Preparation of Activated Carbon Functional Ceramics From Coal Pitch

30卷4期结构化学( JEGOU HUAXUE)Vol 30. No 420l1.4Chinese J. Struct. ChemPreparation of Activated CarbonFunctional Ceramics From Coal PitchLAI Shou-Lian( Chemistry and Material School of Fujian Normal University, Fuzhou 350007, China)AbSTRACT The influences of different impregnation temperatures, pre-oxidation, carbonizationtemperatures and activation conditions on the iodine value and carbon deviations was discussed.SEM, EDS, and BET techniques were used to investigate the microstructures and properties ofmaterials. Results showed that activated carbon functional ceramic exhibited excellentcomprehensive properties when porous ceramics adsorbed the coal pitch at 150 C for 0.5 h,oxidized at 420 C for 1.0 h, and carbonizated at 700 C for 1.0 h and then activated by using KOH(20wt%)as agent at 800C for 1.0 h, as confirmed by the high iodine value(162.6 mg/g) and highspecific surface area( 83.5 m/g)Keywords: diatomite activated carbon coal pitch, functional ceramic1 INTRODUCTIONhas abundant resources with low price and a greatnumber of micropores, so it is an ideal material forActivated carbon is one kind of carbon with strong preparing porous ceramics). In this study, the diato-adsorption obtained from the carbon sources that is mite is taken as the carrier, coal pitch is the preprocessed with carbonization, activation procedures decessor of carbon, and activated carbon functionaland so on. The activated carbon has such advanta- ceramic is prepared with KOH activation method9-121ges as large specific surface area, strong adsorptive In this paper, the diatomite was used to loacapacity, fine chemical stability and so forth. It is activated carbon to prepare activated carbon ceramic,extensively utilized in foodstuff, medicineand the new composite material achieves com-petroleum, organic synthesis, gas purification,plementarity in function and advantage. Under thePresently, most activate carbon products are powder premise that advantageous properties of these twoor granular shape, and there are such problems as materials are maintained, it can not only overcomelow strength, fragile, non-forming, short life, such disadvantages as loose form, low strength,difficulty in recycling and generating, causing difficult forming and recycle difficulty of activatedsecondary pollution and so on4-71carbon, but also increase one new functionalDiatomite has such advantages as huge specific material with the activated carbon function for thesurface, strong adsorptive capacity, small electric ceramics field. We in this paper mainly discuss theconductivity and so on, and it has been extensively influence of impregnation, carbonization, activationutilized in sewage treatment, different filling ma-and中国煤化工 microstructurerials, coating additives and so forth. The diatomite andYHaET, SEM. EDSCNMHGReceived 2 June 2010; accepted 6 August 2010①The2comespondingauthorBomin1964,femaleseniorengineermajoringinfunctionalcompositematerialE-mail:Lsliany2@yahoo.com.cn2011 Vol 30结构化学( JIEGOU HUAXUE) Chinese J. struc.Chemand so on are used to characterize the change of The diatomite, clay and pore- forming material werematerial structures as well as the properties in mixed homogeneously; the dry-formed material wasdifferent preparation stagesprepared based on the powder water proportion of5: 1. The sample was formed in a manual manner2 EXPERIMENTAL METHODThe resulting sample was dried in a dry oven of 80AND PROCESSC, placed into the computer kiln(model: M1231PKCK596; SKUTT (USA) for sintering(sintering2. 1 Preparation of the porous ceramicperature800℃, heating rate200℃h, holdingThe foodstuff level diatomite sold by Zhedong1.0 h), and finally cooled within the furnaceDiatomite Company was taken as the raw material 2.2 Loading of the activated carbonwith the following formulation(8). crude diatomite For the preparation of the activated carbon ceramic50%, sintered diatomite 45%, clay 5%, adding wood refer to Fig. 1chip(pore-forming material) 5%Coal pitdDiamotie porousmpregnaPre-oxid aCarbon记 zatonActivationceramic carnerPerformance test+- sample+ Rinsing and dryFig. 