evaporators and evaporation under reduce pressure

P r e s e n t a t i o n

INDUSTRIAL PHARMACY

*Evaporators & *Evaporation under reduce pressure.

Topic:-

EVAPORATORS

A Apparatus used to vaporize some part or all of the liquid from a solution is called as evaporator, and the phenomenon is known as Evaporation.

Evaporation

Evaporation is a phase transition from liquid phase to vapor phase below the boiling point at a given temperature.

Evaporation usually occurs on the surface of the liquid.

Importance of EvaporatorsWith the used of

Evaporator we can get the following actions:

Improve product storage life

Prepare the products for next operations like drying.

Minimize the chances of chemical reactions which may deteriorate

the product.

Decrease the impact of microbial growth.

•Temperature  The rate of evaporation is directly proportional to the rate of temperature.

• Surface area The rate of evaporation is directly proportional to the surface area of the vessel exposed to evaporation.

• Agitation

Factors Affecting Evaporation

Selection of Evaporator

*Type of Product required

E. g. Evaporating pans or stills may be used to produce liquid or dry products but film evaporators may be used to get solid or viscous products.

*Economic Factors

*Availability of Required operating media, electric power, cleaning agents, spare parts, etc.

*Capacity and operational hours including quantities of material required.

Types of Evaporators

Difference is made: According to the method and

capacity of their work.

1) Small Scale Methods

2) Large Scale Methods

Small Scale Methods

Small quantities of liquids may be evaporated in a porcelain or glass dish. Generally there are 2 different methods used in small scale evaporation.

1) Direct Heating Methods: These methods are applied by Bunsen

burner or electric hot plates, but it should not be employed commonly, as direct heating leads to decomposition of the substances’ towards the end of evaporation.

2) Indirect Heating Methods Water bath, Sand Bath and Oil bath Mainly

used. A fixed maximum temperature can easily be

attained by employing these apparatus. A water bath is most suitable when the

liquids are to be heated up to 100°C. Sand bath or oil bath containing liquid

paraffin or soft paraffin may be used when higher temperatures up to 300 °C are required.

Advantages of Small Scale Methods:-*Simple and inexpensive

*Limited resources are required

*Quick process.

Applications of Small scale Methods:- * Used commonly in laboratory scale procedures and preparations of products.

Large Scale Methods

1) Evaporating pan

On a manufacturing scale, solutions containing water in large quantity are evaporated through open pans Called evaporating pans. They consist of hemispherical or shallow pans made of copper, stainless steel, aluminum or other metal surrounded by a steam jacket.

Advantages:

They are simple, easy and cheap to construct.

They are easy to use and clean.

Stirring of the evaporating liquids can be done easily.

Disadvantages:The whole of liquid is

heated all the time which may lead to

decomposition of the components.

On the evaporating surface, scum is rapidly formed which decreases evaporation. Solids may

be deposited at the bottom which makes stirring necessary.

These pans can only be used for evaporating aqueous and thermo-

stable liquids extracts. They cannot be used for

evaporating extracts containing organic

solvents like alcohols etc.

The room in which evaporating pans are

used for evaporating the liquids, must be fitted with efficient exhaust

fans otherwise the room will be filled with dense

fog of condensed vapours and water will start falling from the

room and along the sides of walls.

2) Evaporating Stills: Evaporating stills are quite similar to evaporating

pans. It consists of a vessel made up of copper or stainless steel, with a cover which is fitted with a water condenser so that the solvent is condensed and collected in a receiver. At the lowest point of the pan, a tube fitted with a tap is connected for the removal of product from the pan. The pan is surrounded by a steam jacket. For cleaning the pan or easy removal of the product the cover of the vessel may be fitted with quick-release system of clamps.

Advantages

They are easy to construct and quite easy to clean and

maintain.

As the vapours are condensed. It increases the rate

of evaporation.

A receiver a vacuum pump can be fitted to the

apparatus by which evaporation under reduce pressure can be carried out at low temperature.

The still can be used for evaporation of both aqueous and organic solvents.

Disadvantages:

The whole of the liquid is to be heated all the times which may lead to deterioration of the product.

