共查询到20条相似文献,搜索用时 78 毫秒
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以Ni/ZrO_2为催化剂催化乙酰丙酸加氢制备γ-戊内酯,制备了5种不同Ni含量的Ni/ZrO_2催化剂,采用氮气物理吸附、X射线衍射和透射电镜等对催化剂进行表征,并考察了催化剂的Ni含量、反应温度、反应时间、氢气压力和反应溶剂等条件对加氢催化活性的影响。结果表明:随着Ni含量的增加,乙酰丙酸的转化率也相应增加,Ni的质量分数为50%的Ni/ZrO_2催化剂的乙酰丙酸转化率最高,Ni的质量分数为30%的Ni/ZrO_2催化剂中单位Ni的比活性(TO_F)最高;提高反应温度可加快反应速率;溶剂二氧六环比水更能促进反应的进行;而Ni含量及不同的反应条件对反应的选择性均没有显著的影响。在二氧六环中,温度200℃,氢压5MPa下,反应9h得到最高的乙酰丙酸转化率及γ-戊内酯收率,分别为99.1%和91.6%。 相似文献
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5-羟甲基糠醛在稀硫酸催化下的降解反应动力学 总被引:2,自引:0,他引:2
5-羟甲基糠醛脱羧生成乙酰丙酸是生物质资源出发制备乙酰丙酸过程中的关键步骤之一。为了研究低硫酸浓度下水解生物质制备乙酰丙酸工艺的可行性,系统地测定了在压力5 MPa、初始浓度1~9 mg·ml-1、硫酸浓度0.05%~0.4%(质量分数)、温度150~190℃条件下,5-羟甲基糠醛在稀硫酸催化下的降解反应动力学数据,并以主反应生成乙酰丙酸、副反应生成腐黑质的平行反应动力学模型对数据进行了拟合,拟合结果表明,在实验范围内,主、副反应对5-羟甲基糠醛均为一级反应;主反应对H+浓度为1.16级,反应的活化能为78.5 kJ·mol-1;副反应对H+浓度为0.722级,反应的活化能为98.0 kJ·mol-1。研究结果表明,降低温度和提高硫酸浓度有利于提高生成乙酰丙酸的选择性。 相似文献
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Interfacial polycondensation of diphenolic acid (DPA) and isophthaloyl chloride (IPC) in various solvent/water systems was investigated with tetrabutyl ammonium chloride as a phase transfer catalyst. It was found that a large mass of capsules were formed at the beginning of the reaction for all solvents examined but the capsule morphology and reaction results depended on the solvents. It is believed that the capsule shells make up of the reaction zone and a mechanism of the interfacial polycondensation is proposed accordingly. The effect of the solvents on the reaction was interpreted from the interaction between the polymer and the solvent according to the mechanism. The reaction conditions were optimized, and poly(DPA-IPC) with high intrinsic viscosity was prepared in high yield under the optimal condition. It is an amorphous polymer with glass transition temperature of about 160°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
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Martino Colonna Corrado Berti Enrico Binassi Annamaria Celli Maurizio Fiorini Paola Marchese Massimo Messori Daniel J. Brunelle 《Polymer International》2011,60(11):1607-1613
Weatherable semicrystalline polyesters based on 1,4‐cyclohexanedimethanol, 1,4‐cyclohexanedicarboxylic acid (CHDA) or dimethyl 1,4‐cyclohexane dicarboxylate (DMCD) can be prepared under normal melt‐phase conditions, using titanium tetrabutoxide as catalyst. The effect of monomer ratio, reaction temperature and catalyst loading on the final polymer properties was studied. Under the proper polymerization conditions, poly(1,4‐cyclohexylenedimethylene‐1,4‐cyclohexanedicarboxylate) polymers with high molecular weight can be obtained. During polymerization, isomerization can occur towards the thermodynamically stable cis‐trans ratio of 34–66 mol%. Carboxylic acid end groups can catalyze the isomerization and therefore the polymerization is more critical starting from CHDA rather than DMCD. Moreover, temperature control becomes a key factor to avoid or to limit isomerization. The study of the isomerization of the different monomers permitted a better understanding of the isomerization and therefore of the polymerization process. Copyright © 2011 Society of Chemical Industry 相似文献
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The aliphatic polyesters with high molecular weight have been prepared according to two methods. First is the synthesis of the polyesters by polycondensation of dimethyl succinate (DMS) with 1,4‐butanediol (BD) using various metal alkoxides as a catalyst. Among the metal alkoxides used, titanium tetraisopropoxide [Ti(OiPr)4] gave the best results (highest molecular weight and yield). Thus, we have prepared aliphatic polyesters using a variety combinations of diesters [MeOOC—(CH2)x—COOMe, x = 2–8] with BD by the catalysis of Ti(OiPr)4. The polyesters with high number‐average molecular weight (Mn > 35,000), except dimethyl adipate (DMA, x = 4)/BD polyester (Mn = 26,900), were obtained in high yield. The melting temperatures (Tm) of polyesters were relatively low (43.4–66.8°C) except that (115.6°C) of the DMS/BD polyester. Second is the synthesis of high molecular weight polyesters by chain extension reaction of lower molecular weight (Mn = 15,900–26,000) polyesters using hexamethylene diisocyanate (HDI) as a chain extender. The Mn values of chain‐extended polyesters consequently increased more than two times (Mn = 34,700–56,000). The thermal properties of polyesters hardly changed before and after chain extension. Enzymatic degradations of the polyesters were performed using three different enzymes (cholesterol esterase, lipase B, and Rhizopus delemar lipase) before chain extension. The enzymatic degradability varied depending on both thermal properties of polyesters [melting temperature and heat of fusion (crystallinity)] and the substrate specificity of enzymes, but it was the following order: cholesterol esterase > lipase B > R. delemar lipase. The 1H‐NMR spectrum of water‐soluble degraded products of the polyester indicated that the polyester was degraded into a condensation product of diol with diester in a monomer form. The enzymatic degradation of chain extended polyesters was slightly smaller than that before chain extension, but proceeded steadily. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 340–347, 2001 相似文献
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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
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2,5-呋喃二甲酸(FDCA)是合成聚(呋喃二甲酸乙二醇酯)(PEF)等生物基聚酯的重要单体,具有广阔的应用前景。FDCA能否实现低廉、高效的大规模生产,是生物基聚酯开发的关键。目前,FDCA合成的研究广受关注,工业化开发也正在进行中。本文对合成生物基单体FDCA的5-羟甲基糠醛(HMF)路线进行综述,重点介绍了水、高沸点有机溶剂、低沸点有机溶剂、双相体系和离子液体中的糖类脱水合成HMF,无碱水溶液、碱性水溶液和有机溶剂中的HMF氧化合成FDCA以及糖类一锅法合成FDCA的研究进展。在比较各种合成方法的基础上,认为当前应着重研究开发低沸点溶剂中糖类脱水合成HMF以及无碱水溶液或有机溶剂中低廉高效的HMF氧化新方法,并向着糖类一锅法合成FDCA的方向发展。 相似文献