Hui Sun

Thermodynamics of Methane Adsorption on Copper HKUST-1 at Low Pressure

Metal-organic frameworks (MOFs) can be engineered as natural gas storage materials by tuning the pore structures and surface properties. Here we report the direct measurement of CH4 adsorption enthalpy on a paddlewheel MOF (Cu HKUST-1) using gas adsorption calorimetry at 25 °C at low pressures (below 1 bar). In this pressure region, the CH4-CH4 intermolecular interactions are minimized and the energetics solely reflects the CH4-MOF interactions. Our results suggest moderately exothermic physisorption with an enthalpy of -21.1 ± 1.1 kJ/mol CH4 independent of coverage. This calorimetric investigation complements previous computational and crystallographic studies by providing zero coverage enthalpies of CH4 adsorption. The analysis of the new and literature data suggests that in initial stages of adsorption the CH4-HKUST-1 interaction tends to be more sensitive to the pore dimension than to the guest polarizability, suggesting a less specific chemical binding role for the open Cu site.

Oxidative regeneration of deactivated binderless 5A molecular sieves for the adsorption–separation of normal hydrocarbons

Abstract The deactivation of binderless 5A molecular sieves for the adsorption–separation of normal hydrocarbons was investigated on a fixed-bed adsorber. The deactivated molecular sieves were regenerated by removing the coke deposited through oxidation under various conditions. They showed lower surface area, smaller pore volume, and larger pore diameter than the fresh sample because certain passages of small pore in the molecular sieves were blocked by the coke deposited. With the increase of the coke content in the molecular sieves, the deactivation rate decreased gradually. With the increase of oxidation temperature from 582 K to 787 K, the coke removal efficiency was elevated from 64% to 100%. At 787 K, the coke deposited in the molecular sieves was completely removed and the adsorption activity of the molecular sieves was recovered; however, the surface area and pore volume of the regenerated molecular sieves could not be restored to the original values of the fresh samples. Under 685–884 K, the removal of coke from the binderless 5A molecular sieves by the oxidative treatment could be expressed with a macrokinetic formula: ln(C0/C) = 0.013exp(−28122.1/T) (po2)0.32t.

Adsorptive removal of dimethyl disulfide from methyl tert-butyl ether using an Ag-exchanged ZSM-5 zeolite

Ion-exchange modification can largely change the adsorption ability of various adsorbents of zeolite. A series of Ag-exchanged ZSM-5 zeolites were prepared using an ion-exchange method and used to remove dimethyl disulfide (DMDS) from methyl tert-butyl ether (MTBE). The structural properties and acidity of the modified zeolite were examined using X-ray diffraction, N2 adsorption, NH3-TPD and Py-IR. The effects of the ion-exchange level on DMDS adsorption were investigated. In addition, the adsorption isotherms and adsorption kinetic data were measured and interpreted. Introduction of Ag+ into ZSM-5 contributes to the adsorption ability and increases the adsorption capacity by 7.7 times through enhancing the interactions between DMDS and zeolite. Strong acidity and Lewis acid sites are considered favorable for DMDS adsorption. The adsorption isotherms and kinetics results reveal that DMDS adsorption onto AgZSM-5 was endothermic chemisorption having an activation energy of 7.4 kJ mol−1. The adsorbents can be regenerated at 300 °C in an air atmosphere.

Liquid-Phase Adsorption Kinetics of n-Paraffins on 5A Zeolite

Abstract The adsorption kinetics of n-hexane from liquid-phase on 5A zeolite crystals, binderless pellets, powder with binder, and pellets with binder are investigated in order to develop the diffusion control mechanism. The adsorption kinetics of n-C5–n-C8 from liquid-phase are studied on binderless 5A zeolite pellets and the pellets containing binder. Adsorption rate of n-paraffins on binderless pellets is controlled by micropore diffusion while it is controlled by macropore diffusion on 5A zeolite pellets with binder. For the same adsorbate, the apparent diffusional time constants on the binderless pellets are about 6–11 times larger than those on others.

Optimization of vacuum resid solvent deasphalting to produce bright stock and hard asphalt

ABSTRACT To prepare bright stock (BS) and 30# hard asphalt simultaneously, propane solvent deasphalting (SDA) of Oman vacuum residue was optimized. Result showed the optimal process conditions were as follows: extraction tower top temperature of 64°C, settling tower top temperature of 74°C, extraction pressure of 3.35 MPa, solvent ratio of 5. Compared with SDA of Oman VR to prepare bright stock and 70# asphalt, the yields of light deasphalted oil (LDAO) and heavy deasphalted oil (HDAO) were 26.8% and 24.7%, and increased by 1.7% and 5.2% respectively; carbon residue of LDAO was less than 1.2%, conformed to the feed requirement of furfural refining to produce bright stock. The yield of DOA was 48.5%, and DOA could be directly used to produce 30# hard asphalt. The PG grade of 30# asphalt was PG 76–22 and the 30# asphalt mixture had high rut dynamic stability and water resistant stability. HDAO could be used as feedstock of catalytic cracking and light yield oil (gasoline and diesel) was 65.99%.

Optimizing the Utilization of Natural Gas Condensate through the Separation of n-Paraffins

To improve the utilization efficiency of gas condensate and effect the proper use of the hydrocarbon components, AKS gas condensate was separated, through the use of a fixed-bed adsorption process employing 5A molecular sieves, into the raffinate oil which is rich in non-normal hydrocarbons and the desorption oil which is rich in n-paraffins. The adsorption breakthrough curves of n-paraffins were investigated. Relative to the gas condensate, the aromatic potential content and the research octane number (RON) of the raffinate oil increased by 12.9% and by over 20 units, respectively. As a result, the raffinate oil is more suitable for use as the feedstock in the catalytic reforming process and as the blending component of high-octane gasoline. Under similar conditions, the ethylene yield of the steam cracking process using the desorption oil as the feedstock increased by 6.5% compared to the situation when the gas condensate was employed as the feedstock.