Methods for separating hydrocarbons

Abstract

Methods described herein may include separating a mixed feed stream into a light fraction and a heavy fraction, compressing the light fraction to form a first compressed light fraction, and further compressing a first portion of the first compressed light fraction to form a second compressed light fraction. The method may include cooling the second compressed light fraction, separating a portion of the cooled second compressed light fraction into a vapor stream and a liquid stream, and combining the vapor stream with a second portion of the first compressed light fraction to form a combined stream. The method may include passing the combined stream to a first heat exchanger to form a cooled combined stream by heat exchange with a portion of the heavy fraction, further cooling the cooled combined stream to form a sub-cooled combined stream, combining the liquid stream with the sub-cooled combined stream to form a reflux stream, and passing the reflux stream to the first separator.

Description

METHODS FOR SEPARATING HYDROCARBONSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 594,103 filed October 30, 2023, the contents of which are incorporated in their entirety herein.TECHNICAL FIELD

[0002] Embodiments described herein generally relate to methods and systems for separating hydrocarbons.BACKGROUND

[0003] Various hydrocarbons, such as ethylene, ethane, propylene, propane, and heavier hydrocarbons, may be recovered from a variety of streams obtained from chemical reactors. Mixtures of the various hydrocarbons may be separated to form one or more product streams having desired hydrocarbon compositions.SUMMARY

[0004] Various separation processes may be used to form product streams from mixed hydrocarbon streams. These separation processes may include processes for separating olefins from paraffins. The separation of olefins from paraffins may be energy intensive due to the similar structures and boiling points of olefins and paraffins having the same number of carbon atoms, such as, for example, propylene and propane. Accordingly, there is a need for methods for separating olefins and paraffins with improved energy efficiency. These needs may be met by embodiments described in the present disclosure.

[0005] As described in greater detail herein, embodiments of the present disclosure may include separating a mixed feed stream into a light fraction and a heavy fraction in a separator. The light fraction may be compressed by one or more compressors. Heat generated by compressing the light fraction may be transferred from the compressed light fraction to at least a portion of the heavy fraction in a heat exchanger. This may improve the energy efficiency of the system. Additionally, the compressed light fraction may be further cooled before being introduced to the separator as a reflux stream. Further cooling of the compressed light fraction before it ispassed to the separator as a reflux stream may reduce the likelihood that the reflux stream is flashed in the separator, which may improve the performance of the separator.

[0006] According to one or more embodiments of the present disclosure, a method for separating a mixed feed stream may comprise separating the mixed feed stream into a light fraction and a heavy fraction in a first separator, wherein the mixed feed stream comprises C3 olefins. The method may further comprise compressing the light fraction to form a first compressed light fraction, further compressing a first portion of the first compressed light fraction to form a second compressed light fraction, and cooling the second compressed light fraction to at least partially condense the second compressed light fraction to form a cooled second compressed light fraction. The method may further comprise passing a first portion of the cooled second compressed light fraction to a second separator, wherein a second portion of the cooled second compressed light fraction is a product stream. The method may further comprise separating the first portion of the cooled second compressed light fraction into a vapor stream and a liquid stream in the second separator, combining the vapor stream with a second portion of the first compressed light fraction to form a combined stream, and passing the combined stream to a first heat exchanger to form a cooled combined stream by heat exchange with at least a portion of the heavy fraction. The method may further comprise further cooling the cooled combined stream in a second heat exchanger to form a sub-cooled combined stream, combining the liquid stream with the sub-cooled combined stream to form a reflux stream, and passing the reflux stream to the first separator.

[0007] Additional features and advantages of the technology disclosed herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the technology as described herein, including the detailed description which follows, the claims, as well as the appended drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawing, where like structure is indicated with like reference numerals and in which:

[0009] FIG. 1 schematically depicts a system for separating hydrocarbons, according to one or more embodiments disclosed herein.

[0010] It should be understood that the drawings are schematic in nature, and do not include some components of a separation system commonly employed in the art, such as, without limitation, temperature transmitters, pressure transmitters, flow meters, pumps, valves, and the like. It would be known that these components are within the spirit and scope of the present embodiments disclosed. However, operational components, such as those described in the present disclosure, may be added to the embodiments described in this disclosure.

