Methanol To Olefins Process Research Articles

Mechanism of methanol-to-olefin (MTO) reaction

The full name of MTO is methanol to olefin, which is a new chemical reaction process to gain an important chemistry industry raw material. In this paper, we mainly talk about several general reaction process as well as the mechanism of the reaction. The use of molecular sieve catalytic process is a key point where the new MTO process different form the original simple petroleum cracking in order to again olefin. In this work we mainly discuss how the MTO process could happen with the assist of the molecular sieve catalyst. There are direct mechanism Carbene mechanism and Methane-formaldehyde mechanism. The effect of the direct mechanism is to gain some simple and short Carbon-Carbon product. And then the indirect mechanism will take on to control the rate of the reacting process and the ration of different products. By studying on the mechanism of the MTO reaction, we can figure out how a powerful catalyst, molecular sieve catalyst, works in the reaction. Also, the MTO process is a meaningful way to take place of the origin cracking process to gain olefin, as the storage of petroleum is decreasing fast recently.

Spatial-temporal self-attention network based on bayesian optimization for light olefins yields prediction in methanol-to-olefins process

Methanol-to-olefins (MTO), as an alternative pathway for the synthesis of light olefins (ethylene and propylene), has gained extensive attention. Accurate prediction of light olefins yields can effectively facilitate process monitoring and optimization, as they are significant economic indexes and stable operation indicators of the industrial MTO process. However, the nonlinearity and dynamic interactions among process variables pose challenges for the prediction using traditional statistical methods. Additionally, physical-based methods relying on first-principle theory are always limited by an insufficient understanding of reaction mechanisms. In contrast, data-driven methods offer a viable solution for the prediction based solely on process data without requiring extensive process knowledge. Therefore, in this work, a data-driven approach that integrates spatial and temporal self-attention modules is proposed to capture complex interactions. Furthermore, Bayesian optimization is employed to determine the optimum hyperparameters and enhance the accuracy of the model. Studies on an actual MTO process demonstrate the superior prediction performance of the proposed model compared to baseline models. Specifically, 24 process variables are selected as the high-dimensional inputs, and yields of ethylene and propylene, as the low-dimensional outputs, are successfully predicted at various prediction horizons ranging from 2 to 8 h.

Investigating the Sole Olefin-Based Cycle in Small-Cage MCM-35-Catalyzed Methanol-to-Olefins Reactions.

Small-pore zeolites catalyze the methanol-to-olefins (MTO) reaction via a dual-cycle mechanism, encompassing both olefin- and aromatic-based cycles. Zeolite topology is crucial in determining both the catalytic pathway and the product selectivity of the MTO reaction. Herein, we investigate the mechanistic influence of MCM-35 zeolite on the MTO process. The structural properties of the as-synthesized MCM-35 catalyst, including its confined cages (6.19 Å), were characterized, confirming them as the catalytic centers. Then, the MTO reactions were systematically performed and investigated over a MCM-35 catalyst. Feeding pure methanol to the reactor yielded minimal MTO activity despite the formation of some aromatic species within the zeolite. The results suggest that the aromatic-based cycle is entirely suppressed in MCM-35, preventing the simultaneous occurrence of the olefin-based cycle. However, cofeeding a small amount of propene in methanol can obviously enhance the methanol conversion under the same studied reaction conditions. Thus, the exclusive operation of the olefin-based cycle in the MTO reaction, independent of the aromatic-based cycle, was demonstrated in MCM-35 zeolite.

A vinyl-pedant triazine-based covalent organic framework for efficient C3H6/C2H4 separation

The separation of propylene (C3H6) and ethylene (C2H4) during the methanol-to-olefin (MTO) process is crucial yet challenging. Herein, we report a covalent organic framework (TzDva) featuring favorable nitrogen adsorption sites and vinyl modification for the capture of C2H4 from C3H6/C2H4 mixtures. TzDva exhibits enhanced crystallinity and porosity as well as reduced pore size compared to its vinyl-free counterpart (TzPA), as revealed through comprehensive characterization. The excellent performance of TzDva for C3H6/C2H4 separation combined with its excellent recyclability was confirmed by both static adsorption and dynamic breakthrough experiments. Particularly, it exhibits a C2H4 productivity of 4.29 mmol g−1 at 298 K with C3H6/C2H4 (10/90) mixture. With decreasing temperature to 273 K, the performance can be further enhanced. Theoretical calculations and in-situ infrared analysis suggested that the remarkable selectivity of TzDva towards C3H6 stems from its favorable pore environment, which facilitates a greater number of interactions with C3H6 compared to C2H4 guests. These results underpinned the effective separation of gas mixtures relevant to the MTO process.

