The Pore Structure Variation of Coal Char during Pyrolysis and Its

Sep 27, 2012 - Se-Joon Park , Dong-Wook Lee , Young-Joo Lee , Jong-Soo Bae , Jai-Chang ... Ju-Hyoung Park , Young-Joo Lee , Min-Ho Jin , Se-Joon Park ...
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The Pore Structure Variation of Coal Char during Pyrolysis and Its Relationship with Char Combustion Reactivity Dong-Wook Lee, Jong-Soo Bae, Se-Joon Park, Young-Joo Lee, Jai-Chang Hong, and Young-Chan Choi* Clean Fuel Department, High Efficiency and Clean Energy Research Division, Korea Institute of Energy Research (KIER), 71-2, Jang-dong, Yuseong, Daejeon 305-343, Republic of Korea S Supporting Information *

ABSTRACT: We investigated the pore-structure variation of coal char during the devolatilization process of Baganuur coal (BC) and Shievee Ovoo coal (SOC) from Mongolia, and reported the relationship between the char pore structure and its combustion reactivity. SOC char showed much higher combustion reactivity than BC char at real-power-plant temperatures (1100−1400 °C) as well as at the low temperature range below 900 °C. Meanwhile, the surface area of the SOC char was much higher than that of the BC char, and it was confirmed that their surface areas were dominantly derived from their ash pore structure. In addition, the ash phase dispersion of the SOC char was better than that of the BC char. Thus, it was concluded that the higher surface area and better dispersion of ash phase leads to a higher combustion reactivity of the SOC char.

1. INTRODUCTION In a pulverized coal combustion process, there are two major reactions of coal devolatilization and char combustion. Raw coal fed to a boiler first releases volatile matters, and then the released volatile matters and coal char are burned by supplied oxygen.1 In general, a char combustion rate is much slower in comparison with a devolatilization rate of coal, which means that the rate-determining step is combustion of coal char.2 Accordingly, char combustion properties are very crucial factors for improvement in energy efficiency of the pulverized coal combustion process. Moreover, it is very important to investigate influential factors on char combustion properties in depth. Over the past few decades, the combustion reactivity of coal char and the influential factors on it were reported on not a few of publications.3−12 Several research groups previously came to conclusions that structural ordering of coal into graphite occurs during heat treatment at high temperature and the ordered and unreactive graphite matrices give rise to a falloff in the combustion reactivity of char.2,5,7 Borrego and co-workers reported effects of inertinite content on char structure and combustion reactivity and confirmed that the reactivity of char decreases with an increase in inertinite content.4 Shen et al. investigated the combustion characteristics of char prepared from bituminous coal at different devolatilization temperatures and their pore structure change.3,13 Wells et al. reported that combustion reactivity of pyrolyzed coal char is highly associated with porosity and catalytic elements, such as alkali and alkalineearth metal oxides. In addition, the order of catalytic elements is sodium > magnesium > calcium.6 That is, the catalytic role of ash elements such as sodium, magnesium, calcium and so on is a very important factor for the combustion reactivity of coal char, and surface area is one of the most significant factors in catalysis. These facts imply the considerable effect of ash surface area on combustion reactivity. However, to the best of our knowledge, there are no publications reporting the relationship between ash pore © 2012 American Chemical Society

properties and char combustion reactivity. In this study, we investigated the pore structure variation of coal char and ash during the devolatilization process. The effect of ash pore properties on char combustion rate and temperature was observed by using thermal gravimetric analysis (TGA), nitrogen sorption, mercury intrusion, X-ray dot mapping, and X-ray diffraction (XRD).

2. EXPERIMENTAL SECTION Coal Char and Ash Preparation. Baganuur coal (BC) and Shievee Ovoo coal (SOC) from Mongolia were employed for all experiments in this study. BC and SOC were utilized as received without any chemical modifications. Before devolatilization for char preparation, the raw BC and SOC were crushed to a particle size below 75 μm by using a jaw crusher for coarse crushing and a pin type mill system for fine grinding. The finely crushed BC and SOC were devolatilized for 3 h in a fixed bed reactor shown in Figure 1. N2 carrier gas was constantly fed to the reactor at 100 mL/min and devolatilization temperatures were 600, 700, and 800 °C. After the reactor temperature reached each devolatilization temperature, 400 g of coal sample in a coal storage place was fed to the reactor at once by using a butterfly valve, followed by conducting devolatilization of coal for 3 h at each temperature. BC and SOC char samples prepared by a devolatilization process are denoted by BC-x and SOC-x, where x is devolatilization temperature. In addition, ash samples for each BC-x and SOC-x were also prepared by calcination of BC-x and SOC-x char at 700 °C for 5 h in air, and they are designated by BC-x-ash and SOC-x-ash, respectively. Characterization. To characterize volatile matter, ash, and fixed carbon content for BC and SOC samples before and after Received: Revised: Accepted: Published: 13580

