Ind. Eng. Chem. Res. 2003, 42, 1145-1150
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KINETICS, CATALYSIS, AND REACTION ENGINEERING Pyrolysis of Polypropylene in a Nitrogen Plasma Reactor Lan Tang,* H. Huang, Zengli Zhao, C. Z. Wu, and Y. Chen Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, 81 Xian Lie Zhong Road, Guangzhou, 510070 China
Plasma pyrolysis of polypropylene is studied for the purpose of converting waste plastics into gaseous fuel and useful chemicals. The plasma reactor has a dc arc nitrogen plasma generator with a maximum electric power input of 62.5 kV‚A and a reaction chamber of 50 mm inner diameter and 1000 mm height. The results of a series of experiments show that, under our optimum experimental conditions of a power input of 35.2 kV‚A and a feed rate of 60 g/min, the concentration of hydrogen in the gaseous product can reach up to 18% and that of acetylene up to 5%. Steam injection is introduced for improving the product quality and extending the application range; by water steam injection, the sum of hydrogen and carbon monoxide can reach up to 40% in the gaseous product, while the decrease of the acetylene concentration is slight. A solid conversion of 96% and a gas productivity of 2160 mL/g are achieved. The results indicate that plasma-assisted thermal decomposition of polypropylene may be a useful way for recovering energy and useful chemicals of waste plastics. Introduction In recent years, as a result of changes in people’s consumption patterns, large amounts of waste plastic are available in municipal solid waste (MSW). With an annual increase rate of 48%, in 1996, 12.6% of the annual generation of MSW was comprised of waste plastic in Beijing,1 reaching the level of developed countries; for example, in Western Europe, 6-10% of MSW was composed of plastic (9.3 million tons in 1992).2 In 2000, the production of plastic in the world had reached 150 million tons. According to the formula that the yield of waste plastic is about 70% of the plastic product in the corresponding period, the yield of waste plastic is 105 million tons.3 In our country, 70% of the MSW is disposed of as landfill.1 Because landfilling not only wastes the resources but also engrosses land with pollution with macromolecules of plastic that are not biodegradable, it is important to find an efficient strategy to treat them. Disposal means such as incineration, pyrolysis, and gasification have been studied actively. Among these processes, plasma pyrolysis is a new technology. It has a number of unique advantages. For example, it provides conditions of high temperature and high energy for the reaction; that is, the sample is heated to a high temperature rapidly, and the reaction velocity is fast. Some reactions can take place that would not appear in conventional pyrolysis. There have been a number of previous laboratory studies of plasma pyrolysis of biomass4 and coal;5-8 the main products from hightemperature plasma pyrolysis of a hydrocarbon material could be hydrogen and acetylene.4 Our present study is * To whom correspondence should be addressed. Phone: 86-20-87787136. Fax: 86-20-87608586. E-mail: tanglan@ ms.giec.ac.cn.
concerned with polypropylene (PP) as a representative of plastic waste. PP is a hydrocarbon polymer made from petrochemicals; it has a large amount of volatile matter (>99 wt %) with high heating value and low ash content (
