PROCESS FOR PREPARING A CARBONACEOUS SLURRY

Abstract: A process for preparing a carbonaceous slurry which utilizes a reduced amount of dispersing agent. In this process, a grinding mixture which is comprised of from 60 to 82 volume percent of carbonaceous solid material and from 18 to 40 volume percent of carrier liquid is provided. The optimum concentration of dispersing agent for this grinding mixture is then determined by a specified test. Thereafter, the grinding mixture is ground until a slurry with specified properties and a specified particle size distribution is obtained; during the grinding, a total of from 10 to 90 weight percent of the optimum concentration of dispersing agent is added to the grinding mixture by adding at least two separate portions of dispersant at at least two separate times.

Description: PROCESS FOR PREPARING A CARBONACEOUS SLU RRY TECHNICAL FIELD A process for preparing a carbonaceous slurry which uses a reduced amount of dispersing agent is disclosed. In this process, a grinding mixture which is comprised of from 60 to 82 volume percent of carbonaceous sol id material is provided. The optimum concentration of dispersing agent for this grinding mixture is then determined by a specified test. Thereafter, the grinding mixture is ground until a slurry w ith specified properties and a specified particle size distribution is - Cbbtained; during the grinding, a total of from 10 to 90 weight percent of the optimum concentration of dispersing agent is added to the grinding mixture by adding at least two separate portions of dispersant at least two separate times. BACKGROUND ART United States patent 4,282,006 discloses a carbonaceous slurry which, despite the fact that it contains at least 55 weight percent of solid material, is readily pumpable and has a relatively low viscosity. The slurry of said patent contains at least one dispersing agent. The process of this invention provides a coal-water slurry with properties comparable to those of U.S. patent 4,282,006, but it uses substantially less dispersing agent than is required by the process described in said U.S. patent. Thus, the slurry of the instant case is cheaper to prepare than the slurry of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS The present invention w ill be more fully understood by reference to the following detailed description thereof, when read in conjunction with the attached draw ings, wherein l ike reference numbers refer to l ike elements and wherein: Fig. I is a chart showing the correlation between the zeta potential of coal particles in a fluid and the specific conductance of the fluid as a function of percent dispersing agents for two dispersants; and Fig. 2 is a flow chart of a process for preparing a carbonaceous slurry. OMPI DISCLOSURE OF THE INVENTION The process of this invention comprises the steps of providing a specified grinding mixture and, while grinding it to obtain a slurry with specified properties, adding from 10-90 weight percent of the optimum amount of dispersing agent to it in at least two separate portions at at least two separate times. In the first step of the process, a grinding mixture comprising from 60 to 82 volume percent of carbonaceous solid material and from 18 to 40 volume percent of carrier liquid is provided. As used herein, the term " "carbonaceous" refers to a carbon-containing material and includes, e.g., coal, coke, graphite, and the like. The preferred carbonaceous materials are carbonaceous fuels. In one preferred embodiment, the carbonaceous solid material is coal. In another preferred embodiment, the carbonaceous solid material is coke such as, e.g., petroleum coke. Mixtures of carbonaceous solids also can be used in the grinding mixture. By way of illustration, one can use a mixture of a coarse carbonaceous fraction which contains less than about 30 weight percent of volatilizable hydrocarbons .such as, e.g., anthracite or low volatile bituminous coal) and a fine carbonaceous fraction which contains more than about 35 weight percent of volatil izable hydrocarbons(such as, e.g., lignite or high volatile bituminous coal). Some of the liquids which can be used in the grinding mixture include, by way of illustration: water; aromatic and aliphatic alcohols containing I-I0 carbon atoms, such as methanol, ethanoi, propanol, butanol, phenol, and the like; pine oil; petroleum liquids such as, e.g., number 2 fuel oil, number 4 fuel oil, number 6 fuel oil; gasoline, naphtha, and the like; hydrocarbon solvents such as, e.g., benzene, toluene, xylene, kerosene, and derivatives thereof; and mixtures thereof. In one preferred embodiment, the l iquid used in the grinding mixture is carrier water. As used herein, the term "carrier water" means the bulk of free water dispersed between the coal particles and contiguous to the bound layers on the particles, and it is to be distinguished from bound water. The term "bound water" means water retained in the "bound water layer", as defined and illustrated in Kirk-Othmer, Encyclopedia of Chemical Technology, 2d Edition, Vol. 22, pages 90-97(at page 91). Mixtures of two or more liquids can be used in the grinding mixture. Thus, by way of illustration, one may use mixtures of water and ethanoi , water and o il , water and gasol ine, and the l ike. One can use mixtures comprised of from I to 99 volume percent of alcohol and from 99 to I volume percent of water. In one embodiment , the mixture contains from I- 15 volume percent of alcohol , w ith the remainder of the l iquid consisting essentially of water; in this embodiment, it is preferred that the alcohol be monohydric and that it contain from I to I0 carbon atoms. In another embodiment , at least 90 weight percent of the ..carrier l iquid used in the grinding mixture is water and less than I0 weight percent of the carrier l iquid used in the grinding mixture is petroleum l iquid, which is preferably selected from the group consisting of naphtha, high gas oil , low gas oil , catalytic cracked recycle oil , m ixtures thereof, and other similar petroleum products. In the process of this invention, the grinding mixture is ground for a time sufficient to produce a carbonaceous slurry which: (l)comprises at least 5 weight percent(by weight of said dry carbonaceous sol id material) of col loidal particles of carbonaceous material which are smaller than 3 microns; (2)comprises from 60 to 82 volume percent of dry carbonaceous sol id material and from about 18 to 40 volume volume percent of carrier l iquid; (3)has a Brookfield viscosity of less than 5,000 centipoise when the slurry is tested at a solids content of 60 volume percent, a shear rate of I00 revolutions per minute, and under ambient temperature and pressure conditions; (4)has a yield stress of from 3 to 18 Pascals; and (5)contains a consist of finely-divided carbonaceous particles dispersed in said slurry, wherein said consist has a specific surface area of from 0.8 to 4.0 square meters per cubic centimeter and an