Improvement of Simulated Distillation Methods by Gas Chromatography in Routine Analysis

Abstract

Simulated distillation (SD) by gas chromatography (GC) is a technique which advantageously replaces traditional distillation methods for rapid checking of petroleum products yields. If the principle is simple (separation of the components according to their boiling point by the GC column) the implementation is less obvious. The first problem concerns the choice of the stationary phase to obtain good agreement with the real distillation curves; the second is the stability of this phase at the maximum temperatures used. There are many interdependent parameters involved in these two problems. Although several methods have been standardized their applications give rise to a number of difficulties in routine use: need to choose operating conditions (standard methods indicate only some possibilities), determination of the procedure (calibration, blank, quantification, etc. ) compatible with automation and reproducibility of the method, data processing to assure a good result. The arrival in the last few years of very stable metal capillary columns have provided better control of the experimental parameters. With these columns the determined final boiling point of SD methods has been extended and some procedures have been defined to use these methods in routine analysis. Results of SD are in good agreement with the physical distillation. An automation of these methods has become feasible by developing a software which carries out the raw data processing, the calculation of the SD curve and controls all parameters of the defined procedure.