Abstract
For the production of sustainable biofuels from lipid biomass it is essential to develop non-noble metal catalysts with high conversion and selectivity under inert gas atmospheres. Herein, we report a novel cobalt-based catalyst supported on zeolite NaX via ion-exchange synthesis. The resultant bifunctional cobalt-based NaX zeolite catalyst displayed high conversion of stearic acid to liquid fuels. In addition, the effect of reaction temperature and catalyst loading was studied to evaluate the order of reaction and activation energy. Decarboxylation and decarbonylation were the dominant deoxygenation pathways. Stearic acid was successfully deoxygenated in N2 atmospheres using Co/NaX catalysts with a conversion as high as 83.7% and a yield to heptadecane up to ~28%. Furthermore, we demonstrate that higher reaction temperatures resulted in competing pathways of decarboxylation and decarbonylation. Finally, the fresh and recycled catalysts were characterized showing modest recyclability with a ~12.5% loss in catalytic activity.
Highlights
Fatty acids are readily extracted from non-edible plants [1,2], algae oil [3], and tallow [4].These abundant compounds make ideal candidates for the production of biofuels and chemicals.Homogeneous base catalysis of fatty acids yields first-generation fatty acid methyl esters (FAME) by transesterification
A clear trend is the reduction in the low pressure uptake of nitrogen, correlated to the surface area, due to the incorporation of cobalt in the zeolites under the alkaline synthesis conditions
When comparing the catalyst loading (15, 150, 250 mg) to a first order rate expression calculated from the stearic acid conversion, a linear relationship was observed order rate expression calculated from the stearic acid conversion, a linear relationship was observed (R2 = 0.999), indicating a pseudo-first-order reaction (Figure 7A)
Summary
Fatty acids are readily extracted from non-edible plants [1,2], algae oil [3], and tallow [4].These abundant compounds make ideal candidates for the production of biofuels and chemicals.Homogeneous base catalysis of fatty acids yields first-generation fatty acid methyl esters (FAME) by transesterification. Fatty acids are readily extracted from non-edible plants [1,2], algae oil [3], and tallow [4]. These abundant compounds make ideal candidates for the production of biofuels and chemicals. Homogeneous base catalysis of fatty acids yields first-generation fatty acid methyl esters (FAME) by transesterification. FAMEs have a lower energy density, higher cloud and smoke point, and poor cold flow properties compared to conventional fuels limiting their potential as a “drop-in”. Many researchers have turned to heterogeneous catalysts for the selective deoxygenation of fatty acids with the aim of producing diesel range alkanes. Two predominant pathways for the production of alkanes are hydrodeoxygenation resulting in the retention of the parent molecule’s carbon number under hydrogen replete atmospheres and decarboxylation which removes one carbon atom as a carboxylate group under hydrogen deplete atmospheres [5]
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