AirScience Oxygen Depletion System
DeOxo is principally used in the production of high purity hydrogen and is also used in the upgrading of landfill gas to pipeline quality gas where allowable oxygen content is generally very low.
AirScience experience with oxidation with precious metal catalyst goes back to the early years of the company with the supply of large catalytic reactors for the oxidation of hydrogen bromide (HBr) in the purified terephtalatic acid (PTA) industry. Such as the PTA plants in Montreal, Canada and Altamira, Mexico have used AirScience CaTox units for many years.
More recently AirScience specialized in the valorization of coke oven gas for the primary steel industry. Such gas valorization pathway produces high purity hydrogen from coke oven gas. In the process, oxygen needs to be depleted, and it is done by a DeOxo unit. AirScience has several such installations in operation producing 99.99% pure hydrogen.
Today, AirScience is putting this experience to the purification of biogas/landfill gas. One of the impurity in the gas is oxygen and it is removed through catalytic oxidation of methane in presence of a platinum based catalyst (the DeOxo process) at a temperature range of 350°C (662°F) to 500°C (932°F). One mole of methane depleting two moles of oxygen in the process. The reaction produces one mole of carbon dioxide (CO2) and two moles of water as well as heat equivalent to the heat of combustion one mole of methane.
DeOxo Process Temperature
The oxidation reaction is exothermic and as the reducing agent is the quasi sole constituent of the gas, the oxidation reaction is only limited by the amount of oxygen present in the gas. As the DeOxo reaction needs a minimum temperature to proceed and the reaction produces heat, the maximum concentration of oxygen that the DeOxo reactor can accept is limited by the maximum temperature the catalyst can safely accept without any degradation. Taking into consideration the necessary safety factors, AirScience generally limits the catalyst exit temperature at 500°C (932°F).
In cases where the oxygen content is higher that a single DeOxo stage can accept, the unit will be designed with two catalyst stages with a inter-cooling stage between the two catalyst beds. In the production of sulfuric acid from hydrogen sulfide, the catalytic oxidation unit can have up to four beds, each separated by a cooling stage.
The DeOxo unit is generally followed by a thermal swing adsorption (TSA) gas dryer to remove the water vapour produced by the oxidation reaction. In the case of hydrogen production, the CO2 produced must also be removed. In the case of biomethane for pipeline injection the amount of CO2 produced is not significant enough to require its removal from the product gas.
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