Subcritical Hydrothermal Conditions Research Articles

Research on a harmless treatment method for oily sludge in coal chemical wastewater and the pollutant transformation mechanism of oily sludge during the treatment process

This study developed an ultrasound synergistic subcritical hydrothermal treatment method (U-SHT) to address the challenges posed by the high oil and water content, complex composition, and hazardous nature of oily sludge (OS) generated during the pretreatment of coal chemical wastewater. The study investigated the efficiency of this method for the harmless disposal and resource recovery of OS, and the migration-transformation mechanism of hazardous organic pollutants in OS. The findings revealed that U-SHT achieved a removal efficiency of chemical oxygen demand in OS of 91.16 %, an oil resource recovery efficiency of 96.60 %, and a residual oil rate of 0.28 %, meeting API emission standards. Further research indicated that the solubilizing effect of the surfactant on the oil enhanced the demulsifying effect of ultrasonic cavitation on the emulsified structure of OS, enabling ultrasound to efficiently release and disperse pollutants within OS. This promoted the decomposition and transformation of pollutants under subcritical hydrothermal conditions, with synergistic removal efficiencies for typical pollutants such as long-chain alkanes, polycyclic aromatic hydrocarbons, and phenols reaching 96.61 %, 97.63 %, and 97.76 %, respectively. Economic evaluation indicated that the cost of OS treatment was $29.66/m3, significantly lower than existing methods, demonstrating promising practical application prospects.

Extraction of valuable metals from waste lithium iron phosphate batteries by subcritical water leaching method with synergistic waste polyvinyl chloride

In this paper, the effect of leaching valuable metals from waste lithium iron phosphate (LiFePO4) using waste polyvinyl chloride (PVC) as a source of hydrochloric acid under subcritical water treatment conditions was investigated. The effects of various parameters including temperature, reaction time, PVC/LiFePO4 mass ratio, and solid-to-liquid ratio on metal leaching were investigated. The results showed that the leaching of metals and dechlorination of PVC could be achieved simultaneously under subcritical hydrothermal conditions. The solid residues were analyzed using XRD, XPS and SEM-EDS elemental mapping to identify the compounds in the leached solids. ICP-OES analysis showed that optimal reaction conditions, including a temperature of 275 °C, a reaction time of 120 min, a PVC/ LiFePO4 mass ratio of 3:2, and a solid/liquid ratio of 1:10 (g/mL), could effectively leach 99.10 % of Li and 83.12 % Fe. Finally, the Li in the leachate was recovered in the form of Li3PO4 by precipitation. These findings suggest that subcritical water synergistic waste PVC technology is a promising and eco-friendly method to recover Li and Fe from waste lithium iron phosphate.

Thermal conversion of blended food production waste and municipal sewage sludge to recoverable products

Renewable fuels are necessary energy sources as bio-based combustible fuels can be utilized in existing infrastructure while lowering the dependence on petrochemical based fuels. Current bio-fuels are predominantly crop-based which require tillable land, fertilizer, chemicals, irrigation, and fuel to cultivate the biomass feedstock. This study investigated the hydrothermal conversion of underutilized waste streams for biomass feedstock. This work blended municipal sewage sludge solids, poultry dissolved air flotation solids, and used cooking oil to form a waste slurry that was thermally converted to renewable fuel products. Blended waste processing provides flexibility and robustness in the future of bio-based fuels, and the authors believe this is the first documented hydrothermal processing of this specific blended waste. The waste slurry was heated under subcritical hydrothermal conditions, where solids were separated, and then heated in a second pressurized reaction to complete the thermal conversion process of wastes to recoverable products. Prior to processing, the blended waste slurry contained 8,490 kJ/kg (3,650 BTU/lb). Following processing, the recovered gas products contained 38,747 kJ/kg (16,658 BTU/lb) and 42% methane. The recovered renewable oil contained 40,468 kJ/kg (17,398 BTU/lb) and 0.012% ash. The effluent produced water was appraised for nutrient content and was found to contain 1,689 mg/L of nitrogen, which has potential as a liquid fertilizer product. The produced gas fuel, produced liquid fuel, solid char, and produced nutrient laden water were determined to be potential marketable products.

