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Title:
乳酸乙酯在MoVNbOx基催化剂上催化氧化脱氢反应的研究
Author: 赵雪媛
Degree Level: 硕士
Issued Date: 2016-06
Degree Grantor: 中国科学院研究生院
Place of Degree Grantor: 北京
Supervisor: 李学兵 ; 唐斯甫
Keyword: 氧化脱氢 ; 乳酸乙酯 ; 丙酮酸乙酯 ; MoVNbOx ; 动力学
Subject: 工业催化
Alternative Title:
Major: 化学工程
Abstract: 丙酮酸及其衍生物(丙酮酸盐、丙酮酸酯)是一类重要的有机中间体,广泛应用于化工、制药、食品等行业。随着社会经济的发展,丙酮酸及其衍生物的需求不断增加。目前,国内生产丙酮酸的主要方法为酒石酸脱水脱羧法,生产过程中会产生大量SOx,不仅对环境造成污染,而且存在耗能高、成本高、原子经济性低等问题,该工艺将面临淘汰。以乳酸或其酯类化合物为原料经氧化脱氢反应合成丙酮酸或丙酮酸酯,具有原子经济性高、绿色环保和成本低等优点,被公认为最理想及最具应用前景的生产工艺。 本论文采用浆料法合成Mo-V-Nb-Ox基复合金属氧化物催化剂。用于常压固定床反应器上乳酸乙酯(ethyl lactate,EL)催化氧化脱氢制备丙酮酸乙酯(ethyl pyruvate,EP)反应的研究。一方面考察了MoVNbOx/TiO2催化剂的催化活性及通过分析产物选择性,建立了相关的反应路径网络,并重点开展了反应动力学的研究;另一方面通过改变制备条件对MoVNbOx催化剂进行改性,研究了催化剂的物理化学性质与催化反应性能的相互关联。本论文得到的主要结论如下: (1)MoVNbOx/TiO2催化剂相比于MoVNbOx催化剂具有更高的催化效率和更低的表观活化能。随着乳酸乙酯转化率的增加,目标产物丙酮酸乙酯的选择性在90-93%范围内保持稳定;同时,乙醇作为主要副产物,其选择性在4%左右,其它副产物的选择性均小于1%。根据反应产物的分布情况建立了相关反应路径网络,其中乳酸乙酯氧化脱氢生产丙酮酸乙酯为主反应,乳酸乙酯、丙酮酸乙酯的水解及进一步氧化为副反应,导致乙醇、乳酸、丙酮酸及乙酸等副产物的产生。反应动力学的实验结果表明,在动力学条件范围内乳酸乙酯的转化速率相对于氧气分压的反应级数为一级,但与乳酸乙酯的分压无关。基于Mars-van-Krevelen(MvK)反应机理,我们分析了乳酸乙酯氧化到丙酮酸乙酯反应的基元步骤,推导并简化了反应速率方程;在催化剂表面空穴是最丰富物种的假设下乳酸乙酯的反应速率只与氧气分压有关且为一级,这与反应动力学的实验结果相一致。 (2)在600 ºC下,分别在氮气和空气气氛中焙烧制备MoVNbOx复合金属氧化物催化剂。催化反应结果表明,氮气气氛下焙烧的催化剂表现出更高的催化活性,乳酸乙酯的转化率高达90%,丙酮酸乙酯的选择性为91%;该反应连续进行50 h,乳酸乙酯转化率和丙酮酸乙酯选择性均无明显的变化,表明该催化剂具有良好的稳定性。通过对催化材料的一系列表征发现,氮气和空气气氛下焙烧制备的催化剂具有明显的结构差异,其中,氮气焙烧的MoVNbOx催化剂主要为MoO2相和金红石结构的Mo-V氧化物混合相,而空气焙烧的催化剂主要为Mo5O14相、尖晶石型的α-MoO3相及V2MoO8相。与空气焙烧的MoVNbOx催化剂相比,氮气焙烧的MoVNbOx催化剂具有较高的低温可还原性能和比表面积,以及更多的表面V4+物种,这是导致其更高催化活性的主要因素。 (3)在氮气气氛下分别采用不同的焙烧温度制备了一系列MoVNbOx催化剂。催化反应结果表明,当焙烧温度在400-700 ºC范围内,乳酸乙酯的转化率随着焙烧温度的增加呈先增加后减小的趋势,其中,600 ºC焙烧制备的催化剂催化活性最好。催化材料表征结果表明,500 ºC、600 ºC和700 ºC焙烧的催化剂结构无明显差别,400 ºC焙烧的催化剂为无定型态。600 ºC焙烧的催化剂具更高的低温可还原性能及比表面积,这是导致其最优催化活性的主要因素。
English Abstract: Pyruvic acid and its derivatives are organic intermediates, widely applied in chemical, pharmaceutical and food industries. With the development of social economy, the commercial demand for pyruvate has been increasing. Currently,pyruvic acid is produced mainly via dehydrative decarboxylation of tartaric acid. A large amount of SOx is produced in the process, which results in serious environmental pollution. Moreover, high energy consumption, high cost, low atomic efficiency and low yield are the main defective problems in this technology. So this process will be eliminated. However, a process for production of pyruvic acid or its esters by the oxidative dehydrogenation (ODH) of lactic acid (LA) or esters is developed. The reaction pathway shows excellent atomic efficiency and provides an eco-friendly route and has characteristic of low cost, which is recognized as the most ideal production technology and the most promising process. In this thesis, the MoVNbOx based composite oxides were synthesized by a slurry method and used as catalysts for the catalytic oxidative dehydrogenation of ethyl lactate (EL) to ethyl pyruvate (EP) in a continuous fixed-bed reactor under atmospheric pressure. Firstly, the catalytic activities of MoVNbOx/TiO2 composite oxides and the selectivity of productions had been studied. In addition, we studied the reaction pathways in the catalytic system and the reaction kinetics. Secondly, through to the modification of the MoVNbOx catalysts by changing preparation conditions, we studied the relationship between the catalytic characterization and performance. The main conclusion of this thesis is summarized as follows: (1) MoVNbOx/TiO2 catalyst presented much higher conversion rate of ethyl lactate and relatively lower apparent activation energy in comparison with that over MoVNbOx. With the increase of the ethyl lactate conversion, the selectivity for ethyl pyruvate as the target product maintained stable