The Research On Application Of Ultrasound Technology In Pretreatment And Enzymatic Hydrolysis Of Lignocelulose

With the energy and environmental problems in the world getting worse and worse, fuel ethanol production from lignocellulosic materials is an important alternative to solve these problems and maintain social suastainable development. There are a lot of researches on the pretreatment and enzymatic hydrolysis of lignocellulosic materials, but most researches are focus on the traditional methods of pretreatment and enzymatic hydrolysis of lignocellulosic materials. The research on the pretreatment and enzymatic hydrolysis of rice straw as the lignocellulosic materials via ultrasound technology has not been reported to our knowledge.Firstly, the optimal conditions of acid(H₂SO₄) pretreatment, alkali(NaOH) pretreatment, ultrasound-assisted acid pretreatment and ultrasound-assisted alkali pretreatment were investigated, and the optimal conditions for traditional acid and alkali pretreatment were rice straw in 2% H₂SO₄ or NaOH solution for 60 minutes, the optimal conditions for ultrasound/acid or ultrasound/alkali pretreatment condition were that the rice straw in 2% H₂SO₄ or NaOH solution which was ultrasound-irradiated for 30 minutes at 120W.Secondly the main chemical composition of rice straw which was pretreated by the four different pretreatment was analyzed, The results showed that in contrast to the acid or alkali alone pretreated rice straw, the application of ultrasound technology in acid or alkali pretreatment could make pretreated rice straw has higher cellulose content and lower hemicelluloses and lignin content.Then The enzymatic hydrolysis conditions of these four kinds of pretreated rice straw were optimized by an orthogonal test, and the optimal enzymatic hydrolysis conditions of all the four methods were the same: pH 4.8, temperature 45℃and enzyme loading 20 mg·g-1 substrate. In this condition, the process of enzymatic hydrolysis of four different pretreated rice straw was watched and analyzed, it was indicated by the results that rice straw pretreated by ultrasound-assisted with acid or alkali had the highest concentration of reducing sugar by 26.4 g·L^-1 or 33.0 g·L^-1 after an 108 h enzymatic hydrolysis, and the rice straw pretreated by acid or alkali only had 26.2 g·L^-1 or 32.7 g·L^-1after an 120 h enzymatic hydrolysis.Finally, the main chemical composition of the hydrolysate by the four different pretreatments was analyzed. And the rice straw pretreated by ultrasound-assisted had a higher hydrolysis rate and produced a hydrolysate with higher glucose content and lower xylose content which is more suitable for subsequent fermentation in comparison with the one by acid or alkali alone.In all, the pretreatment with the ultrasound technology has a better result compare to the traditional acid or alkali alone pretreatment.