Investigation of the relevance between biomass pyrolysis polygeneration and washing pretreatment under different severities: Water, dilute acid solution and aqueous phase bio-oil

Cooperative production of monophenolic chemicals and carbon adsorption materials from cascade pyrolysis of acid hydrolysis lignin

A novel cascade pyrolysis upgrading process for acid hydrolysis lignin (AHL), consisting of pyrolysis, catalytic upgrading of pyrolysis vapors, and pyrolysis char, was developed to improve the yield of value-added products (monophenolic chemicals and carbon materials). Pyrolysis of AHL at 450 °C and subsequent catalytic upgrading of pyrolysis vapors over Ni/H-ZSM-5 boosted the concentration of monophenolic chemicals in pyrolysis liquids by 58%. The carbon material prepared from pyrolysis char using KOH as activating agent exhibited a large specific surface area of 2902.5 m2/g and a large total pore volume of 1.45 cm3/g, thus affording good adsorption capacity for methylene blue (824.87 mg/g) and iodine (2333.17 mg/g). Moreover, the cascade pyrolysis upgrading of AHL achieved a yield of 68.52% desired products, which was much higher than the reported results (single production of monophenols and pyrolysis char). In summary, this work provides a potential reference for efficient utilization of lignin in large-scale applications.

Catalytic pyrolysis and in situ carbonization of walnut shells: poly-generation and enhanced electrochemical performance of carbons

In this study, walnut shell (WS) was used as feedstock, incorporating lithium carbonate (LC), sodium carbonate (SC), potassium carbonate (PC), and potassium hydroxide (PH) as pyrolysis catalysts and carbonization activators. A one-step method that allows catalytic pyrolysis and carbonization to be carried out consecutively under their respective optimal conditions is employed, enabling the concurrent production of high-quality pyrolysis oil, pyrolysis gas, and carbon materials from biomass conversion. The effects of LC, SC, PC, and PH on the yield and properties of products derived from WS pyrolysis as well as on the properties and performance of the resulting carbon materials were examined. The results indicated that the addition of LC, SC, PC, and PH enhanced the secondary cracking of tar, leading to increased solid and gas yields from WS. Additionally, it increased the production of phenolic compounds in bio-oil and H2 in syngas, concurrently yielding a walnut shell-based carbon material exhibiting excellent electrochemical performance. Specifically, when PC was used as an additive, the phenolic content in the pyrolysis oil increased by 27.64% compared to that without PC, reaching 74.9%, but the content of ketones, acids, aldehydes, and amines decreased. The hydrogen content increased from 2.5% (without the addition of PC) to 12.75%. The resulting carbon (WSC-PC) displayed a specific surface area of 598.6 m2 g-1 and achieved a specific capacitance of 245.18 F g-1 at a current density of 0.5 A g-1. Even after 5000 charge and discharge cycles at a current density of 2 A g-1, the capacitance retention rate remained at 98.16%. This method effectively enhances the quality of the biomass pyrolysis oil, gas, and char, contributing to the efficient and clean utilization of biomass in industrial applications.

Dry torrefaction and continuous thermochemical conversion for upgrading agroforestry waste into eco-friendly energy carriers: Current progress and future prospect

Agroforestry Waste (AW) is seen as a carbon neutral resource. However, the poor quality of AW reduced its potential application value. Even more unfortunately, chlorine in AW led to the formation of organic pollutants such as dioxins under higher temperatures. Alkali and alkaline earth metals (AAEMs) in ash may deepen the reaction degree. Co-pretreatment of dry torrefaction and de-ashing followed by thermochemical conversion is a promising technology, which can improve raw material quality, inhibit the release of organic pollutants and transform AW into eco-friendly energy carriers. In order to better understand the process, theoretical basis such as the structural characteristics, thermal properties and separation methods of structural components of AW are described in detail. In addition, dry torrefaction related reactors, process parameters, kinetic analysis models as well as the evaluation methods of torrefaction degree and environmental impact are systematically reviewed. The problem of ash accumulation caused by dry torrefaction can be well solved by de-ashing pretreatment. This paper provides a comprehensive discussion on the role of the two- and three-stage conversion technologies around dry torrefacion, de-ashing pretreatment and thermochemical conversion in products quality enhancement. Finally, the existing technical challenges, including suppression of gaseous pollutant release, harmless treatment and reuse of torrefaction liquid product (TPL) and reduction of torrefaction operating costs, are summarized and evaluated. The future research directions, such as vitrification of the reused TPL (after de-ashing or acid catalysis) and integration of oxidative torrefaction with thermochemical conversion technologies, are proposed.

