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Methanol dehydration to dimethyl ether over strong-acid-modified diatomite catalysts
(2016-11-01)
Pranee, Watcharakorn
;
Neramittagapong, Sutasinee
;
Assawasaengrat, Pornsawan
;
Neramittagapong, Arthit
Dimethyl ether synthesis via methanol dehydration over strong-acid-modified (with sulfuric, hydrochloric and nitric acid) diatomite (DM) catalysts was conducted in a fixed-bed reactor with elevated temperature reaction from 250 to 350°C. The modified DM catalysts were characterized by using X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, fourier transform Raman spectroscopy, temperature-programmed desorption of ammonia, temperature-programmed of carbon dioxide, thermal gravimetric analysis, and solid-state 27Aluminum magic angle spinning/nuclear magnetic resonance spectroscopy. It was found that sulfuric-acid-modified DM catalyst yielded the highest DME selectivity (~99%). It was also revealed that methanol conversion depended on Al ions. The methanol conversion increased with Al(IV) but decreased with Al(V) and Al(VI).
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Methanol conversion to dimethyl ether over beta zeolites derived from bagasse fly ash
(2016-10-17)
Assawasangrat, Pornsawan
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Neramittagapong, Sutasinee
;
Pranee, Watcharakorn
;
Praserthdam, Piyasan
Catalytic performance of beta zeolites derived from bagasse fly ash for methanol dehydration to dimethyl ether, alternative fuel, was investigated. Amorphous silica extracted from bagasse fly ash, a tetraethylammonium hydroxide (TEAOH) were used as a precursor and a template for synthesis of beta-zeolites, respectively. Beta zeolites could be synthesized at a constant hydrothermal temperature of 135°C and a constant initial pressure of 3 bars under the nitrogen atmosphere. The crystallization time and Si/Al ratio were 48 h and 15, respectively. These conditions gave the highest crystallinity for beta zeolites with a crystal size of 0.51 μm as well as a Brunauer–Emmett–Teller surface area of 844 m2 g−1. Beta zeolites with the Si/Al ratios of 15.8 and 24.6 were used as catalysts for methanol conversion to dimethyl ether. Beta zeolites with the Si/Al ratios of 15.8 and 24.6 have the % yields of 84 and 60, respectively. According to the result of NH<inf>3</inf>-TPD, the beta zeolites with the Si/Al ratio of 15.8 showed higher acidity than beta zeolites with a Si/Al ratio of 24.6. Therefore, the beta zeolites with a Si/Al ratio of 15.8 were more efficiency in methanol conversion reaction than beta zeolites with a Si/Al ratio of 24.6.
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Dimethyl ether synthesis from methanol over diatomite catalyst modified using nitric acid treatment
(2016-08-02)
Pranee, Watcharakorn
;
Neramittagapong, Sutasinee
;
Assawasaengrat, Pornsawan
;
Neramittagapong, Arthit
Dimethyl ether synthesis from methanol over diatomite catalysts modified using nitric acid was investigated. The catalytic performance of diatomite was tested in a fixed-bed reactor under atmospheric pressure and within the temperature range of 250–350°C. It was discovered that high acidity of the catalyst yielded a higher methanol conversion rate. Moreover, it was revealed that the acidity of the catalyst surface was controlled by Al(IV) ions whereas basicity of the catalyst surface was determined by Al(V) and Al(VI) ions. From this finding, the authors were able to propose the mechanism of DME synthesis from methanol over treated diatomite.

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