A REDUCED VAPOR PRESSURE EQUATION BASED ON THE THEOREM OF CORRESPONDING STATES

A reduced vapor pressure equation based on the theorem of corresponding states is proposed in this work by the use of the third parameter to and the fourth parameter X. This equation yields an overall average absolute deviation of 1.09% for 111 normal fluids involving a total of 6968 vapor pressure data points, and 0.67% for 20 polar fluids involving a total of 1516 data points, respectively. A relationship of estimating acentric factors is obtained by applying the reduced vapor pressure equation at the normal boiling point. This relationship is very accurate for the prediction of the values of the acentric factor     

Effective carbon number molecular weight carbon number Pressure Temperature

A method based on the effective carbon number (ECN) has been developed for the prediction of the vapor pressures of carboxylic acids over a range of temperatures. Good representation of the vapor pressures is obtained in the range 1 kPa to HOkPa with an overall average absolute deviation of 2.26%for 31 carboxylic acids which included saturated as well as unsaturated acids. The method requires a knowledge only of the normal boiling point or the boiling point at 1.3 kPa (lOmmHg) of the substance     

Vapor pressure and normal boiling point predictions for pure methyl esters and biodiesel fuels

Temperature dependent vapor pressures of the methyl esters of fourteen fatty acids that are commonly present in biodiesel fuels were predicted by the Antoine equation and a group contribution method. The predicted boiling points of these esters up to a pressure of 100 mmHg were within ±1.0% of reported data for these two methods. Normal boiling points were determined from both the predicted vapor pressure and a correlation equation and the prediction errors were less than 5 K comparing to available published data. The vapor pressure and normal boiling points of 19 real-world biodiesel fuels were predicted and compared with reported data where available. The prediction errors of normal boiling points were less than 1.0%, and the predicted vapor pressures were also observed to closely match the reported data among the methyl esters of soybean oil, rapeseed oil and tallow. The predicted results showed that, except for coconut and butterfat, most of the methyl esters of the vegetable oils and animal fats had a normal boiling point in the range of 620–630 K. A sensitivity analysis indicated that the variation of fatty acid composition and the uncertainty of the normal boiling point of C18:2 were the main factors that affected the predicted normal boiling points of the biodiesel fuels.     

Estimation of flash point

A general correlation has been obtained for estimation of closed-cup flash point of organic compounds from their normal boiling points. Estimated flash points are within a deviation of about 10% of reported values. However, separate correlations have been obtained and recommended for acids and alcohols for estimation of flash points for more accurate results.     

定位分布贡献方法估算有机物正常沸点

A new position group contribution model is proposed for the estimation of normal boiling data of organic compounds involving a carbon chain from C2 to C18. The characteristic of this method is the use of position distribution function. It could distinguish most of isomers that include cis- or trans-structure from organic com-pounds. Contributions for hydrocarbons and hydrocarbon derivatives containing oxygen, nitrogen, chlorine, bro-mine and sulfur, are given. Compared with the predictions, results made use of the most common existing group contribution methods, the overall average absolute difference of boiling point predictions of 417 organic com-pounds is 4.2 K; and the average absolute percent derivation is 1.0%, which is compared with 12.3 K and 3.2% with the method of Joback, 12.1 K and 3.1% with the method of Constantinou-Gani. This new position contribution groups method is not only much more accurate but also has the advantages of simplicity and stability.     

CH_3CF_3的蒸汽压与临界参数实验研究

测量了CH_3CF_3 230K以上的蒸汽压与临界参数.蒸汽压测量精度为|△T|≤28mk和|△р|≤1.4Pa,结果对文献蒸汽压方程呈明显偏差.基于汽液界面消失位置和临界乳光现象,测定了临界密度ρ_c=442±4kg/m~3、临界温度T_c=346.16±0.05K,由本文蒸汽压方程算出临界压力ρ_c=3.781±0.006MPa.文中还给出了一个新的正常沸点推算值T_b=225.69K.     

The vapour-liquid equilibrium of ternary systems with limited miscibility at atmospheric pressure

The complete study of the vapour-liquid equilibrium of ternary systems with limited miscibility requires vapour-liquid equilibrium determinations and liquid-liquid equilibrium determinations at boiling point. The vapour-liquid equilibrium was determined by means of an equilibrium still based on the principle of Giilespie but modified in such a way that an accurate boiling point measurement, even for systems with heterogeneous liquid was possible and that the vapour phase was analysed without previous condensation. Two ternary systems have been studied: the system methanol-ethylacetate-water and the system ethanol-ethylacetate-water. The ternary data have been predicted by means of the equation of Renon and Prausnitz. The parameters are determined by correlating the binary data. The ternary vapour-liquid equilibrium are predicted within 1-2. 10 ^?2 mol fraction for the vapour composition and 1°C for the boiling point. The position of the predicted tielines of the liquid-liquid equilibrium at boiling point was almost coinciding with the position of the experimental tielines. There was a slight deviation of the predicted and experimental binodal.     

