Activated carbon industrial manufacture

High surface area activated carbon fibers were first prepared by direct carbonization and activation of phenolic fibers in steam/CO2 environment at temperatures around 1000°C (Economy and Lin 1976). These activated carbon flbers, manufactured in the form of a fabric, have received increased attention as adsorbents in air treatment processes. Because these fabrics are easy to handle, there is an increasing demand for them in various applications such as protective fabrics, filtration devices, odor absorbents, and for a wide range of ancillary industrial applications. The high cost of these fabrics has limited their potential use for a number of applications. High cost is also an issue for their use in military applications (Mangun et al. 1999). 

Process Stream Separations. Differences in adsorptivity between gases provides a means for separating components in industrial process gas streams. Activated carbon in fixed beds has been used to separate aromatic compounds from lighter vapors in petroleum refining process streams (105) and to recover gasoline components from natural and manufactured gas (106,107). 

Other industries of interest are (1) the manufacturing of spices and flavorings, which may use activated carbon filters to remove odors from their exhaust stream (2) the tanning industry, which uses afterburners or activated carbon for odor removal and wet scrubbers for dust removal and (3) glue and rendering plants, which utilize sodium hypochlorite scrubbers or afterburners to control odorous emissions. 

Three other forms of carbon are manufactured on a vast scale and used extensively in industry coke, carbon black, and activated carbon. The production and uses of these impure forms of carbon are briefly discussed in the Panel on p. 274. 

Water treatment, 26 102-152. See also Aeration water treatment, Industrial water treatment ABS manufacture, 7 421-422 activated carbon application, 4 752 aerators, 26 158-170 alkanolamines from nitro alcohols, 2 120 coagulation and flocculation in,... 

The major source of carbon tetrachloride in air is industrial emissions. Carbon tetrachloride has been detected in surface water, groundwater and drinking-water as a result of industrial and agricultural activities. Carbon tetrachloride has also been found in wastewater from iron and steel manufacturing, foundries, metal finishing, paint and ink formulations, petroleum refining and nonferrous metal manufacturing industries (United States National Library of Medicine, 1997). 

Water supplied to industry has to meet stringent specifications. For example, process water for the chemical and biotechnology industries is routinely purified beyond potable water standards. Boiler feed water for steam generation must contain a minimum of silica. Reverse osmosis units designed specifically for these purposes are in widespread use today. For example, reverse osmosis/distillation hybrid systems have been designed to separate organic liquids. For semiconductor manufacture, reverse osmosis is combined with ultrafiltration, ion exchange, and activated carbon adsorption to produce the extremely clean water required. 

Manufacturing of industrial of industrial carbons, graphite electrodes, anodes, midget electrodes, graphite blocks, graphite crucibles, gas carbons, activated carbon, synthetic diamonds, carbon black, channel black, and lamp black... 

Activated carbon is a finely divided form of amorphous carbon manufactured from the carbonization of an organic precursor, which possesses a microporous structure with a large internal surface area. The ability of the hydrophobic surface to adsorb small molecules accounts for the widespread applications of activated carbon as gas filters, decoloring agents in the sugar industry, water purification agents, and heterogeneous catalysts. 

One of the major uses of activated carbon is in the recovery of solvents from industrial process effluents. Dry cleaning, paints, adhesives, polymer manufacturing, and printing are some examples. Since, as a result of the highly volatile character of many solvents, they cannot be emitted directly into the atmosphere. Typical solvents recovered by active carbon are acetone, benzene, ethanol, ethyl ether, pentane, methylene chloride, tetrahydrofuran, toluene, xylene, chlorinated hydrocarbons, and other aromatic compounds [78], Besides, automotive emissions make a large contribution to urban and global air pollution. Some VOCs and other air contaminants are emitted by automobiles through the exhaust system and also by the fuel system, and activated carbons are used to control these emissions [77,78],... 

Over a period of almost a century activated carbons have remained the most widely used of all the general-purpose industrial adsorbents. In 1995, the world annual production of activated carbons was estimated to be in the region of400 000 tonnes, with consumption increasing at about 7% per annum (Derbyshire et al., 1995). They are manufactured from a variety of precursors, but cheap and readily available materials such as wood, peat, coal and nut shells are still generally used for large-scale production (Baker, 1992). 

Although there has been a rapid decline in commercial destructive distillation of wood, manufacture of activated carbon by the pyrolysis of cellulosic materials still constitutes a major commercial operation. Finally, the possibility of developing new processes for production of special chemicals by the pyrolysis of cellulose, or the adaptation of the old process to the economy of developing nations blessed with rich forest resources, cannot be overlooked. Controlled pyrolysis of cellulose and cellulosic materials to provide a totally impermeable carbon and other industrial products is an example of the former possibilities. 

