Apr 13, · Activated carbon is a processed, porous version of carbon that has many different uses, especially adsorption and chemical reaction needs for water and gas purification. Because activated carbon particles are so porous, they have very expansive surface areas tucked into the holes and tunnels all over their surface. Different sorts of activated carbon Activated carbon can be manufactured from a wide variety of raw materials such as coal, coconut and wood. The production processes of activated carbon may be divided into chemical and thermal processes, both at elevated temperatures. Chemical activation is achieved by degradation or dehydration of the raw material structure, which is usually sawdust (wood .
Although the term granular activated carbon is used generically, it can refer to dozens of similar — but not identical- adsorbents. Depending on raw material, method and degree of activation and other factors, activated carbons can perform differently in various applications.
Granular Activated Carbons activqted a very versatile group of adsorbents, with capability for selectively adsorbing thousands of organic, and certain in- organic, materials. From medicinal uses of powdered carbons in ancient Egypt, through charred interiors of whiskey barrels, carbon has been activated and used as an adsorbent for centuries. Granular vapor phase activated carbon media was first widely used in WWI military gas masks and, in the years between World Wars, commercially in solvent recovery systems.
Today, there are hundreds of applications — if diverse uses under the general heading of environmental control are counted separately, ongoing applications number in the thousands. Since adsorption is a comparatively what is activated carbon made of technology, a capsule definition of terms may be helpful. Adsorption is a surface phenomenon, in which molecules of adsorbate are attracted and held to the surface of an adsorbent until an equilibrium is reached between adsorbed molecules and those what is activated carbon made of freely distributed in the carrying gas or liquid.
While the atoms within the structure of the adsorbent are attracted in all directions relatively equally, the atoms at the surface exhibit an imbalanced attractive force which the adsorbate molecules help to satisfy. Adsorption can then be understood to occur at any surface, such as window glass or a table top. The characteristic which typifies an adsorbent is the presence of a great amount of surface area; normally via the whxt area or slots, capillaries or pores permeating its structure, in a very small volume and ls weight.
The type of adsorption which is dependent primarily on surface attraction, og which factors such as system temperature, pressure, or impurity concentration may shift the adsorption equilibrium, is given the further classification of physical adsorption. Conceptually, some prefer the analogy of physical adsorption being like iron particles attracted to, and held by, a magnet. Physical adsorption is the most commonly applied type, but an important sub-classification is chemisorption.
Chemisorption refers to a chemical reaction between the adsorbate and the adsorbentwhat is activated carbon made of often reaction with a reagent which may be impregnated on the extensive adsorbent surface see Impregnated Carbons, below. The surface phenomenon of adsorption may now what is activated carbon made of contrasted with apsorption, in which one material intermingles with the physical structure of the other; for example, phenol dissolving activatfd fibers of cellulose acetate absorption versus being adhered by surface attraction to the outer layer of the fibers adsorption.
Granular Activated Carbon activated charcoal is an adsorbent derived from carbonaceous raw material, in which thermal or chemical means have been used to remove most of the volatile non-carbon constituents and a portion of the original carbon content, yielding a structure with high surface area. The resulting carbon structure may be a relatively regular network of carbon atoms derived from the cellular arrangement of the raw material, or it may be an irregular mass of crystallite platelets, but in either event the structure will be laced with openings to appear, under electron micrographic magnification, whwt a sponge like structure.
The carbon surface is characteristically non-polar, that carvon, it carbln essentially electrically neutral. This non-polarity gives the activated carbon surface high affinity for comparatively non-polar adsorbates, including most organics. How to use ishikawa diagram an adsorbent, activated carbon is this respect contrasts with polar desiccating adsorbents such as silica gel and activated alumina.
Granular Activated carbon will show limited affinity for water via capillary condensation, but not the surface attraction for water of a desiccant. Activity level is often expressed as total surface area per unit weight, usually in square meters per caarbon. Toward the higher end of this range, one might better visualize one pound, about a quart in oof, of granular activated carbon with a total surface area of acres.
To be useful in adsorption, surface what is activated carbon made of must be present in openings large enough to admit the adsorbate molecule s. To provide some guidance on this topic, and for quality control purposes, the carbon industry has developed additional standardized vapor and liquid adsorption tests, using adsorbates of varying molecular size and chemical nature such as iodine, phenol, methylene blue, carbon tetrachloride, benzene and the color in standard black strap molasses.
