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Influence of conversion parameters of waste tires to activated carbon on adsorption of dibenzothiophene from model fuels
Accepted Manuscript Influence of conversion parameters of waste tires to activated carbon on adsorption of dibenzothiophene from model fuels Gaddafi I. Danmaliki, Tawfik A. Saleh PII:
S0959-6526(16)00052-4
DOI:
10.1016/j.jclepro.2016.01.026
Reference:
JCLP 6614
To appear in:
Journal of Cleaner Production
Received Date: 29 June 2015 Revised Date:
1 January 2016
Accepted Date: 11 January 2016
Please cite this article as: Danmaliki GI, Saleh TA, Influence of conversion parameters of waste tires to activated carbon on adsorption of dibenzothiophene from model fuels, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.01.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
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M AN U
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Graphical Abstract
ACCEPTED MANUSCRIPT
Influence of conversion parameters of waste tires to activated carbon on adsorption of dibenzothiophene from model fuels
Department of Chemistry, b Environmental Science Department; King Fahd University of
*Corresponding author
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Petroleum & Minerals, Dhahran 31261, Saudi Arabia
E-mail address: [email protected] ; [email protected] (966) 13 860 1734
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Fax:
Phone # (966) 13 860 1734
http://faculty.kfupm.edu.sa/CHEM/tawfik/
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Home Page:
AC C
a
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Gaddafi I. Danmaliki b, Tawfik A. Saleh a*
1
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Abstract Activated carbon was prepared from end-of-life tires, and its surface functional groups were enhanced by
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wet chemical oxidation using nitric acid. The carbonization and activation temperatures were optimized. The obtained material was characterized using a Brunauer-Emmett-Teller surface area analyzer, a Fourier transform infrared spectroscope and a scanning electron microscope coupled with an energy dispersive spectroscope. It was evaluated for adsorptive desulfurization of dibenzothiophene (DBT) in a model fuel.
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Five factors (dosage, concentration of the sulfur compounds, contact time, column length and flow rate) were varied using a 16 factorial design experiment. The optimum carbonization and activation
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temperatures that yielded a 473 m2/g surface area of the adsorbent for 5 hours were 500 °C and 900 °C, respectively. The interaction plot revealed that the adsorbent dosage, column length and dosage had the most influence on the percentage removal of DBT. The kinetic data for the adsorption process complied to a pseudo-second-order kinetic model with an R2 of 0.999, and the surface adsorption and intraparticle
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diffusion were operated concurrently. The equilibrium adsorption is best fitted using the Freundlich isotherm model. The efficiency of the produced carbons is comparable to other studies on adsorptive desulfurization, and the results are promising and should be tested for industrial applications.
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Keywords: carbonization, adsorptive desulfurization, factorial design
1. Introduction
Every aspect of land transportation involves the use of rubber tires. The global production of rubber tires is around one billion, and four billion end-of-life tires (ELTs) are currently in landfills (WBCSD, 2008). These materials are non-biodegradable and pose serious environmental and land management impacts. These materials are mostly burnt off in cement kilns as a management alternative, which leads to the emission of harmful polyaromatic hydrocarbons and heavy metals to the environment. The literature 2
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suggests that these waste materials have been used as a management strategy for diverse applications including mainly: energy and carbon production and adsorption studies (Antoniou et al., 2015; Saleh and AlSaadi, 2015).
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Sulfur is the main important hetero-element found in crude oil and has the most significant effect on refining. It poisons catalyst, corrodes refining equipment, and contributes to the deterioration of air quality, affecting public health and the ecosystem. The maximum allowable sulfur content in highway
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diesel fuel was 15 ppm in 2006 in the US and will be less than 10 ppm by 2017 (USEPA, 2014). Sulfur compounds found in crude oil are divided into aliphatic (mercaptans, sulfides, disulfides) and aromatic
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refractory groups (thiophenes derivatives). The conventional method, hydrodesulphurization, used by refineries for the removal of sulfur from fuel efficiently removes most aliphatic sulfur compounds from fuels. However, it is not efficient in the removal of aromatic refractory sulfur compounds, which pose danger to the environment. Additionally, hydrodesulfurization requires high temperature and pressure and a high dosage of catalyst before achieving the desired objective, which is uneconomical (Shyamal, 2004).
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The use of adsorbents in adsorptive desulfurization (ADS) has been the focus of researchers because of its mild operating conditions. The current area of research focuses on the development of cost effective, efficient and reliable adsorbent materials to reduce the sulfur content of the fuel (Ali 2012; Ali and Gupta
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2006; Ali et al. 2012). Therefore, this study aims to utilize activated carbon (AC) synthesized from ELTs for ADS of dibenzothiophene (DBT). We studied the influence of conversion process parameters of tires
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to AC and the ADS of DBT from model fuels by the obtained AC.
