Separation Of Ethane Research Articles

Diffusion kinetics of ethane, ethylene, and their binary mixtures in ethane-selective adsorbents

Sorption kinetics of single component and binary mixtures of ethane and ethylene in powder and pellet samples of paraffin-selective adsorbents Ni(bdc)(ted)0.5 and ZIF-7 were investigated by zero-length column (ZLC) technique for the purpose of olefin/paraffin separation. The intracrystalline diffusivities were determined at 25 °C and the results were compared in order to investigate the effects of coadsorption for binary gas mixtures and also diffusion in pelletized adsorbents. The diffusion time constants measured for ethane and ethylene through both ZIF-7 and Ni(bdc)(ted)0.5 in powder and pellet forms were similar and found to be in the ranges of 2.68–3.35 × 10−3 s−1 and 1.23–4.07 × 10−3 s−1, respectively, for single component and binary mixtures. Furthermore, diffusion of ethylene for both single component and binary mixture trials revealed the presence of surface resistance due to strong interactions between the CC double bond and the external crystalline surface of the adsorbents. The findings of this study provide novel kinetic characterizations on paraffin-selective adsorbents for the separation of ethane and ethylene.

Separation of Ethane from Natural Gas Using Porous ZIF-8/Water–Glycol Slurry

The high efficiency separation of ethane from natural gas becomes significant due to the occurrence of revolution in shale gas. Herein a new approach of continuous sorption separation was developed...

A Robust Ethane-Trapping Metal-Organic Framework with a High Capacity for Ethylene Purification.

The separation of ethane from ethylene is of prime importance in the purification of chemical feedstocks for industrial manufacturing. However, differentiating these compounds is notoriously difficult due to their similar physicochemical properties. High-performance porous adsorbents provide a solution. Conventional adsorbents trap ethylene in preference to ethane, but this incurs multiple steps in separation processes. Alternatively, high-purity ethylene can be obtained in a single step if the adsorbent preferentially adsorbs ethane over ethylene. We herein report a metal-organic framework, MUF-15 (MUF, Massey University Framework), constructed from inexpensive precursors that sequesters ethane from ethane/ethylene mixtures. The productivity of this material is exceptional: 1 kg of MOF produces 14 L of polymer-grade ethylene gas in a single adsorption step starting from an equimolar ethane/ethylene mixture. Computational simulations illustrate the underlying mechanism of guest adsorption. The separation performance was assessed by measuring multicomponent breakthrough curves, which illustrate that the separation performance is maintained over a wide range of feed compositions and operating pressures. MUF-15 is robust, maintains its performance in the presence of acetylene, and is easily regenerated by purging with inert gas or by placing under reduced pressure.

Boosting Ethane/Ethylene Separation within Isoreticular Ultramicroporous Metal-Organic Frameworks.

The separation of ethane from its analogous ethylene is of great importance in the petrochemical industry, but very challenging and energy intensive. Adsorptive separation using C2H6-selective porous materials can directly produce high-purity C2H4 in a single operation but suffers from poor selectivity. Here, we report an approach to boost the separation of C2H6 over C2H4, involving the control of pore structures in two isoreticular ultramicroporous metal-organic framework (MOF) materials with weakly polar pore surface for strengthened binding affinity toward C2H6 over C2H4. Under ambient conditions, the prototypical compound shows a very small uptake difference and selectivity for C2H6/C2H4, whereas its smaller-pore isoreticular analogue exhibits a quite large uptake ratio of 237% (60.0/25.3 cm3 cm-3), remarkably increasing the C2H6/C2H4 selectivity. Neutron powder diffraction studies clearly reveal that the latter material shows self-adaptive sorption behavior for C2H6, which enables it to continuously maintain close van der Waals contacts with C2H6 molecules in its optimized pore structure, thus preferentially binds C2H6 over C2H4. Gas sorption isotherms, crystallographic analyses, molecular modeling, selectivity calculation, and breakthrough experiment comprehensively demonstrate this unique MOF material as an efficient C2H6-selective adsorbent for C2H4 purification.

