US3387941A - Process for desulfurizing carbonaceous materials - Google Patents

Description

Unite 11 AESTRACT 0F THE BISCLQSURE A method for desulfurizi carbonaceous material by O treating with steam an intimate mixture containing such material and an alkali metal hydroxide, oxide, carbide, carbonate, or hydride at a temperature of about 500 850 C. and at which the hydroxide of said alkali metal is a liquid, while removing the sulfur impurities volatilized during the treatment.

The present invention relates generally to the desulfurization of carbonaceous materials and in particular to a process for the partial desulfurization of carbonaceous materials consisting of or related to coal, char, coke, and petroleum.

The efficient utihzation of such carbonaceous materials has often been greatly impeded due to high sulphur content. This problem can be readily appreciated when considering that for most non-steam fuel uses, coke or coal is required to be at least below 3% by Weight of sulphur and preferably below 2% by weight of sulphur. In foundry uses, coke is required to have a Weight of sulphur of below 1% for satisfactory use as a cupoia fuel. Metallurgical coke having a sulphur content of much greater than 1%, which would otherwise be suitable as blast furnace fuel, is generally regarded as undesirable in the U.S.A. Also, even when used as steam fuel, any of these materials having a high sulphur content, causes corrosion to fines, as well as air pollution.

With respect to petroleum, the presence of relatively high contents of sulphur has proved a distinct disadvantage, in that the cost of refinery maintenance is seriously increased and the quality of end products is generally downgraded in proportion to the amount of sulphur prescut.

The three most common methods of reducing the sulphur content of petroleum coke have been as follows: high temperature calcination in the range of between 120 C. and 1600 C. in the presence of gases such as steam, nitrogen, flue gases or the like; treatment with hydrogen over a period of time at temperatures in the range of between 650 C. and 1090 C.; and treatment with oxygen and hydrogen in accordance with the process for the desulfurization of coke as shown in US. Patent No. 2,721,169, which issued on Oct. 18, 1955. All of the foregoing methods of desulfurization have proved expensive, the patented process is only applicable to the fluid coker type of petroleum coke.

There are several common methods for sweetening or stabiiiziug the form in which sulphur exists in liquid petroleum products. In most cases, such sweetening results in little or no actual reduction of the sulphur content.

A typical method for reducing and stabilizing the sulphur in petroleum and its fractions, is treatment with strong sulphuric acid (90% or higher). This results in the formation of sludges, which may in some instances represent a product loss as high as 20%. Also, sulphuric acid treatment tends to have an adverse effect on the combastion characteristics of lighter distiliates such as motor fuel.

States Patent 0 Another method of stabilizing the sulphur in petroleum is by treatment with a solution of caustic soda odi hydroxide, NaOH). Although this method results in the reduction of hydrogen sulphide, there is very little removal of the other sulphur compounds that usually predominate in petroleum.

Yet another method of stabilizing sulphur in petroleum is by treatment with sulphur and a Water solution of sodium plumbite (Na PbO which is commonly known in the art as the doctor treatment. Although the doctor treatment changes the form of (or stabilizes) some of the sulphur originally present, this method does not actually reduce the sulphur content of the product being treated.

Still another method of stabilizing the sulphur in petroleum is by hypochlorite sweetening with sodium or calcium hypochlorite (NaOCl or Ca(OCl) which has a stabilizing effect generally similar to that of the doctor treatment, except that in some instances the hypochlorite treatment actually results in minor reduction of total sulphur contents.

Another method of reducing sulphur in petroleum is by hydrogen desulfurization which may be employed with a fair degree of economy only in those refineries which also produce hydrogen in large volume for other purposes.

A number of other miscellaneous methods have been proposed for desulfurizing petroleum such as treatment with elemental sodium, with anhydrous aluminum chloride or with caustic soda and alcohol. The employment of such methods in the petroleum industry has been prevented by high cost, hazards of use or other practical considerations.

Broadly, it is an object of the present invention to provide an improved method for the desulfurization of carbonaceous materials. Specifically, it is Within the coutemplation of the invention to provide a method of desulfurizing coal, char, coke, and petroleum which is commercially feasible and relatively inexpensive.

In accordance with the present invention, there is provided a process for the desulfurization of carbonaceous materials with a hydroxide of an alkali metal, an oxide of an alkali metal, a carbide of an alklai metal, a carbonate of an alkali metal or a hydride of an alkali metal, at a temperature in excess of the melting point of the hydroxide of the alkali metal employed.

The above brief description, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred, but nonetheless illustrative embodiments in accordance with the present invention.

