Butadiene extraction uses N-methylpyrrolidone (NMP) as a selective solvent to recover 1,3-butadiene from a crude C4 stream. The technology is recognized worldwide for its high reliability and excellent ecological footprint.
Extractive distillation of Crude C4
Before entering the extractive distillation light components are separated from the crude C4 in a pre-distillation column. Any oxygen traces, which could otherwise initiate polymerisation, are also removed.
Then the feedstock enters the main washer column representing the first stage of the extractive distillation process. Butadiene and a part of the butenes are absorbed in the NMP solvent fed in from the top. The C4 raffinate is drawn off as the overhead product of the main washer column.
In the second extractive distillation stage the after washer and part of the rectifier column separate the C4 acetylenes. Both columns can be integrated into a single divided wall column saving capital expenditure and some plot space.
In the degassing column the hydrocarbons are stripped from the solvent and recycled to the rectifier column using a compressor. The diluted C4 acetylenes are withdrawn as a side stream and, after passing a scrubber, are discharged to battery limits.
The crude butadiene from the second stage of the extractive distillation is sent to the butadiene column for final purification. The butadiene product is withdrawn as a liquid side stream.
A major advantage of the NMP Process licensed by Air Liquide Engineering & Construction is its very high reliability and plant availability.
Delivers highly purified 1,3-butadiene suitable for all polymerization processes