Chemical Reaction Engineering

Hydrogenation of aqueous solutions of sugars from renewable resources

Nowadays, the majority of chemicals are produced from fossil resources like crude oil or natural gas. Considering the high related emissions of carbon dioxide, alternative sustainable processes based on renewable resources such as sugars, sugar alcohols, oils and lignocellulose become more and more attractive. An example for such sustainable syntheses is the production of polyols from sugar. These polyols are applied in the polymer industry and as source material for different plastics. Moreover, some small chain polyols are being used as deicer in the aviation industry. Due to good emulsifying properties of some polyols, they can be used as supporting material for colorants, antioxidants and enzymes in chemical, pharmaceutical, cosmetic and food applications.
The aim of this project is to develop a process for the hydrogenation of aqueous solution of sugars to produce polyols. Besides the selection of a suitable catalyst and reaction conditions, an adequate analysis method for the complex product mixture has to be developed and phase equilibria in the reactor have to be considered. For the determination of the reaction kinetics, systematic experiments at pressures of up to 120 bar are performed in a stirred tank reactor.

Contact: Carina Heisig, M. Sc.

Unsteady-State Methanation of Carbon Oxides

One of the most intensively discussed processes for the chemical storage of renewable energy is the methanation of carbon oxides (CO, CO2). In this process renewable electrical energy is transferred into hydrogen by electrolysis of water, which is used for the hydrogenation of carbon oxides into synthetic natural gas (SNG). The concept, known as “Power-to-Gas”, is complicated by the unsteady state availability of hydrogen, due to the fluctuation in renewable energy supply. However, the unsteady state behaviour of the methanation reaction is still not completely understood. Consequently, the project aims at understanding the unsteady state processing during this reaction in order to contribute to the industrial implementation of the methanation in renewable energy storage.

Contact: Bjarne Kreitz, M. Sc.

Catalytic Methanation of Carbon Dioxide

The reduction of environmental influences, which are caused by fossil fuels, results in a continuous expansion of renewable energy. Due to the considerable fluctuations in performance of these technologies, like wind or solar energy, possibilities of intermediate storage are required. The catalytic methanation is a part of the well-known “power to gas” concept. Therein synthetic methane is produced from hydrogen and a carbon source like carbon dioxide, the methane can be directly fed into the natural gas grid.
Since the reaction is highly exothermic, mass- and heat transport have to be especially considered. Therefore, catalytic fixed bed reactors with different tube diameters and particle sizes are investigated. Additional to heterogeneous reactor models, particle resolved CFD simulations are applied. Especially with small tube- to pellet diameter ratios, the wall effect significantly influences the flow profile. In this project, the flow characteristics around the pellets and the processes at the catalyst surface are studied. The developed model will be integrated into a particle resolved simulation.

Contact: Jan Martin, M. Sc., Steffen Flaischlen, M. Sc.

Micro- and milli-structured fixed bed reactors

 Supported by:

Heterogeneously catalyzed gas-phase reactions such as the synthesis of maleic anhydride, phthalic anhydride or acrolein exhibit highly exothermic behavior. On industrial scale, these reactions are conducted in multi-tubular reactors with up to 30.000 single tubes including the catalytic fixed bed. Due to the limited heat removal in the radial direction of the fixed bed axial temperature profiles with hot spots occur, thus reducing the reactor performance. A significant increase in heat removal can be achieved by reducing the reactor dimensions down to the micro- and milli-structured scale. Thereby the specific surface area for the heat removal is enhanced while the characteristic length of the radial heat conduction through the fixed bed is reduced.
The aim of this project is to investigate this type of process intensification for the selective oxidation of n-butane to maleic anhydride. The main focus of the investigations is to determine the optimal geometric configuration of catalyst and reaction channels with regard to high product yields and low pressure drops. Therefore experiments with different catalyst fractions and channel geometries are conducted with variable concentration of n-butane and volume flow rates of the reactants, which are evaluated with a suitable mathematical reactor model.

Contact: Mauritio Müller, M. Sc.

Experimental studies of high-temperature reactions in a downer reactor

When gas-solid reactions are carried out in a circulating fluidized bed (CFB), the commonly used riser is strongly affected by backmixing of phases because of solid downflow near the wall resulting in a broad residence time distribution (RTD). In a downer reactor, however, backmixing is minimized due to the same direction of gravity and gas flow. Therefore plug-flow behavior can be approximated. In a laboratory scale downer reactor ceramic powders will be studied during different high-temperature chemical reactions. For this purpose, different temperatures, gases, gas velocities and mass flows of solids and gas are going to be used. Furthermore, a mathematical model will be developed which allows for both analysis of the experiments and scale-up of the reactor.

