Methane Coupling to Ethylene and Longer-Chain Hydrocarbons by Low-Energy Electrical Discharge in Microstructured Reactors

Abstract

The direct conversion of methane to longer hydrocarbons, including alkanes and alkenes (i.e., olefins), is achieved with a high energy and atom efficiency through the use of low-energy, nonthermal electric glow discharge plasmas acting on CH 4 / O 2 /N 2 and CH 4 /CO 2 /N 2 in a microstructured reactor. The process is neither dependent on limited lifetime catalysts nor consumable chemicals, enabling continuous operation over long periods. Similarly, it is carried out at atmospheric pressure and ambient temperature, thus simplifying process implementation. Because it does not require high temperatures, energy is not wasted producing sensible heat, allowing for high process energy efficiencies. Also, because it is designed in easy to number up modules, it can be readily scaled to the needs of the methane resource available. The effects of CH 4 /O 2 and CH 4 /CO 2 ratios, electric discharge current, flow rate, gap distance between electrodes, and the number of discharges on product distribution and energy efficiency were studied. Dependent on conditions, energy efficiencies in the order of 80%, methane conversion up to 75%, and carbon selectivity toward C 2+ products up to 90% can be achieved for these processes. The performance of this plasma-chemical microreaction system uses around two-thirds of the energy of that for the current commercial ethylene production process and is thus proposed as a promising alternative for industrial applications including valorization of stranded methane sources.

CO2 Reduction by Multiple Low-Energy Electric Discharges in a Microstructured Reactor: Experiments and Modeling

“…Characterization of Discharges within the Reactor. We have previously reported the I−V behavior of the electric discharge in our reactors, 31 and the I−V curve of the electric discharge with the diagnostic features (kilovolt level voltage, microampere level current, and voltage drop) usually can be divided into four major regimes (dark, spark, glow, and arc). The measurements on this multidischarge microreactor agree with this representative curve.…”

Longevity Demonstration of Methane to C2 via a Nonthermal Plasma Microreactor

“…Synthesis gas (H 2 and CO) has been commonly made in nonthermal plasmas with methane as a key reactant along with air or carbon dioxide. Although syngas production has been the goal of much of this research, ,,− there have also been studies focused on making larger hydrocarbons from methane. , In previous work at OSU, ,, carbon deposition on the electrodes over time harmed the operation of the reactor by making discharges unstable over time. At high methane fractions (>50% by mole), the discharge would short on the order of seconds to a minute.…”

Parametric Study of Hydrocarbon Chain Growth from Methane via a Nonthermal Plasma Discharge Microreactor

“…The reactor used in this work is similar to the one used by this research group in Miao et al to study mixtures of CH 4 /O 2 and CH 4 /CO 2 in a nonthermal plasma. 6 Plasma reforming of methane has been studied previously with the goal of making syngas (H 2 and CO) 3,5,7 rather than the production of larger hydrocarbons. A review of the related research on methane/CO 2 nonthermal plasma systems can be seen in Table S1 in the Supporting Information.…”

“…In the case of methane as the input species, the overall reaction of interest is an electron collision with a methane molecule leading to radical formation. If two of these radicals recombine, longer hydrocarbon chains can be built. In this study, carbon dioxide was used as the makeup gas to prevent rapid carbon deposition from the methane in the microreactor. The reactor used in this work is similar to the one used by this research group in Miao et al to study mixtures of CH 4 /O 2 and CH 4 /CO 2 in a nonthermal plasma . Plasma reforming of methane has been studied previously with the goal of making syngas (H 2 and CO) ,, rather than the production of larger hydrocarbons.…”