| Pretreatment technology is a key process of biomass energy utilization. The research of the influence of chemical pretreatment on biomass inner structure and the characteristics of pyrolysis products has important practical significance and commercial value. In this paper poplar and bamboo were taken as the raw materials, and dilute hydrochloric acid and sodium hydroxide solution were used as the chemical pretreatment reagents. We confirmed the optimum technology conditions of acid and alkali pretreatment by orthogonal experiment and range analysis. The changes of microstructure and chemical compoments were investigated after poplar and bamboo were pretreated with acid and alkali reagents. Besides, we analyzed the thermal chemical characteristics and pyrolysis dynamic of biomass, particularly the characteristics of the biochar.Through orthogonal experiment, we investigated the influence of chemical pretreatment time, temperature and dosage on the solid decrement of bamboo and poplar. The reduction of mass was used as evaluation criteria of pretreatment conditios. The optimum acid conditions of bamboo and poplar were 80℃, 1h,5%(v/v) and 80℃, 3h, 5%(v/v) respectively. It was 80℃, 3h, 3%(m/m) for the optimum alkali pretreatment of bamboo and poplar. After acid and alkali pretreatment, the contents of cellulose and hemicellulose from bamboo increased,while lignin was degraded in the pretreatment. The content of cellulose from poplar remained about the same, but the contents of lignin and hemicellulose decreased. At the same time, the contents of ash from bamboo and poplar decreased,too. As for alkali extracting solution of bamboo, the percent of glucose and xylose from the acid was higher. After acid pretreatment, the conent of C from bamboo and poplar increased, and molar ratio of H to C was smaller. But the opposite occurs after alkali pretreatment, the conent of C from bamboo and poplar decreased, and molar ratio of H to C was bigger.With the analysis of SEM and XRD technology, it showed that after acid pretreatment, the bamboo fiber’s surface structure appeared more holes andcracks, and the surface structure of fiber with alkila pretreatment had the obvious peeling phenomenon. With acid and alkali pretreatment, relative crystallinity of bamboo fiber increased, and the acid pretreatment had a better effectiveness.The experiment of TGA method showed that the amount of residue from bamboo pyrolysis both increased after acid and alkali pretreatment, while the value of residue of poplar with acid pretreatment decreased, and it was found to increas for the poplar with alkali pretreatment. In the main pyrolysis process, the mass loss of bamboo with acid and alkali pretreatment and poplar with acid pretreatment increased, but it decreased for the poplar with alkali pretreatment.After acid and alkali pretreatment, the maximum mass loss rate of bamboo and poplar pyrolysis increased, while the peak of bamboo moved to the high temperature, and it moved to the low temperature for poplar.We researched the kinetics of biomass pyrolysis by Coats-Redfern’s method.The results indicated that after the acid and alkali pretreatment, the reactive activation energy and frequency factor of bamboo increased, and it was the same For poplar,in low temperature,the reactive activation energy and frequency factor increased after alkali pretreatment, and it was opposite to acid pretreatment. But in high temperature, acid and alkali pretreatment had different effect on the reactive activation energy and frequency factor of poplar, it increased for acid pretreatment and decreased for alkali handing.With the analysis of TG-FTIR and TG-GC/MS, it indicated that the gas products of bamboo and poplar pyrolysis contained high concentration of carbon dioxide, followed by H2 O, and finally, Phenols, aldehydes, hydrocarbons, etc.After acid and alkali pretreatment, the carbon dioxide production of bamboo fell,and it fell more for acid pretreatment. While the CO2 production of poplar with alkali pretreatment was higher than the one without pretreatment, and after acid pretreatment, poplar had the lowest production of CO2. The strongest proton abundance of bamboo with acid ang alkali pretreatment appeared at 20.31 min and 20.32 min of retention time respectively, and for bamboo without pretreatment, the abundance was at 18.29 min. There were 15 kinds of pyrolysis products for bamboo without pretreatment, the content of N-methyl-1,3-propanediamine is the highest, followed by4-(2-(Methylamino)ethyl) pyridine. The pyrolysis product kinds of bamboo withacid and alkali pretreatment were 15 and 13, respectively. The main product is quinoline for acid pretreatment, and oxazine for alkali pretreatment. As for bamboo with acid pretreatment, the contents of 2,3-dihydro-benzofuran and2-hexynoic acid were 13.95% and 13.45%, lower than quinoline. There were16.33% of butanal and 10.84% of ethanol producted from bamboo alkali-treated pyrolysis, which was next to the content of oxazine.The experiment of bamboo pyrolysis was taken at laboratory scale, and the results showed that the optimum condition of making biochar was as follow:temperature, 400℃; time, 5min. The production of biochar from bamboo with acid and alkali pretreatment was lower than the one without pretreatment. After acid and alkali pretreatment, the production of biochar decreased from the original 33.41% to 28.30% and 36.71%, respectively. Organic elemental analytical results demonstrated that the highest content of C element in the biochar of bamboo with alkali pretreatment, of which the molar ratio of H to C was smallest. We found that acid and alkali pretreatment increased the values of surface area, pore valume and average pore size of biochar from bamboo pyrolysis. Acid pretreatment had the greatest influence on the characteristics of biochar, and the values of surface area, pore valume and average pore size of biochar increased 10 times. The acid and alkali pretreatment also increased relative crystallinity of biochar, and the acid pretreatment had a better effectiveness.KEY WORDS: biomass, chemical pretreatment, pyrolysis, kinetics, biochar,... |
PDF Full Text Request