Activated carbon


Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed to have small, low-volume pores that greatly increase the surface area available for adsorption or chemical reactions.. The pores can be thought of as a microscopic "sponge" structure. Activation is analogous to making popcorn from dried corn kernels: popcorn is light, fluffy, and its kernels have a high surface-area-to-volume ratio. Activated is sometimes replaced by active.
Because it is so porous on a microscopic scale, one gram of activated carbon has a surface area of over, as determined by gas absorption and its porosity can run 10ML/day in terms of treated water per gram. Researchers at Cornell University synthesized an ultrahigh surface area activated carbon with a BET area of. This BET area value is the highest reported in the literature for activated carbon to date. For charcoal, the equivalent figure before activation is about. A useful activation level may be obtained solely from high surface area. Further chemical treatment often enhances adsorption properties.
Activated carbon is usually derived from waste products such as coconut husks in addition to other agricultural wastes like olive stones, rice husks and nutshell shells which are also being upcycled into activated carbon, diversifying feedstock supply. Furthermore, waste from paper mills has been studied as a possible source of activated carbon. These bulk sources are converted into charcoal before being activated. Using waste streams not only reduces landfill burden but also works to lower the overall carbon footprint of activated carbon production as previously discarded waste is now repurposed. When derived from coal, it is referred to as activated coal. Activated coke is derived from coke. In activated-coke production, the raw coke is ground or pelletized, then "activated" via physical or chemical methods to introduce a porous network, yielding a high-surface-area adsorbent which is referred to as activated coal.

Uses

Activated carbon is used in methane and hydrogen storage, air purification, capacitive deionization, supercapacitive swing adsorption, solvent recovery, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in respirators, filters in compressed air, teeth whitening, production of hydrogen chloride, edible electronics, and many other applications. These multiuse applications make it a versatile form of carbon that is used daily in many industries.

Industrial

There are many industrial applications of activated carbon and its other forms such as areas like metal extraction, water purification, sewage treatment, metal finishing and more. For example, it is the main purification technique for removing organic impurities from bright nickel plating solutions used for metal finishing plants. Expanding on electroplating, a variety of organic chemicals can be added to the plating solutions for improving their deposit qualities and for enhancing properties like brightness, smoothness, ductility, etc. This is due to the passage of direct current and electrolytic reactions of anodic oxidation and cathodic reduction, organic additives generate unwanted breakdown products in solution. Their excessive build up in the solutions can adversely affect plating quality and physical properties of deposited metal if run untreated by the filters. Activated carbon treatment removes such impurities and restores plating performance to the desired level. Its installation costs may vary according to the volume of water it must process, however the average cost can be around USD 1 - 2 million. Additionally, these filters need replacing over time. The cost of replacing the carbon in the GAC filter form is about USD 0.05 - 0.1 per cubic meter of water that is treated in the plant.

Medical

Activated carbon is used to treat poisonings and overdoses following oral ingestion. Tablets or capsules of activated carbon are used in many countries as an over-the-counter drug to treat diarrhea, indigestion, and flatulence. However, activated charcoal shows no effect on intestinal gas and diarrhea, is ordinarily medically ineffective if poisoning resulted from ingestion of corrosive agents, boric acid, or petroleum products, and is particularly ineffective against poisonings of strong acids or bases, cyanide, iron, lithium, arsenic, methanol, ethanol, or ethylene glycol. Activated carbon will not prevent these chemicals from being absorbed into the human body. It is on the World Health Organization's List of Essential Medicines.
Incorrect application results in pulmonary aspiration, which can sometimes be fatal if immediate medical treatment is not initiated.

Analytical chemistry

Activated carbon, in 50% w/w combination with celite, is used as stationary phase in low-pressure chromatographic separation of carbohydrates using ethanol solutions as mobile phase in analytical or preparative protocols.
Activated carbon is useful for extracting the direct oral anticoagulants such as dabigatran, apixaban, rivaroxaban and edoxaban from blood plasma samples. For this purpose it has been made into "minitablets", each containing 5 mg activated carbon for treating 1ml samples of DOAC. Since this activated carbon has no effect on blood clotting factors, heparin or most other anticoagulants this allows a plasma sample to be analyzed for abnormalities otherwise affected by the DOACs.

Environmental

Carbon adsorption has numerous applications in removing pollutants from air or water streams both in the field and in industrial processes such as:
During early implementation of the 1974 Safe Drinking Water Act in the US, EPA officials developed a rule that proposed requiring drinking water treatment systems to use granular activated carbon. Because of its high cost, the so-called GAC rule encountered strong opposition across the country from the water supply industry, including the largest water utilities in California. Hence, the agency set aside the rule. Activated carbon filtration is an effective water treatment method due to its multi-functional nature. There are specific types of activated carbon filtration methods and equipment that are indicated – depending upon the contaminants involved.
In wastewater treatment, granulated activated carbon filters are implemented as an additional treatment step for removal of organic micropollutants such as pharmaceutical products, many of which are not entirely removed in traditional wastewater treatment processes. Pollutants adsorb to the activated carbon granules and are then degraded by microorganisms on the filters.
Activated carbon is also used for the measurement of radon concentration in air.
Biomass waste-derived activated carbons were also successfully used for the removal of caffeine and paracetamol from water.

Agricultural

Activated carbon is an allowed substance used by organic farmers in both livestock production and wine making. In livestock production it is used as a pesticide, animal feed additive, processing aid, nonagricultural ingredient and disinfectant. In organic winemaking, activated carbon is allowed for use as a processing agent to adsorb brown color pigments from white grape concentrates.
It is sometimes used as biochar.

Distilled alcoholic beverage purification

Activated carbon filters can be used to filter vodka and whiskey of organic impurities which can affect color, taste, and odor. Passing an organically impure vodka through an activated carbon filter at the proper flow rate will result in vodka with an identical alcohol content and significantly increased organic purity, as judged by odor and taste.

Fuel storage

Research is being done testing various activated carbons' ability to store natural gas and hydrogen gas. The porous material acts like a sponge for different types of gases. The gas is attracted to the carbon material via Van der Waals forces. Some carbons have been able to achieve binding energies of 5–10 kJ per mol. The gas may then be desorbed when subjected to higher temperatures and either combusted to do work or in the case of hydrogen gas extracted for use in a hydrogen fuel cell. Gas storage in activated carbons is an appealing gas storage method because the gas can be stored in a low pressure, low mass, low volume environment that would be much more feasible than bulky on-board pressure tanks in vehicles. The United States Department of Energy has specified certain goals to be achieved in the area of research and development of nano-porous carbon materials. All of the goals are yet to be satisfied but numerous institutions, including the ALL-CRAFT program, are continuing to conduct work in this field.

Gas purification

Filters with activated carbon are usually used in compressed air and gas purification to remove oil vapors, odor, and other hydrocarbons from the air. The most common designs use a 1-stage or 2 stage filtration principle in which activated carbon is embedded inside the filter media.
Activated carbon filters are used to retain radioactive gases within the air vacuumed from a nuclear boiling water reactor turbine condenser. The large charcoal beds adsorb these gases and retain them while they rapidly decay to nonradioactive solid species. The solids are trapped in the charcoal particles, while the filtered air passes through.

Chemical purification

Activated carbon is commonly used on the laboratory scale to purify solutions of organic molecules containing unwanted colored organic impurities.
Filtration over activated carbon is used in large scale fine chemical and pharmaceutical processes for the same purpose. The carbon is either mixed with the solution then filtered off or immobilized in a filter.