Separation Of Olefins Research Articles

Polysulfone porous hollow fiber membranes for ethylene-ethane separation in gas-liquid membrane contactor

Abstract Separation of olefin from paraffin having same carbon number is one of the most energy intensive separations in petrochemical processes. Employing gas-liquid membrane contactors for olefin/paraffin separation is very attractive. In the present work, the membrane contactor ethylene/ethane separation was investigated based on porous asymmetric polysulfone hollow fiber membranes having mesoporous (dav ∼ 2 nm) skin layer structure in contrast to conventional ultrafiltration membranes (dav ∼ 50–100 nm). Also, the membranes selective layer surface was modified to increase its hydrophobic properties expecting that pore size and surface properties tailoring prevents liquid absorbent penetration into membrane pores. The membrane contactor performance was studied under various operating parameters such as absorbent (aqueous AgNO3) solution concentration and gas and liquid flow rates. Ethylene permeance value was 185 L/(m2 h bar), which is at the level of the best results available in literature for porous membranes, at ethylene recovery rate up to 39%, which is three times higher than that in literature. Modified membranes were characterized after membrane contactor experiments. SEM, EDX and XRD analysis as well as gas permeance measurements showed that silver nitrate crystals deposition in the membranes pore space occurs. However, no noticeable change of membrane contactor performance was observed during two months of experiments on ethylene/ethane separation.

Adsorption performance of MIL-100(Fe) for separation of olefin–paraffin mixtures

Abstract MIL-100(Fe) with a BET surface area of 2558 m 2 g −1 was prepared for the separation of olefin–paraffin mixtures. The sample was characterized by X-ray diffraction (XRD), and scanning electron microscope (SEM). Isotherms of C 2 H 4 , C 2 H 6 , C 3 H 6 and C 3 H 8 were measured with a volumetric method, and the C 2 H 4 /C 2 H 6 and C 3 H 6 /C 3 H 8 adsorption selectivities of the sample were calculated based on the ideal adsorbed solution theory (IAST). The results showed that (a) MIL-100(Fe) adsorbent achieved a superior C 2 H 4 adsorption capacity of 3.8 mmol g −1 and C 3 H 6 7.5 mmol g −1 at 1 atm and 298 K. (b) The isotherms could be well described by the dual-site Langmuir–Freundlich models. (c) The C 2 H 4 /C 2 H 6 and C 3 H 6 /C 3 H 8 adsorption selectivity of MIL-100(Fe) at 1 kPa and 298 K were up to 111 and 70, respectively, which can be attributed to the selective π-complexation between olefins and Fe(II) of MIL-100(Fe).

Superstructure optimization of the olefin separation system by harmony search and genetic algorithms

In this paper a superstructure optimization is applied for the problem of olefin separation system which includes distillation column units, heat exchangers and heat integration. A new algorithm is presented for modeling the separation system and designing the heat integration and heat exchanger networks. The objective is to minimize the total annual cost of the separation superstructure using the presented design methodology and numerical methods such as improved harmony search algorithm. The developed code is validated and verified using standard cases in literature. The solution approach for the superstructure optimization is discussed and the numerical results are presented proving the improvements in the design of the separation superstructure system using the new presented approach.

Olefin Separation Membranes Based on PEO/PDMS-g-POEM Blends Containing AgBF4/Al(NO3)3 Mixed Salts

