Abstract
BackgroundThe forest biorefinery plays an important part in the evolving circular bioeconomy due to its capacity to produce a portfolio of bio-based and sustainable fuels, chemicals, and materials. To tap into its true potential, more efficient and environmentally benign methods are needed to fractionate woody biomass into its main components (cellulose, hemicellulose, and lignin) without reducing their potential for valorization. This work presents a sequential fractionation method for hardwood based on steam pretreatment (STEX) and hydrotropic extraction (HEX) with sodium xylene sulfonate. By prehydrolyzing the hemicellulose (STEX) and subsequently extract the lignin from the cellulose fraction (HEX), the major wood components can be recovered in separate process streams and be further valorized.ResultsUsing autocatalyzed STEX and HEX, hemicellulose (> 70%) and lignin (~ 50%) were successfully fractionated and recovered in separate liquid streams and cellulose preserved (99%) and enriched (~ twofold) in the retained solids. Investigation of pretreatment conditions during HEX showed only incremental effects of temperature (150–190 °C) and hold-up time (2–8 h) variations on the fractionation efficiency. The hydrolyzability of the cellulose-rich solids was analyzed and showed higher cellulose conversion when treated with the combined process (47%) than with HEX alone (29%), but was inferior to STEX alone (75%). Protein adsorption and surface structure analysis suggested decreased accessibility due to the collapse of the fibrillose cellulose structure and an increasingly hydrophobic lignin as potential reasons.ConclusionThis work shows the potential of sequential STEX and HEX to fractionate and isolate cellulose, hemicellulose, and a sulfur-free lignin in separate product streams, in an efficient, sustainable, and scalable process.
Highlights
The forest biorefinery plays an important part in the evolving circular bioeconomy due to its capacity to produce a portfolio of bio-based and sustainable fuels, chemicals, and materials
Fractionation of hardwood by STEX and HEX: analysis and comparison of materials treated under various conditions This study examined three methods for fractionating hardwood: hydrotropic extraction (HEX alone), steam explosion (STEX alone), and the combination thereof (STEX + HEX)
HEX‐alone treatment of hardwood Hardwood chips were treated with HEX as a freestanding process, constituting a base case and benchmark values for comparison
Summary
The forest biorefinery plays an important part in the evolving circular bioeconomy due to its capacity to produce a portfolio of bio-based and sustainable fuels, chemicals, and materials. To tap into its true potential, more efficient and environmentally benign methods are needed to fractionate woody biomass into its main components (cellulose, hemicellulose, and lignin) without reducing their potential for valorization. By prehydrolyzing the hemicellulose (STEX) and subsequently extract the lignin from the cellulose fraction (HEX), the major wood components can be recovered in separate process streams and be further valorized. One application with fractionation at scale is the pulp and paper industry, a sector that is producing a portfolio of renewable products from the single constituents of woody biomass. Apart from dissolving pulp, the value proposition of the process includes valorization of the hemicellulosic monomers and oligomers that are recovered from the prehydrolysis liquid [4] and Kraft lignin [5, 6]. Sulfur-free processes, such as alkali-cooking using anthraquinone [8], can yield the desired delignification; the toxicity of anthraquinone limits its commercial potential and raises considerable environmental concerns [9]
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