Alteration of acidity and porosity of Beta zeolite using fibrous silica for light olefin production

Traditional olefin production heavily depends on fossil fuels, which are a significant contributor to environmental issues. Methanol to olefin (MTO) is among non-fossil fuel alternatives to produce olefinic products from abundant resources, such as biomass, coal, and natural gas. Nevertheless, the catalytic reaction of MTO over commercial zeolite catalysts is hindered by their low activity, mainly due to the micropore structure and excessive acidity within the zeolite. Herein, Beta zeolite with fibrous silica structure was successfully synthesized via the microemulsion and Beta seed-assisted method. The catalysts were characterized using FESEM, N2 physisorption, and ammonia-TPD. FESEM results revealed a well-ordered spherical morphology of HFBETA with uniform particle size distribution. In surface analysis, the HFBETA exhibits higher BET surface area and mesopore volume compared to commercial HBETA by 35% and 86%, respectively. The introduction of fibrous silica within the Beta structure led to a significant drop in the acidity of the catalyst, as shown in ammonia-TPD results. These led to superior catalytic performance of HFBETA in the MTO process.

A versatile electrospinning method to fabricate ZSM-5-decorated MgO nanofibers as a catalyst for methanol to light olefins: Toward remarkable stability and superior performance

In response to the increasing concerns about climate change and the depletion of fossil fuel reserves, the application of zeolite ZSM-5 as a catalyst in the methanol to olefin (MTO) process is considered a promising chemical technique. It holds the potential to produce essential chemical building blocks, such as light olefins, using sustainable raw materials. In this study, electrospun MgO/ZSM-5 nanofibers were synthesized to enhance mass/heat transfer limits during the MTO process and improve catalyst stability. In this synthesis, ZSM-5 nanoparticles with a mean diameter of 600 nm were arranged on magnesium oxide nanofibers with a mean diameter of 200 nm. The catalysts were characterized using various techniques, including XRD, SEM, TEM, EDX-Mapping, NH3-TPD, BET, and TGA. The electrospinning technique prevented nanoparticle accumulation and improved the morphology of the catalyst. In an isothermal fixed-bed reactor, the catalysts were tested at 450 °C, 1 atm, WHSV = 4.5 hr−1, with a methanol-water solution in a 1:1 (v/v) ratio as the feed. The stability of the nanofibers was found to be enhanced compared to ZSM-5 nanoparticles. MgO/ZSM-5-50 nanofibers (50 wt% zeolite), MgO/ZSM-5-80 nanofibers (80 wt% zeolite), and ZSM-5 nanoparticles exhibited methanol conversion rates of 99 %, 88 %, and 76 %, respectively, after 430 min of continuous operation. Furthermore, the amount of coke formed after 10 h for MgO/ZSM-5-50, MgO/ZSM-5-80, and ZSM-5 was 11.83 wt%, 13.63 wt%, and 20.98 wt%, respectively. The reduced coke formation on the electrospun samples compared to ZSM-5 nanoparticles demonstrates improved performance and stability for nanofiber catalysts.

The role of decarboxylation reactions during the initiation of the methanol-to-olefins process

The mechanism for direct CC bond formation during the initiation of the methanol-to-olefins (MTO) process is still under discussion. Carbon dioxide formation is often observed during initiation, but there are only few investigations into the role of decarboxylation. We investigate decarboxylation pathways in the H-SSZ-13 zeolite from methanol to olefins via direct carbon–carbon coupling. Additionally, the rate-determining steps were recomputed in the H-ZSM-5 and H-SAPO-34 zeolite. Gibbs free energy barriers were calculated using periodic density functional theory in combination with CCSD(T) calculations on cluster models. For H-SSZ-13, kinetic batch reactor simulations were performed. We found for H-SSZ-13 that pathways via decarboxylation reactions are equally likely as previously computed pathways including decarbonylation mechanisms (also known as ketene or CO pathway). Lactones formed from ketenes and formaldehyde were identified as the main intermediates. The decarboxylation mechanism has similar barriers in H-SSZ-13, H-ZSM-5, and H-SAPO-34, while the barriers for methylation and decarbonylation reactions are significantly lower in H-ZSM-5 and higher in H-SAPO-34. Decarboxylation reactions of lactones could explain experimentally detected carbon dioxide during the initial phase of the MTO process.

