Qun Cui

Study on the Desorption Process of n-Heptane and Methyl Cyclohexane Using UiO-66 with Hierarchical Pores

UiO-66 (UiO for University of Oslo) is a zirconium-based metal-organic framework with reverse shape selectivity, which gives an alternative way to produce high-purity n-heptane ( nHEP) used for the manufacture of high-purity pharmaceuticals. A couple of studies have shown that UiO-66 gives a high selectivity on the separation of n-/iso-alkanes. However, the microporous structure of UiO-66 causes poor mass transport during the desorption process. In this work, hierarchical-pore UiO-66 (H-UiO-66) was synthesized and utilized as an adsorbent of nHEP and methyl cyclohexane (MCH) for systematically studying the desorption process of n-/iso-alkanes. A suite of physical methods, including X-ray diffraction patterns, verified the UiO-66 structures, and high-resolution transmission electron microscopy showed the existence of hierarchical pores. N2 adsorption-desorption isotherms further confirmed the size distribution of hierarchical pores in H-UiO-66. Of particular note, the MCH/ nHEP selectivity of H-UiO-66 is similar to that of UiO-66 under the same adsorption conditions, and the desorption process of nHEP/MCH from H-UiO-66 is dramatically enhanced; namely, the desorption rates for nHEP/MCH from H-UiO-66 is enhanced by 30%/23% compared with UiO-66 at most. Moreover, desorption activation energy ( Ed) derived from temperature-programmed desorption experiments indicate that the Ed for nHEP/MCH is lower on H-UiO-66; that is, the Ed of MCH on H-UiO-66 is ∼37% lower than that on UiO-66 at most, leading to a milder condition for the desorption process. The introduction of hierarchical structures will be applicable for the optimization of the desorption process during separation on porous materials.

Effect of Macropore Structure on Desorption Diffusion Performance of N-Pentane on 5A Zeolite

Desorption rate curves of n-pentane on 5A zeolites at 418 K and 10-0.03 kPa were determined, and the effects of different macropore structure on desorption performance were analyzed. Results show that macropore distribution of 5A-1 concentrates in 0.25-1.25 μm, while that of 5A-2 ranges from mesopore category to 0.3 μm, but 5A-3 contains both pores of 0.01-0.1 μm and 0.2-2 μm inside, reflecting a broadest distribution; 5A-3, 5A-1 and 5A-2 reach desorption equilibrium after 1100 s, 1400 s and 2000 s respectively at 0.03 kPa, indicating that abundant macropores make n-pentane fastest desorbed from 5A-3, but this advantage gradually disappears with the increasing pressure; the effective desorption diffusion coefficients of n-pentane on 5A-1, 5A-2 and 5A-3 are 4.2×10-15-2.2×10-14 m2/s, 2.0×10-15-2.3×10-14 m2/s, 7.4×10-15-2.4×10-14 m2/s respectively, suggesting that plenty macropores make the diffusivity less affected by the changes of pressure, which can guarantee a fast diffusion rate of n-pentane even at low pressure.

Adsorption Property of Cu-BTC for Dibenzothiophene Sulfide

Cu-BTC was synthesized by hydrothermal method. Adsorption desulfurization performance of Cu-BTC for dibenzothiophene sulfide was investigated. The adsorption property of Cu-BTC for dibenzothiophene and 4-methyldibenzothiophene in stimulated diesel were compared by equilibrium and dynamic experiments. The results show that when the equilibrium concentration is 0~50 mg S/L, the adsorption capacity of Cu-BTC for 4-methyldibenzothiophene is more than that of dibenzothiophene. When the equilibrium concentration is 50 mg S/L, the equilibrium adsorption capacity of Cu-BTC for 4-methyldibenzothiophene and dibenzothiophene are 17.54 mg S/gads and 15.64 mg S/gads, respectively. At the conditions of 30°C, 149.22h-1 and 0.1MPa, the initial concentration of dibenzothiophene and 4-methyldibenzothiophene is about 45.16~46.36 mg S/L, the adsorption property of 4-methyldibenzothiophene is superior than dibenzothiophene, the breakthrough capacity of Cu-BTC for 4-methyldibenzothiophehe is 1.73 times lager than dibenzothiophene. Cu-BTC shows an excellent prospect on diesel desulfurization process.