WO1998013362A1

WO1998013362A1 - Process for the purification of trioxane

Info

Publication number: WO1998013362A1
Application number: PCT/JP1997/003390
Authority: WO
Inventors: Junzo Masamoto
Original assignee: Asahi Kasei Kogyo Kabushiki Kaisha
Priority date: 1996-09-25
Filing date: 1997-09-24
Publication date: 1998-04-02
Also published as: JP3101326B2

Abstract

A process for highly purifying trioxane by subjecting a trioxane-containing distillate obtained by heating an aqueous solution of formaldehyde to extraction with benzene, feeding the obtained benzene solution of trioxane into a distillation column to conduct continuous distillation, and continuously withdrawing trioxane from the bottom of the column while distilling benzene out of the top thereof, characterized in that the distillation column has a number of trays of 30 or more and that the distillation is conducteed in such a way as to meet the following requirements: (i) the above benzene solution of trioxane is extracted with water, (ii) the trioxane concentration X (wt. %) of the solution on the feed tray of the distillation column is kept within the range satisfying a specific relationship, and (iii) the temperature of the column is controlled so that an inflection point can appear in the temperature profile of the column with temperature as the abscissa and the number of trays as the ordinate at a point which is present below the feed tray and apart from the feed tray by at least ten trays and from the bottom by at least five trays.

Description

(57) Summary The present invention relates to a method for extracting a trioxane-containing distillate obtained by heating a formaldehyde aqueous solution with benzene, and using a benzene solution containing the trioxane as a raw material, the distillation column is used in a distillation column. Feed, distills benzene from the top of the column, continuously distills the trioxane from the bottom of the column, and separates and removes the trioxane. The distillation column has a number of stages of B or more, more than 30 in the morning.

Le Korean Book Zayin B-Lu-Vonta

(i) the trioxalte people

Extract the benzene solution containing the country's main runner, Aesurarayansuaravirin, with water,

One L Lord Shitashi Santasin

(ii) Right-click

Next, the trioxane concentration of the liquid composition in the raw material supply stage of the distillation column

Common

X (% by weight) within a range that satisfies a specific relational formula, and

(iii) Temperature of the distillation column with the temperature on the horizontal axis and the number of distillation columns on the vertical axis

MMMMMNNNNMRRSPPLL LL

In the profile, below the raw material supply stage WUDNXEOTODKRUGZ KTVC LLLRS and below the raw material supply stage

Rumomomobo Posumama Loromomo Lorarasirireri

The temperature profile is located at a distance of 0 or more steps and at least 5 steps from the bottom of the tower and at a distance from the bottom of the tower.

W-Idaga

Lulua «Community Acad

The temperature of the distillation column is adjusted so that an inflection point of the distillation column appears.

S Japanese rug

Country

You. God UUUUTVYTTTTZTSS SSSSS WMURTAGNNDGZ EGKSLZJI

Code used to determine the FCT value added to the first page of the gfSS Ig pamphlet that is publicly ffl based on the PCT (Informative)

AL Albania E S Sweden

AM F I Singapore

AT Austria FR Slovenia

AU Australia GA Slovak Republic

AZ Azerbaijan GB Sierra Leone

B A Poznia Elzegovina GE Senegal

BB Barbados GH Swaziland

BE Belgium GM Charid

BF Bulgina Fan GN Togo

BG Bulgaria GW Tajikistan

B J Benin GR Torturamestan

BR Brazil HU Turkey

BY Belarus I D Trinidad and Tobago

CA Canada I E Ukraine

CF Central African Republic I L Uganda

CG Congo I S United States

CH Switzerland I T ゥ zbekistan

C I Coat-Jiboard J P Vie Tonum

CM Cameroon KE Yugoslavia

CN China KG Zimbabwe

CU Cuba KP

CZ Chekko its ft country KR

DE Germany KZ

D Denmark LC

EE Estonia LI International applications published under the Patent Cooperation Treaty

(51) International Patent Classification 6 (11) International Publication Number W098 / 13362 C07D 323/06 A1

(43) International Publication H April 1998 2 fi i02.04.98)

(21) International application number PCT / JP97 / 03390 (81) Designated country CN, DE, JP, KR, SG, US.

