Synthesis, Characterization Of MgAlZnFeCe Hydrotalcite-like Compounds And Application Of Their Complex Oxides In FCC De-SOx

The Fluid Caralytic Cracking (FCC) is one of the major gasoline-producingprocess in refinery.About 5-10% of feed sulfur deposited in the coke on FCCcatalysts is converted into SOx in regenerator,and then emission of SO_x from flue gasof FCC caused the pollution of air.Compared with other measures to control SOxemmision from FCC,sulfur-transfer additives technology is more suitable for thepresent FCC equipments.There are about 2～3% V₂O₅ and 14% CeO₂ in presentSulfur-transfer additive t which are bad for use.At the same time,the sulfur increasesin gasoline.In our research,we have developed a kind of novel sulfur-transfer additives usedMg and Al as the acyive species with transition metal and rare-earth as aids.The novelsulfur-transfer additives aimed to control the increase of sulfur in FCC gasoline and toreduce the toxicity and producing costs is calcined hydrotalcite-like compounds.The rustles are summarized as follows:1.Mg²⁺ in the hydrotalcite can be substituted partially by Zn²⁺and Fe³⁺ in the courseof corprecipitation.SOx adsorption-redution activity of MgAl-LDO(3),MgAlZn-LDO(Zn=5%) and MgAlZnFe-LDO(5%,5%) was studied and the resultsshowed that SOx adsorption rate of MgAlZnFe-LDO increased with the increase ofFe₂O₃ content,and SOx saturation-adsorption capacity increased with the increase ofmolar ratio of Mg to Al,and its activity did not change with ZnO content in LDO to acertainty scope.MgAlZnFe-LDO cannot act as the active material precursor ofsulfur-transfer additive because of its thermal instability.2.SOx adsorption-redution rate of MgAlZnFeCe-LDO increased quickly when CeO₂was introduced because its good ability for the oxidation of SO₂ to SO₃ and theinhibition of particles sintering.SOx adsorption-redution rate of MgAlZnFeCe-LDOdid not change when CeO₂ content reached 8%(wt),and thermal stability ofMgAlZnFeCe-LDO increased obviously at same time.So MgAlZnFeCe-LDO was anice active material precursor of sulfur-transfer additive.3.Effects of Na₂O content,time and temperature of crystallization,raw material andmemory effect on the performance of MgAlZnFeCe-LDO were investigated.Resultsshowed SOx-reduction rate slowered quickly with Na₂O content increasing,thestructure and the particles size of MgAlZnFeCe-LDH (CeO₂=8%) became perfectlyand large,the performance of MgAlZnFeCe-LDH(CeO₂=8%) prepared from nitrateand hydrochloric salts did not show difference.The seasoned temperature for calcined MgAlZnFeCe-LDH was 800℃.4.The physicochemical properties and SOx oxidation-adsorption activity of productsin the pilot trial were as same as those of the sample prepared in lab.Sulfurequilibrium data from circulating fluid vertical riser indicated that sulfur in FCCgasoline was controlled when the sulfur-transfer additive containing ZnO was usedcompared with that without sulfur-transfer additive,but the whole sulfur in productoil increased.5.MgAlZnFeCe hydrotalcite-like precursors were prepared by a hydrothermal method usingMgO as magnesium resource and pseudoboehmite as aluminum resource,and using metalchlorides of Zn,Fe,Ce as catalytic additives.MgAlZnFeCe complex oxides were prepared bydecomposition of MgAlZnFeCe hydrotalcite-like precursors at 700℃for 6 h,and were used forthe removal of SO_x from FCC flue gas.The suitable solids content is 15% to 20%;aging temperature is 150 with 40h.Using this method,hydrotalcite-like compound was the majorcomponent while the minor phase was Mg (OH) 2 as the impure phase.MgAlZnFeCe ComplexOxide achieves high oxidative adsorption rate,short saturation time,and large reductivecapacity.6.Results showed that MgO was the only active material for SOx adsorption,Al₂O₃contributed to the structure of sulfur-transfer additive,Fe₂O₃ was not only the catalystfor oxidating SO₂ to SO₃,but also the catalyst for reducing MgSO₄,CeO₂ was a verynice catalyst for oxidating SO₂ to SO₃,but had no significant contribute to thereduction of MgSO₄,ZnO and Al₂O₃ contributed to control sulfur in FCC gasoline,but ZnO had no activity on SOx oxidation-adsorption.This work will provide the valued data and theoretic bases for the production andapplication in industry scale of sulfur transfer additive.