(405b) Conversion of Polyvinylchloride Containing Solid Wastes into Value-Added Products
Xianglan Bai, Joel Braden
Department of Mechanical Engineering, Iowa State University, Ames, IA, USA, 50011
Municipal Solid Waste (MSW) is a mixture of organic and synthetic materials. The organic material has the potential to be converted into valuable fuels through thermochemical conversion. On the other hand, main plastic wastes, such as PE and PP, can be an excellent source of chemicals or high-density liquid fuels. Previous studies by our group and others have shown that co-conversion of biomass and hydrocarbon-based plastics through catalytic or non-catalytic pyrolysis can be benefited from synergistic effects among the different materials. Nevertheless, MSW also contains significant quantities of halogenated plastics like polyvinyl chloride (PVC) that are difficult to recycle using traditional methods. When MSW is thermally converted (i.e., pyrolysis, gasification and incineration), PVC can not only produce corrosive hydrochloride gas, but also react with organic waste-derived products to form organohalogens and dioxins that create various environmental and health hazards. Our group has investigated a new approach to utilize PVC as an asset to promote MSW conversion to value-added products. We first co-converted cellulose and PVC in heated tetrahydrofuran (THF) solution. It was found that levoglucosan was the major monomer in liquid product. The highest monomeric sugar yield was 42% at 335 ºC and 8 minutes with 2.5% cellulose weight equivalent PVC. The liquid products also contained up to 46% of soluble oligomeric sugars and small amounts of 5-HMF and furfural. Chlorinated organics were nearly absent in either liquid product or the pyrolyzates of the solid residue. Therefore, the results confirmed our hypothesis that hydrochloric acid released during thermal decomposition of PVC acts as an effective catalyst in THF to promote cellulose decomposition to soluble sugars. Encouraged by the result, we also converted a mixture of cardboard, PVC and PE in THF solution. As a result, not only PVC greatly facilitated rapid decomposition of cardboard to liquid product, but the presence of PE also helped to increase the conversion. Up to 68% of cardboard was converted into liquid product containing various organic compounds, such as furans, sugars and phenolics. The remaining solid residues could be easily separated into two fractions. The first fraction was fine char derived from cardboard and it had a HHV of 20.8 MJ/kg, compared to 11.7 MJ/kg with the cardboard. The second fraction of the residue was a waxy material. Upon pyrolyzing, the waxy residue produced a serious of aliphatic hydrocarbons identical to that are produced from pyrolysis of pure PE. More significantly, Cl atom was nearly theoretically converted to HCl and thus can be recovered from the solvent. Overall, we explored an environmentally friendly approach to convert mixed solid wastes into value added products.