| Environmental concerns have resulted in some new gasoline regulations worldwidely toreduce automobile emissions. In China, "Limits and Measurement Methods for Emissionsfrom Light-Duty vehicles (PhaseⅢ,Ⅳ)" standards will be executed on July 1, 2007, inwhich less than 30 vol.％of olefin content, 40 vol.％of aromatic content, and 150μg/g ofsulfur content in gasoline are required to meet the No.Ⅲemission standards.Fluid catalytic cracking (FCC) gasoline, coker gasoline, and straight-run gasoline arelight oil produced in petroleum processing. FCC gasoline accounts for approximate 80％ofthe total gasoline pool in China, which has high olefin content (40～55 vol.％) and high sulfurcontent (200～1500μg/g). It is urgent to develop a novel technology to greatly reduce olefinand sulfur in gasoline, while preserving gasoline octane number. Coker gasoline andstraight-run gasoline can not be used as gasoline blending stocks directly due to the lowoctane numbers (50～60). Currently, the content of aromatics in the typical light oil is about10 to 20 vol.％, whereas the maximum content in the gasoline pool is limited to 40 vol.％.Thus, there is still a big space for increasing the amount of aromatics. It would be desirable todevelop an efficient process that not only removes sulfur but also reduces olefins. In this way,the loss of gasoline octane number due to olefin reduction can be compensated by the increasein isoparaffins and aromatics with higher octane numbers in the process.ZSM-5 zeolites are widely used in hydrocarbons transformation processes due to itsexcellent aromatization, isomerization, and alkylation. The parent HZSM-5 zeolite catalystwith crystals in nanoscale exhibited higher selectivity and higher ability to resist coking thanthe microscale ones because of its smaller crystallite, shorter micropore, and more acidiccenters at external surface. Hydrothermal treatment is usually employed to adjust the acidityof HZSM-5 zeolite and improve its stability. Transition metal nickel and molybdenum haveexcellent desulfurization activity. In the parent study a nanoscale HZSM-5 zeolite wasprepared by hydrothermal treatment and loading transition metal oxides. The catalyticperformance of the prepared catalyst for upgrading of low quality light oil was evaluated.Based on the above investigations, the following conclusions were obtained:1 The nanoscale HZSM-5 was hydrothermally treated at 400℃and 3.0 wt.％La2O3and 1.0 wt.％ZnO was loaded on the treated HZSM-5. The evaluation of the prepared catalystfor upgrading of FCC gasoline was conducted in a flowing system for 300 h. After thehydrotreatment, the olefin content in gasoline decreased from 49.6 to 12.8 vol.％and the aromatic content increased from 11.4 to 24.7 vol.％, Meanwhile, gasoline octane number waspreserved.2 HZSM-5 modified with transition metal oxides indicated the following conclusions:(1) The nanoscale HZSM-5 zeolite was prepared by hydrothermal treatment at 500℃followed by loading of 2.5 wt.％La2O3, 2.0 wt.％NiO, and 9.7 wt.％MoO3 on the treatedHZSM-5. The characterization results showed that after the treatment the total aciditydecreased, the total Lewis/Bronsted acidity increased, and the metal high dispersion occurredon the surface of the catalyst.(2) The evaluation of the prepared catalyst for upgrading of FCC gasoline was conductedin a flowing system for 300 h. After the hydrotreatment, the olefin content decreases from32.5 to 13.9 vol.％, olefin saturation rate 57％; the aromatic content increases from 33.5 to39.8 vol.％; the isoparaffin content increases from 24.1 to 32.7 vol.％; the sulfur contentdecreases form 744 to 178μg/g, desulfurization conversion 76％. Meanwhile, the catalyst canreduce the content of benzene and existent gum. Mass balance calculation showed that theprocess has low chemical hydrogen consumption (0.42 wt.％) and high gasoline yield (95wt.％); the RON of gasoline has only a slight change from 94.1 to 93.9 after the upgradingprocess. The most-significant advantage of this catalyst is that hydrotreatment over thedeveloped catalyst can significantly reduce olefin and sulfur contents without change ofoctane number.(3) Application of DOS catalyst upgrading of coker gasoline and straight-run gasolinecan reduce the sulfur content in light oil significantly and increase the research octane numbergreatly.3 Effect of alumina carriers with different pore structures on the catalytic performancesof the HZSM-5 catalysts upgrading of low quality light oil were also investigated. The resultsshowed that the HZSM-5 catalysts extruded with macroporous alumina exhibits betteraromatization activity, isomerization activity, higher coke-resistant activity, as well as higherability of reducing olefin content in FCC gasoline than the microporous ones.
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