Study of the intereaction of sodium tyocyanate with the mineral acids and investigation of the properties of received products

: 22-27
Lviv Polytechnic National University
Lviv Polytechnic National University
Lviv Polytechnic National University

Hydrogen sulfide gases are formed in many technological processes, in particular, the processing of natural combustible fossil fuels. During the purification of coke oven gas containing cyanadium, from hydrogen sulfide by arsenic-sodic method, sodium thiocyanate is formed together with thiosulfate. Polymer sulfur, which is formed because of the acid decomposition of sodium thiosulfate, contains slightly soluble impurities. They aggravate its rheological properties and cause excessive high ash content of polymer sulfur up to 8%.

To substantiate the expediency of purifying polymer sulfur from impurities formed during the reaction of sodium thiocyanate with mineral acids, the features of this process were studied and the main properties of the formed products were studied.

The research was carried out by the method of potentiometric titration of the NaSCN solution with solutions of nitrate, sulfate and chloride acids. The solubility of the obtained products in inorganic and organic environments was studied gravimetrically.

On the basis of the analysis of the dependence of the redox potential of the system on the volume of nitric acid, it was concluded that it plays the role of a non-reactant that interacts with NaSCN, but a catalyst for the transformation of sodium thiocyanate. Under the action of HNO3 as a strong oxidizer there is a trimerization of thiocyanate to form a slightly soluble triazine-2,4,6-tritiol. Based on the performed calculations, the spatial formula bis-(triazine-4,6-dithiol-yl-2)-disulphide was proposed and the lengths of the bonds between the atoms in this compound were calculated. For excess in the medium of HNO3, bis (triazine-4,6-dithiol-yl-2) -polysulfide is formed. The X-ray diffraction analysis confirmed that the product obtained is amorphous. Its structure was established by the method of infrated spectroscopy.

During the interaction of NaSCN with concentrated sulfate and chloride acids, low molecular weight compounds with a high degree of crystallinity, in particular triazine-2,4,6-tritiol, are formed. They have similar solubility in water and organic solvents.

The high solubility of products formed under the influence of the indicated acids in sodium hydroxide solutions is due to the breakdown of the S-S bond that is inherent in polysulphide systems. However, during the extraction of these products from polymeric sulfur, its destruction will also occur. On the basis of the obtained results, it was concluded that the chemical extraction of low soluble polymer sulfur compounds is not feasible.

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