Patent Description:
Though present in natural settings at minute quantities, ethylene oxide was first synthesized in a laboratory setting in <NUM> by French chemist Charles-Adolphe Wurtz using the so-called "chlorohydrin" process. However, the usefulness of ethylene oxide as an industrial chemical was not fully understood in Wurtz's time; and so industrial production of ethylene oxide using the chlorohydrin process did not begin until the eve of the First World War, due at least in part to the rapid increase in demand for ethylene glycol (of which ethylene oxide is an intermediate) as an antifreeze for use in the rapidly growing automobile market. Even then, the chlorohydrin process produced ethylene oxide in relatively small quantities and was highly uneconomical.

The chlorohydrin process was eventually supplanted by another process, the direct catalytic oxidation of ethylene with oxygen, the result of a second breakthrough in ethylene oxide synthesis, discovered in <NUM> by another French chemist, Thèodore Lefort. Lefort used a solid silver catalyst with a gas phase feed that included ethylene and utilized air as a source of oxygen.

In the ninety years since the development of the direct oxidation method, the production of ethylene oxide has increased so significantly that today it is one of the largest volume products of the chemicals industry, accounting, by some estimates, for as much as half of the total value of organic chemicals produced by heterogeneous oxidation. Worldwide production in the year <NUM> was about <NUM> billion tons. One of the reasons that ethylene oxide is such a widely produced chemical product is its startling versatility - it is the starting point for innumerable derivatives, including ethylene glycol, ethoxylates, ethanolamines, polyols, and glycol ethers, each of which becomes the raw material for numerous high-value products such as fabrics, moldable plastics, surfactants, detergents, solvents and many others.

Increases in annual production have proceeded in parallel and in fact have been enabled by parallel increases in production plant sizes. While larger plants are more efficient, there are of course diminishing returns to increased plant size. In particular, larger plants require ever larger reactors, which is the major capital cost component for an ethylene oxide/ethylene glycol ("EO/EG") plant. An alternative to larger plants and their larger reactors is to operate at higher work rates and higher percentages of ΔEO. Operating at higher work rates (work rate being the kg of EO produced in reactor per hour per m<NUM> of catalyst) and higher ΔEO (defined as moles of ethylene oxide formed in the reactor per <NUM> moles of reactor feed) allows more ethylene oxide to be made with the same reactor size and same amount of catalyst. This mode of operation has been further facilitated in recent years by the development of advanced high selectivity catalysts that have been developed that allow high selectivity performance at higher work rates.

Operating this way (at higher work rates/ ΔEO) is attractive both for greenfield and revamp projects. For new plant operators, nameplate capacity can be increased without increased capital costs, in particular reactor size, which is the major capital cost component for an EO/EG plant. In a similar way, for revamp projects, which increase the work rate/ ΔEO allows for capacity expansion while using essentially the existing equipment, with perhaps only minor additions and replacements. However, this presents difficulties of its own; increasing the work rates/ ΔEO means that more ethylene oxide is produced in the reactor and thus the reactor effluent has a higher ethylene oxide concentration. For purposes of both process efficiency and plant safety, it is imperative that the ethylene oxide be rapidly absorbed, forming the rich cycle water in the scrubber after leaving the reactor. This higher amount of ethylene oxide requires, in turn, a higher volume of water in the scrubber bottoms to absorb the ethylene oxide to form the rich cycle water. The larger volume of cycle water not only increases capital costs because of the upsizing of equipment like the ethylene oxide stripping column, exchangers and cycle water pumps; but also the operational costs due to the increased utility requirements to drive the larger pumps and other equipment and supply the additional steam necessary for stripping the larger quantities of ethylene oxide from the larger quantities of rich cycle water. Similarly, increases in the amount of carbon dioxide made under these more exacting process conditions may require a larger carbon dioxide absorber and more utility import for steam-stripping in the carbon dioxide regenerator.

Document D1, <CIT>, and D2, <CIT>, disclose a process for the preparation of an enriched ethylene oxide stream.

Accordingly, there is a need in the art for efficiently recovering ethylene oxide and separating carbon dioxide from rich cycle water and in an ethylene oxide process operating at higher than typical work rates and ethylene oxide reactor effluent concentrations. By operating more efficiently, higher operating and capital costs can be avoided.

Hereinafter, any values or ranges following the term "about" are interpreted as being as accurate as the method used to measure them. Basically, the maximum margin is ascertained by applying the rounding-off convention to the last decimal place. For instance, for a temperature of about <NUM>, the error margin is <NUM>-<NUM>.

The present invention relates to a process for the preparation of an ethylene oxide stream which includes steps of: providing a reactor effluent containing a concentration of ethylene oxide of from about <NUM> mol% to about <NUM> mol%, preferably about <NUM> mol% to about <NUM> mol%; cooling lean cycle water in a cycle water cooler to a first temperature of about <NUM> to about <NUM>; contacting the reactor effluent with the lean cycle water to prepare a rich cycle water stream and scrubber overheads; separating, in a stripping column, a first stripper column overhead stream from the rich cycle water stream; dividing the scrubber overheads into a treated stream and, optionally, a bypass stream; contacting the treated stream with a carbon dioxide-absorbing solvent to form a remaining gas stream and a rich carbonate solution; separating a regenerator overhead stream from the rich carbonate solution; adding a cycle water chiller and a tempered water system to provide a modified ethylene oxide process; providing to the modified ethylene oxide process a second reactor effluent that contains a concentration of ethylene oxide of from about <NUM> mol% to about <NUM> mol%, preferably about <NUM> mol% to about <NUM> mol%; cooling a second lean cycle water in the cycle water cooler and the cycle water chiller to a second temperature, wherein the second temperature is <NUM> to <NUM> lower than the first temperature; contacting the second reactor effluent with the second lean cycle water to prepare a second rich cycle water stream and second scrubber overheads; separating a second stripping column overhead stream from the second rich cycle water stream; dividing the second scrubber overheads into a second treated stream and, optionally, a second bypass stream; contacting the second treated stream with a second carbon dioxide-absorbing solvent to form a second remaining gas stream and a second carbonate-rich solution; and separating a second regenerator overhead stream from the second rich carbonate solution, wherein the concentration of carbon dioxide in the second regenerator stream is greater than the concentration of carbon dioxide in the regenerator stream and the concentration of the ethylene oxide in the second stripping column overhead stream is greater than the concentration of the ethylene oxide in the first stripping column overhead stream.

