Dry Feed Gas Research Articles

Hydrogen extraction from methane-hydrogen mixtures from the natural gas grid by means of electrochemical hydrogen separation and compression

One interesting option to store and transport hydrogen in the future is to blend it into the natural gas grid. In this paper, we present technological insights regarding electrochemical hydrogen separation and compression (EHC/S), a technology that enables extraction of compressed and purified hydrogen from such blends. Our contribution discusses two use cases, namely i) hydrogen separation to recover purified hydrogen under pressure, and ii) hydrogen removal to protect downstream methane consumers from excessive hydrogen levels. Our experimental work with a laboratory scale EHC/S centers on efficiency aspects. We show that at low hydrogen contents in dry feed gas, gas humidification causes relevant thermal energy consumption, that cannot be provided by EHC/S waste heat. We also show that hydrogen recovery is restricted by mass transport if the residence time in the EHC device is too short. Simultaneous hydrogen separation and compression from 5% hydrogen in methane is demonstrated yielding hydrogen at 6 bara at the cathode.

Zinc-doped titanium oxynitride as a high-performance adsorbent for formaldehyde in air

The potential utility of titanium oxynitride doped with 5% zinc (ZnTON) has been investigated as an adsorbent for the treatment of gaseous formaldehyde (FA) using a fixed-bed adsorption system. The adsorption capacity of ZnTON, when estimated at 10%/100% breakthrough (BT) levels from a dry feed gas consisting of 10 Pa FA, was far superior to two reference materials (i.e., commercial P25-TiO2 and activated carbon (AC)) by factors of 1.7/1.3 and 10/2.5, respectively. The adsorption capacity of ZnTON increased with the increase in the initial feeding concentration of FA (5–12.5 Pa), while decreasing with the rising temperature (25–100 oC). An increase in moisture level (0–100% relative humidity) also led to 5.4- and 2.5-fold reductions in adsorption capacity of ZnTON at 10% and 100% BT levels, respectively. Thermodynamically, the adsorption of FA onto ZnTON is an exothermic (ΔHo = - 9.69 kJ.mol-1) to be feasible in nature based on physisorption mechanism. Further, the adsorption of FA onto ZnTON was governed by surface interactions and monolayer surface coverage (Van der Waal's force/electrostatic attraction), as it obeyed the Langmuir isotherm and pseudo-second-order kinetic models. Regeneration tests indicated a positive effect of moisture on FA desorption and durability of ZnTON (i.e., over three adsorption-desorption cycles). This study offers valuable mechanistic insights into the synthesis of an advanced adsorbent for the efficient removal of hazardous volatile organic compounds under near-ambient conditions.

Washcoat Overlayer for Improved Activity and Stability of Natural Gas Vehicle Monolith Catalysts Operating in the Presence of H2O and SO2

A γ-AlOOH/γ-Al₂O₃ washcoat overlayer, applied to a PdO(Pt/CeO₂)/γ-AlOOH/γ-Al₂O₃ on cordierite (2MgO·2Al₂O₃·5SiO₂) mini-monolith catalyst (400 cells per square inch, 1 cm diameter × 2.5 cm length), is shown to reduce the impact of H₂O and SO₂ on the catalyst activity and stability during CH₄ oxidation at low temperatures (<500 °C). The washcoat overlayer covered the Pd (and Ce and Pt when present) and decreased the catalyst CH₄ oxidation activity in a dry feed gas (0.07 vol % CH₄, 8.5 vol % O₂, 0.06 vol % CO, 8 vol % CO₂) at a gas hourly space velocity (GHSV) of 36 000 h–¹. However, when H₂O (2, 5, and 10 vol %) and SO₂ (2 and 5 ppm) were added to the feed gas, the loss in catalyst activity was reduced and the catalyst stability was improved. The overlayer provided additional sites for both SOₓ and H₂O adsorption, thereby reducing their adsorption on the active phase of the catalysts, and consequently, the catalysts maintained higher activity in the presence of both SO₂ and H₂O over periods of up to 200 h.

