In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitor... more In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitors of gas hydrates as many of those used today suffer from poor biodegradability. In this work, we have investigated experimentally whether ice-structuring proteins (ISPs) found in fish and insect, assumed biodegradable, are capable of inhibiting the growth of methane hydrate (a structure I hydrate). The ISPs investigated were type III HPLC12 (originally identified in ocean pout) and ISP type III found in meal worm (Tenebrio molitor). These were compared to polyvinylpyrrolidone (PVP) a well-known kinetic hydrate inhibitor. The results revealed that adding ISP in sufficient amounts caused the appearance of an initial nonlinear growth period. At a certain point during the growth process the growth pattern changed to linear which is identical to the growth observed for methane hydrate in the absence of inhibitors. The profile of the nonlinear growth was concentration-dependent but also dependent on the stirring rate. ISP type III HPLC12 decreased the growth rate of methane hydrate during the linear growth period by 17-75% at concentrations of 0.01-0.1 wt % (0.014-0.14 mM) while ISP from Tenebrio molitor and PVP decreased the growth rate by 30% and 39% at concentrations of 0.004 wt % (0.005 mM) and 0.1 wt % (0.1 mM), respectively. Considering the low concentration of Tenebrio molitor ISP used, these results indicate that ISP from Tenebrio molitor is the most effective hydrate inhibitor among those investigated. Thermal hysteresis ice formation experiments revealed that ISP from Tenebrio molitor causes higher thermal hysteresis for ice formation compared to type III ISP identified in ocean pout while PVP did not cause thermal hysteresis. This indicates that there might be a direct relationship between ISP performance for ice and hydrate inhibition, and that thermal hysteresis experiments can be used to screen ISPs as kinetic inhibitors.
Carbon dioxide capture using aqueous ammonia is a post-combustion technology that has shown a goo... more Carbon dioxide capture using aqueous ammonia is a post-combustion technology that has shown a good potential. Therefore this process is studied by measuring the rate of absorption of carbon dioxide by aqueous ammonia and by performing process simulation. The rate of absorption of carbon dioxide by aqueous ammonia solvent has been studied by applying a wetted wall column apparatus. The
In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitor... more In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitors of gas hydrates as many of those used today suffer from poor biodegradability. In this work, we have investigated experimentally whether ice-structuring proteins (ISPs) found in fish and insect, assumed biodegradable, are capable of inhibiting the growth of methane hydrate (a structure I hydrate). The ISPs investigated were type III HPLC12 (originally identified in ocean pout) and ISP type III found in meal worm (Tenebrio molitor). These were compared to polyvinylpyrrolidone (PVP) a well-known kinetic hydrate inhibitor. The results revealed that adding ISP in sufficient amounts caused the appearance of an initial nonlinear growth period. At a certain point during the growth process the growth pattern changed to linear which is identical to the growth observed for methane hydrate in the absence of inhibitors. The profile of the nonlinear growth was concentration-dependent but also dependent on the stirring rate. ISP type III HPLC12 decreased the growth rate of methane hydrate during the linear growth period by 17-75% at concentrations of 0.01-0.1 wt % (0.014-0.14 mM) while ISP from Tenebrio molitor and PVP decreased the growth rate by 30% and 39% at concentrations of 0.004 wt % (0.005 mM) and 0.1 wt % (0.1 mM), respectively. Considering the low concentration of Tenebrio molitor ISP used, these results indicate that ISP from Tenebrio molitor is the most effective hydrate inhibitor among those investigated. Thermal hysteresis ice formation experiments revealed that ISP from Tenebrio molitor causes higher thermal hysteresis for ice formation compared to type III ISP identified in ocean pout while PVP did not cause thermal hysteresis. This indicates that there might be a direct relationship between ISP performance for ice and hydrate inhibition, and that thermal hysteresis experiments can be used to screen ISPs as kinetic inhibitors.
