An effective route to improve the catalytic performance of SAPO-34 in the methanol-to-olefin reaction

An effective route to improve the catalytic performance of SAPO-34 in the methanol-to-olefin reaction by simple oxalic acid treatment was investigated. The samples were characterized by XRD, SEM, N2 adsorption-desorption, XRF, TG, 29Si MAS NMR and NH3-TPD techniques. The results indicated that the external surface acidity of SAPO-34 was finely tuned by oxalic acid treatment, and the selectivity to C2H4 on SAPO-34 and the catalyst lifetime in the methanol-to-olefin reaction were greatly improved.

Reaction and deactivation kinetics of methanol-to-olefins process based on a special TGA reactor

Thermax 700 thermo gravimetric analysis （TGA） instrument is introduced for the investigation of the reaction and deactivation kinetics of Methanol-to-Olefins （MTO） process with SAPO-34 catalyst.By the use of a special sample basket,the TGA instrument can be viewed as a plug flow fixed-bed reactor,while the weight change of SAPO-34 during reaction can be recorded online.Kinetic data are acquired in the temperature range of 648.2？748.2 K and space velocities of 7.08？35.91 h^-1 （WHSV）.Catalyst activity is expressed with average coke content,and selectivity for different products is related as a function of coke content and temperature.Methane is also introduced into the lumping kinetic model,and power exponent function with first-order reaction is adopted for model deduction.Exponential function is tested to give the best fit for catalyst activity and product selectivity with the highest correlation coefficient.The nicely agreed results between experimental and calculated data suggest that the overall kinetic model would be meaningful in both product distribution prediction and reactor simulation.

Methanol-to-olefin induction reaction over SAPO-34

The methanol-to-olefin induction reaction over the SAPO-34 was performed using a fluidized-bed system.We found that the whole induction period could be divided into three reaction stages.Further investigation of the reaction kinetics revealed that this induction reaction behavior was different from that over H-ZSM-5 catalyst.Compared with the H-ZSM-5,the generation of initial active centers is easier over SAPO-34 because of its limited diffusivity and the spatial confinement effect of the cages.However,the autocatalysis reaction stage is difficult over SAPO-34 because of the continuous formation of inactive methyladamantanes.

Elucidating the dominant reaction mechanism of methanol-to-olefins conversion in H-SAPO-18: A first-principles study

The reaction mechanism of zeolite- or zeotype-catalyzed methanol-to-olefins（MTO） conversion is still a subject of debate. Employing periodic density functional theory calculations, the olefin-based cycle was studied using tetramethylethene（TME） as a representative olefinic hydrocarbon pool in H-SAPO-18 zeotype. The overall free energy barrier at 673 K was calculated and found to be less than 150 kJ/mol in the TME-based cycle, much lower than those in the aromatic-based cycle（〉 200 kJ/mol）, indicating that olefins themselves are the dominant active hydrocarbon pool species in H-SAPO-18. The similarity of the intermediates involved between the aromatic-based cycle and the olefin-based cycle was also highlighted, revealing that both cycles were pattern-consistent. The selectivity related to the distribution of cracking precursors, such as higher olefins or carbenium ions, as a result of the olefin-based cycle for the MTO conversion. The enthalpy barrier of the crack-ing step scaled linearly with the number of carbon atoms of cracking precursors to produce ethene or propene with ethene being much less favored than propene for cracking of C7 and higher pre-cursors. This work highlighted the importance of the olefin-based cycle in H-SAPO-18 for the MTO conversion and established the similarity between the olefin-based and aromatic-based cycles.

A hybrid spatial-temporal deep learning prediction model of industrial methanol-to-olefins process

Methanol-to-olefins,as a promising non-oil pathway for the synthesis of light olefins,has been successfully industrialized.The accurate prediction of process variables can yield significant benefits for advanced process control and optimization.The challenge of this task is underscored by the failure of traditional methods in capturing the complex characteristics of industrial processes,such as high nonlinearities,dynamics,and data distribution shift caused by diverse operating conditions.In this paper,we propose a novel hybrid spatial-temporal deep learning prediction model to address these issues.Firstly,a unique data normalization technique called reversible instance normalization is employed to solve the problem of different data distributions.Subsequently,convolutional neural network integrated with the self-attention mechanism are utilized to extract the temporal patterns.Meanwhile,a multi-graph convolutional network is leveraged to model the spatial interactions.Afterward,the extracted temporal and spatial features are fused as input into a fully connected neural network to complete the prediction.Finally,the outputs are denormalized to obtain the ultimate results.The monitoring results of the dynamic trends of process variables in an actual industrial methanol-to-olefins process demonstrate that our model not only achieves superior prediction performance but also can reveal complex spatial-temporal relationships using the learned attention matrices and adjacency matrices,making the model more interpretable.Lastly,this model is deployed onto an end-to-end Industrial Internet Platform,which achieves effective practical results.

