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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]

Depolymerization is a potentially viable means of recycling waste polymers, converting them back into monomers or other useful compounds. Terephthalic acid (TPA) and 1,4-butanediol (1,4-BD) are the depolymerization monomer products of polybutylene terephthalate. Their yields from depolymerization in hot compressed water (HCW) were previously found to be lower than reported theoretical values. Thus, the phase behavior, stability, and mechanism of monomers in HCW were investigated in a fused silica capillary reactor (FSCR) and a stainless steel autoclave reactor. Phase change observations showed that TPA was completely dissolved in water at 300°C, was relatively stable at 320 to 350°C, and that its recovery significantly decreased at temperatures above 350°C. The decomposition of TPA increased with increasing heating time. However, the recovery of 1,4-BD decreased rapidly with increasing temperature or heating time. A mechanism for the stability of TPA and 1,4-BD is proposed based on their depolymerization products. The products were quantified by Fourier transform-infrared spectroscopy, high-performance liquid chromatography, and gas chromatography coupled with mass spectrometry. The wall effect of the stainless steel autoclave promoted the decomposition of TPA and 1,4-BD in HCW. POLYM. ENG. SCI., 57:544-549, 2017. © 2016 Society of Plastics Engineers [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 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]

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]