JP3803852B2

JP3803852B2 - Method for producing ammonia synthesis catalyst

Info

Publication number: JP3803852B2
Application number: JP21506899A
Authority: JP
Inventors: 進日数谷; 正義市来
Original assignee: Hitachi Zosen Corp
Current assignee: Kanadevia Corp
Priority date: 1999-07-29
Filing date: 1999-07-29
Publication date: 2006-08-02
Anticipated expiration: 2019-07-29
Also published as: JP2001038210A

Description

【０００１】
【発明の属する技術分野】
この発明は、活性炭からなる担体に貴金属と、アルカリ金属、アルカリ土類金属または希土類金属とを担持してなるアンモニア合成触媒を調製する方法に関する。
【０００２】
【従来の技術】
活性炭を触媒担体としこれに貴金属を担持してなるアンモニア合成触媒において、高活性を得るためには活性炭上の貴金属化合物のアニオンまたは配位子を除去するために貴金属化合物担持活性炭を水素気流下、４５０℃以上の高温で２時間以上加熱処理する必要がある。この処理により、促進剤として添加されるアルカリ金属やアルカリ土類金属から貴金属へ電子が効果的に供与され、アンモニア合成反応の律速段階である貴金属上での窒素の活性化が促進される。
【０００３】
【発明が解決しようとする課題】
アンモニア合成において高活性を得るために必要な上記条件での貴金属化合物担持活性炭の加熱処理は、安全対策を施した設備、および、処理中の監視要員を必要とし、これらが触媒製造コスト高を招く要因となる上に、高温で水素を扱うため危険を伴うものであった。
【０００４】
本発明が解決しようとする課題は、触媒製造コストの増加の要因となる、安全対策を施した設備や監視のための人員が必要でなく、また活性炭上に担持された貴金属化合物のアニオンまたは配位子を安全に除去することができる、アンモニア合成触媒の製造方法を提供することである。
【０００５】
【課題を解決するための手段】
本発明によるアンモニア合成触媒の製造方法は、活性炭からなる担体に貴金属と、アルカリ金属、アルカリ土類金属または希土類金属とを担持してなるアンモニア合成触媒を調製するに当たり、上記貴金属の化合物を担持した活性炭担体を不活性ガス雰囲気下で熱処理して担体上に該貴金属化合物を固定化した後、貴金属化合物担持活性炭を多価アルコール液中で加熱し、担体上の貴金属化合物からそのアニオンまたは配位子を除去することを特徴とする方法である。
【０００６】
活性炭担体上への貴金属化合物の固定化工程において、貴金属化合物担持活性炭を好ましくは不活性ガス雰囲気下、例えば窒素雰囲気下で、好ましくは温度１００〜４５０℃で、好ましくは１〜３時間以上熱処理する。この時の昇温速度は５℃／ｍｉｎ以下とすることが好ましい。この固定化処理によって、後続の貴金属化合物担持活性炭の多価アルコール液中での加熱工程において活性炭担体から貴金属化合物が溶出するのを可能な限り少なくすることができる。
【０００７】
貴金属化合物担持活性炭の多価アルコール液中での加熱工程において、貴金属化合物担持活性炭を多価アルコール液に浸漬し同液を好ましくは温度１２０〜１９０℃に加熱するか、または貴金属化合物担持活性炭を好ましくは温度１２０〜１９０℃の加熱多価アルコール液に浸漬する。この操作により、活性炭に担持されている貴金属化合物と多価アルコールが反応し、貴金属化合物のアニオンまたは配位子が多価アルコールに取り込まれることによって、活性炭担体上の貴金属化合物からそのアニオンまたは配位子が除去される。上記処理の後、多価アルコールから貴金属化合物担持活性炭を取り出し活性炭に付着している多価アルコールを除去するために十分水洗する。
【０００８】
多価アルコールとしてエチレングリコール、プロピレングリコールまたはそれらの混合物を使用することが好ましい。
【０００９】