interstitial porosity of less than 20 volume percent, and wherein said consist has a particle size distribution in accordance w ith a specified "CPFT" formula. In the process of this invention, the grinding mixture is ground until a carbonaceous slurry is produced which contains at least 5 weight percent of colloidal particles. As used herein, the term "colloid" refers to a substance of which at least one componenet is subdivided physically in such a way that one or more of its dimensions l ies in the range of I00 angstroms and 3 microns. It is preferred that , in the slurry consist produced by the process of this invention, from 5 to 70 weight percent of the carbonaceous particles in the consist are smal ler than 3 microns. In an even more preferred embodiment , from 5 to 30 weight percent of the carbonaceous particles in the consist are smaller than 3 m icrons. The carbonaceous slurry produced by the process of this invention OMPI "» contains from 60 to 82 volume percent of at least one carbonaceous sol id material and from 18-40 volume percent of carrier l iquid. It is preferred that said slurry contain from 63 to 80 volume percent of carbonaceous sol id material and from 20 to 37 volume percent of at least one carrier l iquid. ' The slurry produced by the process of this invention has a relatively low Brookfield viscosity of less than 5,000 centipoise. It is preferred that the slurry's Brookfield viscosity be less than 4,000 centipoise and, more preferably, less than 3,000 cent ipoise. It is even more preferred that the slurry viscosity be less than 2,000 centipoise. In the most preferred embodiment, the Brookfield viscosity of the slurry is less than 1 , 000 centipoise. The Brookfield viscosity of the slurry is tested after the sol ids concentration of the slurry is adjusted to 60 volume percent, at a shear rate of I00 revolutions per minute, and under ambient temperature and pressure conditions. The Brookfield viscosity is measured using conventional techniques by means of a Brookfield Synchro- Lectric Viscosimeter(manufactured by the Brookfield Engineering Laboratories, Stoughton , Mass., U.S.A.) The slurry produced by the process of this invention has a yield stress of from 3 to I8 Pascals and, preferably, from 5 to 15 Pascals. In the most preferred embodiment, the yield stress of the slurry is from 7 to 12 Pascals. The yield stress is the stress which must be exceeded before flow starts. A shear stress versus shear rate diagram for a yield pseudoplastic or a Bingham plast ic fluid usual ly shows a non-linear hump in the rheogram at the onset of flow; extrapolating the relatively linear port ion of the curve back to the intercept of the shear stress axis gives the yield stress. See, for example, W.L. Wilkinson 's "Non-Newtonian Fluids, Fluid Mechanics, M ixing and Heat Transfer"(Pergamon Press, New York, I960), pages I-9. The slurry produced by the process of this invention contains a consist of finely-divided carbonaceous particles dispersed in the slurry. The consist has a specific surface area of from 0.8 to 4.0 square meters per cubic centimeter and, preferably, from 0.8 to 3.0 square meters per cubic centimeter. It is more preferred that the specific surface area be from 0.8 to 2.4 square meters per cubic centimeter. In the most preferred embodiment , the specific surface area is from 0.8 to 2.0 square meters per cubic centimeter. As used in this specif ication, the term "specif ic surface area" refers to the summation of the surface area of equivalent spheres in the particle size distribution as measured by sieve analysis and sedimentation techniques; the particle size distribution of the consist in the slurry is first determined, it is assumed that all particles in the consist are spherical , and then one calculates the surface area based on this assumption. The term "consist", as used herein, refers to the particle size distribution of the sol id phase of the sol ids-l iquid slurry. For any given consist, one can determine the particle size distribution by means well known to those skilled in the art. The following means for determining the particle size distributions of pulverized and fine grind carbonaceous particles are preferred: (l)U.S. Series sieves Nos. 16, 20, 30, 40, 50, 70, I00, I40, 200, and 270 are used to determine weights of carbonaceous particles passing through each sieve in the range of from (-) I ISO microns to (-)53 microns. The cumulative volume percents of carbonaceous particles, dry basis, finer than(CPFT) a particular stated sieve size, in microns, is charted against the sizes in microns on a log-log chart, referred to herein as a "CPFT chart", to indicate the nature of the particle size distribution of the 16 mesh x 270 mesh particles. (2)A Sedigraph 5500L(made by Micromeritics Co., Norcross, Ga., U.S.A.) is used to measure particle sizes of numbers of particles of the carbonaceous material in the range of (-)75 microns to 0.2 m.m. The Sedigraph 5500L uses photo-extinction of settl ing particles dispersed in water according to Stoke 's law as a means for making the above determinations. Other instruments, such as a Coulter Counter, can also be used for similar accuracy. The results can be plotted on a CPFT chart. Although these data do not necessarily extend to the size axis at l% CPFT, the "D<- at l%" can be determined by extrapolating the CPFT chart line to this axis and reading the intercept. This number, although not the true Dς , can be effectively used in the computer algorithm to determine percent porosity and specif ic surface area. (3)ln addition to the above methods, particle size measurements can be estimated from methylene blue index measurements to obtain an approximate determination of the weight percent of particles smaller than I mm. such a procedure is described in A.S.T.M. Standard C837-76. This index can be compared w ith the surface area calculated by the CPFT algorithm. OMPI Once the particle size distribution of the consist is determined, it is assumed that each particle in the consist is spherical with a surface area of TfD ; the diameter(D) of the particles in each class of particles in the consist is knownjand the surface area of the particles in each class is calculated and summed. The consist of the slurry produced by the process of this invention has an interstitial porosity of less than 20 volume percent and, preferably, of less than 15 volume percent. It is preferred that the interstitial porosity of the consist be less than 10 volume percent. The interstitial porosity fsa function of the volume between the interstices of the particles in the slurry consist. For any given space full of particles, the interstitial porosity is equal to the "minimum theoretical porosity in accordancxe with the equation presented below. Minimum Theoretical Porosity = 40%(1 - {[l/VAJ ), where VA is defined by the follow ing modified Westman-Hugill algorithm: VA 2 = + A 2 X 2 ±-l VA = E X. + A.X. j=l J i * n-1 VA n = Σ X, + A X • j =1 J n n ' ϋ / i - * _- c= - ~ — __ 1 wherein: ■ +/. A, * = Apparent volume of a monodispersion of the i size part icle , X J = Mass fraction of the i size part icles, VA j = Apparent volume calculated w ith reference to the i size part icles, n = Number of particle s izes, and VA = Maximum value of VAJ = Apparent volume of the m ixture of n particle sizes. To determine the interstitial porosity of any consist, the particle size distribution of said consist can be determined by the method described above w ith reference to the measurement of the specif ic surface area. Thereafter, it is assumed that each particle in the consist is spherical, the volume of the part icles is calculated in accordance w ith this assumption, and the interstitial porosity of the consist is then calculated in accordance w ith the above formula. The slurry produced by the process of this invent ion comprises a compact of finely-divided carbonaceous particles dispersed in fluid. The term "compact" refers to a mass of f inely-divided particles which are closely packed in accordance w ith the CPFT formula. The particles in the compact of said slurry have a part icle size distribution which is substantial ly in accordance w ith the follow ing formula: and v ere if D < D SJ and where if D > Dr . [ s 3 - I _. , n Ή 8 wherein: 1. CPFT is the cumulative percent of the carbonaceous solid finer than a certain particle size D, in volume percent. 2. k is the number of component distributions in the consist, is at least I, and preferably is from I to 30. It is preferred that k be selected from the group consisting of I , 2, 3, and 4. It is even more preferred that k be I. 3.X j is the fractional amount of the component j in the consist, is less than or equal to 1.0, and the sum of all Xj 's in the consist is 1.0. 4. n is the distribution modulus(or slope) of fraction j , is greater than 0.00I, and preferably is from 0.00I to I0. It is preferred that n be from 0.0I to 1.0; it is more preferred that n be from 0.0I to 0.5. 5. D is the diameter of any particle in the consist, and ranges from 0.05 to II80 microns. 6. Oe is the diameter of the smallest particle in fraction j(as measured by extrapolating the CPFT chart l ine, if necessary, to one percent CPFT using data from sieve analyses plus the M icromeritics Sedigraph 5500L) , and it generally is greater than 0.05 microns and is less than D^ - It is preferred that, when k = I, D^ is from 0.05 to 0.4 microns, preferably from 0.05 to 0.25 microns, and even more preferably from 0.05 to 0.20 microns. 7. D | _ is the diameter of the largest particle in fraction j(sieve size or its equivalent), and it ranges from 15 to I ISO microns. Preferably D^ is from 30 to 420 microns, and most preferably it is from I00 to 300 microns. D j _ is the theoretical size modulus of the particle size distribution; when CPFT is plotted against size, the D L value is indicated as the intercept on the upper X axis of the CPFT/D plot. However, as is known to those skilled in the art, because of aberrations in grinding the coarse end of a particle size distribution, the actual top particle size is always larger than the D L obtained by, e.g., the particle size equation described in this case; thus, e.g., a D^ size modulus of 250 microns w ill usually produce a particle distribution with at least 98 percent of the particles smaller than 300 microns. Consequently, said slurry has a compact with a particle size distribution which is substantially in accordance with the CPFT equation; minor deviations caused by the actual top size being greater than the D, are within the scope and spirit of this invention. It is preferred that at least 85 weight percent of the carbonaceous particles in the slurry have a particle size less than 300 microns. It is more preferred that at least 90 weight percent of the carbonaceous particles in the slurry be smaller than 300 m icrons. In the most preferred embodiment, at least 95 weight percent of the carbonaceous particles in the slurry are smaller than 300 m icrons. In one of the preferred embodiments of the process of this invention, the carrier fluid is water, and the colloidal sized carbonaceous particles in the slurry have a net zeta potential of from 15 to 85 millivolts. The following discussion of zeta potential will refer to a coal-water slurry, it being understood that it is equally applicable to other carbonaceous sol ids/water slurries such as, e.g., coke-water slurries. As used in this case, the term "zeta potential" refers to the net potential, be it positive or negative. Thus, a zeta potential of from I5.4 to 70.2 mill ivolts includes zeta potentials from -I5.4 to -70.2 m ill ivolts as well as zeta potentials of from +I5.4 to +70.2 mill ivolts. It is preferred that the zeta potential be from 30 to 70 mill ivolts. As used in this specification, the term "zeta potential" has the meaning given to it in the field of colloid chemistry. Concise discussions and descriptions of the zeta potential and methods for its measurements are found in many sources including, e.g., U.S. patents 3,454,487 and 3,976,582. Zeta potential may be measured by conventional techniques and apparatuses of electroosmosis such as those described, e.g., in Potter, "Electro Chmistry"(CIeaver-Hume Press, Ltd., London, I96I). Zeta potential can also be determined by measuring electrophoretic mobility(EPM) in any of several commercial apparatuses, in the present invention, a Pen Kem System 3000(made by Pen Kem Co. Inc. of Bedford H ills, N.Y., U.S.A.) was used for determining zeta potential . This instrument is capable of automat ically taking samples of coal particles and producing an EPM distribution by Fast Fourier Transform Analysis from which the average zeta potential can be calculated in millivolts. It is preferred that the zeta potential of the colloidal sized coal particles in the carbonaceous consist of the slurry of this invention be negative in charge and be from -I5.4 to -70.2 mill ivolts. It is more preferred that said zeta potential be from -30 to -70 mil l ivolts. One preferred means for measuring the zeta potential is to grind a sample of coal in either a laboratory size porcelain ball mill with porcelain balls in distilled water at 30 weight percent sol ids for approximately 24 hours or in a steel ball mill with steel balls at 30 5 weight percent sol ids for 16 hours or until all of the particles in the coal are less than 10 microns in size. Small samples of this larger sample can then be prepared in a known way by placing them in a vessel equipped with a stirrer with a sample of water to be used as a carrier in the coal-water slurry. Various acidic and basic salts are then added in • j O incremental amounts to vary the pH , and various concentrations of various candidate dispersing agent organic surfactants l ikew ise are added in incremental amounts(e.g., grams per gram coal , both dry basis), alone or in combinations of two or more. These samples are then evaluated in any electrophoretic mobil ity, electroosmosis, or streaming potential - j 5 apparatus to determine electrical data, from which the zeta potential is calculated in a know way. Plots of zeta potential , pH, and specific conductance vs. concentration may then be made to indicate candidate surfactants, or combinations thereof, to be used to produce the optimum dispersion of " coal particles in the carrier water. 