前驱体对完全液相法Cu-Zn-Al催化剂结构及其催化合成气制乙醇性能的影响
发布时间：2018-09-18 16:13
【摘要】：乙醇作为世界公认的绿色环保优质替代性液体燃料和汽油添加剂,相比其它燃料具有辛烷值高、毒性低、硫分灰分低、CO_2排量小的优良特性,应用广泛。传统的乙醇制备方法——粮食发酵法和乙烯水合法具有原料紧缺、能耗大等突出问题,根据我国煤炭相对丰富的现状,煤基合成气制乙醇是一条前景广阔、研究价值高的合成途径。本课题组针对浆态床反应器特点,自主研发了浆态床催化剂完全液相制备工艺,并在前期研究中发现:采用完全液相法制备的Cu-Zn-Al催化剂在催化合成气制甲醇过程中高选择性地生成了乙醇,但是由于高选择性乙醇催化剂对前驱体结构敏感,故重现性和稳定性较差。在后期研究中发现,溶胶制备方法、老化方式以及胶凝剂的种类对催化剂前驱体影响较大,且Al OOH对CO的解离和C链增长有积极作用。针对以上内容,本文采用完全液相法制备催化剂,通过改变制备方法(醇解法、水解法)、Al OOH溶胶的加入量、老化方式(混合老化、分开老化)以及胶凝剂的种类,探索催化剂前躯体结构的优化,以期提高催化剂的稳定性和重现性,并结合XRD、N_2吸脱附、H_2-TPR、NH_3-TPD-MS、FT-IR、TG-DTG、27Al-MAS-NMR、XPS、TEM多种测试手段对催化剂的结构进行了表征分析,获得以下主要结论:(1)一种催化剂制备的新思路:在不添加任何助剂的条件下,分开制备Cu-Zn-Al溶胶(第一铝源)和Al OOH溶胶(第二铝源)得到溶胶前驱体,进而老化、热处理制得催化剂。此法制备的催化剂稳定性高,120 h内未出现失活现象,CO转化率最高可达60%。(2)选用结论1的方法,改变AlOOH溶胶的加入量,当催化剂中n(Cu:Zn:Al:Al OOH)=2:1:0.8:0.6时,催化剂的初始乙醇(Et OH)/总醇(ROH)选择性达最大。此比例下,醇解法比水解法的初始乙醇/总醇选择性大,混合老化比分开老化的初始乙醇/总醇选择性大。醇解法混合老化催化剂的初始Et OH/ROH选择性可达70.3%;醇解法分开老化催化剂的初始Et OH/ROH选择性可达35.4%;水解法混合老化催化剂的初始Et OH/ROH选择性可达27.1%,水解法分开老化催化剂的初始Et OH/ROH选择性可达15.8%。(3)选用结论1的方法,反应前催化剂中铝物种为无定型Al OOH,有五配位铝和六配位铝。反应后催化剂中的铝物种为Al2O3,存在四配位铝和六配位铝,五配位铝消失。结合实验结果推测,当催化剂中六配位铝与五配位铝的量达到合适比例,且五配位铝的量和占比较高时有利于乙醇的生成。当六配位铝的量和占比远大于五配位铝的,且存在四配位铝时有利于DME的生成。(4)选用柠檬酸溶液做胶凝剂的催化剂,初始Et OH/ROH选择性由第一天的29.6%以上升趋势在第四天达42.6%,CO转化率第二天可达37.7%,之后逐渐下降。总之,分开制备Cu-Zn-Al溶胶(第一铝源)和Al OOH溶胶(第二铝源)的催化剂制备方法,使得催化剂的稳定性和重现性显著提高。
[Abstract]:Ethanol is recognized as an environmental friendly and high quality alternative liquid fuel and gasoline additive. Compared with other fuels, ethanol has the advantages of high octane number, low toxicity, low sulfur content and low CO _ 2 emission, so it is widely used. The traditional methods of ethanol preparation, such as grain fermentation and ethylene-water, have outstanding problems such as shortage of raw materials and high energy consumption. According to the relative abundance of coal in our country, coal-based syngas is a promising way to produce ethanol. To study the high value synthetic pathway. According to the characteristics of slurry bed reactor, our team has developed a complete liquid phase preparation process for slurry bed catalyst. In previous studies, it was found that the Cu-Zn-Al catalyst prepared by the complete liquid phase method was highly selective to produce ethanol in the process of synthesis gas to methanol, but the highly selective ethanol catalyst was sensitive to the precursor structure. Therefore, the reproducibility and stability are poor. In the later study, it was found that the preparation method of sol, aging method and the type of gelling agent had great influence on the catalyst precursor, and Al OOH had a positive effect on the dissociation of CO and the growth of C chain. In view of the above, the catalyst was prepared by the complete liquid phase method. The amount of Al OOH sol, the aging mode (mixed aging, separating aging) and the type of gelling agent were changed by changing the preparation method (alcoholysis, hydrolysis method). In order to improve the stability and reproducibility of the catalyst, the structure of the catalyst was characterized and analyzed with XRD,N_2 desorption and desorption H2-TPRN NH3-TPD-MSFT-IRT-TG-DTG 27Al-MAS-NMR-27Al-MAS-NMR-XPSTEM. The main conclusions are as follows: (1) A new way of preparing catalyst: Cu-Zn-Al sol (first aluminum source) and Al OOH sol (second aluminum source) were prepared separately without adding any additives, and then aged. The catalyst was prepared by heat treatment. The