WO2011104738A2

WO2011104738A2 - Process for the production of ethyl-acetate from ethanol

Info

Publication number: WO2011104738A2
Application number: PCT/IT2011/000042
Authority: WO
Inventors: Elio Santacesaria; Martino Di Serio; Riccardo Tesser; Giuseppina Carotenuto
Original assignee: Eurochem Engineering S.R.L.
Priority date: 2010-02-24
Filing date: 2011-02-18
Publication date: 2011-09-01
Also published as: ITNA20100009A1; WO2011104738A3

Abstract

Aim of the present invention in general is to use innovative catalysts of copper chromite/metallic copper/alumina/barium chromate for producing ethyl acetate and pure hydrogen from ethanol. Still another aim of the present invention is the more specific one of a process, which by using the above described catalysts allows a high selectivity and a high productivity to be obtained when producing ethyl acetate and pure hydrogen from ethanol.

Description

Process for the production of ethyl-acetate from ethanol

Field of the Invention

The invention relates to the production of ethyl acetate and pure hydrogen from ethanol by means of the use of catalysts of copper chromite/metallic copper/alumina/barium chromate.

Prior Art

It is well known from the literature the ability of copper catalysts to dehydrogenate ethyl alcohol to yield acetic aldehyde (Inui et al., J. of Mol. Cat. A: Chem. 216, 147-156 (2004)) according to the reaction:

C H_sOH(g)→ CH₃€HQ(g) + ₂

or either ethyl acetate (Franckaerts et al., Chem. Eng. Sci. 19, 807-818 (1964); Fujita et al., React. Kinet. and Cat. Lett. 73, 367-372 (2001); Isawa et al, Bull, of the Chem. Soc. of Japan 64, 2619-2623 (1991)) according to the total reaction

2C_SH₅ O'H→ CH₃COOC^H_s + 2H_s

As it can be seen, hydrogen is obtained as a by-product which can be easily isolated so that it is produced pure. As a matter of fact, with respect to the classic process by steam reforming, no CO is produced. Both ethyl acetate and pure hydrogen have a number of uses, the former as a universal solvent and the latter to feed the combustion cells without the problem of CO presence which poisons the electrodes.

The copper catalysts, due to a peculiar morphology, to the presence of convenient activators and promoters, and to well defined operative conditions, can determine the preeminent formation of acetic aldehyde or either of ethyl acetate. In particular, to promote the production of ethyl acetate different catalysts have been proposed in the literature (Tu et al. J. of Chem. Techn. and Biotechn. 59, 141-147 (1994); Tu et al J. of Mol. Cat. 89,179-189 (1994 ); Kanoun et al., J. of Mol. Cat. 79, 217-228 (1993)) which have shown a fair or good selectivity in appropriate operative conditions, but often problems have arisen due to: (i) catalyst stability, which loses selectivity mostly due to the copper sintering; (ii) selectivity, as acetic aldehyde, which certainly is a reaction intermediate, can originate condensation-dehydrogenation reactions with formation of acetic aldole, cro tonic aldehyde, butandiole, 4-idrossi-butanone, butanol, propanol and acetone.

To stabilize the catalyst, adequate supports are introduced, such as silica (Tu et al. Ind. and Eng. Chem. Res. 37, 2618-2622, (1998); Tu et al. Ind. and Eng. Chem. Res. 40, 5889-5893 (2001); Chang et al. App. Catal. 304, 30-39 (2006)) or alumina (Isawa et al. Bull, of Chem. Soc. of Japan 64, 2619-2623 (1991); Inui et al. App. Catal. A: General 237, 53- 61 (2002)).

Anyway, the presence of acidic sites determines a drop in the selectivity for the ethyl acetate formation, with the appearance if byproducts which are difficult to be separated. To partially get around this inconvenience, in some papers it was proposed to poison the acidic sites by using basic components in the formulation (Inui et al., J. of Mol. Cat. A: Chem. 216, 147-156 (2004)) or either the use of silver (GB 0327514.6 (2003)).

Anyway, Tu et al., (1998) evidenced that for the supported copper catalysts, it is not advisable to use barium oxide as the activator since the activity is slightly improved but the de-activation rate is remarkably increased.