Comparative Study of Different Pretreatment and Combustion Methods on the Grindability of Rice-Husk-Based SiO2

The rice husk (RH) combustion pretreatment method plays a crucial role in the extraction of nanoscale SiO2 from RH as a silicon source. This study examined the effects of diverse pretreatment methods and combustion temperatures on the particle size distribution of nanoscale high-purity amorphous SiO2 extracted from rice husk ash (RHA) post RH combustion. The experiment was structured using the Taguchi method, employing an L9 (21 × 33) orthogonal mixing table. The median diameter (D50) served as the output response parameter, with the drying method (A), combustion temperature (B), torrefaction temperature (C), and pretreatment method (D) as the input parameters. The results showed the torrefaction temperature (C) as being the predominant factor affecting the D50, which decreased with an increasing torrefaction temperature (C). The optimal parameter combination was identified as A2B2C3D2. The verification test revealed that roasting could improve the abrasiveness of Rh-based silica and reduce the average particle size. Torrefaction at medium temperatures might narrow the size distribution range of RHA-SiO2. We discovered that the purity of silica increased with an increasing roasting temperature by evaluating the concentration of silica in the sample. The production of RHA with silica concentrations up to 92.3% was investigated. X-ray diffraction analysis affirmed that SiO2's crystal structure remained unaltered across different treatment methods, consistently presenting as amorphous. These results provide a reference for extracting high-value products through RH combustion.

Elaborating the mechanism of lead adsorption by biochar: Considering the impacts of water-washing and freeze-drying in preparing biochar

This paper examined the impacts of different pretreatments on the characteristics of biochar and its adsorption behavior for Pb2+. Biochar with combined pretreatment of water-washing and freeze-drying (W-FD-PB) performed a maximum adsorption capacity for Pb2+ of 406.99 mg/g, higher than that of 266.02 mg/g on water-washing pretreated biochar (W-PB) and 188.21 mg/g on directly pyrolyzed biochar (PB). This is because the water-washing process partially removed the K and Na, resulting in the relatively enriched Ca and Mg on W-FD-PB. And the freeze-drying pretreatment broke the fiber structure of pomelo peel, favoring the development of a fluffy surface and large specific surface area during pyrolysis. Quantitative mechanism analysis implied that cation ion exchange and precipitation were the driving forces in Pb2+ adsorption on biochar, and both mechanisms were enhanced during Pb2+ adsorption on W-FD-PB. Furthermore, adding W-FD-PB to Pb-contaminated soil increased the soil pH and significantly reduced the availability of Pb.

Machine learning prediction of contents of oxygenated components in bio-oil using extreme gradient boosting method under different pyrolysis conditions

This work aims to develop a prediction model for the contents of oxygenated components in bio-oil based on machine learning according to different pyrolysis conditions and biomass characteristics. The prediction model was constructed using the extreme gradient boosting (XGB) method, and the prediction accuracy was evaluated using the test dataset. The partial dependence analysis (PDA) method was used to derive the pattern of influence of each input feature individually or in combination on the output variable. The results show that the prediction models constructed from biomass ultimate analysis and pyrolysis conditions can predict the contents of oxygenated components in bio-oil more accurately than the models constructed from biomass proximate analysis. Moderate C and O contents, higher H content of biomass, lower flow rate, and higher pyrolysis temperature can improve bio-oil quality.

Co-Pyrolysis for Pine Sawdust with Potassium Chloride: Insight into Interactions and Assisting Biochar Graphitization

This effort aimed to explore the activation and catalytic graphitization mechanisms of non-toxic salts in converting biomass to biochar from the perspective of pyrolysis kinetics using renewable biomass as feedstock. Consequently, thermogravimetric analysis (TGA) was used to monitor the thermal behaviors of the pine sawdust (PS) and PS/KCl blends. The model-free integration methods and master plots were used to obtain the activation energy (E) values and reaction models, respectively. Further, the pre-exponential factor (A), enthalpy (ΔH), Gibbs free energy (ΔG), entropy (ΔS), and graphitization were evaluated. When the KCl content was above 50%, the presence of KCl decreased the resistance to biochar deposition. In addition, the differences in the dominant reaction mechanisms of the samples were not significant at low (α ≤ 0.5) and high (α ≥ 0.5) conversion rates. Interestingly, the lnA value showed a linearly positive correlation with the E values. The PS and PS/KCl blends possessed positive ΔG and ΔH values, and KCl was able to assist biochar graphitization. Encouragingly, the co-pyrolysis of the PS/KCl blends allows us to target-tune the yield of the three-phase product during biomass pyrolysis.

Review of biochar production via crop residue pyrolysis: Development and perspectives

Worldwide surge in crop residue generation has necessitated developing strategies for their sustainable disposal. Pyrolysis has been widely adopted to convert crop residue into biochar with bio-oil and gas being two co-products. The review adopts a whole system philosophy and systematically summarises up-to-date knowledge of crop residue pyrolysis processes, influential factors, and biochar applications. Essential process design tools for biochar production e.g., cost-benefit analysis, life cycle assessment, and machine learning methods are also reviewed, which has often been overlooked in prior reviews. Important aspects include (a) correlating techno-economics of biochar production with crop residue compositions, (b) process operating conditions and management strategies, (c) biochar applications including soil amendment, fuel displacement, catalytic usage, etc., (d) data-driven modelling techniques, (e) properties of biochar, and (f) climate change mitigation. Overall, the review will support the development of application-oriented process pipelines for crop residue-based biochar.

