Low temperature decomposition of hydrogen sulfide on metal catalysts under layer of solvent to produce hydrogen and diatomic sulfur.
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A.N. Startsev,,* O.V. Kruglyakova, Yu. A. Chesalov, E.A. Paukshtis, V.I. Avdeev, S.Ph. Ruzankin, A.A. Zhdanov
Boreskov Institute of Catalysis, Lavrentiev, 5, Novosibirsk, Russian Federation, 630090
Keywords: hydrogen production, H2S decomposition, ambient conditions, diatomic sulfur
1 Introduction
Hydrogen sulfide, H2S, attracts attention of many researchers as an inexhaustible source of hydrogen, but numerous attempts in the development of a suitable technology for hydrogen recovery from H2S were not crowned with success because of high cost of hydrogen produced. However, recently it was shown that the catalytic decomposition of hydrogen sulfide into hydrogen and diatomic sulfur
2 H2S « 2 H2 + S2(gas) (1)
occurs on metal catalysts at ambient conditions with H2S conversion about 15 % [1-3]. Along with hydrogen, diatomic gaseous sulfur appeared to be the reaction product. The paper demonstrates that H2S conversion can be considerably (up to 100 %) upgraded on passing H2S at room temperature through the metal catalyst being immersed into the solvent capable of dissolving sulfur produced [4].
2 Experimental
Experiments were carried out at room temperature in a glass absorber equipped with a magnetic stirrer. Metal catalyst, mainly a chip of stainless steel, was placed into solvent and a mixture of argon with H2S was bubbled through the solution. At the absorber outlet, non-reacted H2S was trapped in the aqueous zinc acetate solution for quantitative analysis. The reaction products, hydrogen and gaseous sulfur, were detected with a gas chromatograph. As a sulfur solvent, aqueous solutions of monoethanolamine (MEA), HOC2H4NH2, and sodium carbonate, Na2CO3, which are widespread in industry to extract hydrogen sulfide from the exhaust gas emissions, were used. Besides, water, ethanol and aqueous hydrazine were tested as well.
3 Results and discussion
On passing H2S through the metal catalyst at room temperature, two gaseous products are formed, hydrogen and diatomic sulfur [1-3], though H2S conversion is relative low. When the catalyst is placed into solvent, H2S conversion increases even in the case of water (Table). In ethanol and, especially, in aqueous hydrazine, H2S conversion increases significantly, however gaseous sulfur formed leaves solvents on blowing-off with argon.
With MEA or soda, only hydrogen is detected in the gas phase, while sulfur is accumulated in the solvent. In 12 hours of experiment, at the steady-state level of hydrogen production (Figure) 3.6 g of sulfur was discovered in the mother solution (Table). In Infrared and Raman spectra of the solution no new bands (in comparison with the initial solvent) were found what unambiguously indicates on the dissolved diatomic gas formed in the reaction (1). An important point is that no other bands like S – S, S – H or S – O were detected with IR and Raman spectroscopy, what means high selectivity in the reaction (1) producing only hydrogen and gaseous diatomic sulfur.
Table. H2S decomposition on the chip of stainless steel placed into solvent. Catalyst mass is 5 g, reaction temperature is ambient. Ar flow is ~ 10 ml/min, H2S flow is ~ 3 ml/min.
| Solvent | Solvent volume, ml | Hydrogen sulfide, mmol | H2S conversion, % | Sulfur mass in solution*, g | |
| fed | non-reacted | ||||
| Gas phase | — | 9.23 | 8.81 | 4.6 | — |
| Water | 180 | 11.8 | 9.7 | 17.2 | 0 |
| Ethanol | 100 | 12.7 | 6.09 | 52.2 | 0.10 |
| 5% hydrazine | 77 | 19.5 | 0.29 | 98.5 | 0.46 |
| 5% MEA | 200 | 110.6 | 2.3 | 97.9 | 3.64 |
| Na2CO3
[Na] = 0.84 % |
100 | 53.4 | 10.9 | 79.6 | 1.30 |
* — X-ray fluorescent analysis data after non-reacted H2S being removed with argon flow
Fig. 1. Hydrogen evolution on passing H2S through the stainless steel chip placed into 5 % MEA aqueous solution.
Main regularities of hydrogen production and sulfur recovery from the solutions are been discussed. The S2 electronic state and the reaction (1) thermodynamics are considered. According to DFT calculations, S2 molecule forms loosely bounded adducts with the solvent molecules. As was suggested, dissolved diatomic sulfur can be used for synthesis of new chemical substances.
4 Conclusions
Hydrogen sulfide decomposition at ambient conditions on metal catalysts under layer of solvents seems to offer new challenges and very promising opportunities to produce hydrogen from renewable inexhaustible resources, at the same time very toxic H2S is utilized.
References
[1] A.N. Startsev, O.V. Kruglyakova, Yu.A. Chesalov, S.Ph. Ruzankin, E.A. Kravtsov, T.V. Larina, E.A. Paukshtis, Top. Catal. 56 (2013) 969.
[2] A.N. Startsev, O.V. Kruglyakova, J Chem Chem Eng. 7 (2013) 1007.
[3] A.N. Startsev, O.V. Kruglyakova, S.Ph. Ruzankin, N.N. Bulgakov, Yu.A. Chesalov, E.A. Kravtsov, V.I. Jeivot, T.V. Larina, E.A. Paukshtis, Russ J Phys Chem. 88 (2014) 943 (in Russian).
[4] A.N. Startsev, A.V. Pashigreva, O.V. Voroshina, I.I. Zakharov, V.N. Parmon. Patent Ru 2,261,838. (10.10.2005). Patent Uk 81,088 (26.11.2007). Patent Kz 57,481 (15.12.2008). Patent US 7,611,685 (20.12.2007).
