Energy valorisation of food processing residues and model compounds by hydrothermal liquefaction

Abstract

International audienceThe upcoming depletion of fossil fuels calls for the development of alternative energies produced from renewable resources. Particularly, energy valorisation of agriculture and food processing wastes is one of the most promising tools for renewable energy production. The amount of food wastes is rapidly increasing due to urbanisation, industrialisation and population growth worldwide. They consequently represent a widely available resource, and their use as a raw material allows reducing the environmental cost associated with their disposal. These resources usually have high moisture content, making dry valorisation processes unattractive because of a costly drying step prior to conversion. Hydrothermal processes are conversely particularly well suited for the valorisation of wet organic wastes in an economical way, since they use water as the reaction medium. More specifically, liquid fuels can be produced using hydrothermal liquefaction (HTL). The process converts wet biomass into a crude-like oil with higher heating values up to 40 MJ/kg using subcritical water (T=250-370 degrees C, P=10-30 MPa). Though this is an active research area, the mechanisms of hydrothermal liquefaction still remain unclear today. Some processes have already been developed at the pilot scale for valorising food processing wastes. However, the development of HTL processes at industrial scales is facing technological and economic challenges. This paper discusses the two main issues to address for development of the process at large scales. On the one hand, hydrothermal conversion of food processing residues and model compounds is necessary to better understand the fundamentals of hydrothermal liquefaction. As well, technological and process integration issues have to be addressed to ensure economic viability of commercial HTL processes

Hydrothermal liquefaction of blackcurrant pomace and model molecules: understanding of reaction mechanisms

“…It decomposes biomass and produces four valuable products: a crude-like bio-oil with higher heating values up to [35][36][37][38][39][40] À1 , a combustible solid residue called 'char', an aqueous phase containing light polar platform chemicals, and a CO 2 -rich gaseous phase also containing certain amounts of hydrogen and light hydrocarbons. Many resources are considered for HTL, such as sewage sludge, 2 food processing residues, 3 and algae. 4 Typical conditions for hydrothermal liquefaction are in the 300 C range at pressures above the saturation pressure of water.…”

“…5 Other important process parameters are the dry matter concentration in the reaction medium (10-20%), and the use of pH-regulating additives to optimise HTL in basic media and increase the production of bio-oils from hydrothermal liquefaction of lignocellulosic biomass. 3 The chemistry behind HTL processes is highly complex. The biomass considered in this work is composed of not only lignocellulosic compounds but also lipids, proteins, and small carbohydrates.…”

“…We provided in a previous paper a review of the main reactions occurring during hydrothermal conversion of model molecules. 3 Polymeric model compounds such as cellulose, 8 10 lignin, 9 proteins 10,11 or triglycerides 10,12,13 have been the subject of many research papers investigating the reaction pathways and degradation kinetics of individual model compounds. Moreover, many model monomers have been used, such as monosaccharides, 14 16 guaiacol, 17 amino acids 18 or fatty acids.…”

“…Butyrolactone formation can be explained by the existence of an intermediate produced by the deamination and decarboxylation of glutamic acid: it is the hydroxybutyric acid, whose intramolecular esterication forms butyrolactone. 58 Finally, 2-pyrrolidone may also be formed from butyrolactone by reaction with NH 3 . 59 Liao and Tuemmler 59 also suggested that 2-pyrrolidone can be formed from succinimide.…”

Recovery of valuable components and inactivating microorganisms in the agro-food industry with ultrasound-assisted supercritical fluid technology

“…The re covered oil is then refined via a sequential process including i) de gumming, ii) acidification and neutralisation, iii) washing, iv) bleaching, v) winterization, and vi) deodorisation. Besides the use of toxic solvent (hexane) that is associated with health, environment, and economic issues, 1) the whole process requires high energy consump tion (approximately 40 and 10 kWh/ton of canola seed processed, for oil extraction and oil refining, respectively) [3], and 2) oil recovered by hexane is of poor quality due to the degradation of thermolabile com pounds, and the low solubility of high added value compounds (i.e. polyphenols) in hexane.…”