Thermochemical Conversion of Lignocellulosic Biomass into Mass-Producible Fuels: Emerging Technology Progress and Environmental Sustainability Evaluation

Accelerated Charge Transfer through Interface Chemical Bonds in MoS2/TiO2 for Photocatalytic Conversion of Lignocellulosic Biomass to H2

Solar photocatalytic H2 production from lignocellulosic biomass has attracted great interest, but it suffers from low photocatalytic efficiency owing to the absence of highly efficient photocatalysts. Herein, we designed and constructed ultrathin MoS2-modified porous TiO2 microspheres (MT) with abundant interface Ti-S bonds as photocatalysts for photocatalytic H2 generation from lignocellulosic biomass. Owing to the accelerated charge transfer related to Ti-S bonds, as well as the abundant active sites for both H2 and ●OH generation, respectively, related to the high exposed edge of MoS2 and the large specific surface area of TiO2, MT photocatalysts demonstrate good performance in the photocatalytic conversion of α-cellulose and lignocellulosic biomass to H2. The highest H2 generation rate of 849 μmol·g-1·h-1 and apparent quantum yield of 4.45% at 380 nm was achieved in α-cellulose aqueous solution for the optimized MT photocatalyst. More importantly, lignocellulosic biomass of corncob, rice hull, bamboo, polar wood chip, and wheat straw were successfully converted to H2 over MT photocatalysts with H2 generation rate of 10, 19, 36, 29, and 8 μmol·g-1·h-1, respectively. This work provides a guiding design approach to develop highly active photocatalysts via interface engineering for solar H2 production from lignocellulosic biomass.

Ectopic Production of 3,4-Dihydroxybenzoate in Planta Affects Cellulose Structure and Organization

Lignocellulosic biomass is a highly sustainable and largely carbon dioxide neutral feedstock for the production of biofuels and advanced biomaterials. Although thermochemical pretreatment is typically used to increase the efficiency of cell wall deconstruction, genetic engineering of the major plant cell wall polymers, especially lignin, has shown promise as an alternative approach to reduce biomass recalcitrance. Poplar trees with reduced lignin content and altered composition were previously developed by overexpressing bacterial 3-dehydroshikimate dehydratase (QsuB) enzyme to divert carbon flux from the shikimate pathway. In this work, three transgenic poplar lines with increasing QsuB expression levels and different lignin contents were studied using small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS). SANS showed that although the cellulose microfibril cross-sectional dimension remained unchanged, the ordered organization of the microfibrils progressively decreased with increased QsuB expression. This was correlated with decreasing total lignin content in the QsuB lines. WAXS showed that the crystallite dimensions of cellulose microfibrils transverse to the growth direction were not affected by the QsuB expression, but the crystallite dimensions parallel to the growth direction were decreased by ∼20%. Cellulose crystallinity was also decreased with increased QsuB expression, which could be related to high levels of 3,4-dihydroxybenzoate, the product of QsuB expression, disrupting microfibril crystallization. In addition, the cellulose microfibril orientation angle showed a bimodal distribution at higher QsuB expression levels. Overall, this study provides new structural insights into the impact of ectopic synthesis of small-molecule metabolites on cellulose organization and structure that can be used for future efforts aimed at reducing biomass recalcitrance.

Towards Negative Emissions: Hydrothermal Carbonization of Biomass for Sustainable Carbon Materials

The contemporary production of carbon materials heavily relies on fossil fuels, contributing significantly to the greenhouse effect. Biomass is a carbon-neutral resource whose organic carbon is formed from atmospheric CO2. Employing biomass as a precursor for synthetic carbon materials can fix atmospheric CO2 into solid materials, achieving negative carbon emissions. Hydrothermal carbonization (HTC) presents an attractive method for converting biomass into carbon materials, by which biomass can be transformed into materials with favorable properties in a distinct hydrothermal environment, and these carbon materials have made extensive progress in many fields. However, the HTC of biomass is a complex and interdisciplinary problem, involving simultaneously the physical properties of the underlying biomass and sub/supercritical water, the chemical mechanisms of hydrothermal synthesis, diverse applications of resulting carbon materials, and the sustainability of the entire technological routes. This review starts with the analysis of biomass composition and distinctive characteristics of the hydrothermal environment. Then, the factors influencing the HTC of biomass, the reaction mechanism, and the properties of resulting carbon materials are discussed in depth, especially the different formation mechanisms of primary and secondary hydrochars. Furthermore, the application and sustainability of biomass-derived carbon materials are summarized, and some insights into future directions are provided.

Making the biochemical conversion of lignocellulose more robust

Lignocellulose is an alternative to fossil resources, but its biochemical conversion is not economically competitive. While decentralized processing can reduce logistical cost for this feedstock, sugar platforms need to be developed with energy-saving pretreatment technologies and cost-effective cellulases, and products must be selected correctly. Anaerobic fermentation with less energy consumption and lower contamination risk is preferred, particularly for producing biofuels. Great effort has been devoted to producing cellulosic ethanol, but CO2 released with large quantities during ethanol fermentation must be utilized in situ for credit. Unless titer and yield are improved substantially, butanol cannot be produced as an advanced biofuel. Microbial lipids produced through aerobic fermentation with low yield and intensive energy consumption are not affordable as feedstocks for biodiesel production.

