College of Mechanical
Engineering Technology
Benghazi
‫كلية تقنية الهندسة‬
‫الميكانيكية‬
‫بنغازي‬
Department
of
Chemical Engineering
‫قسم الهندسة الكيميائية‬
Unit operations and Unit processes II
[ChE- 705]
Lecture notes
By
Adjunct faculty - Khalil Ali Alpelekeya
{ ‫} أس تاذ متعاون – خليل عيل البيلكيه‬
Academic year
2021-2022
Part one
Lectures
Unit Operation and unit process
Unit Operation and unit process
The basic physical operations of chemical engineering in a chemical process plant, that is distillation,
fluid transportation, heat and mass transfer, evaporation, extraction, drying, crystallization, filtration,
mixing, size separation, crushing and grinding, and conveying.
•In simple terms, the operation that involves physical changes are known as unit operation.
•Those operations, which involves chemical changes such as reaction, are known as unit process.
Chemical engineering is all about chemical reactions and elements, factors, and optimization of those
to understand the mechanics of chemical reactions and producing products. The combination of both
unit operation and process is called the manufacturing process or chemical process.
Unit operation
It is a basic step in a process that involves physical change during the process such as evaporation
crystallization, filtration, and other operations.
Examples of Unit operation
Example 1 – Distillation of Methylene dichloride with water
Explanation – In a process, the separation of methylene dichloride with water using a liquid-liquid
separation technique can be called as a unit operation.
Explanation – In the above process, only separation is taking place, which will be done base on density
difference. This is a physical change and no chemical reaction taking place, hence this process is
considered as unit operation.
Example 2 – Distillation of acetone and water
Explanation – The distillation of acetone from the water is an example of unit operation. In the
distillation process, acetone is separated and that is due to boiling point difference or volatility of the
components. This is also a physical change and no chemical reaction is carried out. Hence, distillation
is a unit operation.
Classification of Unit Operation
Now we had seen the definition of unit operation and hereby learned what unit operation is. There are
four classification of unit operation, classification of unit operation are listed below.
1. Material handling, transportation / Fluid flow process
Pumping
Compression
fluidization
2. Mechanical unit operations
Size reduction
Size enlargement
mixing, agitation, blending, etc.
3. Mass transfer Operations
Evaporation
Distillation
Absorption
Extraction
leaching.
4. Heat transfer operations
conduction
convection
radiation
Unit Process
The unit process is a process in which chemical changes take place to the material present in the
reaction and result in the chemical reaction is known as the unit process. This consists of a reaction
between two or more chemical which results in another chemical can also be defined as unit process.
Sulphonation, nitration, oxidation, halogenation, and many more.
Example of Unit process
Example 1 – Electrolysis of sodium chloride solution
Explanation – Here, electrolysis of Nacl is being done and the concentration of sodium chloride is
taken as 305 (around) GPL (gram per liter) concentration is feed to electrolysis cell in which electricity
is passed and sodium hydroxide is produced. In this reaction, decomposition reaction takes place;
hence, this is a unit process.
Example 2 – Production of Hydrogen
Hydrogen is produced using very popular method i.e. Steam-methane reforming reaction. In this
method, methane reacts with steam at a pressure under 3–25 bar pressure in the presence of a Nickel
catalyst to produce hydrogen.
In this Steam-methane reforming reaction, chemical reaction under pressure and temperature is
being conducted to react methane with steam and generate hydrogen. As here the reaction is begin
conducted, this process comes under unit process.
Manufacturing process
What is chemical process?
Manufacturing process consists of a combination of various unit operations and unit processes which
being conducted considering factors like optimization, design of equipment and selection of equipment,
use of suitable utilities, and many more to make product is known as manufacturing process/chemical
process.
Structures of unit operations and unit processes
•These manifesting physical steps are called unit operations.
•The chemical step is called unit process or simply “process”
Example – Manufacturing process of cement
Cement is considered as a product, which is a result of unit operation and unit process. There are
various unit operations and unit processes are involved in the manufacturing process of cement. We
will not go in-depth into the manufacturing process and will consider the relevant things only. For the
manufacturing process of cement. The main raw material of cement is limestone, which is present in
the hard solid rock form. It is crushed into a fine powder using a jaw crusher. Using Jaw crusher, only
physical changes will be conducted hence it is a unit operation. In the chemical process, limestone is
heated and decomposes into lime and carbon dioxide is released which is a unit process.
Difference between unit operation and unit process?
Unit Operation
Process in which only physical changes and not
chemical changes takes place are known as a unit
operation.
Mixing, blending, crushing distillation, etc. are
considered as unit operations
Unit Process
Process in which chemical changes (reaction)
takes place are considered as unit process.
Bromination, halogenation, sulphonation, etc.
are called unit process
Is distillation unit process or unit operation?
Distillation is a unit operation as there is not chemical reaction take place and only physical separation
takes place. Hence, the answer to the question Is distillation a unit operation? Yes, distillation is a
unit operation.
What is unit process example?
Process in which chemical reaction takes place such as nitration, sulphonation, chlorination and many
more are unit process example.
What is unit operation in food industry?
In the food process industry, unit operations such as cleaning, mixing, separation, and filtration are
used.
Basic principles of unit operations and unit processes in chemical industries
Chemical processes usually have three interrelated elementary processes

Transfer of reactants to the reaction zone

Chemical reactions involving various unit processes

Separation of the products from the reaction zone using various unit operations
Processes may involve homogeneous system or heterogeneous systems. In homogeneous system,
reactants are in same phase-liquid, gases or solids while heterogeneous system include two or more
phases; gas liquid, gas–solid, gas-gas, liquid–liquid, liquid solid etc. Various type reactions maybe
reversible or irreversible, endothermic or exothermic, catalytic or non-catalytic. Various variables
affecting chemical reactions are temperature pressure, composition, catalyst activity, catalyst
selectivity, catalyst stability, catalyst life, the rate of heat and mass transfer.
