As Raman spectroscopy enables rapid, non-destructive measurements, the technique appears a most promising tool for on-line process monitoring and analysis in the pharmaceutical industry. This article ...gives a short introduction to Raman spectroscopy and presents several applications in the pharmaceutical field.
Emulsified polycolloid substrate (EPS) was developed and applied in situ to form a biobarrier for the containment and enhanced bioremediation of a petroleum-hydrocarbon plume. EPS had a negative zeta ...potential (−35.7 mv), which promoted its even distribution after injection. Batch and column experiments were performed to evaluate the effectiveness of EPS on toluene containment and biodegradation. The EPS-to-water partition coefficient for toluene (target compound) was 943. Thus, toluene had a significant sorption affinity to EPS, which caused reduced toluene concentration in water phase in the EPS/water system. Groundwater containing toluene (18 mg/L) was pumped into the three-column system at a flow rate of 0.28 mL/min, while EPS was injected into the second column to form a biobarrier. A significant reduction of toluene concentration to 0.1 mg/L was observed immediately after EPS injection. This indicates that EPS could effectively contain toluene plume and prevent its further migration to farther downgradient zone. Approximately 99% of toluene was removed after 296 PVs of operation via sorption, natural attenuation, and EPS-enhanced biodegradation. Increase in total organic carbon and bacteria were also observed after EPS supplement. Supplement of EPS resulted in a growth of petroleum-hydrocarbon degrading bacteria, which enhanced the toluene biodegradation.
•EPS was developed to form a biobarrier for petroleum-hydrocarbon containment.•Toluene has high sorption affinity to EPS (EPS to H2O partition coefficient = 943).•EPS could contain toluene plume and prevent its migration to downgradient aquifer.•EPS enhanced in situ toluene biodegradation under anaerobic conditions.
The aim of the present study was to propose a strategy for the implementation of a Process Analytical Technology system in freeze-drying processes. Mannitol solutions, some of them supplied with ...NaCl, were used as models to freeze-dry. Noninvasive and in-line Raman measurements were continuously performed during lyophilization of the solutions to monitor real time the mannitol solid state, the end points of the different process steps (freezing, primary drying, secondary drying), and physical phenomena occurring during the process. At-line near-infrared (NIR) and X-ray powder diffractometry (XRPD) measurements were done to confirm the Raman conclusions and to find out additional information. The collected spectra during the processes were analyzed using principal component analysis and multivariate curve resolution. A two-level full factorial design was used to study the significant influence of process (freezing rate) and formulation variables (concentration of mannitol, concentration of NaCl, volume of freeze-dried sample) upon freeze-drying. Raman spectroscopy was able to monitor (i) the mannitol solid state (amorphous, α, β, δ, and hemihydrate), (ii) several process step end points (end of mannitol crystallization during freezing, primary drying), and (iii) physical phenomena occurring during freeze-drying (onset of ice nucleation, onset of mannitol crystallization during the freezing step, onset of ice sublimation). NIR proved to be a more sensitive tool to monitor sublimation than Raman spectroscopy, while XRPD helped to unravel the mannitol hemihydrate in the samples. The experimental design results showed that several process and formulation variables significantly influence different aspects of lyophilization and that both are interrelated. Raman spectroscopy (in-line) and NIR spectroscopy and XRPD (at-line) not only allowed the real-time monitoring of mannitol freeze-drying processes but also helped (in combination with experimental design) us to understand the process.
The present work deals with the corrosion inhibition mechanism of API 5L X52 steel in 1 M H2SO4 employing the ionic liquid (IL) decyl(dimethyl)sulfonium iodide DDMS+I–. Such a mechanism was ...elicited by the polarization resistance (R p), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques, both in stationary and dynamic states. The electrochemical results indicated that the corrosion inhibition was controlled by a charge transfer process and that the IL behaved as a mixed-type corrosion inhibitor (CI) with anodic preference. The experimental results revealed maximal inhibition efficiency (IE) rates up to 93% at 150 ppm in the stationary state, whereas in turbulent flow, the IE fell to 65% due to the formation of microvortexes that promoted higher desorption of IL molecules from the surface. The Gibbs free energy of adsorption (ΔG°ads) value of −34.89 kJ mol–1, obtained through the Langmuir isotherm, indicated the formation of an IL monolayer on the metal surface by combining physisorption and chemisorption. The surface analysis techniques confirmed the presence of Fe x O y , FeOOH, and IL on the surface and showed that corrosion damage diminished in the presence of IL. Furthermore, the quantum chemistry calculations (DFT) indicated that the iodide anion hosted most of the highest occupied molecular orbital (HOMO), which eased its adsorption on the anodic sites, preventing the deposition of sulfate ions on the electrode surface.
