Gas To Liquid Research Articles

Synthesis of a phosphomolybdic acid-modified AlPO4-5/SAPO-34 composite catalyst and its catalytic performance in the MTO reaction

SAPO-34 catalysts with high selectivity for light olefins were first synthesized via the introduction of phosphomolybdic acid (HPMo) and AlPO4-5 zeolite into the initial gel. The physical and chemical characteristics of the synthesized catalysts were determined by a series of techniques and the catalytic performance of the modified composite zeolites for the methanol-to-olefin (MTO) reaction was investigated. The results indicated that HPMo-modified SAPO-34 was featured with more Brønsted acid sites, more mesopores, and a smaller crystal size, thereby demonstrating superior catalytic performance. The further combination with AlPO4-5 (16.7 wt%) prolonged the lifetime of the HPMo-modified SAPO-34, which is thought in this paper related to its 12-ring straight channel (0.7–0.8 nm) and the absence of any Brønsted acid sites. The MTO tests showed that the light olefins selectivity for the modified composite zeolites reached 95.1 %, while the catalyst lifetime remained at 445 min

Modeling and analysis of air combustion and steam regeneration in methanol to olefins processes

Light olefins is the incredibly important materials in chemical industry. Methanol to olefins (MTO), which provides a non-oil route for light olefins production, received considerable attention in the past decades. However, the catalyst deactivation is an inevitable feature in MTO processes, and regeneration, therefore, is one of the key steps in industrial MTO processes. Traditionally the MTO catalyst is regenerated by removing the deposited coke via air combustion, which unavoidably transforms coke into carbon dioxide and reduces the carbon utilization efficiency. Recent study shows that the coke species over MTO catalyst can be regenerated via steam, which can promote the light olefins yield as the deactivated coke species can be essentially transferred to industrially useful synthesis gas, is a promising pathway for further MTO processes development. In this work, we modelled and analyzed these two MTO regeneration methods in terms of carbon utilization efficiency and technology economics. As shown, the steam regeneration could achieve a carbon utilization efficiency of 84.31%, compared to 74.74% for air combustion regeneration. The MTO processes using steam regeneration can essentially achieve the near-zero carbon emission. In addition, light olefins production of the MTO processes using steam regeneration is 12.81% higher than that using air combustion regeneration. In this regard, steam regeneration could be considered as a potential yet promising regeneration method for further MTO processes, showing not only great environmental benefits but also competitive economic performance.

Hydrodynamics of a cold circulating fluidized bed for methanol-to-olefins (MTO) process: experimental and computational investigation

The present study aims to investigate the hydrodynamic behavior of gas–solid flow in a pseudo-two-dimensional cold circulation fluidized bed specifically designed to mimic a plane cut of an industrial methanol-to-olefins (MTO) bed. The solid velocity pattern was experimentally examined using the Particle Image Velocimetry with Digital Image Analysis (PIV-DIA) technique. The hydrodynamics of this pseudo-2D bed were studied using the twoPhaseEulerFoam solver in OpenFOAM, and the adjusted solver was validated through solid particle velocity and solid volume fraction comparisons, showing good agreement with experimental data. Additionally, the study explores different geometries, including symmetric and asymmetric baffles, to understand their impact on the mixing characteristics of the circulating fluidized bed for MTO. The findings highlight the significant role of asymmetric baffles in enhancing mixing behavior. Furthermore, the DIA technique was employed to study the effects of bubbles on gas–solid mixing, revealing that the low mixing region of the bed limited the diameter of bubbles.

