Study On Preparation Process And Surface Modification Of Coal Based Activated Carbon Functional Groups

As an important adsorbent, activated carbon has been extensively used inindustries such as environmental protection, chemical industry, food processing andpharmaceutical processing etc. Columnar activated carbon is mainly used in gasadsorption, while briquetting crushing activated carbon utilized in liquid adsorption.The type and quantity of activated carbon surface functional groups determine thechemical properties of activated carbon surface, while the chemisorptioncharacteristics of activated carbon are directly determined by its chemical properties.The surface functional groups of activated carbon are mainly decided by preparationprocess and post-processing technology. And the adsorption capacity of activatedcarbon to particular substances could be improved greatly through the research ofpreparation process and surface modification.In this paper, Shanxi Datong (DT) weak caking coals were used as raw materialsto prepare briquetting crushing activated carbon by steam activation method. AndNingxia Taixi (TX) anthracites were utilized as raw materials to prepare columnaractivated carbon by steam activation method, with coal tar blinder added in. Theeffects of carbonization heating rate, carbonization residence time, carbonization finaltemperature, activation time and activation burn-off rate on the properties of coalbased activated carbon were investigated. Different post-processing methods wereadopted to conduct modification on the surface chemical properties of activatedcarbon. Specifically, high temperature nitric acid oxidation modification andmicrowave radiation modification were adopted for columnar activated carbon whilehigh temperature hydrochloric acid modification and heat treatment modification forbriquetting crushing activated carbon. The changes of surface functional groupscontent, type and adsorption properties of activated carbon obtained from preparationprocessing and surface modification were characterized with the methods of FTIRSpectrum, Zeta potential, Boehm chemical titration, elemental analysis, iodineadsorption value and methylene blue adsorption.In this paper, FTIR spectrum of raw coals gained from heat treatment underdifferent temperature levels was studied. Results showed that DT raw coals containedmore side chains like C-O-C,-CH3and-CH2-and a small amount of-OH and-COOH,while TX raw coals contained a small amount of side chains like C-O-C,-OH、C-O-Cand-CH2-. The side chains of raw coals decomposed at450℃and oxygen-containing functional groups decomposed totally at600℃.In this paper, the effects of different preparation processing conditions on theproperties of coal based activated carbon were also researched. Univariate resultsindicated that briquetting crushing activated carbon prepared under the condition ofheating rate for10℃/min, carbonization final temperature for600℃, carbonizationresidence time for30min, activation temperature for980℃and burn-off rate for50%contained relatively higher surface functional groups content. In contrast to that,columnar activated carbon prepared under the condition of heating rate for10℃/min,carbonization final temperature for700℃, carbonization residence time for60min,activation temperature for980℃and burn-off rate for60%had a relatively highercontent of surface functional groups. It could be included from the FTIR spectrumthat both briquetting crushing activated carbon and columnar activated carboncontained hydroxyl and single bond oxygen functional groups. The change ofpreparation processing conditions had a slight influence on the peak value of the FTIRspectrum, indicating that the influence of it on the type of activated carbon functionalgroups was insignificant.In the last part of this paper, surface modification of activated carbon was focused on.High temperature nitric acid modification and microwave radiation modification wereconducted on columnar activated carbon while high temperature hydrochloric acidmodification and heat treatment modification on briquetting crushing activated carbon.Results showed that nitric acid oxygenization increased the amount of-OH andC-O-C functional groups on columnar activated carbon surface, obviously increasingthe amount of-COO-functional group,namely the content of activated carbon surfaceacidic groups amounting to0.898mmol/g per1.5mol/L. High temperaturehydrochloric acid modification increased the functional groups containing singlebonding oxygen of activated carbon surface and enhanced the surface acidity ofbriquetting crushing activated carbon, namely the content of activated carbon surfaceacidic groups amounting to0.301mmol/g per1.5mol/L. After the modification ofmicrowave radiation treatment, the nitrogenous alkaline groups of activated carbonsurface increased and oxygen-containing functional groups experienced thermaldecomposition, making the PHpzc value of columnar activated carbon surfaceincrease, the alkaline functional groups of activated carbon treated for840Wamounting to0.879mmol/g. In contrast, the relative content of activated carbonalkaline groups increased, the content of alkaline functional groups amounting to 0.684mmol/g for800℃. Compared with conventional heating methods, microwaveradiation heating has a better penetrability, which enables materials to be heatedevenly.