Journal of Industrial and Engineering Chemistry 28 (2015) 37–44

Carbonization of Elaeis guineensis frond fiber: Effect of heating rate andnitrogen gas flow rate for adsorbent properties enhancement

Ling Wei Low, Tjoon Tow Teng *, Abbas F.M. Alkarkhi, Norhashimah Morad,Baharin Azahari

School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia

A R T I C L E I N F O

Article history:

Received 7 January 2014

Received in revised form 15 January 2015

Accepted 22 January 2015

Available online 29 January 2015

Keywords:

Carbonization

Heating rate

Nitrogen gas flow rate

Optimization

BET surface area

A B S T R A C T

Heating rate and nitrogen gas flow rate were found to be influencing carbonization process. Lowering the

heating rate from 30 to 10 8C/min has resulted in the increase of Brunauer–Emmett–Teller (BET) surface

area of the adsorbent from 398.23 to 555.53 m2/g; the percentage of color removal and COD reduction of

Rhodamine B dye have also increased from 27.59 to 99.11% and 25.77 to 98.62%, respectively. The

adsorbent prepared under 100 cm3/min nitrogen flow rate exhibits higher efficiency than that at

500 cm3/min. The carbonization process has efficiently increased the BET surface area of the raw

adsorbent by 99.35%.

� 2015 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

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Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

Introduction

The present study exploited Elaeis guineensis frond fiber (EGFF),a major lignocellulosic rich, agricultural solid waste as anadsorbent for the treatment of Rhodamine B (RB) dye aqueoussolutions. Although, EGFF has been effectively utilized in theproduction of adsorbent [1–3], there is insufficient information onthe production of EGFF with high Brunauer–Emmett–Teller (BET)surface area through carbonization process.

Carbonization is a thermal conversion process of convertingorganic materials to carbon [4]. Carbonization process can also bedefined as aromatic growth and polymerization process [5–7]where aromatic is the vital building blocks for carbon. Other thancarbonization temperature and carbonization duration, there areseveral crucial parameters that affect the properties of charproduced i.e. heating rate, and nitrogen gas flow rate which shouldbe taken into consideration for enhancing further the total surfacearea of the adsorbent.

Carbonization temperatures associated with the amount ofnecessary energy to break the chemical bonds of the raw materialto enrich the carbon content and to create an initial porosity in thechar [4]. It also influences the amount of volatiles released from thematerials and thus the char yield [6]. Studies have shown that,

* Corresponding author. Tel.: +60 4 6532215; fax: +60 4 6573678.

E-mail address: ttteng@usm.my (T.T. Teng).

http://dx.doi.org/10.1016/j.jiec.2015.01.020

1226-086X/� 2015 The Korean Society of Industrial and Engineering Chemistry. Publis

500 8C must be considered as the lowest carbonization tempera-ture as the char yield was almost constant beyond this tempera-ture [8,9].

Carbonization duration (usually varies from 30 min to 2 h) isthe time where material remains in the reactor at a specifictemperature before it is cooled [6,8,9].

The heating rate is one of the carbonization parameters thataffect the composition of the volatiles and the char properties[10]. Carbonization heating rate is usually performed from1 to13 8C/min [11].

The effect of nitrogen gas flow rate in the carbonization processshould also be taken into consideration as the gas plays animportant role in removing the volatile products from char surfaceand reduces the secondary reaction such as repolymerization andrecondensation [12].

Most previous studies [4,6,13–15] employed univariate methodto study the effect of carbonization process (i.e. carbonizationtemperature and duration) on properties of adsorbents. This mightnot attain the authentic optimal operating conditions. Responsesurface methodology (RSM), an amalgamation of mathematicaland statistical techniques has been used in the present study todevelop, improve, optimize and study the interactions of two ormore variables of the carbonization process [16–19].

In the present work, not only studied on the effects ofcarbonization temperature and carbonization duration on theadsorption of RB dye aqueous solutions but also the effects ofheating rate and nitrogen gas flow rate were studied using

hed by Elsevier B.V. All rights reserved.

Fig. 2. Chemical structure of Rhodamine B dye.

