摘要
石油炼制和石油化工过程中副产大量富含丁烯的C_4液化气。长期以来液化气主要作为城市燃气使用,化工利用率低。将液化气进一步优化利用转化成高附加值产品不仅能带来经济效益而且具有重要的社会意义。C_4液化气低温芳构化,目的是将液化气中的烯烃转化成高辛烷值汽油组分,剩余的烷烃可作为蒸汽裂解原料用于生产乙烯、丙烯,或作为车用液化气,是一条非常有意义的液化气综合利用途径。
纳米ZSM-5沸石因具有优异的芳构化、异构化、烷基化以及抗积炭性能,已应用在催化裂化汽油降烯烃的OTA工艺中。本文选取不同晶粒大小ZSM-5沸石制成催化剂,在相对低的反应温度下对比研究了其C_4液化气芳构化反应的性能。ZSM-5沸石的颗粒大小是影响催化剂性能的一个重要参数。与微米HZSM-5催化剂相比,纳米HZSM-5催化剂因其粒度小、孔道短、孔口多等优点,在C_4液化气芳构化反应中表现出较强的容炭能力和良好的芳构化性能。
在此基础上考察了原料中微量杂质及反应条件对C_4液化气在纳米HZSM-5催化剂上芳构化性能的影响。原料中的二烯烃和碱性氮化物都能加速催化剂失活,其中碱性氮化物的失活作用比二烯烃大。反应过程中氢气的存在有利于抑制催化剂上积炭的形成,从而提高芳构化反应稳定性。反应温度、压力和进料重量空速都对催化剂性能有显著影响,最佳反应条件是450℃、2.0 MPa和WHSV_(LPG)=0.83h~(-1)。反应温度、反应压力和进料空速过高都导致催化剂积炭失活速度加快。
在相对优化反应条件下,纳米HZSM-5催化剂连续运转1100h,丁烯转化率基本保持在99%左右,同时C_5~+液体产物中的芳烃含量保持在60%以上,表现出高稳定性和优异的芳构化性能。不同再生方法对三次再生纳米HZSM-5催化剂芳构化性能的影响不明显,表明纳米HZSM-5催化剂具有良好的烧炭再生性能。
C_4 liquefied petroleum(C_4 LPG) gas rich in butylenes is mainly by-produced from the petrolume refining and petrochemical industries. For a long time, the majority of C_4 LPG has been consumed as fuel and the utilization of it for chemical purpose is quite low. Optimization utilization of C_4 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 C_4 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 C_4 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 C_4 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 (H_2) / V (LPG,liquid)= 260 ,WHSV = 0.83 h~(-1), pressure=3.0 MPa and temperature= 450 ℃, the catalytic performance of nano-sized
HZSM-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.
引文
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