US2285858A - Electrolytic process for the production of quinone and hydroquinone - Google Patents

Description

Patented June 9, 1942 2,285,858 ELECTROLYTIC PROCESS FOR THE PRO- DUCTION F QUINON E QUINONE A ND unmo- Sydney Horrobin and RandalGeorge Arthur New,

- Blackley, Manchester, England, assignors to Imperial Chemical Industries Limited, a corpov ration of Great Britain No Drawing.

271,604. In Great Britain May 3, 1938 11 Claims. (Cl. 204-78) This invention relates to the manufacture of p-benzoquinone and hydroquinone. More spe cifically it relates to the manufacture of p-benzoquinone by the electrolytic oxidation of benzene in sulphuric acid medium, and to the manufacture of hydroquinone by the reduction of the p-benzoquinone. In British Patent Specification No. 430,572 there is described a process forthe production of p-benzoquinone wherein benzene is passed through or stirred with an electrolyte, preferably consisting of dilute sulphuric acid or a mixture of sulphuric acid and a soluble sulphate, such as sodium sulphate, and subjected to electrolysis in an electrolytic cell in which an active and stable anode of lead or an alloy of lead and an inactive cathode are disposed, preferably close to each other, the concentration of p-benzoquinone in the cell being kept low by its continuous or frequent removal. In the same specification there is also described an improved process for the production of hydroquinone from the dilute solution of pbenzoquinone in benzene resulting from the electrolytic oxidation, the said process comprising reducing at about the boiling point of benzene and under such conditions that the benzene is immediately distilled off and the hydroquinone obtained dissolved in water.

The above processes have the disadvantage that there is a considerable loss of benzene due to entrainment in the gases which are evolved from the cell. They also have to be operated as batch processes and are not susceptible of continuous operation.

This invention has as an object to devise a new and improved process for the manufacture of p-benzoquinone and hydroquinone. A further object is to devise such a process which can be operated as a continuous process. A further ob. ject is to devise such a process which will avoid substantially all the loss of benzene associated with the known processes. Further objects will appear hereinafter. These objects are accomplished by the following invention. 7

We have now found that instead of passing the benzene through or mixing it with the electrolyte in the cell, as in the above process, the benzene may b electrolysed entirely as a solution in dilute sulphuric acid; and that the use of such a solution has the advantage that the loss of benzene, which occurs with the above mentioned process, and which is due largely to the entrainment of the benzene in the gases which are evolved from the cell, is entirely or almost entirely avoided. We have also found when using such a solution, that if the solution after flowing through the cell, has benzene passed through it, th p-benzoquinone is absorbed in the benzene and at the same time the dilute sulphuric acid is replenished with benzene and so prepared for passing through the cell again, and consequently the process may be made a circulating one. We

have found that such a circulating process has the advantages over the above-mentioned process, firstly that any stoppage of the process to replenish thecell, is avoided, and secondly that agitation is unnnecessary, and consequently electrolytic cells, which are free from moving parts, may be employed.

Our invention accordingly consists of a process for the manufacture of p-benzoquinone by the electrolytic oxidation of benzene in solution in sulphuric acid, using an anode of lead or of an alloy of lead, which has been activated by the 'electrodeposition of a film of lead peroxide on its surface, and a cathode consisting of metal unaffected by the electrolyte, characterised in that the benzene is present in the electrolyte only as a solution in dilute sulphuric acid and that the electrolyte is circulated through the electrolytic cell and outside the cell is brought into contact with benzene in which p-benzoquinone is absorbed and the electrolyte replenished with benzene, the p benzoquinone beingsubsequently removed from the benzene;

In working according to the invention the nature and preparation of the electrodes the current density, the acid strength, and the temperature of the electrolyte may be substantially the same as described in the above-mentioned specification. Thus the lead alloy may consist of a hard alloy of lead containing antimony or bismuth. The temperature of the electrolyte is conveniently 2530 C. The electrodes, however are preferably disposed in the form of closely spaced parallel plates with sheets of cloth placed be-' tween and close to the cathodes, in such a manner that the circulating liquor flows between the cloths and the anodes.

