Method for recovering ethanol from crude ethyl acetate

Abstract

The present invention provides a process for recovering substantially dry ethanol from a feedstock comprising ethyl acetate, ethanol and water, the process comprising: (a) passing the feedstock to a first separation column comprising a first separation column reboiler, and maintained under distillation conditions to form an intermediate bottoms stream comprising ethanol and water and having an ethanol concentration higher than that in the feedstock; (b) passing the intermediate bottoms stream to an azeotropic column maintained under distillation conditions to form an azeotropic column bottoms stream and an azeotropic column overhead stream, the azeotropic column overhead stream comprising ethanol and water and having a higher ethanol concentration than the ethanol concentration in the intermediate bottoms stream; (c) feeding an ethanol make-up stream to the azeotropic column; (d) passing the azeotropic column overhead stream through a water removal section to separate water from ethanol, forming a substantially dry ethanol stream; (e) providing heat in the first separation column reboiler using the substantially dry ethanol stream.

Description

Technical Field

[0001] The present invention relates to a process for recovering substantially dry ethanol from a feedstock comprising ethyl acetate, ethanol and water. Background Art

[0002] A commercial process for producing ethyl acetate employs the dehydrogenation of ethanol to ethyl acetate via acetaldehyde in the gas phase over a copper-based heterogeneous catalyst. The residual aldehydes and ketones in the crude ethyl acetate product, some of which would be difficult to remove from the product by distillation, are selectively hydrogenated back to the alcohol in a liquid phase finishing reactor. Unreacted ethanol and water are then separated from the ethyl acetate in the crude product stream using a double-column pressure swing distillation, with the final column removing heavies from the ethyl acetate product. Examples of this process are disclosed in WO 00 / 20373, WO 00 / 20374, and WO 00 / 20375.

[0003] Pressure swing distillation system requires two towers, a first low-pressure separation tower and a second high-pressure separation tower. The first separation tower is maintained under distillation conditions to form a bottom stream comprising ethanol and water and a tower top stream comprising light components such as ether, methanol, ethane and gases such as hydrogen, methane and carbon dioxide. In the arrangement disclosed in WO 00 / 20373, WO 00 / 20374 and WO 00 / 20375, a side draw comprising ethyl acetate, ethanol and water is taken out from the first separation tower and fed to the second separation tower. The second separation tower is maintained under distillation conditions to form a bottom stream comprising high-purity ethyl acetate and a tower top stream comprising ethyl acetate, ethanol and water, which returns to the first separation tower above the feed point of the crude product stream. Both the first separation tower and the second separation tower in the pressure swing distillation system require a reboiler.

[0004] The unreacted ethanol, water and byproducts in the bottoms stream from the first separation column in the pressure swing distillation system are then recycled to another column, called the azeotrope column. Here, fresh wet ethanol feed is added and the overheads, which mainly contain ethanol, are sent to drying packs to remove water to a low level. The dried ethanol from the drying packs is then used in the feed to the dehydrogenation reactor.

[0005] It is desirable to optimize the energy input to the process, particularly in view of the need to minimize energy use and introduce renewable energy as we transition to a low-carbon to zero-carbon economy. Summary of the invention

[0006] Accordingly, the present invention provides a process for recovering substantially dry ethanol from a feedstock comprising ethyl acetate, ethanol and water, the process comprising:

[0007] (a) passing the feedstock to a first separation column, the first separation column comprising a first separation column reboiler and maintained under distillation conditions to form an intermediate bottoms stream comprising ethanol and water and having an ethanol concentration greater than the ethanol concentration in the feedstock;

[0008] (b) passing the intermediate bottoms stream to an azeotrope column maintained at distillation conditions to form an azeotrope column bottoms stream and an azeotrope column overhead stream, the azeotrope column overhead stream comprising ethanol and water and having a higher ethanol concentration than the ethanol concentration in the intermediate bottoms stream;

[0009] (c) feeding an ethanol make-up stream into the azeotropic column;

[0010] (d) passing the azeotrope column overhead stream through a water removal section to separate water from ethanol to form a substantially dry ethanol stream;

[0011] (e) using the substantially dry ethanol stream to provide heat in the first separation column reboiler.