As a matter of fact, it is known that the catalysts containing very dispersed metallic copper are active but not very selective (Kenvin et al. J. of Cat., 135, 81-91 (1992)) and, in addition, get very easily deactivated (Kanoun et al. App. Cat., 70, 225-236 (1991)). The deactivation is less evident in the presence of hydrogen.

For example, in the application EP 0992482 the catalyst E408TU is used which is available from Mallickrodt Speciality Chemicals, Inc. (82% in weight copper oxide, 8% alumina) with ethanol conversions in the range 23-33% and a selectivity to ethyl acetate in the range between 90 and 76% respectively.

More stable are the catalysts wherein the precursor is copper chromite. The prerogative of copper chromite in this reaction has also been known for quite some time (Church et al. Ind. and Eng. Chem. 43, 1804-1811 (1951); Franckaerts et al. Chem. Eng. Sci. 19, 807-818 (1964); Tu et al. J. of Chem. Techn. and Biotechn. 59, 141-147 (1994); Tu et al. J. ofMol. Cat. 89,179-189 (1994)).

As a confirmation of the low selectivity (most of all at high conversions) of the copper chromite-based catalysts the results of patent EP 0201105 can be reported, which describes the use of copper chromite catalysts with the possible presence of barium oxide: for conversions around 25-26% the selectivity to ethyl acetate is 95-96%, but for conversions around 50% the selectivity gets down to 80-85%. In addition, in EP 0201105 it is said that the efficiency of the reaction is not a function of the catalyst, a suggestion which, combined with Tu et al. (1998), advises against the addition of other metals to the couple Cu/chromite. In EP 0201105 it is said that it is the co-feeding of hydrogen and ethanol that improves the selectivity, in addition the indicated hydrogen concentration is definitely high (0.3-6 mol Eb/mol EtOH). This is supported by the observation that the presence of barium oxide reduces the catalysts activity in the formation of acetic aldehyde, which is the intermediate product for the formation of ethyl acetate; actually, for example Peloso et al. (La Chimica e L'Industria, 58(10) 687-691 (1976)) report that, in the same reaction conditions, a catalyst based on copper chromite only gives a, ethanol conversion of 69,7%, while in case of a copper chromite and barium oxide catalyst the conversion gets down to 55,8%.

Copper chromite catalysts without the presence of barium were claimed as more selective in the dehydrogenation reaction of ethanol to acetic aldehyde and acetic acid also in patent US 4,220,803. Notwithstanding the efforts made in the search for an active and selective catalyst, the formation of by-products of the prior art stays non negligible, so that some processes (GB 2357505; US 6809217; US 7553397) provide, in addition to the reaction step which allows to obtain ethyl acetate, a further hydrogenation step to transform some of the impurities into products which are more easily separated.

It is, therefore still unsolved the issue of the identification of activators/promoters of copper chromite-based catalysts useful for improving their selectivity to ethyl acetate to such a level that the hydrogenation step described before becomes useless.

It has now been found that a catalyst comprising the combination of copper chromite/metallic copper/alumina/barium chromate allows one to obtain high conversions with a high selectivity to ethyl acetate, as evidenced by the experiments herein described.

Summary of the Invention

Aim of the present invention is to generally use catalysts comprising the combination of copper chromite/metallic copper/alumina/barium chromate, for the production of ethyl acetate and pure hydrogen from ethanol.

Still another aim of the present invention is the more specific one of a process which, by using the catalysts described above, allows an elevated selectivity and productivity to obtain ethyl acetate and pure hydrogen from ethanol.

These and other aims, which will be evident from the following description of the invention, are achieved by the process according to the herein appended claims. Description of the Figures

Figure 1 represents the diagram of the plant used for the synthesis of ethyl acetate and hydrogen.

Detailed Description of the Invention

The reaction is carried out in one single step in a tubular reactor, using catalysts based on copper chromite/metallic copper/alumina/barium chromate which surprisingly have definitely better performances with respect to the prior art.

The composition in weight of the catalyst is preferably as follows: copper chromite from 20 to 60%, preferably from 35 to 50%; metallic copper: from 5 to 20%, preferably form 10 to 15%; alumina from 50 to 10%, preferably from 25 to 35%; barium chromate from 1 to 20%, preferably from 7 to 15%.

