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•WGSR is an important reaction for H2 production and CO2 capture.•A comprehensive review of the research progress in the WGSR is given.•State-of-the-art thermodynamic and kinetic ...characteristics of the WGSR are underlined.•WGSR behaviors in certain special environments are emphasized.•WGSR in membrane reactors for carbon capture and H2 production is addressed.
The water gas shift reaction is an important and commonly employed reaction in the industry. In the water gas shift reaction, hydrogen is produced from water or steam while carbon monoxide is converted into carbon dioxide. Over the years, on account of the progress in hydrogen energy and carbon capture and storage for developing alternative fuels and mitigating the atmospheric greenhouse effect, the water gas shift reaction has become a crucial route to simultaneously reach the requirements of hydrogen production and carbon dioxide enrichment, thereby enhancing CO2 capture. This article provides a comprehensive review of the research progress in the water gas shift reaction, with particular attention paid to the thermodynamic and kinetic characteristics. The performance of the water gas shift reaction highly depends on the adopted catalysts whose progress in recent years is extensively reviewed. The behaviors of the water gas shift reaction in special environments are also illustrated, several cases have the ability to proceed with water gas shift reaction without any catalyst. The utilization of several separation technologies on the water gas shift reaction such as carbon capture and storage and membrane reactors for purifying hydrogen and enriching carbon dioxide will be addressed as well. Reviewing past studies suggests that separating hydrogen and carbon dioxide in the product gas from the water gas shift reaction can not only increase efficiency but also enhance the usability for further application. The CO conversion is beyond the thermodynamic limitation after applying membrane for the water gas shift reaction.
•A state-of-the art review on recent research activities in microalgae pyrolysis is given.•Pyrolysis characteristics and kinetics of microalgae via TGA is reviewed.•Kinetic-free, single reaction and ...multiple parallel reaction and distributed activation energy models are introduced.•The kinetic models predicting the thermal degradation of microalgae are examined.•Pros and cons of microalgae pyrolysis using TGA are illustrated.
Pyrolysis is a promising route for biofuels production from microalgae at moderate temperatures (400–600°C) in an inert atmosphere. Depending on the operating conditions, pyrolysis can produce biochar and/or bio-oil. In practice, knowledge for thermal decomposition characteristics and kinetics of microalgae during pyrolysis is essential for pyrolyzer design and pyrolysis optimization. Recently, the pyrolysis kinetics of microalgae has become a crucial topic and received increasing interest from researchers. Thermogravimetric analysis (TGA) has been employed as a proven technique for studying microalgae pyrolysis in a kinetic control regime. In addition, a number of kinetic models have been applied to process the TGA data for kinetic evaluation and parameters estimation. This paper aims to provide a state-of-the art review on recent research activities in pyrolysis characteristics and kinetics of various microalgae. Common kinetic models predicting the thermal degradation of microalgae are examined and their pros and cons are illustrated.
Torrefaction is a mild pyrolysis, which has been explored for the pretreatment of biomass to increase the heating value and hydrophobicity. Due to its potential applications for making torrefied ...pellets, which can be used as a high quality feedstock in gasification for high quality syngas production and as a substitute for coal in thermal power plants and metallurgical processes, torrefaction and densification have attracted great interest in recent years from both academia and bioenergy industry. This paper provides a comprehensive review of research progresses in this area, drawing on major contributions from two major research groups of the authors on torrefaction and densification at Canada and Taiwan as well as literatures. It is revealed that torrefaction of various biomass species and their major components, lignin, cellulose and hemicelluloses have been extensively studied in thermogravimetric apparatus (TGA) under both inert (N2) and oxidative (O2, H2O) environments to elucidate the weight loss as a function of temperature, particle size and time. It was found that the higher heating value and saturated water uptake of torrefied biomass were a strong function of weight loss, which represents the degree of torrefaction. When torrefied sawdust is compressed into torrefied pellets, more mechanical energy is consumed and higher die temperature is required to make torrefied pellets of similar density and hardness as regular pellets. Simple economics analyses based on laboratory scale experimental data showed that because of the potential savings from pellets transport, handling and storage logistics, the overall cost for torrefied pellets can be lower than regular pellets in European market for both European and Canadian pellets. The gasification could be improved in terms of both energy efficiency and syngas quality because of the removal of oxygenated volatile compounds from torrefied biomass.