Efficacy of Ca/ZSM-5 zeolites derived from precipitated calcium carbonate in the methanol-to-olefin process

In the context of heightened environmental consciousness and the growing demand for light olefins,this study explores the promising future prospects for their sustainable production from renewable resources.Light olefins(especially propylene)are a pivotal constituent of the petrochemical industry,and their demand is poised for steady growth driven by various sectors(e.g.,electric mobility,consumer goods and packaging industries),which should not rely solely on traditional petroleum-led routes.Therefore,sustainable pathways,such as the methanol-to-olefin(MTO)process catalyzed by zeolites,are gaining attention.Intending to couple the future olefin demands with the concept of a"methanol economy",this study investigates the synthesis of hierarchical Ca/ZSM-5 zeolites using a cost-effective approach involving Precipitated Calcium Carbonate(PCC)as a hard template,leading to superior catalytic performance.Comprehensive characterization techniques are employed to elucidate the cata-lyst's properties,highlighting the dual importance of mesoporosity and calcium species in optimizing its per-formance.Operando spectroscopy provides in-depth insights into its enhanced anti-coking characteristics.This research contributes to expanding the catalyst toolkit for zeolite-catalyzed MTO processes,focusing on propylene production,thereby addressing the increasing demand for light olefins while promoting sustainability and circular economy principles.

Analysis of the overall pressure balance loop for a methanol-to-olefins dual fluidized bed reactor-regenerator

Development of a comprehensive reactor model is of paramount importance for design and scale-up of methanol-to-olefins (MTO) process in a dual fluidized bed reactor (DFB). These models must integrate suitable reaction kinetic expressions with hydrodynamic models properly descriptive of gas-solid contact in fluidized bed reactors. In this modeling study, our previously developed kinetic models of MTO fluidized bed reactor and regenerator are coupled with overall mass, energy and pressure balances to ensure smooth circulation of catalyst particles between the two fluidized beds. This integrated model was then applied to determine geometric dimensions of a demo-scale MTO DFB configuration and to obtain the mass distribution of catalyst particles throughout the entire system including the pipes connecting the two reactors. Our model is capable of being integrated into simulation software such as Aspen Plus for plant-wide optimization and scale-up studies.

Understanding Zeolites Catalyzed Methanol-to-Olefins Conversion from Theoretical Calculations

Zeolites catalyzed methanol-to-olefins （MTO） conversion provides an alternative process to produce light olefins such as ethene and propene from nonpetroleum resources. Despite of successful industrialization of the MTO process, its detailed reaction mechanism is not yet well understood. Here we summarize our work on the hydrocarbon pool reaction mechanism based on theoretical calculations. We proposed that the olefins themselves are likely to be the dominating hydrocarbon pool species, and the distribution of cracking precursors and diffusion constraints affect the selectivity. The similarities between aromatic-based and olefin-based cycles are highlighted.

High-precision diffusion measurement of ethane and propane over SAPO-34 zeolites for methanol-to-olefin process

The methanol-to-olefin （MTO） process has attracted much attention and many problems including lifetime and selectivity of light olefins have all been connected to the diffusion problems in zeolite crystals. However, a quantitative study of diffusion problems in SAPO-34 zeolites is lacking. In this paper, we performed a high-precision diffusion measurement of the diffusion behavior of ethane and propane, which represent ethylene and propylene respectively, over SAPO-34. The diffusions of ethane and propane over fresh and coked SAPO-34 zeolites with different crystal sizes were carefully studied. Ethane and propane show different diffusion behavior in SAPO-34. The diffusion of ethane is almost not influenced by the crystal size and coke percentage, whereas that of propane is strongly affected. A slower diffusion velocity was observed in bigger crystals, and the diffusion velocity decline signifcantly with the coke percentage increasing. The diffusion coefficient was calculated with both the internal and surface diffusion models, and the results show that the surface diffusion plays a key role in the diffusion process of both ethane and propane. We believe that this work would be helpful for understanding the diffusion of different molecules in SAPO-34 zeolites, and may lay the foundation of MTO research.