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–4438

statistical design techniques. The adsorbent was characterizedusing surface area and pore size analysis, Fourier-transforminfrared (FT-IR), and scanning electron microscope (SEM).

Experimental

Materials

EGFF used as raw material to produce adsorbent in this studywas obtained from a plantation in Nibong Tebal, Malaysia. The barkwas removed and the frond was cut into pieces using band saw.The frond was then cleaned with distilled water and left to dryunder sunlight. Dried EGFF was ground to fine powder and washedthoroughly with boiling distilled water until the residual solutionbecame clear [20]. It was then dried at 100 8C in an oven toconstant weight and sieved to obtain the particle size of <45 mm.The resulted EGFF was kept in dessicator prior to use.

Carbonization of Elaeis guineensis frond fiber

The experimental set-up of the carbonization unit is shown inFig. 1. It basically consists of a stainless steel reactor and a nitrogensupply. A fixed amount of EGFF powder was loaded into a Jenknerretort that is a cylindrical stainless steel fixed bed reactor with alength and inner diameter of 180 mm and 40 mm, respectively.The reactor was externally heated using vertical Carbolite electricfurnace where the temperature was measured by a Ni–Cr–Nithermocouple inside the bed. The maximum operating tempera-ture is 900 8C. Before heating, the system was flushed with drynitrogen for 30 min to remove all traces of oxygen. Aftercarbonization, the final weight of sample was determined tocalculate the biochar yield.

The dried EGFF with particle size of <45 mm was heated tospecific carbonization temperature (500–900 8C), carbonizationduration (1–3 h), heating rate (10–30 8C/min), and nitrogen gasflow rate (100–500 cm3/min). After carbonization the sampleswere cooled to room temperature under constant nitrogen gas flowrate of 100 cm3/min. The carbonized samples were crushed andsieved to obtain particles with sizes less than <45 mm.

Adsorbate

Rhodamine B (C.I. number: 45170; molecular formula:C28H31N2O3Cl; molecular weight: 479.02 g/mol) was obtainedfrom Sigma-Aldrich as a commercially available dye. Fig. 2 showsthe chemical structure of this dye [21,22]. Distilled water was used

Fig. 1. Schematic diagram of the experimental set-up.

throughout the study to prepare the RB dye aqueous solutions of200 mg/L.

Adsorption experiments

Batch adsorption experiments were conducted in 250 mLErlenmeyer flasks containing 100 mL RB dye aqueous solutions.The solution pH was adjusted with 0.1 M HCl and 0.1 M NaOH. Foreach test, 0.5 g of carbonized EGFF powder was used and themixture was agitated at 150 rpm in an orbital shaker for 24 h toensure adsorption equilibrium was attained. Aliquot (80 mL) waswithdrawn after the adsorption process and was centrifugedimmediately at 4000 rpm for 30 min. The supernatant wasused for dye concentration analysis using spectrophotometer(Model DR2800) at the maximum absorption wavelength of(lmax = 547 nm). The amount of RB adsorbed onto the EGFF wasdetermined using

qe ¼ðC0 � CeÞV

W(1)

The percentage of RB removal can be calculated from

RB removalð%Þ ¼ 100C0 � Ce

C0

� �(2)

The percentage of COD reduction can be calculated from

COD reductionð%Þ ¼ 100D0 � De

D0

� �(3)

where qe (mg/g) is the amount of RB adsorbed at equilibrium, C0

(mg/L) and Ce (mg/L) are the initial and equilibrium liquid-phaseconcentration of RB, respectively, w (g) is the adsorbent mass, V (L)is the volume of dye solution. D0 and De are the initial and final CODconcentrations, respectively.

Experimental design

All the experimental sequences received by the Design Expertsoftware (Version 6.0.10, Stat-Ease, Inc., Minneapolis, UnitedStates) were executed. Response surface methodology (RSM)was carried out to study the effect of four independent variables:carbonization temperature A (500–900 8C), carbonization durationB (1–3 h), heating rate C (10–30 8C/min) and nitrogen gas flow rateD (100–500 cm3/min) on decolorization (y1) and COD reduction(y2).

