Chapter 5

INORGANIC AND FINE

CHEMICALS

Contents

Sulfuric Acid

The Chlor-Alkali Industry

Cement Industry

Glass Industry

Fertilizer

Sulfuric Acid

Largest tonnage

Raw material is sulfur

Sources:

Direct mining of underground deposits

Desulfurization of oil and gas (off-gases containing H2S

or SO2)

By-product of metal extraction (copper process, ore

such CuFeS2)

Produced in various strengths

Sulfuric Acid Manufacturing Process

Three major steps in sulfuric acid manufacturing:

1. Burning of sulfur in air:

S + O2 SO2

2. Reaction of SO2 and O2:

2 SO2+ O2 2SO3

3. Absorption of SO3 into water to produce a sulfuric

acid (H2SO4)

Oxidation of Sulfur 1) S + O2 SO2

Air

93% H2SO4

Sulfur

10-12% SO2

Steam

Water

Primary Generation of SO2

-79% Combustion of Sulfur

-9% Recovery from Metallurgic Processes

- 5% Regeneration of Spent Acids

Process:

- Air drying tower with acid

- Air and sulfur are injected into burner

- Reaction temperature 2000°F

- Exothermic reaction must be cooled

- Steam is produced from recovered heat

Oxidation of Sulfur

molten

Oxidation of Sulfur Dioxide SO2 + ½ O2 SO3

Because of the large effect temperature plays on the reaction, multiple catalyst

layers are used (vanadium pentoxide catalyst), with cooling between each step.

As the partial pressure of SO3 increases, further reaction is limited. This is

overcomed by removing the SO3 after the third stage to drive the reaction to

completion.

Gas

Cooling

SO3 Gas

SO3 Gas

SO2 Gas

93% H2SO4

SO2 Gas

Oxidation of Sulfur Dioxide

Oleum

Air

Oxidation of Sulfur Dioxide

• Kinetic Effects

- Oxidation of sulfur dioxide is slow and reversible

- The reaction requires a catalyst and 426.7°C temperatures

-The reaction is exothermic and sensitive to excessive heat

• Equilibrium Constant (The degree at which the reaction proceeds is temp. dependent)

log Kp = 4.956 - 4.678

T

T = absolute temp. in kelvin

Kp = equilibrium constant as a function of partial pressure of gases

Kp = ( PSO3 )

PSO2 PO2

0.5

Absorption of SO3

Sulfuric acid is obtained from the absorption of SO3 and water into

H2SO4 (with a concentration of at least 98%).

The efficiency of the absorption step is related to:-

– The H2SO4 concentration of the absorbing liquid (98.5-99.5%)

– The range of temperature of the liquid (normally 70°C-120°C)

– The technique of the distribution of acid

Dilution of absorber acids The acid produced, normally 95.5%-96.5% or 98.5%-99.5%, is diluted

with water or steam condensate down to the commercial concentrations:

25%, 37%, 48%, 78%, 96% and 98% H2SO4.

The dilution can be made in a batch process or continuously through

in-line mixing.

Sulfuric Acid Contact Process

Oxidation of SO2 is thermodynamically favored by

low temperatures

All SO2 must be converted for environmental

reasons

Catalytic oxidation in adiabatic fixed bed reactors

Multiple catalyst beds with intermediate cooling

Heat from combustion of sulfur is recovered as HP

steam

Sulfuric Acid Contact Process

water

Oleum Production

Oleum is produced in the contact process, where sulfur is oxidized to

sulfur trioxide which is subsequently dissolved in concentrated sulfuric

acid. Sulfuric acid itself is regenerated by dilution of part of the oleum.

20% Oleum contains 20% SO3 by weight in the oleum

Common strengths of oleum are 20, 30, 40, 65 percent.

To produce 20 and 30 percent oleum, only requires an additional

absorption tower.

Oleum is used in reactions where water is excluded

SO3 + H2SO4 H2S2O7 (disulfuric acid)

Oleum Production

Uses of H2SO4

Manufacture of phosphoric acid for fertilizer

Production of ammonium sulfate

Production of ethanol from ethylene

One method of producing TiO2

Production of hydrofluoric acid from calcium

fluoride

Aluminum sulfate

15

The Chlor-Alkali Industry

The Chlor-Alkali Industry

Sodium hydroxide, sodium carbonate, and chlorine are substances

produced on a large scale by the chemical industry.

