HU209668B - Process for purifying of styrene and its derivates - Google Patents

Description

The present invention relates to a process for the purification of styrene and its derivatives as monomers, more particularly to the removal of phenolic inhibitors from these monomers. It is known that these monomers, such as styrene, methylstyrene, alpha-methylstyrene, butylstyrenes or mono- and dibromo-styrenes, and mixtures thereof, can be stored and transported from 5 to 50 p. p. m. concentrations of polymerization inhibitors. The most commonly used inhibitor is para-tert-butylpyrocatechin (TBC), but there are other inhibitors, such as hydroquinone monomethyl ether, dinitrophenols and picric acid. However, these inhibitors can degrade the quality of the polymer compound to be prepared and therefore sometimes need to be removed from the monomer.

Several methods are known for this purpose, for example:

(i) Monomer distillation to remove inhibitor content (in distillation residue). This process is very expensive due to the high power consumption and the use of complex equipment.

ii) Wash with aqueous sodium hydroxide solution. This process requires an intensive aqueous wash after the sodium hydroxide wash to remove any remaining sodium chloride in the monomer. Further, a final drying is usually required thereafter to eliminate residual moisture.

iii) The contaminated monomer is allowed to pass over an anion exchange resin bed (the resin may have tertiary and / or quaternary terminal groups, both free and in salt form; the disadvantages of this process are very common: the resin material is very short lived is used in salt form and the treated monomer has an unpleasant odor due to the presence of trace amounts of amine compounds when the resin is used in free form. There are also known purification processes in which the vinylaromatic monomer is passed through an alumina fixed bed. which are not always compatible with the economics of the process due to the short life of the absorbent material, it is often necessary to replace the bed, which requires a complete set of operations such as removal of the monomer absorbed by the material, emptying and g and loading fresh material.

Methods (i) to (iii) and the above purification procedures are described in detail in British Patent No. 1,386,419.

In order to prolong the life of alumina and thereby reduce the number of operations to replace it, a recent publication (Japanese Patent Publication No. 57,535/1988, the disclosure of which is incorporated herein by reference), proposes that the velocity of the monomer should be very low. For example, it has been found that alumina results in a longer life if the spatial velocity of 0.8 / h is changed to a spatial velocity of 0.01 / h or less. Therefore, the amount of purified monomer that can be obtained - per unit weight (or unit volume) of alumina before the alumina is deactivated - is much higher. The "normal" field velocity values are 0.1 to 10 / hour. However, this method forces the operator to perform complicated operations with the purifying column; furthermore, the total amount of purified monomer that can be recovered before the alumina deactivation threshold is reached is not a high value. During periods of operation characterized by "low" space velocity (below 0.1 / hour), the presence of unwanted products is eliminated.

According to the present invention, the precise choice of all operating conditions provides the opportunity to avoid changing the space velocity, eliminating periods at low space velocities, and surprisingly large increases in the total amount of purified monomer.

In the broadest sense, the present invention relates to a process for the purification of styrene and its derivatives as monomers containing a phenolic polymerization inhibitor. In this process, the contaminated monomer is fed to a fixed bed of alumina particles. The average size of the alumina particles is 0.5 to 3 mm. The monomer has a spatial velocity of 0.5-7.5 / h and a linear monomer velocity of 0.125-45, preferably 1.2-45 m / h. Space speed is defined as the following ratio:

monomer (m / h) _ the apparent volume of alumina (m ³ ) where "apparent volume" is the volume of the empty cleaning space (chamber, vessel), which of course differs from A1 ₂ O ₃ real (true) volume of particles. Linear velocity is the ratio of the flow rate of the monomer to the normal part of the purification space (chamber). The term "monomer" refers to both the monomer alone, for example styrene, and mixtures of styrene with other styrene derivatives. A preferred inhibitor of the process of the present invention is para-tert-butylpyrocatechin.

The monomeric inhibitor to be purified has a content of 5-50 ppm (preferably 5-15 ppm). The preferred specific surface area for alumina is 150-270 m ² / g. The monomer purification devices according to the invention may be of different types. Outstanding results can be achieved by feeding the monomers to be purified into a vertical, cylindrical column with a fixed bed of alumina. The column has an inlet, preferably at the bottom of the cylinder. Aluminum oxide can be spherical (very low loss due to rubbing, wear) or granules (grains with irregular edges). Alumina has a longer life when the particle size is smaller. This result is independent of the form of alumina used (balls, small rolls, granules, etc.). This has never been investigated.

The examples below are only illustrative2

The present invention, however, is not intended to limit the scope of the invention. In the assays, breakage above the threshold (end of absorbent life or "deactivation threshold") has traditionally been measured to coincide with the point at which p-tert-butyl pyrocatechin in the treated monomer is 2 p. p. m. is equal to. This limit is far more cautious (cautious) (an aspect of many polymer compound requirements) than the limit in the cited Japanese disclosure, where this threshold is 8 p. p. m.

Example 1 (comparative study)

Aluminum oxide granules, commercially known as "COMPALOX AN / V-850", manufactured by Martinswerk GmbH, Bergheim (Germany) and having an average size of 5-10 mm, were loaded into a 25 cm high 2.5 cm diameter vertical column. Then, at room temperature (20 ° C), a styrene monomer containing 12 ppm paraterc-butylpyrocatechin was passed through it at a space speed of 6 / hour (linear velocity = 1.5 m / hour). Purification is possible only with 150 volumes of styrene / volume of Al ₂ O ₃ in 1.04 days, which is ahead of the deactivation threshold in time. Data and results are shown in Table 1.

