Properties of activated carbon adsorbent. The larger the surface area, the stronger the adsorption capacity; activated carbon is a non-polar molecule, easy to adsorb non-polar or very low polar adsorbents; activated carbon adsorbent particle size, pore structure and distribution and surface chemical properties also have a great impact on adsorption.
Properties of adsorbents. Depending on its solubility, surface free energy, polarity, adsorbate molecule size and unsaturation, adsorbate concentration, etc.
PH value of wastewater. Activated carbon generally has a higher adsorption rate in acidic solutions than in alkaline solutions.
PH value will affect the state and solubility of adsorbate in water, and thus affect the adsorption effect.
Coexistence substances. In the presence of multiple adsorbates, the adsorption capacity of activated carbon to a certain adsorbate is worse than that of activated carbon containing only such adsorbate.
Temperature has little effect on the adsorption of activated carbon.
Contact time. The contact time between activated carbon and adsorbate should be guaranteed to make the adsorption close to equilibrium and make full use of the adsorption capacity.
Activated carbon chemistry
The adsorption of activated carbon is not only physical adsorption, but also chemisorption. The adsorption of activated carbon depends not only on pore structure but also on chemical composition.
Activated carbon contains not only carbon, but also a small amount of oxygen and hydrogen, such as carbonyl, carboxyl, phenolic, lactone, quinone and ether, which are chemically bound and functionalized. These surfaces contain oxides and complexes, some of which are derived from raw material derivatives, some of which are formed by the action of air or steam during and after activation. Sometimes sulfides and chlorides are formed on the surface. In the activation process, the minerals contained in the raw materials are concentrated in the activated carbon to become ash. The main components of ash are alkali metal and alkaline earth metal salts, such as carbonate and phosphate.
These ash contents can be reduced by washing or pickling.
Catalytic activity of activated carbon
Activated carbon exhibits catalytic activity in many adsorption processes, showing the activity of the catalyst. For example, activated carbon adsorbed sulfur dioxide through catalytic oxidation to three sulfur oxides.
Activated carbon has catalytic activity for a variety of reactions, such as the formation of phosgene from chlorine and carbon monoxide, due to the presence of specific surface oxides or complexes.
Because of the formation of complexes between the active carbon and the carrier, this complex catalyst can greatly increase the catalytic activity. For example, the palladium-supported activated carbon can catalyze the oxidation of olefins even without the presence of copper salt catalyst, and it has high speed and selectivity.
Activated carbon can be used as catalyst support because of its well-developed pore structure, huge inner surface area, good heat resistance, acid resistance and alkali resistance. For example, in organic chemistry, hydrogenation, dehydrogenation, cyclization, isomerization and other reactions, activated carbon is a good carrier of platinum, palladium catalyst.
Mechanical properties of activated carbon
(1) Particle size: A set of standard sieving method was used to calculate the weight of activated carbon left and passed through each sieve, indicating the particle size distribution.
(2) Static density or bulk density: the weight of activated carbon per unit volume of dietary pore volume and intergranular pore volume.
(3) Volume density and particle density: the weight of activated carbon per unit volume of dietary pore volume without dietary pore volume.
(4) strength: the crushing resistance of activated carbon.
(5) wear resistance: wear resistance or abrasion resistance.
These mechanical properties have a direct impact on the application of activated carbon, such as: density affects the size of the container; the size of carbon powder affects the filtration; particle size distribution affects fluid resistance and pressure drop; crushing affects the service life of activated carbon and waste carbon regeneration.
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