Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/30—Active carbon
  • C01B32/354—After-treatment
  • C01B32/384—Granulation

Definitions

• This invention relates to granular activated carbon manufacture, and more particularly to a new and Improved process for making hard granular activated carbon from sub- bituminous coal treated with dilute solution of saturated aliphatic monocarboxylic acid, and to a new and improved hard granular activated carbon made by such process and having properties which make it suitable for use in liquid phase applications such as water and waste water treatment.
• Abrasion number - is a measure of the resistance of the activated carbon granules to degrading on being mechanically abraded. It is measured by contacting a sample with steel balls in a pan on a machine and shaking the contents for a given time and determining the resultant particle size dis ⁇ tribution and hence the mean particle diameter.
• the abra- sion number is the ratio of the final average (mean) particle diameter to the original average (mean) particle diameter (determined by screen analysis) times 100.
• Activated carbon - is a carbon which is "activated” by heating to high temperature preferably with steam or carbon dioxide as the gaseous activating agent in producing an in ⁇ ternal porous particle structure.
• Activation or activating - means heating coal at high temperatures on the order of about 600°C. to about 1100°C. in the presence of a gaseous activating agent, as is well known in the art.
• the heating rate during activation from the minimum activation temperature to the maximum activatio temperature may vary widely, e.g., from about 100 to about 1000°C. per hour, but usually is nearer 100°C. per " hour.
• Adsorption isotherm - is a measurement of the adsorp- tive capacity of an adsorbent (viz. granular activated carb as a function of the concentration, or pressure, of the adsorbate (viz. N 2 ) at a given temperature. It is defined as the constant temperature relationship between the amount adsorbed per unit weight of adsorbent and the equilibrium concentration, or partial pressure.
• Apparent density - is the weight per unit volume of homogeneous granular activated carbon. To assure uniform packing of the granules during measurement, a vibrating trough is used to fill the measuring device.
• Ash - is a principal mineral constituent of coal, car ⁇ bon and pitch. It is normally defined as a weight percent basis after a given amount of sample is reduced to ash.
• Average (mean) particle diameter - is a weighted avera diameter of a granular activated carbon sample. A screen analysis is run and the average particle diameter is calcu ⁇ lated by multiplying the weight of each fraction by its 3. average diameter, adding the products, and dividing by the total weight of the sample. The average diameter of each fraction is taken as the size midway between the sieve opening through which the fraction has passed and the sieve opening on which the fraction was retained. It usually is expressed in mm.
• Carbon tetrachloride activity number - is the steady state percentage increase in the weight of a bed of acti ⁇ vated carbon after air which has been saturated with carbon tetrachloride at 0°C. is passed through the carbon at 25°C. It is expressed as a percentage number.
• Charring - means heating coal at low temperatures on the o)rrddeerr of about 175 C. to about 275 C. in the presence of oxygen.
• Coking value - is usually expressed as percent residual carbon obtained when a dry sample of coal, tar or pitch is vaporized or pyrolized for a specific time at a specific tem ⁇ perature that limits the available oxygen supply (ASTM Method D-2-16).
• the coking value expressed as percent residual carbon, indicates the coke forming properties of the material
• Devolatilizing - means heating coal at intermediate tem ⁇ peratures on the order of about 400 C. to about 600 C. in an oxygen-free atmosphere.
• Direct activation or directly activating - means heating a coal, preferably in a granular form, directly (without prior charring and devolatilization) and rapidly (at a heat ⁇ ing rate of about 500°C. per hour or more) to an activating temperature higher than the devolatilization temperature (of the order of 600° to 1100°C.) in an atmosphere containing a gaseous activating agent and maintaining the desired acti ⁇ vating temperature for the desired period of tirne ⁇ .
• Granular activated carbon - is "activated carbon" whic has a particle size, i.e., "mesh", which is not less than about 60 and preferably not less than about 40.