The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:.

All parts, percentages and ratios used herein are expressed by volume unless otherwise specified.

By "water" it is meant any kind of water suitable for use in chemical and petrochemical processing, including deionized, demineralized, industrial, potable and distilled water.

By the present invention, an improved heat integration scheme has been incorporated into the manufacture of ethylene oxide to improve the efficiency of the process at higher than typical work rates and ethylene oxide reactor effluent concentrations. As a result, the process can be operated at these higher production values without significantly increased operational or capital costs. Specifically, in the present invention, operation at higher work rates and ethylene oxide reactor effluent concentrations results in higher concentrations of ethylene oxide vapor in the stripper overhead (and comparable increases in the carbon dioxide concentration in the regenerator overhead) compared to prior art operation.

The increased amount of available thermal energy due to these higher concentrations of ethylene oxide vapor in the stripper overhead stream and carbon dioxide in the regenerator overhead stream compared to conventional prior art operation makes recirculating streams that provide the hot water driving force for the cycle water chiller. This cycle water chiller in turn reduces the temperature of the lean cycle water supplied to the scrubber to increase the amount of ethylene oxide that is absorbed in the rich cycle water formed in the scrubber.

The use of this invention will now be described in greater detail as a component of an ethylene oxide production process. Specifically the invention will be shown first with respect to a conventional process (<FIG>) and, second with respect to a conventional process that has been modified in accordance with the present invention (<FIG>).

Ethylene oxide is produced by continuously contacting an oxygen-containing gas with an olefin, preferably ethylene, in the presence of an ethylene oxide ("epoxidation") catalyst (described in greater detail below). Oxygen may be supplied to the reaction in substantially pure molecular form or in a mixture such as air. By way of example, typical reactant feed mixtures under operating conditions may contain from about <NUM>% to about <NUM>%, preferably about <NUM>% to about <NUM>% of ethylene and from about <NUM>% to about <NUM>% oxygen, and from about <NUM> % to about <NUM>% carbon dioxide with the balance comprising comparatively inert materials, including such substances as water, inert gases, other hydrocarbons, and the reaction moderators described herein. Non-limiting examples of inert gases include nitrogen, argon, helium and mixtures thereof. Non-limiting examples of the other hydrocarbons include methane, ethane, propane and mixtures thereof. Carbon dioxide and water are byproducts of the epoxidation process as well as common contaminants in the feed gases. Both have adverse effects on the catalyst, so the concentrations of these components are usually kept at a minimum.

Also present in the reaction, as previously mentioned, are one or more reaction moderators, non-limiting examples of which include organic halogen-containing compounds such as C<NUM> to C<NUM> halohydrocarbons; especially preferred are chloride-containing moderators such as methyl chloride, ethyl chloride, ethylene dichloride, vinyl chloride or mixtures thereof. Controlling chloride concentration level is particularly important with rhenium-containing catalysts.

As mentioned above, a usual method for the ethylene epoxidation process comprises the vapor-phase oxidation of ethylene with molecular oxygen, in the presence of an epoxidation catalyst, in a fixed-bed tubular reactor. Conventional, commercial fixed-bed ethylene-oxide reactors are typically in the form of a plurality of parallel elongated tubes (in a suitable shell) approximately <NUM> to <NUM> inches O. and <NUM> to <NUM> inches I. and <NUM>-<NUM> feet long, each filled and packed with catalyst. The reaction feed mixture (described above) is introduced into these tubes, and the resulting reactor effluent gas contains ethylene oxide, un-used reactants, and byproducts.

As mentioned above, in the present invention the reactor is run at higher work rates and ΔEO than conventionally employed. The work rate is the production rate and is represented herein by the units kg/m<NUM>/h. The ΔEO is defined as the moles of EO formed in the reactor per <NUM> moles of reactor feed and essentially represents the concentration of ethylene oxide in the reactor effluent, since the concentration of ethylene oxide in reactor feed must be maintained at very close to zero, indeed typically only a few ppm.

In ethylene oxide process, the typical work rate is between <NUM> and <NUM>/m<NUM>/h, while the ΔEO is between <NUM>% and <NUM>%. By contrast in the present invention, the work rate (EO production rate) is greater than <NUM>/m<NUM>/h, preferably between about <NUM> and about <NUM>/m<NUM>/h. The ΔEO is also comparatively higher than in conventional operation. The feed composition of the reactor inlet after the completion of start-up and during normal operation typically comprises (by volume %): <NUM> - <NUM>% methane, <NUM>-<NUM>% ethylene, <NUM>-<NUM>% O<NUM>; <NUM>% to <NUM>%, preferably <NUM> to <NUM>%, more preferably <NUM> to <NUM>% of CO<NUM>; <NUM>-<NUM>% ethane, an amount of one or more chloride moderators, which are described herein; and the balance of the feed being comprised of argon, methane, nitrogen or mixtures thereof.

Typical operating conditions for the reactor are temperatures (as measured in the shell side coolant of the reactor) in the range from about <NUM> to about <NUM>, and preferably from about <NUM> to about <NUM>, and more preferably from about <NUM> to about <NUM>. The operating pressure may vary from about <NUM> atmosphere to about <NUM> atmospheres, depending on the mass velocity and productivity desired. Higher pressures may be employed within the scope of the invention. Residence times in commercial-scale reactors are generally on the order of about <NUM> to about <NUM> seconds.

<FIG> shows a conventional, prior art ethylene oxide production process <NUM>. The reactor effluent <NUM> flows to the scrubber <NUM>. The reactor effluent <NUM> contains a concentration of ethylene oxide of from about <NUM> mol% to about <NUM> mol%, preferably about <NUM> mol% to about <NUM> mol%. In addition to ethylene oxide, the reactor effluent <NUM> may also contain inert and unreacted gases supplied as components of the reactor feed such as argon, methane, ethylene and oxygen; reaction byproducts, in particular, carbon dioxide, but also ppm levels of formaldehyde, formic acid, acetic acid, and product isomers such as acetaldehyde; and additionally sulfur and other impurities, again typically at ppm or ppb levels. The lean cycle water <NUM> is cooled in a cooler <NUM> before being sent to the scrubber <NUM>. In the scrubber <NUM>, the reactor effluent is contacted with the recirculated lean cycle water <NUM> to scrub the ethylene oxide from the reactor effluent thereby forming rich cycle water. Besides ethylene oxide, the rich cycle water may also contain inerts and unreacted gases supplied as components of the reactor feed such as methane, ethylene, argon, and oxygen; as well as carbon dioxide, the main byproduct of the epoxidation of ethylene; and in addition to ppm levels of impurities and isomers such as formaldehyde, formic acid, acetic acid and acetaldehyde.

