EP4225722A1

EP4225722A1 - Process for preparing methanol

Info

Publication number: EP4225722A1
Application number: EP21794723.3A
Authority: EP
Inventors: Gernot PACHOLIK; Karin FÖTTINGER
Original assignee: Technische Universitaet Wien
Current assignee: Technische Universitaet Wien
Priority date: 2020-10-08
Filing date: 2021-10-08
Publication date: 2023-08-16
Also published as: US20230365481A1; CA3194655A1; AT524247A1; WO2022073055A1; CN116323529A

Abstract

Process for preparing methanol (CH₃OH) from carbon dioxide (CO₂) and hydrogen (H₂), wherein CO₂ is reacted with H₂ over a manganese-promoted molybdenum(IV) sulfide catalyst; and a catalyst for such a process and a preparation process for the catalyst.

Description

PROCESS FOR PRODUCTION OF METHANOL

The present invention relates to a process for the catalytic production of methanol from carbon dioxide and hydrogen. The invention also relates to a catalyst for producing methanol from carbon dioxide and hydrogen. Finally, the invention relates to the use of a catalyst for producing methanol from carbon dioxide and hydrogen.

BACKGROUND OF THE INVENTION

According to the prior art, various processes are available for the fully synthetic production of alcohols. Industrially, processes in which carbon monoxide (CO) or carbon dioxide (CO2) are used as starting materials are of particular importance. These processes are divided into processes for the production of methanol (CH3OH) on the one hand and processes for the production of higher alcohols, i.e. alcohols with more than one carbon atom, on the other hand. Important criteria are the selectivity and the yield of the desired alcohol.

According to the prior art, the industrial production of methanol takes place, for example, via the hydrogenation of carbon monoxide or carbon dioxide, in each case at high pressures, using suitable catalysts. Both reactions occur in the hydrogenation starting from synthesis gas, although the yield of the CCU hydrogenation is in need of improvement.

Liu et al., Journal of the Taiwan Institute of Chemical Engineers, 76 (2017), page 18, describe the production of higher alcohols by means of CCb hydrogenation with a Mo-Co-K sulfide catalyst, where the catalyst can have, inter alia, M0S2 .

Qi et al., Catalysis Communication, 4 (2003), page 339 describe CO hydrogenation using K/M0S2. The addition of manganese to the catalyst is also described, and finally a Ni/Mn/K/MoS2 catalyst is described as suitable for the hydrogenation of CO. The result shows a very high selectivity for alcohols with an overall yield of 81.7%. Of this, 45.8% is methanol and 53.3% higher alcohols (C _n - alcohols with n = 2, 3, 4 and 5). eng et al., Applied Catalysis B: Environmental, 246 (2019), page 232, describe the production of higher alcohols with at least three carbon atoms (C _n -alcohols with n > 3) by CO hydrogenation over potassium-promoted M0S2.

DETAILED DESCRIPTION OF THE INVENTION

The selective processes known from the prior art for the production of methanol are often based on carbon monoxide as the starting material. Processes based on CO2 are either not very selective or they require expensive catalysts or complex process conditions. If CO is to be used as a feedstock, an additional reaction step is required for the production of CO, whereas CO2 is available in practically unlimited quantities (e.g. it is a waste product in the form of flue gas from the combustion of hydrocarbons).

The object of the present invention is to provide a selective and inexpensive process and a catalyst for the selective hydrogenation of CO2 to methanol. The catalyst should also be sulfur tolerant, i.e. tolerant of trace amounts of sulfur compounds in the reaction gas.

This task is solved by a selective process for the production of methanol (CH3OH, MeOH) from carbon dioxide (CO2) and hydrogen (H2), whereby CO2 is reacted with H2 over a manganese-promoted M0S2 catalyst.

The invention is based on the finding that a manganese-promoted M0S2 catalyst catalyzes the CCh hydrogenation in a highly selective manner. In particular, the very high yield of methanol and the high specificity of the formation of methanol are surprising in comparison to already known sulfur-tolerant catalysts. In this process, there is almost no formation of higher alcohols and the amount of by-products formed, such as CO or CH4, is also small.

Although the exact reaction mechanism is not yet known to the inventors, it is a two-stage reaction sequence with an upstream RWGS step (Reverse Water-Gas Shift Reaction) and a subsequent CO hydrogenation to methanol

CO2 + H2CO ₊ H2O

CO ₊ 2H2CH3OH rather improbable, since comparative tests on the manganese-promoted M0S2 catalyst hardly showed any conversion of CO with H2 to CH3OH. The high yield and selectivity is all the more surprising.

