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Journal of Analytical and Applied Pyrolysis 91 (2011) 257–262
Contents lists available at ScienceDirect
Journal of Analytical and Applied Pyrolysis
journa l homepage: www.e lsev ier .com/ locate / jaap
reparation and characterization of activated carbon from bagasse fly ash
handra Wahyu Purnomoa,b,∗, Chris Salima, Hirofumi Hinodea
Department of International Development Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550, JapanDepartment of Chemical Engineering, Gadjah Mada University, Jl. Grafika no 2, Bulaksumur, Yogyakarta 55281, Indonesia
r t i c l e i n f o
rticle history:eceived 1 April 2010ccepted 24 February 2011
a b s t r a c t
Activated carbons from bagasse fly ash (BFA) were prepared by one step chemical activation using ZnCl2as activating agent, or combination method of chemical with CO2 physical activation (physicochemical
vailable online 3 March 2011
eywords:ctivated carbonagasse fly ashhysicochemical activation
activation). The development of porosity was studied in correlation with the method of activation, acti-vation temperature, and also the chemical weight ratio. A typical sample by the combination method at600 ◦C and weight ratio of ZnCl2:BFA = 2 exhibited micropore volume of 0.528 cc/g, mesopore volume of0.106 cc/g and surface area of 1200 m2/g. For determining the adsorption capacity of the carbon samplesin solutions, phenol and methylene blue equilibrium adsorption experiments were conducted. The prop-erties and adsorption capacity of the synthesized activated carbons has been compared to commercial
SX Pl
iquid adsorption activated carbon (Norit®. Introduction
Activated carbons have always become a research interest dueo their continuous usages in many areas. These materials haveeen synthesized from many types of carbonaceous precursors.ormerly, coal has become the major precursor for activated car-on production. Since coal is more valuable to be used for energyeneration, people started to study many type of biomass such asoods [1,2], plant’s shells [3–6] and stones [4,6–8], straw [9,10],ulls [10–12] and sawdust [13,14] as the precursors. The utiliza-ion of several type of biomass for activated carbon production haspositive impact in reducing organic solid wastes.
On the other hand, due to a heavily regulated price of sugary governments especially in developing countries, sugar cane
ndustries are expected to generate revenue from their derivativeroducts beside their main commodity. One of the potential sideroducts from the industries that can be used for producing deriva-ive products is bagasse, a solid waste from sugar juice extractionrocess. At present, the common utilization of bagasse is based on
ts cellulosic content such as for making pulp and particle board.
In fact, bagasse is a valuable solid fuel to be combusted in steamoilers. Most of the industries take this advantage and leave mini-al excess of bagasse during normal milling season. However, the
shes from the combustion process in the form of fly ash (BFA) and
∗ Corresponding author at: Department of International Development Engineer-ng, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550,apan. Tel.: +81 03 5734 32451; fax: +81 03 5734 32451.
E-mail addresses: [email protected], chandra [email protected]. Purnomo).
165-2370/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.jaap.2011.02.017
us).© 2011 Elsevier B.V. All rights reserved.
bottom ash have not yet being commercially utilized causing dis-posal problems. In the case of BFA, some researchers already madean attempt to utilize it as adsorbents by direct usage with minimalpretreatment [15–17]. It is very rare that BFA is being upgraded tobecome advanced material such as high porosity activated carbonbefore being utilized.
Meanwhile, the major problem that should be considered inproducing activated carbon from residual material is its continu-ous supply. In terms of BFA, the supply is steady as long as sugarindustries still use bagasse for fueling their steam boiler. A sugarindustry emits approximately 5.5 kg of fly ash per metric ton of caneprocessed in the flue gases from the bagasse combustion [18]. In thecase of Indonesia with around 2.5 million tons of annual produc-tion of cane, 13,750 tons of BFA per year is produced nationwide.The previous attempts in producing bagasse based activated car-bon used raw bagasse [10,13,19] and also bagasse bottom ash [3]as starting material.
