CA2640857A1 - Methods and compositions for coating sulfur blocks - Google Patents

Abstract

The invention relates to methods and compositions for coating blocks of elemental sulfur for storage. The method of coating a sulfur block against atmospheric exposu re comprises the steps of: a) preparing a coating composition comprising an effective blend of silicone and aqueous sodium silicate; b) applying the coating composition to the elemental sulfur to create a continuous barrier between the elemental sulfur and the atmosphere; and c) allowing the coating composition to cure. The composition for sealing elemental sulfur against atmospheric exposure comprises an effective blend of silicone and aqueous sodium silicate.

Description

METHODS AND COMPOSITIONS FOR COATING SULFUR BLOCKS
FIELD OF THE INVENTION

[0001] The invention relates to methods and compositions for coating blocks of elemental sulfur for storage.

BACKGROUND OF THE INVENTION

[0002] Raw sulfur is obtained in large quantities from several sources including sour natural gas processing, heavy oil upgrading and light oil during refining.

[0003] The vast majority of the hydrogen sulphide removed from the sour gas and oil is converted into elemental sulfur. Elemental sulfur is at various times, sold and shipped in molten liquid form, processed into one of several solid particles for handling and where logistics and/or lack of demand dictate, poured and solidified into aboveground storage blocks. Molten (liquid) sulfur is red in color and when solid is a bright yellow color.

[0004] Elemental sulfur may be sold to customers around the world and is used primarily in the manufacture of sulfuric acid for a variety of uses including the manufacture of phosphate fertilizers. A smaller proportion of the sulfur market/supply is also used in making products including pharmaceuticals, plastics and rubber.

[0005] Importantly, when the sulfur production rate is higher than the demand for sulfur, sulfur is most often stored in blocks near or at a plant site where the sulfur originated with the result that permanent or very long-term storage of sulfur in some locations is required. At such storage facility sites, sulfur blocks may be as much as 20 m in height, 200m wide and have lengths greater than 500m. Smaller size blocks may also be made.
Industry forecasts generally indicate an increasing surplus of sulfur in traditional markets such as Canada and Kazakhstan.

[0006] The long-term storage of sulfur blocks as described above poses a number of problems as discussed below.

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[0007] One problem is fugitive dust emissions from the degradation of sulfur blocks by exposure to the weather, including degradation by sunlight, wind, rain and atmospheric freeze/thaw cycles.

[0008] In addition, degradation may occur by various sulfur consuming bacteria such as thiobacilli oxidans that is omnipresent in the environment and will naturally populate sulfur surfaces. Metabolites from these organisms include sulfuric acid.

[0009] Thus, as a result of these degradation mechanisms, the sulfur itself and the various by-products make their way into the surrounding environment, including the surrounding soil and ground water leading to various levels and types of contamination of the groundwater and the surrounding land. Furthermore, any precipitation that comes into contact with the sulfur and that is trapped by the blocks or in a containment facility requires testing and treatment prior to release of the contaminated water back to the environment.

[0010] Further still, in addition to the environmental issues associated with sulfur block degradation, another problem associated with sulfur blocks is that they are often perceived as unsightly due to the bright yellow color of the elemental sulfur.
Large piles of sulfur are often visible from a great distance and as a result, there is a negative public perception to the presence of sulfur in or around a community.

[0011] Finally, there is a fire-risk associated with large and dormant piles of sulfur. While relatively difficult to ignite, burning sulfur is a highly undesirable and polluting reaction that is potentially fatal to people and may be highly contaminating to the environment depending on the severity of a fire.

[0012] As a result, there has been a need for a technology to minimize the above problems relating to the short, medium and long-term storage of sulfur. More specifically, there has been a need for effective coating compositions that can minimize the risk of degradation, that have long-term stability when exposed to the weather elements, that can enhance the visual appearance of the sulfur blocks and that can minimize the fire-risk associated with the long-term storage of sulfur blocks. In addition, there has been a need for a coating system that is relatively inexpensive and that can be readily removed from the sulfur blocks for ultimate recovery of the sulfur.

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[0013] A review of the prior art indicates that no such coating compositions have been created or used. For example, while the following references teach various coating compositions, none are directed to inexpensive and effective compositions described by the present invention. More specifically, US Patent 4,238,536 discloses a method of coating coal with a gel; US Patent 6,344,236 discloses an acrylic copolymer coating composition; US Patent 5,330,788 discloses a temporary acrylic polymer or copolymer coating composition; US Patent 4,087,572 discloses a method of preventing environmental erosion with an organic polymer latex and a silicone; and US
Patent 2,854,347 discloses a method of erosion control of mineral products with rubber compounds.

SUMMARY OF THE INVENTION

[0014] In accordance with the invention, there is provided a method of sealing elemental sulfur against atmospheric exposure comprising the steps of: a) preparing a coating composition comprising an effective blend of silicone and aqueous sodium silicate and;
b) applying the coating composition to the elemental sulfur to create a continuous barrier between the elemental sulfur and the atmosphere.

[0015] In various embodiments the silicone:sodium silicate composition is 25:75 (w/w) to 75:25 (w/w), preferably 50:50 (w/w) to 30:70 (w/w) and more preferably 50:50 (w/w).

