Research On The Liquefaction Process Of Cornstalk Cellulose In Sub-/supercritical Methanol And Cyclohexane

As a widespread renewable source containing C and H, biomass not only can be converted into liquid fuels, but also directly into chemical products such as ketones, esters, acids and alcohols by thermo-chemical method that containing gasification, pyrolysis, and liquefaction processes. However, direct liquefaction of biomass, especially liquefaction in sub-/supercritical solvent, has proven to be an effective approach to convert lignocellulose materials into low molecular weight chemicals. But how the supercritical organic solvent promote cellulose conversion various types of compounds with high selectivity and the liquefaction mechanism is not clear. This paper can provide theoretical basis for the research of cellulose liquefaction by using methanol and cyclohexane to liquefy cellulose to explore the mechanism and to create reaction paths in the two organic solvent.In this paper, the liquefaction behaviors of cornstalk cellulose in sub-/supercritical methanol(Tc?239.4? or Pc?8.09MPa) and cyclohexane(Tc?280.4? or Pc?4.05MPa) were carried out using stainless-steel autoclave. To explore reaction conditions of cornstalk cellulose for liquefaction,the reaction products were divided into the five lumps: gas lump(GAS), volatile organic compounds lump(VO), water-soluble oil lump(WSO), heavy oil lump(HO) and solid residue(RE).The liquid products and solid residues were characterized by GC-MS and FT-IR to explore mechanism of the methanol free radicals and cyclohexane free radicals on the reaction of cellulose liquefaction and the main compounds formation mechanism. The main research contents and results are as follows:(1) The paper studied the influence of methanol in different reaction conditions of straw cellulose in liquefaction reaction. To explore the influence, the methanol dosage, reaction temperature, reaction time and other factors were studied. The yield of heavy oil increased from 1.7% to 11.61%, the water soluble oil increased from 5.76% to 11.95%, the volatile organic component increased from 9.52% to 48.83%, the gas increased from 0.09% to 28.20%, the residue decreased from 80.71% to 8.74%. The highest conversion percent of cellulose is 91.26%. The influence of methanol free radicals how to promote cellulose liquefaction and control the produce of residue.(2) Using GC-MS and FT-IR analysis, investigated the effects of methanol radical on liquefaction of cellulose of the major product formed, and discussed the reaction mechanism of cellulose liquefied into carbohydrate, hydrocarbons, acids and esters compound reaction in sub/super critical methanol. The C-O-C bonds, hydroxyl radical and C-O bonds of cellulose cleavage to form to active cellulose in high temperature. And the active cellulose transformed into polysaccharide in supercritical methanol, the polysaccharide can react with fracture, isomerizate to methyl oligosaccharides and produce a variety of methyl or two methyl-glucoside, and dehydrated intramolecular to generate levoglucosans. At the same time, polysaccharide can react with ring into the open-loop polysaccharide, which can produce intermediate free radicals. The free radicals interacted and generate into intermediate products such as aldehydes and alcohols. The intermediate products can react with addition and hydrogenation under the effect of H2, CO or CH3· and H· which released by methanol can get hydrocarbons, acids and other substances. Acids can be cracked into small molecule acids intermediates, and under the effect of H·, CH3· and alcohols to form fewer chain ester compounds. The competition among the various compounds, the amount of methanol increased, elevated temperature, reaction time change of cellulose to each kind of compound promoting action on the formation of different, and establish the liquefaction reaction paths of cellulose to form sugars, hydrocarbons, acids and esters.(3) The paper studied the influence of cellulose liquefaction in sub/super critical cyclohexane under different reaction conditions. As the increase of cyclohexane dosage and reaction temperature, the yield of residue decreased gradually. The water soluble oil and heavy oil were gradually increased and then slightly decreased. During a certain dosage of cyclohexane and temperature range, increase the cyclohexane and temperature, is advantageous to the cellulose liquefaction. As reaction time increased, the yield of liquefaction show better between 30 min to 60 min.The bio-oil was characterized by GC-MS and the residue was characterized by FT-IR, the mechanism of ketones, esters and furans formation during cellulose liquefaction in sub-/supercritical cyclohexane. Cellulose pyrolysis into active cellulose at high temperature, and under the effect of cyclohexane free radicals, a large number of C-O-C bonds rupture completely form to cellulose monomer. According to inverse Diels-Alder, cellulose monomer can react with ring-opening cracking, dehydration, aldol condensation, etc, and transform into aliphatic ketones, enol ketones and acids. The acids and alcohols transformed into esters. The cellulose monomer can isomerizate to monosaccharide such as fructose. The C1-O of fructose broken, dehydration, dehydration, hydrogenation, substitution reaction further, and transform into furans. There is a competitive relationship among different kinds of compounds, and different reaction conditions promote different competitive relationships. Based on these, the reaction path of the cellulose to transform into a variety of compounds was established.(4) By making comparisons with cornstalk cellulose in sub-/supercritical methanol and cyclohexane, it found that the ratio of cornstalk cellulose liquefaction and conversion were high with methanol. In sub-/supercritical methanol, the cornstalk cellulose was more likely to tranform into saccharides and hydrocarbon. And the cornstalk cellulose was more likely to tranform into ketones, esters and furans in sub-/supercritical cyclohexane.