EP0157793A1

EP0157793A1 - Method for removing insoluble sulfide pads at oil/water interfaces

Info

Publication number: EP0157793A1
Application number: EP84903311A
Authority: EP
Inventors: Charles L. Kissel; Martin W. Preus; Steven A. Mayer
Original assignee: Magna Corp
Current assignee: Magna Corp
Priority date: 1983-10-12
Filing date: 1984-08-20
Publication date: 1985-10-16
Also published as: JPS60501496A; JPS6333404B2; WO1985001722A1; EP0157793A4; CA1222714A

Abstract

Procédé d'extraction de boues de sulfure métallique insoluble présentes dans des interfaces huile/eau, par l'addition de bioxyde de chlore.Process for the extraction of insoluble metal sulfide sludge present in oil / water interfaces, by the addition of chlorine dioxide.

Description

METHOD FOR REMOVING INSOLUBLE SULFIDE PADS AT OIL/WATER INTERFACES Field of the Invention Solid metallic sulfides are frequently encountered in petroleum processing equipment. In operations involving water and oil phase separations, such as in field dehydration systems, desalting plants, and the like, these solid metallic sulfides are particularly troublesome. They have low solubility in water or brines. The oleophilic characteristics of sulfides cause them to collect at the oil/water interface, to form sludges of a complicated nature. These sludges are generally referred to as "pads". The pads caused by the presence of the troublesome metallic sulfides drastically interfere with the efficient separation of crude oil from the associated aqueous medium. Under these conditions, a clearly defined interface between the oil and water phases is not present due to the emulsification effect exerted by the solid metallic sulfides. As a consequence, phase separation, desalting, and similar processes required in crude oil production and refining are slowed or interrupted. The presence of solid metallic sulfides at the oil/water interface forces large time, chemical, and energy expenditures to be utilized. This holds true for the oil phase, which must be purified before entering refineries, as well as the aqueous phase prior to disposal or discharge. In addition, these metallic sulfide-contain.ing pads create fouling of oil handling equipment, interfere with control and sensing equipment, and produce inherent corrosion at the points of contact within oil field vessels or other metallic equipment. Such effects as these add to the cost and complexity of petroleum processing. In addition, the quality and suitability of the oil for subsequent uses may be reduced by the occurrence of these interfacial sulfide precipitates.

Prior Art In the past, a variety of chemical methods have been employed in an attempt to alleviate the problems caused by solid metallic sulfides present at oil/water interfaces. Earlier efforts to solve this problem include the use of inorganic chloride containing chemicals such as hydrochloric acid, hypochlorous acid, alkali and alkaline earth hypochlorites, and chlorine. In addition, organic chemicals such as acrolein and various nonionic, cationic, and anionic surfactants have been employed.

Most of the inorganic chlorine-containing chemicals are required in relatively high concentrations and are very corrosive to the steels and other metals used in the construction of typical petroleum producing equipment. The pH's of the treated media are typically low under these conditions. The chemicals may also react with the petroleum, yielding hydrochloric acid and organic chlorides by decomposition. This alteration of the petroleum composition creates products that are poisonous to catalysts used in che refining process, which seriously affects refinery operations. Although the rate of solid metallic sulfide removal by hydrochloric acid and chlorine can be economically rapid enough, the action of hypochlorous acid and hypochlorite salts is quite slow.

Acrolein can be quite useful in removing insoluble metallic sulfides. However, typical applications of acrolein generally require long contact periods with the pads at the oil/water interface. Frequently, several applications of acrolein are required to eliminate the total insoluble metallic sulfide pad. The large amounts of acrolein chemical consumed under these circumstances can become quite expensive. Most applications involving nonionic, cationic, and anionic surfactants tend to remove the oil adhering to the solid metallic sulfide pad present in the oil/water interface but do not eliminate the solid metallic sulfides, so the interfacial pads reform quickly. Chlorine dioxide has been known to successfully remove hydrogen sulfide from aqueous media for many decades. U.S. Patent 4,077,879 discloses a process using chlorine dioxide to remove undesirable soluble sulfides from aqueous systems contaminated with small amounts of petroleum oils. However, removal of oil/water interfacial pads in bulk oil/water systems by chlorine dioxide in order to improve oil recovery has not previously been known.

Furthermore, any use of chlorine dioxide to treat soluble metallic sulfides is limited to aqueous media. It is generally known that the effects of solvents on chemical reactions can greatly alter observations. Chlorine dioxide is not known to be effective in treating insoluble metallic sulfides in the presence of oils.

