Use of an artificial neural network algorithm to predict hydrate dissociation conditions for hydrogen+water and hydrogen+tetra-n-butyl ammonium bromide+water systems

In this communication, a feed-forward artificial neural network algorithm is developed to estimate the hydrate dissociation conditions for the hydrogen+water and hydrogen+tetra-n-butyl ammonium bromide+water systems. To develop this algorithm, the experimental data reported in the literature for hydrate dissociation conditions of the latter two systems with different concentrations of tetra-n-butyl ammonium bromide in aqueous phase below its stoichiometric concentration (i.e., ≈0.037 mole fraction or 0.43 mass fraction) have been used. Independent experimental data (not used in training and developing this algorithm) have been employed to examine the reliability of this method. It is shown that the predicted and the experimental data are in acceptable agreement demonstrating the reliability of this algorithm as a predictive tool.     

Phase equilibria of clathrate hydrates of methyl cyclopentane, methyl cyclohexane, cyclopentane or cyclohexane+carbon dioxide

In this work, experimental dissociation data for clathrate hydrates of methyl cyclopentane, methyl cyclohexane, cyclopentane or cyclohexane+carbon dioxide are reported at different temperatures. The experimental data were generated using an isochoric pressure-search method. The reliability of this method is examined by generating new dissociation data for clathrate hydrates of methyl cyclopentane+methane and comparing them with the experimental data reported in the literature. The acceptable agreement demonstrates the reliability of the experimental method used in this work. The experimental data for all measured systems are finally compared with the corresponding literature data in the absence of the above mentioned cyclic compounds to identify their promotion effects.     

Phase equilibria of binary clathrate hydrates of nitrogen+cyclopentane/cyclohexane/methyl cyclohexane and ethane+cyclopentane/cyclohexane/methyl cyclohexane

In this communication, we first report hydrate dissociation conditions for the nitrogen+cyclopentane, cyclohexane or methyl cyclohexane+water and ethane+cyclopentane, cyclohexane or methyl cyclohexane+water systems at various temperatures. The experimental data were generated using an isochoric pressure-search method. The hydrate dissociation data for the aforementioned systems along with the hydrate dissociation data for the methane, carbon dioxide or hydrogen sulfide+cyclopentane, cyclohexane or methyl cyclohexane+water systems collected from the literature are compared with the corresponding literature data in the absence of the aforementioned heavy hydrocarbons in order to study the hydrate promotion effects of cyclopentane, cyclohexane or methyl cyclohexane. It is shown that these effects on ethane simple hydrate are not considerable unlike the corresponding effects on nitrogen, methane, carbon dioxide and hydrogen sulfide simple hydrates.     

四丁基溴化铵-二氧化碳-水体系半笼水合物相平衡数据的测定

水合物相平衡数据是利用水合物捕集二氧化碳的基础数据,利用定容逐步加热的方法测量了四丁基溴化铵-二氧化碳-水三元体系水合物的相平衡数据,实验测量的压力和温度分别为1.0-4.3 MPa,282.75-292.15 K,四丁基溴化铵水溶液的质量分数为5％ -30％.实验结果表明:在一定的温度条件下,与纯水中二氧化碳水合物形...     

Hydrate phase equilibria for hydrogen+water and hydrogen+tetrahydrofuran+water systems: Predictions of dissociation conditions using an artificial neural network algorithm

In this communication, a mathematical model based on feed-forward artificial neural network algorithm is presented, which can estimate hydrate dissociation conditions for the hydrogen+water and hydrogen+tetrahydrofuran+water systems. To develop this algorithm, the experimental data for the hydrate dissociation conditions of the latter two systems with different concentrations of tetrahydrofuran in aqueous phase below its stoichiometric concentration (i.e., ?0.059) have been used. Independent experimental data (not used in training and developing this algorithm) have been employed to examine the reliability of this method. It is shown the agreement between the predictions and the experimental data is acceptable demonstrating the reliability of this algorithm as a predictive tool.     

