Wonderful discussion with Shri jkp SIR Regrading activated carbon , iodine no, surface area and its efficiency
The Principle Of Activated Carbon Filter
Activated carbon adsorption capacity have some certain influences with high or low the water temperature and the water quality .The
higher the temperature, the stronger the adsorption capacity of
activatedcarbon;If the water temperature up to above 30 ℃, the
adsorption capacity reached its limit and is possibility gradually
reduce.When the water quality of acidic, activated carbon adsorption
capacity of anionic substances relative weakening; water quality
alkaline activated carbon adsorption capacity of cationic substances
weakened.Therefore, unstable water quality PH will affect the adsorption
capacity of activated carbon.
Activated carbon adsorption principle : Formed
in the particle surface layer balance the surface concentration, then
the impurities of organic substances adsorbed to activated carbon
particles, the initial highadsorption effect.But over time, activated
carbon adsorption capacity will be weakened to varying degrees, the
adsorption effect also decreases.If the aquarium water turbidity, high
organic content in water,activated carbon will soon be the loss of
filtration function. The activated carbon should be regular cleaning or
replacement.
The size of the granules of activated carbon is also affected on adsorption capacity .In
general, the smaller the carbon particles, the greater the filtration
area.Therefore, the total area of powder activated carbon adsorption
best,but powdered activated carbon is very easy with the water flow into
the aquarium, it is difficult to control, is rarely used.Granular
activated carbon due to the particles forming the easy flow of organic
matter in water and other impurities in the activated carbon filter
layer is not easy to block the adsorption capacity to carry easy to
replace.
Activated carbon adsorption capacity is proportional to the time in contact with water. The
longer the contact time, the better for the filtered water.Note:The
filtered water should be slowly out of the filter layer.The new
activated carbon should be washed clean before the first use, otherwise
the black ink flowing out.Activated carbon in the filter is loaded,
bottom and top overlay 2 to 3 cm thick sponge role is to prevent large
particles of algae and other impurities to penetrate two to three
months, activated carbon, if the filter down effect should bereplace
with a new activated carbon, and the sponge layer should be changed
regularly.
Activated Carbon
Our activated carbon products effectively remove
pollutants, contaminants and other impurities from water, air, food and
beverages, pharmaceuticals and more.
We are a global leader in the research, development,
manufacturing and sale of high-grade activated carbon used in a growing
range of environmental, health, safety and industrial applications.
Building on our more than 90-year history of innovative product
development, we produce a diverse array of products with over 150
different activated carbon formulations engineered from a wide range of
raw materials.
We offer a wide range of industry-leading activated carbon solutions,
each with their own uses and applications, in three major product
groups:
- Powdered activated carbon (PAC)
- Granular activated carbon (GAC)
- Extruded activated carbon
We complement our activated carbon products with on-site systems and services, as well as reactivation solutions, to help meet your specific needs.
Our activated carbon products are also used as colorants, carriers or
catalysts in industrial processes, and the pore size distribution is
highly important in most applications. Activated carbon, also called
activated charcoal, is a form of carbon that has been processed to
create millions of tiny pores between the carbon atoms, resulting in a
dramatically increased surface area. The surface area of activated
carbon makes the material suitable for adsorption, a process by which
impurities are removed from fluids, vapors or gas.
Ideally, the carbon material used should have pore sizes that are
larger in size than the material it is trying to adsorb. The removed
molecules are held within the carbon’s internal pore structure by Van
der Waals forces, electrostatic attraction or chemisorption. The
adsorption process helps carbon reduce hazardous gas, activate chemical
reactions, and act as a carrier of biomass and chemicals.
Properties
A gram of activated carbon can have a surface area in excess of 500 m2, with 1500 m2 being readily achievable.Carbon aerogels, while more expensive, have even higher surface areas, and are used in special applications.
Under an electron microscope, the high surface-area structures of activated carbon are revealed. Individual particles are intensely convoluted and display various kinds of porosity; there may be many areas where flat surfaces of graphite-like material run parallel to each other, separated by only a few nanometers or so. These micropores provide superb conditions for adsorption to occur, since adsorbing material can interact with many surfaces simultaneously. Tests of adsorption behaviour are usually done with nitrogen gas at 77 K under high vacuum, but in everyday terms activated carbon is perfectly capable of producing the equivalent, by adsorption from its environment, liquid water from steam at 100 °C (212 °F) and a pressure of 1/10,000 of an atmosphere.
James Dewar, the scientist after whom the Dewar (vacuum flask) is named, spent much time studying activated carbon and published a paper regarding its adsorption capacity with regard to gases. In this paper, he discovered that cooling the carbon to liquid nitrogen temperatures allowed it to adsorb significant quantities of numerous air gases, among others, that could then be recollected by simply allowing the carbon to warm again and that coconut based carbon was superior for the effect. He uses oxygen as an example, wherein the activated carbon would typically adsorb the atmospheric concentration (21%) under standard conditions, but release over 80% oxygen if the carbon was first cooled to low temperatures.
Physically, activated carbon binds materials by van der Waals force or London dispersion force.
Activated carbon does not bind well to certain chemicals, including alcohols, diols, strong acids and bases, metals and most inorganics, such as lithium, sodium, iron, lead, arsenic, fluorine, and boric acid.
Activated carbon adsorbs iodine very well. The iodine capacity, mg/g, (ASTM D28 Standard Method test) may be used as an indication of total surface area.
