Optimization of nano-sized SAPO-34 synthesis in methanol-to-olefin reaction by response surface methodology

Two-Step Hydrothermal Synthesis of Submicrometric and Hierarchical Hollow SAPO-34 with Superior Catalytic Performance in Methanol to Olefin (MTO) Reaction

A submicrometric and hierarchical hollow SAPO-34 molecular sieve was synthesized by an easy and low-cost two-step hydrothermal method. First, the crystallized mixture was obtained by direct drying after a first-step hydrothermal reaction. Then, the SAPO-34 product was obtained by adding the crystallized mixture to silicon-free gel and using cheap and common template agents. Compared to conventional SAPO-34, the submicrometric and hierarchical hollow SAPO-34 exhibits superior catalytic activity in the MTO reaction.

Multi-Objective Function Optimization of Cemented Neutralization Slag Backfill Strength Based on RSM-BBD

Tailings produced in the beneficiation of Carlin-type gold deposits are characterized by fine particle size and high mud content. When neutralized with wasted acid generated by pressurized pre-oxidation, the tailings turn to neutralized slag and perform as a novel backfill material. To understand the influential behavior of variable factors on the strength and its optimization of cemented neutralization slag backfill, RMS-BBD design test was carried out with 56–60% slurry mass fraction, 12.5–25% cement/(neutralization slag + waste rock) (i.e., C/(S+R)) and 30–40% waste rock content. A modified three-dimensional quadratic regression model was proposed to predict the strength of cemented neutralization slag backfill. The results showed that backfill strength predicted by the modified ternary quadratic regression model was in high coincidence with the data of backfill mixture tests. C/(S+R) was predominant in backfill strength with regard to every single influential factor throughout the curing age, and the mass fraction of slurry had a significant effect on the later strength. From the perspective of economic and engineering operation, a multi-objective function method was further introduced to optimize the backfill strength. The optimal mixture proportion of cemented neutralized slag backfill slurry was: 58.4% slurry mass fraction, 32.2% waste rock content, and 20.1% C/(S+R). The backfill strength of this mixture proportion on days 7, 28 and 56 was verified as 0.42, 0.64 and 0.85 MPa, respectively. RSM-BBD design and multi-objective function optimization proposed a reliable way to evaluate and optimize the strength of neutralized slag backfill with high mud content.

Synthesis and Applications of SAPO-34 Molecular Sieves

Silicoaluminophosphate zeolite (SAPO-34) has been attracting increasing attention due to its excellent form selection and controllability in the chemical industry, as well as being one of the best industrial catalysts for methanol-to-olefin (MTO) reaction conversion. However, as a microporous molecular sieve, SAPO-34 easily generates carbon deposition and rapidly becomes inactivated. Therefore, it is necessary to reduce the crystal size of the zeolite or to introduce secondary macropores into the zeolite crystal to form a hierarchical structure in order to improve the catalytic effect. In this review, the synthesis methods of conventional SAPO-34 molecular sieves, hierarchical SAPO-34 molecular sieves and nanosized SAPO-34 molecular sieves are introduced, and the properties of the synthesized SAPO-34 molecular sieves are described, including the phase, morphology, pore structure, acid source, and catalytic performance, in particular with respect to the synthesis of hierarchical SAPO-34 molecular sieves. We hope that the review can provide guidance to the preparation of the SAPO-34 catalysts, and stimulate the future development of high-performance hierarchical SAPO-34 catalysts to meet the growing demands of the material and chemical industries.

Regulating the size and acidity of SAPO-34 zeolites using dual templates to enhance the selectivity of light olefins in MTO

To understand the relationship between the catalytic performance, crystallite size, and acidity of SAPO-34 zeolites, a series of SAPO-34 zeolites were prepared by hydrothermal crystallization using palygorskite and dual templates.

Effect of various structure directing agents (SDAs) on low-temperature deactivation of Cu/SAPO-34 during NH3-SCR reaction

Cu/SAPO-34(TEA) only exhibited minor deactivation and mostly recovered its original activities, while Cu/SAPO-34(MO) showed major deactivation and was not fully regenerated during low temperature NH₃-SCR reaction.

Presenting a new kinetic model for methanol to light olefins reactions over a hierarchical SAPO-34 catalyst using the Langmuir-Hinshelwood-Hougen-Watson mechanism

In this study, a new kinetic model for methanol to light olefins (MTO) reactions over a hierarchical SAPO-34 catalyst using the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism was presented and the kinetic parameters was obtained using a genetic algorithm (GA) and genetic programming (GP). Several kinetic models for the MTO reactions have been presented. However, due to the complexity of the reactions, most reactions are considered lumped and elementary, which cannot be deemed a completely accurate kinetic model of the process. Therefore, in this study, the LHHW mechanism is presented as kinetic models of MTO reactions. Because of the non-linearity of the kinetic models and existence of many local optimal points, evolutionary algorithms (GA and GP) are used in this study to estimate the kinetic parameters in the rate equations. Via the simultaneous connection of the code related to modelling the reactor and the GA and GP codes in the MATLAB R2013a software, optimization of the kinetic models parameters was performed such that the least difference between the results from the kinetic models and experiential results was obtained and the best kinetic parameters of MTO process reactions were achieved. A comparison of the results from the model with experiential results showed that the present model possesses good accuracy.

Coke suppression in MTO over hierarchical SAPO-34 zeolites

Hierarchical SAPO-34 crystals were synthesized by a facile TEAOH etching post-treatment for the first time.