Comparison of hydrochar- and pyrochar-based solid acid catalysts from cornstalk: Physiochemical properties, catalytic activity and deactivation behavior

Rod-shaped silica promotes cellulose hydrolysis by inducing interior structural breakage via penetrated breaking

Solid acid catalysts have attracted much attention in cellulose hydrolysis due to their high product selectivity, easy preparation and reusability. However, most current researches only focus on modifying their surface functional groups but overlook the impact of carrier shape on hydrolytic performance. Herein, we synthesize a series of rod-shaped silica with varying sizes for cellulose hydrolysis to analyze the shape mode to enhance the breaking of cellulose structure during solid-solid reaction. Experimental results show rod-shaped silica produces particular penetrating mode to enter into the interior of cellulose and thus causing strong disruption. This mode quickly disrupts the aggregated structure of cellulose, fragmenting it in a short time. The cellulose fragments are rapidly converted to glucose in a 0.02 M H+ solution. This process achieves an 83.92 % cellulose conversion rate and a 52.98 % glucose yield. The discovery suggests a new strategy to design one-dimensional solid catalyst for the efficient hydrolysis of cellulose to sugar.

Strong adsorption enhances mass transfer and promotes efficient hydrolysis of cellulose to sugar by solid acids

Efficient conversion of cellulose to glucose is a crucial challenge for the energy and materialization of non-food biomass. Solid acids' adsorption strength is essential to affecting mass transfer efficiency. In this study, solid acids with different particle sizes (from 0.25 to 10.10 μm) modified with -OH and -PO3H2 were obtained by hydrothermal method. Hydrolysis of cellulose at 180 °C for 4 h revealed that the particle size of the solid acids was directly proportional to the cellulose conversion (R2 = 0.925). Still, there was no significant correlation with the glucose yield (R2 = 0.632). Eventually, the cellulose conversion reached 98.9 %, with a 30 % glucose yield. The solid acids demonstrated good stability and recoverability. This study fills the gap in the influence of solid acid particle size and reveals the mechanism of strong adsorptive mass transfer and hydrolysis efficiency. It provides the theoretical basis for the design of high-performance solid acids.

Enhancing humic acids production from cornstalk under fast hydrothermal conditions: Insights into new pathways of skeleton self-polymerization and branch growth

Hydrochar, a sustainable fertilizer rich in humic substances, is made from lignocellulose through hydrothermal conversion. However, hydrothermal humification (HTH) is challenged by low yields and limited selectivity in the resulting hydrochar. This study proved humic-like acids production can be enhanced under fast non-catalytic conditions (260 ∼ 280 °C, 0 ∼ 1 h). A higher yield (by 14.1 %) and selectivity (by 40.2 %) in hydrochar of humic-like acids than conventional HTH (＜250 °C) were achieved. Meanwhile, decreased lignin derivatives, carbonyl and quinone groups, as well as increased sp2-C structures in the humic-like acids were observed. The synthesized humic-like acids exhibited a lower degree of aromatization and a higher molecular weight than commercial variants. Two pathways of humic-like acids formation of self-polymerization and the development of branched sidechains were hypothesized based on mass mitigation, carbon flow and aqueous phase compositions. This research contributes a novel approach to producing humic-like acids rich hydrochar for environmentally friendly fertilizer production.

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.

Sustainable management of tea wastes: resource recovery and conversion techniques

As the demand for tea (Camellia sinensis) has grown across the world, the amount of biomass waste that has been produced during the harvesting process has also increased. Tea consumption was estimated at about 6.3 million tonnes in 2020 and is anticipated to reach 7.4 million tonnes by 2025. The generation of tea waste (TW) after use has also increased concurrently with rising tea consumption. TW includes clipped stems, wasted tea leaves, and buds. Many TW-derived products have proven benefits in various applications, including energy generation, energy storage, wastewater treatment, and pharmaceuticals. TW is widely used in environmental and energy-related applications. Energy recovery from low- and medium-calorific value fuels may be accomplished in a highly efficient manner using pyrolysis, anaerobic digestion, and gasification. TW-made biochar and activated carbon are also promising adsorbents for use in environmental applications. Another area where TW shows promise is in the synthesis of phytochemicals. This review offers an overview of the conversion procedures for TW into value-added products. Further, the improvements in their applications for energy generation, energy storage, removal of different contaminants, and extraction of phytochemicals have been reviewed. A comprehensive assessment of the sustainable use of TWs as environmentally acceptable renewable resources is compiled in this review.