A Scientometric Review: Biomass Gasification Study from 2006 to 2020

Biomass gasification represents a significant way to produce energy from biomass. It features renewable properties and offers great potential for utilization. The application of biomass gasification products, design of the gasifier, type of biomass feedstock, gasification agents, and gasification parameters are key for the biomass gasification process. This work applies bibliometric approaches to provide a comprehensive and objective analysis of worldwide biomass gasification study trends over the period from 2006 to 2020 according to the Web Of Science core collection data. A total of 3222 articles associated with biomass gasification was retrieved, and its number grew annually. The subjects of study are diversified, primarily classified into "Energy & Fuels", "Engineering Chemical", and "Green Sustainable Science Technology". Moreover, Energy was a top published journal in the field of biomass gasification. Austrian contributors had the majority of publications, next to China and the USA. Liejin Luo from Xi'an Jiaotong University possessed the greatest H-index. Keyword evaluation showed that biomass gasification is a current hotspot, among which life-cycle assessment, sustainability, and deep processing of gasification products are future research directions. This work is predicted to offer further research interest in biomass gasification.

Production of biochar from crop residues and its application for biofuel production processes - An overview

A sustainable carbon-neutral society is imperative for future generations, and biochars and biofuels are inevitable choice to achieve this goal. Crop residues (CR) such as sugarcane bagasse, corn stover, and rice husk are promising sustainable resources as a feedstock for biochars and biofuels. Extensive research has been conducted on CR-based biochar production not only in environmental remediation areas but also in application for biofuel production. Here, the distribution and resource potential of major crop residues are presented. The production of CR-biochar and its applications in biofuel production processes, focusing on the latest research are discussed. Finally, the challenges and areas of opportunity for future research in terms of CR supply, CR-biochar production, and CR-biochar utilization for biofuel production are proposed. Compared with other literature reviews, this study can serve as a guide for the establishment of sustainable, economical, commercial CR-based biorefineries.

Involvement of the organics in aqueous phase of bio-oil in hydrothermal carbonization of lignin

Aqueous phase of bio-oil (APBO) is water-rich but also contains some sugar-derivatives and phenolics. APBO has little potential as feedstock for producing biofuel, but can be potentially used as medium for hydrothermal carbonization (HTC) of biomass. In this study, the HTC of lignin in APBO was conducted, aiming to probe the influence of the organics in APBO on property of the hydrochar. The results indicated that the organics in APBO cross-polymerized with lignin derivatives, resulted in the yield of hydrochar to exceed 100%. In addition, APBO promotes the deoxygenation but does not promote dehydrogenation. More aliphatic structures are generated in the hydrochar, reducing its thermal stability. In addition, the hydrochar from APBO also shows the improved combustion performance by lowering the activation energy and the ignition temperature (180 vs 240 °C).

Investigations on the pyrolysis of microalgal-bacterial granular sludge: Products, kinetics, and potential mechanisms

This study investigated the pyrolysis of microalgal-bacterial granular sludge for producing bio-oil and biochar. Results showed that the bio-oil productivity of pyrolyzed MBGS reached 39.5-45.4 wt%, while 23.8-41.2% for the nitrogen-containing bio-oil at the temperature of 673-1073 K. Meanwhile the biochar with a nitrogen content of 3.7-7.0 wt% could also be produced. Moreover, the Van-Krevelen diagram revealed that produced bio-oil had a H/C ratio higher than that from agroforestry biomass, but its O/C ratio was found to be similar to those of coal and biochar. It further appeared from a mass conservation analysis that the highest bio-oil production yield was achieved at a pyrolysis temperature of 773 K, while the pyrolytic kinetics of MBGS in the temperature range studied was governed by the 3-D diffusion mechanism with the activation energy of 224.96 kJ·mol^-1.

Pretreated residual biomasses in fluidized beds for chemical looping Gasification: Experimental devolatilizations and characterization of ashes behavior

The European research project CLARA (G.A. 817841) has studied pretreated residual biomasses for chemical looping gasification. This work investigated devolatilizations of wheat straw pellets (raw, torrefied, and torrefied-washed) at 700 °C, 800 °C, and 900 °C, performed in fluidized beds made of sand or three oxygen carriers (OCs): integral-average values (gas yield, H₂/CO molar ratio, and carbon conversion) were calculated; instantaneous peaks of released syngas were evaluated by regression straight lines. For all biomasses and bed materials, the temperature increase (from 700 to 900 °C) was the dominant parameter, positively affecting all integral-average values. The OCs appeared more active at 900 °C. Biomass pretreatments improved the H₂/CO molar ratio and decreased carbon conversion. SEM analyses showed that the purpose of washing (removal of low-melting elements) may be jeopardized by OCs' composition.