[0011] Reference will now be made in greater detail to various embodiments, some embodiments of which are illustrated in the accompanying drawing.DETAILED DESCRIPTION

[0012] One or more non-limiting embodiments of methods for separating a mixed feed streams are described herein. FIG. 1 depicts an embodiment of a system for separating a mixed feed stream. Embodiments of the methods for separating mixed feed streams may be performed using a system as depicted in FIG. 1. However, it should be understood that the methods for separating mixed feed streams described herein are not limited to the use of the system depicted in FIG. 1. Embodiments of the methods for separating mixed feed streams described herein may be used to separating olefins from paraffins. For example, some embodiments of the methods described herein may be used to separate C3 olefins (propylene) from C3 paraffins (propane).

[0013] Referring now to FIG. 1, a mixed feed stream 102 may be separated into a light fraction 104 and a heavy fraction 106. In one or more embodiments, the mixed feed stream 102 may comprise one or more of C2, C3, and C4 hydrocarbons. The mixed feed stream 102 may comprise olefins and paraffins. For example, the mixed feed stream 102 may comprise one or more of C2, C3, and C4 olefins and one or more of C2, C3, and C4 paraffins. In some embodiments, the mixed feed stream 102 may comprise C3 olefins and paraffins. For example, the mixed feed stream 102 may comprise at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, at least 90 wt.%, at least 95 wt.% or even at least 99 wt.% C3 olefins and paraffins. The mixed feed stream 102 may be any process stream comprising C2, C3, and C4 olefins and paraffins. For example, in some embodiments, the mixed feed stream 102 may be a product stream from a system that produces olefins from paraffins.

[0014] The mixed feed stream 102 may be separated into a light fraction 104 and a heavy fraction 106 in a first separator 202. The first separator 202 may be any suitable separation device. The first separator 202 may be configured to separate olefins from paraffins. In one or more embodiments, the first separator 202 may comprise a distillation column.

[0015] As used in this disclosure, a “separator” refers to any separation device or system of separation devices that at least partially separates one or more chemicals that are mixed in a process stream from one another. For example, a separator may selectively separate differing chemical species or phases from one another, forming one or more chemical fractions. Examples of separators include, without limitation, distillation columns, flash drums, knock-out drums, knock-out pots, traps, scrubbers, expansion devices, membranes, solvent extraction devices, and the like. It should be understood that separation processes described in this disclosure may not completely separate all of one chemical constituent from all of another chemical constituent. It should be understood that the separation processes described in this disclosure “at least partially” separate different chemical components from one another, and that even if not explicitly stated, it should be understood that separation may include only partial separation. As used in this disclosure, one or more chemical constituents may be “separated” from a process stream to form a new process stream. Generally, a process stream may enter a separator and be divided, or separated, into two or more process streams of desired composition.

[0016] In one or more embodiments, the light fraction 104 may comprise one or more C2, C3, and C4 olefins. For example, the light fraction 104 may comprise one or more of ethylene, propylene, and butene. In one or more embodiments, the light fraction 104 may comprise greater than or equal to 75 wt.% of C2, C3, and C4 olefins. For example, the light fraction 104 may comprise greater than or equal to 75 wt.%, greater than or equal to 80 wt.%, greater than or equal to 85 wt.%, greater than or equal to 90 wt.%, greater than or equal to 95 wt.%, or even greater than or equal to 99 wt.% of C2, C3, and C4 olefins. In some embodiments, the light fraction 104 may comprise at least 75 wt.% propylene. For example, the light fraction 104 may comprise greater than or equal to 75 wt.%, greater than or equal to 80 wt.%, greater than or equal to 85 wt.%, greater than or equal to 90 wt.%, greater than or equal to 95 wt.%, or even greater than or equal to 99 wt.% propylene.

