VOCs adsorption

Modification techniques for activated carhon were used to increase the removal capacity by surface adsorption and to improve the selectivity to volatile organic compounds (VOCs). Modified activated carbons (MACs) were prepared by modifying the purified activated carbon with various acids or bases. The effects of adsorption capacity and modified contents on the textural properties of the MACs were investigated. Furthermore, VOC adsorption and desorption experiments were carried out to determine the relationship between the adsorption capacity and the chemical properties of the adsorbents. High adsorption capacity for the selected VOCs was obtained over lwt%-H3P04/AC (lwt%-PA/AC). As a result, MAC was found to be very effective for VOC removal by adsorption with the potential for repeated use through desorption by simple heat treatment. 

Table 1. The prepared MACs and their specific surface area and VOC adsorption on PAC and various 5wt%-MACs...

A wide range of organic pollutants can be adsorbed by MFl, Y and mixtures of the two structure types. In the VOC application fixed beds are comparatively few with most VOC adsorption being done by rotary adsorbers such as are built and sold by Seibu Giken. A few words about rotary adsorption applications follow in Section 9.7. 

Wheeler-Jonas model for VOCs adsorption The Wheeler-Jonas equation is used for adsorption of VOCs using carbons. This equation is of the same form of the Thomas model with some modifications ... 

Characterization of porous solids using low pressure VOC adsorption data... 

In some cases, it is more economical to use air stripping to remove VOCs from water and then u.se a GAC bed to purify the airstream. GAC has a higher capacity for VOC adsorption in the gas phase than in the liquid phase. Also, gas phase adsorption occurs more rapidly, so that shallower beds can be used [84]. 

Pre, P., Delage, F., Faur-Brasquet, C., and Le Cloirec, P. (2002). Quantitative stmcture-activity relationship for the prediction of VOCs adsorption and desorption energies onto activated carbon. Fuel Process TechnoL, 77—8, 345-51. 

Analyses of carbon samples taken from the Plant vessel at different testing periods showed that HaS, VOCs and H2O are adsorbed at different rates [130]. The highest rate was found for H2O and lowest for H2S. H2S is mainly oxidized to elemental sulfur, which precipitates in carbon raicropores blocking their entrances, VOCs and sulfur can substitute adsorbed H2O, H2S is probably adsorbed in pore space available after VOCs adsorption, total adsorption of all component reaches 35 0% wt, VOCs adsorption gradually incareases with tendency of saturation at around 30 %wt The average amount of adsorbed sulfur does not exceed 3 %wt after 3.5 years of operation. 

A multicomponent model of adsorption can be reduced to three main components first, H2S, second, VOC with average properties of found species, and third, H2O. Moreover, H2O adsorption can be described as quasi-equilibrium due to the high concenbation of H2O and the long operation time of the carbon bed. Rectangular type isotherms are used to model the equilibrium of VOC and H2S. The amount of H2S adsorbed depends on available space left after VOC adsorption and it can be described bj equation ... 

The model equations were solved using a numerical method witli known parameters (qs and k) of H2S adsorption corrected for hydrodynamics conditions. The parameters for VOC adsorption and L-V model parameters for H2O adsorption where found by fitting the experimental and calculated data. The results of these fittings are present on Fig. 28, where numbers in the plot legends represent the port location. The initial concentration of H2S was 0.15 ppm. Comparison of the H2S breakthrough capacities received finm the Lab test and the Plant... 

The following techniques are applicable for the removal of VOCs adsorption to activated carbon post combustion biofilter. 

Thus, for example, adsorption of benzene and toluene at low concentrations (200 ppmv) has been carried out at room temperature in a fixed-bed reactor coupled to a mass spectrometer [107-109], Two kinds of ACs have been studied pristine ones and some thermally treated ones (including T in their nomenclature). The purpose of the thermal treatment was to remove most of the oxygen surface groups, to be able to analyze only the effect of porosity on VOC adsorption. 

There are two major types of VOCs recovery refrigerated condensation (Stone 1997) and adsorption, followed by refrigeration (Hussey and Gupta 1997, Kent 1999). Although there are several types of condensation systems the most common adopted is a reverse Rankine cycle where a closed-cycle heat pump with a separate working fluid is used to condense VOCs. Adsorption is a process whereby the VOCs in the air stream are captured physically on the surface of a solid such as carbon. Steam or inert gas is... 

The development of active catalysts for total combustion of volatile organic compounds (VOCs) has been desired from foe viewpoint of environmental protection. Noble metal which possess high activity for total oxidation are widely applied to foe low temperature complete oxidation [1]. Moreover, it was shown that supports play an important role in catalytic activity and zeolites were widely used as powerful catalytic support [2-4]. Therefore, zeolites FAU and BEA exchanged with different alkali metal cations were prepared and 0.5wt% of palladium was incorporated in these supports. The catalysts obtained were calcined, characterised and tested for propene total oxidation. Some of these solids were also tested for VOCs adsorption. 

The content to follow will be presented in the order of CO2 capture, acid-gas removal, VOC adsorption, and radioactive gas adsorption in MOFs, as we described above. The intention is not to present a complete review and summary on all the related research published in the literature, but to try giving a flavor of the research in which MOFs are used to adsorb these harmful gases and share... 

Luebbers et also studied VOC adsorption in ZIF-8 using an inverse gas chromatography methodology. 

The research on VOC adsorption in MOFs is still at its early stage. Experimental studies can only be found on alkane and alcohol adsorption in MOFs. The adsorption of some critical VOCs, such as benzene and formaldehyde, has been studied with molecular simulation or theoretical calculation. Therefore, experimental investigation of the removal of VOCs with MOFs as novel adsorbents, especially VOCs with higher threat to environmental and human health, is urgently needed. An experiment and simulation combinatorial screening study will be important to start the exploration of MOFs for the removal of VOCs. 

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