Article pubs.acs.org/IECR
Upgrading Ash-Rich Activated Carbon from Distilled Spirit Lees Juan Yang, Jian Yu, Wei Zhao, Qiang Li, Yin Wang,* and Guangwen Xu* National Key Laboratory of Multiphase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China ABSTRACT: Activated carbon (AC) was prepared from ash-rich distilled spirit lees via carbonization and successive activation incorporated with different deashing methods. The results show that the alkali treatment of the steam-activated carbon (ATAC) produced the AC with the highest performance in comparison with the NaOH activation and direct alkali treatment of the carbonized carbon (ATCC). The ATAC removed 84.4% of the ash from steam-activated carbon and increased the BET surface area and total pore volume by 92.3% and 109.3%, respectively, resulting in the AC with its ash content of 11 wt %, BET surface area of 620 m2/g, and total pore volume of 0.67 cm3/g. The article also revealed that it is possible to use the alkaline leaching solution from the ATAC, which is mainly composed of sodium silicate, as the major binder to mold the produced powder AC.
1. INTRODUCTION Activated carbons with high specific surface area and large adsorption capacity are the carbonaceous material highly needed for various industrial purifications and water (wastewater) treatments.1,2 The demand for activated carbon (AC) is increasing rapidly with enhanced awareness about environment protection. However, the price of ACs is very expensive due to the fact that most of the commercial AC products are derived generally from costly natural materials such as wood or coal. Therefore, the exploration for a cheap and easily available precursor for AC production is therefore of great importance. There is growing interest in the production of ACs using cheap agricultural and industrial wastes.3−6 Several wastes including coffee husks,7 rice husks,8,9 walnut shells,10,11 cotton stalks,12 coconut husks,13 herb residues,14,15 and corn cobs16 have been investigated as the activated carbon precursors and are still receiving renewed attention because of their cheap prices and abundant resources. Many of the waste-based ACs also enabled comparable or even better performance than the commercial ACs in many applications. Consequently, the conversion of cheap biomass wastes into value-added ACs not only opens a low-cost path for AC production but provides also an efficient way to reduce the environmental pollution caused by disposing agricultural and industrial wastes. Distilled spirit lees are the main byproduct of liquor production. According to statistics,17 about 20 million tons of distilled spirit lees were produced in China in 2009, and this amount is still increasing by 20% annually. The distilled spirit lees have high moisture content (50−80%) and are usually weak acidic so that they are easy to decay and cause serious environmental pollution. Though some of the distilled spirit lees have been used as additives for fertilizers and feeds, the utilization rate is still low due to the potential harmfulness to crops and animals aroused by the weak acidity and alcoholic toxicity of the distilled spirit lees. Therefore, most of the wastes at present have to be landfilled, which not only wastes biomass resources but also causes serious pollution. The distilled spirit lees are rich in cellulose and concentrated, and the conversion of the lees into activated carbon (AC) may be an alternatively © 2012 American Chemical Society
high-value way for their innocent utilization. This in turn also exploits a new path for low-cost production of ACs. It is generally know that the alkali treatment of raw material can greatly increase the BET surface area and total pore volume of the produced AC.8,14 Liou and Wu8 also showed that the acid treatment of the obtained AC can similarly improve the AC quality, although the identified effect was not as obvious as that of alkali treatment. These technical ways, however, have to produce acidic or alkaline wastewater. When we treated a raw biomass material with 0.5 mol/L NaOH,14 we found that the generated waste solution had not only complicated chemical compositions but was also deep black and strong alkaline. Thus, it is highly necessary to advance the alkali or acidic treatment technology for AC or to develop a utilization technology for the generated waste solution. The aim of this study is to explore the possibility of producing AC from distilled spirit lees with various alkali treatment ways which are devoted to the ash removal and carbon activation. Instead of alkali treatment of the raw material, the distilled spirit lees in this article were first carbonized and then subjected to varied methods of alkali treatment and activation process. The leaching solution from the alkali treatment was further tested to be the major binder for molding the prepared typical AC. Consequently, what we have shown in this study is not only an advanced promising way for AC production but also a capable technology for utilizing the ash-derived alkaline waste.
