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1.
高温液态水中木糖无催化分解反应动力学   总被引:3,自引:0,他引:3  
The kinetics of non-catalyzed decompositions of xylose and its decomposition product furfural in high temperature liquid water (HTLW) was studied for temperature from 180 to 220℃ and under pressure of 10MPa. The main products of xylose decomposition were furfural and formic acid, and furfural further degraded to formic acid under HTLW condition. With the assumption of first order kinetics e.quation, the evaluated activation energy of xylose and furfural decomposition was 123.27kJ·mol^-1 and 58.84kJ·mol^-1, respectively.  相似文献   

2.
Levulinic acid is a kind of new green platform chemical with wide application. The kinetics of levulinic acid formation from glucose decomposition at high temperature was investigated. Glucose containing 1%, 3% or 5% H2SO4 was treated at 170℃ or 190℃. For the various experimental conditions assayed, the time-courses of glucose and glucose degradation products (including 5-hydroxymethylfurfural and levulinic acid) were established. These variables were correlated with the reaction time based on the equations derived from a pseudo-homogeneous, first-order kinetic model, which provided a satisfactory interpretation of the experimental results. The set of kinetic parameters from regression of experimental data provided useful information for understanding the levulinic acid formation mechanism.  相似文献   

3.
The kinetics for production of ethyl levulinate from glucose in ethanol medium was investigated. The experiments were performed in various temperatures (433-473 K) and initial glucose concentrations (0.056-0.168 mol·L-1) with extremely low sulfuric acid as the catalyst. The results show that higher temperature can improve the conversion of glucose to ethyl levulinate, with higher yield of ethyl levulinate (44.79%, by mole) obtained at 473 K for 210 min. The kinetics follows a simplified first-order kinetic model. For the main and side reactions, the values of activation energy are 122.64 and 70.97 kJ·mo1-1, and the reaction orders are 0.985 and 0.998, respectively.  相似文献   

4.
In preparation of fuel alcohol from biomass as feedstock, hydrolysis with dilute acid as catalyst is one way to produce fermentable saccharide, xylose and glucose. However, the acid is also the catalyst in degradation of xylose and glucose and the yield of sacchride is dependent on the kinetic behaviors of saccharide. The degradation kinetics of xylose and glucose in the hydrolysate was investigated under the conventional process conditions of hydrogen ion concentration from 0.05 to 0.2 mol/L and temperature from 150 to 200℃. With a numerical calculation method, the kinetic parameters were estimated, and the activation energy of xylose and glucose in the degradation reaction was obtained. The kinetic equations correlating the effect of hydrogen ion concentration on the rate constants of degradation reaction were established. Comparison between the calculated results from the equations and experimental ones proved that the established kinetic model could satisfactorily predict the degradation behavior of xylose and glucose in the acidic hydrolysate.  相似文献   

5.
Levulinic acid is considered as a promising green platform chemical derived from biomass. The kinetics of levulinic acid accumulation in the hydrolysis process of wheat straw was investigated in the study. Using dilute sulfuric acid as a catalyst, the ki-netic experiments were performed in a temperature range of 190-230C and an acid concentration range of 1%-5% (by mass). A simple model of first-order series reactions was developed, which provided a satisfactory interpretation of the experimental results. The kinetics of main intermediates including sugar and 5-hydroxymethylfurfural (5-HMF) were also established. The kinetic pa-rameters provided useful information for understanding the hydrolysis process.  相似文献   

6.
The decomposition kinetics for formation of CO2 hydrates in 90 cm3 wet natural silica sands were studied systematically using the depressurization method at the temperatures ranging from 273.2 to 277.2 K and the pressures from 0.5 to 1.0 MPa. The effects of temperature, pressure, particle diameter, porosity, and salinity of formation water on the decomposition kinetics were investigated. The results show that the dissociation percentage increases as temperature increases or as the initial decomposition pressure decreases. An increase in porosity or a decrease in particle diameter of silica sands accelerates the decomposition. Increasing the salinity of the formation water gives rise to a faster decomposition. However, a combination of the present results with the observa-tions in literature reveals that the effect of the coexisting ionic solute depends on its chemical structure.  相似文献   

