Batch Refining of Oils

Many vegetable oilseeds are available in small quantities at a time at various locations due to various reasons. These oilseeds include edible as well as non-edible oilseeds. Sal, Kokum, Niger, Mango Kernel, etc. are the edible oilseeds. Karanja, Neem, etc. are non-edible oils. Oils are extracted from them on small scale by various processes suitable for the respective oilseeds. The extracted oils are stored in barrels, etc. These oils are refined periodically when substantial quantities become available and can be processed in small capacity batch processing plants.  Animal fats and fish oils are also processed in batch refining plants. Common vegetable oils like soybean, groundnut (peanut), rapeseed (mustard), etc. can also be processed in these batch refining plants; especially when their impurities contents are different than those in 

Low availability of these crude oils and fats, as well as their varying contents of different impurities such as gums, free fatty acids, coloring bodies, odoriferous materials, etc.

BATCH REFINING PLANTS
Typical batch refining plants for vegetable oils (and selected oils of animal or fish origin) consist of several small units carrying out specific unit operations in the refining, such as heating, degumming, alkali refining (neutralization), bleaching and deodorization. Allied equipment like electric heater and small steam generator are also included in a batch refining plant. 

Production capacities of batch oil refining plants vary widely; mostly depending on the availability of minor oils. These capacities vary from one tonne per day to five tonnes per day. However, batch refining plant capacities of 10, 15, 20 and 25 TPD are also available. 

The oils and fats which are to be processed in these batch refining plants are analyzed at the beginning to assess their impurities like free fatty acids, gums or phospholipids, color, and odor. Pre-mixed concentrations of treatment chemicals like phosphoric acid, caustic soda, bleaching earth and activated carbon, are mixed with these oils at specific processing steps in pre-calculated or measured quantities. 

DEGUMMING AND ALKALI REFINING
The crude vegetable oil or animal fat or fish oil is first filtered to remove insoluble matter and then taken in the first reactor which is used for degumming and alkali refining. Measured quantities of phosphoric acid and hot water are mixed with the crude oil to precipitate the hydratable gums. After thorough mixing to ensure complete precipitation of the phospholipids, measured quantities of caustic soda (sodium hydroxide) solution are also added and mixed thoroughly. The mixture is heated to about 60 deg. C. The caustic soda reacts with the free fatty acids in the oil to form soap or soapstock. This precipitate settles at the bottom of the reactor. It is collected in soap pans from the bottom of the neutralizer and dried in pans. The degummed and neutralized oil is washed with water to remove traces of soap.

Depending on the gum or phosphatides content of the crude oil, there could be separate reactors for degumming and alkali neutralization.

This degummed and alkali neutralized oil is then taken to the next reactor vessel, i.e., bleacher or bleaching reactor.

BLEACHING
In this section, coloring bodies or pigments present in the oil are removed. The oil is first heated slightly to remove moisture, if any. Then pre-determined and measured quantities of bleaching earth and activated carbon are mixed with the degummed and neutralized oil in the bleacher. The bleaching earth and activated carbon remove or adsorb the coloring bodies present in the oil. After specified reaction time, the mixture is passed through a suitable filter to remove the spent bleaching earth and activated carbon. The filter type is determined by the quantity of oil processed in each batch. Pressure leaf filters or small sized filter press can also be used. The filtered, bleached oil is of light color and taken to the next reactor for deodorization step.

DEODORIZATION
Degummed, alkali refined and bleached oil still contains some odoriferous compounds like aldehydes, ketones, etc. Minor components like sterols are also present in this oil. Deodorization process removes these chemicals from the oil in the deodorization reactor. The process is carried out by passing open steam from the bottom of the deodorization reactor through the oil charge. The oil is heated to about 110 to 220 deg. C under very high vacuum to remove the air (de-aeration). The open steam is passes through the oil, extracting the odoriferous compounds and carries them to the top of the reactor. This steam loaded with the odor materials is taken to a condenser where they are condensed and stored temporarily. Later, these materials are removed from the condenser and disposed off. The deodorized oil is taken to a cooling tank, from which it is transferred to a larger storage tank.

SUPPORTING EQUIPMENT
The following supporting equipments are needed for a batch oil refining plants. 

Heat conduction oil furnace for heating the oil to high temperature

Steam generator to pass the open steam in the deodorization process

Leaf filter for removing spent bleaching earth and activated carbon

Hot water tank used for washing the oil in various stages

ADVANTAGES OF BATCH REFINING
Batch processing of oils to refine them is advantageous in many respects. The following are the advantages of batch oil refining – 

1. Batch refining enables purifying small quantities of oils, which are not available in large quantities at a given location. Also, many a times, it is not practical to store these oils for longer time due to the resulting deterioration, and hence have to be processed immediately.
2. The batch process also offers good, light colored and odorless oils, which can either be used for edible purpose as well as some industrial applications.
3. The composition and properties of soapstock obtained from different oils and fats are different. Batch refining of these oils helps in obtaining these soapstocks separately and they can be stored separately, eventually, utilizing them in specific applications in large quantities later. The acid oils obtained from these soapstocks are important for their specific fatty acid compositions. 
4. Similarly, the deodorization process results in collection of odoriferous materials including sterols in the condenser. These components obtained from certain oils are of commercial value. Batch refining enables separate collection of these components from selected oils and they can be processed further for downstream value-added products.
5. Batch refining plants are versatile and a wide range of oils and fats can be refined in them.
6. Since these batch refining plants are of lesser capacity, the investment needed to set up these plants is much less as compared to the large-capacity, continuous refining plants. The space or land requirements for batch refining plants are also smaller. In turn, the payback period is also lesser.
7. These batch refining plants are comparatively easier to operate with lesser number of personnel, in most cases.

These advantages make the batch refining plants ideal for setting up in regions where a number of different oilseeds are available in smaller quantities, in many cases, throughout the year.

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