JPH01165534A - Polymerization inhibitor for styrenes - Google Patents

Abstract

PURPOSE:To provide a polymerization inhibitor for styrenes suitable to be used in the high-temperature distillation and recovery of styrenes and composed of piperidin-1-oxyl and its derivative having sufficiently high polymerization inhibiting activity and easily soluble in ethylbenzene and styrene. CONSTITUTION:The objective polymerization inhibitor usable especially in the distillation and recovery of styrenes at a high temperature (about 80-130 deg.C) is compound of piperidin-1-oxyls of formula I [R is H, CH3, C2H5, C3H7 or C4H9; X is H, =0 or -OR' (R' is H, 1-16C alkyl or group of formula II)]. The amount of the inhibitor is >=0.002wt.%, preferably 0.01-0.2wt.%. The polymerization inhibitor is preferably continuously supplied to the distillation column of a styrene-production process in the form of an ethylbenzene solution or a solution in ethylbenzene heavy end.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the production of styrenes, and more particularly to a polymerization inhibitor used when styrenes are distilled and recovered at high temperatures.

[Conventional technology]

Many compounds have been studied as polymerization inhibitors for styrenes. However, the polymerization behavior of styrenes is
Therefore, polymerization inhibitors that are effective at low temperatures often exhibit almost no activity at high temperatures, such as those encountered during styrene distillation (about 80 to 130° C. lf). In addition, although ordinary polymerization inhibitors are generally effective in the presence of dissolved oxygen, the amount of dissolved oxygen in the distillation column during styrene production is extremely small, and therefore some may lose their ability to inhibit polymerization under such conditions. many.

For example, t-butelcatechol, hydroquinone monomethyl ether, or phenothiazine, which have a high inhibitory ability in a low temperature range, show almost no polymerization inhibitory activity in a high temperature range during styrene distillation.

Under these circumstances, sulfur has conventionally been used to prevent styrene polymerization in the distillation column during the final purification distillation step when producing styrene by dehydrogenating ethylbenzene. However, since the ability of sulfur to prevent polymerization is not necessarily sufficient, a multineedle-like distillation residue called styrene bottom is formed. Since such by-products contain sulfur, their incineration poses problems from the viewpoint of air pollution.

Therefore, the development of heavy inhibitors to replace sulfur has been considered, and the following proposals have been made. % opening 48-868
No. 26, No. 49-75541, No. 49-72219, No. 49-124001, No. 49-81325, No. 49-66687, and each publication. However, these known polymerization inhibitors have low polymerization inhibitory ability9, have sublimation or exfoliation properties, have poor thermal stability and easily generate No gas, and have low solubility. , which is not necessarily satisfactory.

Furthermore, methylated benzoquinone-4-oxime (Japanese Patent Publication No. 55-37974), which is one of the most active compounds among known polymerization inhibitors, has a slightly higher solubility in ethylbenzene and styrene. Although there are some, it is still not enough.

[Problems to be Solved by the Invention: 0 Points] Therefore, the properties required as a polymerization inhibitor are: 1) having sufficient polymerization inhibitory activity; 2) Solubility in ethylbenzene and styrene. However, according to conventionally proposed techniques, there is no polymerization inhibitor that completely satisfies these two conditions.

[Means for solving problems]

As a result of extensive research to develop a polymerization inhibitor that satisfies the above two conditions, the present inventors discovered that piperidine-1
It has been discovered that a polymerization inhibitor composed of -oxyls has extremely excellent polymerization inhibiting ability against styrenes and excellent solubility in aromatic compounds such as ethylbenzene and styrene, and has thus arrived at the present invention.

The piperidine-1-oxyls of the present invention are piperidine-1-oxyls represented by the following general formula and derivatives thereof.

凰 (wherein, R is H, CH3, C2H5, C3H7+ C
4H9.

X represents H,=O,-OR', R' is H2
They are a Cl-C16 alkyl group and -C-o. ) The amount of piperidine-1-oxyl to be used should be at least 0.002% by weight, and can be changed depending on the necessary #IK and the usage situation, but generally it is 0.005~
0.5, preferably 0.5. The amount of O is about 1 to 0.2% by weight (all based on styrene).

The polymerization inhibitor of the present invention can be used at any stage from the production of styrene to its storage, but the most advantageous method of use is to take advantage of its high polymerization inhibitory ability and high solubility at high temperatures. This is a method in which ethylbenzene solution or ethylbenzene K [dissolved in the ethylbenzene heavy end produced during ethylbenzene production] is supplied to the distillation column during production. Styrene is usually produced by gas-phase catalytic dehydrogenation of ethylbenzene, but in that case, styrene is obtained as a mixture with unreacted ethylbenzene, which is continuously distilled to separate styrene. The polymerization inhibitor of the present invention is continuously fed to the column as a solution of ethylbenzene or ethylbenzene heavy ends to the above-mentioned extent.

The solubility in ethylbenzene (25°C) of representative compounds of the piperidine-1-oxyls of the present invention and known polymerization inhibitors is shown in the table below.

〔Example〕

Next, the present invention will be explained by giving examples.

Example 1 In a 100 d three-bottle round bottom flask, 4 ogl of purified styrene monomer (SM) and 2.2, 6.
6-titramethelpiperidine-1-oxyl 200 p
pm and bubble high-purity nitrogen into the liquid for 20 minutes to degas the dissolved oxygen in the styrene, then raise the temperature to 110°C and measure the amount of polymer produced after 1 and 2 hours. did.

The amount of polymer produced is calculated by mixing the above monomer liquid with methanol and 1
The turbidity of this solution was determined using a fluorophotometer.

The results were as follows.

Polymer production amount (weight! 1%) After 1 hour 0.0% 2z O, 35% Examples 2 to 4 Polymerization inhibitor was 4-oxo-2,2,6,6-titramethelpiperidine-1-oxyl (Example 2), 4-nonenexy-2,2,6,6-titrametherbiperidine-1-
Oxyl (Example 3) and 4-benzoyloxy-2,2
, 6,6-tetramethylpiperidine-1-oxyl (Example 4). The results are shown in Table IK.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 without adding a polymerization inhibitor. The results are shown in Table-1.

Comparative Example 2.3 The same procedure as in Example 1 was carried out using dinitrophenol (Comparative Example 2) and 2,6-dinitro-p-cresol (Comparative Example 3) as polymerization inhibitors.

The results are shown in Table 1.

(Leaving space below) Table 1 As is clear from the above Examples and Precepts, the piperidine-1-oxyls of the present invention not only have good solubility in aromatic compounds such as ethylbenzene, but also have an excellent polymerization prevention effect. It is an industrially useful polymerization inhibitor.

Patent applicant: Mitsubishi Yuka Co., Ltd. Agent: Patent Attorney Masahisa Nagatani Agent Patent Attorney Takaya Yamamoto

Claims (1)

[Claims] A styrene polymerization inhibitor consisting of piperidine-1-oxyls.