PHASE EQUILIBRIA OF CLATHRATE HYDRATES IN HYDROGEN SULFIDE + DIETHYLENE GLYCOL OR TRIETHYLENE GLYCOL + WATER SYSTEM

In this communication, experimental hydrate dissociation pressures for hydrogen sulfide + diethylene glycol (DEG) + water and hydrogen sulfide + triethylene glycol (TEG) + water systems are reported in the 276.8–288.3 K and 271.3–289.5 K temperature ranges for 0.05 and 0.15 mass fractions of DEG in aqueous solution and 279.0–289.9 K and 276.9–290.6 K for 0.05 and 0.15 mass fractions of TEG in aqueous solution, respectively. The experimental data were generated using an isochoric pressure-search method. The experimental hydrate dissociation data were compared with some selected literature data in the presence of pure water. In the concentration ranges studied in this work, it is shown that both DEG and TEG aqueous solutions have inhibition effects on hydrogen sulfide clathrate hydrates. Approximately the same inhibition effects are found for the DEG and TEG aqueous solutions studied in the presence work.     

1-氨丙基-3-甲基咪唑溴盐水溶液的汽液相平衡

1-氨丙基-3-甲基咪唑溴盐([APMIm][Br])是一种对CO₂有良好吸收性能的功能型离子液体,在工业中可采用水溶液来实现高效能的吸收和解吸循环过程,因此对其水溶液特性的研究至关重要。对[APMIm][Br]水溶液在中低温度下的汽液相平衡进行了测量,获得可靠的实验数据,从而揭示其水溶液特性。实验温度范围为278.15～348.15 K,[APMIm][Br]在水溶液中质量分数分别为10.0%、20.3%、29.5%、40.0%、57.5%、75.3%、84.0%、88.9%、90.9%。考虑了低温下离子液体分子在水溶液中的强缔合特性,采用带缔合惰化因子的离子液体水溶液活度模型对实验数据进行了拟合,实验值与计算结果符合很好,平均相对误差为2.15%。     

Clathrate hydrate dissociation conditions for the methane+cycloheptane/cyclooctane+water and carbon dioxide+cycloheptane/cyclooctane+water systems

In this communication, we report hydrate dissociation conditions for the methane+cycloheptane/cyclooctane+water and carbon dioxide+cycloheptane/cyclooctane+water systems. The experimental data were generated using an isochoric pressure-search method. The dissociation data for clathrate hydrates of cycloheptane or cyclooctane+methane are successfully compared with the literature data demonstrating the reliability of the literature data and the experimental method used in our work. The experimental data for all measured systems are finally compared with the corresponding literature data in the absence of cycloheptane or cyclooctane to study the hydrate promotion effects of the latter two chemicals.     

Thermodynamic and Raman spectroscopic studies on hydrogen+tetra-n-butyl ammonium fluoride semi-clathrate hydrates

Thermodynamic stability and hydrogen occupancy on the hydrogen+tetra-n-butyl ammonium fluoride semi-clathrate hydrate have been investigated by means of phase equilibrium (pressure-temperature) measurements and Raman spectroscopic analyses for two mole fractions, 0.018 and 0.034 (stoichiometric for the cubic structure) of tetra-n-butyl ammonium fluoride aqueous solutions. In the case of higher concentration (0.034), the stability boundary curve of hydrogen+tetra-n-butyl ammonium fluoride semi-clathrate hydrate locates at about 23 K higher temperature than that of hydrogen+tetrahydrofuran mixed gas hydrate. The storage capacity of hydrogen in the cubic structure for the hydrogen+tetra-n-butyl ammonium fluoride semi-clathrate hydrate is smaller than that of hydrogen+tetrahydrofuran mixed gas hydrate. In the case of hydrate prepared from the lower concentration (0.018) of aqueous solution, the Raman spectra and phase behavior reveal that the cubic structure of semi-clathrate hydrate is changed to a different one at about 9 MPa and 299.2 K. The new structure can entrap larger amount of hydrogen than the cubic one. The stability boundary curve of hydrogen+tetra-n-butyl ammonium fluoride semi-clathrate hydrate obtained in the aqueous solution of lower mole fraction (0.018) is shifted to slightly low-temperature or high-pressure side from that of higher mole fraction (0.034).     

Experimental heat capacities of nitrogen-carbon dioxide mixtures at elevated pressures

The heat exchanger method of determining the ratio of heat capacity at a pressure to the heat capacity at a low pressure was used to obtain data on two binary mixtures of nitrogen and carbon dioxide containing 6.77 and 31.70 mole percent nitrogen. The data were obtained at pressures up to 2150 psia in the temperature range from ambient to 90°C. The results are believed to be accurate within ± 0.5% in the regions removed from the pressure maxima and within ± 1% in regions close to the maxima. Heat capacities of the two binary mixtures calculated using the BWR equation of state and new mixing rules compared favourably with the experimental data.     

