Synthesis, Characterization and Evaluation of Sulfur Transfer Catalysts for FCC Flue Gas

China Petroleum Processing and Petrochemical TechnologyScientific Research2014,Vol.16,No.2,p59-64June30.2014Synthesis, Characterization and Evaluation of SulfurTransfer Catalysts for FcC Flue GasJiang Ruiyu; Shan Honghong; Zhang Jiling; Yang Chaohe; Li Chunyi(1. Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province,Proc ancheng Institute of Technology, Yancheng 224051; 2. State Key Laboratory of Heavy Oiling, China University of Petroleum (East China), Qingdao 266580 3 East-China Design branchChina Petroleum Engineering Construction Corporation, Qingdao 266071,Abstract: In this work, Zr-M(M=Cu, Mn, Ce)type sulfur transfer agent was prepared by impregnation method. Under thecondition similar to that in the regenerator of FCC units, the influence of different active metal components and their con-tents on sulfur transfer agent were investigated. Moreover, the crystalline structure of sulfur transfer agent was characterizedby X-ray diffraction(XRD)and Fourier transforms infrared spectroscopy (FT-IR). The result showed that the Zr-Mn sulfurtransfer agent could effectively reduce the SO2 content in FCC regenerator flue gas, featuring high SO2 adsorption capacityThe sulfur transfer agent was inactivated in 40-60 min during the test. In the course of reduction reaction, after several reaction cycles, the formation of SO, ceased and only h, s was detected as the reduction productKey words: fluid catalytic cracking; sulfur-transfer catalyst; flue gas; zirconium1 Introductioncoke deposited on the catalyst in the regenerator of FCCThe emission of So, (SO, and SO, )from either motor As far as the reduction of sulfur oxides emissions derivedvehicles or stationary units causes serious atmosphericfrom the fCC unit is concerned, a variety of methodspollution and destruction of the ozone layer-7.Thus, have been proposed either for treating the fuel beforetheir emission is increasingly restricted by environmen- combustion or for disposing of the flue gas generated durtal legislations. Although the contribution of refineries ing fuel combustion. However, the least costly strategyis relatively small (6%10%)compared with the total is the addition of sulfur transfer additives to the fccamount of SO, emitted from other sources, it can become catalyst. By mixing the FCC catalysts with the additives,very significant in smog-filled areas that are ringed with sulfur oxides can be fixed as sulfates in the regeneratorheavy industry, metal smelters, and coal-fired power in an oxidative atmosphere; then the sulfates formed onplants. It is well known that if the sulfur-containing feed- the additives move together with FCC catalysts to a riserstock is fed into the fluid catalytic cracker unit(FCCU) where they are released as H,S. The discharged gaseouswithout pretreatment, about 45%-55% of the total sul- H, S is sepm the ofur compounds present are released as H, S, and another reduced in the usual way known as the Clause process to35%45% would remain in the liquid products, with form elemental sulfur. This technique is much less costhe rest being deposited on the coke which is formed on than the hydrodesulfurization or stack-gas scrubbing techthe FCC catalysts and transformed to sulfur oxides(with niques, and, from the economical and technical viewpoint,more than 90% of So2 and less than 10%of So, )when it is a very practical and attractive technique 4-3, 12-13, 17-1I8Jthe coke deposits are burned off in the regenerator of FCc The three steps that determine the performance of a sozunit. Therefore, the emission of so. derived from Fccunits can be divided into two parts: one is originated from Recieved date: 2013-09-09; Accepted date: 2014-04-20the combustion of fuel produced from FCC units and the Correspondingano Ruivn Telenhone: +86-515other is from the combustion of the sulfur-containing 88298923 E-mail中国煤化工CNMHGChina Petroleum Processing and