Depolymerization Of Cornstalk Powders In Supercritical Methanol, Product Separation With High-Speed Countercurrent Chromatography And Subsequent Analysis

At present, energy crisis and environmental issues have become the focus of global concern, while the biomass caused widespread concern around the world for its advantages of great production, storage and carbon cycle. It has positive significance to research in efficient conversion of biomass for decreasing environmental pollution, dependence on the fossil fuel and promoting the economic sustainable development.On the bases of the research on depolymerization technology of cornstalk powders in supercritical methanol, the depolymerization product was separated and analyzed systematically by the way of"graded distillation-fractional extraction-separation with high-speed countercurrent chromatography-GC/MS analysis"with a view to providing a theoretical basis for efficient conversion of cornstalk and utilization of product.Effects of solvent species, reaction temperature, reaction time, solvent amount and methods of removing air in the autoclave on depolymerization of cornstalk were investigated by single factor and orthogonal test. The optimum conditions were identified as the follows: 5 g cornstalk with 20 mL methanol was conducted at 300°C for 1h with substitute mode of nitrogen to remove any trapped air, and the residue rate decreased to 26.9%. The depolymerization product was analyzed with FTIR and GC/MS. The results showed that its components were quite complex, and there are a majority of oxygen-containing organic compounds which include esters, phenols, ketones, hydrocarbons, aethers and other compounds in the depolymerization product. The relative content of methyl esters was 38.8% in the depolymerization product of supercritical methanol, the relative content of ethyl esters was 42.7% in the product of supercritical ethanol, while the content of ketones was 22.0% in the product of supercritical ketone. These facts indicate that solvents involve in the depolymerization of the cornstalk powders respectively.The depolymerization product was fractioned by fractional distillation. The light fractions were a homogeneous system with proper caloric value and pH values near neutrality. The species information was relatively simple and these compounds mainly include methyl esters, ketones, phenols, and aethers. The total calorific value of all light fractions was little less than the value of the depolymerization initial sample, so the light fractions could be used as fuel while the remaining liquid could not suitable for fuel. The stability experiment revealed that the species information of the fractions increased gradually as time.The distillation residue was sequentially extracted with n-hexane, carbon tetrachloride, benzene, methanol and acetone in a Soxhlet extractor. Lots of light low-polar esters, heterocyclic compounds, aromatics and alkanes were identified in the fractions of n-hexane, carbon tetrachloride and benzene,respectively, while none were detected in the extracts of methanol and acetone by the GC/MS.The extracts were further separated with a high speed countercurrent chromatography (HSCCC) and then analyzed with HPLC and GC/MS. The original solvent systems of HSCCC established by HPLC were chloroform/carbon tetrachloride/methanol/water(1:3:3:2, v/v), n-hexane/ethyl acetate/methanol/water(3:5:3:5, v/v), ethyl acetate/n-butanol/water(4:1:5, v/v)and ethyl acetate/n-butanol/water (4:1:5, v/v) for distillation residual liquid, extractable fractions with n-hexane, carbon tetrachloride and benzene from distillation residue, respectively. A stepwise elution mode was introduced in the separation and purification and 12, 6, 12 and 12 chromatographic peaks were obtained, respectively. The results of analysis by HPLC and GC/MS showed that the components of every fraction were simple significantly and the number of species decreased markedly. Compared with the direct analysis to the four fractions, there are significant increases in the species number of compounds detected by GC/MS, which was 159, 222, 207 and 125. These compounds were mainly esters, ketones, phenols and hydrocarbons, but there was an obvious difference in type. 11 compounds with high purity were separated successfully from the four fractions, and 4 ketones, 4 esters, 2 phenols and 1 acid amide.These abundant compounds messages and high purity compounds was significant valuable for investigating the comprehensive utilization of the depolymerization products and the depolymerization mechanism of biomass. This result displays a possibility of production of fine chemicals from heavy components through separation approach. The study system of separation and analysis of"graded distillation-fractional extraction-separation with HSCCC-GC/MS analysis"was suitable for separation and analysis of the fractions from light to medium heavy components and the fractions from low polar to medium polar components, and also enriched the study methods of separation and analysis of the organic compounds in the biomass depolymerization products.