GB2163975A - Froth flotation of coal - Google Patents

Abstract

In froth flotation process for coals, the collector comprises an acid or acidester, having a molecular weight of at least 500, an oil, and a sulfonated hydrocarbon compound.

Description

SPECIFICATION High molecular weight carboxylic acids as collectors of coal Background of the invention The use of various materials as collectors for the beneficiation of coal, particularly oxidized coal, has found more and more favor in recent years. These collectors are used in what has been designated as froth flotation, a process which can be applied to both bituminous and anthracite coal, although best results have been achieved on bituminous coal because of its inherent hydrophobicity. Frothers such as methyl isobutyl carbinol, 2-ethyl-hexanol and the like (see U.S. 4,253,944) are usually employed with the collector, which generally comprises at least one oil, such as fuel oil. Froth is created by dispersing air through the apparatus employed. Sun, Trans.AIME, 199, 396-401, 1954 suggests the use of fatty amines as collectors for oxidized coals, how-ever, because these materials also float the ash portion of the coal, very poor grades are recovered.

Published EPO Application No. 0,106,787, April 25, 1984 discloses the use of various acids, esters, salts, nitriles, their epoxidized, hydroxylated, oxidized or alko-xylated derivatives and 12-30 carbon atom fatty alcohols as coal collectors while published European Application 84/109310/18 discloses the use of at least 10C aliphatic N-free carboxylic acids for the same purppse. Also U.S. Patent Nos. 4,253,944; 4,278,533; 4,305,815 and 4,330,339 disclose the use of the reaction products of a fatty acid or ester and various nitrogen containing compounds such as the hydroxy-alkylated reaction product of N-2-aminoethylpiperazine and ethylene oxide; ether amines or hydroxyalkylated ether amines, alkylated polyalkylene polyamines; diethanolamine etc. for the flotation of coal.

While these collectors have proven to be relatively effective for the beneficiation of coal, they are rather expensive and/or difficult to produce. Accordingly, if a collector could be found which is as effective or more effective than the collectors of the prior art, but less expensive, or more easily produced, a step forward in the art could be achieved.

Summary of the invention According to the present invention, coal is beneficiated in a froth flotation process wherein coal particles are floated in a frothing aqueous medium in the presence of a collector comprising an oil, an acid or acid ester having a molecular weight of at least 500 and, a sulfonated hydrocarbon compound. The process is effective on both bituminous and anthracite coal, but is preferred for the treatment of bituminous coal, and particularly, oxidized bituminous coal. The preferred oil is fuel oil and a conventional frothing agent such as 2-ethylhexanol is preferably employed.

Description of the invention Including preferred embodiments The present invention entails a froth flotation process for beneficiating coal which comprises floating coal particles of flotation size in a frothing aqueous medium in the presence of a collector comprising an oil, an effective amount of an acid or acid ester having a molecular weight of at least 500, and, a sulfonated hydrocarbon compound.

As is mentioned above, any oil may be used in the process of the present invention, however, fuel oil is preferred. Other oils such as crystal free neutral oil recovered from coal tar, kerosene and the like may be used.

As the acid or acidester component of the collector crude mixtures of acids such as tall oil, palm oil, cottonseed oil, olive oil, linseed oil and the like all of which materials are available commercially as high molec-ular weight fractions e.g. the Arizona Chemical Company under the tradename Actinol, and from the Hercules Chemical Company under the tradename Dymerex or PolyPalee may be used.

If mixtures of acids are used, the average molec-ular weight of the mixtures should be within the above designation. Useful materials also include dimers, trimers and polymers of unsaturated acids and/ or rosin acids while fractions obtained from tall oil pitches, condensation pro-ducts of long chain acids and polyols, tall oil pitches per se and the like, are preferred.

The preparation of the dimer, trimer and poly- meric acids useful herein from acids or acids esters is taught in the literature, e.g. J.C. Cowan; J. Am. Oil Chemists' Soc. 39, 534-545, 1962; E. C. Leonard, ibid, 56, 782A-785A, 1979. Commercial products are usually prepared by the process of clay catalyzed, high temperature polymerization. The final products consist of mostly 36 carbon atom entities i.e. dimers, although trimeric and polymeric acids are also pro-duced. These products are oftimes fractionated into specific fractions to concentrate dimers, trimers etc.

