Gas phase methanol synthesis with Raman spectroscopy for gas composition monitoring

Applicability of Raman spectroscopy for time-resolved gas composition monitoring during direct methanol synthesis via carbon dioxide hydrogenation was investigated. A series of methanol synthesis experiments with varied reactor conditions was conducted and the reactor outlet stream was analyzed with in-line gas Raman spectroscopy. Concentrations of H₂, CO₂ and CO were determined directly from the acquired spectral data. For evaluation of methanol and water content a data reconciliation algorithm was developed. The algorithm involves estimation of the occurring chemical reactions' extents by iterative minimization of the difference between concentration values acquired from the experimental data and concentration values computed based on the mass conservation principle. The obtained experimental concentrations were compared and validated against the results of the reactor mathematical modeling, which is based upon a well-established kinetic interpretation of the process. The findings indicate good repeatability and accuracy of the developed gas analysis system, which together with the advantageous temporal resolution of the method, make Raman spectroscopy a promising technique for fast response monitoring of the process.

Applicability of Raman spectroscopy for time-resolved gas composition monitoring during direct methanol synthesis via carbon dioxide hydrogenation is investigated.

The noncoincidence phenomenon of acetonylacetone CO stretching in a binary mixture and the aggregation-induced split theory

This article aims to correlate the noncoincidence effect phenomenon with the aggregation state of acetylacetone CO stretching in a binary mixture. CO stretching noncoincidence effect (NCE) was observed not only between IR and Raman spectra but also between the isotropic and anisotropic Raman spectra of acetonylacetone. The difference in CO stretching wavenumbers of the isotropic and anisotropic Raman spectra (NCE value) in a binary mixture at different concentrations has been calculated. We found that both isotropic and anisotropic Raman wavenumbers of CO stretching increase with the dilution of acetonylacetone by CCl₄ while the NCE value decreases. These noncoincidence and concentration effect phenomena seem to go against the quantum theory. Herein, we proposed an aggregation-induced split (AIS) model to explain the NCE phenomenon and concentration effect. The experimental data were consistent with the DFT calculations performed at the B3LYP-D3/6-311++G (d,p) levels based on the proposed model. The dynamics of transformation from monomers to an aggregated structure can be easily controlled by tuning the concentration. Solvent dependent experiments show that the value of NCE decreased with the increase of the solvent dielectric constant at the same concentration, which is in accordance with Logan's theory.

Both the isotropic and anisotropic Raman wavenumbers of the CO stretch increase with the dilution of acetonylacetone by CCl₄, while the separation between isotropic and anisotropic Raman wavenumbers (Δυ) decrease.

Composition-dependent association behavior in the mixture of isopropanol and trichloromethane: a volumetric, vibration spectroscopic and quantum chemical study

Herein the intermolecular associative behaviors in the binary mixture of isopropanol and trichloromethane have been studied via a combined excess volumetric, vibration spectroscopic and quantum chemical approach.

Solvent effect on the vibrational spectra of Carvedilol

Carvedilol (CRV) is an important medicament for heart arrhythmia. The aim of this work was the interpretation of its vibrational spectra with consideration on the solvent effect. Infrared and Raman spectra were recorded in solid state as well in solution. The experimental spectra were evaluated using DFT quantum chemical calculations computing the optimized structure, atomic net charges, vibrational frequencies and force constants. The same calculations were done for the molecule in DMSO and aqueous solutions applying the PCM method. The calculated force constants were scaled to the experimentally observed solid state frequencies. The characters of the vibrational modes were determined by their potential energy distributions. Solvent effects on the molecular properties were interpreted. Based on these results vibrational spectra were simulated.