In-Line Near-Infrared (NIR) and Raman Spectroscopy Coupled with Principal Component Analysis (PCA) for in Situ Evaluation of the Transesterification Reaction

Abstract

Biodiesel was synthesized from different commercially available oils while in-line Raman and near-infrared (NIR) spectra were obtained simultaneously, and the spectral changes that occurred during the reaction were evaluated with principal component analysis (PCA). Raman and NIR spectra were acquired every 30 s with fiber optic probes inserted into the reaction vessel. The reaction was performed at 60-70 °C using magnetic stirring. The time of reaction was 90 min, and during this time, 180 Raman and NIR spectra were collected. NIR spectra were collected using a transflectance probe and an optical path length of 1 mm at 8 cm(-1) spectral resolution and averaging 32 scans; for Raman spectra a 3 s exposure time and three accumulations were adequate for the analysis. Raman spectroscopy showed the ester conversion as evidenced by the displacement of the C=O band from 1747 to 1744 cm(-1) and the decrease in the intensity of the 1000-1050 cm(-1) band and the 1405 cm(-1) band as methanol was consumed in the reaction. NIR spectra also showed the decrease in methanol concentration with the band in the 4750-5000 cm(-1) region; this signal is present in the spectra of the transesterification reaction but not in the neat oils. The variations in the intensity of the methanol band were a main factor in the in-line monitoring of the transesterification reaction using Raman and NIR spectroscopy. The score plot of the first principal component showed the progress of the reaction. The final product was analyzed using (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy and using mid-infrared spectroscopy, confirming the conversion of the oils to biodiesel.

Biodiesel Synthesis Monitoring using Near Infrared Spectroscopy

“…Biodiesel is a renewable fuel [1 -5] considered the main substitute of fossil fuels [1,6,7]. It presents reduced exhaust emissions in comparison to petroleum diesel [8 -10], it is biodegradable [2,4,9,11,12], and it is miscible in all proportions to petroleum diesel [9]. Similar properties of diesel make possible the use of blends between biodiesel and diesel in combustion engines without any modification [1,7].…”

“…In general, works using NIR spectroscopy are based on calibration models built and applied to samples under well-controlled conditions. The standard experimental procedure generally involves sample collection during reaction, sample neutralization and off-line characterization, for a number of transesterification runs carried out at different molar ratios and catalyst concentrations [4,5,12,14,18,21]. These studies involve cumbersome and time-consuming experimental procedures.…”

Virtual Sensors for Biodiesel Production in a Batch Reactor

“…The measurements provide valuable information about the operating conditions and simultaneously give an estimate for critical variables by monitoring the state of a process and verifying that performance is optimal. There are methods to monitor the progress of the reaction, such as gas and liquid chromatography [9][10][11][12], Fourier transform infrared (FTIR), near-infrared (NIR), and nuclear magnetic resonance (NMR) spectroscopy methods [10,[12][13][14][15][16][17], measurement of refractive index [18], and viscosity [19]. Most of these methods require samples to be taken and offline analyses to be performed which include a pre-treatment of the sample.…”

Discriminating the Mineralogical Composition in Drill Cuttings Based on Absorption Spectra in the Terahertz Range

“…With minimal additional effort, PCA provides a roadmap on how to reduce a complex data set to a lower dimension. [39][40][41] In this research, each spectrum was extracted as a single point plotted in PC space, with similar samples plotted close together. The score plot for all samples is shown in Figure 3b.…”