금속산화물 촉매에서 프로필렌 글라이콜로의 글리세롤 수소화 분해반응

Abstract

Glycerol (1,2,3-propanetriol or glycerine), an organic molecule isolated by heating fats in the presence of ash (to produce soap) as early as 2800 BC, is an industrial chemical with tens of applications. Since the late 1940s, and following the discovery of synthetic surfactants, glycerol has been produced from epichlorohydrin obtained from propylene (and thus from fossil oil) as large chemical companies forecasted a glycerol shortage and initiated its synthetic production. Today, however, glycerol plants are closing and others are opening that use glycerol as a raw material as a result of the large surplus of glycerol that is formed as a byproduct (10% in weight) in manufacturing biodiesel fuel by trans-esterification of seed oils with methanol. If crude natural glycerol could be converted to propylene glycol, this technology could be used in biodiesel production plants to increase profitability. Preferred technology would convert crude natural glycerol at moderate temperatures and pressures. Some typical uses of propylene glycol are in unsaturated polyester resins, functional fluids (antifreeze, de-icing, and heat transfer), pharmaceuticals, foods, cosmetics, liquid detergents, tobacco humectants, flavors and fragrances, personal care, paints and animal feed. The antifreeze and deicing market is growing because of concern over the toxicity of ethylene glycol-based products to humans and animals as well. Hydrogenolysis of glycerol to propylene glycol has been previously reported to use several supported transition metal catalysts such as sulfide Ru, Pt, Cu, Raney Ni including some bimetallic catalysts consisting of Pt–Ru, Pt–Re, Rh–Cu, Cu-Cr and Ni–Cu. Selective hydrogenolysis of glycerol to propylene glycol requires cleavage of C–O bonds by H2 without attacking C–C bonds in the glycerol molecule. For this purpose, a number of solid catalysts have been explored, among which Cu-containing catalysts exhibit superior performances. In this study, binary and ternary metal oxide catalysts with Cu contents were carefully prepared by co-precipitation method and microwave-assisted process. Metal oxide catalysts were characterized by gas choromatography (GC) with flame ionization detector (FID), X-ray diffraction (XRD), X-ray fluorescence (XRF), field emission scanning electron microscope (FE-SEM), ammonia temperature-programmed desorption (NH3-TPD), and BET surface area. Among the different mixed-metal oxides that were evaluated for glycerol hydrogenolysis, the Cu/Zn/Al (a molar ratio of 2/2/1) mixed-metal oxides were the most active catalysts, showing selectivity of 72.6~74.0% toward propylene glycol. The optimized conditions for the glycerol conversion and selectivity toward propylene glycol were a hydrogen pressure of 250psig, reaction temperature 200℃, reaction time of 20h, catalyst concentration of 5.0wt%, and glycerol aqueous solution of 20wt%.