DE102014118966A1 - Plant, process and catalyst for the production of dimethyl ether - Google Patents

Abstract

The present invention relates to a plant and the associated process for the preparation of dimethyl ether, comprising a reactor (30) for reacting a methanol-containing starting material mixture to a dimethyl ether and water-containing product mixture over a catalyst under reaction conditions, with at least one control and / or control unit ( 50) for controlling pressure and / or temperature within the reactor (30). The at least one control and / or control unit (50) is designed such that the pressure in the reactor (30) is lower than the saturation partial vapor pressure of water under the reaction conditions.

Description

The present invention relates to a plant for the preparation of dimethyl ether, comprising a reactor for reacting a methanol-containing Eduktgemisches to a dimethyl ether and water-containing product mixture of a catalyst at reaction conditions, with at least one control and / or control unit for controlling pressure and / or temperature within the reactor. Furthermore, the invention relates to a method and a catalyst for the preparation of dimethyl ether.

Dimethyl ether (C ₂ H ₆ O, DME) is an ether with two methyl groups. High-purity dimethyl ether is used as a propellant because, in contrast to CFC hydrocarbons, it does not attack the ozone layer. Due to a cetane number of 55 to 60, dimethyl ether can also be used in diesel engines as a replacement for conventional fuel. This is of particular interest because dimethyl ether can be made from biomass.

The industrial production of dimethyl ether is carried out by acid-catalyzed condensation of methanol with elimination of water:

In this process, methanol vapor is usually passed over a dehydration catalyst-filled reactor. Embodiments of this method are, inter alia, in "Ullmann's Encyclopedia of Chemistry", 6th edition, 1998 electronic release described. The reaction is under normal conditions of 250-450 ° C equilibrium limited, the achievable conversion is about 70-90%.

The condensation reaction of methanol to dimethyl ether is an exothermic reaction. In order to achieve a sufficient conversion of the methanol to dimethyl ether and at the same time to avoid too high, the plant polluting and damaging the catalyst temperatures are typical reaction temperatures between 250 to 450 ° C.

To catalyze the condensation reaction, a catalyst having sufficient acidity for the catalytic reaction is used. Suitable catalysts are zeolites and γ-alumina (γ-Al ₂ O ₃ ).

Zeolites are crystalline aluminosilicates that are found in many modifications in nature, but also produced synthetically. The general composition of the zeolites is: M ^{n +} _{x / n} [(AlO ₂₎ ^- _x (SiO _{2) y]} ∙ zH ₂ O, where M is a cation of an alkali or alkaline earth metal.

γ-Alumina (γ-Al ₂ O ₃ ) is an oxide which can be prepared by careful heating of γ-Al (OH) ₃ (hydrargillite) or γ-AlO (OH) (boehmite) to over 400 ° C. The structure of γ-Al ₂ O ₃ consists of a cubic closest packing formed by the O ² ions in which the Al ³⁺ ions are statistically distributed over the octahedral and tetrahedral voids. This corresponds to a kind of defective spinel structure.

The US Pat. No. 6,740,783 B1 describes catalysts for the production of dimethyl ether from crude methanol. Particularly acidic and hydrophobic zeolites are used, for example USY, mordenite or ZSM. Due to the high Lewis acidity of the zeolites, the formation of hydrocarbons, especially alkanes, and coking of the catalyst has been increasingly observed.

From the US 20050038129 A1 For example, metallic catalyst systems containing copper oxide, zinc oxide and aluminum are known. The preparation of these catalysts is carried out from a slurry.

From the KR 100 966 706 B is the use of ferrite in a zeolite known.

