Methods of producing ferrihydrite nanoparticle slurries, and systems and products employing the same

Abstract

The present disclosure relates to methods of synthesizing slurries comprising ferrihydrite nanoparticles, and systems and methods employing the same. The method may include the steps of preparing an aqueous solution having ferric iron cations, halide anions, and a two-line iron promoter, and precipitating the ferrihydrite nanoparticles in the aqueous solution, thereby producing a ferrihydrite slurry. The ferrihydrite slurries may be useful in treating a polluted fluid having sulfur contaminants therein.

Claims

1. A method for producing a slurry comprising ferrihydrite nanoparticles, the method comprising: (a) preparing an aqueous solution having ferric iron cations, halide anions, and a 2LI promoter, wherein the preparing comprises: (i) adding an iron salt to the aqueous solution; (ii) adding a two-line iron promoter to the aqueous solution; (A) wherein, due to the adding steps (i) and (ii), the aqueous solution comprises a molar ratio of from 1:10 to 1:100 of the two-line iron promoter to iron (Fe) (promoter:Fe); (B) wherein, due to the adding steps (i) and (ii), the aqueous solution realizes an acidic pH; (b) precipitating ferrihydrite nanoparticles in the aqueous solution, thereby producing a ferrihydrite slurry, wherein the precipitating comprises: (i) contacting the aqueous solution with an alkali caustic, thereby raising the pH of the aqueous solution, wherein, after the contacting, the ferrihydrite slurry comprises ferrihydrite, the 2LI promoter, at least some alkali ions, and at least some of the halide anions; wherein the iron salt is selected from the group of consisting of ferrous chloride, ferric chloride and combinations thereof; wherein the 2LI promoter is selected from the group consisting of alcohols, polyols, polysaccharides, alkali metasilicates, and combinations thereof.

2. The method of claim 1, wherein the iron salt is ferric chloride.

3. The method of claim 1, wherein the 2LI promoter is selected from the group consisting of D-sorbitol, sodium metasilicate, and combinations thereof.

4. The method of claim 1, wherein the contacting step (b) comprises contacting the aqueous solution with the caustic at a rate such that at least 80% of the total amount of the caustic is added to the prepared aqueous solution within 2 hours.

5. The method of claim 4, wherein, after the contacting step (a), the aqueous solution is free of akaganeite.

6. The method of claim 5, wherein the ferrihydrite nanoparticles consist essentially of twoline iron nanoparticles.

7. A method for producing a slurry comprising ferrihydrite nanoparticles, the method comprising: (a) preparing an aqueous solution having ferric iron cations, halide anions, and a 2LI promoter, wherein the preparing comprises: (i) adding an iron salt to the aqueous solution; (ii) adding a two-line iron promoter to the aqueous solution; (A) wherein, due to the adding steps (i) and (ii), the aqueous solution comprises a molar ratio of from 1:2 to 1:1000 of the two-line iron promoter to iron (Fe) (promoter:Fe); (B) wherein, due to the adding steps (i) and (ii), the aqueous solution realizes an acidic pH; (b) precipitating ferrihydrite nanoparticles in the aqueous solution, thereby producing a ferrihydrite slurry, wherein the precipitating comprises: (i) contacting the aqueous solution with an alkali caustic, thereby raising the pH of the aqueous solution, wherein, after the contacting, the ferrihydrite slurry comprises ferrihydrite, the 2LI promoter, at least some alkali ions, and at least some of the halide anions; wherein the 2LI promoter is selected from alcohols, polyols, polysaccharides, alkali metasilicates and combinations thereof.

8. The method of claim 7, wherein the 2LI promoter is selected from D-sorbitol, sodium metasilicate, and combinations thereof.

9. The method of claim 7, wherein the iron salt is selected from the group of consisting of ferrous chloride, ferric chloride and combinations thereof.

10. The method of claim 7, wherein the iron salt is ferric chloride.

11. The method of claim 7, wherein the contacting step (b) comprises contacting the aqueous solution with the caustic at a rate such that at least 80% of the total amount of the caustic is added to the prepared aqueous solution within 2 hours.

