Effects of torrefaction temperature and acid pretreatment on the yield and quality of fast pyrolysis bio-oil from rice straw

This study investigated the effects of torrefaction temperatures and dilute acid pretreatment on the quality of pyrolysis bio-oil and the distribution toward gaseous, liquid bio-oil, and char products from rice straw. Torrefaction of rice straw was conducted at different temperatures (225 °C, 250 °C, and 275 °C) for 30 minutes in a Py-GC/MS reactor. After the torrefaction process was completed, fast pyrolysis of torrefied rice straw was then performed at temperatures of 450 °C, 500 °C and 550 °C with a heating rate of 1000 °C/s and held for 20 seconds in the same micropyrolysis reactor. The results showed that the decrease of pyrolysis bio-oil, gas, and water, are observed when the torrefaction temperature increases. However, the decreasing trend of pyrolysis char yield was observed when the torrefaction severity increases at pyrolysis temperatures 450 °C and 500 °C, but an increasing trend was noticeable at pyrolysis temperature 550 °C. The phenolic components in pyrolysis bio-oil from torrefied rice straw were lower compare to raw rice straw. The torrefaction process helps improve the quality of pyrolysis bio-oil in terms of reducing some water, acid, and oxygenated species. The torrefaction temperature of 225 °C with the pyrolysis temperature of 550 °C is indicated as the optimum condition in our study. Additionally, the removal of mineral content from rice straw promoted higher yields of pyrolysis bio-oil, particularly levoglucosan. The acid pretreatment method also improved the pyrolysis product distribution in terms of enhancing bio-oil yield and reducing water, gas, and char.