RU2404959C1 - Method of producing formaldehyde - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing formaldehyde through dehydrogenation of methanol in the presence of an oxide Zn-Na containing catalyst at high temperature. Dehydrogenation of methanol is carried out through chemical conjugation in the presence of hydrogen peroxide taken in an amount which ensures its concentration in methanol of 0.8-1.5%, and in the presence of a catalyst which also contains silicon dioxide with the following initial composition of components, wt %: Na₂O - 1.2-1.4; ZnO - 0.8-1.2; SiO₂ - the rest, at 790-900°C, mainly at 820-850°C.

EFFECT: invention enables to carry out the process with high formaldehyde output of the catalyst and longer life of the catalyst.

2 cl, 6 ex

Description

The invention relates to methods for producing petrochemical products by catalytic dehydrogenation of hydrocarbons and their derivatives, in particular to the preparation of formaldehyde by dehydrogenation of methanol.

Formaldehyde is one of the most important chemical products used in the manufacture of dyes, drugs, explosives, macromolecular compounds, etc.

At present, there are two fundamental technological approaches to methanol dehydrogenation, known from the scientific, technical and patent literature, that is oxidative dehydrogenation and direct dehydrogenation.

The process of oxidative dehydrogenation is a reaction of the removal of hydrogen followed by its oxidation in water and proceeds according to the following mechanism:

A significant drawback of the described process is the release of a large amount of stoichiometric water as a result of the interaction of the split-off hydrogen with molecular oxygen.

In this regard, the problem of separation of water from the final product arises, which is associated with the complication of the technology and hardware design of the process, so we will not consider this method of obtaining formaldehyde.

Direct classical methanol dehydrogenation is a reaction of the removal of a hydrogen molecule with the formation of formaldehyde and has an advantage over oxidative one, due to the absence of this drawback, i.e. lack of allocation of a large amount of water.

In addition, due to the relevance of hydrogen energy, dehydrogenation in the absence of oxygen also has an additional advantage due to the formation of hydrogen, which is used, in particular, in the production of fuel cells.

However, in the transition from the oxidation process to the usual dehydrogenation, significant energy costs arise due to thermodynamic limitations (the reaction proceeds practically significantly with a conversion of more than 50% and a selectivity of at least 70% for formaldehyde at elevated temperatures, 900 ° C and above). At temperatures below 800 ° C, it does not make sense to consider the available data in the literature on direct non-conjugated dehydrogenation: low productivity (less than 3 g / g · h) or low selectivity for formaldehyde (below 60%) lead to unprofitable technologies.

A known process for the preparation of formaldehyde by catalytic dehydrogenation of methanol is described in Ruterana P .; Buffat PA; Prairie M; Renken A. // The structure of the Na ₂ MoO ₄ catalyst for water free dehydrogenation of methanol to formaldehyde. - In: Helvetica Physica Acta, v. 62, 1989, pp. 227-230.

The disadvantage of this process is the short life of the catalyst, which operates in the field of low degrees of conversion with low productivity in the low temperature region.

A known method of producing formaldehyde from methanol by direct dehydrogenation described in DE patent No. 3719055, C07C 45/00, published 15.12.1988, according to which the reaction proceeds at a temperature of from 300 to 800 ° C.

The disadvantage of this method is the low yield of formaldehyde.

A known method for producing formaldehyde by dehydrogenation of methanol on a silver catalyst (Meyer A., Renken A. New catalysts for the dehydrogenation of methanol to water-free formaldehyde // Proc. 9th Int. Congr. Catal. V.4. P.1898-1905 ( 1988).

Dehydrogenation rates are also low here. The methanol conversion on silver, modified with a small amount of tellurium (0.5%) and Na ₂ CO ₃ , is 37% at 800 ° C, but the formaldehyde selectivity does not exceed 7%.

Higher degrees of conversion of methanol to formaldehyde on silver compositions are possible, as described by Usachev N.Ya., Krukovsky and I.M., Kanaev S.A. Non-oxidative dehydrogenation of methanol to formaldehyde // Petrochemistry. 2004.V. 44. P.411 // due to the use of cyclic oxygen supply to the reaction space on the one hand and organization of the post-catalytic space in which chain transformations are realized, on the other.