Therefore, in one aspect, the invention relates to the use of a manganese-promoted M0S2 catalyst for the production of methanol from CO2 and H2.

The object stated at the outset is also achieved by a catalyst comprising manganese-promoted molybdenum(IV) sulfide (M0S2), the manganese-promoted molybdenum(IV) sulfide having a layered structure which can have various disorders. The structure can be described by the limit cases 2H-M0S2 and 3R-M0S2. The proportion of manganese is such that the molar ratio of Mn to Mo is 0.1 to 0.5:1, preferably 0.2 to 0.4:1. Furthermore, XPS studies have shown that manganese can exist in the oxidation states (II) and (III).

Manganese can preferably be present as Mn(II) sulfide and/or Mn(III) sulfide. Manganese can additionally also be present as Mn(II) oxide, Mn(III) oxide, Mn(II) hydroxide, Mn(III) hydroxide or MnOOH.

According to the invention, the manganese-promoted molybdenum(IV) sulfide (M0S2) can be a mixed crystal of manganese sulfide(s) and M0S2, the basic structure being formed by the M0S2 and manganese sulfide(s) being embedded in this basic structure, with manganese oxide(s) optionally also , manganese hydroxide(s) and/or MnOOH are incorporated into the basic structure according to the previous paragraph.

The catalyst can also be promoted with potassium. In this case, a phase of a K(I) salt, preferably K2CO3, is present on the surface of the manganese-promoted molybdenum(IV) sulfide. Such a catalyst is hereinafter referred to as manganese-promoted potassium molybdenum(IV) sulfide.

The catalyst can additionally have a support on which the manganese-promoted molybdenum(IV) sulfide (optionally with potassium) is applied. The carrier can be a porous material. For example, the support can be an aluminum oxide or aluminum oxide hydroxide such as Al2O3 or AlO(OH). The catalyst preferably consists of Mn(0.1 to 0.50)MoS2, preferably Mn(0.2 to 0.4)MOS2, optionally with a support as mentioned above.

The catalyst described above has proved useful for the process. Therefore, in one aspect, the invention relates to such a catalyst.

Furthermore, reaction conditions in the process with a pressure that is higher than standard conditions have proven to be advantageous. Provision is therefore preferably made for the reaction to take place at a pressure of >10 bar. For example, the pressure can be 10 bar to 200 bar or 10 bar to 100 bar. In one embodiment, the pressure was between 18 bar and 23 bar.

In principle, the reaction can take place over a wide temperature range. Suitable temperatures are, for example, between 140°C and 320°C. If a pure manganese-promoted MoS2 catalyst is used, the ideal temperature range is preferably between 170 °C and 220 °C.

If a potassium-added manganese-promoted MoS2 catalyst is used, the ideal temperature range for the reaction is somewhat higher, preferably between 260°C and 300°C.

Provision is preferably made for the partial pressure ratio of CO2 to H2 to be approximately 1:2.5 to 3.5, preferably approximately 3. This means that the partial pressure of hydrogen should be about 2.5 to 3.5 times higher than the partial pressure of CO2.

Surprisingly, it has also been found that the addition of an inert gas to the reaction mixture of CO2 and H2, for example an inert gas (such as helium) or nitrogen, hardly impedes the reaction. The yield fell only slightly. The partial pressure of inert gas can be about 1 to 0.5 to 1.5 in relation to CO2. The realization that inert gas does not interfere with the reaction means that flue gas, which contains mostly nitrogen, can also be used as a source of CO2. In one embodiment variant, the CO2 can therefore come from flue gas. In this case, the process of the present invention is a selective process for the production of methanol from CO2 and H2, where the CCh source is flue gas, where CO2 is reacted with H2 over a manganese-promoted MOS2 catalyst. Such a method is suitable for supplying flue gas for recycling.

Although all manganese-promoted M0S2 catalysts are suitable as catalysts, those that are presented according to the process described next have proven to be particularly efficient. Therefore, in one aspect, the invention relates to a

Process for the production of a manganese-promoted M0S2 catalyst for the production of methanol from CO2 and H2, comprising the steps:

(i) forming a mixture of water, ammonium molybdate (particularly (NH4)6MO?O24'4H2O), thiourea (CH4N2S) and a water-soluble manganese(II) salt;

(ii) Raising the temperature of this mixture in an autoclave to 150-250°C and increasing the pressure to such a level that some of the water remains liquid, maintaining the temperature and pressure until the thiourea decomposes and a sulphide mixture comprising manganese sulphide and M0S2 forms;

(iii) washing the obtained sulphide mixture from step (ii);

(iv) drying the washed sulfide mixture from step (iii);

(v) calcining the dried and washed sulfide mixture from step (iv) under inert gas to obtain the manganese-promoted M0S2 catalyst.

