CS212761B2 - Method of preparing granulated active carbon - Google Patents

Abstract

ACl-l GRANULAR ACTIVATED CARBON MANUFACTURE FROM SUB-BITUMINOUS COAL LEACHED WITH DILUTE INORGANIC ACID Granular activated carbon is manufactured from subbituminous coal by crushing and screening the as received coal containing about 17% moisture by weight to produce 8/30 mesh granules, which are treated by leaching with a dilute aqueous solution of inorganic acid (H2S04, H3P04, or HCl) at a concentration of about 6.5% by weight and at an aqueous solution to coal ration of about 10/1 by weight, by washing off the acid, and by drying. In one case the granules are dried partially to a moisture content of about 15% by weight without the addition of a carbonaceous binder. In the other case the granules are dried thoroughly and mixed with about 10% by weight of coal tar pitch. The so treated granules are ground to more than 65% by weight -325 mesh powder, preferably 75 to 85% by weight -325 mesh, which is compressed into pel lets of 0.5" diameter and 0.5" long under a pressure of 40,000 to 80,000 psi, and then granulated to obtain 6/20 mesh granules. These granules are devolatilized by heating to 450.degree.C at 300.degree.C/hour in an atmosphere of N2 and the volatiles and by maintaining the temperature for 1 hour, and then activated by heating to 800 to 900.degree.C in an atmosphere of N2 and steam and by maintaining the temperature for 4 to 5 hours. The overall yield of granular activated carbon is 25 to 33% by weight of the dry coal, and the activated granules have a surface area of 900 to 1100 m2/gram, an iodine number of 1000 to 1100, an ash content of 5 to 7%, an abrasion number of 70 to 80, and an apparent density of 0.46 to 0.50 gram/cc, which properties make them suitable for use in waste water treatment and other applications.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the preparation of granulated activated carbon which is suitable for use in the treatment of wastewater and other applications, wherein the process is based on semi-carbon. which is leached with dilute inorganic acid.

Granular activated carbon is used in wastewater treatment not only because it is highly effective in treating effluents from urban and industrial sources, but also because it can be easily recovered for reuse. The material to meet these conditions must be somewhat suitable for these purposes, that is to say, it must meet certain conditions, and in particular, the minimum surface area must be about 900 m ² / g in order to achieve an appropriate adsorption capacity, the minimum iodine value must be about 900 to allow adequate adsorption of low molecular weight substances, the maximum ash content must not exceed 12% by weight, and preferably not greater than 8% by weight, to achieve a certain the purity, the minimum abrasion number must be about 70 and preferably not less than 80 in order to achieve the corresponding hardness necessary to maintain granular integrity in use and. . 2 ....

at the regeneration, and a minimum spill density, it must be " higher " than 0.46 g / cm @ 3, preferably up to 0.48 g / cm @ ³ , in order to achieve such a. the density required to 'form' densely packed 'beds' and columns 'which' are used in the 'waste water' treatment.

These 'properties' can be achieved with the resulting product in cases where activated granulated charcoal is prepared from bituminous coal, but to date no method is known to achieve this product by leaching bituminous coal with a dilute aqueous inorganic solution. This material is substantially cheaper as a starting material.

It is well known that when using bituminous coal as a starting material, it is not only necessary to add tar, but also to carry out a separate process of coking the granulated mixture prior to the removal of volatiles and activation. In other words, due to the high tendency of the preferred bituminous coal types to coke, granules are formed. they sinter together during the removal of the volatile species, and thus this material becomes unsuitable both to obtain a product with suitable activation and to obtain the aforementioned desired properties. In addition, when developing the process according to the invention, it has been found that this separate coking is necessary in both cases where the granulation has not been cured with a dilute aqueous solution of inorganic acid prior to the addition of tar and separate coking. only a small, if any, positive effect on both the overall yield of the resulting granulated activated carbon and the aforementioned desired properties.

In addition, it has been found in previous investigations leading to the process of the invention that granulated activated carbon having the aforementioned desirable properties cannot be prepared from semi-charcoal unless the coal is subjected to acid leaching or coking yet This type of coal is usually poorly coking. Furthermore, it has been found that it is possible to prepare granular activated carbon from semi-bituminous coal by a process using only a separate coking process without acid leaching, but the yield in this case is very, low and the properties are best at the interface, or below the minimum accepted threshold for this granulated activated carbon that would be suitable for use in wastewater treatment or others. applications. As a matter of principle, it has been found in the process of the invention that separate coking, commonly considered necessary in the treatment of semi-bituminous coal, can be eliminated by using leaching with a dilute inorganic acid solution, the results being substantially better not only not only in terms of yield, but also in terms of desired properties. It has further been found that while the combination of using a dilute inorganic acid solution for leaching and a coal binder results in optimum yield and resulting product properties, the coal binder may be discharged at an early stage to produce the product. which is obtained with substantially. higher yield and having acceptable properties.

. Numerous different terms will be used in the following, and to facilitate a clear understanding of the spirit of the invention, all of these terms will be precisely, specified.

· Abrasive · No.: · is a measure of the resistance of activated carbon to granules to degrade during mechanical abrasion. This value is determined by contacting the individual material samples with the steel balls in the vessel in the measuring instrument, shaking the contents for a predetermined period of time to determine the resulting particle distribution and hence the mean particle diameter. The abrasion number indicates the ratio of the resultant mean particle diameter to the original mean particle diameter (determined by sieve analysis), increased by a factor of 100.

Activated carbon is coal which is "activated" by heating to a high temperature, preferably in the presence of water vapor or carbon dioxide as the activating agent, in order to achieve an internal porous particle structure.

Adsorption isotherm: is a measure of the adsorption capacity of an adsorbent (see granulated activated carbon) as a function of the concentration or pressure of an adsorbed substance (see nitrogen) at a given temperature, defined as the relationship between adsorbed amount per adsorbent mass unit and equilibrium concentration or partial pressure, temperature.

Bulk density: is the mass of homogeneous granulated coal in the activated state per unit volume. To ensure a uniform distribution of the granules during the measurement, a vibration vessel is used to fill the meter.

Ashes: they are the main mineral component of coal, carbon and tar. Normally this proportion is defined as the weight percent of the sample after the given amount of sample has been converted to ash.

Mean particle diameter: is the mean particle diameter of the activated carbon samples obtained from weighing. After sieve analysis, the mean particle diameter is determined by multiplying the weight of each fraction by its mean diameter, adding up the values thus obtained, and dividing the resulting value by the total weight of the sample. The average diameter of each fraction is the mean value between the sieve opening through which the fraction passes and the sieve opening where the fraction is trapped.

Coking value: normally expressed as a percentage of the residual carbon that is obtained when a dry sample of coal, tar or pitch is evaporated or pyrolyzed for a given period of time and at a given temperature, avoiding oxygen access (ASTM method D-2416) Coking capacity, expressed as · percentage · residual carbon, · indicates the ability of a material to form coke.

Granular activated carbon: is activated carbon having a particle size, expressed in mesh, greater than about 40.

Iodine Number: is the number of milligrams of iodine adsorbed per gram of granulated activated carbon at an equilibrium filtrate concentration of iodine of 0.02 N. This value is determined by contacting the carbon sample with the iodine solution and extrapolating to 0.02 N according to the expected climb isotherms. This number can be considered as the ability of granular activated carbon to adsorb low molecular weight substances.

