顺酐溶剂吸收装置的关键控制工艺分析

吐哈石化厂通过引进意大利CONSER公司的溶剂吸收工艺,对原有水吸收工艺进行改造。通过对CONSER溶剂吸收工艺的研究,分别对溶剂吸收装置中的溶剂吸收系统、溶剂解析系统和溶剂洗涤系统操作过程中的关键控制工艺进行分析,提出了可行的生产控制指导建议。     

Solvent-deficient synthesis of cerium oxide: Characterization and kinetics

The reaction mechanism and kinetics of CeO₂ synthesis using a solvent-deficient method are investigated by simultaneous thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The decomposition process of the cerium(III) nitrate hexahydrate and ammonium bicarbonate precursor mixture with four observed stages is monitored using TGA/DSC measurements in a nonisothermal regime with heating rates of 5, 10, 15 and 20?°C min^?1. The proposed mechanism indicates a complex synthesis with several parallel reactions, some of which occur at room temperature. A detailed kinetic analysis is performed using isoconversional (expanded Friedman, modified Coats-Redfern and Kissinger) and model fitting (N^th order and nucleation and growth models) methods. The first three stages are best described by the N^th order model with activation energy values of 21, 53 and 90?kJ?mol^?1. The last stage, during which ammonium nitrate decomposition occurs, is best fit by the nucleation and growth model and has an activation energy of 129?kJ?mol^?1. The proposed mechanism, supported by the kinetic analysis in our study, indicates that CeO₂ has already formed before the reaction reaches 200?°C. The average crystallite size of CeO₂ synthesized at 300?°C, which was calculated from the XRD measurements and observed in the SEM and TEM data, is between 10 and 20?nm.     

Rational design of novel carboxylic acid functionalized phosphonium based ionic liquids as high-performance extractants for rare earths

Developing the novel ionic liquids as the potential substitutes for conventional organic solvents in extraction of the rare-earth metals is highly desirable but challenges still remain. In this study, the well-designed carboxylic acid functionalized phosphonium based ionic liquids, (4-carboxyl)butyl-trioctyl-phosphonium chloride/nitrate, were synthesized and characterized. The as-prepared samples were tested as the undiluted hydrophobic acidic extractant for rare-earth metal ions, affording the maximal loading of 3 mol/mol towards Nd(III) in aqueous solution and the remarkable stripping performance. The results also reveal their excellent extractability and selectivity for Sc(III) in the mixtures of six rare-earth ions, as well as the outstanding separation properties between rare-earth and first row transition-metal ions (i.e., La/Ni, Sm/Co). Moreover, the extraction mechanism indicates that the extracted rare-earth complex via a proton exchange in the ionic liquid phase is structurally similar to the complexes obtained with neutral extractants. This work presents a prototype for the fabrication of the hydrophobic cation-functionalized ionic liquids for highly efficient rare-earth extraction and provides the future application in recycling of rare-earth metals from the spent magnets.     

Study of Proton Leakage at Interface of Anion-Exchange Membrane in Solutions of Acids,Salts, and Solvents Using Current/Voltage Characteristics

Water dissociation and proton leakage using the anionic exchange membrane (AMH) are studied by means of current/voltage characteristics and confirmed by simulation of transport number using Hittorf's method. The acids used are HCl, HNO₃, and H₂SO₄ and the salts are NaCl, ZnCl₂, and NaNO₃. Concentration polarization of such membrane is accompanied by a change in the electrolyte concentration/solution interface due hydrolysis reactions. The results show that when the concentration of the electrolyte increases, the limiting current density increases linearly and the transmembrane resistance decreases systematically. The thickness of the diffusion layer is always higher in presence of acid than salt, making in evidence the proton leakage through the membrane. Besides, when the membrane is selectively permeable to chloride anion in the case of ZnCl₂, the thickness of the double layer is rather bigger and far exceeds that of the membrane. The voltamperometry method seems reliable and offers some advantages over that of Hittorf because it shows the effects of some parameters on the value of limiting current: concentration, counter-ion types (Cl^?, NO₃^? SO₄^2?), and the gradient of concentration in the anode and cathode compartments. It can, therefore, allow to optimize the value of the current which should be used in electrodialysis in any form and without a great consumption of energy. Moreover, the simulation carried out for transport number of proton, shows its sensitivity toward the variation in concentration in the receiving compartment. In effect, a small decrease in concentration implies an enormous decrease in its value.     