Although some chemical approaches are available for removing metallic sulfide-containing pads at an oil/water interface, high cost or poor performance characteristics are usually encountered. The inventive process described hereinafter utilizes a chlorine dioxide application to treat the bulk properties of the oil/water interfacial pad caused by the solid metallic sulfides. This process is especially useful in that it allows rapid and low cost phase separations in treatment of crude oil to remove water, solids, salts, and other impurities. These steps are required before the petroleum can be sold, transported, and refined.

Specific references to chlorine dioxide removing insoluble iron and manganese sulfides in aqueous media can be found. However, references pertaining to other specific insoluble metals are not prominent in the literature. The inventive discovery of the fast action of chlorine dioxide in removing certain insoluble metallic sulfide pads in oil/water interfaces present in actual oil field tanks was unpredictable from prior processes and quite surprising.

In practicing the inventive process for removing insoluble metallic sulfides in oil/water separation equipment, various water quality improvements may also result as a side effect of the treatment, depending upon the amount of chlorine dioxide used and its point of application. Such improvements may include soluble sulfide removal, biocidal effects and others. However, these benefits are ancillary to the inventive process, which provides oil recovery and phase separation improvements regardless of whether these ancillary benefits are achieved. Summary of the Invention

Chlorine dioxide is used in a process for eliminating the effects of insoluble metallic sulfides in impeding the separation of oils from aqueous phases encountered in petroleum processing systems. This process involves adding aqueous chlorine -dioxide solution to the oil/water mixture containing an insoluble metallic sulfide interfacial pad. The process results in a clearly defined oil/water interface.

Description of the Invention Insoluble metallic sulfide interfacial pads are defined as interfacial interferences caused when metals and metallic ions combine with sulfur, hydrogen sulfide, or soluble sulfide salts to form insoluble metallic sulfides. Examples of such metals and ions include, but are not limited by, Ag, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sn, Ti, and Sn, separately or in any combined ratio. These insoluble metallic sulfides become attracted to the oil phase of an oil/water system, and collect at the oil/water interface. Typical oils found in oil field practices combined with these insoluble metallic sulfide pads can experience troublesome interfacial interferences in contact with aqueous media. This situation can also arise when dissolved gases and undissolved gases are present. Troublesome interfacial sulfide pads can be found in oil field tanks, free-water-knockouts, heater treaters, desalters, refinery distillate receivers, sumps, pits, and the like. These pieces of equipment can be involved in constant-flowing, intermittent-flowing, and static fluid conditions.

Chlorine dioxide solutions can be obtained from a variety of manufacturing processes. Typical processes include acid-chlorite, acid-chlorate, acid-hypochlorous acid-chlorite, acid-hypochlorite salts-chlorite, chlorine-chlorite, and the like, and any variation of these systems comprised of process adjuvants. The application of chlorine dioxide can be made into quiet, nonagitated petroleum processing equipment. Additionally, applications of chlorine dioxide can be accompanied by agitation of fluids within such equipment.

The temperature of the systems to which chlorine dioxide may be applied varies widely. The effectiveness of the inventive process is not very dependent on the temperature, and is found to be useful in petroleum-water separations at temperatures from low ambient to 200°C, or thereabouts. Some systems are operated under pressures to allow higher temperatures and lower fluid viscosities, which is helpful in the sedimentation and separation of phases. Higher temperatures appear to lessen somewhat the amount of chlorine dioxide required.

By the use of chlorine dioxide, insoluble metal sulfides are converted to a soluble form. Presumably, the petroleum oil that wets, i.e., clings to the surface of, the insoluble metal sulfide is able, after chlorine dioxide treatment, to migrate to the petroleum oil phase and is no longer a component of the emulsion. This then permits the clean separation of the petroleum oil from water phases. The mode of action of chlorine dioxide as described is believed to be correct and is given for better understanding, but is not intended to limit the scope of the invention.

Aqueous chlorine dioxide solutions can. be added to oil/water systems in a variety of different ways in order to remove insoluble interfacial sulfide pads. The chlorine dioxide may be added into the inlet lines upstream of the equipment containing the troublesome interfacial sulfide pads, Applications may also be made directly into the individual oil field equipment. The more cost effective applications appear to be those made into the oil phase proper.

Applications of chlorine dioxide can be made into oil field vessels experiencing continuous flowing, intermittent flowing, and stagnant fluid conditions. The time required for complete pad removal is lessened if the vessel can be agitated, e.g., such as rolling tank contents with gas.

