Dimethyl Ether To Olefins Research Articles

Synthesis of n-Butene via Dimethyl Ether-to-Olefin Reaction over P-Loaded Ferrierite Zeolites

In the dimethyl ether (DME)-to-olefin (DTO) reaction over 20 types of P-loaded ferrierite zeolites with different P loading amounts, the synthesis of n-butenes such as 1-butene, trans-2-butene, and cis-2-butene was investigated to maximize the n-butene yield by optimizing the P loading amount. The zeolites were characterized using X-ray diffractometry (XRD), N2 adsorption-desorption isotherms, and NH3 temperature-programmed desorption (NH3-TPD). Micropore and external surface areas, total pore and micropore volumes, and weak and strong acids affected the DTO reaction’s characteristics. The P-loaded ferrierite zeolite with a P loading of 0.3 wt.% calcined at 500 °C exhibited an n-butene yield of 35.7 C-mol%, which exceeds the highest yield reported to date (31.2 C-mol%). Multiple regression analysis using the obtained data showed that the strong acid/weak acid ratio and total pore volume had a high correlation with the n-butene yield, with a contribution rate of 64.3%. Based on the multiple regression analysis results, the DTO reaction mechanism was discussed based on the proposed reaction model involving the dual-cycle mechanism.

Tailoring the acidity of ZSM-5 via surface passivation: Catalytic assessment on dimethyl ether to olefins (DTO) process

In the present study, four different samples having different acidity were synthesized. Two MFI-type zeolites having silicon-to-aluminum ratio equal to 25 and 50 were prepared. Besides, two additional samples were obtained by external passivation of each parent zeolite with a layer of Silicalite-1, leading to a core–shell structure. Each sample was characterized to assess textural properties, structure, composition, and acidity, and then tested for dimethyl ether (DME) conversion at different reaction temperatures between 300 and 375 °C. The analysis of produced mixture revealed the simultaneous presence of hydrocarbons and methanol. DME conversion grew by increasing the temperature. Propylene was the most abundant hydrocarbon detected during all the time-on-stream analyses. Especially at 375 °C, the investigated samples having greater acidity showed faster deactivation due to coking. Samples with lower acidity were thus more stable but, on the other hand, they presented higher methanol selectivity and lower hydrocarbons yield.

Improvement of n-Butene Yield in Dimethyl Ether-to-Olefin Reaction Using Ferrierite Zeolite Catalysts

Various ferrierite zeolites were investigated as catalysts for the dimethyl ether (DME)-to-olefin (DTO) reactions to efficiently synthesize n-butene, such as 1-butene, trans-2-butene, and cis-2-butene except for iso-butene using a fixed-bed flow reactor. Twenty P-loaded ferrierite zeolites with different structural parameters and acidic properties were prepared by the impregnation method by varying the P content and the temperature of air calcination as a pretreatment. The zeolites were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, and NH3 temperature-programmed desorption (NH3-TPD). Micropore surface area, external surface area, total pore volume, micropore volume, and weak and strong acid sites affected the DTO reaction behavior. A high n-butene yield (31.2 C-mol%) was observed, which is higher than the previously reported maximum yield (27.6 C-mol%). Multiple regression analysis showed that micropore surface area and strong acid sites had a high correlation with n-butene yield. Based on our findings, we explained the reaction mechanism for selective n-butene synthesis except for iso-butene in the DTO reaction by the dual cycle model.

Hydrogen transfer reaction contributes to the dynamic evolution of zeolite-catalyzed methanol and dimethyl ether conversions: Insight into formaldehyde

Formaldehyde (HCHO), generating from hydrogen transfer (HT) of reactant, is significant for autocatalysis initiation and deactivation in methanol-to-olefins (MTO), but hitherto, its evolution throughout the reaction has not been thoroughly revealed. Herein, by the established colorimetric analysis method, HCHO in the MTO and dimethyl ether (DME)-to-olefins (DTO) reactions over SAPO-34 was in situ quantitatively monitored, where HCHO was detected in slight and conspicuous amounts at initial and deactivation stages with semi-conversion, also when co-fed with water or high-pressure H2. We reveal the weak HT ability of DME relative to methanol, which enables prominent olefins-based cycle and suppresses reactant-induced HT and deactivation in DTO (which is critical for MTO). A complete dynamic reaction network is disclosed, constituting two simultaneous and interplaying pathways: the main reactions for olefin generation as the open-line and HT reactions as the hidden-line. Especially, co-feeding high-pressure H2 with DME capacitating a long-term and highly efficient operation of DTO by modulating the dynamic reaction network to a more moderate autocatalysis evolution, has great potential in industry application.

