Adsorption-catalytic Process Research Articles

Mathematical Modeling of the Adsorption-Catalytic Process with Internal Heater in a Multisectional Arrangement

Mathematical Modeling of the Adsorption-Catalytic Process with Internal Heater in a Multisectional Arrangement

Low quantity of Pt loaded onto CeCoOx nanoboxes: Surface-rich reactive oxygen species for catalytic oxidation of toluene.

An optimized oxygen activity of catalysts can facilitate oxidation of volatile organic compounds. This work shows the first construction of Ce-Co oxide thin-walled nanoboxes. Bulk-phase lattice oxygen is activated by metal-metal interactions. The subsequent uniform dispersion of low loaded Pt nanoparticles further enhances the surface-adsorbed oxygen content, and creates an oxygen-rich reaction interface. Competitive adsorption of water vapor was also inhibited, and complete catalytic oxidation of toluene was achieved at low temperature (T90 =140°C). A diffuse reflectance infrared Fourier-transform spectroscopy probe was used to investigate the adsorption-catalytic process and the possible synergistic catalytic mechanism (Langmuir-Hinshelwood and Mars-van Krevelen). This work provides a strategy for improving the catalyt Crystal structure ic oxidation performance of nanocatalysts for volatile organic compounds by increasing the catalytic oxygen activity.

The impact of surface chemistry of carbon xerogels on their performance in phenol removal from wastewaters via combined adsorption-catalytic process

The present work explores the influence of the surface chemistry of carbon xerogels (CXs) on their ability to remove phenol from aqueous solutions under mild reaction conditions. The surface of the CXs was functionalized introducing acidic, basic or a combination of weak acid/basic active centers via: (A) hydrothermal method with diluted nitric acid, (B) gas treatments with diluted ammonia and then oxygen, and (C) thermal modification. Obtained CXs with varied acidic-basic surface properties were used for removal of phenol via adsorption or adsorption combined with catalytic wet peroxide oxidation reaction. It was found that both sorption and catalytic properties of CXs depended strongly on the chemical structure of their surfaces. The adsorption of phenol was clearly favored on the basic surfaces (mainly in the presence of quaternary nitrogen) and hindered in the presence of carboxylic groups. Similarly, the activity of these materials in CWPO was affected not only by the total acidity/basicity of the surface of these carbocatalysts, but also by the type of N- and O-type groups present in these samples. Overall, the removal of over 60% of phenol was achieved in the first hour of the process with CX containing quaternary nitrogen and neutral O-groups on the surface.

Adsorption-catalytic process for removal of volatile organic compounds from lean waste gases: Optimization of the adsorbent-catalyst bed geometry

Abtstract The study was dedicated to the adsorbent-catalyst bed geometry optimization in the adsorption-catalytic process for the removal of volatile organic compounds (VOC) by means of the mathematical modeling. The commercial software COMSOL Multiphysics was used for the 2D axisymmetric modeling of the process with internal location of the heater, which initiates the self-sufficient adsorbent-catalyst regeneration. The model took into account the adsorption and oxidation reactions on the internal pellet surface, mass transfer between gas flow and catalyst bed, diffusion in the pellets, and heat transfer in the bed. The simulation showed the failure of adsorbent-catalyst regeneration in the cylindrical bed. At the same time, the beds with inlet part in a shape of truncated cone appeared to be much more efficient. The different cone side angles and inflow gas rates were considered by means of mathematical modeling. The optimal geometry parameters for the best process performance were defined in the study.

On the performance stability of the MnOx/Al2O3 catalyst for VOC incineration under forced adsorption-catalytic cycling conditions

The study is dedicated to experimental investigation of operation stability of the manganese oxide based catalyst under forced periodical temperature and composition cycling, typical for adsorption-catalytic process. Such process is considered as a promising energy-efficient tool for abatement of volatile organic compounds in lean waste and went gases. As shown by experiments, the catalyst successfully undergoes the series of 150 adsorption-regeneration cycles with organic contaminants (styrene, methyl ethyl ketone, acetic acid) without any visible changes of adsorption capacity, oxidation activity, texture, surface and bulk phase composition. Some decrease of oxidation activity is observed in presence of chlorinated substances (methylene chloride), though the deactivation degree is moderate. Strong catalyst deactivation may occur in presence of hydrogen sulfide, but the catalyst oxidation activity may be completely restored by periodical regeneration at high temperatures (900°C). The observed deactivation phenomena are similar to that in the steady-state conditions, therefore, the adsorption-regeneration cycling does not produce any specific loss of catalyst properties. The studied catalyst may be applied in the adsorption-catalytic process with the estimated practical life time of at least 2–3 years.

