EP2539307A1

EP2539307A1 - Process for preparing methanol

Info

Publication number: EP2539307A1
Application number: EP11702934A
Authority: EP
Inventors: Holger Schlichting; Philipp Marius Hackel; Thomas Wurzel
Original assignee: Lurgi GmbH
Current assignee: Air Liquide Global E&C Solutions Germany GmbH
Priority date: 2010-02-22
Filing date: 2011-01-28
Publication date: 2013-01-02
Also published as: CN102770401B; DE102010008857A1; WO2011101081A1; US20120322651A1; CN102770401A

Abstract

In the preparation of methanol by means of a catalytic process with a plurality of serial synthesis stages, in which the severity of the reaction conditions, measured on the basis of the reaction temperature and/or the concentration of carbon monoxide in the synthesis gas, decreases from the first to the last reaction stage in flow direction, the first reaction stage involving flow traversal of synthesis gas uses a first catalyst with low activity but high long-term stability, and the last reaction stage involving flow traversal by synthesis gas uses a second catalyst with high activity but low long-term stability.

Description

Process for the production of methanol

The invention relates to a process for the catalytic production of methanol, in which the economy is significantly improved by optimized selection of the catalysts used compared to a known from the prior art. In particular, the invention relates to a process for optimized methanol synthesis in a multi-stage process. The invention further relates to a process for the conversion of an existing plant for the production of methanol.

Methods for producing methanol by catalytic conversion of synthesis gas containing hydrogen and carbon oxides have been known to the art for a long time. Thus, in Ullmann ^'s Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, chapter "Methanol", subchapter 5.2 "Synthesis" describes a one-step process for the production of methanol. A more modern, two-stage process for the production of methanol is known, for example, from the patent EP 0 790 226 B1. There, a synthesis gas stream containing hydrogen and carbon oxides is reacted in two reaction stages in a water cooled methanol synthesis reactor followed by a gas cooled methanol synthesis reactor. In the last-mentioned reaction stage, the synthesis gas is preheated by indirect heat exchange before it enters the water-cooled methanol synthesis reactor. Usually, the same copper-based methanol synthesis catalysts are used in both synthesis reactors. In the described method

CONFIRMATION COPY For example, the water cooled reactor is typically operated at a higher synthesis gas inlet temperature than a water cooled reactor in a one step methanol synthesis process to provide higher pressure steam. Furthermore, this reactor is charged with not yet reacted synthesis gas. Due to the high exothermicity of the methanol synthesis, therefore, a very good temperature control of the reactor is necessary to avoid overheating of the catalyst, which would lead to its premature deactivation by loss of active metal surface due to coagulation of the metal crystallites, the so-called sintering. In addition to this thermal effect, it is also known from the prior art that metal / support catalysts, as well as the copper-based methanol synthesis catalyst, under the influence of carbon monoxide tend to restructure their surface, which leads to the loss of active metal surface by sintering and thus loss of activity , As an illustrative reference, the publication of Nihou et al., Journal de Chimie Physique et de Physico-Chimie Biologique (1988), 85 (3), pp. 441-488, may be cited in which EPMA studies have shown in that the surface of catalysts of the type CuO / ZnO / Al ₂ O ₃ dynamically restructures in the reaction of carbon oxides with hydrogen under methanol synthesis conditions. This restructuring is more pronounced at high carbon oxide partial pressures than at low carbon oxide partial pressures.

On the other hand, recent developments in catalysts for methanol synthesis are aimed at providing catalysts with high synthesis activity even at low reaction temperatures. For example, product brochures currently available on the market for methanol synthesis refer to their increased synthesis activity at low temperatures; The brochure "MK-121 - High activity methanol synthesis catalyst" (Haldor Topsoe A / S), which is available on the Internet at http://www.topsoe.com/, is an example of this enhanced low-temperature activity . an increased dispersion of the copper on the catalyst surface developments in other catalyst manufacturers are going in the same direction, so that Süd-Chemie AG offers the methanol synthesis catalyst MegaMax ^® 800 as a further development of the catalyst MegaMax ^® 700, with the former, newly developed Catalyst characterized by a higher activity at low temperatures due to optimized copper dispersion (Nitrogen + Syngas 290, 1 1 -12 (2007), 26-42).

