Fluid phase equilibria of the reacting mixture in the dimethyl carbonate synthesis from supercritical CO2

In order to investigate the dimethyl carbonate synthesis from methanol and supercritical CO2, the thermodynamic behaviour of the reacting mixture, i.e. the quaternary methanol/CO2/DMC/water mixture, has to be known. The SRK equation of state with MHV2 mixing rules has been chosen to predict fluid phase equilibria in the reactor. The first part of this work is dedicated to the determination of binary interaction parameters, needed in the use of this model. These parameters are deduced from the fitting of experimental data concerning binary or ternary sub-systems existing in the quaternary mixture. Literature data was used for most of the binary sub-systems, but for the DMC/CO2 and DMC/water mixtures, specific experiments were carried out. The agreement between experimental and predicted fluid phase equilibria was found to be satisfactory. With a view to studying of the operating conditions for the reaction, the thermodynamic model was used to predict fluid phase equilibria in the reactor, by considering several hypothetical feed ratios and conversions. This work shows that CO2 has to be used in large excess in order to be sure of running the reaction in a homogeneous fluid medium

Adsorption of Nitrobenzene from Water onto High Silica Zeolites and Regeneration by Ozone

This work investigates the removal of nitrobenzene (NB), a model pollutant from water, by combining adsorption onto zeolites and regeneration with ozone. The adsorption equilibrium isotherms of NB onto zeolites enabled the best adsorbent to be selected and zeolites with a high Si/Al ratio were the most efficient. The adsorption capacity depended on the Si/Al ratio and on the pore size. In a sequential process coupling adsorption and oxidation by ozone, NB was completely removed from water and the initial adsorption capacity of the zeolite was totally restored. Although no catalytic effect was noticed, the adsorption produced locally high concentrations, thus enhancing the oxidation rate for NB

Oxidation of nitrobenzene by ozone in the presence of faujasite zeolite in a continuous flow gas–liquid–solid reactor

This work investigates the oxidation of nitrobenzene (NB) by ozone in the presence of faujasite zeolite. Experiments were carried out in a gas–liquid–solid reactor were ozone transfer and NB oxidation took place at the same time. Three configurations of the reactor were compared: empty, filled with inert glass beads and filled with faujasite pellets. First, ozone transfer coefficient (kLa) and decomposition rate constant (kC) were determined for each configuration. In presence of solid, kLa was 2.0 to 2.6 times higher and kC was 5.0 to 6.4 times higher compared to the empty reactor. Then, the various configurations were evaluated in terms of NB removal and chemical oxygen demand (COD) decrease. The faujasite reactor showed higher removal of NB and decrease of COD compared to other configurations under the same conditions suggesting that the faujasite increases the oxidation rate of NB. Oxidation of NB in presence of faujasite also proved to be limited by the transfer of ozone from the gas to the liquid phase

Role of Lewis acid sites of ZSM-5 zeolite on gaseous ozone abatement

In this work, chemical interactions between ozone and zeolite surface active sites are studied in order to propose a process for gaseous ozone removal. Synthetic ZSM-5 zeolites with three different Si/Al2 ratios and similar specific surface areas and microporous volumes were used in this study. Zeolite samples were characterised using Fourier Transform InfraRed spectroscopy (FTIR) and pyridine sorption IR studies in order to determine acidic site concentrations and strength. Ozone removal experiments were conducted in a quartz fixed-bed flow reactor, at 20°C and 101 kPa. Experiments using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) were conducted in order to identify adsorbed ozone and/or adsorbed oxygen species on zeolite surface. Pyridine IR measurements evidence two kinds of Lewis acid sites induced by extra-framework aluminium species and electronic aluminium defaults inside zeolite structure. Results obtained here evidence the important role of acidic surface sites of ZSM-5 zeolite on gaseous ozone removal. The total amount of removed ozone is found to be directly proportional to the total content of Lewis acid sites. DRIFTS experiments exhibit two bands around 800 and 1400 cm-1 that could correspond to adsorbed oxygen species linked to zeolite surface. DRIFTS experiments also exhibit a band around 1100 cm-1 that correspond to adsorbed ozone on the zeolite surface. Gaseous ozone removal using ZSM-5 zeolite could be largely attributed to ozone decomposition on Lewis acid sites and also to ozone adsorption on the surface of the zeolites

Removal of volatile organic compounds by heterogeneous ozonation on microporous synthetic alumina silicate

