Investigations on Adsorption Drying at Low Temperatures

Abstract

Communications for viscosities of 0.26 and 25 mPa s. The assumption of a constant diffusion coefficient is based on reference measurements with a comparable system. However, at the highest viscosity of 260 mPa s the measured and calculated values deviate considerably. The main reason for this is that Bravo et al. fitted their coefficients on measured data with much lower viscosity. Thus, of course, their model is applicable only to a limited extent for the measurements discussed here.The packing surface, which is also part of the model, is only useful to a certain extent in the high-viscosity range. This was confirmed by looking inside the column during the measurements with the high-viscosity liquids. The liquid drained very poorly from the packing. The useful surface area was certainly much lower than the value inserted in the model. At lower liquid viscosity the wetting of the packing is much better. ConclusionOn the basis of the investigations with a test column as described here, the following results can be stated: ± The efficiency decreases significantly with increasing viscosity. At a viscosity of 260 mPa s, only 20 % of the reference value was achieved. ± Flooding occurs at considerably lower loading.Distillation with structured packing in high-viscosity systems may be an economically interesting process option. If solvents or monomers must be removed from or exchanged in polymers, only a small number of theoretical stages are necessary. The results presented must be taken into consideration in the design of technical plants. There are some applications in this area at Bayer. Therefore, special liquid distributors and flash arrangements also need to be developed.This kind of development may help extend the application of distillation technology into the area of high-viscosity liquids. Especially in this area it is necessary to provide a better description of mass transfer by improving existing or developing new mass transfer correlations. ProblemThe use of an adsorbent can be advantageous for the gentle drying of temperature-sensitive products. The used adsorbent binds water vapor and causes a driving force for drying to equilibrium, so that drying is possible also at low temperatures in the range of atmospheric pressure. The literature provides comparatively few data on drying of wet, especially biological products.The expected effects should be verified by experimental investigations with model substances and selected biological products. At the same time test methods and a test equipment should be established in order to be able to investigate various products in connection with different adsorbing agents with relatively little effort.For a physically based mathematical modeling of adsorption drying at low temperatures the water vapor adsorption isotherms of the products to be dried and the adsorbing agents at corresponding temperatures must be known. Therefore, they were determined experimentally and modeled mathematically. Experimental Investigations Drying Tests with a Rotating DrumFor the experim...