Resources recycling by advanced techniques for PVC containing waste plastics

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The purpose of research project is the development of advanced techniques for the recycling of PVC containing waste plastics, especially in Japan. The smooth recycling system requires not only the technology but also the consumer acceptance of products. Particularly, the products from waste PVC gave a negative impression because Japanese consumers are afraid to an adverse health effect by the residual Cl species, even the concentration as low as ppb. Thus, in order to dispel concerns about products derived from PVC wastes, a new technology unconstrained existing methods should be developed in Japan. As the alternative method for the production of an activated carbon from carbon residues after the dehydrochlorination, we proposed a potassium activation method, whose advantages are that potassium will act both as the neutralizing agent for residual Cl species and as the activating agent for carbon. Furthermore, residual potassium and potassium chloride in the activated carbon can be used … More as a fertilizer in the agricultural fields but not for sodium due to the salt pollution. We attempted the production of activated carbons and determined the optimal condition for both a glass made apparatus and a batch apparatus equipped with a kerosene burner and a stainless-steel kiln. The activated carbon with a surface area of over 1000 m^2/g was prepared at 750C. It was found that the most important step is the pre-oxidation treatment at 300-400C before the carbonization, which means the formation of non-graphitizable carbon. After the treatment, both yield and quality of activated carbon are improved by the inhibition of melting to form graphitizable carbon during the carbonization. The importance of pre-oxidation treatment is confirmed in the production by the batch apparatus, too. In addition, dioxin concentration in the activated carbon meets environmental standards. Characteristics of activated carbon are as follows: 1) The activated carbon is more hydrophilic than most activated carbons available. 2) A large amount of surface functional groups such as OH and COOH, which are titrated by Boehm method, are formed and correlate contribute to the hydrophilic property. 3) The surface modification is successfully performed by add solutions such as HNO_3 and H_2SO_4 and thin nitric acid solutions are particularly effective for the generation of oxygenate group by the oxidation of C-C bonds. 4) Characteristics of activated carbon are somewhat affected by mixing ratios between PVC and polyolefin and the concentration of polyolefin should be control to be less than 50%. An application to agricultural field is now in progress Less