DE1942094A1 - Process for cleaning up contaminated glycols - Google Patents

Description

P ATc NTA N WA Lt *

dr. w: Schalk dipl.-ing. p. Wirth dipl.-ing. c. Dan ν en be rc DR. V. SCHMIED-KOWARZIK DR.P. WEINHOLD

6 FRANKFURT AM MAIN 1 Q / O Π Q /

OR. ESCHENHEIMER STR. 39 I vj H t U J 4 SK'SK

C-7388-C

Union Carbide Corporation 270 Park Avenue
New York, NY 10 * 01? / UNITED STATES

Process for refining contaminated glycols

The present invention relates to a method of removal the impurities present in glycols, especially in ethylene glycols.

Ethylene glycol is used extensively in the manufacture of polymeric terephthalate esters used. Such polymeric materials can either be obtained by direct esterification of ethylene glycol and terephthalic acid or by heating ethylene glycol with a lower monohydric alcohol ester of the acid such as dimethyl terephthalate. With everyone In the reaction, ethylene glycol is used in excess of the theoretical amount in order to achieve a practically complete reaction of all of the terephthalic acid ensure in the reaction mixture. Some of the excess ethylene glycol can be distilled off during the reaction. After finished However, the reaction is practically all of the ethyl glycol excess van polymeric material (polyester) by distillation, washing with water or a combination of these procedures is removed.

0098Ü9 / 1736

The ethylene glycol recovered from the above process is generally low with minor amounts of impurities such as sodium terephthalate. molecular. Aldehydes, acetals, dioxolanes and phenols contaminated * Die ^;

Presence of one or more of the impurities mentioned confers

the ethylene glycol obtained from the above process, one deep . reddish brown color. Although this ethylene glycol contaminated again could be used to esterify terephthalic acid are those obtained Polyester, of such poor color and quality that it was considered synthetic Fiber production, an important use of these polyesters, are unsuitable. Similarly, the presence of such impurities does in diethylene glycol the glycol for the production of polyesters, the for the production of polyurethane foams, fibers and films are used. can, unsuitable.

The ethylene glycols obtained from the above reactions are referred to below as "used" glycols as opposed to "unused or ^{virgin" 11} ("virgin") glycols obtained by hydrolysis of ethylene oxide. Unused glycols are often contaminated with impurities such as aldehydes, Acetals, dioxolanes and certain oxidative products contaminated by glycols The presence of these contaminants in unused glycols makes them unsuitable for polyester manufacture for use as fiber.

Various methods of purifying glycols have been proposed. For example, U.S. Patent 2,788,373 describes a method of cleaning of ethylene glycol, that with alkali terephthalates, aldehyde polymers and ethylene glycol reactants is contaminated. The described Method consists in diluting the contaminated ethylene glycol with Water, acidifying the obtained aqueous Äfchyleneglykolllösung with a

73 6

suitable acid for precipitating the soluble solid material including the alkali terephthalate, the removal of the precipitated solid .Material from the aqueous solution, the dehydration of the precipitate-free aqueous solution under acidic conditions to hydrolyze the high-boiling one Acetal impurities in low boiling materials that come with water can be distilled off as an azeotrope, neutralizing the dehydration Ethylene glycol and the distillation of the neutralized ethylene glycol.

Another method (see U.S. Patent 3,367,8 ^ 7) uses a Series of VerdarapfunRon and successive folßemie, Ublicho distillations dos contaminated glycols. The end product is filtered through a bed of activated animal charcoal to ensure complete removal of impurities.

t deliver. - , j

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ϊ The multi-step process of US Pat. No. 2,788,373 is quite cumbersome j

and often impractical on a large scale. The removal of the above-mentioned impurities is often difficult to achieve by common distillation processes. i

The present invention therefore relates to a method for cleaning

-if- ' \ "

of used and unused glycols by removing the above impurities through the use of a new distillate process under a critically regulated distillation environment.After purification according to the process according to the invention, the ethylene glycols obtained have proven to be extremely useful and industrially acceptable for the production of FbIy es ^: for Proven fiber purposes

