Methanol and 2-methyl-1-propanol (isobutanol) coupling to ethers and dehydration over Nafion H: Selectivity, kinetics, and mechanism
- Lehigh Univ., Bethlehem, PA (United States)
The dehydration of a mixture of methanol and isobutanol has been studied over the sulfonic acid Nafion H catalyst. Dehydration products consisted of dimethyl ether (DME), di-isobutyl ether (DIBE), methyl-isobutyl ether (MIBE), butenes, octenes, and traces of methyl-tertiarybutyl ether (MTBE). At low temperatures and high alcohol pressures (P [ge] 150 kPa), the dehydration product slate was dominated by ether formation with selectivity within the ethers significantly in favor of the mixed ether, MIBE. The rates of ether and butene formation as a function of alcohol pressure could be described by Langmuir-Hinshelwood kinetics in which competitive adsorption of the two alcohols on the surface -SO[sub 3]H sites was the dominant feature. The kinetics of isobutanol dehydration to isobutene were consistent with a dual-site mechanism involving the cooperative action of a free surface -SO[sub 3]H site and an adjacent adsorbed alcohol molecule. Dehydration to ethers was consistent with the reaction of two adsorbed alcohols, also by a dual-site mechanism. As a consequence, dehydration to symmetric ethers showed saturation-type kinetics as a function of alcohol pressure, while the rate of isobutene formation went through a distinct maximum. Due to the competitive adsorption of methanol and isobutanol, the mixed ether MIBE was formed at a maximum rate with an optimum ratio of partial pressures of the two alcohols. The high selectivity to MIBE was explained by stronger adsorption of isobutanol on the catalyst surface as compared to methanol. The absence of MTBE and the predominance of products such as MIBE and 2,5-dimethylhexene suggests that dehydration to give free carbenium ions that subsequently rearrange to the more stable tertiary intermediate was not occurring. It was proposed that the alcohols react with the -SO[sub 3]H groups to give oxonium ions or esters. These intermediates couple to give the product ethers or octenes. 24 refs., 13 figs., 1 tab.
- DOE Contract Number:
- AC22-90PC90044
- OSTI ID:
- 6298240
- Journal Information:
- Journal of Catalysis; (United States), Vol. 139:2; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
10 SYNTHETIC FUELS
BUTANOLS
DEHYDRATION
ETHERS
CHEMICAL PREPARATION
METHANOL
ADSORPTION
BUTENES
CATALYSTS
CHEMICAL REACTION KINETICS
COUPLING
ESTERS
HETEROGENEOUS CATALYSIS
IONS
METHYL ETHER
OCTENES
OXONIUM IONS
REACTION INTERMEDIATES
SATURATION
SULFONIC ACIDS
ALCOHOLS
ALKENES
CATALYSIS
CHARGED PARTICLES
HYDROCARBONS
HYDROXY COMPOUNDS
KINETICS
MOLECULAR IONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
REACTION KINETICS
SORPTION
SYNTHESIS
400201* - Chemical & Physicochemical Properties
100200 - Synthetic Fuels- Production- (1990-)