Catalysis for clean renewable energy technologies. Moshe Sheintuch Department of Chemical Engineering, Technion, Haifa, Israel

Transcription

1 Catalysis for clean renewable energy technologies Moshe Sheintuch Department of Chemical Engineering, Technion, Haifa, Israel

2 Catalysis for clean renewable energy technologies 1. Introduction 2. Hydrogen production Steam reforming Dry reforming Autothermal reforming Novel reactor concepts: Membrane Reactor ; Millisecond-contact Reactor; 3. From renewable sources to fuels 4. Fuel Cells 5. Hydrogen Storage Outline

3 15% NiO and 85% MgAl2O4 CATALYTIC SCALES (1)

4 CATALYTIC SCALES (2) Fcc(110): The surface atoms on a more open ("rougher") surface have a lower CN - this has important implications when it comes to the chemical reactivity of surfaces fcc (111): All surface atoms are equivalent and have a relatively high CN The surface offers adsorption sites : On-top sites Bridging sites, between two atoms Hollow sites, between three atoms Actual solids: (i) an angled corner (ii) a spherical tip

5 2. Hydrogen Production Methane Steam Reforming CH H 2O = CO 3H 2 ΔH 1 = 206[ kj CO + H + 2O = CO2 H 2 mol 1 ] CO + H + 2O = CO 2 H 2 ΔH 2 = 41[ kj mol 1 ] CH 2 + H 4 + H 2O = CO2 4 2 ΔH 3 = 165[ kj mol 1 ] 1. Equilibrium limitations Steps: Catalyst Selection Reactor Design Drawbacks: Drawbacks: Alternatives: Dry Reforming Autothermal Design 2. CO is poisonous for fuel cells 3. Heat supply is required (combustion, nuclear?) 4. CO2 separation.

6 Motivation Fuel cells are more effective Fuel Cells than internal combustion engines and Hydrogen Fuel cells are quiet and pollution-free; Extremely pure hydrogen is required for effective fuel cell operation Hydrogen has the highest energy content per unit of weight of any known fuel; there is no hydrogen fuel infrastructure Hydrogen fuel is hard to transport Hydrogen can be produced on-board using a smallscale catalytic membrane reactor

7 Steam reforming: Catalyst selection depending on hydrogen source 1-st metal 2 nd - metal Support Promoter Reforming reaction Hydrogen source Co, Ru, Pt, Pd, Rh Al 2 O 3 Rare earth oxide, ZrO 2, IIA oxides Dry R, steam R, Gaseous hydrocarbons: C 1 C 4 Ni, Pt, Ru, Pd, Rh Co, Mo, Re CeO 2, La 2 O 3, ZrO 2, Ce doped ZSM5, Ce/Zr/La doped Al 2 O 3 Gd, Sm All reforming reactions C 8 C 18 Cu Co CeO 2, ZrO 2, Al 2 O 3 ZnO, ZrO 2 Steam R Methanol Pt, Pd, Ni Ru, Cr, Cu, Fe TiO 2, ZnO, La 2 O 3, MgO Li, Na, K Steam R, OSR Ethanol Adapted from Saxena et al, Energy&Fuel, 2007

8 Catalysis for clean renewable energy technologies: 2. Hydrogen production Mechanism of SR on Ni-based catalysts: Theoretical and experimental studies Carbon-induced catalyst deactivation is one of the main problems. DFT calculations demonstrate that the carbon tolerance of Ni can be improved by Ni-containing surface alloys that preferentially oxidize C atoms rather than form C C bonds and have a lower thermodynamic driving force, associated with the nucleation of carbon atoms on low-coordinated Ni sites. Using the molecular insights obtained in the DFT calculations, Sn/Ni surface alloy was identified as a potential carbon-tolerant reforming catalyst in the steam reforming of methane, propane, and isooctane. (a) Transmission electron micrograph of a Ni particle covered by carbon. (b) DFT-calculated reaction energies for various elementary steps in steam reforming of methane on Ni(111). (from E. Nikolla et al, J. Catal. 2007)