[0017] In one or more embodiments, the heavy fraction 106 may comprise one or more of C2, C3, and C4 paraffins. For example, the heavy fraction 106 may comprise one or more of ethane, propane, and butane. In one or more embodiments, the heavy fraction 106 may comprise greater than or equal to 50 wt.% of one or more of C2, C3, and C4 paraffins. For example, the heavy fraction 106 may comprise greater than or equal to 50 wt.%, greater than or equal to 60 wt.%, greater than or equal to 70 wt.%, greater than or equal to 80 wt.%, or even greater than or equal to 90 wt.% of one or more of C2, C3, and C4 paraffins. In some embodiments, the heavy fraction 106 may comprise greater than or equal to 50 wt.% of propane. For example, the heavy fraction 106 may comprise greater than or equal to 50 wt.%, greater than or equal to 60 wt.%, greater than or equal to 70 wt.%, greater than or equal to 80 wt.%, greater than or equal to 90 wt.%, or even greater than or equal to 95 wt.% propane.

[0018] In one or more embodiments, the first separator may be configured to at least partially separate olefins having a certain carbon number from paraffins having the same carbon number. Without intending to be bound by theory, in embodiments where C3 olefins and paraffins are separated in the first separator 202, the light fraction 104 may comprise propylene and the heavy fraction 106 may comprise propane. The heavy fraction 106 may also include any heavier hydrocarbons included in the mixed feed stream 102, such as C4 olefins and paraffins. In a similar manner, the light fraction 104 may also include any lighter hydrocarbons included in the mixed feed stream 102, such as C2 olefins and paraffins.

[0019] Still referring to FIG. 1, the light fraction 104 may be passed to a first compressor 212. In one or more embodiments, the light fraction 104 may be passed directly from the first separator 202 to the first compressor 212. As described herein, when a stream is passed “directly” from one system component to another system component, the stream is not passed through any intervening system components. In some embodiments, the light fraction 104 may be passed directly to the first compressor 212 without being passed through any intervening system components, such as a knock-out drum. Without intending to be bound by theory, passing the light fraction 104 directly from the first separator 202 to the first compressor 212 may reduce the capital cost of the system, while having a minimal impact on the performance of the system. For example, a knock-out drum positioned between the first separator 202 and the first compressor 212 may be eliminated in embodiments where the light fraction 104 is passed directly from the first separator 202 to the first compressor 212, reducing the capital cost of the system.

[0020] In one or more embodiments, the light fraction 104 may be compressed in the first compressor 212 to form a first compressed light fraction 108. The first compressor 212 may be any suitable compressor, including but not limited to, a centrifugal compressor. In one or more embodiments, compressing the light fraction 104 may increase the pressure of the light fraction 104 and increase the temperature of the light fraction 104. In such embodiments, the pressure and temperature of the first compressed light fraction 108 may each be greater than the pressure and temperature of the light fraction 104.

[0021] In one or more embodiments, a pressure of the light fraction 104 may be from 75 psig to 200 psig. For example, a pressure of the light fraction 104 may be from 75 psig to 200 psig, from 100 psig to 200 psig, from 125 psig to 200 psig, from 150 psig to 200 psig, from 175 psig to 200 psig, from 75 psig to 175 psig, from 75 psig to 150 psig, from 75 psig to 125 psig, from 75 psig to 100 psig, or any range or combination of ranges formed from these endpoints. In one or more embodiments, a temperature of the light fraction 104 may be from 0 °C to 35 °C. For example, the temperature of the light fraction 104 may be from 0 °C to 35 °C, from 5 °C to 35 °C, from 10 °C to 35 °C, from 15 °C to 35 °C, from 20 °C to 35 °C, from 25 °C to 35 °C, from 30 °C to 35 °C, from 0 °C to 30 °C, from 0 °C to 25 °C, from 0 °C to 20 °C, from 0 °C to 15 °C, from 0 °C to 10 °C, from 0 °C to 5 °C, or any range or combination of ranges formed from these endpoints.