The sulfide mixture in step (ii) and subsequent steps may include Mn(II) oxide, Mn(III) oxide, Mn(II) hydroxide, Mn(III) hydroxide or MnOOH. These compounds also form, in particular, at the upper end of the temperature range.

The pressure in the autoclave is preferably in a range from 5 to 40 bar, preferably about 15.5 bar.

Optionally, potassium can also be added before the calcination but after drying the washed sulfide mixture. Potassium can be added in the form of an aqueous K(I) solution, for example a K2CO3 solution, with a drying step then being provided before the calcination. The K(I) solution can be added via ultrasonic dispersing. Furthermore, a support for the catalyst can be provided. In this case, prior to the calcination step, the sulfide mixture is admixed with a carrier. The carrier can be a porous material. Aluminum oxides, eg AlO(OH) or Al2O3, have proven suitable as carriers.

Preferably, the carrier is precipitated, preferably from a precursor compound, while raising the temperature of the mixture in the autoclave to 150-250°C and raising the pressure to a value that part of the water remains liquid. The precursor can be e.g. A1(NÜ3)3 and is initially dissolved. The dissolved precursor can then be precipitated as A1(OH)3 or AIO(OH).

DETAILED DESCRIPTION OF THE INVENTION

Further advantages and details of the invention are shown in the accompanying figures and explained in more detail in the following description.

1 shows the reaction yield of methanol from the reaction of CO2 with FE over a manganese-promoted MoS2 catalyst as a function of temperature in a process according to the invention.

Figure 2 shows the yield of the reaction of CO with FE over a manganese-promoted MoS2 catalyst as a function of temperature.

3 shows the reaction yield of methanol from the reaction of CO2 with FE as a function of temperature in a process according to the invention over a manganese-promoted MoS2 catalyst without potassium (■) and with potassium (•).

4 shows a comparison of the reaction yields of methanol or CEE of the reaction of CO2 with FE as a function of temperature in a process according to the invention over a manganese-promoted MoS2 catalyst without potassium (■) and with potassium (•)•

5 shows the comparison of the reaction yield with a cobalt-promoted M0S2 catalyst with potassium starting from CO2 and FE.

6 shows the comparison of the reaction yield with a cobalt-promoted M0S2 catalyst with potassium starting from CO and FE.

Fig. 7 shows different catalysts in the reaction of CO2 with FE as a function of temperature. 8 shows a comparison of the reaction yields of methanol or CO and CFU of the reaction of CO2 with H2 in a process according to the invention over various manganese-promoted MoS2 catalysts with different Mn and Mo contents.

9 shows a comparison of the reaction yields of methanol or CO and CFU of the reaction of CO2 with H2 over a Mn(0.30)MoS2 catalyst in the presence of 20% helium (left) and without helium (right).

Fig. 10 shows a comparison of the reaction yields of methanol or CO and CH4 of the reaction of CO2 with H2 over a Mn(0.25)MoS2 catalyst without a support (left), a M0S2 catalyst with an A1O(OH) support (middle) and a Mn(0.25)MoS2 catalyst with A1O(OH) support (right).

11 shows a comparison of the reaction yields of methanol from the reaction of CO2 with H2 as a function of temperature over a MnMoS2 catalyst and a cobalt-promoted MoS2 catalyst.

12 shows a comparison of the reaction yields of methanol from the reaction of CO with H2 as a function of temperature over a MnMoS2 catalyst and a cobalt-promoted MoS2 catalyst.

The reaction conditions in the examples shown in the figures at the beginning of the reaction, as well as how the gas mixture is passed over the catalyst, are summarized in Table 1.

The total flow of the gas mixture as it is passed over the catalyst is:

300 ml N gkat * h

In this formula, "ml N" stands for milliliters under normal or standard conditions, i.e. at 273, 15 K or 0 °C and 1 bar pressure. The normalization to normal conditions is carried out because under 21 bar 1 ml would have a higher number of moles than under 1 bar; therefore the flow is converted and related to the volume flow under normal conditions.

1 shows the reaction yield of methanol as a function of temperature in a process according to the invention when CO 2 is reacted with FF over a simple manganese-promoted molybdenum(IV) sulfide catalyst. It can be seen very clearly that there is a maximum yield of methanol at around 200 °C to 210 °C, while only a few by-products are formed at this temperature. With increasing temperature, the formation of methane (CH4) increases while the yield of methanol decreases. The amount of carbon monoxide (CO) formed also increases with increasing temperature. The ideal temperature range is therefore around 180 °C to 220 °C.

