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Raman spectroscopy is a nondestructive and in situ analytical technique that could provide information on the chemical structure and structural ordering of carbonaceous materials. Based on the E2g symmetric stretching vibration mode in the aromatic layers (G band, ~1,580 cm−1) and the defect structure in graphite (D band, ~1,350 cm−1), Raman spectroscopy has been used extensively to characterize the structural features of carbonaceous matters since 1970. Coal is a complex organic compound made up mainly by carbon showing characteristic Raman bands. This article reviews the application of Raman spectroscopy for coal structure characterization under room temperature, to determine its chemical structure, crystallite size, coal rank, and combustion reactivity. Future research for collecting Raman spectra during coal pyrolysis at high temperatures is also discussed. The combination of high‐temperature hot stage with Raman spectroscopy technology allows direct collection of Raman spectra at high temperature. [ABSTRACT FROM AUTHOR]

Accurate expansion data for CO 2 in petroleum model compounds (e.g., alkanes, cycloalkanes and aromatics) are fundamental information for CO 2 sequestration and enhanced oil recovery in oil reservoir. In this study, the volume expansion of the CO 2  + octane mixture was measured using a fused silica capillary cell with in situ Raman spectroscopy. A section of water was loaded between octane and CO 2 in the fused capillary tube to seal the octane whilst allowing the diffusion of CO 2 into the octane. Raman spectroscopy was applied during our experiments to verify that the CO 2  + octane mixture reached phase equilibrium. Moreover, a good quadratic relationship was observed between the Raman peak intensity ratio and volume expansion factor. It was verified that this method can be used not only just to obtain more accurate experimental data, but also to protract additional volume expansion factor curves or curved surfaces from measured Raman peak intensity ratio using this equation. Over an extended temperature and pressure range, this method was thus shown to be more efficient and accurate than the traditional pressure–volume–temperature methods. [ABSTRACT FROM AUTHOR]

Hot compressed water (HCW), with its unique properties, is regarded as a promising solvent for industrial applications. A number of methods to measure the solubility of hydrophobic organic compounds (HOCs) in HCW have been reported. However, these methods were conducted in large-scale stainless-steel reactors, and few included an in situ study regarding the dissolution mechanism of HOCs in HCW during the solubility determination process. In this study, a fused silica capillary reactor in combination with Raman spectroscopy was applied to investigate phase changes, determine the solubility, and study the dissolution mechanism of 1,2-dichlorobenzene in HCW. The total dissolution process of 1,2-dichlorobenzene in HCW was observed under a microscope, and the images were recorded continuously using a digital camera. Raman spectroscopy was used to confirm the homogeneity of the 1,2-dichlorobenzene solution during dissolution. The solubility of 1,2-dichlorobenzene increased from 35.9 to 85.7 mg g−1 in water with increasing temperature from 256.7 to 294.1 °C. Furthermore, the dissolution mechanism of 1,2-dichlorobenzene in HCW is proposed based on the Raman spectra of 1,2-dichlorobenzene and water during the dissolution process in the fused silica capillary reactor. The breakage of the fully hydrogen-bonded (tetrahedral) configuration and the consequent change in the static dielectric constant of water are deemed to be compelling reasons for the high solubility of 1,2-dichlorobenzene in HCW. Our experimental method exhibits great potential for determining the solubility of HOCs in HCW and for investigating their dissolution behavior and dissolution mechanism at elevated pressure and temperature conditions. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Significance The solubilities of hydrophobic organic compounds (HOCs) in hot compressed water (HCW) were measured using an optically transparent fused silica capillary reactor (FSCR). The total dissolution temperatures of HOCs in HCW were determined visually; the solution homogeneity in the FSCR during HOCs dissolution was checked using Raman spectroscopy. The solubility of 2,4-dichlorotoluene increased linearly with increasing temperature in the range of 266.3-302.4°C. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2721-2725, 2013 [ABSTRACT FROM AUTHOR]

Abstract: The uncatalyzed hydrolysis of carbon tetrachloride (CCl4) in hot compressed water (HCW) in a fused silica capillary reactor (FSCR) was investigated with in situ Raman spectroscopy at reaction temperatures up to 300°C. The phase behavior of CCl4 in water during heating at 34.1–260.0°C was observed by a microscope, and images were recorded with a digital camera. The phase phenomena showed that the CCl4 gasified between 231.3 and 260.0°C during the heating process. The hydrolysis was monitored by tracking the in situ vapor-phase Raman signals for CCl4 and product CO2. Increases in the CO2 Raman peak area over time were correlated to the hydrolysis yield. The quenched liquid products were analyzed by gas chromatography–mass spectrometry and ion chromatography, and the results indicated that the only hydrolysis products were HCl and CO2. The effect of the gasified CCl4 initial concentration (0.076–0.145g/cm3), CCl4(l):H2O(l) volume ratio (1:2, 1:6, 1:10), and reaction temperature (240–300°C) on the hydrolysis rate was investigated. The CCl4 hydrolysis in the FSCR was found to be mainly a vapor phase reaction. Temperature was the prime determining factor for the hydrolysis rate. The CCl4 hydrolysis rate was also dependent on the initial concentration of vapor-phase CCl4 and the initial CCl4(l):H2O(l) volume ratio. The kinetics of CO2 formation was analyzed, and the result showed that it followed the first order with an activation energy of 95.06±6.71kJmol−1. [Copyright &y& Elsevier]

