Marin, Guy

Navidi, Nima

Thybaut, Joris

English

Ghent University Academic Bibliography

Experimental investigation of ethylene hydroformylation to propanol on Rh and Co based catalystsN. Navidi, 1J. W. Thybaut, G. B. MarinLaboratory for Chemical Technology,  Ghent University,  Krijgslaan 281 – S5, 9000 Ghent Belgium;  tel.  +3292645572,  e-mail:  Nima.Navidi@UGent.be;  1tel.  +3292644519,  e-mail: Joris.Thybaut@UGent.be; tel. +3292645517, e-mail: Guy.Marin@UGent.be.AbstractHydroformylation,  or oxo synthesis,  is an important  process for the production of aldehydes from alkenes.  Alkene  and  aldehyde  hydrogenation  are  undesired  parallel  and  consecutive  reactions. Whereas present-day industrial process configurations typically operate in a homogenous mode, the development  of  a  heterogeneous  hydroformylation  catalyst  is  aimed  at  to  avoid  the  well-known drawbacks  of  homogenous  catalysis  such  as  catalyst  recuperation  and  corrosiveness.  Kinetic measurements have been performed in a high-throughput kinetic test set up. Temperatures varied from 448 to 498 K, with the total pressure ranging from 1 to 3 MPa. A gaseous feed containing CO, C 2H4 and H2 was used with space times varying from 5.4 kgcat.s/molC2H4,in to 149 kgcat.s/molC2H4,in. Three catalysts  have  been  investigated,  i.e.,  5%Rh/Al2O3,  1%Co/Al2O3  and  0.5%Co-0.5%Rh/Al2O3.  The main  products observed were ethane,  propanal  and propanol.  The Rh catalyst  showed the highest  hydroformylation  and  hydrogenation  site  time  conversions  in  the  investigated  range  of  operating conditions. Moreover it was found that on all investigated catalysts, a temperature increase has a more  pronounced effect on hydrogenation than on hydroformylation.Keywords: Heterogeneous catalysts;  Ethylene hydroformylation;  Fischer-Tropsch; High-throughput experiments; Rhodum/Cobalt catalysts1. IntroductionThe ever increasing crude oil  price has led to the exploration of alternative feeds such as natural  gas, and  correspondingly  new  processes  for  the  production  of  hydrocarbons. Hydroformylation, or oxo synthesis, that was discovered by the German scientist Otto Roelen in 1938, is an important process for production of aldehydes from alkenes. Hydroformylation catalysts are also active in double bound hydrogenation converting the reactant alkene into the corresponding  alkane  as  well  as  the  product  aldehydes  into  alcohols  [1].  Typical hydroformylation products are in the carbon number range from 3 to 19. The reactant alkene is selected based on the desired product aldehyde.Aldehydes are useful intermediates in the production of valuable products such as alcohols, carboxylic acids, amines, diols, etc. Recently, hydroformylation is also widely applied in fine chemicals in the production of drugs, vitamins, herbicides and perfumes [2, 3].The name ‘hydroformylation’ becomes clear when looking at the nature of the products that are formed. The reaction entails the addition of a formyl group (CHO) and a hydrogen atom to a carbon – carbon double bond. Depending on the catalyst used, the aldehyde can be further hydrogenated to the corresponding alcohol. The hydroformylation of ethylene that is shown in Figure 1, in particular is a spontaneous, exothermic reaction (ΔHº = -129.0 kJ mol -1, ΔGº = -56.9 kJ mol-1) [4]. Due to high energy barriers, the reaction rate remains low, however.CH2 CH2+ CO + H2 C2H5CHOFigure 1- Ethylene hydroformylation to prapanalIn principle, all the transition metals capable of forming carbonyls, such as Rh, Co, Ir, Ru,.. are potential hydroformylation catalysts. The order of activity from the most to the least active metal, is as follows: Rh > Co > Ir, Ru > Os > Pt > Pd > Fe > Ni [5]. Commercially,  homogeneous  Co  or  Rh  complexes  are  typically  applied  at  temperatures ranging from as low as 360 K up to 573 K [6,7].  