Andrzej Górak

Modelling of reactive separation processes: reactive absorption and reactive distillation

In the last years chemical process industries have shown permanently increasing interest in the development of reactive separation processes (RSP) combining reaction and separation mechanisms into a single, integrated unit. Such processes bring several important advantages among which are increase of reaction yield and selectivity, overcoming thermodynamic restrictions, e.g. azeotropes, and considerable reduction in energy, water and solvent consumption. Important examples of reactive separations are reactive distillation (RD) and reactive absorption (RA). Due to strong interactions of chemical reaction and heat and mass transfer, the process behaviour of RSP tends to be quite complex. This paper gives an overview of up-to-date reactive separation modelling and design approaches and covers both steady-state and dynamic issues. These approaches have been applied to several different RA and RD processes including the absorption of NOx, coke gas purification, methyl acetate synthesis and methyl tertiary butyl ether (MTBE) synthesis.

Process intensification and process systems engineering: A friendly symbiosis

An attempt is presented to define process intensification in relation to the other chemical engineering disciplines, in particular to process systems engineering. It is shown that process intensification is fully in development and, as a consequence, the essential characteristics are subject to debate. The innovative character of process intensification is in nice harmony with the objectives of process systems engineering: a symbiosis between them has high potential.

On the modelling and simulation of sour gas absorption by aqueous amine solutions

A rigorous rate-based model for reactive sour gas absorption by aqueous amine solutions is presented which governs both the coupling of mass transfer and reaction and specific features of electrolyte species. The acceleration of mass transfer due to reactions in the liquid phase is taken into account rigorously, without application of enhancement factors. The model is implemented into the simulation environment Aspen Custom Modeler and validated by comparison of published pilot plant data with the simulation results. It is shown, that the model possesses a good predictivity for pilot plant scale as well as for industrial scale applications. In addition, the influence of reaction kinetics on the absorber performance is studied.

Investigation of ethyl acetate reactive distillation process

In this paper, an extensive study of ethyl acetate synthesis by homogeneously catalyzed reactive distillation is presented. Reactive distillation is a promising operation whereby reaction and separation take place within a single distillation column. The synergistic effect of this combination has the potential to increase conversion, improve selectivity and facilitate separation tasks. The feasibility of ethyl acetate synthesis is examined using the reactive distillation lines diagram. A completely rate-based simulator DESIGNER developed within the framework of a large European research project is used in order to predict concentrations, temperatures and other important process variables. In order to validate theoretical predictions, a set of reactive distillation experiments is performed in a glass tray column with 80 bubble cap trays. The concentrations and temperature profiles computed by DESIGNER agree well with the experimental data.

Determination of gas–liquid reaction kinetics with a stirred cell reactor

Dynamic experiments were carried out in a gas–liquid stirred cell reactor and equations describing the reactor behaviour were derived. Different procedures of applying these equations to obtain the relevant rate parameters from the experimental data were proposed. A rigorous method was developed which takes the liquid bulk load into account. The latter method is advantageous as several experiments can be conducted in series. This procedure was compared with other considered methods and applied to the determination of the reaction kinetics of the system CO2–monoethanolamine. The determined kinetics is in good agreement with those of earlier investigations.

Reactive absorption : Optimal process design via optimal modelling

Optimal design of complex reactive separations is inconceivable unless reliable process models are available. Such models have to be both rigorous enough in order to reflect the process complexity and simple enough in order to ensure feasibility of process simulations. In this respect, an optimal model should represent a kind of a consensus between the rigour and simplicity, and its development requires a comparison of both detailed and simplified process models with experimental data. From this viewpoint, reactive absorption operations with their pronounced kinetic character and complex non-ideal behaviour provide one of the best objects for studying. This work gives a detailed analysis of the problem supplemented by the examples of industrial importance.