Monte Carlo simulation methods for determining fluid-and crystal-phase chemical potentials are us... more Monte Carlo simulation methods for determining fluid-and crystal-phase chemical potentials are used for the first time to calculate liquid water-methane hydrate-methane vapor phase equilibria from knowledge of atomistic interaction potentials alone. The water and methane molecules are modeled using the TIP4P/ice potential and a united-atom Lennard-Jones potential, respectively. The equilibrium calculation method for this system has three components, (i) thermodynamic integration from a supercritical ideal gas to obtain the fluid-phase chemical potentials, (ii) calculation of the chemical potential of the zero-occupancy hydrate system using thermodynamic integration from an Einstein crystal reference state, and (iii) thermodynamic integration to obtain the water and guest molecules' chemical potentials as a function of the hydrate occupancy. The three-phase equilibrium curve is calculated for pressures ranging from 20 to 500 bar and is shown to follow the Clapeyron behavior, in agreement with experiment; coexistence temperatures differ from the latter by 4-16 K in the pressure range studied. The enthalpy of dissociation extracted from the calculated P-T curve is within 2% of the experimental value at corresponding conditions. While computationally intensive, simulations such as these are essential to map the thermodynamically stable conditions for hydrate systems.
International Journal of Greenhouse Gas Control, 2011
In this work, the rate of absorption of carbon dioxide by aqueous ammonia solvent has been studie... more In this work, the rate of absorption of carbon dioxide by aqueous ammonia solvent has been studied by applying a newly built wetted wall column. The absorption rate in aqueous ammonia was measured at temperatures from 279 to 304 K for 1 to 10 wt% aqueous ammonia with loadings varying from 0 to 0.8 mol CO 2 /mol NH 3 . The absorption rate in 30 wt% aqueous mono-ethanolamine (MEA) was measured at 294 and 314 K with loadings varying from 0 to 0.4 as comparison.
... c Parameters determine in this study. d Calculated using the extended UNIQUAC model from MEG(... more ... c Parameters determine in this study. d Calculated using the extended UNIQUAC model from MEG(l) NIST properties. e Determined by Kaj Thomsen, previously unpublished. f Obtained from NIST(25) if not stated otherwise. ...
The rate-based steady-state model proposed by Gabrielsen et al.(Gabrielsen, J.; Michelsen, ML; Ko... more The rate-based steady-state model proposed by Gabrielsen et al.(Gabrielsen, J.; Michelsen, ML; Kontogeorgis, GM; Stenby, EH AIChE J. 2006, 52, 10, 3443− 3451) for the design of the CO2− 2-amino-2-methyl-propanol absorbers is adopted and improved for the design of ...
... from the large number of parameters, the Pitzer model usually gives a more accurate reproduct... more ... from the large number of parameters, the Pitzer model usually gives a more accurate reproduction of experimental data than the extended UNIQUAC model. ... The parameter estimation was carried out by a least-squares minimization procedure as described by Thomsen et al. ...
Pressure parameters are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (M... more Pressure parameters are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (Modeling of vapor-liquid-solid equilibrium in gas-aqueous electrolyte systems. Chemical Engineering Science 54, 1787Science 54, -1802Science 54, , 1999). The improved model has been used for correlation and prediction of solid-liquid equilibrium (SLE) of scaling minerals (CaSO 4 , CaSO 4 ·2H 2 O, BaSO 4 and SrSO 4 ) at temperatures up to 300 • C and pressures up to 1000 bar. The results show that the Extended UNIQUAC model, with the proposed pressure parameters, is able to represent binary, ternary and quaternary solubility data within the experimental accuracy in the temperature range from −20 to 300 • C, and the pressure range from 1 to 1000 bar.
Different types of data are used for modeling and they cover a very wide range of conditions. Vap... more Different types of data are used for modeling and they cover a very wide range of conditions. Vaporliquid equilibrium (VLE) data for the aqueous alkanolamine systems containing CO 2 in the pressure range of 313,000 kPa and temperatures of 25200 °C are used. The ...
