The impacts of deacetylation prior to dilute acid pretreatment on the bioethanol process

Abstract

BackgroundDilute acid pretreatment is a promising pretreatment technology for the biochemical production of ethanol from lignocellulosic biomass. During dilute acid pretreatment, xylan depolymerizes to form soluble xylose monomers and oligomers. Because the xylan found in nature is highly acetylated, the formation of xylose monomers requires two steps: 1) cleavage of the xylosidic bonds, and 2) cleavage of covalently bonded acetyl ester groups.ResultsIn this study, we show that the latter may be the rate limiting step for xylose monomer formation. Furthermore, acetyl groups are also found to be a cause of biomass recalcitrance and hydrolyzate toxicity. While the removal of acetyl groups from native corn stover by alkaline de-esterification prior to pretreatment improves overall process yields, the exact impact is highly dependent on the corn stover variety in use. Xylose monomer yields in pretreatment generally increases by greater than 10%. Compared to pretreated corn stover controls, the deacetylated corn stover feedstock is approximately 20% more digestible after pretreatment. Finally, by lowering hydrolyzate toxicity, xylose utilization and ethanol yields are further improved during fermentation by roughly 10% and 7%, respectively. In this study, several varieties of corn stover lots were investigated to test the robustness of the deacetylation-pretreatment-saccharification-fermentation process.ConclusionsDeacetylation shows significant improvement on glucose and xylose yields during pretreatment and enzymatic hydrolysis, but it also reduces hydrolyzate toxicity during fermentation, thereby improving ethanol yields and titer. The magnitude of effect is dependent on the selected corn stover variety, with several varieties achieving improvements of greater than 10% xylose yield in pretreatment, 20% glucose yield in low solids enzymatic hydrolysis and 7% overall ethanol yield.

Development and characterization of a high-solids deacetylation process

“…This step, termed deacetylation, has been demonstrated to solubilize approximately 80 % of acetyl groups present in native corn stover, which can then be separated from the biomass prior to pretreatment though a wash process. Deacetylating corn stover prior to a typical dilute sulfuric acid pretreatment improved both glucose and xylose yields during enzymatic hydrolysis and ethanol yields relative to the control experiments using dilute-acid pretreatment of native corn stover [4].…”

“…While promising, previous work on the deacetylation process was conducted at low (~10 %) total solids loadings, and at fixed conditions (0.4 % w/w NaOH, 80 °C, 120 min) [4]. Thus, many questions have been left unanswered, including the relationship between sodium hydroxide loading and acetate and xylan solubilization, as well as the impact of temperature and residence time on the process efficacy.…”

“…Dilute-acid pretreatment experiments were carried out in a 4-L steam explosion reactor, the construction and operation of which has been previously described [4]. Prepared deacetylated and acid-impregnated corn stover feedstock were loaded into the reactor (500 g) and heated to the target temperature by direct steam injection.…”

Continuous succinic acid production from xylose by Actinobacillus succinogenes

“…Furthermore, current promising pretreatment technologies are able to generate xylose-rich hydrolysates from corn stover, a model lignocellulosic feedstock [29][30][31]. Therefore, it is necessary to determine the feasibility and limits of SA production on a clean xylose feed to establish a baseline for lignocellulosic fermentations, and to gain insight into the extent to which C5 carbohydrates can be utilised by A. succinogenes.…”

Phylogeny, classification and metagenomic bioprospecting of microbial acetyl xylan esterases

“…The potential role of AcXEs in enhanced lignocellulosic biomass degradation processes has been extensively reviewed [3,5,6,9,19,[151][152][153][154][155]. While alkaline and certain non-alkaline pretreatment methods in current use remove most acetyl groups from lignocellulosic biomass, they each have their drawbacks based on factors such as type of lignocellulosic feedstock, temperature requirements, intensity of pre-treatment, detoxification requirements and economic viability [154][155][156]. No single pre-treatment method can be considered to be ideal for deacetylation of xylans.…”