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(A) XRD plots of the 2 mm alumina and TS-1 membrane; (B) XRD plots of the zirconia and TS-1 membranes on different sizes of zirconia surfaces; FT-IR plots (C) and UV−vis plots (D) of the TS-1 powders on different carrier kettle bottoms.
Source publication
Titanium silica (TS-1) membrane catalysts grown on the surfaces of spherical substrates can both exploit the high catalytic performance and facilitate their separation from products after the reaction. In this work, a simple static crystallization method was used to perform the in situ construction of a TS-1 membrane on the surfaces of micron-sized...
Contexts in source publication
Context 1
... achieve miniaturization of the carrier size, 2 mm alumina and 400 μm zirconia microspheres were used as the substrates, and we attempted to grow TS-1 membranes on their surfaces. According to the XRD spectra of the molecular sieve membranes shown in Figure 2A,B, we concluded that the TS-1 membrane was already present on the carrier surfaces when compared with the characteristic XRD peaks of the pure carriers. The characteristic peaks of the MFI topology appeared at 2A = 7.8°, 8.8°, 23.2°, 23.8°, and 24.5°, as shown by the marks in Figure 2A,B. ...
Context 2
... to the XRD spectra of the molecular sieve membranes shown in Figure 2A,B, we concluded that the TS-1 membrane was already present on the carrier surfaces when compared with the characteristic XRD peaks of the pure carriers. The characteristic peaks of the MFI topology appeared at 2A = 7.8°, 8.8°, 23.2°, 23.8°, and 24.5°, as shown by the marks in Figure 2A,B. According to the FT-IR spectrum shown in Figure 2C, we found that the intensity of the characteristic peak of 960 cm −1 was lower than that of the zirconia support when the substrate consisted of alumina. ...
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... characteristic peaks of the MFI topology appeared at 2A = 7.8°, 8.8°, 23.2°, 23.8°, and 24.5°, as shown by the marks in Figure 2A,B. According to the FT-IR spectrum shown in Figure 2C, we found that the intensity of the characteristic peak of 960 cm −1 was lower than that of the zirconia support when the substrate consisted of alumina. The characteristic peak at 960 cm −1 was likely caused by the asymmetric stretching vibration of the Si−O−Ti bond or the disturbance of the Si−O bond caused by titanium atoms in the framework. ...
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... peak generally indicated that titanium atoms entered the framework of the molecular sieve. 39 The UV−vis spectrum depicted in Figure 2D visually shows that the kettlebottom molecular sieve powder had a more pronounced peak representing anatase at 330 nm when alumina was used as the carrier. The reason for the above phenomenon was possibly because alumina was dissolved in an alkaline crystallization environment to produce Al 3+ , which inhibited the formation of TS-1 and affected the entry of Ti species into the molecular sieve skeleton, causing the titanium atoms to convert to nonskeleton titanium. ...
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... addition, during the static crystallization process, the membrane layer on the surface of the carrier was not uniform and smooth, with clusters of the molecular sieve on the surface of the membrane layer, where the smaller the size of the carrier, the more the clusters observed. The film layers shown in Figure 3C−F were b-oriented; however, the corresponding (0k0) peak was not dominant in Figure 2B. The main reasons for this were likely due to the molecular sieve crystals on the zirconia surface, which grew on the curved support and were overlapped and stacked, and due to the distances between the crystal planes being different. ...
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... to the spherical membrane on the 2 mm carriers, as the loading capacity of the molecular sieve and the utilization rate of the bed improved, nearly 100% conversion of hydrogen peroxide was achieved when the size decreased to 400 μm. The TS-1@ 400 μm ZrO 2 sample had a higher effective utilization rate of H 2 O 2 than the TS-1@2 mm Al 2 O 3 sample, which confirmed the phenomenon shown in Figure 2D, where the framework titanium content of the TS-1@400 μm ZrO 2 sample was higher than the TS-1@2 mm Al 2 O 3 sample. In addition, compared to the extruded sample, the TS-1@400 μm ZrO 2 sample showed better catalytic performance, possibly because more active sites could be exposed by the spherical membrane catalyst. ...