Petrochemical Technology2014,16(2):59-64transfer catalyst are shown below[ZrOCl2 8H2O] and ammonium hydroxide [Nd, H2O](1)Oxidation of SO 2 to SO3 in the FCC regenerator, typi- were used as starting materials to prepare catalysts. First-cally at a reaction temperature in the range of from 700C ly, two precursors were completely dissolved in distilledto730℃,SO2(g)+1/2O2(g)→SO(g)water at a ph value of between 9-10. The precipitate(2) Trapping of SO, on the catalyst to form sulfates, was formed and filtered, washed with distilled water, andMO(s)+SO(g)→MSO(s)soaked in ethanol for 36 h and then filtered. Then the fil-(3)Reduction of sulfates to release sulfur as H,s in Fcc ter cake was dried for 8 h to remove moisture at 120 Criser, typically at a reaction temperature in the range of 500C The dried solid was calcined in a muffle furnace for 2 h atto 530C, MSO4(S) +4H,(g)MO(s)+3H, O(g)+H,s(g)700C and then ground. The solid particles with a size ofMany efforts have been made to improve the activ- 80-120 mesh were collected through sievingity of SOx uptake catalysts. MgAlO-spinel or Mg/Al- 2.2 Preparation of ZrO, -M(M-Cu, Mn, Ce)HTLCs) have been attracting much attention because ZrO2-M catalysts were prepared by the impregnationthey offer a large capacity for adsorption of SO, Different method. Zirconia and metal nitrates were mixed in differmetallic oxides such as those of Ce, Cu. Co. V. Cr and Fe ent proportions. The solution was dried for 2 h to removeare incorporated into HTLCS either via impregnation or moisture from the solid material at 120 C. The dried catacoprecipitation, as the best way to prepare the solid solu- lyst was calcined in a muffle furnace for 2 h at 700Ctions of mixed oxides/spinels with both basic and redox 2.3 Characterization of samplesproperties required for good performance in the De-SOXprocess+-5, 10, 12-13,17, 19. Lately, Henriques/ 9, 6 and co-workAll samples were characterized by X-ray diffractioners demonstrated that Mg, Mn and Al-oxides with the(XRD)on a DANalytical X'Pert PROMPD spectrometricdiffractometer(using Cu-Ka radiation), and by FT-IRspinel structure would be promising as additives for SOremoval in FCC unit. In addition to the spinel systemsspectrometry on a Micromeritics Nexu STM spectrometerusing the K Br-disk methodwe preliminary used zirconia as carrier loaded alkalinespecies functioning as a sulfur oxide transfer agent. Zir- 2.4 Catalytic performance tests/7-a/conia can be used as the catalyst and also the catalyst car- Experiments were performed in a tubular reactor placedrier thanks to its acid-base property, redox performance, in a vertically installed electric furnace filled with 0.5 ggood thermal stability and mechanical strength. As a support, zirconia favors the dispersion and stability of active gram of experimental setup for this study. Gas entered thecomponent Furthermore, it is also involved in catalytic top of reactor with its flow rate being controlled by a massreactions because the presence of zirconia could increase flowmeter. The concentration of SO, was 2 730 mL/L; inthe mobility of lattice oxygen to improve the oxidationorder to carry out SO, oxidative adsorption, a stream withreduction property. In this experiment, the preliminary a flow rate of 131 mL/min containing 2 730 mL/L of soexploration of load-based FCC flue gas sulfur transferagent was carried out under FCC conditions. The effectof different active metal components on the adsorption ofSO, in flue gas was studied and characterized by X-raydiffractometry (XRD)and the Fourier transform infrared(FT-IR) spectroscopy.2 Experimentalcon2.1 Preparation of ZrOZrO, was prepared by means of the ammonia com-Flue gas analvzerIn中国煤化工plexation method. Zirconium oxychloride octahydratector unitCNMHGiang Ruiyu, et al. Synthesis, Characterization and Evaluation of Sulfur Transfer Catalysts for FCC Flue Gasand 1. 