Development of a Pre-combustion CO2 Capture Process Using High-Temperature PBI Hollow-Fiber Membranes

Abstract

This paper describes a process for high-temperature separation of CO2 from a syngas stream containing CO2, H2, CO, steam, and other trace-level gases using polybenzimidazole (PBI) hollow fiber membranes (HFM). SRI International developed the asymmetric HFMs for gas separation applications using commercially available, high-temperature stable PBI polymer blends. In the PBI-based membrane separation, non-fuel gases will retain the high temperature (~ 225C) and high pressure (20 to 40 atm) of the feed syngas, while the fuel gas H2 and steam permeates through compact, hollow, asymmetric PBI fibers for use in gas and steam turbines. An analysis by Department of Energy-National Energy Technology Laboratory (DOE-NETL) reports the net power plant efficiency is increased by 1 to 3 percentage points by preserving the heat in the syngas stream. Additionally, in the PBI-HFM process, CO2 (> 95%) is captured at high pressure, significantly reducing the compression energy cost in the CO2 capture system. The PBI-HFM gas separation technology was successfully demonstrated with syngas at the National Carbon Capture Center (NCCC) in 2017 under air-blown gasifier conditions. A transportable membrane test skid mounted with 4-in fiber modules made of Generation 1 (GEN-1) microstructure fibers was used for this field demonstration. Tests involved long term and parametric studies at bench scale level using actual coal-derived syngas from an air-blown gasifier under realistic conditions. The next generation of PBI-HFMs (GEN-2) developed at SRI showed far superior H2/CO2 selectivity than GEN-1 HFMs in lab- and preliminary bench-scale testing. A new project is underway for field demonstration of GEN-2 HFMs under realistic pre-combustion conditions using a syngas stream derived from an oxygen-blown coal gasifier.

Keywords: Hollow fiber membrane; Pre-combustion; CO2 capture; Syngas;Gas separation