RU1796244C - Method for preparation of iron-molybdenum catalyst - Google Patents

Abstract

Usage: petrochemical synthesis. SUMMARY OF THE INVENTION: Powdered iron oxide and powdered molybdenum acid are poured into a paddle mixer. Mixed. Distilled water is added, mixed to a pasty paste. Molded into granules. Granules sag in the air. Calcined at increasing temperature to. 400 ° C for 6 hours, then at 400 ° C for 2 hours and 550 ° C for 2 hours. Catalyst characteristic: specific surface 4.7 m2 / g, mechanical strength up to. 53 kg / cm2. 1 tab.

Description

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The invention relates to the field of producing a catalyst for the selective oxidation of methanol to formaldehyde, in particular to a method for producing an iron-molybdenum catalyst.

A known method for the preparation of a iron-molybdenum catalyst, comprising Al1Is, in impregnating powdered iron oxide with a solution of ammonium paramolybdate, followed by drying the resulting mass, calcining it, tableting it and heat treatment to 420 ° C. The catalyst contains from 4 to 20 wt.% MoOz and from 80 to 96 wt.% ReaOz.

The method avoids wastewater formation in the preparation of the catalyst. However, the technology is quite complex, and the activity and selectivity of the resulting catalyst is low.

The closest to the described method in terms of the achieved effect and essential features is a method of preparing an iron-molybdenum catalyst, which consists in mixing powdered iron oxide (ReaO3) and ammonium paramolybdate ((MH4) 4HaO), first in a dry and then wet state, followed by molding of the resulting plastic mass into granules, their drying and heat treatment at increasing temperature. The final calcination is carried out at a temperature of 550-700 ° C. The catalyst contains 29-65 wt.% MoOz and 71-35 wt.% ReaOz.

The activity of the catalyst is characterized by the constant of methanol oxidation rate Ki (basic reaction). Selectivity is characterized by a constant oxidation rate of formaldehyde K2 (side reaction), as well as a ratio of "2 / Ki. Tests show that the activity of the catalyst obtained

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in a known manner, not high enough: Ki 2.5-4.0 ml / g-s. In addition, the known method for preparing an iron-molybdenum catalyst does not completely eliminate harmful emissions and requires the disposal or neutralization of ammonia waste during calcination. The ammonia yield can reach 86 thousand liters per 1 ton of catalyst. The average Johannic crushing strength of the obtained catalyst along the axis of 35 kg / cm t;, i

An object of the present invention is to provide an iron-molybdenum catalyst with increased activity and mechanical strength and reduced production waste.

The object of the invention is achieved by the described method of preparing iron with 6 L and a base catalyst, which consists in mixing powdered molybdenum compounds, which are used as molybdenum acid (HMOSC). and iron oxide (ReaO3) or iron hydroxide (Fe (OH) h), followed by wetting, molding the resulting plastic mass into granules, drying and heat treatment at a temperature of 550-70 ° C. The starting components are taken in such a ratio that the catalyst contains May 29-65.% MoO3 and, respectively, May 71-35.% F6203.

A distinctive feature of the shadow invented is the use of another molybdenum-containing compound, molybdenum acid (H2MoQ / i), instead of ammonium paramolybdate ((MH4) 4 H20). The use of this compound allows to reduce the amount of waste in the preparation of the catalyst, and also to obtain a catalyst with increased activity and mechanical strength .; at:

Catalytic tests were carried out under conditions of complete mixing in a flow-circulation system at 300 ° C, a methanol concentration in the air-alcohol mixture of 6.5%, a contact time of 0.3-0.35 sec. In order to obtain the characteristics necessary for industrial use, the catalysts are tested in the form of granules with a grain size of 4.3x4.3-5.0x5.0 mm. The weighed portion is 2 g. The activity and selectivity are characterized by the constant oxidation rate of methanol - Cp (ml / g-s) and formaldehyde (side reaction) - K2 (mg / g-s), calculated according to the kinetic equations of the first order. Selectivity is also characterized by the ratio of constants Ka / Ki, and a higher value means worse

selectivity. The selectivity, as the ratio of the useful conversion of methanol to formaldehyde and the total conversion of methanol, for the prepared samples is 95%. The invention is illustrated by the following examples.

Example 1. In a paddle mixer. 30 g of powdered iron oxide ReaO3 (specific surface area 19 m / g) and 35.5 g of powdered molybdenum acid NaMoSm are added (grade and stirred for 30 minutes. 20 ml of distilled water are added and mixed in One hour before receiving dough-like paste 5 (humidity 22%). The paste is formed by extrusion into granules, dipped; it is air-dried for a day, then calcined at an increasing temperature up to 40 ° C for 6 hours, then at 400 ° С - 2 hours and 5500С - 2 hours. The finished catalyst contains 50 ma . Reabz% and 50 wt.% MoOz. Granule size of finished catalyst 4,3x4,3 mm. The specific surface area of 4.7 m2 / g. The average mechanical strength of the catalysts was torus 5 is 36 kg / cm2.

Tests in the flow-circulation installation show: KI - 5.2 ml / g-s; K2 0.21 ml / g-s; K2 / Ki -0.04.

Example 2, The catalyst is prepared according to Example 1. The ratio of the starting reagents is taken based on the preparation of a catalyst with a composition of 29 wt% MoO3 and 71% wt,% Pb20z. The granule size of the finished catalyst is 4.3x4.3 mm. Specific surface area 5 14 m2 / .g. The average mechanical strength of the catalyst is 38 kg / cm2.