[0022] In one or more embodiments, a pressure of the first compressed light fraction 108 may be from 160 psig to 205 psig. For example, a pressure of the first compressed light fraction 108 may be from 160 psig to 205 psig, from 170 psig to 205 psig, from 180 psig to 205 psig, from 190 psig to 205 psig, from 200 psig to 205 psig, from 160 psig to 195 psig, from 160 psig to 185 psig, from 160 psig to 175 psig, from 160 psig to 165 psig, or any range or combination of ranges formed from these endpoints. In one or more embodiments, a temperature of the first compressed light fraction 108 may be from 20 °C to 60 °C. For example, a temperature of the first compressed light fraction 108 may be from 20 °C to 60 °C, from 30 °C to 60 °C, from 40 °C to 60 °C, from 50 °C to 60 °C, from 20 °C to 50 °C, from 20 °C to 40 °C, from 20 °C to 30 °C, or any range or combination of ranges formed from these endpoints.

[0023] In one or more embodiments, a first portion of the first compressed light fraction 110 may be further compressed in second compressor 214 to form a second compressed light fraction112. The second compressor 214 may be any suitable compressor including but not limited to, a centrifugal compressor. In one or more embodiments, compressing the first portion of the first compressed light fraction 110 may increase the pressure and increase the temperature of the first portion of the first compressed light fraction 110. In such embodiments, the pressure and temperature of the second compressed light fraction 112 may each be greater than the pressure and temperature of the first portion of the first compressed light fraction 110.

[0024] In one or more embodiments, the second compressed light fraction 112 may have a pressure from 190 psig to 250 psig. For example, the second compressed light fraction 112 may have a pressure from 190 psig to 250 psig, from 200 psig to 250 psig, from 220 psig to 250 psig, from 230 psig to 250 psig, from 240 psig to 250 psig, from 190 psig to 240 psig, from 190 psig to 230 psig, from 190 psig to 220 psig, from 190 psig to 210 psig, from 190 psig to 200 psig, or any range or combination of ranges formed from these endpoints. In one or more embodiments, the second compressed light fraction 112 may have a temperature from 25 °C to 75 °C. For example, the second compressed light fraction 112 may have a temperature from 25 °C to 75 °C, from 35 °C to 75 °C, from 45 °C to 75 °C, from 55 °C to 75 °C, from 65 °C to 75 °C, from 25 °C to 65 °C, from 25 °C to 55 °C, from 25 °C to 45 °C, from 25 °C to 35 °C, or any range or combination of ranges formed from these endpoints.

[0025] The second compressed light fraction 112 may be cooled, such as by heat exchanger 210. The second compressed light fraction 112 may be cooled by any suitable means including cooling against air, or ambient cooling. Cooling the second compressed light fraction 112 may at least partially condense the second compressed light fraction 112 to form a cooled second compressed light fraction 114. In one or more embodiments, cooling the second compressed light fraction 112 may condense greater than or equal to 90 wt.%, greater than or equal to 95 wt.%, greater than or equal to 97 wt.%, or even greater than or equal to 99 wt.%, of the second compressed light fraction 112. In some embodiments, cooling the second compressed light fraction 112 may condense substantially all of the second compressed light fraction 112.

[0026] In one or more embodiments, the second compressed light fraction 112 may be cooled against a cooling medium in heat exchanger 210. The cooling medium may be any suitable cooling medium. In one or more embodiments, the cooling medium may comprise air. In some embodiments, the cooling medium may comprise water. In one or more embodiments, the coolingmedium may have a temperature from 10 °C to 70 °C before passing through heat exchanger 210. For example, the cooling medium may have a temperature from 10 °C to 70 °C, from 20 °C to 70 °C, from 30 °C to 70 °C, from 40 °C to 70 °C, from 50 °C to 70 °C, from 60 °C to 70 °C, from 10 °C to 60 °C, from 10 °C to 50 °C, from 10 °C to 40 °C, from 10 °C to 30 °C, from 10 °C to 20 °C, or any range or combination of ranges formed from these endpoints.

[0027] Still referring to FIG. 1 , a first portion of the cooled second compressed light fraction 116 may be passed to a second separator 204. A second portion of the cooled second compressed light fraction 114 may be a product stream 118. The product stream 118 may exit the system. As described herein, a “product stream” refers to a stream exiting the system. It should be noted that a “product stream” may be further processed in another system, or used as a feedstock in another system. In one or more embodiments, the product stream 118 may comprise greater than or equal to 75 wt.%, greater than or equal to 80 wt.%, greater than or equal to 85 wt.%, greater than or equal to 90 wt.%, greater than or equal to 95 wt.%, or even greater than or equal to 99 wt.% of C2, C3, and C4 olefins. In some embodiments, the product stream 118 may comprise greater than or equal to 75 wt.%, greater than or equal to 80 wt.%, greater than or equal to 85 wt.%, greater than or equal to 90 wt.%, greater than or equal to 95 wt.%, or even greater than or equal to 99 wt.% propylene.