The homogeneous character of industrial process configurations leads to inherent operational problems such as difficulties in catalyst separation from products, expensive metal losses and corrosivity of catalytic solutions. The successful implementation of an active and stable heterogeneous hydroformylation catalyst would allow avoiding these drawbacks. Although the research into heterogeneously catalysed hydroformylation is in an early stage, a wide range of research activities has been performed on  experimental  heterogeneous  hydroformylation  with  various  reactants,  catalysts  and operation conditions [8-17].The present work concentrates on heterogeneous ethylene hydroformylation on a series of Rh and  Co  based  catalysts.  Gas  phase  experimentation  was  performed  in  a  high-throughput kinetics setup to compare the Rh and Co catalysts and to investigate the effect of the operation conditions on the main and by product formation rates on these catalysts. The results of this study provide key insight into the corresponding reaction mechanism that may be exploited in further catalyst design.2. ProceduresGas phase hydroformylation measurements have been performed in a high-throughput kinetic test set up. The setup consisted of eight reactors in parallel and each individual reactor had three  feed  lines  for  gases  and  one  feed  line  for  a  liquid  with  corresponding  mass  flow controllers. The reactor temperature and pressure were controlled per reactor pair. A reactor tube  was  made  of  AISI  316  cold  worked  steel  with  890mm  height  and  11mm  internal diameter. The reactors are capable of operating up to 600˚C and 15 MPa, i.e., far beyond the operating range  as  required  for  hydroformylation.  A  three-zone  reactor  temperature  control  was established, the catalyst being situated at the bottom of the second zone and the top of third zone. Between 1 and 10 g of 5%Rh/Al2O3, 1%Co/Al2O3 and 0.5%Rh-0.5%Co/Al2O3 was pelletized. The  fraction  with  a  diameter  between  0.3  and  0.5mm  was  retained  and  mixed  with  an identical  mass  of  dilution  material  prior  to  loading  into  the  reactor  tubes  of  the  high-throughput set up. Considering the investigated operating conditions in the literature and some preliminary experiments that were conducted in the lab, the following operating conditions were selected. Temperatures varied from 448 to 498 K, with the total pressure ranging from 1 to 3 MPa. A gaseous feed containing CO, C2H4 and H2 was used with space times that varied from 5.4 kgcat.s/molC2H4,in to 149 kgcat.s/molC2H4,in.Online  effluent  analysis  was  performed  with  a  four  channel  Agilent  3000  micro  gas chromatograph equipped with thermal conductivity detectors (TCDs). Argon as an internal standard has been added to the reactants stream in order to verify the mass balances. The conversions and product molar flow rates were calculated using calibration factors as reported by Diets [18]. In order to compare the performance of the mentioned catalysts under identical experimental  conditions  the  conversions  were  reported  versus  the  site  time.  At  first,  for calculating the site time, space time (kgcat..s./moli) was divided by standard atomic weight of metal catalyst to be converted to (molcat.  