There is currently interest in the detergent industry in concentrated detergent products. These products provide advantages to the consumer, who has a product which can be used in lower amounts and is more easily stored, and to the producer and intermediates, who have lower transportation and warehousing costs. A major difficulty, though, is finding an inexpensive and efficient way to produce a high active detergent particle for inclusion in a concentrated detergent product. By "high active" is meant greater than about 50% active by weight of the detergent particles is anionic surfactant.
The traditional method for producing detergent granules is spray drying. Typically, detergent ingredients such as surfactant, builder, silicate and carbonate are mixed in a mix tank to form a slurry which is about 35% to 50% water. This slurry is then atomized in a spray drying tower to reduce moisture to below about 10%. It is possible to compact spray dried particles to make dense detergent granules. See U.S. Pat. No. 4,715,979, Moore et al., issued Dec. 29, 1987. However, the use of spray drying to make condensed granules has some disadvantages. Spray drying is energy intensive and the resulting granules are typically not dense enough to be useful in a concentrated detergent product. Spray drying methods generally involve a limited amount (less than 40%) of organic components such as surfactant for environmental and safety reasons.
One way to reduce the energy required to spray dry detergent granules is to reduce the moisture in the slurry which is atomized in the spray drying tower, i.e., by reducing the evaporative load. An alternative method for making a high active detergent particle is by continuous neutralization in, for example, a continuous neutralization loop. There are continuous neutralization loops available to which relatively concentrated caustic can be added. Using a caustic solution which is about 50% sodium hydroxide allows reduction of moisture in the resulting neutralized surfactant paste to about 16% water.
The following publications describe ways to make free-flowing high active particles without drying, using surfactant paste, and made with a continuous neutralization system: Japanese Patent 61-118500, Hara et al., laid-open June 5, 1986, Japanese Patent 60-072999, Satsusa et al., laid open Apr. 25, 1985, U.S. Pat. No. 4,515,707, Brooks, issued May 7, 1985, U.S. Pat. No. 4,162,994, Kowalchuk, issued July 31, 1979, and European Patent 266847-A.
The use of polyethylene glycol and ethoxylated nonionic surfactants in granular detergent compositions is known in the art: e.g. Japanese Patent 61-231099, Sai et al., laid-open Oct. 15, 1986, Japanese Patent 62-263299, Nagai et al., laid-open Nov. 16, 1987, U.S. Pat. No. 4,639,326, Czempik et al., issued Jan. 27, 1987, and U.S. Pat. No. 3,838,072, Smith et al., patented Sept. 24, 1974.
The following patents describe processes and/or surfactant compositions comprising viscosity modifiers such as polyethylene glycol and ethoxylated (E.sub.20-60) alkyl (C.sub.6-12) phenol: U.S. Pat. No. 4,482,470, Reuter et al., issued Nov. 13, 1984, U.S. Pat. No. 4,495,092, Schmid et al., issued Jan. 22, 1985, U.S. Pat. No. 4,532,076, Schmid et al., issued July 30, 1985, U.S. Pat. No. 4,675,128, Linde et al., issued June 23, 1987, and U.S. Pat. No. 4,772,426, Koch et al., issued Sept. 20, 1987.
It has been found that an improved high active surfactant paste, and therefore better detergent granules, can be made by adding to a continuous neutralization system, along with the acid form of an anionic surfactant and alkali metal hydroxide, an .alpha.-aminodicarboxylic acid selected from the group consisting of glutamic acid, aspartic acid, aminomalonic acid, aminoadipic acid, and 2-amino-2-methylpentanedioic acid, or their alkali salts, particularly monosodium glutamate. Monosodium glutamate (MSG) is popular throughout the world as a flavor enhancer. It is used in many Western packaged foods and in Asian countries alongside salt and pepper. Kirk-Othmer Encyclopedia of Chemical Technology. H. F. Mark et al., John Wiley & Sons, NY (1978), 3rd ed., vol. 4, pp. 410-421. These .alpha.-aminodicarboxylic acids are not to our knowledge known to be useful in detergent-making processes, for preventing discoloration of high-active detergent particles or for improving processability.
The following publications describe detergent compositions containing amino di-acid components such as glutamic acid and its salts.
U.S. Pat. No. 3,872,020, Yamagishi et al, issued Mar. 18, 1975 discloses a detergent composition having good transparency and detergency, which preserves freshness of food and the like, and which comprises a certain sucrose ester component and an organic acid component. The latter is malic acid and/or tartaric acid and/or alkaline salts of either. The composition preferably further includes a saccharide component and/or an amino acid component, typically glutamic acid, alkali salts of glutamine acid, glycine and/or alkali salts of glycine. The amino acid component, e.g. sodium glutamate, is added to impart a freshness preservation ability to food to be washed (Col. 4, lines 10-16).
U.S. Pat. No. 4,046,717, Johnston et al, issued Sept. 6, 1977, discloses a bar soap which is said to be given a skin moisturizing effect by including a water soluble lactate and/or glutamate salt. The glutamate salt and/or lactate are described as additives effective to increase the water content of human skin (Col. 1, lines 17-29).
Japanese Publication 61-108387 discloses a method for stabilizing alkali proteases in detergent compositions by combining amino acid or its salt and, for improved stabilization, calcium salt.
Japanese Publication 60-243199 discloses a two-phase liquid detergent composition containing 10-50 wt. % of at least one anionic and/or nonionic surfactant, and 2-30 wt. % carboxylic acid. The components of the composition are said to separate on standing and can be mixed together.
German Offen. 1,942,236 discloses enzyme-containing detergent compositions containing anionic, zwitterionic, or nonionic surfactants and builders, and for improved protein stain-removing efficiency, 2-15% S-free C.sub.4-11 -amino acid or its water-soluble salt; optionally containing .gtoreq.1 additional CO.sub.2 H or amino group (including glutamic acid).
Copending patent application Ser. No. 516,292, Wise et al, filed May 4, 1990 describes light duty liquid or gel dishwashing detergent compositions containing an alkyl ethoxy carboxylate surfactant. Disodium glutamate is mentioned as a preferred buffer therein.