Cleaning through perhydrolysis conducted in dense fluid medium

Abstract: The invention provides a cleaning agent and method for removing stains from fabrics comprising a combination of dense gas, a source of hydrogen peroxide and an organic bleach activator therefor.

Description: 1. Field of the Invention The invention provides a method and composition for cleaning, e.g., the removal of stains from fabrics, by using a combination of a dense gas, such as densified carbon dioxide, a source of hydrogen peroxide and an organic bleach activator therefor, the combination providing a source of organic peracid. 2. Brief Statement on Related Art There has been limited recognition in the use of carbon dioxide for cleaning. Carbon dioxide has been used as a standard propellant in the delivery of foaming cleaning products, e.g., Harris, U.S. Pat. No. 4,219,333. Maffei, U.S. Pat. No. 4,012,194, described a dry cleaning system in which chilled liquid carbon dioxide is used to extract soils adhered to garments. The liquid carbon dioxide is converted to gaseous carbon dioxide, the soils removed in an evaporator and the gaseous carbon dioxide is then recycled. Maffei, however, does not teach, disclose or suggest the use of additional cleaning adjuncts in connection with his chilled liquid carbon dioxide dry cleaning system. More recently, the use of supercritical fluids, e.g., carbon dioxide whose temperature has been elevated to past a so-called critical point, has been studied for the purposes of solvent extraction, as in, e.gs., Kirk-Othmer, Encycl. of Chem. Tech., 3d Ed., Vol. 24 (Supplement), pp. 872-893 (1983) and Brogle, "CO₂ in Solvent Extraction," Chem. and Ind. , pp. 385-390 (1982). This technology is of high interest because of the need for little or no organic solvents in such extraction processes, which is very desirable from an environmental standpoint. In DE-A-3,904,514, there is described a process for the cleaning and washing of clothes and domestic textiles etc., in which there is as cleaning or washing medium a supercritical fluid, for example carbon dioxide, carbon monoxide or inert gases. Polar substances may be added to the supercritical media as washing or cleaning improvers. Examples of such improvers are detergents. In EP-A-0,396,287 there is described a bleaching product for use in an aqueous wash solution comprising a peracid precursor and a source of hydrogen peroxide together with means for generating acid after substantial production of the peracid. However, none of the prior art discloses, teaches or suggests the combination of dense gas, a source of hydrogen peroxide and an organic bleach activator therefor as a cleaning agent. Nor does the art teach, disclose or suggest the use of such combination of densified carbon dioxide, a source of hydrogen peroxide and an organic bleach activator therefor in a dry cleaning process, the novel combination providing an environmentaly safe alternative to the use of ordinary dry cleaning materials such as Stoddard solvent or perchloroethylene ("perc"). SUMMARY OF THE INVENTION AND OBJECTS The invention provides, in one embodiment, a method for cleaning comprising: contacting said stains with a dense gas, a source of hydrogen peroxide and an organic bleach activator therefor. In a further embodiment is provided a cleaning agent for cleaning comprising a mixture of dense gas, a source of hydrogen peroxide and an organic bleach activator therefor. It is therefore an object of this invention to provide a novel cleaning agent which uses a combination of a dense gas, a source of hydrogen peroxide and an organic bleach activator therefor. It is another object of this invention to provide a method for the dry cleaning of fabrics while avoiding significant use of such solvents as perchloroethylene and Stoddard solvent, or similar hydrocarbon solvents. It is yet another object of this invention to clean stained fabrics with a combined densified carbon dioxide/perhydrolysis system which has better performance than dense carbon dioxide alone. It is a still further object of this invention to clean any surface, or any substance, by using a combination of dense gas a perhydrolysis system containing an organic activator and a source of hydrogen peroxide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention provides a cleaning agent and method for removing stains from fabrics comprising a combination of dense gas, a source of hydrogen peroxide and an organic bleach activator therefor. As noted above, a particularly preferred application of the invention is in the use of the cleaning admixture for the nonagueous cleaning of stained fabrics