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A novel core–shell species for the adsorption-based separation of carbon dioxide (CO2) from methane (CH4) is introduced by hydrothermal synthesis of Ni-MOF-74 on mesoporous spherical Al2O3 carrier substrate. The material was characterized and the shell thickness determined by means of optical and scanning electron microscopy as well as volumetric adsorption and fluid displacement experiments. Kinetic experiments with Ni-MOF-74@Al2O3 core–shell composites carried out at 303.15 K and at pressures up to 10 bar expose remarkably dominating uptake rates for CO2 over CH4. In the contrary Ni-MOF-74@Al2O3 appears to be unselective according to equilibrium data at the same conditions. Dynamic breakthrough experiments of binary CH4/CO2-mixtures (at 303.15 K and 5 bar) prove the prevailing effect of adsorption kinetics and the storage function of the mesoporous core. This statement is supported by a considerable boost in CO2-selectivity and capacity compared to adsorption equilibria measured on pure Ni-MOF-74 by the factor of 55.02 and up to 2.42, respectively.

Kinetics and quantity of crystallization fouling on different polymeric surfaces are studied for the model salts of calcium sulfate and calcium carbonate and compared with those on stainless steel. The promising low scaling affinity of the polymers is attributed to their different surface properties compared to stainless steel. The crystallization kinetics and quantity are also affected by the degree of supersaturation due to higher local temperatures and concentrations. The results can be utilized in thermal desalination plants.

The corrosive process conditions in common multi-effect distillation (MED) plants require heat transfer surfaces consisting of high-grade metal alloys. However, corrosion resistant polymers can be a reasonable alternative to expensive metals. But it is necessary to use thin polymer films, which must be mechanically stabilized by a spacer grid, to compensate the low thermal conductivity of polymers. A falling film plate evaporator with heat transfer surfaces made out of the high performance polymer polyetheretherketone (PEEK) was already developed based on those considerations. Experimentally measured overall heat transfer coefficients with the prototype heat exchanger at MED process conditions are presented in this publication. They are comparable to typical values of metallic falling film heat exchangers. Furthermore, the heat transfer within the prototype heat exchanger was modeled and compared with the obtained experimental results. It will be shown that correlations valid for falling film heat transfer on a vertical wall are not applicable for a spacer stabilized polymeric heat transfer surface, but they can be used after modifications.

Multi-effect distillation (MED) is a well-established process in seawater desalination. Heat transfer surfaces used in MED-plants are exposed to highly corrosive process conditions due to direct contact to evaporating seawater. The use of polyetheretherketone (PEEK) might be a low cost and less corrodible alternative to expensive metal alloys. PEEK seems to be best suited for application in MED-plants, because it possesses an excellent mechanical and chemical resistance. One drawback of polymers is their poor thermal conductivity. Typical MED process conditions require a wall thickness of about 25 μm for PEEK to get overall heat transfer coefficients comparable to metallic heat transfer surfaces. Therefore, it is necessary to investigate the mechanical behavior of PEEK films, to ensure that they can withstand the mechanical and thermal loads in MED-plants. Stress-strain and creeping behavior of PEEK films in water were investigated at elevated temperatures and described by empirical correlations. Mechanical calculations were carried out to determine tensile loads of the polymer film in a falling film plate evaporator at typical MED process conditions. Parameter variations reveal the limitations of use for PEEK film heat transfer surfaces, but the results also show that PEEK films can withstand the mechanical loads in MED-plants.

Multi-effect distillation (MED) plants with co-current flow show moderate process conditions with respect to temperature and pressure differences between consecutive effects. Thus, polymers seem to be best suited as a low-cost and less-corrodible alternative to metal alloys. Furthermore, polymer surfaces are less susceptible to scaling. In order to proof this concept, a falling film plate evaporator with heat transfer surfaces made of polyetheretherketone (PEEK) films was built. One of the main challenges is to assure a sufficient mechanical stability of the polymer film and simultaneously provide a low thermal resistance for heat conduction. Calculations and experiments show that a polymer film thickness of 25 μm, in combination with an appropriate spacer geometry, is sufficient for mechanical stability in MED plants. This low film thickness results in a thermal resistance for heat conduction comparable to 1.5 mm thick stainless steel. In order to demonstrate the applicability of polymer films for heat t...