The Polymer Cracking Process Consortium Project

Texaco has conununicated the following acceptance criteria for its process (a.l). Depending on the design of the purification step after gasification, the process can deal well with up to 10% PVC in its feedstock. The tolerance to non-plastic materials like inorganics and paper is thought to be around 10%. Other acceptance criteria include  

Before MPW is fed into the process, a basic separation of the non-plastic fraction and size reduction is needed. This prepared feedstock is then introduced in the heated fluidised bed reactor which forms the core of the process. The reactor operates at approximately 500 °C in the absence of air. At this temperature, thermal cracking of the plastics occurs. The resulting hydrocarbons vapourise and leave the bed with the fluidising gas. Solid particles, mainly impurities formed from, e.g., stabilisers in plastics, as well as some coke formed in the process mainly accumulate in the bed. Another fraction is blown out with the hot gas and captured in a cyclone. 

Any chlorine in the feedstock (e.g., from PVC in the MPW) is converted into HCl, and the gas is purified with lime. The main result is a CaCl2-fraction that has to be landfilled. 

By cooling the gas is condensed and then available as hydrocarbon feedstock for other processes (some 85% of the MPW input). The light hydrocarbon gas (15% of the MPW input) that remains after cooling is compressed, reheated and returned to the reactor as fluidising gas. It can also be used as a fuel for the cracking process, though other recovery options are being studied as well. 

Impurities like chlorine are effectively re-used. At an input of 1% of chlorine in the MPW (2% PVC), the products will contain around 10 ppm Cl. This is somewhat higher than the specifications of 5 ppm typical for refinery use. However, in view of the high dilution likely in any refinery or petrochemical application, BP assumes that this is acceptable (a.5). Also, metals like Pb, Cd and Sb can be removed to very low levels in the products. Tests have shown that all the hydrocarbon products can be used further in refineries. 

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