atoms.s./moli) thereafter, this value was multiplied by the fraction of exposed metal atoms to calculate the numbers of accessible moles. The fraction exposed was calculated employing the relation between the particle size and dispersion [19]. In order to estimate the particle sizes, Transmission Electron Microscopy (TEM) method was used. TEM  specimens  were  prepared  by  applying  simple  immersion  of  a  carbon-supportfilm  on  a  nickel  grid  into  the  catalyst  powder  followed  by  careful  shakingoff  the  excess  powder.  A  microscope  JEOL  JEM2200FS-Cs-corrected,  operatedat  200  kV  and  equipped  with  Schottky-type  FEG,  EDX  JEOL  JED-2300D  and  JEOLin-column omega filter, was used.It was verified by using the proper correlations, that at the selected operating conditions so-called intrinsic kinetics are measured, i.e., the observations are not affected by mass or heat transfer limitations [20].3. Results and discussion3.1 catalyst comparisonThe measured particle sizes and corresponding fractions exposed of the mentioned catalysts are reported in Table 1.Table 1- Fraction of exposed metal, accessible metal atoms and site time conversions per catalystCatalystParticle size (nm)TEMFraction of exposed metal (%)Accessible metal atoms (mol/gcat.)CO site time conversion(molCO, converted /molcat. atoms /s)*C2H4 site time conversion(molC2H4,converted /molcat. atoms /s)*5%Rh/Al2O3 2 51.11 2.4757×10-4 0.01356 0.040711%Co/Al2O3 11 12.38 0.2098×10-4 0.00359 0.014860.5%Rh-0.5%Co/Al2O3 4.3 for Co 35 for Rh 28.10 for Co 3.81 for Rh0.2575×10-4 0.00746 0.02626* at 473 K, 2.0 MPa and equimolar C2H4/CO/H2 gas phase compositionBased on the TEM results, the 5%Rh catalyst as it is depicted in Figure 2 has well dispersed particles with a small size (2nm) resulting a high fraction of exposed metal. On the contrary, in the 1%Rh-Co catalyst rhodium was observed in big particles or clusters (20-50nm).Figure 2- TEM image of 5%Rh/Al2O3 catalystFigures 3 and 4 show the observed CO and C2H4  conversion as a function of the site time at 473 K and 2 MPa. An equimolar feed composition containing CO, C2H4 and H2 was used with space times that were varied 5.4 kgcat.s/molC2H4,in to 149 kgcat.s/molC2H4,in Figure  3-  CO  conversion  versus  molar  site  time.  Temperature  473K;  Pressure (C2H4:CO:H2:Ar=30:30:30:10), 2 MPaFigure  4-  C2H4 conversion  versus  molar  site  time.  Temperature  473K;  Pressure (C2H4:CO:H2:Ar=30:30:30:10), 2 MPaThe accessible number of metal atoms and site time conversions are also reported in Table 1. As it can be seen in these figures and the table, the Rh catalyst shows the highest site time conversions at the investigated operating conditions. Based on the site time conversions obtained in monometallic catalysts and the knowledge of the fractions exposed on the bimetallic catalyst, see Table 1, an expected site time conversion on this bimetallic catalyst  amounting to 0.00429 molCO, converted  /molcat.  atoms  /s was calculated, which is lower than the experimentally observed site time conversion. Considering the size of Rh  clusters  in  Rh-Co  catalyst,  this  metal  cannot  show  considerable  activity  in  the hydroformylation reaction, so the reason that bimetallic catalyst shows slightly higher activity than pure cobalt catalyst can be explained by the fine Co particles in the Rh-Co catalyst that enhances the activity of this catalyst. It has been already reported in the literature [8, 14] that small metal particles exhibit higher hydroformylation activity than large metal clusters.3.2 Temperature effect In order to investigate the temperature effect on hydroformylation, a series of experiments were carried out on