A number of methods are known for the direct dehydrogenation of methanol in the presence of Zn-Na catalysts: Usachev N.Ya., Belanova E.P., Kazakov A.V. et al. // Stud. Surf Sci. Catal. (Zeolites and Mesoporous materials at the dawn of the 21st century). V.135. P.206 (2001); N.Ya. Usachev, E.L. Belanova, I.M. Krukovsky and others // Izv. RAS, Ser. Chem. T.52. P.1839 (2003) [Russ. Chem. Bull. 2003. V. 52. P.1940 (Engl. Transl.)].

However, in the mentioned studies, the formaldehyde yield does not exceed 5% with a selectivity of 60% and 15% with a selectivity of 42%.

The literature references to the possibility of increasing the yield of formaldehyde to 50% under mild conditions (600 ° C) are contradictory.

So, in the work of Sagou M., Deguchi T., Nakamura S. // Stud. Surf Sci. Catal. (Successive Design of Catalysts). V.44. P.139 (1988) and Japanese Patent No. 1880209, C07B 61/00, 10.21.1994; U.S. Pat. 4788347, СВВ 61/00, 11/29/1988 and European patent No. 0261867, С07С 47/00, 02/01/92, the preparation of formaldehyde is described by the direct deoxidation of methanol in the presence of zinc - silicon catalytic complexes.

However, the performance of the catalyst in these studies was either not indicated in individual experiments or indicated as extremely low (not more than 1 g / g · h), while the formaldehyde selectivity is also extremely low.

Closest to the proposed technical solution is the direct methanol dehydrogenation method described in the work “Catalytic properties of non-acid zinc-containing systems based on zeolites of type Y, X and A in the conversion of methanol” N.Ya. Usachev, E.P. Belanova, A.S. Fomin et al. // Petrochemistry. T.42. P.95 (2002) [Petrol. Chem. 2002 V.42. P.78 (Engl. Transl.)].

In the described method, dehydrogenation is carried out in the presence of an oxide Zn-Na containing catalyst, the preparation method of which affects the activity of these systems in the dehydrogenation of methanol in the temperature range 500-750 ° C.

The disadvantage of the process is the insufficiently high productivity (not more than 5 CH ₂ O g / g cat. · H) and a low formaldehyde yield of not more than 22% with a continuous operation time of not more than 9 hours, and the catalytic system becomes unstable when the temperature rises above 600 ° FROM. The use of cyclic oxygen supply in the technology translates the process into the class of indirect catalytic dehydrogenation, which assumes the presence of post-catalytic space and cyclic oxygen supply. The service life of the catalyst (up to 9 hours) and the cycle time of its continuous operation without introducing oxygen into the system also reduces the advantages of the proposed technology for producing formaldehyde.

The objective of the invention is to develop a method for producing formaldehyde by dehydrogenation of methanol, which would eliminate the disadvantages of both known basic methods and oxidative and direct dehydrogenation, namely the process in conditions of low water and high catalyst productivity on formaldehyde.

The problem is solved in that a method for producing formaldehyde by dehydrogenation of methanol in the presence of an oxide Zn-Na containing catalyst at an elevated temperature, in which conjugated dehydrogenation of methanol is carried out in the presence of hydrogen peroxide, taken in an amount ensuring its concentration in methanol of 0.8-1.5% , and in the presence of a catalyst additionally containing silicon dioxide in the following ratio of components, wt.%:

Na ₂ O - 1.2-1.4

ZnO - 0.8-1.2

SiO ₂ - the rest.

The process of obtaining formaldehyde by dehydrogenation of methanol is carried out mainly in the temperature range from 790 to 900 ° C.

The technical result that can be obtained using the present invention is to increase the productivity of the catalyst for formaldehyde, increase the life of the catalyst, and also reduce the coking rate of the contact surface.

