M. Awais Yaqoob2011-ch-32

(University of Engineering and Technology, Lahore)

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.

These are the two main basic vessel types:

• tank• pipe

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.

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

Reaction Types• Direct Combination or Synthesis

ReactionA + B = AB

• Chemical Decomposition or Analysis Reaction

AB = A + B

• Single Displacement or Substitution Reaction

A + BC = AC + B• Metathesis or Double

Displacement ReactionAB + CD = CB

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

Endothermic Reactions

• “within- heating” describes a process or reaction that absorbs energy in the form of heat.

Exothermic Reactions

• Release energy in the form of heat, light, or sound.

• ∆S > 0 • ∆H < 0

Reaction Rate• Speed at which a chemical

reaction proceeds, in terms of amount of product formed or amount of reactant consumed per unit time

Factors Influencing Reaction Rate

• Concentration• The nature of reaction• Temperature• Pressure• Catalyst

Modeling Principle:

• Inputs + Sources = Output + Sink + Accumulations

Basic Reactor Element

•Material Balances•Heat Transfer and Mass Transfer

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 .

Mathematically the mass balance for a system without a chemical reaction is

as follows:

•Input = Output + Accumulation

Applications of Differential Mass Balance

• Ideal (stirred) Batch reactor• Ideal tank reactor, also named

Continuous Stirred Tank Reactor (CSTR)

• Ideal Plug Flow Reactor(PFR)

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.

Heat Transfer• Is the transition of thermal energy

from a heated item to a cooler item.

• Transfer of Thermal Energy

Modes Of Heat Transfer• jacket,

• internal coils,

• external heat exchanger,

• cooling by vapor phase condensation

• fired heater.

Jacket

Internal Coil

External Heat Exchanger

Cooling by Vapor Phase Condensation

Heat Exchange in Packed Reactors

Chemical Reactor can be operated in:

1. Batch Modes 2. Semi Continuous Modes 3. Continuous Modes

BATCH REACTOR

• One in which feed material is treated as a whole for a fixed period of time.

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.

Single External Jacket

• 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

Half Coil Jacket

•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

Constant Flux Cooling Jacket

SCHEMATIC DIAGRAM OF CRUDE SEWAGE

Semi Batch Reactor• One or more reactant is in a batch

modes, while co reactant is fed and withdrawn continuously.

Schematic Diagram of Semi Batch

Stirred TankReactor

Consist of a tank fitted with a mechanical agitator and a cooling jacket or coils.

Continuous Stirred-Tank Reactor(CSTR)

• One or more fluid reagents are introduced into a tank reactor.

• Residence time – average amount of time a discrete quantity of reagents spend inside the tank

• Residence time = volumetric flow rate volume of the tank

Some Important Aspects of the CSTR:

• At steady state, the flow rate in must be equal the mass flow rate out.

• All calculations performed with CSTR’s assume perfect mixing.

• The reaction proceeds at the reaction rate associated with the final (output) concentration.

• Economically beneficial to operate in series or in parallel

• Small CSTR operating in series would be equivalent to a PFR.

Plug Flow Reactor(PFR)

One or more fluid reagents are pumped through a pipe or tube

Some Important Aspects of the PFR:

• All calculations performed with PFR’s assume no upstream or downstream mixing.

• Reagents may be introduced into the reactor’s inlet

• Has a higher efficiency than a CSTR at the same value.

Schematic Diagram of Plug Flow Reactor

Tubular Flow Reactor(TFR)

are generally used for gaseous reactions but are also suitable for some liquid-phase reactions.

Some Important Aspects of the TFR:

• Chemical reactions take place in a stream of gas that carries reactants from the inlet to the outlet

• The catalysts are in tubes

• Uniform loading is ensured by using special equipment that charges the same amount of catalyst to each tube at a definite rate.

CATALYSIS

CATALYSIS

• It is the acceleration of chemical reaction by means of substance called catalyst.

Principles of Catalysis:

∙Typical mechanism: A + C → AC (1) B + AC → ABC (2) ABC → CD (3) CD → C + D (4)

•Catalysis and reaction energetic.

What is Phase?

Two Types of Catalyst:

∙Homogeneous∙Heterogeneous

Homogeneous• the catalyst in the same phase as the reactants.

Heterogeneous• Involves the use of a

catalyst in a different phase from the reactants.

How the heterogeneous catalyst works?

•Adsorption•Active Sites•Desorption

Adsorption

•Is where something sticks to a surface.

Active Sites

• Is a part of the surface which is particularly good at adsorbing things and helping them to react.

Desorption

• means that the product molecules break away.

Kinds of Catalyst• Strong Acids• Base Catalysis• Metal oxides, Sulfides, and Hydrides• Metal and Alloys • Transition-metal Organometallic

Catalysts

Strong Acids

• Is an acid that ionizes completely in an aqueous solution

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.

Metal Oxides

• Form a transition between acid/base and metal catalysts.

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

Transition-metal Organometallic Catalysts

•More effective hydrogenation than are metals such as platinum.

Fluid and Solid Catalysis

• Multitubular reactors• Fluidized beds• Fixed Bed • Spray Tower• Two-Phase Flow

Multitubular reactors

• These reactors are shell-and-tube configuration and have catalyst in the tubes.

Multi tubular Reactor

Fluidized Bed

• Device that can be used to carry out a variety of multiphase chemical reactions.

• A catalyst possibly shaped as tiny spheres.

Fluidized Bed Reactor

Fixed Bed • Fixed bed reactor is a

cylindrical tube, randomly filled with catalyst particles, which may be spheres or cylindrical pellets.

Fixed Bed Reactor

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

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.

Two-Phase Flow

• occurs in a system containing gas and liquid with a meniscus separating the two phases.

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

Goodbye!!!!!

Eating Time!!!! Thank You!!!!