GB2091580A

GB2091580A - Chromatographic method for recovery of ethylene glycol

Info

Publication number: GB2091580A
Application number: GB8138793A
Authority: GB
Original assignee: Nippon Rensui Co; Mitsubishi Kasei Corp; Mitsubishi Petrochemical Co Ltd; Mitsubishi Petrochemicals Engineering Co Ltd
Current assignee: Nippon Rensui Co; Mitsubishi Kasei Corp; Mitsubishi Petrochemical Co Ltd; Mitsubishi Petrochemicals Engineering Co Ltd
Priority date: 1980-12-24
Filing date: 1981-12-23
Publication date: 1982-08-04
Also published as: DE3151452A1; NL8105847A

Abstract

Ethylene glycol contained in washings discharged from an ethylene oxide production process by gas phase oxidation of ethylene with oxygen, is recovered by passing the washings along pipe 6 to a chromatographic separation column 1 whose lower part is packed with a cation exchange resin 2 in salt form. Water from pipe 3 is used to elute the column 1, the effluent from the column 1 being divided into at least three fractions of which at least one is an ethylene glycol-rich fraction, the others containing e.g. organic acids or coloured materials. At least one of the other fractions which contains low concentrations of ethylene glycol is recycled via pipe 7. <IMAGE>

Description

SPECIFICATION Method for recovery of ethylene glycol The present invention relates to a method for recovering ethylene glycol from an aqueous solution containing ethylene glycol discharged from an industrial process for production of ethylene oxide. More particularly, the present invention relates to a method for recovering ethylene glycol from a solution that is discharged from the industrial process of production of ethylene oxide from ethylene and which contains ethylene glycol, organic acids, and colored materials.

Ethylene oxide is an important basic chemicals and produced in large quantities. It is used as an insecticide. It is used in the production of polyethyleneglycol and polyethoxylates useful as nonionic surfactants. Most ethylene oxide, however, is hydrated to produce ethylene glycol.

Ethylene oxide is produced by catalytic gas-phase oxidation of ethylene with oxygen. The reaction gas containing ethylene oxide from the reactor is supplied to an absorption column where it is washed with water and absorbed in it. The washings containing ethylene oxide are fed to a stripping column where they are stripped to release ethylene oxide. The ethylene oxide is further purified, if desired, and used for many purposes above described. The process for the production of ethylene oxide is described, for example, in the following publications. PHILIP L. WALKER Jr. and PETER A. THROWER ed. "Catalysis Reviews - Science and Engineering", vol. 23, Nos. 1 and 2, p. 163 to 183 (1981) and "Industrial Organic Chemistry - Main Materials and Intermediates" translated by MITSUAKI MUKOYAMA, etc.

published by Tokyo Kogaku, Dozen, p. 137 to 154, Dec. 1 5, 1978.

The washings from which ethylene oxide has been released are returned to the absorption column.

The process for the production of ethylene oxide is described in further detail below.

Gas-phase catalytic oxidation of ethylene is typically performed by passing a mixed gas containing ethylene and oxygen through a fixed bed of a silver-based catalyst. Usually, the mixed gas also contains inert gases such as nitrogen and methane, as well as a trace amount of an inhibitor such as ethylene dichloride, which prevents excessive oxidation. A large volume of nitrogen is contained in the mixed gas when air is used as the oxygen source. Ethylene oxide is usually recovered from the reaction gas and purified using from one to three washing stages.

