Separation Of Propylene Research Articles

Separation of propylene and propane with a microporous metal–organic framework via equilibrium‐kinetic synergetic effect

AbstractAdsorption separation of olefin and paraffin can greatly lower the energy consumption associated with the currently utilized distillation technique but remains a great challenge. Herein, we report the efficient separation of propylene (C3H6) and propane (C3H8) in a phosphate anion‐functionalized metal–organic framework (MOF) ZnAtzPO4 by synergetic effect of equilibrium and kinetics. The material features periodically expanded and contracted apertures decorated with electronegative groups, offering eligible pore shape and pore chemistry to effectively trap C3H6 under moderate isosteric heat of adsorption (27.5 kJ mol−1) while obstruct the diffusion of C3H8. It simultaneously combines excellent thermodynamic selectivity (uptake ratio of 1.71) and kinetic selectivity (~31) for C3H6/C3H8 separation, meanwhile can be easily regenerated. Breakthrough experiment for C3H6/C3H8 gas mixture was conducted and confirmed the outstanding separation capability of ZnAtzPO4. The equilibrium and kinetics cooperative C3H6/C3H8 adsorption separation was for the first time found in anion‐functionalized MOFs, and further confirmed by computational studies.

Doubly Interpenetrated Metal-Organic Framework of pcu Topology for Selective Separation of Propylene from Propane.

Adsorptive separation is an appealing alternative technology to reduce the high energy and capital cost of the distillation separation of propylene/propane; however, it is very challenging to realize. A new flexible metal-organic framework (MOF) material [Zn2(BDC-Cl)2(Py2TTz)] with a doubly interpenetrated pillared paddle wheel structure of pcu (primitive cubic) topology has been realized for this difficult separation for the first time. Through a judicious choice of linkers, the framework has small pore apertures that lead to much more propylene adsorption than propane. The selective adsorption relies on the sieving effect of the flexible framework. The column breakthrough experiment further demonstrated that efficient separation can be achieved under dynamic conditions.

An Ultramicroporous Metal-Organic Framework for High Sieving Separation of Propylene from Propane.

Highly selective adsorptive separation of olefin/paraffin through porous materials can produce high purity olefins in a much more energy-efficient way than the traditional cryogenic distillation. Here we report an ultramicroporous cobalt gallate metal-organic framework (Co-gallate) for the highly selective sieving separation of propylene/propane at ambient conditions. This material possesses optimal pore structure for the exact confinement of propylene molecules while excluding the slightly large propane molecules, as clearly demonstrated in the neutron diffraction crystal structure of Co-gallate⊃0.38C3D6. Its high separation performance has been confirmed by the gas sorption isotherms and column breakthrough experiments to produce the high purity of propylene (97.7%) with a high dynamic separation productivity of 36.4 cm3 cm-3 under ambient conditions. The gas adsorption measurement, pore size distribution, and crystallographic and modeling studies comprehensively support the high sieving C3H6/C3H8 separation in this MOF material. It is stable under different environments, providing its potential for the industrial propylene purification.

Solution processable metal-organic frameworks for mixed matrix membranes using porous liquids.

The combination of well-defined molecular cavities and chemical functionality makes crystalline porous solids attractive for a great number of technological applications, from catalysis to gas separation. However, in contrast to other widely applied synthetic solids such as polymers, the lack of processability of crystalline extended solids hampers their application. In this work, we demonstrate that metal-organic frameworks, a type of highly crystalline porous solid, can be made solution processable via outer surface functionalization using N-heterocyclic carbene ligands. Selective outer surface functionalization of relatively large nanoparticles (250 nm) of the well-known zeolitic imidazolate framework ZIF-67 allows for the stabilization of processable dispersions exhibiting permanent porosity. The resulting type III porous liquids can either be directly deployed as liquid adsorbents or be co-processed with state-of-the-art polymers to yield highly loaded mixed matrix membranes with excellent mechanical properties and an outstanding performance in the challenging separation of propylene from propane. We anticipate that this approach can be extended to other metal-organic frameworks and other applications.

