(255e) Membrane Reactor With Water Selectve Zeolite Membrane for Esterification of Acetic Acid

Membrane reactoris expected to improve the level of esterification conversion, displacing equilibrium by selective removal of by‐product, water. In this study, we performed a simulation study on the behavior ofthe membrane reactorforthe esterification of acetic acid (AcOH) with ethanol as well as the experiments using mordenite‐type zeolite membrane, in which mordenite is a kind ofzeolite having both high stability in acidic media and hydrophilic nature. Recently, we successfully synthesized compact mordenite membrane [1], which selectively permeated and separated water from alcohol[2]. A compact mordenite membrane was prepared on the outer surface of an  α‐alumina
tubular support by a secondary growth method, following the procedure described elsewhere [2]. The membrane tube was set inside a stainless steel module. A hundred
milligramofsolid acid catalyst, Amberlyst‐15, was placed on the outersurface ofmembrane. The exposure area of zeolite membrane was 6.28 cm². The feed for the esterification consisted of an equimolar mixture of AcOH and ethanol (both 0.1 mol). The retentate was circulated at a flow rate of 1 mL min⁻¹. The permeate side of membrane was vacuumed during the esterification.

Use of membrane increased the level of conversion from about 60 (equilibrium value)to >90 % at 403 K. Repeated use of the membrane gave reproducible results. In the simulation model, we integrated a perfectly‐mixed batch reactor with a pervaporation unit. The expression of the rate of the esterification in the membrane reactor is controlled by both the rates of reaction and permeation. All the parameters for the simulation such as the rates of reaction and permeation were determined by the experiments: No fitting parameters were used. We confirmed that the simulation model developed in thisstudy sufficiently explainsthe experimentalresults. We carried out the sensitivity analysis of the model. Water removal from the reaction side contributed to improving the level of AcOH conversion by displacing the equilibrium. However, an increase of water permeance above 1.0×10^–6 mol m^–2 s^–1 Pa^–1would not be effective to improve the level of conversion because the concentration of water in the reactorside is kept very low throughoutthe reaction. The simulation was done with different separation factors, namely water/AcOH, water/ehanol and water/ethylacetate. When the separation factor of water against AcOH or ethanol was too small, the reacants passed through the membrane, resulting in a decrease of attainable level of conversion. When the separation factor of water against ethyl acetate was too small, the yield of ethyl acetate has a maximum with time course, because produced ethyl acetate was lost to the permeate side. As a result, we concluded that separation factor should be larger than 100 for water/AcOH and water/ethanol, and larger than 1000 for water/ethyl acetate. Mordenite membrane developed satisfies such requirements for separation factors.

References
[1] Matsukata, M. et al.,J. Membr. Sci., 316, 18−27 (2008).
[2] Sawamura, K. et al.,J. Chem. Eng.Jpn., 41, 870−877 (2008).
[3] Li,G. et al.,J. Membr. Sci., 218, 185−194 (2003).