METHOD AND APPARATUS FOR SULFUR REMOVAL

Abstract

Provided is a method for removing hydrogen sulfide from a gas stream. The method includes contacting the gas stream with a reactor that is configured to remove the hydrogen sulfide. The reactor includes at least one nano-sized metal.

Claims

1. A method for removing hydrogen sulfide (H.sub.2S) from a gas stream, the method comprising: contacting the gas stream with a reactor configured to remove the H.sub.2S, wherein the reactor comprises at least one nano-sized metal.

2. The method of claim 1, wherein the at least one nano-sized metal of the reactor is heated between approximately 200 C. and approximately 255 C. during the removal of the H.sub.2S.

3. The method of claim 1, wherein the at least one nano-sized metal acts as a catalyst to remove the H.sub.2S.

4. The method of claim 3, wherein the H.sub.2S is decomposed on a surface of the catalyst, and the decomposition produces hydrogen (H.sub.2) and Sulfur (S).

5. The method of claim 4, wherein the S is removed from the reactor by sublimation, and a substantial amount of the S does not remain in the reactor.

6. The method of claim 1, wherein the at least one nano-sized metal is not consumed during the removal of the H.sub.2S.

7. The method of claim 1, wherein the at least one nano-sized metal is copper.

8. The method of claim 1, wherein the at least one nano-sized metal is iron.

9. The method of claim 8, wherein an amount of the H.sub.2S removed from a gas stream is at least two times an amount of the iron in the reactor.

10. The method of claim 8, wherein the iron acts as a catalyst for at least seven cycles during the removal of the H.sub.2S, when heated to approximately 210 C.

11. The method of claim 8, wherein the iron acts as a catalyst for at least six cycles during the removal of the H.sub.2S, when heated to approximately 255 C.

12. A method for removing hydrogen sulfide (H.sub.2S) from a gas stream, the method comprising: contacting the gas stream with a reactor configured to remove the H.sub.2S, wherein the reactor comprises biochar and at least two nano-sized metals.

13. The method of claim 12, wherein the at least two nano-sized metals are not consumed to remove the H.sub.2S.

14. The method of claim 12, wherein a substantial amount of unconverted H.sub.2S does not accumulate within the reactor.

15. The method of claim 12, wherein the at least two nano-sized metals are copper and iron.

16. The method of claim 12, wherein the at least two nano-sized metals of the reactor are heated between approximately 200 C. and approximately 255 C. during the removal of the H.sub.2S.

17. The method of claim 12, wherein the at least two nano-sized metals act as a catalyst to remove the H.sub.2S.

18. The method of claim 17, wherein the H.sub.2S is decomposed on a surface of the catalyst, and the decomposition produces hydrogen (H.sub.2) and Sulfur (S).

19. The method of claim 18, wherein the S is removed from the reactor by sublimation, and a substantial amount of the S does not remain in the reactor.

20. An apparatus for removing hydrogen sulfide (H.sub.2S) from a gas stream, the apparatus comprising: a reactor configured to contacting the gas stream and remove the H.sub.2S, wherein the reactor comprises biochar and at least two nano-sized metals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other aspects, features and advantages of certain embodiments of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0023] FIG. 1 is a diagram of an H.sub.2S removal unit utilized to perform the examples described herein;

[0024] FIG. 2a is a graph of breakthrough curves of four biochar samples at 23 C.;

[0025] FIG. 2b is a graph of breakthrough curves of four biochar samples at 100 C.;

[0026] FIG. 2c is a graph comparing total H.sub.2S removal capacity of four samples;

[0027] FIG. 3 shows output obtained at an outlet of a packed bed reactor of the H.sub.2S removal unit of FIG. 1;

[0028] FIG. 4 is a graph showing percentage H.sub.2S output over time from the removal unit using a 2 g nano-iron oxide moderated with 1 g layer of biochar, heated to 200 C.;

[0029] FIG. 5 is a graph showing percentage H.sub.2S output over time from the removal unit using a 5 g nano-iron oxide moderated with 1 g layer of biochar, heated to 200 C.; and

[0030] FIG. 6 shows output obtained at an outlet of a packed bed reactor of the H.sub.2S removal unit of FIG. 1 for nano-iron oxide and a reactor temperature of 110 C.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

[0031] The following detailed description of the preferred embodiments will be made with reference to the accompanying drawings. In the description provided herein, explanation of related functions or constructions known in the art are omitted for the sake of clarity in understanding while avoiding obscuring the concept with unnecessary detail.

