Preparation And Characterization Of Black Liquor High Molecular Lignin-Based Carbon Nanofibers

Pulping and papermaking black liquor is rich in lignin,which is a kind of plant biomass resource.Currently,lignin is mainly considered as a by-product of cellulose utilization.Lignin is usually used for burning to release heat energy,resulting in resource waste.Only a small part of the industrial lignin has been processed and utilized.In addition,with the increasing shortage of petroleum based energy,it is particularly important to develop and utilize biomass resources to supplement or partially replace fossil energy.Therefore,due to the characters of low-cost,biodegradable,aromatic rich renewable,lignin is regarded as a promising raw material for the preparation of carbon fiber.Bamboo pulp is used as a raw material for non-wood pulp and paper.Compared with wood pulp black liquor,bamboo pulp black liquor not only contains lignin,but also contains more silicon,which is easy to produce "silicon interference" problem.This paper took bamboo pulp black liquor as raw material source.Aluminum sulfate was used as precipitator to partially separate lignin from black liquor of bamboo pulp.The structure and composition of aluminum sulfate lignin were characterized and analyzed.The results showed that the silicon was removed synchronously during the separation of lignin by aluminum sulfate.A small amount of Na,S,Cl and K ions were also detected,which came from the previous stage of alkali recovery.In addition,aluminum ions are introduced into lignin.The content of Si ions and Al ions detected by ICP-AES was 4.26 mg/g and 22.51 mg/g,respectively.The FT-IR detection structure further showed that Si-O-Si symmetric telescopic vibration and flexural vibration absorption peaks occurred at 831 cm-1 and 470 cm-1,respectively.It is proved that adding aluminum sulfate to black liquor can precipitate silica and lignin.An effective method is provided for the separation of bamboo pulp black liquor lignin and simultaneous silicon removal.It is of great significance for the recovery of non-wood silicone-containing lignin.Carbon nanofibers were prepared from aluminum lignin sulfate and polyacrylonitrile(PAN).First,aluminum lignin sulfate nanofibers were prepared by electrostatic spinning by mixing aluminum lignin sulfate with PAN.Then,through 200? pre-oxidation and 700? carbonization,aluminum lignin sulfate based carbon nanofibers were obtained.The results showed that pure aluminum sulfate lignin formed electrospray particles in the process of electrostatic spinning.When the proportion of aluminum sulfate lignin is 60%or less,the fiber with good shape can be formed in the process of electrostatic spinning.And the diameter decreases with the proportion of aluminum sulfate lignin increasing.When the proportion of lignin was 60%,the minimum diameter of carbon fiber was 187 nm.Silicon and aluminum elements were detected in the electrospinning fibers,indicating that they had no effect on the process of electrostatic spinning.In the heat treatment process,compared with the lignin obtained by sulfuric acid separation,the electrospun fiber of aluminum lignin sulfate is easier to maintain the fiber shape and avoid melting and structural collapse.The structure of carbon fiber obtained is made of random layer of graphite and the carbon is amorphous carbon.This study confirmed that non-wood silicone-containing lignin,which is rich in source,is expected to be a material for the preparation of high-performance and low-cost carbon fiber.It provides a new method for the efficient utilization of lignin,which is a byproduct of non-wood pulping and paper making.The application of aluminum sulfate lignin-based carbon nanofibers in the field of capacitors was studied.It was used as electrode material to test the electrochemical performance of supercapacitors.Cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy were tested.At the same time,carbon fibers prepared from lignin separated from sulfuric acid were tested for comparison.The results showed that the performance of aluminum lignin sulfate based carbon fiber as electrode material was more outstanding,which was reflected in the performance of double-layer capacitance.The capacitance performance increased with the increasing of aluminum sulfate lignin content.Capacitance performance is best when the additive quantity is 60%.The approximate rectangle enclosed by the cyclic voltammetry curve of the sample has the largest area.The constant current charge-discharge curve is a typical isosceles triangle,and the longest time to complete a charge-discharge is 676s.Moreover,the retained capacitance was 94.50%after 1000 electrochemical cycles.The results showed that the carbon fiber with silicon-containing lignin as raw materials has good capacitance and cyclic stability.It can be used precursor for preparing electrode materials for supercapacitors.This part of research provides a theoretical basis for the application of non-wood pulping black liquid high molecular silicone-containing lignin in the field of supercapacitors.At the same time,it provides a new way to realize the high value utilization of biomass resources.