The term CHLOR-ALKALI PROCESS refers to the industrial

production of (alkali sodium hydroxide, NaOH, and chlorine, Cl2 from

the common salt (sodium chloride, NaCl).

The importance of these chemicals, produced in the millions of tons

annually, is illustrated by the table next slide. However, this part includes:

1. NaOH (Caustic Soda)

2. Chlorine

3. HCl

4. Sodium Hypochlorite (NaOCl)

Uses for NaOH, NaOCl, Na2CO3 and Cl2

NaOH Na2CO3 Cl2

Manufacture of

Soap

Ceramics

Numerous organic chemicals

Various sodium salts

NaOCl

Manufacture of

dairies

Paper and laundries as a bleaching agent

Manufacture of

Paper

Glass

Various sodium salts

Manufacture of:

Plastics

Paper industry

Insecticides

Hydrochloric acid

Numerous organic chemicals

Used for:

Bleaching

Water purification

18

Electrolysis of sodium chloride:

Sodium hydroxide and chlorine are produced industrially by the electrolysis

of brine, which is a near-saturated solution of sodium chloride, NaCl. The

reactions involved are

When a current is passed through brine (an aqueous solution of sodium

chloride), hydrogen gas is produced at the cathode, since H+ ions are more

easily discharged than Na+ ions. The depletion of H+ ions near the cathode

means that hydroxide(OH-) ions, as sodium hydroxide, accumulate in the

cathode compartment. Chlorine gas is produced at the anode. Three

processes are used, 1- the MEMBRANE CELL,

2- the DIAPHRAGM CELL,

3- the MERCURY PROCESS.

20

Sulphate Removal

Demin. Water

Chlorine Packing, Filling

Vaporization

Hypo Product

Chlorine Storage

Brine Saturation

Primary Treatment

Secondary Treatment

Brine Dechlorination

Electrolysis

Salt

DC Rectification

AC Power Supply

Demineralized Water

Hydrogen Handling

Caustic Storage

Chlorine Compression

Chlorine Drying

HCl Storage

Chlorine Liquefaction

Caustic Product

HCl Product

Hypo Production

Hypo Destruction

Chlorine Product

Sodium Sulphite

Chlorate Destruction

Hypo Storage

HCl Production

Caustic Concentration

Sulphuric Acid Carbon Dioxide

To Hypo HCl

HCl

Sulphuric Acid

NaOH

NaOH

Electrolysis

Types of Electrolytic Cells

Three important types of cells are employed:

Mercury

Diaphragm

Membrane

Mercury Cells1/4

Saturated sodium chloride solution is fed continuously into a container

fitted with titanium anodes. The bottom of the cell consists of a layer of

mercury, circulated by means of a pump. This layer serves as cathode.

Under the conditions that prevail, sodium ions are preferentially discharged.

The sodium metal dissolves in the mercury to form an amalgam. This

amalgam is reacted with water in a "decomposer", producing hydrogen gas

and sodium hydroxide solution:

De Nora CELL Mercury Cells2/4

mercury

Mercury Cells3/4

Mercury Cell Operation

Mercury Cells4/4

Advantages

Lower brine purity requirements

High purity NaOH and KOH product

NaOH and KOH produced directly at 50% concentration

Disadvantages

Highest power consumption

Mercury Emissions

27

In the diphragm (Nelson) cell, saturated sodium chloride solution is fed

continuously into a steel-mesh container lined with an asbestos diaphragm

in which a carbon anode is placed. Chlorine gas is produced at the carbon

anode, and escapes out of the cell for further treatment.

Hydrogen is produced on the outside of the asbestos, and escapes out of

the cell, where it is collected.

A steam is used to create a heated environment, and, through condensation

on the steel mesh, washes out the sodium hydroxide, which is collected at

the bottom of the cell, from where it is drawn off.

This process is being phased out, as asbestos is harmful to the workers,

causing fatal lung diseases generally called ASBESTOSIS.