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Figure 1. A schematic diagram of fixed bed reactor for coal devolatilization.

devolatilization, proximate analyses were conducted by utilizing a TGA-701 thermogravimeter (LECO Co., St. Joseph, MI, USA). To observe a char combustion rate, TGA for BC-x and SOC-x was carried out in the temperature range of 25−900 °C at a heating rate of 20 °C/min on a Q500 TA Instruments. Nitrogen carrier gas was replaced by air at 600 °C, and the carrier gas flow rate was 100 mL/min. For further investigation on combustion patterns at real-power-station temperatures, TGA was also conducted isothermally at 1100, 1200, 1300, and 1400 °C. The micropore and mesopore properties of BC-x, SOC-x char, and their ash samples, such as surface area, pore volume, and BJH desorption pore size, were taken by nitrogen sorption tests with a Micromeritics ASAP 2020 instrument. Finely ground char samples were employed for nitrogen sorption tests, and the samples were degassed for 7 h at 200 °C before nitrogen adsorption tests. BET surface area was calculated from the slope and intercept of the BET equation. Mesopore surface area was obtained from the slope of the tplot, and micropore surface area was calculated by subtracting the mesopore surface area from the BET surface area. Single point total pore volume was taken from the volume of N2 adsorbed at P/Po = 0.995, and micropore volume was calculated from the intercept of the t-plot. Pore size distribution was obtained by the BJH method. Moreover, for their macropore size distributions, mercury intrusion tests were conducted on Autopore IV Micromeritics. To observe the crystalline phase for BC-x and SOC-x char samples, their XRD patterns were collected on a Rigaku D/MAX-2200 V instrument operated at 1.6 kW. X-ray dot mapping of Si and Al was carried out to investigate distribution of ash components on the coal surface. The ash content of the BC and SOC char was taken by using inductively coupled plasma−atomic emission spectroscopy (ICP−AES). Kinetics. The shrinking core model is used to observe the reaction kinetics of char combustion at high temperature.14−16 When the chemical reaction at surface is a rate-determining step, the shrinking core model can be described as

1 − (1 − X )1/3 =

k t 3

where t, k, and X are the reaction time, reaction rate constant, and char conversion, respectively. After collecting t values and calculating X from Figure 3, a (1 − X)1/3 versus t graph was plotted. Then k from the slope of the graph at 1100, 1200, 1300, and 1400 °C was calcuated. Subsequently, the activation energy (Ea) can be estimated by the Arrhenius plot (ln k vs 1/ T).

3. RESULTS AND DISCUSSION Combustion Behavior of Coal Char. To investigate the relationship between combustion reactivity and pore properties of char such as surface area and pore volume, BC-x and SOC-x char samples were prepared by devolatilization of raw BC and SOC samples at different temperature, and the combustion reactivity of devolatilized char was observed by using TGA. Figure 2 presents nonisothermal combustion patterns (TGA profiles) of BC and SOC char samples with different devolatilization temperature. After nitrogen carrier gas was replaced by air at 600 °C, the combustion of BC-x and SOC-x was initiated. In the case of SOC char, the combustion of all samples was terminated below 750 °C regardless of devolatilization temperature. In contrast, for BC char samples, the combustion reaction proceeded slowly and was not terminated until 900 °C. Moreover, from DTG curves in Figure 2, it was revealed that the combustion rate of SOC char samples is much higher than that of BC char, and combustion temperature of SOC char was lower than BC char. For further investigation on the char combustion pattern at real-power-station temperatures (1000−1500 °C), TGA for BC-800 and SOC-800 char was conducted isothermally at 1100, 1200, 1300, and 1400 °C (Figure 3). Using the reaction rate constant at each temperature calculated from the TGA results with the shrinking core model, the Arrhenius plots for BC and SOC char were obtained, whereby the activation energy for BC and SOC char could be calculated (Figure 4). As a result, the activation energy of SOC char (7.16 kJ/mol) was 13581

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Figure 2. Nonisothermal combustion patterns (TGA profiles) of (a) BC and (b) SOC char samples at low temperature range below 900 °C (room temperature to 600 °C, nitrogen; 600−900 °C, air).

