Thermochemical Conversion Techniques Research Articles

Combustion and co-combustion of biochar: Combustion performance and pollutant emissions

Biomass is a renewable and clean energy source, offering the potential to reduce fossil fuel consumption and greenhouse gas emissions when it is used as a biofuel. However, the disadvantages of raw biomass such as poor grindability, high moisture content, and low calorific value hinder its widespread industrial combustion. Thermochemical conversion techniques are widely used to convert biomass to biochar, which serves not only as an adsorbent and soil amendment but also as solid fuels alternative to fossil energy. The upgraded biochar exhibits better physicochemical properties and improved combustion performance. This paper focuses on the properties and combustion behavior of biochar as a solid fuel, reviewing common production techniques of biochar and their effects on yields and properties of biochar. It also examines the combustion characteristics and kinetics of biochar in single- and co-combustion scenarios with other fuels, such as coal, sludge, and petroleum coke, analyzing the influencing factors of combustion behavior and kinetic parameters. This study further investigates the emission characteristics during the combustion of biochar, including gaseous pollutants (such as CO, NOx, SOx, and HCl), ash-related issues, and particulate matter (PM) emissions. Additionally, a new fuel type named “bioslurry”, which is developed with biochar as a main material, is introduced. Furthermore, this paper discusses the techno-economic and environmental aspects of biochar application, exploring the feasibility of its industrial production and utilization.

Towards the production of 1,4:3,6-dianhydro-α-d-glucopyranose from biomass fast pyrolysis based on oxalic acid-assisted torrefaction pretreatment

Pyrolysis, a promising thermochemical conversion technique, can convert lignocellulosic biomass into various value-added products. Herein, the selective production of 1,4:3,6-dianhydro-α-d-glucopyranose (DGP) was achieved through fast pyrolysis of cellulose based on oxalic acid-assisted torrefaction (OAT) pretreatment. The mixture of cellulose and oxalic acid first underwent torrefaction, followed by fast pyrolysis to yield DGP. Simultaneously, the air atmosphere was considered to facilitate the formation of esterification intermediates, thereby promoting the formation of DGP. The effects of torrefaction temperature, oxalic acid amount, as well as pyrolysis temperature were carefully explored for DGP production. A yield of 9.6 wt% and a selectivity of 57.5 % for DGP were achieved from the micro-scale pyrolysis of cellulose under the optimized conditions. In lab-scale tests, the DGP yield reached 12.5 wt% from cellulose. The OAT-based pyrolysis was confirmed to be applicable to the waste cellulose-rich materials, with a DGP yield of 8.2 wt% from waste cotton and 6.0 wt% from spent paper in lab-scale experiments. Additionally, the OAT-based pyrolysis also showed the potential for poly-generation of DGP and formic acid at different stages.

Influence of reaction parameters on biofuels derived from solvothermal liquefaction of Citrus limetta fruit wastes

Citrus limetta or sweet lime is a widely consumed fruit worldwide. The wastes generated from their processing are enormous and are discarded without any value-addition. Biomass liquefaction in hydrogen-donor solvent is an effective thermochemical conversion technique to produce value added products such as biocrude and biochar from wet biomasses directly. Thus, liquefaction studies of Citrus limetta peel and pulp were conducted using solvent methanol at temperatures of 240 °C–280 °C, 30 min residence time as well as 1:2, 1:3 and 1:4 ratios of biomass to solvent. The impact of temperature as well as biomass to solvent ratio on yield of biocrude and biochar were investigated herein. Biocrude produced from Citrus limetta peel at 240 °C and 1:3 ratio of biomass to solvent is maximum (12.5 wt. %). At reaction parameters of 280 °C and 1:4 ratio of biomass to solvent, biocrude from Citrus limetta pulp showed higher heating value of 27.18 MJ kg−1 which was the maximum obtained in this study. The gas-chromatography mass-spectrometry (GC-MS) indicated presence of alcohols, phenols, alkanes, ketones, ethers, esters and fatty acid methyl esters as major compounds. The characteristics and energy content of biochar demonstrated their potentiality for bioenergy applications.

