Methanol Conversion To Olefins Research Articles

Boosted regeneration of coked SAPO-34 catalyst in MTO fluidized bed reactor by diluted air at elevated temperatures

SAPO-34 zeolite as an excellent catalyst for methanol-to-olefins (MTO) reaction suffers rapid deactivation by prevalent coking. Herein, regeneration of coked-SAPO-34 in a fluidized-bed reactor was successfully intensified by altering temperature (550–650 °C) and oxygen content (7–21 vol.%). Fresh, used, and regenerated catalysts were characterized by different methods to understand the correlation between regeneration conditions, coke content, and catalyst performance. The minor residual coke over the regenerated catalyst comprised active hydrocarbon pool intermediates (like naphthalene, benzaldehyde, phenol, and derivatives), which increased by decreasing regeneration temperature and promoted the selectivity to light olefins at earlier reaction times. The restored microporosity and lifetime of regenerated catalyst were superior by increasing temperature. However, higher attrition at 650 °C, as confirmed by SEM images, caused a partial weight loss of the catalyst and a slight decline in relative crystallinity, hence 600 °C was preferred with additional advantage of less energy consumption. Meanwhile, introducing lower oxygen not only moderated the coke oxidation rate but also enhanced the recovery of beneficial catalytic features for the MTO conversion. Consequently, considering an excellent regeneration as well as lower emission of CO2 detected in the flue gas, diluted air containing 14 vol.% O2 at 600 °C was suggested as the most promising method.

Design and fabrication of the alumina nanofibers decorated with isolated ZSM-5 using electrospinning method: A novel catalyst for methanol conversion to light olefins

ZSM-5 nanoparticles are widely used as the catalyst in the methanol conversion to olefins (MTO) process due to their high surface area and short diffusion path length. However, agglomerate formation is a challenge for this catalyst. To address this issue, in this study, electrospinning was used for the first time to synthesize fibrous catalysts comprised of ZSM-5 nanoparticles embedded in the alumina nanofibers. The catalysts were characterized using XRD, FTIR, SEM, TEM, EDX-map, BET, and NH3-TPD analyses. In the synthesized samples, ZSM-5 nanoparticles with an average particle size of 683 nm are uniformly and homogeneously dispersed over alumina nanofibers with a 300 nm diameter. These composites form core-shell structures and have a reactor porosity of 0.85, which is higher than that of parent ZSM-5. In the MTO process, electrospun catalysts demonstrate superior catalytic activity and a longer lifespan than powder catalysts. 80 wt% ZSM-5- 20 wt% Al2O3 with 47.76 % light olefin selectivity and complete methanol conversion after 321min on stream performed better than 50 wt% ZSM-5-50 wt% Al2O3. Moreover, a lower coke formation of about 3.28 % was achieved for the 80 wt% ZSM-5- 20 wt% Al2O3 sample. The reduced bulk density of the electrospun samples increases the probability of reactant and catalyst contact. Additionally, electrospinning is an effective method for reducing particle aggregation and improving catalytic process efficiency.

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.

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.

Microwave Radiation Effects on the Acidic Properties of Fe/ZSM-5 Catalysts for Methanol Conversion

Aim: To use the microwave radiation as the post-treatment method to tune the acidic properties of Fe/ZSM-5 catalyst. Background: ZSM-5 zeolite is a widely used standard catalyst in the methanol conversion to olefins and high-octane gasoline range hydrocarbons. However, the coke deposition and the concentration of acid sites determine its overall catalytic activity. Thus, the concentration of acid sites more precisely, the number of Brønsted acid sites, is vital in determining the activity of ZSM-5 zeolite and product distribution in the methanol-to-hydrocarbons reaction. Objective: (1) To modify ZSM-5 using an iron solution to form Fe/ZSM-5 via the impregnation method. (2) To tune the acidic properties of Fe/ZSM-5 using microwave radiation. (3) To check and determine the concentration of acidic sites using n-propylamine temperature-programmed surface reaction. (4) To check the effect of microwave radiation and acidic properties in the methanol conversion (product distribution) via methanol temperature-programmed surface reaction. Methods: Two sets of zeolites were used, with iron being introduced by ion-exchange from ferric nitrate (Fe(NO3)3 9H2O, Sigma Aldrich, ≥ 98% metal) solutions. These two series were designated as Z (0.5FeZ10/0-700) and X (0.5FeX10/0-700) after microwave treatment. The Z and X series possess the Si/Al framework ratio of 30 and 80, respectively. The TPSR studies were then conducted for characterization and catalytic tests. Result: From the C3H9N-TPSR experiments, it was found that the concentration of Brønsted acid sites decreased with increasing microwave power level. Both X and Z series exhibited high selectivity to propene than ethene. Microwave treated catalysts (0.5FeZ10/280 and 0.5FeX10/462) with decreased concentration of Brønsted acid sites showed the highest propene/ethene ratios of 1.67 and 5.27, respectively. Conclusions: From the results obtained, it was found that the amount of methane evolved (as a measure of coke deposited) and the concentration of Brønsted acid sites decreased with increasing microwave power level (0-700 Watts). High selectivity to propene was found when using both X series (0.5FeX10/0-700) and Z series (0.5FeZ10/0-700) as catalysts. After decreasing the concentration of Brønsted acid using microwave treatment, the highest P/E ratios were observed for 0.5FeX10/280, 0.5FeX10/462, 0.5FeZ10/280 and 0.5FeZ10/462 catalysts. Other: It is reasonable to suggest that microwave radiation could be a feasible post-synthesis modification step to produce ZSM-5 based catalysts that exhibit reduced concentration of Brønsted acid sites, reduced methane formation, increased catalytic activity and selectivity.

