亚/超临界乙醇中羟基和氢自由基作用下的纤维素液化行为

以水杨酸为羟基自由基(HO·)捕捉剂、四氯化碳为氢自由基(H·)捕捉剂,采用间歇高压反应釜对玉米秸秆纤维素在亚/超临界乙醇中的液化行为进行了研究,通过考察自由基捕捉剂用量、反应温度和反应时间对纤维素液化行为的影响,研究亚/超临界乙醇产生的HO·和H·自由基对纤维素的液化作用。结果表明,随着水杨酸用量增加(0-4mL),HO·浓度升高,生物油收率由29.3%提高至47.9%,固体残渣收率从26.7%降低至24.3%;反应温度从250℃升高至320℃,HO·活性随之增强,生物油收率由35.9%升高至58.2%,固体残渣收率由51.8%降低至20.4%;随着四氯化碳用量由0增加为2mL时,H·浓度降低,生物油收率由24.7%降低至20.7%,固体残渣收率由54.1%增加至59.1%;反应时间从0到30min,液化作用不断增强,生物油收率从8.7%升高至28.5%,固体残渣收率由86.3%下降至60.9%;30min之后,四氯化碳对H·活性的抑制加强,导致液化作用减弱,生物油收率有所下降。实验结果表明,乙醇在亚/超临界状态下能够产生HO·和H·,且HO·和H·浓度和活性与反应条件相关,对纤维素液化产物的收率及其分布具有明显的影响。

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.