Process and catalyst for treatment of synthesis gas

Syngas treatment process and catalyst

Technical field

The present invention relates to a water gas shift reaction and a material suitable as a water gas shift catalyst. The water gas shift reaction (abbreviation: shift reaction) is a gas phase equilibrium reaction:

For any process involving synthesis gas, that is, steam reforming, ammonia synthesis, hydrogen and reducing gas production, etc., reaction balance is critical.

Therefore, the exhaust gas from the steam reforming process can be enriched with hydrogen by contacting the gas stream with a catalyst that promotes the shift reaction.

The water-gas shift reaction can also be used in the reverse way to produce carbon monoxide by hydrogenation of carbon dioxide. The production of carbon monoxide is usually achieved by minimizing the amount of water in the process gas and balancing the water gas shift reaction at high temperatures.

Our purpose is that the present invention can be applied in hydrogen production and carbon monoxide production.

Background technique

The shift reaction is exothermic and low temperature is conducive to CO conversion. Therefore, as long as the gas is in contact with a sufficiently active shift catalyst, the lower the temperature, the more the syngas shifts to CO2+H2. However, due to the exothermic nature of the shift reaction, the synthesis gas is usually balanced in at least two stages, where the first stage is operated at a higher temperature than the second stage. The usual practice is to distinguish between shift reaction at low temperature (usually 180-300°C, low temperature shift) and shift reaction at high temperature (usually 300-500°C, high temperature shift).

At present, the catalyst used for high temperature shift is iron oxide, which is usually mixed with chromium oxide. However, this catalyst has the disadvantage that if the syngas contains steam that is much lower than the carbon content-that is, if the oxygen/carbon ratio falls below a certain critical value (which is a function of temperature), it forms Methane. At temperatures exceeding 500°C, some methane formation is always observed. In addition, at 500°C and above, the catalyst deteriorates very quickly.

The catalyst material of the present invention contains a microscopic mixture of manganese oxide and zirconium oxide (Mn-Zr oxide), may optionally include other oxidation promoters, and may optionally include metal promoters.

The catalyst material of the present invention has the advantages of very high stability to water gas shift reaction and high selectivity (that is, no hydrocarbon formation), so it can replace or supplement traditional iron-based catalysts. If copper is used as the accelerator of the material of the present invention, the activity can be significantly improved. The use of metallic silver as a promoter of Mn-Zr oxide produces a similar effect, although the significant effect of increasing the activity is lower.

Compared with traditional high-temperature water-gas shift catalysts, another advantage of the catalyst of the present invention is that these materials have superior adhesion properties to other ceramic materials and metals. Therefore, the catalyst of the present invention is very suitable for the manufacture of catalytic hardware (hardware), and it can be applied in fixing and automatic devices that require water-gas shift active catalysts.

As we all know, manganese oxide and zirconium oxide have certain activity to catalyze the water gas shift reaction. But it is very surprising that there is a strong synergistic effect between these oxides. Therefore, the catalytic activity of the microscopic mixture of manganese oxide and zirconium oxide is much higher than that of any pure oxide, especially after a short time in the gas stream. This is proven in the examples of the present invention. Under comparable conditions at 450°C, pure manganese oxide has a conversion rate of 41-42%, pure zirconia has a conversion rate of 9-11%, and mixed manganese-zirconium oxide The catalyst has a conversion rate of 58-60%. In all cases, the equilibrium conversion under operating conditions is equal to 65%.

From the fact that the same prepared Mg/Zr and Mn/Ti oxides have very low activity, the synergistic effect of manganese oxide and zirconium oxide is particularly surprising. In fact, Mn/Ti oxide has even lower activity than pure manganese oxide (under the same conditions as in the above example, the conversion rate is 8-16%). Mg/Zr oxide has a slightly higher activity than pure zirconia (under the same conditions as the above example, the conversion rate is 14-17%), but this is because magnesium oxide itself is a more active transformation than zirconia Because of the reaction catalyst.

In addition, the mixed manganese-zirconium oxide catalyst has the surprising advantage of extremely high selectivity. This is demonstrated in the examples of the present invention, even if these materials are exposed to dry syngas, they will not result in the formation of any appreciable amount of methane. When the space velocity (GHSV) is 10000Nl/g/h, only 100ppm methane (0.01%) is formed at 500°C, and only 1000ppm methane (0.1%) is formed at 600°C. In fact, it can be shown that the selectivity is even higher, because under these conditions, even many microscopic impurities of transition metals will lead to the formation of methane.

