What is Henry’s law and Raoult’s law

Henry’s law

It states that partial pressure of the solute gas is proportional to a mole fraction of that component in liquid phase but proportionality constant is H

p_A = H* x_A=Y_A . P

       where

• p_A = equilibrium partial pressure of pure liquid 'A'
• H = Henry's law constant for A in specific solvents
• x_A= mole fraction of A in the liquid phase
• Y_A = mole fraction of A in the vapor phase
• P = equilibrium pressure
• Henry's law is valid when x_A is close to zero that is for a dilute solution of 'A'

Raoult’s law

It states that the equilibrium partial pressure of components 'A' is equal to the product of vapor pressure and mole fraction of 'A' in the liquid phase.

         Mathematically

p_A = P_A⁰* x_A=Y_A . P

      where

• P_A⁰ = vapor pressure of pure liquid A
• Raoult's law is valid when x_A is close to 1 that is when the liquid phase is almost pure

DIFFERENCE BETWEEN UNIT OPERATION AND UNIT PROCESS

Difference between Unit operation and Unit process

• The chemical process is a combination of unit processes and Unit operation. Hence the Difference between Unit operation and Unit process as follows.

Unit process

The unit process involves a chemical change or sometimes it referred to as chemical changes along with physical change leading to the synthesis of various useful product

• It also provides basic information regarding the reaction temperature and pressure, the extent of chemical conversions and yield of product of the reaction, nature of reaction whether endothermic or exothermic, type of catalyst used.
• Example: hydrogenation, oxidation, nitration, etc

Unit operations

The operations carried out in the chemical process industry involving physical changes in the materials handled or in the system under consideration are called Unit operations

• Hence unit operations involve the physical separation of the products obtained during various unit processes.
• It is very important in chemical industries for separation of various products formed during the reaction.
• Individual operations have common techniques and are based on the same principles.

Above figure shows the unit process flow diagram for the production of benzene from toluene via various unit operations which are carried out in reactor, gas separator and still

Types of unit operations are as follows

1. Mechanical operations:-Example:- size reduction, conveying, filtration
2. Fluid flow operations:- In these operations, pressure difference act as a driving force.
3. Heat transfer:- In these operations, temperature difference act as a driving force. Example:- Evaporation
4. Mass transfer:- In these operations, the concentration difference act as a driving force. Example:-Distillation

WHAT IS MOLALITY

Molality

Molality is defined as the mole of the solute dissolved in one kilogram of solute.

Example: -
A solution of caustic soda contains 20 % NaOH by weight of a solution. The density of the solution is 1.196kg/lit. Find the molality
Solution ⇒

Given: - 20 % NaOH in the caustic soda solution
Basis: - 100 kg of solution

Formula:-

As the Solution contains 20 % of NaOH

∴ Weight of NaOH = 100 * 0.2 = 20 kg.................(1)

Weight of water (solvent ) = 100 - 20 = 80 kg..............(2)

As we know

CONTINUITY EQUATION

Continuity equation

• The continuity equation is a mathematical expression for the law of conservation of mass.
• The equation of continuity is useful for calculating the velocity of a fluid flowing through pipes of different diameters.

It states that for a steady flow system, the rate of mass entering the flow system is equal to that leaving as accumulation is either constant or nil in the flow system under steady conditions

• Rate of mass entering the flow system = ρ1 u1 A1
• Rate of mass entering the flow system = ρ2 u2 A2
• According to the law of conservation of mass

Mass entering the tube = Mass leaving the tube

per unit time       per unit time

• This is the equation of continuity.
• It is applicable to compressible as well as incompressible fluids.
• when ρ1 = ρ2

where

Continuity equation

IN PLACE & HEAP LEACHING

In place leaching

• In place leaching is also called solution mining in which minerals are recovered through boreholes drilled into the deposit.
• In this process, the solvent is pumped through the borehole into the ore body.
• Then the solvent is circulated through the porous rock of dissolving ore.
• Then the leach solution is extracted via the second borehole.

Example

• For salt deposit fresh water used as the solvent, for copper deposit acid used as the solvent and for uranium ores acid or sodium bicarbonates used as the solvent.

Heap Leaching

• Heap leaching is an industrial mining process. 
• In this process, precious metals are extracted from ore via a series of chemical reactions that absorb specific minerals and then reseparate them after their division from earth metal.
• In this process, mined ore is usually crushed into the small lump and heaped on an impermeable plastic or clay lined leached pad.
• Then the solvent is passed through it or sprinkled on it to dissolve valuable materials.
• Then the leach solution is percolated through the heap and then collected, treated in the process plant.

Example

• Copper has leached from pyritic ores.

Types of reactor

Types of reactor

• The confines in which chemical reactions occur are called reactors.
• In chemical engineering chemical reaction or set of reactions is carried out in a reaction vessel that is in chemical reactors.
• 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.
• While doing any operation we have to first decide what reactor type and reactor shape to select and whether it would be advantageous to operate in batch or continuous mode.
• Ideal reactors have three ideal flow or contacting patterns. They are main basic type of chemical reactor

1. Batch reactor
2. Flow reactor

• Continuous Stirred-Tank Reactor(CSTR)
• Plug Flow Reactor (PFR)

Batch reactor

• Whether the system does not exchanges mass with its surroundings, then the system is called a batch reactor.
• The batch reactor is simply a container with an agitator and an integral heating/cooling system.

