Extractives Of Pretreated Lignocellulose And Its Effect On Saccharification And Fermentation

The rapid development of the economic bring burden to the environment,and looking for sustainable clean energy become more and more urgent for solving the environmental problem and economy development.Because the lignocellulose is rich and renewable,cellulosic ethanol is considered as a promising new clean energy.During the production of bioethanol,lignocellulose must to be pretreated firstly for breaking the natural biomass resistibility by destroying tight and complex structure of lignocellulose,which improve enzymatic digestibility of biomass.However,the structure and properties of cellulose,hemicellulose,and lignin of lignocelluloses are changed,and extractive content from lignocellulose is often increased after different methods pretreatment.The chemical components of water extractives are complex,which may affect the accuracy measurement of sugars in pretreated lignocelluloses and enzymatic hydrolysis and ethanol fermentation.The accurate determination of three components of lignocellulose is the important for the research and evaluation of enzymatic digestibility and biocoversion of cellulose to ethanol.The understanding on effect of extractive components on enzymatic hydrolysis and ethanol fermentation is also important for improving bioconversion efficiency of cellulose.The thesis studied the effect of extractive of lignocellulose on analysis of chemical components and saccharification and fermentation of lignocellulose.The results are as follows:?1?The contents of water-and alcohol-extractives of poplar are increased after different methods pretreatment,especially acid pretreatment?dilute H₂SO₄ and acidic sodium sulfite?.There are many oligosaccharides and monosaccharides such as glucose,xylose,etc.resulted from cellulose and hemicellulose in water extractives of pretreated poplar because the sugars are easily extracted out by water,but there are little sugars in ethanol extractives.Therefore,it is recommended that the contents of the sugars extracted by water should be determined by acidic hydrolysis on the suitable conditions and be calculated separately to the cellulose and hemicellulose content of pretreated biomass for more truly reflecting the sugars contents of biomass and calculating the conversion ratio of cellulose to ethanol during bioconversion of lignocelluloses.?2?Effect of acidic hydrolysis time on sugars contents in hydrolysis liquor in the stage of acidic hydrolysis with 4%H₂SO₄ during determination of chemical components of untreated,acidic NaHSO₃ and alkaline NaHSO₃ pretreated poplar based on NREL method are studied.It is found that the cellulose and hemicellulose of pretreated poplar is easily degraded,which should because of their structure and chemical characteristics changing after pretreatment.Therefore,it is recommended that the duration of acidic hydrolysis stage in the component analysis process should be appropriately shortened according to the actual situation to prevent the excessive degradation of carbohydrates,especially for acidic pretreated raw materials.?3?Chemical components of water extractives are analyzed and found that there are more by-products,such as furfural,5-HMF,formic acid and acetic acid,etc.in the water extractives of acid pretreated poplar,which inhibited saccharification and fermentation of cellulose in lignocelluloses.In the ethanol extractives of acidic NaHSO₃ pretreated poplar,for example,it is found by GC-MS analysis that there are aldehydes,phenols,ketones,acids,alcohols,lipids,and so on.The components inhibited the saccharification and fermentation of lignocellulose through inhibiting the activity of cellulase or unproductive adsorption on cellulase protein.?4?After pretreated poplar was washed by water,enzymatic digestibility of dilute H₂SO₄ and acidic NaHSO₃ pretreated poplar could be improved.We also found that it is more effective for improving enzymatic hydrolysis by increasing washing water volume and washing frequency compared with increasing washing time.Relatively,the cyclic washing is an effective method for improving enzymatic hydrolysis of pretreated biomass after choosing a suitable water volume.?5?It was also shown that although ethanol yield can be increased during Q-SSF of dilute H₂SO₄ pretreated poplar by water washing,ethanol yield during Q-SSF of acidic NaHSO₃ pretreated poplar is decreased by water washing.Lignosulphonate could be produced during acid NaHSO₃ pretreatment of poplar.It is found that water extractive containing lignosulphonate could promote the Q-SSF of lignocelluloses and avicel.The Q-SSF of avicel is also promoted during Q-SSF after adding pure lignosulphonate.And yeast strain number is increased in culture medium after by adding water extractive and pure lignosulphonate,speculated that lignosulphonate may play a role in promoting Q-SSF process of lignocellulose by promoting growth of yeast,which will be investigated in further work.