【作者】 程文萍；

【导师】 何鸣元； 杨建国；

【作者基本信息】 华东师范大学 ， 物理化学， 2008， 博士

【摘要】 流化催化裂化（FCC）装置中,原料油中所含的硫约45-55%转化成H₂S随蒸汽排出,而35～45%留在液态产品中,还有5～10%的硫则沉积在待再生催化剂的焦炭上,进入再生器后焦炭上的硫被氧化生成SO_x（SO₂+SO₃）随再生烟气排出。随着高硫原料油加工量的提高以及FCC装置进料中渣油和重质油的比例不断增加,FCC再生烟气中SO_x含量增加,导致装置腐蚀严重,同时污染环境、危害人类健康。与原料油加氢脱硫和烟道气洗涤法控制FCC再生烟气中SO_x排放的措施相比,采用硫转移剂技术降低再生烟气中SO_x的含量,不需要改造装置,且操作简便,是一条经济有效的技术途径。硫转移剂是在FCC装置的反应器和再生器之间循环使用,在再生器中将SO_x氧化吸附形成稳定的金属硫酸盐,然后在反应器和汽提器中,所形成的硫酸盐被还原,生成H₂S直接释放。再生后的硫转移剂则进行下一次的循环使用。目前报道的硫转移剂还存在着硫氧化物脱除率低、再生性能较差和毒性大等一系列问题。本文以不同的制备方法和原料合成了CuMgAlFe类水滑石前驱体,再经过焙烧制得CuMgAlFe-LDOs硫转移剂。通过X射线衍射（XRD）、组成分析（XRF）、热分析（TG-DTA）、氮吸附脱附、扫描电镜（SEM）和红外光谱（FT-IR）表征,考察了不同方法和原料对制备的类水滑石前驱体及硫转移剂结构和物化性能的影响;并在改装的WRP-3热重天平上,在模拟典型FCC的反应—再生条件下,评价了不同硫转移剂的氧化还原性能。结果表明:1.通过共沉淀法制备的类水滑石为前驱体得到的MgAl3-LDOs、8%CuMgAl3-LDOs与MgAl3Fe8%-LDOs硫转移性能比较发现,MgAl3-LDOs氧化吸硫速率较慢,饱和吸附硫容较低,并且生成的硫酸盐在600℃不能被还原脱附。8%CuMgAl3-LDOs氧化吸硫速率最快,6 min饱和吸附硫容达到1.22 g SO_x/g,但是化学吸附的硫酸盐在600℃不能被完全还原脱附。MgAl3Fe8%-LDOs氧化吸硫速率较快,20 min饱和吸附硫容为0.93 g SO_x/g,并且在600℃时,10 min即可完全还原。这一结果表明:MgO是化学吸附SO_x的主要活性组分;Al₂O₃起保持材料结构的作用,支撑孔结构,防止烧结现象,增加其金属元素的分散性能,同时Al₂O₃可以起到抑制FCC汽油中硫含量升高的作用;Fe₂O₃既是氧化SO₂的促进剂又是还原MgSO₄的促进剂;CuO是一种很好的氧化SO₂的促进剂。2.以浸渍法合成Cu-MgAlFe硫转移剂。首先,通过研究不同镁铝比和铁含量对载体硫转移性能的影响发现,MgAl5Fe8%-LDOs的氧化吸硫和还原脱硫性能较好,氧化吸硫速率较快,25 min饱和吸附硫容为1.45 g SO_x/g,并且在600℃完全还原。因此MgAl5Fe8%-LDOs是优良的硫转移剂的活性载体。其次,MgAl5Fe8%-LDOs载体通过浸渍法引入CuO以后,Cu-MgAlFe复合氧化物的氧化吸硫速率明显加快,饱和硫容也有所增加。1.0Cu-MgAlFe仅仅6 min即可饱和吸附SO_x1.60 g SO_x/g,氧化吸硫的速率是MgAl5Fe8%-LDOs载体的4.6倍;经过八次循环使用后,硫转移性能基本保持稳定,再生性能好。3.采用常规的共沉淀法,首先以不同金属盐作为原料均可以得到晶形较好的类水滑石前驱体,焙烧后得到CuMgAlFe-LDOs。其中以硝酸盐得到的复合氧化物,其氧化吸硫速率较快,饱和吸附硫容较高,并且在600℃被完全还原。然后通过以改变不同镁铝比和铁、铜含量制备类水滑石前驱体的研究发现,CuMgAlFe-LDO6复合氧化物,在氧化吸硫条件下,仅仅需要6 min达到饱和吸附,饱和硫容达到1.62 g SO_x/g;在还原条件下,8 min即可完全还原;经过八次循环使用后,硫转移性能基本保持稳定,表现出很好的再生性能。4.以铝酸钠为铝源,通过共沉淀法,均可以得到晶形较好的类水滑石前驱体,焙烧后得到CuMg（Al）Fe-LDOs。通过改变不同镁铝比和铁、铜含量制备类水滑石前驱体的研究发现,CuMg（Al）Fe-LDO6的饱和硫容仅需6 min即达到1.74 g SO_x/g;在还原条件下,8 min即可完全还原;并且CuMg（Al）Fe-LDO6水滑石前驱体制备的复合氧化物也表现出非常好的再生性能。5.以MgO为镁源,拟薄水铝石水为铝源,Fe、Cu的硝酸盐为助催化剂通过水热法合成了类水滑石材料,实验条件下得到的类水滑石含有Mg（OH）₂和Al（OH）₃杂晶,焙烧后得到Cu（MgAl）Fe硫转移剂。Cu（MgAl）Fe-LDOs8复合氧化物具有较大的饱和硫容和较快的氧化吸硫速率,6 min即可达到1.69 gSO_x/g吸附饱和,但是还原脱硫能力较差。因此水热合成类水滑石前驱体制备硫转移剂的方法还需要进一步的研究。6.通过浸渍法,常规共沉淀法,水热法和以铝酸钠为原料共沉淀法分别制备的CuMgAlFe复合氧化物均有较好的硫转移性能,其中以铝酸钠为原料得到的CuMg（Al）Fe硫转移性能最佳。更多还原

【Abstract】 In the feedstock of fluid catalytic cracking（FCC）process,there exist many different types of sulfur-containing organic compounds.When the feedstock containing organic sulfur is fed into FCC units about 45～55%of the sulfur in the feedstock is converted to hydrogen sulfide in the reactor of FCC units,about 35～45% is still remained in the liquid products,and the rest of the sulfur of about 5～10%is deposited in the coke formed on the FCC catalyst.The sulfur deposited in the coke is transferred to SO_x（SO₂+SO₃）when the coke is combusted in the regenerator of FCC units.With the increase of throughput of FCC units and of sulfur content in crude oil, emission of SO_x from flue gas of FCC units is increased.These