[0012] The inventors have surprisingly discovered that the substantially dry ethanol stream leaving the water removal package (azeotrope column in combination with the water removal stage) can be used to supplement or completely replace the external heat input required for the first separation column reboiler. This additional heat integration increases the overall energy efficiency of the process for forming ethyl acetate by dehydrogenation of ethanol and has benefits in terms of both cost and minimized energy consumption because less steam needs to be generated and therefore less fuel is consumed in the boiler. Water consumption is also minimized, for example because less water coolant is required to condense the substantially dry ethanol stream.

[0013] Also provided is a process for producing ethyl acetate by dehydrogenation of ethanol, the process comprising the process of the present invention for recovering substantially dry ethanol from a feedstock comprising ethyl acetate, ethanol and water. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the method of the present invention.

[0015] Figure 2 A schematic diagram of another aspect of the present invention.

[0016] Figure 3 is a schematic diagram of another aspect of the present invention.

[0017] Figure 4 is a schematic diagram of another aspect of the present invention.

[0018] Figure 5 is a schematic diagram of another aspect of the present invention.

[0019] Figure 6is a schematic diagram of another aspect of the present invention. DETAILED DESCRIPTION

[0020] Raw material can be the crude product stream recovered from producing ethyl acetate by ethanol dehydrogenation, and should not contain the compounds that can cause separation problems if the raw material is directly refined. For example, because their boiling point is close to the boiling point of ethyl acetate, and because ethyl acetate tends to form distillate or azeotrope with such compounds. Such compounds include acetaldehyde, n-butyraldehyde and butan-2-ketone. Usually, these compounds are removed from raw material by selective hydrogenation (also referred to as refining) using a suitable selective hydrogenation catalyst (for example, as described in WO 00 / 20375). Therefore, raw material is generally substantially free of aldehydes and ketones. For example, raw material will contain aldehydes and ketones less than about 0.01 weight %. Therefore, the present invention is used for the method for producing ethyl acetate by ethanol dehydrogenation and will generally also include the refining step of selective hydrogenation before the inventive method for reclaiming substantially dry ethanol.

[0021] The feedstock will typically contain about 10% by weight or less water, and preferably about 5% by weight or less water. In addition to ethyl acetate, ethanol and water, the feed stream typically contains light components and heavy components. The term "light" component means a component having a boiling point lower than ethyl acetate and its azeotropes with water and ethanol. The term "heavy" component means a component having a boiling point higher than ethanol and ethyl acetate.

[0022] The first separation tower is maintained under distillation conditions to form an intermediate bottoms stream comprising ethanol and water and having an ethanol concentration higher than that in the raw material. An overhead stream comprising light components such as ether, methanol, ethane and gases such as hydrogen, methane and carbon dioxide is also formed. The side drawdown comprising ethyl acetate, ethanol and water can be taken out from the first separation tower and fed to the second separation tower as a part of a pressure swing distillation system for recovering substantially pure ethyl acetate, for example, as disclosed in WO 00 / 20373. Alternatively, the overhead stream can be partially condensed and then sent to a light component tower, in which the light component is discharged to a flare or a fuel header. Most of the light component tower bottoms stream is then returned to the first separation tower as reflux, and the remainder is fed to the second separation tower. The first separation tower is typically operated at a pressure less than about 4 absolute pressures, preferably about 1 absolute pressure to about 2 absolute pressures.

[0023] The intermediate bottoms stream comprising ethanol and water formed in the first separation column will typically also contain any heavy components, for example by-product organic components such as butanol and butyl acetate. The intermediate bottoms stream will typically contain about 2.0 wt % or less water, preferably about 1.0 wt % or less water. Typically, the intermediate product stream will contain at least about 0.5 wt % water. The intermediate bottoms stream will typically contain at least about 80 wt % ethanol, and preferably at least about 90 wt % ethanol.

[0024] The azeotropic column is so called because it provides an overhead stream comprising ethanol and water, which is generally in an ethanol / water azeotropic composition. The azeotropic column may contain any suitable internals, such as packing or trays. One skilled in the art can determine what packing to use and, for example, how many trays are needed, which can be determined, for example, by the concentration of water passing through the column. The azeotropic column rejects water and heavy components, which are generally present in the intermediate bottoms stream at a higher concentration than is preferred when ethanol is recycled back to the dehydrogenation reactor in a process for producing ethyl acetate by dehydrogenation of ethanol.