FIG. 2 shows, in comparison to the example of FIG. 1, that the reaction yield of methanol as a function of temperature is extremely low in a process in which CO is reacted with H 2 over a manganese-promoted molybdenum(IV) sulfide catalyst is. As the temperature rises, the formation of CO2 and CH4 begins. CO should therefore play no role in the formation of methanol over this catalyst.

In Fig. 3 the reaction yields of the reaction CO2 + 2 FF - CH3OH over a simple manganese-promoted MoS2 catalyst (•; see example of Fig. 1) and over a manganese-promoted MoS2 catalyst additionally with potassium (• ) compared as a function of temperature in the method according to the invention. As already described in FIG. 1, the course of the reaction shows a maximum yield at about 200 to 210° C. in the case of simple manganese-promoted molybdenum(IV) sulfide. In the case of the manganese-promoted MoS2 catalyst with potassium, the maximum yield shifts to around 280 °C. The addition of potassium thus shifts the maximum yield towards higher temperatures, while at the same time a reduction in the yield (mol% based on the CO2 used) from just under 0.7% to approx. 0.4% can be observed. The disadvantage of the use of the manganese-promoted M0S2 Catalyst with potassium in the form of lower yield at the same time higher ideal temperature range, however, is accompanied by the benefit of a significant decrease in the formation of CFU, which CFU is an undesirable by-product. This relationship is also shown in FIG. 4, where it can be seen in this diagram that the maximum yield of CH3OH in the case of simple (ie potassium-free) manganese-promoted molybdenum(IV) sulfide at approx. 200 to 210° C. already shows a significant increase in CFU yield. In the case of the manganese-promoted MoS2 catalyst with potassium, the methane yield is still low at the maximum yield for CH3OH at 280 °C.

Figure 5 shows the reaction yield of the reaction CO2 + 2H2 - CH3OH as a function of temperature in a process over a cobalt-promoted MOS2 catalyst. The maximum yield is around 280 °C. It is not difficult to see that, compared to the manganese-promoted MoS2 catalysts (with and without potassium), not only is the amount of CEU formed comparatively high, but also that the amount of CO formed is so high that this catalyst is largely unselective for the formation of methanol. The yield of CO is already several orders of magnitude higher than that of methanol at around 200 °C, and the yield of CEU also increases significantly from around 280 °C.

Figure 6 compares the example of Figure 5 to the reaction yield of methanol as a function of temperature in a process where CO reacts with EU over a cobalt-promoted MOS2 catalyst with potassium. The yields of methanol and methane are slightly higher overall, but CO2 is the main product even at low temperatures and from about 300 °C the CH4 yield exceeds the amount of CH3OH formed.

7 shows a comparison of the yield of methanol formed in the reaction of CO2 with H2 over various catalysts. A nickel-promoted M0S2 catalyst with potassium ( A) gives the lowest yields. A cobalt-promoted M0S2 catalyst shows only a slightly higher methanol yield (•). An M0S2 catalyst with K (■) shows significantly better yields, but the highest yields can be found in processes according to the invention with manganese-promoted M0S2 with potassium (▼).

The diagram of FIG. 8 shows the comparison of the reaction yields of methanol (MeOH) or CO and CH4 of the reaction of CO2 with H2 in a process according to the invention over various manganese-promoted MoS2 catalysts with different Mn and Mo shares shown. The abscissa shows the molar proportion of manganese in relation to molybdenum. The maximum methanol yield is from 0.2 to 0.4. (Reaction conditions: 21 bar, 180 °C, 20% CO ₂ , 60% H ₂ , 20% He, 300 mlN/(gkatai _yS ator*h)

The bar graph of FIG. 9 shows the reaction yields of methanol, CH4 and CO from the reaction of CO2 with H2 over a Mn(0.30)MoS2 catalyst in the presence and absence of helium as the inert gas. The left diagram shows the yields of a mixture of 20% CO2, 60% H2 and 20% He, the right diagram shows a mixture of 25% CO2 and 75% H2. It can be seen that the yield of methanol decreases only slightly in the presence of He; surprisingly, the yield of CO decreases at the same time by a significant amount. (The reaction conditions are in each case 21 bar, 180° C., 300 mlN/(gcatalyst*h)).