Advances in the fabrication, modification, and performance of biochar, red mud, calcium oxide, and bentonite catalysts in waste-to-fuel conversion

Various catalysts are being used in fuel production from biomass and polymeric waste for the obtention of an alternative energy source with both environmental friendliness and economic viability. Biochar, red mud bentonite, and calcium oxide have been shown to play a pertinent role as catalysts in waste-to-fuel conversion processes, such as transesterification and pyrolysis. In this line of thought, this paper has provided a compendium of the fabrication and modification technologies of bentonite, red mud calcium oxide, and biochar, together with their various performances in their application in the waste-to-fuel processes. Additionally, an overview of the structural and chemical attributes of these components is discussed regarding their efficiency. Ultimately, research trends and future points of focus are evaluated, and it is observed that techno-economic optimization of catalyst synthetic routes and investigation of new catalytic formulations, such as biochar and red mud-based nanocatalysts, are potential prospects. This report also offers future research directions that are anticipated to contribute to the development of sustainable green fuel generation systems.

Effect of Acidic Hydrochar on Plastic Crude Oil Produced from Hydrothermal Liquefaction of Waste PVC

In this study, the effect of hydrothermal liquefaction (HTL) of waste PVC was investigated in the presence of acidic hydrochar. The hydrochar was prepared by hydrothermal carbonization of pineapple waste at 250 °C and at 1 h in the presence of citric acid. Hydrochar was acidic, stable, and porous and contained acidic functional groups. Hydrochar was co-fed with PVC during HTL to enhance HTL conversion and quality of the plastic crude oil. HTL experiments were performed at 300–350 °C, 0.25–4 h of reaction times, and 0–20 wt% hydrochar-to-PVC ratio. The plastic crude oil was separated from the solid residue to evaluate HTL conversion and to analyze elemental compositions, boiling point distribution, alteration of chemical bonds, and chemical compositions. The results showed that acidic hydrochar enhances HTL conversion with a maximum value of 28.75 at 5 wt% hydrochar content at 350 °C and 0.5 h. Furthermore, plastic crude oils contained no chloride but contained significantly high carbon and hydrogen, resulting in a higher heating value of up to 36.43 MJ/kg. The major component of the plastic crude oil was 3, 5 dimethylphenol produced ranging from 61.4 to 86.4% (percentage of total identified area) according to gas chromatography mass spectroscopy (GCMS) data.

Strategic thermosonication-mediated modulation of lactic acid bacteria acidification kinetics for enhanced (post)-fermentation performance

This study explored the feasibility of thermosonication (TS)-prestressed inoculum with different fermentation patterns for regulating microbial (post)-fermentation acidification kinetics. Through a Box-Behnken design, stimulative (20 min, 400 W, 33 kHz, 25 °C) and inhibitive (10 min, 600 W, 33 kHz, 20 °C) effects on the acidification capability of Lactobacillus plantarum A3 were achieved without observing greatly activated/inactivated strains growth, further confirmed by lactose fermentation performed by Streptococcus thermophilus and Lactobacillus bulgaricus. Lactic acid was the major contributing factor responsible for TS-induced acidification modifications corresponding to the potential fluctuations of CoA biosynthesis, fatty acid degradation and chain elongation pathways to TS prestress. Microscopy observations and quantitative extracellular substance assays showed palpable stress disturbance on microbes, but causing insignificant effects on product characteristics. This investigation demonstrated the potential of controlled sonication prestress strategies to achieve dual engineering effects on microbial metabolic behavior, for alleviating post-acidification problem or enhancing process efficiencies.

Effects of different low temperature pretreatments on properties of corn stover biochar for precursors of sulfonated solid acid catalysts

In this study, the effects of different pretreatment methods including phosphoric acid (PA), freeze drying (FD) and phosphoric acid-freeze drying combined (PA-FD) pretreatment on corn stover characteristics and pyrolysis of corn stover samples was investigated. The results demonstrated that the physiochemical properties of biochars varied significantly. In comparison, PA pretreatment could effectively remove a large portion of inorganics and improve the fuel characteristics. PA-CSB-600 had a greater HHV, lower O/C and H/C ratios, and a lower biochar energy yield (Y_e), indicating the possibility for an attractive fuel source. PA-FD pretreatment would significantly affected cell volume and caused mechanical damage to corn stover structure. As a sulfonated solid acid catalyst precursor, the results of cellulose catalytic hydrolysis indicated that the density of -SO₃H in FD-CSA was much higher than PA-FD-CSA, but lower surface special area. Specifically, PA-FD-CSB prepared at 600 °C resulted in the maximum increase of cellulose conversion by 34.7-81.3%.

The hydrochar activation and biocrude upgrading from hydrothermal treatment of lignocellulosic biomass

The production of hydrochar and biocrude from hydrothermal treatment of lignocellulosic biomass is getting increasing attention, but the quality of hydrochar and biocrude need further improvement before utilization. Many attempts have been carried out on the hydrochar activation and biocrude upgrading. However, different methods play different roles on the property of hydrochar and biocrude, this topic received scant attention in recent review papers. Therefore, the influence of different activation methods on hydrochar property, and the potential application of hydrochar were summarized in this study. Meanwhile, the research progress on biocrude upgrading is reported. Besides, the techno-economic analysis of hydrochar and biocrude from hydrothermal treatment of lignocellulosic biomass are also discussed. Finally, the research needs and future directions on hydrochar activation and biocrude upgrading were proposed. This paper could provide insights for further studies on the utilization of hydrochar and biocrude.

