Vipin K. Saini

Ethane Selective IRMOF-8 and Its Significance in Ethane–Ethylene Separation by Adsorption

The separation of ethylene from ethane is one of the most energy-intensive single distillations practiced. This separation could be alternatively made by an adsorption process if the adsorbent would preferentially adsorb ethane over ethylene. Materials that exhibit this feature are scarce. Here, we report the case of a metal-organic framework, the IRMOF-8, for which the adsorption isotherms of ethane and ethylene were measured at 298 and 318 K up to pressures of 1000 kPa. Separation of ethane/ethylene mixtures was achieved in flow experiments using a IRMOF-8 filled column. The interaction of gas molecules with the surface of IRMOF-8 was explored using density functional theory (DFT) methods. We show both experimentally and computationally that, as a result of the difference in the interaction energies of ethane and ethylene in IRMOF-8, this material presents the preferential adsorption of ethane over ethylene. The results obtained in this study suggest that MOFs with ligands exhibiting high aromaticity character are prone to adsorb ethane preferably over ethylene.

Natural clay binder based extrudates of mesoporous materials: improved materials for selective adsorption of natural and biogas components

The effects of natural clay binder based extrusion, on the selective adsorption properties of mesoporous materials were investigated in context of natural gas and biogas purification. Two mesoporous adsorbent materials, namely porous clay heterostructures (PCH) and MCM-41 were shaped into cylindrical extrudates, using a natural montmorillite clay binder. The effect of extrusion with clay binder was evaluated in three steps; (i) effects on structural properties, which were studied with low temperature nitrogen adsorption and XRD techniques; (ii) effect on adsorption capacity, which were evaluated with high pressure adsorption isotherms (up to 1000 kPa) for three main natural gas and biogas component gases which are CO2, C2H6, and CH4; (iii) effects of extrusion on selective adsorption properties of materials were investigated, for two commercially significant binary separations (CO2/CH4 and C2H6/CH4). Results show that, in general, extrusion caused an increase in mesoporosity of the final material; but in the case of MCM-41, an increase in microporosity has also been noticed. The order of maximum adsorption was found to be CO2 > C2H6 > CH4 with each material and the capacity of adsorption decreases to a different extent (dependent on gas) on extrusion. Variation in selectivity of these materials with pressure was studied and discussed. Both extrudates show satisfactorily high selectivity values than minimum requisite for an adsorbent to be used in separation process. However among all the four materials, the extrudate of MCM-41 was found most suitable, in terms of separation possibilities/applications.

High Pressure Adsorption Studies of Ethane and Ethylene on Clay-Based Adsorbent Materials

Bentonite clay is tailored in three different ways to produce porous materials viz. PCH1, PCH2, and PILC, where PCH1 and PCH2 are two different clay heterostructures and PILC is a Zr-oxide pillared clay. Surface characterization materials shows that both of PCHs have a higher surface area than PILC, and have micro and mesoporosity, where PILC is basically a microporous. DRIFT and X-ray techniques were used to investigate the surface-groups and height of micropores in PCHs and PILC, respectively. Adsorption isotherms of ethane and ethylene were measured on these materials up to high pressure (1000 kPa) under different temperatures, and by processing the obtained data these materials were evaluated for their aptness for ethane ethylene separation. Isosteric heats of adsorption were observed higher for ethylene than ethane during initial surface coverage for each material-gas system. Interaction in each material-gas system with gradual increase in pressure was elucidated with the help of isosteric heat curves. Adsorption performances of these materials were compared with already studied materials (reported by other workers for ethane/ethane separation). Comparison was based on selectivity and working capacity, which are the two decisive parameters for screening suitability of any adsorbent material (for PSA application).

Development of metal organic framework-199 immobilized zeolite foam for adsorption of common indoor VOCs

Reticulated foam shaped adsorbents are more efficient for the removal of volatile organic compounds (VOCs), particularly from low VOC-concentration indoor air streams. In this study composite structure of zeolite and metal organic frameworks (MOFs), referred as ZMF, has been fabricated by immobilization of fine MOF-199 powder on foam shaped Zeolite Socony Mobil-5 (ZSM-5) Zeolitic structure, referred as ZF. The ZMF possess a uniform and well-dispersed coating of MOF-199 on the porous framework of ZF. It shows higher surface area, pore volume, and VOCs adsorption capacity, as compared to ZF-structure. Post-fabrication changes in selective adsorption properties of ZMF were studied with three common indoor VOCs (benzene, n-hexane, and cyclohexane), using gravimetric adsorption technique. The adsorption capacity of ZMF with different VOCs follow the order of benzene>n-hexane>cyclohexane. In comparison with MOF-199 and ZF, the composite structure ZMF shows improvement in selectivity for benzene from other two VOCs. Further, improvement in efficiency and stability of prepared ZMF was found to be associated with its high MOF loading capacity and unique morphological and structural properties. The developed composite structure with improved VOCs removal and recyclability could be a promising material for small to limited scale air pollution treatment units.