BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to surfactants having low foaming powers, and thus useful in cleaning applications where excessive foam is undesirable. More particularly, the invention relates to a new use of polyether-substituted chlorohydrins as cleaning assistants useful in the industrial spray cleaning of metals, as a rinse aid in automatic dishwashers, and similar applications where low foaming, caustic stable, nonionic surfactants are in demand.
2. Brief Description of the Prior Art
Polyether-substituted chlorohydrin compounds, and specifically, epichlorohydrin capped alcohol ethoxylates, are known compounds, and have heretofore been utilized as chemical intermediates in the preparation of other compounds. For example, such epichlorohydrin capped alcohol ethoxylates are employed in the process described in Gaertner U.S. Pat. No. 3,102,893 as intermediates in the preparation of glycidyl ethers, which are, in turn, intermediates in the preparation of polyether-substituted hydroxypropanesulfonates.
To my knowledge, no one has previously appreciated properties of any epichlorohydrin capped alcohol ethoxylate compound which suggest its use as a nonionic surfactant having high wetting power, but low foaming power, or if such properties may have been known, they have not led to a suggestion or proposal from any quarter for using these compounds in any type of cleaning application. In fact, though certain ethoxylated alcohols have themselves been reported as possessing good wetting power and low foaming power, it is nevertheless known that capping long-chain monohydric alkanol ethoxylates with propylene oxide, a compound somewhat similar to epichlorohydrin, does not yield a low foaming compound satisfactory for use in cleaning applications where a low foam, nonionic surfactant is required. It is therefore somewhat unexpected that long-chain monohydric alkanol ethoxylates capped with epichlorohydrin should exhibit very low foam characteristics, as well as good wetting properties and good caustic stability.
With the discovery of these properties of these particular polyether-substituted chlorohydrin compounds, I have now appreciated and confirmed that these materials possess significant utility in both household and industrial cleaning applications. In the industrial field, conventional nonionic surfactants usually produce foaming to an extent rendering them unsuitable in spray metal cleaning formulations. Here violent agitation is involved at temperatures ranging from room temperatures up to 80° or 90° C. Many presently available nonionics are also unsuitable as textile wetting agents, and other instances of industrial applications where low foaming, caustic stable, nonionic cleaning agents are needed could be cited. In the household, conventional nonionic surfactants give too high a foam level for satisfactory use as a rinse aid in mechanical dishwashers. Excessive foam is objectionable here because it may cause overflow of the machine, and even moderate amounts of foam will interfere with proper rinsing. Low foaming can often be achieved by the addition of defoaming agents, but this approach generally does not give adequate wetting or detergency properties.
OBJECTS OF THE INVENTION
The present invention has as its basic objective that of providing low foam, caustic stable, nonionic surfactants consisting essentially of known polyether-substituted chlorohydrin compounds whose utility in this respect has not previously been recognized, and which therefore have not previously appeared in this market. Subsidiary to this basic objective of demonstrating this new use of these compounds, further objectives of the invention are to demonstrate:
a. That these compounds produce relatively low foam over a wide range of temperatures, and compare well in this respect to presently used, commercially available, low foam, nonionic surfactants;
b. That these compounds compare well with commercially available, low foam, nonionic surfactants in wetting characteristics;
c. That these compounds are generally better in their ability to lower surface tension than commercial nonionics; and
d. That these compounds generally have better cloud point properties than currently used low foam, nonionic materials.
SUMMARY OF THE INVENTION
The present invention is broadly directed to a new use of known polyether-substituted chlorohydrins, and more specifically, epichlorohydrin capped alcohol ethoxylates, and most specifically, compounds having the structural formula
where R is a C4 -C20 n-alkyl group attached to the oxygen atom through a primary or secondary carbon atom, n is a number from 5 to, and including 25, and m is a number from 1 to, and including 5. The new use is broadly that of use as a cleaning agent or cleaning assistant, and is more specifically that of use as a low foam, caustic stable, nonionic surfactant.
