Ethane separation using low temperature heat exchangers

Abstract

A method and apparatus integrates a deethanizer with a cryogenic heat exchanger by reboiling the deethanizer with a refrigerant stream and / or cooling a deethanizer overhead line in a cryogenic heat exchanger. High purity hydrogen in a net gas stream and an ethane rich tail gas stream can be obtained using a single stage separator and a single deethanizer, whereas conventionally, two stage separators and two deethanizers, respectively, would be required to achieve equivalent purities.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Provisional Application No. 63 / 169,415, filed April 1, 2021, the full text of which is incorporated herein by reference. Technical Field

[0003] This field relates to the separation of hydrogen and light hydrocarbons at low temperatures. More specifically, this field relates to the recovery of propylene from light hydrocarbons. Background Technology

[0004] Hydrocarbon dehydrogenation is an important commercial hydrocarbon conversion method due to the existing and growing demand for dehydrogenated hydrocarbons used in the manufacture of various chemical products such as detergents, high-octane gasoline, oxygenated gasoline blending components, pharmaceutical products, plastics, synthetic rubber, and others well known to those skilled in the art. Specifically, the demand for propylene in the petrochemical industry has grown significantly due to its use as a precursor in the production of polypropylene for packaging materials and other commercial products. Other downstream uses of propylene include the manufacture of acrylonitrile, acrylic acid, acrolein, propylene oxide and glycols, plasticizer oxyalcohols, cumene, isopropanol, and acetone. One route for producing propylene is propane dehydrogenation.

[0005] A method for converting alkanes to olefins involves passing an alkane feed stream through a highly selective catalyst, where the alkanes are dehydrogenated to the corresponding olefins, producing a dehydrogenation reactor effluent. The dehydrogenation reactor effluent is cooled and separated into hydrocarbon-rich and hydrogen-rich vapor fractions (a portion of which is a non-recirculated net gas) in a cryogenic separation system. This cryogenic separation system requires refrigeration to cool the process stream in order to separate hydrogen from the light hydrocarbon liquid. Conventional cryogenic separation systems cool the process stream separately to remove hydrogen from the light hydrocarbons. However, further fractionation is required to separate the C2-material from the C3 hydrocarbons in the dehydrogenation effluent in a deethanizer, which typically also requires refrigerated packaging.

[0006] Improvements to cryogenic separation systems are necessary to make propylene production and purification more economical. Summary of the Invention

[0007] We have discovered improved methods and apparatus for integrating a deethaner with a cryogenic heat exchanger by reboiling the deethaner with a refrigerant feed and / or cooling the deethaner top line in a cryogenic heat exchanger.

[0008] These and other features, aspects, and advantages of this disclosure are further explained by the following detailed description, accompanying drawings, and appended claims. Attached Figure Description

[0009] The accompanying drawings are schematic diagrams of the methods and apparatus of this disclosure.

[0010] definition

[0011] The following detailed description is exemplary in nature only and is not intended to limit the application and use of the described embodiments. Furthermore, it is not intended to be bound by the foregoing background art or any theory presented in the following detailed description.

[0012] The term "connectivity" means that material flow is operatively permitted between enumerated components.

[0013] The term "downstream connectivity" means that in downstream connectivity at least a portion of the material flowing toward the main body can be operatively flowed from the object with which it is connected.

[0014] The term "upstream connectivity" means that at least a portion of the material flowing out of the main body in an upstream connectivity can be operatively flowed to the object connected to it.

[0015] The term "direct connection" means that the flow from the upstream component to the downstream component does not change in composition due to physical fractionation or chemical transformation.

[0016] The term "bypass" means that an object loses downstream connectivity with the bypassed entity, at least within the scope of the bypass.

[0017] As used herein, the term "separator" refers to a vessel having an inlet and at least one overhead vapor outlet and a bottom liquid outlet, and may also have an outlet for a water-containing feed stream from a boot. A flash tank is a type of separator that can maintain downstream communication with a separator capable of operating at higher pressures.

[0018] As used herein, the terms “major” or “most” mean greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0019] Term "C" x "This should be understood as referring to a molecule having the number of carbon atoms indicated by the subscript "x". Similarly, the term "C" x "-" refers to a molecule containing x carbon atoms or less, and preferably x and fewer. The term "C" x "+" refers to a molecule that has x or more carbon atoms, and preferably x and more.

[0020] The term "tower" refers to one or more distillation columns used to separate one or more components with different volatility. Unless otherwise specified, each column includes a condenser at the top of the column for condensing a portion of the overhead feed and returning it to the top of the column, and a reboiler at the bottom of the column for evaporating a portion of the bottom feed and returning it to the bottom of the column. The feed to the column may be preheated. Top pressure is the pressure of the overhead vapor at the column outlet. Bottom temperature is the liquid temperature at the bottom outlet of the column. Unless otherwise specified, top and bottom lines refer to the net lines returning or reboiling from the downstream of the column to the column. Alternatively, the stripping feed may be used as a heat input near the bottom of the column.

