Process for quantitative determination of fatty acid esters in fuels

Abstract

The present invention provides a method for the quantitative determination of contaminants in the form of fatty acid esters in jet fuels, wherein the analyte is the fatty acid ester fatty acid methyl ester (FAME) and/or the fatty acid ester fatty acid ethyl ester (FAEE), wherein the analyte undergoes a chemical reaction which is selective for it and which influences the intensity for the carbonyl band of the respective ester group with the formation of a modified analyte and the variation in the concentration of analyte in the sample, which is the jet fuel together with FAME and/or FAEE, is measured using the reduction in the intensity of the carbonyl band and/or the increase in the concentration of the modified analyte is measured using the increase in the intensity of a band which is characteristic for the modification.

Claims

1. A method for the quantitative determination of contaminants in the form of fatty acid esters in jet fuels, wherein the analyte is the fatty acid ester fatty acid methyl ester (FAME) and/or the fatty acid ester fatty acid ethyl ester (FAEE), wherein the analyte undergoes a chemical reaction which is selective for it and which influences the intensity for the carbonyl band of the respective ester group with the formation of a modified analyte and the variation in the concentration of analyte in the sample, which is the jet fuel together with FAME and/or FAEE, is measured using the reduction in the intensity of the carbonyl band and/or the increase in the concentration of the modified analyte is measured using the increase in the intensity of a band which is characteristic for the modification.

2. The method as claimed in claim 1, characterized in that the measurement of the variation in the concentration of analyte is carried out using IR spectroscopy.

3. The method as claimed in claim 2, characterized in that the measurement of the variation in the concentration of analyte is carried out using FTIR spectroscopy.

4. The method as claimed in claim 2, characterized in that the measurement of the variation in the concentration of analyte is carried out using quantum cascade lasers.

5. The method as claimed in claim 2, characterized in that the measurement of the variation in the concentration of analyte is carried out by means of IR spectroscopy with the aid of the reduction in the carbonyl band at 1749 cm.sup.−1 or 1742 cm.sup.−1.

6. The method as claimed in claim 5, characterized in that the measurement of the variation in the concentration of analyte is carried out by means of IR spectroscopy with the aid of the reduction in the carbonyl band at 1749 cm.sup.−1 by symmetrical evaluation about 1742 cm.sup.−1 or with the aid of the reduction in the carbonyl band at 1742 cm.sup.−1 by symmetrical evaluation about 1749 cm.sup.−1.

7. The method as claimed in claim 1, characterized in that FAME/FAEE is transformed into the corresponding amide by adding an amine, wherein the variation in the concentration of FAME/FAEE in the sample is measured-with the aid of the reduction in the intensity of the carbonyl band for the ester and/or the increase in the intensity of the amide band for the amide which is formed.

8. The method as claimed in claim 7, characterized in that the reaction is enzymatically catalysed.

9. The method as claimed in claim 1, characterized in that FAME/FAEE is transformed into the corresponding other ester by adding another alcohol under suitable reaction conditions and the variation in the concentration of FAME/FAEE in the sample is measured with the aid of the reduction in the intensity of the carbonyl band for the ester and/or the increase in the intensity of the carbonyl band of the other ester.

10. The method as claimed in claim 9, characterized in that the reaction is enzymatically catalysed.

11. The method as claimed in claim 1, characterized in that in addition to the quantitative determination, the method additionally comprises a qualitative determination using the reaction kinetics or reaction kinetics.

12. Use of a method as claimed in claim 1, characterized in that the method is used for identification of the contaminant or for the exclusion of the contaminant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures:

(2) FIG. 1: shows the degradation of FAME (1) with the aid of the reduction of the carbonyl stretching frequency at 1749 cm.sup.−1 and the sufficiently spectrally displaced increase in the corresponding amide as a reaction product (2) in the infrared absorption spectrum.

(3) FIG. 2: shows the kinetics for the enzymatically catalysed reaction of FAME and amine to the corresponding amide (points) with an exponential fit (line) for the purposes of predicting the measurement.

(4) FIG. 3: shows the comparison of the reaction kinetics for transesterification and aminolysis.

(5) FIG. 4: shows the reactions of fatty acid esters and other analytes measured on a measurement system with FTIR in accordance with the method in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

(7) The present invention will now be explained in more detail with the aid of the cited examples, although the invention is not limited to the examples.

(8) The following determinations were carried out: FAME in jet fuel by means of aminolysis FAEE in jet fuel by means of aminolysis glyceryl trioleate in jet fuel by means of aminolysis FAME in diesel by means of aminolysis FAME in jet fuel by transesterification

(9) For the determination of FAME in jet fuel by means of aminolysis, additional measurements were carried out: approved jet fuel additives jet fuel screening.

(10) General Method

(11) In a preferred embodiment, measuring instruments for carrying out the method consist of a flow cell, an infrared source (for example: Globar with or without spectral filter or QCL) together with a detector, pumps, valves, a system for dosing the reagents as well as a multi-way cartridge which contains the catalyst. The layer thickness of the flow cell is typically tailored to the illumination power of the infrared source used and to the IR transmission of the sample matrix.

