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 treating a H.sub.2S-containing fluid stream, the method comprising: (a) contacting a H.sub.2S -containing fluid stream with a ferrihydrite slurry, wherein the ferrihydrite slurry includes ferrihydrite nanoparticles and a 2LI promotor wherein the contacting step results in (i) a treated fluid stream comprising less H.sub.2S than the H.sub.2S -containing stream and (ii) a used slurry including ferrous sulfide, a 2LI promotor, and a first sulfur concentration of sulfur obtained from the H.sub.2S -containing stream; (b) regenerating the used slurry to obtain elemental sulfur and a regenerated ferrihydrite slurry, wherein regenerating includes: (i) contacting the used slurry with an oxidizing agent thereby converting at least some of the sulfur in the used slurry into elemental sulfur and converting at least some of the ferrous sulfide in the used slurry into regenerated ferrihydrite thereby forming regenerated ferrihydrite slurry; and (ii) separating the elemental sulfur from the regenerated ferrihydrite slurry, wherein the regenerated ferrihydrite slurry includes ferrihydrite nanoparticles and a 2LI promotor and a second sulfur concentration less than the first sulfur concentration of the used slurry; wherein the 2LI promotor is selected from the group consisting of D-sorbitol, alkali metasilicates and combinations thereof.

2. The method of claim 1, wherein steps (a) through (b) are repeated with the regenerated ferrihydrite slurry.

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

4. The method of claim 2, wherein the H.sub.2S -containig fluid stream is natural gas.

5. The method of claim 2, wherein the H.sub.2S -containing fluid stream is off-gas.

6. The method of claim 2, wherein the H.sub.2S -containig fluid stream is sour crude oil.

7. The method of claim 2, wherein the H.sub.2S -containig fluid stream is sour water.

8. The method of claim 2, wherein the H.sub.2S concentration of the treated fluid stream is 4 ppm or less.

9. The method of claim 2, wherein the oxidizing agent is oxygen from air.

10. The method of claim 2, wherein the regenerated ferrihydrite slurry realizes a six-cycle activity of at least 6.0, and at least three of the cycles realize a slurry activity of at least 1.0.

11. The method of claim 2 wherein the regenerated ferrihydrite slurry realizes a six-cycle loss of not greater than 45%.

12. The method of claim 2 wherein the regenerated ferrihydrite slurry realizes a six-cycle capture efficiency average of at least 92% and a six-cycle standard deviation of not greater than 1.75%.

13. The method of claim 2 wherein elemental sulfur is separated from the used slurry in a regenerator.

14. The method of claim 13 wherein an output of the regenerator is regenerated ferrihydrite slurry that is used in a subsequent contacting operation.

15. The method of claim 2, wherein the oxidizing agent is air.

16. The method of claim 2, wherein the H.sub.2S -containig fluid stream is a gas containing CO2.

17. The method of claim 2, wherein the contacting further comprises: flowing the H.sub.2S -containing fluid stream into a contactor containing the ferrihydrite slurry; and removing the treated fluid stream comprising less H.sub.2S than the H.sub.2S -containing stream from the contactor.

18. The method of claim 2, wherein regenerating further comprises: transferring used slurry from a contactor that performs the contacting operation a) to a regenerator that performs the regeneration operation b); and transferring regenerated ferrihydrite slurry from the regenerator to the contactor.

19. The method of claim 2, further comprising: flowing the H.sub.2S-containing fluid stream into a contacting column containing the ferrihydrite slurry; removing the treated fluid stream comprising less H.sub.2S than the H.sub.2S -containing stream from the contacting column; transferring used slurry from a contactor that performs the contacting operation a) to a regenerator that performs the regeneration operation b); and transferring regenerated ferrihydrite slurry from the regenerator to the contactor.

20. The method of claim 19 wherein the contactor is a first column and the regenerator is a second column.

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 H.SUB.2.S 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 moles of Average sulfur captured per Loss Capture Standard Cycle 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 H.SUB.2.S 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 H.SUB.2.S 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 H.SUB.2.S 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 H.SUB.2.S 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 H.SUB.2.S 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 H.SUB.2.S 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 Invention Cycle Cycle Run-to- Capt. Stand. 1.0 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.