VOCs adsorbent

The prepared MAC adsorbents were tested for benzene, toluene, 0-, m-, p-xylene, methanol, ethanol, iso-propanol, and MEK. The modified content of all MACs was 5wt% with respect to AC. The specific surface areas and amounts of VOC adsorbed of MACs prepared in this study are shown in Table 1. The amounts of VOC adsorbed on 5wt%-MAC with acids and alkali show a similar tendency. However, the amount of VOC adsorbed on 5wt%-PA/AC was relatively large in spite of the decrease of specific surface area excepting in case of o-xylene, m-xylene, and MEK. This suggests that the adsorption of relatively large molecules such as 0-xylene, m-xylene, and MEK was suppressed, while that of small molecules was enhanced. It can be therefore speculated that the phosphoric acid narrowed the micropores but changed the chemical nature of surface to adsorb the organic materials strongly. 

The variation of amount of VOC adsorbed and the variation of BET surface area with modified contents were shown in Fig. 1. The optimum modified content was lwt% for benzene, toluene, p-xylene, methanol, ethanol and iso-propanol, but the amount of o-xylene, m-xylene, and MEK adsorbed were decreased with increasing modified contents. Interestingly, the amount of benzene, p-xylene, and ethanol adsorbed on lwt%-PA/AC was 1.5 to 2 times that on purified AC. The BET surface area of lwt%-PA/AC (1109m /g) took the maximum value. 

The chemical product used in the design project (chapter 12) is a household appliance designed to deliver clean air by removing and killing airborne microorganisms, and converting carbon monoxide and common VOCs found indoor into harmless carbon dioxide and water. It also dehumidifies indoor air and maintains a comfortable humidity level that suppresses fungal proliferation. The appliance is intended to maintain its performance without maintenance for at least two years and is expected to have a functional life of at least five years. The product contains an active formulation of (1) low temperature oxidation catalyst, (2) VOCs adsorbent and (c) desiccant. 

The team agreed that the production of (1) low temperature oxidation catalyst, (2) VOCs adsorbent and (3) desiccant should be the core business of the new enterprise and the appliance manufacture should be conducted through strategic partnerships with Chinese OEMs. The enterprise will produce the catalyst, adsorbent and desiccant in suspension, paste and powder forms as needed for their incorporation in the appliance. Honeycomb filter made of the formulated powders will also be one of the main products. The enterprise will design the appliance and provide the blueprint along with components containing the active formulation to the OEM partners. The OEM manufacturers will be responsible for the manufacture of mechanical and electrical components and their assembly into an appliance. 

The design employs filters for particulate removal, a desiccant-VOCs adsorbent wheel for simultaneous air dehumidification and purification. The catalyst was coated on a separate sleeve directly across the hot air stream. This design eliminates the need for separate wheels and is both cheaper and simpler to manufacture. The higher temperature and pollutant concentration in the regeneration stream mean higher catalyst activity. However, the small flow rate and high moisture content of the regeneration stream can result in a poorer overall performance. 

The design employs filters for particulate removal, a single desiccant wheel coated with both low temperature VOCs oxidation catalyst based on nanostructured catalyst and regenerable VOCs adsorbent made from modified mesoporous silica. The distribution of the active elements along the wheel thickness was optimized and shown in Fig. 12.8-6. The adsorbents are coated along two-thirds of the wheel thickness and all catalysts are concentrated on one... 

Adsorption/separation processes are based on adsorption isotherms (thermodynamics) and intracrystalline diffusivity (kinetics). Figure 16.1 illustrates various shapes of adsorption isotherms depending on the VOC nature, trichloroethylene (TCE) and tetrachloroethylene (PCE), and of the zeolite, MFI with Si/Al > 500 and FAU (Si/Al > 100) (14). The isotherms of VOCs adsorbed on FAU present a more or less S-shape which corresponds to type V of the IUPAC classification. In contrast, the isotherms of VOCs on MFI are more of type I, with the additional particularity of a step at 4 molecules per u.c. for PCE adsorption. The... 

As a conclusion, we provide a new experimental procedure which allows to reach the Henry area for VOC/adsorbent systems. It provides both the adsorption isotherms and the heat of adsorption. Comparison studies with existing data at high temperature should be performed prior to the data acquisition at lower temperatures. 

Activated carbon is commonly acknowledged to be very efficient as a VOC adsorbent. However, in the last decade, interests arose to develop new materials, such as alumni-silicate molecular sieve, towards operating conditions for which activated carbon was inappropriate due to its inflammability and adsorption capacity dependence on effluent relative humidity. Apart from hydrophobicity, the advantages of High Silica Zeolites (HSZ) are notably a thermal and chemical stability, a high steric selectivity and a complete regeneration at low temperatures [11]. Yet, for adsorption and separation processes development, organic compounds properties impact on adsorption and crystalline framework influence on selectivity are to be clarified and efficiently modeled. 

In order to evaluate the VOC adsorbing capacity, several small ceramic rotor (10cm diameter, 40cm length) were prepared, and the adsorption and desorption characterstics were measured using static adsorption / desorption test equipment. In the experiment, VOC laden gas was artificially made and provided by bubbling air into VOC liquid. The concentration of the VOC was adjusted between 150 ad 420 ppm, and its flow rate was from 150 to 600 liter/min. 

With this experiment, the proper type of adsorbent and the amount of impregnation was determined, and the operation parameter such as adsorption / desorption / cooling area ratio, rotational speed, required size of VOC adsorbing honeycomb rotor was designed... 

Experimental studies to determine adsorption and desorption rates show wide differences in values depending on the sink material and the VOC adsorbate. Because of the large munber of possible combinations of indoor surfaces and VOCs, only a few of these combinations have been evaluated. References that give values of k and kj for a variety of indoor sink surfaces and indoor pollutants based on dynamic small chamber testing are provided in Table 1. 

The amount of VOC retained on the carbon may be represented by adsorption isotherm, which relate the amount of VOC adsorbed to the equilibrium pressure (or VOC concentration) at a constant temperature. The adsorptive capacity of the carbon (expressed as VOClb/Clb) depends not only on properties on the carbon, but also on the properties of the organic. Generally, the adsorptive capacity increases with ... 

Redesign the VOCs adsorber of Example 9.15 for a breakthrough time of 4.0 h. The pressure drop through the bed [calculated using the Ergun equation, (2-91)] should not exceed 1.0 kPa. Calculate the new dimensions of the bed and the total amount of activated carbon required. 

These values are useful to calculate the adsorption exothermic heat or the energy to be introduced into the system in order to regenerate the porous media [83,84]. An example of a model presenting the heat and mass transfer in a VOC adsorber will be given in section 4.1.5. 

Fig, 16. Schematic representation of an industrial VOC adsorber with in situ regeneration by steam and solvent recovery. 

Similarly, VOCs adsorbed from air samples onto Tenax or activated charcoal can be sealed and stored for several months prior to analysis. Losses have been reported only with cyclic and aliphatic ketones (catalytic oxidation) and esters (hydrolysis) [ 14.5]. For these groups of substances, losses approach a maximum of 20 % after a four-week storage period. No losses were observed with benzene, toluene, and xylenes over a 24-month storage period [146]. Samples containing analytes of lower volatility can be stored in suitable containers for a few days at -i4 °C, and for several months deep-frozen at -18 °C or lower. 

Drobek M, Figoli A, Santoro S, Nanascues N, Motuzas J, Simone S, et al. PVDF-MFl mixed matrix membranes as VOCs adsorbers. Microporous Mesoporous Mater 2015 207 126-33. 

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