Maria MADEJ-LACHOWSKA – Institute of Chemical Engineering, Polish Academy of Sciences, Gliwice; Department of Applied Chemistry and Mechanics, Opole University of Technology; Aleksandra KASPRZYK-MRZYK*, Henryk MOROZ – Institute of Chemical Engineering, Polish Academy of Sciences, Gliwice; Andrzej I. LACHOWSKI – Department of Applied Chemistry and Mechanics, Opole University of Technology; Hildegarda WYŻGOŁ – Institute of Chemical Engineering, Polish Academy of Sciences, Gliwice, Poland Please cite as: CHEMIK 2014, 68, 1,
Introduction Methanol is an important feedstock for the production of many chemicals. It is the key material for the C1 chemistry. It is used for manufacturing other chemicals such as formaldehyde, acetic acid, chloromethane and many others. Moreover, it is an outstanding solvent and recently it is used as a clean synthetic fuel [1, 2, 3]. Methanol can be also converted via the steam reforming to the hydrogen-rich gas, which can be fed to a fuel cell to generate electric power. A breakthrough in the synthesis of methanol occurred when it was found that the presence of CO2 in the reaction mixture is favorable for methanol synthesis.The main reactions that occur in carbon dioxide hydrogenation are following: CO2 + 3H2 CH3OH + H2O (1) – a direct synthesis of methanol from carbon dioxide and hydrogen CO2 + H2 CO + H2O (2) – the reverse water gas shift reaction. Both reactions are exothermic and reversible. However, the cost of such process, where CO2 hydrogenated is higher than the cost of using CO+CO2 mixture. On the other hand, there is a need of utilization of CO2, which is a waste gas in many chemical processes. Methanol synthesis by hydrogenation of CO2 gives great opportunity to achieve this goal. The industrial methanol synthesis catalysts developed for the synthesis gas containing hydrogen, carbon monoxide and only small amounts of carbon dioxide in the presence of larger quantities of carbon dioxide deactivate. Accordingly, there is a need for develop a new methanol synthesis catalyst useful for carbon dioxide gas rich. This is evidenced by a number of works on this subject that appeared in the scientific journals. In numerous studies have been attempted to increase the efficiency and improve selectivity of industrial methanol synthesis catalyst from CO2 rich gas [4]. Most researchers consider that not copper but Cu/ZnO system is responsible for the activity of copper catalysts [5, 6]. The molar compositions of Cu:Zn in the industrial Cu/ZnO-based catalysts, prepared by a co-precipitation method, is about 70:30 [6]. Fujitani et al. found linear relationship between methanol synthesis activity and copper surface area. Many authors have found that the Cu catalysts containing zirconia are active in the synthesis of methanol from CO2 and H2 [4, 8, 9]. Ortelli et al. [9] considered zirconia supported catalysts as mechanically and thermal stable, with relatively high specific surface area. Development of a new, active in the presence of carbon dioxide catalyst demands not only selecting appropriate components (promoters) but also estimating their concentration. Among the number of literature reports we selected: gallium [4, 7, 10÷14], cerium [15÷18], palladium [19], lanthanum [20÷22] and chromium [17÷24] as additions to CuO/ZnO/ZrO2 catalyst.
