Dimethyl ether formation

The carbon monoxide selectivity was well below 2% for all samples. As a by-product, substantial amounts of dimethyl ether were found for all samples the highest selectivity of 23% was detected over pure ceria. Only traces of another by-product, methyl formate, were measured. The dimethyl ether formation was attributed to separate dehydration of the methanol on the alumina surface. 

The background theory for estimating free energy barriers using constrained dynamics is covered in more detail in a similar study of dimethyl ether formation from methanol in zeolites Hytha, M., Stich, L, Gale, J.D., Terakura, K. 

An H-ZSM-5 catalyst which has been heated to 500 in air does not form hydrocarbons when methanol is passed over it at e.g. 220 °C. (But it is very active for DME ( dimethyl ether ) formation, so methanol, DME, and water are virtually equilibrated. )... 

Homologation experiments were conducted in a 300 ml pressure reactor ( M/s Parr Inst., Co. U.S.A ). In a typical run, known amount of catalyst is mixed with known volumes of aqueous HI and methanol (total volume 50 ml) and placed in the reaction vessel. The reactor was pressurized to 30 atm CO and was maintained at 150 C. After 11 h contact time, the reactor was cooled to room temperature and analyzed for the products. Dimethyl ether formation was confirmed by passing the gaseous product through iodine in CS2 solution which gave tany colour. It was quantitatively analyzed by gas chromatography using molecular sieve 13X packed s.s column and TCD detector. Acetic acid and dimethylacetate were analyzed by GC ( Shimadzu, Japan ) and confirmed by their standards. 

Aluminium oxide as promotor can increase dimethyl ether formation considerably, above all at the top end of the temperature range approaching the copper catalyst application limit... 

Men and coworkers investigated methanol steam reforming over Cu/Ce02/Al203 catalysts [12-14] in a 10-fold screening reactor developed by Kolb et al. [3]. At a reaction temperature of 250 °C and an S/C ratio of 0.9, the atomic ratio of copper to ceria was varied from 0 to 0.9, revealing the lowest conversion for pure ceria and a sharp maximum for a ratio of 0.1. The carbon monoxide selectivity was lower than 2% for all samples. As byproduct, substantial amounts of dimethyl ether were observed for all samples the highest selectivity of 23% was detected for pure ceria. The dimethyl ether formation was attributed to separate dehydration of methanol on the alumina surface. 

Dimethyl ether formation was also observed by Men et al. for Cu/ZnO/Al203 catalysts [15]. Lowering the WHSV to 10 Lh g J was required at an S/C ratio of 2 to achieve full conversion of the methanol without byproduct formation. Under these conditions, around 1 vol.% of carbon monoxide was detected in the reformate. 

A kinetic study of methanol oxidation over stoichiometric iron molybdate catalyst was performed in a fixed-bed integral reactor showing kinetic influences of reaction products. In the temperature range of 548-618 K it was not possible to fit the fomoation rate data to a single power rate law. Dimethyl ether formation presents only a second order dependence with respect to methanol. CO formation seems to be inhibited by water and formaldehyde and rate data fit well to the power rate law ... 

Let us consider dimethyl ether formation from methanol, which proceeds through a consecutive reaction mechanism I 1. Figure 4.13a illustrates the reaction intermediates for the first reaction step in which the C-0 bond in methanol is cleaved. The calculated reaction energy diagram for this reaction is shown in Fig. 4.13b. The reaction products that form are water and adsorbed methoxy. 

Dimethyl ether formation is favoured by decreasing the reaction temperature [53]. 

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