THE VEGETABLE OIL EXTRACTION. INTRODUCTRY TO CHEMICAL ENGINEERING. EXTRACTION. Extraction is one of the most useful and widely used chemical seperation methods. There are two types of extraction process: Solid – Liquid Extraction Liquid – Liquid Extraction. Solid – Liquid Extraction.
Extraction is one of the most useful and widely used chemical seperation methods.
There are two types of extraction process:
Solid – Liquid Extraction
Liquid – Liquid Extraction
Leaching generally refers to the removal of a substance from a solid via a liquid extraction media. The desired component diffuses into the solvent from its natural solid form.
Examples of leaching include the removal of sugar from sugar beets with hot water and the removal of nickel salts or gold from their natural solid beds with sulfuric acid solutions.
There are many different types of equipment used for leaching. Most of these pieces of equipment fall into one of two categories:
The solvent is contacted with the solid in a continuous or batch method. This method is popular for in-place ore leaching or large scale "heap" leaching. Popular for extreme amounts of solids.
The solids are usually crushed into small pieces before being contacted with solvents. This is a popular leaching method when an especially high recovery rate can economically justify the typically higher operating cost (Ex/ gold extraction)
Liquid extraction (or solvent extraction) refers to an operation in which the components of a liquid mixture are separated by contacting it with a suitable insoluble liquid solvent which preferentially dissolves one or more components.
In this operation, the separation of the components depends upon the unequal distribution of the components between the immiscible liquids. The feed solution represents one phase and the solvent to be used to effect separation represents the second phase. The mass transfer of the solute liquid takes place from the feed solution to the solvent phase.
Typical liquid-liquid extraction operations utilize the differences in the solubilities of the components of a liquid mixture. The basic steps involved include:1. Contacting the feed with the extraction solvent.2. Separation of the resulting phases, and 3. Removal/recovery of solvent from each phase.
Typical liquid-liquid extraction operations utilize the differences in the solubilities of the components of a liquid mixture. The basic steps involved include:1. Contacting the feed with the extraction solvent.2. Separation of the resulting phases3. Removal/recovery of solvent from each phase.
Some Basic Steps & Extractor Design
Various small-scale techniques are available to enable people in rural areas to process their own oilseeds locally. Careful consideration is needed to select the system that will best suit the local circumstances. These circumstances include the scale of operation required, the availability of a power source, and a number of other factors.
Some oilseeds have a hard outer shell which must be removed before processing. This process is called decortication. Palm kernel is an example of a seed that must be decorticated prior to processing. The extraction of oil from other oilseeds which can be processed without decorticating them first, such as sunflower, may be aided by removing a proportion of the hulls before processing.
It is essential to winnow and sieve oilseeds, prior to expelling, to remove as much dirt, dust, sand and small stones as possible. The presence of sand results in high wear on critical components of expellers such as cages, wormshafts and chokes. Using clean oilseed for expelling will greatly increase the time that the expeller can be used before replacement parts are needed.
Generally, small oilseeds (such as sesame or rapeseed) can be processed directly, while larger seeds (such as copra or shea nuts) need to be ground before processing. At the domestic level, grinding is usually carried out with a pestle and mortar (Plate I) while larger quantities may be ground in a village maize mill (Plate II). Hand-operated meat mincing machines can also be used in certain circumstances. The most common type of powered mill used for small-scale operations is the hammer mill.
Rolling a seed generally results in an improvement in oil extraction by increasing the surface area of the seed while at the same time retaining channels for the flow of oil. The flakes should be very fine and preferably thinner than 0.1 mm. Rolling before processing in a bridge press is said to increase oil yields by 10% for palm kernel, groundnut and sunflower.
Oilseeds are nearly always conditioned before large-scale expelling. Small-scale expellers minimize the need for pre-treatment by using a relatively fast wormshaft speed which shears the oilseed as it passes through the expeller and produces frictional heating within the expeller barrel. This assists oil expulsion by raising the temperature of the oilseed.
In wet extraction methods water is used to extract oil from oilseeds. The distinction should be made between wet methods and water-assisted methods of oil extraction.
Wet extraction methods involve the use of a relatively large amount of water so that the oilseed is suspended in the water and the extracted oil floats on the surface.
Involve the addition of a small quantity of water to the oilseed before the oil is extracted by manual kneading. These methods are discussed later. They are not classified as wet methods because all the water used is absorbed by the oilseed and no separate water layer is apparent.
The hot water flotation (HOOF) method of edible oil extraction is traditionally used in the rural areas of many developing countries. Usually, decorticated oilseed is used. The oilseed kernels are heated and ground by pounding in a pestle and mortar. The ground seed is then suspended in boiling water and boiled for at least 30 min. Liberated oil floats to the surface. Further quantities of water are sometimes added after boiling to replace that lost by evaporation, and to encourage the oil to float to the surface. The oil is carefully scooped from the surface of the water using a shallow dish and is then heated over a fire to remove residual moisture.
Series of small scale oil expeller These small scale screw type oil expeller are advanced oil processing machinery, characterized by their high oil output rate with good quality, simple design, easy to use and continuous operation. They can use for various raw material, such as peanut, beans, rape and cotton seeds, sesame, olive, sunflower, coconut, grass seed etc
Expellers are continuous in operation and work by grinding and pressing the raw material as it is carried through a barrel by a helical screw.The pressure inside the barrel, and hence the yield of oil, are adjusted using a ‘choke’ ring at the outlet. The equipment has higher production rates than similar sized presses but is more expensive to buy and operate.
These presses are used in the rolling stage of the oil extraction. They help the extraction by widening the extraction surface area.
Coconuts grow in the coastal areas of the tropics.
Major producing countries are: The Philippines, Indonesia, Malaysia, Sri Lanka, India, C’ote d'Ivoire, Mozambique, Tanzania, and the Pacific Islands.