The problem of the suitable for the production of dimethyl ether acidity of the catalyst used by utilizing the deactivation of the active centers by water is in the US 2009/0023958 A1 addressed. To solve the problem, it is proposed in this case to first pass the raw methanol-containing educt mixture over a zeolite catalyst having a high acidity and then to feed it to a less acidic catalyst, in particular γ-aluminum oxide (γ-Al ₂ O ₃ ). In addition, the reaction is carried out in an adiabatic reactor, so that the highly active zeolites initially increase the reaction temperature, which favors the selectivity of the conversion to dimethyl ether of the less active γ-alumina. Finally, an adjustment of the acidity of the catalysts by the addition of foreign ions, in particular alkali and alkaline earth metals, is proposed.

For the use of all described catalyst systems in processes and plants for the production of dimethyl ether the achievable service life is of crucial importance. The sooner deactivation of the catalytically active centers occurs, the more frequently the catalyst has to be changed or regenerated, which leads to undesirable downtimes in the production. In the industry but typically lives of at least one year, preferably 2-4 years, better> 4 years are expected.

It is therefore an object of the present invention to provide a system and a method with which the service life of a catalyst used for the preparation of dimethyl ether can be improved. The invention also provides a catalyst which exhibits an improved service life in the production of dimethyl ether.

This object is achieved with a system having the features of claim 1. For this purpose, a reactor is provided for reacting a methanol-containing Eduktgemisches to a dimethyl ether and water-containing product mixture. The educt mixture consists at least partially of methanol, preferably of methanol with a purity of A, particularly preferably purity AA. The reaction takes place under reaction conditions on a catalyst, which is preferably present in solid form. Furthermore, in the system according to the invention at least one control and / or control unit for controlling pressure and / or temperature within the reactor is provided, wherein the at least one control and / or control unit is designed such that the pressure in the reactor is lower than the saturation partial vapor pressure of water under these reaction conditions.

By the prevailing pressure in the reactor is lower than the saturation partial vapor pressure of water under these reaction conditions, a condensation of water is reliably avoided. The pressure is preferably 10% lower, more preferably 20% lower than the saturation partial vapor pressure of water under the prevailing reaction conditions. By avoiding the condensation of water on the catalyst, according to the idea underlying the invention, the service life of the catalyst can be prolonged, since obviously liquid water damages the active centers of the catalyst.

The saturation vapor pressure of a substance according to the invention corresponds to the pressure at which the liquid or solid and gaseous state of matter of the substance are in equilibrium. So there is no evaporation, sublimation or condensation. This saturation vapor pressure is dependent both on the temperature and on the composition of the substance under consideration. The saturation vapor pressure of a pure substance at a given temperature T can be deduced from the Clapeyron equation:

If it is a matter of a mixture of different substances, it is still decisive which proportions the individual substances have on the substance mixture. With regard to gaseous mixtures, these proportions are also expressed by the partial vapor pressure of the corresponding individual substances. To account for this fact, the invention speaks of the saturation partial vapor pressure, which illustrates the influence of the corresponding proportions (partial pressures) of the individual pure substances in the mixture.

Assuming that the volume of the gaseous substance is substantially greater than that of the liquid substance, the volume change on evaporation can be replaced to a good approximation by the volume of the gas. For an ideal gas, the volume can still be calculated according to the general gas equation. Taking into account these two formulations, one obtains the so-called Clausius-Clapeyron equation:

wobei p' der Dampfdruck des Reinstoffs bei der Temperatur T' ist. Wird nun der Dampfdruck p' durch den Partialdruck der entsprechenden Substanz eines Gemisches ersetzt, so erlaubt die obige Gleichung eine Ermittlung des Sättigungspartialdampfdruckes des entsprechenden Stoffes bei gegebener Zusammensetzung und Temperatur.Assuming further that the enthalpy of vaporization ΔH _v does not depend on the temperature, the Clausius-Clapeyron equation can be integrated:

where p 'is the vapor pressure of the pure substance at the temperature T'. If now the vapor pressure p 'is replaced by the partial pressure of the corresponding substance of a mixture, the above equation allows a determination of the saturation partial vapor pressure of the corresponding substance at a given composition and temperature.

