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Pre-treating lignocellulosic biomass is a major technological challenge. Recycling the liquid fraction may reduce chemical inputs and water use but may have lower efficiency. Seven chemical pre-treatments of sugarcane bagasse were compared: four acids (sulfuric, citric, phosphoric, and oxalic), two alkaline (sodium and calcium hydroxides) and an oxidative (alkaline hydrogen peroxide). The liquid fractions resulting from these pre-treatments were reused up to five times. After each pre-treatment cycle, the solid fraction was hydrolyzed with Celluclast 1.5L enzyme in a 1:10 solid-liquid ratio. Sulfuric and oxalic acids solubilized 80% of the hemicellulose over the cycles. Sodium and calcium hydroxides and hydrogen peroxide removed lignin until the fourth cycle. About 70% of lignin were removed with alkaline hydrogen peroxide. This pre-treatment lead to the highest glucose release after the enzymatic hydrolysis, above 50% in the three cycles analyzed. The best efficiency in enzymatic hydrolysis followed the order H2O2-alkaline > NaOH > oxalic acid > phosphoric acid > H2SO4 > citric acid > Ca (OH)2. With the recycling, more than 62% in reagents used in the pre-treatment of sugarcane bagasse were saved, enabling an economy in the costs at this stage of the process.

Lignocellulosic biomass is the most abundant biological resource on the planet and has been extensively researched to produce cellulosic ethanol. However, there is a consensus that the presence of lignin hinders the biomass conversion. Lignin is often considered a villain in cellulosic ethanol production studies due to its adverse effects on cellulases and yeasts. Despite this, recent studies indicate that lignins can be transformed into useful inputs to produce cellulosic ethanol. These approaches aim to establish closed-loop biorefineries to improve economic metrics and reduce the environmental impact due to the substitution of products based on fossil sources. The present review addresses the successful cases in transforming lignin into chemicals and materials to increase cellulosic ethanol titers. A contextualization was first carried out, considering aspects of biomass characteristics and lignin valorization. The impact of lignin-based chemicals and materials in the pretreatment, detoxification, and enzymatic hydrolysis steps was discussed in detail. Economic aspects and future perspectives were also included in this review. These reports open a new point of view on lignin valorization and its integration with the cellulosic ethanol production chain.

Cactus pear biomass has the potential for bioethanol production in dry regions. However, its low solids concentration and pH variations may hinder the process of alcoholic fermentation. The objectives of this study were as follows: (1) to evaluate the effects of harvest time and season on biomass pH and dry matter concentration of cladodes of two cactus pear species commonly used as forage (Nopalea cochenillifera and Opuntia stricta); (2) to compare the hydrolysis of fresh and dried biomass (10% w v−1 solids); (3) to compare increasing periods of two temperatures (65 °C or 105 °C) to concentrate the biomass to 10% and 30% solids; and (4) to perform enzymatic hydrolysis and fermentation of biomass dried to 30% solids. Biomass pH ranged from 3.0 to 5.6, from early morning to late afternoon, with higher diurnal variation during the dry season, when their solids concentrations were higher than in the rainy season (12–16% × 7–10%). Hydrolyzed fresh and dried biomass had similar glucose, xylose, and galacturonic acid concentrations. Drying at 105 °C for 12 h was the best temperature and period to reach 30% of solids. The enzymatic hydrolysis of the biomass dried to 30% solids yielded 65.3 and 80.0 g of glucose L−1. After fermentations (33 °C; 8 h; Saccharomyces cerevisiae), ethanol was produced to 29.4 and 37.5 g L-1 from N. cochenillifera and O. stricta biomasses, respectively. Therefore, early morning during the dry season is the best moment to harvest the cladodes, whose biomass can be partially dried at 105 °C for 12 h to 30% solids load before being hydrolyzed and fermented for bioethanol production. This procedure reduces the time, energy, and inputs needed in the process.

Pre-treatment is one of main economic and technological challenges to render feasible the production of biofuels and chemical compounds from lignocellulosic biomass. Alkaline hydrogen peroxide (AHP) is the most used pre-treatment and recycling of its liquid fraction can help reduce production costs. The effects of four AHP concentrations (1, 3.5, 5 and 7.5% v/v) on the recycling performance of the liquid fraction of pre-treated corn stover was evaluated for five consecutive cycles. Delignification rates increased with increasing AHP concentrations in the first cycle: 15, 26, 43 and 76% with 1, 3.5, 5 and 7.5% v/v H2O2, respectively. In the following cycles, the rates decreased linearly reaching less than 40% in the last two recycles. These delignification rates and hemicellulose solubilization were corroborated by spectroscopic analyses with Fourier transformation showing reductions in lignin and hemicellulose absorbance and increases in crystallinity indices. Considering the low delignification rates in the last two cycles, the pre-treated biomasses obtained until the third cycle were submitted to enzymatic hydrolysis at 1:10 solid–liquid ratio. The delignification rates affected the efficiency of the enzymatic hydrolysis at all AHP concentrations and all recycles. The highest AHP concentration (7.5% v/v) was required to efficiently remove lignin and solubilize hemicellulose, maintaining cellulose conversion into glucose greater than 50% up to three recycles. Therefore, the technology of recycling the liquid solution of AHP pre-treatment is recommended with high initial concentrations (7.5% v/v).

