Abstract
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.
Highlights
People’s lifestyles are beginning to be severely affected by climate change and the continuous depletion of the world’s limited supply of natural resources
(an equal amount of alkali compared to Na2 CO3 ) sodium hydroxide of the black liquor’s dry matter was added, the carbon yield rose from 61% to 64% compared to when no NaOH was added, while the bio-oil HHV on an as-received basis was 25 MJ/kg and 34.2 MJ/kg on a dry ash-free basis
By its very nature, contains large quantities of alkali salts. Because of their low solubility in hydrothermal conditions, and the risk of corrosion, they can cause a lot of problems for the processing equipment by fouling up the pipes and vessels
Summary
People’s lifestyles are beginning to be severely affected by climate change and the continuous depletion of the world’s limited supply of natural resources. The resulting product is a biocrude, which can be further upgraded into transportation fuel in an oil refinery This membrane filtration process has been successfully demonstrated at SP Energy Technology Center in. There have been numerous HTL studies of various feedstocks, no comprehensive review article has been published on the HTL of black liquor or of its derived products Those HTL review articles that do exist either focus on the HTL of biomasses from different sources [21,22], the HTL of pure lignin compounds [23], or the HTL of a specific biomass, such as wood [24], algae [25,26,27], agricultural and forestry waste [28], and even swine manure [29].
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