촉진수송은 기존의 고분자 막에서는 힘든, 투과도와 선택도를 동시에 향상시킬 수 있는 기술 중 한 가지이다. 촉진수송 분리막을 이용한 올레핀/파라핀 분리는 기존의 증류공정을 대체할 수 있는 기술로써 많은 관심을 받아왔다. 본 연구에서는 테트라플루오로붕산은/질산알루미늄의 혼합염이 포함된 고분자 블렌드 기반의 촉진수송 올레핀 분리막을 제조하였다. 자유 라디칼중합법을 이용하여 폴리다이메틸실록세인-g-폴리옥시에틸렌 메타크릴레이트 가지형 공중합체를 합성하였다. 또한, 폴리다이메틸실록세인-g-폴리옥시에틸렌 메타크릴레이트 매질에 폴리에틸렌옥사이드를 다양한 비율로 혼합하였다. 폴리에틸렌옥사이드를 폴리다이메틸실록세인-g-폴리옥시에틸렌 메타크릴레이트 가지형 공중합체 질량 대비 70%를 혼합하였을 때, 혼합기체 선택도 및 투과도는 5.6 및 10.05 GPU에 도달하였다. 이와 같은 복합막의 올레핀 분리 성능이 향상된 이유는, 분리막에 첨가된 은이온이 올레핀 기체분자의 선택적인 촉진 수송을 하였고, 또한 고투과성의 고분자 블렌드가 사용되었기 때문이다. 또한 은이온의 은나노입자로의 환원을 억제시키는 질산알루미늄의 첨가로 인해 복합막의 장시간 안정도를 향상시킬 수 있었다. 【Facilitated transport is one of the possible solutions to simultaneously improve permeability and selectivity, which is challenging in conventional polymer-based membranes. Olefin/paraffin separation using facilitated transport membrane has received much attention as an alternative solution to the conventional distillation process. Herein, we report olefin separation composite membranes based on the polymer blends containing $AgBF_4/Al(NO_3)_3$ mixed salts. Free radical polymerization process was used to synthesize an amphiphilic graft copolymer of poly(dimethyl siloxane)-graft- poly(ethylene glycol) methyl ether methacrylate (PDMS-g-POEM). In addition, poly(ethylene oxide) (PEO) was introduced to the PDMS-g-POEM graft copolymer to form polymer blends with various ratios. The propylene/propane mixed-gas selectivity and permeance reached up to 5.6 and 10.05 GPU, respectively, when the PEO loading was 70 wt% in polymer blend. The improvement of olefin separation performance was attributed to the olefin facilitating silver ions as well as the highly permeable blend matrix. The stabilization of silver ions in the composite membrane was achieved through the introduction of $Al(NO_3)_3$ which suppressed the reduction of silver ions to silver particles.】

Silver assisted separation of n-decane/1-decene using distillable CO2-derived alkyl carbamate ionic liquids

A series of distillable alkyl carbamate ionic liquids (ALKCARB ILs) have been prepared from CO2 and an amine, and then treated with silver (I) oxide to give the task specific ionic liquids. The synthesized ionic liquids have been used for the separation of 1-decene selectively from the mixture of n-decane/1-decene at room temperature. Presence of CO2 to form carbamate with alkyl amine in the synthesis of ionic liquids remarkably enhanced the separation of olefin from mixture; however in its absence silver containing amine solvent provided very poor separation under identical conditions.

Microfluidic Separation of Ethylene and Ethane Using Frustrated Lewis Pairs.

Separation of gaseous olefins and paraffins is one of the most important separation processes in the industry. Development of new cost-effective technologies aims at reducing the high energy consumption during the separation process. Here, we took advantage of the reaction of frustrated Lewis pairs (FLPs) with ethylene to achieve reactive extraction of ethylene from ethylene-ethane mixtures. The extraction was studied using a microfluidic platform, which enabled a rapid, high-throughput assessment of reaction conditions to optimize gas separation efficiency. A separation factor of 7.3 was achieved for ethylene from a 1:1 volume ratio mixture of ethylene and ethane, which corresponded to an extracted ethylene purity of 88 %. The results obtained in the microfluidic studies were validated using infrared spectroscopy. This work paves the way for further development of the FLPs and optimization of reaction conditions, thereby maximizing the separation efficiency of olefins from their mixtures with paraffins.

Upgrading FCC gasoline through adsorption separation of normal hydrocarbons

The octane number and the olefin content are two crucial indices for FCC gasoline. FCC gasoline was upgraded by a separation process that was superior to chemical processes including hydrogenation. The adsorption separation of normal paraffins and normal olefins in FCC gasoline was performed in a fixed-bed adsorber packed with 5A zeolites. The content of low octane normal paraffins decreased from 5wt% to less than 0.1wt% by the shape-selective separation of zeolites, leading to an increase in research octane number from 88.9 to 92.3. The olefin content decreased from 35.23wt% to 29.02wt% due to the removal of normal olefins. The adsorbabilities observed from the breakthrough curves of normal paraffins and normal olefins were consistent with the adsorption energies. The desorption oil, which was rich in normal hydrocarbons, showed excellent cracking performance for producing ethylene in a steam cracker.