Our invention also comprises a process for the production of hydroquinone which comprises the reduction of the p-benzoquinone obtained in solution in benzene as described immediately above, the reduction being effected for example, as described in the above-mentioned specification.

The following example illustrates how the process of the invention may be carried into effect but does not limit the invention.

r 1 Example The electrolytic cell employed contains two anodes, both sides of each being used in electrolysis, the total anode area being about 17 dmF, and 4 cathodes each used on one side only. The anodes and cathodes are both of pure lead, the former consisting of plain sheets and the latter of perforated sheets. Each anode is separated from each of the adjacent cathodes by /2 inch sheets of woollen cloth bein fixed between close to the surface of the cathode. linlets and outlets for the electrolyte are provided at the bottom of the cell, which is so arranged that the acid flows consecutively over each of the 4 anode surfaces. The cathodic hydrogen passes through holes in the cathode to a compartment at the back isolated from the rest of the cell. 7

To activate the anodes the cell is filled with a 10% solution of sulphuric acid, and a current of 40 amps. passed with the anodes positive. As soon as the voltage is seen to rise rapidly the current is reversed. This procedure is carried on for about 1 hour, and a steady current of 40 amps. is then passed, with the anodes positive, for a further hour. In this way an active surface is produced on the anodes. The cell is then ready for use.

10% sulphuric acid containing dissolved benzene is now circulated at the rate of 30 litres per hour through the cell, down a glass column and back through the cell, continuously. The temperature of the acid is 25-30" C. and a current of 40 amps. corresponding to an anode current density of 2.4 amps./dm. is passed through the cell. The glass column, 185 cms. long and ofinternal diameter 5.5 cms. is packed with inch unglazed porcelain rings. Benzene from a reservoir rises up the glass column at a rate of to 1 litre per hour thus meeting and intermingling with the sulphuric acid which has come from the cell and extracting therefrom the quinone, which is then reduced to hydroquinone by iron and acid as described in British Specification No. 430,572.

The cell is kept in continuous operation until the acid becomes fouled with oxidation products of benzene which dissolve in the electrolyte. The electrolyte is then discarded, the acid renewed, and the cell put into operation again after the anodes have been activated as already described.

As many apparently widely different embodimentsof this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A process for the manufacture of p-benzoquinone which comprises subjecting a solution of benzene in an electrolyte to electrolytic oxidation in a cell forming p-benzoquinone, withdrawing from said cell electrolyte containing p-benzoquinone, passing said electrolyte outside said cell in contact with additional benzene thereby extracting said p-benzoquinone and replenishing said electrolyte with benzene, removing benzene containing the extracted p-benzoquinone from contact with said electrolyte, and returning to said cell the electrolyte containing benzene abscrbed from the aforesaid contact.

2. A process for the manufacture of p-benzoquinone which comprises subjecting a solution of benzene in dilute sulphuric acid to electrolytic oxidation in a cell forming p-benzoquinone, withdrawing from said cell dilute sulphuric acid conquinone, passing said electrolyte outside said cell lit in counter-current contact with additional benzene thereby extracting said p-benzoquinone and replenishing said electrolyte with benzene, removing benzene containin the extracted p-benzoquinone from contact with said electrolyte, and returning to said cell the electrolyte containing benzene absorbed from the aforesaid contact.

l. In a process for the manufacture of hydroquinone by reduction of p-benzoquinone, the steps which comprise subjecting a solution of benzene in an electrolyte to. electrolytic oxidation in a cell forming p-benzoquinone, withdrawing from said cell electrolyte containing pbenzoquinone, passing said electrolyte outside said cell in contact with fresh benzene thereby extracting said p-benzoquinone, forming a solution thereof in said fresh benzene and replenishing said electrolyte with benzene, removing fresh. benzene containing the extracted p-benzoqui- I none entirely in solution from contact with said electrolyte for reduction of the p-benzoquinone entirely in solution in said fresh benzene to hydroquinone, and subjecting benzene absorbed in the electrolyte from said contact step to electrolytic oxidation as aforesaid.