貴金属化合物としてはルテニウムの塩化物をはじめとする水溶性化合物、およびＲｕ₃（ＣＯ）₁₂をはじめとするルテニウムのカルボニル化合物および錯体を使用するのが好ましい。貴金属（例えばルテニウム）換算濃度で好ましくは１〜１００ｇ／ｌの貴金属化合物溶液に、活性炭からなる担体を好ましくは１〜２４時間浸漬し、貴金属化合物を活性炭に担持する。その後貴金属化合物溶液から活性炭を取り出し充分垂れ切りを行う。
【００１０】
活性炭としては下記の方法で前処理を施したものが好ましく用いられる。すなわち、活性炭を好ましくは温度１００〜１２０℃で好ましくは１〜３時間乾燥し、この乾燥活性炭をＫＯＨ、ＮａＯＨをはじめとするアルカリ金属水酸化物水溶液またはアルカリ土類金属水酸化物水溶液に通常は室温で好ましくは１〜２４時間浸漬し、その後充分水洗し、好ましくは温度１００〜１２０℃で好ましくは１〜３時間乾燥する。この前処理を行うことにより、触媒に悪影響を及ぼす活性炭中の酸性官能基が除去される。
【００１１】
アルカリ金属、アルカリ土類金属または希土類金属を貴金属化合物担持活性炭に担持する工程において、アルカリ金属、アルカリ土類金属または希土類金属の水溶性化合物を用いる。該水溶性化合物としてはアルカリ金属、アルカリ土類金属または希土類金属の硝酸塩、炭酸塩が好ましい。貴金属化合物担持活性炭を上記水溶性化合物の水溶液に好ましくは１〜２４時間浸漬し、アルカリ金属、アルカリ土類金属または希土類金属を同活性炭に吸着および／または含浸により担持する。その後、これを水溶液から取り出した後、水素またはアンモニア合成ガス（水素＋窒素）雰囲気下で通常は１１０℃程度まで徐々に昇温しこの温度で好ましくは１〜３時間保持した後、好ましくは温度４５０℃程度まで徐々に昇温しこの温度で好ましくは２〜５時間保持し、上記水溶性化合物からアニオンを除去する。
【００１２】
活性炭からなる担体はそのままの形態で用いてもよいが、板状、ハニカム状等の、基体に保持された形状をなすものであってもよい。
【００１３】
【発明の実施の形態】
つぎに、本発明を実施例により具体的に説明する。
【００１４】
実施例１
(1) バインダーとして酸化珪素−酸化アルミニウムを約３０％含有する活性炭ハニカムを１１０℃で１時間乾燥した。乾燥後の重量は約０．８ｇであった。乾燥した活性炭ハニカムを１Ｎ水酸化カリウム水溶液４０ｍｌに浸漬した。これを２４時間後水酸化カリウム水溶液から取り出し、イオン交換水で水洗後、１００ｍｌのイオン交換水中に浸漬した。これを２４時間後イオン交換水から取り出し１１０℃で１時間乾燥した。
【００１５】
(2)上記前処理を施した活性炭ハニカムをルテニウム換算で４０ｇ／ｌの塩化ルテニウム水溶液２０ｍｌに浸漬した。これを２４時間後水溶液から取り出し充分垂れ切りを行った後、窒素雰囲気下、３００℃で１時間熱処理した。
【００１６】
(3) 得られたルテニウム化合物担持活性炭ハニカムを常温でエチレングリコール液に浸漬し、オイルバス上でエチレングリコール液を１６５℃まで加熱しこの温度に保持し、担持されたルテニウムの塩化物アニオンを除去した。加熱の際、ルテニウム化合物担持活性炭ハニカムからルテニウム化合物が幾分溶出しエチレングリコール液が褐色に着色した。液の色は１６５℃保持の間に黒色に変化し最後は透明になった。この時点で処理を終了した。
【００１７】
上記処理の後、ルテニウム化合物担持活性炭ハニカムをエチレングリコール液から取り出し、十分水洗し、活性炭に吸着したエチレングリコールを除去した。
【００１８】
(4) 水洗後のルテニウム担持活性炭ハニカムを０．０９２ｍｏｌ／ｌに調整した硝酸バリウム水溶液に一晩浸漬した。
【００１９】
これをバリウム水溶液から取り出した後、アンモニア合成ガス雰囲気（Ｈ₂ ／Ｎ₂ ＝３）下、２００℃／ｈの速度で１１０℃まで昇温しこの温度に１時間保持し、更に１０℃／ｍｉｎの速度で４５０℃まで昇温しこの温度に２時間保持し、触媒中の硝酸根を除去した。その後これを所定の温度まで冷却しアンモニア合成触媒を得た。
【００２０】
実施例２
実施例１の工程(2) において、塩化ルテニウム水溶液浸漬後の活性炭ハニカムを窒素雰囲気下で熱処理する際、処理温度を変化させた点以外、実施例１と同様の操作を行い、８種のアンモニア合成触媒を得た。
【００２１】
比較例１
実施例１の工程(3) の代わりに、ルテニウム担持活性炭ハニカムを水素気流下、温度４５０℃で２時間処理した点以外、実施例１と同様の操作を行い、アンモニア合成触媒を得た。
【００２２】
性能試験
ａ）実施例１および比較例１で得られたアンモニア合成触媒について、下記の条件でそれぞれアンモニア合成の反応速度を測定した。測定結果を表１に示す。
【００２３】