Mesh (or mesh size): is the size of the individual granules, determined according to the specified US Sieve Series or Tyler Series sizes. Generally, this term refers to the mesh sizes of two sieves, in one or the other. For example, “8/30 mesh” (or otherwise “8 times 30 mesh” or “8 X 30 · mesh”] means that 90 percent by weight of a given sample goes through sieve # 8 but is retained on sieve # 8 30. Similarly, the term refers to the maximum particle size and thus defines the fineness of the powder material, for example, "65% by weight - 325 mesh" referring to powder means that 65% by weight of the sample passes sieve 325 mesh.

Tar: is a black or dark colored viscous substance obtained as a residue from the distillation of organic materials and in particular pitch.

Powder: means a particle size given in the mesh of less than about 40. A larger mesh number means a smaller particle size.

Bituminous coal: is the intermediate phase of coal that lies above lignite and brown coal but below bituminous coal. Under the conditions adopted, the analysis of this material is as follows (percentages given are by weight):

1) component analysis:

up to 25% moisture, 35 to 45% volatile component, 2 to 5% ash and 25 to 45% carbon

2. elementary analysis:

up to 75% carbon, 4 to 8% hydrogen, 0.5 to 2% nitrogen and 0.5 to 1.0% sulfur.

Surface area: is expressed as the surface area per unit of granulated activated carbon mass. This value is determined from the nitrogen adsorption isotherm according to the Brunauer, Emmet and Teller (BET) method and is expressed in m ² / g.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel improved process for preparing granular activated carbon from bituminous coal, which is inexpensive instead of bituminous coal, eliminating the separate coking required for bituminous coal treatment with a dilute inorganic acid solution. without addition of coal binder. It is also an object of the present invention to provide granulated activated carbon which exhibits desirable adhesion, surface area and iodine number properties, as well as hardness and bulk densities that make this material suitable for use in wastewater treatment and other applications.

The process for the preparation of granulated activated carbon suitable for use in waste water treatment and other applications in which the coal is ground into granules is carried out according to the invention by treating the granules by mixing with inorganic acid, then removing the volatiles. the granules by heating in an oxygen-free atmosphere at a temperature higher than that used for low temperature oxidative heat treatment, followed by activating said volatile-free granules by heating in an atmosphere containing a gaseous activating agent at a temperature higher than the temperature at which the volatilization is carried out, while reducing the cost of the coal used while obtaining a granular activated carbon of adequate hardness to maintain the granular integrity on the other hand intended use and regeneration, expressed as a minimum abrasion number of 70.

The process according to the invention consists in using semi-charcoal, whereby the granules are cured with a dilute aqueous solution of inorganic acid at a concentration ranging from 1 to 50% by weight, followed by elution of the acid solution, drying the washed granules, at least partially to maximum moisture content of 25% by weight, and optionally mixing the dried granules with 5-15% by weight of coal binder, the granules thus treated being comminuted to a powder which is compressed and then comminuted to reformed granules which are then heated directly to a temperature wherein the removal of volatiles in an oxygen-free atmosphere is carried out without prior low-temperature oxidative heat treatment. ·

In a preferred embodiment of the process of the present invention, a bituminous coal having a maximum moisture content of - 25% by weight and a maximum ash content of 5% by weight is used.

Sulfuric acid, phosphoric acid or hydrochloric acid is preferably used as a dilute aqueous solution of inorganic acid. The preferred ratio of the aqueous acid solution to the amount of charcoal to be treated is at least 2: 1.

In a preferred embodiment of the process of the invention, the granules are comminuted to form a powder having a dispersive degree such that the proportion of particles having a size of 0.044 mm is greater than 65 percent by weight. This powder is preferably compressed to a minimum pressure of 276 MPa.

In order to obtain granulated activated carbon of increased hardness, the granules are preferably processed by mixing the dried granules with a carbon binder in an amount ranging from 5 to 15% by weight.

Phosphoric acid at a concentration ranging from 1 to 20% by weight of the aqueous solution is preferably used to obtain granular activated carbon in an increased yield, with a minimum solution to carbon weight ratio of 4: 1.

In order to eliminate any mixing with the binder, the granules are preferably processed by drying partially to a moisture content in the range of 10 to 25% by weight, without the addition of a coal binder.

It is also preferred to use phosphoric acid at a concentration ranging from 1 'to 20% by weight of the aqueous solution, with a minimum solution to carbon weight ratio of 4: 1, increasing the overall yield of the granular activated carbon.

An advantage of the process according to the invention is that the granular activated carbon is prepared from bituminous charcoal, which is inexpensive, instead of bituminous charcoal, which is substantially more expensive, eliminating separate coking and increasing the overall yield of the granular activated carbon. The quenching is carried out with a dilute inorganic acid solution and the addition of a coal binder is also used or not. The resulting granular activated carbon product is suitable for wastewater treatment and other applications due to improved properties.

Generally, the process for preparing granular activated carbon comprises the following steps: preparing granules from semi-carbon, treating the granules by curing with a dilute inorganic acid solution, washing the acid and drying, comminuting the processed granules into powder, compressing the powder into pellets, processing the pellets into reformed granules , removing the volatiles from the reformed granules, activating and removing the volatiles from the granules.

In a particular embodiment of the process of the present invention, the treated charcoal has a moisture content of from 10 to 25% by weight, wherein the acid is selected from the group consisting of sulfuric acid, phosphoric acid, hydrochloric acid and theirs. mixtures, at a concentration ranging from. 1 to 50% by weight, preferably. In the range of from 1 to 20% by weight, and the weight ratio of the aqueous solution to the amount of coal is at least 2: 1, the treated granules are milled to a minimum of 2: 1. powder with a particle size of at least 65% by weight - 32'5 mesh, the comminuted granules are devolatilized by heating in an oxygen-free atmosphere and the devolatilized granules are activated by heating in an atmosphere containing an activating agent.

In another particular embodiment, the granules are processed by partial drying to a moisture content in the range of from about 10 to about 25% by weight without the addition of a coal binder.

According to another alternative embodiment, the granules are treated by intensive drying and then mixed with the coal binder in an amount ranging from 5 to 16% by weight, preferably from 7 to 12% by weight, preferably the coal binder. binder tar pitch.

It is also possible to carry out the process according to the invention in that the granules of bituminous coal have a moisture content. from about 10 to about 25% by weight, with a dilute aqueous solution of inorganic acid at a concentration ranging from 1 to 10% by weight, and the weight ratio of the solution to coal is at least 4: 1, wherein the ground granules are devolatilized by heating to 450 ° C at a rate of increasing the temperature of 300 ° C / h, under an atmosphere of nitrogen and volatile volatiles, and maintained at that temperature for about 1 hour. The volatile-free granules are activated by heating to a temperature in the range of 800 to 900 ° C in an atmosphere of nitrogen and water vapor, and maintained at this temperature for a period of from 4 to 5 hours to achieve a total yield of granulated of activated carbon in the range of from 25 to 33% by weight, based on dry matter. Granular activated carbon having a surface area in the range of about 900 to 1100 m ² / g, an iodine value in the range of about 1000 to 1100, an ash content in the range of about 5 to about 7% by weight can be obtained. , an abrasion count in the range of 70 to 80 and a bulk density in the range of about 0.46 to 0.50 g / cm ³

In an alternative embodiment of the process according to the invention, the granules are processed by partial drying to a moisture content of about 15% by weight, without the addition of a coal binder, the total yield being from 25 to 30% by weight based on dry matter. granulated activated carbon having a surface area in the range of about 900 to 1100 m ² per gram, an iodine value in the range of about 1000 to 1100, an ash content in the range of 5 to 7% by weight, an abrasion number in the range of about 70 and a bulk density in the range of 0.46 to 0.50 g / cm ³ .

