Microwave Plasma Pyrolysis of Biomass: Process and Applications

In order to meet the growing demands of an increasing global population without irreversibly depleting the planet’s resources in the face of a rapidly changing climate a sustainable circular economy will need to be adopted, one based on renewable biologically derived materials. The Microwave Plasma Pyrolysis (MPP) process detailed in this dissertation is intended to help enable this transition by establishing a standard methodology for the conversion of renewable biological material feedstocks like hemp and fungi into high-value end products capable of replacing non-renewable or petroleum-based products in a scalable and efficient manner. To this end a custom MPP system is designed and built around a common kitchen microwave oven and tested with commercially available hemp-based canvas fabrics as well as fungal samples collected from the Dallas ecosystem. It is found that the MPP process converts biomass into a matrix of carbon phases including graphite and a form of diamond called Ultrananocrystalline Diamond (UNCD) while retaining the original sample’s superstructure. The pyrolyzed biomass is investigated via a variety of complementary physical and chemical characterization techniques and is shown to possess hierarchical porosity at the macro, micro, and nanoscales. Being that this is the first time it has been reported that diamond can be produced from a biological source in such a rapid and efficient manner, a mechanism is discussed to explain this unique transformation, with comparisons to conventional methods of diamond growth and production. The application demonstrated in this dissertation as an air filtration membrane is influenced by the global COVID-19 viral pandemic, which exposed serious failure modes in conventional facemask systems based on non-woven electro-spun or melt-blown polypropylene fibers. Since a fully sized facemask derived from pyrolyzed fungal mycelium or hemp canvas was not feasible during this dissertation research, a unique methodology derived from TEM grid particle sampling research was developed utilizing additive manufacturing and tested in collaboration with an industry standard FDA aerosol mask testing setup using electrostatically neutral salt particles. Further functionalization and enhancement of the plasma pyrolyzed biomass is demonstrated through Microwave Plasma Chemical Vapor Deposition (MPCVD), used to deposit additional layers of diamond and other nanocarbons including graphite and graphene. Prior work in the literature investigating applications of conventionally pyrolyzed biomass have included energy storage in the form of high surface area nanocarbons for battery electrodes and as performance enhancing additives in composites.