Particle size reduction of RDX by sequential application of solvent–antisolvent recrystallization and mechanical methods

ABSTRACT

Solvent–antisolvent recrystallization produced ~8 µm average size RDX particles (UF-RDX) that were subsequently subjected to mechanical methods of ultrasonication and ball-milling to find further achievable reduction in particle size. Long duration ultrasonication for 20 h and 300 rpm ball milling for 4 h of UF-RDX decreased its average particle size to ~2 µm. RDX produced by all the three processes (solvent–antisolvent recrystallization, ultrasonication and ball-milling) was similar to coarser RDX in structure and thermal decomposition behavior. However, UF-RDX produced by solvent–antisolvent recrystallization was significantly less impact sensitive than that produced by ball-milling and ultrasonication. The issues of residual solvent and the metal contamination during RDX processing were addressed by process parameter optimization. Solvent–antisolvent recrystallization and mechanical methods even when used sequentially could not bring average particle size of RDX to nano-scale.     

Systematic optimization of low bandgap polymer/[6,6]-phenyl C70 butyric acid methyl ester blend photodiode via structural engineering

Synthetic approaches for optimizing polymer-based organic photodiodes (OPDs) by systematically analyzing the effects of the hole-blocking layer, the electron-blocking layer, and the thickness and morphology of the active layer with respect to the dark current and detectivity have been reported. PBDTT-DPP with a repeating alkylthienylbenzodithiophene (BDTT) and diketopyrrolopyrrole (DPP) units is used as a p-type polymer for achieving both broadband absorption and a high absorption coefficient in conjunction with n-type [6,6]-phenyl C₇₀ butyric acid methyl ester (PC₇₀BM) for constructing photoactive layers. Through systematic investigations of various interfacial layers, we found that the thickness of the active layer and the energy level of the hole/electron blocking layer were critical for minimizing the dark current of OPDs. By changing the deposition method of the PBDTT-DPP/PC₇₀BM blend and using post treatment, we discovered that the morphology of the active layer was directly related to the photocurrent of OPDs. Furthermore, we conducted a comparative study between a bulk heterojunction and a planar heterojunction (PHJ) to demonstrate the effectiveness of the PHJ for suppressing the dark current. Consequently, we realized a high detectivity of 5.3 × 10¹² Jones with an optimized device architecture and morphology. This work shows the importance of a synthetic approach for optimizing OPDs that requires both a high photocurrent and a low dark current in the reverse saturation regime.     

Recovery and Separation of Metal Ions from Aqueous Solutions by Solvent‐Impregnated Resins

The recovery and separation of metals from aqueous solutions is one of the research hotspots in hydrometallurgy, environment protection, analytical chemistry, etc. Much attention has been paid to solvent‐impregnated resins (SIRs) since these were firstly proposed for the extraction of metals. SIRs are characterized by high efficiency and selectivity, convenient preparation, and easy operation because they combine the unique advantages of solvent extraction and ion exchange. The preparation and features of SIRs are summarized and their applications in the extraction of various metals from solutions are reviewed. In addition, the equilibrium, thermodynamics, and sorption kinetics of the metals onto SIRs are elucidated in detail.     

