Effect of Crystal Size on Acetone Conversion over SAPO-34 Crystals

Hirota, Yuichiro; Nakano, Yoshifumi; Watanabe, Kazuo; Uchida, Yoshiyuki; Miyamoto, Manabu; Egashira, Yasuyuki; Nishiyama, Norikazu

doi:10.1007/s10562-012-0797-1

Cited by 7 publications

(4 citation statements)

References 16 publications

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“…The main product of ethanol conversion on SAPO‐34 is ethylene, together with some byproducts as diethyl ether, acetaldehyde, and propylene . Acetone can be converted into isobutene and also, to a much smaller degree, into other hydrocarbons such as ethylene, propylene, and C 1 –C 4 saturated alkanes in a reaction proceeding mainly at the outer surface of SAPO‐34 crystals . The identification of these products is beyond the scope of this study.…”

Section: Resultsmentioning

confidence: 98%

“…When using SAPO‐34 to purify the effluent of the Si‐LTA column, trace amounts (<0.25 wt %) of other impurities were detected in the product stream. The catalytic activity of SAPO‐34 with regard to small alcohols is well known; SAPO‐34 is often used as a catalyst in the methanol‐to‐olefin process (MTO), but also in ethanol‐to‐olefin (ETO) and even acetone‐to‐olefin (ATO) processes, which usually take place at high temperatures (>350 °C). At lower temperatures, SAPO‐34 demonstrates only a reduced catalytic activity .…”

Section: Resultsmentioning

confidence: 99%

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Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

et al. 2017

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A vapor-phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanol-ethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in the vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape-selective all-silica zeolites CHA and LTA were prepared and evaluated with single-component isotherms and breakthrough experiments. These zeolites show opposite selectivities; adsorption of ethanol is favorable on all-silica CHA, whereas the LTA topology has a clear preference for butanol. The molecular sieving properties of both zeolites allow easy elimination of acetone from the mixture. The molecular interaction mechanisms are studied by density functional theory (DFT) simulations. The effects of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior are investigated. Desorption profiles are studied to maximize butanol purity and recovery. The combination of LTA with CHA-type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows butanol to be recovered in unpreceded purity and yield. A butanol purity of 99.7 mol % could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

et al. 2017

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“…When using ZSM-5 (MFI zeolite, 10-membered rings), isobutylene is formed within the crystal pore by decomposition of diacetone alcohol (dimer), not by decomposition of an acetone trimer (pholone and iso-pholone), due to spatial limitations of the MFI zeolite (10-membered rings) [25,26]. In contrast, when using SAPO-34 (CHA zeolite, 8-membered rings), the aldol condensation of acetone proceeds mostly on the acid site located on the external surface, where the acetone dimer and trimers are formed, followed by decomposition to produce isobutylene, because the pore size of SAPO-34 is smaller than the molecular size of acetone [89]. The isobutylene produced reacts with itself to produce C 8 hydrocarbons followed by cyclization/cracking to form C 8 aromatics (xylene) and propylene [76].…”

Section: Acetone-to-olefins (Ato) Reaction Over Nano-sized Zeolitementioning

confidence: 99%

Size-Controlled Synthesis of Nano-Zeolites and Their Application to Light Olefin Synthesis

et al. 2012

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For the application of zeolites as heterogeneous catalysts, low diffusion resistance for hydrocarbons within the micropore is essential for improving product selectivity and catalyst lifetime. This problem has been overcome by reducing the crystal size. This review introduces size-controlled preparation of nano-sized zeolites via hydrothermal synthesis in water/surfactant/organic solvent (emulsion method) and their application to heterogeneous catalysts. The ionicity of the hydrophilic group in surfactant molecules and the concentration of the Si source affected the crystallinity and morphology of zeolites prepared using the emulsion method. When using a non-ionic surfactant, mono-dispersed silicalite-1 nanocrystals approximately 60 nm in diameter were successfully prepared. Nano-and macro-ZSM-5 zeolites with crystal sizes of approximately 150-200 nm and 1.5 µm, respectively, were prepared and applied to n-hexane cracking and acetone-to-olefin reactions to investigate the effect of zeolite crystal size on catalytic stability and light olefin yield. Application of nano-zeolite to light olefin production was effective in achieving faster mass transfer of hydrocarbon molecules within the micropore, which led to improvements in olefin yields and catalyst lifetime.