9 Membrane reactor concept Schematic Representation: A typical lab-scale MR: A+B C+D A, B, C, D D D D A, B A+B C+D Shift in reaction equilibrium 1 High perm-selectivity yields high purity products 2 Changes in total olefin yield (f), cracking (y3) and isomerisation (yn) products during isobutane dehydrogenation in a Pd-tube packed with catalyst at 500 o C (Sheintuch and Dessau, 1996)

10 H 2 Separation Membranes Dense Metallic Pd, Pd alloys Supported Pd Almost 100% selectivity, high fluxes Nanoporous Ceramic Silica Zeolitic Lower selectivities and fluxes Well-developed preparation technology Under-development preparation technology High cost Potentially low cost

11 MEMBRANE ASSISTED FLUIDIZED BED REACTOR FOR H 2 PRODUCTION BY STEAM REFORMING OF CH 4 C. S. PATIL, et al, Chem. Eng. Research and Design, 2006, (Pd/Inconel membrane) CO selectivity is strongly suppressed due to the selective extraction of H 2.

12 Thermal Balancing Methane Steam Reforming (MSR) CH 2 + H 4 + H 2O = CO2 4 2 ΔH 3 = 165[ kj mol endothermic 1 ] Methane Oxidation (MOx) CH4 + 2 O2 = CO2 + 2H2O Δ = 803[ kj mol H Ox exothermic 1 ] The heat required for the endothermic reaction is supplied by the exothermic reaction reaction coupling 3 concept

13 MEMBRANE REACTOR Figure 2: Schematic diagram of the double-jacketed membrane reactor (Hou et al, CES 54, , 1999.) 900h of operation.

14 Combining Membrane Separation Reactor schematic: and Thermal Balancing Cross-sectional view: H 2 N 2 CO 2 +H 2 O Membrane compartment CO 2 H 2 CH 4 + air CH 4 H 2 O Endothermic compartment (steam reforming) Exothermic compartment (catalytic oxidation)

15 Reactor Analysis CH 2 + H 4 + H 2O = CO2 4 2 Y M SR = ( F Y Y = 4(1 P / ) 2 t P M SR H, out / Fmf ) / max max t

16 Challenges: 1.Experimental verification. 2. Cheaper durable membranes. 3. CO2 sequestration. 4. Integrated vs. distributed design. 5. Alternative designs: Autothermal

17 2. Hydrogen production: Methane Oxidative Steam Reforming Addition of small amount of Pd to Ni 0.2 Mg 0.8 Al 2 O 4 enhanced the catalytic activity and stability for the oxidative SR of methane, where Ni 0.2 Mg 0.8 Al 2 O 4 deactivated due to the oxidation of Ni and carbon deposition. Formation of Pd Ni alloy located preferentially on the surface improved the reducibility of Ni and the resistance to the carbon deposition. Surface modification of Ni with Pd by a sequential impregnation method (Pd/Ni) was effective for the suppression of hot-spot formation during oxidative SR of methane (from K. Tomishige et al 2007)

18 Thermo-catalytic decomposition, TCD TCD process, to produce hydrogen and carbon, is an alternative to reforming processes for small-to-medium size facilities TCD of methane has several advantages over SMR process: no CO is obtained and the production of the ultra pure hydrogen is simpler and cheaper. Although theoretical hydrogen yield for SMR is twice of that for TCD, high reaction endothermicity and CO2 sequestration would significantly reduce the net yield of hydrogen produced by SMR. Metallic and carbonaceous catalysts have been used., The use of carbon catalyst offer several advantages: (i) higher fuel flexibility, (ii) lower price and (iii) the carbon formed can be used as catalyst precursor. But the direction of the ethanol reaction changed, when carbons were applied as a support.