009809/1736

According to the invention, used or unused glycol is in any suitable form Distillation device in the presence of a controlled amount of water in the stripping section of the distillation device. The presence distilled of water increases * the coefficient of effectiveness of those present in the glycol Impurities and facilitates their removal with the distillate stream. Therefore, this distillation process is referred to in the present application as "Enhanced distillation" denotes the removal of impurities by increasing the activity coefficient of the impurities in the glycol is achieved. In other words, the presence of regulated amounts of water

«In the stripping section of the still causes an increase (Enhancement) of the relative volatilities of the impurities with respect to the Glycol, which enables it to be removed overhead in the distillate stream Then the bottom product consisting of the glycols becomes a common one Subjected to distillation to obtain ethylene glycol from the above mentioned impurities is practically free.

Thus, the method according to the invention comprises in principle a primary (reinforced) Distillation stage through which the used or unused glycol is distilled in the presence of a regulated amount of water in the Abs tripp section will · Virtually all impurities are considered to be overhead with the water Distillate removed The bottom product from the primary distillation stage of glycols, which is practically free of the above-mentioned impurities, is refined (distilled) in a second distillation stage to obtain the desired glycol.

The temperature at the top of the primary destination zone is usually the boiling point of water at working pressure, while the temperature at the bottom of the primary distillation zone is below the decomposition temperature of the material to be recovered

Glycols

009809/1736

must lie. This decomposition temperature is usually below about 25O ⁰ C, and for each special glycol is usually van expert readily ascertainable ·

• ·

The pressure in the primary distillation zone should be between approximately 50 mm Hg Section. up to about atmospheric pressure, preferably from about 100 mg Hg abs up to about 300 mm Hg abs, be

As mentioned, a sufficient amount of water must be present as liquid in the stripping section, the enhanced distillation stage, in order to achieve the necessary degree of enhancement of the activity coefficients of the impurities. Thus, the concentration in the boiler (digester) should be kept between about 0.05-2 wt .-%, preferably about 0.1-0.5 wt .- % , based on the weight of glycol. A water concentration of about 30-80 wt. #, Preferably about ² K) -OO wt.

. To ensure practically complete removal of the impurities in the primary distillation zone, the weight ratio of reflux to distillate can be varied from about 0.1-5 _f 0, preferably from about 0.2-2.

That made up of glycols, a little water and small amounts of non-volatile residues existing bottom product from the primary distillation zone is converted into a second distillation zone in which the desired, of the above Impurities practically free glycol is obtained, raiELniert, d »h * distilled · The working conditions in the second distillation zone are invented. duly not per se decisive and voa specialist for the acquisition of each *

009809/1736

- 6 special glycols easily identifiable.

In some cases, e.g. if the glycol (used or unused) is in its, previous refining during its production of a heavy thermal or inferior to oxidative decomposition and / or hydrolyzable impurities it may be necessary to add the primary distillation zone " add a mineral acid such as sulfuric acid, phosphoric acid, hydrochloric acid, etc., to ensure complete removal of most of the impurities present in the glycol. The amount of acid added in these cases must have a pH below about?, preferably between about 2-5, im Stripping section of the primary distillation zone result.

In general, acidification is in the removal of hydrolyzable impurities in contrast to or difference from non-hydrolyzable impurities necessary. The hydrolyzable impurities include dioxolanes, acetals, and compounds that combine by reaction with water Release glycol. In contrast, the non-hydrolyzable impurities are aldehydes, carbonyls and oxidative products, which are usually produced during manufacture these glycols are formed.

When cleaning glycols with these hydrolyzable contaminants you get a better quality product if you check the pH of the soil product from the increased distillation stage to a value above about? Set before refining.

[Both distillations are preferably carried out continuously, although they are also

j can be carried out semi-continuously or intermittently. Self-

j. ■ '

Continuous work is of course more desirable and of technical aspects Point of view more economical.

009809/1736 '*. .

If appropriate, that obtained from the secondary distillation column can be used Ethylene glycol through a bed of activated charcoal or a similar absor-

■ ·· ■ bating material can be filtered to remove trace amounts of impurities, which have not been removed in the primary distillation column, too remove.

The glycols to be purified by the process according to the invention can through

the following general formula can be represented:

R.

