阅读说明：本技术 回收环氧乙烷的方法 (Process for the recovery of ethylene oxide ) 是由 布莱恩·奥泽罗 于 2019-05-14 设计创作，主要内容包括：通过以下操作来进行环氧乙烷纯化：在将含气态环氧乙烷的流通入环氧乙烷吸收器以形成稀环氧乙烷和二氧化碳水溶液之前,急冷和洗涤环氧乙烷反应器流出物,然后在环氧乙烷汽提塔中汽提该溶液以产生含气态环氧乙烷和二氧化碳的塔顶蒸汽,然后将该塔顶蒸汽通入再吸收器,其中环氧乙烷和部分二氧化碳蒸汽被吸收以形成再被吸收物水溶液,将二氧化碳从其中去除以生成含环氧乙烷的溶液,通过以下操作来改进环氧乙烷纯化：将从急冷洗涤获得的含杂质的液体排出物流通入第二个小的急冷排出汽提塔,在所述汽提塔加入蒸汽和二氧化碳,并且来自该急冷排出汽提塔的气态塔顶馏出物被通入再吸收器,用于回收环氧乙烷和除去甲醛和其他杂质。(Ethylene oxide purification was performed by: prior to passing the gaseous ethylene oxide-containing stream to an ethylene oxide absorber to form a dilute ethylene oxide and carbon dioxide aqueous solution, quenching and scrubbing the ethylene oxide reactor effluent, then stripping the solution in an ethylene oxide stripper column to produce an overhead vapor containing gaseous ethylene oxide and carbon dioxide, which is then passed to a re-absorber where ethylene oxide and a portion of the carbon dioxide vapor are absorbed to form an aqueous reabsorbent solution from which carbon dioxide is removed to form an ethylene oxide-containing solution, improving ethylene oxide purification by: the liquid effluent stream containing impurities resulting from the quench wash is passed to a second small quench vent stripper where steam and carbon dioxide are added and the gaseous overhead from the quench vent stripper is passed to a re-absorber for recovery of ethylene oxide and removal of formaldehyde and other impurities.)

1. A process for purifying ethylene oxide, the process comprising:

quenching and washing ethylene oxide reactor effluent by contact with an aqueous base, passing the gaseous ethylene oxide-containing stream obtained from said quenching/washing into an ethylene oxide absorber, wherein the ethylene oxide is absorbed by water to form a dilute aqueous solution comprising ethylene oxide and carbon dioxide, then stripping the dilute solution in an ethylene oxide stripper to produce an overhead vapor comprising gaseous ethylene oxide and carbon dioxide, then passing the overhead vapor to a re-absorber, wherein ethylene oxide and carbon dioxide are absorbed to form a concentrated aqueous solution, then passing the re-absorbate to a carbon dioxide and light ends stripper to release gaseous carbon dioxide, and recovering the ethylene oxide-containing solution for use or further treatment; and

passing the impure liquid stream obtained from the quench/wash into a second stripping column, such as a purge stripper column or a quench vent stripper column, introducing steam and carbon dioxide into the second stripping column, feeding the gaseous overhead from the quench vent stripper column into the re-absorber, and removing the impure bottoms from the quench vent stripper column.

2. The process of claim 1, wherein the carbon dioxide fed to the second stripping column is recycled carbon dioxide obtained from a point downstream of the residual absorber.

3. The process according to claim 1 or claim 2, wherein the pH in the second stripping column is less than 8.0 after feeding carbon dioxide to the second stripping column.

4. The method of claim 1, 2 or 3, wherein the CO is added₂Steam is fed into the stripping steam to provide a minimum of 0.07 bar of CO₂Partial pressure.

5. The process according to any preceding claim, wherein 10% to 90%, more preferably 20% to 80%, most commonly 25% to 30% of the dilute ethylene oxide solution obtained from the absorber is passed directly to the re-absorber without passing through the stripper.

6. The process according to any preceding claim, wherein a separate quench tower (or bottom section of the absorber) is provided to thoroughly scrub the ethylene oxide reactor vent gas with a recycled, cooled dilute alkaline solution (typically 1% to 30%, preferably 1% to 15% alkaline hydroxide solution) to neutralize the organic acids and absorb a maximum amount (about 90% to 98%) of formaldehyde and other heavy (in water) aldehyde impurities.

7. The process of claim 6, wherein the scrubbing gas from the quench section is passed through a high efficiency demister apparatus to remove entrained quench solution, and then scrubbed with a small amount of single pass (and/or recycle) fresh water to remove any entrained quench liquid and absorb more formaldehyde.

8. The method according to claim 1, for removing carbon monoxide from a gas containing ethylene oxide, CO₂Ethylene oxide is recovered from a vapor reaction stream of formaldehyde, acetaldehyde and an organic acid compound comprising: absorption of said CO in ethylene oxide and water₂Formaldehyde, acetaldehyde and a portion of the organic acid compound to form an absorption stream; contacting the absorption stream with steam to strip ethylene oxide, CO from the absorption stream₂Formaldehyde, acetaldehyde and an organic acid compound to form a stripper overhead vapor stream; condensed water, formaldehyde, the ethylene oxide, acetaldehyde and a portion of the organic acid compound; recovering a vapor ethylene oxide product stream; and contacting the vapor ethylene oxide product stream in an ethylene oxide absorber in which the ethylene oxide is absorbed by countercurrent scrubbing with recycled ethylene oxide-free process water to produce an ethylene oxide-containing absorbate; wherein the improvement comprises sending a portion of the ethylene oxide-containing dilute absorbate comprising from 10% to 90% from the ethylene oxide absorber directly to an ethylene oxide reabsorber/residual absorber, wherein the ethylene oxide-containing dilute absorbate absorbs additional ethylene oxide from ethylene oxide stripper overhead vapor to produce an ethylene oxide/water solution having a desired high ethylene oxide concentration, the solution being suitable for use as a feed to an ethylene oxide purification column or an ethylene glycol production reaction system, the amount of stripping steam required for the ethylene oxide stripper being reduced in proportion to the amount of ethylene oxide absorbate bypassing the ethylene oxide stripper.

9. The process of claim 9 wherein the vapor reaction stream from the alkaline quench wash section is fed to a water wash section where it is washed with fresh process water and dehazed and then fed to the bottom of the ethylene oxide absorber where high purity ethylene oxide containing absorbate is produced, 10% to 90% of which can be fed directly to an ethylene oxide re-absorber to absorb more ethylene oxide and produce a higher concentration of high purity ethylene oxide-water solution, which can then be fed to the ethylene glycol reaction section to produce fiber grade MEG or to a high purity ethylene oxide column to produce high purity ethylene oxide.