The response y is a function of the levels of independentvariables:

y2or2 ¼ f ðA; B; C; DÞ þ e (4)

where e is the error observed in the response y1 or 2. The expectedresponse is represented by

Eðy1or2Þ ¼ f ðA; B; C; DÞ ¼ h (5)

Table 1Independence factors and corresponding levels used for optimization.

Variables Real values of coded

levels

�1 1

Carbonization temperature (8C) 500 900

Carbonization duration (h) 1 3

Heating rate (8C/min) 10 30

Nitrogen gas flow rate (cm3/min) 100 500

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–44 39

and the surface area is represented by

h ¼ f ðA; B; C; DÞ (6)

where h is the response surface.Experimental data was analyzed to fit the following second-

order model:

h ¼ bo þXk

i¼1

bixi þXk

i¼1

biix2i þ

X Xi < j

bi jxix j (7)

where bo, bi, bii, and bij are regression coefficients, and xi are thecoded variables. The relationship between the natural variable ji

and the coded variables xi is

xi ¼jiðHigh level þ Low levelÞ=2

ðHigh level þ Low levelÞ=2(8)

Adsorbent characterization

The char (carbonized powder) was characterized by surfacearea and pore size analyzer (model: NOVA 2200e). Prior to gasadsorption measurements, the carbon was degassed at 110 8C in avacuum condition for a period of 8 h. Nitrogen adsorption isothermwas measured over a relative pressure (P/Po) range fromapproximately 10�6 to 1 where Po is the saturation pressure.The BET surface area was calculated from the isotherms by usingthe Brunauer–Emmett–Teller (BET) equation [4,23].

Functional groups in a molecule of the EGFF powder wasdetected using FTIR spectroscopy (model: Thermo scientific FTIR-Is10) within the range of wavelength region between 400 and4000 cm�1.

Surface morphology of the adsorbent was detected using SEM(model: Leo Supra 50 VP Field Emission SEM equipped with an

Table 2The results of statistical analysis.

Carbonization

temperature (8C)

Carbonization

duration (h)

Heating rate

(8C/min)

Nitrogen gas flow

rate (cm 3/min)

Exp

rem

500 1 10 100 27

900 1 10 100 99

500 3 10 100 26

900 3 10 100 99

500 1 30 100 15

900 1 30 100 27

500 3 30 100 19

900 3 30 100 99

500 1 10 500 22

900 1 10 500 43

500 3 10 500 27

900 3 10 500 79

500 1 30 500 24

900 1 30 500 20

500 3 30 500 26

900 3 30 500 77

500 2 20 300 19

900 2 20 300 99

700 1 20 300 18

700 3 20 300 34

700 2 10 300 27

700 2 30 300 21

700 2 20 100 35

700 2 20 500 25

700 2 20 300 22

700 2 20 300 22

700 2 20 300 24

700 2 20 300 25

700 2 20 300 25

Oxford INCA 400 Energy Dispersive X-ray Microanalysis (EDS)system) before and after adsorption.

Results and discussion

Statistical analysis

Each independent variable i.e. carbonization temperature A,carbonization duration B, heating rate C, nitrogen gas flow rate Dprovides significant effects on the adsorbent properties. It is crucialto study the effect of interaction between independent variables inorder to attain authentic optimal operating conditions.

Table 1 shows the levels of each independent variable used inthe present study. Optimization of the carbonization process ofEGFF was performed according to the design matrix and thecorresponding results are listed in Table 2. The results of 29 runsusing face centered composite design (FCCD) with four factors(carbonization temperature A, carbonization duration B, heatingrate C, nitrogen gas flow rate D) are able to cover all feasiblecombinations of various selected levels. The runs are distributed as24 = 16 factorial points, 8 axial (star) points, and 5 replicates at thecenter. All runs were accomplished randomly to avert unexpectederror in the observed response. The range of color removal and COD

erimental color

oval (%)

Experimental COD

reduction (%)

Predicted color

removal (%)

Predicted COD

reduction (%)