7.
The adsorption of dibenzofuran (DBF) on three commercial granular activated carbons (GAC) was investigated to correlate the adsorption equilibrium and kinetics with the morphological characteristics of activated carbons. Breakthrough experiment was conducted to determine the isotherm and kinetics of dibenzofuran on the activated carbons. All-the experiment runs were performed in a fixed bed with a process temperature of 368 K. The effects of adsorbent morphological properties on the kinetics of the adsorption process were studied. The equilibrium data are found satisfactory fitted to the Langmuir isotherm. An intraparticle diffusion model based on the obtained Langmuir isotherm was'developed for predicting the fixed bed adsorption of dibenzofuran. The result indicated that this model fit all the breakthrough curves well. The surface diffusion coefficients of dibenzofuran on the activated carbon are calculated, and a relationship with the microporosity is found. As it was expected, the dibenzofuran molecule finds more kinetic restrictions for the diffusion in those carbons with narrower pore diameter.  相似文献   

8.
The kinetic model of glucose metabolism was established and successfully applied to batch cultures of rCHO and rBHK cells. It was found that a large amount of glucose was utilized for cell maintenance, and the overwhelming majority of maintenance energy from glucose was by its anaerobic metabolism in both rBHK and rCHO cell cultures. The overall maintenance coefficients from aerobic metabolism were 1.9?10-13 mmol/(cell·h) for rCHO cells and 7?10-13 mmol/(cell·h) for rBHK cells. In addition, all GO/T and EO/T gradually increased with the same trend as the cell growth in the culture of both rCHO and rBHK cells. The overall molecule yield coefficients of lactate to glucose were 1.61 for rCHO cells and 1.38 for rBHK cells. The yield coefficients of cell to glucose were 4.5?108 cells/mmol for rCHO cells and 1.9 ?108 cells/mmol for rBHK cells, respectively.  相似文献   

9.
Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Redfern's equation was used to determine the apparent activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640℃, which was 180℃lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151kJ·mol-1 while the literature value for normal calcite was approximately 200kJ·mol-1. The order of magnitude of pre-e  相似文献   

10.
Computational fluid dynamics (CFD) combined with detailed chemical kinetics was employed to model the filtration combustion of a mixture of methane/air in a packed bed of uniform 3 mm diameter alumina spherical particles. The standard k-ε turbulence model and a methane oxidation mechanism with 23 species and 39 elemental reactions were used. Various equivalence ratios (1.47, 1.88, 2.12 and 2.35) were studied. The numerical results showed good agreement with the experimental data. For ultra-rich mixtures, the combustion temperature exceeds the adiabatic value by hundreds of centigrade degrees. Syngas (hydrogen and carbon monoxide) can be obtained up to a mole fraction of 23%. The numerical results also showed that the combination of CFD with detailed chemical kinetics gives good performance for modeling the pseudo-homogeneous flames of methane in porous media.  相似文献   

11.
高温液态水中有机酸对果糖分解反应动力学的影响   总被引:13,自引:0,他引:13       下载免费PDF全文
研究了压力10MPa下、温度453.15~493.15K范围内高温液态水中有机酸(甲酸、乙酸)对果糖分解反应动力学的影响. 实验结果表明,在有机酸存在下,果糖分解反应速度大大加快.在相同浓度有机酸存在时,甲酸对果糖分解反应的促进作用明显大于乙酸.对不同温度、有机酸和反应停留时间对果糖分解的主要产物——5-羟甲基糠醛(5-HMF)和乙酰丙酸(LA)收率的影响进行了考察. 果糖分解反应主要由果糖分解为中间产物5-HMF和5-HMF进一步分解成LA两步组成,乙酸的加入加快了第一步反应速度,而对第二步反应无明显影响,因而中间产物5-HMF收率可高达83%;甲酸的加入可同时加快果糖分解为中间产物5-HMF和5-HMF进一步分解为LA的速度,因此LA的收率得到了较大的提高.  相似文献   

