Coal suspensions and process for preparing same

A suspension containing (A) water and (B) the product resulting from the reaction of (1) coal having a neutral equivalent of about 150 to about 485 with (2) a base. The process for preparing such suspension is also claimed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to coal suspensions containing (A) water and (B) the 
product resulting from the reaction of (1) coal having a neutral 
equivalent of about 150 to about 485 with (2) a base and to a process for 
preparing such suspension. 
2. Description of the Prior Art 
Coal suspensions are well-known and are widely used, for example, in 
transporting coal, as fuel mixtures, in coal reactions or conversions, 
etc. It is an object herein to provide a suspension requiring the presence 
therein of only the coal to be suspended therein and water. 
SUMMARY OF THE INVENTION 
We have prepared stable coal suspensions containing solely (A) water and 
(B) the product resulting from the reaction of the coal to be suspended 
therein, said coal having a neutral equivalent of about 150 to about 485 
with (2) a base. 
The suspensions prepared herein can utilize any of the well-known coals. 
Thus, bituminous and subbituminous coal, lignitic materials and other 
types of coal products are exemplary of coals that are suitable in the 
preparation of the novel coal suspensions claimed herein. Some of these 
coals in their raw state will contain relatively large amounts of water. 
These can be dried prior to use, if desired, and preferably can be ground 
in a suitable attrition machine, such as a hammermill, to a size such that 
at least about 50 percent of the coal will pass through a 40-mesh (U.S. 
Series) sieve. The carbon and hydrogen content of the coal are believed to 
reside primarily in multi-ring aromatic and non-aromatic (condensed and/or 
uncondensed), heterocyclic compounds, etc. On a moisture-free, ash-free 
basis the coal can have the following composition: 
TABLE I 
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Weight Per Cent 
Broad Range Preferred Range 
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Carbon 49-95 60-85 
Hydrogen 2.2-8 5-7 
Oxygen 2-46 8-40 
Nitrogen 0.7-3 1-2 
Sulfur 0.1-10 0.2-5 
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In order to suspend the above-identified coal in water to form the novel 
suspension defined herein, it is critical that such coal first possess 
sufficient carboxylic acid functions such that it possesses a neutral 
equivalent in excess of about 150 but not greater than about 485, 
preferably in excess of about 180 but not greater than about 480. By 
"neutral equivalent" we mean the grams of such coal needed to neutralize 
one mol of sodium hydroxide. When coals are used having a neutral 
equivalent in excess of about 485 the suspension prepared using such coal 
is not stable. On the other hand, when suspensions are prepared using 
coals having a neutral equivalent below about 150, such coals become 
soluble therein. By "stable" we mean to define a water-coal suspension 
wherein no appreciable amount of the coal portion thereof will precipitate 
or settle out from the water component thereof for at least about eight 
days, generally for a period of about 10 to about 90 days. 
If the coal to be used does not already possess the neutralization 
equivalent values defined above, the coal is first subjected to any 
conventional or suitable treatment sufficient to obtain a coal product 
possessing such neutralization equivalent values. For example, a stirred 
aqueous slurry containing coal in particulate form, as defined above, with 
or without a catalyst, such as cobalt, manganese, vanadium, or their 
compounds, can be subjected to a temperature of about 15.degree. to about 
225.degree. C. and an oxygen pressure of about atmospheric (ambient) to 
about 2000 pounds per square inch gauge (about atmospheric to about 13.8 
MPa) for about 0.12 to about 20 hours. The product so obtained can then be 
subjected to mechanical separation, for example, filtration, and the solid 
residue can be washed with water, if desired. The coal so treated is then 
treated with a base, as will be defined hereinafter, and then added to 
water to form the desired novel suspension. 
A preferred procedure for preparing the coal having a neutral equivalent 
within the critical range required herein involves subjecting a slurry 
containing coal in particulate form to mild oxidation with dilute nitric 
acid, following, for example, the procedural steps employed in U.S. Pat. 
No. 4,052,448. Thus, an aqueous slurry containing coal can be contacted 
with aqueous nitric acid having a concentration of about one to about 90 
weight percent, preferably about three to about 70 weight percent, at a 
temperature of about 15.degree. to about 200.degree. C., preferably about 
25.degree. to about 100.degree. C., and a pressure of about atmospheric to 
about 2000 pounds per square inch gauge (about atmospheric to about 13.8 
MPa), preferably about atmospheric to about 500 pounds per square inch 
gauge (about atmospheric to about 3.4 MPa), for about 0.12 to about 15 
hours, preferably about two to about six hours. The oxidation with nitric 
acid can, if desired, be carried out in an atmosphere containing molecular 
oxygen, following, for example, the procedure outlined in U.S. Pat. Nos. 
4,195,185 and 4,195,186 to Schulz et al. The resulting product can then be 
subjected to mechanical separation, for example, filtration, and the solid 
residue can be washed with water, if desired, and dried to produce the 
coal component having the neutralization values defined above for use in 
preparing the novel suspensions claimed herein. 
