Fluorosilicate-polyamine complexes for producing hf

Abstract

A method to make HF including the steps of mixing a first solution of hexafluorosilicic acid a second solution of a polyamine wherein an FSA-PA complex is formed, and degrading at least a portion of the FSA-PA complex to yield HF.

Description

Fluorosilicate-Polyamine Complexes for Producing HFCarlos E. Cardenas-Daw Paloma Venegas Rodriguez Luis A. Gutierrez L.Rosa Rivera MartinezGabriel A. Garcia MartinezBACKGROUND

[0001] Hydrogen fluoride (HF) (typically encountered as hydrofluoric acid - an aqueous solution of HF) is commonly produced by reacting enriched calcium fluoride, CaF2, the most common mineral form of fluorine, with sulfuric acid (H2SO4). Alternatively, HF can be produced from fluorosilicic acid ( / .e., hexafluorosilicic acid, 2H+[SiF6]2'; "FSA") solutions treated with concentrated sulfuric acid. See Dahlke et al (2016) "Production of HF from H2SiFg," Procedici Engineering 138: 231-239. FSA is spontaneously formed as a dilute aqueous solution when silicon tetrafluoride (SiF4), a common gaseous by-product of the phosphate industry, is trapped in scrubbers. SiF4is also a common by-product of in the HF industry because the calcium fluoride feedstocks used to make HF often contain siliceous sub-components. Some of that silicon ends up as the Si F4by-product.

[0002] Because FSA solutions are dilute and hazardous to transport, their use as HF precursors is inherently limited. Alternatives to bypass these disadvantages by the production of a solid / condensed intermediate have been developed.

[0003] U.S. Pat. No. 3,421,853, issued January 14, 1969, to R.R. Hennig, describes the synthesis of stable alkali or alkaline earth metal salts of FSA and their use as precursors to make HF. Specific examples include salts of Ca, Na, K, and Ba. As condensed forms of FSA, these salts are safe and economical to transport. Nevertheless, the generation of HF requires melting the salts at temperatures in the range of from about 1,300 to about 1,600 °C. The large amount of energy required to reach these temperatures vitiates the other advantages of this approach.

[0004] Chinese Patent CN 113816340A describes generating HF from the sodium salt of fluorosilicic acid. On one hand, and in contrast to the fusion method described in the Hennig patent, the approach here proceeds at a more reasonable temperature range of from about 500 to about 600 °C. On the other hand, the method requires adding hot HCI gas to the reaction - a potentially dangerous step that requires special handling and safety equipment.

[0005] Chinese Patent CN 103332655A is specific to the calcium salt of FSA, and describes an energy-efficient reactor design to treat a pre-heated precursor with super-heated steam to generate HF. The reaction takes place at an overall reaction temperature range of from about 800 to about 950 °C. Like the other methods discussed above, however, the process requires large amounts of super-heated steam, and thus requires a large energy input.

[0006] Alkaline routes have also been developed to generate HF from fluorosilicic acid. See, for example, U.S. Pat. No. US 3,128,152, issued April 7, 1964, to Secord and Le Roy. This patent describes adding excess ammonia to hydrolyze FSA in solution and simultaneously precipitating SiOa- The solid SiO2is separated via filtration. The residual liquid is evaporated partially or completely to obtain a highly concentrated solution of NH4F or crystalline NH4F, respectively. The NH4F is then burned to produce HF. This method requires large amounts of ammonia and energy due to the dilute condition of the FSA precursor.

[0007] Alternatives to solve the low concentration disadvantage and proceed with the alkaline route have been described. For example, U.S. Pat. No. 9,663,375, issued May 30, 2017, to Berry et al., describes using commercial anionic exchange resins to remove contaminants from an FSA precursor. (The FSA precursor adsorbs to the resin.) The FSA precursor is thereby concentrated. The process requires H2SO4to liberate the precursor from the resin (thereby regenerating the resin). The solution is then treated with ammonia and Na2CO3to produce the bifluoride salt NaHF2, from which HF can be generated by thermal treatment.

[0008] European Published Patent Application EP 3,792, 219A1 (17 March 2021; Applicant Novye Khimicheskie Produkti) describes precipitating the alkali, alkaline earth, or ammonium salts of FSA through controlled, partial a Ika linization. These precursors are isolated and subsequently treated with excess ammonia to hydrolyze the fluorosilicate anion and separate solid SiOs, in a fashion similar to U.S. Pat. No. 3,128,152. Likewise, the resulting NH4F aqueous solution is burned to produce HF in an energy-intensive process. CO2, N2and H2O by-products must be separated first.

