Thermochemical Conversion Technologies Research Articles

Optimization of waste biomass demineralization through response surface methodology and enhancement of thermochemical and fusion properties

This study examines the impact of leaching with dilute hydrochloric acid solution on the reduction of ash content and the thermal degradation behavior of sugarcane bagasse. Response surface methodology (RSM) was used to statistically design the experiments and investigate the effect of three independent variables: treatment time, solid-to-liquid ratio, and reagent concentration. The leaching conditions were further optimized and experimentally validated for maximum ash reduction for suitability of treated biomass as feedstock for thermochemical conversion technologies. Reagent concentration and treatment time directly affected ash reduction, while the solid-to-liquid ratio inversely influenced it. Concentration had the highest impact, and treatment duration had the least. The maximum 78.2% ash reduction was achieved by treating the biomass with 1 M HCl for 80 min at a solid-to-liquid ratio of 50:1 (wt/vol). This ash reduction also resulted in a 9.82% increase in higher heating value (HHV). Hemicellulose hydrolysis during leaching was observed through chemical composition and Fourier-transform infrared spectroscopy (FTIR). Ash fusion temperatures increased, indicating more thermally stable biomass. Thermogravimetric analysis (TGA) showed elevated maximum degradation temperature and activation energy.

Systematic analysis of mixing and segregation patterns of binary mixtures in fluidised beds for multi-functional processes

Fluidized beds are increasingly used in renewable energy and chemical production due to their versatility in handling different solids for multi-functional industrial applications. The diversity in size and density of solid particles impacts fluidization, influencing mixing and segregation behaviours critical for optimizing chemical processes and reactor design. This study investigates the expansion and segregation behaviours of mixed Geldart group powders in binary systems, simulating polydispersed beds with different materials and catalysts. By applying a modified Cheung equation and an adapted Gibilaro-Rowe model, the study analyzes segregation behaviours of Geldart Group A and B materials at varying mixing rates and gas flow velocities. Results show a good match between experimental data and model predictions. Using novel non-invasive X-ray imaging, the study provides real-time analysis of mixing and segregation at different fluidization regimes and temperatures. These findings aid in designing and optimizing advanced thermochemical conversion technologies, enhancing process efficiency and resilience.

A Review on Machine Learning-Aided Hydrothermal Liquefaction Based on Bibliometric Analysis

Hydrothermal liquefaction (HTL) is an effective biomass thermochemical conversion technology that can convert organic waste into energy products. However, the HTL process is influenced by various complex factors such as operating conditions, feedstock properties, and reaction pathways. Machine learning (ML) methods can utilize existing HTL data to develop accurate models for predicting product yields and properties, which can be used to optimize HTL operation conditions. This paper presents a bibliometric review on ML applications in HTL from 2020 to 2024. CiteSpace, VOSviewer, and Bibexcel were used to analyze seven key bibliometric attributes: annual publication output, author co-authorship networks, country co-authorship networks, co-citation of references, co-citation of journals, collaborating institutions, and keyword co-occurrence networks, as well as time zone maps and timelines, to identify the development of ML in HTL research. Through the detailed analysis of co-occurring keywords, this study aims to identify frontiers, research gaps, and development trends in the field of ML-aided HTL.

Rapid pyrolysis of cellulose: Revealing the role of volatile matter and char structure evolution

