NTA. Properties and I&I Applications NTA TRISODIUM NITRILOTRIACETATE MONOHYDRATE

Transcription

1 NTA Properties and I&I Applications NTA TRISODIUM NITRILOTRIACETATE MONOHYDRATE TABLE OF CONTENTS INTRO 1 CHEMICAL & PHYSICAL PROPERTIES 1 I&I APPLICATIONS 7 STARTER FORMULARY USING NTA 10

2 INTRODUCTION Sodium Nitrilotriacetate Monohydrate, N(CH 2 CO 2 Na) 3 H 2 O (NTA, mwt.275.1), is one of the several commercially available aminopolycarboxylates. Its principal function is the control of polyvalent metal ions in aqueous solutions by sequestration. NTA is also an effective buffering agent. NTA exhibits some deflocculating properties and is stable in both strongly acidic and basic solutions over a wide temperature range. These properties, together with its excellent solubility, are especially useful in liquid applications. One use of NTA is in Industrial and Institutional (I&I) laundry detergents as a builder. NTA softens the wash water by sequestering metal ions. NTA is also used in a number of surface cleaning applications including hard surfaces, metals, and vehicles. In boilers, NTA prevents and removes scale formation. In the textile industry, NTA fulfills a number of unique functions in the scouring, bleaching and dyeing of materials. The primary agricultural function of NTA is a carrier for micronutrient trace metals, e.g. iron and zinc. These and many other established and potential uses are discussed in the following pages. (NOTE: Throughout this bulletin, the abbreviation NTA refers to the stable crystalline, monohydrate trisodium salt form.) CHEMICAL & PHYSICAL PROPERTIES SEQUESTRATION The ability of NTA to sequester metal ions is an essential property for its utilization in a variety of applications. Sequestration is the phenomenon of binding metal ions in soluble complexes, thereby preventing the formation of undesirable precipitates or the occurrence of detrimental side reactions. For example, NTA will combine with the calcium and magnesium ions found in hard water to form soluble but strongly associated complexes which remain in solution in the presence of precipitating anions. In other words, sequestration effectively ties up these metal ions and prevents their reactions with other components in the solution which would yield insoluble compounds as precipitates. In practical applications, the sequestering power of NTA is utilized in cleaning compounds to reduce or minimize the various negative effects of hardness ions. NTA is also useful in the reverse reaction. For example, NTA can re-dissolve hard water mineral deposits such as CaCO 3 in processing equipment or on textiles. The determination of sequestration is dependent upon a variety of experimental conditions such as method of measurement, temperature, solution ph, etc. Consequently, one must use caution in the comparison of data on sequestering agents. The best comparison can be made by the user / formulator under actual application conditions. The two most common methods of reporting data on sequestering are via sequestration values and stability constants. Sequestration Values estimate the capacity of the various sequestration agents. On the other hand, Stability Constants measure the strength with which the metal is held. 1

3 Sequestration Values (Capacity) Sequestration values provide the most practical basis for comparing or selecting sequestration agents. These values are obtained by determining the weight of the metal ion that can be kept in solution per unit weight of sequestering agent. These measurements can be made by nephelometric (precipitation) titrations or by specific ion electrode. These results are method and condition sensitive, and comparisons should only be made within a given set of experiments. Figure 1 illustrates the relative calcium sequestration power of NTA and sodium tripolyphosphate (STP) at 25ºC and 60ºC as a function of solution ph. Note the importance of maintaining solution ph in an optimum range to achieve maximized performance from both NTA and STP. These data also show the higher Calcium sequestration value of NTA relative to STP at optimum ph. Figure 1 also demonstrates that NTA maintains its sequestration power at lower temperatures whereas STP loses some power at lower temperatures. Thus as lower wash temperatures are used to save energy, NTA becomes an even more attractive sequestrant on a cost/performance basis. FIGURE 1 Comparison of Calcium Sequestration (Ability of NTA and STP) g Ca/100 g. Sequestrant ph of Solution STP 60ºC NTA 60ºC STP 25ºC NTA 25ºC 2

