JP2943386B2 - Purification method of acrylamide aqueous solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper removal method for purifying an aqueous solution of acrylamide obtained by a contact hydration method of acrylonitrile. Acrylamide (hereinafter abbreviated as AM) is an industrially useful monomer that is used for producing acrylamide-based polymers used for paper strength agents, flocculants, and the like, and for various applications.

[0002]

2. Description of the Related Art A method for producing AM by catalytic hydration of acrylonitrile in the presence of a copper metal catalyst is already well known. It is unavoidable that a trace amount of copper is eluted into the AM-containing reaction solution obtained using this copper-based catalyst. When a polymer is to be produced from an AM aqueous solution, the dissolved copper inhibits the polymerization reaction and
This causes the commercial value of the M aqueous solution to be significantly reduced. Therefore, in order to use an AM aqueous solution obtained from the AM reaction solution as a polymer raw material, it is necessary to remove dissolved copper. As a method of removing dissolved copper, a method of treating with a chelate resin or a method of treating with an ion exchange resin is used, and usually, a method of treating an AM aqueous solution with a cation exchange resin is employed. In this case, the column may be filled with a cation exchange resin and passed therethrough, or a method may be used in which the column is filled and stirred as necessary.

[0003]

However, since the obtained AM is highly reactive, it is extremely difficult to industrially remove dissolved copper in the AM reaction solution without a loss such as polymerization. It is particularly difficult to remove copper ions with a cation exchange resin. Even if they are free acid type (hereinafter abbreviated as H type), they are sodium salt type (hereinafter abbreviated as Na type). Also, there is a problem that AM polymerizes inside the resin tower (or tank) and clogs the resin tower (or tank), so that stable production cannot be performed or the quality of the product is significantly reduced.

On the other hand, it is well known that an AM aqueous solution is stabilized by the presence of dissolved oxygen (hereinafter abbreviated as DO) (Kishore, K. and Bhanu, VA; J. Polym. Sc).
i., Part A: Polym. Chem., 26 (10), 2831-3 (1988); Kisho
re, K. and Bhanu, VA; J. Polym. Sci., Part A: Polym.
Chem., 24 (2), 379-81 (1986)). For example, regarding the polymerization stability of an AM aqueous solution, according to the findings of the present inventors, it has been reported that AM
The aqueous solution is polymerized in 3 hours in a state where the AM aqueous solution is replaced with nitrogen gas under the condition of a concentration of 50% and 60 ° C. and there is no dissolved oxygen at all. On the other hand, when the dissolved oxygen in the aqueous AM solution is adjusted to 0.1 ppm by a mixed gas of air and nitrogen, the polymer of AM is not observed even when the solution is kept for 40 days under the same conditions, and is extremely stable.

There is also a method in which a stabilizer is separately added in order to avoid polymerization of AM in the step of removing copper.
For example, as a polymerization inhibitor in an aqueous AM solution, organic compounds such as hydroquinone, methoxy-hydroquinone, anthraquinone, P-tert-butylcatechol, 2,5-di-tert-butyl-hydroquinone, pyrogallol, and P-hydroxyldiphenylamine , Dithiobenzoyl sulfide, phenyl β-naphthylamine, picric acid, etc., and as inorganic ones, ferric chloride, cupric chloride, copper powder, titanium trichloride, red blood salt, yellow blood salt, manganese sulfate, There is a method of adding a cobalt complex salt, a chromium complex salt, or the like.

However, in this method, since the added polymerization inhibitor causes the quality of the AM monomer product as a raw material of the AM polymer to be remarkably deteriorated, it is necessary to remove those additives in a later step. The disadvantages. On the other hand, in the method of preventing AM polymerization by dissolved oxygen, when polymerizing an AM monomer product to produce a polymer, oxygen gas can be easily removed by replacement with an inert gas such as nitrogen gas. Therefore, A
As a method of stabilizing the M aqueous solution, stabilization by dissolved oxygen is most preferable.

