JP6789523B2 - Ammonium ion adsorbent - Google Patents

Description

The present invention relates to an adsorbent for ammonium ions in a liquid.

Methane fermentation is one of the technologies for converting organic matter into fuel and utilizing it for power generation, etc., and is widely used. For example, sewage sludge, agricultural waste such as livestock manure, etc. are used as raw materials. Methane fermentation is a method in which methane-fermenting bacteria are added to a suspension (digestive solution) containing organic matter under anaerobic conditions to generate methane, and a part of carbon contained in the organic matter is converted into fuel as methane. On the other hand, most of the nitrogen, which is also abundant in organic matter, is decomposed into ammonia. Most of the ammonia remains as ammonium ions in the digestive juices.

It is known that a high concentration of this ammonium ion inhibits methane fermentation. It is known that inhibition occurs at 4,500 to 5,000 ppm or more in medium-temperature fermentation fermented at about 35 ° C., and at 2,500 ppm or more in high-temperature fermentation fermented at about 55 ° C. (Non-Patent Document 1). ). In particular, chicken manure and food waste containing a large amount of protein have a high nitrogen content, and particularly high ammonium ion concentration is often a problem when methane fermentation is carried out using them.

On the other hand, ammonium ions are also contained in ammonia, ammonium compounds, nitrite compounds and nitric acid compounds, which are restricted by the uniform wastewater standards specified by the Ministry of the Environment. Furthermore, when the concentration of ammonium ions increases in water, there is concern about the effects on aquatic organisms. For example, according to the standards for aquatic water, the total nitrogen content is 0.2 to 1.0 mg / L in fresh water and 0.3 to 1.0 mg in seawater. A standard of extremely low concentration of / L is shown (Non-Patent Document 2).

As a method of solving these problems, there is a method of using an adsorbent that adsorbs a large amount of ammonium ions. By using the adsorbent, it is expected that the device can be made compact and the energy cost can be reduced because heating is not required. As an example of using an adsorbent, Non-Patent Document 3 describes an example of using an adsorbent that is heated after impregnating sulfuric acid to an organic substance. However, since this adsorbent cannot be regenerated, there is a problem in the cost of the adsorbent.
On the other hand, Patent Document 1 also introduces that a metal cyano complex can be used as an ammonium ion adsorbent and can be reused. Furthermore, in order to increase the adsorption capacity of ammonium ions, it is introduced that it is important to control the composition and increase the alkali metal in the composition. However, Non-Patent Document 4 introduces that the metal cyano complex changes to a stable composition when washed with water, and in the case of the metal cyano complex, adsorption by ion exchange with the originally contained alkaline ion is introduced. Therefore, a change in composition as shown in Non-Patent Document 4 is directly linked to a decrease in adsorption capacity. Further, the composition control important for the content of alkaline ions is the content ratio of metal ions and hexacyanometal ions, and the control is controlled by the mixing ratio of the raw materials. However, the desired composition is not always obtained by the method, and when the required composition cannot be obtained by simply controlling the mixing ratio, a method for solving the problem has not been shown.

WO2015 / 186819

Outline of methane fermentation technology and its application prospects, Lee Yu Yu, JEFMA 2005, 53, 4-18. Fisheries Water Standards (2005 edition) Ammonia removal from air stream and biogas by a H2SO4 impregnated adsorbent originating from waste wood-shavings and biosolids, Xuejun (Jack) Guo, Jin Kwon Tak, Richard L. Johnson, Journal of Hazardous MaterialsVolume 166, Issue 1, 15 July 2009, Pages 372-376 Chemical composition control of potassium copper hexacyanoferrate by rinse with cross-flow filter, Akira Takahashi, Keiko Noda, Hokuto Hariu, Hisashi Tanaka, Shin-ichi Ohkoshi, Manabu Ishizaki, Masato Kurihara, Tohru Kawamoto, 41st International Conference on Coordination Chemistry (ICCC) , 2014, Jul., Singapore

As described above, as the ammonium ion adsorbent, a material having a large adsorption capacity is required, whose capacity does not change even after cleaning.

The present invention has been made in view of this situation, and it is an object of the present invention to provide an ammonium ion adsorbent which can adsorb ammonium ions and has a high adsorption amount of ammonium ions even if the adsorbent is washed. Is to be.

As a result of various studies, the inventors, in order to solve this problem, control the binding force of the metal ion in the metal cyano complex, and the metal in a state where the composition containing a large amount of alkali metal is maintained even after washing. We realized that we needed to synthesize a cyano complex. Then, they have found that these problems can be solved by using a metal cyano complex of a combination of specific metal ions as an ammonium ion adsorbent. The inventors have obtained knowledge about the adsorption behavior and function addition by synthesizing a metal cyano complex using various metal ions and compositions and appropriately performing an adsorption test of ammonium ions.