In this study, BFA has been upgraded using ZnCl2 chemicalactivation and simultaneous combination of chemical and CO2physical activation methods to produce activated carbons whichhave unique textural and chemical properties. The attempt inemploying simultaneous combination method is to synergize theeffects of chemical agents with atmospheric gases during onestep heat treatment toward the precursors. However, the previ-ous study on simultaneous activation method which employingZnCl2 and CO2 are still very few [6,12], especially in address-
ing the comparison of porosity development between chemicalactivation and simultaneous physical and chemical activationfor a specific precursor. Then after synthesizing the activatedcarbons, the adsorption characteristics of several samples werestudied using two model pollutants which were phenol (PH) and
258 C.W. Purnomo et al. / Journal of Analytical and Applied Pyrolysis 91 (2011) 257–262
Table 1Composition analysis and porosity of BFA particles.
Proximate (wt%) Initial porosity Ultimate analysis (wt%)
VM FC Ash Vmic (cc/g) Vmes (cc/g) SBET m2/g C H N Oa
V
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2
2
Ybsmcszonso1(Ab
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sSarm5
2
nSvp
42.5 44.4 8.8 0.176 0.018
M = volatile matters; FC = fixed carbon.a By difference (Total weight − (C,H and N) weight − ash weight).
ethylene blue (MB) and to be compared with the commercialne.
In addition, behaviors of impregnated samples during heatreatment in an activation method can be studied using ther-
ogravimetric (TG) analysis. By employing this analysis, severalptimal activation variables, i.e. activation temperature, chemicalatio and holding time can be predicted. This is based on a widelyccepted assumption that there is a significant correlation betweeneight loss during activation process and pore development of acti-
ated carbon. Thus, trial steps during activation experiments can bevoided. Earlier reports have mostly utilized this tool for evaluatinghe activated samples thermal behavior in relation with activa-ion mechanism determination [20–22], and given less stressingn design purposes.
. Experimental
.1. Activated carbon preparation
BFA was obtained from PT Madukismo, a sugar company inogyakarta province, Indonesia. Before being used for activated car-on precursor, received fly ash has been sieved to obtain particleize from 0.7 to 1.4 mm. The properties of the BFA particles are sum-arized in Table 1. From the table, it is shown that BFA has a high
arbon content which is suitable to be an activated carbon precur-or. Then, sieved fly ash underwent chemical impregnation usinginc chloride with certain chemical weight ratios (R) ZnCl2:BFA = 2r 3 prior to heat treatments between 500 and 700 ◦C. The impreg-ation was done by manual mixing BFA with ZnCl2 concentratedolution at room temperature and then drying in an oven at 100 ◦Cvernight. The dried mixture then subjected to heat treatment by5 ◦C/min of heating rate in a horizontal automatic tubular furnaceISUZU, EPKR-12K) under continuous nitrogen flow of 150 cc/min.fter reaching the final temperature, the heating was hold for 1 hefore cooling to room temperature.
In addition, the combination of physical activation using CO2as done in the heat treatment step after the impregnation pro-
edure as discussed earlier. This method was done simply bywitching nitrogen with CO2 during the holding time with the sameow rate as nitrogen at final temperature. After activation, all sam-les were subjected to washing by 0.5 N HCl solutions and followedy hot distilled water until neutral pH.
The samples were labeled as ZxTyC for the chemically activatedamples and ZxTyCQ for the physicochemical activated samples.mall x indicates the chemical ratio value, while y states thectivation temperature in hundreds (◦C). For example, Z1T5CQ rep-esents a typical sample that synthesized by combination activationethod using chemical ratio of 1 and activation temperature of
00 ◦C.
.2. Carbon characterization
The samples textural properties have been characterized usingitrogen adsorption at 77 K by Autosorb 1 from Quantachrome.urface area was calculated using BET method, while microporeolume (Vmic) has been determined using DR method. Then, meso-ore volume (Vmes) has been calculated by subtracting pore volume
408 75.2 1.7 0.4 13.9
obtained from adsorption at P/Po = 0.95 by Vmic value. Meanwhile,DFT method has been employed to obtain pore size distribution ofthe samples.
The chemical property analyses were done by measuring thezero point charge pH or pHZPC and also analyzing the surfacefunctional groups using FTIR spectra analysis. The method of deter-mining pHZPC was based on the method that proposed by Noh andSchwarz [23], while the FTIR study was done using Jasco FT/IR6200 equipment. Before analysis, a carbon sample was mixed byKBr using weight ratio of carbon:KBr = 1:500 and then pressed toproduce thin transparent pellets.