One of the largest gas phase applications for activated carbon is in the recovery of solvents from industrial process effluents. Examples of industries that produce solvent-contaminated air streams are dry cleaning, the manufacture of paints, adhesives and polymers, and printing. In many cases, the solvent concentration is high (of the order of 1-2%). The highly volatile nature of many solvents can create unacceptable problems if they are vented to the atmosphere they can create health, fire, and explosion hazards as well as pollute the environment. The solvents must therefore be removed before the air streams are vented to the atmosphere. There are economic benefits if the recovered solvent can be reused. 

These modifications obviously represent ideal structures and a number of deviations in the arrangement of the carbon layers is ob.served. In this chapter industrially manufactured forms of carbon, e.g. carbon black or activated carbon, are dealt with as carbon modifications since their structures are in principle based upon those of diamond and graphite. 

One answer can be found in the manufacturing problems that are involved. Although activated carbon can be prepared with relative ease on a laboratory scale, the industrial production is attended by enjineering difficulties. The corrosive action of many activation conditions requires special structural materials that were not then available. Moreover, the successful industrial production of activated carbon depends on the skill of the manufacturer in controlling the environment of activation within narrow limits, and suitable instrumentation for such control is a relatively recent development. 

The first powdered commercial carbon, Eponite, was produced in Europe in 1909, using wood as a source material and working under the Ostrejko patents.1 Norit, an activated carbon manufactured in Holland, first appeared about 1911 and soon became widely known in the sugar industry. 

The first activated carbon produced in America was developed accidently from an endeavor to find utility for leached black-ash, a waste product in the manufacture of soda pulp.26 When pulverized, black-ash resembles lamp black, and a factory was erected to process it into a pigment. Because of certain cblor characteristics, however, the finished pigment was not generally accepted by the paint and ink industries. Vigorous efforts to find other sales outlets were of no avail and the factory was about to be abandoned, when, quite by accident, one of the workers stumbled on the discovery that black-ash has decolorizing power. The product, now named Filtchar, was sold as a substitute for bone char and fuller s earth. Marketing difficulties soon developed because of uneven quality of the product some batches were satisfactory, others were not. Very few tests were then available to measure decolorizing power and none were suitable for quality control of the Filtchar. 

Although activated carbon had been manufactured for some years, the soft powdered types were not suitable for gas masks. Consequently new materials had to be selected and new processing equipment developed. Coconut char proved to be a suitable source material because of its great potential adsorptive capacity combined with the required resistance to abrasion. The rapid development of effective methods of production constitutes a brilliant episode in the annals of industrial chemistry. 

The interest that had been aroused by the publicity given to the use of carbon in gas masks in World War I extended to liquid-phase purification, and workers in many industries began to explore possible benefits from the use of activated carbon. Considerable enthusiasm also developed in the direction of additional facilities for manufacturing activated carbon. As a result the period following World War I was marked by intense competition. Of the hundred or more brands of commercial carbon developed during that period, only a few remain. The quest for survival led to continual advancement in the quality of activated carbon. Within a space of twelve years, the process based on black-ash went through four major changes in method of manufacture. 

The way in which testing methods keep in touch with changing market patterns is illustrated by excerpts taken from the history of the original process for making activated carbon in America. The source material for that process was black-ash residue, a waste product from the manufacture of soda pulp. Although this early activated carbon had much less adsorptive power than brands of today, it was found useful for decolorizing coconut oil, phosphoric acid, and other industrial products. Complaints were received from customers stating that the quality was uneven, and as these complaints became more frequent it was necessary to institute quality controls. 

Porous carbon materials are used for many applications in various industrial or domestic domains adsorption (air and water purification, filters manufacture, solvents recovery), electrochemistry (electrodes for batteries, supercapacitors, fuel cells), catalyst support (industrial chemistry, organic synthesis, pollutants elimination),. .. Porous carbons used at the present time are generally activated carbons, i.e. materials prepared by pyrolysis of natural sources, like fhiit pits, wood or charcoal. Pyrolysis is followed by a partial oxidation, under steam or CO2 for instance, leading to the development of the inner porosity. 

Most processes in the fine chemical industry are typically carried out in batch mode, where the powdered catalyst is suspended in the reaction medium. For the production of bulk chemicals extruded or granulated carbon-supported catalysts are used in fixed-bed reactors. To date, the most important carbon supports from an industrial point of view is activated carbon and carbon black. The main reason for the success of those materials is their commercial availability and variety of different grades, so that the final calalyst can be lailored to the end user s requirements. On a worldwide basis, 908,000 metric tons of activated carbon was produced in 2005 [5], Only a small fraction of that is used as catalyst support. Other carbon supports, such as carbon aerogels and carbon nanotubes, are in the focus of modem catalytic research but so far have not been used in commercial processes. Since there are various scientific pubhcations in the field of carbon and its use as catalyst support, the focus of this contribution is on the industrial importance of carbon supports for precious metal powder catalysts, their requirements, properties, manufacturing, and industrial applications. 

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