A Study On Synthesis, Characteristics And Properties Of New Sulfur-transfer Additives For FCC Flue Gas DeSOx

About 5～10% of feed sulfur deposited on FCC catalysts in the coke is converted to SO_X in regenerator and then emitted in flue gas in fluid catalytic cracking (FCC) process. With the increase of throughput of FCC units and sulfur content in crude oil, harmfulness of SO_X from flue gas of FCC units is becoming serious. Compared with other measures for controlling SO_X emission from FCC unit, sulfur-transfer additive technology is more suitable for the present FCC units. 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, (3) to control the increase of sulfur in FCC gasoline.The results of this thesis can be concluded as following:1. SO_X adsorption rate of MgAlZnFe-HTlc increased with the increase of Fe₂O₃ content, SO_X saturation capacity became large when the ratio of Mg to Al changed from 2 to 5, ZnO content of HTlc had no significant effect on SO_X adsorption-reduction performance of MgAlZnFe-HTlc. MgAlZnFe-HTlc was not the most efficiently active material precursor of sulfur-transfer additive owing to its thermal instability.2. SO_X adsorption rate of MgAlZnFeCe-HTlc increased rapidly and its thermal stability was also improved obviously when CeO2 was introduced into MgAlZnFe-HTlc(5%, 5%). So MgAlZnFeCe-HTlc(CeO₂=8%) was an efficient active material precursor of sulfur-transfer additive.3. SO_X-reduction rate decreased quickly when Na₂O content of MgAlZnFeCe-HTlc (CeO₂=8%) increased, SO_X-adsorption profile of MgAlZnFeCe-HTlc(CeO₂=8%) prepared through coprecipitation was higher than that synthyzed with impregnation to introduce CeO₂, the structure and the particles size of MgAlZnFeCe-HTlc(CeO₂=8%) became perfectly and large with the increase of time and temperature of crystallization, MgAlZnFeCe-HTlc(CeO₂=8%) prepared from nitrate and hydrochloric salts had no difference on physicl-chemical properties and SO_X adsorption-reduction activity.4. Sulfur-transfer additive matching with FCC catalyst in physical-chemical properties was prepared using spray drying unit ( 2t/d ) used for FCC catalyst production through the special matrix material and binder suitable for alkaline active material.5. Both physical-chemical properties and SO_X adsorption-redution activity of sulfur-transfer additive were better than that of sulfur-transfer additive reported on literatures. Results of ACE, fixed fluid bed and vertical riser pilot reactor showed that H₂S content in dry gas increased 10～20%, SO_X and NO_X in flue gas decreased 87% and 32% respectively, and the conversion and selectivity of the valuable products did not be modified when sulfur-transfer additive was added to the catalyst inventory in an amount of 2%(wt) compared with that without it. Sulfur equilibrium data from vertical riser pilot reactor indicated that sulfur of FCC gasoline was controlled when the sulfur-transfer additive containing ZnO was used, but the whole sulfur of product oil still increased.6. MgAlZnFe-S prepared from pseudoboehmite as support and aluminium source in situ through impregnation and calcination exhibited high SO_X adsorption-reduction activity compared with kaolin, SiO₂ and equilibrium FCC catalyst supports, and its SO_X saturation capacity became large with the increase of active material content. Spinal phase could form on the surface of pseudoboehmite after calcination at 700 ℃ for 6 h, however, which is not the only active material for SO_X adsorption.7. MgAlZnFeCe-Pseud. was prepared under different calcination temperature using pseudoboehmite as support and aluminium source. Results indicated that SO_X adsorption rate of MgAlZnFeCe-Pseud. increased rapidly, CeO₂ could restrain spinal phase growing on the surface of pseudoboehmite and MgAlZnFeCe-Pseud. particles sintering. Spinal phase on the surface of pseudoboehmite became intense with calcination temperature increasing, however, surface area and pore volume of MgAlZnFeCe-Pseud. decreased quickly when calcination temperature was over 700 ℃, thus SO_X adsorption profile decreased. The optimal calcination conditions for preparation of MgAlZnFeCe-Pseud. in situ were: 700 ℃ 6 h.8. Results showed that MgO was the only active material for SO_X adsorption, Al₂O₃ contributed to the structure of sulfur-transfer additive, Fe₂O₃ played a dual role as an oxidizing and a reducing promoter, CeO₂ was an efficient promoter for oxidating SO₂ to SO₃, but had no significant contribute to the reduction of MgSO₄, ZnO and Al₂O₃ controlled sulfur content of FCC gasoline in synergic effect, but ZnO exhibited no activity for SO_X oxidation-adsorption.9. Physical-chemical properties and SO_X oxidation-adsorption performance of MgAlZnFeCe-HTlc(CeO₂=8%) prepared in 20 L bath (1.2～1.5 Kg MgAlZnFeCe-HTlc/bath) were as same as that of the sample prepared in 1 L bath.The innovation of this thesis can be concluded as following :1. A method of coprecipitation and heat treatment suitable for production of the active material of sulfur-transfer additive has been brought forward, which was testified to be feasible in pilot test.2. Expensive and toxic vanadium element was completely replaced by cheap and nontoxic iron element, which not only reduced pollution to workers and environments during the produce of sulfur-transfer additive, but also avoided vanadium poisoning of FCC catalyst which could make the structure of zeolite collapsed.3. Cerium content can be reduced after a small amount of iron was introduced into HTlc after the study on the synergic effect between iron and cerium in HTlc, which decreased the producing costs of sulfur-transfer additive.4. A method of adding ZnO into the active material of sulfer-transfer additive to control sulfur content of FCC gasoline was developed, which could control the increase of sulfur of FCC gasoline during the application of sulfer-transfer additive in FCC unit.5. The abrasion resistance ability of sulfur-transfer additive was improved through the spray drying method and the special matrix material and binder suitable for alkaline active material. 6. A novel method for preparation of sulfur-transfer additive in situ through pseudoboehmite as support and aluminium source had been brought forward, which was feasible and the performance of sulfur-transfer additive prepared was very good.This thesis will be the theory base for the production and application of sulfur-transfer additive in industry scale, and will provide complete data at the same time.