US1640314A - Process of manufacture of alkali-metal sulphides - Google Patents

Description

Patented Aug. 23, 1927.

UNITED STATES PATENT OFFICE.

HORACE FREEMAN, OF VANCOUVER, BRITISH COLUMBIA, CANADA, ASSIGNOR 0F ONE-HALF TO CANADA CARBIDE COMPANY, LIMITED, OF MONTREAL, CANADA.

PROCESS OF MANUFACTURE OF ALKALI-METAL SULPHIDES.

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This invention relates to improvements in the manufacture of sodium sulphide, and the primary object is to obtain a higher yield of an improved product, and in a less time than has heretofore been the case.

A further object is to overcome the inherent difliculties in dealing with sodium sulphide arising from its practically infusible nature.

A still further object is to render the electric furnace available for this manufacture.

At present sodium sulphide is commercially produced by heating to a bright red heat in a fuel fired furnace, a mixture of sodium sulphate with a carbonaceous reducingagent, such as coal or sawdust.

As sodium sulphate is fusible, and sodium sulphide is not fusible at temperatures which are commercially practicable in this art, it is found that when the proportion of sulphate predominates, as during the earlier stages of the reduction, the charge remains liquid. When about fifty per cent of sulphide is formed, the mass thickens and becomes more solid; as a consequence the necessary contact between the reacting particles is prevented and the reduction is checked.

For this reason, the product of this method of operation seldom contains more than sixty-five per cent of sodium sulphide and is obtained from the furnace in the form of a semi-solid mass, which is practically electrically non-conductive even when hot.

In carrying out this process I have found that the imperfections of this method of production, viz, the low grade of the fuel fired furnace product and the long period required for the reaction, are due to the in fusibility of sodium sulphide, which also introduces complications in its removal from the furnace.

An object of this invention is to render the furnace charge fusible throughout the period of operation and in some instances at a lower temperature than is generally used for the reduction. The charge being fluid, the reaction is more complete and the yield of sodium sulphide is greater also owing to its fluidity, the charge is electrically conductive enabling use of the electric furnace for heating in all stages, and further enabling the sulphide to be tapped from the furnace.

I have found that sodium sulphide which,

Serial No. 619,030.

in the pure state is infusible, or practically so, forms readily fusible compounds when mixed with other sulphides, such as those of potassium, calcium, barium, strontium, copper, zinc, lead, iron and many others.

During the course of a long investigation of the products so obtained, I have found that the lowering of the fusing point of sodium sulphide is particularly great when potassium sulphide is added to it: Thus, a mixture in proportion of one mole of sodium sulphide to one mole of potassium sulphide melts to a thin mobile liquid at 420 degrees centigrade, while the addition of only ten per cent of potassium sulphide to sodium sulphide produces a mixture melting at 570 degrees centigrade.

Furthermore, the double sulphides of sodium with lead, with zinc, with iron and With copper are very mobile liquids at tem' peratures much below 700 degrees centigrade. Also the double sulphides of sodium with the alkaline earth metals fuse readily at relatively low temperatures.

Of the alkaline earth metal sulphides, barium sulphide and calcium sulphide have an additional characteristic in common with the heavy metal sulphides, namely, they are insoluble in concentrated aqueous solutions of sodium sulphide. In this connection it may be noted that iron and barium sulphides are to some extent soluble in very dilute solutions of sodium sulphide.

In carrying out this process for the production of sodium sulphide the above described properties are made use of in the following manner according to the product it is desired to obtain.

If the product required is hydrated sodium sulphide, free from admixture with other sulphides, the reduction of sodium sulphate is carried out with a reducing agent, such as coal, in the ordinary manner, but when or before the previously mentioned thickening of the reacting mass takes place, a proportion of an insoluble sulphide is added sufficient to make the charge liquefy or to keep the same liquid. A very small proportion of the added sulphide will liquefy the charge at a temperature of 1000 degrees centigrade, while the addition of a molecular proportion of lead sulphide will cause liquefaction of the sodium sulphide at.550 degrees centigrade, and when a molecular pro'portion of zinc sulphide is used, at 620 degrees centigrade.

The common sulphide ores are used for this purpose or refined or recovered sulphides may be used as obtained in the later steps of the process.

