This work reported on the development of novel nanomaterials of multiwalled carbon nanotubes doped with titania (CNT/TiO2) for the adsorptive desulfurization of model fuel oils. Various analytical techniques such as field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of the nanomaterials. The initial results indicated the effectiveness of the prepared CNT/TiO2 nanomaterials in removing sulfur compounds from model fuel oil. The adsorption of DBT, BT, and thiophene from model fuel onto the derived sorbents was performed using batch mode system. These CNT/TiO2 nanomaterials initially afforded approximately 45% removal of DBT, 55% BT, and more than 65% thiophene compounds from model fuels. The CNT/TiO2 nanomaterials provided an excellent activity towards interaction with organosulfur compounds. More experiments are underway to optimize the parameters for the adsorptive desulfurization processes. We believe that these nanomaterials as adsorbents will find useful applications in petroleum industry because of their operational simplicity, high efficiency, and high capacity.
The amount of sulfur contents in fuels often provides indication to the emission of SO
One-dimensional nanoscale structure of nanotubes with covalent bonding together imparts unusual properties: high tensile strength, high resilience, and good thermal and mechanical stability. Porous carbon also has properties such as uniform and regular pore size and structure, chemically inert, pore network interconnected with tailorable surface properties [
Adsorption of organic sulfur compounds in diesel fuel to composite adsorbents has been reported in recent years. A comparison between activated carbon, alumina, and MWNT and their corresponding composite catalysts with cobalt and molybdenum oxide and sulfide shows that dibenzothiophene (DBT) adsorbs to two kinds of sites, one is the acidic sites and another is on the transition metals with vacant orbits which can accept electrons. In case of sulfide state adsorbent, newly produced active sites on the edges of active phases provide higher adsorption compared with oxide states [
Some approaches have been reported for the synthesis and preparation of TiO2/CNT composite. This includes direct in situ growth, in situ CVD synthesis route, high-intensity ultrasonic radiation method, assembling presynthesized metal oxide nanoparticles as building blocks on CNTs, spontaneous formation of metal oxide nanoparticles on CNTs, hydrothermal crystallization, sol-gel followed by spark plasma sintering process, surfactant wrapping sol-gel method, and chemical precipitation [
We report here a procedure for desulfurization of model fuel oil by adsorption on MWCNTs/TiO2 nanomaterials. Thus, the nanomaterials were synthesized and characterized. The desulfurization activity was evaluated by model fuel of thiophene, benzothiophene, and dibenzothiophene.
Multiwalled carbon nanotubes (CNTs) were with specifications of purity, >95%; outer diameter, 30–50 nm; inner diameter, 5–10 nm; 30–50 nm; length, 10–20
CNTs were purified and oxidized before use. After the purification process, nanotubes were treated with a mixture of HNO3 and H2SO4 as reported earlier [
CNT/TiO2 nanomaterials were prepared by the following steps. Nanotubes were dispersed by sonication for 4 h at room temperature. At the same time the precursor of titania, titanium tetraisopropoxide solution, was hydrolyzed and stirred until it progressively became more viscous. The former, then, was drop-wise added with continuous stirring [
Schematic diagram of preparation of MWCNT/TiO2 nanomaterials.
The characterization of the CNT/TiO2 nanomaterials is important to evaluate the interaction between titania nanoparticles and the nanotubes. Therefore, the characterization was performed by means of field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared absorption spectroscopy (FTIR). The specific surface area of the CNT/TiO2 nanomaterials was determined by the Brunauer-Emmett-Teller (BET) method using adsorption data in a relative pressure range from 0.05 to 0.4.
The surface morphology of the prepared nanotubes/titania nanomaterials was characterized by high resolution field emission scanning electron microscope (SEM). The SEM image is depicted in Figure
High resolution field emission scanning electron microscopy (FESEM) image (a) and enlarged SEM image (b) of the MWCNT/TiO2 nanomaterials.
The EDX analysis was also carried out for the synthesized CNT/TiO2 nanomaterials. The EDX spectrum is depicted in Figure
EDX elemental analysis of the MWCNT/TiO2 nanomaterials.
Element | Weight % | Atomic % |
---|---|---|
C K | 31.80 | 50.85 |
O K | 27.29 | 32.76 |
Ti K | 40.90 | 16.40 |
|
||
Totals | 100.00 |
EDX spectrum and SEM image of the MWCNT/TiO2 nanomaterials.
The nitrogen adsorption-desorption measurement at −160°C indicates that the prepared nanocomposites have a specific surface area of 158 m2
FTIR spectrum (a) and XRD (b) of the MWCNT/TiO2 nanomaterials.
The work was conducted to evaluate the desulfurization activity of the CNT/TiO2 nanomaterials. The desulfurization activity was evaluated by model fuel of thiophene, benzothiophene, and dibenzothiophene. Figure
Gas chromatogram of desulfurized oil by MWCNT/TiO2 nanomaterials; thiophene, benzothiophene (BT), and dibenzothiophene (DBT).
A comparison between the desulfurization activity of CNT, titania, mechanical mixture of titania and CNTs (MM), and the prepared CNT/TiO2 nanomaterials; thiophene (THIO), benzothiophene (BT), and dibenzothiophene (DBT); conditions: reaction time is 60 min; agitation speed is 150 rpm; temperature is 23°C.
The efficiency of sulfur removal is significantly influenced by the amount of adsorbent used. The effect of the mass of adsorbents versus percentages of sulfur adsorbed was investigated for the CNT/TiO2 nanomaterials. The amounts of thiophene, BT, and DBT adsorbed onto the adsorbents are depicted in Figure
Effect of CNT/TiO2 nanomaterials adsorbent dosage on the adsorption of thiophene (THIO), benzothiophene (BT) and dibenzothiophene (DBT).
DBT exhibits higher percentage of removal for each dosage and on all adsorbents due to the ability of DBT to form
In summary, we have evaluated and compared the desulfurization activity of CNT, titania, mechanical mixture of titania and CNTs (MM), and the prepared CNT/TiO2 nanomaterials for the adsorption of thiophene (THIO), benzothiophene (BT), and dibenzothiophene (DBT). It has been observed that prepared CNT/TiO2 nanomaterials have better desulfurization activity than other tested materials. We believe the CNT/TiO2 nanomaterials, as adsorbent, will find useful applications in petroleum industry because of their operational simplicity, high efficiency, and high capacity.
The authors declare that there is no conflict of interests regarding the publication of this paper.
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 & Minerals (KFUPM) for funding this work through project No. 12-PET3009-04 as part of the National Science, Technology and Innovation Plan (NSTIP).