Kinetics Of Monosaccharide Decomposition In High Temperature Liquid Water

With the rapid consumption of non-renewable resources, the renewable biomass resources, in particular lignocellulosics biomass, has received more attention in producing chemicals. Lignocellulose may be converted to bulk chemicals by a hydrolysis reaction. During hydrolysis, the lignocellulose is cleaved to give monosaccharide, which can be decomposed further into useful chemicals. Results of most research showed that the first step (lignocellulose →monosaccharide) was a crucial step and had substantial impact on the selectivity and yield of chemical product. The traditional hydrolysis of biomass used liquid acid as catalysts such as hydrochloric acid and sulfuric acid, but the liquid acid had a negative impact on the reactor and on the global environment. Foucsing on the conversion of bimass in high temperature liquid water (HTLW), following study was did in this paper.Decomposition kinetics of glucose in HTLW was studied in the temperature ranges from 180 to 220℃ and pressure of 10 MPa with a stirred autoclave. The result showed that the glucose could decompose completely at experimental conditions. According to first order reaction mechanism, activation energy of non-catalyzed decomposition of glucose was 118.85 kJ/mol. The decomposition products were 5-hydromethylfurfural (5-HMF), fructose, levulinic acid (LA) and humic substance. At experimental conditions, the maximum yield of 5-HMF was 32.0 mol% and the maximum yield of levulinic acid was 2.0 mol%.Decomposition kinetics of 5-HMF in HTLW was studied at temperature ranges from 180 to 260℃ and pressure of 10 MPa. The decomposition products were formic acid, LA, two unknown products and humic substance. According to first order reaction mechanism, activation energy of non-catalyzed decomposition of 5-HMF was 95.40 kJ/mol.The stability of levulinic acid in HTLW was studied in the temperature ranges from 220 to 280 ℃ and pressure of 10 MPa. The result showed that the conversion of LA was only 7.0 mol% after 32 hours of reaction at 280 ℃. According to first order reaction mechanism, activation energy of non-catalyzed decomposition of LAwas 31.29kJ/mol.A kinetic model according to above experiments was proposed, in which decomposition kinetics of glucose in HTLW in the temperature ranges from 180 to 220℃ was described by a series first-order reactions with parallel by-reaction. The model parameters were correlated from the experimental data and the results calculated by the model were in well accordings with the experimental data.Decomposition kinetics of xylose in HTLW was studied at temperature ranges from 180 to 220℃ and pressure of 10 MPa. The decomposition products were furfural, formic acid and humic substance. The maximum yield of furfural was 50.6 mol%. A kinetic model was proposed, in which the process was described by a series first-order reactions with parallel by-reaction. The model parameters were correlated from the experimental data and the results calculated by the model were in well accordings with the experimental data. Activation energy of non-catalyzed decomposition of xylose was 123.27 kJ/mol.In order to improve the yields of levulinic acid in HTLW, 35w strong acid resin was used as an acid catalyst to prepare levulinic acid from glucose or fructose in this paper. Moreever 35w strong acid resin was also used to catalyze xylose to prepare furfural.The influence of temperature and catalyst loading on the levulinic acid yields in temperature ranges from 130 to 160℃ was studied using a small hydrothermal reactor. The result showed that by adding the resin, monosaccharide conversion was enhanced and levulinic acid formation was promoted. The maximum yield of levulinic acid formed from glucose was 27.4 mol%, and the maximum yield of levulinic acid formed from fructose was 49.7 mol %.The influence of temperature and catalyst loading on the furfural yields at temperature ranges from 130 to 160℃ was also studied. The maximum yield of furfural formed from xylose was 26.3 mol %.