In the simplest process, the reaction gas is washed with water in one step, and the water that has absorbed ethylene oxide is stripped. to release ethylene oxide for recovery. Ethylene oxide of higher purity can be obtained by washing the released ethylene oxide again with water, and then by stripping the water that has absorbed ethylene oxide to release the ethylene oxide. In some cases, these washing and absorption stages may be preceded by a stage where the reaction gas is washed and quenched with water. The water used in these stages of washing is recycled. The reaction gas contains various byproducts which are also absorbed by water in the washing stages; typical by-products are organic acids such as formic acid and oxalic acid, as well as colored materials. The pH of the water using in the washing stages is usually adjusted by caustic soda.Then organic acids in the water are present in the form of sodium salts. The water also contains ethylene glycol (a hydrated form of ethylene oxide) and diethylene glycol (a dimer of ethylene glycol). These components are not released in the stripping stages and accumulate in the water as the water is recycled, so part of the water must be occasionally replaced by a new supply of water. The composition of the water drawn from the stripping column varies with the reaction and washing conditions; for instance, it contains 3 to 7 g of formic acid, 2 to 9 g of diethylene glycol, 0.05 to 0.3 g of oxalic acid, and small amounts of unknown colored materials per 100 g of ethylene glycol.

Several methods have been proposed for recovering ethylene glycol from the water containing ethylene glycol that are discharged in the above-described process for production of ethylene oxide. For instance, Japanese Patent Publication No. 10324/70 described a method for recovering high-purity ethylene glycol by distilling the water and contacting the resultant ethylene glycol fraction with activated carbon to adsorb impurities. U.S. Patent No. 3,904,656 describes a method wherein the water containing ethylene glycol is purified by using ion-exchange resin beds and activated carbon column, then fed to a dehydrating distillation column where aqueous ethylene glycol resulting from hydration of ethylene oxide is distilled.

The present Invention provides an entirely new method wherein the impurities in the water are separated from ethylene glycol by column chromatography.

The invention therefore provides a method for recovering ethylene glycol wherein purified ethylene glycol is recovered by column chromatography from an aqueous solution containing ethylene glycol that is discharged from the process in the production of ethylene oxide.

In the process for the production of ethylene oxide, the reaction gas that contains ethylene oxide obtained by gas-phase catalytic oxidation of ethylene with oxygen is washed with and absorbed in the water; in the next stage, the absorbed ethylene oxide is released from the water, and the water is recycled to the washing stage. A part of the recycled water is removed from the system to prevent accumulation of ethylene glycol and impurities therein. The present invention provides a method for recovering ethylene glycol from the water by chromatography. According to the present invention, ethylene glycol in the water can be recovered in high yield and with less amounts of organic acids and colored materials.

Figs. 1 and 2 are graphs showing examples of chromatograms, that is to say, the elution curves of sodium ion and ethylene glycol in chromatographic column effluent, and examples of dividing the effluent into fractions according to the method of the present invention. In these cases, the aqueous solution discharged from the washing stages is concentrated and then supplied to the chromatographic column followed by elution with only water.

Fig. 3 is a schematic representation of an apparatus that can be used in the practice of the method of the present invention, wherein 1 is a column, 2 is an ion exchange resin bed, 3 is a water supply pipe, 4 is a distributor for washings, 5 is a distributor for the recycled portion, 6 is a supply pipe for washings, and 7 is a supply pipe for the recycled portion.

Figs. 4 and 6 are chromatograms obtained by eluting the washings with only water; and Figs. 5 and 7 show chromatograms obtained according to the same methods used in Figs. 4 and 6 respectively, except that elutions of the washings are carried out with recycled fractions followed by water, and patterns of dividing the effluent into fractions according to the present invention. In these cases, washings are different from one used in Figs. 1 and 2.

The washings that contain ethylene glycol, organic acids and colored materials, which are discharged from the recovery stage of ethylene oxide from the reaction gas that contains ethylene oxide obtained by gas-phase catalytic oxidation of ethylene with oxygen are, after optionally concentrating subjected to chromatography using a cation exchange resin as a packing materials and water as an eluent, and from the resulting effluent, an aqueous ethylene glycol fraction that contains a major part of the ethylene glycol in the washings and has reduced concentrations of organic acids and colored materials is obtained.