Figure 3. Isothermal combustion patterns (TGA profiles) of (a) BC800 and (b) SOC-800 char samples at high temperature range at 1100, 1200, 1300, and 1400 °C (room temperature to each temperature; nitrogen, air atmosphere at each temperature).

much lower than that of BC char (25.27 kJ/mol). Thus, it was confirmed that SOC char provided higher combustion reactivity compared with BC char even at real-power-station temperature. Figure 5 shows proximate analysis results of BC and SOC char samples devolatilized at different temperature. As for the BC samples, when the devolatilization temperature increased from 600 to 800 °C, fixed carbon content gradually increased and volatile matter content was reduced from 23.1 to 7.8 wt %. The SOC char samples also showed a falloff in the content of volatile matter from 17.3 wt % to 7.7 wt %. Considering much lower combustion temperature and higher combustion rate of SOC char than BC char in spite of similar volatile matter content of SOC char to that of BC char samples, the char combustion reactivity is considered to be not much affected by volatile matter content. Mesopore Variation of Char. Such a remarkably high combustion reactivity of SOC char is presumably attributed to its different pore properties from BC char such as specific surface area and pore volume. Investigation on mesopore structure of char might be more significant for confirmation of the relationship between pore properties and char combustion reactivity, because mesopores are a much more important factor for catalysis than macropores. To verify the relationship, nitrogen sorption tests of each SOC and BC char sample were conducted. Figures 6 and Supporting Information, Figure S1 exhibit pore size distributions and isotherms for raw BC, BC-x char, raw SOC, and SOC-x char samples. BC shows a typical type IV isotherm and a H3 hysteresis loop in the relative

Figure 4. Arrhenius plots for BC and SOC char samples in the temperature range from 1100 to 1400 °C.

pressure range of 0.4−1.0, which is commonly associated with slit-like pores derived from aggregates of plate like particles (Supporting Information, Figure S1a). The pore size of raw BC is distributed in the very wide range of 2.5−150 nm with a sharp peak at about 2.8 nm, and the pore size distribution considerably shifted to larger pore size after devolatilization at 600 °C. Above 700 °C, the mesopore surface area of BC char 13582

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Figure 5. Proximate analysis results of (a) BC and (b) SOC char samples devolatilized at different temperatures.

Figure 6. Pore size distributions for (a) raw BC, BC-x char, (b) raw SOC and SOC-x char samples.

samples dramatically decreased after devolatilization. In the case of SOC-x, all of the samples also exhibit type IV isotherms with H3 hysteresis loops in the relative pressure range of 0.46−1.0 (Supporting Information, Figure S1b). However, differently from the BC-x, SOC-x char samples maintained their isotherm pattern even at 800 °C of devolatilization temperature. As shown in Figure 6b, SOC-x char samples show bimodal pore size distributions with sharp peaks at 3−4 nm and broad peaks in the range of 4−200 nm, and the considerable change in their pore size was not observed with an increase in devolatilization temperature. Moreover, as shown in Table 1, it was confirmed that the mesopore surface area and the mesopore volume of SOC-x were higher than those of BC-x. (In this case, the total pore volume can be regarded as mesopore volume because the total pore volume is 2 orders of magnitude higher than the micropore volume.) Although their micropore surface area is similar to each other, the mesopore surface area of SOC-x is about 3 times higher than that of BC-x. Considering the nitrogen sorption results in combination with TGA results for BC-x and SOC-x samples, it was demonstrated that the combustion rate and temperature of coal char is substantially affected by its surface area and pore volume. That is, the higher surface area of coal char gives rise to faster combustion rate and lower combustion temperature. Mesopore Variation of Ash. SOC-x and BC-x char samples are composed of fixed carbon, ash, and a little remaining volatile matter, and the surface area of the char