This study we aimed to identify how the harvest period of the stems from 5 sweet sorghum cultivars influences the production of sugar and ethanol under rainfed conditions in the municipality of Itambe, state of Pernambuco. Subsequently we evaluated the ethanol production from juice and bagasse of the different cultivars. The field experiment was evaluated in a factorial arrangement with two factors (5 cultivars and 3 harvest periods) and fours replications. The fermentation experiments, pretreatment and enzymatic hydrolysis were delineated in a completely randomized design in quadruplicate. Data obtained for all variables evaluated were submitted to an Analysis of Variance and the means compared by the Tukey test at 5% of probability. Results showed that the harvest period influenced the total soluble solids, and the harvest period of soft dough was chosen for assessments of ethanol production of first and second generation. Ethanol production from juice differed among cultivars with the best performance by cultivar SF 15. Significant differences were observed for the chemical composition of bagasses between cultivars, but there where no difference in efficiencies of enzymatic hydrolysis. The average conversion of cellulose in glucose was 64.87%. The cultivars of sweet sorghum biomass developed and adapted for the Northeastern region of Brazil showed potential for ethanol production from the juice and bagasse.

Lignocellulosic biomass is a renewable and abundant resource that is suitable for the production of bio-based materials such as biofuels and chemical products. However, owing to its complex chemical composition, it requires a process that enhances the release of sugars. Pretreatment is an essential stage in increasing the efficiency of enzymatic hydrolysis of lignocellulosic biomass. The most widely used pretreatment methods operate at high temperatures (160–290 °C) and pressures (0.69 to 4.9 MPa) and generate biological growth inhibitors such as furfural and hydroxymethylfurfural (HMF). Thus, there has been a growing need to adopt new approaches for an effective pretreatment that operates at ambient temperature and pressure and reduces the generation of inhibitors. Among these methods, alkaline hydrogen peroxide (AHP) is notable because it is effective for a wide range of lignocellulosic biomass concentrations, and can provide a high degree of enzymatic hydrolysis efficiency. However, few results have been discussed in the literature. Given this, the aim of this study was to investigate the use of alkaline hydrogen peroxide (AHP) as an oxidative pretreatment agent to improve the efficiency of enzymatic hydrolysis for different types of biomass and examine the key areas of the pretreatment. Finally, there is a discussion of the challenges facing a large-scale application of this method.

The optimization of enzymatic hydrolysis, with high solids loading, of two species of cactus pear for bioethanol production was tested evaluating the influence of surfactant Tween 80 and pretreatment with H2O and H2SO4 (1% v/v) (50 °C, 150 rpm, 3 h). XRD and FTIR analyzes were performed. Afterwards, the influence of the factors cellulase (FPU g−1), pectinase (U g−1) and solids load (% w/v), on the hydrolysis of varieties (50 °C, 150 rpm, 48 h), and the fermentation of the optimal point (33 °C, 8 h) were evaluated. The pretreatments and the Tween 80 did not increase the hydrolysis yields and Rotacional Central Compound Design indicated that the pectinase factor was not significant. The best cellulase and solids load conditions were 10 FPU g−1 of biomass and 30% w/v for both species. The fermentation efficiency of hydrolysates for Nopalea cochenillifera and Opuntia ficus-indica were 76.3% and 82.8%, respectively, showing their potential for bioethanol production.

The aim of this study was to evaluate the influence of recycling the liquid fraction of pretreatment with alkaline hydrogen peroxide (AHP) on the hydrolysis of corn stover. Corn stover was pretreated in the traditional condition with 7.5% v/v H 2 O 2 . After pretreatment, the solids were separated from the liquid fraction and five successive reuse cycles of the liquid fraction were tested. The solid fraction from pretreatment in each recycle was submitted to enzymatic hydrolysis. The number of recycles had a linear negative effect (R 2 = 0.98) on biomass delignification efficiency and also affected negatively the enzymatic conversion efficiency. Despite the decrease in efficiency after each recycling step, reuse of the liquid fraction leads to reduction in water, H 2 O 2 and NaOH consumption of up to 57.6%, 59.6% and 57.6%, respectively. These findings point to an efficient recycling technology, which may reduce costs and save water.