The exact structure of the polymerized acids is not yet fully determined. However, a variety of suggestions have been proposed in the literature. One structure is essentially that of a long chain dicarboxylic acid with two alkyl side chains. It appears to contain at least one ethylenic bond and another "linkage" resulting from the polymerization of the two unsaturated acid molecules that form dimer acid. Some idealized possible structures for dimer acids are shown below.

CH=CH(CH2)7C02H cH3(CH2) s (CH2)7C02H CH3(CH2)5 Monocyclic (CH2)7C02H CcH2) 7C02H Iî S CH3(CH2)3CH=CH X I CH3(CH2)3 Bicyclic CH3(CH2)8CH(CH2)7C02 H I CH3(CH2)7CH=C(CH2)7C02 H Acyclic

The molecular weight of these dimer acids is about 560.

"Pure" aliphatic trimer acid is a long-chain tri-carboxylic acid formed by the linking of three unsaturated monobasic acids. The structure is similar to that of dimer acid. The molecular weight of trimer acid is about 800. Polymeric acid is a polybasic acid with molecular weight usually higher than 800.

Besides the commercial process of polymerization, unsaturated acid can be polymerized at 2700-370"C under pressure with or without catalyst. (For example, C. G. Goebel, J. Am. Oil Chemist Soc., 4, 65-68 (1947). The structure of the product has been suggested to be similar to those aforementioned.

Other types of high molecular weight, hydrophobic carboxylic acid useful herein are the polymeric acids which are prepared by the polymerization of rosin acids. The two double-bond abietic-type rosin acids react through a Diels-Alder type mechanism to form dimers, trimers and polymers. Sulfuric acid, an alkyl or metal halide is generally used as the catalyst. The reaction is carried out at room temperature oven an extended period of time. The molecular weight of a "pure" dimeric rosin acid is about 600.

Another method, besides the "synthesis process" described above to obtain high molecular weight, hydrophobic carboxylic acids useful herein is the fractionation of tall oil pitch. Tall oil pitch is the nondistillable residue left during the fractional distillation of crude tall oil. The studies on the composition and fractionation of tall oil pitches obtained from different sources have revealed that these tall oil pitches contain large amounts of high molec-ular weight, hydrophobic carboxylic acid. (V. Era and K.

Noronen, J. Am. Oil Chemists Soc., 56, 992-994 (1979); and B. Holmbom, ibid, 55,.342-344 (1978). These tall oil pitches are mixtures with a broad distribution of molecular weights and contain high concentrations of substance whose molecular weight ranges from 550 to 9,000. For the fraction-ation of tall oil pitch, various techniques have been employed. These include solvent extraction and acid-base extraction.

As used herein, the term "acidester" means an ester which contains at least some functional carboxylic groups.

Examples of useful acidesters are those obtained by the reaction of a suitable alcohol such as isobutyl alcohol with polymers of, for example, maleic anhydride, such as maleic anhydride-octodecene-1 copolymers to produce the re-sultant half-ester. Alternatively, an acid anhydride such as tetralin dianhydride may be reacted with stearyl alcohol to produce the half stearyl ester of tetralin dianhydride.

The third critical component which must be present in the collectors used in the process of the present invention comprises the sulfonated hydrocarbons. SuitabLe examples thereof include sulfonated aromatics such as sulfonated hexadecyl oxybenzene; sulfonated petroleum materials such as petroleum lignosulfonates and the like. Amounts ranging from about 1% to about 30%, by weight, preferably from about 5-20%, by weight, based on the weight of acid or acid ester and oil, are used.

The test for the effectiveness of a coal flotation collector is to determine coal recovery and grade (purity) when the reagent is used in a flotation experiment. The best possible reagent is one which recovers all of the coal in the concentrate and leaves all of the ash minerals in the tailing.

The term "oxidized coal" has come to include any coal that is hydrophilic and poor floating, including surface coals, coals that have been stockpiled for long periods of time after mining or coals of naturally low grade. They are characterized by high oxygen content (i.e. many oxygen-containing functional groups) at least on the coal particle surface.

The term "effective amount", as used herein, is meant to denote the amount of the collector required to increase the recovery of the coal from the coal-bearing charge. Generally, from about 0.1 to about 10.0 Ibs. of collector per ton of coal fed to the flotation cell should be employed. The acid or acidester comprises from about 5 to about 50% of the collector while the oil comprises from about 30-90% thereof and the sulfonated hydrocarbon compound from about 1% to about 30%. Preferred ranges comprise about 20-50% acid or acidester, about 40-80% oil and about 5-20%, sulfonated hydrocarbon, the total in all instances, of course, being 100%.