[0032] A mixed system is provided having the capacity to absorb hydrogen sulfide in a 1:1 mole ratio, i.e., utilizing each available site on the adsorbent and/or absorbent. The adsorbent, e.g., activated carbon, acts as a dispersant. The mixed system contains both the dispersant and a metal oxide. Results of actual runs are described in the following examples, demonstrating efficacy of the combined dispersant and metal oxide.

[0033] Aspects of the system are described below utilizing various comparative example runs carried out with dispersant alone, with the dispersant being an adsorbent that by itself is used commercially for H.sub.2S removal. The adsorbent included a commercial sample and a variety of biochars, with four biochars being derived from four sources as examples: hardwood (BC-1), chicken waste and hardwood (BC-2), switchgrass (BC-3), and switchgrass and rye (BC-4).

Example 1

[0034] A Brunauer, Emmett and Teller (BET) surface area of samples of untreated biochar (UBC) produced from all four samples was measured, providing a measured value of less than 0.5 m.sup.2/g. Same measurements were repeated for samples BC-2, BC-3 and BC-4, with BET measurement values of less than 0.5 m2/g for each of these three samples. Scanning electron microscopy (SEM) imaging showed presence of alkali salts, including Na, Cl, and K on the surface of all biochar samples.

Example 2

[0035] An untreated hardwood biochar adsorbent was tested for H.sub.2S removal efficiency, using the laboratory scale H.sub.2S removal unit shown in FIG. 1, which is a diagram of an H.sub.2S removal unit utilized to perform the examples described herein.

[0036] As shown in FIG. 1, a packed-bed reactor 7 is provided, with the packed-bed reactor 7 being a quartz tube of 0.63 cm O.D. and 16.5 cm length. As shown in FIG. 1, synthetic biogas is provided from vessel 1, the synthetic biogas passes a first valve 2a, and a first pressure of the synthetic biogas is displayed on first pressure display 3a. The synthetic biogas passes a second valve 2b, flows through a first sample port 4a, past a needle valve 5 and a flow meter 6, and into a packed bed reactor 7 that is heated by a heater 8. The synthetic biogas then flows past a second sample port 4b, and a second pressure is displayed at a second pressure display 3b. The synthetic biogas then flows past a third needle valve into a gas chromatograph.

[0037] In a typical run, 0.6 g-1.8 g adsorbent sample BC-1 was placed in the packed bed reactor. A premixed gas of composition 59% CH.sub.4/40% CO.sub.2/1% H.sub.2S was flowed through the reactor with a gas-hourly-space-velocity (GHSV) of 275 h.sup.1. The entering and exiting gas were analyzed using gas chromatography. The measured H.sub.2S removal capacity of UBC-1 was 0.006 g H.sub.2S/g UBC at 100 C.

Example 3

[0038] The UBC-1 was replaced with UBC-2 and the biochar adsorbent sample was tested for H.sub.2S removal efficiency under the conditions listed in Example 2. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.005 g/g at 100 C.

Example 4

[0039] The UBC-1 was replaced with UBC-3 and the biochar adsorbent sample was tested for H.sub.2S removal efficiency under conditions listed in Example 2. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.006 g/g at 100 C.

Example 5

[0040] The UBC-1 was replaced with UBC-4 and the biochar adsorbent sample was tested for H.sub.2S removal efficiency under conditions listed in Example 2. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.006 g/g at 100 C.

Example 6

[0041] A sample of biochar produced from hardwood was oxidized under CO.sub.2 at 900 C. for 60 minutes. The sample was cooled to room temperature under flowing CO.sub.2, and the same treatment was repeated for samples BC-2, BC-3 and BC-4. The BET measurements gave values of 1026, 506, 433 and 344 m2/g, respectively for the four samples confirming a large increase in SA for the samples. Examples 7-11 show the effect of biochar activation on H.sub.2S removal capacity.

