Quantitative analysis of mixtures of fatty alcohols, alkyl acrylates and alkyl m~thacrylates by gas chromatography technique

Transcription

1 Indian Journal of Chemical Technology Vol. 2, July 1995, pp. 1R4-1 RR Quantitative analysis of mixtures of fatty alcohols, alkyl acrylates and alkyl mthacrylates by gas chromatography technique JyotirmoyDas, N C Joshi, A S Sarma& K L Mallik LubrizolIndia Limited,Research& DevelopmentCentre, Leo House,4th Floor, Bombay400025, India Received24 February 1994;accepted15December1994 Separation of a mixture ofcwc 18 alkyl esters of acrylicand methacrylic acid have been simultaneously done in the presence of corresponding alcohol on a Silar 5 cp column using a programmed temperature. condition. The identification and quantification of the different components, in the presence of other impurities are reported and variance in results from expected are discussed. Homopolymers and/or copolymers of long chain alkyl acrylates or alkyl methacrylates are widely used as performance additives in lubricants and other petroleum products, e.g., as pour point depressants and viscosity index improvers in lubricants and as flow improvers and drag reducers in. petroleum crudes and fuels. The monomers used for the production of these polymers, viz., alkyl acrylates and alkyl methacrylates are normally produced by esterification of acrylic acid or methacrylic acid with appropriate fatty alcohols employing usual reaction procedures. The crude esters so produced, often contain unreacted alcohols and the carboxylic acids as impurities. Although the acid impurities can easily be removed in the purification process, the esters can still remain contaminated with f ttty alcohol components. Thus, there arises very often the need for quantitative estimation of mixtures of fatty alcohols, alkyl acrylates and alkyl methacrylates in the process of making monomers for industrial application. There are only a few reports related to the GC analysis of long chain alkyl acrylates or alkyl methacrylates in which the alkyl chain length corresponds 'to a range of carbon atoms12. These investigations do not address the problems of quantification of the individual components3-5. Further there are no reports on the quantitative estimation of mixtures containing acrylate and methacrylate combinations. Hence, a detailed investigation has been taken up to develop a suitable GC method for quantification of ester mixtures of long chain alkyl acrylates and alkyl methacrylates, which contain fatty alcohols as impurities. The objective of the present investigation is to establish an analytical method based on GC technique to quantify the ;;omponents present in a mixture of fatty alcohols, alkyl acrylates and alkyl methacrylates in which the alkyl chain length varies between C IO-C18. The method consist of GC analysis of synthetic mixtures of specific fatty alcohols of known alkyl chain lengths; synthesis of alkyl acrylates and alkyl methacrylates from alcohols containing known alkyl chain length (Cw, C12, C14, CI6 and CIS) and GCanalysis of these alkylacrylates and alkyl methacrylates; GC analysis of mixtures of alkyl acrylates and alkyl methacrylates described above and GC analysis of mixtures of acrylates and methacrylates, further admixed with known quantities of fatty alcohol mixtures. The synthetic mixtures in all the above cases were made using different proportions of the corresponding components. In each case, three sets of experiments were carried out at different levels of component combination. Experimental Procedure Preparation of standard esters-individual fatty alcohols (Ageis Chemical) of 95% and commercial grade of acrylic acid (GSFC) and methacrylic acid (Nippon Sakubai) of approximately 99.8% purity were used. The standard esters were prepared in the laloratory by esterifying acrylic acid or methacrylic acid with specific alcohol in the presence of metljailesulphonic acid as catalyst using standard procedure. The crude esters were purified by normal washing/extraction process, and were used as such without further purification by distillation. Gas chromatographic analysis-a Hewlett Packard Gas Chromatograph, Model 5840A, was used for this study. A stainless steel column 6' x 1/8" filled with Silar 5 cp (l 0%) on Chromosorb WHP was used. Nitrogen was used as carrier gas with a flow rate of 30 ml/min. The injection and detection temperatures were maintained at 280 and 300 C, II ji' III! II Il'I" "I" " Ji I I

