Impact of Hot-Water Extraction on Acetone-Water Oxygen Delignification of Paulownia Spp. and Lignin Recovery

Abstract

A hardwood-based biorefinery process starting with hot-water extraction (HWE) is recommended in order to remove most of the hemicelluloses/xylans before further processing. HWE may be followed by delignification in acetone/water in the presence of oxygen (AWO) for the production of cellulose and lignin. In this study, the HWE-AWO sequence was evaluated for its effectiveness at removing lignin from the fast-growing species Paulownia tomentosa (PT) and Paulownia elongata (PE), in comparison with the reference species, sugar maple (Acer saccharum, SM). HWE might lead to a remarkable increase in lignin accessibility, and as a result, a greater AWO delignification degree was observed for extracted PT, PE, and SM than for unextracted ones. Organosolv lignin was recovered from the spent liquor of AWO delignification of PT with/without prior HWE and characterized to evaluate the benefits of HWE on the lignin structure and purity. The lignin recovered from the spent liquor of HWE-AWO sequence is of higher purity and lighter color than that recovered from the AWO spent liquor. These properties along with low sulfur content are desirable for lignin high-value applications.

Toward Complete Utilization of Miscanthus in a Hot-Water Extraction-Based Biorefinery

“…Determined digester yields were comparatively lower than observed for different hardwoods (such as Paulownia sp. and sugar maple) studied earlier under the same conditions [17]. This result suggests that autohydrolysis reactions taking place during HWE lead to extraction of a higher amount of miscanthus constituents than of hardwood constituents.…”

“…Nevertheless, miscanthus lignin was found to be relatively susceptible to hydrolysis as delignification of >30% was observed at all scales. In contrast, hardwoods have exhibited delignification of <20% under the same conditions of HWE in our previous experiments [17,39,48]. The relatively low molecular weight of lignin in miscanthus and/or abundance of lignin and lignin-carbohydrate acid-labile bonds may contribute to its relatively higher hydrolyzability in comparison to lignin in hardwoods.…”

“…HWE approximately doubled the content of PhOH groups in EMS. This result suggests an extensive cleavage of acid-labile bonds; aryl ether bonds (α-O-4, β-O-4) and/or phenylglycosidic bonds leading to a ready release of lignin fragments and a relatively higher degree of delignification of miscanthus compared to that of hardwoods (based on MK studies DD 30% found for MS vs 10% for Acer saccharum (sugar maple) and 15% for Paulownia tomentosa [17]. The increase in PhOH content of miscanthus after HWE was still less than that observed in sugar maple (0.4 mmol/g lignin before HWE to 1.8 mmol/g lignin after HWE, more than four times increase [39].…”

Chemical Composition of Apricot Pit Shells and Effect of Hot-Water Extraction

“…In addition to removing xylans, hot-water extraction (HWE) results in an increase in cellulose and lignin content, an increase in porosity, a decreased ash content, and cleavage of acetyl groups. These modifications provide for more efficient delignification, enzymatic hydrolysis, and pyrolysis of hot-water extracted biomass as confirmed in recent studies on different hardwoods, including sugar maple, Paulownia species, and eucalyptus [17][18][19][20]. HWE also results in an increase in energy of combustion [21].…”

“…Solid extraction yield of hot water extracted APS (EAPS) was 59.23% (standard deviation 1.75), which indicates that slightly more than 40% of the APS total mass was extracted during HWE. HWE of wheat straw, sugar maple, and Paulownia species under the same conditions resulted in the dissolution of 29.0%-37.5% of total biomass [18,21].…”