Rapid Processing of Abandoned Oil Palm Trunks into Sugars and Organic Acids by Sub-Critical Water

Biomass Deacetylation at Moderate Solid Loading Improves Sugar Recovery and Succinic Acid Production

Biomass deacetylation with alkali prior to dilute acid pretreatment can be a promising approach to reduce the toxicity of the resulting hydrolysates and improve microbial fermentation. In this study, the effect of mild alkaline treatment of oil palm trunk (OPT) biomass on succinic acid production was evaluated. Deacetylation was carried out under different conditions: NaOH loadings (1–5%, w/v) and reaction times (15–90 min) at 100 °C. Deacetylation using 1% (w/v) NaOH within 15 min was sufficient to achieve a high acetic acid removal of 5.8 g/L with minimal sugar loss. Deacetylation under this condition resulted in a total sugar concentration of 55.8 g/L (18.0 g/L xylose and 37.8 g/L glucose), which was 37% higher than that of non-deacetylated OPT. Subsequently, succinic acid production using Actinobacillus succinogenes was also improved by 42% and 13% in terms of productivity and yield, respectively, at 10% (w/v) solid loading. This further demonstrated that mild alkaline treatment prior to dilute acid pretreatment is a promising strategy to improve succinic acid production. This study provides a facile approach for reducing the most influential inhibitory effect of acetic acid, and it can be applied to the exploitation of lignocellulosic biomass resources for succinic acid, biofuels, and/or other biochemical co-production in the future.

Recovery of sugars and amino acids from brewers' spent grains using subcritical water hydrolysis in a single and two sequential semi-continuous flow-through reactors

This study evaluated the subcritical water hydrolysis (SWH) of brewer's spent grains (BSG) to obtain sugars and amino acids. The experimental conditions investigated the hydrolysis of BSG in a single flow-through reactor and in two sequential reactors operated in semi-continuous mode. The hydrolysis experiments were carried out for 120 min at 15 MPa, 5 mL water min^-1, at different temperatures (80 - 180 °C) and using an S/F of 20 and 10 g solvent g^-1 BSG, for the single and two sequential reactors, respectively. The highest monosaccharide yields were obtained at 180 °C in a single reactor (47.76 mg g^-1 carbohydrates). With these operational conditions, the hydrolysate presented xylose (0.477 mg mL^-1) and arabinose (1.039 mg mL^-1) as main sugars, while low contents of furfural (310.7 µg mL^-1), 5-hydroxymethylfurfural (<1 mg L^-1), and organic acids (0.343 mg mL^-1) were obtained. The yield of proteins at 180 °C in a process with a single reactor was 43.62 mg amino acids g^-1 proteins, where tryptophan (215.55 µg mL^-1), aspartic acid (123.35 µg mL^-1), valine (64.35 µg mL^-1), lysine (16.55 µg mL^-1), and glycine (16.1 µg mL^-1) were the main amino acids recovered in the hydrolysate. In conclusion, SWH pretreatment is a promising technology to recover bio-based compounds from BSG; however, further studies are still needed to increase the yield of bioproducts from lignocellulosic biomass to explore two sequential reactors.

Green products from herbal medicine wastes by subcritical water treatment

Herbal medicine wastes (HMWs) are byproducts of medicine factories, which are mainly landfilled for their environmental problems. Only bearing in mind the contamination and concerns caused by the COVID-19 pandemic and environmental emissions, the worth of herbal medicine wastes management and conversion to green products can be understood. In this work, subcritical water treatment was carried out batch-wise in a stainless tube reactor in the pressure range of 0.792-30.0 MPa, varying the temperature (127-327 °C) and time (1-60 min) of extraction. This resulted in new and green material sources, including organic acids, amino acids, and sugars. Amazingly, at very low extraction times (below 5 min) and high temperatures (above 277 °C), about 99% of HMWs were efficaciously converted to clean products by subcritical hydrothermal treatment. The results of hydrothermal extraction after 5 min indicated that at low temperatures (127-227 °C), the total organic carbon in the aqueous phase increased as the residual solid phase decreased, reaching a peak around 220 °C. Acetone soluble extracts or fat phase appeared above 227 °C and reached a maximum yield of 21% at 357 °C. Aspartic acid, threonine, and glycine were the primary amino acids; glycolic acid, formic acid, lactic acid, and acetic acid were obtained as the main organic acids, glucose, fructose, and cellobiose were substantial sugars produced from the aqueous phase after 5 min of hydrothermal subcritical hydrolysis extraction.

Hydrothermal liquefaction of wood chips under supercritical and subcritical water reaction conditions

This work describes batch-type hydrothermal liquefaction (HTL) treatments of conifer wood chips at 180–425 °C, under either air or nitrogen atmosphere. Such experiments allow efficient extraction of 5-hydroxymethyl furfural (HMF) and other valuable chemical substances, such as glycolic acid and acetic acid, from the lignocellulosic biomass. These compounds and their decomposition products present in the samples after HTL are analyzed and quantified using spectroscopic and chromatographic techniques. In general, the relatively higher-pressure nitrogen atmospheric condition is more suitable for obtaining the desired products, relative to the air atmosphere. Based on the quantitative results, the optimal temperatures for producing acetic acid, glycolic acid, and HMF are 300 °C, 250 °C, and 180 °C, respectively. The interesting relationship between HMF yield and temperature is also discussed; as the temperature increases, the yield of HMF first decreases and then increases. This phenomenon is explained by the exothermic nature of the HMF decomposition reaction, which is inhibited by excessively high temperature (in the range from 380 to 425 °C). At moderately high temperatures (optimized conditions; 300 °C), the generation rate of HMF exceeds its decomposition rate, resulting in a high yield of HMF. Based on the results of the experiments conducted in this study, the decomposition mechanism describing HTL treatment of wood chips can be elucidated. This study therefore provides guidance for future work involving HMF extraction from lignocellulosic biomass.