Fe-modified HZSM-5 catalysts for ethanol conversion into light olefins

Availableonlineatwww.sciencedirect.comScienceDirectNATURAL GAS通 CHEMISTRYELSEVIERJournal of Natural Gas Chemistry 20(2011)423-427www.elsevier.com/locate/jngcFe-modified HZSM-5 catalysts for ethanol conversion into light olefinsJiangyin Lu", Yancong Liu, Na liKey Laboratory of oil and Gas Fine Chemicals of Ministry of Education, Xinjiang University, Urumqi 830046, Xinjiang, ChinaI Manuscript received December 28, 2010: revised March 14, 2011AbstractA series of Fe/HZSM-5 catalysts with different iron loadings were prepared by impregnation method. Characterization was performed by n2dsorption-desorption, X-ray diffraction(XRD), NH3 temperature-programmed desorption(NH3-TPD), temperature-programmed reduction(TPR), temperature-programmed oxidation(TPO)and thermogravimetry (TG)analysis. Iron content in the synthesized samples varied from1. 1 wt% to 20 wt%. The obtained samples have been used for ethanol conversion into light olefins. It was found that the amount of strong acidityat 300-550 C on Fe-modified samples was decreased, going with another new acid site appearance at 550-600C and that Fe/HZSM-5catalysts were highly selective towards light olefins, especially the 9FZ sample. In addition, Fe-modified catalysts suppressed the conversionof ethanol to aromatics and paraffins and enhanced their anti-carbon deposit ability.Key wordsbio-ethanol; light olefins; HZSM-5; Fe modification1. Introductionture and acidic amount, leading to a substantial increase inthe selectivities to liquid and gaseous hydrocarbons, preferLight olefins, particularly ethylene and propylene, have ably aromatics. In this paper, the properties of Fe-modifiedHZSM-5 catalyst were studied for ethanol conversion intobeen the basic petrochemicals and organic chemical raw ma- light olefins, and experimental evidence was provided in orderterials. With the steady and rapid development of Chinaseconomy, the long-term demand for resources is in the high to prove the increasing yields of light olefins and the inhibi-tion of coke formationgrowth. Because the per capita resource in China is below av-erage of the world, the work of looking for sustainable, eco-nomic, altermative resources to produce light olefins is attract-2. Experimentaling increasing attention. A novel route, using the renewablebiomass to produce bio-ethanol and subsequently being con- 2.l. Catalyst preparationverted into light olefins, exceeds the traditional preparationof light olefins depending on fossil oil. It is an alternativeHZSM-5 zeolite(molar ratio of SiO2/Al2 O3= 25, Nankaiapproach to conventional naphtha cracking, and hence has be- University, China) was dried for 4 h at 110C; then it wascome a hot research area [1-3impregnated with Fe(NO3)3 9H2O solution under stirring forAs an active catalyst, HZSM-5 zeolite has been exten- 12 h at room temperature. The contents of Fe were 0, 1.1sively investigated in a variety of reactions, such as alkylation wt%, 5.2 wt%, 9.2 wt%, 13.0 wt%, 17.0 wt% and 20.0 wt%[4,5], cracking [6,7], aromatic isomerization and MTO/MTP respectively. The dipping products were dried at 120C for[8-10]. Owing to its relatively high surface area and large 4 h and then calcined at 550C in air for 5h. Finally, theaperture, the obtained products were mainly light olefins, calcined products were compressed, crushed and sieved forparaffins and aromatics. Machado et al. [11-13] found that 40-60 mesh. This series of catalysts were marked as oZ, IFZ,Fe-modified HZSM-5 catalyst not only possessed the quality 5FZ, 9Fz, 13FZ, 17FZ and 20FZ according to the differentof decreasing its acid strength, but also had appropriate aper- contents of Fe correspondinglyCorresponding author. Tel: +86-991-8581012-808: E-mail: yinglu@xju educnThis was supported by the National Natural Science Foundation of China(No. 20963010) and the dgo.070267)中国煤化工Copy1, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. All rights reserved.doi: 10s1003-9953(1060193CNMHG424Jiangyin Lu et al/ Journal of Natural Gas Chemistry VoL. 20 No 4 20112.2. Catalyst characterizationcatalyst deactivation was related with its physical parametersto some extentSurface area and pore volume of the samples were measured