Binderless ZrO2/HZSM-5 fibrillar composites by electrospinning as catalysts for the dimethyl ether-to-olefins process

The upscaling of zeolitic materials to technical catalysts implies the formulation of the active phase with additives that can affect catalytic performance. As an alternative, we herein present fibrillar ZrO2/HZSM-5 composites prepared by electrospinning where HZSM-5 zeolite aggregates are joint through inert ZrO2 fibers. For zeolite loadings of 5, 10 and 20 wt% and SiO2/Al2O3 ratios of 30, 50 and 80, well-dispersed zeolite aggregates smaller than 1.5 μm have been observed. The ZrO2/HZSM-5 composites were tested as catalysts in the dimethyl ether-to-olefins (DTO) process. The maximum olefin selectivity (ca. 70%) but fastest deactivation was observed for a zeolite loading of 5 wt%, with side reaction extent being promoted when increasing zeolite loading or density of acid sites. A comparison with a technical catalyst suggested that secondary reactions are limited due to the homogeneous distribution of the zeolite in the fibrillary material and to the higher accessibility of zeolite crystals.

N-Butene Synthesis in the Dimethyl Ether-to-Olefin Reaction over Zeolites

Zeolite catalysts that could allow the efficient synthesis of n-butene, such as 1-butene, trans-2-butene, and cis-2-butene, in the dimethyl ether (DME)-to-olefin (DTO) reaction were investigated using a fixed-bed flow reactor. The zeolites were characterized by N2 adsorption and desorption, X-ray diffraction (XRD), thermogravimetry (TG), and NH3 temperature-programmed desorption (NH3-TPD). A screening of ten available zeolites indicated that the ferrierite zeolite with NH4+ as the cation showed the highest n-butene yield. The effect of the temperature of calcination as a pretreatment method on the catalytic performance was studied using three zeolites with suitable topologies. The calcination temperature significantly affected DME conversion and n-butene yield. The ferrierite zeolite showed the highest n-butene yield at a calcination temperature of 773 K. Multiple regression analysis was performed to determine the correlation between the six values obtained using N2 adsorption/desorption and NH3-TPD analyses, and the n-butene yield. The contribution rate of the strong acid site alone as an explanatory variable was 69.9%; however, the addition of micropore volume was statistically appropriate, leading to an increase in the contribution rate to 76.1%. Insights into the mechanism of n-butene synthesis in the DTO reaction were obtained using these parameters.

Generating Assembled MFI Nanocrystals with Reduced b-Axis through Structure-Directing Agent Exchange Induced Recrystallization.

Controlling crystal size and shape of zeolitic materials is an effective way to promote their mass transport and catalytic properties. Herein, we report a single step, Na+ - and porogen- free crystallization of MFI hierarchical architecture made up of aligned nanocrystals with reduced b-axis thickness (5-23 nm) and adjustable Si/Al ratios between 35 to 120, employing the commonly used tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) as structure-directing agents (SDAs). Homogeneous nucleation driven by both SDAs and subsequent SDA-exchange induced dissolution-recrystallization are responsible for the formation of such structure. The enhanced textural and diffusion properties account for a notable exaggeration of propene selectivity and catalyst lifetime in dimethyl ether-to-olefins (DTO) conversion. This protocol is extendable to the rational synthesis of other hierarchical zeolites through crystallization process control.

Generating Assembled MFI Nanocrystals with Reduced b‐Axis through Structure‐Directing Agent Exchange Induced Recrystallization

AbstractControlling crystal size and shape of zeolitic materials is an effective way to promote their mass transport and catalytic properties. Herein, we report a single step, Na+‐ and porogen‐ free crystallization of MFI hierarchical architecture made up of aligned nanocrystals with reduced b‐axis thickness (5–23 nm) and adjustable Si/Al ratios between 35 to 120, employing the commonly used tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) as structure‐directing agents (SDAs). Homogeneous nucleation driven by both SDAs and subsequent SDA‐exchange induced dissolution‐recrystallization are responsible for the formation of such structure. The enhanced textural and diffusion properties account for a notable exaggeration of propene selectivity and catalyst lifetime in dimethyl ether‐to‐olefins (DTO) conversion. This protocol is extendable to the rational synthesis of other hierarchical zeolites through crystallization process control.

Composite Nanostructure of Manganese Cluster and CHA-Type Silicoaluminaphosphates: Enhanced Catalytic Performance in Dimethylether to Light Olefins Conversion.

