Chemical Reactors


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  • Catalysts generally react with one or more reactants to form an intermediate that subsequently give the final reaction product, in the process regenerating the catalyst. The following is a typical reaction scheme, where C represents the catalyst, A and B are reactants, and D is the product of the reaction of A and B:
  • Chemical Reactors

    1. 1. M. Awais Yaqoob 2011-ch-32 (University of Engineering and Technology, Lahore)
    2. 2. Chemical Reactors • An industrial chemical reactor is complex device in which heat transfer, mass transfer, diffusion and friction may occur along with chemical reaction with provisions of safety and controls. • Are vessels designed to contain chemical reactions.
    3. 3. These are the two main basic vessel types: •tank •pipe
    4. 4. Basic Principles: • All chemical processes are centered in a chemical reactor. The design of a chemical reactor Is the most important factor in determining the overall process economics.
    5. 5. At the start the design work , the following information is presumably available: . Reaction Type . Need for catalyst . Phases involve . The mode of temperature and pressure control, and . Production capacity
    6. 6. Reaction Types • Direct Combination or Synthesis Reaction A + B = AB • Chemical Decomposition or Analysis Reaction AB = A + B
    7. 7. • Single Displacement or Substitution Reaction A + BC = AC + B • Metathesis or Double Displacement Reaction AB + CD = CB
    8. 8. In addition to the basic data, include: • A heat and mass transfer characteristics • Physical, chemical and thermodynamic properties of components taking part in the reaction. • CORROSION- erosion characteristics of any potential hazard associated with reaction system. • Reaction Rate
    9. 9. Endothermic Reactions • “within- heating” describes a process or reaction that absorbs energy in the form of heat.
    10. 10. Exothermic Reactions • Release energy in the form of heat, light, or sound. • ∆S > 0 • ∆H < 0
    11. 11. Reaction Rate • Speed at which a chemical reaction proceeds, in terms of amount of product formed or amount of reactant consumed per unit time
    12. 12. Factors Influencing Reaction Rate • Concentration • The nature of reaction • Temperature • Pressure • Catalyst
    13. 13. Modeling Principle: •Inputs + Sources = Output + Sink + Accumulations
    14. 14. Basic Reactor Element •Material Balances •Heat Transfer and Mass Transfer
    15. 15. Material Balances • Also called mass balance. • Is an application of conservation of mass to the analysis of physical systems. • The mass that enters a system must, by conservation of mass, either leave the system or accumulate within the system .
    16. 16. Mathematically the mass balance for a system without a chemical reaction is as follows: •Input = Output + Accumulation
    17. 17. Applications of Differential Mass Balance • Ideal (stirred) Batch reactor • Ideal tank reactor, also named Continuous Stirred Tank Reactor (CSTR) • Ideal Plug Flow Reactor(PFR)
    18. 18. Mass Transfer • Is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of atoms and molecules within physical system. • Transfer of mass from high concentration to low concentration.
    19. 19. Heat Transfer • Is the transition of thermal energy from a heated item to a cooler item. • Transfer of Thermal Energy
    20. 20. Modes Of Heat Transfer • jacket, • internal coils, • external heat exchanger, • cooling by vapor phase condensation • fired heater.
    21. 21. Jacket
    22. 22. Internal Coil
    23. 23. External Heat Exchanger
    24. 24. Cooling by Vapor Phase Condensation
    25. 25. Heat Exchange in Packed Reactors
    26. 26. Chemical Reactor can be operated in: 1. Batch Modes 2. Semi Continuous Modes 3. Continuous Modes
    27. 27. BATCH REACTOR •One in which feed material is treated as a whole for a fixed period of time.
    28. 28. Types of Cooling Jacket: Single External Jacket • Consists of an outer jacket which surrounds the vessel. • Heat transfer fluid flows around the jacket and is injected at high velocity via nozzles. • The temperature in the jacket is regulated to control heating or cooling.
    29. 29. Single External Jacket
    30. 30. • The half coil jacket is made by welding a half pipe around the outside of the vessel to create a semi circular flow channel. •A large reactor may use several coils to deliver the heat transfer fluid. Half Coil Jacket
    31. 31. Half Coil Jacket
    32. 32. •Has a series of 20 or more small jacket elements. •The temperature control valve operates by opening and closing these channels as required. Constant Flux Cooling Jacket
    33. 33. Constant Flux Cooling Jacket
    35. 35. Semi Batch Reactor • One or more reactant is in a batch modes, while co reactant is fed and withdrawn continuously.
    36. 36. Schematic Diagram of Semi Batch
    37. 37. Stirred Tank Reactor
    38. 38. Consist of a tank fitted with a mechanical agitator and a cooling jacket or coils.
    39. 39. Continuous Stirred-Tank Reactor (CSTR) • One or more fluid reagents are introduced into a tank reactor.
