GB2185005A - Process for producing powder-like sulphur preparations - Google Patents

Abstract

The process comprises preparation of a sulphur suspension, dehydration thereof to a paste-like state (e.g. 10-20 wt % H2O), followed by granulation of the resulting paste. The process of this invention can be used mainly in the production and a granulated powder of sulphur employed for plant protection in the agriculture as a 0.5-1% aqueous suspension, as well as a vulcanizing agent in the production of rubber engineering goods.

Description

SPECIFICATION Process for producing powder-like sulphur preparations The present invention relates to processing of sulphur and, more particularly, to processes for producing powder-like sulphur preparations.

The most advantageous area of application of the present invention is the production of a granulated wettable powder of sulphur useful in plant protection as a 0.5-1% aqueous suspension. Another field of application of the present invention is the production of ground sulphur in the granulated form employed as a vulcanizing agent in the manufacture of tyres and rubber-engineering goods.

Other applications of the present invention involve processes for producing reagents, dry paints, pigments and other powder-like preparations, their production being characterized by fire and explosion hazards and toxicity of the dust-air mixtures formed.

A conventional process for producing powder-like sulphur preparations comprises grinding of elemental sulphur to the fineness depending on each particular application thereof, followed by mixing it with various additives.

A powder-like sulphur is a hazardous substance which, in addition, has the ability of accumulating electrostatic charges during its processing. This causes a number of undesirable phenomena in the treatment of sulphur: possibility of sparking or flash, bridging of powder-like sulphur in bins or cyclones, its aggregation, film-forming on the walls of pipelines and grinding equipment. A wettable powder of sulphur is also a fire-hazardous material (glowing temperature in a sulphur bed is 1800C), while its mixtures with air are explosive (the lower limit of ignition is 18 g/m3, self-ignition temperature is 455"C). The ignition temperature of ground sulphur is 207 C.

Control of these phenomena requires considerable expenses, special safety measures and does not guarantee a complete elimination thereof.

The modern level of development of the technology of manufacture of powder-like sulphur preparations necessitates a complete exclusion of fire- and explosion-hazard and toxicity in all stages of the production process, while ensuring a high quality of the final product. The main qualitative characteristics of a wettable powder of sulphur are stability of its 0.5% aqueous suspension (at least 75%) and wetting time (at most 2 minutes). To retain high quality during a long-time storage of the product (the use of a wettable powder of sulphur in the agriculture is a season campaign, while its production is effected all year long), an inert filler is added to the final product to prevent its caking, i.e. china clay (about 4%).

Known in the art is a process for producing powder-like disperse sulphur suitable for plant protection by grinding it at a moisture content of from 2 to 20% (cf. FRG Patent No.

1,024,934). The presence of moisture during the grinding process, especially in an amount of above 5%, in an effective measure to control fire- and explosion hazard, but the resulting wet product has a low quality, gets caked in storage and for this reason is not suitable for long-time keeping in storehouses. Upon storage the moisture dries out and on the account of gravitation forces and surface tension, as weil as adhesion, within the mass of the paste-like product non-uniformity of the composition takes place, sulphur particles stick to one another. This necessitates additional expenses for disintegration and homogenization of the product composition.

Also known in the art is a process for producing granulated sulphur from a powder thereof by introducing a binding agent containing a rubber latex, a high-purity mineral oil and a surfactant, followed by extrusion of the mixture through a die with predetermined diameter of its openings. The thus-produced threads are cut into cylinders of an appropriate length and dried (cf. US Patent No.

3,012,985).

This prior art process has disadvantages residing in the fire- and explosion-hazard character of the stage of the production of powderlike sulphur during which sulphur dust is formed which necessitates an obligatory use of an inert medium for sulphur grinding; they also reside in a complicated procedure and high rates of power consumption for a subsequent mixing of powder-like sulphur with the binding agent.

