Catalytic hydrotreatment of non-edible vegetable oil shows great potential for the production of renewable (or biohydrogenated) diesel. This process comprises saturation of C=C double bonds and deoxygenation (via decarboxylation, decarbonylation, and hydrodeoxygenation) of triglycerides, thereby producing a mixture of C₁₅-C₁₈n-paraffins, CO₂, CO and water (Liu et al., 2011; Gong et al., 2012). It is compliant with varied feedstock and can be applied to present hydrotreatment units in petroleum refineries. It provides superior product properties and creates a smaller environmental footprint. Understandably, much effort is now being focused on the production of this promising alternative to petroleum-based diesel.

       In this study, biohydrogenated diesel was produced by the hydrotreatment of Karanja (Pongamia Pinnata) and Jatropha (Jatropha Curcas L.) oils over a commercial Pt/Al₂O₃ catalyst in the 583-643 K range at 3 MPa in a fixed-bed reactor. Although many papers on vegetable oils, model compounds and blends containing vegetable oils and petroleum products were reported (Sotelo-Boyas et al., 2011; Huber et al., 2007; Sebos et al., 2009), there exists scarce information on the catalytic hydrotreatment of Jatropha oil. For example, Liu et al. (2011) investigated hydrotreatment processing using sulfided Ni-Mo and solid acid catalysts, whereas Gong et al. (2012) reported the efficacy of PtPd/Al₂O₃ and NiMoP/Al₂O₃ catalysts. Further, there is no information in the literature on the hydrotreatment of Karanja oil.

Experimental

Physico-chemical properties of the investigated non-edible oils (such as saponification value, iodine value, acid value, density, viscosity, elemental composition, % free fatty acid and fatty acid composition) were determined. Activity trials for 4 h of time-on-stream were performed in a fixed-bed catalytic reactor (diameter=2.54 cm, length=49 cm) at P=3 MPa, H₂/oil ratio=600 (v/v) in the 2.5-7.5 1/h range of WHSV. Analysis of the liquid and gaseous hydrodeoxygenation products was done using gas chromatography (GC 8610, Thermo Fischer). BPX-5 capillary column with FID was used for the liquid-phase analysis (1-methyl naphthalene was the internal standard), whereas Porapak-Q and Molecular Sieve-5A columns with TCD were used for the gaseous phase. C₁₅ and C₁₇n-paraffins were the major reaction products in the liquid phase. The formation of propane and methane in the gaseous product was ascertained. Knowing the saponification values of the feed and the product, oil conversion in each experiment was determined. The reproducibility of results was checked and the error in experimental measurements was <2%. Few useful properties of the product as density, kinematic viscosity, pour point, net heat of combustion and ash content were found. The commercial 0.5% Pt/Al₂O₃ catalyst (pellet size 2.7-3.3 mm) was purchased from Alfa Aesar (Hyderabad, India) and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), H₂ chemisorption and N₂-adsorption desorption (BET) technique.

Results and Discussion

The effects of reaction variables such as temperature, pressure, H₂/oil ratio and WHSV on oil conversion and the product distribution were investigated. The rise in temperature facilitated the hydrotreatment process. Typical conversion values for Karanja oil at 583 and 643 K were 44.3 and 90.5%; for the case of Jatropha oil, these values were 56.6 and 94.2%, respectively.

The total diesel yield (% wt. basis) was determined using a method reported by Kikhtyanin et al. (2010). As the temperature increased from 583 to 643 K, the product yield from Karanja oil increased from 74 to 88.7%; the corresponding values for the case of Jatropha oil were 78 and 91.4%. The WHSV in these experiments was equal to 7.5 1/h.

       Finally, the reaction pathway was comprehensively described and the role of Pt was considered.

References

1.  Liu, Y., Sotelo-Boyas, R., Murata, K., Minowa, T. and K. Sakanishi, Energy Fuels, 25, 4675-4685 (2011).

2.  Gong, S., Shinozaki, A., Shi, M. and E. W. Qian, Energy Fuels, 26, 2394-2399 (2012).

3.  Sotelo-Boyas, R., Liu, Y. and T. Minowa, Ind. Eng. Chem. Res., 50, 2791-2799 (2011).

4.  Huber, G. W., O’Connor, P. and A. Corma, Appl. Catal. A: Gen., 329, 120-129 (2007).

5.  Sebos, I., Matsoukas, A., Apostolopoulos, V. and N. Papayannakos, Fuel, 88, 145-149 (2009).

6.  Kikhtyanin, O. V., Rubanov, A. E., Ayupov, A. B. and G. V. Echevsky, Fuel, 89, 3085-3092 (2010).