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Co-pyrolysis of waste plastics and coal has been considered to be an environmentally friendly and scalable waste treatment technology. This study investigated the influence of polyvinyl chloride (PVC) on the physico-chemical structure and gasification performance of co-pyrolytic char with lignite (PZ) and bituminous (SM) coal. The structure characteristics were explored by applying an X-ray diffractometer and a specific surface area analyzer. The quantitative analysis on the influence of PVC on pore characteristics and carbon microcrystal structure was conducted by the fractal theory and deconvolution method. The gasification performance was explored using a thermogravimetric analyzer. When the PZ blending ratio was larger than 50%, the specific surface area of PVCPZ chars enlarged significantly due to the increment of mesopores. Nevertheless, the effect of SM on the pore structure was not pronounced, and the specific surface area of PVCSM chars was as small as PVC char. A higher PZ blending ratio benefited the formation of mesopores with an aperture smaller than 10 nm for PVCPZ chars, whereas SM had little influence on pore diameter distributions of PVCSM chars attributed to the remarkable coating effects. The values of fractal dimension of co-pyrolytic char were larger than PVC char, revealing that the adjunction of coal increased the pore surface coarseness and improved the complicacy of the pore structure. Quantitative analysis on XRD spectra indicated that the disorder extent of the carbon structure was improved because of coal addition, and the influence of lignite on the disorder degree of the carbon structure was more significant. The gasification reaction of co-pyrolytic char showed significant synergistic effects, resulting in the improvement of gasification performance.

Hydrothermal liquefaction of the third-generation biomass represented by microalgae can produce biocrude. However, the directly obtained biocrude has a high heteroatom content and a low higher heating value (HHV), which cannot meet the standards of biofuel. In this work, water-insoluble biocrude which was directly gained from microalgae hydrothermal liquefaction (HTL) was upgraded under four kinds of solvents (i.e., methanol, ethanol, acetone, and H₂O) and one type of catalyst (H₂O + Ru/C) at 240–400 °C for 1 h. The results show that the HHV and C and H contents of upgraded bio-oil increased and the O/C ratio decreased significantly after solvent upgrading. The highest upgraded bio-oil yield appeared in the case of ethanol upgrading and reached the maximum value of 82.8 wt % at 360 °C. The upgraded bio-oil yield of acetone upgrading increased from 45.8 to 68.2 wt % as the temperature increased within 240–400 °C. Also, esterification reactions between alcohol and acid in the supercritical system remarkably reduced the content of carboxyl-containing organic matter.

Temperature showed obvious effect on the reaction rate and conversion when CuO was used as an oxygen carrier (OC), in which in situ gasification chemical-looping combustion (iG-CLC) occurred at low...

The optimization and mechanism for oxidation of the waste anion exchange resin from the nuclear industry in supercritical water were investigated. To achieve the maximum chemical oxygen demand (COD...

The construction of cyclobutanes has attracted much attention because of its unique four-membered ring skeleton. Herein, we report the highly enantioselective direct vinylogous Michael reaction of β,γ-unsaturated pyrazole amides and nitroolefin using a squaramide catalyst. Cyclobutane derivatives were obtained by subsequent cyclization in good yields (up to 85%) with excellent enantioselectivities (up to 99% ee). Importantly, the large-scale reaction experiment confirmed the reliability of the vinylogous reaction. Furthermore, the synthetic utility of the vinylogous adducts and cyclobutane derivatives has been realized.

Corrosion continues to be a major challenge in developing supercritical water-cooled reactor and supercritical water oxidation system. Corrosion behaviors of candidate alloy materials used in these...

The corrosion behavior and mechanism of Inconel 600 exposed to the oxidizing high-salinity supercritical water (SCW) containing chlorides, sulfates, and phosphates at 450, 500, and 580 °C were investigated and proposed. The corrosion film had an outer layer dominated by NiO, Fe₂O₃, and eutectic phosphate deposit and an inner layer consisting of Cr-rich oxides. Some produced oxides may generate ionic reactions with the low-melting phosphates precipitated out from SCW, triggering the generation of the eutectic FePO₄–Ni₃(PO₄)₂–Na₃PO₄–Na₂HPO₄ salts in the outer layer. The formation and thickening of the outer layer results from the eutectic phosphate disposition and the common solid-state growth mechanism. Nonmolten chlorides and sulfates in SCW predominantly exist on the outmost surface and are easily washed off, being supported by the absence of S and Cl on sample surfaces. Based on this investigation, a comprehensive corrosion mechanism, involving the solid-state growth of oxide scales, salt precipitation, and phosphate melting processes, was proposed and discussed.

