CN1740398A

CN1740398A - Direct electrochemical process of preparing ferrate

Info

Publication number: CN1740398A
Application number: CN 200510027780
Authority: CN
Inventors: 侯惠奇; 郑璐; 张仁熙; 董文博
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2005-07-15
Filing date: 2005-07-15
Publication date: 2006-03-01
Anticipated expiration: 2025-07-15
Also published as: CN100427644C

Abstract

The present invention belongs to the field of chemical preparing technology, and is especially direct electrochemical process of preparing ferrate. The preparation process prepares ferrate inside one diaphragm type cylindrical electrolytic bath with pure sodium hydroxide as electrolyte. While controlling electrolyte concentration, reaction temperature and applied voltage, high concentration sodium ferrate solution is first prepared, and potassium ferrate or barium ferrate is then prepared via adding potassium ion or barium ion. The present invention has simple technological process and low cost, and is suitable for large scale preparation of ferrate.

Description

Method for directly electrochemically preparing ferrate

Technical Field

The invention belongs to the technical field of medicament preparation processes, and particularly relates to a method for directly electrochemically preparing ferrate.

Background

Ferrate refers to a hexavalent iron compound, and is the only stable high-valence iron compound. Because of the many unique properties of ferrate, it has received increased attention in recent years in various fields of application. Firstly, ferrate has strong oxidizing property, and the final product of the reaction with organic matters is non-toxic and harmless ferric ions, so that the ferrate can be used as a multifunctional green water treatment chemical agent integrating oxidation, flocculation and sterilization; moreover, the super-iron battery using ferrate as a cathode material has great attraction due to the characteristics of large capacity, good charging property, strong conductivity, environmental friendliness and the like; in organic synthesis, ferrate has the characteristic of selective oxidation, thereby providing an effective way for the clean production of organic synthesis; ferrate is used as a matrix, transient particles Fe (IV) and Fe (V) can be generated by a pulse radiolysis technology, and the two strong oxidizing particles are researched to fill the blank in the field. With the development of research in these fields, the amount of ferrate required will increase day by day, however, the existing ferrate preparation process has the disadvantages of low yield, high preparation cost and the like, and the industrial production is not yet mature, which limits the practical application thereof.

Ferrate can now be synthesized by three pathways:

wet oxidation (hypochlorite oxidation) -chlorine is introduced into concentrated sodium hydroxide solution, ferric ions are oxidized by virtue of the concentrated sodium hypochlorite generated by the chlorine, and sodium ferrate is generated as the solution becomes purple black. Although this method provides a simple and efficient synthetic route, it has twomajor disadvantages. Firstly, the generation of high-concentration hypochlorite solution requires the use of toxic hazardous gas, namely chlorine gas, and the disposal of high-concentration chlorine-containing waste liquid is a problem to be solved; secondly, since the generated ferrate ions are easily decomposed by the influence of impurity ions (such as transition metals), the method requires the use of highly pure reagents (nearly saturated NaOH and KOH solutions), is quite costly, and is not suitable for large-scale industrial production.

Dry oxidation (fusion) methods-various dry oxidation methods utilize the nitrate, oxide, peroxide or hydroxide of alkali metal to react with iron salt at high temperature and high pressure to produce ferrate. Although this green technology can recycle various iron oxide wastes in the steel production process, the reaction conditions are severe and have high requirements on the materials of the reaction kettle. Research in this area is currently underway.

Electrolytic method-Poggendor et al, as early as 1841, discovered for the first time that ferrate is formed by anodic oxidation when an iron-containing anode is electrolyzed in a concentrated alkaline solution. The electrolysis method provides a feasible way for realizing the industrial production of ferrate by the advantages of less secondary pollution, simple and convenient operation, convenient and easily obtained raw materials, recycling and the like. However, as research progresses, many problems have been found in the preparation of ferrate by electrolysis. Haber and Pick et al found that the necessary conditions for ferrate synthesis were pH ≥ 14; the solubility of ferrate and an electrolysis intermediate product in NaOH is higher than that of KOH and LiOH, and the phenomenon of anode passivation and inactivation is the lightest, so the synthesis effect of using NaOH electrolyte is better than that of KOH and LiOH; the yield isimproved along with the increase of the concentration and the temperature of the electrolyte (40-50% NaOH or KOH, 30-70 ℃). Many documents also emphasize the effect of carbon content in iron anode materials on ferrate yield, although the conclusions are inconsistent. It can be seen that the efficiency of electrochemical synthesis of ferrate mainly depends on the current density, the type of anode material and the composition of electrolyte, and the maximum concentration of ferrate that can be achieved during electrolysis is limited by two factors, namely ferrate instability and anode surface passivation and inactivation. Another problem with the electrolytic process is the energy consumption, which directly affects the cost and market potential of the product. Once these key problems are overcome, the electrolytic method for preparing ferrate can really realize industrialization.