Activators, conditioning reagents, dispersing reagents, depressing reagents etc. may also be used in conjunction with the collector employed in the present process.

The coal may be floated at a pH ranging from about 3.0-9.5 and preferably from about 5.0-7.0. The pH may be adjusted, if necessary, by the addition of pH adjusters in order to assure the most economical and complete beneficiation.

The following examples are set forth for purposes of illustration only and are not to be construed as limita-tions on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

In the examples, a suitable flotation vessel is charged with an aqueous coal slurry of about 4% solids.

Collector reagent is added and mixing is effected for 0.1-5 minutes. Frother is added and air (or nitrogen) is dispersed through the vessel. The resulting coal-laden froth pours over the top of the vessel or is skimmed off for a period of 2-5 minutes. Generally, nearly all the coal is floated within the first two minutes and after five minutes no additional significant amount of coal is realized. Coal recoveries are determined from the weights of the concentrates and tailings, together with the ash content of both of these fractions. (ASTM D 3174).

In the examples below, several different coals are used, all of which are difficult to float with commercially available reagents. These coals include (1) a laboratory-oxidized coal, (2) a naturally oxidized coal from Spain, (3) a naturally oxidized coal from British Columbia, and (4) a coke dust from France. The Spanish and French coals contain naturally large amounts of inorganic ash minerals, while clay is intentionally mixed with the lab oxidized coal; it is necessary not only to float the oxidized coal, but to selectively float it, leaving the inorganic minerals (clay, etc.) behind.

Flotation results are summarized in Tables 1-4, below. The coals are floated with fuel oil alone or with acids and compared to the compositions of the present invention which include a sulfonated hydrocarbon component, an oil and an acid or acidester of a molecular weight of at least 500. The 3 component systems of the present invention produce excellent coal recoveries, while maintaining good concen-trate grades. Most dramatic results are for the worst coals - the British Columbian coal and the French coke dust both of which gave less than 10% recovery with frother alone.

TABLE 1 Flotation of Lab Oxidized CoallClay Blend (a) pH 5.3 Coal Conc.

Recovery Grade pH 7.0 Dose Example (kg)MT)(b) Reagent(c) (%) (% coal) Recovery Grade 1C - Frother only 32.2 93.0 2C 1.0 #2 Fuel Oil 52.0 95.1 3C 2.0 " 59.7 94.5 4C 1.0 90/10 Fuel Oil/SPF 65.9 90.6 52.2 91.0 5C 2.0 " " " 72.6 88.7 55.4 90.9 6C 0.5 90/10 Fuel Oil/USP 65.0 92.7 7C 1.0 " " " 70.6 93.5 8C 2.0 " 74.3 92.9 9C 2.0 20/80 Oleic Acid/Fuel Oil 71.0 93.9 10C 2.0 50/50 " " " 68.6 94.7 11C 2.0 100 " 62.9 95.4 12C 2.0 20/80 Linoleic Acid/Fuel Oil 68.3 93.3 13C 2.0 20/80 FA-1@Fuel Oil 73.5 93.0 14C 2.0 50/50 " " 74.7 92.3 15C 2.0 20/70/10 FA-1/Fuel Oil/SPF 71.8 89.8 16C 2.0 20/80 Abietic Acid/Fuel Oil 74.2 92.4 17C 2.0 20/80 Actintol" FA7002(g)Fuel Oil 80.3 92.0 17A 2.0 20/70/10 FA7002/Fuel Oil/SPF 78.4 91.2 18 0.4 45/45/10 Acintol P(h)/FO/SPF 66.4 93.6 19 0.6 45/45/10 " " " - - 62.0 94.2 20 0.8 " " " " 71.1 92.8 61.7 91.2 TABLE (Continued) Flotation of Lab Oxidized CoallClay Blend (a) pH 5.3 Coal Conc.