In general, however, high dispersion metal / support catalysts are more susceptible to deactivation due to sintering. Monzon et al. in Applied Catalysis A: General 248 (2003), 279-289 show that the rate of dispersion decrease of noble metal / support catalysts follows a kinetic approach of the kind dD _r / dt = ψ o (D _r -D _rr ) ⁿ , where D _{r is} the relative dispersion defined by the relationship D _r = D / D ₀ , where D is the absolute value of the dispersion at time t and D _{0 is} the absolute value of the dispersion at time zero. D _rr is the limit of the relative dispersion for t - oo; ψ ₀ is the kinetic constant of deactivation. n is the kinetic order of the deactivation reaction; in the cited reference it is stated that these can be described satisfactorily for all data published in the literature on the deactivation kinetics of noble metal / supported catalysts due to sintering with n = 1 to 2. It follows that when using a highly dispersed noble metal / support catalyst, under otherwise identical conditions, a faster relative decrease in dispersion is to be expected. A faster dispersion decrease leads to a faster loss of activity and consequently to a lower long-term stability of the catalyst. This is economically particularly disadvantageous because for the newly developed catalyst generations with higher dispersion by manufacturers usually a higher purchase price is required.

The object of the present invention is therefore to avoid the abovementioned disadvantages and to provide a new, robust, economically advantageous and industrially easy to carry out process for the production of methanol while retaining the advantages of the multistage mode of operation.

This object is achieved with the features of the characterizing part of claim 1 in conjunction with the features of the preamble essentially in that in a process for the catalytic production of methanol from synthesis gas, in which at least two catalyst-containing reaction stages are used with different reaction conditions in which each synthesis gas is at least partially converted to methanol, the sharpness of the reaction conditions, measured at the reaction temperature and / or Concentration of carbon monoxide in the synthesis gas decreases from the first to the last reaction stage in the flow direction, a first catalyst with low activity is used in the first reaction stage through which synthesis gas flows, and a second catalyst with high activity is used in the last synthesis stage through which synthesis gas flows.

Although it is known per se from the prior art described above, there is an opposite relationship between dispersion or activity and long-term stability of noble metal / support catalysts. It is interesting in the work of Μοηζόη et al. the use of the limit value D _rr for the relative dispersion below which the relative dispersion does not decrease further even for very long operating times for defined reaction conditions. This means that even for a very long time in use precious metal / support catalysts have a non-zero dispersion and thus residual activity. Surprisingly, it has now been found that this countercurrent correlation between the dispersion or activity, on the one hand, and the long-term stability, observed for noble metal / support catalysts, can be transferred to copper-based catalysts for the synthesis of methanol, leading to a technical teaching which essentially fulfills the object of the present invention Invention solves.

According to a preferred embodiment of the invention, it is provided to use in a process for methanol synthesis with more than two reaction stages, at least one further, third catalyst with average activity. In this way, an optimal adaptation of the catalysts used to the prevailing in the respective reaction stage sharpness of the reaction conditions is achieved. An alternative embodiment of the invention envisages using only two different catalysts with different activity in a process for methanol synthesis with more than two reaction stages. Although in this way a slight Fügig worse adaptation of the catalysts used to the prevailing in the respective reaction stage sharpness of the reaction conditions achieved as in the embodiment described above; however, the restriction to two different types of catalysts leads to logistical advantages and thus to an improved economy of the process.

Advantageously, all catalysts used are copper-based. Methanol synthesis catalysts of the type Cu / Zn / Al ₂ O ₃ are used in virtually all currently operated industrial plants for the synthesis of methanol and are held by the trade with different copper dispersions and therefore different degrees of activity.