[0025] The azeotropic column will typically be operated at a top pressure of at least about 4.0 absolute. The azeotropic column will typically be operated at a top pressure of about 5.0 absolute or less. For example, about 4.6 absolute.

[0026] Because ethanol and water form an azeotrope, it is not possible to remove all of the water from the azeotrope column overhead stream using an azeotrope column alone. Typically, the azeotrope column overhead stream has a water content of about 2.0 wt % to about 6.0 wt %. In order to remove water from this stream, it is passed through a water removal section, which preferably includes a molecular sieve for separating water from ethanol to form a substantially dry ethanol stream, which will be in the vapor phase. Typically, a 100% ethanol stream is used. Zeolite molecular sieve. Water molecules have diameter, while the ethanol molecule has diameter, so Zeolite retains water, but blocks ethanol. Alternatively, the water removal section may include a membrane system for separating water from ethanol. In such a membrane system, any residual water content will be a function of the membrane surface area. A hydrophilic membrane may be used, which will preferentially allow water to pass through, leaving ethanol to concentrate on the high pressure side. Some ethanol may be transmitted through the membrane with water, and the ethanol is returned to the azeotropic column. Substantially dry ethanol streams generally contain about 1.0 % by weight or less water, generally about 0.5 % by weight or less water, preferably about 0.05 % by weight or less water.

[0027] Typically, the azeotropic column overhead stream is superheated to a temperature of at least about 15°C. Typically, the stream is superheated to a temperature of about 50°C or lower, such as about 20°C. The superheating step is to keep the stream away from the dew point before the stream is sent to the water removal section. Based on the size of the pores in the molecular sieve, the molecular sieve selectively absorbs water instead of ethanol. Eventually, the water capacity of the molecular sieve is exhausted, so that the feed more azeotropic column overhead stream will cause water to penetrate into the substantially dry ethanol stream. Since this is undesirable, the azeotropic column overhead stream can be transferred to another molecular sieve empty bed, and the bed saturated with water is regenerated at the same time. Regeneration is carried out by refluxing dry ethanol through the molecular sieve and reducing the pressure in the bed to extract water molecules from the pores of the molecular sieve to remove water. Vacuum conditions can be used to maximize the removal of water. The liquid removed by the regeneration procedure is a mixture of water and ethanol, wherein the water concentration is higher than the ethanol / water azeotrope. This aqueous regeneration stream is collected and can be returned to the azeotropic column at a constant rate to a point lower than the feed. The returned water is sent down the azeotrope and eventually removed from the azeotrope bottoms stream as an aqueous effluent. Typically, the aqueous regeneration stream is condensed under vacuum, so it is difficult to recover any heat from it because the saturation temperature will be too low to use. Therefore, it is usually cooled using cooling water, usually to about 40°C. The aqueous regeneration stream can be reheated before returning to the azeotrope. Advantageously, when the raw material is a crude product stream recovered from the production of ethyl acetate by ethanol dehydrogenation, heat exchange can be provided between the dehydrogenation reactor effluent and the aqueous regeneration stream. This heat exchange advantageously reduces any increased heat load required for the azeotrope to provide a substantially dry ethanol stream with an optimal temperature difference with the first separation tower reboiler. In a typical ethyl acetate production process, the effluent stream is sent through three heat exchangers to preheat other streams in the process. In a specific example, such an effluent stream will have a temperature of about 105°C, and the aqueous regeneration stream can be heated from about 40°C to typically about 95°C. Therefore, the process of the present invention may further comprise the step of regenerating the water removal section, preferably comprising a molecular sieve, to provide an aqueous regeneration stream having a water concentration above the ethanol / water azeotrope and returning the aqueous regeneration stream to the azeotrope column. In the process for producing ethyl acetate, the effluent from the dehydrogenation reactor used to generate the feedstock is used to heat the aqueous regeneration stream before the aqueous regeneration stream is returned to the azeotrope column.