E-waste plastic liquefaction using supercritical Toluene: Evaluation of reaction parameters on liquid products

Solvothermal liquefaction (STL) is a thermochemical conversion technique that employs solvents other than water to transform waste plastics into valuable compounds. The objective of this study was to explore the potential use of supercritical toluene, a nonpolar solvent, for the depolymerization of four electrical waste (e-waste) thermoplastics, namely polyamide (PA), polycarbonate (PC), polyoxymethylene (POM), and polyether ether ketone (PEEK), into liquid products. Depolymerization experiments were carried out in batch reactors at three reaction temperatures (325, 350, and 375 °C), and three residence times (1, 3, and 6 h). The findings revealed that increasing STL temperature and extending the reaction time enhances the depolymerization of e-waste thermoplastics. The highest STL conversation (100 %) was observed for POM, and the lowest STL conversation (32.23 %) was observed for PEEK. Additionally, the ultimate analysis showed that the liquid product obtained from STL at 375 °C and 6 h exhibited higher heating values (HHV) within the range of 31.43 to 35.31 MJ/kg. Thermogravimetric analysis (TGA) demonstrated that the boiling point distributions of liquid products are highly dependent on thermoplastic type. Finally, the reaction mechanisms of STL for PA, PC, POM, and PEEK were proposed based on gas chromatography-mass spectrometry (GCMS) analysis.

Synthesis, performance and reaction mechanisms of Ag-modified multi-functional rice husk solvochar for removal of multi-heavy metals and water-borne bacteria from wastewater

This study introduces a new thermo-chemical conversion technique, solvothermal carbonization on rice husk with alcoholic solvents, ethanol, and isopropanol (IPA) at a low temperature, 280 ℃ with 2 h reaction time to produce innovative char, solvochar. Solvochars were hierarchically activated by potassium hydroxide (KOH), impregnated with silver nanoparticles (AgNPs), and stabilized through the calcination process at high temperatures and residence time. The functionalized solvochar was comprehensively characterized by FTIR, BET-BJH, XRD, XRF and XPS analyses. The maximum surface area, pore diameter and pore volume were obtained, 77.38 m2/g, 18.44 nm and 0.32 cm3/g by IPA-AgNPs. The active units in functionalized solvochars were enhanced surface area-porosity, sp2, and sp3-hybridized aromatic carbon compounds and oxygen-containing alcoholic groups for physio-chemisorption of heavy metal ions. Further, the functionalized solvochars were applied for the adsorption of multi-heavy metal ions, Cu2+, Fe3+, Pb2+, Zn2+, and Mn2+ through fixed-bed flow column adsorption till reaching the saturation stage of two consecutive cycles. The heavy metal ion adsorption uptake for experimented solvochars were ⁓100–230 mg/g Cu2+, ⁓513–569 mg/g Fe3+, ⁓3–9 mg/g Mn2+, ⁓164–190 mg/g Pb2+, ⁓64–100 mg/g Zn2+ for 1st cycle and ⁓2–57 mg/g Cu2+, ⁓6–132 mg/g Fe3+, ⁓3–5 mg/g Mn2+, ⁓3–30 mg/g Pb2+, ⁓2–19 mg/g Zn2+ for 2nd cycle. The adsorption kinetics have been analyzed by intra-particle diffusion (IPD) modelling. Among multi-heavy metal ions, Fe3+ was adsorbed continuously till the saturation stage and R2 was obtained, 0.67–80 through IPD modelling. The post-adsorption characterization of solvochars presented the possibility of recycling. The significant presence of sp3d-hybridized AgNPs in all adsorbents acted as a potent antimicrobial agent against the most common wastewater-relevant bacteria, Escherichia coli, and Staphylococcus aureus. 0.03 wt% loading rate of Ag-functionalized solvochars inhibited both bacteria growths completely. This phenomenon reinforces the potential of the Ag-modified solvochar composites to be applied as potential multi-functional adsorbents for realistic approach.