Effect of CNT over structural properties of SAPO-34 in MTO process: Experimental and molecular simulation studies

The hierarchical silicoaluminophosphate (SAPO-34) catalyst was synthesized using the mixtures of diethylamine (D) and butylamine (B) as a structure-directing agent (SDA), and carbon nanotube (CNT) as a secondary template in the hydrothermal method. The catalysts were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 physisorption, and temperature-programmed desorption of ammonia (NH3-TPD) techniques and evaluated for the catalytic activity in the Methanol to Olefins (MTO) process. The results showed that the use of CNT as the secondary template improved the hierarchical structure of SAPO-34 due to increasing the external surface area and mesoporosity and decreasing the particle size and as a result, made better the performance of the prepared SAPO-34 zeolite in the MTO process. Among all the prepared samples, the CNT-B-D catalyst synthesized by mixing three templates displayed the highest ethylene and propylene selectivity of 49% and 34%, respectively. Also, using CNT in the synthesis of samples increased the catalytic stability. In addition, pure, binary, and ternary adsorption isotherms and diffusivities of the main products and reactants over the SAPO-34 were investigated by theoretical measurements, because sorption and diffusion affect the catalyst stability and C2–C3 selectivity in the MTO reaction. The higher diffusion rate of ethylene leads to following the aromatic-based cycle in the MTO process.

Collaborative removal of fine catalysts particles and insoluble organics from methanol-to-olefins reaction wastewater using horizontal swirl regeneration micro-channel separation (HSRMS)

The methanol-to-olefins (MTO) process is regarded as a crucial approach for ensuring the sustainable growth of China's chemical industry. However, the fine catalyst particles and insoluble organics in the water system poses a serious threat to the stability of the MTO process. A novel horizontal swirl regeneration micro-channel separation (HSRMS) method for purifying the MTO reaction wastewater was developed in this study. On-site experiments were conducted using a device with a capacity of 1 t/h to investigate the separation and regeneration effects under various parameters and to verify the feasibility of this method through a long-term observation. The results showed that this method could effectively remove the fine solids and insoluble organics in the reaction wastewater, and the device operated stably with fluctuations in both the quality and quantity of wastewater for 24 consecutive days. The suspended solids in the effluent was maintained below 5 mg/L, and the average removal efficiency for insoluble organics exceeded 75%. Furthermore, the excellent regeneration performance was achieved, with solid particles and oil in the media reduced to less than 0.2% after regeneration. This method could ensure long-term stable operation of the water system and outperform other commonly used reaction wastewater treatment methods in terms of investment, maintenance cost, freshwater supplementation, and energy consumption.

Microkinetic Simulations of Methanol-to-Olefin Conversion in H-SAPO-34: Dynamic Distribution and Evolution of the Hydrocarbon Pool and Implications for Catalytic Performance