Technical Field

The present invention relates to a process for increasing the purity of Ethylene Oxide (EO) recovered from the gaseous effluent of an ethylene oxide reactor. Such effluents may be used, for example, as feeds to ethylene oxide purification columns and/or integrated ethylene glycol plants that produce polyester grade Ethylene Glycol (EG). More particularly, the present invention relates to an improved quench absorption/stripping system for the recovery of ethylene oxide. Such systems are typically used in the ethylene oxide recovery step of an integrated ethylene oxide/ethylene glycol plant that will produce a higher purity ethylene oxide-water feed for a high purity ethylene oxide column or ethylene glycol plant, while providing substantial savings in operating costs and simplifying plant operation.

Background

When ethylene oxide is produced by partial silver oxide catalyzed ethylene in the molecular oxygen phase, a hot gaseous reactor effluent is obtained. The ethylene oxide content is low and the conventional practice to recover ethylene oxide from the off-gas involves cooling the reaction feed and product gases in a heat exchanger train and absorption in process water to produce a very dilute ethylene oxide solution which also contains various absorbed impurities. The ethylene oxide is then stripped from the dilute solution in a stripper column, which results in a large amount of impurities mixed with the ethylene oxide (such as formaldehyde), which can be a problem for many applications, including in the preparation of certain purity ethylene glycol for the production of polyester fibers (fiber grade ethylene oxide). Thus, the ethylene oxide from the oxidation reactor typically requires additional treatment before or after the absorption/stripping treatment to improve its purity, depending on its intended end use.

In my U.S. patent 7569710, the ethylene oxide reactor effluent is fed to an ethylene oxide absorber which contains a quench section in the lower portion of the absorber column where it is scrubbed with a recycled cooled basic water stream to absorb and neutralize acidic compounds such as acetic acid and formic acid and absorb nearly all trace amounts of by-product formaldehyde. Because the reaction gas contains CO₂The basic quench stream consists essentially of dissolved CO₂(as carbonic acid) buffered sodium bicarbonate, and has a pH value in the range of 7.1 to 8.0. The quench effluent is then used to remove water, an ethylene oxide reaction by-product, which is substantially completely condensed during quenching. The treated gaseous reactant stream from the alkaline quench is passed through a demister and fed to a water wash section where it is washed with fresh process water to remove any entrained quench liquid and absorb any residual formaldehyde vapor, passed through a liquid de-entrainment device, and fed to the bottom of an ethylene oxide absorber where it is counter-currently washed with recycled ethylene oxide-free process water to absorb ethylene oxide and produce a high purity ethylene oxide-containing absorbate. The quench effluent, typically containing from 0.5 to 3.0 wt% ethylene oxide with substantial concentrations of ethylene glycol and sodium salts and low concentrations of formaldehyde (e.g., methylene glycol), is sent to a quench effluent stripper where ethylene oxide is stripped and recovered. The ethylene oxide-free quench stripper bottoms can then be disposed of as a waste stream or separately treated to recover small amounts of technical grade ethylene glycol contained therein.

The alkalinity of the recycle quench condensate stream is typically provided by sodium bicarbonate and carbonate salts formed by the injected caustic solution and a small portion of the CO in the ethylene oxide reactor vent gas₂Formed by the reaction. Potassium hydroxide or potassium carbonate may also be used in place of caustic, but this adds significantly to the chemical cost as they are more expensive than caustic. The designed concentration range of the basic salt in the quenching liquid for complete neutralization of the organic acid in the reaction gas is usually 0.1 to 5.0% by weight. Modern high performance ethylene oxide reaction catalysts are now in demandLow CO required₂Concentration of CO to be introduced into the quench-washed reaction circulating gas₂The concentration is limited to 0.4 to 3.0% v, which corresponds to CO in the range of about 0.07 to 0.6 bar₂Partial pressure.

The published technical literature shows that even with 5.0 wt% sodium bicarbonate and carbonate in the recycle quench solution, and CO₂The partial pressure is only 0.1 bar and the equilibrium molar ratio of bicarbonate to carbonate will also be higher than 100: 1. Since pure sodium bicarbonate in the quench solution has a pH in the range of 8.0 to 8.5, while pure sodium carbonate has a pH in the range of 9.0 to 11.2, the initial pH of the alkaline mixture enriched in pure bicarbonate in the quench solution will be in the range of about 8.2 to 9.0. However, since the quench solution will also contain absorbed CO₂Which forms carbonic acid, which acts as a buffer and lowers the pH by at least 1 unit, the resulting pH in the quench tower will be in the range of 7.3 to 8.0, which facilitates complete neutralization of the organic acid and absorption of formaldehyde from the reaction gas (as evidenced by actual commercial operation).

As described in U.S. patent 7569710, the quench vent stripper is a small column that runs in parallel with the main ethylene oxide stripper at near atmospheric pressure and uses steam to strip the absorbed ethylene oxide. To avoid formaldehyde and entrained acid salts from the small purge stripper from contaminating the main ethylene oxide stripper product steam, the overhead ethylene oxide-rich steam from the quench vent stripper may need to be partially condensed and the contaminated condensate will be returned as reflux out of the stripper. The ethylene oxide-free bottoms product exiting the quench vent stripper should contain nearly all of the formaldehyde and heavy aldehyde impurities as well as all of the (neutralized) acids produced in the ethylene oxide reaction system and can be disposed of as a waste stream or separately treated to recover small amounts of commercial grade ethylene glycol contained therein.

In actual commercial operation, when the stripping steam quench exiting the bottom of the stripper is simply injected directly or generated inside the reboiler, the pH of the stripping section will rise until it is in the range of 9.0 to 10 because of the stripping of the carbonic acid and because there is no CO in the stripping steam₂Most of the hydrogen carbonateSodium is converted to sodium carbonate. Surprisingly, the literature indicates that at pH values above 8.0, the rate of decomposition of methylene glycol will increase exponentially. Thus, a majority of the methylene glycol in the vent stripper feed decomposes in the thermal stripping section to produce formaldehyde that is primarily stripped, so the stripper bottoms purge contains only a small portion of the aldehyde present in the stripper feed. The formaldehyde in the quench vent stripper overhead vapor is then absorbed into the reabsorber bottoms product stream and significantly reduces the purity of the ethylene oxide purification and/or concentrated ethylene oxide-water feed to the ethylene glycol plant.

