SEPARATION AND CONCENTRATION OF NITRATE FROM AQUEOUS SOLUTIONS AND GASEOUS STREAMS

Abstract

A process for recovering nitric acid or salts thereof, comprising: contacting, in the presence of water, an water-immiscible ionic liquid of the formula [A.sup.+][X.sup.−], wherein [A.sup.+] represents a phosphonium or ammonium cation and [X.sup.−] represents a counter anion which is NO.sub.3.sup.−, an halide anion displaceable by NO.sub.3.sup.−, or both, with a fluid which contains HNO.sub.3 and at least one more mineral acid, or precursors of said acids, and partition, under mixing, said acids between aqueous and organic phases and form nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 where Z indicates a molar amount of nitrate held in the ionic liquid beyond the positions occupied by the nitrate counter ions; separating the so-formed mixture into an organic phase comprising a nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 and an aqueous phase consisting of a nitrate-depleted aqueous solution that contains the other mineral acid(s); stripping the nitric acid from said nitrate-loaded ionic liquid to create an aqueous nitrate solution and regenerate ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z≥0 with reduced nitrate loading, or unloaded [A.sup.+][NO.sub.3.sup.−].sub.z=0 ionic liquid.

Claims

1. A process for recovering nitric acid or salts thereof, comprising: contacting, in the presence of water, an water-immiscible ionic liquid of the formula [A.sup.+][X.sup.−], wherein [A.sup.+] represents a phosphonium or ammonium cation and [X.sup.−] represents a counter anion which is NO.sub.3.sup.−, an halide anion displaceable by NO.sub.3.sup.−, or both, with a fluid which contains HNO.sub.3 and at least one more mineral acid, or precursors of said acids, and partition, under mixing, said acids between aqueous and organic phases and form nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 where Z indicates a molar amount of nitrate held in the ionic liquid beyond the positions occupied by the nitrate counter ions; separating the so-formed mixture into an organic phase comprising a nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 and an aqueous phase consisting of a nitrate-depleted aqueous solution that contains the other mineral acid(s); stripping the nitric acid from said nitrate-loaded ionic liquid to create an aqueous nitrate solution and regenerate ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z÷0 with reduced nitrate loading, or unloaded [A.sup.+][NO.sub.3.sup.−].sub.z=0 ionic liquid.

2. The process according to claim 1, wherein the one or more mineral acids is(are) selected from the group consisting of sulfuric acid, phosphoric acid and hydrohalic acids.

3. The process according to claim 1, wherein the ionic liquid [A.sup.+][X.sup.−] with which the process begins is [R.sub.1R.sub.2R.sub.3R.sub.4P.sup.+][X.sup.−] wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and wherein at least two of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are C5-C15 alkyl groups and [X.sup.−] is chloride, bromide or nitrate.

4. The process according to claim 3, wherein the ionic liquid with which the process begins is (CH.sub.3(CH.sub.2).sub.5).sub.3P.sup.+(CH.sub.2).sub.13CH.sub.3][Cl.sup.−] or [(CH.sub.3(CH.sub.2).sub.5).sub.3P.sup.+(CH.sub.2).sub.13CH.sub.3][NO.sub.3.sup.−].

5. The process according to claim 1 wherein the ionic liquid is dissolved in one or more water-immiscible organic solvents.

6. The process according to claim 1, wherein the stripping of the nitrate from the ionic liquid to create an aqueous nitrate solution is achieved with the aid of a stripping reagent selected from the group consisting of water, an aqueous base solution, an aqueous salt solution, or a mixture thereof; or by heating the ionic liquid, optionally under reduced pressure, to release gaseous HNO.sub.3 followed by absorption into an aqueous solution.

7. The process according to claim 6, wherein the stripping reagent is potassium hydroxide or a mixture of potassium hydroxide and potassium nitrate.

8. The process according to claim 1, wherein the fluid is an aqueous acidic solution, the process being applied for producing nitric acid or potassium nitrate through selective liquid-liquid extraction of nitrate from said aqueous acidic solution.

9. A process for producing nitric acid or nitrate salts by liquid-liquid extraction of nitrate from an aqueous stream that contains nitric acid and at least one more mineral acid, said process comprising the steps of: an extraction step, which comprises contacting an extractant which is an water-immiscible ionic liquid of the formula [A.sup.+][X.sup.−], wherein [A.sup.+] represents a phosphonium or ammonium cation and [X.sup.−] represents a counter anion which is NO.sub.3.sup.−, an halide anion displaceable by NO.sub.3.sup.−, or both, with an aqueous solution which contains HNO.sub.3 and at least one more mineral acid, to partition, under mixing, said acids between aqueous and organic phases and form nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 where Z indicates a molar amount of nitrate held in the ionic liquid beyond the positions occupied by the nitrate counter ions; phase separation step, which comprises separating the so-formed mixture into an organic nitrate-loaded extract of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 and an aqueous raffinate comprising the other mineral acid(s); a stripping step, which comprises stripping the nitric acid from said organic extract to create an aqueous nitrate solution and regenerate ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z≥0 with reduced nitrate loading or unloaded [A.sup.+][NO.sub.3.sup.−].sub.z=0 ionic liquid.

10. The process according to claim 9, wherein the one or more mineral acids is(are) selected from the group consisting of sulfuric acid, phosphoric acid and hydrohalic acid.

11. The process according to claim 9, wherein the extractant [A.sup.+][X.sup.−] is [R.sub.1R.sub.2R.sub.3R.sub.4P.sup.+][X.sup.−] wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and wherein at least two of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are C5-C15 alkyl groups and [X.sup.−] is chloride, bromide or nitrate.

12. The process according to claim 11, wherein the extractant is (CH.sub.3(CH.sub.2).sub.5).sub.3P.sup.+(CH.sub.2).sub.13CH.sub.3][Cl .sup.−] or [(CH.sub.3(CH.sub.2).sub.5).sub.3P.sup.+(CH.sub.2).sub.13CH.sub.3][NO.sub.3.sup.−].