[0028] The dew point of the substantially dry ethanol stream is typically at least about 115°C. Typically about 125°C or less. The temperature difference between the dew point of the substantially dry ethanol stream and the temperature of the first separation tower bottoms stream is typically at least about 15°C, typically, the temperature difference is about 25°C or less, typically about 20°C or less. "Temperature difference" means the minimum difference between the temperature of the cold (reboiler) stream and the hot (dew point of substantially dry ethanol) stream. Those skilled in the art will understand that the dew point is the temperature at which superheated vapor begins to condense at a specific pressure; it may also be referred to as the saturation temperature.

[0029] Advantageously, this temperature difference means that the latent heat of condensation from the substantially dry ethanol stream can be used to provide heat in the first separation column reboiler using the heat transfer area of ​​the reboiler that may be used in the real world, which typically has a sump temperature of about 95°C to about 100°C, typically about 99°C to about 100°C. Therefore, the normal consumption of low-pressure steam in the first separation column reboiler is no longer required, thereby reducing the consumption of steam and fuel for generating steam from the boiler. When the temperature difference is not large enough, it is impossible to produce an economical design for the first separation column reboiler due to the need for a very large heat transfer area. Surprisingly, the additional heat requirements of increasing the overhead pressure in the azeotropic column and raising the dew point of the substantially dry ethanol stream do not negate the advantages of the reduced steam and fuel requirements provided by the heat exchange of the present invention. The first separation column may include a supplementary steam reboiler, which may be required, for example, during the startup of the process.

[0030] The ethanol make-up stream takes into account the ethanol that has been converted to ethyl acetate and byproducts in the upstream dehydrogenation process and ensures the ethanol mass balance between the feed to the ethanol dehydrogenation reactor and the first separation column. Typically, the ethanol make-up stream contains about 10.0 wt % or less water, typically about 5.0 wt % or less water, such as 2.5 wt % or less water.

[0031] In the first splitter reboiler, from the substantially dry ethanol stream, produce a condensed ethanol stream that can be partially or completely condensed. The condensed ethanol stream usually leaves the reboiler at a temperature of about 110 ℃ to about 130 ℃ or to about 120 ℃. Heat integration can be provided between the condensed ethanol stream and the ethanol supplementary stream, which is usually fed from a storage tank at ambient temperature (usually about 25 ℃). Therefore, the condensed ethanol stream formed in the first splitter reboiler is used to provide heat to the ethanol supplementary stream before the ethanol supplementary stream is fed into the azeotropic column. If desired, this completes the condensation of the substantially dry ethanol stream, and advantageously offsets the heat load of any increase required in the azeotropic column reboiler, so as to provide the optimum temperature close to the first splitter reboiler to the substantially dry ethanol stream.

[0032] The heavy components introduced into the azeotropic column via the intermediate bottoms stream can be at least partially removed by recovering a liquid side draw containing water and organic matter near the bottom of the azeotropic column. The liquid side draw typically contains less than about 4.0% by weight of ethanol, preferably less than about 0.1% by weight of ethanol to produce a favorable phase separation. Typically, the liquid side draw is recovered near the bottom of the azeotropic column, cooled by passing through a cooler, and then sent to a decanter, wherein the decanter provides an aqueous stream having a higher water concentration than the liquid side draw and an organic stream having a higher organic concentration than the liquid side draw, wherein the aqueous stream is returned to the azeotropic column. Using an azeotropic column decanter to remove the heavy components allows them to be removed without losing ethanol, thereby improving the feed efficiency of the ethyl acetate production process in which the present method is integrated. Typically, the aqueous stream contains at least about 90% by weight of water, and the organic stream contains 20% by weight or less of water. Typically, the liquid side draw is cooled to a temperature of about 30°C to about 50°C, such as about 40°C. Cooling the liquid side draw causes the water and organics to become immiscible and form separate phases of different densities that can be separated using weirs and baffle plates. When the cooled side draw settles in the decanter vessel, two liquid phases are formed, a denser aqueous phase at the bottom and a less dense organic phase on top. This separation allows the oxygen demand of the aqueous effluent from the bottom of the azeotropic column to be reduced and allows the organics to be recovered for use as a fuel without free water.

[0033] Heat integration can be provided between the liquid side draw and the aqueous stream returned from the decanter to the azeotropic column. Thus, the liquid side draw can be used to heat the aqueous stream before it is returned to the azeotropic column, either prior to or without passing through a cooler. This heat exchange advantageously reduces any increased heat duty required in the azeotropic column to provide a substantially dry ethanol stream having an optimal temperature differential with the first separation column reboiler.