(22) International filing date September 24, 1997 (24.09.97)

International Survey Report

(30) Priority data

Japanese Patent Application No. 8/272862 September 25, 1996 (25.09.96) JP

(71) Applicant (for all designated countries except the United States)

Asahi Chemical Industry Co., Ltd.

(ASAHI KASEI OGYO KABUSHI I AISHA) [JP / JP]

〒530 Osaka, Kita-ku, Osaka fthama 1-chome 2-6 Osaka, (JP)

(72) the inventor; and

(75) Inventor / Applicant (US only)

Junzo Masamoto (MASAMOTO, Junzo) [JP / JP]

〒 Castorum Rakuhoku 712, Takano Higashikaicho, Sakyo-ku, Kyoto-shi, Kyoto Prefecture 606, Japan

Kyoto, (JP)

(74) Agent

Patent Attorney Akira Asamura, Outside (ASAMURA, Kiyoshi et al.)

〒100 2-1-1 Otemachi, Chiyoda-ku, Tokyo

Shin-Otemachi Building 331 Tokyo, (JP)

(54) Title: PROCESS FOR THE PURIFICATION OF TRIOXANE

(54) Title of the invention Method for purifying trioxane

(57) Abstract

A process for highly purifying trioxane by subjecting a trioxane-containing distillate obtained by heating an aqueous solution of formaldehyde to extraction with benzene, feeding the obtained benzene solution of trioxane into a distillation column to conduct continuous distillation, and continuously withdrawing trioxane from the bottom of the column while distilling benzene out of the top them, characterized in that the distillation column has a number of trays of 30 or more and that the distillation is conductced in such a way as to meet the following requirements: (i) the above benzene solution of trioxane is extracted with water, (ii) the trioxane concentration X (wl.%) of the solution on the feed tray of the distillation column is kept within the range satisfying a specific relationship, and (iii) the temperature of the column is controlled so that an inflection point can appear in the temperature profile of the column with temperature as the abscissa and the number of trays as the ordinate at a point which is present below the feed tray and apart from the feed tray by at least ten trays and from the bottom by at least five trays.

In the method for continuously distilling and separating lioxane, the trioxane concentration X (weight ¾) of the liquid composition in the raw material supply stage of the distillation column is represented by the following formula (1)

50 50

100 -2 (r-1) ° ² ≤x≤ioo

0.5-0.5 0.5

One 2 (7-1) ^{0 2} + 2 Ru ⁵ (1)

(Where R is the reflux ratio, and a is the weight ratio of the liquid part in the feedstock, q, and the trioxane concentration in the feedstock, C (% by weight).

R (1 -C / 1 0 0) + q

7-(2)

R (l -C / 1 00) is a parameter defined by -C / 1 00 + q)

A method for separating trioxane, characterized in that the trioxane is kept within a range satisfying the relational expression represented by:

McCube's Chile (Mc abe—

According to the theory of Th i e 1 e), the mole fraction y,,, of the steam leaving the j + 1st stage counted from the top is given by the following equation (3)

L + q F W

y, = X, Xw (3)

L + q F-W L + q F-W (for example, see Hirata and Yorimi, “Distillation Engineering Handbook”, pp. 11-11). Where L is the molar flow rate of the descending liquid, F is the raw material supply amount, W is the bottom liquid amount, q is the ratio of the liquid part in the raw material, X, is the molar amount of the liquid leaving the j-th stage counted from the top X is the mole fraction of bottoms.

In this equation, the gradient _の of the recovery section operation line is given by L

+ q

L + q F F

(Four)

L + q F-W then W

+ q

Assuming the ideal conditions, denoted by F F, and the complete separation of the light and heavy components of the binary system, then C

= R (to-

F 1 00

W C

Since the relationship of F 100 is established, when these are substituted into the above equation (4), the following equation (5) is obtained.

C

R () + Q

1 0 0

(Five)

C C

R (1-) one

1 00 1 0 0

Becomes

Therefore, ァ is a power that can be used as a parameter indicating ideal distillation conditions, and the invention of JPB-64 ('89) -10513 and US-Λ-43-2644 described above. Uses this key as a basic parameter and specifies the optimal range experimentally.

