Ion-conducting dual-phase membrane for high temperature CO2 separation

Hang Qi, Alan Thursfield, Evangelos Papaioannou and Ian S. MetcalfeMerz Court, NE1 7RU, Newcastle-upon-Tyne, United Kingdom

The concept of a dual-phase carbonate-electroceramic membrane based on the idea of the molten carbonate fuel cell (MCFC) has been demonstrated recently [1, 2]. The dual-phase system consists of a porous oxygen anion O2- conducting ceramic substrate hosting a guest molten carbonate phase (usually a Li/Na/K carbonate eutectic mixture) infiltrated within the pore network. Carbon dioxide from the feed gas reacts with oxygen ions supplied by the ionic conducting host membrane to form a carbonate (CO3

2-) anion in the molten carbonate phase. The CO3

2- anion is transported through the molten phase carbonate at high temperatures under a chemical potential gradient and released as gasous CO2 on the permeate side. The O2- anion is transported back to the feed side membrane by the substrate [1, 2]. A schematic is presented in Figure 2. In this project, the dual phase membrane was fabricated by yttria stabilized zirconia (8 mol% Y2O3) powder which was mechanically mixed with up to 33 wt% corn starch as a pore former and sintered at 1450 °C.The sintered porous membrane was then infiltrated with a known quantity of a eutectic mixture of; Li2CO3, Na2CO3 and K2CO3 in the molar ratio 51:16:33.

Experimental setup

YSZ-carbonate membrane

Gas outlet tube in permeate side of membrane

Alumina tube support for membrane

Gas inlet tube in permeate side of membrane

Thermal couple

heliumCO2/N2

1:1To mass spectrometer for analysis

References1.Jennifer L. Wade, C.L., Alan C. West, Klaus S. Lackner, Composite electrolyte membranes for high temperature CO2 separation. Journal of Membrane Science, 2011. 369(2011): p. 20-29.2.Matthew Anderson, Y.S.L., Carbonate–ceramic dual-phase membrane for carbon dioxide separation. Journal of Membrane Science, 2010. 357(2010): p. 122-129.

Conceptual schematic of the ion conducting, dual-phase membrane.

50% CO2 and 50% N2 was provided in feed side of membrane; helium was carrier gas in permeate side of membrane.

Silver paste pre-seal the membrane to the alumina tube.

Glass based sealant at edge of the membrane

Clean surface of the dual-phase membrane.

Membrane sealing

ConclusionThe CO2 permeability of a dual-phase YSZ-carbonate membrane was investigated by long term CO2 permeation at 800 °C, 0.009 mol of CO2 was permeated during 50 hours; while 0.0028 mol carbonate ions were infiltrated which indicated that CO2 permeation had occurred. The CO2 permeability at 850 °C was 7×10-11 mol m-1 s-1 Pa-1, while at 800 °C it decreased to 4 mol m-1 s-1 Pa-1 and 2 mol m-1 s-1 Pa-

1 at 780°C. The sealing method gives a ratio of permeated CO2 to leak N2 of 15:1 at 850 °C.

Selected Results

The CO2 permeated over 50 hours was estimated to be 0.009 mol; while the carbonate that was infiltrated into the membrane is 0.28 gram which contains 0.0028 mol of carbonate ions.

The average leak-subtracted CO2 permeability at 850°C was 7×10-11 mol m-1 s-1 Pa-1, while at 780°C it decreased to 2×10-11 mol m-1 s-1 Pa-1. The average selectivity of CO2 over N2 at 850°C is 15:1 and initially 17:1 at 780°C. It decreases to 2:1 after a further one hour as the N2 leak increases.

CO2 permeability dependence on temperature. It can be seen that permeability decreases on a decrease of temperature. This decrease is reversible on returning the membrane temperature to the original value.

Group of Applied Catalysis

Introduction

Figure 2.

Figure 1. Membrane reactor setup Figure 3.

The membrane is 2.4mm thick and diameter is 14mm. The porosity of the host membrane was measured by mercury porosimetry which indicated that 33 wt% of corn starch pore former creates about 47% porosity with an average pore size of around 700 nm. For a 1.5 g porous YSZ host membrane with about 40% porosity, 0.28 gram carbonate (2.2g cm-3) was infiltrated, as one would expect if all of the pore volume was occupied by carbonate.

Figure 4. (a) Flux of CO2 and leak N2; (b) Leak-subtracted CO2 permeability.

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