Modeling and simulation analysis of methanol conversion to olefins (MTO): A critical comparison of a honeycomb monolith and a fixed-bed of cylindrical extruded HZSM-5 catalyst

The performance of a honeycomb monolith and a fixed-bed of cylindrical extruded HZSM-5 catalyst for the methanol to olefins process (MTO) are evaluated and compared using two-scale two-dimensional heterogeneous models in adiabatic and diabatic operations considering two approaches of “restricted comparison” and “free comparison”. The 53-step elementary reaction mechanism of Mihail and coworkers is used to model the MTO reactions. The effects of space-time (0.1–5 s), feed water content (up to 60 mol%), and monolith cell density (200–600 cpsi) on the catalyst temperature, feed conversion, and selectivity and yield of olefins are investigated. “Restricted comparison” indicates that the feed conversion and selectivity and yield of the total olefins in the monolithic reactor are greater than the fixed-bed with a maximum discrepancy of 5%. There is an optimum space-time of ~ 0.3 s at which the yield of total light olefins in the monolith and fixed-bed reactors achieves the maximum values of 0.45 and 0.43, respectively. The results of “free comparison” reveal that a 600 cpsi monolith can produce ~ 43% more light olefins using ~ 75% less catalyst mass at the optimal space-time of 0.3 s compare with a fixed-bed reactor at an identical specific surface area.

Catalytic roles of the acid sites in different pore channels of H-ZSM-5 zeolite for methanol-to-olefins conversion

H-ZSM-5 zeolite is a typical catalyst for methanol-to-olefins (MTO) conversion. Although the performance of zeolite catalysts for MTO conversion is related to the actual location of acid sites in the zeolite framework, the catalytic roles of the acid sites in different pore channels of the H-ZSM-5 zeolite are not well understood. In this study, the MTO reaction network, involving the aromatic cycle, alkene cycle, and aromatization process, and also the diffusion behavior of methanol feedstock and olefin and aromatic products at different acid sites in the straight channel, sinusoidal channel, and intersection cavity of H-ZSM-5 zeolite was comparatively investigated using density functional theory calculations and molecular dynamic simulations. The results indicated that the aromatic cycle and aromatization process occurred preferentially at the acid sites in the intersection cavities with a much lower energy barrier than that at the acid sites in the straight and sinusoidal channels. In contrast, the formation of polymethylbenzenes was significantly suppressed at the acid sites in the sinusoidal and straight channels, whereas the alkene cycle can occur at all three types of acid sites with similar energy barriers and probabilities. Consequently, the catalytic performance of H-ZSM-5 zeolite for MTO conversion, including activity and product selectivity, can be regulated properly through the purposive alteration of the acid site distribution, viz., the location of Al in the zeolite framework. This study helps to elucidate the relation between the catalytic performance of different acid sites in the H-ZSM-5 zeolite framework for MTO conversion, which should greatly benefit the design of efficient catalyst for methanol conversion.