Further, a low foam cleaning solution which is effective for spray cleaning metal and for rinsing the mechanical dishwasher applications is provided which consists essentially of an aqueous solution containing up to about 1 percent by weight of an epichlorohydrin capped ethoxylated alcohol compound as defined in Equation 1.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The epichlorohydrin capped alcohol ethoxylates which have been determined to be useful as low foam nonionic cleaning agents have the structural formula (1 ) set out above, and thus include compounds which are properly termed 1-alkoxypolyethenoxy-3-chloro-2 propanols. The alkyl group (R) in the structural formula representative of the compounds used in the invention is a straight chain (normal) alkyl group containing from 4 to 20 carbon atoms, and has either a primary or secondary carbon atom bonded to the oxygen atom to form the alkoxy group. The number of carbon atoms in the alkyl group is preferably from 8 to 16, and most desirably from 8 to 12, subject to the character of the remaining portion of the molecule of the compound as hereinafter explained. Epichlorohydrin capped compounds derived from the ethoxylation of mixtures of C8, C10, and C12, n-alkanols, are especially suitable, and are easily derived from readily available starting materials.
The number of moles of ethylene oxide (designated in n in the structural formula) which are incorporated in the compound during ethoxylation of the alcohol can range from 5 to 25, but is preferably from about 8 to about 12, and most desirably from 8.5 to 10. Again the optimum number of ethoxy groups in any given compound will depend upon the influence of the remaining portion of the molecular structure on such properties as water solubility, foaming characteristics and biodegradability. The number of moles, m, of epichlorohydrin which are used in capping the ethoxylates also depends upon the remaining molecular structure, but in general, is from 1 to 5, and preferably is 1. As a practical matter, the epichlorohydrin does not react quantitatively with the ethoxylated alcohol, and the reaction products are mixtures of capped and uncapped molecules. An especially suitable mixture for surfactant usage is one which contains an average of from about 0.9 to about 1.1 chlorohydrin groups per molecule.
The molecular structure which is most suitable for the surfactant use of these chlorohydrins contemplated by the present invention is dictated by the interaction of the several functional groups in the molecule, and the effect of each group on such properties as water solubility, product color and biodegradability. With respect to water solubility, it is desirable that a 1 weight percent aqueous solution of the capped ethoxylates have a cloud point of at least 75° F., with a higher cloud point being indicated of greater solubility. Lengthening of the alcohol chain decreases water solubility, whereas increasing the number of ethenoxy groups in the molecule increases solubility. Higher epichlorohydrin content also reduces solubility. Increasing the length of the alcohol chain also increases the foam developed or sustained by the surfactant. Increasing the number of ethenoxy groups much above 12 tends to lessen the biodegradability of the compounds. Reducing the average number of moles of epichlorohydrin per mole of ethoxylated alcohol in the reaction product mixture to less than 0.9 increases foaming, and imparts an undesirable color to the product when mixed with caustic.
Considering these criteria, the optimum compounds for low foam, nonionic surfactant use appear to be those derived from C8 -C14 primary and secondary normal alkanols and including from 8 to 12 moles of ethylene oxide and an average (in the mixture) epichlorohydrin content of from about 0.9 to about 1.1.
Methods of preparing the 1-alkoxypolyethenoxy-3-chloro-2-propanols which I have discovered to be excellent low foam, nonionic surfactants are well known in the art. General and specific methods of preparation are described, for example, in U.S. Pat. No. 3,102,893 to Gaertner. The method used to prepare these compounds therefore does not constitute a part of the present invention, and the description of one such method here is solely for the purpose of providing a more complete description of the background of the invention, and the prior knowledge essential to its practice.
In the preferred method of preparing the surfactants useful in the invention, primary or secondary monohydric n-alkanols containing from 4 to 20 carbon atoms, and preferably of the chain length hereinbefore described, or mixtures of such alcohols, are reacted with ethylene oxide in the presence of an acidic or basic catalyst of the specific types comprehensively listed in the cited patent. Preferably, a basic catalyst is used for this ethoxylation reaction, and most preferably, from about 0.1 to about 0.3 weight percent of NaOH is utilized, based on the weight of the alcohol. The ethoxylation reaction is carried out under anhydrous conditions to avoid formation of byproducts, and at a temperature which is preferably in the range of from about 310° F. to about 390° F. The reaction may be carried out at substantially atmospheric pressure, although it is preferably carried out in an autoclave at pressures of from about 10 p.s.i.g. to about 80 p.s.i.g.