(12) At the start of a sequence of measurements, the measuring instrument is rinsed with the sample liquid to be analysed, and then a background is recorded with QCL or FTIR. After adding one of the reagents listed below, the sample liquid is pumped between flow cells and a cartridge containing the catalyst in a circuit. The analyte thereby undergoes a chemical reaction which is selective for it, which influences the intensity of the carbonyl bands for the relevant ester group, with the formation of a modified analyte and the variation in the concentration of analyte in the sample is measured using the reduction in the intensity of the carbonyl band and/or the increase in the concentration of the modified analyte being formed is measured using the increase in the intensity of a band which is characteristic for the modification. The kinetics of the reaction allow early threshold warnings to be determined, allow the entire course of the reaction to be monitored, and by measuring standard samples, allow the remaining activity of the catalyst in the reusable cartridge to be determined. After the reaction is complete, the measuring instrument is rinsed with sample liquid again in order to measure a second background. From the variation in the measured intensity between the background (I.sub.0) and the reacted sample (I), the absorption (Abs) is determined using the Lambert-Beer law:
Abs=log(I.sub.0/I)

(13) From this, and by comparison with calibration curves, the concentration of the analyte is given by:
concentration of analyte [mg/kg]=(Abs*k+d)*ρ.sub.C/ρ.sub.S

(14) in which:

(15) k=slope of calibration curve

(16) d=axial intercept of calibration curve

(17) ρ.sub.C=density of calibration matrix, in kg/m.sup.3

(18) ρ.sub.S density of sample, in kg/m.sup.3

(19) As an example, for a measurement of jet fuel supplemented with 49.9 mg/kg of FAME, for a measured absorption of 17.81 mAU with the calibration curve k=2.79 mAU.sup.−1 and d=−0.18 mg/kg, the calculated FAME concentration is 49.51 mg/kg. The density of the calibration matrix and of the sample were identical in this example.

(20) FAME in Jet Fuel Using Aminolysis:

(21) Aminolysis has been shown to be an advantageous variation, because under enzymatic catalytic conditions, it is complete in less than 20 minutes for FAME concentrations of less than 500 mg/kg (see accompanying FIG. 2).

(22) TABLE-US-00001 TABLE 1 FAME in jet fuel using aminolysis Added Calculated concentration concentration Matrix Analyte [mg/kg] [mg/kg] Jet fuel FAME mix from B7 0.0 −0.02 Jet fuel FAME mix from B7 5.5 5.34 Jet fuel FAME mix from B7 11.1 11.26 Jet fuel FAME mix from B7 22.1 21.66 Jet fuel FAME mix from B7 199.3 200.19 Jet fuel FAME mix from B7 400.4 399.98

(23) Table 1 shows examples of results for jet fuels which had been supplemented with a FAME mix (20% RME—Rape Methyl Ester, PME—Palm Methyl Ester, TME—Tallow Methyl Ester, SME—Soy Methyl Ester und UCOME—Used Cooking Oil Methyl Ester, as a seven percent solution in diesel; B7) in various concentrations.

(24) The results show that 0-250 mg/kg FAME in jet fuel can be measured with an accuracy of <1 mg/kg. In order to determine FAME in jet fuel without the influence of FAEE and alcohols, all of the data were evaluated symmetrically around 1742 cm.sup.−1.

(25) The method in accordance with the invention was not only tested with the FAME mix cited above, which was tailored to the European market, but also with individual FAME types. The measurement results with a concentration around the permitted maximum of 50 mg/kg are listed in Table 2 below.

(26) From Table 2, it can be seen that the accuracy for individual FAMEs was somewhat lower because FAME from different sources typically have different chain lengths. With short chain methyl esters such as CME (Coconut Methyl Ester, used in particular in South-Eastern Asia and therefore not a part of the FAME mixes designed for Europe) with shorter carbon chain lengths and therefore a lower molar mass, adding a concentration in mg/kg resulted in a greater quantity of carbonyl groups, and thus in a known systematic agreement. These deviations can easily and simply be corrected by a specific calibration. The currently approved methods can either not determine CME (GC-MS, GC-Heart Cut and HPLC), or have the same systematic agreement (FTIR Rapid Screening Method).

(27) TABLE-US-00002 TABLE 2 FAME alone compared with FAME mix from B7 calibration Added Calculated concentration concentration Matrix Analyte [mg/kg] [mg/kg] Jet fuel RME from B7 48.5 54.77 Jet fuel PME from B7 48.4 49.44 Jet fuel TME from B7 47.7 48.48 Jet fuel SME from B7 49.0 46.86 Jet fuel UCOME from B7 48.7 47.37 Jet fuel CME from B7 48.1 66.50

(28) Additives:

(29) At the maximum permitted concentration in jet fuel of 15 permitted additives of various types (Static Dissipator, Lubricity Improver, Fuel System Icing Inhibitor, Metal Deactivator, Antioxidant & Cetane Improver, Biocide), an error in the measured value of <±5 mg/kg was measured. This is within the limits of the expected reproducibility of the method.

