Methanol 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. 

Gas chromatography was employed for analysis of the reaction products Hi, CO and CO2 were analyzed by thermal-conductivity detector (TCD) methanol, dimethyl ether, methyl formate and hydrocarbons were analyzed by the flame ionization detector (FID). 

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. 

Recent data, published and unpublished, provide strong evidence that the common views on the reaction mechanism of the MTH reaction are not tenable. The data rather point to ethene and propene formation from an adsorbate hydrocarbon pool, probably of aromatic nature. There are strong indications that the catalytic cycle is based on arenes that are continually methylated by methanol/dimethyl ether, and dealkylations leading to ethene, propene and most likely also isobutene via molecular rearrangements. Penta- and hexamethylbenzene appear prone to undergo this reaction. However, there is also clear evidence that higher alkenes, if present in substantial amount, may take part in the classical homologation system. 

Substrates belonging to this group, such as water, methanol, dimethyl ether etc., have been studied intensively [S]. Another typical candidate is anunonia (14). The primary n adduct 15 (triplet ground state) is stable enough to be detected by IR spectroscopy and does not spontaneously isomerize into the insertion product 16. However, this rearrangement with formation of aminosilylene 16 occurs upon photoexcitation (X, = 436 nm) of 15. Secondary irradiation of 16 (X, >310 nm) leads — as is already known [6] — to iminosilylene 17. 

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. 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-cataly2ed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] cataly2ed reaction, methyl acetate carbonylation is considered to go through formation of ethyUdene diacetate (33) ... 

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

The reaction occurs in the liquid phase at relatively low temperatures (about 50°C) in the presence of a solid acid catalyst. Few side reactions occur such as the hydration of isohutene to tertiary hutyl alcohol, and methanol dehydration and formation of dimethyl ether and water. However, only small amounts of these compounds are produced. Figure 5-8 is a simplified flow diagram of the BP Etherol process. 

It is proposed that the primary step in the formation of olefins involves the formation of a carbenoid species, [ CH2], which then inserts into a C—H bond of either methanol or dimethyl ether ... 

Wender and coworkers conclude that cobalt-catalyzed benzyl alcohol homologation involves the intermediate formation of car-bonium ions (8). However, since the methyl cation (CH3+) is unstable and difficult to form (9), it is more likely that methanol homologation to ethanol proceeds via nucleophilic attack on a protonated methyl alcohol molecule. Protonated dimethyl ether and methyl acetate forms have been invoked also by Braca (10), along with the subsequent formation of methyl-ruthenium moieties, to describe ruthenium catalyzed homologation to ethyl acetate. 

Methanol has been considered as a fuel for fuel-cell vehicles with on-board fuel processors for some time. Dimethyl ether (DME) has been suggested as a fuel alternative for diesel engines in Japan and Sweden. The synthesis of DME is based on methanol synthesis followed by DME formation ... 

Finally, an additional approach to using hydrocarbon fuels with Ni-based anodes involves using methanol and ethanol, molecules that carry sufficient oxygen to avoid carbon formation.Unlike the case with low-temperature fuel cells, methanol crossover is not an issue with ceramic membranes. Since methanol decomposes very readily to CO and H2. SOFC can operate with a very high performance using this fuel. ° ° In addition, recent work has shown promising performance levels with limited carbon deposition using dimethyl ether as fuel. ° ° ... 

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