[0009] Thus, there remains a long-felt and unmet need for a safer, less energy-intensive method to produce HF.SUMMARY OF THE INVENTION

[0010] Disclosed herein is a method to make HF. The method comprises mixing a first solution comprising hexafluorosilicic acid ("FSA") with a second solution comprising a polyamine ("PA") for a time, and at a temperature, wherein an FSA-PA complex is formed. At least a portion of the FSA-PA complex so formed is precipitated, separated, and subsequently degraded to yield HF. The first and second solutions are preferably mixed at a temperature between 0 °C and 100 °C, and more preferably still at a temperature between 4 °C and 50 °C. It is also much preferred that wherein the first and second solutions are aqueous solutions. However, any solvent capable of dissolving the FSA and PA reactants may be used.

[0011] The PA is may optionally be selected from the group consisting of an ethyleneamine, a linear, branched, or dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), and a macrocyclic polyamine. In other versions, the PA may be selected from the group consisting of ethylenediamine, diethylenetriamine (DETA), aminoethylpiperazine (AEP), triethylenetetramine (linear-TETA), tris(2-aminoethyl)amine (branched-TETA), N,N'-bis-(2- aminoethyl)piperazine) (bis-AEP), N-[(2-aminoethyl)2-aminoethyl]piperazine), piperazinoethylethylenediamine (PEEDA), tetraethylenepentamine, pentaethylenehexamine, linear, branched, and dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), 1,4,7-triazacyclononane, 1,4,7, 10-tetraazacyclododecane ("cyclen"), 1,4,8,11- tetraazacyclotetradecane ("cyclam"), tris(2-aminoethyl)amine, and 1,1,1- tris(aminomethyl)ethane.

[0012] Prior to degrading the FSA complex to yield HF, optionally at least a portion of any solvent remaining after the mixing of the first and second solutions may be removed by any suitable means (e.g., evaporation).

[0013] The FSA-PA complex is preferably thermally degraded at a temperature at or above 200 °C, or at or above 250 °C, or at or above 300 °C. Optionally, the FSA-PA complex may be degraded in the presence of super-heated steam.

[0014] The first (FSA) solution may optionally be from about 0.1 wt% to about 50 wt% FSA. The concentration of the second (PA) solution may also vary widely, based on the nature of the PA chosen, but also may optionally be from about 0.1 wt% to about 35 wt% PA. More highly concentrated solutions are generally preferred.

[0015] Explicitly disclosed herein are the following:

[0016] 1. A method to make HF, the method comprising: mixing a first solution comprising hexafluorosilicic acid ("FSA") with a second solution comprising a polyamine ("PA") for a time, and at a temperature, wherein an FSA-PA complex is formed; and (b) degrading at least a portion of the FSA-PA complex to yield HF.

[0017] 2. The method of claim 1, wherein the first and second solutions are mixed at a temperature between 0 °C and 100 °C.

[0018] 3. The method of claim 1, wherein the first and second solutions are mixed at a temperature between 4 °C and 50 °C.

[0019] 4. The method of claim 1, wherein the first and second solutions are aqueous solutions.

[0020] 5. The method of claim 1, wherein the PA is selected from the group consisting of an ethyleneamine, diethylentriamine, triethylentetramine, tetraethylenpentamine, a linear, branched, or dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), a macrocyclic polyamine, and combinations thereof.

[0021] 6. The method of claim 1, wherein the PA is selected from the group consisting of ethylenediamine, diethylenetriamine (DETA), aminoethylpiperazine (AEP), triethylenetetraamine (linear-TETA), tris(2-aminoethyl)amine (branched-TETA), N,N'-bis-(2- aminoethyl)piperazine) (bis-AEP), N-[(2-aminoethyl)2-aminoethyl]piperazine), piperazinoethylethylenediamine (PEEDA), tetraethylenepentamine, pentaethylenehexamine, linear, branched, and dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), 1,4,7-triazacyclononane, 1,4,7, 10-tetraazacyclododecane ("cyclen"), 1,4,8,11- tetraazacyclotetradecane ("cyclam"), tris(2-aminoethyl)amine, and 1,1,1- tris(aminomethyl)ethane.

[0022] 7. The method of claim 1, wherein step (b) comprises thermally degrading at least a portion of the FSA-PA complex of step (a) to yield HF.

[0023] 8. The method of claim 7, wherein the FSA-PA complex is degraded at a temperature at or above 200 °C.

[0024] 9. The method of claim 7, wherein the FSA-PA complex is degraded at a temperature at or above 250 °C.

[0025] 10. The method of claim 7, wherein the FSA-PA complex is degraded at a temperature at or above 300 °C.