13. The process according to claim 9, comprising stripping the nitric acid from the organic extract with potassium hydroxide or a mixture of potassium hydroxide and potassium nitrate.

14. The process according to claim 1, wherein the fluid is an oxidized flue gas that contains NO.sub.2 and SO.sub.2, the process being applied for producing nitric acid or salts thereof by scrubbing the oxidized flue gas with the ionic liquid in the presence of an aqueous oxidizer and partition, under mixing, HNO.sub.3 and H.sub.2SO.sub.4 between an aqueous phase and the organic phase to form nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25.

15. A process for producing nitric acid or salts thereof by removing NO, from a flue gas, said process comprising the steps of: passing an oxidized flue gas stream that contains NO.sub.2 and SO.sub.2 through a gas-liquid contactor, where the flue gas is brought into intimate contact with an water-immiscible ionic liquid of the formula [A.sup.+][X.sup.−], wherein [A.sup.+] represents a phosphonium or ammonium cation and [X.sup.−] represents a counter anion which is NO.sub.3.sup.−, an halide anion displaceable by NO.sub.3.sup.−, or both, in the presence of an aqueous oxidizer, and form nitrate-loaded ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z>0.25 where Z indicates a molar amount of nitrate held in the ionic liquid beyond the positions occupied by the nitrate counter ions; releasing a purified flue gas into the atmosphere; withdrawing ionic liquid-containing stream from the gas-liquid contactor and feeding regenerated ionic liquid stream back into the gas-liquid contactor through a circulation loop, wherein the ionic liquid-containing stream flows through said circulation loop where it is subjected to regeneration treatment comprising the steps of: separating the ionic liquid-containing stream, optionally after addition of water, into a first organic stream consisting essentially of H.sub.2SO.sub.4-free and HX-free ionic liquid [A.sup.+][NO3.sup.−].sub.z>0.25 and a first aqueous acidic stream which contains H.sub.2SO.sub.4 and optionally HX, wherein X is halide; stripping the nitrate from the organic stream consisting of the ionic liquid [A.sup.+][NO3.sup.−].sub.z>0.25 to create a second aqueous stream which contains HNO.sub.3 or salt thereof; and regenerating ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z≥0 with reduced nitrate loading (i.e., reduced Z value), or unloaded [A.sup.+][NO.sub.3.sup.−].sub.z=0 ionic liquid; leading said [A.sup.+][NO.sub.3.sup.−].sub.z≥0 with reduced Z value back to the gas-liquid contactor; and recovering H.sub.2SO.sub.4 solution from said first aqueous acidic stream and optionally HX solution, wherein X is halide, or salts thereof, and from the second aqueous stream a nitrate salt or nitric acid solution.

16. The process according to claim 15, wherein the ionic liquid used to scrub the flue gas in the liquid-liquid contactor is [R.sub.1R.sub.2R.sub.3R.sub.4P.sup.+][X.sup.−] wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and wherein at least two of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are C5-C15 alkyl groups and [X.sup.−] is chloride, bromide or nitrate.

17. The process according to claim 16, wherein the ionic liquid used to scrub the flue gas in the liquid-liquid contactor is (CH.sub.3(CH.sub.2).sub.5).sub.3P.sup.+(CH.sub.2).sub.13CH.sub.3][Cl.sup.−] or [(CH.sub.3(CH.sub.2).sub.5).sub.3P.sup.+(CH.sub.2).sub.13CH.sub.3][NO.sub.3.sup.−].

18. The process according to claim 15, wherein the stripping of the nitrate from the ionic liquid to create an aqueous nitrate solution is achieved with the aid of a stripping reagent selected from the group consisting of water, an aqueous base solution, an aqueous salt solution, or a mixture thereof; or by heating the ionic liquid, optionally under reduced pressure, to release gaseous HNO.sub.3 followed by absorption into an aqueous solution.

19. The process according to claim 15, wherein the flue gas further comprises mercury, which is recovered from the organic phase consisting of the ionic liquid.

20. The process according to claim 1, wherein loading of the ionic liquid with nitrate creates [A.sup.+][NO.sub.3.sup.−].sub.z>0.75.

21. A liquid-liquid extraction process for separating nitrate from dilute aqueous solution of nitric acid or salts thereof, with initial nitrate concentration C.sub.i0.01%, and produce concentrated aqueous solution of nitric acid or salts thereof, arriving at final nitrate concentration C.sub.f which is at least twofold greater than C.sub.i, which comprises: contacting said dilute aqueous nitrate solution with water-immiscible ionic liquid of the formula [A.sup.+][X.sup.−], wherein X.sup.− is NO.sub.3.sup.− or halide anion displaceable by NO.sub.3.sup.−, generating nitrate-loaded ionic liquid [A.sup.+][NO.sub.3.sup.−].sub.z>25, stripping the nitrate from said nitrate-loaded ionic liquid to create a concentrated solution thereof and regenerate an ionic liquid of the formula [A.sup.+][NO.sub.3.sup.−].sub.z≥0 with lesser nitrate loading, or unloaded [A.sup.+][NO.sub.3.sup.−].sub.z=0 ionic liquid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 shows results of HNO.sub.3 extraction from aqueous HNO.sub.3+H.sub.2SO.sub.4+HCl mixture.

[0059] FIG. 2 shows results of HNO.sub.3 extraction from HNO.sub.3 stream.

[0060] FIG. 3 shows results of HNO.sub.3 extraction from HNO.sub.3 stream.

[0061] FIG. 4 illustrates HNO.sub.3 stripping results from loaded ionic liquid at different temperatures.

[0062] FIG. 5 shows the results of Examples 1 and 2 together.

[0063] FIG. 6 is a selectivity versus [H.sub.2SO.sub.4] plot based on HNO.sub.3 extraction from aqueous HNO.sub.3+H.sub.2SO.sub.4 mixtures.

[0064] FIG. 7 shows results of HNO.sub.3 extraction from aqueous HNO.sub.3+H.sub.3PO.sub.4 mixture.

[0065] FIG. 8 is Z versus concentration plot comparing the performance of two ionic liquids.