[0028] In one or more embodiments, the pressure of the first portion of the cooled second compressed light fraction 116 may be reduced to at least partially vaporize the first portion of the cooled second compressed light fraction 116 before the cooled second compressed light fraction 116 is passed to the second separator 204. Reducing the pressure of the first portion of the cooled second compressed light fraction 116 may comprise throttling the first portion of the cooled second compressed light fraction 116 through a valve 216. Valve 216 may be any suitable valve for pressure reduction.

[0029] The first portion of the cooled second compressed light fraction 116 may be separated into a vapor stream 120 and a liquid stream 122 in the second separator 204. The second separator 204 may be any suitable separator, including but not limited to a flash drum or any other vapor / liquid separator.

[0030] In one or more embodiments, the vapor stream 120 may be combined with a second portion of the first compressed light fraction 124 to form a combined stream 126. The combinedstream 126 may be passed to first heat exchanger 206. The combined stream 126 may provide heat to the first heat exchanger 206 to form a cooled combined stream 128. In one or more embodiments, the cooled combined stream 128 may have a temperature that is less than the temperature of the combined stream 126. In one or more embodiments, cooling the combined stream 126 in the first heat exchanger 206 may at least partially condense the combined stream 126.

[0031] In one or more embodiments, the combined stream 126 may have a temperature from 30 °C to 50 °C. For example, the combined stream 126 may have a temperature from 30 °C to 50 °C, from 35 °C to 50 °C, from 40 °C to 50 °C, from 45 °C to 50 °C, from 30 °C to 45 °C, from 30 °C to 40 °C, from 30 °C to 35 °C, or any range or combination of ranges formed from these endpoints. In one or more embodiments, the cooled combined stream 128 may have a temperature from 20 °C to 40 °C. For example, the cooled combined stream 128 may have a temperature from 20 °C to 40 °C, from 25 °C to 40 °C, from 30 °C to 40 °C, from 35 °C to 40 °C, from 20 °C to 35 °C, from 20 °C to 30 °C, from 20 °C to 25 °C, or any range or combination of ranges formed from these endpoints.

[0032] In one or more embodiments, a portion of the heavy fraction 107 may be passed to the first heat exchanger 206. The portion of the heavy fraction 107 may be heated in the first heat exchanger 206 to produce a heated portion of the heavy fraction 109. In one or more embodiments, the heated portion of the heavy fraction 109 may have a temperature that is greater than the temperature of the portion of the heavy fraction 107. In one or more embodiments, at least part of the portion of the heavy fraction 109 may be vaporized in the first heat exchanger 206. In one or more embodiments, the heated portion of the heavy fraction 109 may be passed from the first heat exchanger 206 to the first separator 202. According to one or more embodiments, the first heat exchanger 206 may act as a reboiler.

[0033] In one or more embodiments, passing the combined stream 126 to the first heat exchanger 206 may allow at least a portion of the heat generated in the first compressor 212 and the second compressor 214 to be used to heat the portion of the heavy fraction 107 such that the heated portion of the heavy fraction 109 may be returned to the first separator 202. As described hereinabove, the first compressor 212 may heat the light fraction 104 and the second compressor 214 may heat the first portion of the first portion of the first compressed light fraction 110. Atleast a portion of the heat generated in the first compressor 212 and the second compressor 214 may be transferred to the portion of the heavy fraction 107 in heat exchanger 206 through combined stream 126. Without intending to be bound by theory, using heat generated by the first compressor 212 and the second compressor 214 to heat the portion of the heavy fraction 107 before it is returned to the first separator 202 may improve the energy efficiency of the process and reduce the need for external heating sources.

