CA1056751A - Desulphurizing char - Google Patents

Abstract

ABSTRACT
Char, especially coal char, is desulphurized by first washing the char with an acid. e.g. an aquoous mineral acid, to react with and leach out inorganic compounds in the char, whereafter the acid-washed char is treated with a gas comprising hydrogen. The gas may contain sulphur-bearing gases without adverse effects on the desulphurization of the acid-washed char, so that it is feasible repeatedly to recycle the gas.

Description

This invention concerns reduc-tion of the sulphur con-tent of char.
Present methods commercia]ly ernployed for the desulphur-ization of chars, such as those made from coal, only remove a portion of the sulphur present therein. This is inadequate to comply with air purity standards that permit only limited amounts of sulphur dioxide to be produced by the combustion o-f coals, chars, and other carbonaceous materials. The neecl for a relatively sulphur-free char, and especially a coal char, has therefore become very impor-tant, especially in view of the abundant supplies of coal and the dwind]ing supplies of oil and natural gas.
One desulphurization method used on coa] is to treat the coal with hydrogen gas to react with the sulphur in the coal to form hydrogen sulphide gas. This method may work well with coal but not as well wlth chars made from coal because the sulphur appears to be more resistant to reaction with hydrogen after being converted into char.
A further problem is that in methods involving treatment of coal or char with hydrogen gas, the latter has usually to be repeatedly recycled to accomplish its economic utilization. As a result unless elaborate and complex techniques are employed to remove hydrogen sulphide and other sulphur-bearing gases from the hydrogen before it is recycled, the ga.s used to treat the eoal or char will eontain small amounts of sulphur-bearing gases that tend to inhibit the desulphurization reaetion and may even baek-reaet to inerease the sulphur eontent of the treated eoal or ehar.
It has been discoverecl that greatly improved results in ~0 desulphurizing char with hydrogen gas may be realized if the ~ '

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char is first washed with an acid before the treatment with the hydrogen gas. The acid washing is believed to make the sulphur in the char more reactiye with hydrogen gas, by reacting with the inorganic compounds to form metallic salts that are removed from the char in the acid wash. These inorganic compounds include sulphides, such as iron sulphide and calcium sulphide, and other inorganics which generally comprise the ash content of the char. The organic sulphur in the char is not believed to be affected by the acid wash but the removal of the inorganic compounds by the acid wash appears to make the organic sulphur more susceptible to removal by the subsequent hydrogen treatment.
It has further been discovered that when char is washed with an acid before treatm~nt with hydrogen gas, the presence of sulphur-bearing gases, such as hydrogen sulphide in the hydrogen, may be tolerated without any substantial inhibition of the desulphurization reaction.
It has also been discovered that pretreating char with acid before desulphurization with hydrogen gas will cause the desulphurization to proceed at a greater rate than in the absence of the acid pretreatment.
Based on these discoveries, the invention provides a method of desulphurizing char, comprising: first washing the char with a mineral acid to react with and leach out the inorganic compounds therein, and thereafter treating said acid washed char with a gas comprising hydrogen.
In practicing the method of the invention, coal, for instance, is converted into char and thereafter introduced into an acid bath. The char need not be specially treated or prepared and may be introduced into the acid bath in its as-manufactured condition. The acid bath is preferably ~J -3-~056751 an aqueous solu-tion of a mineral ac:id, such as for example, hydrochloric acid, sulphuric acicl, nitric acid, phosphoric acid, or a combination of mineral acids such as these, In preferred embodiments, the acid concentration is molar but the concentration may be as low as about 0.05 M. or even lower if the residence time of the char in the acicl is suitably increased. The ratio of acid to char should be maintained at a level which will effect maximum reaction between the inorganic compounds present in the char and the acid. In pre~erred embodiments, this ratio is at least two parts of a molar aqueous solution of acid to one part of char. This ratio, however, may be varied depending upon the concentration of the acid and the residence time of the char in the acid. Thus, when the acid bath has a relatively low concentration and long residence times are employed, the acid to char ratio may have to be increased to effect the necessary reaction with the inorganics. ~-Preferably the char is continually agitated in the acidbath, e.g. by means of a motor-driven stirrer or other equivalent means, to provide a thorough mixing of the char with the aqueous acid solution for intimate contact therebetween. An inert medium, such as nitrogen gas, may be added to the char-acid mixture to purge oxygen therefrom and to prevent the possibility of any reactions therewith. The elimination of oxygen from the bath, however, is not essential.
The acid bath may be maintained at room temperature but the rate of reaction with the inorganic compounds will be increased if the bath is maintained at suitably elevated temperatures.
The residence time of the char in the acid bath should be at least about five minutes when using a molar acid solution at a ra-tlo of` about two parts of acid to one part of char. The residence time, however, like the acid-to-char ratio, is a variable depending on the acid concentration, bath temperature, and the acid-to-char ratio.
After an appropriate residence time, the char is removed by fil-tration from the aqueous acid bath.The char is thereafter preferably washed with water to remove the acid therefrom. Tlhe inorganic salts formed by -tlle reaction between the inorganic sulphides in the char and the acid may be separated from the 10 acid to permit this to be recycled for further use. -In preferred practice, after washing as descr:ibed~ the char is introduced into a reactor containing hydrogen gas maintained at a pressure between about 15 to 125psia (1.05to 8.79kg/cm ;
1.02 to 8.51ats) at a temperature of between about 1100 to about 1800F. (595 to 980 C.), and is held in said reactor from about one minute to about two hours. In preferred embodiments, the char is treated with hydrogen gas at a pressure of about 65psia (4.57kg/cm2; 4.42ats) and a temperature of about 1600F. (870 C.) for about five minutes.
The hydrogen reacts with the sulphur in the char to form hydrogen sulphide, mercaptans and other sulphur-bearing gases.
These sulphur-bearing gases and excess hydrogen are passed out of the reactor and the hydrogen is separated therefrom and recycled for further reaction with the char. Some trace amounts of hydrogen sulphide and other sulphur-bearing gases remain in the recycled hydrogen. However, the presence of these small amounts of sulphur-containing gases does not cause any reaction with the acid-washed char to increase its sulphur content, and only slightly reduces the extent of char desulphurization by 30 hydrogen gas. Up to about 3 to 5/0 of sulphur-containing gases _ 5 _ _ ., _, .. .......