Step washing: A modified pretreatment approach for industrial applications to improve chemical composition of agricultural residues

To improve the efficiency and applicability of the washing pre-treatment for combustion, pyrolysis and gasification, a modified approach was developed in the present study. Two novel washing approaches were tested using wheat straw and empty fruit bunches of oil palm: multiple-step washing with fresh water (SWFW) and wastewater recirculation (SWWR). SWFW showed the high removal of K (<68%), Cl (<99%), S (<80%), N (<58%), and ash (<52%) reducing fouling, slagging, and corrosion propensity of the biomass. Furthermore, with one-third the amount of water used in SWFW, SWWR showed similar to higher efficiency than SWFW with relatively better energy (98%) yields. Industrial-scale pilot testing was also conducted for the validation of the SWWR approach, which showed similar findings as the lab-scale results. The effect of a high washing temperature and pressing on washing efficiency and characterisation of wastewater was also determined. Overall, SWWR with pressing is recommended for industrial applications.

Effect of basic washing parameters on the chemical composition of empty fruit bunches during washing pretreatment: A detailed experimental, pilot, and kinetic study

The present study aimed to evaluate the effect of basic washing parameters on the chemical composition of empty fruit bunches of oil palm (EFB) and to determine the optimal parameters for large-scale applications of washing pre-treatment. Three basic washing parameters were studied in detail: washing duration, temperature, and solid/liquid (S:L) ratio. The leaching kinetics of ash and troubling elements such as K, Cl, N, and S were also evaluated with respect to washing time. About 82-98% Cl, 64-80% S, 38-77% K, 34-67% ash, and 24-63% N removal was noted after washing EFB, which follows a second-order leaching kinetics on increasing washing duration. Two pilot washing tests were also conducted to evaluate the effectiveness of the pre-treatment on a large scale, which showed similar trends as the laboratory results. The recommended EFB washing conditions for large-scale applications are 10 min washing with a 1:15 S:L ratio at 50 °C.

Investigation of element migration characteristics and product properties during biomass pyrolysis: a case study of pine cones rich in nitrogen

To further understand the element migration characteristics and product properties during biomass pyrolysis, herein, pine cone (PC) cellulose and PC lignin were prepared, and their pyrolysis behavior was determined using thermogravimetric analysis (TGA). Subsequently, the PC was pyrolyzed in a vertical fixed bed reactor system at 400–700 °C for 60 min. The characteristics of element migration and the physicochemical properties of the pyrolysis products were analyzed and discussed. In the pyrolysis temperature range from 200 °C to 500 °C, there were two distinct weight loss peaks for PC. During the pyrolysis process, the C element was primarily retained in the biochar, while the O element mainly migrated into liquid and gaseous products in the form of compounds such as CO₂, CO, and H₂O. Besides, 28.42–76.01% of the N element in PC migrated into biochar. Of the three-phase products, the gases endow the lowest energy yield, while the energy of the biochar dominates the pyrolysis of the PC. Additionally, the N content and specific surface area for the PC-derived biochar obtained at 400 °C in a N₂ atmosphere were higher than those of the biochar derived from fiberboard.

To further understand the element migration characteristics and product properties during biomass pyrolysis, herein, pine cone (PC) cellulose and PC lignin were prepared, and their pyrolysis behavior was determined using thermogravimetric analysis (TGA).

Eco-friendly rice husk pre-treatment for preparing biogenic silica: Gluconic acid and citric acid comparative study

Carboxylic acid leaching has been established eco-friendly pre-treatment method for producing biogenic silica (BSi) from rice husk. The most urgent issue is for carboxylic acid to promote new readily biodegradable acids and enhance carboxylic acid sustainability in BSi preparation. This research investigates gluconic acid (GA) applicability for biogenic silica preparation from rice husk compared with citric acid (CA). The results demonstrated that GA was preferable to CA on BSi recovery with 89.91% efficiency. Although GA leaching promoted slightly higher silica loss, the primary metal alkali impurities, such as K₂O, Na₂O, and Al₂O_3, were effectively removed at 92-93%, 89-93%, 95-97%, respectively. The combination effect of silica loss and high removal impurities resulted in lower rice husk thermal decomposition activation energy. The characteristics of BSi prepared by GA leaching were comparable with CA leaching, mainly mesoporous with 114.06 m²/g of specific surface area and 0.23 cm³/g of the pore volume. In addition, GA leaching was environmentally better than CA leaching, indicated by minor contribution to all environmental impact indices. The findings suggested that GA could be a potential replacement for prevalent carboxylic acids in BSi preparation.