[0034] Still referring to FIG. 1, the cooled combined stream 128 may be further cooled in a second heat exchanger 208 to form a sub-cooled combined stream 130. As used in the present disclosure, a stream may be “sub-cooled” when it has undergone multiple cooling steps and has a temperature that is less than the temperature of the stream from which it is formed. For example, combined stream 126 may be cooled in first heat exchanger 206 to form cooled combined stream 128, and cooled combined stream 128 may be further cooled in the second heat exchanger 208 to form the sub-cooled combined stream 130. The sub-cooled combined stream 130 may have a temperature that is less than a temperature of the cooled combined stream 128. In one or more embodiments, the cooled combined stream 128 may be passed directly from the first heat exchanger 206 to a second heat exchanger 208.

[0035] In one or more embodiments, the sub-cooled combined stream 130 may have a temperature from 15 °C to 35 °C. For example, the sub-cooled combined stream 130 may have a temperature from 15 °C to 35 °C, from 17 °C to 35 °C, from 19 °C to 35 °C, from 21 °C to 35 °C, from 23 °C to 35 °C, from 25 °C to 35 °C, from 27 °C to 35 °C, from 29 °C to 35 °C, from 21 °C to 35 °C, from 33 °C to 35 °C, from 15 °C to 34 °C, from 15 °C to 32 °C, from 15 °C to 30 °C, from 15 °C to 28 °C, from 15 °C to 26 °C, from 15 °C to 24 °C, from 15 °C to 22 °C, from 15 °C to 20 °C, from 15 °C to 18 °C, from 15 °C to 16 °C, or any range or combination of ranges formed from these endpoints.

[0036] In one or more embodiments, the cooled combined stream 128 may be cooled against a stream comprising one or more alkanes 134 in the second heat exchanger 208. In such embodiments, the method may comprise passing the stream comprising one or more alkanes 134 to the second heat exchanger 208 to provide cooling in the second heat exchanger 208. The stream comprising one or more alkanes 134 may comprise one or more of C2, C3, or C4 alkanes. For example, the stream comprising one or more alkanes 134 may comprise ethane, propane, orbutane. In one or more embodiments, the stream comprising one or more alkanes 134 may comprise greater than or equal to 70 wt.%, greater than or equal to 80 wt.%, greater than or equal to 90 wt.%, or even greater than or equal to 95 wt.% of one or more of C2, C3, or C4 alkanes. In some embodiments, the stream comprising one or more alkanes 134 may comprise propane. In one or more embodiments, the stream comprising one or more alkanes 134 may comprise greater than or equal to 70 wt.%, greater than or equal to 80 wt.%, greater than or equal to 90 wt.%, or even greater than or equal to 95 wt.% propane.

[0037] In one or more embodiments, at least a portion of the stream comprising one or more alkanes 134 may be vaporized before being passed to the second heat exchanger 208. Vaporizing at least a portion of the stream comprising one or more alkanes 134 may cool the stream comprising one or more alkanes 134 before it is passed to the second heat exchanger 208. This may increase the amount of cooling that the stream comprising one or more alkanes 134 may provide in the second heat exchanger 208. In one or more embodiments, the at least a portion of the stream comprising one or more alkanes 134 may be vaporized by passing the stream comprising one or more alkanes 134 through valve 218 prior to passing the stream comprising one or more alkanes 134 to the second heat exchanger 208.

[0038] In one or more embodiments, the stream comprising one or more alkanes 134 may have a temperature of from -30 °C to 0 °C before being passed to the second heat exchanger 208. For example, the stream comprising one or more alkanes 134 may have a temperature of from - 30 °C to 0 °C, from -25 °C to 0 °C, from -20 °C to 0 °C, from -15 °C to 0 °C, from -10 °C to 0 °C, from -4 °C to 0 °C, from -30 °C to -5 °C, from -30 °C to -10 °C, from -30 °C to -15 °C, from -30 °C to -20 °C, from -30 °C to -25 °C, or any range or combination of ranges formed from these endpoints.

[0039] In one or more embodiments, the stream comprising one or more alkanes 134 may be heated in the second heat exchanger 208 to produce a warmed stream comprising one or more alkanes 136. Warmed stream comprising one or more alkanes 136 may have a temperature that is greater than stream comprising one or more alkanes 134. In one or more embodiments, warmed stream comprising one or more alkanes 136 may be passed to a reactor to be used as a hydrocarbon feedstock. For example, in some embodiments, the warmed stream comprising one or more alkanes 136 may comprise propane, and the warmed stream comprising one or more alkanes 136may be passed to a propane dehydrogenation reactor as a feedstock for the propane dehydrogenation reactor. It should be noted that this is merely one example of a reactor to which the warmed stream comprising one or more alkanes 136 may be passed and that the type of reactor is not necessarily limited to dehydrogenation reactors.

[0040] Without intending to be bound by theory, using the stream comprising one or more alkanes 134 as coolant in the second heat exchanger 208 may improve the energy efficiency of the system. For example, using the stream comprising one or more alkanes 134 as a coolant in the second heat exchanger 208 may reduce or even eliminate the need for external cooling to further cool the cooled combined stream 128.

[0041] Still referring to FIG. 1, the sub-cooled combined stream 130 may be combined with the liquid stream 122 to form a reflux stream 132. The sub-cooled combined stream 130 and the liquid stream 122 may be combined in any suitable manner, including but not limited to any suitable mixing device or apparatus. In one or more embodiments, the reflux stream 132 may be passed to the first separator 202.

[0042] The reflux stream 132 may have a temperature and pressure suitable for introduction into the second separator 202. In one or more embodiments, the reflux stream 132 may have a temperature from 10 °C to 20 °C. For example, the reflux stream 132 may have a temperature from 10 °C to 20 °C, from 12 °C to 20 °C, from 14 °C to 20 °C, from 16 °C to 20 °C, from 18 °C to 20 °C, from 10 °C to 19 °C, from 10 °C to 17 °C, from 10 °C to 15 °C, from 10 °C to 13 °C, from 10 °C to 11 °C, or any range or combination of ranges formed from these endpoints. In one or more embodiments, the reflux stream 132 may have a pressure from 100 psig to 120 psig. For example, the reflux stream 132 may have a pressure from 100 psig to 120 psig, from 105 psig to 120 psig, from 110 psig to 120 psig, from 115 psig to 120 psig, from 100 psig to 115 psig, from 100 psig to 110 psig, from 100 psig to 105 psig, or any range or combination of ranges formed from these endpoints.

[0043] Without intending to be bound by theory, further cooling the cooled combined stream 128 in the second heat exchanger 208 before introducing the reflux stream 132 into the first separator 202 may reduce the likelihood of the reflux stream 132 flashing upon being passed to the first separator 202. For example, reducing the enthalpy of the reflux stream 132 by subcooling the stream may result in less flashing of the reflux stream 132 when the pressure is letdown. Reducing the likelihood of the reflux stream 132 flashing upon introduction in to the first separator 202 may improve the separation performance of the first separator 202 and may reduce the load of compressor 212.EXAMPLES

[0044] Various embodiments of the processes and systems for separating a mixed feed stream will be further clarified in the following Example. The Example is illustrative in nature, and should not be understood to limit the subject matter of the present disclosure.

[0045] Example 1

[0046] Example 1 was conducted using an integrated separation train process model in Aspen plus for the system depicted in FIG. 1 for the separation of C3 olefins and paraffins. Table 1 shows temperatures, pressures, and mass fractions ratios of streams depicted in FIG. 1. The numbering of the streams included in Table 1 is consistent with the numbering of the streams in FIG. 1 and the numbering used throughout the detailed description. It should be noted that Table 1 includes mass fraction information for each stream listed in the table. The mass fraction information includes the mass fraction of the Total C2, Total C3, and Total C4 in each stream. Additionally, the mass fraction information includes the mass fraction of propylene and propane in each stream to illustrate the separation of propylene from propane in the system. It should be noted that the sum of the mass fraction of propylene and propane for each stream in Table 1 is the mass fraction of Total C3 in Table 1.Table 1.Table 1 Cont.Table 1 Cont.