Modification of the pore environment in UiO-type metal-organic framework toward boosting the separation of propane/propylene

The separation of propane (C3H8) from propylene (C3H6) to obtain high purity C3H6 as a petrochemical raw material is an important, but challenging process. In the traditional industrial process, the separation mainly relies on energy-intensive cryogenic distillation. One alternative process that is currently becoming more attractive in the separation of C3H6 is adsorptive separation technology. Using porous materials, especially C3H8 selective adsorbents, high purity C3H6 can be directly obtained and thus, significantly simplifies the process. Herein, a series of functionalized ligands were introduced into UiO-type materials to finely regulate the C3H8 separation performance. Single-component adsorption isotherms reveal that BUT-10 has a distinct binding affinity for C3H8 over C3H6 over a wide range of temperature from 298 to 338 K and thus, achieved by far the highest C3H8 capture capacity (105 cm3 g−1 at 0.1 bar and 298 K) reported among the C3H8-selective materials reported to date. A combination of Grand Canonical Monte Carlo and density-function theory simulations demonstrate that the favorable pore environment provided by the multiple host-guest interactions toward C3H8 result in the higher C3H8 binding affinity observed in the separation process. Breakthrough experiments indicate that BUT-10 can selectively separate C3H8 from C3H8/C3H6 (1/1 and 1/15, v/v) mixtures and thus, directly produces high purity C3H6 (>99.99%) under ambient conditions.

All-silica DD3R zeolite for adsorptive separation of propylene from propane: Equilibrium and kinetic data

Abstract Propylene/propane separation by adsorption is an energy-efficient process which is considered as an alternative for energy-intensive separation by cryogenic distillation. The main part of the adsorption process is the design of an efficient adsorbent. All-silica DD3R zeolite is a special adsorbent for the proposed process. In this paper, two different sizes of that zeolite are synthesized. Adsorption isotherms of propylene were experimentally measured on large DD3R zeolite crystals (~12 μm) at 303–423 K and up to 1000 kPa. Due to the very slow adsorption kinetics of propane, full equilibrium was not reached on large-sized DD3R crystals and even on small crystals (~2 μ m) after 3.5 days at 303 K. However, for the first time, real propane adsorption isotherms have been successfully measured on small-sized DD3R particles at higher temperatures, i.e., 373–473 K, up to 500 kPa. Experimental adsorption kinetics of propylene and propane were tested at various pressures and temperatures, and finally the diffusion coefficients were predicted. The investigation revealed that diffusivities increase with both pressure and temperature. Estimated high values of propylene/propane kinetic selectivities, i.e., 9.76 × 103 and 3.66 × 103 at 373 and 423 K at 80 kPa, respectively, revealed that DD3R zeolite is a superior kinetic-based adsorbent for propylene/propane separation.

High-throughput screening of metal–organic frameworks for kinetic separation of propane and propene

We apply molecular simulations to screen a database of reported metal-organic framework structures from the computation-ready, experimental (CoRE) MOF database to identify materials potentially capable of separating propane and propene by diffusion. We report a screening workflow that uses descriptor analysis, conventional molecular dynamics (MD), and Nudged Elastic Band (NEB) energy barrier calculations at both classical force field and Density Functional Theory (DFT) levels. For the first time, the effects of framework flexibility on guest transport properties were fully considered in a screening process and led to the identification of candidate MOFs. The hits identified by this proof-of-concept workflow include ZIF-8 and ZIF-67 previously shown to have large differences in propane and propene diffusivities as well as two other materials that have not been tested experimentally yet. This work emphasises the importance of taking into account framework flexibility when studying guest transport in porous materials, demonstrates the potential of the data-driven identification of high-performance materials and highlights the ways of improving the predictive power of the screening workflow.

Investigation on Adsorption and Separation Behavior of Propane/Propene Mixtures in Zeolites.