commonly known as dry cleaning. Dry cleaning is conducted primarily by small businesses, many of which have been in operation for many years prior to the onset of stringent environmental legislation regarding the use and disposal of organic solvents, e.g., perc and Stoddard solvent. Because of the ever-growing concern that ground waters may become contaminated by the widescale use of such solvents and because of the health risks of the solvents acting as possible carcinogens, much of this new legislation has been promulgated to regulate such use and disposal. Consequently, there is a great need for alternate ways of cleaning fabrics avoiding the use of such solvents, while obtaining effective cleaning for garments and other fabrics for which aqueous washing is contraindicated. In the present invention, it has been found that using dense gases to essentially deliver a peracid from a perhydrolysis system has unique benefits. For example, a generated peracid is generally a stronger oxidant than such common oxidant bleaches as sodium perborate, or other peroxides. Moreover, the generated peracid can effectively remove diverse stains at relatively low concentrations of peracid. And, in the case of surface active peracids, such generated peracids will actually be fabric substantive, leading to better soil removal. Next, because the organic bleach activator can be embedded in the fabric to be cleaned, pretreatment of the stained fabric can be achieved, allowing "targetting" of stains. Also, because the organic bleach activator is much more stable than its equivalent peracid, the release of the generated peracid is controllable and can be delayed or "metered" as desired. Finally, as indicated hereinbefore, organic peracids are unstable, volatile compounds and keeping them in storage is very problematic. By using the predecessor organic bleach activator, typically, a very stable ester, storage and stability are very advantageous versus the generated peracid. Thus, when the peracid is actually generated, one can have the peracid available at "full strength." In the present invention, numerous definitions are utilized: "Densified carbon dioxide" means carbon dioxide, normally a gas, placed under pressures generally exceeding preferably 5,516 kPa (800 psi)at standard temperature (21°C). "Organic Bleach Activator" and "Peracid Precursor" are considered synonymous terms and describe organic compounds, typically carbonyl compounds, such as, without limitation, esters, nitriles, imides, oximes, carboxylic acids, acid anhydrides, and the like, which, in the presence of a source of hydrogen peroxide, typically, in an aqueous medium, react to form a corresponding organic peracid. Additionally, as described hereinbelow, these terms encompass the phenomenon of enzymatic perhydrolysis in which a normally poor activator, e.g., a triglyceride, can be catalyzed by the use of an esterase (e.gs., lipase or protease) in the presence of hydrogen peroxide to generate peracid. Since the peracid is generated in the presence of an enzyme, this type of perhydrolysis is referred to as enzymatic perhydrolysis. "Supercritical" phase means when a substance, such as carbon dioxide, exceeds a critical temperature (e.g., 31°C), at which point the material cannot be condensed into the liquid phase despite the addition of further pressure. Co-pending European Patent Application No. 92305338.3 corresponding to EP-A-518653 concerns itself with subject-matter similar to that of the present invention. 1. Dense Gas The term dense gas applies to gases which are subjected to greater than usual (atmospheric) pressure or lower than usual temperature (room temperature, 21.1C°) to enhance its density. A preferred gas for densification is carbon dioxide. Carbon dioxide (CO₂) is a colorless gas which can be recovered from coal gasification, synthetic ammonia and hydrogen generation, fermentation and other industrial processes. ( Kirk-Othmer , Encycl. Chem. Tech. , 3rd Ed., Vol. 4, pp. 725-742 (1978). In the invention, densified carbon dioxide is used as a cleaning agent for removing soils and stains from fabrics, in conjunction with the perhydrolysis mixture. Densified carbon dioxide is carbon dioxide which has been placed under greater than atmospheric pressure or low temperature to enhance its density. In contrast to carbon dioxide used in pressurized cannisters to deliver foamed products, e.g., fire extinguishers or shaving creams, densified carbon dioxide is preferably at much greater pressures, e.g., 5,516 kPa (800 p.s.i.) and greater. It has been found that density, rather than temperature or pressure alone, has much greater