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)

Preparation and characterization of palladium ceramic alumina membrane for hydrogen permeation.

In this study, a tubular palladium membrane has been prepared by an electroless plating method using palladium II chloride as a precursor with the intent of not having a completely dense film since its application does not require high hydrogen selectivity. The support used was a 15 nm pore sized tubular ceramic alumina material that comprised of 77% alumina and 33% titania. It has dimensions of 7 mm inner and 10 mm outer diameters respectively. The catalyst was deposited on the outside tube surface using the electroless deposition process. The membrane was morphologically characterized using scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDXA) and liquid nitrogen adsorption/desorption analysis (BET) to study the shape and nature of the palladium plating on the membrane. The catalytic membrane was then inserted into a tubular stainless-steel holder which was wrapped in heating tapes so as to enable the heating of the membrane in the reactor. The gases used for permeation tests comprised H2, N2, O2 and He. Permeation tests were out at 573 K and at pressure range between 0.05 and 1 barg. The results showed that hydrogen displayed a higher permeation when compared to other gases that permeated through the membrane and its diffusion is also thought to include solution diffusion through the dense portions of the palladium in addition to Knudsen, convective and molecular sieving mechanisms occurring through cracks and voids along the grain boundaries. While high hydrogen selectivity is critically important in connection with hydrogen purification for fuel cells and in catalytic membrane reactors used to increase the yield of thermodynamically limited reactions such as methane steam reforming and water–gas shift reactions whereby the effective and selective removal of the H2 produced from the reaction zone shifts the equilibrium, it is not so important in situations in which the membrane has catalytic activity such that it is possible to carryout the reaction in situations where the premixed reactants are forced-through the membrane on which the catalysts is attached. This type of catalytically active membranes is novel and has not been tested in gas-solid-liquid reactions and liquid-solid reactions before. With such a reactor configuration, it is possible to achieve good feed stream distribution and an optimal usage of the catalytic material. The preparation and characterization of such membrane catalysts has gained increased interest in the process industries because it can be adapted to carryout the chemical reactions if one of the reactants is present in low concentration and an optimal reactant distribution results in a better utilization of the active catalytic material. However, there are concerns in terms of the high cost of palladium membranes and research on how to fabricate membranes with a very low content of the palladium catalyst is still ongoing. Work is currently underway to deploy the Pd/Al2O3 membrane catalysts for the deoxygenating of water for downhole injection for pressure maintenance and in process applications

Transport in catalytically active porous membrane application in seawater deoxygenation for pressure maintenance.

In this study, inorganic tubular ceramic membranes with highly-dispersed catalytic metal: palladium and platinum were produced on both meso and macro-porous membranes. The membranes were characterised by energy dispersive x-rays (EDAX), scanning electron microscopy (SEM), BET liquid nitrogen adsorption and hydrogen gas transport behaviour. They were tested for sea water deoxygenation by feeding seawater saturated with hydrogen under various operating conditions and monitoring the downstream oxygen removal rate. The results far exceeded those of a traditional fixed be catalytic reactor

Predicting multicomponent gas transport in hybrid inorganic membranes.

A repeated dip-coating technique has been used to prepare novel inorganic multilayered membranes. The membranes have been characterizated by Scanning Electron Microscopy (SEM) and nitrogen adsorption (ASAP 2010) respectively. The three-parameter model incorporating the gas transport characteristics of the hybrid membranes has been adequately described using a combination of Knudsen and Viscous flows. The model has been used to predict gas transport rates through the membranes over a wide range of gas compositions and good agreement has been observed with experimental data. The model has also been applied to estimate the separation layer thickness. The estimated value of 1.6m is in good agreement with that of 1.62m observed by scanning electron microscopy. The gases studied include O2, N2, He, H2 and mixtures of CO2/N2 and O2/N2, respectively. All experiments were carried out at room temperature and were found to possess both Knudsen and viscous flow as predicted by the model

Thermo-neutral methane reforming using a flow-through porous Rh-impregnated membrane catalyst reactor for carbon capture and utilisation.

A thermo-neutral process has been developed and tested for the carbon dioxide (CO2) reforming of methane (CH4) with oxygen (O2) and steam (H2O). A catalytic membrane reactor in which the catalytic material is dispersed within the straight through porous network was used to study this process. This design suggests an elegant route for the utilisation of waste gas streams such as vent gas and flue gas streams. It can also be used in the monetisation of stranded gas assets containing large volumes of CO2. Results have demonstrated complete conversion of all the feedstocks into synthesis gas (CO, H2) with a composition of H2/CO = 2. Synthesis gas with this composition or ranging from 1 to 2 has been identified as a key to the production of major heavy chemicals using the Fischer-Tropsch synthetic route

Utilization of CO2 for syngas production by CH4 partial oxidation using a catalytic membrane reactor.

