Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU) Tobias Mattisson

Transcription

1 Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU) Tobias Mattisson Department of Energy and Environment Division of Energy Technology

2 Aim of this work Explore the possibilities of combined manganese oxides as oxygen carrier materials Investigate the potential of a series of binary and ternary materials for use as oxygen carrier in chemical-looping with oxygen uncoupling: - System 1: Mn y MgO x - System 2: CaMnO 3 - (Fe 0.25 Mn 0.75 ) 2 O 3 - System 3: CaMnO 3 - (Fe 0.67 Mn 0.33 ) 2 O 3 - System 4: CaMnO 3 - MnMgO x - System 5: MnMgO x - (Fe 0.25 Mn 0.75 ) 2 O 3 - System 6: Mn 2 SiO x - Fe 2 SiO x More specifically the following parameters were evaluated: Mechanical strength Uncoupling properties (CLOU) Reactivity with methane Reactivity with char for system 6

3 Chemical-looping with oxygen uncoupling (CLOU) Fuel Reactor (FR) (2n+½m) MeO x (2n+½m) MeO 1-x + (n+¼m) O 2 (g) C n H m + (n+¼m) O 2 (g) n CO 2 (g) + (½m) H 2 O(g) Oxygen Depleted Air O 2, N 2 MeO x Combustion Products CO 2, H 2 O Air Reactor (AR) (2n+½m) MeO 1-x + (n+¼m) O 2 (g) (2n+½m) MeO x AR FR Air O 2, N 2 MeO x-1 Fuel C n H m Sum of reactions identical to chemical-looping combustion (CLC). Different reaction mechanism for oxidation of fuel, i.e. release of O 2 (g). Capable of oxidizing solid fuels directly, i.e. no need for gasification. Complete conversion of gaseous fuels, perfect mixing unnecessary.

4 Monometallic oxygen carriers 4CuO 2Cu 2 O + O 2 (g) 6Mn 2 O 3 4Mn 3 O 4 + O 2 (g) 2Co 3 O 4 6CoO + O 2 (g) 800 o C 960 o C Copper oxide examined by several groups with excellent results. Cobalt oxide has poor cost, health and environmental characteristics. Manganese oxide seemingly has very slow oxidation kinetics.

5 The case for combined Mn-oxides Combined oxides of manganese and certain metald can have advantageous thermodynamic and kinetic effects with respect to CLOU. Some examples: a) 6(Mn,Fe) 2 O 3 4(Mn,Fe) 3 O 4 + O 2 (g) b) CaMnO 3-δar CaMnO 3-δfr + ½(δ fr -δ ar ) O 2 (g) c) ( 2 / 3 )Mn 7 SiO SiO 2 ( 14 / 3 )MnSiO 3 + O 2 (g) Other metals of interest are Cu, Ni, Mg, which all affect the performance of manganese oxide.

6 Example of combined oxide system: (Fe x,mn 1-x ) 2 O 3 (Fe x,mn 1-x ) 3 O 4

7 Investigated materials in this work (Fe 0.25 Mn 0.75 ) 2 O 3 (Fe) (Fe 0.66 Mn 0.33 ) 2 O 3 (Fe2) MgMnO x (Mg) Mn 2 SiO x (MS) CaMnO 3 (Ca) System Ca+0.67Fe 0.5Ca+0.5Fe 0.67Ca+0.33Fe 1Ca+0Fe System Ca+0.67Fe2 0.5Ca+0.5Fe2 0.67Ca+0.33Fe2 1Ca+0Fe System 4 0Ca + 1Mg 0.33Ca+0.67Mg 0.5Ca+0.5Mg 0.67Ca+0.33Mg 1Ca+0Mg MgMnO x (Mg) System Mg+0.67Fe 0.5Mg+0.5Fe 0.67Mg+0.33Fe 1Mg+0Fe Fe 2 SiO x (FS) System FS+0.67MS 0.5FS+0.5MS 0.67FS+0.33MS Basis for the analysis are the combined manganese oxide oxygen carriers: CaMnO 3, (Fe 0.25 Mn 0.75 ) 2 O 3, (Fe 0.66 Mn 0.33 ) 2 O 3, Mn 2 SiO x, MnMgO x

8 Investigated materials in this work

9 Batch fluidized bed reactor

10 Experiment with Ca 0.33 MnMg 0.67 O x at 950 C

11 Oxygen uncoupling and reactivity of Mn-Mg-O

12 Reactivity with CH 4 at 950 C as a function of Mn/Mg Reactivity and oxygen uncoupling increases with the Mg content

13 System 5: Combination of MnMgOx - (Fe0.25Mn0.75)O3

14 System 6: Combination of Mn2SiOx and Fe2SiOx

15 (Mn 0.67 Fe 0.33 )SiO x with wood char at 950 C Oxygen carrier mass: 10 g Wood char: 0.6 g Fluidizing gas: N 2

16 Conversion of (Mn 0.67 Fe 0.33 )SiO x as a function of time

17 XRD analysis for the systems based on Mn-Mg and Mn-Fe-Si System 1 Molar composition Phases identified in fresh sample Phases identified in used sample 1 MnMgO x Mg 2 MnO 4 Mg 2 MnO 4 1 Mn 1.5 MgO x Mg 2 MnO 4, MgMn 2 O 4 Mn 3 O 4, MgO 1 Mn 2 MgO x MgMn 2 O 4, Mg 2 MnO 4 MgMn 2 O 4 6 (Fe 0.33 Mn 0.67 ) 2 SiO x (Mn x Fe 1-x ) 2 O 3 (B), SiO 2 (Mn x Fe 1-x ) 3 O 4, SiO 2, MnSiO 3 6 (Fe 0.5 Mn 0.5 ) 2 SiO x (Mn x Fe 1-x ) 2 O 3 (B), SiO 2, (Mn x Fe 1-x ) 3 O 4 (Mn x Fe 1-x ) 3 O 4, SiO 2 6 (Fe 0.67 Mn 0.33 ) 2 SiO x (Fe x Mn 1-x ) 2 O 3 (H), SiO 2, (Mn x Fe 1-x ) 3 O 4 n.a.

18 Phase diagram of Mn-Fe-Si system

19 Conclusions A series of combined manganese oxides were prepared by spray-drying and investigated with respect to criteria important for CLC/CLOU. Several systems were identified as promising based on reactivity, uncoupling behaviour and mechanical strength, especially systems based on Mn-Mg and Mn-Fe-Si. For (Mn 0.67 Fe 0.33 ) 2 SiO x the reaction mechanism is primarily through the transition bixbyite to spinel, which is predicted from thermodynamics and confirmed through XRD. The direct reaction (CLC) is probably the dominant oxygen transferring reaction for (Mn 0.67 Fe 0.33 ) 2 SiO x. The binary system of Mn-Mg-O has considerable uncoupling of oxygen and also high reactivity. Oxygen is likely released through transition of Mg 2 MnO 4 to (Mg 2-x Mn 1+x )O 4. As these type of oxygen carriers can be produced with cheap raw materials, they could certainly be of promise for chemical-looping.