Recycling of gas-to-liquid sludge as a potential organic amendment: Effect on soil and cotton properties under hyperarid conditions

Gas-to-liquid (GTL) sludge is a specific wastewater treatment by-product, which is generated during the industrial process of natural gas conversion to transportation fuels. This least studied sludge is pathogen-free and rich in organic carbon and plant nutrients. Therefore, it can be reused for soil enhancement as a sustainable management strategy to mitigate landfill gas emissions. In this field study, we compared the performance of soil treatments with GTL sludge to the more conventional chemical fertilizers and cow manure compost for the cultivation of cotton under hyperarid conditions. After a complete growing season, GTL sludge application resulted in the enhancement of soil properties and plant growth compared to conventional inputs. As such, there was a significant dose-dependent increase of soil organic matter (4.01% and 4.54%), phosphorus (534 and 1090 mg kg−1), and cumulative lint yield (4.68 and 5.67 t ha−1) for GTL sludge application rates of 1.5% and 3%, respectively. The produced fiber quality was adequate for an upland cotton variety (Gossypium hirsutum var. MAY 344) and appeared more dependent on the prevailing climate conditions than soil treatments. On the other hand, the adverse effects generally related to industrial sludge reuse were not significant and did not affect the designed agro-environmental system. Accordingly, plants grown on GTL sludge-amended soils showed lower antioxidant activity despite significant salinity increase. In addition, the concentrations of detected heavy metals in soil were within the standards’ limits, which did not pose environmental issues under the described experimental conditions. Leachate analysis revealed no risks for groundwater contamination with phytotoxic metals, which were mostly retained by the soil matrix. Therefore, recycling GTL sludge as an organic amendment can be a sustainable solution to improve soil quality and lower carbon footprint. To reduce any environmental concerns, an application rate of 1.5% could be provisionally recommended since a two-fold increase in sludge dose did not result in a significant yield improvement.

Relay Catalysis for Highly Selective Conversion of Methanol to Ethylene in Syngas.

The precise C-C coupling is a challenging goal in C1 chemistry. The conversion of methanol, a cheap and easily available C1 feedstock, into value-added and largely demanded olefins has been playing a game-changing role in the production of olefins. The current methanol-to-olefin (MTO) process, however, suffers from limited selectivity to a specific olefin. Here, we present a relay-catalysis route for the high-selective conversion of methanol to ethylene in syngas (H2/CO) typically used for methanol synthesis. A bifunctional catalyst composed of selectively dealuminated H-MOR zeolite and ZnO-TiO2, which implemented methanol carbonylation with CO to acetic acid and selective acetic acid hydrogenation to ethylene in tandem, offered ethylene selectivity of 85% at complete methanol conversion at 583 K. The selective removal of Brønsted acid sites in the 12-membered ring channel of H-MOR favors the selectivity of acetic acid in CH3OH carbonylation. The high capabilities of ZnO-TiO2 in the adsorption of acetic acid and the activation of H2 play key roles in selective hydrogenation of acetic acid to ethylene. Our work provides a promising relay-catalysis strategy for precise C-C coupling of C1 to C2 molecules.

Bayesian optimization of multiscale kernel principal component analysis and its application to model Gas-to-liquid (GTL) process data

Kernel methods map the data from original space into a higher-dimensional space in which linear methods are applied. In many applications, the inverse mapping is also important, and the pre-image of a feature vector must be found in the original space. Kernel principal component analysis (KPCA) based kernel density estimation (KDE) has been developed to solve this problem. However, the performance of the KPCA technique greatly depends on the choice of some parameters which can lead to poor modeling performance when these parameters are not well identified. Thus, fully Bayesian optimization KPCA (BOKPCA) is proposed to enhance the performance of the KPCA model. BOKPCA method aims to automatically select the best parameters of the KPCA model. Generally, kernel methods struggle to handle nonlinear data contaminated with high levels of noise. This is because the noise affects every principal component, making it challenging to mitigate its influence during the reconstruction step. Consequently, to further enhance the ability of KPCA and BOKPCA models, we propose to integrate multi-scale filtering with these two models. The efficiency of the proposed methods are evaluated using a simulated nonlinear process and real data generated from a bench-scale Fischer–Tropsch (FT) process.

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.