significance for enhancing the solvent-like properties of carbon dioxide. See , H. Brogle, "CO₂ as a Solvent: its Properties and Applications, " Chem. and Ind. , pp. 385-390 (1982). Types of dense gases which would be of utility herein includes densified carbon dioxide, supercritical carbon dioxide and liquid carbon dioxide. The concept of dense carbon dioxide encompasses these others types of carbon dioxides. Other supercritical fluids appear suitable for use as dense gases, and include liquids capable of gassification, e.gs., ammonia, lower alkanes (C₁₋₅) and the like. The amount, or volume, of densified carbon dioxide or other supercritical fluid would depend on the type of substrate, temperature and pressure involved, as well as the volume of the container for such densified gas. Generally, an amount which is effective to remove the stain is used. Thus, for the purposes of this invention, cleaning-effective amounts are used. 2. Perhydrolysis System By itself, densified carbon dioxide has relatively poor soil removal performance. Surprisingly, applicants have discovered that the addition of a source of hydrogen peroxide and an organic bleach activator therefor can unexpectedly improve the removal of soils. This is surprising considering that dense gas by itself may not necessarily be very effective at removing such soils from fabrics. The perhydrolysis system comprises two essential components: a source of hydrogen peroxide and an organic bleach activator therefor. The source of hydrogen peroxide is hydrogen peroxide, or may be an aqueous solution in which is placed a soluble hydrogen peroxide source selected from the alkali metal salts of percarbonate, perborate, persilicate and hydrogen peroxide adducts. Most preferred is hydrogen peroxide, which typically is available as a 35% solution. Of the inorganic peroxides, most preferred are sodium percarbonate, and sodium perborate mono- and tetrahydrate. Other peroxygen sources may be possible, such as alkaline earth and alkali metal peroxides, monopersulfates and monoperphosphates. The range of peroxide to activators is preferably determined as a molar ratio of peroxide to activator. Thus, the range of peroxide to each activator is a molar ratio of from 100:1 to 1:100, more preferably 25:1 to 1:25 and most preferably 1:1 to 10:1. This is also the definition of a bleach effective amount of the hydrogen peroxide source. It is preferred that this activator peroxide composition provide 0.005 to 100 ppm peracid A.O., more preferably 0.01 to 50 ppm peracid A.O., and most preferably 0.01 to 20 ppm peracid A.O., in aqueous media. A description of, and explanation of, A.O. measurement is found in the article of Sheldon N. Lewis, "Peracid and Peroxide Oxidations," In: Oxidation , 1969, pp. 213-258. Determination of the peracid can be ascertained by the analytical techniques taught in Organic Peracids , (Ed. by D. Swern), Vol. 1, pp. 501 et seq. (Ch.7) (1970). The organic bleach activator is typically a carbonyl-containing compound. These activators react with the source of hydrogen peroxide to provide a corresponding peracid. Among the carbonyl compounds are, without limitation, esters, nitriles, imides, oximes, carboxylic acids, acid anhydrides, and the like, which, in the presence of a source of hydrogen peroxide react to form a corresponding organic peracid. Esters are preferred activators. One group of such activators is phenol esters. The substituted phenol esters are described in great detail in Bolkan et al., U.S. Patent 5,002,691, Chung et al., U.S. Patent 4,412,934, Thompson et al., U.S. Patent 4,483,778, Hardy et al., U.S. Patent 4,681,952, Fong et al., U.S. Patents 4,778,618 and U.S. 4,959,187, Rowland et al., published EP 390,393. Other examples of phenol esters are those described in U.S. Patents 4,778,618 and 4,959,187 and EP 390,393, which refer to substituted phenyl esters known as alkanoyloxyglycoylbenzene (also known as alkanoyloxyacetyloxybenzene), further abbreviated as "AOGB," and alkanoyloxyglycoylphenyl sulfonate (also known as alkanoyloxyacetyloxyphenyl sulfonate), further abbreviated as "AOGPS." The first compound, AOGB, has the structure: wherein n₁ is preferably 0-20. The second compound, AOGPS, has the structure: wherein n₁ is preferably 0-20, and M is H, alkali metal or ammonium cation. AOGB/AOGPS preferably have an alkyl group with a carbon chain length of C₁₋₂₀, more preferably C₄₋₁₂. The latter chain lengths are known to result in surface active peracids, which apparently perform better at the fabric surface than more soluble peracids, such as peracetic acid. Particularly preferred AOGB/AOGPS compounds include