By reducing the pH of the stripping section below 8.0, the amount of formaldehyde quenched to purge the stripper bottoms can be increased and maximized, which fundamentally reduces the rate of methylene glycol decomposition in the stripping section. This may be accomplished by injecting a dilute acid-water solution, such as acetic acid or sulfuric acid, to neutralize excess sodium carbonate and sodium bicarbonate in the quench bottoms bleed stream before the quench bottoms bleed stream is sent to the quench vent stripper. However, the necessary addition of acid storage, dilution, injection and pH control facilities will increase capital and chemical costs and significantly complicate the operation of quenching the effluent stripper.

The invention is achieved by injecting sufficient CO byproduct into the stripping steam₂Steam to provide CO at a minimum of 0.07 bar₂Partial pressure, provides an equally effective, much lower cost and much simpler design alternative for injecting acid solution to reduce the pH below 8.0 in the quench stripper.

Disclosure of Invention

Accordingly, the present invention provides a process for the purification of ethylene oxide, said process comprising quenching and scrubbing ethylene oxide reactor effluent by contact with a recycled, cooled, alkaline water stream, passing a gaseous ethylene oxide-containing stream obtained from said quenching and scrubbing into an ethylene oxide absorber wherein said ethylene oxide is absorbed in ethylene oxide-free, single pass process water to form an aqueous dilute absorbate solution comprising ethylene oxide and carbon dioxide, then stripping said dilute absorbate solution in an ethylene oxide stripper to produce an overhead vapor comprising ethylene oxide and carbon dioxide, then passing said overhead vapor into a re-absorber wherein said ethylene oxide and a portion of the carbon dioxide vapor are absorbed to form an aqueous re-absorbate solution, then passing said solution into a carbon dioxide stripper to remove dissolved carbon dioxide, recovering the ethylene oxide-containing solution free of light ends for use as a high purity feed to an ethylene oxide distillation system or FG MEG reactor; and

passing a liquid contaminant-containing effluent stream obtained from said quench wash to a second small quench vent stripper, introducing steam and carbon dioxide into said second stripper, sending said gaseous overhead from said quench vent stripper to said re-absorber for recovery of ethylene oxide, and removing formaldehyde and a contaminant-containing bottoms product from said quench vent stripper.

In a preferred embodiment, the carbon dioxide fed to the quench vent stripper is recycled carbon dioxide from other parts of the plant, such as a carbonate rich flash vessel or CO₂A carbon dioxide stripper of the removal section.

In another preferred embodiment, 10% to 90%, more preferably 20% to 80%, most commonly 25% to 30% of the dilute ethylene oxide solution obtained from the absorber is passed directly to the re-absorber without passing through the ethylene oxide stripper, thus reducing the stripping steam consumed in the ethylene oxide stripper by 25% to 30%.

In a further preferred process, a separate quench tower (or the bottom of the ethylene oxide absorber) is designed to thoroughly scrub the ethylene oxide reactor vent gas with a recycled, cooled dilute alkaline solution (typically 1% to 30%, preferably 1% to 15% alkaline hydroxide solution) to neutralize the organic acids and absorb the maximum amount (about 90% to 98%) of formaldehyde and other soluble (in-water) aldehyde impurities. Preferably, the scrubbing gas from the basic quench scrubbing section will pass through a high efficiency demister apparatus to remove entrained quench solution, and then be scrubbed with a small amount of once-through (or recycle) fresh water to remove any entrained quench liquid and absorb most of the remaining formaldehyde. The effluent wash water from the wash section may then be discharged into a lower quench section to reduce the concentration of formaldehyde and absorbed impurities and more completely remove them in the quench solution.

The scrubbed recycle gas, which is almost completely free of formaldehyde and heavy impurities and also completely free of acids, is typically passed through a demister unit to remove entrained scrubbing liquid and then thoroughly scrubbed in an ethylene oxide absorber with ethylene oxide-free once-through process water (recovered from the stripper and glycol unit) to completely absorb the ethylene oxide and produce a dilute (1 to 5 wt%) ethylene oxide-water solution.

Drawings

Figure 1 is a schematic diagram of a simple form of the invention.

FIG. 2 is a schematic representation combining all of the preferred features described above, but it should be recognized that each of these preferred features can be used independently of the other.

FIG. 3 is a schematic diagram of the integration of the improved process into a flow scheme of a prior art recovery system such as that described in U.S. Pat. No. 3,964,980, which consists of a new wash/quench tower and quench purge stripper, and the addition of an ethylene oxide rich absorbate stream that bypasses the ethylene oxide stripper, flows directly to the ethylene oxide reabsorber, and after CO removal₂And light ends, into a high purity ethylene oxide column and/or MEG reactor.

Fig. 4 is a schematic diagram of the incorporation of the improved process into a flow scheme of a prior art recovery system such as that described in U.S. patent No. 4,822,926, which consists of an improved wash/quench tower and an improved ethylene oxide stripping system wherein the ethylene oxide rich absorber stripper bypass stream is injected into the residual absorber to absorb more ethylene oxide and then sent directly to the high purity ethylene oxide column.

Detailed Description

The simplest form of the invention is depicted in FIG. 1, where the effluent from the ethylene oxide reactor is fed via line 1 to the lower portion of quench tower 2. Part of the quench bottoms is recycled to the quench tower after cooling, for example by means of a heat exchanger.

An aqueous alkaline solution, such as sodium hydroxide, is fed into the quench tower through inlet 3 above inlet 1. The recycle section of the quench bottoms product may conveniently be combined with base and introduced via inlet 3 and a separate inlet may be provided for the recycle bottoms product, but this is not essential. An aqueous sodium hydroxide solution having a concentration of 10 to 20% by weight is generally used. The overhead of the quench tower, including ethylene oxide, is passed via line 4 to the bottom of absorber 5. The net bottoms of the quench tower is passed via line 9) to the upper part of the purge stripper 10.

It is preferred to include a demister in the upper portion of the quench tower to minimize the amount of entrained liquid passing into the absorber. It is also possible to combine the quench tower and the absorber in a single tower with the absorber section located above the quench section.

Cold absorption water is fed to the upper absorber 5 through inlet 6 and the reaction effluent gas is contacted counter-currently with water to absorb substantially all of the ethylene oxide entering via conduit 4. The non-condensable reaction gas leaving the top of the absorber 5 is substantially free of ethylene oxide and is returned to the ethylene oxide reaction system via conduit 7. The dilute ethylene oxide-water solution formed in absorber 5 is withdrawn from the bottom of the absorption section via conduit 8 and passed to the top of ethylene oxide stripper 11. Steam enters the ethylene oxide stripper through inlet 12. The absorbate is stripped of ethylene oxide by countercurrent contact of the absorbate and steam within stripper 11, which is withdrawn from the top of stripper 11 via conduit 13 along with steam, carbon dioxide, light ends and trace impurities. The stripped (lean) absorbate, now substantially free of ethylene oxide, is withdrawn from the bottom of stripper 11 via conduit 14. This lean absorbate may be cooled and recycled to the absorber 5 if desired. The overhead from stripper 11 contains ethylene oxide, as well as steam, carbon dioxide, light ends, non-condensable gases, and trace impurities. The overhead passes via conduit 13 to the lower portion of the re-absorber 15.