gases are among the major atmospheric pollutants and are acid rain precursors,posing a serious problem to the protection of the environment.Both flue gas scrubbing and feedstock hydrodesulfurization are all effective means of SO_x control,but they are laborious and expensive.Compared with the two techniques for controlling SO_x emission from FCC units,sulfur-transfer additive technique is more practical and attractive for the present FCC units.It is very important to design high effective SO_x reducing materials for this purpose.Potential SO_x transfer catalyst must be able to oxidize SO₂ to SO₃ under the FCC regenerator conditions,be able to chemisorb the SO₃ in the form of stable metal sulfates in the FCC regenerator,be able to reduce sulfates to release sulfur as H₂S in the FCC reactor and stripper.Study on sulfur-transfer additive should aim at the following questions（1）to improve the activity and abrasion resistance ability of sulfur-transfer additive,（2）to reduce the toxicity and production costs of sulfur-transfer additive.The CuMgAlFe-HTlcs were prepared by different synthetic methods and different materials,and The CuMgAlFe complex oxides used for the removal of SO_x from FCC flue gas were prepared by decomposition of CuMgAlFe hydrotalcite-like compounds precursors at 700℃for 6 h.These catalysts were characterized by XRD, XRF,TG-DTA,BET,SEM and FT-IR techniques and first evaluated as potential SO_x transfer catalysts by thermogravimetric techniques under conditions similar to those of a typical FCC.The MgAl3-LDOs、8%CuMgAl3-LDOs and MgAl3Fe8%-LDOs mixed oxides were obtained from the hydrotalcite-like precursors which were synthesized by coprecipitation method.The results of SO_x adsorption-reduction tests showed that MgAl3-LDOs displayed the lowest adsorption capacity in the longest saturation time, and MgAl3-LDOs can not be regenerated at 600℃.8%CuMgAl3-LDOs exhibited the highest adsorption rate,and total saturation adsorption capacity with 1.22 g SO_x/g in 6 min,but its sulfates can not be completely reduced at 600℃.MgAl3Fe8%-LDOs reached total saturation adsorption capacity with 0.93 g SO_x/g in 20 min,its sulfate reduction ability was much better than that of MgAl3-LDOs and 8%CuMgAl3-LDOs at 600℃.The results indicated that MgO was the only active material for SO_x adsorption,and formed very stable MgSO₄ compounds,restricting the additive regeneration.Al₂O₃ showed a low SO_x removal capacity because the Al₂（SO₄）₃ formed is very unstable at the regenerator temperature so it releases the sulfate species as produced in the regenerator.But Al₂O₃ contributed to the structure of sulfur-transfer additive,and Al₂O₃ controlled sulfur content of FCC gasoline in synergic effect.Fe₂O₃ played a dual role as an oxidizing and a reducing promoter, CuO was an efficient promoter for oxidating SO₂ to SO₃,but had no significant contribute to the reduction of metal sulfates.Cu-MgAlFe catalysts