PRECIPITATION CATALYST FOR THE HYDROGENATION OF ETHYL ACETATE CONTAINING COPPER ON ZIRCONIA

Abstract

A process for the preparation of a copper/zirconia-catalyst for the hydrogenation of ethyl acetate to ethanol comprising the steps: a) preparation of an aqueous solution of water-soluble copper and zirconium salts; b) precipitation of a solid from this solution by addition of a basic precipitating agent, and optionally aging of the solid; c) separation and washing of the solid; d) drying of the solid; e) calcination of the solid; characterized in that the precipitation of the solid in step b) is carried out at a pH in the range of from 7 to 7,5, and the basic precipitation agent contains a mixture of Na.sub.2CO.sub.3 and NaOH.

Claims

1-14. (canceled)

15. A process for the preparation of a copper/zirconia-catalyst for the hydrogenation of ethyl acetate to ethanol comprising the steps: a) preparation of an aqueous solution of water-soluble copper arid zirconium salts; b) precipitation of a solid from this solution by addition of a basic precipitating agent, and optionally aging of the solid; c) separation and washing of the solid; d) drying of the solid; e) calcination of the solid; characterized in that the precipitation of the solid in step b) is carried out at a pH in the range of from 7 to 7.5, and the basic precipitation agent contains a mixture of Na.sub.2CO.sub.3 and NaOH.

16. The process of claim 15, further comprising the steps: f) shaping the solid obtained from step e) to give shaped bodies; or g) modifying the solid obtained from step c), d) or e) to give powders of modified particles; and h) optionally forming shaped bodies from the powders obtained in step g); optionally further calcination of the shaped bodies or powders obtained from step f), g) or h); wherein the shaping step f) can also be carried out between drying step d) and calcination step e).

17. The process according to claim 15, wherein the copper salt is copper nitrate Cu(NO.sub.3).sub.2 and the zirconium salt is zirconyl nitrate ZrO(NO.sub.3).sub.2.

18. The process according to claim 15, wherein the atomic ratio of Cu:Zr in the aqueous solution is in the range of from 1:3 to 2:5.

19. The process according to claim 15, wherein the ratio of Na.sub.2CO.sub.3:NaOH in the precipitation agent is in the range of from 2:1 to 10:1.

20. The process according to claim 15, wherein the precipitation agent is employed as an aqueous solution containing from 5 to 30% by weight of Na.sub.2CO.sub.3 and NaOH.

21. The process according to claim 15, wherein in step b) the precipitated solid is aged at a pH in the range of from 7.0 to 7.5.

22. The process according to claim 15, wherein the solid obtained in step c) is dried at a temperature of from 80 to 160 C.

23. The process according to claim 15, wherein the dry solid obtained in step d) is calcined at a temperature of from 350 to 650 C.

24. A catalyst for the preparation of a copper/zirconia-catalyst for the hydrogenation of ethyl acetate, obtainable by the process as claimed in claim 15.

25. The catalyst according to claim 24, containing from 18 to 30% by weight of CuO and from 72 to 80% by weight of ZrO.sub.2.

26. The catalyst according to claim 24, having a specific surface (BET) area in the range from 100 to 130 m2g.sub.1 and an average pore diameter (BJH) in the range from 2.6 to 3.6 nm.

27. The catalyst according to claim 24, which is X-ray amorphous.

28. A method of use of the catalyst according to claim 24, wherein ethyl acetate is hydrogenated to ethanol at a hydrogen pressure of from 1 to 200 bar and a temperature from 200 to 300 C. in the pressure of said catalyst.