含盐异丙醇溶液饱和蒸汽压的测定和关联

<正>为了考察电解质-盐类对汽液平衡的影响,研究挥发性溶剂在不同盐浓度下的饱和蒸汽压与温度的关系,对于理论上了解盐效应的机理,实践中用于恒沸混合物的加盐精馏、有机生物物料的制取分离等都是很有意义的.由丙烯水合制异丙醇的传统过程是得到异丙醇和水的恒沸物,而后再加入第三组分进行特殊精馏,便可得到无水异丙醇.近年来人们试探改革这一传统过程,运用加盐萃取精馏.这是因为盐效应可较大地改变各组分的相对挥发度,以致消除恒沸.由于氯化锌较其他盐(如CaCl_2)在异丙醇中有较大的溶解度,并有较大的溶解速率,因此研究ZnCl_2-异丙醇溶液的饱和蒸汽压是有现实意义的.     

Estimation of solubility of solids in supercritical carbon dioxide

Peng-Robinson equation of state(PR EOS)was chosen for modeling the thermodynamic be-havior of supercritical(SC)-CO_2/Solid systems.The necessary critical constants and acentric factorof the solute were obtained by the Sigmund and Trebble(1992)method based on the molecular weightand boiling temperature,and the vapor pressure of the solute was calculated by its meltingtemperature and heat of fusion.This approach compared very favorably with the conventional corres-ponding state theory,but without using critical constants and vapor pressure of solutes.Four mixingrules were tested for the calculation of solid solubility in SC-CO_2.van der Waals(vdW)mixing rulewith one parameter was considered to be most suitable for the estimation of solubility.A simplecorrelation was developed for the SC-CO_2/solid binary interaction coefficient k_(ij) with the meltingtemperature of pure solutes.The solubilities of solids in SC-CO_2 were estimated for eleven binarysystems at various temperatures,the total absolute average     

Development of a general model for determination of thermal conductivity of liquid chemical compounds at atmospheric pressure

In this communication, a general model for representation/presentation of the liquid thermal conductivity of chemical compounds (mostly organic) at 1 atm pressure for temperatures below normal boiling point and at saturation pressure for temperatures above the normal boiling point is developed using the Gene Expression Programming algorithm. Approximately 19,000 liquid thermal conductivity data at different temperatures related to 1636 chemical compounds collected from the DIPPR 801 database are used to obtain the model as well as to assess its predictive capability. The parameters of the model comprise temperature, acentric factor, critical pressure, normal boiling temperature, and molecular weight. Nearly 80% of the data set (15,221 data) is randomly assigned to develop the model equation, 10% of the data set (1902 data) is used to validate the model, and the remaining data (1902 data) were implemented to evaluate its predictive power. The average absolute relative deviation of the model results from the DIPPR 801 data is less than 9%. In terms of simplicity and wide range of applicability, this empirical model shows acceptable accuracy. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1702–1708, 2013     

Determination of environmentally relevant physical-chemical properties of some fatty acid esters

Fat models frequently use input parameters that are defined at environmental conditions. In a recently developed gas-liquid chromatography method (GC-VAP), vapor pressures, heats of vaporization, and heat capacity differences (gas-liquid) of fatty acid esters are determined over a large temperature range that includes environmental temperatures. This method also allows an accurate determination of the normal boiling point temperature of a substance. Literature values of vapor pressure, boiling point temperature, and heat of vaporization at 298.15 K for the chosen esters are all in excellent agreement with those determined with the developed method. Correlations between carbon number and heat of vaporization are high.     

正常沸点下液体蒸发焓的基团贡献计算法

用分子热力学方法建立了纯物质汽液平衡的推广vanderWaals模型 ,并据此得到了一个计算正常沸点下液体蒸发焓的方程 .它只含有一个与分子大小有关的参数 .这个参数的值与正常沸点下液体的摩尔体积成正比 ,且具有基团加和性 .为此 ,用 484个有机物回归得到了 45个基团增量 .对这些有机物的蒸发焓计算结果表明 ,与实验值的平均绝对偏差 (AAD)为 1.39% ,优于文献发表的其他方法     

A vapor pressure equation for heavy compounds

A vapor pressure calculation procedure based on a lattice equation is applied to several compounds. Originally, the method was used to predict low vapor pressures of heavy hydrocarbons. In this work, the method is used at low vapor pressure for nonhydrocarbons, and a modified version is employed at high vapor pressure for n-alkanes. As the procedures require the knowledge of one vapor pressure datum only, they work in a predictive mode. Prediction for hydrocarbons is good and for nonhydrocarbons is poor. Prediction of n-alkanes high vapor pressure is good with an overall average relative absolute deviation under 6 percent.     