4 Table 1 provides a theoretical comparison of the sequestering power of NTA compared to Sodium tripolyphosphate (STP) and tetrasodium ethylenediaminetetraacetate (EDTA). These values were calculated by assuming that aminopolycarboxylate sequestering agents and STP complex with metal ions on a 1:1 molar basis. Since the molecular weight of NTA is less than either STP or EDTA, one part of NTA will sequester considerably more metal ion than either STP or EDTA. TABLE 1 Theoretical Comparison fo the Sequestering Value of NTA, EDTA, and STP* Parts by wt. Chelant/One Part by wt. Metal Metal (Atomic Wt.) NTA EDTA STP Aluminum (26.98) Calcium (40.08) Copper (63.54) Iron (55.85) Lead (207.21) Magnesium (24.32) Manganese (54.94) Zinc (65.38) *Calculations assume 1:1 Mole ratio Parts Chelant Mol. Wt. Chelant = One Part Metal At. Wt. Metal Stability Constants Another common manner of comparing sequestering agents is on the basis of stability constants (pk value). These constants are a measure of the extent to which the sequestration reaction proceeds. The stability constant, therefore, is a quantitative measure of the affinity of a sequestering agent for a specific metal ion. Valuable insight into the choice of a sequestrant for a given application can be obtained by comparing stability constants. For example, a comparison of the magnitude of the stability constants of two ligands gives an indication of how much unsequestered metal ion may remain in one system versus the other. The larger the stability constant, the smaller the amount of free ion is remaining in solution. Stability constants also provide data on which metals will be sequestered from a system containing several metal ions. In this regard, a sequestrant will react with metal ions in order of decreasing pk values. Any metal will displace from the complex a metal below it in the sequence. For example, if the hardness ions (Ca +2 and Mg +2 ) in a system are tied up in an NTA complex, the addition of copper or zinc ion will cause the hardness ions to be displaced back into free or uncomplexed state since both the copper and zinc stability constants are sufficiently higher than calcium or magnesium. Care must be taken when comparing stability constants to be sure the same basis is being used, particularly as to the ionic species taking part in the equilibria. The experimental conditions, such as temperature and ionic strength, must also be taken into account when comparing stability constant data. Table 2 provides a comparison of the stability constants for NTA, STP and EDTA. 3

5 TABLE 2 Stability Constants for NTA, STP and EDTA* Stability Constant, pk Metal Ion NTA STP EDTA Aluminum (III) > Calcium (II) Copper (II) Iron (II) Iron (III) Magnesium (II) Manganese (II) Zinc (II) *in 0.1 N KCI or KNO 3 at 20ºC Except for some specialized applications, the binding strength of NTA and STP is normally adequate to obtain the desired performance result. This is particularly true for virtually all cleaning applications. In other words, the superior binding strength of EDTA is not a factor in the majority of sequestrationrelated applications. NTA offers attractive calcium sequestration properties when compared with a series of common builders. Both in terms of sequestration capacity, expressed as mgcaco 3 /g builder and in terms of binding strengths expressed as pk ca, NTA offers properties which make it attractive in I&I formulations. Table 3 shows values for a series of common builders. In terms of pk, NTA binds calcium (at 25ºC and 0.1 M concentration) more tightly than any other builder except EDTA. The value given for citrate pk ca, represents the lowest value that represents effective sequestration strength. Also, NTA is capable of sequestering more calcium (as CaCO 3 ) than any listed builder other than TSPP. Zeolite A does not have a pk value given since its sequestration properties is by ion exchange rather than by chelation-type binding. TABLE 3 Calcium 25ºC & 0.1 M conc. *Calcium removal by ion exchange. Builder pkca mg. CaCO 3 /g. Builder NTA Sodium Tripolyphosphate (STP) Tetrasodium Pyrophosphate (TSPP) Tetrapotassium Pyrophosphate (TKPP) EDTA Citrate Zeolite A * 225 4