In other words, equation (1) shows that the liquid composition of the raw material supply stage is set on an extension of the ideal recovery section operation line, and that gas-liquid separation of benzene and trioxane is possible, and that FIG. 3 shows experimentally the allowable range of the liquid composition in the feed column of the distillation column capable of reducing the content of the chain transfer agent in the trioxane at the bottom of the distillation column.

Note that it is the left side of the above equation (1)

50

100 • 2 (7-1)

r-0.5 is the minimum value of the trioxane concentration in the liquid composition of the distillation column, and is the right-hand side of the above formula (1).

50

100 2 (1) ^{0 2} + 2 R

r -0.5 indicates its maximum value. As is clear from this, the larger the reflux ratio, the wider the allowable range of the liquid composition in the raw material supply stage.

In the conventional method of distilling and separating a benzene solution of trioxane, in the operation of the distillation column, the liquid composition of the raw material supply stage is usually made to coincide with the intersection of the operation line of the concentration section and the raw material line (Q line). (See, for example, Tokyo Chemical Doujinshi, Shigefumi Fujita, Heiichiro Higashihata, "Chemical Engineering II, 2nd Edition, Mass Transfer Operation," pp. 40-47). That is, when the raw material is in a liquid state at a boiling point, the basic operation has been to make the trioxane concentration of the liquid composition in the raw material supply stage approximately equal to the raw material concentration. However, this will result in insufficient removal of the chain transfer agent.

On the other hand, JP-B-64 ('89) -105-13 and US- 4-4 33 32 644 disclose powerful methods for providing highly purified trioxane. ing. However, under certain conditions, employing the methods disclosed in JP-B-64 ('89) -105-133 and US-A-433-264, It has been found that the purification of the trioxane may still be insufficient. The above-mentioned invention of JP-A-3 ('91)-123, 777 aims to improve this point.

For example, a trio obtained by heating an aqueous solution of formalin containing a large amount of methanol It was difficult to extract the xane with benzene and separate the benzene from the resulting benzene solution of trioxane to obtain trioxane containing almost no water, methanol, or formic acid. That is, the purification methods disclosed in JP—A—3 ('91) —1237777 are described in JP—B—64 (′89) -105013 and US—A— In contrast to the method disclosed in 4 3 3 2 6 4 4, it is assumed that a benzene solution containing trioxane extracted with benzene is extracted with water. This is a method for purifying trioxane. By employing such a purification method, it has become possible to purify impurities such as water in trioxane to about 1 ppm.

However, it may require a particularly highly purified trioxane. For example, there may be a case where a trioxane having an impurity such as water of 0.1 0ppm or less is required, and the present invention provides a method for purifying such highly purified trioxane.

Disclosure of the invention

The present inventors have conducted intensive studies on the distillation method in order to find a method for purifying trioxane to a higher degree under all conditions, and as a result, using a distillation column having 30 or more stages, using a distillation column having a number of stages of more than 30. It has been found that trioxane can be purified to a higher degree by creating an inflection point in the temperature profile of the distillation column at the bottom of the distillation column at least 10 stages away and at least 5 stages away from the bottom of the column. The present invention has been completed. That is, in the present invention, a trioxane-containing distillate obtained by heating a formaldehyde aqueous solution is extracted with benzene, a benzene solution containing trioxane is supplied as a raw material to a distillation column, and benzene is distilled from the top of the column. In a method for purifying trioxane, which comprises continuously distilling trioxane from the bottom of a column, separating and extracting the trioxane, the distillation column has 30 or more stages,

(i) extracting the benzene solution containing the trioxane with water,

(U) Next, the trioxane concentration X (% by weight) of the liquid composition in the raw material supply stage of the distillation column is calculated by the following formula (1) 50 50

100 2 (r-l) ≤X≤100

(r -0.5) r -0.5

-2 (r ~ 1) ^{0 2} + 2 R ° ^s (1)

(However, R is the reflux ratio, and a is the weight ratio of the liquid part in the feedstock, q is the trioxane concentration in the raw material supplied, and C (wt%).

