Adsorption of chlorinated volatile organic compounds using activated carbon made from Jatropha curcas seeds

Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2526–2530

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Adsorption of chlorinated volatile organic compounds using activated carbon made from Jatropha curcas seeds Shih-Hong Hsu a, Chin-Sheng Huang a, Tsair-Wang Chung a,*, Shun Gao b a b

Department of Chemical Engineering/R&D Center for Membrane Technology, Chung Yuan Christian University, Chungli, Taoyuan 320, Taiwan Institute of Ecological Forestry, Faculty of Forestry, Sichuan Agricultural University, Wenjiang, Chengdu 611130, Sichuan, China

A R T I C L E I N F O

A B S T R A C T

Article history: Received 4 March 2014 Received in revised form 5 May 2014 Accepted 27 May 2014 Available online 18 June 2014

In the present study, Jatropha curcas seeds (JS) were used as the raw material for the production of activated carbon by simple thermo-chemical activation with NaOH as a chemical activating agent. Various chlorinated volatile organic compounds (carbon tetrachloride, chloroform, dichloromethane, tetrachloroethylene, trichloroethylene, and chlorobenzene) were tested for the single-component adsorption study using the gravimetric adsorption method. The study focused on the adsorption of chlorinated volatile organic compounds, and the effect of the number of chlorine atoms in the molecule to the adsorption uptake. Results from the experiments showed that adsorption by activated carbon increased with increasing number of chlorine atoms and hence, with increasing molecular weight. There is, however, no significant difference between the adsorption of molecules with the same number of chlorine atoms but with different bond orders. It indicates that the influence of molecular weight is more important than the existence of double bonds within the molecule. The reusability of the activated carbon was proved when no significant decrease in its adsorption capacity was observed even after the fourth time of regeneration. ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords: Jatropha curcas seeds Activated carbon Adsorption Isotherm Volatile organic compounds

1. Introduction Volatile organic compounds (VOCs) are among the most common air pollutants emitted from chemical, petrochemical and allied industries. Techniques such as thermal oxidation, catalytic oxidation, biofiltration, absorption, adsorption, condensation and membrane separation have been developed for VOCs removal [1–3]. Among these techniques, adsorption technology nowadays was widely accepted for the removal of VOCs. For the adsorption technique, an appropriate material for VOCs capture is important. Chlorinated volatile organic compound (CVOC) is a subgroup of VOCs containing chlorine compounds. Most of these compounds are man-made and are irritants, toxic, carcinogenic, and flammable [4]. Thus, the removal of these CVOCs is a major environmental concern. Jatropha curcas is a multipurpose non-edible oil yielding perennial and drought tolerant plant. The oil from J. curcas is regarded as a potential fuel substitute [5]. Recently, the usage of J. curcas oil as raw material for making biodiesel became popular, resulting to the huge cultivation of J. curcas plant in many countries

* Corresponding author. Tel.: +886 3 2652500; fax: +886 2652599. E-mail address: [email protected] (T.-W. Chung).

[6–9]. This may lead to the problem associated with its wastes, such as the J. curcas fruit shell, hull and seed cake; these wastes contain low nutrients, abundant cellulose, hemicellulose and lignin, and are not suitable for use as fertilizer. Thus, converting these wastes into activated carbon maybe a good possible solution to alleviate the potential problems [10]. Activated carbon is a form of carbon processed to have a high pore volume with high specific surface area for adsorption or chemical reactions. The methodology used for activated carbon preparation involves physical and/or chemical activation. Generally, physical activation is a two-step process, usually using CO2 or steam as the activating agent. The advantages of physical activation include its ease of operation and environmental friendly nature; however, it demands higher activation temperature and longer activation time [11]. On the other hand, chemical activation offers shorter treatment time and lower activation temperature, making it the method of choice for activation [12,13]. Based on literature, alkaline hydroxides can be used to prepare activated carbon, giving a high specific surface area in the range of 1700–3167 m2 g1 [14]. This study aimed to investigate the relationship between the number of chlorine atoms in the CVOCs and the adsorption capability of the activated carbon. Gravimetric adsorption was used to generate the isotherms for six CVOCs (carbon tetrachloride,

http://dx.doi.org/10.1016/j.jtice.2014.05.028 1876-1070/ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

