ABSTRACT
In the present work, natural mordenite originated from volcanic soils in Greek islands, activated using HCl solution and HCl solution followed by NaOH solution, was used as support for preparing two metallic nickel catalysts (30 wt.% Ni). The catalysts were thoroughly characterized (XRF, N2 adsorption-desorption, SEM, XRD, TEM, H2-TPR, NH3-TPD) and evaluated for biodiesel upgrading to green (renewable) diesel. Double activation of natural mordenite optimized its supporting characteristics, finally resulting in a supported nickel catalyst with (i) enhanced specific surface area (124 m2 g-1) and enhanced mean pore diameter (14 nm) facilitating mass transfer; (ii) easier nickel phase reduction; (iii) enhanced Ni0 dispersion and thus high active surface; (iv) balanced population of moderate and strong acid sites; (v) resistance to sintering; and (vi) low coke formation. Over the corresponding catalyst, the production of a liquid consisting of 94 wt.% renewable diesel was achieved, after 9 h of reaction at 350 °C and 40 bar H2 pressure, in a semi-batch reactor under solvent-free conditions.
ABSTRACT
Four Ni catalysts and one Mo-Ni catalyst supported on montmorillonite were synthesized, characterized by various techniques and evaluated, under solvent-free conditions, for the production of green diesel from waste cooking oil. The optimum Ni content was found to be 20 wt.%. The addition of 2 wt.% Mo to the catalyst resulted in a considerable increase in the amount of green diesel hydrocarbons. The Mo species, moreover, led to a decrease in the (C15 + C17)/(C16 + C18) ratio, which is beneficial from the viewpoint of carbon atom economy. The promoting action of Mo was mainly attributed to the synergy between the oxygen vacancies on the surface of the well-dispersed Mo(V) and Mo(VI) oxides and the neighboring Ni0 sites. The optimum reaction conditions, for achieving a proportion of liquid product in the green diesel hydrocarbons (C15-18) equal to 96 wt.%, were found to be 350 °C, 3 g of catalyst per 100 mL of waste cooking oil and 13 h reaction time. These conditions correspond to an LHSV of 2.5 h-1, a value that is considered quite reliable from the viewpoint of industrial applications. Thus, the cheap and abundant mineral montmorillonite is proved a promising support for developing efficient Ni-Mo catalysts for green diesel production.
