Otto, T.N.

Pfeifer, P.

Pitter, S.

Powietzka, B.

English

Otto, T. N.

KITopen

Thomas N. Otto a, Peter Pfeifer b, Stephan Pitter a, Bernhard Powietzka aa Forschungszentrum Karlsruhe GmbH, ITC-CPV, Postfach 36 40, 76021 Karlsruheb Forschungszentrum Karlsruhe, GmbH, IMVT, Postfach 36 40, 76021 Karlsruhemit der Universität Karlsruhe verbunden into 3,4-epoxy-1-butene „EpB“ (fig. 1) in the gaseous phase is a very attractive process. EpBis a multi-functional molecule and a potential intermediate for the production of other oxygen-containing products. The reason for the efficiency of EpB formation in comparison to propylene epoxidation is caused from the fact that splitting of an allylic methyl group is not possible with 1,3-butadiene. Thus, the direct kinetically controlled oxidation to the corresponding epoxide is preferred. Whether one considers homolytic or heterolytic C-H-bond strength, it is clear that allylic hydrogens are vulnerable to abstraction by reactive oxygen atoms on the catalyst. 1,3-butadieneO2Ag / Cs - Al2O3 O3,4-epoxy-1-buteneFigure 1. Direct epoxidation of 1,3-butadiene over Ag / Cs catalyst on Al2O3to 3,4-epoxy-1-butene. EpB was so far industrially produced by Eastman (Texas) by means of gaseous phase oxidation of 1,3-butadiene with air at Ag / Cs catalyst.[1] In recent years the influence of promoters (Cs / Rb / Ba, Tl) on this process was particularly investigated by combined theoretical and experimental investigations on catalyst surfaces.[2], [3] Motivation, intention and cooperationCombination of chemical developments with micro-reactor technology shall offer alternative routes for important processes. A micro-reactor, developed and manufactured in the Forschungszentrum Karlsruhe[4], was set up to lab-scale to enable investigation. Furthermore a conventional tubular fixed bed reactor with catalyst bed serves the comparison with the industrially used procedure. From the results of attempt alternative technical and economic procedure possibilities are to be derived. Additionally, our research considers  the optimization and development of catalysts on the basis of different supporting materials and promoters. [1]  U.S. Patent No. 6,455,713, Reactivation of Cs-Promoted, Ag Catalysts for the Selective Epoxidation of  Butadiene to 3,4-Epoxy-1-Butene, J. R. Monnier, September 24, 2002.[2]  John R. Monnier, Jerome L. Stavinoha Jr., Robin L. Mingaa, Journal of Catalysis 226 (2004) 401–409[3]  John R. Monnier, Prepr. Pap. -Am. Chem. Soc.,Div. Petr. Chem. 2007, 52 (2), 163 [4]  P. Pfeifer et al., chimica oggi (Chemistry Today) 25 (2007) 42-46[5]  John R. Monnier Journal of Catalysis 203, 362–368 (2001)[6] Mark A. Barteau, Topics in Catalysis Vol. 22, Nos. 1/2, January 2003 [7]  Mark A. Barteau, Topics in Catalysis Vol. 22, Nos. 1/2, January 2003 Lab-scale process Mechanism of catalyzed epoxidationA mixture of C4H6, O2 and Ar (N2) is passed through a catalyst bed (fig.2) at an elevated temperature, pressure and space velocity. R1 represents the tubular fixed bed reactor, R2 represents the micro-reactor (fig.4). R3 serves for complete catalytic treatment of exhaust gases through oxidation over a catalyst (Pd / Al2O3). Fig. 3 shows the lab equipment which make the parallel investigation possible at both reactor types. Figure 2. Schematic representation of the heterogeneously catalyzed EpB process (lab-scale). The guiding hypothesis is that surface oxametallacycles are key intermediate for epoxidation on Ag / Cs catalyst. The intermediate EpB(ads), finally leading to molecular EpB, is probably strongly adsorbed on the catalyst surface indicated by theoretically calculations which also support its identity as an oxametallacycle. The oxametallacycle intermediate is more thermodynamically stable than EpB by approx. 24 kcal / mol (fig.7). Moreover, the transition state for EpB formation from the oxametallacycle intermediate  is actually  lower in energy than the reactants, butadiene and oxygen.[7]Figure 9. Element-specific quantification by EDX of the catalysts (INCA Energy, Oxford).