Study On The Causes Of By-Products Na₂S₂O₃ In The Process Of Tannin Extract Desulfurization Technology

Tannin extract desulfurization process is currently one of the most widely used desulfurizing techniques in coal gas cleanup in China. But it still has disadvantages such as side reactions which exist in all liquid-phase desulfurization technology. When the content of by-products reach to a certain degree,the consumption of sodium carbonate ( Na₂CO₃) increase and desulfurization efficiency will decline. So the causes of the formation of by-products( Na₂S₂O₃)were studied in this paper,and the main conclusions as follows .The effects on the reaction of NaHS and O₂ were carried out in continuous bubbling reactor and the causes of the formation of by-products( Na₂S₂O₃)were studied. The following results were obtained.(1)The Na₂S₂O₃ is the main component of by-products with little Na 2SO4 by quantitative analysis of the possible products.(2)The reaction rate of HS^- and O₂ accelerated with the increase of the initial concentration of sodium hydrosulphide,air velocity, temperature and the PH of solution.(3)The reaction order is 1.0 and the activation energy is 26302.43KJ/mol for NaHS and O₂ under adequate O₂atmosphere.(4)There is no sulfur detected in the products which shows that HS-, 2?S 2O3, SO3 2?and SO 42? in the regenerative process could not convert to sulfur.The effects of Tannin extract and sodium metavanadate on the reaction of NaHS and O₂ were investigated by 314 A-type sulfide ion selective electrode. The results as following:( 1 ) The transformation rate of NaHS increased with the rise of concentration of tannin extract because tannin extract has high oxidation reactivity and enhances the reactivity of O₂. Besides, the transformation rate of NaHS accelerated with the increase of temperature and the PH of solution.(2)The transformation rate of NaHS increased with the rise of concentration of sodium metavanadate due to the high oxidation of sodium metavanadate. Besides,the transformation rate of NaHS accelerated with the increase of temperature and the PH of solution.The reaction of NaHS and NaVO₃ were researched by 314A-type sulfide ion selective electrode. The results as following:(1)The results show that the reaction is complicated with two steps. The rapid reaction reached homeostasis at about 20s, and the oxidation reaction equation of NaHS and NaVO₃ is v = 0.0427CNaHS. (2)The sulfur appeared until the reaction lasted 5 mins which might be illustrated by the reaction mechanism which is a complicated reaction involving the formation of polysulphides as intermediates and S8. The chemical reactions as following:This also explain that polysulphides is one of the resource of by-product contained elemental sulfur.A new method of multi-wavelength spectrophotometric linear regression was used in this paper to determine the concentration of Na₂S₂O₃ and NaSCN in the desufurized solution. The results showed that the concentration of Na₂S₂O₃ and NaSCN is 0.6329 mol/L and 3.9506 mol/L,respectively,and the relative error of the Na₂S₂O₃ and NaSCN were less than 3%. The method is simplified and fast,and is better applied to research on by-products.