The regeneration method of a silver catalyst preparation of formaldehyde

 

(57) Abstract:

The invention relates to the chemical industry, in particular to methods of regeneration of silver catalysts for the preparation of formaldehyde from methanol. The purpose of the invention is development of a method of regeneration of spent silver catalyst by removing coke and iron-bearing sediments with subsequent recovery of the silver content in the catalyst to the initial and subsequent activation of the catalyst, with the exception of the loss of silver in the regeneration process. The technical result is achieved by the fact that the spent silver catalyst, from calcined coke deposits for removal of iron compounds from the surface of the catalyst and recovery of the silver content to the original quantity, and subsequent activation of the catalyst is treated with a mixture of 10-20% nitric acid with a calculated amount of silver nitrate, missing to the initial content of silver in the catalyst, at a temperature of 100-120°C. and bringing the pH of the solution to pH 1-2, the separation of the catalyst from the resulting solution. Removing iron compounds from solution azotnokislogo silver carried out by CCA, from iron compounds with subsequent activation of the catalyst by an additional impregnation of the catalyst with hot filtered solution of silver nitrate, evaporation, drying, calcining and cooling. The proposed method provides the possibility of recovery from the spent silver catalyst activity and selectivity to its original condition, simplifies the technology of regeneration of the catalyst, for repeated regeneration of spent silver catalysts and eliminates the loss of silver from spent catalyst in the regeneration conditions. 1 C.p. f-crystals, 1 table.

The invention relates to the chemical industry, and in particular to methods of regeneration of the silver catalysts of the process of obtaining formaldehyde.

The major industrial process for the preparation of formaldehyde is the process of oxidative dehydrogenation of methanol on silver catalysts, which is held at a temperature of 650-700°C

Disadvantages of the process of oxidative dehydrogenation of methanol to formaldehyde are quick nauglerozhivaniya and decontamination of a silver catalyst by deposition on the catalyst surface coke and soedinenii with the catalyst surface during annealing in the furnace, however, removing iron deposits from the catalyst practically does not occur, and its activity is significantly lower than the activity of freshly prepared silver catalyst.

There is a method of regeneration of silver catalysts for the preparation of formaldehyde, which consists in the fact that superagency the catalyst is unloaded from the reactor, calcined at a temperature of 600-800°C for 5-7 h in a stream of air or oxygen. The calcined catalyst was washed twice with hydrochloric acid, dried at 120°C, then treated with nitric acid, to restore a uniform distribution of silver on the surface of the carrier, dried again at 120°C and calcined at 600-650°C for the decomposition of nitrate of silver.

The calcination at high temperature leads to increased diffusion of silver from the pores of the carrier to the surface, and in places of local overheating occurs the formation of metallic silver, which, in turn, leads to a sharp decrease of the total active silver surface and, consequently, to a significant reduction of General and useful conversion of methanol to reduce the selectivity of the process.

The catalysts regenerated by the oxidation of surface-adsorbed is izvodstva catalyst “silver on the pumice” Kuibyshev refinery SK, 1972 and A. S. No. 799211 from 09.07.79).

The disadvantages of this method of regeneration of the catalyst are:

a) treatment of the catalyst with hydrochloric acid leads not only to the removal of iron compounds, but also to a significant loss of silver from the catalyst,

b) required prolonged washing of the catalyst with demineralised water from the Cl-ions.

The technical nature of the proposed method of regeneration of silver catalysts closest way catalyst regeneration consists in the fact that the spent catalyst is calcined in air flow at a temperature of 560-650°C with subsequent treatment of the catalyst with a solution of 6 N. nitric acid to restore a uniform distribution of silver on the surface of the carrier (Yakovenko H. I., Kruglikov A. A., Kurina L. N., Vorontsov, N. In., Ponomarenko, S. A. Regeneration of catalysts for the synthesis of formaldehyde on the basis of pumice and media SF. //Chem. industry. 1972, No. 9, S. 70).

However, the catalytic activity of the catalyst is restored fully, the selectivity and the yield of formaldehyde on the regenerated silver catalyst on average 10-12% lower than in freshly prepared catalyst.

the coke and iron-bearing sediments with subsequent recovery of the silver content in the catalyst to the initial and subsequent activation of the catalyst; the exception of the loss of silver in the regeneration process.

