Conversion Of Methanol To Light Olefins Research Articles

Formulated Mn-promoted SAPO-34/kaolin/alumina sol micro-size catalyst with a superior performance for methanol to light olefins conversion in a fluidized bed reactor

Formulation of zeolite molecular sieves powder is necessary to prepare an excellent micro-size catalyst for methanol conversion to light olefins (MTO) in a fluidized bed reactor. In this work, new fluidizable micro-meso pore catalysts were successfully fabricated by spray drying a slurry containing Mn(x)SAPO-34 powder, kaolin filler, alumina sol binder, and HCl additive. A mixed template of TEAOH/morpholine with different amounts of Mn ion was used in primary gel during hydrothermally synthesis of the crystals. The catalytic samples were characterized utilizing different methods. A moderate acidity reached by catalyst formulation using kaolin and alumina sol as well as through Mn incorporation into the chabazite cages was helpful for MTO performance of the final shape-selective catalyst in terms of selectivity to light olefins and lifetime. The enhancement effect of Mn promoter on ethylene production was much more than propylene because of entering Mn to the micro-pores and imposing restriction on heavier hydrocarbons diffusion. The uniformity and crystalinity were also appeared to be enhanced once Mn(0.05) was introduced into the gel composition. The suggested spray dried catalyst was SD-Mn(0.05)SAPO-34 (70–120 µm) in which provided a superior selectivity up to 88.4% to light olefins and catalytic lifetime of 330 min in a fluidized bed reactor at 450℃, WHSV = 4 h−1, and XMeOH = 0.75 in the feed.

Catalytic Longevity of Hierarchical SAPO-34/AlMCM-41 Nanocomposite Molecular Sieve In Methanol-to-Olefins Process.

SAPO-34/AlMCM-41, as a hierarchical nanocomposite molecular sieve was prepared by sequential hydrothermal and dry-gel methods studied for catalytic conversion of methanol to light olefins. Pure AlMCM-41, SAPO-34, and their physical mixture were also produced and catalytically compared. Physicochemical properties of materials were mainly investigated using XRD, N2 isothermal adsorption-desorption, FESEM, FT-IR, NH3-TPD, and TG/DTG/DTA techniques. Micro-meso hierarchy of prepared composite was demonstrated by XRD and BET analyses. Catalytic performance of materials illustrated that the methanol conversion of the prepared composite was about 98% for 120 min, showing a higher activity than the other catalysts. The initial reaction selectivity to light olefins of the composite was also comparable with those for the other catalysts. Furthermore, the results revealed that SAPO-34/AlMCM-41 preparation decreased the concentration and strength of active acid sites of the catalyst which could beneficially affect the deposition of heavy molecular products on the catalyst. However, as observed, the prepared composite was deactivated in olefins production faster than pure SAPO-34. The small mean pore diameter of composite could be mainly responsible for its pore blockage and higher deactivation rate. Meanwhile, since the SAPO-34 prepared by dry-gel method had inherently high mesoporosity, the AlMCM-41 introduction did not promote the molecular diffusion in the composite structure. The coke content was found 15.5% for deactivated composite smaller than that for the SAPO- 34 catalyst which could be due to the pore blockage and deactivation of the composite in a shorter period.

Synthesis and catalytic performances of hierarchical SAPO-34 monolith

A novel hierarchical SAPO-34 monolith was prepared by the dry gel conversion of the amorphous silicoaluminophosphate monolith. The obtained material possesses macropores and mesopores besides micropores. The macroporous framework of the hierarchical SAPO-34 is constructed by interconnected spherical aggregates of cubic SAPO-34 crystals and mesopores is formed by the close stacking of cubic SAPO-34 crystals. Catalytic tests show that the hierarchical SAPO-34 possesses high catalytic activity compared with the conventional microporous SAPO-34 for methanol conversion to light olefins (MTO) reaction. The better activity is mainly assigned to the existence of cubic SAPO-34 crystals and the hierarchical porosity.

Influence of Coke Deposition on Selectivity in Zeolite Catalysis

The selectivity of a complex reaction depends on a number of factors, such as the reaction mechanism, operating conditions, catalyst properties and catalyst deactivation. The present work discusses how the selectivity of a complex reaction depends on the formation of coke. For zeolite catalysts, changes in selectivity can be a result of intrinsic selectivity effects or shape selectivity effects. A method is suggested to analyze a complex reaction system with deactivation caused by coke formation, and different cases of selectivity change during deactivation of zeolites are discussed. Transition-state shape selective deactivation is proposed as a mechanism in addition to the deactivation mechanisms suggested by Guisnet and Magnoux (Guisnet, M.; Magnoux, P. Appl. Catal. 1989, 54, 1). By variation of the space velocity, the selectivities to the main products are measured as a function of conversion (optimum performance envelopes). Selectivities at given conversions can then be compared for results obtained with different contact time and with varying degree of catalyst deactivation (space velocity loops). Selective or nonselective deactivation is thereby distinguished. This type of selectivity plot is applied to two different types of reaction, i.e. ethene oligomerization over HZSM-5 and methanol conversion to light olefins (MTO) over SAPO-34. The selectivity of ethene oligomerization was affected only by the decrease in conversion due to coke formation; hence, this is an example of nonselective deactivation. Selective deactivation was found for methanol conversion over SAPO-34.