The insoluble sulphide may be added to the charge of sulphate and its reducing agent prior to feeding them into the furnace, or it may be added at any subsequent stage in order to bring about the desired result, viz, the maintaining of the sodium sulphide in the reaction mixture in a liquid condition so that reduction may proceed to completion. As an alternative a metal sulphate may be added which will reduce to a sulphide to fuse with the sodium sulphide. During the period of reduction the carbon monoxide gas produced, easily and quietly escapes from the mobile liquid. When the evolution of gas ceases, reduction is complete and the charge may be tapped or poured from the furnace.

The product of this operation is sodium sulphide in admixture or combination with an insoluble sulphide. In order to obtain pure sodium sulphide from this material, it is necessary to lixiviate the mass with hot water. The sodium sulphide is readily dis solved in the water but the other metal sulphide remains undissolved in the form of an extremely fine suspension, which, however, quickly settles on account of its high specific gravity. The clear solution'of sodium sulphide is therefore easily separated and allowed to crystallize; the product of crystallization being sodium sulphide free from other sulphides. 1

It is obvious that the fine sludge of th added metal sulphide resulting from this operation is available after drying for re-use in the process of reduction.

If the sulphide product desired is that known as fused sodium sulphide and is to be used without further refinement by crystallization, the presence of an insoluble metal sulphide wouldrbe objectionable. The presence of potassium sulphide or a soluble alkaline earth metal sulphide is ordinarily not objectionable inasmuch as these sulphides will erform the same function as sodium sulphide in many of its various applications in the arts.

As previously stated, potassium sulphide is particularly effective in rendering sodium sulphide fusible in the process of reduction. Less than ten per cent of the potassium sulphide is required and in most cases less than ve per cent of the weight of sodium sulphide is a practicable pro ortion to use, al-

' though I do not desire to e confined to any particular proportion.

My process for producing the fused alkali metal sulphide consists in heating a mixture of sodium sulphate with the desired proportion of potassium sulphate and a carbonaceous reducing agent. Potassium sulphide is formed coincidentally with sodium sulphide and the charge remains liquid while the reduction is carried to completion. As an alternative I may add previously prepared potassium sulphide to the sodium sulphate charge undergoing reduction. The result is the same, i. e., the liquefaction of the charge.

The process may be operated similarly using alkaline earth metal sulphides admixed with the sodium sulphate.

The product can then be tapped or run from the furnace direct into containers for shipping, it may be cooled in moulds, or it may be quickly cooled on a rotating water- .cooled drum and produced in the form of flakes as is now done with caustic soda and with cyanid.

\Vith the process here described the time required for reduction is much shortened and a smaller amount of the reducing agent is used than in the process heretofore practised. The reduction is carried much farther than in the usual process, owing to the mobility of the charge in the furnace and the intimate contact of particles thereby provided.

I do not desire to be confined to any particular form of furnace in carrying out this process, but I prefer and have used an electric furnace for the purpose, utilizing the charge itself as the resistor. The electric furnace is preferred as it is more economical and avoids oxidation of the sulphide product which is apt to take place in a fuel fired furnace. My process for the first time makes the electric furnace available for this manufacture, allowing of the tapping of the liquid product and dispensing with the use of moving devices for stirring the charge.

In carrying out any of the variations of this process I may either add the desired sulphide or sulphides to the charge, or I may, as described, add the corresponding sulphate or sulphates or any other salts which will be reduced to sulphides coincident with the reduction of sodium sulphate. The roduct of the process here described contains lar er percentages of available sulphide than 1s at all possible by the method now commonly used.

Having now particularly described my invention, I hereby declare that what I claim as new and desire to be protected in by Letters'Patent, is:

1. A process of producing a sodium sulphide product of over 60% sodium sulphide content which consists in fusing sodium sulphate inpresence of a carbonaceous reducmolten condition until after substantially complete reduction of the sodium sulphate is effected.

2. The process ofproducing sodium sulphide which consists in fusing sodium sul phate with a carbonaceous reducing agent llil the presence of another alkali metal sulp ide.

3. The process ofproducing sodium sulphide which consists in fusing sodium sulphate with a carbonaceous reducin agent in the presence of potassium sulphi e.

4. The process of producing a sodium sulphide product of over sodium sulphide content which consists in fusing sodium sulphate in presence of a carbonaceous reducing agent and another sulphate, such as will be reduced to yield a sulphide during the reduction of the sodium sulphate, and heating the reaction to maintain the mixed sulphides in a fluid condition until after reduction of the sulphates is substantially complete.