Effect of algae (Scenedesmus obliquus) biomass pre-treatment on bio-oil production in hydrothermal liquefaction (HTL): Biochar and aqueous phase utilization studies

Environmental concerns due to fossil fuel usage has turned the research interest towards biomass and bioenergy field. Renewable biomass such as microalgae provides numerous advantages as they can grow in wastewater; sequester carbon dioxide, economical and eco-friendly. In this study, effect of pretreatment of microalgae (Scenedesmus obliquus) biomass using post-hydrothermal liquefaction wastewater (PHWW) for bio-oil production through hydrothermal liquefaction at a temperature of 300 °C was studied. Results showed liquefaction of pre-treated biomass yielded 48.53% bio-oil whereas 28.35% was resulted from biomass without pretreatment. The analysis of higher heating value of bio-oil showed that pretreated biomass oil has 36.19 MJ.Kg^-1 against non-pretreated biomass oil, which has 28.88 MJ.Kg^-1. Bio-oil (pretreated biomass) analysis revealed that 60% of compounds are in diesel and gasoline range with 58.09% of energy recovery. Bio-oil was rich in hydrocarbons of C₇-C₂₁ range with less oxygenated compounds. Carbon balance showed that an increase of 13% of carbon was sequestered in solid residue obtained from pretreated biomass and about 146% of increase also obtained in bio-oil.

Influences of the Pretreatments of Residual Biomass on Gasification Processes: Experimental Devolatilizations Study in a Fluidized Bed

The European research project CLARA (chemical looping gasification for sustainable production of biofuels, G.A. 817841) investigated chemical looping gasification of wheat straw pellets. This work focuses on pretreatments for this residual biomass, i.e., torrefaction and torrefaction-washing. Devolatilizations of individual pellets were performed in a laboratory-scale fluidized bed made of sand, at 700, 800, and 900 °C, to quantify and analyze the syngas released from differently pretreated biomasses; experimental data were assessed by integral-average parameters: gas yield, H2/CO molar ratio, and carbon conversion. A new analysis of devolatilization data was performed, based on information from instantaneous peaks of released syngas, by simple regressions with straight lines. For all biomasses, the increase of devolatilization temperature between 700 and 900 °C enhanced the thermochemical conversion in terms of gas yield, carbon conversion, and H2/CO ratio in the syngas. Regarding pretreatments, the main evidence is the general improvement of syngas quality (i.e., composition) and quantity, compared to those of untreated pellets; only slighter differentiations were observed concerning different pretreatments, mainly thanks to peak quantities, which highlighted an improvement of the H2/CO molar ratio in correlation with increased torrefaction temperature from 250 to 270 °C. The proposed methods emerged as suitable straightforward tools to investigate the behavior of biomasses and the effects of process parameters and biomass nature.

Comparative Study on the Pyrolysis Behaviors of Pine Cone and Pretreated Pine Cone by Using TGA-FTIR and Pyrolysis-GC/MS

Pine cone (PC) is a potential biomass energy source and is rich in nonstructural substances (NSS). To understand the impact of these NSS on the pyrolysis behavior and its products, in this study, phenol alcohol extraction was used for the separation of NSS from PC (the PC after separation of NSS was labeled as A-PC), and then thermogravimetric analysis -Fourier transform infrared and PY-gas chromatography/MS detection techniques were used to conduct a systematic comparison of the thermal degradation behaviors and kinetics parameters of PC and A-PC. Results showed that the N content of PC was higher than that of other biomass, and the activation energies of PC and A-PC generally decreased at first and then increased as the conversion rate increased. Furthermore, the activation energy of PC decreased with conversion rates in the range of 0.25-0.30, while A-PC lagged significantly behind PC. On the other hand, the maximum absorption peak of CH₄ for PC was higher than that of A-PC, and the maximum absorption peak of CO₂ was quite the opposite. After extracting NSS from the PC, its activation energy was significantly increased.

Coupling anaerobic digestion and pyrolysis processes for maximizing energy recovery and soil preservation according to the circular economy concept

After press separation of the liquid and solid digestate from an agricultural biogas plant, pyrolysis of solid anaerobic digestate was carried out (i.e., at 500 °C, 1h, and 10 °C/min) to produce biochar (37.6 wt%), bio-oil (33.7 wt%) and syngas (29.3 wt%). The organic phase of bio-oil and syngas exhibited high and low heating values of 28.4 MJ/kg and 12.9 MJ/Nm³, respectively. Then, the synergy of coupling biochar with liquid digestate for agronomic purposes was investigated by leaching experiment and growth plant tests on wheat. Leaching experiments using combination of liquid digestate (170 kg N/ha) and biochar demonstrated that biochar addition increases the cumulative leaching of all nutrients, except nitrate, that have a significant decrease of 82% and 91%, respectively at 50 and 100 t/ha, compared to soil treated only with liquid digestate. The co-application of biochar with liquid digestate on growth wheat plant tests demonstrated that biochar application at 50 t/ha did not exhibit a negative impact on the relative seed germination and improved aerial dry biomass production (up to 27.5%) compared to soil with only liquid digestate addition.

