Acetic Acid Removal from Brine
by UV-Catalyzed Chlorination
J. R. MOYER
C. S. PARMELE
Environmental Research Laboratory
Dow Chemical Company
Midland, Michigan
INTRODUCTION
A chlor-alkali based company uses much of its chlorine and caustic soda internally.
Dow's phenol process is an example: we chlorinate benzene, then hydrolyze the
chlorobenzene. The aqueous effluent from the process is a brine. Some of these brines are
concentrated enough to serve as feed for chlorine cells, but they contain soluble organic
impurities which interfere with the operation of chlorine cells. With the organics gone,
recycling is possible.
Biological processes don't work in such strong brines. Physical processes such as steam
stripping, extraction, and precipitation remove some, but not all of these organic
impurities. Activated carbon is very effective with aromatic compounds, but less effective
with aliphatics. So we find a hard core of small organic molecules which defy conventional
separation processes. Chief among these small organics is acetic acid. Thermodynamics is
behind it. Aliphatic carboxylic acids are relatively inert, so we see acetic acid turning up
where you wouldn't expect it. Who would predict that the hydrolysis of chlorobenzene gives
some acetic acid?
Let's look at the composition of the waste brine from phenol production (Table I).
When the problem of removing the organics first came up, we found that activated carbon
would take care of the phenol. A multi-pronged attack was made on the sodium acetate.
When decision time came, activated carbon was chosen for acetate removal as well. Since
that time, we have brought along the technology I will describe. It has proven to be a
cheaper process for hot brines and has supplanted activated carbon.
TABLE I
COMPOSITION OF WASTE BRINE FROM PHENOL PRODUCTION
Sodium chloride 18      percent
Phenol 0.01 percent
Sodium acetate 0.1   percent
This work was undertaken on the premise that acetic acid might decompose readily if
one of the methyl hydrogens could first be removed by a free radical. This would puncture
its thermodynamic defenses and give something which could be readily oxidized to C02. We
used aqueous potassium persulfate as a source of free radicals and found that acetic acid
was wiped out in no time. This is impractical, of course, so we turned to chlorine and
ultraviolet light as a cheaper source of free radicals. We were expecting to use four moles of
chlorine to oxidize each mole of acetic acid and to obtain C02 as follows:
CH3C02H + 4 Cl2 = 2 C02 + 8 HC1
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