Method of forming low temperature dispersions

Dispersions with lowered freezing points are provided by dissolving a dispersing agent in water, adding urea, adding a particulate inorganic solid, and then adding alcohol as a freezing point depressant. Dispersions formed in this manner can contain 20 to 75% inorganic solids in suspension without flocculating in the presence of the alcohol. Alternatively, the dispersant can be dissolved in an aqueous urea solution and the fine, particulate inorganic solid can be dispersed in the solution after which the alcohol may be added. These compositions exhibit depressed freezing points and can still be transported as a liquid at lower temperatures.

BACKGROUND OF THE INVENTION 
Attapulgite dispersions in water at 25 to 30% clay solids predispersed with 
TSPP (approximately 2-3% tetrasodium pyrophosphate based on the clay 
weight) are available from commercial sources and can be made in situ by 
the user. Processing in either case consists of dissolving the TSPP 
dispersant in water, adding the clay while agitating and continuing 
agitation until the major portion of the clay is dispersed. The dispersion 
can be used as made or can be processed to remove undispersed impurities. 
Other chemical agents such as small amounts of NaOH can be included as 
functional additives in the dispersion. They are added either before or 
after the incorporation of the clay. 
The dispersion of attapulgite clay at 25 to 30% solids in water using 
condensed phosphates as dispersing agents is an old and well-known 
practice and has been described many times in the literature. The 
technique has also been described as a step in many U.S. Patents where the 
inventive feature has been some further treatment of the dispersion. U.S. 
Pat. Nos. 3,050,863, 3,509,066 and the references cited therein describe 
some methods of further treatment as examples. 
When colloidal grades of attapulgite are used as gelling agents to 
stabilize suspensions or to thicken an undesirably thin aqueous system, 
the user often has the option as to how he will incorporate the clay into 
his system. He may either add the dry clay during processing and disperse 
it by mechanical work input or he may add predispersed clay which has been 
subjected to prior processing as described above. In either case the clay 
must end up with an extended flocculated structure in the final product to 
give the desired thickening or suspension effects. 
The advantages of using predispersed attapulgite are that (1) the clumps of 
needles present in the dry colloidal clay products can be dispersed in 
water using a condensed phosphate dispersant with much less work input 
than is necessary in mechanical dispersion and (2) the efficiency of the 
predispersed clay in its intended use is 2 to 3 times better than that 
achieved in strictly mechanical dispersion. The disadvantages of 
predispersed clay slurries are (1) the poor economics of shipping 75% 
water for long-distance trips and (2) the fact that the freezing point of 
the dispersion is approximately 32.degree. F. This second factor, the 
32.degree. F. freezing point, prevents the shipment and outdoor storage of 
predispersed slurries in many parts of the U.S. during the winter. In many 
parts of the country this would prevent shipment in unheated tank cars and 
trucks from October of one year to April of the next year. This situation 
has been a retarding factor in the development and use of such a desirable 
product. 
Materials normally used as antifreezes, such as methanol, ethanol, 
isopropanol, ethylene glycol, propylene glycol and eutectic salt 
solutions, cannot be used in the above-described predispersions because 
they cause the predispersion to flocculate and become excessively viscous 
so that it can no longer be stirred or pumped. Furthermore, after such a 
flocculation it no longer exhibits the above-mentioned ease of use and 
must be redispersed mechanically for utilization. 
SUMMARY OF THE INVENTION 
The present invention provides a technique to overcome this inherent 
incompatibility of the feasible anti-freeze compounds by having dissolved 
urea present in the particulate dispersion when the antifreeze compounds 
are added as a final addition. 
Urea is essentially a nonionic compound and, because of its lack of 
ionoticity in solution, solutions of urea can be used as a dispersing 
media when using condensed phosphates as dispersants. The beneficial 
results are believed to be related to the interfacial characteristics of 
the urea-solution/particle surface interface which are altered by the 
adsorption from solution of molecular urea in such a manner that, although 
condensed phosphates are still capable of charging up and dispersing the 
solids, the antifreeze compounds (alcohols and glycols) are blocked from 
dehydrating the surface and causing flocculation. Since urea is a 
nitrogenous compound formed from carbon dioxide and ammonia, other 
compounds of similar chemistry are believed to provide similar beneficial 
results. However, urea will not prevent flocculation with eutectic salt 
solutions because the mechanism of flocculation of dispersed particles is 
different with ionic materials. When ionic materials cause flocculation 
the flocculation is caused by the collapse of the protective charged 
double layer and the adsorbed urea evidently does not prevent this 
phenomenon.