Kinetic Assessment of Light Hydrocarbons Separation over Fe-Doped 13X Composite Sorbents Under Multicomponent Feed Conditions

Abstract

Current sorbents investigated for light olefin/paraffin separation usually suffer from low selectivity. Besides, multicomponent analysis of this important separation is usually overlooked in the literature. To enhance the separation efficiency of zeolite 13X, we developed a series of Fe 2 O 3 /13X composite sorbents and assessed their separation performance using binary, ternary, and multicomponent gas mixtures of C 2 H 4 , C 2 H 6 , CH 4 , and H 2 . In these composites, nano-and micro Fe 2 O 3 particles (NPs and MPs) with varied loadings were used, while Fe was also ion-exchanged into the 13X zeolite structure. The microporosity and surface area of the bare sorbent were reduced upon increasing Fe x loading for all particle sizes. However, Fe 1 (NPs)/ 13X demonstrated a higher C 2 H 4 adsorption capacity and C 2 H 4 /C 2 H 6 selectivity despite its lower surface area, which was attributed to its higher surface electron transfer property that enhanced its adsorption performance via electrostatic interactions. Additionally, the incorporation of Fe 1 into the 13X framework resulted in narrowing of the micropore channels, thereby promoting the molecular sieving effect and improving the selectivity toward C 2 H 4 . The dynamic adsorption results revealed the reduction in C 2 H 4 /(C 2 H 6 + CH 4 + H 2 ) selectivity in the presence of impurity gases (CH 4 and H 2 ), from 4.10 to 3.84 and 3.20 for binary, ternary, and multicomponent gas mixtures, respectively. Nevertheless, the C 2 H 4 /C 2 H 6 selectivity was found to be roughly constant at ∼4 across all feed conditions. Moreover, the affinity of Fe 1 (NPs)/13X toward different adsorbates from the most adsorbed to the least adsorbed component was in the order of C 2 H 4 > C 2 H 6 > CH 4 > H 2 , while the rates of species transport were found to be primarily dependent on the rates of molecular diffusion within the pores of the 13X zeolite.