Machine learning models for predicting biochar properties from lignocellulosic biomass torrefaction

This study developed six machine learning models to predict the biochar properties from the dry torrefaction of lignocellulosic biomass by using biomass characteristics and torrefaction conditions as input variables. After optimization, gradient boosting machines were the optimal model, with the highest coefficient of determination ranging from 0.89 to 0.94. Torrefaction conditions exhibited a higher relative contribution to the yield and higher heating value (HHV) of biochar than biomass characteristics. Temperature was the dominant contributor to the elemental and proximate composition and the yield and HHV of biochar. Feature importance and SHapley Additive exPlanations revealed the effect of each influential factor on the target variables and the interactions between these factors in torrefaction. Software that can accurately predict the element, yield, and HHV of biochar was developed. These findings provide a comprehensive understanding of the key factors and their interactions influencing the torrefaction process and biochar properties.

Effects of water washing and KOH activation for upgrading microalgal torrefied biochar

Torrefaction is an effective pathway for microalgal solid biofuel upgrading, and alkali metal activation is also an efficient method to enhance fuel properties. This study explores the comparison of torrefaction alone and KOH activation combined with torrefaction to determine a better operation for biochar production from the microalga Nannochloropsis Oceanica. The results indicate that the HHV ranges of KOH-activated biochar and unactivated biochar are 25.611-32.792 MJ·kg-1 and 25.024-26.389 MJ·kg-1, respectively. Furthermore, KOH-activated biochar is better than unactivated biochar, with less residue, broader pyrolysis and combustion temperature ranges, higher elemental carbon, and less combined carbon. Moreover, KOH-activated biochar is close to the unactivated one from the viewpoint of expense calculation and life cycle assessment and thus possesses a better comprehensive performance. Overall, KOH activation is an efficient method for upgrading microalgal solid biofuel. The results are conducive to exploring further modification of microalgal solid biofuel production with better properties, thus leading to a greener and more efficient approach for upgrading fuel performance.

A case study of metropolitan city

Solid waste management is one of the biggest challenges of the current era. The combustible fractions in the waste stream turn out to be a good energy source if converted into refuse-derived fuel. Researchers worldwide are successfully converting it into fuel. However, certain challenges are associated with its application in gasifiers, boilers, etc. to co-fire it with coal. These include high moisture content, low calorific value, and difficulty to transport and store. The present study proposed torrefaction as a pretreatment of the waste by heating it in the range of 200 °C-300 °C in the absence of oxygen at atmospheric pressure. The combustible fraction from the waste stream consisting of wood, textile, paper, carton, and plastics termed as mixed waste was collected and torrefied at 225 °C, 250 °C, 275 °C, and 300 °C for 15 and 30 min each. It was observed that the mass yield and energy yield decreased to 45% and 62.96% respectively, but the energy yield tended to increase by the ratio of 1.39. Proximate analysis showed that the moisture content and volatile matter decreased for torrefied samples, whereas the ash content and fixed carbon content increased. Similarly, the elemental analysis revealed that the carbon content increased around 23% compared to raw samples with torrefaction contrary to hydrogen and oxygen, which decreased. Moreover, the higher heating value (HHV) of the torrefied samples increased around 1.3 times as compared to the raw sample. This pretreatment can serve as an effective solution to the current challenges and enhance refuse-derived fuel's fuel properties.

Alteration of biomass toxicity in torrefaction - A XDS-CALUX bioassay study

Torrefaction constitutes one of the promising technologies for the management of waste biomass and the production of high-carbon products for combustion, gasification, adsorption of pollutants or soil treatment. Unfortunately, waste biomass may be contaminated with toxic persistent organic pollutants, such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) and dioxin-like biphenyls (dl-PCB). Literature does not provide consistent measurements on how the low-temperature thermochemical processing, such as torrefaction, affects the toxicity of biomass. This contribution assesses how a torrefaction treatment, conducted at 200 °C, modifies the toxicity due to PCDD/PCDF/dl-PCB in biomass. We deploy the XDS-CALUX biotest on five types of waste biomass (sewage sludge, tree bark, cattle manure, spent coffee ground, common reed), before and after treatment. The content of total dioxin- & biphenyl fraction compounds in the raw biomass, investigated in this study, varies from 0.14 to 3.67 pg BEQ·g-1d.m., and in the torrefied biomass between 0.17 and 6.00 pg BEQ·g-1d.m.; BEQ stands for bioanalytical equivalent. This increase is statistically insignificant at p = 0.05, taking into account all types of examined biomass. This proves that low-temperature torrefaction cannot detoxify biomass, i.e., chars, produced from biomass characterized by elevated concentration of PCDD/PCDF/dl-PCB, will reflect the contamination of the feedstocks. With respect to heavy metals, we conclude that only the content of Cd in biomass, and, to a lesser extent, the abundance of Cu and Fe, modify the toxicity of this material during its thermochemical treatment at low temperature.

Experimental strategy for the preparation of adsorbent materials from torrefied palm kernel shell oriented to CO2 capture

In this study, an experimental strategy to obtain biochar and activated carbon from torrefied palm kernel shell as an efficient material for CO2 removal was evaluated. Biochar was obtained by slow pyrolysis of palm kernel shell at different temperatures (350 °C, 550 °C, and 700 °C) and previously torrefied palm kernel shell at different temperatures (220 °C, 250 °C, and 280 °C). Subsequently, activated carbons were prepared by physical activation with CO2 from previously obtained biochar samples. The CO2 adsorption capacity was measured using TGA. The experimental results showed that there is a correlation between the change in the O/C and H/C ratios and the functional groups -OH and C=O observed via FTIR in the obtained char, indicating that both dehydration and deoxygenation reactions occur during torrefaction; this favors the deoxygenation reactions and makes them faster through CO2 liberation during the pyrolysis process. The microporous surface area shows a significant increase with higher pyrolysis temperatures, as a product of the continuous carbonization reactions, allowing more active sites for CO2 removal. Pyrolysis temperature is a key factor in CO2 adsorption capacity, leading to a CO2 adsorption capacity of up to 75 mg/gCO2 for biochar obtained at 700 °C from non-torrefied palm kernel shell (Char700). Activated carbon obtained from torrefied palm kernel shell at 280 °C (T280-CHAR700-AC) exhibited the highest CO2 adsorption capacity (101.9 mg/gCO2). Oxygen-containing functional groups have a direct impact on CO2 adsorption performance due to electron interactions between CO2 and these functional groups. These findings could provide a new experimental approach for obtaining optimal adsorbent materials exclusively derived from thermochemical conversion processes.

Waste to Energy: Steam explosion-based torrefaction process to produce solid biofuel for power generation utilizing various waste biomasses

Currently, humankind is facing a serious environmental and climate crisis, which has accelerated the research on producing bioenergy from waste biomass as a carbon-neutral feedstock. In this study, the aim was to develop an upcycling strategy for waste biomass to solid-type biofuel conversion for power generation. Various types of waste biomass (i.e., waste wood after lumbering, sawdust-type mushroom waste wood, kudzu vine, and empty fruit bunches from palm) were used as sustainable feedstocks for steam explosion-based torrefaction. The reaction conditions were optimized for each waste biomass by controlling the severity index (Ro); the higher heating value increased proportional to the Ro increase. Additionally, component analysis revealed that steam explosion torrefaction mainly degraded hemicellulose, and most of the torrefied waste biomass met the Bio-Solid Refuse Fuel quality standard. The results provide not only a viable waste-to-energy strategy but also insights to address global climate change.