Description

EXAMPLES

[0062] Catalyst Preparation

Example 1 and Comparative Examples C1-C3

[0063] Four Cu/ZrO.sub.2 catalysts with identical copper loading were synthesized by co-precipitation in a batch process varying the precipitating agent and the pH. Initially, ZrO(NO.sub.3)23 H.sub.2O and Cu(NO.sub.3).sub.23 H.sub.2O were dissolved in water. For a 18.3 wt % CuO/ZrO.sub.2, 6.0317 g ZrO(NO.sub.3).sub.2. 3H.sub.2O and 1.6677 g Cu(NO.sub.3)2.3 H.sub.2O were dissolved together in 45 mL water. During the coprecipitation, the metal nitrates were pumped (ICP pump, ISMATEC) continuously into the precipitation reactor filled with 200 mL HPLC water. Simultaneously, the pH was kept constant at pH 10.5 or pH 7 with 25 wt % NaOH (OH-10, OH-7) or 7:1 Na.sub.2CO.sub.3/NaOH (saturated solution/25 wt %) (CO.sub.3-10, CO.sub.3-7) as precipitating agents. The addition of the precipitating agent was controlled by an autotitrator (Titroline alpha, Schott) connected with a pH electrode (Schott) located in the precipitation reactor. After co-precipitation, the solution containing the precursor was aged for 15 min. Subsequently, the precursor was filtered, washed with 0.75 L water until the nitrate anions were removed, and dried at 378 K for 18 h. Finally, the dried precursor was calcined in synthetic air at 763 K for 3 h with a heating rate of 2 K min.sup.1. After calcination, the catalyst was characterized by XRD, N.sub.2 physisorption, TPR, and N.sub.2O-RFC and tested after reduction in the gas-phase hydrogenation of ethyl acetate.

TABLE-US-00001 TABLE 1 List of precipitation agents, pH and catalyst samples Example Precipitation agent pH Label C1 NaOH 10 OH-10 C2 NaOH 7 OH-7 C3 Na.sub.2CO.sub.3/NaOH 10 CO.sub.3-10 1 Na.sub.2CO.sub.3/NaOH 7 CO.sub.3-7

[0064] Characterisation:

[0065] N.sub.2 physisorption measurements were performed at 77 K with 200 mg calcined catalyst using a BELSORP-max volumetric sorption set-up (BEL Japan, Inc.). Before the measurement, the catalyst was heated to 473 K for 2 h under vacuum to remove surface water. X-ray powder diffraction measurements were carried out to characterize the phase composition of the calcined catalysts and the catalysts after hydrogenation of ethyl acetate. Diffraction patterns were recorded in reflection geometry with an Empyrean Theta-Theta diffractometer (Panalytical, Almelo) equipped with a copper tube, 0.25 divergent slit, 0.5 antiscatter slit, 7.5 mm high antiscatter slit, 0.04 rad incident and diffracted beam soller slits, as well as a position sensitive PIXcel-1d detector. For qualitative phase analysis, the catalyst was scanned in the range of 5 -80 2 with a step width of 0.0131. Afterwards, the qualitative phase analysis was processed by the ICDD powder diffraction file (PDF2) in conjunction with the HighScore Plus software (Panalytical, Almelo). Additionally, the Cu particle size of the catalysts after hydrogenation was calculated using the Scherrer equation with =0.053. Temperature-programmed reduction (TPR) and N.sub.2O reactive frontal chromatography (RFC) experiments were performed in a flow-set-up with 100 mg catalyst loaded in a glass-lined stainless steel U-tube reactor. The calcined catalyst was heated up to 513 K with 1 K min.sup.1 in a 84 mL min.sup.1 flow of 5% H.sub.2/Ar. Simultaneously, the hydrogen consumption was measured with a thermal conductivity detector. After cooling to room temperature, N.sub.2O-RFC was carried out with a 10 mL min.sup.1 flow of 1% N.sub.2O/He. The hydrogenation of ethyl acetate was performed in a flow-set-up described below. 100 mg catalyst was loaded in a glass-lined stainless steel U-tube reactor. The catalyst was reduced in a 10 mL min.sup.1 flow of 2% H.sub.2/He with a temperature plateau at 398 K. The maximum temperature during reduction was set to 573 K. For the hydrogenation of ethyl acetate, the reduced catalyst was heated up from room temperature to 513 K with 0.5 Kmin.sup.1 in a gas flow of 50 mL min.sup.1 containing 1% ethyl acetate and 68% hydrogen. After holding the maximum temperature for 1 h, the temperature was reduced to room temperature with 0.5 mL min.sup.1. All gases were analyzed by a calibrated quadrupole mass spectrometer (QMS, GAM422, Balzers).