Graphical abstract Highlights • O 2 and CO 2 were quantitatively and qualitatively analyzed by Raman spectroscopy. • The mineralization rate of o-DCB was evaluated with Raman peak height of CO 2. • O 2 demand and consumption were described during the reaction process. • The kinetic analysis was performed on the oxidation process of o-DCB. Abstract A fused quartz tube reactor (FQTR) and Raman spectroscopy were employed to investigate the decomposition of H 2 O 2 and o-dichlorobenzene (o-DCB) in hot compressed water (HCW). The results showed that o-DCB can be effectively degraded in HCW, and exhibited applicability as a powerful tool to quantitatively and qualitatively analyze O 2 and CO 2 using Raman spectroscopy combined with an FQTR. The decomposition rate of H 2 O 2 reached 95.4% at 8 min, and it completely decomposed after 23 min at 400 °C in the closed heating system. When the oxygen stoichiometric ratio (OSR) increased from 50% to 200% after 90 min at 400 °C, the degradation rate of o-DCB significantly increased from 67.5% to 100%. The conversion data for the kinetic analysis of o-DCB indicated that the reaction followed pseudo first-order kinetics and exhibited reaction rate constants of k 0.5 = 0.00782 s−1, k 1.0 = 0.01412 s−1, k 1.5 = 0.02675 s−1, and k 2.0 = 0.03509 s−1, respectively. [ABSTRACT FROM AUTHOR]

To ascertain the reaction variables on o -chloroaniline (o -ClA) mineralization, total nitrogen (TN) removal rate, and N-species distribution, o -ClA was subjected to catalytic supercritical water oxidation (CSCWO) in a fused quartz tube reactor (FQTR). The findings demonstrated that when the temperature, reaction time, and excess oxidant were 400 °C, 90 min, and 150%, respectively, the mineralization rate of o -ClA could reach more than 95%. Moreover, potential degradation pathways of o -ClA in supercritical water oxidation (SCWO) was proposed according to the GC-MS results. TN removal rate is significantly impacted by Ru/rGO, despite the fact that its catalytic effect on the mineralization of o -ClA was not particularly noteworthy. Compared with no catalyst, the TN removal rate of o -ClA obviously increased from 44.1% to 90.3% at 400 °C, 10 wt% Ru loading, 90 min and 200% excess oxidant. In addition, N-species distribution in SCWO and CSCWO were also investigated. Results indicated that the Ru/rGO catalyst could accelerate the oxidation of ammonia-N and convert it to nitrate-N, promoting N 2 generation. Finally, the possible N transformation pathway in CSCWO of o -ClA was proposed. As a result, this work offers fundamental information about o -ClA catalytic oxidation removal in the SCWO process. [Display omitted] • CSCWO of o -ClA was investigated in a FQTR coupled with Raman spectroscopy system. • The potential degradation pathways of o -ClA in SCWO was proposed. • Ru/rGO has a significant effect on the removal rate of TN. • Ru/rGO accelerate the oxidation of ammonia-N to nitrate-N, promoting N 2 generation. • Possible nitrogen transformation pathway in CSCWO of o -ClA was proposed. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the effects of different concentrations of camellia tea oil on surimi gel physicochemical properties and protein secondary structure. With the increase of camellia tea oil concentration (0–8 g/100 g of surimi), surimi gel hardness, whiteness, WHC, overall acceptability, storage modulus (G′) and the indexes of ionic bonds and hydrophobic interactions were increased significantly (P < 0.05). Cryo-scanning electron microscopy (Cryo-SEM) showed that the oil occupied the void spaces of the protein matrix and formed a firmer structure. The Raman spectroscopy study showed that there was a decreased trend in α-helix content and increased trend in β-sheet content in surimi protein as the oil content increased. Correlation analysis showed that the hardness was negatively correlated to the α-helix content (r = −0.958, P < 0.01) and positively correlated to the β-sheet content (r = 0.958, P < 0.01) and hydrophobic interactions (r = 0.944, P < 0.01) of surimi gels. These results suggest that the presence of the oil could change the micro-environment and molecular structure of surimi proteins and further affect the physicochemical properties of surimi gels. In general, when the concentration of camellia tea oil was 8 g/100 g of surimi, the surimi gel showed the most favorable properties. [ABSTRACT FROM AUTHOR]