The temperature of the lean cycle water <NUM> is regulated in order to maximize the amount of ethylene oxide absorbed into in the rich cycle water and minimize the presence of other components in the rich cycle water. Typically, the lean cycle water <NUM> is cooled in the cooler <NUM> prior to entering the scrubber <NUM> to increase the amount of ethylene oxide that is absorbed into the rich cycle water. The temperature of the lean cycle water <NUM> is in the range of about <NUM> to about <NUM>. The pressure in the scrubber <NUM> is maintained within a sufficient range so that the "light" gases that have a volatility greater than that of ethylene oxide are directed by pressure differential to rise upwardly to the top of the scrubber <NUM> forming the scrubber overheads, while the ethylene oxide solute stays largely solubilized within the rich cycle water stream in the liquid bottoms (some light gases may be metastably solubilized in the rich cycle water but they will quickly flash out into the scrubber overhead leaving only traces of light gases still dissolved in the rich cycle water). These more volatile "light" gases that compose the scrubber overheads include the aforementioned inert, unreacted or byproducts found in the reactor effluent, including of course carbon dioxide. Accordingly, in order to ensure the balance between flashing the more volatile light solutes while maintaining high solubility of ethylene oxide in the rich cycle water, the pressure in the scrubber <NUM> is maintained in a range about <NUM> atm to about <NUM> atm. Nonetheless, traces of ethylene oxide may also vaporize with the more volatile light gases in the rich cycle water stream. These small amounts of ethylene oxide that effervesce out of the rich cycle water (preferably the scrubber overheads contain less than <NUM> ppm of ethylene oxide), and rise into the scrubber overhead with the light gas solute vapor are recovered subsequently at a later point that is not relevant to this invention. The resulting first rich cycle water produced in the first scrubber <NUM> contains from about <NUM> wt% to about <NUM> wt% ethylene oxide.

The first rich cycle water in the scrubber <NUM> bottoms flows as stream <NUM> and is pumped to the top portion of the stripping column <NUM> and as the first rich cycle water moves downward in the stripping column <NUM>, separation by steam-stripping of the rich cycle water takes place with upwardly-moving steam contacting the rich cycle water and separating an ethylene oxide rich steam from the rich cycle water to form a gaseous stripping column overhead. The ethylene oxide rich-gaseous stripping column overhead comprises ethylene oxide, water vapor, carbon dioxide and additional impurities in trace amounts. Ethylene oxide is removed as a result of this stripping action. The stripping column <NUM> is operated at a pressure of about <NUM> atm to about <NUM> atm, while the bottoms temperature of the stripping column <NUM> is about <NUM> to about <NUM> and the bottoms contains a lean cycle water solution having had all or most of its ethylene oxide separated away so that it contains less than <NUM> molar ppm ethylene oxide. Steam <NUM> is provided to the stripping column <NUM> in order to effect the separation by steam stripping. This steam is supplied from either: (<NUM>) steam generated elsewhere in the ethylene oxide production facility, e.g., in the reactor steam drum or (<NUM>) medium- or high-pressure steam supplied externally/OSBL; or a combination of these two sources. The separation efficiency of EO from the rich cycle water may also be enhanced by use of a steam ejector system well-known to those skilled in the art.

The stripping column overhead <NUM> contains a significant amount of excess heat because of the steam <NUM> that is directly provided for the steam-stripping that takes place in the stripping column <NUM> in order to separate the ethylene oxide from the rich cycle water. The temperature of the stripping column overhead <NUM> is then reduced in a cooler <NUM> to partially condense the water and ethylene oxide thereby forming a liquid-vapor mixture (not shown). The cooler <NUM> may be an air cooler such as, for example, a fin fan cooler (illustrated in <FIG> and <FIG>) and sent for further processing. From the cooler <NUM>, the resulting liquid-vapor mixture is directed to an ethylene oxide reabsorber (not shown), in which the uncondensed ethylene oxide vapor is reabsorbed in water. A predominance of the carbon dioxide and gaseous inerts which remain unabsorbed are readily separated as gaseous overhead stream from this reabsorption step. An aqueous solution is thus obtained which contains the reabsorbed ethylene oxide and aldehyde impurities, such as formaldehyde and acetaldehyde, as well as dissolved carbon dioxide and other gaseous impurities, and which ethylene oxide must be either further treated to either provide purified ethylene oxide or reacted in various proportions with water to make an ethylene glycol homolog.

Having previously described the scrubber bottoms at the other end the scrubber overhead treated stream <NUM> travels to the carbon dioxide absorber <NUM>. The treated stream <NUM> contains valuable hydrocarbons and therefore in order increase the economic efficiency of the ethylene oxide process it is imperative that these be recovered and recycled back to the reactor inlet feed. In particular, the treated stream <NUM> may contain between about <NUM> mol% to about <NUM> mol% ethylene and about <NUM> mol% to about <NUM> mol% methane. In addition to trace amounts of other light gases, the scrubber overhead also, of course, contains carbon dioxide. As mentioned above carbon dioxide is a byproduct of the epoxidation process and it has an adverse effect on the performance of high selectivity catalysts. This carbon dioxide must be removed from the treated stream <NUM> so that the ethylene and methane in treated stream <NUM> can be recycled back to the reactor.

Carbon dioxide removal occurs in the carbon dioxide absorber <NUM>, where the carbon dioxide solubilized in the treated stream <NUM> is removed. The resulting remaining gas stream <NUM>, which contains ethylene and methane can then be recycled back to the reactor inlet feed allowing for the recovering and reused of these gases. At least a portion and up to <NUM>% of the scrubber overheads is sent as the treated stream <NUM> to the carbon dioxide absorber <NUM>. This is illustrated in <FIG>, in which a treated stream <NUM> from the scrubber overheads is sent to the carbon dioxide absorber <NUM> for carbon dioxide removal while a bypass stream <NUM> is preferably recycled back to the reactor inlet without treatment in the carbon dioxide absorber to remove carbon dioxide.

