Process for making acid activated bleaching earth using high susceptibility source clay and novel bleaching earth product
Bleaching Earth Abstract
A process for making acid-activated bleaching earth from a crude attapulgite clay. A crude is selected which is mildly acidic and contains at least about 90% attapulgite. The process involves treating such clay with low levels of activating acid which are mixed with the dried and ground clay, or spray dried from slurries containing the clay-acid mixture. Advantages include: lower acid costs/unit mass of clay treated, lower production costs (no washing, filtering, or waste treatment steps) and environmental soundness (no harmful environmental waste products are produced).
Bleaching Earth Claims
We claim:
1. A method for producing bleaching earth which comprises selecting a naturally-occurring acidic attapulgite clay having a pH in the range of 5 to 7 and a pore volume in the range of 0.25-0.50 cc/gm, mixing said clay with an acid solution in amount corresponding to an acid dosage in the range of 10 to 30%, heating said mixture at a temperature in the range of 77.degree. to 220.degree. F. to react said clay with said acid and, without washing the resulting reaction product, recovering it for use as a bleaching earth.
2. The method of claim 1 wherein said selected clay contains no more than about 5% CO.sub.2 by weight on a moisture free basis.
3. The method of claim 1 wherein said selected clay contains less than 1% CO.sub.2 on a moisture free basis.
4. The method of claim 1 wherein said selected clay is dried and ground before mixing with said acid.
5. The method of claim 1 wherein said mixture of clay and acid is heated while it is spray dried.
6. The method of claim 1 wherein said mixture of clay and acid is formed by spraying acid solution onto dried clay.
7. The method of claim 1 wherein said clay is dried and ground, mixed with acid solution, filtered after heating, and filtrate is recycled.
8. The method of claim 1 wherein said acid is sulfuric.
9. The bleaching earth product obtained by the method of claim 1.
Bleaching Earth Description
RELATED APPLICATIONS
This application is related to USSN 352,578 filed concurrently herewith.
1. Field of the Invention
The invention relates to a process for making acid-activated bleaching earth from attapulgite clay and to novel acid-activated bleaching earth products obtained thereby.
2. Background
Acid-activated clays of high activity are used to adsorb colored pigments (carotenoids, chlorophyll) and colorless pigments (phospholipids) from edible and inedible oils. This process is called "bleaching" and serves both cosmetic and chemical purposes. Thus, bleaching reduces color, whereby very clear, almost water white oils are produced that meet with consumer expectations. Bleaching also stabilizes the oil by removing colored and colorless pigments which tend to "destabilize" the oil, resulting in oils that rancidify more easily if they are not removed. The current, and expected long term trend, favors the use of highest possible bleaching efficiency clays with this process because: (i) the smaller amounts of the high activity clays needed to produce desired refined oil properties mean that lower inventories can be maintained by the oil refiner; (ii) refined oil losses depend somewhat on the amount of clay used because less of high activity clay needs to be used and therefore oil losses are lower; and (iii) less spent clay is produced when using high activity clay, and hence land-fill disposal costs are lower.
The conventional process for producing acid-activated bleaching clays utilizes calcium bentonite clays and requires relatively high acid dosages to achieve maximum bleaching efficiencies. The calcium bentonites used in the process are hydrated sodium calcium aluminosilicates which typically are mildly basic. The manufacture of highest quality commercial bleaching earths typically require 70-90 grams of 96% H.sub.2 SO.sub.4 /100 grams of dry clay or 67.2-87.4% acid dosage where: % Acid ##EQU1## Extensive leaching of the clay structure in the form of solubilized salts takes place and these are removed in the process. Because of these high acid dosages, and the extensive leaching that takes place during the leaching process, the yield of bleaching clay is low (typically in the range of 75-85 wt %). The acidic salts formed during activation and residual acid must be washed off and separated by filtration from the product clay. If high levels of unused acid and acidic salts (iron and aluminum sulfates) are left in the clay, the quality of the bleached oil is impaired. High residual acid levels generate undesirable free fatty acids from the fatty acid triglycerides in the oil. Finally, the leachate (acidic salts and residual acid) is a waste stream that contains materials harmful to aquatic life and therefore must be neutralized or otherwise disposed of in an environmentally acceptable manner. This constitutes an additional expense of producing bleaching clays from pure calcium bentonites.
Clay sources used in the past to provide acid-activated bleaching clay of high activities have been primarily restricted to calcium bentonites, i.e., clays in which the principal exchangeable cation is a calcium ion, and these are sometimes also referred to as sub-bentonites.
Another type of naturally-occurring clay simply requires heat to impart bleaching activity. These are the clays rich in the minerals attapulgite or sepiolite, now frequently classified as palygorskite clays. Mineralogically, the palygorskite clays are readily distinguishable from the bentonites (smectites or montmorillonites) and rarely are palygorskites and bentonites used interchangeably.
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