Natural Gas Conversion VI (eBook)

T.H. Fleisch, Enrique Iglesia, J.J. Spivey (Herausgeber)

eBook Download: PDF | EPUB

2001 | 1. Auflage
576 Seiten
Elsevier Science (Verlag)
978-0-08-053731-3 (ISBN)

Infos

This volume contains peer-reviewed manuscripts describing the scientific and technological advances presented at the 6^th Natural Gas Conversion Sumposium held in Alaska in June 2001. This symposium continues the tradition of excellence and the status as the premier technical meeting in this area established by previous meetings.

The 6^th Natural Gas Conversion Symposium is conducted under the overall direction of the Organizing Committee. The Program Committee was responsible for the review, selection, editing of most of the manuscripts included in this volum. A standing International Advisory Board has ensured the effective long-term planning and the continuity and technical excellence of these meetings.

Inhalt

Front Cover 1
Natural Gas Conversion VI 4
Copyright Page 5
Table of Contents 10
Chapter 1. Modeling Millisecond Reactors 16
Chapter 2. Molecular Design of Highly Active Methanol Synthesis Catalysts 28
Chapter 3. Partial Oxidation of Methane to Syngas over NiO/l.-Al2O3 Catalysts Prepared by the Sol-Gel Method 36
Chapter 4. Mo/MCM-22: A Selective Catalyst for the Formation of Benzene from Methane Dehydro-aromatization 42
Chapter 5. The Synthesis of Dimethyl Ether from Syngas Obtained by Catalytic Partial Oxidation of Methane and air 48
Chapter 6. Development of the High Pressure ITM Syngas Process 54
Chapter 7. An Integrated ITM Syngas / Fischer-Tropsch Process for GTL Conversion 60
Chapter 8. LiLaNiO/./-Al2O3 Catalyst for Syngas Obtainment by Simultaneous Catalytic Reaction of Alkanes with Carbon Dioxide and Oxygen 66
Chapter 9. Impact of Syngas Generation Technology Selection on a GTL FPSO 72
Chapter 10. Developments in Fischer-Tropsch Technology and its Application 78
Chapter 11. An Innovative Approach for Ethylene Production from Natural Gas 84
Chapter 12. Methane Conversion via Microwave Plasma Initiated by a Metal Initiator 90
Chapter 13. Production of Ethylbenzene by Alkylation of Benzene with Dilute Ethylene Obtained from Ethane Oxidative Dehydrogenation with CO2 96
Chapter 14. Oxidative Dehydrogenation of Ethane with Carbon Dioxide to Ethylene over Cr-loaded Active Carbon Catalyst 102
Chapter 15. Catalytic Performance of Hydrothermally Synthesized Mo-V-M-O (M= Sb and Te) Oxides in the Selective Oxidation of Light Paraffins 108
Chapter 16. A Novel Two-stage Reactor Process for Catalytic Oxidation of Methane to Synthesis Gas 114
Chapter 17. Composite Steam Reforming Catalysts Prepared from Al2O3/Al Matrix Precursor 120
Chapter 18. Relation Between the Structure and Activity of Ru-Co/NaY Catalysts Studied by X-ray Absorption Spectroscopy (XAS) and CO Hydrogenation 126
Chapter 19. Development of a High Efficiency GTL Process Based on CO2/Steam Reforming of Natural Gas and Slurry Phase FT Synthesis 132
Chapter 20. Kinetic Modeling of the Slurry Phase Fischer-Tropsch Synthesis on Iron Catalysts 138
Chapter 21. Mechanism of Carbon Deposit/Removal in Methane Dry Reforming on Supported Metal Catalysts 144
Chapter 22. New Catalysts Based on Rutile-type Cr/Sb and Cr/V/Sb Mixed Oxides for the Ammoxidation of Propane to Acrylonitrile 150
Chapter 23. ALMAX Catalyst for the Selective Oxidation of n-butane to Maleic Anhydride: A Highly Efficient V/P/O System for Fluidized-bed Reactors 156