HO (CH ₉ -CHO) H <η

in which R can stand for hydrogen or a methyl or ethyl group and η is an integer of 1 to 4 · So means the above Foraek, when R is hydrogen, methyl or ethyl, ethylene glycol, propylene glycol or butylene glycol and, depending on the value of n, is that Glycol either mono-, di-, tri- or tetraethylene glycol, propylene glycol or -butylene glycol If R is, for example, hydrogen and n-1, then the above means Formula monoethylene glycol. It is further noted that where R represents a methyl or ethyl group, the above formula also includes various isomeric glycols means with head-to-head, tail-to-swan * or head-to-tail structure.

Glycols are e.g. monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, monopropylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, monobutylene glycol, dibutylene glycol, tributylene glycol and Tetrabutylene glycol or mixtures thereof.

The following examples illustrate the present invention without it su restrict.

009809/1736

Example 1 and 2

These examples show the purification of unused Monoäthyfengfykol by sucked, "dry" and "wet". Distillation.

The device used in these examples was the same and consisted of a first Öldershaw column with 20 trays and one with 22

Bottomed second Oldershaw columnEach column was provided with a back

(Kettle) Equipped with a flow boiler and reflux condenser.

The feed in each example was about 40 wt% monoethylene glycol Water and non-hydrolyzable impurities (aldehydes, carbonyls and oxidative products). Each time the charge was made for the introduction to the first Oldershaw column evaporates. The products obtained from the liquid and vapor streams are shown in Table 1.

Table 1

example 1 Steam- 2 98.1 more fluid
current 1.9 composition 98.3 liquid vapor
current - Water; Gew.-Ji 36.9 1.7 - Monoethyleglycolj wt .- ^ 59.7 - 39.7 100.0 , _ Diethylene glycol; Wt * - £ 3.3 57.2 Triethylene glycol and tetra
ethylene glycol; Weight % 0.1 100.0 3.0 all in all 100.0 0.1 100.0

In Example 1, the steam feed (essentially water) was used Liquid feed (-an monoethylene glycol rich) to the lo. or 5 * floor introduced above the boiler of the first Oldershaw column, while in Example 2 the steam feed as 5 x tray and the liquid feed was introduced on the 10th floor.

009809/1736

In both examples, the bottom product from the first column was used for the 10th Tray introduced above the kettle in the second Oldershaw column. A liquid sidestream (monoethylene glycol) became the second at the 20th floor Column withdrawn; To examine the purity of the glycol obtained, its UV transmission values were determined.

In both examples, water and impurities were removed overhead from the first column. The bottom product containing the glycols and some water was distilled in the second column, where refined monoethylene glycol was obtained as a liquid side stream. The bottom product in the second column consisted essentially of diethylene glycol, triethylene glycol, tetraethylene glycol and non-recovered monoethylene glycol. The working conditions in the first column are shown in Table 2, while the working conditions in the second column are shown in Table 3. The percentage. The permeability of the monoethylene glycols obtained in both examples is given in table b .

Table 2

example 009809 / 1 2 Pressure: mm Hg abs. 215 215 Temperature; ⁰ G ₀ head 68-113 78-113 10. Soil 132-138 116-121 Steam loading 95 95 Liquid feed 95 95 Soil material 165 165 " Weight ratio of reflux A O r \ 0 to distillate U, Ä U, <c Feed; G fluid 3723 5Ο56 steam 21 ^ 9 28 ^ 6 Distillate; G ¥ H5 5 & 7 Soil material; % 1561 2077 1736

- 10 - example Table 4 1 example 1 Example 2 upper 1942094 Tabel Pressure; now Hg abs. 100 Upper distillate wavelength distillate Temperature} ⁰ C. η »/ U bypass flow 2 head 122-130 350 83Λ 98.9 95.1 100 upper side stream of the 20 · floor 275 22.2 78.8 30.7 feed 95 220 0.0 26.7 0.0 136 Soil material 175 139 Weight ratio of reflux to
distillate 100 95 Feed; G 804 175-. ■ Distillate; G 24 100 upper side stream; G 536 1295 21 percentage permeability 915 Sidestream 100.0 97.9 76.9

As can be seen from Table 4, the moon ethylene glycol obtained in Example 2 had a higher permeability than the monoethylene glycol from Example 1 »Sq. For example, the secondary stream withdrawn from the second column in Example 2 had significantly higher values of the percentage UV permeability than that from the second column in Example 1 withdrawn secondary flow. The improved transmission is clearly visible when measuring at wavelengths of 275 and 220 mm. The permeability values at these wavelengths are precise crisis criteria for purity monoethylene glycol than that in 350 ml ^{of n} values obtained.

