JPH08281099A - Adsorbent for organic chlorine compound - Google Patents

Abstract

PURPOSE: To obtain an adsorbent for removing an org. chlorine compd. in an aq. soln. CONSTITUTION: This adsorbent is a carbon compd. having <=0.1meq/g acidic functional group existing on the surface. Since the amt. of acidic functional groups is reduced and pore distribution is made optimum, adsorption sites of a large specific surface area peculiar to activated carbon are effectively utilized and the diffusion of an org. chlorine compd. in pores in water can be improved. As a result, the useful life of this adsorbent at the time of adsorbing and removing an org. chlorine compd. in water can be considerably prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an adsorbent for removing organic chlorine compounds in an aqueous solution. Specifically, it is an adsorbent for removing compounds collectively called trihalomethane.

[0002]

2. Description of the Related Art Organic chlorine compounds in water are not only odorous,
Due to the problem of carcinogenicity, its removal has been strongly desired, and the development of a high-performance adsorbent has been urgently needed. Conventionally, activated carbon has been used to remove organic chlorine compounds in water. Attempts to increase the adsorption performance by increasing the specific surface area and using activated carbon with a fibrous shape in order to improve the removal performance of organochlorine compounds and thereby increasing the probability of contact between the organochlorine compound and the adsorbent. Has been done. However, as disclosed in JP-A-6-100310, the conventional production method has a problem that the removal performance of an organochlorine compound typified by trihalomethane deteriorates at 1500 m ² / g or more, so that the specific surface area is simply changed. Increasing it did not solve the problem. Further, an attempt to utilize activated carbon having a fibrous shape is disclosed in Japanese Patent Laid-Open No. 10616/1994.
As shown in 2, there is an essential problem in that the packing density cannot be increased. That is, in the above conventional method, when the content of the organochlorine compound is low as in drinking water (1 p
At pm or less), water molecules present in a large excess occupy the pores, the adsorption of the organochlorine compound reaches saturation early, and the adsorptivity decreases early, which is the essential adsorption performance for the organochlorine compound, In particular, the improvement in performance of withstanding long-term use has not been achieved.

[0003]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned problems of the prior art, that is, when removing an organic chlorine compound from an aqueous solution containing the organic chlorine compound, it is necessary to remove water from a large amount of water. Another object of the present invention is to provide an adsorbent which makes it easier to adsorb an organic chlorine-based compound and has a longer life than the conventional adsorbents.

[0004]

The present invention relates to an adsorbent characterized in that the amount of acidic functional groups present on the surface is a porous carbon material in the range of 0.1 meq or less per 1 g of the adsorbent. is there.

The present invention also relates to E. FIG. T. Specific surface area is 1
The adsorbent is characterized in that the volume of pores having a diameter of 10 to 20Å is 500 m ² / g or more and 0.3 cc or more per 1 g of the adsorbent. The present invention also has a diameter of 10-20.
The adsorbent is characterized in that the volume of the pores of 14 to 20 Å occupies 70% or more of the volume of the pores of Å. The porous carbon material in the present invention, coconut shell and sawdust, natural organic matter such as wood, synthetic organic matter such as various synthetic resins and synthetic fibers, or coal, coal-based pitch,
It is a carbonaceous substance obtained by further subjecting activated carbon made from petroleum pitch or the like as a raw material to an appropriate treatment described later. Coconut shell activated carbon is a preferred raw material from which high specific surface area activated carbon suitable for the present invention can be produced.

The organic chlorine compounds in the present invention include chloroform, bromodichloromethane, dibromochloromethane, tribromomethane, etc., which are usually called trihalomethanes. Further, a halogen compound having 2 carbon atoms, which is represented by dichloroethane, trichloroethane, trichloroethylene, etc., is also included.

In the adsorbent for organic chlorine compounds, 2
We have to solve one problem. 1: The physical properties of carbon, which is the material of the adsorbent, are optimized and have a selective adsorption property for the organochlorine compound, 2: The pore structure is optimal for the adsorption of the organochlorine compound, that is, It was thought that the above two points are important, having an optimal pore distribution, and having a structure in which an organochlorine compound easily diffuses to an adsorption site and is difficult to desorb, and as a result of intensive studies, the present invention has been accomplished.