12.
Reaction of d-glucose in water to yield 5-hydroxymethylfurfural (5-HMF), 1,2,4-benzenetriol (BTO) and furfural was studied at high temperatures (up to 400 °C) and high pressures (up to 80 MPa) using a continuous flow reactor. Maximum temperature and pressure conditions gave maximum furfural yield. Increasing pressure from 40 to 70 and 80 MPa enhanced dehydration reactions to 5-HMF, but also enhanced hydrolysis of 5-HMF leading to the production of BTO and thus lead to lower yields of 5-HMF (below 10%). Remarkably, the dehydration reaction to 5-HMF and the hydrolysis of 5-HMF were both enhanced by the increase in water density at 400 °C.  相似文献   

13.
Production of 5-hydroxymethylfurfural (5-HMF) from glucose and fructose catalyzed by TiO2 and ZrO2 under microwave irradiation was studied. For the case of TiO2 used in the fructose reaction, 5-HMF yield was 38.1% for a fructose conversion of 83.6% for 5 min reaction time. A 5-HMF yield of 30.5% for a fructose conversion of 65% was obtained for 5 min reaction time in the presence of ZrO2. The ZrO2 was found to promote isomerization of glucose to fructose, in which the selectivity of fructose from glucose became higher than 60% for about 50% glucose conversion for a reaction time of 1 min. Under the conditions (5 ml of 2 wt% fructose solution, 0.05 g of TiO2, 200 °C, and 3 min), fructose conversion and HMF yields by microwave heating (73% and 35%, respectively) were higher than those by sand bath heating (27% and 12%, respectively).  相似文献   

14.
The conversion of fructose into 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA) was investigated and catalyzed by indium trichloride (InCl3) in water. 79% 5-HMF yield (15 min) and 45% LA yield (60 min) were obtained at 180 °C with 2.5 mol% InCl3. Additionally, comparative studies of glucose/fructose mixture with different ratios as substrates were carried out to manifest the isomerization process between glucose and fructose during the conversion of monosaccharides into chemicals. It was shown that InCl3 was not only active in the isomerization of glucose to fructose and the reverse direction, but also demonstrated an excellent activity in the dehydration and conversion of monosaccharides. InCl3–H2O system presented a remarkable catalytic effect on the dehydration and conversion of monosaccharides.  相似文献   

15.
Hydrothermal conversion is an interesting process to transform (very) humid biomass into high energy vectors or valuable products in the liquid or solid state. In the supercritical domain, water becomes a solvent for organics as well as a reactant, and thus the cellulosic content is effectively hydrolyzed into glucose, largely considered as its model molecule.The kinetics of glucose decomposition during the heating step in the batch reactor were investigated through the analysis of glucose concentration. Glucose reacts totally before reaching the supercritical point of water. Among the operating parameters that influence supercritical water gasification, this paper presents only the effect of reaction temperature through gas composition, liquid carbon content and structure of the solid. Glucose gasification in a batch process (5 wt% glucose, 0.5 wt% catalyst, 600 °C, 25 MPa, 60 min) produced 1.5 mol of hydrogen per mol of glucose. The gas has energetic properties (H2, CH4, C2H6) while the liquid contains substances that could be used as platform molecules (5-HMF). The solid phase is composed of carbon (almost pure) in two distinct phases: spherical nanoparticles and an amorphous phase.  相似文献   

16.
Solid acid catalysts based on graphite-like mesoporous carbon material Sibunit were developed for the one-pot solubilization–hydrolysis–dehydration of cellulose into glucose and 5-hydroxymethylfurfural (5-HMF). The catalysts were produced by treating Sibunit surface with three different procedures to form acidic and sulfo groups on the catalyst surface. The techniques used were: (1) sulfonation by H2SO4 at 80–250 °C, (2) oxidation by wet air or 32 v/v% solution of HNO3, and (3) oxidation-sulfonation what meant additional sulfonating all the oxidized carbons at 200 °C. All the catalysts were characterized by low-temperature N2 adsorption, titration with NaOH, TEM, XPS. Sulfonation of Sibunit was shown to be accompanied by surface oxidation (formation of acidic groups) and the high amount of acidic groups prevented additional sulfonation of the surface. All the Sibunit treatment methods increased the surface acidity in 3–15 times up to 0.14–0.62 mmol g?1 compared to pure carbon (0.042 mmol g?1). The catalysts were tested in the depolymerization of mechanically activated microcrystalline cellulose at 180 °C in pure water. The main products 5-HMF and glucose were produced with the yields in the range of 8–22 wt% and 12–46 wt%, respectively. The maximal yield were achieved over Sibunit sulfonated at 200 °C. An essential difference in the composition of main products obtained with solid acid Sibunit carbon catalysts (glucose, 5-HMF) and soluble in water H2SO4 catalysts (formic and levulinic acids) as well as strong dependence of the reaction kinetics on the morphology of carbon catalysts argue for heterogenious mechanism of cellulose depolymerization over Sibunit.  相似文献   

