Patent Publication Number: US-2005115910-A1

Title: Formaldehyde releaser and process for treating aqueous systems

Description:
The present invention relates to stable compositions that release formaldehyde and a process for treating aqueous systems directly with one or more biocides including the formaldehyde releasing composition. More particularly, the invention is directed to a stable urea formaldehyde composition that, when combined with one or more biocides including isothiazolones, slowly releases low levels of formaldehyde.  
      Stabilization of biocides including isothiazolones against thermal degradation and storage degradation often involves combining them with metal salts and formaldehdye. Unfortunately, significant amounts of free formaldehyde and other odorous, volatile organic compounds (VOC) are released as a result. It is therefore desirable to provide a stable concentrated formaldehyde releasing composition that is low odor and compatible with one or more biocides, including isothiazolones, and that releases low levels of free formaldehyde and VOC.  
      U.S. Pat. No. 3,970,625 discloses a method for providing a urea-formaldehyde concentrate for use as urea releasing nitrogenous fertilizers. The concentrate is prepared in two steps by combining a buffered solution of aqueous formaldehyde and formic acid with urea in aqueous ammonia such that the resulting mixture contains a molar ratio of 4.4 to 7.3 moles of formaldehyde for each mole of urea. The pH of the mixture is adjusted to between 8.8 and 9.5, the mixture is heated and water is removed by distillation under reduced pressure to provide the concentrate. However, the urea formaldehyde polymer product is odorous and contains high amounts of free formaldehyde in addition to other VOC.  
      Inventors have discovered a one step process for preparing a stable liquid urea-formaldehyde concentrate that is low cost and is compatible with a wide variety of biocides, including isothiazolones. The concentrate is a clear solution with low odor and a high proportion of bound formaldehyde that provides low levels of free formaldehyde. In addition, the formaldehyde releaser concentrate alone exhibits biocidal activity and in combination with one or more biocides, synergistic biocidal activity is observed. Inventors have also discovered a process for treating aqueous systems with the formaldehyde releaser alone and in combination with one or more biocides, including isothiazolones.  
      Accordingly, the invention provides a formaldehyde releasing composition comprising urea, formaldehyde and paraformaldehyde in a urea:formaldehyde molar ratio of 1:3; wherein the composition is a colorless clear liquid having a density less than 1.3 g/mL, less than 40% by weight of VOC and free formaldehyde level of less than 3% by weight based on the weight of the composition.  
      The invention also provides a biocide composition comprising one or more isothiazolones and a formaldehyde releasing composition comprising urea, formaldehyde and paraformaldehyde in a urea: formaldehyde molar ratio of 1:3, wherein the composition has a density less than 1.3 g/mL, less than 40% by weight of VOC and a free formaldehyde level of less than 3% by weight based on weight of the composition.  
      The invention also provides a process for manufacturing a formaldehyde releasing composition comprising the step of: mixing aqueous formaldehyde, sodium hydroxide, urea and paraformaldehyde, heating the mixture to 90° C. until the solids liquefy, and adjusting the pH from 4 to 5. The process provides a formaldehyde releasing composition that is a colorless clear liquid having a density less than 1.3 g/mL, less than 40% by weight of VOC and a free formaldehyde level of less than 3% by weight based on weight of the composition.  
      The invention also provides a method of treating aqueous systems comprising the step of adding one or more isothiazolones in combination with a formaldehyde releasing composition comprising urea, formaldehyde and paraformaldehyde in a urea:formaldehyde molar ratio of 1:3, wherein the composition has a density less than 1.3 g/mL, less than 40% by weight of VOC and a free formaldehyde level of less than 3% by weight based on weight of the composition.  
      As used herein, the term aqueous system refers to any system including water. The term VOC refers to volatile organic compounds. The term volatile refers to organic compounds having a vapor pressure of 100° C. or less at atmospheric pressure. Many volatile organic compounds can be detected from the odor they emit as a result of their vapor pressure.  
      The formaldehyde releasing (FR) composition comprises a mixture of urea, formaldehyde and paraformaldehyde in a urea:formaldehyde molar ratio of 1:3. Typically, the FR composition is a clear, colorless liquid. The FR composition has a density less than 1.3 g/mL, less than 40% by weight of VOC and a free formaldehyde level of less than 3% by weight, based on the weight of the composition. The FR concentrate is low odour, consistent with having a high proportion of bound formaldehyde present. The FR composition provides effective release of formaldehyde in an aqueous system alone and in combination with one or more biocides, including isothiazolones. In addition, the FR concentrate is effective at controlling the growth of microorganisms alone and in combination with one or more biocides, including isothiazolones.  
