Juhani Aittamaa

An integrated tool for synthesis and design of reactive distillation

Abstract The consortium consisting of the companies BP Chemicals (Great Britain), Hoechst (Germany), BASF (Germany), Snamprogetti (Italy), Neste Oy (Finland) and universities of Clausthal (Germany), Dortmund (Germany), Aston (Great Britain), Bath (Great Britain) and Helsinki University of Technology (Finland) has just finished the three-year project “Reactive distillation” initiated by SUSTECH and supported by EU in the frame of the BRITE-EURAM program. The paper presents an overview of the achievements gained in the project. The authors of this paper are only representatives of a group of over 20 researchers involved in the project.

An improved correlation for compressed liquid densities of hydrocarbons. Part 1. Pure compounds

A new model for calculating compressed liquid densities is proposed. In the new model, the Hankinson-Thomson correlation (Hankinson and Thomson, 1979) is used to calculate saturated liquid densities, and a slightly modified Chang-Zhao equation (Chang and Zhao, 1990) is used in the compressed liquid region. n nParameters of the new model are fitted from a data base consisting of 4426 density points for 29 pure alkanes and alkenes. The new model is compared with HBT (Thomson et al., 1982) and Chang-Zhao (Chang and Zhao, 1990) models, and it is found to be the most accurate of the three models. With the new model, densities of compressed liquids can also be calculated in the near critical region with good accuracy. The average absolute deviation was 0.38% for the region Tr < 0.95 and 0.44% for the whole region Tr < 1.0. n nThe new model is also tested against compressed liquid density data for several other organic substances and inorganic light compounds, that were not included in the data set used to fit the parameters. The average absolute deviation was 0.72% for the region Tr < 0.95 and 0.86% for the whole region Tr < 1.0 indicating that though fitted from alkane and alkene data, the new model can be applied to many other compounds.

The liquid phase hydrogenation of benzene and substituted alkylbenzenes over a nickel catalyst in a semi-batch reactor

Abstract The liquid phase hydrogenation kinetics of benzene, toluene, ethylbenzene and cumene was studied in a three-phase semibatch reactor at pressures of 20–40 bar and at temperatures of 95–140°C. The experimental kinetics was described with a rate equation based on rapid adsorption and desorption steps and slow consecutive hydrogen steps. A pseudo-homogeneous model neglecting the diffusion resistances in the catalyst particles was able to phenomenologically describe the observed kinetics, but numerical simulations showed that there exist significant concentration gradients in the particles. Therefore a complete dynamic heterogeneous model was developed for the reactor and the catalyst particles including the reaction-diffusion process. The kinetic parameters were re-determined using the heterogeneous reactiondiffusion model. The model enables the investigation of the reaction-diffusion effects and the dynamics of the catalyst particles.

An improved correlation for compressed liquid densities of hydrocarbons. Part 2. Mixtures

Abstract A recently presented model for compressed liquid densities of pure hydrocarbons (Aalto et al., 1995) is extended to mixtures. Mixing rules for the parameters V ∗ , Tc. HBT, ωSRK and Pc are given. A collection of mixing rules was compiled. 75 combinations of the mixing rules were evaluated using a compressed liquid density data base. The data base was collected during this work and it contained 4223 density data points for 49 binary and ternary hydrocarbon systems. The set of mixing rules recommended in this work gave an average absolute deviation (AAD) of 0.45%. The new model was compared to the original HBT correlation (Thomson et al., 1982), which gave an AAD of 0.57%. Based on the comparison done, it was found that the new model is more accurate than HBT and it can be used at higher temperatures near the vapor-liquid critical point. No binary interaction parameters are needed.

Approximate high flux corrections for multicomponent mass transfer models and some explicit methods

Abstract New approximate simplifications are made to the high flux correction matrix for the film model and the penetration model, as derived from the Maxwell–Stefan mass transfer theory. Approximations are valid for both predetermined total flux, when explicit method results, and equivalently when total fluxes must be iterated. These presented simplifications are simple enough so as to be always includable in the mass transfer calculations, and the zero total flux assumption (equimolar transfer) is never needed for computational reasons in practical calculations.

