A PROCESS FOR BENEFICIATION OF COAL BY SELECTIVE CAKING

Abstract: A process is disclosed for beneficiation of coal by selective caking, in which process a caking mixture is em­ ployed consisting of: - one or more solvents selected among the light hydrocar­ bons having boiling points not higher than 70°C; - one or more non-ionic additives selected among oil-­ soluble propoxylated or propoxylated-ethoxylated phenolic or alkylphenolic compounds; - possibly one or more heavy co-caking agents selected among coal-derived oils having boiling points between 200°C and 400°C, or the residual products of petroleum refining, or mixtures thereof.

Description: This invention relates to a process for beneficiation of coal through selective caking. The best known processes for the beneficiation of coal are mainly founded on the difference between physical properties of the predominantly organic matter and the predominantly inorganic matter. For example, such materials can be separated on the basis of their particle sizes or of their densities, or or their different electric or magnet behaviour. Said processes are not always conveniently applicable when the physical properties of the materials to separate are similar. A solution to that problem is given by the exploitation of another property of the phases to separate: their different affinities for water, which are typically exploited in caking and foam flotation processes. In particular, the caking process consists in forming a water-coal dispersion to which an organic compound of hydrocarbon nature is added under stirring, in order to obtain the formation of caked masses mainly consisting of pure coal and a water dispersion containing solid matter which is predominantly inorganic in nature. Fuel oils of petroleum origin, heavy oils from distillation of coal pyrolysis tars, petroleum middle distillates (such as kerosene, gasoil, and so on) are employed as organic caking compounds. A drawback of such procedure consists in the fact that oil employed for causing coal to cake is normally left behind in the product, with a consequent remarkable increase in the costs of processing. On the other hand, the recovery of the caking agent possibly performed would cause an economic burden that would be onerous at the same or even at a higher extent because of the poor volatility of the products mentioned. In order to obviate such drawbacks, use has been made of volatile hydrocarbon solvents and their derivatives as caking agents, which compounds can be recovered after the inorganic matter has been removed. The light hydrocarbon solvents employed are mainly n-pentane, n-hexane, petroleum ethers and their fluoro-chloroderivatives (Freons). Said solvents generally show selectivities higher than heavy solvents, but they show the drawback with respect to the latter of having lower bridging power, so that some coals having more unfavourable surface properties cake with heavier oils but they do not cake with light oils. A caking process has been recently claimed in the Japanese Patent Application published before examination (kokay) JP 84/105089, said process employing together with a caking agent (selected among paraffin oil, light oil (petrol), crude oil, asphalt, oil from coal liquefaction, low-temperature tar, high-temperature tar, all kinds of residual oil and fuel oil (the preferred solvent)) also a non-ionic, oil soluble compound as an additive, and in particular ethoxylated nonylphenol in maximum amounts of 5 % by weight with respect to the caking agent. According to the Authors of said Patent Application, the process they claim is characterized by higher caking speeds, as well as by lower amounts of the caking agent employed and higher dehydration (i.e., lower water concentrations in the caked product), said process also allowing less amounts of ashes to be obtained in the final product. Accordingly, such process is an improvement with respect to the use of the above mentioned products alone, but it is unsuitable for a final economic recovery of the caking agent because of the poor volatility of the claimed liquids. Moreover, no mention is made of the possibility of so processing partially oxidized coals that are otherwise uncakable. This latter problem had been tackled by other researchers, such as D.V.Keller, in US-A-4 484 928, claiming the use, together with light or heavy caking agents, of several additives, such as carboxylic acids, oleic acid and its salts, amines, alcohols and their derivatives, and others, in caking operations performed on partially oxidized coals. The patent in question also reports the use of an ethoxylated phenol (composition not disclosed) as a method for shortening the caking times considerably for a coal which is cakable as itself. However, using acidic or basic products or ethoxylated