Enhanced methanol to gasoline performance using nanosheet-like SAPO-11 catalyst

Herein, spherical and nanosheet-like SAPO-11s were successfully synthesized hydrothermally and utilized to catalyze the methanol-to-gasoline (MTG) process. The nanosheet-like SAPO-11 (SAPO-11-A) had a thickness of about 10 nm, while the spherical SAPO-11 (SAPO-11-B) had a particle size of around 11 μm. Compared to SAPO-11-B, the property of SAPO-11-A was enhanced by 42.9% in specific surface area (SSA), 38.1% in mesopore volume (Vme) and 20.2% in acid amounts, respectively. In terms of catalytic performance during the MTG reaction, SAPO-11-A demonstrated superior results not only in the methanol conversion (95.82%), gasoline-range hydrocarbons selectivity (58.76%) and iso/nparaffin ratio (8.17) but also in suppressed coke deposition (2.56%) compared with those (90.63%, 50.95%, 4.75 and 5.73%, respectively) of SAPO-11-B. Additionally, the optimal MTG process conditions were identified utilizing SAPO-11-A, demonstrating a methanol conversion rate of 98.34%, a gasoline hydrocarbon selectivity of 67.61%, an isoparaffin selectivity of 36.01% and an iso/nparaffin ratio of 10.94 at 380 °C, weight hourly space velocity (WHSV) of 2 h−1 and 1 MPa. These results highlight the potential of nanosheet SAPO-11 to produce gasoline-range hydrocarbons rich in isoparaffins.

Co-Hydroprocessing of Fossil Middle Distillate and Bio-Derived Durene-Rich Heavy Ends under Hydrotreating Conditions

Methanol-to-gasoline (MTG) and dimethyl ether-to-gasoline (DTG), as industrially approved processes for producing greenhouse gas-neutral gasoline, yield byproducts rich in heavy mono-ring aromatics such as 1,2,4,5-tetramethylbenzene (durene). Due to its tendency to crystallize and the overall poor fuel performance, the heavy fuel fraction is usually further processed using after-treatment units designed for this purpose. This research article discusses the co-hydroprocessing (HP) of bio-derived heavy gasoline (HG) with fossil middle distillate (MD), drawing on available refinery hydrotreaters. Co-HP experiments were conducted in a laboratory-scale fixed bed reactor using an industrial CoMo/γ-Al2O3 catalyst, varying the space-time between 0.7 and 4.0 cmCat3 h cmFeed−3 and the reaction temperature between 340 and 390 °C. In addition to the durene conversion, special attention was paid to the octane and cetane numbers (CN) of gasoline and MD, respectively. A six-lump model with ten parameters was developed to predict relevant fuel yields dependent on the process conditions. Under stable catalyst conditions, C10 aromatic conversions of more than 60% were obtained, while the CN remained close to that of pure MD. Harsh process conditions increased the gasoline yield up to 20% at the cost of MD, while the kerosene yield remained almost constant. With an optimized lumping model, fuel yields could be predicted with an R2 of 0.998. In this study, co-HP heavy aromatic-rich MTG/DTG fuels with fossil MD were proven to be a promising process strategy compared to a stand-alone after-treatment.

Intergrowth Zeolites, Synthesis, Characterization, and Catalysis.

Microporous zeolites that can act as heterogeneous catalysts have continued to attract a great deal of academic and industrial interest, but current progress in their synthesis and application is restricted to single-phase zeolites, severely underestimating the potential of intergrowth frameworks. Compared with single-phase zeolites, intergrowth zeolites possess unique properties, such as different diffusion pathways and molecular confinement, or special crystalline pore environments for binding metal active sites. This review first focuses on the structural features and synthetic details of all the intergrowth zeolites, especially providing some insightful discussion of several potential frameworks. Subsequently, characterization methods for intergrowth zeolites are introduced, and highlighting fundamental features of these crystals. Then, the applications of intergrowth zeolites in several of the most active areas of catalysis are presented, including selective catalytic reduction of NOx by ammonia (NH3-SCR), methanol to olefins (MTO), petrochemicals and refining, fine chemicals production, and biomass conversion on Beta, and the relationship between structure and catalytic activity was profiled from the perspective of intergrowth grain boundary structure. Finally, the synthesis, characterization, and catalysis of intergrowth zeolites are summarized in a comprehensive discussion, and a brief outlook on the current challenges and future directions of intergrowth zeolites is indicated.

