Viscous gel-like species form in vegetable oils during frying. After fatty acid formation, thermal oxidation of unsaturated chains causes polymerization. Heat treatment of oleic acid was employed to produce and identify the initial polymerization products. Spectroscopic studies revealed that heating oleic acid (210 C, open to air) causes the formation of oligomers cross-linked by ester groups. The absence of esters, before thermal treatment, facilitated observation of cross-links (ester groups) that propagate to produce heavier insoluble products.

Oxidative polymerization of plant oils and lipids is poorly understood yet widely encountered. Oils and fats are renewable resources providing biofuels and polymers. Oil oxidation is accelerated at high temperatures, typically above 110°C, where triacylglycerides are converted into toxic compounds and viscous deleterious polymers. Polymerization of mono‐unsaturated oil (210°C, 3 h, open to air) was investigated by comparing four similar sized molecules with different functional groups: oleic acid, methyl oleate, trans‐7‐tetradecene, and stearic acid. Non‐volatile products identified by NMR spectroscopy are minor ketones for saturated fatty acid (stearic acid), epoxides for acyl chains without acid groups (methyl oleate, tetradecane) and copious oligomerization, through ester cross‐links, for acyl chains with acid, and olefinic groups (oleic acid). Long range CH coupling clearly shows ester (not ether) cross‐links, contradicting long‐held beliefs. Chain fragmentation also occurs for heated oleic acid as revealed by formation of a species with a methylene group bonded to oxygen of an ester, CH2OC(O). Large size (slow diffusion) of the first oligomer (trimer) formed from oleic acid, used to represent hydrolyzed vegetable oil, was evidenced by DOSY (diffusion‐ordered spectroscopy). Combined NMR results show oligomers found in heated oleic acid are fatty acid estolides. Model oil reactions demonstrate why olefin and carboxylic acid groups are required for polymerization.

No abstract

Oxidative polymerization of plant oils and lipids is poorly understood yet widely encountered. Oil oxidation is accelerated at high temperatures, typically above 110°C, where tri-acylglycerides are converted into toxic compounds and viscous deleterious polymers. Polymerization of mono-unsaturated oil (210°C, 3h, open to air) was investigated by comparing four similar sized molecules with different functional groups: oleic acid, methyl oleate, trans-7-tetradecene and stearic acid. Non-volatile products identified by NMR spectroscopy are minor ketones for saturated fatty acid (stearic acid), epoxides for acyl chains without acid groups (methyl oleate, tetradecane) and copious oligomerization, through ester cross-links, for acyl chains with acid and olefinic groups (oleic acid). Long range C-H coupling clearly shows ester (not ether) cross-links, contradicting long held beliefs. Chain fragmentation also occurs as revealed by species with methylene groups bonded to oxygen, -CH2-O-C(=O)-R. Large size (slow diffusion) of the first oligomer (trimer) formed by thermal oxidation of oleic acid, (representing hydrolyzed vegetable oil) was evidenced by DOSY (diffusion ordered spectroscopy). Since the first oligomers formed still have reactive groups (olefin, carboxylic acid), poly-ester formation is inevitable at longer oxidation times. Model oil reactions monitored by NMR spectroscopy are important for resolving the complex chemistry of vegetable oil polymerization.

Allocation of production fluids is a key aspect for reservoir management purposes. Many consolidated techniques exist, but they have the drawback of being expensive (multiphase flowmeters, production logging tool, spectral noise logging) or not directly portable at wellhead (geochemical production allocation). For these reasons, we developed a new rapid and accurate method employing Fourier Transform InfraRed (FTIR) spectroscopy coupled with regression methods, and successfully applied to a real case of reservoir commingled fluids. After testing different spectroscopic techniques, we realized that FTIR was the best method to perform allocation. FTIR spectra were acquired with a portable spectrometer operated in transmission mode on oils loaded in standard cells for liquids (0.1 mm optical path, KBr windows). The portable instrumentation yielded equally informative signals as the laboratory one for our needs. After suitable baseline subtraction, a machine learning workflow written in R language was applied to select the most informative spectral regions for the deconvolution of single component contribution in analysis of mixtures. Through a minimization algorithm, we are able to get the concentration of end members samples into the commingled samples. To validate our technology, we first took the end member oils (coming from two different layers of the same reservoir), we mixed them, performed the IR analysis with our portable instrument and then applied our regression modelling approach, getting results that are both accurate and precise (less than 2% of average error). Based on that, we applied our workflow directly on 9 real commingled samples coming from the same aforementioned reservoir, getting results that are in very good agreement with multi-phase flowmeters measurements. We then think that the technology is very promising and can be considered a real, low-cost and affordable opportunity among all the reservoir allocation best practices. Combination of spectroscopic portable IR hardware with regression software for the sake of allocation directly at wellhead is an innovative solution for the old problem of allocation.