Description of the prior art The industrial water gas shift is described in several publications, such as L. Lloyd et al. in MVTwigg (ed.) "Catalyst Handbook" Manson Publ., 1996; K. Kochloefl, Ch. 3.3 in G. Ertl , H.Kntzinger and J.Weitkamp (eds.) "Handbook of Heterogeneous Catalysis" Volume 4, Wiley-VCH, 1997; and JRRostrup-Nielsen & PEHφjlund-Nielsen in J.Oudar & H.Wise(eds. .) "Deactivation and Poisoning of Catalysts" Marcel Dekker, 1985.

For industrial high temperature water gas shift, the currently used catalysts are based on iron as the active metal component. The preferred formulation is always an iron-chromium catalyst as disclosed in US Patent No. 4,861,745. In EP0634990B1, chromium-free high temperature shift catalysts are required, but these catalysts are still based on iron as the active metal. Iron-based catalysts are also mentioned in EP062410B1.

The application of manganese oxide in combination with specific other components is known from the literature. Therefore, FMGottschalk and GJ Hutchings reported in Applied Catalysis 51, 127-139 (1989) the performance of cobalt manganese oxide, copper manganese oxide and iron manganese oxide as water gas shift catalysts. However, their research only involved the use of these materials at temperatures below 400°C. In addition, their research did not involve mixed manganese-zirconium oxide as a water-gas shift catalyst, which is the object of the present invention.

It can be understood from the literature that mixed manganese-zirconium oxide is used as an adsorbent for removing NO and NO2 from completely different aspects. This topic has been discussed in many papers, I. Matsukuma et al. in Applied Catalysis B 37, 107 (2002), K. Eguchi et al. in Applied Catalysis B 16, 69 (1998), K. Eguchi et al. in Journal of Catalysis 158, 420 (1996), K. Eguchi et al. in Bulletin of the Chemical Society of Japan 68, 1739 (1995). This field does not involve water gas shift reactions.

Various oxidizing compounds have been declared in ZA2001/3424 as catalysts for water-gas shift reactions at temperatures above 400°C. Among them are zirconia and manganese oxide supported on other oxides. However, this patent does not involve mixed Mn/Zr oxides. In addition, the activity of the catalyst of the present invention is much higher-without loss of selectivity-any catalyst composition required in the above-mentioned patents. Finally, the synergistic effect between manganese oxide MnO and zirconium oxide ZrO2 is amazing, and it produces the best activity for a relatively small range of combinations of these materials. As demonstrated in the examples of the present invention, although it is known that MgO is similar to MnO in chemical and physical properties, this synergistic effect does not therefore exist between magnesium oxide and zirconium oxide.

Summary of the invention

The purpose of the present invention is to provide a catalyst for catalyzing the water-gas shift reaction at high temperature without the formation of hydrocarbons.

The present invention can be used to enrich the synthesis gas with hydrogen and/or enrich the synthesis gas with carbon monoxide. With the help of the present invention, the production of hydrogen and carbon monoxide can be controlled by controlling the temperature and the amount of steam in the synthesis gas.

In a general embodiment of the present invention, at least 50% by weight of the catalyst in the reduced state is composed of manganese oxide and zirconium oxide, wherein the Mn/Zr ratio is between 0.05-5.00, more preferably between 0.05-1.00, and most preferably between Between 0.10-0.80.

In a specific embodiment of the present invention, copper is also used as a catalyst promoter, and its content is between 0.1% and 8.0% based on the weight of Cu in the reduction catalyst, more preferably between 0.1% and 4.0%.

In yet another specific embodiment of the present invention, the catalyst can be in the form of a sphere, extrudate, monolithic or geometrical body, and can be used as a coating on the wall of a tube for transporting the synthesis gas to be treated.

In a specific embodiment of the present invention, the catalyst is set in an adiabatic zone and operated at a temperature of 400°C-1000°C, more preferably between 500°C and 900°C.

In another specific embodiment of the present invention, the catalyst is arranged in the cooling zone in the flow direction of the processing gas. In this way, the inlet temperature is between 500°C and 1000°C, more preferably between 700°C and 900°C, The outlet temperature is between 400°C and 800°C, more preferably between 400°C and 700°C.

detailed description

The following examples are used to demonstrate the beneficial properties of the manganese/zirconium oxide catalyst in terms of activity, selectivity and stability for the water gas shift reaction.

The composition of the catalyst AW of the present invention with a general process including a comparative catalyst is listed in Table 7. Except for the remaining K, which is also listed in Table 7, the catalyst AH contains only Mn and Zr metal ions. Also includes catalysts I and J for comparison. Catalyst I contains Mg and Zr, while catalyst J contains Mn and Ti. The catalyst KO contains Zr, Mn ions, and another oxide-forming metal, while the catalyst QV contains Zr, Mn, and one of Cu or Ag. Catalysts P and W are commercial water gas shift catalysts for comparison.

Unless otherwise specified, all examples use the following process and process parameters.