In another embodiment of the present invention, the phosphoric acid is used and the total yield is in the range of about 26% to about 30%. Granular activated carbon having a surface area ranging from 900 to 1100 m 2 / g, iodine number: about 1000, ash content ranging from 5 to 6% by weight, based on dry weight, is obtained. an abrasion number of about 70 and a bulk density in the range of '0.48. up to 0.50 g / cm ³ . .

In another embodiment of the process of the invention, the granules are processed by proper drying and then mixed with the coal binder, i.e., tar, in an amount of from about 7 to about 12% by weight, the total yield being from 25 to 33% by weight. based on dry weight, granulated charcoal is obtained having a surface area in the range of from about 900 to 1100 m 2 / g, an iodine value in the range of from about 1000 to 1100, an ash content in the range of from about 5 to 7% by weight, an abrasion number of about 80 and a bulk density ranging from 0.48 to 0.50 grams per cm @ -1.

Alternatively, phosphoric acid may be used and the total yield will be from about 30 to 33% by weight of the dry matter to produce a granular activated carbon having a surface area of about 1050, iodine number. in the range of 1000 to 1100, an ash content of about 6% by weight,. an abrasion number of about 80 and a bulk density in the range of 0.48 to 0.50 g / cm ³ .

Other features and advantages of the process of the invention will be apparent from the following detailed description of the exemplary embodiments and from the following description. of the accompanying drawing, which shows a block diagram of the individual phases of the process and which shows schematically the individual steps constituting the process according to the invention.

In accordance with the diagram in the accompanying figure, the starting coal is first granulated and the moisture content is simultaneously monitored. This starting bituminous coal either has the desired moisture content, i.e. at most 25% by weight, or is dried. This is followed by treatment of the granules by leaching with a dilute inorganic acid solution, followed by acid elution and drying. At this stage, either tar is added or not added as a coal binder, as will be further elaborated in. in the following examples, according to the moisture content of these granules. Next, the granules are pulverized, pelletized, regranulated, referred to herein as regranulation, and then the volatiles are removed and the product thus obtained is activated. The result is granulated activated carbon which is suitable for wastewater treatment and other applications. The conditions of the various stages of the process according to the invention will be described in detail in the following examples, in which the significance of carrying out the individual stages of the process will also be explained.

In the following, ten examples of practical implementation of the process of the invention will be given, examples 1 and 6-8 refer to embodiments that preceded the process of the invention, while examples 2-5, 9 and 10 describe the process itself. In addition, the order of the examples was chosen to show a higher effect according to the invention, starting with Example 1, which is an attempt to apply the known coking process to it. preparing granular activated carbon from bituminous coal to bituminous coal, through examples 2-5 using acid leaching, to examples 6, and 7,. which compare the results obtained using progressive acid leaching (Example 7j together with the known separate coking (Example 6) in the preparation of granulated activated carbon from bituminous coal with the same methods applied to semi-bituminous coal) and to Example 8, which shows that progressive acid leaching it cannot be applied with equal success to lignite, except finally for examples 9 and 10, which illustrate the importance of fine powdering (example 9) and the possibility of using hydrochloric acid (example 10) as well as sulfuric acid (example 4) and phosphoric acid (example 4). Example 5) 10

Example 1

Preparation of granulated activated carbon by coking of semi-carbon

In the preparation of granulated activated carbon from bituminous coal, it has been found that it is necessary to undergo a separate coke treatment prior to activation as described in Examples 6 and 7 below. in this case, to show what product can be obtained from the bituminous coal. The starting material was. in this example, as well as in the following examples 2-5, 9 and 10, Wyoming bituminous coal having the following composition, all percentages being by weight:

Component analysis

humidity 17 % volatile components 441 % ash 2.05 % bound carbon 35 % Elementary analysis carbon 66.8 % hydrogen 5.41 % nitrogen 0.9 % sulfur 0.55%

This composition is typical of semi-coal. The coal was crushed to very fine particles, more than 65% by weight of the material passed through a 325 mesh sieve, preferably 75 to 85% by weight passed through a 325 mesh sieve. The obtained powder was then compressed at a pressure ranging from 20 to 50 psig to cylindrical pellets having a diameter of about 1.27 cm and a height of about 1.27 centimeters. The bulk density of the pellets thus prepared ranged from 1.1 to 1.2 g / cm 3. The pellets were then granulated to a pellet. 6 x 20 mesh granules, with bulk density. these granules ranged from 0.64 to 0.68 g per cm ³ . In the course of the experiments, as will be shown in Examples 2 and 3, it has been found that if the aim of the process is to prepare compact granules (which are suitable for the preparation of hard granular activated carbon) without using a coal binder such as for example coal tar pitch, then it is very important to maintain a certain moisture content of the bituminous coal and the granules to be processed. Too low a moisture content, i.e. below about 10% by weight, or a too high moisture content, i.e. above about 25% by weight, leads to poor compaction of the particles, and thus. the granules become soft and less dense. Similarly, if the moisture content of the coal is too high, for example as a result of rain, then the material must be dried to the desired moisture content range prior to granulation. Otherwise, it is too difficult to crush and sieve. In this example, coal with a moisture content of 17% by weight was used, this value being within the prescribed range and therefore it was not necessary to dry the material separately in the first stage.

600 grams of the granules prepared above were placed in a cylindrical vessel made of 5 mesh. The vessel was then placed on a cylindrical shaft and the whole was placed in a cylindrical furnace while the granule vessel was slowly rotated.

The obtained granules were then subjected to a separate coking treatment, which is a low-temperature oxidation heating, in which the granules were heated in an atmosphere of air and nitrogen (in the absence of air), to a temperature of 200 ° C, at a temperature increase rate of 100 ° C / h. the granules were then held at that temperature for an hour. During this procedure, the granules slowly and uniformly rotated inside the furnace (speed ranging from 1 to 8 rpm) while exposed to oxygen. During the experimental work, it has been found that higher temperatures and / or higher oxygen contents in the atmosphere lead to poor process control and possibly poor product quality. The weight loss in this coke was between 5 and 10 percent by weight based on dry coal.

The granular material was then subjected to a treatment to remove volatiles. The granules were then placed in the aforementioned furnace, which was heated to 450 ° C, at a rate of increasing the temperature of 300 ° C / h, in an oxygen-free atmosphere (in this case a nitrogen-containing atmosphere and - volatiles which - were released from the granules), and this temperature, at which the volatiles were removed, was maintained for 1 hour, and then the material was cooled. During the experiments, it has been found that the separate coking and volatile removal steps can be carried out at the same time so as to: - do not need to cool the material; and - the atmosphere only changes to be almost oxygen free. Deň: 32 ° C. It has also been found in these experiments that the presence of oxygen at these higher temperatures leads to higher losses, poorer product yield and granulated activated carbon being of only inferior quality.

The yield of the granules after the removal of the volatiles was about 00% by weight, based on the coke granules, and their bulk density was about 0.6 g / cm ³ .

The volatile-free granules obtained were then placed in a cylindrical furnace and subjected to activation by heating the granules to a temperature ranging from 800 to 900 ° C in an atmosphere composed of a carrier gas which was - nitrogen, and water vapor, the activation temperature being maintained for 4-5 hours. The amount of water vapor supplied was pre-determined to be in the range of 1 to 3 grams of water vapor per gram of charge per hour.

The yield of granular activated carbon to be removed from this step ranged from 30 to 45% by weight, based on the volatile material-free material. The granular product obtained had a surface area in the range of 900 to 1000 m ² / g, an ash content in the range of 7 to 10% by weight, an abrasion number ranging from 60 to 70 and the bulk density was in the range of from 0.45 to 0.48 g / cm 3.

The total yield, based on dry coal, ranged from 20 to 22% by weight, the granules obtained having adsorption properties, ash content, bulk density and hardness that were below or below acceptable levels, which are determined for granulated activated carbon, which is used in wastewater treatment and other applications.