Exploring Potential Beryllium-free, Deep-Ultraviolet Optical Crystals in the Rare Earth Fluoride Carbonate–Water System

Rare earth fluoride carbonates have been proven to be potential deep-ultraviolet optical materials, but lacked the systematic study on phase stability domains to guide synthesis. In this work, detailed investigations of the Na2CO3–GdF3–H2O system have been done in subcritical hydrothermal conditions. A series of sodium-rare earth carbonates crystals NaGdCO3F2 (1), Na2GdCO3F3 (2), Na3Gd(CO3)3 (3), and Na3Gd(CO3)3·6H2O (4) have been synthesized. NaGdCO3F2 (1) is composed of a three-dimensional (3-D) [GdCO3F2]− framework with Na+ as the charge balance cation. Na2GdCO3F3 (2) showed two-dimensional (2-D) [GdCO3F3]2– layers along the c-axis and further bridged by Na+ to form a 3-D framework. Na3Gd(CO3)3 (3) is made up of alternately stacked layers [Na(CO3)2]∞ along the a-axis and [Na2Gd(CO3)2]∞ in the bc plane, forming a 3-D framework. Na3Gd(CO3)3·6H2O (4) exhibits an intricate 3-D structure composed of a [Gd(CO3)3(H2O)3]3– complex and bridging Na+ ions. The results from the UV–vis diffuse reflectance spectrosc...

ChemInform Abstract: Structural Modulation of Anionic Group Architectures by Cations to Optimize SHG Effects: A Facile Route to New NLO Materials in the ATCO3F (A: K, Rb; T: Zn, Cd) Series.

AbstractCrystals of KCdCO3F (I), RbCdCO3F (II), KZnCO3F (III), and RbZnCO3F (IV) are grown under subcritical hydrothermal conditions, using e.g. a 1:6:2 molar mixture of CdCl2, KF, and K2CO3 in H2O for KCdCO3F (autoclave, 220 °C, 5 d).

Structural Modulation of Anionic Group Architectures by Cations to Optimize SHG Effects: A Facile Route to New NLO Materials in the ATCO3F (A = K, Rb; T = Zn, Cd) Series

A new series of alkali-transition metal fluoride carbonates (KCdCO3F, RbCdCO3F, KZnCO3F, and RbZnCO3F) have been synthesized under subcritical hydrothermal conditions. All crystals are isostructural with the acentric space group P6c2 (188). They were structurally characterized by X-ray single crystal diffraction and exhibited the stacking of alternating [AF]∞(A = K, Rb) and [TCO3]∞(T = Zn, Cd) layers connecting adjacent layers by infinite T–F–T (T = Zn, Cd) chains parallel to c-axis. We found that all [TCO3](T = Zn, Cd) building units aligned perfectly parallel in any given layer, but the rotation from one layer to the next resulted in the nonparallel arrangement of [CO3] groups between two adjacent [TCO3]∞ (T = Zn, Cd) layers. In this work, the relative rotation of [CO3] groups between two successive layers was successfully controlled by introducing cations of different sizes into the structures, which led to different relative rotation angles of [CO3] groups, yielding varying second harmonic generation...