2. EXPERIMENTAL SECTION 2.1. AC Preparation and Molding. The activation method used in the present study was divided into two stages, including carbonization and activation. For carbonization, approximately 100 g of the dried distilled spirit lees were placed in a quartz reactor which was inserted into a horizontal tube heating furnace. The whole system was purged with 500 Received: Revised: Accepted: Published: 6037
December 9, 2011 April 8, 2012 April 12, 2012 April 12, 2012 dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
Industrial & Engineering Chemistry Research
Article
Table 1. Proximate and Ultimate Analyses of Distilled Spirit Lees and XRF Analysis of Their Ash Proximate Analysis (wt %) volatile
ash
fixed carbon
66.91
12.07
16.92
Ultimate Analysis (dry-base wt %) moisture
C
4.10 43.80 Ash Analysis via XRF (oxide-based wt %)
H
N
S
6.31
3.42
0.77
SiO2
MgO
Al2O3
P2O5
K2O
CaO
TiO2
Fe2O3
MnO2
other
77.15
1.12
4.56
8.47
4.78
1.49
0.19
2.15
0.07
0.03
Table 2. BET Surface Area, Pore Characteristics, and Adsorption Capacities of Activated Carbons Prepared under Different Conditions of Carbonization and Steam Activation pore volume (cm3/g) sample
a
AC-450-750 AC-450-800 AC-450-850 AC-650-800 AC-750-800
2
pore volume distribution (%)
SBET (m /g)
VTotal
VMicro
VMeso
VMicro/VTotal
VMeso/VTotal
348 372 324 360 324
0.26 0.38 0.32 0.32 0.32
0.12 0.14 0.10 0.11 0.10
0.14 0.24 0.22 0.21 0.22
46.2 36.8 31.2 34.4 31.2
53.8 63.2 68.8 65.6 68.8
adsorption (mg/g) DAb
(nm)
2.99 3.37 3.97 3.52 3.94
iodine
MB
525 581 524 521 463
50 90 99 87 82
a The samples are named as follows: “AC-carbonization temperature-activation temperature”. bDA refers to the average pore size calculated as 4V/A by BET.
filtered to remove the ethanol. The resultant solid was compressed into disks using a tiny pressing machine at a pressure of 4 MPa. The obtained disks were dried at 105 °C and then calcined at 500 °C in N2 atmosphere for 1 h to get the fixed molded AC. 2.2. Material and Characterization. The distilled spirit lees tested in this article were from Luzhou Laojiao Company, China. Although the virgin lees had a water content of about 60 wt %, they were dried at 110 °C for 24 h to remove the moisture for the use in the reported tests. Table 1 shows the results of the proximate and ultimate analyses for the tested distilled spirit lees. The raw distilled spirit lees have relatively high contents of volatile and carbon, potentially suitable for making AC. The ash content is relatively high but is dominated by SiO2 (shown in Table 1) so that it can easily be removed by alkali treatment. The specific surface areas and pore structure characteristics of prepared ACs were determined by nitrogen adsorption at −196 °C (Micromeritics ASAP2020). The BET surface area (SBET) was calculated from the isotherms using the BET equation. The total pore volume (VTotal) was assessed by converting the amount of nitrogen gas adsorbed (expressed in cubic centimeters per gram at STP) at a high relative pressure (∼0.99) to the volume of liquid adsorbate. The t-plot method was used to calculate the micropore volume (VMicro). The mesopore volume (VMeso) was determined by subtracting the micropore volume from the total pore volume while the micropore and mesopore percentages were based on the total pore volume. The mesopore size distribution of AC was also calculated from the N2 adsorption isotherm according to the Berret−Joyner−Halenda (BJH) method. The ash composition in the virgin distilled spirit lees was determined with an X-ray fluorescence spectrometry (AXIOS). The mechanical strength of the molded activated carbon was determined by an automatic particle strength tester (ZQJ-II). In order to evaluate the adsorption capacity of the AC products, both iodine and methylene blue (MB) absorption values were measured according to the China national standards GB/T 12496.81999 and GB/T 12496.10-1999, respectively. The ash content
mL/min nitrogen for 20 min to remove the oxygen. Then the reactor was heated to a preselected carbonization temperature with a heating rate of 10 °C/min and was held at this temperature for 1 h before it was cooled to room temperature. The heating and cooling processes were carried out under the protection of nitrogen flow. For steam activation, 5 g of the carbonized carbon (CC) was first placed in a quartz reactor which was inserted into a vertical electric furnace and, then, heated to a desired activation temperature at a heating rate of 10 °C/min under the protection of nitrogen flow (200 mL/ min). After the activation temperature was reached, the gas was switched to steam (0.1 mol/g·h) and the sample was kept under this condition for 1 h before it was finally cooled in nitrogen flow. For chemical activation, 5 g of the CC was mixed with NaOH solution at a specified ratio of 1.0 (defined as the mass ratio of activation agent to CC), and the mixture was kept at room temperature for 48 h and then dried at 105 °C. The resulting sample was finally heated to a preselected activation temperature at a heating