Separation of isoprene from biologically-derived gas streams

ABSTRACT

Renewable organic precursors, including olefinic compounds such as isoprene, have attracted interest from the polymer and pharmaceutical industries. Biologically-derived processes can generate these target compounds; however, their gaseous product streams are complex mixtures of condensable organic vapors (COVs), water vapor, carbon dioxide (CO₂), and/or nitrogen (N₂). Because COVs, CO₂ and water vapor are known to alter polymer membranes, mixed gas separations data at ambient and elevated temperatures are limited. This study focused on two classes of polymer membranes, glassy [polyetherimide (Ultem®)] and a rubbery [polydimethylsiloxane (PDMS)] with results indicating that isoprene separation is possible in humidified gas environment (2–4 vol% water). Gas permeabilities of these membranes did not noticeably change in the presence of humidity; however, the selectivity of these membranes was significantly lower compared to their performance under dry conditions. The role of water vapor in gas transport was derived from the energy of activation of permeation (E_p) for PDMS and Ultem® from 30–80°C in humidified mixed gas streams. For both polymers, E_p data shows a slight decrease in selectivity with the other gases (hydrogen, N₂, CO₂, and methane) at elevated temperatures in the presence of water vapor. Thus, these COVs separations are feasible with polymer membranes in the presence of humidified gas streams, even in the case of glassy and rubbery membranes in series.

KEYWORDS:

• Polyetherimide
• polydimethylsiloxane
• polymer membrane separations
• isoprene
• gas permeation analysis
• water vapor

Acknowledgements

We appreciate the technical assistance regarding biologically-derived isoprene from Dr. Dayna L. Daubaras, a research scientist at Idaho National Laboratory, Idaho Falls, Idaho.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the United States Department of Energy through contract DE AC07-05ID14517 and by Laboratory Directed Research and Development (LDRD) at the Idaho National Laboratory..