The distribution of solutes and solvent between an aqueous solution of salt and an ion exchange r... more The distribution of solutes and solvent between an aqueous solution of salt and an ion exchange resin has been measured at ambient temperature. The experiments have been performed for aqueous solutions of KNO 3 , KCl, Ca(NO 3 ) 2 and CaCl 2 in the concentration range of 0-3N. The absorption has been measured for three gel-type and three macroreticular resins with a degree of cross-linking varying from 10.5 to 18.5%. The experimental results have been modeled with the Extended UNIQUAC model combined with an elastic term taking the elastic properties of the resin structure into account. The model shows very good predictions with varying degree of cross-linking, and the deviations between model results and experimental data are all within the experimental error.
... 00981354 95 9.50 + 0.00 SYNTHESIS AND ANALYSIS OF PROCESSES WITH ELECTROLYTE MIXTURES KAJ THO... more ... 00981354 95 9.50 + 0.00 SYNTHESIS AND ANALYSIS OF PROCESSES WITH ELECTROLYTE MIXTURES KAJ THOMSEN, RAFIQUL GANI and ... KEYWORDS Electrolyte system; Fractional crystallization; Solubility diagram; Extended UNIQUAC; SLE; Steady state simulation. ...
To simulate cyclohexane oxidation reactors using a dynamic model linking kinetics, thermodynamics... more To simulate cyclohexane oxidation reactors using a dynamic model linking kinetics, thermodynamics and hydrodynamics, the acquisition and modeling of vapor-liquid equilibria of the key components, under the process conditions, are essential. In this work, the vapor-liquid equilibria of the cyclohexane + cyclohexanol system were determined at temperatures 424, 444, 464 and 484 K. The measurements were carried out using an apparatus based on the "static-analytic" method, with two ROLSI TM pneumatic capillary samplers. The generated data are successfully correlated using two equations of state, the Peng-Robinson (PR) and the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT). A comparison of model performances reveals the former being better in data representation, while the latter has a broader applicability over larger range of temperatures.
... The extended UNIQUAC model of Thomsen et al. (1996) is used here, but any other reliable mode... more ... The extended UNIQUAC model of Thomsen et al. (1996) is used here, but any other reliable model can be used. * Corresponding author. ... The extended UNIQUAC model (Thomsen et al, 1996) has been used for all calculations. ...
A thermodynamic model for the description of vapor-liquid-solid equilibria is introduced. This mo... more A thermodynamic model for the description of vapor-liquid-solid equilibria is introduced. This model is a combination of the extended UNIQUAC model for electrolytes and the Soave-Redlich-Kwong cubic equation of state. The model has been applied to aqueous systems containing ammonia and/or carbon dioxide along with various salts. Model parameters valid in the temperature range 0-110°C, the pressure range from 0-100 bar, and the concentration range up to approximately 80 molal ammonia are given. The model parameters were evaluated on the basis of more than 7000 experimental data points. Edwards et al. (1975) used an extended form of the Debye-Hu¨ckel law for the liquid-phase activity coefficients, and the virial equation of state for the pure component fugacity of each component in the vapor phase. Vega and Vera (1976) calculated liquid-phase activity coefficients with a semi-empirical equation. Henry's law constants at reference concentrations were used to calculate the vapor pressures. Similarly to the model of van Krevelen et al. and the SWEQ model, Vega and Vera's model only apply to the low-pressure region where the vapor phase can be considered ideal.
The Extended UNIQUAC model for electrolyte solutions is an excess Gibbs energy function consistin... more The Extended UNIQUAC model for electrolyte solutions is an excess Gibbs energy function consisting of a Debye-H uckel term and a term corresponding to the UNIQUAC equation. For vapor-liquid equilibrium calculations, the fugacities of gas-phase components are calculated with the Soave-Redlich-Kwong equation of state. The model only requires binary, temperature-dependent interaction parameters. It has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures and aqueous electrolyte systems containing methanol. It has been found to be an adequate model for representing solid-liquid-vapor equilibrium and thermal property data for strongly non-ideal systems. In this work, the model is extended to aqueous salt systems containing higher alcohols. The calculations are based on an extensive database consisting of salt solubility data, vapor liquid equilibrium data, and liquid-liquid equilibrium data for solvent mixtures and for mixed solvent-electrolyte systems.