This work developed a new method for measuring the volume expansion of a CO 2 + n -dodecane mixture, using a fused silica capillary cell (FSCC), combined with a heating-cooling stage and a confocal Raman spectrometer. The cell was constructed on the micron scale to reduce the temperature gradient and reagent consumption. The results confirmed the feasibility of this method that using Raman spectra to verify phase equilibrium, a digital camera to record images of the CO 2 + n -dodecane mixture and a micrometer to measure the volume, a section of water (water seal) between n -dodecane and gas phase to prevent n -dodecane from evaporating. It was shown that the volume expansion factor of the mixture increased with pressure going from 1.0 to 10.0 MPa, but decreased as the temperature was raised from 30 to 80 °C. In addition, a positive quadratic relationship ( R 2 > 0.99) was obtained between Raman peak intensity ratio and volume expansion factor, such that more volume expansion factors could be obtained according to the equations with measured Raman peak intensity ratio data. This experiment widens the ranges of temperature and pressure in the measurements of the volume expansion, and provides more volume expansion data for CO 2 -enhanced oil recovery. [ABSTRACT FROM AUTHOR]

The solubility of 4-chlorotoluene in subcritical water was measured using an optically transparent fused silica capillary reactor (FSCR). The total dissolution temperature of 4-chlorotoluene in subcritical water was visually determined. The dissolution uniformity of 4-chlorotoluene in subcritical water was confirmed by Raman spectroscopy. The solubility of 4-chlorotoluene linearly increased with increasing temperature in the range 262.3–293.8 °C. The dissolution mechanism of 4-chlorotoluene in subcritical water is proposed based on the Raman spectra of 4-chlorotoluene and water during the dissolution process in the FSCR. [ABSTRACT FROM AUTHOR]

Abstract: Decomposition of 1,1,1-trichloroethane (TCA) in hot compressed water, with or without an oxidizer, was studied using an optically transparent anti-corrosive fused silica capillary reactor (FSCR), and Raman spectroscopy. The phase behavior of TCA in water during hydrolysis/oxidation was observed continuously under a microscope and recorded with a digital-camera/recording system, A new phase behavior of TCA was found in the presence of excess H2O2; TCA was first gasified during heating, followed by liquefaction under increasing internal pressure as a result of the formation of O2 from the decomposition of H2O2, and subsequently gasified again during further heating up to 400°C. The gaseous products of TCA oxidation in hot compressed water were monitored quantitatively and qualitatively using Raman spectroscopy. The effects of the operating parameters, namely the stoichiometric amount of oxidizer, temperature, and reaction time, were investigated. In our experiments, it was found that 100% CO2 yield was achieved with a 175% stoichiometric amount of H2O2 at 420°C after 360s. Temperature plays a key role in the decomposition of TCA and the formation of CO2 in the supercritical water oxidation (SCWO) process. Based on our results, a reaction mechanism for TCA decomposition in hot compressed water was proposed. The global reaction kinetics showed that the formation of CO2 in the SCWO of TCA was a first-order reaction. [Copyright &y& Elsevier]

Degradation of phenol by sodium persulfate (SPS) in hot compressed water (HCW) was investigated in a lab-built fused quartz tube reactor (FQTR) coupled with Raman spectroscopy system. The species of S 2 O 8 2−, SO 4 2−, HSO 4 −, SO 3 2− and HSO 3 − in the reaction system were qualitatively and quantitatively analyzed by Raman spectroscopy. The hydrothermal stability of phenol and SPS at different temperature and the degradation of phenol by SPS were also studied. The results indicated that phenol was not stable in aqueous solution above 200 °C, and that only SO 4 2− was generated in the hydrolysis of SPS at temperatures below 50 °C, and SO 4 2− and HSO 4 − were generated at higher temperatures. The maximum conversion rate (90.93%) and mineralization efficiency (38.88%) of phenol by SPS was obtained at reaction temperature of 300 °C with 180 min reaction time. During the degradation of phenol by SPS, HSO 4 − was the main product and S∗ (not detected by Raman spectroscopy) exhibits a positive correlation with temperature. In addition, a degradation pathway of phenol by SPS was proposed. The degradation data for the kinetic analysis indicated that the reaction followed pseudo first-order kinetics, and the reaction rate constants (k s) were given as k 50 °C = 0.0083 min−1, k 100 °C = 0.0197 min−1, k 200 °C = 0.0498 min−1, k 300 °C = 0.0619 min−1 and k 400 °C = 0.0505 min−1 at 30 min reaction. Moreover, the activation energy (12.580 kJ mol−1), the enthalpy change (9.064 kJ mol−1) and the entropy change (−222.104 J mol−1) of the reaction were also calculated. • A lab-built fused quartz tube reactor coupled with Raman spectroscopy system was developed. • Degradation of phenol by sodium persulfate in hot compressed water was investigated. • Hydrothermal stability and products distribution of phenol and SPS were discussed. • The fate of S during the degradation process was qualitative and quantitative analyzed by Raman. • A degradation pathway of phenol by SPS was proposed. [ABSTRACT FROM AUTHOR]