CA1164110A - Conditioner for flotation of oxidized coal - Google Patents

Abstract

ABSTRACT
Condensation products of a fatty acid or fatty acid ester and a hydroxyalkylated polyalkylenepolyamine are useful as conditioners to improve the recovery of clean coal in a froth flotation process. The presence of these condensation products in the flotation medium is particu-larly effective to enhance the recovery of oxidized bitu-minous coal.

28,127-F

Description

1~64~10 CONDENSATES OF FATTY ACIDS AND
HYDROXYALKYLATED POLYALKYLENEPOLYAMINES
AS AIDS IN FROTH FLOTATION OF COAL

This invention relates to the froth flotation of coal-containing ashes, coal sludge or coal-containing residues to recover coal containing a lower percentage of impurities. In particular, this invention relates to the use of a condensation product of a fatty acid or fatty acid ester and a N-hydroxyalkylated polyalkylenepolyamine com-pound as a conditioner for the flotation of finely-divided coal in the presence of a fuel oil collector.

The process of cleaning and classifying coal inherently deposits some non-combustible mineral matter in association with the combustible carbonaceous solids.
Large fragments of non-combustible material can be removed by screening or other gravity concentration techniques, but other cleaning methods more efficiently remove fine material intimately associated with the car-bonaceous solids. Froth flotation of coal is used in the art to upgrade finely-divided raw coal. Bltuminous coals generally possess a natural hydrophobicity, which results in the coal being floatable in the presence of 28,127-F -l-~641~10 a frother, such as methyl isobutyl carbinol, desirably with a relatively mild collector, such as kerosene. How~
ever, anthracite coals, as well as coals of all grades in which the surface has been at least partially oxidized, float poorly in such a medium, resulting in the loss of significant amounts of combus-tible material with the tail fraction from the flotation.

The loading of the oil-type collector is gen-erally 0.5 to 2 pounds (0.228-0.91 kg) per 1000 kg of coal feed for bituminous coals of intermediate or low grade, with the loading being relatively greater for the flota-tion of lignite and anthracite coals. However, good recovery of oxidized coals or lignite coals can only be effected at such high loadings of the oil-type collector that significant amounts of inert material are floated along with the combustible materials. Sun suggests in Trans. AIME, 199:396-401 (1954), that fatty amines can be utilized as co-collectors in the flotation of oxidized coals to effect enhanced recovery.
~Iowever, even these amine collectors float substantial amounts of ash along with the coal and effect only partial recovery of combustible material.

The defects of the prior techniques mentioned above have been substantially overcome by the present invention, which is a froth flotation process for the upgrading of coal which comprises floating coal particles of flotation size in a frothing aqueous medium in the presence of a fuel oil collector and an effective amount of a condensation product of (a) a fatty acid represented by the formula D-C-O~

wherein D is an aliphatic radical having 4 to 22 carbon atoms or an ester thereof and (b) a compound represented by the formula I

28,127-F - Z -~ .

- 3 - ~ ~ 6 4 ~ ~ 0 R ~ R R
\ N ~ CH2~yN ~ 2 y \

wherein x is a whole number from 1 to 4; each y is 2 or 3; R is independently hydrogen or -CH-CH-OH
T T

with the proviso that at least one R is not hydrogen, and wherein each T is independently hydrogen, methyl or ethyl; said condensation product being prepared in a molar ratio of at least one mole of fatty acid or ester for each mole of the compound of formula I and said condensation product being employed in its free form or as an acid derivative.

Preferred examples of the compounds of formula I
include hydroxyalkylated diethylenetriamine, triethylene-tetramine, tetraethylenepentamine, pentaethylenehexamine, and analogous compounds in which at least one propylene moiety is present instead of an ethylene group, or mixtures thereof. Mixtures of the aforementioned hydroxyalkyated polyalkylenepolymaines are preferred. Hydroxyalkylated polyethylenepolyamines and mixtures thereof are especially preferred. Hydroxyalkylated diethylenetriamine, triethylene-tetramine and mixtures thereof are the most preferred poly-alkylenepolyamine reactants for the condensate.

