Polybutadiene Production from n-Butane

The process under analysis comprises 4 major sections: (1) n-Butane dehydrogenation; (2) 1,3-Butadiene purification; (3) Polymerization; and (4) Rubber molding.

n-Butane dehydrogenation. Butane and butenes are heated to dehydrogenation temperature. They pass through fixed beds of chromia-alumina catalysts in the reactors and are converted into butadiene.

1,3-Butadiene purification. The reactor product is quenched for removal of polymeric compounds. The quenched gas is compressed and partially condensed. The liquid condensate, containing butadiene, is fed to a series of distillation columns, from which a butadiene-rich C4 stream is obtained. This stream is then submitted to extractive distillation in the presence of N-methylpyrrolidinone used as solvent, yielding high-purity Butadiene. Recovered butane and butenes are recycled to dehydrogenation, while other hydrocarbons are used as fuel.

Polymerization. High-purity Butadiene is pre-treated for removal of polymerization inhibitors as well as residual impurities. The treated Butadiene is dissolved in hexane and fed to a series of two continuously stirred polymerization reactors. Polymerization takes place in those reactors and is only interrupted by stopping agents when the desired molecular-weight is achieved.

Rubber molding. The polymer slurry from polymerization is passed through a flasher and subsequently through a steam stripper for hexane solvent recovery. Hexane recovered by flashing is directly recycled while hexane recovered via stripping must be further separated from water before being recycled. A crumb-water slurry is obtained and fed to a drying step. The dried crumbs are cooled with air, weighed, baled and stored.