Abstract:

SiO₂ supported cesium catalyst was prepared and its performance in the aldol condensation of formaldehyde and methyl propionate was studied in a fixed-bed reactor. X-ray diffraction, field emission scanning electron microscopy, X-ray fluorescence spectroscopy and thermal analysis were used to determine the composition and structure changes of the catalyst. The conversion of methyl propionate of 13%~15%, that of formaldehyde of 60%~65%, and the selectivity to MMA based on methyl propionate of 93%~95% were achieved. During the reaction, the crystal structure and morphology of the catalyst did not change significantly with insignificant aggregation and loss of the active component Cs and the amount of carbon deposition increased. After in-situ regeneration by carbon burning, the catalytic activity was restored, and the initial activity was even higher than that of the fresh catalyst. With the progress of the reaction, formaldehyde and methyl propionate conversions approached the average level before regeneration. For a long-term run for about 1700h, the MMA selectivity based on methyl propionate maintained at 93%~95%. Technical and economic analysis showed that the new coal-based MMA synthesis route with the core step of aldol condensation is safer, more environmentally friendly, more economical and more efficient than the traditional routes of acetone cyanohydrin and isobutylene oxidation, and hence is quite suitable for using in China, which has rich coal, lean oil, and little gas in resource structure. The route fits the national coal chemical policy, which not only can break through the patent blockade of C2 and C4 routes so as to change the existing technology pattern of the MMA industry, but also can provide an important way for coal chemical companies to enter the MMA synthesis technology field to enrich the coal chemical product chain by consuming the excess production capacities of formaldehyde, acetic acid and a large amount of low-value by-product methyl acetate.

Key words: methyl methacrylate(MMA), aldol condensation, acid-base catalyst, techno-economics

摘要：

制备了Cs/SiO₂催化剂，在固定床反应器中研究了其催化甲醛与丙酸甲酯羟醛缩合反应性能，并采用X射线衍射、场发射扫描电镜、X射线荧光光谱分析和热分析等手段，对催化剂组成和结构变化跟踪分析。采用80%的浓缩甲醛为甲醛源，单程1000h反应过程中，丙酸甲酯转化率13%~15%，甲醛转化率60%~65%，丙酸甲酯为基准的甲基丙烯酸甲酯（MMA）选择性93%~95%。长周期反应后，催化剂晶型结构和形貌未发生显著变化，活性组分Cs未出现明显聚集和流失，积炭量有所增加。原位烧碳再生后，催化剂活性得到恢复，初始活性高于新鲜催化剂，随着反应的进行，甲醛、丙酸甲酯转化率等指标逐渐趋稳，接近再生前的平均水平。在近1700h的反应时长内，丙酸甲酯为基准的MMA选择性93%~95%，催化剂总体稳定性较好。技术经济分析表明，以羟醛缩合为核心技术的煤基MMA合成新路线，较传统的丙酮氰醇法和异丁烯氧化法MMA技术安全环保、经济高效，契合我国富煤、贫油、少气的资源结构和国家煤化工产业升级鼓励政策，可突破C2和C4路线商业技术的专利封锁，改变MMA行业现有技术格局，为煤化工企业进军MMA合成技术领域提供重要途径，同时可消化国内乙酸、甲醛的过剩产能以及大量低值化利用的副产乙酸甲酯，丰富我国煤化工产品链。

关键词: 甲基丙烯酸甲酯, 羟醛缩合, 酸碱催化剂, 技术经济性