Nonetheless, a sufficiently high amount of the overhead gases in the scrubbing column <NUM> must be sent as the treated stream <NUM> to the carbon dioxide absorber <NUM> in order to reduce the amount of carbon dioxide to produce a remaining gas stream <NUM> with a relatively low level of carbon dioxide. Removing as much of the carbon dioxide as possible allows the recycling back to the reactor of the hydrocarbon feedstock, such as ethylene and methane, in the remaining gas stream <NUM>. So for example, when about <NUM>% of the scrubber overheads is fed to the carbon dioxide absorber <NUM> the amount of carbon dioxide present in the remaining gas stream <NUM> will be of such a quantity that the inlet reactor feed will be about <NUM> vol. % carbon dioxide. However, for lower carbon dioxide concentrations, for example to maintain <NUM> vol. % carbon dioxide in the inlet reactor feed, substantially all of the scrubber overheads must be fed to the carbon dioxide absorber <NUM>.

As mentioned above, the bypass stream <NUM> is 'preferably' recycled back to the reactor inlet because while it would be possible to simply vent the untreated bypass stream to the atmosphere, this would almost never be done intentionally given the loss of valuable hydrocarbons in the bypass stream and the requirement for extensive emissions treatment prior to venting. Nonetheless, it is a possible under the operational constraints of emergencies that the bypass stream could be partially vented.

Any process or technique known to the person of ordinary skill for removing carbon dioxide from a gaseous feed is acceptable in the present invention. Preferably, a carbon dioxide-containing stream is contacted with a carbon dioxide-absorbing solvent so that carbon dioxide is readily solubilized and absorbed into solvent. Specifically, as shown in <FIG>, the treated stream <NUM> from the carbon dioxide-containing scrubber overhead is contacted with a carbon dioxide-absorbing solvent in the carbon dioxide absorber <NUM> to form a carbon dioxide-rich solvent phase and a carbon dioxide-depleted gas phase. Preferably the carbon dioxide-absorbing solvent is potassium carbonate; the carbon dioxide reacts with the potassium carbonate to form potassium bicarbonate thereby removing the carbon dioxide. In a particularly preferred embodiment the steps in the carbon dioxide absorber are carried out by reactive distillation.

At the bottom of the carbon dioxide absorber the carbon dioxide-rich solvent phase exits the carbon dioxide absorber <NUM> as the rich carbonate solution <NUM> and flows by pressure differential to the regenerator <NUM>, which operates at near atmospheric pressure. In the regenerator <NUM>, the carbon dioxide is separated from the carbon dioxide-rich solvent using steam to yield a gaseous carbon dioxide-rich regenerator overhead stream <NUM> and a lean solvent <NUM>, the lean solvent <NUM> then being returned to the carbon dioxide absorber <NUM> ready to absorb additional carbon dioxide.

The regenerator overhead <NUM> contains a significant amount of excess heat because of the aforementioned steam-stripping that takes place in the regenerator in order to separate the carbon dioxide from the rich carbonate solution. As was the case with the stripping column overhead <NUM>, the temperature of the gaseous carbon dioxide-rich regenerator overhead <NUM> is reduced in a cooler <NUM>. For the choice of the appropriate cooler, see the discussion above with respect to the type of cooler <NUM> used to cool the first stripping column overhead <NUM>.

Now referring to <FIG> and <FIG>, which show a modified ("inventive") ethylene oxide process <NUM> in accordance with the present invention in which the tempered water system <NUM> is added to the ethylene oxide process <NUM>. As mentioned above, in this modified ethylene oxide process <NUM>, the reactor is operated at higher work rates and ethylene oxide reactor effluent concentrations. Accordingly, the second reactor effluent <NUM> contains a higher concentration of ethylene oxide than the reactor effluent <NUM> in ethylene oxide process <NUM>. Specifically, the second reactor effluent <NUM> contains a concentration of ethylene oxide of from about <NUM>% mol% to about <NUM> mol%, preferably about <NUM> mol% to about <NUM> mol%.

As can be seen in <FIG>, in the modified ethylene oxide process <NUM>, the cooler <NUM> of the ethylene oxide process <NUM> is supplemented with a tempered water system <NUM> as shown in <FIG> thereby greatly improving the efficiency and economics of the process. Referring to <FIG> and <FIG>, as presently illustrated, the tempered water system <NUM> has ends on the second stripping column overhead <NUM> and the regenerator overhead <NUM> which provide indirect heating to the first tempered water loop <NUM>, and a second tempered water loop <NUM>, respectively. The loops <NUM> and <NUM> of the tempered water system combine at point A to form the combined heated stream <NUM> which feeds and powers the cycle water chiller <NUM>. Having passed through the cooler <NUM>, the second lean cycle water <NUM> then passes through the cycle water chiller <NUM> and this second lean cycle water <NUM> then enters the second scrubber <NUM>. Thus, the second lean cycle water <NUM> is cooled by being passed through both the cooler <NUM> and the cycle water chiller <NUM> to temperatures lower than in conventional ethylene oxide processes. Specifically, the stream <NUM> is <NUM> to <NUM> cooler than the temperature of stream <NUM>. As mentioned above, the chiller- second lean cycle water <NUM> passes from the cycle water chiller <NUM> to the second absorber <NUM> where it is ready to absorb even higher concentrations of ethylene oxide from the second reactor effluent <NUM> than is absorbed by the first scrubber <NUM>.

It should be noted that the additional power required to run the tempered water system <NUM> is more than offset by the power saving due to the lower condensation requirements of the regenerator overhead <NUM> and stripper overhead <NUM> in coolers <NUM> and <NUM>, respectively.

The cycle water chiller <NUM> is a hot water-driven absorption chiller. In the present invention, the hot water-driven absorption chiller is preferred to other coolers such as electrically-operated or steam-operated since the latter two refrigeration technologies require outside utility supply. By contrast, the hot water-driven absorption unit of the present invention makes use of the waste heat from the regenerator and stripper overhead streams to heat the aforementioned tempered water streams and the combined heated stream <NUM> for providing the hot water driving force for the hot water driven absorption chiller. Any suitable hot water driven absorption refrigeration unit or technology known to those of ordinary skill can be used in the present invention.