Diaphragm Cells1/3

Diaphragm Cells2/3

Diaphragm Cells3/3

Advantages

Lower brine purity requirements than membrane cells

Lower power consumption than mercury cells

Simpler cell equipment than mercury cells

Disadvantages

NaOH and KOH produced at ~25% concentration, ie low product purity

Solid salt produced during evaporation

Asbestos traditionally used for diaphragm, which is harmful

The membrane cell is the most modern and has economic and

environmental advantages.

The two other processes generate hazardous wastes (containing

mercury or asbestos).

In the membrane process, the chlorine (at the anode) and the

hydrogen (at the cathode) are kept apart by a selective polymer

membrane that allows the sodium ions to pass into the cathodic

compartment and react with the hydroxyl ions to form caustic

soda

Membrane Cells1/4

31

In the membrane process, the anode and cathode compartments are

separated by an ION EXCHANGE MEMBRANE that allows water and

sodium ions to diffuse through, but not chloride ions.

•In the anode compartment, chloride ions migrate to the titanium anode,

where they are discharged to form chlorine gas.

•In the cathode compartment, hydrogen ions migrate to a nickel cathode,

where hydrogen is produced.

•Electrical neutrality is maintained by sodium ions moving through the

membrane from the anode compartment to the cathode compartment.

•This is the preferred industrial method for the preparation of chlorine and

sodium hydroxide. A very pure product NaOH is obtained, with minimal

effects on the environment. The energy requirements of this cell are said

to be more advantageous than with the diaphragm or mercury cells.

Membrane Cells2/4

32

Membrane Cells3/4

Membrane Cells4/4

Advantages

Lowest power consumption

High purity NaOH and KOH product

No mercury or asbestos emissions

Disadvantages

Significantly higher brine purity requirements

NaOH and KOH produced at ~30% concentration, ie low

product purity

High capital cost

34

Polymer membrane of Membrane Cells

Electricity Consumption by Production Process

Sodium Hypochlorite Production

The most common method for manufacturing sodium

hypochlorite is by the treatment of sodium hydroxide

solution with gaseous chlorine.

2NaOH + Cl2 → 2NaOCl + NaCl + H2O

Sodium hypochlorite is employed as:

a disinfectant and deodorant in dairies, creameries, water

supplies, sewage disposal, and households.

It is also used as bleach in laundries. As a bleaching agent,

it is very useful for cotton, linen, jute, rayon, paper pulp,

and oranges.

Cement Industry

WHAT IS CEMENT????

Material with adhesive and cohesive

properties

Any material that binds or unites -

essentially like glue

• Cement is a basic material for building and civil

engineering construction.

FUNCTION OF CEMENT

to bind the sand and coarse aggregate

together

to fill voids in between sand and coarse

aggregate particle

to form a compact mass

Types of Cement

Two types of cement normally used in

building industry are as follows:

a) Hydraulic Cement

b) Non-hydraulic Cement

Hydraulic Cement

Hydraulic Cement sets and hardens by

action of water. Such as Portland Cement

In other words it means that hydraulic

cement are:

“ Any cements that turns into a solid product

in the presence of water (as well as air)

resulting in a material that does not

disintegrate in water.”

Non-hydraulic Cement

Any cement that does not require water to

transform it into a solid product.

2 common Non-hydraulic Cement are

a) Lime

- derived from limestone / chalk

b) Gypsum

PORTLAND CEMENT

Chemical composition of Portland Cement:

a) Tricalcium Silicate (50%)

b) Dicalcium Silicate (25%)

c) Tricalcium Aluminate (10%)

d) Tetracalcium Aluminoferrite (10%)

e) Gypsum (5%)

FUNCTION :TRICALCIUM SILICATE

Hardens rapidly and largely responsible for

initial set & early strength

The increase in percentage of this compound

will cause the early strength of Portland

Cement to be higher.

A bigger percentage of this compound will

produces higher heat of hydration and

accounts for faster gain in strength.

FUNCTION :DICALCIUM SILICATE

Hardens slowly

It effects on strength increases occurs at ages

beyond one week .

Responsible for long term strength

FUNCTION :TRICALCIUM ALUMINATE

Contributes to strength development in the

first few days because it is the first compound

to hydrate .

It turns out higher heat of hydration and

contributes to faster gain in strength.

But it results in poor sulfate resitance and

increases the volumetric shrinkage upon drying.

Cements with low Tricalcium Aluminate

contents usually generate less heat,

develop higher strengths and show greater

resistance to sulfate attacks.

