Design and testing of an integrated catalytic membrane reactor for deoxygenating water using hydrogen for down-hole injection and process applications.
Water obtained from the sea contains dissolved oxygen (DO) and is considered to be undesirable for use in down-hole water injection or other process applications. The presence of DO leads to corrosion and other related problems and hence the need for its removal. Various methods are in place for sea water deoxygenation, but with requirements of floating facilities to meet smaller footprint, compact deoxygenating methods have been proposed. Presently, Minox and Seaject processes are the most compact deoxygenating methods in place, but research is still ongoing on devising even more compact means. One attractive method for water deoxygenation is the reaction of hydrogen and dissolved oxygen over a wider highly catalytic dispersed surface area, and this can be seen to be achievable by employing membrane technology. Membrane technologies provide compactness and are already applicable in other water treatments like reverse osmosis. In this study, inorganic tubular ceramic membranes with highly dispersed catalytic metals: palladium and platinum were produced on both meso and macro porous membranes. They were characterised and tested in membrane reactors by feeding hydrogen saturated water under varying operating conditions and the results compared to that of a fixed-bed reactor. The catalytic activities of the different membranes resulted in different deoxygenating efficiencies. The 6000nm palladium membrane was found to give the highest oxygen conversion of over 80% on the range of the saturated feed flow rate of 200 -1000 mL/min, with a 97% DO reduction at the lowest flow rate of 200 mL/min. Increase in hydrogen gas flow rate and catalytic loading were observed to lead to improved removal of DO. Reaction run time was found to play an important role in the DO removal rate efficiency. Only when the reaction time of a flowrate was longer than 30 minutes under the experimental condition was a very low DO level attained. The reaction order for reactant oxygen was found to follow a pseudo-first order kinetics for both the fixed-bed and membrane reactor. The effect rate of reaction of oxygen showed a strong dependence on the hydrogen total pressure to the power of 3, albeit with a low rate constant. The values for the rate constant for the rate of reaction of oxygen were calculated to be (mol.s-1.gcatalyst-1.mg-1.L) for fixed-bed (k1) and (mol.s-1.gcatalyst-1.mg-1.L) for CMR (k2) respectively. The value of "k" for the dependency on hydrogen pressure for the fixed-bed reactor (k3) was calculated to be (mol.s-1.g-1catalyst.atm-3)