6 BUFFERING Buffering is the ability to maintain ph in a narrow region despite the addition of moderate amounts of acid or base. For example, the sodium salts of weak acids are alkaline materials and will increase both alkalinity and buffering capacity for detergent systems. As the alkalinity is reduced by complex formation as shown in Figure 2, the ability to act as a buffer is decreased. The presence of sodium silicate in the formulation will maintain the alkalinity level and in combination with the builders can accomplish buffering in the ph range. Changes in the ph of most cleaning solutions under practical conditions do not exceed ca. 0.5 ph units. The alkalinity level provided by builders varies from builder to builder and is often hardness dependent as shown in Figure 2. It can be seen that the amount of alkalinity provided by NTA is greater than that from STP and the alkalinity from each builder at 50 ppm hardness is greater than that at 150 ppm hardness. This loss of alkalinity with increasing hardness is due to release of protons from protonated ligands during complex formation. SOLUBILITY The high solubility of NTA makes it a versatile product which can be used in both powder and liquid applications. Ascend supplies NTA either as a powder or as a 40% solution. The actual solubility of NTA is greater than 40% 0ºC, 25ºC; and 50ºC. In addition, a 40% solution of NTA has a freezing point of -22.5ºC (-8.5ºF). FIGURE 2 Effect of Water Hardness on the Buffer Capacities of Sodium Tripolyphosphate and Trisodium Nitrilotriacetate Monohydrate* Solution ph ppm 150 ppm 50 ppm 0 ppm STP NTA Milliliters of 0.02N HCI *Solution Strength, 750 ppm., at 25ºC using Ca +2 / Mg +2 in 3/2 ratio to prepare water hardness. 5

7 DEFLOCCULATION Deflocculation is the process whereby aggregates of solid particles are broken up into individual particles, and the individual particles are dispersed throughout the solution. These particles remain dispersed and suspended due to the interaction which occurs when soil particles unite with a deflocculating agent. NTA exhibits some deflocculating properties. See Figure 3 which compares the deflocculating properties of NTA, STP and sodium sulfate. Deflocculation finds commercial application in detergent solutions where NTA can disperse insoluble soils and prevent their redeposition on the articles being cleaned. The same phenomenon is applicable with drilling muds for oil well operations to control viscosity. STP NTA Na 2 SO 4 FIGURE 3 Clay Deflocculation, 70ºC 200 ppm. CaCO V Hardness 70 % Transmittance DETERGENCY In simple terms, a detergent is any material capable of removing soil from a surface. A key property of NTA is its synergistic effect on cleaning when used in combination with soaps and synthetic surfactants. Soaps and synthetics built with NTA show substantially greater detergency than either compound alone. Both anionic and nonionic surfactants built with NTA exhibit excellent detergency in hard and soft water on all types of fabrics and across a wide range of wash temperatures. The performance of NTA-built detergent products is particularly strong at cooler wash temperatures Increasing Deflocculation Concentration (ppm) CHLORINE STABILITY NTA and chlorine sources (hypochlorites and chlorinated isocyanurates) are not compatible in dry or liquid formulations due to chemical interactions. However, chlorine sources such as sodium hypochlorite can be added to laundry systems containing NTA at normal wash temperatures with minimal loss of chlorine activity during the normal wash cycle. Figure 4 shows the effect of NTA on the level of available chlorine in distilled water solutions at 120ºF (49ºC). The NTA levels noted, ppm, correspond to 5-40% NTA in a formulation used at 0.15% concentration in the wash system. Starting available chlorine level was 220 ppm. FIGURE 4 Retention of Sodium Hypochlorite in Solutions Containing NTA & STP % NaOCl Remaining Normal Wash Cycle 750ppm STP 75ppm NTA 150ppm NTA & 150ppm NTA +600 ppm STP 300ppm NTA & 300ppm NTA +450ppm STP Contact Time in Minutes 6 600ppm NTA