rate of 10 °C/min and activated at this temperature for 1 h. In this process, a nitrogen flow (200 mL/ min) was applied to the reactor as the purge gas and also the coolant gas after activation. The obtained solid product was thoroughly washed with distilled water until the pH value of the washing solution was around 7 and, then, dried at 105 °C for subsequent analyses. The obtained CC or AC was also subjected to an alkali treatment to remove its ash and upgrade the carbon quality. It was done by mixing the carbon and a specified NaOH solution according to a solid/liquid ratio of 1:5 (g/mL) and refluxed in a glass flask for a period of time. Finally, the alkaline solution was separated by vacuum filtration and the obtained solid was thoroughly washed with distilled water until the pH value of the washing solution was about 7. The AC molding was implemented by first treating 3.0 g ashcontaining AC with 15 mL NaOH (2 M) for 30 min (i.e., the deashing process) and further blending a given amount of carboxymethylcellulose (CMC) and acidic alumina sol (in some experiments the alkaline solution was drained out before the addition of CMC and alumina sol). The resulting mixture was in turn thoroughly washed with ethanol and vacuum 6038
dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
Industrial & Engineering Chemistry Research
Article
of AC was determined using the standard ASTM procedure D2866-94.
3. RESULTS AND DISCUSSION 3.1. ACs from Steam Activation. This section is devoted to making and further characterizing the ACs based on steam activation. Table 2 summarizes the characteristics of the ACs obtained with different conditions of carbonization and activation. The BET surface area and total pore volume was highest at the activation temperature of 800 °C (carbonized at 450 °C). Up to 800 °C, the gradually enhanced reaction between steam and carbon resulted in more developed pore structures. When the activation temperature was over 800 °C, the reactions between steam and carbon start to be diffusioncontrolled and thus cause a nonhomogeneous reaction in the particle, resulting in the reactions mainly focusing on the external parts that have little contribution to pore generation. Furthermore, the reaction between steam and carbon became to too violent to widen the pores and cause some micropores to be converted into mesopores and macropores, thus decreasing the specific surface area and total pore volume. This was demonstrated by the fact that the AC activated at 850 °C had a smaller micropore volume than that activated at 800 °C. Table 2 further shows that the mesopore percentage and the average pore size gradually increased with increasing activation temperature, indicating the widening of pores at high activation temperatures as well. Comparing all the data for the activation temperature of 800 °C in Table 2 clarifies that increasing the carbonization temperature from 450 to 750 °C decreased the BET surface area and total pore volume of the prepared AC. The carbonization at higher temperature would lead to a rather compact char, which in turn hinders the diffusion and reaction of the activator (steam) in the carbon activation and thus decreases BET surface area and total pore volume of the resulting AC. On the other hand, the thermogravimetric data for the tested distilled spirit lees demonstrated that the carbonization should be at temperatures above 400 °C to achieve a sufficiently high kinetic rate of carbonization (data not shown). Consequently, the carbonization temperature of 450 °C is adopted for all the experiments hereafter. Figure 1a shows the nitrogen adsorption−desorption isotherms of ACs made with different carbonization and steam activation conditions. The ACs from relatively low carbonization and activation temperatures (AC-450-750 and AC-450-800) exhibited the behavior of type I isotherm with a characteristic H4 hysteresis loop. Although the isotherms had a rapid increase at low P/Po values and a relatively horizontal plateau at the higher P/Po (the characteristics of type I isotherm), there are apparent hysteresis loops when P/Po increased to 0.4 (the characteristics of type IV isotherm), indicating the development of the mesoporosity. These features are in agreement with the pore volume distribution shown in Table 2 which is characterized with a higher mesopore volume than the micropore volume for each AC. For ACs made with carbonization at temperatures over 450 °C or activation at temperatures above 800 °C, their isotherms were with more characteristics of the type IV isotherm because the N2 uptakes for such ACs increased more obviously at P/Po higher than 0.6. Figure 1b shows the BJH pore size distributions of all ACs characterized in Figure 1a. The ACs from carbonization at 750 °C (⧫) or activation at 850 °C (▲) had obviously fewer pores of 3−5 nm but more pores above 5 nm. This provided evidence
Figure 1. (a) Nitrogen adsorption−desorption isotherms and (b) BJH pore size distributions of activated carbons obtained under different activation conditions.
