【作者】 龙化云；

【导师】 王祥生； 孙万付；

【作者基本信息】 大连理工大学 ， 工业催化， 2012， 博士

【摘要】 本文研究了烯烃在纳米HZSM-5上的反应过程,考察了分子筛物化性质、钾改性、水热处理条件和金属改性对烯烃反应过程的影响,研究了烯烃和硫化物共存时的反应过程及相互影响,开发了以ZnLaP改性纳米HZSM-5的芳构化催化剂和先芳构后脱硫的全馏分FCC汽油改质工艺,得到了如下结论：与微米HZSM-5相比,纳米HZSM-5表现出更高的芳构化活性和反应稳定性。反应温度影响烯烃反应的类型和产物分布。高温有利于芳烃的生成和产品辛烷值的提高,但同时会导致芳烃组成中苯含量上升和产品液收下降。反应压力对正辛烯芳构化和芳烃组成影响不大。氢气在芳构化过程中起到了消炭作用。正辛烯首先发生分子内的双键和骨架异构,再裂解生成C3-C5的小分子烯烃中间体,中间体发生聚合、环化和氢转移生成芳烃和烷烃。正辛烯芳构化需要酸强度Ho<+2.27的酸中心的参与才能发生。结焦反应会优先发生在Ho<-3.0的酸中心上。酸中心数量影响烯烃中间体的分布,从而影响产物中芳烃的组成。水热处理能有效脱除HZSM-5骨架铝,降低分子筛酸量。强酸中心和弱酸中心的下降在抑制结焦方面能起到协同作用。纳米HZSM-5经过锌改性后,总酸量和B酸中心下降,L酸中心增加。适当的L酸和B酸分布可以提高催化剂的芳构化活性。纳米HZSM-5上硫化物的脱除能力不同。烯烃可吸附在催化剂活性位上,对硫化物的脱除有抑制作用。一定浓度的硫化物不会对芳构化和异构化活性造成明显影响。纳米HZSM-5经过500℃水热处理和ZnLaP改性后,总酸量为0.49mmol/g,Ho<+2.27的酸量为0.07mmol/g,L／B值为2.3。镧的加入提高了芳构化活性中心锌物种的分散度,增强锌物种和载体的相互作用,增加了[Zn(OH)]+物种含量,改善了催化剂的芳构化活性。磷的添加提高了锌物种在催化剂内表面的浓度,改善了催化剂的稳定性。镧磷的协同作用进一步增加了[Zn(OH)]+物种含量,延缓了锌物种的流失,提高了催化剂芳构化活性和稳定性。通过先芳构后脱硫工艺采用ZnLaP/HZSM-5催化剂对全馏分FCC汽油改质,产品中芳烃含量由原料的15.2%上升至19.3%,烯烃由40.1%下降至27.2%,异构烷烃含量从35.4%上升至38.4%,硫含量则由产品的190ppm下降至47ppm。产品的辛烷值为90.4,相比原料RON损失为0.3个单位。原料干点为187℃,产品干点上升至197℃。实验结果表明采用先芳构后脱硫的改质工艺,可以生产满足国IV标准的清洁汽油。更多还原

【Abstract】 The effect of physicochemical properties of ZSM-5, hydrothermal treatment and metal modification conditions on the olefin transformation were investigated over nanoscale HZSM-5. The interaction effect of olefin and sulfur compounds on the aromatization and hydrodesulfurization activities was studied. The ZnLaP/HZSM-5aromatization catalyst and the two steps process applying the sequence that aromatization followed by desulfurization were developed. Based on the investigations, the following conclusions were reached:Nanoscale HZSM-5zeolite was more stable and showed higher aromatization activity than microscale HZSM-5. The reaction type and product distribution were strongly influenced by reaction temperature. High temperature was favorable to the aromatization activity and the increase of the product RON. But it resulted in the increase of benzene content and the decrease of the product yield. Pressure showed unobvious effect on the aromatization activity and the distribution of aromatics. The eliminating carbon ability of H2was found in the aromatization process.Double bond isomerization and skeletal isomerization of n-octene was the first step of n-octene transformation. Propene, butene and pentene were produced as intermediates. These olefins were oligomerized and then cracked to produce a wide distribution of olefins with different carbon atoms. These intermediates were quickly transformed into aromatics and alkanes by hydrogen transfer. The strong acid sites with acid strength H0≤+2.27were indispensable to the transformation of n-octene into aromatics. Coking reaction firstly occurred in the acid sites with acid strength H0≤-3.0. The distributions of olefin intermediates and aromatics were influenced by the acidic amount of HZSM-5.Hydrothermal treatment was a very effective dealumination method and reduced the acidic amount of HZSM-5obviously with the increase of the hydrothermal treatment temperature. The synergistic effect of strong and weak acid sites in improving the deactivation behavior of catalyst was found. The amount of Bronsted acid sites decreased and the amount of Lewis acid sites increased with the addition of the zinc into nanoscale HZSM-5. The maintenance of appropriate Bronsted and Lewis acid sites distribution greatly improved the aromatization stability.The hydrodesulfurization activities of sulfur compounds were different over nanoscale HZSM-5. The inhibiting effect of olefin on the removal of sulfur compounds was caused by the adsorption of olefins on the acid sites and was irreversible. The presence of200ppm sulfur compounds did not influence the aromatization and isomerization activities of nanoscale HZSM-5.The total acidic amount of nanoscale HZSM-5after hydrothermal treated at500℃and modified with Zn, La and P decreased to0.49mmol/g and the ratio of L/B was2.3. Zinc species were the active sites of aromatization. The addition of La improved the dispersion degree of zinc species, increased the zinc species-support interaction and the amount of [Zn(OH)]+species and therefore enhanced the aromatization activity of the catalyst. The addition of P increased the amount of the zinc species located in the channels of nanoscale HZSM-5and therefore enhanced the stability of the catalyst. The synergistic effect of La and P increased the amount of [Zn(OH)]+species, decreased the loss of zinc species and consequently increased the activity for FCC gasoline aromatization and the stability of the catalyst. The evaluation of ZnLaP/HZSM-5catalyst for upgrading of FCC gasoline was conducted in two steps process applying the sequence that aromatization followed by desulfurization. The results showed that the aromatics content increased from15.2%to19.3%, the olefins content decreased from40.1%to27.2%, the i-paraffins content increased from35.4%to38.4%and the sulfur content decreased from190ppm to47ppm. The RON of the product was90.4and the loss of the RON was0.3. The dry point increased from187℃of the feed to197℃of the product. The product can meet the National IV standard with sulfur content less than50ppm and the loss of RON less than one unit by the two steps process applying the sequence that aromatization followed by desulfurization.更多还原