catalytic processes for the conversion of natural …...gtl_march2016 catalytic processes for the...

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Colorado School of Mines Earth • Energy • Environment

GTL_March2016

Catalytic processes for the conversion of natural gas to logistics fuels and chemicals

Robert J. Kee, Canan Karakaya, and Huayang Zhu Mechanical Engineering

Colorado School of MinesGolden, CO 80401

[email protected](303) 273-3379

Presented:KAUST Future Fuels Workshop

March 8, 2016

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GTL_March2016

The recent abundance of inexpensive natural gas presents new opportunities

Gas is often “stranded” • Transportation is impractical • Convert to liquids

Opportunities for products • Logistics fuels • Commodity chemicals

Gas-to-liquids technology • Via syngas • Oxidative coupling • Direct dehydrogenation

Process intensification • Micro-channel reactors • Membrane reactors

Fracking technology has fundamentally changed the energy landscape

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Process intensification is defined broadly in terms of greatly increasing efficiency and reducing plant size

Fundamentals • Heterogeneous catalysis • Gas-phase kinetics • Chemically reacting flow • Membrane electrochemistry • Reforming, gas-to-liquids,…

Reactor engineering • Process intensification • Thermal management • Process up-scaling • Model-predictive control

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In addition to combustion, there are numerous choices and processing pathways for natural gas

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The feed stoichiometry and the catalyst affect the reforming process and end-use of the syngas

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Natural-gas reforming is practiced on a very large industrial scale (over 50 million tonnes annually)

Significant opportunities for process intensification and efficiency improvement

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Rostrup-Nielsen & Sehested, Stud. Surf. Sci. Catal., 139:1, 2001

Equilibrium provides reasonable guidance

Avoiding coke and controlling H2/CO ratios are important process considerations

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There are numerous challenges in developing reaction mechanisms for heterogeneous catalysis

Typical “Deutschmann” reaction mechanism

Establish the reaction pathways • Conceptual

Develop rate expressions • Modified Arrhenius form • Mean field approximation

Consistent with experimental measurements • Packed beds • Washcoated monoliths • Stagnation flows • Surface science

Microscopic reversibility • Need surface thermodynamics

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Microchannel reactors and integrated heat exchangers offer opportunities for major process intensification

Closely couple endothermic and exothermic processes

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Microchannel heat-exchangers and reactors have some inherent benefits

High performance and Compact

Low-Reynolds number flow • Constant Nusselt numbers • Constant Sherwood numbers

Small channel dimensions (< 1 mm) • High heat and mass transfer

Manifold design can be complex • Especially for counter flow • Cross flow is easier

Catalyst integration • Washcoat can be difficult • Replacement can be difficult

Kee, et al., Appl. Thermal Eng., 31:2004-2012, 2010

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Internal manifolds can be difficult to fabricate, especially for counter-flow designs

Kee, et al., Appl. Thermal Eng., 31:2004-2012, 2010

Fabrication processes affect manifold design

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There are numerous challenges and opportunities in designing and developing micro-reactor technology

Thermal balance and alignment • Exotherms • Endotherms

Materials • Metals (more mature) • Ceramics (in development)

Manifold design • Counter-flow more difficult • Cross-flow easier

Catalyst maintenance • Regeneration • Replacement • Removable plates

Thybaut, et al., Chem. Ing. Tech., 86:1588–1870, 2014

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Three-dimensional modeling of the reactive flow and conjugate heat transfer assist design

Very large three-dimensional problem • Opportunities to accelerate chemistry via ISAT • Approximate small-channel flow as plug flow

Blasi and Kee, Comp. Chem. Eng., 84:36-42, 2016

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Our ceramic microchannel reactors show good performance for steam reforming and partial oxidation

Blakeley and Sullivan, Int. J. Hydrogen Energy, 41:3794-3802, 2016

S/C = 2.5GHSV=50000 h-1

Inert = 750 C

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Hydrogen and oxygen permselective membranes can improve reforming processes

H2: Palladium alloy Ceramic ion-transport

O2: Ceramic ion-transport Nano-porous ceramic

Membranes • Assist chemistry • Assist thermal control

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Air separation provides many opportunities for process intensification

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Ion-transport membranes represent a new and maturing technology for air separation

Opportunities for membrane-based in-situ air separation

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Miller, Chen, Carolan, Foster, Catal. Today, 228:152, 2014

An oxygen-transport membrane reactor integrates air separation and catalytic partial oxidation

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A composite tubular reformer integrates air separation, steam reforming, and partial oxidation

Integrated design achieves thermal integration

US Patents: 7686856 B2 (2010); 9115045 B2 (2015)

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Large-scale Fischer-Tropsch technology is mature, but process intensification is increasingly important

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Fischer-Tropsch synthesis can be controlled to achieve desired syncrude compositions

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Refinery-scale Fischer-Tropsch synthesis is being practiced commercially

Fixed-bed reactor Slurry-bubble reactor

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Velocys has developed and scaled microchannel reactor technology to commercial viability

Component scale • Millimeter-scale channels • Pressurized water coolant • Fe- or Co-based catalysts

Meter-scale reactorwww.velocys.com

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Oxidative coupling of methane (OCM) provides a “direct” route for converting methane to ethylene

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Oxidative coupling of methane provides a “direct” route to ethylene synthesis

• First reported by Keller and Bhasin, 1982• Process is controlled by methyl-radical formation• Catalyst is required, but gas-phase contributes significantly• H2O, CO2, and CO are unavoidable side products• Typical conditions 5 < CH4/O2 < 10 (inhibit full oxidation)

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Oxidative coupling of methane can be accomplished with two types of catalysts

• These catalysts are more complex than single metals• Much current modeling uses the Staunch mechanism

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Species and temperature profiles contribute great insight about the OCM process

Zohour, Noon, Senkan, ChemCatChem, 6:2815-2820, 2014

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GTL_March2016Zohour, Noon, Senkan, ChemCatChem, 6:2815-2820, 2014

Staging the catalyst bed and oxygen addition improves OCM performance

Limit local temperature excursions • Decrease full oxidation • Decrease catalyst degradation • Suggests oxygen membrane

Single-bed yield: 16% C2H4Double-bed yield: 21% C2H4

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Thybaut, et al., Chem. Eng. Tech., 86:1588-1870, 2014

Segmented unit processes can potentially deliver process intensification

• Two complementary product streams• Approach isothermal conditions• Segmentation improves both processes

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Segmented compression and expansion with intercooling and reheating improves gas turbines

Multistaging gas turbines improves efficiency • The Brayton cycle approaches the higher efficiency Ericsson cycle • Isothermal compression and expansion provides benefits

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Segmented designs can assist process efficiency, control, and maintenance

• Large number of segments approaches membrane behavior• Reactors can be easily removed and replaced• Spatially segmented oxygen/steam addition can be beneficial • Membranes do not easily accommodate local oxygen/steam control

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There are likely ways to to exploit similarity principles in chemical processing

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Swirling tubular reactors may provide a route to achieve process uniformity in a OCM process

Achieve axial independence in long membrane tubes

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Methane dehydroaromatization (MDA) promises a ‘’direct” route from methane to benzene

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Methane dehydroaromatization (MDA) is a potential route to produce benzene from methane

Ideal global reaction • 6 CH4 = C6H6 + 9 H2

Process limitations • Equilibrium limit (~12% conversion) • Carbon deposits • Catalyst deactivation (few hours)

Hydrogen membranes • Remove H2, increase conversion • Competition with naphthalene

Steam addition • Attack naphthalene (C10H8) • Extend catalyst lifetime

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Bi-functional Mo/Zeolite catalysts are known to deliver MDA functionality

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The active Mo structure is Mo2C incorporated into the zeolite structure

• Incorporate MoOx into the zeolite • Carburize MoOx to Mo2C during • Mo2C is active for CH4 activation • Mo deactivates zeolite acid sites • Typical Mo loading is 1-10 wt. %

Zhou, Zuo, Xing, J. Phys. Chem. C, 116:4060-4070, 2012

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TEM and XRD confirm that crystal structure is preserved through processing

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MDA chemistry on Mo/ZSM5 can be described by 54 elementary reaction steps

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Catalytic packed-bed models are developed to incorporate membrane transport

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Removing only H2 increases conversion, but competition with naphthalene is problematic

T = 700 ˚CGHSV = 1500 ml/g/h

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Steam can play a beneficial role in preventing (or delaying) catalyst fouling coke or PAH deposits

Low-concentration (~2%) steam is beneficial • Crack coke deposits on surfaces1

• Crack naphthalene, interrupt PAH growth2

Too much H2O is detrimental • Promote reforming chemistry • De-aluminate zeolite catalysts

Detailed kinetics remain to be developed • Reported experiments use excess H2O • Need low-level steam-naphthalene expts.

Models can use detailed reaction mechanisms • Assist design and operation

1.  Ma, et al., Appl. Catal. A., 275:183-187, 20042.  Buchireddy, et al., Energy Fuels, 24:2707-2715, 2010

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Our ongoing experiments are designed to elucidate the naphthalene-steam chemistry

Data needed for mechanism development

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A diverse set of membrane materials can be applied in gas-to-liquids technology

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Ion transport within ceramic mixed conductors can be represented with Nernst-Planck-Poisson models

Zhu, Ricote, Coors, Kee, Faraday Discussions, 182:49-74, 2015

Zhu and Kee, Intl. J. Hydrogen Energy, 41:2931-2943, 2016

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There are numerous opportunities for process and reactor development across greatly disparate scales

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Acknowledgements

Office of Naval Research • Dr. Michele Anderson

CoorsTek, Inc. • Dr. Grover Coors

Colorado School Mines • Prof. Greg Jackson • Prof. Rob Braun • Prof. Sandrine Ricote • Prof. Ryan O’Hayre • Prof. Neal Sullivan (CFCC)

Air Force Office of Scientific Research Drs. Chiping Li and Mike Berman

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Market forces can significantly affect the course of research and development for new technologies

Markets are volatile • Price cycles can be short

Sustained investments needed • 10-20 year development cycle

catalytic processes for the conversion of natural …...gtl_march2016 catalytic processes for the...

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