Carbon dioxide capture using an omniphobic membrane for a gas-liquid contacting process

Long-term stability of PVDF-SiO2-HDTMS composite hollow fiber membrane for carbon dioxide absorption in gas-liquid contacting process

Hybrid polyvinylidene fluoride-silica-hexadecyltrimethoxysilane (PVDF-SiO₂-HDTMS) membranes were fabricated via a non-solvent-induced phase-inversion method to create stable hollow-fiber membranes for use in the membrane contact absorption of carbon dioxide (CO₂). The surface properties, performance characteristics, and long-term performance stability of the prepared membranes were compared and analyzed. The outer surfaces of the prepared membranes were superhydrophobic because of the formation of rough nanoscale microstructures on the surfaces and their low surface free energy. The addition of inorganic nanoparticles improved the mechanical strength of the PVDF-SiO₂-HDTMS. Long-term stable operation experiments were carried out with a mixed inlet gas (CO₂/N₂ = 19/81, v/v) at a flow rate of 20 mL/min. The absorbent liquid in these experiments was 1 mol/L diethanolamine (DEA) at a flow rate of 50 mL/min. The mass transfer flux of CO₂ through the PVDF-SiO₂-HDTMS membrane decreased from an initial value of 2.39 × 10^-3 mol/m²s to 2.31 × 10^-3 mol/m²s, a decrease of 3% after 20 days. The addition of highly stable and hydrophobic inorganic nanoparticles prevented pore wetting and structural damage to the membrane. The PVDF-SiO₂-HDTMS membrane was found to have excellent long-term stable performance in absorbing CO₂.

Predominant Effect of Material Surface Hydrophobicity on Gypsum Scale Formation

Scale formation is an important challenge in water and wastewater treatment systems. However, due to the complex nature of membrane surfaces, the effects of specific membrane surface characteristics on scale formation are poorly understood. In this study, the independent effect of surface hydrophobicity on gypsum (CaSO₄·2H₂O) scale formation via surface-induced nucleation and bulk homogeneous nucleation was investigated using quartz crystal microbalance with dissipation (QCM-D) on self-assembled monolayers (SAMs) terminated with -OH, -CH₃, and -CF₃ functional groups. Results show that higher surface hydrophobicity enhances both surface-induced nucleation of gypsum and attachment of gypsum crystals formed from homogeneous nucleation in the bulk solution. The enhanced surface-induced nucleation is attributed to the lower nucleation energy barrier on a hydrophobic surface, while the increased gypsum crystal attachment results from the favorable hydrophobic interactions between gypsum and more hydrophobic surfaces. Contrary to previous findings, the role of Ca²⁺ adsorption in surface-induced nucleation was found to be relatively small and similar on the different SAMs. Therefore, increasing material hydrophilicity is a potential approach to reduce gypsum scaling.

Materials and logistics for carbon dioxide capture, storage and utilization

The efforts to curtail carbon dioxide presence in the atmosphere are a strong function of the available technologies to capture, store and usefully utilize it. Materials with adequate CO₂ sorption kinetics that are both effective and economical are of prime importance for the whole capture system to be built around. This work identifies such materials that are currently used in CO₂ adsorption beds/columns at different global locations, along with their vital operational parameters, logistics and costs. Three main classes of materials currently in use to that end are discussed in detail here, namely solid sorbents, advanced solvents membrane systems. These materials are then compared in terms of their potential CO₂ uptake, operating parameters and ease of use and implementation of the respective technology. Tabular data are appended to each technology covered with the most relevant advantages and disadvantages. With such comprehensive survey of the recent state-of-the-art materials, recommendations are also made to facilitate the selection of systems based on their CO₂ yield, price and suitability to the geographical location.