Materials of pharmaceutical plant construction - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes

 Materials of pharmaceutical plant construction

Contents of this session

Factors affecting selection of plant material

Physical, chemical and economic factors

Classification of materials

Metals and non-metal materials

Non Ferrous metals

Thermosetting Plastic

Polystyrene

Learning objectives

Enlist the factors affecting selection of plant material

Understand the physical, chemical and economic factors

Classify materials

Discuss the metal and non-metal materials

Enlist the non-ferrous materials

Discuss non-metals used for plant construction

Discuss thermoplastics

Factors affecting selection of material for pharmaceutical plant construction

The success or failure of s new chemical plant or in the improvement of an existing facility depends on

1.       Design of equipment-easy to clean, install, operate

2.       Selection of material-Physical, chemical, Economical

Physical

·         Strength: to withstand the stress and and rigours

·         Mass: to transport

·         Wear and tear: to mill and grind

·         Thermal conductivity: evaporators, dryers

·         Thermal Expansion: material should maintain size, should not expand.

·         Cleansing: Smooth and polished surfaces

·         Sterilization: Material should withstand the heat and pressure.

·         Transparency: permits the visual observation of reactions and processes.

Chemical

Contamination: Substance’s such as glass, silica, lead, cast iron, steel, tinned iron and variety of alloys are used in construction of pharma plant and most of them produce contamination. Ex: Heavy metals inactivates penicillin, Appearance changes, may be toxic etc

Reactivity with chemicals: At extreme pH, temperature and pressure, materials get corroded.

Economical

Cost of the material plays an important role in the design of the plant.

Cost and utility of the material is studied before making buying decision.

Classification of material

Metal

1.       Ferrous

·         Cast Iron

·         Steel Carbon

·         Stainless steel

2.       Non ferrous

·         Aluminium

·         Nickel

·         Lead

Non metal

1.       Inorganic

·         Glass

·         Asbestos

2.       Organic

·         Rubber

·         Timber

FERROUS METALS

Iron metal is one of the used materials for the construction of plants because of its mechanical strength, abundent availability and lower cost.  Some varieties of iron are discussed.

1. Cast iron:

It consists of iron with a proportion of carbon (>15 %). The properties of iron depend on the amount of iron present in it.

Cast iron is abundently available, inexpensive and therefore widely used. A number of types of cast iron are available.

Advantages:

Cast iron is cheap. Therefore, it is used in place of expensive plant material for coating

Since cast iron has low thermal conductivity, it is used for the construction of outer surface of jackets of steam pans.

Low melting temperatures 1140/1200*C

Disadvantages:

Cast iron is very hard and brittle. Therfore, it is difficult to machine. This disadvantage can be overcome by the addition of different materials to improve his performance.

Cast iron is attacked by dil.H2SO4, dil. Nitric acid and dilute as well as con HCl.

It is resistant to conc. H2SO4, nitric acid and alkalis.

Since cast iron has low thermal conductivity, it cannot be used for heat transfer in steels.

Uses:

It is commonly used for the construction of: 

·         Supports for plant

·         Jackets of steam pans

·         Linings with enamel, plastic or suitable protective material.

Modification of cast iron: Cast iron is not considered corrosion resistant. The characteristics of cast iron can be altered by alloying with other elements such as silicon, nickel and chromium

Commercial types: duriron and durichlor.

2. Carbon steel

Carbon steel is an iron alloy, which contains only a small % of carbon.

Advantages:

Carbon steel is cheapest. Therefore, it is preferred.

It is easily weldable and is freqently used in fabrication

 

Disadvantages:

Carbon steel has limited resistance to corrosion. This property can be improved by preparing alloys.

It reacts with caustic soda, brine and sea water. Alloying it can reduce this reactivity.

Uses:

Carbon steel is used for the construction of bars, pipes and plates. It is used to fabricate large storage tanks for water,  sulphuric acid, organic solvents etc.

It is used for supporting structures such as grinders and bases for plant vessels.

VARIENTS OF CARBON STEEL:

The properties of carbon steel can be altered by alloying it with other metals.  Some of the metals and their properties are:

Nickel (Ni) – improves toughness, corrosion resistance and low temperature properties.

Chromium (Cr)/ increase hardness, more abrasive resistant and resistance to oxidation.

Silicon (Si)/ increase hardness, more abrasive resistant and resistance to oxidation.

Molybdenum (Mb)/ provides strength at elevated temperatures.

3. Stainless steel

It is an alloy of iron. Usually, it contains chromium and nickel, which make the steel corrosion resistant.

Stainless steel is stabilized by the addition of titanium, niobium,                and tantalum. Minor amount of other elements             such as copper, molybdenum selenium are added. Stainless and steel also has the advantage of ease in fabrication.

The abundant use of stainless steel is due to the properties such as 

Heat resistance

Corrosion Resistance

Ease of fabrication 

Cleaning and sterilization

Tensile strength

Depending on the composition, stainless steel alloys are available in 3 groups viz., martensitic, ferritic and austenitic.

