PVC MEDICAL PLASTIC WASTES DEGRADATION IN MICROWAVE DIELECTRIC HEATING

摘要

Accumulation of enormous amounts of plastic waste produced all over the world has negative implications on the environment. Pyrolysis of these plastic wastes not only reduces the volume of these wastes but it could also have an important role in converting these wastes into economically valuable hydrocarbons. These hydrocarbons could be used either as fuels or as feedstock in the petrochemical industry. Using microwave energy to pyrolyze plastics is a new technology. It combines the advantages of the pyrolysis technology with the fast heating capacity of microwave heating. In this study, the decomposition of polyvinylchloride (PVC) and PVC blood bags through pyrolysis by microwave dielectric heating was investigated. The decomposition of PVC resin was determined using a TGA-50 instrument. A microwave pyrolyzer system was fabricated using a Whirlpool domestic microwave oven with a capacity of 1,000 watts and a frequency of 2,450 MHz. The particle size of PVC was less than 2 mm while the charcoal powder was 0.01 mm. The charcoal powder acts as a microwave absorber. Pyrolysis temperature was set to approximately 520°C. The parameters used in this study are residence time and weight ratio of PVC over charcoal. The pyrolytic oil was condensed at a temperature of 8 to 10°C using a Graham condensing system. The correlations of the percentages of decomposition, pyrolytic oil product yield, residual amount with the residence time and different plastic to charcoal weight ratio were investigated. A biological test was performed to determine the population of microorganisms on the simulated PVC plastic wastes before pyrolysis. The results of the present study can be summarized as follows: (1) PVC resin had two decomposition temperature zones in microwave irradiation. The first zone was in the range between 280 and 400°C in which the dehydrochlorination of PVC occurred while the second zone was between 450 and 550°C in which the hydrocarbons of PVC were released; (2) The optimum conditions for pyrolyzing the samples were for 1/1.5 weight ratio of PVC/charcoal and 20 minutes residence time at 520°C. It was also noted that PVC could not decompose any more even if the residence time was increased to 30 min; (3) Results in analyzing PVC resin and PVC blood bags showed that the produced hydrocarbons were almost the same and theywere not dependent on either the residence time or weight ratio of PVC and charcoal. The main components of pyrolytic oil were benzene, toluene, heptane, heptene and some benzene derivatives; (4) The results of the biological tests show that there are around 1.3 × 10~6 colonies in one gram of simulated PVC blood bag. The ability to pyrolyze PVC resin and PVC blood bags using the microwave pyrolyzer emphasizes the fact that pyrolysis technology could not only solve the problems of waste disposal but also turn these plastic wastes into a source of renewable energy. On the other hand, pyrolysis is also a suitable technology for the treatment of hazardous wastes.