In one embodiment of the present invention, the effluent from the chromatographic column is divided into two fractions an aqueous ethylene glycol fraction containing a major amount of the ethylene glycol contained in the washings and a waste fraction containing a major amount of the organic acids and colored materials in the washings. The aqueous ethylene glycol fraction is distilled to yield ethylene glycol. For example, the aqueous ethylene glycol fraction is purified with ion exchange resins or ion exchange resins and activated carbon, then fed into a process for production of ethylene glycol from ethylene oxide and distilled therein, in accordance with a method described in U.S. 3,904,656.

In another embodiment, the effluent is divided into at least three fractions, i.e., a first fraction that contains organic acids and colored materials in high concentrations but which contains little ethylene glycol, a second fraction that contains organic acids, colored materials and ethylene glycol in low concentrations, and a third fraction that contains little of the organic acids and colored materials, but which contains ethylene glycol in high concentration.

The first fraction is delivered to a sewage treatment plant. The second fraction is recycled to the washing stages in the process for producing ethylene oxide or is mixed with washings and supplied to the chromatographic column again. The third fraction is recovered as aqueous ethylene glycol solution.

In this embodiment, ethylene glycol contained in the washings discharged from the washing stages is recovered into the third fraction in high yield.

In still another embodiment, the second fraction is supplied to the chromatographic column following the washings and thereafter water is supplied thereto; that is to say, the washings supplied into the chromatographic column is eluted with the second fraction and water successively. In this embodiment, the concentration of ethylene glycol in the third fraction can be made higher.

In the method of the present invention, the washings containing ethylene glycol that are discharged from the washing stages in the process for producing ethylene oxide may be directly subjected to chromatography, but it is preferred that they be preliminarily concentrated because the subsequent chromatography can be performed in a small apparatus using a small amount of water as an eluent. Generally, in the method according to the present invention, the washings are concentrated to an ethylene glycol concentration of at least 200 g per liter before they are subjected to chromatography.

A cation exchange resin is used as a packing material for chromatography. The cation exchange resin may be a weakly acidic or medium acidic resin of the carboxylic acid type. A strong acid cation exchange resin, especially, a cross-linked polystyrene-based strong acid cation exchange resin is preferred. A sulfonated product of styrene/divinyl benzene cross-linked copolymer is usually used.

Cation exchange resins of this type are commercially available under the trademark "Diaion" (registered trademark for a series of ion-exchange resins manufactured by Mitsubishi Chemical Industries, Limited, Japan) and under many other trademarks. The cation exchange resin is preferably pre-loaded with the same kind of cations as contained in the washings to be subjected to chromatography. Resins which have no ability to decompose neutral salts are generally used after they are loaded with cations, but when washings containing caustic soda is supplied to chromatographic column, they may be used in hydrogen form.

The chromatography can be carried out by a conventional method. In the simplest form, a column is filled with the cation exchange resin and water, and water is drawn to the surface of the resin bed, and then, a predetermined amount of the washings containing ethylene glycol is supplied to the column As water is drawn from the bottom of the column, the washings are allowed to descend in the column.

When the surface of the washings becomes level with that of the resin bed, water is supplied to the column to elute the washings. By alternately supplying washings and water to the column, chromatography can be carried out continuously. The effluent coming out of the bottom of the column is divided according to its composition. For instance, by continuously measuring the ethylene glycol concentration with a refractometer, that of the organic acids with a conductivity meter and that of the colored materials with a spectrophotometer, respectively, an effluent fraction having the desired composition can be recovered as an aqueous ethylene glycol solution.

For instance, Fig. 1 is an embodiment showing a chromatogram of the column effluent obtained by the above procedures. In the figure, the effluent is divided into two fractions. Fraction I is disposed of as waste liquor, and fraction II is recovered as aqueous ethylene glycol solution. Thus most of the ethylene glycol contained in the washings can be recovered in the fraction 11. Further, the ratio of impurities to ethylene glycol in the recovered aqueous ethylene glycol solution is much lower than that in the washings.