[0026] 11. The method of claim 7, wherein the FSA-PA complex is degraded in the presence of super-heated steam.

[0027] 12. The method of claim 1, wherein the first solution is from about 0.1 wt% to about 35 wt% FSA.

[0028] 13. The method of claim 1, wherein the second solution is from about 0.1 wt% to about35 wt% PA.

[0029] 14. The method claim 1, further comprising, after step (a) and before step (b): (a)(i) precipitating at least a portion of the FSA-PA complex formed in step (a) and removing at least a portion of any solvent remaining after step (a) to yield an intermediate; and wherein step (b) comprises degrading at least a portion of the FSA-PA complex in the intermediate to yield HF.

[0030] 15. A method to make HF, the method comprising: mixing a first solution comprising hexafluorosilicic acid ("FSA") with a second solution comprising a polyamine ("PA") for a time, and at a temperature, wherein an FSA-PA complex is formed; and precipitating at least a portion of the FSA-PA complex formed in step (a) and removing at least a portion of any solvent remaining after step (a) to yield an intermediate; and degrading at least a portion of the FSA-PA complex in the intermediate to yield HF.

[0031] 16. The method of claim 15, wherein the first and second solutions are mixed at a temperature between 0 °C and 100 °C.

[0032] 17. The method of claim 15, wherein the first and second solutions are aqueous solutions.

[0033] 18. The method of claim 15, wherein the PA is selected from the group consisting of an ethyleneamine, diethylentriamine, triethylentetramine, tetraethylenpentamine, a linear, branched, or dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), a macrocyclic polyamine, and combinations thereof.

[0034] 19. The method of claim 15, wherein the PA is selected from the group consisting of ethylenediamine, diethylenetriamine (DETA), aminoethylpiperazine (AEP), triethylenetetraamine (linear-TETA), tris(2-aminoethyl)amine (branched-TETA), N,N'-bis-(2- aminoethyl)piperazine) (bis-AEP), N-[(2-aminoethyl)2-aminoethyl]piperazine), piperazinoethylethylenediamine (PEEDA), tetraethylenepentamine, pentaethylenehexamine, linear, branched, and dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), 1,4,7-triazacyclononane, 1,4,7, 10-tetraazacyclododecane ("cyclen"), 1,4,8,11- tetraazacyclotetradecane ("cyclam"), tris(2-aminoethyl)amine, and 1,1,1- tris(aminomethyl)ethane.

[0035] 20. The method of claim 15, wherein step (c) comprises thermally degrading at least a portion of the FSA-PA complex in the intermediate of step (b) to yield HF.

[0036] ABBREVIATIONS AND DEFINITIONS

[0037] FSA = hexafluorosilicic acid, 2H+[Si Fg]2-. FSA is miscible in water. It is available commercially from a host of international suppliers, including Thermo Scientific Chemicals (formerly Alfa Aesar), Ward Hill, Massachusetts, United States.

[0038] PA = polyamine. As used herein "polyamine" refers to all types of polyamines, natural or synthetic, without limitation, having two or more amino groups (internal or terminal). Thus, the term "polyamine," includes (by way of example and not limitation) linear polyamines such as, ethylenediamine, spermidine, spermine, longer homologs thereof, and the like; ethyleneamines such as diethylenetriamine (DETA), aminoethylpiperazine (AEP), triethylenetetraamine (linear- TETA), tris(2-aminoethyl)amine (branched-TETA), tetraethylenpentamine (TEPA), N, / V'-bis-(2- aminoethyl)piperazine) (bis-AEP), A / -[(2-aminoethyl)2-aminoethyl]piperazine) or piperazinoethylethylenediamine (PEEDA), tetraethylenepentamine, pentaethylenehexamine, and the like; linear, branched, and dendritic poly(ethylenimines) generally; other amine- containing polymers such as aziridne oligomers, polydiallyldimethylammonium chloride (polyDADMAC) and the like; macrocyclic polyamines such as 1,4,7-triazacyclononane, 1,4,7,10- tetraazacyclododecane ("cyclen"), 1,4,8,11-tetraazacyclotetradecane ("cyclam"), and the like; and branched and dendritic polyamines such as tris(2-aminoethyl)amine, 1,1,1- tris(aminomethyl)ethane, and the like. Polyamines are available commercially from many international suppliers, including the Sigma-Aldrich subsidiary of MilliporeSigma, Burlington, Massachusetts, United States.

[0039] All references to singular characteristics or limitations of the disclosed method shall include the corresponding plural characteristic or limitation, and vice-versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made. The indefinite articles "a" and "an" mean "one or more." The word "or" is used inclusively and should be read as "and / or."

