Estimation of solid vapor pressures from supercritical CO2 + biomolecule systems using a PSO algorithm

A method to estimate the solid vapor pressures of biomolecules using a biologically deriver algorithm is presented. The solid vapor pressure is usually small for most solid compounds and in many cases available experimental techniques cannot be used to obtain accurate values. Therefore, estimation methods must be used to obtain these data. Five binary gas-solid phase systems of supercritical CO₂ + biomolecule containing caffeine, artemisinin, capsaicin, cholesterol, and β-carotene are considered in this study. Particle swarm optimization is used for minimize the difference between calculated and experimental solubility. Then, the solid vapor pressures of biomolecules are calculated from solubility data. The Peng-Robinson equation of state with the Wong-Sandler mixing rules are used to evaluate the fugacity coefficient on the systems. The results show that the method presented is reliable enough and can be used with confidence to estimate the solid vapor pressure of any organic biomolecule.     

Thermal Decomposition of NTO: An Explanation of the High Activation Energy

Burning rate characteristics of the low‐sensitivity explosive 5‐nitro‐1,2,4‐triazol‐3‐one (NTO) have been investigated in the pressure interval of 0.1–40 MPa. The temperature distribution in the combustion wave of NTO has been measured at pressures of 0.4–2.1 MPa. Based on burning rate and thermocouple measurements, rate constants of NTO decomposition in the molten layer at 370–425 °C have been derived from a condensed‐phase combustion model (k=8.08⋅10¹³⋅exp(−19420/T) s⁻¹. NTO vapor pressure above the liquid (ln P=−9914.4/T+14.82) and solid phases (ln P=−12984.4/T+20.48) has been calculated. Decomposition rates of NTO at low temperatures have been defined more exactly and it has been shown that in the interval of 180–230 °C the decomposition of solid NTO is described by the following expression: k=2.9⋅10¹²⋅exp(−20680/T). Taking into account the vapor pressure data obtained, the decomposition of NTO in the gas phase at 240–250 °C has been studied. Decomposition rate constants in the gaseous phase have been found to be comparable with rate constants in the solid state. Therefore, a partial decomposition in the gas cannot substantially increase the total rate. High values of the activation energy for solid‐state decomposition of NTO are not likely to be connected with a sub‐melting effect, because decomposition occurs at temperatures well below the melting point. It has been suggested that the abnormally high activation energy in the interval of 230–270 °C is a consequence of peculiarities of the NTO transitional process rather than strong bonds in the molecule. In this area, the NTO molecule undergoes isomerization into the aci‐form, followed by C3‐N2 heterocyclic bond rupture. Both processes depend on temperature, resulting in an abnormally high value of the observed activation energy.     

平均吸引势模型状态方程用于固体在超临界流体中溶解度的计算

基于膨胀液体概念，把超临界流体看作是被气体膨胀了的液体，并假设体系的分子吸引势为范德华气体和凝聚液体吸引势的体积平均值、导出了一个平均吸引势模型状态方程。该方程较好地关联了纯溶剂蒸汽压及超临界二氧化碳的Ｐ－Ｖ－Ｔ关系；并关联了１４种固体溶质在超临界二氧化碳中的溶解度数据，结果优于ＲＫ、ＳＲＫ及ＰＲ方程。     

Vapor-liquid equilibria for the binary monoethanolamine+ water and monoethanolamine+ethanol systems

Isobaric vapor-liquid equilibrium data for monocthanolamine (MEA)+water and monoethanolamine (MEA)+ ethanol were measured in an equilibrium cell circulating both the vapor and liquid phases. The measurements of the boiling temperatures and corresponding equilibrium compositions for two binary mixtures were carried out at the atmospheric pressure. The results were checked for thermodynamic consistency by the point test method. The activity coefficients for nonideality of the liquid phase were calculated by using the Wilson, NRTL, and UNIQUAC equations. The fugacity coefficients for nonideality of the vapor phase were calculated from the virial equation of state with the second virial coefficient. The experimental data were verified to be thermodynamically consistent and showed a good agreement with the calculated values.     

Prediction of Saturated Air Dew Points at Elevated Pressures Using a Simple Arrhenius‐Type Function

In compressed air systems, condensed water vapor can have corrosive effects on metals and wash out protective lubricants from tools, equipments, and pneumatic devices. Therefore, it is necessary to be able to predict the dew point temperature of atmospheric air and the air dew point at elevated pressures in order to design and apply the appropriate type of drying. A simple tool is presented here for the prediction of the dew point of atmospheric moist air as a function of temperature and relative humidity and of the compressed saturated air dew point as a function of pressure and dew point of atmospheric moist air at a given temperature using an Arrhenius‐type asymptotic exponential function. The developed tool can be of immense practical value for engineers and scientists as a quick check of the dew points of atmospheric moist air and relative humidity and compressed saturated air under various conditions.     