catalyst prepared by this method has high stability and no deactivation within 120 hours. (2) the method of conclusion 1 is chosen to change the amount of AlOOH sol. When n (Cu:Zn:Al:Al OOH) is 2: 1: 0.8: 0.6 in the catalyst, The initial ethanol (Et OH) / total alcohol (ROH) selectivity of the catalyst was the highest. In this ratio, the selectivity of the initial ethanol / total alcohol was higher than that of the hydrolysis method, and the selectivity of the mixed aging was higher than that of the separated aging method. The initial Et OH/ROH selectivity of the mixed aging catalyst for alcoholysis can reach 70.3, the initial Et OH/ROH selectivity of the catalyst separated by alcoholysis can reach 35.4and the initial Et OH/ROH selectivity of the mixed aging catalyst by hydrolysis method can reach 27.1%, and the initial Et OH/ROH selectivity by hydrolysis method can be as high as 27.1g. The initial Et OH/ROH selectivity of the catalyst can reach 15.8%. (3) the method of conclusion 1 is selected. The aluminum species in the catalyst before the reaction are amorphous Al OOH, with five coordinated aluminum and six coordinated aluminum. After the reaction, the species of aluminum in the catalyst were Al2O3, with four coordinated aluminum and six coordinated aluminum, and the five coordinated aluminum disappeared. Combined with the experimental results, it was inferred that the amount of six-coordinated aluminum and five-coordinated aluminum in the catalyst reached an appropriate proportion, and the amount and proportion of five-coordinated aluminum were higher in favor of ethanol production. When the amount and proportion of hexa-coordinated aluminum is much larger than that of five-coordinated aluminum, and the existence of four-coordinated aluminum is favorable to the formation of DME. (4) citric acid solution is used as the catalyst for gelling agent. The initial Et OH/ROH selectivity increased from 29.6% on the first day to 42.6% on the fourth day, and the conversion rate of CO reached 37.7% on the second day, and then decreased gradually. In a word, the stability and reproducibility of Cu-Zn-Al sol (first aluminum source) and Al OOH sol (second aluminum source) were improved significantly.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ223.122
[Abstract]:Ethanol is recognized as an environmental friendly and high quality alternative liquid fuel and gasoline additive. Compared with other fuels, ethanol has the advantages of high octane number, low toxicity, low sulfur content and low CO _ 2 emission, so it is widely used. The traditional methods of ethanol preparation, such as grain fermentation and ethylene-water, have outstanding problems such as shortage of raw materials and high energy consumption. According to the relative abundance of coal in our country, coal-based syngas is a promising way to produce ethanol. To study the high value synthetic pathway. According to the characteristics of slurry bed reactor, our team has developed a complete liquid phase preparation process for slurry bed catalyst. In previous studies, it was found that the Cu-Zn-Al catalyst prepared by the complete liquid phase method was highly selective to produce ethanol in the process of synthesis gas to methanol, but the highly selective ethanol catalyst was sensitive to the precursor structure. Therefore, the reproducibility and stability are poor. In the later study, it was found that