This study investigated the optimum operating conditions on hydrothermal liquefaction (HTL) for the production of biocrude oil from animal carcass. HTL experiments were carried out at various reaction temperatures (230−350 °C), residence times (10−80 min), solid concentrations (5−20 wt%), and pressures (15−30 MPa). Detailed chemical composition analysis of biocrude oil was performed by gas chromatography-mass spectrometry, Fourier transform infrared spectroscopic analysis, and element analysis. The results showed that the biocrude oil was composed of fatty acids, hydrocarbons, amides, esters, and N-heterocyclic compounds. The maximum biocrude oil yield of 55.6 wt% was obtained at 320 °C, 10 wt% solid concentration for a residence time of 60 min. Pressure imparts little on the yield of biocrude oil. The higher heating value of the biocrude oil ranging from 39.7 to 42.5 MJ·kg−1 was comparable to that of petroleum crude (42.9 MJ·kg−1). What is more, the general reaction pathways for HTL of animal carcass was...

Nano/micro crystalline copper is widely used in catalysts and it has potential for being used as conductive additive to ink for inkjet printed electronics. Copper is attractive, because it has excellent electrical conductivity and low cost compared to noble metals. The nucleation and phase transitions from the precursor to the final micrometer sized Cu in supercritical methanol have been studied for the first time using in-house in situ powder X-ray diffraction (PXRD). Temperatures have a significant impact on the reduction process of Cu2+, at low synthesis temperature (250 °C), it was observed how the Cu2+ precursor initially formed copper hydroxy nitrate (Cu2(OH)3NO3) and transformed to copper(II)oxide (CuO) i.e no reduction took place. At 300 °C multiple phase transformation could be observed from initial copper hydroxy nitrate to zero-valent copper, the in situ investigations reveal the following reaction scheme; CuII2(OH)3NO3 → CuIIO → CuI2O → Cu0. Increasing the synthesis temperature causes the pure Cu0 to form much faster; at 350 °C, it takes 8.7 min to produce phase pure Cu0, while at 450 °C, the formation takes ∼0.7 min. Increasing the initial concentration of Cu2+ in the precursor causes formation of larger Cu0 crystallites in the final product. Finally, the in situ observations were used as guidance for making Cu0 using a supercritical flow setup.

Supercritical water oxidation is a promising alternative for treatment of wastewater and sludge. The addition of auxiliary fuel can achieve the optimization of the system. Owing to the discrepancy ...

Hydrothermal liquefaction of microalgae produces water-insoluble biocrude that spontaneously separates from aqueous phase by gravity. A small proportion of water-soluble biocrude can be obtained via organic solvent extraction from the aqueous phase. This work explored catalytic hydrothermal upgrading of the water-soluble biocrude with five varieties of catalysts (i.e., Pt/C, Pd/C, Ru/C, Pt/C + Pd/C, and newly synthesized CoNiMoW/γ-Al2O3) for the first time. The results show that the upgraded oil by Pt/C had the highest yield and energy recovery but the second lowest quality with respect to elemental composition and heating value. Pd/C led to the highest heating value and the lowest yield and energy recovery of upgraded oil, as well as the largest yields of CH4 and C2H6 simultaneously. Both Pt/C and CoNiMoW/γ-Al2O3 performed well in converting high-boiling-point macromolecules into smaller molecular compounds in water-soluble biocrude upgrading. More than 70% of components in upgraded oils were in the dist...

Reactor corrosion and plugging problems severely hinder commercial application of supercritical water oxidation. A transpiring wall reactor can overcome these two problems by forming a protective water film on the inner surface of a porous transpiring wall to isolate corrosive substances and inorganic salt. This work proposed water film coverage rate and inorganic salt concentration in water film as evaluation indexes of water film characteristics. A computational fluid dynamics model of a new transpiring wall reactor was built to explore the characteristics of water film under key operating parameter conditions by numerical simulation together with experiment validations. The results show that water film coverage rate raised either with transpiration intensity and transpiration water temperature increasing or with feedstock flow rate and feedstock preheating temperature decreasing. Inorganic salt concentration in water film declined as transpiration intensity and transpiration length increased. Two equat...

Copper(II) oxide ultrafine particles are of great interest as a new material for multiple applications. This paper expounds the synthesis and characterization of copper(II) oxide submicrometer particles formed by a facile and simple supercritical hydrothermal synthesis method. The copper(II) nitrate, copper salt, was used as a precursor aqueous solution heated by a preheated sand bath to reach supercritical conditions. The effects of process operating parameters, such as temperature, pressure, the addition of sodium hydroxide, and precursor concentrations on the morphology and the size of copper(II) oxide submicrometer particles have been investigated. The copper(II) oxide particles formed, with particle sizes of ca. 100 nm, were hexagon-flake-like and spindle-like and free of impurities. The average particle size decreased with the increase of temperature under subcritical conditions and decrease of pressure. It decreased with the increase of precursor concentration at lower concentration conditions and ...

