CN100493700C - A kind of preparation method of ruthenium-based ammonia synthesis catalyst - Google Patents

Abstract

An Ru-based catalyst for synchronizing ammonia from H2 and N2 is composed of Ru as active center and metal oxide (MgO) as carrier, and is prepared through adding the aqueous solution of ammonia to the aqueous solution of magnesium nitrate, filtering to obtain Mg(OH)2 deposit, washing, baking, calcining, adding it to the solution of reducer, stirring, cooling in ice water bath, stirring while evaporating, filling H2 to obtain Ru/MgO, adding it along with nitrate of alkali metal (MNO3) to solvent, laying aside, stirring while evaporating, and filling H2.

Description

A kind of preparation method of ruthenium-based ammonia synthesis catalyst

technical field

The present invention relates to an ammonia synthesis catalyst, in particular to a method for preparing a highly active novel ammonia synthesis catalyst with ruthenium (Ru) as the active center and metal oxides such as magnesium oxide (MgO) as the carrier, suitable for hydrogen and nitrogen Ammonia synthesis reaction.

Background technique

At present, the problem of energy depletion has become a global concern and an urgent problem to be solved. Before alternative energy sources are found, reducing energy consumption has become an important means to slow down energy depletion and ensure sustainable economic development. The ammonia industry consumes a lot of energy, consuming about 1% of the world's energy every year. At present, the industrial ammonia synthesis catalysts used at home and abroad mainly use multi-promoted iron-based catalysts, usually made of selected magnetite and a series of additives with different contents (such as Al2O ₃ , K20, CaO, MgO, BaO, etc.) Mixed, made by melting and cooling. The cost of this traditional catalyst is low, but it needs to react under high temperature and high pressure conditions, and the energy consumption is too high. The energy crisis will lead to a substantial increase in the cost of ammonia synthesis. To reduce costs, energy consumption must be reduced. Ammonia synthesis catalysts are one of the most direct factors for reducing energy consumption. The development of a catalyst with higher activity at lower temperature and pressure is beneficial to reduce energy consumption, reduce costs and enhance the competitiveness of enterprises. The supported ruthenium-based ammonia synthesis catalyst has the characteristics of high activity at low temperature and low pressure. It is known as a new generation of ammonia synthesis catalyst and has been extensively studied in the world. In November 1992, BP and Kellogg (Report Article in ApplCatal A: General. 93 (1993) N16) jointly developed a carbon-supported ruthenium-based ammonia synthesis catalyst, which was applied to the KAAP process and was first industrialized at the Ocelot ammonia plant in Canada. This process has high synthesis efficiency, less catalyst consumption, mild reaction conditions, 1.06×106kJ reduction in energy consumption per ton of ammonia, and the renewable use of precious metal ruthenium in the catalyst, which is a major technological revolution in the ammonia synthesis industry.

Under the reaction conditions of high temperature and high pressure, methanation of ordinary activated carbon will lead to the loss of active components, thereby greatly reducing the activity of the catalyst. British Petroleum BP developed graphite-containing carbon in 1974 (Chemical Engineering. Chementator. 3 (1993) 19), which has better stability and activity than ordinary activated carbon. However, graphite-containing carbon has poor mechanical strength, and needs to be prepared by secondary high-temperature treatment and primary oxidation treatment. The energy consumption and production cost are relatively high, and the production operation and control are relatively complicated. Therefore, in recent years, researchers of ammonia synthesis catalysts tend to choose difficult-to-reduce metal oxides as supports for ruthenium-based catalysts.

Domestic researchers are also committed to the research of highly active supported ruthenium-based ammonia synthesis catalysts. For example, the patent application whose publication number is CN1270081A discloses an ammonia synthesis catalyst with ruthenium as the active center, activated carbon as the carrier, and alkaline earth metals, rare earths, etc. as auxiliary agents. The loading amount of ruthenium is 0.1%-16%wt, and the molar ratio of ruthenium to additive is 0.01-10. It is prepared by dipping. The patent application with publication number CN1481933A discloses a new type of catalyst for ammonia synthesis production, which uses ruthenium as the active component, alkali metal or alkaline earth metal fluoride as an auxiliary agent, and a highly active ammonia synthesis catalyst with magnesium oxide as a carrier and its preparation method. The loading amount of Ru Ru/MgO is 3%-8%, the molar ratio of Ru to MFx is 0.5-8, and the solvent used is water or an organic solvent capable of dissolving RuCl ₃ ·nH ₂ O or ruthenium carbonyl. It is prepared by impregnation method or mechanical mixing calcining and impregnation method respectively.