S.-H. Hsu et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2526–2530

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Table 1 Properties of the sorbates of chlorinated volatile organic compounds. Structure

Pour point (8C)

Density (g/cm3)

Vapor pressure (kPa)

Polarity (debye)

22.92

1.5867

12.2

1.7

19

1.622

2.1

61.2

63.5

1.483

21.3

4.1

131.39

87.2

73

1.46

8.0

1.0

CH2Cl2

84.93

39.6

96.7

1.33

54.3

3.1

C6H5Cl

112.56

45

1.11

1.2

2.7

Formula

Molecular weight (g/mol)

Boiling point (8C)

CCl4

153.82

C2Cl4

165.83

121.1

CHCl3

119.38

C2HCl3

76.72

131

chloroform, dichloromethane, tetrachloroethylene, trichloroethylene, chlorobenzene) with J. curcas seed activated carbon as the sorbent. 2. Materials and methods 2.1. J. curcas seed activated carbon preparation The JS received from India was washed with deionized water to remove some particles and dried in an oven at 110 8C for 24 h. The dried seeds were ground and sieved into particle size smaller than 500 mm. The JS powder was placed in an oven at 400 8C for 1 h under nitrogen flow. After carbonization, the sample was cooled to room temperature and was mixed with 1 M NaOH at 70 8C for 24 h. Then, the sample was dried in an oven to remove the moisture. The sample was activated at 800 8C for 2 h under nitrogen flow. It was then cooled to room temperature and washed with distilled water and HCl solution until the pH value reached 7. Afterwards, it was dried at 110 8C for 24 h producing the final product. The pore

–

diameter, surface area and pore volume of the JS activated carbon were measured using the nitrogen adsorption/desorption isotherms (BET sorptometer, QUANTACHROME NOVA N-1000e). The thermo-gravimetric analysis was performed using the TA Instrument/TGA Q500. Approximately, 5 mg of the sample was heated from 25 to 900 8C with the heating rate 20 8C/min under controlled atmosphere of nitrogen flow. The surface functional group was measured using FT-IR (Fourier Transform-Infrared Spectroscopy, Spectrum One model, Perkin Elmer Co.). The activated carbon was encapsulated in KBr as the testing pellet. A total of 128 scans were recorded per spectrum at a resolution of 4 cm1. 2.2. CVOCs equilibrium adsorption experiment The CVOCs used in this study are listed in Table 1. For the equilibrium adsorption experiment, the activated carbon was first placed in a vacuum oven at 100 8C for 24 h to remove the impurities and moisture of the sorbent. In order to avoid other gases, the freeze–vacuum–thaw cycles was used to degas the

Fig. 1. Gravimetric adsorption experimental set-up.

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2528

Fig. 2. Thermo-gravimetric analysis of Jatropha curcas seeds.

solvent. On the basis of the authors’ previous work [15], the gravimetric adsorption experimental setup is shown in Fig. 1. 50 mg of JS activated carbon was placed in the micro-balance. The weight of the sorbent was recorded when the vacuum pressure of the system reached below 0.5 torr. The valve was then simultaneously opened to let the CVOCs pass through the system. When the entering CVOCs reached the desired value for pressure, the valve was closed to start the adsorption of the CVOCs onto the sorbent on the microbalance. Adsorption equilibrium was achieved when the microbalance reading remained constant. The weight reading shown on the microbalance was recorded together with the final system pressure. This process (started at P/ P0 = 0.1) was repeated, and more CVOCs vapor was added into the system until the final pressure can be reached in this system and the temperature was kept at room temperature. Experimental data are presented as the equilibrium isotherm obtained by plotting the adsorption uptake versus the relative pressure (P/P0) of adsorbate gas at room temperature. Langmuir isotherm model was used to fit the equilibrium data, which is defined by the following equation: q

qm bC ð1 þ bCÞ

or

(1)

