Studies On The Aromatization Performance Of HZSM-5 Modified By Ga And Zn

Gasoline standards have become more and more stringent since the development of auto industry and human notice on environment protection. In China, the latest standard in which less than 50 ppm sulfur content, no more than 25V% olefins content and no more than 60V% aromatics plus olefins content is required has been executed in some city.In China, about 80% gasoline comes from FCC gasoline which has high sulfur and olefins content while aromatics still has growth room. The conventional hydrotreating technology results in the significant reduction of RON dut to the saturation of olefins in FCC gasoline. Aromatization can transfer olefins to aromatics to keep the octane number. The quality of straight run gasoline can also be improved by aromatization.ZSM-5 has been used in many hydrocarbon conversion reactions due to its excellent aromatization, isomerization and alkylation ability. The parent nano-HZSM-5 exhibited the properties of smaller crystallite, shorter micropore, and more acidic centers at external surface. Hydrothermal treatment can modify the acidity of HZSM-5 and its stability on the basis of retaining crystal structure. HNO3 treatment can remove the non-framework Al in the zeolite channel. Ga and Zn are excellent active component on aromatization process. In the study nano-HZSM-5 were prepared by hydrothermal & HNO3 treatment and loading Ga, Zn and other metal oxides. The aromatization performances of prepared catalysts for FCC and straight run gasoline were evaluated.Based on the above investigations, we got the following conclusions.(1) The Ga/HZSM-5 after nanoscale HZSM-5 was hydrothermal treated at 600℃showed the best aromatization performance (aromatization and C3+C4 contents were 58.3V%and 7.6V%, respectively) at reaction temperature 480℃, WHSV=1 h-1.(2) The total acid amount (including Leswis and Br(?)nsted acid) and strength decreased, and the ratio of L/B of prepared HZSM-5 increased as the hydrothermal treatment temperature rising.(3) Catalyst Ga/HZSM-5 which modified by Fe, Cu and Cr didn't show any advanced aromatization performance on FCC gasoline in the selected reaction conditions.(4) Catalyst Zn/HZSM-5 modified by La and P showed better aromatization performance than catalyst modified by Cu and Ni respectively. The evalution of the prepared catalyst which was loaded with 2% wt.Zn and 1wt.% La for FCC gasoline aromatization was conducted at 380℃, WHSV=1.5 h-1. After aromatization, the aromatic content in gasoline increased from 15.2V% to 22.1V%, and olefin content decreased from 40.1V% to 25.7V%. Meanwhile, gasoline RON was 89.7.(5) HZSM-5 modified by Ga and Zn followed the same mechanism in the aromatization process no matter what the active component was.