The dominating hydrocarbon pool species (HCPs) in zeolites for methanol-to-olefin (MTO) conversion have been the subject of intense debate for decades due to the diversity of structures and the complexity of reaction networks. We performed microkinetic simulations in a three-site model to study the MTO conversion in industrially relevant H-SAPO-34 zeolite under a wide range of operating conditions. The energetics of 229 and 342 elementary reaction steps were employed, respectively, in the aromatic-based and olefin-based cycles. The dynamic distribution and evolution of the retained aromatic or olefinic HCPs and the origin of olefin products were revealed with respect to reaction conditions. We corroborate that the olefin-based cycle dominates the MTO conversion in H-SAPO-34 under most reaction conditions, and the contribution of the aromatic-based cycle increase with increasing temperature, decreasing pressure, and/or decreasing water partial pressure. The paring route, dedicated highly to propene formation, prevails in the aromatic-based cycle; the side chain route, favoring exclusively ethene formation, only prevails at extremely lower temperatures, higher pressures, and higher water contents. The inherent activity of each aromatic HCP via the paring cycle increases, while its population retained in H-SAPO-34 usually decreases, with the methylation degree remarkably from tetramethylbenzene to hexamethylbenzene. The contents of higher methylbenzenes increase with decreasing water partial pressure, leading to the enhanced contribution of the aromatic-based cycle. The olefin-based cycle contributes to the formation of both ethene and other olefins, and the product distribution is drastically sensitive to reaction conditions. Ethene predominantly comes from the cracking of C5 and C6 species, and propene comes from C5 to C7 species. The olefin-based cycle shifts from the interconversion of C2–C7 olefins toward C2–C5 ones with increasing temperature and water partial pressure to enhance ethene formation. Under industrially relevant conditions, the conversion rate of methanol via the olefin-based cycle is 40-fold greater than that via the aromatic-based cycle (6.6 vs 0.15 s–1), and the former agrees unexpectedly with the experimental value in low-silica AlPO-34 (7.0 s–1). This work thus solves the puzzle of dominating HCPs as a function of reaction conditions in H-SAPO-34 and provides mechanistic insights into the kinetic behaviors, which are the basis for the optimization of the MTO catalyst and process.

Cavity-controlled methanol conversion over zeolite catalysts.

The successful development and application in industry of methanol-to-olefins (MTO) process brought about an innovative and efficient route for olefin production via non-petrochemical resources and also attracted attention of C1 chemistry and zeolite catalysis. Molecular sieve catalysts with diversified microenvironments embedding unique channel/cavity structure and acid properties, exhibit demonstrable features and advantages in the shape-selective catalysis of MTO. Especially, shape-selective catalysis over 8-MR and cavity-type zeolites with acidic supercage environment and narrow pore opening manifested special host-guest interaction between the zeolite catalyst and guest reactants, intermediates and products. This caused great differences in product distribution, catalyst deactivation and molecular diffusion, revealing the cavity-controlled methanol conversion over 8-MR and cavity-type zeolite catalyst. Furthermore, the dynamic and complicated cross-talk behaviors of catalyst material (coke)-reaction-diffusion over these types of zeolites determines the catalytic performance of the methanol conversion. In this review, we shed light on the cavity-controlled principle in the MTO reaction including cavity-controlled active intermediates formation, cavity-controlled reaction routes with the involvement of these intermediates in the complex reaction network, cavity-controlled catalyst deactivation and cavity-controlled diffusion. All these were exhibited by the MTO reaction performances and product selectivity over 8-MR and cavity-type zeolite catalysts. Advanced strategies inspired by the cavity-controlled principle were developed, providing great promise for the optimization and precise control of MTO process.

A computational investigation of the decomposition of acetic acid in H-SSZ-13 and its role in the initiation of the MTO process

The zeolite-catalyzed reaction of acetic acid is important in the direct utilization of biomass and also plays a role in the reactivity of oxygenates in the methanol-to-olefins (MTO) process.

A Simultaneous Design and Optimization Framework for the Reaction and Distillation Sections of Methanol to Olefins Process

The reaction and separation sections are the keys to the methanol-to-olefins (MTO) chemical processes, and they should be optimized to reduce the cost of production. This work develops a framework for the simultaneous design and optimization of the reaction and distillation sections. An optimization model with shortcut and rigorous methods combined is established for distillation columns to improve accuracy and efficiency. With the auxiliary devices and the selection of utilities considered, the reaction and distillation sections are integrated to maximize profits. The genetic algorithm targets the optimal parameters, including the catalyst’s coke content and reaction temperature, each column’s operating pressure, and the allocation of utilities and auxiliary devices. For the studied MTO process, the optimal reaction temperature and catalyst’s coke content were identified to be 496 °C and 7.8%, respectively. The maximum profit is 15.3% greater than that identified with only the separation section optimized, and the minimum total annual cost (TAC) of the separation section is 3.73% less.

