Hydrothermal liquefaction of lignocellulose for value-added products: Mechanism, parameter and production application

Hydrothermal formation mechanism of lignocellulose-derived carbon dots: From sawdust to carbon nanomaterials with blue fluorescence

The conversion of lignocellulose into fluorescent lignocellulose-derived carbon dots (LCDs) via hydrothermal carbonization (HTC) has attracted significant attention. However, the degradation pathways of lignocellulose components, their contributions to LCDs formation, and the temporal evolution of LCDs' formation remain unclear. Given that HTC conditions influence LCDs' structure and fluorescence properties, an orthogonal design was applied to investigate these effects. Results show that HTC temperature and feedstock type are two key factors due to the diverse hydrolysis behaviors of components. A temperature of 190 °C effectively balances fluorescence clusters' generation and consumption, and the softwood, Pinus sylvestris var. mongolic, with its high hemicellulose and G-type lignin content, is an ideal feedstock. During HTC, LCDs are formed with a carbon core of conjugated cyclic structures from cross-linked, polymerized, and carbonized carbocyclic compounds, and a shell of polymer clusters from aliphatic hydrolysates. Here, hemicellulose and amorphous cellulose contribute to aliphatic and carbocyclic compounds, imparting hydrophilicity and fluorescence, while lignin supplies carbocyclic compounds essential for fluorescent carbon cores. As conjugation increased, the maximum fluorescence quantum yield (FQY) of LCDs reached 3.4 %. This work offers a theoretical basis for feedstock selection and explains the temporal formation process of LCDs, which is of great significance for the high-value utilization of lignocellulosic biomass and the regulation of LCDs' structures and optical properties.

Sequential hydrothermal liquefaction of lignocellulose-rich livestock manure: A new perspective on enhancing the production and quality of low-phenolic biocrude

The treatment and valorization of bulk livestock manure rich in lignocellulose demand efficient processing techniques. Hydrothermal liquefaction (HTL) has emerged as a promising approach for waste-to-energy conversion, effectively transforming lignocellulosic biomass into renewable biocrude. However, the advances in the utilization of HTL-derived biocrude have been hindered by its poor oil quality due to several factors including high phenolic compound content. This study focuses on enhancing the production and quality of low-phenolic biocrude via a sequential HTL process. The results revealed that sequential HTL achieved a high biocrude yield of 59.9%, with a concurrent reduction in phenolic content to 4.2%. This represents an 84.2% decrease in phenolic content compared to biocrude derived from direct HTL (280 ℃), achieving a tradeoff between biocrude yield and quality. Notably, GC-MS revealed that the biocrude produced through sequential HTL was enriched with fatty acids and esters accounting for 80.5%, contributing to the production of hydrocarbon fuels. Additionally, FT-ICR MS revealed that sequential HTL enhanced the biocrude quality and encouraged the production of light fuels. The petroleum fractionation analysis further revealed that sequential HTL-derived biocrude was more desirable in the downstream petroleum refining industry. The model compounds experiments revealed that phenols were likely to to be transferred to the oil phase at relatively high temperatures. Overall, it is the first study to elucidate the phenols removal mechanism and quality improvement of biocrude through the sequential HTL, demonstrating its potential for sustainable disposal and valorization of waste lignocellulosic biomass, and contributing to the development of renewable energy.

Hydrothermal liquefaction: Exploring biomass/plastic synergies and pathways for enhanced biofuel production