R (1 -C / 100) + q

7 = (2)

R (1—C / 1 00)-Parameter defined by -C / 1 00 + q)

Is maintained within a range that satisfies the relational expression represented by, and

(iii) In the temperature profile of the distillation column, where the horizontal axis represents the temperature and the vertical axis represents the number of distillation columns, the lower stage than the raw material supply stage is at least 10 stages away from the raw material supply stage and 5 stages from the bottom of the column. The above method for purifying trioxane, wherein the temperature of the distillation column is adjusted so that an inflection point of the temperature profile appears at a position apart from the above.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, by extracting a benzene solution containing a trioxane with water, impurities such as methanol, formic acid, and formaldehyde dissolved in the solution are transferred to an aqueous phase, and trioxane is subsequently distilled. Can be easily purified. Therefore, the content of impurities such as water, methanol, and formic acid in trioxane obtained by a distillation operation performed after the extraction operation is extremely low. The mechanism of this effect is unclear, but formaldehyde dissolved in the benzene solution containing trioxane is transferred to the aqueous phase by extraction with water, which facilitates the purification of trioxane in the subsequent distillation step. It is estimated that there is.

The extraction operation with water is performed by a batch extraction method using a tank or a continuous extraction method using a tower. As a preferable method, water is flowed from the upper part of the tower, a benzene solution containing trioxane is flowed from the lower part of the tower, and a step or a filler such as a filler is placed in the tower. A so-called counter-current contact method is employed, in which an auxiliary substance for improving the interfacial contact between water and a benzene solution containing trioxane is contained. The ratio of the water used and the benzene solution containing trioxane is from 0.01: 1 to 1: 1, preferably from 0.03: 1 to 0.3: 1, more preferably 0.05: From 1 to 0.2: 1. If the amount of water used is small, the extraction effect is insufficient, and if it is too large, loss of trioxane and the like is large and uneconomical.

The formaldehyde concentration of the benzene solution containing trioxane after the water extraction treatment varies depending on the target degree of purification, but is usually 1% or less, preferably 0.2% or less, and particularly preferably. 0.05% or less.

From the benzene solution containing trioxane subjected to the extraction treatment with water in this way, benzene is then separated in a distillation column, and trioxane with a low content of impurities such as water is obtained from the bottom of the column.

At this time, as for the operating conditions of the distillation column, it is necessary to adjust the liquid composition of the raw material supply stage of the distillation column as shown by the above formula (1). If the trioxane concentration of the liquid composition in the raw material supply liquid is kept lower than the lower limit of the range represented by the formula (1), it becomes difficult to separate trioxane and benzene, while if it is kept higher than the upper limit, the chain transfer agent The power to lower the content of << becomes difficult.

The concentration of trioxane in the feed stage can be controlled by increasing or decreasing the amount of rising steam at the bottom of the column, changing the temperature profile in the column, and other methods. In the present invention, the temperature profile in the distillation column is particularly important.

In the temperature profile of the distillation column with the temperature on the horizontal axis and the number of distillation columns on the vertical axis, the inflection point of the temperature profile below the raw material supply stage is separated by more than 10 stages from the raw material supply stage. By providing the column at least five steps away from the bottom of the column, highly purified trioxane can be obtained. The position of the inflection point is located at least i0 step from the raw material supply step, but preferably at least 15 step. The reason why it is necessary that the position of the inflection point be at least 10 stages away from the raw material supply stage is not clear, but it is due to the relationship between the temperature profile in the distillation column and the distillation separation behavior of trace impurities. Guessed.

In order for the inflection point of the temperature profile to appear at a position below the raw material supply stage, at least 10 stages away from the raw material supply stage, and at least 5 stages away from the bottom of the column, distillation The position of the inflection point may be adjusted by appropriately changing the supply amount of the raw material, the reflux ratio, the supply amount of steam used as a heating source, and the like.

In the distillation separation of trioxane and benzene, the reflux ratio varies depending on the trioxane concentration of the feed solution, but is usually in the range of 1.1 to 8. Reflux ratios higher than 8 can be used, and use of an unnecessarily high reflux ratio only results in energy loss and is disadvantageous. A preferred reflux ratio is from 1.2 to 6, more preferably from 1.5 to 4.

Usually, a multi-stage distillation column is used for continuous distillation. In the present invention, the number of stages of the distillation column is 30 or more, but the number of stages actually used varies depending on the intended separation accuracy, the feed material used, the reflux ratio, and the like.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to these Examples.