phenols is not such as to render difficult coals to become cakable or agglomerable, since the bridging power of the caking liquids employed, such as Freons (Trade Mark), n-pentane, n-hexane, petroleum ethers, is poor, as will be better seen in the examples hereof. US-A-4 331 447 discloses the use of a blend of a heavy hydrocarbon with a surfactant as a caking agent, the surfactants being an ethoxylated compound, a propoxylated compound, or a propoxyated and ethoxylated compound, including propoxylated alkylphenols. US-A-4 484 928 discloses the use of blends of a light hydrocarbon, such as pentane and 2-methylbutane, with a surfactant. The Applicants have surprisingly ascertained that, by employing a particular agglomerating mixture, it becomes possible to cake uncakable or difficult-to-cake coals even in the presence of light solvents, while concurrently achieving very good results as to selectivity and recovery. As a matter of fact, high-volatiles bituminous coals, such as the Russian and the Colombian, and sub-bituminous coal, such as the Italian one from Sardinia (Sulcis), which do not cake with pentane alone or the added ethoxylated phenol due to their poor surface hydrophobicity, can be caked, this notwithstanding, when using the process of this invention, with the attendant advantage of the low concentration of the products used in the caking solvent which permits to dispense with recovery. The present invention, therefore provides a process for the beneficiation of coal by selective agglomeration, characterized in that the agglomerating mixture consists of: (a) at least one solvent selected among the light hydrocarbons having a maximum boiling point of 70°C, in an amount of from 2% to 50% by weight relative to the coal to be agglomerated; (b) at least one nonionic additive selected from the oil-soluble phenol compounds, alkylphenol compounds, ethoxylated phenol compounds and ethoxylated alkylphenol compounds, in an amount of from 0,02% to 1% by weight relative to the coal concerned, having the general formula: wherein R-OH, the substrate for the propoxylation and the facultative ethoxylation, is selected from: phenol, monosubstituted phenol, disubstituted phenol wherein the substituents R I and R II , when present, are equal to, or different from one another, and are selected from hydrogen, methyl, ethyl and propyl, x is from 2 to 100, and y is from 0 to 20, the x:y ratio being greater than 2,3 when y is other than zero. According to another aspect of the process according to the present invention, the agglomerating mixture further contains at least one heavy agglomerant selected from oils derived from coal and having a boiling point of from 200°C to 400°C, and the residues of crude oil processing or admixtures of the foregoing, in a maximum amount of 3% by weight relative to the coal to be agglomerated. The preferred range of the solvent amount is from 3% to 20% by weight relative to the coal, and preferred members are n-pentane, n-hexane and petroleum ethers. The preferred range of the additive amount is from 0,05% by weight to 0,3% by weight relative to the coal to be agglomerated. Th oil soluble propoxylated phenolic or alkylphenolic compounds can additionally be ethoxylated, if so desired. The preferred substrate for the propoxylation and the possible ethoxylation is phenol as such or as the mono-or di-substituted phenols, the substituting groups being R I and R II . In addition to the additive or to the additives selected among the oil soluble, propoxylated (and possibly also ethoxylated) phenolic or alkylphenolic compounds, the caking mixture can also possibly be made up of other non-ionic additives selected among the ethoxylated alkyl phenols. The oil soluble ethoxylated compounds can be selected among the ethoxylated alkylphenols, having an alkyl group preferably with 8-12 and more preferably with 8-10 carbon atoms, and preferably with 3-8 and more preferably with 3-5 ethoxy groups, among which the octylphenol and the nonylphenol, ethoxylated with 3 or 4 ethoxy groups, are herein mainly mentioned. Also in case the additives employed are selected among ethoxylated alkylphenols, it is preferable that the total amount of all additives is not higher than 1 % with respect to coal. The heavy co-caking agent or agglomerants wich are facultatively present are preferably contained in amounts between 0 and 3 % by weight with respect to coal, and more preferably between 0.2 and 2 % by weight. Such products, employed in so reduced amounts, can be conveniently left behind in the beneficiated coal without heavy economic burdens. Coal-derived oils can be obtained through pyrolysis or through coking or through hydroliquefaction of coal itself. In particular, they can be obtained from coke-oven tar, and more particularly from distillation of