The worsening environmental conditions, diminishing fossil fuel reserves, and increasing waste accumulation have redirected the attention of researchers and scientists towards the exploration of sustainable and non-exhaustive energy sources, as well as waste mitigation techniques. Among the various thermochemical technologies producing biofuels, hydrothermal liquefaction stands out as an effective technique for the simultaneous waste valorization and the production of sustainable biofuels. Under optimal conditions, hydrothermal liquefaction converts 70-80 % of feedstock energy into bio-oil, representing approximately 30-50 % of the feedstock's original mass. The review meticulously discusses and summarizes the process and reaction mechanism along with the influence of various factors on the hydrothermal liquefaction process, including the types of feedstocks (lignocellulosic biomass and plastic waste), operating conditions (temperature, residence time, pressure, substrate-to-water ratio, particle size, and heating rate), and catalyst types. According to the data documented in existing literature, the preferred temperature and residence time for attaining maximum bio-oil yields are reported to be within the range of 260-340 °C and 10-30 min for biomass, and 300-425 °C and 15-30 min for plastics. This review highlights the critical challenges in developing and scaling up the HTL process, proposing potential solutions to enhance feedstock conversion into value-added products. Additionally, it emphasizes the significance of understanding the chemical composition and synergistic interactions between lignocellulosic biomass and plastic waste to optimize product yields and enhance the overall process efficiency. Moreover, it discusses the different products of the hydrothermal liquefaction process-bio-oil, biochar, aqueous phase, and gaseous fraction-and their potential applications, while proposing techniques to upgrade the quality of biocrude.

Exploring the catalytic hydrothermal liquefaction of Namibian encroacher bush

An urgent ecological issue is the threat posed by invasive species, which are becoming more widespread especially in Africa. These encroachments damage ecosystems, pose a threat to biodiversity, and outcompete local plants and animals. This article focuses on converting Acacia Mellifera from Namibia, commonly known as encroacher bush (EB) into high-quality drop-in intermediates for the chemical and transport industry via hydrothermal liquefaction (HTL). HTL tackles the growing need for sustainable energy carriers while simultaneously halting the spread of the invasive species. A surface response methodology was used to optimize the HTL process for the following operational conditions: temperature (250-340 °C), residence time (5-60 min) and catalyst loading (0-10 wt%). The catalyst of choice was determined after evaluating the energy recovery (ER) of four different catalysts (Zeolite, La2O3, Hydrotalcite, Ni/SiO2-Al2O3) under the same HTL operational conditions. The results indicate that the addition of hydrotalcite results in high yields of bio-crude oil (13-28 wt%), without compromising the high heating value (HHV, 26-31 MJ/kg), water content (0.47 wt%) or increasing the content of oxygenated compounds compared to the non-catalytic experiment. For the experimental conditions tested, we observed a global maximum in conversion in the 330 °C and 30 min range. Our findings indicate that the most significant factor on the conversion of EB into bio-crude oil was temperature, followed by the catalyst loading. Furthermore, biochars produced at 330 °C and 30 min show potential as solid biofuels with HHVs up to 28.30 MJ/kg.

Coupling hydrothermal liquefaction and anaerobic digestion for waste biomass valorization: A review in context of circular economy

In light of the substantial global production of biomass waste, effective waste management and energy recovery solutions are of paramount importance. Hydrothermal liquefaction (HTL) and anaerobic digestion (AD) have emerged as innovative techniques for converting biomass waste into valuable resources. Their integration creates a synergistic framework that mitigates inherent limitations, leading to improved efficiency, enhanced product quality, and the comprehensive utilization of biomass. This review paper investigates the integration of HTL and AD, highlighting its significance and potential benefits as well as the optimal sequencing (HTL followed by AD and AD followed by HTL). The review encompasses experimental procedures, factors influencing both sequencing options, energy recovery characterizations, final product outcomes, as well as toxicological assessments and discussions on reduction. Additionally, it delves into the transition towards a circular bioeconomy and discusses the challenges and opportunities intrinsic to these processes. The findings presented in this review offer valuable insights to shape future research in this evolving field.

Lignocellulosic biomass fertilizers: Production, characterization, and agri-applications

The growing focus on sustainable agriculture and optimal resource utilization has spurred investigations into lignocellulosic biomass as a potential source for producing environmentally friendly fertilizers. This paper reviews recent advancements in the production and application of innovative fertilizers derived from lignocellulose. It highlights potential in enhancing agricultural productivity and reducing environmental impacts such as carbon footprint and water pollution. The paper outlines various methods for conversion, highlighting the unique advantages of chemical, enzymatic, and microbiological processes, for converting lignocellulosic biomass into nutrient-rich fertilizers. The study compares the efficacy of lignocellulosic fertilizers to traditional fertilizers in promoting crop growth, enhancing soil health, and reducing nutrient losses. The results demonstrate the potential of lignocellulosic biomass-derived fertilizers in promoting resource efficiency and sustainable agriculture. While this research significantly contributes to the existing body of knowledge, further studies on long-term impacts and scalability are recommended for the development of innovative and sustainable agricultural practices.