Effects of cation types in persulfate on physicochemical and adsorptive properties of biochar prepared from persulfate-pretreated bamboo

The adsorption behaviors of biochar are largely impacted by biomassfeedstock. In this study, two biochars were prepared from torrefaction of ammonium persulfate- and potassium persulfate-pretreated bamboo and then activated by cold alkali, which are named as ASBC and KSBC, respectively. The two biochars were characterized by different instruments, and their adsorption properties over cationic methylene blue (MB) were compared. The type of persulfates little affected the specific surface areas, but significantly impacted O (29.54 % vs. 35.113 %) and N (12.13 % vs. 3.74 %) contents, functional groups, and zeta potentials of biochars. MB adsorption onto ASBC/KSBC is a single-layer chemical endothermic process and ASBC/KSBC exhibit high adsorption capacity over MB (475/881 mg·g-1) at 303 K. Obviously, the sorption capacity of MB onto KSBC much surpasses that of MB onto ASBC. These results indicate biomass pre-treatment is a cheap and convenient method to prepare biochars with unique physicochemical and adsorptive properties.

Effect of torrefaction on fuel properties of biopellets

The study aimed to determine the effects of torrefaction on the fuel properties of pellets. Therefore, firstly, torrefaction parameters of rose (Rosa Damascena Mill.) oil distillation solid waste and red pine sawdust were determined through the torrefaction optimization process in terms of temperature and holding time. Then, using the selected torrefaction parameters, 14 different raw and torrefied pellets containing RP, PS, and Turkish Elbistan Lignite were prepared in different weight ratios. Finally, the fuel properties of the prepared raw and torrefied pellets, namely dimensions, proximate analyses, higher heating values, tensile strength, durability, abrasive resistance, and water uptake resistances, were investigated. The findings demonstrated that the higher heating values and carbon content of raw biomass samples increased while their volatile matter content decreased. The use of lignite at high concentrations led to an increase in ash content and a decrease in the strength and durability of pellets, which should be emphasized. In addition, red pine sawdust was used in place of solid waste from rose oil distillation solid waste to produce pellets with greater strength. All pellet mixtures with torrefaction had higher heating values and energy densities despite the fact that their mass and energy efficiency had decreased. It was determined that torrefaction increased the pellets' resistance to absorbing water and gave them a more hydrophobic structure. Thus, it was determined that torrefaction could enhance the crucial fuel parameters of the biomass samples.

Catalytic torrefaction effect on waste wood boards for sustainable biochar production and environmental remediation

Wood boards used in construction are generally treated with toxic chemicals, making them unsuitable for further use and causing environmental pollution. This study evaluates the possibility of using catalytic torrefaction as a pretreatment to improve wood pyrolysis and combustion for greener biochar production. Waste beech boards were impregnated with different K2CO3 solutions (0-0.012 M), then torrefied between 5 and 60 min at 275 °C. The ICP-AES showed that the board's surface held more potassium than the core. Torrefaction coupled with potassium decreased the C-O and -OH stretches. Thermogravimetric analysis of torrefied wood showed that the board's internal heating degraded the core more than the surface. The exothermic reactions made potassium's catalytic action more efficient in the core. Interactions between the potassium content and torrefaction duration decreased the pyrolysis' maximum devolatilization temperature. During combustion, potassium decreased the ignition temperature by up to 9% and 3% at the surface and core, respectively, while the torrefaction increased it. The catalytic torrefaction significantly decreased the devolatilization peak during combustion, thus making the wood's combustion similar to that of coal, having only the char oxidation step. These findings highlight the advantages and challenges of waste wood's catalytic-torrefaction for biochar production to reduce environmental pollution.

Low-temperature biochar production from torrefaction for wastewater treatment: A review

Biochar, a carbon-rich and por ous material derived from waste biomass resources, has demonstrated tremendous potential in wastewater treatment. Torrefaction technology offers a favorable low-temperature biochar production method, and torrefied biochar can be used not only as a solid biofuel but also as a pollutant adsorbent. This review compares torrefaction technology with other thermochemical processes and discusses recent advancements in torrefaction techniques. Additionally, the applications of torrefied biochar in wastewater treatment (dyes, oil spills, heavy metals, and emerging pollutants) are comprehensively explored. Many studies have shown that high productivity, high survival of oxygen-containing functional groups, low temperature, and low energy consumption of dried biochar production make it attractive as an adsorbent for wastewater treatment. Moreover, used biochar's treatment, reuse, and safe disposal are introduced, providing valuable insights and contributions to developing sustainable environmental remediation strategies by biochar.

Torrefaction interpretation through morphological and chemical transformations of agro-waste to porous carbon-based biofuel

In the current study, two agro-waste lignocellulosic corncob (CC) and rice husk (RH) were thermally torrefied at 200-300 °C into a porous carbon-enriched biofuel. The scanning electron microscopy (SEM) of produced biofuel confirmed the rounded, homogenous, and spherical structure of the produced biofuels with higher porosity at a temperature between 250 and 300 °C with 60 min retention time. Brunauer-Emmett-Teller (BET) analysis indicated the high surface area (CC: 1.19-2.87 m2 g-1 and RH: 1.22-2.67 m2 g-1) and pore volume (CC: 1.23-2.81 ×10-3 m3 g-1 and RH: 1.46-2.58 ×10-3 m3 g-1). Crystallinity index decline percent (CC= 62.87% and RH=57.10%) estimated thermal stability and rise in amorphous cellulose reformation during (250-300 °C)/60 min that would efficiently hydrolyze during oxidative pyrolysis carbon reactive sites the rise in surface area and total pore's volume, having higher conversion rate as compared to raw materials. Carbon content was upgraded to 94% by eliminating hydrogen and oxygen from lignocellulosic agro-waste to produce energy-dense CC and RH. The lignin macromolecule transformation extent was estimated by O/C trend, which was equal to 63% and 47% for CC and RH, respectively, at 300 °C for 60 min. Due to low bulk density and pre-grinding energy requirements, torrefied biofuel with decomposed fibrous structure have lower transportation costs.

Dataset on the performance characteristics of briquettes from selected agricultural wastes using a piston-type briquetting machine

Densification of agricultural wastes for briquette production has considerable potential to meet the growing energy demand and contribute towards a safe environment worldwide. The datasets contained in this paper are the performance characteristics of raw and torrefied briquettes produced from sawdust (SD), cassava peels (CP), cornhusk (CH), and their blends using a developed piston-type briquetting machine. The physicomechanical, chemical, structural, and combustion indices including the kinetic parameters, were determined using standard methods. The result obtained show that each briquettes sample has the infrared transmittance of C-H, OH, C-O, and C=C with the SD sample having the highest and CP, the lowest. The feedstock mixture and increase in torrefaction temperature enhance the physicomechanical properties of the briquettes through water preconditioning. The combustion characteristics show that the torrefied briquettes and their blends could be co-fired with coal, and are well suited for heating applications and reduce environmental pollution. The activation energy, pre-exponential factor, and R2 values of the briquettes ranged between 39.70-60.76 kJ/mol, 5.52-9.17 min-1, and 0.95-0.98, respectively. The data provided in this paper will therefore be useful for energy enthusiasts and coal engine design, and assist in choosing the appropriate briquette blends with increased calorific value for heating applications.