hexanoyloxyglycoylbenzene, heptanoyloxyglycoylbenzene, octanoyloxyglycoylbenzene, nonanoyloxyglycoylbenzene, decanoyloxyglycoylbenzene, undecanoyloxyglycoylbenzene, and mixtures thereof; and hexanoyloxyglycoylphenyl sulfonate, heptanoyloxyglycoylphenyl sulfonate, octanoyloxyglycoylphenyl sulfonate, nonanoyloxyglycoylphenyl sulfonate, decanoyloxyglycoylphenyl sulfonate, undecanoyloxyglycoylphenyl sulfonate, and mixtures thereof. Other, non-surface active homologs, such as phenoyloxyglycoylbenzene and compounds depicted in Zielske et al, U.S. Patents 4,956,117 and 4,859,800, and Zielske, U.S. Patent 4,957,647, may also be useful herein. It was surprisingly found that AOGB and AOGPS have proficient soil removal performance on fabrics. It has been found that the AOGB type esters are more easily soluble in dense carbon dioxide gas. Because of such observed phenomenon, it is expected that these types of esters may work more proficiently in a bulk medium, i.e., with a large amount of fabric (e.g., soiled clothing) in a large volume of carbon dioxide dense gas. The AOGPS type activator, being less soluble in CO₂ dense gas, is expected to work more proficiently when applied directly to the stain/soil. Where either type activators are used, then their solubility characteristics may be modified or manipulated by the use of emulsifiers, such as surfactants, hydrotropes, or other suitable, dispersing aids. See also, Kirk-Othmer, Encyclopedia of Chemical Technology , Third Edition, Vol. 22, pages 347-387, and McCutcheon's Detergents and Emulsifiers , North American Edition, 1983. Further adjuncts may be useful herein. For example, buffers could be used to adjust the pH of the perhydrolysis environment. It is, for example, known that modifying pH conditions can improve perhydrolysis or performance of the formed peracids. See., EP-A-396,287, referred to above. Other compounds of interest herein are alkanoyloxybenzene, sometimes referred to as "AOB." This compound has the structure: wherein n₂ is preferably 0-20. Still more compounds of interest are alkanoyloxybenzene sulfonate, sometimes referred to as "AOBS," with the structure shown below. wherein n₂ is preferably 0-20, and M is H, alkali metal or ammonium cation. Yet other, useful activators are expected to include simple alkyl esters, such as, without limitation, methyl acetate, methyl propionate, methyl butyrate, methyl pentanoate, methyl hexanoate, methyl heptanoate, methyl octanoate, methyl nonanoate, methyl decanoate, methyl undecanoate and methyl dodecanoate, and other alkyl esters such as, without limitation, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, phenyl, acetate and other ester nuclei. These types of esters are not ordinarily expected to provide good perhydrolysis in the absence of a catalyst, e.g., a lipase, or the like. See, Weyn, U.S. 3,974,082, Additionally, other organic activators useful in the practice of this invention include the products of enzymatic perhydrolysis. In enzymatic perhydrolysis, an esterolytic enzyme, e.g., esterase, lipase (see U.S. 5,030,240 and E.P. 253,487,) or a protease (see EP-A-359,087), is combined with a source of hydrogen peroxide and a substrate, therefor, which, in combination with the enzyme and hydrogen peroxide, will produce peracid. The substrate is a chemical which, in combination with the hydrogen peroxide and the selected enzyme generates at least a significant amount of peracid of greater than about 0.5 ppm A.O. The enzymatically generated peracid is distinct from chemical perhydrolysis, which is the reaction of a bleach activator (typically, an ester) with hydrogen peroxide to produce peracid. Generally, the substrate and the hydrogen peroxide will not produce any discernible peracid in the absence of the enzyme. Exemplary substrates include: (a) when the enzyme is a lipase or esterase: (i) glycerides having the structure wherein R₁=C₁₋₁₂, and R₂, or H; (ii) an ethylene glycol derivative or ethoxylated ester having the structure wherein n=1-10 and R₁ is defined as above; and (iii) a propylene glycol derivative or propoxylated ester having the structure wherein n and R₁ are defined as above. Within the preferred structures referred to immediately above, R₁ is more preferably C₆₋₁₀ and most preferably C₈₋₁₀, R₂ and R₃ have more preferably a C₆₋₁₀ alkyl group and most preferably a C₈₋₁₀ alkyl group, or H. The use of glycerides, especially diglycerides and triglycerides, is particularly preferred when the esterolytic enzyme is lipase or esterase, since diglycerides and triglycerides have more than one acyl group which can yield peracid when combined with the selected enzyme