Durian rind wastes are an important raw material for activated carbon production due to their renewable sources and low-cost materials. The efficiency of increasing surface area and the quantity of oxygen groups on the surface of activated carbon were studied for the preparation of activated carbon. The preparation of activated carbon has been studied with the different methods as follows: activation by acid, activation by base, hydrothermal and activation by acid, and hydrothermal and activation by base. The results showed that hydrothermal and activation by acid had high iodine number which was chosen to determine the optimum condition for activated carbon preparation. The optimum condition for preparation of durian rind activated carbon was studied by Box-Behnken design. Solid/water ratio, solid/acid ratio and temperature were chosen as the important parameters for achieving the optimum reaction condition. The reaction products were analyzed by iodine number. Based on the results, the optimum condition for preparation of durian rind activated carbon was predicted using RSM. The maximum iodine number of 626.47 mg/g was expected at the optimum condition: solid/water ratio (1:175, g/mL), solid/acid ratio (1:23, g/mL) and temperature (500°C). The preparation of durian rind activated carbon at the optimal condition was carried; the percentages of iodine number achieved (666.73 ± 6 mg/g) were close to the maximum predicted value (666.73 mg/g), thus verifying the model. At the optimum condition, the functional group on surface of durian rind activated carbon was characterized by FT-IR. The result showed that the oxygen content on surface was increased in the form of carbonyl and sulfonyl group.
Durian rind is the waste from durian fruit consumption. In durian season, a lot of durian rind waste is produced in Thailand every day. Direct disposal of durian peel will increase the amount of agricultural waste. Therefore, it would be economically attractive if durian peel can be utilized as a raw material to produce an effective activated carbon [
Activated carbons are widely used for adsorbing gaseous- and liquid-phase pollutants. In the processing units, they are used for several industrial sectors, such as chemical industries, food- and beverage-processing industries, pharmaceuticals, petroleum, and many manufacturing industries [
The high surface area, large porosity, well-developed internal pore structure, and a functional group appear on the surface of AC make it a useful material which has a lot of applications in many areas, but mostly in the environmental area [
There are two main steps for preparing an activated carbon including carbonization of the raw materials in an inert atmosphere and activation of char in the presence of the appropriate oxidizing agents. By pyrolytic decomposition, most of the non-carbon elements, such as H2 and O2, are removed as the gaseous form in carbonization, giving a carbon with the fixed mass and the structure of rudimentary pore. To increase the diameter of particle pores and to create new pores, the activation step is then used for developing the adsorptive power of the carbonization product [
Activation can be conducted by either chemical or physical method. Commonly within the process of chemical activation, carbonization and activation occur at the same time as accommodated by the chemical activating agents, that is, dehydrating agents and oxidants. On the contrary, for physical activation, the precursor carbonization takes place in priority, followed by the activation at high temperatures in the presence of the suitable activating agents such as CO2 or steam. It has been found that the physical activation process usually emerges at a temperature higher than the chemical activation process [
The precursor-material impregnation using chemical agents such as FeCl3, ZnCl2, H3PO4, and KOH can restrain the formation of tar and reduce the amount of the volatile-matter evolution also, achieving the high precursor-to-carbon conversion [
This study aimed to determine the good durian rind activated carbon preparation method and the physical and chemical activation processes of activated carbon derived from durian peel. The response surface methodology (RSM) was used for optimization of durian rind activated carbon preparation parameters including solid/water ratio, solid/acid ratio and temperature.
Durian rinds were collected from local markets in Bangkok, Thailand, washed many times with distilled water in order to remove the dust and other inorganic impurities. After that, it was cut into approximately 1 cm × 1 cm size and dried at 60–80°C for 24 hrs to reduce its moisture content. The dried durian rind was grounded in the hammer mill and then stored in desiccators to prevent it from moisture. Potassium hydroxide (KOH; ACS reagent) and sulfuric acid (H2SO4; ACS reagent) were purchased from UNILAB (Thailand) and LAB SCAN (Thailand), respectively. The proximate analysis of durian rind which was conducted according to ASTM standard E 870-82 was given in
Proximate | Results, % |
---|---|
Moisture content | 7.00 |
Ash content | 3.00 |
Volatile content | 89.50 |
Fixed carbon content | 0.50 |
Firstly, the durian rind biochar was prepared, which was put into the furnace, then was heat at 400°C for 1 hr. Secondly, the durian rind biochar was activated by the four different methods including activation by acid (A1), activation by base (A2), hydrothermal and activation by acid (A3), and hydrothermal and activation by base (A4).
