Current trends in biochar application for catalytic conversion of biomass to biofuels

Enhancement of dark fermentative hydrogen production using metal-modified biochar from sugarcane residues: Optimization, characterization, and metabolic analysis

This study investigated the enhancement of dark fermentative hydrogen production (HP) using metal-modified biochars derived from sugarcane bagasse (SB) and sugarcane leaves (SL). The biochars were modified with Fe and Ni, with optimal conditions identified through Box-Behnken Design as 6.09 g/L biochar: SB, 5.38 g/L biochar: SL + Fe, and 7.66 g/L biochar: SL + Ni. This optimization achieved a maximum hydrogen yield of 108.77 mL-hydrogen (H2)/g-glucose, a 58.77 % increase over the control. Metal modification enhanced biochar surface properties and selectively enriched H2-producing bacteria, particularly Clostridium sensu stricto 1 and Paraclostridium sp. Metabolic pathway analysis showed enhanced glucose catabolism and increased H2-producing enzyme abundance. The study demonstrates that sugarcane-derived biochar can effectively enhance bio-HP, though careful optimization of metal concentrations is crucial to avoid inhibitory effects.

Sustainable synthesis and advanced optimization of Prosopis juliflora biomass catalyst for efficient biodiesel production and environmental impact assessment

The present research focuses on developing an innovative biochar-based heterogeneous catalyst from Prosopis Juliflora biomass waste using response surface methodology and genetic algorithm (GA) to optimize pyrolysis parameters, achieving a 46.31% PJBC yield from 60 mg of biomass at 790 °C for 60 min. The pyrolyzed PJBC is characterized using SEM, FTIR, XRD, EDX, BET, XPS analyses, and physico-chemical measurements to confirm its catalytic activity. Now, the newly synthesized PJBC serves as an efficient catalyst for waste Trichosanthes cucumerina seed biodiesel (WTSB) production from waste Trichosanthes cucumerina seed bio-oil through trans-esterification, achieving a maximum yield of 97.42%. Also, the WTSB exhibits excellent physico-chemical properties that meet most of the ASTM D6751 standards for biodiesel and closely align with the characteristics of conventional diesel fuel. Therefore, this research utilized neat WTSB and WTSB/diesel blends (WTSB25, WTSB50, and WTSB75) in a direct injection (DI) diesel engine at variable load settings. Among all WTSB blends, the WTSB25 blend showed closer variations of 1.65% lower BTE and 9.29% higher BSEC when compared to conventional diesel fuel readings. Its peak in-cylinder pressure and heat release rate were similar to those of diesel fuel at 100% engine load. Emission analysis indicated that the WTSB25 reduced specific HC, CO, and smoke opacity emissions by 8.39%, 13.97%, and 4.18%, respectively. However, specific NO emissions increased slightly by 3.05% compared to diesel fuel. Thus, WTSB25 is validated as a viable diesel alternative requiring no significant engine modifications. The environmental impact, lifecycle and economic feasibility are also discussed.

Sewage sludge pyrolysis 'kills two birds with one stone': Biochar synergies with persulfate for pollutants removal and energy recovery

The disposal and resource utilization of sewage sludge (SS) have always been significant challenges for environmental protection. This study employed straightforward pyrolysis to prepare iron-containing sludge biochar (SBC) used as a catalyst and to recover bio-oil used as fuel energy. The results indicated that SBC-700 could effectively activate persulfate (PS) to remove 97.2% of 2,4-dichlorophenol (2,4-DCP) within 60 min. Benefiting from the appropriate iron content, oxygen-containing functional groups and defective structures provide abundant active sites. Meanwhile, SBC-700 exhibits good stability and reusability in cyclic tests and can be easily recovered by magnetic separation. The role of non-radicals is emphasized in the SBC-700/PS system, and in particular, single linear oxygen (1O2) is proposed to be the dominant reactive oxygen. The bio-oil, a byproduct of pyrolysis, exhibits a higher heating value (HHV) of about 30 MJ/kg, with H/C and O/C ratios comparable to those of biodiesel. The energy recovery rate of the SS pyrolysis system was calculated at 80.5% with a lower input cost. In conclusion, this investigation offers a low-energy consumption and sustainable strategy for the resource utilization of SS while simultaneously degrading contaminants.