2. Material and methods 2.1.
Conversion of ELTs to Porous Carbon
ELTs received from tire shop were cut into small pieces, cleaned and thoroughly washed with deionized water three times to remove impurities until they become neat and clean. The tire was dried in an oven at 110 ◦C for 2 h, and the tire pieces were cut into smaller pieces to fit into a crucible. 3
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Carbonization: An initial sample mass of approximately 20 g was carbonized. The sample was kept inside a stainless steel adsorber for exactly 2 h at different temperatures of 250, 300, 350, 400, 450, 500 and 550 °C, respectively, for optimization. Note: the produced liquid hydrocarbon and gases were trapped
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and collected. After heating for 2 h, the heating was stopped, and the system was allowed to cool, then the sample was taken out of the adsorber. The percentage yield of both carbon black and liquid hydrocarbon were calculated. The carbon particles were ground to fine particles using pestle and mortar. The
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procedure was repeated for different samples to optimize the time by keeping the temperature constant at 500 °C and varying the time to 30, 60, 120, 180, 240 and 300 min in a muffle furnace. We oxidized all
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adhering impurities on the surface of the adsorbent upon treatment with a hydrogen peroxide solution. The obtained material was washed with deionized water and dried in a vacuum oven. Activation: The materials were activated in a muffle furnace for 5 h, at different temperatures, 400, 500, 600, 700, 800 and 900 °C respectively. The material was then treated with 4 M HNO3 for 3 h at 90 °C to remove the ash content and develop oxygen functional groups on the surface of the AC adsorbent. We
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washed the AC adsorbent with deionized water and dried in an oven at 120 ◦C overnight. The materials were characterized using Scanning electron microscope (SEM), Energy dispersive spectroscope (EDX),
(FTIR).
Adsorption Experiment
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2.2.
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Brunauer-Emmett-Teller (BET) Surface Area analyzer and Fourier transform infrared spectroscope
The model diesel fuel was prepared by adding the refractory sulfur compound viz DBT (150 ppm) in hexane (85 %) and toluene (15 %). Then, the batch and fixed bed column adsorption experiments were conducted. Factorial design for the fixed bed adsorption of DBT: Minitab software (version 16, Minitab Inc., USA) was used for the design of experiments to understand the most significant factors affecting the fixed bed adsorption (Vining 1998). Five factors were selected with high and low values, namely: concentration, flow rate, column length, dosage and contact time, as they were the significant factors
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affecting the adsorption. Half-factorial design 2 (5-1) with 16 experimental runs without a center point and without randomization was used for the analysis. A gas chromatograph, with a sulfur chemiluminescence detector, model 7890A system Agilent equipped with auto sampler (7693) and splitless injector, analyzed
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the concentration of the refractory sulfur compounds. The column used was Agilent 19091S-001: 263845555 50 m × 0.2 mm dimensions and a film thickness of 0.5 µm methyl siloxane stationary phase. The injection volume was 1 µL with a flow rate of 0.839 mL/min. The maximum temperature was 325 0C with
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an oven temperature programing of 60 °C for 1 min, then 10 °C/min to 230 °C for 2 min.
3.1.
Carbonization
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3. Results and discussion
Influence of temperature: The yield of gases and liquid hydrocarbons increases with pyrolysis temperature by around 500 °C where the percentage yield starts declining. This can be attributed to the fact that higher temperatures tend to give stronger thermal pyrolysis, in turn reducing the yield of the
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liquid hydrocarbons and gases. The yield of carbon black decreases until a temperature range of 500-550 °C where it starts stabilizing. This means that treating ELTs to 500 °C was the optimum for effective decomposition of all its components and the sole production of aggregates of carbon that are randomly
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linked together (Shah et al., 2006).
Influence of time: By fixing the temperature at 500°C and varying the time from 30 min to 5 h, the initial
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mass and final mass of the adsorbent were recorded. The recovery percentage was later calculated. The results indicated that treatment for 30 min to 1 h had the greatest influence on the carbon black recovery. Increasing the time from 2 h to 5 h did not show significant influence on the carbon surface. However,
the current work fixed the timing at 5 h for effective decomposition of the ELTs.
Activation: We fixed the time at 5 h for each experiment, and we varied the temperature from 400 to 500 °C. The initial mass and final mass of the adsorbent was recorded to calculate the recovery
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percentage. There was a continual reduction in the recovery percentage of the AC signifying continuous enhancement of the porosity and the decomposition of functional groups present in the ELTs. It is believed the adsorbent produced at 900°C with a 27.20 % recovery rate was the best and its surface area
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was taken after the experiment. The surface modifications on the adsorbent was carried out using nitric acid and sodium hydroxide to enhance the surface area and oxygen containing functional groups (Saleh, 2011). However, we conducted the subsequent experiments with the adsorbent that gave the highest
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surface area. Characterization
The sample expresses Type I isotherm with a hysteric loop and was observed at a relatively high pressure
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(0.8 to 1) indicating the presence of mesopores (Deng et al., 2009). In addition, a minor uptake of nitrogen was observed at relative pressures between 0 and 0.2 signifying the presence of small amounts of micropores within the samples (Min et al., 2006). The surface has a pore volume of 0.76 cm3/g and a pore size of 6.022 nm. The sample has a surface area of 473.35 m2/g and a pore volume of 0.70 cm3/g. Table 1 compares the pyrolysis and activation temperatures, residence times and BET surface areas of AC
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produced from ELTs in our study with those in literature.
Table 1: Pyrolysis, activation temperatures and BET surface areas of AC from ELTs BET Reference Pyrolysis Activation (m²/g)
600
Activating Agent
4 min
850
2h
Steam
528
800
1h
850
3h
CO2
496
800 500 500 800 800
45 min 5h 2h 6h 5h
950 900 950 900 900
2.4 h 2h 3h 2h 2h
Steam HNO3 CO2 Steam Steam
472 397 437 465 473
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Aranda et al., 2012 Gonzalez et al., 2006 Zabaniotou et al., 2004 Gupta et al., 2012 Choi et al., 2014 Saleh et al., 2015 This Study
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Temperature Residence Temperature Residence (°C) time (°C) time
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The SEM/EDX results of the AC sample after activation and treatment with HNO3 are depicted in Fig. 1 a & b respectively. The sample after activation showed the presence of sulfur in the EDX analysis because of the vulcanization process that uses sulfur to bind most of the polymers such as styrene and
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butadiene together in the tire formation process. This means that the pyrolysis and activation processes did not completely convert the waste materials into elemental carbon though the concentration of the sulfur from the EDX analysis was very low. Treatment with HNO3 removed all adhering impurities and
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showed the presence of carbon and oxygen as the only elemental compositions of the adsorbent. The acid treatment showed significant improvement in the oxygen content from 10.64 wt % after activation to
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14.39 wt % after treatment meaning that oxygen containing functional groups increased significantly.