Again, referring to the modified ethylene oxide process <NUM> in <FIG>, the second reactor effluent <NUM> flows to the second scrubber <NUM>. As in the conventional or prior art ethylene oxide process, the second lean cycle water <NUM> flows through and is cooled in the cooler <NUM> and then additionally, the second lean cycle water <NUM> is cooled in the cycle water chiller <NUM> and then recirculated to the second scrubber <NUM>. In the second scrubber <NUM>, the reactor effluent <NUM> is contacted with recirculated second lean cycle water <NUM> to form the second rich cycle water in the second scrubber <NUM> bottoms in which nearly all of the ethylene oxide from the second reactor effluent <NUM> is absorbed. In the present invention, the second lean cycle water stream <NUM> is cooled in the cooler <NUM> and cycle water chiller <NUM> well below the temperature level of the comparable second lean cycle water <NUM> in order to increase the amount of ethylene oxide that can be absorbed in the second lean cycle water <NUM> in the second scrubber <NUM>; in this way, the same volume of lean cycle water as was used in ethylene oxide process <NUM> can absorb the larger quantity of ethylene oxide that is produced in the ethylene oxide process <NUM> by running the reactor at a higher work rate. Preferably the temperature of the second lean cycle water <NUM> as supplied to and upon entering the scrubber <NUM> is between about <NUM> to about <NUM>, preferably about <NUM> to about <NUM>. At these lower temperatures, the amount of ethylene oxide absorbed in the second rich cycle water is much higher, from about <NUM> mol% to about <NUM> mol% - this is as much as twice the level of ethylene oxide found in the rich cycle water stream <NUM> of the ethylene oxide process <NUM>. However, additional energy is required to power the second chiller <NUM> to provide this additional cooling of the second lean cycle water <NUM> to increase the amount of ethylene oxide absorbed. In the present invention, this additional cooling is provided by the tempered water system <NUM> as mentioned above and discussed in further detail below.

The second rich cycle water in the second scrubber <NUM> bottoms flows as stream <NUM> and enters into the top portion of the second stripping column <NUM> and as the second rich cycle water moves downward in the column, separation by steam-stripping of the product solution takes place as described above with respect to the second stripping column <NUM> in the conventional ethylene oxide process <NUM>. A second steam stream <NUM> provides a first amount of steam to the stripping column <NUM> for steam-stripping, however, in the inventive process <NUM> the second amount of steam provided in the second steam stream <NUM> is less than the first amount of steam because the second rich cycle water is more enriched than the first rich cycle water and therefore requires less steam for stripping. Similarly, compared to the second stripping column overhead <NUM> in the separation section of the conventional ethylene oxide process <NUM>, the second stripping column overhead <NUM> of the present invention is more enriched in ethylene oxide, and less enriched in water vapor-steam; preferably the second stripping column overhead <NUM> in the inventive modified ethylene oxide process <NUM> contains about <NUM> wt% to about <NUM> wt% ethylene oxide with the balance vapor-steam.

With respect to the operational temperatures and pressures of the second stripping column <NUM>, the second stripping column <NUM> is operated at a pressure of about <NUM> atm to about <NUM> atm, while the bottoms temperature of the stripping column <NUM> is about <NUM> to about <NUM>. The second stripping column overhead stream <NUM> has a temperature of about <NUM> to about <NUM>. As mentioned above with respect to the conventional ethylene oxide process <NUM>, in the inventive process <NUM> it is necessary to cool and condense the second stripping column overhead <NUM>. In the conventional ethylene oxide process <NUM> described above this is done in an air cooler with the excess heat being treated as waste and released into the atmosphere. This imposes an economic and process efficiency penalty not only because of the wasted heat but because of energy to power the equipment to dissipate it, like electrically operated fin fan coolers. This penalty gets worse in circumstances like those of the present invention, where the high concentration of ethylene oxide increases the amount of heat that must be removed.

However, in the inventive ethylene oxide process <NUM> rather than simply treat this as waste heat, the excess thermal energy provided by the higher ethylene oxide content of the second stripping column overhead stream <NUM> makes the stream highly useful for heat integration. Specifically, in the present invention this stream <NUM> helps provide the hot water driving force for the second chiller <NUM> via the tempered water system <NUM>. Specifically, the second stripping column overhead steam <NUM> passes through the first heat exchanger <NUM> with first tempered water loop <NUM> coming from the second chiller <NUM> on the other side of the exchanger. The first tempered loop <NUM> is thus heated by indirect heat exchange with the second stripping column overhead stream <NUM> in the first heat exchanger <NUM> so that the temperature of the first tempered water loop <NUM> is raised from a temperature of about <NUM> to about <NUM> prior to entering the first heating exchanger <NUM> to a temperature of about <NUM> to about <NUM> for the heated first tempered water loop <NUM> after exiting after the heat exchanger <NUM>.

After exchanging heat in the exchanger <NUM> with the first tempered water loop <NUM> the second stripping column overhead <NUM> may require still additional cooling which takes place in cooler <NUM>. For the choice of the appropriate type or design of the cooler see the discussion above with respect to the type of cooler used to cool the first stripping column overhead <NUM>. As above with respect to the stripping column <NUM> and the cooler <NUM>, the second stripping column overhead <NUM> is partially condensed in cooler <NUM> with the water and ethylene oxide thereby forming a second liquid-vapor mixture <NUM>. The second liquid vapor mixture is then directed to a second ethylene oxide reabsorber (not shown) which is operated as the reabsorber described above.

The treated stream <NUM> from the scrubber overheads travel to the carbon dioxide absorber <NUM>. As described above the scrubber overhead treated stream <NUM> contain valuable hydrocarbons that must be recycled back to the reactor inlet feed. (The bypass stream <NUM> is also illustrated). The carbon dioxide absorber <NUM> is operated as described above with respect to the comparable carbon dioxide absorber <NUM> in the conventional ethylene oxide process <NUM>. However, removal of carbon dioxide is particularly important in the inventive ethylene oxide process <NUM> because higher work rates mean more carbon dioxide is produced and thus, carbon dioxide concentrations are considerably higher in the scrubber overhead treated stream <NUM> than in the corresponding scrubber overheads of the conventional ethylene oxide process <NUM>.

Rather than being sent to the second carbon dioxide absorber <NUM>, an optional second bypass stream <NUM> may be recycled back to the reactor inlet stream without treatment in the carbon dioxide absorber to remove carbon dioxide. As mentioned above, in the present invention carbon dioxide concentrations in the reactor outlet and hence in the rich cycle water and second scrubber overhead treated stream <NUM> are higher and so generally a high proportion of the second scrubber overhead stream <NUM> are treated in the carbon dioxide absorber <NUM>. Specifically, the volume ratio of stream <NUM>: stream <NUM> is about <NUM>:<NUM> to about <NUM>:<NUM>.