coke-oven tar. Normally, oils derived from distillation of coke-oven coal tars can be obtained from various successive fractionations through distillation. For instance, two products that can be employed as co-caking agents are obtained already from the first distillation process, i.e., a crude anthracene oil from the first distillation (with boiling point between 230 and 400°C), and an anthracene oil from the second distillation (boiling point: 270-400°C), and a lighter product that cannot be employed as such. However, after dephenolizing and further redistillation, other cuts are obtained from said lighter product, the heaviest cuts (the gas washing oil or "debenzolizing oil", with boiling point 235-300°C and "pasty" anthracene oil (300-400°C)) being usable as co-caking agents. Such oils deriving from distillation of coke-oven coal tar, can be employed alone or as mixtures of the same. A particular mixture of such oils is for instance creosote oil which is made up of mixtures of anthracene oils. Products which are not liquid at room temperature ("pasty" products) can be employed as such or in the fluidized state through previous controlled crystallization and filtration of the starting "pasty" product. A typical composition of a pasty anthracene oil is reported in the following Table 1. The "fluidized" variant contains about less 40 % of anthracene and carbazole, whereas the higher homologues keep in the filtered product because they are liquid for the most part. The residual products of petroleum refining can be those coming from the bottoms of atmospheric distillation processes, of vacuum distillation or of cracking processes. Said residual products or bottoms can be employed as such or they can can be previously "flushed" with middle distillates (gasoil,kerosene and so on). The "flushed" bottoms are called more usually fuel oils. The stages which the process of the present invention is made up of are those already known, i.e., the following: milling coal to particle sizes not larger than 4 mm, preferably not larger than 1 mm; dispersing the milled coal into water at a concentration between 5 % and 30 % by weight with respect to the dispersion itself; adding the caking mixture, as such or as a water emulsion previously prepared to the dispersion so formed; stirring the dispersion at high speed for times ranging preferably between 1 and 20 minutes; possible stabilizing and growing the coalescence products through gentle stirring for times ranging preferably between 1 and 10 minutes; separating the caked mass from the inorganic matter dispersed in the water phase by screening and possibly by washing said agglomerated mass, or by skimming or by decantation. In order to better illustrate the meaning of the present invention, some examples are reported in the following, which are not to be considered as limitative of the invention itself. The following table illustrates some properties of coals processed in the examples mentioned above; in particular, for better differentiating the three types of high-volatile bituminous coals, the comparative results are herein reported as obtained from the analysis of the surface composition through XPS (X-ray photo Spectrometry). It is evident that the coals from Russia and from Columbia show the lowest tendency to caking or agglomeration (as confirmed in the following examples), whereas for the Italian coal (from Sulcis) such aspect is already put into evidence by its type. Example 1 A high-volatile bituminous coal from Russia, containing 14 % by weight of ashes, is milled to a maximum granulometry of 750 µm. 50 g of such coal is dispersed in 200 ml of water and stirred in a suitable reactor provided with baffles and a blade double turbine stirrer, in order to allow a complete wetting to be obtained of the phase richest in inorganic matter. The stirring time is of 5 minutes, at a speed of 1,000 rounds per minute (rpm). After increasing the speed to 2,000 rpm, the caking mixture is added, said mixture consisting of 7 g of light solvent (n-hexane, 14 % by weight on the coal basis (c.b.)), 0.05 g of mixed cresols (the ortho-meta-para cresols) propoxylated with 6 (average) oxypropylenic units (0.1 % by weight c.b.) and 0.5 g of a fuel oil commercially available (1 % by weight c.b.). The stirring at high speed is kept for two minutes in order to allow the caking packet to develop an efficient action; then the mixture is stirred for additional 5 minutes at 1,000 rpm in order to obtain a further increase in the sizes of the caked products. Finally the caked or agglomerated product is recovered through screening with a screen having meshes of 750 µ. The cake product is characterized in terms of weight and composition (percentage of ashes). The results so obtained were as follows: Recovery of the heat value 93.5 % by