Search Results (5)

Hydrothermal liquefaction (HTL) technology has garnered immense research interest due to its potential to convert wet biomass into petroleum-like biocrude. Understanding the reaction mechanism and kinetics of HTL is crucial for understanding the process better, estimating the yields, and scaling up. On the other hand, reaction mechanisms and kinetics largely depend upon the feedstock composition and reaction parameters of HTL. However, the literature lacks an in-depth analysis of the reaction mechanism and kinetics concerning biocrude yield and product distribution for a single to multi-feedstock scenario. This review focuses on the reaction mechanisms of various biomolecular components of lignocellulosic biomass, proteins, and lipids in the HTL process under sub- and supercritical conditions. Furthermore, the HTL reaction kinetics, effect of reaction conditions on reaction mechanisms, and product distribution are explored. The findings agree that reaction temperature and retention time follow inverse relations for high biocrude yield. A high heating rate is recommended for higher biocrude yield to avoid cracking and recombination processes. A high solvent/feedstock ratio, depending on feedstock composition, was favored for optimum biocrude yield. In addition, catalysts and reaction solvents, especially organic solvents, effectively contribute towards high biocrude yield, even up to 70%. Heterogeneous catalysts are favored due to reusability and improved biocrude quality. Also, hydrothermal co-liquefaction (multi-feedstock) use for improving biocrude yield was debated. A detailed discussion on the reaction kinetics of various biomolecular components in the HTL process revealed that reactions in HTL normally follow the first-order rate law. Finally, the authors outline the pointers for future research in HTL for industrial upscaling. Full article

Hydrothermal liquefaction (HTL) is an emerging technology for bio-crude production but faces challenges in determining the optimal temperature for feedstocks depending on the process mode. In this study, three feedstocks—wood, microalgae spirulina (Algae Sp.), and hydrolysis lignin were tested for sub-supercritical HTL at 350 and 400 °C through six batch-scale experiments. An alkali catalyst (K₂CO₃) was used with wood and hydrolysis lignin, while e (Algae Sp.) was liquefied without catalyst. Further, two experiments were conducted on wood in a Continuous Stirred Tank Reactor (CSTR) at 350 and 400 °C which provided a batch versus continuous comparison. Results showed Algae Sp. had higher bio-crude yields, followed by wood and lignin. The subcritical temperature of 350 °C yielded more biocrude from all feedstocks than the supercritical range. At 400 °C, a significant change occurred in lignin, with the maximum percentage of solids. Additionally, the supercritical state gave higher values for Higher Heating Values (HHVs) and a greater amount of volatile matter in bio-crude. Gas Chromatography and Mass Spectrometry (GCMS) analysis revealed that phenols dominated the composition of bio-crude derived from wood and hydrolysis lignin, whereas Algae Sp. bio-crude exhibited higher percentages of N-heterocycles and amides. The aqueous phase analysis showed a Total Organic Carbon (TOC) range from 7 to 22 g/L, with Algae Sp. displaying a higher Total Nitrogen (TN) content, ranging from 11 to 13 g/L. The pH levels of all samples were consistently within the alkaline range, except for Wood Cont. 350. In a broader perspective, the subcritical temperature range proved to be advantageous for enhancing bio-crude yield, while the supercritical state improved the quality of the bio-crude. Full article

In the present study, the protein-extracted grass residue (press cake) was processed through hydrothermal liquefaction under sub and supercritical temperatures (300, 350 and 400 °C) with and without using a potassium carbonate catalyst. The results revealed that bio-crude yield was influenced by both temperature and the catalyst. The catalyst was found to be effective at 350 °C (350 Cat) for enhancing the bio-crude yield, whereas supercritical state in both catalytic and non-catalytic conditions improved the quality of bio-crude with reasonable HHVs (33 to 36 MJ/kg). The thermal behaviour of bio-crude was analysed and higher volatile contents (more than 50% under the range of 350 °C) were found at supercritical conditions. The overall TOC values in the residual aqueous phase varied from 22 to 38 g/L. Higher carbon loss was noticed in the aqueous phase in supercritical conditions. Furthermore, GCMS analysis showed ketones, acids and ester, aromatics and hydrocarbon with negligible nitrogen-containing compounds in bio-crude. In conclusion, the catalytic conversion of grass residue under subcritical conditions (350 Cat) is favourable in terms of high bio-crude yield, however, supercritical conditions promote the deoxygenation of oxygen-containing compounds in biomass and thus improve HHVs of bio-crude. Full article

To mitigate global warming, humankind has been forced to develop new efficient energy solutions based on renewable energy sources. Hydrothermal liquefaction (HTL) is a promising technology that can efficiently produce bio-oil from several biomass sources. The HTL process uses sub- or supercritical water for producing bio-oil, water-soluble organics, gaseous products and char. Black liquor mainly contains cooking chemicals (mainly alkali salts) lignin and the hemicellulose parts of the wood chips used for cellulose digestion. This review explores the effects of different process parameters, solvents and catalysts for the HTL of black liquor or black liquor-derived lignin. Using short residence times under near- or supercritical water conditions may improve both the quality and the quantity of the bio-oil yield. The quality and yield of bio-oil can be further improved by using solvents (e.g., phenol) and catalysts (e.g., alkali salts, zirconia). However, the solubility of alkali salts present in black liquor can lead to clogging problem in the HTL reactor and process tubes when approaching supercritical water conditions. Full article

In this study, hydrothermal liquefaction (HTL) of wheat straw (WS) in sub (350 °C) and supercritical (400 °C) water with and without alkali catalyst was performed to investigate the potential of WS for the production of biocrude. The influences of temperature and catalyst were studied for the HTL products. Results showed that maximum biocrude yield (32.34 wt. %) with least solid residue (4.34 wt. %) was obtained at subcritical catalytic condition, whereas the carbon content was slightly higher in biocrude at supercritical. The higher heating value (HHV) for biocrude is around 35 MJ/kg for all four conditions. The major compounds in biocrude were observed as ketones, alcohols, acids, and hydrocarbons. At 350 °C, 44–55% of the carbon recovered into biocrude. The products were characterized in terms of elemental composition, higher heating values, organics, and inorganic compounds in different phases. To keep in consideration the scale-up of HTL process for continuous plant, aqueous phase from HTL was also recirculated which showed the fruitful outcomes by increasing the biocrude yield at each cycle. Full article