20 Figure I illustrates one means of evaluating the effectiveness of surfactants for any given solid material. The curves of Fig. 1 represent data obtained using both a purported nonionic polyumer CW-II made by the Diamond Shamrock Process Chemicals Co., and an anionic lignosulfonate Polyfon-F made by Westvaco, Inc., adsorbed on an Australian coal. The 25fine coal ground to about 100% finer than 10 microns is slurried in distilled water at 0.01 weight percent solids. Aliquots are placed in test tubes, and increasing amounts of any candidate surfactant are added to each test tube. The test tube samples are thoroughly mixed and inserted into a sampler carousel. The Pen Kem System 3000 Electrophoretic 3gMobility Analyzer automatically and sequentially samples each test tube and measures the electrophoretic mobility of the coal particles and the specific conductance of the carrier liquid. In Fig. 1 , the left ordinate gives the calculated zeta potential of the particles in millivolts, the right ordinate gives the specific conductance in micromhos of the carrier 35liquid. These variables are both measured as a function of the percent addition of each surfactant on a dry coal basis, which is plotted on the abscissa. Figure I shows that the purported nonionic CW-II surfactant does have some anionic character. CW-II has a zeta potential of -50 m.v. at 300% addition on 0.01 % dry coal. Polyfon-F has a zeta potent ial of -55 mill ivolts at 200% addition on 0.01 percent dry coal. Furthermore, the specific conductance of the Polyfon-F at -55 m.v. zeta potential is greater than CW-II at -50 m.v. These data establ ish Polyfon-F as a more chemically effective surfactant for use on this particular Austral ian coal. During the time that the grinding mixture used in the process of this invention is being ground to produce said slurry, from 10 to 90 weight percent of the optimum amount of dispersing agent is added to the grinding mixture by adding at least two separate portions of dispersing agent to the grinding mixture at at least two separate times. It is preferred to add from 20 to 80 weight percent of the optimum amount of dispersing agent to the grnding m ixture during the t ime it is being ground, and it is even more preferered to add from 30 to 70 weight percent of said optimum amount of dispersant during grinding. In an even more preferred embodiment, from 40 to 60 weight percent of the optimum amount of dispersing agent is added to the grinding mixture while it is being ground. In the most preferred embodiment, from 45 to 55 weight percent of the optimum amount of dispersing agent is added to the grinding mixture while it is being ground. It is preferred to add at least three separate portions of dispersing agent to the grinding mixture while it is being ground. It is even more preferred to add at least four separate portions of dispersing agent to the grinding mixture while it is being ground at at least four separate times. In one embodiment, there is added at least five separate portions of dispersing agent to the grinding mixture at at least five separate t imes. Regardless of how many separate portions of dispersing agent are added to the grinding mixture, the total amount of dispersant added never exceeds about 90 weight percent of the optimum amount of dispersing agent. The term "opt imum amount of dispersing agent", as used in this specification, refers to the dispersing agent concentration as determined by the test mentioned below. Any given mixture of carbonaceous material(s) and l iquid(s) w ill have a specified sol ids content, n, D j_ , and D^ . The "optimum concentration" of dispersing agent(s) must be separately determined for each given mixture of carbonaceous material and liquid, for it w ill vary from mixture to mixture. Similarly, for a given mixture, the "optimum concentration of dispersing agent" mus be OMPI •-^ _. IPO * VJ separately determined for each dispersing agent or combination of dispersing agents, for it may vary for a given system - with different dispersing agent systems. For a given dispersing agent system and a given m ixture of carbonaceous material(s) and liquid(s) , different concentrations of the dispersing agent system are added prior to time the mixture is ground, the mixture is then ground until at least 98.5 weight percent of the carbonaceous material in the mixture passes through a 50 mesh screen, and the viscosity of the mixture is then determined. That concentration of dispersing agent which, for a given mixture and dispersing agent, yields the lowest viscosity after the mixture is ground to a particle size 98.5% less than 50 mesh, " is "optimum" for that dispersing agent and that mixture. In one of the preferred embodiments of the process of this invention, the total amount of dispersing agent added up to any one point in the grinding cycle is related to the specific surface area of the slurry consist which exists at that point. In this embodiment, the optimum concentration of dispersing agent(s) is determined for a particular system in accordance with the aforementioned procedure. The optimum concentration of dispersing agent ia added in one step to the carbonaceous material-liquid slurry system, the system is then ground until 98.5 weight percent of its carbaonaceous particles are smaller than 50 mesh(300 m icrons), and during the grinding samples are periodically w ithdrawn from the system and analyzed for specific surface area. The ratio of the surface area generated at any one point in the grinding to the final surface area(when the final slurry product, which contains at least 98.5 weight percent of carbonaceous particles smaller than 300 microns is obtained) must be I.O or less. In this embodiment, the total amount of surfactant added up to any one point in time does not exceed the surface area ratio at that point in time times the optimum dispersant concentration times a factor of from about 0.1 to about 0.9. Thus, by way of illustration, if the optimum dispersing agent concentratin for a particular coal-water system is 0.7 weight percent of dispersing agent(by weight of dry coal) and if, at 60 minutes into the grinding cycle, the specific surface area of the slurry consist is 0.5 times as much as the final specific surface area which will be obtained when grinding is completed, then only enough additional dispersant should be added so that, at time 60 minutes, the total amount of surfactant in the system does not exceed: (0.7 we ight percent of dispersing agent) x (0.5) x (from 0.I to 0.9) = from 0.035 to 0.3I5 weight percent of dispersing agent. Lesser amounts than 0.3I5 we ight percent of dispersant