• Iodine number - is the milligrams of iodine adsorbed b one gram of granular activated carbon at an equilibrium fil trate concentration of 0.02 N iodine. It is measured by co tacting a single sample of carbon with an iodine solution and extrapolating to 0.02 N by an assumed isotherm slope. This number can be correlated with the ability of . granular activated carbon to adsorb, low molecular weight substances.
• Mesh - is the particle size of granules as determined by the U.S. Sieve Series or the Tyler Series. Usually, this term refers to the sizes of the twoScreens, in either of the above Series, between which the bulk of a sample falls. For example, “8/30 mesh” (or “8 by 30 mesh” or “8 x 30 mesh”) means that 90% by weight of the sample wi pass through a No. 8 screen but will be retained on a No. 3 screen. Likewise, 6/0 mesh means that 905? by weight will pass through a No. 6 screen, with no lower limit on granula size. Alternatively, this term refers to a maximum particl size, such as in defining the fineness of powder material. For example, "65$ by weight -325 mesh powder” means that 65 by weight of a given sample passes through a No. 325 mesh screen.
• Molasses number - is calculated from the ratio of the optical densities of the filtrate of a molasses solution treated with a standard activated carbon and the activated carbon in question.
• Pitch - is a black or dark viscous substance obtained as a residue in the distillation of organic materials and especially tars.
• Powder - means powdered activated carbon which has a particle size, i.e., "mesh", which is smaller than about 4 ( 3 and preferably smaller than about 60. The larger the mesh number, the smaller the size.
• Sub-bituminous coal - is an intermediate stage coal which ranks above lignite and brown coals, but below bitu in- ous coal. In the as received condition it has, by weight, (1) a proximate analysis of: from about 10J? to about 25$ moisture, from about 35$ to about 45$ volatile material, from about 2 % to about 5 % ash, and from about 25$ to about - ⁇ 5% fixed carbon, and (2) an ultimate analysis of: from about 65% to about 75$ carbon, from about k % to about 8% hydrogen, from about 0.5$ to about 2.05? nitrogen, and from about 0.5# to about 1.0J. sulfur. See ASTM Standard D-388-66.
• Surface area - is the amount of surface area "" per unit weight of granular activated carbon; it is determined from the nitrogen adsorption isotherm by the Brunauer, Emmet and Teller (BET) method, and it is expressed in m /gram.
• BET Brunauer, Emmet and Teller
• volumetric Iodine and Molasses Numbers - are determined by multiplying by the apparent density, in order to express these properties independently of such density.
• Granular activated carbon is particularly useful in li ⁇ quid phase applications, such as water and waste water treat ⁇ ment, not only because it is highly effective in purifying the intake, as well as the effluent from municipal and industrial systems but also because it can be regenerated for repeated use. In order to accomplish these objectives, however, it must possess certain properties, namely, a
• Hard granular activated carbon can be obtained from bituminous, sub-bituminous and brown coals, such as dis ⁇ closed in U.S. Patents 4,144,19-3, 4,032,476, 4,131,566, 4,149,994, 4,149,995, and 4,157,314.
• each of the aforesai patents discloses the elimination of the charring or low temperature heat oxidation step foun to be necessary in dealing with bituminous coal.
• both the acid treatment and charring steps were fou to be necessary for attaining the desired results when trea ing low rank agglomerating but not good coking bituminous the '314 patent, it has been found that both the charring and devolatilization steps could be eliminated prior to the acti ⁇ vation step in heat treating the sub-bituminous granules.
• the disclosures of U.S. Patents 3,483,134, 3,876,505, and 4,014,817 are of interest, but each discloses the necessity for the charring or low temperature heat oxi ⁇ dation step, and none discloses a hard granular activated carbon product.
• coals are composed essen ⁇ tially of organic carbonaceous materials of varying volatiles together with portions of inorganic salts and other com ⁇ pounds.
• the object of processes for the formation activated carbon is to produce carbon in an active form within a suitable physical environment - that is, with a suitable pore size, density and hardness. It is highly desirable that the ash content be as small a percentage of the total mass of product as Is possible, this to improve the physical characteristics of said product.