The complexity of the cellulose structure hinders its energy conversion and utilization. Pyrolysis is not only an independent thermochemical conversion technology but also a necessary stage in the gasification process. The real-time capture of volatile components in cellulose pyrolysis is difficult, and the evolution of char structures is lacking, which is extremely challenging. In this work, elemental analysis, industrial analysis, thermogravimetric analysis, infrared spectroscopy (FTIR), Raman spectroscopy (Raman), and X-ray diffraction spectroscopy (XRD) were used to characterize the raw materials and products. Combined with rapid pyrolysis experiments, the pathways of cellulose pyrolysis volatiles and char structure evolution were explored. Dehydrated sugars are the initial products formed below 350 ℃, which quickly dehydrate to form furan compounds at 400 ℃ and then break CC bonds at 600 ℃ to generate fatty aldehydes, ketones, and carboxylic acids. Biochar generated at low temperatures (<300°C) has strong lipid solubility. An increase in pyrolysis temperature leads to a continuous decrease in the content of H and O in biochar, which destroys its functional groups and physical structure, and ultimately tends to form graphite-type char with aromatic structures. Based on the correlation between the volatile matter release characteristics and the evolution of the semichar structure, a cellulose pyrolysis pathway was established, providing theoretical support for the high-value utilization of cellulose.

A review on environmental assessment of thermochemical conversion technologies for energy generation from crop residue

A review on environmental assessment of thermochemical conversion technologies for energy generation from crop residue

Automated machine learning-aided prediction and interpretation of gaseous by-products from the hydrothermal liquefaction of biomass

Hydrothermal liquefaction (HTL) is a thermochemical conversion technology that produces bio-oil from wet biomass without drying. However, by-product gases will inevitably be produced, and their formation is unclear. Therefore, an automated machine learning (AutoML) approach, automatically training without human intervention, was used to aid in predicting gaseous production and interpreting the formation mechanisms of four gases (CO2, CH4, CO, and H2). Specifically, four accurate optimal single-target models based on AutoML were developed with elemental compositions and HTL conditions as inputs for four gases. Herein, the gradient boosting machine (GBM) performed excellently with train R2 ≥ 0.99 and test R2 ≥ 0.80. Then, the screened GBM algorithm-based ML multi-target models (maximum average test R2 = 0.89 and RMSE = 0.39) were built to predict four gases simultaneously. Results indicated that biomass carbon, solid content, pressure, and biomass hydrogen were the top four factors for gas production from HTL of biomass. This study proposed an AutoML-aided prediction and interpretation framework, which could provide new insight for rapid prediction and revelation of gaseous compositions from the HTL process.

Hydrochar from winemaking industry wastes as solid biofuel: A thermal and kinetic analysis of pyrolysis and combustion

Pyrolysis and combustion behavior of the hydrochar (HY) from co-hydrothermal carbonization (co-HTC) of vine pruning (VP) and exhausted grape marc (EGM) by using vinasse as wet catalytic vector was investigated through thermogravimetric analysis (TGA). For both raw- and co-HTC biomass, different iso-conversional methods were used for kinetic analysis, and the thermodynamic parameters were determined. Overall, even if HY exhibited a lower activation energy compared to EGM and VP during both pyrolysis and combustion, HTC has positive effects on the hydrochar’s structure, which achieved a more thermodynamically stable, structurally ordered, and energetically favorable state. The obtained kinetic and thermodynamic parameters would contribute to the development of biomass thermochemical conversion technologies and the application of hydrochar-based energy systems.

A data-driven framework to inform sustainable management of animal manure in rural agricultural regions using emerging resource recovery technologies

Thermochemical conversion technologies are emerging as preferred resource recovery practices for managing animal manure in agricultural regions. Although the implementation of such technologies has been previously studied, difficulties exist in maintaining balance between high rate of resource recovery and low environmental, economic, and social impacts, particularly in rural regions with limited resources. We developed a data-driven framework by integrating machine learning with life cycle thinking that can be used as an open-source tool to help overcome these barriers. The framework was applied to compare two emerging technologies: pyrolysis versus hydrothermal carbonization for managing the excess poultry litter in a rural agricultural region. Among different machine learning models, random forest regression was the most successful to predict resource recovery of both technologies. Next, sustainability analysis indicated that the environmental (global warming), economic (annual worth), and social (system intrusiveness) impacts of pyrolysis was lower than hydrothermal carbonization. Finally, the framework revealed that implementation of pyrolysis at 600 °C for 1 h with the heating rate of 20 °C/min would result in the highest rate of resource recovery that corresponded to the lowest impacts. These results can be helpful in providing operational conditions for implementing emerging resource recovery technologies in rural agricultural regions.