Monolithic Adsorbent-Based Rapid-Cycle Vacuum Pressure Swing Adsorption Process for Carbon Capture from Small-Scale Steam Methane Reforming

Steam methane reforming is the primary route to convert natural gas into hydrogen, both at small and large scales. Most of the effort from the scientific and industrial community has been directed toward CO2 capture from large-scale reforming plants. This Article, therefore, proposes an intensified 8-bed, 14-step vacuum pressure swing adsorption unit to capture CO2 from a high partial pressure stream in a small-scale steam methane-reforming process. The unit employs a monolithic adsorbent, rather than adsorbent pellets or beads; this allows the cycle time to be much shorter than that for pelleted adsorbent systems. The specific energy penalty for carbon capture has been minimized by regulating the blowdown and evacuation pressure, while also meeting the CO2 purity and recovery constraints. The minimum penalty is realized when the CO2 purity and recovery are fixed at the minimum allowable values of 95% and 90%, respectively. The model predicts a specific electrical energy penalty of 9.03 kJ/mol CO2 for a fixed feed processing capacity of 7.10 mol of feed/m3/s. The corresponding productivity of the monolithic VPSA process in terms of its CO2 production capacity was estimated to be 0.951 mol CO2/m3/s. The productivity was found to be almost double than the values reported in the literature for state-of-the-art MDEA-based capture plants for large-scale steam methane-reforming applications. A dry feed gas was initially assumed for modeling; the presence of moisture was found to cause a drop in CO2 recovery by approximately five percentage points. The monolithic adsorbent system has also been compared to an equally sized fixed bed, packed with pelleted adsorbent. The pelleted adsorbent system was found to have a lower working capacity between the same blowdown and evacuation pressure. The working capacity could only be improved with reducing the regeneration (evacuation) pressure, resulting in a higher vacuum pump penalty.

The Impact of CeO2 Loading on the Activity and Stability of PdO/γ-AlOOH/γ-Al2O3 Monolith Catalysts for CH4 Oxidation

This study reports on the activity and stability of PdO/γ-AlOOH/γ-Al2O3 monolith catalysts, promoted with varying amounts of CeO2, for CH4 oxidation. Although the beneficial effects of CeO2 have been reported for powdered catalysts, this study used a cordierite (2MgO.2Al2O3.5SiO2) mini-monolith (400 cells per square inch, 1 cm diameter × 2.5 cm length; ~52 cells), washcoated with a suspension of γ-Al2O3 combined with boehmite (γ-AlOOH), followed by sequential deposition of Ce and Pd (0.5 wt.%) by wetness impregnation. The monolith catalysts’ CH4 oxidation activity and stability were assessed in the presence of CO, CO2, H2O and SO2 at low temperature (≤550 °C), relevant to emission control from lean-burn natural gas vehicles (NGVs). The CeO2 loading (0 to 4 wt.%) did not significantly impact the adhesion and thermal stability of the washcoat, but CeO2 reduced the inhibition of CH4 oxidation by H2O and SO2. The catalyst activity, measured by temperature-programmed methane oxidation (TPO) in a dry feed gas with 0.07 vol.% CH4, showed that adding CeO2 to the γ-AlOOH/γ-Al2O3 washcoat suppressed the activity of the catalysts; whereas, CeO2 improved the catalyst activity when H2O (2 and 5 vol.%) was present in the feed gas. Moreover, adding CeO2 decreased catalyst deactivation that occurred in the presence of 10 vol.% H2O and 5 ppmv SO2 at 500 °C, measured over a 25 h time-on-stream (TOS) period. The highest catalyst activity and stability for CH4 oxidation in the presence of H2O was obtained by adding 2 wt.% CeO2 to the washcoat.

Fabrication and field testing of spiral-wound membrane modules for CO2 capture from flue gas

A spiral-wound membrane module comprising face compression “O” rings for effective seal of gases was developed, including a spiral-wound membrane element, Plexiglas fiber-reinforced plastic tube, and membrane housing. The spiral-wound membrane modules demonstrated essentially no leakage. The concentration polarization phenomenon was observed at a dry feed gas flow rate of less than 1000 sccm before humidification. Hence, the performances of the spiral-wound membrane modules were evaluated using both dry feed and sweep gas flow rates each at 1000 sccm before humidification at the typical flue gas temperature of 57 °C. The feed and sweep gas pressures were at 1.5 and 1 psig, respectively. By using either a simulated flue gas or an actual flue gas, the spiral-wound membrane modules showed similar performance results with a CO2 permeance of greater than 800 GPU and a CO2/N2 selectivity of more than 140, which were essentially identical to the results obtained from the flat-sheet membrane used for the module fabrication and tested in laboratory with the simulated flue gas. The pressure drops of the modules were satisfactory, i.e., less than 1.5 psi/m. During the field test using the actual flue gas at the National Carbon Capture Center in Wilsonville, Alabama, the performances of the modules revealed some unexpected issues including the feed spacer indentations on the membrane selective layer and the leakage at glue lines. These issues were resolved by improving the spiral-wound membrane module fabrication using a smoother feed spacer and a longer glue curing time. The field test results of the modules have shown their good potential for the post-combustion CO2 capture from coal-fired power plants.

