CO_2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO_2 purification in H_2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H₂-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the CO₂ concentration to less than 100 ppm via the aforementioned process. The CO₂ adsorption capacity of potassium-promoted hydrotalcite at elevated temperatures under different adsorption (mole fraction, working pressure) and desorption (flow rate, desorption time, steam effects) conditions was systematically investigated using a fixed bed reactor. It was found that the CO₂ residual concentration before the breakthrough of CO₂ mainly depended on the total amount of purge gas and the CO₂ mole fraction in the inlet syngas. The residual CO₂ concentration and uptake achieved for the inlet gas comprising CO₂(9.7 mL/min) and He (277.6 mL/min) at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and 0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual CO₂ concentration compared to purging with an inert gas. The residual CO₂ concentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/CO₂ purification.