Study On The Low-temperature Aromatization Of C₄ Liquified Petroleum Gas Over Nano-sized ZSM-5 Zeolite

C₄ liquefied petroleum(C₄ LPG) gas rich in butylenes is mainly by-produced from the petrolume refining and petrochemical industries. For a long time, the majority of C₄ LPG has been consumed as fuel and the utilization of it for chemical purpose is quite low. Optimization utilization of C₄ LPG for products with high additional value is not only an important way to improve economic benefit, but also has profound social significance. In this study, we focuse on the utilization of C₄ LPG to produce high octane number gasoline via the low-temperture aromatization of butylenes.After the complete conversion of butylenes,the residual alkanes can be used to produce propylene and ethylene by steaming cracking or used as fuel for motors.Nano-sized ZSM-5 zeolite has been applied in OTA process for FCC gasoline upgrade duo to its excellent performance for aromatization, isomerization , alkylation and stronge ability to resist coking. In this paper, the aromatization of the butylenes of C₄ LPG is comparatively studied with HZSM-5 catalysts with different crystal size under mild temperature. The crystal size of zeolite is an important factor that affects the properties of the catalyst. Results show that nano-sized HZSM-5 catalyst possesses high tolerance ability for coke and favorable aromatization performance due to its small size and shorter channel of micropore.On the basis, the effects of feeding impurities and reaction conditions on the aromatization of the butylenes of C₄ LPG over nano-sized HZSM-5 catalyst are investigated. Results show that, both diene and alkaline nitrogen-containing compounds all have negative influences on the aromatization stability of the catalyst under mild temperature. Comparatively, the negative influence of the alkaline nitrogen-containing compounds is much stronger than that of diene.The aromatization stability is obviously improved under the hydrogen ambience duo to coking prohibition during the reaction.Reaction temperature, pressure and WHSV_LPG also show significant influences on the performance of the catalyst. The optimum reaction conditions are centered around 450℃, 2.0 MPa and WHSV_LPG=0.83 h^-1. High coking speed of the catalyst is seen when high temperature, pressure and WHSVlpg conditions are used.Under the optimum conditions of V (H₂) / V (LPG,liquid)= 260 ,WHSV = 0.83 h^-1, pressure=3.0 MPa and temperature= 450 ℃, the catalytic performance of nano-sizedHZSM-5 catalyst keeps stable at least within 1100 hour continuous operation. The percentage of aromatics (mainly C6^Cc>) in the product maintain 60.0 %.The conversion of butylenes is as high as 99%. The catalytic performance of nano-sized HZSM-5 catalyst can be kept after three times deactivation-regeneration.