Raw materials for production of activated carbon
Activated carbons can be obtained from various carbon containing raw materials, including wood, coal andbrown coal, etc. In production of activated carbons, coal, coconut shells and wood serve most of all as raw materials
Activated carbon is an adsorbent
The adsorbent’s qualities depend
on surface area Pores sizes Pores distribution structure
The adsorbed substance is the substance that should be adsorbed (removed from water). It is very important to know exactly the characteristics of adsorbed substance, as it possible to find the size and molecular structure of the substance being absorbed. There are three reasons to learn the size of molecules; growth of molecules causes drop in solubility; growth of molecules caused draw in adsorptionas molecules cannot penetrate in the adsorbent’s pores; the bigger the molecules are the more time it takes for them to penetrate into pores
As a rule activated carbon is applied in three forms.PowderAC (PAC),Granulated AC (GAC),Compressed AC (CAC). PAC consists mainly of particles smaller than 80 mesh (mesh – is a cell, 80 mesh corresponds to diameter of 0,177 mm) and is used mainly for refinement of liquids inbakery PAC is mixed with water after adsorption of mixtures it goes through mechanical filter or is precipitated GAC is mainly formed from big particles of coal 50 mesh (0,297 mm) and used for refinement of liquids (water and liquid products) and gases. Sometimes used GAC (for some applications) can be reactivated and used again. Drum-like CAC grains are used for refinement of gases as catalysts and in recovery of gold Application of CAC is similar to that of GAC. CAC can also be reactivated and used again
Production of active carbon and its application
First of all carbon-containing raw materials are subjected to carbonization, i.e. kilning at high temperature, inert atmospherewith no air access. However, the resultant carbonate has pure adsorption qualities, as it is of small size.
That’s why the carbonate is subjected to activation to receive specific structure and to improve adsorption properties.
Saw dust is the best material for production of activated carbon.
To obtain 5-6 tons/day it is required to have 50-52m3 of sawdust/day or 1400-1500 m3/month, thickness of the fraction10-80 mm, ash content:≤2%, moisture - 30%.
Fir and pine sawdust is preferable.
For high quality it is better to use brown coal and high-moor peat, the quality of carbon made of low-moor peat, shredded stalks of straw, corn, reeds etc is lower .
It is more difficult to use black coal, as it becomes fluid as the temperature reaches 450 C, so its caking and further coking intsted of activation take place, so the whole process should be premanently supervised .
Activation
There are two methods of coal activation
The first method -treatment withwater vapor. We make the equipment that activated coal by water vapors. Water vapor activation is performed at temp. of 800-1000 C, under thorough control, causing chemical reaction between vapor and coal. This results in the developed pores structure and in increase of internal surface of coal. Using such a process it is possible to obtain coal possessing various adsorption properties. Activation by water vapor allows to obtain carbon with internal surface up to 1500m2/gr. Owing to such surface area activated carbons can display brilliant adsorbents qualities. Nevertheless, only part of this surface area is good for adsorption because large molecules of adsorped substances cannot penetrate into small pores.
The second method is activation of coal by special chemical agents. This method is muhc more expensive.
Activating part
| Raw materials | Additive, no less than required by PR China standards | Molecular formula | Standards |
| Phosphoric acid | 1% - 900 kg | H3PO4 | GB2091—80 |
| Sulphuric acid | 1% - 900 kg | H2SO4 | GB625—89 |
| Hydrochloric acid | 1% - 900 kg | HCL | GB622—89 |
| Water | 40 tons/1 ton of coal | H2O |
Carbon containing substances are activated by high-temperature vapor (800-1000°C) or dehydrating chemicals.
Chemical activation
Chemical activation consists in heating initial materials to 400-500°C in presence of strong chemical dewatering agent (phosphoric acid, zinc chloride etc) After that some materials are subjected to acid washing. Acid washing eliminates metals, ash and other water-soluble substances (such as silicon) that can be washed out during operations
Pores structure
There are three types of pores in active carbons, namely, macropores, transition pores and micropores, these types differ in sorption mechanisms of vapors and gases.
