Methods of synthesizing chelated chromium

Abstract

Methods of synthesizing chelated chromium are described. The methods may include a step of combining a chromium precursor and a reducing agent to thereby provide a reduced chromium compound, wherein the chromium precursor comprises Cr(VI) and the reduced chromium compound comprises Cr(III). The methods may further include a step of combining the reduced chromium compound and a ligand to thereby provide chelated chromium. In some embodiments, the methods described herein are specifically used to synthesize CrEDTA or CrPDTA.

Description

METHODS OF SYNTHESIZING CHELATED CHROMIUMTECHNICAL FIELD

[0001] This disclosure is generally directed to methods of synthesizing chelated chromium. The methods may include a step of combining a chromium precursor and a reducing agent to thereby provide a reduced chromium compound, wherein the chromium precursor comprises Cr(VI) and the reduced chromium compound comprises Cr(lll). The methods may further include a step of combining the reduced chromium compound with a ligand to thereby provide chelated chromium.BACKGROUND

[0002] The creation of highly pure material forms of chromium chelates such as CrEDTA (chromium ethylenediamine tetraacetate) and CrPDTA (chromium propylenediamine tetraacetate) is a desirable goal for several industries. For example, the battery industry requires highly pure chromium chelates for use in electrolyte materials. However, obtaining highly pure material forms of chromium chelates can be both difficult and expensive. Most known methods for synthesizing, e.g., CrEDTA and CrPDTA, use Cr(lll) precursors and result in the creation of salt byproduct that diminishes the chromium chelate purity. Costly separation processes are therefore needed to remove these salts from the chromium chelate final product. Alternative methods for synthesizing chromium chelates have used Cr(VI) precursors, but these syntheses require a strong reducing agent or a strong acid, both of which result in the formation of similar undesirable salt byproducts as are formed when Cr(lll) is used as a precursor, which thus also diminishes the purity of the chromium chelates and requires expensive separation techniques to remove.

[0003] Accordingly, a need exists for new methods of synthesizing chelated chromium complexes without forming byproducts, such as salts, that diminish the purity of the chelated chromium complexes.SUMMARY

[0004] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary, and the foregoing Background, is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter.

[0005] In some embodiments, a method of synthesizing chelated chromium generally includes a step of combining a chromium precursor, a reducing agent, and an organic acid to thereby provide a reduced chromium compound, wherein the chromium precursor comprises Cr(VI) and the reduced chromium compound comprises Cr(lll); and a step of combining the reduced chromium compound and a ligand to thereby provide chelated chromium. In some embodiments, the methods described herein are specifically used to synthesize CrEDTA or CrPDTA. In some embodiments, the organic acid is acetic acid.

[0006] These and other aspects of the technology described herein will be apparent after consideration of the Detailed Description and Figures herein. It is to be understood, however, that the scope of the claimed subject matter shall be determined by the claims as issued and not by whether given subject matter addresses any or all issues noted in the Background or includes any features or aspects recited in the Summary.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Non-limiting and non-exhaustive embodiments of the disclosed technology, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0008] FIG. 1 is a flow diagram illustrating a method of synthesizing chelated chromium configured in accordance with various embodiments described herein.DETAILED DESCRIPTION

[0009] Embodiments are described more fully below with reference to the accompanying Figures, which form a part hereof and show, by way of illustration, specificexemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense.

[0010] Described herein are low-cost, scalable methods for synthesizing chelated chromium compounds at high concentrations. The described methods produce little to no salt byproduct, and therefore eliminate the need for costly separation processes. The methods described herein generally use Cr(VI) precursor material, which is less expensive than Cr(lll) precursor used in most previously known methods. The methods described herein also rely on lower cost reducing agents, and minimize reaction time as compared to previously known synthesis methods.

[0011] The chelated chromium compounds described herein are identified as, e.g., CrEDTA, CrPDTA, etc. It should be appreciated, however, that CrEDTA, CrPDTA, etc., are anions with a -1 charge. As such, the pure material forms of the chelated chromium compounds described herein will have a cation counter, such as H+, Li+, K+, Na+, NH4+, Cs+, Rb+, etc., to make the chelated chromium compound neutral in its solid form. Non-limiting examples of the neutral form of the disclosed chelated chromium compound include NaCrEDTA and KCrPDTA. For the sake of simplicity, however, the chelated chromium compounds described herein are referenced with respect to their anion form.

