【作者】 张丽霞；

【导师】 王兴国；

【作者基本信息】 江南大学 ， 粮食、油脂及植物蛋白工程， 2010， 博士

【摘要】 酸催化剂是酯化反应常用催化剂,目前仍有许多反应过程采用液体矿物酸为催化剂,这就存在着腐蚀设备、副产物多、后处理复杂和污染环境等一系列问题。开发环境友好型酸催化剂日益受到重视。本论文以凹凸棒土为原料,研究制备磷钨酸(H3PW12O40, HPW)或其铯盐的载体材料——改性凹凸棒土。采用FTIR、XRD、TGA/SDTA、N2吸附脱附、XPS、FESEM-EDS和TEM等表征方法,比较凹凸棒土改性和固载HPW前后的结构变化,研究其改性和固载机理,并以酯化反应为催化反应模型研究固载HPW的催化活性。凹凸棒土的酸处理研究发现,酸处理凹凸棒土的活性度越大,经γ-氨丙基三乙氧基硅烷(KH550)改性后含氮量越高。此外,酸处理的凹凸棒土含有丰富的吸附水、结合水、结构水和结构羟基。在无水甲苯回流体系中进行偶联剂KH550的有机改性,KH550的乙氧基团能够与凹凸棒土的羟基在凹凸棒土结构内水分子的催化作用下直接缩合,实现有效改性,并形成均匀的改性层。用硅烷偶联剂KH792和KH550分别对凹凸棒土有机改性(记作KH792-Pa和KH550-Pa)。它们对HPW溶液的吸附过程的研究表明:单层氨基的数目决定HPW的吸附量;在相同吸附条件下,KH792-Pa和KH550-Pa对HPW的平衡吸附量分别达到189 mg·g-1和175 mg·g-1;对HPW的吸附过程符合拟一级动力学方程,化学吸附是吸附过程的速率控制步骤,在吸附过程的前5min,KH792-Pa和KH550-Pa对HPW的吸附率都超过80%;在所研究温度下吸附等温线均满足Langmuir方程。对吸附HPW后固体(分别记作HPW/KH792-Pa和HPW/KH550-Pa)的结构性质进行表征,FTIR和XPS的结果显示HPW阴离子与载体的氨基形成强的离子对,有效地固载在KH792-Pa和KH550-Pa表面;XRD的图谱没有观察到HPW的特征衍射峰,说明HPW是均匀分散的,与Langmuir方程的假设相一致;以DRIFT和NH3-TPD表征酸性质的结果表明HPW/KH792-Pa和HPW/KH550-Pa仍旧保持强的Bronsted酸性和总酸性。以KH792-Pa为载体,通过浸渍方法制备不同HPW量的固载催化剂(HPW/KH792-Pa)。活化温度影响催化剂的酸性。在酯化合成乙酸丁酯的反应中,活化温度在160℃时,催化剂活性最强。固载催化剂的催化活性随固载量的增加而增大,在重复使用过程中,20%HPW/KH792-Pa的催化活性最稳定,重复使用6次,丁醇的转化率仍在60%左右。催化乙酸丁酯的反应符合Eley-Rideal机理,丁醇在20%HPW/KH792-Pa活性位点上的吸附过程是整个反应过程的速率控制步骤,反应速率与丁醇浓度在动力学上符合拟一级动力学方程。同样在油酸甲酯的合成反应中,20%HPW/KH792-Pa仍然能够显示强的催化活性和高的重复利用性,合适条件下油酸的转化率可达90%。这些说明凹凸棒土表面经硅氨基改性有助于杂多酸的稳定化。研究表明,磷钨酸铯盐酸(CsHPW)固载在活化凹凸棒土时,CsHPW均匀地分布在凹凸棒土的棒晶上,仍然保持体相CsHPW的晶体结构,在油酸甲酯化反应中有强的催化活性和好的重复使用性,克服了CsHPW在极性反应体系中易形成胶体而难以过滤的问题。在合适反应条件下,CsHPW/Pa催化油酸甲酯化的转化率可达73%。更多还原