Modeling and optimization of the yield of pyrolytic oil from waste face masks using RSM‐ANN‐LM hybrid approach

AbstractPyrolysis is one of the most widely practiced thermochemical conversion technique to convert biomass into bio fuel. In this investigation, waste surgical masks were taken for pyrolysis process and the pyrolysis oil yield was determined experimentally. The experiments were designed and optimized based on Box Behnken Design (BBD) with operating parameters (feed size, temperature, and time) to study the effect on the yield of the pyrolysis oil and char. Experiments were conducted by varying the feed size (10–50 mm), pyrolysis temperature (400–600°C), and time (30–90 min). A hybrid Response Surface Methodology –Artificial Neural Network‐ Levenberg–Marquardt algorithm (RSM‐ANN‐LM) modelling approach has been to optimize the process parameters for the prediction of pyrolysis oil yield. The optimized network architecture was found to be 3‐10‐1 and the authenticity of the developed model has been evaluated using Regression Co‐efficient (R2) and Mean Squared Error (MSE). The developed RSM‐ANN‐LM model has outperformed the RSM model on predicting the pyrolytic oil yield. For the optimized conditions of 10 mm size, 600°C of pyrolysis temperature and 90 min pyrolysis time, 85.30% oil yield was obtained.

Role of in situ (in contact with biomass) and ex situ (in contact with pyrolysis vapors) transition metal catalysts on pyrolysis of cherry pits

While energy dense liquid biofuels can be produced from sustainable waste feedstocks via thermochemical conversion techniques, these biofuels are plagued by high acidity and low stability, largely due to the presence of oxygenated functional groups. By utilizing transition metal catalysts during pyrolysis either in situ within the biomass, or ex situ (directly downstream supported on an alumina substrate) acting on the pyrolysis vapors, the quality of the bio-oil can be improved via deoxygenation. Four transition metals (Cu, Mn, Ni, Zn) were either wet impregnated on cherry pit biomass, or were impregnated on alumina wool fibers placed downstream of the biomass to act on the devolatilized gases. The in situ catalysts Cu, Mn and Zn increase the pyrolysis bio-oil yield. The Mn, Ni and Zn used as ex situ catalysts increase the total non-condensable gas produced, suggesting that these downstream catalysts crack the pyrolyzed molecules into smaller organics and water. The ex situ catalysts result in larger quantities of especially oxygen-containing gases like CO2, which in turn lowered the bio-oil’s O/C ratio. However, such reactions also increase the water content of the resulting bio-oil. Both Mn and Zn used in either location enhance the concentration of alcohols relative to aromatic carbons, and when used ex situ, Mn shows a decrease in the ratio of aromatic to aliphatic carbon content.

Application of polysaccharide-rich solution derived from waste macroalgae Enteromorpha prolifera in cherry tomato preservation and utilizing post-extraction residue for crude bio-oil production

Preservative is of importance to retard fruit deterioration and prolong the shelf-life. The suitability of using water-soluble polysaccharide extracted from waste macroalgae Enteromorpha prolifera (EPP) for cherry tomato preservation was evaluated. As compared with the control, the EPP-treated cherry tomatoes exhibited better fruit appearance, lower disease index and rot index during storage. Around 47 % EPP-treated cherry tomatoes were commercially acceptable after 36 days, which was however only 15.6 % for untreated cherry tomatoes, indicating the satisfactory preservation effectiveness of EPP-rich solution for cherry tomatoes. The post-extraction residue was commonly underutilized, we herein attempted to employ an emerging thermochemical conversion technique, hydrothermal liquefaction, to produce crude bio-oil (biocrude) from post-extraction E. prolifera. A biocrude yield of ∼23 wt% (dry-ash-free, daf) was obtained, and fatty acids and phenolics were identified to be the two main components in biocrude. The biocrude contained ∼70 % carbon and the higher heating value was ∼30 MJ/kg.

Toward Native Hardwood Lignin Pyrolysis: Insights into Reaction Energetics from Density Functional Theory