The technical result is achieved by the fact that the spent silver catalyst is subjected to calcination in air in a furnace at 580-620°C for 6-8 h to remove coke deposits, and after cooling, determine the content of iron and silver in the catalyst (calcined catalyst). Then from calcined coke passerby the catalyst was treated with a mixture of 10-20% HNO3c estimates of the total amount of silver nitrate, missing to the initial content of silver in the catalyst. The purpose of dissolution of iron-bearing sediments of the process is conducted at 100 to 120°C and bring the pH of the solution to pH 1-2. Then a solution of silver nitrate and iron compounds are separated from the catalyst, the catalyst is washed with demineralized water at a temperature of 70 to 80°C. Then a solution of silver nitrate to dissolved iron compounds and the washing water is heated to 70 to 80°With and neutralize the ammonia water (25 wt.% NH3) to pH 5-6, the solution stands out the iron hydroxide in the form of fine sediment. A hot solution of silver nitrate (70-80°C) is filtered from the iron hydroxide several times to porntranny hot solution of silver nitrate and the washing water is poured back into the bowl with washed passerinum the catalyst and evaporated solution with constant stirring to a friable state of the catalyst. The catalyst discharged into trays and calcined in a furnace at 350 to 450°C for 2-3 h until complete decomposition of silver nitrate, then at 450°C under stirring for 2-3 h at 650°C for 1-2 h, after which the catalyst is cooled in the furnace without air to room temperature (regenerated catalyst).

Restoring the activity and selectivity of spent silver catalyst to its original condition is achieved by removing not only coke, and iron deposits, and subsequent reduction of the silver content to the original quantity in the catalyst, by means of its additional additional in the process of regeneration and subsequent activation of the catalyst. The proposed method provides the possibility of recovery from the spent silver catalyst activity and selectivity to its original condition, simplifies the technology of regeneration of the catalyst due to the exclusion of a number of stages (treatment with hydrochloric acid, washing from Cl-ions), for repeated regeneration of spent silver catalysts and eliminates the loss of silver from spent catalyst in the regeneration conditions.

We offer umyshlennogo passarinho catalyst (2-3 mm fraction) after the 3rd cycle (3×3=9 months) in the industrial process of oxidative dehydrogenation of methanol to formaldehyde is subjected to calcination in air in a furnace at 580-620°C for 5-7 h to remove coke deposits, then cooled in the furnace to room temperature and determine the content of iron and silver in the catalyst. Then from calcined coke catalyst for removal of iron compounds twice treated with 10% hydrochloric acid and washed with demineralised water to remove Cl-ions. Thereafter, the catalyst is treated with a mixture of 20% HNO3c dissolved nitrate of silver, missing to the initial content of silver in the catalyst, and evaporated under stirring to a friable state of the catalyst. Baking the dried catalyst was loaded into an oven and calcined at 350 to 450°C to complete decomposition of silver nitrate, the catalyst is calcined at a temperature of 450°C under stirring for 2-3 h at a temperature of 650°C for 3-4 h and cooled without access of air to room temperature. After that regenerated passerinum the catalyst determine the content of iron and silver.

Example 2 (the prototype). In the same way as in example 1, but instead of 3 g supereeego industrial passarinho catalyst after the 3rd cycle (3×3=9 months) take 3 g supereeego industrial personalabteilung of methanol to formaldehyde.

Example 3. 3 g supereeego industrial passarinho catalyst (fraction 2-3 mm) after 1 cycle (3 months) in the industrial process of oxidative dehydrogenation of methanol to formaldehyde is subjected to calcination in air in a furnace at 580-620°C for 6-8 h to remove the coke deposits and after cooling in the furnace to room temperature, determine the content of iron and silver in the catalyst. Then from calcined coke passerby the catalyst was treated with a mixture of 20% HNO3and AgNO3c estimated quantity of silver missing to the initial content of silver in the catalyst. The purpose of dissolution of iron-bearing sediments of the process is conducted at 100 to 120°C and bring the pH of the solution to pH 1-2. Then a solution of silver nitrate and iron compounds are separated from the catalyst and the catalyst is washed with demineralized water at a temperature of 70 to 80°C. Then a solution of silver nitrate to dissolved iron compounds and the washing water is heated to 70 to 80°C and neutralize ammonia water (25 wt.% NH3) bringing the pH of the solution to pH 5-6, the solution stands out the iron hydroxide in the form of fine sediment. Gorogo the precipitate of iron hydroxide from the solution, the filter is washed with demineralised water. Then filtered hot solution of silver nitrate together with the washing water is poured back into the bowl with washed passerinum the catalyst and evaporated solution with constant stirring to a friable state of the catalyst. Thereafter, the catalyst was unloaded in the trays and calcined in a furnace at 350 to 450°C for 2-3 h until complete decomposition of silver nitrate and then calcined at 450°C under stirring for 2-3 h at 650°C for 1-2 h, then the catalyst was cooled in the furnace without air to room temperature. After that, regenerated and restored passerinum the catalyst determine the content of iron and silver.

Example 4. In the same way as in example 3, but instead of 3 g supereeego industrial passarinho catalyst after the 1st cycle (3 months) take 3 g supereeego industrial passarinho catalyst after the 2nd cycle (2×3=6 months) in the industrial process of oxidative dehydrogenation of methanol to formaldehyde and from calcined coke passerby the catalyst was treated with a mixture of 20% HNO3and 10% HNO3and AgNO3c races the example 5. In the same way as in example 3, but instead of 3 g supereeego industrial passarinho catalyst after the 1st cycle (3 months) take 3 g supereeego industrial passarinho catalyst after the 3rd cycle (3×3=9 months) in the industrial process of oxidative dehydrogenation of methanol to formaldehyde.