2 DAS et al: ANALYSIS OF MIXTURES OF FATI'Y ALCOHOLS 185 respectively. The oven temperature was kept between C with an initial hold for three minutes at 160 Cfollowed by increase in temperature at a rate of 6 C per min. Total time of analysis was kept for 30 min to allow any higher boiling point components to elute. The retention times were measured from the time of sample injection by a reporting integrator. The values were calculated based on three to five measurements which had a good repljducibility. Complete Tim!!,mln Fig. I-Typical gas chromatogram of a mixture of alkyl acrylate!;. methacrylates and alcohols in Silar 5 cp column; Peaks (I) C 10 Alcohol. (2) CIOAcrylate, (3) CIOMethacrylate, (4)C12 Alcohol, (5) C12 Acrylate, (6) CI2 Methacrylate, (7) CI4 Alcohol, (8) CI4 Acrylate, (9) C'4 Methacrylate. (10) CI6 Alcohol, (II) CI6 Acrylate, (12) CI6 Methacrylate. (13) CIM Alcohol. (14) CIM Acrylate. (15) C IMMethacrylate ) resolution was achieved for all the alcohols, acrylates and methacrylates as well as mixtures thereof, with no overlap of peaks in any case. The weight percent of each component taken was computed giving due weightage of the other constituents present in the mixture. The total weight of individual components thus taken were compared with the area percent response of the individual constituents. The weight percent of esters and alcohols present has been found to be equal to the area percentage response which has been used for quantification. Results and Discussion Fig. 1corresponds to typical gas chromatographs of mixtures. From the figure 'can be seen that there is a distinct resolution of peaks even in the case of three-component system containing alkyl acrylates, alkyl meth;:lrylates and fatty alcohols. The resolution Oi aks with respect to specific alkyl chain length of the compom"ats is complete and all the fifteen peaks expected in such a mixture are distinctly seen. Based on the results the retention times are found in the order: Methacrylate > acrylate > alcohol. As expected, thef"eis a systematic increase in retention time with the increase in carbon chain length of the alkyl group in a homologous series. Quantitative analysis Typical gas chromatographic results obtained are shown in Tables 1-7. Table I depicts the results obtained on synthetic mixtures of fatty alcohols containing different proportions of components. Tables 2 and 4 show the quantitative data obtained in 3 different synthetic mixtures of alkyl acrylates or alkyl methacrylates containing varied proportions of components. Tables 3, 5 and 6 show quantitative data obtained on three categories of synthetic mixtures Wt% % Deviation Theoretical \ Found Theoretical Found Table SET-2 SET-3 I-Quantitative Wt% analysis of alkyl alcohols in a mixture Wt% - % Deviation Theoretical Fund Theoretical - Found Table SET-2 2-Quantitativeanalysis SET-3 Wt% of alkyl acrylate in a mixture

3 \ Table 3-Quantitative analysis of alkyl acrylate in combination with alcohol SET-2 SET-3 Acrylate W.t% Alcohol Wt% Acrylate Wt% Alcohol Wt% Acrylate Wt% Alcohol Wt% Carbon ± ± ± IO % tical Theore Deviation Theoretical Found tion Found Theoretical % Theon- Theore- Found Devia- SET-2 Found SET-3 Wt% % Devia- Wt% : Theore tical : Found tion % Methacrylate Theore- Devia- Alcohol Found Wt% Wt /.) Wt% % Table Devia- 5uantitative SET-2 SET-3 analysis of alkyl methacrylate in combination with alcohol :; Z () :I: tt1 trl () :I: Z o.r C t( \0 \0 U1 t-.i.-

4 +8.92 ± Il.l II Theore tical 10.8 s:::, : , :> ' Found 13.4 Methacrylate % Theore- Devia- Acrylate Found Alcohols Wt% Wt% Acrylate % Wt% Devia- en - >< % Deviation Theoretical Wt% Table SET-2 SET-3 6--Quantitative analysis of alkyl acrylate in combination with alkyl methacrylate en 0 Found 5.30 Theoretical Found 0en "T1 h :> ::c ::: J

5 188 INDIAN J. CHEM. TECHNOL., JULY 1995 i.e., alkyl acrylate in combination with alcohol, alkyl methacrylate in combination with alcohol, and alkyl acrylate in combination with alkyl methacrylate, respectively. Finally, Table 7 presents data on composite mixtures of alkyl acrylates, alkyl methacrylatcs and fatty alcohols in different proportions. For a quantitative estimation point of view, the results in each set of experiments have been analysed in two respects, i.e., observed variations between experimental results and expected (theoretical) results, with regard to estimation of the overall quantities of alcohols, alkyl acrylates and alkyl methacrylates in a mixture of these three category of components. In this case, the individual components in each category arising from the differences in the carbon chain length of the alkyl groups were not taken into account. Observed variations between experimental results and. expected results. with regard to quantitative estimation of components, wherein the components were further differentiated in terms of the carbon chain length of the alkyl groups. From the results it is seen that mostly the quantitative results obtained are within 10% variation from the theoretically expected results. This observation is foood to be valid in all the seven sets of experiments carried out in the case of the mixture of alkyl acrylates, alkyl nl'thacrylates and alkyl alcohols. The few deviations observed in actual results as compared to expected results, can be attributed to experimental errors. From the above data, it can also be seen that the variations between experimental and theoretical results in the three sets of experiments are upto a maximum of 7.0% for alcohols, 1.1% for alkyl acrylates, and 5.2% for alkyl methacrylates. Conclusion Complex mixtures containing alkyl agr.ylates, alkyl methacrylates and fatty alcohors with alkyl chains corresponding to a range of carbon atoms (CIO-C1S) can be analysed by gas chromatographic technique using packed columns. The resolution of components in such mixtures is quite effective, with each component appearing as a disti,nct peak. The repeatability/reproducibility results indicate that the retention times of components are almost constant (variation of the order of min). A quantitative estimation of the components in such mixtures is possible and the variation in quantitative results are generally less than 10%, even in the case of three-component systems containing alcohols, alkyl acrylates and alkyl methacry lates. Acknowledgements The authors thank Lubrizol India Limited for permitting to publish these results. References I Homa A. Taborsky J & Churacek J. J ChromatoKr, 89 (1986) Homa A. Taborsky J. Dofka O. Matousek P & Churacek J. J Chromatogr. 325 (1987) Germain R W & Haken J K. J Chromatogr. 43 (1969) Ashes J R & Haken J K. J Chromatogr. III (\ 975) Linkiewicz M. Szocik A & Smolik M. ChClII Anal (Warsaw), 26 (1981) 153. 'I 'I'!'!'I"'I' I" I