Process and apparatus for separating nitroaromatics from wastewater

Abstract

The invention relates to a process for the electrochemical treatment of aromatic nitro compounds, which comprises the steps: introducing an aqueous composition comprising at least one aromatic nitro compound into the anode space of an electrolysis cell and carrying out an electrolysis at an anodic current density in the range from 0.1 to 10 kA/m 2 and a cell potential in the range from 4 to 15 V.

1 . A process for the electrochemical treatment of aromatic nitro compounds, which comprises the steps:
 a) introducing an aqueous composition comprising at least one aromatic nitro compound into the anode space of an electrolysis cell,
 where the electrolysis cell has at least one anode space and at least one cathode space which are separated from one another by a separator, 
 and the electrolysis cell has at least one anode which comprises at least one anode segment comprising platinum or an anode segment consisting of a support material and a coating, where the support material comprises at least one metal selected from the group consisting of niobium (Nb), tantalum (Ta), titanium (Ti) and hafnium (Hf), and the coating consists of boron-doped diamond; 
   b) carrying out an electrolysis at an anodic power density in the range from 0.1 to 10 kA/m 2  and a cell potential in the range from 4 to 15 V.   
     
     
         2 . The process according to  claim 1 , wherein the aqueous composition is alkaline process wastewater from the nitration of aromatic compounds. 
     
     
         3 . The process according to  claim 1 , wherein the aromatic nitro compounds are at least one compound selected from the group consisting of nitrobenzene (NB), dinitrobenzene (DNB), trinitrobenzene (TNB), mononitrotoluene (MNT), dinitrotoluene (DNT), trinitrotoluene (TNT), nitrochlorobenzene (NCB), mononitroxylenes, dinitroxylenes, trinitroxylenes, mononitrocresol, dinitrocresol, trinitrocresol, mononitrophenol, dinitrophenol, trinitrophenol, mononitrobenzoic acid, dinitrobenzoic acid, trinitrobenzoic acid, mononitroxylenols, dinitroxylenols and trinitroxylenols, with all isomeric forms of the compounds mentioned being encompassed. 
     
     
         4 . The process according to  claim 1 , wherein the aqueous composition comprises at least one aromatic nitro compound in suspended form. 
     
     
         5 . The process according to  claim 1 , wherein the aqueous composition comprising at least one aromatic nitro compound additionally comprises a redox mediator. 
     
     
         6 . The process according to  claim 1 , wherein the temperature of the aqueous composition in the anode space in the electrolysis is in the range from 30 to 90° C. 
     
     
         7 . The process according to  claim 1 , wherein the electrolysis cell has an anode which comprises at least one anode segment comprising platinum and the electrolysis is carried out at an anodic current density in the range from 2.5 kA/m 2  to 10 kA/m 2  and a cell potential in the range from 4 to 15 V. 
     
     
         8 . The process according to  claim 1 , wherein the electrolysis cell has an anode which comprises at least one anode segment consisting of platinum, wherein the anode segment is in the form of foils, sheet or woven wire mesh and is fastened to a base frame comprising at least one metal selected from among niobium (Nb), tantalum (Ta), titanium (Ti) and hafnium (Hf), and the anode segment covers the surface of the base frame to an extent of not more than 30%. 
     
     
         9 . The process according to  claim 1 , wherein the electrolysis cell has an anode comprising at least one anode segment comprising a support material and a coating, where the support material comprises at least one metal selected from the group consisting of niobium (Nb), tantalum (Ta), titanium (Ti) and hafnium (Hf); the coating comprises boron-doped diamond; the anode segment is fastened to a base frame comprising at least one metal selected from among niobium (Nb), tantalum (Ta), titanium (Ti) and hafnium (Hf) and the electrolysis is carried out an anodic current density in the range from 0.1 kA/m 2  to 2 kA/m 2  and a cell potential in the range from 4 to 15 V and the coating of boron-doped diamond on the support material has a layer thickness in the range from 5 to 50 μm. 
     
     
         10 . An apparatus for the electrochemical treatment of aromatic nitro compounds, which comprises at least one electrolysis cell,
 wherein the electrolysis cell has at least one anode space and at least one cathode space which are separated from one another by a separator,   and the electrolysis cell has at least one anode which comprises at least one anode segment comprising platinum or an anode segment comprising a support material and a coating, where the support material comprises at least one metal selected from the group consisting of niobium (Nb), tantalum (Ta), titanium (Ti) and hafnium (Hf) and the coating comprises boron-doped diamond.   
     
     
         11 . The apparatus according to  claim 10 , wherein the separator is selected from among unspecific separators based on inorganic or organic porous materials, cation-exchange membranes based on polyethylene composite polymers and/or polyvinyl chloride composite polymers and/or polyvinylidene fluoride (PVDF) and/or polytetrafluoroethene (PTFE) and anion-exchange membranes. 
     
     
         12 . The apparatus according to  claim 10 , wherein the electrolysis cell has a spacer between the separator and the anode, where the spacing between anode and cathode is in the range from 2 to 12 mm. 
     
     
         13 . The apparatus according to  claim 10 , wherein the spacer between anode and cathode is a multilayer woven mesh composed of nonconductive polymer, with the various layers having a gradated aperture.