The reaction may be carried out in batch, semi batch or continuous. Reactors may be batch,
plugflow, CSTR. It may be isothermal or adiabatic. Catalytic reactors may be packed bed,
movingbed or fluidized bed.
Along with knowledge of various unit processes and unit operation following information are very
important for the development of a process and its commercialization [Austin, 1984]
Basic Chemical data: Yield conversion, kinetics





Material and energy balance, raw material and energy consumption per ton of product,
energy changes
Batch vs. Continuous, process flow diagram
Chemical process selection: design and operation, pilot plant data, equipment required, and
material of construction.
Chemical process control and instrumentation

Chemical process economics: Competing processes, material and, energy cost, labor,
overall cost of production
Market evaluation: Purity of product and uniformity of product for further processing

Plant location

Environment, Health, safety and hazard

Construction, Erection and commissioning


Management for productivity and creativity: Training of plant personals and motivation
at all levels.
Research, Development and patent

Process Intensification
In order to improve productivity and make the process cost effective and for improving
overall economy, compact , safe, energy efficient and environmentally sustainable plant,
process intensification has become very important and industry is looking beyond the
traditional chemical engineering.
Unit processes and unit operation in chemical process industries
Chemical process is combination of unit processes and unit operation. Unit process involves
principle chemical conversions leading to synthesis of various useful product and provide basic
information regarding the reaction temperature and pressure, extent of chemical conversions and
yield of product of reaction nature of reaction whether endothermic or exothermic, type of catalyst
used. Unit operations involve the physical separation of the products obtained during various unit
processes. Various unit processes in chemical industries are given in table M-I 3.1. Various
chemical reactions and its application in process industries are given in table M-I 3.2.
Table M-I 3.1: Unit processes in chemical process industries
Table M-I 3.2: Important chemical reaction and their application inchemical process industries
NITRATION
Nitration involves the introduction of one or more nitro groups into reacting molecules using
various nitrating agents like fuming, concentrated, aqueous nitric acid mixture of nitric acid and
sulphuric acid in batch or continuous process. Nitration products find wide application in chemical
industry as solvent, dyestuff, pharmaceuticals, explosive, chemical intermediates. Typical
products: TNT, Nitrobenzene, m-dinitrobenzene, nitro acetanilide, alpha nitro naphthalene,
nitroparaffins.
Example Preparation of TNT (trinitrotoluene)
TNT is produce in a three-step process: First, toluene is nitrated with a mixture of sulfuric
acid and nitric acid to produce mono-nitro toluene or MNT. The MNT is separated and then
reiterated to trinitrotoluene or DNT. In the final step, the DNT is nitrated to trinitrotoluene or TNT
using an anhydrous mixture of nitric acid and oleum.
HALOGENATION
Halogens involve introduction of one or more halogen groups into an organic compound for
making various chlorine, bromine, iodine, fluorine organic derivatives. All though chlorine
derivatives find larger application, however some of the bromine and fluorine derivatives arealso
important. Various chlorinating agents are chlorine, HCl, phosgene sulfuric chloride, hypochlorite,
bromination, bromine, hydrobromic acid, bromide, bromated, alkalinehypobromites. In iodination
iodine, hydroiodic acid and alkali hypoiodites.
Example
Typical important chemicals are chlorinated products: Ethylene dichloride, chlorinated methanes
Chloroform, Carbon tetra chloride etc.) Chlorinate ethane, Chloro propane, chloro butanes,
Chloroparaffins, chlorination of acetaldehyde (Chloral), alkyl halhides, Chlorobenzene,
Ethylenedioxide, Chlorofluorocarbon (CFCs).
Preparation of chloroform and chlorofluorocarbon (CFCs)
SULPHONATION AND SULPHATION
Sulphonation involves the introduction of sulphonic acid group or corresponding salt like
sulphonyl halide into an organic compound while sulphationinvolves introduction of -OSO2OH or
-SO4-. Various sulphonating agents are sulphur trioxide and compounds, sulphurdixide,
sulphoalkylating agents. Some of the sulphaming agents are sulphamic acid. Apart from
sulfonation and sulphamate sulpho chlorinated, sulfoxidation is also used. Typical application of
sulphonation and sulphation are production of lingo sulphonates, linear alkyl benzene sulphonate,
Toluene sulphonates, phenolic sulphonates, chlorosulphonicacd, sulphamates for production of
herbicide, sweetening agent (sidiumcyclohexysulphamate). Oil soluble sulphonate, saccharin
Preparation of Saccharin
The industrial synthesis entails the reaction of hydrogen chloride with a solution of sulfur
trioxide in sulfuric acid. Sulfonation by chlorosulfonic acid gives the ortho and para substituted
chlorosulfones. The ortho isomer is separated and converted to the sulfonamide with ammonia.
Oxidation of the methyl substituent gives the carboxylic acid, which cyclicizes to give saccharin.
HCl + SO3 → ClSO3H
OXIDATION
Oxidation used extensively in the organic chemical industry for the manufacture of a large number
of chemicals. Oxidation using oxygen, are combinations of various reactions like oxidation via
dehydrogenation using oxygen, dehydrogenation and the introduction of oxygen and destruction
of carbon, partial oxidation, peroxidation, oxidation in presence of strong oxidizing agent like
KMnO4, chlorate, dichromate, peroxides H2O2, PbO2, MnO2; nitric acid and nitrogen tetra oxide,
oleum, ozone. Some of the important product of oxidation are aldehyde, ketone, benzyl alcohol,
phthalic anhydride, ethylene oxide, vanillin, bezaldehyde, acetic acid, cumene, synthesis gas from
hydrocarbon, propylene oxide, benzoic acid, maleic acid, benzaldehyde, phtathalic anhydride.