can be used. It is preferred that the dispersing agent used in the process of this invent ion be a surfactant. The term "surfactant" indicates any substance that alters energy rel at ionships at interfaces such as , e.g., wetting agents , detergents, penetrants, spreaders, dispersing agents, foaming agents , etc. The term also incl udes synthetic or natural organic compounds which display surface act ivity. The surfactant used in the process of this invention is preferably an organic surfactant selected from the group consisting of anionic surfactants, cationic surfactants, and amphoteric surfactants. In one preferred embodiment, the surfactant is anionic and its solubil izing group(s) is selected from the group consisting of a carboxylate group, a sulfonate group, a sulfate group, a phosphate group, and m ixtures thereof. In another preferred embodiment , the surfactant is cationic and its solubil izing group(s) is selected from the group consisting of a a primary am ine group, a secondary amine group, a tertiary am ine group, a quaternary amine group, and mixtures thereof. In one of the preferred embodiments, the surfactant used in the process of th is invention is the alkal i metal salt of a condensed mono naphthalene sulfonic acid. Th is salt , whose preparat ion is described in U.S. patent 3,067,243, can be prepared by sulfonating naphthalene w ith sulfuric acid , condensing the sulfonated naphthalene w ith formaldehyde, and then neutralizing the condensate so obtained w ith a hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonium hydroxide. In another preferred embodiment , a comparable surfactant w ith a benzene rather than a naphthalene nucleus is used in the process of th is invention. Another preferred class of surfactants is the l ignosulfonates. These lignosulfonates have an equivalent weight of from I00 to 350, contain f rom 2 to 60 phenyhl propane units(and, preferably, from 3 to 50 phenyl propane units) , and are made up of cross-l inked polyaromat ic chains. In one embodiment , the dispersing agent used in the process of th is invention is a polyelectrolyte which, preferably, is organic. As used in this specification , the term "polyelectrolyte" indicates a polymer which can be changed into a molecule with a number of electrical charges along its length. It is preferred that the polyelectrolyte have at least one 14 site on each recurring structural unit which, when the polyelectrolyte is in aqueous solution, provides electrical charge; and it is more preferred that the polyelectrolyte have at least two such sites per recurring structural un it. In a preferred embodiment, said sites comprise ionizable groups selected from the group consisting of ionizable carboxylate, sulfonate, sulfate, and phosphate groups. Suitable polyelectrolytes include, e.g., the alkali metal and ammonium salts of polycarboxylic acids such as, for instance, polyacryclic acid; the sodium and ammonium salts of condensed naphthalene sulfonic acid; polyacryiamide; etc. ■ j g In one preferred embodiment, the slurry produced by the process of this invention contains, in addition to said dispersing agent, from 0.05 to 2.0 weight percent(by weight of dry carbonaceous material) of an electrolyte which, preferably, is inorganic. The total concentration of the dispersing agent and electrolyte(if any) •J5 in the slurry is from 0.05 to 4.0 weight percent. Although it is not essential for there to be electrolyte in the slurry produced by the process of this invention, it is essential that said slurry contain dispersing agent. The term "electrolyte" refers to a substance that dissociates into 2o two or more ions to some extent in water or other polar solvent. Suitable electrolytes include, e.g., the ammonium or alkali metal salts of hexametaphosphates, pyrophosphates, sulfates, carbonates, hydroxides, and halides. Alkal ine earth metal hydroxides can be used. Other inorganic electrolytes known to those in the skilled in the art also can be used. 25 It is preferred that the electrolyte be selected from the group consisting of sodium hydroxide and potassium hydroxide. The grinding mixture used in the process of this invention may be comprised of one or more consists of carbonaceous material. The term "consist" means the particle size distribution of the solid phase of the 30 carbonaceous slurry. For example, the term "8 mesh x 0", when applied to coal ", indicates coal with a graded size, or consist, of coal particles distributed in the range of 8 mesh and zero(dust). In one aspect of this invention, a grinding mixture is ground in a ball mill at a reduced critical speed until a carbonaceous slurry which 35Contains a compact whose particle size distribution is in substantial accordance with said CPFT formula is obtained. The grinding mixture contains from 60 to 82 volume percent of carbonacoeous materϊal(such as coal), less than 40 volume percent of carrier liquid(such as water) , and from 0.0I to 4.0 weight percent of dispersant(based on weight of dry coal). In th is embodiment, the grind ing mixture is ground in a bal l mill at a ball mill speed of less than 70 percent of the ball mill critical speed. It is preferred that the bail m ill speed be less than 60 percent of the ball mill critical speed, and it is even more preferred that the ball mill speed be less than 55 percent of the ball mill critical speed. However, it is generally preferred to run the ball m ill at a speed no lower than about 50 percent of the ball mill critical speed. The critical speed of the ball m ill is the theoretical speed at which the centrifugal force an a ball in contact w ith the mill shell at the height of its path equals the force on it due to gravity, and it is def ined by the equation: N = 76.6 c D wherein N is the critical speed(in r.p.m.), and D is the diameter of the m ill(feet) for a ball diameter that is small w ith respect to the ball mill. Several typical means of practicing the process of the invention are illustrated in Fig. 2. The follow ing description of the process of Fig. 2 w ill refer to coal(as the carbonaceous material) and water(and the carrier l iquid). It is to be understood, however, that other carbonaceous material(s) and/or other l iquid(s) can be used in said process. In a wet grinding method, coal is charged to crusher I0. Any of the crushers known to those skilled in the art can be used as crusher I0. Thus, one can use, e.g., a rod mill, a gyratory crusher, a roll crusher, a jaw crusher, a cage mill , etc. Generally, the coal is crushed to a size of I/4" x 0, although coarser and finer fractions can be used. The crushed coal is fed through line 12 to mill 14. Mill 14 can be either a tumbl ing mill(such as a ball m ill, pebble mill , rod mill , tube mill , or compartment mill) , or a non-rotary ball or bed mill. Liquid(such as water) and diluted dispersing agent are fed through l ines 16 and 18, respectively, to mill 14. The m ill I4 will have sufficient coal and l iquid fed to it so that it w ill contain from 