A novel fructose-based adsorbent with high capacity and its ethane-selective adsorption property

Separation of ethane/ethylene mixture at normal temperature and pressure is a challenging issue in the petrochemical industry. Herein, we synthesized Fructose-based carbon materials (C-Frus) with characteristic of ethane-selective adsorption for the energy-effective separation of ethane and ethylene. The as-synthesized sample C-Fru-4-700 exhibited narrow micropore size distribution and high micropore volume. More importantly, these samples presented preferential adsorption of C2H6 over C2H4, of which the ethane capacity of the sample C-Fru-4-700 reached as high as 7.94 mmol/g at 25 °C and 100kPa, much higher than that of many MOFs, and its selectivity for equimolar C2H6/C2H4 mixture reached 4 at low pressure. These excellent properties made C2H6/C2H4 mixture be well separated by fixed bed at 25 °C. Computational simulations revealed that the surface Osite1, Osite2 and Osite3 sites of the materials are the favorably adsorptive sites of C2H6. Fructose-based carbon materials are promising for separation of ethane/ethylene mixture at normal condition.

Synthesis of the zeolitic imidazolate framework ZIF-4 from the ionic liquid 1-butyl-3-methylimidazolium imidazolate.

A new synthesis route for the zeolitic imidazolate framework ZIF-4 using imidazolium imidazolate is reported. Additionally, the ionic liquid-derived material is compared to conventional ZIF-4 with respect to the powder X-ray diffraction pattern pattern, nitrogen uptake, particle size, and separation potential for olefin/paraffin gas mixtures. Higher synthesis yields were obtained, and the different particle size affected the performance in the separation of ethane and ethylene.

Selective Adsorption of Ethane over Ethylene in PCN-245: Impacts of Interpenetrated Adsorbent.

The separation of ethane from ethylene using cryogenic distillation is an energy-intensive process in the industry. With lower energetic consumption, the adsorption technology provides the opportunities for developing the industry with economic sustainability. We report an iron-based metal-organic framework PCN-245 with interpenetrated structures as an ethane-selective adsorbent for ethylene/ethane separation. The material maintains stability up to 625 K, even after exposure to 80% humid atmosphere for 20 days. Adsorptive separation experiments on PCN-245 at 100 kPa and 298 K indicated that ethane and ethylene uptakes of PCN-245 were 3.27 and 2.39 mmol, respectively, and the selectivity of ethane over ethylene was up to 1.9. Metropolis Monte Carlo calculations suggested that the interpenetrated structure of PCN-245 created greater interaction affinity for ethane than ethylene through the crossing organic linkers, which is consistent with the experimental results. This work highlights the potential application of adsorbents with the interpenetrated structure for ethane separation from ethylene.

C2 adsorption in zeolites: in silico screening and sensitivity to molecular models

Selective zeolitic frameworks for adsorptive separation of ethane and ethylene are identified using molecular modeling with improved force fields.

Control of zeolite framework flexibility and pore topology for separation of ethane and ethylene.

The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.

Process design of carbon dioxide and ethane separation using ionic liquid by extractive distillation

AbstractBACKGROUNDCarbon dioxide and ethane easily form a binary azeotrope under liquefied conditions. An extractive distillation process for the separation of carbon dioxide and ethane using the ionic liquids [bmim][Tf2N], [emim][Tf2N] and [emim][EtSO4] as solvents was explored. The thermodynamic and physical property parameters of each ionic liquid and their thermo‐physical properties that correlated with the experimental data were used to create the ionic liquid components and conduct the process simulation.RESULTBased on the analysis of its physical properties and relative volatilities, [emim][Tf2N] is the best option as a solvent for extractive distillation separation compared with other ionic liquids. Based on the sensitivity analysis optimization procedure, the minimum total annual cost, carbon dioxide emissions and thermodynamic efficiency were calculated. Compared with traditional extraction distillation, the total annual cost and carbon dioxide emissions of the process using [emim][Tf2N] as a solvent decreased by 62% and 31%, respectively. The thermodynamic efficiency (η) of the electricity generated from hydropower increase by 0.7%.CONCLUSIONThe results show that an ionic liquid extractive distillation process using an ionic liquid as the entrainer performs better than a process using traditional organic solvents in terms of economics. Due to the non‐volatility of ionic liquids, a flash tank was used instead of a solvent recovery column to efficiently realize solvent recovery. © 2017 Society of Chemical Industry

