Analysis of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-  Stability Enhancement Using a Two Step Reactor Design Jovan Trujillo

What a membrane reactor does Some reactions require pure oxygen Ceramic membranes provide an economical method for providing pure oxygen from air An example is providing pure oxygen and methane to create syngas (CO/H 2 ) Syngas is used to create long chain alkanes from shorter chains

Membrane Reactor Shell side Air Methane CO, CO 2, others Tube side Ceramic membrane

Current Problems Ceramics like Sr-Fe-Co-O, Ba-Sr-Fe-Co-O, La-Sr-Fe-Co-O mixtures quickly become brittle and break during use. Low oxygen permittivity. Low product yield.

Current Research Explore composition and processing methods to improve oxygen permittivity and membrane durability. Explore different catalysts for product yield. Boumeester et al. suggest separating catalyst from membrane to improve lifespan of reactor.

Rational for two stage Research shows higher oxygen partial pressure improves stability. Lower membrane concentration gradient improves stability. Boumeester’s design separated Ni/  -Al 2 O 3 catalyst from membrane to lower concentration gradient and raise oxygen partial pressure within membrane.

Reactor model Assume plug flow isothermal reactor model Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-  is the membrane General mass balance is: (1)

Permeation flux of O 2 Operating temperature of 800 o C chosen because more data was found at that temp Paper by Wang et al. provided: Air flows > 150 cm 3 /min provided constant flux Methane flow is 60 cm 3 /s (2)

Permeation flux of O 2 Shell side gas is dry air at 1 atm. Constant shell side oxygen partial pressure is 0.21 atm. Initial tube side oxygen partial pressure is atm before reactant flow at steady state.

Gas phase reactions Paper by Lane and Wolf provided: These are predominant gases found under model conditions. Methane pressure is 1 atm. Four ODE’s solved simultaneously using Matlab® (3)

Wang and Lu provided the effect of Ni/  - Al 2 O 3 : Boumeester added Co 3 O 4 to membrane, this was omitted from model. Effect of cobalt oxide in membrane approximated by Klvana et al.’s results with La 0.4 Sr 0.6 Fe 0.4 Co 0.6 O 3 : (4) Effect of catalysts (5)

Model conditions Air pressure of 1 atm giving oxygen partial pressure of 0.21 atm flowing 150 cm 3 /min Overall temperature of 800 o C. Tube side initial condition of atm O 2. Methane pressure of 1 atm flowing at 60 cm 3 /min. Tube length of cm provides 1 hour residence time. Inner radius 4.56 mm, outer 7.96 mm. 45 gm Ni/  -Al 2 O 3 catalyst for single stage design Common 1 gm Co 3 O 4 catalyst, doubled for single stage design.

Simulation Results Generally tube side partial pressure of O 2 always low. Generally low conversion of methane Generally low production of CO Ni/  -Al 2 O 3 catalyst had no effect Co 3 O 4 catalyst had an effect

Figure 1. Comparison of tube side oxygen partial pressure in atm. Shell side O2 partial pressure was held constant at 0.21 atm using a flow rate of 150 cm3/min. Tube side O2 partial pressure started at atm and rose to atm for both reactor designs. It is evident that the Ni/  -Al2O3 catalyst has no effect on oxygen consumption. Ni/  -Al 2 O 3 Effect on Oxygen Partial Pressure Tube Side

Figure 2. Methane consumption down the length of the reactor gave 11% conversion. Equal levels of cobalt oxide and Nickel Aluminum Oxide catalyst in both designs. Starting partial pressure of methane was 1 atm, which decreased in both designs to atm. Simulation conditions were the same as for figure 1. Ni/  -Al 2 O 3 Effect on Methane Consumption

Figure 3. Oxygen profile comparison with cobalt catalyst content altered. For the two-step membrane the catalytic content of the membrane was assigned to be 1 gram. For the one-step membrane this content was doubled to 2 grams, simulating the addition of Co4O4 to the inner membrane surface. Both started with an oxygen content of atm. For the two-step design oxygen increased to atm (36% increase). For the one-step design oxygen content decreased to atm (4% decrease). Cobalt oxide effect on tube side oxygen partial pressure

Figure 4. Methane with and without cobalt catalyst doubled. Starting partial pressure of methane was 1 atm. Single stage decreased to atm. Two-stage decreased to atm. Cobalt changed conversion from 11% to 14%. Simulation conditions were the same as for figure 3. Cobalt Oxide Effect on Methane Consumption

Figure 5. Carbon monoxide production with single and two stage membrane design. The low yield may be indicating a problem with the model.

Conclusion Co 3 O 4 catalyst had lowered O 2 because it converts O 2 to CO 2. Therefore keep Co 3 O 4 away from membrane, unlike what Bouwmeester did. Ni/  -Al 2 O 3 did not lower O 2 because it only converts CO 2 to CO. This reaction is not fast enough to affect other reactions. Cobalt content in membrane may be contributing to degradation. Experiments following this model are needed to verify.