Jozef Markoš

Kinetics of pyrolysis and properties of carbon black from a scrap tire

The pyrolysis of rubber from the sidewall and tread of a passenger car tire was carried out in a nitrogen flow at a wide range of final temperatures. Derivative thermogravimetric analysis (DTG) was applied to examine the kinetics at the different process conditions of completed pyrolysis. Two characteristic stages were observed in the DTG curves. The first stage corresponded to the decomposition of processing oil, plastifier, and additives, whereas the rubber polymer was decomposed in the second stage. Several properties of the carbon black formed by the pyrolysis such as ash content, specific surface area, and pore size distribution were determined. A change of the internal structure of the rubber particle in the meso-and macroregions of the pore size was observed.

Impact of mathematical model selection on prediction of steady state and dynamic behaviour of a reactive distillation column

The objective of this paper was to compare the prediction of the equilibrium (EQ) and nonequilibrium (NEQ) models during safety analysis of a reactive distillation column focusing on the identification of hazardous situations or particular operability problems. The safety and operability analyses are based on application of the HAZOP procedure integrated with a mathematical model with the aim to determine the column response to deviations from normal operation conditions or during a nonstandard procedure, e.g. the start-up of the reactive distillation column. A significant part of the safety and operability problems analysis is the identification of multiple steady states and their stability. A reactive distillation column can in general exhibit multiple steady states which reduce the column operability and controllability during perturbations of the manipulated variables and particularly during the start-up and shut down procedures. The EQ and NEQ models were compared focusing on prediction of the multiple steady states phenomenon and of the consequences which can result from this phenomenon.

Reactive distillation — experimental data for propyl propionate synthesis

A set of experimental data for heterogeneously catalysed esterification of propan-1-ol and propionic acid to propyl propionate in a pilot scale reactive distillation column is presented. The catalytic section of the column was equipped with the structured packing Katapak SP-11. Both, rectifying and stripping, sections consisted of the non-reactive structured Sulzer BX packing. As catalyst, the strongly acidic ion-exchange resin Amberlyst 46 was used. The experimental results show concentration as well as temperature profiles along the column height and therefore exhibit reliable data for model validation purposes.

Modeling of enzymatic reaction in an airlift reactor using an axial dispersion model

This work was focused on modeling of biochemical processes in a 40-L internal-loop airlift reactor. Due to different mixing in the specific zones of the reactor four main sections, bottom, riser, separator and downcomer, were recognized. Each zone was modeled by an adequate mixing model: bottom and separator sections by the model of ideally-stirred reactor; riser and downcomer sections by the model of plug-flow reactor with axial dispersion. In the model, the effects of mass transfer, hydrodynamics, and reaction kinetics were taken into account. The model of the reactor was experimentally verified by the aerobic enzymatic oxidation of glucose to gluconic acid. Simulations are in good agreement with experimental data.

Safety analysis and risk identification for a tubular reactor using the HAZOP methodology

A model approach to Hazard and Operability (HAZOP) analysis is presented based on the mathematical modeling of a process unit where both the steady-state analysis, including the analysis of the steady states multiplicity and stability, and the dynamic simulation are used. Heterogeneous tubular reactor for the ethylene oxide production from ethylene and oxygen was chosen to identify potential hazards for real system. The computer code DYNHAZ was developed consisting of a process simulator and a generator of the HAZOP algorithm.

Intensive 2-phenylethanol production in a hybrid system combined of a stirred tank reactor and an immersed extraction membrane module

Bioconversion of l-phenylalanine to 2-phenylethanol using Saccharomyces cerevisiae is connected with the growth of biomass strongly limited by product inhibition. Therefore, fermentation can proceed only at low conversions of l-phenylalanine with very low yield of the desired product, which allows reaching the maximum concentration of 2-phenylethanol, 4 g L−1, in an ordinary batch, fed-batch, or chemostat bioreactor. To minimize capital and operating costs in the bioproduction of chemical specialties where the product inhibits the bioreaction, using a hybrid system based on the application of membrane extraction integrated in the bioreactor to remove the product is a suitable solution. Integration can be done by an external module for membrane extraction or, as a more efficient solution, by an extraction membrane module immersed directly in the bioreactor. Such a hybrid system can be used to remove 2-phenylethanol from the fermentation media and thus to overcome the product inhibition of the biotransformation process. In this paper, a hybrid system consisting of a stirred tank bioreactor (3.5 L) and an immersed extraction hollow fiber membrane module was studied. In the proposed system, the kinetics of 2-phenylethanol extraction from a water solution with and without biomass in the bioreactor to alkanes at different operational conditions was measured. Extraction kinetics was compared with the predictions obtained by a mathematical model. In the hybrid system, two extractive biotransformation experiments were performed and compared with that without product removal. Experimental data were also mathematically predicted with good accuracy between the simulation and the experiment.

