Effects of hydroxyl and hydrogen free radicals on the liquefaction of cellulose in sub/supercritical ethanol

With salicylic acid as hydroxyl radical (HO·) trap and carbon tetrachloride as hydrogen radical (H·) trap, the effects of HO· and H· radicals on the liquefaction of cornstalk cellulose in sub/supercritical ethanol was investigated in an autoclave. The results indicated that the concentration of HO· radical increases with the increase of salicylic acid amount added in the feed from 0 to 4 mL; meanwhile, the bio-oil yield is increased from 29.3% to 47.9%, whereas the residue yield is decreased from 26.7% to 24.3%. The activity of HO· increases with the increase of reaction temperature from 250 to 320 ℃; meanwhile, the bio-oil yield is increased from 35.9% to 58.2%, whereas the residue yield is reduced from 51.8% to 20.4%. On the other hand, the concentration of H· radical decreases with the increase of carbon tetrachloride from 0 to 2 mL; meanwhile, the bio-oil yield is decreased from 24.7% to 20.7%, whereas the residue yield is increased from 54.1% to 59.1%. The liquefaction of cellulose is enhanced within 30 min due to the increase of H· activity; after that, the bio-oil yield begins to decline due to the inhibition of H· activity by CCl₄. Current results proved that ethanol can produce HO· and H· radicals under sub/supercritical state; the concentration and activity of HO· and H· radicals are dependent on the reaction conditions, which may determine the product yield and distribution for the liquefaction of cellulose in sub/supercritical ethanol.