RU2296745C1 - Method of preparing iron(iii) formate in presence of hydrogen peroxide - Google Patents

Abstract

FIELD: inorganic synthesis.

SUBSTANCE: invention relates to preparation of salts of transition metals with organic acids, in particular to formic acid ferric salt. Method is accomplished via oxidation of ferrous formate with hydrogen peroxide in presence of formic acid and in absence of any dorm of iron as reducer in order to prevent reduction of ferric salt into original ferrous salt. As reducer, ferrous formate is used preliminarily recrystallized and dried or filtered off from reaction mixture suspension. Process is carried out in upright bead mill in two steps. In the first step, ferrous formate powder or precipitate is combined, stepwise or in one go, with 85% formic acid or mixture of filtrate with wash water formed during isolation of desired product to form pasty slurry ensuring stable functioning of bead mill. Second-step operation is effected in bead mill functioning mode involving forced cooling through side surfaces of reactor and continuous introduction of 12.5-25% hydrogen peroxide solution at a rate of 3.25-4.24 g H₂O₂ per 1 kg starting charge until degree of Fe(II) salt conversion achieves 85-90%. Supply velocity is then lowered until complete conversion is reached. Resulting product slurry is separated from beads and filtered. Filter cake is washed with 85% formic acid and recrystallized in saturated ferric formate solution containing 20-30% of formic acid. Wash liquid is combined with filtrate and used in the first step as described above.

EFFECT: increased yield of target product and simplified its isolation step.

1 tbl, 8 ex

Description

The invention relates to a technology for the production of ferric salts and low molecular weight fatty acids and can be used in various fields of industrial and laboratory chemistry, in scientific research and in the analytical control of various objects.

A known method of producing iron (II) formate by the interaction of iron (II) sulfate and sodium formate, in which it is noted that the product is quite poorly soluble in water and is resistant to oxidation in air (US Pat. No. 2688032 from 08.31.1954). It is these product properties that ensure the implementation of the exchange process specified in the patent.

On the other hand, there is no reason to believe that a similar type of exchange process can be implemented to obtain iron (III) formate. In addition, there is no information about the solubility of ferric salt, which is of paramount importance in shifting the equilibrium of the metabolic process in the desired direction.

Closest to the claimed is a method for the preparation of basic indium formate and acetate (AS USSR No. 454198), in accordance with which the metal is reacted with acid in the presence of hydrogen peroxide with periodic heating to 80-100 ° C and subsequent product isolation by evaporation solution.

The disadvantages of this method are

1. The complete uncertainty of how hydrogen peroxide will lead in a suspension of ferrous formate, in particular, will prevail oxidation of Fe ²⁺ in Fe ³⁺ or will catalysis of homolytic and heterolytic decomposition of peroxide dominate with the formation of oxygen as an oxidation product under the influence of salt ferric iron, etc. In any case, iron and indium as metals are far from the same thing and it is hardly legitimate to draw any conclusions by analogy.

2. Temperatures of 80-100 ° C for most heterolytic reactions of hydrogen peroxide are too high. On the contrary, such temperatures should contribute to the homolytic and induced decomposition of this oxidizing agent.

3. In the above system with indium, there is no abundant solid phase of salt in the reaction mixture, which must be evaporated to isolate the product. In the case of iron (II) formate, the solid phase must be necessary due to the poor solubility of this salt. It can be expected that it will also be in the presence of iron (III) formate in the reaction mixture. It is not at all obvious how such solid phases will affect the stability and effectiveness of hydrogen peroxide as an oxidizing agent.

4. An iron (III) salt is capable of oxidizing the metal itself to form an iron (II) salt. Therefore, it is not at all obvious that in the presence of hydrogen peroxide the product will be an iron (III) salt, and not a ferrous salt.

5. Isolation of the salt product by evaporation is a long and energy-intensive operation, which should be avoided if possible.

