In naphtha cracking process, C4R3 refers to C4 residual obtained after separation of 1,3-butadiene, isobutylene, and 1-butene from C4 raffinate stream which mainly consists of cis- or trans-2-butene, n-butane, and unseparated 1-butene. Normally C4R3 is being process through a selective hydrogenation unit (SHU) and CDHydro deisobutenizer unit to produce isobutylene as a feed to tert-butyl alcohol  plant.