JP2988999B2 - Catalyst regeneration method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for regenerating a chromium oxide catalyst used for producing chlorine by catalytic oxidation of hydrochloric acid.

Chlorine is produced on a large scale by the electrolysis of salt, and its demand is increasing year by year. However, during the electrolysis of sodium chloride, caustic soda is also produced at the same time, and its demand is smaller than that of chlorine. Therefore, it has become difficult to adjust the respective balances well.

On the other hand, hydrogen chloride is by-produced in large amounts during the chlorination reaction of organic compounds or the reaction with phosgene, but the amount of by-products is much larger than demand, so a large amount of hydrogen chloride requires considerable processing costs. It is wasted and wasted.

Therefore, if chlorine can be efficiently recovered from hydrogen chloride,
The demand for chlorine can be met without causing imbalance with caustic soda.

[Problems to be solved by conventional technology and invention]

Deacon has a long history of producing chlorine by oxidizing hydrogen chloride.
Also known as a reaction. In 1868, the copper-based catalyst according to the invention of Deacon is considered to exhibit the highest activity in the past, and many catalysts in which various compounds are added as third components to copper chloride and potassium chloride have been proposed.

However, in order to oxidize hydrogen chloride at an industrially sufficient reaction rate using these catalysts, the reaction temperature must be 450 ° C.
C. or higher, which causes a problem such as a reduction in catalyst life due to scattering of catalyst components. Furthermore, the oxidation reaction of hydrogen chloride is an equilibrium reaction, and the higher the temperature, the lower the amount of chlorine produced. Therefore, it is necessary to develop a catalyst that is active at a temperature as low as possible.

In view of the above, catalysts other than copper-based catalysts have been proposed, but no catalyst having sufficiently practical performance has been found.

Chromium oxide is more stable and durable at high temperatures than copper-based catalysts and the like, and there are proposals to use it as a catalyst for oxidizing hydrogen chloride, but no results showing sufficient activity have been reported.

For example, a chromic anhydride or chromium nitrate aqueous solution is impregnated on a suitable carrier, and hydrogen chloride is passed around a catalyst prepared by thermal decomposition at about 400 ° C. to generate chlorine, and after the catalyst is deactivated, hydrogen chloride is added. A method has been proposed in which the supply of hydrogen is stopped, the air is circulated to regenerate the catalyst, and then the supply of air is stopped and hydrogen chloride is circulated again (UK Patent No. 584,790).
issue).

In addition, hydrogen chloride and oxygen-containing gas are reacted at a reaction temperature of 420 to 430 ° C. and a space velocity of 380 hr- ¹ by using a catalyst in which dichromate or dark green chromium oxide is supported on a carrier, and an equilibrium value of 67.4 is obtained. % Conversion of hydrogen chloride has been obtained (GB 676,667). At this time, space velocity 680Hr ^-1
Then the conversion is 63%. The reaction is also observed at 340 ° C., in which case the space velocity is as low as 65 Hr ⁻¹ with only a 52% conversion.

Since these methods have a high reaction temperature and a low space velocity, they cannot be industrially practiced.

On the other hand, it has been found that a chromium oxide catalyst obtained by calcining a compound obtained by reacting an aqueous solution of chromic acid with ammonia at a temperature of 800 ° C. or less has high activity in the oxidation reaction of hydrogen chloride (particularly). The use of this catalyst has made it possible to produce chlorine at a lower temperature and a higher space-time yield than conventionally known catalysts.

On the other hand, as a problem of the catalyst, when it is used for the oxidation reaction of waste hydrogen chloride gas, the activity is reduced several months after the start of the reaction. As an activation method, a method of contacting with a hydrogen chloride gas and / or an oxygen-containing gas in a high-temperature gas phase has been proposed (JP-A-62-25484).
6) When the catalyst activated by this method is used in the oxidation reaction of waste hydrogen chloride gas, the activity returns to the same level as the new catalyst for several days after the start of the reaction, but the activity decreases after one week or more,
There is a problem that it cannot withstand long-term use.

[Problems to be solved by the invention]

An object of the present invention is to provide a useful method for regenerating a chromium oxide catalyst having reduced activity when producing chlorine by oxidizing hydrogen chloride.

[Means for solving the problem]

In order to solve the problems of the present invention, the present inventors have intensively studied a method for regenerating a chromium oxide catalyst used for producing chlorine by oxidizing hydrogen chloride.

As a result, the impaired catalyst is impregnated with an aqueous solution of chromium salt or chromium oxide, and then calcined at a temperature of 800 ° C. or less to activate and regenerate the decreased activity catalyst, and can be used for industrial use for a long time. The inventors have found that the present invention can withstand, and have completed the present invention.