First, the first problem was solved by the following means. The amount of all surface acidic functional groups per 1 g of the adsorbent determined by the method of Boehm et al. Is 0.1 meq or less, and more preferably 0.05 meq or less. When the total amount of acidic functional groups on the surface is more than 0.1 meq, the hydrophilicity of the activated carbon surface increases, and the cluster formed by water molecules by adsorption in the aqueous solution stays in a state of blocking the entrance of the pore. In such a state, the molecules of the low molecular weight organochlorine compound such as chloroform are prevented from diffusing and reaching the surface of the fine pores serving as the adsorption site, and the adsorption ability of the organochlorine compound is reduced. On the contrary, if the total surface acidic functional group is an adsorbent having the amount in the above range, the diffusion of the molecules of the organochlorine compound is not hindered, and at the same time, the hydrophilic group is formed on the surface of the fine pores serving as adsorption sites. Since there is almost no, the molecules of the hydrophobic organochlorine compound can be selectively adsorbed.

Heating in a nitrogen atmosphere is the best method for reducing the amount of surface acidic functional groups. However, it is difficult to obtain sufficient effects as in the present invention by simply heating in an atmosphere in which nitrogen gas is replaced. A method is effective in which nitrogen gas is circulated during the heating time so as to have an effect as a carrier gas, and the gas generated by the decomposition of the acidic functional group is removed. The flow rate of nitrogen gas is
It is preferably 1 N liter / min or more for 5 kg of the adsorbent to be treated. In addition, it is important to control the impurity gas concentration during heating and circulation, and the content of oxygen and water vapor becomes a problem. Oxygen concentration is 0.5ppm or less, water vapor concentration is 1
It is necessary to heat in a nitrogen gas atmosphere of ppm or less. The heating temperature is preferably 400 to 1200 ° C.
The same effect can be obtained in the above heat treatment by using an inert gas other than nitrogen, such as argon gas, as the atmosphere gas. A method is also effective in which the temperature of the inert gas is raised to a predetermined temperature and then the flow of the gas is stopped and the heating is performed under vacuum. In this case, it is desirable to continue to maintain the vacuum degree of 0.1 mmHg or less.

Here, the total amount of acidic functional groups on the surface is Boehm.
Report (Angew. Chem., Intern.Ed. Engl., 5, 533
(1966)). They are shown as the equivalent of alkali consumed after adding activated carbon to an alkaline solution and shaking. The amount of alkali consumed is determined by acid titration. Specifically, 0.5 g of the adsorbent in a dry state is immersed in 60 ml of a 0.02 mol / l sodium hydroxide aqueous solution, shaken for 4 hours, and then 25 ml of the solution is sampled to obtain 0.02 mol / l hydrochloric acid. The amount of total acidic functional groups was determined from the amount of alkali consumed.

The second problem is solved by the following means. Diameter of 1 for adsorption of organochlorine compounds
As a result of examination, it was revealed that micropores in the range of 0 to 20Å are effective. When molecules are adsorbed on the surface of the porous adsorbent, the interaction potential between the molecules and the surface of the adsorbent becomes larger as the pores become smaller, and the molecules are strongly adsorbed on the surface of the pores. Chloroform, which is a typical molecule of an organochlorine compound, has a molecular diameter of about 4.7Å
Is. The strong interaction potential works on the chloroform molecule from the pore wall of the adsorbent up to a distance of at most two molecules. Therefore, it is estimated that pores up to about 4 times the diameter of the chloroform molecule up to about 20 Å, that is, pores in a range generally called micropores, are effective for adsorbing chloroform.

Among the micropores in the above range, the diameter 14
It has been conventionally considered that very small pores of Å or less have a particularly large interaction potential between the surface of the pores and the adsorbed molecules and are particularly effective for adsorption. However, in such a small pore, there arises a problem that the diffusion rate of molecules becomes extremely slow. This phenomenon is unlikely to appear as a problem in the measurement of the equilibrium adsorption amount (a measurement method in which adsorption is performed in a closed system until complete equilibrium) is performed in the laboratory as a performance evaluation of the adsorbent, but the aqueous solution is passed through the adsorbent layer. As a result of the investigation, it became clear that it is a particularly serious problem when it is used in the adsorption type, that is, the adsorption type which is industrially common.