60 to 82 volume percent of coal. Generally, one should charge from 0 to I0 volume percent more coal to mill 14 than he desires in the final slurry product, subject to the limitation that in no event should one charge more than 82 volume percent coal to the mill. In general , less than 40 volume percent of l iqu id and from 0.0I to 4.0 weight percent of dispersant(based on weight of dry coal) w il l be fed in l ines I6 and 18, respectively, to mill 14. However, no more than from I0 to 90 weight percent of the optimum amount of dispersing agent is fed through l ine 18 to the mill , and it is fed in at least two separate portions at at least two separate times during the grinding. Ground slurry from m ill I4 is passed through line 20 through sieve 22. Sieve 22 may be 40 mesh sieve which allows underflow slurry of sufficient fineness(less than 420 microns) through to line 24; overflow particles wh ich are greater than 420 microns are recycled via l ine 26 back into mill I4, wherein they are subjected to further grinding. A portion of the underflow slurry from line 24 flows through line 28, vϊscometer 30, density meter 32, and particle size distribution analyzer 34; the remaining portion of the underflow slurry flows through l ine 36. The viscometer 30 indicates the viscosity of the ground slurry. If the viscosity of the ground slurry is higher than desired, then the underflow slurry should be subjected to further tests(in density meter 32 and particle size distribution analyzer 34). Density meter 32 indicates the density of the underflow slurry, which directly varies w ith its solids content. If the density of the underflow slurry is higher or lower than desired , the underflow slurry should then be subjected to further tests in particle size analyzer 34 to determ ine what the particle size distribution of the underflow slurry is and its attendant surface area and porosity. Particle size distribution analyzer 34 analyzes the particle size distribution of the compact of the underflow slurry. From the data generated by analyzer 34, the specific surface area and the porosity of the compact of underflow slurry can be determined. if the solids content, the viscosity, the specif ic surface area, and the porosity properties of the underflow slurry are as desired, then the underflow slurry is passed through l ine 38 to final trim tank 40. If, however, either the sol ids content or the viscosity or the specific surface area or the porosity of the underflow slurry is not as desired, then a portion of the underflow slurry is passed through line 36 to mill 42. Depending on how badly the underflow slurry is out of specification, from I to 30 volume percent of the underflow slurry is passed to mill 42 and the remainder is passed to trim tank 40. Recycl ing the slurry to mill 17 42 and, after regrinding, to mill 14, increases the qual ity of the slurry com ing out of mill 14. Water is fed into mill 42 through l ine 44 so that the sol ids concentration of the ground slurry fed through l ine 36 w ill be adjusted 5 to 30 to 60 volume percent. The diluted slurry in m ill 42 is then ground in mill 42 until at least 95 volume percent of the particles in the slurry have diameters less than 20 microns and, preferably, less than 15 microns. It is more preferred to grind until at least 95% of the particles are smaller than I0 microns and, most preferably, smaller than •) 0 5 microns. The slurry ground in mill 42 is then passed through line 46 to high shear mixer 48. Dispersing agent can be passed through l ine 50 to high shear mixer 48 in order to optimize the zeta potential of the col loidal particles in the slurry. However, the amount of dispersant aded in line 15 50 should be such that the total amount added in lines I8 and 50 does not exceed from I0 to 90 weight percent of the optimum amount of dispersant. In general , the ground slurry can be mixed w ith water and dispersant in mixer 48 for from 3 to 15 minutes. The mixture from mixer 48 is then passed through l ine 52 and through viscometer 54, density meter 56, and 0 particle size distribution analyzer 58. If the properties of the mixed slurry are not suitable, then the water flow to mill 42 through line 44 and/or the slurry flow to mill 42 through l ine 36 and/or the dispersant flow to mixer 48 through line 50 are adjusted unt il the properties are suitable. If the properties of the mixed slurry from mixer 48 are 5 suitable, then the mixed slurry is recycled to trim tank 40 or to mill 14 through line 60, where it is mixed w ith and ground with crushed coal from l ine 12, water from l ine I6, and dispersant from l ine I8. Fig. 2 also illustrates a dry grinding process for preparing stabil ized slurry. In this process, crushed sol id material , such as 0 petroleum coke, from crusher I0, is passed through l ine 62 to dry grinder 64, where it is dry ground until it is pulverized, i.e., unitl it is a consist of 40 mesh x 0. The ground carbonaceous material from dry grinder 64 is passed through line 66 to trim tank 40. Water and dispersing agent are passed 5through lines 68 and 70, respectively, to trim tank 40. The total amount of dispersant added to trim tank 40 from line 68 and/or line 38 and/or line 92 should not exceed from I0 to 90 weight percent of the optimum dispersant concentration, and it should be added in at least two stages 1 8 at at least two separate times. The carbonaceous material/water/dispersant mixture is stirred by stirrer 72, and the stirred mixture is passed through l ine 74 to high shear mixer 76. The qual ity of the slurry produced in m ixer 76 is evaluated by passing it through fine 78 to zeta potential analyzer 80, particle size distribution analyzer 82, Haake viscometer 84(for measuring yield stress) , and density meter 86. If the net zet potential of the colloidal particles is from 10 to 90 mill ivolts, the sol ids content is from 60 to 80 volume percent, the yield stress is from 3 to I8 Pascals, the specific surface area is from 0.8 to 4.0 square meters per cubic centimeter, the porosity is less than 20 volume percent, and the particle size distribution of the compact is in accordance w ith the CPFT equation , then the slurry produced by the dry grinding is satisfactory. However, if the slurry is not up to specifications, then a portion of the ground material from l ine 66 is passed through l ine 86 to be dry ground in a micronizer fluid energy(jet) mill. The f ine particles from jet mil l 88 are passed through l ine 90 to trim tank 40 where they are mixed with the ground material from l ine 66, the water from line 68, and the dispersant from l ine 70. Thereafter, the slurry produced in trim tank 40 is again evaluated in zeta potential analyzer 80, particle size distribution analyzer 82, Haake viscometer 84, and density meter 85 to determine whether the slurry is up to specifications. The process can be fine-tuned by this method until the properties of the slurry are as required; alternatively, or additionally, one can alter the rate of flow of