As described above, the bottom product of the quenching tower 2 is fed via conduit 9 into the upper part of the purge stripping column 10. Steam is fed to the lower part of the purge stripper as in conventional plants. However, according to the invention, carbon dioxide is also introduced into the lower part of the purge stripper. The introduction of steam and carbon dioxide may be through separate inlets, such as inlets 16 and 17 shown in fig. 1, but preferably the steam and carbon dioxide should be mixed and introduced together through a single inlet. By injecting sufficient by-product CO into the stripping steam₂Steam to provide CO at a minimum of 0.07 bar₂Partial pressure, introducing an amount of carbon dioxide to reduce the pH in the purge stripper to below 8.0. More preferably, the pH is brought within the range of 7.3 to 7.9, and CO₂The partial pressure is in the range from 0.1 to 0.3 bar. The carbon dioxide used may conveniently be recovered from other parts of the system. For example, carbon dioxide may be obtained from an ethylene oxide production plant in which the carbon dioxide is in CO₂Removed from the ethylene oxide in the removal section. Such CO₂The removal section may produce steam containing 95% or more carbon dioxide. By monitoring the pH of the bottoms purge and adjusting the CO entering the purge stripper₂The flow rate can control the pH value of the purge stripping tower. CO if required to reach the desired pH₂Too large an amount may affect further adjustment of the pH by adding an acid such as acetic acid or sulfuric acid.

The bottoms product from purge stripper 10, which contains most of the formaldehyde, salts and a small amount of ethylene glycol, is sent via outlet 18 to waste treatment or industrial grade ethylene glycol recovery. The overhead from the purge stripper 10 containing ethylene oxide, steam and carbon dioxide is passed via conduit 19 to re-absorber 15, optionally after being combined with the overhead from stripper 11 in line 13. Cold water is introduced into the upper portion of the re-absorber 15 through inlet 20. The non-condensable gases are exhausted through an exhaust port 24. The bottom product from the re-absorber 15 is recovered via line 21 and after passing through the carbon dioxide stripper 22 the ethylene oxide containing stream is passed to an ethylene glycol production reactor or subjected to further ethylene oxide distillation.

Most of the water formed in the ethylene oxide reactor is condensed in the quench scrubber. To maintain water balance in the quench water system, a clean purge of the alkaline quench water and wash water is required. Since the total quench bottoms purge will also contain a low concentration (1 wt% to 4 wt%) of ethylene oxide, its ethylene oxide content will be stripped off in a small purge stripper, which will run in parallel with the main stripper. To avoid formaldehyde and entrained acid salts from the small purge stripper from contaminating the main stripper product ethylene oxide vapor, the overhead ethylene oxide-rich vapor from the purge stripper will be partially condensed and the contaminated condensate will be returned to the purge stripper as reflux. Thus, the ethylene oxide-free bottoms from the quench purge stripper will contain almost all of the formaldehyde and heavy aldehyde impurities as well as all of the (neutralized) acid produced in the ethylene oxide reaction system. Since the amount of ethylene glycol in such small purge (resulting from hydration of ethylene oxide in quench scrubbers and purge strippers) is very small, it is generally not necessary to install a dedicated purge ethylene glycol recovery facility and can be sent directly to most facilities for waste treatment. Alternatively, the quench/purge may be treated as a technical grade product to recover ethylene glycol.

The dilute ethylene oxide-bottoms stream from the absorber (free of organic acids, substantially free of formaldehyde and heavy contaminants) will be completely stripped of ethylene oxide and dissolved gases in the main ethylene oxide stripper. The overhead ethylene oxide and water-rich vapor are cooled and partially condensed in an overhead heat exchanger, which may be cooled using air or cooling water. Unlike the process described in U.S. patent No. 3,964,980, both the vapor and condensate effluents of the main stripper condenser are sent to the reabsorber because the ethylene oxide-rich condensate is also substantially free of impurities. This increases the efficiency of the ethylene oxide stripping/reabsorption step compared to the prior art.

In the process, high purity ethylene oxide-water bottoms product from the ethylene oxide absorber, if CO is being removed₂And other absorbed non-condensable gases are then used as feed to an integrated glycol plant that will produce fiber grade glycol. Unfortunately, based on industry information, in commercial ethylene oxide reaction systems, the concentration of ethylene oxide in the dilute ethylene oxide absorbate is too low to be economically used as a direct to ethylene glycol reactor and vaporization systemFeeding.

The water balance in the absorber-stripper system can be maintained by injecting the low pressure process steam extracted from the ethylene glycol plant directly into the ethylene oxide stripper to provide up to 100% of the required stripping steam, which is an additional advantage of the present invention, or by recovering water from the evaporation section of the ethylene glycol plant for use as absorption water.

In the preferred process of the present invention as shown in fig. 2, the majority of the ethylene oxide absorbate need not be stripped of its ethylene oxide in the main ethylene oxide stripper, but rather can be sent directly to an ethylene oxide reabsorption system to absorb more ethylene oxide so that it can be used as a direct feed to an ethylene glycol reactor or high purity ethylene oxide column. This reduces the operating and capital costs of the ethylene oxide absorption system and makes the use of water/ethylene oxide molar ratios above 25:1 more economical.

The flow chart shown in fig. 2 includes all of the preferred features described above, but as previously mentioned, each of the preferred features may be used independently of the other. Parts common to fig. 1 and 2 have the same reference numerals in both figures.

The flow chart in fig. 2 differs from the flow chart in fig. 1 in the following:

1) the quench tower 2 is provided with a demister to remove entrained liquid from the gas stream passing to the absorber 5. Two demisters are typically used, but the actual number may vary depending on the conditions of use. When two demisters are used, they will be located in the quench tower, one above the other, with the fresh water feed located between the two demisters. Thus, in the quench tower 2 of FIG. 2, material rising from the quench section below the base feed inlet first passes through a demister apparatus 25, is washed with fresh water fed through inlet 27, and then passes through an upper demister apparatus 26 before exiting the quench tower through the top duct 4. The water added in this way is included in the quench bottoms which is sent to purge stripper 10. Typically, most of the quench bottoms removed via line 9 will be cooled and recycled to the quench tower below the lower demister network 25.