High-pressure phase behavior of carbon dioxide in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Phase equilibrium data of carbon dioxide in the ionic liquid 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]) are presented at high pressures up to about 30 MPa and at temperatures between 298.15 K and 343.15 K. The solubilities at a given temperature were determined by measuring the bubble point pressure of the ionic liquid solution with carbon dioxide dissolved using the high-pressure equilibrium apparatus equipped with a variable-volume view cell. Solubility results are reported for carbon dioxide concentrations ranging from 0.21 up to 0.80 mole fraction. Carbon dioxide gave very high solubilities in the ionic liquid at lower pressures, while the equilibrium pressure increased very steeply at higher concentrations of carbon dioxide. The solubility of carbon dioxide in the ionic liquid decreased with an increase in temperature.     

Bubble point pressures and densities of hexamethyldisiloxane–carbon dioxide binary mixture using a constant volume view cell

The phase behavior of hexamethyldisiloxane (HMDS)–carbon dioxide (CO₂) binary mixture was investigated using a constant volume view cell. The accuracy of the measurement technique was inspected against the bubble point pressure data in the literature for ethanol (C₂H₅OH)–carbon dioxide (CO₂) binary mixture. The bubble point pressures for C₂H₅OH–CO₂ agreed well with the literature values. The bubble point pressures of HMDS–CO₂ binary mixture were determined at five different temperatures (T = 298.2 K, 308.2 K, 313.2 K, 323.2 K, 333.2 K) and at various compositions. The bubble point pressures increased with increasing temperature and CO₂ mole fraction in the binary mixture. The phase behavior of the binary mixture was modeled using the Peng–Robinson Stryjek–Vera equation of state (PRSVEoS). The binary interaction parameters were regressed from experimental bubble point pressures at each temperature and were found to exhibit a linear dependency on temperature. The HMDS–CO₂ binary mixture was also found to exhibit Type II phase behavior. Additionally, P–T–ρ measurements for the same binary system were conducted and excess molar volumes were calculated.     

Modeling of Nitrogen and Carbon Dioxide Solubility in Alternative Fuels at High Pressures Using the Soave‐Redlich‐Kwong Equation of State

In this paper, the Soave‐Redlich‐Kwong equation of state with quadratic mixing rule has been tested for correlation of vapor‐liquid equilibria (VLE) at high pressures in the binary nitrogen + dimethyl ether, dimethyl ether + methanol, nitrogen + methanol, carbon dioxide + dimethyl ether and carbon dioxide + methanol systems. The interaction parameters k_ij were evaluated for each binary pair and used for prediction of VLE in the ternary nitrogen + dimethyl ether + methanol and carbon dioxide + dimethyl ether + methanol systems at high pressures. The results of correlation and prediction are discussed.     

Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) system

This article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF₆], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time-dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume-of-fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.     

Phase equilibria of hydrates from ternary mixtures of methane + ethane + propane and methane + propane + carbon dioxide

Hydrate–liquid–vapour (HLV) equilibrium of aqueous clathrates formed from gas mixtures can be complex compared to hydrates formed with single guests. Typically, pressure and temperature are controlled to obtain these data, but for multicomponent systems, it is necessary to control/report more intensive variables, namely, composition. Metastability, manifested as impractically long experimental times, has been reported to be a challenge with some multicomponent systems. We present HLV equilibrium conditions of two ternary gas mixtures: methane + ethane + propane (90:7:3 molar ratio) and methane + propane + carbon dioxide (55:5:40 molar ratio). Conditions varied in the temperature range of 275–285 K and the pressure range of 1.24–4.75 MPa. Experimental standard uncertainties were on average 0.10 K and 0.005 MPa for methane + ethane + propane and 0.19 K and 0.005 MPa for methane + propane + carbon dioxide. Our technique allowed us to bypass the limitations reported in the literature and provided fast, reproducible HLV equilibria for gas-dominated systems.     