samples could be derived from ash or fixed carbon phase. To verify the origin of their porosity, ash samples were separated from each char sample by burning fixed carbon and the remaining volatile matter in char samples at 700 °C for 5 h in air, and nitrogen sorption tests for the remaining ash samples were conducted. Figures 7 and S2 present pore size distributions and isotherm curves of BC-x-ash and SOC-x-ash samples. All of the samples give a typical type IV isotherm and a H3 hysteresis loop, which is nearly consistent with BC-x and SOC-x char samples before elimination of fixed carbon phase. However, SOC-x-ash has higher nitrogen adsorption volume in comparison with BC-x-ash, indicating that the pore volume of SOC ash samples is larger than that of BC ash samples. As if BC-x and SOC-x showed bimodal pore size distribution in a wide pore size range, BC-x-ash and SOC-x-ash also give broad pore size distribution between 2 and 150 nm along with several sharp peaks in a several nanometer range, indicating that pore structure of char is almost consistent with that of ash. Table 1 exhibits mesopore properties of BC-x-ash and SOCx-ash samples. The mesopore surface area and total pore volume of SOC-x-ash are much higher than those of BC-x-ash. In addition, SOC-x-ash samples have about 4.3−8.7 times higher mesopore surface area and 2.9−4.6 times higher mesopore volume compared with SOC-x char samples. The BC-x-ash showed about 2.2−5.1 times higher mesopore surface area and 2.4 times higher pore volume than BC-x char. Accordingly, it can be concluded that the mesopore properties of BC and SOC char is dominantly derived from the ash phase 13583

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Table 1. Pore Properties of SOC-x, BC-x, SOC-x-ash, and BC-x-ash Samples sample raw SOC SOC-600 SOC-700 SOC-800 raw BC BC-600 BC-700 BC-800 SOC-600-ash SOC-700-ash SOC-800-ash BC-600-ash BC-700-ash BC-800-ash

SABET (m2/g)a

SAme (m2/g)b

SAmi (m2/g)c

Vtot (cm3/g)d

Vmi (cm3/g)e −3

D (nm)f

6.9 6.2 9.6 6.0 2.5 4.3 g

6.3 3.9 5.3 3.2 2.0 1.3

0.6 2.3 4.3 2.8 0.5 3.0

0.030 0.028 0.041 0.036 0.015 0.017

0.14 0.93 1.86 1.16 0.16 1.27

× × × × × ×

10 10−3 10−3 10−3 10−3 10−3

16.0 20.7 22.9 22.3 21.6 34.5

36.5 31.4 33.6 12.0 11.2 13.2

28.9 23.2 27.8 2.9 5.2 6.6

7.6 8.2 5.8 9.1 6.0 6.6

0.13 0.12 0.12 0.04 0.04 0.04

3.19 3.53 2.42 3.54 2.60 2.71

× × × × × ×

10−3 10−3 10−3 10−3 10−3 10−3

14.8 15.7 14.7 26.6 14.7 17.2

a

BET surface area calculated from the slope and intercept of the BET equation. bMesopore surface area (SA) calculated from the slope of t-plot. Micropore surface area calculated by subtracting the mesopore surface area from the BET surface area. dSingle point total pore volume taken from the volume of N2 adsorbed at P/Po = 0.995. (In this case, the total pore volume can be regarded as mesopore volume because the total pore volume is 2 orders of magnitude higher than the micropore volume.) eMicropore volume calculated from the intercept of t-plot. fBJH desorption average pore diameter. gNot measured. c

The Proposal of Mesopore Variation Mechanism. An investigation of the variation of specific surface area with an increase in devolatilization temperature in Table 1confirms that whereas mesopore properties of SOC-x-ash samples are almost constant with an increase in devolatilization temperature, the mesopore surface area and total pore volume of SOC-x char increase and decrease with a rise in temperature. As coal devolatilization proceeds, the weight fraction of ash phase occupying most of the coal surface area increases by a falloff in volatile matter content, resulting in an increase of coal surface area. However, above 700 °C, the specific surface area starts to decrease despite continuously rising in ash content. In the case of BC char, mesopore surface area and pore volume dramatically decreased at 700 and 800 °C, whereas BC-700ash and BC-800-ash maintained their high surface area. On the basis of these results, it can be inferred that the ash phase exposed on the coal surface was covered by thermoplastic deformation of coal particles during devolatilization at high temperature. During the thermoplastic deformation process, coal particles swell and their physical structures are changed, sometimes resulting in the plugging of original pores or the reduction of original pore size.3 We illustrate the mesopore− structure variation mechanism of coal char with increasing devolatilization temperature in Figure 8. XRD Analysis of Char. In general, the significant variation in pore properties of oxides is usually attributed to crystallization or transformation of the crystal phase.17−19 That is, X-ray diffraction patterns of oxides are a reliable measure to anticipate the significant variation of pore properties indirectly. For further investigation on the stability of ash pore structure, XRD analyses for BC-x and SOC-x were carried out. Figure 9 shows XRD patterns of BC-x and SOC-x char. BC-x char gave several diffraction peaks, which corresponds to quartz phase of silica (Figure 9a). The major crystalline phase inside BC-x char, which can be detected by XRD, was quartz. Moreover, the intensity and fwhm (full width of halfmaximum) of quartz changed little regardless of increasing devolatilization temperature, and nucleation and crystallization of other ash components were not observed. As shown in Table

