ASTIMAR ABDUL AZIZ* and MOHAMAD DERAMAN**
* Malaysian Palm Oil Board,
6 Persiaran Institusi, Bandar Baru Bangi, 43000 Kajang, Selangor, Malaysia.
E-mail: [email protected]
** School of Applied Physics, Faculty Science and Technology, Universiti Kebangsaan Malaysia,
43600 Bangi, Selangor, Malaysia.
aBsTRaCT
Porous carbon granules were prepared from the H2SO4 treated carbon pyro-polymers from oil palm empty fruit bunch (EFB) fibres. The carbon pyro-polymers were prepared by a slow pyrolysis process of the EFB carried out at 280oC under vacuum. Two concentrations of H2SO4 (0.2 M and 0.6 M) were used for the pre-treatment of the carbon pyro-polymers. The untreated carbon pyro-polymer was used as a standard.
The treated and untreated carbon pyro-polymers were analysed for the elemental content (CHNO), thermal behaviour (TGA) and the particle size. The green pellets were produced from the treated carbon pyro-polymers and were carbonised at three carbonisation temperatures (600oC, 700oC and 800oC) under nitrogen. The porosity of the activated carbon granules was studied using Brunauer-Emmett-Teller (BET) analysis and the results were correlated to the interlayer spacing (d002), stack height (Lc) and stack diameter (La) of the trubostratic crystallites in the carbon crystallite estimated from the XRD analysis. Data showed that: (a) the d002 of the carbons decreased with increasing carbonisation temperatures, and (b) the d002 of carbon prepared from 0.2 M H2SO4 show a decrease as compared to untreated carbon, but an increase was observed for the carbon prepared from 0.6 M H2SO4 treatment. The La shows an increase for the effect of increase in H2SO4 treatment and an increase with increase in the carbonisation temperatures. These findings indicated significant effect of H2SO4 and carbonisation temperatures toward the porosity and micro-structure of the activated carbon granules.
Keywords: activated carbon, carbon pyro-polymers, empty fruit bunches, porosity, BET.
Date received: 3 January 2011; Sent for revision: 12 January 2011; Received in final form: 13 June 2013; Accepted: 14 June 2013.
PORE sTRUCTURE OF CaRBOn GRanULEs PREPaRED FROM sLOW PYROLYsis OF OiL
PaLM EMPTY FRUiT BUnCH FiBREs
inTRODUCTiOn
Empty fruit bunch (EFB) is one of the biomasses being produced from the palm oil mill. Basically the yield is being calculated based on 22% of the fresh fruit bunch processed. Fibres from EFB contain about
77.7% holocellulose, which consists of 44.2% and 33.5% of a-cellulose and hemicellulose respectively, and 20.4% of lignin (Astimar et al., 2002). These components contribute to the carbon content of the EFB and it has also been reported that the carbon content of EFB is in the range of 42%-43% (wet basis) (Gurmit et al., 1990). The abundance of EFB from the mills has attracted many researchers in pursuing the R&D for the preparation of many value-added products, including the activated carbons and carbon products. Studies on the preparation of solid carbon products from EFB were initiated in the 1990s (Mohamad, 1993; 1995; Mohamad et al., 2003), which later advanced into the production of
glassy carbon. Persuant to this, the glassy carbons have been further studied for the advanced carbon products applications (Astimar et al., 2008).
Activated carbons are the oldest industrially manufactured adsorbents and currently, with the advanced technology on tailoring the porosity of the activated carbon, they have been used in many applications such as gas separation, gas filtration and as catalysts (Suzuki, 1994; Marsh and Rodriguez- Reinos, 2006). Agricultural waste products have been used for the production of carbon adsorbents, and as for Malaysia, the major raw material for the production of activated carbon are coconut shells and palm kernel shells. Previous researchers have reported that high porosity activated carbons could be obtained from coconut shells (Iwasaki et al., 2001;
Sekar et al., 2004; Su et al., 2006) and palm kernel shells (Hu and Srinivasan, 1999; Guo et al., 2007) and are suitable for used for toxic gas filtration.