Oxidation maybe carried out either in liquid phase or vaporphase.
Preparation of synthesis gas from hydrocarbon
By using the Fischer–Tropsch process, or Fischer–Tropsch synthesis, is a collection of chemical
reactions that converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons.
H2O + CH4
CO + 3 H2
Synthetic gas
HYDROLYSIS
Hydrolysis is used both in inorganic and organic chemical industry. Typical application is in oil
and fats industry during soap manufacture where hydrolysis of fats are carried out to obtain fatty
acid and glycerol followed by addition of sodium hydroxide to form soap. Other application is in
the manufacture of amyl alcohols. Some of the major product using hydrogen is ethylene from
acetylene, methanol, propanol, butanol, production of alcohol from olefins (e.g. Ethanol from
ethylene). Various types of hydrolysis reaction may be pure hydrolysis, hydrolysis with aqueous
acid or alkali, dilute or concentrated, alkali fusion, hydrolysis with enzyme and catalyst.
Preparation of ethanol from ethylene:
CH2 = CH2(g) + H2O(g)
catalyst
CH3CH2OH(g)
H = - 45 kJ mol -1
HYDROGENATION
Hydrogenation involves the reaction of a substance with hydrogen in the presence of a catalyst.
Some of the other reaction involving hydrogen are hydrodesulphurization, hydrocracking, hydro
formulation, Oxo synthesis, hydroammonylsis, and synthesis of ammonia.
Preparation of aldehyde (Hydro-formulation):
H2 + CO + CH3CH=CH2
HCo(CO)PBu3
CH3CH2CH2CHO
ESTERIFICATION
Esterification is an important unit process in the manufacture of polyethylene terephthalate, methyl
metha acrylate, cellulose ester in viscose rayon manufacture (xanthation of alkali cellulose with
carbon disulphide), nitroglycerine.
ALKYLATION
Alkylation involves the introduction of an alkyl radical into an organic compound by substitution or
reduction. Products from alkylation find application in detergent, lubricants, high-octane gasoline,
photographic chemicals, plasticizers, synthetic rubber, chemicals etc. Some of thealkylating agents
are olefins, alcohols, alkyl halides. Although sulphuric acid and phosphoricacid were commonly
used as catalyst in alkylation process, however due to the corrosive nature of these acid now solid
acid catalyst is finding wide application in new alkylation processes.
Preparation of toluene
Alkylation is the transfer of an alkyl group from one molecule to another.
POLYMERIZATION
Polymerization is one of the very important unit processes, which find application in manufacture
of polymer, synthetic fiber, synthetic rubber, polyurethane, and paint and petroleum industry for
high-octane gasoline. Polymerization maybe carried out either with single monomer or with
comonomer. Polymerization reaction can be addition or condensation reaction. Various
Polymerization methods may be bulk, emulsion, solution, suspension. Typical important product
from polymerization are, Polyethylene, PVC, poly styrene, nylon, polyester, acrylic fibre, poly
butadiene, poly styrene, phenolic, urea, melamine and alkyd resins epoxy resin, silicon polymers,
poly vinyl alcohol etc.
Preparation of Polyethylene or polythene
It is the most common plastic.
NITRIC ACID
INTRODUCTION
Nitric acid (HNO3), also known as aqua fortis (strong water) and spirit of niter, is
• A highly corrosive strong mineral acid.
• The pure compound is colorless, but older samples are yellowish in color due to the
accumulation of oxides of nitrogen.
• Commercially available nitric acid having concentration of 68% HNO3, while the solution
containing more than 86% HNO3, is referred to as fuming nitric acid.
• Depending on the amount of nitrogen dioxide present, fuming nitric acid is further
characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above
95%.
MANUFACTURE
Nitric acid is manufactured by three methods.
1. From Chile saltpeter or nitrate
2. Arc process or Baekeland and eyed process
3. Ostwald's process or Ammonia oxidation process
1. From Chile saltpeter or nitrate
It is the first commercial process of manufacture of nitric acid from sodium nitrate extracted from
Chile saltpeter. The process is now become obsolete since second decade of nineteenth century.
Raw materials
Sodium Nitrate
Sulfuric acid
Sources of raw material
Sulfuric acid can be obtained by contact process.
Sodium nitrate can be obtained from caliche ore. Also, it is manufactured by neutralization of soda
ash with nitric acid as well by reaction of ammonium nitrate and sodium hydroxide.
Reaction
NaNO3 + H2SO4
NaHSO4 + HNO3
2. Arc process or Birkeland and eyed process:
N2 + O2 ----2NO endo.
2NO + O2 ---2NO2
4NO+H2O --HNO3
3. Ostwald's process or Ammonia oxidation process:
Raw Materials
• Ammonia
• Air
• Platinum
• Water
• Steam credit
• Power
Reaction
Major reactions
4NH3 + 5O2
4NO + 6H2O
ΔH = - 216.6kcals ---- (1)
2NO+O2
2NO2
ΔH = - 27.1kcals ---- (2)
3NO2+H2O
2HNO3+
ΔH = - 32.2 kcals .... (3)
1
3
NH3+O2
N2O +2 H2O
ΔH = - 65.9kcals ... (4)
2
Manufacture
Nitric acid is made by the oxidation of ammonia, using platinum or platinum- 10% rhodium as catalyst,
followed by the reaction of the resulting nitrogen oxides with water.
