Carbon dioxide removal pore structure

Since the molecular size of SO2 is around 0.43 nm (LJ parameter o i = 0.429 nm) the presence of pmes smaller than 0.8 nm in the structure of carbon should be crucial for physical adsfflption of this molecule. Indeed the importance of such pores in the proces of SO2 removal was pointed out in the literature. Raymundo-Pinero and coworkers studied the dependence of the amount adsorbed on various carbons on the porosity measured using Dubinin-Radushkevich method, CO2 adsorption and the total pore volume calculated from nitrogen adsorption [26]. The results obtained show the relatively px)d correlation for the volume of micnopotes calculated form carbon dioxide adsorption. It has to be pointed out here that it is believed that CO2 at experimental conditions chosen in that research adsorbs only in pores smaller than 0.7 nm. Such correlation is found only when oxygen is present in the system. Lack of oxygen decreases the amount adsorbed by a factor of two to six depending on the type of carbon. 

Rayon-based ACFs are used in the adsorption of many volatile organic compounds including formaldehyde (80), methyl ethyl ketones (81), and benzene (81). ACFs are also finding uses in natural gas storage (82), electrodes for batteries (83), catalyst supports (84), and NO removal (85). Stabilized rayon fibers are carbonized and then activated with air (80), steam (86), or carbon dioxide (87), much as in granular carbon activation. The extent of pyrolysis governs the pore structure, carbon yield, and surface area of the fiber, while activation impacts the presence of functional groups on the pore surface (12). Properties of some commercial ACFs are summarized in Table 6. 

The physical AC preparation process involves two separate stages, the first being carbonisation, i.e. pyrolysis of the raw material at temperatures usually between 873-1073 K, in an inert atmosphere, where the pore network is developed and the non-carbon species are essentially removed. In the subsequent step of activation, the substrate is heated under an oxidizing agent (Carbon dioxide, air, water) at about 1073-1173 K. This process aims to improve the characteristics of the pore structure, e.g. increase of pore volume and surface area, tuning of the pore size etc. This step, which is a heterogeneous solid-gas reaction. 

Microporous materials have become of increasing economic importance as new processes and products are developed. Carbons have been used for hundreds of years for the removal of odours and colours from gases and solutions. Methods for their manufacture have been developed so that by controlling their pore structure a range of properties is available. Predominantly, carbons form slit-shaped pores, ideal for the adsorption of flat molecules of carbon dioxide and of aromatic organic substances, hence their common use in vapour extraction. 

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