1. Processing flow of activated carbon functional ceramicsThe coal pitch commercially available in Fuzhou discuss the influence of impregnation temperaturemarket was heated up to fusion with an electric oven, (130-180 C), pre-oxidation temperature(400-into which the porous ceramic sample was placed 480 C), carbonization temperature(550--750 C)for impregnation and adsorption for 0.5 h and then activation temperature(700-900 C)and activationtaken out. After cooling, the coal pitch in surface time (0.5-2.5 h)on the properties of activatedwas removed. The impregnated sample was placed carbon ceramic.into a computer kiln(M123IPK CK596; SKUTT 2. 3 Sample test and characterization(USA))with a filling method for carbonization, and The adsorptive value of the activated carbonthen cooled within the oven. The carbonized sample against iodine was determined according to thewas soaked with the KOH activation agent(analy- National standard(GB/T124968-1999). The sampletical reagent, Sinopharm Chemical Reagent Co, Ltd carbon content was determined on a Vario EL IlIsolution. After vacuum soaking for 4.0 h in the elemental analyzer( Elementar(Germany)); the auto-vacuum dry oven, the sample was taken out after matic specific surface was measured on a porositysoaking, and then placed into the oven of 80 C for analyzer(ASAP 2010: Max(USA)), the SEMdrying. It was placed into the computer kiln with a compo V凵中国煤化工 FEI (Hollandfilling method for sintering. The activated sample wasCNMHGcrotopography,was placed into distilled water, and then rinsed with and the micro-zone composition analysis was madeboiling water to be neutral. Finally, the sample was on an attached energy spectrometerplaced into the oven of 80 C for use. We hereLAI S. L: Preparation of Activated Carbon Functional Ceramics From Coal Pitcho.43 RESULT ANALYSISceramic was placed into the coal pitch fusion underAND DISCUSSIONdifferent temperature for impregnation for 0.5 h.After taking out the ceramic, the redundant coal3. 1 Influence of impregnation temperature on pitch on the surface was removed for weighing. Thethe load factor of coal pitchinfluence of different temperature on the load factorThe coal pitch was heated to fusion with an electric (load factor- adsorbed coal pitch mass/mass of theoven and the temperature was controlled at 130, 140, porous ceramic after adsorption)of the coal pitch150, 160, 170 and 180 C, respectively. The porous was tested, as shown in Fig. 2.Adsorption teFig. 2. Influence of adsorption temperature on the load rate of coal tar pitchAccording to Fig. 2, although the coal pitch has position, reduces the content of low-moleculeshown fusion state under 130 C, it has greater composition, increases the content of fixed carbon,viscosity, poor fluidity and lower load factor. When and makes the coal pitch to be under easy subse-raising the temperature, the liquidity of coal pitch quent carbonization and activation, which are goodincreased,and the load rate rose from 25.8% at the for the production and development of pores.Theof130℃to37.9%at140under 150 C, the coal pitch has better liquidity,tion degree of coal pitch in some degree. Thethe load factor reached the peak of 43. 1%; with the oxidation product can be prepared by rising the coalcontinuous temperature rising to 160 C, the coal pitch temperature up to 400, 420, 440, 460 and 480Cpitch decomposed into volatile substances with low at a heating rate of 150 C/h for 1.0 h and then℃forl.0h,volatile caused the increase of coal pitch viscosity, 800 C for 1.0 h to produce the activated ceramicand the matrix is difficult to make adsorption. Thus, Fig 3 shows the influence of pre-oxidation temperathe load rate of coal pitch under higher temperature ture on iodine value of the samplereduced, and it dropped down to 38. 2% at 180 CAccording to Fig. 3, the oxidation degree of coal3. 2 Influence of pre-oridation temperature on pitch was low when the oxidation temperature wasthe activated carbon ceramic property中国煤化工Pre-oxidation treatment actually transfers the ther-coapletely, which wasmoplastics of coal pitch to thermosetting property, notCNMHGiodine value wasimproves the carbon-hydrogen compound aroma- affected, 160.2 mg/g in this case; when the tempetizetion or polymerism depth in the asphalt com- rature rose to 420 C, deep oxidation appearedVol 30结构化学(IEGOU HUAXUE) Chinese Struct. Chemduring the condensation of aromatic rings, the coal cause carbon loss, carbon content reduced, and thepitch transferred to show thermosetting property, the sample adsorptive property reduced; up to 480 Cvolatile content reduced, the iodine value was the sample iodine value reduced to 137.8 mg/g. Thus,increased to 178.5 mg/g; after the coal pitch was the optimal pre-oxidation temperature wasoxidized to some degree the temperature rise would determined to be 420 COxidation temperature/rFig 3. Influence of oxidation temperature on the iodine values Fig 4. Influence of carbonization temperatureon the yield of carbonization and iodine value3. 