•
•
•
Compressed air is mixed with anhydrous ammonia, fed to a shell and tube convertor designed so that
the preheater and steam heat recovery boiler-super heater are within the same reactor shell. The
convertor section consists of 10-30 sheets of Pt-Rh alloy in the form of 60-80 mesh wire gauge packed
in layers inside the tube. Contact time, of the gas passes downward in the catalyst zone 2.5 X 10-4 sec,
and are heated at 8000C.
Product gases from the reactor that contain 10-12% NO, are sent through heat recovery units consisting
of heat recovery boiler, super heater and quenching unit for rapid cooling to remove large fraction of
product heat, and into the oxidizer-absorber system. Air is added to convert NO to NO2 at the more
favorable temperature (40-500C) environment of the absorption system.
The equipment in the absorption train may be series of packed or sieve tray vertical towers or a series
of horizontal cascade absorbers. The product from this water absorption system is 57- 60% HNO3
solution which can be sold as or concentrated as follow:
1. Concentration by H2SO4
2. Concentration by Mg(NO3)2
The process involves four steps
1. Catalytic oxidation of ammonia with atmospheric oxygen to yield nitrogen monoxide.
2. Oxidation of the nitrogen monoxide product to nitrogen dioxide or dinitrogen tetroxide.
3. Absorption of the nitrogen oxides to yield nitric acid.
4. Concentration of nitric acid.
Catalyst for oxidation of ammonia
• Platinum/rhodium alloy containing 10% rhodium is the only industrially viable catalyst.
• Rhodium not only improves the catalytic properties of platinum but also improves mechanical and
anti-abrasive properties of material under the operating condition such as to counter the severe
corrosion and oxidation atmosphere.
• 4–10 % of rhodium used in Pt/Rh supported catalyst. Knitted gauzes can achieve higher
efficiencies and smaller platinum losses.
• The metallic alloy catalyst is prepared into very fine threads of diameter 0.05mm, which are woven
into meshes with more than 1000stiches/cm2. Two to four or even more of these meshes are placed
on top of one another inside the reactors when these are put into operation.
• Catalyst threads are smooth, bright and less active at initial stage, as the time progresses they
becomes dull and wrinkled whereupon their activity rises to the maximum. Finally, they become
spongy with activity falling off.
• When it is in most active state, ammonia oxidation yields up to 98% of NO are obtained.
• Ammonia conversion efficiency is a function of pressure and temperature.
• As the pressure increases, higher temperatures are needed to obtain the high conversion efficiency.
An increased flow rate and the presence of several layers of the catalyst help to minimize undesirable side
reactions. However, high flow rates increase the catalyst loss, which leads to search for non-platinum
catalysts for ammonia oxidation. The most prospective non-platinum catalysts are based on oxides of Co,
Fe or Cr.
Catalyst poison
• Sulfates, H2S, chlorides, Arsenic and its oxide, Si, P, Pb, Sn and Bi are permanently poisoning
the catalyst. These elements lead to the formation of inactive compounds in the wires resulting in
decreasing of the catalytic activity.
• Traces of acetylene, ethylene, Cr, Ni and Fe temporarily reduce the conversion efficiency which
can be restored by treatment with HCl. There so air should be freed from all above impurities along
with suspended particles of lubricants, fats, fine dust and abrasive powder. Also, suspension of
Fe2O3 from ammonia is removed. For that efficient filtration system along with magnetic
separators are provided.
SULFURIC ACID
Introduction
Sulfuric acid (H2SO4) is a highly corrosive strong mineral acid. It is a colorless to slightly yellow viscous
liquid which is soluble in water at all concentrations. It is one of the most important heavy industrial
chemicals due to it has a number of large-scale uses particularly in the phosphate fertilizer industry. About
60 % of the sulfuric acid produced is utilized in fertilizer manufacture.
Sulfuric acid was called "oil of vitriol" by Medieval. The study of vitriol began in ancient times.
Sumerians had a list of types of vitriol that classified according to substance's colour.
Johann Glauber prepared sulfuric acid by burning sulfur together with saltpeter (potassium nitrate, KNO3),
in the presence of steam in the 17th century. Decomposition of saltpeter followed by oxidation produces
SO3, which combines with water to produce sulfuric acid. Joshua Ward used the method for the first largescale production of sulfuric acid in 1736.
John Roebuck, produce less expensive and stronger sulfuric acid in lead-lined chambers in 1746. The
strength of sulfuric acid by this method is 65%. After several refinements, this method, called the "lead
chamber process" or "chamber process", remained the standard for sulfuric acid production for almost two
centuries. The process was modified by Joseph Louis Gay-Lussac and John Glover which improved
concentration to 78%. However, the manufacture of some dyes and other chemical processes require a
more concentrated product. Throughout the 18th century, this could only be made by dry distilling
minerals in a technique similar to the original alchemical processes.
Pyrite (iron disulfide, FeS2) was heated in air to yield iron(II) sulfate, FeSO4, which was oxidized by
further heating in air to form iron(III) sulfate, Fe2(SO4)3, which, when heated to 4800C, decomposed to
iron(III) oxide and sulfur trioxide, which could be passed through water to yield sulfuric acid in any
concentration. But the production expenses are very high.
More economical process i.e. the contact process was patented by Peregrine Phillips in 1831. Today,
nearly all of the world's sulfuric acid is produced using this method.
MANUFACTURE
The Industrial manufacture of sulfuric acid is done mainly by two processes ;
1. The Lead Chamber process
2. The Contact process
1. The lead chamber process
The Lead Chamber process for the manufacture of sulfuric acid dates back about 200 years. Although less
efficient than the contact process, it is still of considerable commercial importance.