Example 7

[0042] The activated biochar (ABC) sample was tested for H.sub.2S removal efficiency using the laboratory scale H.sub.2S removal unit shown in FIG. 1. In a typical run, 0.6 g-1.8 g activated adsorbent hardwood based sample ABC-1 was placed in the packed bed reactor. A premixed gas of composition 59% CH.sub.4/40% CO.sub.2/1% H.sub.2S was flowed through the reactor with a gas-hourly-space-velocity (GHSV) of 275 h.sup.1. The entering and exiting gas was analyzed using gas chromatography. The measured H.sub.2S removal capacity was 0.097 g/g at 23 C.

Example 8

[0043] ABC-2 was replaced and the biochar adsorbent sample was tested for H.sub.2S removal efficiency under conditions listed in Example 7. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.057 g/g at 23 C.

Example 9

[0044] The biochar sample ABC-1 was replaced with ABC-3 and the biochar adsorbent sample was tested for H.sub.2S removal efficiency under conditions listed in Example 7. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.035 g/g at 23 C.

Example 10

[0045] The biochar sample ABC-1 was replaced with ABC-4 and the biochar adsorbent sample was tested for H.sub.2S removal efficiency under conditions listed in Example 7. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.050 g/g at 23 C.

Example 11

[0046] The biochar sample ABC-1 was replaced with commercial activated carbon (SA=1100 m.sup.2/g) and the sample was tested for H.sub.2S removal efficiency under conditions listed in Example 7. The gas chromatographic analysis established the H.sub.2S removal capacity to be negligible at 23 C.

[0047] Examples 12-16 show the effect of increased temperature on H.sub.2S removal capacity of the adsorbent, with temperature increased from 23 C. to 100 C.

Example 12

[0048] With conditions the same as in Example 7 and with biochar sample ABC-1, the test temperature was raised to 100 C. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.059 g/g at 100 C. from 0.097 g/g at 23 C. The decrease in capacity is attributed to an increased desorption at a higher temperature.

Example 13

[0049] With conditions the same as in Example 7 and with biochar sample ABC-2, the test temperature was raised to 100 C. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.038 g/g at 100 C. from 0.057 g/g at 23 C., similar to that observed with ABC-1.

Example 14

[0050] With conditions the same as in Example 7 and with biochar sample ABC-3, the test temperature was raised to 100 C. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.047 g/g at 100 C. from 0.035 g/g at 23 C.

Example 15

[0051] With conditions the same as in Example 7 and with biochar sample ABC-4, the test temperature was raised to 100 C. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.036 g/g at 100 C. from 0.050 g/g at 23 C.

Example 16

[0052] With conditions the same as in Example 11 and with the same commercial activated carbon sample, the test temperature was raised to 100 C. The gas chromatographic analysis established the H.sub.2S removal capacity to be 0.033 g/g at 100 C. from 0.0 g/g at 23 C.

[0053] Examples 1-16 show that the biochar serves as an adsorbent and is effective for H.sub.2S removal from a gas flow that contains 1% H.sub.2S. However, such systems are not very efficient because, once saturated, the packed bed must be either replaced or readied for reuse. If replaced, the packed bed must be disposed of most likely in a landfill, which is challenging. Alternatively, for reuse, the bed is heated to drive out the adsorbed H.sub.2S in a separate step, making the process more cumbersome. Either way, an energy penalty is realized.