Alloys of stainless steel (SS): are allowed with other metal so an to modify its properties. The metals incorporated into SS are,

Titanium (Ti)

Niobium (Nb)

Tantalum (Ta)

Chromium (Cr)

Carbon (C)

Silicon (Si)

Nickel (Ni)

Manganese (Mn)

Copper (Cu)

Non Ferrous metals

Aluminium

Lead

Copper

Nickel

Chromium

Silver

Platinum

ALUMINIUM

A number of aluminium items are used in regular day to day life.  Aluminium is cheap, light in weight and offers adequate mechanical strength. In addition, aluminium equipment can be easily fabricated. Further, aluminium can be strengthened by cold working. Their maintenance and cleaning is also easy.  Hence, its utility is mostly recommended. However the use of aluminium in the construction of plant and equipment is limited.

Advantages:

High resistance to atmospheric conditions, industrial fumes, vapour and fresh or salt waters. Aluminium can be used with conc. Nitric acid (above 82%) and acetic acid.

Thermal conductivity of aluminium is 60% that of pure copper. 

Disadvantages:

The mechanical strength decreases greatly above 150*C.

aluminium cannot be used with strong caustic solution.

Many mineral acids attack aluminium.

Oxide and hydro/ oxide films are formed rapidly, when its surface is exposed. Normally this film is thickened by chemical and electrolytic means. This provides so called anodised finishes.

SILVER

Because of its high cost, silver is used only as a material of plant construction in special cases and usually silver coated material is used rather than solid silver.

It is not resistant to concentrated HCl or H2SO4, any strength of nitric acid, and sulphur and sulphur compounds.

It is resistant to organic acids and their salts. It is even more malleable and ductile than copper and, therefore, capable of being readily worked. It has a higher thermal conductivity than all other metals.

A few e.g. of its special uses are – plant for the manufacture of salicylates and acetic acid; a silver/ plated basket for a hydroextracter used in vitamin crystallisation; a solid silver vessel in a cast/ iron jacket for bromination.

TITANIUM

Titanium has become increasingly important as a construction material. It is strong and of medium weight.

Titanium is usually not bothered by impingement attack, crevice corrosion, and pitting attack in seawater. Its general resistance to seawater is excellent.

Titanium is not easy to form, it has a high spring back

NICKEL

Nickel is resistant to oxidation and alkalis but is attacked slowly by dilute mineral acids and rapidly by concentrated acids.

It is resistant to the weak organic acids occuring in pharmaceutical preparations, e.g. citiric, tartaric and stearic.

It is also resistant to phenols. Its salts are non oxic. It is useful for such plant as pans, vats, tanks, mixers, valves, and pumps, nickel wire may be woven to form filter cloths.

 

CHROMIUM

Although Hard and resistant to corrosion, chromium is not normally used as material of plant construction.

It forms resistant alloy with nickel and, probably, its most important use is in the manufacture of stainless steel.

It is also, of course, used as a plating to protect steel.

Non Metals

Glass

Rubber

Plastic

·         Thermosetting Plastic

·         Thermoplastic

General properties

Resistant to chemicals

Resistant to contamination

Corrosion resistant

Easy to fabricate

Application

Flooring

Roofing

Windows & doors

Piping

Storage tanks

Insulation materials

Thermosetting Plastic

Permanently shaped to rigid structure during manufacturing.

·         Phenol formaldehyde

·         Bakelite (cookwear handle)

·         Melamine (iron)

Thermoplastic

Soften under the influence of heat

·         Poly vinyl Chloride (PVC)

·         Polyethylene/Polypropylene

·         Polystyrene

·         Acrylonitrile Butadiene Styrene (ABS)

·         Cellulose Acetate Butyrate (CAB)

Poor resistance to organics

Polyvinyl chloride

Clear, tough, inert

Stabilizer or colorant can be incorporated

Resistant to acids

Resistant to alkali

Crack readily (plasticizer added to reduce this)

Turn yellow when exposed to UV

Polyethylene

Economical

Density (0.91-0.96) determine stiffness, transluscency, vapour transmission

More density-> more stiffness, less permiable, less, resistant to cracking

Pipe of Polyethylene must be fully supported

Stable upto 1200F

Polyporopylene

Good resistance to chemical, acids, alkali

Tough and flexible

Resistance to fatigue (weakening of a material caused by repeatedly applied loads)

Stable upto 2500F

Brittle at low temperature, Used for manufacturing piping systems

Polystyrene

High mechanical strength

Chemical resistant

Rigid

Clear

Easy to scratch

Brittle (rubber or acrylic compounds can be mixed to improve properties)

Stable upto 1900F

Acrylonitrile Butadiene Styrene (ABS)

Acid resistant

Resistant to organic solvents

Not resistant to alkali

Summary

The success or failure of s new chemical plant or in the improvement of an existing facility depends on:

1.       Design of equipment

2.       Selection of material

Alloys of stainless steel (SS): are allowed with other metal so an to modify its properties.

A number of aluminium items are used in regular day to day life.  Aluminium is cheap, light in weight and offers adequate mechanical strength. In addition, aluminium equipment can be easily fabricated.

Although Hard and resistant to corrosion, chromium is not normally used as material of plant construction. It forms resistant alloy with nickel and, probably, its most important use is in the manufacture of stainless steel.

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