Bleaching Earths

The term bleaching effectively means decolorisation. Clays with high specific surfaces have great importance in removal of unwanted substances, most of which are colored, from liquids through adsorption. Those clays are called bleaching earths.

We have been the representatives and distributors of Oil-Dri Corp.of America, one of the largest manufacturers of hormitic clays in the world. Oil-Dri manufacture their products from fullers earth (a natural mixture of attapulgite and bentonite) where  most of the other clays in the market are produced from calcium type bentonites.

Oil-Dri’s "Pure-Flo ®" branded products are used for bleaching of both vegetable and mineral oils worldwide and in our country. There are four main types of these clays

1.    Pure-Flo Natural B-80 : This is a naturally active bleaching and clarifying adsorbent which has a surface area more than 400 m²/g. It has no effect on double bonds because it does not contain any mineral acid. It can be used between % 0.5 - 8 depending on the nature of the oil, and/or blended with a acid activated clay where necessary.

2.    Pure-Flo Supreme B-81 :  It is an acid activated adsorbent with a surface area around 200 m²/g and have a pH around 4. It can be used for bleaching all kinds of oils, especially for removal of red color. It gives the best results for the stability of the oil. Dosage used may be between % 0.3 - 2.0 depending on nature of the oil.

3.    Pure-Flo Supreme Pro-Active / Perform 4000 :  These varieties are acid activated clays with a pH around 3. They are most effective in removal of  the metal-containing color bodies and compounds containing oxygen in their structure.

4.    Pure-Flo Perform 6000 : This products is developed from Perform 4000 for treatment of most oxidized oils. It has pH around 2.5 and it is the most expensive of  Oil-Dri’s bleaching clays.  

Pure-Flo ® products are manufactured from a different kind of raw material, which is an intergrowth hormite and smectite minerals, then their counterparts in the market as was mentioned before, and one of the most important aspects of the material is its sensitivity to soaps. It adsorbs soaps, hence rise in free fatty acids is not observed during bleaching unlike that with other bleaching clays.

These adsorbents have a particle size distribution between 1-100 microns (with averages at around 20-30 microns) as can be seen in their specifications, are usually mixed with the liquids at a temperature of 90-100°C for 15-20 minutes, and under vacuum to minimize oxidative and other catalytic effects of the clay. The clay is seperated from the fluid by filtration after processing is completed.

5.    Ultra-Clear® : Other than the powdered products described above, Oil-Dri have also granular clays branded as Ultra-Clear® which are used for removal of moisture and surfactants in petroleum derivatives and organic fluids. These are used by percolation of the liquid throgh the clay filled as packed beds in vertical columns or in cartridges.  

The effect of the solid/liquid ratio on the reaction kinetics is often overseen in the use of both powdered and granular clays in bleaching. Caution is adviced in  determining a dosage, in interpreting lab data and estimating scale-up, in employing filtration equipment or using packed beds, that the solid/liquid ratio is few percent during mixing or in the reaction vessel while it would be about 1:1 during filtration or percolation.