Accordingly, the reaction conditions to be set, namely temperature, pressure and composition can be calculated or estimated in a first approximation by the formula III also for non-ideal (actually occurring) systems.

Due to the mutual influence of the individual reaction conditions (pressure, temperature and composition), it is possible according to the invention to specify part of the reaction conditions and to regulate the other reaction conditions, so that at a given temperature, the pressure in the reactor is lower than the saturation partial vapor pressure of water in the reaction conditions. So it can be controlled a suitable pressure and the temperature can be controlled in the reactor. Likewise, the temperature can be controlled and the pressure in the reactor controlled such that the pressure in the reactor is lower than the saturation partial vapor pressure of water at the reaction conditions. A regulation of the pressure is more dynamic and therefore the preferred embodiment.

Because of the described coupling of the individual reaction conditions, wherein the composition prevailing in the reactor is essentially determined by pressure and temperature, the control unit according to the invention is designed to regulate pressure and / or temperature within the reactor.

Preferred catalysts for the system according to the invention contain γ-aluminum oxide, since this shows good conversions and selectivities with respect to the target product dimethyl ether. The damaging effect of liquid water on a γ-alumina-containing catalyst manifests itself in the fact that there is a conversion of catalytically active γ-alumina to catalytically inactive boehmite (AlO (OH)). The system according to the invention can prevent or at least delay this structural transformation.

It has also proven to be favorable when the reactor is designed as a fixed bed reactor. Thus, a uniform flow through the catalyst can be ensured.

The plant according to the invention preferably has a reactor with at least one catalyst bed.

In an alternative embodiment, the reactor is designed as a tray reactor with at least two trays, each with a separate inlet and outlet. The different hordes allow a stepwise reaction of the reactant mixture to the product mixture and allow a high conversion of methanol with low formation of by-products to achieve in absolute terms high yields of dimethyl ether .. (Higher reaction temperatures lead to a faster implementation, but at the same time decreases the achievable Turnover due to the limitation described as the reaction is exothermic and more by-products form at higher temperatures, such as methane or carbon oxides, resulting in an optimal temperature window for highest DME yields.)

It is particularly preferred if at the respective outlet of the reactor or in a design as a tray reactor at the outlet of each tray a control and / or control unit is arranged so that the pressure in the reactor at the corresponding Horde is lower than the saturation partial vapor pressure of the water at the reaction conditions at the corresponding horde. This prevents local condensation of water and thus local damage to the catalyst.

The invention further relates to a catalyst for the preparation of dimethyl ether from a methanol-containing educt mixture according to claim 5. The catalyst according to the invention contains at least 90% by weight of γ-aluminum oxide and between 0.1 and 10, preferably 0.2 and 5% by weight. Carbon.

It has been found that the service life of the catalyst used is significantly improved by the proportion of carbon according to the invention. In particular, a conversion of the active γ-aluminum oxide to inactive boehmite (AlO (OH)) is prevented or at least slowed down. Preferably, a carbon content between 0.1 and 10, preferably 0.2 and 5 wt .-% stabilizes the active γ-alumina and slows or even prevents a conversion to the inactive boehmite.

In a preferred embodiment of the catalyst according to the invention before use in the production of dimethyl ether for at least 24 hours, preferably at least 48 hours and more preferably at least 100 hours to a temperature between 120 and 300 ° C, preferably a temperature above 180 ° C and heated with the exclusion of condensing water. This also leads to a solidification of the proportion of γ-alumina, whereby the service life of the catalyst is considerably extended.

The invention further relates to a process for the preparation of dimethyl ether having the features of claim 7.

In the process of the invention, a methanol-containing reactant mixture is reacted in a reactor on a catalyst under reaction conditions to a dimethyl ether and water-containing product mixture, wherein pressure and / or temperature in the reactor are controlled and / or controlled so that the pressure is lower than that Saturation partial vapor pressure of water under the reaction conditions.