8 I&I APPLICATIONS CLEANING PRODUCTS Laundry Detergents: Several benefits can be obtained from using NTA as a builder in I&I Laundry Detergents. Primarily, NTA reduces the harmful effects of hard water by sequestering hardness ions. It has been shown that NTA is more effective than STP in sequestering calcium, magnesium and iron ions (See Figure 1 and Table 1). By reducing water hardness, NTA significantly reduces ash content of cotton fabric, thus reducing the graying and increasing the softness of the fabric. NTA also exhibits greater buffering capacity than STP on an equal weight basis, as well as a greater solubility and stability towards hydrolysis in water. Furthermore, the superior performance of NTA-built detergents in cold water is particularly valuable in today s energy conscious world. NTA is compatible with most of the other major and minor ingredients found in I&I laundry detergent formulations. In fact, NTA will often enhance the performance of these ingredients. In liquid formulations, because of its greater sequestering power, NTA allows a lower solids content and provides a lower viscosity and greater ease of mixing and handling. NTA s solubility also permits higher levels of performance to be built into liquid detergents. Typical examples of both powder and liquid NTA-built detergent formulations can be found in the formulary section. Other Cleaning Products: The benefits from using NTA in I&I laundry detergents are also available when NTA is used in hard surface and specialty cleaning formulations. Pound for pound, equal or better performance results are observed when other builders are replaced with NTA. The formulary section contains some typical hard surface cleaning formulations, both liquid and concentrate and spray type. VEHICLE WASH The vehicle wash market is an established and growing market for many detergent ingredients. Changing conditions, such as new paints, alloys and mechanical cleaning systems along with safety and environmental concerns are placing new demands on the vehicle wash industry. For example, aluminum alloys have replaced the heavier carbon steel as a means of improving fuel efficiency and clear overcoat lacquers are becoming more prevalent on new automobiles. NTA can be formulated into effective vehicle wash cleaning formulations. The removal of road film without the use of the corrosive HF give these formulations a distinct advantage from the point of view of safe handling for operators and users. Extensive testing in our laboratories have shown that these NTA formulations are particularly effective over a range of soiling conditions and are superior to most of the commercially available products that were tested. In addition, in our testing, no corrosion was found on the paint and lacquer finishes and no attack on the rubber components in hosing was found. WATER TREATMENT NTA softens water by chemically sequestering metal ions through soluble complex formation. This event prevents the precipitation of the metal salts. Furthermore, NTA has the capability to dissolve metal salt precipitates such as scale. Boiler water treatment with NTA is particularly effective. Lower levels of NTA provide equal or better scale preventing capacity than EDTA. When using NTA or other chelating agents for boiler treatment, oxygen-scavenging chemicals (e.g. sodium sulfite) should be added before the chelating agent. Chelating agents complex the trace metals added to catalyze the oxygen removal reactions. Table 4 shows a comparison of NTA and EDTA in their effectiveness to prevent scale formation. 7

9 TABLE 4 Scale Preventing Capacities of NTA and EDTA in Boiler Water Treatment Pressure NTA EDTA Pressure Scale Scale PSI PPM Prevention % PPM Prevention % Just as NTA can be used to prevent scale formation, it also can be used to remove scale after it has formed in cases where it is uneconomical or otherwise undesirable to continuously treat with NTA. In these cases, it does an excellent job of cleaning and offers the additional advantage of cleaning in neutral or basic solutions. This greatly reduces corrosion problems caused by the usual acid cleaning. AGRICULTURE In agriculture, NTA can be used as a carrier for micronutrient trace metals and as a stabilizer in herbicide formulations. As a micronutrient trace metal carrier, NTA has been demonstrated to be equally or more effective than other chelating agents. Chelated forms of iron, zinc, manganese, and copper are known to be much more efficient than inorganic forms of these metals in either foliar or ground applications. On a cost-performance basis, it is frequently more economical to use the chelated forms of these metals. TEXTILES In scouring, bleaching and dyeing, NTA performs a number of unique functions. The ability of NTA to form soluble complexes with metallic ions and hold them in solution is important in all phases of textile operations. In scouring formulations, NTA effectively prevents precipitation of insoluble compounds during wet finishing and the precipitation of insoluble soaps. NTA reduces the ash content of the fabric, increases the cleaning stage effectiveness and removes metal ions which would be harmful in subsequent bleaching and dyeing operations. NTA functions as a peroxide stabilizer in aqueous hydrogen peroxide bleaching baths. In cases where it is added directly to the bath, it stabilizes the bath by chelating trace metals which catalytically decompose the peroxide at undesirable rates. Adding NTA as a Mg +2 salt imparts additional stability to the bleaching bath. With perborate bleaches, transition metal salts of NTA (especially the Cu +2 salt) have been reported to improve bleaching efficiency at moderate temperatures. In dyeing, NTA effectively removes calcium and magnesium ions which, left untreated, could lead to loss of color yield and rub fastness, turbidity and other detrimental effects. NTA can remove other metallic ions and prevent formation of interfering metal lakes, spotting and streaking. Other uses for NTA in the textile industry are as a stabilizer for copperized azo dyes and sodium aluminate; as a gas-fading inhibitor for acid fumes; as an anti-tarnishing agent for indigoid vat dye compositions and as a brightening agent for metalized dyes. 8