In the course of the experimental work, it was found that when the semi-coal is treated as described above but without separate coking, the resulting product is soft and has little activity, indicating that coking of bituminous coal (at its processing] is very important, even if this kind of coal is not very well coking.

The following examples 2-5 illustrate embodiments of the process according to the invention, which are schematically shown in the attached figure. In terms of performing the procedure, this progressive procedure comprises the following steps; granulating semi-bituminous coal, either having a predetermined moisture content, under predetermined conditions ranging from 10 to 25% by weight, or dried, as shown in the attached figure on the right side of the diagram, the moisture content is checked prior to granulation, followed by treatment of the granules by leaching with a dilute aqueous solution of inorganic acid, acid washing and drying, powder formation, pelletizing, regranulation, volatile removal, activation, the aim of these steps being to prepare granular activated carbon desired properties and which would be suitable for use in wastewater treatment as well as in other applications. The following Examples 2- and 3 represent two embodiments of the process in which the treated granules are leached with a dilute aqueous solution of sulfuric acid and phosphoric acid, the product obtained is washed and dried to the desired preferred moisture content as described above. preferably to a moisture content of 15% by weight, followed by powder formation and further steps, this process being carried out without the addition of tar, as shown in the alternative embodiment. Examples 4 and 5 show two different and more preferred embodiments of the process according to the invention in which the granules are leached with a dilute aqueous solution of sulfuric acid and phosphoric acid, followed by acid washing, proper drying and mixing with tar such as coal prior to powder formation. as shown in the attached figure on the right.

Example 2

Preparation of granulated activated carbon using leaching of semisolid coal with dilute aqueous sulfuric acid solution (without tar addition)

A batch of Wyoming bituminous coal, the analysis of which has already been described in Example 1, was crushed and then sieved to obtain granules of 8 X 30 mesh. Then 300 grams of these granules were placed in a 41 liter vessel, to which a total amount of dilute aqueous acid solution was also added, which was 150 cm @ 2. sulfuric acid at a concentration of 98% by weight and 2.85 liters of water (the acid concentration was about 6.5% by weight or 5% by volume). The total content, consisting of granules and acid solution, was heated to 80 ° C and held at this temperature for 5 hours, with the granules being continuously stirred. During these experiments, it was found that the size of the granules, the leaching temperature (which is usually below 100 ° C because of the dilute aqueous acid solution used), the leaching time, the acid concentration and the dilute aqueous acid to coal ratio were all large. the importance and importance for the further processing of coal into granular activated carbon. For this reason, the specific values set forth not only in this but also in the following examples are illustrative only, and are not intended to limit the scope of the invention in any way. For example, it may be noted that the use of coarser and finer granules during leaching with a dilute aqueous acid solution results in corresponding results when a longer leaching time is used for coarser granules than finer granules.

The contents of the vessel were then allowed to cool and the solution was decanted, with the granules being rinsed thoroughly with water so that the washing water leaving this wash had a -pH value of 6-7. To terminate this processing step, the leached granules were partially dried to an approximate moisture content of 15% by weight, which is advantageous for good densification in pellet formation and for achieving the required hardness and bulk density without using a coal binder.

The treated granules, which contained approximately 15% by weight of moisture, were milled to very fine particles, with more than 65% by weight of the material passing through a 325 mesh sieve, preferably 75 to 85% of the material passed through a 325 mesh sieve as this is further elaborated in Example 9 below. The powder obtained was compressed into cylindrical pellets with a diameter of 1.27 cm and a height of 1.27 centimeters using a pressure ranging from 281.2 MPa to 562.4 MPa, and the bulk density of the resulting pellets varied ranging from 1.1 to 1.2 grams per cm ³ . The pellets were then regranulated into 6 X 20 mesh granules having a bulk density ranging from about 0.64 to 0.68 g / cm ³ . The reformed granules were placed in a cylindrical furnace and further volatiles were removed as described in Example 1 by heating the granules at a temperature of 450 ° C at a temperature increase of 300 ° C / h in the atmosphere. relatively oxygen-free and maintained at this temperature for 1 hour.

During the experiments, it has been found that a separate coking step as described in Example 1 is not necessary in the preparation of hard granular activated carbon with good adsorption properties. At this point it was noted that two batches of the same starting material treated by cure with a dilute aqueous acid solution as described above were treated, one batch being subjected to a separate coking treatment and one not. While yields varied in both specific processes, the overall yield and activity of the resulting granulated activated carbon were the same in both cases, meaning that a separate degree of coking can be completely eliminated by using this material. This is probably the result of coal treatment where curing with a dilute aqueous acid solution was used.

The granules from which the volatiles were removed and had a bulk density of 0.60 g per cm 3 were placed in a cylindrical furnace and then subjected to activation by heating the granules to a temperature ranging from -80 to 90 ° C in an atmosphere composed of nitrogen and water vapor, the granules were maintained at this temperature for 4-5 hours. The amount of water vapor introduced into the furnace was preset to a value ranging from 1 to 3 grams of water vapor per gram of charge per hour.

The total yield of granulated activated carbon obtained, based on dry carbon, was in the range of 25 to 28% by weight, as opposed to Example 1, where the yield was 20 to 22% by weight. The resulting granules had a surface area in the range of 900 to 1100 m ² / g, as compared to Example 1, which was 900 to 1000 m ² / g, iodine number 1000, an ash content in the range of 5 to 6% by weight, in compared to Example 1, where this value was 7 to 10% by weight, furthermore the abrasion number 70, compared to Example 1, where this value ranged from 60 to 70, the bulk density ranged from 0.46 to 0.48 g / cm ³ , as compared to Example 1, where the value was in the range of 0.45 to 0.48 grams per cm ³ .

Using this example, granules were prepared which were hard, had a high adsorption capacity, low ash content, and were comparable in most parameters to carbon quality, which is advantageous for use in wastewater treatment and other applications. It should also be noted that this process not only makes it possible to prepare an acceptable granular product, activated carbon, from the bituminous coal, without the dense use of a coal binder, such as coal tar pitch, and without the need for separate coking, leaching with a dilute aqueous solution of inorganic acid substantially contributes to the reduction of ash content, while the yield increases with increased adsorption capacity, all compared to Example 1. It is also noteworthy that granulated activated carbon can be prepared by this process, which is hard (having an abrasion number 'of 70) without the need to add a coal binder.

Example 3

Preparation of granulated activated carbon by curing of semi-bituminous coal granules with dilute aqueous phosphoric acid solution (without tar addition)

The Wyoming semi-charcoal charge, as exemplified in Example-1, was ground and sieved to provide 8 X 30 mesh granules, and 300 grams of these granules were placed in a 41 liter kettle. To this batch was added a dilute aqueous acid solution containing 150 cm 3 of 75% by weight concentrated phosphoric acid and 2.85 liters of water (about 6.5% by weight). The granules and the acid solution were heated to 80 ° C and maintained at this temperature for 5 hours while stirring continuously. The product obtained was allowed to cool, the solution was decanted and the granules were thoroughly rinsed with an amount of water such that the leaving wash water had a pH ranging from 6 to

7. This step was completed by partially drying the cured and washed granules to an approximate moisture content of 15% by weight, as in Example 2.

These processed granules, which contained approximately 15% by weight of moisture, were ground to a powder of a particle size such that 65% by weight of the material passed through a 325 mesh sieve, preferably 75 to 85% of the material passed through a sieve. size 325 mesh.