In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally ... more In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally using a stirred batch reactor. The experiments have been performed isothermally recording the pressure as a function of time. Experiments were conducted at different stirring rates, but in the same supersaturation region. The experiments showed that the gas dissolution rate rather than the induction time of propane hydrate is influenced by a change in agitation. This was especially valid at high stirring rates when the water surface was severely disturbed. Addition of polyvinylpyrrolidone (PVP) to the aqueous phase was found to reduce the gas dissolution rate slightly. However the induction times were prolonged quite substantially upon addition of PVP. The induction time data were correlated using a newly developed induction time model based on crystallization theory also capable of taking into account the presence of additives. In most cases reasonable agreement between the data and the model could be obtained. The results revealed that especially the effective surface energy between propane hydrate and water is likely to change when the stirring rate varies from very high to low. The prolongation of induction times according to the model is likely to be due to a change in the nuclei--substrate contact angle.
... KAJ THOMSEN, PETER RASMUSSEN* and RAFIQUL GANI Department of Chemical Engineering, Technical ... more ... KAJ THOMSEN, PETER RASMUSSEN* and RAFIQUL GANI Department of Chemical Engineering, Technical University of Denmark, DK2800 Lyngby, Denmark (First received 3 November 1995; accepted in revised form 14 December 1995) AbstractAn extended UNIQUAC ...
Three activity coefficient models for electrolyte solutions were evaluated and compared. The acti... more Three activity coefficient models for electrolyte solutions were evaluated and compared. The activity coefficient models are: The electrolyte NRTL model (ElecNRTL) by Aspentech, the mixed solvent electrolyte model (MSE) by OLI Systems, and the Extended UNIQUAC ...
In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitor... more In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitors of gas hydrates as many of those used today suffer from poor biodegradability. In this work, we have investigated experimentally whether ice-structuring proteins (ISPs) found in fish and insect, assumed biodegradable, are capable of inhibiting the growth of methane hydrate (a structure I hydrate). The ISPs investigated were type III HPLC12 (originally identified in ocean pout) and ISP type III found in meal worm (Tenebrio molitor). These were compared to polyvinylpyrrolidone (PVP) a well-known kinetic hydrate inhibitor. The results revealed that adding ISP in sufficient amounts caused the appearance of an initial nonlinear growth period. At a certain point during the growth process the growth pattern changed to linear which is identical to the growth observed for methane hydrate in the absence of inhibitors. The profile of the nonlinear growth was concentration-dependent but also dependent on the stirring rate. ISP type III HPLC12 decreased the growth rate of methane hydrate during the linear growth period by 17-75% at concentrations of 0.01-0.1 wt % (0.014-0.14 mM) while ISP from Tenebrio molitor and PVP decreased the growth rate by 30% and 39% at concentrations of 0.004 wt % (0.005 mM) and 0.1 wt % (0.1 mM), respectively. Considering the low concentration of Tenebrio molitor ISP used, these results indicate that ISP from Tenebrio molitor is the most effective hydrate inhibitor among those investigated. Thermal hysteresis ice formation experiments revealed that ISP from Tenebrio molitor causes higher thermal hysteresis for ice formation compared to type III ISP identified in ocean pout while PVP did not cause thermal hysteresis. This indicates that there might be a direct relationship between ISP performance for ice and hydrate inhibition, and that thermal hysteresis experiments can be used to screen ISPs as kinetic inhibitors.
