Comparison of adsorption mechanism and filtration principle of desulfurized activated carbon
The desulfurized activated carbon is accompanied by a catalytic reaction in many adsorption processes, exhibiting the activity of the catalyst. For example, desulfurization activated carbon adsorbs sulfur dioxide by catalytic oxidation to sulfur trioxide. Since the desulfurized activated carbon has a specific surface oxygenate or complex, it has a catalyst activity for various reactions, for example, chlorine gas and carbon monoxide to generate phosgene. Due to the formation of a complex between the desulfurized activated carbon and the support, the complex catalyst greatly increases the catalytic activity, such as desulfurized activated carbon carrying a palladium salt, and the oxidation reaction of the olefin can be catalyzed even in the presence of a catalyst without a copper salt. It is carried out with high speed and high selectivity. Since the desulfurized activated carbon has a developed pore structure, a large internal surface area, and good heat resistance, acid resistance and alkali resistance, it can be used as a carrier for the catalyst. For example, in the reaction of hydrogenation, dehydrocyclization, and isomerization in organic chemistry, the columnar activated carbon is an excellent carrier of platinum and palladium catalysts.
Desulfurization activated carbon adsorption mechanism
(1) Physical adsorption theory
The desulfurized activated carbon crystal is composed of a plurality of crystal faces. The carbon atoms on the crystal face are arranged in a hexagonal lattice. Each carbon atom is bonded to the adjacent three carbon atoms by a covalent bond, and holes or voids are formed in the crystal lattice. At the edge of the crystal, these holes or voids will have an unsaturated bond and have an adsorption activity. The higher the porosity, the larger the surface area, and the more active sites there are, the greater the adsorption activity will be. The adsorption of activated carbon is due to physical adsorption caused by van der Waals forces.
(2) Electrochemical adsorption theory
When the activated carbon is in contact with oxygen, it is reduced to a hydroxyl group, and hydrogen peroxide is precipitated. The carbon loses electrons and is positively charged, so that an anion can be adsorbed, and the reaction is:
N02+2H20+2e-→H202+20H-
n
C-2e→C2+
(3) Ion exchange theory
Au(CN)2- in the gold-containing leachate stays on the active center of the inner wall of the micropores of the activated carbon when it is activated with activated carbon. This active center (called the oxidizing point) can release anions and associate with Au(CN)2. - Perform an ion exchange reaction to adsorb Au(CN)2- - on activated carbon.
(iv) Double layer said
The gold cyanide ion [Au(CN)2-] adsorbs on the activated pores of the activated carbon to form a local negative electric region. Under the action of static electricity, the positive ion Me+ in the slurry produces directional motion and Au(CN)2 Forming an electric double layer, the electric double layer is unstable and further forms an ion couple Me·Au (CN) 2 . Under the redox action of CO, H2 and H2O, the ion couple finally forms Au(CN)2, Au and Au3CN.
Desulfurization activated carbon adsorption principle:
Classification
Van der Waals force - physical adsorption
Chemical bond - chemical adsorption
Project adsorption type
Physical adsorption chemisorption
Force molecular gravity (van der Waals force) residual chemical bond force
Selectivity is generally non-selective and selective
The single-molecule or multi-molecular adsorption layer forming the adsorption layer can form only a single-molecular adsorption layer.
The heat of adsorption is small, generally larger within 41.9kJ/mol, generally between 83.7~418.7kJ/mol
The adsorption speed is fast, almost no activation energy is slow, and a certain activation energy is required.
Reversible is easier to desorb chemical bond bond force, adsorption is irreversible
Temperature exothermic process; low temperature is conducive to adsorption temperature increase, adsorption speed increases
2. Adsorption isotherm
1) Adsorption equilibrium and adsorption capacity
(1). Adsorption equilibrium Adsorption and desorption are a reversible equilibrium process. When the adsorption rate and the desorption rate are equal, the adsorption equilibrium is reached. The adsorption amount is the weight of the adsorbate adsorbed on the unit weight adsorbent at the time of adsorption equilibrium. It can indicate the amount of adsorbent adsorption capacity. In a certain volume and a certain concentration of the adsorbate solution, a certain adsorbent is added, and the mixture is stirred and mixed until the adsorption equilibrium, that is, the residual adsorbate concentration in the solution is determined, and the adsorption amount is as follows:
2) adsorption isotherm
The amount of material adsorbed by a certain adsorbent is related to the nature of the substance and its concentration and temperature. It is shown that the relationship between the amount and concentration of the adsorbate becomes an adsorption isotherm.