The proposed method for producing formaldehyde is a type of direct dehydrogenation and relates to conjugated reactions, in particular to a conjugated dehydrogenation reaction of substances, when a reaction occurs using an inductor, the presence of which stimulates the main process:

CH ₃ OH = CH ₂ O + H ₂

Adverse Reactions:

CH ₂ O = CO + H ₂

CH ₃ OH + CO = CH ₄ + CO ₂

Apparently, when H ₂ O ₂ is introduced into the system, it interacts with the hydroxylated surface of the catalyst with the formation of mobile surface radicals that block the formation of coke on the surface:

H ₂ O ₂ + ZOH → ZHO ₂ + H ₂ O

In this case, the chain partially develops on the contact surface, and partially in the reaction zone:

In the reaction initiation, in the general case, two activated particles migrate in a homogeneous heterogeneous chain process between the catalyst surface and the reaction volume — OH ^• HO ₂ ^• . At the same time, chemical conjugation and the self-regenerating properties of the contact surface are ensured.

The possibility of conjugated dehydrogenation is indicated in the monograph by T. M. Nagiyev “Chemical conjugation” M .: Nauka, 1989. 216 s, in which, using the example of dehydrogenation of ethylbenzene to styrene, the effect of hydrogen peroxide used as a dehydrogenation inductor is described.

However, such a conjugation reaction for the dehydrogenation of methanol to formaldehyde was not found either in the patent or in the scientific and technical literature.

It should be noted that in each specific process the effect of hydrogen peroxide is specific. Therefore, it does not make sense to consider and dwell on the mechanism of conjugated action in the process of dehydrogenation of ethylbenzene to styrene in this case.

However, we note that activation with the subsequent decomposition of hydrogen peroxide occurs thermodynamically noticeably at temperatures above 790 ° C, and the use of this method at lower temperatures loses its meaning.

The following examples illustrate the invention, but in no way limit the scope of its application relative to similar catalyst systems in the reactions of direct dehydrogenation of compounds.

Catalyst K-1 is prepared by impregnating silicon oxide with a solution of sodium nitrate and zinc chloride, followed by drying at 120 ° C for 1 h and step-by-step calcination for 2 h at each next temperature of 200, 400 and 600 ° C.

The activity testing experiments are carried out in a standard quartz cylindrical reactor loaded with K-1 catalyst and located in an oven heated to temperatures of 790-920 ° C.

The methanol stream is diluted with hydrogen peroxide with a concentration of 0.8-1.5%. In the evaporation zone, the methanol stream is mixed and picked up by a stream of nitrogen gas in a molar ratio of CH ₃ OH: N ₂ = 1: 0.5-1.3.

Product analysis is carried out chromatographically.

In all experiments, a 30% hydrogen peroxide solution was used, in connection with which the amount of water in all examples was artificially maintained constant in order to compare the results obtained.

Example 1 ("blank", in the absence of hydrogen peroxide). Methanol was passed through 20 cm ^{3 of} a K-1 silicon-containing catalyst (bulk density 0.75 g / cm ³ ) containing 1.0 wt.% ZnO and 1.0 wt.% Na ₂ O at a rate of 3.65 g / min . In the evaporation zone, the methanol stream is mixed with the nitrogen gas stream in a molar ratio of CH ₃ OH: N ₂ = 1: 1. At a temperature of 920 ° C, the formaldehyde yield is 41%, and the hydrogen selectivity of the process is 86%. The methane yield is 0.5%.

The total conversion of methanol is 94%.

The mass of 20 cm ^{3 of} catalyst is 15 g.

Raw Material Load:

W = 3.65 · (60:15) = 14.6 g / g · h (60 min, 15 g of catalyst)

The formaldehyde catalyst productivity is calculated taking into account the formaldehyde yield as

14.6 × 0.41 = -5.99 g / g · h

and is 5.99 g / g · h, compared with 5 g / g · h in the prototype.

The rate of coke formation, determined by weight, thermogravimetric and control atomic-adsorption independent methods, is 0.08 g / g · h.

Coke yield

(0.08: 14.6) × 100 = 0.55 wt.%.

The time of continuous operation to tangible signs of decreased activity is 20 hours. Next, air regeneration at 900 ° C for 2 hours is required.