Fig. 1. SEM/EDX result of AC sample after activation (a) and after treatment with HNO3 (b)
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FTIR Spectroscopy: FTIR spectra of the synthesized AC were taken to understand the functional groups present on the surface of the synthesized AC and the result is given in Fig. 2. The sample shows a sharp peak centering around 3430 cm−1 that can be ascribed to O-H stretching vibrations of hydroxyl or
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carboxylic groups due to chemisorbed water. There are noticeable development peaks at 2854 and 2924 cm−1 due to the presence of aliphatic C-H stretch of CH, CH2 and CH3. The small and broad peaks at 1700 and 1640 cm−1 are due to C=O stretching vibrations in ketones (such as ion radical or quinone structure that are highly conjugated) and carboxyl groups in carboxylic acid respectively. The peak around 1400
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(Paul et al., 2004; Wu et al., 2013; Tazibet et al., 2013).
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cm−1 can be attributed to the presence of C=O stretching vibrations of the O=C-OH and nitrate structures
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Fig. 2. FTIR Spectra of AC synthesized from ELTs
3.2.
Design of Experiment (DOE) Results of desulfurization
Fig.3 depicts the main effect plot and interaction plots of these experimental factors. The main effect plot (Fig. 3a) shows that the column study is best conducted at higher column length and dosage because the longer the column the better the interaction between the sulfur compounds and the adsorbent, while the 8
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higher the dosage the more active sites will be present for sulfur compound adsorption. On the contrary, the lower the concentration and flow rates the better the percentage removal because the adsorbent can only take the maximum sulfur compounds at any given time before reaching saturation. The lower the
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flow rate the better the interaction of the model fuel with the adsorbent. Contact time did not show any significant influence because the adsorption of the refractory sulfur compounds on the surface of the AC is a rapid process attaining equilibrium at 5-10 min.
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Results from the interaction plot, Fig. 3b, shows that the interaction between dosage and concentration, dosage and flow rate, and dosage and column length gave the most profound influence on the adsorption
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experiment. It shows that whether or not column length, concentration and flow rate are high or low when
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the dosage of the adsorbent is high, the percentage removal of the DBT tends to be very high.
(a)
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(b) Fig. 3. Main effects plot (a) and Interaction plot (b) for the removal of DBT
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First order, second order, and intraparticle diffusion models were used in the kinetic studies, see the Appendix (Langergren 1898; Webber and Morris 1963; Ho and McKay 1998). The kinetic analysis of the adsorption results in Table 2 suggests the experimental data was well fitted to a pseudo second order
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model with an R2 of 0.999, indicating a sort of interaction between DBT and the carbon surface. Fitting the data to the Intraparticle diffusion model indicated that surface adsorption and intraparticle diffusion
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were operating concurrently. The linear forms of Langmuir and Freundlich equations were used for the isotherm analysis (Ho, 2004). Table 3 suggests that the experimental data was well fitted to Freundlich Isotherm with an R2 of 0.998 and n>1, indicating a favorable adsorption process on heterogeneous systems or multilayer sorption (Freundlich, 1906).
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AC
DBT
1.22
0.062
Pseudo first order Calculated qe (mg/g) R2
Pseudo second order model K2 Calculated g/(mg•min) R2 qe (mg/g)
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Compound
K1 (1/min)
0.06
0.9935
3.375
1.22
Intraparticle diffusion Ki C mg/(g•min) (mg/g) R2
0.999
0.0045
1.17
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Adsorbent
Experimental qe (mg/g)
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Table 2: Pseudo first order, pseudo second order and intraparticle diffusion parameters for adsorption of DBT on AC derived from ELTs
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Table 3: Langmuir and Freundlich Isotherms constants for adsorption of DBT on AC derived from ELTs Langmuir Isotherm constant
Adsorbents
Compound
AC
DBT
Freundlich Isotherm constant
qm (mg/g)
KL (L/mg)
R2
RL
KF (L/g)
n
1/n
R2
6.43086817
7.893401
0.5648
0.002527
4.611255
8.9311
0.111968
0.9986
11
0.87
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4. Conclusion ELTs were converted to AC under the optimum carbonization temperature of 500 °C for 5 h. Factorial
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design of the experiment showed that the adsorbent had high percentage removal of the refractory sulfur compound DBT. A pseudo second order kinetic model and Freundlich isotherm best fit the experimental results, indicating the adsorption to be governed by heterogeneous or multilayer adsorption patterns. The
Appendix
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The equation of Pseudo first order linear equation is:
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prepared AC exhibited dual advantages of being inexpensive and of double benefits to the environment.
ln − = −
Where, qe and qt are the amounts of adsorbent adsorbed at equilibrium and time t, respectively. k1 is the rate constant of the Pseudo first order kinetics model.
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The equation of Pseudo second order linear equation is: 1 = +
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Where qt is the amount of adsorbent at a time t. k2 is the adsorption rate constant.