Effects of Fe3+ on Hydrothermal Humification of Agricultural Biomass

Hydrothermal humification technology for the preparation of artificial humic matters provides a new strategy, greatly promoting the natural maturation process. Iron, as a common metal, is widely used in the conversion of waste biomass; however, the influence of Fe3+ on hydrothermal humification remains unknown. In this study, FeCl3 is used to catalyze the hydrothermal humification of corn straw, and the influence of Fe3+ on the hydrothermal humification is explored by a series of characterization techniques. Results show that Fe3+ as the catalyst can promote the decomposition of corn straw, shorten the reaction time from 24 h to 6 h, and increase the yield from 6.77 % to 14.08 %. However, artificial humic acid (A-HA) obtained from Fe3+ -catalysis hydrothermal humification contains more unstable carbon and low amount of aromatics, resulting in a significantly decreased stability of the artificial humic acid. These results provide theoretical guidance for regulating the structure and properties of artificial humic acid to meet various maintenance needs.

Semi-continuous hydrothermal processing of pine sawdust for integrated production of fuels precursors and platform chemicals

This research reports data for the integrated obtaining of fermentable sugars (FSs), bio-oil (BO), and hydro-char (HC) - all fuel precursors - as well as platform chemicals (PCs - acetic, formic, and levulinic acid, besides furfural, and hydroxymethylfurfural) through semi-continuous hydrothermal processing of sawdust from pine wood. The influence of temperature (260, 300, and 340 °C) and the water-to-biomass ratio (25 and 50 g H2O (g biomass)-1) were the parameters considered to evaluate the mass yields, kinetic profiles, and BO properties. For FSs (and PCs), a detailed analysis considering the kinetic profiles of obtaining cellobiose, glucose, xylose, and arabinose is presented. For the conditions evaluated, a distinct behavior concerning the process parameters was observed, where 7.11 and 9.28 g (100 g biomass)-1 of FSs and PCs were synergistically obtained, respectively, after 30 min, 20 MPa, 260 °C, and 50 g H2O (g biomass)-1. Contextually, 17.59 g (100 g biomass)-1 of BO was obtained at 340 °C and the same water/biomass ratio. FTIR analysis of the BO samples suggested the presence of aldehydes, carboxylic acids, ketones, hydrocarbons, ethers as well as aromatic, alcohols, and nitrogenous compounds. Similar HC yields were achieved among the conditions analyzed, where 24.68 g (100 g biomass)-1 were obtained at 340 °C and 50 g H2O (g biomass)-1 for a higher heating value of 29.14 MJ kg-1 (1.5 times higher than the in natura biomass).

Pulp-paper industry sludge waste biorefinery for sustainable energy and value-added products development: A systematic valorization towards waste management

The pulp-paper industry is one of the main industrial sectors that produce massive amounts of residual sludge, constituting an enormous environmental burden for the industries. Traditional sludge management practices, such as landfilling and incineration, are restricted due to mounting environmental pressures, complex regulatory frameworks, land availability, high costs, and public opinion. Valorization of pulp-paper industry sludge (PPS) to produce high-value products is a promising substitute for traditional sludge management practices, promoting their reuse and recycling. Valorization of PPIS for biorefinery beneficiation includes biomethane, biohydrogen, bioethanol, biobutanol, and biodiesel production for renewable energy generation. Additionally, the various thermo-chemical technologies can be utilized to synthesize bio-oil, hydrochar, biochar, adsorbent, and activated carbon, signifying potential for value-added generation. Moreover, PPIS can be recycled as a byproduct by incorporating it into nanocomposites, cardboard, and construction materials development. This paper aims to deliver a comprehensive overview of PPIS management approaches and thermo-chemical technologies utilized for the development of platform chemicals in industry. Substitute uses of PPIS, such as making building materials, developing supercapacitors, and making cardboard, are also discussed. In addition, this article deeply discusses recent developments in biotechnologies for valorizing PPIS to yield an array of valuable products, such as biofuels, lactic acids, cellulose, nanocellulose, and so on. This review serves as a roadmap for future research endeavors in the effective handling of PPIS.