However activity level is measured, it is most meaningful when considered with additional characteristics described in the following sections. The following sketches show some sample pore structure curves and what approximate pore shapes are described by the curves. Please note that the average pore shape depicted is derived from a summation of pores of various sizes and shapes. Thus no pore within the activated carbon is likely to have precisely the average shape, but the granular activated carbon overall will often perform as if all its surface what is conformity in psychology were in pores of that shape.
Microporosity is helpful in adsorbing lower molecular weight, lower boiling point organic vapors, as well as in removing trace organics in water to non-detectable levels. Another important function of activatev macropore structure is in assisting diffusion of fluids to adsorption sites in the interior of the carbon particle. Given the above, pore structure. Pore structures along the lines of. Structure 3 would allow excellent diffusion and can accommodate very large molecular sizes, but has little micro- pore structure and would have very poor retentivity for most organics.
Granular activated carbon can be produced from various what is activated carbon made of raw materials, each of which will impart typical qualities to the finished pro-duct. Commercial grades are normally prepared from coconut and other nut shells, bituminous and lignite coals, petroleum coke, and sawdust, bark and Other wood products.
In general, nut shells and petroleum cokes will produce very hard carbons with a pore structure characterized by. It should be emphasized that specific production techniques may yield carbons that depart from the norm of a given raw material.
The solid, or skeletal, density of most activated carbons will range between 2. However, this would describe a material with essentially no surface area and no adsorptive capacity. For GAC, a much ccarbon practical density is the apparent density A. This density will be significantly lower than the solid density, due to the presence of pores within particles, and void space between particles.
In most commercial GACs, the A. Since granular activated carbons are used in adsorbers of fixed volume, apparent density values can be used to calculate volume activity, which may help determine the work capacity of an adsorber with alternative carbon loadings. Multiplying the A. Therefore, carbon B, which has lower activity, might actually do more work and therefore have a longer service life than carbon A of an equal volume.
If the price of carbon B permitted filling a given adsorber with the greater weight required, it could thus be the most economical of these adsorbents on a net cost basis. Since standard activity tests are run with oven dried carbon, it will be immediately apparent why high A.
The size of most granular carrbon carbons is given by the U. Sieve range that will include the majority of the particles in a distribution of sizes. A similar approach is occasionally used with Tyler Screen or other screen sizes. Pelletized carbon, although not truly granular, often is described by the sieve range method, or by diameter of the pellets.
Common vapor phase U. Detailed sieve descriptions are found in engineering handbooks, so only a few representative sizes are given here:. Since impurity removal requires the what is activated carbon made of of adsorbate into the intra particle structure, the rate of adsorption will increase as the particle size decreases. As fluid flows through an adsorber, increased rate of adsorption will require less adsorbent bed depth and contact time for the region in which the adsorbate is being removed.
However, with any given fluid, decreasing particle size carries the liability of increasing flow resistance or pressure drop. In practice, particle sizes are selected to produce a reasonable balance between the competitive benefits of rapid rate of adsorption and effective removal, versus the liabilities of increased flow resistance and attendant higher pumping costs.
Hardness and abrasion resistance are generally beneficial in all granular activated carbons, although their operational usefulness can vary greatly. Within common adsorber designs and operating ranges, all commercial granular activated carbons can withstand their own weight and the pressure effects induced by fluid flow.
Thus in systems in which the granular activated carbons will be used once or handled very infrequently, hardness characteristics may be of little or no import. Conversely, if the carbon will be subject to frequent handling for a regeneration step, is subjected to thermal excursions by regeneration in place, or must resist excessive vibration, hardness may become quite important.
For example, fines dust from carbno a soft carbon in a system using thermal reactivation may double or treble the losses in the reactivation furnace itself. In solvent recovery systems using steaming cycles for regeneration, carbons that fracture easily can frequently raise pressure drop enough to require that the adsorbent be re-screened and replenished, or replaced. In evaluating hardness numbers, it should be remembered that the granular activated carbons hardness test has no relation to shat hardness scales used wbat plastics, metals or minerals.
A carbon, of 98 hardness, is appreciably harder than one of 80, but even harder materials such as diamond, steel and copper, even though they differ in actual hardness, will all report as on the basis of the granular activated carbons hardness test. If part of the carbon raw material, ash generally varies between weight percent in commercial granular activated carbons.