Agglomeration behaviour of various biomass fuels under different air staging conditions in fluidised bed technology for renewable energy applications

The most common technology for thermochemical conversion of solid fuel through the process of gasification, such as coal, varieties of residues from biomass and agriculture are the bubbling fluidised bed or fluidised bed systems. However, there are some disadvantages within these systems including the formation of eutectic mixtures, increased process of melting and bed agglomeration. Hence, the current study aimed to evaluate the agglomeration behaviour of various biomass fuels. Characteristics of five biomass fuels (miscanthus, peanut, straw, domestic wood and industrial wood) in a bubbling fluidised bed (BFB) combustor were studied by SEM-EDX, XRD and XRF analysis of bed materials and ash samples. The influence of bed temperatures on the fuel ash composition and bed particles was evaluated, as well as fuel ash components, their interaction with the particles from the bed sand and morphology of the bed material. The combustion efficiency ranged from 95.5 to 99.5% with the highest value obtained for miscanthus under SA conditions. The peanut and straw had the highest K content, whereas the industrial wood ash contained the highest Ca content compared to other biomasses. The XRF results showed that most of the potassium (K) from the wheat straw biomass was converted to K2O with 19%. No bed agglomeration was noticed without staging-air (WSA) and with staging-air (SA) combustion conditions, even with temperatures up to 850 °C during the testing period. Overall obtained results demonstrated that agglomeration is unlikely expected to be a major problem during fluidised bed combustion of tested biomass fuels.

Life cycle and techno-economic assessment of bioresource production from wastewater

Thermochemical conversion technologies present an opportunity to flip the paradigm of wastewater biosolids management operations from energy-intense and expensive waste management processes into energy-positive and economical resource extraction centers. Herein, we present a uniform “grading framework” to consistently evaluate the environmental and commercial benefits of established and emerging wastewater biosolids management processes from a life cycle and techno-economic perspective. Application of this approach reveals that established wastewater biosolids management practices such as landfilling, land application, incineration, and anaerobic digestion, while commercially viable, offer little environmental benefit. On the other hand, emerging thermochemical bioresource recovery technologies such as hydrothermal liquefaction, gasification, pyrolysis, and torrefaction show potential to provide substantial economic and environmental benefit through the recovery of carbon and nutrients from wastewater biosolids in the form of biofuels, fertilizers, and other high-value products. Some emerging thermochemical technologies have developed beyond pilot scale although their commercial viability remains to be seen.

A novel intelligent system based on machine learning for hydrochar multi-target prediction from the hydrothermal carbonization of biomass

Hydrothermal carbonization (HTC) is a thermochemical conversion technology to produce hydrochar from wet biomass without drying, but it is time-consuming and expensive to experimentally determine the optimal HTC operational conditions of specific biomass to produce desired hydrochar. Therefore, a machine learning (ML) approach was used to predict and optimize hydrochar properties. Specifically, biochemical components (proteins, lipids, and carbohydrates) of biomass were predicted and analyzed first via elementary composition. Then, accurate single-biomass (no mixture) based ML multi-target models (average R2 = 0.93 and RMSE = 2.36) were built to predict and optimize the hydrochar properties (yield, elemental composition, elemental atomic ratio, and higher heating value). Biomass composition (elemental and biochemical), proximate analyses, and HTC conditions were inputs herein. Interpretation of the model results showed that ash, temperature, and the N and C content of biomass were the most critical factors affecting the hydrochar properties, and that the relative importance of biochemical composition (25%) for the hydrochar was higher than that of operating conditions (19%). Finally, an intelligent system was constructed based on a multi-target model, verified by applying it to predict the atomic ratios (N/C, O/C, and H/C). It could also be extended to optimize hydrochar production from the HTC of single-biomass samples with experimental validation and to predict hydrochar from the co-HTC of mixed biomass samples reported in the literature. This study advances the field by integrating predictive modeling, intelligent systems, and mechanistic insights, offering a holistic approach to the precise control and optimization of hydrochar production through HTC.Graphical

