Study On The Treatment Of Nitropyrazole Wastewater

Nitropyrazole is currently an important organic intermediate in the synthesis of pharmaceuticals,pesticides,energetic materials,and other important organic intermediates.Nitropyrazole synthesis uses nitrate-sulfur mixed acids as the nitrification system.During the nitrification process,a large amount of DNP-containing acidic wastewater will be generated,while crude DNP will generate weakly acidic washing wastewater during the refining process.Improper treatment of these two types of wastewater will cause serious harm to the ecosystem and human health.It is of great practical significance to study the treatment of wastewater generated in the synthesis and refining processes of nitropyrazole.In this paper,the extraction process and single factor conditions of nitrification wastewater generated during the preparation of DNP(3,4-dinitropyrazole)were studied using extraction,Fenton method,and electrochemical methods,respectively,and a better wastewater treatment scheme was obtained.(1)Extraction method: By using high-performance liquid chromatography and ion chromatography,the main components of nitrification wastewater were determined to be DNP and sulfuric acid.The organic solvent extraction method was used to recover DNP.The extraction effects of different solvents were compared,and different extraction processes were investigated to obtain optimized extraction conditions.Choosing ethyl acetate as the optimal extractant for extracting nitrification wastewater,the optimal extraction ratio is nitrification wastewater: ethyl acetate=12:1,and the recovery rate of DNP is 94.4%.The remaining acidity after extraction is mainly generated by sulfuric acid,which can be concentrated and recycled for the synthesis of nitropyrazole.The main component of weak acidity of refined wastewater is DNP.The optimal extraction ratio of refined wastewater is ethyl acetate=8:1.The recovery rate of DNP is 96.2%.After extraction and dilution,the chemical oxygen demand(COD)is less than 150 mg/L,which meets the national wastewater discharge standard.It can be discharged to the factory wastewater treatment system,and the preliminary cost estimation of the recovery process is made.(2)Fenton method: By examining the influencing factors of Fenton method on the treatment of nitrification wastewater,it was found through UV visible absorption spectrum analysis that the absorbance of the raw water sample significantly decreased after Fenton oxidation treatment in the UV visible region,with a DNP removal rate of 97% and a COD removal rate of 62.9%.Meanwhile,through reaction kinetics analysis,the removal process of DNP in the Fenton oxidation reaction follows a pseudo second-order reaction kinetics equation.(3)Electrochemical method: By examining the influencing factors of electrochemical method on the treatment of nitrification wastewater,the UV visible absorption spectrum analysis shows that the absorbance of the raw water sample significantly decreases after electrolytic oxidation treatment in the UV visible region,indicating that the organic matter in the wastewater is significantly oxidized and removed,with a DNP removal rate of 90% and a COD removal rate of 58%.(4)By comparing the effectiveness of extraction method,Fenton method,and electrochemical method in treating wastewater,it can be concluded that the extraction method has significant economic benefits.It can be calculated that extracting 1 ton of nitrifying wastewater yields a benefit of 11015 RMB,and extracting 1 ton of refining wastewater yields a benefit of 30602.5 RMB.Fenton method and electrochemical method still have shortcomings in the treatment of wastewater,and there may be some secondary pollution issues.In summary,extraction and recovery of DNP can be used as a better solution for nitropyrazole wastewater treatment.