First-Principles Investigation of Two-Dimensional CuPP-Grid Molecular Sieves for C₄ Hydrocarbon Purification by a Double-Bond Effect

Separation and purification of C₄ hydrocarbons are critical processes in the petrochemical industry. The purification performance of a 2D CuPP-Grid molecular sieve membrane is systematically explored by first-principles calculations. A “double-bond effect” will reduce the penetration diameter of molecules, the transferred electrons, and the charge density overlaps between molecules and the molecular sieve, thus making a C₄H₆ molecule with two carbon–carbon double bonds pass through a pore without a diffusion barrier. An i-C₄H₁₀ molecule without a double bond has the highest diffusion barrier of 0.52 eV. Interestingly, the passing i-C₄H₁₀ molecule will cause the reversal of the magnetic property of the CuPP-Grid membrane, which can be applied for detection. Remarkably, under 150–400 K, the C₄H₆/n-C₄H₈, C₄H₆/i-C₄H₈, and C₄H₆/i-C₄H₁₀ selectivities of the CuPP-Grid membrane are in the relatively high range of 10²–10²⁶ with superior permeance. Our research theoretically verifies the feasibility of designing a kind of 2D nanomolecular sieve material for the efficient purification of 1,3-butadiene in the petrochemical industry.