A possible catalyst is the commercial BASF catalyst Cu-1234 (composition in weight: about 45% of copper chromite, about 30% of alumina, about 13% of metallic copper, about 11% of barium chromate, about 1% of copper oxide).

Before use, the catalyst is suitably pre-treated for at least 1 hour by fluxing it with a mixture of hydrogen and inert gas at temperature within 100-300°C e at 1-5 bar pressure, preferably 1 bar.

The mixture contains in between 2-10% of hydrogen in volume, with a preference of 3% volume. In these conditions, most part of the copper is reduced to metallic copper, but is resistant to sintering, the main cause for de-activation.

The reaction process according to the invention is usually carried out in the presence of hydrogen which can or cannot be diluted with an inert gas. Preferably a hydrogen stream is used at 5-7% in volume, preferably about 6% in nitrogen.

It is to be pointed out that the ratio hydrogen/ethanol is definitely smaller than the one disclosed in EP 0201105 (0.3-6 mol H₂/mol EtOH). This is in favour of the possibility to obtain higher conversions, being the reactions involved equilibrium dehydrogenation reactions and, therefore, not being favoured by the presence of hydrogen. In the process of the invention it is preferable to keep the hydrogen/ethanol ratio in the range 0.001-0.050 mol H₂/mol EtOH, preferably 0.001- 0.030, more preferably 0.0015-0.010, most preferably 0.0020-0.0080 mol H2 mol EtOH. The reaction, moreover, is favoured for its activity and selectivity by a moderate pressure, 10-40 bar with a preference for 15-30 bar and a temperature of 180-260 with a preference for 220- 240°C.

Preferred contact times of ethanol with the catalyst tipically are in the range 20-500 ghmol ¹, preferably 30-150 ghmol -¹.

By using the catalysts and the operative conditions described above a good activity and a very high selectivity to ethyl acetate are surprisingly obtained, combined with a noteworthy stability of the catalyst. All the tests reported in Table 1 were carried out with the same catalyst, in average each test lasted 8-10 hours, as a consequence the catalyst was kept working for about 240 hours.

With the catalysts and the operative conditions mentioned before a negligible quantity of by-products. Actually, the only by-product present in a significant quantity is acetic aldehyde, which can easily be recovered and recycled within the plant itself. So, it will not be necessary in the industrial plant to provide a hydrogenation section for the by-products, with evident and notable advantages with respect to the current technology which widely justify the present invention. The catalyst peculiarity is in its composition, which provides the presence of metallic copper/copper chromite/alumina and barium chromate at the same time. This type of composition had never been used before and surprisingly the performance obtained are definitely better with respect to the prior art both in terms of yield and selectivity, and in terms of purity of the hydrogen obtained (no CO), which can be used directly in the electronics industry.

In the following Examples the detailed use of catalysts based on copper chromite/metallic copper/alumina/barium chromate is described, useful for the high productivity and selectivity production of ethyl acetate and pure hydrogen, only with the aim to illustrate and not to limit the present invention.

Examples Example 1

Ethyl Acetate and Hydrogen Production. Effects of the Temperature

In this example and in the following ones a tubular, fixed-bed, stainless steel AISI-316 reactor was used, with a volume of 60 cm³ charged with 50 g of the catalyst. The catalyst used in the dehydrogenation reaction of ethanol to ethyl acetate is the commercially available BASF catalyst Cu-1234 (composition in weight: 45% copper chromite, 30% alumina, 13% metallic copper, 11% barium chromate, 1% copper oxide). The catalyst is previously treated for about 16 hrs with a mixture of ¾ (6% v/v) in N2 with a flow rate of 25 cm³/min, introduced into the reaction system by means of a flow rate regulator, to the temperature of 200°C. The ethanol is fed by means of an HPLC pump to a sprayer kept at a temperature of 200°C. The gaseous phase mixture made of ethanol, hydrogen and nitrogen is fed to the reactor. The reaction products are analyzed online or condensed and analyzed by means of a gas chromatographer. The simplified plant diagram is shown in Figure 1 wherein the meaning of the abbreviations is: Al- Ethanol reservoir; A- 2 HPLC pump for the ethanol; A3, A5- Non Return Valves; A4- safety valve; A6- flow rate regulator; A7- H2 mixture in N2; A8- pre-heater and pre-mixer; A9- tubular, fixed-bed reactor; A10- pressure regulator; All- heat exchanger; A13, A14- product collecting reservoir; A12, A15- liquid nitrogen reservoir; SI, S2, S3- temperature sensor; S4, S5- pressure sensor.