5. The process of producing a sodium sulphide compound, which consists in heating a mixture of sodium sulphate and potassium sulphate with a'reducing agent at a temperature sufficient to maintain the reaction product in a molten condition.

6. The product which comprises sodium sulphide fused and associated with a sulphide of another alkali metal.

7 The product which includes sodium sulphide in amount upwards of 60%. of the whole and another metal sulphide, the said product being capable of liquefaction at temperatures a little over 1000 C.

8. The process of making sodium sulphide which comprises fusing together sodium sulphate equivalent to more than 60% sodium sulphide content of the final product and the sulphate of another metal in presence of a carbonaceous reducing agent, and maintaining the sulphide content of the mass molten until evolution of gas ceases.

9. The process of making sodium sulphide which comprises reducing together sodium sulphate equivalent to more than 60% sodium sulphide content of the final product and the sulphate of another metal by heating the same in presence of a carbonaceous reducing agent and maintaining the sulphide content of the reacting mass constantly in a molten condition.

10. In the manufacture of sodium sulphide by reduction of sodium sulphate with a carbonaceous reducing agent, the step of maintaining the formed sodium sulphide molten until substantially all the sodium sulphate has been reduced, which comprises carrying out the reduction in presence of less than 10% of the sulphide of another metal.

11. In the manufacture of sodium sulphide by reduction of sodium sulphate with maintainin a carbonaceous reducing agent, the step of the formed sodium sulphide molten unt1l substantially all of the sodium sulphate has been reduced, which comprises simultaneously reducing the sulphate of another metal in amount less than 10% of the sodium sulphate and retaining the formed sulphide in the reaction in presence of the sodium sulphide undergoing reduction.

12. In the manufacture of sodium sulphide by reduction of sodium sulphate with a carbonaceous reducing agent, the step of lowering the fusion temperature of the mixed sulphate and sulphide when containing'over 60% sulphide and maintaining the same molten at a temperature under 1500 C., which comprises carrying out the reduction in presence of the sulphide of another metal.

13. The process of producing sodium sulphide which comprises melting sodium sulphate with less than 10% of a soluble sulphide of another metal in presence of a carbonaceous reducing agent.

14. A process of making sodium sulphide by reduction of sodium sulphate with a carbonaceous reducing agent, which comprises fusing the sulphate in presence of the reducing agent and when the charge commences to thicken fluxing the same with the sulphide of another metal in amount suflicient to flux the formed sodium sulphide and maintain the same freely fluid until after substantially complete reduction of the sodium sulphate is effected.

15. A process of making sodium sulphide by reduction of sodium sulphate with'a carbonaceous reducing agent, which comprises fusing the sulphate in presence of the reducing agent and when the charge commences to thicken fiuxing the same with the sulphide of another metal in amount sufficient to flux the formed sodium sulphide and maintain the same freely fluid at a temperature over 1000 C. until after substantially complete reduction of the sodium sulphate is effected.

16. A process of making sodium sulphide which comprises heating sodium sulphate with a reducing agent to a temperature over 1000 C. in presence of less than 5% of the sulphide of another metal, whereby the sodium sulphide. is maintained in molten condition until after substantially complete reduction of the sodium sulphate is effected.

17. A process of making sodium sulphide which comprises heating sodium sulphate with a reducing agent to a temperature over 1000 C. in presence of less than 5%. of potassium sulphide, whereby the sodium 125 sulphide is maintained in molten condition until after substantially complete reduction of the sodium sulphate is efiected.

18. A process of making a fused sodium sulphide product of over 80% sodium sulphide content, which comprises fusing sodium sulphate with the sulphate or sul- Iphide of another metal in presence of a car- 'onaceous reducing agent.

19. A process of making a sodium sulphide product with substantially no sodium carbonate content, which comprises heating sodium sulphate with the sulphate of an other metal in presence of a carbonaceous reducing agent at a temperature over 1000 C.

20. A process of making'a sodium sul phide product with substantially no Sodium carbonate content, which comprises heating sodium sulphate with the sulphide of another metal in presence of a carbonaceous reducing agent at a temperature of approximately 1000 C.

21. A process of producing a sodium sulphide product of over 60% sodium sulphide content, which consists in fusing sodium sulphate in presence of a carbonaceous re-.

ducing agent and along with the sulphides of any other metals serving to flux the formed sodium sulphide and maintain the same in molten condition until after substantially complete reduction of the sodium sulphate is effected.

In testimony whereof I affix my signature.

HORACE FREEMAN.