The BASF process uses n-methylpyrrolidone (NMP) as solvent to produce a high-purity butenes stream from a mixture of butanes and butenes. The feedstock is typically the raffinate byproduct of a butadiene extraction process or an “onpurpose” butene process.
The C4 feed, containing a mixture of butanes and butenes, is fed to the butenes absorber column (1), which produces an overhead butanes stream containing only a few percent butenes. The bottoms stream from this column contains butenes absorbed in the solvent. The butenes are stripped from the solvent in the butenes stripper (2). The overhead of the butenes stripper is a butenes stream that contains a few percent butanes.
The vapor overheads of both the absorber and stripper are condensed with cooling water, generating the respective butanes and butenes products. Each column has a small reflux flow that washes the overhead product to minimize solvent losses.
The bottoms of the stripper is lean solvent, which is cooled against process streams and then cooling water before being sent to the butenes absorber. The butenes stripper is reboiled using medium pressure steam.
Yields and product quality: Typical product qualities are 5% butanes in the butenes product and 5% butenes in the butanes product. Higher quality products can be achieved if required. C4 losses are essentially zero.
Licensor: BASF/Lummus Technology