Example 2

The test was carried out under the conditions described in Example 1, but using alumina having a particle size of 1-3 mm, sold under the trade name "COMPALOX AN / V-813", with a specific surface area of 170 m ² / g. The amount of styrene that can be purified is much higher in 12.50 days (1800 volumes of styrene / 1 volumes of Al ₂ O ₃ ).

Example 3

The test was performed under the conditions described in Example 2, but using a space velocity of 0.5 / hr (linear velocity = 0.125 m / hr). Amount to be purified: 4500 volumes of styrene / 1 volumes of Al ₂ O ₃ 375 days.

Example 4

The test was carried out under the conditions described in Example 1, but the alumina used had an average particle size of 0.5 to 2 mm and was sold under the trade name "COMPALOX AN / V-802". The amount of purified styrene is greater than 2500 volumes of styrene / volume of alumina in more than 17.36 days.

Example 5 (Comparative Study)

The tests were performed under the conditions described in Example 2, but at a much higher field speed (14 / h) (linear speed = 3.5 m / h). The amount of purified styrene is 1.550 volumes of styrene / volume of alumina in 4.61 days.

Example 6

The alumina granulate of Example 2 was loaded into a column 4.5 cm in diameter and 6 m high. 10 p.m. p. m. Styrene monomer containing para-tert-butylpyrocatechin was added to the column at a rate of 7.1 / h (linear speed = 42.6 m / h). The amount of styrene to be purified was 2200 volumes of styrene / volume of alumina in 12.91 days.

Example 7 (Comparative Study)

The alumina granules of Example 2 having a particle size of 1-3 mm were loaded into a column 4.5 cm in diameter and 3 m high. Then 10 p. p. m. styrene monomer containing para-tert-butylpyrocatechin was passed through it at a space speed of 14 h (linear velocity = 42.0 m / h). 1250 volumes of styrene / 1 volumes of alumina were purified in 3.72 days.

Example 8 (Comparative Study)

Spherical aluminum oxide, traded under the trade name "ALUMINE-ACTIVATE A 2-5" and Rhone Poulenc (France) with a particle size of 2-5 mm, was loaded into a 6 m high 4.5 cm diameter column. Then 9 p.m. p. m. styrene monomer containing para-tert-butylpyrocatechin was added to the column at a space velocity of 6.4 / hr (linear velocity = 38.4 m / hr). Feeding volume: 1200 volumes of styrene / 1 volumes of alumina in 7.81 days.

Example 9

A spherical aluminum oxide with a particle size of 1.5-2.5 mm and a specific surface area of 270 m ² / g, trade name "ALUMINE ACTIVÉE A 1.5-2.5", was loaded into a 6 m high 4.5 cm diameter column. Styrene monomer containing 9 ppm para-tert-butylpyrocatechin was then added to the column at a space speed of 6.8 hours (linear rate = 40.8 m / hour). In 13.4 days, 2200 volumes of styrene / 1 volumes of alumina were purified.

Example 10 (Comparative Study)

6.4 mm spherical alumina, traditionally Alcoa H151, manufactured by Alcoa Chemicals Division (USA), was loaded into a column 25 cm high by 28 mm in diameter. Average 12 p. p. m. The styrene monomer containing p-tert-butylpyrocatechin was then fed into the column at a space speed of 4 h (linear velocity = 1.0 m / h). In 1.56 days, only 150 volumes of styrene / 1 volume of alumina were purified.

Table 1 shows the data and results for each example.

HU 209 668 B

Table 1

Example 1 (*) 2 3 4 5 (*) 6 7 (*) 8 (*) 9 10 (*) Form of A1 ₂ O ₃ G G G G G G G S S s A1 ₂ O ₃ 0 (mm ² ) 5-10 1-3 1-3 0.5-2 1-3 1-3  1-3 2-5 1.5-2.5 6.4 column 0 (cm) 2.3 2.3 2.3 2.3 2.3 4.5 4.5 4.5 4.5 2.8 column height) 0.25 0.25 0.25 0.25 0.25 6 3 6 6 0.25 inhibitor (p. m.) 12 12 12 12 12 10 10 9 9 12 space speed (hours ^-1 ) 6 6 0.5 6 14 7.1 14 6.4 6.8 4.0 linear speed (m / h) 1.5 1.5 0,125 1.5 3.5 42.6 42.0 38.4 40.8 1.0 purified styrene (v / v) 150 1800 4500 more than 2500 1550 2200 1250 1200 2200 150 deactivation threshold (days) 1.04 12.50 375 more than 17.36 4.61 12.91 3.72 7.81 13.48 1.56

G = granulate S = spherical (*) comparator

Claims (8)

A process for purifying styrene and its derivatives containing a phenolic polymerization inhibitor as a monomer by passing over a fixed bed containing alumina particles to a monomer spatial velocity of 0.5-7.5 / h and a linear monomer velocity of 0.125-45 m / hours, characterized in that the cleaning step uses alumina having a particle size of 0.5 to 3.0 mm. The method of claim 1, wherein the linear velocity is set to 1.2 to 45 m / h. The process according to claim 1 or 2, wherein the monomer to be purified is styrene. The process according to claim 1 or 2, wherein the inhibitor is para-tert-butylpyrocatechin. The process according to claim 1 or 2, wherein the amount of inhibitor is from 5 to 50 µg. p. m. is set to. 6. The method of claim 5, wherein the amount of inhibitor is from 5 to 15. p. m. is set to. 7. A process according to any one of claims 1 to 3, characterized in that alumina with a specific surface area of 150-270 m ² / g is used. 8. A process according to any one of claims 1 to 3, characterized in that spherical alumina particles are used.