Using response surface method to analyze the effect of hydrothermal post-treatment on the performance of extrudates HZSM-5 catalyst in the methanol to propylene reaction
25 Jan 2019-Reaction Kinetics, Mechanisms and Catalysis (Springer International Publishing)-Vol. 127, Iss: 1, pp 375-390
TL;DR: In this article, ZSM-5 was synthesized via the hydrothermal method and then extruded using aluminophosphate as a binder, and the experimental design and analysis of the results, especially the relation of characterization results and reactor performance, are performed by optimal response surface method in Design Expert Software.
Abstract: In this study, ZSM-5 was synthesized via the hydrothermal method and then extruded using aluminophosphate as a binder. Before using it as a catalyst in methanol to propylene reaction, it was tried to eliminate the undesired contributions of the used binder by hydrothermal post- treatment. The experimental design and the analysis of the results, especially the relation of characterization results and reactor performance, are performed by optimal response surface method in Design Expert Software. The effects of the exposing time and the temperature during the steaming procedure on the catalytic characteristics and the performance of this system were investigated for two different average particle sizes (75 and 150 µm) of this catalyst. The results of the post-treatment represent the main dependency on the catalyst particle size, where the catalyst with smaller particle size showed lower methanol conversion and selectivity towards light olefins. It was concluded that an increase in the particle size of the catalyst intensifies the transport restrictions within the zeolite structure, which consequently increases the intra-particle residence time for production of higher hydrocarbons and then facilitates their cracking in order to produce more light olefins. This needs to be taken into consideration while synthesizing the catalyst for large-scale application.
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TL;DR: In this article, a series of hierarchical ZSM-5 aggregates with a relatively low SiO2/Al2O3 ratio was successfully synthesized using Cetyltrimethylammonium bromide (CTAB) as mesogenous template.
Abstract: A series of hierarchical ZSM-5 aggregates with a relatively low SiO2/Al2O3 ratio (~ 50) were successfully synthesized using alkali-treated commercial ZSM-5 as seeds and cetyltrimethylammonium bromide (CTAB) as mesogenous template. The effect of the amounts of CTAB on the physicochemical and catalytic properties of the synthesized catalysts was characterized by XRD, FE-SEM, FE-TEM, N2 physical adsorption, ICP-OES, NH3-TPD, Py-IR and TGA. Moreover, the possible formation mechanism of the hierarchical ZSM-5 aggregates was studied. The results indicated that the mesoporosity of the hierarchical ZSM-5 aggregates was greatly enhanced with the addition of CTAB. The primary crystal size of the ZSM-5 aggregates significantly decreased owing to the protective effect of CTAB, which inhibits the further crystal growth. The hierarchical ZSM-5 aggregates prepared with addition of a suitable amount of CTAB showed large specific surface areas and large external surface areas, abundant intercrystalline mesopores and appropriate concentration of acid sites, which resulted in excellent catalytic performance in the methanol to gasoline reaction. The stability of the catalyst was remarkably improved and the gasoline yield was given a rise of 10% compared with the catalyst prepared in the absence of CTAB.
13 citations
TL;DR: In this article, a cost-effective route has been developed for the synthesis of nano-sized triclinic SAPO-34 zeolite via seed-assisted grinding method using lower dosage of morpholine as the sole template.
Abstract: A cost-effective route has been developed for the synthesis of nano-sized triclinic SAPO-34 zeolite via seed-assisted grinding method using lower dosage of morpholine as the sole template. The synthesis conditions including silica source, silica concentration, crystallization temperature and time were refined to obtain SAPO-34 zeolite with high phase purity and crystallinity. Particularly, seed crystals preactivated by different methods were utilized to induce the synthesis of nano-sized SAPO-34 zeolites in the subsequent study. The resultant SAPO-34 samples were characterized by XRD, SEM, N2 physisorption and NH3-TPD techniques. It was found that the introduction of seed crystals activated by mechanical milling for 20 min and chemical etching with 0.0001 M and 0.01 M H3PO4 can not only effectively reduce the crystal size of SAPO-34 zeolites from 3–4 μm to 500–800 nm level, but also can modify their texture and acid properties. This nano-sized SAPO-34 catalyst exhibits a remarkably prolonged catalytic lifetime in methanol to olefins (MTO) reaction in comparison to the conventional micron-sized counterpart. Analogous to solvent-free synthesis of zeolites, this seed-assisted grinding synthesis method is simpler, more efficient than conventional hydrothermal synthesis. More importantly, this method provides a new avenue for preparing superior MTO catalyst.
10 citations
TL;DR: In this article, a mixed organic agent system was employed to achieve mesoporous highly crystalline ZSM-5 zeolite using Decyltrimethylammonium bromide (DeTAB) and tetramethyl ammonium hydroxide (TMAOH).