According to the International Union of Pure and Applied Chemistry (IUPAC), the pores of a porous material are classified into three groups:
micropores (width d <2 nm), mesopores (2 nm < d
< 50 nm) and macropores (d >50 nm) (Gregg and Sing, 1982). The typical evaluation of the porosity and pore size distribution in porous material is by using gas adsorption isotherms as suggested by Barrett, Joyner and Halenda (BJH method) (Barrett et al., 1951).
The analysis of certain carbon structures can be made in terms of the dimension [stack height (Lc) and width (La)] of the graphite-like crystallites that are randomly distributed and oriented throughout the samples through the X-ray diffraction (XRD) analysis. Each crystallite consists of a number of near-parallel carbon layers that form the stacks height and width, and the nearest layers are separated by an interlayer spacing d002. Both Lc and La were found to change simultaneously during carbonisation (Takahashi et al., 1965), and Lc was observed to be dependent on the crystallinity of the carbon precursors (Dae et al., 2001).
The use of acids for the activation of the lignocellulosic materials to prepare high surface area porous carbon has been studied for many materials (Mochida et al., 1985; Guo et al., 2005; Legrouri et al., 2005). Basically, acids are an oxidation agent, which promote the dehydration and redistribution of biopolymers in lignocellulosic materials (Song and Lee, 1984). It involves the cleavage of the ether bonds between the lignin and the cellulose, followed by recombination reactions in which larger structural units are formed, resulting in a rigid cross linked solid (Helm and Young, 1989; Sabio et al., 1995; El-Hendawy, 2003). Based on this hypothesis, sulphuric acid (H2SO4) treatment of the carbon precursors of EFB is targeted to alter the chemical
and physical structures of the lignocellulosic materials, thus increasing some of the porosity and physical properties of the activated carbon produced.
Previous study shows that the treatment of carbon pyro-polymers of EFB with H2SO4 increased the self- adhesive binding property of the pyro-polymers and thus increased the physical and mechanical properties of the carbon pellets prepared (Astimar et al., 2004). Meanwhile, from the following study, it was found that there is a very low porosity of the carbon pellets which was correlated to the effect of the particle sizes and the compression added during the preparation of the green pellets (Astimar et al., 2005). The carbonisation temperature of 1000oC was also found contributed to the low porosity.
This article studies the porosity and structure of the activated carbon granules prepared from different H2SO4 concentrations treatment of the EFB carbon pyro-polymers, carbonised under lower different carbonisation temperatures.
EXPERiMEnTaL
Preparation of EFB Carbon Precursors
EFB used for this study were in the form of chips, obtained from the chipping of dried EFB using MAIER D-33649 chipper. The carbon pyro-polymers were prepared by slow pyrolysis process under vacuum. Six hundred grammes of EFB chips were slowly pyrolysed in the box pyrolysis system, and heated at 280οC for 3 hr under vacuum condition. The box furnace is a Thermoline Furnace which has been modified by taking out the door, and was inserted with a hollowed sample container and a vacuum extractor that will attach tightly to the furnace.
The extractor is equipped with a vacuum suction and the thermocouple for temperature controlling.
The design of the facilities and the vacuum slow carbonisation system is illustrated in Figure 1.
This pre-carbonisation process was attempted to eliminate the low molecular weight and volatile components from the fibres, basically hemicellulose and extractives. This step will partially expose the lignin part of the EFB fibres which later contributes to the self-adhesive properties of the carbon pyro- polymers (Astimar et al., 2003). The pre-carbonised EFB (which has lost weight of around 40%), was then ground into powdered form using a ball milling process into sizes less than 100 mm. For the chemical treatment, 100 g of the carbon pyro- polymers was dissolved in 500 ml of H2SO4 at different concentrations (0.2 M and 0.6 M) and was heated at 100oC for 5 min before drying in oven.
These two concentrations were chosen based on the previous study which showed both gave the best
physical characteristics of carbon pellets for carbon electrode (Astimar et al., 2004). The untreated carbon pyro-polymers were used as a standard.
