Environmental assessment of metal-organic framework DUT-4 synthesis and its application for siloxane removal

International audienceIn this study, the effect of different solvents in metal-organic framework (MOF) synthesis was evaluated in a technical study and an environmental study. The technical study considered the octamethylcyclotetrasiloxane (D4) adsorption on MOF DUT-4 for biogas purification, while the environmental study was implemented using the Life Cycle Assessment (LCA) methodology. In addition, the obtained DUT-4 adsorbents were characterized by X-ray diffraction, N2 adsorption-desorption isotherms, solid-state 27Al magic-angle spinning nuclear magnetic resonance, scanning electron microscopy, and Fourier transform infrared spectroscopy techniques. The results indicated that technically similar materials are obtained through solvothermal synthesis with similar D4 siloxane adsorption capacities (9.8 mg/g). Conversely, hydrothermal synthesis led to a low D4 siloxane adsorption capacity (1.8 mg/g). The environmental study demonstrated that the solvothermal synthesis had the highest contribution to the environmental damage due to the use of toxic solvents in the synthesis, cleaning, and solvent exchange stages (environmental score factor up to 244 mPt). In addition, a techno-environmental impact factor was introduced to identify the most suitable synthesis route of DUT-4. The overall results pointed out that solvothermal synthesis is the best scenario for DUT-4 production due to its low environmental impact/adsorption capacity ratio (11.44). This study is a step toward a more holistic approach integrating technical and environmental criteria in MOF synthesis for adsorption applications

Siloxane removal for biogas purification by low cost mineral adsorbent

International audienceThe potential use of raw and expanded perlite as low-cost adsorbents for biogas purification has been investigated. The thermal expansion of perlite causes a reduction in the density of silanol groups from 2515.43 to 653.75 OH/nm2; in contrast, the specific surface area of perlite increased two-fold due to the thermal expansion. To determine the equilibrium adsorption capacity and the adsorption kinetics batch experiments were conducted. The adsorption capacities are in the following order: activated carbon (6.8 mg/g) andgt; silica gel (6.6 mg/g) andgt; expanded perlite (5.8 mg/g) andgt; raw perlite (5.6 mg/g) when compared at the same experimental conditions. The equilibrium adsorption data showed that perlite can be used to reduce the octamethylcyclotetrasiloxane concentration below 28 mg/m3, as recommended by leading manufacturers. The adsorption kinetics of octamethylcyclotetrasiloxane onto raw and expanded perlite followed the Linear-Driving Force model suggesting that the mass transfer is the rate-controlling step. In addition to its low cost, expanded perlite has the advantage of requiring lower desorption temperature (200 °C) for regeneration in comparison to the reported values for activated carbon (andgt;400 °C) and fast desorption kinetics (20 min), which could contribute to a cleaner production of biogas

Electrospun Al-MOF fibers as D4 Siloxane adsorbent: Synthesis, environmental impacts, and adsorption behavior

International audienceHere, we unveil the great potential of metal-organic framework (MOF) composite fibers produced by the electrospinning method to remove D4 siloxane from gaseous solutions. The fibers are based on polyacrylonitrile (PAN) and a microporous aluminum-based MOF known as DUT-4. The electrospinning configuration and DUT-4:PAN ratio in the precursor solutions play an important role in the textural properties of the fibers. Characterizations of morphology and textural properties demonstrated that the best dispersion on the fiber surface was achieved using coaxial electrospinning with a relationship of 1:1.4 of DUT-4:PAN. The Al-MOF fiber composite was evaluated as a D4 siloxane adsorbent, reaching over 85% of the D4 siloxane uptake capacity of individual DUT-4 crystals but with faster adsorption kinetics (effective diffusion coefficient 3.31 times higher). In addition, the synthesis of the composite showed a lower environmental impact and better thermal stability than that observed for DUT-4. This work shows the novel DUT-4 fibers have an outstanding potential for siloxane removal from biogas streams