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.

Highlights

  • Fossil fuels are the primary energy sources for the transportation sector which consumes about 28% of the global energy production [1]

  • In the frame of this program, we have successfully developed nickel catalysts supported on mineral palygorskite and mordenite, for the production of third-generation green diesel [65,66,67]

  • We extend our studies by developing nickel and molybdenum–nickel catalysts supported on mineral montmorillonite for the production of third-generation

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Summary

Introduction

Fossil fuels are the primary energy sources for the transportation sector which consumes about 28% of the global energy production [1]. Biodiesel (a mixture of fatty acid methyl esters) presents unfavorable cold flow properties and delivers lower fuel mileage compared to fossil diesel. This is due to the presence of oxygen in its ester structure. The ratio of oxygen to the combustible carbon and hydrogen atoms in a molecule of triglyceride is relatively small This justifies the intensive research effort over the last decades regarding the transformation of natural triglycerides and related compounds into n-alkanes in the diesel range (green diesel) via hydrotreatment [8,9,10,11]. There are increasing numbers of studies dealing with the utilization of residual fatty raw materials for the production of third-generation green diesel, such as waste cooking oils [19,20,21,22], yellow grease and hemp seed oils [23], brown grease oil [24], distilled fatty acids [24,25,26,27], oil from chicken fat [28,29] and oil extracted from spent coffee grounds [30,31,32,33,34]

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