[0040] All combinations of method steps disclosed herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

[0041] The method disclosed herein can comprise, consist of, or consist essentially of the essential elements and steps described herein, as well as any additional or optional ingredients, components, or limitations described herein or otherwise useful in organic / inorganic chemistry.DETAILED DESCRIPTION OF THE INVENTION

[0042] Disclosed herein are novel fluorosilicate-polyamine organic / inorganic complexes. The complexes are made by combining aqueous solutions of hexafluorosilicic acid (2H+[Si F6]2'; "FSA") and a polyamine ("PA").

[0043] Precursor solutions may be of varied concentrations and combined in different ratios, defined as moles / molarity of silicon atoms in the fluorosilicic acid solution versus moles / molarity of nitrogen atoms in the amine functional groups of the PA solution. The control of these solution parameters is a results-effective variable. The ratio of the molarities of the two solutions prior to mixing dictates whether the final product forms a stable colloid or precipitates from solution as a solid complex.

[0044] It has been found by the current inventor that the purity of the FSA solution is not critical to formation of the FSA-PA complexes. Because FSA appears as a by-product in the production of phosphoric acid and HF, and further because those production processes utilize a wide variety of feedstocks, the FSA solution may contain other ions depending on its origin. For the most part, these additional ions remain in solution and do not interfere with formation of the complexes (although a small mole fraction of these other ions fraction may be incorporated into the FSA-PA complexes).

[0045] As defined above, any PA, without limitation, may be used. The PA may comprise a well- defined "small" molecule (see exemplary small-molecule PA's above), a polymeric material of linear, branched, or dendritic structure, or a combination of them. Polyethylenimine, polyDADMAC, ethylendiamine, diethylentriamine (DETA), triethylentetramine (TETA), and tetraethylenpentamine (TEPA) are preferred polyamines:Polyethylenimine PolyDADMAC Ethylenediamine(wherein "n" is an integer greater than 1)Diethylentriamine (DETA) Triethylentetramine (TETA)Tetraethylenpentamine (TEPA)

[0046] Fatty amines (e.g., octyl amine, lauryl amine, stearyl amine, oleyl amine, and the like) may also be added to the PA solution as hydrophobization agents.

[0047] The FSA-PA complex in its dried form exhibits different F-to-Si ratios depending on the conditions under which the FSA solution and the PA solution are mixed. An F-to-Si ratio of 6 in the final complex indicates that the [SiFe]2anion in the FSA reactant solution was preserved intact forms at least part of the cationic portion of the final complex. F-to-Si ratios < 6 (and as low as about 1) can be obtained and indicate high levels of defluorination of the Si atom during the complexation reaction. These complexes may be accompanied by the concurrent formation of silicon oxides or suboxides. F-to-Si > 6 can also be obtained. This outcome results when additional HF molecules are either present in one of the reactant solutions, or forms during the complexation reaction. The total content of fluorine in the final complex also depends on variations in the relative content of organic versus inorganic mass in the product.

[0048] The dried complexes are thermally stable at temperatures ranging from 100°C up to 300°C depending on the molecular weight of the amine. Weight losses of < about 5% were observed at temperatures below the stability threshold. Exposing the complex to temperatures above its stability threshold results in the liberation of HF from the complex. The release of HF is facilitated in the presence of super-heated steam.

[0049] Given these properties, the FSA-PA complexes disclosed herein are highly useful to produce HF in-situ, without the need for additional, hazardous reactants and at much lower temperatures than conventional methods. The method is thus useful to transport the needed reactants to make HF in a safe condition and to make the HF without specialized equipment and without additional inputs ( / .e., without catalysts or additional co-reactants). The method disclosed herein thus stands in stark contrast to current commercial methods, which require large amounts of a strong acid or ammonia and / or huge energy inputs.

[0050] An exemplary, non-limiting example of the method is as follows:

[0051] Concentrated diethylentriamine (DETA) was added dropwise into an 18 wt% FSA aqueous solution under vigorous stirring. A total of 21.5 g DETA was added per L of FSA solution. This corresponds to a total of 2 N atoms per Si atom in the mixture. The formed solid was then separated and allowed to dry under vacuum at room temperature. To generate HF, the dried solid was placed in an HF-resistant distillation system, in this case instance a perfluoroalkoxy alkane ("PFA")-lined steel distillation column and associated plumbing. The system was heated up to 300°C. Vapors were cooled to < 100°C to separate a condensate rich in DETA. The remaining vapors were separated and further cooled to < 20°C to condense essentially pure HF.

