Manganese gluconate, A greener and more degradation resistant agent for H2S oxidation using liquid redox sulfur recovery process

Abstract

Iron chelate liquid redox sulfur recovery (LRSR) has been one of the most frequently recommended technologies for the oxidation of H 2 S in natural gas into elemental sulfur, particularly when the acid gas has a high CO 2 /H 2 S molar ratio. The process is however known to suffer from extensive oxidative ligand degradation that results in high operational costs. Moreover, poor biodegradability or toxicity of the existing ligand has become a concern. In this research, we demonstrated that gluconate, a naturally greener ligand, when coupled with manganese as the metal, has considerable potential to be a better redox agent. Manganese gluconate solution was more resistant against ligand degradation compared with iron NTA. As required, aerated solution was capable of converting dissolved NaHS into elemental sulfur. At sufficiently high pH, manganese gluconate solutions were stable enough from precipitation of manganese hydroxide, carbonate, or sulfides. An equilibrium calculation has been developed to understand the precipitation behavior.

Inhibition of iron chelate degradation in liquid redox desulfurization by nanoscale MnO2 through H2O2 decomposition

“…4,5 It is well known that hydroxyl radicals (OH) formed during the reoxidation of ferrous chelate to ferric chelate, which is usually associated with a 'Fenton reaction', is responsible for the oxidative degradation of the iron chelate. [6][7][8] To inhabit the iron chelate degradation, three approaches were previously investigated: (i) development of chelating ligands that are resistant to hydroxyl radical attack; [8][9][10][11][12][13][14] (ii) use of novel nonaqueous redox couple systems instead of the aqueous iron chelate; [15][16][17] and (iii) application of hydroxyl radical scavengers. 6,18,19 Since it is widely acknowledged that a replacement of the commercially available chelating agent is not yet available 5 and reports on application of non-aqueous phase redox desulfurization processes are rare, a hydroxyl radical scavenger such as 5-8% (w/w) thiosulfate is the best option for a commercial LO-CAT system.…”

“…• O 2 − by • OH in Eqn(14) is the way to produce O 2 from the decomposition of H 2 O 2 , it is worth noting that little O 2 is obtained in the acid Fenton reaction of Fe 2+ and H 2 O 2 in the absence of Fe 3+ ,40 indicating that Fe 3+ has an important effect on the decomposition of H 2 O 2 to H 2 O and O 2 in the Fenton reaction. The rate constant reported for the oxidation of OH in in Eqn(14) was higher than that by Fe 3+ -EDTA in Eqn (15);26,41 however, the half-life time of• OH and • O 2 − was 10 −10 and 10 −6 s, respectively; 42 therefore, it was possible that Fe 3+ -EDTA instead of • OH became the predominant oxidizer of O 2 obtained from the decomposition of H 2 O 2 .…”

H2S–CO2 gas separation with ionic liquids on low ratio of H2S/CO2

“…The biological method was used to convert dissolved H 2 S to elemental sulfur using sulfur-oxidizing bacteria such as Thiobacillus. A similar concept was applied in liquid redox system that applying chemicals instead of microorganism [7,8]. In comparison, the indirect electrolysis method can be a very promising method that converts H 2 S in gas streams to produce both sulfur and hydrogen simultaneously using vanadium dioxide in acidic aqueous media [9].…”

The promising performance of manganese gluconate as a liquid redox sulfur recovery agent against oxidative degradation

“…Several investigations have been carried out to overcome or reduce degradation problems [ 3 , 4 ]. One of which was our work that suggested manganese gluconate could be a potential, greener, more economical, and stable redox agent for the LRSR process [ 5 ]. However as this is still a novel concept, to our knowledge no information on manganese gluconate degradation in LRSR systems has been reported in the open literature.…”