Iron oxide-miec hybrid materials for hydrogen production using chemical looping technologies Cristina Dueso, Ian S. Metcalfe

Transcription

1 Iron oxide-miec hybrid materials for hydrogen production using chemical looping technologies Cristina Dueso, Ian S. Metcalfe 5 th High Temperature Solid Looping Network Meeting 2-3 September 2013 Cambridge, United Kingdom

2 Hydrogen production Steam Methane Reforming (SMR) Ni CH 4 + H 2 O + 3 H 2 H 1100 K = kj/mol Combustion products H 2 O 2, H 2 O, N 2, O 2 CCS Shift Reactor Chemical absorption H 2 O H 2,CH 4, 2, Air PSA H 2 CH 4 PSA offgas (CH 4, H 2,, 2 ) CH 4 + H 2 O 2 diluted in the combustion gases Energy penalty

3 Hydrogen production Steam Methane Reforming (SMR) Autothermal Methane Reforming (ATR) CH 4 + ½ O H 2 Reforming gas, H 2, 2, CH 4, H 2 O Shift Reactor H 1100 = kj/mol H 2 O H 2 O N 2 ATR Hydrogen separation H 2 ASU Air O 2 CH 4 + H 2 O CH 4, H 2,, 2 High cost and energy consumption

4 CLR Chemical looping reforming Air reactor N 2 + O 2 unreacted Cyclone Fuel reactor CH 4 + MeO + 2 H 2 + Me DH 1200K =211 kj/mol CH 4 + H 2 O + 3 H 2 DH 1200K =226 kj/mol Reactor de oxidación 4 Me + 2 O 2 4 MeO DH 1200K =-234 kj/mol H 2 O Shift Reactor Hydrogen separation H 2 Fuel reactor 2 CH 4 + H 2 O Air

5 Fuel reactor Steam reactor 2 H 2 Steam-iron process H 2 O Fe 3 O FeO FeO + H 2 O Fe 3 O 4 + H 2 DH 850 ºC = 12.7 kj/mol DH 850 ºC = kj/mol

6 2 H 2 Steam-iron process Fuel reactor Steam reactor Air reactor N 2 (+O 2 ) H 2 O Air Fe 2 O Fe Fe + 4 H 2 O Fe 3 O H 2 4 Fe 3 O 4 + O 2 6 Fe 2 O 3 DH 850 ºC = kj/mol DH 850 ºC = kj/mol DH 850 ºC = kj/mol

7 Steam-iron process o Different configurations have been proposed for the steam-iron process, such as fixed bed or circulating fluidized bed reactors. Circulating fluidized bed reactors Fixed bed reactor 2 H 2 N 2 (+O 2 ) 2 H 2 N 2 (+O 2 ) H 2 O Air H 2 O Air

8 Steam-iron process o o Different configurations have been proposed for the steam-iron process, such as fixed bed or circulating fluidized bed reactors. Iron oxide has been traditionally used as OCM in the steam-iron process. Favourable thermodynamics Low cost & environmentally friendly Slow reaction kinetics with carbonaceous fuels Low stability after several redox cycles

9 CL-Membranes 2 H 2 + O 2 H 2 O H 2 + O H 2 O Hydrogen is produced by water splitting with both methods No further purification of hydrogen is needed

10 CL-Membranes 2 H 2 + O 2 H 2 O H 2 + O H 2 O The same materials could be used: PEROVSKITES ABO 3 A B O

11 Perovskites Lower H 2 production during the first cycles compared to Fe-based OCM H 2 production more stable with La 0.7 Sr 0.3 FeO 3-d (LSF731) FeAl 2 O 4 No structural changes after use for 150 redox cycles A. Murugan, A. Thursfield, I.S. Metcalfe, Energy & Environmental Science 4 (2011) 4639

12 Objective o To obtain materials with hybrid structures composed by iron oxide and MIEC, such as LSF731 and CeO 2, to improve the stability and the reactivity for hydrogen production using the steam-iron process. MIEC Iron oxide Red. 2 Ox. H 2 O H 2 The MIEC material facilitates the O 2- ion mobility and transport from the bulk to the fuel due to the presence of oxygen vacancies

13 Material preparation LSF731 Fe 2 O 3 CeO 2 30% Fe 2 O 3 Pellets were prepared in a press using LSF731 or Fe 2 O 3 powders or a mixture of CeO 2 and Fe 2 O 3 Calcination at 1200 o C for 4 hours Crushing and sieving ( mm)

14 Material preparation LSF wt.% Fe 2 O 3 Modified Pechini method 0.7 [La(NO 3 ) 3 6H 2 O] Sr(NO 3 ) 2 + Fe(NO 3 ) 3 9H 2 O C 6 H 8 O NH 4 NO 3 La 0.7 Sr 0.3 FeO H 2 O N 2 Iron oxide particles (20-60 nm)are added to the solution to get the desired concentration in the final material 30 wt.% Fe 2 O 3 Calcination at 800 o C for 2 hours to convert the amorphous gel into crystalline LSF731 Pellet formation, calcination at 1200 o C, crushing and sieving

15 Characterization SEM-EDX x 1E3 cps Fe Sr O La Distance / µm Iron was accumulated in specific areas, confined inside the LSF731 structure.