[0012] References to EDTA, PDTA, NTA, and DTPA herein should be understood to refer to a ligand that is fully protonated or fully deprotonated or partially deprotonated or mixtures of the fully protonated, fully deprotonated, and partially deprotonated ligand. EDTA or PDTA as used herein can refer to the free form of the ligand or the form of the ligand bound to Cr with one or more arms.

[0013] The technology described herein also refers in several instances to PDTA (propylenediamine tetra-acetic acid), such as when referring to the ligand to which the chromium bonds to form the chelated chromium compound. Several isomer forms of PDTA exist. When used as the ligand for the chelated chromium compound, it should be appreciated that reference herein to PDTA means 1 ,3-PDTA, 1 ,2-PDTA, or mixtures thereof.

[0014] With reference to FIG. 1 , a method 100 for synthesizing chelated chromium generally includes a step 110 of combining a chromium precursor, a reducing agent, and an organic acid to thereby provide a reduced chromium compound; and a step 120 of combining the reduced chromium compound and a ligand to thereby provide chelated chromium. Method 100 can also optionally step 115 of drying the reduced chromium compound and / or step 125 of drying the chelated chromium.

[0015] Step 110 generally includes combining a chromium precursor and a reducing agent and reacting these two materials to provide a reduced chromium compound reaction product. Accordingly, step 110 may be carried out in any manner that allows for the chromium precursor and the reducing agent to react, and in some embodiments, may be carried out in a specific manner that encourages a reaction between the chromium precursor and the reducing agent. As discussed in more detail below, this may include also combining an acid with the chromium precursor and the reducing agent such that the pH is maintained at a low level, thus allowing the reaction between the chromium precursor and the reducing agent to go to completion.

[0016] In some embodiments, which may be a preferred embodiment, the chromium precursor is a compound that comprises Cr(VI); that is to say, the compound includes chromium in its hexavalent form. Non-limiting examples of a suitable chromium precursor (i.e. , a compound including Cr(VI)) include sodium chromate, sodium dichromate, potassium chromate, potassium dichromate, ammonium chromate, ammonium dichromate, lithium chromate, and lithium dichromate. Other chromium precursors that may be suitable for use in the methods described herein include chromium (VI) oxide, chromyl chloride, and calcium chromate.

[0017] It is hypothesized that the use of a Cr(VI)-based chromium precursor in the formation of a chelated chromium compound has traditionally been avoided for several reasons. To begin with, Cr(VI) is a strong oxidant in acidic conditions and can oxidize organic compounds, including chelating agents, if they are mixed together. Therefore, Cr(VI) has generally been avoided, at least as compared to synthesis methods using, e.g., Cr(lll), in order to avoid destroying organic molecules that may be present. Additionally, Cr(VI) can oxidize ligands such as EDTA under traditional conditions used in the synthesis of chelatedchromium compounds, which thereby undesirably reduces the amount of chelated chromium compound formed. This has further resulted in Cr(VI) not being used in previously known processes. Finally, processes using Cr(VI) for synthesizing chelated chromium compound, at least as compared to methods using Cr(lll), generally require an additional step, wherein Cr(VI) is reduced to Cr(lll). This additional step has traditionally been seen as adding undesirable complexity to the process. The technology described herein addresses each of these concerns to thereby provide a relatively simple method for synthesizing chelated chromium compounds using Cr(VI) precursor.

[0018] The reducing agent used in step 110 may be any suitable reducing agent capable of reacting with the chromium precursor to reduce the chromium component of the chromium precursor. Non-limiting examples of reducing agents that may be used in step 110 include methanol, ethanol, isopropanol, hydrogen peroxide, and hydrogen. In some embodiments, these reducing agents may be preferred reducing agents, as they are generally lower cost than reducing agents that may have been required in previously known methods for synthesizing chelated chromium. Other reducing agents that may be suitable for use in the methods described herein include ammonia, hydrazine, sodium hydride, potassium hydride, sodium sulfide, lithium aluminum hydride, sodium borohydride, hydrogen sulfide, sulfite, formic acid, ascorbic acid, glucose, tin chloride, and sodium thiosulfate.