Disclosure of Invention

The invention aims to provide a preparation method of ferrate with high electrolysis efficiency and low preparation cost.

The preparation method provided by the invention is a direct electrochemical preparation method, namely, the ferrate is prepared by using pure NaOH as an electrolyte and utilizing a diaphragm type electrolytic cell for electrolysis. The method comprises the following steps: preparing 15-16 mol/L NaOH solution as an anolyte, and pouring the anolyte into an anode compartment; preparing 1-2 mol/L NaOH solution as a cathode electrolyte, and pouring the cathode electrolyte into a cathode compartment; controlling the temperature of the electrolyte at 35-40 ℃, inserting an electrode, and electrolyzing for 60-70 min under the condition that the applied voltage is 8-11V to obtain a high-concentration purple-black sodium ferrate solution.

In the invention, after the high-concentration sodium ferrate solutionis prepared, the solution is put into an ice-water bath, KOH or Ba (OH) is added₂Continuously stirring the solid to 1-1.5 mol/L until purple black crystals are separated out, quickly performing suction filtration at 0 ℃, and drying in a vacuum drier for 20-30h to obtain the dry and stable K₂FeO₄Or BaFeO₄And (3) solid powder. The flow is shown in figure 1.

In the present invention, the diaphragm material, the housing material, the electrode material and the structural arrangement of the diaphragm electrolytic cell are selected and improved as shown in fig. 2. The electrolytic cell adopts a concentric cylinder type structure, the outer cylinder adopts polyvinyl chloride material, the inner cylinder adopts polyvinyl chloride framework, and the surface of the inner cylinder is attached with an N-961TX perfluorinated ion membrane; the anode adopts a galvanized iron wire mesh with the iron content of 95-96%, the diameter of 0.3-0.35 mm and the mesh of 10-15, and is arranged on the inner wall of the outer cylinder; the cathode is made of a copper wire with the diameter of 0.1-0.15 mm, the copper wire is suspended in the center of the inner barrel, and the electrode distance is 2.3-2.5 cm. 35mL of catholyte is contained in the inner cylinder, and 60mL of anolyte is contained in the interlayer between the outer cylinder and the inner cylinder.

The electrode reactions that occur during electrolysis are as follows:

anode:

cathode:

and (3) total reaction:

the N-961TX perfluorinated ion membrane system used in the invention is a reinforced composite membrane of sulfonic acid/carboxylic acid in 900 series developed by Du Pont company in the United states, and is suitable for a narrow-polar-distance or zero-polar-distance electrolytic tank in the chlor-alkali electrolysis industry. Has the advantages of high current efficiency, low voltage, high alkali-resistant concentration, long service life and the like. In the electrolytic process of the experiment, the ionic membrane not only effectively transfers current, but also prevents the mixing of the anode electrolyte and the cathode electrolyte, and lays a foundation for generating high-concentration sodium ferrate.

The invention adopts the preparation method of different concentrations of the cathode compartment and the anode compartment, which not only improves the electrolysis efficiency, but also reduces the preparation cost, wherein the anode zone is 15-16 mol/L sodium hydroxide solution, and the cathode zone is 1-2 mol/L sodium hydroxide solution.

The anode material used in the invention is a galvanized iron wire mesh adopting a cold plating technology, and the material is easy to purchase and is cheap. In the experiment, the yield of sodium ferrate of pig iron, hot galvanized iron wires and cold galvanized iron wires is compared, and the conclusion is that the cold galvanized iron wires have the best effect, the anode passivation phenomenon is not obvious, the capability of generating sodium ferrate by dissolving the anode is durable, and a high-concentration sodium ferrate solution can be prepared.

The concentration of sodium ferrate in the experiment was determined by chromate titration.