[0021] As used herein, the term "rich component stream" refers to a rich stream exiting a container with a higher component concentration than the feed into the container.

[0022] As used herein, the term "lean stream" refers to a lean stream exiting a container with a lower component concentration than the feed into the container. Detailed Implementation

[0023] This disclosure relates to methods and apparatus for integrating the separation of hydrogen, C2-hydrocarbons, and C3+ hydrocarbons into a single system with a single refrigeration package. The single refrigerant system facilitates cooling and condensation over a wide temperature range. The methods and apparatus utilize a cryogenic heat exchanger integrating the deethanizer, thereby eliminating the use of steam for reboiling and leveraging the refrigeration system within the cryogenic heat exchanger to significantly reduce fractionation costs. The methods and apparatus allow the use of a single deethanizer instead of two conventional deethanizers, reducing capital expenditure and operational complexity. The methods and apparatus provide reduced compressor stages, equipment count, and facility usage.

[0024] The method and apparatus include conveying a reactor feed stream containing hydrocarbons and hydrogen from reactor feed line 2 to dehydrogenation reactor 4 to provide a dehydrogenation reactor effluent stream in effluent line 6. The reactor feed stream in line 2 may be preheated in a heat-combining feed exchanger 5 before being conveyed to dehydrogenation reactor 4.

[0025] The reactor feed stream contains propane. In some embodiments, the reactor feed stream contains other light alkanes, such as ethane, butane, n-butane, isobutane, pentane, or isopentane. In some embodiments, the reactor feed stream contains at least one alkane having 2 to 30 carbon atoms. The molar ratio of hydrogen to hydrocarbons in the feed stream is in the range of 0.005 to 0.6.

[0026] In dehydrogenation reactor 4, which is maintained under dehydrogenation conditions, a preheated reactor feed stream is contacted with a dehydrogenation catalyst to produce a dehydrogenation reactor effluent stream containing hydrogen, unconverted alkanes, and olefins in effluent line 6. Dehydrogenation reactor 4 can be a reaction zone comprising multiple stages or reactors typically connected in series.

[0027] The dehydrogenation catalyst can be a highly selective platinum-based catalyst system. An example of a suitable catalyst for dehydrogenation methods of light alkanes is a catalyst composite material comprising a Group VIII noble metal component, a Group IA or Group IIA metal component, and a component selected from tin, germanium, lead, indium, gallium, thallium, or mixtures thereof, all of which are situated on an alumina support.

[0028] Dehydrogenation conditions include temperatures ranging from 400°C to 900°C, pressures ranging from 0.01 to 10 atmospheres, and operating times ranging from 0.1 to 100 hours. -1 The liquid hourly space velocity (LHSV) is crucial. Generally, for n-chain alkanes, the lower the molecular weight, the higher the temperature required to achieve a comparable conversion. The pressure in dehydrogenation reactor 4 is maintained at the lowest feasible level, consistent with equipment limitations, to maximize the chemical equilibrium advantage. The dehydrogenation reaction is typically endothermic.

[0029] The reactor feed stream in reactor feed line 2 can exchange heat with the reactor effluent stream in line 6 in a heat-combining feed exchanger 5. The dehydrogenation reactor effluent stream in line 6 is cooled by heat exchange with the reactor feed stream 2 in the heat-combining feed exchanger 5 and compressed in the reactor effluent compressor 11 to provide a compressed reactor effluent stream. The compressed reactor effluent stream in reactor effluent line 6 is then fed to a cryogenic separation system 10 to provide olefin and hydrogen streams.

[0030] The reactor effluent stream may contain light hydrocarbons and hydrogen. In alkane dehydrogenation, the desired product is typically propylene, which must be separated from other light hydrocarbons such as propane and hydrogen. Propane can be recycled back to dehydrogenation reactor 4 for propylene production. Hydrogen is a valuable byproduct and can be used elsewhere in the refinery, such as as fuel for combustion heaters used in dihydrogenation processes. Some hydrogen can be recycled back to reactor 4 to control the dehydrogenation reaction.

[0031] To effectively separate hydrogen from light hydrocarbons, the reactor effluent stream is cooled by condensing hydrocarbons in a cryogenic heat exchanger 16. In the cryogenic heat exchanger 16, the reactor effluent stream in line 6 is guided through an effluent passage 7, where it is cooled by heat exchange with other streams carried through the cryogenic heat exchanger, thus providing a cooled reactor effluent stream in line 8.

[0032] The single-stage separator 20 maintains downstream communication with the effluent passage 7. The cooled reactor effluent stream in the separation line 8 of the single-stage separator 20 provides a hydrogen-rich net gas overhead stream in the separator overhead line 22 extending from the top of the single-stage separator, and a hydrocarbon-rich separator bottom stream in the separator bottom line 24 extending from the bottom of the single-stage separator. The single-stage separator 20 can operate at temperatures between -150°C (-101°F) and 66°C (150°F), and more commonly between -95°C (-138°F) and -40°C (-40°F), and at gauge pressures between 690 kPa (100 psig) and 1.4 MPa (200 psig).

[0033] By fully condensing hydrocarbons in the single-stage separator 20, the net gas overhead stream in separator overhead line 22 is sufficiently pure hydrogen from a separation stage. The net gas overhead stream can have a hydrogen purity of at least 94 mol%, suitably at least 95 mol%, preferably at least 96 mol%, and most preferably at least 96.5 mol% molecular hydrogen. Hydrogen recirculation line 25 can recirculate a portion of the net gas from separator overhead line 22 to the reactor feed stream in line 6 via a control valve thereon to provide the hydrogen required for the reaction. The net gas overhead stream can be directed to the cryogenic heat exchanger 16 to be heated by passing it through separator overhead passage 23, providing a product hydrogen stream that can be used elsewhere in the refinery or plant. Separator overhead passage 23 can maintain direct downstream communication with separator overhead line 22 of the single-stage separator 20. The heated exhaust gas stream can be supplied at temperatures ranging from 32°C (90℉) to 60°C (140℉) and gauge pressures ranging from 760 kPa (110 psig) to 1.2 MPa (170 psig).

[0034] The separator bottom stream is rich in hydrocarbons that can be refined for valuable products. The separator bottom stream in separator bottom line 24 can be pumped and expanded on expander 26 to evaporate the hydrocarbons and conveyed through cryogenic heat exchanger 16. The evaporated hydrocarbons are cooled by releasing the heat of evaporation, thus contributing to the cooling of the reactor effluent stream conveyed through cryogenic heat exchanger 7 from line 6. The separator bottom stream is heated by conveying it through deethanizer feed passage 27 in cryogenic heat exchanger 16 to provide deethanizer feed stream in deethanizer feed line 28.

[0035] The deethanizer feed stream in line 28 contains ethane and propane that must be separated from each other. Therefore, the deethanizer feed stream in line 28, with temperatures between -31°C (-25°F) and -3°C (25°F), is fed to deethanizer 30 for fractionation. An optional polypropylene plant recycle stream containing light fractions can be added to the deethanizer feed stream in line 28. Deethanizer 30 separates the deethanizer feed stream in deethanizer feed line 28 into an ethane-rich deethanizer overhead stream in deethanizer overhead line 32 extending from the top of the deethanizer, and a propane-rich deethanizer bottom stream in deethanizer bottom line 34 extending from the bottom of the deethanizer. The deethanizer overhead feed in line 32 is conveyed to the cryogenic heat exchanger 16 and then through the deethanizer overhead passage 33 in the cryogenic heat exchanger for cooling, thereby further condensing C3+ hydrocarbons and providing a cooled deethanizer overhead feed in the cooled deethanizer overhead line 35. The deethanizer overhead passage 33 can remain downstream connected to the deethanizer overhead line 32 of the deethanizer 30.

[0036] The cooled deethanizer overhead feed in line 35 is returned to deethanizer receiver 36. Deethanizer receiver 36 is a separator that separates the gas from the condensate. Deethanizer receiver 36 can maintain downstream communication with deethanizer overhead passage 33 in cryogenic heat exchanger 16. Deethanizer receiver operates at temperatures from -32°C (-25°F) to -60°C (-75°F) and gauge pressures from 690 kPa (100 psig) to 1.1 MPa (160 psig). The deethanized tail gas feed in deethanizer receiver overhead line 38, extending from the top of deethanizer receiver 36, carries the C2-rich tail gas feed to cryogenic heat exchanger 16. The tail gas feed in line 38 is heated by heat exchange in tail gas passage 39 passing through cryogenic heat exchanger 16 to provide a heated tail gas feed. The heated exhaust gas stream can be supplied at temperatures ranging from -32°C (90°F) to 60°C (140°F) and gauge pressures ranging from 690 kPa (100 psig) to 1.1 MPa (160 psig).

[0037] The C3+ hydrocarbon-rich bottom feed stream in the deethanizer bottom line 34 can extend from the bottom of the deethanizer and be split into two or three streams. The net deethanizer bottom feed stream can be taken from the bottom feed stream in line 34 and used as feed to the splitter in the net deethanizer bottom line 40. The splitter feed stream containing propylene and propane can be conveyed in the net deethanizer bottom line 40 to the propylene-propane splitter 50. The propylene-propane splitter 50 can remain downstream connected to the deethanizer bottom line 34. The bottom feed stream of the first reboiler deethanizer can be extracted from the bottom feed stream of the deethanizer in line 34 through the first reboiler deethanizer bottom line 42 and conveyed through the first side of the first deethanizer reboiler heat exchanger 44, boiled by heat exchange with the hot refrigerant on the second side of the first deethanizer reboiler heat exchanger, and returned to the lower end of the deethanizer 30. The first side of the first deethanizer reboiler heat exchanger 44 may be kept in downstream communication with the bottom line 34 of the deethanizer. The second side of the first deethanizer reboiler heat exchanger may be kept in downstream communication with the refrigerant separator top line 102 and / or the first refrigerant compressor 66 and possibly the second compressor 68 and / or the second refrigerant passage 63 through the cryogenic heat exchanger 16, all of which will be described below.

[0038] In one embodiment, the bottom feed stream of the second reboiler deethanizer can be taken from the bottom feed stream of the deethanizer in line 34 in the second reboiler bottom line 46 and conveyed through the first side of the second deethanizer reboiler heat exchanger 48, boiled by heat exchange with the second compressed diverter overhead stream in the second diverter overhead line 58 (described below) in the second side of the second deethanizer reboiler heat exchanger, and returned to the lower end of the deethanizer 30. The first side of the second deethanizer reboiler exchanger 48 may be in downstream communication with the bottom line 34 of the deethanizer, and the second side of the deethanizer reboiler exchanger may be in downstream communication with the diverter compressor 53. The bottom of the deethaner can be operated at a temperature of 16°C (50℉) to 43°C (120℉) and a gauge pressure not exceeding 1.7 MPa (250 psig), preferably between 690 kPa (100 psig) and 1.4 MPa (200 psig).

[0039] A refrigerant stream supplied from the second side of the first deethaner reboiler heat exchanger 44 in refrigerant line 70 can be mixed with a liquid refrigerant stream in line 72 and cooled in cryogenic heat exchanger 16. Cryogenic heat exchanger 16 operates with a refrigerant stream, which may include a mixed refrigerant stream containing nitrogen and some or all of C1 to C5 hydrocarbons. The refrigerant stream is conveyed by the combined refrigerant line 60 through a first refrigerant passage 61 in cryogenic heat exchanger 16. In line 60 prior to the first refrigerant passage, the refrigerant can be at a temperature of 16°C (60℉) to 43°C (110℉) and a gauge pressure of 3.3 MPa (485 psig) to 3.9 MPa (565 psig). In the first refrigerant passage 61, the refrigerant stream is cooled by heat exchange with other streams in cryogenic heat exchanger 16 and exits the cryogenic heat exchanger. The first refrigerant passage 61 of the combined refrigerant line 60 in the cryogenic heat exchanger 16 can maintain downstream communication with the second side of the first deethaner reboiler 44. The cooled refrigerant stream expands and evaporates in the refrigerant expander 62, thereby cooling it to provide a cold refrigerant stream with a temperature of -67°C (-90℉) to -101°C (-150℉) and a gauge pressure of 310 kPa (45 psig) to 1 MPa (140 psig). The cold refrigerant stream is passed through the second refrigerant passage 63 in the cryogenic heat exchanger 16 to cool all other streams passing through the cryogenic heat exchanger while simultaneously heating the cold refrigerant stream. The second refrigerant passage 63 of the combined refrigerant line 60 in the cryogenic heat exchanger 16 can maintain downstream communication with the refrigerant expander 62. The heated refrigerant stream can be at a temperature of 10°C (50℉) to 54°C (130℉) and a gauge pressure of 276 kPa (40 psig) to 931 kPa (135 psig) when it leaves the cryogenic heat exchanger after the second refrigerant passage 63 in the heated refrigerant line 64.

[0040] The heated refrigerant stream exiting the cryogenic heat exchanger 16 from the second refrigerant passage 63 in line 64 is at low pressure and is in vapor form. Therefore, it is compressed to increase its pressure. The heated refrigerant stream in line 64 can be compressed by the first refrigerant compressor 66 and possibly by the second refrigerant compressor 68 to provide a compressed refrigerant stream in the compressed refrigerant line 74. An air cooler 67 can be installed to cool the compressed refrigerant between the first refrigerant compressor 66 and the second refrigerant compressor 68. A slap can (not shown) can be installed upstream of each compressor to remove liquid from the compressor inlet. The compressed refrigerant stream in line 74 can be at a temperature of 107°C (225℉) to 152°C (275℉) and a gauge pressure of 4.5 MPa (650 psig) to 5.2 MPa (750 psig).