The chromium oxide catalyst used in the process of the present invention comprises a mixture of chromium salt such as chromium nitrate, chromium chloride or a chromium salt of an organic acid, ammonia or a compound releasing ammonia such as urea, a reactant, and silica. 800 ℃
It is manufactured by firing at the following temperature. The mixture of chromium and silica is usually, but not particularly limited to, the weight ratio of Cr ₂ O ₃ to SiO ₂ , which is the form after final calcination of the catalyst, and Cr ₂ O ₃ / SiO ₂ = The range of 30/70 to 95/5 is frequently used.

The raw material hydrogen chloride used in the oxidation reaction of hydrogen chloride is usually hydrogen chloride produced as a by-product during chlorination of organic compounds or reaction with phosgene.

An oxygen-containing gas is used as an oxidizing material for hydrogen chloride, and oxygen gas or air is usually used frequently. In the case of a fluidized bed type reactor, oxygen gas is often used, and in the case of a fixed bed type reactor, air is often used.

The molar ratio of hydrogen chloride used in the reaction to oxygen in the oxygen-containing gas is about 1/4 mole (equivalent) of oxygen to 1 mole of hydrogen chloride, and oxygen is usually used in an excess of 5 to 200% of the equivalent. Often do.

The amount of hydrogen chloride supplied to the catalyst bed is 200-1800Nl / Hr.Kg
The cat range is suitable.

The reaction temperature is frequently used at 300 to 450 ° C, particularly 360 to 420 ° C.

Under the above reaction conditions, the catalyst used for the reaction for several months to half a year has a reduced activity, and the conversion of hydrogen chloride is initially 70 to 80.
The percentage is 50-60%.

The activity of the reduced catalyst can be recovered by washing with water, impregnating with an aqueous solution of chromium salt or chromium oxide, and calcining at a temperature of 800 ° C. or lower.

The temperature for washing with water is usually preferably from 25 to 100 ° C, particularly preferably from 50 to 80 ° C. The washing amount is not particularly limited, but is usually 0.5% of the catalyst amount.
Use up to 10 times.

Specific examples of the chromium salt of the present invention include water-soluble chromium salts such as chromium nitrate and chromium chloride. Examples of the chromium oxide include a water-soluble chromium oxide such as chromic anhydride. The concentration of chromium salt or chromium oxide is 5
A range of 45% is preferred. The aqueous solution of chromium salt or chromium oxide may be impregnated once and a predetermined amount may be impregnated, but preferably the predetermined amount is impregnated in several times. In the case of impregnation by dividing into several times, the operations of impregnation and pre-firing at 150 to 300 ° C. are repeated several times, and finally firing at a temperature of 800 ° C. or less.

When impregnating a predetermined amount at one time, baking is directly performed at a temperature of 800 ° C. or less. The impregnation amount of the chromium salt or chromium oxide is not particularly limited, but when the catalyst is used for the oxidation reaction of hydrogen chloride, a part of the chromium oxide is volatilized, and the amount is preferably sufficient to compensate for the volatilization.

That is, the weight ratio of Cr ₂ O ₃ and SiO ₂ , which is a form obtained by finally firing the catalyst, is such that Cr ₂ O ₃ / SiO ₂ = 30/70 to 95/5. Is preferred.

In the present invention, it is essential to impregnate a catalyst containing chromium oxide as a main component with an aqueous solution of chromium salt or chromium oxide, and chromium oxide obtained by simply thermally decomposing an aqueous solution of chromium salt does not become a highly active catalyst. . The firing temperature of the catalyst is
It is necessary to keep the temperature below 800 ° C, and the one fired at 800 ° C or higher has low catalytic activity. Preferred firing temperature is 450-6
50 ° C.

[Action and effect of the invention]

According to the method of the present invention, the catalyst is used for a long period of time in the oxidation reaction of hydrogen chloride, the catalyst having reduced activity is impregnated with an aqueous solution of a chromium salt or chromium oxide, and activated and regenerated by firing at a temperature of 800 ° C or lower. Can be. The regenerated catalyst thus obtained has a high activity, and has the same performance as the new catalyst in a long-term life test.

〔Example〕

Hereinafter, the method of the present invention will be described more specifically with reference to examples.

Example 1 Chromia 70% by weight, Silica 30% by weight, particle size 5m /
50 g of a catalyst having a length of 6 m / m and a length of 6 m / m were filled in a 1-inch inner diameter SUS-316L reaction tube. 800ml / min waste hydrogen chloride gas, 4 oxygen
Flow into the catalyst bed at 00ml / min, and outside the reaction tube with sand fluidized bath
The reaction was carried out by heating to 370 ° C.