Internal reuse of methanol-to-olefin wastewater based on micro-channel separation coupling hydrocyclone regeneration

Methanol-to-olefin (MTO) is a typical new coal chemical industry example. Due to the large volume of generated wastewater, complex composition including catalysts, aromatics and various oxygen-containing compounds, and serious environmental hazard, wastewater recycling is critical for sustainable industrial development and ecological protection. Herein, a swirl regenerating micro-channel separation (SRMS) technology was proposed to integrate deep filtration and hydrocyclone-enhanced regeneration. A small-scale experimental investigation was first conducted to verify the feasibility of the MTO wastewater treatment. A pilot SRMS device with a treatment capacity of 20 m3/h was constructed, and the device's continuous operation effect and stability were comprehensively evaluated. The separation performance of the SRMS device at different solution pH values and the impact of the hydrocyclone-enhanced regeneration of separation media were discussed in detail. At low solution pH values (<7), the SRMS device exhibits an average separation efficiency of 92.0% for fine particulate matter in wastewater, and the median particle size, d50, decreases from 1.55 to 0.6 μm. As the solution pH increases, the repulsive energy barrier for the medium-contaminant and contaminant-contaminant increases, inhibiting the deposition behavior of particulate pollutants. In addition, hydrocyclone desorbs contaminants deposited on the separation media and the average contaminant residual rate decreases from 3.3 to 0.2 wt%. We propose an industrial application for treating and reusing MTO wastewater (200 m3/h) using the SRMS technology based on the experimental results. The costs of the wastewater treatment process are as low as 0.25 CNY/m3, and the wastewater reuse rate is over 97% without chemical consumption. This work can provide an environmentally friendly and economically sustainable approach to the source management of MTO wastewater.

Experimental study of Gas-To-Liquid (GTL) and diesel fuel blends evaporation behaviour and droplet lifetime through Leidenfrost effect

Gas to Liquid (GTL) fuel is considered a clean alternative fuel and has been given much attention to replacing conventional fuel. Evaporation behaviour and droplet lifetime are critical aspects that need to be determined as these aspects can affect the fuel spray properties and improve the combustion process. In this study, a set of GTL–diesel fuel blends are prepared, which are G20, G50, G80, and G100 (the number represents the GTL percentage fuel ratio in the fuel blends). Subsequently, using a single droplet drop test on the hot plate (Leidenfrost effect), the GTL fuel blends droplet lifetime and evaporation behaviour are visualised using a high-speed camera connected to long-distance microscopy. An image processing system and a MatLab were used to measure and analyse the droplet evaporation data. Comparing the fuel characterisation of the GTL fuel and conventional diesel fuel, the GTL fuel shows a lower value in all properties tested except for the calorific value, cetane number, and vapour pressure. The qualitative results through the Leidenfrost effect have shown that increasing the GTL fuel ratio (20% to 100%) decreases the heating phase duration (37.3 % to 14.4 %) and evaporation rate (1.29 mm 2/s to 1.10 mm 2/s) while increasing their steady evaporation phase duration and droplet lifetime. The shorter period to achieve steady evaporation is beneficial as the spray inside the chamber has a limited time to evaporate for combustion.

Insight into the effect of F− on acidity of H-SAPO-18 and its catalytic performance for conversion of methanol to olefins

In this study, F− was added to the synthesis gel to regulate the acid property of SAPO-18 molecular sieve and enhance its catalytic performance for the methanol-to-olefin (MTO) reactions. The results indicate that adding an appropriate amount of F− during synthesis can increase the crystallinity of SAPO-18 molecular sieve and reduce the overall strong acid density and external surface acid content. The H-SAPO-18-I-20-0.0025 molecular sieve exhibits a much higher catalytic lifetime (1000 min) and light olefins selectivity (45.2% to propene and 96.1% to C2-5=) in MTO at 400 °C than those of the traditional H-SAPO-18-1-0. The results of the isotope labeling experiments, GC-MS, and 13C MAS NMR results provided direct evidence that the aromatic-based cycle contributes more to the conversion of methanol into light olefins, and hexamethylbenzene serves as the most abundant hydrocarbon species that produces propene via the paring route.