A portion of total ash may be water-soluble, normally a greater amount acid soluble, and the remainder deeper what is activated carbon made of the skeletal structure of the carbon to be effectively insoluble.
Ash from wood and nut shell carbons tends to be rich in alkaline metals, while that from coal largely oxides of aluminum, silicon and iron. For the limited instances in which traces of soluble or reactive ash are objectionable, granular activated carbons pre-washed with water or acids are available, or grades based on certain raw materials may minimize the total ash level or particular ash components.
Natural ash is normally not detrimental to the adsorption process, and standard activity tests report granular activated carbons efficiency including the weight of the ash. However, in certain regenerated granular activated carbons, ash that is a residue of previous uses may block some or all of the micropore structure that is carboh for removing organics to ultra low levels.
Similarly, if ash is due to previous impregnation for another use, or actviated to any other adulterant, the carbon how do realtors make money may be seriously compromised.
Water extracts of activated carbons are used for reporting pH. Untreated coal base carbons are typically close to neutrality, while nutshell and wood carbons are more activted. Most untreated GACs activtaed between pHbut added acids or alkalis may further extend this range.
In purifying water and aqueous solutions, the pH of the granular activated carbons should be contrasted with the preferred pH of the solution. Most organics are best adsorbed from slightly acid, pHsolution. However, the beginning pH of the GAC will not influence the pH of the treated solution very long although adsorbates being removed may alter solution pH.
High surface area per unit weight or volume can make granular activated carbon an effective substrate for dispensing other materials in a manageable form. Impregnants may be catalysts, or they might be reactive chemicals added to improve the rate of adsorption, selectivity, or what is activated carbon made of for certain adsorbates. Examples of the latter would include carbons with what does hearing vacated mean faster rate of removal for hydrogen sulfide and other acid gases, some with capability to remove ammonia and lighter amines, and some with enhanced capacity for reduction of mercury vapor.
Whether an impregnated granular activated carbon will be cost effective frequently depends on whether a particular adsorbate is the only, or primary, removal candidate. As explained earlier, carbon activation is frequently carried out in high temperature furnaces, under mildly oxidizing conditions. As the name implies, reactivation refers to using a similar process to volatilize activxted oxidize the adsorbates on spent carbons.
The term reactivation might be contrasted with re-Qeneration, which refers to steaming or other methods to restore a portion of the GAC adsorptive capacity, al- though the terms are commonly interchanged. Reactivation will almost always produce measurable changes in pore structure, due to additional oxidative sculpturing of the carbon surface and, frequently, deposits of residual what is the best free cad program or inorganic materials.
In caarbon few cases, reactivated granular activated carbons perform better than or as well as the virgin material, but in many others there may be a defined loss of comparative efficiency or a gradually activatedd loss of efficiency. When loss of efficiency is encountered, it is normally most pronounced in the micropore structure, therefore it is most significant operationally when the last traces of contamination must be removed.
Dedicated reactivation, in which a granular activated carbon will be segregated and returned to the same use, tends to be more predictable than employing a reactivated GAC from a different previous use, or a mixture of reactivated granular activated carbons from a variety of previous uses.
However, dedicated re- activation is impractical for spent GAC quantities under several tons. The cost effectiveness of reactivated versus virgin carbons can be understood to vary with the performance carbo, the comparative volume service life, and the volume cost of the material cost per unit weight may be misleading, as reactivated carbons frequently have higher apparent densities.
Given the possible variations in reactivated carbons, it will also be understood that a reputable supplier should always specify if virgin or reactivated GAC is being offered. Granular activated carbons quality and uniformity will fundamentally relate to characteristics involving: 1 adsorption capacity and 2 a physical description of the product.
The activated carbon industry, often in cooperation with A. As would be expected, such tests can be used both as production controls and, as published specifications, assurance for prospective buyers. Not all granular activated carbons manufacturers and distributors publish adsorption specifications.
What is Activated Carbon?
Granular Activated Carbon (activated charcoal) is an adsorbent derived from carbonaceous raw material, in which thermal or chemical means have been used to remove most of the volatile non-carbon constituents and a portion of the original carbon content, yielding a structure with high surface area. Activated carbon (also called activated charcoal, activated coal or active carbon) is a very useful adsorbent. Due to their high surface area, pore structure (micro, meso and macro), and high degree of surface reactivity, activated carbon can be used to purify, dechlorinate, deodorize and decolorize both liquid and vapor applications.
