Catalyst preparation from noble metals by strong electrostatic adsorption technique for biodiesel production

Abstract

This research studied the preparation of noble metal catalysts (5wt.% Pd/graphene) using the Strong Electrostatic Adsorption (SEA) technique. The Pd metal nanoparticles were reduced under a hydrogen environment. The pH shift of graphene was determined, and the point of zero charge (PZC) was obtained at a pH of 4.6. The cation Pd precursor (i.e., [Pd (NH3)413-- tetraamminepalladium(I) nitrate, PdTA) were adsorbed over low PZC in high pH solutions (PH = 12). The maximum metal surface density (Fmetal) was corresponding to = 0.59 umol/ m . The Pd loading of 5wt.% catalyst was controlled by the initial concentration of PdTA. The ring pattern from electron diffraction (ED) and the spectra from X-Ray diffraction (XRD) confirmed the crystalline morphology of Pd particles with the face cubic centered (FCC) formation. The average Pd nanoparticle size of approximately 2-3 nm and give good dispersion onto graphene. The catalysts were used to convert stearic acid or crude palm oil (CPO) to a liquid biofuel product in a semi- batch reactor. This research studied the effect of operating parameters such as the amount of catalyst, reaction time, carrier gas, and gas pressure in the deoxygenation reaction. Moreover, the liquid products from the deoxygenation process were examined by gas chromatography-mass spectrometry (GC-MS). This study of the deoxygenation reaction was divided into the three parts. First, this research studied the effect of two operating parameters on the deoxygenation process of stearic acid: the amount of catalyst (0.25 - 1.0 g) and the effect of reaction time (2, 6 h) under helium gas. The results showed that when the mass of Pd/G catalyst increased, the gas products also increased. This indicates that reactions (1) and (2) occurred better when the amount of catalyst increased. During the reaction time of 2 h, it was found that all stearic acid was not enough converted to products. While, 6 h of deoxygenation reaction and increasing the amount of catalyst can effectively convert up to nearly 100% of the stearic acid to products. The results showed that 0.8 grams of 5wt.%Pd/G was highest conversion. Second, this research studied the effect of two operating parameters for the deoxygenation process of stearic acid: the amount of catalyst (0.2 - 1.0 g) and the effect of gas pressure (10, 20 bar) in 10%H/He gas. Under the 10%H/He gas (10 bar) reaction conditions, the results indicated that 5wt.% Pd/G can increase selectivity to give a liquid product in the bio-diesel range, C16-21. Also, this amount of catalyst (>0.6 g) was stable to selectively give products with the number of carbon atoms in the range of C16-21 (83.60%). This amount of catalyst (>0.6 grams) can almost completely convert stearic acid to the liquid products ( 100%). However, the 1.0 grams of this catalyst selectively gave the highest number of carbon atoms in the product, C16-21 (90.27%). Under the 10%H/He gas (20 bar) reaction conditions, deoxygenation with 5wt.%Pd/G (0.6 grams) was most effective in changing stearic acid to the highest amount of heptadecane with the number of carbon atoms in the range of C16-21 (96.19%). Third, this research studied the effect of gas pressure on converting crude palm oil to liquid product in a deoxygenation reaction. This research studied 0.6 g of 5%wt. Pd/G catalyst for converting CPO to liquid products under 10%H/He at various gas pressures (5, 10, 20 bar) with a reaction time of 6 h. The results showed that increasing the gas pressure up to 20 bar can convert CPO to a liquid product in a condenser (25.6 wt.%o) and a heavy oil (20.00 wt.%) in semi-batch reactor. At low gas pressure (5, 10 bar), the main liquid products had the number of carbon atoms in the range of <C7 and C7-1 1, while the gas pressure of (20 bar) could selectively convert CPO to products with the number of carbon atoms in the range of gasoline (C7-11) and kerosene (C12-15). The results suggest that the catalysts prepared by the SEA technique in this work successfully facilitated the deoxygenation reaction by converting fatty acids into alkane hydrocarbons with heptadecane as the main product. Snare and Maki-Arvela et al. were reported.