【表１】

表１から明らかなように、実施例１の触媒は比較例１のものに比べ遜色のないアンモニア合成活性を示した。
【００２４】
ｂ）実施例２で得られた８種のアンモニア合成触媒について、上記の条件でそれぞれアンモニア合成の反応速度を測定した。測定結果を図１に示す。
【００２５】
図１から明らかなように、ルテニウム担持後の窒素雰囲気下での熱処理温度を３００℃付近で行ったものが高いアンモニア合成活性を示した。
【００２６】
【発明の効果】
本発明により、触媒製造コストの増加の要因となる、安全対策を施した設備や監視のための人員が必要でなく、また活性炭上に担持された貴金属化合物のアニオンまたは配位子を安全に除去することができる、アンモニア合成触媒の製造方法が提供される。
【図面の簡単な説明】
【図１】ルテニウム担持後の窒素雰囲気下での熱処理温度とアンモニア合成活性の関係を示すグラクである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preparing an ammonia synthesis catalyst in which a noble metal and an alkali metal, alkaline earth metal or rare earth metal are supported on a support made of activated carbon.
[0002]
[Prior art]
In an ammonia synthesis catalyst in which activated carbon is used as a catalyst support and a noble metal is supported thereon, in order to obtain high activity, the noble metal compound-supported activated carbon is removed under a hydrogen stream in order to remove anions or ligands of the noble metal compound on the activated carbon. It is necessary to perform heat treatment at a high temperature of 450 ° C. or higher for 2 hours or longer. By this treatment, electrons are effectively donated from the alkali metal or alkaline earth metal added as a promoter to the noble metal, and the activation of nitrogen on the noble metal, which is the rate-limiting step of the ammonia synthesis reaction, is promoted.
[0003]
[Problems to be solved by the invention]
Heat treatment of precious metal compound-supported activated carbon under the above conditions necessary for obtaining high activity in ammonia synthesis requires equipment with safety measures and monitoring personnel during the treatment, which lead to high catalyst production costs Besides being a factor, handling hydrogen at high temperatures is dangerous.
[0004]
The problem to be solved by the present invention is that there is no need for safety-equipped equipment or monitoring personnel, which causes an increase in catalyst production costs, and the anion or arrangement of noble metal compounds supported on activated carbon. It is an object of the present invention to provide a method for producing an ammonia synthesis catalyst capable of removing a ligand safely.
[0005]
[Means for Solving the Problems]
The method for producing an ammonia synthesis catalyst according to the present invention comprises carrying the above precious metal compound when preparing an ammonia synthesis catalyst comprising a support made of activated carbon supporting a noble metal and an alkali metal, alkaline earth metal or rare earth metal. After heat-treating the activated carbon support in an inert gas atmosphere to immobilize the noble metal compound on the support, the noble metal compound-supported activated carbon is heated in a polyhydric alcohol solution, and the anion or ligand is converted from the noble metal compound on the support. It is the method characterized by removing.
[0006]
In the step of immobilizing the noble metal compound on the activated carbon support, the noble metal compound-supported activated carbon is preferably heat-treated in an inert gas atmosphere, for example, in a nitrogen atmosphere, preferably at a temperature of 100 to 450 ° C., and preferably for 1 to 3 hours or more. . It is preferable that the temperature increase rate at this time shall be 5 degrees C / min or less. By this immobilization treatment, it is possible to minimize the elution of the noble metal compound from the activated carbon support in the subsequent heating step of the activated carbon supporting the noble metal compound in the polyhydric alcohol solution.
[0007]
In the heating step of the noble metal compound-supported activated carbon in the polyhydric alcohol solution, the noble metal compound-supported activated carbon is immersed in the polyhydric alcohol solution and the solution is preferably heated to a temperature of 120 to 190 ° C, or the noble metal compound-supported activated carbon is preferably used. Is immersed in a heated polyhydric alcohol solution having a temperature of 120 to 190 ° C. By this operation, the noble metal compound supported on the activated carbon reacts with the polyhydric alcohol, and the anion or ligand of the noble metal compound is taken into the polyhydric alcohol, so that the anion or coordination from the noble metal compound on the activated carbon support. The child is removed. After the above treatment, the activated carbon carrying the noble metal compound is taken out from the polyhydric alcohol and washed sufficiently with water to remove the polyhydric alcohol adhering to the activated carbon.
[0008]
It is preferable to use ethylene glycol, propylene glycol or a mixture thereof as the polyhydric alcohol.
[0009]
As the noble metal compound, water-soluble compounds such as ruthenium chloride, and ruthenium carbonyl compounds and complexes such as Ru ₃ (CO) ₁₂ are preferably used. A support made of activated carbon is preferably immersed in a precious metal compound solution of 1-100 g / l in terms of precious metal (for example, ruthenium), preferably for 1 to 24 hours, and the precious metal compound is supported on the activated carbon. Thereafter, the activated carbon is taken out from the noble metal compound solution and sufficiently suspended.
[0010]
