JPS58103506A - Removal of acrylonitrile monomer - Google Patents

Abstract

PURPOSE:To carry out economical and efficient removal of acrylonitrile from a synthetic resin, by injecting steam into a synthetic resin in hot water to reduce the acrylonitrile content to a specified value and then adding an aqueous alkali solution to the mixture. CONSTITUTION:Steam is blown into an acrylonitrile synthetic resin containing unreacted acrylonitrile monomer under agitation in hot water to reduce the acrylonitrile monomer content to below 5,000ppm, preferably below 3,000ppm. Then, an aqeous alkali solution is added to the mixture to transfer the residual acrylonitrile monomer into the aqueous phase and thereby reduce markedly the content of the residual acrylonitrile in the synthetic resin. Thus, it is possible to reduce easily the content of acrylonitrile remaining in the resin to below 50ppm. As the acrylonitrile synthetic resins which are applicable, there can be mentioned As resins, ABS resins, acrylonitrile resins, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing acrylonitrile monomer from synthetic resins.

Recovery and removal of unreacted acrylonitrile monomers in acrylonitrile-based synthetic resins is extremely important from the economic standpoint and from the standpoint of hygiene issues such as odor and toxicity.

41, when acrylonitrile resins are used in applications where they come into direct contact with food or people I, the toxicity of residual acrylonitrile monomers becomes a problem, and extremely strict removal is required.

However, in the case of any acrylonitrile-based synthetic resin, it is economically difficult to carry out polymerization until all of the acrylonitrile monomers used are converted into polymers.
Also, since it is not desirable in terms of quality, some unreacted 7-crylonitrile monomer remains in the polymerized resin.

It is necessary to remove the tolyl monomer, and various methods have been developed for K to date.

That is, 7 acrylonitrile monoi-
Conventional methods for removing acrylonitrile monomer include (1) heating a resin containing unreacted acrylonitrile monomer, extruding it into a string and treating it under reduced pressure; (2) using an extruder with a pent; (3) ) method using steam distillation, (4) extraction method using a solvent, etc. however,
Such conventional methods have the following drawbacks.

In other words, method (1) has a large surface area for volatilization, but the surface is not renewed, resulting in poor deaeration efficiency and efficiency.Method (2) requires multi-stage venting to improve deaeration efficiency. In addition, it is necessary to raise the resin temperature to apply external heating or shearing force, and if the molecular weight of the polymer decreases or the resin contains an elastic material, dispersion of a rubber-like elastic material may be necessary. This results in particle destruction and resin deterioration. Although method (3) is relatively easy to operate, it is far from economical because it requires a large time loss and consumes a large amount of steam energy to remove the acrylonitrile monomer to a low concentration. In addition, method (4) requires a complicated process due to the recovery of the solvent and the like.

Although any of the methods K(1) to (4) are said to be the best, one of the challenges in the industry is to efficiently remove residual acrylonitrile monomers from acrylonitrile-based synthetic resins.

The inventors of the present invention aimed to improve conventional methods, particularly steam distillation, and arrived at the present invention after repeated studies with the aim of economically and efficiently removing acrylonitrile monomers.

In the present invention, a synthetic resin containing an acrylonitrile monomer is mixed in hot water and blown with steam to bring the content of the acrylonitrile monomer to 5000 ppm or less, preferably 3000 ppm or less, and then an alkaline aqueous solution is added to remove the remaining acrylonitrile monomer. This is a method for removing acrylonitrile monomer from a synthetic resin, which is characterized by transferring the acrylonitrile monomer into an aqueous phase.

Examples of the acrylonitrile-based synthetic resin used in the present invention include AS resin, AB8 resin, and acrylonitrile resin.

As an alkaline aqueous solution, sodium hydrosulfide (Na1l
H) - Sodium sulfide (Nat8) * There is an aqueous solution such as sodium hydroxide (NaOH), and the amount added is 0, 1 to 2.0 mol to the remaining acrylonitrile monomer, and 0.5 to 1.0 mol to 41. The corresponding amount and contact time are usually about 10 to 120 minutes, preferably about 30 to 120 minutes.

In this project @, by adding an alkaline aqueous solution to the acrylonitrile-based synthetic resin dispersion containing a trace amount of acrylonitrile monomer after steam distillation, the acrylonitrile monomer is changed into a hydrophilic substance, transferred to the aqueous phase, and absorbed into the synthetic resin. It becomes possible to significantly reduce the amount of residual acrylonitrile monomer, and the amount of acrylonitrile monomer in the normal resin can be reduced to 1FjK 50 ppm or less.

The method of the present invention does not require any special extractant (for example, methanol, etc.), the process is simple, and the processing time is short. It is preferable to apply

Examples 1 to 8 An A8 resin suspension containing about 2 weight of unreacted acrylonitrile monomer was heated in hot water at 95° C. for 5 k).
/cst" G saturated steam was blown in for 70 to 90 minutes to perform steam distillation, and the acrylonitrile monomer concentration in the As resin was 1000 to 2000 ppm.

Add sodium hydrogen sulfide (Na8H) to this suspension as an aqueous solution and add 0.0% to the 7-acrylonitrile monomer in the As resin.
5 to 1.0 molar phase was added, and the mixture was allowed to stay at a temperature of 85 to 95° C. for a certain period of time, and this dispersion was sampled, and the acrylonitrile monomer in the As resin was measured by the gas grottograph method.

The concentration of acrylonitrile monomer in the As resin after steam distillation We (ppy*) e The concentration of acrylonitrile monomer in the As resin after addition and residence of the sodium bisulfide aqueous solution Ws (ppm) The reduction results are shown in Table IK.

Examples 9-16 An A8 resin suspension containing about 2 wt. of unreacted acrylonitrile monomer was mixed in 95° C. hot water for 5 k).
/am''G saturated steam was blown in for 70 to 90 minutes to perform steam distillation, so that the acrylonitrile monomer concentration in the A8 resin was 1000 to 2000 ppm.

An aqueous solution of sodium hydroxide (NaOH) was added to this dispersion, and the amount of sodium hydroxide (NaOH) was added to the dispersion to give an acrylonitrile monomer in A8 resin.
An amount equivalent to 5 to 1.0 moles was added, and the mixture was allowed to stay at a temperature of 85 to 95°C for a certain period of time.

The results are shown in Table 2.

Examples 17-20 5 kg/lx"G saturated steam was blown into a coagulated suspension of Al11 resin containing about 0.6 g of unreacted acrylonitrile monomer for 20-30 minutes while mixing in hot water at 95°C. By performing steam distillation, the acrylonitrile monomer concentration in MuB8 resin was approximately 1000 ppm.

To this suspension, sodium bisulfide or sodium hydroxide was added in an amount equivalent to 0.5 to 1.0 mole, respectively, based on the acrylonitrile monomer in the AB8 resin, and the suspension was allowed to stay at a temperature of 90° C. for a certain period of time.

The results are shown in Table 39 and Table 4.

Claims (1)

[Claims] Synthetic resin containing acrylonitrile monomer is mixed with hot water and steam is blown into it to create acrylonitrile monomer! - A method for removing acrylonitrile monomer from a synthetic resin, which comprises reducing the content of acrylonitrile to 5000 ppm or less, and then adding alkaline water SII to transfer the remainder of the acrylonitrile monomer into an aqueous phase.