[0034] Heat integration can also be provided between the azeotropic column bottoms stream and the aqueous stream before the aqueous stream is returned to the azeotropic column. Thus, the azeotropic column bottoms stream can be used to heat the aqueous stream before the aqueous stream is returned to the azeotropic column. This heat exchange also advantageously reduces any increased heat load required for the azeotropic column to provide a substantially dry ethanol stream having a temperature close to the optimum temperature of the first separation column reboiler.

[0035] In some arrangements, there may be a brief interruption sometimes in the substantially dry ethanol stream from the water removal section. For example, if a molecular sieve is used in the water removal section, the molecular sieve arrangement may include two or more molecular sieve beds, and as mentioned above, when the water capacity of the first molecular sieve bed is exhausted, the stream may be transferred to another molecular sieve bed, while the first molecular sieve bed is regenerated. The regenerated molecular sieve bed generally involves reducing the pressure, and then the fluid is refluxed through the bed. When the regenerated bed is restored online, it is necessary to repressurize it. If the bed is refluxed and / or repressurized using a substantially dry ethanol stream, this will cause the substantially dry ethanol stream to significantly reduce the flow of the first separation tower reboiler for a period of time. Reflux generally uses a lower flow rate for a longer time, and repressurization generally uses a higher flow rate for a shorter time. Therefore preferably, in addition to the first separation tower reboiler, a quick start reboiler is provided on the first separation tower. The quick start reboiler is preferably a reboiler that can be started in less than 10 minutes, preferably less than 5 minutes and more preferably less than 1 minute. The quick start reboiler is preferably an electric reboiler. It should be understood that conventional steam reboiler may need time to heat, therefore may not be suitable for the situation that needs short time heating.Quick start reboiler (preferably electric reboiler) can be used for reducing or interrupting the substantially dry ethanol feed stream to provide heat during the flow of the first separation tower reboiler.Alternately or additionally, when there is an increased demand for ethanol in water removal section, for example, during the repressurization or reflux of a part (such as molecular sieve bed) of water removal section, other ethanol source (generally ethanol vapor) can be provided to be fed to the water removal section.In this way, even when additional ethanol (generally ethanol vapor) is needed in water removal section, the flow rate of the substantially dry ethanol feed stream entering the first separation tower reboiler can also be maintained.Other ethanol source is preferably ethanol supplementary stream.Therefore, ethanol supplementary stream can be further connected to the water removal section, preferably via evaporator, most preferably electric evaporator, so that the ethanol from ethanol supplementary stream can also be supplied to the water removal section. It will be appreciated that supplying ethanol from the ethanol make-up stream to the water removal section may be in addition to, rather than a replacement for, feeding the ethanol make-up stream to the azeotrope column. An increase in the amount of ethanol make-up required is not a problem because the ethanol make-up stream is typically drawn from a storage tank, so an increased supply is possible while ethanol from the ethanol make-up stream is also being supplied to the water removal section.

[0036] The invention will now be described by way of example with reference to the accompanying drawings. It will be appreciated by those skilled in the art that the drawings are illustrative and that other items of equipment may be required in a commercial plant, such as reflux drums, pumps, vacuum pumps, compressors, gas recirculation compressors, temperature sensors, pressure relief valves, control valves, flow controllers, level controllers, etc. The provision of such ancillary items of equipment does not form part of the present invention and is in accordance with conventional chemical engineering practice.

[0037] like Figure 1 As shown in, the raw material comprising ethyl acetate, ethanol and water is fed to the first knockout tower I in pipeline 15. The raw material comes from the refining hydrogenation step after ethanol dehydrogenation on a copper-based heterogeneous catalyst. This part of the method is not shown. The raw material will also contain light components such as ether, methanol, ethane and gases such as hydrogen, methane and carbon dioxide and heavy components such as butanols and butyl acetate. The raw material will usually contain liquid phase components and gas phase components, and its composition depends on upstream conditions and is not critical for this method.

