【作者】 于维钊；

【导师】 郑经堂；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2008， 博士

【摘要】 燃料油品中含硫化合物的脱除是清洁油品生产中的关键过程。作为非加氢脱硫技术的一种,基于吸附过程的脱硫技术得到研究者的广泛关注。该方法可以在常温常压的条件下选择性地脱除油品中的含硫化合物,因而具有潜在的应用前景。研究显示具有选择性吸附脱除噻吩类化合物能力的吸附剂种类较多,但现有研究大多集中在吸附材料的筛选方面,对吸附剂和吸附质之间的作用方式和油品中竞争吸附物对吸附过程影响的研究还比较薄弱。因此,本文以炭材料为吸附材料,以模型汽油溶液为处理对象,系统考察了氧化改性对活性炭表面性质的改变及其对吸附脱除噻吩类化合物性能的影响、模型竞争组分对炭材料吸附脱硫性能的影响及其机理,以及活性炭吸附噻吩过程的热力学和动力学特征,并对新型吸附脱硫炭材料的制备及其吸附脱硫性能进行了初步的研究;同时也考察了炭材料对催化裂化(FCC)汽油的吸附脱硫效果。对多种炭材料进行初步筛选,确定采用椰壳活性炭作为吸附研究的基础材料。然后分别采用过硫酸铵溶液和臭氧作为氧化介质,对椰壳活性炭进行了氧化改性以改变其表面化学性质,以吸附脱除噻吩-环己烷溶液中噻吩的能力作为考察指标,确定了两种改性方法的最佳条件。结果表明,经过硫酸铵和臭氧氧化改性后,活性炭噻吩的静态平衡吸附容量(以单位质量活性炭的硫容量计)由8.47 mg-S/g分别提高为15.52和21.50 mg-S/g,动态吸附的穿透容量由2.03 mg-S/g分别提高到8.10和14.21 mg-S/g。分别以环己烯和甲苯作为汽油中烯烃和芳烃的模型化合物,以环己烷、正庚烷和正癸烷作为汽油中烷烃的模型化合物,考察了这些化合物对噻吩在活性炭表面的竞争吸附作用。结果表明,烯烃和芳烃对噻吩的吸附具有强烈的竞争作用,导致活性炭对噻吩的吸附容量大大降低,其中芳烃的竞争作用高于烯烃;而烷烃化合物对噻吩的竞争吸附作用较弱。分别采用N2吸附、Boehm滴定、FT-IR和XPS等表征手段对活性炭的孔结构和表面化学性质进行了表征,结果表明过硫酸铵氧化对活性炭孔结构的影响低于臭氧氧化;两种氧化过程均使炭表面的含氧官能团数量大量增加,两种氧化方法增加的酚羟基数量接近,而臭氧氧化能够在炭表面引入更多的羧基。通过关联活性炭的物理、化学性质与其噻吩吸附性能,发现活性炭对噻吩的吸附能力主要决定于其表面化学性质,即氧化过程引入的含氧官能团是氧化改性活性炭对噻吩吸附能力增强的主要原因。从微观角度对活性炭与吸附质分子的相互作用进行了分析,并采用硬软酸碱(HSAB)理论对模型汽油体系中的各种化合物的化学硬度进行了计算,结果表明,各种化合物的化学硬度与其竞争吸附作用的强弱具有很高的相关性,表明化学硬度能够作为评价化合物在炭表面吸附能力的指标。对活性炭进行氧化改性也能够改变其表面的局部化学硬度,使其与目标脱除物质分子的化学硬度相匹配,从而提高吸附选择性和吸附容量。活性炭对噻吩吸附过程的热力学研究表明,噻吩在活性炭表面的吸附等温线可很好地符合Langmuir吸附模型;热力学函数的分析显示活性炭吸附噻吩的过程为放热、减熵的自发过程,氧化处理能够提高炭表面对噻吩分子的亲和力。吸附动力学考察显示噻吩在活性炭上的吸附过程可用拟二级吸附动力学方程来描述,颗粒内扩散是该过程的速率控制步骤之一,吸附速率同时还受颗粒外扩散过程的控制。将对模型汽油吸附脱硫性能较好的臭氧氧化改性活性炭用于FCC汽油的处理,对该方法中的吸附条件进行了考察,确定了最优条件。在优化吸附条件下,可使硫含量为796μg/g的FCC汽油的初始流出液的硫含量降低到18μg/g。饱和吸附后的活性炭经再生3次后使用,仍能使初始流出液的硫含量降低到45μg/g。以酚醛系弱酸性阳离子交换树脂为炭前驱体,制备了负载金属的球形活性炭材料,并对其吸附脱硫性能进行了初步的考察。对模型汽油的处理结果显示,由于金属负载对噻吩吸附作用方式的改变,该材料对竞争吸附物具有比较好的抑制作用。对FCC汽油的处理结果显示该材料对汽油中的噻吩类化合物的选择性吸附脱除能力较强。更多还原