Sustainable synthesis of AEI/CHA intergrowth zeolites for methanol-to-olefins conversion

The conventional hydrothermal synthesis of zeolites is inevitably accompanied by the production of mother liquors containing plentiful unreacted raw materials and organic templates. The direct emission or improper use of these mother liquors will cause not only the environmental contamination but also the waste of resources. Here we report a promising synthetic strategy for the effective recycle of mother liquors produced from the industrial production of SAPO-34 zeolites. Mother liquors with the addition of extra Si, P and Al were spray-dried and subsequently converted to the crystal seeds by vapor-phase-transport (VPT) method. Zeolite products with improved porosity and altered acidity were eventually acquired by VPT-Seeds-assisted hydrothermal crystallization, in which the topologic structures (e.g., CHA, AEI or AEI/CHA intergrowth) of zeolites depended significantly on the crystalline phase of VPT-Seeds. We demonstrated further via FT-IR and kinetics study that VPT-Seeds accelerated the crystallization of zeolites dramatically without the severe dissolution during the whole stage of synthesis. The as-synthesized AEI/CHA intergrowth zeolites showed the enhanced catalytic lifetime (increased at least by 27.6%) and higher selectivity in (C2H4+C3H6) (increased by 2.5%) during methanol-to-olefins (MTO) reactions than the pure CHA zeolites synthesized by the conventional hydrothermal method. Zeolites synthesized using the secondary recycled mother liquors in the same way also showed the comparable catalytic performances in MTO process, again verifying the feasibility of our methods to recycle mother liquors. The sustainable synthesis route developed in this work should be applicable to the industrial production of a wide variety of zeolites.

Electronic structure of chabazite zeolites H-SSZ-13 and H-SAPO-34

H-SSZ-13 and H-SAPO-34 are chabazite (CHA) zeolites and successful methanol-to-olefins (MTO) catalysts. In order to understand their intrinsic origin of catalytic activity and compare their properties, the electronic structure of H-SSZ-13 and H-SAPO-34 referencing to neutral SiO2-CHA and AlPO4-CHA was studied in this work exhaustively. Based on the results, the following conclusions can be made. (1) The catalytic activity of acidic zeolites stems from that the electronic distribution of the valence band maximum (VBM) is highly localized in the acid catalytic center. (2) The acidity of H-SAPO-34 is weaker than that of H-SSZ-13 because the strength of H–O bond in H-SAPO-34 is stronger than that in H-SSZ-13. (3) From the Bader Charge analysis, the acidic center of H-SAPO-34 possesses stronger polarization ability than peripheral framework, while in H-SSZ-13 the polarization ability of the acidic center is almost equal with the outer framework. Thus, small gas molecules are easy to reach active centers and so H-SAPO-34 are more efficient for MTO process.

Cooperative physical separation of oil and suspended solids from methanol-to-olefin wastewater: A pilot study

Methanol-to-olefin (MTO) is an important non-petroleum chemical process for the preparation of light olefins. However, the MTO process consumes copious amounts of water and produces large amounts of untreated effluent. Therefore, the realization of efficient wastewater treatment and recycling is key to the green low-carbon development of MTO. Here, a cooperative process combining swirl regenerating micro-channel separation (SRMS) and combined fibrous coalescence (CFC) technologies was proposed to separate high contents of oil and suspended matter in MTO wastewater. Using a pilot device with a treatment capacity of 1 m3/h, the average oil content in MTO wastewater decreased from 750 mg/L to <30 mg/L, while the average content of suspended matter decreased from 108 mg/L to <15 mg/L. Compared with a commercial MTO wastewater treatment process (olefin production capacity of 0.6 million tons per annum), the proposed method could reduce wastewater discharges and costs by 57% and US$ 0.23 million per annum respectively. Equipment costs and operational energy consumption were also reduced by 30% and >95% respectively. The combined process may provide the basis for the green and sustainable treatment of MTO wastewater and its recycling.

Kinetic modeling of methanol-to-olefins process over SAPO-34 catalysts in a dual fluidized bed reactor–regenerator

Based on a lumped methanol-to-olefins (MTO) reaction kinetic model over SAPO-34 catalyst particles, a one-dimensional two-phase model was developed for bubbling fluidized bed reactor and catalyst regenerator. Comparison of the model predictions with literature experimental data showed good agreement over wide ranges of operating conditions both on a bench-scale unsteady-state bubbling fluidized bed reactor as well as pilot and demo-scale steady-state dual fluidized bed reactor–regenerator. The two-phase reactor model was also applied for catalyst coke content combustion with diluted air to design the regenerator of the dual fluidized bed reactor. Finally, the heat duty required for cooling circulating catalyst particles is obtained from overall energy balances. This integrated reactor–regenerator simulation allows for seamless analysis of MTO process. The trade-off between the complexity and applicability of the model makes it a useful choice for conceptual process designs, scale-up, integration with simulation software, optimization, process control and economic analyses.