The proximate analysis of BFA by ASTM 5142-04 method[24] and thermal weight loss behaviors during heat treatment ofimpregnated BFA samples were conducted using thermogravime-try (Thermo Plus TG 8120, Rigaku). Elemental analyses of C, H and Nwere performed on a Yanaco MT-6 CHN recorder elemental analysisinstrument. For observing morphological changes by the activationsteps, SEM analysis was performed (JSM5310LV, JEOL).
2.3. Liquid adsorption
Liquid adsorption equilibrium of several selected samples hasbeen carried out in a batch system. A small amount of a carbonsample ca. 0.05 g was put into 100 mL stoppered Erlenmeyer flasksconsist of 50 mL solution of MB or PH in a specific concentrationranged from 50 to 300 mg/L. Initial pH of the solutions, without pHadjustment, were around 5.2 for PH and about 5.5 for MB solutionthat were measured using pH meter (Horiba D-51). After 72 h ofadsorption in a water bath shaker at 30 ◦C, concentration of themodel pollutant in the supernatant solution was determined usingUV spectrophotometer (UV-1800, Shimadzu). The adsorption pro-cedure was repeated in triplicate then the data of each sample wasfitted by Langmuir equation:
Q = QmK · C
1 + K · C(1)
where Q is the amount of MB or PH adsorbed (mg adsorbate/gadsorbent), Qm is the monolayer adsorption capacity (mg adsor-bate/g adsorbent), K is the affinity constant (L/mg adsorbate), andC is the equilibrium solution concentration of adsorbate (mg/L).
3. Results and discussion
3.1. Thermal behaviors
As shown in Fig. 1a, weight loss versus temperature curves ofseveral impregnated samples with different chemical ratio (R) andalso pure ZnCl2 during heat treatment up to 800 ◦C in nitrogenatmosphere at a 15 ◦C/min of heating rate are provided. Based onthe TG and derivative thermogravity (DTG) curves of impregnatedones, the largest weight loss occurred at about 400 ◦C and com-
pleted around 600 ◦C. This loss was mainly due to ZnCl2 and volatilematerial release which created porosity inside BFA. For the sampleusing R equal to 2 and 3, the gradual weight loss was steady after600 ◦C. This temperature can be a hint of a completion of the mainactivation process.
C.W. Purnomo et al. / Journal of Analytical and Applied Pyrolysis 91 (2011) 257–262 259
Fh
amatpstacadewcso
3
FsIwbotb
large micropore (LMP) with pore width between 10 and 20 A andmesopore with pore width larger than 20 A up to 500 A. Observ-ing the effect of increasing activation temperature, the significantchange in samples of similar R is the increase of pore in SMP range.
Table 2Textural properties of carbon samples.
Sample Vmic (cc/g) Vmes (cc/g) SBET (m2/g)
Z2T5C 0.218 0.034 506Z2T6C 0.308 0.080 709Z2T7C 0.352 0.057 827Z3T5C 0.321 0.196 723Z3T6C 0.417 0.157 946Z3T7C 0.525 0.138 1168Z2T5CQ 0.434 0.058 1005
ig. 1. TG and DTG curves of different R (a); and TG curve of R = 2 sample duringeat treatment to 600 ◦C (b).
DTG curve for R = 1 sample shows a significant loss of weightt about 800 ◦C after the largest loss, which represents the require-ent of higher temperature treatment of R = 1 samples to complete
ctivation process than the higher R samples. It can be a hint thathe chemical ratio should be chosen above this value for com-lete development of porosity in relatively low temperature. Fig. 1bhows the weight changes of R = 2 and 3 samples during the heatreatment up to 600 ◦C within 1 h holding time in N2 atmosphere at15 ◦C/min of heating rate. It can be seen that there was no signifi-ant change of weight after 40 min of holding time for R = 2 samplend even shorter for R = 3 sample. Thus, 60 min of holding timeuring activation experiment chosen in this study was sufficientnough to develop optimal porosity. The other interesting findingas the similarity of the two samples final weight at about 10%. By
onsidering that R = 3 samples has less precursor weight than R = 2ample, it is obvious that ZnCl2 impregnation can increase the yieldf activated carbon products.
