Hydrothermal liquefaction of biomass: A review of subcritical water technologies
TL;DR: In this paper, the authors present a review of the current status of the hydrothermal liquefaction of biomass with the aim of describing the current state of the technology, which is a medium-temperature, high-pressure thermochemical process which produces a liquid product, often called bio-oil or bi-crude.
About: This article is published in Energy.The article was published on 2011-05-01. It has received 1451 citations till now. The article focuses on the topics: Hydrothermal liquefaction & Liquefaction.
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TL;DR: In this paper, the authors briefly enlightened a few concepts of HTL such as the elemental composition of bio-crude obtained by HTL, different types of feedstock adopted for HTL processes, possible process flow diagrams of both wet and dry biomass and energy efficiency of the process.
Abstract: The rapid depletion of conventional fossil fuels and day-by-day growth of environmental pollution due to use of extensive use of fossil fuels have raised concerns over the use of the fossil fuels; and thus search for alternate renewable and sustainable sources for fuels has started in the last few decades. In this context biomass derived fuels seems to be the promising path; and various routes are available for the biomass processing such as pyrolysis, transesterification, hydrothermal liquefaction, steam reforming, etc.; and the hydrothermal liquefaction (HTL) of wet biomass seems to be the promising route. Therefore, this article briefly enlightened a few concepts of HTL such as the elemental composition of bio-crude obtained by HTL, different types of feedstock adopted for HTL, mechanism of HTL processes, possible process flow diagrams for HTL of both wet and dry biomass and energy efficiency of the process. In addition, this article also enlisted possible future research scope for concerned researchers and a few of them are setting up HTL plant suitable for both wet and dry biomass feedstock; analysing influence of parameters such as temperature, pressure, residence time, catalytic effects, etc.; deriving optimized pathways for better conversion; and development of theoretical models representing the process to the best possible accuracy depending on nature of feedstock.
755 citations
TL;DR: This review describes the recent results in hydrothermal liquefaction (HTL) of biomass in continuous-flow processing systems, and process models have been developed, and mass and energy balances determined.
729 citations
TL;DR: In this article, a review of the available literature is presented, analyzing the influence of parameters such as temperature, holding time and catalyst dosage on the yield and properties of the different product fractions.
Abstract: Among the various types of biomass, microalgae have the potential of becoming a significant energy source for biofuel production in the coming years. Currently, research is mainly focusing on optimization of the cultivation methods and the conversion of just a single microalgae fraction (lipids for biodiesel production). Hydrothermal liquefaction is a method for thermochemical conversion of wet microalgae, producing a liquid energy carrier called ‘bio-oil’ or ‘biocrude’, next to gaseous, aqueous and solid by-products. A review of the available literature is presented here, analyzing the influence of parameters such as temperature, holding time and catalyst dosage on the yield and properties of the different product fractions. Also, the strain selection and the status of the technology for hydrothermal processes are analyzed. Finally, based on the findings obtained from the literature review, directions for future research are suggested.
608 citations
TL;DR: In this article, a comprehensive review of the strategies to produce furfural, new approaches and numerous possibilities to utilize it in industrial and laboratory sector for the production of fuel additives and value-added chemicals are discussed.
Abstract: As our high dependence on the supply of diminishing fossil fuel reserves raise great concerns in its environmental, political and economic consequences, utilization of renewable biomass as an alternative resource has become increasingly important. Along this background, furfural as a building block, offers a promising, rich platform for lignocellulosic biofuels and value-added chemicals. These include 2-methylfuran and 2-methyltetrahydrofuran, furfuryl alcohol, tetrahydrofurfuryl alcohol, furan, tetrahydrofuran as well as various cyclo-products (e.g., cyclopentanol, cyclopentanone). The various production routes started from furfural to various fuel additives and chemicals are critically reviewed, and the current technologies for efficient production are identified. Their potential applications as well as the fuel properties of these products are discussed. Challenges and areas that need improvement are also highlighted in the corresponding area. In short, we conduct a comprehensive review of the strategies to produce furfural, new approaches and numerous possibilities to utilize furfural in industrial and laboratory sector for the production of fuel additives and value-added chemicals.
545 citations
TL;DR: In this paper, the physicochemical properties of water under subcritical and supercritical conditions and the interactions of water with biomass are discussed in the present paper, and the characteristics of various types of hydrothermal processing products are identified.
Abstract: Hydrothermal processing is an important thermochemical conversion process that is used to convert biomass into valuable products or biofuel. The process is usually performed in water at 250–374 °C under pressures of 4–22 MPa. The biomass is degraded into small components in water. Based on the target products, i.e., bio-oil, bio-gas or bio-carbon, the process conditions (temperature, pressure and time) are chosen. There has been significant effort in evaluating various biomass resources for hydrothermal processing because the process is suitable for any type of biomass including the co-utilization of biomass with waste materials. Additionally, because most biomass resources have high moisture contents, the most efficient way to process them is through hydrothermal processing. To understand hydrothermal biomass processing and the degradation pathway of biomass, it is necessary to understand the properties of water under hydrothermal conditions (i.e., subcritical and supercritical). In this respect, the physicochemical properties of water under subcritical and supercritical conditions and the interactions of water with biomass are discussed in the present paper. This review focuses on the hydrothermal processing of biomass and identifies the characteristics of various types of hydrothermal processing products. Additionally, this review provides an overview of the available biomass, the use of biomass as an energy source and related conversion technologies.
491 citations
References
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TL;DR: Simultaneous saccharification and fermentation effectively removes glucose, which is an inhibitor to cellulase activity, thus increasing the yield and rate of cellulose hydrolysis, thereby increasing the cost of ethanol production from lignocellulosic materials.
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TL;DR: Several biomass hydrothermal conversion processes are in development or demonstration as mentioned in this paper, which are generally lower temperature (200-400 °C) reactions which produce liquid products, often called bio-oil or bio-crude.
Abstract: Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.
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