The ethylene oxide-alkanol reaction is primarily an addition reaction resulting, under controlled conditions, primarily in the ethoxylated alcohol. The amount of ethylene oxide introduced to the reaction zone and the duration of reaction time, determines the number of moles of ethylene oxide added to the alcohol. As has previously been discussed, the water solubility of the product compounds is related to the number of ethenoxy groups in the molecule, and it is further desirable to maintain the number of ethenoxy groups below about 12 in order to avoid loss of biodegradability. It is therefore desirable to limit the addition to from 8 to 12 moles of ethylene oxide, which corresponds to from about 65 weight percent to about 77 weight percent of a final product derived from C10 to C12 alcohols.
After the alkaline catalyst is neutralized, and the ethoxylated alcohol is recovered, the ethoxylated product is reacted with epichlorohydrin in the presence of an acid-type catalyst, preferably boron trifluoride. From 1 to 5 moles of epichlorohydrin may be used per mole of the alcohol starting material, but a product containing a single epichlorohydrin group in each molecule is preferred. Since an addition type-capping reaction is involved, development of this preferred product is realized by using about 1 mole of epichlorohydrin for each mole of alcohol starting material. As has been indicated, however, the addition of the epichlorohydrin is not quantitative, and is therefore most desirable to use a quantity of the epichlorohydrin reactant sufficient to yield a product mixture in which the average epichlorohydrin addition is from about 0.9 to about 1.1 mole per mole of alcohol.
The amount of BF3 used in the capping reaction can vary over a wide range of from about 0.1 weight percent to about 5 weight percent, based on the weight of the alcohol reactant used, but preferably is from about 0.1 to about 1 weight percent. Since an undesirable darkening of the chlorohydrin capped reaction product occurs even when amounts of catalyst above about 0.5 weight percent are employed, the most suitable amount is from about 0.1 to about 0.5 weight percent.
The capping reaction can be carried out at room temperature, but proceeds slowly here, so that it is more desirable to heat the reaction mixture to from 50° C. to about 100° C. During the reaction, the epichlorohydrin is dripped into the ethoxylated alcohol while the reaction mixture is blanketed with an inert gas.
In producing the low foaming cleaning solution of the present invention which is effective for spray cleaning a metal and for rinsing in mechanical dishwashers, an aqueous solution is employed which contains up to about 1 percent of the epichlorohydrin capped ethoxylated alcohol compound as hereinbefore described. While the amount of the epichlorohydrin alcohol compound will vary somewhat, desirable results have been obtained wherein the aqueous solution contains from about 0.1 to 0.25 weight percent of the epichlorohydrin capped ethoxylated alcohol compound.
In order to more fully illustrate the low foam cleaning solution and the nonionic low foam surfactant composition of the present invention, the following examples are set forth; however, it is to be understood that these examples are for illustrative purposes and as such are not intended to limit the scope of the present invention.
In order to provide a more complete appreciation of the product evaluation test data hereinafter appearing, the manner in which the tested compounds were prepared will be described. An alcohol mixture containing about 85 percent normal 1-decanol, about 8.3 weight percent normal 1-dodecanol, and about 6.7 weight percent 1-tetradeconal ethoxylated in the manner hereinbefore described, using NaOH catalysis to yield a product containing 73.5 weight percent ethylene oxide. The NaOH catalyst was then neutralized with glacial acetic acid and the ethoxylated alcohol isolated.
207 grams (0.33 moles) of the ethoxylated alcohol was then charged to a 500 ml. three-necked flask equipped with a stirrer, reflux condenser, thermometer and dropping funnel. The system was purged well with nitrogen, and 0.5 grams of boron trifluoride gas was dissolved in the ethoxylate. 31 grams (0.33 moles) of epichlorohydrin was charged to the dropping funnel. The ethoxylate was heated to 30° C. and the epichlorohydrin was dripped into the ethoxylate. A nitrogen blanket was maintained over the reaction mass during the entire procedure. The reaction did not readily go at 30° C., so the temperature was raised to 60° C. At the temperature, the reaction proceeded readily. The product was post stirred for 30 minutes at 60° C. After the chlorohydrin addition.
