Esterification for biodiesel production with a phantom catalyst: Bubble mediated reactive distillation

Abstract

The initial aim of the paper is to dramatically improve the pretreatment stage of biodiesel production, which converts problematic free fatty acids to fatty acid methyl esters, by introduction of a microbubble mediated reactive distillation stage instead of acid pretreatment. This will shift the conventional esterification process towards completion with a yield higher than 80%, even without high excess methanol. Application of ozone microbubbles has the advantage over acid gas catalysis in that it gives higher conversion and leaves no catalyst residue and requires no further catalyst recovery separation steps (a "phantom" catalyst). Unreacted ozone breaks down into oxygen, so the off-gases are just a humid air stream that can be vented. Importantly, ozonolysis breaks carbon-carbon double bonds into aldehydes and carboxylic acids. Many ester species were found after contacting the feedstock with ozone-rich microbubbles, depending on the molecular structure of the alcohols for the ozonolysis of oleic acid with alcohols, i.e., methanol, ethanol, n-propanol, iso-propanol, and n-butanol. In the case of ozonolysis of used cooking oil mixed with methanol, the results from the GC-MS show that all saturated free fatty acids (including palmitic acid, stearic acid, and myristic acid) are converted to methyl esters within 20 hours of 60°C ozonolysis, whereas trace amounts of these chemicals remain at lower temperatures. The results also show that the conversion of oleic acid to form oleic acid methyl ester is 91.16% after 32 hours of ozonolysis at 60°C. Therefore, the free fatty acid content in used cooking oil is less than 1.33%, which makes it suitable as a reactant for biodiesel production via transesterification. However, this result is different from the result provided by ASTM D974 in that the acid numbers decrease dramatically by 25% at the beginning of ozonolysis followed by a plateau. Moreover, if the fluidic oscillator is used to generate bubbles in ozonolysis of oleic acid mixed with methanol, the results show that the yields of ozonolysis product 1-nonanal increase by 30%. This observation means that ozonolysis of oleic acid is relative to the specific interfacial area, and favoured at low liquid temperatures.

Fluidic Oscillators Mediating Generation of Microbubbles (Survey)

“…In [41] are presented laboratory tests results of biodiesel production with the microbubble removal of water, as well as esterification, which is important for biodiesel production with a phantom catalyst. There is already a monograph [33] published on the problems associated with biofuels from algae.…”

ZnO/Ionic Liquid Catalyzed Biodiesel Production from Renewable and Waste Lipids as Feedstocks

“…At the same time, the ionic liquid assumes the crucial role of phase transfer catalyst (PTC) by carrying methoxide anions into the oil phase [40][41][42]. In the absence of this component, catalytic action of ZnO becomes disappointing (see Figure 1b).…”

Advances in Enzyme and Ionic Liquid Immobilization for Enhanced in MOFs for Biodiesel Production

“…The catalytic activity has also been found to increase with the atomic radius of metal ions [2]. When tetrabutylammonium iodide (TBAI) was used as a phase transfer agent, the catalytic activity was improved due to the inherent lipophilic nature of the IL and its ability to provide methoxide anions in the oil phase [160,161]. High biodiesel yields were also achieved under mild operation conditions using the TBAI-ZnO system in different oil sources, including lard, fish, waste cooking oil, linseed, soybean, and jatropha.…”