Recovery Grade pH 7.0 Dose Example (kg/MT)(b) Resgent(c) (%) (% coal) Recovery Grade 21 1.0 45/45/10 Acintol P(h) FO/SPF - - 81.4 92.3 22 1.2 " " " 74.8 93.7 70.5 94.1 23 1.6 " " " 84.7 90.3 24 2.0 " " " 87.8 88.6 77.2 91.9 25C 2.0 50/50 Acintol P/Fuel Oil 72.5 92.7 26C 2.0 20/80 " " " 72.7 92.8 27 2.0 20/70/10 " " " SPF 83.7 92.0 28C 2.0 20/80 Hexane Insol fraction(i) of Acintol P/Fuel Oil 81.2 93.0 29C 2.0 20/80 Hexane Sol. fraction of Acintol P/Fuel Oil 76.0 92.8 30C 2.0 20/80 Acidic fraction of Acintol P/Fuel Oil 81.2 93.6 31C 2.0 20/80 Nearly neutral (j) fraction Acintol P/Fuel Oil 79.8 93.8 32C 2.0 20/80 Acintol R(k)/Fuel Oil 71.6 93.5 33C 2.0 20/80 Dymerex Resin(1)/' 66.5 92.6 34C 2.0 20/80 Poly Pale 2 Resin(1)/ 71.0 92.5 Fuel Oil 35 2.0 20/70/10 Acintol R/Fuel Oil/ SPF 76.3 91.4 36 2.0 20/70/10 Dymerex/Fuel Oil/SPF 79.6 92.4 37 2.0 20/70/10 Poly Pale 2/Fuel Oil/ SPF 83.2 90.6 TABLE (Continued) Flotation of Lab Oxidized CoallClay Blend (a) pH 5.3 Coal Conc.

Recovery Grade pH 7.0 Dose Example (kg/MT)(b) Reagent(c) (%) (% coal) Recovery Grade 38C 2.0 20/80 Linoleic acid heated to 350 C under pressure/Fuel 73.7 93.2 Oil 39C 2.0 20/80 Linolenic acid heated 76.1 92.4 to 350 C under pressure/Fuel Oil 40C 2.0 20/80 High mol. wt. fraction 80.7 92.6 of Acintol P/neutral oil (m) Designation for Tables C = Comparative a)W.Va.bitumenous coal heated @ 150 C for 200 hrs./Belden Clay (50% coal/50% clay).

b) Kilogram per metric ton.

c) + 40 l/l 2-ethylhexanol as frother.

f) Arizona Chem. Co. (fatty acids, mostly oleic and linoleic) (M.W.#280).

g) Arizona Chem. Co. (fatty acids dimers (54%) + trimers (21%) (ave. mol. wt.

600) (Acid No. = 151) h) Arizona Chem. Co. (tall oil pitch) (avg. mol. wt. #1000) (Acid No. = 56).

i) Avg. mol. wt. 1900.

j) Acid No. = 12 k) Arizona Chem. Co. tall oil rosin acids (mol. wt. #300).

l) Hercules Chemical Co. (polymerized tall oil rosin acids -mol. wt. # 500).

m) Koppers Chemical Co. (crystal free neutral oil - from coal tar).

USP = Product produced according to USP 4,253,944 SPF = sulfonated petroleum fraction FO = Fuel Oil TABLE 2 Flotation of Oxidized Coal, from British Columbia Coal Conc.

Dose Recovery Grade Example {kglMT) Collector(e) pH (%) (% Coal) 41C - Frother only 6.8 7.0 85.7 42C 1.0 90/10 Fuel Oil/SPF 6.8 40.4 87.3 43C 2.0 " " " 6.8 46.4 87.3 44 0.5 20/70/10 Acintol P/Fuel Oil/SPF 6.8 52.6 87.5 45 1.0 " " " ,' 6.8 62.4 87.1 46 1.5 " " " " 6.8 79.4 86.1 47 2.0 " " " " 6.8 92.7 85.9 48C 2.0 20/80 FA7002/Fuel Oil 6.8 70.1 87.1 49 2.0 45/45/10 Acintol P/Fuel Oil/SPF 6.8 87.1 85.7 50 2.0 " " " " 5.2 79.4 87.4 d) 82% coal, 18% ash e) + 40 l/l 2-ethylhexanol also added as frother TABLE 3 Flotation of Spanish Oxidized Coal (n) Coal Conc.

Dose Recovery Grade Example {kglMT) Collector (o) pH (%) (% Coal) 51 2.0 45/45/10 Acintol P/Fuel Oil/SPF 3.8( ) 54.0 86.9 52 3.0 " " " 3.8 60.7 83.0 53C - Frother Only 5.3 27.5 87.3 54C 2.0 90/10 Fuel Oil/SPF " 56.3 86.8 55C 2.0 70/30 " " 60.4 84.5 56C 2.0 90/10 " /USP " 57.8 86.9 57 2.0 10/80/10 Acintol P/Fuel Oil/SPF " 69.4 82.6 58 2.0 15/75/10 " " " " 74.1 81.8 59 2.0 20/70/10 " " " " 80.2 80.8 60 2.0 30/60/10 " " " " 78.0 79.6 61 2.0 40/50/10 " " " " 75.6 80.0 62 2.0 45/45/10 " " " " 65.6 83.5 n) Feed grade is 65% coal (35% ash).

o) + 40 l/l 2-ethylhexanol as frother TABLE 4 Flotation of French Coke Dust P Coal Conc.

