JPS59243B2 - Method for treating formaldehyde-containing gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Formaldehyde is known as a compound useful in resin compositions such as melamine, fiber processing agents, preservatives, and the like.

Formaldehyde is a harmful gas with a unique irritating odor, and the odor can be felt even at extremely dilute concentrations such as 0.25 ppm, and it strongly irritates the throat even at concentrations as low as 5 ppm.

In working environments where formaldehyde gas is normally generated, such as factories manufacturing formaldehyde or its derivatives or plywood factories using urea resin, formaldehyde gas is present in the air at a concentration of 10 to 1009%, and formaldehyde-containing gas There is a strong demand for processing equipment.

Traditionally, this type of formaldehyde-containing gas has been treated by washing it with aqueous ammonia and treating it as hexamethylenetetramine, or by heating it at 200 to 300°C on a catalyst made of a platinum metal compound supported on alumina or the like.
Methods have been proposed to render it harmless through catalytic oxidation at a temperature of .

However, the former wet method generally poses difficulties in wastewater treatment, and the latter catalytic oxidation method requires expensive catalysts and the need to heat dilute formaldehyde-containing gas to the temperature at which catalytic oxidation occurs. There was, and the cost of abatement was also high.

In view of these circumstances, the present inventors have made extensive studies and found that formaldehyde in gas can be effectively decomposed by using activated carbon with a pH of 7 or less, and based on this new knowledge, the present invention has been developed. It was completed.

That is, the present invention provides (1) acid-treated activated carbon with a pH of 7 or less (3 g of it mixed with 1 1 of distilled water).
001rLl, heated to 90°C, cooled to 20°C, and electrically measured the pH of this suspension.
is 7 or less.

) of formaldehyde-containing gas in the presence of oxygen.
A method for treating a formaldehyde-containing gas, comprising contacting at a temperature of ~200°C.

(2) Acid-treated activated carbon with a pH of 7 or less that supports iron, cobalt, vanadium, copper, nickel, or manganese (3 g of it is suspended in 100 mA' of hot tube water, heated to 90°C, cooled to 20°C, and this suspension is A liquid whose pH is 7 or less when measured electrically.

) to formaldehyde-containing gas in the presence of oxygen.
This is a method for treating formaldehyde-containing gas, which is characterized by contacting at a temperature of ~200°C.

The activated carbon with a pH of 7 or less used in the present invention refers to activated carbon produced by, for example, treating ordinary activated carbon with an acid, followed by heat treatment in an inert gas stream, and its acidity (pH) is determined as described later. measured.

The activated carbon used may be a moderately activated activated carbon with a BET surface area of about 500 to 1500 m.

The acid treatment is carried out with an aqueous solution of an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or an organic acid such as trichloroacetic acid or succinic acid at any concentration, for example 0.1 to 10 weight ratio.

After immersing the activated carbon in an acid aqueous solution or sprinkling the acid aqueous solution on the activated carbon, the activated carbon is soaked in an inert gas such as nitrogen or helium for about 30 minutes at a temperature of about 100 to 500°C.
Heat treat for 5 hours.

These operations produce stable activated carbon with a pH of 7 or less, preferably a pH of 5 or less.

Here, the pH of activated carbon means the pH when activated carbon is suspended in distilled water.

As a general measurement method, for example, distilled water (pH 7,
0) A method is to suspend 3 g of activated carbon in 100 g, heat it to 90°C, cool it to 20°C, and electrically measure the pH of this suspension.

(1474 in Japanese Industrial Standards) Activated carbon produced in this way is
It exhibits excellent performance in decomposing formalin at relatively low temperatures, but the effect of the present invention cannot be obtained at a pH of 7 or higher.

This decomposition performance can be further improved by adding transition metal elements.