Effect of coating with silica on acidic and catalytic properties of SAPO-18 in MTO conversion

Abstract Silicoaluminophosphate with AEI structure has been modified by silica coating using polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) as silica sources. The single step procedure including deposition of 0.5, 1.0, 1.5 and 2.0 wt% of silicon in one step and the multistep procedure including stepwise deposition of silica source by small portions corresponding to 0.5 wt% of silicon with intermediate calcination steps have been applied. The modified materials have been characterized by X-ray fluorescence spectroscopy, X-ray diffraction analysis, low temperature nitrogen adsorption, 29Si MAS NMR, thermoprogrammed desorption of ammonia and FTIR spectroscopy of adsorbed 2,6-ditertbutylpyridine (2,6-DTBPy). The results show that multistep procedure leads to the gradual increase of silicon content and results in the deposition of 2 wt% of Si in 4 steps, whereas single step procedure does not lead to the desired result. Coating with silicon leads to poisoning of Bronsted acid sites located on the external surface of SAPO-18 crystal. This effect is more pronounced in the case of PDMS due to more uniform silica deposition in this case. Coated materials show higher stability of catalytic activity with time on stream in methanol to olefins conversion (MTO) and higher selectivity to light olefins. The mechanism of silica coating with PDMS and TEOS is discussed.

Synthesis of mesoporous SAPO-34 catalysts in the presence of MWCNT, CNF, and GO as hard templates in MTO process

In order to study the effect of carbon nanostructures as hard templates, three silicoaluminophosphate samples using carbon nanotubes (SAPO-34/CNT), carbon nanofiber (SAPO-34/CNF) and graphene oxide (SAPO-34/GO) as well as one sample in the absence of nanocarbon structures were successfully synthesized. The effect of each of the hard templates on the physicochemical properties of the synthetic samples was studied using XRD, FESEM, BET, FTIR and NH3-TPD analyses. Furthermore, the catalytic activity of the synthetic catalysts was compared in the methanol to olefin conversion (MTO) at atmospheric pressure, temperature of 400 °C and WHSV of 4.0 h−1. The results of the investigation of physical characteristics of the catalysts indicate that varying the structure type changes such parameters as crystallinity and mesoporosity. This difference also results in different catalytic behavior in MTO reaction. Of the three carbon nanostructures used, graphene oxide had the greatest effect on the mesoporosity and pore size of SAPO-34 catalyst.

Synthesis of mesoporous beta catalysts in the presence of carbon nanostructures as hard templates in MTO process

Abstract Three Beta catalyst samples using carbon nanotubes (Beta/CNT), carbon nanofiber (Beta/CNF) and graphene oxide (Beta/GO) templates and one sample in the absence of nanostructured carbon templates have been successfully prepared to investigate the impact of carbon nanostructures as hard templates. Tetraethylammonium hydroxide has been applied as the template in each of the samples. XRD, FESEM, BET, FTIR and NH3-TPD analyses were used to study the effect of each of the hard templates on the physicochemical properties of the synthetic samples. In addition, the catalytic activity of the catalysts prepared was compared in the methanol to olefin conversion (MTO) reaction at atmospheric pressure, temperature of 400 °C and WHSV of 8.0 h−1. Variations in the structure type change parameters such as crystallinity and mesoporosity as well as the catalytic behavior in MTO reaction, according to the results of the investigation of physical characteristics of the catalysts. Graphene oxide was the most effective template on the mesoporosity and pore size of Beta catalyst. The catalyst lifetime and performance were improved by increasing the mesoporosity.

Effect of CNT, CNF, and GO carbon nanostructures as co-templates on ZSM-5 synthesis in MTO process

Three ZSM-5 catalyst samples synthesized using carbon nanotubes (ZSM-5/CNT), carbon nanofiber (ZSM-5/CNF) and graphene oxide (ZSM-5/GO) templates as well as one sample containing no template have been studied to study the effect of carbon nanostructured hard templates. The template in each sample was tetrapropylammonium hydroxide. The impact of each of the hard templates on the physicochemical properties of the synthetic samples was investigated via XRD, FESEM, BET, NH3-TPD and FTIR analyses. Moreover, the catalytic activity of the catalysts synthesized was compared in the methanol to olefin conversion (MTO) reaction at atmospheric pressure, temperature of 450 °C and WHSV of 8.0 h−1. Considering the results of the investigation of the physical properties, variations in the type of nanostructured carbon templates affect parameters such as cystallinity and mesoporosity. These differences result in different catalytic activity in the MTO reaction. Among the three carbon nanostructures used, graphene oxide was the most effective on the number of mesoporous cavities and pore sizes of ZSM-5 catalyst. The increased number of mesopores and modified acidity increase the selectivity of the catalysts and make their performance more appropriate.

Mesoporogen-Free Synthesis of Hierarchical SAPO-34 with Low Template Consumption and Excellent Methanol-to-Olefin Conversion.

