(583de) Hydrotreating of Jatropha Oil to Hydrocarbons On Al2O3 Supported NiMo Catalysts

Three kinds of Al₂O₃ (acidic Al₂O₃ (pH = 4.5±0.5 in 10% water suspension), neutral Al₂O₃ (pH = 7.5±0.5 in 10% water suspension) and basic Al₂O₃ (pH = 9.5±0.5 in 10% water suspension)) were used as supports in the catalytic hydrogenation of Jatropha oil to produce hydrocarbons. The supported NiMo on these supports (4wt % Ni, 12wt % Mo) were prepared by wet co-impregnation of aqueous solutions of (NH₄)₆Mo₇O₂₄ and Ni(NO₃)₂. Elemental analysis of Ni and Mo were determined by X-Ray Fluorescence (S4 Pioneer, Bruker). The specific surface area and pore size of the catalysts were determined by N₂ adsorption and desorption isotherms using Micromeritics TriStar 3000. The NH₃-TPD (ammonia temperature programmed desorption) experiments were carried out using a Chemisorption Physisorption Analyzer (AMI-300, Altamira Instruments) to measure the acid sites in catalysts. The organic liquid products were qualitatively determined using an Agilent 5795 gas chromatography/massspectrometry (GC/MS). A gas chromatographs (Agilent 7890A), equipped with an FID (flame ionization detector) and a commercially column (PONA, 50 m × 0.20 mm × 0.5μm) was used to analyze the hydrocarbons in the organic liquid phase.

The pore sizes of these three aluminum oxides are all in the range of 3-4 nm and the surface area are also the similar. The acid sites in these three catalysts are all weak and medium acid and no strong acid site. The total acid sites for the three catalysts were in the order: NiMo/Al₂O₃ (basic) < NiMo/Al₂O_3. (neutral) < NiMo/Al₂O₃ (acidic).

The hydrotreatment of Jatropha oil were conducted in a fixed-bed flow reactor at the temperature of 653 K, pressure of 3 MPa, LSHV (liquid hourly space velocity) = 3.8 h^-1, and H₂/oil ratio of 500 (v/v). Almost total conversion was obtained over all three catalysts and the products obtained were all hydrocarbons without any other product produced. The same ratio of C₁₇/C₁₈ and (C₁₅+C₁₇)/(C₁₆+C₁₈) shows that the oxygen removal was through the same pathways with decarboxylation, decarbonylation and hydrodeoxygenation. However, the different of acid nature in the three catalysts influence the secondary reaction especially the cracking reaction on the product distribution. For the Al₂O₃ (basic) which showed alkaline as support, the lowest acidity was detected in NiMo/Al₂O₃ (basic) catalyst and the highest of organic liquid yield (93 %) and selectivity to C₁₆-C₁₈ hydrocarbons (89.7 %) and the lowest of selectivity to C₄-C₈ hydrocarbons (1.5 %) were obtained. While for the Al₂O₃ (acidic) showing acidic supported NiMo with the highest total acid sites, the lowest organic liquid yield (80.1 %), selectivity to C₁₆-C₁₈ hydrocarbons (83.2 %) and highest of selectivity to C₄-C₈ hydrocarbons (8.1 %) were obtained.