Theoretical investigation of the side-chain mechanism of the MTO process over H-SSZ-13 using DFT and ab initio calculations

The side-chain mechanism of the methanol-to-olefins process over the H-SSZ-13 acidic zeolite was investigated using periodic density functional theory with corrections from highly accurate ab intio calculations on large cluster models.

Presenting a Four-Lump Dynamic Kinetic Model for Methanol to Light Olefins Process over the Hierarchical SAPO-34 Catalyst Using Power Law Models

Objectives: A four-lump dynamic kinetic model on the hierarchical SAPO-34 catalyst in the methanol to light olefins (MTO) process has been presented using the power law models. Since decreased catalyst activity in the MTO process is common, for the applicability of the proposed model, the function of catalyst activity was computed as a function of the coke percentage deposited on the catalyst. Materials and Methods: The reactant and products were divided into four lumps, including methanol and dimethyl ether (DME), light olefins (ethylene and propylene), light paraffin (methane, ethane, and propane) and heavier hydrocarbons from C4. The one-dimensional ideal plug reactor was used for the simulation of the MTO reactor. The kinetic parameters and the catalyst activity function were predicted using the particle swarm optimization (PSO) algorithm. Results: The comparison of product distribution in the experimental mode and the results of the kinetic model indicated the high accuracy of the presented model. The effect of operational parameters such as temperature and weight hourly space velocity (WHSV) on the mole percent of light olefins was investigated using the proposed kinetic model. The optimized value of temperature and WHSV to reach the maximum yield of light olefins was respectively 460 ˚ C and 4.2 h-1 . Conclusion: The passive kinetic coefficients were estimated in the reaction rate constant and catalyst activity function with the help of the PSO optimization algorithm. The mole fraction of different products and the reactant arising from modeling at the reactor outlet was compared with experimental results, which indicated the high accuracy of the presented kinetic model. The results also revealed that the selection of high and low temperatures and WHSV decreases the yield of light olefins and the lifetime of the catalyst.

Comparative Synthesis and Characterization of Nanostructured SAPO-34 Using TEA and Morpholine: Effect of Mono vs. Dual Template on Catalytic Properties and Performance toward Methanol to Light Olefins

Aim and Objective: Production of light olefins from methanol was studied over SAPO-34 molecular sieves exploring the effect of mono and dual templates. Herein, the single templates of TEA, morpholine and mixed template of TEA/morpholine (equal molar ratio of TEA and morpholine) were used to synthesize SAPO-34 catalysts. Materials and Methods: The prepared samples were prepared via hydrothermal synthesis method and characterized with XRD, FESEM, PSD, EDX, BET and FTIR techniques. Results: It was found that the crystallinity decreased upon applying TEA as template and also it can be noted that the intensity of the SAPO-34 phase peaks increased by increasing the morpholine in template mixture. Production of much smoother particles for the catalyst synthesized with binary template mixture of TEA/morpholine can be depended on the crystallinity increase. Si incorporation value was decreased for the catalyst with a major phase of SAPO-5 (topological structure of AFI). It is indicative that the TEA application would facilitate the formation of AFI structure which is incapable of the incorporating higher amounts of Si in to the crystallite framework. Conclusion: The nature of the template determines the morphology of final product due to different rate of crystal growth obtained in accordance with XRD and FESEM results. Therefore, the catalyst synthesized with TEA/morpholine mixture shows the best performance among synthesized samples in terms of life time in the MTO process sustaining light olefins selectivity at higher values (about 90% after 630 min TOS).

CFD modeling of methanol to light olefins process in a sodalite membrane reactor on SAPO-34 catalyst with in situ steam removal

Aims and Objective: In this work, the performance of sodalite membrane reactor (MR) in methanol to olefins (MTO) process was evaluated for ethylene and propylene production with in situ steam removal using 3-dimensional CFD (computational fluid dynamic) technique. Methods: The local information of component concentration for methanol, ethylene, propylene, and water was obtained by the proposed CFD model. Literature data were applied to validate model results, and between experimental data and predicted results using CFD model, a good agreement was attained. In the sodalite MR model, a commercial SAPO-34 catalyst in the reaction zone was selected. The influence of key operation parameters including pressure and temperature on methanol con-version, water recovery, and yields of ethylene, propylene, and water was studied to evaluate the performance of sodalite MR. Permeation flux through the sodalite membrane was increased by an increase of reaction temperature which led to enhance-ment of water stream recovered in the permeate side. Result and Conclusion: The CFD modeling results showed that the sodalite MR in MTO process has higher performance regarding methanol conversion compared to the fixed-bed reactor (methanol conversion of 97% and 89% at 733 K for sodalite MR and fixed-bed reactor, respectively).