28,127-F - 3 -~, .

_4~ ~41~0 The compounds of formula I are readily prepared by reacting the corresponding polyalkylenepolyamine with an alkylene oxide in a manner known to the art. Representa-tive alkylene oxides include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, isobutylene oxide and 2,3-pentylene oxide. The hydroxyalkylation reac-tion is conveniently effected by contacting in the stoich-iometric ra~io the polyalkylenepolyamine and the alkylene oxide in the li~uid phase at a temperature of from about 50C to about 150C. Multiple hydroxyalkyl groups can be added to the polyethylenepolyamine by employing more than one equivalent of alkylene oxide for each equivalent of the polyalkylenepolyamine. The preferred alkylene oxide reactants are ethylene oxide and propylene oxide. Mix-tures of the aforementioned alkylene oxides are also operable.

The fatty acid condensed with the compounds of formula I can operably be an acid represented by the formula o D-C-OH

wherein D is an aliphatic radical having 4 to 22 carbon atoms. Oleic, lauric, linoleic, palmitic, stearic, myris-tic acids, mixtures thereof and similar fatty acids are operable. The esters corresponding -to these fatty acids, such as glycerides, are also operable, but less preferred.
For reasons of economy, it is preferred to use crude mix-tures of fatty acids, rosin acids, lignin and unsaponifi-able material, such as tall oil, coconut oil, palm oil, 28,127-F -4-_5 ~ O

palm kernel oil, cottonseed oil, olive oil, linseed oil, peanut oil, and fish oil. Tall oil or tall oil heads are an especially preferred mixtures of fatty acids and rosin acids. Preferably, the tall oil reactant contains less than about 40 percent rosin acids by weight. Tall oil and tall oil heads are well-known compositions described in the Kirk-Othmer EncYclopedia of Chemical TechnoloqY, 2nd Ed., Vol. 19, pp. 614-629 (1969).

The compound of formula I is condensed with a fatty acid or its ester by mixing these reactants and heating until the desired degree of condensation has taken place, as indicated by the water distilled overhead or infrared spectrophotometric analysis of the condensa-tion product. Generally, a reaction temperature of from about 120C to about 250C is operable. This reaction is termed a condensation to distinguish it from the formation of the ammonium salt of the carboxylic acid, which occurs at lower reaction temperatures. Dependent on the reactant, the condensation product may be an ester, an amide or both.
Although it is desirable that the condensation reaction is substantially complete to make most efficient use of the reactants, the condensation product is operable, but less effective, as a conditioner for coal in the presence of a substantial amount of unreacted fatty acid and the uncon-densed ammonium salt of the acid. The term "conditioner"indicates that the condensation product is primarily effective to enhance the hydrophobicity of the coal sur-face. The use of the descriptive term "conditioner" is not intended to exclude the possibility that this conden-sation product acts as a co-collector with the fuel oil or kerosene collector. The term "condensation product", 28,127-F -5-as used herein, refers to not only the condensation prod-uct in its free form, but also acid derivatives thereof, as described hereafter.

The above-described condensation products neu-tralized or partially neutralized with inorganic or organic acids are operable as conditioners in the instant flotation process, but are generally less effective than the conden-sates in their free form. These derivatives are frequently more readily dispersed in the aqueous flotation medium than are the parent compounds. These acid derivatives may be either a salt, partial salt or acid complex, depending on the acid and condensate employed. Common inorganic acids which can be used to prepare these derivatives include phosphoric, nitric, boric, hydrochloric, hydrobromic, sul-furic and alkane sulfonic acids. Organic carboxylic acidswhich can be used include aliphatic mono-, di-, or tricar-boxylic acids; lower alkyl carboxylic acids; mono- or dihydroxy lower alkyl carboxylic acids and amino-substi-tuted compounds thereof; and unsaturated aliphatic acids.
Examples of these organic acids include formlc, acetic, hydroxyacetic, propionic, butyric, isovaleric, lactic, gluconic, aminoacetic, malonic, succinic, adipic, malic, tartaric, glutaric, maleic, fumaric, citric, lsocitric, aconitic, oxalic, salicylic, benzoic, and naphthenic acids. Fatty acids can also be employed for this pur-pose, but are not as desirable as other lower organic acids. The C1 to C~ organic acids are preferred. Ace tic acid is particularly preferred to prepare so called partial acetate salts by the partial neutralization of the conde~sation product with acetic acid.

