Precombustion CO2 Capture Pemperature PBI Hollow Fiber Membranes

Separation of CO2 from the fuel gas stream from a coal gasifer at elevated temperature (above the dew point of the gas stream) increases the efficiency of electric power generation from coal. We are using polybenzimidazole (PBI), which has showed promise as a membrane material for precombustion-based capture of CO₂ by separating H₂ and CO₂ at elevated temperatures (200° to 250°C). Membranes that permeate H₂ preserve the CO₂streams at high pressures, thereby reducing the energy for compression to pipeline pressures. SRI is developing a process, under U.S. Department of Energy funding,  the last 5 years a separation process based on the high temperature stable PBI polymer.  We fabricated hollow PBI fibers of <0.5 mm OD with an asymmetric structure with ~1 µm dense layer and a 0.1 mm wall thickness.  The performance of SRI fiber was evaluated over 50 days, representing the performance over 1000 hours.  The selectivity for H₂/CO₂ improved with time increasing from 35 to 50, exceeding the design target of 40. The H₂ permeance value at 225°C remained at about 80 GPU throughout the test period and this value is also above the target value.  At the end of the 1000-h test period, the H₂ permeance was measured to be 130 GPU at 250°C.   The experimental observations and analytical calculations are very encouraging that a technically viable and cost-effective method can be developed for separating CO₂ from fuel gas streams into a high pressure CO₂-rich gas stream suitable for use in enhanced oil recovery or sequestered underground.