High pressure adsorptive separation of ethylene and ethane on Na-ETS-10

Previously, we reported that Na-ETS-10 can be used to separate a mixture of ethylene and ethane from an industrial process stream under low pressure (101 kPa) with a binary bed selectivity of 5 at 298 K and 101.3 kPa. In this study, we show that selectivity improves considerably under high pressure conditions. Na-ETS-10 was used as a packed bed adsorbent to separate an ethylene/ethane 59/41 mixture over a pressure range of 101–2580 kPa and at two different temperatures (273 and 298 K). At these pressures, pure ethane gas raffinate streams prior to ethylene breakthrough are obtained. The extract phase obtained following desorption from the packed bed column contained up to 94% ethylene. The separation performance improved as adsorption column pressures increased. The ethylene/ethane bed selectivity achieved at 298 K and 2580 kPa was ∼11, more than double the previously reported selectivity under low pressure.     

Extraction of ethane from natural gas at high pressure by adsorption on Na-ETS-10

Methane/ethane separation was achieved using Na-ETS-10 as a packed-bed adsorbent over a pressure range of 450–5600 kPa at 298 K. At these pressures, pure methane gas raffinate streams were obtained prior to ethane breakthrough. The extract phase obtained following desorption from the packed-bed column was enriched in ethane. Extract phases containing up to 75% ethane were achieved following separations of a 93/7 methane/ethane feed mixture. Separation performance did not deteriorate as adsorption column pressures increased. Selective adsorption of a synthetic natural gas mixture using an Na-ETS-10 packed-bed column resulted in hydrocarbon outlet compositions ranging from pure methane (up to ∼60 bed volumes at standard temperature and pressure) to ∼93% methane, ∼5% ethane and ∼2% propane (∼150 to ∼850 bed volumes at standard temperature and pressure). In all cases, following desorption, the extract phase was highly enriched in the larger and more valuable hydrocarbons.     

Separation of ethylene/ethane mixtures by adsorption on small-pored titanosilicate molecular sieves

Adsorptive separation of ethylene and ethane may represent a less energy-intensive alternative to current sub-ambient distillation methods. In this approach, ethylene and ethane are separated by inverse-phase gas chromatographic and gravimetric isotherm techniques on ion-exchanged forms of ETS-4 and RPZ titanosilicate molecular sieves. Gas chromatography reveals that kinetic separation of ethylene from ethane is possible using ETS-4 and RPZ adsorbents exchanged with Zn and mixed Ca/H. Gas chromatographic selectivities of 4–40 for the adsorptive separation of ethylene and ethane were measured for these adsorbents, and the limiting selectivity calculated from gravimetric adsorption isotherms was between 4 and 12. In accordance with the ideal adsorbed solution theory, ethylene/ethane selectivity increases with pressure in all cases studied, especially for strontium- and barium-exchanged ETS-4. Due to the molecular sieving character of the adsorbents, steric effects were observed for the adsorption of ethylene and ethane, and contact time between the adsorbent and the gas mixture was the key factor in the separation of the gases. ETS-4 and RPZ materials exchanged with Zn or Ca/H are excellent candidates for the commercial adsorptive separation of ethylene and ethane.     

共沸精馏分离乙醇-异丙醇

为了分离乙醇-异丙醇混合物,研究了共沸精馏在乙醇-异丙醇物系中的应用。根据共沸剂的选取原则选定出1-己烯作为共沸精馏分离乙醇-异丙醇混合物的共沸剂,使用ASPEN模拟软件模拟连续和间歇共沸精馏分离乙醇-异丙醇工艺流程,并通过间歇共沸精馏实验考察了所选共沸剂的分离效果。结果表明：使用1-己烯作为共沸剂能成功的分离乙醇-异丙醇混合物;采用有30块理论板的填料塔,回流比为25,共沸剂1-己烯与乙醇的质量比为4∶1,塔釜异丙醇的质量分数达到99.77%。     

