Investigation of Aerogel Production Processes: Solvent Exchange under High Pressure Combined with Supercritical Drying in One Apparatus

Abstract

This work aims to contribute to the theoretical and experimental research of supercritical processes for intensification and combination in one apparatus. Investigation is carried out to improve production technology of organic alginate aerogels. It is proposed within the investigation to carry out the solvent exchange stage, an important stage of organic aerogels production, under pressure in a carbon dioxide medium in the same apparatus used for supercritical drying. The phase behavior in the system “carbon dioxide–water–2-propanol”, which arises during such a solvent exchange stage, is studied theoretically. An experimental study of the process of step-by-step solvent exchange under pressure was carried out through multiphase and homogeneous regions of the phase diagram of such a system. As a result, new highly efficient technology for the production of organic aerogels was proposed, which can be implemented by combining the two main stages of the process.

Surface Properties of Graphene and Graphene Oxide Aerogels for Energy Storage Applications

“…The first stage is considered essential in determining the exact composition of the aerogel. In contrast, the second and third stages are essential to maintain the final shape of the aerogel [36]. Aerogels can be synthesized using some materials, such as graphene, semiconductors, transition metal oxides, carbon nanotubes, and silica.…”

The effect of synthesis conditions and process parameters on aerogel properties

“…If supercritical drying is used, solvent exchange is especially important for the gels that are prepared in aqueous solutions or in solvents which are not soluble in scCO 2 ( Lebedev A. et al, 2021 ). Thus, they should be exchanged with more suitable solvents, commonly alcohols or acetone, with lower critical points and chemical activities to perform supercritical drying under more convenient and economic conditions ( Subrahmanyam et al, 2015 ; Gurikov P et al, 2019 ).…”

“…Moreover, the use of additional zeolites in the same bath to adsorb water kept the concentration gradients high, which increased the speed of diffusion and thus lowered the duration of the solvent exchange. Based on various factors affecting the solvent exchange, understanding its kinetics is a challenging task as the duration of the solvent exchange can vary significantly from hours to several days ( Lebedev A. et al, 2021 ; Schwan et al, 2021 ). In that regard, Raman et al employed a kinetic model to better describe and quantify the solvent exchange kinetics ( Subrahmanyam et al, 2015 ).…”

“…To reduce the time spent on the solvent exchange process, it can be combined with the supercritical drying in one apparatus ( Lebedev A. et al, 2021 ). Instead of placing wet gels several times in pure or mixed solvents, the water inside the pores can be replaced with an organic solvent under pressurized CO 2 .…”

“…The mass transfer under those conditions will be faster than atmospheric pressure, which in turn will reduce the duration of solvent exchange. Lebedev et al developed a model to determine the parameters of the most efficient solvent exchange process under pressure ( Lebedev A. et al, 2021 ). They used 2-propanol as the solvent and studied the ternary system “carbon dioxide-water-2 propanol”.…”