Study On HMWPVC Heat-resistant And Anti-corrosive Packing Rings

In the production processes of chlor-alkali industry, a variety of packing rings are widely used in cooling, scrubber and absorber towers. In such a case, it is of important significance researching and preparing polymer packing rings in order to meet the specific requirements.Ordinary polyvinyl chloride (PVC) Raschig rings usually have to be replaced after six months owing to its unsatisfying heat resistance and anti-corrosive property. Although the heat resistant property of polypropylene Raschig rings improves compared with that of ordinary polyvinyl chloride, it is susceptible to corrosion, embrittlement and surface whitening. Polyvinyl chloride resin with high polymerization degree (HMWPVC) has advantage of heat resistance, fatigue resistance and high mechanical performance, etc. In this thesis, the processing, thermal property and corrosion resistance of HMWPVC samples were investigated with different types and amounts of thermal stabilizers and plasticizers.Firstly, different types and amounts of plasticizers and stabilizers were applied. In order to improve the Vicat softening temperature of HMWPVC samples, we chose plasticizer trimellitate trioctyl (TOTM) and auxiliary plasticizer epoxidized soybean oil. Liquid barium-zinc, barium-chromium-zinc complex stabilizers, solid tribasic lead sulfate, dibasic lead phosphate or antimony mercaptide were studied as heat stabilizers. We tested the mechanical and physical properties, corrosion and heat resistance of HMWPVC samples based on different types and amounts of plasticizers and stabilizers, and chose the best formula. It was found that HMWPVC samples had better compressive strength, tensile strength and heat resistance property. At normal temperature, the compressive strength of HMWPVC Raschig ring was much higher than that of ordinary PVC. At 60-80℃, HMWPVC Raschig ring could also meet the process requirement, and there were no dense holes appeared on HMWPVC Raschig rings without adding calcium carbonate. However, if the operation temperature exceeded 90 ℃, the performance of HMWPVC Raschig ring could not reach the required process conditions.Secondly, in order to achieve the requirement of chlorine scrubber, in which the temperature could reach 95℃, we applied methyl methacrylate-maleimide-styrene copolymer (MPS) as anti-high temperature modifier in order to develop better heat-resisting packing rings. It was found that by adding MPS, the Vicat softening temperature of packing rings could be increased to above 100 ℃. But poor compatibility of MPS with HMWPVC needs to be solved by using appropriate processing aids.Finally, we put the two kinds of HMWPVC packing rings into scrubber tower and chlorine cooling tower. After a period of time, we took them out to test the properties, and compared them with the performances of packing rings made from ordinary polyvinyl chloride and imported heat-resistant PVC. We found that the two kinds of HMWPVC packing rings had good performances and could meet the process criteria.