Catalytic Contactor Research Articles

SiC Foams for the Photocatalytic Degradation of Methylene Blue under Visible Light Irradiation.

SiC foams were synthesized by impregnating preceramic polymer into polyurethane foam templates, resulting in a photo-catalytically active material for the degradation of methylene blue. The crystalline structure, electronic properties, and photocatalytic performance of the SiC foams were characterized using a series of experimental techniques, including X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, N2 physisorption measurements, UV-visible spectroscopy, and methylene blue photodegradation tests. The original polyurethane template's microporous structure was maintained during the formation of the SiC foam, while additional mesopores were introduced by the porogen moieties added to the preceramic polymers. The prepared SiC-based photocatalyst showed attractive photocatalytic activity under visible light irradiation. This structured and reactive material offers good potential for application as a catalytic contactor or membrane reactor for the semi-continuous treatment of contaminated waste waters in ambient conditions.

Nitrate hydrogenation by microtubular CNT-made catalytic membrane contactor

Microtubular CNT-made catalytic membrane contactor is proposed for heterogeneous three-phase (i.e. solid-liquid-gas) catalytic processes aimed at hydrogenation and oxygenation of aqueous pollutants. The contactor comprises a mesoporous CNT-made microtube with an internal diameter of ≈ 1.5 mm, wall thickness of ≈ 0.2 mm, pore diameter of ≈30 nm, loaded with a nano-scale metal catalyst. In this study the concept of CNT-made contactors was proved for hydrogenation of nitrate ions. The CNT-made microtubes were fabricated by infiltration of CNT suspension through the polypropylene microfiltration membrane. The CNT-made microtubes were loaded with Pd-Cu catalysts using the wet-impregnation method followed by reduction by H2 gas or sodium borohydride. The catalytic contactors were investigated for nitrate reduction at varied pH (5–9) and H2 pressure (0.5–2.5 bar) in pure KNO3 solutions and groundwater. Lower pH and higher H2 promoted higher nitrate reduction rates but lower selectivity towards the nitrogen gas. The highest catalytic activity of 2.6 mgN/min/gPd was obtained at pH5.0 and H2 gauge pressure of 0.5 bar. The highest selectivity (79%) towards nitrogen gas was achieved at pH7.0 and H2 pressure of 0.1 bar. Hydrogen utilization efficiency of 93.4% (±7.6%) was obtained. Operation in groundwater resulted in lower selectivity to nitrogen than in experiments conducted on KNO3 solutions in deionized water.

Polymeric catalytic membrane for ozone treatment of DEET in water

The ozone treatment of N,N-diethyl-meta-toluamide (DEET) in water was carried out in a membrane reactor that uses ozone-resistant polymer membranes for ozone distribution, catalytic contactor and water separation. Iron oxide (ferrihydrite) nanoparticles supported on powdered activated carbon (CAT1) were used as catalyst, and were coated on the surface of the membrane contactor/distributor. Ferrihydrites promote ozone dissolution and transformation to reactive hydroxyl radicals, and accelerate the conversion and mineralization of DEET. The powdered activated carbon helped retain the organic pollutants in the reaction zone leading to greater conversion and deeper mineralization. Consistently, the catalytic membrane contactor/distributor displayed the highest DEET conversion and TOC reduction over the entire studied range of ozone dosage and reaction residence time. The selective removal water by the membrane separator had the desired effect of concentrating the organic pollutants resulting in their improved treatment. The compact membrane reactor unit equipped with catalytic membrane contactor/distributor and membrane water separator outperformed a semi-batch ozone reactor with 60% DEET conversion compared to 20%, and 30% TOC reduction versus 5%.

Dry reforming of methane in contactor and distributor membrane reactors

Despite the well-known benefits of catalytic membrane reactors, they are still far from industrial implementation. Researchers who work in this area traditionally use catalytic membrane extractor reactors, which require the application of the most difficult to made catalytic membranes. Catalytic contactor and distributor membrane reactors are as yet imperfectly explored, although they have advantages over extractor reactors in many characteristics. This study is an attempt to fill, at least partially, the gap in understanding of the catalytic membrane process. On the assumption that a membrane-supported catalyst is a type of heterogeneous catalysts, the parameters of methane dry reforming in three catalytic reactors: a catalytic fixed-bed reactor, a contactor membrane reactor, and a distributor membrane reactor have been compared in terms of the classical kinetic method. The investigation has been carried out using the same catalytic system having tungsten carbide as the active component. It has been found that membrane reactors afford higher performance characteristics in the process of the dry reforming of methane, which occurs at high temperatures.

