Samia A. Hanafi

Recent Trends in the Cleaning of Diesel Fuels via Desulfurization Processes

Abstract This article is a selective review of new approaches and emerging technologies for ultra-clean (ultra-low sulfur) diesel fuels. The issues of diesel deep desulfurization are becoming more serious because the crude oils are getting higher in sulfur content, while the regulated sulfur limits are becoming lower and lower. Deep reduction of diesel sulfur (from 500 to <15 ppmw sulfur) is dictated largely by 4,6-dimethyldibenzothiophene, which represents the least reactive sulfur compounds that have substitutions on both 4- and 6-positions. The deep hydrodesulfurization (HDS) problem of diesel streams is exacerbated by the inhibiting effects of co-existing poly aromatics and nitrogen compounds in the feed as well as H2S in the product. New and more effective approaches and continuing catalysis and processing research are needed for producing affordable ultra-clean diesel fuels, because meeting the new government sulfur regulations in 2006–2010 is only a milestone. Desulfurization research should also take into consideration the fuel-cell fuel processing needs, which will have stringent requirements on desulfurization.

Para-xylene Maximization—Part VI: Shape-Selective Platinum-Promoted Methylation of Toluene

Abstract The need for increased production of para-xylene, which is the primary material for producing the polyester fibers, activated this research. Although the alkylation reaction is acid catalyzed, we found that a Pt promoter activates this reaction by virtue of the presence of a vacant d-orbital in the Pt atom. In this work, a series of catalysts containing 0.1, 0.2, or 0.3% Pt in H-ZSM-5 zeolite was tested for alkylating toluene with methanol, aiming to produce the xylenes and maximizing para-xylene production in a temperature range of 300°C–500°C in the presence of hydrogen flow in a continuous-flow fixed-bed reactor. The catalysts were characterized by temperature programmed desorption (TPD) of ammonia for acid sites distribution analysis and platinum dispersion in the catalysts by hydrogen chemisorption. Moreover, the diffusion resistance extent in the current catalysts during the alkylation reaction has been evaluated via estimation of the Thiele modulus, Φ L . The selectivity for para-xylene production was found to increase systematically with increasing the Pt content in the catalysts, whereas the unloaded zeolite did not follow this order. The Φ L values calculated were accordingly found to increase also with increasing Pt content in the catalysts. Although para-xylene was the highest on the 0.3% Pt/H-ZSM-5 catalyst, the heavy undesired trimethylbenzenes were the lowest to be formed on this catalyst.

Characterization and Catalytic Activities of ZrO2-TiO2 Supported Hydrodesulfurization Catalysts

Abstract Pure ZrO2, TiO2, and ZiO2-TiO2 mixed oxides are prepared by urea hydrolysis. Hydrotreating catalysts containing 8 wt% (MoO3) and 3 wt% (NiO) are prepared using these oxides and characterized by the Brunauer, Emmett, and Teller (BET) surface area, pore volume, X-ray diffraction, Fourier transform infrared, differential thermal analysis, and scanning electron microscopy. Thiophene hydrodesulfurization, cyclohexene hydrogenation, and cumene hydrocracking are taken as model reactions for evaluating catalytic activities in a micro-catalytic reactor at 350°C and atmospheric pressure. Sulfided catalysts showed a wide range of activity variation as a function of support composition, which established that NiMo sulfided active phases strongly depend on the nature and composition of the support. It is found that catalytic activities increase with increasing zirconia content in mixed oxide and reach maximum values for 20% zirconia content. (20%) Zr/Ti mixed oxide supported catalyst was tested at high pressure with real gas oil feedstock. A thorough study of the relationship between operating conditions and product quality would contribute much to the optimization of hydrotreatment processes.

The Support Effect on Hydrogenolysis of Thiophene and Gas–Oil

Abstract Results are reported on the support effect on the catalytic activity in thiophene hydrodesulfurization (HDS) of sulfided Ni-Mo catalysts supported on pure niobia, mixed oxides of Nb2O5-TiO2 prepared by sol-gel method, and Nb2O5/TiO2 and Nb2O5/Al2O3 prepared by surface deposition. The prepared samples were characterized using N2 adsorption at −196°C, X-ray diffraction (XRD), and temperature-programmed reduction (TPR) techniques. This study showed activity variation as a function of support composition. The activity of niobia-rich catalysts was no longer promoted by the synergy between Ni and Mo. The absence of synergy between molybdenum and nickel on niobia can be explained by the strong interaction of each metal with niobia at the expense of interaction with each other. It was found that 5 wt% Nb2O5/TiO2-supported catalyst was the better catalyst for thiophene HDS. It was shown that by means of an adequate support design it is possible to significantly increase the functionalities of HDS catalysts. Semiconducting supports like TiO2 can improve the HDS activity by exerting electronic effects on the active phase, helping in this way the formation of sulfur vacancies. The 5 wt% Nb2O5/TiO2 was also tested at high pressure with gas oil feedstock. It is observed with the hydrogeolysis of sulfur compounds against time-on-stream that the activity of this catalyst decreases fast with time.

Can Mesoporous TiO2-Al2O3-Supported NiMoS OR CoMoS Effectively Perform in Ultra-Deep Desulfurization of Gas Oil?

Waste aluminum foil was used for preparation of mesoporous TiO2-Al2O3 using starch as a textural modifier. The catalytic species, Mo and Ni or Co were loaded onto the mesoporous support, following incipient wetness sequential impregnation. To gain an insight into the pore dimensions effect, Ni and Mo species with the same mass ratio were loaded onto the TiO2-Al2O3, prepared from analytical grade chemicals without templating. TPR spectra, TEM images and BET analysis showed how the promoter (Ni or Co), TiO2 and the template (starch) affect the ease of reduction of Mo species, the morphology of the active MoS2 phase and the pore dimensions of the catalysts. The catalysts were employed in hydro-desulfurization process of gas oil using a fixed bed down flow microreactor at varying operating conditions, viz., temperature (320–400°C), Liquid hourly space velocity (0.5–4 h–1), H2/oil ratio of 450 v/v, and 6 MPa operating pressure. The results showed that the promotion effect prevails over the textural effect, where Ni promoted catalyst (with lower surface parameters) exhibits higher activity than Co promoted one. The dual layer catalytic bed system achieved the sulfur level less than 10 ppm.

Study of the Role of Lanthanum Containing Titania in Hydrogenolysis of Thiophene and Gas Oil

Abstract Pure La2O3 and La2O3-TiO2 mixed oxides are prepared by sol-gel method. Hydrodesulfurization catalysts containing 8 wt% MoO3 and 3 wt% NiO are prepared using these oxides and characterized by Brunauer, Emmett, and Teller (BET) surface area, pore volume, X-ray diffraction, differential thermal analysis, Fourier transform infrared and scanning electron microscopy. The effects of support composition have been investigated in order to determine their influence on hydrodesulfurization catalytic process. Hydrodesulfurization of thiophene model molecule reaction was carried out in a micro-catalytic reactor at 250°C–425°C and atmospheric pressure. Sulfided catalysts showed a wide range of activity variation as a function of support composition, which established that NiMo sulfided active phases strongly depend on the nature and composition of support. It is found that 10% La/Ti supported catalyst was the better catalyst for thiophene hydrodesulfurization. It was also tested at high pressure with a real feed Gas oil.