The powder obtained was compressed into cylindrical pellets with a diameter of 1.27 cm and a height of 1.27 centimeters, using a pressure ranging from 281.2 MPa to 562.4 MPa, and the bulk density of these pellets ranged 1.1 to 1.2 g / cm 3. These pellets were regranulated to obtain 6 X 20 mesh granules having a bulk density ranging from 0.58 to 0.62 g / cm 3.

These re-formed granules were then placed in a cylindrical furnace and subjected to a volatile removal as described in Example 1, but in this case no separate coking of the granules was performed prior to the volatile removal. Volatile granules having a bulk density ranging from 0.58 to 0.60 g per cm 3 were then activated in the same manner as in Example 1.

The total yield of granular activated carbon, based on dry carbon, was in the range of 26 to 30% by weight, compared to Example 1, which was in the range of 20 to 2.2% by weight, and Example 2, where the value ranged from 25 to 28% by weight. The granules obtained had a surface area in the range of 900 to 1100 m 2 / g, as compared to Example 1, where the value was 900 to 1000, the iodine number was 1000, the ash content ranged from 5 to 6% by weight, compared to with Example 1, where the value was 7 to 10% by weight, the abrasion number was 70, compared to Example 1, where the value was in the range of 60 to 70, the bulk density was in the range of 0.48 to 0. 50 g / cm 3, compared to Example 1, where the value was in the range of 0.45 to 0.48, and Example 2, where the value was in the range of 0.46 to 0.48 g / cm 3 . The yield and bulk density were somewhat higher than the same values in Example 2 (leaching with dilute aqueous sulfuric acid).

According to the above process, activated carbon granules were obtained which were hard, had good adsorption capacity, low ash content, and were comparable in most parameters to the quality of granular activated carbon, which is preferably used for wastewater treatment and other applications. At this point it should be noted again that this product can be prepared from bituminous coal and does not need to be used.

In addition, a coal binder is added during the process, and there is no need to carry out a separate coking process, wherein leaching with a dilute inorganic acid solution significantly reduces ash content while increasing yield and absorbency compared to Example 1. With respect to the use of sulfuric acid or phosphoric acid as an inorganic acid in aqueous solution, it should be noted that phosphoric acid is considered to be a more efficient acid in the preparation of granular activated carbon in high yield. As can be seen from the above text and the examples, the rate of increase in yield depends on the specific leaching conditions and other conditions used.

Example 4

Preparation of granulated activated carbon 1ου. by spreading the bituminous coal granules with a dilute sulfuric acid solution (with the addition of tar

In this case, the procedure of Example 2 was repeated after drying, since in this case partial drying was not carried out to a moisture content of 15% by weight, but the granules were dried properly, and then, as shown in the middle on the right side of the production diagram. of the attached figure, processing was completed by mixing the granules with coal tar pitch No. 125 having the following properties:

Softening point 129.2 ° C benzene-insoluble matter 33.2% by weight;

13.1% by weight, coking power (according to Conradson). .

61.1 wt.%, Ash 0.17 wt.

The properly dried granules and the tar mentioned above were mixed at a rate of 90 g of coal per 10 g of tar (i.e. 10 parts by weight of tar per 100 parts by weight of coal), and the mixture was ground to a particle size of which at least 65 percent by weight a 325 mesh screen, and then the powder obtained was compressed into pellets having a diameter of 1.27 centimeters and a height of 1.27 cm using a pressure ranging from 2 to 31.2 MPa. The bulk density of the pellets ranged from 1.1 to 1.2 g / cm 3, and the granules were regranulated to obtain 6/20 mesh granules having a bulk density of 0.68 g / cm 3.

600 g of the granules thus prepared were placed in a cylindrical vessel and then degassed in the same manner as in Example 2 without separate coking of the granules. The volatile-free grains had a bulk density of 0.62 g / cm ³ and a yield of 60% by weight based on the weight of the dry tar-coal mixture.

Granulation and removal of the volatiles provided a product which was then placed in a cylindrical furnace and subjected to activation in the same manner as in Example 2.

The total yield of granulated activated carbon in this preferred embodiment of the present invention was in the range of 25 to 30% by weight based on the weight of the dry coal / tar mixture as compared to Example 1, which was 20 to 22% by weight. The granules obtained had a surface area of 1050 m ² / g, as compared to Example 1, which was 900 to 1000 m ² / g, the iodine number ranging from 1000 to 1100, compared to Examples 2 and 3, where this value was 1000, the ash content was 6% by weight, as compared to Example 1, where this value was in the range of 7 to 10% by weight, the abrasion number was 80 compared to Example 1, k.de this value was in the range of 60 to 70, and with Examples 2 and 3 where this value was 70, and the bulk density was in the range of 0.48 to 0.50 g / cm ³ , compared to Example 1, where this value it was 0.45 to 0.48 g / cm ³ , and with Example 2, which was in the range of 0.46 to 0.48 g / cm 3.

Granules of sufficient hardness, good adsorption capacity, low ash content and in all parameters were comparable to the quality of activated granulated charcoal, which is advantageously used in wastewater treatment and other applications. it should be noted that it is remarkable and utterly unexpected that, compared to the process of Example 1, in which a separate coking step was applied and which was carried out without leaching with a dilute inorganic acid solution. in this case, the overall yield was greatly increased, which can be attributed to the leaching of the coal with a dilute aqueous solution of inorganic acid and subsequent mixing with the coal binder, in this case with tar, with a simultaneous increase in yield having excellent adsorption capacity, bulk density. and abrasion resistance In comparison with Example 2, where leaching with a dilute aqueous sulfuric acid solution without tar was added, there was a slight increase in adsorption capacity (expressed as iodine value) and a substantial increase in abrasion resistance. and bulk density values. In comparison to the procedure of Example 3, in which leaching was carried out with phosphoric acid and not using tar addition, there was a slight increase in absorbency (expressed as iodine212761) and a significant increase in abrasion resistance.

Example 5

Preparation of granulated activated carbon by leaching semi-bituminous coal with dilute phosphoric acid solution (with tar addition)

In this case, the same procedure as in Example 4 was followed except that 75% by weight of concentrated phosphoric acid (in a 6.5% by weight solution relative to the granules to be treated) was used instead of sulfuric acid. . The bulk density of the converted granules was 0.65 g per cm ³ , instead of the 0.68 value obtained in Example 4, wherein the volatile-free granules exhibited a bulk density ranging from 0.59 to 0.61 g / cm ³ , compared to the value of 0.62 achieved in the previous example, and the yield ranged from 60 to 65% by weight, based on the dry coal / tar mixture, compared to the value of 60% by weight achieved in the previous example.

The total yield of granulated activated carbon in this preferred embodiment of the present invention was in the range of 30 to 33% by weight, based on the weight of the dry coal / tar mixture, as compared to Example 1, which was 20-22% by weight. and Example 2, where the value was between 25 and 28% by weight, and Example 3, where the value was between 26 and 30% by weight, and Example 4, where the value was between 25 and 30% by weight. The resulting granules had a surface area of 1050 m ² / g, as compared to Example 1, which was in the range of 900 to 1000 m ² / g, the iodine number was in the range of 1000 to 1100, compared to Examples 2 and 3, where the value was 1000, the ash content was 6% by weight, as compared to Example 1, where the value was in the range of 7 to 10% by weight, the abrasion number was 80, compared example 1, where this value was from 60 to 70, and Examples 2 and 3; in which the value was 70, and the bulk density in this example was in the range of 0.48 to 0.50 g / cm ³ , compared to Example 1, where the value was in the range of 0.45 to 0.48 g / cm ³ , and with Example 2, wherein the value was in the range of 0.46 to 0.48 g / cm ³ .

