Mirko Skiborowski

Conceptual Design of Distillation-Based Hybrid Separation Processes

Hybrid separation processes combine different separation principles and constitute a promising design option for the separation of complex mixtures. Particularly, the integration of distillation with other unit operations can significantly improve the separation of close-boiling or azeotropic mixtures. Although the design of single-unit operations is well understood and supported by computational methods, the optimal design of flowsheets of hybrid separation processes is still a challenging task. The large number of operational and design degrees of freedom requires a systematic and optimization-based design approach. To this end, a structured approach, the so-called process synthesis framework, is proposed. This article reviews available computational methods for the conceptual design of distillation-based hybrid processes for the separation of liquid mixtures. Open problems are identified that must be addressed to finally establish a structured process synthesis framework for such processes.

Recycling homogeneous catalysts simply via organic solvent nanofiltration: New ways to efficient catalysis

Organic solvent nanofiltration is a convenient method for the recovery of homogeneous transition metal catalysts. The long chain olefin 1‐dodecene is hydroformylated continuously, and the commercially available catalyst complex is separated efficiently using a commercially available nanofiltration membrane. An advantage of this method is that both reaction and separation take place in a single liquid phase. Only continuous operation shows interactions of reaction and separation in the long run. Low energy demand, high scalability as well as transferability to other reactions make this method promising for new industrial applications.

Synthesis of Intensified Processes from a Superstructure of Phenomena Building Blocks

Abstract This paper presents a method for phenomena-based process synthesis that automatically generates flowsheet variants by means of superstructure optimization. By composing processes of phenomena instead of predefined unit operations, the creativity during process synthesis is maximized and process intensification principles can be considered even beyond already existing equipment. The optimization-based method generates promising phenomena-based flowsheet variants which can further be interpreted and translated into equipment by using databases or proposing new equipment that implements the phenomena-based design. The applicability of the developed method is demonstrated for the case study of ethanol dehydration. The method automatically generates conventional as well as innovative flowsheet variants, some of which even show an improved performance estimate.

Conceptual Design of Post-Combustion CO2 Capture Processes - Packed Columns and Membrane Technologies

Abstract CO 2 removal from flue gas emitted by coal fired power plants is an important objective for process sustainability. However, solvent regeneration in state-of-the-art absorption processes results in power plant efficiency losses of 7 to 15 % (Neveux et al., 2013). Process intensification, combining different and innovative technologies for gas separation, can result in highly efficient processes capable of reducing the energy penalty caused by CO 2 capture. Current approaches for conceptual process design (CPD) however rarely consider emerging technologies like membrane contactors or hybrid process configurations. We present a multi-stage approach to overcome this drawback, which bases on process decomposition in different levels, combined with an efficient screening of promising materials and process design variants by means of shortcut methods. The approach follows the idea of an iterative refinement, in which the modeling accuracy increases while the number of process variants decreases.

Shortcut method for the design of extraction columns for multi-component mixture separations

Abstract Shortcut methods are valuable tools for the fast evaluation of different units and flowsheets in separation process design. In this paper, a systematic method for the estimation of the minimum solvent flow rate required in counter-current extraction columns is presented. A key element is the identification of a mode of operation under saddle-pinch control, characterizing multi-component extractive separations. The criterion defining this mode leads to a new shortcut method, which provides both, a systematic calculation of all pinch points and a criterion for minimum solvent flow rate estimation. It requires low computational effort, it is robust and does not need any specific initialization. Furthermore, the shortcut method is fully algorithmic and thus, at least in principle, applicable to any number of components. Its features are highlighted by means of an example of an extractive separation of a four component mixture.

Efficient optimization-based design of energetically intensified distillation processes

Abstract Although suffering from low energy efficiency, distillation is still the most widespread separation technique in industry. Different means for the improvement of energy efficiency, such as heat-pump assisted and thermally coupled distillation columns, have been developed. However, the comparison of these different configurations and the identification of the most energy or economicly beneficial option for a specific separation is an elaborate task. Therefore, an efficient optimization-based method for the evaluation of the different options is proposed. In contrast to most previous approaches, the method is based on a superstructure equilibrium tray model including rigorous thermodynamics. It is therefore directly applicable to the separation of non-ideal mixtures and considers a broad range of different options for energetically intensified distillation processes. For illustration purposes the design method is applied to the separation of a ternary non-ideal mixture.

