Hallvard F. Svendsen

Computational chemistry study of reactions, equilibrium and kinetics of chemical CO2 absorption

Abstract The chemical reactions involved in CO 2 absorption in amine systems are studied. For each mechanism, available experimental data are considered and quantum mechanical calculations carried out. Base-catalyzed bicarbonate formation is found to be a likely mechanism for all amine bases, not only tertiary amines. Direct formation of bicarbonate species from carbamate species is found to be unlikely. The carbamate formation has been proposed to take place through a single-step termolecular reaction, or through a two step mechanism with a zwitterionic intermediate. Quantum mechanical calculations suggest that if there is such a zwitterionic intermediate, it is likely to be short-lived. Quantum mechanical calculations together with solvation models are shown to predict the base strength and carbamate stability of different amine solvents with a useful degree of accuracy. Solvent effects and electron donation and withdrawal through bonds are identified as important factors in determining the overall reactivity of different amine solvents. Results suggest a strong correlation between the carbamate stability and base strength of amine solvents and their reaction kinetics.

Liquid circulation , bubble size distributions, and solids movement in two- and three-phase bubble columns

Abstract One two-phase bubble column and two three-phase slurry reactors have been experimentally characterised with special emphasis on bubble size distribution, liquid circulation and solids movement. The measurements in the two phase bubble column were based on a five point conductivity probe method and on a steady state heat tracer technique. For the solids movement, the CARPT technique was used. By numerical simulations using a two fluid model, new models for bubble size distribution and solids presence have been tested. The new bubble size model is found to improve the size distribution predictions compared to prior models, but is still not satisfactory. Temperature profiles were well predicted by the model. For the solids movement, two circulation cells were found experimentally in the reactors tested. This has also been verified by numerical simulations. The formation of secondary cell structures of magnitude approximately equal to the column diameter, are indicated by the experimentally determined Reynolds stress patterns.

A model for turbulent binary breakup of dispersed fluid particles

Abstract Accurate predictions of particle size distributions, and therefore of the underlying processes of fluid particle breakup and coalescence are of vital importance in process design, but reliable procedures are still lacking. The present paper aims at developing a modular formulation for the turbulent particle breakup process. The model is to be included in a population balance model which is formulated such as to facilitate the direct future implementation into a full multifluid CFD model. The breakup process is described without introducing adjustable parameters. The current model is a further development of an existing model by Luo and Svendsen (AIChE J. 42 (5) (1996) 1225), which has been expanded and refined, and where an inherent weakness regarding the breakup rate for small particles and small daughter particle fragments are removed. A new criterion regarding the kinetic energy density of the colliding turbulent eddy causing breakup has been introduced. This new criterion is a novel concept describing the breakup process. The details are thoroughly discussed together with possible further modifications. The results from the new model are encouraging because the breakup rate is greatly reduced when the dispersed fluid particles are reduced in size. Further, the response to changes in system variables is reasonable and the distribution of daughter sizes vary in a reasonable way for the different collision possibilities.

Effect of viscosity on droplet-droplet collision outcome: Experimental study and numerical comparison

The influence of viscosity on droplet-droplet collision behavior at ambient conditions was studied experimentally and numerically. N-decane, monoethyleneglycol (MEG), diethyleneglycol (DEG), and triethyleneglycol were used as liquid phase providing viscosities in the range from 0.9to48mPas. Collision Weber numbers ranged approximately from 10 to 420. A direct numerical simulation code, based on the volume-of-fluid concept, was used for the simulations. Experimentally, observations of two droplet streams using a modified stroboscopic technique (aliasing method) were used to investigate the whole range of impact parameters during one experimental run. The experimental method has previously been verified for the water/air system [C. Gotaas et al., Phys. Fluids 19, 102105 (2007)]. In the present work, it was tested and validated for the n-decane/air system. Measured data agree well with those published in the literature. Well-defined regions of stretching separation and coalescence were identified, while refl...

Explicitly representing the solvation shell in continuum solvent calculations.