Enhanced methanol-to-olefins(MTO) performance over SAPO-34 molecular sieves synthesized using novel sources of silicon and aluminium

As the core technology of methanol-to-olefins(MTO),the development of a high-efficiency and low-cost molecular sieve catalyst has always been the most important challenge.Herein,SAPO-34 molecular sieves were synthesized by using three different compositions of amorphous aluminium silicate as both Si and Al source under the same conditions.The structure and composition of synthesized SAPO-34s were investigated using X-ray diffraction and X-ray fluorescence,while the morphology and physical properties were characterized using scanning electron microscopy,N2 adsorption-desorption and ammonia temperature-programmed desorption measurements.Compared to the silica sol as the Si source,the SAPO-34s prepared with amorphous aluminium silicate show the higher solid yields and crystallinity,larger surface area and lower numbers of acid sites.Besides the effect of Si,the effect of the Al source on the textural structure and catalytic performance of SAPO-34s in MTO reactions was investigated in detail.The results confirmed that the SAPO-34s prepared using amorphous aluminium silicate have low Si content and hierarchical structure,which results in a longer catalytic lifetime and higher selectivity for light olefins.The sample S2 exhibited the longest lifetime of 214 min and the highest selectivity for light olefins of 85.37%.This also provides a potential for the approach to obtain a high-efficiency catalyst with enhanced catalytic performance and low cost.

Coking and decoking chemistry for resource utilization of polycyclic aromatic hydrocarbons(PAHs)and low-carbon process

Low-carbon process for resource utilization of polycyclic aromatic hydrocarbons(PAHs)in zeolitecatalyzed processes,geared to carbon neutrality-a prominent trend throughout human activities,has been bottlenecked by the lack of a complete mechanistic understanding of coking and decoking chemistry,involving the speciation and molecular evolution of PAHs,the plethora of which causes catalyst deactivation and forces regeneration,rendering significant CO_(2) emission.Herein,by exploiting the high-resolution matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry(MALDI FT-ICR MS),we unveil the missing fingerprints of the mechanistic pathways for both formation and decomposition of cross-linked cage-passing PAHs for SAPO-34-catalyzed,industrially relevant methanol-to-olefins(MTO)as a model reaction.Notable is the molecule-resolved symmetrical signature:their speciation originates exclusively from the direct coupling of in-cage hydrocarbon pool(HCP)species,whereas water-promoted decomposition of cage-passing PAHs initiates with selective cracking of inter-cage local structures at 8-rings followed by deep aromatic steam reforming.Molecular deciphering the reversibly dynamic evolution trajectory(fate)of full-spectrum aromatic hydrocarbons and fulfilling the real-time quantitative carbon resource footprints advance the fundamental knowledge of deactivation and regeneration phenomena(decay and recovery motifs of autocatalysis)and disclose the underlying mechanisms of especially the chemistry of coking and decoking in zeolite catalysis.The positive yet divergent roles of water in these two processes are disentangled.These unprecedented insights ultimately lead us to a steam regeneration strategy with valuable CO and H_(2) as main products,negligible CO_(2) emission in steam reforming and full catalyst activity recovery,which further proves feasible in other important chemical processes,promising to be a sustainable and potent approach that contributes to carbon-neutral chemical industry.

Insight into the topology effect on the diffusion of ethene and propene in zeolites: A molecular dynamics simulation study

Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products.Besides the topology effect on reaction kinetics,the topology influences the diffusion of reactants and products in catalysts as well.In this work,by using COMPASS force-field molecular dynamics method,we investigated the intracrystalline diffusion of ethene and propene in four different zeolites,CHA,MFI,BEA and FAU,at different temperatures.The self-diffusion coefficients and diffusion activation barriers were calculated.A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA.This ratio decreases with the increase of temperature in the four investigated zeolites.The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.

One-Pot Synthesis of Hierarchically Nanoporous SSZ-13 for Conversion of Methanol to Olefins

The main disadvantage of microporous SSZ-13 catalyst used in the methanol to olefins(MTO) process is its rapid deactivation due to its relatively low coke resistance. Meanwhile, the hierarchical zeolites usually exhibit improved catalytic stability thanks to their better mass transfer ability. Herein, the hierarchically nanoporous SSZ-13 zeolites were one-pot synthesized by using N,N,N-trimethyl-1-adamantanammonium hydroxide as a microporous structure directing agent and C_(18)H_(37) N^+(CH_3)_2 C_6H_(12) N^+(CH_3)_2 C_6 H_(13)(Br^-)_2(hereinafter abbreviated as C_(18-6-6) Br_2) as a mesoporogen. The hierarchically nanoporous SSZ-13 catalyst was characterized by XRD, N_2 physisorption, SEM, TEM, TG-DTG, ^(27) Al and ^(29) SiNMR spectroscopy and NH_3-TPD techniques. The results showed that the hierarchical SSZ-13 zeolite synthesized in the presence of the C_(18-6-6) Br_2 surfactant exhibits aggregates of primary nanocrystals and contains the well-developed mesopores and excellent acidity. Compared to its conventional counterpart, the hierarchical SSZ-13 zeolite has longer catalytic lifetime and higher selectivity for ethylene and propylene in the MTO reaction, which can be attributed to the synergistic effect of their good acidity and improved diffusion properties resulted from the hierarchical pore structure.

