WO2013060580A1

WO2013060580A1 - Method for producing vinyl acetate

Info

Publication number: WO2013060580A1
Application number: PCT/EP2012/070261
Authority: WO
Inventors: Christoph RÜDINGER
Original assignee: Wacker Chemie Ag
Priority date: 2011-10-25
Filing date: 2012-10-12
Publication date: 2013-05-02
Also published as: DE102011085165A1

Abstract

The invention relates to a method for producing vinyl acetate, wherein ethylene is reacted with acetic acid and oxygen into vinyl acetate in a heterogeneously catalyzed oxacylation reaction on a noble metal catalyst. The invention is characterized in that the ethylene has been obtained by dehydrating ethanol of biological origin, and the ethylene inflow to the reactor has a CO concentration of 30 to 500 parts per million volume (ppmv).

Description

Process for the preparation of vinyl acetate

The invention relates to a process for the preparation of vinyl acetate.

Vinyl acetate is an important monomer for the industrial production of vinyl acetate homopolymers and vinyl acetate-ethylene copolymers. Vinyl acetate can be prepared by various methods. The most economical and correspondingly dominant process today is the oxacylation of ethylene with acetic acid and oxygen in a heterogeneously catalyzed gas-phase process. Catalysts used in this process are noble metal-containing catalysts (for example WO 2010/056299 or ÜS Patent Application 20100022796).

The production of ethylene from fossil raw materials is especially based on hydrocarbons such as ethane, butane, naphtha (petroleum refining) and the purification, ie the removal of impurities specific to the production process, of the ethylene thus obtained, to marketable quality levels. Due to the finiteness of fossil raw materials and the ever-increasing prices of crude oil-based products, efforts have been made to produce chemical starting compounds, especially ethylene and vinyl acetate, from renewable raw materials. The currently preferred process for producing ethylene for this purpose is the dehydration of ethanol obtained from vegetable raw materials. Processes for the production of ethylene from ethanol are described inter alia in WO 2008/138775 and WO 2008/062157. Starting from this ethylene, chemical intermediates may include, but are not limited to, vinyl acetate and polymers such as e.g. Polyethylene or the polyvinyl acetate-ethylene copolymers are produced on a renewable raw material basis (WO 2010/010291, WO 2010/055257, CN 101798265 machine translation).

Many processes that use ethylene as a starting material use catalysts. These catalysts are impaired by catalyst poisons in their function. Ethylene for these processes must therefore meet special purity requirements. customarily example, crude ethylene is purified by cryogenic distillation. For this purpose, the crude gas is first compressed in a 4- to 5-stage ompression process to a pressure of 3.2 to 3.8 MPa and then subjected to a very complex process of acid gas washing and drying in order to prevent interfering impurities during the low-temperature pressure distillation to separate, eg C0 ₂ <0.2 ppm. The ethylene is then fractionated by 100 at top pressures of 1.7 to 2.8 MPa and top temperatures of 0 to -50 ° C. with high reflux ratios (about 4) and very high soil numbers (Heinz Zimmermann and Roland Walzl, Ethylene, et al. Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH Verlag GmbH & Co. KGaA., Weinheim, Germany, Vol.12, pp. 531 to 583). This complex ethylene purification determines a high proportion of ethylene production costs.

In the production of ethylene from ethanol of vegetable origin, other impurities are produced than in the established production of ethylene in crackers from hydrocarbons. There has been no lack of attempts to use this obtained from ethanol ethylene directly without further purification

(CN 101798265 machine translation). In the context of the experiments leading to the present invention, it has been found that the ethylene obtained by dehydration by known methods in ethanol contains impurities which inhibit the use of this ethylene in noble metal catalyst processes (Pd.

Au, Rh, Ir, Ru, Pt), since these noble metal catalysts are partially or even completely poisoned.