However, before the coal product having the required neutralization value 
can be used to prepare the novel suspensions claimed herein, it must first 
be treated or reacted with a base. Any base, including the corresponding 
or basic salt, organic or inorganic, that can react with a carboxyl 
function, can be used to react with the coal. Thus, hydroxides of the 
elements of Group IA and Group IIA of the Periodic Table can be used. Of 
these we prefer to use potassium, sodium or calcium hydroxide. In 
addition, ammonium hydroxide can also be used. Among the organic bases 
that can be used are aliphatic amines having from one to 12 carbon atoms, 
preferably from one to six carbon atoms, such as methylamine, ethylamine 
and hexamethylenediamine; aromatic amines having from six to 60 carbon 
atoms, preferably from six to 30 carbon atoms, such as aniline and 
naphthylamine; aromatic structures carrying nitrogen as a ring 
substituent, such as pyridine and quinoline; etc. By "basis salt" we mean 
to include salts of the elements of Group IA and IIA of the Periodic Table 
whose aqueous solutions exhibit a pH in the basic region, such as 
potassium carbonate, sodium metasilicate, calcium acetate, barium formate, 
etc. 
The reaction between the coal having the designated neutral equivalent 
value and the base is easily effected. The amounts of reactants are such 
that on a weight basis the coal and the base are in the range of about 
100:1 to about 6:1, preferably about 50:1 to about 8:1. Mechanically, the 
reaction can be carried out, for example, by dissolving the base in an 
aqueous medium, such as water, and adding the coal thereto while stirring. 
These reactions can be carried out over a wide range of temperatures and 
pressures, for example, a temperature of about 5.degree. to about 
150.degree. C., preferably about 15.degree. to about 90.degree. C., and a 
pressure of about atmospheric to about 75 pounds per square inch gauge 
(about atmospheric to about 0.52 MPa), preferably about atmospheric. Water 
can be removed from the reaction in any convenient manner, for example, by 
filtration. If desired, however, the water need not be removed from the 
resulting mixture and the total, together with additional water, if 
needed, can be used to prepare the novel suspension herein. 
The amount of (1) water and (2) the product resulting from the reaction of 
coal having a neutral equivalent of about 150 to about 485 with a base 
present in the novel suspension can be varied over a wide range, for 
example, on a weight basis, from about 4:1 to about 1:4, preferably from 
about 2:1 to about 1:2. 
The suspensions defined and claimed herein are easily prepared. A 
convenient procedure involves introducing the product resulting from the 
reaction of coal having a neutral equivalent of about 150 to about 485 
with a base into water while mixing the two, for example, for about 0.01 
to about 10 hours, sufficient to obtain the desired suspension. Mixing can 
be effected in any suitable manner, for example, using propeller 
agitation, turbine agitation, a colloid mill, etc. The suspensions so 
obtained are stable, as noted, in that there is no separation of water 
from the coal. When desired, however, the suspensions herein can easily be 
broken, for example, mechanically by bringing the same into contact with a 
body, for example, a filter, or chemically, for example, by contact with 
an acid solution, such as hydrochloric acid. The coal and the water can be 
separated from each other in any suitable manner, for example, by 
filtration, and the coal so obtained can be used as desired, for example, 
as a fuel for burning in a furnace.

DESCRIPTION OF PREFERRED EMBODIMENTS 
A Coal (A) was prepared as follows. To a one-gallon glass reactor equipped 
with a mechanical stirrer and heating and cooling coils there were charged 
320 milliliters of water and 100 milliliters of 70 weight percent aqueous 
nitric acid. The reactor was heated to 80.degree. C. and maintained at 
this temperature during the entire run. To the resulting mixture there was 
added 800 grams of Kentucky No. 9 coal having an average particle size 
such that about 50 percent passed through a 40-mesh sieve and 1140 
milliliters of 30.7 weight percent aqueous nitric acid over a five-hour 
period. The Kentucky No. 9 coal analyzed as follows: 1.1 weight percent 
water, 67.93 weight percent carbon, 4.83 weight percent hydrogen, 1.50 
weight percent nitrogen, 13.03 weight percent oxygen, 4.34 weight percent 
sulfur and 7.37 weight percent metals. The resulting mixture was held at 
80.degree. C. for one hour, with stirring, and then cooled to room 
temperature and removed from the reactor and filtered. The recovered 
solids were washed three times with water (1000 milliliters of water each 
time), dried in a vacuum oven, resulting in the production of 819.1 grams 
of treated particulate coal. To obtain the neutral equivalent one gram of 
this product was placed in a 100-milliliter beaker containing a magnetic 
stirring bar and 40 milliliters of water was added. With stirring there 
was then added to the beaker 0.2 N sodium hydroxide until a pH of 11 was 
reached and remained constant for one-half hour. The resulting mixture was 
back titrated to a pH of 8.0 using 0.2 N HCl and the resulting calculation 
showed that the treated coal had a neutral equivalent of 473. Neutral 
equivalents of the remaining coals used hereinafter were similarly 
determined. 