In a copper-lined tubular reactor (with an outer diameter of 9.53 mm and an inner diameter of 4.6 mm) embedded in a self-ventilating furnace, 1.00 g of catalyst was arranged in a fixed bed manner. The loaded catalyst is in the form of particles with a particle size of 0.71-0.85 mm. Before entering the reactor, dry gas and steam are mixed at a temperature of 200°C and a selected reaction pressure. The reaction pressure is usually 25 barg. The size of the reactor allows the gas to be further heated to the desired temperature before reaching the catalyst. The temperature is controlled and monitored externally by a thermocouple on the reactor outside the center of the catalyst bed. Cool the exhaust gas at the rear of the catalyst zone and depressurize it to ambient conditions. The water in the exhaust gas is condensed in the separator, and the CO and CO2 in the remaining dry gas are continuously analyzed by the BINOS infrared sensor to monitor the influence of the catalyst on the gas composition during the heating and cooling process. Starting from about 200°C, the temperature of the reactor is increased at a rate of 4°C min-1 until it reaches a temperature T, which is usually 500°C, and stays. In this heating stage, the CO content in the dry exhaust gas (continuously measured by the BINOS device) is used to obtain the CO conversion rate as a function of temperature. The dry exhaust gas is periodically analyzed by gas chromatography (GC) at a residence temperature that allows the measurement of CO, CO2, H2, CH4, higher hydrocarbons and Ar. Use Ar as the internal standard. The mass balance (C, H and O) calculated based on the GC data and the weight of the condensed water is accurate to ±5%.

Introduce dry raw gas with a composition of 74.4% H2, 12.6% CO, 10.0% CO2, 3.0% Ar at the usual rate of 10.0Nl h-1, and at the same time supply at a usual rate of 4.25g h-1 with a steam/dry gas ratio of 0.53-0.54 is equivalent to water.

The catalyst stays in the gas stream at the residence temperature for 12-24 hours. While still in the gas stream, the reactor was cooled to 200-300°C and heated to T stay again in order to determine the activity of the spent catalyst. Sometimes, the catalyst has to be cooled and heated repeatedly.

Table 1-3 lists the observed CO conversion rates of various catalysts at four different temperatures. In each case, the maximum conversion rate specified by the equilibrium composition is included.

Example 1 The catalyst A was tested according to the general procedure above.

In the first heating stage, the CO conversion rate at 400°C was 6%, and the maximum conversion rate at this temperature was 79% (recorded as 6(79) in Table 1). At 425°C, 450°C, and 475°C, the observed conversion rates (equilibrium conversion rates) were 11 (79)%, 20 (69)%, and 30 (63)%, respectively. Stabilize the temperature and periodically analyze the exhaust gas by GC. At 500°C, the first GC analysis obtained within 1 hour confirmed the equilibrium composition of H2, CO, and CO2 in the gas, and showed that no hydrocarbons were formed. After 19 hours of gas flow, the exhaust gas was still found to be in equilibrium and free of hydrocarbons. Reduce the temperature to 220°C and increase it again at a rate of 4°C/min. The conversion rates at 400°C, 425°C, 450°C and 475°C are 10(79)%, 21(79)%, 36(69)% and 49(63)%, respectively.

Examples 2-6 were tested according to the procedure described in Example 1 for catalysts B, C, D, E, and F. The results are shown in Table 1. With these catalysts, the equilibrium conversion rate was maintained at 500°C, and no hydrocarbon formation was observed.

These examples demonstrate the effect of changes in the Mn/Zr ratio. When considering both activity and stability, catalysts C and D are the most preferable.

Examples 7-10 (comparative examples)

Catalysts G, H, I, and J were tested according to the procedure described in Example 1, and the results are shown in Table 1.

Catalyst G is pure zirconia, and catalyst H is pure manganese oxide. Catalyst I is a mixed magnesium-zirconium oxide with a Mg/Zr ratio of 0.38; that is, the composition is the same as that of catalyst C, but magnesium is substituted for manganese. Similarly, catalyst J is a mixed manganese-titanium oxide with a Mn/Ti ratio of 0.38. Thus, titanium replaces zirconium in this catalyst.

It is surprisingly found that these comparative catalysts all have very little activity compared to Catalyst C and other mixed Mn/Zr oxides.

Example 11 tested catalyst E according to the procedure described in Example 1, except that the difference was that the T stay was 650°C. As expected, the initial conversion rate is very close to the previous test of Catalyst E (Example 5); the difference is due to the uncertainty of the test. Due to the higher T retention value, the conversion rate of the gas stream after 21 hours is lower than that of Example 5.

Example 12 tested Catalyst D as described in Example 1, except that the difference was that the total pressure was changed between 2 barg and 25 barg. The results are shown in Table 1.

This example is used to demonstrate that these catalysts can be used in a wide range of working pressures.