Catalyst-Enhancing Hydrothermal Carbonization of Biomass for Hydrochar and Liquid Fuel Production-A Review

The research impact of catalysts on the hydrothermal carbonization (HTC) process remains an ongoing debate, especially regarding the quest to enhance biomass conversion into fuels and chemicals, which requires diverse catalysts to optimize bio-oil utilization. Comprehensive insights and standardized analytical methodologies are crucial for understanding HTC's potential benefits in terms of biomass conversion stages. This review seeks to understand how catalysts enhance the HTC of biomass for liquid fuel and hydrochar production, drawing from the following key sections: (a) catalyst types applied in HTC processes; (b) biochar functionality as a potential catalyst; (c) catalysts increasing the success of HTC process; and (d) catalyst's effect on the morphological and textural character of hydrochar. The performance of activated carbon would greatly increase via catalyst action, which would progress the degree of carbonization and surface modification, alongside key heteroatoms. As catalytic HTC technology advances, producing carbon materials for thermochemical activities will become more cost-effective, considering the ever-growing demands for high-performance thermochemical technologies.

Recent advances in the synthesis and application of magnetic biochar for wastewater treatment

Magnetic biochar (MBC) is a novel bio-carbon material with both desired properties as adsorbent and magnetic characteristics. This review provides an up-to-date summary and discussion on the latest development of MBC, which covers the progress on its synthesis, application, and techno-economic analysis. The review indicates that the direct hydrothermal synthesis has been catching more research attention to produce MBC due to its mild reaction conditions. Instead of the Fe-loaded MBC, there is a trend of using Mn for the magnetization. For the MBC application, how to improve its adsorption performance for water decontamination, ideally to match that of the biochar (BC) or activated carbon, is important. In addition, more studies on the environmental impacts of MBC and life-cycle assessment decoding the process optimization options are necessary. This review will provide valuable references for the development of MBC and MBC-based materials for wastewater treatment.

A Review of the Design and Performance of Catalysts for Hydrothermal Gasification of Biomass to Produce Hydrogen-Rich Gas Fuel

Supercritical water gasification has emerged as a promising technology to sustainably convert waste residues into clean gaseous fuels rich in combustible gases such as hydrogen and methane. The composition and yield of gases from hydrothermal gasification depend on process conditions such as temperature, pressure, reaction time, feedstock concentration, and reactor geometry. However, catalysts also play a vital role in enhancing the gasification reactions and selectively altering the composition of gas products. Catalysts can also enhance hydrothermal reforming and cracking of biomass to achieve desired gas yields at moderate temperatures, thereby reducing the energy input of the hydrothermal gasification process. However, due to the complex hydrodynamics of supercritical water, the literature is limited regarding the synthesis, application, and performance of catalysts used in hydrothermal gasification. Hence, this review provides a detailed discussion of different heterogeneous catalysts (e.g., metal oxides and transition metals), homogeneous catalysts (e.g., hydroxides and carbonates), and novel carbonaceous catalysts deployed in hydrothermal gasification. The article also summarizes the advantages, disadvantages, and performance of these catalysts in accelerating specific reactions during hydrothermal gasification of biomass, such as water-gas shift, methanation, hydrogenation, reforming, hydrolysis, cracking, bond cleavage, and depolymerization. Different reaction mechanisms involving a variety of catalysts during the hydrothermal gasification of biomass are outlined. The article also highlights recent advancements with recommendations for catalytic supercritical water gasification of biomass and its model compounds, and it evaluates process viability and feasibility for commercialization.

Life Cycle Assessment (LCA) of Biochar Production from a Circular Economy Perspective

Climate change and environmental sustainability are among the most prominent issues of today. It is increasingly fundamental and urgent to develop a sustainable economy, capable of change the linear paradigm, actively promoting the efficient use of resources, highlighting product, component and material reuse. Among the many approaches to circular economy and zero-waste concepts, biochar is a great example and might be a way to push the economy to neutralize carbon balance. Biochar is a solid material produced during thermochemical decomposition of biomass in an oxygen-limited environment. Several authors have used life cycle assessment (LCA) method to evaluate the environmental impact of biochar production. Based on these studies, this work intends to critically analyze the LCA of biochar production from different sources using different technologies. Although these studies reveal differences in the contexts and characteristics of production, preventing direct comparison of results, a clear trend appears. It was proven, through combining life cycle assessment and circular economy modelling, that the application of biochar is a very promising way of contributing to carbon-efficient resource circulation, mitigation of climate change, and economic sustainability.