C 1 C ¼ þ q qm b qm

(2)

where C (ppm) is the equilibrium concentration of CVOCs, q (mg/g) is the amount of CVOCs adsorbed at equilibrium, qm (mg/g) is the maximum loading to complete coverage of the surface by the CVOCs and b (L/mg) is the adsorption-equilibrium constant. 3. Results and discussion 3.1. Thermo-gravimetric analysis Thermo-gravimetric analysis was used to identify the composition of J. curcas seeds. Fig. 2 shows the TGA data. According to previous studies [16–18], the first stage of weight loss (25–180 8C) is due to the moisture and some volatile components. The second stage has a greater weight loss (180–375 8C), which corresponds to the primary carbonization. The weight loss in the third stage (375– 900 8C) became stable, which indicates the decomposition of lignin and the formation of the structure of activated carbon.

Fig. 3. Fourier transform infrared spectroscopy of Jatropha curcas seeds (JS), carbonized Jatropha curcas seed (CJS), and activated carbon of Jatropha curcas seed (ACJS).

The second stage has a greater weight loss (180–375 8C), which corresponds to the primary carbonization. This stage presented the release of light VOCs occurs from degradation of cellulose and hemicellulose. The weight loss in the third stage (375–900 8C) became stable, which indicates the decomposition of lignin and the formation of the structure of activated carbon. Above 600 8C, the weight loss was minor indicating that the main structure of char was formed. 3.2. Fourier transform infrared spectroscopy analysis Generally, the pore structure development is influenced by many factors, which were the amount of chemical activating agent, activation temperature and activation time. However, it is accepted that pore structure development is also influenced by impurities and structure of carbon. Fourier transform infrared spectroscopy of JS, CJS, and ACJS was shown in Fig. 3. For the JS (J. curcas seed) sample, the following IR bands were observed: a peak at around 3398 cm1 (–OH vibrational stretching of hydroxyl group), peak at 2919 cm1 (aliphatic groups), peak at 1636 cm1 (C5 5O), peak at 1411 cm1 and 1375 cm1 (both corresponding to oxygen functionalities such as highly conjugated C5 5O stretching and C–O stretching in carboxylic groups), peak at 1052 cm1 (C–O stretching in acids, alcohols, phenols, ethers, and esters), and peak at 617 cm1 (in-plane ring deformation) [10]. The intensity of the FT-IR spectra in the CJS (carbonized JS) sample decreased at 2919 cm1 and 617 cm1, which is possibly due to the removal of impurities and volatile compounds. For the ACJS (activated carbon of JS) IR spectra, the –OH band decreased distinctly while the peaks for the other functional groups disappeared; this is a characteristic close to that of the commercial activated carbon used. 3.3. ACJS surface property analysis Adsorption ability depends on the surface area, pore volume and pore diameter of the sorbent. As shown in Table 2, the surface

Table 2 Surface properties of the ACJS. Material

Activation method

Activation agent

SBET (m2/g)

Averaged pore diameter (A˚)

Averaged pore volume (cm3/g)

Jatropha curcas seed

Thermo-chemical

NaOH

1758

23.39

0.9238

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2529

400 350 550 300 500

Uptake(mg/g)

Quantity Adsorbed (cm3/g STP)

600

450 400

Adsorption Desorption

350

250

1st ACJS 2nd ACJS 3rd ACJS

200 150 100 50

300 0.0

0.2

0.4

0.6

0.8

1.0

0

Relative Pressure (P/Po)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Relative pressure(P/Po)

Fig. 4. Adsorption/desorption isotherms of ACJS.