Lignin is one of the three structural components of lignocellulosic biomass and the only renewable source for sustainably producing aromatic chemicals. Despite lignin’s promise for targeted valorization to fine chemicals, fuels, and polymer composites, a major roadblock is an ambiguity associated with its molecular structure. Due to the lack of an established molecular structure, all types of computational studies from reaction mechanism to reaction energetics are performed with model lignin compounds. Among several thermochemical conversion techniques, lignin pyrolysis has been an active research area for both experimental and computational investigations. Historically, computational studies on the pyrolysis of lignin have mainly been limited to dimeric or trimeric models using electronic structure methods. Very recently, model oligomers up to the size of decamers have been studied with density functional theory (DFT) calculations. While these studies used very simplified models to study lignin’s pyrolysis behavior, theoretical investigations on a more realistic lignin structure are warranted to advance its state-of-the-art. To address this, we have modeled a native hardwood lignin polymer consisting of 20 repeating units, including all three monolignols, i.e., guaiacyl (G), syringyl (S), and p-hydroxy coumaryl (H) units, and multiple types of linkages, i.e., β-O-4, 4-O-5, β–β, and β-5. This more realistic molecular model for the wild-type poplar lignin is based on a proposed lignin structure reported in a previous experimental study. The initial stage in lignin pyrolysis involves the homolytic cleavage of β-O-4 linkages present in lignin. The activation energy for homolysis of this linkage is considered to be slightly greater than the bond dissociation enthalpy (BDE) required to cleave it. We used a composite method using molecular mechanics-based conformational sampling and quantum mechanically based density functional theory (DFT) calculations to determine the reaction energetics for this reaction, which indicates the activation energy required for the early stage of lignin pyrolysis. In addition, we calculated standard thermodynamic properties for all species, including enthalpy of formation, heat capacity, entropy, and Gibbs free energy of formation as a function of temperature. This study provides the reaction energetics and standard thermodynamic quantities that could be used in kinetic and reactor modeling for biomass conversion. Additionally, these predictions would be particularly helpful in advanced-generation biorefinery, where hardwoods can be used as a potential feedstock. Moreover, the predictions reported in this study will benefit further computational studies and cross-validation with pyrolysis experiments, ultimately contributing to solving the puzzle of the structural ambiguity of lignin.

Waste to energy and materials through pyrolysis: a review

Waste biomass, such as agricultural waste, is emerging as a promising renewable energy resource because of its abundance and carbon-neutral nature. It has a high potential to be used as an alternative source of energy by employing thermochemical conversion techniques. Pyrolysis is the most efficient technique for the conversion of biomass-based waste in manufacturing renewable fuels and chemicals. However, despite pyrolysis being a well-known method to provide solid fuel (charcoal) and chemicals, the technological pathways for producing chemicals and liquid fuels at an industrial scale are not fully developed. This review addresses the relevance of pyrolysis for waste-to-energy and materials, the fundamentals of pyrolysis, different reactors, process conditions, and its products from the perspective of energy and materials recovery. Accordingly, the purpose of this review is to analyse the current application level of pyrolysis for waste management, identify gaps in our current understanding, and recommend future research directions.

Thermochemical Recycling of Solid Biomass Materials for Achieving Sustainable Goal: A Complete Characterization Study on Liquid Yield Products

In order to achieve sustainability goals, biomass is a renewable energy source that lowers emissions of greenhouse gases and other hazardous gases. Biochemical and thermochemical methods are both used to produce bioenergy from biomass. Pyrolysis is an effective thermochemical conversion technique used for the conversion of biomass into energy-rich bio-oil. In this study, the pyrolysis characteristics and bio-oil obtained from the residues of Ricinus communis were investigated. The experimental run was designed to analyze the impact of bed temperature on product yield by varying the process temperature from 350°C to 750°C. In this study, a maximum of 46.5 wt% of bio-oil was produced at 500°C. The maximum conversion was recorded at temperatures ranging from 450°C to 550°C. The bio-oil obtained at maximum yield conditions was analyzed using different analytical techniques. The Fourier transform infrared spectroscopy (FT-IR) and gas chromatography and mass spectroscopy (GC-MS) analyses of the bio-oil revealed that the oil has a significant amount of phenol derivatives, oxygenated chemicals, acids, and esters. The physical properties of the bio-oil showed that it is viscous and has a medium heating value compared with commercial fossil fuel.