.36 29.27 32.84 33.8

.11 98.62 86.6 85.94

.29 25.14 19.92 19.44

.98 99.54 112.68 111.94

14.27 8.84 8.42

.59 25.77 43.36 41.96

.14 18.52 19.52 18.5

.97 99.54 93.04 92.4

.86 22.94 25.2 25.7

.41 42.41 49.16 48.28

.8 27.31 18.16 16.98

.52 78.44 81.12 79.92

23.85 17.44 17.32

.37 19.94 22.16 21.3

.03 24.73 34 33.04

.05 76.05 77.72 77.38

.76 19.72 32.37 32.66

.87 99.54 81.11 80.9

.32 17.43 12.47 11.95

.1 33.03 33.79 32.81

.89 26.6 28.62 28.38

.8 21.9 14.92 14.42

.77 34.4 33.47 32.83

.85 25.4 21.99 21.27

.28 21.56 27.67 27.28

.19 23.85 27.67 27.28

.55 24.31 27.67 27.28

.83 25.23 27.67 27.28

.03 24.31 27.67 27.28

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–4440

reduction of RB dye varied from 15 to 99.98% and 14.27 to 99.54%,respectively.

The quadratic equations for predicting the optimum pointwas acquired according to the FCCD and input variables, andthen the empirical relationship between the responses (colorremoval and COD reduction) and the independent variables(carbonization temperature A, carbonization duration B, heatingrate C, nitrogen gas flow rate D) in the coded units wereintroduced in Eqs. (9a) and (9b).

Color removalð%Þ ¼ 27:67 þ 24:37A þ 10:66B � 6:85C � 5:74D

þ 29:07A2 � 4:54B2 � 5:90C2 þ 0:060D2

þ 9:75AB � 4:81AC � 7:45AD þ 5:90BC

þ 1:47BD þ 4:06CD

(9a)

COD reductionð%Þ ¼ 27:28 þ 24:12A þ 10:43B � 6:98C � 5:78D

þ 29:50A2 � 4:90B2 � 5:88C2 � 0:23D2

þ 10:09AB � 4:65AC � 7:39AD þ 6:11BC

þ 1:41BD þ 4:25CD

(9b)

Positive coefficients for each term designate to thesynergistic effect of the factor on the response, whilst thenegative sign denote the antagonistic effect of the factor on theresponse [17,24]. The regression models in Eqs. (9a) and (9b)are assured as the coefficient of determination (R2) values are0.9277 and 0.9269, respectively, which mean that more than92% of the entirety variation is enlightened by the regressionmodels.

Tables 3a and 3b give the results of analysis of variance ANOVAfor the percentage of color removal and COD reduction, respec-tively. The ANOVA implies that the authentic correlation betweenthe responses and significant variables represented by theequations are accurate. The significance of the coefficient termis established by the values of F and p. Higher F value and smallerp value show more significant of the coefficient term in thecarbonization process [25–27]. The ANOVA tables show that themain linear effect is significant for all selected factors (A, B, C, D).The effect of carbonization temperature in the carbonization

Table 3aANOVA for color removal.

Source Sum of

squares

DF Mean

square

F value Prob > F

Model 21,289.30 14 1520.66 12.83 <0.0001

A 10,688.68 1 10688.68 90.15 <0.0001

B 2045.01 1 2045.01 17.25 0.0010

C 844.19 1 844.19 7.12 0.0184

D 593.06 1 593.06 5.00 0.0421

A2 2184.46 1 2184.46 18.42 0.0007

B2 53.29 1 53.29 0.45 0.5135

C2 90.15 1 90.15 0.76 0.3979

D2 9.44 � 10�3 1 9.44 � 10�3 7.962 � 10�5 0.9930

AB 1521.00 1 1521.00 12.83 0.0030

AC 369.60 1 369.60 3.12 0.0993

AD 888.04 1 888.04 7.49 0.0161

BC 556.72 1 556.72 4.70 0.0480

BD 34.34 1 34.34 0.29 0.5989

CD 263.25 1 263.25 2.22 0.1584

Residual 1659.94 14 118.57

Total 22949.24 28

R-squared 0.9277

process is more significant than carbonization duration, followedby heating rates and nitrogen gas flow rates. The quadraticcontribution over the linear effect displays highly significant effectof carbonization temperature (A) with the p value of 0.0007. Inter-actions between carbonization temperature and carbonizationduration, carbonization temperature and nitrogen gas flow rate,carbonization duration and heating rate, and heating rate andnitrogen gas flow rate exhibit significant effect on both thepercentage of color removal and COD reduction of RB dye aqueoussolutions.

