Otimização de metodologia analítica para determinação de hidrocarbonetos, compostos sulfurados e gases permanentes em gás natural

Abstract

The analysis of natural gas samples is as much intrinsic as it is routine in the petrochemical industry with a variety of objectives such as product certification, process control adjustment and even legislation compliance. All of these samples have some properties that are analyzed by gas chromatography in laboratory and the optimization of this type of method is crucial to acquire results as fast and trustworthy as possible. In those samples, the complexity of the analytical matrix involves the use of two methodologies for the complete characterization of natural gas, with one part for the analysis of hydrocarbons and fixed gases and a second part for the sulfur compounds. With the study of parameters like oven temperature and column flow, it was possible to comply to both normative methodologies with a single injection of sample, thus resulting in a simplified analysis. During development it was possible to optimize the methods previously used with a 50% reduction on analysis time through finding the optimal flow with the Van Deemter equation as well as utilizing the existent resources of the equipment to reduce usage of carrier gas. The optimized method was validated in terms of repeatability and accuracy in reference material through evaluation of relative standard deviation and relative error. For the accuracy, it was made by comparison of the current method and the optimized in terms of reproducibility of the standards used, in addition the evaluation of intermediate precision of variation between different days of analysis. The optimized method showed good repeatability in reference material as well as in samples and good accuracy in those materials. In comparison between methods it was noticed some diverging results, due to samples analyzed had composition outside of the expected scope from the methods, but it maintained stable when varying the day of analysis.