Study On The Formation Of Byproducts And Effect Factors In Tannin Extract Desulfurization Technology

The tannin extract desulfurization technology (TEDT) belongs to the wet desulfurization technology used to remove H2S. At present, the technology is widely applied in the field of coking, fertilizer and oil refining et al. However, practice shows that the problem on by-products in this technology has become a stumbling block restricting the development of TEDT and is one of problems to be solved urgently. According to the literature, the research on side reaction is less and lacks theoretical depth. Therefore, in order to solve this problem, the studies on side reaction, formation mechanism of by-products and influencing factors in TEDT, was done for the first time.Through the study on side reaction and the component analysis of desulfurization solution and sulfur paste in TEDT, It is concluded that the main by-products are NaSCN and Na2S2O3. This conclusion is a base to research the formation cause of by-products further. And the study also showed that the content of elementary sulfur is about 50 percent in sulfur paste which is one of by-products in TEDT, and the purity of elementary sulfur is more than 95 percent after dried sulfur paste was extracted by toluene. According to the literatures, by-products will influence on the normal operation of TEDT, when its content accumulates to a certain amount. So the influence of by-products on TEDT was studied in third chapter of this paper. The results show that the pH value of desulfurization solution reduced with the increase of by-products. The pH value is relative to the absorption of H2S and the existence state of sulfur species, so its decrease will lead to the fall of desulfurization efficiency. Moveover, the accumulation of by-products results in the increase of the viscosity and density of desulfurization solution also, which will affect the normal operation of TEDT.In order to settle the problem of side reaction effectively, the research on reaction between HS- and V(V) was carried out in detail with theoretical and experimental method in this paper for the first time. By analyzing the E-pH diagram of V-H2O system, it is concluded that in normal operating conditions of TEDT, quinquevalent vanadium species is HV2O73- and tetravalent is V4O92-. Furthermore, through the thermodynamic analysis and compute, the E-pH diagram was creatively drawn for the reaction system of HS- and V(V), and the concept of Sx2- was introduced in this system, according to which, it is concluded that in the reaction between HS- and V(V), the Sx2- was generated prior, then Sx2-transformed into element sulfur. By combining theory analysis with experimental research, the reaction mechanism of HS- and V(V) is as follows: HV2O73-+2HS-→S22-+HV2O5-+2OH- 2S22(?)S2-+S32-2S32-(?)S22-+S42-(?)S2-+S52-2S42-(?)S32-+S52-(?)S22-+S62-(?)S2-+S72-2S52-(?)S42-+S62-(?)S32-+S72-(?)S22-+S82-(?)S2-+S92-S92-+H+(?)S8↓(乳黄色)+HS-2HV2O5-→V4O92-+H20In this reaction mechanism,the transformation process from HS- to Sx2- is a quick step,but the process from Sx2- to S8 is a slow step.Besides,The study also found that a unknown black precipitate appeared in the bottom of reactor,while increasing the concentration of HS- and V(V) simultaneously. After measuring and analyzing, this precipitate should be VO(OH)2 instead of VOS which was regard as precipitate formerly.Finally,this paper studied the formation cause of sulfur-containing and its influence factor,and analysed the formation mechanism of by-products of TEDT using theoretical means for the first time,and investigated the reaction condition of by-products formation,which offered a valuable conclusion for optimizing TEDT further.Studies show that the HS- and Sx2- are the source of sulfur in by-products.And Sx2- is more livelier than HS- in solution,so it is oxidized by oxygen easily and generates by-products S2O32-.The Sx2- will be more livelier with x value minishing.Because the electrode potential of S042-/HS- is larger than the electrode potential of 02/OH-,S042- couldn't been generated directly in the reaction between HS- and O2.Thought meaturing quantificationally the oxidation products after reacting 2 hours between HS- and O2, the main product is S2O32-, there are less SO42- and not element sulfur. Then the formation mechanism of by-products is as follows:Moreove, by a continuous bubbling reactor, the reaction conditions of HS-and O2 were discussed in regenerate process and their kinetic equation was set up, the influence of tannin and vanadium as catalysts in desulfurization solution on this reaction were investigated also.In short, these studies in this paper are the supplement and perfection of tannin extract desulfurization mechanism, and theory foundation of developing TEDT further.