The above process yielded very hard granules having a good adsorptive capacity, low ash content, and in all parameters the granules were comparable to the quality of carbon used as granular activated carbon for wastewater treatment and other applications. It should be noted at this point that it is remarkable and utterly unexpected that the overall yield has increased considerably not only with respect to Examples 2, 3 and 4, but of course 1 with respect to Example 1, while also increasing the adsorption, purity product, abrasion resistance and density. Similarly, in this case, there was a substantial increase in abrasion resistance relative to Examples 2 and 3 and a significant increase in density relative to Example 2.

The process according to the invention improves the properties of the granulated activated carbon, such as hardness, density, adsorption ability, which can be attributed to the treatment of semi-porous coal with a dilute aqueous solution of an inorganic acid, in particular phosphoric acid in this case. Furthermore, these improved properties can be considered to be comparable to those obtained with a more valuable bituminous coal than a traditional raw material. More importantly, this completely unexpected result is achieved by eliminating the separate degree of coking that is considered necessary in the processing of bituminous coal.

The following two exemplary embodiments show how the process of the invention results in bituminous coal, in the first case without leaching with a dilute aqueous solution of an inorganic acid (Example 6) and in the second case using this leaching.

Example 6

Preparation of granulated activated carbon from bituminous coal and tar addition

In this case, the starting material was a feedstock of bituminous coal, which showed the following analyzes (in percent by weight):

Component analysis:

Given material Dried material

% moisture 2.04 - % ash 1.20 1.26 % volatile material 33, IQ 33.80 % bound carbon : 63,60 64.90

The material

Dried material

Elementary analysis:

% humidity i 2.04 - % carbon 83.30 84.00 % hydrogen 5.20 5.29 % nitrogen 1.30 1.33 % sulfur 0.34 0.35 % ash 1,23 1.26 The calorific value was for the material concerned, 33,9 MJ / kg; and for dried material 34,6

MJ / kg.

The values from these analyzes are typical of eastern bituminous coal. These types of coal are also well coking and contain little ash. The dried coal was milled to a particle size of 8 X 30 mesh granules which were then mixed with coal tar pitch No. 125 described in Examples 4 and 5 at a ratio of 90 grams of charcoal. 10 grams of tar pitch (which means 10 parts per 100 parts by weight).

The mixture thus obtained was ground to a very fine powder having a particle size such that 65% by weight of the powder passed through a 325 mesh sieve. The ground powder was compressed into pellets of 1.27 centimeters in diameter and 1.27 cm in terms of pellet height using a pressure ranging from 281.2 MPa to 562.4 MPa. These pellets had a bulk density of 1.18 g / cm ³ and were further granulated into 6 X 20 mesh granules having a bulk density of 0.65 g / cm ³ .

The granules were placed in a cylindrical furnace in an amount of 600 g and were subjected to a separate coking treatment in the same manner as in Example 1. In this case, the separate coking was carried out by heating the granules from ambient to temperature. 250 ° C at a temperature rise rate of 100 ° C / h and were then maintained at that temperature for 2 hours. The furnace was then supplied with a stream of gas, which consisted of 1.4158 nitrogen. 10 ^-2 m ³ / h at a pressure of 0.1 MPa and ambient temperature, and from air in an amount of 1.4158. . ² m ³ / h at a pressure of 0.1 MPa and ambient temperature, with the cylindrical vessel rotating in the furnace at a speed ranging from 1 to 4 rpm.

During the experimental part, it has been found that the rate of temperature increase, the gas composition (particularly the amount of oxygen present in the gas), the temperature and the time it is maintained are critical values whose changes have a significant effect on the granule quality if their applicability for further processing into hard granular activated carbon. For example, if too short a time interval is used to maintain the granules at the above coking temperature (less than 0.5 hours) or too low a temperature (less than 200 ° C), there will be difficulties in further processing the granules. If a process without suitable coking is used, the granules are sintered during the removal of the volatiles and are unsuitable for further activation and the desired properties of granular activated carbon cannot be achieved.

In the above-mentioned separate coking process, the yield of the granules was 69% by weight based on the weight of the coal / tar mixture, the granules having a bulk density of 0.62 g / cm 2.

The cracked granules were then degassed and further activated in the same manner as in Example 1.

After completion of the process, activated carbon granules were obtained with a total yield of 34% by weight based on the weight of the dry coal / tar mixture. These granules had a bulk density of 0.50 g / cm ³ , an iodine number of 1080, a surface area of 1040, an ash content of 2.2% by weight, and an abrasion number of 80.

The granules obtained were very hard, had good adsorption capacity, low ash content and were comparable in all parameters to the quality of activated carbon, which is preferably used in waste water treatment and other applications. In this case it should be noted that hard granular activated carbon cannot be obtained from bituminous coal by a process in which the granules would not be subjected to a separate coking and activation treatment. During implementation. In the experiments, the granules were devolatilized without being subjected to separate coking to obtain a sintered mass (instead of granules) which was unsuitable for activation, indicating the necessity and importance of performing separate coking for this type of coal.

Example 7

Preparation of granulated activated carbon by leaching bituminous coal with phosphoric acid using tar addition

In this example, the procedure of Example 6 was repeated, including initial granulation. Then 300 grams of the recovered charcoal granules were placed in a 41 liter vessel. To these granules was added a dilute aqueous acid solution containing 150 grams of concentrated 75% w / w phosphoric acid and 2.86 kg water (equivalent to 6.5% w / w). The mixture was heated to 80 ° C and left at this temperature for 5 hours with continuous stirring. The resulting contents were allowed to cool, the acidic solution was decanted, and the charcoal was properly washed with water in an amount such that the analyzed effluent stream had a pH in the range of 6 to 7.

The leached coal was thoroughly dried and then mixed uniformly with the coal tar pitch, as analyzed in Example 4, in the same amount, i.e. 90 g of coal per 10 g of coal pitch. The mixture was milled to a particle size of 6; 5% by weight - 325 mesh, and the powder was then compressed into pellets having a diameter of 1.27 cm and a height of 1.27 cm using a pellet ^; to a pressure ranging from 281.2 MPa to 562.4 MPa. The bulk densities of the pellets thus formed ranged from 1.1 to 1.2 g / cm 3 and were then regranulated into 6 x 20 mesh granules. which had a bulk density at this stage of 0.64 g per cm 3.

The granules were then placed in a cylindrical furnace in which they were subjected to a separate coking treatment as described in Example 6, the yield of the granules after this step being 71% by weight and the bulk density was 0.63 g / cm 3. During the experiments, it has been found that even when leaching bituminous coal with a dilute inorganic acid solution is used, separate coking as a preliminary step is necessary to obtain a suitable granulated activated carbon.

The obtained coke granules were devolatilized and then activated, both steps being carried out in the same manner as described in Example 1.

Upon completion of the activation, a hard product, granulated activated carbon, was obtained with a total yield of 35% by weight based on the weight of the dry coal / tar mixture. The granules had a bulk density of 0.50 g / cm 3, a surface area of 1000 · m 2 / g, an iodine number of 1050, an ash content of 2.4% by weight and an abrasion number of 82.

By this process, hard granules were obtained which had good adsorption capacity, low ash content and were comparable in all parameters to the quality of activated carbon, which is preferably used in wastewater treatment and other applications. It should also be noted that it is noteworthy that it is not possible to prepare a hard granulated active product from bituminous coal without subjecting the granules to the separate coking described above, even if the coal is leached with a dilute aqueous solution of inorganic acid. In this respect, the result is very different from the process for preparing granulated activated carbon from bituminous coal, where leaching with a dilute aqueous solution of inorganic acid has made it possible to eliminate separate coking to produce a product with acceptable properties.

