Drective Control Porous Sturcture And Utilization Of Nutshell Activated Carbon

A well-developed multi-level pore structure and surface chemical structure (surfacefunctional groups) is formed by graphitized microcrystalline carbon and non-graphitizedamorphous carbon in activated carbon. It has an extensive application in all fields likeadsorption, separation, food, medicine, catalyzing, electronics, storing energy and so on. Withthe development of science and technology, carbon materials with concentrated and orderedpore size will be more widely needed in modern science, industry and engineering. Therefore,it has been the core of preparation technology to regulate pore structure in activated carbon. Itnot only help to enrich and improve the theoretical system of activated carbon manufacturing,but also contributes to enlarge its practical approaches. Coconut shell and camellia shell wereused as raw materials in this research. Preparation methods using KOH as activating agent ofmicroporous activated carbon with ultra-high specific surface area were discussed. Pyrolysisactivation, catalytic carbonization and polymerization carbonization methods were applied toregulate micropores, catalytic oxidation and reactivation methods using chemical agents formesopores in activated carbon. Influence of controlled conditions to ordered pore structure andregulation mechanism was explored. Pore structure analyzer, TG-MS, FT-IR, SEM, TG-DTGand XPS are applied to characterize activated carbon's pore structures. The regulated activatedcarbons' applications in electrochemistry, adsorption of CO2, removal of radio iodine-131,adsorption of tannic acid and decolorization of glycerol were investigated. The main contentand structure of this paper are as follows:1. Preparation technology of microporous super activated carbonCarbide of coconut shell was used as raw material, KOH as activating agent in thisresearch. Microporous super activated carbon was obtained by controlling process parameters,like mixing ratio of KOH to carbide, activation temperature and activation duration. And itsBET specific surface area is3326m~2/g, with pores distributed between1.5-2.5nm. It also hasa very good adsorption property (Qiodine2779mg/g, QMB570mg/g). It is revealed that carbideas raw material instead of fresh coconut shell has higher carbon content, more stable structure,and channels between cell cavities are preliminary formed. KOH enters more easily, and lessdose of reagent would get microporous activated carbon with a high specific surface area. Theproduct has a promising prospect in the fields of natural gas storage and electrode materials forsuper-capacitor.2. Preparation of microporous coconut shell activated carbon with pyrolytic self-activation A new clean method to prepare microporous activated carbon without any activating gasor reagents was created. Some kinds of shell and sawdust materials were pyrolyzed in a closedenvironment. Simultaneously structures of materials would reform, and self-activationoccurred. Firstly, a lot of gas was released by pyrolysis of natural tissue of coconut shell, whichcontained vapor, CO2and CO. Adding the air in the reactor and the raw material itselfadsorbed, mixing activating atmosphere was formed, and pressure may emerge with theincrease of temperature in the closed reactor. Secondly, because of the pressure, tissue structureof coconut shell would be impacted when the gas in tissue cell forced to escape. This couldimprove the tissue structure, and promote the form and development of micropore in activatedcarbon. Thirdly, pyrolytic product reacted with mixing activating atmosphere. At the same time,pressure in the reactor increased, which speeded up the self-activation reaction. No activatingreagents or vapor was used in this research. Influences of pyrolysis temperature, pyrolysisduration, increasing rate of temperature, and atmosphere to gas composition in self-activation,pore structure and adsorption properties of activated carbon were discussed. The pore-formingmechanism and kinetics of pyrolytic self-activation for preparing activated carbon withnutshell were studied, which could enrich the preparation and application system of activatedcarbon. The new process is very fast and easy. The pyrolytic self-activation experiment takesonly1h, which had greatly shortened the production cycle, improved efficiency, and savedenergy. Cost could be low, and environmental pollution could be less because of no chemicalreagents. Therefore, it has an extensive prospect of development to prepare coconut shellactivated carbon with well-developed micropore and high resistance at low cost using this newmethod conveniently and cleanly.4. Regulation of activated carbon micropores by catalytic carbonization with K2CO3Sylvite was added to develop the micropore structure and adsorption properties ofcamellia shell activated carbon by controlling parameters in catalytic carbonization. The resultsshowed that sylvite played an important role in the development of micropore structure andincrease of specific surface area. Activated carbon with developed micropores was obtained bycontrolling parameters as follows: adding4%K2CO3, activation temperature at800℃andlasting for4h, whose micropores were90.3%, Qiodine971mg/g and QMB75mg/g. It wasshowed by TG-DTG results that potassium could greatly catalyze pyrolysis reaction anddecrease temperature for pyrolysis. Coke yield increased at the same time. XRD results showedthat potassium helped to form microcrystalline structure of nutshell activated carbon. Therefore,microporous activated