Cu-BTC and Fe-BTC metal-organic frameworks: Role of the materials structural features on their performance for volatile hydrocarbons separation

The separation of alkanes (nC5 to nC9), propane and propylene, and aromatic (benzene, toluene and o-xylene) hydrocarbons using the metal-organic frameworks Cu-BTC and Fe-BTC as stationary phase was evaluated from inverse gas chromatography data. Both materials were found able to separate mixtures of these volatile hydrocarbons. The nature of such behavior is discussed according to the possible guest-host interactions during the molecules adsorption and retention in the column and considering the molecules size and shape and the porous framework topology. From the recorded chromatographic profiles, the retention times for the considered hydrocarbons were calculated and then used to obtain the involved differential adsorption heats and the values for the separation coefficient. Cu-BTC is a long-range ordered crystalline material while Fe-BTC shows gel-like features. Such structural differences modulate the pore accessibility and the adsorption interactions. In this contribution, the effects of these structural differences on the molecules adsorption and separation are discussed. From the recorded adsorption data, information on the pore volume, adsorption potentials and probable pore topology for Fe-BTC was obtained.

Exergetic evaluation of renewable light olefins production from biomass via synthetic methanol

In this paper, an exergetic evaluation was conducted on a two-step biomass-derived light olefins system established using ASPEN PLUS. This system linked methanol synthesis via entrained-flow gasification to a methanol-to-olefins (MTO) process. The mass yield of the system was 0.248kg light olefins per kg biomass, which is relatively higher than the literature results. The energetic and exergetic efficiencies of this system were 54.66% and 47.65%, respectively. The results of an exergetic analysis indicate that the biomass gasification, steam cycle, methanol separation, CO2 removal and olefins separation produce most of the system inefficiencies. By identifying the occurrence mechanism of the exergy losses, the potential for improvement can be obtained. A further increase of exergetic performance can be obtained from (1) improvement of gasification process via combining biomass torrefaction, and (2) enhancement of energy integration processes via heat network optimization and power generation from the produced steam.

Addition of ethylene to a π-conjugated two-dimensional nickel-based organometallic framework with implications for olefin separation

We have investigated the mechanism for the reversible addition of ethylene to a periodic 2D network of square-planar nickel centers ([Ni(SC)4]n) using density functional theory. The mechanism is analogous to that for homogeneous olefin binding to metal bis(dithiolene) complexes. We considered periodic boundary calculations (PBC) as well as clusters containing up to 12 nickel atoms using a screened hybrid density functional to obtain accurate reaction barriers. Several different products were analyzed. The lowest-energy route begins with the addition of ethylene across the nickel-sulfur bond, which has previously not been considered for this system. The effect of the addition of several alkene molecules simultaneously on the surface was investigated to determine the potential efficiency of this material. This material is a candidate for alkene purification as it exhibits similar reactivity to its molecular analog in terms of the relative stability of products, energy barriers, and molecular efficiency while also providing the intrinsic technical benefits of heterogeneous catalysis.

Capillary column coated with graphene quantum dots for gas chromatographic separation of alkanes and aromatic isomers

A GQD coated capillary column has been employed for the first time for successful separation of alkanes and aromatic isomers at low temperature in a short time.

Enhancing Liquid-Phase Olefin–Paraffin Separations Using Novel Silver-Based Ionic Liquids

This paper describes the extraction of C5–C8 linear α-olefins from olefin/paraffin mixtures of the same carbon number using silver(I)/N,N-dimethylbenzamide bis(trifluoromethylsulfonyl)imide ([Ag(DMBA)2][Tf2N]) or silver(I)/propylamine bis(trifluoromethylsulfonyl)imide ([Ag(PrNH2)2][Tf2N]) as the extracting agent. The separation performance of the system increased with increasing chain length. [Ag(DMBA)2][Tf2N] appeared to outperform [Ag(PrNH2)2][Tf2N] in terms of both selectivity and distribution coefficient. The [Ag(DMBA)2][Tf2N] system was successfully modeled using the universal quasi-chemical activity coefficient (UNIQUAC) model. These results support the potential future development of amine/amide-based ligands for producing soluble silver complexes useful for the separation of olefins from paraffins.