[0019] The reaction mechanism in which the chromium component is reduced generally includes the formation of a reduced chromium compound; that is to say, a new compound is formed, the new compound including a reduced form of chromium as compared to the chromium component of the chromium precursor. In some embodiments, which may be a preferred embodiment, the reduced chromium component comprises Cr(lll). A non-limiting example of a reduced chromium compound that may be formed from the reaction between the chromium precursor and the reducing agent is NaCr(CH3COO)4, in which the Cr component of this compound is Cr(lll).

[0020] Step 110 further includes the addition of an organic acid to the mixture of chromium precursor and reducing agent, with the primary aim of the organic acid being to control (i.e. , maintain at low level) the pH of the mixture, which thereby allows the reaction between the chromium precursor and the reducing agent to proceed to completion. In someembodiments, the amount / concentration of organic acid used in step 110 is selected in order to maintain the pH level within a range of from 1 to 5. In some embodiments, the organic acid is a carboxylic acid. In some embodiments the organic acid is acetic acid, but can also be, e.g., formic acid, propionic acid, or butyric acid. The organic acid component is not consumed during the two-step method 100, and as such, behaves like a quasi-catalyst to the reaction between the chromium compound precursor and the reducing agent. Because organic acids may be volatile acids, they can be removed from the reaction product and possibly recycled through evaporation or distillation.

[0021] Step 110 may further utilize a solvent as part of forming the mixture. Any suitable solvent may be used. In one non-limiting example, the solvent used is deionized water.

[0022] In some embodiments, the amount of chromium precursor used in the methods described herein is relatively high as compared to previously known methods for synthesizing chelated chromium. In some embodiments, the concentration of chromium precursor in the mixture formed in step 110 is in the range of from 0.1 to 4 M. In some embodiments, the chromium precursor concentration can be lower than 0.1 M. The higher concentration of chromium precursor that can be used in the methods described herein allows for the production of more final material per synthesis batch, and is thus more economical than some previously known methods using lower concentrations.

[0023] In order to promote reaction between the reducing agent and the chromium precursor, the mixture may be subjected to, e.g., heating and / or agitation. Heating of the reaction may be in the range of, e.g., 20°C to 300°C and at a pressure in the range of from about 1 atm to about 218 atm. For example, in some embodiments, the mixture is heated at 90°C for 4 hours while stirring the mixture.

[0024] Following completion of the reaction between the chromium precursor and the reducing agent, optional step 115 may be carried out to dry the reaction product. Any suitable drying techniques can be used, including industrial drying techniques, provided the drying serves to dry the reaction product, such as by evaporating off any remaining solvent and / or acid used in step 110.

[0025] In some embodiments, drying step 115 includes heating the reaction product. The reaction products can be heated to any suitable temperature provided the reaction products themselves (i.e., the reduced chromium product) are not damaged or negatively impacted by the heating. In some embodiments, the reaction products are heated to a temperature in the range of from 20°C to 300°C, such as from 20°C to 140°C, to about room temperature, or from 140°C to 300°C. Heating as part of the heating step can also be carried out at an adjusted pressure, such as at a pressure below atmospheric pressure. In some embodiments, the drying step is carried out at a pressure in the range of from about 1 mTorr to about 760 Torr. The duration of the heating step is also generally not limited, again provided that prolonged heating doesn’t damage or negatively impact the reaction product. In some embodiments, the heating step is carried out for a duration of up to 24 hours.

[0026] Spray dryers and other industrial drying processes can also be used as part of drying step 115.

[0027] Step 120 generally comprises combining the reduced chromium compound produced in step 110 and a ligand to thereby provide chelated chromium. Accordingly, step 120 may be carried out in any manner that allows for the reduced chromium compound and the ligand to react, and in some embodiments, may be carried out in a specific manner that encourages a reaction between the reduced chromium compound and the ligand. In some embodiments, the mixture of reduced chromium compound and ligand may be subjected to, e.g., heating and / or agitation to promote reaction. For example, in some embodiments, the mixture is heated at 100°C for 1 to 4 hours while stirring the mixture.