Hydrothermal flame is a promising solution for problems in the preheating process of supercritical water oxidation (SCWO) technology. A detailed chemical kinetics coupled with a simple flow model is developed and validated to reflect the characteristic of hydrothermal flame. Analysis of free radicals accumulation show that the high quantity of free radicals induced by high methanol concentration leads to ignition. A method to approach the ignition temperature through ignition delay time calculation with a specific reactor model is proposed, which shows good agreement with the existing experimental data and directs further design quantitatively. Extinction limits are discussed by laminar flame speed and the perfect stirred reactor (PSR) model comparatively. Ultimate extinction temperatures of different methanol concentrations are approached and suggest the possible improvement of hydrothermal flame stability at higher methanol concentration through flow field optimization.

Liquid foam, as a complex fluid, provides an observable prototype for studying a discrete fluid system. In this work, a numerical study on the settling behavior of a round particle in wet polydisperse foam has been conducted on the bubble scale. The local and nonuniform distribution of bubble pressure, as well as the localized plastic events, is presented. It shows a foam region of higher pressure in front of the settling particle due to the extrusion deformation of the bubbles applied by the particle. Additionally, the forces exerted on the particle by the disordered wet foam are measured during the sedimentation. It exhibits in particular a power-law dependence of the drag force caused by the bubble as a function of the foam quality. Moreover, sedimentation experiments are demonstrated to verify this power-law relation. The evolution of the components of drag force is demonstrated when a plastic event occurs in front of the settling particle. The result shows that both the contributions of the pulling force of foam films and the bubble pressure to the drag force decrease in that case. Likewise, the variation of both these contributions to the drag force is illustrated as well when a bubble in the wake detaches from the particle. These results assist in understanding the mesoscopic response of wet foam to a settling particle.

Co-pyrolytic technology of plastic wastes and coal has been widely studied as a promising method to dispose of plastic wastes. Evaluation on pyrolytic behavior and product properties is important for optimizing this technology. In this work, pyrolytic behavior of poly(vinyl chloride) (PVC) blended with two typical coals from northern China (Pingzhuang lignite and Shenmu bituminous) was investigated by applying a nonisothermal thermogravimetric analyzer. Furthermore, scanning electron microscopy technique (SEM) was applied to explore the surface morphology of residual chars. Thermal analysis curves of PVC/coal blends showed nonadditivity performance meaning the existence of synergistic effects between PVC and coal during co-pyrolysis. Negative synergistic effects were observed in the temperature below about 370 °C, whereas positive synergistic effects happened at high temperature. In the final pyrolytic temperature, the formation of volatiles was promoted due to synergistic effects. In addition, isoconvers...

Co-pyrolysis of the coal blend with lignocellulosic biomass has a significant influence on final product composition of co-gasification and co-combustion. Successful evaluation of the product distribution during co-pyrolysis is very important to understand the overall co-thermochemical process. In this paper, product distribution, especially the gaseous product evolution during a kind of bituminous coal from northern of China blended with lignocellulosic biomass, major model components (cellulose, hemicellulose, and lignin) were explored in a drop-tube furnace from 600 to 1000 °C. The addition of three model components showed different synergistic effects in the product yields and gaseous product composition. Positive synergistic effects in the gas and tar yields were observed during co-pyrolysis of bituminous coal and cellulose, indicating that the addition of cellulose promoted the formation of volatile products. On the contrary, gas yields from co-pyrolysis of bituminous and lignin mixtures showed a ne...

Co-pyrolysis of coal and lignocellulosic biomass has the potential to mitigate the emission of greenhouse gases from an energy supply. Successful application of this technology requires proper inve...

The mixing process of metal salt solutions and supercritical water is essential to supercritical water hydrothermal synthesis (SWHS) to produce nanoparticles. A computational fluid dynamics (CFD) model was developed for predicting mixing efficiency and crystallization kinetics in SWHS mixers. The mixing efficiency was calculated from the micromixing model, and the kinetics model of crystallization was built from the population balance equation. The effects of the fluid dynamics of mixing (Reynolds number and mixer diameter) on the mixing efficiency and crystallization kinetics (nucleation rate and growth rate) were investigated. The results showed that faster mixing can lead to a higher crystallization rate and the production of smaller particles with a narrower particle size distribution.