in the hydrogen gas may be tolerated, depending upon the particular char, without impairing the commercial acceptabili*y of the treated char.
EXAMPLE I
To demonstrate the effect of acid washing on the desulphurization of char by hydrogen gas, 100 grams of Hamilton coal was converted into char by heating at 1600F. (870C.) for one hour. Hamilton coal is a high volatile, bituminous coal from seam No. 11 in Western Kentucky, and was beneficiated by floating the coal in a zinc chloride solution having a specific gravity of 1.55. The beneficiation is not necessary but it allows the pyritic sulphur (FeS2), which has a specific gravity greater than 1.55J to settle out from the coal floating on the surface and thus reduces the amount of acid needed in the subsequent washing step. The char was ground and screened to -150 to +400 (United States Standard) mesh. Eight, 10-gram specimens of char were prepared for treatment. Four of the specimens were not washed with any acid, and three of these specimens were treated in a fluidized bed quartz reactor at 1600F. (870C.), and 65 psia (4.57kg/cm2; 4.42ats) for four hours with hydrogen gas or a mixture of hydrogen sulphide-hydrogen gas as described in Table I hereinbelow. The four specimens were analyzed for their sulphur content and iron content and the results made noted as set forth in Table I.
The remaining our specimens were washed with one litre of lM HCl at 176F. (80C.) for five minutes. The char was separated therefrom and then washed a second time with 1 litre of lM HCl for five minutes at 176F. (80C.).
The char was separated after the second wash, washed with water to re ve the acid therefrom. Three of the four specimens were treated in a fluidized bed quartz reactor at 1600F. (870C.) and 65 psia (4.57kg/cm2; 4.42ats) for four hours 10567~1 with hydrogen gas or mixture of hydrogen gas and hydrogen sulphide as set forth in Table I. The specimens were thereafter analy~ed for their sulphur content and iron content and the results noted in Table I hereinbelow.