Contents of the invention

The object of the present invention is to provide a kind of preparation method of novel ruthenium-based ammonia synthesis catalyst for the problems of its low activity and poor stability of the existing loaded-type nail-based ammonia synthesis catalyst, which catalyst (with hydrogen and nitrogen as raw materials In the production process of synthetic ammonia), it has a higher activity of nitrogen and hydrogen into ammonia and better stability.

Said catalyzer of the present invention is the Ru-MNO 3 /MgO system that the noble metal ruthenium and a kind of alkali metal nitrate on the nano magnesium oxide (12～14nm) are supported on the Ru-MNO ₃ /MgO system, said catalyzer is active component with Ru, with MgO is used as a carrier, and alkali metal nitrate _MNO3 is used as an auxiliary agent. The loading capacity of Ru Ru/MgO is 2Wt%-8Wt%, the molar ratio of _MNO3 to Ru is 0.5-8, and the reducing agent used is hexanediol, One of formaldehyde and hydration trap, etc., and the solvent of impregnation aid is one of hexylene glycol, water and ethanol, etc. The loading amount of Ru is preferably 2Wt%-6Wt%, and the molar ratio of MNO ₃ to Ru is preferably 1-5. Ru can come from RuCl ₃ ·nH ₂ O or ruthenium carbonyl, etc., where n is the number of crystal water, the amount of reducing agent used is 10-50ml per gram of MgO, and the amount of solvent is 10-30ml per gram of Ru/MgO.

The concrete steps of the said preparation ruthenium-based ammonia synthesis catalyst of the present invention are:

1) Add ammonia solution to the aqueous solution of magnesium nitrate until the pH value is 8-11, filter the Mg(OH) ₂ precipitate, wash it with deionized water, and then dry it;

2) Calcining at 400-700°C for 0.5-3h, then calcining at 400-700°C for 3-8h under _N2 atmosphere;

3) Add RuCl ₃ ·nH ₂ O to MgO in a ratio of 3 to 25:100 by mass to the reducing agent solution, stir evenly and cool in an ice-water bath;

4) stirring and evaporating to dryness;

5) Pass hydrogen at 325-425°C to obtain Ru/MgO;

6) Add the prepared Ru/MgO and the auxiliary agent alkali metal nitrate MNO ₃ into the solvent in a mass ratio of 100:5-20;

7) stirring and evaporating to dryness;

8) Through hydrogen to obtain the target product.

In step 1), add a certain amount of ammonia solution to the aqueous solution of magnesium nitrate until the pH value is 11, filter the Mg(OH) _precipitate , wash it with deionized water at least once, and then dry it at 80 ~180°C.

In step 1), the drying temperature is 100°C.

In step 2), calcination was performed at 600 °C in air for 1 h, followed by calcination at 600 °C for 5 h under _N2 atmosphere.

In step 3), stir evenly at 60-180° C. and cool in an ice-water bath.

In step 4), stirring and evaporating to dryness at 160-250°C;

In step 6), the prepared Ru/MgO and the auxiliary alkali metal nitrate MNO ₃ are added to the solvent in a mass ratio of 100:5-20, stirred for 3-12 hours and then left to stand.

In step 7), stir and evaporate to dryness at 160-250°C.

In step 8), pass hydrogen gas at 325-425° C. to obtain the target product.

It can be tabletted, crushed and sieved (35-60 mesh) before use.

The catalyst mentioned in the invention is used for catalytically synthesizing ammonia with nitrogen-hydrogen mixed gas.

Compared with existing similar catalysts, the advantage of the said catalyst of the present invention is that the ruthenium metal colloids with better particle size and crystal structure are reduced under certain temperature conditions by utilizing reducing agents such as hexanediol and make it uniformly loaded on the on nano-magnesium oxide. The catalyst prepared by using hexylene glycol as the solvent impregnation aid has the highest activity, and no water solvent is used in the whole preparation process, which avoids the formation of Mg(OH) ₂ , improves the dispersion of Ru and the utilization rate of the metal surface, and at the same time has a good Controlling the size of ruthenium particles greatly improves the catalytic activity. The catalytic ammonia synthesis activity of the said catalyst of the present invention has very high activity at low temperature and low pressure, at 385 ℃, pressure 0.2MPa, its activity is as high as 6341.5μmolh-1g-1-cat under the flow rate of 2100ml/h. 10 to 13 times that of the same type of ruthenium-based catalyst prepared by the method.

Detailed ways

The following examples will illustrate the present invention in more detail.

