Clean production method for epoxypropane using the chlorohydrination process with a chlorine close-loop circulation

A clean production method for epoxypropane using the chlorohydrination process with a chlorine closed-loop circulation, the clean production method comprises the following steps:

• (1) a chlorohydrination process:
• initially dissolving chlorine in water at a temperature of 35-45°C through a chlorine dissolver to produce hypochlorous acid and then feeding into a chlorohydrination reactor, introducing propylene through a propylene distributor according to a molar ratio of chlorine to propylene of 1:1.01-1.1, wherein a reaction pressure is normal pressure, or above normal pressure but not higher than 10 KPa (gauge pressure), a reaction temperature is within the range of 50-70°C, thereby producing a chloropropanol-containing solution having a concentration within the range of 3.0 wt %-6.0 wt %, which contains hydrochloric acid with an equal molar concentration with chloropropanol, washing a tail gas obtained from the flash evaporation process with a NaOH electrolyte, and feeding the tail gas back to a propylene recovery system;
• (2) a causticization process:
• mixing the chloropropanol-containing solution having a concentration within the range of 3.0 wt %-6.0 wt % obtained from step (1) with a NaOH electrolyte having a concentration within the range of 10 wt %-20 wt % according to a molar ratio of 1.0-1.2:1 of sodium hydroxide to the total amount of chloropropanol and hydrochloric acid, feeding the mixture to a tubular causticization reactor to perform a causticization reaction to obtain a reaction solution, wherein a causticization reaction temperature is within the range of 90-95°C, a reaction time is within the range of 0.5-2 seconds, and then feeding the reaction solution into a stripping tower to obtain a crude epoxypropane with a content within the range of 90 wt %-95 wt %, an absolute pressure of the stripping tower top is within the range of 25-65 KPa, and obtaining a causticization wastewater having a NaCl content within the range of 2.5-5.5 wt % from the stripping tower bottom;
• (3) a rectification process:
• feeding the crude epoxypropane with a content within the range of 90 wt %-95 wt % generated in the causticization process into a front distillation tower and a fractionating tower which are connected in series, the crude epoxypropane initially passes through the front distillation tower, a finished product epoxypropane is extracted from the top of the front distillation tower, high-boiling-point components are discharged from the top of the fractionating tower, both the front distillation tower and the fractionating tower are operated under normal pressure, the fractionating tower bottom temperature is within the range of 50-85°C, and the fractionating tower bottom causticization wastewater is discharged from the fractionating tower bottom;
• (4) a causticization wastewater treatment process:
• subjecting the causticization wastewater obtained from the stripping tower bottom, a tail gas washing waste liquid and a fractionating tower bottom causticization wastewater to a supercritical gasification reaction and separation by electromagnetic heating to generate a synthesis gas, a purified water and a NaCl slurry, diluting the NaCl slurry with a part of purified water to a concentrated brine with a concentration of 31.5 wt %-36.1 wt %, and then returning the concentrated brine to a chlorine-alkali electrolytic bath for recycling, and returning the remaining purified water to the chlorohydrination process;
• (5) a NaCl solution electrolysis process:
• electrolyzing the concentrated brine with a concentration of 31.5 wt %-36.1 wt % in the chlorine-alkali electrolytic bath, recycling the obtained chlorine to the chlorohydrination process for generating hypochlorous acid, and returning the NaOH electrolyte with a concentration of 10 wt %-20 wt % to the causticization process for carrying out the causticization reaction.