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ARTICLE IN PRESSHERD-614; No. of Pages 6
chemical engineering research and design x x x ( 2 0 1 0 ) xxx–xxx
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Chemical Engineering Research and Design
journa l homepage: www.e lsev ier .com/ locate /cherd
reparation of SAPO-34 catalyst and presentation of ainetic model for methanol to olefin process (MTO)
iloufar Fatourehchia, Morteza Sohrabia,b,∗, S. Javid Royaeea,c, S. Mahdi Mirarefina
Amirkabir University of Technology, Chemical Engineering Department, Tehran 15914, IranThe Academy of Sciences of Iran, Engineering Division, Tehran 19717, IranRefining Technology Development Division, Research Institute of Petroleum Industry, Tehran, Iran
a b s t r a c t
Conversion of methanol to light olefins (MTO) using acidic SAPO-34 molecular-sieve as the reaction catalyst was
studied in a differential fixed bed reactor within the temperature range of 375–425 ◦C and under 4 bar pressure.
The importance of MTO process is due to the increasing demand for light olefins in recent years. SAPO-34 was
synthesized by hydrothermal method, applying morpholine as the template. The latter compound was then changed
into protonated form by ion exchange method with ammonium chloride at 80 ◦C. A simple stoichiometric scheme
has been presented for MTO. In addition a mechanism for this process based on Langmuir–Hinshelwood formulation
has been put forward and the kinetic parameters have been evaluated as functions of temperature.
© 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Methanol to olefin (MTO); SAPO-34; Catalytic reaction; Kinetic model
ined for the MTO process. However, SAPO-34 was observed to
. Introduction
ethanol is a major chemical building block used to manufac-ure formaldehyde, MTBE, acetic acid and a wide range of otherhemical products. The reduction in MTBE demand, mainlyue to the decision taken by some of the states in the US andertain countries in the world to eliminate its use in the gaso-ine, is causing some of the producers in the world to explorelternate applications for their existing methanol plants. Oneuch utilization is the conversion of methanol to olefins (MTO)Al Wahabi, 2003).
Olefins can be produced using several processes and feedtocks. In every process a range of products and byproductsre formed. The percentage of the different output productsepend on the process and the feedstock used. Currently,here are three main industrial methods for olefins forma-ion, steam cracking of hydrocarbons (naphtha, ethane, gas oilnd LPG), fluid catalytic cracking in oil refineries and paraffinehydrogenation. In addition to these commercial processes,here are some non-commercial technologies under varioushases of development such as oxidative coupling of methane
Please cite this article in press as: Fatourehchi, N., et al., Preparation of SAolefin process (MTO). Chem Eng Res Des (2010), doi:10.1016/j.cherd.2010.10
OCM), oxidative dehydrogenation of paraffins and methanolo olefins (MTO) process (Al Wahabi, 2003).
∗ Corresponding author at: Department of Chemical Engineering, AmirkE-mail address: [email protected] (M. Sohrabi).Received 3 October 2009; Received in revised form 7 August 2010; Acc
263-8762/$ – see front matter © 2010 The Institution of Chemical Engioi:10.1016/j.cherd.2010.10.007
The production of light olefins from methanol was firstrealized around 1977, during the development of Mobil’smethanol to gasoline (MTG) process. In the MTG process,where ZSM-5 is used as a catalyst, methanol is first dehydratedto dimethylether (DME). The equilibrium mixture of methanol,DME and water is then converted to light olefins. A final reac-tion step leads to a mixture of higher olefins, n/iso-paraffins,aromatics and naphthenes (Al Wahabi, 2003).
Methanol to olefin (MTO) process provides a conventionalmethod for production of ethylene and propylene. This pro-cess has some advantages over the current steam cracking ofNGL, naphtha or other light fractions of petroleum, due to thefact that MTO can provide a wider and more flexible range ofethylene to propylene ratio relative to those of conventionalprocesses to meet market demand. In addition, methanol maybe produced from synthesis gas, that can be formed from anysource of carbon-containing materials such as coal, petroleumresidue, biomass and natural gas (Eng et al., 1998a,b; Vora etal., 1997).
A number of molecular sieve catalysts have been exam-
PO-34 catalyst and presentation of a kinetic model for methanol to.007
abir University of Technology, Tehran 15914, Iran.
epted 5 October 2010
be a more efficient catalyst in terms of activity and selectiv-ity for light olefins (Wilson and Barger, 1999). Several studies
neers. Published by Elsevier B.V. All rights reserved.