[0066] FIG. 9 is selectivity versus concentration plot comparing the performance of two ionic liquids.

[0067] FIG. 10 is a schematic illustration of extraction of nitrate from an aqueous mixture of acids.

[0068] FIG. 11 is a schematic illustration of an apparatus used for purifying flue gases and recovering nitrate therefrom.

[0069] FIG. 12 is a schematic illustration of a process of purifying flue gases and recovering nitrate, HCl and H.sub.2SO.sub.4 therefrom.

[0070] FIG. 13 is Phosphorous-31 NMR spectrum of ionic liquids described herein.

DETAILED DESCRIPTION

[0071] Trihexyl(tetradecyl)phosphonium chloride (CYPHOS IL-101) was purchased from Holland Moran, Israel. Potassium chromate K.sub.2CrO.sub.4, Phenolphthalein and Sodium hydroxide solution (0.1 N) were purchased from Sigma-Aldrich, Israel. Silver nitrate solution (AgNO.sub.3) 2.5% (w/v) was purchased from Sigma-Aldrich, Israel. Potassium fluoride was purchased from Merck Israel. Mercury chloride and aliquat336 were purchased from Sigma-Aldrich, Israel. phosphoric acid 85% solution was purchased from Sigma-Aldrich, Israel. Decane was purchased from Sigma-Aldrich, Israel.

Preparation 1

[0072] Preparation of nitrate ionic liquid (IL-NO.sub.3)

[0073] 15 gr of Trihexyl(tetradecyl)phosphonium chloride and 17 gr of KNO.sub.3 (10% solution) were mixed at 98° C. for 5 minutes, then left for 20 minutes in order to enable phase separation. The clear aqueous phase (the lower level phase) was removed and fresh 17 gr KNO.sub.3 (10% solution) was added. The mixture was stirred at 98° C. for 5 minutes. After phase separation the clear aqueous phase was removed. Fresh 17 gr KNO.sub.3 10% solution was added, and the mixture was stirred at 98° C. for 5 minutes. After phase separation the clear organic liquid was collected. To determine that chloride ions were fully displaced by the nitrate, the ionic liquid was analyzed for the presence Cl. The chloride (Cl.sup.−) concentration was determined using standard AgNO.sub.3 (0.05 N with indicator 5% K.sub.2CrO.sub.4) titration. The Cl concentration in the resultant ionic liquid solution was 0.02mo1/kg , indicating that 99% of the Cl ions were replaced by NO.sub.3.

[0074] The nitrate ionic liquid that was obtained is named hereinafter IL-NO.sub.3.

Preparation 2

[0075] Preparation of nitrate ionic liquid (aliquat336-NO.sub.3)

[0076] 10 gr of Trioctylmethylammonium chloride (aliquat® 336) and 25 gr of KNO.sub.3 (10% solution) were mixed at 80° C. for 5 minutes, then left for 20 minutes to enable phase separation. The clear aqueous phase (lower phase) was removed and fresh 25 gr KNO.sub.3 (10% solution) was added. The mixture was stirred at 80° C. for 5 minutes. After phase separation the clear aqueous phase was removed. Fresh 25 gr KNO.sub.3 10% solution was added, and the mixture was stirred at 80° C. for 5 minutes. After phase separation the clear organic liquid was collected. To determine that chloride ions were fully displaced by the nitrate, the ionic liquid was analyzed for the presence Cl. The chloride (Cl.sup.−) concentration was determined using standard AgNO.sub.3 (0.05 N with indicator 5% K.sub.2CrO.sub.4) titration. The Cl concentration in the resultant ionic liquid solution was 0.035 mol/kg, indicating that 98.6% of the Cl ions were replaced by NO.sub.3 ions.

[0077] The nitrate ionic liquid that was obtained is named hereinafter aliquat336-NO.sub.3.

EXAMPLE 1

Separation of nitric acid from a Mixture of Strong Acids with IL-NO.SUB.3

[0078] A series of experiments (1-6) were made to measure the distribution of HNO.sub.3, HCl and H.sub.2SO.sub.4 with the ionic liquid of Preparation 1 (IL-NO.sub.3). To this end, Solution A1 (consisting of 6.9 wt % HNO.sub.3, 21.1 wt % H.sub.2SO.sub.4 and 6.4 wt % HCl in water), IL-NO.sub.3 and water were mixed at various proportions set out in Table 1, using a vortex mixer for 5 minutes at 98° C.

TABLE-US-00001 TABLE 1 experiment solution A1 water IL-NO.sub.3 number (gr) (gr) (gr) 1 0.1014 0.478 0.333 2 0.1676 0.2312 0.2838 3 0.2140 0.1486 0.2653 4 0.3305 0 0.285 5 0.5164 0 0.2836

[0079] In all cases, the resultant liquid consists of a clear IL-NO.sub.3 phase and aqueous phase. Concentrations of the three acids were determined as follows:

[0080] [H.sup.+] was determined separately in each phase by titration with standard sodium hydroxide (0.1 N solution using Phenolphthalein indicator).

[0081] [Cl.sup.−] was determined separately in each phase using the standard AgNO.sub.3 (0.05 N with indictor 5% K.sub.2CrO.sub.4) titration.

[0082] [NO.sub.3] in the aqueous phase was measured by NO.sub.3 electrode (Nitrate Ion Meter NO3-11 electrode from HORIBA).

[0083] [NO.sub.3] in the IL-NO.sub.3 was calculated by mass balance (NO.sub.3(IL)=NO.sub.3(tot))-NO.sub.3(aqua).

[0084] [SO.sub.4] in the IL-NO.sub.3 was calculated by the difference between H.sup.+ and the Cl.sup.− and NO.sub.3.sup.− concentration.

[0085] [SO.sub.4] in the aqueous phase was calculated by mass balance.

[0086] The distribution coefficient is defined by the ratio [Y].sub.ILNO3/[Y].sub.Aqueous phase; Y indicates the acid under consideration.