[0054] Examples 2-5 show that untreated biochar, i.e., the UBC samples, with SA of less than 0.5 m.sup.2/g has very low efficiency for H.sub.2S removal, ranging from 0.005-0.006 g/g. When the UBC samples were activated, the SA increased from 394-1026 m.sup.2/g, and the corresponding H.sub.2S removal efficiency also increased dramatically. In examples 7-11 at 23 C., the H.sub.2S removal values for ABC samples were 0.035-0.097 m.sup.2/g. When the temperature increased to 100 C. in examples 12-15, the values ranged from 0.036-0.059 m.sup.2/g. The values for ABC samples were higher when compared to a commercial activated carbon sample (SA: 1100 m.sup.2/g) for which the values were zero and 0.033 m2/g. Accordingly, the overall performance of biochar is better than commercial activated carbon for H.sub.2S removal. Thus, examples 2-16 provide baseline runs with non-activated and activated adsorbent based treatments to identify an adsorbent usable for a hybrid process that combines a two-step process into a one-step process that allows continuous H.sub.2S adsorption and subsequent decomposition on the same bed; and catalytic decomposition that allows bed volume to shrink from 22.4 liters to 32 g when H.sub.2S continually decomposes to H.sub.2 and yellow sulfur (S.sub.8). The hybrid process avoids frequent bed replacement, is more environmentally efficient and is more economical.

[0055] A metal oxide is used as the basic catalyst, with the metal oxide selected from metals that that are known to show stoichiometric (not catalytic) H.sub.2S removal property. Also, the catalyst is nano-sized, as described in the following examples.

Example 17

[0056] Nano-sized metal oxides precursors were prepared from commercially available precursors, and metals were selected from copper, nickel, iron, cobalt, and other metals using a sonicator, e.g., Misonix model 2020 with 600 watts power, to provide fixed frequency sound waves that are used to break bonds to produce nano-sized metal particles, with particles as small as less than 10 nm.

[0057] For the sonolysis, a tapered four-necked borosilicate glass flask was used to allow maximum solution in the middle of the flask for adequate immersion of the sonication probe. A series of O-rings and standard greased ground-glass joints ensured tight seals to maintain rigorous exclusion of air or gas leakage from the flask during sonication. A gas collection set-up quantified any gas evolved during sonication by collection and analysis. A bath was used to immerse the flask to maintain a constant temperature.

[0058] In a run of the cobalt system, a 0.2 g CO.sub.2(CO).sub.8 precursor was added to 50 mL n-decane as a solvent and the resulting slurry was thoroughly degassed with argon or nitrogen. The degassed solution was then sonicated at 100% intensity and 80% pulsed cycle settings. Sonication of the solution resulted in gas formation which was collected and analyzed. Within minutes of starting the sonication the solution turned into a black slurry and the gas started to evolve, with a theoretical carbon monoxide (CO) evolution as 5 mole times the added cobalt. When gas evolution ceased, the black product was centrifuged and the upper solvent layer was decanted to separate the product. The remaining black solid was washed three times with n-hexane to remove any residual solvent. The process of sonication allows cleavage of metal-carbon bonds in the metal precursor and results in nano-sized metal particles.

Example 18

[0059] The cobalt precursor was replaced by 0.015 mol iron pentacarbonyl, a yellow homogeneous formed and the same procedure was followed. The theoretical CO was 0.075 mol. After 8 hours, 90% reaction was complete. After the work-up, a black powder was produced. Transmission Electron Microscopy (TEM) of the black powder showed that the particles were less than 10 nm size. The X-ray Diffraction (XRD) spectrum of the sample matched well with that of Fe.sub.3O.sub.4 (magnetite). In other cases, the reaction time was varied from 2 hours to 8 hours.

Example 19

[0060] The cobalt precursor was replaced by 0.015 mol Ni tetracarbonyl, a colorless homogeneous formed and the same procedure was followed, taking care when handling due to the high toxicity of the nickel carbonyl complex. The theoretical CO was 0.060 mol. After 15 minutes, greater than 90% reaction was complete. After the work-up, a black powder was produced. The TEM of the black powder showed that the particles were 10-20 nm in size and the XRD spectrum of the sample matched well with that of NiO.

Example 20

[0061] The cobalt precursor was replaced by 0.015 mol copper chloride or acetate, a green hue homogeneous solution formed and the same procedure was followed. After about four hours, greater than 90% reaction was complete.