Tests at different temperatures were carried out, 200°C (test 1), 220°C (test 2), 240°C (test 3) and 260°C (test 5). These tests were carried out at a constant pressure of 20 bar and at the constant contact time of 97.45 ghmol ¹. The results reported in Table 1 show the conversions and the selectivities obtained in said conditions.

From the results of Table 1 it is evident that the rise in temperature causes a rise in the ethanol conversion. On the other hand, with the rise in temperature a formation of byproducts which lowers the selectivity to ethyl acetate is observed. The best results in terms of conversion and selectivity are obtained with temperature values of 220-240°C.

Example 2

Ethyl acetate and Hydrogen production. Pressure effects

Tests were carried out following the same procedures described in Example 1. The reaction was carried out with constant contact times of 97.45 ghmol"¹ and at a constant temperature of 220°C, with a variable practice pressure (10 bar (test 5) and 30 bar (test 6)). In Table 1 the operative conditions used for these tests and the results obtained are summarized.

By comparing the results of test 2 (20 bar), test 5 (10 bar) and of test 6 (30 bar), carried out in the same conditions apart from the different pressure, it can be concluded that while the activity, even though modestly, rises with the pressure, the selectivity is maximal at around 20 bar. Table 1

Operative conditions and Results obtained in the tests carried out in

Examples 1-5.

Operative Tests

Conditions 1 2 3 4 5 6 7 8 9 10

Temperature _{2QQ 22Q 24Q 26Q 22Q 22Q 220 200 200 2}40

Pressure 20 20 20 20 10 30 20 30 10 10 bar

Ethanol flow _, 0.5 0.5 0.5 0.5 0.5 1.5 0.1 0.5 0.5 rate cm³/min

mixture 6% 25 25 25 25 25 25 25 25 25 25 cm³/min

H./Ethanol

mol/mol x 7.4 7.4 7.4 7.4 7.4 7.4 2.4 36.8 7.4 7.4

1000

Ethanol

contact time ^ 97.45 97.45 97.45 97.45 97.45 32.48 487.3 97.45 97.45 ghmoH

Product Analysis (%mol)

Ethanol 49.58 57.33 64.83 70.63 51.44 63.21 47.21 60.08 45.3 61.8 6£ Conversion

Ethyl- etanoate 98.79 99.33 99.58 94.25 96.10 96.84 96.91 97.65 96.2 96.5 93 Selectivity

aldehyde 1.21 0.66 0.42 0.52 2.90 0.59 1.92 0.58 3.2 1.1 1 Selectivity

Selectivity 0.01 - 5.23 1 2.57 1.17 1.77 0.6 2.4 5 (Other)

Operative Tests

Conditions 12 13 14 15 16 17 18 19

Temperature

200 260 240 260 220 240 260 240 °C

Pressure

bar 30 30 20 20 30 30 30 20

Ethanol flow

0.5 0.5 1.5 1.5 1.5 1.5 1.5 0.5 rate cm'/min

mixture 6% 25 25 25 25 25 25 25 25

cm³/min

Hii/Ethanol

7.4 7.4 2.4 2.4 2.4 2.4 2.4 7.4 mol/mol x 1000

Ethanol

contact time

ghmoH 97.45 97.45 32.48 32.48 32.48 32.48 32.48 97.45

Product Analysis (%mol)

Ethanol

67.2 61.2 67.5 42.4 60.9 65.6 61.2

Conversion

Ethyl-etanoate

96.0 96.1 95.2 96.1 95.8 93.8 98.5

Selectivity

Acetic

aldehyde 1.3 0.8 1.8 1.7 2.0 2.1 2.6 0.9

Selectivity

0.8 3.2 2.1 3.0 1.9 2.1 3.6 0.6 (Other)

Example 3

Ethyl acetate and hydrogen production. Effects of contact time.

A test was carried out (test 7) following the same procedures described in Example 1. Test 7 was carried out in the same conditions as in Test 2 of Example 1, but for a shorter contact time (32.48 ghmol ¹ instead of 97.45 ghmol ¹). In Table 1 are summarized the operative conditions adopted for this test and the results obtained.

