Comparison of ethanol production from corn cobs and switchgrass following a pyrolysis-based biorefinery approach

Abstract

BackgroundOne of the main obstacles in lignocellulosic ethanol production is the necessity of pretreatment and fractionation of the biomass feedstocks to produce sufficiently pure fermentable carbohydrates. In addition, the by-products (hemicellulose and lignin fraction) are of low value, when compared to dried distillers grains (DDG), the main by-product of corn ethanol. Fast pyrolysis is an alternative thermal conversion technology for processing biomass. It has recently been optimized to produce a stream rich in levoglucosan, a fermentable glucose precursor for biofuel production. Additional product streams might be of value to the petrochemical industry. However, biomass heterogeneity is known to impact the composition of pyrolytic product streams, as a complex mixture of aromatic compounds is recovered with the sugars, interfering with subsequent fermentation. The present study investigates the feasibility of fast pyrolysis to produce fermentable pyrolytic glucose from two abundant lignocellulosic biomass sources in Ontario, switchgrass (potential energy crop) and corn cobs (by-product of corn industry).ResultsDemineralization of biomass removes catalytic centers and increases the levoglucosan yield during pyrolysis. The ash content of biomass was significantly decreased by 82–90% in corn cobs when demineralized with acetic or nitric acid, respectively. In switchgrass, a reduction of only 50% for both acids could be achieved. Conversely, levoglucosan production increased 9- and 14-fold in corn cobs when rinsed with acetic and nitric acid, respectively, and increased 11-fold in switchgrass regardless of the acid used. After pyrolysis, different configurations for upgrading the pyrolytic sugars were assessed and the presence of potentially inhibitory compounds was approximated at each step as double integral of the UV spectrum signal of an HPLC assay. The results showed that water extraction followed by acid hydrolysis and solvent extraction was the best upgrading strategy. Ethanol yields achieved based on initial cellulose fraction were 27.8% in switchgrass and 27.0% in corn cobs.ConclusionsThis study demonstrates that ethanol production from switchgrass and corn cobs is possible following a combined thermochemical and fermentative biorefinery approach, with ethanol yields comparable to results in conventional pretreatments and fermentation processes. The feedstock-independent fermentation ability can easily be assessed with a simple assay.

An Assessment of Potential Resources for Biomass Energy in Nigeria

“…Maize residues have been converted to more efficient solid fuels through briquetting [132][133][134]. Ethanol has been produced from corn residues by [125,135,136]. Corn stover has also been used to produce saturated and monounsaturated aliphatic methyl ketones in the C 11 to C 15 (diesel) range [137,138].…”

Effect of Non-Structural Organics and Inorganics Constituents of Switchgrass During Pyrolysis

“…Levoglucosan is a useful starting chemical that can be converted into platform chemicals such as levulinic acid, levulinic esters, and 5-(hydroxymethyl) furfural (Yin et al, 2016). Levoglucosan can also serve as a precursor for bioethanol production through hydrolysis followed by fermentation (Luque et al, 2016). However, high severity pretreatment conditions, including high temperature, long reaction time, and high acid concentration, lead to the decomposition of the biomass matrix through the hydrolysis of cellulose and hemicellulose (Eom et al, 2011).…”

Levoglucosan: a promising platform molecule?

“…The efficiency of ethyl acetate was also pointed out by Lian et al 75 who found ethyl acetate to be the best solvent to extract phenolic compounds in the organic phase, leaving LG and acetic acid in the aqueous phase. The group of Luque et al 82 suggested that hydrolysis of bio-oil, followed by neutralization and extraction with ethyl acetate was the best system to generate glucose and remove the major amounts of inhibitors. Islam et al 83 obtained 8.62 g L −1 of ethanol from detoxified hydrolysate of waste cotton bio-oil.…”