Propane/propene separation is among the most energy-intensive separation processes in the petrochemical industry. Separation based on adsorption on a nanoporous material (e.g., zeolites) has spawned new ideas for this process. Therefore, we conducted grand canonical ensemble Monte Carlo simulations to investigate the adsorption and separation of propane and propene in one-dimensional (ATS, MOR, and AWO), two-dimensional (MWW, FER, and BOG) and three-dimensional (MFI, BEA, FAU) zeolites. The computation of pure components indicates that the adsorption capacity is affected by the zeolite pore diameter, dimensionality, and isosteric heat. For a given diameter, three dimensional zeolites exhibit better adsorption properties than two or one-dimensional zeolites. Zeolites with diameters ranging from 4.8 Å to 5.4 Å show high propane and propene affinity. In binary mixture simulations, the separation capacity of propane and propene increases with elevated pressure and decreased temperature. Among these zeolites, AWO exhibits the best separation performance due to its eight-ring window channel, which is consistent with experimental results. Thus, our results provide better understanding on propane and propene adsorption and separation in different zeolites, as well as insight into how production conditions could be upgraded.

Microporous ZIF-8 and ZIF-67 membranes grown on mesoporous alumina substrate for selective propylene transport

Defect free microporous ZIF-8 and ZIF-67 membranes were successfully developed from the secondary growth technique to separate propylene from propylene/propane gas mixture. The characterization and gas permeation results demonstrate that ZIF-8 and ZIF-67 membranes have the potential for the separation of propylene from propylene/propane gas mixture with the highest separation factor of 76 and 5, respectively. While ZIF-67 membrane did not perform as expected in term of the selectivity, its permeance was found to be considerably higher than the ZIF-8 membrane. ZIF-67 membrane exhibited the highest propylene permeance of 196 × 10−10 mol·m−2·s−1·Pa−1, whereas ZIF-8 membrane exhibited the highest permeance of 86 × 10−10 mol·m−2·s−1·Pa−1. The difference in the permeation performance was largely due to the better inter-grown grain boundary structure of ZIF-8 membrane than that of ZIF-67 membrane.

Separation of propylene oxide-methanol-water mixture via enhanced extractive distillation: Design and control

The ternary azeotropic mixture of propylene oxide-methanol-water generally occurs in the direct oxidation of hydrogen peroxide and needs to be separated effectively. This paper explores two energy-efficient configurations with water as solvent, namely extractive dividing-wall column (EDWC) and side-stream extractive distillation (SSED), in terms of the potential economic advantages compared to conventional extractive distillation (CED) and the dynamic control. Several steady-state designs with the minimum total annual cost (TAC) by using a sequential iterative optimization method are achieved and compared. Regarding the controllability, four control structures for the SSED are developed and examined via introducing the feed flow and composition disturbances as well as one control structure for the EDWC. Similar to the EDWC, the SSED can be well controllable via an optimal control structure relying on only temperature measurements.

Mechanical Control of the Kinetic Propylene/Propane Separation by Zeolitic Imidazolate Framework‐8

AbstractOne intriguing feature of many porous MOFs is their stimulus‐induced flexibility, which makes them unique compared to standard adsorbents. Here we propose an innovative concept to achieve an efficient kinetic separation of species with similar properties by the mechanical fine‐tuning of the pore architecture of the flexible zeolitic imidazolate framework ZIF‐8. This unprecedented approach was applied to one of the most challenging societally relevant separations: the separation of propylene and propane, which is of vital importance in the petrochemical industry. It was demonstrated that the application of an external pressure creates a gradual enhancement in the propylene/propane diffusion selectivity to more than one order of magnitude at 1 GPa pressure. A detailed analysis of the molecular simulations was further able to unravel the origin of this unusual behavior at the atomistic level.

Mechanical Control of the Kinetic Propylene/Propane Separation by Zeolitic Imidazolate Framework-8.

One intriguing feature of many porous MOFs is their stimulus-induced flexibility, which makes them unique compared to standard adsorbents. Here we propose an innovative concept to achieve an efficient kinetic separation of species with similar properties by the mechanical fine-tuning of the pore architecture of the flexible zeolitic imidazolate framework ZIF-8. This unprecedented approach was applied to one of the most challenging societally relevant separations: the separation of propylene and propane, which is of vital importance in the petrochemical industry. It was demonstrated that the application of an external pressure creates a gradual enhancement in the propylene/propane diffusion selectivity to more than one order of magnitude at 1 GPa pressure. A detailed analysis of the molecular simulations was further able to unravel the origin of this unusual behavior at the atomistic level.