Ethylene from the prior art dehydration of ethanol (Heinz Zimmermann and Roland Walzl, Ethylene, Ullmanns

Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany Vol.12, pp. 531 to 583;

Kochar et al. , CEP, June 1981; Bijlani et al. Chemical Age of India, Vol. 32, No. 5 (1981); Arenamnart et al. Internat. J. of Applied Science and Engineering, (2006) 4, 1: 21-32, US

1,914,722; US 3,244,766; U.S. 4,134,926, U.S. 4,423,270; US

No. 4,698,452, US Pat. No. 4,670,620) usually contains 100 to more than 1000 directly from the production process without further purification ppmv (parts per million by volume) carbon monoxide. The higher the productivity and conversion rate in ethanol dehydration, the higher the CO content in the ethylene produced will usually be. This concentration of carbon monoxide contamination is too high for direct use of ethylene in noble metal catalyst processes. Carbon monoxide in such a high concentration poisons the noble metal centers of the catalysts and drastically reduces the activity of the catalysts. The target reaction therefore comes to a standstill or is slowed down considerably, which makes the economics of the processes uneconomical when using such an ethylene with too high a carbon monoxide content.

In the use of ethylene prepared by dehydration from ethanol of biological origin in the oxacylation of ethylene with acetic acid and oxygen to vinyl acetate with noble metal-containing catalysts (Pd, Au, Rh, Ir, Ru, Pt), especially On Pd / Au catalysts, especially on Si0 ₂ catalyst carriers, there is a drastic reduction in the space-time performance {RZL s. Comparative Example). The space-time performance of the catalyst is, in addition to the selectivity, the decisive factor for the economic efficiency of the process, since a 50% reduction of the RZL means a halving of the production capacity of a plant.

Established market specifications for ethylene from fossil fuels for general industrial use are between 1 and 10 ppmv CO upper limit (Heinz Zimmermann and Roland Walzl, Ethylene, Ulimanns Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH Verlag GmbH & Co. KGaA. , Weinheim, Germany, Vol.12, pages 531 to 583 and Eastman's sales specifications up to 5 ppm CO, GHC standard specification Ethene 3.5 10 ppm CO, Petkim Ethylene 2 ppm CO, Sinopec Premium grade max. 1 ppm CO, Sabic max 2 ppm CO, Sunoco max 5 ppm CO, brazil max 2 ppm CO). It is known in the art that for the use of ethylene as starting material for the production of vinyl acetate, a quality specification of 2-10 ppmv CO is considered sufficient (Chemical Process Design: Computer Aided Case Studies, Wiley ~ VCH Verlag, Weinheim, ISBN 978-3-527-31403-4, pp. 287 to 311). However, the removal of carbon monoxide to such a low concentration is costly and expensive. Thus, the ethylene derived from the ethanol dehydration has, without further measures, too high a carbon monoxide content to be used directly in processes with noble metal catalysts without additional purification or reduced productivity in the subsequent processes. The aim of the invention was to provide a most economical process for the production of vinyl acetate using a noble metal catalyst and ethylene prepared from ethanol, which was obtained from renewable raw materials available.

This object is achieved by a process in which in a reactor ethylene is reacted with acetic acid and oxygen in a heterogeneously catalyzed oxacylation reaction on a noble metal catalyst to vinyl acetate, characterized in that the ethylene was obtained by dehydration of ethanol of biological origin and the ethylene feed to Reactor has a CO concentration 30 to 500 part per million volume {pprnv). Preferably, the CO concentration is 50 to 150 pprnv.

Preferably, the catalyst contains one or more of the metals Ru, Rh, Pd, Ir and Pt, more preferably the catalyst contains palladium or palladium / gold.