Applicability of the Perturbed Hard Chain Equation of State for Simulation of Distillation Processes in the Oleochemical Industry. Part II: Purification of Glycerol

Abstract

Glycerol is a major by-product in the oleochemical industry with extensive end-use markets. Synthetic and natural glycerine fractions are currently purified using steam distillation at subatmospheric pressures. Due to the increasing interest of the pharmaceutical industry in ultrapure glycerol, supercritical fluid extraction followed by appropriate fractionation steps are also employed. It would therefore be convenient to utilize a single thermodynamic model that is capable of predicting all thermodynamic properties needed, and that also covers the whole pressure range which is currently applied in both industries. Different equations of state and activity coefficient models were scanned, and the perturbed hard chain equation of state (PHC-EOS) provided better results than those obtained using activity coefficient models. Pure component parameters were computed using vapor pressure data for glycerol. The fitted parameters were incorporated in the PHC-EOS and resulted in good reproduction of binary vapor—liquid equilibria. Calculations of multicomponent mixtures were performed using these binary parameters. A flow-sheeting program was utilized to simulate a steam distillation process consisting of two integrated columns, operated at subatmospheric pressures, for the purification of different glycerine feedstocks. The simulated flow rate, concentration, and temperature profiles were compared with some operating data obtained from a major oleochemical plant. Analysis of this comparison revealed that the PHC-EOS is very well suited for simulating different distillation processes for the purification of crude glycerine feedstocks.     

Modeling of solid–liquid equilibria for polyethylene and polypropylene solutions with equations of state

We modeled solid–liquid equilibria (SLEs) in polyethylene and polypropylene solutions with a Soave–Redlich–Kwong (SRK) cubic equation of state (EOS) and a perturbed‐chain statistical associating fluid theory (PC‐SAFT) EOS. Two types of mixing rules were used with SRK EOS: The Wong–Sandler mixing rule and the linear combination of the Vidal and Michelsen mixing rules (LCVM), both of which incorporated the Bogdanic and Vidal activity coefficient model. The performance of these models was evaluated with atmospheric‐pressure and high‐pressure experimental SLE data obtained from literature. The basic SLE equation was solved for the equilibrium melting temperature instead of for the composition. The binary interaction parameters of SRK and PC‐SAFT EOS were estimated to best describe the experimental equilibrium behavior of 20 different polymer–solvent systems at atmospheric pressure and 31 other polymer–solvent systems at high pressure. A comparison with experimental data showed that SRK–LCVM agreed very well with the atmospheric SLE data and that PC‐SAFT EOS was more efficient in high‐pressure conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A New Method for Determining the Vapor Pressure of Nitroglycerine Above Solid Rocket Propellants

Measuring the vapor pressure of compounds such as nitroglycerine (NG) which have a low volatility has not been a straightforward task in the past. There are a wide range of values in the literature for the vapor pressure of NG and furthermore, there is little information regarding the vapor pressure of this compound above solid rocket propellant formulations. We have devised a new method for determining the vapor pressure of NG both above the pure material and solids containing this nitrate ester. The values obtained for pure liquid NG are in good agreement with some previously published values. It was also found that the vapor pressure of this compound is slightly lowered when it is incorporated into solid rocket propellant formulations.     

Vapor pressure equilibrium of stearic acid in triglyceride and in high paraffin solutions

Summary The vapor pressure equilibrium of stearic acid has been determined at 180°C. in peanut oil and highparaffin solutions. Positive deviation from Raoult’s law has been observed in both of the systems; it was however essentially stronger in the nonpolar high-paraffin. Extrapolation of the vapor pressures obtained in paraffin to infinite dilution indicated that monomer stearic acid in free state would have a vapor pressure of 3.9 mm. Hg. at 180°C. in comparison with 0.80 mm. of the pure stearic acid itself, which is a mixture of monomer and dimer molecules. Quantitative relationships could be established between degree of association and vapor pressure. For pure dimeric acid at 180°C. a vapor pressure of 0.015 mm. Hg. has been calculated.     

