Gactivc

carbon Granular activated . has the ability to absorb thousands of organic materials and some inorganic materials In ancient Egypt, for centuries, carbon powder prepared from half-burning whiskey barrels was used as an absorbent for medicinal purposes. The vapor phase of granular activated carbon was first widely used in World War I, in military combat masks, and found commercial use in the interwar years to improve solvents. The liquid phase of granular activated carbon was used for the first time after the First World War in the purification of antibiotics and the decolorization of sugar.

Adsorption activated carbon is effective for various industrial purposes, this material has a high ability in surface absorption due to its high specific surface area, surface energy (high surface activity) and developed porous structure. Activated carbon is usually used to absorb organic compounds, remove chemical compounds with unpleasant odor and taste in drinking water. The two main types of activated carbon are: granular activated carbon (GAC) and powdered activated carbon (PAC); In the following, granular activated carbon will be discussed. Among the important features of granular activated carbon are:

Characteristics of granular activated carbon

• Adsorption
• surface activity (surface energy)
• Porous structure
• Apparent density
• Particle size
• Hardship
•  PH

Granular activated carbon surface adsorption

Adsorption is a surface phenomenon, in fact, it is the interaction of the electric force between activated carbon as an absorbent material and an absorbent material such as Elained. which are absorbed to the surface of the adsorbent until the equilibrium between the absorbed molecules and the free molecules in the fluid is established. The type of adsorption mainly depends on factors such as system temperature, pressure or impurity concentration (because it causes changes in the adsorption equilibrium). Activated carbon is a granule with a regular or irregular network structure of carbon atoms, with a spongy structure. The carbon surface is distinctly non-polar. This non-polarity makes the active carbon surface absorb more.

Surface activity of granular activated carbon

The surface activity of most surfaces with the ratio of the total surface in

The unit of weight (square meters per gram) is expressed. The active surface of the granule is usually ^{in the range of 600-1200 m 2} expressed /g. In this way, the higher the active surface, the more absorbing parts.

The porous structure of granular activated carbon

In carbon structures, materials with smaller hole diameters form micro structures and have the highest energy absorption. These small holes with a diameter of less than 20 are useful for removing dilute pollutants in water. Large pores with a diameter of more than 50 will cause more sedimentation and are useful for very large adsorbents such as the absorption of dye molecules in sugar solutions. The existence of holes is effective in diffusion of fluids to the absorbent sites inside the carbon particles. This porous structure attracts molecules of different sizes. The more the number of activated carbon cavities, the more active the granular activated carbon is.

The apparent density of granular activated carbon

GAC usually has a diameter between 1.2 and 1.6 mm and an apparent compressibility between 25 and 31 Ib/ft, depending on the materials used and the production process. It should be noted that the base compressibility is 10% less than the apparent compressibility (so to determine the amount of GAC required to fill the filter, the size of the filter must be determined.)

Particle size of granular activated carbon

Granular activated carbon is produced in different sizes. In the vapor phase of the granule, the particle size is about 4×6, 4×8, 4×10, 6×16, 12×30. Granule liquid phase is somewhat smaller and is common with sizes 8×30, 12×20, 12×40, 20×50. It should be noted that the particles in the liquid phase with a size of 50×20 are composed of particles that pass through a sieve with a particle size of 0.94 mm, but do not pass through a sieve with a particle size of 0.47 mm. Therefore, it can be said that usually 85-95% of it remains in the sieve. Granule with smaller particles has better performance, but it causes pressure drop. While granular activated carbon with a larger particle size has a lower specific surface area, therefore, the penetration rate of the attracted material plays an important role in larger size adsorbents. As a result, these carbons are mostly used to absorb fluids that cause faster penetration. In fluids, increasing the particle size increases the rate of absorption. Granules in aqueous solutions with sizes of 12×40, 8×30 will create a balance between size, specific surface and thermal properties, so it can be introduced as the best size of activated carbon.

Granular activated carbon hardness

The hardness in granular activated carbon is not very important if it is used for one time. But in activated carbons that are used repeatedly and may be under pressure during the regeneration process (vibration, thermal regeneration), it is an important consideration. Although measuring the hardness of granular activated carbon is not related to the measurement of hardness materials such as steel and diamond, it can be stated that if the hardness of diamond and steel is 100, the hardness of granular activated carbon can have values ​​lower than 98 and it should be noted that Activated carbon, like other materials, its hardness of 98 is significantly harder than activated carbon with hardness of 80.

PH granular activated carbon:

One of the important characteristics of activated carbon is its pH. Because pH can be effective in the amount of absorption and retention of absorbed substances. The pH of carbons made from coal is usually neutral. While the activated carbon prepared from the shell of hazelnuts, almonds, etc. and wood is more alkaline. The pH level of granular activated carbon usually varies between 6-10. But the addition of acids or alkaline substances to the activated carbon solution may expand this pH range. (The absorption of substances can change the pH)

Application of granular activated carbon

Today, granular activated carbon has many applications in the chemical, food and water treatment industries as flat adsorbents. Also in alcohol purification, drinking water preparation, biodiesel refining, caffeine refining, air filter (in air purifiers – fragrances, industrial purifiers), chloramine removal, water purification of large commercial aquariums, sugar decolorization And sugar, which weakens the carbon dioxide in fruit storage, gas purification (removing oil vapors, odors and other hydrocarbons from the air), metal extraction (gold recycling), is used.

One of the most important applications of granular activated carbon is drinking water purification, which includes the following two common methods:

• Adsorption after filtration, in this method, GAC is placed in the filtration station after the normal filtration process. figure 1)
• Absorption Filtration In absorption filtration, some or all of the filter media is placed in a granular filter media (filter media filled with GAC). figure 2)

In the process, filtration after adsorption removes GAC, with the highest quality of water-soluble compounds.

In this method, compared to the absorption filtration method, the contact time of the filter with water is longer, and in addition to removing dissolved organic compounds in water, it has the ability to remove water mud, solid particles, and biological stabilizers. In sand filters, the absorption filtration process can be performed many times by replacing the granule, as a result, the costs are significantly reduced. Also, absorption filtration has a shorter execution time than filtration after absorption and should be used more.

Activated carbon raw materials

Granular activated carbon can be produced from carbonaceous materials. In the industry, it is often prepared from coconut skin (skin of products such as walnut skin, pistachio, etc.), coal, crude oil coke, sawdust, fruit kernels (such as dates, apricots, peaches, etc.). It should be emphasized that special production techniques make the wood and leather materials of all types of recycled activated carbon products leave their original raw state.

Production of activated carbon:

Thermal and chemical processes are usually used to convert active carbon raw materials into granules. In the thermal process, the steam injection method is used, and in the chemical process, the method of adding non-ferrous materials to the raw materials at low temperature is used.

Regeneration of granular activated carbon:

It is economically viable to rebuild spent carbon recycling systems on-site or off-site. Because GAC has turned into spent GAC after absorbing pollutants, and before disposal, they may deal with contaminated water and underground water and soil containing pollutants, but they cannot perform the purification process, thus due to concerns about Remediation of spent GAC is typically possible through the following methods:

• Steam
• thermal
• Chemical

Among them, the thermal regeneration method is the most commonly used method.

Thermal regeneration technology to remove organic materials absorbed by granule activated carbon, include:

• Electric infrared ovens
• Furnaces with fluid bed
• rotary kiln