Abstract:
A suspension containing coal, water and the product resulting from the reaction of (1) polycyclic, polycarboxylic acids obtained as a result of the oxidation of coal with (2) a base. The process for preparing such suspensions is also claimed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a uniform coal suspension containing coal, water and the product resulting from the reaction of (1) polycyclic, polycarboxylic acids obtained as a result of the oxidation of coal 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 coal suspension prepared using a relatively inexpensive dispersing agent that is easily prepared and is stable in storage. 
     SUMMARY OF THE INVENTION 
     We have prepared stable coal suspensions using as an inexpensive dispersing agent therefor the product resulting from the reaction of (1) polycyclic, polycarboxylic acids obtained as a result of the oxidation of coal with (2) a base. 
     In preparing the stable suspensions herein we require only three components: water, coal and the product resulting from the reaction of (1) polycyclic, polycarboxylic acids obtained as a result of the oxidation of coal with (2) a base. 
     Any suitable or conventional coal can be used herein in the preparation of the defined suspensions. For example, any of the coals defined hereinafter as being suitable for the preparation of the polycyclic, polycarboxylic acids can be employed. The size of the coal particles can vary over a wide range, for example, from particles whose average length can be as about one inch (2.54 centimeters), or more, to as small as about 500 mesh, although, in general the average length will probably be no longer than about one-half inch (1.27 centimeters) but no smaller than about 200 mesh. 
     The polycyclic, polycarboxylic acids employed in the reaction with a base to obtain the product used to prepare the suspensions herein can be obtained by any conventional or suitable procedure for the oxidation of coal. Bituminous and subbituminous coals, lignitic materials and other types of coal products are exemplary of coals that are suitable 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 compounds (condensed and/or uncondensed), heterocyclic compounds, etc. On a moisture-free, ash-free basis the coal can have the following composition: 
     
                       TABLE I______________________________________     Weight Percent     Broad Range                Preferred Range______________________________________Carbon      45-95        60-85Hydrogen    2.2-8        5-7Oxygen       2-46         8-40Nitrogen    0.7-3        1-2Sulfur      0.1-10       0.2-5______________________________________ 
    
     Any conventional or suitable oxidation procedure can be used to convert the coal to the desired polycyclic, polycarboxylic acids. For example, a stirred aqueous slurry containing coal in particulate form, with or without a catalyst, such as cobalt, manganese, vanadium, or their compounds, can be subjected to a temperature of about 60° to about 225° 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 one to about 20 hours. The product so obtained can then be subjected to mechanical separation, for example filtration, and solid residue can be washed with water, if desired, and dried. The solid product remaining will be a mixture of water-insoluble polycyclic, polycarboxylic acids, hereinafter referred to as &#34;water-insoluble coal carboxylate&#34;. A preferred procedure for preparing such coal carboxylate involves subjecting a slurry containing coal in particulate form to oxidation with nitric acid. An exemplary procedure for so converting coal to coal carboxylate is disclosed, for example, in U.S. Pat. No. 4,052,448 to Schulz et al. Thus, a slurry containing coal can be subjected to reaction with aqueous nitric acid having a concentration of about one to about 90 percent, preferably about three to about 70 percent, at a temperature of about  15° to about 200° C., preferably about 25° to about 100° 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 3.5 MPa), for about five minutes 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, as, for example, in U.S. patent applications Ser. Nos. 923,953 and 924,054, filed July 12, 1978 of Schulz et al. The resulting product is then subjected to mechanical separation, for example, filtration, and the solid residue can be washed with water, if desired, and dried to produce the water-insoluble coal carboxylate. 
     The entire mixture of water-insoluble coal carboxylate so obtained, or any portion thereof, can be used in the reaction with a base herein, if desired. An example of a portion of the entire mixture of water-insoluble coal carboxylate that can be used in the reaction with a base is the extract obtained as a result of the extraction of the entire mixture of water-insoluble coal carboxylate with a polar solvent as defined in U.S. Pat. No. 4,052,448 to Schulz et al. Another example of a portion of the water-insoluble coal carboxylate that can also be reacted with a base herein is that portion of the water-insoluble coal carboxylate that is insoluble in a polar solvent as defined in U.S. Pat. No. 4,147,882 to Schulz et al. Still another example of polycyclic, polycarboxylic acids that can be reacted with a base herein are the water-soluble polycyclic, polycarboxylic acids present in the filtrate obtained when coal is oxidized and the resulting product is subjected to filtration, as for example, the water-soluble, polar solvent-soluble carboxylic acids obtained in U.S. Pat. No. 4,136,481 to Schulz et al. These can be referred to as &#34;water-soluble coal carboxylate&#34;. For simplicity, all of these acids can be referred to as &#34;coal carboxylate&#34;. 
     The individual components of the coal carboxylate are believed to be composed of condensed and/or non-condensed aromatic and non-aromatic rings, with an average number of such rings in the individual molecules ranging from about one to about ten, but generally from about two to about eight. On the average it is believed the number of carboxyl groups carried by the individual molecules will range from about two to about eight, generally from about three to about eight. The average molecular weight can range from about 200 to about 3000, but generally can be from about 300 to about 3000 and the average neutral equivalent from about 50 to about 900, generally from about 70 to about 600. A typical analysis of the coal carboxylates on a moisture-free and ash-free basis that will be reacted with the base herein is set forth below in Table II. 
     