[0062] Examples 17-20 show production of nano-sized particles of metals using sonication in which a black product was produced. The spectroscopic measurements showed that: [0063] 1) particles with surface area ranging from 195-34 m.sup.2 g.sup.1 were produced when using n-decane, while surface areas ranging from 76-16 m.sup.2 g.sup.1 were produced using hexadecane; [0064] 2) sonication time between 2-3 hours led to particles of 100-200 nm in diameter and 4-8 hours led to particles of greater than 30 nm in diameter; [0065] 3) increasing sonication time from four hours to eight hours resulted in 25% and 8% increase in surface area of particles produced in n-decane and hexadecane, respectively; and [0066] 4) the reaction processed at a lower rate in n-decane than hexadecane, thus resulting in lower product yield.

[0067] The following examples show sulfur removal performance of the prepared nano metals. The examples generally involved packing nano metal as a packed bed in a glass tube, and plugging both sides of the tube with glass wool to avoid aerosoling that would otherwise result in a slow material loss from the packed bed. The impure gas containing H.sub.2S was then flowed through the tube and the gas was analyzed before and after passing through the bed. The data were used to plot breakthough curves provided in FIGS. 2a-2c, and establish the nanometal catalytic properties.

[0068] FIG. 2a is a graph of four biochar samples at 23 C., FIG. 2b is a graph of four biochar samples at 100 C., and FIG. 2c is a graph comparing total H.sub.2S removal capacity of four samples. FIG. 2c compares total H.sub.2S removal capacity by nano-sized iron oxide (HD-2), nano-sized iron oxide (HD-3), CO, and iron oxide (FO) samples. The HD-2 and HD-3 samples are differentiated by two and three hours of sonication, yielding surface areas of 16.5 and 53.7 m.sup.2 g.sup.1, respectively.

Example 21

[0069] H.sub.2S removal was conducted in the unit of FIG. 1 with a packed-bed reactor of 0.63 cm diameter and 16.5 cm. The commercial copper oxide catalyst (0.2-2.0 g) was filled in the center (2.28 cm) and the reactor was plugged with glass wool on both sides to ensure that there was no catalyst attrition when the impure gas was flowing through the reactor. The reactor temperature was set at 23 C. The gas mixture (CH.sub.4: 59%; CO.sub.2: 40%; H.sub.2S: 10,000 ppm) was started through the reactor and the gas hourly space velocity was maintained at 1690 h.sup.1. The breakthrough curve showed the same H.sub.2S concentration as initial (10,000 ppm) indicating total inactivity.

Example 22

[0070] Copper oxide (CO) is used and the temperature of the reactor was raised to 110 C., and the setup and other conditions of Example 21 were maintained. As shown in FIG. 2c, no H.sub.2S appeared at the outlet for 60 min when 100 ppm H.sub.2S was measured. The total H.sub.2S removal was 0.02 g/g catalyst, indicting activity in comparison to the peak 0.097 g/g biochar (ABC) of Example 7.

Example 23

[0071] The temperature of the reactor was raised to 210 C., and the setup and other conditions of Example 21 were maintained, and the H.sub.2S concentration at the outlet was not measured for 65 hours. As shown in FIG. 2c, the total H.sub.2S removed was 1.91 g/g catalyst for commercial micron-sized copper oxide (CO), indicting activity in comparison to the activity of ABC sample in Example 7, with the activity of copper being higher by a factor of at least 19.

Example 24

[0072] The temperature of the reactor was raised to 255 C., and the setup and other conditions of Example 21 were maintained. As shown in FIG. 2c, the same H.sub.2S concentration at the outlet decreased, with the total H.sub.2S removal was 0.73 g/g catalyst, indicating high activity.

Example 25

[0073] The catalyst was changed to micron-sized nickel oxide, and all other conditions of Example 21 were maintained, showing the same H.sub.2S concentration as initial (10,000 ppm), indicating total inactivity.

Example 26

[0074] The catalyst was changed to nano-sized nickel oxide and the reactor temperature was maintained at 23 C., and all other conditions of Example 21 were maintained. The same H.sub.2S concentration was shown as initial (10,000 ppm), indicating total inactivity.

Example 27

[0075] The reactor temperature was maintained at 110 C., and all other conditions of Example 25 were maintained. The same H.sub.2S concentration was shown as initial (10,000 ppm), indicating total inactivity.