Claims

Claims1. A method to make HF, the method comprising:(a) mixing a first solution comprising hexafluorosilicic acid ("FSA") with a second solution comprising a polyamine ("PA") for a time, and at a temperature, wherein an FSA-PA complex is formed; and(b) degrading at least a portion of the FSA-PA complex to yield HF.

2. The method of claim 1, wherein the first and second solutions are mixed at a temperature between 0 °C and 100 °C.

3. The method of claim 1, wherein the first and second solutions are mixed at a temperature between 4 °C and 50 °C.

4. The method of claim 1, wherein the first and second solutions are aqueous solutions.

5. The method of claim 1, wherein the PA is selected from the group consisting of an ethyleneamine, diethylentriamine, triethylentetramine, tetraethylenpentamine, a linear, branched, or dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), a macrocyclic polyamine, and combinations thereof.

6. The method of claim 1, wherein the PA is selected from the group consisting of ethylenediamine, diethylenetriamine (DETA), aminoethylpiperazine (AEP), triethylenetetraamine (linear-TETA), tris(2-aminoethyl)amine (branched-TETA), N, / V'-bis-(2- aminoethyl)piperazine) (bis-AEP), A / -[(2-aminoethyl)2-aminoethyl]piperazine), piperazinoethylethylenediamine (PEEDA), tetraethylenepentamine, pentaethylenehexamine, linear, branched, and dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), 1,4,7-triazacyclononane, 1,4,7, 10-tetraazacyclododecane ("cyclen"), 1,4,8,11- tetraazacyclotetradecane ("cyclam"), tris(2-aminoethyl)amine, and 1,1,1- tris(aminomethyl)ethane.

7. The method of claim 1, wherein step (b) comprises thermally degrading at least a portion of the FSA-PA complex of step (a) to yield HF.

8. The method of claim 7 , wherein the FSA-PA complex is degraded at a temperature at or above 200 °C.

9. The method of claim 1, wherein the FSA-PA complex is degraded at a temperature at or above 250 °C.

10. The method of claim 7, wherein the FSA-PA complex is degraded at a temperature at or above 300 °C.

11. The method of claim 1 , wherein the FSA-PA complex is degraded in the presence of superheated steam.

12. The method of claim 1, wherein the first solution is from about 0.1 wt% to about 35 wt% FSA.

13. The method of claim 1, wherein the second solution is from about 0.1 wt% to about 35 wt% PA.

14. The method claim 1, further comprising, after step (a) and before step (b):(a)(i) precipitating at least a portion of the FSA-PA complex formed in step (a) and removing at least a portion of any solvent remaining after step (a) to yield an intermediate; and wherein step (b) comprises degrading at least a portion of the FSA-PA complex in the intermediate to yield HF.

15. A method to make HF, the method comprising:(a) mixing a first solution comprising hexafluorosilicic acid ("FSA") with a second solution comprising a polyamine ("PA") for a time, and at a temperature, wherein an FSA-PA complex is formed; and(b) precipitating at least a portion of the FSA-PA complex formed in step (a) and removing at least a portion of any solvent remaining after step (a) to yield an intermediate; and(c) degrading at least a portion of the FSA-PA complex in the intermediate to yield HF.

16. The method of claim 15, wherein the first and second solutions are mixed at a temperature between 0 °C and 100 °C.

17. The method of claim 15, wherein the first and second solutions are aqueous solutions.

18. The method of claim 15, wherein the PA is selected from the group consisting of an ethyleneamine, diethylentriamine, triethylentetramine, tetraethylenpentamine, a linear, branched, or dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), a macrocyclic polyamine, and combinations thereof.

19. The method of claim 15, wherein the PA is selected from the group consisting of ethylenediamine, diethylenetriamine (DETA), aminoethylpiperazine (AEP), triethylenetetraamine (linear-TETA), tris(2-aminoethyl)amine (branched-TETA), / V, / V'-bis-(2- aminoethyl)piperazine) (bis-AEP), A / -[(2-aminoethyl)2-aminoethyl]piperazine), piperazinoethylethylenediamine (PEEDA), tetraethylenepentamine, pentaethylenehexamine, linear, branched, and dendritic poly(ethylenimine), polydiallyldimethylammonium chloride (polyDADMAC), 1,4,7-triazacyclononane, 1,4,7, 10-tetraazacyclododecane ("cyclen"), 1,4,8,11- tetraazacyclotetradecane ("cyclam"), tris(2-aminoethyl)amine, and 1,1,1- tris(aminomethyl)ethane.

20. The method of claim 15, wherein step (c) comprises thermally degrading at least a portion of the FSA-PA complex in the intermediate of step (b) to yield HF.

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