Abstract: A mixed organic agent system was employed to achieve mesoporous highly crystalline ZSM-5 zeolite. Decyltrimethylammonium bromide (DeTAB) and tetramethyl ammonium hydroxide (TMAOH) were used as the mesogenous and molecular templates respectively in the synthesis gel with a composition of 60SiO2: 1Al2O3:12Na2O:3150H2O:xDeTAB:8TMAOH. The sole presence of DeTAB as the mesogenous template in the synthesis gel led to the high degrees of mesoporosity in the ZSM-5/xD samples but negatively affected the intrinsic properties of zeolites. At the high concentration of DeTAB (x = 0.7), the mesopore volume dramatically increased while the relative crystallinity and the total acid sites critically decreased. By adding the TMA+ ions as a microporous template to the ZSM-5/0.7D synthesis gel, not only a zeolite with well-developed mesoporosity was obtained but also its crystal structure and the intrinsic acidity were preserved. The catalyst samples were characterized by FESEM, TEM, XRD, FT-IR, nitrogen adsorption–desorption isotherms, NH3-TPD and TGA techniques. The ZSM-5/0.7D/T exhibited higher surface area, higher mesopore volume, higher crystallinity and more acid sites than the ZSM-5/0.7D. The catalytic conversion of methanol to gasoline was conducted in a fixed bed reactor at T = 390 °C and WHSV = 4.74 h−1. In ZSM-5/0.7D/T catalyst the mesoporosity formation without severely damaging the crystal structure and the acidity of the zeolite led to the best catalytic performance including the highest liquid hydrocarbon yield, most stable catalytic performance and longest catalytic lifetime.
9 citations
15 Oct 2021
8 citations
TL;DR: In this article, the regenerability of spent catalysts after methanol to olefins (MTO) reaction was studied and the modified hierarchical type 34 silicoaluminophosphate (SAPO-34) catalysts containing manganese were synthesized in the presence of carbon nanotube as mesopore template.
Abstract: The hierarchical type 34 silicoaluminophosphate (SAPO-34) catalysts containing manganese were synthesized in the presence of carbon nanotube as mesopore template and tested in the transformation of methanol to light olefin. Also, the regenerability of spent catalysts after methanol to olefins (MTO) reaction was studied. In order to investigate the effect of manganese on the framework and extra framework of SAPO-34 structure, manganese species were added to SAPO-34 by isomorphous substitution and impregnation methods. The physicochemical properties of modified hierarchical samples such as crystallinity, acidity, porosity and reducibility were strongly dependent on the metal addition method. The modified hierarchical samples showed superior performance in the terms of activity and longevity compared to unmodified hierarchical SAPO-34. Among the samples, hierarchical MnAPSO-34 catalyst prepared by isomorphous substitution exhibited the best performance in the MTO reaction. The characterization of the used hierarchical catalysts by TGA analysis revealed that the deposited coke on modified samples was lower compared to unmodified hierarchical SAPO-34. The regenerated modified hierarchical SAPO-34 samples showed more enhanced ethylene selectivity in the MTO reaction and longer lifetime due to the existence of more methylated naphthalenes and methylated benzenes in the residual coke after regeneration.
6 citations
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29 Aug 1995TL;DR: Using a practical approach, this book discusses two-level factorial and fractional factorial designs, several aspects of empirical modeling with regression techniques, focusing on response surface methodology, mixture experiments and robust design techniques.
Abstract: From the Publisher:
Using a practical approach, it discusses two-level factorial and fractional factorial designs, several aspects of empirical modeling with regression techniques, focusing on response surface methodology, mixture experiments and robust design techniques. Features numerous authentic application examples and problems. Illustrates how computers can be a useful aid in problem solving. Includes a disk containing computer programs for a response surface methodology simulation exercise and concerning mixtures.
10,104 citations
TL;DR: It is shown that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolites that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell.
Abstract: Zeolites-microporous crystalline aluminosilicates-are widely used in petrochemistry and fine-chemical synthesis because strong acid sites within their uniform micropores enable size- and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion. This has been realized by synthesizing zeolite nanocrystals, by exfoliating layered zeolites, and by introducing mesopores in the microporous material through templating strategies or demetallation processes. But except for the exfoliation, none of these strategies has produced 'ultrathin' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on the mesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.
1,839 citations
TL;DR: This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.
Abstract: Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2). The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.
1,379 citations
TL;DR: In this paper, a controlled reduction in the effective dimensions of the catalyst pore openings, and/or channels, along with deactivation of acidic surface sites, has been proposed as a mechanism for the selective production of p-xylene.
513 citations
TL;DR: In this paper, a chemical model for the phosphorus-zeolite interaction is proposed in which the framework aluminum pairs are stabilized by extra-framework cationic species formed by protonation of orthophosphoric acid, and the influence of isolated versus pairs of aluminum on activity and selectivity after steaming is discussed.
353 citations