Gas-pressurized torrefaction of biomass wastes: The optimization of pressurization condition and the pyrolysis of torrefied biomass

A novel gas-pressurized (GP) torrefaction with high oxygen removal efficiency at mild temperature was proposed in our previous work. However, the optimal condition of the GP torrefaction and subsequent pyrolysis of the torrefied biomass were not clear. In this work, the effect of pressure on the GP torrefaction and pyrolysis product properties of the torrefied biomass were studied in detail. The results show that the pressure increasing from 1.7 MPa to 5.0 MPa just slightly contributed to further oxygen removal, and 1.7 MPa was thus selected as the optimum pressure. The GP torrefaction significantly improved the product property of biomass pyrolysis compared to the conventional torrefaction (AP torrefaction). The acids content in bio-oil was reduced from 15-20% to less than 5%, and the calorific value of biogas increased to as high as 16.57-19.31 MJ/Nm³. Furthermore, an overall conversion mechanism of combined GP torrefaction and subsequent pyrolysis of biomass was proposed.

Modification on biochars for applications: A research update

Biochars are the solid product of biomass under pyrolysis or gasification treatment, whose wholesale prices are lower than commercial activated carbons and other fine materials now in use. The employment of biochars as a renewable resource for field applications, if feasible, would gain apparent economic niche. Modification using physical or chemical protocol to revise the surface properties of biochar for reaching enhanced performances of target application has attracted great research interests. This article provided an overview of biochar application, particularly with the respect to the use of modified biochar as preferred soil amendment, adsorbent, electrochemical material, anaerobic digestion promotor, and catalyst. Based on literature works the current research trends and the prospects and research needs were outlined.

Hydrothermal liquefaction of Prosopis juliflora biomass for the production of ferulic acid and bio-oil

The objective of this work was to study the hydrothermal liquefaction (HTL) of Prosopis juliflora biomass for the production of ferulic acid and bio-oil. Biomass was processed with various solvents (NaOH, KOH, HCl and H₂SO₄) to produce ferulic acid (FA). FA oxidation was carried out using the Nano ZnO catalyst to produce an optimum vanillin yield of 0.3 g at 70 °C with 0.4% catalyst loading for a time of 60 min. The spent solid residue was then processed using HTL at 5 MPa pressure and a temperature range of 240-340 °C. Various biomass loading (2.5 g to 12.5 g) was taken for a fixed water content of 200 mL. Bio-oil optimum yield was 22.5 wt% for 10 g/200 mL of biomass loading ratio. The optimum temperature was 300 °C for a processing time of 1 h. The catalyst showed the reusable capability of two three consecutive cycles.

Features and Commercial Performance of a System of Biomass Gasification for Simultaneous Clean Heating and Activated Carbon Production

Biomass is a renewable and clean energy. Moreover, clean heating plays a vital role in solving issues related to the heating source structures in northern China. This paper reports on our novel technology: a system of biomass (mainly fruitwood waste, referred to in short as FWW) gasification for simultaneous clean heating and fruitwood activated carbon (FAC) production. In particular, we will discuss the features of our gasification system and product characteristics, as well as energy efficiency, environmental benefits, and economic benefits. The results showed that the energy conversion from FWW gasification was as follows: 48.10% hot gas, 49.08% fruitwood gasified carbon (FGC), and 2.82% energy loss. The NO _x emissions of this system were about 126 mg/Nm³. The iodine adsorption values of the derived FGC and FAC were about 550 and 1000 mg/g, respectively. The system of gasification consumed 36 t of FWW per day, obtained 10 t of FGC, and produced 5 t of FAC. The emissions of CO₂ were neutral during the operation, and the clean heating area was 4100 m²/d in Chengde, Hebei, China, with the payback period under one heating season. These results show that the system is practical, economical, energy-saving, and environmentally friendly.

Product Distribution of Chemical Product Using Catalytic Depolymerization of Lignin

Lignin depolymerization is a very promising process which can generate value-added products from lignin raw materials. The main objective of lignin depolymerization is to convert the complex molecules of lignin into small molecules. Nevertheless, lignin is natural polymer which the molecules of lignin are extremely complicated due to their natural variability, and it will be a big challenge to depolymerize lignin, particularly high water yield. The various technology and methods are developed to depolymerize lignin into biofuels or bio chemical products including acid/base/metallic catalyzed lignin depolymerization, pyrolysis of lignin, hydroprocessing, and gasification. The distribution and yield of chemical products depend on the reaction operation condition, type of lignin and kind of catalyst. The reactor type, product distributions and specific chemicals (benzene, toluene, xylene, terephthalic acid) production of lignin depolymerization are intensive discussed in this review. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Hydrothermal liquefaction of Scenedesmus obliquus using a novel catalyst derived from clam shells: Solid residue as catalyst for hydrogen production

This study explores the catalytic application of waste clam shell in hydrothermal liquefaction (HTL) of microalgae (Scenedesmus obliquus) for liquid hydrocarbons production. Novel catalyst (calcium hydroxide) was derived from clam shells. Catalytic HTL was performed at varying temperature of 240-320 °C for catalyst load (0.2-1 wt%) at a reaction time of 60 min. Bio-oil yield was maximum (39.6 wt%) at a temperature of 300 °C for catalyst load of 0.6 wt% at a reaction time of 60 min with calorific value of 35.01 MJ/kg. Compounds like phenols, aromatic hydrocarbons, acids and aldehydes were detected in bio-oil through Gas Chromatography Mass Spectrophotometry (GC-MS). Gasification of microalgae with waste solid residue obtained from HTL was carried out for hydrogen production. Valuable hydrogen gas production was maximum (37 wt%) at a temperature of 400 °C for 3 wt% of solid residue. Water-gas shift, methanation and steam reforming reactions favoured the hydrogen gas production.