As the activated carbon, those pretreated by the following method are preferably used. That is, the activated carbon is preferably dried at a temperature of 100 to 120 ° C., preferably for 1 to 3 hours, and this dried activated carbon is usually used as an aqueous alkali metal hydroxide solution or alkaline earth metal hydroxide aqueous solution including KOH and NaOH. It is preferably immersed at room temperature for 1 to 24 hours, and then sufficiently washed with water, and preferably dried at a temperature of 100 to 120 ° C., preferably for 1 to 3 hours. By performing this pretreatment, acidic functional groups in the activated carbon that adversely affect the catalyst are removed.
[0011]
In the step of supporting the alkali metal, alkaline earth metal or rare earth metal on the noble metal compound-supported activated carbon, a water-soluble compound of alkali metal, alkaline earth metal or rare earth metal is used. The water-soluble compound is preferably an alkali metal, alkaline earth metal or rare earth metal nitrate or carbonate. The precious metal compound-supported activated carbon is preferably immersed in the aqueous solution of the water-soluble compound for 1 to 24 hours, and an alkali metal, alkaline earth metal or rare earth metal is supported on the activated carbon by adsorption and / or impregnation. Then, after taking it out of the aqueous solution, the temperature is gradually raised to about 110 ° C. in a hydrogen or ammonia synthesis gas (hydrogen + nitrogen) atmosphere, and this temperature is preferably maintained for 1 to 3 hours. The temperature is gradually raised to about 450 ° C., and this temperature is preferably maintained for 2 to 5 hours to remove anions from the water-soluble compound.
[0012]
Carrier consisting of activated carbon may be used in unmodified form, but plate-shaped, honeycomb-shaped, etc., or may be a shape which is retained in the proximal body.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be specifically described with reference to examples.
[0014]
Example 1
(1) An activated carbon honeycomb containing about 30% of silicon oxide-aluminum oxide as a binder was dried at 110 ° C. for 1 hour. The weight after drying was about 0.8 g. The dried activated carbon honeycomb was immersed in 40 ml of 1N potassium hydroxide aqueous solution. This was taken out from the potassium hydroxide aqueous solution 24 hours later, washed with ion-exchanged water, and immersed in 100 ml of ion-exchanged water. This was taken out of the ion exchange water after 24 hours and dried at 110 ° C. for 1 hour.
[0015]
(2) The activated carbon honeycomb subjected to the above pretreatment was immersed in 20 ml of a ruthenium chloride aqueous solution of 40 g / l in terms of ruthenium. This was taken out from the aqueous solution after 24 hours and sufficiently suspended, and then heat-treated at 300 ° C. for 1 hour in a nitrogen atmosphere.
[0016]
(3) The obtained activated ruthenium compound-supported activated carbon honeycomb is immersed in an ethylene glycol solution at room temperature, and the ethylene glycol solution is heated to 165 ° C. on an oil bath and kept at this temperature to remove the supported ruthenium chloride anion. did. During the heating, some ruthenium compounds were eluted from the ruthenium compound-supported activated carbon honeycomb, and the ethylene glycol liquid was colored brown. The color of the liquid changed to black while being kept at 165 ° C. and finally became transparent. At this point, the process was terminated.
[0017]
After the above treatment, the ruthenium compound-supported activated carbon honeycomb was taken out from the ethylene glycol solution, washed thoroughly with water, and the ethylene glycol adsorbed on the activated carbon was removed.
[0018]
(4) The ruthenium-supported activated carbon honeycomb after washing with water was immersed in an aqueous barium nitrate solution adjusted to 0.092 mol / l overnight.
[0019]
After removing this from the barium aqueous solution, the temperature was raised to 110 ° C. at a rate of 200 ° C./h in an ammonia synthesis gas atmosphere (H ₂ / N ₂ = 3), and maintained at this temperature for 1 hour, and further 10 ° C./min. The temperature was raised to 450 ° C. at this rate and maintained at this temperature for 2 hours to remove nitrate radicals in the catalyst. Thereafter, this was cooled to a predetermined temperature to obtain an ammonia synthesis catalyst.
[0020]
Example 2
In the process (2) of Example 1, when the activated carbon honeycomb immersed in the ruthenium chloride aqueous solution was heat-treated in a nitrogen atmosphere, the same operation as in Example 1 was carried out except that the treatment temperature was changed, and 8 types of ammonia were obtained. A synthesis catalyst was obtained.
[0021]
Comparative Example 1
An ammonia synthesis catalyst was obtained in the same manner as in Example 1 except that the ruthenium-supported activated carbon honeycomb was treated at 450 ° C. for 2 hours in a hydrogen stream instead of step (3) in Example 1.
[0022]
Performance Test a) Regarding the ammonia synthesis catalyst obtained in Example 1 and Comparative Example 1, the reaction rate of ammonia synthesis was measured under the following conditions. The measurement results are shown in Table 1.
[0023]