A new vapor pressure equation for pure substances

A new simple equation for prediction of vapor pressure of pure substances is proposed. The equation which has the Clausius-Clapeyron (C-C) equation form consists of three parameters: critical temperature, critical pressure and normal boiling point. Experimental data for organic and inorganic substances have been used to calculate equation parameters in the boiling point ranges from 169.45 to 457.55 K and critical temperature ranges from 282.75 to 699.15 K. Comparison of proposed equation estimation results with experimental data shows that the new equation has minor average error. The new equation is also 68 percent more accurate than the C-C equation     

Benedict-webb-rubin parameters for ethanol

Experimental PVT measurements available in the literature for ethanol have been utilized to establish the BWR parameters for this substance using a nonlinear regression analysis involving 300 experimental points for reduced densities up to ρ_R = 1.80. The resulting parameters reproduce pressures for these 300 points, with an average deviation of 2.60% and predict the vapor pressure behavior between the normal boiling point and the critical point with an average deviation of 0.91%. This treatment is applied for the first time to the PVT behavior of an alcohol and indicates that the BWR equation of state could well be extended in application to include other oxygenated organic compounds receiving considerable interest in the currently changing energy emphasis.     

Estimation of vapor pressure of liquid oxygen between the triple and critical points

The existing vapor pressure measurements available in the literature for the liquid oxygen between the triple and critical points have been utilized to establish the constants and exponent of the modified Frost-Kalkwarf vapor pressure equation in the reduced form as follows: $$\ln P_r = 6.372408 - \frac{{6.637925}}{{T_r }} - 1.975760 \ln T_r + 0.265517T_r^5 $$ In order to calculate the vapor pressure, only the normal boiling point (T_b=90.180 K) and the critical pressure (P_c=5037.17 kPa) and critical temperature (T_c=154.33 K )are necessary to obtain an overall average deviation of 0.36 % for 540 experimental vapor pressure data.     

Flash point prediction of organic compounds using a group contribution and support vector machine

The flash point is one of the most important properties of flammable liquids. This study proposes a support vector regression (SVR) model to predict the flash points of 792 organic compounds from the DIPPR 801 database. The input variables of the model consist of 65 different functional groups, logarithm of molecular weight and their boiling points in this study. Cross-validation and particle swarm optimization were adopted to find three optimal parameters for the SVR model. Since the prediction largely relies on the selection of training data, 100 training data sets were randomly generated and tested. Moreover, all of the organic compounds used in this model were divided into three major classes, which are non-ring, aliphatic ring, and aromatic ring, and a prediction model was built accordingly for each class. The prediction results from the three-class model were much improved than those obtained from the previous works, with the average absolute error being 5.11–7.15 K for the whole data set. The errors in calculation were comparable with the ones from experimental measurements. Therefore, the proposed model can be implemented to determine the initial flash point for any new organic compounds.     

估算有机物正常沸点的基团贡献法的研究进展

有机物的正常沸点是重要的物性数据之一。尽管文献中有很多化合物正常沸点的实验值,但一些物质的正常沸点不能由实验获得,可以通过建立数学模型来估算缺少的有机物正常沸点,其中基团贡献法是人们获得正常沸点的最重要研究方法。本文对估算有机物正常沸点的基团贡献法进行了综述。主要介绍了Joback法、C—G法、许文法、定位分布贡献法、元素和化学键法等方法的原理、优缺点及应用范围;并对这些方法进行简单的比较;最后指出了有机物正常沸点的基团贡献法的发展趋势。     

甲基苯基二乙氧基硅烷饱和蒸汽压的测定与关联

静态法测定了甲基苯基二乙氧基硅烷在378.10—423.84 K之间的饱和蒸汽压数据。采用非线性回归的方法得到Antoine常数A,B,C的值分别为8.809 9,3 935.933,87.61,饱和蒸汽压的计算值与实验值之间的误差介于0—2.36%;在2.27—101.325 kPa之间,沸点计算值与文献值的绝对误差不超过3.80 K,以开尔文温度表示的最大相对误差不超过0.77%。通过Clausius-Clapeyron方程计算得到甲基苯基二乙氧基硅烷在378.10—423.84 K之间的平均摩尔蒸发热为50 653.79 J/mol,常压沸点为494.66 K。     

Calculating the Vapor Pressure of Associated Acyclic Aliphatic Compounds

A model based on Prigogine's molecular–statistical theory of solutions is suggested for estimating the vapor pressure and boiling temperature of associated acyclic aliphatic compounds. To calculate the vapor pressure between 0.1 and 760 mm Hg by the equations of this model, it is sufficient to know the saturation vapor pressure and temperature at one boiling point.