Preferably, the ethylene is recovered from ethanol by dehydration, the dehydration process being modified such that the carbon monoxide content in the ethylene produced is below 500 ppmv, more preferably below 150 ppmv, more preferably below SOppmv, without further external purification. The CO content in the ethylene from the dehydration of ethanol can be adjusted in various ways to a value according to the invention. By dilution with a stream having a lower CO content, the CO content in ethylene from the dehydration of ethanol of biological origin can be reduced to the value required according to the invention, so that no disruptive blocking of the noble metal centers on the catalyst occurs more. A concentration of CO in the ethylene which is sufficient according to the invention for the process for the oxacylation of ethylene with acetic acid and oxygen to vinyl acetate is between 50-500 ppmv CO, depending on the reaction conditions in the oxacylation process and the specific properties of the oxacylation catalyst. Suitable reaction conditions for the oxacylation process are preferably a reaction pressure of 1-25 bar overpressure, preferably 6-16 bar overpressure, particularly preferably 8-10 bar overpressure. The oxygen concentration in the reaction gas before the reactor at the inlet to the catalyst bed must be below the oxygen limit concentration at which the reaction gas mixture is no longer flammable. Depending on the temperature, the pressure and the rest of the gas composition, this oxygen limit concentration is in the range of 10-12% by volume of oxygen under the said usual reaction conditions of the oxacylation. Accordingly, an oxygen content below 10% by volume is preferred for the oxacylation, and between 5-8% by volume is particularly preferred. The ethylene content in the reaction gas is between 25 and 80% by volume. The coolant temperature of the reactor is preferably selected in the range between 100 and 200 ° C, wherein a catalyst temperature of preferably 120 to 200 ° C should set.

Another way to reduce the CO content of ethylene to a concentration according to the invention is the conversion of CO in C0 ₂ , since C0 _2, the catalyst for the production of vinyl acetate significantly less affected than CO. This conversion can be stoichiometric over easily oxygen-emitting substances, or with the help of a catalyst with other oxygen carriers or gaseous oxygen. Suitable methods are, for example, from US 7,544,634; US

6,548,446; US 6,849,571; US 7,560,410 or US 5,045,297.

Another way to reduce the CO content of ethylene to a concentration according to the invention is the conversion of CO into CH ₄ , since CH ₄ affects the catalyst for the preparation of vinyl acetate much less than CO. For this purpose, the gas mixture to be treated is treated with reducing, hydrogen-transferring reagents, preferably a hydrogenation or methanation catalyst and molecular hydrogen. Such methods are for example US

4,172,053, US 2010/0093525, or US 7,560,496.

However, the carbon monoxide can also be separated with a liquid or solid absorbent directly or after conversion of the CO to C0 ₂ or another compound from the ethylene. Preference is given to using an adsorbent which binds carbon monoxide more strongly than ethylene (C ₂ H). Particularly suitable are liquid or solid adsorbents containing copper (US

4,277,452; US 2010/0115994; US 5,922,640; US 4,950,462; US 3,658,463; JA Hogendoorn et al. , The Chemical Engineering Journal 59 (1995) 243-252). Suitable commercial adsorbents include the Festadsorbentien, type PuriStar ^® R3-16 commercially available from BASF and PolyMax ^® 301 commercially available from Süd-Chemie AG.

Carbon monoxide and ethylene can also be separated via their different membrane permeation, or the carbon monoxide content in the ethylene can be reduced. It is preferable to use a membrane that allows carbon monoxide to pass more easily against C ₂ H.

All experiments described in the examples were carried out in a reaction system shown in FIG. 1 at a reaction overpressure of 8.8 bar. About the dosage 1 acetic acid, the dosage 2 ethylene and the dosage 3 argon fed to an evaporator. Consisting of homogeneously mixed gas Ar, C ₂ H ₄ and CH ₃ COOH are mixed in the mixing nozzle 4 with oxygen 4a. The gas mixture of O ₂ , C ₂ H ₄ , Ar and CH ₃ COOH is fed to a tubular reactor 5 with oil-cooled outer wall (oil cooler 5 a) containing a fixed-bed catalyst bed 6. The catalyst used is an alloy catalyst of the Pd / Au type as described, for example, in US 20100022796, WO / 1998/052688, US Pat. No. 5,691,267 or US Pat. No. 6,207,610, preferably on an annular, purely mesoporous SiO _{2 support} . By passing the gas mixture over the catalyst, vinyl acetate is produced. The vinyl acetate-containing gas mixture is passed via the line 7 to the condenser 8. In the condenser 8, a vinyl acetate-depleted gas phase is obtained which is fed to an exhaust gas combustion 9 after an analytical determination of the components of this mixture. The liquid phase from the condenser 8 is discharged via line 10 and fed to the determination of the water, acetic and vinyl acetate content and mass flow of the further use.