Gas-pressurized torrefaction of lignocellulosic solid wastes: Low-temperature deoxygenation and chemical structure evolution mechanisms

A novel gas-pressurized (GP) torrefaction realizes deeper deoxygenation of lignocellulosic solid wastes (LSW) to as high as 79 % compared to traditional torrefaction (AP) with the oxygen removal of 40 % at the same temperature. However, the deoxygenation and chemical structure evolution mechanisms of LSW during GP torrefaction are currently unclear. In this work, the reaction process and mechanism of GP torrefaction were studied through follow-up analysis of the three-phase products. Results demonstrate gas pressure causes over 90.4 % of cellulose decomposition and the conversion of volatile matter to fixed carbon through secondary polymerization reactions. Above phenomena are completely absent during AP torrefaction. A deoxygenation and structure evolution mechanism model is developed through analysis of fingerprint molecule and C structure. This model not only provides theoretical guidance for optimization of the GP torrefaction, but also contributes to the mechanism understanding of pressurized thermal conversion processes of solid fuel, such as coal and biomass.

Biochar production from microalgae: a new sustainable approach to wastewater treatment based on a circular economy

The generation of wastewater due to human activities are the main responsible for environmental problems. These problems are caused by the large amount of organic and inorganic pollutants related to the presence of pesticides, metals, pathogens, drugs and dyes. The photosynthetic treatment of effluents emerges as a sustainable and low-cost alternative for developing wastewater treatment systems based on a circular economy. Chemical compounds present in wastewater can be recovered and reused as a source of nutrients in microalgae cultivation to produce value-added bioproducts. The microalgal biomass produced in the cultivation with effluents has the potential to produce biochar. Biochar is carbon-rich charcoal that can be obtained by converting microalgae biomass through thermal decomposition of organic raw material under limited oxygen supply conditions. Pyrolysis, torrefaction, and hydrothermal carbonization are processes used for biochar synthesis. The application of microalgal biochar as an adsorbent material to remove several compounds present in effluents is an effective and fast treatment. This effectiveness is usually related to the unique physicochemical characteristics of the biochar, such as the presence of functional groups, ion exchange capacity, thermal stability, and high surface area, volume, and pore area. In addition, biochar can be reused in the adsorption process or applied in agriculture for soil correction. In this context, this review article describes the production, characterization, and use of microalgae biochar through a sustainable approach to wastewater treatment, emphasizing its potential in the circular economy. In addition, the article approaches the potential of microalgal biochar as an adsorbent material and its reuse after the adsorption of contaminants, as well as highlights the challenges and future perspectives on this topic.

Identification of differences and comparison of fuel characteristics of torrefied agro-byproducts under oxidative conditions

Torrefaction is a pretreatment method for upgrading biomass into solid fuels. This study aimed to investigate the properties of agro-byproducts pretreated under different oxidative conditions at temperatures of 210-290 °C for 1 h to determine optimal operating conditions for upgrading biomass. The mass yields of lignocellulosic and herbaceous biomass were 90.27-42.20% and 92.00-45.50% and 85.71-27.23% and 88.09-41.58% under oxidative and reductive conditions, respectively. The calorific value of lignocellulosic and herbaceous biomass under oxidative conditions increased by approximately 0.14-9.60% and 3.98-20.02%, respectively. Energy yield of lignocellulosic and herbaceous biomass showed 63.78-96.93% and 90.77-44.39% showed 88.09-41.58% and 92.38-27.23% under oxygen-rich and deficit conditions. A decrease in oxygen and an increase in carbon dioxide and carbon monoxide were confirmed through gas measurements. Torrefaction evaluations were conducted using energy-mass co-benefit index (EMCI). Decreases of ΔEMCI were observed under certain conditions. Both oxidative and reductive conditions can be employed for pepper stems, wood pellets, and pruned apple branches. Based on standards, the optimal temperatures for pepper stems, wood pellets, and pruned apple branches in oxidative conditions were 250, 270, and 250 °C, respectively.

Heat balance analysis for self-heating torrefaction of dairy manure using a mathematical model

A self-heating torrefaction system was developed to overcome the difficulties in converting high-moisture biomass to biochar. In self-heating torrefaction, the ventilation rate and ambient pressure must be set properly to initiate the process. However, the minimum temperature at which self-heating begins is unclear because the effects of these operating variables on the heat balance are not theoretically understood. The present report presents a mathematical model for the self-heating of dairy manure based on the heat balance equation. The first step was to estimate the heat source; experimental data showed that the activation energy for the chemical oxidation of dairy manure is 67.5 kJ/mol. Next, the heat balance of feedstock in the process was analyzed. Results revealed that the higher the ambient pressure and the lower the ventilation rate at any given pressure, the lower the temperature at which self-heating is induced. The lowest induction temperature was 71 °C at a ventilation rate of 0.05 L min^-1 kg-AFS^-1 (AFS: ash-free solid). The model also revealed that the ventilation rate significantly affects the heat balance of feedstock and drying rate, suggesting an optimal range for ventilation.

Production of biochar from tropical fruit tree residues and ecofriendly applications - A review

Environmental contamination is considered a major issue with the growing urbanization and industrialization. In this context, the scientific society is engaged in searching for a sustainable, safe, and eco-friendly solution. Sustainable materials such as biochar play an important role in environmental contamination. It has some specific properties such as micropores which increase the surface area to bind the pollutants. This review endeavors to analyze the potential of fruit wastes especially tropical fruit tree residues as potential candidates for producing highly efficient biochar materials. The review discusses various aspects of biochar production viz. pyrolysis, torrefaction, hydrothermal carbonization, and gasification. In addition, it discusses biochar use as an adsorbent, wastewater treatment, catalyst, energy storage, carbon sequestration and animal feed. The review put forward a critical discussion about key aspects of applying biochar to the environment.

Spent coffee ground torrefaction for waste remediation and valorization

Spent coffee grounds (SCGs) are a noticeable waste that may cause environmental pollution problems if not treated appropriately. Torrefaction is a promising low-temperature carbonization technique to achieve waste remediation, recovery, and circular bioeconomy efficiently. This study aims to maximize lipids retained in thermally degraded SCGs, thereby upgrading their fuel quality to implement resource sustainability and availability. This work also analyzes the lipid contribution to biochar's calorific value under various carbonization temperatures and times. Torrefaction can retain 11-15 wt% lipids from SCG, but the lipid content decreases when the pyrolysis temperature is higher than 300 °C. Extracted lipid content consisting of fatty acids echoed the results of diesel adsorption capacity. The lipid content in the biochar from SCG torrefied at 300 °C for 30 min is 11.00 wt%, and its HHV is 28.16 MJ kg^-1. In this biochar, lipids contribute about 14.84% of the calorific value, and the other carbonized solid contributes 85.16%. On account of the higher lipid content in the biochar, it has the highest diesel adsorption amount per unit mass, with a value of 1.66 g g^-1. This value accounts for a 22.1% improvement compared to its untorrefied SCG. Accordingly, torrefaction can sufficiently remediate SCG-derived environmental pollution. The produced biochar can become a spilled oil adsorbent. Furthermore, oil-adsorbed biochar (oilchar) is a potential solid fuel. In summary, SCG torrefaction can simultaneously achieve pollution remediation, waste valorization, resource sustainability, and circular bioeconomy.