Conceptual design of distillation columns sequence for separation of pentane and hexane from C5+ stream of LPG unit

ABSTRACTThe principal role of an LPG (Liquefied Petroleum Gas) unit is the separation of propane and butane from other products in a gas refinery. One of the other main products of the LPG unit is C5+ which is sold at the same price of crude oil after it is added into gas condensate. In this research, sixth refinery (Phases 15 and 16) of South Pars gas filed was selected as a case study example to find an efficient design for enriching the C5+ stream. Analysis of the C5+ stream exited from the LPG unit demonstrates that it contains more than 70 wt. % of valuable solvents such as pentane and hexane which are more expensive than crude oil. Therefore, the main goal of this research is to do calculations related to the separation of these solvents from the C5+ stream using the direct and indirect sequence of distillation columns. For this purpose, an optimum algorithm is recommended based on Fenske-Underwood-Gilliland (FUG) method in which design parameters (column pressure and reflux ratio) are optimized so that the objective function that represents the total annual cost (TAC) is minimized. Programming with MATLAB shows that the theory of the direct sequence of distillation columns is more economical than the indirect sequence (an annual income of 40,309,012$ is estimated with a fixed cost of 1,047,555 $). Economic calculations also revealed that the rate of return (ROR) and annual profit would be 38.48% and 650,000,000 $.year−1, respectively, if the optimal direct sequences of distillation columns are performed in all the gas refineries of South Pars.

K-RANK: AN EVOLUTION OF Y-RANK FOR MULTIPLE SOLUTIONS PROBLEM

ABSTRACT Y-rank can present faults when dealing with non-linear problems. A methodology is proposed to improve the selection of data in situations where y-rank is fragile. The proposed alternative, called k-rank, consists of splitting the data set into clusters using the k-means algorithm, and then apply y-rank to the generated clusters. Models were calibrated and tested with subsets split by y-rank and k-rank. For the Heating Tank case study, in 59% of the simulations, models calibrated with k-rank subsets achieved better results. For the Propylene / Propane Separation Unit case, when dealing with a small number of sample points, the y-rank models had errors almost three times higher than the k-rank models for the test subset, meaning that the fitted model could not deal properly with new unseen data. The proposed methodology was successful in splitting the data, especially in cases with a limited amount of samples.

Ultrathin, fine-tuned microporous coating modified 5A zeolite for propane/propylene adsorptive separation

Abstract Adsorptive separation of propylene from propane is very challenging because of their very similar sizes (propylene: 0.431 nm; propane: 0.446 nm) and other similar physical properties. In this study, we further explored the potential of the previously developed concept, pore misalignment, for precisely adjusting pore mouth size of 5A zeolite for propane/propylene adsorptive separation. Pore size of the ultrathin microporous TiO2 coating on 5A zeolite was fine-tuned from 0.8 to 0.6 nm by combining molecular layer deposition (MLD) and atomic layer deposition (ALD). As a result, average pore mouth size of 5A zeolite was adjusted to be between propane and propylene and an ideal adsorption selectivity of about 22 was achieved. Meanwhile, diffusivity ratio of propylene to propane also increased drastically from about 1 for 5A zeolite to 75 for MLD/ALD modified 5A zeolite. The resulting composite 5A zeolite adsorbent, therefore, favors propylene separation from propane both thermodynamically and kinetically. Our work suggests that MLD combined with ALD might be an effective way of precisely adjusting zeolite pore mouth size for separation of propane/propylene mixtures and potentially for other mixtures composed of molecules with very small size differences.

Conformation-Controlled Molecular Sieving Effects for Membrane-Based Propylene/Propane Separation.

Membrane-based separation is poised to reduce the operation cost of propylene/propane separation; however, identifying a suitable molecular sieve for membrane development is still an ongoing challenge. Here, the successful identification and use of a metal-organic framework (MOF) material as fillers, namely, the Zr-fum-fcu-MOF possessing an optimal contracted triangular pore-aperture driving the efficient diffusive separation of propylene from propane in mixed-matrix membranes are reported. It is demonstrated that the fabricated hybrid membranes display a high propylene/propane separation performance, far beyond the current trade-off limit of polymer membranes with excellent properties under industrial conditions. Most importantly, the mechanism behind the exceptional high propylene/propane selectivity is delineated by exploring theoretically the efficiency of sieving of different conformers of propane through the hypothesized triangular rigid pore-aperture of Zr-fum-fcu-MOF.

