Increase the value of steam-cracker C4 cuts via low-temperature selective hydrogenation and hydroisomerization catalysis. Several options exist: removal of ethyl and vinyl acetylenes to facilitate butadiene extraction processing downstream; conversion of 1, 3-butadiene to maximize 1-butene or 2-butene production; production of high-purity isobutylene from crude C4 cuts; high conversion MTBE and superfractionation to produce polymer-grade butene-1; total C4 cut hydrogenation; and total hydrogenation of combined C3/C4 and C4/C5 cuts for recycle to cracking furnaces or LPG production.
Each application uses a specific process, catalyst and operating conditions. The basic process for maximizing 1-butene consists of sending a combined butadiene-rich C4 cut, recycled C4s, makeup hydrogen to the main reactor (1) where acetylenes and 1, 3-butadiene (in the case of hydroisomerization to a specified product distribution) are hydrogenated. A finishing reactor (2) is used if required. Reactions take place in the liquid phase at low temperatures to provide significant advantages in the area of heat removal, approach to equilibrium, catalyst life and reaction homogeneity. Information here is for the C4 selective hydrogenation process applied to maximize 1-butene. It is typically completed with high-conversion MTBE (using Axens, reactive distillation called Catacol) to convert isobutylene and superfractionation delivering the highest quality butene-1 used as a copolymer in LLDPE.
The process is different in the case of high-purity isobutylene production where a reactor and distillation column operate on the C4 stream simultaneously.