Polyaspartic Acid and Its Salts for Dispersing

Europaisches Patentamt (19) European Patent Office Office europeenpeen des brevets EP 0 688 347 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) intci.6: C08L 77/04, C08K5/17, of the grant of the patent: B01F 17/28, C08G 69/10, 24.11.1999 Bulletin 1999/47 C08G 73/06, B01F 17/00, C02F5/12 (21) Application number: 94909749.7 C11D3/37, (22) Date of filing: 15.02.1994 (86) International application number: PCT/US94/01886 (87) International publication number: WO 94/19409 (01.09.1994 Gazette 1994/20) (54) POLYASPARTIC ACID AND ITS SALTS FOR DISPERSING SUSPENDED SOLIDS VERWENDUNG VON POLYASPARAGINSAURE UND DEREN SALZEN ZUR DISPERSION VON SUSPENDIERTEN FESTSTOFFEN ACIDE POLYASPARTIQUE ET SES SELS UTILISES POUR DISPERSER DES SOLIDES EN SUSPENSION (84) Designated Contracting States: • LOW, Kim C. DE FR GB IT NL La Grange, Illinois 60525 (US) (30) Priority: 16.02.1993 US 18008 (74) Representative: Eddowes, Simon et al Hepworth Lawrence Bryer & Bizley, (43) Date of publication of application: Merlin House, 27.12.1995 Bulletin 1995/52 Falconry Court, Bakers Lane (73) Proprietor: DONLAR CORPORATION Epping, Essex CM16 5DQ (GB) Bedford Park, IL 60501 (US) (56) References cited: (72) Inventors: EP-A- 0 686 657 WO-A-92/16463 • KOSKAN, Larry, P. US-A- 3 846 380 US-A- 4 640 943 Orland Park, IL 60462 (US) DO Is- ^- CO 00 00 CO Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU Printed by Jouve, 75001 PARIS (FR) EP 0 688 347 B1 Description Technical Field 5 [0001] This invention relates to certain water-soluble polyaspartic acid salts and their use as dispersants. Background of the Invention [0002] The inhibition and dispersion of a broad variety of mineral and metal oxide scales and particulates in water 10 is a common technology used in many different industries. For example, it is used widely in water treatment to prevent scale form forming on heat transfer surfaces and in pipes, in laundry and cleaning products to prevent suspended particles such as dirt from re-adhering to cleaned surfaces, in toothpastes and mouth washes as an anti-tartar agent, in paints and coatings to suspend pigments for ease of shipping, mixing and uniform application, and in polymer systems where emulsion droplets need to be suspended, to name a few. 75 [0003] Examples of the different types of scale and particulates dispersed include CaC03, CaS04, BaS04, Fe203, clays such as kaolin, Ti02, Zn(OH)2, Ca3(PO)4, Mg(OH)2, Mn203, and many others. [0004] Most dispersants used today are of the synthetic variety, usually a water soluble polymer made from acrylic acid, acrylamide, their derivatives, maleic acid, vinyl esters, and the like. These polymers are non-biodegradable and potentially toxic to the Environment, a-polyaspartic acid also has been suggested as a dispersant; however, its use for 20 this purpose has not met with widespread acceptance by the industry. Starch and lignin based dispersants, although biodegradable, tend to be poorer performers compared to their polyacr- ylate counterparts. [0005] There are a variety of methods for producing polyaspartic acid, several of which may be found in U.S. Patent No. 4,534,881 to Sikes et al. The Sikes et al patent teaches the use of certain polyaspartic acids for use in calcium 25 carbonate scale inhibition. Additionally, "Inhibition of Calcium Carbonate and Phosphate Crystallization by Peptides Enriched in Aspartic Acid and Phosphoserine", by Sikes et al, ACS Symposium Series 444 (1991), teaches that it is known to use certain polyaspartic acids to inhibit calcium phosphate crystallization. Summary of the Invention 30 [0006] Water soluble salts of p-polyaspartic acid are excellent agents for suspending in water a variety of inorganic and organic particles. Due to biodegradability of p-polyaspartic acid, its salts are acceptable for use in a variety of industrial products and processes. 35 Brief Description of the Drawings [0007] In the drawings, Figure 1 depicts temperature versus time reaction curves for thermal condensation of L- aspartic acid; the interrupted line indicates the oil temperature in the reactor and the continuous line the reaction mixture temperature; and 40 FIGURES 2-4 depict other temperature versus time reaction curves for thermal condensation of L-aspartic acid; again the interrupted line indicates the oil temperature in the reactor and the continuous line indicates the reaction mixture temperature. Description of Preferred Embodiments 45 [0008] The starting polysuccinimides (anhydropolyaspartic acids) from which the a-polyaspartic acids are synthe- sized are produced by the thermal condensation of powdered L-aspartic acid at controlled temperatures to produce polysuccinimide in high yields. The term "yield" as used herein means the theoretical yield based on