[0087] The selectivity constant is defined by the ratio:

[0088] [Y1].sub.IL-NO3/[Y1].sub.aqueous phase: [Y2].sub.IL-NO3/[Y2].sub.aqueous phase

[0089] where Y1 and Y2 indicate a pair of acids under consideration.

[0090] The results are tabulated in Table 2 and are also presented graphically in FIG. 1.

TABLE-US-00002 TABLE 2 Aqueous phase IL-NO.sub.3 phase Distribution Selectivity composition composition coefficient constant HCl HNO.sub.3 H.sub.2SO.sub.4 HCl HNO.sub.3 H.sub.2SO.sub.4 HCl HNO.sub.3 H.sub.2SO.sub.4 HNO.sub.3/ HNO.sub.3/ wt % wt % wt % wt % wt % wt % Kd Kd Kd HCl H.sub.2SO.sub.4 0.75 0.76 3.2 0.44 0.61 0.88 0.59 0.80 0.27 1.4 2.9 2.41 1.04 7.9 0.71 2.28 1.40 0.29 2.19 0.18 7.5 12.4 3.17 1.17 11.2 1.07 3.52 1.77 0.34 3.00 0.16 8.9 19.0 5.09 1.33 18.9 1.80 5.82 2.61 0.35 4.39 0.14 12.4 31.9 4.74 1.65 20.7 1.63 8.55 0.94 0.34 5.18 0.05 15.0 114.2

[0091] The abscissa and ordinate of each point in the graph are: [0092] { [Y].sub.aqueous phase; [Y].sub.IL-NO3}.sub.i, where [Y].sub.aqueous phase indicates the concentration of the acid in the aqueous phase and [Y].sub.IL-NO3 indicates the concentration of the acid in the ionic liquid for each of the six experiments (i=1,2,3,4,5, 6), based on the data tabulated in Table 2. From the results one can see that the distribution coefficient of HNO.sub.3 is surprisingly very high relative to the distribution coefficients of H.sub.2SO4 and HCl between IL-NO.sub.3 phase and the aqueous phase. The extraction of nitric acid by the ionic liquid is very efficient even al low HNO.sub.3 concentration. The efficiency of HNO.sub.3 extraction in diluted HNO.sub.3 solutions is surprisingly good, bearing in mind the high solubility of nitrate in water. It is also seen that HCl and the H.sub.2SO.sub.4 distribution coefficients decrease with increasing NO.sub.3 loading onto IL-NO.sub.3. That is, when the ionic liquid is fully loaded with HNO.sub.3 in the second position (Z>1-NO.sub.3-NO.sub.3 loading).

EXAMPLE 2

Separation of HNO.SUB.3 .from Dilute Nitric Acid Solution Using IL-NO.SUB.3

[0093] A series of experiments were made to measure the distribution of HNO.sub.3 between IL-NO.sub.3 and aqueous phase. To this end, 50% HNO.sub.3 solution, water and IL-NO.sub.3 were mixed at various proportions set out in Table 3 using a vortex mixer for 5 minutes at 98° C.

TABLE-US-00003 TABLE 3 HNO.sub.3 50% solution Water IL-NO.sub.3 (gr) (gr) (gr) 0.040 1.46 1 0.037 1.46 1 0.053 1.45 1 0.16 1.34 1 1.46 0.04 1 1.18 0.32 1 0.71 0.79 1 0.53 0.97 1 0.31 1.19 1

[0094] In all cases, the resultant liquid consists of a clear IL-NO.sub.3 phase and aqueous phase. Both phases were analyzed for H+ by titration with standard sodium hydroxide (0.1 N solution using phenolphthalein indicator). The results are shown in Table 4 and in FIGS. 2 and 3.

TABLE-US-00004 TABLE 4 Aqueous phase IL-NO.sub.3 Phase Distribution HNO.sub.3 HNO.sub.3 coefficient Wt % Wt % Z IL-NO.sub.3\Aqua 0.73 0.75 0.059 1.02 0.78 0.82 0.065 1.06 1.12 0.99 0.078 0.89 3.5 2.81 0.225 0.8 5.5 7.03 0.589 1.27 10.6 10.6 0.922 1 15.9 11.5 1.011 0.72 29.3 15.2 1.4 0.52 37.4 17 1.601 0.46

[0095] The abscissa and ordinate of each point in the graph (the first and second coordinates of a point} are: [0096] { [HNO.sub.3].sub.aqueous phase; [HNO.sub.3].sub.IL-NO3}.sub.i, where [HNO.sub.3].sub.aqueous phase indicates the concentration of the acid in the aqueous phase and [HNO.sub.3].sub.IL-NO3 indicates the concentration of the acid in the ionic liquid for each of the nine experiments (i=1,2,3,4,5, 6,7,8, 9), based on the data tabulated in Table 3. FIG. 3 is Z versus concentration [HNO.sub.3].sub.aqueous phase plot.

EXAMPLE 3

Separation of Nitric Acid from Aqueous Phase Using IL-NO.SUB.3 .that is Formed in Situ from IL-Cl

[0097] Experiment was carried out to measure the distribution of HNO.sub.3 with IL-Cl. To this end, 0.85 gr 5.6% HNO.sub.3 solution and 0.3274 gr Trihexyl(tetradecyl)phosphonium chloride (IL-Cl) were mixed using a vortex mixer for 5 minutes at 98° C. The resultant liquid consists of a clear ionic liquid phase and aqueous phase. Both phases were analyzed in order to determine acids concentration in different phases. The results are shown in Table 5.

TABLE-US-00005 TABLE 5 Aqueous phase composition IL-Cl phase composition HNO.sub.3 HCl HCl HCl HNO.sub.3 HNO.sub.3 H+ NO3/IL Cl/IL Selectivity wt % wt % mol/kg wt % wt % mol/kg mol/kg Mol/mol Mol/mol HNO.sub.3/Cl 0.63 2.60 0.33 1.2 11.3 1.8 0.33 1.071 0.197 39.4

[0098] It is noted that the NO.sub.3.sup.−/IL molar ratio is more than 1, indicating Z>0.