again that the higher carbonization and activation temperatures would convert the narrowly sized pores into pores with wider size as well as some extremely large pores. Table 2 also shows the iodine and methylene blue adsorption values measured for all the compared ACs. As we know, both iodine and methylene blue have been widely adopted as the model substances in screening the carbons for water treatment.1,11,18,19 While the iodine adsorption quantifies the numbers of micropores, the methylene blue adsorption provides a quantitative indication of the mesopore numbers present in the material. In Table 2, the AC-450-800 enabled the highest iodine adsorption (581 mg/g), while the AC-450-850 exhibited the highest methylene blue adsorption (99 mg/g). This verifies again that higher activation temperature resulted in more mesopores. The realized iodine adsorption also decreased with increasing carbonization temperature (450−750 °C), indicating the conversion of some micropores into rather large pores or the collapse of some pores. Nonetheless, the methylene blue adsorption did not show a big difference among the tested three carbonization temperatures, indicating possibly that it is rather hard to create or enlarge pores for the carbon from high-temperature carbonization. Hereafter, the tests of ash removal and quality upgrading are thus conducted with respect to both AC-450-800 and AC-450-850. 3.2. Upgrading AC with Alkali Treatment. Considering the SiO2-dominant high ash content in the ACs from distilled spirit lees, alkali treatment was introduced to remove the ash and upgrade the ACs. The alkali treatment took NaOH 6039
dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
Industrial & Engineering Chemistry Research
Article
removed via the successive filtration. When NaOH concentration was below 2 mol/L, the ash removed efficiency increased with increasing NaOH concentration. Further increasing the NaOH concentration, however, affected the ash content little in the carbon product. Figure 3b shows further that the ash content and ash removal efficiency were almost constant after 10 min of alkali treatment, indicating that the ash in CC and AC can be easily removed. On the basis of Figure 3, the NaOH concentration of 2 mol/L and the treating time of 30 min were adopted in the studies herein. Table 3 lists the yields and ash contents for the ACs prepared via different ash-removal methods. Taking the ATAC as an
solution as the alkali reagent and was applied to both the carbonized carbon (denoted as ATCC) and activated carbon (denoted as ATAC). Meanwhile, the chemical activation with NaOH was also viewed as an ash-removal method and tested in this section. Figure 2 summarizes the technical steps involved in all the examined ash-removal methods.