009809/1738

- ii - 19A209A

The improved permeability values of the secondary stream obtained in Example 2 show a lower level of impurities. Since in the process of Example 1 the water is mainly above the liquid feed * kungpunktes was present in the first column, there was an insufficient one There was water in contact with ethylene glycol in the stripping section of this Column. Therefore, the activity coefficients of the impurities present in the feed were not sufficiently enhanced and were therefore substantial Quantities of the same remained in the glycol.

In contrast, Example 2 describes a distillation process in which a substantial amount of water is allowed to be present in the stripping section of the first column , since the steam feed in this case was introduced below the liquid feed, contrary to the relative introduction points of the liquid and vapor feeds in Example 1. Therefore . the presence of substantial amounts of water in contact with the glycol increases the relative volatilities of the contaminants with respect to the glycols. Accordingly, the bottoms from the first distillation column contains a very small amount of impurities and the ethylene glycol recovered in the second distillation column is virtually free of impurities, as shown by the percent UV transmittance values in Table 4.

009809/1736

Example 2

This example shows the cleaning of used, terephthalic acid, Containing terephthalic acid esters and carbonyl compounds as impurities Monoethylene glycol.

• ·

\ The used glycol charge, which also contains smaller amounts of diethylene,.

j -

■ Glycol and triethylene glycol were absent, was ion exchanged with an equal amount Mixed with water and used as a hot charge (75 ° C) for 10

! Bottom (above the bubble) of a 2-tray Oldershaw column introduced, in which the impurities were removed as a distillate stream. _#

The bottom product from the above distillation consisted essentially of dry monoethylene glycol (about 0.15 wt .- # water) and smaller amounts • «on diethylene glycol and triethylene glycol; it became the 5 floor (above the

■ Bladder) of a 15-tray Oldershaw column was introduced. As a liquid side stream

Purified monoethylene glycol was sucked off from the 10th floor above the bladder; then its UV transmission value is determined. The results The examples are given in Tables 5 and 6. Table 5 shows the distillation results in the first Oldershaw column, while Table 6 shows those of the second distillation, i.e. the refining of the bottom product indicates from the first distillation column.

Table 5

Pressure on head; ran Hg abs 215 Temperature; ⁰ C. head 69 feed 80 + 10 Beechidongsboden (iq. Floor) 75 ~ Bladder 163-165 Weight ratio of reflux to λ η distillate 0.2 Feed; G 5122 Distillate; G 2871 Floor materiali g 009809/17 36 225V

- 13 - ; G 100 Table 6 134 140 142 145 »· 50 62o 18th 558

Table 6 /

Pressure on the head; mm-.Hg abs.
Temperature; ⁰ C.
head

10. Soil
Loading floor
bladder

Weight ratio of reflux to
distillate

Evil nicking; G

Distillate;

liquid sidestream from 10th floor; G

(1) = contains a maximum of 1.7 wt .- # ethylene glycol as determined by the potassium dichromate / sulfuric acid oxidation process.

The UV transmittances of the liquid secondary stream were 350.272 and 220 mm 100.0, 99.5 and 81.0, respectively

Example 4

This example shows the purification of used Mono ethyleng Iy kol, the in addition to terephthalic acid, terephthalate and carbonyl compounds, phenolic compounds Contains impurities.

The used GIy kolbe delivery was on the 35 * tray of a 40-tray Oldershaw column and water introduced into this column as water vapor at the 5 x tray above the bubble at a water / glycol weight ratio of 3.3. the The column was operated at atmospheric pressure, a bottom temperature of 189 ° C. and a weight ratio of reflux to distillate of 0.2. the end this column became overhead water along with practically all impurities removed · This overhead material contained a maximum of 0.12 wt .- ^ " Ethylene glycol according to the method specified in Example 3.

