Electrically Mediated Hydrocarbon Conversion Processes

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1 Electrically Mediated Hydrocarbon Conversion Processes Guido P. Pez 3/6/16 Theme: Conversion of saturated C 1,C 2 &C 3 HC s to chemicals by any means that involves electricity. 1. Limiting economics. 2. Direct hydrocarbon fuel cells (DHCFC s): Chemicals from FC s? 3. Electrochemically promoted catalysis (EPC): Methane to syn-gas (CO/H 2 ) via (non-faradaic) Electroreforming. 4. Methane to C 2 HC s via electrical plasma processes.

2 1. Limiting Economics Natural gas $2.67 / MMBtu (2015 ave. price) Ideally 0.9 cents/kwh Electricity cost: 8-12 cents/kwh (Pa 2015) Currently NG,lowest cost fuel for electric power generation. But electricity is a relatively costly reagent if it s required for endothermic hydrocarbon (HC) conversion processes (eg CH 4 to C 2 HC s or syn gas via plasma). Consider first an (exothermic) selective anodic oxidation of HC s that provides both electricity and chemicals- in a tailored direct hydrocarbon fuel cell (DHCFC)* (*Review:) F. Alcaide, P.-L. Cabot, E. Brillas, J. of Power Sources 153 (2006) 47 )

3 Fuel Cell Fundamentals: The H 2 -O 2 FC Figure from p 62 of Li s book Figure 1 on p 14 of Gasteiger H 2 + ½ O 2 = H 2 O(g) E Rev = 1.17 V 80C Rev. Efficiency (η r ) = (ΔH - TΔSS)/ΔH Xianguo Li Principles of FC s Taylor &Francis Publ at Polarization Curve ( E Cell vs Current) Losses from: mass transp. res.( ηtx), Ohmic.res.,but mainly slow O 2 redn. kinetics(η ORR ). Gasteiger, Wagner et al, Appl. Cat. B 56 (2005), 9

4 Thermodynamically feasible FC s for chemicals and energy cogeneration 1. Ethane to ethylene. C 2 H 6 + 1/2O 2 = C 2 H 4 + H 2 O(g) 2. Methane coupling to ethane. 2CH 4 + O 2 = C 2 H 6 + H 2 O(g) 3. Methane coupling to ethylene. 2CH 4 + O 2 = C 2 H 4 + 2H 2 O(g) 4. Methane to methanol. CH 4 + ½ O 2 = CH 3 OH(g) E = V at ( 80 C ); V (500 C) E = V at 80 C; V (500 C) E= V at 80 C ; V (500 C) E= V at 80 C ; V (500 C) Hydrogen/Oxygen FC. H 2 + ½ O 2 = H 2 O (g) Methane /Oxygen FC CH 4 + 2O 2 = CO 2 +2H 2 O(g) E= 1.17 V at ( 80 C) ; V (500 C) E = V at (80 C) ; V (500 C)

5 Ethane to Ethylene FC : C 2 H 6 + 1/2O 2 = C 2 H 4 + H 2 O See Figure from Abstract, for the overall cell design. For performance data see Fig 4A on p 764 Fig 5,on p765 Anode: (Pr 0.4 Sr 0.6 ) 3 (Fe 0.85 Mo 0.15 ) 2 O 7 /Co-Fe alloy nanoparticles C 2 H 6 C 2 H 4 + 2H + + 2e - H + Electrolyte : BaCe 0.7 Z r0.1 Y 0.2 O 3-δ Cathode: (La 0.6 Sr 0.4 ) 0.95 Co 0.20 Fe 0.80 O 3-δ O 2 + 2e- + 2H + 2H 2 O Button cell, 0.2 cm 2, A replacement for steam-ethane cracking? S.Liu, K.T. Chuang and J-L. Luo (Univ. of Alberta), ACS Catal. 2016, 6, 760 By-Products: CH 4,CO(trace),no CO 2