Raw Materials
Basis: 1000kg Sulfuric acid (98% yield)
Sulfur = 400kg
Air = 399kg
Manufacture
Block diagram of manufacturing process
Diagram with process equipment
Animation
Sulfur dioxide is obtained by burning sulfur or by roasting pyrites. There are two function of burner
1. To oxidize sulfur to maximum extent
2. To produce and constant supply of gas containing maximum concentration of SO2
The burner of the furnace should expose large surface of melted sulfur and should be provided secondary
air in order to burn sublimed burner. This is necessary due to low heat of combustion and high vapour
pressure of sulfur. At about 4000C, pyrite (FeS2) decompose in to FeS and sulfur vapour, the later
oxidized to SO2 in presence of excess air. The residual FeS also oxidizes to Fe2O3 and SO2. Iron oxide
(Fe2O3) slightly catalyzed oxidation of SO2 to SO3. Burner gas should contain sufficient oxygen for carry
out further oxidation of SO2 to SO3.
The burner gases which contain SO2, N2, O2 and dust or fine particle of pyrites are passed through dust
chamber followed by Cottrell electrical precipitator or centrifugal separator in order to remove dust or fine
particle of ore. Dust chambers are provided with horizontal shelves or baffles followed by filtration
through crushed coke or similar material.
Now, burner gases are passed through niter oven made of cast iron in which equimolecular proportion of
NaNO3 and H2SO4 is heated. Resulting nitric acid reacts with SO2 to give mixture of nitric oxide (NO)
and nitrogen dioxide (NO2) which are carried with burner gases.
In modern plant oxides of nitrogen are produced by passing mixture of ammonia and air through heated
platinum gauze acting as catalyst (same as manufacture of HNO3 by ammonia oxidation process) . After
passing burner gases to dust chamber and niter oven, they pass through 5 meter square and 10 -15meter
high Glower tower which is packed with flint stone, quartz, tile or acid resisting bricks. The packing in the
tower is loosely stacked at the bottom to facilitate mixing of hot gases. The hot burner gases passes up this
tower is at 450-6500C and dilute H2SO4 from the lead chamber and nitrosyl sulfuric acid from GayLussac tower are made to trickle down the Glower tower by means of sprayers. Here, burner gases are
cooled down to 70-800C, dilute chamber acid is concentrated up to 78% and nitrosyl sulfuric acid (nitrous
vitriol) is denigrated by action of water. The tower acid is drawn off from the bottom of the tower and
collected in the container called acid egg. The acid from base of Glower tower is cooled to 400C by air
coolers.
The mixture of SO2, Oxides of nitrogen and air is then passed to series of rectangular vessels made of lead
(lead chamber) having 15-45 meter length, 6-7 meter width and 7 meter length. The number of chambers
depends upon the size of plant, but usually they are 3 to 6 in number. The chambers are arranged in two
parallel rows. Steam from low pressure boiler or pure filtered water is sprayed from top of the chamber.
Mixture of gases is converted into H2SO4 having 65-70%v strength is collected at the bottom of the
chamber. Dilute sulfuric acid obtained in any of the chamber is called chamber acid. A part of chamber
acid is pumped to Glower tower, and the rest is sent for concentration.
The unabsorbed remaining gases contain oxides of nitrogen and SO2 from lead chamber are then passed
through Gay-Lussac tower at the top of which Glower acid is sprayed to recover oxides of nitrogen.
The oxides of nitrogen recovered in the form of nitroso sulfuric acid are pumped to Glower tower to again
regenerate oxides of nitrogen.
When pyrite is used as raw material, the chamber acid may contain arsenious oxide (from pyrite), lead
sulfate from lead chamber are removed by treatment of H2S and dilution of acid respectively. Dilute acid
may be further concentrated into Glower tower.
Kinetics and thermodynamics
Above reaction is rate controlling step in the chamber process. The exothermic forward reaction is
favoured by decrease in temperature. As the reaction proceeds with decrease in volume, the formation of
NO2 would be favoured by increase in pressure. It has been observed that the rate of oxidation is slow at
ordinary temperature and rate is proportional to the square of the absolute pressure. At lower temperature,
the production of chamber acid has been found to be greater. All these facts are in good agreement with
the fact that the oxidation of NO to NO2 is the rate controlling step in this process.
The dilution of nitrosyl sulfuric acid within the Glover tower leads to its decomposition and nitrous fumes
produced catalyze the synthesis of sulfuric acid when they come in contact with sulfur dioxide and water.
Reaction (2) can be shown in chain as follow
Reaction (2) can be repeated cyclically by the partial reoxidation of the nitric oxide produced by excess air
which forms part of the sulfurous gas coming from the combustion chamber.
Reaction (2) and (3) mainly occur in chambers following the Glover tower until the SO2 has been
exhausted.
The recovery of nitrous gases is important task of Gay Lussac towers but it is difficult. A reverse reaction
of reaction (1) is taking place here. In effect, this typical equilibrium reaction is particularly sensitive to the
mass action effect by water
or reversible reaction
Above reaction is displaced to the right in the Glover tower where water is relatively abundant and to the
left in the Gay Lussac tower which is supplied with sulfuric acid which is transformed into nitrosyl sulfuric
acid by absorbing equimolecular mixture of NO and NO2 on account of its high concentration (78%).
Reason for obsolesce
As discussed above, overall reaction consisting of number of partial reactions, which takes place in liquid
phase, the development of surfaces, which are covered in this liquid, is a factor of fundamental importance
in promoting the synthesis of sulfuric acid. Maximum strength of sulfuric acid obtained by chamber
process is 78%. However, in manufacture of some dyes and chemical processes require more concentrated
H2SO4. There so, the process is largely replaced by contact process.