Experimental Study of Silver-Loaded Mesoporous Silica for the Separation of Ethylene and Ethane

Three kinds of mesoporous silica materials including SYSG (commercial silica gel), SBA-15, and KIT-6 are used as the carrier for supporting silver nitrate via incipient-wetness impregnation method. The resultant materials Ag/SYSG, Ag/SBA-15, Ag/KIT-6 are characterized by low-temperature nitrogen adsorption/desorption, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy and also are used as adsorbents for ethylene and ethane separation. It is found that both the surface area and the dispersion of Ag cations have significant influences on the separation performances. The surface modification by AgNO3 has the adsorption mechanism changed through π-complexation, which is in contrast to the physical adsorption through van der Waals force that is usually dominated by the surface area. The loss of surface area weakens the physical adsorption of ethane, whereas the well-dispersed Ag cations could promote the adsorption of ethylene; therefore, the selectivity is improved. As a result, Ag/SBA-15 shows the best separation performances among the tested materials.

Synthesis of zeolitic imidazolate framework-69 for adsorption separation of ethane and ethylene

The zeolitic imidazolate framework ZIF-69 with topology of GME has been synthesized successfully via a facile hydrothermal synthetic method, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption measurements, thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The ethane/ethylene separation potential was measured by single-component adsorption isotherms, and the selectivity was calculated based on the ideal adsorbed solution theory (IAST). SEM and TEM images confirmed that the as-synthesized seeds possessed a well-crystallized and uniform morphology, appearing as a flat hexagonal prism with double hexagonal pyramid heads. The obtained ZIF-69 exhibited a higher adsorption capacity of C2H6 over C2H4 at 100 kPa, and the C2H6/C2H4 adsorption selectivity was about 1.7 at below 100 kPa. The outcome would provide a new insight into the study on the effective separation of ethane/ethylene using different topological structures of ZIFs.

Asphalt-derived high surface area activated porous carbons for the effective adsorption separation of ethane and ethylene

We reported novel asphalt–based activated carbons (A-ACs) with high C2H6/C2H4 adsorption capacity and selectivity. A series of A-ACs were prepared by a one-step preparation method and characterized. The adsorption performances of A-ACs for ethane/ethylene were examined. Results showed that the sample A-ACs prepared at 800°C and the KOH/asphalt ratio=4 exhibited ultra-high BET area of 3111m2/g and its pore volume reached 1.92cm3/g. Their surface O and N contents gradually decreased with activation temperature or KOH/asphalt ratio at which A-ACs were prepared. More interestingly, A-ACs showed significantly preferential adsorption of C2H6 over C2H4. It could be ascribed to the stronger interaction of C2H6 with the surfaces of A-ACs by hydrogen bonds compared to C2H4, which were revealed by Density functional theory calculation. Its C2H6 adsorption capacity was up to 7.2mmol/g at 100kPa and 25°C and its C2H6/C2H4 adsorption selectivity for typical cracked gas mixture (15:1 ethylene/ethane) was in the range of 3.2–16.3 at the pressure below 100kPa, higher than the most reported ethane-adsorbents. Additionally, the isosteric heat of ethane and ethylene adsorption on A-ACs were lower than those on π-complexation adsorbents. Therefore, these excellent adsorption properties would make A-ACs as a type of promising adsorbents for adsorption separation of C2H6/C2H4.

