better activity, but in general, the ethylene hydrogenation activity is relatively low. The ethylene selectivity is much better when acetylene hydrogenation reaction occurred at high temperature(250℃), but most of acetylene polymerize into carbon fibers, a little of acetylene hydrogenates into ethylene, therefore in order to overcome or relax polymerization of acetylene, we choose the way of adding promoter palladium to increase the acetylene conversion. The experimental results show that catalyst bed jams phenomenon eased, the most important is that the ethylene selectivity main a high level,99% as the temperature is 250℃, and the largest space velocity is 1.54×106 cm3/g.h.We tested the metal silver and gold belonging to same main group whether they have similar properties like copper, the experimental results suggested that:acetylene didn't polymerize on silver and gold, and when dealt with acetylene before reaction they don't display much higher activity yet.In addition, we further investigated the acetylene selective hydrogenation activity of cupric oxide, the experimental result suggested that cupric oxide also has the similar properties with copper, we can say that cupric oxide also can form the active phase with acetylene.