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“…Previous investigations of acetone condensation to isobutene have focused on the use of Brønsted acid zeolites, e.g., SAPO-34, H-MFI and H-BEA, as the catalyst. These studies suggest that isobutene is formed by successive aldol condensation and self-deoxygenation. − While Brønsted acidic zeolites are demonstrated to be very active for acetone conversion to isobutene, low isobutene selectivity and rapid catalyst deactivation due to coking have discouraged their further development.…”

Section: Introductionmentioning

confidence: 99%

Mechanism and Kinetics of Acetone Conversion to Isobutene over Isolated Hf Sites Grafted to Silicalite-1 and SiO₂

Zhang

Lund

et al. 2021

J. Am. Chem. Soc.

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Isolated hafnium (Hf) sites were prepared on Silicalite-1 and SiO 2 and investigated for acetone conversion to isobutene. Characterization by IR, 1 H MAS NMR, and UV−vis spectroscopy suggests that Hf atoms are bonded to the support via three O atoms and have one hydroxyl group, i.e, (SiO) 3 Hf−OH. In the case of Hf/Silicalite-1, Hf−OH groups hydrogen bond with adjacent Si−OH to form (SiO) 3 Hf−OH•••HO−Si complexes. The turnover frequency for isobutene formation from acetone is 4.5 times faster over Hf/Silicalite-1 than Hf/SiO 2 . Lewis acidic Hf sites promote the aldol condensation of acetone to produce mesityl oxide (MO), which is the precursor to isobutene. For Hf/SiO 2 , both Hf sites and Si−OH groups are responsible for the decomposition of MO to isobutene and acetic acid, whereas for Hf/Silicalite-1, the (SiO) 3 Hf−OH•••HO−Si complex is the active site. Measured reaction kinetics show that the rate of isobutene formation over Hf/SiO 2 and Hf/Silicalite-1 is nearly second order in acetone partial pressure, suggesting that the rate-limiting step involves formation of the C−C bond between two acetone molecules. The rate expression for isobutene formation predicts a second order dependence in acetone partial pressure at low partial pressures and a decrease in order with increasing acetone partial pressure, in good agreement with experimental observation. The apparent activation energy for isobutene formation from acetone over Hf/SiO 2 is 116.3 kJ/mol, while that for Hf/Silicalite-1 is 79.5 kJ/mol. The lower activation energy for Hf/Silicalite-1 is attributed to enhanced adsorption of acetone and formation of a C−C bond favored by the H-bonding interaction between Hf−OH and an adjacent Si−OH group.

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Effect of Crystal Size on Acetone Conversion over SAPO-34 Crystals

Cited by 7 publications

References 16 publications

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

Size-Controlled Synthesis of Nano-Zeolites and Their Application to Light Olefin Synthesis

Mechanism and Kinetics of Acetone Conversion to Isobutene over Isolated Hf Sites Grafted to Silicalite-1 and SiO₂

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Effect of Crystal Size on Acetone Conversion over SAPO-34 Crystals

Cited by 7 publications

References 16 publications

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

Size-Controlled Synthesis of Nano-Zeolites and Their Application to Light Olefin Synthesis

Mechanism and Kinetics of Acetone Conversion to Isobutene over Isolated Hf Sites Grafted to Silicalite-1 and SiO2

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Product

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Mechanism and Kinetics of Acetone Conversion to Isobutene over Isolated Hf Sites Grafted to Silicalite-1 and SiO₂