ZSM-5分子筛催化甲醇制丙烯过程研究

【作者】 张锋涛；

【导师】 陈立宇；

【作者基本信息】 西北大学 ， 化学工程， 2010， 硕士

【摘要】 丙烯生产的主要原料是石油,而石油资源又十分有限,以甲醇为原料制取丙烯,即MTP (Methanol to Propylene)技术越来越受到关注。MTP技术的研究重点在于催化剂的开发,主要集中在ZSM-5分子筛催化剂的改性研究。本文以ZSM-5分子筛为催化剂,在固定床积分反应器上研究了催化剂硅铝比、各种元素改性对催化剂性能的影响,并确定了最佳工艺条件。考察硅铝比对催化剂性能的影响,发现硅铝比对丙烯的选择性有较大影响,硅铝比越大甲醇转化率越低,丙烯选择性却随硅铝比增加而增加。且不同硅铝比催化剂其最佳的反应温度存在一定差异。最终确定在硅铝比50和硅铝比200的ZSM-5催化剂反应温度分别选取400℃和450℃。采用非金属元素P,过渡金属Zn、Cu、Co、Ag,稀土元素Ce、La,碱及碱土金属K、Mg分别对两种硅铝比催化剂进行改性研究。表明K改性硅铝比200的ZSM-5催化剂具有最佳的丙烯收率。进一步考察了K浓度对改性催化剂性能的影响。最终确定质量分数2%的K改性硅铝比200的ZSM-5催化剂为甲醇制丙烯反应的适宜催化剂。通过热重测试考察了K改性对催化剂稳定性的影响,结果发现,2%K改性对催化剂的稳定性起到了进一步的促进作用。改性后催化剂积碳量更少,表面的活性中心在反应过程受到的影响更小,从而使催化剂的寿命增加。在2%K改性ZSM-5分子筛催化剂基础上,考察了反应温度、进料空速、原料组成等因素对改性催化剂反应性能的影响,发现温度升高有利于提高甲醇转化率和丙烯选择性,但温度升高的同时,催化剂的结焦失活也进一步加快。空速提高甲醇转化率和丙烯收率都下降,这种趋势在空速大于3h-1后加剧。同时水在原料中的比重增加,甲醇转化率和丙烯收率下降,而水可以作为热载体将反应热及时移除,确保催化剂的寿命更长。确定最佳工艺条件为：反应温度450℃,原料进料空速为3h-1,纯甲醇进料。以异丁烯模拟碳四烯烃回收过程,考察以2%K改性的ZSM-5分子筛为催化剂,反应温度450℃,甲醇进料空速3h-1,常压条件下固定床积分反应器中反应对甲醇转化率和丙烯选择性的影响。发现当异丁烯与进料甲醇摩尔比为0.1时,在保持甲醇转化率在98.7%的同时,丙烯选择性可达44.5%。更多还原

【Abstract】 Propylene is one of the most basic organic chemical materials, global propylene demand is increasing. Because oil is the main raw material for propylene production by now, which is very limited over the world. There is lots of concern about methanol as raw materials for preparation of propylene, that is MTP technology(Methanol to Propylene). The focus of MTP technology is development of catalysts which has good performance on methanol to propylene. It is mainly based on the modification of ZSM-5 used as catalyst. Therefor, ZSM-5 zeolite was used as catalyst, the impact of silica alumina ratio and the various elements on the catalytic properties were studied, and optimum process conditions were determined.First, We investigated the effect of silica alumina ratio on the performance of catalytic activities. It was found that silica alumina ratio had a greater impact on the selectivity of propylene, and different silica alumina ratio corresponded to different optimum reaction temperature. Such as ZSM-5 zeolites with Si/Al ratio 50 and 200,reaction temperature 400℃and 450℃.ZSM-5 zeolites with silica alumina ratio 50 and 200 were modified using non-metallic elements P, transition metals Zn, Cu, Co, Ag, rare earth elements Ce, La, alkali and alkaline earth metals Mg, K respectively The experimental results shown that under the evaluation conditions of the catalyst, K-modified ZSM-5 catalyst with silica alumina ratio of 200 had the best yield of propylene. The effect of the concentration of K on the modification of the catalyst studied as well, the mass fraction of 2% of the K-modified Si-Al-ZSM-5 with silica alumina ratio 200 catalysts is the best candidate for the reaction of methanol to propylene catalysts, the methanol conversion rate was 98.6%,43.93% selectivity of propene was selectivity. Meanwhile the catalyst stability of catalyst modified by K was investigated using thermogravimetric method, the test found that the catalyst stability of catalyst was improved. At the same conditions, the coke deposition on the surface of the modified catalyst was less than that of the original catalyst, the active sites on the surface of the modified catalyst was suffered less effect, thereby increasing the life of the catalyst.The influences of reaction temperature, feed space velocity, material composition and other factors on performance of modified catalyst were researched based on 2% K-modified ZSM-5 zeolite catalyst. We found that high temperature was beneficial to enhance the methanol conversion rate and selectivity of propylene, but high temperature resulted the catalyst coking deactivation at the same time. Increasing space velocity was harmful to the methanol conversion and yield of propylene, this trend was intensified with the space velocity more than 3Kg (Methanol)/Kg (cat.)-h. At the same time increasing the proportion of water in the raw material leaded to the decreasing rate of methanol conversion and yield of propylene, and the water can be used as heat carrier would promptly remove the reaction heat, ensuring a longer life of the catalyst. The optimum conditions for methanol to propylene were as follows:reaction temperature 450℃, raw material feed space velocity 3Kg (methanol)/ Kg (cat.)·h, pure methanol feed at the same time. Isobutylene represents carbon 4 olefins, which was used for backing to the reactor during the methanol to propylene process, the activity of 2%K modified catalyst was investigated under reaction temperature 450℃, feed space velocity 3h-1, atmospheric pressure, The results showed that, when the molar ratio of isobutylene and methanol was 1:10, the selectivity of propylene could reach 44.5% when the methanol conversion rate was 98.7%.更多还原