Assessment of thermochemical technologies for wastewater sludge-to-energy: An advance MCDM model

In the recent past the tremendous growth of populace, industrial development, and urbanization adds to the inevitable production of wastewater sludge (WWS), needing more sludge disposal and renewable energy generation technologies. The thermochemical technologies namely combustion/or incineration, pyrolysis, and gasification have a great prospect of energy recovery with the possibility to be feasible when considering costs and efficiencies. This research paper seeks an investigation on the selection of the finest or feasible thermochemical conversion technology to treat, dispose and generate gas energy in turn heat and electric power. This can be achieved through an advance multi-criteria decision making (MCDM) model using analytical hierarchy process (AHP) and the technique for order of preference by similarity to ideal solution (TOPSIS) to form a AHP-TOPSIS focused on technical and economic criteria. Results show that combustion or/incineration is the most viable technology due to its ability to lessens enormous sludge volume, recuperate energy, demolish pollutants. Gasification is favourable due to benefits such as high efficiency, continual volumetrically heating, and fast thermal reaction. With regards to pyrolysis conversion technology, this process is regarded among of the most feasible thermochemical technologies with zero-waste production, it can gas recover energy and materials such as biogas, biochar, water, tar, etc. With the aforesaid advance thermochemical technologies, the sludge treatment and energy conversion difficulties are foreseen to be limited or lessened. • The conversion of wastewater sludge or sewage sludge to energy. • Thermochemical energy conversion techniques. • Multi-Criteria Decision Making. • Analytical Hierarchy Process (AHP). • Technique for Order of Preference by Similarity to Ideal Solution (AHP).

Integrated role of algae in the closed-loop circular economy of anaerobic digestion

Following the surging demand for sustainable biofuels, biogas production via anaerobic digestion (AD) presented itself as a solution for energy security, waste management, and greenhouse gas mitigation. Algal-based biorefinery platform serves an important role in the AD-based closed-loop circular economy. Other than using whole biomass of micro- and macroalgae as feedstock for biogas production, the integration of AD with other bio- or thermochemical conversion techniques can achieve complete valorization of biomass residue after processing or valuable compounds extraction. On the other hand, anaerobic digestate, the byproduct of AD processes can be used for microalgal cultivation for lipid and pigments accumulation, closing the loop of resource flow. Furthermore, algae and its consortium with bacteria or fungi can be employed for combined biogas upgrading and wastewater treatment. Innovative strategies have been developed to enhance biogas upgrading and pollutant removal performance as well as minimize O2 and N2 content in the upgraded biomethane.

Diluted Bitumen: Physicochemical Properties, Weathering Processes, Emergency Response, and Recovery

Bitumen, an unconventional crude oil, has received much attention with the increasing consumption and the shrinking storage of conventional crude oils. Bitumen is highly viscous and, thus, is commonly diluted for transportation purposes. Spills of diluted bitumen could occur during the transportation from reservoirs to refineries via pipeline, rail, and marine vessels. Although some laboratory and numerical modeling studies have been contributed to study the spill of diluted bitumen from different aspects, there is no systematic review in the field yet. Therefore, this study first conducted a review on different types of diluted bitumen based on their physicochemical properties, followed by their weathering processes including spreading, evaporation, emulsification, photooxidation, biodegradation, and sinking. Second, the numerical modeling on the fate and behavior of spilled diluted bitumen was summarized and analyzed. Finally, the techniques for spilled oil recovery were discussed, as well as the disposal/treatment of oily waste. Currently, a rare attempt has been made to turn the recovered oily waste into wealth (reutilization/valorization of oily waste). Using the recovered oily waste as the feedstock/processing medium for an emerging thermochemical conversion technique (hydrothermal liquefaction of biomass for crude bio-oil production) is highly recommended. Overall, this article summarized the state-of-the-art knowledge of the spill of diluted bitumen, with the hope to create a deep and systematic understanding on the spill of diluted bitumen for researchers, relevant companies, and decision makers.

Synthesis of Biochar From Lignocellulosic Biomass for Diverse Industrial Applications and Energy Harvesting: Effects of Pyrolysis Conditions on the Physicochemical Properties of Biochar