Light olefins, especially ethylene and propylene, are important chemicals in petrochemical industries with an increasing demand and play an essential role in the global consumption. In this regard, there have been extensive studies to design efficient catalysts for the light olefins productions. In this study, we report a new protocol to induce Mn nanoclusters (MnNC) into the mesopore of a CHA-type silicoaluminaphosphates via a one-pot synthesis of MnNC@SAPO-34 catalysts. The catalysts are characterized by a series of technology, such as TEM, XRD, NH3-TPD, 27Al MAS NMR, ICP-MS, XPS, and as well as N2-physical adsorption methods. The Mn nanoclusters of Mn2O3 and MnO2 species are well dispersed in the framework of the SAPO-34 silicoaluminaphosphates, modifying the porosity and acidic property of the SAPO-34: Giving rise to more mesoporous and improving the acid density. The MnNC@SAPO-34 catalysts exhibit decent 100% conversion and 92.2% olefins selectivity in the dimethyl ether to olefins (DTO) reactions, which is considerably higher than that for SAPO-34 silicoaluminaphosphates (79.6% olefins selectivity). The higher olefins selectivity over the MnNC@SAPO-34 is deemed to associate with the strong acid density and intensity of the silicoaluminaphosphates. Further, the Mn particles largely improve silicoaluminaphosphates’s durability.

Reactor–Regenerator System for the Dimethyl Ether-to-Olefins Process over HZSM-5 Catalysts: Conceptual Development and Analysis of the Process Variables

The dimethyl ether (DME)-to-olefins (DTO) process is an interesting alternative to the methanol-to-olefins process because of the easier production of DME, its higher reactivity, and the moderate d...

The Synthesis of YNU-5 Zeolite and Its Application to the Catalysis in the Dimethyl Ether-to-Olefin Reaction.

During prior investigations of the synthesis of the novel zeolite YNU-5 (YFI), it was found that a very slight amount of an impurity phase contaminated the desired zeolitic phase. This impurity was very often ZSM-5 (MFI). The phase composition was determined to be sensitive to the water in the synthesis mixture, and it was possible to obtain a pure phase and also to intentionally generate a specific impurity phase. In the present work, trials based on the dimethyl ether-to-olefin (DTO) reaction using a fixed-bed downflow reactor were performed to assess the effect of the purity of YNU-5 on its catalytic performance. Dealuminated pure YNU-5 exhibited rapid deactivation due to coking at time on stream (TOS) values exceeding 5 min. Surprisingly, this deactivation was greatly suppressed when the material contained a trace amount of ZSM-5 consisting of nano-sized particles. The formation of ZSM-5 nanoparticles evidently improved the performance of the catalytic system during the DTO reaction. The product distributions obtained from this reaction using highly dealuminated and very pure YNU-5 resembled those generated by 12-ring rather than 8-ring zeolite catalysts. The high selectivity for desirable C3 and C4 olefins during the DTO reaction over YNU-5 is beneficial.

A green route for the synthesis of nano-sized hierarchical ZSM-5 zeolite with excellent DTO catalytic performance

Nano-sized hierarchical ZSM-5 zeolite with high crystallization was prepared by a novel green strategy, that is, the consecutive freezing and vacuum drying route. In comparison with the traditional synthesis process, only 1/5 amount of TPAOH (tetrapropylammonium hydroxide) template was involved. Moreover, hierarchical structured zeolites can be formed even in the absence of mesoporous template (e. g. cetyltrimethylammonium bromide, CTAB). Moreover, the hierarchical ZSM-5 with a wide range of SiO2/Al2O3 ratio (25–200) can be modulated. The effects of the consecutive freezing and vacuum drying methods on the formation process, pore characteristics, crystallinity, morphology and acidity of the ZSM-5 zeolites were explored. It is noted that the abundant intra-crystal mesopores and nanoparticles structure were generated from the porous structure on the surface of the freeze-dried powder. The constructed nano-sized and hierarchical ZSM-5 catalyst exhibits a prolonged lifetime of 110 h in dimethyl ether-to-olefin (DTO) reaction, which is around 3.7-fold lifetime compared to the conventional microporous ZSM-5.