Therefore, when removing the dissolved copper in the AM aqueous solution by a resin tower (or tank) filled with a cation exchange resin, it is conceivable that dissolved oxygen is present in the AM aqueous solution in advance to stabilize it. However, A
When removing the dissolved copper in the M aqueous solution by the resin tower (or tank) filled with the cation exchange resin, the AM aqueous solution was previously secured and DO was stabilized in the resin tower (or tank). However, there is a problem that polymerization may be clogged, and stable operation cannot always be performed.
The present inventors have conducted intensive studies on a method of removing copper while reliably preventing the polymerization of AM in purifying an AM aqueous solution obtained by a contact hydration method of acrylonitrile with a cation exchange resin. Was completed.

[0008]

That is, when the acrylamide aqueous solution obtained by the contact hydration method of acrylonitrile is decoppered with a cation exchange resin, the dissolved oxygen concentration in the acrylamide aqueous solution is measured at the outlet of the resin tower or the resin tank. At least 2 ppm, more preferably 5 ppm
By keeping the above, AM polymerization is reliably avoided,
It has been found that the dissolved copper can be removed stably, and the present invention has been completed.

Hereinafter, details of the present invention will be sequentially described. The AM aqueous solution used in the present invention is obtained by a usual contact hydration method using acrylonitrile as a raw material. That is, acrylonitrile was charged together with water into a pressure-resistant reactor, and was heated at a temperature of 70 to 150 ° C. in the presence of a copper metal catalyst.
Let react for ~ 3 hours. Since unreacted acrylonitrile remains in the obtained reaction solution, it is usually removed in advance. The AM concentration in the AM aqueous solution thus obtained is 20 to 50%, and usually 10 to 50 ppm
Contains copper.

Next, in order to improve the copper removal performance in the cation exchange resin tower, the liquid obtained in this way is passed through an H-type weakly acidic ion exchange resin tower in advance and the AM
The pH of the aqueous solution is adjusted to 6 or less. Examples of the H-type weakly acidic ion exchange resin used here include commercially available Amberlite IRC-76, Diaion WK-10, and WK-1.
1, WK-20 and the like.

When the dissolved copper in the AM aqueous solution thus obtained is removed by a cation exchange resin, DO is previously secured before passing the solution through a resin tower (or tank) in order to stabilize the AM aqueous solution. Nevertheless, AM may polymerize in some cases. For example, even when the AM aqueous solution is passed through a cation exchange resin tower, it is brought into contact with air at atmospheric pressure in advance to stabilize the AM aqueous solution to bring DO to 10 ppm, and even when ordinary copper removal is performed. AM inside the resin tower
Was polymerized in some cases. DO10ppm in this case is
In the polymerization stability test at 60 ° C. of the AM aqueous solution described above, it was actually 1 compared with 0.1 ppm which was stable for 40 days.
That is, the amount was 00 times, and it could not be predicted at all from the effect of stabilizing dissolved oxygen in the AM aqueous solution.
As can be seen from this example, it is not possible to stably remove the dissolved copper simply by keeping the DO of the AM aqueous solution at the entrance of the resin tower.

This indicates that the stability of the AM aqueous solution inside the resin tower is greatly different from the stability outside the resin tower. That is, when removing the dissolved copper with the cation exchange resin from the AM aqueous solution, even if the AM aqueous solution secures its DO at the entrance of the resin tower, the AM aqueous solution is not necessarily stabilized in the resin tower, and the AM is not polymerized. There is no guarantee. The present inventors have studied in more detail a method in which AM polymerization does not occur inside the resin tower, and as a result, have found that stable operation can be achieved by keeping the dissolved oxygen concentration at the outlet of the resin tower substantially at 2 ppm or more. Further, in order to keep the dissolved oxygen concentration at the outlet of the resin tower at 2 ppm or more, it is conceivable to control the dissolved oxygen at a certain concentration or more at the inlet of the resin tower. Even if the dissolved oxygen concentration in the AM aqueous solution is always constant at the inlet, the dissolved oxygen concentration at the resin tower outlet does not always show a stable value.

