Abstract:
Two-stage microwave pretreatment (microwave/NaOH pretreatment followed by microwave/H2SO4 pretreatment) successfully released monomeric sugars from various types of Thai grasses, namely. Mission grass (Pennisetum polystachyon). Kans grass (Saccharum spontuneum). Giant reed (Arundo donax), and Tiger grass (Thyscmolaenu maxima). The optimum conditions of the pretreatment were investigated, and the maximum monomeric sugar yields were compared. The microwave-assisted NaOH and H2SO4 pretreatments with 15:1 liquid-to-solid ratio were studied by varying chemical concentration, reaction temperature, and reaction time to optimize the amount of the monomeric sugars. The changes in structure of grasses were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). Of all grasses studied, the one giving the most amount of monomeric sugar was chosen to study the ethanol production. After the grass underwent through the two-stage pretreatment, it was subjected to enzymatic hydrolysis. Glucose, the source of ethanol fermentation, was obtained after the hydrolysis process. The grass hydrolyzate was over limed at various pHs; and then sodium sulfite was added to remove inhibitory compounds and degradation products, such as furfural and hydroxymethylfurfural. Yeast population count was studied under a microscope. The change of glucose concentration in the hydrolyzate was detected by high performance liquid chromatography (HPLC), and the production of ethanol was determined using gas chromatography (GC).