009809/1736

- i4 - y

Consisting essentially of ethylene glycol, and 1.5 wt _o - / 6 v / ater existing soil was product as a hot liquid (about 100 ⁰ C.) at the bottom of a 35- ^15; bottom Oldershaw column, which at a pressure of 100 mm Hg abs. and a floor temperature of 189 ° C. worked introduced · In the bladder was hooh? Diethylene glycol of high purity was introduced to act as a cooking medium and a small stream of distillate was withdrawn from this column at a weight ratio of reflux to distillate of 70 to ensure the removal of all impurities and residual water. This distillate stream consisted essentially of "water and some ethylene glycol.

Refined ethylene glycol was stripped from the 25th floor; its UV transmittance at 350, 272 and 220 m «u wavelength was 99> 1 | 90.8 and 72.0, respectively. These UV transmission values indicate the practical absence of impurities in the

recovered Gtykol.

Example 5 '

This example shows the purification of diethylene glycol, _r containing the typical "during the production of glycol impurities formed. These include oxidation products, aldehydes, carbonyls, and excess temperature contaminants.

Diethylene glycol with the above impurities, mono-, tri-, and Tetraathylenglykol has been mixed with ejmen equal volume of ion-exchanged water prior to the introduction as feed hot (90 ⁰ C) 2ura 20th plate of a 21-tray Oldershaw column · The column operated at atmsphärischem Pressure has a weight ratio of reflux to distillate of 1.0 and an overhead temperature of 99-5 ° C. The bottoms contained about 1.8 wt% water indicating the presence of a substantial amount of water in the stripping portion of the column.

0 0 9809/17 36

The bottoms product from the above column was as hot feed (9O ⁰ C.) for 5 · the bottom of a second 20-tray Oldershaw column, the mn at 35 Hg, abs. worked, introduced. A small stream was withdrawn overhead as distillate and refined diethylene glycol was removed from the 10th tray above the pot.

The refined diethylene glycol was prepared according to the method described below Sulfuric acid process tested and had a sulfuric acid color of 15 Pt-Go compared to 28 Pt-Co for one obtained by conventional methods Diethylene glycol. '

In the sulfuric acid color test used here, 95 ecm of diethylene glycol with 5 ecm of conc. Sulfuric acid mixed at room temperature. The mixture was heated to 100 ° C. for 30 minutes, then the color was determined by a standard color scale such as platinum-cobalt (Pt-Co). Lower color values indicate glycols of higher purity. Example 6

This example shows the effect of changing the pH of the feed to the purification of diethylene glycol containing the same impurities as the feed in Example 5.

# It became a feed mix of about an equal weight ratio made from diethylene glycol and triethylene glycol. The pH of the resulting mixture was about 11. Two separate portions of this mixture were used acidified with phosphoric acid to pH values of about 7 and 2, respectively. So there were three separate feed mixes with pH four of 11, 7 and 2. Each portion

was used as a hot liquid (9O ⁰ C.) sum 10 floors of a 25-floor Oldershaw

column, which at 4 am Hg abs. worked, introduced. About 1.5 wt Feed were used as overhead material at a weight ratio of return

009809/1736

- 16 - 19A209A

to distillate of about 60, and about 90% by weight of the diethylene glycol charge were withdrawn from the bottom as refined glycol. the Sulfuric acid color tests and the values of the UV transmittance of the refined Diethylene glycols are given in Table 7 in each case.

Table 7

■ *

pH «value d. # UV transmittance values; at tn / U sulfuric acid paint} charge ~ J ~ ^ ¹ ^ Pt-Co

11 100 77 Λ2 35

-7 100 78 ^ Z 30

2 98 66 31 60 ' _f

The above results show that the diethylene glycol was of poor quality won "The reason for the unvols tändige distance of impurities _(Cleaners in the original feed. However, it is noted that the feed .this example before refining any increased subject to distillation had been, and that the impurities were not completely removed
! B is ρ ie I 7

! This example shows the effect of a change in the pH of the Beschik-, kung the Reinigtmg of diethylene glycol with the same contaminants) as the feed in Example 6. However, before the feed was

subjected to refining to an increased distillation.

