Light Olefins Synthesis from Methanol and Dimethylether over SAPO-34 Nanocrystals

The Oxygenate-Mediated Conversion of COx to Hydrocarbons─On the Role of Zeolites in Tandem Catalysis

Decentralized chemical plants close to circular carbon sources will play an important role in shaping the postfossil society. This scenario calls for carbon technologies which valorize CO2 and CO with renewable H2 and utilize process intensification approaches. The single-reactor tandem reaction approach to convert COx to hydrocarbons via oxygenate intermediates offers clear benefits in terms of improved thermodynamics and energy efficiency. Simultaneously, challenges and complexity in terms of catalyst material and mechanism, reactor, and process gaps have to be addressed. While the separate processes, namely methanol synthesis and methanol to hydrocarbons, are commercialized and extensively discussed, this review focuses on the zeolite/zeotype function in the oxygenate-mediated conversion of COx to hydrocarbons. Use of shape-selective zeolite/zeotype catalysts enables the selective production of fuel components as well as key intermediates for the chemical industry, such as BTX, gasoline, light olefins, and C3+ alkanes. In contrast to the separate processes which use methanol as a platform, this review examines the potential of methanol, dimethyl ether, and ketene as possible oxygenate intermediates in separate chapters. We explore the connection between literature on the individual reactions for converting oxygenates and the tandem reaction, so as to identify transferable knowledge from the individual processes which could drive progress in the intensification of the tandem process. This encompasses a multiscale approach, from molecule (mechanism, oxygenate molecule), to catalyst, to reactor configuration, and finally to process level. Finally, we present our perspectives on related emerging technologies, outstanding challenges, and potential directions for future research.

A Review on SAPO-34 Zeolite Materials for CO2 Capture and Conversion

Among several known zeolites, silicoaluminophosphate (SAPO)-34 zeolite exhibits a distinct chemical structure, unique pore size distribution, and chemical, thermal, and ion exchange capabilities, which have recently attracted considerable research attention. Global carbon dioxide (CO₂ ) emissions are a serious environmental issue. Current atmospheric CO₂ level exceeds 414 parts per million (ppm), which greatly influences humans, fauna, flora, and the ecosystem as a whole. Zeolites play a vital role in CO₂ removal, recycling, and utilization. This review summarizes the properties of the SAPO-34 zeolite and its role in CO₂ capture and separation from air and natural gas. In addition, due to their high thermal stability and catalytic nature, CO₂ conversions into valuable products over single metal, bi-metallic, and tri-metallic catalysts and their oxides supported on SAPO-34 were also summarized. Considering these accomplishments, substantial problems related to SAPO-34 are discussed, and future recommendations are offered in detail to predict how SAPO-34 could be employed for greenhouse gas mitigation.

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.

Life Time Improvement of Hierarchically Structured SAPO-34 Nanocatalyst in MTO Reaction via Applying Clinoptilolite: Investigating of Composite Design via RSM

AIM AND OBJECTIVE

The research focuses on recent progress in the production of light olefins. Hence, as the common catalyst of the reaction (SAPO-34) deactivates quickly because of coke formation, we reorganized the mechanism combining SAPO-34 with a natural zeolite in order to delay the deactivation time.

MATERIALS AND METHODS

The synthesis of nanocomposite catalyst was conducted hydrothermally using experimental design. Firstly, Clinoptilolite was modified using nitric acid in order to achieve nano-scaled material. Then, the initial gel of the SAPO-34 was prepared using DEA, aluminum isopropoxide, phosphoric acid and TEOS as the organic template, sources of Aluminum, Phosphor, and Silicate, respectively. Finally, the modified zeolite was combined with SAPO-34's gel.

RESULTS

20 different catalysts due to D-Optimal design were synthesized and the nanocomposite with 50 weight percent of SAPO-34, 4 hours Crystallization and early Clinoptilolite precipitation showed the highest relative crystallinity, partly high BET surface area and hierarchical structure.

CONCLUSION

Different analyses illustrated the existence of both components. The most important property alteration of nanocomposite was the increment of pore mean diameters and reduction in pore volumes in comparison with free SAPO-34. Due to the low price of Clinoptilolite, the new catalyst renders the process as economical. Using this composite, according to the formation of multi-sized pores located hierarchically on the surface of the catalyst and increased surface area, significant amounts of Ethylene and Propylene, in comparison with free SAPO-34, were produced, as well as the deactivation time was improved.

Lower olefins from methane: recent advances

Modern methods for methane conversion to lower olefins having from 2 to 4 carbon atoms per molecule are generalized. Multistage processing of methane into ethylene and propylene via syngas or methyl chloride and methods for direct conversion of CH4 to ethylene are described. Direct conversion of syngas to olefins as well as indirect routes of the process via methanol or dimethyl ether are considered. Particular attention is paid to innovative methods of olefin synthesis. Recent achievements in the design of catalysts and development of new techniques for efficient implementation of oxidative coupling of methane and methanol conversion to olefins are analyzed and systematized. Advances in commercializing these processes are pointed out. Novel catalysts for Fischer – Tropsch synthesis of lower olefins from syngas and for innovative technique using oxide – zeolite hybrid catalytic systems are described. The promise of a new route to lower olefins by methane conversion via dimethyl ether is shown. Prospects for the synthesis of lower olefins via methyl chloride and using non-oxidative coupling of methane are discussed. The most efficient processes used for processing of methane to lower olefins are compared on the basis of degree of conversion of carbonaceous feed, possibility to integrate with available full-scale production, number of reaction stages and thermal load distribution.