Chapter 24. Oxygen Transport Membranes for Syngas Production 162
Chapter 25. Deactivation of CrOx/Al2O3 Catalysts in the Dehydrogenation of i-Butane 168
Chapter 26. Selectivity of Fischer-Tropsch Synthesis: Spatial Constraints and Forbidden Reactions 174
Chapter 27. Effect of CaO Promotion on the Performance of a Precipitated Iron Fischer-Tropsch Catalyst 180
Chapter 28. Partial Oxidation of Methane at High Temperatures over Platinum and Rhodium Monolith Catalysts 186
Chapter 29. The Promoting Effect of Ru and Re Addition to Co/Nb2O5 catalysts in the Fischer-Tropsch Synthesis 192
Chapter 30. Comparative Studies of the Oxidative Dehydrogenation of Propane in Micro- Channels Reactor Module and Fixed-Bed Reactor 200
Chapter 31.Catalyst-assisted Oxidative Dehydrogenation of Light Paraffins in Short Contact Time Reactors 206
Chapter 32. Catalytic Decomposition of Methane: Towards Production of CO-free Hydrogen for Fuel Cells 212
Chapter 33. CO2-CH 4 Reforming with Pt-Re/.-Al2O3 Catalysts 218
Chapter 34. The Catalytic Properties of Alkaline Earth Metal Oxides in the Selective Oxidation of CH4-O2-NOx (x=1,2) 224
Chapter 35. Production and Storage of Hydrogen from Methane Mediated by Metal Oxides 230
Chapter 36. Oxidative Dehydrogenation over Sol-Gel Mo/Si:Ti Catalysts: Effect of Mo Loading 236
Chapter 37. NOx -Catalyzed Partial Oxidation of Methane and Ethane to Formaldehyde by Dioxygen 242
Chapter 38. Comparative Study of Partial Oxidation of Methane to Synthesis Gas over Supported Rh and Ru Catalysts Using in situ Time-Resolved FTIR and in situ Microprobe Raman Spectroscopies 248
Chapter 39. Optimisation of Fischer-Tropsch Reactor Design and Operation in GTL Plants 254
Chapter 40. Catalytic Partial Oxidation of Methane to Syngas: Staged and Stratified Reactors with Steam Addition 260
Chapter 41.Natural Gas Conversion in Monolithic Catalysts: Interaction of Chemical Reactions and Transport Phenomena 266
Chapter 42. Direct Synthesis of Acetic Acid from Methane and Carbon Dioxide 274
Chapter 43. Partial Oxidation of Methane to Form Synthesis Gas in a Tubular AC Plasma Reactor 280
Chapter 44. Selective Hydrogenation of Acetylene to Ethylene During the Conversion of Methane in a Catalytic DC Plasma Reactor 286
Chapter 45. The Nigerian Gas-to-Liquids (GTL) Plant 292
Chapter 46. Pt-Promotion of Co/SiO2 Fischer-Tropsch Synthesis Catalysts 298
Chapter 47. Catalytic Dehydrogenation of Propane over a PtSn/SiO2 Catalyst with Oxygen Addition: Selective Oxidation of H2 in the Presence of Hydrocarbons 304
Chapter 48. Selectivity and Activity Changes upon Water Addition during Fischer-Tropsch Synthesis 310
Chapter 49. Synthesis Gas Production by Partial Oxidation of Methane from the Cyclic Gas-solid Reaction using Promoted Cerium Oxide 316
Chapter 50. Hydroconversion of a Mixture of Long Chain n-Paraffins to Middle Distillate: Effect of the Operating Parameters and Products Properties 322
Chapter 51. Ethylene Production Via Partial Oxidation and Pyrolysis of Ethane 328
Chapter 52. The Role of Gallium Oxide in Methane Partial Oxidation Catalysts: An Experimental and Theoretical Study 334
Chapter 53. Low Temperature Routes for Methane Conversion, and an Approach Based on Organoplatinum Chemistry 340
Chapter 54. NAS (Novel Aluminosilicates) as Catalysts for the Selective Conversion of Propane to Fuels and Chemicals- Effects of Chrystallinity on Catalytic Behaviour 348
Chapter 55. The Oxidative Dehydrogenation of Propane with CO2 Over Supported MO2C Catalyst 354