two of the mentioned catalysts, i.e., 5%Rh/Al2O3 and 1%Co/Al2O3. A temperature increase leads to a more pronounced increase of the C2H4 site time conversion than of the CO site time conversion on both tested catalysts. As a result, as it is depicted in Figure  5,  the  apparent  activation  energy  for  ethane  formation  exceeds  that  for  propanal formation. The above observations correspond with an increasing selectivity towards ethane with the temperature, which is confirmed by the literature [9, 12]. It was observed by Balakos et. al.,  that  in  heterogeneous  ethylene  hydroformylation  on  4%Rh/SiO2 with  increasing  the temperature  from  483  K  to  573  K  the  hydroformylation  selectivity,  defined  as TOFpropanal/TOFC2H6, decreased from 0.136 to 0.039 [9].Figure 5- Relation between space-time yield and temperature for hydrogenation site time conversion on Rh(♦)  and Co (▲) and hydroformylation site time conversion on Rh(■) and Co (×)The more pronounced temperature effect on hydrogenation than on hydroformlation can be explained by investigating the selected heterogeneous ethylene hydroformylation mechanism that is shown in Figure 6 in some more detail.The depicted mechanism is constituted by the following elementary steps:1- Ethylene molecular chemisorption : C2H4 + 2M ↔ MMC2H42- Hydrogen dissociative chemisorption : H2 + 2M ↔ 2 MH3- Partial ethylene hydrogenation : MM C2H4 + MH ↔ MC2H5 + 2M4- Reductive elimination towards paraffin: MC2H5 + MH ↔ C2H6+ 2M5- CO molecular chemisorption : CO + 2M ↔ MMCO6- CO insertion: MC2H5 + MMCO ↔ MC2H5CO7- Hydrogen addition to metal bound carbonyl: MC2H5CO + MH  ↔ MMC2H5CHO8- Desorption of aldehyde: MMC2H5CHO ↔ C2H5CHO + 2MWith increasing temperature,  adsorbed C2H4 molecules apparently exhibit a higher affinity towards reductive elimination into ethane (step 4 in Figure 6) than reacting with adsorbed CO molecule (step 6) on the catalyst surface. This can be related to the expected evolution in the hydrogen and CO surface concentrations. Because the chemisorption heat of CO is typically about the double of that of hydrogen, the CO concentration will decrease much faster with increasing temperature than the hydrogen concentration. As a result, the relative importance of  hydrogenation  in  the  overall  ethylene  conversion  will  increase  at  the  expense  of hydroformylation.Figure 6: Proposed reaction mechanism for ethylene hydroformylation to propanol [21]4. ConclusionGas  phase  hydroformylation  measurements  have  been  performed  on  5%Rh/Al2O3, 1%Co/Al2O3  and  0.5%Co-0.5%Rh/Al2O3  catalysts  in  a  high-throughput  set  up.  The  main products observed were ethane, propanal and propanol. The Rh catalyst showed the highest hydroformylation  and hydrogenation  rates  compared  to  other  catalysts  at  the  investigated operation  conditions.  Bimetallic  catalyst  shows  slightly  higher  activity  than  pure  cobalt catalyst since the fine Co particles in the Rh-Co catalyst enhances the activity of this catalyst. On all investigated catalysts, increasing the temperature has a more pronounced effect on the hydrogenation rate than on the hydroformylation rate. The overall activation energy for ethane formation  exceeds  that  for  propanal  formation  which  can  be  related  to  a  higher  heat  of chemisorption for CO than for hydrogen. In addition, metal particle size effects also play a significant  role  in  the  selectivity  between  hydrogenation  and  hydroformylation.  