The method provides a new way for large-scale and diversified production of ferrate. The invention utilizes the high efficiency of preparing sodium ferrate by NaOH; the proper anode material is selected, so that the problem of anode passivation is solved; the problems of diaphragm corrosion and current efficiency are solved by selecting a proper diaphragm material; the optimal experimental device and reaction conditions are adopted, so that the sodium ferrate with the highest concentration can be produced with the lowest energy consumption; the potassium ferrate and the barium ferrate are crystallized to separate out a solid by utilizing the characteristic of low solubility of the potassium ferrate and the barium ferrate, and are stored in a drying way, so that the problem that the ferrate is unstable in a humid environment is solved. The invention provides a set of feasible scheme for the industrialization of preparing ferrate by an electrolytic method.

Drawings

FIG. 1 is a schematic process flow diagram of the present invention.

FIG. 2 is a schematic diagram of a diaphragm electrolytic cell device for preparing sodium ferrate.

Reference numbers in the figures: 1 is an anode electrolytic cell outer cylinder, 2 is a galvanized iron wire mesh anode, 3 is a cathode electrolytic cell inner cylinder, and 4 is a copper wire cathode.

Detailed Description

The invention is further described below by way of examples.

In the examples, analytically pure NaOH was used as a raw material, and sodium ferrate was produced by electrolysis in a cylindrical diaphragm cell.

In example 1, 16mol/L NaOH solution is prepared as an anolyte, 2mol/L NaOH solution is prepared as a catholyte, the temperature of the electrolyte is controlled at 40 ℃, the applied voltage is 8.5V, and the concentration of sodium ferrate obtained after electrolysis is 22.14g/L after 69 min.

Example 2, 15mol/L NaOH solution is prepared as the anolyte, 2mol/L NaOH solution is prepared as the catholyte, the temperature of the electrolyte is controlled at 40 ℃, the applied voltage is 10.8V, and the concentration of the sodium ferrate obtained after electrolysis is 22.99g/L after 60 min.

Example 3, 15mol/L NaOH solution was prepared as the anolyte, 2mol/L NaOH solution was prepared as the catholyte, the temperature of the electrolyte was controlled at 35 ℃ and the applied voltage was 8.5V, and after 70min of electrolysis, the concentration of sodium ferrate was 18.66 g/L.

Example 4g of KOH were added in portions to 22.14g/L of Na obtained in the above example₂FeO₄In the solution, the mixture is stirred in ice-water bath until purple black crystals are separated out, and then is subjected to suction filtration at zero degree and vacuum drying to obtain the K with the purity of 49.6 percent₂FeO₄And (3) powder.

Claims

1. A method for directly electrochemically preparing ferrate is characterized in that pure NaOH is used as electrolyte, a diaphragm type electrolytic cell is adopted, and the method comprises the following specific steps: preparing 15-16 mol/L NaOH solution as an anolyte, and pouring the anolyte into an anode compartment; preparing 1-2 mol/L NaOH solution as a cathode electrolyte, and pouring the cathode electrolyte into a cathode compartment; controlling the temperature of the electrolyte at 35-40 ℃, inserting an electrode, and electrolyzing for 60-70 min under the condition that the applied voltage is 8-11V to obtain a high-concentration purple-black sodium ferrate solution.

2. The method according to claim 1, wherein the sodium ferrate solution is further prepared by placing it in an ice-water bath, adding KOH or Ba (OH)₂Solid to 1-1.5 mol/L, and continuously stirring until purple black crystals are obtainedSeparating out, vacuum filtering at 0 deg.C, and drying in vacuum drier for 20-30 hr to obtain dry and stable K₂FeO₄Or BaFeO₄And (3) solid powder.

3. The preparation method according to claim 1 or 2, characterized in that the diaphragm type electrolytic cell is a concentric cylinder type structure, the outer cylinder is made of polyvinyl chloride material, the inner cylinder is made of polyvinyl chloride framework, and the surface of the inner cylinder is attached with an N-961TX perfluorinated ion membrane; the anode adopts a galvanized iron wire mesh with the iron content of 95-96%, the diameter of 0.3-0.35 mm and the mesh of 10-15, and is arranged on the inner wall of the outer cylinder; the cathode is made of a copper wire with the diameter of 0.1-0.15 mm, the copper wire is suspended in the center of the inner barrel, and the electrode distance is 2.3-2.5 cm.