Enabling Kinetic Light Hydrocarbon Separation via Crystal Size Engineering of ZIF-8

Recent increases in shale gas production provide an excellent opportunity for advancements in the energy-efficient separation of natural gas liquids because these are increasingly used as fuel sources and chemical feedstocks. Current fractionation schemes generally involve cryogenic distillation of C1–C4 hydrocarbons and are extremely energy-intensive. Here, we describe the first steps toward a lower-energy, kinetic pressure-swing-adsorption cycle for the separation of ethane, propane, propylene, and butane using ZIF-8 as a diffusionally selective adsorbent. Crystal engineering techniques were employed to control the diffusive time scale of the separation, allowing for multiple separations using the same adsorbent within reasonable process times. Equimolar separation of ethane/propane mixtures at 293 K exhibited separation factors of 2.7 in the gas phase under nonoptimized conditions, which enhances the concentration of the feed mixture to 75 mol % propane. The separation performance was shown to improve ...

Process optimization-based adsorbent selection for ethane recovery from residue gas

The design and optimization of a pressure/vacuum swing adsorption process for the separation of ethane (C2) from residue gas (2.4 mol% ethane and the rest being methane) is presented. To achieve this, experimental measurements, modeling and optimization tools are developed to characterize the adsorbents, define the cycle configuration, and find the optimal operating conditions for the process. Adsorbents from two different families, namely, titano-silicate (Na-ETS-10) and activated carbons are chosen. Experimental high-pressure isotherms were measured and described using a dual-site Langmuir model. A rigorous one-dimensional model is developed to simulate the adsorption process. Two different pressure/vacuum swing adsorption (PVSA) cycle configurations are proposed and assessed based on C2 purity and recovery. The effect of feed temperature is studied and is shown to have a high impact on the separation. Finally, a multi-objective optimization study is performed to identify the material that offers the best trade-off between the two objective functions: C2 purity; and recovery. Among the adsorbents examined, Na-ETS-10 is found to provide the best performance with a possibility of obtaining ≈76% purity at a recovery of 68%.

Ethane selective adsorbent Ni(bdc)(ted)0.5 with high uptake and its significance in adsorption separation of ethane and ethylene

We reported a novel ethane selective metal–organic framework material Ni(bdc)(ted)0.5 with a high uptake of C2H6 and a decent selectivity towards C2H6/C2H4 separation. This material was synthesized with double ligands (bdc and ted) by a hydrothermal method. Its C2H6 and C2H4 isotherms were subsequently measured. The BET surface area of the synthesized Ni(bdc)(ted)0.5 reached 1701m2/g. Successful assembling of the two organic ligands into Ni(bdc)(ted)0.5 was indicated by FT-IR. TGA indicated that Ni(bdc)(ted)0.5 was stable in the temperature region below 673K. Ni(bdc)(ted)0.5 exhibited decent adsorption capacities of C2H6 and C2H4 with a superior high C2H6 adsorption capacity of 6.93mmol/g at 100kPa. More importantly, it exhibited preferential adsorption of C2H6 over C2H4. Its C2H6/C2H4 adsorption selectivity was in the range of 2–7.8 at pressure below 100kPa, higher than the reported adsorbents possessing the characteristic of preferential adsorption of C2H6 over C2H4. In addition, the isosteric heat of C2H6 and C2H4 adsorption on Ni(bdc)(ted)0.5 were much lower compared to those π-complexation sorbents adsorbing olefin preferentially by binding with the π bond of olefin. The high ethane adsorption capacity, high ethane/ethylene selectivity and low isosteric heat of adsorption of Ni(bdc)(ted)0.5 would make it a promising adsorbent for the effective separation of ethane/ethylene.

Alternative extractive distillation system for CO2–ethane azeotrope separation in enhanced oil recovery processes

CO2 is a common constituent of natural gas. Standards for its maximum concentration differ from about 2% for pipeline to 50 ppm for liquefaction. All natural gas constituents absorb CO2 to some degree when in the liquid phase, requiring multi-step natural gas treatment processes. The existence of a minimum-boiling temperature azeotrope between ethane and carbon dioxide particularly complicates CO2 separation. Extractive distillation with higher molecular weight hydrocarbons as the solvent represents the most competitive means for the separating CO2 from ethane. The conventional separation method involves two distillation columns in series and rather high amount of energy.This investigation proposes an efficient method for CO2–ethane separation that produces all products at high purity with less capital and operating costs in comparison with the conventional system. The new operating flowsheet includes three columns: a CO2 recovery column, a solvent recovery column, and a concentrator column. The proposed system requires 10% less total annual cost (TAC) and 16% less energy compared to the conventional system at the same purification. Additionally, unlike the conventional system, the proposed design separates CO2 in the form of a liquid product, which avoids the high amount of energy required for the liquefaction. Thus, this technology provides a useful alternative toward the less expensive CO2–ethane separation process.

