The catalytic performance of commonly used heteropoly acids(H_3 PW_(12)O_(40). H_4 SiW_(12)O_(40) and H_3 PMo_(12)O_(40)) for the synthesis of 4,4'-methylenedianiline(4.4'-MDA) from aniline and formaldehyde was evaluated and the result showed that H_4 SiW_(12)O_(40) with moderate acid strength exhibited the best catalytic performance. Then H_4 SiW_(12)O_(40)@MIL-100(Fe) was prepared by encapsulating H_4 SiW_(12)O_(40) within the pores of MIL-100(Fe) to facilitate its recovery and reuse. The prepared H_4 SiW_(12)O_(40)@MIL-100(Fe) was characterized by means of FT-IR, N_2 adsorption-desorption, XRD, TG and then the catalytic performance was evaluated. The result showed that H_4 SiW_(12)O_(40) was highly dispersed in the pores of MIL-100(Fe), and both the Keggin structure of H_4 SiW_(12)O_(40)and the crystal skeleton structure of MIL-100(Fe) could be effectively preserved. Furthermore. H_4 SiW_(12)O_(40)@MIL-100(Fe) showed excellent catalytic performance under the following reaction conditions: a molar ratio of aniline to formaldehyde = 5, a mass ratio of catalyst to formaldehyde = 1.2, a reaction temperature of 120 ℃and a reaction time of 6 h. Under the above reaction conditions, the conversion of aniline was 41.1%, and the yield and selectivity of 4.4'-MDA were 81.6% and 79.2%, respectively. Unfortunately, an appreciable loss in the catalytic activity of the recovered H_4 SiW_(12)O_(40)@MIL-100(Fe) was observed because of the blocking of the pores and the change of the acidity resulted from the adsorption of alkaline organics such as aniline and 4,4'-MDA.The adsorbed alkaline organics could be cleaned up when the recovered catalyst was washed by methanol and DMF. Then the catalyst was effectively reused up to three cycles without much loss in its activity.
Yunhuan KongXiaomeng ChengHualiang AnXinqiang ZhaoYanji Wang
为了提高泡沫分离甘草中甘草酸的分离效果,开发了甘草麻黄配伍泡沫分离工艺,并就麻黄对浸提液泡沫性能的影响进行了研究。结果表明,麻黄强化了甘草酸的提取,但降低了浸提液中甘草苷的浓度,使得浸提液的泡沫性能发生变化而影响泡沫分离甘草酸的分离效果。以甘草酸的富集比和回收率为评价指标,研究了温度、气体体积流量、甘草酸初始浓度和甘草麻黄质量配比对分离效果的影响。结果表明当温度为40℃、气体体积流量为100 m L×min^(-1)、甘草酸初始浓度为0.2 g×L^(-1)和甘草麻黄质量配比为5:3时,获得甘草酸的富集比和回收率分别为8.34和62.5%。与单独泡沫分离甘草中甘草酸相比,甘草酸的富集比提高了121.7%,而回收率并未明显降低。因此,麻黄的引入有效地提高了泡沫分离甘草酸的分离效果。