The closest prior art process most resembling that of the present invention as to the subject matter thereof is a process for producing a wettable powder from ground sulphur described in the USSR Inventor's Certificate No. 647248. The process comprises mixing ground sulphur with an aqueous solution of reagents (ammonium lignosulphonate and ammonia water), wet grinding of the mixture (secondary grinding), dehydration (drying) of the resulting suspension in the atmosphere of an inert gas, washing the gas with a cooled filtered return water and recycling the latter to mixing with sulphur. This prior art process for producing sulphur powder preparations has a disadvantage of fire- and explosion-hazards inherent to a preliminary stage of sulphur grinding (dry grinding in an inert atmosphere), drying and packing.It can be explained by dust formation at the above-mentioned stages, resulting in sulphur losses (up to 3%) and worsening of the personnel working conditions.

This prior art process has a disadvantage residing in a low quality-i.e. stability of the aqueous suspension of the powder not exceeding 70%. This is due to the fact that during the drying of the powder in a spray drier stability is reduced by 10-15% because of sintering of sulphur particles and fusing thereof. To minimize caking in a long-term storage, an inert filler such as china is added to the final product prior to packing thereof, but preparation and addition of the filler to the product requires additional expenses.

A process for the production of powder-like sulphur preparations according to the present invention comprises preparation of a suspension of sulphur, dehydration thereof to a paste-like state, followed by granulation of the resulting paste.

The process according to the present invention makes it possible to fully eliminate dust formation in all stages, including the preconditioning stage. This full elimination of dusting makes it possible to exclude fire- and explosion-hazard and toxicity during the manufcture and use of the product.

The process for producing sulphur preparations according to the present invention enables an essential improvement in quality of the final product. When used as a wettable powder of sulphur this improved quality is exhibited in a higher stability of an aqueous suspension of the preparation and uniformity of granules in respect of their mechanical strength in the use thereof in the manufacture of tyres and rubber-engineering goods. In contrast to drying to a dry powder-like state lowering stability of the product by 10-15%, the dehydration to a paste-like state and granulation do not lower the quality of the final product. The residual moisture in the product makes it possible to avoid overheating, sintering and fusing of sulphur particles.

Furthermore, the manufacture of the product in a granulated form suitable for application in, for example, agriculture, enables elimination of incorporation of inert additives for anti-caking purposes, thus reducing expenses for the manufacture of the final product.

In the preferred embodiment of the process according to the present invention the suspension dehydration is conducted to a moisture content of 10-20% by mass. This enables granulation of the mixture without impairing quality of the final product. The lower limit of the moisture content in the paste-like material is 10% owing to the fact that the subsequent stage of granulation at a moisture content below 10% requires considerable energy consumption, since the compressive strength during granulation is sharply increasing, thus making the process economically inefficient. Furthermore, as a result of growing forces of friction and compression a local heating of the paste is increased which results in aggregation of sulphur particles due to sintering and fusing, i.e. the final product quality is reduced.

The upper value of the moisture content in the paste prior to granulation (20%) is limited by the side effect of sticking of the resulting granules to one another.

It is advisable that the produced granules be subjected to drying. The granules produced by the process according to the present invention can be substantially immediately used in the agriculture or in the manufacture of tyres and rubber-engineering goods. However, in a longtime storage granules stick to each other.

Dried granules, on the contrary, do not lose their quality even in a long-time storage, since they are sufficiently durable.

Drying of the granulated product makes it possible to avoid the use of an inert gas for the production of which a considerable amount of fuel and energy resources is conumed (gas, mazout and the like).

It is desirable that the drying of granules be conducted at a temperature of not higher than 105"C.

At a temperature above 105"C the final product inferior in quality is obtained due to sintering of sulphur particles. This results in a lower stability of a wettable sulphur powder and non-uniformity of the granules produced in respect of their mechanical strength.

It is advisable in certain cases that the resulting large-size granules of the final product be subjected to disintegration (crushing). This enables a greater contact surface of the sulphur preparation with water in the production of an aqueous solution of a wettable powder of sulphur and with the basic rubber mix employed in the manufacture of tyres and rubberengineering articles.