6 Methane to Ethane-Ethylene FC Fig 1 Cell Schematic p1462 Fig 5 on p 1466 YSZ (Yttrium stabilized zirconia) tubular. Membrane. Surface Area = 148 cm2; 1.5 mm thick Anode Cat.: La 1.8 Al 0.2 O 3 O 2- ion conducting YSZ tube electrolyte Cathode Cat: La 0.85 Sr 0.15 MnO 3 CH 4 Conversion and Products Selectivity vs Temperature. (Max. 91% Selectivity for C 2 s, at 23.7% Conversion of CH 4 at 1273K ). Note: C 2 H 4 >> C 2 H 6 Fig 9 (b) on p1468 W. Kiatkittipong et al, J. Chem. Eng. Japan 2004,37(12), 1461 (Data here) M.R. Quddus et a, Chem. Eng. J. (Amsterdam) 2010,165,639 (Review, modelling, FC diagram) Cell voltage and power vs current

7 Electrolytically induced catalytic methane to methanol conversion. No reports of a direct methane + ½ O 2 to methanol FC (E= V at 80 C). However,: A. CH 4 + ½ O 2 (+ Power) CH 3 OH (+ CO 2 ) B. CH 4 + H 2 O (+ Power) CH 3 OH + H 2 (+ CO 2 ) Cathode : ½ O 2 + 2H + + 2e- H 2 O Cathode : 2H 2 O + 2e- 2OH - +H 2 ; Pt cat H + H 2 O OH - H 2 O Anode : CH 4 + H 2 O CH 3 OH + 2H + +2e- (+CO 2 ) Anode : CH 4 +2OH - CH 3 OH + H 2 O + e- (+CO 2 ); Ni(OH) cat. (V2O5/SnO2) Fig 3 (c) on p237 of Lee Hibino Methanol conc. vs anode (applied) potential using V 2 O 5 /SnO 2 anode for wt % V 2 O 5,at 100 C. Max: 61% current efficiency and 88% selectivity for CH 3 OH B. Lee, T. Hibino, J. Catal. 2011, 279, 233 See also: Anodic oxidation of CH4 CH 3 OH,HCHO,C 2 H 5 OH over NiO-ZrO 2 ; CO -- 3 [O]- donor electrolyte. N. Spinner,W.E. Mustain Feed CH, J. 4 (top curve), and Products : CH 3 OH, CO 2 and Electrochem. Soc. 160 (11) F1275 (2013) O 2 at anode. Qinbai Fan, US Pat. Appl. 2015/

8 Electrode catalyst design: The Direct Methane FC Figures 3 D & E Figure: Schematic of cell design from Abstract Voltage-Current Polarization Curve for OMC tethered catalysts. Key Novelty : Pt complex, molecular CH 4 activation catalyst,tethered to an ordered mesoporous carbon (OMC) support. CH 4 +2H 2 O = CO 2 + 8H + +8e- 2O 2 + 8H + + 8e- = 4H 2 O Net: CH 4 +2O 2 = CO 2 + 2H 2 O(g), E 1.033V at 80 C M. Joglekar, V. Nguyen, S. Pylypenko, C. Ngo., Q. Li,M.E. O Reilly, T.S. Gray, W.A Hubbard, T. B. Gunnoe, A. M. Herring, B.G. Trewyn J. Am. Chem. Soc. 2016,

9 Electrochemical Promotion of Catalysis (EPOC) or Non-Faradaic electrochemical modification of catalytic activity (NEMCA) (a) Faradaic : Stoichiometric use of electron as a reactant, (a) (b) Eg n= 12el / mole C 2 H 4 reacted. (b) Non-Faradaic: Non- stoichiometric use of electron, with n potentially much larger. (Ʌ > 1,) often Ʌ > > 1 Oxide ion conducting YSZ disc, Pt catalyst-electrode coating. Following C 2 H 4 Oxidation rate as a function of applied potential. Faraday Efficiency, Ʌ = r/r e = 74,000 r/r 0 = 25 Mechanism: (as for CO, CO 2 reactants on Pt / YSZ solid el.) Figure 3 of K. p887 Fig 1 p866 of Katsaounis K. Katsaounis J. Appl. Electrochem ; C.G. Vayenas et al (2001) in Electrochemical activation of catalysis Kluwer/Plenum. Pub. Ethylene Oxidation rate increases of up to 25 X ( r) with applied potential of ca. 0.6 V (375 C)