28l127-F -6-- ~L16~1~0 The effectiveness of the instant organic car-boxylic acid condensation product is greatest when the reactants are condensed in a specific range of mole ratios. Advantageously, at least about one equivalent of fatty acid or ester is condensed with each equivalent of a hydroxy or secondary amine moiety. To avoid waste of fatty acid or ester, the number of moles of fatty acid and/or ester reacted with the compound of formula I
should not exceed the number of moles of the compound of formula I multiplied by the average number of reactive sites on a molecule of the compound. The term "reactive sites" refers to the exchangeable hydrogen substituents on the amine group(s) and the reactlve hydroxyl substitu~
ents on the hydroxyal~yl group(s), which will react with the fatty acid or fatty acid ester to produce amides and esters, respectively. In the foregoing mole ratios, the moles of fatty acid in crude mixtures derived from natu-ral sources do not include the moles of such minor gener-ally inert compounds as unsaponifiable matter.

The loading of the condensation product in the flotation medium which affects the greatest recovery of combustible carbonaceous matter with a tolerable amount of inert matter is dependent upon such factors as the size, grade, degree of oxidation and inert matter content of the coal feed, as well as the loading of frother and other adjuvants. The term effective amount is used herein to denote the amount of said compounds required to increase the recovery of coal by froth flotation in the presence of fuel oil and a frother. Generally, where this condi-tioner is employed with only fuel oil and a frother, thecondensate is advantageously employed in a ratio of from 28,127-F -7-~6fl~10 about 0.01 to about 1.0, preferably about 0.005 to about 0.5 kilograms, of condensate per 1000 kg of coal flota-tion feed.

The instant conditioner can be utilized in conjunction with co-collectors or other adjuvants, such as activators, conditioning reagents, dispersing reagents, frothing reagents and depressing reagents. Fuel oil is employed in the flotation medium as a collector and/or dis-persing reagent. Representative fuel oils include diesel oil, kerosene, Bunker C fuel oil, and mixtures thereof.
The fuel oil can generally be advantageously employed in a ratio of from about 0.25 to about 2.5 kilograms fuel oil per 1000 kg of coal flotation feed. The optimal loading of fuel oil in the flotation medium is influenced by num-erous factors, such as the size, degree of oxidation and grade of the coal to be floated and the loading of condi-tioner and frother. Therefo.re, the loading of the fuel oil should be optimized empirically to effect the great-est selectivity and recovery during flotation. It is generally desirable to introduce the condensation prod-uct to the flotation medium in a fuel oil emulsion.

A frothing agent should be present in the flotation medium to promote formation of a froth. Con-ventional frothers, such as pine oil, cresol, isomers of amyl alcohol and other branched C4 to C8 alkanols are suitable for this purpose. However, methyl isobutyl car-binol and polypropylene glycol alkyl or phenyl ethers are preferred as frothers, with polypropylene glycol methyl ethers having a weight average molecular weight of from 200 to 600 being more preferred. The optimal loading of frother in the flotation medium is influenced 28,127-F -8-i4~1V
g by a number of factors, most important of which is the particle size, grade and degree of oxidation of the coal.
Generally, a ratio of from 0.05 to about 0.5 kilogram of frother per 1000 kg of coal feed is advantageous.

The coal to be floated by the instant process can suitably be anthracite, bituminous, or subbituminous.
This process is preferably employed to float coal which cannot be floated with conventional frothers alone and is particularly effective in the flotation of bituminous coal o~ intermediate or low grade, where the surface of the coal is oxidized to an extent which significantly impedes the flotation of the coal by conventional methods.