Another important and significant fact is that leaching bituminous coal with a dilute aqueous phosphoric acid solution did not mean a significant change in yield (from 34 wt% to 35 wt%). This result is very different from the process using semi-charcoal as described in Example 5, in which the leaching of semi-charcoal with a dilute aqueous solution of inorganic phosphoric acid substantially changed the yield compared to Example 1, which was in the range of 20 up to 22% by weight, up to a value ranging from 30% to 33% by weight in Example 5, very close to the yield values in the range of 34 to 35% by weight reported in the last two examples. These results are truly unique and unexpected if they are. regarding semi-tiny coal. .

The following example is an attempt to apply the leaching technique with a dilute aqueous solution of an inorganic acid according to the invention to lignite which is lower than semi-bituminous coal.

Example 8

Preparation of granulated activated carbon by curing lignite charcoal with dilute aqueous phosphoric acid solution (tar addition).

The starting material used in this example was a charge of lignite coal, which was analyzed as follows (percentages are by weight):

The material

Dried material

Component analysis:

° / o moisture% ash / volatile matter ° / o bonded carbon

30.3

9.9

50.0

9.8

14.2

71.7

14.0

Elementary analysis:

Given material Dried material

% moisture 30.30 -. % carbon 41.50 59.5 % hydrogen 3.15 4,5 % nitrogen 3.50 5.0 % sulfur 0.73 1.4 % ash 9.90 14.2

This composition is generally typical of this type of coal, and these species generally have a high ash content compared to other types of coal. The charcoal was milled into 8 X 30 mesh granules and 300 g of the granules were placed in a 41 liter vessel and 150 cm ^{3 of} concentrated phosphoric acid (75% by weight) and 2.85 l of water (corresponding to acid concentration 6.5% (w / w). The granules and the dilute aqueous acid solution were then heated to 80 ° C and held at this temperature for 5 hours while stirring continuously. The resulting product was allowed to cool, the solution was decanted, and the granules were rinsed thoroughly with water such that the pH of this effluent analyzed was in the range of 6 to 7. The obtained granules were thoroughly dried and mixed with coal tar pitch at a weight of 10% parts of tar per 100 parts by weight of coal, using the same tar as in Examples 3 and 4.

The resulting mixture was thoroughly pulverized, with 65% by weight of the powder passed through a 325 mesh sieve, preferably 75 to 85% by weight of the powder passed through a 325 mesh sieve. The powder was then compressed into cylindrical pellets having a diameter of 1.27 centimeters and a height of 1.27 cm at a pressure of between 281.2 MPa and 562.4 MPa, and the bulk density of these pellets ranged from 1 to 200 psi. 1 to 1.2 g / cm ³ . These pellets were regranulated into 6 X 23 mesh granules having a bulk density ranging from 0.64 to 0.66 g / cm ³ . The granules were placed in a cylindrical furnace where they were devolatilized as described in Example 1. In this example, two batches were used which were devolatilized in the same manner, with one batch being subjected to separate coking as described. in Example 1, and the second batch was not subjected to separate coking, as was the case in Examples 2 to 5. These two batches were similar in terms of overall yield and activity, meaning that separate coking is not necessary for this kind of coal. .

The volatile-free granules were activated in the same manner as described in Examples 1 to 5. The granules had a very low bulk density, 0.36 g / cm ³ , surface area of 850 m ² / g, iodine number 900, ash content 11 These experiments were repeated to improve the properties of the final product, although, although there was some improvement, the desired bulk density of at least 0.48 g / cm ³ and an abrasion number of at least 70 were not achieved, or higher values. For this reason, it can be stated that it is not possible to prepare an acceptable activated carbon from lignite coal which is sufficiently hard and suitable for wastewater treatment under the above conditions.

It is evident from this and the above exemplary embodiments that:

A) The leaching of bituminous coal with a dilute aqueous solution of inorganic acid does not have any particular effect in processing this kind of coal into hard granulated activated carbon and has no particular effect on the overall yield of the process, while leaching with a dilute aqueous inorganic acid solution does not eliminate the need for separate coking.

B) Lignite charcoal leaching with a dilute inorganic acid solution does not affect the acceptability of the granular activated charcoal obtained from lignite, since this type of charcoal is too light and too soft.

C) Conversely, it has been clearly demonstrated, in demonstrating a preferred embodiment of the invention, that hard granulated activated carbon suitable for wastewater treatment and other applications can be prepared from12761 but from bituminous coal, the treated coal being leached with a dilute aqueous acid solution. (since very hard granulated activated carbon cannot be prepared from untreated coal), and this processing is reflected in the quality of the final product in an entirely unexpected and therefore progressive manner, as well as in the total yield of granular activated carbon from bituminous coal. comparable to the yield obtained in the treatment of bituminous coal by comparing Example 5 with Examples 6i and 7.

D) Another totally unexpected result in the treatment of semiconductor coal by craving with dilute aqueous solution is that separate coking, considered necessary in the treatment of treated and untreated bituminous coal and untreated bituminous coal, can be completely eliminated in the preparation of hard, dense, granulated activated carbon. . good adsorption capacity of treated semi-bituminous coal.

Design · acc. Another example is a similar embodiment to Example 5, but emphasizes the need and importance of finely grinding the treated granules before pelletizing.

Examples

Preparation of granulated activated carbon by curing of semi-bituminous carbon with dilute phosphoric acid solution by fine grinding of granules to powder

In this example, a procedure similar to that described in Example 5 and shown in the figure with a variation to the right was performed. The leached granules were washed with water in such. The amount of effluent analyzed from this wash showed a value. pH in the range of 6 to 7, the granules were thoroughly dried and then mixed with coal tar pitch in an amount of 10 parts by weight of tar # 125 per 100 parts by weight of coal. The mixture was then divided into two equivalents.

The first portion was ground to a fine particle size powder such that 60 to 65% by weight of the powder passed through a 325 mesh sieve. Pellets of 1.27 cm diameter and height were prepared from this powder. 1.27 cm, using a pressure ranging from 281.2 MPa to 562.4 MPa, and a bulk density thereof. the pellets ranged from 1.1 to 1.2 g / cm ³ . These pellets were regranulated into 6 X 20-mesh granules. and a bulk density in the range of 0 · 64 to 0.66 g / cm 3. These granules were devolatilized in the same manner as in Example 5, and the density of the granules ranged from 0.57 to 0.59 g / cm 3. The granules were activated in the same manner as in Examples 1 and 5, wherein the activated granules had a bulk density in the range of 0.44 to 0.47 g / cm 3, an iodine number in the range of 1000 to 1100, · Ranged from 900 to 1050 m2 / g, ash content ranging from 5 to 6% by weight, abrasion number ranging from 55 to 65. The obtained granules were substantially softer and therefore were not suitable for use in waste water treatment since this use and regeneration resulted in large losses of material because these granules were not hard enough.

The second crop was ground to a very fine powder of a particle size such that 75 to 85% by weight of the particles passed through a 3:25 mesh screen. The powder obtained was compacted as described above into pellets having a density ranging from 1.1 to 1.2 g / cm 3, and the pellets were regranulated to granules having a density of 0.65 to 0.68 g / cm ³ . The granules so obtained were devolatilized as described in Example 5, the granule density being in the range of 0.60 to 0.62 g / cm 3. Finally, the granules were subjected to activation in the same manner as above, and the bulk density of these granules in the activated state ranged from 0.48 to 0.50 g / cm 6. The granules thus prepared had an iodine number in the range of 1000 to 1100, a surface area in the range of 900 to 1050 m ² / g, an ash content in the range of 5 to 6% by weight, and an abrasion number of 80.