The excessive dependency on fossil fuel resources could be curtailed by the efficient conversion of lignocellulosic biomass. Biochar, a porous carbonaceous product synthesized exploiting thermochemical conversion pathway, could be an environment-friendly replacement of fossil fuel resources. Slow pyrolysis, a sub-class among various thermochemical conversion techniques, has gained immense popularity owing to its potential to convert biomass to biochar. Furthermore, biochar obtained as the by-product of slow pyrolysis has attracted enormous popularity due to its proven role and application in the multidisciplinary areas of engineering and environmental remediation applications. The physicochemical quality of biochar and its performance is significantly dependent on the feedstock type and pyrolysis process parameters. Therefore, further experimental research and investigations in terms of lignocellulose biomass type and pyrolytic process parameters (temperature, heating rate and reaction time) are essential to produce biochar with desired physicochemical features for effective utilization. This review presents an updated report on slow pyrolysis of lignocellulosic biomass, impact of different pyrolysis parameters and degradation pathway involved in the evolution properties of biomass. The influence of the feedstock type and lignocellulosic composition on the biochar properties are also discussed meticulously. The co-relationship between biochar yield at different pyrolysis temperatures and the development of textural properties provides valuable information for their effective utilization as a functional carbon material. Additionally, an extensive study was undertaken to collate and discuss the excellent physicochemical characteristics of biochar and summarizes the benefits of biochar application for diverse industrial purposes. Biochar is acknowledged for its excellent physicochemical properties owing to the thermal treatment and as a result its prospective diverse industrial applications such as for soil treatment, carbon sequestration, adsorbent (wastewater treatment or CO2 capture), producing activated carbon for gold recovery, energy storage and supercapacitor are summarized systematically in this review paper. For instance, biochar when applied in soil have shown improvement in soil respiration by 1.9 times. Furthermore, biochar when used to capture CO2 from flue gas stream under post-combustion scenario has demonstrated superior capture performance (2.8 mmol/g) compared to commercial activated carbon. This paper identified the knowledge gaps and outlooks in the field of the advancements of biochar from slow pyrolysis for targeted engineering applications mainly in the field of environmental remediation and energy harvesting.

Estimation of Higher heating Value of Biomass from Proximate and Ultimate Analysis: A Novel Approach

Biomass is the organic matter formed by photosynthesis that occurs on the earth’s surface. They contain all forms of waste compost, including urban solid waste, municipal bio solids, animal wastes, forestry and agricultural wastes, and some industrial wastes. Efficient use of biomass oil would aid in the resolution of issues caused by fossil fuels. However, the biggest issue about using this energy is due to the gas composition of biomass material. As a result, properties of biomass are the critical parameter for assessing the fuel content of a special biomass substance in energetic applications. Gasification is the most mature thermo-chemical conversion technique available among the various methods of transforming biomass materials to bio resources. In this context, proximate and ultimate analysis has been used to classify two groups of biomass material that carry out in this experiment. The proximate analysis results have been obtained by the TGA technique while the ultimate analysis results will obtain by the GC mechanism. Then, based on the proximate analysis data various empirical equations containing linear and nonlinear terms were evaluated in order to predict the higher heating values (HHV) of the entire sample range. Since, the biomasses used in this analysis have different properties and fuel characteristics, the estimated HHV for the wood pellet sample are between 15.33 and 19.71 MJ/kg, while the rubber seed sample is between 15.18 and 18.64 MJ/kg. According to the experimental findings, the HHV of wood pellet is at around 2.95 MJ/Nm3 while the HHV of rubber seed of about 4.99MJ/Nm3. The comparison on the theoretical analysis have been show 0.19% compared to the results on wood pellet while the rubber seed have at around 2.07% difference compare each other. The experimental results on wood pellets, the findings reveal a 15.35% difference, while rubber seed indicates a 13.81% difference. Nonetheless, the finding and analysis on the properties, the results can be considered within reasonable limits.

Microalgal-based biochar in wastewater remediation: Its synthesis, characterization and applications

Microalgae are drawing attentions among researchers for their biorefinery use or value-added products. The high production rate of biomasses produced are attractive for conversion into volatile biochar. Torrefaction, pyrolysis and hydrothermal carbonization are the recommended thermochemical conversion techniques that could produce microalgal-based biochar with desirable physiochemical properties such as high surface area and pore volume, abundant surface functional groups, as well as functionality such as high adsorption capacity. The characterizations of the biochar significantly influence the mechanisms in adsorption of pollutants from wastewaters. Specific adsorption of the organic and inorganic pollutants from the effluent are reviewed to examine the adsorption capacity and efficiency of biochar derived from different microalgae species. Last but not least, future remarks over the challenges and improvements are discussed accordingly. Overall, this review would discuss the synthesis, characterization and application of the microalgal-based biochar in wastewater.