Carbon dioxide capture using aqueous ammonia is a post-combustion technology that has shown a goo... more Carbon dioxide capture using aqueous ammonia is a post-combustion technology that has shown a good potential. Therefore this process is studied by measuring the rate of absorption of carbon dioxide by aqueous ammonia and by performing process simulation. The rate of absorption of carbon dioxide by aqueous ammonia solvent has been studied by applying a wetted wall column apparatus. The
In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitor... more In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitors of gas hydrates as many of those used today suffer from poor biodegradability. In this work, we have investigated experimentally whether ice-structuring proteins (ISPs) found in fish and insect, assumed biodegradable, are capable of inhibiting the growth of methane hydrate (a structure I hydrate). The ISPs investigated were type III HPLC12 (originally identified in ocean pout) and ISP type III found in meal worm (Tenebrio molitor). These were compared to polyvinylpyrrolidone (PVP) a well-known kinetic hydrate inhibitor. The results revealed that adding ISP in sufficient amounts caused the appearance of an initial nonlinear growth period. At a certain point during the growth process the growth pattern changed to linear which is identical to the growth observed for methane hydrate in the absence of inhibitors. The profile of the nonlinear growth was concentration-dependent but also dependent on the stirring rate. ISP type III HPLC12 decreased the growth rate of methane hydrate during the linear growth period by 17-75% at concentrations of 0.01-0.1 wt % (0.014-0.14 mM) while ISP from Tenebrio molitor and PVP decreased the growth rate by 30% and 39% at concentrations of 0.004 wt % (0.005 mM) and 0.1 wt % (0.1 mM), respectively. Considering the low concentration of Tenebrio molitor ISP used, these results indicate that ISP from Tenebrio molitor is the most effective hydrate inhibitor among those investigated. Thermal hysteresis ice formation experiments revealed that ISP from Tenebrio molitor causes higher thermal hysteresis for ice formation compared to type III ISP identified in ocean pout while PVP did not cause thermal hysteresis. This indicates that there might be a direct relationship between ISP performance for ice and hydrate inhibition, and that thermal hysteresis experiments can be used to screen ISPs as kinetic inhibitors.
Monte Carlo simulation methods for determining fluid-and crystal-phase chemical potentials are us... more Monte Carlo simulation methods for determining fluid-and crystal-phase chemical potentials are used for the first time to calculate liquid water-methane hydrate-methane vapor phase equilibria from knowledge of atomistic interaction potentials alone. The water and methane molecules are modeled using the TIP4P/ice potential and a united-atom Lennard-Jones potential, respectively. The equilibrium calculation method for this system has three components, (i) thermodynamic integration from a supercritical ideal gas to obtain the fluid-phase chemical potentials, (ii) calculation of the chemical potential of the zero-occupancy hydrate system using thermodynamic integration from an Einstein crystal reference state, and (iii) thermodynamic integration to obtain the water and guest molecules' chemical potentials as a function of the hydrate occupancy. The three-phase equilibrium curve is calculated for pressures ranging from 20 to 500 bar and is shown to follow the Clapeyron behavior, in agreement with experiment; coexistence temperatures differ from the latter by 4-16 K in the pressure range studied. The enthalpy of dissociation extracted from the calculated P-T curve is within 2% of the experimental value at corresponding conditions. While computationally intensive, simulations such as these are essential to map the thermodynamically stable conditions for hydrate systems.
International Journal of Greenhouse Gas Control, 2011
In this work, the rate of absorption of carbon dioxide by aqueous ammonia solvent has been studie... more In this work, the rate of absorption of carbon dioxide by aqueous ammonia solvent has been studied by applying a newly built wetted wall column. The absorption rate in aqueous ammonia was measured at temperatures from 279 to 304 K for 1 to 10 wt% aqueous ammonia with loadings varying from 0 to 0.8 mol CO 2 /mol NH 3 . The absorption rate in 30 wt% aqueous mono-ethanolamine (MEA) was measured at 294 and 314 K with loadings varying from 0 to 0.4 as comparison.
... c Parameters determine in this study. d Calculated using the extended UNIQUAC model from MEG(... more ... c Parameters determine in this study. d Calculated using the extended UNIQUAC model from MEG(l) NIST properties. e Determined by Kaj Thomsen, previously unpublished. f Obtained from NIST(25) if not stated otherwise. ...