Hydrothermal liquefaction of municipal sludge and its products applications

Hydrothermal liquefaction (HTL) is an effective medium-temperature, high-pressure thermochemical process to dispose municipal sludge (MS), and biocrude (a crude bio-oil) is its main product. Many efforts are continued extensively to improve conversion efficiency and to promote industrial application of this technology. This work focuses on critical influencing factors (e.g., reaction temperature, residence time, atmosphere, solvent, catalyst, and pretreatment) and fundamental transformation mechanisms of main components (i.e., lipids, proteins, and carbohydrates) in MS HTL. It also analyzes migration behavior of heavy metals during MS HTL, which can provide a reference for subsequent recovery of nutrients from HTL products. Moreover, the applications of MS HTL products are systematically expounded, and potential challenges and opportunities are highlighted as well. It is necessary to develop advanced methods of catalyst recovery and innovative biocrude upgrading methods so as to reduce HTL investment and operating costs. Reusing aqueous phase and solid phase products as reaction medium and catalyst carrier separately after MS HTL is feasible to realize resource utilization of MS. This information can provide valuable guidance to promote MS HTL industrialization.

Exploitation of lignocellulosic-based biomass biorefinery: A critical review of renewable bioresource, sustainability and economic views

Urbanization has driven the demand for fossil fuels, however, the overly exploited resource has caused severe damage on environmental pollution. Biorefining using abundant lignocellulosic biomass is an emerging strategy to replace traditional fossil fuels. Value-added lignin biomass reduces the waste pollution in the environment and provides a green path of conversion to obtain renewable resources. The technology is designed to produce biofuels, biomaterials and value-added products from lignocellulosic biomass. In the biorefinery process, the pretreatment step is required to reduce the recalcitrant structure of lignocellulose biomass and improve the enzymatic digestion. There is still a gap in the full and deep understanding of the biorefinery process including the pretreatment process, thus it is necessary to provide optimized and adapted biorefinery solutions to cope with the conversion process in different biorefineries to further provide efficiency in industrial applications. Current research progress on value-added applications of lignocellulosic biomass still stagnates at the biofuel phase, and there is a lack of comprehensive discussion of emerging potential applications. This review article explores the advantages, disadvantages and properties of pretreatment methods including physical, chemical, physico-chemical and biological pretreatment methods. Value-added bioproducts produced from lignocellulosic biomass were comprehensively evaluated in terms of encompassing biochemical products , cosmetics, pharmaceuticals, potent functional materials from cellulose and lignin, waste management alternatives, multifunctional carbon materials and eco-friendly products. This review article critically identifies research-related to sustainability of lignocellulosic biomass to promote the development of green chemistry and to facilitate the refinement of high-value, environmentally-friendly materials. In addition, to align commercialized practice of lignocellulosic biomass application towards the 21st century, this paper provides a comprehensive analysis of lignocellulosic biomass biorefining and the utilization of biorefinery green technologies is further analyzed as being considered sustainable, including having potential benefits in terms of environmental, economic and social impacts. This facilitates sustainability options for biorefinery processes by providing policy makers with intuitive evaluation and guidance.

