Slow-pyrolysis of biomass for the production of biochar, a stable carbon-rich solid by-product, has gained considerable interest due to its proven role and application in the multidisciplinary areas ...of science and engineering. An alternative to slow-pyrolysis is a relatively new process called hydrothermal carbonization (HTC) of biomass, where the biomass is treated with hot compressed water instead of drying, has shown promising results. The HTC process offers several advantages over conventional dry-thermal pre-treatments like slow-pyrolysis in terms of improvements in the process performances and economic efficiency, especially its ability to process wet feedstock without pre-drying requirement. Char produced from both the processes exhibits significantly different physiochemical properties that affect their potential applications, which includes but is not limited to carbon sequestration, soil amelioration, bioenergy production, and wastewater pollution remediation. This paper provides an updated review on the fundamentals and reaction mechanisms of the slow-pyrolysis and HTC processes, identifies research gaps, and summarizes the physicochemical characteristics of chars for different applications in the industry. The literature reviewed in this study suggests that hydrochar (HTC char) is a valuable resource and is superior to biochar in certain ways. For example, it contains a reduced alkali and alkaline earth and heavy metal content, and an increased higher heating value compared to the biochar produced at the same operating process temperature. However, its effective utilization would require further experimental research and investigations in terms of feeding of biomass against pressure; effects and relationships among feedstocks compositions, hydrochar characteristics and process conditions; advancement in the production technique(s) for improvement in the physicochemical behavior of hydrochar; and development of a diverse range of processing options to produce hydrochar with characteristics required for various industry applications.
Greenhouse gases emitted from the excessive use of fossil fuels are threatening the environment, and thus alternative resources like biomass are being considered as a replacement. Biomass with high ...moisture content is better treated by hydrothermal carbonization method than any other process to generate biofuel. Research on this method on a lab scale has progressed recently. However, due to the complex reaction mechanisms and operational barriers, more improvements are required to make it a commercial technology. This paper aims to review the development of hydrothermal carbonization with a focus on the practical aspects of the process. Many references have been reviewed critically to provide a well-structured source for improving this process. After providing information about the biomass structure and general knowledge of hydrothermal carbonization, the challenges faced in attempts to improve the process have been identified as lack of valid kinetic and heat transfer models and insufficient data on continuous and large-scale reactors. Useful and practical suggestions have been presented to tackle all these challenges.
•Hydrothermal carbonization (HTC) should be industrialized to valorize wet biomass.•Effect of operational parameters should be studied in both lab and industrial-scale.•Kinetic and energy modeling are more challenging due to unknown chemical reactions.•The approaches to address the gaps have been clearly explained.•Combining HTC with other processes has been proposed.
Single-atom-thick graphene is a particularly interesting material in basic research and applications owing to its remarkable electronic, mechanical, chemical, thermal, and optical properties. This ...leads to its potential use in a multitude of applications for improved energy storage (capacitors, batteries, and fuel cells), energy generation, biomedical, sensors or even as an advanced membrane material for separations. This paper provided an overview of research in graphene, in the area of synthesis from various sources specially from biomass, advanced characterization techniques, properties, and application. Finally, some challenges and future perspectives of graphene are also discussed.
Graphic Abstract
Torrefaction improves the thermochemical properties of biomass that are relevant to combustion, co-combustion with coal, or gasification. This study examines torrefaction of rice husks and four other ...agriculture residues (sawdust, peanut husks, bagasse, and water hyacinth) in nitrogen. Two main operating parameters of torrefaction, temperature and residence time for the process, were varied in the range of 250−300 °C and 1−2 h, respectively. Product evolution and mass and energy losses during torrefaction were measured. Similar to other work, the torrefied products in the present work were characterized by a more brownish color, reduced moisture content and volatile matter, and increased ash, fixed carbon content, and energy density. The difference between the mass and energy yield was shown to improve for the higher torrefaction temperatures investigated. For the biomass studied, the torrefied bagasse at 300 °C and 1.5 h resulted in the highest higher heating value (HHV) of 25.68 MJ/kg of product, which was comparable to the HHV of lignite. Dependent upon the severity of the torrefaction conditions, the torrefied fuel can contain up to 98% of the original energy content on a mass basis. The combustion behavior of both raw and torrefied rice husks was studied in a spout-fluid bed combustor by measuring its temperature history at different zones. It is observed that torrefied husks ignite faster and raise the bed temperature to a higher level because of its low moisture content.
