Activated carbon extrudates

Pelleted Activated Carbon - extruded and cylindrical shaped with diameters from 0.8 to 5 mm. These are mainly used for gas phase applications because of their low pressure drop, high mechanical strength and low dust content. 

There are several reasons for the production of shaped GAC. These differ depending on the activation production method employed. Thus, in the case of the thermal activation (mainly steam activation), one of the reasons is to ensure that the particle has a relatively high internal porosity. This facilitates the diffusion of the activating gas and ensures a homogeneous activation throughout the whole particle. Another important point is that shaped carbons have a higlier density and hardness and a lower abrasion index than broken GAC. Most cylindrical shaped GAC produced by steam activation are based on extrusion, and are frequently called activated carbon extrudates. 

The production of activated carbon extrudates by steam activation does not follow the general scheme of Fig. 8. In this case, after crushing the raw mato ial is first devolatilized at high temperature and then finely pulverized, resulting in a powdered char. The powdered char is then mixed with appropiate binders to form a paste with lubricant properties, which is extruded. Normally several binders are used to form the paste because they each have different tasks a) to provide lubricant properties to allow the extrusion of the paste b) to transform the wet extrudates into hard and consistent short cylinders during the drying step (low temperature binder), and c) to act as a high temperature binder in the activation step. The type and composition of the hinder is a matter for further research, since the final hardness and abrasion index is dependent on the binders. Consequently, it is not unusual for them to be a mixture of three binders, each with a specific mission. 

A new preparation method is described to synthesize porous silicon carbide. It comprises the catalytic conversion of preformed activated carbon (extrudates or granulates) by reacting it with hydrogen and silicon tetrachloride. The influence of crucial convoaion parameters on support properties is discussed for the SiC synthesis in a ftxed bed and fluidized bed chemical vapour deposition reactor. The surface area of the obtained SiC ranges ftiom 30 to 80 m /g. The metal support interaction (MSI) and metal support stability (MSS) of Ni/SiC catalysts are compared with that of conventional catalyst supports by temperature programmed reduction. It is shown that a Ni/SiC catalyst shows a considnable Iowa- MSI than Ni/Si(>2- and Ni/Al203-catalysts. A substantially improved MSS is observed an easily reducible nickel species is retained on the SiC surface after calcination at 1273 K. 

Composition and specific surface area of converted activated carbon extrudates... 

Figure 3. Pore size distribution of activated carbon extrudates applied as catalyst and catalyst carrier.

For application in flow reactors the nanocarbons need to be immobilized to ensure ideal flow conditions and to prevent material discharge. Similar to activated carbon, the material can be pelletized or extruded into millimeter-sized mechanically stable and abrasion-resistant particles. Such a material based on CNTs or CNFs is already commercially available [17]. Adversely, besides a substantial loss of macroporosity, the use of an (organic) binder is often required. This material inevitably leaves an amorphous carbon overlayer on the outer nanocarbon surface after calcination, which can block the intended nanocarbon surface properties from being fully exploited. Here, the more elegant strategy is the growth of nanocarbon structures on a mechanically stable porous support such as carbon felt [15] or directly within the channels of a microreactor [14,18] (Fig. 15.3(a),(b)), which could find application in the continuous production of fine chemicals. Pre-shaped bodies and surfaces can be... 

Catalyst-supporting materials are used to immobilize catalysts and to eliminate separation processes. The reasons to use a catalyst support include (1) to increase the surface area of the catalyst so the reactant can contact the active species easily due to a higher per unit mass of active ingredients (2) to stabilize the catalyst against agglomeration and coalescence (fuse or unite), usually referred to as a thermal stabilization (3) to decrease the density of the catalyst and (4) to eliminate the separation of catalysts from products. Catalyst-supporting materials are frequently porous, which means that most of the active catalysts are located inside the physical boundary of the catalyst particles. These materials include granular, powder, colloidal, coprecipitated, extruded, pelleted, and spherical materials. Three solids widely used as catalyst supports are activated carbon, silica gel, and alumina ... 

The microporosity is often reported in recent research papers as nanoporosity. Commercial activated carbon grades have an internal surface area of 500 up to 1,500 m2/g. Powdered activated carbon comes with particle size 1-150 pm. There are also granulated or extruded materials with granule size in the 0.5 4-mm range. 

Most research and development has focused on the use of granular or extruded activated carbons, and all commercial processes to date use this technology. However, within the last several years there has been appreciable research to examine the application of activated carbon fibers. Activated carbon fibers (ACEs) have... 