water and surfactant through l ines 68 and 70, respectively, the rate of flow of material from line 66(by varying the speed of the mill and/or the rate at which crushed material is fed to the mill through line 62) , and the like. Alternatively, ground material from dry grinders can be fed directly back to mills 14 or 42 and as feed for the wet grinding circuits. In yet another method illustrated in Fig. 2, the amount of very finely ground slurry material in trim tank 40 can be increased by passing a portion of the mixed slurry from h igh speed mixer 48 through l ine 92 into trim tank 40. Alternatively, or additionally, the amount of moderately finely ground slurry material in trim tank 40 can be increased by passing a portion of the ground slurry from ball mill 14 thourh l ine 38 to slurry tank 40. This scheme al lows various fractions of slurries from wet grinders 14 and 42 to be blended with various fractions of dry consist from dry grinders 64 and 88. The fol low ing Examples are presented to il lustrate the claimed invent ion and are not to be deemed l imitative thereof. EXAMPLE I -- PROCEDU RE FOR SCREEN ING D ISPERSING AGENTS A surfactant, or combination of surfactants, effective for use in the process of the invent ion, can be screened by either of the follow ing two methods: (a)Zeta potential measurement: This method is discussed on pages I0-I I of this case. A Pen Kem System 3000 apparatus is used in the determination described and can process 40 samples in about 6 hours. (b)AIternate method for est imating equivalent zeta potent ial : A large sample of coal is ground in water as described in (a) above at 50 weight percent sol ids for about 24 hours to produce a slurry. Smaller samples, about 500 m.I., of this slurry are then deflocculated by adding various candidate dispersing agent surfactants and surfactant combinat ions to the sample of slurry, as above, dry or, preferably, in solut ion, dropw ise, blending gently, and then measuring the viscosity at some constant shear rate(e.g., using a Brookfield LVT viscometer at 30 r.p.m.). A surfactant system which is found to produce an acceptably low(preferably the lowest) viscosity at the lowest amount(e.g., in weight percent) of addition on a dry coal basis is thereby identified as the most effect ive surfactant. EXAMPLE 2- PREPARATION OF COAL SAMPLES FOR MEASUREMENTS. (a)Sieve analysis: Although any standard procedure may be used to measure particle sizes of coal particles from a coal , the procedure used in obtaining data discussed herein w ill be described. A weighed sample, e.g., 50 grams dry weight of coal , is dispersed in 400 m.I. of carrier water contain ing I.O weight percent of Lomar D(which is the sodium salt of. condensed mono naphthalene sulfonic acid which is sold in powder form at a concentration of 86-90% by D iamond Shamrock Process Chem icals, Inc.) , based on the weight of coal , dry basis, and the slurry is mixed for I0 minutes w ith a Hamilton Beach mixer. The slurry is then al lowed to stand quiescent for 4 hours, or, preferably, overnight. (This step is usually not necessary if the slurry was mil led w ith surfactant.) The sample is then remixed very briefly. It is then poured slowly onto a stack of tared U.S. Standard sieves over a large vessel. The sample is carefully washed w ith running water through the top sieve w ith the rest of the stack intact until all of the s ievable material on that sieve is washed through the sieve into the underlying sieve. The top sieve is then removed, and each sieve in the stack, as it becomes the top sieve, is successively washed and removed until each sieve has been washed. The sieves are then dried in a dryer at 105 degrees centigrade, and the residue on each one is weighed in a known way. (b)Sedigraph analysis: A separate sample finer than 140 mesh sieve size is carefully stirred, and a representative sampIe(about 200 m.I.) is taken for analysis. The rest may be discarded. About 2 eyedroppers of the dilute slurry are further diluted in 30 m.I. of distilled water with 4 drops of Lomar D added. The sample is stirred overnight with a magnetic stirrer. Measurement is them made with the Sedigraph 5500L. The data from the sieve and Sedigraph is combined to prepare a CPFT chart. D at I % is read from the CPFT line. COMPARATIVE EXAMPLE 3 To an Abbe ball mill were charged I6.3 pounds of a 4 x 0 mesh Pittston Moss #l coal with a Hardgrove grindability index of about 72 and a free swelling index of about 7, 4.6 pounds of water, 3.7 grams(0.05 weight percent) of sodium hydroxide, and 51.8 grams(0.7 weight percent, by weight of dry coal) of "Lomar D"; the grinding mixture thus formed contained 78 weight percent of coal. The Abbe ball mill used was model number 2, and it was manufactured by the Paul O. Abbe Company of Little Falls, New Jersey; the ball mill had 35 volume percent ball charge of 2.0 inch top Bond ball mix. The ball mill was run at a speed of 34 r.p.m. (51% of its critical speed) for about 130 minutes, until at least 99.34 weight percent of the coal particles in the slurry were smaller than 50 mesh(297 microns). A sample of the slurry so produced was diluted to a solids content of 75 weight percent, and its Brookfield viscosity was tested at 100 revolutions per minute on a Brookfield RVT viscometer. The Brookfeild viscosity of the slurry was 1100 centipoise. EXAMPLE 4 The procedure of Example 3 was substantially followed, with the exception that only 25.2 grams(0.34 weight percent, by weight of dry coal) of "Lomar D" was used, and portions of the lomar D were added throughout the grinding cycle to the mill, as shown in Table I. 98.02 weight percent of the coal particles in the slurry produced were finer than 50 mesh. The slurry had a Brookfield viscosity of 1150 centipoise at 75 weight percent of solids. 21 Table 1 Weight Percent of Dispersing Time at which the Addition Agent Added to the Abbe Mill of the Dispersing Agent to the Mill was made. Minutes 0.02 0 0.04 5 0.035 10 0.02 15 0.025 20 0.07 25 D 0.095 30 0.06 35 0.045 40 0.03 45 0.03 50 15 0.03 55 0.03 60 0.03 65 0.03 70 0.03 75 20 0.03 80 0.03 85 0.03 90 0.03 95 0.03 100 25 0.03 105 0.03 110 0.03 115 0.03 120 0.06 125 0 Total-0.34 22 Example 5 The procedure of Example 4 was substantially followed. Only 25.2 grams (0.34 weight percent, by weight of dry coal) of Lomar D was used, and portions of Lomar D were added throughout the grinding cycle to the mill. Table 2 shows how the Lomar D was added during this Experiment. Table 2 Weight Percent of Dispersing Time at which the Addition Agent Added to the Abbe Mill of the Dispersing Agent to the Mill was made. Minutes 0.02 0 0.125 10 0.045 20 0.165 30 0.105 40 0.60 50 0.60 60 0.60 70 0.60 80 0.60 90 0.60 100 0.60 110 0.60 120 Total-0.34 96.77 weight percent of the coal particles in the slurry produced were finer than 50 mesh. The slurry had a Brookfield viscosity of 1200 centipoise at 75 weight percent of solids. Example 6 23 The procedure of Example 5 was substantially followed, with