固体酸碱催化剂的制备及在酯交换法制备生物柴油反应中的应用

发布时间：2018-04-02 21:31

本文选题：生物柴油　切入点：酯交换　出处：《吉林大学》2011年博士论文

【摘要】：近些年来,随着能源危机的日益加剧以及环境问题的日益严重,迫使人们去寻找一些可再生、清洁、环境友好的能源。生物柴油作为一种可再生的能源,不仅有着与矿物柴油相似的燃烧与动力性能,而且还具有对环境友好的特性,因此正逐渐吸引着越来越多的能源工作者及环境工作者的注意。合成生物柴油主要有四种方法,即直接混合法、微乳化法、高温裂解法和酯交换反应法。其中前两者属于物理方法,后两者属于化学方法。使用物理方法虽然能降低油脂的粘度,但燃烧中产生的积炭及润滑油污染等问题仍然难以解决,而高温裂解法会产生大量小分子化合物,主要产物是生物汽油而非生物柴油。相比之下,采用动植物油和甲醇为原料、经酯交换反应制取生物柴油的方法是一条简单有效、可操作性强的工艺路线。该反应可用酸或碱作为催化剂,其中常用的均相酸、碱催化剂包括硫酸、盐酸、磷酸、氢氧化钠、氢氧化钾以及钠和钾的醇盐。使用均相酸、碱催化剂不仅会对仪器设备造成腐蚀,反应后催化剂无法回收还会产生一定量的中和废弃物,导致生产成本增加的同时还易造成环境污染。用多相催化剂代替均相催化剂就可以解决上述问题。目前已报道的多相酸性催化剂有固体超强酸、杂多酸、离子交换树脂等：碱性催化剂有：分子筛、负载型碱金属及碱土金属催化剂,负载型有机碱、复合金属氧化物以及水滑石等。但上述催化剂大多存在活性较低或是活性组分易流失等问题,因此制备一种高效、稳定的催化剂是十分有意义的。基于上述情况,本论文主要开展了固体酸、碱催化材料的制备及表征工作,并尝试将这些材料作为多相催化剂用于合成生物柴油的酯交换反应中。同时结合各种表征手段,研究了各种酸、碱材料的结构及表面性质,着重探讨了载体表面性质对负载的活性中心(物种)的结构、酸碱性质的影响,并与催化剂的反应性能进行了关联。此外,还针对性能优异的多相催化剂体系进行了催化反应动力学方面的研究,确定了反应动力学的主要参数(包括反应速率常数、表观活化能以及指前因子等)。论文主要研究内容和结果如下：一.介孔钛硅复合材料在三乙酸甘油酯与甲醇的酯交换反应中的应用采用柠檬酸路线制备了具有高钛含量的钛硅复合材料,通过制备生物柴油的模型反应一三乙酸甘油酯与甲醇的酯交换反应评价了其催化性能,并与采用传统的溶胶-凝胶法制备的钛硅材料进行了对比分析。发现采用柠檬酸路线制备的钛硅复合材料在相同的反应条件下对该反应具有较好的催化活性及稳定性,循环使用三次后反应活性基本保持不变。通过X射线衍射、紫外、程序升温脱附以及吡啶吸附红外光谱等表征手段证明了钛硅复合材料中的钛物种不是以Ti02晶相或孤立的钛物种形态存在的,而主要是以低聚的TiO、形态存在且高分散在二氧化硅表面上的。为了弄清钛物种的存在状态对材料的催化性能的影响,分别采用硫酸以及硫酸铵对钛硅复合材料进行处理,使材料表面的Ti02物种发生聚集形成大的颗粒(晶体)。催化反应评价结果表明处理后的催化剂反应活性明显降低。综合各种因素,可以认为在二氧化硅表面存在的高分散的钛物种应该是酯交换反应中的主要活性中心。二.多孔炭负载CaO催化剂的制备、表征及在三乙酸甘油酯与甲醇的酯交换反应中的应用采用浸渍法分别以四种炭材料(介孔炭NC-2、活性炭AC、碳分子筛CMS以及介孔炭CMK-3)为载体制备了负载型CaO催化剂,考察了它们在三乙酸甘油酯与甲醇的酯交换反应中的催化活性。