Specifically, for example, V, Mn. Fe, Co, Ni, C
u or their compounds (e.g. ammonium vanadate, manganese nitrate, ferric sulfate, cobalt sulfate, nickel sulfate, copper nitrate) are added to the aforementioned acid aqueous solution and impregnated on activated carbon, or activated carbon is added in the activated carbon manufacturing process. These elements or compounds may be supported by any method such as adding them to raw materials.

The thus produced activated carbon having a pH of 7 or less is brought into contact with a formaldehyde-containing gas in the presence of oxygen.

Here, the formaldehyde content in the formaldehyde-containing gas may be at any concentration, but in particular about ip
pm to 10,000p is preferred.

Specific means for bringing a formaldehyde-containing gas into contact with activated carbon having a pH of 7 or less include (1) If the formaldehyde-containing gas is already in the coexistence of oxygen, it may be directly heated and passed through an activated carbon layer having a pH of 7 or less; Or a means of passing it through a heated activated carbon layer with a pH of 7 or less, (2) p
Formaldehyde-containing gas and approx. 1
(3) Formaldehyde in the formaldehyde-containing gas is adsorbed on activated carbon in advance, and formaldehyde is passed through the air or oxygen-containing gas preheated to the above temperature. Examples include means for passing a desorption gas containing formaldehyde through an activated carbon layer having a pH of 7 or less while desorbing the activated carbon and regenerating the activated carbon.

When a formaldehyde-containing gas is brought into contact with activated carbon by the method described in (2) above, the ratio of formaldehyde-containing gas to air or oxygen-containing gas may be as long as the amount of oxygen is at least the amount theoretically required for complete oxidation of formaldehyde, and the activated carbon layer The space velocity at is preferably 5,000 to 40,0OOH-1.

In addition, when contacting by means of (3) above, the space velocity of air or oxygen-containing gas is usually 1,000 to 20
,0OOH-l.

A gas flow time of about 0.5 to 2 hours is sufficient.

Generally, when the contact temperature is below 100°C, the oxidation activity of the activated carbon is insufficient, formaldehyde may be detected in the exhaust gas, and in some cases, formic acid may be generated. preferable.

As the activated carbon for formaldehyde adsorption used in the method (3) above, regardless of its raw material or manufacturing method, BE
Activated carbon with developed micropores and a surface area of about 700 to 2,000 7g is mentioned.

In particular, activated carbon having a pH of 7 or less is preferable because it has excellent formaldehyde adsorption performance at room temperature.

For example, the normal BET surface area is 1.000 rt? / g
Formaldehyde ioppm of activated carbon activated to a certain degree
The equilibrium adsorption amount of formaldehyde in air containing air at 20°C is said to be about Oo1 weight factor, but the equilibrium adsorption amount of coconut shell activated carbon at pH 4.5 activated to the same extent under the same conditions is 0.5 weight. It was found that the amount increased to a certain degree.

The temperature at which formaldehyde is adsorbed onto activated carbon is preferably as low as possible, particularly preferably about 0 to 60°C.

The formaldehyde thus adsorbed on the activated carbon may be removed by passing an oxygen-containing gas or air through it, and then treated according to the method (1) below.

Since this means can concentrate formaldehyde in the gas through the first adsorption/desorption step, it is particularly preferred when treating dilute formaldehyde-containing gas.

According to the method of the present invention, the unit price is low because no expensive white metal compounds are used, and the space velocity can be increased, so the amount of activated carbon used can be reduced. ■ Since it is a dry process, wastewater treatment ■Meaning (3) above has the advantage that fuel consumption can be extremely reduced because only a small amount of heat needs to be supplied intermittently during the decomposition process, and it is extremely efficient compared to conventional treatment methods. Economical.

EXAMPLES The present invention will be specifically explained below with reference to Examples and Comparative Examples.

Example I BET surface area 1.000 rrl/,! 9. Particle size 4~
A glass cylinder was filled with 6 mesh coconut shell activated carbon (pH-6) at a temperature of 20°C and a space velocity of 10.0OOH-1.
Formaldehyde was adsorbed onto the activated carbon by passing 10 to 15 pins of formaldehyde-containing air under these conditions.