In other words, it is not necessary to bring the AM aqueous solution into contact with oxygen or an oxygen-containing gas at the inlet of the resin tower and stabilize it in order to reliably remove copper while reliably preventing polymerization inside the resin tower. However, this is not enough by itself, and there is no guarantee that polymerization will not occur in the resin tower. Therefore, it is essential to constantly control the dissolved oxygen concentration at the outlet of the resin tower in order to reliably and stably remove the dissolved copper in the AM aqueous solution without causing polymerization in the resin tower. And
As for the concentration of dissolved oxygen to be maintained, 0.1 ppm, as in the case where no resin is present, is quite insufficient, and a large amount of dissolved oxygen of 2 ppm or more, more preferably 5 ppm or more, is required. Thus, DO in the AM aqueous solution at the outlet of the resin tower was reduced by 2%.
Only when the concentration is substantially maintained at ppm or more, extremely stable operation becomes possible without polymerization of AM in the resin tower. Such a retention management method is a method that has not been known until now.

[0014] Advantages of controlling the dissolved oxygen concentration of the AM aqueous solution at the outlet of the resin tower include the following. The danger of polymerization of AM inside the resin tower can be predicted, and a damaged tower of equipment due to polymerization can be prevented beforehand. Depending on the dissolved oxygen concentration at the outlet of the resin tower, the amount of oxygen gas supplied for stabilizing AM at the inlet of the resin tower can be economically controlled. In addition, as a method of managing the DO of the resin tower (or tank) outlet liquid,
A method in which the DO of the resin tower (or tank) outlet liquid is managed online by a dissolved oxygen meter. A method in which a resin tower (or tank) outlet liquid is sampled so as not to come into contact with outside air, and DO is measured and managed by a dissolved oxygen meter, a modified Miller method, a Winkler sodium azide method, or the like. And the like.

The method of (1) is preferable because a measurement result is immediately obtained. By these methods, the resin tower (or tank)
When the DO of the outlet AM aqueous solution is controlled and the liquid is passed while adding an operation to raise the DO when the amount of DO decreases, the polymerization inside the resin tower (or tank) does not occur for a long time for the first time. Stable operation is possible. As an operation for raising the DO, a method of increasing the oxygen concentration of the gas to be brought into contact with the AM aqueous solution before passing through the resin tower. A method of pressurizing a container for bringing an AM aqueous solution into contact with oxygen or an oxygen-containing gas before passing through a resin tower. Is taken. By these methods, the dissolved oxygen concentration at the outlet of the resin tower can easily be substantially maintained at 2 ppm or more.

As the cation exchange resin to be used, ordinary styrene cation exchange resins (for example, Amberlite IR-120B, IR-124, Diaion S)
K-1B, SK-10, etc.). Next, the AM aqueous solution from which copper has been removed is concentrated to 50% by a concentration device, and after decoloring with activated carbon, a good AM monomer can be obtained as a raw material of an AM polymer.

[0017]

Next, the present invention will be described in more detail with reference to examples. Example 1 An aqueous AM solution was synthesized by catalytic hydration of acrylonitrile using a copper-containing catalyst (K-product: improved CDT-60). A 20 L stainless steel reaction tank was used as a reactor. 2.2 kg of the above catalyst was previously charged in a reaction tank, and acrylonitrile and water were supplied thereto at a rate of 2.8 kg / Hr and 6.53 kg / Hr, respectively, and the reaction was carried out at 120 ° C. with stirring. Note that copper nitrate was added as a reaction promoting stabilizer so that the copper ion concentration in feed water was 5 ppm.

The reaction product is separated from the catalyst by a filter and extracted, and then unreacted AN is distilled off under reduced pressure.
A 25% aqueous solution of M was obtained. This solution contains 30 copper ions.
ppm dissolved, and its pH was 6.5. This A
The M aqueous solution was passed through a column filled with 1.0 L of an H-type cation exchange resin Amberlite IRC-76 at SV 4.0 / Hr and LV 3.0 m / Hr at a temperature of 40 ° C. while being in contact with air. The resulting solution had a pH of 5.5, copper ions of 15 ppm, and a dissolved oxygen concentration of 10 ppm.

