JPS5850971B2 - Formaldehyde separation and purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and purifying formaldehyde from a formaldehyde mixture containing water, methanol, etc., and particularly to a purification method characterized by the adsorbent used at that time.

Formaldehyde is one of the substances that plays a major role in the chemical industry.

Industrial methods for producing formaldehyde include an excess air method and an excess methanol method. (1) Both methods use methanol as a main raw material and produce products containing formaldehyde, water, and methanol as main components.

The composition of the above three components in the product is determined by the manufacturing method.
Formaldehyde concentration 20% to 70%, water concentration 20%
A mixture having a composition with a methanol concentration of 1 to 20% and a methanol concentration of 1 to 20% is called formalin and is commercially available.

On the other hand, with the development of industries that require highly purified formaldehyde as a raw material for chemical industries, for example, industries that produce polymers called polyacetals by polymerizing formaldehyde as a monomer, the need for high-purity formaldehyde has increased.

For this reason, separation techniques for formaldehyde have been studied in recent years, and separation and purification methods using precision distillation, extraction, hemi-secure, freezing, and combinations thereof have been devised.

However, in either method, many difficulties remain in separating and purifying formaldehyde in a highly efficient manner.

The first reason is that formaldehyde and water form a complex and there is an equilibrium relationship, the second is that formaldehyde is chemically very unstable and easily decomposes and polymerizes, and the third is that it is highly purified. Industries that require formaldehyde, such as the polyacetic industry, require a stable and continuous supply of formaldehyde that is as pure as possible and has a certain purity.

For example, in order to obtain higher purity formaldehyde from a mixture of equal amounts of formaldehyde and water, firstly, formaldehyde and water are separated to some extent by means such as distillation, then an alcohol compound and a hemiacetal adduct are created, and this adduct is separated and separated. A method has been adopted in which the purity of the formrdehyde generated by decomposition is further improved by using a method such as a freezing method.

Such means have poor efficiency in each step and result in a large loss of formaldehyde.

In addition, there are many troubles in each process, and it is industrially difficult to stably obtain formaldehyde of extremely high purity.

Formaldehyde is a highly active compound, as is well known (0), and the adsorption phenomenon brings about some kind of interaction between the adsorbent and the adsorbent, so many adsorbents are used to prevent the decomposition and polymerization of formaldehyde. It can't be used because of this.

Furthermore, since there is no major difference in the polarity, dielectric constant, and other characteristics of formaldehyde and water, adsorbents with weak interactions have similar adsorption characteristics for formaldehyde and water, making it difficult to use them for efficient separation. Achieved f1. (
1).

The present inventors have extensively studied organic adsorbents such as ion exchange resins and activated carbon, inorganic adsorbents such as synthetic zeolite, silica gel, and activated clay, and adsorbents used for separation analysis such as gas chromatography. A method for vapor phase separation of formaldehyde using A-type synthetic zeolite consisting mainly of cations or potassium ions was already disclosed in Japanese Patent Application Laid-Open No. 5
It is provided in the invention of No. 289570.

However, in formaldehyde separation and purification methods using these synthetic zeolites, a portion of formaldehyde decomposes and polymerizes during the separation operation, resulting in by-products such as carbon dioxide gas and methyl formate, and the synthetic zeolites are used for a long period of time. In this case, sugar precipitation is observed on the surface of the synthetic zeolite.

Carbon dioxide gas, methyl formate, etc. generated by side reactions are mixed into formaldehyde products, reducing purity and causing loss of formaldehyde.

Furthermore, the precipitation of sugar on synthetic zeolite makes it difficult to use the zeolite for a long period of time, making it extremely difficult to use the synthetic zeolite industrially.

As a result of intensive studies to solve this problem, the inventors of the present invention discovered that A-type synthetic zeolite exchanged with a specific cation was treated by bringing it into contact with a specific compound, and used it as an adsorbent. We have discovered a surprising phenomenon in which gas-phase separation and purification of formaldehyde can be carried out while almost completely suppressing the decomposition and polymerization of formaldehyde.