Hydrophobic Platinum Honeycomb Catalyst to Be Used for Tritium Oxidation Reactors

We have developed two types of hydrophobic platinum honeycomb catalyst to be used for tritium oxidation reactors. One is the hydrophobic platinum catalyst on a metal honeycomb. The other is the hydrophobic platinum catalyst on a ceramic honeycomb made of silicon carbide. The activity of these catalysts was evaluated with tritium. The effects of hydrogen concentration (0.02 to 1000 ppm) and water concentration (100 or 22000 ppm) in the gaseous feed on the activity were investigated. The fine platinum particles around a few nanometers significantly improve the catalytic activity for the oxidation tritium at a very small concentration. The hydrogen concentration in the gaseous feed slightly affects the overall reaction rate constant for hydrogen oxidation. Due to the competitive adsorption of hydrogen and water molecules on platinum surface, the overall reaction rate constant has the bottom value at the hydrogen concentration of 100 ppm with the dry feed gas. We have experimentally confirmed the activity of these honeycomb catalysts is as good as that of granular hydrophobic catalyst. The results support the hydrophobic honeycomb catalysts can be used for tritium oxidation reactors.

Microporous Ceramic Tubule Based and Dendrimer-Facilitated Immobilized Ionic Liquid Membrane for CO2 Separation

A solvent evaporation method has been used to prepare a supported ionic liquid (IL) membrane in a microporous ceramic tubule-based module; its separation performance for CO2–N2 and CO2–He mixtures has been reported here over a pressure range of 50−250 psig (344.7−1724 kPag) and temperatures up to 100 °C. Solutions of IL-ethanol having different IL contents were used to prepare 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]) membranes having different thicknesses. Membranes prepared from 25 wt % IL in ethanol solution showed the best gas permeation and separation performance. Ionic liquid membranes prepared from 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim][Tf2N]) under the same conditions displayed a slightly higher gas permeance, but its separation capability was somewhat lower. Tests at higher temperatures using the [bmim][DCA] membrane generated obviously higher gas permeances, but the ideal separation factors of CO2 over N2 and He dropped sharply. These tests were carried out with a dry feed gas. Adding polyamidoamine (PAMAM) dendrimer generation 0 to IL did not show any improvement when the feed gas was dry. After the feed gas was humidified, both the permeance and the separation factor of CO2 over N2 and He were improved greatly. This is due to lower viscosity caused by dissolved water in the IL membrane and additional reactions between CO2 and tertiary amine units of dendrimer in the presence of water. A set of gas mixture-based test results confirmed the facilitating effects of dendrimer to enhance CO2 permeation with humidified feed gas.

Hydrogen separation by Pd–CaZr 0.9Y 0.1O 3− δ cermet composite membranes

A cermet composite membrane composed of a hydrogen-transporting metal (Pd) embedded in a thermodynamically stable, proton-conducting, ceramic matrix (CaZr 0.9Y 0.1O 3− δ ) was proposed to achieve the successful combination of high permeability and chemical stability in a CO 2-containing atmosphere at elevated temperatures (>600 °C). The influence of both applied hydrogen chemical potential gradient and temperature on the hydrogen permeation properties of 0.5-mm-thick, Pd–CZY cermet membranes were studied using dry feed gases with 20–80% H 2. The hydrogen permeation flux increased from 1.3 to 2.3 cm 3(STP)/min-cm 2 with increasing temperature and p H 2 gradient. The effect of the ceramic matrix on the permeability of the Pd–cermet membranes was also compared. The proton-conducting ceramic matrix exhibited the maximum hydrogen permeation flux, which was attributed to the additional ambipolar hydrogen permeation through the cermet membrane. Finally, the hydrogen permeability in CO 2-containing gas streams was investigated using a dry feed gas stream comprised of 30% CO 2, 20% H 2 and 50% He. The decrease in hydrogen permeation flux with increasing temperature was ascribed to the decrease in the H 2 content in the feed gas stream as calculated using the Gibbs energy minimization method.

