Tracking swelling of lignocellulosic biomass during acid hydrolysis by using size-exclusion chromatography to evaluate molecular size

The two-step concentrated acid hydrolysis process is very efficient in producing fermentable sugars from lignocellulosic biomass, but acid recovery is important for the economic viability of the process. During mem-brane or precipitation-based separation of the acid catalyst from sugar oligomers and monomers, the molecular sizes of the sugar molecules will influence sugar entrainment with the acid. This study applied size-exclusion chromatography to determine the molecular size distribution of the water-soluble sugar molecules generated during the concentrated acid swelling of lignocellulosic biomass. Two indicators were calculated from the chromatograms to describe the distribution: the relative area of the chromatogram and the ratio of small mol-ecules versus large molecules. Measurable changes in these indicators could be related to changes in the oper-ating conditions of the swelling step, and to downstream hydrolysis performance. This approach provided important information about the swelling progression that will be useful for optimizing the hydrolysis process, and especially when implementing an acid recovery step.