The reactivity and activation parameters for the ring-opening metathesis polymerization of eight norbornene esters in the presence of a N-chelating Hoveyda-Grubbs II type catalyst were determined ...using
in situ
1
H-NMR. The ester molecules differ in the structure of substituent and the location of ester groups. Kinetic studies have shown that effective polymerization constants and activation parameters highly depend on the monomer structures. It was demonstrated that the elongation of the aliphatic chain does not significantly affect the reactivity of the ester, but has a high impact on the activation parameters of the reaction. Branching of the aliphatic substituent has a significant influence on the reactivity and activation parameters. Furthermore, the orientation of the ester substituents in the norbornene ring substantially affects the activation parameters.
The reactivity and activation parameters for the ROMP of eight norbornene esters in the presence of a N-chelating Hoveyda-Grubbs II type catalyst were determined. Kinetic studies prove that these parameters highly depend on the monomer structures.
This article considers the thermodynamic aspects, thermo- and rheokinetics of
endo
-dicyclopentadiene polymerization in the presence of the original metathesis second Hoveyda-Grubbs catalyst with an
...N
-chelating ligand. The activation energy of
endo
-dicyclopentadiene polymerization was determined as 88.9–89.2 kJ/mol. The thermal effect of the ring-opening metathesis
endo
-dicyclopentadiene polymerization reaction reaches 52.7 kJ/mol. This is lower than the values for molybdenum- and tungsten-containing catalysts reported in the literature, which can be explained by a different microstructure of the polymer produced in the presence of ruthenium-based metathesis catalysts.
In this paper, Fourier transform infrared spectroscopy (FTIR) was applied to examine the metathesis copolymerization of dicyclopentadiene with a mixture of exo,exo- and ...endo,endo-2,3-dicarbomethoxy-5-norbornene using a Hoveyda-Grubbs II type catalyst. The obtained data allowed us to calculate the monomer reactivity ratios of dicyclopentadiene and the isomers of 2,3-dicarbomethoxy-5-norbornenes. The relative reactivity of dicyclopentadiene was around eight times lower than the reactivity of the isomer mixtures.
Pt-loaded H-beta zeolite was identified as a highly active catalyst for the bifunctional transformation of citronellal to menthol, with isopulegol as the intermediate. With a 2 wt% Pt-loaded ...catalyst, citronellal is fully converted within 12 h, with only 2.5 wt% catalyst with respect to citronellal, and with a citronellal to Pt molar ratio of 2500.
1
,
4
-Dioxane is the best reaction solvent, because it minimizes the unwanted direct hydrogenation of citronellal and promotes its stereoselective cyclization to isopulegol, leading to high menthol yields. The stereoselectivity can be improved moderately by using a Zr-impregnated support and more substantially by performing high-temperature (750 °C) treatment of the calcined and reduced catalyst. This treatment presumably creates extra Lewis acidity on the catalyst and results in 88% stereoselectivity for the desired menthol. Overall, an 85% yield of (–)-menthol was obtained.
FT-Raman spectroscopy (in combination with a fibre optic probe) was evaluated as an in-line tool to monitor a blending process of diltiazem hydrochloride pellets and paraffinic wax beads. The mean ...square of differences (MSD) between two consecutive spectra was used to identify the time required to obtain a homogeneous mixture. A traditional end-sampling thief probe was used to collect samples, followed by HPLC analysis to verify the Raman data. Large variations were seen in the FT-Raman spectra logged during the initial minutes of the blending process using a binary mixture (ratio: 50/50, w/w) of diltiazem pellets and paraffinic wax beads (particle size: 800–1200
μm). The MSD-profiles showed that a homogeneous mixture was obtained after about 15
min blending. HPLC analysis confirmed these observations. The Raman data showed that the mixing kinetics depended on the particle size of the material and on the mixing speed. The results of this study proved that FT-Raman spectroscopy can be successfully implemented as an in-line monitoring tool for blending processes.
The thermal stability of polymers is a main issue when used as friction elements under dry sliding. Cast polyamide grades processed with either natrium or magnesium catalysors are slid on a ...small-scale and a large-scale test configuration to reveal the effect of softening or degradation on the sliding stability and to investigate possibilities for extrapolation of friction and wear rates between both testing scales. The combination of softening and afterwards transition into the glassy state is detrimental for the sliding stability of natrium catalysed polyamides, characterised by heavy noise during sliding. A transfer film formed under continuous softening also provides high friction. Melting during initial sliding is necessary for stabilisation in both friction and wear, and eventual softening of a molten film near the end of the test then not deteriorates the sliding stability. Softening of magnesium catalysed polyamides is favourable for the formation of a coherent transfer film resulting in more stable sliding than natrium catalysed polyamides. The differences in softening mechanisms of both polyamide grades is correlated to structural changes investigated by thermal analysis and Raman spectroscopy: the γ crystalline structure prevails in magnesium catalysed samples and the α crystalline structure is predominant in natrium catalysed samples. For internal oil lubricated polyamides, a time dependent degradation of the polyamide bulk deteriorates the supply of internal oil lubricant to the sliding interface, resulting in high friction and wear under overload conditions. As the degradation mechanisms during sliding are strongly correlated to the test set-up, extrapolation is only possible for friction in a limited application range, while wear rates cannot be extrapolated.