[0038] The first separation column I includes a reboiler M. A substantially dry ethanol stream 23 in the vapor phase is used to provide heat to the reboiler M. This replaces the steam reboiler present in conventional processes and provides the advantages discussed herein. The ethanol stream 24 leaving the reboiler M is then cooled in an ethanol condensate cooler N and can be fed back into the ethanol dehydrogenation process. There may also be a gas reboiler K, in which heat from a vapor stream 22 produced in another part of the ethyl acetate production process can be utilized, such as a high pressure second separation column in a pressure swing distillation system.

[0039] The intermediate bottom stream 19 is recovered from the bottom of the first separation tower I and conveyed through a pump L, and then fed to the azeotropic column A as stream 1 at or near the top of the azeotropic column. After a period of operation, a purge of the intermediate bottom stream 19, for example up to 1.5% by weight, may be performed in stream 20 to stop the accumulation of undesirable by-products. A tower top stream 16 containing light components such as ether, methanol and ethane is formed. Stream 16 is partially condensed and then sent to a light component column (not shown), where the light components are discharged to a combustion column or a fuel header. Most of the light component column bottom stream is returned to the first separation tower as reflux in stream 17, and the remainder is fed to a high-pressure second separation tower (not shown) as part of a pressure swing distillation system. Stream 18 is a condensed tower top stream from the second separation tower, which is in a high-pressure azeotropic composition and is therefore deficient in ethyl acetate relative to stream 16.

[0040] Azeotropic column A is operated at a top pressure of about 4.6 absolute pressure to obtain an azeotropic column top stream 3 with a temperature of about 123°C. Azeotropic column top stream 3 contains ethanol and water, with a water content of about 2.2% to about 5.5% by weight. This stream is then superheated by about 20°C and passed through a molecular sieve pack H, which removes water from the stream. The substantially dry ethanol stream 23 leaves the molecular sieve pack at a temperature of about 122°C and a slightly reduced pressure. This temperature means that the latent heat of condensation from the substantially dry ethanol stream can be advantageously used to provide reboil heat to the bottom of the first separation column via a reboiler M, which has a sump temperature of about 99°C. Therefore, the normal consumption of low-pressure steam of the first separation column is no longer required, thereby reducing the consumption of steam and fuel for generating steam from the boiler. The azeotropic column uses a reboiler B heated with steam 12, which provides an additional heat load imposed on the azeotropic column by a higher operating pressure. Surprisingly, the additional heat requirement here does not negate the advantages of reduced heat and steam consumption provided by the heat exchange of the present invention.

[0041] An aqueous regeneration stream 10 containing removed water produced during the regeneration of the molecular sieve is returned to the azeotropic column at a constant rate to a point below the feed point of stream 1. A mainly aqueous bottoms stream 4 is recovered from the bottom of the azeotropic column A by pump C, cooled with a water coolant stream 14 in a bottoms cooler D and discarded as an aqueous effluent.

[0042] An ethanol make-up stream 2 is fed from a storage tank (not shown) to the azeotropic column A near the top (below the top tray if trays are used) at ambient temperature. This stream contains water, which is why it is best to add it to the system at this stage in the ethanol dehydrogenation process. In addition, the water in the make-up stream can promote the deactivation of the ethanol dehydrogenation catalyst.

[0043] A liquid side draw 6 is recovered near the bottom of the azeotrope column. This side draw contains water and organic heavy components, which are separated in a decanter F after cooling in a cooler E with an aqueous coolant stream 13. The decanter contains a baffle and a weir to remove the two phases separately and provide an aqueous stream 8 to be returned to the azeotrope column A via a pump G. The organic phase is discarded as an organic purge stream 9.

[0044] exist Figure 2 In the arrangement shown, after the substantially dry ethanol stream leaves the first separation column reboiler 24, there is heat integration between the substantially dry ethanol stream and the ethanol make-up feed 2. In this arrangement, heat is provided by stream 24 to the ethanol make-up stream 2 in heat exchanger O. By heating the ethanol make-up stream, the sensible heat required by the azeotropic column reboiler B is reduced, thereby reducing its steam consumption. This also completes the condensation of the substantially dry ethanol stream in the vapor phase, if necessary, to provide stream 11.