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Ma et al. [4] in their review paper report that the addition of Ga or Cr to Cu/Zn/Al catalyst increases catalyst activity with respect to Cu surface area. Fornero et al.[10] obtained the highest methanol synthesis activity for 2wt% Cu/6 wt%Ga2O3/ZrO2 catalyst while Toyir et al. [14] during investigating gallium promoted copper-based catalyst chose ZnO as the better then SiO2 support. Fujitani et al. [7] claim that copper surface area of Cu/ZnO/Ga2O3 catalyst containing 20–30 wt% of Ga2O3 is about 40% higher than the copper surface area of Cu/ZnO and Cu/ZnO/Al2O3 catalysts. Huang et al. [24] described the significant improvements of the activity of skeletal copper catalyst for the methanol synthesis reaction by adding small amount of Cr2O3 to the surface of copper. Nonetheless, overloading the Cu surface with Cr2O3 reduced the copper surface area and the positive catalytic effect. The literature reports refer to completely different catalytic systems, so it is difficult or practically impossible to predict how the above-mentioned promoters affect for the activity of CuO/ZnO/ZrO2 catalyst. The aim of this work is the study of the influence of promoters on the activity of the CuO/ZnO/ZrO2 catalyst in the process of methanol synthesis from CO2. Preparation and characterization of the catalysts The homogenization method using citric acid was selected in order to prepare the catalysts. The oxide precursors of the catalysts containing CuO, ZnO, ZrO2 and one of the promoters – Ce, Cr, Ga, La, Pd were obtained by decomposing the citrate complex of the metals according to the method described by Courty et al. [25]. The required amounts of nitrates of Cu, Zn, Zr and promoter were added in small portions under intense stirring to 2 M solution of citric acid. The solution was evaporated in a revolving flask in vacuum at 380 K, up to get the solid phase. The catalyst decomposition took place in Buechi oven, in order to obtain oxides. Then it was calcinated at temperature from 373 to 573 K.
Photo 1. Tubular Buechi oven – decomposition of catalyst
The calcinated catalyst was turned into pills by using the hydraulic press. Then the pills were crashed and sieved to a range of 0.8–1.0 mm to perform the reaction.
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Methanol Synthesis from Carbon Dioxide and Hydrogen over CuO/ZnO/ZrO2 promoted catalysts
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A tubular, flow, high-pressure, fixed bed reactor, made of stainless steel was used in the experiments. The bed consisted of 2 g of the catalyst placed between two layers of ceramic grains. The catalyst was reduced in a steam of diluted hydrogen (7% H2 in N2 under atmospheric pressure). The catalyst activity in the methanol synthesis was determined under the following range of conditions: the temperature from 433 to 513 K, the pressure 8 MPa and the reaction gas composition: H2‒66%, N2‒12%, CO2‒22%. After leaving the reactor, the reaction mixture was analyzed chromatographically with the Varian Star 3800 apparatus. The methanol content was determined by the flame ionization detector (FID) with CP-Wax column. Gases were analyzed by the thermal-conductivity detector (TCD) with Carbo Plot column. The pictures of the testing equipment are presented in Figure 1 and Photo 2.
Table 1 Composition, specific surface area BET and Cu active area values of tested Catalyst
Promoter
CuO
ZnO
ZrO2
%wt
%wt
%wt
62.4
25.0
12.6
—
Cu/Zn/Zr/Ce 65.3
26.3
4.5
Ce2O3
Cu/Zn/Zr/Cr 65.2
26.3
7.7
Cu/Zn/Zr/Ga 65.3
26.3
Cu/Zn/Zr/La 65.3 Cu/Zn/Zr/Pd 65.2
Cu/Zn/Zr
Promoter concentra-tion %wt
SBET m2g-1
Cu active area m2gkat-1
20
6.1
3.9
15
7.9
Cr2O3
0.7
24
8.7
4.5
Ga2O3
3.9
21
8.7
26.3
4.5
La2O3
3.9
16
7.3
26.3
4.5
PdO
3.9
24
6.7
Fig. 1. Installation scheme Fig. 2. Pore volume distribution
The results of the catalytic tests are presented in the form of graphs: the dependence of CO2 degree of conversion (Fig.3), the selectivity towards methanol (Fig.4), the methanol efficiency (Fig.5) and (Tab.2).