Temperature influence on layered double hydroxide tailored corncob biochar and its application for fluoride removal in aqueous media

Exposure to excess fluoride is a controversial public health concern as it can cause dental/skeletal fluorosis as well as renal toxicity. The study intended to evaluate the synergistic interaction of clay intercalation and thermochemical modification on corncob biochar to remove fluoride from aqueous solutions. Layered double hydroxide was assorted with thermally activated (torrefaction and pyrolysis) corncob biochar at 1:1 (w/w) ratio to obtain composites called LDH-CCBC250 and LDH-CCBC500. Physicochemically characterized adsorbents were assessed against the pH (3-9), reaction time (up to 12 h) and initial fluoride concentration (0.5-10 mg L^-1) for defluoridation. The porous structure of biochar was found to be richer compared to biocharcoal. The adsorption performance of LDH-CCBC500 was 6-fold higher compared to LDH-CCBC250 signifying the pronounced effect of thermal activation. Fluoride adsorption was pH dependent, and the best pH was in the range of pH 3.5-5.0 and there was no ionic strength dependency. Fluoride uptake by LDH-CCBC500 follows pseudo-second order and Elovich kinetic models, which suggests a chemisorption process followed by physisorption. The most expected way to eliminate fluoride by LDH-CCBC500, which had a maximum adsorption capacity of 7.24 mg g^-1, was cooperative chemical adsorption upon the Langmuir and Hills isotherm (r² = 0.99) parameters. Layered double hydroxide intercalated corncob biochar derived from slow pyrolysis is best performing in acidic waters.

Microwave processing of oil palm wastes for bioenergy production and circular economy: Recent advancements, challenges, and future prospects

The valorization and conversion of biomass into various value-added products and bioenergy play an important role in the realization of sustainable circular bioeconomy and net zero carbon emission goals. To that end, microwave technology has been perceived as a promising solution to process and manage oil palm waste due to its unique and efficient heating mechanism. This review presents an in-depth analysis focusing on microwave-assisted torrefaction, gasification, pyrolysis and advanced pyrolysis of various oil palm wastes. In particular, the products from these thermochemical conversion processes are energy-dense biochar (that could be used as solid fuel, adsorbents for contaminants removal and bio-fertilizer), phenolic-rich bio-oil, and H₂-rich syngas. However, several challenges, including (1) the lack of detailed study on life cycle assessment and techno-economic analysis, (2) limited insights on the specific foreknowledge of microwave interaction with the oil palm wastes for continuous operation, and (3) effects of tunable parameters and catalyst's behavior/influence on the products' selectivity and overall process's efficiency, remain to be addressed in the context of large-scale biomass valorization via microwave technology.

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.

Torrefaction characteristics of cellulose loaded with boric acid

To explore the catalytic effect of boric acid on biomass, cellulose loaded with boric acid was roasted by a tubular furnace. The gaseous products were adsorbed by activated carbon and then analyzed by GC-MS. Boric acid was shown to improve the selectivity of the product levoglucosenone (LGO). The effects of the parameters such as boric acid loading, nitrogen flow, and temperature on the torrefaction behavior of cellulose were investigated. In the studied temperature range of 240-420 °C, the yield of LGO first increases and then decreases. In addition, its yield increases directly with increasing nitrogen flow rate. The results show that the highest LGO yield of 6.64% (analytical value) can be obtained under 10% (w/w) boric acid loading, 380 °C and nitrogen flow rate of 65 ml/min conditions.

A rational and feasible approach to the co-management of condensates from biomass torrefaction and carbon-rich fly ash from fluidized-bed coal gasification

This study explored a promising approach to the co-management of torrefaction condensates (TCs) from biomass and carbon-rich fly ash (FA) derived from an industrial fluidized-bed coal gasifier. TC was a low-quality liquid product consisting mostly of water and a small amount of organic acids and other oxygenated organics. FA was the ultra-fine particulates with high carbon content (40-70%) and some extreme characteristics such as ultra-low volatiles, low reactivity, and high ignition temperature. The blending of FA and TC induced most of the organic components in TC to be chemically or physically adsorbed by FA, accounting for 3-13 wt% of the resultant mixtures of FA and TC (FATCs) and 11-33 wt% of the TCs. The acidic components in TC dissolved locally aggregated Ca minerals in FA, resulting in more evenly dispersed Ca on the surface of FA as an in-situ catalyst. As a result, FATCs exhibited a many-fold improvement in CO2 gasification reactivity compared to FA. And the syngas evolution rate of FATC gasification in steam-oxygen atmosphere was also remarkably elevated. In addition to the promoting effect on gasification, the combustion performance of FATCs was also greatly improved. Specifically, the ignition and burnout temperatures of FATCs were 46.5-68.5 °C and 12.4-31.7 °C lower than those of raw FA, respectively. The lower activation energy also demonstrated the higher reactivity of FATC gasification and combustion.

Torrefaction of organic municipal solid waste to high calorific value solid fuel using batch reactor with helical screw induced rotation

The potential of producing high calorific value (CV) solid fuel was investigated in a helical screw rotation-induced (HSRI) fluidized bed reactor based on mechanical fluidization. The study revealed that the HSRI torrefaction improved the torrefied product properties. For the 40 and 0 rpm conditions, the CV, fixed carbon, and ash contents of torrefied solid fuel increased with an increase in temperature. In contrast, volatile matter, moisture content, mass and energy yields decreased. The CV of torrefied solid fuel increased by a factor of 1.43 and 1.58 at 280 °C for the 40 and 0 rpm conditions, respectively. HSRI torrefaction enhanced the removal of hydroxyl functional group. HSRI torrefaction improved the hydrophobicity of the torrefied solid fuel. Therefore, the HSRI fluidized bed reactor promotes uniform temperature distribution, a higher heat transfer rate within the sample particles in the reactor, and a homogenous torrefied solid product compared to the fixed bed reactor.

The effect of torrefaction temperature and catalyst loading in Microwave-Assisted in-situ catalytic Co-Pyrolysis of torrefied biomass and plastic wastes

In the current study, the effect of torrefaction temperatures (125-175 °C) and catalyst quantity (5-15 g) on co-pyrolysis of torrefied sawdust (TSD) and polystyrene (PS) are investigated to obtain value-added products. The role of torrefaction in co-pyrolysis of TSD: PS was analyzed to understand the product yields, synergy, and energy consumption . As the torrefaction temperature increases, oil yield (48.3-59.6 wt%) and char yield (24.3-29 wt%) increase while gas yield (27.4-11.4 wt%) decreases. Catalytic co-pyrolysis showed a significant level of synergy when compared to non-catalytic co-pyrolysis. For the conversion (%), a positive synergy maximum (-2.6) exists at a torrefaction temperature of 175 °C and 15 g of KOH catalyst. To develop the model, polynomial regression-based machine learning was used to predict pyrolysisproduct yields and energy usage variables. The developed models showed significant prediction accuracy (R2 > 0.98), suggesting the experimental values and the predicted values matched well.

