Treatment of tallow and like fatty materials

[57] ABSTRACT

Fatty material such as tallow contaminated by synthetic polymeric impurities such as polyethylene is purified by adjusting the temperature to above the melting point of the fatty material but not above about 95°C, thereby rendering the impurities insoluble in the fatty material, and separating such insoluble materials.

Claims, No Drawings

3,758,533

TREATMENT OF TALLOW AND LIKE FATTY MATERIALS

This invention relates to the treatment of tallow and like fatty materials. Tallow is used on a large scale as a raw material in the manufacture of soap.

During the last few years, soap manufacturers have experienced new difficulties such as the increased occurrence of black specks in kettle and finished soaps, the formation of a layer of black intractable mud between the clear lye bottom layer and the settled nigre soap upper layer during the nigre graining operation, coating of transfer lines and heat exchanger surfaces, and clogging of centrifuges and filters. These difficulties are attributable to contamination of the raw tallow with polyethylene and possibly other synthetic polymeric material. This contamination may arise from the use of polyethylene bags and drum liners for shipping of fats and butchers’ trimmings, and also from polyethylene-prepacked condemned foods, all of which are sources of industrial tallow.

According to the present invention, a process for removing synthetic polymeric impurities from fatty material comprises adjusting the temperature of the fatty material to about 95°C or below but above the melting point of the fatty material to render the polymeric impurities insoluble in the fatty material and separating the polymeric impurities from the fatty material.

In one form of the invention a process for treating tallow contaminated with polyethylene comprises bringing the tallow to a temperature below 90°C but at which the tallow is still fluid, and separating from the tallow polyethylene which comes out of solution.

The invention is based on the appreciation that while at temperatures in excess of about 95°C polyethylene melts and is soluble in tallow in the concentrations in which it is normally present as a contaminant (e.g. up to about 500 parts per million), but that at temperatures below about 95 °C the polyethylene comes out of solution in the form, initially, of fine particles. These particles grow in size and tend to become flake-like or filament-like, particularly as the temperature of the tallow is lowered. In this form, the polyethylene is readily separable from the still fluid tallow, for example by filtration or centrifuging.

For optimum results, the temperature of the tallow should be lowered as far as practicable below 95°C. As the temperatures is reduced, a point is reached at which the tallow tends to lose fluidity and become mushy which would make separation of the polyethylene more difficult. Temperatures as low as about 55°C can be used. However, temperatures in the range 75° to 90°C are, in general, preferred.

if the separation is to be conducted by filtration, a filter aid may be employed. Filter aids are particulate solid materials which encourage the growth of the polytheylene particles and aid in their retention on a filter bed. Such filter aids may be, for example “Celite”, carbon black or Fuller’s earth. Fuller’s earth is preferred as this is also useful for bleaching the tallow. The filter aid will normally be used in an amount of between about 0.5 to 2 percent based upon the weight of the tallow. During the filtration step, the filter aid and the polyethylene particles are held back by the filter, the fluid tallow passing through the filter.

For application of the filter aid, use may be made of a so-called earth bleach tank and a filter press such as are conventionally employed for bleaching tallow for soap manufacture. The temperature in the earth bleach tank is usually in the range 100° to 110°C, and for the purpose of cooling the molten tallow on its way from the earth bleach tank to the filter press, a heat exchanger may be interposed. The coolant in the heat exchanger may be water.

When starting up the plant after the introduction of new filter cloths into the filter press, hot tallow containing filter aid, at a temperature of 100° to 110°C, may first be passed through the filter press in order to line the new cloths with filter aid particles, the outflow from the filter being returned to the earth bleach tank. Thereafter, the heat exchanger can be brought into operation so that the tallow enters the filter press at a temperature in the range 75° to 90°C. When the filter cloths need replacement, the cycle described is repeated, the old filter cloths together with the separated polyethylene and filter aid being discarded.

It is also possible to carry out the separation in other ways, for example by means of a centrifuge, or by the interposition of a special filter at some other point in the plant at which the tallow is, or can be, brought to the appropriate temperature. It is not feasible to separate the polyethylene simply by settling since the density of polyethylene is only a little greater than that of tallow.

EXAMPLE

A batch of tallow in an amount of 25 tons is removed from storage at a temperature of about 60°C. The tallow contains 350 parts per million of polyethylene. It is passed to a conventional vacuum bleach tank where it is heated to a temperature of 102°C under a vacuum of 27 mmHg and maintained at this temperature and pressure until substantially all of the water is removed. Fullers’ earth in an amount of 560 pounds is then thoroughly admixed with the molten tallow, and the mixture is then cooled to a temperature of 85°C and passed to a conventional plate and frame filter press which removes the polyethylene together with the Fullers’ earth.

The filtered tallow is removed and tested and found to contain 15 parts per million of polyethylene, which amount is well below the acceptable maximum of about 50 parts per million.