Magnesium oxide stabilized magnesioferrites for solar thermochemical fuel production

Transcription

1 Magnesium oxide stabilized magnesioferrites for solar thermochemical fuel production Kelvin Randhir 1, Nathan R. Rhodes, Like Li 1, Nicholas AuYeung 3, David W. Hahn, Renwei Mei and James F. Klausner 1 1 Michigan State University, University of Florida, 3 Oregon State University

2 Motivation for study Fig. Phase diagram of the ZrO FeO system.(source: Bechta et al.journal of nuclear materials. 6 Jan 1;348(1): Loss in activity of zirconia supported ferrites can be attributed to formation molten slag traces upon high temperature reduction. In air High melting point of phases formed on mixing Magnesium oxide with iron oxide. Higher melting point decreases chances of sintering. Lowering the sinteribility may lead higher reactive stability. Fig. Phase diagram of Fe O 3 O-MgO system in Air (source: Jung et al. Journal of Physics and Chemistry of Solids. 4 Oct 31;65(1): )

3 Chemical reactions Fe 3 O 4 and excess MgO mixture upon elongated heat treatment in air forms MgFeO4 + MgO From literature survey the following simplified chemical equations may be envisaged for thermochemical fuel production ( - x) Thermal reduction : MgFeO4 εmgo heat (1 ε)mgo ( x)feo xfeo1.5 O 4 ( - x) ( - x) Oxidation: (1 ε)mgo ( x)feo xfeo1.5 HO/CO MgFeO4 εmgo H/CO (Mg Spinel,Fe,Fe3 )[Mg,Fe,Fe3,Va] O 4 Magnesiowustite(MW) MgO FeO FeO 1.5 With higher Mg content slag formation disappears and magnesio wustite phase forms at lower P O Region of interest Fig. Phases present at 15 C at different Mg/ (Fe + Mg) ratios. source: Jung et al. Fig. Phase diagram of FeO-MgO-FeO3 at 14 C with isobaric lines (Source: Jung et al.)

4 Material synthesis : Solid state reaction Heat treatment in air at 15 for 4 hours Ball milling x mole % Fe 3 O 4 and MgO for 4 hours crushing sieving Particles used for comparative test μm ( to be optimized) Fig. Synthesis of x mole% Fe 3 O 4 in MgO (x=.5, 5, 1 and )

5 CONVERSION (Δm/m total ) CONVERSION (Δm/m total ) CONVERSION (Δm/m total ),15,5 -,5,1,5, -,5 -,1, -,5 -,1 -,15 -, Validation of hypothesis using.5 mole% Fe 3 O 4 in MgO : TGA experiments (a) Tred = 15 C and Tox = 11 C Conversion Temperature (b)tred = 16 C and Tox = 11 C Conversion Temperature (c) Isothermal redox cycles at 15 C on.5 FM Conversion Temperature TEMPERATURE [ ] TEMPERATURE [ ] TEMPERATURE [ ] TGA REDOX test conditions for 1mg material Process reduction Ramp down oxidation Temperature 1 hour a)15⁰c b) 16⁰C c) 15⁰C Argon flow 14 SCCM 5⁰C min hour a)11⁰c b) 11⁰C c) 15⁰C SCCM Ramp up 14 5⁰C min -1 SCCM SCCM Fig. TGA mass change of 1 mg.5fm: (a) reduction at 15 C, oxidation at 11 C (b) reduction at 16 C, oxidation at 11 C (c) Isothermal redox cycles at 15 C. CO flow 1 SCCM

6 O RELEASED [cm 3 g -1 ] H RELEASED [cm 3 g -1 ] H RELEASED [cm 3 g -1 ] (a) P O =1-4 atm x=.5 x=5 x=1 x= H productivity calculated from CALPHAD models O RELEASED [cm 3 g (b) P O =1-5 atm x=.5 x=5 x=1 x= 8, 7, 6, 5, 4, 3,, 1, x= x=1 x=5 x=.5 (a) T RED =145 C at P O =1-4 atm 8, 7, 6, 5, 4, 3,, 1, (b) T RED =135 C at P O =1-4 atm x= x=1 x=5 x= T RED [ C] T RED [ C] Fig. Amount of O released per gram of completely oxidized x mole% Fe 3 O 4 in MgO (x=.5, 5, 1 and ) (a) P O =1-4 atm; (b) P O =1-5 atm, T OX [ C], T OX [ C] Fig. Amount of H released per gram of x mole% Fe 3 O 4 in MgO (x=.5, 5, 1 and ) when reduced at P O = 1-4 atm and oxidized with steam (m HO / m material = 4) (a) T RED =145 C (b) T RED =135 C