Preparation and hydrothermal corrosion behavior of Cf/SiCN and Cf/SiHfBCN ceramic matrix composites

Cf/SiCN and Cf/SiHfBCN-based ceramic matrix composites (CMC) were fabricated using the precursor infiltration and pyrolysis technique (PIP). Their behavior in subcritical hydrothermal conditions was investigated at 150–250°C using exposition times of 48, 96 and 240h and shown to rely on active corrosion.The data of the mass loss as a function of the corrosion time and temperature at S/V of 0.075 were used to rationalize the corrosion kinetics of the CMCs. Both materials have been shown to exhibit excellent stability in subcritical hydrothermal conditions. The corrosion rates of Cf/SiHfBCN were lower than those determined for Cf/SiCN; furthermore, SEM investigation indicates that spallation occurred in the Cf/SiCN samples; whereas the ceramic matrix was still attached on the individual carbon fibers in Cf/SiHfBCN. The results indicate that the incorporation of Hf and B into SiCN matrix leads to a significant improvement of its hydrothermal corrosion performance.

Lanthanum lead oxide hydroxide nitrates with a nonlinear optical effect.

Two new lanthanum lead oxide hydroxide nitrates with acentric structure, [LaPb8O(OH)10(H2O)](NO3)7 (1) and [LaPb8O(OH)10(H2O)](NO3)7·2H2O (2), have been prepared under subcritical hydrothermal conditions and crystallize in the space groups of Cc and P2(1)2(1)2(1), respectively. The crystal structure of compound 1 consists of the novel [LaPb8O(OH)10(H2O)](7+) clusters regularly arranged along the ab plane with nitrate ions as the counterions around the clusters by Pb-O bonds, developing into a three-dimensional net framework, while the structure of compound 2 is composed of [LaPb8O(OH)10(H2O)](7+) clusters and [NO3](-) groups as the bridging groups, forming a three-dimensional net framework with crystallized water molecules filling in the gaps. The experiments confirmed that compound 1 is the residue of compound 2 after efflorenscence. Besides, the [LaPb8O(OH)10(H2O)](7+) clusters present mirror symmetry in structures of the two compounds. The second-harmonic-generation (SHG) measurements for the two nitrates indicate that the SHG responses for compounds 1 and 2 are 1.3 and 1.1 times that of KH2PO4, respectively. Theoretical calculations confirmed that the SHG efficiency of compounds 1 and 2 mainly arises from the NO3(-) groups in the structure.

ChemInform Abstract: Syntheses, Characterization and Nonlinear Optical Properties of Sodium—Scandium Carbonate Na5Sc(CO3)4·2H2O.

AbstractNa5Sc(CO3)4·2H2O (I) is prepared under subcritical hydrothermal conditions using stoichiometric amounts of Na2CO3, NaF, and Sc(NO3)3 (autoclave, 22 °C, 5 d, 91% yield).

ChemInform Abstract: Series of Lead Oxide Hydroxide Nitrates Obtained by Adjusting the pH Values of the Reaction Systems.

AbstractPb(II) oxide hydroxide nitrates are prepared under subcritical hydrothermal conditions by adjusting the pH values of the Pb(NO3)2—NaOH reaction system.

Alternative Solid Fuel Production from Paper Sludge Employing Hydrothermal Treatment

This paper aims to investigate the alternative solid fuel production from paper sludge employing hydrothermal treatment (HTT) in a lab-scale facility for implementation of the pilot-scale plant. The paper sludge was subjected to the HTT under subcritical hydrothermal conditions. In the lab-scale experiment, the temperature conditions were 180 °C, 200 °C, 220 °C, and 240 °C, respectively, while it was 197 °C in the pilot plant as the optimum condition. The holding time was 30 min in both cases. The hydrothermally produced solid fuel was evaluated for the fuel property, the water removal performance, and the mass distribution. Furthermore, the energy balance of the process was studied. The higher heating value of the HT pretreated paper sludge was slightly improved. In addition, the produced solid fuel had comparable H/C and O/C atomic ratios with that of coal, indicating the presence of carbonization during the HTT process. Using the mechanical dewatering, only 4.1% of moisture in the raw paper sludge can be removed while the solid fuel production from paper sludge by HTT at 200 °C showed 19.5% moisture reduction. According to the energy balance of the pilot plant, the recovered energy was significantly higher than the energy input, showing the feasibility of employing the HTT to produce alternative solid fuel from paper sludge.