Other objects and advantages of the present invention will now become more fully apparent from the following detailed description thereof illustrated by some specific examples of its particular embodiment.

The process for producing powder-like sulphur preparations according to the present invention comprises preparation of a sulphur suspension, dehydration thereof to a paste-like state, preferably to a moisture content of 10-20% by mass, granulation of the resulting paste and, when necessary, drying of the resulting granules at a temperature of not higher than 105"C and a further disintegration (crushing) thereof.

The suspension of sulphur is prepared by any conventional method (by wet grinding, in the course of processing of gas-purification masses, from solutions of a polysulphide by evaporation and the like); it is then delivered to dehydration which is also effected by any conventional method known in the art (filtration, centrifugation, mixing with the recycle of the dry final product) using conventional equipment currently employed in the industry. The granulation of the paste of sulphur can be also effected using any conventional apparatus currently employed in the art for this purpose. In the case of a long-time storage of the sulphur preparation the resulting granules are subjected to drying with the use of, for example, air or any other gas-carrier preheated to a temperature of not above 105"C.The disintegration stage is used where granules of a large particle size are obtained and it is necessary to have a lesser size thereof for a subsequent use.

Example 1 A suspension of sulphur with the stability of 90% produced by wet grinding of sulphur is dehydrated in a roll drier to the moisture content of 13%. The resulting paste is subjected to granulation by extrusion through a die in the form of threads with the diameter of 3 mm, then dried by air at the temperature of 80"C on a band drier. The stability of the thus-obtained sulphur preparation has remained unchanged and equal to 90%.

The resulting granulated product is not caked in storage and does not lose its quality for a long time.

A wettable powder of sulphur produced by the prior art process from a suspension of the same quality (90%) after drying in a spray drier has stability of 75%. Furthermore, its quality is considerably reduced during a long time storage due to caking thereof.

Example 2 A suspension of a wettable powder of sulphur (stability of 90%) produced by a wet grinding is supplied into a settling centrifuge with a screw-type discharge means. The paste dehydrated to the moisture content of 12% is subjected to granulation and drying at the temperature of 100 C. The final product has stability of 88%.

Example 3 A paste with the moisture content of 15% is produced by mixing a sulphur suspension with the recycle of the final product. The granulation and granule drying stages are conducted in a manner similar to that described in Example 1 hereinbefore. The final product stability is 90%.

Example 4 A suspension of sulphur produced by wet grinding is subjected to dehydration in a roll drier to the moisture content of 13%. The paste is then granulated and dried following the procedure described in Example 1.

The mechanical strength of the resulting granules (the amount of material passing through a sieve with a screen No. 09K, after tests, %) is the following: Sample 1 2.35-3.09 Sample 2 1.22-2.76 The analysis of the moisture evolved after dehydration and of the air employed for drying of granules in all of the Examples 1 to 4 has shown a complete lack of sulphur and the employed reagents in them.

Claims (8)

1. A process for producing powder-like sulphur preparations comprising preparation of a suspension of sulphur, dehydration thereof to a paste-like state, followed by granulation of the resulting paste.

2. A process according to Claim 1, wherein said dehydration of the suspension is conducted to a moisture content within the range of from 10 to 20% by mass.

3. A process according to Claim 1 or 2, wherein the resulting granules are subjected to drying.

4. A process according to Claim 1, 2 or 3, wherein said drying of the granules is effected at a temperature not exceeding 105"C.

5. A process according to Claim 1, 2, 3 or 4, wherein the granules are subjected to disintegration.

6. A process according to any of the foregoing Claims 1 to 5, substantially as described in the Specification.

7. A process for producing powder-like sulphur preparations, substantially as described herein with reference to Examples 1 to 4.

8. Powder-like sulphur preparations when produced in accordance with any preceding claim.