I am working on edible oils extracted from new plant and insect sources. Traditionally we use bleaching earth to decolorize the oil. But they have a few limitations:
1. The recovery of edible oil is very low (a large quantity of oil sticks to bleaching earth and its hard to remove).
2. In most cases the process takes place on temperatures above 100°C, which usually degrades the nutritional quality of the oil (especially if more unsaturated fatty acids are present in the oil).
3. Bleaching earth are usually non-renewable, we can't use them again and again.
Keeping in mind all the above points I would like some suggestions about a desirable bleaching agent.
Modern bleaching processes use a substantial range of different bleaching agents including:-
• Natural bleaching earths (used with only limited colour-reducing effect but are particularly useful in treating animal fats)
• Acid-activated bleaching earths (widely used for removing all kinds of impurities)
• Activated carbon (used to remove polyaromatic hydrocarbons and ensure removal of a wide range of specific pollutants)
• Synthetic amorphous silica compounds (used largely in wet bleaching, with a focus on selectively removing phosphatides, trace metals and soaps).
Dry bleaching can also be done in which the oil is heated before it is mixed with bleaching earth. If the process requires it, a citric acid solution is mixed with the hot oil to bind trace metals and decompose any residual soap. After this treatment, the oil is mixed with bleaching earth, activated carbon or a mixture of these two. Operating the process at a vacuum of about 70 torr, greatly reduces the humidity in the oil. Heat exchangers can be used for heating and cooling the oil efficiently, both before and after the bleaching process to prevent any degradation. After bleaching, the bleaching agent is normally removed using pressure leaf filters. Naturally, the filter cake that accumulates here still contains oil which can be recovered by steam-blowing the contents of filters.
Modern bleaching processes use a substantial range of different bleaching agents including:-
• Natural bleaching earths (used with only limited colour-reducing effect but are particularly useful in treating animal fats)
• Acid-activated bleaching earths (widely used for removing all kinds of impurities)
• Activated carbon (used to remove polyaromatic hydrocarbons and ensure removal of a wide range of specific pollutants)
• Synthetic amorphous silica compounds (used largely in wet bleaching, with a focus on selectively removing phosphatides, trace metals and soaps).
Dry bleaching can also be done in which the oil is heated before it is mixed with bleaching earth. If the process requires it, a citric acid solution is mixed with the hot oil to bind trace metals and decompose any residual soap. After this treatment, the oil is mixed with bleaching earth, activated carbon or a mixture of these two. Operating the process at a vacuum of about 70 torr, greatly reduces the humidity in the oil. Heat exchangers can be used for heating and cooling the oil efficiently, both before and after the bleaching process to prevent any degradation. After bleaching, the bleaching agent is normally removed using pressure leaf filters. Naturally, the filter cake that accumulates here still contains oil which can be recovered by steam-blowing the contents of filters.
Dear Dr. Tripathi,
Thanks for the reply!
But the main addons I need are:
1. the process should be preferably at room temperature or even lower and
2. the recovery of the oil from bleaching agent.
Another thing is the oil which I am investigating have lots of minor components and I lose them by using above adsorbents. So I am still in hunt of a suitable bleaching agent.
Bleaching earths (silicates) through which aluminia has leached down. These earths should be activated by acid
Dear Aman
100 C is not too much high process to degrade unsaturated fatty acids. If you are facing still problem at high temperatyure you may use slightly vacum conditions. If you will be using activated carbon instead of bleaching earth you will come across more losses of oil. If you are using some HTST technique it will be more valuable and losses of oil will be less.
blanching angents to edible oil, take care you need natural agents or synthetic, i read montomorplronit or caolonit stone ginding stones as a natural filter ( Ph.D. thesis in agric. fac., cairo univ, Egypt 2000)
I will try to use natural filtration or chemical like sodium hydroxide 5 - 10%
You may be interested in stripping the oil on a column using activated charcoal or similar and then recovering the stripped oil and thereafter eluting the other fractions with the other minor components
I see through the discussion the lack of knowledge on bleaching clays. The words like "montomorplronit" or "caolonit" are actually "montmorillonite" and "kaolinite". Montmorillonite is now better known as bentonite. Kaolinite can never be a better choice as bleaching agent, montmorillonite would also not be superior. The best bleaching/decoloration agent would be palygorskite (and sepiolite). We found palygorskite of good quality in Pakistan if someone wants to try in bleaching of edibil oils through natural agents.
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