Growth control of cobalt oxide nanoparticles on reduced graphene oxide for enhancement of electrochemical capacitance

The high capacitance and cyclic stability of graphene nanosheets decorated with Co₃O₄ nanoparticles as a material for supercapacitor electrodes are reported here. Hydrothermal method is adopted to deposit cobalt oxides on the reduced graphene oxide (RGO) sheets in a mixture of water and dimethylformamide (DMF) as the solvent with different volume ratios. The water volume ratio presents a crucial factor in the nucleation and growth process. In addition, it affects dispersion, particle size and the amount of nucleated cobalt oxide particle on the graphene sheets. By decreasing the water volume, the nucleation and growth occur mainly on graphene rather than in solution. According to the obtained results from transmission electron microscopy, scanning electron microscopy and thermogravimetric analysis, a model for growth of nanoparticles on graphene sheets is proposed. Based on the obtained results, the presented model can also be used for the synthesis of other graphene-metal (oxide) composites. Electrochemical measurements indicate that water volume ratio in the mixture solvent influences on capacitance of the RGO/Co₃O₄ composite electrodes. The highest obtained specific capacitance is 440.4 F g⁻¹ with 50% volume ratio of water at current density of 5 A g⁻¹.     

A critical review on solvent extraction of rare earths from aqueous solutions

Rare earth elements have unique physicochemical properties that make them essential elements in many high-tech components. Bastnesite (La, Ce)FCO₃, monazite, (Ce, La, Y, Th)PO₄, and xenotime, YPO₄, are the main commercial sources of rare earths. Rare earth minerals are usually beneficiated by flotation or gravity or magnetic processes to produce concentrates that are subsequently leached with aqueous inorganic acids, such as HCl, H₂SO₄, or HNO₃. After filtration or counter current decantation (CCD), solvent extraction is usually used to separate individual rare earths or produce mixed rare earth solutions or compounds. Rare earth producers follow similar principles and schemes when selecting specific solvent extraction routes. The use of cation exchangers, solvation extractants, and anion exchangers, for separating rare earths has been extensively studied. The choice of extractants and aqueous solutions is influenced by both cost considerations and requirements of technical performance. Commercially, D2EHPA, HEHEHP, Versatic 10, TBP, and Aliquat 336 have been widely used in rare earth solvent extraction processes. Up to hundreds of stages of mixers and settlers may be assembled together to achieve the necessary separations. This paper reviews the chemistry of different solvent extractants and typical configurations for rare earth separations.     

Study on separation of heavy rare earth elements by solvent extraction with organophosphorus acids and amine reagents

The present work describes a study of the separation of rare earth elements (REE) from heavy REE concentrate through solvent extraction. Seven extractants were investigated: three organophosphorus acids (DEHPA, IONQUEST^®801 and CYANEX^®272), a mixture of DEHPA/TOPO (neutral ester) and three amines (ALAMINE^®336, ALIQUAT^®336 and PRIMENE^®JM-T). The organophosphorus extractants were investigated in hydrochloric and sulphuric media whereas the amines performance was assessed in a sulphuric medium. The variables investigated were: concentration of the extractant agent, aqueous phase acidity, aqueous/organic volumetric ratio, contact time, stripping agent concentration (hydrochloric acid solution) and the selective stripping step. In the extraction step, the best separation factors for the adjacent elements were obtained with DEHPA and IONQUEST 801. For 1.0 mol L⁻¹ DEHPA in an initial acidity of 0.3 mol L⁻¹ H⁺, the separation factor was 2.5 Tb/Dy, 2.1 Dy/Ho, 1.9 Ho/Er, 2.0 Ho/Y and 1.1 Y/Er; for 1 mol L⁻¹ IONQUEST 801 in 0.3 mol L⁻¹ of H⁺ it was 2.7 Tb/Dy, 2.4 Dy/Ho, 2.1 Ho/Er, 2.1 Ho/Y e 1.5 Y/Er. The study concluded that for the extractants investigated, IONQUEST 801 is the most indicated for the separation of heavy REE because it has lower affinity with the REE compared to the affinity of DEPHA/REE, which makes the strip of the REE from Ionquest 801 easier than from DEHPA. Moreover, the number of stages necessary for the stripping of the REE from IONQUEST 801 is much lower than that observed when DEPHA is employed.