Example 28

[0076] The reactor temperature was raised and maintained at 210 C., and all other conditions of Example 25 were maintained. The same H.sub.2S concentration was shown as initial (10,000 ppm), indicating total inactivity.

Example 29

[0077] The reactor temperature was raised and maintained at 255 C., and all other conditions of Example 25 were maintained. The same H.sub.2S concentration was shown as initial (10,000 ppm), indicating total inactivity.

Example 30

[0078] The catalyst was changed to nano-sized iron oxide (HD-2) with a mean particle diameter (MPD) less than 10 nm, and all other conditions of Example 21 were maintained. At the reactor temperature of 23 C., the breakthrough curves showed an H.sub.2S concentration at the outlet being the same, indicating that the catalyst was inactive.

Example 31

[0079] For a nano-iron oxide catalyst with a surface area (SA) of 16.5 m.sup.2/g, the temperature of the reactor was raised to 110 C., and all other conditions of Example 21 were maintained. The breakthrough curves showed an H.sub.2S concentration at the outlet of 1136 ppm after 40 minutes, with a total H.sub.2S removal of 0.03 g/g catalyst, indicating some activity.

[0080] FIG. 3 shows output obtained at an outlet of a packed bed reactor of the H.sub.2S removal unit of FIG. 1. The circle 210 of FIG. 3 shows formation of a yellow color, i.e., sulfur removed from the H.sub.2S stream, output at the top of the reactor. The yellow color indicates accumulation of sulfur removed from the gas stream.

Example 32

[0081] A quartz tube 61 cm in length and 2.34 cm O.D. was filled with 2 g nano-iron oxide (magnetite) and moderated with 1 g layer of biochar, then heated to 200 C. The gas velocity of simulated landfill gas containing 1% H.sub.2S passed through the quartz tube filled iron at 100 mL/min. The time-resolved H.sub.2S exiting the tube was measured, with the results of the measurement being shown in FIG. 4.

[0082] FIG. 4 is a graph showing percentage H.sub.2S output over time from the removal unit using a 2 g nano-iron oxide moderated with 1 g layer of biochar, heated to 200 C. The total H.sub.2S removal was 0.0312 mol H.sub.2S, indicating that the mixture of Example 32 is far more effective than the adsorbent in Example 12.

Example 33

[0083] Example 32 was scaled up to 5 g iron oxide filled in the quartz tube and then moderated with biochar. The gas velocity of simulated gas composition similar to Example 35, with the gas stream increased to 1544 mL/min, maintaining the other conditions of Example 21. The time-resolved exit H.sub.2S gas measurement is shown in FIG. 5, which is a graph showing percentage H.sub.2S output over time from the removal unit using a 5 g nano-iron oxide moderated with 1 g layer of biochar, heated to 200 C.

[0084] The run of Example 33 lasted more than two hours at the increased high gas velocity before the catalyst became ineffective. A total of 0.339 g H.sub.2S was removed, indicating that 2.30 mol H.sub.2S per mole of Fe was removed. The data establishes that the reaction is catalytic as the removed S was 2.3 times the amount of iron added.

Example 34

[0085] Nano-iron oxide having an SA of 53.2 m2/g was used, and the temperature of the reactor was raised to 110 C., keeping other set-up and reaction conditions of Example 21 maintained.

[0086] The breakthrough curves show the H.sub.2S concentration at the outlet after 64 minutes, with a total H.sub.2S removal of 0.27 g/g catalyst, indicating some activity.

[0087] FIG. 6 shows output obtained at an outlet of a packed bed reactor of the H.sub.2S removal unit of FIG. 1, based on example 34. As shown in FIG. 6, yellow color forms at the top of the reactor (see circle), which is elemental sulfur (S8) formed by the decomposition of H.sub.2S.