The heating surface is limited

Calandria Type Evaporators

3) Calandria type Evaporator:

Commonly it is known as short tube or single effect evaporator.

Features:-

Vertical type of evaporator. Tubes sheets extending across the body and central down take. Material which has to be evaporated is introduced in tubes. The tube may be about 1.2m long and 5 cm in diameter, but the

size varies with the nature of the substances. There is space below containing a steam coil to give extra heating

capacity and large enough to afford circulation of liquid.

Diagram:

Advantages:

High heat transfer rates at high temperature differences leads to quick process.

Ease of cleaning

Relatively inexpensive

Disadvantages:

*Large floor space and weight

*Poor heat transfer at low temperature differences.

*Not use for thermo-labile products

Climbing film Evaporators

4) Climbing film Evaporator: It is also known as long tube or rising film

evaporator.

Advantages:

*Reduced floor space requirement

*Relatively high heat transfer coefficient

*Ability to handle foamy and viscous liquids.

Disadvantages:

High head room requirement

Hydrostatic head at the bottom may increase product temperature and cause temperature sensitivity problems.

Thermo-labile products are not preferred.

Horizontal Film Evaporator

5) Horizontal Film Evaporator

Also known as falling film evaporator.

Advantages:

They require small head room.

Evaporation occurs at low temperature difference that is suitable for heat sensitive products.

Disadvantages:

Dry patches and incrustations can b occur which may lead to completely tubes clogged due to extreme dryness of material or with non-wetted material.

Rising-falling film Evaporator

6)Rising-falling film Evaporator:- Rising and falling film evaporators are some time

combined in to a same unit. When a high ratio of evaporation to feed is required and concentrated liquid is viscous, a tube bundle can be divided in to two sections with the first section functions as a rising film evaporator and the second section serves as falling film evaporator.

Advantages:

Low cost and small floor space

Suitable for viscous material

Large units for handling high evaporation load

Disadvantages:

High headroom required

Recirculation is frequently required

Evaporation Under Reduce Pressure

*It is also known as Vacuum Evaporation.

Description: Vacuum evaporation is the process of causing

the pressure in a liquid-filled container to be reduced below the vapor pressure of the liquid, causing the liquid to evaporate at a lower temperature than normal.

When the process is applied to food and other products and the water is evaporated and removed, the food can be stored for long periods of time without spoiling. It is also used when boiling or heating a substance at normal temperatures would chemically change the consistency of the product.

Vacuum evaporation is used whenever possible because there is a saving of time, heat and labour.

1) Single-Effect Vacuum Evaporator

Single-effect Vacuum Evaporator A single effect evaporator is utilized using water

as feed and condensed water and liquid water as product. This evaporator may be run with and without a vacuum at different steam pressures. Running the evaporator under a vacuum proved to be more efficient with respect to steam usage for evaporation.

Single-effect evaporator is discussing briefly in above heading of Calandria-type evaporator.

In this type of evaporator the vapor from boiling liquid is condensed and discarded.

Diagram:

Applications:Cheap supply of steam available.

Vapours are contaminated.

Disadvantages:

It uses steam inefficiently.

Triple-effect Vacuum Evaporator

Features: This equipment adopts the principle of multitubular

circulation out-heating working principle to keep the short heating time of materials, rapid evaporation speed, large concentration ratio, so that to keep the raw-effect of materials effectively.

Energy will be well saved 70% than single-effect evaporator. Materials are evaporated & concentrated under sealed state which is clean and comfortable. Besides, it is equipped with special foam-removing device to prevent the material running phenomenon.

All the parts touched with materials are made of stainless steel and be polished. The equipment has the properties of good corrosion-proof, easy of cleaning in accordance with requirements of Pharmacy, Food Hygiene. It can be matched with PC control system and be easy of operation and stable effects.

Diagram:

Advantages:

Suitable for large scale and for continues operations.

Highly economical when compared to single-effect evaporator.

Applications of Evaporators in Pharmaceutical Industry

Concentration of products by removal of extra water .

To insure the stability of products for longer period of time.