The recovered aqueous ethylene glycol solution is further purified to get ethylene glycol of commercial grade. For example, the aqueous ethylene glycol solution is treated with ion exchange resins to remove ionic substances and colored materials and then distilled to get ethylene glycol of commercial grade. In another embodiment, after the treatment with ion exchange resins or ion exchange resins and activated carbon, the aqueous ethylene glycol solution is fed to a process for producing ethylene glycol by hydration of ethylene oxide according to the method described in U.S.

Patent 3,903,656. One advantage of this method is that it requires no special distillation apparatus since the ethylene glycol recovered by chromatography from the washings is treated together with the ethylene glycol produced by hydration of ethylene oxide. As was above mentioned, the aqueous ethylene glycol solution recovered by chromatography usually contains small amounts of organic acids and colored materials, so these impurities are preferably removed before the aqueous solution is distilled to get pure ethylene glycol. To remove these impurities, the aqueous ethylene glycol solution may be treated with a cation and anion exchange resin to which these impurities are adsorbed. The cation exchange resin is usually a styrene/divinyl benzene crosslinked copolymer based strong acid cation exchange resin.The anion exchange resin is usually a strongly basic anion exchange resin based on a styrene/divinyl benzene cross-linked copolymer having a quaternary ammonium group introduced as a functional group. A weakly basic anion exchange resin having primary to tertiary amino groups as a functional group may also be used. These ion-exchange resins may be used separately or in mixture. The ion exchange resins used to purify the aqueous ethylene glycol solution can be regenerated by a conventional method using an acid, e.g., hydrochloric acid or sulfuric acid, or an alkali, e.g., caustic soda.

In the above described procedures, the column effluent is divided into two fractions, i.e., waste liquor and aqueous ethylene glycol solution, but other ways to divide the effluent may be applied. Fig. 2 is an embodiment showing another way to divide the effluent. Fig. 2 shows an embodiment to divide the effluent into three fractions, i.e., waste liquor, recycled fraction and a fraction of aqueous ethylene glycol solution.

In Fig. 2, the portion that comes out of the column first which is rich in the colored materials and organic acids and which contains little ethylene glycol, is recovered as the first fraction, and is disposed of as a waste liquor. The subsequent portion that contains the colored materials, organic acids and ethylene glycol in low concentrations is recovered as the second fraction, which is recycled to the process of ethylene oxide production to use as washings. Alternatively the second fraction is mixed with washings discharged from the process for ethylene oxide production and supplied again to the chromatographic column. Thus, the second fraction is directly or indirectly supplied to the chromatography, and ethylene glycol in that fraction is recovered as the third fraction which is described hereunder.If the water balance permits, the second fraction is recycled to the process of ethylene oxide production with advantage.

Finally, a portion that comes out of the column subsequent to the second fraction and which is rich in ethylene glycol and contains little of the organic acids and colored materials is recovered as the third fraction, which is further purified by distillation for recovery of ethylene glycol. It is preferred to contact the third fraction, before distillation, with cation exchange resin and anion exchange resin, or these resins and activated carbon to adsorb impurities, as already described. The terminal portion of the third fraction has a decreasing concentration of ethylene glycol, and if the washings and water are supplied to the column alternately, the colored materials and organic acids contained in subsequently supplied washings may enter into terminal portion of the third fraction.

Therefore, preferably, the portion IV in which the concentration of ethylene glycol lowered is recovered separately from the third fraction and is mixed with the second fraction for subsequent treatments. According to the method shown in Fig. 2, ethylene glycol may be recovered in higher yield and the concentrations of impurities in recovered aqueous ethylene glycol solution may be lowered than in Fig. 1.

In other embodiment of the present invention, the fraction containing ethylene glycol in a low concentration, which is obtained from column effluent, is fed to the column, subsequent to the washings and then water is supplied to the column. These procedures are preferable, in view that the fraction of aqueous ethylene glycol solution having higher concentration of ethylene glycol may be recovered from the column effluent. This is because that the washings fed to the column is first eluted by the recycled fraction containing ethylene glycol in a low concentration.