[0028] The reduced chromium compound used in step 120 is generally used “as is”; that is to say, no purification steps, isolation steps, and / or separation steps are carried out on the reduced chromium compound prior to its use in step 120. The exception here is the previously described drying step, which for purposes of this disclosure, is not considered a purification, isolation, or separation step. The drying step is merely a step for removing volatile components from the reduced chromium compound such that the reduced chromium compound is provided in a dry form.

[0029] The ligand used in step 120 may be any suitable ligand capable of reacting with the reduced chromium compound to thereby provide chelated chromium. Non-limiting examples of ligands that may be used in step 120 include ethylenediamine tetra-acetic acid (EDTA), propylenediamine tetra-acetic acid (PDTA), diethylenetriamine pentaacetatic acid (DTPA), and nitrilotriacetic acid (NTA). When EDTA is used as the ligand, the resulting chelated chromium compound is CrEDTA. When PDTA is used as the ligand, the resulting chelated chromium compound is CrPDTA. When NTA is used as the ligand, the resulting chelated chromium compound is CrNTA. When DTPA is used as the ligand, the resulting chelated chromium compound is CrDTPA. In some embodiments, the ligand may be any am inopolycarboxy late.

[0030] In some embodiments, the methods described herein use as close to a 1 :1 ligand: Cr ratio as possible. By avoiding excess ligand, the process is less expensive. In some embodiments, a relatively slight excess of ligand is used, such as up to 5% excess ligand.

[0031] Step 120 may optionally further include the addition of a solvent to the mixture of reduced chromium compound and ligand. The solvent, such as water, may be used to dissolve the reduced chromium compound produced in step 110 and dried in step 115.

[0032] In some embodiments, the pH of the reaction product resulting from step 120 is in the range of from about 2 to about 4. As discussed in further detail below, additional steps may be carried out to further adjust the pH level of the reaction product (i.e., chelated chromium).

[0033] Following completion of the reaction between the reduced chromium compound and the ligand, optional step 125 may be carried out to dry the reaction product. Step 125 may be similar or identical to optional step 115 described previously. Any suitable drying techniques can be used, including industrial drying techniques, provided the drying serves to dry the reaction product, such as by evaporating off any remaining solvent used in step 120.

[0034] In some embodiments, drying step 125 includes heating the reaction product. The reaction product can be heated to any suitable temperature provided the reactionproduct themselves (i.e. , the chelated chromium) are not damaged or negatively impacted by the heating. In some embodiments, the reaction products are heated to a temperature in the range of from 20°C to 300°C, such as from 20°C to 140°C, to about room temperature, or from 140°C to 300°C. The duration of the heating step is also generally not limited, again provided that prolonged heating doesn’t damage or negatively impact the reaction product. In some embodiments, the heating step is carried out for a duration in the range of from 0.5 hours to 24 hours.

[0035] Spray dryers and other industrial drying processes can also be used as part of drying step 125.

[0036] In some embodiments, at least one aim of the drying step 125 is to completely remove acid from the chelated chromium. As described previously, the organic acid is generally not consumed in the various reactions carried out to provide chelated chromium, and as such, the acid component is still present upon producing the chelated chromium. Any manner of ensuring complete removal of acid from the chelated chromium can be used. In some embodiments, one or more cycles of drying are carried out on the mixture of materials produced via step 120 in order to fully remove the acid component from the chelated chromium. Following each drying step, the solids are redissolved so that further drying can be carried out to remove residual acid not removed from the previous drying cycle or cycles. Any suitable acid removal step or steps can be used, such as, but not limited to, rotovaping.

[0037] As noted previously, method 100 may further include a step of adjusting the pH of the chelated chromium produced from step 120 (and optionally dried in step 125). Any suitable method of adjusting the pH level can be used. In some embodiments, the chelated chromium reaction product is combined with a solvent (e.g., water) and a base (e.g., sodium hydroxide) to raise the pH level. As noted previously, the chelated chromium produced from step 120 may have a pH in the range of 2 to 4. The addition of a base may be used to increase the pH level to within a range of about 4 to about 6. That being said, the final pH of the chelated chromium may be in the range of from about 2 to about 7. A pH level below 2 can also be used in some embodiments.