12. The method of claim 11, wherein, after the contacting step (a), the aqueous solution is free of akaganeite.

13. The method of claim 7, wherein the ferrihydrite nanoparticles consist essentially of twoline iron nanoparticles.

14. A method for producing a slurry comprising ferrihydrite nanoparticles, the method comprising: (a) preparing an aqueous solution having ferric iron cations, halide anions, and a 2LI promoter, wherein the preparing comprises: (i) adding an iron salt to the aqueous solution; (ii) adding a two-line iron promoter to the aqueous solution; (A) wherein, due to the adding steps (i) and (ii), the aqueous solution comprises a molar ratio of from 1:2 to 1:1000 of the two-line iron promoter to iron (Fe) (promoter:Fe); (B) wherein, due to the adding steps (i) and (ii), the aqueous solution realizes an acidic pH; (b) precipitating ferrihydrite nanoparticles in the aqueous solution, thereby producing a ferrihydrite slurry, wherein the precipitating comprises: (i) contacting the aqueous solution with an alkali caustic, thereby raising the pH of the aqueous solution, wherein, after the contacting, the ferrihydrite slurry comprises ferrihydrite, the 2LI promoter, at least some alkali ions, and at least some of the halide anions; wherein the 2LI promoter is selected from D-sorbitol, sodium metasilicate, and combinations thereof.

15. The method of claim 14, wherein the iron salt is selected from the group of consisting of ferrous chloride, ferric chloride and combinations thereof.

16. The method of claim 15, wherein the ferrihydrite nanoparticles consist essentially of twoline iron nanoparticles.

17. The method of claim 15, wherein the iron salt is ferric chloride.

18. The method of claim 15, wherein the contacting step (b) comprises contacting the aqueous solution with the caustic at a rate such that at least 80% of the total amount of the caustic is added to the prepared aqueous solution within 2 hours.

19. The method of claim 18, wherein, after the contacting step (a), the aqueous solution is free of akaganeite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic flow diagram of one embodiment of a method for producing a ferrihydrite slurry as described in this patent application.

(2) FIG. 2 is a schematic view of one method of producing an aqueous solution having ferric iron cations, 2LI promoter, and halide anions therein.

(3) FIG. 3 is a schematic view of one method of precipitating ferrihydrite nanoparticles from the aqueous solution shown in FIG. 2.

(4) FIG. 4a is a schematic view of an arrangement for a ferrihydrite slurry to treat a polluted fluid.

(5) FIG. 4b is a schematic view of an arrangement for regenerating a used ferrihydrite slurry via an oxygen-containing fluid.

(6) FIG. 4c is a schematic view of a dual column approach to using batches of ferrihydrite slurry so as to facilitate continuous treatment of a polluted sulfur-containing stream.

(7) FIG. 4d is a schematic view of a dual column approach employing continuous recirculation so as to facilitate continuous treatment of a polluted sulfur-containing stream. The ferrihydrite slurry of FIG. 4d may be continuously regenerated.

(8) FIGS. 5a-5b are SEMs of the ferrihydrite nanoparticles of Example 1.

(9) FIG. 5c is a graph showing the ferrihydrite slurry activity and capture efficiency for the ferrihydrite slurry of Example 1.

(10) FIGS. 6-12 are graphs showing the ferrihydrite slurry activity and capture efficiency for the ferrihydrite slurries of Examples 3-9, respectively.

DETAILED DESCRIPTION

Example 1Synthesis of a 1 wt. % Ferrihydrite Slurry Using Ferric Chloride and D-Sorbitol

(11) An aqueous slurry comprising 1 wt. % two-line iron, 0.05 mole of D-sorbitol and 3 mole of sodium chloride for every 1 mole of ferric iron was made by the following synthesis procedure. A total of 0.6 g of anhydrous D-sorbitol was added to 304.7 mL of deionized water, followed by the addition of 10.1 g of anhydrous ferric chloride. The resulting solution had a molar ratio of D-sorbitol to iron of about 1:20. Once the salt was dissolved and the solution cooled to ambient temperature, 1M sodium hydroxide at room temperature was added from a burette at a fast rate with stirring until the solution reached a pH of about 3. Additional sodium hydroxide was added at a slow dropwise rate until pH of about 7 was reached for a total sodium hydroxide addition of approximately 187.4 mL. The total time to reach pH 7 was approximately 30 minutes. An XRD analysis confirmed that the iron nanoparticles formed in this synthesis consist essentially of two-line iron nanoparticles. The two-line iron nanoparticles had an average surface area of about 306 m.sup.2/g as determined by BET (N.sub.2) and a particle size less than 100 nanometers as determined by SEM.

