Valorization of organic waste with the aid of solar hydrothermal liquefaction technology

Abstract

Solar Hydrothermal Liquefaction technology is a relatively novel and less developed area of solar fuels category. It enhances the circular economy by promoting both the environmental sustainability and the production of added value products, since its feedstock is comprised of organic waste and their water content that takes over the double role as reactant and catalyst. The present study focuses on the lab-scale screening of different organic waste in terms of their bio-oil production yield, with an immediate next step being the HTL system coupling with Concentrating Solar Technologies (CST). The relative lab-scale solar experiments will be carried out in APTL/CERTH’s high flux solar simulator and solar furnace with the use of a dedicated batch reactor, while pilot-scale experiments will be performed in using a reactor coupled with a parabolic trough system. The feedstocks examined in the current work were peach stones, food waste and dairy waste processed in two different temperatures (300 and 350oC) and two initial pressures (1 and 20 bar) for a retention time of 30 minutes. Based on the findings, GC/MS analysis has shown that the main compounds of the bio-oil consisted of fatty acids, phenols and long-chain alkanes, whereas the primary gas-phase products (GC analysis) were CO2, CO, CH4, C2H4, C2H6, C3H8 and C3H6. Dairy waste had the highest bio-oil yield efficiency (up to 22 wt%), by employing dichloromethane as a solvent at a reaction temperature of 300oC and 1 bar initial N2 pressure. An increase of water/feedstock ratio by adding surplus water had a significantly positive effect on the bio-oil yield with an up to 98% increase.