Ilkka Turunen

Kinetics of nitrate reduction in monolith reactor

Abstract The kinetics of nitrate reduction with hydrogen was studied in a metallic monolith reactor, where the catalytically active material was Cu-doped Pd supported on Al 2 O 3 . The experiments were carried out at 60°C and at hydrogen pressures of 2 atm and 4 atm. The reactor was operated in semibatch with respect to hydrogen, whereas the liquid phase was in batch recirculating through a storage tank. The main reaction products were nitrogen and ammonia; nitrite was formed as an intermediate product. The reduction kinetics was described with a rate model based on a mechanism where absorbed NO is the key intermediate on the catalyst surface. The mass transfer parameters were estimated from correlations and the mass transfer model was combined to the kinetic model. The reaction kinetics and the mass transfer were included in a plug-flow type of model for the monolith and the kinetic parameters were estimated with non-linear regression analysis. Simulation of the experimental conditions showed that the rate model can be used in nitrate hydrogenation.

Kinetics of oxidation of ferrous sulfate with molecular oxygen

Abstract The oxidation kinetics of Fe 2+ ions to Fe 3+ in concentrated H 2 SO 4 –FeSO 4 solutions was studied with isothermal and isobaric experiments carried out in a laboratory-scale pressurized autoclave. The experiments were performed at temperatures between 60 and 130°C, and the oxygen pressures between 4 and 10 bar. The kinetic results revealed that the oxidation rate increases with temperature and pressure. A rate equation was derived for the oxidation process, based on the assumption that stepwise complexation of Fe 2+ with dissolved oxygen is rate determining. The rate equation has the form r = a 1 c 2 FeII c O /(1+ a ′= c FeII ), where c FeII and c O are the concentrations of Fe 2+ ions and dissolved oxygen, respectively a 1 and a ′ are experimentally determined kinetic parameters. A comparison of the experimental data with the model fit revealed that the proposed rate equation is applicable for the prediction of the Fe 2+ -oxidation kinetics in acidic solutions.

Mass transfer in tubular reactors equipped with static mixers

Abstract Gas—liquid mass transfer was studied in horizontal tubular reactors equipped with static mixers. In such reactors, it often makes sense to leave empty spaces between mixer elements to avoid excessive pressure drops. Increasing the length of these spaces improves the reactor performance because of the reduced pressure drop but, on the other hand, worsens it because of the decreased mass transfer efficiency. Pressure drop and mass transfer efficiency can also be affected by liquid velocity. A detailed model, including a description of mass transfer and pressure drop, is presented. A novel approach was developed to evaluate the interfacial area in the transition zones between the flow patterns in the mixers and in the empty spaces. The parameters of the model were estimated from a large set of experimental results obtained by two different methods, a chemical and a physical one. Utilization of the model in reactor optimization is demonstrated.

Experimental design with steady-state and dynamic models of multiphase reactors

Abstract The verification of multiphase reactor model parameters is a complicated practical problem because of the diversity of phenomena involved in the reaction process. Due to this complexity, designing experiments for selecting and estimating the essential parameters affecting the mechanisms of simultaneous mass transfer and reaction is challenging. To our knowledge, there are not much published information on experimental design with these very models. This paper presents some of our recent studies in which experimental design methods were applied for analyzing mass transfer and reaction in stirred gas—liquid and gas—liquid—solid reactors. The first case deals with a moderately fast gas—liquid reaction in a continuous—flow reactor. Transport characteristics were described by a steady-state one-response model based on material balances in the bulk of the liquid and the interfacial film. The effective experimental design proved to be beneficial since only five sequentially designed experiments in addition to ten screening experiments were required. Experimental strategy with dynamic model of a three-phase catalytic slurry system is illustrated secondly. The system was studied in three stages: gas—to—liquid absorption, liquid—to—solid adsorption and the surface reaction.

Phenomenon driven process design methodology: Industrial case

Abstract This work reports how to use Phenomenon driven process design methodology proposed for RD from management level, up to detailed models. The successful fit of the methodology encourages to use the methodology and to develop the computer tool further.

Expero — an advanced support system for hydrogen peroxide process control

Abstract This paper presents a multifunctional support system, EXPERO, developed to help in control, training and research activities at Kemiras hydrogen peroxide plants. The knowledge included in EXPERO and the structure of the system are described. The most important knowledge in the system is deep, algorithmic knowledge in the form of very detailed simulation models. In addition there is experience-based knowledge in the form of rules and descriptive information of the process presented in hypertext fashion. The support system runs on 386/486 PC under OS/2. This PC is connected to the process control system which enables the transfer of real process measurements to EXPERO. The user interface is completely graphical and it closely mimics the displays in the process control system. EXPERO and its user interface have been developed using Object/1 which provides link to underlying FORTRAN simulator.

The simulation of a co-current bubble reactor

We consider the modelling of gas-liquid reactions in a cocurrent packed bubble reactor: both gas and liquid are fed in from the bottom of the column and removed from the top. The liquid froms a continuous phase in the column and the gas flows in the form of bubbles through the liquid phase. The desired product accumulates in the liquid as a result of a chemical reaction taking place both in the bulk liquid and at the gas/liquid interface. The column is operated continuously and is therefore in a steady state.