When the total amount of acidic functional groups on the surface is controlled to improve the affinity as in the present invention, pores having a diameter of 14Å or more are suitable in terms of diffusion rate. In the usage type with large influence of diffusion rate (adsorption by liquid passage method), the pore distribution of the adsorbent is such that the pore volume in the diameter range of 14 to 20Å is 70% or more of the pore volume in the diameter range of 10 to 20Å. And more preferably 75% or more. As described above, by solving the above-mentioned two problems by controlling the chemical and physical structures, the adsorbent which has been considered insufficient until now can be effectively used despite the high specific surface area of 1500 m ² / g or more. I was able to utilize it.

In the present invention, activated carbon having a high specific activation and a specific surface area and a fine pore volume as shown below can be used particularly effectively. B. which is a general parameter of activation degree. E. FIG. T. The specific surface area is 1500 m ² / g or more is preferable, and more preferably in the range of 1600~2000m ² / g. The pore volume is 0.
3cc / g or more is desirable, and more desirably 0.35
It is cc / g or more. B. E. FIG. T. Specific surface area is 2000
If it is larger than m ² / g, the strength of the adsorbent becomes weak,
It is not preferable because it becomes fine powder when the aqueous solution is poured.

Pore distribution of the adsorbent in the present invention and B. E. FIG. T. The specific surface area was measured by the adsorption isotherm of nitrogen gas at the liquid nitrogen temperature, the Cranston-Inkley method, and B. E. FIG. T. Calculated by the method. Specifically, it was measured by using Carlo Erba Co., Sorptomatic, SSII-80, and then the adsorption isotherm was converted to a pore distribution curve from the relationship between pore diameter and critical relative pressure based on the Inkley method. . BET specific surface area is saturated vapor pressure Po and equilibrium pressure P
, And P / Po was calculated by using the adsorption amount data in the range of 0.05 to 0.3. The method of determining the pore distribution and BET specific surface area by the Inkley method is described in detail in Keicho Tomicho, "Adsorption", Kyoritsu Shuppan, 1965.

The adsorbent of the present invention may be in the form of powder, granules, fibers or the like, but as described above, in terms of packing density, granules or powdered products are processed. It can be used effectively. Among them, granular materials are the most excellent and effective in terms of handling. The particle size is 50
It is desirable to be between ~ 300 microns. Diameter is 3
When it is larger than 00 microns, the outer surface area of the particles becomes small, and when the flow rate of the aqueous solution is high, the diffusion of the organochlorine compound becomes insufficient and the adsorption amount decreases. If the diameter is smaller than 50 microns, the pressure loss when the aqueous solution is circulated becomes extremely high, which is not desirable.

Heating in a nitrogen atmosphere is the best way to reduce the amount of surface acidic functional groups. However, it is difficult to obtain sufficient effects as in the present invention by simply heating in an atmosphere in which nitrogen gas is replaced. A method is effective in which nitrogen gas is circulated during the heating time so as to have an effect as a carrier gas, and the gas generated by the decomposition of the acidic functional group is removed. The flow rate of nitrogen gas is
It is preferably 1 N liter / min or more for 5 kg of the adsorbent to be treated. In addition, it is important to control the impurity gas concentration during heating and circulation, and the content of oxygen and water vapor becomes a problem. Oxygen concentration is 0.5ppm or less, water vapor concentration is 1
It is necessary to heat in a nitrogen gas atmosphere of ppm or less. The heating temperature is preferably 400 to 1200 ° C.

In the above heat treatment, the same effect can be obtained even when an inert gas other than nitrogen, such as argon gas, is used as the atmosphere gas. A method is also effective in which the temperature of the inert gas is raised to a predetermined temperature and then the flow of the gas is stopped and the heating is performed under vacuum. In this case, it is desirable to continue to maintain the vacuum degree of 0.1 mmHg or less.

[0019]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 Commercially available coconut husk-based granular activated carbon (Kitamura Chemical = SZP-W)
1.5 kg that were pulverized and sieved in the range of 180 to 355 microns were previously dried at 120 ° C. for 5 hours (this is referred to as Comparative Example 1), and 1 kg of this was dried under a nitrogen atmosphere (oxygen concentration: 0. 3 ppm or less, water vapor concentration of 0.
2ppm or less, nitrogen flow rate 2Nl / min),
The adsorbent of Example 1 was obtained by raising the temperature to 1000 ° C. in 2 hours, holding it at 1000 ° C. for 5 hours, and then allowing it to cool to room temperature in the same atmosphere.