2% of air was introduced through the catalyst bed introduction of Mn is good for the oxidative adsorption700C in 10 min. A simulated FCC gas was used to of SO, to form the related sulfates. Furthermore, with theinvestigate the effect of desulfurization. The gases exit- continuous reduction of Mn species, the SO2 concentra-ing the reactor were automatically analyzed by a flue gas tion firstly increased and then declined. a Zr/Mn ratio ofanalyzer(Model Testo 350 M/X, made in Germany). The 2 was better because with increase in the metal amourSO, content was calculated from the relevant datamore active components could migrate into the metalcarrier holes, which would cause deposition on the pore3 Results and discussionwalls and fast deactivation of the catalyst It is reasonable if3.1 Catalytic performancewe suppose that Mn(Ill) may function as the active species,which can promote the oxidation of so2 to SO, with itself3.1.1 Effect of the Zr/Cu ratios on desulfurization ef- being simultaneously reduced to Mn(ID, while the excessficiencyO2 will subsequently oxidize Mn(Il) to Mn(II)), 201To investigate the influence of the different zr/Cu ratiosTable 2 Effect of different Zr/Mn ratios on thedesulfurization performance, a series of tests weredesulfurization efficiencyconducted to measure their desulfurization efficiency. ItZr/Mn=1 Zr/Mn=2 Zr/Mn=10 Zr/Mn=20can be seen from Table I that the group effect of sulfurAmount of So,(in thetransfer agent was not very good, but it showed that Cu51564Ist 20 min), mL/Lhad some effect on SO2 adsorption. The catalyst with a Amount of SO, (in the 82Zr/Cu ratio of 2 worked relatively well probably because2nd20min),μL/Lthe role of zro, as well as Cu in the micro-surface reacAmount of So, (in the13905633rd20min),μLL2061tion process showed a relatively unique performanceZrO, not only played the role of support, but also favored 3.1.3 Effect of the Zr/Ce ratios on the desulfurizationion and stability of active component. Frourtheefficiencymore, ZrO, might be involved in catalytic reaction, and The data listed in Table 3 are in agreement with those decould shape up the active center with Cu co-catalystpicted in Table 1. The group effect of sulfur transfer agentTable 1 Effect of different Zr/Cu ratios on thwas not very good, but it also showed that Ce had somedesulfurization efficiencyeffect on SO, adsorption. a Zr/ Ce ratio of l worked relaAmount of So, (in the Ist 20 min), HL/Ltively well. This fact has confirmed that Ce atoms wereZr/Cu=lthe active sites for SO2 oxidative adsorption in this seriesZr/Cu21359although the formation of a crystalline phase could not be1652detected according to the thermodynamic studZr/Cu=201723Table 3 Effect of different Zr/Ce ratios on thedesulfurization efficieney3.1.2 Effect of Zr/Mn ratios on the desulfurizationZr/Ce=0.5 Zr/Ce=0.67 Zr/ Ce=1 Zr/Ce=efficiencyAmount of so, (in thelst20min),μLL14191331564Upon comparing the role of zirconia used as the mn conlining carrier, it is recognized that its performance wasbetter than the catalyst containing Cu as depicted in Table 3.2 XRD analysis1. The effect of Zr/Mn ratio in the sulfur transfer agent The XRD spectrograms of the as-synthesized sample andon adsorption of so2 at 700C during the simulated cata- the used sample are shown in Figure 2. With respect tolytic cracking process is presented in Table 2. The sulfur the sample(a), small diffraction peaks corresponding tocapacity of sulfur transfer agent was smaller because Mn, a Mn2O3-bixbyite C, the syn-type phase, were observedwhich possessed a shorter atomic radius than that of Zr, along with中国煤化 ating that aalready changed the structure of zirconium oxide. The part of MnYHSCNMHGMn' duringChina Petroleum Processing and Petrochemical Technology2014,16(2):59-64the synthesis process, as previously suggested by Velu, et could be observed and it could be attributed to the inter-al. With respect to the sample (b), a similar behavior was action between the hydroxyl radicals and oxygen latticeobserved for the virgin and the used samples. Besides in the framework due to the water