      Suitable examples of biocides that are usefully employed in accordance with the present invention include isothiazolones as described in U.S. Pat. Nos. 3,523,121; 3,761,488; 4,954,338; 5,108,500; 5,200,188; 5,292,763; 5,444,078; 5,468,759; 5,591,706; 5,759,786; 5,955,486 and European Pat. Nos. EP 0 302 701; EP 0 490 565; EP 0 431 752; EP 0 608 911; EP 0 608 912; EP 0 608 913; EP 0 611 522 and EP 0 648 414.  
      According to one embodiment of the invention, isothiazolones useful in the invention are 2-methyl-3-isothiazolone, 5-chloro-2-methyl-3-isothiazolone 2-octyl-3-isothiazolone, 4,5-dichloro-2-cyclohexyl-3-isothiazolone, 4,5-dichloro-2-octyl- 3-isothiazolone and combinations thereof  
      Other suitable examples of biocidal active ingredients include benzisothiazolone, dibromonitriloproprionamide (DBNPA), 2-(thiocyanomethylthio)benzthiazole (TCMTB), iodopropargylbutylcarbamate (IPBC) and parabens.  
      It is well known in the art that the performance of microbiocides is frequently enhanced by combining with one or more other microbiocides. In fact, there have been numerous examples of synergistic combinations of biocides. We have found that other known microbiocides are combined advantageously with the formaldehyde releasing composition of the invention to treat aqueous systems.  
      The FR composition is compatible with isothiazolones and acts as a stabilizer for many isothiazolones. When it is desired to package the isothiazolone with the FR (e.g. in can), the amount of FR employed will be from about 1 percent to about 25 percent. The isothiazolone may be present in a bulk form or packaged or encapsulated in some manner, including a form for controlled release. The ratio of FR to isothiazolone is preferably from about 1.5:1 to 1:7.  
      Solvents are optionally used to dissolve the isothiazolones and the solvent includes any organic solvent which dissolves the isothiazolones, are compatible with the proposed end use, do not destabilize the isothiazolone and do not react with the isothiazalone or FR. Suitable solvents include, but are not limited to, hydroxylic solvents such as, for example, polyols, such as ethylene glycol, polyethylene glycols, alcohols, ethers, polyethers and combinations thereof. The solvents are also usefully employed in preparing FR compositions according to a separate embodiment.  
      According to a separate embodiment, small amounts of solvents may be used in admixture to assist in forming a stable microemulsion. Typical examples of solvents include alcohols such as, for example, methanol, ethanol and ethylene glycol, mixtures of water and alcohols, ethers, polyethers and combinations thereof. Hydroxylic solvents, for example, polyols, such as glycols, monoethers of glycols, alcohols, and the like, may be used. A hydroxylic coalescent, such as for example trimethyl-1,3-pentanediol monoisobutyrate also may be used. In certain formulations, hydrocarbons, either aliphatic or aromatic, are useful solvents. Typical solvents also include dipropylene glycol, dipropylene glycol monoethyl ether, xylene, and mineral spirits.  
      In a yet another separate embodiment, small amounts of one or more non-polar, water immiscible solvent selected from the group consisting of benzyl alcohol, benzyl acetate, pine oil, phenethyl alcohol, xylene, phenoxyethanol, butyl phthalate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and alkylbenzene, said solvent being capable of dissolving at least 5% by weight of biocides at room temperature, is used to dissolve the biocidal active ingredient(s) or assist in formation of a stable microemulsion.  
      Because isothiazolone biocides are so active, the low level required to achieve stabilization also makes them ideal in combination with the FR composition when compared to many known biocides because at the low levels required they are not likely to interfere with other components in systems requiring protection or with systems upon which the protected systems will be applied.  
      Microbiocide (including isothiazolones) formaldehyde releaser combinations of the invention are useful in many areas of preservation including disinfectants, sanitizers, cleaners, deodorizers, liquid and powder soaps, hide removers, oil and grease removers, food processing chemicals, dairy chemicals, food preservatives, animal food preservatives, wood preservation, polymer latices, paint, lazures, stains, mildewicides, hospital and medical antiseptics, medical devices, metal working fluids, cooling water, air washers, petroleum production, paper treatment, pulp and paper slurries, paper mill slimicides, petroleum products, adhesives, textiles, pigment slurries, latexes, leather and hide treatment, petroleum fuel, jet fuel, laundry sanitizers, agricultural formulations, inks, mining, non-woven fabrics, petroleum storage, rubber, sugar processing, tobacco, swimming pools, photographic rinses, cosmetics, toiletries, pharmaceuticals, chemical toilets, household laundry products, diesel fuel additives, waxes and polishes, oil field applications, and many other applications where water and organic materials come in contact under conditions which allow the growth of undesired microorganisms. Other active ingredients are useful as fungicides, miticides, herbicides, insecticides, and plant growth regulators.  