[0047] As shown in Example 1, a mixed feed stream 102 may be separated into a light fraction 104 comprising greater than 99 wt.% propylene and a heavy fraction 106 comprising greater than 98 wt.% propane. It should be noted that not every stream labeled in FIG. 1 and described hereinabove is listed in Table 1.

[0048] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”

[0049] It should be understood that where a first component is described as “comprising” a second component, it is contemplated that, in some embodiments, the first component “consists of’ or “consists essentially of’ that second component. Additionally, the term “consisting essentially of’ is used in this disclosure to refer to quantitative values that do not materially affect the basic and novel characteristic(s) of the disclosure. For example, a chemical composition “consisting essentially of’ a particular chemical constituent or group of chemical constituents should be understood to mean that the composition includes at least about 99.5% of a that particular chemical constituent or group of chemical constituents.

[0050] It should be understood that any two quantitative values assigned to a property may constitute a range of that property, and all combinations of ranges formed from all stated quantitative values of a given property are contemplated in this disclosure.

[0051] The subject matter of the present disclosure has been described in detail and by reference to specific embodiments. It should be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that the component or feature is essential to the particular embodiment or to any other embodiment. Further, it should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.

Claims

CLAIMS1. A method of separating a mixed feed stream, the method comprising: separating the mixed feed stream into a light fraction and a heavy fraction in a first separator, wherein the mixed feed stream comprises C3 olefins and C3 paraffins; compressing the light fraction to form a first compressed light fraction; further compressing a first portion of the first compressed light fraction to form a second compressed light fraction; cooling the second compressed light fraction to at least partially condense the second compressed light fraction to form a cooled second compressed light fraction; passing a first portion of the cooled second compressed light fraction to a second separator, wherein a second portion of the cooled second compressed light fraction is a product stream; separating the first portion of the cooled second compressed light fraction into a vapor stream and a liquid stream in the second separator; combining the vapor stream with a second portion of the first compressed light fraction to form a combined stream; passing the combined stream to a first heat exchanger to form a cooled combined stream by heat exchange with at least a portion of the heavy fraction; further cooling the cooled combined stream in a second heat exchanger to form a subcooled combined stream; combining the liquid stream with the sub-cooled combined stream to form a reflux stream; and passing the reflux stream to the first separator.

2. The method of claim 1, further comprising passing a stream comprising one or more alkanes to the second heat exchanger to provide cooling to the second heat exchanger.

3. The method of claim 2, wherein the stream comprising one or more alkanes comprises C3 alkanes.

4. The method of claim 2 or claim 3, further comprising vaporizing at least a portion of the stream comprising one or more alkanes prior to passing the stream comprising one or more alkanes to the second heat exchanger.

5. The method of any one of claims 2 to 4, further comprising passing the stream comprising one or more alkanes to a reactor.

6. The method of any one of claims 1 to 5, wherein the light fraction is passed directly from the first separator to a first compressor.

7. The method of any one of claims 1 to 6, wherein the light fraction comprises greater than or equal to 75 wt.% propylene.

8. The method of any one of claims 1 to 7, wherein the heavy fraction comprises greater than or equal to 50 wt.% propane.

9. The method of any one of claims 1 to 8, wherein a cooling medium is used to cool the second compressed light fraction, and the cooling medium has a temperature from 10 °C to 70°C.

10. The method of claim 9, wherein the cooing medium comprises water.

11. The method of any one of claims 1 to 10, wherein cooling the second compressed light fraction condenses at least 95 wt.% of the second compressed light fraction.

12. The method of any one of claims 1 to 11, wherein the portion of the heavy fraction is heated in the first heat exchanger and passed to the first separator.

13. The method of any one of claims 1 to 12, wherein cooling the combined stream in the first heat exchanger at least partially condenses the combined stream.

14. The method of any one of claims 1 to 13, further comprising reducing a pressure of the first portion of the cooled second compressed light fraction to at least partially vaporize the first portion of the cooled second compressed light fraction before separating the first portion of the cooled second compressed light fraction into the vapor stream and the liquid stream.

15. The method of claim 14, wherein reducing the pressure of the first portion of the cooled second compressed light fraction comprises passing the first portion of the cooled second compressed light fraction through a valve.

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