Advancements, Challenges, and Pathways to Sustainable Biofuel Production

AbstractThe discovery of new energy sources plays a vital role to fulfil the needs of energy and depletion of fossil fuel sources. An inclusive review of all available technologies for the synthesis of biofuels from biomass is presented. Amongst the innovative biomass conversion technologies, thermochemical technology encompasses significant potential practices and is required for expansion. Universally, biofuels are gaining importance due to the depletion of non‐renewable fuel sources in transport and industries by equivalent work proficiencies. The reaction mechanism thoroughly explores all aspects associated with reaction conditions, types of reactor, and products. Biomass thermochemical conversion technologies will be influential in producing sustainable biofuels.

Simulation of waste tire gasification in bubbling fluidized bed by Aspen: Contribution ratio analysis

Waste tire gasification in a bubbling fluidized bed is a promising thermochemical conversion technology that not only utilize waste tire but also produce energy. To reveal the gasification performance of waste tire in a bubbling fluidized bed, two Aspen models were developed to simulate the effect of gasification agent types (such as air, steam, carbon dioxide and their mixtures), considering chemical reactions that reached thermodynamic equilibrium (CRTM) or were controlled by kinetics (CRK). The simulated gas compositions (H2, CO, CO2 and CH4) and lower heating value (LHV) were compared with experimental data under various operating conditions. The results showed that CRK model exhibited much better performance than the CRTM model. These two models were further utilized to analyze the effect of gasification agent type on gas composition and LHV. The contribution ratios of different chemical reactions were detailed analyzed, such as hydrogen combustion, carbon monoxide combustion, methane combustion, carbon combustion, steam gasification, water gas shift reaction and carbon dioxide gasification. The established Aspen model for waste tire gasification in a bubbling fluidized bed could be served as a guideline for selecting operation conditions to achieve high hydrogen composition, carbon conversion, and gas yield.

Kinetic reaction mechanism of lignocellulosic biomass oxidative pyrolysis based on combined kinetics

The kinetics knowledge of lignocellulosic biomass decomposition is essential to develop efficient thermochemical conversion technology. However, the simplification of reaction mechanisms in existing oxidative pyrolysis studies largely compromises the application of kinetic models. To explore more exact kinetic parameters and reaction mechanism of lignocellulosic biomass oxidative pyrolysis, an updated oxidative pyrolysis kinetic model (seven-step reaction combined kinetics model) coupled with an optimization algorithm is proposed. Based on a series of thermogravimetric experiments in an air atmosphere, the extra oxidative pyrolysis kinetic parameters are obtained by the Shuffled Complex Evolution method. The proposed kinetic model is validated based on the degradation process of each component (hemicellulose, cellulose, and lignin). Furthermore, the obtained kinetic parameters are applied to predict the oxidative pyrolysis behavior, and the predicted mass loss rate is in good agreement with the experimental data. Eventually, according to the key combined kinetics parameters, it is found that the oxidative pyrolysis mechanisms of hemicellulose, cellulose, and lignin correspond to the power law, nucleation & growth, and chemical reaction order, respectively, while the combustion of char corresponds to the reaction order mechanism.

A thematic review on livestock manure treatment strategies focusing on thermochemical conversion.

