Energy & Fuels 2005, 19, 1717-1722
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Hydrogen Sulfide Separation Using Tetra-n-butyl Ammonium Bromide Semi-clathrate (TBAB) Hydrate Yasushi Kamata,* Yukiyasu Yamakoshi, Takao Ebinuma, Hiroyuki Oyama, Wataru Shimada, and Hideo Narita National Institute of Advanced Industrial Science and Technology (AIST), Tsukisamu-higashi, Toyohira-ku, Sapporo 062-8517, Japan, and Hokkaido Industrial Research Institute, Kita-19, Nishi-11, Kita-ku, Sapporo 060-0819, Japan Received November 15, 2004. Revised Manuscript Received April 27, 2005
Biogas mixtures include methane (which is useful), carbon dioxide, and hydrogen sulfide (which can be a nuisance). To remove hydrogen sulfide from biogas, we conducted separation experiments using tetra-n-butyl ammonium bromide semi-clathrate hydrate (hereafter referenced as TBAB hydrate). TBAB hydrate is stable under atmospheric pressure and can cage gas molecules in their empty small cage. A solution of 10 wt % TBAB was enclosed in a pressure vessel with a gas mixture containing hydrogen sulfide, and then TBAB hydrate was formed in the solution by cooling. Because of the selective incorporation of hydrogen sulfide into TBAB hydrate, >90% of the hydrogen sulfide in the vapor phase was removed during the hydrate growth. We also determined that the removal efficiency of hydrogen sulfide was not dependent on the initial pressure or the cooling rate. The results showed that TBAB hydrate was an effective material for desulfurization.
Introduction Biogas is generated during the processing of animal manure, and it contains 50%-65% of methane (CH4), several percent of hydrogen (H2), 30%-40% of carbon dioxide (CO2), and 90% of the H2S in the vapor phase of the biogas was removed under certain conditions. Experimental Method The experimental apparatus is shown in Figure 1. The inner volume of the pressure vessel was 1.26 × 10-3 m3. A spargertype fin was installed to stir the solution at a speed of 1000 rpm with microbubbling. The temperature in the pressure (1) Davidson, D. W. WatersA Comprehensive Treatise; Franks, F., Ed.; Plenum Press: New York, 1973; Vol. 2, Chapter 3. (2) Fukushima, S.; Takao, S.; Ogoshi, H.; Ida, H.; Matsumoto, S.; Akiyama, T.; Otsuka, T. NKK Tech. Rep. 1999, 166, 65 (in Jpn.). (3) Shimada, W.; Ebinuma, T.; Oyama, H.; Kamata, Y.; Takeya, S.; Uchida, T.; Nagao, J.; Narita, H. Jpn. J. Appl. Phys. 2003, 42 (2A), L129.
10.1021/ef0497098 CCC: $30.25 © 2005 American Chemical Society Published on Web 07/20/2005
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Figure 1. Experimental apparatus for forming tetra-n-butylammonium bromide semi-clathrate (TBAB) hydrates and gas hydrates. The inner volume of the pressure vessel was 1.26 × 10-3 m3. vessel was controlled by running refrigerant in a cooling jacket, which was connected to a circulating thermostat. The temperature and pressure were collected once per minute on a recorder (Yokogawa, model µ1800). Gas was introduced into the pressure vessel from the gas cylinder. A gas chromatograph (Shimadzu, model GC-14B) was connected to the pressure vessel to measure the gas composition of the mixed gas in the vapor phase at equilibrium condition. CH4 and CO2 were measured within an error of 0.2%, and H2S was measured to the parts per million level, because of its small amount. We poured 500 g of 10 wt % TBAB aqueous solution into the pressure vessel, and then the inside gas of the vessel was evacuated. A gas mixture was added at a fixed pressure. Biogas (CH4 + CO2 + H2S), a CH4 + H2S mixture, and a CO2+ H2S mixture were used in this experiment. In either case, the H2S concentration was 90% of the H2S in the pressure vessel was included in TBAB hydrate. The distribution coefficient of H2S was higher than that of (5) Kamata, Y.; Oyama, H.; Shimada, W.; Ebinuma, T.; Takeya, S.; Uchida, T.; Nagao, J.; Narita, H. Jpn. J. Appl. Phys. 2004, 43 (1), 362365.
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Figure 4. H2S extraction ratio from the listed gas mixtures at various total pressures. Table 1. Distribution Coefficients of Each Component Gas Included in TBAB Hydrate Initial Amount (mol) CH4
CO2
3.57 × 10-1 3.57 × 10-1 3.51 × 10-1 3.55 × 10-1 3.06 × 10-1
2.10 × 10-1
Amount in TBAB Hydrate (mol) H2S 9.01 × 10-2 4.00 × 10-2 2.18 × 10-3 3.92 × 10-4 7.79 × 10-3
5.45 × 10-1 5.09 × 10-1 5.02 × 10-1 5.22 × 10-1 5.43 × 10-1 5.43 × 10-1 5.52 × 10-1
4.93 × 10-3 5.44 × 10-3 4.70 × 10-3 2.62 × 10-3 1.01 × 10-3 4.82 × 10-4 4.26 × 10-5
4.54 × 10-3
1.74 × 10-1
CH4
CO2
CH4 + H2S Gas Mixture 1.38 × 10-1 6.94 × 10-2 1.16 × 10-1 1.22 × 10-1 5.45 × 10-2 CO2 + H2S Gas Mixture 2.14 × 10-1 1.94 × 10-1 1.87 × 10-1 7.44 × 10-2 2.03 × 10-1 2.21 × 10-1 2.06 × 10-1
C)
P-1y 1-y
H2S
CH4
8.63 × 10-2 3.97 × 10-2 2.12 × 10-3 3.90 × 10-4 7.74 × 10-3
0.39 0.19 0.33 0.35 0.18
4.60 × 10-3 4.90 × 10-3 4.40 × 10-3 2.36 × 10-3 9.50 × 10-4 4.61 × 10-4 4.01 × 10-5
CH4 + CO2 + H2S Gas Mixture (Biogas) 8.27 × 10-2 4.01 × 10-3 8.25 × 10-2
other component gases. It was clarified that H2S was selectively included in TBAB hydrate. Therefore, it is possible that an initial biogas sample of 0.5% H2S might be desulfurized to