    40. 40. • Residence time – average amount of time a discrete quantity of reagents spend inside the tank • Residence time = volumetric flow rate volume of the tank
    41. 41. Some Important Aspects of the CSTR:
    42. 42. • At steady state, the flow rate in must be equal the mass flow rate out.
    43. 43. • All calculations performed with CSTR’s assume perfect mixing.
    44. 44. • The reaction proceeds at the reaction rate associated with the final (output) concentration. • Economically beneficial to operate in series or in parallel
    45. 45. • Small CSTR operating in series would be equivalent to a PFR.
    46. 46. Plug Flow Reactor (PFR) One or more fluid reagents are pumped through a pipe or tube
    47. 47. Some Important Aspects of the PFR:
    48. 48. • All calculations performed with PFR’s assume no upstream or downstream mixing. • Reagents may be introduced into the reactor’s inlet
    49. 49. • Has a higher efficiency than a CSTR at the same value.
    50. 50. Schematic Diagram of Plug Flow Reactor
    51. 51. Tubular Flow Reactor (TFR) are generally used for gaseous reactions but are also suitable for some liquid-phase reactions.
    52. 52. Some Important Aspects of the TFR:
    53. 53. • Chemical reactions take place in a stream of gas that carries reactants from the inlet to the outlet • The catalysts are in tubes
    54. 54. • Uniform loading is ensured by using special equipment that charges the same amount of catalyst to each tube at a definite rate.
    55. 55. CATALYSIS
    56. 56. CATALYSIS •It is the acceleration of chemical reaction by means of substance called catalyst.
    57. 57. Principles of Catalysis: ∙Typical mechanism: A + C → AC (1) B + AC → ABC (2) ABC → CD (3) CD → C + D (4)
    58. 58. •Catalysis and reaction energetic.
    59. 59. What is Phase?
    60. 60. Two Types of Catalyst: ∙Homogeneous ∙Heterogeneous
    61. 61. Homogeneous • the catalyst in the same phase as the reactants.
    62. 62. Heterogeneous •Involves the use of a catalyst in a different phase from the reactants.
    63. 63. How the heterogeneous catalyst works? •Adsorption •Active Sites •Desorption
    64. 64. Adsorption •Is where something sticks to a surface.
    65. 65. Active Sites •Is a part of the surface which is particularly good at adsorbing things and helping them to react.
    66. 66. Desorption • means that the product molecules break away.
    67. 67. Kinds of Catalyst • Strong Acids • Base Catalysis • Metal oxides, Sulfides, and Hydrides • Metal and Alloys • Transition-metal Organometallic Catalysts
    68. 68. Strong Acids •Is an acid that ionizes completely in an aqueous solution
    69. 69. Base Catalysis • Is most commonly thought of as an aqueous substance that can accept protons. • Base the chemical opposite of acids. • Often referred to as an alkali if OH− ions are involved.
    70. 70. Metal Oxides •Form a transition between acid/base and metal catalysts.
    71. 71. Metal and Alloy • Metal is a chemical elements whose atoms readily lose electrons to form positive ions (cations), and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms. • The principal industrial metallic catalyst, are found in periodic group VII
    72. 72. Transition-metal Organometallic Catalysts •More effective hydrogenation than are metals such as platinum.
    73. 73. Fluid and Solid Catalysis • Multitubular reactors • Fluidized beds • Fixed Bed • Spray Tower • Two-Phase Flow
    74. 74. Multitubular reactors •These reactors are shell- and-tube configuration and have catalyst in the tubes.
    75. 75. Multi tubular Reactor
    76. 76. Fluidized Bed • Device that can be used to carry out a variety of multiphase chemical reactions. • A catalyst possibly shaped as tiny spheres.
    77. 77. Fluidized Bed Reactor
    78. 78. Fixed Bed • Fixed bed reactor is a cylindrical tube, randomly filled with catalyst particles, which may be spheres or cylindrical pellets.
    79. 79. Fixed Bed Reactor
    80. 80. SPRAY TOWER • Are a form of pollution control technology. • Consist of empty cylindrical vessels made of steel or plastic and nozzles that spray liquid into the vessels
    81. 81. Two types of Spray Towers: 1.Cocurrent Flow -are smaller than countercurrent-flow spray towers 2.Crosscurrent Flow - the gas and liquid flow in directions perpendicular to each other.
    82. 82. Two-Phase Flow • occurs in a system containing gas and liquid with a meniscus separating the two phases.
    83. 83. Two-phase flow may be classified according to the phases involved as: • gas-solid mixture • gas-liquid mixture • liquid-solid mixture • two-immiscible-liquids mixture
    84. 84. Goodbye!!!!! Eating Time!!!! Thank You!!!!