Solid surface adsorption of dissolved and colloidal substances in aqueous solution
Freundlich adsorption isotherm - low concentration
Langmuir adsorption isotherm - monolayer
Desulfurization activated carbon mechanical properties
(1) Particle size: A standard sieve sieving method was used to determine the weight of the desulfurized activated carbon remaining in and passing through each sieve to indicate the particle size distribution.
(2) Static density or bulk density: the weight of the columnar activated carbon per unit volume of the dietary pore volume and the interparticle void volume.
(3) Bulk density and particle density: the weight of the columnar activated carbon per unit volume of the dietary pore volume without the inter-particle void volume.
(4) Strength: the crushing resistance of the coal-like columnar activated carbon.
(5) Abrasion resistance: that is, wear resistance or anti-friction performance.
These mechanical properties directly affect the application of coconut shell activated carbon, for example: density affects the size of the container; the thickness of the powder affects the filtration; the particle size distribution of the carbon affects the fluid resistance and pressure drop; the fracture affects the service life of the columnar activated carbon and the regeneration of the waste carbon.
[Water Purifier Spherical Activated Carbon Filtration Principle]
Spherical activated carbon removes odor and taste, color, residual chlorine, colloids, organic matter (synthetic detergents, pesticides, herbicides, insecticides, synthetic dyes, trihalomethanes, haloacetic acids, endocrine disruptors such as o-benzaldehyde) Acid ester PAES, etc., heavy metals (such as mercury, silver, cadmium, chromium, lead, nickel, etc.), radioactive materials, etc., are the earliest and most widely used water purification materials in water purifiers. Not only general activated carbon water purifiers, but also in household reverse osmosis water purifiers, as well as most ultrafiltration, ceramics, KDF, UV and other water purifiers, will use activated carbon.
Spherical activated carbon and KDF can remove residual chlorine in water, but KDF reacts with chlorine to form zinc ions (Zn2+), which may lead to excessive zinc in water. However, there is no such concern when using activated carbon to remove chlorine.
The spherical activated carbon forms a large number of fine pores of various shapes during the activation process, and constitutes a huge surface area with adsorption. The specific surface area is 500-1200 m 2 /g, and the larger the specific surface area, the better the adsorption effect.
What is the principle of spherical activated carbon filtration? The removal of impurities from spherical activated carbon is based on the active surface of spherical activated carbon and unsaturated chemical bonds.
Since the spherical activated carbon has a large surface area (500 to 1500 m 2 /g). In addition, the surface is covered with micropores having an average diameter of 2 to 3 nm, so the activated carbon has a high adsorption capacity.
At the same time, since the carbon atoms on the surface of the spherical activated carbon are not equal in energy, these atoms contain unsaturated bonds, so they have a tendency to chemically interact with foreign molecules or groups, and have strong adsorption to certain organic substances. force.
Studies have shown that the adsorption of chlorine by spherical activated carbon is not entirely a physical adsorption of chlorine on the surface, but rather a catalytic effect due to the activated carbon table, which promotes the hydrolysis of free chlorine and accelerates the process of generating new ecological oxygen.
The standards for activated carbon for water purification currently include:
(1) GB/T7701.4 - 1997 "Coal Granular Activated Carbon for Purification"
(2) GB/T13803.2 - 1999 "wooden activated carbon for water purification"
(3) DL/T582 - 2004 "Guidelines for the Use of Activated Carbon for Water Treatment in Thermal Power Plants"
(4) LY/T1331 - 1999 "Silver Activated Carbon for Water Purification"
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