Preparation of activated Carbon Granules
The weighed treated carbon pyro-polymers were then used to produce green-pellets by compressing it in a mould at 10 Newton, and were then carbonised at different temperatures of 600oC, 700oC and 800oC using the multi-steps heating profile in the Vulcan Box Furnace 3-1750 in nitrogen atmosphere. The multi-steps heating profile involves heating up to 320oC at a rate of 1.0oC min-1 and a holding period of 60 min. Further, temperature was increased to the selected carbonisation temperature (600oC, 700oC or 800oC) at a rate of 3.0oC min-1 and a holding period of 5 min. After completing the carbonisation process, the cooled carbon pellets were then kept in the desiccator chamber before further processing.
The activated carbon granules were prepared by crushing the carbon pellets with mortar and were sieved at sizes < 2 mm of granules. Prior to that, the density of the carbon pellets was measured by dividing the weight by the volume of the pellets.
Characterisation
Mettler Toledo STAR System Thermal Analyser was used to obtain the thermograms (TGA analysis) of the EFB carbon pyro-polymers in the temperature range up to 600οC in the inert atmosphere at the heating rate of 20οC min-1. The elemental analysis (CHNO) for the carbon precursors was carried out using Eager 300 Thermo Finnigan pyrolysis instrument. The effect of the H2SO4 concentrations on the particle size of the carbon pre-cursors was analysed using MICROTRAC-X100 Particle Size Analyser.
The X-ray diffraction measurements on activated carbon disks were conducted using a Siemens (D5000) diffractometer which employed Cu K (0.1542 nm) radiation. The X-ray diffraction patterns will show the disordered graphitic which are assigned to two broad peaks at 002 plane and 10 plane (overlapped 100 and 101), respectively (Ryu et al., 2002). The interlayer spacing (d002) was calculated using Bragg equation (Jenkins and Kawamura, 1976) and the stacking diameter (La) was calculated from the linear relationship between interlayer spacing and stack diameter proposed by Richards (1967). The stacking height (Lc) was calculated from angular width of the half maximum intensity of the diffraction peak (002) (Jenkins and Kawamura, 1976).
Nitrogen adsorption isotherms at 77K were obtained using Micromeritics instrument (Model ASAP 2000) at the relative pressure ranging from
0.01 to 1. Before the measurement all the samples were degassed at 150oC for 1 hr. Surface areas and micropores volume of the carbon pellets were determined from the application of the Brunauer- Emmett-Teller (BET) and Dubinin-Radushkevich (D-R) equations, respectively. The t-plot method was applied to calculate the micropore volume and external surface area (mesopore surface area). The total pore volumes were estimated based on the liquid volume of adsorbate (N2) at a relative pressure of 0.98 (Gregg and Sing, 1982).
REsULTs anD DisCUssiOn
The preparation of EFB pyro-polymer was discussed earlier, whereby the vacuum carbonisation has reduced the EFB fibres into pre-carbonised fibres (Astimar et al., 2003). Table 1 shows the effect of the H2SO4 treatments towards the characteristics of the pyro-polimers. The H2SO4 as an activation agent caused a weight loss of the pyro-polimers in which the 0.2 M and 0.6 M resulted in a weight loss of 20.3%
and 25.9% respectively. The trend was also observed in the C, N and O; and also in the particle size of the carbon pyro-polymers.
The H2SO4 has significantly reduced the particle size of the carbon pyro-polymers and this can be explained by the hydrolysis effects of the acid on the polysaccharides chains as well as the conversion of the lignin molecules into low molecular weight components or monomers. The H2SO4 hydrolyses the hemicellulose and cellulose content of the EFB into monomers such as xylose and glucose respectively (Esteghlalian et al., 1997; Aguilar et al., 2002). The oxidation of the polymers may also be explained by the reduction of the C element contents in the treated carbon, which have bonded with the O element thus releasing gases in the form of CO or CO2 during the pyrolysis process (as also indicated by the reduction of O elements content).
