Preparation Of Silica-supported Copper Catalysts And Its Performance In Continuous Hydrogenation Of Dimethyl Maleate

Dimethyl maleate(DMM) is an important chemical intermediate, whose hydrogenation products are γ-butyrolactone(GBL), 1, 4-butanediol(BDO) and tetrahydrofuran(THF), all of which are high value-added products and widely used in medicine, pesticide, chemical, automobile and other industries. With the technology development in the preparation of n-butane oxidation to maleic anhydride and reduction in production costs, the development of downstream products of maleic anhydride will have important practical significance. The process route by maleic anhydride and methanol in acid-catalyzed esterification reaction of DMM, and then by the DMM continuous hydrogenation of BDO cogeneration GBL and THF, which is considered to be the most promising technology at this stage, and the process is both economical and technological green synthetic routes. For the realization of this process, the core is the development of DMM hydrogenation catalyst. Copper-based catalyst is currently the most commonly used DMM hydrogenation catalyst, but some problems still exist: unclear active ingredient, low product selectivity, poor thermal stability, etc.By using different preparation methods and adding alkaline promoters, this article was to explore the relationship between catalyst structure and catalytic performance, focusing on the effects of copper valence on DMM hydrogenation performance, and revealing the composition of active site. According to XRD, TPR, FT-IR, XPS and other analysis, the initial conclusions were as follows:Cu/SiO2 catalysts prepared by different preparation methods were compared to found that AE-Cu/SiO2 prepared by ammonia evaporation had higher catalytic activity than WI-Cu/SiO2 prepared by impregnation. According to the characterization, it was found that the reduced WI-Cu/Si O2 only contained Cu0, while the reduced AE-Cu/SiO2 contained Cu+ besides Cu0; the further researches also suggested that the Cu0 and Cu+ were originated from the precursor CuO and copper phyllosilicate, respectively. In addition, the result showed that the dispersion of Cu species in AE-Cu/SiO2 was much better than that in WI-Cu/SiO2. To further explore the effects of copper valence on DMM hydrogenation performance, TOF value of the two catalysts was calculated and it showed that TOF value of AE-Cu/SiO2(11.16h-1) was significantly greater than that of WI-Cu/Si O2(6.57h-1), which suggested a synergistic effect existed between Cu+ and Cu0. Considering that WI-Cu/SiO2(only containing Cu0) could catalyze DMM hydrogenation individually, and thus we concluded that Cu0 was the main active site in DMM hydrogenation, and the synergistic effect between Cu+ and Cu0 could further improve catalytic activity.To further achieve the modulation of product selectivity on hydrogenation of DMM, this article introduced alkaline promoters(Mg, Ca, Sr, Ba, La) to improve the performance of Cu/SiO2. A preliminary study showed that adding alkaline promoters could promote the dehydrogenation of BDO to GBL in basic sites(mainly in middle strong alkali) to enhance the selectivity of GBL. By evaluating and screening, it was found that Cu-La/SiO2 catalyst had the highest activity.Through the study of reaction conditions, we have come to appropriate reaction conditions of DMM hydrogenation: T=473~513 K, p=4~6 MPa, LHSV=0.6~0.9 h-1, H2/DMM=50. Several regularities have been found as follow:(a) In a suitable acid site, a higher temperature and pressure will contribute to produce THF;(b) Under the conditions of avoiding acid site, a lower temperature and higher pressure will contribute to produce BDO, a higher temperature and lower pressure will do good to produce GBL.