首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 140 毫秒
1.
The characteristics of depolymerization of PBT in supercritical methanol were investigated in the range of 453-533 K by using a high-pressure reactor. Based on the qualitative and quantitative analyses of the products, a depolymerization-reaction model was proposed to explain the depolymerization and reaction mechanism, i.e. ester exchange reaction occurred randomly along the chain of PBT. It was suggested that the process of depolymerization consisted of subcritical region, transitional region and supercritical region. In the first region, PBT mainly showed a swelling process in the methanol with slow decrease in molecular weight and little conversion. In the second region, PBT dissolved quickly with high depolymerization rate. While in the third region, the molecular weight of PBT decreased quickly with a thorough depolymerization in few minutes. DMT and BG obtained from the depolymerization of PBT in supercritical methanol reached 98.5% and 72.3%, respectively.  相似文献   

2.
超临界甲醇降解对苯二甲酸丁二酯的研究   总被引:4,自引:0,他引:4  
作为一种综合性能优良的新型工程塑料,对苯二甲酸丁二酯(PBT)工程塑料及其各种合金在全球范围内已经广泛用于电子电气、汽车、机械及民用等各个领域,而中国是其中需求量最大的国家.  相似文献   

3.
聚酯在超临界甲醇中的降解特性   总被引:1,自引:0,他引:1  
研究在间歇高压反应器中聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)及聚碳酸酯(PC)在超临界甲醇中的降解反应;通过建立聚酯在超临界甲醇中的降解反应模型,探讨了聚酯在甲醇中降解的机理。结果表明:PET、PBT和PC在甲醇溶液中的降解具有共性,均可分为超临界区、非临界区和中间过渡区三个区域。在超临界区聚酯完全溶于甲醇并降解为原料单体,且对苯二甲酸二甲酯(DMT)和碳酸二甲酯(DMC)的收率均大于90%;聚酯的降解是在聚合物分子链的无规断裂和聚酯进行酯交换反应的双重作用下发生的。  相似文献   

4.
The characteristics of depolymerization of PC in supercritical ethanol were investigated in the range of 483-563 K by using a high-pressure batch autoclave reactor. Based on the qualitative and quantitative analyses of the products, a depolymerization-reaction model was proposed to explain the reaction mechanism, i.e. random scission and ester exchange reaction occurred simultaneously during the process of depolymerizaition of PC. It was suggested that the process of depolymerization consisted of subcritical region, transitional region and supercritical region. It was indicated that PC degraded with slow decrease of molecular weight determined by GPC and with the conversion of 7.5% at 513 K in subcritical region. While in the supercritical region, the molecular weight of PC decreased quickly and degraded completely in 30 min at 563 K. Continuous-distribution kinetics could be used to describe the mechanism of polymer degradation and the energy of activation for the random scission of PC in the supercritical region was 97.2 kJ/mol. Moreover, PC could be degraded completely into diethyl carbonate (DEC) and bisphenol A (BPA) with the yields of 89% and 90%, respectively, in supercritical region.  相似文献   

5.
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   

6.
A comparative study on the thermal and catalytic degradation of polybutylene terephthalate (PBT) at atmospheric pressure was conducted. The weight loss of PBT under thermal degradation was significantly influenced by the temperature between 360 °C and 380 °C, but little affected by the PBT particle size. Four groups of catalysts include metal chloride, metal oxide, metal acetate, and metal copper powder were used to test PBT degradation activity. Copper (II) chloride is the most active one for increasing the percentage PBT weight loss more than 100% in comparison with the result of thermal degradation at a temperature of 360 °C for 30 min. PBT and catalyst mixtures can be prepared by impregnation and physical method, the former resulted in a better PBT degradation. The percentage PBT weight loss in the presence of CuCl2 increased steadily between 320 °C and 380 °C which was different from the results of thermal degradation. The time for obtaining a same percentage PBT weight loss reduced effectively when compared to the catalytic to thermal degradation. The weight ratio of CuCl2/PBT was tested between 0 and 0.2 and the optimal ratio was 0.1. The gaseous product distribution analyzed by GC/MS for PBT thermal and catalytic degradation revealed almost the same and the major products were ethane, carbon monoxide, carbon dioxide, 1-butene, 2-butene, 1,3-butadiene, and butadiene dimmer. But the relative abundance of major products was changed, especially for 1,3-butadiene increased dramatically, and a new chlorocompound was produced in catalytic degradation. In condensed liquid product, both the number and the molar mass of components were more and greater than that of in gaseous product and 4-heptylacetophenone was the most abundance product. In PBT catalytic degradation, 4-heptylacetophenone and some products were decreased and some even disappeared completely while the abundance of benzoic acid increased and three new products were generated.  相似文献   

7.
The degradation of polycaprolactone (PCL) was studied in subcritical and supercritical toluene from 250 to 375 °C at 50 bar. The degradation was also investigated in various solvents like ethylbenzene, o-xylene and benzene at 325 °C and 50 bar. The effect of pressure on degradation was also evaluated at 325 °C at various pressures (35, 50 and 80 bar). The variation of molecular weight with time was analyzed using gel permeation chromatography and modeled using continuous distribution kinetics to evaluate the degradation rate coefficients. PCL degrades by random chain scission in subcritical conditions (250-300 °C) and by chain end scission (325-375 °C) in supercritical conditions in toluene. The degradation of PCL in other solvents at 325 °C was by chain end scission under both subcritical and supercritical conditions indicating that the mode of scission depends on the temperature and not on the supercriticality of the solvent. The thermogravimetric analysis of PCL was investigated at various heating rates (2-24 °C/min) and the activation energy was determined using Friedman, Ozawa and Kissinger methods. It was shown that PCL degrades by random scission at lower temperatures and by chain end scission at higher temperatures again indicating that the mode of scission is dependent on the temperature.  相似文献   

8.
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   

9.
Sub- and supercritical glycolysis of polyethylene terephthalate (PET) with ethylene glycol (EG) to bis(2-hydroxyethyl) terephthalate (BHET) was investigated for the purpose of developing a PET recycling process. Supercritical glycolysis was carried out at 450 °C and 15.3 MPa while subcritical glycolysis was carried out at 350 °C and 2.49 MPa or at 300 °C and 1.1 MPa. High yields (gt; 90%) of the monomer BHET were obtained in both super- and subcritical cases. For the same PET/EG weight ratio of about 0.06, the optimum reaction time was 30 min for supercritical glycolysis and 75 and 120 min for two cases of subcritical glycolysis. GPC, RP-HPLC, 1H NMR and 13C NMR, and DSC were used to characterize the polymer and reaction products. Supercritical glycolysis will be suitable to a process requiring a high throughput due to its short reaction time.  相似文献   

10.
The predominant degradation reaction in the γ-irradiation of nine poly(olefin sulfone)s was found to be C-S bond scission with elimination of SO2 and olefin. The extent of depolymerization, measured by the yields of the two comonomers, increased over five irradiation temperatures from 0 to 150° C and could be correlated with the ceiling temperature. Thus G (total volatile products) increased from 10 to 10,000 over this temperature range. Minor radiolysis products included the alkanes corresponding to (1) loss of the side chain group and (2) scavenging of the side chain radical by monomer olefin. There was a deficiency of olefin relative to SO2, except at high temperatures, and isomerization of the product olefin in some cases. These observations are attributed to reactions of radiation-induced polymeric cations.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号