Hydrothermal liquefaction of lignocellulosic biomass with potassium phosphate and iron and their binary mixture: A comprehensive investigation on the yields and compositions of biocrude and solid residue

Hydrothermal liquefaction of corn, soybean, rice and wheat straws with K3PO4, Fe and Fe + K3PO4 at 320 °C for 30 min was examined. The addition of K3PO4 led to the highest biocrude yields from hydrothermal liquefaction of rice straws (39.20 wt%). Particularly, the biocrude yields from K3PO4-catalyzed hydrothermal liquefaction of corn and rice straws were ∼ 10 wt% higher than those from non-catalytic run (19.4 and 27.8 wt%). Catalytic hydrothermal liquefaction with K3PO4 had minimal impact on the elemental compositions of biocrudes and solid residue. Furthermore, K3PO4 promoted the enrichment of low-boiling components in biocrudes by 2.02 wt%. for hydrothermal liquefaction of wheat straw. Moreover, the incorporation of K3PO4 induces the occurrence of dense porous structure on the surface of solid residue, making it highly suitable as an adsorbent or catalyst carrier. Finally, potential reaction network and mechanisms of catalytic hydrothermal liquefaction of straw have been proposed and discussed detailly.

Treatment of industrial ferric sludge through a facile acid-assisted hydrothermal reaction: Focusing on dry mass reduction and hydrochar recyclability performance

Large amounts of Fenton sludge and waste activated sludge (WAS) are mixed as ferric sludge (FS) in most industrial wastewater treatment plants. The treatment of such waste represents a challenge and quantity-dependent cost, so that a reliable way for FS waste reduction is required. In this study, we develop a facile acid-assisted hydrothermal treatment (HT) for the cost-efficient treatment of hazardous FS waste. Sulfuric acid was dosed at 0.25 mL/g dry solid (DS) to the HT process, which significantly increased the total solid mass reduction (TMR) by 25.1 % and dry mass reduction (DMR) by 104.4 %. The participation of sulfuric acid during the HT process changed the HT reaction pathway from dehydration to demethylation based on the analysis of the derivative thermogravimetric and Van Krevelen diagram. The addition of sulfuric acid improved the release of Fe from FS by 52.9 %, which contributed to the DMR. During the acid-assisted HT, Fe(III) was effectively reduced to Fe(II) within the produced hydrochar, which can be recycled for the Fenton reaction during the degradation of actual industrial wastewater such as pharmaceutical wastewater. Moreover, Sulfuric acid facilitated the generation of sulfonated hydrochar, which was efficient as an adsorbent for the complete removal of some metals such as Cu(II) - cation metal (98.8 %) and Cr(VI) - anion metal (99.9 %). This study firstly provides a novel and reliable approach for hazardous FS reduction and pointed out the recycling of hydrochar as the supplement for the Fenton reaction and adsorbents for some hazardous heavy metals.

Advances in process design, techno-economic assessment and environmental aspects for hydrothermal pretreatment in the fractionation of biomass under biorefinery concept

The development and sustainability of second-generation biorefineries are essential for the production of high added value compounds and biofuels and their application at the industrial level. Pretreatment is one of the most critical stages in biomass processing. In this specific case, hydrothermal pretreatments (liquid hot water [LHW] and steam explosion [SE]) are considered the most promising process for the fractionation, hydrolysis and structural modifications of biomass. This review focuses on architecture of the plant cell wall and composition, fundamentals of hydrothermal pretreatment, process design integration, the techno-economic parameters of the solubilization of lignocellulosic biomass (LCB) focused on the operational costs for large-scale process implementation and the global manufacturing cost. In addition, profitability indicators are evaluated between the value-added products generated during hydrothermal pretreatment, advocating a biorefinery implementation in a circular economy framework. In addition, this review includes an analysis of environmental aspects of sustainability involved in hydrothermal pretreatments.

Value addition through biohydrogen production and integrated processes from hydrothermal pretreatment of lignocellulosic biomass

Bioenergy production is the most sought-after topics at the crunch of energy demand, climate change and waste generation. In view of this, lignocellulosic biomass (LCB) rich in complex organic content has the potential to produce bioenergy in several forms following the pretreatment. Hydrothermal pretreatment that employs high temperatures and pressures is gaining momentum for organics recovery from LCB which can attain value-addition. Diverse bioprocesses such as dark fermentation, anaerobic digestion etc. can be utilized following the pretreatment of LCB which can result in biohydrogen and biomethane production. Besides, integration approaches for LCB utilization that enhance process efficiency and additional products such as biohythane production as well as application of solid residue obtained after LCB pretreatment were discussed. Importance of hydrothermal pretreatment as one of the suitable strategies for LCB utilization is emphasized suggesting its future potential in large scale energy recovery.