The second scrubber overhead treated stream <NUM> is contacted with a second carbon dioxide-absorbing solvent in the second carbon dioxide absorber <NUM>. Preferably, a second carbon dioxide-containing stream is contacted with a carbon dioxide absorbing solvent so that carbon dioxide is readily solubilized and absorbed into solvent. Specifically, the second carbon dioxide-containing second scrubber overhead treated stream <NUM> is contacted with a carbon dioxide-absorbing solvent in the second carbon dioxide absorber <NUM> to form a carbon dioxide-rich solvent phase and a carbon dioxide-depleted gas phase. Thus, from the second treated stream <NUM> two additional streams are created: (<NUM>) a second carbonate-rich solution <NUM> which is sent to the second regenerator <NUM> from the bottom of the carbon dioxide absorber <NUM>; and (<NUM>) in the overhead second remaining gas stream <NUM> reduced in carbon dioxide concentrationspecifically having a carbon dioxide content of between about <NUM> mol% and <NUM> mol%.

Preferably the carbon dioxide-absorbing solvent is potassium carbonate; carbon dioxide reacts with the potassium carbonate to form potassium bicarbonate thereby removing the carbon dioxide. In a particularly preferred embodiment, the steps in the carbon dioxide absorber are carried out by reactive distillation.

Although not shown in the figure, the second remaining gas steam <NUM> is preferably subjected to additional process steps before being fed back to the inlet reactor feed. Specifically, the second remaining gas stream <NUM> from the second carbon dioxide absorber <NUM> is preferably subjected to a cooling step by direct contact with cooled wash water reducing the water content of the second remaining gas stream <NUM> while also scrubbing it of contained carbonate, which would deleteriously affect the ethylene oxide catalyst were it to be returned to the ethylene oxide reactor through the reactor inlet feed. High concentrations of water may also hurt catalyst performance and by cooling the water content of the second remaining gas stream <NUM> is reduced to a level that does not inhibit catalyst activity. See, e.g., <CIT>.

The second regenerator <NUM> is constructed and operated as described above with respect to the regenerator <NUM> in the conventional ethylene oxide process <NUM> above. Carbon dioxide is separated from the carbon dioxide-rich solvent stream <NUM> using steam stripping to yield a second lean solvent <NUM> recycled through the bottoms back to the second carbon dioxide absorber <NUM> and a carbon dioxide-rich gaseous second regenerator overhead stream <NUM> having a temperature of about <NUM> to about <NUM>. It is preferable that special column internals (not shown) be positioned that at the top of the regenerator to minimize carbonate solution entrainment into the vapor and reduce the carbonate that is carried away in the second regenerator overhead <NUM>.

Because of the higher carbon dioxide content in the second regenerator overhead stream <NUM>, the excess thermal energy in this stream is highly useful for heat integration. (This is analogous to the higher ethylene oxide content in the stripper overhead stream <NUM>, as discussed above). Specifically, the second regenerator overhead stream <NUM> has a carbon dioxide concentration of between <NUM> % and <NUM>% higher than the carbon dioxide concentration of stream <NUM>. The second regenerator overhead <NUM> passes through the second heat exchanger <NUM> and exchanges heat with the second tempered loop <NUM> coming from the chiller on the other side of the exchanger <NUM>. The second tempered loop <NUM> is thus heated by indirect heat exchange with the second regenerator overhead <NUM> so that after passing through the exchanger <NUM> the temperature of the heated second tempered water loop <NUM> is raised from a temperature of about <NUM> to about <NUM> prior to entering heat exchanger <NUM> to a temperature of about <NUM> to about <NUM> after exiting.

After exchanging heat in the exchanger <NUM> with the second tempered loop <NUM>, the second regenerator overhead <NUM> may require still additional cooling which takes place in cooler <NUM>. For the choice of the appropriate type or design of the cooler see the discussion above with respect to the type of cooler used to cool the first stripping column overhead.

Although not shown in the figure, the carbon dioxide absorber <NUM> may be directly affixed to the scrubber <NUM>. In this embodiment the absorber <NUM> is directly and permanently affixed to the top surface of the scrubber <NUM>, by for example, welding. However, this is not a necessary part of the invention and they may be prepared as entirely separate components/columns.

Under the circumstances of process streams, specifically the stripping column overhead having a higher than conventional ethylene oxide concentration, operators will continue to maintain appropriate safety standards that are always observed when producing, handling or storing ethylene oxide. As always, measures must be taken to prevent reactions or events that could result in ignition, combustion, deflagration, detonation or explosion of any gas stream, but especially those containing higher than typical concentrations of ethylene oxide. Accordingly, to prevent such events relief valves may be used to relieve or reduce undesirable pressure built-up in the process, reaction, or separation systems or elsewhere in the ethylene oxide plan both upstream and downstream of what is illustrated. In the present invention such risk is extremely small given that the ethylene oxide-enriched reactor effluent is quickly absorbed into an aqueous stream. Additionally, the separation in the stripper is very effective so that nearly all of the ethylene oxide in the rich cycle water that enters the stripper is successfully separated and recovered from the rich cycle water and leaves the stripper as vapor overhead while only a small portion leaves the stripper as liquid bottoms.

In the present invention, the conventional ethylene oxide process <NUM> is modified to the ethylene oxide process <NUM> by incorporating the chiller <NUM> and supplementing with the tempered water system <NUM>, It is an advantage of the present invention in order to modify the ethylene oxide process <NUM> to the ethylene oxide process <NUM> requires the process be only briefly taken off-line. No equipment modifications are necessary and it is easy to erect new equipment during normal plant operation followed by a brief process interruption while the new equipment is incorporated into the process. This also provides extra flexibility in cases where docurnentation fails to accurately describe the as-built conditions of the plant and further modifications need to be made. In such cases, the plant can continue to operate normally while such changes are made.

Accordingly, in one embodiment the conventional ethylene oxide process is not permanently replaced by the modified ethylene oxide process operation. Rather, in this embodiment, the present invention provides sufficient flexibility to alternate between the conventional ethylene oxide process (with the lean cycle water is cooled in the cooler <NUM>) and the modified ethylene oxide process operation (with the lean cycle water is cooled in the chiller <NUM> and its accompanying tempered water system <NUM>) when the plant operator wishes to do so in the event that technical or economic circumstances make one process particularly more desirable than the other.