Although the granules were subjected to the same processing conditions for the first portion and for the second portion, it should be noted that finer grinding of treated semi-granular granules (75 to 85 W - 325 mesh) resulted in denser yields. granules and hence the hard granular product. By way of comparison, the procedures of Examples 6 and 7, wherein the bituminous coal was milled to a particle size of 65% by weight - 325 mesh, resulted in the resulting granulated product being hard.

Thus, the fineness of grinding the granules prior to compaction, which is necessary for semi-bituminous coal, as compared to bituminous coal, is a completely unexpected condition which could not be derived from the prior art and therefore constitutes an advantageous feature of the process of the invention.

The following and last exemplary embodiment illustrates the use of hydrochloric acid as a dilute aqueous solution of an inorganic acid in the progressive process of the invention.

Example 10

Preparation of granulated activated carbon by curing semi-bituminous coal with dilute hydrochloric acid solution (with addition of tar)

A batch of Wyoming bituminous coal having the same composition as in Example 1 was ground and sieved to obtain 8 XX 30 mesh granules. The granules were placed in an amount of 300 g in a 41 liter vessel, and to these granules was added a dilute aqueous acid solution containing 300 cm ³ of concentrated 37.5% hydrochloric acid and 2700 cm ^{3 of} water (5% by volume or 6% by volume). , 5% by weight). The granules and the acid solution were then heated to 80 ° C and held at that temperature for 5 hours, while the total contents of the vessel were mixed continuously.

The contents of the vessel were then allowed to cool, the solution was decanted, and the granules were rinsed thoroughly with an amount of water such that the analysis of the leaving wash water showed a pH in the range of 6 to 7. The granules were then dried in two ways:

(a) to a moisture content of 15% by weight, the further processing being carried out without the addition of a carbon binder, as in the case of the procedures of Examples 2 and 3, to the resulting activated carbon granules, or:

b) complete drying by adding a coal binder, namely tar, in an amount of 10 parts by weight of tar per 100 parts by weight of coal, and carrying out the process in the same manner as in Examples 5 and 4.

The coal / tar mixture or only coal was ground to fine particles, with at least 65% by weight of the particles passing through a 325 mesh sieve, preferably from 75 to 85% by weight of the particles passing through a 325 mesh sieve. The powder thus prepared was compressed to form pellets having a diameter of 1.27 cm and a height of 1.27 cm using a pressure ranging from 281.2 MPa to 562.4 MPa, the bulk density of these pellets being in the range of from 1.1 to 1.2 g / cm ³ . The pellets were regranulated into 6 X 20 mesh granules having a bulk density ranging from 0.60 to 0.65 grams per cm ³ , and further depleted of the volatiles without coking and finally activated , in the same manner as in Examples 2 to 5.

A) The resulting total yield of granulated activated carbon, based on tar-free dry coal, was in the range of 25 to 28% by weight. The obtained granules had a surface area in the range of 900 to 1100 m ² / g, the iodine number was in the range of 1000 to 1100, the ash content ranged from 5 to 7% by weight, the abrasion number was 70 and the bulk density was 0.46 g / cm ³ . Compared to Example 1, the yield, adsorption and abrasion resistance were substantially increased, and the ash content was substantially reduced. In comparison with Examples 2 and 3, the yield and other properties are comparable to those obtained according to the procedure of Example 1. 2 (leaching with dilute sulfuric acid solution), while compared to Example 3 (leaching with dilute phosphoric acid solution) the yield and bulk density are somewhat less.

B) The total yield of granulated activated carbon obtained, based on the dry tar / coal mixture, was in the range of 25 to 30% by weight, and the granules had a surface area in the range of 900 to 1100 m ² / g, iodine number in the range of 1000 to 1100, an ash content ranging from 5 to 7 percent by weight, an abrasion number of 80 and a bulk density of 0.48 g / cm ³ . Compared to the procedure of Example 1, the yield, abrasion number and bulk density increased substantially. Compared to the processes of Examples 2 and 3 with the above process (a), carried out without the addition of tar, it can be noted that with respect to example <2 а and the above process (a) the abrasion resistance has increased substantially and the yield and bulk density increased slightly. Compared to Examples 4 and 5, the yield was slightly reduced relative to Example 4 (dilute sulfuric acid leaching and tar addition) and substantially reduced relative to Example 5 (dilute phosphoric acid leaching and tar addition).

When treating the bituminous coal with a dilute aqueous hydrochloric acid solution, in both cases (a) and (b) above, an increase in yield, an increase in adsorption capacity, an increase in abrasion resistance and an increase in product purity has been achieved to produce a carbon that is suitable for waste water treatment and other uses, eliminating the need for separate coking.

It will be apparent from the foregoing examples how the various objects of the invention are achieved. Similarly, the invention has been described and illustrated by way of example only with respect to certain preferred embodiments, which are illustrative only and are not intended to limit the scope of the invention in any way.

Claims (10)

A process for the preparation of granulated activated carbon suitable for use in wastewater treatment and other applications, wherein the coal is milled to form granules, which granules are treated by mixing with inorganic acid, followed by the removal of volatile substances from said granules. OF THE INVENTION by heating in an oxygen-free atmosphere at a temperature higher than that used for low temperature oxidative heat treatment followed by activating said volatile-free granules by heating in an atmosphere containing gaseous activating agent at a temperature above the temperature at which provides a reduction in the cost of spent coal while providing a granular activated carbon of adequate hardness to maintain granular integrity in reuse and regeneration, expressed as a minimum abrasion number of 70, characterized in that the starting material is used . The granules are treated by leaching with a dilute aqueous solution of inorganic acid at a concentration ranging from 1 to 50% by weight, followed by elution of the acid solution, drying the washed granules, at least partially, to a maximum moisture content of 25% by weight, and optionally mixing dried granules with 5 to 15% by weight coal binder, the granules thus treated being comminuted to a powder which is compressed and then comminuted to reformed granules which are then heated directly to a temperature at which the volatile matter removal in the an oxygen-free atmosphere, without prior low temperature oxidative heat treatment. 2. Process according to claim 1, characterized in that semi-charcoal with a maximum moisture content of 25% by weight and a maximum ash content of 5% by weight is used. 3. The process according to claim 1, wherein an aqueous solution of sulfuric or phosphoric acid or hydrochloric acid or a mixture of these acids is used. 4. Process according to any one of the preceding claims 1 to 3, characterized in that an aqueous acid solution is used at a weight ratio of this solution to coal of at least 2: 1. Process according to any one of the preceding claims 1 to 4, characterized in that the treated granules are comminuted to form a powder with a dispersion degree such that the proportion of particles having a size of 0.044 mm is greater than 65% by weight. Method according to any one of the preceding claims 1 to 5, characterized in that the powder is compressed at a minimum pressure of 276 MPa. 7. A process according to any one of the preceding claims 1 to 6, characterized in that, in order to obtain granulated activated carbon of increased hardness, the granules are processed by mixing the dried granules with an amount of coal binder in the range of 5 to 15% by weight. 8. The method of claim 7, wherein the phosphoric acid is used in a concentration ranging from 1 to 20% by weight of the aqueous solution, wherein the minimum solution to carbon weight ratio is 4: 1 to increase the total yield of granular activated carbon. Process according to any one of the preceding claims 1 to 6, characterized in that the granules are dried to a partial moisture content in the range of 10 to 25% by weight, without the addition of a coal binder, thereby eliminating any mixing with the binder. 10. The process of claim 9, wherein the phosphoric acid is used in a concentration ranging from about 1% to about 20% by weight of the aqueous solution, wherein the minimum solution to carbon weight ratio is 4: 1, increasing the total yield of granular activated carbon. .