TABLE I

Gas Used Weight Per- Weight Per- Weight Per-Treatment of to treat cent of Sul- cent Fe in cent Ash in Char _ Charphur in Char Char Char Not washed with acid None 1. 61 1 . 0 12 ~ 05 Not washed with acid II2 - 58 Not washed 1 1% H2S
with acid and 1. 36 - -98. 9% H2 Not washed 3 ~ 3% H2S
with acid and 1. 82 96 . 7% H2 Washed with acid None , 1.60 0.73 10.68 Washed with acid H2 ~4 Washed 1-1% H2S 0 . 76 with acid and - 98. 9% H2 Washed 3 . 3% H2S 0. 95 with acid and 96.70/o H

3o 1056751.

EXAMPI,E Il To further demonstrate the effect of acid washing on the desulphurization of char by hydrogen gas, the procedures as set forth in Example I were repeated, except that a run of the mine type of Hamilton coa] having a high ash, higll sulphur and high iron content were used and -the char was manufactured at 1400 F. (760 C.) and treated in the fluidized bed quartz reactor a-t 1400 F. (760 C.). The char was also analyzed for its ash content. Thc resul-ts are set forth hereinbelow in Table lI.

T~BLE II

Gas Used Weight Per- Weight Per- Weight Per-Treatment of to Treat cent of Sul- cent Fe in cent ~sh Char Char phur in Char Char in Char Not washed with acid None 2.87 2.12 14.2LI

Not washed with acid 2 0.72 _ 18.80 Not washed 2.740/o H2S 2.22 _ 18.07 with acid and 97. 260/o H2 Washed with None 2 . 70 o . 64 10 . 63 acid Washed with H2 0.32 - 14. 17 acid Washed with 2 . 740/o H2S 1 . 08 - 13.40 acid and 97.260/o H2 1~56751 EXAMPLE III
To demonstrate the effect of acid washing in removing iron, calcium, and ash content of the char whiçh comprises the total inorganic content of the char, the same Hamilton coal as ~ described in Example I hereinabove was converted into char at 1600 ~. (870 C.) for one hour under a nitrogen blanket in a fluidized quart~ bed reac-tor. The char was ground to -200 mesh and three, 50-gram samples thereof were prepared. Tl1e first specimen was analyzed in terms Or its ash, iron, and calcium content. The second specimen was mixed with 200 ml of 0.1M HC1 and allowed to stand at room temperature for three hours.
Thereafter the specimen was filtered from the acid and washed with water and analyzed in terms of its ash, iron and calcium content. The third specimen was added to 200 ml of 0.05M H2S04 and allowed to stand at room temperature for three hours.
Thereafter the char was filtered from -the acid and washed with water and analyzed for its ash, iron and calcium content. The res~lts are set forth in Table III hereinbelow.

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- TABLE III

Treatment Weight Percent Weight Percent Weight Percent of Char ~e in Char Ca in Char _ Ash in Char Not washed with acid 1.63 0.25 11.86 Washed with HC1 o.86 0.062 10.26 Washed with H2S04 0.88 0.062 10.14 3o _ g _ 10567Sl EXAMPLE IV
To demonstrate the effect of temperature upon the desulphurizatio of an acid washed char treated with hydrogen gas, the same Hamilton coal as used in Example I hereinabove was conver~ed into char and six specimens thereof were washed with HCl by the same procedure set forth in Example Io Five of the six acid-washed-char specimens were thereafter treated in a fluidized bed quartz reactor at 65 psia ~4.57Kgtcm2; 4.42ats) for four hours at five different temperatures as set forth in Table IV hereinbelow. Each of the specimens were thereafter analyzed for its sulphur content and the results are set forth in Table IV hereinbelow.

