Acidity Tuning Of HZSM-5 Zeolite By Ion Exchange And Its Effects On The Supercritical Catalytic Cracking Of N-dodecane

With the development of science and technology,almost all countries are committed to the development of military core technology,the researchers found that high speed flight vehicle design is affected by the flight environment,large amount of heat generated by the friction between the aircraft and atmosphere needs to be colded down in time.,and chemical heat sink is one of the most important solutions,endothermic hydrocarbon fuel,as a kind of excellent coolant,have attracted much attention duing to its excellent chemical properties.HZSM-5 zeolite catalyst is a commonly used catalyst for the catalytic cracking of heat-absorbing hydrocarbon fuel under supercritical conditions.In order to prevent the carbon deposition and deactivation of HZSM-5 zeolite catalyst during the catalytic cracking of fuel,it is urgent to prepare efficient and stable HZSM-5.In this paper,the acidity of HZSM-5 zeolite catalyst was regulated by ion exchange method for optimizing its catalytic activity in the supercritical catalytic cracking of n-dodecane.The change of catalyst activity during pyrolysis was analyzed by gas chromatography,the acid content of HZSM-5 after ion exchange with Na Cl was determined by potentiometric titration,the catalyst was characterized by XRD and n-propylamine pyrolysis and the carbon deposited on the catalyst after supercritical catalytic cracking was analyzed by TPO.XRD results showed that Na Cl solution had no effect on the crystal structure of HZSM-5 zeolite through ion exchange.Potentiometric titration and n-propylamine TPD acid analysis indicate that Na Cl ion exchange is an effective method to achieve acid control of molecular sieve.In this exchange process,the p H value of the solution shows an oscillating downward trend with the time of ion exchange,which may be caused by the negative charge on the surface of HZSM-5 particles and the formation of unstable double layers disturbed by shear action caused by Na~+and H~+in the adsorption liquid phase.The results of supercritical catalytic cracking of n-dodecane showed that neither high nor low acid content of the catalyst was conducive to the transformation of n-dodecane,resulting in a high degree of deactivation of the catalyst.When the concentration of Na Cl was 0.6-0.8 M,the acid strength and acid amount of the catalyst after ion exchange were moderate,which could not only maintain a certain catalytic activity,but also effectively inhibit the generation of carbon deposition,thus effectively enhancing the effective activity of the catalyst in the process of n-dodecane supercritical catalytic reaction.