GB2058104A - Processing of sulphur - Google Patents

Abstract

A release agent which is durable when used in the release of sulphur during its processing comprises (A) a polydimethylsiloxane fluid having a viscosity at 25 DEG C of 20 to 100,000 centistokes, (B) a siloxane composed of SiO2 and (CH3)3SiO1/2 units in a ratio of 1:0.6 to 1:1.2, (C) a solvent for (B), and (D) a titanate. The release agent is dried on a metal substrate and molten sulphur is subsequently solidified on the substrate treated with the release agent whereby the release of the solidified sulphur from the substrate is enhanced.

Description

SPECIFICATION Processing of sulphur This invention relates to the processing of sulphur.

One of the significant sources of sulphur is as a by-product of sour gas refining. In the processing of such sulphur it is commonly placed in molten form on a metal belt where it is cooled to form a "slate" about 0.635 to 0.95 cm. thick, which slate is subsequently broken into chunks for ease of handling and shipping.

Problems occur in releasing the sulphur from the metal substrate. Thus there exists a need in the sulphur processing art for a release agent, preferably one with a reasonable degree of durability on the metal substrate. Moreover, if such a release agent were available, it would have utility in processing the sulphur into "bar" or other solid forms which involve the release from metal substrates.

U.S. Patent No. 4,011,326 describes certain carboxyfunctional siloxane fluids for improving release characteristics of metal substrates. Particular uses of such release agents are for metal fuser rolls in duplicating machines and for release of nylon from metal substrates.

U.S. Patent No. 4,076,695 discloses the incorporation of certain carboxy-functional siloxane fluids in polyurethane compositions for reaction injection moulding processes which imparts better release of the moulded part.

U.S. Patent No. 3,047,528 discloses that mixtures of certain carboxy-functional siloxanes, fillers, and a polyvalent metal compound can be heat-cured to form elastomeric products useful, inter alia, as gaskets and electrical component encapsulants. Titanium is disclosed as one of seventeen suitable polyvalent metals, with the compound tetrabutyl titanate being specifically disclosed.

The present invention relates to an improvement in the processing of sulphur which process includes the steps of placing molten sulphur on a metal substrate, cooling the molten sulphur to solid sulphur, and subsequently releasing the solidified sulphur from the metal substrate, the improvement comprising, prior to the time the molten sulphur is placed on the metal substrate, placing on the metal substrate a composition as defined below and then drying the composition on the metal substrate, whereby the release of the solidified sulphur from the metal substrate is facilitated.

The composition employed in the process according to the invention comprises (A) 70 to 85 percent (preferably 75 to 80) percent by weight of a trimethylsilyl endblocked polydimethylsiloxane fluid having a viscosity in the range of 20 to 100,000 centistokes at 25"C; (B) 5 to 15 percent (preferably 9 to 12 percent) by weight of a siloxane composed of SiO2 units and (CH3)3SiO112 units wherein the ratio of the SiO2 units to the (CH3)3SiO"2 units is in the range of 1:0.6 to 1:1.2; (C) 3 to 20 percent (preferably 8 to 12 percent) by weight of a solvent in which (B) is soluble; and (D) 0.1 to 10 percent (preferably 0.2 to 0.5 percent) by weight of a titanate having the general formula Ti(OR')4 wherein R' is an aliphatic hydrocarbon or a hydroxylated aliphatic hydrocarbon radical containing 1 to 12 carbon atoms.

One essential component in this composition is a titanate having the general formula Ti(OR')4. The R' radical can be any aliphatic hydrocarbon radical or any hydroxylated aliphatic hydrocarbon radical containing less than 13 carbon atoms. R' can be, for example, a methyl, ethyl, isopropyl, butyl, 2-ethylhexyl, decyl, dodecyl, octylene glycolyl, ethylene glycolyl or hexylene glycolyl radical. The R' groups can be the same or different, e.g. Ti(OCH3)2(OC2H5)(OC5H11).

As a general rule it should be remembered that as the amount of titanate used increases, the gel time changes and the pot life or useful length of time decreases.

Another essential component in the above composition is a trimethylsilyl endblocked polydimethylsilox ane fluid having a viscosity in the range of 20 to 100,000 centistokes at 25"C. Preferably this siioxane fluid has a viscosity in the range of 50 to 10,000 centistokes. Such siloxane fluids are well known throughout industry and are commercially available from a variety of sources.

