COMPARISON OF ACID CATALYSTS FOR THE DEHYDRATION OF METHANOL TO DIMETHYL ETHER
Advancing the chemical engineering fundamentals
Catalysis - II (T2-13b)
Keywords: DME synthesis, methanol dehydration, acid function
The acid function g-Al2O3 is used widely in the dehydration of methanol to dimethyl ether (DME). Good performance is reported in the literature for this and other acid functions in the transformation of synthesis gas to DME in a single step on bifunctional catalyts such as CuO-ZnO-Al2O3/g-Al2O3 and CuO-ZnO-Al2O3/NaHZSM-5. These catalysts are made up of a metallic function for methanol synthesis and an acid function for dehydration of methanol to DME [1,2].
The aim of this paper is to compare the performance of three acid functions in the second reaction step (dehydration of methanol to dimethyl ether). These acid functions are: g-Al2O3, NaHZSM-5 (obtained from NaZSM-5 zeolite subsequent to ion exchange with 1M NH4Cl), and HZSM-5 zeolite pretreated with 0.2M NaOH dissolution. Both partial ion exchange and pretreatment with NaOH allow for obtaining moderate acid sites in the zeolite, which on the one hand are active in the dehydration of methanol and, on the other, are of low activity in the formation of hydrocarbons [3].
The following operating conditions have been used: temperature, in the 200-275 ºC range; pressure, 15 bar; space time, 5.6 g of catalyst h-1 (mol of methanol)-1. DME yield is measured as the percentage of carbon atoms fed in methanol that convert to DME. Higher DME yields are obtained with the catalyst based on ZSM-5 zeolite than with g-Al2O3.
DME yield is almost the same (between 90 and 93 %) up to temperatures of 260 ºC, for NaHZSM-5 and HZSM-5 pretreated with NaOH and there is a slight difference above this temperature. The more severe treatment with NaOH allows for obtaining a zeolite with a more suitable acid strength for avoiding the formation of olefins and the decrease in the DME yield above 275 ºC with NaHZSM-5 zeolite.
References
[1] Ereña J., Garoña R., Arandes J. M., Aguayo A. T., Bilbao J., Int. J. Chem. Reactor Eng., Vol. 3 (2005) A44.
[2] Ereña J., Garoña R., Arandes J. M., Aguayo A. T., Bilbao J., Catal. Today, 107-108 (2005) 467.
[3] Garoña R., Ph.D. Thesis, University of the Basque Country, Bilbao, Spain, 2006.
See the full pdf manuscript of the abstract.
Presented Thursday 20, 11:20 to 11:40, in session Catalysis - II (T2-13b).