Tests on a flow-circulating installation show: Ki 4.2 ml / g-s; Ka 0.17 ml / g-s; K2 / K1 - 0.04.

Example 3. The catalyst is prepared according to Example 1. The ratio of the starting reagents is calculated on the basis of the preparation of the catalyst — the composition is 65 wt.% MoO3 and 35 wt.% Pb20z. The granule size of the finished catalyst is 4.3x4.3 mm. The specific surface area is 5.7 m2 / g. The mechanical strength of the catalyst is 40 kg / cm2,

Tests in a flow-through installation show: Ki -3.4 ml / g-s; K2 0.12 ml / g-s; K2 / Ki 0.035.

Example 4. To prepare the catalyst, 40 g of iron hydroxide (Fe (OH) h) (grade h) and 41.5 g of molybdenum acid (H2Mo04) were taken. The catalyst is prepared according to Example 5 according to Example 1. Catalyst composition: 50 wt.% MoO3 and 50 wt.% Pb20z. The granule size of the catalyst is 4.3x4.3 mm. The specific surface of 3m / g. The mechanical strength of the catalyst is 53 kg / cm2.

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Tests in a flow-through installation show: Ki 4.0 ml / g-s; Ka 0.13 ml / g-s; "2 / Ki 0.033.

Example 5. A catalyst with a composition of 50 wt.% Pb203 and 50 wt.% MoO3 is prepared according to Example 4. After calcining at 550 ° C, the finished catalyst is calcined at 700 ° C for 2 hours. The granule size of the finished catalyst is 4.3x4.3 mm The specific surface is 1.5 m2 / g, the mechanical strength is 53 kg / cm.

Tests in a flow-through installation show: KI 2.7 ml / g-s; K2 0.06 ml / g s; K2 / K1 0.022.

Example 6 (for comparison).

A) The catalyst composition of 50 wt.% Re20z and May 50. % MoO3 is prepared according to the procedure of the prototype. The granule size of the finished catalyst is 5x5 mm. The specific surface area is 4.3 m2 / g. Ammonia emissions from the preparation of the catalyst reach 7 liters per 100 g of catalyst. Mechanical strength 35 kg / cm2.

Tests in a flow-through installation show: K2 4.0 ml / g-s; K2 0.16ml / g s; K2 / K1 0.04. : .B) A catalyst with a composition of 29 wt.% MoO3 and 71 wt.% Rb20z was prepared according to the prototype. Granule size 5x5 mm. The specific surface area is 9.4 m2 / g. Ammonia emissions during cooking reach 4 L per 100 g of catalyst. Mechanical strength 33 kg / cm2.

Tests in a flow-through installation show: Ki 3.2 ml / g-s K2 0.14 ml / g-s; K2 / Ki 0.044.

B) A catalyst with a composition of 65 wt.% MoO3 and 35 wt.% P203) is prepared according to the prior art. Granule size 5x5 mm. The specific surface area is 3.2 M2 / g. Ammonia emissions during cooking reach 9 liters per 100 g of catalyst. The mechanical strength of the catalyst is 31 kg / cm2

Claims (1)

The claims A method of preparing an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde by mixing the molybdenum-containing compound with iron oxide, first in the dry, then in the wet state, followed by Tests in a flow-through installation show: KI 2.6 ml / g-s; K2 0.09 ml / g; K2 / Ki 0.035. D) A catalyst prepared according to the prototype under conditions analogous to Example 5 (i.e. calcined at 700 ° C). shows the following results during testing: Ki 2.5 ml / g-s, K2 0.08 ml / g-s, K2 / Ki 0.032. The mechanical strength of the catalyst is 34 kg / cm2. The test results of the catalysts are presented in the table. As can be seen from the table, the catalyst obtained by the present method has an activity higher than the catalyst obtained by the known method. So, for example, a catalyst containing 50% MoO3 obtained by the present method has a constant of methanol oxidation rate Ki of 5.2 ml / g-s, a similar catalyst obtained by a known method has a Kg of 4.0 ml / g- e. Depending on the content of MoOs, Ki varies from 2.7 to 5.2 ml / g-s on the catalyst obtained by the present method and from 2.5 to 4.0 ml / g-s on the catalyst obtained by the known method . Moreover, the selectivity expressed by the Kg / Ki ratio is approximately the same on both catalysts. In addition, the use of molybdenum acid instead of ammonium paramolybdate avoids the formation of harmful ammonia emissions during the preparation of the catalyst. The catalyst obtained by this method also has a higher mechanical crushing strength. axis. The mechanical strength of the catalyst obtained by the known method is 31-35 kg / cm2, the mechanical strength of the catalyst obtained by the present method is from 36 to 53 kg / cm2. molding the obtained pestle into granules, drying and heat treating it at 550-800 ° C, characterized in that, in order to obtain a catalyst with increased activity and mechanical strength, to reduce production waste, molybdenum-containing compound is used as molybdenum acid. The oxidation rate constants of methanol (Id) and formaldehyde (K2) obtained in flow conditions (Т 300 ° С, 6.5% СНЗОН, contact time 0.35 s, catalyst grain size (4.3 x 4.3) - (5.0 x 5.0) mm Table continuation