10 METAL CLEANING AND FINISHING NTA is an excellent material for formulating alkaline cleaning and/or derusting solutions. It imparts not only excellent buffering capacity and building action but can stabilize and prolong the life of a cleaning bath. NTA can provide many beneficial functions in aqueous electroplating baths. For example, it can act as the source of the plating metal, the plating regulator or as a brightness regulator. NTA will also complex interfering metal ions and prevent sludge formation. RUBBER AND POLYMER PROCESSING NTA has many potential uses in the rubber and polymer industry. For example, as a catalyst for the initiation of styrene polymerization, the CU +2 salt of NTA gives equivalent performance to the Cu +2 salt of EDTA. NTA can be used as the catalyst for the polymerization of vinyl acetate and vinyl compounds, polyamines and mono-and diolefins. NTA as a stabilizer inhibits the polymerization of acrylonitrile and imparts heat stability to tin-catalyzed polyurethane foams. It inhibits dark spots in freshly spun viscose fibers and acts as a preservative for rubber latexes. PULP AND PAPER NTA can be useful in several processing areas of the pulp and paper industry. In peroxide and hydrosulfite bleaching, it is a stabilizer and metal ion scavenger. NTA can remove metal ions from paper for use in capacitors and from coatings where metal ions adversely affect the printing ink. PETROLEUM PRODUCTION NTA uses in petroleum applications are varied - from production to refining. During the well drilling process, NTA can be added to the drilling fluids to prevent scale formation and control viscosity of drilling muds. It can also be used during acid treatments of wells, again to chelate and remove scale formation. In addition, NTA has found use in corrosion inhibition packages and in both emulsification and emulsionbreaking treatments. PETROLEUM REFINING NTA chelates have found use in the removal of hydrogen sulfide from sour, acid gas (sweetening the gas). During this process, ferric iron is reduced to the ferrous form and sulfide is oxidized to elemental sulfur and removed. The net reaction is: H 2 S + 1/2 O 2 S + H 2 O However, the overall reaction pathway involves catalysis by the NTA chelate of iron: 2 Fe +3 NTA + H 2 S 2 Fe +2 HNTA + S 2 Fe +2 HNTA + O 2 2 Fe +3 NTA + H 2 O MISCELLANEOUS Corrosion Inhibitor: NTA can be used as a corrosion inhibitor in photographic ferricyanide bleach solutions, in ammonium phosphate fire fighting formulations, in anti-freeze compositions, in engine coolants in general, in mineral oils, in dimethyl sulfoxide and in many other applications. Stabilizer: NTA is used in a number of products as a stabilizing agent; for example, in sodium silicate solutions against precipitation and in ammonium nitrate propellants. 9

