Process and system for the electrochemical reduction of oxalic acid
The present disclosure concerns a process and a system for the electrochemical reduction of oxalic acid to glyoxylic acid. The process involves withdrawing a portion of oxalic acid-depleted catholyte from the process and contacting it with a quantity of solid oxalic acid to provide a concentrated oxalic acid solution which is re-entered into the process.
1. A process for the electrochemical reduction of oxalic acid to glyoxylic acid, wherein the process is performed in an electrochemical cell comprising a cathode compartment containing a cathode, an anode compartment containing an anode, and an ion exchange membrane separating the anode compartment from the cathode compartment, wherein the process comprises the steps of:
(a) feeding an anolyte comprising an acid to the anode compartment;
(b) feeding a liquid catholyte comprising an aqueous oxalic acid solution to the cathode compartment, wherein the liquid catholyte is moving in a catholyte loop by being passed from a catholyte holding tank into the cathode compartment, over the surface of the cathode, being removed from the cathode compartment as an oxalic acid-depleted catholyte and returned to the catholyte holding tank;
(c) applying an electric potential difference between the cathode and the anode sufficient to produce a glyoxylic acid recoverable from the cathode compartment,
wherein during the process one or more quantities of concentrated oxalic acid solution are provided to the liquid catholyte by the steps of:
(d) withdrawing a portion of the oxalic acid-depleted catholyte and contacting it with a quantity of solid oxalic acid to provide a concentrated oxalic acid solution; and
(e) feeding at least a portion of the concentrated oxalic acid solution to the catholyte holding tank.
2. The process according to claim 1 , wherein the oxalic acid-depleted catholyte is withdrawn from the catholyte holding tank.
3. The process according to claim 1 , wherein the oxalic acid-depleted catholyte is withdrawn from the catholyte loop upstream of the catholyte holding tank.
4. The process according to claim 1 , wherein the withdrawn portion of oxalic acid-depleted catholyte is contacted with the quantity of solid oxalic acid by feeding it through a column comprising solid oxalic acid to provide the concentrated oxalic acid solution.
5. The process according to claim 1 , wherein the concentration of oxalic acid in the catholyte loop is determined intermittently or continuously.
6. The process according to claim 1 , wherein the concentration of oxalic acid is determined in the catholyte loop upstream of the cathode compartment.
7. The process according to claim 1 , wherein the one or more quantities of concentrated oxalic acid solution are provided to the liquid catholyte if the concentration of oxalic acid in the liquid catholyte fed to the cathode compartment fails below a predetermined level.
8. The process according to claim 1 , wherein the concentration of oxalic acid in the catholyte holding tank is maintained in the range of 0.05 to 10 M.
9. The process according to claim 1 , wherein the concentration ratio of glyoxylic acid to oxalic acid in the cathode compartment is maintained in the range of 0.2:1 to 12:1.
10. The process according to claim 1 , wherein the concentration of oxalic acid in the liquid catholyte fed to the cathode compartment is measured continuously.