Chapter 56. Decomposition/Reformation Processes and CH4 Combustion Activity of PdO Over Al2O3 Supported Catalysts for Gas Turbine Applications 360
Chapter 57. Effect of Periodic Pulsed Operation on Product Selectivity in Fischer-Tropsch Synthesis on Co-ZrO2/SiO2 366
Chapter 58. Synthesis and Characterization of Proton-Conducting Oxides as Hydrogen Transport Membranes 372
Chapter 59. Methane to Syngas: Development of Non-coking Catalyst and Hydrogen- Permselective Membrane 378
Chapter 60. Site Reactivity of Fischer-Tropsch Synthesis Catalysts Studied by 12CO . 13CO Isotope Transients 384
Chapter 61. Surface Carbon Coverage and Selectivity in FT Synthesis: A Simple Model for Selectivity Correlations 390
Chapter 62. Perovskites as Catalysts Precursors for Methane Reforming: Ru Based Catalysts 396
Chapter 63. Fischer-Tropsch Synthesis Catalysts Based on Fe Oxide Precursors Modified by Cu and K: Structure and Site Requirements 402
Chapter 64. Catalytic Dehydrocondensation of Methane Towards Benzene and Naphthalene on Zeolite-supported Re and Mo -Templating Roles of Micropores and Novel Mechanism 408
Chapter 65. Lurgi's Mega-Methanol technology Opens the Door for a New Era in Down-stream Applications 414
Chapter 66. Selecting Optimum Syngas Technology and Process Design for Large Scale Conversion of Natural Gas into Fischer-Tropsch products (GTL) and Methanol 420
Chapter 67. CANMET's Integrated Acetic Acid Process: Coproduction of Chemicals and Power from Natural Gas 426
Chapter 68. Rhenium as a Promoter of Titania-Supported Cobalt Fischer-Tropsch Catalysts 432
Chapter 69. Market Led GTL: The Oxygenate Strategy 438
Chapter 70. Gas-to-Liquids R& D: Setting Cost Reduction Targets
Chapter 71. Syngas for Large Scale Conversion of Natural Gas to Liquid Fuels 450
Chapter 72. CO2 Reforming for Large-scale Methanol Plants - an Actual Case 456
Chapter 73. Water-gas Shift Reaction: Reduction Kinetics and Mechanism of Cu/ZnO/Al2O3 Catalysts 462
Chapter 74. Design/Economics of an Associated (or Sub-Quality) Gas Fischer-Tropsch Plant 468
Chapter 75. Expanding Markets for GTL Fuels and Specialty Products 474
Chapter 76. Development of Dense Ceramic Membranes for Hydrogen Separation 480
Chapter 77. Methane Oxyreforming over Al2O3 Supported Rhodium Catalyst as a Promising Route of CO and H2 Mixture Synthesis 486
Chapter 78. Catalytic Partial Oxidation of Ethane to Acetic Acid over Mo1Vo.25Nb0.12Pd0.0005Ox – Catalyst Performance, Reaction Mechanism, Kinetics and Reactor Operation 492
Chapter 79. A Non Stationary Process for H2 Production from Natural Gas 498
Chapter 80. From Natural Gas to Oxygenates for Cleaner Diesel Fuels 504
Chapter 81. Some Critical Issues in the Analysis of Partial Oxidation Reactions in Monolith Reactors 510
Chapter 82. Indirect Internal Steam Reforming of Methane in Solid Oxide Fuel Cells 516
Chapter 83. Catalytic Properties of Supported MoO3 Catalysts for Oxidative Dehydrogenation of Propane 522
Chapter 84. Quantitative Comparison of Supported Cobalt and Iron Fischer Tropsch Synthesis Catalysts 528
Chapter 85. CO2 Abatement in Gas-To-Liquid Plants 534
Chapter 86. Study on Stability of Co/ZrO2/SiO2 Catalyst for F-T Synthesis 540
Chapter 87. Partial Oxidation of Methane to Formaldehyde on Fe-doped Silica Catalysts 546
Chapter 88. Production of Light Olefins from Natural Gas 552
Chapter 89. Novel Techniques for the Conversion of Methane Hydrates 558
List of authors 564
Studes in Surface Science and Catalysis 568

