The Distribution of Bio-Oil Components with the Effects of Sub/Supercritical Ethanol and Free Radicals during Cellulose Liquefaction

Abstract

Hydroxyl radicals (HO•) and hydrogen radicals (H•) produced from sub/supercritical ethanol have an obvious contribution on cellulose liquefaction for bio-oil production. Salicylic acid was employed as the HO• trap and CCl4 was employed as the H• trap to investigate the role of HO• and H• on the formation pathways of dominant chemical components in bio-oil during cellulose liquefaction in sub/supercritical ethanol (mostly ketones and esters). The yield of bio-oil decreased from 24.7% to 20.7% with the addition of CCl4, while the bio-oil yield increased from 29.3% to 47.9% with the addition of salicylic acid. Gas chromatography/mass spectrometry results showed that the yields of ketones, esters, and phenols in the bio-oil were 22.3%, 8.8%, and 4.7%, respectively, without salicylic acid or CCl4. The highest yields of esters and phenols increased to 21.6% and 36.9%, respectively, in the presence of salicylic acid. The yield of ketones decreased to 14.1%. Experimental data indicated that the cleavage of C-O-C and C-C bonds in the cornstalk cellulose initially generated many active cellulose fragments. Then, platform chemicals were formed from these fragments through aromatization, isomerization, aldol condensation, Baeyer-Villiger oxidation, and trans-Diels-Alder ringopening with the redox of HO• and H•.

Upgrading of Coffee Biocrude Oil Produced by Pyrolysis of Spent Coffee Grounds: Behavior of Fatty Acids in Supercritical Ethanol Reaction and Catalytic Cracking

“…Supercritical ethanol acts as an effective reactant medium by reducing the viscosity of biocrude oil. Ethanol can also produce hydroxyl and hydrogen radicals in reactions with biocrude oil in the supercritical state [14,15]. Among lignocellulosic biomass, coffee has a huge potential for biomass feedstock, simply because it is one of the most popular beverages worldwide.…”

Investigation of cornstalk cellulose liquefaction in supercritical acetone by FT-TR and GC-MS methods

“…The reason was presumed that supercritical solvents can produce hydroxyl radicals, hydrogen radicals and alkyl radicals, then the C-O-C, C-C, C-H and -OH bonds were cleave under the attack of radicals which had a contribution on cellulose converting to liquid products (8,20,21). Additionally, it was found that ketones, esters, alkanes and aromatics were in high content in the liquid product of cellulose liquefaction in supercritical solvents (22)(23)(24)(25), these green platform chemicals were widely used as important chemical materials. Therefore, supercritical liquefaction of biomass was also proved to be a promising method for producing platform chemicals.…”