With the implementation of new policies supporting renewable natural gas production from organic wastes, Canada began replacing traditional disposal methods with highly integrated biogas production ...strategies. Herein, data from published papers, Canadian Biogas Association, Canada’s national statistical agency, and energy companies’ websites were gathered to gain insight into the current status of anaerobic digestion plants in recovering energy and resource from organic wastes. The availability of materials prepared for recycling by companies and local waste management organizations and existing infrastructures for municipal solid waste management were examined. Governmental incentives and discouragements in Canada and world anaerobic digestion leaders regarding organic fraction municipal solid waste management were comprehensively reviewed to identify the opportunities for developing large-scale anaerobic digestion in Canada. A range of anaerobic digestion facilities, including water resource recovery facilities, standalone digesters, and on-farm digesters throughout Ontario, were compared in terms of digestion type, digester volume, feedstock (s), and electricity capacity to better understand the current role of biogas plants in this province. Finally, technology perspectives, solutions, and roadmaps were discussed to shape the future in terms of organic fraction municipal solid waste management. The findings suggested that the biogas industry growth in Canada relies on provincial energy and waste management policies, advanced technologies for diverting organic waste from landfills, improving biogas yield using existing pretreatment methods, and educating farmers regarding digester operations.
Hydrothermal carbonization (HTC) is a promising method for the production of energy dense coal-like material from low quality lignocellulosic biomass. The process takes place in the presence of water ...and therefore is unaffected by feedstocks containing a high moisture content. However, the substantial water requirement and disposal concerns for a large scale HTC plant may outweigh its advantages from an economical and environmental point of view. The work presented in this study proposes a solution to the aforementioned problem. Miscanthus feedstock was treated hydrothermally at three different reaction temperatures (190, 225, and 260 °C) for 5 min with a solid load ratio of 1:6. The liquid by-product from each experiment was characterized for chemical composition. The results show that the HTC process water was rich in organic acids (acetic, formic, levulinic, and glycolic acid), Hydroxy-methyl-furfural (HMF), and total organic carbon (TOC). The acidity and the concentration of intermediate products in the HTC process water increased with an increase in reaction temperature. The HTC process water produced at 260 °C was examined for the recirculation of process water. The results show that, during successive recirculation of HTC process water, the mass yield of the hydrochar samples increases by 5–10% and the energy yield of the hydrochar samples increased up to 15% compared to the HTC-reference sample (hydrochar sample produced at initial run). Most importantly, the HHV of hydrochars increased from 18.9 (raw biomass) to 26.6 MJ/kg (maximal value) during recirculation of process water. As a result, the recirculation of process water can increase the overall system’s efficiency and reduce both the operating costs and environmental impact of a commercial HTC plant.
Influential spreaders are the crucial nodes in a complex network that can act as a controller or a maximizer of a spreading process. For example, we can control the virus propagation in an ...epidemiological network by controlling the behavior of such influential nodes, and amplify the information propagation in a social network by using them as a maximizer. Many indexing methods have been proposed in the literature to identify the influential spreaders in a network. Nevertheless, we have notice that each individual network holds different connectivity structures that we classify as complete, incomplete, or in-between based on their components and density. These affect the accuracy of existing indexing methods in the identification of the best influential spreaders. Thus, no single indexing strategy is sufficient from all varieties of network connectivity structures. This article proposes a new indexing method Network Global Structure-based Centrality (ngsc) which intelligently combines existing kshell and sum of neighbors' degree methods with knowledge of the network's global structural properties, such as the giant component, average degree, and percolation threshold. The experimental results show that our proposed method yields a better spreading performance of the seed spreaders over a large variety of network connectivity structures, and correlates well with ranking based on an SIR model used as ground truth. It also out-performs contemporary techniques and is competitive with more sophisticated approaches that are computationally cost.
