Electrochemical process and reactor

Abstract

A solid ion-conductive material can be used in a compartment of an electrochemical cell, such as between an anion exchange membrane and a cation exchange membrane, for improving energy efficiency and at least partially replacing electrolyte solution. The formed product can be obtained for instance in demi water.

Claims

1. A reactor system comprising an electrochemical cell reactor, wherein the electrochemical cell reactor comprises an anode, a cathode, a cation exchange membrane and an anion exchange membrane, wherein said anion exchange membrane is adjoined to said cathode or defines a catholyte compartment with said cathode, wherein the electrochemical cell reactor further comprises a product compartment between said cation exchange membrane and said anion exchange membrane, wherein said product compartment comprises an outlet for a liquid stream, wherein said product compartment comprises a solid ion-conductive material, wherein said solid ion-conductive material comprises an ion exchange material and has channels configured to permit a liquid to flow through said solid ion-conductive material to said outlet, wherein the product compartment has no inlet opening for liquids.

2. The reactor system according to claim 1, wherein said solid ion-conductive material is in contact with both said cation exchange membrane and said anion exchange membrane.

3. The reactor system according to claim 1, wherein said cathode is a gas diffusion electrode.

4. The reactor system according to claim 1, wherein said anion exchange membrane, said cation membrane, or both, are impermeable for convective flow of liquids.

5. A process for the electrochemical production of hydrogen peroxide in the reactor according to claim 1, the process comprising: producing H.sup.+ cations at the anode, producing HO.sub.2.sup.− anions at the cathode, transporting said H.sup.+ cations through the cation exchange membrane into the product compartment of said electrochemical cell, transporting said HO.sub.2.sup.− anions through the anion exchange membrane into said product compartment, wherein hydrogen peroxide is formed in said product compartment; and withdrawing a hydrogen peroxide solution with a concentration of at least 50 g H.sub.2O.sub.2/l through an outlet from said product compartment, wherein water molecules migrate with said anions through the anion exchange membrane and/or with said cations through the cation exchange membrane due to electro osmosis drag, and wherein all water is supplied into the product compartment through the membranes.

6. The process according to claim 5, wherein said solid ion-conductive material comprises cation exchange material and/or anion exchange material.

7. The process according to claim 5, wherein the hydrogen peroxide solution has an electrical conductivity of less than 50 mS/cm.

8. The process according to claim 5, wherein said product compartment comprises a fixed packed bed comprising cation exchange material resin beads.

9. The process according to claim 8 wherein said packed bed further comprises anion exchange material resin beads.

10. The process according to claim 5, wherein said solid ion-conductive material comprises a spacer comprising an ion exchange material.

11. The process according to claim 10, wherein said spacer is in the form of a woven or non-woven fabric and comprises fibers of the ion exchange material.

12. The process according to claim 5, wherein the pH of said hydrogen peroxide solution at said outlet is lower than 8.

13. The process according to claim 5, wherein said hydrogen peroxide solution has an electric conductivity lower than 5 mS/cm at said outlet.

Description

EXAMPLE 1

Comparative

(1) A plate-and-frame type electrochemical cell having 10 cm.sup.2 active surface area, with a compartment thickness of 2 mm was used and equipped with platinized titanium as anode from DeNora, with Nafion 115 as cation exchange membrane, with Neosepta AHA as anion exchange membrane and a gas diffusion electrode supplied by Gaskatel, Germany, i.e. with an anolyte compartment and a catholyte compartment. 75 ml 0.4 M KOH aqueous solution was used as catholyte, 40 ml 0.5 M K.sub.2SO.sub.4 aqueous solution as concentrate (in the middle compartment) and 75 ml 0.4 M H.sub.2SO.sub.4 aqueous solution as anolyte and were circulated from double walled glass vessels into the electrochemical cell and back into the glass vessels at 80 ml/min. Circulating concentrate illustrates no water feed to the concentrate compartment. Pure oxygen was supplied to the GDE at 80 ml/min. A Neslab RTE 7 thermostatic bath was used to maintain temperature between 10 and 25° C. Delta Elektronika ES 030-5 was used as power supply and set to 0.5 A, the cell voltage was monitored with a Metrahit 26M multimeter. The level of the electrolyte solutions was used to determine the volume during the experiment. Periodic sampling of catholyte and concentrate samples was done for determine hydrogen peroxide concentration by redox titration. Results are given in Table 1. The overall current efficiency was 83% with an energy consumption of 7.5 kWh/kg hydrogen peroxide. This example is comparative because no resin beads (or other solid ion-conductive materials) are used in the compartment between AEM and CEM.