After about 20 hours, formaldehyde was detected in the exhaust gas from the activated carbon packed bed.

At this point, the flow of formaldehyde-containing air was stopped, and the outlet of the adsorption tower was connected to the inlet of a separately prepared activated carbon layer with a pH of 7 or less, and air preheated to 150° C. was flowed at the same space velocity.

Both the adsorption layer and the activated carbon layer with a pH of 7 or less are immediately
No formaldehyde was detected in the exhaust gas from the activated carbon layer, which reached a temperature of 0° C. or higher and a pH of 7 or lower.

It was confirmed that the formaldehyde decomposition process using heated air was completed in about 40 minutes from analysis of formaldehyde in the gas at the outlet of the adsorption tower.

It was also confirmed that the performance of each process did not change by repeating this operation.

The activated carbon used in the decomposition step of this example was made by immersing activated carbon made of coal raw material with a BET surface area of 700 x 7 g and a particle size of 4 to 6 mesh in a 5 weight part nitric acid aqueous solution for 10 hours, then draining the liquid and placing it in a nitrogen stream. It was produced by heat treatment at a temperature of 170° C. for about 1 hour, and its pH was 4.3.

Example 2 BET surface area 1. o o o Coconut shell activated carbon with a particle size of 7 g and a particle size of 4 to 8 mesh was sprayed with a sulfuric acid aqueous solution of 10 parts by weight containing ferric sulfate, pre-dried at 110°C, and heat-treated at a temperature of 300°C for about 1 hour. Activated carbon for decomposition process was produced.

The activated carbon was filled and the same operation as in Example 1 was repeated, but it was confirmed that formaldehyde in the desorbed gas was decomposed and rendered harmless at the temperature of the activated carbon layer of 110°C.

Analysis of the activated carbon revealed that its pH was 5.5 and the amount of iron supported was 1.0% by weight as Fe.

Example 3 and Comparative Examples BET surface area 1.000 m/g, pH 7, 4,
Coconut shell activated carbon with a particle size of 4 to 6 mesh and 1 to 6 mesh of this
A formaldehyde decomposition performance test was conducted under the following conditions for activated carbons of pH 2.7 and pH 6.2 produced by immersing them in a 10% weight acid aqueous solution and subjecting them to the above-described treatment.

Test conditions Gas composition: Relative humidity 50 parts containing formaldehyde 50 fermentation Air space velocity: 20,000 H-1 Reaction area temperature: 110°C, 130°C, 150°C The results of the performance test are as shown in the following table. Ta.

Example 4 A transition metal was added to activated carbon made of coal raw material with a BET surface area of 700 x 7 g and a particle size of 4 to 6 mesh by the method described above,
The following activated carbons A to E having a pH of 7 or less were produced.

Details regarding the production of the activated carbon and the results of the same performance test as in Example 3 are shown in the following table.

Claims (1)

[Claims] Acid-treated activated carbon with a pH of 7 or less (3 g of it dissolved in 100 ml of distilled water)
When suspended in WLl, heated to 90°C, cooled to 20°C, and electrically measured the pH of this suspension, the pH was 7.
Refers to the following. ) to formaldehyde-containing gas in the presence of oxygen.
A method for treating a formaldehyde-containing gas, comprising contacting at a temperature of ~200°C. 2 Acid-treated activated carbon of 17 or less carrying iron, cobalt, vanadium, copper, nickel or manganese (part 31!
9 in 100 g of distilled water, heated to 90°C, and then heated to 20°C.
When the pH of this suspension was measured electrically after cooling to
The pH is 7 or less. ) to formaldehyde-containing gas in the presence of oxygen.
A method for treating a formaldehyde-containing gas, comprising contacting at a temperature of ~200°C.