Research On Simultaneous Saccharification And Fermentation For Ethanol With Raw Corn And Kinetic

Fuel ethanol,as a biofuel with promising prospect,always attracts tremendous attention.In china,fuel ethanol is mainly produced by microbial fermentation and the most widely used starch materials is corn.Compared with traditional fermentation,the simultaneous saccharification and fermentation with uncooked materials can not only reduce energy consumption and simplify the processes,but it also has advantages in decreasing the viscosity and substrate inhibition.However,the uncooked fermentation technology also has some drawbacks,such as bacterial contamination.What's more,the enzymes,yeast and raw materials are in one same fermentation tank,which makes the fermentation process become difficult to control and forecast.How to improve the product concentration and analyze the fermentation process quantitatively has become an important step in fermentation research.In this paper,the influence of common process factors on the simultaneous saccharification and fermentation with uncooked corn material was studied.In addition,two reparameterized fermentation kinetic models were applied to correlate the ethanol concentration,which were obtained by the analogy of the yeast growth kinetic.The models can be used to represent the kinetics behavior of ethanol concentration in fermentation,which not only have potential to predict ethanol concentration in industry but provide the theoretical basis for fermentation process optimization and prediction.By measuring total sugar,reducing sugar,ethanol concentration and pH with time,we analyzed the influence of substrate concentration,particle size,initial pH on the fermentation and found that the concentration of ethanol would be affected by the process factors.Firstly,the ethanol concentration and residual total sugar concentration would increase with increasing of the substrate concentration,but was almost not affected by the particle size.The simultaneous saccharification and fermentation with uncooked corn was carried out under the following conditions:3.5‰yeast addition amount,the ratio of material to water 1:2.0,over100 mesh sieve and natural pH.In this condition,the largest ethanol concentration was 102.37g/L.Secondly,using acid to adjust the initial pH in the fermentation tank could help to inhibit the bacteria,thus lowering the fermentation tank liters acidity and improving ethanol concentration.Considering the real conditions in industry,the simultaneous saccharification and fermentation with the uncooked corn was conducted under the following conditions:over40 mesh;the ratio of material to water 1:2.0,initial pH 4.5.In this condition,the maximum ethanol concentration was 102.59 g/L and the optimum quantity of yeast was 3.5‰g/?g.raw material?.Different from traditional Logistic model,the reparameterized fermentation kinetic models?Logistic model and Gompertz model?were applied to describe the ethanol concentration vary with the time under the different conditions of the ratio of material to water and mesh factors.The imitation degrees R² of two reparameterized fermentation kinetic model were all bigger than 0.9200.Therefore,the reparameterized fermentation kinetic models have potential to predict ethanol concentration in industrial fermentation.The parameters P_max,v_max and?in two models all increased with increasing the ratio of material to water,which could explain the influence of different substrate concentration on the simultaneous saccharification and fermentation perfectly.Compared reparameterized Logistic model with reparameterized Gompertz model,the modified Gompertz model could describe fermentation process with higher R² value than reparameterized Logistic model,in addition,the Gompertz model predicted values were closer to experimental values and the relative error was smaller.Therefore,the modified Gompertz may be more effective in the prediction of the ethanol fermentation process than the Logistic model.