3D printed triply periodic minimal surfaces as advanced structured packings for solvent-based CO2 capture

Point-source CO2 capture is a critical technology for industrial decarbonization and certain CO2 removal processes. Solvent-based CO2 absorption is a mature process, but the capital investment and energy requirements are substantial, especially when economic drivers for its deployment are tenuous. We utilized additive manufacturing and computational fluid dynamics to screen and prototype structured packings in the vast design space accessible via advanced manufacturing and computer-aided design. 3D-printed triply periodic minimal surfaces (TPMS) were tested as advanced packing geometries for CO2 capture from simulated flue gas (10% CO2) and evaluated alongside a representative industrial packing geometry, Mellapak 250Y. 1D model fits of experimental absorption data revealed 49-61% increases in mass transfer performance (kLaeff) and 91-140% increases in effective gas-liquid interfacial area in TPMS packings (Gyroid and Schwarz-D) compared to 250Y. These advanced structured packings also featured similar or better maximum fluid loads and pressure drops than 250Y, reinforcing their industrial potential. Together with the capability to natively distribute fluid shown by the TPMS geometries, the performance improvements realized could reduce absorber capital costs by more than 30%.</p

Kinetic and Mechanistic Examination of Acid–Base Bifunctional Aminosilica Catalysts in Aldol and Nitroaldol Condensations

The kinetic and mechanistic understanding of cooperatively catalyzed aldol and nitroaldol condensations is probed using a series of mesoporous silicas functionalized with aminosilanes to provide bifunctional acid–base character. Mechanistically, a Hammett analysis is performed to determine the effects of electron-donating and electron-withdrawing groups of para-substituted benzaldehyde derivatives on the catalytic activity of each condensation reaction. This information is also used to discuss the validity of previously proposed catalytic mechanisms and to propose a revised mechanism with plausible reaction intermediates. For both reactions, electron-withdrawing groups increase the observed rates of reaction, though resonance effects play an important, yet subtle, role in the nitroaldol condensation, in which a <i>p</i>-methoxy electron-donating group is also able to stabilize the proposed carbocation intermediate. Additionally, activation energies and pre-exponential factors are calculated via the Arrhenius analysis of two catalysts with similar amine loadings: one catalyst had silanols available for cooperative interactions (acid–base catalysis), while the other was treated with a silanol-capping reagent to prevent such cooperativity (base-only catalysis). The values obtained for activation energies and pre-exponential factors in each reaction are discussed in the context of the proposed mechanisms and the importance of cooperative interactions in each reaction. The catalytic activity decreases for all reactions when the silanols are capped with trimethylsilyl groups, and higher temperatures are required to make accurate rate measurements, emphasizing the vital role the weakly acidic silanols play in the catalytic cycles. The results indicate that loss of acid sites is more detrimental to the catalytic activity of the aldol condensation than the nitroaldol condensation, as evidenced by the significant decrease in the pre-exponential factor for the aldol condensation when silanols are unavailable for cooperative interactions. Cooperative catalysis is evidenced by significant changes in the pre-exponential factor, rather than the activation energy for the aldol condensation

Sequence of Hydrophobic and Hydrophilic Residues in Amphiphilic Polymer Coatings Affects Surface Structure and Marine Antifouling/Fouling Release Properties

Amphiphilic polymers, specifically combinations of hydrophilic and hydrophobic residues, have been shown to be effective as antifouling materials against the algae <i>Ulva linza</i> and <i>Navicula</i> diatoms. Here we use the inherent sequence specificity of polypeptoids made by solid-phase synthesis to show that the sequence of hydrophilic (methoxy) and hydrophobic (fluorinated) moieties affects both antifouling and fouling release of <i>U. linza</i>. The platform used to test these sequences was a polystyrene-<i>b</i>-poly­(ethylene oxide-<i>co</i>-allyl glycidyl ether) (PS-<i>b</i>-P­(EO-<i>co</i>-AGE)) scaffold, where the polypeptoids are attached to the scaffold using thiol–ene click chemistry. The fluorinated moiety is very surface active and directs the surface composition of the polymer thin film. The position and number of fluorinated groups in the polypeptoid are shown to affect both the surface composition and antifouling properties of the film. Specifically, the position of the fluorinated units in the peptoid chain changes the surface chemistry and the antifouling behavior, while the number of fluorinated residues affects the fouling-release properties