Dry reforming of methane using dense palladium membrane supported on porous stainless steel

Abstract

In this research, the electroless plating technique had been used for palladium plating on porous stainless steel. The plating condition was determined using normal and porous stainless steel disks. The appropriate plating condition was at 60ºC for 90 minutes and palladium layer thickness was measured gravimetrically and compared with the results from SEM. By using SEM-EDS, the metal diffusion from stainless steel to palladium layer was found when the temperature was higher than 500ºC. Two palladium membrane tubes with effective surface area of 20 cm² and average pore size 0.1 µm, Tube 1 (19.3 µm thickness) and Tube 2 (17.5 µm thickness), were prepared. The performance testing of these tubes were investigated by assembling it in the reactor. Helium flux and hydrogen permeation flux were then measured at 350- 450ºC and pressure differences 1-3 atm. The helium flux was not detected for Tube 1 and only a trace of helium flux was found for Tube 2. Therefore, palladium membranes of both tubes were proved to be dense. Higher conversion of methane and carbon dioxide using palladium membrane tube reactor containing Tube 1, comparing to conventional tube reactor utilized 1% Pt/Al₂O₃ as the catalyst at the same reaction condition was resulted which was monitored by gas chromatographic technique. It was also found that higher conversions were obtained when the temperature of reactor increased. Furthermore, when argon was used as a sweep gas, higher conversion was obtained and increased with increasing sweep gas flow rate. To prevent the metal diffusion, several kinds of materials as the incremental layer on porous stainless steel disks were generated before palladium plating, i.e. silver-tungsten, silica, chromium, and chromium oxide. After the exposure at 500ºC for 24 hours in helium, the intermetallic diffusion of these disks was investigated by SEM. It was found that no intermetallic diffusion was observed in case of Cr₂O₃ layer. The palladium membrane tube with palladium layer thickness of 32µm, Tube 3, was then prepared with Cr₂O₃ intermetallic diffusion barrier at the thickness of 2µm. It was confirmed to have dense palladium membrane by helium flux measurement. Its hydrogen permeation flux at 500ºC was not declined, which was in contrast to the previous result when the other palladium membrane tube without Cr₂O₃ layer was used, implying that Cr₂O₃ acted as the good intermetallic diffusion barrie