Optimization of preparation process of activated carbon from chestnut burs assisted by microwave and pore structural characterization analysis

Figures & data

Table 1. Factors and levels in Box-Behnken design (BBD) of experiment.

	Symbol		Coded Level
Factor	Uncoded	Coded	−1	0	1
Irradiation time (min)	X1	x1	15	20	25
Impregnation time (min)	X2	x2	120	180	240
Mass ratio of alkali-to-char	X3	x3	1:1	1.25:1	1.5:1

Figure 1. Effects of (a) irradiation time, (b) impregnation time, and (c) mass ratio of alkali-to-char on the iodine adsorption value.

Table 2. Experimental design and results for response surface methodology (RSM).

				Iodine Adsorption Value (mg/g)
Run	x1	x2	x3	Experimental Y	Predict Y
1	−1	0	1	1084.05	1074.54
2	1	−1	0	960.11	970.79
3	0	0	0	1046.03	1053.04
4	−1	0	−1	790.07	794.08
5	0	−1	−1	998.69	978.50
6	1	0	−1	874.44	883.95
7	0	0	0	1087.60	1053.04
8	−1	−1	0	972.26	988.44
9	−1	1	0	1035.41	1024.73
10	0	0	0	1050.62	1053.04
11	0	1	1	1108.44	1128.63
12	0	0	0	1038.62	1053.04
13	0	0	0	1042.35	1053.04
14	0	1	−1	973.14	979.82
15	1	1	0	964.17	947.99
16	0	−1	1	1123.14	1116.47
17	1	0	1	894.27	890.27

Table 3. Analysis of variance for the regression equation.

Source	Sum of Squares	df	Mean Square	F value	P value Prob > F
Model	122711.50	9	13634.61	27.74	0.0001**
x1	4455.68	1	4455.68	9.06	0.0196*
x2	90.86	1	90.86	0.19	0.6802
x3	41121.38	1	41121.38	83.65	<0.0001**
x1x2	872.91	1	872.91	1.78	0.2244
x1x3	18789.56	1	18789.56	38.22	0.0005**
x2x3	29.43	1	29.43	0.060	0.8137
x1^2	46510.18	1	46510.18	94.62	<0.0001**
x2^2	5170.95	1	5170.95	10.52	0.0142*
x3^2	5837.90	1	5837.90	11.88	0.0107*
Residual	3440.98	7	491.57
Lack of fit	1869.38	3	623.13	1.59	0.3252
Pure error	1571.60	4	392.90
Cor total	126152.48	16
R^2	0.9727
R^2adj	0.9377
CV (%)	2.21

Notes: *P < 0.05; **P < 0.01.

Figure 2. Response surface polts showing the effects of variables (X₁ = irradiation time, min; X₂ = impregnation time, min; and X₃ = the mass ratio of alkali-to-char) on the iodine adsorption value.

Figure 3. Adsorption isotherms of CBAC prepared under optimal conditions.

Table 4. Comparisons of activated carbons for the characterization of the microstructure.

Raw Materials	Activation Method	Activator	Activation Time (min)	The BET Surface Area (m^2/g)	Pore Volume (m^3/g)	Average Pore Size (nm)	Micropore Area (m^2/g)	Micropore Volume (cm^3/g)	Reference
Chestnut burs	Microwave heating	KOH	17	1254.5	0.6565	2.093	1204.8	0.5727	Present study
Oil palm fiber	Microwave heating	KOH	5	707.79	0.3805	2.211	—	—	Foo and Hameed, 2011b
Date stones	Microwave heating	KOH	8	856	0.4680	2.182	—	—	Foo and Hameed, 2011d
Oil palm empty fruit bunch	Microwave Heating	KOH	15	807.54	0.45	2.193	—	—	Foo and Hameed, 2011e
Pistachio nut shells	Microwave heating	KOH	7	700.53	0.375	2.144	—	—	Foo and Hameed, 2011c
Rice husks	Microwave heating	KOH	7	752	0. 64	3.414	346	0.26	Foo and Hameed, 2011a
Cotton stalk	Microwave heating	KOH	10	729.33	0.38	2.08	529.46	0.26	Deng et al., 2010a,b

Figure 4. HK-pore size distribution of CBAC prepared under optimal conditions.

Figure 5. SEM micrographs of (a) char (2000×) and (b) CBAC (2000×).

Figure 6. FTIR spectrum of CBAC.

Foo, K.Y., and B.H. Hameed. 2011b. Microwave-assisted preparation of oil palm fiber activated carbon for methylene blue adsorption. Chem. Eng. J. 166: 792–795. doi:10.1016/j.cej.2010.11.019

 Web of Science ®Google Scholar

Foo, K.Y., and B.H. Hameed. 2011d. Preparation of activated carbon from date stones by microwave induced chemical activation: Application for methylene blue adsorption. Chem. Eng. J. 170:338–341. doi:10.1016/j.cej.2011.02.068.

 Web of Science ®Google Scholar

Foo, K.Y., and B.H. Hameed. 2011e. Preparation of oil palm (Elaeis) empty fruit bunch activated carbon by microwave-assisted KOH activation for the adsorption of methylene blue. Desalination 275:302–305. doi:10.1016/j.desal.2011.03.024

 Web of Science ®Google Scholar

Foo, K.Y., and B.H. Hameed. 2011c. Preparation and characterization of activated carbon from pistachio nut shells via microwave-induced chemical activation. Biomass Bioenergy 35:3257–3261. doi:10.1016/j.biombioe.2011.04.023

 Web of Science ®Google Scholar

Foo, K.Y., and B.H. Hameed. 2011a. Utilization of rice husks as a feedstock for preparation of activated carbon by microwave induced KOH and K2CO3 activation. Bioresour. Technol. 102:9814–9817. doi:10.1016/j.biortech.2011.07.102

 PubMed Web of Science ®Google Scholar

Deng, H., G.X. Li, H.B. Yang, J.P. Tang, and J.Y. Tang. 2010a. Preparation of activated carbons from cotton stalk by microwave assisted KOH and K₂CO₃ activation. Chem. Eng. J. 163:373–381. doi:10.1016/j.cej.2010.08.019

 Google Scholar

Deng, H., G. Zhang, X. Xu, G. Tao, and J. Dai. 2010b. Optimization of preparation of activated carbon from cotton stalk by microwave assisted phosphoric acid-chemical activation. J. Hazard. Mater. 182:217–224. doi:10.1016/j.jhazmat.2010.06.018

 Google Scholar