1,4-butanediol Selective Dehydration To 3-buten-1-ol Over CaO/ZrO₂ Doped With SiO₂ Catalysts

Because of the special molecular structure,3-Buten-1-ol (BTO) can be used in a variety of fine chemical fildes such as platic lens, edible flavor, oil processing, et al. Especially, in the medical field, BTO is an important intermediate for the production of antiproliferatice drugs, antitumor drugs and anti-aids drugs. In recent years, the market demand for BTO has been increasing year by year. Up to now, the BTO production methods include formaldehyde addition to propylene, reduction of 3,4-epoxy-1-butene by formic acid, reduction of 3-butenonic acid,3-butyne-l-ol hydrogenation and vapor phase dehydration of 1,4-butanediol (BDO), et al. Among the above methods, the gas phase selective dehydration of BDO to BTO represents some advantages such as mild reaction conditions, environmental friendliness and a simple experiment procedure.BTO can be synthesised from BDO selective dehydraion by the synergetic effect between acid and base sites. Our previous studies had shown that the ZrO2 catalyst modified by CaO, which had rich acid and base active centers, showed an excellent catalytic activity in BDO selective dehydration to BTO. In addition, M1-O-M2 structure in binary oxides can generate unbalance charge sites then produce new acid sites, meanwhile, the unbalance charge sites can prompt the dispersion of third component. This suggests that the amount of acid and basic sites in CaO/ZrO2 catalyst may be improved by doping SiO2. Then an superior catalyst for gas phase selective dehydration of BDO to BTO can be obtained.On the basis of our previous studies, SiO2 doped SiO2-ZrO2 carrier was prepared by sol-gel method combined with supercritical fluid drying technique. Then, CaO/SiO2-ZrO2 catalysts were prepared by incipient impregnation method. N2 physisorption, XRD, FT-IR, NH3-TPD and CO2-TPD techniques were used to characterize the catalysts. The effect of doping SiO2, SiO2 content and CaO content on the texture, structure, and surface properties of CaO/SiO2-ZrO2, as well as the catalysis performance of BDO dehydration were investigated. The main results are listed as follows:1. CaO/SiO2-ZrO2 and CaO/ZrO2 catalysts were characterized by various characterization methods and the catalytic performance in BDO selective dehydration to BTO were investigated. The results showed that the texture, the structure, and surface acid-base properties of CaO/ZrO2 were regulated by doping SiO2. CaO/SiO2-ZrO2 exhibited rich acid-base active centers, further more, the intensity of acid and base were concentrated. Evaluations showed that the conversion rate of BDO and the selectivity to BTO increased from 75.4% and 51.3% for CaO/ZrO2 to 94.8% and 73.7% for CaO/SiO2-ZrO2, respectively. Doping SiO2 effectively improved the catalytic performance of gas phase selective dehydration of BDO to BTO.2. The effect of SiO2 content on catalytic performance of CaO/SiO2-ZrO2 was systematically investigated. With increasing of SiO2 content in carriers, acid sites on surface catalysts gradually increased, and base sites firstly increased then decreased. When SiO2 content was 1.0 mol%, both rich acid centers and base centers were obtained in catalysts, which showed optimical catalytic performance of BDO dehydration to BTO. With the further increase in SiO2 content, a lot of medium and strong acid centers were generated. There are strong interaction between medium and strong acid sites and terminal hydroxyls of BDO, and by-product THF were produced.3. Based on the above work, choosing 1.0SiO2-ZrO2 as carrier, the effect of CaO content in CaO/SiO2-ZrO2 catalyts on the acid-base properties and catalytic performance were investigated. With the increasing of CaO content, weak acid centers on catalysts surface maintained a constant, the medium acid gradually reduced, and weak, medium, strong base centers increased. When the CaO content was 9 wt%, the highest selectivity (80.4%) of BTO was obtained. However, the BTO selectivity decreased with the further increasing CaO content. The possible reason was that more medium and strong basic sites generated on catalyst surface enhanced the interaction between catalyst and the β-H in BDO, products likes 2-buten-1-ol similar with BTO were produced.