Waste-to-plastics: process alternatives

Rapport, 2006

In this report, processes for converting woody biomass to plastics (BTP) and waste plastics into plastics (PTP) are examined. The technologies evaluated are thermochemical conversion of the raw material into polyethylene (PE) and polypropylene (PP). The core strategy is to take the biomass or plastic waste through gasification, water gas shift (WGS), methanol production, methanol to olefins (MTO) and finally plastic production. The environmental attractiveness of these emerging technologies is evaluated using a combination of process modelling and life cycle assessment (LCA) methodology. Several tools and simulation softwares have been combined to carry out the study, including Aspen’s HYSYS, LCAiT and Excel. Important factors have been identified and evaluated, like climate change mitigation, feedstock availability, recycling loops and technological improvements. Various improvements of the processes are evaluated with respect to green house gases emissions potential for the system. The most important outcomes of the study include: 1. Production of plastic waste from biomass and plastic waste seems possible using the BTP and PTP processes, respectively. 2. As a plastic production system, the BTP seems more advantageous than PTP regarding green house gases emissions. 3. The gasification unit, with the air separation unit to produce oxygen, is the main contributors to CO2 emissions. A case with an improved gasifier for plastic waste shows significant improvements. 4. To use hydrogen surplus from a chemical plant as a hydrogen fuel cells feedstock is not the only option available. Hydrogen surplus could be use to greatly improve the BTP and PTP routes - or similar processes - as shown in this report. 5. The method, which combines LCA and process modelling, enables an effective early-design phase evaluation.