Fig. 5 shows a way to divide the effluent when recycled fraction recovered from the preceding effluent is used as a part of eluent. In the figure, the effluent is divided into four portions, i.e., a fraction I containing colored materials and organic acids in high concentrations but containing little ethylene glycol, a fraction II containing ethylene glycol in high concentration, a fraction Ill containing ethylene glycol in low concentration and a fraction IV containing ethylene glycol in lower concentration. The fraction I is disposed of as a waste liquor, since it contains a large quantity of impurities. The fraction II contains major amount of ethylene glycol contained in the washings and is recovered as a fraction of aqueous ethylene glycol solution. The fraction II is further purified, as is described above, to recover ethylene glycol.The fraction Ill is a recycling fraction and fed to the column following the washings. The supply of washings, the recycled fraction and water, in this order, does not lead to an alteration in the elution position and curves of organic acids and colored materials compared with those established on a supply of washings and water in this order. However, the elution curve for ethylene glycol has a higher peak, although its elution position remains almost the same. Thus, the concentration of ethylene glycol in the fraction of the aqueous ethylene glycol solution becomes higher by feeding the recycled fraction to the column, subsequent to the washings. The fraction IV is disposed of, or returned to the process for producing ethylene oxide to use as washings.The fraction IV may be mixed with recycled fraction and used as eluent but it is not preferable because the concentration of ethylene glycol in the recycled fraction lowers.

Fig. 7 shows another way to divide the effluent when the recycled fraction is used as a part of eluent In the figure, the effluent is divided into five fractions I to V. The fraction I is disposed of as waste liquor, the fraction ill is a fraction of the aqueous ethylene glycol solution and is further purified to recover ethylene glycol. The fractions II and IV are recycled fractions and fed to the column subsequent to the washings. The fractions II and IV may be supplied to the column either separately or in mixture.

When supplied separately, the washings, the fraction II, the fraction IV and water are supplied in this order. The fraction V contains little ethylene glycol and, thus it is disposed of, or returned to the process for production of ethylene oxide to use as washings, as is the same as the fraction IV in Fig. 5.

When the washings and the eluent are fed to the column alternately, the fraction V and fraction I of next operation come out in series and they may be taken as one fraction.

It is preferred to recover a fraction of aqueous ethylene glycol solution which contains ethylene glycol as much as possible. Usually at least 70%, preferably more than 85% of ethylene glycol contained in the washings is recovered in the fraction of aqueous ethylene glycol solution. Further the concentration of ethylene glycol in the recovered fraction of aqueous ethylene glycol solution is preferably kept at least 0.2 times, especially 0.3 times of the concentration of ethylene glycol concentration of the washings.

One preferred embodiment for practising the method of the present invention is now described by reference to Fig. 3, in which the reference numeral 1 indicates a chromatographic column the lower part of which is filled with a cation exchange resin bed 2. The upper part of the column 1 is void, and a water supply pipe 3 opens to the top of the column 1. Close to the surface of the resin bed 2 are arranged a distributor for washings 4 and a distributor for recycled fraction 5 which are respectively connected to a supply pipe for washings 6 and a supply pipe for recycled fraction 7.The operation of this chromatograph is as follows: water is supplied through the pipe 3 to fill the upper part of the column; then washings is supplied to the column through the pipe 6 via the distributor 4, and at the same time, the effluent is allowed to flow from the bottom of the column at a rate substantially equal to the supply rate of the washings. Since the washings has a greater specific gravity than water, the two do not mix, and form a distinct interface close to the surface of the resin bed. When a predetermined amount of the washings has been supplied to the column, its supply is ceased, and, instead, the recycled fraction of the effluent is supplied at the same rate through the pipe 7 via the distributor 5. The amount of the recycled fraction supplied is usually equal to the amount of the recycled fraction to be recovered in one cycle of chromatography.After a predetermined amount of the recycled fraction has been supplied through the pipe 7, its supply is stopped, and instead, water is supplied through the pipe 3. In this procedure, there is little chance of the washings, recycled fraction and water to intermingle in the upper part of the column, and hence, high separation efficiency is achieved. The effluent that flows from the bottom of the column during this operation is divided into at least three fractions by continuous measurements of the concentration of ethylene glycol, organic acids, and colored materials. The concentration of ethylene glycol is easily determined by a refractometer, that of the organic acids by a conductmeter, and that of the colored materials by a spectrophotometer.

