Production of Motor Fuel Grade Alcohol by Concentration Swing Adsorption

Abstract

A new cyclic process concept called “concentration swing adsorption” for separation of bulk binary liquid mixtures is described. The process carries out the primary separation by selective liquid-phase adsorption of one of the components of the feed mixture on an adsorbent. The adsorbed component is then desorbed by a desorbent liquid which is equally or more strongly adsorbed than the slectively adsorbed component of the feed mixture. The desorbent liquid is removed from the adsorbent by displacing it with the less strongly adsorbed component of the feed mixture so that the adsorbent can be resused. The process also includes a complementary step where the adsorbent is rinsed with the more strongly adsorbed component of the feed mixture so that two essentially pure products are produced from the feed mixture with high recoveries of both components. At least one simple distillation is also required by the process which separates the desorbent liquid from the less strongly adsorbed component of the feed mixture. The process can be used to separate liquid mixtures with close boiling components or azeotropic mixtures which require energy intensive distillation. A very efficient separation can be achieved in these cases by spending only a fraction of the distillation energy. An example of such an application, viz., separation of a bulk ethanol–water mixture for motor fuel grade alcohol production, is described. A local equilibrium model of the process is used to evaluate the performance of the process for that separation using an activated carbon as the adsorbent and acetone as the desorbent liquid. Experimentally measured equilibrium adsorption characteristics for ethanol–water, acetone–water, and acetone–ethanol binary liquid mixtures on the carbon as well as adsorption column dynamics for the steps of the process are reported.     

Improved film evaporator for mechanistic understanding of microwave-induced separation process

Microwave-induced film evaporation separation process has been reported recently to separate the polar/nonpolar mixture. However, the efficiency of the separation is still too low for practical applications, which requires further enhancement via different strategies such as optimization design of evaporator structure. In addition the depth understanding of the separation mechanisms is great importance for better utilization of the microwave-induced separation process. To carry out these investigations, a novel microwave-induced falling film evaporation instrument was developed in this paper. The improvement of the enhancement effect of microwave-induced separation was observed based on the improved film evaporator. The systematic experiments on microwave-induced separation with different binary azeotropic mixtures (ethanol-ethyl acetate system and dimethyl carbonate (DMC)-H₂O system) were conducted based on the new evaporator. For the ethanol-ethyl acetate system, microwave irradiation shifted the direction of evaporation separation at higher ethanol content in the starting liquid mixture. Moreover, for DMC-H₂O system microwave-induced separation process broke through the limitations of the traditional distillation process. The results clearly demonstrated the microwave-induced evaporation separation process could be commendably applied to the separation of binary azeotrope with different dielectric properties. Effects of operating parameters are also investigated to trigger further mechanism understanding on the microwave-induced separation process.     

Pervaporative Separation of Methanol–Methyl Acetate Mixtures with Commercial PVA Membranes

Pervaporation may successfully be implemented for the separation of azeotropic mixtures which generally requires energy intensive separation procedures. Separation of methanol from methyl acetate by pervaporation is a representative application. In this study the commercial polyvinyl alcohol (PVA)-based membranes PERVAP^TM 4155-30, PERVAP^TM 4155-70, and PERVAP^TM 4155-80 were used to recover methanol from binary methanol–methyl acetate mixtures. The separation performance was investigated for various operating parameters such as feed composition, feed temperature, and permeate pressure and discussed in terms of permeance and selectivity. An empirical model was developed to quantify the effect of membrane swelling on the permeate flux.     

Batch‐Rektifikation azeotroper Gemische in Verstärkungs‐ und Abtriebskolonnen

Batch distillation is an efficient unit operation which allows the separation of a multicomponent mixture into its pure constituents in a single column. However, the separation of azeotropic mixtures by distillation is quite difficult because at the azeotrope the liquid and the gas have the same composition and, in turn, the driving force for distillation disappears. A systematic presentation of batch distillation processes for the separation of binary azeotropic mixtures using an entrainer is given.     

