Transmutation Of Structure And Properties In The Preparation Of Chestnut Shell Based Biochar

The discarding and directly burning of a large number of chestnut shell, have caused some environmental pollution and resources waste, so it will be benefit to our society, economy and environment to make good use of the abandoned chestnut shell. Chestnut shell based biochar with high calorific value has been made through pre-oxidation and carbonization in two cases, without and with catalyst, according to the innate advantages of chestnut shell at carbon content and calorific value. The pyrolysis behaviors and the transmutation of both the structure and properties during the carbonization were investigated.The pyrolysis behaviors of chestnut shell have been studied by TG and GC-MS. Results show that there are three stages of pyrolysis of the chestnut shell and the TG curve slightly shifts to higher temperature as the heating rate increases. With catalyst, the TG curve slightly shifts to low temperature at the same heating rate. With the pyrolysis temperature increasing, the weight proportion of CO2 in pyrolysis products goes up, acetic acid and levoglucosan emerge earlier, while furans decrease obviously. The catalyst restrains the levoglucosan's generation, and helps furans increase when temperature goes up.The transmutation of elements composition, groups and crystalline structure in pre-oxidation and carbonization have been investigated by element analysis tester, FT-IR and XRD respectively. As the process temperature increases, carbon element content increases gradually and carbon network grows up. When adding catalyst, element contents of every stage change, hydrogen and oxygen eliminate more often by the form of H2O, and the carbon network forms earlier.The microstructure of samples, without or with catalyst, in pre-oxidation and carbonization has been studied by SEM. As the process temperature increases, the holes on surface shrinks and the porosity of cross section become bigger, while network structure grows to be regular. The catalyst makes the network structure of cross section emerge earlier and the surface becomes turtle shell shape. The yield and density of samples in pre-oxidation and carbonization, without or with catalyst, have been studied, and the transmutation of calorific value has been investigated by oxygen bomb calorimeter. Results show that the yield decreases as the process temperature increases, and the transformation of density is undulation. Calorific value goes up slowly in pre-oxidation process, while in carbonization, it increases quickly. The chestnut shell based biochar with 38.17% yield and 30.75MJ/Kg calorific value has been prepared at 750℃. Adding catalyst has improved the density, yield and calorific value. With the catalyst, the chestnut shell based biochar with 44.31% yield and 35.48MJ/Kg calorific value has been obtained at 750℃.