• The reactants are initially charged into a container, are well mixed, and are left to react for a certain period.
• The resultant product mixture is then discharged.
• This is an unsteady-state operation where composition changes with time; however, at any instant the composition throughout the reactor is uniform
• During the operation, no addition or withdrawal is made.
• The experimental batch reactor is usually operated isothermally and at constant volume because it is easy to interpret the results of such runs.
• This reactor is a relatively simple device adaptable to small-scale laboratory set-ups, and it needs but little auxiliary equipment or instrumentation.
• Thus, it is used whenever possible for obtaining homogeneous kinetic data.

Advantages

• Suitable for small scale production
• Suitable for processes where a range of different products or grades is to be produced in the same equipment
• Suitable for reactions requiring long reaction times
• Suitable for reactions with superior selectivity

Limitation

• Not suitable for large batch sizes.
• It is a closed system in which once the reactants are added in the reactor, they will come out as products only after the completion of the reaction.

Application

• Batch processes are used in chemical (inks, dyes, polymers) and food industry.

Continuous Stirred-Tank Reactor (CSTR)

• The flow reactor is used primarily in the study of the kinetics of heterogeneous reactions.
• The first of the two ideal steady-state flow reactor is called the mixed reactor, the backmix reactor, the ideal stirred tank reactor, CSTR, or the CFSTR (constant flow stirred tank reactor)
• As its names suggest, it is a reactor in which the contents are well stirred and uniform throughout.
• In CSTR the reactants are fed to the reactor and the products or byproducts are withdrawn in between while the reaction is still progressing.

• The CSTR is normally run at steady-state and is usually operated so as to be quite well mixed.
• This type of flow is mixed flow, hence this reactor also called the mixed flow reactor or MFR.
• The exit stream from this reactor has the same composition and temperature as the fluid within the reactor.
• Continuous reactors are usually preferred for large scale production.

Advantages

• Highly flexible device
• By products may be removed in between the reaction.
• It is economically beneficial to operate several CSTRs in series or in parallel.
• Reaction can be carried out in horizontal as well as vertical reactors.

Limitation

• More complex and expensive than tubular units.
• All calculations performed with CSTRs assume perfect mixing.
• At steady state, the flow rate in must equal the flow rate out, otherwise the tank will overflow or go empty.

Application

• Chemical industry especially involving liquid/gas reactions.

Plug Flow Reactor (PFR)

• The other ideal steady-state flow reactors are variously known as the plug flow, slug flow, piston flow, ideal tubular, and unmixed flow reactor.
• It consists of a cylindrical pipe and is normally operated at a steady-state, as is the CSTR.

• This reactor is known as the plug flow reactor, or PFR because the flow in the reactor is highly turbulent and the flow field may be modeled by that of plug flow.
• It is characterized by the fact that the flow of fluid through the reactor is orderly with no element of fluid overtaking or mixing with any other element ahead or behind.
• Actually, there may be lateral mixing of fluid in a plug flow reactor; however, there must be no mixing or diffusion along the flow path.
• Hence in the tubular reactor, the reactants are continually consumed as they flow down the length of the reactor.
• The necessary and sufficient condition for plug flow is for the residence time in the reactor to be the same for all elements of fluid.

Advantage

• Higher efficiency than a CSTR of the same volume
• PFRs may have several pipes or tubes in parallel
• Both horizontal and vertical operations are common
• They can be jacketed
• Reagents may be introduced at locations even other then inlet

Limitation

• Not economical for small batches

Application

• The tubular reactor is especially suited to cases needing considerable heat transfer, where high pressures and very high or very low temperatures occur

AFFINITY LAWS OF PUMP

The Affinity Laws of pump

• The Affinity Laws of centrifugal pumps or fans indicates the influence on volume capacity, head (pressure) and/or power consumption of a pump or fan due to

1. change in speed of wheel - revolutions per minute (rpm)
2. geometrically similarity - change in impeller diameter

• Hence, the Affinity Laws are mathematical expressions that define changes in pump capacity,head, and BHP when a change is made to pump speed, impeller diameter, or both.
• Affinity laws are useful when an existing pump must be modified ti give a higher or lower head or different capacity
• The Affinity Laws are valid only under conditions of constant efficiency.

According to Affinity Laws:Capacity, Q: changes in direct proportion to impeller diameter D ratio, or to speed N ratio:

Head, H: changes in direct proportion to the square of impeller diameter D ratio, or the square of speed N ratio:

BHP: changes in direct proportion to the cube of impeller diameter ratio, or the cube of speed ratio:

• Where the subscript: 1 refers to initial condition, 2 refer to new condition
• If changes are made to both impeller diameter and pump speed the equations can be combined to: