Search

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]

Abstract: The co-liquefaction of coal and polypropylene or polystyrene in hot compressed water was carried out in a 50mL batch stainless steel autoclave reactor. The effects of the polymer ratios by weight (10–40%), reaction temperatures (360–430°C), and reaction time (30–120min) were investigated. The main products were analyzed qualitatively by Fourier transform infrared spectroscopy and high-performance liquid chromatography. The results showed that the synergistic effect was demonstrated and the polymer stimulated coal liquefaction as a hydrogen donor during co-liquefaction in hot compressed water. The reaction temperature was the critical factor because the process of oil and gas generating by hydro-cracking, ring-opening and hydrogenation clearly occurred above 400°C and the conversion and yield of oil and gas reached a maximum of 75.92% and 69.11% at 420°C, respectively. The phase behavior during co-liquefaction in a fused-silica capillary reactor was recorded by a microscope during the heating and cooling processes, demonstrating that polypropylene melted to form a liquid phase as the reaction medium and hydrogen donor during co-liquefaction. [Copyright &y& Elsevier]

Abstract: Poly(trimethylene terephthalate) (PTT) was depolymerized in hot compressed water (HCW) using a fused-silica capillary reactor (FSCR) and a batch-type autoclave reactor. The phase behavior of PTT in water during the heating, reaction, and cooling processes was observed in an FSCR with a microscope and recorded by a digital camera. It was found that PTT can dissolve in water in a temperature range of 240–320 °C and form a homogeneous aqueous solution. The effects of the reaction temperature (240–320 °C) and reaction time (5–60 min) were evaluated in a batch-type autoclave reactor. The main depolymerization products of PTT were terephthalic acid (TPA) and 1,3-propanediol (1,3-PDO), which were identified by liquid chromatography mass spectrometry, Fourier-transform infrared spectroscopy, gas chromatography mass spectrometry, Raman spectroscopy, and quantified by high-performance liquid chromatography as well as gas chromatography. Additionally, it was found that 1,3-PDO was converted to 1,5-dioxocane partly in the presence of TPA. Under optimal reaction conditions, i.e. 300 °C, 15 min, with a water/PTT ratio of 8:1 (w/w), complete depolymerization was achieved, and the yields of TPA and 1,3-PDO reached 90.5% and 69.03%, respectively. Based on the results, a reaction mechanism for PTT depolymerization in HCW was proposed. [Copyright &y& Elsevier]

Abstract: Zinc acetate (Zn(Ac)2) catalyzed depolymerization of polyethylene terephthalate (PET) in hot compressed water (HCW) was carried out in a batch autoclave reactor, as a potential method for chemical recycling of waste PET. The effects of the ratio of Zn(Ac)2 to PET (0–3%), temperature (220–300°C), and reaction time (5–60min) were investigated. The optimal conditions for complete catalytic depolymerization of PET were temperature 240°C, pressure 3.2MPa, reaction time 30min, and Zn(Ac)2/PET ratio 1.5%. The main products of catalytic depolymerization were identified and quantified as terephthalic acid and ethylene glycol by Fourier-transform infrared spectroscopy, high-performance liquid chromatography, gas chromatography/mass spectrometry, and gas chromatography. The maximum yield of terephthalic acid reached 90.5%. The phase behavior of PET with or without a catalyst in water during heating and cooling was studied in a fused-silica capillary reactor. According to the phase change data, the temperature of PET dissolution in HCW to form a homogeneous aqueous solution was decreased by adding Zn(Ac)2. [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]

• Catalytic oxidation of o -ClA and nitrogen transformation in HCW were investigated. • A flexible micro-reactor platform consist of FQTR and Raman spectroscopy was developed. • Mn 2 O 3 improved the degradtion of ammonia-N and inhibited the production of nitrate-N. • o -Chlorophenol was the main intermediate product of o -ClA in HCWO process. • The potential degradation pathway of o -ClA was proposed. Catalytic oxidation of o -chloroaniline (o- ClA) in hot compressed water (HCW) was investigated in a fused quartz tube reactor (FQTR) to determine the effects of catalyst, temperature, oxygen stoichiometric ratio (OSR) and reaction time on o- ClA mineralization, total nitrogen (TN) removal rate and nitrogen-containing products distribution. The results showed that o -ClA can be effectively degraded in HCW. With the increased of OSR, retention time and temperature or added of Mn 2 O 3 as catalyst, the mineralization rate of o -ClA and the removal rate of TN increased. Ammonia-N was the main nitrogen-containing intermediate product of o -ClA degradation, however, when the oxidant was excessive, ammonia-N was oxidized to form nitrate-N. Althought the catalytic effect of Mn 2 O 3 on the mineralization of o -ClA was not outstanding, it promoted the removal of ammonia-N from the benzene ring, improved the degradtion of ammonia-N, and inhibited the production of nitrate-N. GC–MS analyzed results indicated that o -chlorophenol was the main degradation intermediate product of o -ClA in HCWO process. Meanwhile, the potential degradation pathway of o -ClA was proposed. This work thus provides basic knowledge about o -ClA catalytic oxidation removal in HCW process. [ABSTRACT FROM AUTHOR]

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]