The liquid thus obtained is brought into contact with air to replenish DO to 10 ppm, and a column filled with 1.0 L of Na-type cation exchange resin Amberlite IR-120B is charged with SV 4.0 / Hr, LV 3.0m / Hr, temperature 40 ° C
Under the conditions described above, the solution was passed while monitoring the dissolved oxygen concentration of the liquid at the outlet of the tower with an online dissolved oxygen meter. On the third day after the start of the flow, the DO of the outlet liquid became 5 ppm. Therefore, oxygen is mixed with the air that is replenishing DO, and the air: oxygen ratio is adjusted to 85:
It was 15. The DO in the AM aqueous solution at the entrance of the resin tower at this time
Was 15 ppm, and the DO of the liquid at the outlet of the resin tower was as high as 8 ppm. After another 5 days, DO at the outlet of the resin tower is 5 ppm
The oxygen supply was further increased, and the air: oxygen ratio was 57:43. D at the entrance of the resin tower at this time
O was 25 ppm, and DO at the outlet of the resin tower rose to 10 ppm. By repeating such an operation, DO at the outlet of the resin tower was kept at 2 ppm or more. As a result, 30
The operation was extremely stable without producing a polymer of AM for one day, and the copper concentration of the obtained liquid was 10 ppb or less.

Comparative Example 1 In the same manner as in Example 1, DO was supplied with air before passing through the resin tower, and the operation was continued without controlling the DO of the AM aqueous solution at the outlet of the resin tower. At this time, D at the entrance of the resin tower
O was usually 10 ppm. On the third day after the start of the passage, the DO of the outlet liquid became 5 ppm, and two days later, the D
When the amount of O became 1 ppm, a polymer of AM was confirmed inside the resin tower, and the passage of liquid was impossible, so that the operation could not be continued.

Comparative Example 2 Instead of the air of Comparative Example 2, a mixture of air and oxygen at a ratio of 57:43 was brought into contact with an AM aqueous solution to flow through a resin tower. At this time, the DO of the AM aqueous solution was constantly controlled at 25 ppm. On the 10th day after the start of the passage, the DO at the outlet decreased to 5 ppm, but the operation was continued. Two days later, the DO at the outlet of the resin tower was 1 ppm.
Then, a polymer of AM was confirmed in the resin tower, and the passage of liquid was impossible, so that the operation could not be continued.

Comparative Example 3 The solution after copper removal in Example 1 was concentrated to give an aqueous solution of 50% AM. 700 ml of this AM aqueous solution was charged into a 1 L glass container, and the AM aqueous solution was brought into contact with a mixture of nitrogen and air at a ratio of 45: 1 while the A solution was heated at a temperature of 60 ° C.
An M aqueous solution was subjected to a polymerization stability test. At this time, the dissolved oxygen concentration in the AM aqueous solution was 0.1 ppm. Further, even after 40 days from the start of the test, the AM aqueous solution remained in the AM aqueous solution.
No polymer was found.

[0023]

According to the present invention, it is possible to remove a trace amount of copper from an aqueous acrylamide solution for a long time, stably and economically by a catalytic hydration reaction of acrylonitrile, which is extremely large for industrial production of acrylamide. It gives profit.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Kazuo Nakayasu 2-3-3 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Denko KK Kawasaki Plant (56) References JP-A-52-100418 (JP, A) 52-91818 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C07C 231/24 C07C 233/09

Claims (1)

(57) [Claims] 1. Purification of an aqueous acrylamide solution obtained by a contact hydration method of acrylonitrile with a cation exchange resin while maintaining the dissolved oxygen concentration in the aqueous acrylamide solution at the outlet of a resin tower or a resin tank at 2 ppm or more. A method for purifying an aqueous acrylamide solution, comprising: