US 3325413 A
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United States Patent Ofifice 3,325,413 Patented June 13, 1957 PROCESS OF PRODUCiNG DETERGENT CUMPUSI- TIGNS CONTAINING ALKALI METAL SILICATES Darwin A. Novak, Jr., St. Louis, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Deiaware No Drawing. Filed Oct. 5, .1964, Ser. No. 401,687
6 Claims. (Cl. 252--135) This invention relates to improved methods for manufacturing detergent compositions that contain hydrated alkali metal tripolyphosphate. More specifically, this invention relates to improved processes for manufacturing detergent compositions, in which processes alkali metal trimetaphosphate is utilized as a raw material.
In copending United States patent application Ser. No. 135,718, filed Sept. 5, 1961 (the disclosure of which is hereby incorporated into the present patent application by reference), processes for manufacturing heat dried detergent compositions that contain, for example, sodium tripolyphosphate hexahydrate are disclosed. The preferred processes of the invention detailed in said copending patent application involve, basically, reacting together alkali metal trimetaphosphate and an appropriate strong inorganic alkali metal cation-containing base (such as alkali metal hydroxide, alkali metal carbonate, strong alkali metal silicate, and the like) in a fluid aqueous slurry (containing more than sufficient water to hydrate all of the alkali metal tripolyphosphate ultimately present in the slurry, but preferably at least about 20 weight percent of Water) to form a hydrated tripolyphosphate. Thus, when sodium trimetaphosphate and sodium hydroxide are utilized:
(2) NasPaow 61120 NHPHO10-6H2O sodium sodium tripolyphostripolyphosphate phate hexahydrate In the preferred processes of said copending patent application, so-called heavy-duty detergent compositions are prepared by first making a slurry containing at least about 20 weight percent of water, at least about 5 weight percent (and preferably between about 10 and about 70 .weight percent) of alkali metal trimetaphosphate, and
sufficient strong base to furnish from about 1.5 to about 4 moles of hydroxyl ion (per mole of alkali metal trimetaphosphate in the slurry). Then, after at least about.
contain from about 3 to about 20, and preferably from about 5 to about 10 weight percent. of alkali metal silicate (the ratio of alkali metal oxide to silicon dioxide [i.e., MgO/SlOg] of such alkali metal silicate generally falling within the range of from about 0.4 to about 1). For use in detergent compositions, generally cost and availability considerations require that of the alkali metal silicates (of which any alkali metal, including, for example, lithium, rubidium and cesium is useful as an anti-corrosion agent), sodium and potassium silicates be preferred.
Mo t of the alkali metal silicates falling within the ratio ranges detailed above are available as raw materials for detergent processes only in the form of fluid aqueous dispersions or solutions, generally (for the sake of stability) containing at least about 25 weight percent of Water, and at most about 55 weight percent of silicate solids (non-volatile at about C., under atmospheric pressure). Because of their fluid aqueous nature, these silicates [having ratios of M O/SiO (where M is an alkali metal cation) of from about 0.4 to about 1] have become well known in the art as simply the liquid silicates. Due to their relatively moderate alkalinity, the liquid silicates have become very widely used by manufacturers of heavy duty detergent compositions.
Because of the economic necessity for keeping the amount of free water at minimum in any given detergent slurry that is to be heat dried eventually, detergent manufacturers who utilize any of the liquid silicates in their formualtions had to take into consideration the amount of water in the liquid silicate material. As a matter of fact, in conventional commercial detergent processes, because of the manufacturers concern about maximizing slurry solids (and thus minimizing the slurrys Water content) for most efficient production of the finished detergent, the liquid silicate portion of the detergent raw materials has heretofore been one of the first of the raw materials introduced into the crutcher. For example, when those processes of the invention of said copending patent application involving the use of extremely high detergent solids (i.e., 65 weight percent of solids or more) were practiced, it was believed (prior to the present invention) that the presence of the liquid silicate (when it was used) in the crutcher during the early stages of the formulation was necessary, and that the aqueous portion of the liquid silicate thus contributed to lower slurry viscosities during the subsequent addition of the usually dry raws such as alkali metal trimetaphosphate, alkali metal sulfate, alkali metal tripolyphosphate, carboxymethyl cellulose, and the like.
It was discovered by the inventors of the invention of said copending patent application that many surprising benefits can result from practicing their invention. Such benefits included, for example (as compared, in each instance, with a process involving the use of conventional procedures for the manufacture of an otherwise identical detergent, in which process anhydrous sodium tripolyphosphate was used as the source of hydrated tripolyphosphate), (a) significantly lower slurry viscosity for a given solids level, (b) significantly lower crutching time cycle, (0) elimination of hard, gritty lumps from the slurry, (d) higher bound moisture levels in the final, heat dried detergent product, (e) higher tripolyphosphate assay in the final detergent product, (f) greater water-solubility of the final detergent product, and (g) a substantial increase in spray drying tower capacity when a plant is operated under full capacity conditions.
In spite of all of the aforesaid valuable advantages that can result from practicing .the processes disclosed in said copend-ing patent application, a still further reduction in slurry viscosity; or conversely, the attainment of higher slurry solids while the slurry remains handleable in practical or conventional crutching, pumping and spraying equipment (over that possible via the procedures detailed in said patent application); could result in substantial additional reduction in processing costs for any given detergent manufactured via such processes. Such reduction in slurry viscosity represents an extremely desirable goal for researchers in the detergent processing art.