Effect of hydrothermal pretreatment on the demineralization and thermal degradation behavior of eucalyptus

Effective removal of alkali and alkaline earth metals (AAEM) is of great significance for promoting biomass pyrolysis. In this study, demineralization via hydrothermal pretreatment was performed, and the effect on the pyrolysis behavior was evaluated by thermogravimetric analysis (TGA) and thermal pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). The effects of reaction temperature, time, and pH on the dissolution rate of K⁺, Ca²⁺, and Mg²⁺ were investigated. The optimal total dissolution rate of the metal elements was 42.10%. Compared with acid leaching, hydrothermal pretreatment allowed a higher crystallinity index. It significantly changed the pyrolysis behavior. The relative content of sugar in pyrolysis products was as high as 58%. The chemical compound distribution was concentrated in the range between C6 and C9, which was conducive for the refinement of gasoline by upgrading. This means that hydrothermal pretreatment has efficient demineralization, which promoted the thermal degradation behavior of biomass.

Upgrading of bio-oil via solar pyrolysis of the biomass pretreated with aqueous phase bio-oil washing, solar drying, and solar torrefaction

In this study, three types of biomass were first pretreated with an aqueous phase bio-oil instead of traditional acid washing. Then, the washed samples were pretreated with drying (100 ℃, 30 min) and torrefaction (250 ℃, 30 min) using a parabolic-trough solar receiver system. The subsequent pyrolysis was performed at 550 ℃ for 10 min using a parabolic-dish solar receiver system. Results showed that the solar energy can effectively ensure the temperature required for biomass drying, torrefaction, and pyrolysis, having thus a potential to replace the conventional electric heating or fossil fuel heating. Such a strategy combines the advantages of the independent pretreatments, i.e., leaching out of metallic species and reduction of oxygen content. Consequently, the high heating value of bio-oil increased remarkably, the generation of acids was strongly inhibited, whereas the formation of phenols and anhydrosugars was promoted. Therefore, the method proposed herein is promising for upgrading of biomass and bio-oil.

Enhancement of hydrocarbons production through co-pyrolysis of acid-treated biomass and waste tire in a fixed bed reactor

The elution of metallic content from cotton stalk (CS) and its co-pyrolysis with waste tires (WT) was investigated in fixed bed reactor. Hydrochloric acid (HCl) was used for leaching and successful removal of metals from cotton stalk was observed. Removal efficiencies of 86%, 58%, 48%, 58% and 35% for potassium, calcium, magnesium, sodium, and iron metals were achieved, respectively. Pyrolysis and co-pyrolysis using various mixing ratios of raw (R-CS) and acid washed cotton stalk (W-CS) with waste tire were carried out at 550 °C. Co-pyrolyzing W-CS with WT not only resulted in increased liquid yield with reduced char and gas yields, but also improved the quality of pyrolytic oil evincing the occurrence of strong positive synergistic effect. The addition of WT reduced oxygenates, density and water content of oil whilst pH and calorific value are increased compared to both, R-CS and W-CS pyrolytic oils. Relative percentage area of hydrocarbons increased to 65% in co-pyrolysis of WT with W-CS as compared to 47% for that of R-CS at optimum blend ratio (CS:WT 1:3). Likewise, 19% higher reduction in oxygenated compounds was observed in W-CS and WT co-pyrolytic oil. Co-pyrolyzing WT with R-CS and W-CS resulted in improved quality of oil. However, the synergistic effect was less significant for R-CS suggesting that the presence of intrinsic metals in R-CS hampered the occurrence of synergistic effects.

A green route for pyrolysis poly-generation of typical high ash biomass, rice husk: Effects on simultaneous production of carbonic oxide-rich syngas, phenol-abundant bio-oil, high-adsorption porous carbon and amorphous silicon dioxide

Rice husk is a widespread agriculture waste in rice-farming country. High silica content in rice husk prevent its efficient utilization. So in this work, concept of poly-generation was introduced to improve its utilization value. This study provided CO-rich syngas, phenol-abundant bio-oil, high-adsorption porous carbon and amorphous SiO₂ as four end products for first time via combination of acid washing and activated carbon catalyst. Specifically, acid washing effectively decreasedsoluble ash, which altered pyrolysis paths, increased volatiles release and reduced impurities in bio-char. After catalytic pyrolysis, phenol content of 65.56% and CO of 56.09 vol% were detected in bio-oil and syngas from AWRH. For solid products, acid washing benefited both bio-char and silica. A low-cost porous carbon with developed pores and rich surface functional groups was prepared for water absorption. And high purity amorphous SiO₂ was recycled from alkali etching solution. Finally, a green process with no waste emission was proposed.