• the ash which arises primarily from the inorganic material present in the starting coal, may be minimized either by removal of the Inorganic materials prior to activation or by increasin the overall proportion of carbonaceous materials retained i the product during the course of its production.
• the Inorganic mineral. acid treat ⁇ ment taught by certain of the patents referred to above serves to fix relatively volatile carbonaceous materials of the starting material coal in a relatively non-volatile for thus minimizing loss of carbonaceous material via volatiliz tion during the course of production.
• the salutary propert and yield resulting from the inorganic treatment are though to be directly attributable, at least In part, to this fixation effect.
• inorganic acids used in the aforementioned treatment processes as being inorganic materials from which ash may form, makes it clear that removal thereof prior to further production Is essential to a minimization of ash co tent in the product.
• the often elaborate washing procedure which is necessary to effect this removal adds measureably the cost of production.
• subsequent drying of the washed coal is hindered by the residual inorganic acid.
• saturated aliphatic monocarboxylic organic acids offers salutary benefit to the production of granular activated carbon from sub- bituminous coal.
• These organic acids are believed to be as effective in fixing volatile carbonaceous materials of sub- bituminous coal as are inorganic acids, but such organic acids do not require elaborate washing procedures prior to further processing.
• these organic acids are carbonaceous materials in their own right, and are not inorganic, failure to remove the totality of the treating organic acid will not lead to a significant increase in the ash content of the products.
• these organic acids are, in general, volatile and can be recovered upon heating of the treated coal. Thus, simple decantation of the organic acid from the coal or a simple rinsing pro ⁇ cedure will generally suffice without further washing.
• a general primary objective of the present invention Is (1) to provide a new and improved process for making hard granular activated carbon from low cost sub- bituminous coal wherein the charring step necessary for pro ⁇ cessing bituminous coal is eliminated, while the overall yield of granular activated carbon is increased significantly by appropriate treatment of sub-bituminous coal with a dilute aqueous solution of saturated aliphatic monocarboxylic organic acid, with or without the addition of carbonaceous binder; (2) as well as to provide a new and improved hard granular activated carbon made by such process and having the afore ⁇ mentioned desired properties of adsorption (as measured by volumetric Iodine number), decolorization (as measured by volumetric Molasses number), purity (as measured by ash con ⁇ tent), hardness (as measured by abrasion number) and density (as measured by apparent density), which make it suitable for use in liquid phase applications, such as water and waste water treatment.
• adsorption as measured by volumetric I
• the invention includes (1) a process for making hard granular activated carbon, comprising: forming granules from sub-bituminous coal; reducing the granules to form fine powder; compressing the powder to form shapes; reducing the shapes to reform granules, and thereafter sub ⁇ jecting the reformed granules to heat treatment, without charring, until activated, wherein the improveme .n r_t comprises: treating the initially formed granules with a dilute aqueous solution of saturated aliphatic monocarboxylic acid, at a 1 0 .
• a specific primary objective is to provide (1) such process wherein the preferred saturated aliphatic monocar ⁇ boxylic acid is formic acid, at a preferred concentration of from about 3% to about 6% by weight, and (2) hard granul activated carbon made by such process and having an abrasio number of not less than about 70.
• Another specific primary objective is to provide (1) such process wherein the treated granules are mixed within from 0 to about 1 % by weight of a carbonaceous binder, and (2) hard granular activated carbon made by such process and having an abrasion number of not less than about 80.
• the single figure is a block diagram or flow sheet illustrating schematically the various steps of the process as well as the resulting product, both embodying the inven ⁇ tion.