CFD study of the reactive gas-solid hydrodynamics in a large-scale catalytic methanol-to-olefin fluidized bed reactor

Lacking the understanding of multiphase flow in the fluidized bed methanol-to-olefin (MTO) process hinders the reactor design, operation, and optimization. Accordingly, a three-dimensional multiphase particle-in-cell model is established to study hydrodynamics and thermochemical characteristics during the MTO process in a fluidized bed reactor. After model validation, the influences of several critical operating parameters on reactor performance are discussed. The results show that particles in the medium part and freeboard of the reactor have heterogeneous velocity, temperature, and heat transfer coefficient (HTC) distributions. Thermal quantities of gas and solid phases are uniformly distributed in the medium part and freeboard of the reactor. The particle-averaged HTC under ranges from 60 to 120 W/(m2·K). Increasing wall temperature enlarges the particle HTC due to the enhanced exothermic reactions. Decreasing the particle diameter gives rise to a larger particle HTC. The vertical particle dispersion coefficient (Dz) is in the range of 0.01 m2/s to 0.03 m2/s. Methanol converts into olefin in a short period. Increasing methanol to catalyst ratio and wall temperature increases olefin including C2H4, C3H6, C4H8, and C5H10, and promotes the gas thermal properties. Particles with multi-sizes show a better MTO conversion performance than those with mono-sizes regarding the particle HTC and gas products.

Probing into the building and evolution of primary hydrocarbon pool species in the process of methanol to olefins over H-ZSM-5 zeolite

It is well known that the reaction process of methanol to olefins (MTO) keeps to the hydrocarbon pool (HCP) mechanism; however, there is no clear consensus over how the primary HCP species are built and how they evolve in the transition period of MTO. In this work, the building and evolution of the primary HCP species for MTO over H-ZSM-5 zeolite were probed through combined pulse-quench, GC–MS and 13C-methanol labeling techniques. The results indicate that propene/ethene carrying the first C–C bonds formed in the induction period can quickly constitute long chain alkenes through oligomerization. Subsequently, the long chain alkenes are inclined to form methylcyclopentadienes (MCPdienes) via cyclization. After that, methylbenzenes (MBs) are produced through the ring expansion of MCPdienes. Both MCPdienes and MBs can boost the production of light olefins in MTO; MCPdienes decompose or convert to MBs easily at elevated temperature, whereas MBs accumulate gradually on the zeolite channels and contribute more greatly to the production of olefins at steady stage and high temperature. As a result, MCPdienes are identified as the primary HCP intermediates in the early transition period of MTO and their appearance promotes the build-up of aromatic HCP (dominated by MBs) and drives the MTO process from the induction period to the steady period. The insight shown in this work helps to clarify the reaction mechanism of MTO in the initial period, which should be of benefit to further researches into MTO.

Conversion of Methanol to Olefins over Modified OSDA-Free CHA Zeolite Catalyst

Methanol to olefins (MTO) is an essential process that produces olefins from both renewable and fossil fuels resources. Chabazite (CHA) is an efficient catalyst for MTO process due to its distinct properties that promote light olefins (i.e., ethylene and propylene) production. Herein, we report a series of chabazite-based catalysts (OSDA-free with enhanced textural properties) that facilitate the MTO reaction. The synthesized CHA was modified by steam injection (CHA-S), acid treatment (CHA-A), steam and acid treatment (CHA-SA), and metal incorporation (CHA-SA (Mg), CHA-SA (Ca), and CHA-SA (Ba)). The catalysts were characterized by several characterization techniques. The structure was investigated using X-ray diffraction (XRD) and nuclear magnetic resonance, while the morphology and physical properties were studied by field emission scanning electron microscopy (FE-SEM), N2 adsorption/desorption, and ammonia temperature-programmed desorption (NH3-TPD). The catalysts were evaluated at 450 °C until deactivation. CHA modified by only acid treatment showed higher selectivity to olefins from ca. 92 to 95 wt.% but suffered quick deactivation. CHA modified with both steam and then acid treatment was more stable in the MTO process.