A method is presented to explicitly represent the first solvation shell in continuum solvation calculations. Initial solvation shell geometries were generated with classical molecular dynamics simulations. Clusters consisting of solute and 5 solvent molecules were fully relaxed in quantum mechanical calculations. The free energy of solvation of the solute was calculated from the free energy of formation of the cluster, and the solvation free energy of the cluster was calculated with continuum solvation models. The method has been implemented with two continuum solvation models, a Poisson-Boltzmann model and the IEF-PCM model. Calculations were carried out for a set of 60 ionic species. Implemented with the Poisson-Boltzmann model the method gave an unsigned average error of 2.1 kcal/mol and a rmsd of 2.6 kcal/mol for anions; for cations the unsigned average error was 2.8 kcal/mol and the rmsd 3.9 kcal/mol. Similar results were obtained with the IEF-PCM model.

The interaction between mass transfer effects and morphology in heterogeneous olefin polymerization

The interaction between mass transfer effects and morphology in heterogeneous olefin polymerization

Dynamic simulation and optimization of a catalytic steam reformer

Abstract The operational performance of a heated fixed-bed reactor has been studied. Previous work indicates that the distribution of heat transfer resistances is important. No generally accepted correlation exists for the wall heat transfer coefficient and the effective radial thermal conductivity, and correlations proposed in the literature have been tested and evaluated. It is found that the outer reactor tube wall temperature is very sensitive to the applied correlation for the wall heat transfer coefficient and none of the evaluated correlations match the real situation perfectly. However, the methane conversion is rather insensitive to the choice of correlation. The effective radial thermal conductivity can be determined from the assumption of equal radial heat- and momentum Peclet number. It is found that using spatially varying physical properties and gas velocities only has a minor effect on the temperature distribution. Thus, the inlet conditions can be used to determine the effective radial thermal conductivity. By applying the correlation by De Wasch and Froment (1972) for the wall heat transfer coefficient, the resulting model is demonstrated for two simulation scenarios: (1) stop in steam supply and (2) stop in gas feed supply (CH 4 , H 2 , CO and CO 2 ). Finally, the optimal methane conversion is obtained for changing feed flow with a limiting value for the outer reactor tube wall temperature applied as a constraint.

Desorber Energy Consumption Amine Based Absorption Plants

A computational model of the regeneration system of a monoethanolamine (MEA) based absorption plant for CO2 removal has been developed and used for an operational parameter study. Several parameters have been identified and varied over a given span in order to see the performance effects for the regeneration system, which determines the majority of the operational cost of the overall gas cleaning process. The results show that major energy savings can be realized by optimizing the loading level in the amine system as well as reboiler pressure. A more efficient heat exchanger followed by a flash prior to the desorber does not improve the overall stripping performance to a significant extent. The quality of equilibrium data is of crucial importance in the simulation and optimization of the desorber unit. They are much more important in the case for modeling the desorber compared to modeling the absorber.

Modeling temperature dependency of amine basicity using PCM and SM8T implicit solvation models.

PCM and SM8T continuum solvation models are used to study the temperature dependency of a set of amines in the temperature range 273-393 K using density functional theoretical calculations. Gaseous phase calculations are done using B3LYP and M06 functionals at the 6-311++G(d,p) basis set level. pK(a) values calculated computationally are compared with experimental values in the given temperature region using both continuum solvation models. The continuum solvation models predict the temperature trends of pK(a) compared to experimental trends very nicely. Accurate pK(a) values at 298 K are however required as input to the model. The absolute values of pK(a) values are not reproduced well by these continuum solvation models, and a correction term is therefore introduced. A set of 10 amines, which have potential for CO(2) capture, and where also a large experimental data set of temperature dependent pK(a) values is available, were studied in this work. The temperature dependency of pK(a) values of amines provides a basis for selection for optimum solvents for postcombustion CO(2) capture processes.

NMR study and quantum mechanical calculations on the 2-[(2-aminoethyl)amino]-ethanol-H2O-CO2 system.

13C and 1H NMR spectra were obtained for AEEA (2-[(2-aminoethyl)amino]-ethanol)-H2O-CO2 systems and quantum mechanical calculations were carried out for the different AEEA species. The results suggest that the main AEEA species under the conditions studied are free amine, primary carbamate, and secondary carbamate. There is also some indication that a dicarbamate species is formed, this species does however only appear to be formed in small amounts. Comparison between experimental data and quantum mechanical calculations suggest that most AEEA species take on conforms with some degree of intramolecular hydrogen bonding.