A Two-Step Crystallization Route for Hierarchical SAPO-34 Molecular Sieves: Unique Structural Features and Catalytic Property for DTO

The hierarchical structure can significantly improve the diffusion efficiency of the catalyst and regulate the product distribution. Therefore, the preparation of hierarchical SAPO-34 molecular sieve has been a hot research topic. With Cetyltrimethyl Ammonium Bromide (CTAB) and Diethylamine (DEA) as templates, a two-step crystallization process was employed to synthesize hierarchical SAPO-34 molecular sieves. We found that the aging process is vital for the formation of pure phase SAPO-34. It was investigated the relationship of crystallinity trend and mesoporous content with the crystallization time. The results showed that the prolongation of crystallization time was beneficial to enhance the crystallinity of the molecular sieve, but unfavourable to the retention of mesoporous structure. The formation process of hierarchical SAPO-34 molecular sieve involved agglomeration, disintegration, crystallization, re-agglomeration and growth. The hierarchical SAPO-34 molecular sieve with a satisfactory crystallinity and considerable mesoporous structure could be obtained after 36 hours of crystallization. Moreover, the sample had the most suitable acid strength as well as acid amount. The catalytic activity was investigated by catalytic dimethyl ether (DME) to olefin (DTO) reaction. It revealed that the conversion of DME and the selectivity to olefins over the hierarchical SAPO-34 molecular sieve were significantly enhanced with comparison to that over microporous SAPO-34 molecular sieve. The amount of coke deposition of the hierarchical SAPO-34 molecular sieve (14.2%) was lower than that over the microporous molecular sieve (16.5%). Meanwhile, the propylene selectivity of hierarchical SAPO-34 was higher than that of microporous SAPO-34 in the whole reaction. In a word, the hierarchical SAPO-34 molecular sieve synthesized in this study showed a longer catalytic life, higher coke deposition resistance and higher propylene selectivity.

Controllable synthesis of hierarchical porous petal-shaped SAPO-34 zeolite with excellent DTO performance

Abstract A hierarchical porous petal-shaped SAPO-34 zeolite was successfully synthesized via one-pot method by using the polymer of polyethylene glycol 20000 (PEG-20000) as structure-directing agents and the low-cost template of morpholine. The physicochemical properties of as-synthesized samples were investigated by XRD, SEM, TEM, FT-IR, EDS, N2 adsorption-desorption and NH3-TPD measurement. The SEM and TEM results showed that many thin nanosheets with the thickness of 50–100 nm and the slit-porous channels could be observed in the petal-shaped SAPO-34 crystals. The nanosheets could significantly shorten the diffusion length and hierarchical porous structure could enhance the mass transfer. The catalytic test of dimethyl ether to olefins (DTO) revealed that the hierarchical porous petal-shaped SAPO-34 catalysts exhibited higher catalytic performance and longer catalyst lifetime compared with the conventional microporous cube-like SAPO-34 catalysts.

Differences in Product Distribution Measured with Flame Ionization Detector Gas Chromatography and Thermal Conductivity Detector Gas Chromatography during the Dimethyl Ether-to-Olefins and Methanol-to-Olefins Processes

It is generally accepted that the products of dimethyl ether (DME)-to-olefins (DTO) and methanol-to-olefins (MTO) processes are hydrocarbons; therefore, gas chromatography (GC) equipped with a flame ionization detector (FID) rather than a thermal conductivity detector (TCD) is usually used to measure their product distribution for the higher response sensitivity of FID than TCD. Product distributions of DTO and MTO processes over SAPO-34 and metal-oxide-modified SAPO-34 catalysts were measured in this research work with GC equipped with FID and TCD. Results showed that product distribution over SAPO-34 measured with FID GC alone was similar to that measured with TCD + FID GC when the DME or methanol conversions were close to 100% and the main products were hydrocarbons, with only trace amounts of H2 and carbon oxides in the products. When using metal-oxide-modified SAPO-34 as the catalyst, it was found that the product distribution measured by TCD + FID GC was greatly different from that measured by FID G...

Synthesis of AEI/CHA intergrowth zeolites by dual templates and their catalytic performance for dimethyl ether to olefins

A series of SAPO molecular sieves were hydrothermally synthesized by employing mixture template of diethylamine (DEA) and N, N′-diisopropylethylamine (DIEA). The influences of template composition and crystallization time were investigated systematically. The results revealed that the crystalline products switched from SAPO-34/5 to SAPO-18/34 and finally to SAPO-18, the crystal size and acidity decreased with the increasing of DIEA ratio in the mixed template. Furthermore, crystallization time was also found to play a significant role in the particulate properties of the zeolites, the metastable AEI phase converted into more stable CHA phase, the Si content and acidity increased with the prolonged crystallization time. Dimethyl ether (DME) to olefins (DTO) reactions showed that the extending of the crystallization time was against the formation of light olefins, but favorable for the formation of light alkanes, due to the increase in CHA/AEI ratio, particle size and acidity may increase the probability of unfavorable hydrogenation of the target light olefins.