2) As described in us patent 7569710, if purity sufficient to produce fiber grade ethylene glycol or ethylene oxide for some other use is desired, the majority of the energy cost in an ethylene oxide recovery unit is in the conventional stripping of all material passing from the absorber. The invention described in us patent 7569710 is based on the recognition that: ethylene oxide of the desired purity can be obtained even if only a portion of the absorbate from the absorber passes through the stripper. This knowledge is equally applicable to the present invention. In the flow diagram of fig. 2, the absorbate from the absorber 5 via line 8 is split between two conduits. Some enter the stripper via conduit 28 and the remainder enter the re-absorber 15 via conduit 29. Typically, the dilute ethylene oxide solution obtained from the absorber 5 is fed directly to the re-absorber 15. Thus, in a commercially significant feature of one aspect of the invention, 10% to 90%, preferably 20% to 80%, most commonly 25% to 30%, of the contaminant free ethylene oxide absorber bottoms product can be sent directly to the reabsorption system, bypassing the ethylene oxide stripper, and then continuing to remove dissolved carbon dioxide without passing through the ethylene oxide stripper. The maximum potential stripper bypass rate (and associated stripper energy savings) increases with increasing ethylene oxide concentration in the absorbate and decreases the production of heavier ethylene glycol with increasing water to ethylene oxide ratio in the ethylene glycol reactor feed. The flow of reabsorption feed water, possibly recycled water from the ethylene glycol plant evaporation (and ethylene oxide purification section), is reduced proportionally to produce the desired ethylene oxide concentration (typically 6 to 12 wt%) at the bottom of the reabsorber (or light ends column).

3) Carbon dioxide introduced into the purge stripper 10 is recycled from the carbon dioxide removal section via line 17 and mixed with steam from line 16 prior to injection into the stripping section.

As noted above, it may be desirable to recycle the bottoms product from stripper 11 after cooling to the top of absorber 5. The hot bottoms from the stripper may then need to be passed through outlet 14 through a heat exchanger where it heats the material fed to the top of stripper 11.

The process of the present invention is applicable to SD and shell ethylene oxide recovery systems as described above to adjust the pH in what is commonly referred to as a purge stripper in the SD process or a quench vent stripper in the shell process.

In embodiments where a large amount of absorbate bypasses the stripper and is passed directly to the re-absorber, further major savings in the modified SD-type ethylene oxide scheme result from the elimination of the expensive stripper bottoms (recycle water) discharge treatment system, such as described in U.S. patent No. 3,904,656, or a separate byproduct ethylene glycol concentration and recovery facility, such as described in U.S. patent No. 6,417,411.

The modified stripper bypass scheme allows the ethylene oxide recycle water to enter the ethylene glycol plant at a very high "bleed" rate without the need for expensive pretreatment. Thus, the equilibrium ethylene glycol concentration in the ethylene oxide absorber-stripper cycle water can be reduced to very low concentrations (<1 wt%), while standard stripper systems typically correspond to higher concentrations (3 wt% to 6 wt%). The lower ethylene glycol concentration reduces the tendency of the water absorbent material to foam in the ethylene oxide absorber and ethylene oxide stripper columns, thereby increasing the capacity and efficiency of the trays or packing in these columns. Thus, applying the present invention to an ethylene oxide absorber-stripper system in a new plant will save initial investment and continued energy usage.

The stripper bypass concept also has great benefit for existing ethylene oxide plants where it is desirable to expand the capacity of their existing ethylene oxide reaction and recovery sections. Application of the present invention will very simply debottleneck the ethylene oxide absorber-stripper system with minimal capital cost and also significantly reduce energy consumption (and CO)₂Yield), which has become a major environmental and economic consideration.

Removing substantially all of the formaldehyde produced in the ethylene oxide reactor from the feed stream to the ethylene glycol plant will result in less uv-absorbing impurities being produced in the ethylene glycol reactor and improved quality fiber grade ethylene glycol. Thus, another major potential benefit of applying the present invention to a SD-type ethylene oxide reaction/recovery system similar to that described in U.S. patent No. 3,964,980 is that it allows the use of ultra-high selectivity ethylene oxide catalysts, which (as known in the industry) can generate large amounts of formaldehyde, which typically adversely affects the uv quality of ethylene glycol produced in standard SD-type integrated ethylene glycol plants that produce only fiber-grade MEG.

The shell type ethylene oxide process, as described in U.S. patent No. 4,822,926, includes a quench scrubber and quench stripper, which are the basic steps of the improved ethylene oxide recovery process. However, as described in the patent, these two process steps do not produce an ethylene oxide absorber bottoms product that is completely contaminant free and suitable as a direct feed to a fiber grade ethylene glycol reactor, and in the patent flowsheet, 100% of the ethylene oxide absorbate is ultimately sent to the ethylene oxide stripper. By incorporating the present invention and increasing the impurity absorption efficiency of the quench section by adding water washes and reducing interstage and interstage entrainment in the quench scrubber, the ethylene oxide rich absorbate will be sufficiently pure for use as a direct feed to the ethylene glycol plant. Thus, a significant portion (15% to 75%) of the ethylene oxide absorbate may be injected directly into the stripper overhead ethylene oxide recovery section to absorb more ethylene oxide and then fed directly into the ethylene oxide purification column, thereby bypassing the ethylene oxide stripper altogether.

Furthermore, to avoid any contamination from the quench bleed solution in the present improved scheme, the ethylene oxide-rich overhead vapor from the quench stripper (e.g., in a shell process) will be partially condensed and the condensate contaminated with entrained salt and condensed formaldehyde will be returned to the quench stripper as reflux. The net ethylene oxide vapor and uncondensed vapor will flow directly to the residual ethylene oxide absorber to recover ethylene oxide vapor as the ethylene glycol reactor feed. The ethylene oxide-free bottoms product from the improved quench vent stripper will contain substantially all of the formaldehyde and heavy aldehyde impurities as well as all of the (neutralized) acid produced in the ethylene oxide reaction system. Since the amount of ethylene glycol in such small purge (resulting from hydration of ethylene oxide in quench scrubbers and stripper columns) is very small, if existing purge ethylene glycol recovery facilities are not available, the ethylene glycol can be sent directly to waste treatment with minimal economic loss.

The current ultraviolet transmittance index ranges are as follows:

the primary cause of impurities in the glycol hydration reactor is formaldehyde, which can adversely affect the ultraviolet transmittance of the fiber grade glycol product, is introduced via the treated recycle water effluent and accumulates in the glycol reaction recycle water.

