Development of Carbon Molecular Sieves Hollow Fiber Membranes based on Polybenzimidazole Doped with Polyprotic Acids with Superior H2/CO2 Separation Properties (Final Report)
- Univ. at Buffalo, NY (United States)
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Trimeric Corporation, Buda, TX (United States)
The goal of this project was to develop a highly efficient membrane-based process to capture CO2 from coal-derived syngas with 95% CO2 purity, achieving the cost of electricity (COE) 30% below the baseline capture approaches (i.e., Selexol process) when coupled with the advancement in other areas of the power generation facility. Our core approach is based on high-permeance hollow fiber membranes (HFMs) with superior H2/CO2 separation properties at the syngas process conditions, which can then be further utilized to design membrane reactors for process intensification of H2 production and purification and CO2 capture. Three organizations with complementary skills collaborated to achieve the goal, including the University at Buffalo (UB), Los Alamos National Laboratory (LANL), and Trimeric Corporation (Trimeric). We formulated logical steps to bring the membrane technology from Technology Readiness Level (TRL) 3 (Experimental proof of concept) to TRL 4 (Laboratory scale validation in relevant environment). During the budget period (BP) 1, we screened various polymeric materials and identified polybenzimidazole doped with inorganic polyprotic acids as the desirable platform. The acid doping increases the H2/CO2 selectivity, and the sequential carbonization increases H2 permeability while retaining the high selectivity. By manipulating the acid type and doping level and the carbonization temperature, we demonstrated advanced carbon molecular sieving (CMS) materials with H2 permeability of above 200 Barrer (1 Barrer = 10-10 cm3(STP) cm cm-2 s-2 cmHg-1) and H2/CO2 selectivity of above 40 at 200-300°C with simulated syngas containing CO and water vapor. For example, the PBI-(H3PO4)0.11 carbonized at 700 °C exhibits H2 permeability of 200 Barrer and H2/CO2 selectivity of 60 at 200 °C, and H2 permeability of 240 Barrer and H2/CO2 selectivity of 54 at 225 °C, which meets the targeted properties and surpasses Robeson’s upper bound. During the BP2, we focused on the conversion of the advanced CMS materials to stable HFMs. Membranes with H2 permeance of 1,090 GPU (1 GPU = 10-6 cm3(STP) cm-2 s-2 cmHg-1) and H2/CO2 selectivity of 57 at 300 °C were successfully fabricated. The effects of temperature, gas compositions, pressure, and time on the separation properties were systematically investigated. Pencil modules were continuously evaluated for 219 h (dry pure gas) and 669 h (dry simulated syngas) and showed initial decline in permeance and increased H2/CO2 selectivity over time, ultimately achieving a steady state stable value, indicating that the ageing phenomena in the nanoporous structures of the membranes during the test. Membrane reactors were fabricated based on the CMS membranes and evaluated for water-gas shift (WGS) reaction. The use of membranes slightly improves the conversion of the CO. However, parametric tests of the membrane reactors at various temperatures and flow rates need to be conducted, as well as the membranes with improved separation performance. We performed a sensitivity analysis on the impact of H2/CO2 selectivity on the COE based on a hybrid process of a membrane unit and cryogenic unit developed by Membrane Technology and Research, Inc. (MTR). Three H2/CO2 selectivity (40, 60, and 15) cases were developed and compared with the baseline capture process (Case B5B) provided by the DOE report. Increasing the membrane H2/CO2 selectivity reduces COE, but the rate of the decrease of COE also diminishes. The COE values for H2/CO2 selectivities of 40 and 60 were nearly the same. As the H2/CO2 selectivity increases, the inert recycling decreases, leading to smaller equipment, less auxiliary power requirements, and less heating, cooling, and refrigeration duty. The refrigeration system used to liquefy the CO2 is the most expensive piece of equipment and consumes the most electricity within the CO2 capture process. Increasing the CO2 concentration in the recycle stream would improve the economics of the process by reducing the refrigeration duty requirement of the unit and also allow for higher liquefaction temperatures. The high H2-selective membrane developed by our team may be applicable in other separation processes where lower pressure H2 retains value. Typically, hydrogen retains its pressure when it is separated from syngas components. Residual components may be used as low-quality fuel and then vented to the atmosphere. Applications might include control of H2/CO ratios or mitigation of the water gas shift reaction by CO2 recycling to the feed of a gasifier or steam methane reformer. To summarize, we have developed industrial HFMs with the best H2/CO2 separation performance reported in the literature. The membranes demonstrate stability with simulated syngas and show great potential for membrane reactors for WGS reactions, lowering the cost of blue H2 production.
- Research Organization:
- Univ. at Buffalo, NY (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE), Clean Coal and Carbon Management
- DOE Contract Number:
- FE0031636
- OSTI ID:
- 1876358
- Report Number(s):
- DOE-UatB-31636
- Country of Publication:
- United States
- Language:
- English
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