in the range of 90–93%, and ethanol was the most abundant byproduct with the selectivity around 4.0%. The selectivities of other products were all below 1.5%. According to the distribution of reaction products, the reaction path network was established, in which the oxidative dehydrogenation of ethyl lactate into ethyl pyruvate was the dominant reaction. Besides, the hydrolysis and further oxidation of ethyl lactate and ethyl pyruvate were side effects, which resulted in the production of byproducts,such as ethanol, lactic acid, pyruvate and acetic acid. The reaction kinetics of the experimental results showed that the conversion rate of ethyl lactate was first order reaction towards the O2 concentration but none of any relation with the concentration of ethyl lactate in the kinetic condition. The analysis of elementary reaction steps of ethyl lactate into ethyl pyruvate and the derivation of reaction rate equation were performed based on Mars-van Krevelen (MvK) redox mechanism. The results showed that the conversion rate of ethyl lactate was first order reaction, which was only related to the partial pressure of O2 in the precondition of considerably abundant surface oxygen vacancies. The results were in good accordance with the experimental kinetics results. (2) The MoVNbOx composite metal oxides were prepared at calcination atmosphere of 600 ºC in nitrogen and air atmosphere, respectively. The studied showed that N2-calcined catalyst exhibited remarkable better activity than air-calcined catalyst. The conversion of EL and the selectivity of EP were 90% and 91%, respectively. The reaction was carried out continuously for 50h, the conversion of EL and selectivity of EP were maintained, which showed that the catalyst had a remarkable catalytic stability. Through a series of characterization of catalytic materials found that N2-calcined MoVNbOx catalysts were significantly different to the recorded of air-calcinated MoVNbOx catalysts. N2-calcinated MoVNbOx catalysts existed MoO2 phases and rutile structure of Mo-V phase. Air-calcinated MoVNbOx catalysts existed Mo5O14 phase, α-MoO3 phase and V2MoO8 phase. Compared to air-calcinated MoVNbOx catalysts, N2-calcinated MoVNbOx catalysts presented relatively higher low-temperature reducibility and specific surface area and had more available V4+ species on the surface than air-calcinated MoVNbOx catalysts. These were mainly responsible for the remarkable enhancement of the catalytic activity. (3) A series of MoVNbOx catalysts were prepared by changing the calcination temperatures at N2 atmosphere. The results showed that the conversion of ethyl lactate first increased and then decreased as the calcination temperatures from 400 ºC to 700 ºC. Among all samples, the catalyst at 600 ºC of calcination temperatures exhibited the best catalytic performance. The results of catalytic material characterization showed that the structure of catalysts, which were calcinated at 500 ºC, 600 ºC and 700 ºC, was no significant difference. However, the catalysts were amorphous at calcination temperature of 400 ºC. MoVNbOx catalysts at calcination temperatures of 600 ºC presented relatively higher lowe-temperature reducibility and specific surface area than other catalysts. These reasons may be lead to high catalytic activity of the N2-calcinatied catalyst.
Language: 中文
Department: 多相催化转化团队
Available Date: 2020-07-01
DOC Type: 学位论文
Content Type: 学位论文
URI: http://ir.qibebt.ac.cn/handle/337004/9786
Appears in Collections:多相催化转化团队_学位论文

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description.institution: 中国科学院青岛生物能源与过程研究所

Recommended Citation:
赵雪媛. 乳酸乙酯在MoVNbOx基催化剂上催化氧化脱氢反应的研究[D]. 北京. 中国科学院研究生院. 2016.
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