For the activation by acid and base, the charcoal was chemically activated by H2SO4 or KOH at the several ratios, then washed with DI water until the pH value was 5.5–6.0. The washed charcoal was carbonized in the furnace at the several temperatures for 1 hr.
For hydrothermal and activation by acid and base, the charcoal was immersed in DI water with the several ratios and then transferred to the thermal reactor, which was heated at 110°C for 24 hr. After that, it was activated by H2SO4 or KOH at the several ratios, then washed with DI water until the pH value was 5.5–6.0. The washed charcoal was carbonized in the furnace at the several temperatures for 1 hr.
In this study, the optimization of the preparation of durian rind activated carbon was applied by Box-Behnken design (BBD) technique under response surface methodology (RSM), which is a collection of mathematical and statistical techniques for designing experiments, building models, and evaluating the effects of factors. This method allows evaluating not only the main factors affecting the preparation of durian rind activated carbon, but also the interaction between these factors. The complete model is based on the simultaneous variation of 3 factors at 3 levels with 30 experiments. The independent variables reaction, i.e., solid/water ratio, solid/acid ratio, and temperature, were coded with the low level as –1 and the high levels as +1 in BBD and the results with the experimental conditions were shown in
RunOrder | Solid/water |
Solid/acid |
Temperature (°C) | Iodine number (mg/g) | Predicted value |
---|---|---|---|---|---|
1 | 1:150 | 1:10 | 450 | 549.43 | 556.09 |
2 | 1:200 | 1:10 | 450 | 549.20 | 561.67 |
3 | 1:150 | 1:30 | 450 | 589.49 | 588.91 |
4 | 1:200 | 1:30 | 450 | 558.10 | 567.65 |
5 | 1:150 | 1:20 | 400 | 597.42 | 596.64 |
6 | 1:200 | 1:20 | 400 | 590.76 | 582.06 |
7 | 1:150 | 1:20 | 500 | 627.88 | 623.41 |
8 | 1:200 | 1:20 | 500 | 620.26 | 622.31 |
9 | 1:175 | 1:10 | 400 | 607.57 | 604.59 |
10 | 1:175 | 1:30 | 400 | 607.57 | 611.94 |
11 | 1:175 | 1:10 | 500 | 627.88 | 626.05 |
12 | 1:175 | 1:30 | 500 | 665.96 | 657.51 |
13 | 1:175 | 1:20 | 450 | 630.42 | 631.69 |
14 | 1:175 | 1:20 | 450 | 632.96 | 631.69 |
15 | 1:175 | 1:20 | 450 | 630.42 | 631.69 |
16 | 1:150 | 1:10 | 450 | 560.30 | 556.09 |
17 | 1:200 | 1:10 | 450 | 572.03 | 561.67 |
18 | 1:150 | 1:30 | 450 | 590.43 | 588.91 |
19 | 1:200 | 1:30 | 450 | 579.65 | 567.65 |
20 | 1:150 | 1:20 | 400 | 605.03 | 596.64 |
21 | 1:200 | 1:20 | 400 | 582.19 | 582.06 |
22 | 1:150 | 1:20 | 500 | 610.11 | 623.41 |
23 | 1:200 | 1:20 | 500 | 615.19 | 622.31 |
24 | 1:175 | 1:10 | 400 | 594.88 | 604.59 |
25 | 1:175 | 1:30 | 400 | 605.03 | 611.94 |
26 | 1:175 | 1:10 | 500 | 635.50 | 626.05 |
27 | 1:175 | 1:30 | 500 | 655.81 | 657.51 |
28 | 1:175 | 1:20 | 450 | 632.96 | 631.69 |
29 | 1:175 | 1:20 | 450 | 632.96 | 631.69 |
30 | 1:175 | 1:20 | 450 | 630.42 | 631.69 |
The surface area, pore volume and average pore diameter of the activated carbon were determined by nitrogen adsorption-desorption measurements (Autosorb IQ, Quantachrome). The crystalline structure of the durian rind and the activated carbon were characterized by X-ray diffraction (XRD 6100, Shimadzu) using Cu Kα radiation (
The durian rind biochar was activated by the different methods which were divided into 4 methods including activation by acid (A1), activation by base (A2), hydrothermal and activation by acid (A3), and hydrothermal and activation by base (A4). The iodine number is targeted as to choose the activation method for optimization as shown in
Raw material | Activation method | Iodine adsorption number (mg/g) |
---|---|---|
Durian rind | Activation by acid | 146.73 |
Activation by base | 118.81 | |
Hydrothermal and activation by base | 162.78 | |
Hydrothermal and activation by acid | 198.21 |
The Box-Behnken design (BBD) with three factors at three levels, as well as the results of the preparation of durian rind activated carbon were shown in
In
One of the purposes of the experimental design was to allow a simple and reliable model efficient of relating to directly response to the most significant variables. In
The accuracy of model fit was verified by the coefficient of determination R2, which was 0.9504, indicating that 0.9504 of the variability in the response could be described by the model. The statistical significance of this model equation was assessed by the F-test for ANOVA (
