Development of a continuous reactor for the electro-reduction of carbon dioxide to formate – Part 1: Process variables

Abstract

This paper reports an experimental investigation into the effects of five process variables on the performance of a bench-scale continuous electrochemical reactor used in the reduction of CO 2 to potassium formate, and interprets the data in terms of reactor engineering for a (speculative) industrial process for electro-reduction of CO 2 . The process variables: temperature, catholyte species, catholyte conductivity, cathode specific surface area and cathode thickness were studied, along with CO 2 pressure and current density, in a set of factorial and parametric experiments aimed to unravel their main effects and interactions. These variables showed complex interdependent effects on the reactor performance, as measured by the current efficiency and specific energy for generation of formate (HCO 2 ) ). The ''best'' result has a formate current efficiency of 86% at a superficial current density of 1.3 kA m )2 , with a product solution of 0.08 M KHCO 2 and specific electrochemical energy of 260 kWh per kmole formate. The combined results indicate good prospects for process optimization that could lead to development of an industrial scale reactor. NomenclatureC catholyte composition CE current efficiency (dimensionless) E cathode potential (VSHE) E cell full-cell operating voltage (absolute value) (V) E o Standard equilibrium electrode potential (VSHE) GDE gas diffusion electrode i geometric (superficial) current density (kA m )2 ) i max maximum geometric (superficial) current density (kA m )2 )Me cathode material P CO 2 pressure (Bar(abs) or kPa(abs)) P cathode cathode side pressure (kPa (abs)) T temperature (K) t operating time (h) X 1 , X 2 , X 3 factorial variables defined in Tables 6, 9, 10, 13, 14, 16 and 17 y volume fraction (i.e. mole fraction) in gas phase (dimensionless) s thickness of 3D cathode (m)

Formic Acid Manufacture: Carbon Dioxide Utilization Alternatives

“…Energy consumption is in the form of electricity or steam according to the nature of each individual process. Mass balances are based on the reaction of the CO 2 ER shown in Table 1, assuming neutral to alkaline conditions [29,30]. CO 2 and water are injected in the cathode.…”

Electrochemical Processing of Carbon Dioxide

“…This 3D tin cathode was incorporated into a single-cell laboratory reactor, whose configuration, specifications, and operating conditions are summarized in Figure 1 and Table 3. [30][31][32] The electrochemical reactor shown in Figure 1 was set up in the testing apparatus outlined in Figure 2, with provision to control and/or measure the relevant process variables such as the current and voltage, flow rates, pressures, temperatures, and stream compositions. A wide range of factorial and parametric experiments were carried out with this apparatus to observe the effects and interactions of the main process variables on the performance of the reactor (and in a smaller (14 A) reactor used in earlier work).…”

Development of a continuous reactor for the electro-reduction of carbon dioxide to formate – Part 2: Scale-up

“…superficial current density >1 kA m À2 and current efficiency >50%), followed by scaling-up to a multi-cell ''industrial'' reactor in an economically viable continuous electro-chemical process. Our previous communications [3,4] report work on the electro-reduction of CO 2 to formate in a laboratory benchscale single-cell continuous reactor with a cation membrane separator and ''trickle-bed'' 3D cathode 30 mm wide by 150 mm high (i.e. 45 · 10 À4 m 2 ), designated presently as Reactor A.…”