Full life cycle characterization strategies for spatiotemporal evolution of heterogeneous catalysts

The sustainable development of the chemical industry requires novel and efficient catalysts and catalytic processes,especially eco-friendly and intrinsically safe processes.The idea is to improve the selectivity,activity,and stability of the catalyst in an appropriate reactor.Therefore,it is of great academic and industrial significance to conduct in-situ characterization of a working catalyst while testing its catalytic performance.This is beneficial for a comprehensive study on the dynamic evolution of the catalyst structure under real conditions,deepening the understanding of the structure-performance relationship of catalysts,and providing a scientific basis for the development of future generation catalytic technology.Thus far,it is still a great challenge to realize full life cycle characterization of heterogeneous catalysts from catalyst formation and function to deactivation under real world conditions.In this mini review,we summarize the characterization strategies for heterogeneous catalysts,using zeolite,metal,and metal oxide catalysts as typical examples.The research strategies for the approximation of industrial conditions,multi-scale in-situ characterization devices,and computational modeling of realistic conditions should provide insight for the research and development of industrial catalysis.

Effect of SiO_(2)/Al_(2)O_(3)ratio on the conversion of methanol to olefins over molecular sieve catalysts

A series of SAPO-34 molecular sieves with different SiO_(2)/Al_(2)O_(3)ratios have been synthesized for the methanol-to-olefin(MTO)reaction.Their physico-chemical properties are characterized by various techniques such as X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),Fourier transform infrared spectroscopy(FT-IR)and N2 adsorption-desorption.The results are compared with those of the commercial HZSM-5,which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO_(2)/Al_(2)O_(3)ratio.The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO_(2)/Al_(2)O_(3)ratio of 0.4 exhibits the highest BET surface area.FT-IR spectra indicate that HZSM-5 has both Brǿnsted and Lewis acid sites and Brǿnsted acid sites are stronger,whereas SAPO-34 samples are dominated only by Lewis acid sites.When the SiO_(2)/Al_(2)O_(3)ratio increases,propylene and butylenes become the predominant product of the MTO reaction over HZSM-5.In contrast,the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene.According to the product distribution,the reaction mechanism over HZSM-5 catalysts is proposed.

Confinement effects in methanol to olefins catalysed by zeolites： A computational review

Small pore zeolites, containing 8-rings as the largest, are widely employed as catalysts in the process of methanol-to-olefins （MTO）. Reactants and products dif- fuse with constraints through 8-rings and this is one of the reaction bottlenecks related to zeolite micropore topology. Small pore zeolites and silicon-aluminophosphates （SAPOs） containing cavities, where olefins are mainly formed through the hydrocarbon pool （HP） mechanism, are frequently tested for MTO. Shape selectivity of transition states within the side-chain methylation will be reviewed as this is one of the controlling steps of the MTO process, with particular attention to the role of hexam- ethylbenzene （HMB） and heptamethylbenzenium cation （HeptaMB~）, which are the most tipically detected reaction intermediates, common to the paring and side-chain routes within the HP mechanism. The relative stability of these and other species will be reviewed in terms of confinement effects in different cage-based zeolites. The role of the different alkylating agents, methanol, dimethyl ether （DME）, and surface methoxy species （SMS） will also be reviewed from the computational viewpoint.

Insight into the Dual Cycle Mechanism of Methanol-to-OIefins Reaction over SAPO-34 Molecular Sieve by Isotopic Tracer Studies

Methanol-to-olefins(MTO)reaction is one of the important non-petroleum routes to produce light olefinsover acidic molecular sieves.In this study,the complete reaction course of MTO on SAPO-34 molecular sieve with retained organics evolution from induction period to deactivation period was investigated systematically at different weight hourly space velocities(WHSV)of methanol.By the aid of 12C/3C-methanol isotopic switch experiment,the dual cycle mechanism involving aromatics-based cycle and alkenes-based cycle was evaluated during the whole reac-tion process.The detailed reaction route varied with the evolution of the retained organics in the catalyst at different reaction stages.The aromatics-based cycle and alkenes-based cycle alternately dominate the reaction process.In the efficient reaction period,aromatics-based cvcle is the main reaction mechanism,while in the induction and deactiva-tion periods.the contribution of alkenes-based cvcle mechanism will become more important.