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1.
Chemical conversion of cellulose as treated in supercritical methanol   总被引:6,自引:0,他引:6  
The chemical conversion of cellulose as treated in supercritical methanol was studied using a batch-type reaction vessel at temperatures from 220 to 450°C and pressures from 14 to 72MPa. Supercritical methanol treatment at 350°C and 43MPa for 7min was sufficient to convert microcrystalline cellulose (avicel) to the methanol-soluble. To study the kinetics of the decomposition of cellulose, the decomposition rate constants were obtained, and rapid increase was observed at about 270°C which was about 30°C higher than the critical temperature of methanol. The main products from cellulose decomposition were methylated cellotriose, methylated cellobiose, methyl - and -D-glucosides, levoglucosan and 5-hydroxymethylfurfural. Monomeric compounds such as methyl - and -D-glucosides were stable in supercritical methanol, allowing high yields of monomeric products by supercritical methanol treatment. Based on these results, a pathway of cellulose decomposition treated in supercritical methanol was proposed. These findings suggest that the supercritical methanol treatment of various cellulosic materials may be suitable to obtain useful chemicals and liquid fuels without using fossil resources.  相似文献
2.
In recent years, non-catalytic supercritical processes for biodiesel production have been proposed as alternative environmentally friendly technologies. However, conditions of high temperature and pressure that occur while biodiesel is in supercritical fluid can cause fuel degradation, resulting in low yield. In this study, we performed the thermal decomposition of fatty acid methyl esters (FAMEs) in supercritical methanol at temperatures ranging from 325 °C to 420 °C and pressure of 23 MPa to investigate the degradation characteristics and thermal stability of biodiesel. The primary reactions we observed were isomerization, hydrogenation, and pyrolysis of FAMEs. The main pathway of degradation was deduced by analyzing the contents of degradation products. We found that if FAME has shorter chain length or is more saturated, it has higher thermal stability in supercritical methanol. All FAMEs remained stable at 325 °C or below. Based on these results, we recommend that transesterification reactions in supercritical methanol should be carried out below 325 °C (at 23 MPa) and 20 min, the temperature at which thermal decomposition of FAMEs begins to occur, to optimize high-yield biodiesel production.  相似文献
3.
Dimethyl carbonate was synthesized by transesterification reaction between ethylene carbonate and methanol under supercritical conditions without any catalyst. Experimental results showed that the residence time and the molar ratio of methanol to ethylene carbonate all can affect the conversion of ethylene carbonate. When the molar ratio of methanol to ethylene carbonate was 8:1, 81.2% conversion can be achieved at 9.0 MPa and 250℃ after 8 h.  相似文献
4.
生物柴油;超临界甲醇;萃取;酯交换法;油菜籽;原位  相似文献
5.
超临界流体技术在绿色化工过程中的应用范围不断拓宽。由于超临界甲醇具有独特的物理和化学性质,它既是反应介质,也是反应物,因此,超临界甲醇下的化学反应研究得到人们广泛的关注。本文在介绍超临界甲醇独特的物理化学特性的基础上,综述了近年来超临界甲醇体系在有机合成、生物柴油的制备、生物质处理和高聚物的降解等方面的应用研究进展,重点对超临界甲醇下各种反应的影响因素进行了分析讨论。最后,展望了超临界甲醇在甲醇化工中的应用前景。  相似文献
6.
The depolymerization of polybutylene terephthalate (PBT) in supercritical methanol was investigated by using a batch autoclave reactor. Continuous kinetics analysis was applied to experimental data. It was observed that PBT could dissolve into supercritical methanol quickly and decompose completely in a homogeneous phase. PBT with average molecular weight of about 29 700 was converted to oligomer with that of 4200 within 10 min and with that of 2700 in 15 min at 513 K and converted into monomer completely within 22 min. The main reaction products decomposed of PBT were dimethylterephthalate (DMT) and 1, 4-butanediol (BG) by methanolysis. The yields of monomer components of the decomposition products, including byproducts were measured. The yields of DMT and BG could reach 94.5% and 70.1%, respectively, at 563 K for 75 min. Based on the qualitative and quantitative analyses of the products, a depolymerization-reaction scheme was proposed to explain the reaction mechanism, i.e. the degradation of PBT in supercritical methanol mainly includes random scission and chain-end scission reactions and side reactions for monomer components. With the process of degradation, some oligomers could be decomposed into small molecular products by side reactions. Continuous-distribution kinetics theory was developed to analyze the decomposition behavior. The energy of activation for the random scissions of PBT in the supercritical methanol was 86.53 kJ/mol.  相似文献
7.
The recycling of cross-linked polyethylene (XLPE) by a decross-linking reaction in supercritical methanol was studied using a batch reactor. XLPEs with initial gel contents of 45, 55 and 65% were employed and subjected to reaction temperatures between 320 and 360 °C. Complete decross-linking of XLPE was achieved in 10 min in supercritical methanol at 360 °C and 15 MPa. For the first time, chemical kinetics for the decross-linking reaction is proposed based on the gel concentration, and applicable to the reactor design. With respect to the gel concentration, the first-order reaction model agreed well with the experimental results. The evaluated kinetic constant was 0.0867 ± 0.0082 cm3/mg min at 350 °C, and the activation energy was 578 ± 25 kJ/mol.  相似文献
8.
向丽  程健 《燃料化学学报》2008,36(1):111-114
超临界甲醇中的酯化和酯交换反应是利用植物油、动物油或废油脂制备生物柴油的新工艺.它的最大特点是不需要添加催化剂,超临界甲醇既是反应媒介,又是反应物.  相似文献
9.
Benzoic acid esterification and ethyl benzoate transesterification with subcritical methanol were carried out at 220 °C without any catalyst. A procedure for biodiesel production from vegetable oil under indicated conditions was proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 102–104, January, 2008.  相似文献
10.
Acid-base equilibria between 2,5-dichlorophenol (DCP) and various bases (LiOH, NaOH, and KOH) were studied in ambient to supercritical methanol, by measuring the absorption spectrum of DCP at alkali metal hydroxide molalities ranging up to 10 mmol⋅kg−1, at temperatures up to 250 °C and a pressure of 25.0 MPa. The spectrum was deconvoluted into contributions for the acidic (HA) and basic (A) forms of DCP, taking into account a blue shift of the phenolate (A) spectrum due to the effect of ion pairing with an alkali metal cation. Degrees of dissociation of DCP determined from the spectra suggested that the dissociation constant of DCP has a maximum around 150 °C, whereas that of KOH decreases with temperature. The phenolate-alkali metal ion pairing was examined from the peak shift of the phenolate spectrum in the presence of Li+, Na+, and K+. A smaller cation radius and higher temperature (thus a lower dielectric constant for methanol) give rise to stronger electrostatic interaction in the ion pair. The basicities of the alkali metal hydroxides in supercritical methanol were compared using DCP as an indicator, and were shown to follow the order LiOH < NaOH ≤ KOH. This order is the same as that for the catalytic effect of alkali metal hydroxides on the methylation of phenol in supercritical methanol (Takebayashi et al.: Ind. Eng. Chem. Res. 47:704–709, 2008). Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.  相似文献
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