Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Pat. Ser. No. 696,142, filed June 14, 1976 and now abandoned. 
    
    
     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° F. This second factor, the 32° 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. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Urea concentrations in water for use within this invention are 3 to 30% by weight of the dispersion. Particulate materials of interest include clays such as sepiolite and attapulgite (palygorskite) at concentrations of 20 to 30% solids and kaolin, calcium carbonate and titanium dioxide at concentrations of up to 65 to 75% solids. Dispersants of utility are the condensed phosphate dispersants normally used with minerals such as TSPP (tetrasodium pyrophosphate), STP (sodium tripolyphosphate), Calgon, etc. at 0.2 to 4% by weight of the solid particles. Antifreezes useable with this invention are methyl alcohol, ethyl alcohol, ethylene glycol, propylene glycol, isopropanol and desirable mixtures thereof in amounts of 9 to 30% by weight of the dispersion. The primary intended fields of interest for the inventive dispersions with depressed freezing points include suspensions of: fertilizer, soil treating material, animal feed, paint pigments and powdered coal. 
     Freezing point depressions in water as listed in the Encyclopedia of Chem. Tech., Kirk-Othmer, Ed. 2, Vol. 2, p. 547, for the antifreeze compounds used within this invention are: 
     
         ______________________________________         Freezing Points (% by vol.)  Density  20% in water 30% in water______________________________________Methanol 0.80       +9° F.                            -4° F.Ethanol  0.80       +18° F.                            +5° F.Ethylene 1.13       +17° F.                            +6° F. Glycol______________________________________ 
    
     The addition of urea to water depresses the freezing points further than listed above and also modifies the freezing characteristics of the resulting solution. 
     To demonstrate some of the possibilities of this invention, the examples listed on Table 1 were made using a Sterling multi-mixer. The dispersants in each of the examples were dissolved in water prior to the addition of the urea and then the urea was dissolved before the dispersion was made by adding the solid particles. The antifreeze component, methanol, was added as the last ingredient in all the examples listed. p The particulate material used in the examples is Min-U-Gel 200, a colloidal attapulgite product of the Floridin Co., Pittsburgh, Pa. 
     To determine the feasibility of using ethanol as a freezing point depressant in accordance with this invention, the processing previously described was repeated using ethanol in place of methanol. The formulations and results shown in Table II for each of the examples listed show that ethanol can be used as an effective freezing point depressant in the urea-STP suspensions whereas methanol was effective for both urea-TSPP and urea-STP suspensions. 
     
                                           TABLE 1__________________________________________________________________________ Ingredient  Methanol FormulationsWeight %     Example 1              Example 2                    Example 3                          Example 4                                Example 5                                       Example 6                                             Example                                                   Example__________________________________________________________________________                                                   8Water        61.72 43.20 49.38 55.55 49.34  57.00 49.38 61.72TSPP          0.77  0.77  0.77  0.77  0.77  --    --    --STP          --    --    --    --    --     --     0.77  0.77Urea         --    18.52 12.34  6.17 12.33  18.00 12.34 --Min-U-Gel 200        25.72 25.72 25.72 25.72 25.70  25.00 25.72 25.72Methanol     11.79 11.79 11.79 11.79 11.79  --    11.79 11.79        100.00              100.00                    100.00                          100.00       100.00                                             100.00                                                   100.00Comments     Very thick              Thin  Thin-med.                          Med.  *5 Drops                                       Couldn&#39;t                                             Thin  V. thick                          Thickness                                50% Caustic                                       get all                                (0.07%)                                       of the                                100.00 clay inComponents In Solution% Urea       0     24.92 16.62  8.31 16.60  24    16.62 0% Methanol   15.88 15.88 15.88 15.88 15.86  0     15.88 15.88Brookfield Visc., cpsInitial 10 RPM        --    1000  3600  6000  5200   --    1500  --   20 RPM        --     850  1950  3200  2750   --    850   --   50 RPM        --     520  1000  1420  1400   --    420   --   100 RPM        --     300   560   820   740   --    270   --1 Week  10 RPM        2500  1500  4600  7700  7000   --    1100  --   20 RPM        1500  1100  2600  4000  3800   --    1000  --   50 RPM         700   720  1080  1700  1600   --    600   --   100 RPM         490   530   630   960   930   --    410   --2 Weeks 10 RPM        2050  1700  4850  8000  7500   --    600   --   20 RPM        1350  1375  2525  Discarded    --    850   --   50 RPM         700   840  1120  too thick    --    700   --   100 RPM         385   555   580               --    470   --Low Temp.Characteristics        Slush at              V. thin                    --    --    --     --    V. thin        -15° C.              at -12° C.              at -12° C.__________________________________________________________________________ 
    