Contact: Prof. Dr.-Ing. Thomas Turek

Heterogeneously catalyzed reactive extraction for the hydration of olefins

 Supported by:

Within this project a new process for the hydration of butene to secondary butyl alcohol in presence of an acid ion-exchanger will be developed. The goal is to gain information for different arrangements of the catalyst for a scale-up to an industrial plant. Therefore kinetics, mass transfer, equilibrium data as well as fluid dynamics are investigated, to get a good basis for a mathematical model. The new process is a multiphase-system with the solid catalyst phase and two fluid phases. Under operating conditions one of them is a liquid and the other one is a supercritical phase. The chemical reaction takes place in the liquid aqueous phase and the product is extracted into the supercritical organic phase simultaneously.

Contact: Frank Schwering, M. Sc.

Innovative development process for optimal foam pellets as catalyst carrier for fixed bed reactors

  Supported by:

Fixed Bed Reactors (FBR) are the most used reactor type in the chemical industry. The catalyst pellets in FBR are usually made of ceramic pellets. In order to overcome the limitations of these ceramic pellets and for reactor performance enhancement, the use of novel pellets made of metal foams are recommended. Computational Fluid Dynamic (CFD) simulations should speed up the development of new possible shapes. The design parameters (e.g. shape, porosity) of this new catalyst supports in chemical engineering perspective are not yet completely aware. The development in high performance computing and advances in numerical techniques and algorithms, allowed CFD to become a powerful tool in analyzing flow patterns, heat and mass transfer processes in chemical reactors. Recently, Prof. Wehinger (TU Clausthal) has developed a CFD modelling approach for the reactors composed of ceramic pellets. The main objective of this study is to adapt the already developed CFD techniques for the study of foam pellets and to predict the optimal shape for the defined reaction conditions. This study also comprises the validation of CFD model with adequate experimental data, which will be monitored by Alantum Europe. By this approach, the development process of new metallic foams can be accelerated and the time required to introduce it in the market can be reduced. The algorithm can also be used to react quickly on changes in the requirements.

Ansprechpartner: Ginu George, M. Sc.

Electrochemical Engineering

The bio-electrical fuel cell as a component of an energy producing wastewater treatment equipment

 Supported by: ERWAS Joint Project

Goals of the subproject at the Institute of Chemical and Electrochemical Process Engineering (ICVT):

  • Selection of materials and material combinations for the electrode production
    Mainly carbon-polymer compounds of the cooperation partner Eisenhuth GmbH shall be examined referring to their performance as components for bio-electrical fuel cells. Those compounds are, by methods of polymer processing, producable in large quantities.
  • Selection and processing of catalysts and their precursors to obtain catalytically active layers
    The laminating methods available at the institute, especially a wet spraying process, shall come into operation. The potentials of laminating carbon-polymer compounds with materials on which biofilms can grow, shall be examined.
  • Operation of test fuel cells in a fuel cell testing equipment
    These procedures will be useful to identify appropriate materials, material combinations and operating procedures for test cell prototypes, as basic know-how for a future pilot plant designing and operation, concerted with the project partners.

Contact: Prof. Dr.-Ing. Ulrich Kunz

Wastewater Treatment by Radicals - RADAR

 Supported by:

Numerous organic trace compounds as well as drug residues are found in municipal wastewater, which is insufficient purified by the biology of sewage treatment plants. Moreover, many process waters of the chemical industry are contaminated with organic compounds, too.
In order to remove the trace elements, an electrochemical wastewater treatment concept is developed for the first time within RADAR project (RADAR: german abbreviation for „Radikalische Abwasserreinigung; English: wastewater treatment by radicals). The developed concept will be realized up to demonstration scale. The basis of the new concept is a combination of a boron-doped diamond electrode and a gas diffusion electrode for generating highly oxidative species simultaneously. Furthermore, auxiliary electrodes are examined to avoid scaling on cathode side.
In the subproject of the Institute of Chemical and Electrochemical Process Engineering, the electrochemical evaluation of electrodes and the identification of best operating points will be done.

Gas diffusion electrodes of the project partner Covestro AG, diamond electrodes of the company Condias GmbH as well as auxiliary electrodes of Eisenhuth GmbH are evaluated. For the systematic exploration laboratory-scale reactors are used to identify degradation rates and the decalcification potential.

Aim of research is the identification of the most promising electrode material combination and an appropriate process engineering design, which is suitable for the technical realization of a novel electrochemical pollutant elimination.

Contact: Thorben Muddemann, M. Sc.