Fig. 3 shows the application of an embodiment of the present invention to the apparatus described in U.S. patent No. 3,964,980. Referring to fig. 3, the vent gas from the ethylene oxide-containing ethylene oxide reaction system is introduced directly into the bottom section of quench tower 352 via conduit 302. The quench bottoms solution is recycled to the top of the quench wash section via conduits 353 and 355A, cooler 354, and conduits 355B and 357. Concentrated sodium hydroxide (10 to 20 wt% aqueous solution) is injected via conduit 356 into the recirculating quench solution to convert to sodium carbonate and bicarbonate and neutralize the organic acids. The cooled wash vapor (free of organic acid vapors, but containing some formaldehyde and entrained quench liquid) from the top of the quench section 352 is passed through a demister apparatus 359 to remove entrained liquid and enters the upper wash section 361.

The filtered quench gas exiting the quench demister 359 is then washed with fresh process water and introduced via conduit 362 to completely remove any remaining entrained quench liquid and absorb most of the remaining formaldehyde and heavy impurities. Preferably, a counter-current water wash is used, before which it may be passed through a recycle water wash section to obtain maximum vapor-liquid contact. The net wash water from the bottom of the water wash section can be discharged into the top of the lower quench section 352 to dilute the concentration of formaldehyde and other impurities in the quench liquid and reduce the equilibrium concentration of these impurities in the wash gas feed to the ethylene oxide absorber. The net quench bottoms effluent containing condensed water, wash water, absorbed impurities and some ethylene oxide flows via conduits 353 and 365 to quench vent stripper 366.

The wash steam from the top of the water wash section passes through a demister apparatus 363 to remove any entrained wash water and enters the bottom of the ethylene oxide absorber 303 via a conduit 364. Cold absorbed water is introduced into the upper section of absorber 303 via conduit 321B and the reaction effluent gas is counter-currently contacted with water to absorb substantially all of the ethylene oxide entering via conduit 364. The non-condensable reactant gas leaving the top of the absorber 303 is substantially free of ethylene oxide and is returned to the ethylene oxide reaction system via conduit 304. The dilute ethylene oxide-water solution formed in absorber 303 is withdrawn from the bottom of the absorption section via conduit 305.

In fig. 3, the quench/scrubber tower is shown as a separate vessel for clarity of illustration. However, in a practical plant, the ethylene oxide absorber, water wash and base quench sections may be combined into one housing to minimize pressure drop and capital cost.

In this flow diagram, a portion of the ethylene oxide absorbate in conduit 305 bypasses ethylene oxide stripper 311 and flows directly to ethylene oxide re-absorber bottom recycle cooler 329 via conduits 310 and 333A. The by-pass varies between 15% and 75%, depending on the ethylene oxide concentration in the absorbate and the desired ethylene oxide concentration in the bottom of the reabsorber (and the ethylene glycol reactor feed), and can be determined using tables, equations or graphs.

The remaining absorbate is introduced into stripper preheater exchanger 307 via conduit 308 and the hot rich absorbate from preheater 307 is sent to the upper section of ethylene oxide stripper 311 via conduit 309. Stripping steam extracted from the ethylene glycol plant is introduced into the lower portion of stripping column 311 via conduit 338 or is generated internally by a reboiler (not shown). The absorbate is stripped of ethylene oxide by countercurrent contact of the absorbate and steam within stripper 311, which is withdrawn from the top of stripper 311 via conduit 313A along with steam, carbon dioxide, light ends and trace impurities. A stripped (lean) absorbate that is substantially free of ethylene oxide is withdrawn from the bottom of stripper 311 via conduit 319A and cooled in heat exchanger 307, thereby releasing heat to the rich absorbate feed. The cooled lean absorbate from cooler 307 is combined with recycle water from the glycol plant in conduit 321A via conduit 319B to heat exchanger 320 where it is further cooled and the total lean absorbate stream is recycled back to absorber 303 via conduit 321B.

The absorbate feed to stripper 311 may contain from about 1 wt% to about 5 wt% ethylene oxide, and the stripper is operated to recover greater than 95% and typically greater than 99% of the ethylene oxide contained in the stripper feed. Although the stripper is typically operated at near atmospheric pressure, the temperature within the column is high enough to thermally hydrate in the range of 0.5% to 3.0% of the ethylene oxide feed to ethylene glycol. The ethylene glycol produced in the ethylene oxide stripper will accumulate to a low equilibrium concentration controlled by the absorbate bypass (via stream 310) which serves as a very large recycle water ethylene glycol effluent.

The stripper overhead vapor withdrawn via conduit 313A typically contains about 20 to 30 mole percent ethylene oxide. The primary diluent in this vapor stream is water, but about 7% to 10% can be generally referred to as a non-condensable gas, primarily CO2, but also including nitrogen, argon, oxygen, methane, ethylene, and ethane. The stripper overhead vapor is cooled in heat exchanger 312 and the total effluent mixture of uncondensed vapor and condensate flows to reabsorber 327 via conduits 313B and 316.

The net vent bottoms stream from quench tower 352 consists primarily of ethylene oxide reaction by-product water that is partially condensed in the quench scrubber plus make-up wash water, and contains some basic salts and absorbed ethylene oxide. This stream is sent via conduit 365 to a small purge stripper 366 in which the contained ethylene oxide is stripped off using stripping steam injected via conduit 371 or generated in a reboiler (not shown). The purge stripper feed/bottoms heat exchanger can also be used to reduce reboiler heat duty and/or stripping steam amount. The purge stripper overhead vapor is cooled in heat exchanger 368 to a temperature such that a majority, preferably at least 60%, of the contained water condenses. The contaminated condensed phase from condenser 368 is vented or pumped back to purge the upper portion of stripper 366 via conduit 369. Uncondensed purge stripper overhead vapor is withdrawn from condenser 368 via conduit 370, combined with the ethylene oxide and condensate mixture from main stripper condenser 312 in conduit 316, and introduced into the lower portion of re-absorber 327. The ethylene oxide-free aqueous bottoms from purge stripper 366, containing most of the formaldehyde, salts and small amounts of ethylene glycol, is sent via conduit 372 to waste treatment or to industrial grade ethylene glycol recovery.

Some of the circulating cold water is introduced into the upper portion of the re-absorber 327 via conduit 351B. In the upper section of the re-absorber, the light gases and water in the stripper overhead vapor are countercurrently contacted to absorb the maximum possible amount of ethylene oxide contained in the vapor. Uncondensed gases (typically containing only trace amounts of ethylene oxide) from the top of the re-absorber 327 are vented via conduit 328. Since this vent stream contains significant amounts of hydrocarbons (consisting primarily of ethylene and methane), it is preferably compressed and recycled back to the ethylene reactor gas system to (partially) recover the contained ethylene. In some plants, particularly those with relatively low production capacity, the reabsorber effluent gas is vented to the atmosphere or preferably incinerated to avoid atmospheric pollution.