3 Influence of carbonization temperature on determined to be the proper carbonization tempethe activated carbon ceramic propertyrature of the coal pitch by comprehensive conside-The porous ceramic matrix pre-oxidized under 420C rationwas carbonized under 550, 600, 650, 700 and 750C, 3. 4 Influence of activation temperature on therespectively with holding for 1.0 h. The carbonizedactivated carbon ceramic propertysample was soaked for 4.0 h in a 20% KOH solution. Fig. 5 shows the influence of different activationFinally, the sample was activated under 800 C for temperature(700, 750, 800, 850 and 900 C)on the1.0 h. lodine adsorption test was conducted for the activated carbon yield and iodine value when thesamples. For results, refer to Fig. 4.coal pitch was under the pre-oxidation temperatureAccording to Fig 4, the carbon yield reduced with of 420 C, carbonization temperature of 700 Cthe rise of carbonization temperature, from 82.3% at holding time of 1.0 h, activating agent KOH con-550C to 63. 1%at 750 C. The sample iodine value centration of 20% and activation time of 1.0h.firstly rose to one peak from 136.4 mg/g at 550 C to According to Fig. 5, the activation temperature had168. 9 mg/g at 700 C and then reduced to 153. 2 greater influence on the activated carbon yield andmg/g. The main reason is that the volatile was iodine value. The sample iodine value firstly incontinuously removed with the temperature rise, creased to the peak at 162.6 mg/g and then reducedcarbonization degree of the coal pitch increased, and with increasing the activation temperature Increasethe carbon yield reduced. With further carbonization, of the activation temperature could significantlythe arrangement of carbon structure became more improve the micropore content of the activatederfect, and the structure of the final solid residue carbon and improve the adsorptive capacity,and thewas similar to that of graphite. This is not good sample iodine value rose from 142. 1 to 162.6 mg/gfor the reaction between activating agent and the however, too high activation temperature wouldcarbon material during activation, thus increasing chang v凵中国煤化工 tivated carbonthe difficulty of reaction because this can not ceramCNMHGviously reducedproduce a great number of mircopores and therefore activated carbon yield. At 900 C, the iodine valuethe adsorptive capacity reduced. Thus, 700C was was 150.2 mg/gLAI S L: Preparation of Activated Carbon Functional CeraNo 43.5 Influence of activation time on the activated the coal pitch was under the pre-oxidation tempecarbon ceramic propertyrature of 420 C, carbonization temperature of 700 Cig. 6 shows the influence of activation time chan- holding time of 1.0 h, activating agent KOH concen-ge on the activated carbon ceramic property when tration of 20%, and activation temperature of 800CActivation time/inFig. 5. Influence of activation temperatureFig. 6. Influence of activation time on theon the yield of activation and iodine valueyield of activation and iodine valueAccording to Fig. 6, the influence of activationactivated carbon ceramictime on the activated carbon ceramic was similar to Fig. 7 shows the SEM pattern of activated carbonthat of activation temperature. Namely, with the ceramic at different preparation stagesextension of activation time to 1.0 h, the sample In Fig. 7, (a) shows the SEM photo of porous cera-iodine value reached a peak of 161.3 mg/g, and then mic matrix. According to the photo there was ait began to reduce. When the holding time was unique bamboo basket structure of diatomite, andextended to 2.5 h, the activated carbon iodine value the distribution of air pores in porous ceramic matrixreduced to 142.8 mg/g. This indicated that the was fairly homogenously. (b)shows the porousextension of activation time could increase the ceramic matrix after loading coal pitch. It can bedegree of activation reaction. There would be a great clearly found that the porous ceramic matrix hadnumber of micropores in the matrix, so adsorptive been fully wrapped with coal pitch; there was a layercapacity could be improved. However, if the time of glass phase coal pitch in the surface of the matrixwas too long, the reaction will be excessive, the (c)shows the SEM photo of porous ceramic