That is, in the present invention, the main part of the exchangeable cations consists of elements of group IA, period 4.5.6 and mA group, period 6 of the periodic table, that is, potassium, rubidium, cesium, and barium ions. The A-type synthetic zeolite consisting of at least one selected from the group further contains ammonia, an amine compound,
The present invention relates to a method characterized in that a product treated with a carboxylic acid compound or a phosphoric acid compound is used as an adsorbent for purification.

The adsorbent used in the present invention is platform zeolite, crystal classification 3, chemical composition (oxide display) Na20Al2
o3H2StO2H4,5) (2o (exchangeable cations are expressed as sodium ions), density 1.99gr, /c,
c, unit cell volume 1870λ3, unit cell constant a=1
2.32 people (condensed cell) a2 24.64 people (true cell), void volume 0.47 c, c, /c, c, cage type: α and β, non-hydrated opening diameter 4.2A , velocity aperture diameter 3.
Starting material is a 9λ and 3.6A zeolite.

This is generally known as type A synthetic zeolite.

(Hereinafter, this will be referred to simply as the starting material.) The exchangeable cation of the starting material is exchanged by a cation within the scope of the invention in a manner already known.

For example, by contacting a starting material of the sodium type with an aqueous solution of a water-soluble potassium salt, or barium salt, or a mixture of potassium and barium salts, the exchangeable cations of the starting material are converted to potassium ions. , or barium ions, or a mixture of potassium and barium ions.

In order to facilitate cation exchange, it is desirable to use exchange ions in excess of the exchange capacity of the starting material and to heat the material.

Type A synthetic zeolite is mainly exchanged with cations other than the cations within the scope of the present invention, such as commonly used cations such as sodium ions, calcium ions, lithium ions, magnesium ions, zinc ions, cadmium ions, and tin ions. During separation and purification operations, formaldehyde is decomposed and polymerized, making it impossible to use it.

The exchange rate of exchangeable cations is important to the present invention.

That is, a small amount of cations outside the scope of the present invention that are present in type A synthetic zeolite tend to partially decompose and polymerize formaldehyde, and often do not always produce good results.

Therefore, as much as possible, the exchangeable cations in the A-type synthetic zeolite should be exchanged with ions within the scope of the present invention.

However, it is difficult to exchange cesium ions and rubidium ions with the entire amount of cations in A-type synthetic zeolite due to the ionic radius, so the remaining exchangeable cations are replaced with potassium ions or barium ions. is desirable.

The exchange rate of cations used in the present invention needs to be 60% or more, preferably 80% or more, and more preferably 90% or more.

The cation exchange rate can be confirmed by atomic absorption spectrometry after dissolving type A Hewei zeolite in a strong acid.

Ammonia treatment of cation-exchanged zeolite is usually carried out in the gas phase at a temperature of about 120°C to 2000°C, and the treatment time can be easily determined by experiment, depending on the need for suppressing side reactions. I can do it.

Furthermore, the amine compound, carboxylic acid compound, or phosphoric acid compound is preferably treated in a liquid phase, particularly in an aqueous solution, an alcohol solution, an acetone solution, or a dioxane solution at room temperature. treatment concentration,
The coverage of these compounds on the zeolite can be easily determined through experiments depending on the degree of suppression of side reactions.

Formaldehyde used in the present invention can be sufficiently used as long as it is obtained by simple evaporation of formalin or thermal decomposition of paraformaldehyde and has a purity of 35 to 10%.

Also, ammonia is commercially available with a purity of 95% to 100%.
% can be used as is.

The amine compounds used in the present invention include aliphatic monoamines and diamines such as methylamine, ethylamine, trimethylamine, diethylamine, and hesyl-methylenediamine, alkanolamines such as ethanolamine and triethanolamine, and aniline, 〇- Aromatic amines such as toluidine, pyridines such as pyridine and lutidine, and urea, N, N'-diphenyl-N, N'
Ureas such as diethyl urea are used, but amine compounds having a vapor pressure of 5 mrnHg or less at 130°C are more preferably used.

