Ammonia Fiber Explosion (AFEX) is considered a leading biomass pretreatment process for cellulosic biomass. AFEX treats biomass with concentrated ammonia under pressure at temperatures up to about 100 ^oC. After a few minutes under these conditions, the pressure is rapidly released (the “explosion”). The ammonia evaporates and is recovered. The treated biomass is now much more easily converted by enzymes to sugars and thence to ethanol. In a recent comparative economic evaluation of advanced pretreatments by the National Renewable Energy Laboratory, AFEX performed better than all other pretreatments studied except for the dilute acid process. Improved understanding of the morphological changes and chemical compounds formed during AFEX may further improve the pretreatment performance.

In this presentation we give a broad outline of the morphological changes before and after AFEX process, using scanning electron micrograph (SEM) and laser confocal scanning (LCSM) imaging pictures. The chemical compounds released during the AFEX process are given by liquid chromatography followed by mass spectroscopy (LC-MS) and gas chromatography followed by mass spectroscopy (GC-MS). Supporting insights on lignin phenolics formed and their deposition on the biomass are obtained through the Prussian blue method and Electron Spectroscopy for Chemical Analysis (ESCA), respectively. The potentially inhibitory role of the chemical compounds formed during AEFX on subsequent enzymatic hydrolysis and fermentation will be discussed.