The Ni-based alloys Incoloy 800, Incoloy 825, Inconel 625, and Hastelloy C-276 exposed to subcritical water (350 °C, 25 MPa) and supercritical water (450 °C, 25 MPa) with high concentrations of chloride and oxygen were analyzed by using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. There is a strong synergistic effect between salt and oxygen, leading to severe corrosion. The selective dissolution of nickel is the severest of all alloying elements, and a stable oxide in oxidizing condition is formed by chromium. Molybdenum improves the resistance to pitting corrosion when chromium is present. Without molybdenum, Incoloy 800 exhibits the severest pitting corrosion of the test alloys under subcritical condition. Inconel 625 and Hastelloy C-276 exhibit good corrosion resistance under the condition of oxygen and salt existing. NiO, NiCr2O4, and Cr2O3 are the three main components of oxide films on Ni-based alloys. The possible corrosion mechanisms of Ni-based alloys are...

Methanol acting as a co-oxidation component was introduced in supercritical water oxidation experiments of acetic acid and phenol which were identified as the most common and refractory intermediates during supercritical water oxidation of many complex organics. Experiments were performed in a tubular flow reactor at 25 ± 0.5 MPa. The concentrations of acetic acid and phenol were constant at 0.17 and 0.067 mol/L, respectively, with varying methanol concentrations ranging from 0.0313 to 0.6563 mol/L. Computational simulations based on the elementary reaction model for the supercritical water oxidation of two binary mixtures were also carried out to understand the co-oxidation mechanism of methanol for these two compounds. For the binary mixture of methanol/acetic acid, the experimental results showed that the acetic acid conversions in the mixture were higher than those in the absence of methanol, and as the methanol concentration increased, the accelerating effect was more notable. For the methanol/phenol...

Lurgi coal-gasification wastewater was degraded in supercritical water using Mn2O3, Co2O3, and CuO as catalysts. The experiments were performed in a batch reactor at temperatures of 380–460 °C and oxygen ratios of 1.5–3.5. The results involved evaluation of TOC and NH3–N removal efficiencies; detection of the main products in the effluent; XRD, SEM, and BET analyses of the catalysts; and detection of metal ions leached from the catalysts. Maximum TOC and NH3–N removals were found with Co2O3 catalyst at 460 °C and OR = 3.5. The effluent quality could meet class-I criteria of the Integrated Wastewater Discharge Standard (GB 8978-1996). The catalytic effects on pollutant removal were in the order Co2O3 > Mn2O3 > CuO. The major phase of Mn2O3 transformed into MnO2 with a decreasing BET surface area at 460 °C and an oxygen ratio of 3.5. Serious Cu-ion leaching occurred during the process and intensified with increasing temperature.

Abatement of aniline in supercritical water was explored in a tubular-flow reactor using oxygen as the oxidant. The effects of the reaction temperature, oxidant stoichiometric ratio, residence time, and initial aniline concentration on the product distribution were investigated. Aniline was primarily hydrolyzed to phenol and ammonia, and thereby, abatement of aniline was converted into the co-oxidation of phenol and ammonia in supercritical water. Phenol was the main carbon-containing intermediate, and ammonia was the exclusive nitrogen-containing intermediate on the pathway to the end products N2, N2O, and NO3–. Owing to the adsorption of aniline and catalysis on the reactor wall (made of Hastelloy C-276), the disappearance of ammonia during aniline supercritical water oxidation (SCWO) was markedly faster than that during SCWO of ammonia alone. Ammonia was mainly converted to N2 (heterogeneous mechanism), and low levels of N2O and NO3– were also produced (homogeneous mechanism).

Chemical looping combustion (CLC) of coal was conducted with 12 CuO-based oxygen carriers supported on SiO2, Al2O3, TiO2, and ZrO2 prepared by mechanical mixing. The influence of an inert support and the effect of particle size on the reactivity of CuO-based oxygen carrier particles were studied. Five mixed oxide oxygen carriers composed of different amounts of CuO and Fe2O3 on TiO2 were prepared to study the synergistic effect between two active metallic oxides. It was found that CuO-based oxygen carriers showed high reactivity in redox reactions. The onset temperature of the reduction reaction decreased when TiO2 was added as an inert support. The particles of CuXTi950 showed the highest reactivity to convert the coal. Although the smaller particle size of the oxygen carrier can enhance the coal conversion, it also makes it more difficult in the separation of the oxygen carrier from fly ash and unburned carbon. For mixed oxygen carriers, the synergistic effect between different active oxides was observe...

Phenol, a substance difficult to be gasified, is often an intermediate product from biomass gasification in supercritical water. In this study, 1 wt % phenol is gasified in supercritical water with...