结果表明：以表面含氧基团相对较少的碳分子筛(CMS)和介孔炭(CMK-3)为载体制备的负载型CaO催化剂虽然初始活性较高,但稳定性很差；而以表面含氧基团较丰富的介孔炭(NC-2)和活性炭(AC)为载体制备的负载型CaO催化剂则对该反应表现出非常高的反应活性和稳定性,且催化剂可多次循环使用。针对CaO/NC-2体系,系统考察了CaO的负载量、催化剂的用量、催化剂的焙烧温度以及反应温度等参数对催化反应性能的影响。优化了反应工艺条件,同时确定了一些反应动力学参数。实验结果表明,在通常的反应条件下,反应速率常数不受传质过程的影响,反应遵循一级动力学模式,催化反应的表观活化能为44.9 kJ/mol。结合各种表征结果,我们认为炭负载氧化钙催化剂具有相对较高的催化活性应主要归结于大量的具有强碱中心性质的CaO物种的存在；载体表面的性质,特别是含氧基团的存在则对CaO物种的分散形态及结构稳定性起到了关键作用,是催化剂具有高稳定性的主要原因。由此我们推测,在具有高活性、高稳定性的炭负载氧化钙催化剂上至少存在两种形式的CaO物种。第一种形式的CaO是不完全堆积的,它与炭载体表面的含氧基团通过强相互作用键合(会导致其碱性变弱),从而使氧化钙粒子与载体之间能够形成有效的链接。第二种形式的CaO是高度堆积的,存在于第一种CaO物种之上,与炭载体之间的相互作用较弱,但具有较强的碱性和较高的催化活性。这两种形式的CaO可以看作一个整体(例如一个小的CaO簇或粒子)高分散在炭载体的表面。三.氧化石墨负载CaO催化剂的制备及在大豆油与甲醇酯交换制备生物柴油反应中的应用分别以氧化石墨(GO)以及热处理后的氧化石墨(GO-T)为载体制备了负载型CaO催化剂,并通过大豆油与甲醇的酯交换反应评价了其催化性能。结果表明：CaO/GO催化剂对该反应表现出较好的催化活性以及稳定性,而CaO/GO-T催化剂虽然也具有较高的初始活性,但稳定性相对较差,在循环反应中,催化剂的活性明显下降。催化反应以及表征结果进一步证实了我们之前的推测：即炭载体表面的含氧基团对活性物种(CaO)起到锚定的作用,从而使高分散在炭载体表面的CaO粒子与载体之间形成一个稳定的连接,最终形成了具有高活性和高稳定性的负载型CaO催化剂。此外,通过对比研究发现CaO/GO催化剂的酯交换反应活性与CaO/NC-2催化剂的活性基本相当。二者的主要差别在于CaO/GO催化剂的初始活化温度或再生处理所需的温度均明显低于CaO/NC-2催化剂。初步表征结果证明,载体GO与NC-2相比,在相同条件下,其表面的含氧基团更易与活性物种发生相互作用,形成最终的负载型CaO催化剂。综上所述,本论文主要针对制备生物柴油的酯交换反应开展了几种固体酸、碱催化剂即钛硅复合氧化物、多孔炭负载CaO催化剂以及氧化石墨负载CaO催化剂的制备、表征及催化性能研究工作。得到了几种性能优异的固体催化剂,对催化剂的活性中心性质、反应机理和催化反应动力学等方面有了较为深刻的认识,希望能为今后生物柴油的制备研制出新型高效的固体酸、碱催化剂提供参考依据。
[Abstract]:In recent years , with the increasing of the energy crisis and the growing environmental problems , it has forced people to look for some renewable , clean and environmentally friendly energy sources .