It has high heat generation and reactive

with soils and water containing moderate

to high sulfate concentrations so it’s least

desirable.

FUNCTION: TETRACALCIUM

ALUMINOFERRITE

Assist in the manufacture of Portland Cement

by allowing lower clinkering temperature.

Also act as a filler

Contributes very little strength of concrete

eventhough it hydrates very rapidly.

Also responsible for grey colour of Ordinary

Portland Cement

49

gypsum is used to assist in retard the

setting time of cement when it is mixed

with water.

FUNCTION: GYPSUM

MANUFACTURING OF PORTLAND

CEMENT

The 3 primary constituents of the raw

materials used in the manufacture of

Portland Cement are:

a) Lime

b) Silica

c) Alumina

Lime is derived from limestone or chalk

Silica & Alumina from clay, shale or bauxite

There are four main steps for cement manufacturing

1- Quarry,

2- raw grinding,

3- burning, grinding,

4- storage & packing

THE CEMENT MANUFACTURING PROCESS

1. BLASTING : The raw materials that are used to manufacture cement (mainly limestone and clay)

are blasted from the quarry.

2. TRANSPORT : The raw materials are loaded into a dumper

3. CRUSHING AND TRANSPORTATION : The raw materials, after crushing, are transported to the

plant by conveyor. The plant stores the materials before they are homogenized.

Quarry face

1. BLASTING 2. TRANSPORT

quarry

3. CRUSHING & TRANSPORTATION

crushing

conveyor

dumper

storage at the

plant

loader

THE CEMENT MANUFACTURING PROCESS

1. RAW GRINDING

Raw grinding and burning

2. BURNING

1. RAW GRINDING : The raw materials are very finely ground in order to produce the raw mixture.

mostly, using raw mill.

2. BURNING : The raw mix is preheated, using cyclone, before it goes into the kiln, which is heated by

a flame that can be as hot as 2000 °C. The raw mix burns at 1500 °C producing clinker which, when

it leaves the kiln, is rapidly cooled with air fans. So, the raw mix is burnt to produce clinker : the basic

material needed to make cement. Natural gas, petroleum or coal are used for burning.

conveyor Raw mix

kiln

cooling

preheating

clinker

storage at the

plant

Raw mill

THE CEMENT MANUFACTURING PROCESS

1.GRINDING : The clinker and the gypsum are very finely ground , using ball mill , giving a “pure

cement”. Other secondary additives materials can also be added to make a blended cement.

2. STORAGE, PACKING, DISPATCH :The cement is stored in silos before being dispatched either in

bulk or in bags to its final destination.

1. GRINDING

Grinding, storage, packing, dispatch

2. STORAGE, PACKING, DISPATCH

clinker

storage

Gypsum and the secondary additives are added to

the clinker.

silos

dispatch

bags

Finish grinding

CEMENT CLINKERS

1. The cement manufacturing process begins when limestone,

the basic raw material used to make cement, from the

limestone quarry is transported to the cement plant.

2. The limestone is combined with clay, ground in a crusher and

fed into the additive silos. Sand and iron are then combined

with the limestone and clay in a carefully controlled mixture

which is ground into a fine powder in a 2000 hp roller mill.

3. Next, the fine powder is heated as it passes through the

Pre-Heater Tower into a large kiln, which is about 100 meters

length and up to 4 meters in diameter. In the kiln, the powder is

heated to 1500oC, and the created new product is called

clinker.

4. The clinker is combined with small amounts of gypsum and

limestone and finely ground in a finishing mill.

5. The cement is, then, stored in silos before being dispatched

either in bulk or in bags to its final destination.

The mill is a large revolving cylinder containing 250 tones of

steel balls that is driven by a 4000 hp motor. The finished

cement is ground to a fine product.

Fuel: Natural gas, petroleum or coal are used

for burning. High fuel requirement may make

it uneconomical compared to dry process.

Process Type

There are two main process that can be used in manufacturing of Portland Cement, the raw material process and the clinker burning process are each classified into:

i) wet process

ii) dry process

Wet Process

Raw materials are homogenized by crushing,

grinding and blending so that approximately

80% of the raw material pass a No.200 sieve.

The mix will be turned into form of slurry by

adding 30 - 40% of water.