An example is provided for comparison with pairing and is related to the following examples.

Example 2

Methanol was passed through 20 cm ^{3 of} a K-1 silicon-containing catalyst containing 0.8 wt.% ZnO and 1.4 wt.% Na ₂ O at a rate of 3.8 g / min. In the evaporation zone, the methanol stream is mixed with the nitrogen gas stream in a molar ratio of CH ₃ OH: N ₂ = 1: 1. The concentration of hydrogen peroxide in methanol is 1%.

At a temperature of 820 ° C, the formaldehyde yield is 55%, and the hydrogen selectivity of the process is 92%. The yield of CO _{2 is} 0.3%. No methane detected.

The total conversion of methanol is 95%.

Raw Material Load:

W = 3.8 × (60:15) = 15.2 g / g · h (60 min, 15 g of catalyst)

The formaldehyde catalyst productivity is calculated taking into account the formaldehyde yield as

15.2 × 0.55 = 8.36 g / g · h

and is 8.36 g / g · h, compared with 5 g / g · h in the prototype.

The coking rate determined by weight, thermogravimetric and control atomic adsorption independent methods is 0.03 g / g · h.

Coke yield

(0.03: 15.2) × 100 = 0.20 wt.%.

Within 200 hours of the reaction cycle, no decrease in activity was observed. The catalyst does not coke to the extent that blocking of active sites occurs.

Example 3

After 20 cm of silicon containing catalyst K-1, containing 1.2 wt.% ZnO and 1.2 wt.% Na ₂ O, methanol was passed at a rate of 3.4 g / min. In the evaporation zone, the methanol stream is mixed with the nitrogen gas stream in a molar ratio of CH ₃ OH: N ₂ = 1: 0.8. The concentration of hydrogen peroxide in methanol is 1.5%. At a temperature of 800 ° C, the formaldehyde yield is 69%, the selectivity of the process for hydrogen is 95%. The yield of CO _{2 is} 0.1%. The methane yield is 0.5%.

The total conversion of methanol is 95%.

Raw Material Load:

W = 3.4 × (60:15) = 13.6 g / g · h (60 min, 15 g of catalyst)

The formaldehyde catalyst productivity is calculated taking into account the formaldehyde yield as

13.6 × 0.69 = 9.38 g / g · h

and is 9.38 g / g · h, compared with 5 g / g · h in the prototype.

The coking rate determined by weight, thermogravimetric and control atomic adsorption independent methods is 0.01 g / g · h.

Coke yield

(0.01: 13.6) × 100 = 0.07 wt.%.

Within 200 hours of the reaction cycle, no decrease in activity was observed. The catalyst does not coke to the extent that blocking of active sites occurs.

Example 4

After 20 cm ^{3 of} silicon containing catalyst K-1 containing 1.0 wt.% ZnO and 1.0 wt.% Na ₂ O, methanol was passed at a rate of 2.5 g / min. In the evaporation zone, the methanol stream is mixed with the nitrogen gas stream in a molar ratio of CH ₃ OH: N ₂ = 1: 1.3. The concentration of hydrogen peroxide in methanol is 1.0%. At a temperature of 790 ° C, the formaldehyde yield is 51%, the selectivity of the process for hydrogen is 92%. The release of CO _{2 is} not observed. The methane yield is 1.5%.

The total conversion of methanol is 91%.

The formaldehyde catalyst productivity is

5.92 g / g

Raw Material Load:

W = 2.9 × (60:15) = 11.6 g / g · h (60 min, 15 g of catalyst)

The formaldehyde catalyst productivity is calculated taking into account the formaldehyde yield as

11.6 × 0.51 = 5.92 g / g · h

and is 5.92 g / g · h, compared with 5 g / g · h in the prototype.

The coking rate determined by weight, thermogravimetric and control atomic-adsorption independent methods is 0.04 g / g · h.

Coke yield

(0.04: 11.6) × 100 = 0.34 wt.%.

Within 200 hours of the reaction cycle, no decrease in activity was observed. The catalyst does not coke to the extent that blocking of active sites occurs.