16 Experimental Thermogravimetric analysis Temperature programmed reduction o o C, 5ºC/min o Reduction: 5% H 2 in N 2 Operating conditions: o T = 850 o C o Reduction: 10% in N 2,, 30 min o Oxidation: 10% 2 in N 2, 20 min o The samples were fully oxidized in a third stage with air Liu W, Dennis J.S., Scott S.A. Ind Eng Chem Res 2012, 51, The reducible oxygen of the solids was determined from a 3-hour reduction experiment using 5% H 2 in N 2 as fuel

17 Weight loss (mg) TPR 0 Iron oxide Fe 3 O 4 FeO Fe Temperature (ºC) Solid conversion Iron oxide can be fully reduced to metallic iron at temperatures below 900 ºC

18 Weight loss (mg) TPR LSF Temperature (ºC) Solid conversion The flat line corresponds to the maximum amount of oxygen released in a 3-hour reduction with 5% H 2 in N 2 at 850 C 6% O in LSF731 is used in the reduction At temperatures above 850 ºC, LSF731 is reduced again. Oxygen strongly bound in the lattice of the LSF structure Easy to reduce at temperatures as low as ºC Oxygen in the surface of the LSF particle

19 Weight loss (mg) TPR LSF731 Pec 30% Fe 2 O Temperature (ºC) 3 3 different reaction steps

20 Weight loss (mg) TPR LSF731 Pec 30% Fe 2 O 3 Step At temperatures below 500 ºC, 1 LSF731 LSF731 is reduced creating paths to allow the access of the fuel to the particle inside and Fe 2 O 3 reduction O 2- O 2- O Temperature (ºC) O 2- O 2-3 different reaction steps O 2- O 2- LSF731 Fe 2 O 3 O 2- O 2- O 2-

21 Weight loss (mg) TPR LSF731 Pec 30% Fe 2 O 3 Step Iron oxide is completely LSF731 reduced The black line corresponds to the maximum amount of 2 reducible O at 850 ºC Fe 2 O Temperature (ºC) 3 different reaction steps LSF731 Fe 2 O 3

22 Weight loss (mg) TPR LSF731 Pec 30% Fe 2 O 3 Step LSF731 in the particle is LSF731 reduced again at temperatures higher than 850 ºC Fe 2 O Temperature (ºC) 3 O 2- O 2-3 different reaction steps O 2- O 2-

23 Solids conversion Reactivity Reduction LSF731 LSF Pec-30 Fe 2 O 3 LSF reacts very fast but only 6% of the total oxygen is available for the reaction at this temperature CeO 2 30% Fe 2 O 3 Fe 2 O 3 The reaction between iron oxide and is very slow, as expected Time (min) An increase in the reactivity of the iron oxide is observed when Fe 2 O 3 is included in the LSF matrix The use of CeO 2 as support also increases the reactivity of the iron oxide. In this case, 10% of the oxygen in the ceria is reducible

24 Solids conversion Hydrogen production Oxidation 1.0 Clear improvement of the reactivity in the OCM with hybrid structure dn O /dt LSF Pec-30 Fe 2 O CeO 2 30% Fe 2 O dn O2 /dt Fe 2 O 3 LSF Time (min) Time (min)

25 Conclusions Hybrid materials composed by MIEC, LSF731 and CeO 2, and 30 wt.% Fe 2 O 3 were prepared by a modified Pechini method and mechanical mixing. The use of MIEC together with iron oxide increases the reactivity during both the reduction with and the oxidation with 2 with respect to LSF731 or iron oxide alone. The amount of hydrogen produced is higher. The MIEC material facilitates the O 2- ion mobility and transport from the bulk to the fuel due to the presence of oxygen vacancies A reaction model has been proposed for the hybrid materials, including several steps. Initial reaction of the LSF creates pathways for the fuel and the oxygen to go inside the OCM particles that allow Fe 2 O 3 reduction.

26 Many thanks to Dr. Stuart Scott, Wen Liu and Mohammad Ismail from Cambridge University Financial support: Iron oxide-miec hybrid materials for hydrogen production using chemical looping technologies C. Dueso, I.S. Metcalfe 5 th High Temperature Solid Looping Network Meeting 2-3 September 2013 Cambridge, United Kingdom

27 Any questions? Iron oxide-miec hybrid materials for hydrogen production using chemical looping technologies C. Dueso, I.S. Metcalfe 5 th High Temperature Solid Looping Network Meeting 2-3 September 2013 Cambridge, United Kingdom