The objective of the proposed solution is to select such conditions for the oxidation of the suspension of iron (II) formate with hydrogen peroxide, which would ensure almost quantitative conversion of the ferrous salt to ferric salt, while refusing to evaporate as a mandatory operation in the isolation of the target product.

This goal is achieved in that the process is conducted in the absence of iron as a reducing agent in any form, as a reducing agent, pre-crystallized and dried or freshly filtered from a suspension of the reaction mixture formate of iron (II) obtained in any way, and the process is carried out in a vertical type bead mill in two stages: at the first, a powder or a freshly filtered precipitate of iron (II) formate by fractional input, if necessary, the selection of the optimal amount or in one go when preliminarily If the optimum amount of 85% formic acid is found or obtained by separating iron (III) formate, the filtrate in a mixture with washing formic acid in the episodic mixing mode is turned into a rather mobile and easily mixed greyish-green paste, and on the second, stirring is switched on in the constant mode operation, cooling is fed through the side and bottom surfaces of the reactor and begin continuous dosage 12.5-25% solution of hydrogen at a rate perokida 3,25-4,24 g H ₂ O ₂ per min per 1 kg of starting zag narrow, and up to 85-90% of the degree of expenditure of iron (II) formate, which is close to constant, and at the final stages it decreases, and in this mode the process is brought to an almost complete conversion of the iron (II) salt to the iron (III) salt, after whereupon the dosage of the peroxide solution, stirring and cooling are stopped, the suspension of the brick-red-brown product is separated from the beads and sent for filtration; the precipitate obtained is washed with 85% formic acid on the filter and sent to recrystallization from 20-30% formic acid in saturated solution of iron (III) formate at room temperature, and the washing liquid is combined with the filtrate and used to prepare a solution for recrystallization of the product , to transfer the powder or precipitate of iron (II) formate into a suspension paste or accumulate for subsequent strengthening and allocation of additional quantities of iron (III) formate.

Characteristics of the raw materials used

Iron (II) formate was prepared as follows:

1. By direct interaction of crushed iron and its alloys (steels, cast iron) with 4.5-10 mol / kg of aqueous formic acid at 45-65 ° C in the presence of a stimulating additive of iodine in an amount of 0.016-0.164 mol / kg of the liquid phase and bubbling air.

2. By direct interaction of crushed iron and its alloys (steel, cast iron) in any mass ratio with each other at room temperature in the presence of iodine (bromine) containing a stimulating additive and continuously supplied to the reaction zone of hydrogen peroxide as an oxidizing agent.

3. By direct interaction of the crushed iron and its alloys with 23-46% formic acid in a bead mill at 55-75 ° C in the presence of Fe ₂ O ₃ or Fe ₃ O ₄ as an additional oxidizing agent and the main supplier of cations for the target salt -product.

4. By direct interaction of the crushed iron and (or) its alloys in any mass ratio with each other with formic acid in a solution of an organic solvent and water in a mass ratio of solvent: formic acid: water 100: (85 ÷ 100) :( 15 ÷ 0) in the presence of 0.03-0.10 mol / (kg of liquid phase) of iodine as a stimulating additive, as well as Fe ₂ O ₃ and (or) Fe ₂ O ₄ as an additional oxidizing agent and the main cation supplier for the target salt product.

5. By the exchange interaction between iron (II) sulfate and sodium formate in the mode of US patent No. 2688032.

Used: freshly filtered precipitate of iron (II) formate, obtained 1-5 - methods, as well as recrystallized and dried product.

Formic acid according to GOST 5848-73.

Hydrogen peroxide according to GOST 10929-76.

Distilled water according to TU 6709-72.