the starting mo- lecular weight of the aspartic acid. The presently attainable relatively high yields optimally occur above the initiation so temperature of 187.8°C (370°C), preferably occur above about 215.6°C (420°F), and most preferably occur above about 226.7°C (440°F). [0009] While a reactant temperature of less than 187.8°C (370°F) may produce polysuccinimide over a period of many hours, the theoretical yields will be low. Usually, the conversion of the L-aspartic acid to polysuccinimide will be less than 70% and will require a reaction time period of many days. On the other hand, we have found that as the 55 reactant temperature is increased in a controlled manner to above 187.8°C (370°F), the percent conversion increases to greater than 90% and the reaction times become greatly reduced. [0010] The thermal condensation of L-aspartic acid to polysuccinimide using the above reaction conditions produces a characteristically shaped "temperature vs. time" reaction curve characterized by an initial, rapid rise in reactant tem- 2 EP 0 688 347 B1 perature which is followed by an endotherm signalling the beginning of the reaction. Immediately following the onset of the endotherm there is evaporative cooling, followed first by a temperature rise, and then by a second endotherm, which is followed by an evaporative cooling plateau. The temperature then rises to a substantially constant temperature plateau. The condensation reaction has gone to at least 95% conversion at a temperature approximately midway 5 between the final plateau and the time the temperature begins to rise to that plateau. [0011] In the following examples, the color of each product sample was noted. [0012] The color of L-aspartic acid is white. Polysuccinimides vary in color according to the temperature of the sample taken during the course of the reaction. From low temperature to high, the colors vary as follows: light pink, to pink, to tannish pink, to tan, to light yellow, to yellow. These colors generally correspond to the percent conversion of the L- 10 aspartic acid, in the same order with light pink indicating the lowest percent conversion and yellow indicating the highest percent conversion. Products exhibiting the pink colors were found to have less than 70% conversion. Heretofore, the technical literature has never reported any other color but pink for thermally condensed L-aspartic acid. The polysuccinimides suitable for making the present dispersants for the practice of the method aspect of this invention are free of pure pink color. The polysuccinimides used to prepare the polyaspartic acid dispersants of this invention have a is water content less than 1%. Usually such polysuccinimides are substantially water-free. [0013] A series of experiments were conducted to thermally polymerize solid phase L-aspartic acid. In each instance, the powdered L-aspartic acid was added to an oil-jacketed reaction vessel and heated. Samples were taken throughout the polymerization reaction. Those samples were analyzed for percent conversion to the polysuccinimide. The color and temperature of the samples were noted as well. 20 [0014] Each of conversion, color, and production of polyaspartic acid are described below. [0015] The conversion of L-aspartic acid to polysuccinimide was determined as follows: A specific amount of the reaction mixture or product was dissolved in an aliquot of dimethylformamide (DMF). The dissolution was allowed to proceed for 4 to 5 hours until all of the polysuccinimide dissolved in the DMF Unreacted L-aspartic acid was filtered out. Conversion of L-aspartic acid was determined using the following formula: 25 % CONVERSION ^r6- * 100% = A Where: 30 A = weight of initial sample B = weight of residue (unreacted L-aspartic acid) [0016] The percent conversion of the L-aspartic acid to the polysuccinimide in the reaction can be increased in 35 reduced time periods by increasing the temperatures used in a manner discussed in greater detail hereinbelow. [0017] Where a thermal fluid is used to heat the L-aspartic acid and as its temperature is brought to a maintenance temperature of at least 248. 9°C (480°F) in a reasonable time period, at least 90% conversion can be effected within 4 hours. [0018] Where the thermal fluid used to heat the L-aspartic acid is brought to a maintenance temperature of at least 40 287. 8°C (550°F) within a reasonable time period, at least 90% conversion can be effected within 2 hours. [0019] Continuous and batch processes can be used. Some process examples include fluidized bed, stirred reactor, and indirectly heated rotary driers. [0020] Once initiation temperature is achieved, temperatures in the range of 215.6-271 .1°C (420-520°F) produce polysuccinimide at yields greater than 80%.

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