甲烷的状态方程研究及应用

本文以MH方程为基础,用甲烷在90－400K,0．01－50MPa范围内的PVT数据,对方程的形式和常数进行显著性检验,得到了一个适用于气液两相的27常数方程。新的方不但较重现了PVT和汽液平衡性质,而且很好地预测了焓、熵和等压热容等性质。改进方程的计算结果达到或优于改进的BWR方程。可以作为甲烷的一个较满意的状态方程。     

EXTENSION OF SOAVE EQUATION OF STATE TO LIQUID DENSITY

On the basis of vapor pressures, volumes of saturated vapor and liquid, both parameters "a" and "b" in Soave equation of state are treated as temperature dependent and an extended Soave equation is proposed in this work. The VLE for 38 pure components including polar substances have been calculated. The comparison of calculated results with experimental data shows the prediction of liquid density is improved over Soave equation without losing the accuracy of prediction in vapor pressure and vapor density.     

Reliable computation of binary homogeneous azeotropes of multi-component mixtures at higher pressures through equation of states

A method to compute binary homogeneous azeotropes in multi-component mixtures at elevated pressures through the equation of state approach is developed. The method is capable of predicting the homogeneous azeotropes and is in close agreement with experimental data. At higher pressures, vapor and liquid phase non-idealities are incorporated using vapor and liquid phase fugacity coefficients from Peng-Robinson-Stryjek-Vera equation of state with Wong-Sandler mixing rules. The method is also capable of predicting the exact value of bifurcation pressure where homogeneous azeotropes may appear or disappear. The method can predict the azeotropes at elevated pressures and is independent of equation of state and mixing rules. The method is also capable of predicting the double azeotropy in binary mixtures. The method is tested with Ethanol-Water, Isopropanol-Water, Carbon dioxide-Ethane-Ethylene and Ammonia-R-125 systems. The highly non-linear system of equations is solved by homotopy continuation approach.     

Application of the redlich-kwong-soave equation of state to solid-liquid equilibria calculations

The application of the Redlich-Kwong equation of state, in the modified form introduced by the author, to the calculation of the solid-liquid-vapour equilibria of systems composed by carbon dioxide and the lighter paraffinic hydrocarbons, is shown.By slight adjustments of their critical constants and the acentric factors, pure liquid components vapour pressures can be reproduced to a high degree at accuracy.Solid carbon dioxide vapour pressure can also be correlated tightly by using proper values of the latent heat of fusion and heat capacity difference between solid and liquid.From the experimental solubities of solid CO₂ in single hydrocarbons the values of the binary interaction constants are derived, which are used to reproduce experimental solubities of carbon dioxide in mixed solvents, and can be used successfully for vapour-liquid equilibrium calculations also.     

Estimation of saturated air water content at elevated pressures using simple predictive tool

In a compressed air system, condensed water vapor can have corrosive effects on metals and wash out protective lubricants from tools, equipments and pneumatic devices. To protect against such undesirable effects in a compressed air system, it is necessary to be able to predict the water content of air in order to design and apply the appropriate type of drying to be used in the system. In this work, a simple predictive tool, which is easier than currently available models and involves a fewer number of parameters, requiring less complicated and shorter computations, is presented here for the prediction of water content of air as a function of temperature and relative humidity as well as for compressed saturated air as a function of pressure and temperature using an Arrhenius-type asymptotic exponential function. The proposed method predicts the amount of air water content for temperatures up to 45 °C, pressures up to 1400 kPa and relative humidities up to 100%. Estimations are found to be in excellent agreement with the reliable data in the literature with average absolute deviation being less than 1.4 and 2.2% for atmospheric air and saturated compressed air, respectively. The tool developed in this study can be of immense practical value for engineers and scientists to have a quick check on the water content of atmospheric air and saturated compressed air at various conditions without opting for any experimental measurements. In particular, engineers and scientists would find the approach to be user-friendly with transparent calculations involving no complex expressions.     

Isothermal vapor-liquid equilibria for the binary systems of ethylene glycol monopropyl ether with 2,2-dimethylbutane and 2,3-dimethylbutane

Isothermal vapor liquid equilibria for the binary system of ethylene glycol monopropyl ether with 2,2-dimehylbutane and 2,3-dimethylbutane were measured in a circulating water bath at 303.15, 318.15, and 333.15 K. The apparatus was in-house designed and manufactured. Consistency testing of the apparatus was done by comparing the measured vapor pressures to the calculated vapor pressures from the Antoine equation. The measured systems were correlated with a Peng-Robinson equation of state (PR) combined with Wong-Sandler mixing rule for the vapor phase, and NRTL, UNIQUAC, and Wilson activity coefficient models for the liquid phase. All the measured systems showed good agreement with the correlation results.     

