Extraction, recovery, and characterization of lignin from industrial corn stover lignin cake

Lignin utilization in value-added co-products is an important component of enabling cellulosic biorefinery economics. However, aqueous dilute acid pretreatments yield lignins with limited applications due to significant modification during pretreatment, low solubility in many solvents, and high content of impurities (ash, insoluble polysaccharides). This work addresses these challenges and investigates the extraction and recovery of lignins from lignin-rich insoluble residue following dilute acid pretreatment and enzymatic hydrolysis of corn stover using three extraction approaches: ethanol organosolv, NaOH, and an ionic liquid. The recovered lignins exhibited recovery yields ranging from 30% for the ionic liquid, 44% for the most severe acid ethanol organosolv condition tested, and up to 86% for the most severe NaOH extraction condition. Finally, the fractional solubilities of different recovered lignins were assessed in a range of solvents and these solubilities were used to estimate distributions of Hildebrand and Hansen solubility parameters using a novel approach.

Effect of alkali treatment on enzymatic hydrolysis of p-toluenesulfonic acid pretreated bamboo substrates

The comprehensive separation and utilization of whole components of lignocellulosic materials has received extensive attention in present research. This study focused on the efficacy of alkali treatment for enzymatic saccharification of cellulose based on p-toluenesulfonic acid (p-TsOH) pretreated bamboo substrate. The results showed that the cellulose to glucose conversion yield was 94.69 % under optimized conditions of 0.4 g NaOH/g, 160 °C and 4 h (soaked), which after only 6 h enzymatic hydrolysis time. Alkali lignin recovery was 88.51 %, with potential for conversion to lignin derivatives. The yield of hemicellulose in the pretreated filtrate was 51.85 % after the 4th cycling reuse of p-TsOH. This work has borrowed the advantages of p-TsOH pretreatment of depolymerized hemicellulose from bamboo, combined with a low-priced weak alkali secondary treatment method, which can be effectively applied to the co-production of lignin, xylooligosaccharide, xylose and glucose, and the whole process is green and economically sustainable.

Aqueous ethanol organosolv process for the valorization of Brewer's spent grain (BSG)

Brewers spent grain (BSG), the main solid byproduct of brewing, is annually generated by ca 37 million tons worldwide, which due to limited application, mostly ends up in landfills. This study aims to separate BSG's fractions (lignin, cellulose, and hemicellulose) by ethanol organosolv pretreatment. Lignin-rich fractions were recovered using a two-step separation technique. The effects of temperature, retention time, and ethanol concentration on the quantity and quality of fractions were studied. The temperature considerably impacted the quality and quantity of obtained fractions, while other parameter effects greatly depended on the temperature. Substantial hemicellulose removal (90 %) along with lignin removal (56 %) and recovery (57 %) were obtained at 180 °C. The highest lignin purity (95 %) was obtained at the pretreatment conditions of 180 °C, 120 min, and 50 % ethanol concentration. This work provides an alternative route for BSG utilization, mitigating its environmental impact while enhancing the economy of a brewery.

A review on physico-chemical delignification as a pretreatment of lignocellulosic biomass for enhanced bioconversion

Effective pretreatment of lignocellulosic biomass (LCB) is one of the most important steps in biorefinery, ensuring the quality and commercial viability of the overall bioprocess. Lignin recalcitrance in LCB is a major bottleneck in biological conversion as the polymerization of lignin with hemicellulose hinders enzyme accessibility and further bioconversion to fuels and chemicals. Therefore, there is a need to delignify LCB to ease further bioprocessing. The efficiency of delignification, quality and quantity of the desired products, and generation of inhibitors depend upon the type of pretreatment employed. This review summarizes different single and integrated physicochemical pretreatments for delignification. Additionally, conditions required for effective delignification and the advantages and drawbacks of each method were evaluated. Advances in overcoming the recalcitrance of residual lignin to saccharification and the methods to recover lignin after delignification are also discussed. Efficient lignin recovery and valorization strategies provide an avenue for the sustainable lignocellulose biorefinery.