Whereas small metal particles exhibit high hydroformylation activity, large metal clusters rather favour hydrogenation reactions.AcknowledgementsThis work was supported by the European research project “TOPCOMBI” (contract NMP2-CT2005-515792) and Methusalem program. References[1] Cornils B., H.W.A., Rasch M., Otto Roelen, pioneer in industrial homogeneous catalysis. Angewandte Chemie International Edition, 1994. 33(21): p. 2144 - 2163.[2] Van Leeuwen P.W.N.M., C.C., Rhodium catalyzed hydroformylation. 2002, N.Y Springer.[3]  Breit,  B.  and  Seiche,  W.,  Recent  advances  on  chemo-,  regio-,  and  stereoselective hydroformylation, Synthesis, 2001, 1–36[4]  Otsuka K., Ando T., Yamanaka I.,  Hydroformylation of Ethylene via Spontaneous Cell  Reactions in the Gas Phase, Journal of catalysis 165, 221-230, 1997.[5]  Cornils B., H.W.A.,  Applied Homogeneous Catalysis with Organometallic Compounds. 1996, Weinheim: VCH[6]  Zeelie.  H.,  Root.  A.,  Krause.  A.O.I.,  Rh/fibre  catalyst  for  ethane  hydroformylation: Catalytic activity and characterization, Applied Catalysis A: General 285, 2005, 96-109[7] Ullmann's Encyclopedia of Industrial Chemistry. 6 ed. 2002: John Wiley & Sons.[8]  Zeelie,  T.,   Rhodium  and  cobalt  catalysts  in  the  heterogeneous  hydroformylation  of  ethane, propene and 1-hexene. 2007[9]  Balakos,  M.W.  and  S.S.C.  Chuang,  Dynamic  and  LHWW  Kinetic-Analysis  of  Heterogeneous Catalytic Hydroformylation. Journal of Catalysis, 1994. 151(2): p. 266-278.[10]  Haza, U. J., Diaz-Abin. O., Wilhelm, A. M., Delmas, H.,  Supported Aqueous phase  catalysis in the pores of silica support: kinetics of the Hydroformylation of 1-Octene, Ind. Eng. Chem. Res. 2005, 44, 9636-9641[11] Tomishige. K., Furikado. I., Yamagishi. T., Ito. S., Kunimori. K., Promoting effect of Mo on  alcoholformation  in  hydroformylation  of  propylene  and  ethylene  on  Mo-Rh/SiO2., Catalysis Letters Vol. 103, Nos. 1-2, 2005[12] Brundage. M. A., Balakos. M. W., Chaung. S.S.C., LHHV and PSSA kinetic analysis of  rates and adsorbate coverages in CO/H2/C2H4 reactions on Mn-Rh/SiO2, 1998., Journal of catalysis 173, 122-133[13]  Zapirtan.  V.  I.,  Mojet.  B.  L.,  Ommen.  J.G.V.,  Spitzer.  J.,  Lefferts.  L.,  Gas  phase hydroformylation of ethylene using organometalic Rh-complexes as heterogeneous catalysts, Catalysis Letters. Vol. 101. Nos. 1-2, 2005[14]  Hanaoka.  T.,  Arakawa.  H.,  Matsuzaki.  T.,  Sugi.  Y.,  Kanno.  K.,  Abe.  Y.,  Ethylene  hydroformylation and carbon monoxide hydrogenation over modified and unmodified silica  supported rhodium catalysts, Catalysis Today. Vol. 58, Issue 4, 2000. p: 271-280[15]  Xiao.  F.S.,  Ichikawa.  M.,  Catalytic  Performance  and  Mechanism  for  oxygenated  compound formation for ethylene hydrformylation over supported Ru-M bimetallic carbonyl  Cluster-Derived catalysts, Journal of catalysis 147, 578-593, 1994[16]  Pittman,  C.  U.,  Jr.,  and  Wilemon,  G.  M.,  1-pentene  hydroformylation  catalyzed  by  polymer-bound ruthenium complexes, J. Org. Chem. 46 (1981) 1901–1905.[17]  Junfan, W., Juntan, S., Hong, L. and Binglin, H., The stability of a polymersupported Rh  complex in the batch hydroformylation of 1-hexene, Reactive Polymers 12 (1990) 177–186.[18] Dietz, W. A., Response factors for gas chromatographic analyses, J. Gas. Chromatogr. 5, 1967 68-71[19] Borodzinski. A., Bonarowska. M.,  Relation between crystallite size and dispersion on  supported metal catalysts. Langmuir, Vol. 13, No. 21, 1997.[20] Berger, R.J. et al, Cattech Journal. Vol. 5. Issue 1. 2001 30-60[21] Brundage. M. A., Chaung. S.S.C., Experimental and modelling study of hydrogenation  using  deuterium  step  transient  response  during  ethylene  hydroformylation,  Journal  of catalysis 164, 94-108 1996.