It is then heated to about 1510ºC in

horizontal revolving kilns (76-153m length

and 3.6 - 4.8 m in diameter).

Dry Process

Raw materials are homogenized by crushing,

grinding and blending so that approximately

80% of the raw material pass a No.200 sieve.

Mixture is fed into kiln & burned in a dry state

This process provides considerable savings in

fuel consumption and water usage but the

process is dustier compared to wet process

that is more efficient than grinding

Dry process kilns may be as short as half in

length of that in wet process.

In the kiln, water from the raw material is

driven off and limestone is decomposed into

lime and Carbon Dioxide.

limestone lime + Carbon Dioxide

In the burning zone, portion of the kiln, silica

and alumina from the clay undergo a solid

state chemical reaction with lime to produce

calcium aluminates.

silica & alumina + lime calcium aluminates

Dry Process & Wet Process-kiln Reactor

The rotation and shape of kiln allow the

blend to flow down the kiln, submitting it to

gradually increasing temperature.

As the material moves through hotter regions

in the kiln, calcium silicates are formed

These products, that are black or greenish

black in color are in the form of small

pellets, called cement clinkers

Cement clinkers are hard, irregular and ball

shaped particles about 18mm in diameter.

The cement clinkers are cooled to about

51ºC and stored in clinker silos.

When needed, clinker are mixed with 2-5%

gypsum to retard the setting time of cement

when it is mixed with water.

Then, it is grounded to a fine powder and

then the cement is stored in storage bins

or cement silos or bagged.

Cement bags should be stored on pallets in

a dry place.

KILN

CEMENT SILO

67

Glass Industry

Chemistry

Common

Name

Chemical Name Chemical

Formul

a

Glass

Compon

ent

Sand Silica or Silicon

Dioxide

SiO2 SiO2

Soda Ash Sodium Carbonate Na2CO3 Na2O

Limestone Calcium Carbonate CaCO3 CaO

What is Glass? Glass is a manufactured material formed when a

mixture of sand, soda, and lime is heated to a high

temperature and assumes a molten, or liquid, state.

69

Glass Manufacturing

Commercially produced glass can be classified as

soda-lime glass, since it constitutes 77 percent of total

glass production.

The manufacture of such glass is carried out in four

phases:

(1) preparation of raw material,

(2) melting in a furnace,

(3) forming and

(4) finishing.

See diagram for typical glass manufacturing, next slide

70

71

Glass production

involves two main methods –

The float glass process, which produces sheet glass, and

The glassblowing which produces bottles and other containers.

Glass container production

Modern glass container factories are three-part operations:

1- batch house : handles the raw materials

2- hot end : handles the manufacture proper: in which the molten glass

is formed into glass products, beginning when the batch is fed into the

furnace at a slow, controlled rate. The furnaces are natural gas- or fuel

oil-fired, and operate at temperatures up to 1,575°C. then, to the

annealing ovens, and forming machines;

3- Cold end

The role of the cold end is to inspect the containers for defects,

package the containers for shipment and label the containers.

72

Annealing

As glass cools it shrinks and solidifies. Uneven cooling

causes weak glass due to stress. Even cooling is achieved

by annealing. An annealing oven (known in the industry as

a Lehr)

The glass cools to approximately 600 oC by the time it

actually enters the annealing lehr. Inside the lehr, the

glass undergoes a controlled cooling process, depending

on the glass thickness, over a 20 – 6000 minute period

Float Glass

In 1952 Alistair Pilkington invented the float glass

process. The float glass process is the most common

method of flat glass production in the world.

This process involves melting recycled glass, silica

sand, lime, potash and soda in a furnace and floating

it onto a large bed of molten tin. This mass slowly

solidifies over the molten tin as it enters the

annealing oven where it travels along rollers under a

controlled cooling process.

From this point the glass emerges in one continuous

ribbon where it is then cut and further processed to

customer's needs.

Float Glass Process1/4

Batching of raw materials

The main components of Soda Lime glass:

Silica sand (73%),

Calcium oxide (9%),

Soda (13%) and

Magnesium (4%),

All are weighed and mixed into batches

to which recycled glass (cullet) is added.

Melting of raw materials in the furnace

The batched raw materials pass from a mixing silo to a five-chambered furnace where they become molten at a temperature of approximately 1500°C. Every operation is carefully monitored.

