CO2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO2 purification in H2-rich gas

Abstract

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.