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1. WO2020109595 - ELECTROCHEMICAL REACTOR AND ITS CLEANING OR REGENERATION

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[ EN ]

Claims

1. An electrochemical reactor, suitable for reducing a dye to its leucodye, comprises at least four electrolytic cells (4), wherein the electrolytic cells are provided in the form of at least two stacks (6) of at least two electrolytic cells (4), said stacks (5) are connected in parallel and allow the separation of at least one stack (5) at a time for washing/regeneration of the cathode during suspension preparation while catholyte solution is circulated through the remaining one or more stacks (5), wherein the electrolytic cells (4) of each stack (5) are connected in parallel and wherein the electrolytic cells comprise a cathode compartment (41) and an anode compartment (42) separated by a separator (43), in particular a separator comprising a semipermeable mem brane, said cathode compartment (41) comprises a multi tude of freely suspended conductive, in particular non-spherical granules in contact with a conductor forming at least the side wall opposite to the separator, said cath ode compartment (41) is provided with an upper grid and a lower grid, the width of the mesh and the positioning of said grids are chosen such that the liquid catholyte can pass through them but the granules are prevented from passing through them so that they are retained in the cathode compartment (41), wherein the anode compartment (42) has a wall opposite to the common side wall formed by an electrode, wherein said cathode compartment (41) is connected to a main vessel (1) via a catholyte supply pipe (151) and a reduced catholyte return pipe (412b) for circulating catholyte through the cathode compartment (41), and said anode compartment (42) is connected to an anolyte vessel (3) via an anolyte supply pipe (31) and an anolyte return pipe (422b), wherein said cathode compart-ment (41) and said anode compartment (42) are also pro vided with means for supplying acidic cleaning solutions and water and optionally basic solution to the cathode compartment (41) and the anode compartment (42), said means comprise at least one cleaning medium supply pipe (61) and at least one cleaning medium removal pipe (62) at opposite ends of the cathode compartment (41) and of the anode compartment (42) for supplying and removing acidic cleaning solutions and water and preferably also a basic solution, said cleaning medium supply pipes (61) and said cleaning medium removal pipes (62) can be by passes of the catholyte supply pipe (151) and/or the anolyte supply pipe (31) , or independent pipes with own inlets and outlets adjacent to the ones of a catholyte circulation loop (15) or an anolyte circulation loop (33), said at least one cleaning medium supply pipe (61) is connected to at least one vessel (63a, 63b) for sup-plying acid and optionally base and is also connected to a water line supplying deionized water, and the at least one cleaning medium removal pipe (62) is connected to a waste water treatment plant (WWTP) or to a waste water vessel .

2. The electrochemical reactor of claim 1 comprising at least 6 stacks (5) and each stack comprising from 2 to 10 electrolytic cells (4), preferably 4 to 6 electrolytic dells, in particular 5 electrolytic cells, the at least 6 and preferably 6 stacks being connected such that at any time at least one of them and preferably one of them can be separated for being supplied with cleaning medium or water while the remaining stacks are connected such that the catholyte solution comprised in the stacks and the connecting pipes can be circulated through them.

3. The electrochemical reactor of claim 1 or 2 wherein the first vessel (2) and/or the main vessel (1) used for catholyte preparation are/is connected with the cathode compartments (41) of the electrolytic cells (4) of each stack (5) such that the first and/or main vessel can be supplied with water through each one of the stacks (5) independently.

4. The electrochemical reactor of any of the preceding claims, further comprising circulation means (64) allowing the acidic cleaning solutions and option ally the basic solution to be circulated via the cathode compartment (41) and/or the anode compartment (42) prior to being removed, said circulation means (64) preferably comprising at least one particle filter and/or at least one adsorption filter.

5. The electrochemical reactor of any of the preceding claims, wherein the cleaning medium supply pipes (61, 62) are connected with the catholyte supply pipes (151) and/or the anolyte supply pipes (31) feeding each stack.

6. The electrochemical reactor of any of the preceding claims, wherein the anodes of each stack are connected with the cleaning medium and water supply pipes (61) such that they can be individually controlled and e.g. washed simultaneously with or preferably inde pendently from the cathodes of the respective stack (5) .

7. The electrochemical reactor of any of the preceding claims, wherein at least the catholyte direc tion can be inverted, i.e. the inlet becomes the outlet and vice versa.

8. The electrochemical reactor of any of the preceding claims wherein the anode compartment (42) is placed in an anolyte circulation loop (33), said anolyte circulation loop being provided with an adsorption filter (332) for removing molecular impurities.

