Intrinsic Kinetics For The Indirect Hydrogenation Of Acetic Acid To Ethanol On The Cu-Zn/Al₂O₃Catalyst

Ethanol is used as an important chemical material as well as clean fuel with huge consumption. Currently, traditional methords of grain fermentation and hydration of ethylene are mainly adopted to produce ethanol. But the former process consumes a lot of precious grain and the latter consumes expensive and depleting oil resources.Currently, coal-based acetic acid industry is trapped in an awkward situation, namely low price, seriously excessive capacity and saturated downstream demand. The development of ethanol from acetic acid can not only utilize excessive acetic acid but also create huge economic and environmental benefits. The process of catalytically indirect hydrogenation of acetic acid——esterification first and then hydrogenation of the ester——was chosen to produce ethanol. The details are as follows:1) Characterization of the Cu-Zn/Al2O3catalystICP (inductive coupled plasma emission spectrometer), XRD (x-ray diffraction), BET (specific surface area), H2-TPR (temperature-programmed reduction) are used to characterize the catalyst. The ICP results show that the main element of the catalyst is Cu, whose mass fraction is53.8%in CuO, the carrier of Al2O317.1%and the promoter of ZnO1.6%. XRD pattern shows that CuO exists as amorphous type on the carrier with good dispersion. The BET specific surface area of the catalyst is87.35m2/g, and the average pore diameter is9.43nm. The proportion of the well-distributed holes with diameter of2-10nm is maximum. H2-TPR indicates that the Cu element goes through the status of Cu2+to Cu+to Cu0with the reduction of the catalyst and the temperature range of221～305℃is suitable for the reduction.2) The intrinsic kinetics of producing ethanol from ethyl acetate(EA)The influences of temperature, pressure, LHSV and n(H2):n(EA) to the catalyzed reaction was measured in an isothermal integral tubular reactor. Under the optimal conditions derived from the single factor experiment, namely t=210℃, p=3.0MPa, LHSV=1.0g/(g·h) and n(H2):n(EA)=30, the ethyl acetate conversion and the selectivity of ethanol reached to97.3%and99.4%, respectively. Within the range of t=180～230℃, p=1.0-5.0MPa, LHSV=0.7-1.9g/(g-h), n(H2):n(EA)=20-50, the L9(34) orthogonal experiment was designed to gain the data of the intrinsic kinetics. Runge-Kutta-Felhberg (4,5) algorithm was selected as the numerical integration method, and the kinetic model parameters were estimated by means of Levenberg-Marquardt method. Then the power-law kinetic equation was derived, which was acceptable and reliable for the catalytic hydrogenation of ethyl acetate to ethanol on the Cu-Zn/Al2O3catalyst.