It is a major object of the present invention to provide improved processes for .the manufacture of detergent slurries, which slurries can contain a higher proportion of solids (i.e., materials that are non-volatile at a temperature of about 105 C.) than was heretofore possible.
It is another object of the present invention to provide improved processes by means of which manufacturers of heat-dried, formulated detergent compositions can reduce the overall processing cost of such detergent compositions.
These objects, as well as others which will become apparent from the following discussion and claims, can be accomplished by withholding the alkali metal liquid silicate portion of the formulation from the slurry until at least about half of the trimetaphosphate in the formulation has been converted to tripolyphosphate.
The reasons for the surprising advantages that result from practicing the present invention are not understood. Since viscosity in the detergent slurries containing fairly large amounts of crystalline sodium tripolyphosphate hexahydrate is greatly influenced by the actual crystalline form, size, etc., of the hexahydrate, apparently the mechanism of tripolyphosphate hexahydrate crystal formation differs, depending upon whether or not alkali metal silicate is present in the slurry during the formation of such crystals. The nature of such differences in mechanisms, if they exist, is not known. However, as illustrated by the following examples, which represent some of the preferred embodiments of the present invention, a knowledge of why the invention can be performed is not at all necessary for the successful practice thereof. In these examples, all parts given are by weight unless otherwise specified.
Example 1 Into a conventional detergent crutcher are charged 5510 parts of water, 77 parts of sodium carboxymethylcellulose, 2120 parts of sodium dodecylbenzene sulfonate, 200 parts of sodium toluene sulfonate, 4160 parts of sodium trimetaphosphate, 1930 parts of sodium sulfate, and 200 parts of lauryl monoisopropanolamide. The resulting mixture (at an initial temperature of about 60 C.) is stirred for about 5 minutes, during which time 2180 parts of a 50 weight percent aqueous solution of sodium hydroxide are blended into the mixture. Stirring is continued for about 20 minutes, during which time the temperature of the slurry is observed to increase to about 95 C. At this point, 1070 parts of a liquid sodium silicate (containing 46.9 weight percent of solids having an SiO /Na O ratio of 2.40). The maximum viscosity of the resulting formulated slurry (temperature about 95 C.), in which practically all of the sodium trimetaphosphate has been converted to sodium tripolyphosphate hexahydrate, is about 900 centipoises (at a 200 sec? shear rate). By comparison, in a similar experiment, except that the liquid sodium silicate is present in the slurry during the conversion (of trimetaphosphate to tripolyphosphate) reaction, the viscosity at a similar point in the conversion reaction (at C.) is 2100 cent-ipoises (sarneshear rate). Total solids of these slurries at the time their viscosities are measured is approximately 66 weight percent.
Other liquid silicates have beneficial effects similar to those illustrated in Example 1, above (when they are added to the slurries after at least about half of the trimetaphosphate conversion reaction has taken place, in accordance with the processes of the present invention as set out above), in apparently all of those instances in which significant amounts (i.e., at least about 3 weight percent, anhydrous basis) of alkali metal silicates are utilized in the overall detergent formulation. The foregoing benefits can be obtained even though a small amount of alkail metal silicate is present in the slurry even prior to the conversion (of trimetaphophate) reaction. However, this amount must be not more than about 1 weight percent, and is preferably less than about 0.5 weight percent, based on the alkali metal silicate solids.
What I claim is:
1. In a process for manufacturing a detergent composition containing alkali metal silicates wherein sodium trimetaphosphate is reacted in a fluid aqueous slurry at a temperature above about 75 C. with a strong base, selected from the group consisting of sodium hydroxide and sodium carbonate, to form sodium tripolyphosphate hexahydrate, and said slurry is thereafter dried to produce said detergent composition, said slurry initially containing at least about 10 weight percent, based on the weight of said detergent composition, of sodium trimetaphosphate, from about 1.5 to about 4 mols of said base for each mol of sodium trimetaphosphate, and suflicient water to maintain said slurry in a fluid condition, the improvement which comprises maintaining the level of water-soluble alkali metal silicates in said slurry below about 1 weight percent until at least about one-half of said sodium trimetaphosphatate has reacted with said strong base, and thereafter intermixing with the resulting slurry from about 3 to about 20 weight percent, based on the weight of said detergent composition, of a water-soluble alkali metal silicate.
2. A process as in claim 1, wherein said alkali metal silicate is sodium silicate.
3. A process as in claim 1, wherein said alkali metal silicate is potassium silicate.
4. A process as in claim 1 wherein said slurry is maintained free of water-soluble alkali metal silicate until at least about one-half of said sodium trimetaphosphate has reacted to form sodium tripolyphosphate hexahydrate and wherein said base is sodium hydroxide.
5. A process as in claim 4, wherein said alkali metal silicate is sodium silicate.
6. A process as in claim 4, wherein said alkali metal silicate is potassium silicate.
References Cited UNITED STATES PATENTS 2,365,190 12/1944 Hatch 252 2,712,529 7/1955 Mills et al 252-135 X 3,189,551 6/1965 Metcalf et a1. 252135 LEON D. ROSDOL, Primary Examiner.
J. T. FEDIGAN, Assistant Examiner.