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Microemulsification-Based Method: Analysis of Monoethylene Glycol in Samples Related to Natural Gas Processing

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journal contribution
posted on 17.12.2015, 09:39 by Jaqueline G. da Cunha, Leandro Y. Shiroma, Gabriela F. Giordano, Bruno C. Couto, Rogério M. Carvalho, Angelo L. Gobbi, Lauro T. Kubota, Renato S. Lima
The determination of monoethylene glycol (MEG) in samples related to natural gas processing by using the microemulsification-based method (MEC) is portrayed herein. MEC was recently proposed by these authors like a powerful way for the development of point-of-use technologies. It relies on effect of the analyte on formation of microemulsions (MEs), changing the minimum volume fraction of amphiphile needed to get ME. This fraction is the analytical signal in MEC, and its detection depends on a binary chemical information: the cloudy-to-transparent conversion that occurs with microemulsification. Hence, this signal can be precisely detected with naked eyes ensuring not only screening analyses as the most of colorimetry-based rapid testing methods, but also precise determinations. The investigations reported herein are essential for a deeper understanding of the approach. These studies relate to tests of ionic strength-function robustness, considerations about the analytical signal profile, and analyses of MEG in complex samples of regeneration after the use of this dialcohol in pipes of liquefied natural gas processing. The dispersions were composed of water, oleic acid, and ethanol such as hydrophilic (W), hydrophobic (O), and amphiphilic phases, respectively. Analytes were added in the W phase to attain the analytical curves by first preparing W–O mixtures (1:1 v/v) and, then, adding ethanol amphiphile until cloudy-to-transparent transition. For application, the samples were directly used as the W phase. The media were prepared in bottles with the aid of micropipette, whereas the analytical signal was detected in solution by naked eyes. Robustness was expressed as a function of absolute errors calculated for concentrations of analyte (volume fraction of MEG to water, % v/v). Such errors were because changes in ionic strength of W phase by adding the salts: 10.0 and 500.0 mmol L–1 NaCl and 10.0 mmol L–1 Na2SO4, CaCl2, and FeCl3. Conductivities of the W phase ranged from 0.1 to 32.1 mS cm–1. MEC was somewhat robust with absolute errors of 0.18 to 6.47% (v/v). Furthermore, our hypotheses on MEC signal profile were in accordance with experimental results indicating an inverse relationship between the signal and the surface activity phenomenon. Concerning the application, the samples presented color, particulate, high conductivity, and diverse compounds. Despite these drawbacks, MEC outstandingly provided accurate measurements (compared to data of iodometry titration) after simple dilution of the samples in water.