Another component essential to the composition according to the invention is a siloxane composed of SiO2 units and (CH3)3SiO, 2 units wherein the ratio of the SiO2 units to the (CH3)3SiO1 2 units is in the range of 1:0.6 to 1:1.2. These siloxanes are also well known materials.

Afinal essential componentforthe composition ofthis invention is a solvent. The solvent employed must be one in which the siloxane containing SiO2 and (CH3)3SiO12 units is soluble. Because this siloxane is produced in a solvent solution, the siloxane-solvent solution as made can serve as the source of the solvent for the compositions of this invention. Also, the solvent and the amount of solvent in the compositions can be controlled by removal or addition of solvent by conventional techniques to achieve the desired level in the final composition. Specific examples of the organic solvents useful herein include benzene, toluene, xylene, trimethylpentanediol isobutyrate, perchloroethylene, Stoddard solvent and naphtha mineral spirits.

Generally speaking the hydrocabon solvents are preferred.

So far as is known at this time, the best method for preparing the compositions of this invention is first to mix the titanate and solvent and then to mix in the other ingredients. Other orders of mixing can be used but tend to cause the formation of gels.

The use of the above compositions in the process of this invention can be accomplished in a relatively simple and straightforward manner. The process involves applying the composition to the metal substrate which will be coming in contact with the molten sulphur and then drying the substrate is altered in some manner as by the deposition of a film thereon whereby the release of the sulphur therefrom is facilitated. The compositions can be applied to the metal substrate by any manner convenient to the user such as by spraying, brushing, dipping, flooding or wiping the composition thereon. Likewise, drying can be accomplished in any convenient manner as by simple air-drying (e.g. standing), by blowing air or other dry gas over the surface, or by heating to speed up the drying process.The amount of the composition applied to the substrate is not critical except in so far as enough must be applied to achieve the degree of improved release of the sulphur from the substrate that the processor desires. Obviously there will be a maximum amount which can be applied beyond which no additional benefit can be seen, and to use more would be wasteful.

The following Examples are given by way of illustration of the present invention. All parts and percents given herein are by weight, and all viscosities measured at25 C., unless otherwise specified.

Spatula Release Test In the following examples the various compositions described were evaluated for release characteristics using the following test procedure. A clean stainless steel spatula blade is dipped into the composition to be tested and the composition allowed to air dry on the blade at room temperature. The spatula blade is then laid flat on a table and a metal washer laid flat on top of the blade. Molten sulphur is then poured into the 1.43 cm. diameter hole (center) of the washer filling it, and the sulphur is allowed to solidify. A wire attached to a spring gauge (0 -2000 g) is hooked through a hole which has previously been drilled in the rim of the washer. The spring gauge is used to pull the sulphur (and washer) from the spatula, the pulling being done horizontally in a direction parallel to the surface of the spatula blade.The process is repeated to determine the number of times (releases) that a force of 1000 g. or less is required to release the sulphurfrom the spatula blade when the blade has been coated only once with the composition being tested. Crosshairs drawn on both the spatula blade and washer aid in positioning the washer in the same spot for the repeated tests in a series. When no coating is applied to the spatula blade in this test, a force of about 1500 g. to release the sulphur is required.

Example 1 The following compositions were prepared for evaluation in the above described spatula release test.

Compositions 1,2,3, 11, 12 and 13 were included for purposes of comparison while the other compositions represent various aspects of the invention.

1. (Comparison) A trimethylsilyl-endblocked polydimetylsiloxane fluid having a viscosity of 20 cs.

2. (Comparison) A carboxy functional siloxane fluid having the average general formula: (CH3)3SiO[(CH3)2SiO]46[(CH3)HOOCCH2SCH2CH2)SiO]2Si(CH3)3 3. (Comparison) A composition consisting essentially of 79 percent of a trimethylsilyl-endblocked polydimethylsiloxane fluid having a viscosity of 100 cs., 10.5 percent of a siloxane composed of SiO2 units and (CH3)3SiO1,2 units in which the ratio of the SiO2 units to the (CH3)3SiO1j2 units was in the range of 1:0.6 to 1:1.2 and 10.5 percent ofxylene.

4. A composition consisting essentially of 20 g. of composition (3), and 0.05 g of tetraisopropyl titanate.

5. A composition identical to composition (4) except 0.58 g of the titanate was used.

6. (Comparison) A carboxy-functional siloxane fluid having the average formula (CH3)3SiO[(CH3)2SiOJ95[(CH3)(HOOCCH2SCH2)SiOj3Si(CH3)3 7. (Comparison) A composition consisting essentially of 20 g of a siloxane composed of SiO2 units and (CH2)3SiO1,2 wherein the ratio of the SiO2 units to the (CH3)3SiO112 units is in the range of 1:0.6 to 1:1.2 and 0.58 g of tetraisopropyl titanate.