This prevents condensation of the water in the reactor. Also in the process of the invention, it is possible to prescribe (control) part of the reaction conditions (pressure, temperature and composition) in the reactor and to adjust the other reaction conditions so that the pressure is lower than the saturation partial vapor pressure of water in the reaction conditions.

The invention further relates to a method for starting or stopping a plant for the production of dimethyl ether with the features of claim 8.

Usually plants for the production of dimethyl ether are started by a medium with reaction temperature is passed through the plant. Favorable here is the use of water vapor due to the low deployment costs. The same applies to cooling.

According to the invention, water vapor is passed through a reactor and catalyst for heating or cooling at a pressure and a temperature, the pressure and / or temperature in the reactor being controlled and / or controlled such that the pressure is lower than the saturation partial vapor pressure of water this pressure and temperature. This reliably prevents damage to the catalyst.

In the method according to the invention has been found to be favorable that the temperature in the reactor between 180 and 320 ° C, preferably 220 to 280 ° C. In this area, high conversion rates are achieved without locally reaching temperatures that could lead to increased formation of by-products such as methane or carbon oxides or even damage to the catalyst.

The pressure in the reactor is preferably between 5 and 35 bar, more preferably between 10 and 20 bar.

In order to prevent the condensation of water on the catalyst according to the invention, in a preferred embodiment the pressure at the outlet or the temperature at the inlet is regulated so that a combination results which prevents condensation in each zone of the reactor. The temperature itself then increases in the reactor or in the respective horde in accordance with the adiabatic temperature increase and the conversion achieved per reactor or per horde. At the same time, the turnover also increases the water partial pressure during passage through the reactor. The inlet temperature is chosen so low that the catalyst is still there sufficient activity for the implementation of the methanol, but at the same time a high selectivity for the formation of DME and low selectivity for the formation of undesirable by-products such as methane or carbon oxides is suppressed and just the given Pressure of the saturation partial pressure of water is never exceeded.

It is favorable to carry out the process according to the invention with a catalyst which contains at least 90% by weight of γ-aluminum oxide, since a particularly strong deactivation takes place in this catalyst by condensation of water, which can be prevented by the process according to the invention.

Preferably, the process is carried out with a γ-alumina catalyst containing between 0.1 and 10, preferably 0.2 and 5 wt .-% carbon. According to the invention, the carbon content increases the service life of the catalyst.

In a preferred embodiment of the process according to the invention, a pretreatment of the catalyst is provided in which the catalyst prior to use of the catalyst at least 24 hours, preferably at least 48 hours and more preferably at least 100 hours to a temperature between 120 ° C and 300 ° C, preferred 180 and 300 ° C was heated. Also, this pre-treatment increases the service life of the catalyst and prevents or at least slows down the conversion of the active γ-alumina to the inactive boehmite.

Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described features alone or in any combination form the subject matter of the invention, also independent of their summary in the claims or their dependency.

It shows:

1 schematically a plant according to the invention for the production of dimethyl ether.

Via wire 1 is crude methanol as methanol with a residual water content or as methanol with a purity of A for pre-cleaning in a distillation column 2 fed. From the distillation column 2 will be over line 7 withdrawn the vapor in the column head and at least partially in a condenser 8th liquefied again. The condensate can via line 9 in the column 2 be recycled, while the consisting of low-boiling distillate via lines 10 and 15 is discharged from the distillation process.

The pre-purified methanol is from the bottom of the column 2 withdrawn and divided into a methanol stream and a reflux stream. The return flow is via line 4 in an evaporator 5 and from there via wire 6 back to the column 2 during the methanol flow of the column 2 via wire 11 is dissipated.

From the pre-purified methanol in line 11 can a part via wire 13 fed directly to the DME production, while the rest of the methanol stream via line 14 first as a detergent in a scrubber 20 is directed. It can also be a partial stream of crude methanol via line 17 directly to the scrubber (Scrubber) 20 be supplied and there are available as detergent.