Norit Row activated carbon (type 0.8 supra) is supplied by Norit Company (USA) in the form of 0.8 mm (diameter) cylindrical extrudate. The physical and structural properties of the adsorbent and the measurement procedures of adsorption isotherm and kinetics were given in our previous work [16]. 

Europe increasing quantities of extruded activated carbon cylinders are being produced, 2 to 12 mm in length and 0.8 to 5 mm thick. Japanese manufacturers supply thin activated carbon fibers in small quantities (< 1000 t/a). 

Many solid adsorbents liberate gas as a result of desorption of volatile liquids under the influence of heat. Typical adsorbents with microporous structures such as activated carbons, or precipitated silicas and renewable resources have been used as a coblowing agent in producing low-density extruded polystyrene foam boards. Incorporation of corn cobs or other renewable vegetable matter containing about 10% water together with a primary PBA into polystyrene in the extrusion process produced a low-density polystyrene foam board with bimodal cellular structures. This type of foam with bimodal cell structures has about 10-15% lower K-factor than similar foams without bimodal cellular structures. Similar results were obtained with a precipitated silica for producing a low-density extruded polystyrene foam with bimodal cellular structures. ... 

To return to activated carbons, these can occur in very different physical forms granular (or particulate), powdered, fibrous, or even membrane (the latter can be either unsupported, or, more commonly, supported). These basic physical forms can be combined with binders and extruded to form pellets, monoliths, or even paper. All of these materials, which are very frequently used as adsorbents, differ significantly in shape, but not in their intrinsic nanotextural features. All of them are isotropic and have their BSUs randomly oriented. 

Commercial activated carbons are generally produced in granular, bead, pellet, or extrudate forms. The particles contain a complex network of meso-macro pores (pore diameters ranging between 30 A to several microns) and micropores (pore diameter <30 A) of different shapes and sizes. The larger pores act as arteries for the gas molecules to be transported from the external gas phase to the mouth of the micropores. Most of the adsorption capacity of a gas on the carbon is created by adsorption within the micropores. Figure 22.2 shows the cumulative pore size distribution of the carbons of Table 22.2 [18]. They were also obtained from the manufacturers data sheet. 

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. 

The characteristics mentioned above also apply for fixed-bed catalysts. However, the requirements for granulated and extruded activated carbons in regard to the mechanical strength and attrition resistance are even higher. To meet the demand of high attrition resistance, preferably activated carbons from coconut shells are used. 

Conventionally, PAG, GAC, or extruded activated carbon serves as adsorbents for contaminants from treated waters directly (Fig. 11, solid lines) or indirectly (dotted lines in the Fig. 11). In the latter option, volatiles from water are first transferred to the gas phase by air stripping [45]. The contaminated air is subsequently passed throu the carbon bed, which enables the effective removal of the stripped compounds. The removal of contaminants Irom waters with the use of carbon adsorption systems is particularly effective for final purification of water discharges from other remedial technologies. 

It should be mentioned that silica-based monohthic columns are even more widely used in CEC and HPLC compared with various polymeric rods (see, e.g.. Journal of High Resolution Chromatography, Special issue on monolithic columns, vol. 23, Nl, 2000 or [423]). In addition, even carbon-type monohths have started to be commercially available. They are manufictured (MAST Carbon Ltd., Guildford, UK) by carbonization and subsequent activation of extruded phenoHc resins [424]. The MAST Carbon square... 

A direct activated carbon method is specified for determination of volatiles loss of calendered, extruded, and cast films and sheeting. The standard also contains a graph of maximum volatile loss vs. film thickness. 

The model adsorbent we used is an activated carbon in the form of extrudate having a diameter of 1.7 mm. The properties of this activated carbon are summarised in the following table. 

ACs are the most commonly used form of porous carbons for a long time. Typically, they refer to coal and petroleum pitch as well as coconut sheUs-based AC. In most cases, ACs are processed to be filled with rich micropores that increase the surface area available for gas sorption and separation. For this category, to get a definite classification on the basis of pore structure is difficult due to their countless products as well as their complex pore features. Based on the physical characteristics, they can be widely classified into the following types powdered, granular, extruded, bead ACs, etc. For the pore structure of ACs, actually, all the three types of pores (micropore, mesopore, and macropore) are included in one product (Fig. 2.1), with a wide pore size distribution [1, 2]. Up to now, many kinds of ACs have been well commercialized in gas sorption/separation including CO2 capture. For example, the BPL type with specific area of 1,141 m g is able to adsorb 7 mmol g CO2 under the conditions of 25 °C and 35 bar, while under the same conditions MAXSORB-activated carbon with specific area of 3,250 g can capture up to 25 mmol g [3]. 

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