Hybridized enzymatic-chemocatalytic conversion of cellulosic biomass towards sustainable bioenergy

Abstract

An environmentally sustainable cellulase immobilized magnetic-photoactive iron (CIMPI) chemo- biocatalyst was synthesized at varying Fe3O4 concentrations for the valorization of waste banana pseudostem (WBP) into fermentable sugar (FS) employing an energy-efficient carbon-infrared irradiated (100 W, 750–1400 nm) vibrating batch reactor (CIIVBR). To improve the efficiency of WBP pretreatment for delignification, peracetic acid treatment was conducted in the CIIVBR. The pretreated WBP (PWBP) was saccharified in the CIIVBR using CIMPI as per L9 Taguchi experimental design (L9TED) to maximize the fermentable sugar yield (73.40%) corresponding to 60 min batch time, 50°C CIIVBR temperature,3:1 (w/w) water: PWBP, and 3.5 wt.%. CIMPI concentration. The optimal CIMPI was characterized using XRD, SEM, EDAX, TGA, FTIR, BET, UV-Vis, and PL analyses. CIMPI exhibited a bandgap of 3.01 eV, confirming its photoactive nature.CIMPI could be recovered conveniently due to its magnetic properties and even after recycling for 6th cycle, it could retain upto71% of its initial activity. The CIIVBR could save 80% energy compared to the conventional batch reactor (CBR)at the optimal condition, underscoring the superior energy-efficiency of the novel CIIVBR. The optimally produced FS, was subsequently converted into bio-ethanol using dry yeast viz. Saccharomyces cerevisiae yielding a maximum of 24.2g/l. Life cycle assessment (LCA) of the overall WBP photoactive-chemo-bioconversion process substantiated remarkable reduction in the Global Warming Potential (GWP100) by 37.5%, Acidification Potential (AcidP) by 18.36%, and Water Depletion Potential (WDP) by 27.27% compared to conventional process. Another novel chemo-biocatalyst, cellulase immobilized photoactive tin (CIPSn), was synthesized via the calcination of tin chloride to tin oxide and following the similar method. Characterization techniques including X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier- transform infrared spectroscopy (FTIR) were employed to analyze the structural and chemical properties of the CIPSn catalyst. Subsequently, pineapple leaves underwent pretreatment, and the saccharification process was conducted using CIPSn. Optimization of the saccharification process was achieved using L9 Taguchi experimental design (L9TED). The results indicated that a maximum fermentable sugar (FS) yield of 56.7% could be obtained using the optimized conditions. Additionally, the formation of other chemicals was observed during the saccharification process. This study presents a promising approach for the efficient conversion of biomass into fermentable sugars using a novel immobilized chemo-biocatalyst, CIPSn.