A biorefinery approach for sequential extraction of commercial grade xylan and alkali lignin from alkali pretreated sugarcane tops hydrolysate

Abstract

Sequential extraction of xylan and lignin from alkali pretreated sugarcane tops (apSCT) hydrolysate was carried out. The xylan extracted from apSCT hydrolysate (apSCTx) was 26.5 g and the alkali lignin (apSCTal) was 8.5 g from 100 g of raw SCT. The composition analysis of apSCTx by high performance liquid chromatography showed 74% D-xylose, 15% D-glucuronic acid and 11% L-arabinose residues. The analysis of apSCTx by high performance size exclusion chromatography showed molecular size, ∼58 kDa. The first derivative of thermogravimetric analysis of apSCTx showed a Td (thermal degradation temperature) at 275ºC. The elemental (CHNS) analysis of apSCTx displayed the presence of only carbon and hydrogen. The absence of nitrogen and sulfur in the extracted apSCTx displayed that the xylan is pure and without the protein and lignin. The specific activity of recombinant clostridial endoxylanase (CtXyn11A) was 1823 ± 51 U/mg. Liquid Chromatography-Mass Spectroscopy and Thin-layer chromatography analyses of CtXyn11A hydrolyzed apSCTx displayed a series of linear xylooligosaccharides ranging between 2 and 5 degrees of polymerization. apSCTx can serve as a potential commercial substrate and also for xylooligosaccharides production. The characterization of apSCTal by Field-Emission Scanning Electron Microscopy showed the exposed spherical structures of alkali lignin. Fourier Transform Infrared spectroscopic analysis of apSCTal displayed the peaks corresponding to those obtained from commercial alkali lignin. CHNS analysis of apSCTal confirmed the absence of protein impurities. The first derivative of the thermogravimetric analysis of apSCTal showed Td at 362ºC, similar to the previously reported softwood lignin. The extracted apSCTal can be used as feedstock for the production of aromatic chemicals. The biorefinery approach of sequential extraction of apSCTx and apSCTal from alkali pretreated SCT hydrolysate waste can enhance the economics of the extraction process.