The rate-based steady-state model proposed by Gabrielsen et al.(Gabrielsen, J.; Michelsen, ML; Ko... more The rate-based steady-state model proposed by Gabrielsen et al.(Gabrielsen, J.; Michelsen, ML; Kontogeorgis, GM; Stenby, EH AIChE J. 2006, 52, 10, 3443− 3451) for the design of the CO2− 2-amino-2-methyl-propanol absorbers is adopted and improved for the design of ...
... from the large number of parameters, the Pitzer model usually gives a more accurate reproduct... more ... from the large number of parameters, the Pitzer model usually gives a more accurate reproduction of experimental data than the extended UNIQUAC model. ... The parameter estimation was carried out by a least-squares minimization procedure as described by Thomsen et al. ...
Pressure parameters are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (M... more Pressure parameters are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (Modeling of vapor-liquid-solid equilibrium in gas-aqueous electrolyte systems. Chemical Engineering Science 54, 1787Science 54, -1802Science 54, , 1999). The improved model has been used for correlation and prediction of solid-liquid equilibrium (SLE) of scaling minerals (CaSO 4 , CaSO 4 ·2H 2 O, BaSO 4 and SrSO 4 ) at temperatures up to 300 • C and pressures up to 1000 bar. The results show that the Extended UNIQUAC model, with the proposed pressure parameters, is able to represent binary, ternary and quaternary solubility data within the experimental accuracy in the temperature range from −20 to 300 • C, and the pressure range from 1 to 1000 bar.
Different types of data are used for modeling and they cover a very wide range of conditions. Vap... more Different types of data are used for modeling and they cover a very wide range of conditions. Vaporliquid equilibrium (VLE) data for the aqueous alkanolamine systems containing CO 2 in the pressure range of 313,000 kPa and temperatures of 25200 °C are used. The ...
The distribution of solutes and solvent between an aqueous solution of salt and an ion exchange r... more The distribution of solutes and solvent between an aqueous solution of salt and an ion exchange resin has been measured at ambient temperature. The experiments have been performed for aqueous solutions of KNO 3 , KCl, Ca(NO 3 ) 2 and CaCl 2 in the concentration range of 0-3N. The absorption has been measured for three gel-type and three macroreticular resins with a degree of cross-linking varying from 10.5 to 18.5%. The experimental results have been modeled with the Extended UNIQUAC model combined with an elastic term taking the elastic properties of the resin structure into account. The model shows very good predictions with varying degree of cross-linking, and the deviations between model results and experimental data are all within the experimental error.
... 00981354 95 9.50 + 0.00 SYNTHESIS AND ANALYSIS OF PROCESSES WITH ELECTROLYTE MIXTURES KAJ THO... more ... 00981354 95 9.50 + 0.00 SYNTHESIS AND ANALYSIS OF PROCESSES WITH ELECTROLYTE MIXTURES KAJ THOMSEN, RAFIQUL GANI and ... KEYWORDS Electrolyte system; Fractional crystallization; Solubility diagram; Extended UNIQUAC; SLE; Steady state simulation. ...
To simulate cyclohexane oxidation reactors using a dynamic model linking kinetics, thermodynamics... more To simulate cyclohexane oxidation reactors using a dynamic model linking kinetics, thermodynamics and hydrodynamics, the acquisition and modeling of vapor-liquid equilibria of the key components, under the process conditions, are essential. In this work, the vapor-liquid equilibria of the cyclohexane + cyclohexanol system were determined at temperatures 424, 444, 464 and 484 K. The measurements were carried out using an apparatus based on the "static-analytic" method, with two ROLSI TM pneumatic capillary samplers. The generated data are successfully correlated using two equations of state, the Peng-Robinson (PR) and the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT). A comparison of model performances reveals the former being better in data representation, while the latter has a broader applicability over larger range of temperatures.