• the starting material for this and each of the following examples was a batch of Wyoming sub-bituminous (Elkol) coal, that being used in this Example having the following analy ⁇ sis percent by weight, in the as received and dry conditions respectively:
• the sub-bituminous coal employed in this Example had the following analysis:
• Example 1 The procedure of Example 1 was repeated, except as follows. 800 grams of 6/20 mesh granules were stirred for 1 hour at 95°C. with an aqueous solution of 150 cc of 90% formic acid in 3020 cc of water (about 5-1% acid and about 4/1 solution to coal ratio). The acid was decanted from the coal, which was quickly rinsed with water and decanted again. The treated coal was dried at 120°C. for 1/2 hour to a mois ⁇ ture content of about 2 or 3%, with 1592 grams of the dried coal being mixed with 102 grams of coal tar pitch (6% pitch), and this mixture was ground in a hammer mill to yield a fine powder of 77% -325 mesh. The powder then was compressed into the aforesaid cylindrical pellets in a hydraulic press operat ⁇ ing at 80,000 psi, which pellets were then crushed into granules, those of 6/20 mesh being collected.
• Example 2 300 grams of this material were activated as in Example 1, but the temperature was Increased to 1000 C, with the steam rate corresponding to 750 cc of water per hour and the temperature maintained over a period of 1/2 hour.
• this acid treatment is believed to have a beneficial effect on the coal resulting in increased activi as will be evident from the substantial increase in the Io ⁇ dine number from 722 in Example 1 to well over 900 in this and in each of the remaining inventive Examples. Expressed in percentages, the Iodine number was increased by at least 25% (this Example) and as much as 45% (Example 4).
• the sub-bituminous coal used herein had the following analysis:
• this acid treatment is believed to have a beneficial effect on the coal resulting in increased activity, as will be evident from the substantial increase in the Io ⁇ dine number from 722 In Example 1 to well over 900 in this and in each of the remaining inventive Examples. Expressed in percentages, the Iodine number was increased by at least 25% (this Example) and as much as % (Example 4).
• the sub-bituminous coal used herein had the following analysis:
• the granules were placed in a controlled atmosphere rotary kiln as described above. They were then heated to 1020 C. under a nitrogen flow, at which time steam carried by flowing nitrogen was passed through the system at a rate corresponding to 750 cc of water per hour. This was con ⁇ tinued for 52 minutes. The material was allowed to cool to room temperature' under a nitrogen atmosphere to produce 116 grams of granular activated carbon corresponding to an activation yield of 38.7% and an overall yield of 23.3%.
• the activated carbon had the following properties: apparen density -503 gram/cc; abrasion number 84; mean particle dia meter 1.49 mm; Iodine number 1050 (volumetric 528); Molasses number 253 (volumetric 127); and ash content 9-4%.
• EXAMPLE 5 (Acetic Acid + Pitch)
• the sub-bituminous coal in this Example had the following approximate analysis:
• T product had the following properties: apparent density .52 gram/cc; abrasion number 82; mean particle diameter 1.46 mm Iodine number 922 (volumetric 48l); Molasses number 247 (volumetric 128.9); and ash content 8.09%.
• hard granular activated carbon suitable for use in liquid phase applications can be obtained by treatment with a dilute aqueous solution of saturated aliphatic monocarboxylic acid, such --a-s. formic acid and acetic acid, with formic acid being preferred.
• saturated aliphatic monocarboxylic acids such as pro- panoic, butanoic, pentanoic and hexanoic acids, with the ac concentration required being increased with the decrease in strength of the acid.

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• 1980
  • 1980-03-21 NZ NZ193206A patent/NZ193206A/xx unknown
  • 1980-07-14 EP EP80104080A patent/EP0025099B1/en not_active Expired
  • 1980-07-14 DE DE8080104080T patent/DE3062735D1/de not_active Expired
  • 1980-07-28 JP JP50192780A patent/JPS56501007A/ja active Pending
  • 1980-07-28 WO PCT/US1980/000933 patent/WO1981000399A1/en not_active Ceased
  • 1980-07-28 GB GB8109657A patent/GB2069991A/en not_active Withdrawn
  • 1980-07-29 PH PH24364A patent/PH15934A/en unknown
  • 1980-07-30 PL PL1980225979A patent/PL122803B1/pl unknown
  • 1980-07-31 DD DD80223006A patent/DD152524A5/de unknown

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