[0041] To cool the compressed refrigerant stream in line 74, it can be heat-exchanged with the depropanizer side stream in line 76 at the upper depropanizer reboiler heat exchanger 78 to provide a cooled compressed refrigerant stream in the cooled compressed refrigerant line 80 and a heated depropanizer side stream in the depropanizer return line 82. The upper depropanizer reboiler heat exchanger 78 has a first side communicating with the depropanizer side stream 76 from the depropanizer 90 and a second side communicating with the compressed refrigerant line 74. The second side of the upper depropanizer reboiler heat exchanger is downstream of the first refrigerant compressor 66 and / or the second refrigerant compressor 68. A valved bypass is provided on the compressed refrigerant line 74 leading to the cooled compressed refrigerant line 80 to regulate the heating amount at the upper depropanizer reboiler heat exchanger 78.

[0042] The cooled compressed refrigerant stream in the cooled compressed refrigerant line 80 can be further cooled in an air cooler and conveyed to the refrigerant separator 100 to separate it into a vapor refrigerant stream in the top refrigerant line 102 extending from the top of the refrigerant separator and a liquid refrigerant stream in the bottom refrigerant line 104 extending from the bottom of the refrigerant separator. The refrigerant separator 100 can maintain downstream communication with the second side of the upper reboiler heat exchanger 78 of the depropanizer. The vapor refrigerant stream in the top refrigerant line 102 can be further cooled by conveying it through the second side of the first deethaner reboiler heat exchanger 44 to exchange heat with the first reboiler bottom deethaner stream in line 42 conveyed through the first side of the first deethaner reboiler heat exchanger 44. The second side of the first deethaner reboiler heat exchanger 44 can maintain downstream communication with the top refrigerant line 102 of the refrigerant separator. The condensed refrigerant stream is returned from the first deethanizer reboiler 44 in the condensed refrigerant line 70 to reassemble the combined refrigerant stream in the combined refrigerant line 60 to restart the cycle. A valved bypass is provided on the top refrigerant line 102 to regulate the amount of heat exchange in the first deethanizer reboiler heat exchanger 44. Before exchanging heat with the bottom deethanizer stream in line 42 in the first deethanizer reboiler 44, the refrigerant stream is compressed in compressor 66 and possibly 68 to provide sufficient heat for reboiling.

[0043] The liquid refrigerant stream in the bottom refrigerant line 104 also possesses heat that can be recovered. The liquid refrigerant stream in line 104 can exchange heat with the combined net split column bottom stream to heat the combined net split column bottom stream in the combined net split column bottom line 124 in the selective hydrogenation feed exchanger 108. A first side of the selective hydrogenation feed exchanger 108 can maintain downstream communication with the net split column bottom line 106, and a second side can maintain downstream communication with the refrigerant separator bottom line 104. A valved bypass is provided on the bottom refrigerant line 104 to regulate the amount of heat exchange in the selective hydrogenation feed exchanger 108. The cooled liquid refrigerant stream in liquid refrigerant line 72 is returned from the selective hydrogenation feed exchanger 108 to allow the combined refrigerant stream in line 60 and the condensed refrigerant stream in line 70 to recombine and restart the refrigeration cycle. After heat exchange with the bottom stream of the first deethane reboiler in the first deethane reboiler heat exchanger 44, the refrigerant stream in the combined refrigerant line 60 is cooled in the low-temperature heat exchanger 16.

[0044] The splitter feed stream in line 40 contains propane and propylene, which must be separated to obtain the propylene product and the propane recycled to reactor 4. The propylene-propane splitter 50 fractionates the splitter feed stream into a propylene-rich splitter overhead stream in splitter overhead line 52 extending from the top of the splitter and a propane-rich splitter bottom stream in splitter bottom line 54 extending from the bottom of the splitter. The splitter overhead stream is compressed in a splitter compressor 53, which condenses the splitter overhead stream and provides the compressed splitter overhead stream in a compression splitter line 55. The splitter compressor 53 may remain downstream of the splitter overhead line 52. The compressed splitter overhead stream in line 55 may be further cooled by a cooling water heat exchanger. The compressed diverter overhead feed in line 55 can exhibit temperatures from 48°C (80℉) to 71°C (160℉) and gauge pressures from 1.2 MPa (175 psig) to 1.9 MPa (275 psig). After heat exchange, the temperature of the compressed diverter overhead feed can decrease by 3°C (5℉) to 6°C (10℉).