The feed was the same as in Example 6, i.e. a mixture of equal weights of diethylene glycol and triethylene glycol. This was mixed with an equal volume of ion-exchanged water, and the three separate portions of the resulting aqueous feed were kept at pH values from 11,? or 3 distilled. Each batch of feed was separated on 15 · Bottom of a 20-tray Oldershaw column, which with a head pressure of

00 9809/173 6

100 in the Hg abs. and a pressure differential across the column of 30-35 mm Hg worked. Most of the water and low boiling impurities was removed as the distillate at a weight ratio of reflux to d'estiliate of about 0.2.

The bottom product consisted in each case of diethylene glycol, triethylene glycol, and 0.3 wt% water, which creates a water-rich environment in the stripping section this column indicated. So three soil products were obtained from three separate distillation stages, each at different pH values were carried out.

Each bottoms product from this pre-distillation stage was refined (distilled) in a 25-tray Oldershaw column under acidic, neutral and basic conditions, the pH being adjusted with either phosphoric acid or sodium hydroxide. A total of 9 distillations were carried out, each at a head pressure of 3-10 mm Hg abs. In each case, the feed was introduced as a hot liquid (90 °) at the 10th tray of the 25-tray column, and the remaining water was introduced together with the remaining impurities removed as distillate at a weight ratio of reflux to distillate of about ^ O. 75-83% by weight of the diethylene glycol contained in the feed was withdrawn as a secondary liquid stream from the bottom as a refined product. The results of this example are listed in the following table.

098 0 9/1730

PH value d. shipment - 18 - 87 - - 1942094 first second Table 8 82 Verse. column column for UV transmission 86 at the, fU sulfuric acid 11th 11th 350 81 /
ο Pn colour 11th 7th 98 83 CcXJ Pt-Co 1 11th 5 99 8th? 38 20th 2 7th 10 100 87 55 7.5 3 7th 7th 100 81 50 10 7th 99 52 10 5 3 10 100 ho 20th 6th 3 7th 99 48 2.5 ? ' 3 3 99 6o 7.5 8th 99 6o 7.5 9 48 15th

A comparison of the results of Tables 7 and 8 shows that the results in Example 7 obtained glycols have higher UV transmission values and lower color values than had the corresponding glycols of Example 6. This means higher UV transmission values and lower color values, higher quality glycols.

Experiments 7 and 8 (in Table 8) _{9 also show} that it is particularly advantageous to carry out the primary distillation at a pH of 3 and to record the pH of the soil product from the primary distillation before refining? or 10.

009809/1736

Claims (1)

P a t, β .n ^ t ans priiche Process for the purification of a glycol contaminated with impurities the general forael HO (CH ₂ -CHO) _n H in which R stands for hydrogen or a methyl or ethyl group and η is an integer with a value from 1 to ¹ J-I, characterized in that this glycol is introduced into a distillation zone, it is distilled in the presence of water in the stripping section of the distillation zone wherein water is maintained at the feed point and in a substantial portion of the stripping section in an amount of about 30-80 weight percent based on the weight of the glycol to enhance the volatilities of the contaminants with respect to the glycol and a pressure of about 50 mm Hg abs. up to about 1 atm. is maintained, the impurities are removed with the distillate from the distillation zone, the bottom product practically free of these impurities is removed from the distillation zone and the purified glycol is recovered from the bottom product. 2 · - Method according to claim 1, characterized in that the pH value of Materials kept below about 7 in the stripping section of the distillation zone will* 3 · - Method according to claim 2, characterized in that the pH value of Materials in the stripping section of the distillation zone wipe about 2-5 is held. k.- The method according to claim 1 to 3 t, characterized in that the amount of water is about 40-60 wt .- ^ of the glycol 5 · - Process according to claims 1 to k _9, characterized in that the glycol is ethylene glycol. 009809/1736 6.- The method according to claim 1 to 5, characterized in that the pH of the bottom product is set above about 7. 1 to 7 · - Process according to Claim / 6, characterized in that the glycol Diethylene glycol is used. The patent attorney: 009809/1736