9. The electrochemical reactor of any of the preceding claims comprising a main vessel (1) for preparing a catholyte to be reduced by circulating a main suspension through a main suspension circulation loop (14) equipped with a main suspension circulation pump (P03) and preferably an ultrasound apparatus (141) and option ally a heating means, preferably a heat exchanger, in particular for raising the temperature to e.g. about 50°C to 65°C, preferably about 60°C.

10. The electrochemical reactor of any of the preceding claims comprising a main vessel (1) for prepar ing a catholyte, said main vessel (1) comprising a catho-lyte outlet (12), a catholyte circulation loop (15) with a catholyte supply pipe (151) equipped with a catholyte supply pump (P01) and optionally and preferably at least one of an ultrasound apparatus (154), a particle filter (152) in particular for removing particles of >50 to 100 pm and a catholyte heating means (153), in particular for raising the temperature to e.g. about 50°C to 65°C, said catholyte circulation loop (15) also comprising a cathode compartment (41) and a reduced catholyte return pipe (412b) returning the reduced catholyte via reduced catholyte inlet (13) into main vessel (1) .

11. The electrochemical reactor of any of the preceding claims comprising a first vessel (2) upstream of the main vessel (1), said first vessel (2) comprising a first suspension circulation loop (22) equipped with a first suspension circulation pump and an ultrasound appa-ratus (221) , preferably a cylindrical ultrasound appa ratus .

12. A method for cleaning electrochemical cells comprising a particulate cathode of an electrochem ical rector of any of the preceding claims, said method comprising

- removing the catholyte solution except the amount needed for suspension preparation and the amounts filling the elctrochemical cells and their connecting pipes,

- separating at least one stack (5) at a time for washing/regeneration of the cathodes during catholyte suspension preparation,

- circulating catholyte solution through the not separated one or more stacks (5) ,

- supplying deionized water through the cath ode compartments of the separated at least one stack (5) of electrolytic cells (4) into the main vessel (1) or the first vessel ( 2 ) ,

- isolating the separated at least one stack (5) from any catholyte suspension preparation and/or cir- culation,

- washing at least the cathode compartments (41) of the separated at least one stack (5) with acidic solution,

- optionally washing at least the cathode compartments (41) of the separated at least one stack (5) with basic solution, then

rinsing the acid and optionally base washed cathode compartments (41) of the separated at least one stack (5) with deionized water until neutral,

- joining the separated at least one stack

(5) with the other stacks (5) and starting catholyte re duction,

wherein the washing and rinsing is performed by supplying the washing solution or the rinsing water to one end of the electrochemical cell (4) and removing it at the opposite end and

wherein the washing solutions and the rinsing water removed from the compartments are forwarded to a waste water treatment plant (WWTP) or to a waste water vessel.

13. The method of any claims 12, wherein all anodes of one stack are cleaned together during the prep aration of a new batch of catholyte suspension but sepa rately from cathode cleaning, wherein anode washing com-prises the following steps:

- removing the catholyte solution except the amount needed for suspension preparation and the amounts filling the elctrochemical cells and their connecting pipes ,

- separating at least one stack (5) at a time for washing/regeneration of the anodes during catholyte suspension preparation,

- circulating catholyte solution through all stacks ( 5 ) ,

- washing the anode compartments (42) of the separated at least one stack (5) with acidic solution,

- optionally washing the anode compartments

(42) of the separated at least one stack (5) with basic solution, then

- rinsing the acid and optionally base washed anode compartments (42) of the separated at least one stack (5) with deionized water until neutral,

- joining the separated at least one stack (5) with the other stacks (5) and starting catholyte re duction,

wherein the washing and rinsing is performed by supplying the washing solution or the rinsing water to one end of the anode compartments and removing it at the opposite end and

wherein the washing solutions and the rinsing water removed from the anode compartments is forwarded to a waste water treatment plant (WWTP) or to a waste water vessel .

14. The method of claim 12 or 13, wherein the washing is performed with strong acids (pK < 1) by circulating the acidic solution through at least the cathode compartments (41) of the at least one separated stack (5) followed by rinsing the compartments (41) with water, op tionally and preferably after washing the compartments (41) with a base, preferably caustic soda.

15. The method of any of claims 12 to 14, wherein the strong acid is selected from the group con sisting of HC1, H2SO4, HNO3 and mixtures thereof.

16. The method of any of claims 12 to 15, wherein the catholyte is an indigo suspension and the catholyte solution is a leucoindigo solution.