الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 75 |  |  |
| | | from | 75 | | |
Abstract
Currently, continuous worldwide concern is paid toward the development of efficient and cost-effective processes for the removal of toxic and hazardous components, such as sulfur and nitrogen compounds, from fossil fuel fractions. In an agreement with this trend, this thesis reports enhanced disposal of sulfur, nitrogen and aromatic compounds from both heavy vacuum gas oil (HVGO) and diesel fuel feedstocks using various techniques.
Particularly, adsorptive removal of such compounds using novel adsorbents made of blending polystyrene (waste or synthesized polymer) with imidazole and its derivatives had been carried out at various operating conditions. The essential characteristics of prepared adsorbents were firstly investigated using Fourier transform infrared (FT-IR), BET surface area analysis, scanning electron microscopy (SEM) and molecular weight. Then, these adsorbents could successfully attain reasonable eliminations for both sulfur and nitrogen compounds. However, maximum removals of 40 and 75 wt. % for sulfur and nitrogen compounds respectively (from heavy vacuum gas oil) at 60 oC, 6 h and adsorbent-to-feed ratio of 1:5 had been obtained by butyl-Imidazole blended waste polystyrene (WPS). The sulfur and nitrogen compounds removals could be respectively increased to 46 and 85 Wt. %, at same operating conditions, using the same composition of adsorbent while introducing a synthesized polystyrene instead of WPS. This adsorbent could also achieve respective percentages of sulfur and nitrogen removals (from diesel fuel feedstock) equal 50.91 and 87.35.
Another technique had been also employed during this thesis for the purpose of sulfur, nitrogen and aromatic compounds removal from the previously stated petroleum fractions. Specifically, catalytic hydrotreatment (HT) using tri-metallic catalysts supported on different structures (CeO2 and Al2O3) had been performed. Feasibility of doping different percentages of CeO2 to Al2O3 to obtain
Summery and conclusion
163
developed binary supported catalysts to enhance efficiency of hydrotreatment process was also investigated. Properties of prepared structures were acquired by
X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photo-spectroscopy (XPS) and BET surface area analysis. In reference to XRD analysis of original supports, it could be revealed that the CeO2 made a solid solution with alumina in 10% and 15% CeO2-Al2O3 samples while the CeAlO3 was formed in considerable amount in 10% CeO2-Al2O3 sample. Moreover, 10% CeO2-Al2O3 sample showed the lowest lattice size and hence possess a larger surface area with uniform pore size and volume. Meanwhile, 25% CeO2-Al2O3 samples possessed only ceria coverage of alumina surface with small surface area. Nanostructure of all samples were also proved by TEM and confirmed that 10% CeO2 content could allow formation of the smallest particle size. The prepared structures were then forwarded to designated application in this study.
Effect of pressure, temperature and liquid hour space velocity (LHSV) on quality of hydrotreatment process was tested. The catalytic activity results demonstrated that CeO2 (10%) doped catalyst had shown the highest affinity toward desulfurization and denitrogenation of HVGO. It could attain as high sulfur and nitrogen removal as 94.8 and 93.6 % respectively. This composite catalyst had been also capable to respectively reduce sulfur and nitrogen contents of diesel fuel by 95.1 and 95.28 %. The formerly observed elimination degree were picked at temperature of 360 oC, Pressure equal 40 bar and LHSV of 1 h-1.
The increased catalytic performance of this catalyst over the other ones had been attributed to its high surface area. Furthermore, it can be as a result of the attained phase separation between metals active sites and alumina due to presence of ceria particles. Hence, formation of metals/Al2O4 as inactive structure, could be avoided. Although contents of both sulfur and nitrogen compounds in the acquired HVGO and diesel fuel were strongly reduced, they have not been satisfying (according to global demands).
Summery and conclusion
164
Thus, a combination between the prior reported techniques had been done to further reduce sulfur compounds in obtained products.
As a third stage of this research study, produced HVGO and diesel fuel (at optimum conditions) from adsorptive treatment were used as secondary feedstocks to the catalytic HT process. The catalyst which contains 10% ceria within its composition was used to perform this stage applying the pre-determined optimum operating conditions from the second technique. It could be noted that sulfur and nitrogen compounds are respectively reduced by 98.29 and 96.63 % (for HVGO) as well as by 99.34 and 98.85 % (in case of diesel fuel).
By completion of this investigation, it can be concluded that the presented adsorptive treatment can be counted as promising competitive method for hazardous compounds removal due to its low energy consumption and mild operating conditions compared to solvent extraction and ordinary hydrodesulphurization methods. Additionally, the adsorptive pretreatment of feedstocks before HT process can establish a new platform for production of ultra-low sulfur petroleum fractions industrially. Moreover, it helps to subsequently conserve the catalyst lifetime via avoiding its deactivation and its superior removal of large sulfur compounds before HT process. Hence, high economics of sulfur removal process can be provided. Furthermore, it can be recommended the addition of 10 % ceria to alumina in order to obtain binary-supported tri-metallic catalyst of enhanced catalytic activity. The use of ceria result in a phase separation between alumina and metallic site, thus formation of inactive species such as metals-aluminate could be avoided. Therefore, the catalytic activity of the produced catalysts could be strongly increased. Additionally, incorporation of ceria with alumina could subsequently produce active sites of metals oxides onto the surfaces of supports. Hence, enhancement of catalytic activity of presented tri-metallic catalyst could also be attained