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With growing awareness of a circular economy, it is necessary to utilize all lignocellulose biomass components as a resource to maintain sustainability. We have selectively targeted the one-step conversion of hemicellulose in sugarcane bagasse to xylooligosaccharides (XOS), which are useful dietary supplements, while keeping the cellulose and lignin relatively intact. In addition to the circular economy and green processing chemistry, we pursue plasma treatment of carbon materials as a global effort to produce metal-free carbon-based catalysts. Herein, activated carbon (AC) was subjected to two different treatments: plasma irradiation to create a porous honeycomb structure and redistribute surface oxygenate functional groups (phenolics –OH), lactonics, and (–COOH) and acid impregnation with HNO3 to enhance the overall acidic functional groups of the carbon, especially the –COOH groups. The functionalized AC was effective to selectively depolymerize sugarcane bagasse hemicellulose to XOS in water as a solvent. High XOS yields of 50.0% (composed of xylobiose (14.1%), xylotriose (11.9%), xylotetraose (8.8%), xylopentaose (9.1%) and xylohexaose (6.0%)), and 15% xylose were obtained. No undesirable sugar degradation products – furans – were detected. Thus, we propose that the tandem sequence of plasma and acid modification of AC is a facile one-step new method to depolymerize hemicellulose from lignocellulosic biomass.

We have examined a sustainable biorefinery process for the conversion of cotton gin trash (CGT), a waste from the cotton industry to multiple high value products. Herein, we found CGT native lignin to have unique features as it not only contains the p-hydroxyphenyl (H), guaiacol (G) and syringol (S) units, but structures of flavonoids, tyrosine, and phenylalanine associated with it. We have used the lignin-first approach to exploit its features in CGT and depolymerize it using argon gas and ethanol over Pd/C. The results show that 50% of the bio-aromatics is trans-isoeugenol, a precursor to produce vanillin. The cleavage of N-compounds from CGT during the fractionation process follows similar path as the rate of formation of the bio-aromatics. CGT impurities were shown to affect the reusability of the Pd/C catalyst. The fractionated cellulose-rich portion of CGT was converted to 39 mol% (80% purity) of 5-chloromethylfurfural (CMF), and a solid fuel which has a higher heating value of 20 MJ kg−1. The liquid extract, removed prior to CGT processing, was hydrogenated to produce C13–C17 liquid hydrocarbons, and the solid extract rich in nutrients is suitable for crops and plants growth.

Bio-oil produced from the hydrothermal liquefaction (HTL) of biomass is unstable and cannot be transported over long distances to a refinery for upgrading to transportation fuel. This study examined the effect of the liquefaction solvent on the stability of bio-oils derived from the HTL of sugarcane bagasse. The accelerated aging test (0–8 days at 80 °C) was used to assess the stability of these oils with the aid of indicators such as water content, molecular weight range, functional groups present, phase separation, thermal stability, and the amount of residue after thermal analysis of the oils. The HTL solvent mixture of ethanol/water was found to produce the most stable bio-oil when compared to crude glycerol/water or water on its own. The light oils fractionated by solvent extraction were more stable than their corresponding bio-oils. The higher heating values (HHVs) of the light oils during the agiging process were relatively stable and were between 33 and 35 MJ/kg. The maximum boiling temperature of the first peak in the DTG thermogram of the aged light oil derived from ethanol/water is 147 °C (cf. diesel of 157 °C), while that of crude glycerol/water light oil is up to 190 °C. The stabilities of the oils derived from either ethanol or crude glycerol are related to alkylation, esterification, and acetalization reactions. This study has demonstrated that the HTL of sugarcane bagasse in the presence of ethanol/water produces oils of good quality that have long shelf-lives and have been projected to be stored for up to 8 years with minor compositional and structural changes.

This paper investigates the carbonization of cotton gin trash (CGT) into carbon structures shaped under the influence of different operating conditions including the impact of endogenous fatty acids impurities present in CGT. As expected, both KOH activation and high carbonization temperature increase the material surface area and porosity. Furan and arene groups are formed from 400 °C to 800 °C but the proportion of the furan groups are highest at 600 °C. This is due to the conversion of the fatty acids in CGT to furan units. XRD data reveals the presence of three aromatic layers at 400 °C, followed by structural rearrangement to the formation of five stacks aromatic layers at 800 °C consisting mainly of protonated and non-protonated condensed arene groups. Interestingly, a reduction in the number of aromatic structures is observed if no acid pretreatment of CGT to remove inorganic impurities is conducted prior to pyrolysis to 600 °C. Two potential applications of the synthesised carbons are shown; one for the formation of 5-hydroxymethylfurfural (80%) from fructose, which compares favorably to other porous carbon materials produced under harsher conditions, and another derived CGT carbon material which shows a good uptake of hydrogen for storage.

A lactic acid/chlorine chloride-based deep eutectic solvent (DES) was used for the extraction of high-purity lignin (up to 94.7 %) in high yield (up to 75 %) from the hydrolysis/fermentation residue corn stover hydrolysate (CSH), which was generated from a pilot-plant-scale biorefinery. A range of extraction conditions were investigated, which involved varying reaction temperature, time, and DES composition. The relationship between lignin yield, purity, and structural characteristics with DES treatment conditions was determined. The extraction of high-purity lignin from hydrolysis/fermentation residues presents a promising approach for enhancing the economic feasibility of a lignocellulose biorefinery. It was also determined that DES extraction can produce lignin with a controlled range of molecular weight and functional group content

In the time of rapidly depleting petroleum resources, worldwide food shortages, and solid waste problems, it is imperative to promote dedicated research into using an appropriate pretreatment technique utilizing regeneratable raw materials such as lignocellulosic biomass. However, not all pretreatment techniques are viable alternatives for industrial practice. Pretreatment is an important step to upgrade different kinds of lignocellulosic biomass into more valuable products, including biofuels and bio-based industrial chemicals. Most of the pretreatment techniques have their limitations or weaknesses, including high operational costs and temperature, toxicity and corrosiveness to the instrument, etc., while, some other pretreatment methods such as biological and plasma pretreatment are green procedures that can also be used to alter the physical and chemical properties of lignocellulosic materials. Although our present understanding is still low and not much research has been done to guarantee which pretreatment method is the reliable alternative, the combination of different pretreatment methods could be a good strategy to overcome the limitations of each approach. This review presents an overview of different pretreatment methods of lignocellulosic biomass to increase the rate and the degree of cellulose hydrolysis and subsequent processing steps as well as future perspectives.