The Hydrolysis Of Cellulose To Glucose By Solid Acid Catalyst And Dietary Safety Evaluation Of Glucose Concentrate

Glucose is one of the most important fundamental materials in food,biological,medicinal,chemical and energy industry.However,the problem of food security caused by the traditional way of hydrolysis of starch to provide glucose is becoming more and more serious.Cellulose is the main component of biomass,which exists widely in nature.Therefore,the hydrolysis of cellulose to glucose has great scientific value and economic value.At present,acid hydrolysis,enzymatic hydrolysis and super/subcritical hydrolysis are the commonly used methods reported in the literature,but these methods have many shortcomings,which have seriously hindered the hydrolysis of cellulose to high quality glucose industrial development.Because the drawbacks of the hydrolysis of cellulose,the concept of heterogeneous catalytic hydrolysis of cellulose emerges at a historic moment.The solid acid catalyst is put forward in this case.Compared with other methods,the hydrolysis of cellulose by solid acid catalyst has many advantages: the product is easy to be separated,and the catalyst is recyclable,little corrosion to the equipment and environment friendly.Silica sulfuric acid is a kind of solid acid supported on silica gel.At present,silica sulfuric acid is mainly used for the study of the synthesis of organic compounds.My study is associated with the application of silica sulfuric acid in the hydrolysis of cellulose in order to provide a new green method for converting cellulose into glucose.Silica sulfuric acid catalyst was prepared by silica gel and chlorosulfonic acid firstly.Then,the production process of glucose by the hydrolysis of cellulose with silica sulfuric acid was optimized,and the technological conditions of decolorization and detoxification of cellulose hydrolysate were studied.Finally,the toxicological evaluation of glucose concentrate was made.The results of the study are as follows:1.Silica sulfuric acid catalyst was prepared by using silica gel and chlorosulfonic acid as raw materials.The catalyst was characterized for functional groups,surface morphology,thermal stability and surface properties by infrared spectroscopy（IR）,scanning electron microscopy（SEM）,X ray diffraction（XRD）,differential scanning calorimetry（DSC）and acid-base titration analysis.IR analysis showed that besides the comman vibrational peaks of the functional groups with silica gel,the antisymmetric stretching vibration peak and the symmetric stretching vibration peak of O=S=O,as well as the stretching vibration peak of S-O bond were found in the catalyst.These features indicated that the sulfonic acid group was successfully introduced into catalyst.Through SEM and XRD spectrum analysis,we know that the particle size of catalyst was smaller than silica gel and it had no definite shape.DSC curve showed that the chemical interaction of chlorosulfonic acid and hydroxyl group on the surface of the carrier successfully took place,which means the formation of silica sulfonic acid group.Neutralization titration indicated that the catalyst surface acid was 6.8 mmol/g.The surface acidity on sulfuric acid catalyst in my study was higher than sulfuric acid catalyst prepared by shaterian research group.The possible reason may be that the quality of chlrosulfonic acid and the hydroxyl of silica gel were more.2.The prepared silica sulfuric acid was used to catalyze the hydrolysis of cellulose,and the cellulose conversion and glucose yield were used as the indexes to evaluate the catalytic activity.On the basis of result of single factor experiments,the experiment by using Box-Behnken design involving the reaction temperature,time,dosage of catalyst and the amount of water was carried out.Data fitting by using Design-expert software indicated that the optimum reaction conditions for preparing glucose were reaction temperature 137.64℃,reaction time 2.16 h,catalyst dosage 0.5 g,the amount of water 11.67 ml.The calculation via the regression equation showed that the conversion rate of cellulose was 80.09% and the yield of glucose was about 50.99%.Considering the operability,the optimum process conditions were modified to be reaction temperature 138℃,reaction time 2.2 h,catalyst dosage 0.5 g and the amount of water 12 ml.Under the conditions,the conversion rate of cellulose and yield of glucose were 82.23% and 51.15% respectively,which were consistent with the theoretical predictions,proved that the model was reliable.GC-MS was used for qualitative analysis of the by-products in hydrolysate under the optimum conditions,which showed that the main by-products in the hydrolysate were mainly 5-hydroxymethylfurfural,levulinic acid,furfural,acetic acid and formic acid.3.Combaining excess Ca（OH）₂ neutralization with activated carbon adsorption method was used for detoxification and decolorization of the cellulose hydrolysate.Firstly,the cellulose hydrolysate was pretreated by Ca（OH）₂ to remove some of the furan impurities,and then activated carbon was used for decolorization of the cellulose hydrolysate.In order to get the best decolorizing process of activated carbon to the hydrolysate,the investigation of effects of carbon content,pH and decolorization time on the decoloration effect of cellulose hydrolysate by single factor experiments were carried out,and then on the basis of the single factor experiments,the orthogonal experiment was used to optimize the conditions of amount of activated carbon,pH and decoloration time.The optimum conditions of decolorization process were as the following: activated carbon dosage 4 g/L,pH6.0 and decolorization time 20 min.4.The toxicological evaluation on the safety of glucose concentrate obtained by decolorization,detoxification and rotary evaporation was carried out.The healthy SPF Kunming mice were selected as the subjects,and the acute toxicity test and the 30 day feeding test were carried out orderly.Through acute toxicity test of glucose concentrate,we know that there were no obvious symptoms of poisoning and no deaths by fourteen observation after intragastric administration.In addition,no abnormality was found in mice viscera after dissection and there were no significant differences in body weight,organ coefficient,hematological index between the testing and control groups.The obove results showed that the oral LD50 of the glucose concentrate in Kunming mice is greater than 19.2 g/kg,which means that the glucose concentrate was non-toxic according to China’s food acute toxicity grading standards.The results also showed that there were no significant differences in body weight,organ coefficient and histopathological examination between the testing and control groups after 30 d feeding test.However,there was a significant difference in total cholesterol compared the high dose group of female mice with the same sex in control group,but it was still within the reference range of our laboratory and no dose-response relationship,so it had no toxicological significance.The results showed that the glucose concentrate didn’t damage the liver,spleen,lung and kidney of mice.