EXAMPLE 4

Stripping of Nitric Acid from HNO.SUB.3.-Lloaded IL-NO.SUB.3 .by Evaporation Process

[0099] Separation of HNO.sub.3 from HNO.sub.3-loaded IL-NO.sub.3 was achieved by bubbling N.sub.2 through the ionic liquid at 98° C. or 155° C. N.sub.2 30 ml/min was bubbled through 2.83 gr IL-NO.sub.3 z=1.1 at 98° C. or 155° C. Samples were taken from the nitrate-loaded ionic liquid at different times over a period of 280 minutes and analyzed for H+by titration with standard sodium hydroxide. The results are set out in Table 6 and presented graphically in FIG. 4.

TABLE-US-00006 TABLE 6 Time(min) Z 98 C° Z 155 C° 0 1.12 0.89 20 1.07 40 0.20 50 1.04 90 0.92 130 0.88 ′150 0.17 180 0.90 280 0.89

[0100] Z versus time plot shown in FIG. 4 indicates that HNO.sub.3 is readily separable from the ionic liquid at increased temperature (T=155° C.).

EXAMPLE 5

Stripping of HNO.SUB.3 .from HNO.SUB.3.-Loaded [IL-NO.SUB.3.].SUB.z=1.01 .using NaHCO.SUB.3 .Solution

[0101] The stripping of HNO.sub.3 from loaded IL-NO.sub.3 was achieved with the aid of a base. 0.415 gr HNO.sub.3-loaded IL-NO.sub.3z=1.01 and 0.263 gr NaHCO.sub.3 solution (20.3 wt %) were mixed using a vortex mixer for 5 minutes at 98° C. Then the ionic liquid was analyzed for H.sup.+ by titration with standard sodium hydroxide. The results are shown in Table 7.

TABLE-US-00007 TABLE 7 IL- NO.sub.3 phase composition after stripping Initial condition HNO.sub.3 in IL-NO.sub.3 NaHCO.sub.3/HNO.sub.3 IL- NO.sub.3 wt % Z mole/mole wt % Z 12.6 1.01 0.8 2.5 0.203

[0102] Nitrate is effectively stripped from the ionic liquid by sodium bicarbonate alkaline solution. Note that the ionic liquid was present in molar excess relative to the bicarbonate, and hence Z was reduced from 1.01 to 0.203. But with the aid of larger amount of NaHCO.sub.3full stripping could have been achieved.

EXAMPLE 6

Stripping of HNO.SUB.3 .from HNO.SUB.3.-Loaded [IL-NO.SUB.3.].SUB.z=1.01

[0103] The stripping of HNO.sub.3 from loaded IL-NO.sub.3 was achieved with the aid of an alkaline potassium nitrate solution (stripping solution consisting of KOH 2 wt % in 25 wt % KNO.sub.3 solution).

[0104] 0.8428 gr [IL-NO.sub.3].sub.z=1.01 and 4.087 gr of a solution composed of 25% KNO.sub.3+2.13 wt % KOH were mixed using a vortex mixer for 5 minutes at 98° C. The resultant clear organic and aqueous phases were analyzed for H+ by titration with standard sodium hydroxide. The results are shown in Table 8.

TABLE-US-00008 TABLE 8 IL-NO.sub.3 Aqua phase phase composition composition HNO.sub.3 HNO.sub.3 KNO.sub.3 wt % Z wt % wt % 1.0 0.080875 0.02 28.8

[0105] The stripping reaction that liberates the HNO.sub.3 from the ionic liquid and transforms it into potassium nitrate solution is:

IL-NO.sub.3-HNO.sub.3+KOH.fwdarw.IL-NO.sub.3+KNO.sub.3+H.sub.2O

[0106] The extraction of HNO.sub.3 from the IL-NO.sub.3 phase with KOH solution is very efficient. The aqueous solution obtained after the extraction is at natural pH.

EXAMPLE 7

action of Ntric Aid from a Mxture of Srong Aids and Sripping into Aueous Pase at Hgher Cncentration

[0107] FIG. 5 emphasizes an important finding emerging from the results reported in Example 1 (extraction of HNO.sub.3 from an aqueous mixture of acids with the aid of the ionic liquid) and Example 2 (separation of HNO.sub.3 from HNO.sub.3 aqueous stream).

[0108] The coordinates of the triangle points are: [0109] { [HNO.sub.3].sub.aqueous phase; [HNO.sub.3].sub.IL-NO3}.sub.i, where [HNO.sub.3].sub.aqueous phase indicates the concentration of HNO.sub.3 in the aqueous phase and [HNO.sub.3].sub.IL-NO3 indicates the concentration of HNO.sub.3 in the ionic liquid for each of the six experiments (i=1,2,3,4,5,6), based on FIG. 1, which is related to the separation of HNO.sub.3 from a mixture of strong mineral acids (HNO.sub.3+H.sub.2SO.sub.4+HCl mixture).

[0110] The coordinates of the circle points are: [0111] { [HNO.sub.3].sub.aqueous phase; [HNO.sub.3].sub.IL-NO3}.sub.j, where [HNO.sub.3].sub.aqueous phase indicates the concentration of HNO.sub.3 in the aqueous phase and [HNO.sub.3].sub.IL-NO3 indicates the concentration of HNO.sub.3 in the ionic liquid for each of the nine experiments (i=1,2,3,4,5, 6,7,8,9), based on FIG. 2, which is related to the separation of HNO.sub.3 from dilute HNO.sub.3 stream.