by N2 adsorption-desorption (Micromeritics ASAPTable 1. Properties of Fe/HZSM-5 samples2010). The determination of crystallinity was carried outSample BET surface area(m /g) Micropore volume(cm g)by XRD(Mac Science M18XHF22-SRA, Cu Ka radiation,5FZ0.17100<20<60,2/min). Coke amount of catalyst was con9FZ2430.16ducted on TG measurement (Netzsch STA449C, o2 flow of200 mL/min, heating rate of 10C/min from 30-900C3FZ229.70.16It is well known that the acidity of the catalysts plays an20FZ206.6nportant role in the conversion of ethanol to light olefins.Used 9Fz catalystThe effect of iron incorporation on the acidity of zeolites wasevaluated by means of NH3-TPD(Autosorb-TP-5080, Xianquan). After pretreatment in a flow of He at 400C for I h,XRD patterns of the samples with different Fe contentsare presented in Figure 1. All samples exhibited typicaladsorption of NH3 at room temperature for 0.5 h and desorp- HZSM-5 zeolite structure, suggesting that the impregnationtion of physically adsorbed NH3 at 120C, TPd profiles wereobtained under He flow with the temperature varying from method with Fe modification did not damage the framework120°Cto900° C at a heating rate of 10°minof HZSM-5 zeolite. The intensity diffraction lines of Fe2 O3crystalline structure(26=3315°,35.65°,40.64°,49.04°andchen the reduction behaviors of Fe/HZSM-5 catalysts were 53.60%)were hardly detected at low Fe contents in Figure 1characterized by TPR(Autosorb-TP-5080, Xianquan). 50 mg It is probably due to the high dispersion of Fe203 with amor-sample was placed in the adsorption tube and preheatedflowing N2 at 200C for 0.5 h, then cooled down to room tem-phous state on zeolite surface. Nevertheless, with the increaseperature. After adsorption of H2 for 0.5 h, TPR profiles were of iron loadings, the intensity of these lines was enhanced,such as samples 17FZ and 20FZ It suggested that Fe2 O3 crys-obtained under the conditions of N2 flow with the temperature tals agglomerated on the carrier surface which was consistentvarying from3o°Cto900° at a heating rate of 10°minTemperature-programmed oxidation(TPO)was used towith the result in Table 1. Combined with the catalytic tests, itcan be found that Fe2 O3 agglomeration affectes the total acid-analyze the amount of carbon deposited on the catalyst sur- ity of catalysts. Therefore, it is disadvantageous to obtain theface. The TPO process was similar to TPR, expect that the light olefins by ethanol pyrolysiscarrier gas and the adsorbed gas were changed into He andO2/He mixture(5%O2)2.3. Catalytic activitye FeO,Catalytic tests were carried out in a fixed-bed microreactor(0.3 g catalyst) with an inner diameter of 6 mm by passinga gaseous ethanol(WHSV=3.16h-)in a n2 atmosphere(to-tal pressure of 1 atm). Previous activation in situ was done under nitrogen flow(48 mL/min) for I h at 500C. The ethanol人feeding was supplied by an infusion pump(Elite P2001l)at120C. The products were analyzed on line using a gas chro-matograph(SP-3420)equipped with a 50 m capillary columnof AT PEG-20M and flame ionization detector(FID)///// wwAn3. Results and discussion3.1. Characterization of catalystsFigure 1. XRD pattems of HZSM-5 and Fe/HZSM-5 catalystsTable 1 shows the N2 adsorption-desorption results of thesamples. It can be seen that BEt surface area and microp-Figure 2 presents NH3-TPD profiles of HZSM-5 andore volume decreased after Fe modification, which can be at- Fe/HZSM-5 catalysts in the 50-700C regions. The sam-tributed to the deposition of iron species on the catalyst sur- ples showed two peaks at 100-300 C and 300-600C,cor-face. Table 1 also lists the physical parameters of the used responding to the weak acid sites and the strong acid sitescatalyst. As shown in Table 1, the surface area and microop- 4) respectively. NV中国煤化工 rved in Figore volume had an obvious decrease. This may be due to the ure 2 that there w-d sites. corre-coke accumulation on the zeolite surface, indicating that the sponding to 300-53YHCNMHbectively. andJournal of Natural Gas Chemistry Vol. 20 No 4 2011425some authors proposed that the latter peak had some connection with the acidity of catalyst surface [15]. As showedFigure 2, with the continuous increase of Fe contents, the firstpeak transferred to lower temperatures