In this research, a synthetic flue gas mixture with added methane was used as the feed gas in the process of dry reforming with partial oxidation of methane using a laboratory scale catalytic membrane reactor to produce hydrogen and carbon monoxide that can present the starting point for methanol or ammonia synthesis and Fischer-Tropsch reactions. 0.5% wt% Rh catalyst was deposited on a γ-alumina support using rhodium (III) chloride precursor and incorporated into a shell and tube membrane reactor to measure the yield of synthesis gas (CO and H2) and conversion of CH4, O2 and CO2 respectively. These measurements were used to determine the reaction order and rate of CO2. The conversion of CO2 and CH4 were determined at different gas hourly space velocities. The reaction order was determined to be a first-order with respect to CO2. The rate of reaction for CO2 was found to follow an Arrhenius equation having an activation energy of 49.88 × 10−1 kJ mol−1. Experiments were conducted at 2.5, 5 and 8 ml h−1 g−1 gas hourly space velocities and it was observed that increasing the hourly gas velocities resulted in a higher CO2 and CH4 conversions while O2 conversion remained fairly constant. CO2 had a high conversion rate of 96% at 8 ml h−1 g−1. The synthesized catalytic membrane was characterized by Scanning Electron Microscopy (SEM) and the Energy Dispersive X-ray Analysis (EDXA) respectively. The micrographs showed the Rh particles deposited on the alumina support. Single gas permeation of CH4, CO2 and H2 through the alumina support showed that the permeance of H2 increased as the pressure was increased to 1 × 105 Pa. The order of gas permeance was H2 (2.00 g/mol) > CH4 (16.04 g/mol) > N2 (28.01 g/mol) > O2 (32 g/mol) > CO2 (44.00 g/mol) which is indicative of Knudsen flow mechanism. The novelty of the work lies in the combination of exothermic partial oxidation and endothermic CO2 and steam reforming in a single step in the membrane reactor to achieve near thermoneutrality while simultaneously consuming almost all the greenhouse gases in the feed gas stream

A comparative evaluation of the hydrogen separation, purification and transport behavior of α-alumina membrane and γ-alumina membranes modified with ALOOH sol.

The main purpose of this work is to investigate the hydrogen permeation behavior of a commercial ceramic alumina membrane and compare same with that of a γ-alumina membrane graded with an AlOOH sol using the dip coating method. The permeance of hydrogen and 5 other single gases (He, N2, CH4, CO2 and Ar) were investigated at high temperatures. Mixed gas permeation tests for a H2 gas mixture were also carried out. Results showed that the permeance of H2 increased with increasing temperature for the graded γ- Al2O3 membrane while it decreased for the α-Al2O3 support. For the single gas tests, the α-Al2O3 support show higher permeance of up to 9.45 x 10-3 mol m-2 s-1 Pa -1 compared to 1.03 x 10-3 mol m-2 s-1 Pa-1 for the γ-Al2O3 but the graded substrate was permeable to only H2 at fifth coating. The mixed gas tests for a gas mixture (H2= 50%, CO= 28%, CO2=10% CH4=8%, N2=4%) show lower H2 permeance which was attributed to the inhibition effect of CO2 in the gas mixture. The H2/N2 permselectivity for both membranes was close to the theoretical Knudsen value of 3.73 which suggests a combined viscous and Knudsen flow transport mechanism

Morphological characterization and gas permeation of commercially available ceramic membrane.

This work presents experimental results relating to the structural characterization of a commercially available alumina membrane. A {esc}gc{esc}s-alumina mesoporous tubular membrane has been used. Nitrogen adsorption-desorption, scanning electron microscopy and gas permeability test has been carried out on the alumina membrane to characterize its structural features. Scanning electron microscopy (SEM) was used to determine the pore size distribution of the membrane. Pore size, specific surface area and pore size distribution were also determined with the use of the Nitrogen adsorption-desorption instrument. Gas permeation tests were carried out on the membrane using a variety of single and mixed gases. The permeabilities at different pressure between 0.05-1 bar and temperature range of 25-200oC were used for the single and mixed gases: nitrogen (N2), helium (He), oxygen (O2), carbon dioxide (CO2), 14%CO2/N2, 60%CO2/N2, 30%CO2/CH4 and 21%O2/N2. Plots of flow rate verses pressure were obtained. Results got showed the effect of temperature on the permeation rate of the various gases. At 0.5 bar for example, the flow rate for N2 was relatively constant before decreasing with an increase in temperature, while for O2, it continuously decreased with an increase in temperature. In the case of 30%CO2/CH4 and 14%CO2/N2, the flow rate showed an increase then a decrease with increase in temperature. The effect of temperature on the membrane performance of the various gases is presented in this pape

Design and Evaluation of Gas Transport through a Zeolite Membrane on an Alumina Support

This chapter details the synthesis and applications of zeolite membranes (gas separation and zeolite membrane reactors). Gas separation is still not carried out at industrial level for zeolite membranes. Related areas, such as the possibility of incorporating a zeolite membrane in a reactor for possible catalytic action of the zeolite particles and scale-up issues are also discussed. The basic concept of mass transport through the zeolite layer has been presented. Zeolites can enhance the selectivity of methane more which can lead to the reduction of greenhouse gases in the atmosphere

Comparison of hydrogen transport in dense and porous ceramic membrane systems.

In this study, hydrogen permeation behaviour was investigated for both dense and porous ceramic composite membranes. Selected porous supports were tested and highly active metallic species was impregnated into the porous structure using the repeated dip coating technique. Thin palladium films deposited onto a 15 nm pore size porous ceramic alumina support using both conventional and modified electroless plating methods were also studied. The hydrogen transport behaviours of the membranes were investigated, including the effect of high-temperature treatment including on the hydrogen transport. The value of the permeance in both the dense and porous systems were compared and the exponential factor n depicting the rate limiting step to hydrogen permeation in the dense membranes was also investigated. Deviations from Sievert’s Law were observed from the palladium membranes when compared to the porous systems investigated in this work