Successful applications utilize up to about three moles chlorine dioxide per mole of insoluble metallic sulfide. These conditions result in lowering the pH of a given system by two or less pH units for an initial system pH range of 4 to 10 for metallic substances containing chromium, iron, manganese and vanadium, Systems comprised of cadmium, cobalt, lead, silver, tin, and tantalum appear to require more acidic final pH values. Lower amounts of chlorine dioxide, and subsequently lower drops in system pH levels, are realized if the process is carried out at higher temperatures.

The invention describing a method for removing insoluble metallic sulfide pads at oil/water interfaces is demonstrated by the following non-limiting examples; EXAMPLE 1

Ten screw cap test tubes were each filled with 1.0 mL ferric chloride solution (0.037M) and 1.0mL freshly prepared sodium sulfide solution (0.037M). Black iron sulfide precipitates formed immediately. These heterogeneous mixtures were diluted with 5.0 mL ASTM brine solution (4.2%, American Society Testing Materials, formula a, A.S.T.M. D-1141-52, Table 1, section 4). These solutions gave 3.7x10^-5 moles of sulfide and had a pH of 7.0. Then, 1.0 mL Nujol (trademark) mineral oil was added, the tubes were capped, and shaken vigorously for one minute. A heavy iron suifide pad formed at the oil/water interface in all tubes. Next, various amounts of chlorine dioxide solution (0.0266M) were added to each of the tubes and the results recorded.

This example demonstrates the ability of chlorine dioxi .de to remove an iron sulfide pad in a synthetic oil/water system, It is also clearly shown the pad can be removed without causing the pH of the aqueous solution to drop by more than 0.9 of a pH unit.

EXAMPLE 2 Three screw cap test tubes were each filled with 0.5 mL ferric chloride solution (0.037M) and 0.5 mL freshly prepared sodium sulfide solution (0.037M). The black iron sulfide precipitates were diluted with 2.0 mL deionized water and vigorously shaken with 0.5 mL various oils to provide a heavy pad at the oil/water interfaces. Then, 3.0x10^-6 moles chlorine dioxide were added. The initial pH of 6.5 fell to 6.0 after treatment with the chlorine dioxide, at a ratio of 0.62 moles of sulfide to 1.0 moles of chlorine dioxide.

TABLE 2 Oil Used Results

Mineral oil Pad removed; did not reform

23º API California Crude Pad removed; did not reform 35° API Arkansas Crude Pad removed; did not reform This example demonstrates that chlorine dioxide is effective in removing pads not only at the oil/water interface of synthetic oils, but also at interfaces between aqueous phases and actual crude oils.

EXAMPLE 3 Eight screw cap test tubes were charged with equal amounts of 0.037M ferric chloride and 0.037M sodium sulfide solutions. Then, 4.2% ASTM brine solution and mineral oil were added. The tubes were capped and shaken to obtain a heavy oil/water interfacial pad. These solutions had an initial pH of 7.0. Then, 1.11x10^-5 M chlorine dioxide solution was added, and the observations recorded.

TABLE 3

Moles of Ferric Chloride mL 4.2% mL Final a Sodium Sulfide ASTM Brine Nujol pH Observations

3 . 7 x 10^-6 5 . 0 1. 0 No pad formed initially

1.85 X 10-5 5.5 1.0 4.0 Pad removed

3.7 x 10-5 6.0 1.0 4.0 Pad removed

3.7 X 10^-6 10.0 1.0 No pad formed initially

3.7 X 10^-5 21.0 1.0 6.0 Pad removed

3.7 X 10^-5 6.0 5.0 6.0 Pad removed

3.7 X 10^-5 4,0 10.0 7.0 Pad removed

3.7 X 10^-5 11.0 10.0 7.0 Pad removed

These xamples demonstrate the ability of chlorine dioxide to remove various amounts of interfacial pads in varying oil to water systems.

EXAMPLE- 4 The ability of chlorine dioxide to remove oil/water interfacial sulfide pads in systems with varying pH's can also be demonstrated. Several screw cap test tubes were charged with 1.48x10 moles of ferric chloride and 1.48x10^-6 moles sodium sulfide. Each of these mixtures was diluted with 1.0mL various .pH buffer solutions and 0.5mL mineral oil. Upon shaking, heavy interfacial pads formed. Then, 0.037M chlorine dioxide solution was added and, in all cases, the pad was removed.

