New palladium oxalate hydrodeoxygenation catalyst for production of drop-in paraffinic biofuels
17 August 2014
Researchers in Malaysia and Oman have developed a novel palladium oxalate catalyst supported on zeolite A (PdOx/ Zeol) with increased acidity for the hydrodeoxygenation and isomerization of bio-feedstocks into paraffinic (drop-in) biofuels. In a paper in the ACS journal Energy & Fuel, they report the hydrodeoxygenation (HDO) of stearic acid (SA) (one of the most common saturated fatty acids found in nature following palmitic acid) into paraffinic biofuel.
Their best observed conditions for the process were 360 °C, 20 bar, 100 mL/min, and 25 mg to achieve 92% biofuel production from 35 g SA. The biofuel product distribution showed 71% n-C18H38, 18% iso-C18H38, and 3% C17H36.
A good catalyst for the production of biofuel is expected to produce both normal and iso-paraffin in order to have a reasonably high cetane number as well as improve the biofuel cold flow properties. The presence of iso-paraffin enhances the cold flow properties of biofuel by lowering the freezing point of the fuel; for example, the freezing point of the C16−C18 n-paraffin lies between 18 and 28 °C, while with the presence of 20% iso-paraffin it can be reduced to about 10−12 °C.
… Among the best reported active metals used in the hydrodeoxygenation (HDO) process to remove oxygen molecules from feed stocks is palladium. … available reports on the use of supported Pd for the production of biofuel also do not report the presence of iso-paraffins.
… it is imperative to synthesize acidified supported Pd catalyst that can achieve both HDO and isomerization in one single processing step to enhance the overall process economics. Therefore, in this study, we functionalized palladium with OxA to develop a novel palladium oxalate catalyst supported on zeolite A (PdOx/ Zeol) with increased acidity. Zeolite A was selected because of its thermal and structural stability, and in addition, it is currently being cheaply produced from coal fly ash (CFA), which hitherto is the waste product of combustion of coal in coal-fired power stations with about 800 million tons per annum CFA production. The catalyst was characterized for the physical and chemical properties and its HDO and isomerization activities were tested on stearic acid.—Ayodele et al.
The activity of the PdOx/Zeol tested on the HDO of SA showed that temperature, pressure, gas flow rate, and PdOx/Zeol loading have significant effects on the HDO process. Increasing the values enhances the efficiency up to a certain threshold—the conditions noted above—beyond which further increases lowers HDO efficiency.
They ascribed the presence of iso-C18H38, which is an excellent biofuel value-added-component due to its low freezing point to the functionalization of Pd with OxA, which increases PdOx/Zeol acidity.
The results showed that PdOx/Zeol is a prospective catalyst toward further research and commercialization of HDO process of SA.—Ayodele et al.
O. B. Ayodele, Hazzim F. Abbas and Wan Mohd Ashri Wan Daud (2014) “Hydrodeoxygenation of Stearic Acid into Normal and Iso-Octadecane Biofuel with Zeolite Supported Palladium-Oxalate Catalyst” Energy & Fuels. doi: 10.1021/ef501325g
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