matrixmicropore structure was damaged, a large amount of after pre-oxidation. It can be found that Co, cO2carbon was consumed, and the yield of activated H20 and low-molecular compounds and otherrbon was reducedvolatiles were eliminated. The coal pitch showedBased on the analyses above, we determined the shrinkage and agglomeration because of cross-optimum parameters for the preparation of activatedking, dehydrogenation and cylization during thecarbon ceramic to be follows: the porous ceramic oxidation process, and the sample surface showed ancarrier is impregnated in the coal pitch of 150 C for irregular shape In some areas, the surface hole of0.5 h, pre-oxidized at 420 C for 1.0 h, soaked with diatomite could be found again, and the hole porous20wt% KOH for 4.0 h; the activated carbon ceramic matrix showed holes in different sizes onceactivation temperature is 800 C, the activation time moreibits Porous ceramic matrix aftertimum iodine value of activated carbol中国煤化工 d aroundcarbon ceramic is 162.6 mg/g, and the specific wereCNMHGafter coal pitchsurface area is 83.5 m/g3.6 Microstructure of theture!3. Compared with(a), the position around the结构化学( JIEGOU HUAXUE) Chinese Struct.Chem597diatomite in(e)was filled with activated carbon. test was conducted respectively, as shown in Fig 8Sampling two points of(a) and(b), energy spectrum(point b)(a)Diatomite porous ceramic matrix;(b) Diatomite porous ceramic absorbing the coal pitch(c) Diatomite porous ceramic after oxidation; d) Diatomite porous ceramic after carbonization(e)Diatomite porous ceramic after activationFig. 7. Microtopography of the stages of activated carbon porous ceramic中国煤化工CNMHG(a) Energy spectrum analysis figure for point a598LAI S L. Preparation of Activated Carbon Functional Ceramics From Coal Pitch. No 4V230457(b) Energy spectrum analysis figure for point bFig 8. EDS pattern of the activated carbon porous ceramicsPoint a was the agglomeration around the diatomite. 4 CONCLUSIONEnergy spectrum analysis gave the followingcontents: C 66.62%, Si 11.34%, and O8.07%, which (1)Pre-oxidation and carbonization techniquesrevealed that the activated carbon agglomerated in have important influence on the activated carbonthe gaps in the diatomite bamboo basket. Point b ceramic. The optimum pre-oxidation technique is aswas the diatomite surface. After activation, its follows: heating rate 150 C/h, holding time 1.0 h atsurface was covered with one layer of activated 420 C; the optimum carbonization technique is ascarbon. With energy spectrum analysis, the c below: heating rate 200 C/h, holding time 1.0 h atcontent was 18.45%, Si 40.5%, and 0 21.34%, so 700 C. After carbonization, the sample iodine valuethe activated carbon was actually loaded on the is 43. 8 mg/gdiatomite surface. The tested sample surface had (2)During the preparation of activated carbonbeen under metal spraying, and thus there was Au in ceramic, the activation technique has the greatestthe photo, and other microelements like K, Fe and so influence on the sample iodine value. When theon were impurities carried into by diatomite. 20wt% KOH solution is used as the activating agent,Thereby, the microstructure of activated carbon the optimum activation technique is given as followsceramic prepared with coal pitch showed in impregnation time 4.0 h, activation temperature 8004.hogeneity, the ceramic surface was fully covered C and activation time 1.0 h. The iodine value ofith activated carbon, and it can be reckoned that activated carbon ceramic prepared under thesethe final ceramic adsorptive capacity will be directly conditions is 162.6 mg/g, the specific surface area isrelated to the loaded quantity of activated carbon.83.5 m/g and the activated carbon yield is 59.5%REFERENCES( )Shen, Z.M.; Zhang, W H; Zhang, x J Chemical Industry Publisher 2006, 1-20(2)Xie, C.中国煤化工()Jia, G; Wang, S. X; Yan, L C. Journal of Colloid and Interface Science 2005, 281HCNMHG(4)Cui, J; Zhao, N, Q. Li, JJ Carbon Technique 2005, 24, 26-31(S)Streitwieser, D A; Popovska, N; Gerhard, H Journal of the European Ceramic Society 2006, 26,2381-2387.20l1vol.30结构化学( EGOU HUAXUE) Chinese struct.Chem(6)Zeng, L. K; Hu, D L; Shui, A. Z; Ren, X. T Liu, P A Wang. H Cheng, X.S. China Ceramics 2008, 44, 7-11(Wu, H. P Wu, R. P; Yu, Y; Huang, M. L. Bulletin of the Chinese Ceramic Society 2009, 28, 641-645.(8)Xic, Y. B. Zhang, W. Y; Zhang, R; Cheng, G: Zhang, C. x; Ling, L. C. 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