Direct methane-to-ethylene conversion in a nanosecond pulsed discharge

Abstract

We report that gas phase plasma-assisted non-oxidative methane coupling can lead to formation of ethylene as major product at ~20 % yield per pass. This is attained by using a nanosecond pulsed discharge (NPD) reactor, featuring rapid product quenching rates, (recyclable) hydrogen co-feeding (CH4:H2=1:1) and elevated pressures (5 bar) at which NPD is ignited.

Process Modeling and Evaluation of Plasma-Assisted Ethylene Production from Methane

“…Three mass flow controllers (GF40 Series, Brooks Instrument, Hatfield, PA, USA) were employed to control reactants feed flowrates namely, CH 4 :H 2 = 1:1 v/v mixture, C 2 H 6 and CO 2 . H 2 was cofed with CH 4 to suppress carbon formation [11] and facilitate longer and stable operation, while C 2 H 6 and CO 2 were added to simulate shale gas composition. Detailed description of the experimental setup and plasma reactor performance optimization are reported in our previous works [11,12].…”

“…Nanosecond pulsed discharge (NPD) reactors, a relatively new technology of non-equilibrium plasma, are currently of great interest due to their high energy efficiency [10]. Ethylene can be produced as major product from methane in NPD reactors: (i) In one-step process, operating at elevated pressures (5 bar) [11], (ii) in two-step process, at atmospheric pressure, employing hybrid plasma-catalytic reactors, in which the acetylene produced in the plasma zone is subsequently hydrogenated to ethylene by a hydrogenation catalyst placed in the post-plasma zone at no additional cost [12]; this is because both heat and hydrogen required for the hydrogenation reaction are provided by methane cracking that takes place upstream, inside the plasma zone.…”

“…Two process alternatives are conceptually designed to deliver high purity ethylene (≥99% v/v): (i) A one-step plasma-assisted methane-to-ethylene route operating at 5 bar, and (ii) a hybrid plasma-catalytic methane-to-ethylene route operating at atmospheric pressure. The proof of concept of both processes has been successfully demonstrated in our lab [11,12]. Both process alternatives are simulated and also consider the technical limitations of the real industrial environment, while the economically favorable operating window (range of operating conditions at which the target product purity is met at minimum utility cost) is defined via sensitivity analysis using the Aspen Plus V10 process simulator.…”

Non‐oxidative methane conversion in diffuse, filamentary, and spark regimes of nanosecond repetitively pulsed discharge with negative polarity

“…The intensity of the OES depends on the population of the excited state produced by the excitation reactions. Luque et al [33,34] investigated the CH(A 2 Δ → X 2 Π) of DBD in detail, and suggested that the electron impact dissociative excitation of methane is the most likely channel for CH(A) state production as shown in Equations (11,12). Other mechanisms, such as direct excitation from the ground state CH, were not well known.…”

“…Other mechanisms, such as direct excitation from the ground state CH, were not well known. The Equations (11,12) are intermediate processes of the step-by-step electron dissociation as shown in Equation (6). It means the electron dissociation reactions are important in both diffuse discharge and filamentary discharge, but they are negligible in the spark discharge.…”