[0066] The XRD diffraction patterns of the calcined CuO/ZrO.sub.2 catalyst precursors are shown in FIG. 1 together with the reference patterns of t-ZrO.sub.2 and CuO. In the XRD patterns of the CuO/ZrO.sub.2 catalysts OH-10, OH-7, and CO.sub.3-7, two very broad peaks in the range of 20 to 40 and 45 to 65 2 were observed suggesting the presence of essentials amorphous t-ZrO.sub.2. In addition to the two very broad peaks of OH-7, the main reflection for t-ZrO.sub.2 was detected weakly. Therefore, OH-10 and CO.sub.3-7 are essentially X-ray amorphous without detectable crystallinity, and OH-7 is mainly amorphous with some crystallized t-ZrO.sub.2. In contrast, for CO.sub.3-10 the main reflections of t-ZrO.sub.2 were clearly observed at 30.2, 35.3, 50.3 , and 60.2 2. Furthermore, for CO.sub.3-10 the main reflections of CuO were identified at 35.6 and 38.8 2. Consequently, crystalline t-ZrO.sub.2 and CuO nanoparticles are present in the calcined catalyst precursor CO.sub.3-10, whereas the other precursors are all X-ray amorphous.

[0067] The determined surface areas (BET method), average pore diameters (BJH method), and average pore volumes derived from N.sub.2 physisorption results are summarized in Table 2. These results have to be interpreted carefully due to the complex pore network. The specific surface areas of the X-ray amorphous catalysts OH-10, OH-7, and CO.sub.3-7 are in the range from 111 to 119 m.sup.2g.sup.1. The average pore diameters are similar amounting to about 2.7 nm. In comparison to the X-ray amorphous catalysts, the specific surface area of the crystalline catalyst precursor CO.sub.3-10 is smaller by 2/3, and the average pore diameter of 6.7 nm is about twice the size. The average pore volumes are comparable for all four samples.

TABLE-US-00002 TABLE 2 Specific surface areas, average pore diameters and average pore volumes of the calcined CuO/ZrO.sub.2 precursors precipitated with NaOH and Na.sub.2CO.sub.3/NaOH at pH 10.5 and 7 Average pore Specific BET Average pore volume/ Example Sample surface/m.sup.2g.sup.1 diameter/nm cm.sup.3g.sup.1 C1 OH-10 119 2.7 0.08 C2 OH-7 111 2.4 0.07 C3 CO.sub.3-10 38 6.7 0.06 1 CO.sub.3-7 114 3.1 0.09

[0068] The degrees of reduction derived from TPR experiments were approximately 100% and are summarized in Table 3 together with the reduction temperatures and specific copper surface areas derived from N.sub.2O reactive frontal chromatography (RFC) performed with the reduced Cu/ZrO.sub.2 catalysts. Obviously, CuO was fully reduced to metallic Cu. The reduction temperatures of these catalysts were shifted depending on the chemical nature of the oxidic Cu precursor. The lowest reduction temperature of 399 K was found for CO.sub.3-7 followed by the reduction temperature of 407 K for OH-10. For OH-7, a reduction temperature of 415 K was detected, whereas the reduction profile for CO.sub.3-10 was found to extend over a broad temperature range with a peak at 429 K. Thus, the reduction temperature was 30 K higher than that of CO.sub.3-7. The reduction temperature of pure CuO which is not shown in this work is estimated to 526 K. The specific Cu surface areas were in the range of 1.4 m.sup.2g.sub.cat.sup.1 to 5.2 m.sup.2g.sub.cat.sup.1.

TABLE-US-00003 TABLE 3 TPR and N.sub.2O-RFC results of CuO/ZrO.sub.2 catalysts precipitated with NaOH and Na.sub.2CO.sub.3/NaOH at pH 10.5 and 7 Degree of Reduction Specific Cu surface Example Sample reduction/% temperature/K area/m.sup.2g.sub.cat.sup.1 C1 OH-10 96 407 1.4 C2 OH-7 100 413 2.1 C3 CO.sub.3-10 100 429 4.0 Ex. 1 CO.sub.3-7 100 399 5.2

[0069] Hydrogenation

Example 2 and Comparative Examples C4-C6

[0070] Microreactor Setup:

[0071] The hydrogenation of ethyl acetate and the IR studies were performed in a stainless steel microreactor flow setup with coupled FT-IR.