the preparation method of sol, aging method and the type of gelling agent had great influence on the catalyst precursor, and Al OOH had a positive effect on the dissociation of CO and the growth of C chain. In view of the above, the catalyst was prepared by the complete liquid phase method. The amount of Al OOH sol, the aging mode (mixed aging, separating aging) and the type of gelling agent were changed by changing the preparation method (alcoholysis, hydrolysis method). In order to improve the stability and reproducibility of the catalyst, the structure of the catalyst was characterized and analyzed with XRD,N_2 desorption and desorption H2-TPRN NH3-TPD-MSFT-IRT-TG-DTG 27Al-MAS-NMR-27Al-MAS-NMR-XPSTEM. The main conclusions are as follows: (1) A new way of preparing catalyst: Cu-Zn-Al sol (first aluminum source) and Al OOH sol (second aluminum source) were prepared separately without adding any additives, and then aged. The catalyst was prepared by heat treatment. The catalyst prepared by this method has high stability and no deactivation within 120 hours. (2) the method of conclusion 1 is chosen to change the amount of AlOOH sol. When n (Cu:Zn:Al:Al OOH) is 2: 1: 0.8: 0.6 in the catalyst, The initial ethanol (Et OH) / total alcohol (ROH) selectivity of the catalyst was the highest. In this ratio, the selectivity of the initial ethanol / total alcohol was higher than that of the hydrolysis method, and the selectivity of the mixed aging was higher than that of the separated aging method. The initial Et OH/ROH selectivity of the mixed aging catalyst for alcoholysis can reach 70.3, the initial Et OH/ROH selectivity of the catalyst separated by alcoholysis can reach 35.4and the initial Et OH/ROH selectivity of the mixed aging catalyst by hydrolysis method can reach 27.1%, and the initial Et OH/ROH selectivity by hydrolysis method can be as high as 27.1g. The initial Et OH/ROH selectivity of the catalyst can reach 15.8%. (3) the method of conclusion 1 is selected. The aluminum species in the catalyst before the reaction are amorphous Al OOH, with five coordinated aluminum and six coordinated aluminum. After the reaction, the species of aluminum in the catalyst were Al2O3, with four coordinated aluminum and six coordinated aluminum, and the five coordinated aluminum disappeared. Combined with the experimental results, it was inferred that the amount of six-coordinated aluminum and five-coordinated aluminum in the catalyst reached an appropriate proportion, and the amount and proportion of five-coordinated aluminum were higher in favor of ethanol production. When the amount and proportion of hexa-coordinated aluminum is much larger than that of five-coordinated aluminum, and the existence of four-coordinated aluminum is favorable to the formation of DME. (4) citric acid solution is used as the catalyst for gelling agent. The initial Et OH/ROH selectivity increased from 29.6% on the first day to 42.6% on the fourth day, and the conversion rate of CO reached 37.7% on the second day, and then decreased gradually. In a word, the stability and reproducibility of Cu-Zn-Al sol (first aluminum source) and Al OOH sol (second aluminum source) were improved significantly.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ223.122
【参考文献】
相关期刊论文 前10条
1 张小雨;黄伟;高志华;张琳;时培祥;边仲凯;;完全液相法中Cu源对Cu-Zn-Al催化剂结构及性能的影响[J];燃料化学学报;2016年10期
2 游向轩;樊金串;黄伟;周由之;魏s，
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