Manipulation of the pore size of clinoptilolite for separation of ethane from ethylene

Naturally occurring zeolites are uniquely useful for small molecule separations due to the effective size of their pores. While the crystal structure of clinoptilolite has large 12-ring pores, the effective pore size of the zeolite excludes molecules larger than ~0.4nm. In this work, the structure of a naturally occurring clinoptilolite was modified through ammonium exchange, calcination, and post-calcination steam treatment. The ammonium exchange removed some fraction of the structural cations, which caused the framework to expand, while steam treatment at 600°C causes a contraction in the structure. The effective pore size of the modified clinoptilolite allowed it to adsorb ethylene and exclude ethane in a dynamic adsorption experiment. By incrementally changing the pore size of clinoptilolite, a new rate-based adsorbent for the adsorptive separation of ethylene from ethane was created.

Solubilities of small hydrocarbons, viscosities of diluted tetraalkylphosphonium bis(2,4,4‐trimethylpentyl) phosphinates

Tetraalkylphosphonium bis(2,4,4‐trimethylpentyl)phosphinates show large solubilities for methane, ethane, ethylene, and propane. In these ionic liquids, solubilities of ethane are larger than those of ethylene. Therefore, these ionic liquids may be useful solvents for separation of ethane and ethylene; because the vapor pressure of ethylene is higher than that of ethane, the relative volatility ethylene/ethane is enhanced. However, the viscosities of these ionic liquids are too high for an industrial process. Low‐viscosity 1‐butyl‐3‐H‐imidazolium acetate([BHMIM][AC]) is a suitable diluent for reducing the large viscosities of trihexyl tetradecylphosphonium bis(2,4,4‐trimethylpentyl) phosphinate ([P(14)666][TMPP]) and tetrabutylphosphonium bis(2,4,4‐trimethylpentyl) phosphinate ([P4444][TMPP]). Addition of 20 wt % [BHMIM][AC] gives a dramatic drop in the viscosities of these ionic liquids. Mixtures of [P(14)666][TMPP] or [P4444][TMPP] with 20 or 50 wt % [BHMIM][AC] show high solubilities for the four solutes when compared with those in other ionic liquids. In these mixtures, the solubility for ethane is higher than that for ethylene. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2607–2612, 2014

Thermodynamic adsorption data of CH4, C2H6, C2H4 as the OCM process hydrocarbons on SAPO-34 molecular sieve

Adsorption of CH4, C2H6 and C2H4, the feed and main products of oxidative coupling process of methane (OCM) has been studied on silicoalumina-phosphate molecular sieve (SAPO-34) in mild conditions. The experiments were conducted in a batch system based on volumetric adsorption measurement technique for determination equilibrium adsorption capacity in the absolute pressure range of 100–1000kPa and at the isothermal temperatures of 303, 313 and 323K. Various isotherm equations were fitted on the adsorption equilibrium data and the model parameters were predicted as a function of temperature. Isosteric heats of adsorption were determined using Clausius–Clapeyron equation at different surface coverage. Maximum capacity of SAPO-34 was observed at 303K and 880–900kPa equilibrium pressure with 1.25, 2.02 and 4.67mmol/g adsorbed amount for methane, ethane and ethylene adsorption, respectively. The adsorption selectivity of ethane and ethylene against methane were determined and the appropriate potential of SAPO-34 was observed for separation of OCM products from methane. The isotherm models and enthalpy of adsorption can be efficiently used for the simulation of the adsorption process constructed at the downstream of the OCM process for separation of ethane and ethylene from methane.