Propane/Propylene Separation by Simulated Moving Bed II. Measurement and Prediction of Binary Adsorption Equilibria of Propane,Propylene, Isobutane,and 1-Butene on 13X Zeolite

Abstract

The design of a simulated moving bed (SMB) process relies on valid thermodynamic predictions of multicomponent adsorption built up from accurate binary adsorption equilibrium data. Experimental adsorption equilibria of binary mixtures constituted by propane, propylene, isobutane and 1-butene on 13X zeolite were determined using breakthrough experiments at 373 K and 150 kPa. In addition, these binary adsorption experiments allow to confirm the choice of isobutane as an interesting desorbent for the separation of propane-propylene by SMB, since it has an intermediate selectivity between the two species to separate. Various prediction models are available in the literature but only a few of them have both physical and thermodynamical consistency. The ideal adsorbed solution theory (IAST), the thermodynamically consistent extended Toth model (TCET), and the physically-consistent extended Toth isotherm (PCET) were used to predict binary adsorption equilibria from pure component adsorption isotherms parameters. The PCET model was found suitable for representing the adsorption equilibrium of the different hydrocarbon mixtures with a reasonably good accuracy.     

DISTILLATION UNDER ELECTRIC FIELDS

ABSTRACT

Distillation is the most common separation process used in the chemical and petroleum industry. Major limitations in the applicability and efficiency of distillation come from thermodynamic equilibria, that is, vapor-liquid equilibria (VLE), and heat and mass transfer rates. In this work, electric fields are used to manipulate the VLE of mixtures. VLE experiments are performed for various binary mixtures in the presence of electric fields on the order of a few kilovolts per centimeter. The results show that the VLE of some binary mixtures is changed by electric fields, with changes in the separation factor as high as 10% being observed. Batch distillation experiments are also carried out for binary mixtures of 2-propanol and water with and without an applied electric field. Results show enhanced distillation rates and separation efficiency in the presence of an electric field but decreased separation enhancement when the electric current is increased. The latter phenomenon is caused by the formation at the surface of the liquid mixture of microdroplets that are entrained by the vapor. These observations suggest that there should be an electric field strength for each system for which the separation enhancement is maximum.

     

Einfluß der Diffusion auf die Selektivität der Schleppmittel-Destillation

Influence of diffusion on the selectivity of entrainer distillation . The selectivity of azeotropic distillation generally depends not only on the relative volatility but also upon the rate of diffusion of the participating components in the liquid and the gaseous phase. If the less volatile material diffuses faster in the gas phase than the more volatile material, then the former can also accumulate in the gas phase. In such a case the azeotropic points do not necessarily represent separation limits. This effect might also be utilized in the separation of azeotropic mixtures in specific cases. On the other hand, a large diffusion resistance in the liquid phase can override any selectivity. An estimate shows that selective drying of porous materials containing binary solvent mixtures is therefore practically impossible. Azeotropic distillation is also suitable for investigating column plates and packings with the aim of isolating the hydraulic and kinetic reasons for the imperfect equilibration always observed. These questions, overcoming azeotropic points, non-selective drying, and the reasons for imperfect equilibration in separation columns, are discussed in the light of theoretical results and experimental data obtained for practical azeotropic distillations.     

Separation of Liquid Mixtures by Pervaporation

Separation of various mixtures, especially liquid mixtures, is a very necessary unit operation in industry. A large number of such techniques are available, such as distillation, adsorption, liquid-liquid extraction, and fractional crystalization [l]. The development of this type of technology became necessary to effect separation of azeotropic liquid mixtures. For liquid mixtures having components with similar boiling ranges, however, such conventional separation techniques are energy intensive and add considerably to the cost of the final product. With the advent of the necessity of reducing the energy requirements of Unit options, membrane separation has been recognized as an alternative to the conventional methods.     