in the presence of hydrogen peroxide. Thus, glyceride may be particularly effective in achieving very efficient perhydrolysis in the presence of the lipase/esterase and a source of hydrogen peroxide. The glyceride substrate is characterized by carboxylic acid moieties having from about one to eighteen carbon atoms. Mixtures of varying chain length glycerides are also preferred. Exemplary triglyceride substrates are triacetin, trioctanoin, trinonanoin, tridecanoin, and tristearin. As discussed previously, where the solubility characteristics of perhydrolysis system are desired to be modified or manipulated, then emulsifiers, such as surfactants, hydrotropes, or other suitable, dispersing aids, can be used. See again, Kirk-Othmer, Encyclopedia of Chemical Technology , Third Edition, Vol. 22, pages 347-387, and McCutcheon's Detergents and Emulsifiers , North American Edition, 1983. Other exemplary substrates include: (b) when the enzyme is a protease: wherein R' = C₁₋₁₀ alkyl; Z = O, (CH₂CH₂O) m -, NH, SO₂, or NR'' (wherein m = 0-10 and R'' = phenyl or C₁₋₄ alkyl); n = 2-10; X = OH, -OR'' or -NR''₂; and X may be pendent on or terminate the hydrocarbyl chain. Exemplary substrates here include C₁₋₁₀ alkyl esters, e.gs, methyl octanoate, methyl acetate; substituted esters, e.gs., methylmethoxyacetate, (2-hexyloxyethoxy) acetic acid, (2-hydroxypropyl) ester, 2-hydroxypropyloctanoate. Thus, the perhydrolysis system can be broadly defined herein as either (a) an organic compound, such as an ester, which reacts with hydrogen peroxide to form a corresponding peracid; or (b) a substrate for an esterolytic enzyme, which, in the presence of the designated enzyme and hydrogen peroxide produces peracid enzymatically. In the practice of the best mode of this invention, reference is conveniently made to the drawing, Fig. 1, which is a schematic depiction of the dry cleaning process and equipment suited thereto. In Fig. 1 is generally depicted the dry cleaning operation 2. A pressurized gas cylinder 8 contains densified CO₂, whose outflow can be regulated by in-line valve 4A. The gas cylinder is connected by means of tubing to pump 10, e.g, an electrically driven LDC pump, which pressurizes the CO₂ along with regulator 12. A further valve 4B passes densified CO₂ to be read by pressure gauge 14. The densified CO₂ is fed into autoclave 18, in which the soiled fabrics are placed. The temperature of the densified CO₂ is controlled by a heat exchange coil 16 located in autoclave 18. The temperature is measured by a digital thermometer 20 connected to a thermocouple (not shown). The densified CO₂ and soil is then passed through valve 4C which is in line with heated control valve 6, which controls the extraction rate. Further downstream, an expansion vessel 22 collects the extracted soils, while flow gauge 24 measures the rate of extraction. The gas meter 26 measures the volume of CO₂ used. Using the operation outlined above, extractions of soils were undertaken using a preferred embodiment of the invention, in which the stained fabric was contacted with AOGB or AOGPS and hydrogen peroxide with dense CO₂ in a reaction chamber. EXPERIMENTAL In order to ascertain whether perhydrolysis (and therefore, bleaching) was actually being achieved, two separate organic bleach activator compounds representative of AOGB and AOGPS were contacted on wool swatches. (Wool is a frequently dry-cleaned fabric since aqueous washing and drying often leads to shrinkage of such fabrics.) The respective compounds were nonanoyloxyglycoylbenzene ("NOGB") and nonanoyloxyglycoylphenyl sulfonate ("NOGPS"). The swatches were previously stained with spaghetti sauce, coffee, grass and clay, to provide a series of "diagnostic" stains. Effectiveness of the invention could therefore be assayed by comparing performance against this broad spectrum of cleaning challenges. A 300 ml chamber was used. The swatches were placed in two separate batches or runs for each treatment in order to obtain reproduceable results. The chambers were then filled with dense carbon dioxide to 17,237 kPa (2,500 psi) at 20°C and the reaction allowed to take place for 1 hour. In the TABLE below, comparisons were made among CO₂ alone, CO₂ and H₂O₂, and CO₂/H₂O₂/activator. In the data, stain removal is indicated as %stain removal versus untreated, stained swatches. Treatment Stain Spaghetti Sauce Coffee Grass Clay CO₂ 37 4 6 9 CO₂/H₂O₂ 47 8 7 34 CO₂/H₂O₂/NOGB 64 14 -- -- CO₂/H₂O₂/NOGPS 59 42 37 58 The foregoing results demonstrate the unexpected benefits of the inventive cleaning composition and method over the use of dense CO₂ used singly or in combination with H₂O₂.