Biomass for activated carbon production has had been gaining interest in a wide variety of applications such as water filtration, gas adsorption, and electrochemical devices as a renewable carbon ...source while meeting desired porosity, surface area, conductivity, and stability requirements. Activated carbon production has been extensively investigated, proving to provide high performance in applications including electrochemical devices. Hydrothermal carbonization (HTC) has shown potential as a pretreatment method for activated carbon production, especially when surface functionalization is desired. However, research into catalytic HTC is still limited. In this review, the processing methods used to convert biomass waste products into high value activated carbon are briefly reviewed, with a focus on recent progress in catalytic HTC as a pretreatment method to activated carbon. Areas of interest for catalytic HTC for activated carbon production are identified. Recent studies have found that the use of catalysts enhances the degree of carbonization, surface modification, and introduction of key heteroatoms significantly augmenting the performance of activated carbon. With further development of catalytic HTC technology, more competent carbon material for electrochemical devices can be produced cost-effectively and move towards meeting the ever-increasing demands of activated carbons for high-performance electrochemical devices.
Graphic Abstract
Two state-of-the-art electrodes were successfully synthesized and used to assemble both symmetric and asymmetric type supercapacitors. 3DFAB was fabricated by direct pyrolysis of green macroalgae in ...the presence of NaOH. Possible NaOH activation mechanisms are proposed, which explains the formation of oxygen functional groups through quick penetration of OH- and NaOH into the vacancies. To obtain CoTLM, the tile-like architecture of cobalt oxides was introduced to the 3D interconnected functional algal biochar (3DFAB) by a simple one-pot hydrothermal method under mild conditions. For the symmetric supercapacitors, the maximum specific capacitance of RAB, 3DFAB, and CoTLM were 158, 296, and 445 F g
at the current density of 1 A g
. Regarding cobalt-based asymmetric systems, the maximum capacitance for the 3DFAB//CoTLM was 411 F g
. This asymmetric supercapacitor device also retained 100.9% of its initial capacitance after 4000 cycles at the current density of 4 A g
. Unbuffered aqueous electrolyte and the unique morphological structure used in this study might catapult forward commercialization of such advanced energy storage devices.
Developing and applying a novel and sustainable energy crop is essential to reach an efficient and economically feasible technology for bioenergy production. In this study, plant tissue culture, also ...referred to as in vitro culture, is introduced as one of the most promising and environmentally friendly methods for the sustainable supply of biofuels. The current study investigates the potential of in vitro -grown industrial hemp calli obtained from leaf, root, and stem explants as a new generation of energy crop. For this purpose, the in vitro grown explants were first fully characterized in terms of elemental and chemical composition. Secondly, HTL experiments were designed by Design Expert 11 with a particular focus on biocrude. Finally, the chemical components, functional groups, and petroleum-like hydrocarbons present in the biocrude were identified by PY-GCMS. A 22.61 wt.% biocrude was produced for the sample grown through callogenesis of the leaf (CL). The obtained biocrude for CL consisted of 19.55% acids, 0.42% N compounds, 15.44% ketones, 16.03% aldehydes, 2.21% furans, 20.01% aromatics, 5.2% alcohols, and 19.88% hydrocarbons. To the best of the authors' knowledge, this is the first report that in vitro -grown biomass is hydrothermally liquefied toward biocrude production; the current work paves the way for integrating plant tissue culture and thermochemical processes for the generation of biofuels and value-added chemicals.
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