A hybrid process combining adsorption and ozonation was examined as an alternative treatment for odorous volatile organic compounds (VOCs). Methyl ethyl ketone (MEK) was chosen to study the influence of operating parameters. Two synthetic aluminosilicates (faujasite-Y and ZSM-5) were tested for adsorption and reactivity with ozone. The adsorption equilibrium measurement on both adsorbents showed that adsorption performance depends on temperature but is not sensitive to relative humidity, due to the hydrophobic properties of the materials. Adsorbed VOCs were oxidized at low temperature when ozonated flow was sent to the reactor. Regeneration of the fixed bed was achieved at the same time, releasing mainly CO2 and H2O. Intermediates of oxidation, such as 2,3-butanedione and acetic acid, were identified, leading to incomplete mineralization. The influence of concentration and humidity are discussed. Four successive cycles were tested: after the first adsorption/ozonation cycle, the adsorption efficiency was not affected during subsequent cycles. These results show that the same sample of adsorbent can be used in the treatment process for a long time. Ozonation regeneration is a promising process for VOC removal

Comparison of Activated Carbon and Hydrophobic Zeolite Efficiencies in 2,4-Dichlorophenol Advanced Ozonation

This study aims at comparing the removal of 2,4-dichlorophenol (2,4-DCP) by 3 methods; adsorption using hydrophobic zeolite (faujasite) or activated carbon (S-23 and L-27), conventional ozonation and hybrid adsorption/ozonation treatment. On the one hand, the three materials correctly adsorb 2,4-DCP; however the adsorption kinetics using zeolite is very low. On the other hand, ozonation totally removes 2,4-DCP after 1 h experiment and the simultaneous combination of adsorbent and ozone does not change the 2,4-DCP degradation. But, though ozonation and hybrid process appear to be equivalent for 2,4-DCP removal, activated carbons are able to decompose ozone and to improve chemical oxygen demand (COD) removal, whereas the zeolite does not show this catalytic effect. Similar results were also observed in a former study with nitrobenzene. Adsorbent degradation is evaluated by Brunauer, Emmet and Teller (BET) and differential thermogravimetric (DTG) analysis, which evidence that Faujasite and S-23 activated carbon are resistant to ozone exposure whereas the pore volume and the surface area of L-27 activated carbon decrease during ozonation

Urban Wastewater Treatment by Catalytic Ozonation

This study focuses on the catalytic ozonation of organic matter recalcitrant to usual water treatment technologies. Experiments aimed to investigate the efficiency of the process TOCCATA®, which uses a granular catalyst coupled with ozonation. Comparison was made between single ozonation, single adsorption onto the catalyst and catalytic ozonation. Adsorption was proven to contribute to decreased dissolved organic carbon. Catalytic ozonation enhanced organic matter removal and ozone transfer compared to single ozonation. Catalytic ozonation was modeled with global apparent first-order kinetics and single adsorption with pseudo–second-order sorption kinetics

Combined Ozonation Using Alumino-Silica Materials for the Removal of 2,4-Dimethylphenol from Water

This study deals with an advanced oxidation process combining adsorption and ozonation for treating petrochemical effluents. The compound 2,4-dimethylphenol (DMP) was the paradigm molecule and faujasite-Y, mordenite, ZSM-5 and γ-alumina were tested. Single ozonation showed rapid DMP degradation but limited by gas to liquid ozone transfer. No catalytic effect occurred during ozonation combined with any of+ the adsorbents: DMP removal was not accelerated. However, a good synergistic effect was observed for TOC removal with γ-alumina, yet the various zeolites are less efficient. Some specific oxidation by-products produced during ozonation are eliminated by adsorption in the presence of γ-alumina, although they persist in the other cases

Gaseous ozone decomposition over high silica zeolitic frameworks

For several decades, it has been known that ozone emissions are harmful to humans, plants, and animals. Heterogeneous catalytic decomposition is an efficient process for removing ozone from air. This study examines the effect of the zeolite's framework and pore width on efficiency for decomposing gaseous ozone. Four highly hydrophobic zeolites are used: a large cavity zeolite (Faujasite/H‐FAU), a medium pore zeolite with parallel channel (Mordenite/H‐MOR), and two medium pore zeolites with interconnected channels (H‐ZSM‐5/H‐MFI and Na‐ZSM‐5/Na‐MFI). Experiments were conducted in fixed‐bed flow reactors loaded with zeolite at ambient conditions (20 °C and 101 kPa). Zeolite surfaces were analyzed during the experiments in order to understand the influence of physical and chemical surface properties on the ozone decomposition mechanism. A higher amount of ozone is eliminated using H‐MOR, compared with the zeolite samples H‐FAU, H‐MFI, and Na‐MFI. Pore width and micropore framework size distribution (channel and cages) appear to be key factors. A narrow channel or cage, slightly larger than the ozone molecule size, seems to promote ozone interactions with Lewis acid sites. Fourier transform infrared spectroscopy shows that Lewis acid sites (LAS), located on the walls of zeolite pores, decompose ozone. This leads to the formation of atomic oxygen species that could react with another ozone molecule to form dioxygen. Hence, LAS are regenerated, ready to decompose another ozone molecule once more