Optimalizace přípravy uhlíkatých materiálů ze zemědělské biomasy v mikrovlnném poli

Abstract

This bachelor thesis deals with preparation of carbonaceous materials by microwave pyrolysis of two waste agricultural raw materials - corn cob and red mombin seeds. Thermo-chemical properties of both raw materials are studied. Via optimizing of individual parameters of preparation/microwave pyrolysis (i.e. weight of raw material batch - 20 g versus 60 g, nitrogen atmosphere - flow versus batch and addition of activating agent ZnCl2) biochars and activated carbons are prepared, their elemental and chemical composition, textural and structural properties are characterized. The effect of individual parameters of preparation/microwave pyrolysis of both waste raw materials on the composition of pyrolytic gas is also evaluated. It was revealed that both raw materials possess similar elemental composition and contain the same amount of fixed carbon and volatile combustibles, but the corn cob contains more ash and less moisture than red mombin seeds. Biochars prepared from corn cob show lower fixed carbon content and higher ash content than biochars prepared from red mombin seeds. The addition of activating agent ZnCl2 to corn cob, regardless of the raw material mass, reduces the fixed carbon content and increases the volatile combustibles content in prepared activated carbon, suggesting that pyrolysis of this activated feedstock in a microwave field could take few minutes longer. The addition of ZnCl2 to red mombin seeds in 20 g batch reduces the fixed carbon amount and increases the volatile combustibles amount, which indicates prolonged pyrolysis time, in 60 g batch reduces the fixed carbon amount and increases the ash amount, indicating carbon structural changes or insufficient removal of activator transferred to ash. While biochars from both raw materials are microporous materials with inhomogeneous low-surface mesopore/macropore network, activated carbons are highly microporous-mesoporous materials. The addition of ZnCl2 to both raw materials contributes to formation of extensive high-surface mesopore network (with pore-size < 20 nm) and enlargement of micropore-size of activated carbons, but does not affect the micropore volume. Biochars from corn cob, but activated carbons from red mombin seeds are the best from the texture view. The rate of carbon graphitization cannot be clearly evaluated. Regarding the composition of pyrolytic gas, the addition of ZnCl2 to both raw materials leads to the increase in H2 production and decrease in CH4 production. Changing the weight of raw material with activator (from 20 g to 60 g) leads to the increase in CO2 production.