.2. Textural properties
Nitrogen adsorption isotherms of several samples, as shown inig. 2, can be used for analyzing qualitatively the porosity in eachamples. Except the commercial carbon, most samples reshape theUPAC isotherm classification of type I that represent porous solid
ith micropore domination. From the similarity of the isothermsefore and after activation, it gives indication that the pore devel-pments by the activation procedures were using initial pore as aemplate. This can be more easily observed from PSD plots that wille explained later. Then, for higher R of chemically activated sam-
Fig. 2. Nitrogen adsorption isotherms of several activated samples.
ples (Z3TyC) a significant development of pore in mesoporous rangecan be observed by a transformation from the flat shape isothermof the type I into type II that can be easily observed in higher partialpressure (P/Po).
For ZxTyCQ samples, the development of mesoporosity is not assignificant as the chemical activated ones with same R. This can bea sign that CO2 mainly enhanced the development of pore in micro-pore range. For R = 2 samples, the combination method was able toimprove the porosity development as shown by Z2T6CQ isothermcompared with Z2T6C isotherm. Meanwhile, the commercial car-bon isotherm (SX Plus) shows that the material has large amountof microporous as well as mesoporous. When it is compared toZ2T6CQ sample, this material has less small pores but significantexcess in large pores.
Quantitative results of porosity and surface area for all sampleshas been summarized in Table 2, with PSD plots of selected sam-ples are shown in Fig. 3. Chemical activated carbon samples showa general trend of enhancement of porosity by increasing activa-tion temperature and chemical ratio. Surface areas of the activatedsamples, which represent the total porosity, have a positive corre-lation with Vmic data, but it is not always in line with Vmes. Thus,the total surface area of the samples is mostly determined by thesurface area in micropores range.
From the PSD plots in Fig. 3a, the chemical activation increasesthe porosity of the raw material in every pore size range. In gen-eral, the PSD indicate three modal pore distribution that can beclassified to small micropore (SMP) with pore width less than 10 A,
Z2T6CQ 0.528 0.106 1200Z3T5CQ 0.266 0.068 607Z3T6CQ 0.266 0.041 619BFA 0.141 0.065 315SX Plus 0.491 0.331 1104
260 C.W. Purnomo et al. / Journal of Analytical and Applied Pyrolysis 91 (2011) 257–262
Fs
AtTliii
bttebotte
cmowiTiob
and Vannice [25]. Beside this method, surface properties can bestudied by observing heteroatom site densities that can be esti-mated from ultimate analysis data normalized by the weight of thecarbon (Table 3). This table shows the atomic (H, N and O) densityon the surface of selected carbon samples which can represent the
Table 3Chemical properties of several samples.
Sample Density (mmol/g carbon)
[H] [N] [O]
Z3T6C 17.80 0.44 6.23
ig. 3. PSD of chemically activated samples and BFA (a); combination activationamples and SX Plus (b).
ccording to the data in Table 2, increase of 100 ◦C of the treatmentemperature will increase about 0.1 cc/g of the micropore volume.hen as indicated from the isotherms analysis above, the usage ofarger R developed pores in mesopore range further. However, thencrease of the activation temperature up to 700 ◦C does not alwaysncrease the mesoporosity, even in some samples show a reductionn this pore size range.
The combination activation method using R = 2 produced car-on samples that have better porosity development compared tohe chemical activated samples with the same activation tempera-ure as suggested from the nitrogen isotherms analysis above. Thenhancement of porosity located in microporous range as showny increase of Vmic value for Z2TyCQ samples compared with Z2TyCnes in Table 2. As stated earlier, this might be used for evidencehat CO2 enhanced more the development in micropore ratherhan mesopore. According to the PSD plots in Fig. 3b, the specificnhancements are peaked at about 5A and 12A.
An interesting result has been shown by the sample of higherhemical ratio of R = 3. By using the ratio in simultaneous activationethod, the porosity was lower compared to chemically activated
nes. The Z3T6CQ sample porosity is dominated by small microporehile pore development in mesopore range of the samples seemed
nhibited as it still resembles the pore distribution of the precursor.he three-modal of PSD turned into unimodal for this sample which
s peaked at about 6 A. The possibility of this kind of PSD evolutionf bagasse based carbons by different activation mechanism haseen previously reported [19].Fig. 4. SEM images of BFA particle surface before (a) and after activation (b).
