Electrolytic oil purifying method

Abstract

Sulfur is removed from liquid hydrocarbon oils such as crude oil by subjecting a mixture of the oil and an electrolyte to a direct current field at a relatively high current and low voltage for causing oxidation, reduction or other electrochemical reaction of the sulfur or sulfur-containing material enabling ready separation and removal of the sulfur from the oil.

Description

The present invention relates to the removal of sulfur from hydrocarbon liquids, especially hydrocarbon oils such as crude oil.

It is an object of the present invention to reduce the sulfur content of hydrocarbon liquids, particularly crude oil.

It is another object of the invention to provide a process for purifying crude oil and other hydrocarbon liquids which is readily carried out at relatively low cost.

A particular object of the invention is to provide a process of the above type wherein the sulfur content is reduced by electrochemical means.

Other objects and advantages will become apparent from the following description and the appended claims.

With the above objects in view, the present invention in one of its aspects relates to the method of electro-chemically removing sulfur from hydrocarbon liquids including sulfur-containing materials which comprises mixing the hydrocarbon liquid with an ion-producing compound selected from the group consisting of inorganic electrolytes and ionizing organic solvents, and subjecting the thus obtained mixture to an electrical DC field having a voltage in the range of about 2 to 120 volts and a current of at least about 0.001 amperes per square centimeter, and recovering the hydrocarbon liquid in which the sulfur-containing materials have been substantially reduced.

In general, it has been found in accordance with the invention that the use of relatively high current at low voltages in the electrolyte-oil mixture promotes the oxidation (or reduction, as the case may be) of sulfur contaminants in the oil, resulting in precipitation or volatilization of sulfur compounds which are thereby removed from the oil mixture.

As will be understood, the sulfur components in crude oil may be of various types. It is known that the sulfur content of petroleum may vary from less than 0.1% to 10% by weight depending upon the source. This sulfur may be present as free sulfur, hydrogen sulfide, mercaptans, disulfides, cyclic sulfides or thiophenes. The present refinery methods for removal of sulfur, such as hydro-desulfurization, require the use of relatively cumbersome apparatus and expensive processes. The electrochemical process of this invention, on the other hand, is a relatively simple inexpensive desulfurization method.

In the electrolysis of any particular oil-electrolyte mixture to produce an electrochemical reaction in accordance with the invention, under the same conditions certain sulfur compounds may be oxidized, others may be reduced, some may be precipitated, some may be volatilized and others may be deposited on the electrode surfaces. From experiments carried out in the course of practicing the invention, it appears that oxidation is the predominant reaction, and oxidation products such as sulfonic acids and sulfur oxides have been identified. The reduction of sulfur compounds has been indicated by the production of H.sub.2 S volatilized during the process.

The removal or reduction of sulfur in accordance with the principles of the invention may be carried out using various sulfur-containing hydrocarbon liquids or oils mixed with various ion-producing compounds. For example, hydrocarbons such as mineral oil and crude oil from various geographical sources have been satisfactorily treated by the electrochemical process of the invention.

The inorganic electrolyte with which the hydrocarbon liquid may be mixed may be in the form of an aqueous solution of a salt or alkali base in concentrations high enough to obtain an electrically conducting system. Such solutions may contain, for example, a salt or base such as sodium chloride, lithium chloride, potassium chloride, strontium chloride, sodium nitrate, lithium nitrate, potassium nitrate, sodium carbonate, potassium carbonate, calcium carbonate, barium carbonate, sodium hydroxide, potassium hydroxide, calcium hydroxide, and barium hydroxide.

Ionizing organic solvents which may be used in combination with the hydrocarbon liquid include methanol, benzene, nitrobenzene, toluene, xylene, and glacial acetic acid. Many other inorganic and organic compounds will also be found suitable for use in practicing the present invention.

In general, the electrolysis of the oil-electrolyte mixture is carried out in a DC electrical field having a voltage in the range of about 2 to 120 volts and a current of between .001 to 25 amperes per square centimeter, with a preferred voltage range of about 2 to 10 volts being used in most cases. The concentration of the ionizing compound employed in the mixture will depend mainly on the spacing, surface area and configuration of the electrodes. For any particular conditions, the amount of the ionizing material used should be such as to provide a conductivity which results in a voltage of the system in the range set forth above.

The process of the present invention will be illustrated by the following examples, it being understood that the invention is not intended to be limited thereby. In the experiments described below, the electrolysis was carried out in a 100 ml flask equipped with two standard platinum electrodes. The anode was a cylinder of platinum mesh 1/2" in diameter and 2" long. The cathode was a mesh cylinder 13/8" in diameter and 2" long.