Adsorption of ethane and ethylene on modified ETS-10

Ethylene and ethane adsorption isotherms were measured for Engelhard Titanosilicate (ETS-10) both as made in the sodium form and ion exchanged with different mono-, di-, and trivalent cations. Isotherms for Na-, K-, and Ag-ETS-10 were found to be nearly rectangular indicating very strong adsorption. In contrast, isotherms for Li-, Ba-, and Cu-ETS-10 show substantial curvature. Isotherms for some mixed cation forms (such as Ba/H and La/H) demonstrate the weakest adsorption with substantial adsorption swing capacity between 1 and 200 kPa. Using the ideal adsorption solution theory (IAST), it was determined that ethylene/ethane adsorption selectivity decreases in the order Na>K>Li>Cu≈Ba>Ba/H>La/H, while the adsorption swing capacity (from 1 to 200 kPa) shows an exactly reversed trend. It is thus probable to find the right balance between selectivity and swing capacity in order to design appropriate pressure swing adsorption (PSA) processes for the separation of ethylene and ethane under a wide range of conditions.     

Extraction of ethane from natural gas by adsorption on modified ETS-10

Ethane was extracted from a synthetic natural gas mixture at 298 K and 101.3 kPa using modified ETS-10 as a packed bed adsorbent. Ethane was completely separated from the mixture for a prolonged period until the initial stages of breakthrough. The adsorptive properties of several cation-exchanged forms of ETS-10, a large-pored titanosilicate molecular sieve, were compared. Na-, Ba- and Ba/H-ETS-10 were all found to be selective for ethane over methane. Na-ETS-10 showed the highest Henry's selectivity (α=52) for ethane over methane of the three ETS-10 materials tested. Ideal Adsorbed Solution Theory (IAST) models indicate that significant selectivity should persist at high pressures. Ethane is commonly removed from raw natural gas by energy-intensive cryogenic methods and these results reflect the potential for an alternative and efficient separation process using cation-exchanged ETS-10 as an adsorbent.     

Reversed ethane/ethylene adsorption in a metal-organic framework via introduction of oxygen

Separation of ethane from ethylene is a very important but challenging process in the petrochemical industry. Finding an alternative method would reduce the energy needed to make 170 million tons of ethylene manufactured worldwide each year. Adsorptive separation using C₂H₆-selective porous materials to directly produce high-purity C₂H₄ is more energy-efficient. We herein report the “reversed C₂H₆/C₂H₄ adsorption” in a metal-organic framework Cr-BTC via the introduction of oxygen on its open metal sites. The oxidized Cr-BTC(O₂) can bind C₂H₆ over C₂H₄ through the active Cr-superoxo sites, which was elucidated by the gas sorption isotherms and density functional theory calculations. This material thus exhibits a good performance for the separation of 50/50 C₂H₆/C₂H₄ mixtures to produce 99.99% pure C₂H₄ in a single separation operation.     

Reverse selectivity of zeolites and metal-organic frameworks in the ethane/ethylene separation by adsorption

Major advances in the ethane/ethylene separation will be related with the discovery of adsorbents that present preferential adsorption of ethane over ethylene. Metal-organic frameworks (MOFs) are crystalline materials consisting of metal ions, or ion clusters, and organic ligands. Gas chromatography (GC) is most informative for materials screening for the ethane/ethylene separation since it needs only few mg of sample and gives selectivity results at various temperatures. This is illustrated by the methodology presented in this work where materials from two types of families (zeolites and MOFs) were used to show the reversed selectivity that can be found towards the ethane/ethylene separation.     

Breakthrough behaviour of a binary gas mixture with azeotropic adsorption equilibrium

This contribution reports on the breakthrough behaviour of binary gas mixtures with ideal and non-ideal multicomponent adsorption equilibria. Investigations were carried out on mixtures CO₂/C₂H₄ and C₂H₄/C₂H₆, both adsorbed on molecular sieve 5A (ms5A). The adsorption equilibrium of the system CO₂/C₂H₄/ms5A may exhibit azeotropic behaviour, which subsides with decreasing active pressure (= sum of partial pressures of adsorbable components) or on raising the temperature. In contrast, the system C₂H₄/C₂H₆/ms5A maintains its ideal behaviour also at higher active pressures or lower temperatures. Attempts to calculate the non-ideal adsorption equilibrium from measured single component isotherms have failed when known models were applied. The investigation of the effect of azeotropic equilibrium on the fixed bed adsorption led to intersecting breakthrough curves of the two components. This behaviour is due to a displacement of equilibrium caused by the change in the active pressure and partial pressures, and a superposed temperature effect. This can be shown by calculating the breakthrough curves with the equilibrium model.     