3.3. Morphological properties
By visual observation, the grain shape and texture of activatedcarbon samples was still similar with the origin. Therefore, thephysical destruction was minor by employing the both activationmethods. From SEM image in Fig. 4, it shows that the activationprocedure did not alter so much the morphological properties ofactivated sample surface compared with the raw material. The mor-phology of BFA is preserved during all the treatments. The onlychange is the appearance of fine holes and defects on the surface ofactivated samples as shown in Fig. 4b.
3.4. Chemical properties
Functional group determined by FTIR study in this report wasbased on infrared assignment identification reported by Fanning
Z3T7C 16.26 0.44 5.69Z3T6CQ 17.55 0.45 6.33BFA 22.85 0.39 10.25
C.W. Purnomo et al. / Journal of Analytical and Applied Pyrolysis 91 (2011) 257–262 261
Table 4Adsorption characteristics of carbon samples in solutions.
Sample pHZPC Qm PH (mg/g) Qm MB (mg/g) SPH (m2/g) SMB (m2/g) SPH/SBET (%) SMB/SBET (%) VT = Vmic + Vmes (cc/g)
Z2T6C 5.2 154 141 547 483 65 68 0.388Z3T5C 3.9 132 143 470 490 77 68 0.517Z3T6C 5.2 169 208 604 715 64 76 0.574Z3T7C 5.9 170 164 608 563 52 48 0.662Z2T6CQ 5.4 189 156 674Z3T6CQ 5.1 130 116 465SX Plus 6.8 128 263 458BFA 8.2 105 98 375
pFf9elTgwv
atpoopidw
less attractive for small molecule adsorption. Meanwhile, the high-
TS
Fig. 5. FTIR spectra of several activated samples and BFA.
opulation of related functional groups. From the FTIR spectra inig. 5, the raw BFA has four major peaks that can be assigned to aunctional group. Its first peak is a broad overlapping peak between00 and 1300 cm−1 which can be assigned for C–O bond in ethers,ster and some bonds in phenolic group. The present of pheno-ic group is also confirmed by the broad band around 3500 cm−1.his band also might be assigned to C–H stretching groups, alcoholroups (O–H), as well as N–H group. Then, the other two peaks areeak peak at 1580 and 1400 cm−1 due to aromatic C C stretching
ibration and carboxyl and carbonate structure, respectively.For activated carbon samples, in general, there are no new peaks
ppear as a result of activation procedures. The effects of activa-ion are only reducing and also intensifying the precursor’s initialeaks. The Z3TyC samples (y equal to 5–7) shows the reductionf the broad peak between 3000 and 3600 cm−1 by the increasef activation temperature. And the band diminishes almost com-
letely by heat treatment at 700 ◦C. The other reduction of intensitys 1400 cm−1 peak for carboxyl-carbonate structure. These peaksecline by increasing the activation temperature has an agreementith the reduction of O and H species as indicated in Table 3. The
able 5ugar cane bagasse based activated carbon properties.
Precursor Activationagent
R Activationtemperature(◦C)
H(h
Bagasse bottom ash Steam na 800 1Bagasse bottom ash CO2 na 800 1Bagasse H3PO4 0.65 (v/v) 900 2Bagasse CO2 na 900 1Bagasse H3PO4 1.5 (w/w) 500 1Bagasse ZnCl2 0.9 (w/w) 600 1Bagasse fly ash ZnCl2/CO2 2 (w/w) 600 1
537 56 45 0.634467 75 64 0.307904 41 82 0.822316 92 82 0.194
only intensifying peak is 1580 cm−1 especially for low temperaturetreatment. This can be a sign of more ordered aromatic structureafter activation. Then, the similarity of the O, N and H density andalso the FTIR spectra between Z3T6C and Z3T6CQ have verified thatCO2 treatment has not affected so much the chemical properties ofthe samples.
3.5. Adsorption performance
Some selected sample have been measured their capacity inadsorbing two different molecules PH and MB which have a sig-nificant different in size and charge in solution. These variationscan be a good tool for evaluating the characteristics of each car-bon samples. Considering the area of the phenol molecule to be0.558 nm2 [26] and the methylene blue molecule to be 1.62 nm2
[27], the surface of carbon occupied by these adsorbates (SMB andSPH) were calculated (Table 4).