Livestock manure (LSM) management is emerging as a challenge due to increasing livestock consumption. Owing to the decreased agricultural land area, it is necessary to ensure LSM utilization in non-agricultural fields. LSM can be a valuable resource if managed as a circulating resource. This study discusses research trends based on a literature review and classifies LSM treatments. The analysis of each treatment is presented according to research trends, and implications for the future LSM processing are discussed. "Biological treatment" accounted for the largest portion at 48%, "manure management," which suggests improvement in manure treatment through systematic thinking or LSM management practices, accounted for 16%, and "thermochemical conversion" accounted for 11%. In addition, "life cycle assessment (LCA) research," "solid-liquid separation approach," and "nutrient-recovery/losses" were derived. Studies on biological treatments are increasing. Although anaerobic digestion (AD) is the most used method, it has the disadvantages of long processing time and waste generation after processing. As a key supplement, thermochemical conversion (TCC) technology, which could overcome the disadvantages of AD, was reviewed.

Management of Agri-Food Waste Based on Thermochemical Processes towards a Circular Bioeconomy Concept: The Case Study of the Portuguese Industry

Sustainable biomass production has a significant potential for mitigating greenhouse gas emissions, providing an alternative to produce eco-friendly biofuels, biochemicals, and carbonaceous materials for biological, energetic, and environmental applications. Biomass from agroforestry and agricultural wastes is the richest natural carbon source and a sustainable option for woody biomass from a circular economic perspective. The European Union (EU) is estimated to produce 1.3 billion tons of agri-food waste annually. Portugal has a large supply of residual biomass, as well as other byproducts and wastes from forestry, agriculture, and the food industry, and has a high availability of residual biomass. By using biomass waste to create high-value products, Portugal envisages an improvement in its economic performance, while reducing its dependence on energy imports and fossil fuel use. This review explores the potential of agri-food waste obtained from Portuguese industries through thermochemical conversion technologies as a promising sustainable substitute for wood-based biomass for the development of eco-friendly biofuels, biochemicals, and high-value carbonaceous materials, and their applications. This strategy, based on the circular bioeconomy concept, can help reduce reliance on fossil fuels, reduce greenhouse gas emissions, fulfil the needs of the growing population, and offer a sustainable waste management solution.

Investigation of pyrolytic characteristics of three oily sludges with focus on properties of oil product

Pyrolysis is an important thermochemical conversion technology to recover the oily sludge resources and reduce the harmfulness of waste. This work aims to investigate the pyrolysis behaviors of three different oil sludges by using a thermogravimetric analyzer and two fixed-bed reactors. An attempt was made to determine a wide range of properties of liquid products. Three oily sludges included a tank bottom sediment (OS-1), an oil-water separator scum (OS-2), and a wastewater sediment concentrate (OS-3). OS-1 had a high content of oil, whereas OS-2 and OS-3 were characteristic of high contents of water and oxygen. The pyrolysis of as-received oily sludge in a vertical tubular reactor at 700 °C attained the oil yield up to 69.2 % for OS-1, against the oil yields ranged in 34.4–35.5 % for OS-2 and OS-3. These yields of pyrolysis oil were higher than or close to those of extraction oil. Through characterizing the molecular composition of pyrolysis oil and extraction oil, it was revealed that the pyrolysis promoted the cracking of long-chain alkanes and O/N-containing functional groups accompanied by the conjugation, cyclization and aromatization reactions. The analysis of the pyrolysis oils obtained from the horizontal tubular reactor showed that the liquid products derived from all three oil sludges had very low ash contents and viscosities, and the water-free pyrolysis oils had higher HHVs than the parent dried oil sludges.