[0112] It is seen that the partition coefficient of nitric acid Kd.sub.HNO3 increases in the presence of other acids in the aqueous stream from which HNO.sub.3 is to be removed, as indicated by the sharp slope of the curve formed by triangle points. On the other hand, Kd.sub.HNO3 measured for the series of experiments in which HNO.sub.3 was extracted from aqueous stream devoid of other acids is roughly 1. Consequently, one can benefit from the enhanced affinity displayed by [A.sup.+][NO.sub.3.sup.−].sub.z=0 towards nitrate in the presence of sulfate or chloride, in comparison with the ability of the ionic liquid to capture nitrate from dilute HNO.sub.3 solutions, by loading the ionic liquid with nitrate from a first aqueous solution consisting of a mixed acidic solution, reaching an equilibrium state wherein [HNO.sub.3].sub.IL-NO3 >> [HNO.sub.3].sub.first aqueous solution, and after removal of the readily washable acids (H.sub.2SO.sub.4, HCl) from the ionic liquid (if needed), stripping the nitrate from the ionic liquid to release HNO.sub.3 into a second aqueous solution. That is, moving from a point in the ‘triangle curve’ horizontally to a point on the ‘circles curve’ to create a second aqueous solution characterized in that the [HNO.sub.3].sub.second aqueous solution>> [HNO.sub.3].sub.first aqueous solution.

EXAMPLE 8

Separation of Nitric Acid from Aqueous Mixtures of HNO.SUB.3 .and Varying Concentrations of H.SUB.2.SO.SUB.4.with the Aid of IL-NO.SUB.3

[0113] A series of experiments (1-8) were made to correlate the distribution of HNO.sub.3 and H.sub.2SO.sub.4 with ionic liquid of Preparation 1 after HNO.sub.3 addition (11.7% HNO.sub.3). To this end, four solutions with different H.sub.2SO.sub.4 and HNO.sub.3 concentrations (see Table 9) were mixed at various proportions (see Table 10), using a vortex mixer for 5 minutes at 80° C.

TABLE-US-00009 TABLE 9 H.sub.2SO.sub.4 HNO.sub.3 (wt %) (wt %) solution 1 7.62 11.2 solution 2 0 12 solution 3 30.3 4.69 solution 4 37.2 1.4

TABLE-US-00010 TABLE 10 solution 1 solution 2 solution 3 solution 4 Water IL-NO.sub.3 + 11.7% Exp. (gr) (gr) (gr) (gr) (gr) HNO.sub.3 (gr) 1 0.449 0.734 5.28 2 0.615 0.34 4.96 3 0.843 5.17 4 1.052 1.654 5.44 5 0.582 0.365 5.23 6 0.806 0.224 4.97 7 0.779 5.06 8 0.89 5.3

[0114] In all cases, the resultant liquid consists of clear IL-NO.sub.3 phase and aqueous phase. Concentrations of the two acids in the two phases were determined as follows:

[0115] [H.sup.+] in the aqueous and IL-NO.sub.3 phases was determined by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0116] [NO.sub.3.sup.−] in the aqueous phase was measured by NO.sub.3 electrode (nitrate Ion Meter NO.sub.3-11 electrode from HORIBA).

[0117] [NO.sub.3.sup.−] in the IL-NO.sub.3 was determined by calculating the difference between the H+ and the SO.sub.4.sup.2− concentration.

[0118] [SO.sub.4.sup.2−] in the IL-NO.sub.3 was measured by washing the acids from the IL-NO.sub.3 with water and H.sub.2O.sub.2 then measuring by visocolor sulfate test (Machery-Nagel).

[0119] [SO.sub.4.sup.2−] in the aqueous phase was determined by calculating the difference between the H+ and the NO.sub.3.sup.− concentrations.

[0120] The results are tabulated in Table 11.

TABLE-US-00011 TABLE 11 Distribution Selectivity aqueous phase Ionic liquid phase coefficient constant Exp. HNO.sub.3 H.sub.2SO.sub.4 HNO.sub.3 H.sub.2SO.sub.4 NO.sub.3 H.sub.2SO.sub.4 NO.sub.3/SO.sub.4 No. wt % wt % t % t % Kd d selectivity 1 1.4 3.8 1.7 0.113 1.03 0.030 35 2 2.5 4.3 12.1 0.10 0.97 0.024 40 3 9.31 7.0 11.7 0.16 1.26 0.023 56 4 4.54 12.0 10.9 0.46 2.39 0.038 62 5 3.71 20.8 11.3 0.83 3.04 0.040 76 6 3.05 27.2 12.2 1.25 4.02 0.046 87 7 2.00 32.2 12.0 1.81 6.00 0.056 107 8 1.00 36.5 12.7 2.04 12.79 0.056 228

[0121] Results are also presented graphically in FIG. 6, where selectivity is plotted versus concentration of sulfuric acid. Counterintuitively, it is seen that distribution coefficient and the selectivity of nitrate removal by the ionic liquid increase with increasing concentration of the sulfate “competitor”.

EXAMPLE 9

Separation of Nitric Acid from a Mixture of H.SUB.3.PO.SUB.4 .and HNO.SUB.3 .with IL-NO.SUB.3

[0122] A series of experiments were made to measure the distribution of HNO.sub.3 and H.sub.3PO.sub.4 with ionic liquid of Preparation 1 (IL-NO.sub.3). To this end, solution C1 (which consists of 4.3 wt % HNO.sub.3 and 18.4% H.sub.3PO.sub.4 in water) or solution C2 (which consist of 7.5 wt % HNO.sub.3 and 21 wt % H.sub.3PO.sub.4 in water) and IL-NO.sub.3 were mixed at various proportions set out in Table 12, using a vortex mixer for 5 minutes at 850° C.

TABLE-US-00012 TABLE 12 Solution C1 Solution C.sub.2 IL-NO.sub.3 Experiment No. (gr) (gr) (gr) 1 0.613 0.928 2 0.752 0.9 3 0.758 2.0 4 0.840 0.840 5 0.868 0.868 6 1.370 1.370

[0123] In all cases, the resultant liquid consists of clear IL-NO.sub.3 phase and aqueous phase. Concentrations of the two acids were determined as follows:

[0124] [H+] was determined separately in each phase by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0125] [NO.sub.3.sup.−] in the aqueous phase was measured by NO.sub.3 electrode (nitrate Ion Meter NO.sub.3.sup.−11 LAQUA twin electrode from HORIBA).