[Table 1]

As is clear from Table 1, the catalyst of Example 1 exhibited ammonia synthesis activity comparable to that of Comparative Example 1.
[0024]
b) Regarding the eight ammonia synthesis catalysts obtained in Example 2, the reaction rate of ammonia synthesis was measured under the above conditions. The measurement results are shown in FIG.
[0025]
As is clear from FIG. 1, a high ammonia synthesis activity was obtained when the heat treatment temperature in the nitrogen atmosphere after supporting ruthenium was about 300 ° C.
[0026]
【The invention's effect】
The present invention eliminates the need for safety-equipped equipment and monitoring personnel, which increase catalyst production costs, and safely removes anions or ligands of precious metal compounds supported on activated carbon. A process for producing an ammonia synthesis catalyst is provided.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between heat treatment temperature and ammonia synthesis activity in a nitrogen atmosphere after loading ruthenium.

Claims

In preparing an ammonia synthesis catalyst in which noble metal and an alkali metal, alkaline earth metal or rare earth metal are supported on a support made of activated carbon, the activated carbon support supporting the above-mentioned noble metal compound is heat-treated in an inert gas atmosphere. Then, after immobilizing the noble metal compound on the support, the noble metal compound-supported activated carbon is heated in a polyhydric alcohol solution to remove the anion or ligand from the noble metal compound on the support. Manufacturing method.

2. The ammonia synthesis catalyst production according to claim 1, wherein in the step of immobilizing the noble metal compound on the activated carbon support, the activated carbon carrying the noble metal compound is heat-treated at 100 to 450 ° C. for 1 to 3 hours in an inert gas atmosphere. Method.

In the heating step of the noble metal compound-supported activated carbon in the polyhydric alcohol solution, the noble metal compound-supported activated carbon is immersed in the polyhydric alcohol solution and the solution is heated to a temperature of 120 to 190 ° C, or the noble metal compound-supported activated carbon is heated to a temperature of 120 to The method for producing an ammonia synthesis catalyst according to claim 1 or 2, wherein the anion or ligand of the noble metal compound is reacted with the polyhydric alcohol by being immersed in a heated polyhydric alcohol solution at 190 ° C.

The method for producing an ammonia synthesis catalyst according to any one of claims 1 to 3, wherein ethylene glycol, propylene glycol or a mixture thereof is used as the polyhydric alcohol.

The method for producing an ammonia synthesis catalyst according to any one of claims 1 to 4, wherein the noble metal compound is a chloride.

The method for producing an ammonia synthesis catalyst according to any one of claims 1 to 5, wherein the noble metal compound is a ruthenium compound.

The production of an ammonia synthesis catalyst according to any one of claims 1 to 6, wherein the activated carbon is immersed in an aqueous solution containing an alkali metal hydroxide or an alkaline earth metal hydroxide and then washed with water. Method.

The ammonia synthesis catalyst according to any one of claims 1 to 7, wherein a water-soluble compound of an alkali metal, an alkaline earth metal, or a rare earth metal is used in the step of supporting an alkali metal, an alkaline earth metal, or a rare earth metal. Manufacturing method.

The method for producing an ammonia synthesis catalyst according to any one of claims 1 to 8, wherein the activated carbon carrier has a plate-like or honeycomb-like shape.