Glucose is a key pillar in producing bio-based alternatives to conventional chemicals, but finding industrially viable, non-food-competitive sources for glucose has proven challenging, due to the difficulty in obtaining glucose from hemicellulosic materials, such as woody biomass, in a cost -competitive way. Now, the ongoing search for an alternative glucose feedstock has led to the development of a process that also tackles another persistent environmental challenge — the accumulation of textile waste. Research conducted by Avantium N.V. (Amsterdam, The Netherlands; www.avantium.com) and the University of Amsterdam (www.uva.nl) discovered that the cotton content in polyester-cotton (polycotton) textiles could be selectively recovered and converted into glucose using a modified version of the century-old Bergius process, which uses concentrated hydrochloric acid (HCl) to hydrolyze cellulose. Avantium has already done a great deal of development work related to Bergius principles — previously constructing a pilot plant focused on processing woody biomass — but is now tailoring the process to instead handle polycotton.
“Cotton is much simpler to process than wood, because it only has cellulose, and you don’t have any hemicellulose. The glucose produced from cotton remains very pure because there are no other sugars present,” says Gert-Jan Gruter, chief technology officer of Avantium. In initial laboratory tests, researchers showed that cotton could be completely hydrolyzed to glucose at room temperature and ambient pressure with concentrated HCl. Not only does this demonstrate a feasible pathway for glucose production, but it also enables the recovery of recycled polyester, which is not typically possible using traditional textile recycling. “Polycotton is not easily recyclable because polyester melts at 265°C, but these temperatures thermally degrade the cotton. Because we are able to process the cotton at room temperature, the polyester is completely unaffected,” explains Gruter. Once glucose is recovered, the resulting polyester residue includes all pigments from the textile, which can subsequently be removed using any number of established chemical recycling processes. The HCl is also easily washed out, resulting in a recycled polymer product that is over 99% polyester.
Crucial to the process’ efficiency is high acid concentration and effective acid recovery and recycling, which typically is quite costly in other Bergius HCl processes because it involves energy-intensive evaporation, dilution and reconcentration of the acid. Avantium has devised a lower-energy approach to acid recovery that employs extraction, rather than evaporation, with no heating or dilution. This also enables the use of higher acid concentrations. At its pilot plant, Avantium is now processing polycotton waste instead of woody biomass, scaling up from 1-L laboratory tests to 230-L reactors.