Sodium–rare earth carbonates with shorite structure and large second harmonic generation response

Two non-linear optical crystalline carbonates (Na3Y(CO3)3 and Na3Gd(CO3)3) were synthesized under subcritical hydrothermal conditions, and both of them crystallized in the non-centrosymmetric space group Ama2 (40). Their crystal structures, analogous to shorite, can be described as alternate stackings of [Na(CO3)2]∞ and [Na2RE(CO3)2]∞ (RE = Y, Gd) layers, which are parallel to the bc plane. Second harmonic generation (SHG) studies indicated that Na3Y(CO3)3 and Na3Gd(CO3)3 have large SHG responses of approximately 3.57 and 3.54 times that of KH2PO4 (KDP), respectively, and the SHG responses were phase-matchable in the visible region. Furthermore, they exhibited wide transparent regions from UV to near IR with short UV cut-off edges at about 220 nm, suggesting that these crystals are promising UV non-linear optical (NLO) materials.

Rapid and continuous synthesis of cobalt aluminate nanoparticles under subcritical hydrothermal conditions with in-situ surface modification

The synthesis and in-situ organic surface modification of spinel cobalt aluminate nanoparticles were carried out under subcritical reducing hydrothermal conditions (250°C, 30MPa). Single nanoparticles of cobalt aluminate were obtained using a continuous flow-type reactor; in contrast, Co1−xAlx layered double hydroxide (Co-Al-LDHs) became the main product when a batch-type reactor was used. The addition of a surface modifier, hexanoic acid, to the flow-type reaction system changed the hydrophilic surface of the nanoparticles to a hydrophobic surface. Cobalt aluminate nanoparticles modified with hexanoic acid were well dispersed in hexane. The in-situ surface modification during the synthesis of the nanoparticles reduced the particle size from 15nm to 10nm.

Phase stability regions in the Na 2CO 3[sbnd]YF 3[sbnd]H 2O system at 190 °C

Phase stability domains in the Na 2CO 3 YF 3 H 2O system are investigated in sub-critical hydrothermal conditions with microwave heating in Teflon lined autoclaves. At T = 190 °C , t = 1 h and P = 11 × 10 5 Pa , five phases are obtained for [YF 3] ⩽ 1.0 M and [ Na + ] / [ Y 3 + ] < 30 : NaY(CO 3)F 2, Na 2Y(CO 3)F 3, Na 3Y(CO 3) 2F 2, Na 2Y(CO 3) 2(OH,F), and Na 4Y(CO 3) 2F 3⋅H 2O. All phases are characterized by powder or single crystal X-ray diffraction, thermogravimetric or chemical analyses. NaY(CO 3)F 2 is the rare mineral horváthite. Na 2Y(CO 3)F 3, and Na 2Y(CO 3) 2(OH,F) are isostructural with Na 2Eu(CO 3)F 3 and Na 2Yb(CO 3) 2F, respectively; the Na 3Y(CO 3) 2F 2 and Na 4Y(CO 3) 2F 3⋅H 2O phases were still unknown. The average structure of Na 3Y(CO 3) 2F 2 is determined in the monoclinic P2 1/n space group with a = 7.047 ( 6 ) Å , b = 14.840 ( 3 ) Å , c = 7.192 ( 3 ) Å , β = 113.32 ( 5 ) ° ; V = 690.7 ( 6 ) Å 3 ; Z = 4 ; R = 0.076 and R w = 0.278 (1965 unique reflections). The structure is built up from ∞[NaY(CO 3) 2F 2] layers; Y 3+ and Na + cations are disordered in these (010) layers which are separated by other Na + cations. The structures of Na 3Yb(CO 3) 2F 2, previously described, and Na 3Y(CO 3) 2F 2 are correlated. Disorder between sodium and ytterbium or yttrium occurs and it is shown by transmission electron microscopy that both structures are noncommensurate.