8. (Comparison) A composition identical to composition 7 except that 0.05 g of the titanate was used.

The results of the spatula release testing of the above compositions are set forth in the table below.

Composition Number of Releases Average of Tests Before 1000 g (1)* 4,7, 4 5 (2)* 9,9 9 (3)* 13,8 10.5 (4) 15,17,18 16.7 (5) 11,20,23 18 (6)* 6 6 (7)* 3 3 (8)* 2 2 * Included for comparison.

Example 2 This example illustrates the effect of the amount of solvent and titanate used.

The following compositions were prepared and evaluated in the spatula release test.

1. A composition consisting essentially of 15.8 g of a trimethylsilyl-endblocked polydimethylsiloxane fluid having a viscosity of 100 cs., 2.1 g of a siloxane composed of SiO2 units and (CH3)3SiO112 units in which the ratio of the SiO2 units to the (CH3)3SiO112 units was in the range of 1:0.6 to 1 :1.2, 2.19 of xylene and 1.5 g oftetraisopropyl titanate.

2. A composition identical to composition (1) except that 0.58 g of the tetraisopropyl titanate was used.

3. A composition identical to composition (1) except that 0.05 g of the tetraisopropyl was used.

The results of the spatula release testing of the above composition are set forth in the table below.

Composition Number of Releases Average of Tests Before 1000 9 (1) 16,14 15 (2) 11,20,23 18 (3) 15,17,18 16.7 Example 3 The compositions described hereinafter were prepared and evaluated in the spatula release test, the test results being set forth in the table following the description of the compositions.

1. A composition consisting essentially of about 2.86 g of a siloxane composed of SiO2 units and (CH3)3SiO1,2 units wherein the ratio of SiO2 units to the (CH3)2SiO112 units was in the range of 1:0.6 to 1:1.2, about 16.19 g of a trimethylsilyl-endblocked polydimethylsiloxane fluid having a viscosity of 100 cs., about 0.95 g of xylene, and 1.8 g of tetraisopropyl titanate.

2. A composition identical to composition (1) except that 0.96 g of the titanate was used.

3. A composition identical to composition (1) except that 0.79 of the titanate was used.

Composition Number of Releases Average of Tests Before 1000 9 (1) 14,10,11 11.7 (2) 19,11 15 (3) 15,12 13.5

Claims (5)

1. A process for processing sulphur which comprises placing molten sulphur on a metal substrate, cooling the molten sulphur until it solidifies and subsequently releasing the solidified sulphur from the substrate wherein, prior to the placement of the molten sulphur on the substrate, a composition is placed on the metal substrate and dried thereon whereby the release of the solidified sulphur from the substrate is enhanced, and wherein the composition comprises: (A) 70 to 85 percent by weight of a trimethylsilyl-endblocked polydimethylsiloxane fluid having a viscosity in the range of 20 to 100,000 centi-stokes at 25"C; (B) 5 to 15 percent by weight of a siloxane composed of SiO2 units and (CH3)3SiO1,2 units wherein the ratio of the SiO2 units to the (CH3)3SiOs 2 units is in the range of 1:0.6 to 1::1.2; (C) 3 to 20 percent by weight of a solvent in which (B) is soluble; and (D) 0.1 to 10 percent by weight of a titanate having the general formula Ti(OR')4 wherein R' is an aliphatic hydrocarbon or a hydroxylated aliphatic hydrocarbon radical containing from 1 to 12 carbon atoms.

2. A process according to claim 1, wherein the composition comprises 75 to 80 percent of component (A); 9 to 12 percent of component (B); 8 to 12 percent of component (C); and 0.2 to 0.5 percent of component (D).

3. A process according to claim 1 or 2, wherein component (A) has a viscosity in the range of 50 to 10,000 centistokes; component (C) is a hydrocarbon solvent; and in component (D) R' is an aliphatic hydrocarbon radical.

4. A process according to claim 3, wherein component (A) has a viscosity of substantially 100 centistokes; component (C) is xylene; and component (D) is tetraisopropyl titanate.

5. A process according to claim 1, substantially as herein described with reference to any of the specific Examples.