Full GC-PIONA Carbon Number Analysis Performed by On-Line Process NMR Spectroscopy
A 60 MHz process FT-NMR spectrometer has been installed on the feedstream to a naphtha cracker in several locations to provide detailed PIONA analysis, every two minutes, for input into APC/optimization packages. The NMR technique utilizes high-resolution FT-NMR proton spectra in conjunction with partial least squares modeling techniques to obtain highly linear and robust predictive models. Modeling requirements are limited and on-line models contain only around 300-500 data points with minimum model maintenance required. Single predictive models are used to predict across the entire variability range of each property. Table A shows the performance of the NMR models compared to the laboratory GC over a four month period where the NMR was available for >99.5%.
Table A – Correlation and Standard Deviation Summary of NMR-Lab GC Reproducibility
The following figures show the spectral variability observed in various naphtha streams as well as the lab-NMR agreement plots for several of the detailed PIONA parameters.