were prepared by the impregnation with copper on the mixed oxides MgAl5Fe8%-LDOs.First,MgAl5Fe8%-LDOs reached total saturation adsorption capacity with 1.45 g SO_x/g in 25 min,its sulfate reduction ability was much best in all MgAlFe-LDOs with different Mg/Al ratios and Fe contents at 600℃. So MgAl5Fe8%-LDOs was an efficient active material precursor of sulfur-transfer additive.Second,Cu-MgAlFe catalysts showed the higher adsorption rates which are reflected in lower saturation times compared with that of MgAl5Fe8%-LDOs. 1.0Cu-MgAlFe reached total saturation adsorption capacity with 1.60 g SO_x/g in 6 min,its adsorption rate was 4.6 times higher than that of MgAl5Fe8%-LDOs,and 1.0Cu-MgAlFe showed similar adsorption capacities after the eighth SO₂ adsorption-reduction cycle.CuMgAlFe-LDOs complex oxides used for the removal of SO_x from FCC flue gas were prepared by decomposition of CuMgAlFe hydrotalcite precursors synthesized by coprecipitation method at 700℃for 6 h.The influence of different metal salts in the sulfur transfer catalyst was investigated.The results of SO_x adsorption-reduction test showed that CuMgAlFe-LDOs prepared from nitrates achieved high oxidative adsorption rate,short saturation time,and large reductive capacity.CuMgAlFe-LDOs with different Mg/Al ratios,Fe and Cu contents in the sulfur transfer catalyst were found that CuMgAlFe-LDO6 presented the greatest total adsorption capacity（1.62 g SO_x/g）in 6 min,and was regenerated completely in 8 min, which was also remained at constant after the eighth cycles.CuMg（Al）Fe-LDOs complex oxides were prepared by decomposition of CuMg（Al）Fe hydrotalcite precursors with NaAlO₂ as aluminium source synthesized by coprecipitation method at 700℃for 6 h.The influence of different Mg/Al ratios, Fe and Cu contents in the sulfur transfer catalyst was investigated.This indicated that CuMg（Al）Fe-LDO6 showed the greatest total adsorption capacity（1.74 g SO_x/g）in 6 min,and was regenerated completely in 8 min,which was also remained at constant after the eighth cycles.Cu（MgAl）Fe hydrotalcite-likes compounds（includes Mg（OH）₂ and Al（OH）₃） were synthesized with MgO,pseudoboehmite,Fe（NO₃）₃ and Cu（NO₃）₂ by hydrothermal method.Cu（MgAl）Fe-LDOs complex oxides were prepared by decomposition of Cu（MgAl）Fe hydrotalcite-likes precursors at 700℃for 6 h. Cu（MgAl）Fe-LDO8 reached total saturation adsorption capacity with 1.69 g SO_x/g in 6 min,but it exhibited bad regeneration performance.So Cu（MgAl）Fe hydrotalcite-likes compounds as precursors for CuMg（Al）Fe-LDOs complex oxides were prepared by the hydrothermal method need be further researched.All CuMgAlFe catalysts with different methods exhibited excellent adsorption capacities,adsorption-reduction rates,and reduction percentages at 600℃.To compare the CuMgAlFe sulfur-transfer additives performance,CuMg（Al）Fe-LDOs showed the better SO_x absorption-reduction ability than the other catalysts.更多还原