The size of the coal flotation feed is impor-tant as generally particles larger than about 28 mesh (U.S. Sieve Size) are difficult to float. In typical operations, coal particles larger than 28 mesh, advanta-geously larger than 100 mesh, are separated from both the inert material mined therewith and more finely divided coal by gravimetric separation techniques. However, if a substantial fraction of the coal in the flotation feed is contained in particles larger than 28 mesh, it is desirable that the feed is comminuted prior to flotation.

The sized coal flotation feed in preparation for flotation is first optionally washed and then mixed with sufficient water to prepare an aqueous slurry having a concentration of solids which promotes rapid flotation.
Generally, a solids concentration of from about 2 to about 20 weight percent solids, more preferably about 5 to about 15 weight percent, is preferred. The aqueous coal slurry 28 ,127-F -9-is desirably conditioned with the condensation product, a frother, fuel oil and any other adjuvants by mixing or agi-tating the slurry prior to flotation in a manner known to the art. Generally for coal that is difficult to float, it is advantageous to mix the coal slurry with the condi-tioner and fuel oil for a period of time prior to flota-tion, so as to cause intimate contact of the conditioner and fuel oil with substantially all of the coal. Where the aqueous coal slurry is prepared in a container dis-tinct from the flotation cell and then is conveyed to theflotation through conduits, the desired intimate contact can conveniently be attained by introducing the con~i-tioner and fuel oil to the slurry upstream from the flo-tation cell. The frother, however, should be introduced to the slurry shortly before or during flotation to pro-vide maximum frothing.

The coal is operably floated at the natural pH of the coal in the aqueous slurry, which can vary from about 3.0 to about 9.5 depending upon the composition of the feed. However, a pH-adjusting composition is option-ally used when necessary to adjust and maintai~ the p~ of the aqueous coal slurry prior to and during flotation to a value from about 4 to about 9, preferably about 4 to about 8, which generally promotes the greatest coal recov-ery. If the coal is acidic in character, the pH-adjusting composition can be an alkaline material, such as soda ash, lime, ammonia, potassium hydroxide or magnesium hydroxide, with sodium hydroxide being preferred. If the aqueous coal slurry is alkaline in character, a carboxylic acid such as acetic acid, or a mineral acid such as sulfuric acid or hydrochloric acid, is operable to adjust the pH.

28,127-F -10-6~1~V

The conditioned and pH-adjusted aqueous coal slurry is aerated in a conventional flotation machine or bank of rougher cells to float the coal. Any conventional rougher flotation unit can be employed.

The practice of the process of the instant invention can be used to upgrade coal without the aid of secondary processes . Alternatively, the process can be used in conjunction with secondary flotations follow-ing the instant process to effect even greater upgrading of the coal.

The following examples illustrate this inven-tion. Unless otherwise indicated, all parts and percent-ages are by weight.

Exam~les 1-5 In a series of substantially identical flota-tion runs that differ principally in the identity of the frother and presence or absence of a conditioner, 200 grams of comminuted coal is diluted with deionized water to a slurry of 6.67 percent solids. The coal is a low grade, bituminous coal having a highly oxidized surface as indicated by the high oxygen content (14.3 percent) of the coal. The fraction of the coal feed consisting of particles larger than 25 mesh (U.S. Sieve Series) is sepa-rated, comminuted and then recombined with the remainder of the coal prior to dilution. The comminuted coal feed is more than 90 percent particles smaller than 80 mesh (U.S. Sieve Series). The coal as charged to the slurry contains 14.7 percent ash.

28,127-F

-12- ~16~10 The conditioner is prepared in a two-step pro-cess. In the flrst step, 1 equivalent of diethylenetri-amine (DETA) is reacted with 1, 3 or 5 equivalents of ethylene oxide (EO) at a temperature of from 100 to 135C for from 2 to 8 hours. The resulting hydroxyeth-ylated product is then condensed with 2, 3 or 4 equiva-lents of a tall oil fatty acid (TOFA) at a temperature from about 130C to about 225C until the reaction is substantially complete. Infrared spectrophotometric analysis is employed to confirm that the reaction is substantially complete in each instance. This tall oil fatty acid according to analysis by conventional methods contains 39 percent rosin acids, 29.3 percent oleic acid, 23 percent linoleic acid, 3.7 percent conjugated lino-leic acid, 1.8 percent stearic acid and about 3 percentother acids and components.