The room-temperature performance for vinyl acetate was calculated in all examples according to the following formula: ZLVA _C = vinyl acetate production [g / h] / catalyst volume [1]

The selectivity of the reaction to vinyl acetate was calculated in all examples as follows:

S _V Ac = vinyl acetate production [mol / h] * 4 / (vinyl acetate production [mol / h] * 4 + C0 ₂ - production [mol / h]) No carbon monoxide could be detected in the reactor effluent (detection limit 10 ppmv). The technically usual recycling of the vinyl acetate process with recycling of the noncondensable fractions of the reactor effluent (ethylene / argon / CO ₂ ) to the reactor inlet is therefore also with a carbon monoxide content of 30-500 ppmv without accumulation of the carbon monoxide in the recycle gas of the process possible. Example 1 (Comparative Example not according to the invention) shows the performance achieved in the oxacylation of ethylene with acetic acid and oxygen when ethylene from fossil sources with a CO specification <10 ppmv is used.

Example 2 (comparative example not according to the invention) shows the performance achieved in the oxacylation of ethylene with acetic acid and oxygen when using ethylene originating from the dehydration of ethanol of biological origin, used without further purification and a CO content of 850 ppmv.

Example 3 shows the performance achieved in the 0-acylation of ethylene with acetic acid and oxygen when using ethylene derived from the dehydration of ethanol of biological origin and having a CO content of about 289 ppmv.

Example 4 shows the performance achieved in the oxacylation of ethylene with acetic acid and oxygen when using ethylene derived from the dehydration of ethanol of biological origin and having a CO content of about 278 ppmv. Example 5 (comparative example not according to the invention) shows the performance achieved in the oxacylation of ethylene with acetic acid and oxygen when using, under the experimental conditions of Examples 3 and 4, fossil sources of ethylene with a CO specification <10 ppmv.

Example 6 (according to the invention) shows the performance achieved in the 0-acylation of ethylene with acetic acid and oxygen when using ethylene derived from the dehydration of ethanol of biological origin and having a CO content of 90 ppmv.

Example 7 (comparative example, not according to the invention) shows the performance in the oxacylation of ethylene with acetic acid and oxygen is achieved when using under the experimental conditions of Example 6 (according to the invention) ethylene, which had a CO content of less than 10 ppmv.

Table 1 Summary of the test results at a reaction overpressure of 8.8 bar.

Claims

Claims:

A process for the preparation of vinyl acetate in which reacting in a reactor ethylene with acetic acid and oxygen in a heterogeneously catalyzed oxacylation reaction on a noble metal catalyst to vinyl acetate, characterized in that the ethylene was obtained by dehydration of ethanol of biological origin and the ethylene feed to the reactor CO concentration 30 to 500 part per million volume (ppmv).

2. The method according to claim 1, characterized in that the CO concentration is between 50-150 ppmv.

3. The method according to claim 1 or 2, characterized in that the noble metal catalyst one or more of the metals Ru, Rh, Pd, Ir and Pt, preferably palladium or palladium / gold.

4. The method according to claim 1 to 3, characterized in that the CO concentration in the ethylene by oxidation of CO to C0 _{2 is} lowered.

5. The method according to claim 1 to 3, characterized in that the CO concentration in the ethylene is lowered by hydrogenation of CO to CH ₄ .

6. The method according to claim 1 to 3, characterized in that the CO concentration in the ethylene is lowered by adsorption of CO on a liquid or solid selective adsorbent.

7. The method according to claim 5 u. 6, characterized in that the selective adsorbent contains copper.

8. The method according to claim 1-3, characterized in that the ethylene is obtained from ethanol by dehydration and the dehydration process is modified so that that the carbon monoxide content ira produced ethylene without further external purification measures below 500 ppmv, preferably below 150 ppmv, more preferably below 50 ppmv.