The feed amount of the washings for each supply to the column is 0.05 to 0.4 times by volume, preferably 0.1 to 0.25 times by volume to the amount of resin bed volume. The feed rate of the washings, the recycled fraction, and water are preferably the same, but may be different each other. The feed rate may varies widely, but preferably is in the range of 0.5 to 5 and more preferably 2 to 4 in terms of Space Velocity.

The present invention is now described in greater detail by reference to the following Examples, but the invention is not limited thereby, and various modifications are possible.

EXAMPLE 1 A cylindrical column 50 mm in diameter and 2000 mm high was filled with a 1000 mm-high bed of a strong acid cation exchange resin (sodium salt of sulfonated styrene/divinyl benzene copolymer, gel type). A supply pipe for the washings was provided in the column 50 mm above the surface of the resin bed. The upper part of the column was filled with water that was supplied through a pipe connected to the top of the column. The washings having the formulation indicated in Table 1 was fed to the column through the supply pipe for 4 minutes and 20 seconds at a rate of 70 ml/min, and then, water was supplied to the column at the same rate through the water pipe. At the same time that the supply of the washings started, the effluent began to be drawn from the bottom of the column at a rate of 70 ml/min.

The curves of elution of sodium ion and ethylene glycol in the effluent is shown in Fig. 1. The colored materials come out at almost the same position as sodium ion, but the peak of the elution curve of the colored materials is present at the position of 0.53 in terms of bed volume, i.e., slightly preceding that of sodium ion. Since substantially all the sodium ion in the washings was present in the form of organic acid salts, it may be safely concluded that the elution curve of sodium ion is a direct indication of the elution curve of organic acids. From the effluent, 830 ml of a waste liquor fraction and 1230 ml of an aqueous ethylene glycol fraction were taken. The analysis of these fractions is shown in Table 1.Table 1 shows that ethylene glycol solution recovered contains about 88% of ethylene glycol, 4% of organic acids and less than 10% of colored materials contained in the washings. Therefore the method of the present invention is capable of recovering in high yield of ethylene glycol containing only very low concentration of organic acids and colored materials.

TABLE 1 Compositions of the Washings Supplied and the Fractions Recovered Ethylene Glycol Ethylene Glycol Waste Solution Washings Solution Liquor Treated with Ion Supplied Recovered Recovered Exchange Resin Conc. of ethylene glycol 300 65 10.7 65 (s/l) Conductivity(yS/cm) 9100 387 12350 3.15 pH 6.28 5.8 6.3 7.0 Formic acid (g/l) 20 0.19 6.95 < 0.01 Oxalic acid (g/l) 0.20 0.0025 0.07 < 0.01 Color degree 1.3 0.03 0.31 0 N.B.) 1. Analysis of ethylene glycol, formic acid and oxalic acid was carried out by liquid chromatography using Diaion~ CK08 as packing materials and 1% aqueous solution of phosphoric acid as an eluent.

2. The color degree is indicated by the absorbance at 420 nm. Measurement was carried out with "Hitachi Double-beam Spectrophotometer Type 200-20" with 10 mm cell.

