Optimization of mild alkaline pretreatment and acid hydrolysis of Typha Australis stems for biofuel conversion

Abstract

Global energy challenges are leading to research into new non-food plant substrates for liquid biofuels. The viability of raw materials plays a crucial role in the efficient biofuels production. Typha Australis, an invasive plant species with high cellulose content, has great potential for alcohol biofuel production; however, it must first be hydrolyzed to liberate fermentable sugars. In this study, typha stems were pretreated with sodium hydroxide (NaOH) at relatively low concentration to enhance its hydrolysis under varying operating variables, central composite design (CCD) was thoroughly examined, i.e. reaction time, temperature and NaOH concentration to predict the lignin removal. And the acid hydrolysis was optimized with a full factorial design. The crystallinity, surface microstructural change and functional group change of both optimally pretreated and untreated typha stem samples were studied. The suitable operating conditions optimized for NaOH pretreatment and acid hydrolysis were as follows: for the pretreatment condition: temperature 119 °C; 2.95% NaOH concentration and 58 min removed high amount of lignin and for the acid hydrolysis: temperature 130 °C concentration acid 3% for 15 min produced high amount of reducing sugar. The predict R² (0.97) was in good agreement with adjusted R² (0.95) for NaOH pretreatment the same also with acid hydrolysis with R²pre = 0.922 and R²adj = 0.863. X-ray diffraction (XRD) determination and scanning electron microscope (SEM) observation showed that the crystallinity index decreased and typha stems surface suffered from serious erosion after the pretreatment. The mild NaOH pretreatment of typha stems significantly enhanced its potential as a promising biomass to produce biofuels.