Abstract
Short-chain fatty acids (SCFAs) have been used as raw materials in wide range of chemical and medical applications. One technique to produce SCFAs is oxidative cleavage of long-chain fatty acids (LCFAs). However, unless the LCFAs are unsaturated, the yield of SCFAs is often very low because the carboxylic group of the fatty acid is more active than other part of the molecule. This work explores the idea of introducing a double bond into saturated LCFA, i.e., stearic acid, via selective dehydrogenation using commercial heterogeneous catalysts. However, cracking of the LCFA is also catalysed. Different type of metals was therefore investigated to study the effect of metals on the cracking and dehydrogenation. The experiments were conducted in an autoclave reactor under inert atmosphere. The temperature was in the range of 250–350°C. The products were analysed by gas chromatography equipped with mass spectroscopy (GC/MS). The results reveal that the introduction of double bond in the aliphatic chain of the stearic acid is possible although the yields of the unsaturated LCFAs are low. Effects of various parameters, such as temperature, pressure, and reaction time, were also investigated and reported.
Highlights
Nowadays, demands of fatty acids (FAs) have been increased in many industries, especially for SCFAs
A recent study demonstrated that an oxidative cleavage can lead to specific cracking at the location of double bond on the long aliphatic chain of FAs, leading to FAs with shorter hydrocarbon chain (Enferadi et al, 2015)
Thereby, specific SCFAs could be obtained from saturated fatty acids (SFAs), For saturated FAs, they should be dehydrogenated to introduce a double bond into their aliphatic chain first
Summary
Demands of fatty acids (FAs) have been increased in many industries, especially for SCFAs. Thereby, specific SCFAs could be obtained from saturated fatty acids (SFAs), For saturated FAs, they should be dehydrogenated to introduce a double bond into their aliphatic chain first. Snare et al revealed that an aliphatic tail dehydrogenation could be done like a homogeneous catalyst by using bifunction catalysts (Snåre et al, 2006; Berenblyum et al, 2012) These catalysts are comprised of dehydrogenation component, often a noble metal, and acid site on a support (Weitkamp, 2012). These findings are in line with the study of Wang et al that the main function of noble metals is to dehydrogenate substrate molecules (Simakova et al, 2009; Na et al, 2010). The gas from the reactor was collected into a gas bag for GC-FID analysis
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