Figure 7. Pore size distributions of (a) BC-x-ash and (b) SOC-x-ash samples.

rather than the fixed carbon phase. In other words, the mesopore surface area and pore volume of the ash phase inside the char samples play a very significant role in char combustion reactivity. 13584

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Figure 8. A schematic diagram for the mesopore−structure variation mechanism of coal char with increasing devolatilization temperature.

Macropore Variation of Char and Ash. For further investigation on their pore structure in a macropore range above 50 nm, mercury intrusion tests for BC and SOC char were conducted. Figure 10 exhibits pore size distributions of BC-x char, BC-700-ash, SOC-x char and SOC-700-ash obtained from mercury intrusion tests. All of the char and ash samples showed broad bimodal distributions comprising the small macropore range of 0.05−8 μm and the large macropore range of 8−50 μm. In addition, the pore volume of BC-700-ash and SOC-700-ash is remarkably higher in comparison with that of BC-700 and SOC-700. It means that most of the macroporosity in BC and SOC char is derived from the ash phase, as is their microporosity and mesoporosity. In the case of BC-x, the macropore volume of BC char decreased by increasing devolatilization temperature from 600 to 700 and 800 °C, which implies the plugging of the original ash pores via thermoplastic deformation of coal particles. As for SOC-x, after devolatilization temperature rose from 600 to 700 °C, the macropore volume increased substantially. The increase of macropore volume at 700 °C is attributed to an increase in ash/char weight ratio through a decline in volatile matter content. In contrast, the macropore volume and distribution pattern of SOC char changed not much after rising devolatilization temperature from 700 to 800 °C. This is because an increase of the macropore volume by a rise in ash/ char weight ratio was compensated by a decrease in the macropore volume through the thermoplastic deformation. Accordingly, it was confirmed that the macropore-structure variation of BC and SOC char by rising devolatilization temperature is almost consistent with their mesopore-structure variation mechanism suggested in Figure 8. Dispersion of Ash on Char Surface. Figure 11 exhibits Xray maps for major ash elements on BC-800 and SOC-800 surface (Si and Al element are marked with red and green dots, respectively). BC-800 showed phase separation between Si, Al,

2, the calculated crystalline size of quartz is 41−47 nm and is not affected by devolatilization temperature until 800 °C. In the case of SOC-x, char samples provided sharp diffraction peaks ascribed to quartz and anhydrite crystalline phase (Figure 9b). In common with BC-x, SOC-x showed a nearly constant crystalline size for each crystal phase with increasing devolatilization temperature, indicating that the crystalline growth did not occur in the ash phase of char. On the basis of the results in Figure 9 and Table 2, it was revealed that crystallization, crystalline growth, and phase transformation were not observed in the ash phase until 800 °C, which leads to the thermally stable pore structure of the BC-x-ash and SOC-xash. Micropore Variation of Char and Ash. In the same manner as mesopore properties, micropore properties of ash samples were much higher than those of char samples. That is, SOC-x-ash samples have about 2.0−3.3 times higher micropore surface area and 1.4−3.4 times higher micropore volume compared with SOC-x char samples. The BC-x-ash provided about 2.0−3.1 times higher micropore surface area and 2.8 times higher micropore volume than BC-x char. Thus it was also confirmed that micropore properties of char is mainly derived from ash phase. Moreover, the micropore surface area and micropore volume of SOC-x char also increase and decrease with increasing devolatilization temperature. The mesopore surface area of SOC char and ash was higher than the micropore surface area of that, whereas the mesopore surface area of BC char and ash was lower than the micropore surface area. Significantly, the micropore surface area of SOC ash samples was very similar to that of BC ash, while SOC ash provided about 4.2−10.0 times higher mesopore surface area compared with BC ash samples. Thus we can deduce that a higher combustion reactivity of SOC char is attributed to higher mesopore properties of SOC than those of BC. 13585

