Chlorohydrin process is one of the widely used production methods of
ECH, in which dehydrochlorination reaction of dichloropropanol (DCP)
with hydrated lime is an essential step,27 and
it
can be a great reference for the ring-closure process of chlorohydrin
ester intermediate (EPDA-M) to produce EPDA by dehydrochlorination
reaction with sodium hydroxide. The temperature and alkali concentration
are two most important factors of the reaction. When the temperature
higher than 70 oC was applied, EPDA degradation caused
by the hydrolysis of ester bonds became obvious. Therefore, it is a
better option to carry out the reaction in the temperature range of
40~60 oC. According to the
experimental results shown in Scheme 6 , it is hard to
completely convert EPDA-M when excessive alkali was fed in one-time.
This is because the alkali concentration, more specifically referring to
the concentration at the organic-aqueous interface, decreases as the
reaction proceeds, leading to the significantly reduction of the
ring-closure reaction rate.
In order to maintain relatively high concentration of the alkali in the
late stage of the ring-closure reaction, we adopted a two-step alkali
treatment process which is introduced in the Experimentsection. The first alkali treatment process was carried out by adding 40w % NaOH solution (0.8 equiv). The conversion of
60~65% can be achieved after 1 hour at 50oC. Then, the secondary alkali treatment was applied
by adding 40 w % NaOH (1 equiv) after phase separation. The total
addition of 1.8 equivalent NaOH is the same as the one-time experiment,
but the final conversion of EPDA-M can exceed 97% within 2 hours’
treatment (including two steps).
Table 5 . Effects of alkali concentration and treatment time in
the second step on the ring-closure reaction.