Experimental investigation of ethylene hydroformylation to propanol on Rh and Co based catalysts

Laboratory for Chemical Technology, Ghent Universityhttp://www.lct.UGent.beExperimental Investigation of Ethylene Hydroformylation to Propanol on Rh and CoNima Navidi, Joris W. Thybaut and Guy B. Marin1CHISA 2012, 25-29  August 2012, PragueIntroduction● Hydroformylation (oxo synthesis): production of aldehydes from alkenesTransition metal catalyst is required (Rhodium, Cobalt,..) ● It can be used as a method for easy separation of “ethylene” from the methaneoxidative coupling productsIndustrial application: plasticizers, detergents, polymers, … 2CHISA 2012, 25-29  August 2012, Prague, ,2 4 2 2 5p T CatalystC H CO H C H CHO+ + →- Exploration of alternative feedstocks such as natural gas- New processes to convert light hydrocarbons into morevaluable productsIntroductionCurrent industrial processes operate in a homogeneous mode3CHISA 2012, 25-29  August 2012, PragueHigh activitiesHigh selectivitiesMetal lossesSeparation difficultiesCorrosivitySolubility limitationsHomogeneoushydroformylation Heterogeneoushydroformylation Overview• Introduction• Catalyst characterization– BET, XRD, TPD, TPR– STEM EDX, TEM• Kinetics measurements– Catalyst comparison– Temperature and Pressure effect– Inlet composition effect• Conclusion4CHISA 2012, 25-29  August 2012, PragueCatalysts characterization 5CHISA 2012, 25-29  August 2012, Prague● Tested catalysts:- 5%Rh/Al2O3- 1%Co/Al2O3 - 0.5%Co-0.5%Rh/Al2O3Catalyst characterisation:- BET - XRD- TPD, TPR- STEM EDX, TEMCatalysts characterization 6CHISA 2012, 25-29  August 2012, Prague● BET surface area with N2 physisorption- Supported material determined the BET surface area instead of the metal - The catalyst with highest loading has the lowest surface areaCatalystBET surface area (m2/g)5%Rh/Al2O3 1200.5%Rh-0.5%Co/Al2O31471%Co/Al2O3 143Catalysts characterization ● X-ray diffraction (XRD) • The XRD patterns mainly show the alumina peaks for all catalysts• XRD, TPD and TPR tests failed to give proper results to find particle sizes• Why?the small size of the metal particles, i.e., high dispersion the low metal loading on the surface7CHISA 2012, 25-29  August 2012, PragueCatalysts characterization ● Transmission Electron Microscopy method (TEM)- 5%Rh/Al2O3EDX test proved the presence of RhSmall particle size high dispersion8CHISA 2012, 25-29  August 2012, PragueCatalysts characterization - 1%Co/Al2O3  Rather big particle size low dispersion                 low activity  9CHISA 2012, 25-29  August 2012, PragueCatalysts characterization - 0.5%Co-0.5%Rh/Al2O3- Rh metals were observed in big particles or clusters (20-50nm) - Co particles were identified in small size (3-6 nm)- Fraction exposed (dispersion):   High for CoLow for Rh10CHISA 2012, 25-29  August 2012, PragueOverview• Introduction• Catalyst characterization– BET, XRD, TPD, TPR– STEM EDX, TEM• Kinetics measurements– Catalyst comparison– Temperature and Pressure effect– Inlet composition effect• Conclusion11CHISA 2012, 25-29  August 2012, PragueKinetic measurementsGas phase hydroformylation tests using a high-throughput set up 12CHISA 2012, 25-29  August 2012, PragueKinetic measurements- Two reactors with 890 mm height and 11 mm ID - 3 gas feed lines per reactor- Fully automated control of set up- Various loading amounts of catalysts (1 to 10 grams) - Online product detection using Agilent