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The intraparticle diffusion model equation is: = / +
where C is the intercept related to the boundary layer thickness. kid is the slope which represents the intraparticle diffusion rate constant. The linear form of the Langmuir isotherm equation is: 1 = +
13
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where qe is the amount adsorbed at equilibrium concentration Ce. qm is the constant of the Langmuir isotherm representing maximum monolayer capacity. KL is the constant of the Langmuir isotherm related to the energy of adsorption.
1 ln = ln +
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The linear form of the Freundlich isotherm equation is:
where qe is the amount of absorbed material on absorbent surface. KF is the Freundlich isotherm constant indicating the adsorption capacity. n is the Freundlich isotherm constant indicating whether the adsorption
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process is favorable or unfavorable.
Acknowledgement
The authors would like to acknowledge the support provided by King Abdulaziz City for Science and Technology (KACST) through the Science & Technology Unit at King Fahd University of Petroleum &
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Minerals (KFUPM) for funding this work through project No. 13-PET393-04 as part of the National Science, Technology and Innovation Plan.
References
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Ali, I., 2012. New generation adsorbents for water treatment, Chem. Revs., 112, 5073-5091.
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Ali, I., Asim, M., Khan, T.A., 2012. Low cost adsorbents for removal of organic pollutants from wastewater, J. Environ. Manag., 113, 170-183. Ali, I., Gupta, V.K., 2006. Advances in Water Treatment by Adsorption Technology, Nature London, 1, 2661-2667. Antoniou, N., Zabaniotou, A., 2015. Experimental proof of concept for a sustainable End of Life Tyrespyrolysis with energy and porous materials production, J. Clean. Prod., 101, 323-336. DOI:10.1016/j.jclepro.2015.03.101 Deng, H., Yang, L., Tao, G., Dai, J., 2009. Preparation and characterization of activated carbon from cotton stalk by microwave assisted chemical activation- Application in methylene blue adsorption from aqueous solution, J. Hazar. Mater. 166, 1514-1521. DOI:10.1016/j.jhazmat.2008.12.080 Freundlich, H., 1906. Adsorption in solutions (in German). Zeitschrift für Physikalische Chemie, 57, 385-470. 14
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Ho, Y. S., 2004. Selection of optimum sorption isotherm. Carbon, 42, 113–2130 DOI:10.1016/j.carbon.2004.03.019 Ho, Y.S., McKay G., 1998. Sorption of dye from aqueous solution by peat. Chem Eng Journal 70, 115-124 DOI:10.1016/S0923-0467(98)00076-1 Min, A., Harris, A.T., 2006. Influence of carbon di oxide partial pressure and fluidization velocity on activated carbons prepared from scrap car tyre in a fluidized bed. Chem. Eng. Sci. 61, 8050–8059. DOI:10.1016/j.ces.2006.09.047 Paul, C.J., Shunnian W. 2004. Acid/Base-Treated Activated Carbons: Characterization of Functional Groups and Metal Adsorptive Properties. Langmuir, 20, 2233-2242. DOI: 10.1021/la0348463 Lagergren, S. (1898), About the theory of so-called adsorption of soluble substances (in German), Kungliga Svenska Vetenskapsakademiens Handlingar, 24 (4): 1-39. Saleh T.A., 2011. The influence of treatment temperature on the acidity of MWCNT oxidized by HNO3 or a mixture of HNO3/H2SO4, Applied surface science 257 (17), 7746-7751 Saleh, T.A., AlSAadi, A.A., 2015. Surface characterization and sorption efficacy of tire-obtained carbon: experimental and semiempirical study of rhodamine B adsorption, Surf. Interface Anal. 47, 785–792. DOI: 10.1002/sia.5775 Shah, J., Rasul, J.M., Mabood, F., Shahid, M., 2006. Conversion of Waste Tyres into Carbon Black and their Utilization as Adsorbent. J. Chin. Chem. Soc-Taip, 53, 1085-1089. DOI: 10.1002/jccs.200600144 Shyamal, K.B., 2004. Revamping of diesel hydro-desulfurizers: Options available and future research needs” Fuel Process. Technol 85, 13, 1503–1517. DOI: 10.1016/j.fuproc.2003.07.002 Tazibet, S., Boucheffa, Y., Lodewyckx, P. 2013. Heat treatment effect on the textural, hydrophobic and adsorptive properties of activated carbons obtained from olive waste. Micropor Mesopor Mat. 170, 293−298. DOI:10.1016/j.micromeso.2012.12.008 United States Environmental Protection Agency (USEPAa) 2014. EPA sets tier 3 motor vehicle emission and fuel standards. EPA-420-F-14-009. www.epa.gov/otaq/documents/tier3/420f14009.pdf Vining, G. G. Statistical Methods for Engineers; Duxbury-Brooks/Cole: Pacific Grove, CA, 1998. Weber Jr. W. J., Morris J. C., 1963. Kinetics of adsorption on carbon from solution, J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, 31-60. World Business Council for Sustainable Development (WBCSD 2008): Managing End of Life Tires-Full Report. Atar Roto Presse SA, Switzerland http://www.rubberassociation.ca/files/ELT%20Full%20Report,%202008.pdf Wu, X.H., Hong, X.T., Luo, Z.P., Hui, K.S., Chen, H.Y., Wu, J.W. 2013. The effects of surface modification on the super-capacitive behaviors of novel mesoporous carbon derived from rod-like hydroxyapatite template. Electrochim. Acta 89, 400−406. DOI:10.1016/j.electacta.2012.11.067 15