The bar graph of FIG. 10 shows the reaction yields of methanol, CH4 and CO from the reaction of CO2 with H2 over three different catalysts. The left panel shows the yields over a manganese-promoted MoS2 catalyst (Mn(0.25)MoS2), the middle panel shows yields over a “simple” M0S2 catalyst, and the right panel over a manganese-promoted MoS2 catalyst ( Mn(0.25)MoS2) deposited on an A1O(OH) support. A significantly higher selectivity of the two manganese-promoted MoS2 catalysts in relation to methanol can be seen, in particular the significantly lower yields of the undesired by-product CH4 are striking (reaction conditions: 21 bar, 180 °C, 20% CO2 60% H ₂ 20% , He 300 mlN/(gkatal _y sator*h))

11 shows the comparison of the reaction yields of a manganese-promoted MoS2 catalyst and a cobalt-promoted MoS2 catalyst with potassium on methanol of the reaction of CO2 with H2 as a function of temperature. The reaction yields are not only higher with the manganese-promoted MoS2 catalyst, but are also shifted to lower temperatures. (Reaction conditions: each 21 bar, 180 °C, 20% CO2 60% H2 20% He, 300 mlN/(gcatalyst*h).

Furthermore, the comparison of the reaction yields of a manganese-promoted MoS2 catalyst and a cobalt-promoted MoS2 catalyst with potassium on methanol of the reaction of CO with H2 as a function of the temperature is shown in FIG. In this representation is the Selectivity of the manganese-promoted MoS2 catalyst is even clearer. (Reaction conditions: each 21 bar, 180 °C, 20% CO 60% H2 20% He, 300 mlN/(gkataiysator*h).) Since flue gas can contain residual amounts of CO, the high selectivity when using flue gas as a source for CO2 an advantage over other catalysts.

In contrast to the prior art with sulfur-resistant catalysts, the selective formation of methanol by means of CO2 hydrogenation on a manganese-promoted M0S2 (with or without potassium) catalyst is significantly greater.

Claims

EXPECTATIONS

1. A process for producing methanol (CH3OH) from carbon dioxide (CO2) and hydrogen (H2), characterized in that CO2 is reacted with H2 over a manganese-promoted molybdenum(IV) sulfide catalyst.

2. The method according to claim 1, characterized in that the reaction takes place at a pressure of> 10 bar.

3. The method according to claim 1 or claim 2, characterized in that the partial pressure ratio of CO2 to H2 is about 1:2.5 to 3.5, preferably about 3.

4. The method according to any one of claims 1 to 3, characterized in that while CO2 is reacted with H2 over the manganese-promoted molybdenum(IV) sulfide, an inert gas is additionally present.

5. Process according to one of Claims 1 to 4, characterized in that the manganese-promoted molybdenum(IV) sulfide catalyst has a composition Mn(0.1 to 0.50)MOS2.

6. The method according to any one of claims 1 to 5, characterized in that the reaction takes place at a temperature between 160 °C and 240 °C.

7. The method according to any one of claims 1 to 6, characterized in that the CO2 source is flue gas.

8. Use of a manganese-promoted molybdenum(IV) sulfide catalyst for the production of methanol (CH3OH) from carbon dioxide (CO2) and hydrogen (H2).

9. A catalyst comprising manganese-promoted molybdenum(IV) sulfide, wherein the manganese-promoted molybdenum(IV) sulfide catalyst has a composition Mn(0.1 to 0.50)MOS2.

10. Catalyst according to claim 11, characterized in that the catalyst consists of Mn(0.1 to 0.50)MoS2, preferably Mn(0.2 to 0.4)MoS2.

11. A process for preparing a manganese-promoted molybdenum(IV) sulfide catalyst, characterized by the steps:

(i) forming a mixture of water, ammonium molybdate ((NH^eMovCh d^O), thiourea (CH4N2S) and a water soluble manganese(II) salt in the desired molar ratio;

(ii) raising the temperature of this mixture in an autoclave to 150-250°C and increasing the pressure to such a level that part of the water remains liquid, the temperature and pressure being maintained until the thiourea decomposes;

(iii) washing the mixture from step (ii);

(iv) drying the washed mixture from step (iii);

(v) calcining the dried and washed mixture from step (iv) under inert gas to obtain the manganese-promoted MOS2 catalyst.

12. The method according to claim 11, characterized in that prior to step (v) of calcination, the mixture is mixed with a carrier.

13. The method according to claim 12, characterized in that the carrier is precipitated from a precursor compound during step (ii).

14. Catalyst for the reaction of carbon dioxide (CO2) and hydrogen (H2) to form methanol (CH3OH), characterized in that the catalytically active part of the catalyst consists of Mn(0.1 to 0.5)MoS2, preferably Mn(0, 2 to 0.4)MoS2.

15. Catalyst according to claim 14, characterized in that the catalyst has a support, the support preferably having AlO(OH) and/or Al2O3.