The ethylene glycol fraction thus obtained passes through a column (l.D. 22 mm) packed with 100 ml of regenerated strong acid cation exchange resin (DIAlON~ SKIB) at a rate of 250 ml/hr and subsequently through a column (I.D. 22 mm) packed with 100 ml of regenerated strong basic anion exchange resin (DIAION -- Registered Trade Mark -- SAIOA) at a rate of 250 ml/hr. The results are shown in the Table 1. The results indicate that not only the ionic substances but also the colored materials were removed by passing through the column packed ion with exchange resins.

EXAMPLE 2 A column 1.8 cm in diameter was filled with 1 82 ml of a strong acid cation exchange resin (sodium salt of sulfonated styrene/divinyl benzene copolymer, gel type; 95% had a particle size of from 210 to 500 ,u). Through the column, 27 ml of washings having the formulation indicated below was passed at Space Velocity (hereinafter abbreviates SV) = 2 and then water was fed at SV = 2. The elution curves of ethylene glycol, organic acids and colored materials in the column effluent is shown in Fig. 4.

TABLE 2 Formulation of the Washings Ethylene Glycol ca. 530 g/l Sodium Ion* 15,430 mg/l Absorbance (420 my) 1.48 (10 mm cell) * The sodium ion was present mostly as sodium formate, and partly as sodium oxalate. A very small amount might be present.

EXAMPLE 3 A column as used in Example 2 was supplied with 27 ml of washings of Table 2 at SV = 2.

Subsequently, a fraction obtained from the effluent in Example 2 which flowed at a zone from 1.10 to 1.30 Bed Volume (hereinafter abbreviate BV) was fed at SV = 2, and finally water was fed at SV = 2.

The 1.10-1.30 (BV) fraction of the column effluent was recovered to use as a part of eluent in the next operation of chromatography. Four more runs of the same procedure were carried out. The elution curve of ethylene glycol, organic acids and colored materials in the column effluent is shown in Fig. 5.

Comparing with Fig. 4, the peak of the curve for ethylene glycol in the effluent is much higher than that in Fig. 4, but, on the other hand, the curves of absorbance and electric conductivity remain the same.

Therefore, by using a part of the effluent as an eluent in subsequent chromatography, ethylene glycol fraction of higher concentration of ethylene glycol and substantially of the same concentrations of impurities may be recovered.

EXAMPLE 4 A column as used in example 2 was supplied with 23 ml of washings shown in Table 2 at SV = 1.18, and subsequently water was fed at SV = 1.18. The elution curves of ethylene glycol, organic acids and colored materials are depicted in Fig. 6.

EXAMPLE 5 A column the same as used in Example 2 was fed with 23 ml of washings shown in Table 2 at SV= 1.18, and subsequently, a mixture of the 0.75-0.80(BV) and 1.10-1.30 (BV) fractions of the effluent obtained in Example 4 was fed at SV = 1.18, and finally water was fed at SV = 1.18. The 0.75-0.80 (BV) and 1.10-1.30 (BV) fractions of the column effluent was recovered to use as a part of eluent in subsequent chromatography. Four more runs of the same procedure were carried out. The elution curves of ethylene glycol, organic acids and colored materials in the column effluent is shown in Fig. 7.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims

1. A method for recovering ethylene glycol from washing discharged from a process for production of ethylene oxide by gas phase catalytic oxidation of ethylene with oxygen, and containing ethylene glycol, organic acids and colored materials, which comprising subjecting the washings to chromatography wherein a salt form of cation exchange resin is used as a packing material, water is used as an eluent, and at least one fraction rich in ethylene glycol is recovered from the effluent of the chromatography.

2. A method according to Claim 1, wherein the fraction rich in ethylene glycol contains at least 70 weight % of ethylene glycol based on the amount of ethylene glycol contained in the washings, and its ethylene glycol concentration is more than 0.2 times that of the washings.