By line 21 be the low boilers from the scrubber 20 with the electricity from pipe 10 united and over lead 15 deducted. The methanol stream is recycled with the recovered DME 22 from the scrubber 20 withdrawn and with the methanol from line 13 united. Via wire 24 the methanol enters a heat exchanger 25 from which it, preferably in vapor form, by conduction 26 in a cross heat exchanger 27 arrives.

The in the cross heat exchanger 27 further heated electricity is sent via line 28 in a dimethyl ether reactor 30 brought in. In this DME reactor 30 methanol is continuously reacted preferably by acid-catalytic condensation, preferably at a temperature in the range of 150 to 450 ° C and a pressure of 1 to 40 bar, to dimethyl ether. The condensation reaction is preferably carried out on a γ-alumina-containing catalyst within the reactor. Preferably, the catalyst contains a carbon content of 0.1 to 10 wt .-%, preferably 0.2 to 5 wt .-%.

The resulting product mixture is with line 31 in the cross heat exchanger 27 introduced, where it is cooled and at the same time the reactant stream from line 26 heated. By administration 32 the cooled product stream becomes the distillation column 40 transported. Overhead are from the column 40 in line 41 deducted the gaseous components, which then at least partially in a condenser 42 be condensed out. The liquid portions of the stream from pipe 43 be over line 45 back to the column 40 fed while headed by 44 the product dimethyl ether (DME) is removed. The water-rich bottom product of the column 40 will be over line 46 deducted and via wire 47 in the evaporator 48 and from there by lead 49 back to the column 40 fed.

The control and / or control unit 50 is intended to control pressure and / or temperature within the reactor. According to the invention, the reaction conditions, namely temperature, pressure and composition, are controlled within the reactor such that the pressure in the reactor is lower than the saturation partial vapor pressure of water at the reaction conditions present in the reactor.

This regulation or control prevents water from condensing out, both during the production of dimethyl ether and during the startup or shutdown of the plant, in particular of the reactor. As a result, damage to the catalyst used is prevented or at least slowed down and thus increases the service life of the catalyst.

From the over head of the DME column 40 withdrawn low-boiler stream (line 33 ) is in the scrubber 20 by means of a partial flow of the stabilized feed methanol from electricity 14 and or 17 Dimethyl ether recovered, which due to the light-ends (low boilers) in the head of the DME column 40 not condensed and over power 33 was attributed to this point.

Examples

example 1

The influence of the phase state of alumina or alumina on the catalyst activity is shown in Table 1 and the accompanying 2 shown. It was carried out in an isothermally operated reactor at a temperature of 300 ° C and atmospheric pressure. The space velocity, defined as the ratio of the educt mass flow to the catalyst mass, is 2 h ^-1 . Table 1: Catalytic activity measured on methanol conversion (X (MeOH) for different catalysts catalyst γ-alumina [% by weight] Boehmite [% by weight] Conversion (MeOH) [% by weight] A (reference) 100 0 82.6 B 39.0 60.5 37.9 C 0 99.5 2.7

It is clear that boehmite shows a much lower catalytic activity than - γ-alumina.

Example 2

In Example 2, the conditions favoring the phase transformation of γ-alumina to boehmite are examined. The results are shown in Table 2. Table 2: Catalyst composition as a function of operating conditions run Running time (h) treatment T (° C) p (bar) t (h) Dew point undershot γ-alumina (wt%) Boehmite (% by weight) 1 Fresh without - - - No 100 0 2 Fresh Steam 230 5 1 No 100 0 3 > 5000 Steam 240 16 4 No 10 0 4 Fresh water 190 11.4 2 Yes 32 68 5 Fresh water 190 11.4 72 Yes 7 93

It is confirmed that, in the presence of liquid water, a phase transformation of γ-alumina to boehmite apparently occurs, whereas pure water vapor does not show this effect. To the catalyst Activity must not be affected, so the conditions must be selected so that the dew point is not exceeded.