Intensified Reaction and Separation Systems

Process intensification follows four main goals: to maximize the effectiveness of intra- and intermolecular events, to give each molecule the same processing experience, to optimize the driving forces/maximize specific interfacial areas, and to maximize the synergistic effects of partial processes. This paper shows how these goals can be reached in reaction and separation systems at all relevant time and length scales and is focused on the structuring of reactors and separation units, on the use of different energy forms to improve the reaction and separation, on combining and superimposing of different phenomena in one integrated unit or reactor, and on the application of oscillations for intensification of reaction and separation processes.

Dynamic catalytic distillation: Advanced simulation and experimental validation

Abstract Reactive distillation offers a number of potential advantages, so that many traditional operations are currently being investigated in order to discover further applications of this technology. Increasingly, it is performed in columns with catalytic packings that combine the advantages of normal structured packings and heterogeneous catalysts. Analysis of reactive distillation is difficult due to strong physico-chemical interactions, and it is even more complicated for catalytic distillation (reactive distillation in catalytic packings), where the knowledge of column hydraulics, as e.g. hold-ups, pressure drop, and liquid distribution, is more important than in the case of traditional unit operations. In this paper, a detailed rate-based approach for modeling and simulation of catalytic distillation is presented, including all major aspects of the description of column hydraulics, mass and energy transfer, chemical reactions and thermodynamic non-idealities. The model equations have been implemented into the ABACUSS large scale modeling environment. Even in the frame of such sophisticated modeling, a variety of experimental parameters have to be determined. It is shown how these parameters appear in the model equations and how experiments and computer simulation interact. For a completely new class of catalytic packings all experimental parameters have been derived in accordance with the model assumptions in the form of correlations. All models have been formulated for dynamic operation and numerical implications of the dynamic modeling are addressed. For the semi-continuous catalytic distillation of the quaternary reactive mixture of acetic acid, methanol, methyl acetatem and water, simulated and experimental results are presented and compared. Based on the integration of detailed modeling, experimental parameter determination and a modern simulation platform it is possible to predict the dynamic, non-linear and non-ideal process behavior successfully.

Investigation of different column configurations for the ethyl acetate synthesis via reactive distillation

Abstract The ethyl acetate synthesis via reactive distillation is studied theoretically and experimentally using different catalytic packings. Experiments are carried out at laboratory scale in a 50 mm diameter column with a packing height of 3 m, and at semi-industrial scale in a 162 mm diameter column with a packing height of 12 m. The experimental set-up is similar for both cases. The commercially available packings studied are KATAPAK®-S and two different variants of MULTIPAK®. Modelling is performed with a rate-based stage model. The simulation environment ASPEN Custom Modeler™ is used for the implementation and solution of the model equations. The results of the rate-based simulations agree well with the corresponding experimental results. In addition, suitable operating conditions and the influence of the selected catalytic internal on conversion and product purity are investigated. The developed model enables the scale-up from laboratory to industrial size columns, based on the respective packing characteristics.

Review of the application of ionic liquids as solvents for chitin

Abstract Chitin is one of the most abundant biopolymers, but due to its high crystallinity, it is completely insoluble in most organic and inorganic solvents. Chitin is soluble only in solvents that can destroy intersheet and intrasheet H-bonds, and many of these solvents are toxic, corrosive, nondegradable, or mutagenic. Because of these drawbacks, there is a search for more environmentally friendly solvents for chitin. It has been shown that ionic liquids (ILs) can dissolve chitin at elevated temperatures (80°–110°C) or with application of microwave irradiation. The highest solubility of chitin in an IL was about 20% (1-ethyl-3-methylimidazolium acetate), whereas chitin was shown to be insoluble in 1-allyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium formate. Dissolved chitin can be regenerated by mixing with water or methanol, where the polymer precipitates from the solution. X-ray diffraction patterns of native polymer and precipitates have been compared and only small changes in crystallinity have been observed. In addition, Fourier transform infrared spectra remained similar for both forms of chitin, native and regenerated. Presented data hold great promise for the improvement of the chemistry of chitin and open new routes for chemical and enzymatic modifications of this polymer.