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Table 2. Crystalline Size of BC-x and SOC-x Ash Phase crystalline size [nm]a samples

quartz

anhydrite

BC-600 BC-700 BC-800 SOC-600 SOC-700 SOC-800

47 41 45 46 46 45

b

27 25 28

a

Calculated by using Scherrer equation from the quartz peak at 26.6° and the anhydrite peak at 25.3°. bNot detected.

Figure 10. Pore size distributions of BC-x char, BC-700-ash, SOC-x char, and SOC-700-ash obtained from mercury intrusion tests: (a) BCx char and BC-700-ash, (b) SOC-x char and SOC-700-ash.

Compared with BC-800, SOC-800 showed better dispersion of ash components on the char surface and had a larger interfacial area between fixed carbon and the ash phase, contributing to faster combustion rate and lower combustion temperature. From the results, we can deduce that, besides the surface area and pore volume, a good dispersion of ash phase on the char surface could influence an increase in the char combustion reactivity. Ash Composition. The alkali and alkaline-earth metal salts or oxide could enhance the reactivity of coal char, and the order of catalytic reactivity is potassium, sodium, magnesium, and calcium.6,20 As shown in Table 3, SOC char showed higher K2O and MgO content compared with BC char samples; however,

Figure 9. XRD patterns of (a) BC-x and (b) SOC-x char samples with different devolatilization temperature. (Q, quartz; A, anhydrite).

and fixed carbon, indicating that the ash phase with high surface area is not dispersed well on char. However, in the case of SOC-800, Si and Al elements are distributed well on the whole range of SOC-800 char surface. Moreover, the phase separation between silica and alumina in the ash phase is relatively slight. 13586

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°C, the surface area and pore volume of SOC char was reduced, and those of BC char dramatically decreased. (2) BC and SOC ash samples gave much higher surface area and pore volume than BC and SOC char, indicating that the pore properties of BC and SOC char samples are dominantly derived from the ash phase rather than fixed carbon phase. (3) BC and SOC ash samples maintained their high surface area and pore volume despite increasing devolatilization temperatures up to 800 °C. This is because there are not crystallization, crystal growth, and phase transformation of ash components until 800 °C by which the pore structure of ash could collapse significantly. (4) During devolatilization at low temperature, the surface area and pore volume of coal char increase by a rise in the weight fraction of ash phase having much higher pore properties than fixed carbon. However, during devolatilization at high temperature, the surface area and pore volume start to decrease despite the continuously rising ash/char weight ratio, because the pores of the ash phase exposed on char surface were plugged by thermoplastic deformation of coal particles. (5) The higher ash surface area leads to faster combustion rate and lower combustion temperature. Moreover, the good dispersion of ash phase on the char surface also contributes to an improvement in char combustion reactivity due to an increase of the interface between fixed carbon and the ash phase.

■

ASSOCIATED CONTENT

S Supporting Information *

Additional figures as described in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

■

Figure 11. X-ray maps for major ash elements on BC-800 and SOC800 surface (Si and Al element are marked with red and green dots, respectively).

Corresponding Author

*E-mail: [email protected]. Notes

Table 3. Ash Analysis Results for BC and SOC Char sources

BC-800

SOC-800

SiO2 Al2O3 Fe2O3 CaO MgO K2O MnO P2O5 TiO2

53.69 10.78 15.47 15.75 0.32 0.83 0.43 0.49 1.20

45.89 18.34 14.45 10.35 0.77 0.92 0.72 0.82 0.96

AUTHOR INFORMATION

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

This work was supported by a primary project of the Korea Institute of Energy Research (KIER).

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their content is too small to give catalytic activity. In the case of CaO, SOC char provided lower content than BC char, but the absolute quantity of CaO for SOC char was higher than that for BC char due to about two times higher ash content of SOC compared with BC. That is, besides higher surface area of SOC, SOC char also provided higher content of catalytic components in comparison with BC char.

4. CONCLUSIONS (1) The surface area and pore volume of BC and SOC char increased during devolatilization at low temperature below 700 °C. In contrast, at high devolatilization temperature above 700 13587

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