[0045] The first compressed top feed stream in the first compressed top feed line 56 is taken out from the compressed top feed stream in line 55. The second compressed top feed stream in the second compressed top feed line 58 is taken out from the compressed top feed stream in line 55. The second deethanizer bottom feed stream in the second deethanizer bottom line 46 is reboiled by exchanging heat with the second compressed top feed stream in line 58 in the second deethanizer reboiling heat exchanger 48. The first side of the second deethanizer reboiling heat exchanger 48 can be kept in downstream communication with the deethanizer bottom line 34, and the second side of the second deethanizer reboiling heat exchanger 48 can be kept in downstream communication with the top feed compressor 53. The heat exchange in the second deethanizer reboiling heat exchanger 48 is used to cool the second compressed top feed stream in line 58. The propylene product stream in pipeline 59 can be taken out from the cooled top stream of the second compression diverter, and the top stream of the second reflux diverter in the second reflux diverter pipeline 110 can be returned to the propylene diverter 50 as a second reflux stream under compression pressure.

[0046] The bottom feed stream of the reboiler diverter is taken out from the bottom feed stream of the diverter in the bottom line 54 of the diverter in the bottom line 112 of the reboiler diverter, and reboiled by exchanging heat with the top feed stream of the first compressed diverter in the bottom line 56 of the first compressed diverter in the diverter reboiler heat exchanger 114. The diverter reboiler heat exchanger 114 has a first side that is connected downstream to the diverter bottom line 54 and a second side that is connected downstream to the diverter compressor 53. The top feed stream of the first compressed diverter in the bottom line 56, cooled by heat exchange with the bottom feed stream of the reboiler in the line 112 in the diverter reboiler heat exchanger 114, is returned to the diverter 50 as a first return stream under compression pressure. The bottom flow of the diversion tower in line 54 can exhibit temperatures from 21°C (70℉) to 32°C (90℉) and gauge pressures from 62 kPa (---90 psig) to 1034 kPa (150 psig).

[0047] The net split column bottoms stream is taken from the split column bottoms stream in the net split column bottoms line 106. This net split column bottoms stream is rich in propane and can be recycled to reactor 4. However, dienes and acetylene can damage the dehydrogenation catalyst and should be converted to monoolefins in the selective hydrogenation reactor 120. Therefore, hydrogen from the hydrogen stream 122 is added to the net split column bottoms stream to provide a combined net split column bottoms stream in line 124 (which is heated in the selective hydrogenation feed heat exchanger 108). The combined net split column bottoms stream in the combined net split column bottoms line 124 can exchange heat with the liquid refrigerant stream in the bottom refrigerant line 104 in the selective hydrogenation feed heat exchanger 108 and is then fed into the selective hydrogenation reactor 120.

[0048] In selective hydrogenation reactor 120, the combined net split column bottom stream is selectively hydrogenated in the presence of hydrogen and a selective hydrogenation catalyst. Selective hydrogenation reactor 120 is typically operated under relatively mild hydrogenation conditions. These conditions typically result in the hydrocarbons being present as liquid-phase material, and therefore the reactants are typically held at a minimum pressure sufficient to maintain them as liquid-phase hydrocarbons. Therefore, a wide range of suitable operating gauge pressures extends from 276 kPa (40 psig) to 5516 kPa (800 psig), or from 345 kPa (50 psig) to 2069 kPa (300 psig). Relatively moderate temperatures are typically employed between 25°C (77°F) and 350°C (662°F), or between 50°C (122°F) and 200°C (392°F). The liquid hourly space velocity (LHSV) of the reactants through the selective hydrogenation catalyst should be greater than 1.0 hr. -1 and 35.0hr -1To avoid unwanted saturation of a significant amount of monoolefin, the molar ratio of hydrogen to diene in the combined net split column bottom stream entering the selective hydrogenation catalyst bed is maintained between 0.75:1 and 1.8:1. Any suitable catalyst capable of selectively hydrogenating dienes can be used. Suitable catalysts include, but are not limited to, catalysts containing copper and at least one other metal (such as titanium, vanadium, chromium, manganese, cobalt, nickel, zinc, molybdenum, and cadmium) or mixtures thereof. For example, the metal is preferably supported on an inorganic oxide support (such as silica and alumina).

[0049] The net splitter bottom stream containing propane, selected for hydrogenation, is fed in hydrogenation effluent line 126 (possibly after gas separation) and added to the fresh propane feed stream in line 128, and both are fed into depropanizer 90. Depropanizer 90 may remain downstream connected to splitter bottom line 54. Depropanizer 90 separates the net splitter bottom stream from the selectively hydrogenated propane stream and the fresh propane feed stream to provide a propane-rich depropanizer overhead stream in overhead line 92 extending from the top of the depropanizer, and a C4+ hydrocarbon-rich depropanizer bottom stream in bottom line 94 extending from the bottom of the depropanizer.