[0016] The method may further include adding a coloring agent to the coating composition.

[0017] The invention also provides a composition for sealing elemental sulfur comprising an effective blend of silicone and aqueous sodium silicate.

DETAILED DESCRIPTION

[0018] In accordance with the invention, effective sealing and coating compositions for coating sulfur blocks are described together with methods of coating sulfur blocks to provide an effective and removable weather-resistant barrier to the sulfur blocks, which at the same time allows the sulfur to `breathe'.

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[0019] As described below, preferred compositions for preparing sulfur block coatings in accordance with the invention include those that:

a. can be readily applied onto the exterior surfaces of sulfur blocks to provide an even coating;

b. are heat and cold resistant to and beyond normal atmospheric temperatures;

c. have good adherence to the sulfur;

d. are resistant to the penetration of water and sulfur bacteria;

e. allow for gases but not water to pass through the coating composition;
f. can be readily removed from the sulfur blocks;

g. are fire-resistant;

h. are relatively inexpensive; and i. can be colored.

[0020] Suitable compositions in accordance with the invention include effective mixtures of silicone and sodium silicates. In addition, the mixtures may include appropriate coloring agents. Neutral browns/greens/blues are preferred colors but any color is possible and may be selected in accordance with the invention.

[0021] The practical range of blends of silicone:silicates are 25:75 (w/w) to 75:25 (w/w), preferably 50:50 (w/w) to 30:70 (w/w) and more preferably 50:50 (w/w). A
preferred blend of 50:50 wt lo silicone:silicates provides effective liquefying/heat-spraying properties enabling the use of the composition with conventional spraying equipment. In addition, this composition after application onto a sulfur block can be readily removed by scraping. Silicone:silicates blends in the range of 50:50 wt% and 30:70 wt%
were particularly fire-resistant. Coloring agents may be added to the composition to impart desired colors. Alternatively, paints may be applied to the exterior of a cured coating.

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Sodium Silicate

[0022] Sodium silicate is a highly effective sealant. Commercial solutions of sodium silicate typically include approximately 40 wt% sodium silicate in water. The solutions have the appearance of clear water and can be applied to surfaces as paint.

Silicone

[0023] Silicone, or more specifically polymerized siloxanes or polysiloxanes, are mixed inorganic-organic polymers with the general chemical formula [RZSiO],,, where R =
organic groups such as methyl, ethyl, and phenyl. These materials consist of an inorganic silicon-oxygen backbone (...-Si-O-Si-O-Si-O-...) with organic side groups attached to the silicon atoms. In some cases organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions and can vary in consistency from liquid to gel to rubber to hard plastic.
Curing of silicones is highly variable and is based on the specific chemistry of the silicones. One class of silicones is moisture curing silicones that cure upon exposure to atmospheric moisture. In accordance with the invention, silicate/silicone solutions having sufficient viscosity to enable effective working properties and that result in a rubbery cured product while maintaining acceptable non-flammability properties are within the scope of the invention as understood by those skilled in the art.

[0024] Compositions in accordance with the invention are prepared by mixing appropriate volumes of sodium silicate (in water) with the silicone to create the desired wt% mixtures in the cured product. The water in the sodium silicate solution will promote composition curing (and will be substantially vaporized during curing) over a time period sufficient to enable acceptable composition working times. Generally, compositions in accordance with the invention will be a balance between the desired properties of final cured consistency (flexible rubber to hard rubber), fire-resistance and working time.
Increasing silicate concentration in the final composition will generally improve fire resistance properties and working time but will result in a product that is more rigid and less viscous. In contrast, increasing silicone concentration will result in a more flexible coating (thereby providing a thicker coating) but that will have decreased fire resistance.
Increased silicone concentration is also more expensive. Conventional residential I

silicone caulking materials from a local hardware store were utilized in preparing test compositions.

Methods of Application

[0025] In order to effectively apply the silicone:silicates coating compositions, it is preferred that the silicone:silicate compositions are applied at a temperature of at least C. While with appropriate equipment the compositions may be applied at lower temperatures, practically temperatures above 5 C are preferred. A texture gun or an air spray gun with a wide nose can be used for spraying the silicone and sodium silicate solution in addition to brushing equipment.

Surface Preparation

[0026] The coating compositions should be applied to clean surfaces. If necessary, the outer surfaces of the sulfur blocks should be cleaned of debris such as dust and dirt and should be dry.

Application

[0027] The silicone:silicate solutions may be applied by spraying, rolling, brushing or the like. Multiple coats of the solution may be applied and will usually require approximately 2 hours drying time between applications depending on the atmospheric conditions.

[0028] Silicone:silicate compositions may be applied by appropriate spraying equipment that may heat the composition to promote curing of the composition. Brushing or rolling of a silicone:silicates composition may also be used.

[0029] Ideally, thicknesses in the range of 1-5 mm and preferably 3mm will provide both satisfactory coating and performance properties at a reasonable price.