Introduction to polymerization technology
Definitions and Nomenclature
Polymer: Polymers are large chain molecules having a high molecular weight in the range of 103 to 107.
These are made up of a single unit or a molecule, which is repeated several times within the chained
structure. Monomer: A monomer is the single unit or the molecule, which is repeated in the polymer
chain. It is the basic unit, which makes up the polymer.
Thermosetting Polymer: There are some polymers which, when heated, decompose, and hence, cannot be
reshaped. Such polymers have a complex 3-D network (cross-linked or branched) and are called
Thermosetting Polymers. They are generally insoluble in solvents and have good heat resistance quality.
Thermosetting polymers include phenol-formaldehyde, urea-aldehyde, silicones and alleys.
Thermoplastic Polymer: The polymers in this category are composed of monomers, which are linear or
have moderate branching. They can be melted repeatedly and casted into various shapes and structures.
They are soluble in solvents, but do not have appreciable thermal resistance properties. Vinyl, cellulose
derivatives, polythene and polypropylene fall into the category of thermoplastic polymers.
Polymer Manufacturing Processes
Polythene (PE)
Polymer Chemistry: The manufacture of polyethylene follows addition polymerization kinetics involving
catalysis of purified ethylene. Its molecular formula is - (CH2-CH2)n- with a molecular weight of 1,500 to
100,000. Its melting point is 85 – 110oC. its density is 0.91 -0.93 , when produced by high pressure process
and 0.96, when produced by low pressure process.
Technology:
There are three processes by which polyethylene is manufactured –
a .High Pressure Process : This process was developed in the UK by ICI. It uses peroxide catalyst at 100300 oC and produces low density randomly oriented polymer, which have a low melting point. The process
is run at pressure of 1000 – 2500 atms. This process yields Low Density Polyethylene (LDPE).
b .Intermediate Pressure Process : This process was developed in the USA by Phillips Petroleum Co. for
preparing high density polymer with increased rigidity, crystallinity, tensile strength and softening point.
The process uses MoO3 and Cr2O3 on alumina as catalyst and is operated at 30 – 100 atms.
c .Low Pressure Process: This process was originally developed in Germany for preparing high density
polyethylene (HDPE). The catalyst used in this process consists of aluminium triethylactivated with heavy
metal derivatives such as TiCl4.
In the process flow sheet (Figure 39.1), is the description of Low Pressure Ziegler Process to produce
polyethylene. At the very onset, through the process of desulphurization and removal of light ends, high
purity ethylene is prepared. The ethylene is further treated to remove traces of oxygen and its compounds,
which can possibly deactivate the catalyst.
The ethylene is first pumped into a reactor where it is mixed with catalyst diluents stream. The optimum
temperature and pressure maintained should be 70oC and 7 atms gage. The effluent stream then follows
across a series of flash drums in order to remove the solvent from the catalyst. The residual catalyst at this
point is removed by adding water.
The flashed solvent is thereafter recycled to the catalyst make –up unit after appropriate drying and
redistillation. The slurry, which results, is then centrifuged to remove the water, and the water is treated to
remove the catalyst before recycle. The final products of polyethylene solids are then dried, extruded and
given the required final forms.
Figure. Manufacture of Polythene.
POLYVINYL CHLORIDE (PVC)
Polymer Chemistry: The manufacture of Polyvinyl Chloride (PVC) follows addition type kinetics and
produces linear polymers. Its molecular formula is given as –
The vinyl chloride monomer (VCM) has a boiling point of 13.4oC and is a gas at room temperature and
pressure. The vapor pressure of VCM over the typical polymerization temperature range of 50oC to 70oC is
800 – 1250 KPa.
Technology
The two most commercially use methods for the manufacture of PVC are Emulsion Polymerization and
Suspension Polymerization. The Suspension Polymerization process provides 80 % of the world
production. The Suspension Polymerization process is actually a bulk polymerization process, which is
carried out in millions of droplets. Each of these droplets act as small reactors. The liquid vinyl chloride is
dispersed in water by vigorous stirring in a reactor. The reactor is fitted with baffles for optimum agitation
and has a condenser for heat removal. In the reactor, small droplets of size 30 - 40µm diameter are formed.
A monomer soluble free radical initiator is chargedinto the reactors. After charging, the reactor
temperature is increased to 45 – 75 o C . The heat decomposes some of the initiators to free radicals, and
the monomers in these droplets begin to polymerize. the reaction is highly exothermic and the heat is
removed via cooling jackets or by boil – off to the condenser. Thereafter, the condensed monomer is
returned to the reactor. Although the PVC is insoluble in its monomer, it is swollen by VCM to form a
coherent gel. Even in the gel phase, the polymerization continues. The polymerization is rapid at first, but
slowly, as the conversion reaches 80 – 85 %, the rate is reduced due to monomer starvation.
At a predetermined pressure, the reaction is ended by adding a chain terminator or by venting the
unreacted monomer to a recovery plant. Even after venting, the aqueous slurry contains 2 – 3 % unreacted
monomer, which is then removed by stripping in a Stripping Column. The unreacted monomer is
recovered and stored for later polymerization stages. The slurry is then passed through a heat exchanger
and is passed through a continuous centrifuge to give a wet cake with 20 – 30 % moisture.
Figure. Manufacture of Poly (Vinyl Chloride).
Unit operation in chemical industries
Unit operations are very important in chemical industries for separation of various products formed during
the reaction. Table M-I 3.3 give the details of unit operation in chemical process industries.