TABLE IV

Temperature of H Weight Percent Treatment F.(C.2? of Sulphur Ambient Temperature no H2 Treatment 1.82 1400 (760) 0.32 1500 (815) 0.24 1600 (870) 0.27 1700 (925) 0.33 1750 (955) 0.35 f 1 0 -105675~ `
EXAMPL~ V
To further demonstrate the effect of acid washing on the desulphurization of char by hydrogen gas, the same coal as used in Example I was converted into char in a pilot plant and thereafter subjected to the same procedures as set forth in Example I excep-t that the char specimens were;treated with hydrogen or the hydrogen-hydrogen sulphide gas mixtures at 1700 F.
(925 C.) and at 65psia (Ll .57kg/cm ; 4.42ats).
To manufacture the char in the aforesaid pllot plant, the coal was pulverized -to a size of approximately 80% -200 mesh.
The coal was then pyrolyzed by contacting it witl~ a circulating stream of heated char in a 4" (100mm) diameter reactor. The temperature of the circulating char was approximately 1400 ~.
(760 C.). The resultant pyrolysis temperature was about 1100 l~.
(595 C.) at a coal feed rate of 50 lbs./hr. (22.7kg/hr). The reactor essentially consisted of a 20 foot (6m) length of 4 inch (100mm) diameter stainless steel pipe and the char and coal mixture flowed vertically upward through this pipe at a velocity of approximately 20 ft./sec. (6m/sec.). Separation of gases and char was effected by a cyclone with the gases going to the liquid collection system.
The results of treating the char with hydrogen or the hydrogen-hydrogen sulphide gas mixtures are noted in Table V
hereinbelow.

3o -- 1 1 _ TABLE V

Gas used to Weight Percent of Treatment of Char Treat Char Sulphur in Char Not washed wi-th acid H2 1. 62 Not washed with acid O.40/o H2S and 4 ~ 17 99 . 60p H2 Not washed with acid 1, 0/c H2S and 1l,51.
99 ~ % ~12 Not washed wi-th acid 1. 9% I-I2S and - 4 . 43 98 . 1 % l-I2 Not washed with acid 3 . 3% JI2S and 4. 85 . 96, 7% II2 Washed with acid H2 O. 1 Washed with acid 0, 40/o I-l2S and 0.25 9 9 ~ 6 /o 2 Washed with acid 1. 0/0 H2S and 0.~l5 99 . 0% H2 Washed with acid 1, 9/0 II2S and 0.5 98~ 1% ll2 Washed with acid 3. 3% H2S and o. 68 j 96 ~ 7% II2 _ 12 -EXAMPLE VI
To demonstrate the effect of acid washing on the rate of char desulphurization by hydrogen, a parallel set of char hydrodesulphurization tests were conducted using the same char and procedures described in Example I. In one tes-t, the char specimen was treated with hydrogen at a temperature of 1600F.
(870 C.) for a period of five minutes. The tes-t was then repeated with a char specimen which had been acid washed in advance of -the hydrodesulphur:ization The results are summarized below and indicate that the acid washing treatment significantly enhances the rate of char hydrodesulphurization.

Quantity of Sulphur Removed During Sample a ~-minute Treatment with Tl Gas ., - ~ .
Acid-treated char 0. ooo86 lb. of` sulphur/Ft3 of H2 (0.014 g Sulphur/litre H2) Untreated char 0.00011 lb. of sulphur/Ft3 of H2 (0.0~8 g Sulphur/litre H2) While the embodiments and examples set forth herein are for the p~rpose of illustrating the invention, it is to be understood that this invention is not limited to said embodiments and examples. Moreover, while the invention has been described in relation to the treatment of coal chars, the invention is not limited thereby but comprehends the desulphurization of chars made from any carbonaceous material.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of desulphurizing char, comprising: first washing the char with a mineral acid to react with and leach out the inorganic compounds therein, and thereafter treating said acid washed char with a gas comprising hydrogen.

2. The method of claim 1, in which said gas is comprised of hydrogen and lesser amounts of sulphur-bearing gases.

3. The method of claim 1 or 2, in which said char is washed for at least one minute with an aqueous mineral acid having a concentration of at least about 0.05 M., and in an amount of at least about two parts of acid for every part of char.

4. The method of claim 1, in which said acid-washed char is treated with said gas for a period of about one minute to about two hours, at a temperature from about 1100°F (595°C) to about 1800°F (980°C) and at a pressure of about 15 to 125 psia (1.05 to 8.79 kg/cm2; 1.02 to 8.51 ats).

5. The method of claim 4, in which said acid concentration is about 1 M, and the treatment with said gas is at pressure of about 65 psia (4.57 kg/cm2; 4.42 ats) at a temperature of about 1600°F (870°C) for about five minutes.

6. The method of claim 5, in which said gas is comprised of hydrogen and lesser amounts of sulphur-bearing gases.