Hydrothermal Liquefaction of Lignocellulosic and Protein-Containing Biomass: A Comprehensive Review

Hydrothermal liquefaction (HTL) is a thermochemical depolymerization technology, also known as hydrous pyrolysis, that transforms wet biomass into biocrude and valuable chemicals at a moderate temperature (usually 200–400 °C) and high pressure (typically 10–25 MPa). In HTL, water acts as a key reactant in HTL activities. Several properties of water are substantially altered as the reaction state gets closer to the critical point of water, which can result in quick, uniform, and effective reactions. The current review covers the HTL of various feedstocks, especially lignocellulosic and high protein-containing feeds with their in-depth information of the chemical reaction mechanisms involved in the HTL. Further, this review gives insight and knowledge about the influencing factors such as biomass pretreatment, process mode, process conditions, etc., which could affect the efficiency of the hydrothermal process and biocrude productivity. In addition, the latest trends, and emerging challenges to HTL are discussed with suitable recommendations.

A review on potential of green solvents in hydrothermal liquefaction (HTL) of lignin

One of the greatest challenges in biorefinery is to reduce biomass' recalcitrance and enable valorization of lignin into higher value compounds. Likewise, green solvents and hydrothermal liquefaction (HTL) with feasible economic viability, functionality, and environmental sustainability have been widely introduced in extraction and conversion of lignin. This review starts with the underscore of disadvantages and limitations of conventional pretreatment approaches and role of green solvents in lignin extraction. Subsequently, the effect of process parameters along with the reaction mechanisms and kinetics on conversion of lignin through HTL were comprehensively reviewed. The limitations of green solvents in extraction and HTL of lignin from biomass were discussed based on the current advancements of the field and future research scopes were also proposed. More details info on HTL of biomass derived lignin which avoid the energy-intensive drying procedures are crucial for the accelerated development and deployment of the advanced lignin biorefinery.

Highly Efficient Transfer Hydrogenation of Biomass-Derived Furfural to Furfuryl Alcohol over Mesoporous Zr-Containing Hybrids with 5-Sulfosalicylic Acid as a Ligand

The catalytic transfer hydrogenation of biomass-derived furfural to furfuryl alcohol under mild conditions is an attractive topic in biorefinery. Herein, mesoporous Zr-containing hybrids (Zr-hybrids) with a high surface area (281.9−291.3 m2/g) and large pore volume (0.49−0.74 cm3/g) were prepared using the biomass-derived 5-sulfosalicylic acid as a ligand, and they were proven to be highly efficient for the Meerwein−Ponndorf−Verley reduction of furfural to furfuryl alcohol at 110 °C, with the highest furfuryl alcohol yield reaching up to 97.8%. Characterizations demonstrated that sulfonic and carboxyl groups in 5-sulfosalicylic acid molecules were coordinated with zirconium ions, making zirconium ions fully dispersed, thus leading to the formation of very fine zirconia particles with the diameter of <2 nm in mesoporous Zr-hybrids. The interaction between the 5-sulfosalicylic acid ligands and zirconium ions endowed mesoporous Zr-hybrids with relatively higher acid strength but lower base strength, which was beneficial for the selective reduction of furfural to furfuryl alcohol. A recycling study was performed over a certain mesoporous Zr-hybrid, namely meso-Zr-SA15, demonstrating that the yield and selectivity of furfuryl alcohol remained almost unchanged during the five consecutive reaction cycles. This study provides an optional method to prepare hybrid catalysts for biomass refining by using biomass-derived feedstock.