Table 3. Typical Yield and Ash Content after Removing Ash via Different Methodsa Figure 2. Technical steps for preparing ACs with different alkali treatment methods.
sample
b
dried distilled spirit lees carbonized carbon (CC) alkali-treated CC ATCC-AC steam activation AC (SAAC) ATAC-AC NaCA-AC
Figure 3 shows the ash content in the resulting carbon and ash removed efficiency varied with the NaOH concentration
product mass (g)
one-step yield (wt %)
overall AC yield (wt %)
100
ash content (wt %)
ash removal efficiency (%)
12.1
39.0
39.0
39.0
28.7
31.5
80.8
31.5
13.8
17.4 23.6
55.2 60.5
17.4 23.6
24.3 43.2
14.5 18.1
61.4 46.5
14.5 18.1
11.2 19.2
61.1
84.4 69.0
a
All the data was based on treating 100 g dried raw material. The carbonization temperature was 450 °C, the activation temperature was 850 °C, the concentration of NaOH solution was 2 mol/L, and the alkali treatment time was 30 min for ATCC and ATAC. The activation temperature was 800 °C for NaOH activation. bATCC refers to “alkali treatment of carbonized carbon”, ATAC refers to “alkali treatment of activated carbon”, and NaCA denotes the NaOH chemical activation.
example, one can see that treating 100 g dried distilled spirit lees (with 12.1 wt % ash) produced 39.0 g CC, 23.6 g steam activation AC (SA-AC), and 14.5 g ATAC-AC. The ash contents were correspondingly 28.7 wt % for CC, 43.2 wt % for SA-AC, and 11.2 wt % for the ATAC-AC. Thus, by ATAC the ash removal from the SA-AC was 84.4%, referring to a practically high ash removal efficiency. The alkali treatment for CC (ATCC) removed about 61% ash, indicating a relatively lower ash removal than the abovementioned ATAC. This may be related to the more developed pore structure of SA-AC (compared to CC), which made the ash more accessible for the reaction with alkali in SA-AC than in CC. Meanwhile, the ash content in SA-AC (43.2 wt %) was higher than that in CC (28.7 wt %), which would also promote the reactions between ash and alkali. Because of its lower ash removal, the ATCC also allowed a higher overall AC yield than the ATAC (17.4 vs 14.5%). Table 4 shows the BET surface areas and pore structure characteristics of the ACs prepared with different methods. Both the ATCC and ATAC are beneficial to the improvement on the BET surface area and pore volume of the resulting AC. Nonetheless, the ATAC method showed much better enhancing effect than the ATCC method to achieve higher BET surface area and larger total pore volume. This was possibly because the ATAC method removed more ash that
Figure 3. Effects of (a) NaOH concentration and (b) NaOH treatment time on ash content and ash removal efficiency of the resulting carbon products (carbonization and activation were at 450 and 850 °C, respectively): (●) alkali treatment of AC; (★) alkali treatment of CC.
and alkali treatment time. When the CC or AC was boiled in water (0 mol/L NaOH) for 3 h (Figure 3a), the ash content was only slightly reduced (from 28.7 to 27.5% for CC and from 43.2 to 41.0% for AC), and this removed part referred to the water-soluble ash components (e.g., K2O). Treating the samples with NaOH solution decreased the ash content of the resulting carbon distinctively. The SiO2 in ash can react with NaOH and dissolve in the alkaline solution and then be 6040
dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
Industrial & Engineering Chemistry Research
Article
Table 4. Characterization of Activated Carbons from Different Alkali Treatment Methodsa pore volume (cm3/g) sample SA-800 ATCC800 ATAC800 SA-850 ATCC850 ATAC850 NaCA800
pore volume ratio(%)
SBET (m2/g)
VTotal
VMicro
VMeso
VMicro/ VTotal
VMeso/ VTotal
DA (nm)
372 549
0.34 0.62
0.14 0.13
0.20 0.49
41.2 21.0
58.8 79.0
3.37 4.53
623
0.56
0.19
0.37
33.9
66.1
3.58
324 554
0.32 0.61
0.10 0.13
0.22 0.48
31.3 21.3
68.8 78.7
3.97 4.40
623
0.67
0.16
0.51
23.9
76.1
4.33
423
0.35
0.14
0.21
40.0
60.0
3.28
Carbonization temperature was 450 °C, and the samples are named as “alkali treatment method-activation temperature”. The meaning of all abbreviations under the sample column are the following: SA for steam activation with no alkali treatment, ATAC for alkali treatment of activated carbon, ATAC for alkali treatment of activated carbon, and NaCA for NaOH chemical activation.