µGC with 4 TCD columns13CHISA 2012, 25-29  August 2012, PragueCatalyst comparisonExperimental operation conditions14CHISA 2012, 25-29  August 2012, PragueCatalyst Temperature Pressure Space time range Feed Composition5%Rh/Al2O31%Co/Al2O31%Co-Rh/Al2O3473 K 2 MPa5.4 kgcat.s/molC2H4,inTo149 kgcat.s/molC2H4,inCO/C2H4/H21/1/1- Intrinsic kinetics: measured at these conditions & verified using the proper correlations*- The main products observed: ethane, propanal and propanol*Berger, R.J. et al., CattechJournal. Vol. 5. Issue 1.(2001)30-60C2H4 + H2  + CO                  C2H5CHOC2H6 C2H7CHO+ H2 + H2Catalyst comparison15CHISA 2012, 25-29  August 2012, PragueSite timethe equivalent of the spacetime which has beencorrected for the metalloading on the catalyst andthe fraction of exposed metalatomsSpace time (kgcat..s/ molA, in) × 103 (gcat./ kgcat.)(gcat..s/molA, in) ×Metal loading (%) ÷Atomic Weight (gcat./molcat. atom)(molcat. atom .s/ molA, in)× Fraction exposed (%)Site time (molcat. atom.s/ molA, in)Catalyst comparison16CHISA 2012, 25-29  August 2012, PragueTo compare the performance of these catalysts under identical experimental conditions the conversions were reported versus site time2 MPa & 473 K 2 MPa & 473 KCatalyst comparison17CHISA 2012, 25-29  August 2012, Prague- An expected site time conversion on the bimetallic catalyst amounting to 0.00429molCO, converted /molcat. atoms /s  was calculated- Rh catalyst shows the highest conversions and site time conversionsCatalystParticle size (nm)TEMFraction of exposed metal (%)Accessible metal atoms (mol/gcat.)CO site time conversion(molCO, converted /molcat. atoms /s)C2H4 site time conversion(molC2H4,converted /molcat. atoms /s)5%Rh/Al2O3 2 51.1 2.4757×10-4 0.01356 0.040711%Co/Al2O3 11 12.4 0.2098×10-4 0.00359 0.014860.5%Rh-0.5%Co/Al2O34.3 for Co35 for Rh28.1 for Co      3.8 for Rh0.2575×10-4 0.00746 0.02626Catalyst comparison18CHISA 2012, 25-29  August 2012, Praguesmaller particles  higher dispersion  better CO insertion  increased oxo-selectivity*Propanal+propanol selectivity of Co-Rh > propanal+propanol selectivity of CoBig size of Rh clusters in Rh-Co catalyst  Activity should be very lowbutActivity of Rh-Co catalyst > Activity of pure Co catalystSmall cobalt particles in the Rh-Cocatalyst enhance the activityCatalystParticle size (nm)TEMFraction of exposed metal (%)5%Rh/Al2O3 2 51.11%Co/Al2O3 11 12.40.5%Rh-0.5%Co/Al2O34.3 for Co35 for Rh28.1 for Co3.8 for Rh*Zeele. T . et al. Applied Catalysis A: General 285, 2005, 96-109Why?!Why?!T and P effect19CHISA 2012, 25-29  August 2012, PragueExperimental operation conditions:Catalyst Temperature Pressure Space time range Feed Composition5%Rh/Al2O3 1%Co/Al2O3448 to 498 K 1 to 3 MPa5.4 kgcat.s/molC2H4,inTo149 kgcat.s/molC2H4,inCO/C2H4/H21/1/1The effect of Temperature and Pressure on the conversion was studied at fixed P and TIntrinsic kinetics are measured at these conditions & verified using the proper correlations**Berger, R.J. et al., Cattech Journal. Vol. 5. Issue 1.