... The extended UNIQUAC model of Thomsen et al. (1996) is used here, but any other reliable mode... more ... The extended UNIQUAC model of Thomsen et al. (1996) is used here, but any other reliable model can be used. * Corresponding author. ... The extended UNIQUAC model (Thomsen et al, 1996) has been used for all calculations. ...
A thermodynamic model for the description of vapor-liquid-solid equilibria is introduced. This mo... more A thermodynamic model for the description of vapor-liquid-solid equilibria is introduced. This model is a combination of the extended UNIQUAC model for electrolytes and the Soave-Redlich-Kwong cubic equation of state. The model has been applied to aqueous systems containing ammonia and/or carbon dioxide along with various salts. Model parameters valid in the temperature range 0-110°C, the pressure range from 0-100 bar, and the concentration range up to approximately 80 molal ammonia are given. The model parameters were evaluated on the basis of more than 7000 experimental data points. Edwards et al. (1975) used an extended form of the Debye-Hu¨ckel law for the liquid-phase activity coefficients, and the virial equation of state for the pure component fugacity of each component in the vapor phase. Vega and Vera (1976) calculated liquid-phase activity coefficients with a semi-empirical equation. Henry's law constants at reference concentrations were used to calculate the vapor pressures. Similarly to the model of van Krevelen et al. and the SWEQ model, Vega and Vera's model only apply to the low-pressure region where the vapor phase can be considered ideal.
The Extended UNIQUAC model for electrolyte solutions is an excess Gibbs energy function consistin... more The Extended UNIQUAC model for electrolyte solutions is an excess Gibbs energy function consisting of a Debye-H uckel term and a term corresponding to the UNIQUAC equation. For vapor-liquid equilibrium calculations, the fugacities of gas-phase components are calculated with the Soave-Redlich-Kwong equation of state. The model only requires binary, temperature-dependent interaction parameters. It has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures and aqueous electrolyte systems containing methanol. It has been found to be an adequate model for representing solid-liquid-vapor equilibrium and thermal property data for strongly non-ideal systems. In this work, the model is extended to aqueous salt systems containing higher alcohols. The calculations are based on an extensive database consisting of salt solubility data, vapor liquid equilibrium data, and liquid-liquid equilibrium data for solvent mixtures and for mixed solvent-electrolyte systems.
In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally ... more In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally using a stirred batch reactor. The experiments have been performed isothermally recording the pressure as a function of time. Experiments were conducted at different stirring rates, but in the same supersaturation region. The experiments showed that the gas dissolution rate rather than the induction time of propane hydrate is influenced by a change in agitation. This was especially valid at high stirring rates when the water surface was severely disturbed. Addition of polyvinylpyrrolidone (PVP) to the aqueous phase was found to reduce the gas dissolution rate slightly. However the induction times were prolonged quite substantially upon addition of PVP. The induction time data were correlated using a newly developed induction time model based on crystallization theory also capable of taking into account the presence of additives. In most cases reasonable agreement between the data and the model could be obtained. The results revealed that especially the effective surface energy between propane hydrate and water is likely to change when the stirring rate varies from very high to low. The prolongation of induction times according to the model is likely to be due to a change in the nuclei--substrate contact angle.
... KAJ THOMSEN, PETER RASMUSSEN* and RAFIQUL GANI Department of Chemical Engineering, Technical ... more ... KAJ THOMSEN, PETER RASMUSSEN* and RAFIQUL GANI Department of Chemical Engineering, Technical University of Denmark, DK2800 Lyngby, Denmark (First received 3 November 1995; accepted in revised form 14 December 1995) AbstractAn extended UNIQUAC ...
Three activity coefficient models for electrolyte solutions were evaluated and compared. The acti... more Three activity coefficient models for electrolyte solutions were evaluated and compared. The activity coefficient models are: The electrolyte NRTL model (ElecNRTL) by Aspentech, the mixed solvent electrolyte model (MSE) by OLI Systems, and the Extended UNIQUAC ...
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