Isobaric ternary vapour-liquid equilibria system: Benzene-cyclohexane-n-butanol

Vapour/liquid equilibrium data for the system, benzene-cyclohexane-n-butanol, were obtained at 760 ± 1 mm Hg pressure using a modified Colburn equilibrium still. No ternary azeotrope was observed. The experimental activity coefficient data were correlated with Wohl's three-suffix symmetrical and three-suffix Margules equations with and without using a ternary constant. From an estimate of the average errors in Y¹, Y², and Y³, Wohl's three-suffix Margules equations seem to fit the data fairly well using a ternary constant, C = ?0.1042. From the equilibrium curve drawn for the ternary system on a n-butanol-free basis with percent, n-butanol as parameter, it was found that the azeotrope disappeared at 90–95% n-butanol.     

The equilibrium phase properties of the propane-methanol and n-Butane-methanol binary systems

Vapor and liquid equilibrium phase compositions were determined at 310.7, 352.2, 393.0 and 474.3 K for the propane-methanol system and at 469.9 K for the n-butane–methanol system. Measurements were made at pressures from the vapor pressure of the less volatile component to the maximum pressure where two phases coexisted either as an azeo-trope or at the critical condition, depending on the system. Azeotropic behavior was observed at 310.7 and 352.2 K for the propane-methanol system. Equilibrium ratios were calculated at each temperature from the phase composition data. The temperature dependence of the azeotrope pressure and of the corresponding azeotrope composition was expressed analytically.     

Natural gas sweetening using low temperature distillation: simulation and configuration

ABSTRACT

Hypothesis: Separation of CO₂ from a stream of natural gas using low-temperature distillation process is complicated not only because of the existence of ethane (C₂) and CO₂ azeotrope but owing to the freezing of CO₂. A modified process based on an existing Ryan–Holmes process in the form of a low-temperature distillation is presented here for the separation of sour gases. In addition, solvents were employed to prevent CO₂ freezing and to avoid formation of the C₂-CO₂ azeotrope.

Simulation: Simulation calculations were carried out using a natural gas stream containing CO₂ and H₂S. The process was designed and simulated using Aspen HYSYS 9.

Findings: A low-temperature process for the separation of a feed stream containing up to 30 mole% CO₂ and 2.5 mole% H₂S was achieved, which lowered the levels of these gases to within 50 and 4 ppm, respectively. These values conform to liquefied natural gas specifications. The compositions of the product streams, the required solvent circulation flow rates, and the total energy requirements were estimated. The reported process successfully separated H₂S and produced CO₂ at a pressure of 25.0 bar and a temperature of ?13°C, thereby ensuring its suitability for application in enhanced oil recovery. This described process also delivered the desired natural gas product at 35 bar and ?90°C ready for liquefaction and further cooling.     

On Determination of Azeotrope Coordinates from gE for Binary Isothermal and Isobaric Systems

A relatively simple procedure is described to calculate the coordinates, temperature (T_az), pressure (P_az), and composition (x_1az), of an azeotrope (for either an isothermal or isobaric binary system at low pressure and with a single or double homogeneous azeotrope) from an expression for the liquid‐phase excess molar Gibbs function (g^E). General results are based on (?g^E/?x₁)_az = RT_az ln[p₂*(T_az)/p₁*(T_az)], and P_az = (γ₁p₁*)_az = (γ₂p₂*)_az, where R is the gas constant, p* is saturation vapour pressure, and γ is liquid‐phase activity coefficient. Specific results are given for the Redlich‐Kister, van Laar, Wilson, and NRTL equations. Numerical examples are provided for both an isothermal and an isobaric system. The procedure provides a means to obtain azeotrope coordinates that are consistent with a g^E expression obtained either from experimental data or from a model. It is applicable to polyazeotropy, whereas the criteria given previously are generally not applicable to polyazeotropy.     