Preparation and Self-Cleaning Performance of Carbon-Based Superhydrophobic Coatings Based on Non-Fluorine and Non-Toxic Corn Straw

Recently, superhydrophobic surfaces with self-cleaning ability have attracted broad research interest due to their huge potential in daily lives and industrial applications, but the use of fluorinate, toxic organic compounds, and expensive feedstocks make superhydrophobic materials a great challenge in practical application. In this study, we present a facile dip-coating strategy to prepare superhydrophobic coatings with self-cleaning properties based on a non-fluorine and non-toxic system by using eco-friendly corn straw as raw material. During this process, aromatic carbon particles with rough hierarchical structures were prepared firstly via a simple fast pyrolysis process, followed by modification with polydimethylsiloxane (PDMS) in absolute ethanol solvent to decrease the surface free energy. Research shows these natural straw-derived carbons display a microstructure of several protrusions which is similar to the lotus leave’s and the resulted coatings exhibit an outstanding superhydrophobic property with a static water contact angle (WCA) of 151.67 ± 1.36 degrees. In addition, the as-prepared coatings possessed excellent self-cleaning performance: no contaminations were observed on the surfaces after examining with sludge, calcimine, water, and common liquids such as tea, milk, soybean milk as well as ink, which have a broad range of potential application in the field of antifouling, waterproofing, and anticorrosive.

Current understanding in conversion and application of tea waste biomass: A review

Along with the increasing consumption of tea and its extracts, the amount of tea waste grows rapidly, which not only results in huge biomass loss, but also increases environmental stress. In past years, interest has been attracted on utilization of tea waste biomass, and a lot of work has been carried out. This review summarized the progress in conversion of tea waste by thermo-chemical and biological technologies and analyzed the property of the derived products and their performance in applications. It was found that biochar derived from tea waste had relatively large surface area, porous structures, and abundant functional groups, and could be used as bio-adsorbents and catalysts and electrochemical energy storage, while the cost of its largescale production should be evaluated. Profoundly, biological conversion, including ensiling and composting, was suggested to be an effective way to develop the tea waste biomass in practice due to its low-cost and specific functions.

Evaluating river driftwood as a feedstock for biochar production

Driftwood in river catchments might pose a hazard for the safety of infrastructures, such as dams and river dwellers, and thus is often removed. Génissiat dam in France presents a case study where annually approximately 1300 tons of driftwood are removed to prevent driftwood sinking and to protect the dam infrastructure. Collected river driftwood is rarely studied for utilization purposes and is commonly combusted or landfilled. However, driftwood can be valorized for biochar production through pyrolysis or hydrothermal carbonization (HTC). This study follows a novel approach in characterizing river driftwood by identifying the different common genera present at Génissiat dam on the upper Rhône, France. Moreover, the research provides for the first time a comprehensive analysis of river driftwood different physico-chemical properties, such as moisture content, major elemental composition (CHNSO), HHV, and macromolecular composition (cellulose, hemicellulose, lignin, and extractives). The study shows that the transportation of driftwood through rivers can enhance its properties by reducing the bark content resulting in lower ash content. Results indicate that driftwood can be mixed and further processed as a feedstock regardless of their genera and type for biochar production by pyrolysis or hydrothermal carbonization.

Hydrochar: A Review on Its Production Technologies and Applications

Recently, due to the escalating usage of non-renewable fossil fuels such as coal, natural gas and petroleum coke in electricity and power generation, and associated issues with pollution and global warming, more attention is being paid to finding alternative renewable fuel sources. Thermochemical and hydrothermal conversion processes have been used to produce biochar and hydrochar, respectively, from waste renewable biomass. Char produced from the thermochemical and hydrothermal decomposition of biomass is considered an environmentally friendly replacement for solid hydrocarbon materials such as coal and petroleum coke. Unlike thermochemically derived biochar, hydrochar has received little attention due to the lack of literature on its production technologies, physicochemical characterization, and applications. This review paper aims to fulfill these objectives and fill the knowledge gaps in the literature relating to hydrochar. Therefore, this review discusses the most recent studies on hydrochar characteristics, reaction mechanisms for char production technology such as hydrothermal carbonization, as well as hydrochar activation and functionalization. In addition, the applications of hydrochar, mainly in the fields of agriculture, pollutant adsorption, catalyst support, bioenergy, carbon sequestration, and electrochemistry are reviewed. With advancements in hydrothermal technologies and other environmentally friendly conversion technologies, hydrochar appears to be an appealing bioresource for a wide variety of energy, environmental, industrial, and commercial applications.