It is particularly advantageous that the at least two reaction stages are integrated into a cycle for unreacted synthesis gas. Even with the highly active catalysts for methanol synthesis available today, only one partial conversion of the synthesis gas to methanol is achieved per pass through a reaction stage, so that the recycling of unreacted synthesis gas to the reaction stages is economically sensible and necessary. The circulation method also serves in a conventional manner for temperature control in the reaction stages due to the highly exothermic reaction.

In a further development of the invention, at least one further, catalyst-containing reaction stage is arranged upstream of the synthesis loop as a pre-reactor for the partial conversion of synthesis gas to methanol, wherein the catalyst has a lower activity than the first reaction stage fluid within the synthesis gas cycle. The use of pre-reactors in the synthesis of methanol before the synthesis gas cycle is known per se and is described for example in the document DE 10126719 A1. Since the reaction conditions in the prereactor are characterized by particularly high sharpness, the use of a methanol synthesis catalyst with low activity but high long-term stability offers particularly great advantages in this case. Furthermore, the process according to the invention is further developed in that, downstream of the synthesis gas cycle, at least one further reaction stage containing catalyst is arranged as a post-reactor for the partial conversion of synthesis gas to methanol, the catalyst having a higher activity than the last reaction stage within the synthesis gas cycle. Since the synthesis gas entering the secondary reactor has already largely reacted, the higher activity of the catalyst can be optimally utilized here. Since the previously synthesized methanol is removed by cooling and condensation prior to the task of the synthesis gas, the high activity of the methanol synthesis catalyst can advantageously be exploited by introducing the synthesis gas before it enters the postreactor in comparison to the last methanol synthesis reactor within the synthesis loop lower temperatures must be heated, which improves the energy balance of the overall process. In a further development of the invention, a catalyst of lesser activity is not commercially obtained, but such a catalyst is provided by using a partially de-activated methanol synthesis catalyst already used in a process for catalytic methanol synthesis as a catalyst of lesser activity in the process according to the invention. A particular embodiment of this development provides for removal of the partially deactivated catalyst from the last reaction stage of the reaction, filling this reaction stage with fresh, highly active catalyst and using the previously removed, partially deactivated catalyst in an upstream, for example the first reaction stage. For this purpose, it may be necessary to inertize the partially deactivated catalyst prior to its removal from the last reaction stage in the manner known to those skilled, for example by controlled oxidation, and this after installation in a flow upstream reaction stage, for example by treatment with reducing gases reactivate. In this procedure, only fresh, highly active catalyst is obtained from the market, whose period of use can be extended according to the invention, resulting in further economic advantages and the amount of catalyst to be disposed of deactivated, is reduced. According to a preferred embodiment of the invention, two reaction stages are present within the synthesis gas cycle, wherein the reaction of the synthesis gas takes place first in a water-cooled reactor and then in a gas-cooled reactor.

The invention further relates to a process for the conversion of an existing plant for the production of methanol from synthesis gas, wherein at least two catalyst-containing reaction stages are used with different reaction conditions, in which each synthesis gas is at least partially converted to methanol, wherein the severity of the reaction conditions, as measured the reaction temperature and / or the concentration of carbon monoxide in the synthesis gas decreases from the first to the last reaction stage in the flow direction, which is characterized in that the catalyst is removed in the first reaction stage through which the synthesis gas flows and exchanged for a catalyst with low activity. An alternative embodiment of this method provides, in the regular decommissioning of a method for methanol synthesis with water and gas-cooled reactor according to the prior art to leave the aged, partially deactivated catalyst in the water-cooled reactor and the likewise aged, partially deactivated catalyst in the gas-cooled reactor against fresh to replace highly active catalyst.

Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features alone or in any combination form the invention, regardless of their combination in the claims or their dependency.