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Highlight Activated carbon was prepared from waste rubber tires Wet chemical oxidation was performed for the enhancement of surface functionalities
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M AN U
SC
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Activated carbon was evaluated for adsorptive desulfurization of dibenzothiophene
S0959-6526(16)00052-4
DOI:
10.1016/j.jclepro.2016.01.026
Reference:
JCLP 6614
To appear in:
Journal of Cleaner Production
Received Date: 29 June 2015 Revised Date:
1 January 2016
Accepted Date: 11 January 2016
Please cite this article as: Danmaliki GI, Saleh TA, Influence of conversion parameters of waste tires to activated carbon on adsorption of dibenzothiophene from model fuels, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.01.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Graphical Abstract
ACCEPTED MANUSCRIPT
Influence of conversion parameters of waste tires to activated carbon on adsorption of dibenzothiophene from model fuels
Department of Chemistry, b Environmental Science Department; King Fahd University of
*Corresponding author
M AN U
SC
Petroleum & Minerals, Dhahran 31261, Saudi Arabia
E-mail address: [email protected] ; [email protected] (966) 13 860 1734
TE D
Fax:
Phone # (966) 13 860 1734
http://faculty.kfupm.edu.sa/CHEM/tawfik/
EP
Home Page:
AC C
a
RI PT
Gaddafi I. Danmaliki b, Tawfik A. Saleh a*
1
ACCEPTED MANUSCRIPT
Abstract Activated carbon was prepared from end-of-life tires, and its surface functional groups were enhanced by
RI PT
wet chemical oxidation using nitric acid. The carbonization and activation temperatures were optimized. The obtained material was characterized using a Brunauer-Emmett-Teller surface area analyzer, a Fourier transform infrared spectroscope and a scanning electron microscope coupled with an energy dispersive spectroscope. It was evaluated for adsorptive desulfurization of dibenzothiophene (DBT) in a model fuel.
SC
Five factors (dosage, concentration of the sulfur compounds, contact time, column length and flow rate) were varied using a 16 factorial design experiment. The optimum carbonization and activation
M AN U
temperatures that yielded a 473 m2/g surface area of the adsorbent for 5 hours were 500 °C and 900 °C, respectively. The interaction plot revealed that the adsorbent dosage, column length and dosage had the most influence on the percentage removal of DBT. The kinetic data for the adsorption process complied to a pseudo-second-order kinetic model with an R2 of 0.999, and the surface adsorption and intraparticle
TE D
diffusion were operated concurrently. The equilibrium adsorption is best fitted using the Freundlich isotherm model. The efficiency of the produced carbons is comparable to other studies on adsorptive desulfurization, and the results are promising and should be tested for industrial applications.
AC C
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Keywords: carbonization, adsorptive desulfurization, factorial design
1. Introduction
Every aspect of land transportation involves the use of rubber tires. The global production of rubber tires is around one billion, and four billion end-of-life tires (ELTs) are currently in landfills (WBCSD, 2008). These materials are non-biodegradable and pose serious environmental and land management impacts. These materials are mostly burnt off in cement kilns as a management alternative, which leads to the emission of harmful polyaromatic hydrocarbons and heavy metals to the environment. The literature 2
ACCEPTED MANUSCRIPT
suggests that these waste materials have been used as a management strategy for diverse applications including mainly: energy and carbon production and adsorption studies (Antoniou et al., 2015; Saleh and AlSaadi, 2015).
RI PT
Sulfur is the main important hetero-element found in crude oil and has the most significant effect on refining. It poisons catalyst, corrodes refining equipment, and contributes to the deterioration of air quality, affecting public health and the ecosystem. The maximum allowable sulfur content in highway
SC
diesel fuel was 15 ppm in 2006 in the US and will be less than 10 ppm by 2017 (USEPA, 2014). Sulfur compounds found in crude oil are divided into aliphatic (mercaptans, sulfides, disulfides) and aromatic
M AN U
refractory groups (thiophenes derivatives). The conventional method, hydrodesulphurization, used by refineries for the removal of sulfur from fuel efficiently removes most aliphatic sulfur compounds from fuels. However, it is not efficient in the removal of aromatic refractory sulfur compounds, which pose danger to the environment. Additionally, hydrodesulfurization requires high temperature and pressure and a high dosage of catalyst before achieving the desired objective, which is uneconomical (Shyamal, 2004).
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The use of adsorbents in adsorptive desulfurization (ADS) has been the focus of researchers because of its mild operating conditions. The current area of research focuses on the development of cost effective, efficient and reliable adsorbent materials to reduce the sulfur content of the fuel (Ali 2012; Ali and Gupta
EP
2006; Ali et al. 2012). Therefore, this study aims to utilize activated carbon (AC) synthesized from ELTs for ADS of dibenzothiophene (DBT). We studied the influence of conversion process parameters of tires
AC C
to AC and the ADS of DBT from model fuels by the obtained AC.