Study on the Sugar-Producing Effect of High-Temperature Anaerobic Straw Biosaccharification Strain

The utilization of straw waste cellulose will be beneficial by economic, social, and environmental means. The present study sought to screen the high-efficiency cellulose sugar-producing strain from corn straw. The 16S high-throughput sequencing method and the combination of morphological, physiological, and biochemical characteristics of the strain confirmed the strain to be Clostridium thermocellum, which was named Clostridium thermocellum FC811. Moreover, the single factor experiment was conducted to investigate the effect of environmental factors on saccharification efficiency. The optimal saccharification conditions of cellulose saccharification of FC811 strain selected through response surface analysis were as follows: temperature of 58.9 °C, pH of 7.21, culture time of 6.60 d, substrate concentration of 5.01 g/L, and yeast powder concentration of 2.15 g/L. The soluble sugar yield was 3.11 g/L, and the conversion rate of reducing sugar was 62.2%. This study will provide a reference for resource and energy utilization of straw materials, simultaneous fermentation of sugar and hydrogen production, and their large-scale production and application.

Feasibility of Old Bark and Wood Waste Recycling

The pulp and paper industry leads to the formation of significant amounts of bark and wood waste (BWW), which is mostly dumped, causing negative climate and environmental impacts. This article presents an overview of methods for recycling BWW, as well as the results of assessing the resource potential of old bark waste based on physicochemical and thermal analysis. It was found that using BWW as a plant-growing substrate is challenging because it was observed that bark waste is phytotoxic. The C:N waste ratio is far from optimum; moreover, it has a low biodegradation rate (less than 0.15% per year). The calorific value content of BWW ranged from 7.7 to 18.9 MJ/kg on d.m., the ash content was from 4% to 22%, and the initial moisture content was from 60.8% to 74.9%, which allowed us to draw conclusions about the feasibility of using hydrothermal methods for their processing to obtain biofuel and for the unreasonableness of using traditional thermal methods (combustion, pyrolysis, gasification).

Performance Evaluation of Combined Hydrothermal-Mechanical Pretreatment of Lignocellulosic Biomass for Enzymatic Enhancement

Pretreatment is a crucial process in a lignocellulosic biorefinery. Corncob is typically considered as a natural renewable carbon source to produce various bio-based products. This study aimed to evaluate the performance of the hydrothermal-mechanical pretreatment of corncob for biofuels and biochemical production. Corncob was first pretreated by liquid hot water (LHW) at different temperatures (140–180 °C) and duration (30, 60 min) and then subjected to centrifugal milling to produce bio-powders. To evaluate the performance of this combined pretreatment, the energy efficiency and waste generation were investigated. The results indicated that the maximum fermentable sugars (FS) were 0.488 g/g biomass obtained by LHW at 180 °C, 30 min. In order to evaluate the performance of this combined pretreatment, the energy efficiency and waste generation were 28.3 g of FS/kWh and 7.21 kg of waste/kg FS, respectively. These obtained results indicate that the combined hydrothermal-mechanical pretreatment was an effective pretreatment process to provide high energy efficiency and low waste generation to produce biofuels. In addition, the energy efficiency and waste generation will be useful indicators for process scaling-up into the industrial scale. This combined pretreatment could be a promising pretreatment technology for the production of biofuels and biochemicals from lignocellulosic valorization.

The Fractionation of Corn Stalk Components by Hydrothermal Treatment Followed by Ultrasonic Ethanol Extraction

The fractionation of components of lignocellulosic biomass is important to be able to take advantage of biomass resources. The hydrothermal–ethanol method has significant advantages for fraction separation. The first step of hydrothermal treatment can separate hemicellulose efficiently, but hydrothermal treatment affects the efficiency of ethanol treatment to delignify lignin. In this study, the efficiency of lignin removal was improved by an ultrasonic-assisted second-step ethanol treatment. The effects of ultrasonic time, ultrasonic temperature, and ultrasonic power on the ultrasonic ethanol treatment of hydrothermal straw were investigated. The separated lignin was characterized by solid product composition analysis, FT-IR, and XRD. The hydrolysate was characterized by GC-MS to investigate the advantage on the products obtained by ethanol treatment. The results showed that an appropriate sonication time (15 min) could improve the delignification efficiency. A proper sonication temperature (180 °C) can improve the lignin removal efficiency with a better retention of cellulose. However, a high sonication power 70% (840 W) favored the retention of cellulose and lignin removal.