adsorbed on the surfacethe Mn2O3-bixbyite C, the syn-type phase, diffraction of the sample. This band shifted towards higher frequenlines were also observed, but it was difficult to identify cies if the temperature was increased. Hereby, we mainlywhether there was a manganese sulfate phase According focused on the absorption bands ranging from 2 000 cmto the redox potentials, the oxidation of Mn to Mn to 400 cm. After 20 min of adsorption, the samples(a)s highly favorable in a basic medium in the course of and(b)indicated intense absorption bands at 1 140 cmcatalyst synthesis%, 20)and 1 020 cm. However, with regard to the sample(d)only one inferior absorption band appeared at 1 140 cmThe above bands were assigned to the asymmetric andsymmetric O=S=O and O-S-O stretching vibration of sur-WWwface and bulk-like sulfates. The Ft-ir study confirmed theexistence of stable sulfur complexes formed from stronchemisorption or reaction of So, with the active sites4, 2n13.4 Analysis of adsorptive desulfurization mechanism of sulfur transfer agent010203040506070There are many mechanisms relating to flue gas desulFigure 2 XRD patterns of different samplefurization. Different researchers have proposed differenta-Virgin Zr/Mn=2: b-Used Zr/Mn=2desulfurization mechanisms according to experimentalphenomena. By studying the absorptive property of zi3.3 FT-IR analysisMn type spinels, the representative results show that SOmainly forms MgSO4. Experimental results also indicateTo identify the changes of virgin sulfur-transfer catalystthat theand sulfur species after SO2 oxidative adsorption, FT-IRining spinel is a promisingfur transfer agent. After the reduction of the sulfated addimeasurements of the samples such as virgin Zr/Cu, Zr/MnZr/Ce sulfur-transfer catalysts with different metal contents tives. when the reduction temperature reached 500C. SOwere carried out with the results presented in Figure 3was formed as the initial product during the reduction ofsulfated species, which was different from that observedduring the regeneration process starting at 530 C, whereno So, was detected at all. After several reaction cyclesthe formation of SO2 ceased and only H,s was detected asthe reduction product4 ConclusionsUnder conditions similar to those existing in the regenerator of fcc units the influence of different active metal200018001600140012001000800600400components and their contents were investigated theresults showed that the Zr-Mn based sulfur transfer agentFigure 3 IR spectra of different samples(a)Used Zr/Mn=2; (b) Used Zr/Ce=1;(c)Virgin Zr/Mn=2ould effectively reduce SO2 content in the FCC regenerad)Used Zr/ Cu=2;(e)virgin Zr/Ce=;(f)virgin Zr/Cu=2tor flue gas, leading to higher rate for adsorption of soThe sulfur transfer agent was deactivated in 40--60 minAccording to the literature information), a very wide The FT-IR中国煤化工 ated that0band in the range of between 3 410 cm and 3 450 cm" was mainlyayH-ulfur transferCNMHGJiang ruiyu, et al. Synthesis, Characterization and Evaluation of Sulfur Transfer Catalysts for FCC Flue Gasagent is an active promoter to enhance the ability of Sox [8] Jiang Ruiyu, Shan Honghong, Zhang Qiang, et al. The influadditives in the regenerator of FCC units. Further studence of surface area of De-SOx catalyst on its performance []ies must be done to improve the additive performance forSeparation and Purification Technology, 2012, 95: 144-148simultaneous removal of So. In the course of reduction [9] Pereira H B, Polato C, Monteiro J L F, et al. Mn/Mg/Alreaction, when the reduction temperature reached 500 Coinels as catalysts for SOx abatement: Influence of CeO2SO2 was formed as the initial product during the reducincorporation andcatalytic stability [J]. Catalysis Today,tion of sulfated species. After several reaction cycles, the2010,149(3/4):309-315formation of so2 ceased and only H,S was detected as the [10] Yoo JS,Bhattacharyya A, Radlowski C, et al. 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