2. Material and methods 2.1.
Conversion of ELTs to Porous Carbon
ELTs received from tire shop were cut into small pieces, cleaned and thoroughly washed with deionized water three times to remove impurities until they become neat and clean. The tire was dried in an oven at 110 ◦C for 2 h, and the tire pieces were cut into smaller pieces to fit into a crucible. 3
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Carbonization: An initial sample mass of approximately 20 g was carbonized. The sample was kept inside a stainless steel adsorber for exactly 2 h at different temperatures of 250, 300, 350, 400, 450, 500 and 550 °C, respectively, for optimization. Note: the produced liquid hydrocarbon and gases were trapped
RI PT
and collected. After heating for 2 h, the heating was stopped, and the system was allowed to cool, then the sample was taken out of the adsorber. The percentage yield of both carbon black and liquid hydrocarbon were calculated. The carbon particles were ground to fine particles using pestle and mortar. The
SC
procedure was repeated for different samples to optimize the time by keeping the temperature constant at 500 °C and varying the time to 30, 60, 120, 180, 240 and 300 min in a muffle furnace. We oxidized all
M AN U
adhering impurities on the surface of the adsorbent upon treatment with a hydrogen peroxide solution. The obtained material was washed with deionized water and dried in a vacuum oven. Activation: The materials were activated in a muffle furnace for 5 h, at different temperatures, 400, 500, 600, 700, 800 and 900 °C respectively. The material was then treated with 4 M HNO3 for 3 h at 90 °C to remove the ash content and develop oxygen functional groups on the surface of the AC adsorbent. We
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washed the AC adsorbent with deionized water and dried in an oven at 120 ◦C overnight. The materials were characterized using Scanning electron microscope (SEM), Energy dispersive spectroscope (EDX),
(FTIR).
Adsorption Experiment
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2.2.
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Brunauer-Emmett-Teller (BET) Surface Area analyzer and Fourier transform infrared spectroscope
The model diesel fuel was prepared by adding the refractory sulfur compound viz DBT (150 ppm) in hexane (85 %) and toluene (15 %). Then, the batch and fixed bed column adsorption experiments were conducted. Factorial design for the fixed bed adsorption of DBT: Minitab software (version 16, Minitab Inc., USA) was used for the design of experiments to understand the most significant factors affecting the fixed bed adsorption (Vining 1998). Five factors were selected with high and low values, namely: concentration, flow rate, column length, dosage and contact time, as they were the significant factors
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affecting the adsorption. Half-factorial design 2 (5-1) with 16 experimental runs without a center point and without randomization was used for the analysis. A gas chromatograph, with a sulfur chemiluminescence detector, model 7890A system Agilent equipped with auto sampler (7693) and splitless injector, analyzed
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the concentration of the refractory sulfur compounds. The column used was Agilent 19091S-001: 263845555 50 m × 0.2 mm dimensions and a film thickness of 0.5 µm methyl siloxane stationary phase. The injection volume was 1 µL with a flow rate of 0.839 mL/min. The maximum temperature was 325 0C with
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an oven temperature programing of 60 °C for 1 min, then 10 °C/min to 230 °C for 2 min.
3.1.
Carbonization
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3. Results and discussion
Influence of temperature: The yield of gases and liquid hydrocarbons increases with pyrolysis temperature by around 500 °C where the percentage yield starts declining. This can be attributed to the fact that higher temperatures tend to give stronger thermal pyrolysis, in turn reducing the yield of the
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liquid hydrocarbons and gases. The yield of carbon black decreases until a temperature range of 500-550 °C where it starts stabilizing. This means that treating ELTs to 500 °C was the optimum for effective decomposition of all its components and the sole production of aggregates of carbon that are randomly
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linked together (Shah et al., 2006).
Influence of time: By fixing the temperature at 500°C and varying the time from 30 min to 5 h, the initial
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mass and final mass of the adsorbent were recorded. The recovery percentage was later calculated. The results indicated that treatment for 30 min to 1 h had the greatest influence on the carbon black recovery. Increasing the time from 2 h to 5 h did not show significant influence on the carbon surface. However,
the current work fixed the timing at 5 h for effective decomposition of the ELTs.
Activation: We fixed the time at 5 h for each experiment, and we varied the temperature from 400 to 500 °C. The initial mass and final mass of the adsorbent was recorded to calculate the recovery
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percentage. There was a continual reduction in the recovery percentage of the AC signifying continuous enhancement of the porosity and the decomposition of functional groups present in the ELTs. It is believed the adsorbent produced at 900°C with a 27.20 % recovery rate was the best and its surface area
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was taken after the experiment. The surface modifications on the adsorbent was carried out using nitric acid and sodium hydroxide to enhance the surface area and oxygen containing functional groups (Saleh, 2011). However, we conducted the subsequent experiments with the adsorbent that gave the highest
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surface area. Characterization
The sample expresses Type I isotherm with a hysteric loop and was observed at a relatively high pressure
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(0.8 to 1) indicating the presence of mesopores (Deng et al., 2009). In addition, a minor uptake of nitrogen was observed at relative pressures between 0 and 0.2 signifying the presence of small amounts of micropores within the samples (Min et al., 2006). The surface has a pore volume of 0.76 cm3/g and a pore size of 6.022 nm. The sample has a surface area of 473.35 m2/g and a pore volume of 0.70 cm3/g. Table 1 compares the pyrolysis and activation temperatures, residence times and BET surface areas of AC
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produced from ELTs in our study with those in literature.
Table 1: Pyrolysis, activation temperatures and BET surface areas of AC from ELTs BET Reference Pyrolysis Activation (m²/g)
600
Activating Agent
4 min
850
2h
Steam
528
800
1h
850
3h
CO2
496
800 500 500 800 800
45 min 5h 2h 6h 5h
950 900 950 900 900
2.4 h 2h 3h 2h 2h
Steam HNO3 CO2 Steam Steam
472 397 437 465 473
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Aranda et al., 2012 Gonzalez et al., 2006 Zabaniotou et al., 2004 Gupta et al., 2012 Choi et al., 2014 Saleh et al., 2015 This Study
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Temperature Residence Temperature Residence (°C) time (°C) time
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The SEM/EDX results of the AC sample after activation and treatment with HNO3 are depicted in Fig. 1 a & b respectively. The sample after activation showed the presence of sulfur in the EDX analysis because of the vulcanization process that uses sulfur to bind most of the polymers such as styrene and
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butadiene together in the tire formation process. This means that the pyrolysis and activation processes did not completely convert the waste materials into elemental carbon though the concentration of the sulfur from the EDX analysis was very low. Treatment with HNO3 removed all adhering impurities and
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showed the presence of carbon and oxygen as the only elemental compositions of the adsorbent. The acid treatment showed significant improvement in the oxygen content from 10.64 wt % after activation to
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14.39 wt % after treatment meaning that oxygen containing functional groups increased significantly.