while the second peak(300-550C)leaned to higher temperatures. For the strongacid site it contains Bronsted acid site and Lewis acid site:therefore, for the peak at 550-600C, this may be due tone formation of more Lewis acid site. Furthermore the to-I amount of acid reduced in different degree with increasing iron contents, which suggested that a certain amount of'e2O3 gradually agglomerated on zeolite surface and coveredthe active sites of catalyst. For the generation of propylene,when the amount of bronsted acid achieved a certain valuethe amount of Lewis acid may impact the selectivity to propy-lene; however, too much may cause the formation of carbonon the catalysts.Figure 3. NH3-TPD profiles of used samples with reaction for I h at 450C20FZOFZSFZOFZ9FZ13FZ10020FZFigure 2. NH3-TPD profiles of Fe/HZSM-5 catalysts200300700800In this article, the determination of the acidity overFigure 4. Desorption profiles of CO2 during TPO over Fe/HZSM-5 catalystsFe/HZSM-5 with I h reaction time is shown in Figure 3. Com-pared with the fresh catalyst, the amount of the acid sitesFor Fe/HZSM-5 catalysts prepared by impregnationof the used samples decreased with increasing iron loading, method, iron was dispersed on the zeolites with the main formespecially the strong acid sites. This may be attributed to of Fe2 O3, and the dispersity of Fe2 O3 may impact the activithe coke deposited on the zeolite surface and covered the ties of the catalysts In the TpR profiles presented in Figure 5strong acid sites. Therefore, the tpo profiles of the coke one can observe that all the samples revealed two reductionamount are presented in Figure 4. Large amount of CO2 peaks: the first peak at 240 C is related to the transformationwere released from the used catalysts during TPO, which of Fe2O3 into Fe304 [16, 17] and the second peak at 320Cindicated that carbon deposition was formed on the cata- is due to the reduction of Fe3 O4 to Fe0. Since the iron inlysts. The amount of CO2 decreased in the following or- the lattice was not reducible, the final reduced portion posder: 1FZ>OFZ>5FZ>9FZ>13FZ>20FZ. It can be obtained sessed only 30%[16]; and this portion of unreducible ironthat the amount of coke decreased was related to the decrease species may be related to the reactive activity. In additionof Bronsted acid site. For used catalysts, two peaks of CO2 with the increase of Fe content, the first peak shifted to lowwere observed at around 100-250C and 250-600C, cor- temperature, indicating that Fe+ ions had the trend of mi-responding to low temperature coke and high temperature gration, which might be attributed to the impregnated amountcoke, respectively. Obviously, the amount of high tempera- of Fe(NO3)3. 9H2O. However, the second reduction peak miture coke was larger than that of the low temperature coke, grated to high tempindicating that the high temperature coke was main over the Fe3 O4 into Feo beck中国煤化conversion ofcatalystsson may be that theHCNMHGsed and even426Jiangyin Lu et al./ Journal of Natural Gas Chemistry VoL. 20 No. 4 2011that iron species accumulated on the zeolite surface which de-Combined with the NH3-TPD results, the possible rea-creased the dispersity of Fe2 O3. Therefore, this may result in son for those changes is that with increasing iron contentsa decrease in the selectivity to light olefins with too much iron the acid amount of catalysts continuously decreased, whichsuppressed the hydrogen transformation, polymerization andolefins. With further increasing iron contents, iron sn."ghtaromatization, and it was beneficial to the formation of lightaccumulated on the surface of the catalysts and choked thechannels which reduced the effective catalyst surface area, re-sulting in the drop in selectivity. Different from the olefins selectivity, the aromatics selectivity decreased constantly withthe increase of iron loadings. It can be obtained that theolefins had the best selectivity with the iron loadings at92-130wt%The results of Figure 6 suggests that sample 9FZ hashigher selectivity to light olefins, so more investigation was13FZcarried out at different reaction temperatures Table 2 exhibitshe results of catalytic testIt can be seen that a very high ethanol conversion canbe obtained at the