Carbon monoxide is not well adsorbed by activated carbon. This should be of particular concern to those using the material in filters for respirators, fume hoods or other gas control systems as the gas is undetectable to the human senses, toxic to metabolism and neurotoxic.
Substantial lists of the common industrial and agricultural gases adsorbed by activated carbon can be found online.
Activated carbon can be used as a substrate for the application of various chemicals to improve the adsorptive capacity for some inorganic (and problematic organic) compounds such as hydrogen sulfide (H2S), ammonia (NH3), formaldehyde (HCOH), mercury (Hg) and radioactive iodine-131(131I). This property is known as chemisorption.
Iodine number
Many carbons preferentially adsorb small molecules. Iodine number
is the most fundamental parameter used to characterize activated carbon
performance. It is a measure of activity level (higher number indicates
higher degree of activation), often reported in mg/g (typical range
500–1200 mg/g). It is a measure of the micropore content of the
activated carbon (0 to 20 Å, or up to 2 nm)
by adsorption of iodine from solution. It is equivalent to surface area
of carbon between 900 m²/g and 1100 m²/g. It is the standard measure
for liquid phase applications.
Iodine number is defined as the milligrams of iodine adsorbed
by one gram of carbon when the iodine concentration in the residual
filtrate is 0.02 normal. Basically, iodine number is a measure of the
iodine adsorbed in the pores and, as such, is an indication of the pore
volume available in the activated carbon of interest. Typically, water
treatment carbons have iodine numbers ranging from 600 to 1100.
Frequently, this parameter is used to determine the degree of exhaustion
of a carbon in use. However, this practice should be viewed with
caution as chemical interactions with the adsorbate
may affect the iodine uptake giving false results. Thus, the use of
iodine number as a measure of the degree of exhaustion of a carbon bed
can only be recommended if it has been shown to be free of chemical
interactions with adsorbates and if an experimental correlation between
iodine number and the degree of exhaustion has been determined for the
particular application.
Molasses
Some carbons are more adept at adsorbing large molecules. Molasses number or molasses efficiency is a measure of the mesopore content of the activated carbon (greater than 20 Å, or larger than 2 nm)
by adsorption of molasses from solution. A high molasses number
indicates a high adsorption of big molecules (range 95–600). Caramel dp
(decolorizing performance) is similar to molasses number. Molasses
efficiency is reported as a percentage (range 40%–185%) and parallels
molasses number (600 = 185%, 425 = 85%). The European molasses number
(range 525–110) is inversely related to the North American molasses
number.
Molasses Number is a measure of the degree of decolorization of a
standard molasses solution that has been diluted and standardized
against standardized activated carbon. Due to the size of color bodies,
the molasses number represents the potential pore volume available for
larger adsorbing species. As all of the pore volume may not be available
for adsorption in a particular waste water application, and as some of
the adsorbate may enter smaller pores, it is not a good measure of the
worth of a particular activated carbon for a specific application.
Frequently, this parameter is useful in evaluating a series of active
carbons for their rates of adsorption. Given two active carbons with
similar pore volumes for adsorption, the one having the higher molasses
number will usually have larger feeder pores resulting in more efficient
transfer of adsorbate into the adsorption space.
Tannin
Tannins are a mixture of large and medium size molecules. Carbons with a combination of macropores and mesopores
adsorb tannins. The ability of a carbon to adsorb tannins is reported
in parts per million concentration (range 200 ppm–362 ppm).
Methylene blue
Some carbons have a mesopore (20 Å to 50 Å, or 2 to 5 nm) structure which adsorbs medium size molecules, such as the dye methylene blue. Methylene blue adsorption is reported in g/100g (range 11–28 g/100g).
Dechlorination
Some carbons are evaluated based on the dechlorination
half-life length, which measures the chlorine-removal efficiency of
activated carbon. The dechlorination half-value length is the depth of
carbon required to reduce the chlorine level of a flowing stream from 5
ppm to 3.5 ppm. A lower half-value length indicates superior
performance.
Apparent density
The solid or skeletal density of activated carbons will typically range between 2.0 and 2.1 g/cm
3
(125–130 lbs./cubic foot). However, a large part of an activated carbon
sample will consist of air space between particles, and the actual or
apparent density will therefore be lower, typically 0.4 to 0.5 g/cm
3 (25–31 lbs./cubic foot)
Higher density provides greater volume activity and normally indicates better-quality activated carbon.
Hardness/abrasion number
It is a measure of the activated carbon’s resistance to attrition. It
is an important indicator of activated carbon to maintain its physical
integrity and withstand frictional forces imposed by backwashing, etc.
There are large differences in the hardness of activated carbons,
depending on the raw material and activity level.
Ash content
Ash reduces the overall activity of activated carbon and it reduces the efficiency of reactivation. The metal oxides (Fe
2O
3)
can leach out of activated carbon resulting in discoloration.
Acid/water-soluble ash content is more significant than total ash
content. Soluble ash content can be very important for aquarists, as
ferric oxide can promote algal growths. A carbon with a low soluble ash
content should be used for marine, freshwater fish and reef tanks to
avoid heavy metal poisoning and excess plant/algal growth.
Carbon tetrachloride activity
Measurement of the porosity of an activated carbon by the adsorption of saturated carbon tetrachloride vapour.
Particle size distribution
The finer the particle size of an activated carbon, the better the
access to the surface area and the faster the rate of adsorption
kinetics. In vapour phase systems this needs to be considered against
pressure drop, which will affect energy cost. Careful consideration of
particle size distribution can provide significant operating benefits.
31.08.2015