ARTICLE IN PRESSCHERD-614; No. of Pages 6
2 chemical engineering research and d
Nomenclature
E activation energy (J)F0 molar rate of feed (mol/h)kr kinetic parameter of dimethylether production
(mol/g h)ke kinetic parameter of ethylene production
(mol/g h)kp kinetic parameter of propylene production
(mol/g h)kparaffin kinetic parameter of paraffin production
(mol/g h barn)k0 Arrhenius constantKd equilibrium constant of dimethylether produc-
tionKm equilibrium constant of methanol productionPw partial pressure of water (bar)Pmethanol partial pressure of methanol (bar)n order of reactionrdimethylether rate of dimethylether production (mol/g h)rEthylnene rate of ethylene production (mol/g h)rPropylene rate of propylener production (mol/g h)rParaffin rate of paraffin production (mol/g h)U0 inlet gas velocity (m/s)Umf minimum fluidizing velocity (m/s)W weight of catalyst (g)
caton MTO process using chabazite and ZSM-5 have been alsoconducted. Single event kinetics was used to build a kineticmodel for MTO on ZSM-5. Since SAPO-34 seems to be a desir-able catalyst for MTO, and this process has a great potential forcommercialization, detailed research on the products changewith the reaction conditions applying SAPO-34 catalyst wouldbe important and beneficial (Wu et al., 2004).
In the present study, SAPO-34 has been synthesized andthe activity of the latter has been measured applying a differ-ential fixed bed reactor. In addition, a kinetic model has beenproposed and the kinetic parameters have been evaluated.
2. Methods and materials
2.1. Materials
The materials applied in this study were all analytical grades.
2.2. Catalyst preparation
The catalyst was prepared according to the hydrothermalmethod outlined by Song (Song, 2001; Lok et al., 1984) andPrakash and Unnikrishnan (1994) using aluminum isopropox-ide, phosphoric acid, fumed silica and morpholine. The firststep was hydrolysis of isopropoxide. Specified amount ofaluminum isopropoxide [98% Al(O-i-C3H7)3, Alfa Aesar (Karl-sruhe, Germany)] was mixed with distilled water. The mixturewas heated to 80 ◦C to accelerate the hydrolysis. The hydrol-ysis was completed in 2 h with vigorous stirring, resulting ina homogeneous white gel. Isopropyl alcohol, the product ofthe hydrolysis, was left in the gel without further treatment.The second step was to mix phosphoric acid [85% H3PO4, Alfa
Please cite this article in press as: Fatourehchi, N., et al., Preparation of Solefin process (MTO). Chem Eng Res Des (2010), doi:10.1016/j.cherd.2010.10
Aesar (Karlsruhe, Germany)] with the white gel. Phosphoricacid was added drop wise to aluminum gel within 5 min withstirring. The resulting white homogenous gel comprised part
esign x x x ( 2 0 1 0 ) xxx–xxx
(A) of the final mixture. The second step was to prepare part(B) of the final mixture. Morpholine [99% C4H9O, Merck (Darm-stadt, Germany)] was mixed with specified amount of fumedsilica [95% SiO2, Alfa Aesar (Karlsruhe, Germany)]. The mix-ture was stirred until a homogenous solution was formed.Part B was then added to part A with stirring. The final mix-ture was further stirred for 2 h, resulting in a semi-transparenthomogenous white gel. The final gel mixture having the pH 8was transferred into a high-pressure stainless steel autoclave.The autoclave was sealed and maintained at 200 ◦C for 48 hwithout stirring. The pressure inside the autoclave was equalto the autogeneous pressure of water at 200 ◦C. The autoclavewas slowly cooled down after 48 h. As-synthesized SAPO-34was recovered from the autoclave; washed three times with200 ml distilled water; dried at 120 ◦C for 24 h and calcined at600 ◦C for 10 h. The product was then transformed into pro-tonated form by ion exchange process with 2-M ammoniumchloride solution at 80 ◦C. The synthesized catalyst dried at120 ◦C for 24 h and calcined at 500 ◦C for 10 h.
