Removal and renewal of catalytic coatings from lab- and pilot-scale microreactors, accompanied by life cycle assessment and cost analysis

Microstructured reactors with a layer of heterogeneous catalyst deposited on their walls are widely recognized for their potential applications in chemical industry. However, what is the most preferable way to handle these catalytic reactors once they are deactivated? Is it better to dispose them together with the catalytic layer or is it more preferable to remove the catalytic coating and recycle the microreactor substrate? These questions were followed in the current study by experimental investigations as well as by consideration of environmental concerns and cost evaluation to get a holistic basis for decision making. Uniform Ru/alumina catalytic coatings were synthesized and deposited on stainless steel microstructured substrates. The Ru/alumina sols were applied on lab- and pilot-scale plates (50 x 35 x 1 mm and 150 x 225 x 2 mm, respectively). The quality of the coatings was checked by porosity measurements (N2 adsorption), surface and cross-section imaging (SEM). Afterwards, the mentioned catalytic coatings were successfully removed from the substrates by means of treatment by acidic, neutral and basic solutions. The influence of the removal procedure on the characteristics of the plates (surface roughness) and catalytic coatings (specific surface area, re-coating) was investigated. All methods showed good ability in coating removal without any further mechanic treatment. The best renewal of the catalytic coating was achieved to be 90% depending on the composition of the removal solution which also influences the Ru/alumina properties. In parallel, an analysis of costs and environmental impacts was performed to support the decision towards the most preferable treatment method. For cost evaluation the costs of chemicals and energy provision as well as labour costs and costs of laboratory equipment were considered. The environmental impacts of the catalytic coating and the removal of the coatings were estimated by a simplified Life Cycle Assessment (LCA) taking into account the up-stream processes of chemicals, substrates and energy supply as well as the disposal of process wastes in addition to the coating and removal procedure. Especially by cost analysis, but also by LCA the benefit of the recycling methods became obvious against the disposal of the plates. However, the advantage of the recycled plates was (partially) counterbalanced by the removal procedure. Furthermore, the procedures applied to the plates for pilot scale applications seemed to be more efficient than the procedures for the laboratory scale plates.