Study On The Pretreatment, Hydrolysis And Fermentation Of Corn Cob

Lignocellulose was widely existed in the nature of renewable resources, amongwhich there were a large number of agricultural by-products such as straw, corn cobs,therefore effective reuse of the agricultural by-products was significant. On the onehand, it could alleviate the energy crisis brought by the lack of coal, oil and otherenergy, on the other hand, it also could solve the environment pollution of burning theagricultural by-products in the traditional way. Many countries were activelydeveloping lignocellulose-ethanol conversion technology, and the United States,Brazil and other countries already had mature production system. In recent years, ourcountry began to constantly develop the lignocellulose energy conversiontechnologies, also for some relatively mature production process, but there stillexisted some factors which were impact on a large scale industrial production, such asthe high cost, low rate of cellulose decomposition etc. So for our country as anagricultural country, lignocellulose-ethanol fermentation technology was particularlyimportant.This paper was divided into three parts, respectively regarding to the conditionsand optimization of pretreatment, hydrolysis and fermentation of corn cob. In the firstpart, corn cob was pretreated by phosphoric acid-sulfuric acid mixed concentratedacid, and the influence of the mass ratio of different mixed acid and pretreatment timeon the cellulose decomposition rate was discussed by calculating the amount of sugargenerated. Experiments show that when the rate of phosphoric acid-sulfuric acid is50:50, pretreatment time is6h, pretreatment achieves the best effect. As can be seenfrom the SEM images, with the increase of pretreatment time, more non-crystallineloose structure of lignocellulose is destructed. The FT-IR spectrum of the residuesindicate that there still exist a cellulose characteristic peak, which means cellulosestructure is not completely broken down. XRD spectra show that after thepretreatment, degree of crystalline of pretreated residual is higher than that of the rawmaterials, which means hemicelluloses and oligosaccharides are destroyed in theprocess of pretreatment. TGA curves of raw material and pretreated residue show thatthe pretreatment of raw materials can change the raw biomass structure, so the thermal stability is changed. This chapter also discussed how ultrasonic affect theeffect on the rate of cellulose decomposition. It shows that adding ultrasonic does nothave obvious effect on the decomposition of cellulose. Finally, the pretreatment effectof the ice acetic acid-sulfuric acid and phosphoric acid-sulfuric acid was compared,founding mixing phosphoric acid-sulfuric acid treatment effect is better in sugarproduction.In the second part, hydrolysis under the best condition of pretreatment is studied,and the effect of hydrolysis temperature and hydrolysis time are respectivelydiscussed to find the highest cellulose decomposition rate of size, and also putting theamount of sugar as the testing standard. Experiments prove that when the hydrolysistemperature is90℃and hydrolysis time is2h, the hydrolysis effect is best. As canbe seen from the SEM images, the hydrolysis of corn cob samples have significantchanges compared with that before the hydrolysis, and cellulose structure damage isobvious. The FT-IR spectrum of the residues indicate that there still exist a cellulosecharacteristic peak, which means cellulose structure is not completely broken down.XRD spectra show that the diffraction peak which refers to the sample of thehydrolysis of cellulose characteristic obviously disappear and crystalline structuregreatly reduced, and it also shows that the hydrolysis process is indeed greatly destroythe structure of cellulose in the corn cob. The TGA curves of raw materials and theresidues show that the hydrolysis can change the biomass cod strcture on the greaterdegree, increase its thermal stability, and residue is increased significantly at the sametime. FT-IR spectrum shows that the hydrolysis has obvious characteristic peaks ofglucose, has generated the glucose, and at the same time, there are a few otherimpurities generated. Finally, the hydrolysis effect of the ice acetic acid-sulfuric acidand phosphoric acid-sulfuric acid was compared, founding mixing phosphoric acid-sulfuric acid treatment effect is better in sugar production.In the third part, the optimal conditions of efficient saccharomyces cerevisiaewas firstly studied, and putting the generated amount of ethanol and the left amountsugar as the testing standard, including the temperature, substrate concentration,inoculation quantity, initial pH and fermentation time and other factors. The resultsshow that the best fermentation condition of angel efficient saccharomyces cerevisiaeis that fermentation temperature:27℃, the substrate concentration:75g/L, thequantity:0.5%, initial pH value:5.0, the fermentation time:65h. Under the condition of the hydrolysate of before fermentation, the ethanol yield equivalent is45%oftheoretical value.