T H E U N I V E R S I T Y O F L A H O R E

ASSIGNMENT

SUBMITTED by;

UMAiR HANiF, JAVAID JOIYA, SULMAN MAlik, MUHAMMAD IKRAM, OBAID-UR-REHMAN, SHABIR HUSSAIN, SAMDANI KHAN

SUBMITTED TO:

DR. NAJAM

SUBMITTED DATE:

20-12-2010.

COURSE TITLE:

PHARM-D- VII.

SUBJECT: INDUSTRIAL PHARMACY-I

Topic:

Evaporators

Evaporation under Reduce Pressure

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EVAPORATORS

Evaporators are used for reducing product volume, remove water prior to drying, and to improve product storage life.

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.

Importance of Evaporators:-

This equipment is used to get the following actions:

Improve product storage life Reduce transportation costs Prepare the products for next operations like drying and crystallization. Recovery of solvent Minimize the chances of chemical reactions which may deteriorate the product Decrease the impact of microbial growth.

Factors Affecting Evaporation:-

Factors which are affecting the rate of evaporation are in following:

1) Temperature:- The rate of evaporation is directly proportional to the rate of temperature. Higher the temperature higher will be rate of evaporation but evaporation is maximum at boiling point of the liquid. Thermo stable products can be evaporated at high temperatures but thermo labile products will have to be evaporated at low temperatures. Many substances like glycosides, alkaloids, hormones, enzymes and antibiotics may decompose even at below 100°C hence they should be evaporates at a careful temperature. Extremely heat sensitive products may be evaporated under reduce pressure. But the time required for evaporation is also very critical.

2) Surface Area:- The rate of evaporation is directly proportional to the surface area of the vessel exposed to evaporation. Greater the surface exposed to evaporation higher will be rate of evaporation.

3) Agitation:- During evaporation the upper layer of liquid to be evaporated has a tendency to form a scum or layer which lowers the rate of evaporation. Therefore it becomes

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necessary to agitate or stirrer the solution under evaporation. This will also prevent the decomposition of product at the bottom due to excessive heat and will also prevent the settling of solids at the bottom of container.

SELECTION OF EVAPORATOR

The choice made on the selection of evaporator equipment is based on following points:

Type of Product required:- The selection of method and apparatus to be used for evaporation depends upon the type of product required and Product characteristics, including heat sensitivity, viscosity and flow properties, foaming tendency, fouling and precipitation, boiling behavior, etc. Evaporating pans or stills may be used to produce liquid or dry products but film evaporators may be used to get liquid products.

Economic Factors:- While selecting the method and apparatus employed for evaporation, due consideration must be given to economy of labour, fuel, floor area and materials. The recovery of solvents and the utilization of ‘waste’ heat are also important factors which contribute significantly in the reduction of overall costs.

Capacity and operational data, including quantities, concentrations, temperatures, annual operating hours, change of product etc.

Required operating media, such as steam, cooling water, electric power, cleaning agents, spare parts, etc.

Standards and conditions for manufacture delivery, acceptance, etc. Site conditions, such as available space, climate (for outdoor sites), connections for

energy and product, service platforms, etc.

TYPES OF EVAPORATORS

There are different types of evaporators that are differing from each other according to the method and capacity of their work. Briefly evaporators are classified as:

Small Scale Methods Large Scale Methods

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Small Scale Methods:-

Small quantities of liquids may be evaporated in a porcelain or glass dish. Generally direct heating by Bunsen burner or electric hot plates used for evaporation, but it should not be employed, as direct heating leads to decomposition of the substances’ towards the end of evaporation. A fixed maximum temperature can easily be attained by employing different types of baths as a source of indirect heating. A water bath is most suitable when the liquids are to be heated up to 100°C.They are simple and inexpensive. Sand bath or oil bath containing liquid paraffin or soft paraffin may be used when higher temperatures up to 300 °C are required. To prevent decomposition, whole of the liquid should not be evaporated to dryness. The last traces of solvent from the concentrated liquid may be removed under controlled temperatures.

