As an alternative way to produce diesel hydrocarbons, the hydrocracking of rapeseed oil was studied on three different types of bifunctional catalysts: Pt/H-Y, Pt/H-ZSM-5, and sulfided NiMo/γ-Al 2 O 3 . Experiments were carried out in a batch reactor over a temperature range of 300-400 °C and initial hydrogen pressures from 5 to 11 MPa. The reaction time was limited to 3 h to prevent a high degree of cracking. The Pt-zeolite catalysts had a strong catalytic activity for both cracking and hydrogenation reactions, and therefore a higher severity was required to reach a relatively high oil conversion into liquid hydrocarbons. With dependence on the activity of the acid sites of the catalysts, the results show a trade-off between the yield of green diesel and the degree of isomerization, which had a direct effect on the cold properties of the diesel. Among the three catalysts, hydrocracking on Ni-Mo/γ-Al 2 O 3 gave the highest yield of liquid hydrocarbons in the boiling range of the diesel fraction, i.e., green diesel, containing mainly n-paraffins from C 15 to C 18 , and therefore with poor cold flow properties. While for both zeolitic catalysts, hydrotreating of rapeseed oil produced more iso-than n-paraffins in the boiling range of C 5 to C 22 , which included significant amounts of both green diesel and green gasoline. The gas chromatography (GC) analysis of the gaseous phase revealed the presence of mainly CO 2 , CO, propane, and remaining hydrogen. It was observed that both pressure and temperature play an important role in the transformation of triglycerides and fatty acids into hydrocarbons.
Biohydrogenated diesel (BHD) and liquefied petroleum gas (LPG) fuel were produced by the hydrotreatment of vegetable oils over Ni–Mo-based catalysts in a high-pressure fixed-bed flow reaction system at 350 °C under 4 MPa of hydrogen. Because triglycerides and free fatty acids underwent the hydrogenation and deoxidization at the same time during the reaction, various vegetable oils (jatropha oil, palm oil, and canola oil) were converted to mixed paraffins by the one-step hydrotreatment process although they contained quite different amounts of free fatty acids. Ni-Mo/SiO2 formed n-C18H38, n-C17H36, n-C16H34, and n-C15H32 as predominant products in the hydrotreatment of jatropha oil. These long normal hydrocarbons had high melting points and thus gave the liquid hydrocarbon product over Ni-Mo/SiO2 a high pour point of 20 °C. Either Ni-Mo/H-Y or Ni-Mo/H-ZSM-5 was not suitable for producing BHD from jatropha oil because a large amount of gasoline-ranged hydrocarbons was formed on the strong acid sites of zeolites. When SiO2-Al2O3 was used as a support for the Ni-Mo catalyst, the pour point of the liquid hydrocarbon product decreased to −10 °C by converting some C15–C18 n-paraffins to iso-paraffins and light paraffins on SiO2-Al2O3. Because SiO2-Al2O3 had a proper solid acidic strength, both the chemical composition and the pour point of liquid hydrocarbon product over Ni-Mo/SiO2-Al2O3 were similar to those of a normal diesel bought from a petrol station. Meanwhile, the glycerin groups in the vegetable oils were converted to propane over Ni-Mo/SiO2-Al2O3 by the hydrogenation and deoxidization. Therefore, the liquid hydrocarbon product can be directly used as a BHD fuel for the current diesel engines, and the gas hydrocarbon product can be used as a liquefied petroleum gas (LPG) fuel in the hydrotreatment of vegetable oils over Ni-Mo/SiO2-Al2O3.
A fundamental kinetic model for the catalytic reforming process has been developed. The complex network of elementary steps and molecular reactions occurring in catalytic reforming was generated through a computer algorithm characterizing the various species by means of vectors and Boolean relation matrices. The algorithm is based on the fundamental chemistry occurring on both acid and metal sites of a Pt-Sn/Al 2 O 3 catalyst. The number of rate coefficients for the transformations occurring on the metal sites was reduced by relating them to the nature of the involved carbon atoms. The single event concept was applied in the development of rate expressions for the elementary steps on the acid sites. This approach allows obtaining rate coefficients that are independent of the feedstock, owing to their fundamental chemical nature. The Levenberg-Marquardt algorithm was used to estimate the rate coefficients. The estimation was based on data reported from a previous naphtha reforming study in a fixed bed reactor with Pt-Sn/Al 2 O 3 as a catalyst. The agreement between the experimental and estimated yields is excellent. The statistical tests were also satisfied. The kinetic model was used in pseudo-homogeneous and heterogeneous reactor models simulating an industrial three-bed adiabatic catalytic reformer with centripetal radial flow.
Jatropha oil containing 15 wt % free fatty acids (FFAs) was converted to green diesel by hydrotreatment in a fixed-bed reactor over sulfided Ni–Mo/SiO2–Al2O3 catalyst with functions of hydrogenation, deoxygenation, and isomerization/cracking.
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