Pharmaceutical Engineering

1. Materials of Pharmaceutical
Plant Construction

2. In selecting materials for its construction of
satisfactory plant, the pharmaceutical engineers
encounter problems involving chemical, physical
and economic factors.
1.Chemical factors: Two aspects of chemical action
must be considered, namely:
a. The possible contamination of the product by the
plant martial.
b. Effect on the plant material by the drug/chemicals
being processed.
These become important when impurities, even in
traces have considerable physiological effects or
cause the product to decompose.
e.g. inactivating effects of heavy metals on penicillin.

3. 2. Physical factors: These include-
a. Strength: should have sufficient mechanical
strength to withstand the stresses and will be suited to
the size of the plant.
b. Weight: in most cases weight will be reduced to a
minimum, especially in plants that may have to be
moved from place to place.
c. Wearing qualities: these are particularly
important where there is a possibility of friction
between moving parts. e.g. grinding surfaces of mills.
d. Ease of fabrication: must be possible to process
the material in order to fabricate the various units i.e.
materials enabled to be cast, welded, forged or
machined.

4. e. Thermal expansion: the design of plant may be
complicated by the materials that have high
coefficient of expansion. This increases the stresses
and the risk of fracture with temperature change.
f. Thermal conductivity: In plant such as evaporators
or other heating devices, a good thermal
conductivity is desirable.
g. Cleansing: smooth polished surfaces simplify
cleansing processes. The materials that can be
finished with such surfaces are ideal.
h. Sterilization: If any the materials should be
capable of withstanding the necessary treatment,
usually steam under pressure.
i. Transparency: may be a useful property if it is
possible. This is one reason for increasing use of
borosilicate glass in the construction of
pharmaceutical plant.

5. 3.Economic factors: cost and maintenance
of plant must be economic. Not to obtain the
best costly material, rather a higher initial
cost is more economical in long run
(maintenance cost gets lower).

6. The commonly used materials of construction is therefore
given under the simple classification:

 Materials
 Metals Non-metals
 Ferrous Non-ferrous Inorganic Organic

 eg. Cast iron eg. Copper eg. Glass eg. Plastics
 Steels Copper alloys Glass linings Rubber
 Stainless steels Stone ware Timber
 Aluminum Stone, brick & concrete
 Lead Asbestos
 Tin
 Silver
 Nickel
 Chromium etc

7.  Ferrous Metals
Cast iron: consists of iron with a
proposition of carbon. The amount of
carbon varies, giving products with
different properties, may also be altered
by alloying with other elements e.g.
silicon, nickel, chromium etc.
 It is cheap & commonly used as
the supports for plants, the jackets of
steam pans etc.

8. Steels: Mild steel is an iron alloy that
contains a small percentage of carbon,
Unlike cast Iron,
 - It can be worked by welding,
machining.
 - Much greater mechanical strength
 - Much less brittle
 - Resistance to attack by chemicals.
 It may be used for vessels & pans. Also for
supporting structures to grinders, pipe
lines, nuts & bolts etc.

9. Stainless Steels: These are steel alloys,
usually with nickel (8%) and chromium
(18%), characterized by their high
resistance to corrosion.
It can be used for most practical plants of
various shapes and size, including storage
& extraction vessels, evaporators, small
apparatus like funnels, measuring vessels,
sinks, bench tops etc.

10. Non-ferrous Metals
Copper: It is easily fabricated, thermal
conductivity 8 times greater than steel
but corroded by a number of
substances, particularly oxidizing
agents.
It is used for evaporators, pans
of various kinds, columns etc.

11. Copper Alloys: Includes alloys with Zinc, tin,
aluminum, silicon, nickel etc but importantly -
Copper-Zinc Alloys (Brasses): Corrosion resistance is
less but their tensile strength is greater. They are
easily worked in various shapes.
It is used for tube plates are evaporators &
condenser, extensively used in making valves, nuts,
bolts, rods etc.
Copper-Tin Alloys (Bronzes): Usually contain 2 to 13%
tin with a small amount of phosphorus. Harder & more
durable.
They are used for filler gauzes, strirers, pumps,
high pressure pipes, autoclaves and tablet punches &
dies.

