Impact on the Polyester Value Chain of Using p-Xylene Derived from Biomass

Life cycle assessment has been used to investigate the environmental impacts associated with using p-xylene produced from biomass rather than from the processing of naphtha in the production of polyethylene terephthalate (PET). The cases investigated were for polymer production and distribution facilities in the United States. The types of biomass considered were corn stover, willow, and sugar cane (both juice and bagasse). The best case for minimizing global warming potential and fossil energy use involved producing p-xylene from sugar cane juice, while the sugar cane bagasse was burnt to generate electricity. Compared with conventional processing, a net reduction in global warming potential of 87% and a 26% reduction in fossil energy use were obtained. Furthermore, it has been shown that savings can be made by producing ethylene glycol from sugar cane bioethano1.1 This would enable the production of a PET bottle sourced completely from biomass. The production of such a bottle would result in an overall 114% reduction of global warming potential, i.e. the system, as defined, is effectively sequestering CO2 from the atmosphere, and 39% reduction in fossil energy use. However, the total use of energy, i.e. fossil and renewable, increases by 81%. Other environmental impacts were also quantified, e.g. eutrophication, for which the biomass systems are generally at a disadvantage compared with production from petrochemicals. Land use and water use were also considered. The current p-xylene market is discussed, and biomass routes face significant barriers to entry. Finally, the sensitivity of the conclusions to different methods of allocation is assessed.