Applications of Small Scale Methods:

Used commonly in laboratory procedures and preparations of products.

Advantages of small scale methods:

Simple and inexpensive Limited resources are required Quick process

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Large Scale Methods:-

Different evaporating equipments are used in large scale manufacturing of products.

Which are described briefly in following:

1) Evaporatoring Pans : 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.

The hemispherical shape is most suitable because it affords the best surface/volume ratio for heating. These pans may be fixed or made to tilt to remove the product.

For convenience in emptying the fixed pans, a tube passes from the lowest point of inner pan, through the jacket, which fitted with the tap to withdraw the evaporated liquid from the pan when desired.

Advantages:

They are simple, easy and cheap to construct.5

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.

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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 o be heated all the times which may lead to deterioration of the product.

The heating surface is limited.

Note: This method of evaporation is used widely in pharmaceutical industries when small batches of liquids are to be evaporated.

3) Long tube Evaporators: Long tube evaporators have wide range. Most frequently used long tube evaporators are discuss in following.

a) Calandria type evaporator: Commonly it is known as short tube or single effect evaporator. Generally tubes are employed in order to get sufficient heating surfaces with steam on the outside and liquid inside. In same order still further to increase the capacity the tubes are multiplied forming a Calandria.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.

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Advantages: High heat transfer rates at high temperature differences Ease of cleaning Relatively inexpensive

Disadvantages: Large floor space and weight Poor heat transfer at low temperature differences

Not use for thermolabile products

b) Climbing film Evaporators:- It is also known as long tube or rising film evaporator.The theory of climbing film evaporator’s working is that the ascending force of this steam produced during the boiling causes liquid and vapors to flow upwards in parallel flow. At the same time the production of vapor increases and the product is pressed as a thin film on the walls of the tubes, and the liquid rises upwards. This co-current upward movement against gravity has the beneficial effect of creating a high degree of turbulence in the liquid. This is advantageous during evaporation of highly viscous products and products that have a tendency to foul the heating surface.

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Usually there must be a rather high temperature difference between the heating and boiling sides of this type of evaporator. Otherwise the energy of the vapor flow is not sufficient to convey the liquid and to produce the rising film. The length of the boiling tubes will typically not exceed 23 ft (7m).

Advantages: Reduced floor space requirement Relatively high heat transfer cofficient Ability to handle foamy liquids

Disadvantages: High head room requirement Hydrostatic head at the bottom may increase product temperature and cause

temperature sensitivity problems.

c) Horizontal Film Evaporator:- Also known as falling film evaporator.

This type of evaporator is generally made of long tubes (4-8 meters in length) which are surrounded by steam jackets. The uniform distribution of the solution is important when using this type of evaporator. The solution enters and gains velocity as it flows downward. This gain in velocity is attributed to the vapor being evolved against the heating medium, which flows downward as well. This evaporator is applicable to highly viscous solutions so it is frequently used in the chemical, food, and fermentation industry.

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Falling Film Evaporator with boiling inside the tubes. The feed to the evaporator is fed to the top of the Calandria through efficient liquid distributors. Steam is given on the shell side. The concentrate is collected at the bottom. The same operation is repeated in multiple effects to achieve steam economy. 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 materail.

D) 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.

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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

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It is also known as Vacuum Evaporation.

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.

Types of Vacuum Evaporators:-

There are different types of evaporators that are based on the principle of reducing pressure evaporation; some of them which are describing in following are widely used.

Single effect vacuum evaporator

Multi-effect/ triple-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.

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Applications:

It is used when

Through put is low

Cheap supply of steam

Vapours are contaminated

Disadvantages:

It uses steam inefficiently.

Triple-effect Vacuum Evaporator

Features:

(1) 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.(2) 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.(3) 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.

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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

Recovery of solvents

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References:-

Introducing to PHARMACEUTICS-1 by Ashok.K GUPTA 4th Addition.

BENTLEY’S TEXT-BOOK OF PHAMRCEUTICS.

www.niroinc.com/evaporators.../evaporation_systems.asp

en.wikipedia.org/wiki/Evaporator

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