Study On The Interaction Between Binuclear Sulfonated Phthalocyanine Cobalt With Sodium Sulfide In PDS Desulfurization System

PDS desulfurization technology is one of the wet catalytic oxidation desulfurization technologies,which is widely used in coking,fertilizer,oil refineries and other industries.Theoretically,H₂S removal only consumes O₂ in the air to generate water and sulfur,and other materials in the system can be recycled.This is just an ideal state,however,in the actual process,part of the H₂S will be transformed into S₂O₃^2-,SO₃^2-and SO₄^2-by-products,which brings low desulfurization,affects the normal operation of desulfurization process,increases the operation cost,and causes equipment corrosion and secondary water pollution as so on.Therefore,the by-products problem has become an urgent scientific problem to be resolved.However,the post-treatment process is a main method to purify the by-products.This method has high energy consumption,cumbersome operation and high recovery cost.In addition,the treatment process of by-products terminally is much more complicated than the process itself.Therefore,in order to reduce or inhibit by-products being,we have to get deeper understanding of the mechanism of desulfurization and find the source of by-products and put forward resolving methods from the source.The reaction process between the binuclear sulfonated phthalocyanine cobalt（bi-CoPc）with sodium sulfide was studied by UV-Vis,FTIR,CV and HPLC technologies for PDS desulfurization system in this paper.And existence form of polysulfide ions in solution was investigated.The main conclusions were as follows:1.The results of UV-Vis show that the bi-CoPc is easier in water to form polymer than monomer,and mainly exists as a polymer within pH range of the PDS desulfurization system.Moreover,S_x^2-is quickly formed in the investigated reaction system,however,under the condition of concentration in this experiment,the conversion rate is not high.At the same time,it is also concluded that reaction temperature at 40^oC is conducive to the formation of S_x^2-and the monomer form is the main part of playing catalytic role in the bi-CoPc.In addition,by the FTIR analysis,S_x^2-conversion rate to S₈ is slow.And under aerobic conditions,S_x^2-conversion rate to S₈ will be accelerated,but also will generate by-product S₂O₃^2-.2.The results of CV show that the oxidation process of Na₂S and Na₂S_x on glassy carbon electrode is an irreversible process controlled by concentration diffusion.And the transformation from S_x^2-to S₈ is not a one-step process,but firstly transformed into the intermediate,S_x^2-,then further converted into S₈.Moreover,it is deduced that only 20%of S^2-involved in the reaction is converted into S₈,the remaining sulfur substances exist in the solution with the form of S_x^2-and unreacted S^2-.S_x^2-existed two mainforms within the range of S₂^2-S₉^2-in reaction system.With concentration change,the existence forms of S_x^2-also change.When the concentration is greater than 0.12 mol/L,S_x^2-existed a mainform within the range of S₂^2-S₉^2-.When the concentration is 0.024 mol/L,S_x^2-existed some mainforms.When the concentration is within the range of2.4×10^-42.4×10^-33 mol/L,S_x^2-existed two mainforms,but the specific existence forms cannot be determined.In addition,the addition of carbonate buffer solution can maintain the high catalytic activity of bi-CoPc,and reacts with Na₂S in carbonate buffer solution,S₂^2-is formed firstly,meanwhile,the valence state of cobalt is reduced from bivalent to monovalent,then S₂^2-can be autocatalyzed to form longer chain S_x^2-,finally converted to S₈.3.UV-Vis spectrum can only determine the concentration of total sulfur,but it is not possible to detect the individual polysulfide species.¹H NMR can be used to detect substances with sulfur atoms number x≤3 in molecules,however,there are no significant differences in the proton deviations for the number of sulfur atoms x>4 in the molecule,therefore,the ¹H NMR technology are not sufficient for analysis methyl polysulphides.HPLC is suitable for the separation of methyl polysulphides with sulfur atoms number x≥3,but it is not ideal to separate S^2-and S₂^2-.At the same time,when x ranges from 3¹0,the logarithm of retention time has a linear relationship with the number of sulfur atoms x,and the relation is ln（R_t）=0.203x+1.49.4.The results show that concentration change have significantly impact on the presence forms of S_x^2-in aqueous solution is S₃^2-,S₄^2-,S₅^2-and S₉^2-by HPLC.Within the concentration range studied,S₆^2-,S₇^2-,S₈^2-and S₁₀^2-are basically stable.When the concentration is 0.024 mol/L,existance main form S₄^2-and S₅^2-,followed S₃^2-and S₆^2-,S₈^2-and S₁₀^2-finally.When the concentration is 4.8×10^-3mol/L,existance main form S₅^2-and S₆^2-,followed S₄^2-and S₉^2-,with the lowest content of S₃^2-,S₈^2-and S₁₀^2-.When the concentration is 2.4×10^-3 mol/L,existance main form S₅^2-,S₆^2-and S₉^2-,followed S₄^2-and S₇^2-,with the lowest content of S₃^2-and S₁₀^2-.When the concentration is 4.8×10^-4 mol/L,existance main form S₉^2-,with the lowest content of S₃^2-and S₁₀^2-cannot be detected.In the range of 30⁹0oC,with the increase of temperature,S₃^2-and S₉^2-change significantly,S₄^2-,S₅^2-and S₆^2-fluctuate slightly,S₇^2-,S₈^2-and S₁₀^2-are basically stable.In the range of temperature studied,S_x^2-always exists in solution mainly in the form of S₄^2-and S₅^2-.With the increase of temperature,the proportion of S₃^2-decrease by 6.76%,and S₃^2-increase by 6.86%,the lowest proportion was always S₁₀^2-.5.The reaction system of bi-CoPc and Na₂S was studied by HPLC,the results show that the maximum number of sulfur atoms detected was 5,and S_x^2-main form is S₃^2-,followed S₄^2-,with part in the form of S₅^2-in the solution.