Textauszug

Modeling Millisecond Reactors

Lanny D. Schmidt    Department of Chemical Engineering and Materials Science University of Minnesota Minneapolis MN 55455

ABSTRACT

Catalytic partial oxidation processes at very short contact times have great promise for new routes to chemical synthesis from alkanes because they are capable of producing highly nonequilibrium products with no carbon formation using reactors that are much smaller and simpler than with conventional technology. We summarize some of the considerations which may be important in modeling and in interpreting partial oxidation processes. The gradients in these monolith reactors are typically 106 K/sec and 105 K/cm, and reactions are fastest in the regions of highest gradients. Therefore a conventional one-dimensional model may be highly inaccurate to describe these processes, particularly when used to attempt to decide between different reaction mechanisms. We argue that detailed modeling which includes detailed descriptions of reactor geometry, gas and solid properties, and surface and homogeneous reaction kinetics will be necessary to develop reliable descriptions of these processes. Even with detailed modeling, it may be necessary to consider the validity of these parameters under extreme reaction conditions.

INTRODUCTION

Oxidation processes in monolithic catalysts exhibit features not observed in conventional packed bed reactors because they operate with gas flow velocities of ~ 1 m/sec with open channel catalyst structures for effective contact times of the gases on the catalyst of typically 1 millisecond and produce kilograms of product per day with less than a gram of catalyst. These processes are autothermal and nearly adiabatic because the exothermic oxidation reactions heat the gases and the catalyst from room temperature to typical operating temperatures of ~ 1000 °C and the rate of heat generation is too large for effective wall cooling. After lightoff, the reactions usually run to completion of the limiting reactant, so conversion and selectivities are independent of flow rates over typically an order of magnitude of residence time.

A recently explored example is methane oxidation to synthesis gas

4+1/2O2→CO+2H2,

which occurs with 100% O2 conversion, > 90% CH4 conversion, and > 90% selectivity to CO and H2 (based on C and H respectively) on Rh catalyst coated on α-alumina foam monolith[1]. Another example is alkane oxidation to olefins[2], for example,

2H6+1/2O2→C2H4+H2O,

which occurs with 100% O2 conversion, > 70% C2H6 conversion, and ~ 85% selectivity to ethylene on Pt- Sn catalyst coated on α-alumina foam monolith. As a final example, the total oxidation of alkanes to CO2 and H2O

4+2O2→CO2+2H2O

can be attained with > 99% fuel conversion[3]. The oldest examples of monolith reactors with millisecond contact times are the Ostwald process to prepare nitric acid by ammonia oxidation

3+5/4O2→NO+3/2H2O,

and the Andrussow process to prepare HCN[4],

4+NH3+O2→HCN+2H2O+H2.

Both of these processes take place on multiple layers of woven Pt-10%Rh gauze catalysts operating at 800 and 1100 °C.

All of these processes occur with approximately millisecond contact times with the exothermicity of the reactions providing the energy to heat the gases and catalyst from room temperature to operating temperatures from 800 to 1200 °C in < 10− 3 s.

We [3–6] and many others[7] have attempted to model these processes in detail to try to determine the mechanisms by which these product distributions are formed and to find conditions to optimize a particular product. We argue that these apparently simple processes are in fact far more complicated than the usual packed bed catalytic reactor assumptions used for typical modeling. First, the temperatures are sufficiently high that some homogeneous reaction may be expected to occur, even at very short reaction times. Second, the gradients in all properties are so large that all conventional assumptions may be inaccurate. It is the purpose of this manuscript to address these issues.

ONE-DIMENSIONAL MODELS

We first consider the geometry of millisecond reactors. These typically occur in open monolith catalyst structures which may consist of extruded, foam, or fiber ceramics or woven or sintered metal structures, as sketched in the left panel of figure 1. All of these structures can be approximated as a collection of tube wall reactors of length L and channel diameter d.