Example 2 Commercially available coconut husk-based granular activated carbon (Takeda Yakuhin = LGK-498, which was crushed, sieved and dried in the same manner as in Comparative Example 1)
(Comparative Example 2) 1 kg, in a nitrogen atmosphere (oxygen concentration 0.3ppm or less, water vapor concentration 0.2ppm or less, nitrogen flow rate 2Nl / min), 1000 ℃ for 2 hours
After heating up to 1000 ° C. for 5 hours and then allowing to cool to room temperature in the same atmosphere, an adsorbent of Example 2 was obtained.

Example 3 Using char, which is a charcoal of coconut shell, as a raw material, impurities metals and the like were sufficiently removed by washing, and then the temperature was raised to 750 ° C. for 1 hour in a nitrogen atmosphere, and then the water vapor concentration was 15 in a nitrogen atmosphere. %
Activated gas was flowed, and activation was carried out for 50 hours while maintaining the temperature at 750 ° C. to obtain activated carbon. Furthermore, in a nitrogen atmosphere (oxygen content 0.3 ppm or less, water vapor concentration 0.2 ppm or less,
800 for 2 hours at a nitrogen flow rate of 2 Nl / min)
The adsorbent of Example 3 was obtained by heating to 800 ° C., holding at 800 ° C. for 5 hours, and then allowing to cool to room temperature in the same atmosphere.

Comparative Example 3 Commercially available coconut husk-based granular activated carbon (Takeda Yakuhin = granular Shirasagi WH
2C) was crushed and sieved in the range of 180 to 355 micron, dried at 120 ° C. for 5 hours, and then used for measurement.

Example 4 Commercially available granular activated carbon (Kuraray Chemical = Kuraray Coal GW) pulverized, sieved and dried in the same manner as in Comparative Example 1.
In a nitrogen atmosphere (oxygen concentration 0.3 ppm or less, water vapor concentration 0.2 ppm or less, nitrogen flow rate 2 N liter / min), the temperature was raised to 1000 ° C. in 2 hours, and then 1000
After being kept at 0 ° C. for 5 hours, the adsorbent of Example 4 was obtained by allowing to cool to room temperature in the same atmosphere.

The removal performance of the organic chlorine-based compounds of the adsorbents obtained in Examples 1 to 3 and the granular activated carbons of Comparative Examples 1 to 4 was compared as follows using chloroform as a typical example of the organic chlorine-based compound. did. That is, each of the adsorbents of Examples 1 to 3 or 1 g of granular activated carbon of Comparative Examples 1 to 4 was packed in a glass column having an inner diameter of 10 mm, and a chloroform aqueous solution adjusted to a concentration of 40 ppb and a temperature of 20 ° C. was supplied at a flow rate of 150 m 3 / min. The solution was passed through the column. The chloroform concentration of the aqueous solution after passing the solution was measured by a gas chromatography mass spectrometer equipped with a purge & trap to determine the removal rate.

Table 1 shows the physical properties of the obtained adsorbents of Examples 1 to 3 and the granular activated carbons of Comparative Examples 1 to 4 and the performance of removing chloroform. Here, the chloroform removal performance is defined as the cumulative flow rate of the chloroform aqueous solution that has passed through the adsorbent until the above chloroform removal rate drops to 50%.
It is represented by the number of liters per 1 g of the adsorbent.

[0026]

[Table 1]

[0027]

INDUSTRIAL APPLICABILITY As described above, the adsorbent of the present invention reduces the amount of acidic functional groups and at the same time optimizes the pore distribution, thereby effectively utilizing the adsorption site of activated carbon having a high specific surface area. It was possible to improve the diffusion of organochlorine compounds in water into the pores. As a result, it has become possible to significantly improve the life in the adsorption removal of organic chlorine compounds in water.

Claims (3)

[Claims] 1. An adsorbent for an organochlorine compound, which is a porous carbon material in which the amount of acidic functional groups present on the surface is within a range of 0.1 meq or less per 1 g of the adsorbent. 2. B. E. FIG. T. Adsorbent 1 has a specific surface area of 1500 m ² / g or more and a volume of pores having a diameter of 10 to 20 Å
The adsorbent according to claim 1, wherein the adsorbent is 0.3 cc or more per g. 3. The adsorbent according to claim 2, wherein the volume of the pores having a diameter of 10 to 20Å occupies 70% or more of the volume of the pores having a diameter of 10 to 20Å.