A review on the operating conditions of producing bio-oil from hydrothermal liquefaction of biomass

Abstract

Hydrothermal liquefaction (HTL) is a promising technology that involves converting biomass into a liquid energy carrier called bio-oil in sub/supercritical water. The unique physico-chemical properties of bio-oil, particularly its remarkably high energy density, renewability, and sustainability, can address current global environmental challenges and energy crisis. This review assesses the influence of operating parameters, including biomass type, reaction temperature, holding time, biomass/H 2 O ratio, heating rate, pressure, and atmosphere, and catalysis, on the yield and quality of bio-oil. The existing problems in HTL are also analyzed, and its further development is explored.

Treatment technologies for urban solid biowaste to create value products: a review with focus on low- and middle-income settings

“…Publications report liquefaction of wood, forest and agricultural residues, urban biowastes, sewage sludge, manure, and algae (Ramirez et al 2015). Lignocellulosic and algal biomass are the most commonly used feedstock types, with cellulose exhibiting higher bio-oil conversion than lignin (Xue et al 2016). HTL of 18 types of Indonesian agricultural and forest residues was reported in Minowa et al (1998), producing bio-oil with a heating value comparable to high rank coal and revealing a positive energy balance.…”

“…Water is an important reactant and catalyst, and thus wet biomass can be directly converted without an energy consuming drying step (Arturi et al 2016;Toor et al 2011;Xue et al 2016). The thermochemical processes of HTL and fast pyrolysis are sometimes confused with each other as both can convert feedstock organic compounds into liquid products.…”

“…Almost all of these gaseous-, aqueous-, and solid-phase byproducts can be utilized in the field of advanced carbon materials, chemicals, or as fuel for the transportation industry (Xue et al 2016). HTL biooil is semi-liquid, dark-colored and has a smoke-like smell (Ramirez et al 2015).…”

“…alkaline hydroxides and carbonates) lower the amount of solid residue and improve the yield of bio-oils (Srirangan et al 2012). Akhtar and Amin (2011) and Xue et al (2016) discuss the influence of operating parameters such as biomass type, biomass/H 2 O ratio, particle size, reaction temperature, heating rate, solvent density, pressure, residence time, catalysts and reducing gas/hydrogen donors on bio-oil yield and quality.…”

“…reactor corrosion, precipitation of inorganic salts, coking and deactivation of heterogeneous catalysts), which all need to be resolved before hydrothermal technologies can be piloted and ultimately scaled up (Peterson et al 2008;Tran 2016). Challenges regarding feedstock and upgrading of bio-oil include questions about decomposition of lignin in the HTL process, as well as the challenge of high oxygen and nitrogen levels in the bio-oil (Xue et al 2016). Although technologies for the upgrading of the bio-crude exist, applications of these techniques are limited by economic considerations .…”