The process of the claimed method in a bead mill is as follows. First, the iron (II) formate selected as a reducing agent is transferred into a rather fluid and readily moving paddle suspension with a paddle mixer. For this, the powder of recrystallized and dried iron (II) formate or a freshly filtered precipitate of this compound is moistened with formic acid or the filtrate (a mixture of filtrate and wash acid) obtained by isolation of the final product, i.e. iron (III) formate. The amount of liquid phase to be wetted depends on whether iron (II) formate powder or a freshly filtered precipitate is taken. In the first case, it is the largest; in the second, it tends to a minimum. This amount is determined experimentally by the method of fractional input of the liquid phase and occasional mixing after each input. In those cases when it is known, the entire liquid phase can be introduced in one go.

After the specified paste-suspension of the reducing agent is prepared (which indicates the completion of the first stage), they include mechanical stirring of the contents of the reactor in continuous operation, cooling of the reactor through its side and lower surfaces is introduced, and a continuous dosage of an aqueous solution of hydrogen peroxide is started at a controlled speed: first with close to constant, at the final stage - with decreasing. The process is carried out at as close as possible to room temperature up to the almost complete consumption of the entire loaded reducing agent. Upon reaching this point, the dosage of hydrogen peroxide, stirring and cooling are stopped, the suspension of the iron (III) salt (product) is separated from the glass beads and fed to the filter. The resulting filter cake was washed with a formic acid solution and sent for recrystallization from formic acid solution saturated with iron (III) formate. The washing liquid is combined with the filtrate and used to wet the initial reducing agent, to prepare the initial solution to recrystallize the product, or simply accumulate for subsequent strengthening and isolation of additional quantities of iron (III) formate as the target product.

Example No. 1

In a vertical-type bead mill with a glass case and a mechanical stirrer (1440 rpm) of the vane type, the shaft and blade of which are made of Teflon, 100 g of glass beads, 45 g of iron (II) formate powder and 5 g of 85% formic are loaded acids. Scroll the mixer manually to more or less evenly distribute the loaded mass in the reaction zone of the apparatus. After 5 minutes, a second portion of formic acid was added in an amount of 5 g and the mechanical stirrer was manually turned again. The operation of fractional input of formic acid of 5 g at intervals of 5 minutes and manual scrolling of the mixer shaft is carried out 2 more times. All this is done at room temperature. As a result, the introduced iron (II) formate powder turns into a grayish-greenish suspension-paste suspension, which is easily mixed with a stirrer. At this preparatory stage is completed.

The reactor vessel is placed in a cooling water bath, mechanical stirring and a continuous supply of a 12.5% hydrogen peroxide solution at a mass rate of 3.84 g of H ₂ O ₂ / (min · kg load) are included. This moment is taken as the beginning of the process. They control the color transitions in the reaction zone and the sampling method for the conversion of the iron (II) salt to the iron (III) salt. First, a red-brown spot appears at the peroxide injection site, which is rather quickly washed off at the edges as a result of mixing of the reaction mass. Then the whole mass blushes, the color gradually turns into brick-red and then into brick-brown-red and deepens all the time. By the end of 48 minutes, more than 85% of the starting iron (II) salt has time to react. The mass feed rate of peroxide is initially reduced by a factor of 2, and then by a further 3 times after 5 minutes. After 15 minutes of this regime, the degree of conversion of the loaded iron (II) formate to the iron (III) salt is brought to almost 100%. The temperature of the reaction mixture at this moment was 33 ° C.

The continuous supply of hydrogen peroxide to the reaction zone is stopped, mechanical stirring is turned off, and the forced cooling of the reactor is removed. The latter is disconnected from the lid with the automatic oxidizer supply system and the return condenser-condenser, stuffing box, loading hatch and sampler socket located on it. The reaction mixture is separated from the beads by filtration through a mesh instead of a filter septum, and then filtered. The brown-brown precipitate is washed on the filter with 85% formic acid in order to complete the conversion of the basic iron (III) formate to the middle ferric salt, after which it is sent for recrystallization from formic acid-saturated formate iron (III) with the content of the latter 20 % The recrystallized salt is filtered and dried without any restrictions on contact with air. As a result, 57 g of a powder of brick-brown color are obtained, according to the analysis corresponding to the formula Fe (OS (O) H) ₃ .

