COAL/POLYMER COPROCESSING WITH EFFICIENT USE OF HYDROGEN

Inadequacies of current recovery and disposal methods for mixed plastic wastes drive the exploration of viable strategies for plastics resource recovery. The combination of diminishing landfill space and increasing usage of plastic products poses a significant dilemma, since current recovery methods are costly and ill-suited to handle contaminants. Coprocessing of polymeric waste with other materials may provide potential solutions to the deficiencies of current resource recovery methods, including unfavorable process economics. By incorporating plastic waste as a minor feed into an existing process, variations in supply and composition could be mediated, permitting continuous operation. One attractive option is the coprocessing of polymeric waste with coal under direct liquefaction conditions, allowing for simultaneous conversion of both feedstocks into high-valued products. Catalyst-directed coliquefaction of coal and polymeric materials not only has attractive environmental implications but also has the potential to enhance the economic viability of traditional liquefaction processes. By exploiting the higher H/C ratio of the polymeric material and using it as a hydrogen source, the overall process demand for molecular hydrogen and hydrogen donor solvents may be reduced. A series of model compound experiments has been conducted, providing a starting point for unraveling the complex chemistry underlying coliquefaction of coal and polymeric materials. Tetradecane (C{sub 14} H{sub 30} ) was used as a polyethylene mimic, and 4-(naphthylmethyl)bibenzyl (NBBM) was used as a coal model compound. Neat and binary mixture reactions of tetradecane and NBBM were carried out in an inert atmosphere at both low and high pressures to establish a thermal baseline for subsequent catalytic experiments. Work in the past six months has focused on analysis of light gaseous products for neat reactions of tetradecane, resulting in mass balances greater than 94%. The experimental protocol developed in the previous project period was used to conduct experiments at elevated pressures more representative of coal liquefaction conditions, and both neat and binary mixture reactions of tetradecane and NBBM were examined. Mechanistic modeling studies were also initiated in order to support and quantify the mechanistic ideas put forth to explain the experimental observations