      Typical aqueous systems treated by the process of the invention include, for example, recirculating cooling units, open recirculating cooling units that utilize evaporation as a source of cooling, closed loop cooling units, heat exchanger units, reactors, equipment used for storing and handling liquids, boilers and related steam generating units, radiators, flash evaporating units, refrigeration units, reverse osmosis equipment, gas scrubbing units, blast furnaces, paper and pulp processing equipment, sugar evaporating units, steam power plants, geothermal units, nuclear cooling units, water treatment units, food and beverage processing equipment, pool recirculating units, mining circuits, closed loop heating units, machining fluids used in operations such as for example drilling, boring, milling, reaming, drawing, broaching, turning, cutting, sewing, grinding, thread cutting, shaping, spinning and rolling, hydraulic fluids, cooling fluids, oil production units and drilling fluids. 
    
    
      Some embodiments of the invention are described in detail in the following Examples. All ratios, parts and percentages are expressed by weight unless otherwise specified, and all reagents used are of good commercial quality unless otherwise specified.  
     EXAMPLE 1  
     One Pot Preparation of Formaldehyde Releasing Composition  
      To a two liter 4-necked round bottom flask equipped with a mechanical stirrer, condenser, thermometer and pH meter were added 344 g (34.4%) of aqueous formaldehyde solution (37% wt./wt.) The solution was stirred and 8.5 g (0.9%) of 50% by weight aqueous solution of NaOH was added to raise the pH togreater than to 10.5. Urea solids (241.4 g, 29.1%) were added to the basic mixture with stirring, as were 351.3 g (35.1%) of paraformaldehyde resin as beads (90%). The dense mixture of solids and liquids was heated to 90° C. with stirring and this temperature was maintained for 1 hour. The solids liquefied and the reaction went from hazy to clear in appearance. The pH of the reaction was adjusted to from 4 to 5 using a 32% by weight aqueous solution of hydrochloric acid (4.8 g, 0.5%) and the reaction was heated for an additional hour. The solution was cooled to afford a product (FR 2) having the following properties as summarized in Table 1.  
               TABLE 1                          Formaldehyde releasing (FR) compositions.                         Analyses   FR 1   FR 2               Appearance   colourless,   colourless, clear           clear liquid   liquid           (slightly turbid)                                 Density 20° C.   1.2537   g/ml   1.2541   g/ml                         Refraction index n20/D   1.4472   1.4474                                 Viscosity 10° C.   49   mPa · s   45   mPa · s       Viscosity 15° C.   46   mPa · s   37   mPa · s       Viscosity 20° C.   38   mPa · s   29   mPa · s       Viscosity 25° C.   30   mPa · s   21   mPa · s       Viscosity 90° C.   23   mPa · s   14   mPa · s                         Gardner   &lt;1   &lt;1       Cloud point    −10° C.    −6° C.       Flash point open cup   &gt;100° C.   &gt;100° C.       Low volatile matter   38.2%   37.8%       pH, 10% in water deion.   4.96   7.29       pH, direct   5.50   7.81       Formaldehyde, free (acetyl   2.88%   2.61%       acetone meth.)       Formaldehyde, free (hydroxyl   2.66%   2.53%       amine meth.)       Formaldehyde, total   24.3%   26.1%       (iodometr./NaOH)       Formaldehyde, total (acidic dist./   40.7%   40.5%       ac. acetone)                  
 
     EXAMPLE 2  
     Combination of FR with CMI/MI  
      Stability Test for 5 -Chloro- 2-methylisothiazolin-3-one/2-Methylisothiazolin-3-one The 3:1 mixture of 5-chloro-2-methylisothiazohin-3-one (CMI)/2-methylisothiazolin-3-one (MI) is mixed at 14% by weight total active ingredient (AI) with 49 wt. % FR. The retention of AI is measured after four weeks at 40° C. and after one and two weeks at 70° C. HPLC is used to measure AI. This is compared with a 3:1 mixture of 5-chloro-2-methylisothiazolin-3-one, CMI/2-methylisothiazolin-3-one, MI stabilized with magnesium nitrate (15%).