One researcher said logistics will be the primary challenge to commercialization.

Chevrons lead researcher on the project was Stephen J. Miller, the patent holder for the companys Isodewaxing wax isomerization technology. Chevron and numerous other refiners have used that technology in mineral oil refineries to make Group II and Group III base oils. Isodewaxing was part of the process that Miller and Kentuckys Naresh Shah and Gerald P. Huffman used in their work on recycling plastics.

The plastics they tested were mostly polyethylene. They began by pyrolyzing the material, heating it in a furnace in the absence of air to break down molecules to form a waxy fluid with molecular weight in the range of lube oil. Isomerization dewaxed the fluid to produce diesel and base oil. The base oil yield varied between 30 percent and 40 percent by weight, although that output could be increased by oligomerizing short-chain olefins, the main byproduct of the process.

According to the researchers, the quality of the base oil was consistent and exceptionally high – viscosity of between 3.4 centistoke and 5.4 cSt, pour points ranging from minus 13 to minus 37 degrees C, and viscosity index of 150 to 160.

This is probably about as good as youre going to get in a base oil, said Miller, a fellow and senior consulting scientist at Chevron Energy Technology Co. in Richmond, Calif.

Miller said he undertook the project with a waste management bent.

Plastic is the fastest-growing part of the waste stream in the United States and now accounts for more than 10 percent, Miller told Lube Report. Very little of it gets recycled, and this is becoming a major issue in California and elsewhere because of the growing costs of landfills. So if we can turn it into a high-value product, it will reduce those costs and conserve resources.

The research showed that is indeed feasible, Miller said, but he acknowledged that prospects of employing the process on a broad scale are mixed. On the plus side, numerous municipalities and businesses already operate recycling programs that separate polyethylene. It would be up to such programs to redirect the materials to facilities that could turn them into base oil.

Our company isnt going to do that, Miller said. My thinking is that we would have to work in cooperation with someone else, perhaps local governments who are dealing with these escalating disposal costs.

But even if waste polyethylene is channeled, volumes would probably not be sufficient to sustain a commercial-scale plant. The researchers therefore envisioned it being used in conjunction with other feedstocks.

Through their tests they found that pyrolyzed polyethylene can be processed with wax produced by Fischer-Tropsch, the core technology in gas-to-liquids plants. GTL refineries are under construction or planned in several locations around the world, but are generally expected to be built in less-developed regions. As Miller observed, such areas are less likely to have proximity to large volumes of waste plastic.

We always looked at this as more of a supplemental feed, rather than a primary feedstock, Miller said. You may not have GTL plants in areas where [waste] plastic is generated, but maybe you could use this as a component of a gas-to-liquid plant that starts with coal, or even a biomass gasification plant. Both of those also use Fischer-Tropsch.

An article detailing the research by Chevron and the University of Kentucky appears in the July 20 issue of Energy and Fuels, a peer-reviewed journal published by the American Chemical Society.