By comparing the results of Test 2 (ethanol contact time 97.45 ghmol ¹) and those of Test 7 (ethanol contact time 32.48 ghmol -¹), it can be concluded that by rising the contact time a significant rise in the conversion of ethanol and in the selectivity to ethyl acetate to the detriment of acetic aldehyde is obtained, which is a byproduct deriving from the first dehydrogenation step of ethanol.

Example 4

Production of ethyl acetate and hydrogen. Verification of catalyst's stability.

In this Example the performance if the system under study with the variation of catalyst's stability are studied. Test 19 was carried out in the same conditions as test 3 described in Example 1. From the results shown in the Table, it is evident that, notwithstanding the long operating times of the catalyst (160 h), only a small decrease in activity and selectivity was seen, which anyway stay high (selectivity above 93% for conversions above 60%).

Example 5 (Comparison Example)

As a comparison, example reaction tests were carried out with different copper-based catalysts. In particular, two other commercially available catalysts were used:

A) BASF K-310 (CuO/ZnO/Al₂0₃ 40/40/20% weight) in cylindrical pellets with 4.5 mm diameter.

B) Sud-Chemie T-4466 (a copper chromite catalyst, CuO/Cr₂0₃ 53/45 %) in tablets of 3x3 mm.

In Table 2 are reported the test conditions and the results obtained by comparison with those of the catalyst with metallic copper/copper chromite/alumina/barium chromate shown in Table 1. The hydrogen/ethanol feeding ratio is the same as the one used in Examples 1-4. As it can be seen, the results shown in Table 2 are definitely worse than the ones of Table 1, confirming that the new formulation gives particularly active and selective catalysts to obtain ethyl acetate.

Table 2

Operative conditions and Results obtained in the Tests of Example 5 Operative Tests

Conditions 1 2 3 4

Catalyst A B B B

Temperature

200 200 220 260

°C

Pressure bar 20 20 20 20

Ethanol

contact time 98.70 98.23 98.23 98.23 ghmol^"1

Products Analysis (%moD

Ethanol

29.2 39.63 50.4

Conversion

Ehyl-etanoate

96.8 95.8 95.8

Selectivity

Acetic

aldehyde

selectivity

Selectivity

26.7 1.0 1.6 2.6

(other)

Claims

1. Use of a catalyst comprising a combination of copper chromite/metallic copper/alumina/barium chromate for producing ethyl acetate and CO-free hydrogen from ethanol.

2. The use according to the previous claim wherein the combination has the following % composition in weight: copper chromite from 20 to 60%, preferably from 35 to 50%; metallic copper: from 5 to 20%, preferably from 10 to 15 %; alumina from 50 to 10%, preferably from 25 to 35%; barium chromate from 1 to 20%, preferably from 7 to 15%.

3. A process for producing ethyl acetate from ethanol in one step, comprising the step of contacting ethanol with a catalyst comprising a combination of copper chromite/metallic copper/alumina/barium chromate.

4. The process according to claim 3 wherein ethanol is fed together with hydrogen and possibly an inert gas at a partial pressure of the hydrogen comprised between 0.1 and 4 bar, preferably between 0.4 and 2 bar.

5. The process according to claims 3-4 carried out at a temperature maintained within the range 150-280°C, preferably 200-240°C and at a pressure maintained within the range 10-40 bar, preferably 15-25 bar.

6. The process according to claims 3-5 carried out with contact times of the reagent ethanol with the catalyst kept within the interval 20-5000 ghmol ¹, preferably 40-100 ghmol ¹.

7. The process according to claims 4-6 carried out with a^v hydrogen/ethanol ratio within the range 0.001-0.050 mol H mol EtOH, preferably 0.001-0.030, more preferably 0,0015-0.010, most preferably 0.0020-0.0080 mol HVmol EtOH.

8. The process according to claims 3-7 wherein the catalyst is preventively subjected to a pre-treatment with a mixture of hydrogen and inert gas, carried out at pressures of 1-5 bar, preferably 1-2 bar, and at 100-300°C, preferably 200-250°C.

9. Process according to claim 8 wherein the composition of the mixture hydrogen/inert in molar fraction is comprised in between 0.01 and 1, preferably 0.03-0.1.