Green diesel production over nickel-alumina co-precipitated catalysts

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A series of nickel-alumina co-precipitated catalysts with varying nickel loading in the range (0–100wt% nickel) was prepared under close control of the preparation parameters. The catalysts were characterized using nitrogen adsorption-desorption isotherms, NH3-TPD, XRD, XPS, SEM and HRTEM. They were tested for the selective deoxygenation (SDO) of sunflower oil into hydrocarbons in the diesel range under solvent-free conditions at 310°C and hydrogen pressure of 40bar for various reaction times up to 9h using a semi-batch reactor and a “volume of oil (ml)/mass of catalyst (g)” ratio equal to 100. The products were analyzed using GS and GC–MS.The preparative procedure resulted to high specific surface area mesoporous materials with nanocrystals of nickel phases in close contact with alumina nanograins, thus providing high nickel surface area. Normal-alkanes in the diesel range were produced whereas intermediate stearic acid and esters of fatty acids have been also detected. Considerable amounts of high molecular weight esters (intermediate products) are formed during SDO under solvent free conditions. Propane, ethane, methane, CO, and CO2 have been also detected in the gas phase. The conversion of sunflower oil and the total yield to hydrocarbons increases with the nickel content up to the sample containing 60wt% nickel (yield to hydrocarbons equal to 61wt%) and then it decreases. The nickel active surface correlates very well with the total yield to hydrocarbons.