On the third day from the start of the reaction, the conversion of hydrogen chloride was 74%. On the 30th day from the start of the reaction, the conversion was 70%, and on the 65th day, the conversion was reduced to 62%. At this point, the catalyst was withdrawn and washed three times with 30 ml of hot water at 60 ° C. on a Nutze. 40% of this
After impregnating 10 ml of an aqueous solution of Cr (NO ₃ ) ₃ .9H ₂ O, it was baked at 250 ° C. for 3 hours.

Next, the impregnation and calcination of the chromium nitrate aqueous solution as described above were further repeated four times, followed by calcination at 520 ° C. for 5 hours to regenerate the catalyst. 50 g of the catalyst thus regenerated was reacted in the same manner as described above.

The conversion on the third day after the start of the reaction was 79%, and the conversion on the 10th day was 75%.
%Met. On the 30th day from the start of the reaction, the conversion was 69%,
On the day, the conversion was 63%.

Example 2 An average diameter of 60% consisting of 75% by weight of chromia and 25% by weight of silica
40 g of the microsphere fluidized bed catalyst was packed in a 1 inch inner diameter glass fluidized bed reactor. 334ml / mi of waste hydrogen chloride gas
n, oxygen was introduced into the catalyst bed at 167 ml / min, and the outside of the reaction tube was heated to 380 ° C. in an electric furnace to cause a reaction.

The conversion of hydrogen chloride on the third day from the start of the reaction was 72%.
The conversion was 68% on the 30th day from the start of the reaction, and 55% on the 65th day.
Down to At this point, the catalyst was withdrawn and washed three times with 30 ml of hot water at 60 ° C. on a Nutze. Cr (NO ₃ ) ₃
· 9H ₂ O 40% aqueous solution after the 9ml impregnation of, and calcined 3 hours at 200 ° C.. Further, after repeating impregnation and firing three times, firing was performed at 520 ° C. for 5 hours. 40 g of this regenerated catalyst was reacted in the same manner as described above.

The conversion of hydrogen chloride on the third day after the start of the reaction was 77%, and the conversion on the tenth day was 73%. Conversion rate 67% on the 30th day after the start of the reaction
On day 65, 55%.

Example 3 In the same manner as in Example 2, the catalyst whose activity was reduced for 65 days was washed three times with 30 ml of hot water at 60 ° C. on Nutse. This _{Cr (NO 3) 3 · 9H} 2 O 40% aqueous solution after the 30ml impregnation of 520
Calcination was performed at 5 ° C. for 5 hours. This regenerated catalyst (40%) was used in the oxidation reaction of hydrogen chloride in exactly the same manner as in Example 2.

The conversion of hydrogen chloride on the third day after the start of the reaction was 73%, and the conversion on the tenth day was 70%. Conversion rate is 63% on the 30th day from the start of the reaction
And on day 65 the conversion was 50%.

Example 4 Average diameter 62 consisting of 70% by weight of chromia and 30% by weight of silica
1 kg of microsphere catalyst was charged into a 4 inch nickel fluidized bed reactor and heated externally to 400 ° C. in a sand fluidized bath. 35 Nl / Hr of waste hydrogen chloride gas and 200 Nl / Hr of oxygen gas flowed into the catalyst bed to carry out the reaction.

The conversion of hydrogen chloride 3 days after the start of the reaction was 78%,
The number dropped to 76% after 63 days and 63% after 65 days. At this point, the extracted catalyst was placed on Nutsze with 700 ml of 70 ° C warm water.
Washed twice. This _{Cr (NO 3) 3 · 9H} 2 O in 40% aqueous solution of 1
After impregnation of 50 ml, it was baked at 230 ° C. for 3 hours. Further, after the same impregnation and firing were repeated three times, firing was performed at 520 ° C. for 5 hours. 1 kg of this regenerated catalyst was reacted in exactly the same manner as above.

The conversion of hydrogen chloride three days after the start of the reaction was 80%,
75% after 65 days and 64% after 65 days.

Example 5 As in Example 2, the catalyst used for 65 days was washed with hot water.
This was impregnated with 9 ml of a 10% aqueous solution of chromic anhydride and calcined at 200 ° C. for 3 hours. After repeating impregnation and firing three times, 52
It was baked at 0 ° C. for 5 hours. 40 g of this regenerated catalyst was reacted in the same manner as described above.

The conversion of hydrogen chloride on the third day after the start of the reaction was 77%, and the conversion on the tenth day was 73%. Conversion rate is 68% on the 30th day from the start of the reaction
And at day 65 was 54%.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01J 21/00-38/74 C01B 7/04

Claims (1)

(57) [Claims] When regenerating a catalyst containing chromium oxide as a main component, which is used in producing chlorine by oxidizing hydrogen chloride with an oxygen-containing gas, the catalyst is impregnated with an aqueous solution of chromium salt or chromium oxide at 800 ° C. A method for regenerating a catalyst, comprising calcining at the following temperature.