Recovery of purified and substantially anhydrous propylene oxide

A distillation method for the purification of crude propylene oxide containing contaminants comprising water, acetaldehyde and methanol which comprises the steps of:

• charging the crude propylene oxide to a first distillation column and operating the first distillation column under distillation conditions of temperature and pressure selected to provide a first lighter liquid distillation fraction comprising acetaldehyde and a first heavier liquid distillation fraction comprising propylene oxide, water and methanol,
• charging the first heavier distillation fraction to a second distillation column and operating the second distillation column under distillation conditions of temperature and pressure selected to provide a second lighter liquid distillation fraction comprising propylene oxide, less than half of the water charged to the second distillation column and more than half of the methanol charged to the second distillation column and a second heavier liquid distillation fraction comprising more than half of the water charged to the second distillation column and less than half of the methanol charged to the second distillation column,
• charging the second lighter distillation fraction to a third extractive distillation column and also charging an effective amount of a C.sub.8 to C.sub.10 paraffinic hydrocarbon extractive distillation agent thereto and operating the third distillation column under extractive distillation conditions of temperature and pressure selected to provide a third lighter liquid distillation fraction comprising the extractive distillation agent, substantially less than 50% of the water charged to the third distillation column and substantially all of the methanol charged to the third distillation column and a third heavier liquid distillation fraction comprising propylene oxide and than less than half of the water charged to the third distillation column,
• charging the third heavier distillation fraction to a fourth extractive distillation column and also charging an effective amount of a C.sub.8 to C.sub.10 paraffinic hydrocarbon extractive distillation agent thereto and operating the fourth distillation column under extractive distillation conditions of temperature and pressure selected to provide a fourth lighter vapor overhead distillate fraction comprising propylene oxide and less than half of the water charged to the fourth distillation column and a fourth heavier liquid distillation fraction comprising the extractive distillation agent and more than half of the water charged to the fourth distillation column,
• passing said propylene oxide vapor fraction through a drying chamber containing a porous hygroscopic solid absorbent at a temperature of about 34.degree. to about 100.degree. C. and a pressure of about 15 to about 30 psia, to selectively absorb water vapor onto the absorbent,
• and liquefying and recovering the thus-dehydrated purified propylene oxide.

A distillation method for the purification of crude propylene oxide containing contaminating quantities of water, C.sub.5 and C.sub.6 hydrocarbons, methyl formate, acetaldehyde, propionaldehyde, methanol, tertiary butyl alcohol and acetone which comprises the steps of:

• charging the crude propylene oxide to a first distillation column and operating the first distillation column under distillation conditions of temperature and pressure selected to provide a first lighter liquid distillation fraction comprising C.sub.5 hydrocarbons, methyl formate, acetaldehyde and a first heavier liquid distillation fraction comprising propylene oxide, water, methanol, tertiary butyl alcohol, acetone, acetaldehyde, propionaldehyde and C.sub.6 hydrocarbons,
• charging the first heavier distillation fraction to a second distillation column and operating the second distillation column under distillation conditions of temperature and pressure selected to provide a second lighter liquid distillation fraction comprising propylene oxide, less than half of the water charged to the second distillation column, more than half of the methanol charged to the second distillation column, methyl formate, acetaldehyde and C.sub.6 hydrocarbons, and a second heavier liquid distillation fraction comprising more than half of the water charged to the second distillation column, less than half of the methanol charged to the second distillation column, acetone, tertiary butyl alcohol and propionaldehyde,
• charging the second lighter distillation fraction to a third extractive distillation column and also charging an effective amount of a C.sub.8 to C.sub.10 paraffinic hydrocarbon extractive distillation agent thereto and operating the third distillation column under extractive distillation conditions of temperature and pressure selected to provide a third lighter liquid distillation fraction comprising the extractive distillation agent, substantially less than 50% of the water charged to the third distillation column, substantially all of the methanol charged to the third distillation column, methyl formate and acetaldehyde and a third heavier liquid distillation fraction comprising propylene oxide, less than half of the water charged to the third distillation column, and C.sub.6 hydrocarbons,
• charging the third heavier distillation fraction to a fourth extractive distillation column and also charging an effective amount of a C.sub.8 to C.sub.10 paraffinic hydrocarbon extractive distillation agent hereto and operating the fourth distillation column under extractive distillation conditions of temperature and pressure selected to provide a fourth lighter vapor overhead distillate fraction comprising propylene oxide and less than half of the water charged to the fourth distillation column and a fourth heavier liquid distillation fraction comprising the extractive distillation agent, more than half of the water charged to the fourth distillation column, and C.sub.6 hydrocarbons,
• passing said propylene oxide vapor fraction through a drying chamber containing a porous hygroscopic solid absorbent at a temperature of about 34.degree. to about 100.degree. C. and a pressure of about 15 to about 30 psia, to selectively absorb water vapor onto the absorbent,
• and liquefying and recovering the thus-dehydrated purified propylene oxide.