2.3. Packed bed reactor
A differential fixed bed reactor was applied to investigate thekinetic of the reaction and to present a suitable rate model. Thereactor consisted of a 70 cm high cylindrical tube with 1.6 cminternal diameter. The depth of the catalyst bed in the reactorwas 1.5 cm. The heat transfer to the reactor was provided byan electric jacket wrapped around the reactor. Reaction tem-perature was controlled by a PID controller and measured bya thermocouple (PT100) housed in a thermo well located atthe center of the catalyst bed. The reactor’s pressure was reg-ulated by a backpressure system. A schematic diagram of theexperimental set-up is shown in Fig. 1.
2.4. Feed
To increase the olefin’s selectivity and reduce the rate of cata-lyst’s deactivation, the feed was enriched with water vapor.Thus, a feed consisted of 50 mol% methanol and 50 mol%water was applied. Flow of liquid feed was controlled by adosing pump (Milton Roy model H94X (Ivyland, USA)).
2.5. Analytical procedure
In all experimental runs, when steady state conditions wereestablished (usually after about 10 mean residence times) aportion of the gas mixture leaving the reactor was conductedto a GC apparatus connected on line to the reactor’s exit port.Such a procedure was repeated at regular time intervals of7 min.
The GC analyzer (Agilent model 6890, (CA, USA)) wasequipped with a 30 m capillary column made of silica withpolyamide coating, 0.53 mm internal diameter. Helium wasused as the carrier gas and thermal conductivity detector wasapplied. The column temperature was increased linearly from60 to 150 ◦C with a rate of 30 ◦C/min.
3. Results and discussion
3.1. Catalyst synthesis
APO-34 catalyst and presentation of a kinetic model for methanol to.007
H-SAPO34 was synthesized according to Section 2.2 of thepresent paper. SEM image and XRD pattern of the catalyst aregiven in Figs. 2 and 3.
ARTICLE IN PRESSCHERD-614; No. of Pages 6
chemical engineering research and design x x x ( 2 0 1 0 ) xxx–xxx 3
Fig. 1 – Experime
1w5
3
Ipa
s) M
l
m
(
(
Ethylene production:
Fig. 2 – SEM image of catalyst.
Prior to application, the catalyst was regenerated by00 ml/min nitrogen gas in 500 ◦C for 2 h. Flow of nitrogenas controlled by a mass flow controller (MFC) (Brooks model
850E, USA).
.2. Kinetic study
n developing a mechanism for light olefins formation, a sim-le stoichiometric relation was first presented for this processs follows:
Ethylene
Dimethylether Higher olefins
(minute amount
Propylene
ethanol
Paraffin It was further assumed that the reaction mechanism fol-
ows the Langmuir–Hinshelwood formulation.The Langmuir–Hinshelwood–Hougen–Watson (LHHW)
echanism is based upon the following assumptions:
Please cite this article in press as: Fatourehchi, N., et al., Preparation of SAolefin process (MTO). Chem Eng Res Des (2010), doi:10.1016/j.cherd.2010.10
a) Reactants’ molecules adsorb onto the surface of the cata-lyst.
ntal set-up.
b) The adsorbed molecules diffuse across the surface andinteract when they are close.
(c) A product molecule is formed and desorbs into the fluidphase.
A schematic diagram of this mechanism is shown in Fig. 4.According to such a mechanism, methanol molecules
adsorbed at the active site of the catalyst and diffused acrossthe surface, leading to formation of CH3OH·S. IntermediateCH3OH·S was then interacted with another CH3OH·S speciesforming DME·S. Three different paths could be assumed fordecomposition of DME·S, i.e., DME·S could leave the activesite and forms dimethyl ether, or may either convert to ethy-lene or reacts with another CH3OH·S intermediate to producepropylene. Thus, the mechanism may be presented as follows:
CH3OH + Skm�k′
m
CH3OH · S (1)
2CH3OH · Skd�k′
d
CH3OCH3 · S + H2O + S (2)
Dimethylether production:
CH3OCH3 · Skr−→CH3OCH3 + S (3)
PO-34 catalyst and presentation of a kinetic model for methanol to.007
CH3OCH3 · Ske−→C2H4 + H2O + S (4)
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Fig. 3 – XRD pattern of catalyst.
inshe
Fig. 4 – Langmuir–HPropylene production:
CH3OCH3 · S + CH3OH · Skp−→C3H6 + 2H2O + 2S (5)
Please cite this article in press as: Fatourehchi, N., et al., Preparation of Solefin process (MTO). Chem Eng Res Des (2010), doi:10.1016/j.cherd.2010.10
The following kinetic model was derived by taking relations(3)–(5) as the rate determining steps. These reactions wereselected after a number of unsuccessful attempts made by
Table 1 – Kinetic data at different operating conditions.