Example 6. In the same way as in example 3, but instead of 3 g supereeego industrial passarinho catalyst after the 1st cycle (3 months) take 3 g supereeego industrial passarinho catalyst after the 4th cycle (3×4=12 months) in the industrial process of oxidative dehydrogenation of methanol to formaldehyde.

Example 7. In the same way as in example 6, but instead of 3 g supereeego industrial passarinho catalyst after the 1st cycle (3 months) take 3 g supereeego industrial passarinho catalyst after the 5th cycle (3×5=15 months) in the industrial process of oxidative dehydrogenation of methanol to formaldehyde.

Example 8 (comparative). In a flow quartz reactor download 3 cm3(2.5 g) freshly prepared passarinho catalyst with Sanal = 0,315 (consumption of methanol 30,12 g/h, the concentration of methanol in spirtovodnogo a mixture of 70 wt.%, air flow 33,15 l/h, the temperature of the process 695°C). Determine the conversion of methanol and selectivity of the formation of formaldehyde and activity of freshly prepared passarinho catalyst. Activity fresh passarinho catalyst (conversion of methanol) is taken as 100%.

Then determine the conversion of methanol and selectivity of the formation of formaldehyde all regenerated personalbrand catalysts according to the prior art (examples 1-2) and by the proposed method (examples 3-7). The research results are summarized in the table.

The table below shows examples clarify the invention without limiting it.

As can be seen from the table, the content of iron deposits in the calcined personalbrand catalysts with each cycle of operation of the catalyst (deleted only Cox) is increased, for example, the iron content in calcined passerinum the catalyst after the 5th cycle in the oxidation of methanol to formaldehyde is 0,0806 wt.% (example 2, 7), and in the fresh catalyst at 0.020 wt.% (example 8), i.e., the iron content in the exhaust passerinum the catalyst after the 5th cycle increases CPA is Satarov the proposed method is removed from the catalyst surface not only of the coke deposits, but the removal of iron compounds by dissolving them in a mixture of 10-20% nitric acid with a calculated amount of silver nitrate during the process at a temperature of 100 to 120°C and bringing the pH of the solution to pH 1-2. Introduction the estimated number of silver nitrate allows for simultaneous dovnesenie missing in the catalyst of silver.

The iron content in the regenerated passerinum the catalyst even after five cycles in industrial conditions of the process of oxidative dehydrogenation of methanol to formaldehyde (example 7) at the level of freshly prepared passarinho catalyst is 0,0208 wt.% against 0,0292 wt.% the prototype (example 2).

Silver catalyst after five regeneration cycles are fully restores its activity (69,4%) and the selectivity of the formation of formaldehyde (74,8%) in comparison with freshly prepared passerinum catalyst.

As can be seen from the examples of the table, the catalysts (examples 3-7) after the process of regeneration is almost completely restore its catalytic activity in comparison with freshly prepared catalyst (example 8) and have a higher catalytic the spent catalyst to its original condition is achieved by removing not only coke, but iron deposits from the spent silver catalyst, followed by reduction of the silver content in the catalyst to its original amount by additional additional in the process of regeneration and subsequent activation of the catalyst.

Thus, the proposed method for regeneration of spent silver catalysts for the preparation of formaldehyde from methanol provides the ability to recover the spent silver catalyst activity and selectivity to its original condition, allows to increase the overall service life passarinho catalyst, simplifies the technology of regeneration due to the exclusion of a number of stages (treatment with hydrochloric acid, washing from Cl-ions), for repeated regeneration of spent silver catalysts and eliminates the loss of silver from spent catalyst in the regeneration process.

1. The regeneration method of a silver catalyst for the preparation of formaldehyde from methanol, comprising gas-phase oxidation of adsorbed on the surface of the coke deposits, the removal of iron compounds, the recovery of silver content in katalizatoriai from the surface of the catalyst and recovery of silver content to the original content carried out by treating the calcined catalyst with a mixture of 10-20% nitric acid with a calculated amount of silver nitrate, missing to the initial content of silver in the catalyst, at a temperature of 100-120°C and bring the solution pH to 1-2, the separation of the catalyst from the resulting solution, removing iron compounds from solution azotnokislogo silver by precipitation with a solution of ammonia water and filtering the solution containing silver nitrate, iron compounds, with subsequent activation of the catalyst by an additional impregnation of the catalyst with hot filtered solution of silver nitrate with further evaporation, drying, calcining and cooling.

2. The regeneration method of a silver catalyst under item 1, characterized in that the deposition of iron compounds from a solution of silver nitrate is carried out by processing 25% ammonia water at a temperature of 70-80°C and bring the solution pH to 5-6 with subsequent filtering.



 

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