[0126] [NO.sub.3.sup.−] in the IL-NO.sub.3 was measured by washing the acids from the IL-NO.sub.3 with sodium bicarbonate solution and H.sub.2O.sub.2 then measuring by the NO.sub.3 electrode.

[0127] [PO.sub.4.sup.3−] in the IL-NO.sub.3 was determined by calculating the difference between H.sup.+ and NO.sub.3.sup.− concentrations.

[0128] [PO.sub.4.sup.3−] in the aqueous phase was determined by calculating the difference between H.sup.+ and NO.sub.3.sup.− concentrations.

[0129] The results are tabulated in Table 13.

TABLE-US-00013 TABLE 13 Aqueous phase IL-NO.sub.3 phase Distribution Selectivity composition composition coefficient constant HNO.sub.3 H.sub.3PO.sub.4 HNO.sub.3 H.sub.3PO.sub.4 NO.sub.3 H.sub.3PO.sub.4 NO.sub.3/PO.sub.4 wt % wt % wt % wt % Kd Kd selectivity 1 2.35 16.1 3.78 1.9 1.61 0.12 14.0 2 2.95 17.3 4.57 1.9 1.55 0.11 13.9 3 1.17 15.5 1.89 1.9 1.62 0.12 13.3 4 4.95 20.8 6.98 3.4 1.41 0.17 8.5 5 5.73 20.0 6.55 3.3 1.14 0.16 7.0 6 6.38 20.7 7.45 3.3 1.17 0.16 7.2

[0130] The results are also presented graphically in FIG. 7. The abscissa and ordinate of each point in the graph are (rhombuses-HNO.sub.3; squares-H3PO.sub.4): [0131] { [Y].sub.aqueous phase; [Y].sub.IL-NO3}.sub.i, where [Y].sub.aqueous phase indicates the concentration of the acid under consideration in the aqueous phase and [Y].sub.IL-NO3 indicates the concentration of the acid in the ionic liquid for each of the six experiments (i=1,2,3,4,5, 6), based on the data tabulated in Table 13.

EXAMPLE 10

Separation of Nitric Acid from a Mixture of H.SUB.2.SO.SUB.4 .and HNO.SUB.3 .with IL-NO.SUB.3 .in a Solvent

[0132] A series of experiments were conducted to measure the distribution of HNO.sub.3 and H.sub.2SO.sub.4 with the ionic liquid of Preparation 1 (IL-NO.sub.3 70% in decane). To this end, solution D (which consists of 10.1 wt % HNO.sub.3 and 24% H.sub.2SO.sub.4 in water) and IL-NO.sub.3 in decane were mixed at various proportions set out in Table 14, using a vortex mixer for 5 minutes at 650° C.

TABLE-US-00014 TABLE 14 IL-NO.sub.3 70% Solution D in decane Experiment No. (gr) (gr) 1 0.613 1.640 2 0.752 2.290 3 0.758 1.051 4 0.845 0.774 5 1.700 0.808 6 2.800 0.778 7 3.070 0.764

[0133] In all cases, the resultant liquid consists of clear IL-NO.sub.3 phase and aqueous phase. Concentrations of the two acids were determined as follows: [0134] [H+] was determined separately in the aqueous and organic phases by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0135] [NO.sub.3.sup.−] in the aqueous phase was measured by NO.sub.3 electrode (nitrate Ion Meter NO.sub.3.sup.−11 LAQUA twin electrode from HORIBA).

[0136] [NO.sub.3.sup.−] in the IL-NO.sub.3 was measured by washing the acids from the IL-NO.sub.3 with sodium bicarbonate solution and H.sub.2O.sub.2 then measuring by the NO.sub.3 electrode.\

[0137] [SO.sub.4.sup.2−] in the IL-NO.sub.3 was determined by calculating the difference between H+ and NO.sub.3.sup.−concentrations.

[0138] [SO.sub.4.sup.2−] in the aqueous phase was determined by calculating the difference between H.sup.+ and NO.sub.3.sup.− concentrations.

[0139] The results are tabulated in Table 15.

TABLE-US-00015 TABLE 15 Aqueouse phase IL-NO3 in decane Distribution Selectivity composition phase composition coefficient constant Exp. HNO.sub.3 H.sub.2SO.sub.4 HNO.sub.3 H.sub.2SO.sub.4 HNO3 H2SO4 HNO.sub.3 H.sub.2SO.sub.4 HNO.sub.3/H.sub.2SO.sub.4 No. wt % wt % wt % wt % Z Z Kd Kd selectivity 1 0.61 23.6 2.76 2.45 0.35 0.20 4.54 0.10 44 2 0.54 14.9 2.80 1.74 0.35 0.14 5.15 0.12 44 3 1.20 18.2 4.08 1.56 0.51 0.13 3.40 0.09 40 4 2.10 17.8 5.20 1.49 0.66 0.12 2.48 0.08 30 5 3.67 18.9 7.14 0.77 0.92 0.065 1.94 0.04 48 6 4.30 18.7 8.10 0.49 1.05 0.041 1.88 0.03 72

EXAMPLE 11

Separation of Nitric Acid from a Mixture of H.SUB.2.SO.SUB.4 .and HNO.SUB.3 .with Aliquat336-NO.SUB.3

[0140] A series of experiments were performed to measure the distribution of HNO.sub.3 and H.sub.2SO.sub.4 with ionic liquid of Preparation 2 (Aliquat 336-NO.sub.3). To this end, Solution A (which consists of 6.7 wt % HNO.sub.3 and 20% H.sub.2SO.sub.4 in water) and Aliquat 336-NO.sub.3 were mixed at various proportions set out in Table 16, using a vortex mixer for 5 minutes at 800° C.

TABLE-US-00016 TABLE 16 Solution A Aliquat Experiment No. (gr) 336-NO.sub.3 1 2.40 0.919 2 1.22 1.400 3 0.61 1.370 4 1.27 0.686 5 2.20 0.768

[0141] In all cases, the resultant liquid consists of clear Aliquat 336-NO.sub.3 phase and aqueous phase. Concentrations of the two acids were determined as follows: [0142] [H+] was determined separately in the aqueous and organic phases by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0143] [NO.sub.3.sup.−] in the aqueous phase was measured by NO.sub.3 electrode (nitrate Ion Meter NO.sub.3.sup.−11 LAQUA twin electrode from HORIBA).

