Phosphoric acid activation of recalcitrant biomass originated in ethanol production from banana plants

Biomass samples have been studied as activated carbon precursors. Two, denoted as recalcitrant biomass, are ethanol production wastes, one from acid hydrolysis of starch-rich banana (Musa acuminate) fruit and one from enzymatic hydrolysis of banana pseudostem (lignocellulosic material) and a third one is raw banana tree pseudostem. The samples were characterized by proximate, ultimate, forage, morphological and structural analyses. They all have volatile matter contents above 50% but present some remarkable differences. The sample coming from the acid hydrolysis has too high ash content (mostly calcium sulfate) and low cellulose and lignin contents that prevents its use as an activated carbon precursor. Contrarily, the other two samples have lower ash contents, higher carbon percentages and higher cellulose and lignin contents. The activation with phosphoric acid at 450 °C has been investigated. The results are quite reproducible, showing good porosity developments and a strong dependence on the precursor, the H3PO4 concentration and the H3PO4/sample weight ratio used. The activated carbons have quite high apparent surface area, porosity and yield. Interestingly, the phosphoric acid activated carbons prepared in this work have quite well developed mesoporosity which is especially useful for some applications (e.g. for gasoline evaporative control). Our preliminary comparative study, carried out with a well known commercial activated carbon used to control automobile hydrocarbons emissions, has shown that these activated carbons perform very well, being their performance a function of their mesoporosity development. Their oxygenated surface complexes (assessed from TPD experiments) are considerably high.

This research was entirely funded by MAEC-AECID (Ministry of Foreign Affairs and Cooperation-Spanish Agency for International Cooperation) through projects PCI D/010093/07 and D/017484/08.