Pre-Combustion Fuel Decarbonization with Pure Palladium and Palladium Alloy Membranes

 

Integration of Pd or Pd alloy membranes with reforming or WGS reactors, for pre-combustion fuel de-carbonization, is attractive for the reduction in CO2 emissions. Recovery of CO₂ at high pressure and high purity (>90 mol%) as well as carbon conversions in excess of equilibrium limits may be achieved using various process schemes [‎1, ‎2].

 

CRI/Criterion is in the process of commercializing Pd and Pd alloy membranes on sintered porous metal supports. Successful evaluations of CRI/Criterion H₂ separation membranes in membrane steam reformers and as high temperature membrane separators have been performed by CRI/Criterion [‎3 - ‎6], and by third parties [‎7].

 

Figure 1 shows an extended trial of a CRI/Criterion Pd membrane (15cm L x 2.5cm OD) separating H₂ from gas blends (430-450°C, DP 18 – 45 bar). The feed gas composition simulated the partially cooled unshifted product from conventional methane steam reforming: 51.6% H₂, 29.4% H₂O, 12.5 - 14.9% CO₂, 0 - 2.4 % CO and 4.1% CH₄. The pressure was varied to simulate pressure fluctuations in a plant environment. The changes in pressure were carried out in a few seconds.

 

Figure 1: 800 hrs Pd membrane trial under realistic simulated process conditions

The same membrane was then subjected to changes in temperature to demonstrate the robustness to temperature fluctuations as shown in Figure 2

Figure 2: Temperature cycling to demonstrate temperature stability of Pd membranes

Figure 3 shows the hydrogen flux for a Pd membrane for which CO was introduced into the feed gas in a two step process. The compositions in the feed were identical to those tested in the past for CO inhibition. Each time the CO feed was increased; the CO2 in the feed was reduced to keep the total molar feed constant. The results indicate that there was no significant CO inhibition for Pd membranes under the conditions studied (430°C and up 1.3 bara CO partial pressure).

 

      

Figure 3:  CRI/Criterion Pd membrane does not suffer from CO inhibition (430°C and up 1.3 bara CO partial pressure).

Recent on-going tests at 430°C, 29 bar DP with a CRI membrane in a 40% H₂, 19% N₂,  41% H₂O mixture (total feed flow of 1500 SLPH) show a remarkable performance over 5000 hours at present delivering 99.99 % pure Hydrogen in figure 4.

Figure 4 Long term stability testing of a CRI Pd membrane in steam, nitrogen, hydrogen mixture.

CRI Membranes tested in the last two years have shown continued robust performance over long periods of time as indicated in Table 1.

Table 1: Overview of long term testing of CRI Pd membranes

 

CRI/Criterion has produced membranes of this type as large as 2"OD by 48"L, by welding two separate 24"L sections. These membranes can be produced with a hydrogen permeance in the range of 40-70 [Nm³/m².h.bar^0.5]. Both the hydrogen flux and the separation selectivity is stable at temperatures of 300-500°C and differential pressures of 26-42 Bar.

 

 

1.      T.R. Ohrn, R.P. Glasser and K.G. Rackers. Design, Scale Up and Cost Assessment of a Membrane Shift Reactor. published in Carbon Dioxide Capture for Storage in Deep Geologic Formations - Results from the CO2 Capture Project. Volume 1, D.C. Thomas editor. Elsevier. 2005 p. 321-339.

2.      Matzakos, A.N.; Wellington, S.L.; Mikus, T.; Ward, J.M.. U.S. Patent 6,821,501 B2, Nov. 23, 2004.

3.      Clomburg et al.. U.S. Patent Application, US 2008/0179569 A1.

4.      Engwall, E.; Saukaitis, J.; Joshi, M.; Del Paggio, A.. Pre-combustion fuel decarbonization with hydrogen separation membranes, AIChE National Meeting, November 2007.

5.      Nijmeijer, A; Engwall, E; Saukaitis, J.; Del Paggio, A. Pre-combustion fuel decarbonization with Palladium Alloy membranes, NAMS 2010, July 2010

6.      Veenstra, P. et al., “'Integrated approach to CO2 capture in a refinery: fuel gas decarbonisation”, Proceedings 13^th Aachner Membran Kolloquium pp 121(October 2010)

7.      Sanchez, J.M; Marono, M.; Barreiro, M.M.. Separation of CO₂ and H₂ using palladium membranes (for integration in power generation with CO₂ capture). EUROMEMBRANE Conference 2009.