An additional Coal (B) was prepared following the procedure used to obtain 
Coal A, except that with the addition of the Kentucky No. 9 coal there was 
added 740 milliliters of 9.5 weight percent of aqueous nitric acid over a 
period of six hours. The treated coal, amounting to 790.7 grams, was found 
to have a neutral equivalent of 1000. 
A Coal (C) was prepared as follows. To a two-liter beaker, equipped with a 
mechanical stirrer and wet-ice bath, there was added 600 milliliters of 10 
weight percent aqueous nitric acid and 225 grams of North Dakota lignite 
analyzing as follows: 33 weight percent water, 45.7 weight percent carbon, 
2.8 weight percent hydrogen, 11.3 weight percent oxygen, 0.6 weight 
percent sulfur, 0.6 weight percent nitrogen and 6.0 weight percent metals. 
The mixture was stirred for two hours at 25.degree. C. and filtered to 
recover 150.1 grams of treated lignite solids. These solids were then 
processed following the identical procedure employed in obtaining Coal (A) 
to recover a reaction product thereof with sodium hydroxide. The treated 
lignite was found to possess a neutral equivalent of 497. 
The filtrate obtained above in preparing Coal (C) was rotovaced to dryness, 
further dried in a vacuum oven and then extracted with 300 milliliters of 
acetone to recover 4.7 grams of solids of acetone-soluble, water-soluble, 
oxidized coal. This was combined with material from similar runs to 
produce a Coal (D) having a neutral equivalent of 123. 
An untreated North Dakota lignite, of the same composition as that employed 
above in the preparation of Coal (C), was used as Coal (E) having a 
neutral equivalent of 540. 
A Coal (F) was prepared as follows. To a one-liter glass reactor equipped 
with a mechanical stirrer and heating and cooling coils there were charged 
978 milliliters of water and 178.6 milliliters of 70 percent by weight of 
aqueous nitric acid. The mixture was heated to 60.degree. C., with 
stirring, and maintained at this temperature during the run. To the 
resulting mixture there was added a slurry comprised of 800 grams of North 
Dakota lignite, of the same composition as that employed above in the 
preparation of Coal (C), and 800 milliliters of water over a one-hour 
period. The mixture was held at 60.degree. C. for three hours, cooled to 
room temperature and then removed from the reactor and filtered. The 
recovered solids were washed three times with water (1000 cubic 
centimeters each time), dried in a vacuum oven, resulting in the 
production of 560 grams of treated coal having a neutral equivalent of 
200. 
A number of suspensions was prepared as follows. Into a Waring Blender 
there was placed, in each instance, water, solid pellets of potassium 
hydroxide and then one of the coals identified above. These materials were 
mixed, at atmospheric temperature and atmospheric pressure, at low speeds 
(about 500 RPM) for about five minutes, sufficient to obtain reaction 
between the coal and the base. The resulting mixture was mixed at high 
speed (about 20,000 RPM) for about 20 minutes and then examined at various 
intervals of time for stability by noting whether any appreciable settling 
had occurred. The data obtained are tabulated below in Table II. 
TABLE II 
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Example 
Grams of 
Coal 
Grams of 
Neutral Equivalent 
Grams of 
No. Water 
Used 
Coal of Coal KOH Comments* 
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I 200 A 100 473 15 Stable at end of eight days 
II 200 A 100 473 5 Stable at end of eight days 
III 200 B 100 1000 15 Not stable 
IV 200 B 100 1000 5 Not stable 
V 200 C 100 497 15 Not stable 
VI 200 C 100 497 5 Not stable 
VII 200 D 100 123 15 No suspension; coal soluble 
in water 
VIII 200 D 100 123 5 No suspension; coal soluble 
in water 
IX 200 E 100 540 15 Not stable 
X 200 E 100 540 5 Not stable 
XI 200 F 100 200 15 Stable at end of eight days 
XII 200 F 100 200 5 Stable at end of eight 
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days 
*Last day of observation 
In each of Example Nos. I, II, XI and XII no settling of coal particles had 
occurred at the end of the last day of observation. In each of Example 
Nos. III and IV the coal separated and settled within two hours of the 
formation of the suspension. In each of Example Nos. V, VI, IX and X, no 
observations were made until the last day of the test period, that is, the 
eighth day, at the end of which time the coal had separated and settled. 
In each of Examples Nos. VII and VIII, the coal solubilized in the water 
during the mixing procedure. Note that in each of Example Nos. I, II, XI 
and XIII, wherein the coal used had a neutral equivalent between about 150 
and about 485, a stable suspension was obtained. 
Obviously, many modifications and variations of the invention, as 
hereinabove set forth, can be made without departing from the spirit and 
scope thereof and therefore only such limitations should be imposed as are 
indicated in the appended claims.