Process Intensification in Practice: Ethylene Glycol Case Study

Process Intensification (PI) is broadly defined as the development of innovative equipment and technologies that offer drastic improvements in chemical processing. Interest in PI has been increasing steadily for the past 30 years, as confirmed by numerous publications and patents. The outstanding improvement offered by PI technologies is achieved through, for example, the enhancement of physical and chemical phenomena with novel equipment, the integration of functions and the introduction of new driving forces and energy sources. Hence, PI can overcome most difficult process bottlenecks, which cannot be tackled by using classical equipment. Despite its great potential to improve production processes, PI implementations in industry is still limited. Apart from reliance on well-established technologies and a reluctance to use novel processes, the scarcity of PI implementation can be attributed to the lack of knowledge of how and where intensification should be applied. Therefore, systematic methodologies are required that enable to identify the part of the flowsheet that should be intensified and to determine the most adequate PI technology for overcoming current process limitations. To this end, a novel approach for process retrofitting by means of PI is illustrated with an excellent example of ethylene glycol production. Replacing a tubular reactor with a reactive distillation column resulted in significant improvement of ethylene glycol processing: the operating costs were limited by 14%, and the number of required unit operations was decreased by over 70%.

CHAPTER 10:Enzymatic Reactive Absorption and Distillation

In this work, innovative concepts for reactive separation processes, such as reactive absorption and distillation, that make use of bio-based catalysts, in specific enzymes, are discussed. Enzymatic Reactive Absorption (ERA) and Distillation (ERD) offer potential for energy and investment savings or improved selectivity by exploiting enzyme merits like high enantioselectivity and high reaction rates at milder reaction conditions than chemical catalysts. Potential process equipment, application strategies to supply enzyme for ERA and ERD processes as well as suitable modeling and design approaches are presented. Despite the huge potential, addressing these issues is crucial in order to promote ERA and ERD as vital technologies for process intensification in bio-based industries. The application of the enzyme carbonic anhydrase in an ERA column with common MDEA-based solvent can drastically improve the absorption of CO2 by more than 9-fold. Furthermore, the production of butyl butyrate and enantiomerically pure (R)-1-phenylethyl acetate or (S)-2-pentanol were successfully demonstrated in an ERD column. These processes provided high conversion rates of the substrates and purities of the product stream at milder process conditions compared to conventional processes.

Optimization of extractive distillation – integrated solvent selection and energy integration

Abstract The separation of azeotropic mixtures is of particular importance for bio-based processes in the chemical industry. Extractive and heteroazeotropic distillation are oftentimes the favored solution for medium to large scale processes due to their proven robustness and the economics of scale. The feasibility as well as economic efficiency of these processes depends strongly on the selection of a suitable mass separating agent (MSA). Furthermore, energy integration can increase the energy and economic efficiency of these thermal processes. Since, MSA selection, process design and energy integration are usually performed as consecutive steps in process design, potential synergies are easily missed, resulting in sub-optimal choices. In order to determine an optimal process design, including solvent selection and energy integration, an efficient optimization-based approach for the design of extractive distillation processes is proposed. The application of the method is illustrated for the separation of the azeotropic mixture of acetone and methanol. The results highlight that the optimal MSA choice under consideration of energy integration differs from the selection without energy integration.

Analyzing the link between GE-model parameter regression and optimal process design

Abstract The importance of accurate thermodynamic models, capable of describing vapor-liquid and liquid-liquid equilibria, is generally acknowledged for the design of chemical processes. However, the parameterization of thermodynamic models and the development of chemical processes are usually treated as two different disciplines. More importantly, the objectives of each discipline do not necessary align. While the quality of a thermodynamic model is often judged purely on the basis of its average mean deviation from experimental data, process design aims at minimizing the overall process costs, assuming that the underlying thermodynamic models (especially model parameters) are reliable/accurate. Assessing the uncertainty of the thermodynamic model parameters is the link between both disciplines. However, this link is rarely established, and even the effect of the consideration of uncertainties in parameter regression by means of a deterministic process design is rarely investigated. Within this work this effect was taken into account for vapor-liquid equilibrium modeling and optimal design of a distillation column. The results indicate the necessity of a consistent consideration of uncertainties both during parameter regression and process optimization. Furthermore, the results highlight that a special treatment of experimental data and uncertainty information is required for specific applications (e.g. distillation of tangent pinch systems) in order to obtain reliable results in process design.