Continuous Hydrothermal Liquefaction for Biofuel and Biocrude Production from Microalgal Feedstock

Abstract

Microalgal biomass processing by continuous hydrothermal liquefaction (HTL) has recently received much interest and can be used to convert microalgal biomass to biocrude oil and drop‐in fuels. This review focuses on the conversion of microalgae biomass to energy production through continuous HTL processes. In addition, processes for upgrading feedstocks and biocrude are also discussed. The feed of the biomass slurry is treated according to size and moisture regulations. Following separation of the gaseous, liquid, and solid phases, the determination of elemental, physical, and chemical fragments, yield of energy, and other properties of the various products is carried out. Homogeneous or heterogeneous catalysts improve the biocrude yield and quality as does higher moisture content. The high percentage of N2 and O2 in the feedstock results in lower quality products. This may be resolved through pre‐processing of the biomass, controlling of HTL processes conditions, and post‐upgrading processing of the HTL products. The promising potential of microalgae biomass for biocrude and drop‐in fuels may have an important contribution to the world's renewable energy sources through HTL in the near future.

Hydrothermal Treatment of Biomass Feedstocks for Sustainable Production of Chemicals, Fuels, and Materials: Progress and Perspectives

“…Continuous flow reactors (discussed in section ) have been developed for potentially continuous HTC, HTL, and HTG of biomass. − ,,, However, the challenges remain in various stages of large-scale hydrothermal processes (i.e., selection and pretreatment of biomass feedstocks, optimization of continuous flow reactors, and separation and upgrade the bioproducts) . Specifically, continuous HTL and HTG have been explored for the hydrothermal treatment of lignocellulosic − and nonlignocellulosic biomass (e.g., algae, sewage sludge, and food wastes). The following shortcomings still block the scale-up of HTL and HTG.…”

Chlorellaceae Feedstock Selection under Balanced Nutrient Limitation

“…Mineral and trace element levels also vary among microalgae (2-20%) depending on the specific metabolic requirements and the availability in the mediums [38,39]. This ash fraction of the feedstock could later on interfere during the biomass conversion to biocrude and its further upgrading, and it could cause damage to the combustion system [40].…”

Catalytic hydrothermal liquefaction of microalgae cultivated in wastewater: Influence of ozone-air flotation on products, energy balance and carbon footprint

“…produced from a wastewater treatment process. It has been reported that biomass with a high lipids content produces more bio-crude with respect biomass with higher proteins and carbohydrates content [63].…”