Claims: A cleaning composition comprising a combination of dense gas, a source of hydrogen peroxide and an organic bleach activator therefor. A composition as claimed in claim 1 characterized in that said dense gas is selected from the group consisting of densified carbon dioxide, supercritical carbon dioxide, liquid carbon dioxide and liquids capable of gassification. A composition as claimed in claim 1 or claim 2 characterized in that said source of hydrogen peroxide is selected from hydrogen peroxide or an inorganic peroxide. A composition as claimed in any of claims 1-3 characterized in that the organic bleach activator is a carbonyl compound. A composition as claimed in claim 4 characterized in that the carbonyl compound is an ester, in particular a substituted phenol ester. A composition as claimed in claim 5 characterized in that the substituted phenol ester is an alkanoyloxybenzene, preferably an alkanoyloxyglycoylbenzene, particularly of the structure: wherein n₁ is 0 to 20. A composition as claimed in claim 5 characterized in that the substituted phenol ester is an alkanoyloxyglycoylphenylsulfonate preferably of the formula: wherein n₁ is 0-20, and M is H, alkali metal or ammonium cation. A composition as claimed in any of claims 2-7 characterized in that the said densified carbon dioxide has a pressure, at room temperature, of greater than 5,516 kPa (800 psi). A composition as claimed in any of claims 1 to 8 further comprising a dispersant/emulsifier selected from the group consisting of surfactants, hydrotropes and mixtures thereof. A composition as claimed in any of claims 1 to 9 further comprising a buffer for pH modification or maintenance. A method for the removal of stains comprising: contacting said stains with the combination of a fluid medium which is either densified carbon dioxide or supercritical fluid; a source of hydrogen peroxide and an organic bleach activator therefor. A method as claimed in any of claims 1 to 11 further comprising the step of removing said combination and said stains. A method as claimed in claim 11 or claim 12 characterized in that densified carbon dioxide is used as the fluid medium. A method as claimed in claim 13 wherein said densified carbon dioxide is selected from supercritical carbon dioxide and liquid carbon dioxide and preferably has a pressure at room temperature, of greater than 5,516 kPa (800 psi). A method as claimed in any of claims 11 to 14 characterized in that the source of hydrogen peroxide is selected from hydrogen peroxide or an inorganic peroxide placed in aqueous solution. A method as claimed in any of claims 11 to 15 characterized in that the organic bleach activator is a carbonyl compound, preferably an ester, in particular a substituted phenol ester. A method as claimed in claim 16 characterized in that the ester is an alkanoyloxyglycoylbenzene or an alkanoyloxyglycoylphenyl sulfonate.

Inventors: ALVAREZ VINCE, CARTY DANIEL T, LATHAM JAMES R, MITCHELL JAMES D, ALVAREZ, VINCE, CARTY, DANIEL T., LATHAM, JAMES R., MITCHELL, JAMES D.
Applicants: CLOROX CO, THE CLOROX COMPANY
Application year: 1992
Main classification: D06L1
IPC codes: C11D7, C11D11, D06L3, C11D3