Example 1

Add 2g of nano-magnesium oxide and 0.21g of RuCl ₃ ·nH ₂ O into 50ml of hexanediol solution, heat to 180°C in an oil bath, stir for 1.5h, then put it in an ice-water bath and stir for 3h; stir at 160-250°C Evaporate to dryness and remove the organic solution. The obtained solid powder was passed through hydrogen at 425°C for 12 hours to remove chloride ions. Dissolve 0.15g _KNO3 in about 20ml of hexanediol solution, put 1g of the prepared Ru/MgO into the _KNO3 hexanediol solution with stirring and impregnate for 6h, stir and evaporate to dryness at 160-250°C, and the obtained Catalyst at 425 ° C, through hydrogen for 3 hours to remove the remaining hexanediol. Take about 0.2 g of catalyst and place it in a reaction tube to measure its catalyst activity at a pressure of 0.2 MPa and a flow rate of 2100 ml/h. The catalyst KNO ₃ -Ru/MgO-con prepared by the traditional method was also prepared and evaluated under the same conditions. The results show that the activity of the ammonia synthesis catalyst prepared by the new catalyst preparation method is higher than that of the traditional method, as shown in Table 1.

Table 1. Catalyst KNO ₃ -Ru/MgO and reference catalyst KNO ₃ -Ru/MgO-con activity comparison (μ molh-1g-1-cat)

Reaction temperature/K 598 623 648 658 673 698 KNO₃-Ru/MgO 82.1 143.8 410.3 495.6 595.1 656.3 KNO₃Ru/MgO-con 1161.2 2500.9 5001.8 6341.5 5269.6 4287.1

Example 2

Add 2.0g nano-magnesium oxide and 0.21g RuCl ₃ ·nH ₂ O into 50ml of hexanediol solution, heat to 80°C in an oil bath, stir for 2.5h, then put it in an ice-water bath and stir for 5h; at 160～250°C Stir and evaporate to dryness to remove the organic solution. The obtained solid powder was passed through hydrogen at 425°C for 12 hours to remove chloride ions. Dissolve 0.15g _KNO3 in about 20ml of hexanediol solution, put 1g of the prepared Ru/MgO into the _KNO3 hexanediol solution with stirring and impregnate for 6h, stir and evaporate to dryness at 160-250°C, and the obtained The catalyst was passed through hydrogen at 425°C for 3 hours to remove the remaining hexanediol. Take about 0.2 g of catalyst and place it in a reaction tube to measure its catalyst activity at a pressure of 0.2 MPa and a flow rate of 2100 ml/h.

Example 3

Add 2g nano-magnesium oxide and 0.21g RuCl ₃ ·nH ₂ O into 50ml of hexanediol solution, heat to 140°C in an oil bath, stir for 0.5h, then put it in an ice-water bath and stir for 3h; stir at 160-250°C Evaporate to dryness and remove the organic solution. The obtained solid powder was passed through hydrogen at 425°C for 12 hours to remove chloride ions. Dissolve 0.15g _KNO3 in about 20ml of hexanediol solution, put 1g of the prepared Ru/MgO into the _KNO3 hexanediol solution with stirring and impregnate for 6h, stir and evaporate to dryness at 160-250°C, and the obtained Catalyst at 425 ° C, through hydrogen for 3 hours to remove the remaining hexanediol. Take about 0.2 g of catalyst and place it in a reaction tube to measure its catalyst activity at a pressure of 0.2 MPa and a flow rate of 2100 ml/h. The results are shown in Table 2. The results showed that the catalytic activity was the highest when the reduction temperature was 180 °C.

Table 2. Effect of different reduction temperatures on catalyst activity

Reduction temperature/℃ 80 100 120 140 160 180 Activity (μ molh-1g-1-cat) 3210.3 3347.8 4000.0 4194.2 5380.8 6341.5

Example 4

Add 2g of nano-magnesium oxide and 0.105g of RuCl ₃ ·nH ₂ O into 15ml of hexanediol solution, heat to 140°C in an oil bath, stir for 2 hours, then put it in an ice-water bath and stir for 3 hours: Stir and steam at 160-250°C Dry and remove the organic solution. The obtained solid powder was passed through hydrogen at 425°C for 12 hours to remove chloride ions. Dissolve 0.075g _KNO3 in about 15ml of hexanediol solution, put 1g of the prepared Ru/MgO into the _KNO3 hexanediol solution with stirring and impregnate for 6h, stir and evaporate to dryness at 160-250°C, and the obtained Catalyst at 425°C, pass hydrogen for 3 hours to remove remaining hexanediol to obtain K-Ru/MgO.

Example 5

Add 2g nano-magnesium oxide and 0.42g RuCl ₃ ·nH ₂ O into 50ml of hexanediol solution, heat to 140°C in an oil bath, stir for 3 hours, then put it in an ice-water bath and stir for 1 hour; stir and steam at 160-250°C Dry and remove the organic solution. The obtained solid powder was passed through hydrogen at 425°C for 12 hours to remove chloride ions. Dissolve 0.075g KNO ₃ in about 20ml of hexanediol solution, put 1g of the prepared Ru/MgO into the KNO ₃ hexanediol solution with stirring and impregnate for 12h, stir and evaporate to dryness at 160-250°C, and the obtained Catalyst at 425°C, pass hydrogen for 1 hour to remove remaining hexanediol to obtain catalyst K-Ru/MgO.