Three-dimensional response surface plot is given in Fig. 3a andb for color removal and COD reduction, respectively. Both figuresdisplay clear pictures for maximum color removal and CODreduction. It is clearly observed that maximum percentage of colorremoval and COD reduction recline within the chosen interval ofthe factors.

Optimization of the experiment

After the regression models was constructed the decisivefactor for percentage of color removal and COD reduction wasascertained to acquire maximum percentage of color removaland COD reduction. Exploring for the preeminent setting of theprominent factors that give maximum values in RB dye removalcan be attained by using the models in Eqs. (9a) and (9b),simultaneously. The optimum condition for carbonization ofEGFF was obtained at carbonization temperature of 899 8C,carbonization duration of 2.7 h, heating rate of 10 8C/min, andnitrogen flow rate of 243 cm3/min with 99.30% of color removaland 98.88% of COD reduction. Authentication experiments werecarried out by plotting to ensure the optimum conditions andthe results for the predicted and experimental values of colorremoval and COD reduction are close to each other (Fig. 4a andb). As can be seen that the data points were well distributed andclose to a straight line which have the R2 values of 0.9277 and0.9269 for color removal and COD reduction, respectively. Theresults suggest an excellent relationship between the experi-mental and predicted values of the responses, and theunderlying assumptions of the above analysis are appropriate.The results also indicate that the selected quadratic model isadequate in assuming the response variables for the experi-mental data.

Table 3bANOVA for COD reduction.

Source Sum of

squares

DF Mean

square

F value Prob > F

Model 21,180.31 14 1512.88 12.67 <0.0001

A 10,469.04 1 10469.04 87.71 <0.0001

B 1959.38 1 1959.38 16.42 0.0012

C 877.80 1 877.80 7.35 0.0169

D 600.89 1 600.89 5.03 0.0415

A2 2249.69 1 2249.69 18.85 0.0007

B2 62.18 1 62.18 0.52 0.4823

C2 89.52 1 89.52 0.75 0.4011

D2 0.14 1 0.14 1.184 � 10�3 0.9730

AB 1629.33 1 1629.33 13.65 0.0024

AC 346.15 1 346.15 2.90 0.1107

AD 874.09 1 874.09 7.32 0.0171

BC 598.05 1 598.05 5.01 0.0420

BD 31.87 1 31.87 0.27 0.6134

CD 288.49 1 288.49 2.42 0.1423

Residual 1671.10 14 119.36

Total 22,851.41 28

R-squared 0.9269

Fig. 3. Three dimensional response surface plot for (a1) percentage of color removal for carbonization temperature and carbonization duration (a2) percentage of color

removal for heating rate and carbonization duration (b1) percentage of COD reduction for carbonization temperature and carbonization duration (b2) percentage of COD

reduction for heating rate and carbonization duration.

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–44 41

Effect of carbonization temperature on the pore structure of

carbonized EGFF chars

N2 adsorption isotherm can be used to estimate the type ofpores present in the EGFF chars. The N2 adsorption isothermsand characteristics of the EGFF chars prepared under carboni-zation temperature of 500 8C and 900 8C are shown in Fig. 5 andTable 4, respectively. The isotherm of char prepared attemperature 500 8C belongs to type II according to BDDT(Brunauer–Deming–Deming–Teller) classification [28]. Type IIisotherm denotes that monolayer-multi-layer adsorption on astable and open external surface of EGFF, which may be non-porous, macroporous or microporous [23]. The isotherm of charprepared at temperature 900 8C belongs to type I of the BDDTclassification. Type I isotherm refers to relatively small amountof multilayer adsorption on the open surface, which is usuallyexhibited by microporous solids. The main feature of Type Iisotherm is the long plateau [23]. In Fig. 5, the initial part of theplot of 900 8C symbolizes micropore filling, and the slope ofthe plateau at high relative pressure is due to multilayeradsorption on the non-microporous surface, i.e., in mesopores,

in macropores and on the external surface [4,23]. Table 4 showsthe BET surface area (SBET), total volume (Vtotal), microporevolume (Vmicro) and average diameter (Davg) of the chars. Whenthe carbonization temperature was increased from 500 8C to900 8C the SBET increased from 31.80 to 555.53 m2/g, Vtotal

increased from 0.02-0.31 cm3/g, and Vmicro increased from 0.005to 0.14 cm3/g. However the Davg decreased with increasingcarbonization temperature. The results show that the 900 8Ccarbonization temperature char has better developed porestructure as compared with that of 500 8C carbonizationtemperature char.