Calculation of heat balance in burning HMX

Temperature dependences are calculated for a number of physicochemical properties of HMX: the heat capacity of the liquid phase, change in the enthalpy due to heating of the condensed phase to a predetermined temperature, heat of evaporation, saturated vapor pressure, and the vapor diffusion coefficient in low-molecular-weight gases. The data obtained are used to calculate the amount of heat needed to heat the condensed phase to the burning surface temperature in the range of 560–900 K at various degrees of decomposition. The heat of decomposition of HMX under combustion conditions is calculated from the known composition of the reaction products at a pressure of 1 bar. The results of experimental determination of the thermal effects of HMX decomposition by differential scanning calorimetry are presented. The results of the calculations and experiments suggest that at a degree of decomposition ⩾0.6, heat release in the condensed phase can provide heating and evaporation of HMX without heat input from the gas phase. It is shown that the calculated saturation vapor pressures of HMX, which are higher than those presented in the literature, are in better agreement with available experimental data on the HMX vapor concentration profile near the burning surface.     

混空轻烃燃气液相析出成核热力学分析

混空轻烃燃气是将液态轻烃原料汽化、与空气按一定比例混合制成的可燃气体,是一种清洁燃料。但以戊烷为主的轻烃原料常温下为液态,汽化混合后的燃气存在露点较高问题。采用成核热力学理论研究局部温度、压力变化引起的相变/成核驱动力,进而研究液滴的成核能,得到混空轻烃燃气液相析出的成核机理、成核能及其与过冷度和过饱和度的关联关系。结果表明,相变/成核所需过冷度和过饱和度随温度、压力的增加而降低;尽管发生完全相变所需过冷度及过饱和度较高,较难达到,但液相析出成核所需过冷度及过饱和度则极易达到,因此防止燃料露点形成的重点是控制从成核到完全相变的发生。     

甲基叔丁基醚的状态方程

利用公开发表的实验数据开发了甲基叔丁基醚（MTBE）的状态方程,方程以Helmholtz自由能为显式、以温度和密度为自变量。方程计算饱和蒸气压的不确定度430 K以下为1.0%,随着温度的升高,由于缺少实验数据不确定度增大为2.0%。方程计算密度的不确定度由液相区的0.2% 变到临界区和气相区的1.0%。方程计算能量相关物性（如比热容和音速）的不确定度为0.5%。临界区,除了饱和蒸气压,方程计算所有其它热力学性质的不确定度都较高。正如文中分析,本文方程不但能准确的复现实验数据,而且方程的外推性也是合理的。文中对方程进行了详细的分析。     

Phase behavior of 1,3,5-tri-tert-butylbenzene–carbon dioxide binary system

1,3,5-tri-tert-butylbenzene (TTBB) is solid at ambient conditions, and has substantial solubility in liquid and supercritical carbon dioxide. We present the phase behavior of TTBB–CO₂ binary system at temperatures between 298 and 328 K and at pressures up to 20 MPa. Phase diagrams showing the liquid–vapor, solid–liquid and solid–vapor equilibrium envelopes are constructed by pressure–volume–temperature measurements in a variable-volume sapphire cell. TTBB is highly soluble in CO₂ over a wide range of compositions. Single-phase states are achieved at moderate pressures, even with very high TTBB concentrations. For example, at 328 K, a binary system containing TTBB at a concentration of 95% by weight forms a single-phase above 2.04 MPa. TTBB exhibits a significant melting-point depression in the presence of CO₂, 45 K at 3.11 MPa, where the normal melting point of 343 K is reduced to 298 K. With its high solubility in carbon dioxide, TTBB has potential uses as a binder or template in materials forming processes using dense carbon dioxide.     

Formation Mechanism of Cracks During the Freeze Drying of Gelcast Ceramic Parts

The near‐net shaping of gelcast ceramic parts can be achieved using freeze‐drying technology. It was discovered that the cracks probably occurred inside the part during freeze drying due to the formation of liquid water. To explain the formation mechanism of cracks, the electrical resistance method was employed to measure the part's eutectic temperature which can be used to determine the freezing and melting state of the part. Affecting factors on cracking were investigated by testing the temperature and water loss of the part during the drying stage, and the cracks inside the part were detected through computed tomography (CT). It was found that when the temperature of the part was higher than the eutectic temperature, the ice crystals at the sublimation front would melt, resulting in the formation of wet green body. The cracks will occur inside the part because great capillary forces are formed in the wet green body. Cracks could be controlled through reducing heat supply by lowing shelf temperature, decreasing pressure of the drying chamber or lowering the dried layer resistance against water vapor by improving the freezing temperature or reducing the solid loading of the part.