【Abstract】 Liquid mineral acids catalysts, such as H2SO4, HCl, HF, H3PO4 and ClSO2OH, are usually applied in esterification reactions, which cause a series of problems as equipment corrosion, byproducts and environmental pollution. Recently, solid acid catalysts have received considerable attention for their enviromental friendly. Based on the status of the heteropolyacid systematic analysis of the application and development, modified palygorskite was selected as supports for the immobilization of heteropolyacid or its salts as acidic catalyst. An extensive study was performed on the mineral characteristics, modification and immobilization mechanism of palygorskite in terms of chemical composition (FTIR spectroscopy), crystalline structure (XRD), thermal properties (TGA/SDTA), N2 adsorption-desorption, the surface composition chemical states (XPS) and morphology (FESEM and TEM) etc.. The catalytic activity of immobilized heteropolyacid (salt) was tested by esterification models.The nitrogen content in silylated palygorskite withγ-aminopropyltriethoxysilane (KH550) increased with the increasing of activity-degree of acidic palygoeskite. Furthermore, there were lots of waters and hydroxy groups in the palygorskite, with which the ethoxysilane group of KH550 directly reacted with the surface hydroxyl group of palygorskite in refluxing dry tolune. KH550 modified surface presents more stable and homogeneous surface properties, which facilitates the immobilization of heteropolyacid.Palygorskite was modified with different silanes KH792 and KH550. Silylated palygorskite was denoted by KH792-Pa and KH550-Pa, respectively. The results showed that the amount of HPW adsorbed was relayed on the content of monolayer amino group in the supports. KH792-Pa contained larger numbers of adsorption sites (-NH- and -NH2) on its surface and higher nitrogen content (3.02 wt%) than that of KH550-Pa (1.89 wt%), which could trap more amount of HPW. For KH792-Pa and KH550-Pa, the equilibrium adsorption amount of HPW (mg·g-1) was 189 mg·g-1 and 175 mg·g-1, respectively. The adsorption kinetics results demonstrated that the adsorption process of HPW onto silylated-Pa closely followed a pseudo-second-order kinetic model. Equilibrium data were fitted well to the Langmuir adsorption isotherm models at all studied temperatures. The FTIR and XPS characteristic results of HPW/KH792-Pa and HPW/KH550-Pa indicated that heteropolyanion was reacted with NH2 group by chemical reaction;the result of XRD revealed that HPW was finely and effectively distributed on the silylated-palygorskite, which was constent with Langmuir equation. The characteristic of DRIFT and NH3-TPD showed that the Bronsted and total acidity were existed. The different loading HPW/KH792-Pa catalysts were prepared by incipient impregnation (abbreviate as HPW/KH792-Pa). The effect of aging temperature on the catalytic activation was studied and 160℃was proved as suitable aging temperature. The reaction of n-butanol with acetic acid was selected a model reaction, the butanol conversion increased with the HPW loading increasing, 20%HPW/KH792-Pa catalyst showed the best stability during reuseablity and around 60% butanol conversion. The reactions following the Eley-Rideal mechanism takes place between n-butanol chemisorbed on the active sites of the catalyst surface. The rate of the esterification reaction was fitted with a first-order nature. Furthermore, 20%HPW/KH792-Pa showed 90% oleic acid conversion in optimum conditions during the esterification of oleic acid with methanol. From the above, the silylated modification for palygorskite was contributed to the stabilization of heteropolyacid.Acidic Cs salt of 12-tungstophosphoric acid (Cs2.5H0.5PW12O40, CsHPW) was supported on acid-activated palygorskite, which partly overcome the filtration problems in liquid phase reaction because of the tendency of CsHPW to form milky colloid in polar solutions. CsHPW inside CsHPW/Pa was retained intact Keggin anion and highly and uniformly supported on the fibre of Pa, which performed stable catalytic activity for esterification of oleic acid with methanol. Under optimum conditions the conversion of oleic acid reached 73%.Therefore, silylated-Pa should be a suitable candidate for the immobilization of HPW and provide enough encouragement for future exploration.更多还原