Example 6

Add 2g of nano-magnesia and 0.105g of RuCl ₃ nH ₂ O into 50ml of hexanediol solution, heat to 160°C in an oil bath, stir for 3 hours, then put it in an ice-water bath and stir for 1 hour; stir and steam at 160-250°C Dry and remove the organic solution. The obtained solid powder was passed through hydrogen gas at 425°C for 12 hours to remove chloride ions. Dissolve 0.25g _KNO3 in about 50ml of hexanediol solution, put 1g of the prepared Ru/MgO into the _KNO3 hexanediol solution with stirring and impregnate for 6h, stir and evaporate to dryness at 160-250°C, and the obtained Catalyst at 425 ° C, through hydrogen for 6 hours to remove the remaining hexanediol to obtain the catalyst K-Ru/MgO.

Example 7

Prepare the KNO ₃ -Ru/MgO catalyst of different K/Ru mol ratios (1/1～5/1) by the method for example 1, the loading capacity of ruthenium is 4%wt, catalyst consumption 0.2g, at pressure is 0.2MPa, reaction The ammonia synthesis activity was evaluated under the condition that the temperature was 658K, the synthesis gas composition was N ₂ /H ₂ =1/3, and the flow rate was 2100ml/h. The results are shown in Table 3. The results show that when the K/Ru molar ratio is 3, the catalyst activity is the highest.

Table 3. Effect of different K/Ru ratios on catalyst activity

K/Ru molar ratio 1 3/2 2 3 4 Activity (μ molh-1g-1-cat) 5217.4 5460.5 6014.8 6341.5 4410.4

Example 8

The Ru/MgO catalyst was prepared according to the method in Example 1, the loading amount of ruthenium was 4%wt, water was used as the solvent impregnation aid (K/Ru=3), and the catalyst was spun to dryness at 70°C. The amount of the catalyst is 0.2g, the ammonia synthesis activity is evaluated under the conditions of the pressure of 0.2MPa, the reaction temperature of 658K, the synthesis gas composition of N ₂ /H ₂ =1/3, and the flow rate of 2100ml/h. The results are shown in Table 4. The results show that the organic solvent hexylene glycol is a better solvent than water for impregnating aids.

Table 4. Effect of different solvents on catalyst activity

Reaction temperature/K 598 623 648 658 673 698 KNO₃-Ru/MgO(Water) 660.3 776.8 1320.5 1785.2 2252.2 3105.4 KNO₃-Ru/MgO(hexanediol) 1161.2 2500.9 5001.8 6341.5 5269.6 4287.1

Claims (4)

1, a kind of preparation method of ruthenium-base ammonia synthetic catalyst is characterized in that concrete steps are:

1) adding ammonia spirit to pH value in the aqueous solution of magnesium nitrate is 8～11, with Mg (OH) ₂Sedimentation and filtration and spend deionised water after dry;

2) calcine 0.5～3h down at 400～700 ℃, then at N ₂400～700 ℃ of calcining 3～8h under the atmosphere;

3) press RuCl ₃NH ₂The mass ratio of O and MgO is that 3～25: 100 ratio joins in the reductant solution, and cool off in ice-water bath the back that stirs under 60～180 ℃, and described reducing agent is formaldehyde or hydrazine hydrate;

4) stir evaporate to dryness down at 160～250 ℃;

5) logical hydrogen obtains Ru/MgO under 325～425 ℃;

6) with prepared Ru/MgO and additive alkali metal nitrate MNO ₃Ratio in mass ratio 100: 5～20 adds in the solvent, leaves standstill behind stirring 3～12h, and described solvent is an ethanol;

7) stir evaporate to dryness down at 160～250 ℃;

8) logical hydrogen gets target product under 325～425 ℃.

2, a kind of preparation method of ruthenium-base ammonia synthetic catalyst as claimed in claim 1 is characterized in that in step 1), and adding certain density ammonia spirit to pH value in the aqueous solution of magnesium nitrate is 11, with Mg (OH) ₂Sedimentation and filtration and spend deionised water at least 1 time after oven dry, bake out temperature is 80～180 ℃.

3, a kind of preparation method of ruthenium-base ammonia synthetic catalyst as claimed in claim 2 is characterized in that in step 1), and bake out temperature is 100 ℃.

4, a kind of preparation method of ruthenium-base ammonia synthetic catalyst as claimed in claim 1 is characterized in that in step 2) in, in 600 ℃ of following air, calcine 1h, then at N ₂Atmosphere is calcined 5h down for following 600 ℃.