19 Reaction pathways steam reforming (for ethanol) Reaction Steam reforming Steam reforming Dehydrogenation Dehydration Decomposition Methanation Water gas shift reaction (WGSR) Equation C 2 H 5 OH+3H 2 O 2C O 2 +6H 2 C 2 H 5 OH+H 2 O 2CO +4H 2 C 2 H 5 OH C 2 H 4 O+H 2 C 2 H 5 OH C 2 H 4 +H 2 O C 2 H 5 OH CO+CH 4 + H 2 CO+3H 2 CH 4 +H 2 O CO+H 2 O CO 2 +H 2 Remarks Ideal pathway, the highest hydrogen production Undesirable products, lower hydrogen production Reaction pathways for hydrogen production in practice Undesired pathway, main source of coke formation Coke formation, low hydrogen production Reduce coke formation, enhance hydrogen production

20 List of steam reforming using noble metal catalyst (for ethanol) Catalyst Suppo rt Temp. (K) Steam/Etha nol molar ratio Ethanol conversion (%) Hydrogen selectivity (%) Rh (1 wt%) γ-al 2 O : Ru (1 wt%) Pt (1 wt%) Pd (1 wt%) Rh (3 wt%) MgO :1 99 (10 h) 91 Pd (3 wt%) 10 (10 h) 70 Rh (2 wt%) CeO :

21 Cost and Energy Efficiency from the Selected Technologies to Produce Hydroge plant size and technology central plant natural gas steam reforming coal gasification midsize plant methane steam reforming biomass gasification distributed plant water electrolysis natural gas steam reforming water electrolysis cost ($/kg H 2 ) a energy efficiency (%) 66 b 60 c 70 d c 27 c c e

22 Catalysis for clean renewable energy technologies: 3. From renewable sources to fuels Current methods for transformation of biomass into gaseous and liquid fuels (fromg. Huber and J. Dumestic, Catal. Today, 2006

23 Biodiesel from Low Cost Vegetable Oil and Waste Fats:

24 Various biodiesel production TE processes reaction time reaction conditions catalyst free fatty acids yield removal for purification waste glycerin purity process homogeneous catalytic method h C acid or alkali saponified products normal to high methanol, catalyst, and saponified product wastewater low complicated heterogeneous catalytic method h C metal oxide or carbonate methyl esters normal methanol none low to normal complicated Adapted from D. Mohan, Energy&Fuels,2006 enzymatic method 1-8 h C immobilized lipase methyl esters low to high methanol or methyl acetate none normal or triacetylglycerol as byproduct complicated SCMeOH method s C none methyl esters high methanol none high simple

25 Aqueous-phase reforming (ethylene glycol at 483 K and 22 bar ) R.R. Davda, J.W. Shabaker, G.W. Huber, R.D. Cortright and J.A. Dumesic, Appl. Catal. B Environ. 43 (2002), p. 13.

26 Conclusions 1. Hydroprocessing of vegetable oils using transition metal type catalysts is being produced commercially. One of the main drawbacks is that it it requires high pressure. It produces a diesel like products composed of linear hydrocarbons. 2. The use of molecular sieve type catalysts is very promising for the conversion of vegetable oils to highly aromatic gasolines. 3. Heterogeneous catalysis is the backbone of the chemical / petrochemical industry. Few biorefining processes use heterogeneous catalysis. The processing of biomassderived feedstocks is different due to low thermal stability and a high degree of functionality (typically being hydrophilic in nature), thus requiring unique reaction conditions, such as aqueous-phase processing. 4. Catalytic pyrolysis of vegetable oils can be grouped into : (1) molecular sieve catalysts, (2) activated alumina catalysts, (3) transition metal catalysts and (4) sodium carbonate. 5. The applications of novel solid feed mixtures for pyrolysis, catalysts, co-gas feeds, and related approaches have not been explored very much. 7. The electricity costs from biomass, geothermal and solar sources are within the range of US$ 7 25 cents/kwh, compared to the conventional (coal, natural gas, etc.) electricity costs of US$ 4 6 cents/kwh.

27 Hydrogen storage in carbon nanotubes

28 Storage capacity

29 Concluding remarks 1. Short term effort will probably yield small gains using SR with new process designs. 2. Long term effort should be addressed to renewable resources. Its economic advantages still debated, may not be economical here (water). 3. Catalysis is still an art, basic research that allows computational catalyst selection is required.