Efficient separation of propane and propene by a hypercrosslinked polymer doped with Ag(i)

A hypercrosslinked polymer doped with Ag(i) shows high selectivity toward olefins over paraffins under flowing conditions.

Modification of a continuous zeolite membrane grown within porous polyethersulfone with Ag(I) cations for enhanced propylene/propane gas separation

Abstract Current commercial methods for propylene propane separation require energy intensive cryogenic distillation. Significant efforts are underway for alternative methods of separation, and include physical and chemical absorption and adsorption, as well as membrane separations. Polymer membranes have been the most extensively studied. Zeolites are mostly studied as adsorption supports, though there have been a few reports of zeolite membranes for propylene propane separation. The chemical bond between the double bond of olefins and Ag(I) and Cu(I) cations have been exploited in the chemically enhanced separation process for olefins and paraffins, using a variety of supports including polymers and zeolites. We have recently reported that continuous faujasitic membranes grown within an hour in porous polyethersulfone supports, and then covered with a thin layer of polydimethoxysilane can separate CO2 and N2. In this study, we examine these membranes for propylene propane separation. The best separation results were obtained at 50 °C, with average propylene propane selectivity of 2.4 ± 0.8, and propylene permeance of 1211 ± 557 GPU. Membranes were also modified by ion-exchanging with two concentrations of Ag(I). Best results were obtained at 75 °C, with average propylene propane selectivity of 4.8 ± 1.8, and propylene permeance of 1016 ± 661 GPU. Comparison with the few studies that have used zeolite membranes indicate that the selectivity in these studies are higher by a factor of 2–3 as compared to the present study, though the permeance is higher in the present study, in some cases by several orders of magnitude.

Tailor-Made Microporous Metal-Organic Frameworks for the Full Separation of Propane from Propylene Through Selective Size Exclusion.

Adsorptive separation of olefin/paraffin mixtures by porous solids can greatly reduce the energy consumption associated with the currently employed cryogenic distillation technique. Here, the complete separation of propane and propylene by a designer microporous metal-organic framework material is reported. The compound, Y6 (OH)8 (abtc)3 (H2 O)6 (DMA)2 (Y-abtc, abtc = 3,3',5,5'-azobenzene-tetracarboxylates; DMA = dimethylammonium), is rationally designed through topology-guided replacement of inorganic building units. Y-abtc is both thermally and hydrothermally robust, and possesses optimal pore window size for propane/propylene separation. It adsorbs propylene with fast kinetics under ambient temperature and pressure, but fully excludes propane, as a result of selective size exclusion. Multicomponent column breakthrough experiments confirm that polymer-grade propylene (99.5%) can be obtained by this process, demonstrating its true potential as an alternative sorbent for efficient separation of propane/propylene mixtures.

Adsorption Process Intensification through Structured Packing: A Modeling Study Using Zeolite 13X and a Mixture of Propylene and Propane in Hollow-Fiber and Packed Beds

There is scope to intensify the traditional adsorptive separation process which relies on packing a bed with adsorbent pellets. The hollow-fiber bed is one of the several structured configurations that have been proposed to overcome the high pressure drop and inefficient heat transfer of this random packing arrangement. While heat and mass transfer and pressure drop losses are improved in the hollow-fiber bed, the adsorbent packing density is reduced leading to a potential loss of capacity. In this computational study, we performed preliminary parametric comparisons of these bed properties, for equivalent cases in the packed bed and the hollow-fiber bed. Optimized five step single bed cycles for the separation of propylene and propane on zeolite 13X were also studied. For the same recovery and purity, the hollow-fiber bed was found to have a productivity that was five times higher than the packed bed. The hollow-fiber bed also showed higher productivity, when parameters such as the desorption pressure and...