The strong SDA/framework interactions and acidity study of high-silica LTA-type zeolites

The zeolite community spent 50 years in pursuing the synthesis of high-silica LTA-type zeolites, and ultimately succeeded with the pure-silica polymorph by applying specific structure-directing agents (SDA). The high-silica zeolite A has exhibited unique properties and strong potential to be applied as an adsorbent and catalyst in several novel processes. In the present study, the high-silica polymorphs of Si/Al ratios from 15 to ∞ were synthesized and subjected to thorough characterizations using multiple physicochemical methods. It has been revealed that there exists strong interactions between the organic SDAs and the framework. Therefore, removing the SDAs by calcination in air is difficult, and can only be done above 700 °C with a certain degree of framework dealumination. The retained framework structure shows connectivity defects and a unique combination of Brønsted and Lewis acidity. Using methanol-to-olefins (MTO) as a probe reaction, the catalytic performance of high-silica LTA-type zeolites has been evaluated. Compared to the well-studied CHA and MFI-type catalysts, high-silica zeolite A exhibited a shorter life-time and higher selectivity towards C4 olefins, while methane selectivity increased with the deactivation.

Acid Treatment to Improve Total Light Olefins Selectivity of HZSM-5 Catalyst in Methanol to Olefins (MTO) Reaction

Acid Treatment to Improve Total Light Olefins Selectivity of HZSM-5 Catalyst in Methanol to Olefins (MTO) Reaction

Removal of Organic Contaminants in Gas-to-Liquid (GTL) Process Water Using Adsorption on Activated Carbon Fibers (ACFs)

Gas-To-Liquid (GTL) processing involves the conversion of natural gas to liquid hydrocarbons that are widely used in the chemical industry. In this process, the Fischer–Tropsch (F-T) approach is utilized and, as a result, wastewater is produced as a by-product. This wastewater commonly contains alcohols and acids as contaminants. Prior to discharge, the treatment of this wastewater is essential, and biological treatment is the common approach. However, this approach is not cost effective and poses various waste-related issues. Due to this, there is a need for a cost-effective treatment method. This study evaluated the adsorption performance of activated carbon fibers (ACFs) for the treatment of GTL wastewater. The ACF in this study exhibited a surface area of 1232.2 m2/g, which provided a significant area for the adsorption to take place. Response surface methodology (RSM) under central composite design was used to assess the effect of GTL wastewater’s pH, initial concentration and dosage on the ACF adsorption performance and optimize its uptake capacity. It was observed that ACF was vitally affected by the three studied factors (pH, initial concentration and dosage), where optimum conditions were found to be at a pH of 3, 1673 mg/L initial concentration and 0.03 g of dosage, with an optimum uptake of 250 mg/L. Kinetics and isotherm models were utilized to fit the adsorption data. From this analysis, it was found that adsorption was best described using the pseudo-second order and Freundlich models, respectively. The resilience of ACF was shown in this study through conducting a regeneration analysis, as the results showed high regeneration efficiency (~86%) under acidic conditions. The results obtained from this study show the potential of using ACF under acidic conditions for the treatment of industrial GTL wastewater.

Synthesis of SAPO-34 nanocrystallites by epoxy-functional organosilane with improved MTO catalytic performance

Synergic regulation of microstructure, morphology and acidity of SAPO-34 molecular sieve is crucial to enhance its catalytic performance for methanol to olefins (MTO) reaction. Herein, a commercial oxygen-containing organosilane 3-glycidoxypropyltrimethoxysilane (AC-230) was developed as a new mesoporogen to synthesize pure SAPO-34 nanocrystallites together with diisopropylamine and seeds. According to the conditional experiments and systematic characterizations, it was disclosed that AC-230 not only changed the morphology and particle size of the SAPO-34 crystals but also affected its compositions and acidic properties. The addition of seed was indispensable to fasten the crystallization rate and hence assure the crystal growth inhibition function of AC-230. Thanks to the formed shortened diffusion pathway, moderate acid sites and pure CHA structure of the nanosized SAPO-34 product, the catalyst demonstrates excellent catalytic performance with a longer lifetime (395 min) and higher ethylene plus propylene selectivity (82.88%) in comparison to its conventional analogs (259 min and 80.63%).

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.