Development of Cellulose Acetate Propionate Membrane for Separation of Ethanol and Ethyl tert-Butyl Ether Mixtures

Abstract

For pervaporation separation of ethanol and ethyl tert-butyl ether mixtures, a cellulose acetate propionate membrane was chosen as the experimental membrane because of its high selectivity and good mass fluxes. The properties of the membranes were evaluated by the pervaporation separation of mixtures of ethyl tert-butyl ether/ethanol and the sorption experiments. The experimental results showed that the selectivity and the permeates depend on the ethanol concentration in the feed and the experimental temperature. With increases of the ethanol weight fraction in the feed and the temperature, the total and partial mass fluxes increased. With respect to the temperature, ethanol mass flux obeys the Arrhenius equation. The selectivity of this membrane decreases as the temperature and the ethanol concentration in the feed increase. This membrane shows special characteristics at the azeotropic composition. In the vicinity of the azeotropic point, minimum values of ethanol concentration in the permeate and in sorption solution are obtained. The swelling ratios increase when temperature and the ethanol concentration in the feed are increasing. The ethanol concentration in the sorption solution is also influenced by the temperature and the mixture's composition. When the temperature increases, the sorption selectivity of the membrane decreases.     

Synthesis,experiments and simulation of heterogeneous batch distillation processes

The presence of azeotropes in multicomponent mixtures complicates the design of batch distillation separation processes widely used in pharmaceutical and speciality chemical industries. Most of those processes include the use of a homogeneous entrainer to ease the separation. We describe novel methods to break azeotropes using an entrainer that is partially miscible with one of the initial binary mixture components. We depict some of the advantages of heterogeneous batch distillation processes: more design alternatives for the separation of an azeotropic binary mixture than with homogeneous batch distillation, batch distillation boundary crossing thanks to a controlled reflux of the entrainer-rich phase, simplified distillation sequences as a consequence of less distillation tasks. Three examples based on the separation of non-ideal azeotropic or close boiling point binary mixtures through heterogeneous batch distillation are simulated using a commercial batch distillation package. Experiments validate the simulated separation of a minimum boiling azeotropic mixture.     

Separation of Hydrogen-Lean Mixtures for a High-Purity Hydrogen by Vacuum Swing Adsorption

Abstract

High-purity hydrogen is commercially produced by pressure swing adsorption from hydrogen-rich mixtures. In this work, a vacuum pressure swing adsorption cycle is used to produce high purity hydrogen from a hydrogen-lean binary mixture (20/80 H₂/CO) using zeolite 5A as the sorbent. The effects of different process variables on separation performance have been studied. The purity of hydrogen product increases at low throughput, high feed pressure, high end pressure of cocurrent depressurization, low end pressure of countercurrent evacuation, and short cycle time. Also, it was found that for a H₂-lean mixture, the separation is improved at higher ambient temperature. In addition, a new “vacuum purge” step was found to improve the separation and is therefore a promising step for commercial application.     

Liquid Permeation of Isopropanol and Water in a Silicone Rubber

Abstract

The feasibility of using a silicone rubber membrane to separate mixtures of isopropyl alcohol and water, including the azeotropic composition, has been demonstrated and a quantitative measure of efficiency of separation has been developed.

One of the problem areas in studying liquid permeation is the variability in the polymer membrane structure. Such factors as the presence of solvents and plasticizers, previous thermal history, previous solvent history, and the degree of crystallinity of the polymer behavior affect membrane behavior. However, as the polymers are better understood, these drawbacks for the researcher may be of advantage to those tailoring a polymer to a specific use.     

醋酸甲酯和甲醇热集成变压精馏分离工艺模拟与优化

基于对醋酸甲酯与甲醇二元共沸特性的分析,提出热集成变压精馏分离醋酸甲酯和甲醇的工艺. 利用Aspen Plus软件对该分离过程进行模拟,以NRTL活度系数方程为物性计算方法,其二元相互作用参数由气液相平衡数据回归,分析了加压塔和常压塔的理论板数、进料位置及回流比对分离效果的影响,并进行了能耗比较. 结果表明,该工艺能很好地分离醋酸甲酯和甲醇,较佳的工艺条件为：加压塔操作压力909 kPa,理论板数32,第21块板进料,回流比4.2,塔釜醋酸甲酯纯度99.8%;常压塔操作压力101 kPa,理论板数30,第20块板进料,回流比4.6,塔釜甲醇纯度99.0%. 与常规变压精馏相比,热集成变压精馏可节能达45.8%;与以水为萃取剂的萃取精馏分离工艺相比,热集成变压精馏分离工艺更适合醋酸甲酯与甲醇体系的分离.     