Citations
BACKGROUND
The direct epoxidation of allyl chloride is a clean and efficient synthesis method for producing epichlorohydrin (ECH), which is a crucial organic intermediate widely used in the fields of renewable energy and aerospace. However, the presence of multiple azeotropes in the synthesized product using this method complicates the separation process and results in high energy consumption. To efficiently separate high‐purity ECH, this paper investigates and analyzes three separation schemes based on phase‐equilibrium analysis: hybrid extractive distillation (HED), pressure swing distillation (PSD) and three‐column batch distillation (TCBD).
RESULTS
The operating parameters of the three separation processes are optimized by the sequential iterative optimization method such that the minimum total annual cost can reach $493 491 yr⁻¹. The thermal integration method is used for process energy‐saving optimization, and the total annual cost can be further reduced by 6.9%. In addition, a comprehensive evaluation based on economic, energy, environmental and exergy analysis is conducted, and reveals that the TCBD process with thermal integration is optimal. A control structure is designed for the TCBD process to enhance its robustness such that the purity of ECH remains above 99.9 mol% under ±10% disturbances in feed flowrate and composition.
CONCLUSIONS
Compared with the HED and PSD processes, the TCBD process has better economic and environmental benefits, and its control structure can effectively resist disturbances. It is reasonable to believe that the TCBD process can be an excellent solution for the industrial production of ECH. © 2024 Society of Chemical Industry (SCI).
Titanium silicate zeolite (TS-1) is widely used in the research on selective oxidations of organic substrates by H2O2. Compared with the chlorohydrin process and the hydroperoxidation process, the TS-1 catalyzed hydroperoxide epoxidation of propylene oxide (HPPO) has advantages in terms of by-products and environmental friendliness. This article reviews the latest progress in propylene epoxidation catalyzed by TS-1, including the HPPO process and gas phase epoxidation. The preparation and modification of TS-1 for green and sustainable production are summarized, including the use of low-cost feedstocks, the development of synthetic routes, strategies to enhance mass transfer in TS-1 crystal and the enhancement of catalytic performance after modification. In particular, this article summarizes the catalytic mechanisms and advanced characterization techniques for propylene epoxidation in recent years. Finally, the present situation, development prospect and challenge of propylene epoxidation catalyzed by TS-1 were prospected.
TS-1 molecular sieve spherical membranes loaded on small-sized carriers with hierarchical pore structures and high framework-titanium contents could both exhibit high catalytic performances and facilitate the separation from the products after the reaction. In this paper, a simple in situ static crystallization method was used to achieve the construction of hierarchical porous TS-1 molecular sieve membranes on the surfaces of 400-µm spherical ZrO2 carriers using cetyltrimethylammonium bromide (CTAB) and soluble starch as mesoporous templating agents. Through the catalyst characterization and performance evaluation, soluble starch was finally selected as the mesoporous templating agent, and the film-forming mechanism was investigated by examining the effects of the proportion of precursor liquid and the crystallization conditions. In the chloropropene epoxidation reaction, the effective utilization of H2O2 and the selectivity of epichlorohydrin (ECH) reached 96.72% and 93.85%, respectively.
TS-1 molecular sieve spherical membranes loaded on small-sized carriers with hierarchical pore structures and high framework-titanium contents could both exhibit high catalytic performances and facilitate the separation from the products after the reaction. In this paper, a simple in situ static crystallization method was used to achieve the construction of hierarchical porous TS-1 molecular sieve membranes on the surfaces of 400-µm spherical carriers using cetyltrimethylammonium bromide (CTAB) and soluble starch as mesoporous templating agents. Through the catalyst characterization and performance evaluation, soluble starch was finally selected as the mesoporous templating agent, and the film-forming mechanism was investigated by examining the effects of the proportion of precursor liquid and the crystallization conditions. In the chloropropene epoxidation reaction, the effective utilization of H 2 O 2 and the selectivity of epichlorohydrin (ECH) reached 96.72% and 93.85%, respectively.