The role of solvent soaking and pretreatment temperature in microwave-assisted pyrolysis of waste tea powder: Analysis of products, synergy, pyrolysis index, and reaction mechanism

This study focuses on microwave-assisted pyrolysis (MAP) of fresh waste tea powder and torrefied waste tea powder as feedstocks. Solvents including benzene, acetone, and ethanol were used for soaking feedstocks. The feedstock torrefaction temperature (at 150 °C) and solvents soaking enhanced the yields of char (44.2-59.8 wt%) and the oil (39.8-45.3 wt%) in MAP. Co-pyrolysis synergy induced an increase in the yield of gaseous products (4.7-20.1 wt%). The average heating rate varied in the range of 5-25 °C/min. The energy consumption in MAP of torrefied feedstock (1386 KJ) significantly decreased compared to fresh (3114 KJ). The pyrolysis index dramatically varied with the solvent soaking in the following order: ethanol (26.7) > benzene (25.6) > no solvent (10) > acetone (6). It shows that solvent soaking plays an important role in the pyrolysis process. The obtained bio-oil was composed of mono-aromatics, poly-aromatics, and oxygenated compounds.

Post-consumer textile thermochemical recycling to fuels and biocarbon: A critical review

This study aims to look at waste-to-energy (tertiary recycling) of post-consumer textile waste, based on a literature review. Because textiles are mostly made of cotton and polyester, which are carbon and energy sources, they can potentially be converted thermochemically into fuels and biocarbon. The critical parameters determining thermal recycling are summarized and discussed with a focus on pyrolysis, gasification, and torrefaction. For cotton and polyester mixtures, torrefaction presents a low environmental impact and an energy-dense fuel that can be used in cogeneration systems, reducing the energy requirements of these processes by 50-85%. Catalytic pyrolysis of cotton textile waste yields to a high conversion (90 wt%), a liquid fuel of high yields (35-65 wt%), and biocarbon (10-18 wt%), providing carbon and energy closure loops. However, pyrolysis is energy-intensive (T > 500 °C) and produces hazardous chemicals from the conversion of PET, nylon, and polyacrylonitrile. Gasification can handle many types of textile waste, but it needs continuous monitoring of the emissions. More research is needed to overcome existing limitations, LCA and sustainability assessment are required for the thermal recycling processes in order to estimate their future-proofing and sustainability. For the transition to a circular economy, consumers' awareness of resources limits and sustainable use is pivotal to change purchasing behavior and achieve a recycling thinking.

Effect of Reaction Temperature on Properties of Torrefied Kenaf

Torrefaction is a thermal treatment method used to achieve solid-phase biofuel. Raw biomass generally have low heating value and high moisture content; thus, these characteristics should be enhanced before using it as a fuel. In this study, herbaceous biomass kenaf was torrefied at 220, 260, 300, and 340 °C under nitrogen atmosphere for 30 min to investigate the effect of temperature on its properties. The properties of torrefied kenaf were classified into two groups: physical properties such as mass and energy yields, moisture content, and proximate analysis and chemical properties such as functional groups and chemical compositions of sugars and lignin. The mass and energy yield of torrefied kenaf decreased as the reaction temperature increased. In addition, an increase in carbon content and a rapid decrease in oxygen content were observed in torrefied kenaf, which indicated the degradation of compounds such as hemicellulose and cellulose. Elemental analysis, proximate analysis, thermal analysis, Fourier transform infrared spectroscopy, and chemical composition analysis were performed to further investigate the characteristics of torrefied kenaf.

Effect of torrefied biomass on hydrophobicity and mechanical properties of polylactic acid composite

In this study, the physicochemical properties of torrefied biomass (larch and yellow poplar) were investigated based on torrefaction temperature. The effect of torrefied biomass on the hydrophobicity and mechanical properties of a polylactic acid (PLA) composites was evaluated. Hemicellulose was removed from the biomass during torrefaction, whereas the cellulose and lignin contents increased slightly. The color of the biomass changed from brown to black. The grindability of the torrefied biomass improved as the torrefaction temperature increased, which contributed to the production of fine particles (>100 mesh). A PLA composite was prepared using torrefied biomass (10 %) and polylactic acid. At 280 °C, water contact angle was the highest, regardless of the particle size and biomass species. Tensile strength of the PLA composite was slightly lower than that of PLA alone, regardless of the particle size of torrefied biomass. Nevertheless, the strength increased with the torrefaction temperature, except for larch with a relatively large particle size (<100 mesh). The tensile strength of the control was 68.0 MPa, whereas that of the torrefied biomass ranged from 61.1 to 65.8 MPa.

Effects of demineralization and devolatilization on fast pyrolysis behaviors and product characteristics of penicillin mycelial residues

In this study, the effects of demineralization and devolatilization methods including of water washing (WW), torrefaction (TF), washing-torrefaction (WT) and hydrothermal treatment (HT) on the fast pyrolysis characteristics of penicillin mycelial residues were studied. The materials and pyrolysis products were characterized by analysis methods including of thermogravimetric (TG), gas chromatograph (GC), gas chromatography-mass spectrometry (GC-MS), x-ray diffractometer (XRD), fourier transform-infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS), etc. The results showed WW increased the yields of tar and decreased the yields of pyrolysis biochar due to the removal of alkali and alkaline earth metals (AAEMs), while TF and HT showed opposite results due the devolatilization. XPS and FT-IR results proved that the conversion from aliphatic C-(C, H) to aromatic groups C-O-C and CO was the key point for improving the aromatization of biochar. Pretreatments increased the relative proportions of N-containing heterocyclic compounds and phenolic compounds, reduced the proportions of O-containing heterocyclic compounds in pyrolysis tar. And TF and HT could eliminate the residual antibiotic and satisfy the principle of AMR harmless disposal.

Conversion of biomass blends (walnut shell and pearl millet) for the production of solid biofuel via torrefaction under different conditions

The torrefaction of lignocellulose biomass was conducted to produce biochar with properties compatible with coal. Two lignocellulose biomasses, pearl millet (PM) and walnut shell (WS), were torrefied at different process temperatures (230-300 °C), residence times (30-90 min), and different compositional biomass blends to improve the characteristics of the biochar product. The resulting biochar product exhibited favorable changes in their properties. The pure biomasses and their blends obtained a high biochar yield (41-91%). The gross calorific value (GCV) ranged from 22 to 27 MJ/kg, showing an increase of 22-59% compared to the raw biomass. The torrefaction temperature had the most notable effect on the biochar quantity and quality. The biochar samples obtained from the torrefaction of different blends showed a higher GCV and other physicochemical characteristics than the pure biomasses. Scanning electron microscopy showed that these products might also be used for other applications.

Effects of torrefaction on product distribution and quality of bio-oil from food waste pyrolysis in N2 and CO2

Waste food utilization to produce bio-oil through pyrolysis has received increasing attention. The feedstock can be utilized more efficiently as its properties are upgraded. In this work, the mixed food waste (MFW) was pretreated via torrefaction at moderate temperatures (250-275 °C) under an inert atmosphere before fast pyrolysis. The pyrolysis of torrified MFW (T-MFW) was performed in a bubbling fluidized-bed reactor (FBR) to study the influence of torrefaction on the pyrolysis product distribution and bio-oil compositions. The highest liquid yield of 39.54 wt% was observed at a pyrolysis temperature of 450℃. The torrefaction has a significant effect on the pyrolysis process of MFW. After torrefaction, the higher heating values (HHVs) of the pyrolysis bio-oils (POs) ranged from 31.51 to 34.34 MJ/kg, which were higher than those of bio-oils from raw MFW (27.69-31.58 MJ/kg). The POs mainly contained aliphatic hydrocarbons (alkenes and ketones), phenolic, and N-containing derivatives. The pyrolysis of T-MFW was also carried out under the CO2 atmosphere. The application of CO2 as a carrier gas resulted in a decrease in the liquid yield and an increase in the gas product yield. In addition, the carbon and nitrogen content of POs increased, whereas the oxygen was reduced via the release of moisture and CO. Using CO2 in pyrolysis inhibited the generation of nitriles derivatives in POs, which are harmful to the environment. These results indicated that the application of CO2 to the thermal treatment of T-MFW could be feasible in energy production as well as environmental pollution control.