Example 35

[0088] A nano-iron oxide catalyst (SA: 53.2 m.sup.2/g) was used, the temperature of the reactor was raised to 210 C., and the other conditions of Example 34 were maintained. The breakthrough curves showed no H.sub.2S concentration at the outlet for 33 hours. The total H.sub.2S removal was 3.87 g/g catalyst, indicating high activity. For reference, the highest number was 0.097 g/g biochar (ABC) in Example 7. Comparing Example 7 with Example 35 shows an increase in activity by a factor of thirty-nine, indicating that the H.sub.2S removal is catalytic in iron catalyst, and a yellow sulfur deposit was observed at the outlet.

Example 36

[0089] A nano-iron oxide catalyst (SA: 53.2 m.sup.2/g) was used, the temperature of the reactor was raised to 255 C., and the other conditions of Example 34 were maintained. The breakthrough curves showed no H.sub.2S concentration at the outlet for 65 hours. The total H.sub.2S removal was 3.38 g/g catalyst, indicating high activity. Comparing Example 7 to Example 36 shows an increase in activity by a factor of at least thirty-four, and a yellow elemental sulfur (S8) was seen and the H.sub.2S removal was catalytic in iron oxide.

Example 37

[0090] A nano-iron oxide (SA: 16.5 m.sup.2/g) was used, the temperature of the reactor was raised to 210 C., and the other conditions of Example 34 were maintained. The breakthrough curves showed no H.sub.2S at the outlet for 21 hours. The total H.sub.2S removal was 1.67 g/g catalyst, indicating high activity. Comparing Example 7 to Example 37 shows an increase in activity by a factor of at least seventeen, though less than that seen at 210 C.

Example 38

[0091] A nano-iron oxide (SA: 16.5 m.sup.2/g) was used, the temperature of the reactor was raised to 255 C., and the other conditions of Example 34 were maintained. The breakthrough curves showed the H.sub.2S concentration at the outlet decreased. The total H.sub.2S removal was 0.48 g/g catalyst, indicating high activity. Comparing Example 7 to Example 37 shows an increase in activity by a factor of at least five, though less than that seen at 210 C.

[0092] Accordingly, disclosed is a method for removing H.sub.2S from a gas stream, the method including contacting the gas stream with a reactor configured to remove the H.sub.2S, with the reactor comprises at least one nano-sized metal. In the method, at least one nano-sized metal of the reactor is heated between approximately 200 C. and approximately 255 C. during the removal of the H.sub.2S. Also, the at least one nano-sized metal acts as a catalyst during the removal of the H.sub.2S, and the H.sub.2S is decomposed on a surface of the catalyst, and the decomposition produces hydrogen (H.sub.2) and S, with the S being removed from the reactor by sublimation, and not remaining in the reactor.

[0093] In the method, the at least one nano-sized metal is not consumed during the removal of the H.sub.2S, and the at least one nano-sized metal is copper or iron. An amount of the H.sub.2S that is removed from a gas stream is 2.3 times an amount of the iron in the reactor and the iron acts as a catalyst for at least seven cycles during the removal of the H.sub.2S, when heated to approximately 210 C. The iron acts as a catalyst for at least six cycles during the removal of the H.sub.2S, when heated to approximately 255 C.

[0094] Also provided is a method for removing H.sub.2S from a gas stream that includes contacting the gas stream with a reactor configured to remove the H.sub.2S, with the reactor including biochar and at least two nano-sized metals. The at least two nano-sized metals are not consumed during the removal of the H.sub.2S, and unconverted H.sub.2S does not accumulate within the reactor. The at least two nano-sized metals are copper and iron, and the at least two nano-sized metals of the reactor are heated between approximately 200 C. and approximately 255 C. during the removal of the H.sub.2S, with the at least two nano-sized metals acting as a catalyst during the removal of the H.sub.2S. The H.sub.2S is decomposed on a surface of the catalyst, and the decomposition produces H.sub.2 and S, with the S being removed from the reactor by sublimation, and the S does not remain in the reactor.

[0095] Also provided is an apparatus for removing H.sub.2S from a gas stream, with the apparatus including a reactor that contacts the gas stream and remove the H.sub.2S, and the reactor includes biochar and at least two nano-sized metals.

[0096] While the disclosed method and apparatus have been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and equivalents thereof.