a
blocking the existing pores and thus resulted in a more developed pore structure in the AC. For example, the BET surface area and total pore volume of the alkali-treated AC (ATAC-800) were 67.5% and 65.1% higher than those of the AC without alkali treatment (SA-800), respectively. For the case of activation at 850 °C, such increments reached 92.3 and 109.3%, respectively. Literature studies have shown obvious upgrading effect for ACs by treating the raw material with alkali,8,14 but the ATAC tested here appeared to have little influence on the micropore/mesopore ratio and the average pore size. This effectively indicates that the ATAC developed the micropore and mesopore at similar extent. Figure 4a illustrates the nitrogen adsorption−desorption isotherms of the ACs from different alkali treatment methods. The ATCC and ATAC increased the nitrogen uptake at low and high relative pressures, indicative of the increases in both the micropores and mesopores. The hysteresis loops in the isotherms of alkali-treated samples are also more evident than that of the untreated ACs, indicating possibly a more developed mesopore structures from the alkali treatment and being in good agreement with the results in Table 4. Figure 4b shows the BJH pore size distributions of the ACs from different alkali treatment methods. One can see that the both ATCC and ATAC developed mesopores in a wide pore size range of 3− 100 nm and this range covered almost the entire mesopore size range of 2−50 nm. The result refers actually to a difference between the alkali treatment of raw material and carbonized material (ATCC or ATAC). For treating raw material, the increased mesopores are usually concentrated in a narrower pore size range, for example, of 2−5 nm.14 Comparing with the results of literature-reported alkali treatment of raw material, the ATAC, as well as ATCC, method tested above has two advantages. First, after carbonization and activation, the sample is free of tarry matters to make the leaching solution transparent with a simple composition (its main component is sodium silicate). The leaching solution from treating the raw material via alkali is however black and contains lots of organic components, making the solution highly polluting and hard to treat. Also, the alkali treatment of
Figure 4. (a) Nitrogen adsorption−desorption isotherms and (b) BJH pore size distributions of activated carbons from different alkali treatment methods.
the CC or AC allows surely higher efficiency of ash removal than treating the raw material directly because the pores present in the carbon would enhance the reactions between alkali with ash. NaOH chemical activation (NaCA) combined actually the effects of deashing and activation, and the acquired typical results for the materials tested in this study are also compared in Tables 3 and 4. Although the NaCA method was performed under an extremely high temperature of 800 °C, it realized only an ash removal efficiency of 69%, which was comparable to that allowed by the ATCC method and lower than that realized by the ATAC method. Two causes can be considered for the relatively low ash removal efficiency of NaCA method. First, compared with the solid−liquid reactions between ash and NaOH in ATAC or ATCC, the solid−solid reactions in NaCA are harder to achieve and would lead to the realized lower ash removal. Second, in the NaCA method, the undeveloped pore structure of the raw material is an obstacle for the sufficient contact of alkali with ash, which is a prerequisite for high ash removal efficiency. As shown in Table 4, the BET surface area and total pore volume of the AC prepared by NaCA are higher than those of the ACs made by steam activation (SA-AC) but lower than those alkali-treated ACs (ATCC-AC and ATACAC). The relatively low specific surface area and pore volume of NaCA-AC can partly be attributed to the low NaOH/CC (1/1) used, and the performances of NaCA-AC may better than those of ATCC-AC and ATAC-AC if a higher NaOH/CC (e.g., 2/1 or 3/1) is used. Nevertheless, the physical activation is no doubt more economic and environmentally friendly than 6041
dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
Industrial & Engineering Chemistry Research
Article
leaching solution byproduct can be reused as the major binder for molding the produced powder AC. This technology allows the use of material with relatively high ash contents, such as the distilled spirit lees tested in this article, to be the appropriate raw feedstock for AC production.