With the increasing carbonization temperature, polymerizationreaction would further proceed. The diameter of sample woulddecrease gradually and the micropores of sample would develop,giving rise to increases in the SBET, Vtotal, Vmicro of chars. Thepercentage of color removal and COD reduction of chars preparedat carbonization temperature of 500 8C and 900 8C, 1 h carboniza-tion duration, heating rate of 10 8C/min and nitrogen gas flow rateof 100 cm3/min once again show that higher temperature charsoffer higher potential to produce activated carbon of greateradsorption capacity from EGFF.

Fig. 4. Plot of the experimental and predicted (a) color removal (b) COD reduction.

Fig. 5. N2 adsorption isotherm of EGFF char prepared under different carbonization

temperature.

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–4442

Effect of heating rate on the removal of RB dye aqueous solutions

The effect of heating rate on the removal of RB dye aqueoussolutions has been studied under heating rate of 10–30 8C/min,carbonization temperature of 900 8C, carbonization duration of 1 h,and nitrogen gas flow rate of 100 cm3/min. Table 4 shows thatwhen the heating rate was increased from 10 to 30 8C/min, the SBET

decreased from 555.53 to 398.23 m2/g, Vtotal decreased from 0.31 o0.17 cm3/g, and Vmicro decreased from 0.14 to 0.13 cm3/g. Thecarbonization process involves cleavage of C–H and C–C bonds toform reactive free radicals, molecular reassemble, thermalpolymerization, aromatic condensation and elimination of H2

[5,13]. Low heating rate can reduce adverse effects such as

Table 4Characteristics of the EGFF chars prepared under various carbonization temperatures.

Carbonization

temperature (8C)

Carbonization

duration (h)

Heating rate

(8C/min)

Nitrogen gas flow

rate (cm3/min)

Effect of carbonization temperature

500 1 10 100

900 1 10 100

Effect of heating rate

900 1 10 100

900 1 30 100

Effect of nitrogen gas flow rate

900 1 10 100

900 1 10 500

Effect of carbonization duration

900 1 10 100

900 3 10 100

Raw EGFF: SBET = 3.60 m2/g.

Vtotal = 0.002 cm3/g.

Vmicro = 0.001 cm3/g.

Daverage = 12.4 nm.

shrinkage, cracking and thermal stresses that may build up duringcarbonization. High heating rate reduces the restricted effects ofmass transfer and increases the decomposition of the biochar intoliquid product and the mechanical performance of C/C compositesdeteriorates [29,30].

Effect of nitrogen gas flow rate on the removal of RB dye aqueous

solutions

The sweep gas removes the volatile products from char surfacesand reduces the secondary reactions such as repolymerizationand recondensation. The effect of nitrogen gas flow rate on theadsorbent properties was performed under carbonization tem-perature of 900 8C, carbonization duration of 1 h, heating rate of10 8C/min and nitrogen gas flow rate of 100–500 cm3/min. InTable 4, nitrogen gas flow rate of 100 cm3/min shows higher SBET

SBET

(m2/g)

Vtotal

(cm3/g)

Vmicro

(cm3/g)

Daverage

(nm)

% Color

removal

% COD

reduction

31.80 0.02 0.005 5.92 27.36 29.27

555.53 0.31 0.14 4.18 99.11 98.62

555.53 0.31 0.14 4.18 99.11 98.62

398.23 0.17 0.13 3.35 27.59 25.77

555.53 0.31 0.14 4.18 99.11 98.62

98.97 0.05 0.03 6.1 43.41 42.41

555.53 0.31 0.14 4.18 99.11 98.62

555.67 0.31 0.15 4.17 99.98 99.54

Fig. 6. IR spectra of (a) raw EGFF (b) EGFF char.

