| Preparation of erythromycin thiocyanate leads to production of a large amount of wastewater which is complex, toxic and containing thiocyanate. Thiocyanate has some inhibitory effects on the activity of microbes, and brings certain difficulty to the biochemical treatment of wastewater. It has been proposed in this work to separate thiocyanate acid from erythromycin thiocyanate crystallization mother liquor by extraction and use sodium hydroxide solution as the stripping agent to recover thiocyanate and extraction solvent.The research in this work can be summarized as follows:First, screening of suitable extraction system including extraction agent, diluent and cosolvent has been conducted and mixture of trioctylamine (TOA) -n-octyl alcohol sulfonated kerosene has been determined as the applicable extraction solvent. And the effects of many factors on extraction equilibrium of HSCN with this extraction system have been investigated, such as extraction time, composition of extractant, initial concentration of SCN", pH and phase ratio.Second, with extraction system being determined, mechanism and corresponding thermodynamics for the extraction of HSCN has been investigated. It is shown that the mechanism of extracting HSCN with TOA is ionic association, TOA and HSCN form the extraction compound with the molar ratios of 1:1. Based on the thermodynamics study, the extraction of HSCN with TOA is found to be exothermic and spontaneous.Based on technological study, a process for separating HSCN from erythromycin thiocyanate crystallization mother liquor has beeen proposed. The extraction solvent (TOA-n-octyl alcohol-sulfonated kerosene) is used to extract HSCN from the wastewater and NaOH solution is used as the stripping agent to recover extraction solvent. With high yield of extraction and back-extraction of SCN" as criteria for operation objective, suitable process conditions have been determined:â‘ for extraction with TOA-n-octyl alcohol-sulfonated kerosene (10:5:85) and phase ratio of solvent to wastewater of 1:10, two stage crossflow extraction will reclaim 94.52%of SCN- from crystallization mother liqour at initial pH value of 3.50;â‘¡ as for back-extraction, with 38 g/L NaOH solution as stripping liquor and a phase ratio of 5:1 (solvent:NaOH solution), back-extraction rate of SCN- is 96.91%.The aim of this work is to provide theoretical basis and process guidance for establishing the technical route of separation thiocyanate from erythromycin thiocyanate crystallization wastewater which is technicaliy feasible and cost-controllable. |