(2) TABLE-US-00001 TABLE 1 Comparative Example 1 catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 3.8 0 0 3 3.4 0.19 0 15 3.4 1.0 0.02 30 3.5 1.8 0.11 45 3.5 2.7 0.26 60 3.5 3.6 0.53 75 3.5 4.3 0.86 90 3.5 5.0 1.2 120 3.5 6.3 2.4 150 3.5 7.3 3.7 180 3.5 8.2 5.3 240 3.8 9.3 8.9 300 3.8 10.2 53 13.0 13.3 60 2.2

EXAMPLE 2

Comparative

(3) Comparative Example 2 was carried out as Comparative Example 1, except with 80 ml catholyte and anolyte and 60 ml concentrate and operating at 1 A. Results are given in Table 2. The overall current efficiency was 82% with an energy consumption of 10 kWh/kg hydrogen peroxide.

(4) TABLE-US-00002 TABLE 2 Comparative Example 2 catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 — 0 0 3 4.8 0.45 0.04 15 4.8 1.8 0.09 30 5 3.2 0.32 45 5.3 4.8 0.79 60 5.5 5.9 1.4 75 5.5 7.1 2.3 90 5.5 8.1 3.6 120 5.5 9.2 6.5 150 5.8 9.1 9.9 180 5.8 10.5 13.4 240 6.0 11.5 20.0 300 6.0 12.2 52 13.1 25.8 51 2.8

EXAMPLE 3

Comparative

(5) As example 2, except with 100 ml catholyte and anolyte and having demineralized water as concentrate. Delta Elektronika SM120-25D was used as power supply for Example 3 and following examples. Example 3 is comparative. Results are given in Table 3. The overall current efficiency was 77% with an energy consumption of 174 kWh/kg hydrogen peroxide.

(6) TABLE-US-00003 TABLE 3 Comparative Example 3 catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 — 0 0 3 95 0.32 0 15 75 1.6 0.01 30 80 2.5 0.28 45 77 4.0 0.68 60 77 5.2 1.3 75 81 6.3 2.1 90 84 7.2 3.0 120 93 8.4 5.4 0.72 150 86 9.0 8.2 180 85 9.8 11.1 240 96 7.3 16.7 300 97 10.7 48 13.2 21.6 0.84 2.7

EXAMPLE 4

(7) As example 3, except with 90 ml catholyte and anolyte and with the concentrate compartment filled with Nafion NR50 beads resulting in a compartment thickness of 3.5 mm. Example 4 is according to the invention. The overall current efficiency was 80% with an energy consumption of 38 kWh/kg hydrogen peroxide. Results are given in Table 4.

(8) TABLE-US-00004 TABLE 4 Example 4 catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 — 0 0 3 18 0.32 0 15 19 1.6 0.05 30 21 3.3 0.32 45 21 4.6 0.75 60 21 5.8 1.4 75 23 6.8 2.4 90 25 7.7 3.4 120 25 9.0 6.2 150 28 9.9 9.3 180 29 10.5 12.9 240 30 11.2 19.2 300 30 11.7 50 13.1 24.8 1.6 2.4

EXAMPLE 5

Continuous Production

(9) As example 4, except with 10 ml catholyte and anolyte. Example 5 illustrates the invention. Continuous operation for 5820 minutes (97 hours) was enabled by continuous removal of product from the concentrate vessel, thus maintaining 55 ml as concentrate, and replenishing anolyte and catholyte volume using demineralized water to the original level. At t=5520 min. 0.4 M KOH and 0.4 M H.sub.2SO.sub.4 were used to replenish catholyte and anolyte. The overall current efficiency was 64% with an energy consumption of 80 kWh/kg hydrogen peroxide. Results are given in Table 5. The achieved H.sub.2O.sub.2 concentration, e.g. more than 50 g/kg, is acceptable.

(10) TABLE-US-00005 TABLE 5 Example 5 - Continuous production catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 0.0 0.0 3 26 0.31 0.0 15 28 1.4 0.0 30 27 2.7 0.22 45 28 4.0 0.57 60 30 5.6 1.1 75 34 6.0 1.9 90 37 6.9 2.7 120 39 8.3 5.2 150 40 9.0 7.8 180 40 9.9 11.2 240 41 10.3 17.0 300 38 10.9 22.8 301 — 1157 34 13.7 61.3 1158 34 1200 36 8.6 57.1 1260 36 8.4 61.9 1350 35 8.8 63.8 1380 37 9.3 63.9 1440 36 9.6 65.0 1500 35 9.3 63.5 1.24 1560 37 9.9 64.8 1620 35 10.1 64.7 1680 35 10.9 66.1 1682 39 7.1 67.0 2574 34 11.6 69.7 2580 38 6.9 70.0 2640 38 6.7 67.1 1.29 2700 36 7.0 67.8 2822 36 7.5 67.1 2940 36 7.9 68.9 3060 36 8.3 68.5 3065 35 6.0 68.1 0.95 4008 32 13.8 68.7 4020 32 9.7 65.0 4080 33 11.2 66.7 1.25 4144 33 12.2 64.4 4260 33 13.5 64.7 4404 30 14.3 55.8 4500 29 15.2 58.1 4505 24 4.7 57.5 5493 20 16.0 69.6 5520 21 12.2 67.7 5580 21 13.8 68.3 7.1 5640 21 14.7 66.8 5760 23 15.4 66.5 5820 22 15.7 65 13.2 67.2 5.38 1.7