the chemical activation so that the physical activation is still attractive to many applications. 3.3. AC Molding with Leaching Solution. For many applications, molded AC rather than powder AC is required. For AC molding, the use of a certain binder is needed, such as carboxymethylcellulose and acidic alumina sol. This work supposed the use of the sodium silicate-rich alkaline leaching solution as one part of the binding agents for the AC molding. It hopes to explore an effective way to treat and also utilize the leaching solution resulting from the alkali treatment of the highash carbon such as that made from rice husk and the distilled spirit lees tested in this article. Table 5 shows the mechanical strengths and adsorption capacities of the molded ACs with different binding agents. The
■
*Tel.: +86 10 82544886. Fax: +86 10 82629912. E-mail address:
[email protected] (G.X.);
[email protected]. cn (Y.W.). Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors are grateful to the financial supports of National High-Tech Research and Development Program of China (2009AA02Z209), The National Key Technology R&D Program (2010bac66b01), The International (Regional) Cooperation and Exchange (21161140329), and The National Natural Science Foundation of China (21006114).
Table 5. Mechanical Strength and Adsorption Capacities of Activated Carbons Molded under Different Conditionsa adsorption (mg/g)
sample
add leaching solution
alumina sol (dry basis, g)
CMC (g)
mechanical strength (N/cm)
iodine
MB
1 2 3 4
no yes yes yes
0.5 1.0 0 0.5
0.5 0 1.0 0.5
very fragile very fragile 341 212
661 515 464 479
107 93 69 80
AUTHOR INFORMATION
Corresponding Author
■
REFERENCES
(1) Bansal, R.; Goyal, M. Activated carbon adsorption; CRC: Boca Raton, 2005. (2) Dąbrowski, A.; Podkościelny, P.; Hubicki, Z.; Barczak, M. Adsorption of Phenolic Compounds by Activated CarbonA Critical Review. Chemosphere 2005, 58, 1049. (3) Ioannidou, O.; Zabaniotou, A. Agricultural Residues as Precursors for Activated Carbon ProductionA Review. Renew. Sust. Energ. Rev. 2007, 11, 1966. (4) Suhas; Carrott, P. J. M.; Carrott, M. LigninFrom Natural Adsorbent to Activated Carbon: A Review. Bioresour. Technol. 2007, 98, 2301. (5) Paraskeva, P.; Kalderis, D.; Diamadopoulos, E. Production of Activated Carbon from Agricultural by Products. J. Chem. Technol. Biotechnol. 2008, 83, 581. (6) Dias, J.; Alvim-Ferraz, M.; Almeida, M.; Rivera-Utrilla, J.; Sánchez-Polo, M. Waste Materials for Activated Carbon Preparation and Its Use in Aqueous-phase Treatment: A review. J. Environ. Manage. 2007, 85, 833. (7) Oliveira, L. C. A.; Pereira, E.; Guimaraes, I. R.; Vallone, A.; Pereira, M.; Mesquita, J. P.; Sapag, K. Preparation of Activated Carbons from Coffee Husks Utilizing FeCl3 and ZnCl2 as Activating Agents. J. Hazard. Mater. 2009, 165, 87. (8) Liou, T.; Wu, S. Characteristics of Microporous/mesoporous Carbons Prepared from Rice Husk under Base- and Acid-treated Conditions. J. Hazard. Mater. 2009, 171, 693. (9) Kalderis, D.; Bethanis, S.; Paraskeva, P.; Diamadopoulos, E. Production of Activated Carbon from Bagasse and Rice Husk by a Single-stage Chemical Activation Method at Low Retention Times. Bioresour. Technol. 2008, 99, 6809. (10) Gonzalez, J. F.; Roman, S.; Gonzalez-Garcia, C. M.; Nabais, J. M. V.; Ortiz, A. L. Porosity Development in Activated Carbons Prepared from Walnut Shells by Carbon Dioxide or Steam Activation. Ind. Eng. Chem. Res. 2009, 48, 7474. (11) Yang, J. A.; Qiu, K. Q. Preparation of Activated Carbons from Walnut Shells via Vacuum Chemical Activation and Their Application for Methylene Blue Removal. Chem. Eng. J. 2010, 165, 209. (12) El-Hendawy, A. N. A. An Insight Into the KOH Activation Mechanism through the Production of Microporous Activated Carbon for the Removal of Pb2+ Cations. Appl. Surf. Sci. 2009, 255, 3723. (13) Tan, I.; Ahmad, A.; Hameed, B. Preparation of Activated Carbon from Coconut Husk: Optimization Study on Removal of 2, 4, 6-trichlorophenol Using Response Surface Methodology. J. Hazard. Mater. 2008, 153, 709.