Wash water is combined with the primary filtrate and accumulated for subsequent strengthening and the allocation of additional portions of iron (III). Such a mixture can also be used in the main process for the initial wetting of iron (II) formate powder and the preparation of a paste for oxidation with hydrogen peroxide.

Examples No. 2-8

Laboratory installation, bead mill - reactor, reagent loading procedure, process steps, the sequence of operations in them, as well as when separating the reaction mixture from beads and isolating the target product, are similar to those described in Example 1. They differ in the degree of preparation of the initial iron (II) formate, degree cleaning and drying it, with the composition and quantity of the liquid phase added in the first stage in order to convert the initial solid phase of the reducing agent into a paste-mix easily mixed under the conditions of operation of a bead mill retention, the nature of the input of such a liquid phase, the rate of input of the oxidizing agent (in terms of 100% H ₂ O ₂ ) and the nature of its change at the final stages of the process. The results are summarized in table. Designations: SPV - dry recrystallized iron (II) formate; СО N ... - freshly obtained precipitate of iron (II) formate by filtration of the reaction mixture (suspension) obtained by the method described in the characteristics of the feedstock section under the corresponding number; MK - 85% formic acid; SFC - a mixture of filtrate and washing formic acid; α is the degree of conversion of iron (II) formate.

The positive effect of the proposed solution is as follows:

1. An available hydrogen peroxide in a rather wide range of concentrations is used as an oxidizing agent.

2. The process is carried out at room temperature and does not require any specific cooling organization. This also determines the rather simple hardware design of such a process.

3. At room temperatures, iron (III) formate is rather poorly soluble in water and in formic acid solutions and mainly accumulates in the solid phase, which greatly facilitates its release.

4. The product is easily cleaned by conventional recrystallization.

5. The product in the medium used (ie in the absence of iron and other reducing agents) and close to room temperature is stable and does not require any specific additional measures in this regard.

6. Despite the fact that the bulk of the reducing agent used is in the solid phase, the process proceeds quite quickly.

Claims (1)

A method of producing iron (III) formate in the presence of hydrogen peroxide as an oxidizing agent, characterized in that the process is carried out in the absence of iron as a reducing agent in any form, as a reducing agent, iron formate previously recrystallized and dried or freshly filtered from a suspension of the reaction mixture is used as a reducing agent (II ), and the process itself is carried out in a vertical type bead mill in two stages: at the first, a powder or a freshly filtered precipitate of iron (II) formate by fractional input if necessary the ability to select the optimal amount, or in one go with the optimal amount of 85% formic acid previously found or obtained by separating iron (III) formate by filtrate in a mixture with washing formic acid in the episodic mixing mode, is turned into a rather mobile and easily mixed paste the suspension is grayish-green in color, and on the second, stirring is switched on in continuous operation mode, cooling is fed through the side and lower surfaces of the reactor and a continuous dosage is started 12, 5-25% hydrogen peroxide solution at a rate of 3.25-4.24 g H ₂ O ₂ per min per 1 kg of the initial charge, and up to 85-90% degree of consumption of iron (II) formate with a close to constant and at the final stages with decreasing, and in this mode, the process is brought to an almost complete conversion of the iron (II) salt to the iron (III) salt, after which the peroxide solution is dosed, mixed and cooled, the suspension of the brick-red-brown product is separated from beads and sent for filtration; the precipitate obtained is washed with 85% formic acid on the filter and sent to recrystallization from 20-30% formic acid in saturated solution of iron (III) formate at room temperature, and the washing liquid is combined with the filtrate and used to prepare a solution for recrystallization of the product , to transfer the powder or precipitate of iron (II) formate into a suspension paste or accumulate for subsequent strengthening and allocation of additional quantities of iron (III) formate.