Typical thermo gravimetric analysis (TGA) curves of the EFB carbon pyro-polymers are presented in Figure 2 and it clearly shows that the H2SO4 treatment influences the thermal behaviour of each of the carbon precursors, particularly for the 0.6 M H2SO4 treatment, where the existence of the second peak of Pyrolysis Rate, which normally appear at temperatures around 300oC to 340oC (for untreated and 0.2 M H2SO4 treated carbon precursors) have been shifted down to around 340oC to 400oC. According to Byrne and Nagle (1997), this type of trend in wood material (at 300oC-340oC) is normally for the degradation of cellulose and lignin, in which the lignin degradation occurs in the higher temperature. While in this treatment, the H2SO4
had oxidised the lignin into lignin sulphonic which has the same scale of degradation temperature (at
340oC - 400oC). The same finding was applied to the H2SO4 treatment on other biomass (Esteghlalian et al., 1997). When looking at the weight loss during the TGA analysis, a constant weight loss of the 0.6 M H2SO4 treated carbon pyro-polymer at an elevated temperature was also observed. This indicates that mild and constant gases evolved during pyrolysis, and hence this would result in a homogenised structuring of the carbon structure during the
carbonisation process. The H2SO4 treatment also increased the hygroscopic characteristics of the carbon pyro-polymers, shown by the increase of the Pyrolysis Rate in the temperature ranges from 60oC to 120oC (Figure 2). The higher the Pyrolysis Rate at this range of temperatures, indicating the higher moisture content of the carbon pyro-polymers.
The carbon pyro-polymers were then used in the preparation of the green body which were later
Figure 2. Thermo gravimetric analysis profiles of untreated and treated carbon precursors from empty fruit bunch (■ Untreated; ▲ 0.2 Molar H2SO4; * 0.6 Molar H2SO4).
Figure 1. The fibres inside the hollowed container (A) and attached with an extractor (B). This system is inserted inside the box-furnace and screw tightly to maintain the vacuum condition.
TaBLE 1. THE YiELD, PaRTiCLE siZE anD ELEMEnTaL anaLYsis OF THE CaRBOn PYRO-POLYMERs TREaTED WiTH DiFFEREnT COnCEnTRaTiOns OF H2sO4
H2sO4
(Molar) Weight loss
(%) C H n O Particle size
(mm) Untreated
0.20.6
20.3- 25.9
49.32 46.94 42.96
44.45 47.36 53.17
5.905.38 3.64
0.330.30 0.23
30.11 9.01 7.74
Vacuum suction
Weight (%)
Temperature (oC)
Pyrolysis Rate (mg min-1) 100
80
60
40
20
0
61.25 154.88 251.26 350.11 449.09 547.33 14 12 10 8 6 4 2 0
carbonised to get the activated carbon, and Table 2 shows the code number of each of the activated carbon prepared from different treatments and carbonisation temperatures. Table 2 also indicates the results of the density of the activated carbon, which were analysed before the crushing of the activated carbon pellets into granules. The results show that the density of activated carbon increases with an increase in carbonisation temperatures for all the carbon pellets prepared from different H2SO4 treatments (Figure 3). On the other hand, the increase of H2SO4 concentration for the treatment has given the opposite effect towards the density of the activated carbon prepared from different carbonisation temperatures. Kercher and Nagle (2003) explain the mechanism of the increase of carbon density with the increase of temperatures by:
1) the arrangement of the turbostratic carbon into layers of graphene, 2) the increase of high density turbostratic crystallite (per unit volume), and, (3) the shrinkage of the carbon volume. The effect of H2SO4 treatment can be explained by the thermal
TaBLE 2. saMPLE CODE FOR THE saMPLEs anD THE YiELD OF THE aCTiVaTED CaRBOn aFTER THE CaRBOnisaTiOn PROCEss
sample H2sO4
(Molar) Carbonisation
temperature (°C) Density (g cm-3) ACU-600
ACU-700 ACU-800 AC02-600 AC02-700 AC02-800 AC06-600 AC06-700 AC06-800
Untreated Untreated Untreated
0.20.2 0.20.6 0.60.6
600700 800600 700800 600700 800
1.127 1.136 1.206 1.084 1.126 1.190 0.947 1.026 1.043
Figure 3. The density of the activated carbon prepared from different H2SO4 treatment of the empty fruit bunch carbon pyro-polymers.
characteristics of the carbon pyro-polymers (Figure 2). The TGA thermo-grams show that the increase of the H2SO4 concentration for the treatment of the pyro-polymers, increased the weight loss at the end of 600oC pyrolysis temperature. This will therefore reduce the final weight of the carbon pellets and result in a lower density.