Table M-I 3.3: Unit Operations in Chemical Process Industries
Absorption and stripping
Membrane Process: Reverse osmosis, Ultrafiltration,
Dialysis, Electro dialysis, Per evaporation
Adsorption and desorption
Crushing Grinding, Pulverizing and Screening
Pressure Swing adsorption Chromatography
Distillation: Batch distillation Flash distillation, Solid liquid extraction
Azeotropic distillation, Extractive distillation
Reactive distillation
Evaporation
Striping
Fluidization
Sublimation
Crystallization
Solvent extraction
Liquid- Liquid extraction
DISTILLATION
Distillation has been the king of all the separation processes and most widely used separation technology
and will continue as an important process for the for useable future [Olujie et al., 2003]. Distillation is used
in petroleum refining, petrochemical manufacture Distillation is the heart of petroleum refining, and all
processes require distillation at various stages of operations.
MEMBRANE PROCESSES
Membrane processes have emerged one of the major separation processes during the recent years and
finding increasing application in desalination, wastewater treatment and gas separation and product
purification. Membrane technology is vital to the process intensification strategy, and has continued to
advance rapidly with the development of membrane reactors. Catalytic membrane reactor, membrane
distillation, and membrane bioreactors for wide and varied application [Sridhar, 2009]. Membrane process
classified based on driving force. Various type of membrane process and driving force are given in Table
M-I 3.4.
Table M-I 3.4: Membrane Processes
Membrane process
Driving force
Reverse osmosis
Pressure difference
Ultrafiltration
Pressure difference
Microfiltration
Pressure difference
Nano filtration Dialysis
Pressure difference
Concentration difference
Evaporation
Concentration difference
Liquid membrane
Concentration difference
Electro dialysis
Electrical potential
Gas Permeation
Concentration difference
Thermo-osmosis
Temperature difference
Based on lower operating costs, comparable capital cost and only slightly product loss (including fuel),
membranes have demonstrated a flexible, cost, effective alternative to amine treating for some natural gas
processing applications [Cook & Losin, 1995]. Gas membrane and its application areas are mention in
Table M-I 3.5.
Table M-I 3.5: Gas Membrane Application Areas
Common Gas Separation
Application
O2/N2
Generation oxygen enrichment, inert gas
H2 /hydrocarbons
refinery hydrogen recovery
H2/CO
Syn. gas adjustment
H2/N2
Ammonia purge gas
co2/hydrocarbons
Acid gas removal from natural gas
H2O/hydrocarbons
Natural gas dehydration
H2S/hydrocarbons
Sour gas treating
He/hydrocarbons
Helium separation
He/N2
HELIUM RECOVERY
Hydrocarbon/ air
Hydrocarbon recovery
H2O/AIR
Air dehumidification
Membrane distillation is a membrane separation process, which can overcome the limitation of more
traditional membrane process. Membrane distillation has significant advantage over other processes,
including low sensitivity to feed concentration and the ability to operate at low temperature [Patli and
Patil, 2012].
Various type of membrane processes are mention in Table M-I 3.6.
Table M-I 3.6: Various Types of Membrane Processes
Separation Process
Separation Mechanisms
Feed Stream
Microfiltration
Ultra-filtration
Dialysis
Sieving
Liquid or Gas
Sieving
Liquid
Sieving and
Sorption Diffusion
Liquid
Reverse Osmosis
Sorption- Diffusion
Liquid
Evaporation
Sorption- Diffusion
Liquid
Gas and Vapor Permeation
Sorption- Diffusion
Liquid or Vapor
ABSORPTION
Absorption is the one of the most commonly used separation techniques for the gas cleaning purpose for
removal of various gases like H2S, CO2, SO2 and ammonia. Cleaning of solute gases is achieved by
transferring into a liquid solvent by contacting the gas stream with liquids that offers specific or selectivity
for the gases to be recovered. Unit operation and is mass transfer phenomena where the solute of a gas is
removed from being placed in contact with a nonvolatile liquid solvent that removes the components from
the gas.
Solvent: Liquid applied to remove the solute from a gas stream. Solute: Components to be removed from
entering streams.
Some of the commonly used solvents are:
Chemical Absorption
Amine Processes: Mono-ethanol amine (MEA), di-ethanol amine (DEA), tri-ethanol amine (TEA),
diglycol amine (DGA), methyl diethanol amine (MDEA)
Carbonate Process: K2CO3, K2CO3+MEA, K2CO3 +DEA, K2CO3+arsenic trioxide
Physical Absorption
Polyethylene Glycol Dimethyl Ether (Selexol), N-methyl pyrrolidine,NMP (Purisol), Methanol (Rectisol),
Sulphonane mixed with an alkanolamine and water (sulfinol).
ADSORPTION
Adsorption technology is now used very effectively in the separation and purification of many gas
and liquid mixtures in chemical, petrochemical, biochemical and environmental industries and is
often a much cheaper and easier option than distillation, absorption or extraction. Some of the
major applications of adsorption are gas bulk separation, gas purifications, liquid bulk separation,
and liquid purifications. One of the most effective method for recovering and controlling emissions
of volatile organic compounds is adsorption Some of the commercial adsorbent s are silica gel,
activated carbon, carbon molecular sieve, charcoal, zeolites molecular sieves, polymer and resins,
clays, biosorbents. Some of the key properties of adsorbents are capacity, selectivity,
regenerability, kinetics, compatibility and cost [Knaebel, 1995]. Some of the methods used for
regeneration of adsorbent are thermal swing, pressure swing, vacuum (special case of pressure
swing), purge and gas stripping, steam stripping [Crittenden, 1988]. Commercial adsorption
processes is given in Table M-I 3.7. Some of the important criteria of good adsorbent are;
(1) it must selectivity concentrate one or more components called adsorbate to from their fluid phase
levels.