[0045] exist Figure 3 In the arrangement shown, there is also heat integration between the aqueous regeneration stream 10 from the molecular sieve regeneration in the water removal section H and the stream 26 which is the effluent stream from the upstream ethanol dehydrogenation reactor. In this arrangement, heat is provided to the stream 10 by the stream 26 in the heat exchanger P. For regeneration, the azeotropic column top stream 3 is transferred to the molecular sieve empty bed, while the water-saturated bed is regenerated by reflux drying ethanol, and the pressure in the bed is reduced to discharge water molecules. In a conventional ethyl acetate production process, the dehydrogenation effluent stream will have a temperature of about 105°C. The dehydrogenation effluent stream is condensing and has a significantly larger flow rate than the aqueous regeneration stream from the molecular sieve, so the stream can be heated from, for example, 40°C to about 95°C. By heating the aqueous stream 26, the sensible heat required for the azeotropic column reboiler B is reduced, thereby reducing its steam consumption via stream 12.

[0046] exist Figure 4 In the arrangement shown, there is also heat integration between the liquid side draw 6 and the aqueous stream 8 returned to the azeotrope column A after the organic purge in the decanter F. In this arrangement, the liquid side draw 6 is used to heat the aqueous stream 8 in the heat exchanger P before or without passing through the cooler E. This arrangement may be advantageous when the ethanol make-up stream contains a low concentration of water, because the flow of the azeotrope column bottoms stream 4 may not be large enough to allow exchange with the aqueous stream 8 (e.g., Figure 5 shown) is feasible.

[0047] Figure 5 The arrangement shown in Figure 4 An alternative arrangement is shown in which there is heat integration between the azeotropic column bottoms stream 4 and the aqueous stream 8 returned to the azeotropic column A. In this arrangement, heat is provided to the aqueous stream 8 from stream 4 in heat exchanger Q. By heating the aqueous stream 8, the sensible heat required for the azeotropic column reboiler B is reduced, thereby reducing its steam consumption.

[0048] Figure 6 The arrangement shown in Figure 1 . The arrangement includes a fast start-up reboiler in the form of an electric reboiler R on the first separation column I. The arrangement also includes an electric evaporator Q, through which ethanol from the ethanol make-up stream 2 can be supplied to the water removal section H. It should be understood that in any particular embodiment, each of the electric reboiler R and the electric evaporator Q may be present or absent independently of each other, and the electric reboiler R and / or the electric evaporator Q may be included separately or together. Figures 1 to 5 in any arrangement.

[0049] Example

[0050] The illustrated process forms part of a process for producing ethyl acetate by dehydrogenation of ethanol, and the feedstock for the process is therefore a crude product stream recovered from the production of ethyl acetate by dehydrogenation of ethanol, which ethanol has been subjected to finishing hydrogenation.

[0051] The tower was simulated using AVEVA Pro / II Alcohols Package version 10.2.3.

[0052] Example 1

[0053] The following example demonstrates the advantages associated with exchanging heat between the substantially dry ethanol stream and the first separation column reboiler.

[0054] In this example, a comparative process was performed in which the azeotropic column pressure was the conventional 2.75 absolute column top pressure and the heat exchange step of the present invention was not included because it was not feasible. Figure 1 ), where the azeotropic column pressure was 4.6 absolute overhead. This increased the pressure of the substantially dry ethanol vapor leaving the molecular sieve pack, increasing the dew point from 103°C to 121°C, and allowing the temperature difference between the dew point of the substantially dry ethanol vapor and the sump of the first separation column to increase from 6.8°C to 24.8°C. As can be seen in Table 1, at various ethanol make-up stream water concentrations, there is clearly a net steam savings of between 0.62 MWh / TeEA and 0.63 MWh / TeEA. This surprisingly occurred despite the increased duty required for the azeotropic column reboiler.

[0055]

[0056] Table 1

[0057] Example 2

[0058] The following examples demonstrate that the required increase in azeotrope column reboiler duty can be offset by additional heat integration, thereby maximizing the benefits of the present invention.

[0059] In this embodiment, the process of the present invention provides additional heat exchange between the substantially dry ethanol stream exiting the first separation column reboiler and an ethanol make-up stream drawn from a storage tank at ambient temperature (according to Figure 2 As can be seen from Table 2, at different ethanol make-up stream water concentrations, the net steam savings increased to between 0.70 MWh / TeEA and 0.71 MWh / TeEA.

[0060]

[0061] Table 2

[0062] Example 3

[0063] The following examples demonstrate that the required increase in azeotrope column reboiler duty can be further offset by additional heat integration, thereby maximizing the benefits of the present invention.

