Sara Claramunt

The polycondensation reaction to produce polydextrose can be intensified by using micro-process engineering. Fluid Guiding Elements are additively manufactured internal inserts that have already shown their potential to intensify heat transfer in double-pipe heat exchangers. This study investigated the intensification of the polydextrose yield when these internal inserts were used. Different reactor lengths and internal inserts geometries, as well as different operating conditions, were analyzed. The experiments showed that the reactant concentration had no effect on the product yield. Furthermore, it was shown that the process could be intensified at higher temperatures, with relatively low residence times and lower pressures. It was confirmed that the good heat transfer characteristics of the internal inserts allow them to continuously evaporate water during the reaction and to further reach the required reaction temperature, thus shifting the equilibrium towards the desired product. These findings are of special significance for the optimization of the polycondensation reaction of polydextrose.

Hydrophobic membranes were characterized at elevated temperatures. Pressure was applied at the feed and permeate side to ensure liquid phase conditions. Within this scope, the applicability of different polymeric and ceramic membranes in terms of liquid entry pressure was studied using water. The Visual Method and the Pressure Step Method were applied for the experimental investigation. The results show the Pressure Step Method to be an early detection method. The tests at higher pressure and temperature conditions using the Pressure Step Method revealed the temperature as being the main factor affecting the liquid entry pressure. Novel LEP data up to 120 °C and 2.5 bar were obtained, which broadens the application range of hydrophobic membranes.

Hydrophobic porous metallic membranes can be integrated in a microreactor for in situ separation of steam at high temperatures. This study investigates the fabrication and characterization of hydrophobic coatings on metallic substrates. Two different coating methods were explored: (1) Plasma Enhanced—Chemical Vapor Deposition (PE-CVD) to form amorphous carbon silicon-doped a-C:H:Si:O thin films and (2) Direct Immersion in fluoroalkyl silane (FAS-13) solution using dip coating to form Self-Assembled Monolayers. The results on wettability as well as SEM images and EDS/WDS analyses indicate that the coated sintered stainless steel membranes are adequate as hydrophobic surfaces, maintaining the porosity of the substrate and withstanding high temperatures. Especially the FAS-13 coating shows very good resistance to temperatures higher than 250 °C. These findings are of special significance for the fabrication of porous metal membranes for separation of steam in high temperature applications.