General reflection on critical negative azeotropy and upgrade of the Bancroft's rule with application to the acetone + chloroform binary system

The possible shapes of continuous critical loci for binary systems exhibiting a negative azeotrope which persists up to the critical region are reviewed and extensively discussed. Such a review made it possible to prove that the existence of an intersection point – in a (P, T) projection – between the critical line and one of the vaporization curves was a sufficient condition for a binary system to exhibit a critical azeotrope. The Bancroft's rule which until now stated that the existence of an intersection point between the two vaporization curves in a (P, T) plane was a sufficient condition to observe an azeotropic behavior was thus upgraded to take into account the crossing of the critical line and one of the vaporization curves. Such a point was logically called a Bancroft point of the second kind.In a second part, mixture critical points of the acetone + chloroform binary system were measured in order to determine if such a system exhibited a Bancroft point of the second kind and consequently if the negative azeotrope persisted up to the critical region. Along the critical line, the acetone mole fraction was varied between 0.06 and 0.92.     

On Criteria for Occurrence of Azeotropes in Isothermal and Isobaric Binary Systems

Criteria are developed for the occurrence of azeotropes in binary nonelectrolyte systems for both isothermal and isobaric situations in terms of liquid‐phase activity coefficients at infinite dilution (γ^∞). In the case of isothermal systems at temperature T, for a positive azeotrope, γ^∞_lvc≥ p*_mvc/p*_lvc where lvc refers to the less volatile component, mvc to the more volatile component, and p* to saturation vapour pressure at T; for a negative azeotrope, γ^∞_mvc≤ p*_lvc/p*_mvc. In the case of isobaric systems at pressure P, for a minimum‐boiling azeotrope, γ^∞_lvc(T_Bmvc) ≥ P/p*_lvc(T_Bmvc), where T_B refers to the boiling point at P; for a maximum‐boiling azeotrope, γ^∞_mvc (T_Blvc) ≤ P/p*_mvc(T_Blvc). The criteria are also given in terms of the parameters of selected correlations for the excess molar Gibbs function (g^E). Examples of the use of the criteria are provided. Various methods that generate values of γ^∞ can be used in conjunction with the criteria, for example, in screening procedures.     

Design and Control Comparison of Alternative Separation Methods for n‐Heptane/Isobutanol

The binary mixture of n‐heptane and isobutanol forms an azeotrope at atmospheric pressure, with a composition of 66.9 mol % n‐heptane and a temperature of 364 K. Several methods of separation are possible. This study compares the steady‐state economics and the dynamic controllability of three alternative separation techniques: a two‐column extractive distillation process, a two‐column pressure‐swing distillation process, and a single column with a refrigerated condenser.     

Appearance of an internal tangential azeotrope in ternary systems

An internal tangential azeotrope appears at the “ideality” point of the diethylamine-chloroform-methanol system. The mutual arrangement of K= 1 and 6h = 1 lines at this point has been determined.     

Separation of isopropyl alcohol + isopropyl acetate azeotropic mixture: Selection of ionic liquids as entrainers and vapor-liquid equilibrium validation

Based on the COSMO-SAC model, 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium p-toluenesulfonate were selected from 30 ILs as entrainers to investigate the separation of the isopropyl alcohol + isopropyl acetate azeotrope. Two screening indicators, σ-profile and infinite dilution selectivity (S^∞), were adopted as the basis. The isobaric vapor-liquid equilibrium experiments for isopropyl alcohol + isopropyl acetate binary system and isopropyl alcohol + isopropyl acetate + confirmed ILs ternary systems were performed at the pressure of atmospheric pressure. The experimental measurement demonstrated that the adopt ILs enhanced the relative volatility of the above alcohol-ester azeotrope, leading to the elimination of the azeotropic point with a certain amount ILs. Meanwhile, the thermodynamic correlation for two systems containing ILs was explored with the NRTL model, which also reflects the extensive applicability of that by comparing the deviation between experimental and calculated data. And its binary interaction parameters were regressed, which can provide a basis for its simulation process.     

Thermodynamic properties of methanol–benzene mixtures at elevated temperatures

The total pressure and the compositions of the vapour and liquid phases of the methanol–benzene system have been determined under equilibrium conditions at 100°, 120°, 140°, 160°, 180°, 200° and 220° for ten levels of concentration. The corresponding activity coefficients of methanol and benzene are reported; their values indicate that the equilibrium data are thermodynamically consistent. An azeotrope is found at all temperatures, its methanol content increasing as the temperature is increased. The relationship log P_az = 6·5098—(1,766/T) expresses the interdependence of the azeotrope vapour pressure P_az(lb/in² abs.) and temperature T(°K). Estimates of integral heat of mixing (H^E) and entropy change due to mixing (S^E) as functions of liquid composition (x_meth) have been made from the excess free energy of mixing G^E,(T) x_meth functions. Both H^E and S^E at a given x are positive increasing functions of temperature. These phenomena are discussed in terms of the dissociation of methanol ‘polymer’ and the formation of benzene–methanol ‘complexes’.     