     
                                           Table II__________________________________________________________________________ Ingredient  Ethanol FormulationsWeight %     Example 1                 Example 2                       Example 3                             Example 4__________________________________________________________________________Water        61.72    43.20 43.20 49.38TSPP          0.77     0.77 --    --STP          --       --     0.77  0.77Urea         --       18.52 18.52 12.34Min-U-Gel 200        25.72    25.72 25.72 25.72Ethanol      11.79    11.79 11.79 11.79        100.00   100.00                       100.00                             100.00Comments     Too thick                 V. thick                       Med.  Med. to thin        for Et OH        Couldn&#39;t        formulateComponents in Solution% Urea       0        24.9  24.9  16.6% Ethanol    15.9     15.9  15.9  15.9Brookfield Visc. (cps)Initial 10 RPM        --       &gt;10,000                       4600  4000   20 RPM        --       --    2550  2100   50 RPM        --       --    1320  1040   100 RPM        --       --     610   5503 days  10 RPM        --       ˜10,000                       1800  1000   20 RPM        --       --    1400  1000   50 RPM        --       --     800   700   100 RPM        --       --     470   4651 Week  10 RPM        --       10,600                       2700  2100   20 RPM        --       5800  1750  1500   50 RPM        --       2800   960   900   100 RPM        --       1800   590   5602 Weeks 10 RPM        --       10,000                       4400  2000   20 RPM        --       Discarded                       2650  1475   50 RPM        --             1260   840   100 RPM        --              680   510Low Temp.Characteristics        Slush at -15° C.                 --    Pourable at                             Pourable                       -12° C.                             at -12° C.__________________________________________________________________________ 
    
     The control formulations made up with water and either dispersant including urea and M-G 200 (attapulgite clay) were low in viscosity and froze at slightly less than 0° C. and at temperatures lower than -3° C. there were many crystals formed. To determine formulations for ethylene glycol, the previous processing was followed and the examples listed in Table III were prepared. The results show good handling properties with both the urea-TSPP, and urea-STP clay suspensions with ethylene glycol at temperatures as low as -9° C. 
     To determine the results achievable with a low-shear mixer, the formulations shown in Table IV were made up with a Lightnin&#39; mixer. The results indicate that both the ethanol-urea and methanol-urea compositions were pumpable as low as -12° C. (Examples 3, 4 and 5). 
     To determine the gelling efficiency of various pre-dispersions, the predispersions, were evaluated as gellants for a diammonium phosphate solution (DAP) and a urea/ammonium nitrate solution (UAN). The DAP test consisted of 36 g of dispersed clay (25% dispersion) to 264 g of DAP solution (30% DAP; 70% water). The UAN test consisted of 264 g of UAN solution (35.4% urea, 44.3% ammonium nitrate, 20.3% water) to 36 g of predipersion. Mixing for each dispersion was provided by submitting each dispersion to 15 minutes in a Lightnin&#39; mixer. 
     These results shown in Table V indicate that the urea-antifreeze slurries (Examples 3, 4 and 5) are generally equivalent to or better than the controls (Examples 1 and 2) in the UAN and DAP tests at 10 RPM (viscosity reading) without building up excessive readings at 100 RPM. 
     
                                           Table III__________________________________________________________________________Ingredient   Ethylene Glycol FormulasWeight %     Example 1               Example 2*                        Example 3     Example 4                                            Example__________________________________________________________________________                                            5Water        58.87  58.87 (1)                        43.63         48.72 48.72TSPP          0.74   0.74 (2)                         0.74          0.74 --STP          --     --       --            --     0.74Urea         --     --       18.73         12.18 12.18Min-U-Gel 200        24.52  24.52 (4)                        24.65         24.60 24.60Ethylene Glycol        15.87  15.87 (3)                        12.25         13.76 13.76        100.00 100.00   100.00        100.00                                            100.00Initial Comments        Med. to thick               Med.     Med.          Med.  V. thinComponents in Solution% Urea       0      0        24.86         16.2  16.2% Et. Glycol 21.0   21.0     16.26         18.3  18.3Brookfield Visc. (cps)Initial 10 RPM        6500   4700     2550          4000  100   20 RPM        3300   2500     1400          2000  80   50 RPM        1460   1100     820           900   72   100 RPM         860    640     520           540   841 Week  10 RPM        &gt;10,000               &gt;10,000   20 RPM        Discard   50 RPM        Thickening due to intercollation   100 RPM        of the montmorilloniteBrookfield Visc. (cps)       Gelled at -5° C., Pourable                                            Thin at -5°  C.1 Week at   10 RPM               4600          --    400-5° C.   20 RPM        2600            --            400   50 RPM        1320            --            350   100 RPM         940            --            330at -9° C.   10 RPM        5000            --            300   20 RPM        3700            --            250   50 RPM        2440            --            240   100 RPM        1600            --            200__________________________________________________________________________ *numbers in () indicate order of addition 
    
