Study On The Performance Of Slurry Reactor For Ethylene Synthesis By Selective Hydrogenation Of Acetylene

Polyvinyl chloride(PVC) is one of the five engineering plastics. PVC is widely used and developed in various industries for its excellent physical and chemical properties. The world’s mainly synthesis methods of PVC are carbide acetylene method and petro ethylene method. In China, coal resources are very rich, while the petroleum resources are scarce, therefore, the carbide acetylene method become the mainly synthesis method of PVC. At present, about75%of PVC products are produced by the carbide acetylene method. However, the carbide acetylene method uses the HgCl2catalyst, which has toxicity and potentially toxic to the human and environment, in the synthesis process of PVC. So how to eliminate the Hg contamination has been the crucial problem that should be solved.In this paper, we study the process of acetylene selective hydrogenation to ethylene, aiming to use ethylene as raw material for the synthesis of PVC by the petro ethylene method, which avoids the use of Hg catalyst and realizes the free Hg production of PVC.Up to date, the study on acetylene selective hydrogenation to ethylene is only for the removal of traces of acetylene (0.5～2.3%) present in ethylene of ethylene unit. And, the reactor in ethylene is fixed-bed reactor. The reaction of acetylene selective hydrogenation to ethylene is a highly exothermic reaction. Temperature runaway caused by the reaction heat leads to potential safety hazard to the ethylene units. Meanwhile, temperature runaway lead to a large number of polymers formed, which causes the catalyst deactivation and reactivation hardly by covering the surface of catalyst. Slurry reactor is a new type of three-phase reactor. It has many advantages such as simple structure, low investment cost, easy temperature control, iso-thermal operation and so on. The study realizes the combining of carbide acetylene method and petro ethylene method by using slurry reactor for acetylene selective hydrogenation to ethylene. It can not only solve the problem of mercury pollution, but also provides an important way for the clean and efficient use of coal of China.The influence factors on acetylene selective hydrogenation to ethylene such as reaction temperature, superficial gas velocity, solid holdup and catalyst particle size was investigated in the self-made micro-slurry reactor. The study used α-Al2O3supported Pd as catalyst and purified water as the inert medium. The optimized reaction conditions were obtained:temperature T=90℃, superficial gas velocity ug=0.21m/s, solid holdup εs=20%, the diameter of catalyst was200cohorts. The conversion of C2H2increases with rising temperature and declines by the influence of water steam when the reaction temperature is close to the boiling point of water. Based on the results of above, we studied the amplification conditions on the pilot slurry reactor. In order to improve the conversion of C2H2, we adopted liquid paraffin as inert medium. The optimized reaction conditions on the pilot slurry reactor were obtained:temperature T=160℃, superficial gas velocity ug=0.24m/s, solid holdup εs=10%, the diameter of catalyst was200cohorts, the molar ratio of H2:C2H2was1:1. Under the condition, the catalyst stability was very well. Catalyst life was more than100h, the conversion of C2H2could reach70%and the yield of C2H4could reach77%. The conversion of C2H2on Ni catalyst reached87%, but the yield of C2H4reached only45%.