carbon could be obtained by physical activation below1000℃. This isa novel technology to prepare microporous nutshell activated carbon by catalytic carbonization method. And it will provide a new way for the exploration of microporous activated carbonwith low consumption, high yield and good cleanliness.5. Modification of activated carbon micropores by deposition of phenolic resinCoconut shell activated carbon bought was used as carrier. In-site synthesis of phenolicresin was finished in the pores of activated carbon. Carbonization deposition in an inertatmosphere at900℃was taken to regulate micropore structure of activated carbon. N2adsorption/desorption experiments, SEM and adsorption properties were detected tocharacterize the activated carbon samples, and XPS, FT-IR methods were used for mechanismresearch. It turned out that volume and quantities of micropores increased obviously, whileratio of mesopores decreased in coconut shell activated carbon after carbonization deposition.Polymer mainly enters mesopores and macropores. The carbon residue after carbonized isprimarily composed of aromatic ring structure, which forms graphitized microcrystallinearraying orderly in mesopores and macropores. Then mesopores and macropores transform intomicropores to get well-developed microporous activated carbon. Modified nutshell activatedcarbon has a much higher adsorption of CO2than that before modified. Thus, microporouscarbon materials for gas adsorption can be obtained by carbonization modified after in-sitepolymerization of phenolic resin.6. Regulation of camellia shell activated carbon mesopores by chemical methodCamellia shell was impregnated with H3PO4after activated with vapor to research theefforts to control of mesopores in activated carbon. And activated carbon with abundantmesopores was obtained. Results showed that camellia shell activated carbon prepared byvapor activation under820℃was composed of63%micropores, and33%mesopores. TheBET specific surface area was1076m~2/g, total pore volume0.81cm3/g, QMB180mg/g, andQiodine1012mg/g. While, after the second activation using H3PO4under800℃, BET specificsurface area and total pore volume were increased up to1608m~2/g and1.17cm3/g,respectively. The proportion of mesopores were greatly increased from33%to61%,37%ofmicropores remained. QMBand Qiodineof the activated carbon also soared up to330mg/g and1326mg/g.7. Regulation of activated carbon mesopores by catalytic activation with molysiteNutshell activated carbon was used as raw materials. Molysite was added to catalyze thereaction of vapor and carbon on micropore wall in order to enlarge pores. Activationtemperature and additive amount of molysite could be controlled to regulate mesoporestructures of activated carbon. This method is based on micropores existed in activated carbon.And its consumption of catalyst and cost is very low. Therefore, an effective way to regulate nutshell activated carbon mesopores by second activation after vapor is proposed, which couldtake place of technologies that prepare activated carbon with chemical reagents like H3PO4andZnCl2. Results revealed that proportion of mesopores and total volume of nutshell activatedcarbon increased after adding molysite and the second activation. But excessive molysite couldresult in blocking the pores and reducing pore volume. Activation temperature and additiveamount of molysite could be controlled to regulate the development of pores. Mesoporousactivated carbon with90%mesopores whose average pore diameter is5nm was obtained byadding4%molysite under850℃activation for30min.8. Applications of microporous and mesoporous activated carbonBased on the preparation of regulated microporous and mesoporous activated carbon,capacitive character and adsorption of CO2and radioiodine of microporous activated carbonwere studied. Adsorption of tannic acid, decolorization and deodorization of glycerol weredetected to characterize mesoporous activated carbon. The results showed that0.1A chargeand discharge specific capacity of coconut shell activated carbon activated using KOH (KOH:carbon=3:1) under800℃for60min reached323.0F/g, much higher than that of petroleumcoke-based capacitor activated carbon. And smaller capacity decreased with the increase ofcurrent density. The CO2adsorption capacity of coconut shell activated carbon prepared bypyrolytic self-activation method marked AC900was61.22mL/g, more than that of coconutshell activated carbon (36.58mL/g). And AC900adsorption efficiency of I2-131whoseactivity is2552Bq/L reached86.5%, the value could rise up to99.6%by adding marginala0.1%AgCl. The statutory drinking water safety benchmark regulated by nuclear safetycommission of Japan is300Bq/L, and activated carbon prepared by the method in this researchhas reached the purity requirement. Tannic acid value is used as an important index ofactivated carbon using for water-treatment in trade. Because the size of tannic acid molecule isbig, it could reflect mesopores and macropores in activated carbon. The adsorption datashowed that1384mg/L coconut shell activated carbon bought in the market was needed todecrease the concentration of tannic acid from20mg/L to2mg/L However,141mg/Lmesoporous activated carbon AC-6-850that obtained by impregnating molysite and enlargingpores with vapor is enough to do that. Camellia shell mesoporous activated carbon prepared inchapter6was applied in decolorization of glycerol crude products. Refined glycerol productswhose transmittance is more than99.1%could be obtained under90℃, meeting the colorrequirement of food grade glycerol.