Dose Recovery Grade Example (lb.lT) Collector (q) (%) {% Coal) 63C 1.8 80/20 Fuel Oil/FA7002 52.4 81.6 64C 3.6 " " ,' " 57.0 80.0 65C 9.0 " " " 62.0 77.5 66 1.8 70/20/10 Fuel Oil/FA7002/SPF 54.2 79.3 67 3.6 " " " 61.5 74.6 68 9.0 " a, " 63.6 76.4 69C 1.8 70/20/10 Fuel Oil/FA70021XD8390(r) 47.0 80.1 70C 3.6 " " " 53.2 75.1 71C 9.0 " " " 70.0 71.5 72C 1.8 80/20 Acintol P/Fuel Oil 47.1 83.2 73C 3.6 " " r, 53.2 83.2 74C 9.0 " a, a 57.4 81.1 75C 3.6 80/20 Fuel Oil/Hystrene 3680 (s) 49.0 78.4 76C 3.6 " " " 3675 (s) 45.6 81.1 77C 3.6 " " a 5460 (s) 46.8 79.8 78C 1.8 Fuel Oil 0 - 79C 1.8 Dodecylamine 15.4 37.9 p) 47.6% coke (52.4% ash minerals).

q) + 15ffi1/l Aerofroth 77HP as frother.

r) Dow Chemical Co. - frother s) Humko Chemical Co., tall oil dimer + trimer acids (-500-800 mol. wt.) Example 80 10 Parts of a commercially available solid linear polymer derived from maleic anhydride and octadecene-1 (50/50) are heated with isobutyl alcohol under reflux with stirring in a suitable reaction vessel equipped with a reflux condenser protected from the moisture by a drying tube containing anhydrous calcium sulfate, a mechanical stirrer and an external heating source. The charge polymer is initially insoluble in the isobutyl alcohol and gradually dissolves as the half-ester is produced. After 24 hours, the excess isobutyl alcohol is removed by evaporation under reduced pressure to obtain the desired product; half isobutyl ester of poly(maleic anhydride-octodecene-1).

Example 81 10 Parts of tetralin dianhydride are mixed with 18 parts of stearyl alcohol in toluene and heated in a suitable reaction vessel equipped as in Example 80. The reaction mixture is heated under reflux with stirring for 25 hours resulting in a viscous homogeneous solution which is then cooled to room temperature. Ethyl ether is added to the cooled solution which is then transferred to a separatory funnel and washed with water five times. The organic layer is dried over anhydrous sodium sulfate and filtered. The filtrate is concentrated by evaporation under reduced pressure to give a syrupy product, the half stearyl ester of tetralin dianhydride, which solidifies on standing at room temperature.

The half-ester of Example 80 and the half ester of Example 81 are then used in a flotation process with fuel oil and SPF (10/81/9) and (20/72/8) respectively, in accordance with Example 1 see Table I. The dose of both reagents mixtures individually is 2.0 (kg/MT) and the pH of the system is 5.3. A Coal Recovery of 84.0% and 83.2%, respectively, and a Conc. Grade (% coal) of 93.1 and 90.3, respectively, are recorded.

Claims (8)

1. A froth flotation process for beneficiating coal which comprises floating coal particles of flotation size in a frothing aqueous medium containing an effective amount of a conventional frothing agent, and in the presence of a collector comprising an oil, an acid or acidester having a molecular weight of at least about 500 and a sulfonated hydrocarbon compound.

2. A process according to Claim 1 wherein the coal is oxidized coal.

3. A process according to Claims 1 or 2, wherein said oil is fuel oil.

4. A process according to Claims 1 or 2 wherein said acid or acidester is a dimer or trimer.

5. A process according to Claim 1 or 2 wherein said acid or acidester is a tall oil pitch.

6. A process according to Claim 1 or 2 wherein said acid or acidester is a rosin acid.

7. A process according to Claim 1 or 2 wherein said acid or acidester is the half isobutyl ester of poly (maleic anhydride-octadecene-1).

8. A process according to Claim 1 or 2 wherein said acid or acidester is the half stearyl ester of tetralin dianhydride.