[0050] The propane stripper overhead feed in stripper overhead line 92 is cooled and can be completely condensed and fed to stripper receiver 93. The receiver bottom feed exits the bottom of the stripper receiver in stripper receiver bottom line 95. The stripper reflux feed taken from stripper receiver bottom line 95 refluxes the condensed propane back to stripper 90. Stripper receiver 93 operates at temperatures from 20°C (68℉) to 70°C (158℉) and gauge pressures from 1.4 MPa (200 psig) to 1.8 MPa (261 psig).

[0051] The clean propane stripper overhead feed in the clean propane stripper overhead line 96 is expanded on the propane stripper overhead expander 86 to evaporate and cool it, supplemented by hydrogen from the hydrogen recirculation line 25, and further cooled in the reactor feed passage 88 in the cryogenic heat exchanger 16 to provide the reactor feed feed in the reactor feed line 2. The molar ratio of hydrogen to hydrocarbons in the reactor feed feed is controlled within the range of 0.005 to 0.6 by a control valve on the hydrogen recirculation line 25.

[0052] The reactor feed flow in reactor feed line 2, exiting reactor feed passage 88, can be provided at temperatures from 32°C (90°F) to 60°C (140°F) and at gauge pressures from 69 kPa (10 psig) to 0.5 MPa (80 psig).

[0053] The depropanizer side stream taken from depropanizer 90 in depropanizer side line 76 can be reboiled in the upper reboiler heat exchanger 78 of depropanizer by heat exchange with the compressed refrigerant stream in line 74 to provide a cooled compressed refrigerant stream in line 80 and a heated depropanizer side stream (which returns to depropanizer 90 as a vapor stream through its side) in line 82. The depropanizer side stream taken from line 76 is suitably the liquid stream taken from the liquid trap in depropanizer 90.

[0054] The depropanizer bottom stream in depropanizer bottom line 94 is rich in C4+ hydrocarbons. The depropanizer reboiler stream taken from the depropanizer bottom stream in line 94 in line 97 can be heated in the depropanizer reboiler heat exchanger 99 and returned to the bottom of depropanizer 90. The net depropanizer bottom stream containing C4+ hydrocarbons can be taken out as product in net depropanizer bottom line 98. Depropanizer bottom 93 operates at temperatures from 80°C (176℉) to 130°C (195℉) and gauge pressures from 1.5 MPa (217 psig) to 2 MPa (290 psig).

[0055] The method and apparatus enable the use of a single-stage separator 20 and a single deethaner 30 to obtain high-purity hydrogen in the net gas stream in line 23 and high-purity ethane in the tail gas stream in line 38, whereas conventionally, a two-stage separator and two deethaner 30 are required to achieve equivalent purity.

[0056] Specific implementation plan

[0057] While the following description is presented in conjunction with specific embodiments, it should be understood that the description is intended to illustrate, and not limit, the scope of the foregoing description and the appended claims.

[0058] A first embodiment of this disclosure is a method for separating propane from ethane, the method comprising: feeding a deethanizer feed stream containing ethane and propane into a deethanizer to provide an ethane-rich deethanizer overhead stream and a propane-rich deethanizer bottom stream; and reboiling the deethanizer bottom stream by heat exchange with a refrigerant stream. An embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment to the foregoing embodiments of this paragraph, further includes cooling the deethanizer overhead stream by heat exchange in a cryogenic heat exchanger to provide a cooled deethanizer overhead stream. An embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment to the foregoing embodiments of this paragraph, further includes cooling a reactor effluent stream in the cryogenic heat exchanger to provide a cooled reactor effluent stream. One embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes separating the cooled reactor effluent stream in a single-stage separator to provide a net gas overhead stream, and heating the net gas overhead stream in the cryogenic heat exchanger. Another embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes compressing the refrigerant stream before heat exchange with the deethanizer bottom stream. A third embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes cooling the refrigerant stream in the cryogenic heat exchanger after heat exchange with the deethanizer bottom stream, expanding the cooled refrigerant stream to provide a cold refrigerant stream, and heating the cold refrigerant stream in the cryogenic heat exchanger. One embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes separating the cooled deethanizer overhead stream in a deethanizer receiver to provide a tail gas stream, and heating the tail gas stream in the cryogenic heat exchanger. One embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes heating a propane-containing feed stream in the cryogenic heat exchanger and charging the propane stream into a dehydrogenation reactor. One embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes reboiling a portion of the deethanizer bottom stream and feeding the net deethanizer bottom stream to further fractionation. One embodiment of this disclosure, which is one, any, or all of the embodiments described in the first embodiment of this paragraph to the preceding embodiments of this paragraph, further includes operating the deethanizer at a top pressure not exceeding 250 psig.