Unlocking Syngas Synthesis from the Catalytic Gasification of Lignocellulose Pinewood: Catalytic and Pressure Insights

Modern technologies transform biomass into commodity chemicals, biofuels, and solid charcoal, making it appear as a renewable resource rather than organic waste. The effectiveness of Mo, Fe, Co, and Ni metal catalysts was investigated during the gasification of lignocellulosic pinewood. The primary goal was to compare the performance of iron and nickel catalysts in the low- and high-pressure production of syngas from pinewood. This is the first study that has reported high-pressure gasification of pinewood without the use of an external gasifying agent, producing syngas containing hydrogen, carbon monoxide, and carbon dioxide along with considerable amounts of methane with or without a catalyst. Also, the same gasification at low pressures was compared. In this study, the iron catalyst produces syngas more efficiently at higher pressure and 800 °C, and contains 43 mol % H2, 22 mol % CO2, 26 mol % CH4, and 8 mol % CO in comparison to the nickel catalyst. High pressure produces a large amount of methane too. The nickel catalyst produces higher syngas at low pressure and 850 °C, and contains 55 mol % H2, 9 mol % CO2, 5 mol % CH4, and 30 mol % CO. Low-pressure gasification produces less amounts of CH4 and CO2. Also, the H2/CO ratio is ∼1.81 using the nickel catalyst at low pressures, which is good for utilizing syngas as a feedstock. These results highlight the importance of catalyst selection, reactor configuration, and operating circumstances in adjusting gasification product composition. The study's findings provide information about optimizing syngas production from pinewood, which is critical for the development of sustainable and efficient energy conversion technologies.

Catalytic fast pyrolysis of waste pine sawdust over solid base, acid and base-acid tandem catalysts

Catalytic pyrolysis is an effective means for high-value utilization of biomass. This study investigated the effect of solid base catalysts (CaO, calcium aluminate catalysts CaAl-1, CaAl-2, CaAl-3), acid zeolite catalysts (ZSM-5, Fe/ZSM-5, Co/ZSM-5, Ni/ZSM-5, Cu/ZSM-5, Zn/ZSM-5) and base-acid tandem catalysts on pine sawdust pyrolysis using Py-GC/MS. Acid zeolite catalysts exhibited robust deoxidation and aromatization capabilities, favoring aromatics, while solid base catalysts yielded more phenols and ketones. Among the solid base catalysts, CaAl-3 (CaO-Ca12Al14O33) showed comparable deoxygenation activity to CaO and optimal aromatic selectivity with structural stability. Zn/ZSM-5 excelled in deoxygenation and aromatic selectivity (70.42%) among metal-modified ZSM-5 catalysts. Base-acid tandem catalysis promoted the formation of aliphatics and BTX (benzene, toluene, xylene) while suppressing polycyclic aromatics. The highest BTX content (44.35%) was achieved with CaO-Ca12Al14O33&Zn/ZSM-5 tandem catalysts in a 1:3 ratio. This work demonstrates base-acid tandem catalysis as a promising approach for converting pine sawdust into valuable chemicals.

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.

Valorization of cannabis waste via hydrothermal carbonization: solid fuel production and characterization

Hydrothermal carbonization (HTC) was employed to convert cannabis waste into valuable solid fuel (hydrochar) under different operating conditions, including reaction temperature (170-230 °C), biomass-water ratio (1:10-1:20), and residence time of 60 min. The produced hydrochar was examined for their fuel properties including calorific value (HHV), proximate and ultimate analysis, thermal stability and combustion behavior, etc. The results revealed higher HTC temperature led to a higher degree of carbonization, which is beneficial for increasing carbon content and HHV of the hydrochar. The HHV of the hydrochar improved significantly up to 24.65 MJ/kg after the HTC compared to 17.50 MJ/kg for cannabis waste. The energy yield of hydrochar from the HTC process was in a range of 70.41-82.23%. The optimal HTC condition was observed at 230 °C and a biomass-water ratio of 1:10, producing high-quality hydrochar with 24.24 MJ/kg HHV and 72.28% energy yield. The hydrochar had similar fuel characteristics to lignite coal with significantly lower ash content. Additionally, recirculation of liquid effluent showed a positive influence on the HHV of hydrochar besides minimizing the release of wastewater from the HTC process. The study revealed that HTC is a promising technique for valorization of cannabis waste into high-value solid fuel, which can be potentially an alternative to coal.

Thermochemical conversion of large-size woody biomass for carbon neutrality: Principles, applications, and issues

Large-size woody biomass is a valuable renewable resource to replace fossil fuels in biorefinery processes. The preprocessing of wood chips and briquettes is challenging to manage, especially in an industrial setting, as it generates a significant amount of dust and noise and occasionally causes unexpected accidents. As a result, a substantial amount of resources, energy, labor, and space are needed. The thermochemical conversion behavior of large-size woody biomass was studied to reduce energy consumption for chipping. Large-size wood was 1.5 m in length, 0.1 m in breadth, and stacked 90 cm in height. This strategy has many benefits, including increased effectiveness and reduced CO₂ emissions. The target of this paper presents the thermochemical process, and large-size wood was chosen because it provides high-quality product gas while reducing the preprocessing fuel cost. This review examines the benefits of thermochemical conversion technologies for assessing the likelihood of carbon neutrality.