Henrik Raeder

Comparison of a contactor catalytic membrane reactor with a conventional reactor: example of wet air oxidation

Abstract A wet air oxidation reaction was carried out in a gas/liquid catalytic membrane reactor of the contactor type. The oxidation of formic acid was used as a model reaction. The mesoporous top-layer of a ceramic tubular membrane was used as catalyst (Pt) support, and was placed at the interface of the gas (air) and liquid (HCOOH solution) phases. A similar reaction was carried out in a conventional batch reactor, using a steering rate high enough to avoid gas-diffusion limitations, and exactly identical conditions than for the CMR (amount of catalyst, pressure, etc.). At room temperature, the CMR showed an initial activity three to six times higher than the conventional reactor. This activity increase was attributed to an easier oxygen access to the catalytic sites. Nevertheless, the catalytic membrane gradually deactivated after a few hours of operation. Different deactivation mechanisms are presented.

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.

Chapter 21 – Grace: Development of Supported Palladium Alloy Membranes

The Grangemouth Advanced CO 2 Capture Project (GRACE) was a two-year (2002–2003) research program concerned with the capture of CO 2 from a UK refinery site. One of the technologies that were pursued in the program was the development of hydrogen gas separation by membrane technology. Such technology can be used to enhance the water gas shift reaction for CO 2 capture by pre-combustion decarbonization of refinery fuel gas. This chapter presents the development and testing of flat and tubular supported palladium alloy membrane modules. Membranes with thickness in the range of 1 μm are prepared by a two-stage magnetron sputter process using a single crystal silicon wafer as intermediate support and a wire mesh or porous material as final support. Testing of the hydrogen flux through the tubular membranes at 300 °C has shown that permeance values of about 3 × 10 −6 mol/(m 2 s Pa) can be attained. For a flat membrane, peak permeance values of about 6.8 × 10 −6 mol/(m 2 s Pa) is attained at 300 °C. The membranes are able to separate hydrogen gas from nitrogen gas with 100% selectivity within the detection limits of the equipment. Tubular membrane supports that have been reinforced by a steel insert are tested up to 14 bar transmembrane pressure. Although the selectivity drops at high pressure, the tests show that the membrane film does not disintegrate at high pressure even at 300 °C.