Extraction

RECOVERY OF HIGH BOILING SOLVENTS FROM WASTE WATER

DESTROY OR RECOVER?

Industrial  waste  water  often  contains  high  boiling  solvents, such  as  phenol  or  dichlorobenzene,  and  so  cannot  be discharged into a sewage treatment plant without reprocessing and cleaning. Since destruction through burning is not only a bad alternative ecologically but also too costly due to the high water  content,  the  preferred  way  is  phenol  recovery  with simultaneous  cleaning  of  the  waste  water  until  it  can  be discharged into the sewage treatment plant. The example of phenol  is  used  to  describe  the  method  used  repeatedly  by SCS

The  phenol  content,  which  depends  on  the  process,  is normally 2-12%. The low phenol concentrations eliminate separation by distillation, in which the water is evaporated out, due to the high energy requirements. Here, extraction offers  the  decisive  advantage.  Methylisobutylketone (MIBK),  an  extracting  agent,  removes  phenol  from  the waste  water  in  the  extraction  column    K1.  The  charged extracting agent is cleaned again in the distillation columnK2 and returned to the bottom of the extraction. The phenol accumulates in the bottom of the subsequent rectification (column K2) and can be used again in production.

While the waste water flowing out of the extraction K1 may be free of phenol, it carries along traces of the extracting agent, which are recovered in the stripper K3. The MIBK/water az eotrope accumulates at the head of the column, where it is separated in the separator B1 into the light MIBK phase and the heavy water phase. Since the distillation column K2 is operated without water, indirect heating is planned here, while direct steam can be introduced into the stripper.