7 Maximum expected efficiency O Q material + Q reduction Thermochemical reduction (T=T RED ) Redox material Oxidation (T=T OX ) Q steam η solartofuel,max Q material (1 ε)q Q reduction material H Q η η absorption solid,reduced,t absorption reduction 1 RED n Q H pump σt HHV 4 RED IC H H (1 ε)q solid,oxidised, T steam OX n Q O H oxidation O, T RED H O Ɛ Ɛ Q pump n O η RT pump heatelec P ln P η ref O elec-pump Q pump H + unreacted H O Fig. The heat recovery system envisaged to study the implications of heat recovery on efficiency of the process Q PO η elec-pump.4.7log1 Pref n (HH H steam H O (in) O,T HO,98.15K OX )

8 ,3,5 Theoretical efficiency calculated for mole% Fe 3 O 4 in MgO (a)t RED =145 C, T OX = 8 C,5 (b) m H O(in)/m material =.8, Ɛ=9%,4 η solar-to-fuel,max,,15,1,5 η solar-to-fuel,max,3,,1 T RED =145 C, P O =1-5 atm,,,4,6, m HO(in) /m material T OX [ C] Fig. (a) η solar-to-fuel,max vs. m HO(in) /m material calculated at T OX = 8 C with heat recovery at Ɛ=9,75 and %. (Solid lines: P O =1-4 atm, dashed lines: P O =1-5 atm); (b) η solar-to-fuel,max vs. T OX calculated when Ɛ=9% m HO(in) /m material, (solid lines: T RED =145 C, dotted lines: T RED =15 C).

9 Experimental setup for comparative analysis Fig. Experimental setup for comparison of x (.5,5,1 and ) mole % Fe 3 O 4 in MgO

10 O RATE[ cm 3 g -1 min -1 ] H RATE [ cm 3 g -1 min -1 ],9,8,7,6,5,4 a) O RATE Results of the tube furnace experiments X = X = 1 X = 5 X =.5,3,5,,15 b) H RATE X = X = 1 X = 5 X =.5 REDOX test conditions for 5g material Process reduction Temperature minutes at 135 C Argon flow H O flow 5 SCCM Ramp 5 down 1⁰C min -1 SCCM oxidation minutes at 1 C 5SCCM 1 gmin - 1,3,1 Ramp up 1⁰C min -1 5 SCCM,,1 4 6, Fig. Rate of O and H and produced for the last 3 of the 6 cycles of tube furnace experiments at T red = 135 C and T ox = 1 C for x mole% Fe 3 O 4 in MgO (x=.5, 5, 1 and ) ; (a) O (b) H Material Number of cycles Results Average H production in last 3 cycles (cm 3 g -1 ) Average O production in last 3 cycles (cm 3 g -1 ) x= x= x= x=

11 O RATE[ cm 3 g -1 min -1 ] H RATE [ cm 3 g -1 min -1 ],16,14,1,1,8,6,4, Results of the tube furnace experiments a) O X = X = 1 X = 5 X = TIME [ minutes] Fig. Rate of O and H and produced for the last 3 of the 6 cycles of tube furnace experiments at T red = 145 C and T ox = 1 C for x mole% Fe 3 O 4 in MgO (x=.5, 5, 1 and ) ; (a) O (b) H,45,4,35,3,5,,15,1,5 b) H X = X = 1 X = 5 X = TIME [ minutes] REDOX test conditions for 5g material Process reduction Temperature minutes at 145 C Argon flow H O flow 5 SCCM Ramp 5 down 1⁰C min -1 SCCM oxidation Ramp up Material minutes at Number of cycles 1 C 5SCCM 1 gmin -1 1⁰C min -1 5 SCCM Results Average H production in last 3 cycles (cm3g-1) Average O production in last 3 cycles (cm3g-1).5fm FM FM FM