17.
The effects of glucose and inorganic phosphate on mycelium growth and spinosad production with Saccharopolyspora spinosa were studied. The results showed that the increase of glucose concentration from 18.6g·L-1 to 58.8g·L-1 could promote the mycelium growth and spinosad production. And when the glucose concentration increased from 58.8g·L-1 to 79.6g·L-1, no obvious change was detected but a slight drop in spinosad production was observed, whereas, when the glucose concentration increased from 79.6g·L-1 to l15.3g·L-1, substantial decrease in both mycelium growth and spinosad production occurred. The increase of phosphate conccntration from 3.68mmol· L-1 to 29.41mmol·L-1 rendered corresponding increase in mycelium growth and spinosad production. When phosphate concentration increased from 29.41mmol· L-1 to 44.12mmol·L-1, mycelium growth slightly increased and spinosad production dropped, while when phosphate concentration increased from44.12mmol·L-1 to 57.62mmol·L-1, both mycelium growth and spinosad production decreased sharply. Conclusively,the optimal initial concentration of glucose and phosphate is 58.8g·L-1 and 29.41mmol·L-1, respectively. The spinosad fermentation in the production medium containing 58.8g·L-1 glucose and 29.41mmol·L-1 phosphate was scaled up in 5-L fermentation and the spinosad production reached 507mg·L-1, which was 28% higher than that in the flask fermentation.  相似文献   

18.
以琼脂糖为原料,分别采用CuCl2、NiCl2、MnCl2、MgCl2、FeCl3、AlCl3、ZrOCl2、SnCl4为催化剂催化转化制备5-羟甲基糠醛(5-HMF)和乙酰丙酸(LA),筛选适用于琼脂糖转化的优选催化剂,并对制备条件如溶剂含水量、催化剂用量、反应温度以及反应时间等影响因素进行了考察。研究结果表明:以50mg琼脂糖为原料,ZrOCl2为催化剂,二甲基亚砜(DMSO)为反应溶剂,在1 mL DMSO/H2O(体积比为8:2)混合溶剂中,ZrOCl2用量为琼脂糖中单糖物质的量的10%,140℃下反应60 min,5-羟甲基糠醛(5-HMF)的得率为26.9%,乙酰丙酸(LA)的得率为24.7%。对制备机理分析表明:反应过程中琼脂糖首先水解为醛型单糖,然后在催化剂作用下醛型单糖异构化再脱水转化为5-HMF,部分5-HMF在酸的作用下进一步转化为LA。  相似文献   

19.
Baker’s yeast number 6 was selected by screening. It showed good catalytic activity and enantioselectivity for asymmetric reduction of 2,5-hexanedione to produce (2S,5S)-2,5-hexanediol. Gas chromatography-mass spectrometry (GC-MS) revealed that the intermediate was (S)-5-hydroxyhexane-2-one. Reduction of 2,5-hexanedione proceeded in a two-step reaction. The hydroxyketone was initially formed, and this intermediate was further re-duced to the diol. Factors influencing the product yield and the enantiomeric excess of the reduction of 2,5-hexandione catalyzed by baker’s yeast number 6 were investigated. Higher concentration (≤100 mmol•L-1) of 2,5-hexandione did not influence 5-hydroxyhexane-2-one production, but 2,5-hexanediol production was inhibited by excess accumulation (>30 mmol•L-1) of intermediate. The optimal conditions were glucose as the co-substrate at an initial glucose concentration of 20 g•L-1, 34C, pH 7.0 and cell concentration 60 g•L-1 (cell dry mass). Under the optimal condition and an initial substrate concentration of 30 mmol•L-1, the yield of 2,5-hexandiol was 78.7% and the enantiomeric excess of (2S,5S)-2,5-hexandiol was 94.4% for 24-h reduction.  相似文献   

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