Separating mixtures by exploiting molecular packing effects in microporous materials

Krishna, Rajamani

doi:10.1039/c4cp03939d

Cited by 74 publications

(85 citation statements)

References 73 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For a proper comparison of various MOFs, we perform transient breakthrough simulations using the simulation methodology described in the literature535455. For the breakthrough simulations, the following parameter values were used: framework density, ρ (1,146 kg m −3 ); length of packed bed, L (0.12 m); voidage of packed bed, ɛ (0.75); superficial gas velocity at inlet, u (0.00225, m s −1 ).…”

Section: Methodsmentioning

confidence: 99%

Microporous metal–organic framework with dual functionalities for highly efficient removal of acetylene from ethylene/acetylene mixtures

et al. 2015

Self Cite

View full text Add to dashboard Cite

The removal of acetylene from ethylene/acetylene mixtures containing 1% acetylene is a technologically very important, but highly challenging task. Current removal approaches include the partial hydrogenation over a noble metal catalyst and the solvent extraction of cracked olefins, both of which are cost and energy consumptive. Here we report a microporous metal–organic framework in which the suitable pore/cage spaces preferentially take up much more acetylene than ethylene while the functional amine groups on the pore/cage surfaces further enforce their interactions with acetylene molecules, leading to its superior performance for this separation. The single X-ray diffraction studies, temperature dependent gas sorption isotherms, simulated and experimental column breakthrough curves and molecular simulation studies collaboratively support the claim, underlying the potential of this material for the industrial usage of the removal of acetylene from ethylene/acetylene mixtures containing 1% acetylene at room temperature through the cost- and energy-efficient adsorption separation process.

show abstract

Section: Methodsmentioning

confidence: 99%

Microporous metal–organic framework with dual functionalities for highly efficient removal of acetylene from ethylene/acetylene mixtures

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…3,38,39 The technologies used in industrial separations are either pressure swing adsorption (PSA) units 3 or membrane permeation devices. 2,40,41 The operations of fixed bed adsorption units are intrinsically transient in nature, i.e.…”

Section: Diffusion In Microporous Crystalline Materialsmentioning

confidence: 99%

Uphill diffusion in multicomponent mixtures

2015

Self Cite

View full text Add to dashboard Cite

Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations. Key learning points(1) Coupling effects in mixture diffusion may cause uphill transport of a component (2) Uphill diffusion results in transient overshoots and serpentine equilibration trajectories (3) Non-ideal phase equilibrium thermodynamics is often the major source of diffusional coupling effects (4) Chemical potential gradients are the proper driving forces for diffusion (5) Uphill transport can be exploited to achieve difficult and unusual separations

show abstract

“…reviewed entropyeffects on the adsorption of mixtures of alkanes [113] and packing effects in microporous materials. [114] Smit and Maesenr eviewed adsorption ands hape selectivity in zeolites. [115,116] For alkanes, three entropy effects were discovered:1 )size entropy, [117] 2) length entropy, [117] and 3) configurational entropy.…”

Section: Entropymentioning

confidence: 99%

Exploiting Large‐Pore Metal–Organic Frameworks for Separations through Entropic Molecular Mechanisms

Torres‐Knoop

Dubbeldam

2015

ChemPhysChem

View full text Add to dashboard Cite

We review the molecular mechanisms behind adsorption and the separations of mixtures in metal-organic frameworks and zeolites. Separation mechanisms can be based on differences in the affinity of the adsorbate with the framework and on entropic effects. To develop next-generation adsorbents, the separation efficiency of the materials needs to be improved. The performance under industrially relevant conditions largely depends on two factors: 1) the separation selectivity and 2) the pore volume capacity of the material. Enthalpic mechanisms can lead to increased selectivities, but these are mostly restricted to the low loading regime, and hence these mechanisms are unable to make use of all of the large-pore volume that a metal-organic framework can provide. Industrial processes routinely operate in the pore saturation regime. In this Review, we focus on entropic molecular separation mechanisms that are effective under these conditions and, in particular, on a recent methodology to obtain high selectivities at high pore loading.

show abstract

Separating mixtures by exploiting molecular packing effects in microporous materials

Cited by 74 publications

References 73 publications

Microporous metal–organic framework with dual functionalities for highly efficient removal of acetylene from ethylene/acetylene mixtures

Microporous metal–organic framework with dual functionalities for highly efficient removal of acetylene from ethylene/acetylene mixtures

Uphill diffusion in multicomponent mixtures

Exploiting Large‐Pore Metal–Organic Frameworks for Separations through Entropic Molecular Mechanisms

Contact Info

Product

Resources

About