[kcal/ mol][ 6 ][ 5 ]EA for ring closure to EpBEA for EpBring- openingEpB via surface oxametallacycle[ 6 ]REM, EDX, TPR, TPO, ICP , BETOnline-GC, -GAOnline- GC, -GA,GC-MS,  1H-NMR,  13C-NMR140°C – 320°C3,4-Epoxy-1-buteneHe,  N2,  Ar1,3-Butadiene   +  O2280°C – 350°CCO2 +  H2ONPFIDReactor R1 / R2REM, EDX, TPR, TPO, ICP , BETReactants (gas)Ag / Cs- Al2O3 (solid)Products Pd- Al2O3 (solid)ProductsReactor R3 (Exhaust gases)The realization of the experiments is based on different space velocities (SV), different gas compositions (fig. 5) and catalysts formed by a variety of methods. With these parameters the efficiency of the epoxidation, as well as thermal and kinetic behavior in the micro-reactor is to be examined. The limits of operation range were optimized by quantitative analyses of BD-conversion, EpB yield and CO2 formation. From these data conversion curves are generated as depicted in fig. 6.The heterogenously catalyzed epoxidation of butadiene has been successfully carried out in the micro-reactor. EpB selectivity of max. 46% and 8% BD conversion (SV = of 5065h-1, Temp. 235°C, Space time yield = 0,9 kg m-3 h-1) has been reached. It should be pointed out that EpB and CO2 are produced from a common surface intermediate. So far, no better EpBselectivity have been achieved in the micro-reactor, which is currently further optimized. Optimization of the catalyst impregnation method led to higher EpB yields. Nano-scaled silver particles on supporting materials are to be applied in future studies as well as testing additional micro-reactor designs.Results and conclusion ExperimentsHeterogeneously catalyzed epoxidation of 1,3-butadiene to 3,4-epoxy-1-butenemicro-reactor technologyFigure 4. Micro-reactor and its components.Seal (graphite)Metall fritSheet metalSpacer blockHeatingBore holesintered metalFigure 3. Lab equipment with control unit and gas analyzers.On the left side one can see the micro-reactor. Right of it the tubular fixed bed reactor is to be seen (blue frame). Preparation of catalysts takes place by sequential impregnation with AgNO3/ promoters on different types of α-Al2O3 supports (T60 / SLA 92, Almatis, Particle size 0,045 - 0,063 mm, BET-surface 0,8 m2 / g to 1.2 m2 / g). Ag loading is 10 w % and Cs 0,1% ppm. The catalysts are analytically characterized by SEM (fig.8, fig.9), TPO and TPR. For sufficient EpBformation, homogeneous promoter distribution on the Ag surface is decisive. Preparation of catalysts Direct EpoxidationReference Figure 8. Evaluation of the metal distribution on the catalyst (BSE detector, exicationvolume-meet 10kV). Bright spots show Ag. Dark areas show Al2O3.Figure 7. Heat of formation and activation energy for EpB formation from the oxametallacycleintermediate. Ref. [5]Ref. [6]Ref. [6]Figure 5. Phase plot of  1,3-Butadiene, O2, N2 (Ar). The green dashed lines corresponds to the BD / O2 relation. 140 160 180 200 220 240 260 280 300 320 34001020304050RG 5065 h-1BD 19,4 % O2  9,7 % U BD [%] A EpB [%] S EpB [%][%]Temperatur R2 [°C]16           17           1          190            20         21           22           230           24            50     26Figure 6. 1,3-BD conversion, yield of EpB (measured) and EpB Selectivity (calculated) in the micro-reactor (R2), gas temp. = 160°C – 260°C, gasinletBD = 19,4%, O2 = 9,7%, Ar = 80.9%, K=2, SV= 5065h-1, Ag =10w%, Cs = 0,1w%. Smax EpB = 235°C, p gas inlet= 1040 mbar.90 %               80 %         70 %                60 %                50 %             40 %               30 %                20 %                10 %              0 %10 %20 %30 %40 %50 %60 %70 %80 %90 %20 %30 %40 %10 %50 %60 %70 %80 %90 %OEG  72,6 %UEG  1,2 %LuftgeradeSauerstoffgrenz-Volumenanteil  12% OEG  (Luft)  16,4 %UEG  (Luft)  1,3 %C4H6 /   O2 /   N225°C, 1atmK = BD / O2N2 (Ar)C2H6O2K = 1K = 0,5K =2

Heterogeneously catalyzed epoxidation of 1,3-butadiene to 3,4-epoxy-1-butene

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Heterogeneously catalyzed epoxidation of 1,3-butadiene to 3,4-epoxy-1-butene

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