Profitability analysis of thermochemical processes for biomass-waste valorization: a comparison of dry vs wet treatments

Herein pyrolysis, torrefaction and hydrothermal carbonization of olive tree pruning were compared from an economic perspective. For this economic comparison a hypothetical industrial plant of 1250 kg/h of capacity was selected, and the profitability analysis was performed through the discounted cash flow method. A baseline scenario was defined, which serves for basis of later comparison. Results show that under these circumstances, none of the alternatives are profitable, with net present values between -37 M€ and -45 M€. Therefore, different scenarios were studied regarding either the reduction of the associate costs or the improvement of the revenues to analyze the negative economic outputs obtained in the baseline scenario. From the revenues side, breakeven prices for the different solid products between 1.14 and 1.35 €/kg are needed to reach profitability. To reach such values, either subsidies from governments or greater selling product prices are required. When examining the associated costs share, the energy consumption is the main cost factor (representing between 70 and 90% of the total, depending on the technology). This means that a variation on the rest of the parameters will not significantly affect the overall performance. Covering the total investment needed for the plants would still present negative net present values (around -34 M€ for the three alternatives). Similarly, even if the price of electricity could be reduced to 0.02 €/kWh, none of the alternatives would reach profitability. This study reveals the importance of finding economic solutions to evolve towards circular economy societies.

Torrefaction, temperature, and heating rate dependencies of pyrolysis of coffee grounds: Its performances, bio-oils, and emissions

The torrefaction pretreatment is of great significance to the efficient conversion of biomass residues into bioenergy. In this study, the effects of the three torrefaction temperatures (200, 250, and 300 °C) on the pyrolysis performance and products of coffee grounds (CG) were quantified. The torrefaction treatment increased the initial devolatilization and maximum peak temperatures of the CG pyrolysis. Activation energy of CG250 was lower than that of CG and more conducive to the pyrolysis. Torrefaction altered the distributions of the pyrolytic products and promoted the generation of C=C. Torrefaction changed the composition ratio of the pyrolytic bio-oils although cyanoacetic acid and 2-butene still dominated the bio-oils. The joint optimization pointed to pyrolysis temperature > 600 °C and torrefaction temperature ≤ 270 °C as the optimal conditions. Our experimental results also verified that torrefaction of CG may be more suitable at 200 and 250 °C than 300 °C.

Effect of in-situ torrefaction and densification on the properties of pellets from rice husk and rice straw

The research on preparing high-quality pellets by combining torrefaction and densification of biomass has received widespread attention. This paper investigated the influence of torrefaction temperature on biomass and evaluated the quality of three kinds of pellets (raw pellets, ex-situ torrefied densified pellets and in-situ torrefied densified pellets). When the torrefaction temperature was raised to 300 °C, the energy yield of rice straw (RS) and rice husk (RH) quickly decreased to 71.08% and 77.62%, and the cellulose was decomposed significantly. The results proved that 250 °C was an optimum temperature for RS and RH torrefaction. The densities of RS and RH in-situ torrefied densified pellets were 1236.84 kg/m³ and 1277.50 kg/m³ under 150 MPa, respectively. The density, Meyer hardness, hydrophobicity, and mechanical specific energy consumption of the pellet increased with the increase of molding pressure. The in-situ pellets had higher Meyer hardness, hydrophobicity, and lower mechanical specific energy consumption under the same molding pressure than raw pellets and ex-situ torrefied densified pellets. In addition, the bonding mechanism was studied by using scanning electron microscopy and ultraviolet auto-fluorescence. In-situ torrefaction and densification facilitated the formation of self-locking and the migration of lignin between particles. Compared with RH pellets, RS pellets had higher quality due to the higher hemicellulose content, which was necessary for forming stable hydrogen bonds.

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.

Progress in thermochemical conversion of aquatic weeds in shellfish aquaculture for biofuel generation: Technical and economic perspectives

Rapid growth of aquatic weeds in treatment pond poses undesirable challenge to shellfish aquaculture, requiring the farmers to dispose these weeds on a regular basis. This article reviews the potential and application of various aquatic weeds for generation of biofuels using recent thermochemical technologies (torrefaction, hydrothermal carbonization/liquefaction, pyrolysis, gasification). The influence of key operational parameters for optimising the aquatic weed conversion efficiency was discussed, including the advantages, drawbacks and techno-economic aspects of the thermochemical technologies, and their viability for large-scale application. Via extensive study in small and large scale operation, and the economic benefits derived, pyrolysis is identified as a promising thermochemical technology for aquatic weed conversion. The perspectives, challenges and future directions in thermochemical conversion of aquatic weeds to biofuels were also reviewed. This review provides useful information to promote circular economy by integrating shellfish aquaculture with thermochemical biorefinery of aquatic weeds rather than disposing them in landfills.

Thermochemical conversion of municipal solid waste into energy and hydrogen: a review

The rising global population is inducing a fast increase in the amount of municipal waste and, in turn, issues of rising cost and environmental pollution. Therefore, alternative treatments such as waste-to-energy should be developed in the context of the circular economy. Here, we review the conversion of municipal solid waste into energy using thermochemical methods such as gasification, combustion, pyrolysis and torrefaction. Energy yield depends on operating conditions and feedstock composition. For instance, torrefaction of municipal waste at 200 °C generates a heating value of 33.01 MJ/kg, while the co-pyrolysis of cereals and peanut waste yields a heating value of 31.44 MJ/kg at 540 °C. Gasification at 800 °C shows higher carbon conversion for plastics, of 94.48%, than for waste wood and grass pellets, of 70-75%. Integrating two or more thermochemical treatments is actually gaining high momentum due to higher energy yield. We also review reforming catalysts to enhance dihydrogen production, such as nickel on support materials such as CaTiO₃, SrTiO₃, BaTiO₃, Al₂O₃, TiO₃, MgO, ZrO₂. Techno-economic analysis, sensitivity analysis and life cycle assessment are discussed.

Adsorption of methylene blue dye from the aqueous solution via bio-adsorption in the inverse fluidized-bed adsorption column using the torrefied rice husk

In this work, the inverse fluidized-bed bio-adsorption column is applied for the first time and is demonstrated using the torrefied rice husk (TRH) for the removal of methylene blue from the solution. The bio-adsorbents were characterized by BET, FI-IR, and SEM. The inverse fluidized-bed adsorption column using TRH becomes saturated in the 95-min continuous adsorption, during which the breakthrough time is 22 min, the overall MB removal (R) is 84%, and the adsorption capacity (Q_exp) on the TRH is 6.82 mg g^-1. These adsorption characteristics are superior to those in the fixed-bed adsorption column (R of 52% and Q_exp of 2.76 mg g^-1) at a lower flow rate (100 vs. 283 cm³ min^-1). Torrefaction of RH significantly increases the surface area (28 vs. 9 m² g^-1) and enhances the surface functional groups, leading to an improved maximum equilibrium adsorption amount from 21.5 to 38.0 mg g^-1 according to Langmuir model in the batch adsorption system. Besides, the increased Q_exp on the TRH is also obtained in the inverse fluidized-bed (5.25 vs. 2.77 mg g^-1, 89% higher) and the fixed-bed (2.76 vs. 1.53 mg g^-1, 80% higher) adsorption columns compared to that on the RH.

