Study On The Influence Of PH Value And MTO Kinetics In The Synthesis Of SAPO-34 Molecular Sieve

With the progress of national infrastructure and people’s yearning for a better life,the demand for olefins is increasing rapidly.Under the background of my country’s special energy structure,it is very necessary to develop indirect coal-to-olefins,and the potential of methanol-to-olefins(MTO)is huge.The key to the MTO reaction is the performance of SAPO34 molecular sieve and the development of its process package.This paper systematically studied the influence of the pH value of the crystallization precursor liquid on the synthesis of SAPO-34.Based on SAPO-34 molecular sieve with excellent performance,the kinetics study was carried out,and the kinetic model constructed was consistent with the experimental results.Use triethylamine(TEA)as template,in Al2O3:P2O5:SiO2:H2O:TEA=1:1:0.6:60:X system,when X≥2.333 or the pH value of crystallization precursor≥7.343,pure phase SAPO-34 can be synthesized.Through the MTO catalytic reaction,it can be seen that the less template is used in the synthesis of pure phase SAPO-34 molecular sieve,the better the catalytic effect;using phosphoric acid as the phosphorus source,in Al2O3:P2O5:SiO2:H2O:TEA=1:Y:0.6:60:In 2.4 system,Y is 0.8-1.0,and pure phase SAPO-34 is formed.The pH of the crystallization precursor solution is around 7.567-8.769,and pure phase SAPO-34 can be synthesized only when it is weakly alkaline;with silica sol as the silicon source,the influence of silica-aluminum ratio is greater than that of silica sol on the pH of the solution.The kinetics of MTO was studied in an isothermal fixed-bed reactor,and the three factors of temperature,mass space velocity,and water content in methanol were investigated.In the temperature range of 450-500℃,the mass space velocity is 1-5 h-1,and the methanol water content(wt)is between 0-40%,the rotating regression test design is carried out,and the components of the molecular sieve just deactivated are calculated by interpolation.Yield.Five lumped kinetic models of oxygen-containing reactants,methane,ethylene,propylene,and others were established,and the fourth-order Runge-Kutta method was used to solve the problem,and the particle swarm algorithm was used for optimization.The R2 test was performed on the solved kinetic parameters.The test results are good and the model is reliable.