Temperature(◦C)
Wcat/F0(g h/mol)
PMethanol(bar)
PDimethylether(bar)
PEthan(bar)
375 2.531646 1.91095 0.009938 0.00143.375527 1.88575 0.011174 0.00225.063291 1.83887 0.012642 0.00566.751055 1.79102 0.014052 0.00908.438819 1.74814 0.015019 0.013610.12658 1.70306 0.015050 0.0172
400 2.531646 1.90852 0.009852 0.00323.375527 1.87855 0.011069 0.00645.063291 1.82771 0.012472 0.01016.751055 1.77315 0.013819 0.01328.438819 1.72727 0.014745 0.019110.12658 1.67528 0.014605 0.0248
425 2.531646 1.90059 0.009395 0.00803.375527 1.87089 0.009999 0.00865.063291 1.81211 0.011364 0.01466.751055 1.75732 0.012641 0.02038.438819 1.70816 0.014010 0.026910.12658 1.65798 0.014448 0.0316
lwood mechanism.
assuming a combination of different steps as the rate limitingrelations. The kinetic models deduced from such assumptionsall provided poor correlations with the experimental data andwere thus discarded.
APO-34 catalyst and presentation of a kinetic model for methanol to.007
rdimethylether = krKdK2mP2
methanol
Pw(1 + KmPmethanol + (KdK2mP2
methanol/Pw))(6)
e PEthylene(bar)
PPropane(bar)
PPropylene(bar)
PWater(bar)
73 0.011372 0.005877 0.013905 2.04752116 0.015331 0.007749 0.019608 2.05907173 0.022119 0.013345 0.028786 2.07940837 0.031566 0.014945 0.036641 2.10340238 0.035049 0.023098 0.046048 2.11960990 0.041218 0.028234 0.055113 2.14077165 0.011381 0.010256 0.011728 2.04376317 0.017741 0.011569 0.017714 2.05763951 0.025876 0.019882 0.026435 2.07802482 0.037101 0.026015 0.033846 2.10378869 0.041422 0.035386 0.041932 2.12097054 0.048290 0.039526 0.052414 2.14587054 0.016278 0.012082 0.009585 2.04452054 0.021151 0.018325 0.014876 2.05720721 0.029680 0.027385 0.024176 2.08081739 0.042622 0.036035 0.030171 2.10216990 0.048921 0.038950 0.039896 2.12377075 0.055216 0.053347 0.046946 2.140423
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Table 2 – Rate of consumption or production of reactants and products.
Temperature (◦C) �′
(bar g h/mol) −rMethanol (mol/g h) rDimethylether (mol/g h) rParaffin (mol/g h) rEthylene (mol/g h) rPropylene (mol/g h)
375 6 0.01448 0.00410 0.00190 0.002532 0.0030327.5 0.01431 0.00400 0.00205 0.002531 0.00307510 0.01400 0.00403 0.00230 0.002500 0.00309012.5 0.01370 0.00402 0.00255 0.002431 0.00317315 0.01350 0.00390 0.00280 0.002325 0.00320017.5 0.01310 0.00388 0.00305 0.002181 0.003175
400 6 0.01590 0.00400 0.00282 0.002460 0.0026207.5 0.01495 0.00410 0.00300 0.002520 0.00265010 0.01420 0.00402 0.00330 0.002500 0.00270012.5 0.01410 0.00406 0.00361 0.002301 0.00276315 0.01440 0.00395 0.00390 0.002002 0.00280117.5 0.01455 0.00382 0.00411 0.002101 0.002785
425 6 0.01531 0.00405 0.00402 0.003084 0.0019887.5 0.01501 0.00401 0.00405 0.003113 0.00198410 0.01430 0.00403 0.00410 0.003101 0.00198112.5 0.013780 0.00397 0.00415 0.003001 0.00197315 0.01350 0.00386 0.00420 0.002851 0.00196817.5 0.01310 0.00371 0.00424 0.002810 0.001965
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Table 3 – Kinetic parameters at different temperatures.
Temp. (◦C) Parameter
Km Kd kr (mol/g h) ke (mol/g h) kp (mol/g h) kParaffin (mol/g h barn) n
375 2.22 4.683 0.00045 0.0028 0.0366 0.009268 0.342400 1.187 3.757 0.00058 0.0035 0.0184 0.010023 0.31425 0.898 2.601 0.00071 0.005
Table 4 – Values of k0 and E for dimethyl ether andethylene.