[0038] When a pH adjustment step is used as described previously, a further drying step may be carried out. For example, the pH adjusted chelated chromium may be heated at a temperature of about 100°C for 1 to 4 hours while stirring in order to dry the chelated chromium (primarily by evaporating off the solvent and base). Industrial spray drying processes may also be used to dry the pH adjusted chelated chromium.

[0039] The chelated chromium resulting from the methods described herein contains substantially no or no byproduct salts. As such, the produced chelated chromium produced by the methods described herein may be considered pure. By virtue of not having any byproduct salts, the methods described herein are less expensive than previously described methods for synthesizing chelated chromium since the methods described herein eliminate the need for expensive post processing separation steps aimed at separating the chelated chromium from the byproduct salt. Furthermore, because pure chelated chromium is provided by the methods described herein, solutions can be created at high concentrations.

[0040] The various reactions described herein can be carried out in any suitable equipment or apparatus. In some embodiments, industrial reactors are used so as to allow for high product rates. The industrial reactors can be high pressure and / or high temperature industrial reactors.

[0041] The methods described herein also provide an improvement over some previously known methods for synthesizing chelated chromium by requiring a reduced overall reaction time as compared to some previously known methods. For example, some embodiments of the described technology may take 24 hours or less, whereas previously known methods using, e.g., Cr(lll) may take 72 hours or longer.

[0042] Variations on the methods described herein may include a one step process, wherein steps 110 and 120 are generally combined into a single step. That is to say, the chromium precursor, the reducing agent, the ligand, and other previously described additives (e.g., acids) are combined in one step. In this variation, the reduction of Cr(VI) to Cr(lll) and the chelation of the reduced Cr are carried out in the single mixture of materials as part of one overall multi-step reaction mechanism. In this first variation, previously described additive may or may not be needed. However, this variation may require an excess of reducing agent.

[0043] In another variation of the primary method described herein, the previously described two-step process is generally used, but additional components are used such that Cr(OH)3 is the reduced chromium compound generated from the chromium precursor in the first step, and the Cr(OH)3 is isolated before reacting Cr(OH)swith the ligand. The result of this variation is the same as the primary method: providing a pure chelated chromium with no salt byproduct produced.

[0044] In this variation on the primary two step method, the step of generating a reduced chromium compound from the chromium precursor employs a strong inorganic acid (e.g., hydrochloric acid) when combining the organic acid, chromium precursor, reducing agent, and solvent. Following heating and mixing of this mixture of organic acid, chromium precursor, reducing agent, solvent, and inorganic acid to promote a first reaction, a base (e.g., NaOH) is then added to produce Cr(OH)3 as the reduced chromium compound.

[0045] Following production of Cr(OH)3, the variation of the primary method further includes a step of isolating the Cr(OH)s via any suitable method, such as via centrifuge or filtration. This isolation of Cr(OH)3 may result in NaCI being drained off.

[0046] Solvent and ligand are then added to isolated Cr(OH)s to produce chelated chromium. In one non-limiting example, the chelated chromium is HCrEDTA. In some embodiments, an optional additional step may be carried out to change the cation counter. For example, HCrEDTA may be reacted with a base such as, e.g., NaOH to produce NaCrEDTA.

[0047] Examples of the primary method and each of the previously described variations are provided in the following Examples section.

[0048] EXAMPLES

[0049] Example 1 - Primary Two Step Method (EDTA)

[0050] Combine 5 g sodium dichromate (Cr(VI) precursor), 9 mL ethanol (reducing agent), 76.5 mL acetic acid (acid additive), and 46 mL of DI water (solvent) in a round bottom flask. Heat at 90 °C for 4 hours while stirring to promote reaction between sodium dichromate and ethanol. Heat the first reaction product at 140 °C while stirring uncapped to dryness. Add 33.5 mL water to dissolve resulting first reaction product and add 10 g EDTA(ligand). Heat at 100 °C for 1 to 4 hours while stirring to promote reaction between first reaction product and ligand. Heat resulting chelated chromium (i.e., CrEDTA) to dryness. Add 33.5 mL DI water and NaOH to raise the pH to pH 4 to 6. Heat CrEDTA at 100 °C for 1 to 4 hours while stirring to dryness.