Hydrogenation of nitrates in water using mesoporous membranes operated in a flow-through catalytic contactor

The hydrogenation of nitrates in aqueous solution has been studied using Pd–Cu catalysts deposited in mesoporous ceramic membranes operated in a flow-through catalytic membrane reactor. The effect of the top-layer pore size (5, 10 or 25 nm) on the catalytic activity was explored. The activity increased with trans-membrane flow rate for the three membranes, although moderately with the 25 nm pore membrane. At a similar flow rate, the activity increased when the pore size decreased. Concentration polarization of nitrates was evidenced by ultrafiltration experiments with bare membranes, and was enhanced when the pore size decreased. Concentration polarization appeared effective in improving the catalytic activity, due to a local increase in nitrate concentration in the catalytic top-layer of the membranes.

New approaches in the design of ceramic and hybrid membranes

This paper describes approaches developed for the preparation and also the characterization of innovative inorganic or hybrid membrane materials. Soft chemistry routes, sol–gel methods and plasma-enhanced chemical vapour deposition (PECVD) are used to get tailor-made layers with different architectures. The infiltrated composite membranes are first examined. They exhibit a good thermo-mechanical resistance, a low sensitivity to the presence of defects, a relatively high flow resistance and are attractive for catalytic contactor applications. Preliminary results on supported ceramic membranes with a hierarchical porosity are then presented. Finally, examples are given to illustrate the interest of the PECVD route and of plasma post-treatments for preparing very thin hybrid separative layers.

The “Watercatox” process: Wet air oxidation of industrial effluents in a catalytic membrane reactor: First report on contactor CMR up-scaling to pilot unit

A new and innovative method for oxidation of dissolved compounds in water – the “Watercatox” process – has been developed in order to reduce the chemical oxygen demand and the total organic carbon in industrial wastewaters. This process is the result of a European Fifth Framework Program project. It can operate at much lower temperatures and pressures than conventional wet air oxidation or incineration, and it offers much smaller volume requirements than biological treatment plants. The operating principle of the Watercatox process is the oxidation of the dissolved molecules using oxygen from air within a catalytic membrane reactor in an interfacial contactor configuration. The catalytic contactor membranes, as well as the operating conditions, have been up-scaled from lab-scale to pilot unit. The technological efficiency was demonstrated by the results obtained using the pilot test unit on different industrial effluents from several origins.

A wet air oxidation process using a catalytic membrane contactor

A new process for oxidation of toxic compounds in liquids has been demonstrated. The concept is based on the same principles as catalytic wet air oxidation (CWAO), but the metal catalyst is fixed to a ceramic porous membrane in a catalytic membrane reactor of the contactor type (CMR-C). Air is flowing along the surface of the contactor, and the waste liquid is supplied from the other side of the contactor through the porous contactor wall. In this way, the gas and liquid phases are driven to contact in the porous network of the catalytic contactor separating them. Fifty percent of conversion of formic acid model solution (5 g/l) was obtained in initial reactor experiments at 150 8C and 10 bar pressure, but the observed oxidation rate was low: about 0.13 mmol/s per gPt. TEM and EDS investigations of the contactor showed that 5 � /10 nm Pt particles were evenly distributed close to the surface of the mesoporous TiO2 top layer. After the experiments, a 10 � /50 nm thick aluminium-rich amorphous deposit was observed in the porous structure. The low conversion rate has been attributed to this deposit causing deactivation by encapsulation of the catalyst and plugging of the mesoporous layer of the contactor. The deposits are believed to be caused by chemical instability of a-Al2O3 in acidic aqueous environment at elevated temperature. a-Al2O3 is present in the coarse-grained membrane support. # 2003 Elsevier Science B.V. All rights reserved.

COMPARISON OF THE DATA OF YAMAZAKI AND MIYAUCHI WITH THE BUBBLING BED MODEL

The data of Yamazaki and Miyauchi9) for heat transfer between emulsion phase and gas bubbles in fluid-bed catalytic contactors are analyzed in terms of the Bubbling Bed Model of Kunii and Levenspiel5). It is shown that the effective bubble size needed to fit the Bubbling Bed Model to the reported transport rates is much smaller than the actual bubble size; however, more realistic assumptions regarding temperature measurements indicate that their reported transport rates are much too high. Temperature-corrected data are shown to be reasonably estimated by the Bubbling Bed Model using the measured bubble size.