[0064] In this example, the process according to Example 2 is carried out, wherein an additional heat exchange is carried out between the aqueous regeneration stream from the molecular sieve in the water removal section and the effluent stream from the ethanol dehydrogenation reactor (according to Figure 3 As can be seen from Table 3, at different ethanol make-up stream water concentrations, the net steam savings increased to between 0.74 MWh / TeEA and 0.84 MWh / TeEA.

[0065]

[0066] Table 3

[0067] Example 4

[0068] The following examples demonstrate that the required increase in azeotrope column reboiler duty can be further offset by additional heat integration, thereby maximizing the benefits of the present invention.

[0069] In this example, the process according to Example 3 is carried out, wherein an additional heat exchange is carried out between the liquid side draw taken from the vicinity of the bottom of the azeotrope column and the aqueous stream which is returned to the azeotrope column after separation from the organic matter in the decanter (according to Figure 4 As can be seen from Table 4, at different ethanol make-up stream water concentrations, the net steam savings increased to between 0.74 MWh / Te EA and 0.86 MWh / Te EA.

[0070]

[0071] Table 4

Claims

1. A process for recovering substantially dry ethanol from a feedstock comprising ethyl acetate, ethanol and water, the process comprising: (a) passing the feedstock to a first separation column, the first separation column comprising a first separation column reboiler and maintained under distillation conditions to form an intermediate bottoms stream comprising ethanol and water and having an ethanol concentration greater than the ethanol concentration in the feedstock; (b) passing the intermediate bottoms stream to an azeotrope column maintained at distillation conditions to form an azeotrope column bottoms stream and an azeotrope column overhead stream, the azeotrope column overhead stream comprising ethanol and water and having a higher ethanol concentration than the ethanol concentration in the intermediate bottoms stream; (c) feeding an ethanol make-up stream into the azeotropic column; (d) passing the azeotrope column overhead stream through a water removal section to separate water from ethanol to form a substantially dry ethanol stream; (e) using the substantially dry ethanol stream to provide heat in the first separation column reboiler.

2. The process of claim 1 wherein the azeotropic column is operated at a top pressure of at least about 4.0 absolute.

3. The process of any preceding claim, wherein the substantially dry ethanol stream has a dew point of at least about 115°C.

4. The process of any preceding claim, wherein the temperature difference between the dew point of the substantially dry ethanol stream and the temperature of the first splitter bottoms stream is at least about 15°C.

5. The process of any preceding claim, wherein the ethanol make-up stream contains about 10.0 wt% or less water.

6. A process according to any preceding claim, wherein a condensed ethanol stream formed in the first separation column reboiler is used to provide heat to the ethanol make-up stream prior to feeding the ethanol make-up stream to the azeotropic column.

7. A process according to any preceding claim, wherein a liquid side draw comprising water and organics is recovered from near the bottom of the azeotropic column, cooled by passing through a cooler and then passed to a decanter, wherein the decanter provides an aqueous stream having a higher water concentration than the liquid side draw, and an organic stream having a higher organic concentration than the liquid side draw, wherein the aqueous stream is returned to the azeotropic column.

8. The process of claim 7 wherein the liquid side draw is used to heat the aqueous stream before or without passing through the cooler before the aqueous stream is returned to the azeotropic column.

9. The process of claim 7, wherein the azeotrope column bottoms stream is used to heat the aqueous stream before the aqueous stream is returned to the azeotrope column.

10. A process according to any preceding claim, wherein the feedstock is a crude product stream recovered from the production of ethyl acetate by dehydrogenation of ethanol.

11. The method of claim 10, wherein the feedstock is substantially free of aldehydes and ketones.

12. A process for producing ethyl acetate by dehydrogenation of ethanol, the process comprising the process according to claim 10 or claim 11.

13. The method according to claim 10, 11 or 12, further comprising the steps of: The water removal section is regenerated to provide an aqueous regeneration stream having a water concentration above the ethanol / water azeotrope, and the aqueous regeneration stream is returned to the azeotrope column, wherein effluent from the ethanol dehydrogenation reactor used to generate the feedstock is used to heat the aqueous regeneration stream before it is returned to the azeotrope column.

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