The adsorption capacity of adsorbents for a specific moleculeis mainly determined by the porosity profile and chemical sur-face properties. From PH adsorption data, in general it shows agood correlation between Vmic with uptake capacity of the acti-vated samples. However, the capacity of Z3T5C sample was lowerthan Z2T6C even though the former sample has larger microp-orosity. This might be related to lower pHZPC of Z3T5C sample(Table 4) or less positively charged surface. Since, PH moleculesmay present as anions in solution that are strongly attracted to thehigher pHZPC (more positively charged) surface. The other reasonpossibly because Z3T5C has less SMP that peaked around 5 A asshown in PSD plot (Fig. 3a) in which adsorption of PH moleculeswere occurred intensively.
The lowest adsorption capacity of PH was observed for SXPlus among the activated carbon samples. The reason for thisphenomenon is hard to explain by considering well developedmicroporosity and favorable surface chemistry factors of the sam-ple. But it could be related to porosity profile of the material whichhas broad size distribution of meso and macropore that might be
est adsorption capacity of PH was achieved by Z2T6CQ sample dueto well developed micropore.
In the case of large molecule adsorption, i.e. MB, in general thecapacity is in line with VT (Vmic + Vmes) of each samples. This due
olding time)
Vmes (cc/g) Vtot (cc/g) SBET (m2/g) Ref.
0.133 0.395 595 [3]0.074 0.306 517 [3]na 1.234 320 [13]
5 na 0.698 1165 [19]0.510 1.120 1132 [28]0.132 0.621 1278 [29]0.106 0.634 1200 This study
2 cal an
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62 C.W. Purnomo et al. / Journal of Analyti
o MB molecules ability to penetrate pore size in LMP range, evenhough, cannot access SMP pore range. However, the lower capacityf Z3T7C compared to Z3T6C could be due to the contribution ofts less acidic surface of Z3T7C since MB molecule has positivelyharge. For the commercial carbon, the MB uptake is the highestmong AC samples. Even though the charge of the surface of SXlus is not favorable compare to others, the abundantly availabilityf adsorption sites provided in meso and micropore surpassed it.eanwhile, the lowest adsorption capacity of MB was shown by
3T6CQ as the limited of its larger pore as shown in the PSD (Fig. 3b).For adsorbates coverage inside the pores as represented by the
atio of respective molecule surface area to the total available areaSPH/SBET and SMB/SBET), higher porosity inside the samples is notecessary to always have a higher coverage ratio. It is because notll excess porosity can give a positive contribution to adsorption ofertain molecules. For BFA based activated carbon, the two values quite close each other. This indicates that the activated carbonsosses narrow pore distribution. While for Norit SX Plus, MB cov-rage has a large difference from PH that indicates the existencef wide distribution of mesopore as well as macropore becausearge pores will exert very weak adsorption attraction to smaller
olecule (PH). These results give another stressing that the adsorp-ion mechanism is affected by many factors not only govern byorosity of the adsorbents.
.6. Bagasse based activated carbon
As mentioned in the introduction, bagasse has been previouslytudied as precursor for preparing activated carbon. Before activa-ion with high temperature treatment, bagasse has been carbonizedt high temperature under inert atmosphere or at low temperaturesing some chemical agents such as sulfuric acids [10,13,19,28,29].eanwhile, if the ash of bagasse (bottom or fly ash) is used, it
ecomes unnecessary to do carbonization. Up to now, activated car-on from bagasse fly ash has not been documented. A comparisonetween previous bagasse based carbon samples with this studyan be seen in Table 5. Only the largest surface area of the samplesn the literatures is listed in the table.
. Conclusion
The activation methods were able to enhance the porosity asell as increase significantly the adsorption capacity of BFA in rel-
tively low temperature of activation. Z2T6CQ sample exceeded the
[
[[
[
d Applied Pyrolysis 91 (2011) 257–262
commercial activated carbon (SX Plus) in terms of micropore devel-opment and phenol adsorption. Then, the simultaneous activationmethod can produce higher porosity of activated carbon at lowertemperature treatment compared to employing chemical activa-tion only. This activation route can be proposed to reduce energyconsumption during production of activated carbons. This methodwas also able to synthesis samples that have sharp unimodal PSDat 6 A, as shown by Z3TyCQ samples (y equal to 5 and 6).
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