Microwave assisted carbonization and activation of biochar for energy-environment nexus: A review

Conventional thermochemical conversion techniques for biofuel production from lignocellulosic biomass is often non-selective and energy inefficient. Microwave assisted pyrolysis (MAP) is cost and energy-efficient technology aimed for value-added bioproducts recovery from biomass with less environmental impacts. The present review emphasizes the performance of MAP in terms of product yield, characteristics and energy consumption and further it compares it with conventional pyrolysis. The significant role of biochar as catalyst in microwave pyrolysis for enhancing the product selectivity and quality, and the influence of microwave activation on product composition identified through sophisticated techniques has been highlighted. Besides, the application of MAP based biochar as soil conditioner and heavy metal immobilization has been illustrated. MAP accomplished at low temperature creates uniform thermal gradient than conventional mode, thereby producing engineered char with hotspots that could be used as catalysts for gasification, energy storage, etc. The stability, nutrient content, surface properties and adsorption capacity of biochar was enhanced by microwave activation, thus facilitating its use as soil conditioner. Many reviews until now on MAP mostly dealt with operational conditions and product yield with limited focus on comparative energy consumption with conventional mode, analytical techniques for product characterization and end application especially concerning agriculture. Thus, the present review adds on to the current state of art on microwave assisted pyrolysis covering all-round aspects of production followed by characterization and applications as soil amendment for increasing crop productivity in addition to the production of value-added chemicals, thus promoting process sustainability in energy and environment nexus.

The Effect of Temperature on the Properties of Hydrochars Obtained by Hydrothermal Carbonization of Waste Camellia oleifera Shells.

Hydrothermal carbonization (HTC) is a thermochemical conversion technique that can produce renewable solid biofuel by all types of waste. Waste Camellia oleifera shells (WCOSs) can be used to produce hydrochars via HTC. The effect of HTC temperature on the physicochemical properties and combustion behaviors of hydrochars was analyzed by varying from 150 to 300 °C. The mass yield of hydrochars decreased from 72.45% at 150 °C to 41.88% at 300 °C with the increase in temperature, and the higher heating value increased from 19.22 MJ/kg at 150 °C to 29.97 MJ/kg at 300 °C. The H/C and O/C values reduced from 1.30 and 0.66 of HTC150 to 0.77 and 0.27 of HTC300, respectively. Fourier transform infrared spectroscopy analysis indicated that the functional groups of hydrochar have changed because of the dehydration and decarboxylation reaction. The surface structure of hydrochars was rougher, and many pore structures were found at 240–300 °C by scanning electron microscopy analysis. The combustion behaviors of WCOSs and their hydochars are distinct via thermogravimetric analysis, and the stability of hydrochars was strengthened with the increase in HTC temperature.

Supercritical water gasification (SCWG) as a potential tool for the valorization of phycoremediation-derived waste algal biomass for biofuel generation

Phycoremediation is an emerging technology, where algae-based processes were used to effectively remove nutrients, organic wastes, and toxic heavy metals from the polluted environment. The waste algal biomass obtained after phycoremediation, which may contain residual hazardous materials, could still be used as feedstock to produce biofuels/bioenergy preferably through thermochemical conversion technology. This review proposes a synergistic approach by utilizing the phycoremediation-derived algal biomass (PCDA) as feedstock for efficient hazardous waste treatment and clean energy generation via supercritical water gasification (SCWG). The review provides an in-depth study of catalytic, non-catalytic, and continuous SCWG of algal biomass, aiming to lay out the foundations for future study. In addition, the concepts of heat integration as well as water, nutrient, and CO2 recycling were introduced for a sustainable algae-to-biofuel process, which significantly enhances the overall energy and material efficiency of SCWG. The production of biofuel from algal biomass via other advanced gasification technologies, such as integration with other thermochemical conversion techniques, co-gasification, chemical looping gasification (CLG), and integrated gasification and combined cycle (IGCC) were also discussed. Furthermore, the discussion of kinetics and thermodynamics models, as well as life cycle and techno-economic assessments, appear to provide insights for future commercial applications.