In the middle of the 20th century, it was discovered that epichlorohydrin could be synthesized by the reaction of glycerol with hydrochloric acid and further hydrolyzed by lye. However, due to the high price of glycerin at that time, the research in this field remained in the experimental stage and was not applied to the actual industry. Therefore, in the last decades of the 20th century, few kinds of research were conducted on the synthesis of epichlorohydrin with glycerin. In recent years, due to the changes in the market and technology of epichlorohydrin production, the production method of epichlorohydrin synthesis from glycerin has been gradually put on the agenda.
Introduction to glycerin method
The reaction mechanism of chlorination of glycerol into dichloropropanol is the reaction process of chlorination of glycerol, which is realized under the action of fulvic acid and other catalysts. The reaction mechanism can be explained in the following three steps:
(1) first of all, the combination of ore and oxygen on the carbon base of fuseless acid makes the substrate subdivision and enhances the electropositivity of the carbon base. The nucleophile glycerin attacks the carbon on the diatom to form a tetrahedral intermediate. This intermediate is very unstable, the protons quickly transfer to the trans base end, and then lose a molecule of water and ten, resulting in the formation of the glyceride.
(2) oxygen atoms at the glycerol vinegar end are further protonated after the formation of glycerol. Under the influence of adjacent groups, the bonds of carbon and oxygen are broken and the fusiform is released, forming a ternary epoxy group, and the catalyst is reduced to its original form.
(3)Ternary epoxy groups are vulnerable to attack by chlorine ions, and pogonophile substitution occurs. Chlorine atoms are added to the position of the epoxy group to form monochloropropanediol. At the same time, the position of the epoxy group can also be replaced by extremely small amounts of chlorine atoms to form monochloropropanediol.
Therefore, from a macro point of view, in the acidic reaction environment, the glycerol and the fulvic acid catalyst were first vinegar reaction to produce the fulvic acid glyceride. The chloride ions then combine with the glycerol to form 3-chloropropanediol and 2-chloropropanediol, releasing the catalyst and forming cyclic esterification of the catalyst. Similar to the chlorination process of glycerol, 3-chloropropanediol and 2-chloropropanediol were chlorinated under the action of catalyst, and finally, dichloropropanediol was synthesized
The reaction of glycerin to dichloropropanol
As mentioned above, the first chlorination of glycerol mainly forms 3-chloropropanediol, and thus 1, 3-dichloropropanol (2, 3-dichloropropanol is rare) is mainly obtained during the second chlorination.
The development of the glycerin method is not only due to the decrease of the raw material price of glycerin, but also has many advantages over the traditional synthesis method and the newly developed direct oxidation method of chloropropylene.
(1). Technology has a long history and profound theoretical basis
(2). No need to use special equipment, the equipment investment is low
(3). Chlorine gas and hypochlorous acid are not needed and pollution is greatly reduced
(4). Catalysts are cheap and recyclable
(5). Mild reaction conditions, no high temperature and high pressure, safe and reliable
(6). The majority of dichloropropanol synthesized by chlorination of glycerol is 1, 3-dichloropropanol. Compared with 2, 3-dichloropropanol, this isomer has a faster reaction speed and higher product yield in the process of synthesis of epichloropropanol.
(7). Compared with the direct epoxidation of chloropropylene, the glycerine method is more favorable for industrial production