weight Ash percentage 3.2 % by weight Example 2 With respect to example 1, a caking mixture is employed consisting of n-hexane (7 g; 14 % by weight c.b.), a pasty anthracene oil from the processing of coke-oven tars (0.5 g; 1 % by weight c.b.) and a propoxylated phenol with 12 (average) propoxylene units (0.05 g; 0.1 % by weight c.b.). The time required for the stirring stage at high speed is again of 2 minutes. Results were as follows: recovery of the heat value 94 % by weight ash percentage 3.0 % by weight Example 3 With respect to example 1, a caking mixture is employed consisting of n-hexane (7 g; 14 % by weight c.b.), a pasty anthracene oil (0.5 g; 1 % by weight c.b.) and mixed cresols (ortho-meta-para cresols) propoxylated with 6 (average) propoxylene units (0.05 g; 0.1 % by weight c.b.). The time necessary for the stirring stage at high speed is again of 2 minutes. Results were as follows: recovery of the heat value 94 % by weight ash percentage 3.0 % by weight Example 4 (comparative) With respect to example 1, caking mixtures are employed containing just n-hexane in amounts respectively of 2.5g (5 % by weight c.b.), 5 g (10 % by weight c.b.), 7.5 g (15 % by weight c.b.), 10 g (20 % by weight c.b.) and 15 g (30 % by weight c.b.). For all said amounts, no consistent result is obtained even by prolonging the stirring stage at high speed till 30 minutes, and the recovery of the heat value keeps lower than 20 % by weight in all cases. Example 5 (comparative) With respect to example 1, caking mixtures are employed consisting of n-hexane and propoxylated phenol containing 6 (average) oxypropylene groups in amounts respectively of 5 g (10 % by weight c.b.) and 0.025 g (0.05 % by weight c.b.), 20 g (40 % by weight c.b.) and 0.1 g (0.2 % by weight c.b.). For all said amounts, no consistent result is obtained even by prolonging the stirring stage at high speed up to 30 minutes, and the recovery of the heat value is lower than 20 % by weight in all cases. The example shows that this type of coal requires the addition of a small amount of heavy oil. Examples 6-8 (comparative) With respect to example 1, 3 different caking mixtures are employed consisting of: n-hexane (7 g; 14 % by weight c.b.) and fuel oil (0.5 g; 1 % by weight c.b.) (example 6); n-hexane (6 g; 12 % by weight c.b.) and fuel oil (1.5 g; 3 % by weight c.b.) (example 7) n-hexane (6 g; 12 % by weight c.b.) and anthracene oil (1.5 g; 3 % by weight c.b.) (example 8). Results were as follows: Example Recovery, % Ashes percentage Stirring time at high speed 6 88.3 % wt. 3.1 % wt. 15 min 7 93.5 % wt. 3.8 % wt. 10 min 8 94.0 % wt. 3.2 % wt. 10 min Example 9 A high-volatile bituminous coal from Columbia, containing 10.5 % wt. ashes, is processed as disclosed in example 1, employing the same caking mixture as that used in said example. The time required for the stirring stage at high speed is of 10 minutes. Results were as follows: recovery of the heat value 95.2 % by weight ash percentage 2.2 % by weight. Example 10 With respect to example 9, a caking mixture is employed consisting of n-hexane (6 g; 12 % by weight c.b.), fuel oil (1.5 g; 3 % wt. c.b.) and propoxylated phenol having 6 (average) propoxyl units (0.1 g; 0.2 % by wt. c.b.). The time necessary for the stirring stage at high speed is of 5 minutes. Results were as follows: recovery of the heat value 94.1 % by weight ash percentage 2.7 % by weight Example 11 With respect to example 9, a caking mixture is employed consisting of n-hexane (7 g; 14 % by weight c.b.), fuel oil (0.5 g; 1 % wt. c.b.) and propoxylated phenol having 12 (average) propoxylene units (0.05 g; 0.1 % wt. c.b.). The time necessary for the stirring stage at high speed is of 10 minutes. Results were as follows: recovery of the heat value 92.8 % by weight ash percentage 2.0 % by weight Example 12 With respect to example 9, a caking mixture was employed consisting of n-hexane (7 g, 14 % wt. c.b.), an anthracene oil (0.5 g, 1 % wt. c.b.) and propoxylated cresols (ortho-meta-para cresols) having 6 (average) propoxylene units (0.05 g, 0.1 % wt. c.b.). The time necessary for the stirring stage at high speed is of 10 minutes. Results were as follows: recovery of the heat value 93.1 % ash percentage 2.0 % Example 13 With respect to example 9, a caking mixture was employed consisting of n-hexane (7 g, 14 % wt. c.b.), fuel oil (0.5 g, 1 % wt. c.b.) and propoxylated cresols (ortho-meta-para cresols) having 10 (average) propoxylene units, and next (block) ethoxylated with two oxyethylene units (0.05 g, 0.1 % wt. c.b.). The time necessary for the stirring stage at high speed is of 10 minutes. Recovery of the heat value 93.8 % wt. ash percentage 2.3 % wt. Example 14 (comparative) With respect to example 9, caking mixtures are empolyed containing just n-hexane in amounts respectively