Yahua Shi

Skeletal isomerization of light FCC naphtha

The factors affecting the age of olefin skeletal isomerization catalyst are investigated. Molecular sieves with different acid strength and distribution show different activity and stability. Weak and moderate acid centers are responsible for the skeletal isomerization of olefin (SIO) and strong acid sites catalyze dimerization and cracking reaction under the test conditions. The pore structure of molecular sieve influences the products distribution significantly in the skeletal isomerization of 1-hexene. Choosing suitable modification methods to diminish external surface acid center could reduce the influence of external surface coke on molecular sieve activity. Under the same olefin saturation level, the octane loss of light FCC naphtha decreases remarkably by SIO comparing with direct hydrogenation.

Hydroisomerization of n-hexadecane on zeolite catalysts

Hydroisomerization of n-hexadecane on zeolite catalysts was studied and the reaction mechanism was discussed, which may provide new clues to developing hydroisomerization catalysts with high selectivity. The catalysts were prepared as follows: zeolite and alumina were mixed and then extruded to make a support, after drying and calcination, platinum was loaded on by wet impregnation with Pt(NH3)(4)Cl-2 solution. The hydroisomerization of n-hexadecane was carried out in a continuous fixed-bed reactor with down-flow. The catalysts were loaded in the reactor and reduced for 4 h. Then n-hexadecane was pumped into the reactor at different temperatures. The reaction results indicated that Pt/MCM-22 and Pt/ZSM-5 catalysts show higher activity but lower selectivity than Pt/Hbeta and Pt/SAPO-11 catalysts. The selectivity of Pt/SAPO-11 is the highest, more than 90% at the conversion of 80%. From the cracked product distribution, it could be seen that, for Pt/ZSM-5 and Pt/Hbeta, the fractions of small molecule products, such as C-3, C-4 and C-5, are more than those of long chain products, but for Pt/SAPO-11, the cracked product distribution is nearly symmetrical, which means that there is secondary cracking occurred for Pt/ZSM-5 and Pt/Hbeta but no for Pt/SAPO-11. The symmetrical distribution of cracked products is the characteristics of large-pore zeolites or amorphous catalysts, so it can be concluded that the hydroisomerization takes place on the external surface or at the pore mouth of SAPO-11, but not in the pore channel. The different zeolites showed different behavior for the isomerization, which can be attributed to their different acidity. The strong acidity of MCM-22 and ZSM-5 leads to poor isomerization selectivity. SAPO-11 has high selectivity, indicating that the weak and mild acids are favorable to the isomerization.

Selective hydrodesulfurization technology of cracked gasoline for gasoline pool in 2005

The distribution of sulfur and hydrocarbon of commercial FCC gasoline has been analyzed. The effect of isomerization on octane number is also investigated. Based on the above results, two kinds of hydrotreating processes are chosen for producing low sulfur FCC gasoline with minimal octane loss in order to meet the requirement of European gasoline in 2000 and 2005, respectively.

88 Skeletal isomerization of n-hexene: The influence of structure and acid distribution of molecular sieves

Publisher Summary This chapter introduces the skeletal isomerization of hexene-1. The acid amounts and strengths of different molecular sieves are determined by TPD of ammonia. The ammonia desorption peak temperature is used to characterize acid strength. The weak and moderate acid strength is similar for different molecular sieves. But the amount of acid center and strength of strong acid center are quite different. The products of hexene-1 conversion include C3, C4, C5, C6, and >C6 compounds, neither methane nor ethane was detected. The production of C4, C5, and C6+ indicates that there are dimerization and the following cracking reaction during hexene-1 conversion. The cracking product yield and C6+ products yield may be controlled by acid strength of acid center and pore structure together. SAPO-11 presents a unidimension system with 10-MR opening. The amount of acid center is close to ZSM-5-90, but the strength is much lower. So the dimerization and cracking reaction is blocked. The hexene-1 conversion and iso-C6 yield of SAPO-11 is quite close to Beta and ZSM-5-90, which is correlated to the amount of weak + moderate acid center.