Bubble-point pressures of the binary system carbon dioxide+linalool

A synthetic method was used to investigate high-pressure vapor–liquid equilibria of the binary system carbon dioxide+linalool. The bubble points of this system were measured at carbon dioxide mole fractions from 0.2 up to 0.993 and within temperature and pressure ranges of 283–371 K and 1.4–14.7 MPa, respectively. Critical points of this binary system were also determined experimentally for a carbon dioxide mole fraction range from 0.93 up to 0.993. The results were correlated by the Stryjek–Vera modified version of the Peng–Robinson equation of state using one-fluid van der Waals mixing rules with both one and two interaction parameters.     

Dependence of volume expansion on alkyl chain length and the existence of branched methyl group of CO2-expanded ketone systems at 40 °C

We measured the density and liquid-phase CO₂ mole fraction of CO₂-expanded ketones (acetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl i-propyl ketone, and t-methyl butyl ketone) at 40 °C and evaluated the expansion coefficient on the basis of the experimental results. Volume expansion was slow in the region of a low carbon dioxide mole fraction (<0.7) but rapid in the region of a high carbon dioxide mole fraction (>0.7). The dependence of the expansion coefficient on the carbon dioxide mole fraction could be attributed to the number of molecules in a certain volume. These phenomena were inferred from the partial molar volume estimated using the Peng-Robinson equation of state (PR-EOS).     

Measurement and thermodynamic modeling of partition coefficients in N,N-dimethylacetamide-water-carbon dioxide system

The partition coefficients of N,N-dimethylacetamide (N,N-DMA) between the water and the supercritical and near-critical carbon dioxide (CO₂) phases were measured in the temperature range of 298.15-328.15 K and the pressure range of 8.3-24.1 MPa. The measurements were carried out in a 56 ml vessel by contacting the carbon dioxide and the aqueous phases. The partition coefficients of N,N-DMA increased from 0.05 to 0.150 with increasing pressure at a constant temperature and increased with temperature at a constant density. The bubble point pressures of N,N-DMA-CO₂ mixtures were measured at 298.15 K, 308.15 K and 318.15 K and were found to increase with increasing mole fraction of CO₂. The partition coefficients were modeled using the Peng-Robinson Equation of State (PREOS) combined with modified van der Waals mixing rule. The binary interaction parameters for the CO₂-H₂O pair were taken from the literature and were regressed for CO₂-N,N-DMA and H₂O-N,N-DMA pairs by fitting partition coefficients data. The binary interaction parameter for CO₂-N,N-DMA pair was found to depend linearly on temperature. The bubble point pressures of N,N-DMA and CO₂ were also measured and could be predicted fairly well using the regressed binary interaction parameters.     

Phase Equilibrium Measurements of Sacha Inchi Oil (<Emphasis Type="Italic">Plukenetia volubilis</Emphasis>) and CO<Subscript>2</Subscript> at High Pressures

New data on phase equilibria for Sacha inchi seed oil in carbon dioxide have been measured using a variable volume cell phase equilibria system at temperatures of 303, 313 and 323 K and at pressures ranging from 4.3 to 27.7 MPa. The CO₂ mole fraction varied from 0.7488 to 0.9997. At the studied concentrations, phase transitions of vapor-liquid, liquid-liquid-vapor and liquid-liquid were observed. Sacha inchi oil contains 47% of omega-3 fatty acids, with a ratio of 0.76:1 for omega-6:omega-3, which is good for human health. The Peng-Robinson equation of state was used to describe the experimental data. A qualitative agreement was obtained between experimental and calculated data for the binary system CO₂ and Sacha inchi seed oil.     

水逸度模型预测THF添加剂体系下气体水合物相平衡

加入添加剂降低水合物生成压力是当前水合物法分离混合气体研究热点。本研究以水的逸度模型为基础, 结合PRSV2 状态方程研究了CH₄、O₂、N₂ 及其混合气体水合物在纯水体系下的相平衡条件;通过UNIFAC 基团 贡献法对添加剂四氢呋喃(THF)水溶液进行基团划分,计算该体系下液相各组分的活度,理论研究了添加剂 THF 对气体水合物相平衡条件的影响;结果表明在相应的温度范围内,与其他模型相比,在纯水体系下该模型 预测精度较高,在THF 水溶液体系下该模型对单组分和双组分气体的预测精度平均相对误差在7%左右,随着 THF 浓度增加,气体水合物相平衡压力的降低幅度减小;当THF 摩尔分数达到6%时,对气体水合物相平衡影 响达到最大。相关研究结果为混合气体的大规模工业提纯分离提供了理论基础。