Catalytic Oxidation of Volatile Organic Compounds in Industrial Off-Gases

<p>Processes and apparatuses for catalytic oxidation of VOCs in industrial off-gases are described, including steady state and unsteady state processes, a combined adsorption-catalytic process and an advanced method of ozone induced oxidation for low concentrated exhausts. On the basis of research and development works a series of catalytic incinerators, operating in steady state and unsteady state mode, of various capacity were designed, constructed and tested in the purification of ventilation air and off-gases from VOCs. The principles of operation of different types of catalytic incinerators and possible areas of application are discussed. For VOC concentrations 150-1000 mg/m<sup>3</sup> unsteady state catalytic incinerators of KART type should be used, for concentrations 1000-3000 mg/m<sup>3</sup> steady state KROT apparatuses are recommended, and for concentrations over 3000 mg/m<sup>3</sup> up to 7000 mg/m3 installations TKM-250. It is shown that for the purification of low concentrated gases with the content of organic vapors below 150 mg/m<sup>3</sup> adsorptioncatalytic method or catalytic oxidation with ozone in the installation OKA-3000 are most effective. Main kinetic dependencies of the ozone induced oxidation of toluene and acetone over copper oxide catalyst are given and discussed. It is shown that the efficiency of this method of VOCs removal is based on low operation temperature 313-343 K, by contrast to conventional catalytic incineration by air requiring preliminary heating of the gases to 523-573 K. A special consideration is given to adsorptive damping as an efficient method for leveling the VOCs concentrations in the real industrial exhausts directed to the catalytic treatment. The use of adsorptive dampers filled with carbon allows elimination of large deviations of pollutant concentrations in the gas entering the catalyst bed, thus increasing the VOCs removal efficiency from average values. For calculations of adsorptive dampers, an equation describing the profiles of VOC concentrations in gas phase along the length of the adsorbate bed in the damper was derived.</p>

Modifications of the adsorption-catalytic system for organic impurities removal

The study was dedicated to optimization of the adsorption-catalytic process for abatement of volatile organic compounds (VOC), combining the adsorption of VOC at ambient temperature in the bed of the oxidation catalyst with the periodical regeneration of the catalyst by oxidation of adsorbed species at elevated temperature. The detailed mathematical model, accounting for occurrence of unsteady-state adsorption and oxidation reactions, heat and mass transfer process both in the catalyst bed and the catalyst pellets, was constructed. The good quality of the model was verified by bench experiments. The process simulation has confirmed the high efficiency of the new versions of the adsorption-catalytic processes: the process with the startup heater located directly inside the catalyst bed and the process with the system of parallel beds with non-simultaneous regeneration; these approaches give the way to significantly decrease the specific energy consumption and to level off the peaks of VOC outlet content and outlet gas temperature. The optimal values of process parameters were defined in the study. The developed process may be applied for VOC abatement in different waste gases, being especially advantageous in terms of energy consumption and operation flexibility in processing of lean vent gases with high flow rate.

Removal of aqueous organic pollutants by adsorption-catalytic process using mesoporous carbon beads loaded with metal oxides

Removal of aqueous organic pollutants using an adsorption-catalytic process was examined using metal-loaded carbon cryogel beads (CCBs) which possess numerous mesopores of controlled size. Adsorption isotherms of phenol, as a model organic pollutant, on CCBs could be interpreted based on the Langmuir model, indicating the preferable adsorption of phenol on micropores rather than on mesopores. Removal of aqueous phenol was examined using metal oxide-loaded CCBs in the presence of ozone. Due to the adsorptive-concentration effect of CCBs, it proved possible to increase the phenol removal efficiency by the simultaneous use of ozone with CCBs as compared with ozone only. Of the support materials for loading metal oxides, CCBs showed the highest removal efficiency. The enhancement effect of CCBs in the removal of aqueous phenol was examined with regard to the metal species loaded, the amount of loaded metal, the size of the mesopores, and the carbonization temperature used in the preparation of CCBs.

Adsorption-catalytic process for carbon disulfide removal from air

Adsorption-catalytic process for carbon disulfide removal by means of the use of adsorbent and catalysts on the basis of carbon materials is developed. The process consists of adsorption of carbon disulfide from purified air, its steady desorption in inert gas flow, hydrolysis of carbon disulfide with hydrogen sulfide yielding, and oxidation of generated hydrogen sulfide to elemental sulfur. Efficient catalysts for carbon disulfide hydrolysis (5% TiO 2, 1% CaO/KAU) and hydrogen sulfide oxidation (Fe-EDTA/carbopon) are developed. The most favorable parameters, which provide a complete carbon disulfide removal from air, are determined for all steps of the purification process.

Mathematical modeling of unsteady-state operation taking into account adsorption and chemisorption processes on the catalyst pellet

In this paper the dynamics of hydrocarbons deep oxidation in the catalyst pellet with account of intraparticle diffusion limitations under alternating adsorption stage and oxidation one is studied by means of mathematical modeling. As an example the isopropyl benzene oxidation by oxygen on Cu/Cr/Al oxide catalyst is considered. It is shown that intraparticle diffusion limitation significantly influence both adsorption and oxidation performance. The modeling results demonstrate the existence of the optimal catalyst pellet size, providing the maximum purification efficiency in the adsorption-catalytic process of VOC abatement.