The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] An adsorbent that adsorbs ammonium ions by contacting it with a liquid containing ammonium ions, the main composition of which is a general formula.
Na _x M [Fe (CN) ₆ ] _y · zH ₂ O
An ammonium ion adsorbent containing the metal cyano complex represented by.
[In the formula, M represents one or more metal atoms selected from the group consisting of manganese, cobalt, nickel, and zinc, x is 1.5-2, y is 0.8-1.0, z represents a numerical value from 0 to 6. ]
[2] As a method for synthesizing the ammonium ion adsorbent according to [1], a mixed molar of an aqueous solution in which metal M ions are dissolved and an aqueous solution in which [Fe (CN) ₆ ] is dissolved is mixed. A synthetic method of mixing at a ratio of 1: 1 to 1:50.

According to the present invention, by using a metal cyano complex having a specific metal ion as an ammonium ion adsorbent, an adsorbent that adsorbs ammonium ions and has a sufficiently large ammonium ion adsorption capacity even after washing is provided. it can.

The schematic diagram which shows the typical crystal structure of a metal cyano complex. The figure which shows the mixing ratio dependence of cobalt and hexacyanoferrate ion at the time of synthesis of the ammonium ion adsorption amount of a cobalt-iron cyano complex. The figure which shows the relationship between the adsorption amount of ammonium ion of a cobalt-iron cyano complex, and the sodium ion content before adsorption.

Hereinafter, the present invention will be described in detail. Duplicate explanations will be omitted as appropriate. When "~" is described between two numerical values to represent a numerical range, these two numerical values are also included in the numerical range.
The ammonium ion in the present invention, showing the NH ₄ ^+. However, both NH ₃ and NH ₄ ⁺ are present, and their abundance ratio depends on the pH. For example, when one is adsorbed, the equilibrium may shift. Therefore, in the present invention, ammonium ions are adsorbed. As a result, the concentration of ammonia may decrease, and such an event will be included.

The metal cyano complex in the present invention is referred to as an M-iron cyano complex when its composition is represented by Na _x M [Fe (CN) ₆ ] _y · zH ₂ O and M is identified. For example, when M = cobalt, it is called a cobalt-iron cyano complex. Here, the metal atom M is preferably one or more metal atoms selected from the group consisting of manganese, cobalt, nickel, and zinc, and more preferably manganese, nickel, and cobalt.

Further, a solvent other than water and a material such as other ions as impurities which do not appear explicitly in the composition may be contained.

The crystal structure of the metal cyano complex is generally the face-centered cubic structure shown in FIG. 1, but is not necessarily limited thereto. For example, K _0.67 Zn [Fe (CN) ₆ ] _0.67 · zH ₂ O takes a hexagonal crystal. Further, the number of cyano groups coordinated with Fe is generally 6, but a part of the cyano group may be substituted with a nitro group or the like, and there is no problem as long as it is 4 to 8 or less.

Metal cyano complex adsorbs NH ₄ ⁺ to 1nm or less the size of vacant sites containing therein. At that time, it is considered that the ion exchanges with the Na cation of the composition Na _x M [Fe (CN) ₆ ] _y · zH ₂ O existing in the void site. Therefore, to increase the cation of Na in the composition, it shows a large NH ₄ ⁺ adsorption capacity of.

x is preferably 1.5 to 2, and particularly preferably 1.7 to 2. y is preferably 0.8 to 1, more preferably 0.85 to 1.0. There is no particular limitation on z, and it is sufficient if the expected ammonium ion adsorption force can be achieved. However, when x, y, and z contain a salt as an impurity or the material has water that is not incorporated into the internal structure of the metal cyano complex, the effect must be removed and evaluated.

As a desirable particle size of the metal cyano complex, in general, the adsorption rate is often faster as the specific surface area of the material is higher, and from that viewpoint, the primary average particle size is preferably 500 nm or less, more preferably 300 nm or less. , 100 nm or less is particularly preferable. The lower limit of the particle size is not particularly limited, but it is practically 4 nm or more. In the present invention, the primary particle size refers to the diameter of the primary particle, and the diameter corresponding to the circle may be derived from the half width of the peak of the powder X-ray structural analysis. Further, a ligand or the like may be adsorbed on the particle surface, but even in that case, the primary particle size refers to the particle size excluding the ligand.