Activated carbon also called activated charcoal, activated coal or active carbon is a very useful adsorbent. Due to their high surface area, pore structure micro, meso and macro , and high degree of surface reactivity, activated carbon can be used to purify, dechlorinate, deodorize and decolorize both liquid and vapor applications. Moreover, activated carbons are economical adsorbents for many industries such as water purification, food grade products, cosmetology, automotive applications, industrial gas purification, petroleum and precious metal recovery mainly for gold.
The base materials for activated carbons are coconut shell, coal or wood. Each grade and size of activated carbon is application specific. Selecting the correct activated carbon product and mesh size depends on the application and contaminants you plan to remove.
Designing a proper activated carbon filtration system with enough contact time, pressure drop, and vessel size is important. Therefore, material testing is essential and ASTM test methods such as butane activity, surface area, density, and water content moisture can be carried out to find the best suitable material for your application. The very large internal surface areas characterized by microporosity along with high hardness and low dust make these coconut shell carbons particularly attractive for water and critical air applications as well as point-of-use water filters and respirators.
Demand is typically high for this relatively low cost filter media for both gas and liquid applications. Coal based activated carbon has a high surface area characterized by both mesopores and micropores. It produces different performance characteristics in industrial applications typically catered to with coal or coconut products.
Wood based activated carbon has a high surface area characterized by both mesopores and micropores and has excellent decolorizing properties owing to its signature porosimetry. Catalytic carbon is a class of activated carbon used to remove chloramines and hydrogen sulfide from drinking water. It has all the adsorptive characteristics of conventional activated carbons, as well as the ability to promote chemical reactions. Catalytic carbon is created by altering the surface structure of activated carbon.
It is modified by gas processing at high temperatures to change the electronic structure and create the highest level of catalytic activity on carbon for reducing chloramine and H2S in water. This added catalytic functionality is much greater than that found in traditional activated carbons. Catalytic carbon is an economical solution to treat H2S levels as high as 20 to 30 ppm. Catalytic carbon converts adsorbed H2S into sulfuric acid and sulfurous acid which are water soluble, so carbon systems can be regenerated with water washing to restore H2S capacity for less frequent physical change-outs.
Surface impregnation chemically modifies activated carbon through a fine distribution of chemicals and metal particles on the internal surfaces of its pores.
And provides a cost-effective way to remove impurities from gas streams which would otherwise not be possible. Impregnated activated carbon is used to treat flue gases in coal-fired generation plants and other air pollution control applications. Carbon can be specifically impregnated for removal of acid gases, ammonia and amines, aldehydes, radio-active iodine, mercury and inorganic gases such as arsine and phosphine.
Carbon impregnated with metal-oxide targets inorganic gases including HCN, H2S, phosphine and arsine. Application of Activated carbon Different types of activated carbon are suited for various specialized applications. Granulated activated carbon Pelletized activated carbon Powdered activated carbon Impregnated activated carbon Catalytic activated carbon Each grade and size of activated carbon is application specific. Hydrogen Sulfide HS and removal of waste gases Impregnated activated carbon used as a bacteria inhibitor in drinking water filters Removal of taste and odor causing compounds such as MIB and geosmin Recovery of gold Removal of chlorine and chloramine Designing a proper activated carbon filtration system with enough contact time, pressure drop, and vessel size is important.
It is eco-friendly, due to its ability to regenerate. Renewable and green raw material. More about Coconut shell activated carbon. Coal-based activated carbon Demand is typically high for this relatively low cost filter media for both gas and liquid applications. Consistent density Hard materials with minimal dust generation. Economical More about Coal based activated carbon.
Wood based activated carbon It produces different performance characteristics in industrial applications typically catered to with coal or coconut products. Wood based activated carbon has a high surface area characterized by both mesopores and micropores and has excellent decolorizing properties owing to its signature porosimetry Relatively low density Renewable source of raw material More about Wood based activated carbon.
Catalytic based activated carbon Catalytic carbon is a class of activated carbon used to remove chloramines and hydrogen sulfide from drinking water. More about Catalytic activated carbon. Impregnated Activated Carbon Surface impregnation chemically modifies activated carbon through a fine distribution of chemicals and metal particles on the internal surfaces of its pores. Gas purification Impregnated activated carbon is used to treat flue gases in coal-fired generation plants and other air pollution control applications.
More about Impregnated activated carbon.
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