Analysis of Anti-Icing Additives in Jet Fuel by Infrared Spectrophotometry* Keishi Hasegawa**, Masao Kajikawa**, Masaru Kawaguchi** and Tamotsu Nishijima** Summary: The authors have developed a simple and precise instrumental method applying the infrared spectroscopic analysis for the determination of anti-icing additive which is usually added in a large amount and has an important factor among various additives used in jet fuel. This is a method of infrared spectrophotometric analysis to determine the additive, availing the infrared characteristics spectra of both sample and water-extracted oil based on their C-O-C stretching vibrations (1,130cm-1). The method is more satisfactory than the conventional chemical method both in accuracy and precision, e. g., less than 0.8% in average deviation in the range of 0.05-0.3vol% of concentration and 0.006vol% in detectable concentration. These values are also equivalent to ones which were obtained in applying the infrared spectra due to the stretching vibrations of C-O (1,070cm-1). Even when other additives such as corrosion inhibitor, oxidation inhibitor and metal deactivator were coexisting, they did not influence the analytical results. And the determination of infrared spectra per sample required only 30 minutes of operation time and a minimum amount of 5ml of sample. Introduction Recently anti-icing additives are added to jet fuel to prevent the fuel-icing accident1) which is caused by the minute water contained in the fuel. The mixture of ethyleneglycol-monoalkylether and tertiary alcohol is generally used for this purpose from the view point of its solubility, combustibility and thermal stability for fuel. This additive is used for jet fuel in a comparatively large amount, and the strict control of its content is necessary. The authors have developed the infrared analytical method with the simple operation and a good precision for this quantitative analysis. Anti-icing additive is prepared by the American Air Force Standard (MIL-1-27686A) and has the component of 98vol% of ethyleneglycol-monomethylether and 2 vol% of glycerine, called recently as "Jet Fuel Additive 98-2". Infrared spectra of this anti-icing additive and its components, Table 1 Properties of basic jet fuel Experimental The jet fuel tabulated in Table 1 and D-201B Infrared Spectrophotometer of Japan Spectroscopic Co., Ltd. with 0.1mm and 0.5mm NaCl cells were employed. Infrared Analysis of Anti-icing Additives 1) Infrared absorption characteristics * Received November 4, 1963. Lectured at the 16th annual meeting of Chem. Soc of Japan. ** Toa Nenryo Kogyo Co., Central Research Laboratory Oi-mura, Iruma-gun, Saitama-ken.
Hasegawa, Kajikawa, Kawaguchi and Nishijima: Analysis of Fig. 1 Infrared spectra Bulletin of The Japan Petroleum Institute
Anti-Icing Additives in Jet Fuel by Infrared Spectrophotometry ethyleneglycol-monomethylether (Wako Junyaku Co., analytical grade) and glycerine (Koso Chem. Co., analytical grade), are shown in Fig. 1 (a, b and c). These show that the spectrum of anti-icing additive is nearly the same as that of ethyleneglycolmonoethylether, and the absorptions in characteristic region of glycerine (1, 042, 992, 913, 854cm-1) are not clearly detected. The assignment of absorption peak for the comparatively high absorption intensity in Fig. 1 is as follows; 3,350cm-1 (v OH), 2,900-2,750cm-1 (v CH3, CH2 and CH), 1,130cm-1 (v C-O-C) and 1,070cm-1 (v C-O). 2) Determination of characteristic absorption In order to examine the applicability of the above mentioned four absorpiton peaks to the quantitative analysis, infrared absorption spectra of both jet fuel containing 0.15vol% of anti-icing additive and base fuel oil without additive were measured by the compensation method, using 0.1mm NaCl cell, and the absorption region having the comparatively large absorption difference in both infrared spectra was examined. From the results shown in Fig. 2, the absorption difference caused by O-H, C-O-C and C-O stretching vibrations was found to be large. The linearity between concentration of additive and infrared absorption intensity is shown in Fig. 3, employing jet fuel containing 0.075, 0.10 and 0.15vol% additive and applying compensation method with 0.5mm NaCl cell. O-H stretching vibration near 3,350cm-1 which has the greatest absorption difference in Fig. 2 was Fig. 2 Absorption difference between jet fuel and its base oil
Hasegawa, Kajikawa, Kawaguchi and Nishijima: Analysis of Figs. 3 Infrared spectra for the examination of proportionality between concentration of additive and absorption intensity excluded because of its wrong linearity. C-O-C (1,130cm-1) and C-O (1,070cm-1) stretching vibrations show much better linearity. 3) Measurement of absorption coefficient and minimum detectable concentration Six standard samples were prepared add- (Dow Chemical Co., MIL-27686A Standard) to the jet fuel dried by anhydrous sodium sulfate and filtered through dried filter papers. The absorption coefficient in characteristic absorption band was measured in use of 0.5mm NaCl cell. In this case the minimum detectable concentration was determined through the concentration of additive corresponding to the 1% change of transmission, judging from the stability and precision of the spectrometer. The results are given in Table 2, showing that the average error of transmission measurement in both characteristic absorption bands of 1,130cm-1 and 1,070cm-1 was under 2.8% and that there was no difference between them though the average absorption coefficient of the former was 6% higher than that of the latter. There exists a good proportionality between additive concentration and the absorption intensity for the calibration curves of these two characteristic absorption bands. The infrared spectra for the various concentrations of additive and the calibration curves are shown in Fig. 4. Separation Method of Anti-icing Additive in Jet Fuel There is no difficulty and complexity for the separation of anti-icing additive from jet fuel because of its easy solubility into water. It is possible to extract it into water phase merely through the vigorous agitation of the equivoluminal mixture of fuel and pure water for at least two minutes at room temperature. The infrared spectra of basic oil and water-extracted jet fuel by the above mentioned way show no absorption difference through the compensation method, so it is clear that the residual content of the additive in the treated fuel drops down under the minimum detectable concentration. Interference of Other Additives It is general that two or three kinds of other additives are added to jet fuel except the above-mentioned anti-icing additive, which is added in the largest amount. For the examination of interference effect of these other additives on the analysis of the anti-icing additive, a sample was prepared in which 100ppm of Santolene-C (Monsanto Chem. Co.) as corrosion inhibitor, 50ppm of 2,6-ditert-butyl-4-methylphenol (Ethyl Corp.) as oxidation inhibitor and 20ppm of N.N'-disalithylidene propylenediamine (E. I. Du Pont) as metal deactivator were dissolved in basic fuel. This prepared oil did not show any different spectral behavior Bulletin of The Japan Petroleum Institute
Anti-Icing Additives in Jet Fuel by Infrared Spectrophotometry Table 2 Measured values of absorption coefficient and minimum detectable concentration Infrared spectrophotometers: Japan Spectroscopic Co., Ltd. 201-B type, with 0.5mm NaCl cell.