The ethylene oxide-rich reabsorbent exits the bottom of reabsorbent 327 via conduit 330. The re-absorbate is pressurized using a pump (not shown) and is divided into two parts. A portion that is a net bottoms product flows via conduits 331 and 334 to ethylene glycol reaction system 335 and/or may flow via conduit 344 to ethylene oxide purification unit 345. The aqueous reabsorption bottoms product contains not only the reabsorbed ethylene oxide vapor, but also acetaldehyde, dissolved carbon dioxide and non-condensable gases. The water balance in the absorber-stripper system can be maintained by injecting the low pressure process steam extracted from the ethylene glycol plant directly into the ethylene oxide stripper to provide up to 100% of the required stripping steam (which is an additional benefit of the present invention), or by recycling water from the evaporation section of the ethylene glycol plant for use as absorption water and other organic and inorganic gases.

As described in U.S. patent No. 4,134,797, the ethylene oxide-rich reabsorbent discharged via conduits 330 and 331 will first pass to carbon dioxide stripper 380 where the liquid is stripped of CO₂. The gas-free bottoms of the carbon dioxide stripper are then pumped to an ethylene glycol reaction and ethylene oxide purification unit, as described in U.S. Pat. No. 3,964,980.

The recycled absorbate flowing through conduit 332 is combined with the bypassed rich absorbate in conduit 333A, cooled in heat exchanger 329, and introduced as a cold liquid into the middle of the reabsorber 327 via conduit 333B. Heat exchanger 329 maintains the reabsorber in thermal equilibrium to achieve a predetermined bottom reabsorber temperature and ethylene oxide concentration. Depending on the operating pressure of the re-absorber and the amount of by-pass dilution absorbate, the ratio of re-absorbate circulated via conduit 332 to net re-absorbate discharged via conduit 331 will be in the range of 0-3: 1. Maximum bypass of rich absorbate (not shown) can be achieved when the bypassed absorbate in stream 310 is cooled separately and introduced into the reabsorber 327 at a location above the bottom reabsorbent of the cycle.

The reabsorbent that flows to ethylene oxide purification is preheated in heat exchanger 343 and fed to the lower portion of a single ethylene oxide purification column 345 where it is separated into a purified ethylene oxide product (stream 346) and two crude ethylene oxide purge streams rich in formaldehyde and acetaldehyde (streams 347 and 348, respectively), which are fed to ethylene glycol reactor 335. The ethylene oxide-free bottoms water stream containing most traces of formaldehyde in the purified feed is withdrawn via conduit 349A, cooled in heat exchanger 343, and recycled to re-absorber 327 via conduit 349B.

In ethylene glycol reactor 335, the ethylene oxide in the bottom product of the degassing reabsorber reacts almost completely with water to form ethylene glycol. The effluent from the ethylene glycol reactor 335 is sent to a multi-effect evaporation system 337 in which water is separated from the crude ethylene glycol and then sent to an ethylene glycol purification unit (not shown) via conduit 340. A portion of the water separated in vaporization system 337 is recycled back to the ethylene oxide plant as steam via conduit 338 and directly injected into ethylene oxide stripper 311 to provide up to 100% of the desired stripping steam. The remaining recovered water is condensate that is recycled back to the ethylene oxide plant via conduits 339A and 342, combined with the ethylene oxide refiner 345 bottoms in conduit 351A, cooled in cooling means 350, and sent as reabsorbents via conduit 351B to the top of reabsorber 327. To maintain water balance in ethylene oxide stripper 303, make-up ethylene glycol recycle water may be added via conduits 339B, 321A, and 321B.

The improved flow scheme shown in fig. 3 and described herein will produce a fiber-grade MEG that will significantly exceed the current uv transmittance index range previously shown.

Figure 4 shows the application of an embodiment of the present invention to an integrated ethylene oxide/ethylene glycol plant having an ethylene oxide recovery scheme comparable to that of U.S. patent No. 4,822,926. Referring to fig. 4, the vent gas from the ethylene oxide-containing ethylene oxide reaction system enters the ethylene oxide quench section 652 of the ethylene oxide absorber through conduit 602A, gas cooler 601 and conduit 602B, as previously described. The quench bottoms solution is recycled to the top of the quench wash section 652 via conduits 653 and 655A, cooler 654 and conduits 655B and 657. Sodium hydroxide is injected into the recycled quench solution via conduit 656 to convert to sodium carbonate and bicarbonate and neutralize organic acids. In new plants, the gas cooler 601 may be omitted by increasing the quench recirculation rate and heat duty of the quench cooler, and by adding 1 to 4 more quench trays.

The cooled scrubbing vapor (free of organic acid vapors, but containing some formaldehyde and entrained quench liquid) from the top of the quench section 652 is passed through a demister device 659 to remove entrained liquid and enters the upper scrubbing section 661 via an internal vapor conduit (not shown). The filtered quench gas exiting the quench mist eliminator 659 is then scrubbed with fresh process water (stream 662) to completely remove any remaining entrained quench liquid and absorb most of the remaining formaldehyde and heavy impurities. Preferably, a counter-current water wash is used, before which it may be passed through a recycle water wash section to obtain maximum vapor-liquid contact. Clean wash water from the bottom of the water wash section 661 can be discharged into the top of the lower quench section 652 to dilute the concentration of formaldehyde and other impurities in the quench liquid and to reduce the equilibrium concentration of these impurities in the wash gas feed to the wash section. Containing condensed water, washing water and alkaliThe net quench bottoms solution effluent of saline salts, absorbed impurities and some ethylene oxide flows via conduits 653 and 665 to quench vent stripper 673. Concentrated CO via line 695 injection to quench the stripper vent to lower the pH₂Preferably mixed with steam from line 674. CO2₂CO from ethylene oxide production plant₂Removing the section to obtain. By monitoring pH and adjusting CO entering the purge stripper₂Flow rate, controlling the pH value in the range of 7.3 to 7.9. If the amount of CO2 needed to reach the desired pH is too large, further adjustment of the pH can be effected by adding an acid, such as acetic acid or sulfuric acid.