Development of a rechargeable zinc-air flow battery

 Supported by:

In search of a cost-efficient and eco-friendly battery technology, zinc-air batteries provide a promising alternative to conventional systems. The use as primary battery is already established in hearing devices worldwide. The concept of a rechargeable battery is based on a flow through system, where potassium hydroxide is used as electrolyte. This system includes a porous zinc electrode and a bifunctional gas diffusion electrode. The number of charge and discharge cycles is mainly affected by the degradation of the electrodes. Here the formation of dendrites often occurs at the zinc electrode during charging, which is avoidable by using the pulse-loading method. A further challenge is the stability of the bifunctional gas diffusion electrode, because the oxygen development does provoke the loss of activity. This is due to the release of the catalyst from the electrode matrix.

Within the project appropriate materials for the battery components have to be investigated and evaluated with respect to their long-term stability. The evaluation has to be carried out in half and full cells. Furthermore an examination of the optimum operating conditions has to be done for the development and assembly of a 100 W demonstrator.

Contact: Sascha Genthe, M.Sc.

DFG Research Unit „Multiscale analysis of complex three-phase systems: oxygen-reduction at gas-diffusion electrodes in aqueous electrolyte” (FOR 2397)

 Supported by:

Gas-diffusion electrodes (GDE) are key components for different electrochemical processes. This includes the transformation of chemically stored energy into electrical energy in fuel cells and metal-air batteries as well as the reversal of these energy conversion processes in the chlor-alkali electrolysis. However, in many technologies, gas diffusion electrodes are the limiting components and thus the main cost factor.

To improve the efficiency of GDE, it is necessary to have an overall comprehension of the complex interaction of transport and reaction processes inside the electrodes. In order to investigate these processes, subprojects of seven research facilities in Germany are combined in the DFG Research Unit.

At the ICVT working GDE are produced from silver powders and characterized by different methods. The measurements involve physico-chemical characterization of the pore systems and electrochemical measurements in half-cells. Based on these measurements it is possible to determine quantatively the effect of process conditions and electrode properties on the overpotential of the oxygen reduction reaction. Results of all subprojects will be also used to improve a mathematical model, which describes the stationary overpotential of the GDE.

Further information is given on the website of the DFG Research Unit.

Ansprechpartner: David Franzen, M. Sc., Barbara Ellendorff

Experimental and theoretical investigation of gas purity in pressure-driven alkaline water electrolysis

 Supported by:

Alkaline water electrolysis is a key technology for converting regenerative electrical energy into chemically stored energy. The product gas hydrogen can be converted into electricity by fuel cells or used as a starting material for subsequent processes. For further processing, the hydrogen is usually required at an increased pressure level and with a high gas quality. Under pressurized conditions, the cell efficiency decreases mainly due to increasing contamination of the product gases.

Therefore, an extensive experimental and theoretical study to elucidate the factors influencing the product gas quality in pressure-driven alkaline water electrolysis will be carried out within the scope of the project. Relevant process parameters are current density, process pressure, electrolyte volume flow, electrolyte concentration, operating temperature and lye circulation mode. Stationary and dynamic test series as well as the experimental determination of properties should contribute to the extension and validation of a mathematical model with which optimal operating variants in combination with regenerative energy sources can be determined.

Contact: Jörn Brauns, M. Sc.

New large size bipolar plates for redox-flow batteries produced with the extrusion process

  Supported by:

Redox-flow batteries are suitable for storing electricity from fluctuating renewable energy. At present, commercial systems have a stack performance in the kilowatt range due to the limited size of the bipolar plates. This is significantly lower than required during the future development of the German “Energiewende”. Due to the modular design of redox-flow batteries it is possible to build energy storage devices with higher capacity and power by a numbering up of the existing cells. However, this results in too high specific investment costs. An alternative for providing storage capacities of at least 10 megawatts is a real scale up of the active cell area to 2 m² to 3 m². However, the production of those large bipolar plates with conventional processes such as pressing and injection molding is a challenge as the quality requirements are not yet fulfilled. Therefore this research project examines the production of new large and stable bipolar plates with the extrusion process. The characteristics of the developed bipolar plate are analyzed, and cell designs are proposed with the aid of a mathematical model.

For further information look here.

Ansprechpartner: Eva Prumbohm M. Sc.

Design of a high power redox flow stack

  Supported by:

The two main fields of application for energy storage units are first: shifting the energy generated during the day to times, e.g. in the evening or at night, when it’s most needed and second: to level performance peaks and thereby lower grid connection fees. One of the most promising chemical energy storage systems are the redox flow batteries and particularly vanadium redox flow batteries (VRFB).

To use this technology effectively in a decentralized way, e.g. in SME or apartment buildings, the power density of this stationary energy storage has to be increased significantly compared to state of the art concepts. In order to realize this goal a project in collaboration with our partners Eisenhuth, Volterion and TU-Braunschweig is formed. As part of this project new membrane materials, bipolar plate and flow field concepts are introduced to design and develop a high performance cell-stack that has low cost per kW.

Ansprechpartner: Alexander Kubicka, M. Sc.


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