Carbon Dioxide Separation with Novel Solvents as Liquid Membranes

Glycerol carbonate is studied as a new physical solvent for carbon dioxide separation from CO2/N2 mixtures. CO2-selective behavior of glycerol carbonate is explored in an immobilized liquid membrane (ILM) configuration. Pure glycerol carbonate ILMs retained their CO2/N2 selectivity around 80−130 over a large range of CO2 partial pressures. Its CO2 selectivity was not affected by the absence of humidity in feed and sweep streams. When exposed to dry feed gas conditions, the CO2 permeability through pure glycerol carbonate ILMs was about 100 barrer, which increased to about 350 barrer in the presence of humidified feed streams. Addition of small amounts of facilitating carriers such as poly(amidoamine) dendrimer (generation zero) and sodium glycinate appears to significantly help CO2 facilitation at low CO2 partial pressures. However, at high CO2 feed partial pressures, there was a loss of selectivity with the addition of the carriers. The potential for glycerol carbonate based ILMs in CO2 separation from different CO2-containing gas mixtures is discussed and compared with existing solvent/membrane configurations.

Solid polymer electrolyte composite membranes for olefin/paraffin separation

Ethylene and propylene are produced in larger quantities than any other organic compound. Production of these olefins requires separation of the olefins from the corresponding paraffins. Distillation is currently used but this is an extremely energy-intensive process due to the very low relative volatility of the components. Previous studies have shown that facilitated transport membranes can have high selectivity for olefin/paraffin separation. However, four problems have limited the commercial application of facilitated transport membranes: (i) poor mechanical stability, (ii) the difficulty in preparing thin, high-flux composite membranes, (iii) the requirement of a water-vapor-saturated feed to provide mobility for the olefin-selective carrier, and (iv) poor chemical stability due to carrier poisoning. Solid polymer electrolytes are a novel class of facilitated transport membranes for olefin/paraffin separation. These membranes solve the first three problems listed above. Solid polymer electrolyte membranes are based on rubbery, polyether-based polymers containing a dissolved olefin-complexing metal salt. Solid polymer electrolyte composite membranes made from poly(ethylene oxide) loaded with silver tetrafluoroborate showed an ethylene/ethane selectivity of up to 240 and an ethylene permeance of 8×10 −6 cm 3(STP)/cm 2 s cmHg with a dry feed gas mixture.

Effect of water on the facilitated transport of olefins through solid polymer electrolyte membranes

Polymer electrolyte membranes composed of poly(2-ethyl-2-oxazoline) (POZ) and AgBF 4 are prepared for olefin/paraffin separations. The stability and effect of relative humidity on permeance and selectivity are investigated using propylene/propane mixed gases. The selectivity of propylene over propane remains high on the long time operation with a dry feed gas, indicating that membranes are effective for propylene/propane separation in the absence of water. As humidity of the feed gas increases, both propylene and propane permeances increase, which resulting in the slight decrease of selectivity.

Deactivation of PdO–Al 2O 3 oxidation catalyst in lean-burn natural gas engine exhaust: aged catalyst characterization and studies of poisoning by H 2O and SO 2

A palladium oxide on alumina oxidation catalyst was employed to remove combustible pollutants from the exhaust of a spark-ignited, lean-burn natural gas engine. Rapid deactivation was seen for the oxidation of methane and ethane. Characterization results are consistent with sulfur as the primary source of catalyst activity loss. In microreactor studies, deactivation of the engine aged catalysts was only apparent if water was present in the feed stream. In dry feed gas, the activity of fresh and engine aged samples was the same. SO 2 in dry gas was shown to cause both inhibition and deactivation for methane oxidation. This deactivation is partly reversible at 733 K and completely reversible at 793 K. Water inhibits the rate of methane oxidation and causes some permanent activity loss. Activity studies at 733 and 793 K indicate that activity loss is greater when both water and SO 2 are present. Sulfur oxide groups on the surface increase both the amount of water sorbed and the water desorption temperature in TPD experiments. It is proposed that water and SO 2 compete for adsorption sites on the alumina surface. Enhanced activity loss in the presence of both poisons is attributed to enhanced water inhibition and spillover of sorbed SO 2 and SO 3 species from alumina to the PdO surface.