Summary
Biofuel has emerged as an alternative source of energy to reduce the emissions of greenhouse gases in the atmosphere and combat global warming. Biofuels are classified into first, second, ...third and fourth generations. Each of the biofuel generations aims to meet the global energy demand while minimizing environmental impacts. Sustainability is defined as meeting the needs of the current generations without jeopardizing the needs of future generations. The aim of sustainability is to ensure continuous growth of the economy while protecting the environment and societal needs. Thus, this paper aims to evaluate the sustainability of these four generations of biofuels. The objectives are to compare the production of biofuel, the net greenhouse gases emissions, and energy efficiency. This study is important in providing information for the policymakers and researchers in the decision‐making for the future development of green energy. Each of the biofuel generations shows different benefits and drawbacks. From this study, we conclude that the first generation biofuel has the highest biofuel production and energy efficiency, but is less effective in meeting the goal of reducing the greenhouse gases emission. The third generation biofuel shows the lowest net greenhouse gases emissions, allowing the reduction of greenhouse gases in the atmosphere. However, the energy required for the processing of the third generation biofuel is higher and, this makes it less environmentally friendly as fossil fuels are used to generate electricity. The third and fourth generation feedstocks are the potential sustainable source for the future production of biofuel. However, more studies need to be done to find an alternative low cost for biofuel production while increasing energy efficiency.
• First generation biofuel has the highest biofuel yield and energy efficiency. However, the production of the biofuel opposed many sustainable development goals.
• Third and fourth generation biofuels show potential as a sustainable future green energy.
• Methods of lipid extraction of microalgae biofuel and environmental consequences of the fourth generation biofuel should be further explored.
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•Applications of biomass using TG, FTIR, and their combination are summarized.•Thermal degradation of lignocellulosic and no-lignocellulosic biomass is addressed.•The evolved gases ...including CO2, CO, H2, CH4 during the conversion are summarized.•TG-FTIR is a promising analytical technique for co-pyrolysis and co-gasification.
Effective methods of biomass characterization are needed for energy production due to the increase in biomass to bioenergy conversion capacity and the availability of various biomass sources. The utilization of biomass has been enhanced through thermochemical conversion techniques such as torrefaction, pyrolysis, and gasification. The biomass analytical techniques have been developed to decrease the time and energy required for biomass conversion performance. Thermogravimetric analyzer (TG) and Fourier transform infrared spectroscopic (FTIR) analytical techniques facing several limitations when applied individually. Thus, TG coupled with FTIR (TG-FTIR) was used to analyze the main parameters of biomass and improved the energy crop growing developments. In addition, TG-FTIR can determine the suitable ratio for two different biomass or coal blending during the co-pyrolysis and co-gasification to achieve the optimum synergetic interaction. In this review, thermochemical conversion processes such as torrefaction, pyrolysis, and gasification are presented. The analysis of the thermochemical conversion of biomass with the use of TG and FTIR individually are then discussed. Lastly, this review aims to discuss the applications of TG-FTIR techniques that have been applied to the analysis of evolved gas from the thermochemical processing of biomass to biofuels.
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•Eight conversion routes for waste residues using microwave-assisted heating are reviewed.•Microwaves’ high energy use was offset by shorter duration and better product ...quality.•MW-assisted pyrolysis is the most studied route while other routes are still undermined.•Catalysis and co-processing of two wastes are the recent trends with several routes.•MW-assisted pyrolysis in a vacuum environment is one of the most recent advancements.
With drastic fossil fuel depletion and environmental deterioration concerns, a move towards a more sustainable bioenergy-based economy is essential. Lately, the application of microwave (MW) irradiation for waste processing has been attracting interest globally. MW-assisted heating possesses several advantages such as the provision of high microwave energy into dielectric materials with deeper penetration for internal heat generation, showing beneficial features in improving the heating rate and reducing the reaction time. Consequently, the most recent literature regarding the applications of MW-assisted heating for biomass pretreatment as well as biofuel and bioenergy production was reviewed and consolidated in this study. An impressive increase in the product yield and improvement of the product properties are reported, with the use of MW-assisted heating in several conversion routes to produce biofuels. Despite being a promising technology for biofuel production, some major fundamental data of MW-assisted heating have not been comprehensively identified. Therefore, the feasibility of this technology for large-scale implementation is still subpar. Understanding the interaction between the feedstock and the microwave electromagnetic field, and the optimization of several operational and mechanical parameters are the two main keystones that would propel the industrialization of MW heating in the near future. This provides key insights leading to increased feasibility and more advanced application of MW heating.
Being declared a global emergency, the COVID-19 pandemic has taken many lives, threatened livelihoods and businesses around the world. The energy industry, in particular, has experienced tremendous ...pressure resulting from the pandemic. In response to such a challenge, the development of sustainable resources and renewable energy infrastructure has demonstrated its potential as a promising and effective strategy. To sufficiently address the effect of COVID-19 on renewable energy development strategies, short-term policy priorities should be identified, while mid-term and long-term action plans should be formulated in achieving the well-defined renewable energy targets and progress towards a more sustainable energy future. In this review, opportunities, challenges, and significant impacts of the COVID-19 pandemic on current and future sustainable energy strategies were analyzed in detail; while drawing from experiences in identifying reasonable behaviors, orientating appropriate actions, and policy implications on the sustainable energy trajectory were also mentioned. Indeed, the question is that whether the COVID-19 pandemic will kill us or provide us with a precious lesson on future sustainable energy development.
