C4 Acetylenes Hydrogenation Process
The various solvent extraction processes easily separate butenes from 1,3-butadiene but not the acetylene compounds: vinylacetylene (VAC), 1-butyne (ethylacetylene, ETAC) and propyne (methylacetylene, MAC).
Expensive (investment and utility cost) distillation towers must be then used to meet polymer-grade specifications. Such columns are often bottlenecks in extraction processes. In some cases (modern extraction processes), operators have increased overall butadiene recovery by suppressing the acetylenes' purge, which contains butadiene.
Hydrogenating acetylenes selectively is the ideal way to debottleneck butadiene units. However, VAC forms strong complexes with the catalyst's precious metals, e.g., palladium; the resultant metal leaching causes short lifetimes (a few months) for conventional catalysts. Axens therefore developed a bimetallic catalyst, LD 277, which reduces palladium losses by a factor of ten.