EXAMPLE I

A 43.88 gram sample of crude oil designated Fleisher Lease oil containing 6.13% by weight of sulfur was mixed with 54.06 grams of distilled water containing 1.08 grams of reagent grade NaOH. The mixture, which had a pH of 10, was subjected to electrolysis carried out in the above described reaction vessel. The mixture was subjected to a DC electrical field of 0.100--0.175 amperes, for a total of 64 hours. While holding the current to a maximum of 0.175 amperes during the run, the voltage varied between 25 and 200 volts. At the termination of this experiment, it was found that the sulfur content in the oil had been reduced to 4.57%.

EXAMPLE II

A mixture of 7.14 grams of crushed limestone, 49.73 grams distilled water, 43.03 grams of No. 6 fuel oil, and 0.48 gram Ca(OH).sub.2 and 38.78 grams distilled water was placed in the reaction vessel. The mixture separated into an oil layer and water layer. A DC current of 1 ampere was passed through the system at 15 volts for nearly 12 hours, at which time the current had dropped to 0 and the voltage rose to 45 volts. The sulfur content in the oil layer before the electrolysis began was found to be 0.86%, whereas at the end of the experiment the sulfur content was 0.60%.

EXAMPLE III

In this experiment, 46.7 grams of No. 6 fuel oil and 4.55 grams calcium hydroxide were added to 76.58 grams distilled water, and the mixture was heated to reflux without stirring. A direct current of 1 ampere at 9 volts was passed through the solution. The current dropped to 0 within 50 minutes. At this time a surfactant, available commercially under the name Triton X-100, was added to the mixture, and electrolysis was again initiated at 1 ampere and 20 volts. After 4 hours and 20 minutes the voltage had increased to 50 volts at 1 ampere. The system was allowed to run overnight, during which time the current dropped to 0.4 ampere and the voltage increased to 120 volts. The sulfur content of the oil layer before the experiment was 0.86%, and after the experiment was found to be 0.51%.

EXAMPLE IV

To a solution consisting of 92.55 grams distilled water, 0.39 gram Ca(OH).sub.2 and 5.7 grams limestone, there was added 38.75 grams No. 6 fuel oil cut with 10% by weight of pentane to reduce viscosity. The system was subjected to electrolysis at an initial current of 1 ampere and 7 volts. During a period of 6 hours, the current fell to 0 and the voltage increased to 75 volts. The sulfur content of the oil layer was 0.86% before the experiment and was found to be 0.49% after the experiment.

EXAMPLE V

A solution of 1.13 grams Triton X-100, 126.83 grams water and 10.39 grams calcium hydroxide was mixed with 73.95 grams No. 6 fuel oil. The reaction mixture was heated to reflux and electrolysis was started at 1 ampere and 20 volts. Within 2 minutes the voltage had increased to 120 volts and the current dropped to 0.4 ampere. An additional amount of 2.14 grams Triton X-100 was added and electrolysis continued at 1 ampere and 20 volts. After 3 hours the current had dropped to 0.4 ampere and the voltage increased to 120 volts. Again, 2.15 grams Triton X-100 was added and the electrolysis continued at 0.5 ampere and 120 volts. Within 3 hours, the current dropped to 0.2 ampere and the voltage remained at 120 volts. Before the experiment the sulfur content of the oil layer was 0.86% and after the experiment it was 0.54%.

EXAMPLE VI

This was a control experiment which was carried out to determine whether a reduction in sulfur content in the oil can be achieved with a similar mixture is subjected to electrolysis at much higher voltages.

A mixture of 122.12 grams distilled water, 10.14 grams calcium hydroxide, 4.05 grams Triton X-100 and 73.31 grams No. 6 fuel oil was prepared and mechanically agitated for several days. At the end of this period, the oil layer was placed in the previously described reaction vessel and subjected to a 2000 volt per centimeter DC potential for several hours. At the end of this period the oil was analyzed and found to contain the same sulfur content as the original oil content of 0.86% sulfur.

EXAMPLE VII

To a mixture of 15 ml methanol and 51.13 grams mineral oil there was added 8cc of thiophene. This mixture was subjected to electrolysis at 0.1 ampere and 50 volts. The resistance rapidly increased to 30 ohms within 56 minutes and the mixture changed from an initial colorless condition to a yellow color. Gas collected over the reaction mixture indicated SO.sub.2 and mercaptans were present. The electrolysis was run intermittently for 4 days. During this time 85 ml methanol was added to maintain liquid level. A total of 8.7 ampere hours of electricity were used. During the last two days of operation, the gas evolved from the reaction was found to contain formaldehyde.