Figure 4 shows the adsorption isoterms of the activated carbon granules prepared from all the carbon pyro-polymers treated with different H2SO4 concentrations and different carbonisation temperatures. Based on the original data of the adsorption-desorption isotherms, the porosity characteristics were calculated and are shown in Table 3. The maximum SBET was obtained from the activated carbon AC06-600 (386.51 m2 g-1), indicating the effect of H2SO4 towards the EFB pyro-polymers properties, which eventually affect the activated carbon produced. As was discussed in the TGA analysis, the more homogenised gases are emitted during the carbonisation (due to the breaking down of high molecular weight polymer into low
Density (g cm-3)
Figure 4. Adsorption isotherms of activated carbon prepared from different H2SO4 concentration treatment of carbon pyro-polymers and carbonised at different carbonisation temperatures: (a) untreated, (b) 0.2 Molar H2SO4, and (c) 0.6 Molar H2SO4
(♦ = 600oC; ■ = 700oC, and ♦ = 800oC).
TaBLE 3. sURFaCE PROPERTiEs OF THE aCTiVaTED CaRBOn PREPaRED FROM EMPTY FRUiT BUnCH
sample sBET (m2 g -1) sMiCRO (m2 g-1) sMEsO
(m2 g-1) VMiCRO
(cm3 g-1) ACU-600
ACU-700 ACU-800 AC02-600 AC02-700 AC02-800 AC06-600 AC06-700 AC06-800
56.17 13.29 354.405.30 276.46 23.02 386.51 16.64 10.33
55.58 10.19 272.423.30 204.71 15.71 360.54 13.07 9.42
0.893.10 81.982.00 71.75 25.977.71 3.540.91
0.0185 0.0035 0.0013 0.1062 0.0229 0.0061 0.1461 0.0050 0.0038
Figure 5. The adsorption-desorption isotherm of AC06-600.
140 120 100 80 60 40 20 0 Absorbed volume (cm3 g-1)
Relative pressure (P/Po) Relative pressure (P/Po) Relative pressure (P/Po)
Absorbed volume (cm3 g-1) Absorbed volume (cm3 g-1)
Volume absorbed (cm3 g-1)
Relative pressure (P/Po)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
molecular weight components), the higher the pores formations during the carbonisation process. The adsorption-desorption isotherm of the activated carbon AC06-600 is show in Figure 5.
The adsorption-desorption isotherm of AC06- 600 shows typical Type 1 by Brunauer, Deming, Deming and Teller (BDDT) classification (Barrett et al., 1951) with adsorption increasing fairly rapidly at a low relative pressure in the range of 0.0 – 0.2, followed by a slow uptake of adsorbents at a relative pressure of >0.2. This indicates that the AC06-600 activated carbon is microporous. The hysteresis of the adsorption and desorption isotherms indicates the formation of slit-shape pore due to the rupture of the micropores structure (Gregg and Sing, 1982).
Overall, the results show that the BET surface area (SBET), micropore surface area (SMICRO) and the micropore volume (VMICRO) of all the activated carbons decrease with an increase in the carbonisation temperature. This is predictable based on the theory of carbonisation, and a similar observation on the carbonisation of Babasu endocarp and charcoal (Emmerich et al., 1987; Kercher and Nagle, 2003).