the exception that the addition schedule for the dispersing agent differed. Table 3 shows how the 0.34 weight percent of Lomar D was added. Table 3 Weight Percent of Dispersing Time at which the Addition Agent Added to the Abbe Mill of the Dispersing Agent to the Mill was made. Minutes 0.02 0 0.09 5 0.005 10 0.025 15 0.055 20 0.07 25 0.08 30 0.055 35 0.05 40 0.04 45 0.03 50 0.03 55 0.03 60 0.03 65 0.03 70 0.03 75 0.03 80 0.03 85 0.03 90 0.03 95 0.03 100 0.03 105 0.03 110 0.03 115 0.03 120 0.06 125 Total-0.34 97.05 weight percent of the coal particles in the slurry produced were finer than 50 mesh. The slurry had a Brookfield viscosity of 960 centipoise at 75 weight percent of solids. Example 7 The procedure of Example 5 was substantially followed with the exception that the addition schedule for the dispersing agent differed. Table 4 shows how the 0.34 weight percent of Lomar D was added. Table 4 Weight Percent of Dispersing Time at which the Addition Agent Added to the Abbe Mill of the Dispersing Agent to the Mill was made. Minutes 0.02 0 0.095 10 0.08 20 0.15 30 0.105 40 0.07 50 0.06 60 0.06 70 0.06 80 0.06 90 0.06 100 0.06 110 0.06 120 Total-0.34 97.62 weight percent of the coal particles in the βlurry produced were finer than 50 mesh. The slurry had a Brookfield viscosity of 1170 centipoise at 75 weight percent of solids. OMPI 26 Example 8 The procedure of Example 5 was substantially followed, with the exception that 16.7 grams (0.225 weight percent, by weight of dry coal) of Lomar D was used, and the addition schedule differed. Table 5 shows how the 0.225 weight percent of Lomar D was added. Table 5 Weight Percent of Dispersing Time at which the Addition Agent Added to the Abbe Mill of the Dispersing Agent to the Mill was made. Minutes 0.025 0 0.05 25 0.05 35 0.025 60 0.025 70 0.025 100 0.025 120 0.225 94.39 weight percent of the coal particles in. the slurry produced were finer than 50 mesh. The viscosity of the slurry was 1150 centipoise at a solids content of 75 weight percent. Although these examples have described experiments utilizing Lomar D surfactant, similarly good results are obtainable with other surfactants.

Claims: I claim: 1. A process for preparing a carbonaceous slurry, comprising the steps of: (a) providing a grinding mixture comprising from 60 to 82 volume percent of carbonaceous solid material and from 18 to 40 volume percent of carrier liquid; (b) grinding said grinding mixture for a time sufficient to produce a carbonaceous slurry which: 1. comprises at least 5 weight percent (by weight of said dry carbonaceous solid material) of colloidal particles of carbonaceous material , which are smaller than 3 microns; 2. comprises from 60 to about 82 volume percent of dry carbonaceous solid material and from 18 to 40 volume percent of carrier liquid; 3. has a Brookfield viscosity of less than 5,000 centipoise when the slurry is tested at a solids content of 60 volume percent, a shear rate of 100 revolutions per minute, and under ambient temperature and pressure conditions; 4. has a yield stress of from 3 to 18 Pascals; 5. contains a consist of finely-divided carbonaceous particles dispersed in said slurry wherein said consist has a specific surface area of from 0.8 to 4.0 square meters per cubic centimeter and an interstitial porosity of less than 20 volume percent, and wherein said consist has a particle size distribution substantially in accordance with the following formula: vhere Σ Σ_, - 1.0 and where if D < D. and where if D > Dr. wherein: (a) CPFT is the cumulative percent of said βolid carbonaceous material finer than a certain specified particle size D, in volume percent; (b) k is the number of component distributions in the consist and is at least 1; (c) Xj is the fractional amount of the component j in the consist, is less than or equal to 1.0, and the sum of all of the XJ'S in the consist is 1.0; (d) n is the distribution modulus of fraction j and is greater than 0.001; (e) D is the diameter of any particle in the consist and ranges from 0.05 to 1180 microns; (f) Dβ is the diameter of the smallest particle in fraction j, as measured at IZ CPFT on a plot of CPFT versus size D, is less than _τ_ , and is greater than 0.05 microns; (g) DL is the diameter of the size modulus in frac- t ion j , measured by sieve size or its equivalent, and is from 15 to 1180 microns, (c)during the grinding of said grinding mixture, adding a total of from 10 to 90 weight percent of the optimum amount of dispersing agent to the mixture by adding at least two separate portions of the dispersing agent at at least two separate times. 2. The process as recited in claim I , wherein said k is I. 3. The process as recited in claim 2, wherein said l iquid is water. 4. The process as recited in claim 3, wherein said sol id carbonaceous material is coal. 5. The process as recited in claim 4, wherein said grinding mixture is ground in a ball mill. 6. The process as recited in claim 5, wherein said ball mill grinding is conducted at less than 70 percent of the ball mill critical speed. 7. The process as recited in claim 6, wherein said colloidal sized particles of coal have a net zeta potential of from 15 to 85 millivolts. 8. The process as recited in claim 7, wherein said ball mill grinding is conducted at less than 60 percent of the ball mill critical speed. 9. The process as recited in claim 8, wherein during the grinding of said grinding mixture, a total of from 20 to 80 weight percent of the optimum amount of dispersing agent is added to the grinding mixture by adding at least three separate portions of the dispersing agent at at least three separate times. 10. The process as recited in claim 9, wherein said ball mill grinding is conducted at less than 55 percent of the ball mill critical speed. 11. The process as recited in claim 4, wherein said colloidal sized particles of coal have a net zeta potential of from 15 to 85 mill ivolts. 12. The process as recited in claim II , wherein during the grinding of said grinding mixture, a total of from 20 to 80 volume percent of the optimum amount of dispersing agent is added to the grinding m ixture by adding at least three separate portions of the dispersing agent at at least three separate times. 13. The process as recited in claim 12, wherein a total of from 30 to 70 weight percent of the optimum amount of dispersing agent is added to the grinding mixture. 14. The process as recited in claim 13, wherein a total of from 40 to 60 weight percent of the optimum amount of dispersing agent is added to the grinding mixture by adding at least four separate portions of the dispersing agent at at least four separate times. 15. The process as recited in claim 14, wherein a total of from 45 to 55 weight percent of the optimum amount of dispersing agent is added to the grinding mixture. OMPI

Inventors: FUNK JAMES E, FUNK, JAMES, E.
Applicants: UNIV ALFRED RES, ALFRED UNIVERSITY RESEARCH FOUNDATION, INC.
Application year: 1984
Main classification: C10L1
IPC codes: C10L1