The catalysts K, L, M, N and O of Examples 13-17 all contained additional oxidation promoters; see Table 7. Test the catalyst as described in Experiment 1. In order to measure the loss of activity, the catalyst K was repeatedly heated to 500°C and cooled.

The results are shown in Table 2. It was found that the relative activity loss caused by catalyst aging can be improved by adding oxidation promoters such as yttrium, niobium and other promoters.

In Example 18, the catalyst K was tested in the same manner as described in Example 1 except for the following differences. A catalyst of 0.15 g in quantity and dead-burned alumina particles of 0.85 g in quantity with the same particle size as the catalyst were mixed. The surface area of alumina is 6m2/g, and it is noted that alumina itself has no measurable activity below 600°C. The dry gas flow rate is 11Nl/h, and the steam/dry gas ratio is 0.35. The catalyst was heated to a temperature of 600°C under a pressure of 3 bara, and kept in a gas stream under these conditions for 137 hours, while periodically measuring the CO conversion rate. The results are shown in Table 3.

Considering that the temperature is very high, the loss of activity is surprisingly alleviated. In addition, after about 60 hours in the gas stream, the catalyst deactivation appeared to cease.

Example 19 This example was implemented as described in Example 18, with the difference that the temperature was 550°C.

Examples 20-23 These examples are used to demonstrate the extremely high selectivity of the mixed Mn-Zr oxide shift catalyst.

The catalysts D, E, and B were tested in the same manner as described in Example 1, except that the steam/dry gas ratio and the operating temperature T stay were changed. Examples 20 and 21 demonstrate that the methane formation after the introduction stage is below the detection limit of 15 ppm. At these high temperatures, when using traditional iron-based high temperature shift catalysts, the methane output is very large; see Comparative Example C22.

In Example 23 (see Table 4A), the catalyst B was tested in dry synthesis gas at 500°C, 550°C and finally at 600°C, a common iron-based catalyst would result in excessive hydrocarbon formation. However, with Mn-Zr catalysts, even under these conditions, hydrocarbon formation is very low. This embodiment forms the basis of the second possible application of the present invention, namely the carbon monoxide production process. At all three temperatures, the CO2 conversion rate was found to be close to equilibrium.

Examples 24-30 implement these examples as described in Example 1. Catalyst QS contains different concentrations of copper as a metal promoter component, while catalyst TV contains silver.

The results given in Table 5 clearly demonstrate the beneficial effects of adding silver, especially copper, to the Mn-Zr catalyst of the present invention. No methane formation was observed at any time using the catalyst QV.

Examples 31-34 These examples are used to demonstrate that compared with commercial Cu-Zn-Al low-temperature water-gas shift catalysts, the Mn-Zr oxide catalyst with Cu as a promoter has improved oxygen resistance. Perform the test according to the following method. The reactor settings are the same as the previous examples. 0.5g of inert alumina with the same particle size and 0.5g of catalyst were mixed and filled into the reactor. The reactor was pressurized with synthesis gas to a total pressure of 3 bara. The reactor was heated to 150°C in 10 Nl/h of dry synthesis gas. Then add 5.3Nl/h of steam to the process gas. The reactor is heated to temperature T for oxidation and reduction in the gas stream and stays in the gas stream for 1 hour.

After this initial process, the catalyst is subjected to multiple redox cycles with alternating producer gas and syngas according to the following process. Cut off the process gas flow and replace it with dry air with a flow rate of 10 Nl/h for 15 minutes. Cut off the air and replace it with syngas (10.0Nl/h) and steam (5.3Nl/h) while keeping the temperature at T redox. Then the temperature was lowered to 280°C in the case of catalyst S, and to 200°C in the case of a commercial Cu-Zn-Al oxide catalyst to determine the CO conversion rate.

Table 6 lists the activities in terms of% CO conversion and relative CO conversion after each redox cycle.

Comparing Example 31 and Example C33, it is obvious that even if the operating temperature T is 80°C higher in the case of the Mn-Zr oxide catalyst with Cu as the accelerator than in the case of the Cu-Zn-Al catalyst, Cu is used for promotion. The Mn-Zr oxide catalyst S still has a significantly smaller activity loss than the Cu-Zn-Al oxide catalyst. Comparing Example 32 and Example C34, the same trend can be seen.

Table 1 Activity of MnO-ZrO2 without accelerator and comparative catalyst

Table 2 Activity of catalysts containing oxidation promoters

Table 3 Activity of catalyst K under high temperature, low steam content, high GHSV and low pressure

Table 4 Changes in steam content

NM = not measured Table 4A

Table 5 Activity of catalysts with Cu and Ag as promoters

Table 6 The activity of the catalyst with Cu as the accelerator after exposure to air

Table 7 Catalyst composition

NM = not detected