The silver-based epoxidation catalyst includes a support, and at least a catalytically effective amount of silver or a silver-containing compound; also optionally present is a promoting amount of rhenium or a rhenium-containing compound; also optionally present is a promoting amount of one or more alkali metals or alkali-metal-containing compounds. The support employed in this invention may be selected from a large number of solid, refractory supports that may be porous and may provide the preferred pore structure. Alumina is well known to be useful as a catalyst support for the epoxidation of an olefin and is the preferred support.

Regardless of the character of the support used, it is usually shaped into particles, chunks, pieces, pellets, rings, spheres, wagon wheels, cross-partitioned hollow cylinders, and the like, of a size suitable for employment in a fixed-bed epoxidation reactor. The support particles will preferably have equivalent diameters in the range from about <NUM> to about <NUM>, and more preferably in the range from about <NUM> to about <NUM>. (Equivalent diameter is the diameter of a sphere having the same external surface (i.e., neglecting surface within the pores of the particle) to volume ratio as the support particles being employed. ) Suitable supports are available from Saint-Gobain Norpro Co. , Sud Chemie AG, Noritake Co. , CeramTec AG, and Industrie Bitossi S. Without being limited to the specific compositions and formulations contained therein, further information on support compositions and methods for making supports may be found in <CIT>.

In order to produce a catalyst for the oxidation of an olefin to an olefin oxide, a support having the above characteristics is then provided with a catalytically effective amount of silver on its surface. In one embodiment, the catalytic effective amount of silver is from <NUM>% by weight to <NUM>% by weight. The catalyst is prepared by impregnating the support with a silver compound, complex or salt dissolved in a suitable solvent sufficient to cause deposition of a silver-precursor compound onto the support. Preferably, an aqueous silver solution is used.

A promoting amount of a rhenium component, which may be a rhenium-containing compound or a rhenium-containing complex may also be deposited on the support, either prior to, coincidentally with, or subsequent to the deposition of the silver. The rhenium promoter may be present in an amount from about <NUM> wt. % to about <NUM> wt. %, preferably from about <NUM> wt. % to about <NUM> wt. %, and more preferably from about <NUM> wt. % to about <NUM> wt. % based on the weight of the total catalyst including the support, expressed as the rhenium metal.

Other components which may also be deposited on the support either prior to, coincidentally with, or subsequent to the deposition of the silver and rhenium are promoting amounts of an alkali metal or mixtures of two or more alkali metals, as well as optional promoting amounts of a Group IIA alkaline earth metal component or mixtures of two or more Group IIA alkaline earth metal components, and/or a transition metal component or mixtures of two or more transition metal components, all of which may be in the form of metal ions, metal compounds, metal complexes and/or metal salts dissolved in an appropriate solvent. The support may be impregnated at the same time or in separate steps with the various catalyst promoters. The particular combination of support, silver, alkali metal promoter(s), rhenium component, and optional additional promoter(s) of the instant invention will provide an improvement in one or more catalytic properties over the same combination of silver and support and none, or only one of the promoters.

As used herein the term "promoting amount" of a certain component of the catalyst refers to an amount of that component that works effectively to improve the catalytic performance of the catalyst when compared to a catalyst that does not contain that component. The exact concentrations employed, of course, will depend on, among other factors, the desired silver content, the nature of the support, the viscosity of the liquid, and solubility of the particular compound used to deliver the promoter into the impregnating solution. Examples of catalytic properties include, inter alia, operability (resistance to runaway), selectivity, activity, conversion, stability and yield. It is understood by one skilled in the art that one or more of the individual catalytic properties may be enhanced by the "promoting amount" while other catalytic properties may or may not be enhanced or may even be diminished.

Suitable alkali metal promoters may be selected from lithium, sodium, potassium, rubidium, cesium or combinations thereof, with cesium being preferred, and combinations of cesium with other alkali metals being especially preferred. The amount of alkali metal deposited or present on the support is to be a promoting amount. Preferably, the amount ranges from about <NUM> ppm to about <NUM> ppm, more preferably from about <NUM> ppm to about <NUM> ppm, and even more preferably from about <NUM> ppm to about <NUM> ppm, and as especially preferred from about <NUM> ppm to about <NUM> ppm by weight of the total catalyst, measured as the metal.

Suitable alkaline earth metal promoters comprise elements from Group IIA of the Periodic Table of the Elements, which may be beryllium, magnesium, calcium, strontium, and barium or combinations thereof. Suitable transition metal promoters may comprise elements from Groups IVA, VA, VIA, VIIA and VIIIA of the Periodic Table of the Elements, and combinations thereof.

The amount of alkaline earth metal promoter(s) and/or transition metal promoter(s) deposited on the support is a promoting amount. The transition metal promoter may typically be present in an amount from about <NUM> micromoles per gram to about <NUM> micromoles per gram, preferably from about <NUM> micromoles per gram to about <NUM> micromoles per gram.

The silver solution used to impregnate the support may also comprise an optional solvent or a complexing/solubilizing agent such as are known in the art. A wide variety of solvents or complexing/solubilizing agents may be employed to solubilize silver to the desired concentration in the impregnating medium. Useful complexing/solubilizing agents include amines, ammonia, oxalic acid, lactic acid and combinations thereof. Amines include an alkylene diamine having from <NUM> to <NUM> carbon atoms. In one preferred embodiment, the solution comprises an aqueous solution of silver oxalate and ethylene diamine. The complexing/solubilizing agent may be present in the impregnating solution in an amount from about <NUM> to about <NUM> moles per mole of silver, preferably from about <NUM> to about <NUM> moles, and more preferably from about <NUM> to about <NUM> moles for each mole of silver.

When a solvent is used, it may be an organic solvent or water, and may be polar or substantially or totally non-polar. In general, the solvent should have sufficient solvating power to solubilize the solution components. At the same time, it is preferred that the solvent be chosen to avoid having an undue influence on or interaction with the solvated promoters. Organic-based solvents which have <NUM> to about <NUM> carbon atoms per molecule are preferred. Mixtures of several organic solvents or mixtures of organic solvent(s) with water may be used, provided that such mixed solvents function as desired herein.

The concentration of silver in the impregnating solution is typically in the range from about <NUM>% by weight up to the maximum solubility afforded by the particular solvent/solubilizing agent combination employed. It is generally very suitable to employ solutions containing from <NUM>% to about <NUM>% by weight of silver, with concentrations from <NUM> to <NUM>% by weight of silver being preferred.