【Abstract】 Removal of sulfur containing compounds in fuels is one of the key processes in production of clean fuels. As a kind of non-hydrogenation desulfurization approach, adsorptive desulfurization has gained attention worldwidely. By this means, the sulfur containing compounds can be removed from fuels under ambient temperature and pressure. Many adsorbents show adsorptive removal performance of thiophenic compounds, while most researches focus on screening of materials and only minor efforts have been put on study of interactions of adsorbates and adsorbents, and influences of competitive compounds on adsorption process. In this paper, carbon materials were chosen as adsorption materials and model gasoline chosen as treatment object to explore the adsorptive desulfurization process. The change of surface chemistry of carbon materials by oxidation and its influence on adsorption performance for removal of thiophene, influence of model adsorption competitive compounds on thiophene removal and mechanism, and both thermodynamic and kinetics character of the process were investigated systematically. And a new adsorption carbonaceous material was synthesized for primarily exploring of its adsorptive desulfurization. The desulfurization performance of these materials for FCC gasoline was evaluated as well.Firstly, various carbonaceous materials were screened and coconut activated carbon was chosen for further study. Ammonium persulfate and ozone were used as oxidizing agent to modify coconut activated carbon by changing its surface chemistry. The optimized condition was verified by evaluation of capacity for removal of thiophene in thiophene-cyclohexane solution as model gasoline. Results show that after oxidation by ammonium persulfate and ozone, the static equilibrium adsorption capacity of activated carbon, counted by sulfur capacity per unit mass, has increased from 8.47 mg-S/g to 15.52 and 21.50 mg-S/g, respectively. And dynamic breakthrough adsorption capacity has increased from 2.03 mg-S/g to 8.10 and 14.21 mg-S/g, respectively. With cyclohexene as olefin model compound, toluene as aromatic model compound, and cyclohexane, n-heptane and n-decane as paraffin model compounds, the competitive effects of these compounds for thiophene on carbon surfaces were investigated. Results show that olefins and aromatics strongly competitive with thiophene on carbon surfaces, and aromatics show more severe effect, which makes the adsorption capacity of thiophene reduce enormously. However, the competitive effect of paraffins is weak, which hardly influences thiophene adsorption capacity. The pore structure and surface chemistry of activated carbons was characterized by N2 adsorption, Boehm titration, FT-IR, and XPS. Results show that the influence of ammonium persulfate treatment on pore structure is greater than that of ozonation. Both the two treatments increase oxygen-containing functional groups on carbon surfaces considerably with close number of phenolic groups and more carboxyl groups for ozonation. Correlation of thiophene adsorption performance with physical and chemical properties of activated carbon indicates that the surface chemistry plays an important role in the process of thiphene adsorption, from which it can be deduced that the oxygen-containing functional groups introduced by oxidation is the main reason for thiophene adsorption capacity boosting.The interactions of activated carbon with adsorbate molecules were analyzed within microscopic domain. The chemical hardness in HSAB theory of compounds in model gasoline system was calculated by quantum chemistry method. The chemical hardness of these compounds shows good correlation with results of competitive adsorption experiments, which render the chemical hardness as an acceptable criterion for competitive adsorption ability. The analysis of local chemical hardness of activated carbon also elucidates the change in local chemical hardness can adopt it with adsorbate molecules to increase the interaction strength to improve the adsorption selectivity and capacity. The isotherm of thiophene adsorption on activated carbon fits well with Longmuir model. And analysis of kinetically functions indicates that thiophene adsorption is an exothermic, entropy-reducing, and spontaneous process. Oxidation can improve the affinity of carbon surface with thiophene molecules. Investigation of adsorption dynamics also shows that the process can be described with pseudo-second-order dynamic equation. The intra-particle diffusion is one of the rate-determining steps of the total process, and the adsorption rate is also controlled by external diffusion processes.The ozone-oxidized carbon, with comparatively better thiophene adsorptive removal capacity, was chosen for treatment of FCC gasoline. Optimized conditions were determined by breakthrough experiments. Under optimized conditions, the initial effluent of treated FCC gasoline with sulfur content of 796μg/g is reduced to 18μg/g. The saturated activated carbon can still reduced the initial effluent sulfur content to 45μg/g even after 3 cycles of regeneration. Phenolic weak acidic cation exchange resin was chosen as carbon precursor to prepare metal-loaded spherical activated carbon, and its adsorptive desulfurization performance was investigated primarily. The treatment results for model gasoline show that this type of actived carbon can reduce the competitive effects for thiophene adsorption with altered adsorptive interactions between thiophene and adsorbent. The treatment for FCC gasoline shows its good performance for removal of thiophenic compounds.更多还原