Torrefied herb residues in nitrogen, air and oxygen atmosphere: Thermal decomposition behavior and pyrolytic products characters

The thermal decomposition behavior and pyrolytic products characters of herb residue (HR) torrefied in N₂, air and O₂ were investigated in present work. The clear gradual regularity of samples in Van Krevelen diagram exhibited the severity and some similarities of torrefaction. The activation energy (E) calculated by distributed activation energy model (DAEM) found that the E values of torrefied samples was higher than raw HR if the conversion is below 0.8. Torrefaction treatment would beneficial to increase the yield of gas but inhibit the formation of oil, and the compounds of gas and bio-oil under different torrefaction conditions are also quite different. It should be noticed that the presence of oxygen in the torrefaction atmosphere would reduce the torrefaction temperature significantly, while maintaining the severity of torrefaction and pyrolytic products distribution.

Fast pyrolysis of torrefied holocellulose for producing long-chain ether precursors in a fluidized bed

Combining torrefaction with fast pyrolysis is an achievable route for producing long-chain ether precursors. The results of structural characterization for native and torrefied holocellulose indicated that with increasing torrefaction temperature, the crystallinity index (CrI) decreased slightly and then sharply increased; hydroxyls, O-acetyl branches, ether bond and β-1,4-glycosidic bond were eliminated but carbonyls increased. Maximum mass loss rate and apparent activation energy increased after torrefaction. With an increase in torrefaction temperature, gaseous yield continuously dropped, and liquid product yield climbed to the highest point of 49.04% for holocellulose torrefied at 240 °C (240CS). Torrefaction was unfavorable for the production of small-molecule gases. The bio-oil analysis demonstrated that the yield of acetic acid decreased from 6.35% to 1.43% with torrefaction temperature increasing from 105 °C to 260 °C. Significantly, yields of targeted compounds were dramatically improved after torrefaction, and 240CS afforded the maximum carbon yield of 14.79%.

Torrefaction under mechanical pressure of 10-70 MPa at 250 °C and its effect on pyrolysis behaviours of leucaena wood

In this study, torrefaction under mechanical pressure of 10-70 MPa at 250 °C was proposed as a pretreatment method and its effect on pyrolysis behaviours of Leucaena (LC) was examined at 900 °C. It was found that the mechanical pressure applied during torrefaction could significantly increase the char yield at 900 °C. The char yield increased from 18.7% for Raw to 26.4% and 27.5% for MP40 and MP70, respectively. The %C of biochar prepared from MP40 (MP40-900) was 86.5%, whereas the %C of biochar prepared from raw (Raw-900) was 82.6%. From TG-MS analyses during the pyrolysis of MP, a large amount of oxygen was removed as H₂O and CO₂. The analyses of tars produced from MP showed higher fraction of acids and furans compared with tar produced from Raw. Furthermore, the mechanism of the pyrolysis of LC torrefied under mechanical pressure was discussed.

Energy balance of torrefied microalgal biomass with production upscale approached by life cycle assessment

Torrefaction is a thermochemical process used to convert the biomass into solid fuel. In this study, torrefaction increased the raw microalgal biomass' energy content from 20.22 MJ⋅kg^-1 to 27.93 MJ⋅kg^-1. To determine if more energy is produced than energy consumption from torrefaction, this study identified the energy balance of torrefied microalgal biomass production based on a life cycle approach. The energy analysis showed that, among all processes, torrefaction had the least amount of energy demand. The experimental setup, defined as scenario A, revealed that the principal source of energy demand, about 85%, was consumed on the microalgal growth using a photobioreactor system. A sensitivity analysis was also performed to determine the varying energy demand for torrefied microalgal biomass production. The different types of cultivation methods and various production scales were considered in scenarios B to D. Scenario D, which represented the commercial production-scale, the energy demand drastically decreased by 59.46% as compared to the experimental setup (scenario A). The open-pond cultivation system resulted in the least energy requirement, regardless of the production scale (scenarios B and C) among all the given scenarios. Unlike scenarios A and D, scenarios B and C identified the drying process to consume a high amount of energy. All the scenarios have shown an energy demand deficit. Therefore, efforts to decrease the energy demand on the upstream processes are needed to make the torrefied microalgal biomass a viable alternative energy source.

Green additive to upgrade biochar from spent coffee grounds by torrefaction for pollution mitigation

A green approach using hydrogen peroxide (H₂O₂) to intensify the fuel properties of spent coffee grounds (SCGs) through torrefaction is developed in this study to minimize environmental pollution. Meanwhile, a neural network (NN) is used to minimize bulk density at different combinations of operating conditions to show the accurate and reliable model of NN (R² = 0.9994). The biochar produced from SCGs torrefied at temperatures of 200-300 °C, duration of 30-60 min, and H₂O₂ concentrations of 0-100 wt% is examined. The results reveal that the higher heating value (HHV) of biochar increases with rising temperature, duration, or H₂O₂ concentration, whereas the bulk density has an opposite trend. The HHV, ignition temperature, and bulk density of biochar from torrefaction at 230 °C for 30 min with a 100 wt% H₂O₂ solution (230-100%-TSCG) are 27.00 MJ∙kg^-1, 292 °C, and 120 kg∙m^-3, respectively. This HHV accounts for a 29% improvement compared to that of untorrefied SCG. The contact angle (126°), water activity (0.51 a_w), and moisture content (7.69%) of the optimized biochar indicate that it has higher resistance against biodegradation, and thereby can be stored longer. Overall, H₂O₂ is a green treatment additive for SCGs solid fuel. This study has successfully produced biochar with greater HHV and low bulk density at low temperatures. The green additive development can effectively reduce environmental pollutants and upgrade wastes into resources, and achieve "3E", namely, environmental (non-polluting green additives), energy (biofuel), and circular economy (waste upgrade). In addition, the produced biochar has great potential in the fields of bioadsorbents and soil amendments.

Multiple drivers, interaction effects, and trade-offs of efficient and cleaner combustion of torrefied water hyacinth

Developing cleaner and affordable alternatives to the sole reliance on fossil fuels has intensified efforts to improve the thermochemical conversion property of the second-generation lignocellulosic biomass. This study aimed to explore the effects of the two torrefaction temperatures (200 and 300 °C), the two reaction atmospheres (N₂/O₂ and CO₂/O₂), and the three heating rates (5, 10, and 15 °C/min) on the combustion regime of water hyacinth (WH). Decomposition behaviors, reaction kinetics, thermodynamics, and mechanisms, evolved emissions and functional groups, and fuel microstructure properties were quantified. The deoxygenation and dehydration reactions acted as the main drivers of the torrefaction process, with the peak degree of deoxygenation of 86.21% for WH torrefied at 300 °C (WH300). WH300 significantly reduced the quantity of oxygen-containing functional groups and altered the fuel microstructure properties. The order of the decomposition rates of the pseudo-components were hemicellulose > cellulose > lignin for both WH and WH torrefied at 200 °C (WH200) and cellulose > lignin > hemicellulose for WH300. The average activation energy fell from 197.71 to 195.71 kJ/mol for WH, 287.90 to 195.97 kJ/mol for WH200, and 226.92 to 184.94 kJ/mol for WH300 when the atmosphere changed from N₂/O₂ to CO₂/O₂. The heating rate exerted a stronger control on their combustion behaviors than did the reaction atmosphere. CO₂, NO, and NO₂ emissions dropped by 46.0, 53.1, and 65.9% for WH200 and 29.6, 42.8, and 62.5% for WH300, respectively, when compared to WH. 473.7 °C, 5 °C/min, and the CO₂/O₂ atmosphere were the optimal settings for the maximized combustion efficiency. 717.1 °C was determined as the optimal setting for the minimized combustion emissions. Our study can yield new insights into the large-scale and cleaner combustion of the torrefied water hyacinth.