11 Rare Earth Separations: In the separation of the rare earths, NTA has been extensively investigated. There are several reasons for this the complexes with two moles of NTA per mole of metal are more stable than many other complexes; in combination with oxalate, the rare earths or groups of them can be precipitated at various ph s. As an eluant for ion exchange separations, solutions of NTA are very effective. Other: Aminopolycarboxylates have been used in many other areas. A few of these are listed below. Although NTA has not been specifically studied in most of these areas, there is a reason to believe that the use of NTA would result in the same benefits as derived from other members of the aminopolycarboxylate family: Cement NTA can act as a grinding aid and retard setting rate Varnish NTA may prevent fading due to sunlight Phosphatizing NTA may prevent sludge formation Glass Cleaning NTA acts as an excellent cleaning compound and prevents scale formation STARTER FORMULARY USING NTA The Formulations provided below are considered to be starter formulations only. Each person considering use of these suggestions should run small trial batches to optimize for individual, local conditions. I&I LAUNDRY LIQUID, NO PHOSPHATE NTA 18.0 Sodium Alkylbenzene Sulfonate (LAS) 10.0 Sodium Xylene Sulfonate (40%) 22.5 Fatty Alkanolamide 4.0 RU Silicate (47%) 6.4 Water 39.1 LIQUID, NO PHOSPHATE NTA 10.0 Sodium Alkylbenzene Sulfonate (LAS) 10.0 Alcohol Ether Sulfate (58%) 17.2 Sodium Xylene Sulfonate (40%) 20.0 Soap 0.5 RU Silicate (47%) 4.3 Sodium Carbonate 3.0 Water 35.0 POWDER NTA 30.0 Sodium Alkylbenzene Sulfonate (LAS) 18.0 Sodium Silicate 8.0 Sodium Carbonate 5.0 Sodium Sulfate & Minor Ingredients 39.0 POWDER, WITH PHOSPHATE NTA 15.0 Sodium Tripolyphosphate 24.0 Sodium Alkylbenzene Sulfonate (LAS) 18.0 Sodium Silicate 6.0 Sodium Carbonate 5.0 Sodium Sulfate & Minor Ingredients

12 POWDER NTA 30.0 Alcohol Ethoxylate 10.0 Sodium Silicate 8.0 Sodium Carbonate 5.0 Sodium Sulfate & Minor Ingredients 47.0 POWDER, WITH PHOSPHATE NTA 10.0 Sodium Tripolyphosphate 24.0 Alcohol Ethoxylate 10.0 Sodium Silicate 6.0 Sodium Carbonate 5.0 Sodium Sulfate & Minor Ingredients 45.0 HARD SURFACE CLEANERS LIQUID, CONCENTRATE NTA 10.0 Sodium Alkylbenzene Sulfonate (LAS) 4.0 Alkylphenol Ethoxylate 2.0 Ethylene Glycol Monobutyl Ether 0.5 Sodium Xylene Sulfonate Water As Necessary Balance SPRAY TYPE NTA 2.5 Sodium Alkylbenzene Sulfonate (LAS) 1.0 Alkylphenol Ethoxylate 0.5 Ethylene Glycol Monobutyl Ether 2.5 Sodium Xylene Sulfonate Water As Necessary Balance VEHICLE WASH, POWDER, ALUMINUM BRIGHTENING Sodium Tripolyphsophate (STP) 68.0 Alcohol Ethoxylate G.D. Silicate Shell Chemical, Neodol 91.6 VEHICLE WASH, POWDER, ALUMINUM BRIGHTENING NTA 10.0 RU Silicate (47%) 10.0 Alcohol Ethoxylate Sodium Xylene Sulfonate (40%) 7.5 Water Shell Chemical, Neodol 91.6 TERRAZZO CLEANER Surfactant 8.0 NTA 2.0 Water 90.0 Use Level: 1-3 cups in 3 gal. water. MACHINE DISHWASH, LIQUID Water Acrysol ASE-108 Stabilizer Potassium Hydroxide (45% sol.) 1.33 Tetrapotassium Pyrophosphate 25.0 Trisodium Phosphate, Anhyd. 5.5 NTA 3.0 Surfactant 3.0 Dye 1 Rohm & Haas Co. 11

13 WHITEWALL TIRE CLEANER Surfactant 15.0 NTA 5.0 Water 80.0 Use without further dilution. HARD SURFACE & FLOOR CLEANER Stepanate X Sodium Metasilicate, Anhydrous 3.0 NTA 2.5 Ninol 11 CM Water, Dye, Perfume Stepan Co. BUTYL CLEANER (DEGREASER) Ninol 1281 or NTA 2.0 Tetrapotassium Pyrophosphate 4.0 Stepanate X Butyl Cellosolve or Butyl Carbitol 5.0 Potassium Hydroxide (45% sol.) 10.0 Water Balance 1 Stepan Co. 12