(30) Jet Fuel Screening:

(31) The determination of FAME in 26 different jet fuels showed that throughout, deviations from the nominal value could arise (73%≤5 mg/kg, or 92%≤7.5 mg/kg). Such severe discrepancies are known from global jet fuel surveys from the British Energy Institute (n=189; 85%<5 mg/kg, or 95%<10 mg/kg, measured by means of a FTIR Rapid Screening Method) and can be attributed to the different compositions and thus to spectral differences in real jet fuels.

(32) FAEE in Jet Fuel by Means of Aminolysis

(33) Aminolysis also functions with Fatty Acid Ethyl Ester (FAEE), but compared with FAME, a different wave number has to be evaluated. Table 3 shows the results for a calibration with FAEE, in this case ethyl palmitate, in various concentrations, with a symmetrical evaluation about 1749 cm.sup.−1.

(34) TABLE-US-00003 TABLE 3 FAEE in jet fuel using aminolysis Added Calculated concentration concentration Matrix Analyte [mg/kg] [mg/kg] Jet fuel FAEE 0 0.89 Jet fuel FAEE 50 48.66 Jet fuel FAEE 100 100.23 Jet fuel FAEE 200 200.22

(35) In samples which contained both FAEE and FAME, the choice of wave numbers for the evaluation meant that the two analytes could be determined independently of each other. Table 4 shows, by way of example, the determination of FAME from a sample which contained both FAME and FAEE.

(36) TABLE-US-00004 TABLE 4 Determination of FAME in a mixture of FAME and FAEE Added Added Calculated concentration concentration concentration of FAME of FAEE of FAME Matrix Analyte [mg/kg] [mg/kg] [mg/kg] Jet fuel FAME & 0 103.5 −3.29 FAEE Jet fuel FAME & 198.4 103.5 196.26 FAEE

(37) Glyceryl Trioleate in Jet Fuel Using Aminolysis

(38) The aminolysis of triglycerides leads to the formation of amides and alcohol. This reaction was carried out with glyceryl trioleate in jet fuel with lipase as the catalyst. Table 5 shows the results for various concentrations.

(39) TABLE-US-00005 TABLE 5 Triglyceride in jet fuel using aminolysis Added Calculated concentration concentration Matrix Analyte [mg/kg] [mg/kg] Jet fuel Glyceryl trioleate 0.0 −0.98 Jet fuel Glyceryl trioleate 5.0 3.14 Jet fuel Glyceryl trioleate 19.9 20.18 Jet fuel Glyceryl trioleate 49.8 48.65 Jet fuel Glyceryl trioleate 98.5 99.61

(40) FAME in Diesel Using Aminolysis

(41) In order to show that the method in accordance with the invention can also be extended to other liquid fuels, traces of FAME in a diesel B0 matrix were measured. The results of the enzymatically catalysed aminolysis of FAME in diesel are listed in Table 6.

(42) TABLE-US-00006 TABLE 6 FAME in diesel using aminolysis Added Calculated concentration concentration Matrix Analyte [mg/kg] [mg/kg] Diesel FAME mix from B7 0.0 −0.27 Diesel FAME mix from B7 10.0 10.27 Diesel FAME mix from B7 19.9 20.86 Diesel FAME mix from B7 49.2 50.19 Diesel FAME mix from B7 198.7 198.08

(43) FAME in Jet Fuel by Transesterification

(44) The transesterification of FAME with alcohols results in the formation of other esters. Because of the small separation of the characteristic bands between the analyte and reaction product compared with aminolysis, in the case of transesterification, somewhat poorer values were obtained for the reproducibility of the method and the error in the measured values. It can be seen from the reaction kinetics shown in FIG. 3 that the transesterification took approximately ten minutes longer than the aminolysis. For these reasons, the catalytic-enzymatic aminolysis of FAME in jet fuel was established as the preferred implementation of the method.

(45) Reaction of Fatty Acid Esters and Other Analytes

(46) FIG. 4 shows the reactions of FAME, FAEE, triglycerides, diethylhexyl adipate and 2-ethylhexyl acetate, measured with a measurement system with FTIR in accordance with the method in accordance with the invention. The wave numbers for the evaluation in this regard were tailored to the respective analytes.

(47) From the profile of the curves in FIG. 4, it can be seen that a qualitative prediction of the type of analyte can be made from the reaction kinetics of the analyte. As an example, compared with FAME, FAEE and triglycerides, the plasticizer diethylhexyl adipate and the interferent 2-ethylhexyl acetate have a significantly slower reaction rate. Consequently, FAME, FAEE and triglycerides can be distinguished from the other test analytes which, as interferents, could falsify FTIR measurements in accordance with the prior art and the quantitative determination of FAME, FAEE and triglycerides. By means of the combination of optimized evaluation wave numbers and the profile of the reaction kinetics for the analytes, other substances can be taken into consideration separately from each other. The method for the separate measurement and determination of contamination by fatty acid esters can also be applied to other substances.