Table 2
Selected catalytic test results
Catalyst
Photo 2. Installation for methanol synthesis
Specific surface area of the oxide precursor and catalyst was measured with BET method using an Autosorb-1 Quantachrome apparatus with nitrogen as adsorbate at 77.5 K. The active surface of copper in reduced catalyst was determined with the use of reactive adsorption of N2O at 363 K (VG/ Fisons Quartz 200D). Results During the tests, six different catalyst have been prepared. The compositions of the catalysts, specific surface area BET and active area of Cu are presented in Table 1. The base Cu/Zn/Zr catalyst is characterized by relatively flat pore volume distribution (Fig. 2) and a maximum mean diameter 20 nm. The addition of gallium affects in a visible way on the pore size distribution change. There appeared pores of the average diameters ranging from 3 to 11 nm. This significant increase in pore volume (from 0.0812 cm3/g to 0.1014 cm3/g) has changed the specific surface area SBET.
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Temperature. conversion degree and selectivity for maximum methanol yield
Catalyst activity parameters for T=473 K
α %
WMeOH g(kgkath)-1
SMeOH %
T K
α %
W MeOH g(kgkath)-1
SMeOH %
Cu/Zn/Zr
8
83
61
493
6
68
73
Cu/Zn/Zr/Ce
15
202
69
493
12
146
65
Cu/Zn/Zr/Cr
18
194
68
493
14
148
69
Cu/Zn/Zr/Ga
17
211
71
513
10
120
74
Cu/Zn/Zr/La
17
205
70
493
13
152
67
Cu/Zn/Zr/Pd
17
199
73
513
10
105
80
The CO2 conversion degree and selectivity values were calculated according the following formulas:
where: α – conversion degree of CO2 S – selectivity – inlet stream for component i – outlet stream for compnent i
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science Fig. 3. Temperature impact on CO2 conversion degree
Fig.5. Temperature impact on methanol yield
The analysis of the catalytic test results shows a significant improvement of the catalytic properties caused by promoters introduced to the base catalyst CuO/ZnO/ZrO2. Figure 3 presents the dependence of CO2 degree of conversion from temperature. The highest value of conversion degree reach catalysts with Cr and La.
The methanol yield dependence of temperature is presented in Figure 5. Conversion degree and selectivity have impact on methanol efficiency. A high temperature has positive effect on running the parallel reaction (2), more carbon dioxide is converted into carbon monoxide, thus methanol yield is decreasing [26].For the most active catalysts with Ce, La and Ga additives, that reach high degree of conversion at low temperature range, the curves of methanol yield achieve their maximum. For the rest of catalysts, the curves have rising tendency in the whole temperature range. As we noticed, the differences in the methanol efficiency are really small, they are in the limit of measurement error. The exception is CuO/ZnO/ZrO2/PdO catalyst , which gives slightly lower values of methanol yield in whole temperature range. In our opinion for consideration deserves the catalyst with gallium promoter. Although the catalyst achieves maximum methanol efficiency at 513 K , it is characterized by high selectivity in high temperature range (about 70%). Summary • the addition of suitable promoter has a beneficial impact on the catalytic properties of copper catalysts. Depending on the promoter used, the efficiency of catalyst can be twice as high • the highest methanol yields have been obtained for catalysts with La, Cr or Ce promoter at 493 K • the catalyst with gallium promoter achieves the best parameter for the upper range of temperatures studied. Literature
Fig.4. Temperature impact on selectivity
Figure 4 shows the temperature dependence of the selectivity. It gives a noticeable decrease in selectivity with increasing temperature. The best selectivity show catalyst with palladium promoter and for the high temperature range 493 to 513 K catalyst containing gallium.
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1. Rahimpour M.R., Pourazadi E., Iranshahi D., Bahmanpour A.M.: Methanol synthesis in a novel axial-flow, spherical packed bed reactor in the presence of catalyst deactivation. Chemical Engineering Research and Design 2011, 89, 2457–2469. 2. Pontez F., Liebner W., Gronemann V., Rothaemel M., Ahlers B.: CO2 based methanol and DME – Efficient technologies for industrial scale production. Catalysis Today 2011, 171, 242–250. 3. Centi G., Perathoner S.: Opportunities and prospects in the chemical recycling of carbon dixide to fuels. Catalysis Today 2009, 148, 191–205.