The aqueous coal slurry is introduced into a flotation machine having a three-liter cell. The pH of the slurry (initially 4) is adjusted to 7 by adding sodium hydroxide. The coal slurry is agitated for about seven minutes to thoroughly wet the coal, at which time 0.5 gram of a refined kerosene is added to the slurry to effect a loading of 2.5 kilograms of kerosene per 1000 kg of coal feed. One-half milliliter of a 5 percent solu-tion of one of the aforementioned conditioners in keroseneis added in each of five flotation runs. A single control flotation run is also made, in which no conditioner is added with the kerosene.

Next 0.04 ml of a polypropylene glycol methyl ether frothing agent having an average molecular weight 28,127-F -12-~16~110 of about 400 is added to the medium as a frothing agent.
The aqueous coal slurry is conditioned by agitation for one minute, after which aeration of the medium is initi-ated and continued for four minutes. A frothy concentrate is collected during aeration.

The collected concentrate is first dried in an oven and then weighed. The percent recovery of coal by flotation is determined from the weight of coal in the concentrate divided by the weight of coal (i.e., total weight less weight of ash) in the 200-gram charge.
A one-gram sample of the concentrate is completely burned and the ash content of the concentrate is determined from the weight of the material remaining after combustion.
Table I tabulates the identity of the conditioner for each run as well as the percent recovery of coal and ash con-tent in the concentrate.

TABLE I

Conditioner Coal Ash CompositionRecovery Content 20 Example (Ratio-DETA:EO:TOFA) (%) (%) 1 1:1:4 66.2 10.2

2 1:3:2 50.9 9.9

3 1:3:3 60.2 10.1

4 1:3:4 65.5 10.0 1:5:4 S8.5 9.6 Comparative none 35.9 9.1 Experlment*

*Not an embodiment of this invention.

28,127-F -13-~64~0 Example 6 In a manner otherwise similar to Example 1, a condensate of monohydroxypropylated DETA and 4 equiva-lents of TOFA is employed as the conditioner. This con-ditioner effected coal recovery of 64.6 percent and anash content of 10.4 percent.

Example 7 In a manner otherwise similar to Example 1, a condensate of tetrahydroxyethylated triethylenetetra-mine and 5 equivalents of TOFA is employed as the condi-tioner. This conditioner effected coal recovery of 65.8 percent and an ash content of 10.4 percent.

28,127-F -14-

Claims (8)

1. A froth flotation process for the upgrading of coal which comprises floating coal particles of flotation size in a frothing aqueous medium in the presence of a fuel oil collector and an effective amount of a condensation product of (a) a fatty acid represented by the formula D-?-OH

wherein D is an aliphatic radical having 4 to 22 carbon atoms, or an ester thereof and (b) a compound represented by the formula I

wherein x is a whole number from 1 to 4; each y is 2 or 3; R is independently hydrogen or with the proviso that at least one R is not hydrogen, and wherein each T is independently hydrogen, methyl or ethyl;
said condensation product being prepared in a molar ratio of 28,127-F - 15 -at least one mole of fatty acid or ester for each mole of the compound of formula I and said condensation product being employed in its free form or as an acid derivative.

2. The process as in Claim 1 wherein the coal is a bituminous coal having an oxidized surface.

3. The process as in Claim 1 wherein y at each occurrence in formula I is 2.

4. The process as in Claim 3 wherein x is 1 or 2.

5. The process as in Claim 1 wherein in each moiety of the formula in the compound of formula I, T at one occurrence is hydrogen and T at the other occurrence is hydrogen or methyl.

6. The process as in Claim 1 wherein the conden-sation product is present in its free form.

7. The process as in Claim 1 wherein the conden-sation product is present as an acetic acid neutralized derivative.

8. The process as in Claim 1 wherein the fatty acid or ester is a tall oil fatty acid, tall oil heads, a tall oil fatty acid or a mixture thereof , 28,127-F - 16 -