Study On Preparation Of Activated Carbon Fiber From Coconut Shell Fibers

Activated carbon fiber is a highly efficient carbonaceous adsorption material. Its advantages such as large specific surface area and abundant micropores have made great improvement based on granular activated carbon and powder activated carbon. On the basic of its special physical adsorption properties and surface chemical structure, ACF is widely used in various industrial fields. In this paper, coir as dominant resource of Hainan province with low price was chosen as starting precursors to prepared the activated carbon fiber.Firstly, Van Soest method, single component analysis and national standard analysis of ramie was adopted to measure content of hemi-cellulose, cellulose and lignin in coir and coconut shell. Secondly, thermo-gravimetric analysis TG/DTG was used to test the thermo-properties of both materials. Then, activated carbon fibers were prepared using (NH4)2HPO4as chemical activation agent through pretreatment, carbonization and activation. Effects of reaction parameters such as material-to-agent ratio, pre-oxidation temperature, pre-oxidation time, activation temperature and activation time on adsorption properties of ACF were investigated. The results is as followes:(1) Content of hemi-cellulose in coir was17%-23%, rather than0.15%-0.25%reported in the publications. The accuracy of this data was comfirmed through TG/DTG analysis. Content of cellulose and lignin were30%-36%,28%-36%, respectively. But these composite contents are different in coconut shell, including31%-36%hemi-cellulose,26%-30%cellulose and21%-31%lignin.(2) There were two peaks of weight loss in the second stage of coir and coconut shell thermolysis. The first peak mainly included hemi-cellulose and few lignin pyrolysis. Similarly, the second peak mainly included cellulose and few lignin pyrolysis. Residual lignin, besides, pyrolyze in the third stage of thermolysis. Weight loss rate of coconut shell was higher than coir in the second stage, as opposed to this, their ultimate weight loss rate were almost alike. For the reason that apparent activation energys of coir thermolysis reaction in different thermolysis stage with various heating rate were lower than coconut shell, thus coir can pyrolyze more easily.(3) Based on the method of pre-oxidating material after impregnating, activated carbon fibers with high specific surface area1268.1m2/g, rich micropores and abundant mesopores were prepared using coir as raw material and (NH4)HPO4as chemical agent. Influence degree of various reaction factors on iodine adsorption value:activation time>activation temperature>pre-oxidation temperature>material-to-agent ratio>pre-oxidation time. Influence degree of various reaction factors on methylene blue adsorption value:activation temperature > material-to-agent ratio> pre-oxidation temperature> activation time> pre-oxidation time. Activation mechanism of preparing activated carbon fibers by (NH4)2HPO4is different from that by traditional alkalies and steam activation. Diammonium phosphate resting on coir prevented coir from shrinking during carbonization, as a result of this, abundant micropores were obtained. Moreover, occupied physical space in coir manifested as mesopores. Weak etching ability of phosphorous compounds got an increased degree in high temperature.