Example 1

A 65% aqueous solution of formalin containing 6% of methanol was heated and distilled in the presence of sulfuric acid to obtain a water-soluble distillate (aqueous solution) containing 45% of trioxane and the balance being formaldehyde, methanol and water. This aqueous solution was subjected to countercurrent extraction with benzene to obtain a benzene solution containing 42% of trioxane. The benzene solution containing the trioxane was supplied from the lower part of the packed tower packed with Raschig rings, and water was supplied from the upper part. The ratio of the water to the benzene solution containing trioxane was 0.2: 1 (weight ratio). Here, the formaldehyde in the benzene solution containing trioxane that was extracted and washed with water was 0.055%. The trioxane concentration was 38%.

The benzene solution containing the trioxane is continuously supplied as a liquid having a boiling point of 20 from the top to a distillation column of 65 stages as a raw material supply stage, and rectification is performed under a reflux ratio of 3; Distillation was performed so that the inflection point appeared at the 15th stage from the raw material supply stage in the temperature profile below the raw material supply stage in the distillation column, and benzene was continuously separated from the top of the column, and trioxane was continuously separated from the bottom of the column. . As the operating conditions at this time, the trioxane concentration in the supply stage was maintained at 25% according to the above formula (1).

The chain transfer agent in the obtained trioxane contained 0.1 ppm of water and 0.1 part of formic acid. Otsu, ppm.

Comparative Example 1

The same operation as in Example 1 was performed, except that the benzene solution containing trioxane was not subjected to extraction and washing with water. The water content in the obtained trioxane was 90 ppm and formic acid was 60 ppm.

Comparative Example 2

In Example 1, the same operation as in Example 1 was performed except that the inflection point of the temperature profile below the distillation column raw material supply stage was changed to the seventh stage from the supply stage as the operation conditions of the distillation column. . The water content in the obtained trioxane was 1 ppm and formic acid was 1 ppm.

Example 2

The same operation as in Example 1 was performed, except that the ratio of the amount of water to be subjected to the countercurrent extraction to the benzene solution containing trioxane was 0.15: 1 (weight ratio). Here, the formaldehyde in the benzene solution containing trioxane that had been extracted and washed with water was 0.11%. The trioxane concentration was 39%. Moisture in trioxane after distillation and purification was 0.2 ppm, and formic acid was 0.2 ppm. Example 3

In Example 1, the same operation as in Example 2 was performed except that the position of the inflection point of the temperature profile in the lower stage of the distillation column was set at the 10th stage from the raw material supply stage. The water content in the obtained trioxane was 0.3 ppm, and that of formic acid was 0.3 ppm.

Industrial applicability

The present invention provides trioxane, a highly purified, high quality, polymerized grade for polyacetal resins, which is useful in the polyacetal manufacturing industry.

Claims

The scope of the claims

1. A trioxane-containing distillate obtained by heating a formaldehyde aqueous solution is extracted with benzene, and a benzene solution containing trioxane is supplied as a raw material to a distillation column, and benzene is distilled from the top of the column, and the benzene is distilled from the bottom. A method for purifying trioxane, comprising continuously distilling trioxane, separating and extracting the trioxane, wherein the distillation column has 30 or more plates,

(i) extracting the benzene solution containing the trioxane with water,

(ii) Next, the trioxane concentration X (% by weight) of the liquid composition in the raw material supply stage of the distillation column is calculated by the following equation

50 50

100 2 (r-1) X≤100

7 -0.5 r -0.5

-2 (r-1). ² + 2R ^{0 5} (1)

R (1 -C / 1 00) + q

(2)

R (l— CZ1 00) — defined by CZl 00 + q, 'is a parameter)

(iii) In the temperature profile of the distillation column, where the horizontal axis represents temperature and the vertical axis represents the number of distillation columns, the temperature profile is lower than the raw material supply stage, at least 10 stages away from the raw material supply stage, and 5 mm from the bottom of the column. A method for purifying trioxane, comprising adjusting the temperature of a distillation column so that an inflection point of a temperature profile appears at a position separated by more than one step.

2. In the temperature profile of the distillation column, the temperature profile is lower than the raw material supply stage, at least 5 stages away from the raw material supply stage and at least 5 stages away from the bottom of the column. 2. The method according to claim ¹ , wherein the temperature of the distillation column is adjusted so that the inflection point of appears.