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

Transcription

1 Catalytic processes for the conversion of natural gas to logistics fuels and chemicals Robert J. Kee, Canan Karakaya, and Huayang Zhu Mechanical Engineering Golden, CO (303) Presented: KAUST Future Fuels Workshop March 8,

2 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 2

3 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 3

4 In addition to combustion, there are numerous choices and processing pathways for natural gas 4

5 The feed stoichiometry and the catalyst affect the reforming process and end-use of the syngas 5

6 Natural-gas reforming is practiced on a very large industrial scale (over 50 million tonnes annually) Significant opportunities for process intensification and efficiency improvement 6

7 Avoiding coke and controlling H 2 /CO ratios are important process considerations Rostrup-Nielsen & Sehested, Stud. Surf. Sci. Catal., 139:1, 2001 Equilibrium provides reasonable guidance 7

8 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 8

9 Microchannel reactors and integrated heat exchangers offer opportunities for major process intensification Closely couple endothermic and exothermic processes 9

10 Microchannel heat-exchangers and reactors have some inherent benefits Kee, et al., Appl. Thermal Eng., 31: , 2010 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 10

11 Internal manifolds can be difficult to fabricate, especially for counter-flow designs Kee, et al., Appl. Thermal Eng., 31: , 2010 Fabrication processes affect manifold design 11

12 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: ,

13 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,

14 Our ceramic microchannel reactors show good performance for steam reforming and partial oxidation S/C = 2.5 GHSV=50000 h -1 Inert = 750 C Blakeley and Sullivan, Int. J. Hydrogen Energy, 41: ,

15 Hydrogen and oxygen permselective membranes can improve reforming processes Membranes Assist chemistry Assist thermal control H 2 : Palladium alloy Ceramic ion-transport O 2 : Ceramic ion-transport Nano-porous ceramic 15

16 Air separation provides many opportunities for process intensification 16

17 Ion-transport membranes represent a new and maturing technology for air separation Opportunities for membrane-based in-situ air separation 17

18 An oxygen-transport membrane reactor integrates air separation and catalytic partial oxidation Miller, Chen, Carolan, Foster, Catal. Today, 228:152,

19 A composite tubular reformer integrates air separation, steam reforming, and partial oxidation Integrated design achieves thermal integration US Patents: B2 (2010); B2 (2015) 19

20 Large-scale Fischer-Tropsch technology is mature, but process intensification is increasingly important 20

21 Fischer-Tropsch synthesis can be controlled to achieve desired syncrude compositions 21

22 Refinery-scale Fischer-Tropsch synthesis is being practiced commercially Fixed-bed reactor Slurry-bubble reactor 22

23 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 reactor 23

24 Oxidative coupling of methane (OCM) provides a direct route for converting methane to ethylene 24

25 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 H 2 O, CO 2, and CO are unavoidable side products Typical conditions 5 < CH 4 /O 2 < 10 (inhibit full oxidation) 25

26 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 26

27 Species and temperature profiles contribute great insight about the OCM process Zohour, Noon, Senkan, ChemCatChem, 6: ,

28 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% C 2 H 4 Double-bed yield: 21% C 2 H 4 Zohour, Noon, Senkan, ChemCatChem, 6: ,

29 Segmented unit processes can potentially deliver process intensification Thybaut, et al., Chem. Eng. Tech., 86: , 2014 Two complementary product streams Approach isothermal conditions Segmentation improves both processes 29

30 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 30

31 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 31

32 There are likely ways to to exploit similarity principles in chemical processing 32

33 Swirling tubular reactors may provide a route to achieve process uniformity in a OCM process Achieve axial independence in long membrane tubes 33

34 Methane dehydroaromatization (MDA) promises a direct route from methane to benzene 34

35 Methane dehydroaromatization (MDA) is a potential route to produce benzene from methane Ideal global reaction 6 CH 4 = C 6 H H 2 Process limitations Equilibrium limit (~12% conversion) Carbon deposits Catalyst deactivation (few hours) Hydrogen membranes Remove H 2, increase conversion Competition with naphthalene Steam addition Attack naphthalene (C 10 H 8 ) Extend catalyst lifetime 35

36 Bi-functional Mo/Zeolite catalysts are known to deliver MDA functionality 36

37 The active Mo structure is Mo 2 C incorporated into the zeolite structure Zhou, Zuo, Xing, J. Phys. Chem. C, 116: , 2012 Incorporate MoO x into the zeolite Carburize MoOx to Mo 2 C during Mo 2 C is active for CH 4 activation Mo deactivates zeolite acid sites Typical Mo loading is 1-10 wt. % 37

38 TEM and XRD confirm that crystal structure is preserved through processing 38

39 MDA chemistry on Mo/ZSM5 can be described by 54 elementary reaction steps 39

40 Catalytic packed-bed models are developed to incorporate membrane transport 40

41 Removing only H 2 increases conversion, but competition with naphthalene is problematic T = 700 C GHSV = 1500 ml/g/h 41

42 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 surfaces 1 Crack naphthalene, interrupt PAH growth 2 Too much H 2 O is detrimental Promote reforming chemistry De-aluminate zeolite catalysts Detailed kinetics remain to be developed Reported experiments use excess H 2 O Need low-level steam-naphthalene expts. Models can use detailed reaction mechanisms Assist design and operation 1. Ma, et al., Appl. Catal. A., 275: , Buchireddy, et al., Energy Fuels, 24: ,

43 Our ongoing experiments are designed to elucidate the naphthalene-steam chemistry Data needed for mechanism development 43

44 A diverse set of membrane materials can be applied in gas-to-liquids technology 44

45 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: ,

46 There are numerous opportunities for process and reactor development across greatly disparate scales 46

47 Acknowledgements Office of Naval Research Dr. Michele Anderson Air Force Office of Scientific Research Drs. Chiping Li and Mike Berman 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) 47

48 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 year development cycle 48