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–44 43

(555.53 m2/g), Vtotal (0.31 cm3/g), Vmicro (0.14 cm3/g), 99.11% ofcolor removal and 98.62% of COD reduction as compared tonitrogen gas flow rate of 500 cm3/min with SBET (98.97 m2/g),Vtotal (0.05 cm3/g), Vmicro (0.03 cm3/g), 43.41% of color removaland 42.41% of COD reduction. Demiral and Ayan [31] reportedthat, nitrogen flow rate affects the residence time of the adsorbentproduced by pyrolysis. A rapid flow of 500 cm3/min of N2 wasbelieved to have cooled down the EGFF rapidly from the hot zonethus minimizing the carbonization reaction to occur. The presentstudy suggested that nitrogen gas flow rate of <500 cm3/min issuitable for the carbonization process.

FTIR

Spectra of raw EGFF and char were examined for functionalgroups contributed to the adsorption process; the spectra areshown in Fig. 6.

The FTIR spectrum of raw EGFF (Fig. 6a) indicates the peakslocated at 3418.91, 2921.29, 1737.01, 1636.81, 1426.21, 1376.19,1247.67, and 1053.62 cm�1, identical to the N–H group, C–H group,C55O stretch, C55C group, –CH2 (alkyl), C–CH3 group, CH in planebending, C–O (anhydrides).

The FTIR spectrum of char (Fig. 6b) indicates the peaks locatedat 3386.19, 2918.54, 2846.34, 2361.01, 2340.64, 1426.61, 1121.66,874.51, and 808.22 cm�1, identical to the presence of N–H group,C–H group, two bands of aldehyde, CBC (alkynes), –COOH, –CH2

(alkyl), amines group, CH out-of-plane deformation (two bands),out-of-plane C–H derivatives, respectively.

After carbonization process a few functional groups have beenform i.e. CBC (alkynes), –COOH, amines group, CH out-of-plane

deformation (two bands), and out-of-plane C–H derivatives. It issuggested that, these groups are important in the bond formationamong carbon atoms [32].

SEM

A comparison of the morphology of raw EGFF, char (at optimalcarbonization conditions), and spent EGFF with magnification of1000� is illustrated in Fig. 7a, b and c, respectively. The fibersstarted to rupture and the surface of the char was uneven andrough which increased the surface area of the adsorbent. After theadsorption of RB dye on EGFF, the surface of the adsorbent isenveloped with dye molecules and is rough.

Conclusion

In conclusion, increasing the carbonization temperature andcarbonization duration resulted in an increase in the SBET, Vtotal,Vmicro of char. Heating rate of 10 8C/min has higher SBET Vtotal,Vmicro values as compared to heating rate of 30 8C/min. Reductionof heating rate from 30 8C/min to 10 8C/min increases the surfacearea from 398.23 to 555.53 m2/g. The present study indicatesthat it is not necessary to have a high nitrogen gas flow rate forbetter adsorbent performance in terms of SBET, Vtotal, Vmicro,percentage of color removal and percentage of COD reduction.From the statistical analysis, carbonization temperature,carbonization duration, heating rate, and nitrogen gas flow rateplays a vital role in carbonization process. An effective char withthe BET surface area of 555.53 m2/g, 99.30% RB removal and98.88% of COD reduction were produced in the present study

Fig. 7. SEM micrograph of (a) raw EGFF (b) EGFF char (c) spent EGFF with a

magnification of 1000�.

L.W. Low et al. / Journal of Industrial and Engineering Chemistry 28 (2015) 37–4444

using optimal carbonization parameters at carbonization tem-perature of 899 8C, carbonization duration of 2.7 h, heating rateof 10 8C/min, and nitrogen flow rate of 243 cm3/min.

Acknowledgements

The authors acknowledge the financial support provided byMinistry of Higher Education Malaysia under the program ofMyBrain15 and Universiti Sains Malaysia through RU-PRGS grant1001/PTEKIND/845029. The authors also thank Professor Dr. AbdulRahman bin Mohamed of the School of Chemical Engineering forthe loan of the carbonization unit.

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