The method for synthesizing the metal cyano complex (preparation method) is not particularly limited as long as the desired composition can be synthesized, but in general, an aqueous solution in which the metal M ion is dissolved and an aqueous solution in which the hexacyanoiron ion is dissolved are mixed. , The method obtained as a precipitate is used. However, even if the raw materials are mixed according to the ratio of the desired composition, the desired composition and the amount of ammonium ion adsorbed may not always be obtained. In this case, the amount of ammonium ions adsorbed can be increased by increasing the mixed molar ratio of hexacyanoiron ions to the metal M (hereinafter referred to as Fe / M ratio). In this case, paying particular attention to y, the composition y of the adsorbent is 1 or less, but the Fe / M ratio is preferably 1 or more at the time of synthesis. There is no scientific limit to the upper limit of the Fe / M ratio, but increasing it becomes a cost factor, and it is not realistic to increase it infinitely. From the viewpoint of practical use, the Fe / M ratio is preferably 1: 1 to 1:50. What is important here is that the amount of alkaline ions in the adsorbent used for ion exchange with ammonium ions is not directly linked to the amount of ammonium ions adsorbed as it is. The basic adsorption mechanism is this ion exchange, but not all alkaline ions contribute to ion exchange. Therefore, it is necessary to control the composition, improve the content of alkaline ions, and contain alkaline ions in the adsorbent, which are easier to exchange ions. According to the present invention, the composition cannot be largely controlled by setting the Fe / M ratio to 1 or more, but the amount of ammonium ions adsorbed can be improved. It is not clear why the amount of ammonium adsorbed increases without a large change in composition, but it is because the ratio of sodium ions that are easily desorbed increases by synthesizing with a larger amount of sodium ions contained in the raw material. I'm guessing.

As long as the above mixing ratio can be realized, the mixing method is not particularly limited, but a method capable of uniformly realizing the desired composition is preferable. Further, the surface of the complex may be modified with various materials for the convenience of processing. As a specific method, for example, the methods described in JP-A-2006-256954 and JP-A-2013-173077 can be used.

Further, for various reasons, even if it is compounded with other materials, there is no problem as long as it contains a metal cyano complex and functions as an ammonium ion adsorbent. For example, it may be supported in a fibrous form or mixed with a binder such as a polymer to form granules. Further, in order to efficiently exhibit the catalytic effect, it may be combined with an oxidizing agent, a reducing agent, a conductive material or the like.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not construed as being limited thereto.

(Preparation Example 1)
<Preparation of cobalt-iron cyano complex>
A cobalt-iron cyano complex (Na _x Co [Fe (CN) ₆ ] _y ) was prepared as follows. 4.78 g of cobalt chloride hexahydrate was dissolved in pure water to a concentration of 50 mL to prepare an aqueous solution containing 0.40 mol / L of cobalt ions. Further, 19.36 g of sodium ferrocyanide decahydrate was dissolved in pure water to a concentration of 100 mL to prepare an aqueous solution containing 0.40 mol / L of ferrocyanide ions. 15 mL of each solution was taken out, introduced into a centrifuge tube, and stirred quickly. The centrifuge tube containing the mixed solution was shaken with a constant temperature shaker at a shaking speed of 25 ° C. and 1700 rpm for 3 minutes.

30 mL of the obtained liquid was centrifuged at 2000 rcf for 5 minutes to obtain a green solid. Then, 10 mL of MilliQ water and the solid were mixed, and the mixture was shaken again at a shaking speed of 25 ° C. and 1700 rpm for 3 minutes, and the washing operation was performed 6 times by centrifuging at 5000 rcf for 5 minutes. The obtained solid was vacuum dried to obtain a green powder P1 as an adsorbent after the washing operation.
The composition of the powder P1 was evaluated by the following method. After adding 50 mg of powder P1 to 4 mL of hydrochloric acid and 2 mL of nitric acid and performing microwave decomposition with a microwave decomposition device (PerkinElmer, Multiwave3000), Na, with MP-AES (Agilent Technologies, MP-AES-4100), Co and Fe were quantified. H ₂ O was quantified by thermogravimetric analysis. As a result, the composition of P1 was determined to be Na _1.42 Co [Fe (CN) ₆ ] _0.86・ 2.64H ₂ O.

(Preparation Example 2)
<Preparation of cobalt-iron cyano complex with different composition ratio>
In the same production method as in Preparation Example 1, the cobalt chloride aqueous solution and the sodium ferrocyanide concentration were changed as shown in Table 1 to obtain cobalt-iron cyano complex powders P2 to P4 as an adsorbent after the washing operation. The results of each composition analysis are also shown in Table 1. If the material is obtained according to the raw material ratio at the time of synthesis, the Fe / Co ratio and y are values that match. However, as shown in Table 1, the Fe / Co ratio and y do not always match. Further, it can be seen that y does not exceed 1 even if the Fe / Co ratio> 1.