The carboxylic acid compounds used in the present invention include aliphatic carboxylic acids such as lauric acid and stearic acid, benzoic acid, O-
Aromatic carboxylic acids such as phthalic acid, aliphatic carboxylic acid esters such as ethyl laurate and methyl stearate, and aromatic carbon esters such as ethyl benzoate and dimethyl P-phthalate are used.
More preferred are carboxylic acid compounds having a vapor pressure of:

The phosphoric acid compounds used in the present invention include phosphoric acid or phosphoric acid esters such as phosphoric acid, diethyl phosphate, and triethyl phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, potassium phosphate, and monohydrogen phosphate. Barium hydrogen, phosphoric acid 2
Examples include alkali metal salts or alkali metal salts of phosphoric acid such as rubidium hydrogen, cesium dihydrogen phosphate, sodium dihydrogen phosphate, and magnesium monohydrogen phosphate.

Among the processing agents of the present invention, phosphoric acid is particularly effective.
Also, carboxylic acids such as lauric acid and stearic acid are effective.

Considering the well-known fact that A-type synthetic zeolite dissolves in acids, treatment with phosphoric acid, lauric acid, and stearic acid, which would have been unsuitable as a treatment agent for conventional A-type zeolite, removes certain exchangeable cations. It must be said that the marked improvement in the formaldehyde purification ability of the A-type synthetic acid zeolite having the following is a completely unexpected development.

Even in the treatment of A-type synthetic acid zeolite using carboxylic acid and phosphoric acid, it is usually desirable to carry out the treatment in the liquid phase at room temperature, and the treatment time, treatment concentration and coverage rate can be easily determined by experiment. However, for example, the cation-substituted A-type synthetic zeolite to be treated can be treated with an aqueous or alcoholic solution in which carboxylic acid or phosphoric acid is mixed or dissolved at about 0.002 mol/l to 1.0 mol/l. On the other hand,
Good results can be obtained by treatment under conditions containing carboxylic acid or phosphoric acid corresponding to a coverage of 1% to 20%, more preferably 1% to 10%.

In some cases, even better results may be obtained by removing the excess carboxylic acid or phosphoric acid present on the zeolite surface with water or alcohol after the carboxylic acid or phosphoric acid treatment.

The A-type synthetic acid zeolite used in the present invention can be used in a wide range of shapes, from a 2-micron single substance to a 5-diameter pellet containing about 30% inorganic binder, but the cation exchange rate, In order to increase the rate of adsorption and desorption, it is preferable that the particle size is as small as possible.

On the other hand, from an operational standpoint, reducing the pressure loss in the separation column,
For ease of operation, it is desirable to use particles with a large particle size or pellets.

The substance to be separated used in the present invention is a mixture containing at least formaldehyde and water, but also alcohols such as dimethyl alcohol and ethyl alcohol, gases such as carbon dioxide, carbon monoxide, and nitrogen, and formic acid and acetic acid. Even if lower carboxylic acids and esters such as methyl formate and ethyl formate are present, the present invention can be effectively carried out.

Formaldehyde concentration in the substance to be separated ranges from 30% to 99%.
．． It is possible to effectively separate and purify formaldehyde up to 99%, and over a wide range of water concentrations from 70% to 10 ppm, especially when the water concentration is 500 ppm or less relative to formaldehyde. Using the method of the present invention, the water content of formaldehyde can be reduced to 5
It is possible to obtain formaldehyde with an extremely low water content.

As is known, formaldehyde, under constant pressure,
It is possible to exist stably above a certain temperature.

On the other hand, even though formaldehyde is in a stable gaseous state, it is an unstable compound when adsorbed by an adsorbent, causing decomposition and polymerization.

Further, at higher temperatures, the decomposition reaction becomes more pronounced.

The present invention can be carried out from 20°C to 250°C, more preferably from 12°C to 250°C.
10 mrttHg to 3100 mrttHg, more preferably 500 mrttHg, at a temperature of 0°C to 200°C.
It can be carried out smoothly under formaldehyde partial pressure of 600 mmHg.