The sole FIGURE 1 shows schematically a plant for the production of methanol by the process according to the invention. There, a synthesis gas stream containing hydrogen and carbon oxides is fed via line 1 to a compressor 2 and brought therefrom to the reaction pressure of typically 5 to 10 MPa. The compressed synthesis gas stream is fed via line 3 to a heat exchanger 4 and in this brought to the reaction temperature, wherein usually the heat exchange takes place against the hot product gas stream from the last synthesis reactor (not shown in Fig. 1). The preheated synthesis gas stream enters via line 5 in the gas-cooled synthesis reactor 6, but is not yet chemically reacted here, but initially serves as a cooling gas for receiving the released in reactor 6 heat of reaction. At the same time, the cooling gas is heated to the reaction temperature to a temperature of 220 to 280 ° C and then enters via line 7 in the water-cooled synthesis reactor 8 a. Here, at temperatures between 200 and 300 ° C, the partial reaction of hydrogen with carbon oxides on a methanol synthesis catalyst, wherein a product mixture is obtained which contains methanol vapor, water vapor and unreacted synthesis gas. Via line 9, the product mixture is removed from the water-cooled synthesis reactor 8 and fed to the gas-cooled synthesis reactor 6, wherein in the conduction path of the line 9 optionally another heat exchanger (not shown in Fig. 1) for adjusting the temperature of the entering into the gas-cooled reactor synthesis gas stream be attached can. Here, at temperatures between 150 and 300 ° C, the further reaction of hydrogen with carbon oxides on a methanol synthesis catalyst, wherein a product mixture is obtained, which in turn contains methanol vapor, water vapor and unreacted synthesis gas. In the first, water-cooled synthesis reactor, a methanol synthesis catalyst of normal activity is used (hereinafter also referred to as the standard type), whereas in the second, gas-cooled synthesis reactor, a highly active and for lower reaction temperatures optimized methanol synthesis catalyst is used. The reaction temperature in the second, gas-cooled synthesis reactor is therefore significantly lower than that in the first, water-cooled synthesis reactor in order to minimize the deactivation rate of the highly active methanol synthesis catalyst. Alternatively, it may also be the same as or even higher than that in the first, water-cooled synthesis reactor if the CO content of the synthesis gas has been lowered sufficiently strongly by reaction in the first, water-cooled synthesis reactor. The space velocity is typically 5000 to 30000 m ³ / (m ³ h) both in the water-cooled and in the gas-cooled synthesis reactor. The released reaction heat serves, as explained above, the heating of the synthesis gas to the reaction temperature, as well as the generation of steam in the water-cooled reactor. The "pro- Duktgasgemisch leaves the gas-cooled synthesis reactor via line 10. After cooling in the heat exchanger 1 1, the product gas mixture passes via line 12 into the separator 13, where methanol is separated as crude methanol and fed via line 14 to the further product processing. This can be done in a known per se, but not shown in the figure by distillation or rectification. The gas product obtained in the separator is discharged via line 15 and into a purge stream, which is discharged via line 16, and a circuit Ström, which is supplied via line 17 to the cycle compressor 18, separated. Inert components are discharged from the process via the purge stream. Via line 19, the recycle Ström is returned to the synthesis reactor 6, being introduced via line 20 fresh synthesis gas and combined with the circulating stream. The ratio of cycle stream to fresh synthesis gas stream is called the cycle ratio. It is usually between 0.5 and 7 m ³ / m ³ . The invention thus proposes an economical process for the production of methanol, which is characterized by the fact that existing multistage plants for the synthesis of methanol can be reused without conversions. The lower market price of methanol synthesis reactors of lower activity gives rise to economic advantages of the process according to the invention. Furthermore, partial-deactivated methanol synthesis catalysts can advantageously be used further with the process according to the invention. This increases the useful life of the catalysts. Furthermore, the amount of catalyst to be disposed of is reduced, which results in advantages with regard to the environmental compatibility of the process according to the invention.

Numerical examples

To evaluate the activity and deactivation behavior of two methanol synthesis catalysts type A (standard type, normal activity) and type B (optimized for high activity at lower temperatures) long-term experiments were carried out in similar, parallel-connected fixed bed reactors with boiling water cooling. The reactors were charged with synthesis gas of the same composition and the same volume flow in the straight pass without synthesis gas recirculation. Inlet temperature and pressure were the same in both fixed bed reactors.

