A metal-free route for the synthesis of hyper-cross-linked polymers (HCP) based on Brønsted acids such as trifluoromethanesulfonic acid as well as H2 SO4 is reported. It is an improved method compared to conventional synthesis strategies that use stoichiometric amounts of metal-based Lewis acids such as FeCl3 . The resulting high-performance adsorbents exhibit a permanent porosity with high specific surface areas up to 1842 m(2) g(-1) . Easy scalability of the HCP synthesis is proven on the multi-gram scale. All chemo-physical properties are preserved. Water-vapor adsorption shows that the resulting materials exhibit an even more pronounced hydrophobicity compared to the conventionally prepared materials. The reduced surface polarity enhances the selectivity in the liquid-phase adsorption of the biogenic platform chemical 5-hydroxymethylfurfural.
In biorefinery processes often the downstream processing is the technological bottleneck for an overall high efficiency. On the basis of recent developments, the selective liquid phase adsorption applying highly hydrophobic porous materials opened up new opportunities for process development. In this contribution, the efficiency of selective liquid phase adsorption is demonstrated for the separation and purification of itaconic acid from aqueous solutions for the first time. A wide range of different adsorbents was screened, revealing the surface polarity as well as textural properties as critical parameters for their performance. Adsorption from mixed solutions of itaconic acid and glucose exhibited extraordinary high selectivities for adsorbents with highly hydrophobic surfaces, especially certain activated carbons and hyper-cross-linked polymers. Evaluation of the pH dependence showed that the respective molecular species of itaconic acid/itaconate has a major impact on the adsorption performance. Additionally, experiments on a continuously operated fixedbed adsorber were carried out, and the desorption behavior was evaluated. Overall, the technical feasibility of the selective adsorptive removal of itaconic acid from aqueous solutions with hydrophobic adsorbents is demonstrated as a model system for an alternative technology to conventional separation strategies in biorefinery concepts.
The aqueous Ru/C-catalyzed hydrogenolysis of biomass-based polyols such as erythritol, xylitol, sorbitol, and cellobitol is studied under neutral and acidic conditions. For the first time, the complete product spectrum of C2 C6 polyols is identified and, based on a thorough analysis of the reaction mixtures, a comprehensive reaction mechanism is proposed, which consists of (de)hydrogenation, epimerization, decarbonylation, and deoxygenation reactions. The data reveal that the Ru-catalyzed deoxygenation reaction is highly selective for the cleavage of terminal hydroxyl groups. Changing from neutral to acidic conditions suppresses decarbonylation, consequently increasing the selectivity towards deoxygenation.
Porous organic framework materials such as hypercrosslinked polymers (HCP) show a high chemical stability and dynamic behavior in a variety of solvents while their pore properties exhibit great potential for mixed matrix membrane (MMM) applications. However, their influence as porous filler in MMMs, especially for applications in liquid‐phase filtration is still unexploited. Herein, we demonstrate an HCP‐based MMM for molecular separation in the liquid phase by nanofiltration (NF). Depending on the solvent, the membrane changes its fractional free volume by shrinking or swelling. In connection to that, the pore size is also influenced, hence, providing a tunable permeance and molecular cut‐off. The reduction of the pore volume and size directly correlates to the improvement of the NF performance, while the volume increase completely diminishes it. The extraordinary flexibility and high degree of crosslinking assure permanent porosity and render the dynamic behavior fully reversible. Thereby, a solvent‐responsive “on” and “off” switching of the NF properties is enabled and was experimentally proven. Overall, this provides alternative strategies regarding the fouling and regeneration of membranes as well as the inhibition of pore blocking in membrane‐derived processes by a tunable separation performance.
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