Drawing the molten glass onto the tin bath

The molten glass is "floated" onto a bath of molten tin at a temperature of about 1000°C. It forms a ribbon with a working width of 3210mm which is normally between 3 and 25mm thick. The glass which is highly viscous and the tin which is very fluid do not mix and the contact surface between these two materials is perfectly flat.

Float Glass Process2/4

Cooling the molten glass in the annealing lehr

On leaving the bath of molten tin, the glass - now at a temperature of 600°C - has cooled down sufficiently to pass to an annealing chamber called a lehr.

The glass is now hard enough to pass over rollers and is annealed, which modifies the internal stresses enabling it to be cut and worked in a predictable way and ensuring flatness of the glass.

As both surfaces are fire finished, they need no grinding or polishing.

Float Glass Process3/4

Float Glass Process4/4

Quality checks, automatic cutting, storage

After cooling, the glass undergoes rigorous quality checks and is washed. It is then cut into sheets up to 6000mm x 3210mm which are in turn stacked and stored ready for transport.

The entire production process from the batching of raw materials to cutting and stocking is fully automatic controlled.

Glass Recycling

The used glass containers which you recycle at curb-side or take to your local recycling station are easily recycled into new containers at the glass factory.

Glass companies depend upon local communities and various glass recyclers, usually located near our manufacturing facilities, to supply quality used glass, known as cullet, for their factories.

Already separated by color, the cullet is placed into a hopper and fed onto a belt. The belt carries the cullet through a powerful magnet to remove bottle tops and other metals. It then passes through picking stations to remove contaminants such as ceramic, Pyrex, and other items that cannot be removed mechanically. The final step in processing cullet is to crush the cullet into finer glass particles which will then be added to the Raw Materials as they are fed into the glass furnace.

79

Fertilizer Industry

80

Fertilizer

Most producers of compound fertilizers in the world are producing nitrate based

mineral compound fertilizers under the product name “NP” or “NPK”. These

products contain nitrogen in ammoniacal (NH4) and nitrate (NO3) form,

phosphorus expressed as P2O5, and normally also potassium expressed as K2O.

The content of nutrients (N + P2O5 + K2O) will normally be between 40 and 50%.

In addition the fertilizers may contain magnesium, boron, sulphur and micro-

nutrients.

These compound fertilizers are made by one of the two following important

production routes:

1– The nitric acid route or nitro-phosphate process,

2– The sulfuric acid route or mixed-acid process,

The two processes are based on different technologies, having different investment

costs, economic impact, energy consumptions, emission values and process

integration

Sources for the three primary nutrients are given in Figure next two slide.

Fertilizer

83

Fertilizer Materials

2-Mixed Fertilizers

•The primary advantage of mixed fertilizers is that they contain

all three primary nutrients—nitrogen, phosphorus, and

potassium—and require a smaller number of applications. They

can be liquids or solids.

•The overall percentage of the three nutrients must always be

stated on the container. The grade designation is %N-%P2O5-

%K2O. It is commonly called the NPK value.

•Note that it is an elemental percentage only in the case of

nitrogen. Phosphorus and potassium are expressed as oxides.

Thus an NPK value of 6-24-12 means that 6% by weight is

elemental nitrogen, 24% is phosphorus pentoxide, and 12% is

potash.

85

LIQUIDS VS. SOLIDS

There are many different types of liquid and solid fertilizers but we give

only some generalizations about advantages of each.

Liquid fertilizers:

Are a clear solution, a suspension of a solid in a liquid (aided by a

suspending agent), or a simple slurry of a solid in a liquid, account for 20%

of all NPK mixed fertilizers

Solid fertilizers:

Contain no liquid, Mixed solid fertilizers can be made by either direct

granulation methods or bulk blending.

Bulk blending is made by mechanical mixing of the separate granular

intermediate materials. It is usually done in small plants near the point of

use. This technique is employed because the fertilizer can be "tailor-made"

to fit the exact requirements of the user.

Table next slide summarizes the advantages of liquids and solids

Liquids Solids

Lower capital investment Less corrosion for the equipment

Less labor, handling and conditioning

costs

Better economics of smaller volume

storing cost

More inform composition Solubility restrictions are not present

More uniform distribution on land No crystallization problem in cold weather