(2001) 30-60Temperature effect20CHISA 2012, 25-29  August 2012, Prague1%Co/Al2O3 2 MPa1%Co/Al2O3 2 MPa5%Rh/Al2O3 2 MPa5%Rh/Al2O3 2 MPaTemperature effectA temperature increase leads to a more pronounced increase of the C2H4 site time conversion than of the CO site time conversion on both Rh and Co21CHISA 2012, 25-29  August 2012, PragueThe apparent activation energy for ethane formation exceeds that for propanalformationhydrogenation rate on Rh( ) & Co( )hydroformylation rate on Rh( ) & Co( )2 MPa CO/C2H4/H2 1/1/1Temperature effect22CHISA 2012, 25-29  August 2012, PragueHigher effect of temperature on hydrogenation rate than hydroformylation rateIncreasing ethane selectivityThis can be explained by investigating the selected heterogeneous ethylenehydroformylation mechanismby raising temperatureDecreasing oxygenates selectivityIt can be related to the expected evolution in the H2 and CO surface concentrationsTemperature effectThe chemisorption heat of CO is typically about the double of that of H223CHISA 2012, 25-29  August 2012, PragueCO concentration decrease much faster with increasing temperature than the H2 concentrationThe relative importance of hydrogenation in the overall C2H4 conversion will increase at the expense of hydroformylationPressure effectIncreasing total pressure24CHISA 2012, 25-29  August 2012, Prague(propanal+propanol) selectivity increase slightlyAll conversions and consequently rates increase5%Rh/Al2O3 473K5%Rh/Al2O3 473K1%Co/Al2O3 473K1%Co/Al2O3 473KInlet composition effect25CHISA 2012, 25-29  August 2012, PragueThe effect of varying inlet composition on the conversion was studied at fixed P and TExperimental operation conditions:Catalyst Temperature Pressure Space time range CO/C2H4/H25%Rh/Al2O3 473 K 2 MPa2,68 kgcat.s/molC2H4,inTo80 kgcat.s/molC2H4,in1/1/1 ; 2/1/11/2/1 ; 1/1/2, ,2 4 2 2 5p T CatalystC H CO H C H CHO+ + →Inlet composition effectCHISA 2012, 25-29  August 2012, PragueIncreasing the C2H4 inlet concentrationPositive effect on both hydroformylationand hydrogenation rates Concentrations of other species on thecatalyst surface are not affected byincreasing C2H4 concentrationIncreasing the inlet CO concentrationWhy ?!Low concentration of C2H4 on surfaceConsiderable negative effect on bothhydroformylation and hydrogenationratesInlet composition effect27CHISA 2012, 25-29  August 2012, PragueIncreasing inlet concentrationCO conversion C2H4   conversionC2H4 ++           +CO - -H2 + ++CO is the most abundant surface speciesDecreasing both hydroformylationand hydrogenation rates  higher CO concentration       pronounced decrease of H2 & C2H4 concentration on the catalyst surface Conclusion- Heterogeneous hydroformylation can avoid the drawbacks ofhomogenous reaction- Rh shows higher activity in hydroformylation than Co- The main products observed were ethane, propanal and propanol- Small particle size enhances hydroformylation and oxo-selectivitiy- Increasing the temperature has higher effect on hydrogenation ratethan hydroformylation rate- Ea (reductive elimination) > Ea (CO insertion)- The CO concentration is the highest on the catalyst surface28CHISA 2012, 25-29  August 2012, PragueAcknowledgments• TOPCOMBI: the European Community (contract nr 515792-2)• The 'Long Term Structural Methusalem Funding by the FlemishGovernment'• Hilde Poelman for XRD analysis• Vladimir Galvita and Vitaliy Bliznuk for assisting in TEM analysis29CHISA 2012, 25-29  August 2012, PragueQuestions30CHISA 2012, 25-29  August 2012, PragueThanks for your kind attention

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Experimental investigation of ethylene hydroformylation to propanol on Rh and Co based catalysts

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Ghent University Academic Bibliography

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