Emerging Opportunities for Novel Approaches to Natural Gas Conversion, Electrocatalysis: Guido Pez, consultant

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”.

1. Limiting Economics

Natural gas (NG) @ $2.67 / MMBtu (2015 ave. price)

Ideally

Electricity @ 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)*

Fuel Cell Fundamentals: The H

₂

-O

₂

FC

H₂ + ½ O₂ = H₂O(g) E_Rev = 1.17 V at 80C

Rev. Efficiency (η_r ) = (ΔH - TΔ�)/ΔH

Polarization Curve ( E Cell vs Current) Losses from: mass transp. res.( ηtx), Ohmic.res. ,but mainly slow O₂ redn. kinetics(η_ORR ).

Gasteiger, Wagner et al, Appl. Cat. B 56 (2005), 9 Xianguo Li “Principles of FC’s” Taylor &Francis

Publ. 1962

Figure from p 62 of Li’s book

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) E = 0.693 V at ( 80 °C ); 0.855 V (500 °C)

2. Methane coupling to ethane.

2CH

₄

+ O

₂

= C

₂

H

₆

+ H

₂

O(g) E = 0.815 V at 80 °C; 0.695 V (500 °C)

3. Methane coupling to ethylene.

2CH

₄

+ O

₂

= C

₂

H

₄

+ 2H

₂

O(g) E= 0.748 V at 80 °C ; 0.755 V (500 °C)

4. Methane to methanol.

CH

₄

+ ½ O

₂

= CH

₃

OH(g) E= 0.565 V at 80 °C ; 0.453 V (500 °C)

Hydrogen/Oxygen FC.

H

₂

+ ½ O

₂

= H

₂

O (g) E= 1.17 V at ( 80 °C) ; 1.062 V (500 °C)

Methane /Oxygen FC

CH

₄

+ 2O

₂

= CO

₂

+2H

₂

O(g) E = 1.033 V at (80 °C) ; 1.037 V (500 °C)

Ethane to Ethylene FC :

C

₂

H

₆

+ 1/2O

₂

= C

₂

H

₄

+ H

₂

O

Anode: (Pr_0.4Sr_0.6 )₃(Fe_0.85Mo_0.15)₂O₇/Co-Fe alloy nanoparticles C₂H₆ → C₂H₄ + 2H+ _{+ 2e}-

H+ _{Electrolyte : BaCe}

0.7Zr0.1Y0.2O3-δ

Cathode: (La_0.6Sr_0.4)_0.95Co_0.20Fe_0.80O_3-δ O₂ + 2e- + 2H+ → 2H

2O

“Button” cell, 0.2 cm2 _,

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:

CH₄,CO(trace),no CO₂

See Figure from Abstract, for the overall cell design. For performance data see Fig 4A on p 764

Methane to Ethane-Ethylene FC

CH₄ Conversion and Products Selectivity vs Temperature . (Max. 91% Selectivity for C₂’s, at 23.7% Conversion of CH₄ at 1273K ). Note: C₂H₄>> C₂H₆

Cell voltage and power vs current

YSZ (Yttrium stabilized zirconia) tubular. Membrane. Surface Area = 148 cm2; 1.5 mm thick

Anode Cat.: La_1.8 Al_0.2O₃ O 2- _ion

conducting YSZ tube electrolyte Cathode Cat: La_0.85Sr_0.15MnO₃

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)

Fig 1 Cell

Schematic p1462

Fig 5 on p 1466

Electrolytically induced catalytic methane to methanol conversion

.

No reports of a direct methane + ½ O

₂

to methanol FC (E= 0.565 V at 80 °C). However,:

A. CH₄ + ½ O₂ (+ Power) → CH₃OH (+ CO₂ ) B. CH₄ + H₂O (+ Power) → CH₃OH + H₂ (+ CO₂) Cathode : ½ O₂ + 2H+ _{+ 2e-} → H

2O Cathode : 2H2O + 2e- →2OH- +H2 ; Pt cat.

--- --- H+ ↑ H

2O ↓ OH- ↓ H2O ↑

--- --- Anode : CH₄ + H₂O → CH₃OH + 2H+ _{+2e- (+CO}

2) Anode : CH4 +2OH- → CH3OH + H2O + e- (+CO2); Ni(OH) cat.

(V2O5/SnO2)

Methanol conc. vs anode (applied) potential using V₂O₅/SnO₂ anode for wt % V₂O₅ ,at 100 C. Max: 61% current efficiency and 88%

selectivity for CH₃OH B. Lee, T. Hibino, J. Catal. 2011, 279, 233

See also: Anodic oxidation of CH4→CH₃OH,HCHO,C₂H₅OH over NiO-ZrO₂; CO₃-- _{[O]- donor electrolyte. N. Spinner ,W.E. Mustain , J.}

Electrochem. Soc. 160 (11) F1275 (2013)

Feed CH₄ (top curve), and Products : CH₃OH, CO₂ and O₂ at anode. Qinbai Fan, US Pat. Appl. 2015/0129430 Fig 3 (c) on p237 of Lee Hibino

Electrode catalyst design: The Direct Methane FC

Net: CH₄ +2O₂ = CO₂+ 2H₂O(g) , E 1.033V at 80 C CH₄+2H₂O = CO₂ + 8H+ _{+8e- 2O}

2 + 8H+ + 8e- = 4H2O

Voltage-Current Polarization Curve for OMC tethered catalysts.

Key Novelty : Pt complex, ‘molecular’ CH₄ activation catalyst ,tethered to an ordered mesoporous carbon (OMC) support.