Stepwise periodic distillation—II: Separation of a binary mixture

Stepwise periodic operation of a distillation column in which a binary feed is separated in top and bottoms product is described. A simple but realistic model, both for stepwise periodic and controlled cycling operation and a simulation algorithm are proposed. The results of an extensive parametric study of stepwise periodic operation are presented along those for ideal controlled cycling (no axial mixing).Although in some cases inferior to controlled cycling, it is shown that, for reasonable tray efficiencies and difficult separations, stepwise periodic operation can compare favorably or be superior to ideal controlled cycling.     

减压精馏分离乙醇与异丙醇二元混合和物

乙醇与异丙醇二元混合物因两者存在结构和化学性质相似而难分离.对减压精馏分离乙醇与异丙醇工艺条件进行了探索,因折光率与溶液组成存在一一对应关系,进而利用阿贝折射仪进行纯度分析,考察了填料类型、真空度、溶液组成等对产物分离纯度的影响.实验研究结果表明,在以金属螺旋弹簧柱作精馏柱填料,塔顶真空度为700mmHg(93.33k...     

Isotherms and thermodynamics studies for binary adsorption of methane and ethane on 4A molecular sieve zeolite

The temperature dependency of adsorption behavior for binary mixture of methane and ethane on 4A zeolite was investigated. The volumetric method has been adopted for determination of adsorption isotherm data in the temperature range 303–323 K and pressure up to 225 kPa. Extended Langmuir, modified extended Langmuir, and extended Freundlich isotherms were applied for prediction of binary adsorption data using pure component adsorption data. The data were also simulated by IAST model which showed the best correlation of experimental binary adsorption data along with extended Freundlich isotherm. The selectivity of 4A zeolite to adsorb gases was also studied. The result of this study showed that an increases in temperature increases selectivity for ethane to methane. The heats of adsorption for methane and ethane were also determined and found to be ?23.89 and ?36.78 kJ/mol, respectively, which indicate the exothermic and physisorption natures of adsorption.     

Absorption of ethylene from ethylene‐ethane gaseous mixture by AgNO3 solution in a semi‐continuous process

Ethylene absorption from an ethylene–ethane gaseous mixture in the silver nitrate solution is studied at different temperatures and concentrations. Unlike the previous studies, in which the absorption was studied by batch processes, a semi‐continuous process is applied in the present research. The results show that increase in temperature reduces the amount of absorbed ethylene and absorption time. The amount of absorbed ethylene is increased in solutions with higher concentrations of AgNO₃, whereas the mole ratio of absorbed ethylene per silver nitrate is decreased by increasing the AgNO₃ concentration. Total absorption is modelled as a function of the temperature and concentration of absorbing solution. The estimated values from the model are in good agreement with the experimental data.     

A型分子筛膜在分离乙二醇水溶液中的应用

采用抽空涂晶二次生长法成功地合成出了A型分子筛膜,研究了乙二醇水溶液在A型分子筛膜上的渗透气化和蒸气渗透分离性能,考察了温度、浓度对渗透通量的影响,完成了1000 h的稳定性实验。结果表明,A型分子筛膜对EG水溶液具有非常高的分离选择性和稳定性,分离系数达到10000,在120 ℃透量达到10 kg/(m2•h)。     

Application of John's isotherm to predict the adsorption of a binary gas mixture from the adsorption of individual component gases

It is shown that one can predict the adsorption of a binary gas mixture from the adsorption of individual component gases by means of John's isotherm. It is found that the slope and intercept of John's adsorption isotherm for binary mixture is equal to mean of the slopes and intercepts of individual adsorption isotherms. The relation given by Lewis et al. may be used to prove the validity of the above method.     

Calculation of single adsorption isotherms from gravimetrically measured binary gas mixture adsorption isotherms on activated carbon at high pressures

A method is developed for the calculation of single-component adsorption isotherms from gravimetrically measured binary gas mixture adsorption isotherms at high pressures, at two temperatures and for different mole fractions of the gas phase. The adsorption of nitrogen/methane on active carbon Norit R1 is taken as an experimental example.     

