(642c) Selective H2s/CO2 Separation Using Sterically Hindered Amine Membranes | AIChE

(642c) Selective H2s/CO2 Separation Using Sterically Hindered Amine Membranes

Authors 

Deng, X., The Ohio State University
Han, Y., The Ohio State University
Lin, L. C., The Ohio State University
Ho, W. S. W., The Ohio State University
H2S, an extremely toxic and corrosive gas, is a common contaminant in fuel gas mixtures like syngas and natural gas. The selective removal of H2S from such CO2-containing fuel gases is important for enabling their industrial processing. This work describes the development of amine-based facilitated transport membranes (FTMs) with high H2S/CO2 selectivity at elevated temperature (> 100 °C) and explores the underlying mechanisms of acid gas transport in FTMs.

A series of primary, secondary, and tertiary amine carriers with different alkyl substituents was used to synthesize FTMs. Their H2S/CO2 transport performances were evaluated at 107 °C and 7 bar. Sterically hindered amines showed enhanced H2S/CO2 separation performance, with the H2S/CO2 selectivity rising from 4 to nearly 20 as the amine hindrance was increased. The best performance was obtained using a severely hindered di-tert-butylamine carrier, which showed a high H2S/CO2 selectivity of 19.6 and an H2S permeance of 560 GPU. These results are supported by Density Functional Theory (DFT) calculations. The DFT results indicated that the presence of sterically bulky groups on the N site of the amine can restrict its reactivity to CO2 through the carbamate pathway. Conversely, the amine-H2S reaction was found to be relatively insensitive to steric hindrance. Finally, the carrier saturation behavior of the di-tert-butylamine carrier was investigated at H2S concentrations of 0.5—30%. The carrier was found to be nearly inert to CO2, achieving H2S/CO2 selectivities of 25.4 — 9 and H2S permeances of 760—220 GPU. Overall, the newly synthesized membranes show good potential for syngas desulfurization, and the learnings offer some insight into the design of carriers for acid gas purification.