The bibliography includes 346 references.

Synthesis of SAPO-34 Using Different Combinations of Organic Structure-Directing Agents

The effects of different mixtures of organic structure-directing agents (OSDAs) on the formation of SAPO-34 structure have been investigated. Different OSDAs, namely, triethylamine (TEA), tetraethylammonium hydroxide (TEAOH), and morpholine (Mor) and their combinations were used to synthesize SAPO-34 by a hydrothermal method. The template concentration was optimized by eliminating the competing phases to obtain the purest form of SAPO-34 phase. The as-synthesized samples were analyzed by XRD, FE-SEM/EDS, FT-IR, surface area/pore volume measurements, NH3-TPD, TG/DTA, and 29Si NMR MAS. The selection of template notably impacts the crystal size and physicochemical characteristics of as-synthesized SAPO-34. The sample prepared with 3 Mor : 3 TEA : 1 TEAOH exhibited the highest total acidity, smallest crystal size below 3 µm, and high surface area up to 697 m2/g.

Mechanism of SAPO-34 catalyst deactivation in the course of MTO conversion in a slurry reactor

The mechanism of SAPO-34 deactivation in the course of the MTO conversion has been studied in a slurry reactor in polydimethylsiloxane medium.

The tailored synthesis of nanosized SAPO-34 via time-controlled silicon release enabled by an organosilane precursor

Phenyltrimethoxysilane as a Si source can significantly slow down the crystallization process for SAPO-34 synthesis, leading to the formation of agglomerated nanocrystals (<100 nm).

New insights into catalyst deactivation and product distribution of zeolites in the methanol-to-hydrocarbons (MTH) reaction with methanol and dimethyl ether feeds

The ability of a zeolitic catalyst to dehydrate methanol to dimethyl ether affects catalyst deactivation and product distribution during the methanol-to-hydrocarbons (MTH) reaction.

Synthesis of MFI type ferrisilicate zeolite (Fe-MFI) nanocrystals by a dry gel conversion (DGC) method and their application to methanol to olefin (MTO) reactions

Fe-MFI nanocrystals were synthesized by a dry gel conversion method and showed superior catalytic performance in methanol to olefin reactions.

Development of AEI type germanoaluminophosphate (GeAPO-18) with ultra-weak acid sites and its catalytic properties for the methanol to olefin (MTO) reaction

Incorporating Ge into the aluminophosphate framework generated weakened Brønsted acid sites, leading to prolonged catalyst lifetimes in the MTO reaction.

Performance improvement of nano-sized SAPO-34 molecular sieves synthesised by different combinations of multi templates in MTO reaction

The influence of using two, three and four templates on the catalytic performance of SAPO-34 catalyst during the methanol-to-olefins (MTO) reaction has been studied. SAPO-34 catalysts were prepared hydrothermally by applying various combinations of four organic templates (TEAOH, morpholine, DEA and TEA). The results showed that applying a combination of templates affects the activity and selectivity of samples by prolonging their life time. Comparing with a sample prepared by a single template, using more than one template enhances the methanol conversion and selectively of light olefins. Apart from the effect of the number of templates on the performance of these catalysts, acidity also plays a significant role. It was found that catalysts synthesised by two and four templates give better performance due to their mild acidity, smaller particle size and higher BET surface area.

Catalytic Performance of SAPO-34 Catalysts of Different Crystal Sizes in Methanol-to-Olefins Reactions: Effects of Synthetic Parameters

The catalytic performance of SAPO-34 catalysts which were synthesised hydrothermally under different conditions was investigated in methanol-to-olefins reactions. The significance of template, silicon sources and crystallisation time on catalytic performance, and deactivation of SAPO-34 catalysts, were studied. High methanol conversion and yield of light olefins were obtained over the nano-sized catalyst synthesised with tetraethylammonium hydroxide as template source and tetraethyl orthosilicate as silica source with a crystallisation time of 24 h, owing to its higher crystallinity and smaller crystal size. The SAPO-34 catalysts with larger sizes of crystals deactivate rapidly, while smaller crystals retain their activity for a longer time.

Modeling and optimization of catalytic performance of SAPO-34 nanocatalysts synthesized sonochemically using a new hybrid of non-dominated sorting genetic algorithm-II based artificial neural networks (NSGA-II-ANNs)

The effects of ultrasound-related variables on the catalytic properties of sonochemically prepared SAPO-34 nanocatalysts in methanol to olefins (MTO) reactions were investigated.

Microwave-assisted synthesis of plate-like SAPO-34 nanocrystals with increased catalyst lifetime in the methanol-to-olefin reaction

Microwave mediated synthesis produced SAPO-34 nanocrystals with increased catalyst lifetime in the methanol-to-olefin reaction owing to their plate-like crystal shape.