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. 2016,138 116

Figure: Schematic of cell design from Abstract

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.)

Ethylene Oxidation rate

increases

of up to 25 X (∆r)

with applied potential of ca. 0.6 V (375 C) K. Katsaounis J. Appl. Electrochem. 2010 40 885; C.G. Vayenas et al (2001)

in “Electrochemical activation of catalysis__” Kluwer/Plenum. Pub. Fig 1 p866 of Katsaounis

Non- Faradaic ”Electroreforming” of methane to syn. gas and H

₂

Steam-methane reforming (SMR)

,

current

practice:

CH

₄

+2H

2O ↔ CO + 3H2

+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:

CH₄ 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. 15-25 %

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_0.5Zr_0.5O2 cat. Y. Sekine et al , Int. J. of Hydrogen Energy 2013, 38 ,3003 .

From Cat. Today 2011 Reactor Schematic p118

Electrical Discharges/Plasma for Methane Conversion

Methane to C

₂

H

₂

in spark discharge

Reactor: +/- 30 kV , 0-10 mA ,0- 400Hz Feed: CH₄, 10 ccm ,ambient T, P.

Products: C₂H₂ (90% sel.) ; C₂H₆,C₂H₄ (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)

Methane oxidative coupling in corona discharge , +/- catalyst

Feed: CH₄/O₂ = 4 @ 100 sccm Catalyst: Sr/La₂O₃ , T= 823K Products: C₂H₄,C₂H₆ 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. CH₄ A. Marafee, C.Liu, G.Xu, R. Mallison ,L. Lobban

Ind.Eng.Chem.Res. 1997,36,632

From Kado Fig 1 p1378

Potential for: Hydrocarbons→ Chemicals via

Electrocatalysis

With Electric Power Co- Generation (All exothermic conversions)

With Electric Power Consumption (Exothermic or endothermic conv.)

Hydrocarbon/Air Fuel Cell Systems .

Reports for chem. products (currently) only from SOFC’s

Electrolyte : Polymer (PEM) Phosphoric Acid --- ? Solid Oxide, ceramic (SOFC) Molten Carbonate Carrier Ion: H+ _{, CO}

3 -- H+ O-- , H+ CO3 -- /CO2

Temperature: RT- 200 C 150-200 C 200- 500 C 500-1000 C 600-700C Features: Commercial (H+ _{) Commercial}

Key Issues ORR Acid loss, ORR High Temps., Materials

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 CH₄ to syn gas &H₂ . 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.

(Faradaic processes)

Thank you to Andy Herring ( Co. School of Mines)

for valuable discussions.

Electrode catalyst design: The Direct Methane FC

Net: CH₄ +2O₂ = CO₂+ 2H₂O(g) , E 1.033V at 80 C CH₄+2H₂O = CO₂ + 8H+ _{+8e- 2O}

2 + 8H+ + 8e- = 4H2O

Voltage-Current Polarization Curve for OMC tethered catalysts.

Key Novelty : Pt complex, ‘molecular’ CH₄ activation catalyst ,tethered to an ordered mesoporous carbon (OMC) support.

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. 2016,138 116

Figure: Schematic of cell design from Abstract

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.)

Ethylene Oxidation rate

increases

of up to 25 X (∆r)

with applied potential of ca. 0.6 V (375 C) K. Katsaounis J. Appl. Electrochem. 2010 40 885; C.G. Vayenas et al (2001)

in “Electrochemical activation of catalysis__” Kluwer/Plenum. Pub. Fig 1 p866 of Katsaounis

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:

CH₄ 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. 15-25 %

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_0.5Zr_0.5O2 cat. Y. Sekine et al , Int. J. of Hydrogen Energy 2013, 38 ,3003 .

From Cat. Today 2011 Reactor Schematic p118

Electrical Discharges/Plasma for Methane Conversion

Methane to C

₂

H

₂

in spark discharge

Reactor: +/- 30 kV , 0-10 mA ,0- 400Hz

Feed: CH₄, 10 ccm ,ambient T, P.

Products: C₂H₂ (90% sel.) ; C₂H₆,C₂H₄ (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)

Methane oxidative coupling in corona discharge , +/- catalyst

Feed: CH₄/O₂ = 4 @ 100 sccm Catalyst: Sr/La₂O₃ , T= 823K

Products: C₂H₄,C₂H₆ 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. CH₄ A. Marafee, C.Liu, G.Xu, R. Mallison ,L. Lobban

Ind.Eng.Chem.Res. 1997,36,632

From Kado Fig 1 p1378

Potential for: Hydrocarbons→ Chemicals via

Electrocatalysis

With Electric Power Co- Generation (All exothermic conversions)

With Electric Power Consumption (Exothermic or endothermic conv.)

Hydrocarbon/Air Fuel Cell Systems .

Reports for chem. products (currently) only from SOFC’s

Electrolyte : Polymer (PEM) Phosphoric Acid --- ? Solid Oxide, ceramic (SOFC) Molten Carbonate Carrier Ion: H+ _{, CO}

3 -- H+ O-- , H+ CO3 -- /CO2

Temperature: RT- 200 C 150-200 C 200- 500 C 500-1000 C 600-700C Features: Commercial (H+ _{) Commercial}

Key Issues ORR Acid loss, ORR High Temps., Materials

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 CH₄ to syn gas &H₂ . 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. (Faradaic processes)

Thank you to Andy Herring ( Co. School of Mines)

for valuable discussions.