Source | DF | Adj SS | Adj MS | F-value | |
---|---|---|---|---|---|
Model | 9 | 25043.2 | 2782.6 | 42.55 | 0.000 |
Linear | 3 | 6245.7 | 2081.9 | 31.83 | 0.000 |
Water ratio | 1 | 245.8 | 245.8 | 3.76 | 0.067 |
Acid ratio | 1 | 1506.4 | 1506.4 | 23.03 | 0.000 |
Temperatute | 1 | 4493.5 | 4493.5 | 68.71 | 0.000 |
Square | 3 | 18055.8 | 6018.6 | 92.03 | 0.000 |
Water ratio × water ratio | 1 | 12422.5 | 12422.5 | 189.96 | 0.000 |
Acid ratio × acid ratio | 1 | 3605.1 | 3605.1 | 55.13 | 0.000 |
Temperatute × temperatute | 1 | 1758.4 | 1758.4 | 26.89 | 0.000 |
2-Way Interaction | 3 | 741.8 | 247.3 | 3.78 | 0.027 |
Water ratio × acid ratio | 1 | 360.1 | 360.1 | 5.51 | 0.029 |
Water ratio × temperatute | 1 | 90.9 | 90.9 | 1.39 | 0.252 |
Acid ratio × temperatute | 1 | 290.8 | 290.8 | 4.45 | 0.048 |
Error | 20 | 1307.9 | 65.4 | ||
Lack-of-Fit | 3 | 345.1 | 115.0 | 2.03 | 0.148 |
Pure Error | 17 | 962.8 | 56.6 | ||
Total | 29 | 26351.2 |
Adequacy check of the presented model is an important part of the analysis. Good adequacy can endorse that the approximating model allows an adequate estimation to the real system; however, it may give poor or misleading results [
As shown in
As shown in
As shown in
The effects of temperature on iodine number of activated carbon preparation are shown in
The performance of activated carbon preparation using hydrothermal and activation by acid technique can be evaluated in term of iodine number efficiency, which largely varies with the change and the interactions in variables. Thus, the accommodations between the variables were created and optimized depending on the response from the model for economic motivation. Accordingly, if the iodine number was set at the assumed high iodine number (666.73 mg/g) as the target criteria, the optimum condition of activated carbon preparation was 1:175 g/mL of solid/water ratio 1:23, g/mL of solid/acid ratio and 500°C of temperature. At the optimum condition, the iodine number could be obtained as 666.73 ± 6 mg/g in triplicate actual experiments. The optimum condition showed that the predicted values were closer to the experimental values. Thus, the results confirmed the suitability of prediction model for the iodine number of activated carbons.
The A1, A2, A3, and A4 were prepared by the different techniques from Section 3.1. The iodine adsorption method was investigated for studying the microporous in activated carbon [
The BET surface area of the activated carbon (A4) was 331.02 m2/g while the commercial activated carbon (CarboTech) was 900 m2/g [
The crystallinity of durian rind raw material and activated carbon were studied by XRD. As shown in the
The most characteristic vibrations were selected by the FTIR spectra of durian rind and activated carbon. As shown in
The morphology of durian rind and activated carbon was shown in
Durian rind is a good precursor to produce activated carbons with well-developed surface area and functional group. The durian rind biochar was activated by the different methods which were divided into 4 methods including activation by acid, activation by base, hydrothermal and activation by acid, and hydrothermal and activation by base. The hydrothermal and activation by acid was chosen to optimization which is the highest values obtained from iodine number (198.21 mg/g). The response surface methodology based on 3 variables Box-Behnken design was applied to determine the effects of solid/water ratio (ranging 1:150–1:120 mg/g), solid/acid ratio (ranging 1:10–1:30 mg/g) and temperature (ranging 400–600°C). For each response, the coefficients of the hypothesized model were analyzed based on the experimental responses. The analysis of the responses characterizing the surface area development shows, on one hand, the positive effects of solid/acid ratio and temperature on the iodine number and a negative effect of solid/water ratio on these responses. The R2 values of all factors showed a good fit of the models with the experimental data. Based on the four models obtained, the numerical optimization was performed. The optimum condition was confirmed and fitted the experimental data well. In this optimum condition, the activated carbon shown that the functional group on activated carbon surface are oxygen content including the hydroxyl group, carbonyl group and sulfonyl group, respectively.