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4. Ma J., Sun N., Zhang X., Zhao N., Xiao F., Wei W., Sun Y.: A short review of catalysis for CO2 conversion. Catalysis Today 2009, 148, 221–231. 5. Waugh K.C.: Methanol synthesis. Catalysis Letters 2012, 142, 1153–1166. 6. Behrens M., Studt F., Kasatkin I., Kühl S., Hävecker M., Abild-Pedersen F., Zander S., Gir-gsdies F., Kurr P., Kniep B.-L., Tovar M., Fischer R.W., Nørskov J.K., Schlögl R.: The active Site of Methanol Synthesis over Cu/ ZnO/Al2O3. Industrial Catalyst. Science 2012, 336, 893-897. 7. Fujitani T., Saito M., Kanai Y., Takeuchi M., Moria K., Watanabe T., Kawai M., Kakumoto T.: Methanol synthesis from CO2 and H2 over Cu/Zn/Ga2O3. Chemistry Letters 1993, (1079–1080). 8. Słoczyński J., Grabowski R., Kozłowska A., Olszewski P., Lachowska M., Skrzypek J., Stoch J.: Effect of Mg and Mn oxide additions on structural and adsorptive properties of Cu/ZnO/ZrO2 catalysts for the methanol synthesis from CO2. Applied Catalysis A- General 2003, 249, 129–138. 9. Ortelli E.E., Wambach J., Wokaun A.: Methanol synthesis reactions over a CuZr based catalyst investigated using periodic variations of reactant concentrations. Applied Catalysis A- General 2001, 216, 227. 10. Fornero E.L., Sanguineti P.B., Chiavassa D.L., Bonivardi A.L.: Performance of ternary Cu-Ga2O3-ZrO2catalystsin the synthesis of methanol using CO2-ruch gas mixture. Catalysis Today 2013, 213, 163–170. 11. Ladera R., Perez-Alonso F.J.: Catalytic valorization of CO2 via methanol synthesis with Ga-promoted Cu-ZnO-ZrO2 catalyst. Applied Catalysis .B: Environmental 142‒143 (2013) 241–248. 12. Słoczyński J., Grabowski R., Olszewski P., Kozłowska A., Stoch J., Lachowska M., Skrzypek J.: Effect of metal oxide additives on the activity and stability of Cu/ZnO/ZrO2 catalysts in the synthesis of methanol from CO2 and H2. Applied Catalysis A- General 2006, 310, 127–137. 13. Lachowska M., Skrzypek J., Krupa K.: Uwodornienie dwutlenku węgla w kierunku metanolu na katalizatorze miedziowo-cynkowym z dodatkami Ga oraz Zr. Inżyniera Chemiczna i Procesowa 2004, 25, 1294–1253. 14. Toyir J., Ramoirez de la Piscina P., Fierro J. L.G., Homs N.: Catalytic performance for CO2 conversion to methanol of gallium-promoted copper-based catalysts: influance of metallic precursors. Applied Catalysis B: Environmental 2001, 34, 255–266. 15. Yoo Ch.-J., Lee D.-W., Kim M.-S., Moon D.J., Lee K.-Y.: The synthesis of methanol from CO/CO2/H2 gas over Cu/Ce1-xZrxO2 catalysts. Journal of Molecular Catalysis: A Chemical 2013, 378, 255–262. 16. Arena F., Mezzatesta G., Zafarana G., Trunfio G., Frusteri F., Spadaro L.: How oxide carries control the catalytic functionality of the Cu-ZnO system in the hydrogenation of CO2 to methanol. Catalysis Today 2013, 210, 39–46. 17. Bonura G., Arena F., Mezzatesta G., Cannilla C., Spadaro L., Frusteri F.: Role of the ceria promotor and carrier on the functionality of Cu-based catalysts in the CO2-to-methanol hydrogenation reaction. Catalysis Today 2011, 171, 251–256. 18. Pokrovski K.A., Bell A.: Effect of dopants on the activity of Cu/M0.3Zr 0.7 O2 (M = Ce, Mn and Pd) for CO hydrogenation to methanol. Journal of Catalysis 2006, 244, 43–51. 19. Melian-Cabrera I., Lopez Granados M., Terreros P., Fierro J.L.G.: CO2 hydrogenation over Pd-modified methanol synthesis catalysts. Catalysis Today 1998, 45, 251–256. 