Process for Transforming Waste Polyethylene to Dicarboxylic acids

Executive Summary

Polyethylene is a leading plastic used in a myriad of applications. One consequence of the abundant use of the plastic is the problem of waste which accumulates in landfills. Mechanical recycling waste polyethylene is possible for certain grades and limited applications, and pyrolysis to produce fuels possible but often uneconomical. MSU researchers, have developed a new one pot process for converting collected waste polyethylene into the value added diacarboxylic acids. The process produces clear diacarboxylic acids useful for a range of value-added products with 100% of the carbon coming from recycled material.

Description of Technology

The process involves heterogenous depolymerization in a one pot process using nitric acid, sulfuric acid and a metal catalyst. Depolymerization is done in a single step, at ambient pressure and moderate temperatures (~90-120^oC) for approximately 24-48 hours, depending on the grade of product desired. The process includes recycling filtrate, which enhances the overall efficiency of the depolymerization and avoids side reactions that can discolor the product. The final product is filtered, rinsed and dried to form a high quality blend of primarily aliphatic difunctional acids of moderate (70-150 carbons) and low (4-10 carbons) molecular weights. These valuable products can be converted to greases, waxes, or monomers for further use in polymers such as polyesters or polyamides. 100% of the carbon in the dicarboxylic acids made by this process are obtained from recycled sources. The TRL of this process is currently assessed at 3. Work has been done at the laboratory scale using waste HDPE bags collected from a grocery store.

Benefits