Huiyu Zhao,Feng Wu,Qingwen Han,Chen Wang,Sibei Cao,Jiayu Ma
The solubility of potassium hexafluorosilicate (K2SiF6) in pure water and acid solutions (HCl and H3PO4) was conducted within a temperature range of 5–70 °C by the isothermal method. The stability of K2SiF6 in the systems above was also investigated by analyzing the equilibrium solids obtained in different conditions using X-ray diffraction (XRD), energy dispersive X-ray fluorescence (XRF), scanning electron microscope (SEM), and Fourier transform infrared (FT-IR). The results revealed that the solubility always increases with increasing temperature in all investigated systems. In the presence of hydrochloric acid and phosphoric acid, the solubility first increases and then decreases with the increase of acid concentration due to the increase of H+ concentration in hydrochloric acid, the effect of the stepwise dissociation of phosphoric acid, and the changed average ionic activity in solutions. K2SiF6 is stable in pure water and acid solutions. In addition, the experimental data were successfully correlated by the Apelblat empirical equation.
Fang Jin,Xianqiao Wang,Tieliang Liu,Linbo Xiao,Ming Yuan,Yangchun Fan
A new effective process to improve the utilization of industrial fluorosilicic acid of phosphate fertilizer by-product has been investigated to comprehensive application of the silicon and fluorine source. Two-step ammoniation was applied to recover high-quality silica. The recovered silica can be used to hydrothermal synthesize ZSM-5 zeolite without impurity phase contamination, which was confirmed by XRD, TG, SEM, BET and EDS characteristic techniques. It was found that with the increase of SiO 2 /Al 2 O 3 ratio and the extension of reaction time, the crystal type transform from the orthorhombic to the monoclinic phase. The impurity fluorine content of the recovered SiO 2 from H 2 SiF 6 has great influence on the hydrothermal process for ZSM-5 crystal structure formation. Moreover, the increase of fluorine ions content in the hydrothermal process can control the crystal morphology and size of synthesized ZSM-5. Catalytic properties of synthesized HZSM-5 with different SiO 2 /Al 2 O 3 ratio in transalkylation of toluene and 1,2,4-trimethylbenzene show good and stable catalytic performance. The ZSM-5 synthesized with recovered silica source exhibits similar catalyst life as the performance of small particle size HZSM-5, because the ZSM-5 synthesized with the silica source from industrial hexafluorosilicic acid prefers a thin disk crystal along the b axis direction, which shortens the diffusion distance of generated products.
Determining the Si isotopic compositions of samples of the Earth’s surface is crucial to understanding the implications of the biogeochemistry cycling of Si. This study established an alternative method for high-precision Si isotopic measurement in soil samples using gas-source isotope ratio mass spectrometry, which involved the conversion of Si in the samples into SiF 4 gas, which was purified cryogenically and collected for isotopic analysis. The proposed method was applied to determine the Si isotopic composition of two reference materials (GBW04421 and GBW04422), and the results were found to be in good agreement with the certified values. Moreover, the proposed method exhibited a long-term measurement precision of 0.05 ‰–0.08 ‰ (2 s) for the δ 30 Si values. The δ 30 Si values obtained from ten soil reference materials ranged from −1.84 ‰ to −0.17 ‰, which were within the range of the values reported in the literature (−1.82 ‰ to −0.15 ‰). The sample preparation and analysis method in this study provided an easy and effective approach to determining the Si isotopic composition of solid samples and offers to the promise of being applicable to biogeochemical analyses of the Earth’s surface processes.
Meile Yue,Kankan Bu,Yahong,Zhang,Wei Shen,Hualong Xu,Zhen Huang
Propane dehydroaromatization (PDA) provides a promising route to produce valuable chemicals such as benzene, toluene and xylene via non-petroleum feedstocks, in which Ga-modified MFI zeolites demonstrate high activity but are susceptible to severe coke deposition. The defect-derived silanols (Si-OH) in zeolite formed during synthesis has emerged as a predominant factor, making the prolongation of the catalyst longevity a major challenge. Here, we developed a gallosilicate MFI zeolite with silanol-defect remediated (Ga-MFI-AHFS) through an ammonium hexafluorosilicate post-treatment, which exhibited an extraordinary activity and stability. Ga-MFI-AHFS exhibits a nearly unchanged propane conversion around 82.0 % with aromatics selectivity around 64.5 % compared to a 25.4 % conversion decline on the raw zeolite with defects exposed during the 20-h CO 2 assisted PDA reaction. The results of FTIR and MAS NMR showed a decreased content of silanol nests as well as the internal Si-OH groups, indicating the successful repair of silicon hydroxyl defects. The restored framework endows the Ga-MFI-AHFS zeolite with an excellent coking resistance, giving a much lower coking-rate of 5.8 × 10 −8 mol C /mol C-in-produced-Aromatics , which is one-sixth of that on Ga-MFI. This work developed a facile route to prepare Ga-MFI zeolite with suppressed silanol-defects, which could help to realize a stable dehydroaromatization of light alkanes.
危险品化学品经营许可证（带存储）