[0144] [NO.sub.3.sup.−] in the IL-NO.sub.3 was measured by washing the acids from the IL-NO.sub.3 with sodium bicarbonate solution and H.sub.2O.sub.2 then measuring by the NO.sub.3 electrode.

[0145] [SO.sub.4.sup.2−] in the IL-NO.sub.3 was determined by calculating the difference between H+ and NO.sub.3.sup.− concentrations.

[0146] [SO.sub.4.sup.2−] in the aqueous phase was determined by calculating the difference between H.sup.+ and NO.sub.3.sup.− concentrations.

[0147] The results are tabulated in Table 17.

TABLE-US-00017 TABLE 17 aqueous phase Ionic liquid phase Experiment HNO.sub.3 H.sub.2SO.sub.4 HNO.sub.3 H.sub.2SO.sub.4 NO3 H2SO4 HNO.sub.3 H.sub.2SO.sub.4 NO3/SO4 No. wt % wt % wt % wt % Z Z Kd Kd selectivity 1 1.57 18.8 3.38 4.61 0.24 0.21 2.15 0.25 8.7 2 1.35 14.4 2.60 5.10 0.18 0.23 1.92 0.35 5.4 3 1.21 11.0 2.40 3.15 0.16 0.14 1.98 0.29 6.9 4 3.51 18.9 7.40 2.59 0.53 0.12 2.11 0.14 15.3 5 4.36 19.7 7.53 3.58 0.54 0.17 1.73 0.18 9.5

[0148] The results are shown graphically in FIGS. 8 and 9 (Z versus [HNO.sub.3] in the aqueous solution and selectivity versus [HNO.sub.3] in the aqueous solution, respectively), including the data pertaining to IL-NO.sub.3. The results indicate the better performance of phosphonium ionic liquid (P66614 marked by squares) compared to ammonium ionic liquid (marked by rhombuses).

EXAMPLE 12

Separation of Nitric Acid from a Mixture of HNO.SUB.3., H2SO.SUB.4 .and KF with IL-NO.SUB.3

[0149] An experiment was performed to measure the distribution of NO.sub.3.sup.−, SO.sub.4.sup.2− and F.sup.− with ionic liquid of Preparation 1 (IL-NO3). To this end, 2.9 gr of solution consisting of 8.7% KF, 7.9% HNO.sub.3 and 18.7% H.sub.2SO.sub.4 in water and 3.5 gr IL-NO.sub.3 were mixed using a vortex mixer for 5 minutes at 80° C.

[0150] The resultant liquid consists of clear organic and aqueous phases. Concentrations of the two acids were determined as follows: [0151] [H.sup.+] was determined separately in each phase by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0152] [NO.sub.3] in the aqueous phase was measured by NO.sub.3 electrode (nitrate Ion Meter NO.sub.3.sup.−11 LAQUA twin electrode from HORIBA).

[0153] [NO.sub.3] in the IL-NO.sub.3 was measured by washing the acids from the IL-NO.sub.3 with sodium bicarbonate solution and H.sub.2O.sub.2 then measuring by NO.sub.3 electrode.

[0154] [SO.sub.4] in the IL-NO.sub.3 was measured by washing the acids from the IL-NO.sub.3 with sodium bicarbonate solution and H.sub.2O.sub.2 then measuring by visocolor sulfate test (Machery-Nagel).

[0155] [SO.sub.4] in the aqueous phase was calculated by mass balance.

[0156] HF in the IL-NO.sub.3 was determined by calculating the difference between H+ concentration and the sum of the NO.sub.3.sup.−+SO.sub.4.sup.− concentrations.

[0157] [F] in the aqueous phase was calculated by mass balance.

[0158] The results are tabulated in Table 18.

TABLE-US-00018 TABLE 18 Aqueous phase IL-NO3 phase Distribution composition composition coefficient Selectivity NO.sub.3.sup.− F.sup.− SO.sub.4.sup.− HNO.sub.3 HF H.sub.2SO.sub.4 NO.sub.3.sup.− F.sup.− SO.sub.4.sup.− constant wt % Wt % Wt % wt % Wt % wt % Kd Kd Kd NO.sub.3/F NO.sub.3/SO.sub.4 3.68 1.19 15.8 4.55 0.53 2.4 1.24 0.22 0.13 5.6 9.5

EXAMPLE 13

Separation of Mercury from a Mixture of HNO.SUB.3 .and HgCl.SUB.2 .with IL-NO.SUB.3

[0159] One experiment was performed to measure the partition of water-soluble mercury salt (HgCl.sub.2) between an aqueous solution and an ionic liquid bearing nitrate as counter ion, IL-NO.sub.3. To this end, a solution consisting of 31.2 wt % HNO.sub.3 and 119 ppm HgCl.sub.2 in water and 5.1 gr IL-NO.sub.3 were mixed using a vortex mixer for 5 minutes at 80° C. Sample from the aqueous phase was taken for analysis with DMA-80 by MILESTONE INC mercury analyzer.

[0160] [HNO.sub.3] in the IL-NO.sub.3 was determined by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0161] [HNO.sub.3] in the aqueous phase was determined by titration with standard sodium hydroxide (0.1N solution using Phenolphthalein indicator).

[0162] The results are shown in Table 19.

TABLE-US-00019 TABLE 19 Aqueous phase IL-NO3 phase Distribution composition composition coefficient Selectivity HNO.sub.3 Hg HNO.sub.3 Hg NO.sub.3 Hg constant Wt % ppm Wt % ppm Kd Kd NO.sub.3/Hg 10.71 0.07 10.19 47 0.95 672 0.0014

[0163] The results indicate that mercury ions are captured in the organic (ionic liquid) phase and their escape to the aqueous phase is negligible. The mercury could then be recovered from the ionic liquid.

[0164] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.