The wash steam from the top of the water wash section passes through a demister 661A to remove any entrained wash water and enters the bottom of the ethylene oxide absorber 603 via an internal conduit 660. In the ethylene oxide absorber 603, the ethylene oxide contained in the quenched reaction gas is absorbed by countercurrent contact with cold circulating absorption water introduced via conduit 622. The non-condensable reactant gas leaving the top of the absorber 603 is substantially free of ethylene oxide and is returned to the ethylene oxide reaction system via conduit 604. The ethylene oxide rich absorber bottoms is withdrawn via conduit 605 and a portion (15% to 75%) bypasses the ethylene oxide stripper and is sent directly to the middle section of residual absorber 683, where it absorbs more ethylene oxide, via conduits 606, 682A and 682B and new reabsorption cooler 681.

The remaining rich absorbate flows to gas cooler 601 via existing conduit 605A and enters stripper preheater exchanger 607 via conduit 605B. The hot rich absorbate from preheater 607 is introduced via conduit 609 into the upper portion of ethylene oxide stripper 611. In the ethylene oxide stripper 611, the dissolved ethylene oxide and other light components are stripped away using stripping steam generated in reboiler 617 and/or injected directly as live steam (stream 638). A stripped (lean) absorbate that is substantially free of ethylene oxide is withdrawn from the bottom of stripper 611 via conduit 619A and cooled in heat exchanger 607, thereby releasing heat to the absorbate rich feed. The cooled lean absorbate from cooler 607 is combined via conduit 619B with recycled water from ethylene glycol evaporation and ethylene oxide purification (stream 671) in conduit 621A to cooling unit 620 where it is further cooled and recycled back to absorber 603 via conduits 621B and 622. A portion of the cold lean absorbate from cooler 620 may be sent to the top of residual absorber 683 via conduit 623 to absorb ethylene oxide from the light gas vent. Alternatively, the cold recycle water from the ethylene glycol and ethylene oxide purification unit (stream 684) may be injected directly into the reabsorber to replace all or part of stream 623.

The stripper overhead vapor withdrawn via conduit 613 can be expected to contain about 20 to 30 mole percent ethylene oxide. The primary diluent in the vapor stream is typically water, but about 7% to 15% is a non-condensable gas, primarily CO₂But also nitrogen, argon, oxygen, methane, ethylene and ethane. The stripper overhead vapor is combined with overhead vapor from light ends column 690 in conduit 613A and cooled and partially condensed in heat exchanger 612. The total effluent mixture of uncondensed vapor and condensate from condenser 612 flows via conduit 613B to separator 614 where the vapor and liquid are separated.

The ethylene oxide-rich vapor flows from separator 614 via conduit 616 to the bottom of residual absorber 683. Within the top of the residual reabsorber 683, the light gases in the stripper overhead vapor are countercurrently contacted with cold circulating water to absorb the maximum possible amount of ethylene oxide contained in the vapor. Uncondensed gases (typically containing only trace amounts of ethylene oxide) from the top of the re-absorber 683 are vented via conduit 686A. Since this vent stream contains a significant amount of hydrocarbons (consisting primarily of ethylene and methane), it is preferably compressed in compressor 685 and recycled back to the ethylene reactor gas system to recover the contained ethylene. In some plants with reduced capacity, the residual absorber effluent gas may be vented to the atmosphere or, preferably, may be incinerated to avoid atmospheric pollution.

The ethylene oxide rich reabsorber exits the bottom of residual absorber 683 via conduit 687. The re-absorbate is pressurized using a pump (not shown) and is divided into two parts. Circulation ofFlows through conduit 689 and is cooled in heat exchanger 681 after being combined with the bypass rich absorbate in conduit 682A and enters the middle section of residual reabsorber 683. The net reabsorbed product flows via conduit 688 to separator 614 where it is combined with condensate from condenser 612 and enters the upper portion of light ends column 690 via conduit 615. In the light ends column 690, the reabsorbed solution is stripped of CO₂And other dissolved gases, which are recycled back to the condenser 612 via conduits 691 and 613A.

All light ends-free bottoms from light ends column 690 are then pumped directly to an ethylene glycol reaction and ethylene oxide purification unit (not shown) via conduit 693.

The improved ethylene oxide quench/wash system of the present invention reduces formaldehyde and other contaminants in the ethylene oxide absorbate, making it suitable as a direct feed for ethylene glycol reactions, and improving MEG quality. In addition, the improved ethylene oxide quench cooling system design provided by the improved quench/scrubbing system allows for the omission of the reaction gas cooler and reduces the recycle gas pressure drop, thereby saving power. The improved quench purge column design reduces ethylene oxide re-contamination with the absorbent feed in the ethylene glycol reaction and improves MEG quality. Other glycol reaction improvements resulting from the present invention include: increasing the economically optimal range of water/ethylene oxide ratio in the ethylene glycol reactor feed (ethylene oxide reabsorber) by adding an efficient ethylene oxide stripper bypass, thereby rationalizing very high water ratios (up to 40:1), resulting in a higher MEG production with a lower DEG/TEG production; the low pressure process steam extracted from the ethylene glycol plant is injected directly into the bottom of the ethylene oxide stripper, providing up to 100% of the required stripping steam; passing the water effluent stream from the quench/wash section to a separate purge stripper designed for low liquid holdup time to minimize ethylene oxide hydration to MEG, wherein the absorbed ethylene oxide is completely stripped off for recovery as feed to the fiber-grade MEG reactor; the purge stripper overhead vapor is cooled to condense a major portion (preferably at least 60%) of the water vapor and return entrained salt and condensed formaldehyde-contaminated condensate to the top of the purge stripper. Thereafter, the uncondensed ethylene oxide-rich vapor from the partial condenser is sufficiently pure to combine with the main ethylene oxide stripper overhead vapor to recover its ethylene oxide content in the re-absorber or residual absorber.

Eliminating the need for a previous glycol treatment system saves capital and operating costs. The combination of the current quench/wash and quench purge stripper systems purges most of the formaldehyde generated in the ethylene oxide reaction to waste and radically reduces the accumulation of formaldehyde in the ethylene glycol reaction system, which allows the use of ultra-high selectivity ethylene oxide catalysts. As the water/ethylene oxide ratio in the ethylene glycol reactor feed (ethylene oxide reabsorber) increases, the stripper by-pass can be increased, thereby economically rationalizing very high water ratios (up to 35:1) and resulting in higher MEG production.

The high "purge" rate of the ethylene glycol plant stripper recycle water results in a very low equilibrium ethylene glycol concentration in the recycle water, reduces foaming, increases column efficiency and capacity, and allows for the direct injection of very low pressure process steam extracted from the ethylene glycol plant into the ethylene oxide stripper to provide up to 100% of the required stripping steam.