10 Non- Faradaic Electroreforming of methane to syn. gas and H 2 Steam-methane reforming (SMR), current practice: CH 4 +2H 2 O CO + 3H 2 +H 2 O Ni cat., then WGS to 4H 2 +CO 2 Endothermic React. Heat from external methane combustion. Tubular metal alloy reactors, at ca. 30 atm. Pressure and ca. 800 C. Electroreforming: From Fig 6 p121. Data-results from Cat. Today From Cat. Today 2011 Reactor Schematic p118 CH 4 Conv. vs T(K) for Pt/metal oxide cats. Products yield vs T(K) for conventional (left), Electroreforming Apparatus. Open : Conv. SMR : Dark : Electroreforming. and electroreforming (right), for which the E = 500 V -800 V for I= 3mA of Dramatic decrease in reaction temperature yield exceeds the calc. thermo. equilibrium. Dark current ;Elect. Eff % NEMCA Effect. Faradaic Efficiency, Ʌ (reacted Y. Sekine, et al, (Waseda Univ, Jpn) Catalysis Today, 2011, 116, 125, CH4/mole- electron)= 84 for Pt/Ce 0.5 Zr 0.5O2 cat. Y. Sekine et al, Int. J. of Hydrogen Energy 2013, 38,3003.

11 Electrical Discharges/Plasma for Methane Conversion Methane to C 2 H 2 in spark discharge Methane oxidative coupling in corona discharge, +/- catalyst From Kado Fig 1 p1378 Fig 2 Corona Schematic Reactor: +/- 30 kv, 0-10 ma,0-400hz Feed: CH 4, 10 ccm,ambient T, P. Products: C 2 H 2 (90% sel.) ; C 2 H 6,C 2 H 4 (4 % Sel) El. Efficiency ~ 10% (ie 10X of energy needed for react. endotherm.) S. Kado, K. Uraski. Y. Sekine,K. Fujimoto, Fuel 82, 1377 (2003) Feed: CH 4 /O 2 = 100 sccm Catalyst: Sr/La 2 O 3, T= 823K Products: C 2 H 4,C 2 H 6 Yields (%): Cat. Alone. 0.4% Corona alone. 3.6 % ( 6% conv.) Corona + cat. 5.6 % (14% conv) El. Efficiency At 5.6 W input,~ Heat value of conv. CH 4 A. Marafee, C.Liu, G.Xu, R. Mallison,L. Lobban Ind.Eng.Chem.Res. 1997,36,632

12 Electrolyte : Polymer (PEM) Phosphoric Acid ? Solid Oxide, ceramic (SOFC) Molten Carbonate Carrier Ion: H +, CO -- 3 H + O --, H + CO -- 3 /CO 2 Temperature: RT- 200 C C C C C Features: Commercial (H + ) Commercial Key Issues ORR Acid loss, ORR High Temps., Materials Hydrocarbon/Air Fuel Cell Systems. Reports for chem. products (currently) only from SOFC s (Faradaic processes) With Electric Power Co- Generation (All exothermic conversions) Potential for: Hydrocarbons Chemicals via Electrocatalysis (Non-Faradaic processes ) With Electric Power Consumption (Exothermic or endothermic conv.) Electrochemical Promotion of Catalysis (EPC) : Dramatic rate enhancement in reduction, oxidation & isomerization reactions. Triode operation in SOFC s. Potentially lowest power consumption. Issue: Practical reactor design Electroreforming for endothermic CH 4 to syn gas &H 2. Large rate increases and improved conversion equilibria, at lower temps. Electricity use efficiency, only 15-25% Plasma processes for methane to syn gas. Key issue : High power usage.

13 Thank you to Andy Herring ( Co. School of Mines) for valuable discussions.

Ceramic Processing Research

Journal of Ceramic Processing Research. Vol. 8, No. 3, pp. 224-228 (2007) J O U R N A L O F Ceramic Processing Research Computer modeling of single-chamber SOFCs with hydrocarbon fuel Jeong-Hwa Cha 1,2,