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.