Next, a specific example of gas phase separation according to the present invention will be explained.

A separation column is filled with the zeolite used in the present invention, and the entire separation column is set at a predetermined temperature and pressure.

A mixed gas containing pre-vaporized formaldehyde and water is supplied from above or below to the prepared separation tower.

Separation takes place in the column simultaneously with the supply.

When the mixed gas is supplied from below, a formaldehyde-rich gas flow is obtained from above.

The supply of the mixed gas is stopped before the flow of formaldehyde-rich gas falls below the desired purity of formaldehyde.

This timing is determined by the amount of zeolite used, the supply of mixed gas 'NX.

At the time when the supply of the mixed gas is stopped, a small amount of the mixed gas remains in the column, so this is removed by an inert replacement gas such as nitrogen gas or by suction using a vacuum pump.

In this state, the water adsorbed on the zeolite is removed by the usual heating swing method or pressure swing method, and then the temperature and pressure of the separation column are adjusted to prepare for the next introduction of the mixed gas. is set.

Examples of the present invention are shown below, but the present invention is not limited thereto.

Examples 1 to 18 A jacketed cylindrical separation column with a diameter of 8 mm and a length of 2 QOmm was filled with the A-type synthetic acid zeolite shown in Table 1.

The separation column was maintained at 148°C, and 50 rILl of formaldehyde gas containing 450 ppm of water, which was also adjusted to 148°C, was supplied at a formaldehyde partial pressure of 740 mmH&.

The gas flowing out from the tower was introduced into a gas chromatograph equipped with a highly sensitive TCD detector, and its composition was analyzed.

The results are shown in Table 1.

Comparative Examples 1 to 2 Formaldehyde was separated and purified using the zeolite listed in Table 1 under the same conditions as Examples 1 to 10.

Claims (1)

[Claims] 1. In separating and purifying formaldehyde by contacting a mixture of formaldehyde containing water, methanol, etc. with an adsorbent in a gas phase state, the adsorbent contains potassium, the main part of its exchangeable cations, A modified type A synthetic zeolite made by treating a type A synthetic zeolite containing at least one selected from the group consisting of rubidium, cesium, and barium ions with ammonia, an amine compound, a carboxylic acid compound, or a phosphoric acid compound. A gas phase separation and purification method for formaldehyde, characterized in that it is used. 2. The method for vapor phase separation and purification of formaldehyde according to claim 1, wherein the main portion of exchangeable cations is 60% or more. 3. The method for vapor phase separation and purification of formaldehyde according to claim 2, wherein the main portion of exchangeable cations is 90% or more. 4. The method for vapor phase separation and purification of formaldehyde according to claim 1, wherein the treatment with ammonia is carried out in a gas phase state at 120°C to 200°C. 5. The gas phase separation and purification method for formaldehyde according to claim 1, wherein the treatment with an amine compound, a carboxylic acid compound, or a phosphoric acid compound is carried out in an aqueous solution, an alcohol solution, an acetone solution, or a dioxane solution at room temperature. 6. The method for vapor phase separation and purification of formaldehyde according to claim 1, wherein the processing agent is phosphoric acid. 1. The method for vapor phase separation and purification of formaldehyde according to claim 1, wherein the processing agent is lauric acid. 8. The method for vapor phase separation and purification of formaldehyde according to claim 1, wherein the processing agent is stearic acid. 9 Claim 6 in which the treatment agent is used as an aqueous or alcoholic solution with a concentration of 0.002 to 1.0 mol/l
8. The method for vapor phase separation and purification of formaldehyde according to item 7 or 8. 10. The method for vapor phase separation and purification of formaldehyde according to claim 1, wherein the adsorption treatment using an adsorbent is carried out at a temperature of 20° C. to 250° C. and a formaldehyde partial pressure of 10 mmHg to 3100 mmHg. 11. The method for vapor phase separation and purification of formaldehyde according to claim 10, wherein the adsorption treatment with an adsorbent is carried out at a temperature of 120° C. to 200° C. and a formaldehyde partial pressure of 500 to 1600 mmHg.