Patent DE-102007014504-A1 (DE)
Title: Eluting sodium thiocyanate from a solution containing secondary salt comprises adding alcohol to a partial stream of the solution, separating sodium thiocyanate and partially reintroducing the partial stream into the elution process
Inventor: HOFMANN GUENTER
IPC: C01B17/64
Filed: 2007-03-27
Abstract: Procedure for the elution of sodium thiocyanate from a solution, containing a secondary salt, which is circulated in a desulfurization washing process, particularly circulated in a sulfolin- or Stretford process, comprises adding alcohol to a partial stream of a cyclically flowing solution, separating sodium thiocyanate and at least partially reintroducing the partial stream into the elution process, after elution. Procedure for the elution of sodium thiocyanate from a solution, containing a secondary salt, which is circulated in a desulfurization washing process, particularly circulated in a sulfolin- or Stretford process, comprises adding alcohol to a partial stream of a cyclically flowing solution, separating sodium thiocyanate and at least partially reintroducing the partial stream into the elution process, after elution, where sodium thiocyanate that is eluted from the partial stream is extracted as a salable salt product; the alcohol containing a maximum of 2C-atoms and acting as an anti-solvent for the essential part of the secondary salts that are dissolved in water, is used; the separation of sodium thiocyanate takes place by a displacement crystallization (Drowning-out crystallization) of the main part of the secondary salts that are contained in the partial flow and the extraction of sodium thiocyanate as a highly concentrated salt is carried out by means of crystallization from the mother liquor of the displacement crystallization. Independent claims are included for: (1) a sodium thiocyanate crystallized product, with a purity of at least 99%, preferably at least 99.5%, which is obtained form the process; and (2) a plant for the implementation of the procedure comprising sodium thiocyanate separation mechanism, which is connected over a branch line (5, 8) with the washing cycle (4) of a purification plant (2) for desulfurization of a sulfurous substance (1), and into which a solvent can be fed over a feeder (24), and from which on the one hand a sodium thiocyanate-enriched part of the solution that is led out of the washing cycle over the branch line can be fed back over a return line (15, 18, 20) into the washing cycle and from which on the other hand a sodium thiocyanate-enriched part of the solution that is led out of the washing cycle can be fed over a line into a mechanism for the formation of sodium thiocyanate crystallized product, where the sodium thiocyanate separation mechanism is built as a displacement crystallization system (12), into which an alcohol that acts as an anti-solvent for a substantial part of the secondary salts of the sodium thiocyanate present in the solution can be fed over the feeder, and the mother liquor can be fed over a line (13, 21, 25, 28) from the displacement crystallization system to the sodium thiocyanate crystallization mechanism (29), from which the formed mother liquor that is largely freed from sodium thiocyanate is fed over a mother liquor feedback line (30) to the displacement crystallization system.