Examples

[0030] A mixture of silicone: silicates (National Silicates, Etobicoke, Ontario, 37.5 wt% in water as per Material Safety Data Sheet incorporated herein by reference) was prepared to a final concentration of 50:50 (silicone:silicates) wt%. The liquid mixture was applied to a sulfur block that had been cleared of surface debris by brushing. The semi-solid mixture (having a rubbery texture) was applied by brush to both the vertical and horizontal surfaces and fully solidified on the sulfur block within approximately 12 I

hours. No significant dripping or creep of the mixture was observed on the vertical surfaces. Within 24 hours, the coating had the appearance of a hard stone-like surface.
The coating was flexible and could be broken by hand with difficulty. Small sulfur blocks (a few kilograms each) coated with the coating composition as described above are hereinafter referred to as control blocks.

[0031] Other blocks were prepared with 25:75 wt% (silicone: silicates). The composition prior to coating showed acceptable working viscosity and resulted in a harder but thinner coated surface after curing. A further set of blocks were prepared with 75:25 wt%
(silicone: silicates). The composition showed acceptable working viscosity and resulted in a more rubbery surface after curing.

Burn Test

[0032] Control blocks were subjected to direct heating of the coating with an open flame placed against the coating. This test showed insignificant combustion when the open flame was directly against the coating. The coating would quickly self-extinguish when the open flame was removed. The surface temperature of the coating during this test was 1380 C.

[0033] The coating could subsequently be scraped from the sulfur blocks with a scraping tool and brushed from the control blocks for disposal.

Freeze/Thaw Cycle Test

[0034] In this test, control blocks were a) immersed in water for 24 hours; b) towel-dried and placed in a-20 C freezer for 16 hours and c) stored at 20 C for 24 hours. The above cycle was repeated 10 times. Mass change data was collected as well as photographic data.

[0035] These tests showed that after 10 cycles, the coating on the control blocks did not crack. In some samples, the underlying sulfur block would crumble but the coating remained intact.

Sunlight/Heat Test

[0036] Control blocks were placed in an enclosure and subjected to full spectrum visible light and an ultraviolet source. The enclosure was temperature and humidity controlled cycling between 90 C and 100% humidity to 0 C and 20% humidity over a 7 day I

period. After recovery, the control blocks were immersed in water to measure any mass change.

[0037] These tests showed that the control blocks had satisfactory sunlight/ultraviolet resistance as no appreciable change in the coating was observed at the conclusion of this test.

Abrasion Test

[0038] Control blocks were subjected to a stream of blown sand onto one side of the blocks simulating sand-carrying wind up to 50km/hour.

[0039] These tests showed that the control blocks had satisfactory abrasion resistance as no appreciable degradation in the coating was observed during the test.
Specifically, sand particles were observed bouncing off the coating without eroding the coating surface.

[0040] While the present invention has been described and illustrated with respect to preferred embodiments and preferred uses thereof, it is not to be so limited since modifications and changes can be made therein which are within the full, intended scope of the invention as understood by those skilled in the art.

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Claims (15)

1. A method of coating a sulfur block against atmospheric exposure comprising the steps of: a) preparing a coating composition comprising an effective blend of silicone and aqueous sodium silicate; b) applying the coating composition to the elemental sulfur to create a continuous barrier between the elemental sulfur and the atmosphere; and c) allowing the coating composition to cure.

2. A method as in claim 1 wherein the coating composition is blended to produce a viscosity sufficient to adhere to a vertical surface of a sulfur block to a thickness of at least 1 mm during and after curing.

3. A method as in any one of claims 1-2 wherein the silicone:sodium silicate mixture is 25:75 (w/w) to 75:25 (w/w).

4. A method as in claim 3 wherein the silicone:sodium silicate mixture is 50:50 (w/w) to 30:70 (w/w).

5. A method as in claim 3 wherein the silicone:sodium silicate mixture is 50:50 (w/w).

6. A method as in any one of claims 1-5 wherein the sodium silicate for step a) is 30-40 wt% in water.

7. A method as in any one of claims 1-6 wherein step a) further includes adding a coloring agent to the coating composition.

8. A method as in any one of claims 1-7 wherein the coating composition is applied to the sulfur block by spraying, brushing or rolling.

9. A method of sealing elemental sulfur against atmospheric exposure comprising the steps of applying a coating composition comprising a silicone:sodium silicate mixture ranging from 25:75 (w/w) to 75:25 (w/w) to a sulfur block to create a continuous barrier between the elemental sulfur and the atmosphere wherein the coating composition has a viscosity sufficient to adhere to a vertical surface of a sulfur block to a thickness of at least 1 mm during and after curing.

10. A composition for sealing elemental sulfur against atmospheric exposure comprising an effective blend of silicone and aqueous sodium silicate.

11. A composition as in claim 10 wherein the silicone:sodium silicate mixture is 25:75 (w/w) to 75:25 (w/w).

12. A composition as in claim 11 wherein the silicone:sodium silicate mixture is 50:50 (w/w) to 30:70 (w/w).

13. A method as in claim 12 wherein the silicone:sodium silicate mixture is 50:50 (w/w).

14. A composition as in any one of claims 9-13 further comprising a coloring agent.

15. A composition as in any one of claims 9-14 wherein the sodium silicate is wt% in water.