Fig. 6. System reliability test for ACJS.

area of ACJS is 1758 m2/g, the pore diameter is 23.39 A˚ and pore volume is 0.9238 cm3/g, which is a characteristic of a microporous material. Fig. 4 is the adsorption/desorption nitrogen isotherm of ACJS from BET sorptometer. The adsorption and desorption curves overlapped, which means there is no hysteresis loop. The shape of the curve suggests a Type I isotherm, which is attributed to the microporous solids having relatively small external surfaces. In this type, the adsorption limit is decided by the accessible micropore volume rather than by the internal surface area. Fig. 5 is the pore size distribution of ACJS obtained from the measurement of BET sorptometer, which also presents ACJS as a microporous material. 3.4. System reliability test To confirm the reliability of the system, three ACJS samples were randomly chosen and the equilibrium adsorption isotherm was run with chlorobenzene. Langmuir model was used to regress the data. Fig. 6 shows the reliability of this system, proving the stability of the ACJS. 3.5. Equilibrium isotherm for CVOCs adsorption In order to investigate the ACJS adsorption ability for chloroalkanes, various chloride-containing alkanes were used. Fig. 7 shows the equilibrium isotherms generated in the experiment. It can be observed that the adsorption amounts of tetrachloride, chloroform and dichloromethane in Fig. 7 are directly proportional

to the molecular weight and boiling point of the compound (see Table 1). The results is in agreement with the those obtained by Urano et al. [19] and Giaya et al. [20]. Tetrachloroethylene and trichloroethylene in Fig. 7 were used to investigate the adsorption ability of the activated carbon for chloro-alkenes. Trends similar to those of chloro-alkanes were observed; the adsorption amount is directly proportional to the molecular weight and boiling point of the compound. An inverse proportion to vapor pressure was observed also. Tetrachloroethylene and carbon tetrachloride in Fig. 7 were compared to check the influence of the presence of double bond on adsorption ability. The adsorption amount of carbon tetrachloride is higher even if its molecular weight is lower than that of carbon tetrachloride. It is possibly due to the more significant steric hindrance in tetrachloroethylene. Chloroform and trichloroethylene in Fig. 7 also showed the same trend as tetrachloroethylene and carbon tetrachloride. The adsorption amount of chloroform is higher than trichloroethylene. Based on the results, carbon tetrachloride was best adsorbed by the activated carbon among the chloro-alkanes, while tetrachloroethylene was best adsorbed among the chloro-alkenes. The adsorption behavior of these two chemicals by activated carbon was compared with that of an aromatic compound, chlorobenzene. Fig. 7 shows the adsorption of the compounds in the following order: chlorobenzene > carbon tetrachloride > tetrachloroethylene. The degree of adsorption is directly proportional to chemical polarity but inversely proportional to molecular weight.

300 250

Uptake (mg/g)

Pore Volume(cm 3 /g)

0.08

0.06

0.04

200 CH2Cl2 CHCl3

150

CCl4

100

C2HCl3 C2Cl4

50

0.02

0 0.00 0

20

40

60

80

100

C6H5Cl

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Relative pressure (P/P0)

Pore diameter(nm) Fig. 5. ACJS pore size distribution.

Fig. 7. ACJS adsorption equilibrium isotherm data and regression curves for various CVOCs.

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2530 500

chlorobenzene

450

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jtice.2014.05.028.

400 350

Uptake(mg/g)

Appendix A. Supplementary data

300

References

250 200 150 100 50 0

0

1

2

3

Regeneration time Fig. 8. Regeneration test of ACJS.

3.6. ACJS regeneration test To study the reusability of the ACJS, the adsorption experiment with chlorobenzene was repeated 4 times using the same ACJS. Fig. 8 shows that the adsorption ability of the ACJS did not decrease even after the 4th time of regeneration of ACJS with the regeneration temperature kept at 100 8C for 24 h. 4. Conclusion In the present study, ACJS was successfully produced. The reliability and regeneration tests showed the stability and reusability of the ACJS. The results of the experiments showed that the amount adsorbed by the activated carbon increases with increasing number of chlorine atoms in the adsorbate. Based on this observation, it follows that the adsorption is directly proportional to molecular weight. However, the effect of bond order was observed to be insignificant. Steric hindrance and structure, on the other hand, were both proven to be important factors in the adsorption of chlorinated volatile organic compounds with the same number of chlorine atoms by activated carbon made from J. curcas seeds. Acknowledgements Financial support of NSC101-3011-P-033-002 from National Science Council of Taiwan and part of the financial support of CYCU107044-11 from Chung Yuan Christian University are appreciated.

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