Application Research Of Methyl Esterization Rate Analysis Of Camphor Seed Oil Based On NMR And Raman

Fatty acid methyl ester is a new type of green energy-saving energy.The determination of methyl esterization rate is a key step in the preparation process of fatty acid methyl esters.However,there are certain limitations in the current methods of measuring esterization rate.In order to provide more analytical methods for methyl esterification rate analysis,the NMR spectrum and Raman spectroscopy techniques were used to establish the methyl laurate content in the mixed standard samples（trilaurate and methyl laurate）;the established methods of nuclear magnetic resonance and Raman spectroscopy were applied to the determination of methyl esterification rate in the methyl esterification process of camphor seed oil,and the accuracy of the methods was verified by gas chromatography-mass spectrometr;the fatty acid composition of camphor seed oil and its superiority in preparing fatty acid methyl esters were analyzed.The main contributions of this thesis are as follows:1)Using deuterated chloroform as solvent and tetramethylsilane as internal standard,glycerol trilaurate and methyl laurate were analyzed by NMR spectroscopy,and a q¹H-NMR method for determining the methyl laurate content in samples was established.The results of ¹³C-NMR analysis indicated that glycerol trilaurate and methyl laurate had corresponding characteristic peaks only in the carbonyl spectrum（δ=172～174）and glycerol spectrum（δ=62～70）;with the increase of methyl laurate content in the sample,the peak intensity of the glycerol skeleton carbon atom at δ=62.09 andδ=68.88 gradually weakened,and the peak intensity of the methyl carbon atom with chemical shift at δ=51.41 gradually increased.The trend of the peak intensity of the characteristic peak is consistent with the trend of the relative content of the two in the sample.The results of ¹H-NMR analysis indicated that the peak of methoxy group（-OCH₃）at chemical shift δ=3.67 and the peak of methylene at the glycerol backbone（-CH₂-CH-CH₂-）at chemical shift δ=4.13～4.18 and δ=4.28～4.34 were as the characteristic peak of methyl laurate and trilaurin,the linear regression equations y=-0.97+0.61x（R²=0.9991）and y=34.6-0.35x（R²=0.9998）could be obtained,respectively.Both linear regression equations have good linear correlation coefficients and can be used for quantitative analysis of fatty acid methyl esters.2)Analysis of glycerol trilaurate and methyl laurate using FTIR and Raman to establish a Raman method for quantitative analysis of methyl laurate content in samples.FTIR analysis indicated that the infrared absorption peaks of glycerol trilaurate and methyl laurate were very similar,especially in the functional group,there was almost no difference(4000～1300 cm^-1);in the fingerprint area(1300～670 cm^-1),the peak positions are basically the same,but there is a slight difference in intensity.Raman analysis indicated that Raman analysis of the changes in the structure of glycerol trilaurate and methyl laurate may be more sensitive than FTIR.As the content of methyl laurate in the sample increases,some characteristic regions that can be used for quantitative analysis appear in the Raman spectrum,such as the bending vibration region of-C=O unique to methyl laurate at 423 cm^-1,and the stretching vibration region of-C=O of RC=OOR group at 1730～1750 cm^-1,and-C-H stretching vibration area at 2800～2930 cm^-1;combining five spectral pretreatment methods and RPLS algorithm to extract characteristic bands,a Raman PLS model（R²=0.9919,RMSECV=0.1143）which can accurately predict the methyl laurate content in mixed standard samples is established.3)The methylation rate of camphor seed oil was determined by the established q¹H-NMR method and Raman model,and the fatty acid composition of camphor seed oil and its superiority in preparing fatty acid methyl ester were analyzed.The results of q¹H-NMR measurement indicated that the results of two quantitative methods with-OCH₃ and-CH₂-CH-CH₂-as quantitative peaks were basically the same;the methyl esterification rate of camphor seed oil increased with the increase of methylation time.When the time was 0.1 min,the methyl esterification rate was only 6.0%;when the time was 10 min,the methyl esterification rate reached 99.1%;quantitative analysis results of q¹H-NMR agreed with those of GC-MS,and there was no significant difference（P>0.05）.Therefore,q¹H-NMR method could be used to analyze of the methyl esterification rate of camphor seed oil,with advantages of simple pretreatment and short analysis time.The Raman method indicated that the prediction results of Raman model were similar to those of q¹H-NMR and GC-MS.The methyl esterification rate of camphor seed oil increased with the prolongation of methyl esterification time,and the methyl esterification was complete at 10 min.The Raman method can be effectively used for the analysis of the methyl esterification rate of camphor seed oil,but the accuracy is slightly lower than that of the q¹H-NMR method and the GC-MS method.The fatty acid composition of camphor seed oil and its superiority analysis of fatty acid methyl esters indicated that the main fatty acid composition of eucalyptus seed oil was decanoic acid（51.93%）,lauric acid（43.86%）and oleic acid（2.03%）;the prepared fatty acid methyl ester is superior to the oil crops such as C16 and C18 in physical and chemical indexes such as density,cold filter point,oxidation stability and cetane number,and is an excellent raw material for preparing fatty acid methyl ester.