EXAMPLE 5

Chlorine dioxide can remove oil/water interfacial sulfide pads under a wide variety of temperatures. Several screw cap test tubes were charged with 1.0mL ferric chloride (0.037M) and 1.0mL freshly prepared sodium sulfide (0.037M). The resulting mixtures were diluted with 5.0mL of aqueous medium and 1.0mL mineral oil. Upon vigorous shaking, heavy sulfide interfacial pads formed. Then, the tubes were heated to various temperatures. Chlorine dioxide solution was then added at the elevated temperature and, in all cases, the sulfide interfacial pad was removed.

TABLE 5

Initial Temperature Moles Final

Medium PH (°C) C10₂ PH

4.2% ASTM 7 21 7.8 x 10^-6 6

4.2% ASTM 7 35 5.57 x 10^-6 7

4.2% ASTM 7 46 5.13 x 10^-6 7

These results demonstrate the effect of higher temperature on the ability of chlorine dioxide to remove interfacial sulfide pads. Adding heat to the oil/water system allows less chlorine dioxide to be used to accomplish pad removal. This decrease in the amount of chlorine dioxide produces an aqueous system with a higher pH.

EXAMPLE 6 Agitation of the oil/water system can greatly decrease the time required for a given amount of chlorine dioxide to remove an interfacial sulfide pad. Two 250mL flasks were charged with 5.0mL each of ferric chloride (0.037M) and sodium sulfide (0.037M) solutions. These mixtures were then diluted with 100ml ASTM brine (4.2%) and 50ml mineral oil. These systems were shaken to create a heavy interfacial sulfide pad. Then, 8.1 x 10^-6 moles of chlorine dioxide solution was added to the top portion of one flask without agitation. Six minutes were required to completely remove the pad under the undisturbed conditions. Again, 8.1x10^-6 moles chlorine dioxide was added to top portion of the other flask. A magnetic stirring bar was used to create a minor agitation condition at a spinning rate of 20 cps. Under these conditions, the pad disappeared in 30 seconds.

EXAMPLE 7

Chlorine dioxide can be used to remove oil/water interfacial sulfide pads containing metals other than iron. Several screw cap test tubes were charged with a soluble metallic salt and an equimolar amount of freshly prepared sodium sulfide solution. These mixtures were diluted with 4.2% ASTM brine and mineral oil. Then, chlorine dioxide solution was added which caused removal of the interfacial sulfide pad in all cases. The data are displayed below.

These observat:ions demonstrate that chlorine dioxide can remove interfacial pads formed from a variety of soluble metallic salts, including complex mixtures of these materials (not shown in this example), Chlorine dioxide is effective when added to oil/water systems at pH 1 to pH 11 in ratios of from as low as Is 100 moles of chlorine dioxide per mole of sulfide to as high as three moles of chlorine dioxide per mole of sulfide. These are not necessarily critical upper and lower limits, but generally define the most effective range of chlorine dioxide to sulfide ratios suitable for use in this invention. The concept of the invention, however, contemplates the use of effective amounts of chlorine dioxide being added to oil/water systems either in the oil phase or the water phase, or both, to contact the sulfide oil/water pad and to thereby eliminate the pad or prevent the formation of the sulfide pad.

Industrial Application This invention finds wide application in petroleum production and refining.

Claims

WHAT IS CLAIMED IS:

1. The method of eliminating sulfide pads at oil/water interfaces in the handling and processing of petroleum comprising the steps of introducing an effective amount of chlorine dioxide to the oil/water interface and causing the chlorine dioxide to react at said interface at a pH of from 1 to 11 with sulfides at said interface to disperse said sulfides from the oil/water interface.

2. The method of Claim 1 wherein the reaction is carried out from pH 4 to pH 9.

3. The method of Claim 1 or Claim 2 wherein chlorine dioxide is introduced in an amount to result in a ratio of from 1:100 to 3:1 chlorine dioxide to sulfide at said interface,

4, The method of Claim 1 wherein the chlorine dioxide is introduced in an effective amount of at least one part of chlorine dioxide for every one hundred parts of sulfide at the oil/water interface,

5, The method of Claim 1 wherein the chlorine dioxide is introduced in an effective amount of at least one part of chlorine dioxide for every thirty parts of sulfide at the oil/water interface.

6. The method of Claim 4 or Claim 5 in which causing the chlorine dioxide to react at said interface comprises agitating the oil/water interface.

7. The method of Claim 4 or Claim 5 in which causing the chlorine dioxide to react at said interface comprises heating the oil/water, interface from about 0°C to about 200°C.