•Two-faced impacts of COVID-19 pandemic on global energy system were evaluated.•Opportunities and challenges of the shift progress to clean energy were analyzed.•Drawn lessons, strategies for the future, and policy implications were mentioned.
Torrefaction is a thermal pretreatment process for biomass where raw biomass is heated in the temperatures of 200–300 °C under an inert or nitrogen atmosphere. The main constituents contained in ...biomass include hemicellulose, cellulose and lignin; therefore, the thermal decomposition characteristics of these constituents play a crucial role in determining the performance of torrefaction of lignocellulosic materials. To gain a fundamental insight into biomass torrefaction, five basic constituents, including hemicellulose, cellulose, lignin, xylan and dextran, were individually torrefied in a thermogravimetry. Two pure materials, xylose and glucose, were torrefied as well for comparison. Three torrefaction temperatures of 230, 260 and 290 °C, corresponding to light, mild and severe torrefactions, were taken into account. The experiments suggested the weight losses of the tested samples could be classified into three groups; they consisted of a weakly active reaction, a moderately active reaction and a strongly active reaction, depending on the natures of the tested materials. Co-torrefactions of the blend of hemicellulose, cellulose and lignin at the three torrefaction temperatures were also examined. The weight losses of the blend were very close to those from the linear superposition of the individual samples, suggesting that no synergistic effect from the co-torrefactions was exhibited.
► Torrefactions of hemicellulose, cellulose, lignin, xylan, dextran, xylose and glucose. ► Thermogravimetric analyses of hemicellulose, cellulose, lignin, xylan, dextran, xylose and glucose. ► Analysis of thermal behavior (endothermic and exothermic reactions) of the tested materials. ► Classification of weight loss from the torrefaction of the tested materials. ► Co-torrefaction of the blend of hemicellulose, cellulose and lignin.
The increasing demand for energy and diminishing sources of fossil fuels have called for the discovery of new energy sources. The effective energy conversion process of biomass is able to fulfill ...energy needs. Among the advanced biomass conversion technologies, thermochemical processes hold considerable potential approaches and needed for optimization. Thus, this study presents a comprehensive review of the research and development on the effects of catalysts on the thermochemical conversion of biomass to determine the progress of catalytic thermochemical conversion processes. The effects of catalysts on torrefaction, pyrolysis, hydrothermal liquefaction, and gasification are highlighted. Aspects related to reaction conditions, reactor types, and products are discussed comprehensively with the reaction mechanisms involved in the catalytic effects. Hydrogenation and hydrodeoxygenation can occur in the presence of zeolite catalysts during fast pyrolysis while producing highly aromatic bio-oil. A heterogeneous catalyst in liquefaction increases the hydrocarbon content and decreases viscosity, acid value, and oxygenated compounds in the bio-oil. Thus, expanding and enhancing knowledge about catalyst utilization in the thermochemical conversion technologies of biomass will play an important role in the generation of renewable and carbon-neutral fuels.
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•AAEMs modify the biomass cellulose structure to enhance thermal reactivity.•Zeolites enhance the deoxygenation reactions and aromatic yield.•Heterogeneous catalysts enhance hydrocarbon in bio-oil with high recyclability.•AAEMs and Ni catalysts promote the H2 content in the gasification process.
•Enzymatic transesterification process is less energy intensive and robust.•Nano-materials are promising immobilization supports for lipase.•Packed-bed reactors are appropriate for scale-up ...use.•Potential recombinant, whole cell and recombinant whole cell lipases were enlisted.•Genetic engineering is a promising prospect in biodiesel area.
The world demand for fuel as energy sources have arisen the need for generating alternatives such as biofuel. Biodiesel is a renewable fuel used particularly in diesel engines. Currently, biodiesel is mainly produced through transesterification reactions catalyzed by chemical catalysts, which produces higher fatty acid alkyl esters in shorter reaction time. Although extensive investigations on enzymatic transesterification by downstream processing were carried out, enzymatic transesterification has yet to be used in scale-up since commercial lipases are chiefly limited to the cost as well as long reaction time. While numerous lipases were studied and proven to have the high catalytic capacity, still enzymatic reaction requires more investigation. To fill this gap, finding optimal conditions for the reaction such as alcohol and oil choice, water content, reaction time and temperature through proper reaction modelling and simulations as well as the appropriate design and use of reactors for large scale production are crucial issues that need to be accurately addressed. Furthermore, lipase concentration, alternative lipase resources through whole cell technology and genetic engineering, recent immobilizing materials including nanoparticles, and the capacity of enzyme to be reused are important criteria to be neatly investigated. The present work reviews the current biodiesel feedstock, catalysis, general and novel immobilizing materials, bioreactors for enzymatic transesterification, potential lipase resources, intensification technics, and process modelling for enzymatic transesterification.
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