Interfacial mass transfer in trickle-bed reactor modelling

A rigorous steady-state model was written for trickle-bed reactors. The mass and heat transfer resistances both between the gas phase and the liquid phase and between the liquid phase and the catalyst surface are included in the reactor model. The mass transfer is modelled using both the Maxwell-Stefan equations and the effective diffusivity method. The numerical solution of the model is discussed. The reactor model was attached to a flowsheet simulator that provided all the required physical property and phase-behaviour calculations. Finally, an industrial hydrogenation reactor was simulated as an example. The simulation results were used to examine the importance of local mass and heat transfer resistances in the reactor.

Modelling of speciality chemicals production in liquid–liquid reactors—A case study: synthesis of diols

Abstract Generalized mass balance models were derived for semibatch liquid–liquid reactors, which are frequently used in the production of fine and speciality chemicals. The model comprises the reaction kinetics, liquid–liquid equilibria as well as interfacial mass transfer effects. The reactor model was applied on a case study, homogeneously catalyzed synthesis of diols through aldol condensation and Cannizzaro reaction. Rate equations for the process were obtained by applying steady-state approximations on ionic reaction intermediates. The rate equation were incorporated into the mass balances and tested with experimental kinetic data. The model was able to imitate the experimental behaviour of the two-phase system.

Modelling Emergency Relief for Processes at Near Critical Conditions

Abstract A simulation tool for the preliminary design of a pressure relieving device for processes at near critical conditions is described. The selection of a pressure relieving device can be divided into two stages. The first stage is to determine the required emergency outflow as a function of time, which provides information to select a pressure relief valve or a rupture disk. The second stage is to simulate the process with the pressure relieving device selected at the first stage to find out the behaviour of the process as a function of time. A comparison between the proposed and the API 520 method is shown with the aid of an example.

Investigation of the hydrogenation of some substituted alkylbenzenes in a laboratory scale trickle-bed reactor

The liquid-phase hydrogenation kinetics of toluene, cumene and mesitylene was studied over an alumina-supported nickel catalyst in a laboratory scale trickle-bed reactor operating isothermally at temperature of 75-115°C and at hydrogen pressures of 20-40 bar. The experiments performed in the absence of intraparticular diffusion resistance showed that the catalyst deactivated rapidly at the initial stage of the experiment, after which a virtually stable level of the catalyst activity was attained. The systematic kinetic experiments carried out with a stable aged catalyst revealed that cumene and mesitylene at high concentrations retarded the hydrogenation rate, whereas such an effect was not observable for toluene. The results of the kinetic experiments were interpreted quantitatively with a reaction mechanism involving sequential addition of hydrogen to absorbed aromatic molecules.

CALCULATING DISTILLATION EFFICIENCIES OF MULTICOMPONENT i-BUTANE/ n-BUTANE COLUMN

This paper presents experimental data and estimated distillation efficiencies of an industrial scale distillation column separating i-butane and n-butane. The data gathered from plant instruments and laboratory analysis were reconciled and compared to distillation simulations. The simulations were performed with a number of real plates using the point and the Murphree plate efficiency calculation model. This matrix model of efficiency at first estimates the point efficiencies using the two-film and multicomponent mass transfer theory. The point efficiencies are then converted into Murphree plate efficiencies using a liquid mixing model. The whole method is implemented in a computer program to simulate an industrial distillation column with real plates. Finally the calculated product compositions are compared with reconciled measurements. The values of overall, section, point and Murphree plate efficiencies of multicomponent i-butane/n-butane system are also calculated. The results show that point efficiencies are not adequate for large industrial scale columns. The results also imply that the plate efficiency calculation method can be utilized and employed in the design and simulation of industrial scale columns.