[0051] UV Vis after synthesis shows literature peaks meaning CrEDTA has been made successfully. When the material is put in a redox flow battery (RFB), the cycling data is the same or better as compared to CrEDTA synthesized using previously known methods that use Cr(lll) as the chromium precursor.

[0052] Example 2 - Primary Two Step Method (EDTA) Variation

[0053] Combine 5 g sodium dichromate (Cr(VI) precursor), 9 mL ethanol (reducing agent), 76.5 mL acetic acid (acid additive), and 46 mL of DI water (solvent) in a round bottom flask. Heat at 110 °C for 4 hours while stirring to promote reaction between sodium dichromate and ethanol. Heat the first reaction product at 140 °C while stirring uncapped to dryness. Add 33.5 mL water to dissolve resulting first reaction product and add 10 g EDTA (ligand). Heat at 120 °C for 1 to 4 hours while stirring to promote reaction between first reaction product and ligand. Rotovap resulting chelated chromium (i.e., CrEDTA) to dryness. The resulting pH is between 2-6.

[0054] UV Vis after synthesis shows literature peaks meaning CrEDTA has been made successfully. When the material is put in a redox flow battery (RFB), the cycling data is the same or better as compared to CrEDTA synthesized using previously known methods that use Cr(lll) as the chromium precursor.

[0055] Example 3 - Primary Two Step Method (PDTA)

[0056] Combine 5 g sodium dichromate (Cr(VI) precursor), 9 mL ethanol (reducing agent), 76.5 mL acetic acid (acid additive), and 46 mL of DI water (solvent) in a round bottom flask. Heat at 90 °C for 4 hours while stirring to promote reaction between sodium dichromate and ethanol. Heat first reaction product at 140 °C while stirring uncapped to dryness. Add 33.5 mL water to dissolve first reaction product and add 10.2 g PDTA (ligand). Heat at 100 °C for 1 to 4 hours while stirring to promote reaction between first reaction product and ligand. Heat resulting chelated chromium (i.e., CrPDTA) to dryness. Add 33.5mL DI water and NaOH to raise the pH to pH 4 to 6. Heat CrPDTA at 100 °C for 1 to 4 hours while stirring to dryness.

[0057] UV Vis after synthesis shows literature peaks meaning CrPDTA has been made successfully. When the material is put in a redox flow battery (RFB), the cycling data is the same or better as compared to CrPDTA synthesized using previously known methods that use Cr(lll) as the chromium precursor.

[0058] Example 4 - Primary Two Step Method (PDTA) Variation

[0059] Combine 5 g sodium dichromate (Cr(VI) precursor), 9 mL ethanol (reducing agent), 76.5 mL acetic acid (acid additive), and 46 mL of DI water (solvent) in a round bottom flask. Heat at 110 °C for 4 hours while stirring to promote reaction between sodium dichromate and ethanol. Rotovap first reaction product to dryness. Add 33.5 mL water to dissolve first reaction product and add 10.2 g PDTA (ligand). Heat at 120 °C for 1 to 4 hours while stirring to promote reaction between first reaction product and ligand. Rotovap resulting chelated chromium (i.e., CrPDTA) to dryness.

[0060] UV Vis after synthesis shows literature peaks meaning CrPDTA has been made successfully. When the material is put in a redox flow battery (RFB), the cycling data is the same or better as compared to CrPDTA synthesized using previously known methods that use Cr(lll) as the chromium precursor.

[0061] Example 5 - One Step Variation

[0062] Combine 5 g sodium dichromate (Cr(VI) precursor), 9 mL ethanol (reducing agent), 10 g EDTA (ligand), and 46 mL of DI water (solvent) in a round bottom flask. Heat at 90 °C for 4 hours while stirring to react.

[0063] UV Vis after synthesis shows same peaks as from literature meaning CrEDTA has been made successfully.