12. Aluminum: It has good corrosion resistance to many
substances (by forming a film on the surface,
e.g. Acetic acid forms aluminum sub acetate film),
although attacked by mineral acids.
It is easily fabricated and has excellent thermal
conductivity. Most valuable property is the non-
toxicity, moreover, colorless thus used is biosynthetic
processes and culture methods.
Lead: Much used in chemical industry, due to its
great resistance to corrosion. It is little used in
p'ceutical practice because of the risk of
contamination.
It is used for cold water pipes, waste pipes,
dilution tanks for laboratories.

13. Tin: It has high resistance to variety of
substances, its salts are non-toxic, widely
used in food industry.
However it is weak, main use in
p'ceutical industry as a protective coating
for steel, copper, brass etc.
Silver: High cost made silver use only in
special cases. i.e. plants for manufacture of
salicylates, vitamin etc (resistant to organic
compounds). High thermal conductivity &
ductile, capable of being readily worked.
Usually silver-coated material is used
rather than solid silver.

14. Nickel: It is resistant to oxidation & alkalis but
attacked by acids, it is useful for plant as pans,
vats, tanks, mixers, valves and pump or as wire.
Monel metal: an alloy of nickel (⅔) and
copper (⅓), which is harder & more resistant than
nickel, can replace steel where corrosion resistance
is essential.
Chromium: Hard & resistant to corrosion but not
normally need as a construction material, it’s most
important use in the manufacture of stainless steel.
It is also used as a plating to protect steel.

15. Non-metals
(Inorganic)
Glass: It is very resistant & widely used for
small-scale apparatus. Recently developed as
a construction material for a large scale. i.e.
Borosilicate glass has low thermal expansion
(safety over wide temperature ranges).
Special advantages are easily cleaned &
sterilized. Glass pipe is useful for transporting
liquids (from stage to stage).
Glass fabrics are excellent for heat insulation.

16. Glass linings & Coatings: Metal may be coated with
glass to give protective lining, but dangers are of
uneven expansion of metal & glass, resulting glass
surface accidentally chipping. High resistance to
corrosion & ease of cleaning.
Pipe line & fittings, valves, condensers, columns,
pumps, stirrers and mixers are glass-coated items in
use.
Stone ware: Reasonably cheap, but weight, low
thermal conductivity & fragility give low resistance to
mechanical / thermal shock.
Pipe line, tanks, vessels & filters are the items
made from it; Special interest is bacteria-proof filters.

17. Stone, Brick & concrete: have particular uses
i.e. mill, tanks, drains, culverts etc.
(structural purposes)
Asbestos: a poor heat conductor, used for
heat insulation. It is extremely inert, used
for pipe lining & jointing a fibrous material.

18.  Organic
Plastics: reduce noise production, weight is
about then of iron. Resistance to corrosion except
oxidizing substances & strong alkalis.
Any item-vessels, pipes, fittings, valves, pumps,
fans, ducts, fitters etc. may be made from this.
Metallic surfaces may be protected from
corrosion by plastic coatings but the differences in
thermal expansion of plastic & metal may cause
accidental chipping.
The lining of tanks & vessels, coating stirrers &
fans, plastic guards for moving parts of machines &
asepsis screen are the important uses.

19. Rubber: Hard rubber may be used for
purposes similar to plastics. Soft rubber used
for linings & coatings. But rubber swells in
contact with oils, attacked by some organic
solvents.
However, synthetic rubber have greater
resistance been developed.
Timber: Its lightness is an advantage but the
use of wood for tanks & vats has greatly
diminished due to adsorbing the contents.
Filter presses are sometimes made of
wood (for its lightness).