Organosolv and ionosolv processes for autohydrolyzed poplar fractionation: Lignin recovery and characterization

Biomass fractionation plays a major role in the search for competitive biorefineries, where the isolation and recovery of the three woody fractions is key. In this sense, we have used autohydrolyzed hemicellulose-free poplar as feedstock to compare two fractionation processes, organosolv and ionosolv, oriented to lignin recovery. The recovered lignins were then characterize by different techniques (NMR, GPC, TGA). Both treatments were tested at different temperatures to analyze temperature influence on lignin recovery and properties. The highest lignin recovery was obtained with the ionosolv process at 135 °C, reaching a solid yield of ~70%. Lignin characterization showed differences between both treatments. Lignins enriched in C-O linkages and G units were recovered with the organosolv process, where increasing temperature led to highly depolymerized lignins. However, lignins with higher C-C linkages and S units contents were obtained with the ionosolv process, producing more thermically stable lignins. In addition, increasing temperature caused lignin repolymerization when employing ionic liquids as solvents. Therefore, this work outlines the most important differences between ionosolv and organosolv processes for biomass fractionation, focusing on lignin recovery and its properties, which is the first step in order to valorize all biomass fractions.

Extraction of lignin, structural characterization and bioconversion of sugarcane bagasse after ionic liquid assisted pretreatment

The primary focus of this work was to recover lignin and investigate the structural changes in sugarcane bagasse after pretreatment with ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]oAc). 90% lignin recovery was achieved while bagasse was treated with [EMIM]oAc at 140 °C, 120 min reaction time and 1:20 bagasse to the ionic liquid ratio (w/w). The impact of ionic liquid pretreatment on bagasse was confirmed by qualitative analysis of untreated and pretreated bagasse. Scanning electron microscopy analysis exhibited the porous and irregular structure of bagasse after pretreatment. X-ray powder diffraction analysis verified a decrease in crystallinity as a result of the pretreatment process by showing a 14.7% reduction of Crystallinity index after ionic liquid treatment. The efficacy of [EMIM]oAc on bagasse treatment was also examined by enzymatic hydrolysis which manifested an increase in reducing sugar yield as a result of pretreatment. Maximum yield of 54.3% reducing sugar was obtained after 72 h enzymatic hydrolysis of pretreated bagasse. Recovered lignin was analyzed qualitatively. 1D NMR spectroscopy of lignin revealed the presence of essential functional groups whereas 2D NMR spectroscopy showed the dominance of etherified syringyl unit. Further ionic liquid recovery and reuse were substantiated by Gel permeation chromatography analysis of lignin. Weight average molecular weight (M_w) of lignin extracted by fresh [EMIM]oAc was obtained as 1769 g/mol (in the previous study) while lignin recovered by recycled [EMIM]oAc showed almost equal M_w 1765 g/mol in this study. Thus, the current investigation corroborated satisfactory performance of [EMIM]oAc in lignocellulose processing which further enhanced enzymatic hydrolysis in the subsequent step.

Comparison of sodium hydroxide and calcium hydroxide pretreatments on the enzymatic hydrolysis and lignin recovery of sugarcane bagasse

Sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)₂) respectively dissolved in water and 70% glycerol were applied to treat sugarcane bagasse (SCB) under the condition of 80°C for 2h. NaOH solutions could remove more lignin and obtain higher enzymatic hydrolysis efficiency of SCB than Ca(OH)₂ solutions. Compared with the alkali-water solutions, the enzymatic hydrolysis of SCB treated in NaOH-glycerol solution decreased, while that in Ca(OH)₂-glycerol solution increased. The lignin in NaOH-water pretreatment liquor could be easily recovered by calcium chloride (CaCl₂) at room temperature, but that in Ca(OH)₂-water pretreatment liquor couldn't. NaOH pretreatment is more suitable for facilitating enzymatic hydrolysis and lignin recovery of SCB than Ca(OH)₂ pretreatment.