This column is based on “Polybutadiene Production via Solution Process – Cost Analysis,” a report published by Intratec. It can be found at: www.intratec.us/analysis/polybutadiene-production-cost.
Polybutadiene (also known as butadiene rubber) is produced from the polymerization of 1,3-butadiene. In terms of production volume, polybutadiene is among the largest synthetic rubbers produced. This elastomeric polymer can have a variety of different properties depending on the ratio of its microstructural units and its tacticity. Most polybutadiene is consumed in the production of vehicle tires. It is also used to improve the mechanical properties of plastics.
The production process discussed here is similar to the CB&I Lummus Catadiene process, integrated with a typical solution process. The process comprises four major sections: (1) n-butane dehydrogenation; (2) 1,3-butadiene purification; (3) polymerization; and (4) rubber molding. Figure 1 presents a simplified flow diagram.
n-butane dehydrogenation. Initially, fresh butane, recovered butane and mixed butenes are heated to dehydrogenation temperature. These components then pass through fixed beds of chromia-alumina catalysts in the reactors, where they 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 (NMP), used as a solvent. This step yields high-purity butadiene. Recovered butane and butenes are recycled to the dehydrogenation step, while other hydrocarbons are used as fuel.
Polymerization. High-purity butadiene is pre-treated for the 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, where polymerization occurs. Polymerization is interrupted by stopping agents when the desired molecular-weight of the polymers 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 of polybutadiene are cooled with air, weighed, baled and stored.
Different manufacturing routes for polybutadiene are related to different sources of the butadiene used. In this context, the most typical production routes are based on butadiene produced from isolation of C4 steam-cracker fractions and dehydrogenation of butane and butenes. Different pathways for polybutadiene production are presented in Figure 2.
The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce polybutadiene was about $1,600 per ton of polybutadiene in the second quarter of 2015. The analysis was based on a plant constructed in the U.S. with capacity to produce 120,000 metric tons per year of polybutadiene.
Edited by Scott Jenkins
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