Study On Ethoxylation Over Mixed Metal Oxide Catalysts

Fatty alcohol polyoxyethylene for short alcohol ether is an important nonionic surfactant. The surfactant was synthesized by ethylene oxide (EO) and hydrogen class compound through ethoxylation. At present, the reaction is traditionally carried out in the presence of alkaline catalysts, e.g.,NaOH, KOH in tank reactor. Broad-range-distributed products are obtained, and the catalysts was difficult to separate from the reactants and recycle. The ethoxylation is carried out in a fixed-bed reactor and catalyzed by mixed metal oxides catalysts (MMOs) derived from Mg-Al-M (M is Zr, La, Ce, Fe) hydrotalcite to synthetize ethylene glycol monoethyl ether(EGME). The hydrotalcite-precursors were synthesized by co-precipitation method and characterized by XRD, XRD, FT-TR, SEM, TG-TGA, TPD and N2adsorption/desorption techniques to study the constitute, crystal structure, thermostability, morphology etc. physicochemical property of catalysts. The research also highlighted the effect of the type and content of M, catalyst synthesis method, calcination temperature and reaction condition on the catalyst properties and ethoxylation. The main results are as follows:The Mg-Al-M synthetized by co-precipitation method exhibited typical layer structure of hydrotalcite, mixed metal oxide formed with large surface area and two types of alkaline center after calcination. The Mg-Al-Fe hydrotalcite-precursor exhibited best crystallinity and high catalytic activity after calcination. The Mg-Al-Fe MMO exhibited best catalytic activity when the ratio of Fe/Al is0.2. The impact of the type of M on the catalytic activity of MMO is slight, which has a significant impact on the performance of the conversion fo EO. The conversion of EO reached86.44%on Mg-Al-Fe MMO, which was higher than60.68%of Mg-Al binary MMO. With the increase of the content of iron of the Mg-Al-Fe catalyst, the conversion of EO increased and the selectivity of EGME decreased. The preparation method has slight influence on the catalytic activity of catalysts, although the catalysts showed high crystallinity and regular morphology after hydrothermal crystallization. The calcined temperature seriously affected the surface area and then affect the catalytic activities of the catalysts and500℃was the most appropriate temperature. The result of the study of the reaction conditions on the Mg-Al-Fe catalyst showed that the conversion of ethylene oxide was more than85%and the selectivity of EGME reached90%, under the reaction temperature of120℃, reaction pressure of0.4MPa, with molar rate of ethanol and EO of7.0and LHSV of3h-1.