12 CONVERSION (Δm/m total ) H and O YIELD [cm 3 g -1 ] Reactive stability of mole%fe 3 O 4 in MgO,1,5, -,5 -,1 8 Conversion Temperature Fig. TGA data for 1 mg of FM over cycles. ( T RED =135 C T OX =1 C) Stable mass change corresponds to 8.9 cm 3 g -1 of CO TEMPERATURE [ ] TGA REDOX test conditions for 1mg material Process reduction Temperature 6 minutes at 145 C Argon flow CO flow 14 SCCM Ramp 14 down 5⁰C min -1 SCCM oxidation Ramp up 6 minutes at 1 C SCCM 1 gmin -1 5⁰C min SCCM 6 4 HYDROGEN YIELD OXYGEN YIELD CYCLE NUMBER Fig. H and O produced by 5 g of mole%fe 3 O 4 in MgO in the tube furnace experimental facility ( T RED =145 C T OX =1 C) Tube furnace REDOX test conditions for 5g material Process reduction Temperature minutes at 145 C Argon flow H O flow 5 SCCM Ramp 5 down 1⁰C min -1 SCCM oxidation minutes at 1 C 5SCCM 1 gmin -1 Ramp up 1⁰C min -1 5 SCCM

13 H RATE [ cm 3 min -1 g -1 ] H YIELD [ cm 3 g -1 ] Comparison of H productivity of mole%fe 3 O 4 in MgO with ceria 1,8 1,6 (a)h FM 145 red, 1 ox 14 1 (b)h yield 1,4 1, 1 Ceria- 15 red, 1 ox Ceria red, 1 ox 1 8 FM 145 red, 1 ox Ceria 15 red, 1 ox,8 6 Ceria 145 red, 1 ox,6,4, Fig. Comparison of (a) and (b) yield of H produced from CeO and FM in the tube furnace experimental setup. CeO is reduced at 15 and 145 C and oxidized at 1 C. mole%fe 3 O 4 in MgO is reduced and oxidized at 145 C and 1 C, respectively.

14 P O [atm] Advantage : higher P O requirement for mole%fe 3 O 4 in MgO compared to ceria,16,14,1,1 Ceria 15 red; 1 ox Ceria 145 red; 1 ox FM 145 red; 1 ox Equation used for estimating P O P O = P atm O V O V +V Ar,8,6,4, Fig. Comparison of estimated partial pressure of O during thermal reduction of FM and ceria. V Ar = 5 SCCM for 5 g of material P O required for thermal reduction of mole% Fe3O4 in MgO is higher than that of ceria. This indicated lower energy required for vacuum pumping.

15 Disadvantage: H productivity for mole% Fe 3 O 4 in MgO drops with lower H O flow s H RATE [ cm 3 min -1 g -1 ],6,5,4,3,,1 HO(in)=1.5 g/min HO(in)=1 g/min HO(in)=.8 g/min Oxidation s are very slow compared to ceria. Higher H O flow s are required to enhance the fuel productivity Fig. H production of FM at 1 C at three different steam injection s (Reduction at 145 C).

16 CO YIELD [ cm 3 g -1 ] Attempts to improve productivity % mole Fe3O4 in MgO 33 % mole Fe3O4 in MgO 1% molefesio3 in MgO % mole LiFeO in MgO % mole LaFeO3 in MgO 6 wt% CeO in mole% Fe3O4 in MgO CYCLE NUMBER Fig. CO production of doped magnesioferrite materials ; From TGA ; reduction at 135 C (1hour) and oxidation at 1 C (1hour)

17 Conclusions on magnesioferrites for thermochemical fuel production Reactive stability mole % magnetite in magnesium oxide was found to be suitable for thermochemical water and carbon dioxide splitting. Material has produced 6.1 cm 3 g -1 when reduced at 145 C and oxidized at 1 C. H can be increased by increasing oxidation time or steam input. Oxygen partial pressure required for reduction is higher compared to ceria and reduction kinetics are faster. The material has poor oxidation s compared to ceria and needs larger oxidation time for achieving high H productivity. Rare earth dopants and other dopants such as silica and lithium did not improve the fuel production capacity of the material

18 Thank you