Abstract:
Hydrothermal liquefaction (HTL) is a promising process for converting biomass into liquid fuels, so-called bio-crude. Napier grass is one of fast-growing grasses as well as potential energy crops. Its production yields can reach 6.4 Mg rai-1 yr-1 on dry basis. This work was focused on bio-crude production from HTL of Napier grass in ethanol-water co-solvent. The experiments were carried out in a 500 mL high-pressure reactor. The effect of operating parameters including temperature, initial N2 pressure, stirrer-rotating speed and ethanol concentration on product yields were investigated. In case of pure water as a solvent, the bio-crude yield increased with increasing temperature from 275 to 300 ◦C. The maximum bio-crude yield was found at 300 ◦C. The yield became lower due to thermal decomposition of bio-crude to gas if exposed to higher temperatures of 300-350 ◦C. Bio-crude yield increased with increment of initial N2 pressure from 10 to 20 bar. In case of stirrer-rotating speed, the bio-crude yield slightly increased with increasing rotation speed from 300 to 400 rpm but decreased when the rotation speed is higher than 400 rpm. Using co-solvent of ethanol-water, the highest bio-crude yield of 52.76 wt.% was attained at ethanol concentration of 25 vol.% and initial N2 pressure of 20 bar. This value was also higher than that obtained with a mono-solvent at the same operating conditions. This indicated a synergistic effect when using ethanol-water mixture on HTL. The high heating value of bio-crude was about 27 MJ/kg. The GC-MS results revealed that the bio-crude contains mostly phenolic compounds. It was also found that ester and ketone compounds in the oil increased with increasing the ethanol concentration from 0 to 100 vol.%.