On the other hand, the H2SO4 treatment of the EFB carbon pyro-polymers showed different trend in the results, as shown in Figure 6. Results showed that the treatment of EFB carbon precursors has enhanced the porosity of the activated carbon produced from a carbonisation temperature of 600oC. However, at a higher carbonisation temperature, the increase of H2SO4 concentration beyond 0.2 Molar reduced both the SBET and SMICRO of the activated carbons. Overall, it can be concluded that treatment of EFB carbon pyro-polymers with H2SO4 is capable of improving the porosity of the activated carbon, but the effect is highly dependent on the effect of the carbonisation temperature. The effects of acids in improving the porosity of activated carbon have also been observed
in other lignocellulosic materials using phosphoric acid treatments (Molino-sabio et al., 1995; Guo and Rockstraw, 2007).
The carbon structure of the activated carbon was studied using the X-ray diffraction analysis, with the intensity over an angular range from 6o to 60o. The diffractograms for all the carbons show two significant peaks of the (002) peak (2q ~ 22o – 25o) and the (100) peak (2q ~42o – 45o) (Figure 7). The peaks are more obvious for activated carbons from higher carbonisation temperatures (ACU06-700 and ACU06-800). This indicates that these carbon samples have a turbostratic structure, which means that it contains both crystalline and amorphous carbons (Short and Walker, 1963). The reduced intensity in the 10o-12o region could be due to the decrease of contrast between the scattering length densities of the carbon resulting from the H2SO4
treatment. The untreated sample (ACU-600) does not show the reduced intensity.
The (002) and (100) peaks in Figure 7b are sharper or more obvious than those in Figure 7a, indicating more crystalline carbon in the activated carbon prepared from higher carbonisation temperatures which are also observed in other activated carbon studies (Kaneko et al., 1992). This shows that as the carbonisation temperatures increases, there is a higher growth of crystallites of the carbon, as compared to the slower growth of crystallites from the increase of the H2SO4 concentrations. From both peaks (002) and (100), the values of the d002, Lc
and La have been calculated and shown in Table 4.
The interlayer spacing d002 results show that all the carbon samples had slightly higher d002 as compared that of the graphite (3.54 Å). These activated carbons have shown a better quality of activated carbon as compared to the activated carbon produced from polymer materials, such as the carbon black (3.67
Figure 6. The SBET and SMICRO of activated carbons from different carbonisation temperatures and with increase of H2SO4 concentration: (a) 600oC, (b) 700oC, (c) 800oC (■ = Sbet and □ = Smicro).
Sbet and Smicro (m2 g-1) Sbet and Smicro (m2 g-1) Sbet and Smicro (m2 g-1)
(a) (b) (c)
Å) (Choe and Lee, 1992) and phenolic resin (3.89 Å) (Ryu et al., 2002). The lower d002 indicates that the carbon crystallites are better arranged (Jenkins and Kawamura, 1976). From this study, it is learnt that the best d002 is from the activated carbon of 0.2 Molar H2SO4 treatments that are carbonised at 800oC (3.55 Å). Although the lignocellulosic material is considered as soft-carbon and a non- graphitising carbon, a previous study showed that an activated carbon with d002= 3.36 Å was produced from Cryptomeria japonica wood which is carbonised under catalytic condition (Hata et al., 2004).
The trends of effects of H2SO4 treatment and carbonisation temperatures towards the d002, Lc and La are shown in Figures 8a, 8b and 8c respectively.
The results have showed that the activated carbons prepared from 0.2 M H2SO4 treatments reduced the d002, but it increased with a higher H2SO4
concentration at 0.4 M (Figure 8a). This indicates that the H2SO4 treatment changed the complex polymeric structure of the EFB lignocellulosic and hence, it affected the interaction between carbon layers during the carbonisation. Treatment with H2SO4 was earlier found to reduce the particle size of the carbon precursor (Table 1), and this should contribute to lower interlayer spacing of the
Figure 7. The X-ray diffraction profile of carbon pellet as a function of: (a) carbonisation temperatures at H2SO4 concentration of 0.6 M and (b) H2SO4
concentrations at carbonisation temperature of 600ºC.