Significant interest has emerged in the development of nanometer-sized and hierarchical silicoaluminophosphate zeolites (SAPO-34) because of their enhanced accessibility and improved catalytic activity for methanol-to-olefin (MTO) conversion. A series of nanometer-sized SAPO-34 catalysts with tunable hierarchical structures was synthesized in a Al2 O3 /H3 PO4 /SiO2 /triethylamine(TEA)/H2 O system by using a mesoporogen-free nanoseed-assisted method. The nanometer-sized hierarchical SH -3.0 catalyst (TEA/Al2 O3 =3.0) possessed the highest crystallinity, highest abundance of intracrystalline meso-/macropores, and the most suitable acidity among all obtained catalysts, showing the highest ethylene and propylene selectivity of 85.4 %. This is the highest reported selectivity for MTO reactions under similar conditions. Detailed analysis of the coke produced during the reaction revealed that the small-sized methyl-substituted benzene and bulky methyl-substituted pyrene were mainly located inside the crystals instead of on the surface of the crystals, which provided further insight into understanding the deactivation of the SAPO-34 catalyst during MTO reaction. Significantly, the simple and cost-effective synthetic process and superb catalytic performance of the nanometer-sized hierarchical SAPO-34 is promising for their practical large-scale application for MTO conversion.

Methanol-to-olefin conversion in ABC-6 zeolite cavities: unravelling the role of cavity shape and size from density functional theory calculations.

We report a density functional theory (DFT) study to investigate methanol-to-olefin (MTO) conversion in four types of ABC-6 zeolite cavities (cha, avl, aft and h1) by varying their shape and size. Based on a side-chain alkylation mechanism, the reaction energies and barriers of methylations, deprotonations and eliminations for hydrocarbon pool (HP) intermediates are calculated. In the cha cavity, methylations and eliminations are found to possess low barriers as attributed to the strong confinement effect of the elliptical and small cha cavity. The avl and aft cavities also exhibit low barriers of the first and second methylations, and similar barriers of eliminations for producing olefins as in cha. Due to the narrow shape and large size of the h1 cavity, most of the reaction barriers in h1 are the highest. The stabilities of HP species and transition states in the four cavities are quantified by the Gibbs energy profiles. It is found that aft with a wide dimension is favorable for the stability, especially for the charged HP species. The DFT calculation results reveal that the activity and selectivity of MTO conversion in zeolite cavities are strongly governed by the confinement effect, which depends on cavity shape and size. We also predict that zeolites with aft cavities might have good performance for MTO conversion.

The state-of-the-art synthetic strategies for SAPO-34 zeolite catalysts in methanol-to-olefin conversion

Methanol-to-olefin (MTO) conversion has proven to be one of the most successful non-petrochemical routes for producing light olefins. Silicoaluminophosphate (SAPO) zeolite SAPO-34 is one of the best industrial catalysts for MTO conversion, but suffers from rapid deactivation due to the inherent diffusion bottleneck limited by the narrow eight-ring pore openings. To improve the MTO performance, considerable synthetic efforts have been devoted to decrease the crystal size of zeolites or introduce secondary larger pores in zeolite crystals to form hierarchical structures. This review mainly focuses on presenting the state-of-the-art synthetic strategies for nanosized and hierarchical SAPO-34 catalysts with excellent MTO performance. Furthermore, the industrialization of SAPO-34 catalysts for the MTO reaction, and some current problems and future prospects for the synthesis of SAPO-34 catalysts, are also pointed out. We expect that this review can not only shed some light on the preparation of SAPO-34 catalysts, but also stimulate the future development of high-performance SAPO-34 catalysts to meet the increasing demands of the chemical industry.

Recent advances of the nano-hierarchical SAPO-34 in the methanol-to-olefin (MTO) reaction and other applications

The synthesis and catalytic applications of nano-hierarchical SAPO-34 for MTO conversion have received great significance.

Conversion of methanol to light olefins over H‐MCM‐22 dealuminated with different methods

AbstractBackgroundIn the post‐oil society, the methanol‐to‐olefin (MTO) conversion is a successful non‐oil route for the production of ethene, propene and butene, which are important chemicals in modern chemical industry. Recently, the global demand for propene increased, which makes high propene selectivity attractive in the MTO conversion. However, looking for an effective catalyst is the main challenge.ResultsH‐MCM‐22 zeolite was dealuminated with nitric acid, oxalic acid and ammonium hexafluorosilicate (AHFS). Then, the parent and dealumianted samples were examined in the MTO reaction. The results showed that the total acid amounts decreased and the distribution of Brőnsted acid sites in the pores of H‐MCM‐22 were reregulated after the different dealumination procedures. The results of thermogravimetric (TG) analysis of the spent samples demonstrated that H‐MCM‐22 (10A) dealumination with 10 mmol L−1 AHFS solution had the lowest coking rate and coke selectivity, which makes it exhibit the longest lifetime (54 h), and highest propene and butene selectivity (71.8%).ConclusionDealumination with AHFS is an effective method for H‐MCM‐22. Because it can eliminate almost all the extra‐framework aluminum (AlEF) species and concentrate the Brőnsted acid sites in the sinusoidal channels which promote the propene and butene formation with a resistance to carbonaceous deposition in the MTO reaction. © 2016 Society of Chemical Industry