The inside of the reaction vessel and the stirring bar and cathode were covered with a black deposit insoluble in carbon disulfide, the total weight of the deposit being 0.30 gram. No deposit was detected on the anode.

Analysis of the oil layer showed that initially, prior to electrolysis, the sulfur content was 2.30% while the final oil layer had a sulfur content of 0.625%.

EXAMPLE VIII

A sample consisting of 8cc thiophene, 46.12 grams mineral oil and 46.21 grams distilled water containing 1.17 grams sodium hydroxide was mixed and electrolyzed at 0.175 ampere and 4 volts for 15.4 ampere hours. The aqueous layer turned yellow and a gray deposit formed on the anode, while a black deposit formed on the cathode. A brown deposit formed and floated on top of the liquid phases. At the end of the experiment, 42.83 grams of mineral oil, 40.00 grams aqueous phase, 0.54 gram deposit on the anode, 1.23 gram deposit on the cathode and 0.22 gram brown residue were found. Upon standing several days, the oil layer turned sky blue in color. At the start of the experiment, the oil layer had 1.24% sulfur content, and at the end it had 0.20% sulfur. During the experiment, the sulfur content of the aqueous layer had increased from 0 to 2.96%.

EXAMPLE IX

Into the previously described reaction vessel there was introduced 46.14 grams mineral oil, 47.39 grams distilled water containing 1.13 gram calcium hydroxide and 8cc thiophene. A total of 12.86 ampere hours of DC current was passed through the system at 0.2 ampere and 7 volts. A brown solid phase began to separate from the mixture as electrolysis proceeded. The pH of the system was adjusted by the addition of 1.66 grams Ca(OH).sub.2 after 8.56 ampere hours of operation. Just prior to this addition, the generation of gas was noted. At the start of the experiment, the oil layer had 2.71% sulfur and a pH of 12. At the end of the experiment, the oil layer had 0.252% sulfur and the pH was 5.

EXAMPLE X

To a 50.37 gram sample of mineral oil was added 7.75 cc dibutyl disulfide and 43.5 grams methanol. The mixture was electrolyzed at 0.100-0.150 amperes and 50 volts for 64.5 hours or 9.97 ampere hours. During the run no deposits formed on the electrodes and no color changes were noted in the mixture. At the start, the oil layer contained 3.75% sulfur, and at the end of the experiment it contained 2.57% sulfur.

In all of the above experiments the current density of the system was about 0.008 amperes/cm.sup.2. As previously indicated, it is preferable in accordance with the invention to employ a current density of at least 0.001 amperes/cm.sup.2 because it is economically impractical to operate at lower current densities, while a current density of more than 25 amperes/cm.sup.2 is not feasible due to erosion of the anode surface and cavitation on the electrode surface.

The Triton surfactant material mentioned in the Examples was used to emulsify the oil so as to reduce fouling of the electrodes, while at the same reducing the viscosity of the mixture to enhance the electrochemical reaction.

As a result of our experiments, it appeared to be preferable to maintain the pH of the mixture at a relatively high level, i.e., 8-12, since it appeared that the electro-chemical reaction proceeded at a more rapid rate at such a pH level. However, it is not intended to limit the process of the invention to mixtures of such pH levels, since satisfactory results are obtainable at lower pH values. In adjusting the pH by the addition of a base, it is desirable to use compounds such as Ca(OH).sub.2 to form insoluble sulfur-containing compounds to facilitate the separation and removal of these compounds from the mixture.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.

Claims

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of electrochemically removing sulfur from hydrocarbon liquids including sulfur containing materials which comprises mixing the hydrocarbon liquid with an ionizing organic solvent, and subjecting the thus obtained mixture to an electrical D.C. field having a voltage of about 2 to 120 volts and a current of at least about 0.001 amperes per square centimeter, and recovering said hydrocarbon liquid in which said sulfur containing materials have been substantially reduced.

2. The method as defined in claim 1, wherein said current is not more than about 25 amperes per square centimeter.

3. The method as defined in claim 2, wherein said hydrocarbon liquid is crude oil.

4. The method as defined in claim 3, wherein said ionizing organic solvent is selected from the group consisting of methanol, benzene, toluene, xylene and glacial acetic acid.

5. The method as defined in claim 1, wherein said hydrocarbon liquid is selected from the group consisting of crude oil, mineral oil and petroleum and said voltage is in the range of about 2 to 10 volts.