Acetonitrile method

The solvent is acetonitrile (ACN) with water content of 1096, which consists of extraction, flash evaporation, compression, high-pressure desorption, low-pressure desorption and solvent recovery. The gas phases after low-pressure flash desorption are combined and compressed, condensed and sent to a water washing tower to wash off the solvent, and the gas phase at the top of the tower returns to the raw material distillation tower. Part of the residual gas is sent to the high-pressure desorption tower, and the other part is sent to the bottom of the extractive distillation tower as reboiler gas to provide heat energy. The solvent at the bottom of the washing tower is sent to the solvent recovery and refining system to ensure the quality of the circulating solvent. Raw materials with high alkyne content need hydrotreating, or precise rectification and two-stage extraction to obtain high-purity butadiene.

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Dimethylformamide method

Dimethylformamide method (DMF method), also known as GPB method, includes four processes, namely the first extractive distillation, the second extractive distillation, distillation and solvent recovery. Raw material C4 enters the first extractive distillation column, and solvent DMF is added from the upper part of the column. Butane, butene and C3 increase the relative volatility of butadiene and separate it from the top of the tower. Solvents such as butadiene and alkynes are led out from the bottom of the tower, completely desorbed in the first desorption tower, cooled and compressed by the screw compressor, and then enter the second extractive distillation tower. In order to prevent the explosion of vinyl acetylene and further recover butadiene from the solvent, the rich solvent discharged from the bottom of the second extraction tower is sent to the butadiene recovery tower with crude butadiene at the top. Butadiene and a small amount of impurities distilled from the top of the recovery tower are returned to the compressor inlet in front of the second extraction tower, and the solvent containing alkynes at the bottom of the tower is sent to the second desorption tower. Impurities in crude butadiene obtained by two-stage extractive distillation are removed by ordinary distillation. C3, moisture, etc. 2- Butene with higher volatility than butadiene is removed at the top of the light ends column, while residual 2- Butene, 2- Butene and C5 with lower volatility than butadiene are removed at the bottom of the heavy ends column. Polymer-grade butadiene can be obtained by removing the top of the heavy tower.

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N- methylpyrrolidone method

N- methylpyrrolidone method (NMP method) was successfully developed by BASF company in Germany, and its production process mainly includes extractive distillation, degassing distillation and solvent regeneration. Crude C4 enters the bottom of the main washing tower after vaporization, and N- methylpyrrolidone enters from the top of the tower. Butadiene, more soluble components and part of butane and butene are absorbed, while butane and butene without butadiene are discharged from the top of the tower. The rich solvent at the bottom of the main washing tower enters the rectification tower, and butadiene containing acetylene and propylene is extracted from the side line of the rectification tower in gaseous state and enters the post-washing tower. In the post-washing tower, crude butadiene is evaporated from the top of the tower, then condensed and liquefied to enter the distillation process, and the rich solvent at the bottom of the tower returns to the middle section of the rectification tower. The rich solvent in the distillation tower enters the flash tank for degassing, and then enters the degassing tower for hydrocarbon removal to control the water balance of NMP. A small amount of alkynes leave the degassing tower from the side line, and the remaining hydrocarbons enter the circulating compressor through the cooling tower and finally return to the bottom of the distillation tower. Methylacetylene was removed from the crude butadiene from the afterwashing tower in the first distillation tower, and 1, 2- butadiene and C5 hydrocarbons were removed in the second distillation tower, and butadiene products were obtained from the top of the second distillation tower.

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New progress in production technology

Recently, it has been reported that the traditional butadiene extraction process can be improved by using the partition wall technology, and the energy consumption and investment cost of the device can be reduced. The traditional butadiene extraction process is that the concentrated crude C4 fraction first passes through the absorption process, and then the crude butadiene distilled from the top of the post-scrubber is rectified in two distillation columns. Distilling the light fraction in the first rectifying tower; In the second rectifying tower, the heavy fraction is separated and removed from the bottom of the tower, and the butadiene product is distilled from the top of the tower. After adopting the dividing wall technology, the two-step distillation process can be carried out in one device.