With the AC prepared by carbonization at 450 °C and steam activation at 850 °C.
a
powder AC was made from the distilled spirit lees by carbonization at 450 °C and steam activation at 850 °C. In addition to the leaching solution, both alumina sol and CMC were tested as the binders. Samples 1 and 2 are very fragile, and this indicates that the use of the alkaline leaching solution and CMC are necessary for the AC molding. Sample 3 had the highest mechanical strength, revealing that CMC is a good binding agent. However, the high mechanical strength was at the expense of the adsorption capacities. Although sample 2 had weak mechanical strength, it showed higher adsorption capacities than sample 3, indicating alumina sol had less effect on the pore structure of AC than CMC. Furthermore, for some inorganic molecules, the adsorption sites available on the ACs molded using CMC are somehow limited. This caused the use of the alumina sol to replace CMC by considering that alumina is a good adsorbent for inorganic compounds such as fluoride and arsenate.20−22 The data in Table 5 thus show that the molded AC using less CMC would lower the strength more or less, but the realized mechanical strength, for example, of sample 4 is still comparable to that of the ceramic raschig ring that is widely used as the filler of distillation column. Moreover, sample 4 showed higher adsorption capacities than sample 3 due to the less negative effect of alumina sol as described above. These proved the possibility of using the silicate-rich leaching solution as part of the AC molding binders in producing the application-practical molded ACs. Nevertheless, the molding conditions with the use of the leaching solution need to be further optimized for different ACs.
4. CONCLUSIONS The alkali treatment of ACs provides an effective and economic as well as environmentally friendly method for removing ash and upgrading the AC quality. The sodium silicate-rich alkaline 6042
dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
Industrial & Engineering Chemistry Research
Article
(14) Yang, J. A.; Qiu, K. Q. Development of High Surface Area Mesoporous Activated Carbons from Herb Residues. Chem. Eng. J. 2011, 167, 148. (15) Yang, J. A.; Qiu, K. Q. Experimental Design To Optimize the Preparation of Activated Carbons from Herb Residues by Vacuum and Traditional ZnCl2 Chemical Activation. Ind. Eng. Chem. Res. 2011, 50, 4057. (16) Bagheri, N.; Abedi, J. Preparation of High Surface Area Activated Carbon from Corn by Chemical Activation Using Potassium Hydroxide. Chem. Eng. Res. Des. 2009, 87, 1059. (17) Xu, G. W.; Ji, W. F.; Liu, Z.; Wan, Y. H.; Zhang, X. Y. Necessity and Technical Route of Value-added Utilization of Biomass Process Residues in Light Industry (in Chinese). Chin. J. Process Eng. 2009, 9, 618. (18) Demiral, H.; Demiral, I.; Karabacakoglu, B.; Tumsek, F. Production of Activated Carbon from Olive Bagasse by Physical Activation. Chem. Eng. Res. Des. 2011, 89, 206. (19) Aravindhan, R.; Rao, J. R.; Nair, B. U. Preparation and Characterization of Activated Carbon from Marine Macro-algal Biomass. J. Hazard. Mater. 2009, 162, 688. (20) Lin, T.-F.; Wu, J.-K. Adsorption of Arsenite and Arsenate within Activated Alumina Grains: Equilibrium and Kinetics. Water Res. 2001, 35, 2049. (21) Ghorai, S.; Pant, K. K. Equilibrium, Kinetics and Breakthrough Studies for Adsorption of Fluoride on Activated Alumina. Sep. Purif. Technol. 2005, 42, 265. (22) Tripathy, S. S.; Bersillon, J.-L.; Gopal, K. Removal of Fluoride from Drinking Water by Adsorption onto Alum-Impregnated Activated Alumina. Sep. Purif. Technol. 2006, 50, 310.
6043
dx.doi.org/10.1021/ie202882r | Ind. Eng. Chem. Res. 2012, 51, 6037−6043
