(732f) A Comparison of Environmental Impact of Various Silicas Using Dozn Green Chemistry Evaluator

Silica production constitutes a multi-billion USD market, which continues to grow and include a range of different silica grades/types (e.g. gel, colloids, precipitated, mesoporous, etc.).¹ The increasing demands of precipitated silica from low-value industries (e.g., rubber manufacturing) requires greener production routes which are also economical and efficient. While the high value silicas, such as mesoporous MCM-41 and SBA-15, are highly desired in medicine, pollution control and catalysis, their synthesis is resource and energy intensive.² Learning from biology, bioinspired and potentially sustainable synthesis of high value silica was reported recently with applications in air and water decontamination, biocatalysis, carbon capture, energy storage and drug delivery.³ However, currently, there is a significant lack of data that can inform operational decisions based on sustainability of these different grades of current and emerging silicas.

In order to address this issue, in this study, we compare the environmental impact of a variety of low and high value silicas including fumed, precipitated, sol-gels, mesoporous and bioinspired products. By employing the DOZNâ„¢ tool, which is based on 12 Principles of Green Chemistry, to evaluate different forms of synthesis of chemically identical products, we aim to illustrate the impact of synthetic pathways on the sustainability of a product. Moreover, we quantify the impact of operational decisions, such as calcination vs solvent extraction for purification and drying temperatures. Thus, showing the sustainability costs of operational conditions when working at large scale.

We have found that, although all processes compared resulted in the same chemical product and even started off from largely the same precursors, their synthetic pathways and operational conditions still impacted all major categories of the 12 principles of green chemistry: resource use improvement, energy efficiency and hazard reduction. The results enabled comparison across each of the 12 principles for different silicas in order to identify key differences and reasons behind underpinning the greenness of these products. Therefore, we believe this comparative evaluation represents an ideal case study for the DOZNâ„¢ tool, showing its thoroughness against the simpler E-factors and specific yield analyses, as it includes important considerations like the renewability of feedstocks and the impact of catalysts on the atom economy of processes. Further, it also helps in identifying research areas to focus on in order to make a given synthesis greener.

References:

1. Manning, Brambilaa and Patwardhan, Unified mechanistic interpretation of amine-assisted silica synthesis methods to enable design of more complex materials. Molecular Systems Design & Engineering, 2021, Advance Article DOI: 10.1039/D0ME00131G.
2. Patwardhan, Manning and Chiacchia, Bioinspired synthesis as a potential green method for the preparation of nanomaterials: Opportunities and challenges. Current Opinion in Green and Sustainable Chemistry, 12, 110-116, 2018.
3. Patwardhan and Staniland, Green Nanomaterials, IoP Publishing, Bristol, 2019.