A Novel Preparation of SAPO-18 Molecular Sieve with Enhanced Stability for Dimethyl Ether to Olefins

SAPO-18 molecular sieve is an important catalyst for dimethylether-to-olefins (DTO) reaction. Although the conventional synthesized SAPO-18 using N,N′-diisopropylethylamine (DIEA) alone exhibits nanoparticles and better catalytic performance due to the weaker diffusion resistance, its high cost of preparation and difficult separation of the powder limit the industrial process of this type of molecular sieve. Therefore, reducing the cost and increasing the particle size appropriately become the key issues for its practical application. In this study, SAPO-18 catalysts were synthesized hydrothermally using mixture of triethylamine (TEA) and a small amount of DIEA as templates. The results revealed that fairly pure SAPO-18 molecular sieve with particle size of approximately 1.0 μm could be synthesized under the initial gel composition as: xDIEA:(1.4−x)TEA: 1.0 Al2O3: 0.9 P2O5:0.6SiO2:50H2O, where x varies from 0.2 to 0.6. Furthermore, the catalytic performance for DTO reaction over the novel synthesized SAPO-18 catalysts showed higher selectivities to light olefins and much lower coke deposition than the conventional synthesized SAPO-18 using DIEA alone.

Synthesis of SAPO-18 with low acidic strength and its application in conversion of dimethylether to olefins

SAPO-18 molecular sieve was synthesized by a dry gel conversion (DGC) and hydrothermal (HT) synthesis methods using methyltriethoxysilane as the only Si source (DGC-Me-SAPO-18 and HT-Me-SAPO-18). Their physicochemical and catalytic properties on dimethylether-to-olefin (DTO) reaction were compared with those of conventional SAPO-18 molecular sieves synthesized by a hydrothermal synthesis method (HT-SAPO-18). An NH3-TPD measurement revealed that the desorption peak position of Brønsted acid of the Me-SAPO-18 samples moved to lower temperature, indicating that Brønsted acidic strength of the Me-SAPO-18 samples was lower than that of the HT-SAPO-18 samples. The DME conversions and yields of light olefins over DGC-Me-SAPO-18 decreased at a slower rate than those of HT-SAPO-18. The decreased acidic strength and flake-like morphology of DGC-Me-SAPO-18 could retard the coke formation, leading to the prolonged catalytic lifetime.

Development of desilicated EU-1 zeolite and its application in conversion of dimethyl ether to olefins

Creating mesoporosity in one-dimensional pore zeolites is still a challenging task in zeolite scientific community. Desilicated EU-1 (EUO), an one-dimensional pore zeolite, with Si/Al of 25 was developed using with different NaOH concentrations for different times to extract Si atoms from the framework and to form mesoporosity at fixed treatment temperature. Simple hexamethonium bromide was used as a template for EU-1 synthesis. The effects of concentration of NaOH and time of desilication on Si/Al, crystallinity, acidity and surface area have been investigated. A series of treated EU-1 samples was then applied for conversion of dimethyl ether to olefins (DTO). The sample treated with lower NaOH concentration (0.25 M) had the highest increase in mesopore volume with no significant change in acidity. An increase in mesopore volume contributed to higher selectivity toward propylene. The lower catalytic activity was observed over desilicated EU-1 as compared with the parent sample. The physicochemical properties of desilicated zeolites were analyzed using many characterization techniques. X-ray diffraction (XRD) was used to evaluate the effect of desilication on the crystallinity. Nitrogen adsorption–desorption isotherms and temperature-programmed desorption were used to evaluate the porosity and acidity, respectively. Morphology was analyzed using scanning electron microscope (SEM) and Transmission electron microscope (TEM).

Methanol/dimethyl ether to light olefins over SAPO-34: Comprehensive comparison of the products distribution and catalyst performance

Dimethyl Ether (DME) as a possible reactant for production of light olefins was compared with methanol over a synthesized SAPO-34 catalyst at 400–460 °C and the products' distributions as a function of time on stream and reaction temperature were reported and analyzed. Physiochemical characteristics of the synthesized SAPO-34 catalyst were determined by BET, TPD, XRD, SEM and XRF techniques. The optimum reaction temperature range for methanol conversion to olefins (MTO) seemed to be 400–460 °C with the light olefins' selectivity of 77–78.5% and C2=/C3= molar ratios from 1.6 at 400 °C to 2.4 at 460 °C. Products' distributions in DME to olefins (DTO) reaction were different from MTO reaction specially at methane and light olefins' formation rates. Life time of the catalyst increased while using dimethyl ether as the feed but due to high rates of methanol and methane formation, the light olefins' selectivities were not as high as those of MTO reaction.