【作者】 孙琳；

【导师】 王祥生； 郭洪臣；

【作者基本信息】 大连理工大学 ， 工业催化， 2011， 博士

【摘要】 丁烯芳构化反应是提高炼油副产C4液化气资源附加值的一条重要途径。然而,积炭失活快是传统沸石芳构化催化剂的主要难题。因此,本文重点研究了芳构化催化剂在C4液化气低温芳构化反应中的抗积炭失活性能。着重考察了ZSM-5沸石催化剂的晶粒度、酸度和微孔扩散性对其积炭失活速度的影响。主要研究结果如下：(1)研究了酸度相近,而晶粒度不同的ZSM-5沸石催化剂对C4液化气芳构化反应的影响,发现这些样品表现出了相同的初始活性和不同的稳定性。不同沸石催化剂的反应稳定性顺序为：微米沸石催化剂<小晶粒沸石催化剂<纳米沸石催化剂。纳米ZSM-5沸石催化剂优异的抗积炭失活性能归结为孔道短,外表面积大,丰富的晶间孔以及较多的孔口减少了积炭堵孔的机会。(2)用高温水汽钝化与酸扩孔处理制备了四组催化剂样品,通过XRD、NH3-TPD、Py-IR以及正己烷和环己烷的吸附量表征,研究了C4液化气低温芳构化反应中纳米ZSM-5沸石催化剂的酸度、微孔扩散性与积炭失活的关系。发现酸度较强的纳米ZSM-5沸石催化剂表现出了更快的积炭失活速度。同时,沸石的微孔扩散性能也对催化剂的积炭失活速度有显著影响。微孔约束力(即正己烷和环己烷的吸附量之比,用n-h/c-h表示)越大,积炭失活越严重。纳米HZSM-5沸石催化剂经500-550℃水蒸气处理,以及钝化前后都经过稀硝酸溶液处理后,制得的改性催化剂具有适宜的酸度和良好的微孔扩散性能,因此也表现出优异的抗积炭失活能力。(3)通过综合改性调变了沸石的酸度和微孔扩散性能,研制出一种以纳米ZSM-5沸石为催化剂母体的DLG-1催化剂,表现出了良好的抗积炭失活性能以及C4液化气中丁烯的低温芳构化性能。研究了反应条件、C4液化气原料组成、杂质含量以及反应气氛对DLG-1催化剂上C4液化气低温芳构化反应的影响。发现除了催化剂外,适宜的反应条件、清洁的原料(例如,较低的二烯烃和硫化物含量以及无碱性氮化物)以及临氢反应都对进一步提高催化剂的抗积炭失活性能起到了重要作用。在优化的反应条件下(T=420-450℃、P=2.0-3.0 MPa、WHSVLPG=0.8-0.9 h-1和VH2/VLPG=260), DLG-1催化剂在1104h的长运转过程中丁烯转化率和芳构化活性始终分别保持在99%和60%以上,积炭量和积炭的碳氢摩尔比分别为20.8%和1.32。(4)DLG-1催化剂表现出了优异的再生性能。其经历十次体内烧炭再生后,在1000余小时的长运转过程中芳构化活性仍能保持在60%,丁烯转化率始终稳定在99%。并在放大装置(催化剂装填量200m1)上验证了DLG-1催化剂的芳构化性能：在T=410℃,P=2.0 MPa, WHSVLPG=1.2 h-1和VH2/VLPG=260的条件下反应600 h(运转时间限于C4LPG的供应),丁烯转化率大于99%,芳构化活性稳定在48%左右,干气及焦炭低于2%,氢气消耗低于0.6(wt%)。产物分析表明,放大实验中汽油收率达到76%(以进料丁烯计),上述汽油产品因烯烃含量(1.6%)低、苯含量(1.3%)低以及硫含量(1 ppm)低,而辛烷值(RON>97.8)高,成为理想的汽油调和组分。反应同时联产大量烯烃含量小于1.0%的优质丙、丁烷液化气,可作为乙烯裂解原料。可以预期改性纳米HZSM-5沸石催化剂-DLG-1用于C4液化气低温芳构化反应,具有很好的工业化前景。更多还原

