Alkaline oxidation of hydrosulfide and methyl mercaptide by iron/cerium oxide-hydroxide in presence of dissolved oxygen : possible application for removal of Total Reduced Sulfur (TRS) emissions in the Pulp & Paper industry

Authors: Petre, Cătălin Florin
Advisor: Larachi, Faïcal; Grandjean, Bernard
Abstract: Hydrogen sulfide (H2S) and methyl mercaptan (MM) are the most abundant odor contaminants among the Total Reduced Sulfur (TRS) quartet (H2S, CH3SH, (CH3)2S, (CH3)2S2) contained in the Kraft mill atmospheric emissions. The association of TRS with sufficient oxygen could be taken advantage of, based on the iron chemistry, to convert TRS gases to odorless non-volatile products. The process uses Fe/Ce oxide-hydroxide (Fe/CeOx) slurried in alkaline solutions where both H2S and MM oxidative absorption (in the form of hydrosulfide and methyl mercaptide) is promoted. Capillary electrophoresis protocols were developed for the separation, identification and quantification of hydrosulfide, methyl mercaptide, polysulfides, thiosulfate, sulfate, sulfite and tetrathionate. The kinetics and mechanism of the anoxic reaction between hydrosulfide and Fe/CeOx were studied for pH [8.0-11.0] in a batch slurry reactor. Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-frame of the experiments. Hydrosulfide was converted into polysulfides, thiosulfate and, probably, elemental sulfur, while the leached Fe2+ and thiosulfate dovetailed equimolarly. A detailed reaction pathway of the anoxic oxidation of hydrosulfide by Fe/CeOx was proposed for explaining the formation of above products and whereof a kinetic model was derived to depict the Fe2+ leaching and hydrosulfide consumption rates. In oxic conditions at pH [8.5-11.0], Fe/CeOx will oxidize hydrosulfide via a combined heterogeneous-homogenous pathway to yield the same products as in anoxia. Oxygen enhanced Fe/CeOx-promoted hydrosulfide oxidation by more than a factor three when compared with anoxic reaction. Oxygen is believed to have a double role: first, it re-oxidizes iron from Fe(II) to Fe(III); second, it promotes oxidation of hydrosulfide to polysulfides which in turn transforms into non-volatile, non-odorous thiosulfate. The reaction between methyl mercaptide and Fe/CeOx was studied at different pH values [10.5-12] both in anoxic and oxic conditions. Up to 100% conversions of mercaptide were obtained in oxic conditions, though the mercaptide conversion was found to be tributary to the dissolved oxygen. Interference with hydrosulfide co-mixed with mercaptide caused an inhibition in the conversion for both pollutants, due to the incipient polysulfides formation. The oxidation of methyl mercaptide by the Fe/CeOx/O2 system did not affect the re-oxidative regeneration of surface Fe(III) by O2. Fe/CeOx appears to be a very promising material for a redox-scrubbing process targeting the TRS emissions from Kraft mills, via in situ regeneration of Fe(III) sites by O2.
Document Type: Thèse de doctorat
Issue Date: 2007
Open Access Date: 13 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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