Pretreatment Of Lignin In The Lignocellulose By Atmospheric Pressure Plasma And Investigation Of Its Interaction Mechanism

Atmospheric pressure plasma oxidation, which is a newly developed technology for lignin oxidation and degradation, is believed to have the total effect of UV-photolysis, high energy electron radiation and ozone oxidization. In the process of plasma discharge treatment,hydroxyl radicals(·OH), which shows strong oxidizability, could be produced in large amounts, resulted in obvious effect of decomposing organic compounds into harmless inorganic substances. Comparing with traditional methods for lignin degradation, atmospheric plasma oxidation treatment shows many advantages. Desirable results can be obtained in a very short period of treating time with simple and convenient operations. Besides, there is no secondary pollution through out the process. Moreover, it’s much more economic than any other treating methods. In order to obtain an environmental friendly and effective degradation method, guaiacol solution and lignosulfonates were treated with atmospheric pressure plasma and the treating conditions were optimized respectively. Chemical structure change of lignin under optimum treating conditions was researched.Guaiacol solution, which was one of the typical model compounds of lignin, was oxidized by plasma device. The optimal condition of guaiacol degradation was explored through an orthogonal experiment L25(53). Results showed that concentration 20mg/mL of guaiacol solution, discharge power of 90 w and 10 min were assigned as an optimal degradation condition by plasma. In comparison with W-TiO2 degradation method, plasma treatment shows great potential in application with admirable degradative effect and simple process. UV-visible spectrophotometer(UV), Fourier transformed infrared spectroscopy(FTIR)and nuclear magnetic resonance(1HNMR) were used to characterize the degradation product.It can be concluded that during the reaction process, the benzene ring-opening reaction was occurred while the ultraviolet absorption peak shifts to the long wavelength, as a result, the guaiacol was degraded by plasma.The orthogonal experiment L25(53) was designed to discuss the optimal degradation conditions of lignosulfonates by plasma. The optimum conditions were as follows: the initial concentration of lignosulfonates solution was 15mg/L with the discharge power of 100 w for20min. Besides, the degrade rate could be up to 68.4% under this condition. The reaction products were analyzed by UV, FTIR, analysis showed that the ring-opening reaction of aromatic structure was occurred during the degradation process. In conclusion, the lignosulfonate was degraded and eventually oxidized to small molecules.Microcrystalline cellulose was treated by plasma, it could be learnt that a small amount of cellulose degraded. The degraded sample were analyzed by DNS method, FTIR and SEM,results suggested that the structure of microcrystalline cellulose did not change obviously under oxidization. However, cellulose can be degraded partially with the top rate 8.05%during the discharge process. Luffa and hemp fibers were oxidized in the plasma under the optimal conditions of lignosulfonates and characterized by FTIR and SEM. It can be inferred that the porosity and accessibility of fibers improved significantly.