reaction temperature above 300C in Table 2. raisitemperature, the selectivity to ethylerl00decreased while the selectivities to propylene and paraffinsFigure 5. TPR profiles of Fe/HZSM-5 samples under different iron loadings83.2. Catalytic properties of Fe/HZSM-5 catalystsropyleneIron loading is a very important factor affecting the cataAromaticslyst activity, and appropriate iron loading can improve thetivity of catalysts. Figure 6 shows that the selectivity of lightolefins changed with different iron loadings. It can be seenthat the conversion of ethanol did not change significantly, al20most up to 100%. However, Fe-modified catalysts enhancedthe formation of C2+ olefins and suppressed the formation ofaromatic compounds. For example, in the case of 9.2 wt%iron content, the selectivities to ethylene and butylenes ob-⊥.1LL1tained their maxima of 24.7% and 14.8%, respectively;Fe content(wt%)propylene selectivity achieved its optimal value of 22.6%Figure 6. Influence of Fe content on HZSM-5 catalysts during ethanol consample 13FZversion at 450 C for 45 minTable 2. EfTect of different temperatures on ethanol conversion over Fe/HZSM-5 catalystsProduction selectivity(%)nv(%5)ethyleneparaffins(%)67.560.724.42230.599924.910.03127022.6954.37900952011791364167621Reaction conditions: calcination temperature =550C, Fe content=9.2 wt%, P=l atm, meat=0. g, t=45 min;by TG methodpresented the increasing trend and the selectivitiesand the ethylene over HZSM-5 catalyst is difficult to followbutylenes and aromatics attained their maxima of 10.0% and the conversion into propylene butylenes and Cs+ hydrocar31.2% at 500C, respectively. The following conclusions can bons. When the reced, ethylene isbe drawn: at low temperatures, ethanol dehydration into ethy. converted into paraf中国煤化工th polymerizalene is the main reaction on the active sites of the catalyst, tion, cracking, dehCNMHG transfer pro-Journal of Natural Gas Chemistry Vol 20 No 4 2011427cess; paraffins and C3+ olefins subsequently undergo dehy- [2] Le Van Mao R, Nguyen T M, McLaughlin G P Appl Cataldrogenation and aromatization to generate aromatics. When1989,48(2):265the reaction temperature is higher than 500C, hydrogen 3] Goldemberg J, Coelho S T, Guardabassi P Energy Policy, 2008,transfer, polymerization and aromatization reactions are in-36(6):2086hibited and C4+ olefins, paraffins and aromatic compounds (4 Vosmerikov A V, Korobitsyna L l, ArbuzovaN V Kinet Catal,further cracked into ethylene, methane, ethane and H2. In ad2002,43(2):275dition, in the TG measurement, the coke amount obtained its[5] Narayanan S, Sultana A. Appl Catal A, 1998, 167(1): 103minimum value at 500 C which further confirmed the men-[6] Lu J Y, Zhao Z, Xu C M, Zhang P, Duan A J Catal Commun,2006,7(4):199tioned conclusions[7] Lu J Y, Zhao Z, Xu C M, Duan A J, Zhang P Catal Lett, 2006.109(1-2):654. Conclusions[8] Gayubo A G. Aguayo A T, Castilla M, Olazar M, Bilbao J.Chem eng sci,2001,56(17):5059Characterization of Fe/HZSM-5 catalyst shows that [91 Moser W R, Thompson R W, Chiang C C, Tong H J Catal1989,117(1):19Fe-modification decreases the amount of strong acid at[10] Schulz J, Bandermann F Chem Eng Technol, 1994. 17(3): 179300-550C as well as inhibited the hydrogen transter, arom- [11] Machado N RC F, Calsavara V, Astrath N G C, Matsuda K,atization and coke formation, leading to a good performanceJunior A P, Baesso M L. Fuel, 2005, 84(16): 2064on the conversion of ethanol into light olefins, preferably [12] Machado NRCF, Calsavara V, Astrath N G C, Medina Neto A,propylene. The best result with the selectivities to ethylene,Baesso M L Appl Catal A, 2006, 311: 193propylene and butylene are 24.9%, 12.4% and 10.0%, respec- [13] Calsavara V, Baesso M l, Machado nrCF Fuel, 2008,87( 8-tively, at an ethanol conversion of 100%o is achieved usingsample 9FZ under the reaction temperature of 500C.[14] Tynjala P, Pakkanen TT. J Mol Catal A, 1996, 110(2): 153[15] Lenarda M, Da Ros M, Casagrande M, Storaro L, Ganzerla R.ReferencesInorg Chim Acta, 2003, 349: 195[16] Lobree L J, Hwang I C, Reimer J A, Bell A T J Catal, 1999186(2):242[1] Kochar N K, Merims R, Padia A S Chem Eng Prog, 1981, [17] Pieterse J A Z, Booneveld s, van den Brink R w. Appl Catal77(6)2004,51(4):215中国煤化工CNMHG