Example 2Testing of H2S Capture Efficiency of the Two-Line Iron Slurry Made from Ferric Chloride and D-Sorbitol

(12) A two-line iron slurry synthesized as per Example 1 was tested for its H.sub.2S capture efficiency and regenerability. In particular, H.sub.2S was supplied from a compressed gas cylinder containing a 10% by volume hydrogen sulfide in a balance of nitrogen and mixed with nitrogen to generate an inlet concentration of approximately 2000 ppm H.sub.2S. Alicat Scientific mass flow controllers were used to precisely control the inlet concentration at a total flow rate of 0.5 SLPM. Once mixed, the gases were supplied to the bottom of a 3-foot tall, one-half inch Sch. 80 clear PVC bubble column and went through an EPDM gasket sparger. A total of 20 mL of the 1 wt. % slurry was tested. The outlet hydrogen sulfide concentration was measured by a Shimadzu GC-14A gas chromatograph using a FPD detector and Agilent Hayesep Q 80-100 mesh column. FIG. 5c shows the six-cycle activity and capture efficiency of the slurry. Over the six cycles, the H.sub.2S capture efficiency was consistently greater than 95% until breakthrough. After each cycle, the slurry was regenerated by simple exposure to ambient air for about 30 minutes. Table 2, below, shows collected data for each cycle. The ferrihydrite slurry realizes a six-cycle activity of 7.89, a six-cycle capture efficiency of 98%, a six-cycle loss of 22%, and a six-cycle standard deviation of 0.36%. Further, all six capture cycles realized an activity of at least 1.16, the largest run-to-run loss was 9%, and the largest single capture cycle standard deviation was 0.81. After the first capture cycle, the largest single capture cycle deviation was 0.41%.

(13) TABLE-US-00002 TABLE 2 Slurry activity and loss for two-line iron nanoparticles synthesized from ferric chloride and stabilized with D-sorbitol Activity (cumulative Average moles of sulfur captured Loss Capture Standard Cycle per mole of iron) (run-to-run) Efficiency Deviation 1 1.48 97% 0.81% 2 1.45 2% 99% 0.18% 3 1.33 9% 98% 0.41% 4 1.27 4% 99% 0.33% 5 1.20 6% 98% 0.20% 6 1.16 4% 98% 0.22% TOTAL 7.89 22% 98% 0.36%

Example 3Testing of H2S Capture Efficiency of the Two-Line Iron Slurry Made from Ferric Sulfate and D-Sorbitol

(14) A ferrihydrite slurry similar to Example 1 was prepared, except using ferric sulfate as the iron salt instead of ferric chloride. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2. FIG. 6 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. As shown in Table 3, the six-cycle activity only reaches 6.43, with a total loss in activity of 50%, and a six-cycle standard deviation of 1.82%. Further, three cycles were below an activity of 1.0, the largest run-to-run loss was 31% and the largest standard deviation was 4.34%.

(15) TABLE-US-00003 TABLE 3 Slurry activity and loss for ferrihydrite slurry synthesized from ferric sulfate and stabilized with D-sorbitol Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.32 92% 2.42% 2 1.50 13% 97% 0.26% 3 1.05 30% 92% 2.38% 4 0.94 11% 98% 0.51% 5 0.96 2% 97% 1.03% 6 0.66 31% 96% 4.34% TOTAL 6.43 50% 95% 1.82%

Example 4Testing of H2S Capture Efficiency of the Two-Line Iron Slurry Made from Ferric Chloride without Use of a Two-Line Iron Promoter

(16) A ferrihydrite slurry similar to Example 1 was prepared, except D-sorbitol was not employed. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2. FIG. 7 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. The six-cycle activity was 8.10, the six-cycle loss was 31%, the six-cycle capture efficiency was 96%, and the six-cycle standard deviation was 0.28%. Further, all six capture cycles realized an activity of at least 1.13, the largest run-to-run loss was 11%, and the largest single capture cycle standard deviation was 0.76%. After the first capture cycle, the largest single capture cycle deviation was 0.34%.