Figure 1 Left panels: Different monolith geometries approximated by a straight tube. Center panels: Possible temperature profiles down the reactor. Right panels: Possible locations of homogeneous reaction and flames.

One Dimensional Models

Most simple models of these processes have assumed one-dimensional approximations[3] to the geometries of figure 1. Radial mass and heat transfer are included through effective mass and heat transfer coefficients to the walls. Either plug flow (no axial mass or heat transfer in the gas) or models including axial diffusion (a boundary value problem) are assumed, and the resultant model is easy to solve even for many equations.

The simplest approximation to the temperature is to assume a step change from the feed temperature (25 °C) to the final catalyst and gas temperature (~ 1000 °C) so that the energy balance can be ignored. Monolith temperatures typically vary by less than 100°. from front to back, so the assumption of constant wall temperature is reasonable. Gases should attain the wall temperature within a few channel diameters, so the temperatures should be constant within less than 1 mm of the entrance. The expected temperature profiles for gas and catalyst are sketched in curve a of the center panel of figure 1.

Wall heat conduction is an important mechanism for backflow of heat which maintains the monolith and the gas isothermal, and the temperatures can be calculated by solving simultaneously for the gas and solid temperatures Tg and Ts, still in a one dimensional approximation.

Upon heating from 25 °C to 1000 °C, the kinematic viscosity increases by more than a factor of 10, as do the thermal diffusivity and mass diffusivity. Since reaction occurs very quickly upon entering the monolith, these variations in properties near the entrance must be included in any calculation of reactor performance.

Although Reynolds numbers are sufficiently small that laminar flow is a good approximation and heat transfer coefficients and solid thermal conductivities are sufficiently large that nearly isothermal gas and solid may be assumed, there may be serious problems in the one dimensional, plug flow assumption in approximating reactor behavior. First, most reaction appears to occur within a few tube diameters where the temperatures are varying strongly, so the large gradients in this region may be significant. Second, the gases strongly accelerate in the entrance region (typically by factors of 4 to 10), and the decoupling of the fluid flow from the reaction and temperature equations may lead to significant errors.

TWO-DIMENSIONAL SIMULATION

We have simulated quantitatively the temperature and velocity profiles for cold gases entering a hot tube for the reactions and conditions of the methane to syngas[6] and for ethane to ethylene[7]. These calculations were done using FLUENT to calculate fluid properties. All fluid properties are properly accounted for including temperature and mixture variations of diffusivities, thermal conductivity, and viscosity. We used the Hickman model[5,6] of syngas generation for the surface reaction mechanism.

The CH4, temperature, and axial velocity profiles predicted by this model are shown in figure 2. The calculations shown are for three tube diameters: 0.025, 0.05, and 0.1 cm. These correspond to 80, 40, and 20 pores per linear inch which are typical foam ceramic sizes. The region shown is only the first millimeter near the entrance to the hot catalyst section. This section is preceded by an inert tube which produces a fully developed laminar flow profile before entering the catalytic section.

Figure 2 Calculated methane, temperature, and velocity profiles in a single cell of the reactor for syngas from methane.

The predicted velocity profile is especially interesting. Even though Red < 30 throughout the entrance region and the velocity profiles before and within the catalyst section are parabolic, the axial velocity is not parabolic in the entrance region, and the velocity has a minimum in the center. A very thin boundary layer is established near the entrance to the catalytic section as the temperture and all properties vary strongly in very short distances.

The concentrations predicted by one dimensional calculations must therefore be very different from those calculated using these “exact” calculations. The gradients in temperature, velocity, and composition are so large in the entrance region that only a “complete” simulation should be expected to yield more than qualitative conclusions.

REACTIONS

Mechanisms and heat generation

Many modeling studies of these reaction systems have...

Produkt-Details

• Erscheint lt. Verlag: 1.6.2001
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Umwelttechnik / Biotechnologie
• ISBN-10: 0-08-053731-6 / 0080537316
• ISBN-13: 978-0-08-053731-3 / 9780080537313