(686f) Diazomethane Permeability Study across Teflon AF 2400 Membrane Using Tube-in-Tube Module

Diazomethane, the most atom economic C1 building block in organic chemistry with numerous chemical pathways, has found only limited use on laboratory and industrial scale due to challenging safety profile, particularly in gaseous phase. In-situ adaptation of diazomethane generation, separation, and consumption has been developed over the past decade, most notably the application of Teflon^TM AF2400 membrane tube-in-tube module. This has enabled easy usage and reproducibility of experimental data and represents the state-of-the-art for continuous on-demand delivery of diazomethane at laboratory scale. For scale-up purposes, a known value of diazomethane permeability is required.

Despite permeability characterisation of other small molecules, either by delivery or extraction of gas from or to liquid, safety profile of diazomethane necessitated development of a suitable methodology for measuring permeability across the membrane by handling a liquid phase on both sides.

The aim of this work was to develop an experimental methodology to study the full mass balance of diazomethane within the tube-in-tube reactor with a numerical model to evaluate the experimental results and provide an estimation on the diazomethane permeability across the AF 2400 membrane. Convection-diffusion model was modified for liquid-liquid system and using COMSOL Multiphysics 3.7 software was used to fit computational model to the experimental results, both limited by the solubility limit of diazomethane in organic solvent.

Parameter estimation of diazomethane permeability in AF2400 provided a value of 1,863.55 Barrer. Comparison to molecules of similar kinetic diameter, such as methane (340 Barrer, 3.80 Å) or ethylene (350 Barrer, 3.90 Å), diazomethane (3.86 Å) showed unexpectedly high permeability. This indicates strong influence of its solubility in the membrane, which is directly proportional to its high boiling point of -23°C. Results enable scale-up pathway towards larger membrane modules and the methodology developed herein can be translated for study of alternative membranes suitable for diazomethane separation.