LIST OF REFERENCE NUMBERS

1

 management

2

 MeOH pre-cleaning

3, 4

 management

5

 heat exchangers

6, 7

 management

8th

 heat exchangers

9-17

 management

20

 washer

21-24

 management

25

 heat exchangers

26

 management

27

 Cross heat exchanger

28

 management

29

 compressor

29a

 pump

29b

 Evaporator

30

 DME reactor

31-33

 management

40

 DME-cleaning device

41

 management

42

 heat exchangers

43-47

 management

48

 heat exchangers

49

 management

50

 Control and / or control unit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6740783 B1 [0009]
• US 20050038129 A1 [0010]
• KR 100966706 B [0011]
• US 2009/0023958 A1 [0012]

Cited non-patent literature

• "Ullmann's Encyclopedia of Chemistry", 6th edition, 1998 [0004]

Claims (14)

Plant for the production of dimethyl ether, with a reactor ( 30 ) for reacting a methanol-containing starting material mixture to a dimethyl ether-containing product mixture over a catalyst under reaction conditions, with at least one control and / or control unit ( 50 ) for controlling pressure and / or temperature within the reactor ( 30 ), characterized in that the at least one control and / or control unit ( 50 ) is designed such that the pressure in the reactor ( 30 ) is lower than the saturation partial vapor pressure of water under the reaction conditions. Plant according to claim 1, characterized in that the reactor ( 30 ) is designed as a fixed bed reactor. Plant according to claim 1 or 2, characterized in that the reactor ( 30 ) is designed as a tray reactor with at least two hordes, each with an inlet and outlet. Installation according to one of the preceding claims, characterized in that the at least one control and / or control unit ( 50 ) is provided at the outlet of the reactor. A catalyst for the preparation of dimethyl ether-containing methanol starting material mixture containing at least 90 wt .-% γ-alumina and between 0.1 and 5 wt .-% carbon. Catalyst according to claim 5, characterized in that the catalyst was heated to a temperature between 120 and 300 ° C for at least 24 hours, preferably 48 hours and more preferably at least 100 hours before carrying out the method according to any one of claims 7 to 14. A process for the preparation of dimethyl ether, wherein a methanol-containing educt mixture is reacted in a reactor on a catalyst under reaction conditions to a dimethyl ether and water-containing product mixture, characterized in that pressure and / or temperature in the reactor is controlled and / or controlled so that the pressure is lower than the saturation partial vapor pressure of water under the reaction conditions. Method for starting or stopping a plant for the production of dimethyl ether, wherein catalyst for heating or cooling water vapor at a pressure and a temperature is passed through a reactor with a, characterized in that the pressure and / or temperature in the reactor regulated and / / or controlling that the pressure is lower than the saturation partial vapor pressure of water at that pressure and temperature. A method according to claim 7 or 8, characterized in that the temperature is between 180 and 400 ° C. Method according to one of claims 7 to 9, characterized in that the pressure is between 1 and 50 bar. Method according to one of claims 6 to 10, characterized in that the control and / or regulation of pressure and / or temperature based on a measurement at the outlet of the reactor. Process according to one of Claims 6 to 11, characterized in that the catalyst used is a catalyst containing at least 20% by weight, preferably 90% by weight, of γ-alumina. Method according to one of claims 6 to 12, characterized in that the catalyst contains between 0.1 and 10 wt .-%, preferably 0.2 and 5 wt .-% carbon. Method according to one of the claims 6 to 13, characterized in that the catalyst before carrying out the method according to one of claims 1 to 5 between at least 24 hours, preferably at least 48 hours and more preferably at least 100 hours to a temperature between 120 and 300 ° C, preferably 180 ° C was heated.

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