Mactopores are the largest pores. They have avary highupper limit of radius of curvature (about 2000nm), lower limit - about 100 nm.
Capillar condensation of vapors do not fill them.Specific volume of macropores is the range of 0,2—0,8 cm3/g, specific surface is 0,5—2 м2/g.
Thus, adsorption onthe surface of macroporesisof no practical interest. Their surface is equipotent to that if non-porous carbon sorbent with similar chemical nature, whereas the pores themselves play the role of channels for penetration of substances inside sorbent .
Transientporesare less than macropores, their curvature is inthe range of 1.5 -100 nm, i.e. it is much larger,than the size of the adsorbed molecules. Specific volume of the transient pores is rather small - 0.02 - 0.10 cm3/g, specific surface - 20 -70 m2/g. Capillar consensation of vapors can fill these pores. At concentrations lower than that of corresponding capillar condemsation, the vapors absorption cab take place .
Micropores— are the smallest pores of active carbons with radius of less than 1.5 nm, the sizes of pores are comparable with those of the molecules adsorbed. As differs from the two first types of pores, inmicropores al thepores volumes is the space with adsorption field, therefore any ideaof layer-by-layer filling and of the surface of microporesloses any sense. Specific volume of micropores of active carbons is 0,20—0,60 cm3/g. Thus micropores play the most important part in adsorption .
Field of use of activated carbons
Chemistry:
Refinement of organic acids
Adsorption of organic compounds from solutions
Recuperation of organic solvents
Adsorption of vapors and gases of organic substances
Refinement of mineral oils
Refinements of electrolytes, production of galvanics
Production of electrodes
Palladium catalyst support Vinyl-chloride synthesis catalyst’s support Vinyl-acetate synthesis catalyst’s support
Food industry:
Refinement of liquors
Decoloration of sugar syrups
Refinement ofstarch-treacle solutions
Refinement of xylite and xylitane
Production of organic acids (citric acid, lactic acid, ect)
Refinement and finishing of vegetable and animal oils and fats
Refinement of low alcohol drinks and carbonated drinks
Refinement of starch and treacle solutions, glucose, glucose-galactose alcohols, lactuloses
Refinement and deodorization of edible oils and fats
Production of citric, lactic, propionic etc. organic acids
Decoloration of sugar syrups and xylite
Production of caramels
Pharmaceutics :
Refinemen solutions at production of medical preparations
Production of synthetic rubbers and polyvinylchloride resins.
Support for production of catalysts
Production of bioactive substances
Hemosorbent for medical industry
Production of antibiotics
Production of blood substitutes
Production of carbon tablets
Production of calcium gluconates
Sodium chloride
Production of Allohole tablets
Production of cerebrolysine
Production of heparin
Industrial refining
Refinement vapors and gases
Sulphur refinement and process liquors refinement in gas recovery and processing.
Refinement of solutions, vapors, gases during oil processing
Productions of mineral oils, chemical reagents and paint and varnish product
Elimination of spills of oil and oil products.
Refinement of vapor condensates and boiler waters
Refinement of industrial gases and ventilation exhausts
Production of glassy products
Fuel and energy industry
Refinement of vapor condensate
Refinement of circulating waters
Sulphur refinement and process liquors refinement in gas recovery and processing.
Oil and gas recovering and processing
industry: Productions of mineral oils, chemical reagents and paint and varnish products Elimination of spills of oil and oil products.
Metal manufacture
Gold extraction from cyanide pulps and other solutions
Ore floatation of minerals
Extraction of precious metals
Environmental protection
Preparation of drinkable water
Accessories for additionaldrinkable water refinement filters.
Refinement of sewage
Refinement ofvent exhausts the air of harmful gases.
Application of activated carbon in water treatment