20. Zhang L., Zhang Y., Chen S.: Effect of promoter SiO2, TiO2 or SiO2-TiO2 on the performance of CuO-ZnO-Al2O3 catalyst for methanol synthesis from CO2 hydrogenation. Applied Catalysis A- General 2012, 415–416, 118–123. 21. Guo X., Mao D., Lu G., Wang S., Wu G.: The influence of La doping on the catalytic behavior of Cu/ZrO2 for methanol synthesis from CO2 hydrogenation. Journal of Molecular Catalysis A: Chemical 2011, 345, 60–68. 22. Jia L., Gao J., Fang W., Li Q.: Carbon dioxide hydrogenation to methanol over the pre-reduced LaCr0.5Cu0.5O3 catalyst. Catalysis Communications 2009, 10, 2000–2003. 23. Kameoka S., Okada M., Tsai A.P.: Preparation of Novel Copper Catalyst in Terms of the Immiscible Interaction Between Copper and Chromium. Catalysis Letter 2008, 120, 252–256.
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24. Huang X., Ma L., Wainwright M.S.: The influence of Cr, Zn, Co additives on the performance of the skeletal copper catalysts for methanol synthesis and related reactions. Applied Catalysis A- General 2004, 257, 235–243. 25. Courty Ph., Ajot H., Marcilly Ch., Delmon B.: Powder Technology 1973, 7, 21. 26. Skrzypek J., Lachowska M., Serafin D.: Methanol synthesis from CO2 and H2: Dependence of equilibrium conversions and exit equilibrium concentrations of components on the main process variables. Chemical Engineering Science 1990, 45, 89–96.
Translation into English by the Author
Maria MADEJ-LACHOWSKA – Ph.D., (Eng), graduated from the Faculty of Chemical Technology and Engineering at Silesian University of Technology in Gliwice (1977). She has been working for the Institute of Chemical Engineering, Polish Academy of Sciences, in Research Group on Catalysis and Chemical Kinetics since 1977. She has been working in Department of Applications of Chemistry and Mechanics at Opole University of Technology since May 2013.
[email protected]
Aleksandra KASPRZYK-MRZYK – M.Sc., graduated from the Faculty of Chemical Technology and Engineering at Silesian University of Technology in Gliwice, her major interest are technology and engineering of fine chemicals and specialty materials (2007). She has been working for the Institute of Chemical Engineering Polish Academy of Sciences, in Research Group on Catalysis and Chemical Kinetics since 2008.
[email protected]
Henryk MOROZ – Eng., graduated from the Faculty of Chemistry at Silesian University of Technology in Gliwice, his major interest are organic chemistry and technology(1979). He has been working for the Institute of Chemical Engineering Polish Academy of Sciences, in Research Group on Catalysis and Chemical Kinetics since 1979.
Andrzej I. LACHOWSKI – Ph.D., (Eng), graduated from the Faculty of Chemical Technology and Engineering at Silesian University of Technology in Gliwice (1974). Currently he works as Lecturer in Department of Applications of Chemistry and Mechanics in Opole University of Technology. From 1974 to 2013, he worked for the Institute of Chemical Engineering Polish Academy of Sciences in Gliwice. He is co-author of 47 publications and 42 posters at national and international conferences.
Hildegarada WYŻGOŁ has been employed as technical worker in Research Group on Catalysis and Chemical Kinetics, in the Institute of Chemical Engineering Polish Academy of Sciences since 1992.
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