Study on the FCC Gasoline Selective Cracking over HZSM-5 Zeolite and Paraffin Naphtha Dehydro-aromatization Over Pt/KL Zeolite

Author:Zhao Yun

Supervisor:guo hong chen


Degree Year:2019





In China,olefin-reduction upgrading for FCC(Fuild Catalytic Cracking)gasoline and utilization of paraffin-rich naphtha,such as raffinate oil or coal indirect liquefaction naphtha and so on?are important topics in catalysis research field.Focusing on above-mentioned topics,in this study,catalytic cracking of full range FCC gasoline and paraffin-rich naphtha as well as aromatization of paraffin-rich naphtha have been studied,including modification researches on hydrothermal stability of nano-sized H-ZSM-5 zeolite and attempts in preparation of Pt/KL zeolites.In the first place,in order to enhance hydrothermal stabilty of the naino-sized H-ZSM-5 zeolite and optimize its catalytic performance for FCC gasoline,La(N03)3\Ba(N03).,NH4H2PO4,trimethyl phosphate((CH:O+PO4),and tetraethoxysilane(TEOS)modification have been studied comparatively.Afterwards,researches on co-modification by first impregnating with(CH3)3POa and then silylating with tetraethoxysilane(TEOS)have also been done.With the aid of XRD,NH3-TPD and FT-IR as well as fixed-bed micro-reactor,it was found that phosphorus modification was an effective way to improve the hyrotlhermal stability and cracking performance of nano-sized H-ZSM-5 zeolites,and(CH3)3POa modification showed better effect.The results obtained from solid-state NMR suggested that the advantages of(CH3)3POa modification should be attributed to the strong interaction between zeolite frzamework Al and(CH3)3POa,which facilitated the formation of distorted tetra-coordinated Al species stablized by short-chain phasphates.Under simulated fluidization reaction conditions at 540 ℃,in the catalytic cracking reaction of FCC gasoline,the P and Si co-modified nano-sized H-ZSM-5 zeolite after steamed at 800 ℃(1P2Si-st)showed following results:olefins conversion 60.28%,n-paraffins conversion 75.25%,C2≈-C4=olefins selectivity 92.84 wt.%,Cs+crude gasoline yield 65.64 wt.%.The olefin content of Cs+crude gasoline was reduced to 30.74 wt.%.Comparing with the feedstock,the RON of Cs+crude gasoline was increased by about 2 units,and the olefin content was reduced by about 20 percent points.The above-mentioned results suggested that catalytic cracking of FCC gasoline showed high low-carbon olefins selectivity and have good application potential.In the second place,the P,Si co-modified nano-sized H-ZSM-5 zeolite(steamed at 700℃)was used as the catalyst for catalytic cracking of chain-paraffins in raffinate oil.Under conditions of 540 °C and atmospheric pressure(simulated fluidization reaction conditions),the following results were obtained;n-paraffins conversion 60.09%,i-paraffins conversion 74.28%,Cu=+C3=selectivity in gas product 44.05 wt.%.The reasons why dry gas and propane yield were so high during catalytic cracking reaction of chain-paraffins over solid acid catalysts were investigated by theramodynamic calculations.K and Zn ions co-impregnated nano-sized H-ZSM-5 zeolites with different K ion loading were used as catalysts for raffinate oil aromatization on fixed-bed reactor.Under 470 ℃ and 0.8 MPa,for more than 500 h time on stream,the following results were obtained(K0.5Zn6):dry gas yield was reduced to 10~15 wt.%;aromatics yield attained at 40 wt.%;the sum of aromatics and propane yield attained to more than 70 wt.%.Aromatics plus propane co-production scheme was suggested to solve the problem of high dry gas yield in solid acid catalytic aromatization technologies.Finally,the preparation and dehydro-aromatization performance of Pt loaded KL zeolite,which is a non-solid acid catalyst for chain-alkanes aromatization were preliminarily studied with self-synthesized Pt(NH3)4Cl2 and a commercial KL zeolite supporter.The surface dynamic reaction of the dehydro-aromatization over obtained catalysts was studied by an operando dual-beam FT-IR spectrometer.The influence of Pt precursors(H2PtC14 and Pt(NH3)aCl2),Pt loading,and Ba(NO3)2 co-impregnation on the catalytic performance of Pt/KL zeolites were also investigated.On the fixed-bed reactor and under suitable reaction conditions(500℃,0.4 MPa,1.5 h-,,HZ atmosphere),the Pt/KL catalyst with 1.2 wt.%Pt loading,prepared witlh self-synthesized Pt(NH3)4Cl2,showed excellent n-Heptane dehydro-aromatization performance.The conversion of n-Heptane approached 100%;the aromatics yield reached 66.14 wt.%;H2 yield was 5.6 wt.%;dry gas yield(methane+ethane)was 15.84 wt.%;propane yield was a little higher than 3 wt.%.The reaction stability test of Pt,Ba co-impregnated KL zeolite was lasting about 500 h on the fixed bed reactor.