New Perspective on Wood Thermal Modification: Relevance between the Evolution of Chemical Structure and Physical-Mechanical Properties, and Online Analysis of Release of VOCs

Thermal modification (TM) is an ecological and low-cost pretreated method to improve the dimensional stability and decay resistance of wood. This study systematically investigates the relevance between the evolution of chemical structure and the physical and mechanical properties during wood thermal modification processes. Moreover, the volatility of compounds (VOCs) was analyzed using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TGA-FTIR) and a pyrolizer coupled with gas chromatography/mass spectrometer (Py-GC/MS). With an increase of TM temperature, the anti-shrink efficiency and contact angle increased, while the equilibrium moisture content decreased. This result indicates that the dimensional stability improved markedly due to the reduction of hydrophilic hydroxyl (–OH). However, a slight decrease of the moduli of elasticity and of rupture was observed after TM due to the thermal degradation of hemicellulose and cellulose. Based on a TGA-FTIR analysis, the small molecular gaseous components were composed of H₂O, CH₄, CO₂, and CO, where H₂O was the dominant component with the highest absorbance intensity, i.e., 0.008 at 200 °C. Based on the Py-GC/MS analysis, the VOCs were shown to be mainly composed of acids, aldehydes, ketones, phenols, furans, alcohols, sugars, and esters, where acids were the dominant compounds, with a relative content of 37.05−42.77%.

Hydrothermal liquefaction of Scenedesmus abundans biomass spent for sorption of petroleum residues from wastewater and studies on recycling of post hydrothermal liquefaction wastewater

In this study Scenedesmus abundans was used as a biosorbent material for removing hydrocarbons from simulated petroleum wastewater. Batch experiments resulted in the removal of 92.16% of hydrocarbons from simulated wastewater within 60 min. The spent biosorbent was converted to bio-oil through hydrothermal liquefaction process (HTL) at temperature range from 220 to 320 °C with 1 h holding time. Liquid hydrocarbons (bio-oil) yield was 43.4 wt% at 300 °C with 15 g of spent sorbent loading and possessed HHV of 39.10 MJ/Kg. Additionally the HTL wastewater (aqueous phase) was recycled as reaction medium and studied for its effects on bio-oil yield which increased till second cycle (47.91 wt%). HTL bio-char was employed as adsorbent to remove heavy metals from wastewater. It showed greater removal efficiency of 86.5% to Ni(II) ions. From the results it was concluded that the petroleum residues can be effectively recycled back into liquid hydrocarbons with simple waste management pathway.

Choosing Physical, Physicochemical and Chemical Methods of Pre-Treating Lignocellulosic Wastes to Repurpose into Solid Fuels

Various methods of physical, chemical and combined physicochemical pre-treatments for lignocellulosic biomass waste valorisation to value-added feedstock/solid fuels for downstream processes in chemical industries have been reviewed. The relevant literature was scrutinized for lignocellulosic waste applicability in advanced thermochemical treatments for either energy or liquid fuels. By altering the overall naturally occurring bio-polymeric matrix of lignocellulosic biomass waste, individual components such as cellulose, hemicellulose and lignin can be accessed for numerous downstream processes such as pyrolysis, gasification and catalytic upgrading to value-added products such as low carbon energy. Assessing the appropriate lignocellulosic pre-treatment technology is critical to suit the downstream process of both small- and large-scale operations. The cost to operate the process (temperature, pressure or energy constraints), the physical and chemical structure of the feedstock after pre-treatment (decomposition/degradation, removal of inorganic components or organic solubilization) or the ability to scale up the pre-treating process must be considered so that the true value in the use of bio-renewable waste can be revealed.

Pyrolysis of date palm waste to biochar using concentrated solar thermal energy: Economic and sustainability implications

A system of concentrated solar energy for pyrolysis of date palm waste to biochar is designed and simulated using SuperPro Designer v8.5. Both economic and environmental sustainability implications are evaluated by bench-marking with the conventional process (electric heating-based pyrolysis). Economic analysis shows that this process is more economically viable than the conventional process, with payback time (PBT) of 4 years and 132 days, internal rate of return (IRR) of 14.8%, return on investment (ROI) of 22.9% and gross margin of 35.5%. Environmental impact assessment shows that CO₂ emissions from concentrated solar energy-based pyrolysis accounts for only 38% of that of the conventional pyrolysis, indicating that concentrated solar energy pyrolysis is more environmentally friendly. Sensitivity analysis shows that PBT is more sensitive to changes in biochar selling price than changes in the cost of acquiring date palm waste. This process presents sustainable opportunities for biochar production while reducing life cycle emissions and costs.