5 research outputs found
Direct Determination of Glycidyl Esters of Fatty Acids in Vegetable Oils by LC–MS
An LC–MS method using a single quadrupole mass spectrometer was developed for direct analysis of glycidyl esters of fatty acids in vegetable oils. Without any sample clean-up, this method provided acceptable recovery of seven glycidyl esters, comparable results to a previously-published method utilizing two solid-phase extraction steps, and consistent detection parameters after greater than 200 injections without any cleaning operations performed. This method could readily be implemented as a screening assay for glycidyl esters in most oil laboratories
Intensified and safe ozonolysis of fatty acid methyl esters in liquid CO2 in a continuous reactor
We demonstrate a continuous reactor for performing the ozonolysis of fatty acid methyl esters (FAMEs) using liquid CO2 as solvent. The fast reaction kinetics allows the use of small-volume reactors to completely convert the FAMEs, forming secondary ozonides as the primary products. The short residence times also help maximize the yields of the secondary ozonides by minimizing over-oxidation and the formation of oligomeric products. The liquid CO2 medium promotes safe reactor operation by providing an essential fraction of overall reactor cooling and by diluting the vapor phase organics. We also demonstrate a continuous stirred reactor for the safe thermal decomposition of the secondary ozonides to their corresponding acids and aldehydes. Using a lumped kinetic model for the thermal decomposition of the ozonolysis products, we estimate activation energy values of 108.6 +/- 0.6 kJ mol(-1) for the decomposition of secondary ozonides and 122 +/- 3 kJ mol(-1) for the decomposition of the undesired oligomeric species. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2819-2826, 201
Direct Determination of MCPD Fatty Acid Esters and Glycidyl Fatty Acid Esters in Vegetable Oils by LC–TOFMS
Analysis of MCPD esters and glycidyl esters in vegetable oils using the indirect method proposed by the DGF gave inconsistent results when salting out conditions were varied. Subsequent investigation showed that the method was destroying and reforming MCPD during the analysis. An LC time of flight MS method was developed for direct analysis of both MCPD esters and glycidyl esters in vegetable oils. The results of the LC–TOFMS method were compared with the DGF method. The DGF method consistently gave results that were greater than the LC–TOFMS method. The levels of MCPD esters and glycidyl esters found in a variety of vegetable oils are reported. MCPD monoesters were not found in any oil samples. MCPD diesters were found only in samples containing palm oil, and were not present in all palm oil samples. Glycidyl esters were found in a wide variety of oils. Some processing conditions that influence the concentration of MCPD esters and glycidyl esters are discussed
Key Roles of Lewis Acid–Base Pairs on Zn<sub><i>x</i></sub>Zr<sub><i>y</i></sub>O<sub><i>z</i></sub> in Direct Ethanol/Acetone to Isobutene Conversion
The
effects of surface acidity on the cascade ethanol-to-isobutene
conversion were studied using Zn<sub><i>x</i></sub>Zr<sub><i>y</i></sub>O<sub><i>z</i></sub> catalysts.
The ethanol-to-isobutene reaction was found to be limited by the secondary
reaction of the key intermediate, acetone, namely the acetone-to-isobutene
reaction. Although the catalysts with coexisting Brønsted acidity
could catalyze the rate-limiting acetone-to-isobutene reaction, the
presence of Brønsted acidity is also detrimental. First, secondary
isobutene isomerization is favored, producing a mixture of butene
isomers. Second, undesired polymerization and coke formation prevail,
leading to rapid catalyst deactivation. Most importantly, both steady-state
and kinetic reaction studies as well as FTIR analysis of adsorbed
acetone-<i>d</i><sub>6</sub> and D<sub>2</sub>O unambiguously
showed that a highly active and selective nature of balanced Lewis
acid–base pairs was masked by the coexisting Brønsted
acidity in the aldolization and self-deoxygenation of acetone to isobutene.
As a result, Zn<sub><i>x</i></sub>Zr<sub><i>y</i></sub>O<sub><i>z</i></sub> catalysts with only Lewis acid–base
pairs were discovered, on which nearly a theoretical selectivity to
isobutene (∼88.9%) was successfully achieved, which has never
been reported before. Moreover, the absence of Brønsted acidity
in such Zn<sub><i>x</i></sub>Zr<sub><i>y</i></sub>O<sub><i>z</i></sub> catalysts also eliminates the side
isobutene isomerization and undesired polymerization/coke reactions,
resulting in the production of high purity isobutene with significantly
improved catalyst stability (<2% activity loss after 200 h time-on-stream).
This work not only demonstrates a balanced Lewis acid–base
pair for the highly active and selective cascade ethanol-to-isobutene
reaction but also sheds light on the rational design of selective
and robust acid–base catalyst for C–C coupling via aldolization
reaction