Chromatographic Separation by Foam

Abstract

The development of a unique chromatographic separation method based on liquid foams is described. The sorption bed is liquid foam moving in a tall vertical column in plug flow manner. The foam is eluted from the top counter-currently to its motion. The mechanism of separation of mixtures is based on adsorption to bubble surface and/or utilizing the foam producing surfactant as a selective carrier. It is shown how this technique can be used for pulse as well as for continuous chromatographic separations. Results of some systematic studies on the effect of two independent variables, foam velocity and elution rate, on separation of mixtures of organic dyes is presented and discussed.     

Optimal design of extractive distillation columns—A systematic procedure using a process simulator

The separation of binary mixtures which form azeotropes is not possible through conventional distillation and they are usually separated by extractive or azeotropic distillation. The optimization of extractive distillation columns is usually performed using a process simulator; however, normally, the result is only obtained after several simulations and the simultaneous analysis of several graphs. This paper sets out to present a systematic procedure, using a process simulator (Aspen Plus^®), in order to obtain the optimum condition for extractive distillation columns. The optimization achieved is characterized by the fact that it is not necessary to perform various simulations, and it also avoids the simultaneous analysis of dozens of curves. The dehydration of aqueous mixtures of ethanol using ethylene glycol as solvent was the system chosen as a case study.     

Purification of tetrahydrofuran from aqueous azeotropic solution: continuous adsorption operation using molecular sieves

Abstract

Purification of chemicals is industrially important. Tetrahydrofuran (THF) is a useful chemical and the industrial requirement is minimum 99.5 mass %. THF forms a homogenous minimum boiling aqueous azeotrope due to which purification by distillation is difficult. The present work has used liquid-phase adsorption of the THF–water azeotropic mixture over different adsorbents in order to purify THF. Molecular sieves (3A and 4A) were observed to offer better separation. A methodology to make the process continuous is presented in this work so as to obtain high-purity THF by using adsorption over molecular sieves.     

Effect of temperature on gas adsorption and separation in ZIF-8: A combined experimental and molecular simulation study

In this work, the effect of temperature on adsorption of CO₂, CH₄, CO, and N₂ and separation of their binary mixtures in ZIF-8 were investigated using experimental measurements combining with molecular simulations. The results show that for pure gas adsorption, the effect of temperature is large when strong adsorption occurs, mainly due to the variation of the interaction energy between adsorbate molecules with temperature; while for gas mixtures, systems with large selectivity are more sensitive to temperature. In addition, this work shows that temperature influences the working capacity of CO₂ in temperature swing adsorption (TSA) process with the interplay of pressure, which should be considered in the design of TSA process in practical applications.     

Extractive Distillation of p-Cresol/2,6-Xylenol Mixtures in the Presence of Alkanolamines

Abstract

The separation of p-cresol/2,6-xylenol mixtures has been investigated by extractive distillation in the presence of alkanolamines. The interaction parameters of liquid phase models, such as Wilson, NRTL, and UNIQUAC, have been estimated from binary vapor-liquid equilibrium data. The predicted relative volatility values for the p-cresol/2,6-xylenol mixtures in the presence of the alkanolamines were compared with experimental data.     

Separation of ethylene glycol, 1,2-butanediol and 1,2-propanediol with azeotropic distillation

