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Research Into Chemical Recycling Could Open New Opportunities
The U.S. Department of Energy conducts on-going research on plastics recycling. This report highlights new approaches to chemical recycling. Recycling of plastics can be costly and difficult because of constraints on waste contamination and inadequate separation prior to recycling. Chemical recycling could remove some of those restraints.
Pyrolysis and hydrolysis are two processes that have shown promise in the recovery of basic chemicals and fuels from waste plastics. Pyrolysis is a process in which plastic wastes are heated in the absence of oxygen in a closed chamber. The products of pyrolysis may be used as a chemical feedstock or fuel. Hydrolysis decomposes plastic wastes through a series of chemical reactions.
Research sponsored by the U.S. Department of Energy’s Office of Industrial Technologies at the National Renewable Energy Laboratory has led to the development of a new process based on the pyrolysis of certain waste streams. This process retrieves monomers, the basic building blocks of a polymer, and high-value chemicals that are sufficiently pure to use in making new plastics. The advantage of this process is that the waste plastics do not have to be separated ahead of time, thereby eliminating a labor-intensive step in current processes. It also will reduce the cost of the monomers and chemicals and will reduce consumption of petroleum, the source of chemical feedstocks used to produce plastics.
In the new process, monomers and high-value chemicals are retrieved from manufacturing or post-consumer wastes through sequential pyrolysis. The reaction products undergo detailed chemical analysis to determine conditions that allow control of pyrolysis reactions. This allows the design of a process to collect the desired products in high yields, reducing requirements for subsequent separation and purification of the target product. NREL has filed patent applications to cover the process for a total of seven mixed plastic waste streams.