Membranes and adsorbents in separation of C4 hydrocarbons: A review and the definition of the current upper bounds

C4 hydrocarbons are valuable fractions of the oil and gas processing industry due to their market size and importance as raw materials in the manufacture of several products. C4s are derived from fluid catalytic cracking (FCC) and from natural gas fractionation, and are often produced as mixture of associated hydrocarbons that are typically recovered by cryogenic distillation. Yet, the latter is rather challenging, energy-consuming, and economically inefficient due to the similarity in vapor pressures of the constituents. To this end, technologies to separate these hydrocarbons using membranes and adsorption are being intensively explored as efficient, economical, and energy-saving alternatives. This review presents a critical summary of these technologies and the involved materials along with their comparative performance in C4 hydrocarbon separations. In addition, the current upper bounds of membrane selectivity (~1000) and permeance (~4 × 10⁻⁶ mol/m² s Pa), and adsorbent selectivity (~300) and uptake (~13 mmol/g) are presented for the separation of various C4 pairs of industrial interest.