Evaluation on nitrogen conversion during biomass torrefaction and its blend co-combustion with coal

In this work, biomass torrefaction was combined with coal co-combustion to illustrate the differences in biomass performance and the mechanisms of migration and transformation of nitrogen over the entire course of thermal treatments. XPS analysis illustrated that torrefaction in CO₂ suppressed the conversion of pyrrole-N (N-5) to quaternary-N (N-Q), whereas the trend for an O₂ atmosphere moved in the opposite direction. During co-combustion, the impact on NO emission reduction shifted from positive to negative as the pretreatment temperature was raised, which is closely related to the six elementary reactions involving the intermediacy of NCO and NH, as well as to heterogeneous reduction of NO with char. In addition, torrefaction in a N₂/O₂ atmosphere at a lower temperature of 250 °C improved the properties of biomass and achieved the lowest NO emission during co-combustion, which provides the supporting theory needed for using effluent in power plants as a torrefaction medium.

Thermal decomposition behavior and sulfur release characteristics for torrefied wheat straw during pyrolysis process

Understanding the release characteristics of S for pyrolysis process is crucial to the development of biomass thermochemical conversion. The thermal decomposition behavior and S release characteristics for torrefaction and pyrolysis process as well as the impact of torrefaction on the S release during subsequent pyrolysis process of wheat straw were evaluated. In the case of torrefaction, high reaction temperature promoted the increase in S release percentage, which was linearly proportional to mass loss. For pyrolysis process, the release percentage of S increased rapidly up to 70.50% at 500 ℃, whereas the release percentage curve showed an unchanged trend for further increase of the pyrolysis temperature. Additionally, torrefaction pretreatment enhanced the pore properties of char, which promoted the physical resistance of released S during the diffusion process. Thus, torrefaction pretreatment effectively inhibited the release of S into the gas phase, and has a promoting effect on retaining more S in char.

Pore volume upgrade of biochar from spent coffee grounds by sodium bicarbonate during torrefaction

A novel approach for upgrading the pore volume of biochar at low temperatures using a green additive of sodium bicarbonate (NaHCO₃) is developed in this study. The biochar was produced from spent coffee grounds (SCGs) torrefied at different temperatures (200-300 °C) with different residence times (30-60 min) and NaHCO₃ concentrations (0-8.3 wt%). The results reveal that the total pore volume of biochar increases with rising temperature, residence time, or NaHCO₃ aqueous solution concentration, whereas the bulk density has an opposite trend. The specific surface area and total pore volume of pore-forming SCG from 300 °C torrefaction for 60 min with an 8.3 wt% NaHCO₃ solution (300-TP-SCG) are 42.050 m² g^-1 and 0.1389 cm³·g^-1, accounting for the improvements of 141% and 76%, respectively, compared to the parent SCG. The contact angle (126°) and water activity (0.48 aw) of 300-TP-SCG reveal that it has long storage time. The CO₂ uptake capacity of 300-TP-SCG is 0.32 mmol g^-1, rendering a 39% improvement relative to 300-TSCG, namely, SCG torrefied at 300 °C for 60 min. 300-TP-SCG has higher HHV (28.31 MJ·kg^-1) and lower ignition temperature (252 °C). Overall, it indicates 300-TP-SCG is a potential fuel substitute for coal. This study has successfully produced mesoporous biochar at low temperatures to fulfill "3E", namely, energy (biofuel), environment (biowaste reuse solid waste), and circular economy (bioadsorbent).

Chemically versus thermally processed brown shrimp shells or Chinese mitten crab as a source of chitin, nutrients or salts and as microbial stimulant in soilless strawberry cultivation

Brown shrimp (Crangon crangon) shells and Chinese mitten crab (Eriocheir sinensis) were chemically demineralized and deproteinized (denoted as M1 to M4 for the shrimp shells and M5 to M7 for the Chinese mitten crab), and shrimp shells were torrefied at 200 to 300 °C (denoted as R200, R255, R300), and were compared with a commercially available chitin source (denoted as reference chitin). Based on their chemical characteristics, a selection of chitin sources was tested for their N mineralization capacity. The N release was high for the chemically treated shrimp shells and Chinese mitten crab, but not for the torrefied shrimp shells with or without acid treatment, indicating that treatment at 200 °C or higher resulted in low N availability. Interaction with nutrients was tested in a leaching experiment with limed peat for three thermally and two chemically processed shrimp shells and the reference chitin source. The K concentrations in the leachate for the chemically treated shrimp shells and the reference chitin were lower than for limed peat during fertigation. Irreversible K retention was observed for one source of chemically treated shrimp shells, and the reference chitin. The thermally treated shrimp shells had a significantly higher net release of P, Na and Cl than the treatment without chitin source. Three shrimp shell based materials (M4, R200 and R300) and the reference chitin were tested in a greenhouse trial with strawberry at a dose of 2 g/L limed peat. A very positive and significant effect on Botrytis cinerea disease suppression in the leaves was found for the reference chitin, M4 and R200 compared to the unamended control. The disease suppression of the 3 chitin sources was linked with an increase of the microbial biomass in the limed peat with 24% to 28% due to chitin decomposition and a 9-44% higher N uptake in the plants.

A comprehensive review on the factors affecting thermochemical conversion efficiency of algal biomass to energy

Algae are one of the most viable feedstock options that can be converted into different bioenergies viz., bioethanol, biobutanol, biodiesel, biomethane, biohydrogen, etc. owing to their renewable, sustainable and economic credibility features. Algal biomass to fuel biorefining process is generally classified into three categories as chemical, biochemical and thermochemical methods. The present article aims to provide a state-of-the-art review on the factors affecting the thermochemical conversion process of algal biomass to bioenergy. Further, reaction conditions of each techniques (torrefaction, pyrolysis, gasification and hydrothermal process) influence biochar, bio-oil and syngas yield were discussed. Reaction parameters or factors such as reactor temperature, residence time, pressure, biomass load/feedstock composition, catalyst addition and carrier gas flow affecting process efficiency in terms of product yield and quality were spotlighted and extensively discussed with copious literature. It also presents the novel insights on production of solid (char), liquid (bio-oil) and gaseous (syngas) biofuel through torrefaction, pyrolysis and gasification, respectively. It is found that the energy intensive drying was more efficient mode involved in thermochemical process for wet algal biomass. However other modes of thermochemical process were having unique feature on improving the product yield and quality. Among the various factors, reaction temperature and residence time were relatively more important factors which affected the process efficiency. The other factors signposted in this review will lay a roadmap to researchers to choose an optimal thermochemical conditions for high quality end product. Lastly, the perspectives and challenges in thermochemical conversion algae biomass to biofuels were also discussed.