Batch Reactor

M. Awais Yaqoob2011-ch-32

(University of Engineering and Technology, Lahore)

Mean residence time (t)

• It is taken as the measure of the performance of batch reactor

t =v/υ= volume of reactor Flow rate of feed in the reactor

SynopsisIntroduction

Working principle

Advantages and disadvantages

Applications

• Rate equation• Material balance• Energy balance

Kinetics

Design steps

Introduction

Working Principle

Advantages

limitations

1st Part

Material Balance

Performance Equation

Energy Balance

kinetics

2nd Part

Design steps

Factors

Design of BR

problem

3rd Part

Reactor DesignSize of reactor

• Fix one of the 5 parameter• Vf• Ws• S• Vs• Vr

• Shape• Spherical• cylindrical

• Dimensions• Internals• Inlets & outlets

Type of reactor

• BR• CSTR• PFR• Fixed bed

reactor• Fluidized

bed reactor• Slurry

reactor

Method of operation

• Batch• Continuou

s• Semi-

Continuous

• Intermittent

Method of OperationThermodynam

ic Basis

• Isothermal• Adiabatic• Constant

Volume• Constant

Pressure

Flow Patern

• Counter• Co Current• Cross

Current

Arrangment

• Series• Parallel• Recycle• Or

Combination Of Above

Introduction• The reactants are

initially charged into a container, are well mixed, and are left to react for a certain period.

• The resultant mixture is then discharged.

Working Principle• A batch reactor has neither inflow

nor outflow of reactants or products while the reaction is being carried out

• This is an unsteady-state operation where composition changes with time; however, at any instant the composition throughout the reactor is uniform

Advantages• They are preferred for establishing or

verifying kinetics because they are

o Simple in constructionoRequire little or no auxiliary equipments

• Data can be collected easily if Isothermal reactions are carried out under constant volume condition

• High conversions

Disadvantages/limitations• Intensity of process is localized and not

the global one• Preferred for homogenous reactions only• high labor costs per batch • difficulty of large-scale production.• Long idle time (Charging & Discharging

times) leads to periods of no production• No instrumentation – Poor product quality

Application• Typically for liquid phase reactions that

require long reaction times

• Used only when small amount of product is required

• Favored when a process is in developmental stage or to produce expensive products

• Used to make a variety of products at different times

Material Balance• Also called mass balance.• Is an application of law of

conservation of mass for the analysis of physical systems.

• It states that:• The mass that enters a system must,

by conservation of mass, either leave the system or accumulate within the system

Performance equation

(mA)in - (mA)out + (mA)gen - (mA)cons= (mA)acc/dep

since(mA)cons - (mA)gen = (mA)net cons

In case of BR(mA)in and (mA)out = 0The above equation will become-(mA)net cons = (mA)acc/dep

Dividing the above equation with molar mass of component A

• -(NA)net cons = (NA)acc/dep Since

After Substituting these values we will get

• Rearranging and integrating will give

Corollary• If the density of the fluid remains constant, we

obtain

Energy Balance• It is the application of law of conservation of

energy for the analysis of our physical system under consideration

• The heat that enters a system must, by conservation of heat/energy, either leave the system or accumulate within the system

• Overall energy balance

• heat in – heat out + heat gen – heat cons = heat acc/dep

KineticsRate Law For Zero Order Reaction

• Assumptions:o Isothermalo constant volumeo irreversible reaction

Stoichiometry:

Assumed rate law:

• Integrated rate law

Some Integrated rate equations

First order

Second order

Third order• Irreversible trimoleculer• A + B + D products

nth order

Design StepsFACTORS

• Type Of Reaction• Scale Of Prodution• Cost Of Equipment And Operations• Safety • Stability • Life Expectency• Ease Of Convertibility

Design steps• There is no particular formula for selecting the

parameters of a reactor

•Experience•knowledge of characteristics of reactors•literature surveyHelps us in selection of parameters

A Typical Batch Reactor

Design Measurements

Typical Proportions