Hasegawa, Kajikawa, Kawaguchi and Nishijima: Analysis of Figs. 4 Calibration curve and infrared spectra of various concentrations of additive by the extraction treatment of anti-icing additive, and the spectra by the compensation method using this and the basic oil show no absorption difference in the characteristic bands (1,130cm-1, 1,070cm-1), then it is concluded that other kinds of additives give no effect on this analysis so long as they coexist in general using amount. Analysis of Standard Sample Oils In order to examine the precision of infrared spectral analysis in sections (Infrared Analysis of Anti-icing Additives and Separation Method of Anti-icing Additive in Jet Fuel), four standard sample oils containing 0.050~30vol% of the anti-icing additive and the same content of other kinds of additives as in section (Interference of Other Additives) were prepared and analysed three times respectively. 1) Analytical operation Equivolume of pure water was added to the sample oils and the anti-icing additive was extracted into water phase by the vigorous agitation for at least two minutes, then oil phase was dewatered by anhydrous sodium sulfate and then by filter paper. This dewatered oil was used for the standard sample of compensation method. The spectra in the region of 1,200~000cm-1 were scanned over by the compensation method and the absorption strength of 1,130cm-1 was inserted to the calibration curve to Table 3 Comparison of analytical results Bulletin of The Japan Petroleum Institute
Anti-Icing Additives in Jet Fuel by Infrared Spectrophotometry calculate the content of anti-icing additive. 2) Analytical results In Table 3 analytical data of the standard sample oils by the infrared method and the conventional chemical method2) are given for the examination of the analytical precision. Infrared method gave the sufficient results in its precision and accuracy for the additive concentration of 0.05 to 0.30vol% and its average deviation was under 0.8%. The chemical method is a kind of functional analysis, in which the sample oil is oxidized by dichromic acid under the constant condition using sulfuric acid as catalyst and then determined by the iodometry. This operation is complicated and requires the ice bath and boiling water bath, the end point of the reaction being judged by the naked eyes. The precision of the chemical method is as same as that of the infrared one, however, the accuracy decreases as the concentration of additives becomes high. For instance, the sample of 0.3vol% gave 10% lower value than the true one, and the sample of 0.2vol% of anti-icing additive often gave at maximum 20% lower value though not shown in Table 3. The chemical method seems to have problems in its accuracy. Consideration In the infrared spectrophotometric analysis, the greatest care must be taken in washing the infrared cell. After using the samples containing anti-icing additive it is impossible to wash the cell by carbon disulfide or carbon tetrachloride usually employed, because tertiary alcohol in the additive left adhesively in the cell as its content becomes higher. From the view point of solubility of tertiary alcohol it is considered better to wash it by lower anhydrous alcohol, but because of the danger of cell damage by trace water, the prewashing by the sample or compensation and then rewashing by carbon disulfide were applied. The conventional chemical method requires a running time of 180 minutes in average for one sample, because the operation after water extraction is very complicated chiefly depending on the oxidation-reduction reaction under the constant condition, moreover it has problems in accuracy. On the contrary the infrared method developed by the authors is considered to be the most appropriate analytical method for the daily control work because the operation is very simple with the use of the usual infrared spectrometer and its cell, moreover its accuracy is very high. Conclusion The authors have succeeded in making the quantitative analysis of the anti-icing additive (ethyleneglycol-monomethylether-glycerine type) in jet fuel by the very simple operation of the infrared compensation method using characteristic C-O-C stretching vibration and the fuel extracted by water as compensation oil. In this case the coexistence of corrosion inhibitor, oxidation inhibitor and metal deactivator gives no effect on the analytical results and its average deviation is under 0.8% in the region analytical operation is much more excellent than that of the chemical method both in accuracy and in simplicity, so it is very effective to use this method to the daily work. Moreover, it is possible to apply it to naphtha as well as samples having wider range of concentration of anti-icing additive by selecting the adequate cell length. References 1) French, W. C., Malick, E. A., SAE Paper 356-B (1961). 2) Federal Test Method. 5327. 1T.