Post-synthetic improvement of H-ZSM-22 zeolites for the methanol-to-olefin conversion

Microporous ZSM-22 zeolites (structure type TON) were modified by treatments with different alkaline solutions for introducing mesopores. This surprisingly affected the nature and the density of both SiOH groups and Brønsted acid sites significantly, while the Brønsted acid strength was maintained. The catalyst lifetime in the methanol-to-olefin (MTO) conversion could be enhanced by a factor of up to 2 for an optimum Brønsted acid site density of 0.34 mmol/g, which was also accompanied by the highest propene selectivity of 48%. The product distributions of the parent microporous and the modified mesoporous ZSM-22 catalysts were very similar. This indicates that the shape selectivity of the modified ZSM-22 zeolites in the MTO conversion is mainly determined by the 10-ring pore system and not affected by introduced mesopores. Therefore, it can be excluded that catalysis near the pore mouths plays a significant role in the MTO conversion on ZSM-22 zeolites.

Parameters influencing the selectivity to propene in the MTO conversion on 10-ring zeolites: directly synthesized zeolites ZSM-5, ZSM-11, and ZSM-22

Zeolites ZSM-5, ZSM-11, and ZSM-22 (nSi/nAl=20–1000) were applied as methanol-to-olefin conversion (MTO) catalysts and optimized for high propene selectivities at high methanol conversions, high weight hourly space velocities, and for long catalyst lifetimes. On zeolites ZSM-5 and ZSM-11 with optimized Brønsted acid site densities of 0.13 and 0.15mmol/g, propene selectivities of 51 and 52%, respectively, at a reaction time of 25h were reached. In contrast, zeolite ZSM-22 with an optimized acid site density of 0.30mmol/g showed a maximum propene selectivity of 38% only and a significantly shorter lifetime. Under these conditions, no aromatics could be detected by in situ UV–vis spectroscopy and on-line GC. Thus, an optimized acid site density can suppress the aromatic-based reaction mechanisms by hindering intermolecular hydrogen transfer reactions. Therefore, the acid site optimization could be a promising way for tuning the product selectivity of MTO catalysts on significantly different pore systems.

Aromatic-based hydrocarbon pool mechanism for methanol-to-olefins conversion in H-SAPO-18: A van der Waals density functional study

The reaction mechanism of zeolite-catalyzed methanol-to-olefins (MTO) conversion is still debated. Aromatics and/or olefins themselves may act as hydrocarbon pool species in the reaction. In this work we used periodic density functional theory calculations with the van der Waals density functional to study the aromatic-based hydrocarbon pool mechanism in H-SAPO-18 zeotype with eight-membered ring openings. The distribution of different polymethylbenzenes (MBs) in H-SAPO-18 was evaluated from adsorption and interconversion analysis. Hexamethylbenzene was calculated to be the primary component of MBs in H-SAPO-18. Gibbs free energy analysis on the process of ethyl side chain propagation indicated that hexamethylbenzene was not more reactive than pentamethylbenzene and tetramethylbenzene. The overall Gibbs free energy barriers were calculated to be more than 200 kJ/mol at MTO reaction temperature (673 K). These calculated results would provide some implications for understanding the reaction mechanism and the role of aromatics in MTO conversion.

Preparation and Evaluation of the Modified Nanoparticle SAPO-18 for Catalytic Conversion of Methanol to Light Olefins

Silicoaluminophosphate-18 can be considered as an effective catalyst for methanol conversion to olefins (MTO). A series of SAPO-18 were prepared to investigate the effects of aging pretreatment on crystallization time. The results exhibit that stirring aging, in addition to reducing the overall particle size of SAPO-18, decreases the crystallization time from 168 to 65 h. Also, the effects of addition order of the reagents and crystallization time on physiochemical properties of the SAPO-18 nanoparticles were studied. Finally detailed investigations were carried out on the catalytic performance of the samples in MTO process and the best catalyst was determined.