5. A continuous process for the manufacture of p-benzoquinone which comprises subjecting benzene entirely in solution in a dilute electrolyte to electrolytic oxidation in a cell forming p-benzoquinone, characterized in that only such amount of benzene is present in said electrolyte as can be maintained entirely in solution therein, withdrawing from the cell during said process electrolyte containing p-benzoquinone, removing from said electrolyte outside said cell p-benzoquinone, contacting a dilute electrolyte outside said cell with fresh benzene forming a solution thereof in said electrolyte and introducing to the cell during said process said electrolyte containing benzene entirely in solution.

6. A continuous process for the manufacture of p-benzoquinone which comprises subjectingbenzene entirely in solution in dilute sulphuric acid to electrolytic oxidation in a cell forming 'p-benzoquinone, characterized in that only such electrolytic oxidation in'a cell forming 'p-benzoquinone, characterized in that only such amount of benzene is present in said electrolyte as can be maintained entirely in solution therein, withdrawing from the cell during said process electrolyte containing p-benzoquinone, removing from said electrolyte outside said cell p-benzoquinone, contacting said electrolyte with fresh benzene forming a solution thereof in said electrolyte and recycling to the cell during said process said electrolyte containing benzene entirely in solution.

8. A continuous process for the manufacture of p-benzoquinone which comprises subjecting benzene entirely in solution in dilute sulphuric acid to electrolytic oxidation in a cell forming p-benzoquinone, characterized in that only such amount of benzene is present in said dilute sulphuric acid as can be maintained entirely in solution therein, withdrawing from the cell during said process dilute sulphuric acid containing p-benzoquinone, removing from said dilute sulphuric acid outside said cell p-benzoquinone, contacting said dilute sulphuric acid with fresh benzene forming a solution thereof in said dilute sulphuric acid and recycling to the cell during said process said dilute sulphuric acid containing benzene entirely in solution.

9. In a process for the manufacture of hydroquinone by reduction of p-benzoquinone, the steps which comprise subjecting a solution of benzene in dilute sulphuric acid to electrolytic oxidation in a cell forming p-benzoquinone, withdrawing from said cell dilute sulphuric'acid containing p-benzoquinone, passing said dilute sulphuric acid outside said cell in contact with fresh benzene thereby extracting said p-benzoquinone, forming a solution thereof in said fresh benzene and replenishing said dilute sulphuric acid with benzene, removing fresh benzene containing the extracted p-benzoquinone entirely in solution from contact with said dilute sulphuric acid for reduction of the p-benzoquinone entirely in solution in said fresh benzene to hydroquinone, and subjecting benzene absorbed in the dilute sulphuric acid from said contact step to electrolytic oxidation as aforesaid.

10. A process for the manufacture of p-benzoquinone which comprises subjecting benzene entirely in solution in a dilute electrolyte to electrolytic oxidation in a cell forming 'p-benzoquinone,withdrawing from said cell electrolyte containing p-benzoquinone, passing said electrolyte outside said cell in contact with additional benzene thereby extracting said p-benzoquinone and replenishing said electrolyte with benzene, removing benzene containing the extracted p-benzoquinone from contactwith said electrolyte, and subjecting benzene absorbed in the electrolyte from said contact to electrolytic oxidation as aforesaid.

11. A process for the manufacture of p-benzo- I quinone which comprises subjecting benzene endilute sulphuric acid from said contact to electrolytic oxidation as aforesaid.

SYDNEY HORROBIN. RANDAL GEORGE ARTHUR NEW.