                       TABLE II______________________________________     Weight Percent     Broad Range                Preferred Range______________________________________Carbon      35 to 65     37 to 62Hydrogen    1 to 5       3 to 5Nitrogen    1 to 6       3 to 6Oxygen      20 to 60     30 to 50Sulfur      0.1 to 8     0.1 to 5______________________________________ 
    
     Any base, including the corresponding or basic salt, organic or inorganic, that can react with an acid can be used herein to react with the coal carboxylate. 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, ethanolamine 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 constituent, such as pyridine and quinoline, etc. By &#34;basic salt&#34; 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 carboxylate and the base is easily effected. The amounts of reactants are so correlated that the amount of base used is at least that amount stoichiometrically required to react with all, or a portion (for example, at least about 10 percent, preferably at least about 50 percent), of the carboxyl groups present in the coal carboxylate. This can be done, for example, by dispersing the coal carboxylate in an aqueous medium, such as water, noting the initial pH thereof, adding base thereto while stirring and continuing such addition while noting the pH of the resulting mixture. Such addition can be stopped anytime. In the preferred embodiment wherein a large portion or substantially all of the carboxyl groups are desirably reacted with the base, addition of base is continued until a stable pH reading is obtained. The reactions can be varied over a wide range, for example, using a temperature of about 5° to about 150° C., preferably about 15° to about 90° C., and a pressure of about atmospheric to about 75 pounds per square inch gauge (about atmospheric to about 0.5 MPa), preferably about atmospheric (about 0.1 MPa). The resulting product can then be subjected, for example, to a temperature of about 20° to about 200° C. under vacuum to about 100 pounds per square inch gauge (under vacuum to about 0.69 MPa) for the removal of water therefrom. However, if desired the water need not be removed from the total reaction product and the total reaction product, or after removal of a portion of the water therefrom, can be used to prepare the emulsions as taught herein. 
     The amounts of each component present in the suspension prepared herein can be varied over a wide range. Thus, the weight ratio of coal to water can be in the range of about 19:1 to about 1:6, preferably in the range of about 4:1 to about 1:4. The amount of dispersing agent used, that is, the product resulting from the reaction of coal carboxylate with a base, on a weight basis, relative to water, can be in the range of about 1:199 to about 1:3, preferably in the range of about 1:49 to about 1:4. 
     The suspensions defined and claimed herein are easily prepared. A convenient procedure involves introducing the dispersing agent into water, while mixing, for a time sufficient to dissolve and/or disperse the dispersing agent therein, for example, for a period of about 0.1 to about four hours. If desired, the dispersing agent can be prepared in situ by separately introducing into the water the coal carboxylate and base and following the procedure hereinabove defined. To the mixture so prepared there is then added coal and mixing of the resulting mixture is continued, for example, from 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, colloid mill, etc. The suspensions so prepared are stable, that is, there is no separation of water from the coal and there is no agglomeration of coal into larger size entities. 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. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A mixture of polycyclic, polycarboxylic acids (Coal Carboxylate A) was prepared as follows. To a one-gallon 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 aqueous nitric acid. The mixture was heated to 60° 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 and 800 milliliters of water over a one-hour period. The mixture was held at 60° 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 of water each time), dried in a vacuum oven, resulting in the production of 560 grams of particulate polycyclic, polycarboxylic acids. The North Dakota lignite used analyzed 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. 
     A number of suspensions was prepared as follows. Into a Waring Blender there were placed water, coal carboxylate prepared above and pellets of sodium hydroxide. These materials were mixed at low speeds (about 500 RPM) for about five minutes, sufficient to obtain a reaction between the coal carboxylate and the base. To the resulting solution there was added particulate coal that had passed a 40-mesh (U.S. Series) sieve and the resulting mixture was mixed at high speed (about 20,000 RPM) for about 20 minutes, sufficient to obtain a uniform stable suspension. Four coals were used in the preparation of the suspensions. One, North Dakota lignite, was the same as that used in preparing the coal carboxylate. The English Rank 900 Coal analyzed as follows: 13.6 weight percent water, 63.6 weight percent carbon, 4.3 weight percent hydrogen, 12.9 weight percent oxygen, 1.2 weight percent sulfur, 1.3 weight percent nitrogen and 3.1 weight percent metals. Belle Ayre coal analyzed as follows: 19.0 weight percent water, 58.6 weight percent carbon, 3.84 weight percent hydrogen, 0.81 weight percent nitrogen, 1.21 weight percent oxygen, 0.43 weight percent sulfur and 6.25 weight percent metals. 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 suspensions so prepared were examined at various intervals of time for stability by noting whether or not separation of coal and water had occurred, that is, whether any appreciable settling had occurred. The data obtained are tabulated below in Table III. 
     
                                           TABLE III__________________________________________________________________________           Grams           of           Coal,   Grams of                          GramsExample         Dry Water,                   Coal   of  Stability,No.    Coal     Basis               Grams                   Carboxylate                          NaOH                              Days.sup.(1)__________________________________________________________________________I    Belle Ayre 100 155 10     5   26II   North Dakota Lignite           67  153 10     5   7III  English Rank 900           86.4               113.6                   10     5   7IV   Kentucky No. 9           98.9               101.1                   10     5   7__________________________________________________________________________ .sup.(1) Last day of observation; no settling of coal particles noted. 
    
     The date in Table III above clearly exemplifies the stability of the coal suspensions claimed herein. 
     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.