Fig. 1. SEM/EDX result of AC sample after activation (a) and after treatment with HNO3 (b)
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FTIR Spectroscopy: FTIR spectra of the synthesized AC were taken to understand the functional groups present on the surface of the synthesized AC and the result is given in Fig. 2. The sample shows a sharp peak centering around 3430 cm−1 that can be ascribed to O-H stretching vibrations of hydroxyl or
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carboxylic groups due to chemisorbed water. There are noticeable development peaks at 2854 and 2924 cm−1 due to the presence of aliphatic C-H stretch of CH, CH2 and CH3. The small and broad peaks at 1700 and 1640 cm−1 are due to C=O stretching vibrations in ketones (such as ion radical or quinone structure that are highly conjugated) and carboxyl groups in carboxylic acid respectively. The peak around 1400
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(Paul et al., 2004; Wu et al., 2013; Tazibet et al., 2013).
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cm−1 can be attributed to the presence of C=O stretching vibrations of the O=C-OH and nitrate structures
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Fig. 2. FTIR Spectra of AC synthesized from ELTs
3.2.
Design of Experiment (DOE) Results of desulfurization
Fig.3 depicts the main effect plot and interaction plots of these experimental factors. The main effect plot (Fig. 3a) shows that the column study is best conducted at higher column length and dosage because the longer the column the better the interaction between the sulfur compounds and the adsorbent, while the 8
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higher the dosage the more active sites will be present for sulfur compound adsorption. On the contrary, the lower the concentration and flow rates the better the percentage removal because the adsorbent can only take the maximum sulfur compounds at any given time before reaching saturation. The lower the
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flow rate the better the interaction of the model fuel with the adsorbent. Contact time did not show any significant influence because the adsorption of the refractory sulfur compounds on the surface of the AC is a rapid process attaining equilibrium at 5-10 min.
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Results from the interaction plot, Fig. 3b, shows that the interaction between dosage and concentration, dosage and flow rate, and dosage and column length gave the most profound influence on the adsorption
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experiment. It shows that whether or not column length, concentration and flow rate are high or low when
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the dosage of the adsorbent is high, the percentage removal of the DBT tends to be very high.
(a)
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(b) Fig. 3. Main effects plot (a) and Interaction plot (b) for the removal of DBT
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First order, second order, and intraparticle diffusion models were used in the kinetic studies, see the Appendix (Langergren 1898; Webber and Morris 1963; Ho and McKay 1998). The kinetic analysis of the adsorption results in Table 2 suggests the experimental data was well fitted to a pseudo second order
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model with an R2 of 0.999, indicating a sort of interaction between DBT and the carbon surface. Fitting the data to the Intraparticle diffusion model indicated that surface adsorption and intraparticle diffusion
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were operating concurrently. The linear forms of Langmuir and Freundlich equations were used for the isotherm analysis (Ho, 2004). Table 3 suggests that the experimental data was well fitted to Freundlich Isotherm with an R2 of 0.998 and n>1, indicating a favorable adsorption process on heterogeneous systems or multilayer sorption (Freundlich, 1906).
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AC
DBT
1.22
0.062
Pseudo first order Calculated qe (mg/g) R2
Pseudo second order model K2 Calculated g/(mg•min) R2 qe (mg/g)
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Compound
K1 (1/min)
0.06
0.9935
3.375
1.22
Intraparticle diffusion Ki C mg/(g•min) (mg/g) R2
0.999
0.0045
1.17
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Adsorbent
Experimental qe (mg/g)
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Table 2: Pseudo first order, pseudo second order and intraparticle diffusion parameters for adsorption of DBT on AC derived from ELTs
AC C
Table 3: Langmuir and Freundlich Isotherms constants for adsorption of DBT on AC derived from ELTs Langmuir Isotherm constant
Adsorbents
Compound
AC
DBT
Freundlich Isotherm constant
qm (mg/g)
KL (L/mg)
R2
RL
KF (L/g)
n
1/n
R2
6.43086817
7.893401
0.5648
0.002527
4.611255
8.9311
0.111968
0.9986
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0.87
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4. Conclusion ELTs were converted to AC under the optimum carbonization temperature of 500 °C for 5 h. Factorial
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design of the experiment showed that the adsorbent had high percentage removal of the refractory sulfur compound DBT. A pseudo second order kinetic model and Freundlich isotherm best fit the experimental results, indicating the adsorption to be governed by heterogeneous or multilayer adsorption patterns. The
Appendix
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The equation of Pseudo first order linear equation is:
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prepared AC exhibited dual advantages of being inexpensive and of double benefits to the environment.
ln − = −
Where, qe and qt are the amounts of adsorbent adsorbed at equilibrium and time t, respectively. k1 is the rate constant of the Pseudo first order kinetics model.
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The equation of Pseudo second order linear equation is: 1 = +
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Where qt is the amount of adsorbent at a time t. k2 is the adsorption rate constant.