3. A method according to Claim 1, wherein the fraction rich in ethylene glycol contains at least 85 weight % of ethylene glycol based on the amount of ethylene glycol contained in the washings, and its ethylene glycol concentration is more than 0.2 times that of the washings.

4. A method according to Claim 1,2 or 3, wherein at least two fractions are taken from the effluent, one being an ethylene glycol fraction containing most of the ethylene glycol contained in the washings, and the other being a waste fraction containing most of organic acids and colored materials contained in the washings.

5. A method according to any preceding claim, wherein the fraction rich in ethylene glycol is treated with a cation exchange resin and an anion exchange resin, and then fed to a process for producing ethylene glycol by hydration of ethylene oxide.

6. A method according to Claims 1,2 or 3, wherein the effluent is divided into at least three fractions, of which a first fraction contains organic acids and colored materials in high concentration and contains little ethylene glycol, a second fraction contains organic acids, colored materials and ethylene glycol in low concentration, and a third fraction contains ethylene glycol in high concentration, but contains little organic acids and colored materials, the second fraction being recycled to the process for production of ethylene oxide as washings or admixed with the washings discharged from the process for production of ethylene glycol and supplied to chromatography, and the third fraction being further treated to recover purified ethylene glycol.

7. A method according to Claims 1, 2 or 3, wherein the effluent is divided into at least three fractions, of which a first fraction contains organic acids and colored materials in high concentration and contains little ethylene glycol, a second fraction contains organic acids, colored materials and ethylene glycol in low concentration and a third fraction contains ethylene glycol in high concentration but contains little organic acids and colored materials, the second fraction being used as an eluent in subsequent operation of chromatography, and the third fraction being further treated to recover purified ethylene glycol.

8. A method for recovering ethylene glycol from washings discharged from a process for production of ethylene oxide by gas phase catalytic oxidation of ethylene with oxygen and containing ethylene glycol, organic acids and colored materials, which comprising supplying the washings to a chromatographic column packed with cation exchange resin of salt form, then supplying water to elute the washings, and recovering at least one fraction rich in ethylene glycol from an effluent of the column.

9. A method according to Claim 8, wherein the cation exchange resin of salt form is a strong acid cation exchange resin of sodium form.

10. A method according to Claim 8 or 9, wherein the washings are concentrated a concentration of 200 g/ or more of ethylene glycol before being supplied to chromatography.

11. A method according to Claim 8, 9 or 10 wherein the fraction rich in ethylene glycol contains at least 70 weight % of ethylene glycol based on the amount of ethylene glycol contained in the washings, and its ethylene glycol concentration is more than 0.2 times that of the washings.

12. A method according to Claim 8, 9 or 10 wherein the fraction rich in ethylene glycol contains at least 85 weight % of ethylene glycol based on the amount of ethylene glycol contained in the washings and its ethylene glycol concentration is more than 0.2 times that of the washings.

13. A method according to Claim 8, 9, 10, 11 or 12, wherein the fraction rich in ethylene glycol is treated with ion exchange resin, and distilled to recover purified ethylene glycol.

14. A method according to Claim 8, 9 or 10 wherein the effluent is divided into at least three fractions, of which a first fraction contains major amounts of the organic acids and colored materials contained in the washings, a second fraction contains minor amounts of the organic acids, colored materials and ethylene glycol contained in the washings, and a third fraction contains a major amount of ethylene glycol contained in the washings.

1 5. A method according to Claim 14, wherein the third fraction contains at least 70 weight % of ethylene glycol based on the amount of ethylene glycol contained in the washings, and its ethylene glycol concentration is more than 0.2 times that of the washings.

16. A method according to Claim 14, wherein the second fraction is supplied to the chromatographic column, following the washings, and thereafter water is supplied to the chromatographic column chromatograph separation.

17. A method for recovering ethylene glycol substantially as hereinbefore described with reference to Figure 3 or in any one of Examples 1 to 5.

18. Ethylene glycol when recovered by a method as claimed in any preceding claim.