(2) the ability to release adsorbate so that adsorbent can be reused,
(3) as high as possible delta loading the change of weight of adsorbate per unit weight of adsorbent
between adsorbing and desorbing steps over a reasonable range of pressure and temperature.
Pressure swing adsorption (PSA) is based on the principle of relative adsorption strength, is a
milestone in the science of gas separation [Shiv Kiran and Chakravarty, 2002]. Some of the
commercial application of PSA are air drying, hydrogen purification, bulk separation of paraffins,
air separation for oxygen and nitrogen production,
Chromatography is a sorptive separation process. In chromatography feed is introduce in column
containing a selective adororbent (stationary phase) and separated over the length of the column by
the action of a carrier fluid (mobile phase) that is continually supplied to the column following the
introduction of the feed.
Table M-I 3.7: Commercial Adsorption Processes
Sorbex process
Application
Parex
Separation of paraxylene from mixed C8 aromatics isomers
MX sorbex
Meta xylene from mixed C8 aromatics isomers
Molex
Linear paraffins from branched and cyclic hydrocarbons
Olex
Olefins from paraffins
Crsex
Para cresol or meta cresol isomers
Cymex
Para cymene or meta cymene from cymene isomers
Sarex
Fructose from mixed sugar
UOP ISOSIV process
separation of normal paraffins from hydrocarbon mixture
Kerosene Isoiv process
For separation of straight chain normal paraffins from the kerosene
range(C10-C18) used for detergent industry
The separation occurs as a result of the different partitioning of the feed solutes between the
stationary phases. The separated solutes are recovered at different time in the effluent from the
column [Rangrajan, 2010].
CRYSTALLIZATION PROCESS
Crystallization processes are used in the petroleum industry for separation of wax. The process
involves nucleation, growth, and agglomeration and gelling. Some of the applications of
crystallization is in the separation of wax, separation of p-xylene from xylenes stream. Typical
process of separation of p-xylene involves cooling the mixed xylene feed stock to a slightly higher
than that of eutectic followed by separation of crystal by centrifugation or filtration.
LIQUID –LIQUID EXTRACTION
Liquid –liquid extraction has been commonly used in petroleum and petrochemical industry for
separation of close boiling hydrocarbons. Some of the major applications are:
 Removal of sulphur compound from liquid hydrocarbons



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Recovery of aromatics from liquid hydrocarbon
Separation of butadiene from C4 hydrocarbons
Extraction of caprolactam
Separation of homogenous aqueous azeotropes
Extraction of acetic acid
Removal of phenolic compounds from waste water
Manufacture of rare earths
Separation of asphaltic compounds from oil
Recovery of copper from leach liquor
Extraction of glycerides from vegetable oil Some of the important property of a good solvent
 High solvent power/capacity
 High selectivity for desired component
 Sufficient difference in boiling points of the solvent and the feed for effective
separation
 Low latent heat of evaporation an specific heat to reduce utility requirement
 high thermal an chemical stability
 Low melting point
 Relatively inexpensive
 Nontoxic and non –corrosive
 Low viscosity low interfacial tension.
Technological development in unit operations Distillation, Azeotropic, extractive distillation, reactive distillation, membrane distillation
 Random packing to Structured Packing
 Single and two pass to Multiple down comer
 Rasching rings and berl saddles to Intalox sadles, pall rings, nutter rings, half rings, super
rings,Fleximax
 Pan park to Wire gauge packing, Goodloe, Mellpark, Flexipack, Gempack, Intalox
 Fixed bed to Fluidized bed reactor
 Conventional reactor to Micro reactor
 Ball mill grinding to Vertical roller mill and press roll Mill
 Open circuit grinding to Closed circuit grinding
 Batch digester to continuous digester
 Low speed and low capacity chipper to High speed chipper and high capacity chipper
 Low speed Paper machine to high speed machine
 Drum displacer, Pressure diffuser, Displacement presses, Combined deknotting and Fine
screening,
 High temperature screening before washing, Reverse cleaners
 Adsorption(Olex, Parex and Molex), Crystallisation and Membrane separation processes
 Solvent extraction processes and New solvents
 Conventional distillation Short path distillation, divided wall column
 Conventional bubble cap, sieve plate to valve tray
 Random packing to structured packing
 Axial flow reactor to radial flow reactor
 Conventional instrumentation to smart (intelligent) instrumentation.
Basic Separation Concepts
• General Separation Techniques
- Separation by phase creation
- Separation by phase addition
- Separation by barrier
- Separation by solid agent
- Separation by external field or gradient
General Separation Techniques
• Separation by phase creation
– Create a second phase that is immiscible with the feed phase
– Distillation, crystallization
• Separation by phase addition
– Introduce a second phase in the form of a solvent
– Solvent extraction
• Separation by barrier
– Restrict and/or enhance the movement of certain chemical species
– Membrane separation
• Separation by solid agent
– Add solid particles that act directly or as inert carriers for separation
– Adsorption
• Separation by force field or gradient
– Apply external fields of various types
– Centrifugation
Separation by Phase Addition or Creation
• Energy-separating agent (ESA)
- Heat transfer (heating, cooling)
- Shaft work can be involved together
• Mass-separating agent (MSA)
- May be partially immiscible with one or more of species
- May be completely miscible with a liquid mixture
• Disadvantages of MSA
- Need for an additional separator to recover the MSA for recycle
- Need for MSA makeup
- Possible contamination of the product with the MSA and more difficult design procedures.
Separation techniques
Part two
Experiments
Determination of the reaction rate constant and
effect of residence time on the conversion in the tubular flow reactor.
Results analysis and discussion
Discuss your results.
1. Plot a graph of conversion versus conductivity.
2. Plot a graph of conversion versus residence time.
3.
From the graphs , discuss the findings