(17) TABLE-US-00004 TABLE 4 Slurry activity and loss for ferrihydrite slurry synthesized from ferric chloride Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.65 96% 0.76% 2 1.49 10% 93% 0.34% 3 1.33 11% 96% 0.15% 4 1.25 6% 96% 0.18% 5 1.26 1% 96% 0.16% 6 1.13 11% 98% 0.08% TOTAL 8.10 31% 96% 0.28%

Example 5Production of Ferrihydrite Slurry with Slow Caustic Addition

(18) A ferrihydrite slurry similar to Example 1 was prepared, except NaOH was slowly added at a constant rate over about a 3.5 hour period, resulting in the formation of both two-line iron and akaganeite. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2. FIG. 8 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. The six-cycle activity was 6.92, the six-cycle loss was 28%, the six-cycle capture efficiency was 92%, and the six-cycle standard deviation was 2.85%. Further, two of the capture cycles realized an activity of at less than 1.0, the largest run-to-run loss was 26%, and the largest single capture cycle standard deviation was 4.26%. After the first capture cycle, the largest single capture cycle deviation was 4.26%.

(19) TABLE-US-00005 TABLE 5 Slurry activity and loss for ferrihydrite slurry synthesized from ferric chloride Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.34 89% 3.63% 2 0.99 26% 89% 4.26% 3 1.01 2% 93% 4.10% 4 1.50 48% 93% 0.96% 5 1.12 25% 94% 2.10% 6 0.97 14% 95% 2.06% TOTAL 6.92 28% 92% 2.85%

Example 6Testing of H2S Capture Efficiency of the Two-Line Iron Slurry Made from Ferric Chloride and Sodium Metasilicate

(20) A ferrihydrite slurry similar to Example 1 was prepared, except sodium metasilicate was used in lieu of D-sorbitol and in a molar ratio of 70:1 iron to silicon. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2. FIG. 9 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. The six-cycle activity was 7.96, the six-cycle loss was 19%, the six-cycle capture efficiency was 93%, and the six-cycle standard deviation was 0.74%. Further, all six capture cycles realized an activity of at least 1.14, the largest run-to-run loss was 21%, and the largest single capture cycle standard deviation was 1.15%. After the first capture cycle, the largest single capture cycle deviation was 0.97%.

(21) TABLE-US-00006 TABLE 6 Slurry activity and loss for ferrihydrite slurry synthesized from ferric chloride and sodium metasilicate Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.54 93% 1.15% 2 1.44 6% 91% 0.97% 3 1.14 21% 93% 0.47% 4 1.32 15% 91% 0.54% 5 1.28 3% 93% 0.95% 6 1.25 3% 95% 0.36% TOTAL 7.96 19% 93% 0.74%

Example 7Testing of H2S Capture Efficiency of the Two-Line Iron Slurry Made from Ferric Chloride, D-Sorbitol and Sodium Metasilicate

(22) A ferrihydrite slurry similar to Example 1 was prepared, except sodium metasilicate was used in addition to the D-sorbitol and in a molar ratio of 70:1 iron to silicon. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2. FIG. 10 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. The six-cycle activity was 8.47, the six-cycle loss was 22%, the six-cycle capture efficiency was 97%, and the six-cycle standard deviation was 0.26%. Further, all six capture cycles realized an activity of at least 1.24, the largest run-to-run loss was 9%, and the largest single capture cycle standard deviation was 0.65%. After the first capture cycle, the largest single capture cycle deviation was 0.36%.

(23) TABLE-US-00007 TABLE 7 Slurry activity and loss for ferrihydrite slurry synthesized from ferric chloride, D-sorbitol and sodium metasilicate Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.58 95% 0.65% 2 1.55 2% 97% 0.36% 3 1.41 9% 98% 0.22% 4 1.36 4% 98% 0.08% 5 1.33 2% 97% 0.08% 6 1.24 7% 97% 0.15% TOTAL 8.47 22% 97% 0.26%

Example 8Testing of H2S Capture Efficiency of the Two-Line Iron Slurry Made from Ferric Chloride with Chloride Ions Removed

(24) A ferrihydrite slurry similar to Example 1 was prepared, except the alkali and halide (Cl.sup.) ions were removed by centrifuging, decanting the supernatant, and adding back deionized water a total of five times. In addition, the slurry contained about 0.5 wt. % two-line iron nanoparticles. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2, except the inlet H.sub.2S concentration was approximately 1000 ppm. FIG. 11 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. The six-cycle activity was 6.11, the six-cycle loss was 44%, the six-cycle capture efficiency was 93%, and the six-cycle standard deviation was 0.48%. Further, three of the six capture cycles realized an activity of less than 1.0, the largest run-to-run loss was 14%, and the largest single capture cycle standard deviation was 0.79%.