Membrane extraction of 1-phenylethanol from fermentation solution

Abstract1-Phenylethanol can be produced by biotransformation of acetophenone using microorganisms. The next step is the separation of biomass from the fermentation solution (e.g. using microfiltration) and then the separation of the product. Membrane extraction was studied in the presented work for this purpose. Equilibria of acetophenone and 1-phenylethanol in the equilibrium system solute-organic solvent-water were investigated for three different organic solvents (heptane, toluene, ethyl acetate). On the basis of this investigation, extraction kinetics of both solutes from the model aqueous solution to the heptane organic phase, using a hollow fiber membrane module, were studied. To simulate the extraction kinetics, mathematical model of an experimental parallel flow hollow fiber contactor is presented and verified using experimental values with good agreement. Extraction kinetics for the investigated organic solvents were simulated and compared using the verified mathematical model and the chosen membrane extraction parameters.

Theoretical study on transesterification in a combined process consisting of a reactive distillation column and a pervaporation unit

Steady state analysis of a combined hybrid process consisting of a reactive distillation column, pervaporation unit, and a distillation column is presented. This process configuration was first presented by Steinigeweg and Gmehling (2004) for the transesterification of methyl acetate and butanol to butyl acetate and methanol. This system is characteristic for its low reaction rate and complex phase equilibrium. Steinigeweg and Gmehling (2004) have shown that the combination of reactive distillation and pervaporation is favourable since conversions close to 100 % can be reached with a reasonable size of the reactive section in the reactive distillation column. The aim of this paper is to show that although high conversion can be achieved, very complicated steady state behaviour must be expected. The presented analysis is based on mathematical modelling of a process unit, where the steady-state analysis, including continuation and bifurcation analyses, was used. Multiple steady states were predicted for the studied system; three steady states with conversions higher than 98 %. However, not all predicted steady states met the maximal allowed temperature condition in the reactive section (catalyst maximal operation temperature of 393 K). The presence of multiple steady states reduces the operability and controllability of the reactive distillation column during its start-up and during the occurrence of any variation of operating parameters because the system can be shifted from one steady state to another one (concurrent exceeding the maximal allowed temperature) with unwanted consequences, e.g. production loss. Therefore, design and subsequent operation of such a complicated system is an ambitious task requiring knowledge of any possible system behaviour.

Modelling of enzymatic reaction in an internal loop airlift reactor

Gas-liquid reaction carried out in an internal loop airlift reactor was modelled and subjected to the scale-up procedure. Homogeneous oxidation of glucose to gluconic acid catalyzed by Gluzyme 10000 BG, a commercial product containing the enzymes glucose oxidase and catalase as active components, was chosen as the model system. The kinetic parameters were obtained using a 12-L airlift reactor considered as a CSTR. The behaviour of a large-scale internal loop airlift reactor was modelled dividing the reactor sections into a series of tank reactors. The reliability of the model was verified by comparing experimental measurements with the simulation results obtained employing 40-L and 200-L airlift reactors. The designed model could be suitable to predict the behaviour of large-scale internal loop airlift reactors.

Airlift reactor — membrane extraction hybrid system for aroma production

In recent times, environmental production methods and organic products are increasingly sought after in food, perfume, and cosmetic industries, where the products are consumed or come into direct contact with humans. One such additive is 2-phenylethanol, an alcoholic aromatic rose like smell compound, mainly used as a flavor and aroma. 2-Phenylethanol can be produced by bioconversion from l-phenylalanine using Saccharomyces cerevisiae. This type of biotransformation is strongly limited by product inhibition which allows reaching the maximum concentration of 2-phenylethanol, 4 g L−1, in an ordinary batch, fed-batch, or chemostat bioreactor. The main aim of the presented work was to study the possible yield increase of 2-phenylethanol in a hybrid system consisting of membrane extraction performed by a hollow fiber membrane module immersed in the downcomer of an airlift reactor. Such hybrid system can be used to remove 2-phenylethanol from the fermentation medium and thus to overcome the product inhibition of biotransformation. In this paper, the influence of biomass on membrane extraction of 2-phenylethanol from aqueous solution in an airlift reactor to alkanes at different operational conditions was studied. The measured extraction kinetics was compared with the predictions obtained by a mathematical model. Hydrodynamics of the hybrid system was also studied.