Ethylene Epoxidation over Alumina-Supported Silver Catalysts in Low-Temperature AC Corona Discharge

Abstract

In this paper, the epoxidation of ethylene over different catalysts-namely Ag/(low-surface-area, LSA)a-Al 2 O 3 , Ag/(high-surface-area, HSA)c-Al 2 O 3 , and Au-Ag/ (HSA)c-Al 2 O 3 -in a low-temperature corona discharge system was investigated. In a comparison among the studied catalysts, the Ag/(LSA)a-Al 2 O 3 catalyst was found to offer the highest selectivity for ethylene oxide, as well as the lowest selectivity for carbon dioxide and carbon monoxide. The selectivity for ethylene oxide increased with increasing applied voltage, while the selectivity for ethylene oxide remained unchanged when the frequency was varied in the range of 300-500 Hz. Nevertheless, the selectivity for ethylene oxide decreased with increasing frequency beyond 500 Hz. The optimum Ag loading on (LSA)a-Al 2 O 3 was found to be 12.5 wt.%, at which a maximum ethylene oxide selectivity of 12.9% was obtained at the optimum applied voltage and input frequency of 15 kV and 500 Hz, respectively. Under these optimum conditions, the power consumption was found to be 12.6 9 10 -16 W s/molecule of ethylene oxide produced. In addition, a low oxygen-to-ethylene molar ratio and a low feed flow rate were also experimentally found to be beneficial for the ethylene epoxidation.

Combined Reforming and Partial Oxidation of CO2-Containing Natural Gas Using an AC Multistage Gliding Arc Discharge System: Effect of Stage Number of Plasma Reactors

“…The electrical discharge produced also provides heat to the system, apart from generating radicals and excited species to initiate and enhance the plasma chemical reactions [8]. Furthermore, the plasma reforming processes can be operated at mild conditions with less energy consumption, and they have been employed for many applications [9][10][11][12][13][14][15][16].…”

Ethylene Epoxidation in Low-Temperature AC Dielectric Barrier Discharge: Effect of Electrode Geometry

“…In this work, the feed O 2 /C 2 H 4 molar ratio was investigated in the range of 0.2:1-1:1 (O 2 -lean conditions) [18,19], while the other process parameters were fixed at an applied voltage of 19 kV, an input frequency of 500 Hz, and a feed flow rate of 50 cm 3 /min. Figure 2a illustrates both the C 2 H 4 and O 2 conversions as a function of feed O 2 /C 2 H 4 molar ratio of the cylindrical DBD and parallel DBD reactors.…”

“…From the previous works, even though both of the studied plasma systems provided a high potential for the ethylene epoxidation, the DBD system with a parallel electrode geometry [18] was experimentally proven to exhibit superior epoxidation performance compared to the corona discharge system with a pin-plate electrode geometry [19]. The results indicated the influences of the electrode geometry and the corresponding discharge generation on the ethylene epoxidation activity.…”

“…The high side voltage and current were thereby calculated by multiplying and dividing by a factor of 130, respectively, according to a specification of the transformer. A power analyzer was used to measure power, frequency, and voltage at the low voltage side of the power supply unit [18][19][20][21][22][23]. Reactant gases (ethylene, oxygen, and helium) fed through each of the DBD reactors with different electrode geometries were controlled by a set of electronic mass flow controllers and transducers, supplied by SIERRA Ò Instrument Inc., to obtain a feed gas mixture having different oxygen-to-ethylene molar ratios.…”

“…Recently, non-thermal plasmas, such as in dielectric barrier discharge (DBD) and corona discharge, have been used, for the first time, for ethylene epoxidation by our research group [18,19]; the plasma discharges containing highly energetic electrons can be used to activate the reactant molecules at low bulk-gas temperatures even without the presence of a catalyst. From the previous works, even though both of the studied plasma systems provided a high potential for the ethylene epoxidation, the DBD system with a parallel electrode geometry [18] was experimentally proven to exhibit superior epoxidation performance compared to the corona discharge system with a pin-plate electrode geometry [19].…”