Enhanced adsorption of Cu(II) and Zn(II) from aqueous solution by polyethyleneimine modified straw hydrochar

Heavy metals removal from aqueous phase by adsorption technique has recently attracted a considerable interest. Although various adsorbing materials have been developed, introducing more functional groups is considered as the most efficient way to promote the adsorption capacity of the selected adsorbent. However, this approach is usually limited in costly modification precursor and unguaranteed loading efficacy. In this study, waste corn straw was converted to adsorbent precursor by hydrothermal carbonization. The obtained hydrochar (HC) was chemically activated before being modified by polyethyleneimine (PEI). Multiple analysis methods including Scanning Electron Microscopy, Fourier Transform Infrared analysis, and X-ray Photoelectron Spectroscopy analysis verified the alkali activated hydrochar (alkali-HC) was more efficacy to enhance PEI grafting than acid activation. Based on this, the modified HC materials obtained a better adsorption performance. The sorption process of Cu(II) and Zn(II) on the acid-PEI-HC, alkali-PEI-HC, and pristine HC fitted the pseudo second order kinetic and Freundlich model well, and was dominated by chemisorption. Among these adsorbents, the adsorption capacity of alkali-PEI-HC to metal ions was the maximum, which was 207.6 mg/g to Zn(II) and 56.1 mg/g to Cu(II) at 298 K. Regeneration tests showed a result of no less than 60% of its removal capacity was achieved after five cycles. Therefore, alkali-PEI-HC performed as a promising composite sorbent for metal ions. In addition, the study described here has provided a new basis for the utilization of hydrochar (1.08 kWh kg^-1) derived from agricultural resources as a promising adsorbent precursor.

Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

Enhanced electrochemical degradation of 2,4-dichlorophenol with the assist of hydrochar

Effective treatment of 2,4-dichlorophenol (2,4-DCP) in wastewater is essential, as it could pose great threat to the environment. A hydrothermal biochar (hydrochar) was used to assist the electrochemical oxidation treatment of 2,4-DCP. The removal of 2,4-DCP using hydrochar in anode and cathode area with and without proton exchange membrane (PEM) under 3-9 V of electrolysis was investigated. Enhanced 2,4-DCP degradation in the anode area was achieved compared with the adsorption or electrolysis alone. The highest 2,4-DCP removal (∼76%) was obtained using the hydrochar in the anode area with PEM under 9 V. The mechanism for the 2,4-DCP removal during the electrolysis included adsorption by hydrochar and electrochemical degradation by the reactive oxygen species (ROS) generated by the electrode as well as the persistent free radicals (PFR) on hydrochar. The OH produced from anode was the predominant ROS contributing to the 2,4-DCP degradation under 9 V of electrolysis.

A critical review of the production and advanced utilization of biochar via selective pyrolysis of lignocellulosic biomass

Biochar is a carbon-rich product obtained from the thermo-chemical conversion of biomass. Studying the evolution properties of biochar by in-situ modification or post-modification is of great significance for improving the utilisation value of lignocellulosic biomass. In this paper, the production methods of biochar are reviewed. The effects of the biomass feedstock characteristics, production processes, reaction conditions (temperature, heating rate, etc.) as well as in-situ activation, heteroatomic doping, and functional group modification on the physical and chemical properties of biochar are compared. Based on its unique physicochemical properties, recent research advances with respect to the use of biochar in pollutant adsorbents, catalysts, and energy storage are reviewed. The relationship between biochar structure and its application are also revealed. It is suggested that a more effective control of biochar structure and its corresponding properties should be further investigated to develop a variety of biochar for targeted applications.

Green synthesis of aluminum-hydrochar for the selective isomerization of glucose to fructose

Hydrochar microspheres supported Al catalysts with hierarchically porous structure (Al/HPHMs) for glucose to fructose isomerization were fabricated. Superior catalytic selectivity (93.3%) and fructose yield (32.6%) were achieved in aqueous under 160 °C for 20 min. Hierarchically porous structure was formed after KHCO₃ and K₂CO₃ activation and the roles of KHCO₃ and K₂CO₃ in controlling the Al phase and tailoring morphology of hydrochar supported Al were evaluated. The major active sites were characterized as Al hydroxides including β-Al(OH)₃, γ-Al(OH)₃, γ-AlO(OH), Al-C-O linkages. Active sites by KHCO₃ activation with high contents of Al-C-O and Al(OH)₃ have better selectivity. Oxygen-containing functional groups including aluminum‑oxygen groups on the hydrochar microspheres have contributed to the formation of hydrogen bond and π-π interactions between glucose and Al species. Green process synthesized aluminum-hydrochars have potential for their application as a variety of stable, recyclable, and efficient catalysts for lignocellulosic biorefining.