TaBLE 4. EXPERiMEnT DaTa FROM XRD anaLYsis FOR d002, LC anD La OF THE aCTiVaTED CaRBOn PREPaRED FROM EMPTY FRUiT BUnCH
sample interlayer spacing
(d002) (Å) stack diameter
(Lc) (Å) stack height (La) (Å) ACU-600
ACU-700 ACU-800 AC02-600 AC02-700 AC02-800 AC06-600 AC06-700 AC06-800
3.593.59 3.583.56 3.553.55 3.693.65 3.60
9.82 12.36 13.25 10.659.72 12.73 9.369.63 10.51
2.412.62 3.072.55 2.903.22 2.943.50 4.18
carbons. But with a higher concentration of H2SO4, it is believed that the chemical interactions altered the formation of crystallites during carbonisation, hence increasing the interlayer spacing of the formed carbons. The similar phenomenon was also observed in graphites (Shioyama, 2000). But on the effect of the carbonisation temperature, increasing of temperature has reduced the d002 results.
Figure 8b shows different trends of Lc with the function of different H2SO4 concentrations and carbonisation temperatures. The stack height of the graphitic layers was found to be reduced with the increase of the H2SO4 concentration;
but was increased with increase of carbonisation temperature. The decrease of Lc with the increase of H2SO4 concentrations may indicate that the mobility of the carbon atoms in the directions perpendicular to the graphene layers has been reduced. The same effects of other acid treatments have also been discussed by other researchers (Bhabendra et al., 1999; Katsumi et al., 1998). The similar effect of carbonisation temperature has also been observed in the activated carbons from crystalline cellulose (Dae et al., 2001) and the pith (Yang et al., 2002a).
The results on microcrystalite width, La; of the activated carbons showed the increased trend
1 000 800 600 400 200 0
Intensity
0 10 20 30 40 50 60
Intensity
2Θ
1 000 800 600 400 200 0
0 10 20 30 40 50 60 2Θ
(a) (b)
Figure 8. The d002 (a), Lc (b) and La (c) of all the activated carbon samples prepared from different H2SO4 concentration treatments and different carbonisation temperatures (◊ = 600 oC; □ = 700 oC; ∆ = 800oC).
with the increase of both H2SO4 concentration and carbonisation temperature. This indicates that H2SO4 acid has enhanced the orientation of the grapheme layers in perpendicular during the carbonisation (Emmerich, 1995). The increase of La with the increase of carbonisation temperature is also observed in other studies where the carbon samples prepared from eucalyptus wood (Coutinho et al., 2000) and bituminous coal (Yang et al., 2002b).
COnCLUsiOn
A new method of producing activated carbon granules from soft lignocellulosic material like the EFB was attempted, and the porosity as well as the pore structure of the activated carbons was studied.
The preparation of the activated carbon involves the pre-carbonisation at a low temperature, chemical treatment and the formation of green body before the carbonisation process. The pre-carbonised was carried out using the slow pyrolysis process to obtain the carbon pyro-polymer particles, which after the H2SO4 treatment, exhibits a self-adhesive property that enables the particles to be pelletised using compression process without adding a binder.
The green pellets were then carbonised at different temperatures to obtain the carbon pellets, and the carbon granules were obtained by breaking the carbon pellets and sieved into specific sizes. The porosity and the micro-structure analysis results have shown that the activated carbon produced from EFB is comparable to that of qualities of the activated carbon from hard materials. The highest SBET was from the 0.6 M H2SO4 treatment and carbonised
d002 (Amstrong)
(a)
(b)
(c) Lc (Amstrong)La (Amstrong)
at 600oC (SBET= 386.51 m2 g-1) with more than 93%
micropores. The values of interlayer spacing d002, stacking height (Lc), and width (La) in the activated carbons as a function of H2SO4 concentration and carbonisation temperature have been estimated from the X-ray diffraction data.
aCKnOWLEDGEMEnT
The author first would like to thank MPOB for allowing to publish the findings which are part of her Ph.D thesis and Universiti Kebangsaan Malaysia is gratefully acknowledged for the co-operation rendered.
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