Impregnation of the selected support is achieved using any of the conventional methods; for example, excess solution impregnation, incipient wetness impregnation, spray coating, etc. Typically, the support material is placed in contact with the silver-containing solution until a sufficient amount of the solution is absorbed by the support. Preferably the quantity of the silver-containing solution used to impregnate the porous support is no more than is necessary to fill the pores of the support. A single impregnation or a series of impregnations, with or without intermediate drying, may be used, depending, in part, on the concentration of the silver component in the solution. Impregnation procedures are described, for example, in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>,<CIT>, <CIT>, <CIT> and <CIT>. Known prior procedures of pre-deposition, co-deposition and post-deposition of various the promoters can be employed.

After impregnation of the support with the silver-containing compound, i.e., a silver precursor, a rhenium component, an alkali metal component, and the optional other promoters, the impregnated support is calcined for a time sufficient to convert the silver containing compound to an active silver species and to remove the volatile components from the impregnated support to result in a catalyst precursor. The calcination may be accomplished by heating the impregnated support, preferably at a gradual rate, to a temperature in the range from about <NUM> to about <NUM> at a pressure in the range from about <NUM> to about <NUM> bar. In general, the higher the temperature, the shorter the required heating period. A wide range of heating periods have been suggested in the art; e.g., <CIT> discloses heating for less than <NUM> seconds, and <CIT> discloses heating from <NUM> to <NUM> hours at a temperature of from <NUM>° C to <NUM>, usually for duration of from about <NUM> to about <NUM> hours. However, it is only important that the heating time be correlated with the temperature such that substantially all of the contained silver is converted to the active silver species. Continuous or step-wise heating may be used for this purpose.

During calcination, the impregnated support may be exposed to a gas atmosphere comprising an inert gas or a mixture of an inert gas with from about <NUM> ppm to <NUM>% by volume of an oxygen-containing oxidizing component. For purposes of this invention, an inert gas is defined as a gas that does not substantially react with the catalyst or catalyst precursor under the conditions chosen for the calcination. Further information on catalyst manufacture may be found in the aforementioned <CIT>.

For purposes of illustration only, the following are conditions that are often used in current commercial ethylene oxide reactor units: a gas hourly space velocity (GHSV) of <NUM>-<NUM>,<NUM>-<NUM>, a reactor inlet pressure of <NUM> MPa to <NUM> MPa, a coolant temperature of <NUM>-<NUM>, an oxygen conversion level of <NUM>-<NUM>%, and an EO production rate (work rate) of <NUM> - <NUM> EO/m<NUM> catalyst/hr and a change in ethylene oxide concentration, ΔEO, of from about <NUM>% to about <NUM>%. The feed composition in the reactor inlet after the completion of start-up and during normal operation typically comprises (by volume %) <NUM>-<NUM>% ethylene, <NUM>-<NUM>% O<NUM>; <NUM>% to <NUM>%, preferably <NUM>% to <NUM>%, more preferably <NUM>% to <NUM>% of CO<NUM>; <NUM> - <NUM>% ethane, an amount of one or more chloride moderators, which are described herein; and the balance of the feed being comprised of argon, methane, nitrogen or mixtures thereof.

The invention will now be described in more detail with respect to the following non-limiting examples.

An ethylene oxide process prepared according to a conventional, prior art ethylene oxide process <NUM> and according the present invention <NUM> are shown in <FIG> and <FIG>, respectively, and were simulated using PRO/II software. The conventional ethylene oxide process <NUM> utilizes a cooler <NUM> that is independent of the regenerator overhead <NUM> and the stripping column overhead <NUM>. By contrast, the ethylene oxide process prepared according to the present invention <NUM> includes in addition to cooler <NUM> additionally a tempered water system <NUM> with chiller <NUM>. The chiller <NUM> is powered by tempered water loops <NUM>, <NUM>, which are, in turn, powered by heat exchange with the regenerator overhead <NUM> and the stripper overhead <NUM> in exchangers <NUM>, <NUM> respectively. The compositions of the streams were as follows:.

As described above, in the present invention the stripper column overhead contains higher concentrations of ethylene oxide vapor compared to prior art operation (compare stream #<NUM> to stream #<NUM>).

Furthermore, the benefits of the present invention are represented in Table <NUM>, which compares the heat load necessary for steam-stripping separation in the first and second stripping columns as calculated by the aforementioned simulation. As can be seen, the amount of steam in the second steam stream (present invention/inventive EO process #<NUM>) is considerably reduced compared to the first steam stream (conventional EO process #<NUM>). In fact this reduction is over <NUM>%.

Claim 1:
A process for the preparation of ethylene oxide stream comprising:
(a) providing a reactor effluent containing a concentration of ethylene oxide of from about <NUM> mol% to about <NUM> mol%, preferably about <NUM> mol% to about <NUM> mol%;
(b) cooling lean cycle water in a cooler to a first temperature of about <NUM> to about <NUM>;
(c) contacting the reactor effluent with the lean cycle water to prepare a rich cycle water stream and scrubber overheads;
(d) separating, in a stripping column, a first stripping overhead stream from the rich cycle water stream;
(e) dividing the scrubber overheads into a treated stream and, optionally, a bypass stream;
(f) contacting the treated stream with a carbon dioxide-absorbing solvent to form a remaining gas stream and a rich carbonate solution;
(g) separating a regenerator overhead stream from the rich carbonate solution;
(h) adding a cycle water chiller and a tempered water system to provide a modified ethylene oxide process;
(i) providing to the modified ethylene oxide process a second reactor effluent that contains a concentration of ethylene oxide of from about <NUM> mol% to about <NUM> mol%, preferably about <NUM> mol% to about <NUM> mol%;
(j) cooling a second lean cycle water in the cycle water cooler and the chiller to a second temperature, wherein the second temperature is <NUM> to <NUM> lower than the first temperature;
(k) contacting the second reactor effluent with the second lean cycle water to prepare a second rich cycle water stream and second scrubber overheads;
(l) separating a second stripping column overhead stream from the second rich cycle water stream;
(m) dividing the second scrubber overheads into a second treated stream and, optionally, a second bypass stream;
(n) contacting the second treated stream with a second carbon dioxide-absorbing solvent to form a second remaining gas stream and a second carbonate-rich solution; and
(o) separating a second regenerator overhead stream from the second rich carbonate solution,
wherein the concentration of carbon dioxide in the second regenerator stream is greater than the concentration of carbon dioxide in the regenerator stream and the concentration of the ethylene oxide in the second stripping column overhead stream is greater than the concentration of the ethylene oxide in the stripping column overhead stream.