The Formation of Char, Gaseous and Liquid Products during Lignin Carbonization in Super‐ and Subcritical Solvents

Abstract

The carbonization of lignin was performed using different solvents including ethanol, water and 50 vol% ethanol/water mixture under super-and subcritical conditions at 260 8C. The chars from lignin carbonization in supercritical ethanol provided low O/C ratio (0.09-0.14) and considerable content of surface oxygen-containing group (0.18-0.32 mmol g À1 ). Supercritical ethanol substantially participated in lignin carbonization, while the activity of ethanol was also influenced by the chemical structure of lignin. High carbon recovery of 103.8 % for chars was obtained from dealkaline lignin with guaiacyl characteristics, accompained with the production of H 2 and high valuable C 6 -C 10 esters. IntroductionNowadays, the preparation of carbon-based functional catalysts from renewable bioresources such as waste lignin through hydrothermal route has received increasing attentions. [1] Hydrothermal carbonization of lignin produces biochars with lower BET surface, [2] thermally stable char structure [3] and irregular [4] or melted morphology, [3] and has many advantages such as high oxygen functionality of the obtained chars. [5] Solvents play critical role in the carbonization and other solvothermal conversion of lignin. [6] The hydrothermal carbonization of lignin had two possible mechanisms: 1) lignin was firstly hydrolyzed or degraded to phenols and other water-soluble fragments, and then recondensed to form phenol-type chars, which we called as "homogeneous-like" route; 2) unsoluble lignin was transformed to aromatic-type chars directly after deeper crosslinking of aromatic chains and the removal of excess oxygen functionality, which was "heterogeneous" route. Both two routes were believed to exist in the real hydrothermal carbonization of lignin, [7] and possibly made the morphologies and properties of the obtained chars greatly different. It can be expected that replacing water with organic solvents in biomass carbonization would do some help for changing "heterogeneous" route to"homogeneous-like" one, although it is less studied. A case using organic alcohol to assist biomass carbonization was reported by Zheng et al, [8] who used the mixture of alcohol and water at 550 o C to produce uniform carbonaceous spheroids with different symmetric shape from glucose, sucrose and starch. For lignin carbonization, supercritical ethanol was introduced to prepare lignin chars in our previous work, [9] which were then sulfonated to prepare solid acids and used in the esterification of oleic acid and the transesterification of Jatropha oil to biodiesel. Sulfonated catalyst derived from alcohothermal carbonization of lignin possessed similar surface acidity (5.05 vs. 5.35 mmol [H + ] g À1 ) but much higher BET surface (113.1 vs. 2.7 m 2 g À1 ) than sulfonated pyrolytic char. It was believed that the solvothermal carbonization of lignin in organic solvents was remarkable different from that through hydrothermal or pyrolytic routes, which might influence the performance of sulfonated catalyst. Results and discussionHere, the sol...

Reaction Kinetics and Pathways for Salvianolic Acid B in High Temperature Water

“…Recently, high temperature water has attracted much attention as environmentally benign media for reactions, such as oxidation, extraction, hydrolysis, gasification,, hydrogenation or dehydrogenation, and lignin carbonization, and synthesis . In the present study, we studied the conversion kinetics of compound 2 and 1 in high temperature water.…”