Equilibrium isotherms and adsorption heats analysis for ternary mixture of methane,ethane, and propane on 4A zeolite

Equilibrium isotherms were obtained experimentally and theoretically for adsorption of methane, ethane, and propane mixtures on 4A zeolite at 301 K. The experimental data were measured using constant volume method and analyzed by extended Langmuir, modified extended Langmuir, and extended Freundlich isotherm models. The best correlation was achieved with the extended Freundlich isotherm equation and the negative values for heats of adsorption indicate exothermic adsorption nature for these gases on 4A zeolite. The selectivity of 4A zeolite to adsorb gases was also studied with the observation that ethane was more selectively adsorbed than methane on 4A zeolite, while propane was less selectively adsorbed on this zeolite at the studied temperature. Also, it was found that an increase in initial partial pressure of ethane decreases the adsorbed amount of methane, while the increase in partial pressure of methane had no effect on adsorbed amount of ethane.     

Silylated rice husk MCM-41 and its binary adsorption of water–toluene mixture

Mesoporous material, MCM-41, synthesized from rice husk (RH-MCM-41) was modified by loading silylating agent (either trimethylchlorosilane (TMCS), dimethyl-dichlorosilane (DMCS) or phenyl-trichlorosilane (PTCS)) with different concentrations (1–9 wt.%), and aging times, varied between 1, 6, 9, and 24 h. Properties of the silylated MCM-41 samples were characterized by XRD, FTIR, N₂ adsorption, and the binary adsorption of a water–toluene mixture for the breakthrough curves; afterwards, the hydrophobicity indices were determined. Silylating agent caused RH-MCM-41 to possess smaller average pore size and surface area, compared to parent RH-MCM-41. Using a silylating condition of 1 wt.% TMCS for 1 h, modified RH-MCM-41 showed satisfactory enhancement its of hydrophobicity without any significant surface modification. Due to the substitution of silane group onto RH-MCM-41, the hydrophobicity index was increased.     

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

The influence of niobium on the physicochemical properties of the MoVO system and on its catalytic properties in the oxidation of ethane to ethylene and acetic acid is examined. Solids based on MoV_0.4O_x and MoV_0.4Nb_0.12O_y composition and calcined at 350 or 400 °C were studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. Their reactivity during reduction and reoxidation was examined by in situ XRD and by XPS after pre-treatment. Their stability in air was evaluated by means of Raman spectroscopy during laser heating of particles. Niobium is responsible for both stabilization and nanosize of MoO₃ and (VNbMo)₅O₁₄ crystals. The high global selectivity to ethylene and acetic acid (90–96 mol%) is related to the presence of both phases while higher activity is owed to nanoparticles. The model already proposed by Merzouki et al. (Stud. Surf. Sci. Catal., 72 (1992) 81) suggesting that MoVNbO catalysts could be made up from (VNbMo)₅O₁₄-type microdomains in MoO₃ matrix seems still topical.     

Separation of propene/1-alkene and ethylene/1-alkene copolymers by high-temperature adsorption liquid chromatography

A high performance liquid chromatography column (HPLC) Hypercarb^® packed with porous graphite has proven to discriminate polyolefin molecules due to differences in their adsorption and desorption behaviour. While linear polyethylene (PE) and syndiotactic polypropylene (sPP) are adsorbed on the graphite packing, isotactic polypropylene (iPP) is not adsorbed. The column operates at 160 °C with 1-decanol as sample solvent and mobile phase. We have now tested this HPLC system for separations of random propene/1-alkene and ethylene/1-hexene copolymers: While copolymers of propene with 1-butene, 1-hexene and 1-octene copolymers eluted in size exclusion mode without adsorption, propene/1-octadecene and ethylene/1-hexene copolymers are strongly retained and eluted only after application of a linear gradient starting from 1-decanol and ending with pure 1,2,4-trichlorobenzene. The retention of propene/1-alkene (>11 carbons in the side chain) copolymers increases with the concentration of comonomer, making this HPLC system suitable to separate these copolymers according to their chemical composition. In contrast, the retention of ethylene/1-hexene samples decreases with increasing 1-hexene content. Branching in this case shortens the length of continuous methylene sequences of the polymer backbone, which are expected to adsorb in a planar conformation to the graphite layers. This is the first report on the separation of short chain branched polyolefins by high-temperature adsorption liquid chromatography.