Subcritical hydrothermal liquefaction of barley straw in fresh water and recycled aqueous phase

This project focuses on the investigation of addition of aqueous phase in the production of biofuel from biomass through hydrothermal liquefaction (HTL) technology. Hydrothermal liquefaction is a wet thermal conversion process, which can convert all kinds of biomass to fuels. In this study, barley straw was first liquefied in fresh distilled water with the presence of K2CO3 catalyst at 300 C as the reference run. Afterwards, the aqueous phase which is obtained from liquefaction process in the previous run was recycled and used as the reaction medium from the second to the fourth run. With the addition of recycling aqueous phase in HTL process, it is expected that the amount of the waste water and energy consumption can be reduced. The effect of water recirculation on product yield and properties was investigated in this study. The results showed that bio-oil yield was 34.85 wt% when the barley straw was liquefied in the reference run, while it increased gradually to 38.44 wt% with the addition of recycled aqueous phase. In the meantime, higher solid yield was also observed when the aqueous phase was recycled as the reaction medium, and it increased with the increase in cycle. Elemental analysis showed that the carbon content of bio-oil and solid residues in the recirculation runs was higher compared with that obtained from the reference run. The higher heating values of bio-oil were in the range of 27.29-29.34 MJ/kg. Dehydration reaction was enhanced during the recirculation. TG analysis revealed that bio-oil was more stable in the recirculation runs. FTIR spectra indicated that they contained similar functional groups. The changes in functional groups in raw biomass and solid residues confirmed that certain reactions occurred in HTL process. The experimental results showed that aqueous phase obtained from HTL process can be utilized as an effective solvent.