     
                                           Table IV__________________________________________________________________________Ingredient    Example 1          Example 2Weight % (Control)          (Control)                Example 3                      Example 4                            Example 5__________________________________________________________________________Water    74.44 74.44 45.23 49.5  49.5TSPP     0.74  --    0.77  --    --STP      --    0.74  --    0.75  0.75Urea     --    --    19.39 12.38 12.38Min-U-Gel 200    24.82 24.82 25.57 25.   25.Methanol --    --    9.05  12.37 --Ethanol  --    --    --    --    12.37    100.00          100.00                100.00                      100.00                            100.0Comments Thin  Thin  Hard to get all clay inComponents in Solution% Urea   0     0     26.0  16.5  16.5% Alcohol    0     0     12.2  16.5  16.5Brookfield Visc. (cps) at 70° F.:Initial10 RPM    200   900   2000  500   2000    20 RPM    175   800   1250  400   1250    50 RPM    144   490   700   240   800    100 RPM    130   375   400   175   5453 Days    10 RPM    500   900   2500  450   1000    20 RPM    475   850   1750  400   825    50 RPM    410   640   940   340   580    100 RPM    440   535   610   305   460Low temp.Characteristics    Freezes          Freezes                At -12° C.                      At -12° C.                            At-12° C.    ˜0° C.          ˜0° C.                slushy gel                      thin, slushy                at -10 ° C.                      pumpable                            at -5° C.                thin &amp;      thin                pumpableBrookfield Visc. (cps) at -5° C.:(23° F.)10 RPM    --    --    2000  550   3500    20 RPM    --    --    1720  550   3500    50 RPM    --    --    1320  510   &gt;2000    100 RPM    --    --     990  570   &gt;1000__________________________________________________________________________ 
    
     
                                           Table V__________________________________________________________________________Brookfield Viscosities (cps) at RPM Shown              Test Group                    UAN Test  DAP TestExampleFormula       Table 10 RPM                         100 RPM                              10 RPM                                   100 RPM__________________________________________________________________________1    TSPP (Control)              IV    2500 400  1730 2602    STP (Control) IV    2300 350  1850 2953    TSPP, 26 U/12 M              IV    3000 455  1800 2804    STP, 16.5 U/16.5 M              IV    2500 365  1900 3005    STP, 16.5 U/16.5 E              IV    2550 375  1800 2801    TSPP, O U/16 E (Control)              II    3450 465  2300 3402    TSPP, 25 U/16 E (Control)              II    3500 510  2150 3153    TSPP, 25 U/16 EG              III   3000 445  1950 3005    STP, 16 U/18 EG              III   3100 435  1900 3201    TSPP, O U/16 M              I     2700 435  2000 3052    TSPP, 25 U/16 M              I     3300 500  2000 3107    STP, 17 U/16 M              I     2600 435  2550 3903    STP, 25 U/16 E              II    2600 385  2000 3054    STP, 17 U/16 E              II    2300 340  2000 209__________________________________________________________________________ 
    
     To determine the low temperature effects on the viscosity of some of the examples containing urea, Examples 3, 4 and 5 (from Table 5), were held at 20° F. (-6.7° C.) for two weeks in a freezer. At the end of this period Examples 3 and 4 were flowable and Example 5 was very thick. Example 3 and Example 4 were pumpable and Example 5 was questionable. 
     The preferred embodiments previously described are presented as examples only and it is to be understood that variations in concentrations may be made by those skilled in the art. While the examples are directed to attapulgite clay dispersions, dispersions of other minerals and particulate inorganic solids such as sepiolite, kaolin, calcium carbonate, coal dust and titanium dioxide show the same properties of freezing point depression when dispersed in urea solutions. Dispersants such as TSPP, STP, other condensed-phosphate sodium salts, sodium polyacrylates, sodium polymethacrylates, functional blends of the above dispersants, and TSPP/sodium naphthylene-formaldehyde sulfonate blends do not cause the aforementioned materials to drop out of suspension when anti-freeze additives such as methanol, ethanol and ethylene glycol are added to the urea solution. 
     Examples of other clay dispersions include sepiolite, attapulgite, or palygorskite particles at concentrations of 20 to 30% by weight of dispersion, 1 to 4% dispersant by weight of the solid particles, urea in an amount equal to 3 to 30% by weight of the dispersion, antifreeze in an amount equal to 9 to 30% by weight of the dispersion and water. The preferred concentrations include 2 to 3% dispersant by weight of solid particles and 15 to 30% urea by weight of the dispersion. 
     When using kaolin, titanium dioxide or calcium carbonate, the particle concentration may be increase up to 65 to 75% by weight of the dispersion while using only 0.2 to 1% dispersant by weight of the solid particles. The preferred dispersant concentration is in the range of 0.2 to 0.3% by weight of the solids and the preferred urea concentration is again 15 to 30% by weight of the dispersion. 
     The concentration of antifreeze can generally be varied between 9 to 30% by weight of the dispersion with higher concentrations being uneconomical and lower concentrations not being very meaningful. 
     In addition to the above described method of preparing the dispersion, the urea may first be mixed into the water, followed by the dissolving of the dispersant after which the solids may be mixed into the dispersion with the final step being the addition of the antifreeze. 
     Although the invention is directed to water suspensions of materials, it is to be understood that other liquid suspending means and other particulate materials readily fall within the scope of the invention.