Life cycle assessment of novel aerogels based on lignocellulosic residues from agriculture and forestry

Kurzfassung

The environmental impacts of aerogel synthesis from lignocellulosic residues are analyzed using the Life Cycle Assessment (LCA) approach. All steps in the process chain, cradle-to-gate, are considered: from agricultural processes to cellulose extraction, the preparation of wet-gel beads and alcogels, and aerogels obtained by drying with supercritical carbon dioxide. Two methods of cellulose extraction are discussed. Life cycle inventory was built using primary data from the laboratory and with support of the Sphera LCA for Experts software. Environmental impacts are quantified using the functional unit of 1 kg of lignocellulosic-based aerogel. The focus is to assess the contribution of each process to the overall environmental performance and to identify hotspots during production. A comparison of the individual unit operations of the process chain shows that the alcogel preparation, followed by cellulose extraction, contributes most to the overall impact. This is predominantly caused by the supply of ethanol, acetic acid and 2-methyltetrahydrofuran. As aerogel preparation was carried out on a laboratory scale, these results can be regarded as a conservative estimate and thus serve as a basis for process optimization during scale-up. With the assumed improvements during scale-up and in a scenario for 2050, significant reductions in environmental impacts can be achieved, e.g., by 87 – 92% in terms of the greenhouse gas balance, by 75 – 87% in terms of acidification and by 92 – 94% in terms of resource availability. However, a comparative LCA with chosen benchmarks shows that lignocellulosic-based aerogels are not yet fully competitive.