Material k0 E (J)
Dimethylether 0.266335 34295.25
Wu, X., Abraha, M.G., Anthony, R.G., 2004. Methanol conversionon SAPO-34: reaction condition for fixed-bed reactor. Appl.Catal. A: Gen. 260, 63–69.
Ethylene 31.785175 50557.43
rEthylene = keK2mP2
methanol
Pw(1 + KmPmethanol + (KdK2mP2
methanol/Pw))(7)
rPropylene = kpKdK3mP3
methanol
Pw(1 + KmPmethanol + (KdK2mP2
methanol/Pw))2
(8)
To simplify calculations, the rate of paraffin production wasconsidered as a power law relation:
rParaffin = kParaffinPnParaffin (9)
As it was mentioned in Section 2.3, a differential packed bedreactor (with 1.5 cm depth of catalyst bed) was used to inves-tigate the kinetic of the reaction. Synthesis of methanol wascarried out at 4 bar pressure and 375, 400 and 425 ◦C. The feedwas consisted of 50 mol% methanol and 50 mol% water. As thecatalyst depth did not exceed 1.5 cm, the temperature couldbe effectively controlled and formation of hot spots or frontswas avoided. Results obtained from the kinetic studies arepresented in Table 1.
The rates of formation or consumption of the materialswere determined from the slopes of tangents drawn at vari-ous points on the plots of components concentrations againsttime. Rate data are presented in Table 2.
Values for kinetic parameters at various temperatures arepresented in Table 3.
It may be observed from this table that the rate coefficientfor propylene is declined with increase in temperature. This isprobably due to further conversion of propylene to certain by-products, the rates of which are more temperature sensitivethan that of propylene formation
Please cite this article in press as: Fatourehchi, N., et al., Preparation of Solefin process (MTO). Chem Eng Res Des (2010), doi:10.1016/j.cherd.2010.10
The temperature dependency of the kinetic parameters (kr,ke, kp) was determined assuming the Arrhenius type relation.These values are presented in Table 4.
4 0.013 0.004808 0.048
4. Conclusion
It was found that the two step hydrothermal synthesis ofH-SAPO34 is a convenient method by which such a com-pound may be formed. SAPO-34 was then protonated byion-exchange process into an active catalyst by which trans-formation of methanol to light olefins was achieved. Anappropriate kinetic model was presented and the kineticparameters were evaluated as functions of temperature usinga differential fixed bed reactor.
References
Al Wahabi, S.M., 2003. Conversion of methanol to light olefins onSAPO-34 kinetic modeling and reactor design. Ph.D. Thesis. A& M University, Texas.
Eng, C.N., Arnold, E.C., Vora, B.V., 1998a. Integration of theUOP/HYDRO MTO process into ethylene plants. In: Presentedat the AIChE Spring National Meeting, Session 16,Fundamental Topics in Ethylene Production, Paper 16g, NewOrleans, Louisiana.
Eng, C.N., Arnold, E.C., Vora, B.V., Fuglerud, T., Kvisle, S., Nilsen,H., 1998b. Natural gas utilization and UOP/HYDRO MTOprocess. In: Presented at the AIChE Spring National Meeting,Session 45, Production of Liquid Fuels from Natural Gas, Paper45a, New Orleans, Louisiana.
Lok, B.M., Messina, C.A., Patton, R.L., Gajek, R.T., Cannan, T.R.,Flanigen, E.M., 1984. U.S. Patent 4,440,871.
Prakash, A.M., Unnikrishnan, S., 1994. Synthesis of SAPO-34: highsilicon incorporation in the presence of morpholine astemplate. J. Chem. Soc. Faraday Trans. 90 (15), 2291–2296.
Song, W., 2001. Fundamental studies of methanol to olefin (MTO)catalysis. Ph.D. Thesis. University of Southern California.
Vora, B.V., Marker, T.L., Barger, P.T., Fullerton, H.E., Nilson, H.P.,Kvisle, S., Fuglerud, T., 1997. Stud. Surf. Sci. Catal. 107,87–93.
Wilson, S., Barger, P., 1999. The characteristics of SAPO-34 whichinfluence the conversion of methanol to light olefins.Micropor. Mesopor. Mater. 29, 117–126.
APO-34 catalyst and presentation of a kinetic model for methanol to.007
