Development of a novel Method for Thermal Separation

In the proposed work we intend to find a novel method to achieve higher selectivities in thermal separation processes without chemical reaction, which exceed values of currently available apparatus. Our hypothesis is that the application of microstructures is the appropriate method. The challenging part will be the fundamental research of the design and evaluation of the microstructure. We intend to verify our assumption and method by a demonstrating microstructured device. The prior goals of the proposed project are (1) to achieve higher selectivities in thermal separation processes without chemical reaction, which exceed values of currently available apparatus, by means of the development of a novel micro apparatus; (2) to develop an appropriate analytical or numerical description of the physical process of the method for layout and evaluation of the novel apparatus. The approach of Micro Process Engineering (MPE) will be applied to achieve theses goals. Since MPE is researched for Reaction Technology, the research of physical transport phenomena in thermal separation processes with a gaseous and a liquid phase in microstructures will be new and exciting and requires a deep scientific study. The method can be applied for rectification and/or absorption. The project is divided into 4 phases: Phase 1: The main goal is to find the correlations and analytical formulations of the processes and the calculation of thermodynamics/phase equilibrium in the separation unit, which consists of microstructures. CFD simulations of the basic concept design serve to overhaul, revise and optimize the basic concept. Finally the design of the separation unit of the demonstrating microdevice is available. Phase 2: Based on the basic design of the separation unit a scale-out will be made in order to make a design of an apparatus for higher flow rates. For the design of the manifolds for both phases, CFD will be applied. Additionally, the whole apparatus design of the demonstrating microdevice is available, so that finally the construction of a prototype can be accomplished. Phase 3: A laboratory plant for testing is designed and tests of the microdevice are carried out with 3 different mixtures: 2 Distillation series: Methanol -Water, Cyclohexane - n-Heptan and 1 Absorption serial: Nitrogen-Water. Phase 4: By means of the laboratory tests, the efficiency of the method will be verified, which include the verification of the descriptions of the phase equilibrium and transport processes of Phase 1 and the determination of the actual selectivity. In summary, we intend to develop a new and more efficient method for thermal separation process without chemical reaction, which can be applied in fine chemicals and pharmaceutical industry. Since process intensification is becoming increasingly important, this project will have significant impact and may lead to significant improvements in the field of thermal separation.

The goal of this project was the development and study of a novel method for thermal separation. First of all experimental prestudies of absorption and distillation with a reference device, the FFMR of the Institut für Mikrotechnik Mainz, were accomplished. For the separation of the two-phase flow deriving from the experimental operation, a novel phase separation device was tested, evaluated by computational fluid dynamics and optimized. The optimized device featured separation efficiencies over 90%. For designing the thermal separation device (for absorption and distillation) the flow was also studied by numerical methods. A strong influence of the contact angle was identified. By means of the study of the gas/vapor-liquid contacting of the basic design concept using CFD, stable operation could be shown and a novel concept could be developed, which was implemented in the design of the device. The phase contacting zone was studied by means of the CFD - code (FLUENT 6.3 - 3ddp) using the VOF-approach. All simulations and experiments were accomplished by using the test system CH30HlH20. The novel micro structured device (SMARR) was sized, designed and manufactured according the pressure equipment directive. Stable operation could be shown both in absorption and distillation in experiments. In absorption the separation performance was similar to the FFMR(IITU SMARR: 24-48 [mm], HTUFFMR: 13 -124 [mm]; kLa(SMARR): 0.115 -0.325 [5-1], kLa (FFMR): 0.02 - 0.07 [s-I]). In distillation only rectifying stages could be realized. Due to the extremely small dimensions of the pipes, nozzles, the heat transfer of the metallic connections and the unsteady evaporating behaviour of the microevaporator, the feed was partly two-phase flow. Therefore, the liquid had to be separated from the vapor phase, as mentioned above, by the optimized phase separation device. At flow rates of 0.2 - 1.6 [g/min] and a feed temperature of 79 - 88 [0C] with a low heating power of35 - 55 [%] an average HTU-values of65 [mm] could be reached, which is 15 [mm] lower than the HTU-values of the FFMR. Product rates of 0.12 - 0.42 [g/min] in the bottom and 0.1 - 1.16 [g/min] in the distillate could be achieved. The goal of the following study was to develop the device further to be able to run higher throughput (SMARRII), to reduce the HTU value and to realize both rectifying and stripping stages. On the basis of the previous works within this project, an optimized experimental plant was built and the microdevice was further developed by CFD. At flow rates from 0.09 to 5 [g/min], a feed temperature of 75 - 84 [0C] at very low heating power of 23 - 40 [%] and stable operation a destillate and bottom product amount of 2.5 [g/min] could be generated. The experimental evaluation of SMARRII showed a good separation performance for different other applications/test systems. Compared to SMARR the HTU-value could be reduced 46 [nun] to 19 [mm]. On the one hand this resulted from the successful implementation of stripping stages and on the other hand from the findings derived from CFD and experiments associated with the consequential improvements of the microstructure and the design of the device.