The comparative test was carried out with synthesis gas of the composition indicated below.

C0 ₂ 8 vol%

CO 6 vol%

H ₂ 59.5% by volume

CH ₄ 19.5 vol%

N ₂ 7 vol%

Inlet temperature: 230 ° C (270 ° C between 630 and 700 h)

Pressure: 59 bar

Space velocity: 16,000 m ³ / (m ³ h) The following table shows the measured CO conversion for different catalyst runtimes.

As can be seen from the table, the CO conversions for catalyst types A and B are at a comparable level of 70% and 68%, respectively, after a running time of 120 hours. After 440 h running time the difference between the measured CO sales is already 9%, after 760 h running time even 12%. It should be noted that the reaction temperature was increased from 230 to 270 ° C between 630 and 700 h. Obviously, catalyst type B (optimized for high activity at lower temperatures) tends to more rapidly lose activity under the reaction conditions chosen here, which are typical for methanol synthesis with standard type methanol synthesis catalysts.

LIST OF REFERENCE NUMBERS

1 line

2 compressors

3 line

4 heat exchangers

5 line

6 gas-cooled synthesis reactor

7 line

8 water-cooled synthesis reactor

9 - 10 line

1 1 heat exchanger

12 line

13 separators

14 - 17 line

18 compressors

19 - 20 line

Claims

claims:

1. A process for the catalytic production of methanol from synthesis gas, wherein at least two catalyst-containing reaction stages are used with different reaction onsbedingungen in which synthesis gas is in each case at least partially converted to methanol, wherein the sharpness of the reaction conditions, measured at the reaction temperature and / or the concentration of carbon monoxide in the synthesis gas decreases from the first to the last reaction stage in the flow direction, characterized in that in the first reaction stage through which the synthesis gas flows, a first catalyst with low activity and in the last reaction stage through which synthesis gas flows, a second catalyst with high activity is used.

2. The method according to claim 1, characterized in that at more than two reaction stages, at least one further, third catalyst having average activity and average long-term stability is used.

3. The method according to claim 1 and 2, characterized in that all catalysts are copper-based.

4. The method according to claim 1, characterized in that the at least two reaction stages are integrated into a cycle for unreacted synthesis gas.

5. The method according to claim 4, characterized in that upstream of the synthesis gas cycle at least one further reaction stage containing catalyst is arranged as a pre-reactor for the partial conversion of synthesis gas to methanol, wherein the catalyst has a lower activity than the first reaction stage within the synthesis gas cycle.

6. The method according to claim 4, characterized in that at least one further, catalyst-containing reaction stage is arranged downstream of the synthesis gas cycle as a post-reactor for the partial conversion of synthesis gas to methanol, wherein the catalyst has a higher activity than the last reaction stage fluidly within the synthesis gas cycle.

7. The method according to claim 4, characterized in that two reaction stages are present within the synthesis gas cycle, wherein the reaction of the synthesis gas is carried out first in a water-cooled reactor and then in a gas-cooled reactor.

8. Preparation of catalysts of lower activity, in particular for use in a process according to claim 1, characterized in that the catalysts are deactivated in their use for the synthesis of methanol.

9. Use of highly active, but partially deactivated catalyst in a reaction stage with harsher reaction conditions, measured at the reaction temperature and / or the concentration of carbon monoxide in the synthesis gas, in particular in a method according to claim 1.

10. A process for retrofitting an existing plant for the production of methanol, wherein at least two catalyst-containing reaction stages are used with different reaction conditions, in which each synthesis gas is at least partially converted to methanol, the sharpness of the reaction conditions, measured at the reaction temperature and / or the concentration of carbon monoxide in the synthesis gas decreases from the first to the last reaction stage in the flow direction, characterized

(A) that the catalyst is removed in the first reaction stage through which synthesis gas flows and is exchanged for a catalyst with lower activity or

(B) that the catalyst is removed in the last reaction stage through which synthesis gas flows and exchanged for a catalyst with higher activity, or

(c) that both steps (a) and (b) are performed.