EXAMPLE 6

(11) Example 6 is as example 1, except with 100 ml catholyte and anolyte and 60 ml demineralized water as concentrate with the concentrate compartment constructed out of two Nafion 1110 cation exchange membranes. Horizontal bars of approx. 2-3 mm width were cut out of one of the Nafion 1110 membranes. In this way, example 6 is according to the invention. The compartment construction is schematically illustrated in FIG. 9. Between Nafion 115 as CEM (101) and Neosepta AHA as AEM (104), two CEM membranes (102 and 103) were placed. Membrane 101 has inlet 106 and an outlet 107 opening and membrane 102 has an inlet 108 forming a liquid flow connection from inlet 106 to channels 105, and has outlet 109 forming a liquid flow connection from channels 105 to outlet 107. Hence, membrane 102 is configured for collecting liquid from the horizontal flow channels 105 in membrane 103, at opposed ends thereof, and flow therein into the outlet opening respectively inlet opening for concentrate in membrane 101. Horizontal flow channels 105 are for flow of demineralized water and have 2-3 mm width. Results are given in Table 6. The overall current efficiency was 94% with an energy consumption of 9.4 kWh/kg hydrogen peroxide.

(12) TABLE-US-00006 TABLE 6 Example 6 catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 — 0.0 0.0 3 4.5 0.21 0.02 15 4.8 0.79 0.03 30 5.2 1.6 0.09 45 5.4 2.4 0.17 60 5.6 3.1 0.31 75 5.8 3.9 0.45 90 6.0 4.4 0.68 120 6.0 5.6 1.3 150 6.4 6.7 2.2 180 7.5 7.6 3.4 240 5.2 9.0 6.2 300 5.1 10.0 48 13.2 9.5 4.6 2.2

EXAMPLE 7

(13) As example 6, except with 40 ml demineralized water as concentrate and operating at 1 A. Results are given in Table 7. Example 7 is according to the invention. The overall current efficiency was 68% with an energy consumption of 29 kWh/kg hydrogen peroxide.

(14) TABLE-US-00007 TABLE 7 Example 7 catholyte concentrate Time V.sub.cell H.sub.2O.sub.2 EC pH H.sub.2O.sub.2 EC pH [min] [V] [g/kg] [mS/cm] [—] [g/kg] [mS/cm] [—] 0 — 0.0 0.0 3 6.3 0.14 0.0 15 7.5 1.6 0.07 30 8.1 3.0 0.21 45 8.8 4.4 0.61 60 9.5 5.5 1.2 75 11 6.6 1.9 90 12 7.6 3.1 120 14 8.8 5.7 150 16 9.4 8.6 180 18 9.8 11.0 240 19 10.8 17.1 300 20 11.2 49 13.1 21.6 5.3 1.9

(15) The obtained results and further results are summarized in Table 8. Herein, concentrate refers to the compartment between AEM and CEM. CE is the current efficiency and EC is the electrical conductivity. Q is the energy consumption. For comparing results between concentrate compartments of 2 mm and 3.5 mm thickness, it must be taken into account that reducing the compartment thickness decreases Ohmic drop.

(16) TABLE-US-00008 TABLE 8 overview Time Current Concentrate/ H.sub.2O.sub.2 CE EC pH Q Ex. [h] [A] compartment [g/kg] [%] [mS/cm] [—] [kWh/kg] 1 5 0.5 0.5M K.sub.2SO.sub.4 13.3 83% 60 2.2 7.5 2 5 1.0 0.5M K.sub.2SO.sub.4 25.8 82% 51 2.8 10 3 5 1.0 Demi-water 21.6 77% 0.84 2.7 174 4 5 1.0 NR50 bead + 24.8 80% 1.6 2.4 38 demi-water 5 97 1.0 NR50 bead + ≈65 64% 0.95-5.38 1.7 80 demi-water 6 5 0.5 Nafion 9.5 94% 4.6 2.2 9.4 N1110 7 5 1.0 Nafion 21.6 68% 5.3 1.9 29 N1110