A comparative life cycle assessment of the synthesis of mesoporous silica materials on a small and a large scale†

Silica mesoporous materials have been the subject of wide scientific interest with various applications. However, the environmental impacts associated with their preparation have scarcely been studied. In the present work, we applied the Life Cycle Assessment (LCA) methodology to the materials MCM-41, MCM-48, UVM-7, mesoporous Stober particles, SBA-15, SBA-16, HMS, KIT-5, KIT-6, MSU, FDU, nano-MCM-41 and nano-MCM-48 for small- (grams) and large-scale (several kilograms) production. Furthermore, various improvements are proposed, and the impact associated with each of them is quantified. The results show that the values of a single score, a normalized and weighed combination of the damage categories, and net greenhouse gas emissions (NGHGE) are highly dependent on the synthesis procedures. On a small scale, the main impact is due to the use of energy and solvents. By contrast on a large scale, the use of solvents, tetraethylorthosilicate and the structure directing agent are the main determinants. From the values obtained for the different materials and scenarios, we estimate that the preparation of this class of materials could have an NGHGE of 54 ± 30 and 31 ± 18 kg CO₂ eq. per kg of mesoporous material for small- and large-scale production, respectively. The use of calcination versus extraction, the incorporation of renewable energy and distillation/rectification are initiatives that can contribute to a significant reduction of the environmental impact.