Optimal Synthesis of Ethylene Production Process

This work addresses the energetic and economic optimization for the synthesis of distillation-based ethylene production. We employ a model-based optimization approach to determine the optimal sequencing of processes for olefins separation that involves handling a multicomponent mixture. The optimization model is formulated based on a superstructure that embeds many possible and feasible structural alternatives for processing a number of hydrocarbon components constituting gaseous ethane or liquid naphtha. We adopt linear mass balance reactor models for conversion of materials into desirable products and simple sharp distillation column models based on split fractions for product recovery from a multicomponent feed stream. The formulation leads to a mixed-integer linear program (MILP) with discrete 0–1 variables on task selection and continuous variables on input flowrate to each task. To aid convergence to the optimal system synthesis with minimum total annualized cost, the model incorporates heuristic-based logical constraints that represent design and structural specifications on engineering knowledge, design experience, and rules of thumb. The model is implemented on case studies drawn from actual operating petrochemical plants in Malaysia with reasonable computational results.

DRIFT and Theoretical Studies of Ethylene/Ethane Separation on Flexible and Microporous [Cu2(2,3‐pyrazinedicarboxylate)2(pyrazine)]n

AbstractThe separation of olefins from paraffin is important for the production of industrial chemicals. Therefore, there is a need for a better separation system such as a pressure‐swing adsorption (PSA) process. With regard to adsorbents that enable gas separation by PSA, CPL‐1 {[Cu2(2,3‐pyrazinedicarboxylate)2(pyrazine)]n} is an attractive porous material because of the flexibility and microporosity of the material, which provides it with a unique guest‐responsive nature. Adsorption isotherm studies were conducted to elucidate the ethylene‐selective adsorption properties of CPL‐1, which was further examined by breakthrough experiments with ethylene–ethane binary gas mixtures at near room temperatures. Spectroscopic and computational approaches used to investigate the interaction between CPL‐1 and the C2 gas molecules suggested that hydrogen bonds are important in the selective adsorption of ethylene over ethane.

Accurate Model for Predicting Adsorption of Olefins and Paraffins on MOFs with Open Metal Sites

Metal–organic frameworks (MOFs) have shown tremendous potential for challenging gas separation applications, an example of which is the separation of olefins from paraffins. Some of the most promising MOFs show enhanced selectivity for the olefins due to the presence of coordinatively unsaturated metal sites, but accurate predictive models for such systems are still lacking. In this paper, we present results of a combined experimental and theoretical study on adsorption of propane, propylene, ethane, and ethylene in CuBTC, a MOF with open metal sites. We first propose a simple procedure to correct for impurities present in real materials, which in most cases makes experimental data from different sources consistent with each other and with molecular simulation results. By applying a novel molecular modeling approach based on a combination of quantum mechanical density functional theory and classical grand canonical Monte Carlo simulations, we are able to achieve excellent predictions of olefin adsorption, in much better agreement with experiment than traditional, mostly empirical, molecular models. Such an improvement in predictive ability relies on a correct representation of the attractive energy of the unsaturated metal for the carbon–carbon double bond present in alkenes. This approach has the potential to be generally applicable to other gas separations that involve specific coordination-type bonds between adsorbates and adsorbents.

Gas–liquid membrane contactor for ethylene/ethane separation by aqueous silver nitrate solution

Separation of light olefin from paraffin having the same carbon number is one of the most energy intensive separations in petrochemical processes, which uses very long distillation columns with very high number of trays. This is attributed to the very small differences in the relative volatilities. The purpose of this work is to study the absorption performance of a home-made PVDF hollow fiber membrane fabricated using thermally induced phase separation method. Separation of ethylene from an ethylene–ethane gas mixture, using a hollow fiber membrane based absorption–desorption system with aqueous silver nitrate as absorption solvent, and to enhance separation process with a purchased polypropylene hollow fiber membrane module used for stripping purposes. Experiments on the absorption of ethylene from ethylene–ethane mixture, into silver nitrate solutions were performed. The effects of initial ethylene concentration in feed gas, silver nitrate concentration in the inlet solvent, liquid and gas flow rates were investigated. Results reveal that ethylene/ethane separation factor increases with silver nitrate concentration and liquid flow rates. A two dimensional mathematical model was developed for this purpose. Model predictions were validated with experimental data. Model predictions were in good agreement with experimental results.

Use of water in aiding olefin/paraffin (liquid + liquid) extraction via complexation with a silver bis(trifluoromethylsulfonyl)imide salt

This paper describes the extraction of C5–C8 linear α-olefins from olefin/paraffin mixtures of the same carbon number via a reversible complexation with a silver salt (silver bis(trifluoromethylsulfonyl)imide, Ag[Tf2N]) to form room temperature ionic liquids [Ag(olefin)x][Tf2N]. From the experimental (liquid+liquid) equilibrium data for the olefin/paraffin mixtures and Ag[Tf2N], 1-pentene showed the best separation performance while C7 and C8 olefins could only be separated from the corresponding mixtures on addition of water which also improves the selectivity at lower carbon numbers like the C5 and C6, for example. Using infrared and Raman spectroscopy of the complex and Ag[Tf2N] saturated by olefin, the mechanism of the extraction was found to be based on both chemical complexation and the physical solubility of the olefin in the ionic liquid ([Ag(olefin)x][Tf2N]). These experiments further support the use of such extraction techniques for the separation of olefins from paraffins.

Can Metal-Organic Framework Separate 1-Butene from Butene Isomers?

The separation of 1-butene from the other isomers is an industrially important but challenging task because these isomers mainly differ only by the position of C═C double bond with many of their physical properties very similar. In this work, we propose using first-principles calculations that Fe-MOF-74 can be a promising candidate for the separation of 1-butene from all other isomers with high selectivity. We demonstrate that the underlying mechanism of this olefin separation is the steric interactions; that is, 1-butene with terminal double bond has the smallest steric interactions with the framework and therefore can approach the metal binding sites more closely for stronger π-complexation. This combined effect (π-complexation modulated by steric interactions) in MOFs with open metal sites can offer a promising design strategy for difficult separation of even longer olefin isomers by properly engineering the lengths and functional groups of the MOF linkers.

Olefin separation via charge transfer and dipole formation at the silver nanoparticle–tetracyanoquinoid interface

Charge transfer and dipole formation at silver nanoparticle–tetracyanoquinoid takes place in the solid-state membrane, forming an unprecedented, highly olefin permselective facilitated transport membrane with a mixed gas selectivity of over 100 for a propylene–propane mixture. This provides a potential alternative to the highly energy-intensive cryogenic distillation process for olefin/paraffin separation.

Polymeric ionic liquid membranes containing IL–Ag+ for ethylene/ethane separation via olefin-facilitated transport

This work focuses on the separation of light olefins from their corresponding paraffins using membranes due to their lower energy consumption and operating costs in comparison to the traditionally used methods which are highly energy intensive. Although polymeric ionic liquids (PILs) have attracted much attention as interesting materials to prepare improved gas separation membranes, their exploitation for light olefin/paraffin separation has never been attempted before. In this work, we propose the use of PILs as alternative polymer matrices for olefin/paraffin separation. A new series of facilitated transport membranes of poly([pyr11][NTf2]) incorporating different amounts of the ionic liquid ([pyr14][NTf2]) and the silver salt (AgNTf2) were prepared by a film casting process and their ethane and ethylene permeation properties were measured at 293 K using a time-lag apparatus. The results show that the preparation of PIL/IL composite membranes increases the permeability of both C2H4 and C2H6, overcoming the hindered gas diffusion in the pure PIL. Nevertheless, the presence of the IL in the composite membrane promotes reduced C2H4/C2H6 permselectivity. The addition of the silver salt greatly boosts the solubility of the olefin in the membranes. Furthermore, increasing the silver ion concentration in the PIL/40% IL system leads to enhanced overall C2H4/C2H6 permselectivity surpassing the upper bound for polymeric membranes, indicating that PILs have interesting potential as polymer matrices for olefin-facilitated transport membranes.