Example 5

After 20 cm ^{3 of} silicon containing catalyst K-1, containing 1.0 wt.% ZnO and 1.0 wt.% Na ₂ O, methanol was passed at a rate of 4.5 g / min. In the evaporation zone, the methanol stream is mixed with the nitrogen gas stream in a molar ratio of CH ₃ OH: N ₂ = 1: 1. The concentration of hydrogen peroxide in methanol is 1.2%. At a temperature of 850 ° C, the formaldehyde yield is 57%, the selectivity of the process for hydrogen is 98%. The yield of CO ₂ is 0.1%. No methane output was observed.

The total conversion of methanol is 82%.

Raw Material Load:

W = 4.5 × (60:15) = 18.0 g / g · h (60 min, 15 g of catalyst)

The formaldehyde catalyst productivity is calculated taking into account the formaldehyde yield as

18.0 × 0.57 = 10.26 g / g · h

and is 10.26 g / g · h, compared with 5 g / g · h in the prototype.

The coking rate determined by weight, thermogravimetric and control atomic adsorption independent methods is 0.03 g / g · h.

Coke yield

(0.03: 18.0) × 100 = 0.17 wt.%.

Within 200 hours of the reaction cycle, no decrease in activity was observed. The catalyst does not coke to the extent that blocking of active sites occurs.

Example 6

After 20 cm ^{3 of} silicon containing K-1 catalyst containing 1.0 wt.% ZnO and 1.0 wt.% Na ₂ O, methanol was passed at a rate of 5.0 g / min. In the evaporation zone, the methanol stream is mixed with the nitrogen gas stream in a molar ratio of CH ₃ OH: N ₂ = 1: 0.5. The concentration of hydrogen peroxide in methanol is 1.0%. At a temperature of 880 ° C, the formaldehyde yield is 40%, the hydrogen selectivity of the process is 90%. No CO ₂ output is detected. The methane yield is 1.7%. The yield of CO is 57%.

The total conversion of methanol is 98%.

Raw Material Load:

W = 5.0 × (60:15) = 20.0 g / g · h (60 min, 15 g of catalyst)

The formaldehyde catalyst productivity is calculated taking into account the formaldehyde yield as

20.0 × 0.40 = 8.0 g / g · h

and is 8.0 g / g × h, compared with 5 g / g · h in the prototype.

The coking rate determined by weight, thermogravimetric and control atomic adsorption independent methods is 0.04 g / g · h

Coke yield

(0.04: 20.0) × 100 = 0.20 wt.%.

Within 200 hours of the reaction cycle, no decrease in activity was observed. The catalyst does not coke to the extent that blocking of active sites occurs.

Thus, a method for producing formaldehyde by direct non-oxidative dehydrogenation of methanol is proposed, which allows to increase the productivity of the catalyst up to 10.2 g / g · h, which is 2 times higher than in the prototype and to reduce coking by almost three times (in rel. Units).

However, the achievement of these results is possible when choosing a temperature range from 790 to 900 ° C, mainly 920-850 ° C.

At a process temperature below 790 ° C, the formaldehyde productivity of the catalyst is not high, which is associated with insufficiently effective activation of hydrogen peroxide.

In addition, the service life of the catalyst is increased, as evidenced by the fact that during the 200 hours of the reaction cycle, there is no decrease in the activity of the catalyst system (in the prototype, after 9 hours of catalyst operation, a noticeable decrease in activity is observed).

Claims (2)

1. The method of producing formaldehyde by dehydrogenation of methanol in the presence of an oxide Zn-Na containing catalyst at elevated temperature, characterized in that the methanol is dehydrogenated by chemical conjugation in the presence of hydrogen peroxide, taken in an amount ensuring its concentration in the methanol of 0.8-1.5 %, and in the presence of a catalyst additionally containing silicon dioxide, with the following initial composition of the components, wt.%:
Na ₂ O 1.2-1.4 Zno 0.8-1.2 SiO ₂ rest 2. The method of producing formaldehyde by dehydrogenation of methanol according to claim 1, characterized in that the dehydrogenation is carried out at a temperature of 790-900 ° C, mainly 820-850 ° C.