A comprehensive analysis on the synthesis of value-added chemicals via slow pyrolysis: Valorisation of rapeseed residue, whitewood, and seaweed (Laminaria digitata)

Pyrolysis has emerged as a crucial thermochemical conversion technology in the field of biomass processing. Maximising the valorisation of biomass is an essential area of investigation, as it plays a pivotal role in understanding the economic viability and practical application of these advanced technologies. The novelty of this research is to investigate how slow pyrolysis and process interdependencies influence the synthesis of value-added products (bio-oil and biogas formation alongside biochar) from distinctly different UK-based biomass feedstocks: rapeseed residue, whitewood, and seaweed (Laminaria digitata). This research also analysed the chemical composition of these products to provide a holistic understanding of the reaction mechanisms involved in their formation. The maximum yield of bio-oil from lignocellulose-rich whitewood was due to the higher selectivity of several endothermic reactions including conversions of 5-hydroxymethylfurfural into cyclic C5-ketones and alkoxyphenols into cresols and aliphatic hydrocarbons, minimizing the biochar formation. The improvement of bio-oil yield from protein-rich seaweed and lipid-rich rapeseed residue was enabled by the formation of N-heterocyclics (e.g., via the Maillard reaction, Dieckmann cyclization, and Buchwald–Hartwig amination) and aliphatic hydrocarbons (e.g., via deamination of fatty amides and nitriles and decarboxylation of fatty acids), respectively. Meanwhile, the dealkylation and demethoxylation of alkoxyphenols and alkylphenols were responsible for the increased content of hydrocarbons in biogas. The findings provide valuable insights into the maximum valorisation of different types of UK-based biomass resources in slow pyrolysis for the production of biochars and lighter bio-oils to make pyrolysis a key process in biorefineries.

Retrieving back plastic wastes for conversion to value added petrochemicals: opportunities, challenges and outlooks

Plastic production and its unplanned management and disposal, has been shown to pollute terrestrial, aquatic, and atmospheric environments. Petroleum-derived plastics do not decompose and tend to persist in the surrounding environment for longer time. Plastics can be ingested and accumulate into the tissues of both terrestrial and aquatic animals, which can impede their growth and development. Petrochemicals are the primary feedstocks for the manufacture of plastics. The plastic wastes can be retrieved back for conversion to value added petrochemicals including aromatic char, hydrogen, synthesis gas, and bio-crude oil using various technologies including thermochemical, catalytic conversion and chemolysis. This review focusses on technologies, opportunities, challenges and outlooks of retrieving back plastic wastes for conversion to value added petrochemicals. The review also explores both the technical and management approaches for conversion of plastic wastes to petrochemicals in regard to commercial feasibility, and economic and environmental sustainability. Further, this review work provides a detailed discussion on opportunities and challenges associated with recent thermochemical and catalytic conversion technologies adopted for retrieving plastic waste to fuels and chemicals. The review also recommends prospects for future research to improve the processes and cost-efficiency of promising technologies for conversion of plastic wastes to petrochemicals. It is envisioned that this review would overcomes the knowledge gaps on conversion technologies and further contribute in emerging sustainable approaches for exploiting plastic wastes for value-added products.

Decomposition and characterization of bio-oil from coconut shell waste for bio-coke hybrid application as alternative energy resources

Bioenergy sources continue to be developed to solve environmental problems due to agricultural biomass waste and alternative energy sources. Bioenergy from biomass raw materials through the pyrolysis method is a thermochemical conversion technology that produces bio-oil and bio-char. The conversion process of coconut shell (CS) biomass with a size of 60 mesh at a temperature of 500-700°C without adding a catalyst. The results showed that the optimum decomposition process occurred at a temperature of 700°C. Based on the GC-MS analysis of bio-oil from CS, the compound consisting of 58.18% phenol, 18.86% 2.6 dimethoxy-phenol, 1.35% 1-(acetyloxy)-2-propanone, 6.57% 3,5-dimethoxy-4-hydroxytoluene and 2.55% 4-ethyl-2,6-methoxy-phenol was obtained. While the SEM-EDS characterization of bio-char contains the main constituent elements, including 94.37% carbon and minor elements consisting of 5.50% oxygen, 0.09% sodium and 0.05% chlorine. Comprehensive analysis shows that pyrolysis is an efficient and sustainable method for converting CS biomass into material for hybrid bio-coke applications as an alternative renewable energy source.