[0072] The setup has three major sections: gas supplies, reaction chamber, and on-line analysis using a quadrupole mass spectrometer (QMS). The piping is made of stainless steel, which is heated to 383 K to prevent condensation. The gas flows are regulated by calibrated mass flow controllers (MFCs) and a combination of pneumatic and manual Valco valves. The flow rates, the pneumatic Valco valves, as well as the reactor temperature and the heating rate are controlled by LabView software. Through LabView, there is the possibility to program sequences. Therefore, the pre-treatment and the hydrogenation is performed equally for each catalyst. The use of a saturator allows the vaporisation of a liquid like ethyl acetate, ethanol, and acetaldehyde into the gas phase. The saturator is kept at 273 K by a Lauda Ecoline RE112 cryostat with ethylene glycol as the cooling fluid. The QMS was calibrated using the following gases: 3.2146% ethyl acetate in He (99.9999%), 1.5710% ethanol in He (99.9999%), 43.8451% acetaldehyde in He (99.9999%), 10% CO (99.997%) in He (99.9999%), 4% CO.sub.2 (99.9995%) with 1% Ar (99.9999%) in He (99.9999%), and 2% H.sub.2 in He (both 99.9999%). A glass-lined U-shaped stainless steel tube with an inner diameter of 4 mL is used as a reactor (MR) that is placed in an aluminium block oven for heating with a maximum temperature of 850 K and a maximum heating rate of 20 K. 100 mg of catalyst with a consistent particle size of 250-355 m sieve fraction is loaded into the reactor between two glass wool plugs. The temperature during the pre-treatment and reaction is measured by a thermocouple that is inserted directly into the catalyst bed. The thermocouple for the temperature regulation is set in the aluminium block oven. The temperature regulation is performed by a Eurotherm controller and LabView. The setup is coupled with a Nicolet Nexus FT-IR spectrometer, which contains a nitrogen-cooled mercury cadmium telluride (MCT) detector and a DRIFTS cell with ZnSe windows. The temperature of the cell and the heating rate is controlled by Eurotherm and LabView. The FT-IR data is collected and processed through the Omnic software. The reaction chamber also contains a high-pressure unit

[0073] (HPU) and connections for attachment of a portable reactor (PR) to the setup; which were not utilized in this study. The quadrupole mass spectrometer (QMS, Balzers GAM422) for the time-resolved quantitative on-line gas analysis is composed of a crossbeam ion source and a secondary electron multiplier (SEM). The use of the QMS allows for simultaneous detection of all reactants and products by using the Quadstar software for calculating conversion and yields.

[0074] Hydrogenation: The hydrogenation of ethyl acetate was performed in the microreactor flow set-up described above. 100 mg catalyst was loaded in a glass-lined stainless steel U-tube reactor. The catalyst was gently reduced in 10 ml\per of a flow of 2% H.sub.2/He with a temperature plateau at 398 K to avoid sintering. The maximum temperature during reduction was set to 573 K. For the hydrogenation of ethyl acetate, the reduced catalyst was heated from room temperature to 513 K with 0.5 K/min in a gas flow of 50 ml/min containing 1% ethyl acetate and 68% hydrogen. After keeping the maximum temperature for 1 h, the catalyst was cooled to room temperature with 0.5 K/min.

[0075] The catalytic activity of the Cu/ZrO.sub.2 catalysts was assessed in the hydrogenation of ethyl acetate (EtAc) to ethanol (EtOH). The degrees of ethyl acetate conversion and the yields of ethanol at a reaction temperature of 513 K are summarized in Table 4. The highest conversion of ethyl acetate was observed for CO.sub.3-7 with 50% and an ethanol yield of 41%. Furthermore, also OH-10 was highly active with a conversion of 42% and 35% ethanol yield. Only half the conversion of OH-10 was achieved with OH-7. The lowest activity was obtained with CO.sub.3-10 with a conversion of 18% and a yield of 15%.

TABLE-US-00004 TABLE 4 Degrees of conversion of ethyl acetate and yields of ethanol at 513K and the calculated Cu particle sizes derived from the XRD patterns after reaction Cu particle Example Catalyst X.sub.EtAc/% Y.sub.EtOH/% size/nm C4 OH-10 42 35 5 C6 OH-7 20 16 4 C6 CO.sub.3-10 18 14 9 2 CO.sub.3-7 50 41 5