热集成变压精馏分离乙二胺-水共沸体系的模拟优化

针对乙二胺-水共沸物组成对压力较为敏感的特性,采用部分热集成变压精馏工艺分离该共沸物。先利用Aspen Plus软件对该工艺进行稳态模拟,再以理论塔板数、进料位置、回流比为优化变量,水和乙二胺的纯度为约束,以年度总费用（total annual cost,TAC）为目标函数建立乙二胺-水共沸体系分离系统的优化设计模型。采用列队竞争算法对该分离过程主要工艺参数进行优化,得到了变压精馏分离乙二胺-水体系的最佳工艺操作参数及设备参数。模拟结果表明,利用算法对多变量进行同时优化可得到更具经济效益的分离系统,与传统优化结果相比,可降低TAC约7.31%。在此基础上,对高压塔的操作压力进行优化分析,将其由2atm提升至4atm（1atm=101325Pa）,并对流程其他参数进行优化,可显著降低TAC约24.62%。进一步,采用部分热集成比普通变压双塔精馏降低TAC约21.87%     

Ternary vapour-liquid equilibria of the system acetone+chloroform+tetrachloroethylene

Isobaric vapour-liquid equilibrium data of the ternary system acetone + chloroform + tetrachloroethylene were determined at 760 mmHg total pressure using a modified Colburn still. The activity coefficient data were satisfactorily tested for their thermodynamic consistency by the method of McDermott and Ellis and a satisfactory correlation was also obtained through Wohl's three suffix Margules ternary equations without a ternary constant. No ternary azeotrope was observed.     

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.     

Effects of Ultrasonic Waves on Vapor-Liquid Equilibrium of an Azeotropic Mixture

Abstract

Azeotropic and extractive distillation techniques used to separate azeotropic mixtures are among the most challenging separation processes in the chemical industry. In this work, an innovative distillation technique which employed ultrasonic waves was proposed to intensify the conventional multi-column azeotropic distillation method into a single-column alternative. The effects of ultrasonic intensity on the vapor-liquid equilibrium (VLE) of methyl-tert-butyl-ether (MTBE)-methanol was investigated at 50, 100, 200, and 250 W/A·cm² and at a fixed frequency of 40 kHz. Studies were also done to examine the effects of ultrasonic frequency on the VLE data at 25 and 68 kHz frequencies. It was found that ultrasonic waves at 50 W/A·cm² intensity and 25 kHz frequency gave the highest relative volatility (α) at 2.654 and completely eliminated the MTBE-methanol azeotrope, thereby allowing highly pure MTBE to be recovered in just a single distillation column. The results revealed that ultrasonic waves had the potential to favorably manipulate α, and hence, the VLE of an azeotropic mixture.     

醋酸+二甲基甲酰胺常压汽液平衡数据测定与关联

用改进式Rose釜测定了101.33 kPa下醋酸+二甲基甲酰胺二元体系的VLE数据,结果表明二甲基甲酰胺与醋酸形成了二元最高共沸物。实验数据通过了面积法热力学一致性检验。分别采用NRTL、W ilson、UNQUIC方程对实验数据进行关联,NRTL方程关联结果较好,温度平均偏差0.23℃,醋酸在汽相中的平均偏差为0.009 7。用NRTL方程参数推算了共沸点数据,共沸点温度155.65℃,醋酸摩尔分数0.312 7。     

Isothermal vapour–liquid equilibria for the ethanol–n-octane system

A modified Dvorák & Boublík & recirculation still was used for the determination of isothermal vapour–liquid equilibrium data for the binary system ethanol–n-octane at four temperatures. Liquid activity coefficients, γ, were evaluated, and log γ values were correlated by a three-constant Redlich–Kister equation. Binary azeotrope exists at all four temperatures and the mole fraction of ethanol in the azeotrope increases with increasing temperature.     