【Abstract】 The aromatization of butenes is an important route to the value-added use of C4 LPG by-product sources. However, the fast coking deactivation of conventional zeolite aromatization catalyst has been a major obstacle to be overcomed. Therefore, this dissertation is focused on the anti-coking deactivation of aromatization catalyst during the low-temperature aromatization of C4 LPG. Emphasis was given to the effects of crystal size, acidity, and micropore diffusivity of ZSM-5 zeolite catalyst on its coking-deactivation rate. Following main results are obtained:(1) The aromatization of C4 LPG over different crystal size ZSM-5 zeolite catalysts with similar acidity was studied. Results show that these catalysts exhibit similar initial activity but different stability. The order of reaction stability of different zeolites is:micro-sized ZSM-5< small crystal sized ZSM-5< nano-sized ZSM-5 zeolite catalyst. The nano-sized ZSM-5 zeolite catalyst possesses unique coke deactivation resisting ability, which is attributed to its short channels, large external surface area, abundant intercrystal pores, and much more pore mouths which decrease the chance of coke blockage.(2) Four series of zeolite catalysts are prepared by high-temperature steaming and acid leaching combination. XRD, NH3-TPD, pyridine-FT-IR, adsorptions of n-hexane and c-hexane are used to study the relationships between the zeolitic acidity and micropore diffusivity with the coking deactivation of nano-sized ZSM-5 zeolite catalyst in the low-temperature aromatization of C4 LPG. It is found that, nano-sized ZSM-5 zeolite catalyst with stronger acidity generally shows faster coke deactivation speed. Meanwhile, the diffusivity of the zeolitic micropores also has remarkable influence on the coking deactivation of the catalyst. The stronger the micropore diffusion constraint (the adsorption capacity ratio of n-hexane to c-hexane, denoted by n-h/c-h), the more serious coke deactivation is. By subjecting the nano-sized HZSM-5 zeolite catalyst to steaming treatment under 500-550℃, and leaching the catalyst with dilute HNO3 before and after steaming, the modified catalyst shows proper acidity and micropore diffusibility, and thus possesses satisfactory anti-coking deactivation ability.(3) By optimizing zeolitic acidity and micropore diffusivity with modification combination, DLG-1 catalyst was successfully developed by the nano-sized HZSM-5 zeolite, which exhibits satisfactory performances in both anti-coking deactivation and low-temperature aromatization of butene when fed with C4 LPG. Effects of reaction conditions, C4 LPG feedstock composition and purity, and with or without carrier gas on the low-temperature aromatization of C4 LPG was investigated over this catalyst. It is found that, beyond catalyst, the suitable reaction conditions, high purity feedstock (i.e., low diene and S-compounds content and alkaline N-compounds free) and the use of hydrogen as carrier gas are all very important to further enhance the catalyst’s anti-coking deactivation ability. Under the optimal range of reaction conditions (T=420-450℃, P=2.0-3.0 MPa, WHSVLPG=0.8-0.9 h-1 and VH2/VLPG=260), the conversion of butene and aromatization activity over DLG-1 catalyst, in the low-temperature aromatization, can keep above 99% and 60% after 1104 h time-on-stream, and the coke amount and C/H mole ratio of coke are 20.8% and 1.32 separately.(4) DLG-1 catalyst exhibits excellent regeneration performance. It can keep aromatization activity and butene conversion 60% and 99%, respectively, during more than 1000 hours time on stream after ten times repeated in-situ coke-burning regeneration. The catalyst was also subjected to a scale up reactor (200 ml catalyst loading) evaluation, which was carried out at the conditions of T=410℃, P=2.0 Mpa, WHSVLPG=1.2 h-1, and VH2/VLPG=260 for 600 h (operation was limited by C4 LPG supply), results obtained including butene conversion above 99%, aromatization activity around 48%, the percentage of dry gas and coke are below 2, hydrogen loss no more than 0.6 (wt%). Products study indicated that this scaled up test gave 76% gasoline fraction yield (calculated on butene), said gasoline product is most desired gasoline blending cut for low contents of olefin (1.6%), benzene (1.3%) and sulfur (1 ppm), and high octane number (RON> 97). The low-temperature aromatization also produced large amount of high quality Propane-butane LPG in which olefins content is less than 1%. Such LPG can be used as ethylene cracking feedstock. It is believed that the low-temperature aromatization of C4 LPG over modified nano-sized HZSM-5 zeolite catalyst, DLG-1, has very bright commercialization prospect.更多还原