In the process of the present invention, conditions are established for implementing the reaction of one or more of the hydroxides, oxides, carbides, carbonates or hydrides of the alkali metals which are found in Group 1-A of the Periodic System, including lithium, sodium and potassium, with sulphur present in the carbonaceous material which is being treated. It is necessary to establish a temperature above the melting point of the hydroxide of the particular alkali metal being employed (above the eutectic melting point of their hydroxides when mixtures of compounds of alkali metals are being employed). By treating carbonaceous materials in accordance with the present invention, the sulphur contents can be reduced by at least 35% (thirty five percent) when the carbonaceous material being treatedl initially has sulphur contents of between 1% (one weight percent) and 2% (two weight percent) on a volatilefree basis, and in the cases of carbonaceous material initially having sulphur contents of more than 2% (two Weight percent), the sulphur contents of the carbonaceous material so treated can be reduced by at least 50% (fifty weight percent) on a volatile-free basis.

A typical alkali metal reagent which can be used in the process described herein consists of sodium hydroxide (NaOH) which in its commercial form is commonly known as caustic soda or lye. In order to more clearly appreciate the present invention, the desulfurization of carbonaceous material employing caustic soda will be described herein, but it is to be understood that any of the above-mentioned alkali metal reagents may be substituted for the caustic soda in the method of the instant invention, when corresponding adjustment of the process temperatures and chemical equivalent weights are made.

When solid carbonaceous materials are to be desulfurized, it is preferable that the maximum dimension of any particle be no greater than 0.05 (five hundredths) inch and that the material be in particles of a size range no larger than is commonly described at 16 x (sixteen by zero) US. Standard Sieve. Further, it is usually preferable :to provide caustic soda which is equivalent to at least approximately twice the weight of the sulphur to be removed from the solid carbonaceous materials. In order to achieve optimum desulfurization in a minimum length of time, it is preferable to use caustic soda in excess of this proportion when the initial sulfur content of the carbonaceous materials being treated is less than 3% (three weight percent) on a volatile-free basis.

Dry caustic soda may be mixed with the carbonaceous material to be desulfurized before heating. It is preferable to place the requisite amount of caustic soda in solution with water, and to thoroughly mix the solution with the solid carbonaceous material to be desulfurized at ambient temperatures. This mixture should then be heated to a temperature of at least 500 C., which temperature should be maintained for at least minutes in such a manner that the hot mixture is periodically exposed to an, atmosphere containing at least 2% moisture or steam. In most instances it has been found preferable to maintain the temperature range of between 550 and 850 C. for periods of between 10 minutes and 180 minutes.

The intermittent introduction of steam into the hot mixture in the reactor vessel meets the chemical reaction requirement; but some movement of gas through the material is desirable to sweep out the volatile sulfides which are released by the reaction. Since native volatile matter, which is incidentally driven out of the solid carbonaceous material, may serve as part of this sweep gas, it is preferable to supplement this sweep gas with additional steam as maybe required.

During the reaction period, at least /3 (two-thirds) of the sulphur being removed will be released in gaseous form. Most of the residual sulphur remaining in the mixture in sulfide or hydrosulfide form may be removed by washing with water.

The method of desulfurization of carbonaceous material disclosed herein has been found to have the effect of activating carbon in the solid carbonaceous material to an extent that it is at least proportionate to the amount of sulphur removed. For example, this incidental activation of carbon is adequate in most cases to provide the surface activation prescribed as the first step in the practice for treating fluid petroleum coke described in copending application Ser. No. 218,449.

In order to more fully understand the invention, there is set forth below several illustrative examples for the desulfurization of carbonaceous materials in accordance with the present invention.

EXAMPLES No. 1: A heavy (No. 6 or BunkenC grade) petroleum fuel oil, analyzing 3.2% sulfur, was first heated to 350 C. and was then slowly injected into a bath of molten caustic soda (NaOH) maintained in a temperature range of 500 525 C., in such manner that the oil was forced to bubble up through approximately eight inches of molten caustic soda. Approximately three-fourths of the oil volatilized.

Heavy residual oil floating on the molten caustic soda was decanted, cooled and washed with hot water, after which it analyzed 1.5% sulfur.

COndensable (at room temperature) vapors were collected and the resulting distillate was first washed with a hot 1% caustic soda-water solution and then with hot water, after which it analyzed 0.9% sulfur.

No. 2: An air dried Ohio steam coal sample analyzed 4.75% sulfur, 39.32% volatile, 10.98% ash and 1.93% moisture. This sample of coal was first crushed to 16 x 0 mesh, US. Standard Sieve. It was then devolatilized and activated in a bed fluidized with steam at a temperature between 600 C. and 650 C. for 20 minutes. Following this treatment, the sample analyzed 6.2% volatile, 2.3% moisture, and it had been activated to the extent of approximately 2% carbon loss.