The following examples demonstrate the properties of the 1-alkoxypolyethenoxy-3-chloro-2-propanols which make them excellent surfactants for use in cleaning applications requiring minimum foam, good wetting ability and caustic stability.
The product made in example 1 was evaluated for foam properties in a Hamilton Beach malt mixer test, conventionally used in the art to evaluate surfactant foam characteristics. 200 ml. of 0.1 weight percent aqueous solution was placed in a 1,000 ml. tall form beaker and the solution subjected to high speed stirring for 3 minutes. The solution was allowed to set for 2 minutes and the height of the foam was recorded. The foam test was run at both 75° F. and 140° F. For purposes of comparison, a 1 percent aqueous solution of a widely used, commercial low foam nonionic was subjected to the same test. The results of the test are shown in table I. --------------------------------------------------------------------------- TABLE I
Foam Height Surfactant Solution 75° F. 140° F. __________________________________________________________________________ Capped ethoxylate 1 cm. 0.5 cm. Commercial nonionic 1 cm. 0.6 cm. __________________________________________________________________________
In the Hamilton Beach mixer test, foam heights of less than 5 cm. are generally considered low. Thus, the tabulated results indicate that the capped ethoxylates have excellent low foaming properties and compare favorably with presently used low foam nonionics.
In a Draves cotton skein wetting test, using a 3 gram hook and 10 gram cotton skeins, the surfactant solutions evaluated for foam characteristics in example 2, were tested for textile wetting ability. In running these tests, the time required for the skeins to be wetted to a 0.1 percent concentration was measured, as was the concentration of surfactant required to wet the cloth in 25 seconds. The results of these tests are reported in table II. --------------------------------------------------------------------------- TABLE II
Wetting Time 25 Seconds Surfactant Solution 0.1% Conc. Wetting Concentration __________________________________________________________________________ Capped ethoxylate 17.6 seconds 0.09 percent Commercial nonionic 12.3 seconds 0.07 percent __________________________________________________________________________
In general, wetting to the extent of 0.1 percent or less in 25 seconds time is considered satisfactory for surfactants to be used in low foam nonionic applications.
The capped ethoxylate prepared as described in example 1 and the commercial nonionic tested in examples 2 and 3 were subjected to surface tension evaluation, using a 0.01 percent solution of each. At 75° F. the capped ethoxylate solution has a surface tension of 32.9 dynes/cm2. and the commercial nonionic has a surface tension of 36.1 dynes/cm2.
The water solubility of nonionic surfactants decreases with increasing temperature, and at some temperature, termed the cloud point, the aqueous solutions become turbid and undesirable phase separation commences to occur. In comparative tests of 1 percent aqueous solutions of the example 1 product and the commercial nonionic, the capped ethoxylate exhibited a cloud point of 102° F., and the commercial product has a cloud point of 85° F.
The capped ethoxylate product of example 1 and the comparative commercial nonionic were evaluated for caustic stability. This test consisted of preparing a mixture of 9 grams of the nonionic, 1 gram water and 90 grams flake caustic and observing the time required for noticeable color development. At the end of one week the capped ethoxylate as well as the commercial nonionic remained water white. In the same test, an ethoxylated alcohol (uncapped) derived from a mixture of decanol, dodecanol, and tetradecanol, and containing 6 moles of ethylene oxide, turned dark brown in 1 hour.
A number of cloud point tests of various capped ethoxylates were conducted to determine the effect of the number of various functional groups in the molecule upon water solubility. The results of these tests, using a 1 weight percent solution, are set forth in table III. --------------------------------------------------------------------------- TABLE III
Constitution of Compound Alcohol Moles EO1 Moles Epch2 Cloud Point, °F. __________________________________________________________________________ C10 9.60 1.0 85 C10 9.60 1.2 74.5 C10 -C12 3 4.97 1.0 75 C10 -C12 8.75 1.0 79 C10 -C12 10.4 1.0 102 C12 -C14 4 9.05 1.0 78
Although certain preferred embodiments of the invention have been herein described and illustrated by example, various departures from the specific uses mentioned and compound structures described may be effected without a consequent departure from the basic principles of the invention. Changes and innovations of this type are therefore deemed to be within the spirit and scope of the invention except as they may necessarily be excluded therefrom by the appended claims or reasonable equivalents thereof.