[0064] Example 6 - Two Step Variation

[0065] Combine 5 g sodium dichromate (Cr(VI) precursor), 1 .5 mL methanol (reducing agent), 11 mL hydrochloric acid, 0.5 mL acetic acid (acid additive), and 22.5 mL DI water (solvent) in a round bottom flask. Heat at 60 °C for 30 minutes while stirring to react. Add4 g NaOH (base) to produce Cr(OH)3. Wet / hydrated Cr(OH)3 is isolated via centrifuge or filtration, while solution with NaCI is drained off. To wet / hydrated Cr(OH)3, 33.5 mL DI water (solvent) and 10 g EDTA (ligand) are added. Reflux at 100 °C for 2 hours while stirring to react to HCrEDTA. Add 1 .5 g NaOH (base) to produce NaCrEDTA. Reflux at 100 °C for 1 hour while stirring to dryness.

[0066] UV Vis after synthesis shows literature peaks meaning CrEDTA has been made successfully.

[0067] From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

[0068] Although the technology has been described in language that is specific to certain structures and materials, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures and materials described. Rather, the specific aspects are described as forms of implementing the claimed invention. Because many embodiments of the invention can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

[0069] Unless otherwise indicated, all number or expressions, such as those expressing dimensions, physical characteristics, etc., used in the specification (other than the claims) are understood as modified in all instances by the term "approximately". At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter recited in the specification or claims which is modified by the term "approximately" should at least be construed in light of the number of recited significant digits and by applying rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass and provide support for claims that recite any and all sub-ranges or any and all individual values subsumed therein. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all sub-ranges or individual values that are between and / or inclusive of the minimum value of 1 and the maximum value of 10; that is, all sub-ranges beginning with a minimumvalue of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

Claims

CLAIMSI / We claim:1 . A method of synthesizing chelated chromium, comprising: combining a chromium precursor, a reducing agent, and an organic acid to thereby provide a reduced chromium compound, wherein the chromium precursor comprises Cr(VI) and the reduced chromium compound comprises Cr(lll); and combining the reduced chromium compound and a ligand to thereby provide chelated chromium.

2. The method of claim 1 , wherein the chromium precursor is selected from the group consisting of sodium chromate, sodium dichromate, potassium chromate, potassium dichromate, ammonium chromate, ammonium dichromate, lithium chromate, and lithium dichromate.

3. The method of claim 1 , wherein the reducing agent is selected from the group consisting of methanol, ethanol, isopropanol, hydrogen peroxide, carbon, and hydrogen.

4. The method of claim 1 , wherein the ligand is selected from the group consisting of ethylenediamine tetra-acetic acid (EDTA), propylenediamine tetra-acetic acid (PDTA), diethylenetriamine pentaacetatic acid (DTPA), and nitrilotriacetic acid (NTA).

5. The method of claim 1 , wherein the reduced chromium compound provided from the step of combining the chromium precursor, the reducing agent, and the organic acid is combined with the ligand without performing any purification steps on the reduced chromium compound.

6. The method of claim 1 , wherein the chelated chromium is free or substantially free of salt byproduct.

7. The method of claim 1 , wherein the concentration of chromium precursor in the combination of chromium precursor, reducing agent, and organic acid is in the range of from 0.1 to 4 M.

8. The method of claim 1 , further comprising drying the reduced chromium compound, drying the chelated chromium, or both.

9. The method of claim 8, wherein drying comprises heating at a temperature in the range of from 20°C to 300°C and is carried out for between 0.5 hours and 24 hours.

10. The method of claim 1 , wherein the pH of the chelated chromium is from 2 to 7.

11. The method of claim 1 , wherein combining the chromium precursor, the reducing agent, and organic acid comprises heating the combined chromium precursor, reducing agent and, organic acid at a temperature in the range of from 20°C to 300°C.

12. The method according of claim 1 , wherein the organic acid comprises a carboxylic acid.

13. The method according to claim 12, wherein the carboxylic acid comprises acetic acid.

14. The method of claim 1 , wherein combining the chromium precursor, the reducing agent, and the organic acid further comprises combining an inorganic acid with the chromium precursor, the reducing agent, and the organic acid, and adding a base to the reaction product of the chromium precursor, the reducing agent, the organic acid, and the inorganic acid to thereby provide the reduced chromium compound; and wherein the method further comprises isolating the reduced chromium compound prior to combining the reduced chromium compound and the ligand.

15. The method of claim 14, wherein the reduced chromium compound is Cr(OH)3.

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