萃取精馏分离甲醇-丁酮萃取剂的选择

为了解决工业生产中甲醇-丁酮共沸体系难分离的问题,本研究采用一步法合成了N-乙基吡啶溴盐([EPy][Br])、N-丁基吡啶溴盐([BPy][Br])和N-己基吡啶溴盐([HPy][Br])3种离子液体(IL),测定了101.3 kPa下这3种离子液体对甲醇-丁酮共沸物系的溶剂选择性,并考察了溶剂比对其选择性的影响,同时将离子液体的分离性能与有机溶剂进行了比较。实验结果表明:合成的3种离子液体都可提高甲醇对丁酮的相对挥发度,它们的选择性大小顺序为[EPy][Br]> [BPy][Br]> [HPy][Br],同时,它们的选择性随溶剂比的增加而增大,与常规有机溶剂相比,离子液体作为萃取剂具有显著优势。因此,可以选用[EPy][Br]作为分离甲醇-丁酮共沸物系的萃取剂。     

Comparison of Two Aerodynamic Lenses as an Inlet for a Single Particle Laser Ablation Mass Spectrometer

By means of a newly designed portable aerosol mass spectrometer SPLAT (Single Particle Laser Ablation Time-of-flight mass spectrometer) for the analysis of single atmospheric aerosol particles we investigated the system performance in dependency on two different aerodynamic lenses (Liu and Schreiner type) capable of focusing particles with diameters ranging from 80 nm to 800 nm and 300 nm to 3000 nm, respectively. By using the pressure regulated Schreiner lens, the instrument is independent of variations in atmospheric pressure which would lead to changing dynamical properties of the aerosol particles. Active pressure control inside the inlet system facilitates airborne measurements without complicated corrections. With the Liu setup no pressure regulation was used. Here the overall efficiency of our instrument was 7% while with the Schreiner setup 2% was achieved. The Liu lens setup is optimal for measuring submicron particles at low particle concentrations. To detect supermicron particles the Schreiner lens setup is favored. Together with these experiments we present key details of the SPLAT setup and its characterization. Our instrument is able to measure simultaneously the size and the chemical composition of individual aerosol particles larger than 300 nm in diameter. It uses forward scattered light of single aerosol particles at two positions to determine their vacuum aerodynamic diameter from the flight time between the two lasers. Chemical analysis of the particles is done by laser ablation mass spectrometry utilizing a bipolar time-of-flight mass spectrometer.     

Vapor-liquid equilibrium of ethanol/ethyl acetate mixture in ultrasonic intensified environment

A vapor-liquid equilibrium (VLE) study was conducted on ethanol/ethylacetate mixture as a preliminary step towards developing an ultrasonic-assisted distillation process for separating azeotropic mixtures. The influence of ultrasonic intensity and frequency on the vapor-liquid equilibrium (VLE) of the mixture was examined using a combination of four ultrasonic intensities in range of 100–400W/cm² and three frequencies ranging from 25–68 kHz. The sonication was found to have significant impacts on the VLE of the system as it alters both the relative volatility and azeotrope point, with preference to lower frequency operation. A maximum relative volatility of 2.32 was obtained at an intensity of 300 W/cm2 and a frequency of 25 kHz coupled with complete elimination of ethanol-ethyl acetate azeotrope. Results from this work were also congruent with some experimental and theoretical works presented in the literature. These findings set a good beginning towards the development of an ultrasonic assisted distillation that is currently in progress.     

Optimization of the ETBE (ethyl tert-butyl ether) production process

The synthesis of ETBE (ethyl tert-butyl ether) from the reaction of ethanol with isobutene is an exothermic reaction of equilibrium. To increase the conversion of isobutene requires operating the reaction system at low temperatures and with excess ethanol in order to displace the equilibrium towards the products. ETBE and ethanol form an azeotropic mixture which hinders the recycling of nonreacted ethanol in the process. The purpose of this work is to optimize the synthesis of ETBE eliminating the introduction of water into the system to break the ETBE/Ethanol azeotrope. The production process model proposed here eliminates the recycling of ethanol and suggests the use of the azeotropic mixture (ETBE/Ethanol) in the formulation of gasolines. The direct use of the azeotrope in the formulation of automotive gasolines reduces the implementation and production costs of ETBE.