1,2-butanediol (1,2-BDO) and 1,2-propanediol (1,2-PDO) are inevitably side produced in the ethylene glycol (EG) production processes from non-petroleum routes, but are very difficult to separate by the ordinary distillation method because of the closeness of their boiling temperatures to EG, thus compromise the economy of these processes. The azeotropic distillation process using 1-octanol (CPO) as an entrainer to separate EG and 1,2-BDO mixture with or without 1,2-PDO was studied in this paper. Four binary vapour–liquid equilibrium data of EG-1,2-BDO, EG-CPO, 1,2-BDO-CPO, and 1,2-PDO-CPO were measured using an Ellis equilibrium kettle and regressed with the thermodynamic model of non-random two liquid to obtain the corresponding binary interaction parameters. On this basis, azeotropic distillations with CPO as an entrainer were designed to separate EG and 1,2-BDO with or without 1,2-PDO. The complete separation processes, including the azeotropic distillation and CPO recovery process consisting of extraction with H₂O and subsequent distillation, were simulated and optimized with Aspen Plus for both the EG-1,2-BDO binary mixture and the EG-1,2-BDO-1,2-PDO ternary mixture. The simulation results show that the azeotropic distillation method with CPO as an entrainer can effectively separate the mixture of EG-1,2-BDO and EG-1,2-BDO-1,2-PDO, achieving EG of 99.90% purity with 99.98% recovery and 1,2-BDO of 99.30% purity with 99.45% recovery for the binary mixture, and achieving EG of 99.90% purity with 99.80% recovery, 1,2-BDO of 99.35% purity with 99.35% recovery, and 1,2-PDO of 90.59% purity with 94.38% recovery for the ternary mixture. These processes are promising for industrial application and can significantly improve the economy of non-petroleum EG production.     

Heat Integrated Ethanol Dehydration Flowsheets

Abstract

A theoretical evaluation of heat-integrated heterogeneous-azeotropic ethanol-water distillation flowsheets is presented. Simulations of two column flowsheets using several different hydrocarbon entrainers reveal a region of potential heat integration and substantial reduction in operating energy. In this paper, methods for comparing hydrocarbon entrainers are shown.

Two aspects of entrainers are related to operating and capital costs. The binary azeotropic composition of the entrainer-ethanol mixture is related to the energy requirements of the flowsheet. A temperature difference in the azeotropic column is related to the size of the column and overall process staging requirements. Although the hydrophobicity of an entrainer is essential for specification of staging in the dehydration column, no substantial increase in operating energy results from an entrainer that has a higher water content. Likewise, liquid-liquid equilibria between several entrainer-ethanol-water mixtures have no substantial effect on either staging or operation. Rather, increasing the alcohol content of the entrainer-ethanol azeotrope limits its recovery in the dehydration column, and increases the recycle and reflux streams. These effects both contribute to increasing the separation energy requirements and reducing the region of potential heat integration.

A cost comparison with a multieffect extractive distillation flowsheet reveals that the costs are comparable; however, the extractive distillation flowsheet is more cost effective as operating costs increase.

The destruction of organic model substances by indirect electrooxidation was investigated. The oxidation agent Co(III) was used because of the high redox potential of the Co(III)/Co(II) redox couple (E₀ = 1.808 V).

Several supercritical fluid extraction (SCFE) processes have been proposed for removing toxic and intractable organic compounds from a range of contaminated solids. These include soil remediation and the regeneration of adsorbents used to treat wastewater streams such as granular activated carbon (GAC). As a separation technique for environmental control, SCFE has several distinct advantages over conventional liquid extraction methods and incineration. Most notably, the contaminant is removed from the solvent in a concentrated form via a change in pressure or temperature and can be completely separated upon expansion to atmospheric pressure.

The viability of SCFE hinges on process conditions such as solvent-feed ratio and solvent recycle ratio. The necessity of recycling solvent complicates the contaminant separation step since a complete reduction to atmospheric pressure would create large recompression costs. Because of this, the pressure and temperature dependence of contaminant solubility must be understood so that operating conditions for the separation step can be defined. Fortunately, this is the most developed aspect of SCF technology. However, the mass transfer limitations to removing contaminants from solids change with solvent flow rate.

This paper discusses the use of SCFE for environmental control and presents results for the removal of DDT and 2-chlorophenol from GAC. 2-chlorophenol is almost completely removed with pure CO₂ at 40°C and 101 bar while only 55% of the DDT is removed at 40°C and 200 bar. These differences in regeneration efficiency cannot be understood solely in terms of solubility but point to a need for detailed studies of adsorption equilibrium and mass transfer resistances in supercritical fluid systems.