Conversion rules of sulfur compounds in iron chelate desulfurization system

ABSTRACT

Iron chelate desulfurization is a popular method in the coking industry due to its low generation of secondary salts. The conversion of sulfur compounds in the system plays a crucial role in this process. In this paper, the favorable conditions for the formation of polysulfide ions (S_x^2-) were investigated by ultraviolet-visible spectrophotometry (UV-Vis) in the reaction system of EDTA-Fe and Na₂S. The reaction solution was analyzed by high-performance liquid chromatography (HPLC), aiming to obtain the main forms of the presence of S_x^2- after the reaction. HS⁻ was first converted to S_x^2-, and then to elemental sulfur (S₈). In the experimental range, the concentration of S_x^2- increased with increasing the concentration ratio of reactants (c(Na₂S)/c(EDTA-Fe)) and decreasing the temperature, was maximal at pH 9.84. At c(Na₂S)/c(EDTA-Fe) of 120, the forms of S_x^2- reached a maximum, which was S₃^2--S₁₀^2-. When the concentration ratio reached 130, S₈ was generated, as the concentration ratio increased on this basis, the time for S₈ to appear was shortened from 21 min to 12 min. Therefore, the study of the conversion rules of sulfur compounds in the iron chelate desulfurization system provides both the ideas to suppress the generation of by-salts in this system and new evidence to reveal the common problem of sulfur compounds conversion in the wet catalytic oxidation desulfurization process.

GRAPHICAL ABSTRACT

KEYWORDS:

• Wet catalytic oxidation
• iron chelate desulfurization
• polysulfide ions
• secondary salt
• H₂S

Nomenclature

c(Na2S)/c(EDTA-Fe)	=	the concentration ratio of reactants
c0(Na2S)	=	the initial concentration of S2- in the solution.
c (Na2Sx)	=	the concentration of Sx2- in the solution after the reaction.
$\mathit{X}$	=	polysulfide ions concentration as a percentage of total sulfur concentration
c	=	the concentration of Sx2- in Eq. (2)(2) $\mathit{Abs}=1.18326\mathit{c}+0.00347$(2) .
Abbreviations	=
UV-Vis	=	ultraviolet – visible spectrophotometry
HPLC	=	high-performance liquid chromatography
Sx2-	=	polysulfide ions
S8	=	elemental sulfur
H2S	=	Hydrogen sulfide
Tannin	=	tannin extract
PDS	=	dinuclear cobalt-phthalocyanine sulfonate
Abs	=	Absorbance of the measured substances

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [21606161]; the Shandong Key Laboratory of Multiphase Fluid Reaction and Separation Engineering [2021MFRSE-D01]