AC C
The intraparticle diffusion model equation is: = / +
where C is the intercept related to the boundary layer thickness. kid is the slope which represents the intraparticle diffusion rate constant. The linear form of the Langmuir isotherm equation is: 1 = +
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where qe is the amount adsorbed at equilibrium concentration Ce. qm is the constant of the Langmuir isotherm representing maximum monolayer capacity. KL is the constant of the Langmuir isotherm related to the energy of adsorption.
1 ln = ln +
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The linear form of the Freundlich isotherm equation is:
where qe is the amount of absorbed material on absorbent surface. KF is the Freundlich isotherm constant indicating the adsorption capacity. n is the Freundlich isotherm constant indicating whether the adsorption
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process is favorable or unfavorable.
Acknowledgement
The authors would like to acknowledge the support provided by King Abdulaziz City for Science and Technology (KACST) through the Science & Technology Unit at King Fahd University of Petroleum &
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Minerals (KFUPM) for funding this work through project No. 13-PET393-04 as part of the National Science, Technology and Innovation Plan.
References
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Ali, I., 2012. New generation adsorbents for water treatment, Chem. Revs., 112, 5073-5091.
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Ali, I., Asim, M., Khan, T.A., 2012. Low cost adsorbents for removal of organic pollutants from wastewater, J. Environ. Manag., 113, 170-183. Ali, I., Gupta, V.K., 2006. Advances in Water Treatment by Adsorption Technology, Nature London, 1, 2661-2667. Antoniou, N., Zabaniotou, A., 2015. Experimental proof of concept for a sustainable End of Life Tyrespyrolysis with energy and porous materials production, J. Clean. Prod., 101, 323-336. DOI:10.1016/j.jclepro.2015.03.101 Deng, H., Yang, L., Tao, G., Dai, J., 2009. Preparation and characterization of activated carbon from cotton stalk by microwave assisted chemical activation- Application in methylene blue adsorption from aqueous solution, J. Hazar. Mater. 166, 1514-1521. DOI:10.1016/j.jhazmat.2008.12.080 Freundlich, H., 1906. Adsorption in solutions (in German). Zeitschrift für Physikalische Chemie, 57, 385-470. 14
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Ho, Y. S., 2004. Selection of optimum sorption isotherm. Carbon, 42, 113–2130 DOI:10.1016/j.carbon.2004.03.019 Ho, Y.S., McKay G., 1998. Sorption of dye from aqueous solution by peat. Chem Eng Journal 70, 115-124 DOI:10.1016/S0923-0467(98)00076-1 Min, A., Harris, A.T., 2006. Influence of carbon di oxide partial pressure and fluidization velocity on activated carbons prepared from scrap car tyre in a fluidized bed. Chem. Eng. Sci. 61, 8050–8059. DOI:10.1016/j.ces.2006.09.047 Paul, C.J., Shunnian W. 2004. Acid/Base-Treated Activated Carbons: Characterization of Functional Groups and Metal Adsorptive Properties. Langmuir, 20, 2233-2242. DOI: 10.1021/la0348463 Lagergren, S. (1898), About the theory of so-called adsorption of soluble substances (in German), Kungliga Svenska Vetenskapsakademiens Handlingar, 24 (4): 1-39. Saleh T.A., 2011. The influence of treatment temperature on the acidity of MWCNT oxidized by HNO3 or a mixture of HNO3/H2SO4, Applied surface science 257 (17), 7746-7751 Saleh, T.A., AlSAadi, A.A., 2015. Surface characterization and sorption efficacy of tire-obtained carbon: experimental and semiempirical study of rhodamine B adsorption, Surf. Interface Anal. 47, 785–792. DOI: 10.1002/sia.5775 Shah, J., Rasul, J.M., Mabood, F., Shahid, M., 2006. Conversion of Waste Tyres into Carbon Black and their Utilization as Adsorbent. J. Chin. Chem. Soc-Taip, 53, 1085-1089. DOI: 10.1002/jccs.200600144 Shyamal, K.B., 2004. Revamping of diesel hydro-desulfurizers: Options available and future research needs” Fuel Process. Technol 85, 13, 1503–1517. DOI: 10.1016/j.fuproc.2003.07.002 Tazibet, S., Boucheffa, Y., Lodewyckx, P. 2013. Heat treatment effect on the textural, hydrophobic and adsorptive properties of activated carbons obtained from olive waste. Micropor Mesopor Mat. 170, 293−298. DOI:10.1016/j.micromeso.2012.12.008 United States Environmental Protection Agency (USEPAa) 2014. EPA sets tier 3 motor vehicle emission and fuel standards. EPA-420-F-14-009. www.epa.gov/otaq/documents/tier3/420f14009.pdf Vining, G. G. Statistical Methods for Engineers; Duxbury-Brooks/Cole: Pacific Grove, CA, 1998. Weber Jr. W. J., Morris J. C., 1963. Kinetics of adsorption on carbon from solution, J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, 31-60. World Business Council for Sustainable Development (WBCSD 2008): Managing End of Life Tires-Full Report. Atar Roto Presse SA, Switzerland http://www.rubberassociation.ca/files/ELT%20Full%20Report,%202008.pdf Wu, X.H., Hong, X.T., Luo, Z.P., Hui, K.S., Chen, H.Y., Wu, J.W. 2013. The effects of surface modification on the super-capacitive behaviors of novel mesoporous carbon derived from rod-like hydroxyapatite template. Electrochim. Acta 89, 400−406. DOI:10.1016/j.electacta.2012.11.067 15
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Highlight Activated carbon was prepared from waste rubber tires Wet chemical oxidation was performed for the enhancement of surface functionalities
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Activated carbon was evaluated for adsorptive desulfurization of dibenzothiophene