The reaction can be used as catalyst , wherein the common homogeneous acid and alkali catalyst include sulfuric acid , hydrochloric acid , phosphoric acid , sodium hydroxide , potassium hydroxide and alcohol salt of sodium and potassium .

Based on the above situation , the preparation and characterization of solid acid and alkali catalytic materials are mainly carried out . The structure and surface properties of various acid and alkali materials are studied . The structure and surface properties of various acid and alkali materials are studied . The main research contents and results are as follows :

Application of mesoporous titanium silicon composite material in ester exchange reaction between triacetin and methanol

A titanium - silicon composite with high titanium content was prepared by citric acid route . The catalytic performance was evaluated by transesterification of glycerol triacetin with methanol . It was found that the titanium - silicon composite prepared by citric acid route had better catalytic activity and stability under the same reaction conditions .

In order to understand the influence of the presence of titanium species on the catalytic properties of Ti - Si composites , titanium - silicon composites were treated with sulfuric acid and ammonium sulfate to form large particles ( crystals ) .

Preparation , Characterization and Application of Porous Carbon Supported CaO Catalyst in Ester Exchange Reaction of Triacetate and Methanol

Supported CaO catalysts were prepared by impregnation method with four carbon materials ( mesoporous carbon NC - 2 , activated carbon AC , carbon molecular sieve CMS and mesoporous carbon CMK - 3 ) as carriers . The catalytic activity of them in transesterification of triacetin and methanol was investigated .
and the supported CaO catalyst prepared by using mesoporous carbon ( NC - 2 ) and activated carbon ( AC ) rich in surface oxygen - containing group as a carrier shows very high reaction activity and stability to the reaction , and the catalyst can be recycled for many times .

According to the CaO / NC - 2 system , the influence of the loading amount of CaO , the amount of catalyst , the calcination temperature of the catalyst and the reaction temperature on the catalytic reaction performance were investigated . The reaction conditions were optimized , and some reaction kinetic parameters were determined . The experimental results show that the reaction rate constant is not affected by the mass transfer process under the general reaction conditions . The reaction follows the first order kinetic model , and the apparent activation energy of the catalytic reaction is 44.9 kJ / mol .

In combination with various characterization results , we believe that the carbon - supported calcium oxide catalyst has relatively high catalytic activity and is mainly attributed to the existence of a large amount of CaO species with strong alkali center properties ;
In the first form , CaO is highly accumulated , which is weakly interacting with the oxygen - containing group on the surface of the carbon carrier by strong interaction ( which causes its basicity to become weak ) , but has stronger basicity and higher catalytic activity .

Preparation of CaO catalyst loaded with graphite oxide and its application in preparing biodiesel by transesterification of soybean oil and methanol

The supported CaO catalyst was prepared by oxidation of graphite ( GO ) and oxidized graphite ( GO - T ) after heat treatment . The catalytic performance was evaluated by transesterification of soybean oil and methanol . The results show that the CaO / GO catalyst exhibits better catalytic activity and stability , while the CaO / GO - T catalyst has high initial activity , but the stability is relatively poor . In the recycle reaction , the activity of the catalyst is obviously decreased .

The catalytic reaction and the characterization results further confirm our previous assumption that the oxygen - containing group on the surface of the carbon support acts as an anchor to the active species ( CaO ) , thereby forming a stable connection between the CaO particles dispersed on the surface of the carbon carrier and the carrier , and finally forming a supported CaO catalyst having high activity and high stability .

The results show that the oxygen - containing groups on the surface of CaO / GO catalysts are more likely to interact with the active species under the same conditions to form the final supported CaO catalyst .

In conclusion , the preparation , characterization and catalytic performance of several solid acids , alkali catalysts , Ti - Si composite oxides , porous carbon supported CaO catalysts and oxidized graphite supported CaO catalysts were studied in this paper . Several excellent solid catalysts were obtained . The results showed that the catalysts could be used to prepare new high - efficient solid acids and alkali catalysts for the preparation of biodiesel .

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2011
【分类号】：TE667

【引证文献】