(Preparation Example 3)
<Preparation of metal-iron cyano complex with different metal ions>
The metal-cyano complex was synthesized as follows.
A metal-iron cyano complex (Na _x M [Fe (CN) ₆ ] _y ) was prepared as follows. Manganese chloride tetrahydrate, nickel chloride hexahydrate, zinc chloride, copper chloride dihydrate, and iron chloride tetrahydrate are adjusted with pure water so that the metal ion becomes an aqueous solution of 0.40 mol / L. did. Moreover, the sodium ferrocyanide decahydrate was adjusted with pure water so that the ferrocyanide ion became an aqueous solution of 0.40 mol / L. These solutions were mixed and the resulting precipitate was separated by centrifugation. The obtained precipitate was washed with MilliQ water 6 times and then vacuum dried to obtain green powders P6 to P10 as adsorbents after the washing operation.

(Example 1)
<Adsorption of ammonium ion of cobalt-iron cyano complex from aqueous ammonia>
About 100 mg / L ammonium chloride aqueous solution L1 was prepared as a solution for adsorption test. After immersing 140 mg of P in 40 mL of L1 and shaking, solid-liquid separation was performed, and then the amount of ammonium ions remaining in the liquid was examined. SI-300C (manufactured by AS ONE) was used as a shaker, and the shaking speed was 600 rpm, the temperature was 25 ° C., and the shaking time was 3 hours. Centrifugation was used for solid-liquid separation, and the mixture was separated at 16,000 rcf for 10 minutes, and the obtained supernatant was filtered through a 0.45 μm syringe filter.
To quantify ammonium ions in the filtered supernatant, the mixture was diluted with MilliQ water so that it was within the measurement range, and then analyzed by ion chromatography (Metrohm, 883 Basic IC plus). The amount of ammonium ions adsorbed on the solid was calculated from the difference between the ammonium ion concentration in the obtained liquid and the ammonium ion concentration prepared before the adsorption test. As a result, it was found that after the adsorption test, ammonium ions were transferred to P1, and P1 adsorbed ammonium ions at 68.9 mg / g (3.83 mol / kg).

(Example 2)
<Adsorption of ammonium ions from an aqueous ammonia solution of a cobalt-iron cyano complex with a different composition ratio>
Perform the same operation method as in Example 1 for the samples P2 to P5. The amount of adsorption was evaluated. The results are shown in FIG. The amount of adsorption increased as the Fe / Co ratio approached from 0.5 to 1. Furthermore, the relationship between the amount of sodium ions in the composition and the amount of ammonium ions adsorbed is shown in FIG. From this, when the Fe / Co ratio is 1, the amount of ammonium ions adsorbed is smaller than the amount of sodium ions contained, but by further increasing the Fe / Co ratio, a higher amount of ammonium ion adsorption can be achieved. Understand. Even if the Fe / Co ratio> 1, y does not exceed 1, and the sodium content required for ion exchange is not significantly different, but the adsorption amount is increasing.
In conclusion, when Fe / Co ratio> 1, the amount of sodium ions contained in the adsorbent did not change much, but showed a higher adsorption capacity. From this, it was found that setting the Fe / Co ratio at the time of mixing to 1 or more is effective in increasing the amount of ammonium ion adsorbed.

(Example 3)
<Adsorption of ammonium ions from aqueous ammonia solution of metal-iron cyano complex with different metal ion species>
Perform the same operation method as in Example 1 for the samples P6 to P10. The amount of adsorption was evaluated. The results are shown in Table 2. It was found that the amount of adsorption differs depending on the type of metal, and it was found that Mn>Co>Ni>Zn>Cu> Fe. In particular, the low amount of ammonium ions adsorbed by Cu is due to the fact that metal ions or ferrocyanide ions are eluted during the washing operation and the composition becomes stable, as reported in Non-Patent Document 4, resulting in ion exchange. It is thought that this is because the amount of sodium ions produced decreases.

According to the present invention, an ammonium ion adsorbent having various functions can be used by selecting an appropriate material. It can be used for ammonium ion storage materials, ammonium ion sensors, ammonium ion removal filters, ammonium ion recovery devices, etc., and can be used for energy storage, environmental purification, waste liquid, exhaust treatment, etc.

Claims (2)

An adsorbent that adsorbs ammonium ions by contacting it with a liquid containing ammonium ions, the main composition of which is the general formula.
Na _x M [Fe (CN) ₆ ] _y · zH ₂ O
An ammonium ion adsorbent containing the metal cyano complex represented by.
[In the formula, M represents one or more metal atoms selected from the group consisting of manganese, cobalt, nickel, and zinc, x is 1.5 to 2, y is 0.8 to 1.0, z represents a numerical value from 0 to 6. ] As a method for synthesizing an ammonium ion adsorbent according to claim 1, an aqueous solution in which metal M ions are dissolved and an aqueous solution in which [Fe (CN) ₆ ] is dissolved are mixed in a molar ratio of 1: 1. A synthetic method of mixing at a ratio of 1 to 1:50.

Images