1000 grams of the said devolatilized and preactivated sample, after cooling, was then thoroughly mixed with grams caustic soda mixed in 100 cc. water. The resulting mixture was then placed in a fluid bed reactor and heated to 500 C., without fluidization. Heating continued and, beginning at 500 C., the bed was alternately fluidized with steam for 2 minutes and let rest for 5 minutes over a period of 91 minutes up to a final temperature of 650 C.

The resulting product Was then rapidly cooled and was washed in water before drying.

After drying the sample analyzed 1.4% sulfur.

No. 3: A sample of fluid coker petroleum coke screened through a 16 mesh US. Standard Sieve, analyzing 7.8% sulfur and weighing 1800 grams was thoroughly mixed with 180 grams caustic soda which had previously been dissolved in cc. water.

The mixture was placed in a fluid bed reactor, and Was fluidized with air while heating to 450 C. Heating continued and steam was introduced at 500 C. The bed was so caked that fluidization could not be accomplished at first, but heating continued and approximately 10% air was introduced with the steam at 700 C. Fluidization was established shortly thereafter and continued with heating to 800 C. Fluidization continued and temperature was maintained in the 750 C.800 C. range for 95 minutes.

The mixture was cooled and was then washed with Water. After drying, this desulfurized petroleum coke analyzed 2.95% sulfur.

No. 4: A sample of fiuid coker petroleum coke screened through 16 mesh US. Standard Sieve and analyzing 3% sulfur was first activated by fluidizing it with air for 1 hour at 375 -400 C. to a carbon loss of apapproximately 4%.

1660 grams of the resulting preactivated fluid coker petroleum coke was then thoroughly mixed with 90 grams of caustic soda which had previously been dissolved in cc. water.

The resulting mixture was placed in a fluid bed reactor and was heated to 800 C. Fluidization with steam was initiated at 400 C. and was continued thereafter. This fluidized bed was maintained at 800 C. for 3 hours.

The resulting mixture was cooled and washed with water. After drying this desulfurized fluid coker petroleum coke analyzed 1.22% sulfur.

No. 5: A sample of green delayed coker petroleum coke analyzing 1.9% sulfur, was crushed to pass through a 20 mesh US. Standard Sieve. 1500 grams of this material were thoroughly mixed with 150 grams caustic soda which had first been dissolved in 225 cc. water.

The resulting mixture was placed in a fluid bed reactor and heated to 750 C. Fluidization with steam was initiated at 400 C. and it required 2 hours 22 minutes for the reactor to reach 750 C.

The resulting mixture was cooled and washed with water. After drying, this desulfurized delayed coker petroleum coke analyzed 0.88% sulfur.

Examples 6, 7, 8, 9 and 10 Green (not previously devolatilized) delayed coker petroleum coke analyzing 1.9% sulfur and crushed to pass through a 16 mesh US. Standard Sieve was fluidized with steam for 1 hour over a temperature range of 550 C.- 700 0., thus substantially devolatilizing the coke and activatine it to the extent of approximately carbon loss.

Each of five different 1000 gram samples of this preactivated coke was thoroughly mixed with one or more alkali metal hydroxides as follows:

Each of these five different mixtures was then placed in a fluid bed reactor which was heated. On reaching 550 C. in each case, the bed was initially fluidized with steam for 2 minutes and was then let rest for 5 minutes. Heating was continued with 2 minute periods of steam iiuidization alternated with 5 minute rest periods up to the temperatures and for the times tabulated below.

In each case the resulting mixture was rapidly cooled and was washed with Water. After drying, these different examples of the same delayed coker petroleum coke had been desulfurized as follows:

1. A method of reducing the sulfur content of carbonaceous material containing sulfur impurities comprising treating an intimate mixture containing such material and at least about 1.3 parts, per part by weight of said impurities, of at least one alkali metal hydroxide, oxide, carbide, carbonate, or hydride in the form of a fluidized bed with steam at a temperature of about SOD-850 C. and at which the hydroxide of said alkali metal is a liquid, while removing the sulfur impurities volatilized during the treatment.

2. A method as defined in claim 1 wherein said alkali metal is sodium.

3. A method as defined in claim 1 wherein said material is coke.

4. A method as defined in claim 1 wherein said material is coal.

5. A method as defined in claim 1 wherein said mixture is formed by mixing said material with an aqueous solution of at least one of said alkali metal compounds.

6. A method as defined in claim 1 followed by the step of washing the steam-treated mixture with an aqueous medium to remove soluble substances therefrom.

References Qited UNITED STATES PATENTS 1,145,024 7/1915 Lain 23-2092. 2,878,163 3/1959 Hutchings 23209.2 3,164,545 1/1965 Mattox 208-230 3,166,483 1/1965 Masciantonio 23209.9

OTHER REFERENCES Lukasiewicz et al.: Ind. Eng. Chem, vol. 52, N0. 8, August 1960, pages 675677.

EDWARD I. MEROS, Primary Examiner.