of 2.5 g (5 % wt. c.b.), 5 g (10 % wt. c.b.), 7.5 g (15 % wt. c.b.), 10 g (20 % wt. c.b.) and 15 g (30 % wt. c.b.). For all said amounts, no consistent result was obtained even by prolonging the stirring stage at high speed up to 30 minutes, and in all cases the recovery of the heat value was lower than 20 % wt. Examples 15-17 (comparative) With respect to example 9, 3 different caking mixtures are employed consisting of: n-hexane (7 g, 14 % wt. c.b.) and fuel oil (0.5g, 1 % wt. c.b.) (example 15); n-hexane (6.5 g, 13 % wt. c.b.) and fuel oil (1g, 2 % wt. c.b.) (example 16); n-hexane (6 g, 12 % wt. c.b.) and anthracene oil (1.5 g, 3 % wt. c.b.) (example 17). Results are as follows: Example Recovery, % Ash percentage Stirring time at high speed 15 68 % wt. 2.0 % wt. 30 min 16 75 % wt. 1.9 % wt. 30 min 17 73 % wt. 2.2 % wt. 30 min Example 18 A sub-bituminous Italian coal (from Sulcis), already conditioned by atmospheric agents for a long time and containing 22 % ashes is processed as disclosed in example 1, but employing a caking mixture consisting of n-hexane (6 g, 12 % wt. c.b.), fuel oil (1.0 g, 2 % wt. c.b.), cresols (ortho-meta-para cresols) propoxylated with an average number of 6 propoxylene units (0.1 g, 0.2 % wt. c.b.). The time necessary for the stirring stage at high speed is of 8 minutes. Results are as follows: recovery of the heat value 82 % wt. ash percentage 10 % wt. Example 19 (comparative) With respect to example 18, caking mixtures are employed containing just n-hexane in amounts respectively of 2.5 g (5 % wt. c.b.), 5 g (10 % wt. c.b.), 7.5 g (15% wt. c.b.), 10 g (20 % wt. c.b.) and 15 g (30 % wt. c.b.). For all said amounts, no consistent result is obtained even by prolonging the time of the stirring stage at high speed up to 30 minutes, and the recovery of the heat value is lower than 20 % by weight in all cases. Example 20 A high-volatile bituminous coal from Poland, containing 10.8 % ashes is processed as disclosed in example 1 with the same caking mixture as that employed in said example. The time necessary for the stirring stage at high speed is of 30 seconds. Results are as follows: recovery of the heat value 95.5 % wt. ash percentage 4.0 % wt. Example 21 With respect to example 20, a caking mixture is employed consisting of n-hexane (7 g, 14 % wt. c.b.) anthracene oil (0.5 g 1 % wt. c.b.) and phenol propoxylated with an average number of 12 propoxylene units (0.05 g, 0.1 % wt. c.b.). The time necessary for the stirring stage at high speed is of 30 seconds. Results are as follows: recovery of the heat value 95.0 % wt. ash percentage 4.2 % wt. Example 22 With respect to example 20, a caking mixture is employed consisting of n-hexane (7 g, 14 % wt. c.b.) and propoxylated phenol having 6 (average) propoxylene units (0.025 g, 0.05 % wt. c.b.). The time necessary for the stirring stage at high speed is of 30 seconds. Results are as follows: recovery of the heat value 94.4 % wt. ash percentage 4.0 % wt. Example 23 (comparative) With respect to example 20, a caking mixture is employed containing just n-hexane (5 g, 10 % wt. c.b.). The time necessary for the stirring stage at high temperature is of 3 minutes. Results are as follows: recovery of the heat value 93 % wt. ash percentage 4.0 % wt.

Claims: Process for the beneficiation of coal by selective agglomeration, characterized in that the agglomerating mixture consists of: (a) at least one solvent selected among the light hydrocarbons having a maximum boiling point of 70°C, in an amount of from 2% to 50% by weight relative to the coal to be agglomerated; (b) at least one nonionic additive selected from the oil-soluble phenol compounds, alkylphenol compounds, ethoxylated phenol compounds and ethoxylated alkylphenol compounds, in an amount of from 0,02% to 1% by weight relative to the coal concerned, having the general formula: wherein R-OH, the substrate for the propoxylation and the facultative ethoxylation, is selected from: phenol , monosubstituted phenol, disubstituted phenol wherein the substituents R I and R II , when present, are equal to, or different from one another, and are selected from hydrogen, methyl, ethyl and propyl, x is from 2 to 100, and y is from 0 to 20, the x:y ratio being greater than 2,3 when y is other than zero. Process according to Claim 1 , wherein the agglomerating mixture further contains at least one heavy agglomerant selected from oils derived from coal and having a boiling point of from 200°C to 400°C, and the residues of crude oil processing or admixtures of the foregoing, in a maximum amount of 3% by weight relative to the coal to be agglomerated.

Inventors: MARCOTULLIO, ARMANDO, PASSARINI, NELLO, VETTOR, ANTONIO
Applicants: ENIRICERCHE S.P.A.
Application year: 1988
Main classification: B03B1
IPC codes: B03D3, C10B57, C10L9, C10L5, B03B1