(25) TABLE-US-00008 TABLE 8 Slurry activity and loss for ferrihydrite slurry synthesized from ferric chloride with chlorine anions removed Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.35 92% 0.14% 2 1.20 11% 95% 0.40% 3 1.03 14% 94% 0.55% 4 0.95 8% 93% 0.52% 5 0.83 13% 93% 0.51% 6 0.75 9% 91% 0.79% TOTAL 6.11 44% 93% 0.48%

Example 9Testing of H2S Capture Efficiency of the Lepidocrocite Slurry Made from Ferrous Chloride

(26) A ferrihydrite slurry similar to Example 1 was prepared, except that ferrous chloride was used and NaOH was quickly added until pH 6-7 was reached, after which the solution was oxidized via an air sparger while maintaining the pH of 6-7 via regular NaOH addition. The resulting slurry contained 100% lepidocrocite as determined via IR. This slurry was diluted by deionized water to give a 0.5 wt. % ferrihydrite solution. The H.sub.2S capture efficiency and regenerability of this slurry was measured as per the conditions of Example 2, except the inlet H.sub.2S concentration was approximately 1000 ppm. FIG. 12 shows the capture efficiency of and activity of this ferrihydrite slurry for six cycles. The six-cycle activity was 6.90, the six-cycle loss was 18%, the six-cycle capture efficiency was 93%, and the six-cycle standard deviation was 0.35%. All six capture cycles realized an activity of at least 1.04, the largest run-to-run loss was 10%, and the largest single capture cycle standard deviation was 1.09%. After the first capture cycle, the largest single capture cycle deviation was 0.28%. As shown below, the capture efficiency increased for run 1 was only 85%, but the capture efficiency for runs 2-6 was 93%. Due to the increase in capture efficiency, it is believed that at least some two-line iron nanoparticles were produced when the fresh lepidocrocite slurry was regenerated, and that subsequent regeneration cycles also resulted in generation of two-line iron nanoparticles.

(27) TABLE-US-00009 TABLE 9 Slurry activity and loss for ferrihydrite slurry synthesized from ferrous chloride Average Loss Capture Standard Cycle Activity (run-to-run) Efficiency Deviation 1 1.27 85% 1.09% 2 1.16 9% 93% 0.20% 3 1.24 7% 94% 0.28% 4 1.11 10% 95% 0.27% 5 1.07 4% 94% 0.15% 6 1.04 3% 95% 0.10% TOTAL 6.90 18% 93% 0.35%

Analysis of Examples 1-9

(28) Table 10, below, compares the results of Examples 1-9. As shown, the slurries of Examples 3 and 5 are not considered invention slurries. The other slurries are considered invention slurries, being active, durable, and stable. The slurries of Examples 1 and 7 are particularly preferred, but the slurries of Examples 4, 6 and 8-9 are also useful.

(29) TABLE-US-00010 TABLE 10 Results of Examples 1-9 Six- Six- Cycles Six- Six- Largest Cycle Cycle below 1.0 Invention Cycle Cycle Run-to- Capt. Stand. in Ex. Slurry? Activity Loss Run Loss Effic. Dev. Activity 1-2 Yes 7.89 22% 9% 98% 0.36% Zero 3 No 6.43 50% 31% 95% 1.82% Three 4 Yes 8.10 31% 11% 96% 0.28% Zero 5 No 6.92 28% 26% 92% 2.85% Two 6 Yes 7.96 19% 21% 93% 0.74% Zero 7 Yes 8.47 22% 9% 97% 0.26% Zero 8 Yes 6.11 44% 14% 93% 0.48% Three 9 Yes 6.90 18% 10% 93% 0.35% Zero

(30) While various embodiments of the new technology described herein have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the presently disclosed technology.