[0059] A second embodiment of this disclosure is an apparatus for separating propane from ethane, comprising: a deethanizer having a top deethanizer line exiting the top of the deethanizer and a bottom deethanizer line exiting the bottom of the deethanizer; a reboiling line in communication with the bottom deethanizer line; a compressor for compressing a refrigerant feed stream; and a reboiling heat exchanger having a first side in communication with the bottom deethanizer line and a second side in communication with the compressor. One embodiment of this disclosure, which is one, any, or all of the second embodiment to the preceding embodiments of this paragraph, further includes a refrigerant expander in communication with the second side of the reboiling heat exchanger for cooling the refrigerant. Another embodiment of this disclosure, which is one, any, or all of the second embodiment to the preceding embodiments of this paragraph, further includes a cryogenic exchanger and a passage of a refrigerant line in the cryogenic exchanger in downstream communication with the refrigerant expander. One embodiment of this disclosure is one, any, or all of the embodiments described in the second embodiment of this paragraph to the preceding embodiments of this paragraph, wherein the passage of the refrigerant line in the cryogenic exchanger that maintains downstream communication with the refrigerant expander is a second passage of the refrigerant line, and the embodiment further includes a first passage of the refrigerant line in the cryogenic exchanger that maintains downstream communication with the second side of the reboiler. One embodiment of this disclosure is one, any, or all of the embodiments described in the second embodiment of this paragraph to the preceding embodiments of this paragraph, and further includes an effluent passage for reactor effluent in the cryogenic exchanger and a single-stage separator that maintains downstream communication with the effluent passage. One embodiment of this disclosure is one, any, or all of the embodiments described in the second embodiment of this paragraph to the preceding embodiments of this paragraph, and further includes a separator top passage in the cryogenic exchanger, and the separator top passage maintains direct downstream communication with the top line of the single-stage separator. One embodiment of this disclosure is one, any, or all of the embodiments described in the second embodiment to the foregoing embodiments of this paragraph, and further includes a deethanizer top passage in the cryogenic exchanger, the deethanizer top passage being in downstream communication with the top pipeline of the deethanizer. Another embodiment of this disclosure is one, any, or all of the embodiments described in the second embodiment to the foregoing embodiments of this paragraph, and further includes a deethanizer receiver being in downstream communication with the deethanizer top passage.

[0060] A third embodiment of this disclosure is an apparatus for separating propane from ethane, the apparatus comprising: a deethanizer having a deethanizer top line exiting the top of the deethanizer and a deethanizer bottom line exiting the bottom of the deethanizer; a cryogenic heat exchanger having a refrigerant passage in downstream communication with an expander; and a deethanizer top passage in the cryogenic heat exchanger, the deethanizer top passage being in downstream communication with the deethanizer top line. One embodiment of this disclosure is one, any one, or all of the embodiments described in the third to the preceding embodiments of this paragraph, further comprising a reboiling heat exchanger having a first side in communication with the deethanizer bottom line and a second side in communication with the refrigerant passage in the cryogenic heat exchanger.

[0061] A fourth embodiment of this disclosure is a method for separating hydrogen from ethane, the method comprising: cooling a reactor effluent stream containing hydrogen and ethane in a cryogenic heat exchanger to provide a cooled reactor effluent stream; and separating the cooled reactor effluent stream in a single-stage separator to provide a net gas overhead stream containing at least 94 mol% hydrogen and an ethane-rich bottom stream.

[0062] Although no further detailed description has been provided, it is believed that those skilled in the art will be able to make full use of the invention by employing the foregoing description and will be able to readily identify the essential features of the invention without departing from its spirit and scope, and to make various changes and modifications to adapt it to various uses and situations. Therefore, the foregoing preferred embodiments should be understood as illustrative only and not as limiting the remainder of this disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0063] In the foregoing, all temperatures are expressed in degrees Celsius, and all portions and percentages are by weight unless otherwise specified.

Claims

1. A method for separating propane from ethane, comprising: The feed stream from the deethanizer, which contains ethane and propane, is fed to the deethanizer to provide an ethane-rich overhead stream and a propane-rich bottom stream. The bottom stream of the deethaner column is reboiled by heat exchange with the refrigerant stream; The overhead feed stream of the deethanizer is cooled by heat exchange in a cryogenic heat exchanger to provide a cooled overhead feed stream for the deethanizer; The reactor outflow is cooled in the cryogenic heat exchanger to provide a cooled reactor outflow. The cooled reactor effluent stream is separated in a single-stage separator to provide a clean gas column overhead stream, and the clean gas column overhead stream is heated in the cryogenic heat exchanger. After heat exchange with the bottom stream of the deethaner, the refrigerant stream is cooled in the cryogenic heat exchanger, the cooled refrigerant stream is expanded to provide a cold refrigerant stream, and the cold refrigerant stream is heated in the cryogenic heat exchanger.

2. The method of claim 1, further comprising compressing the refrigerant stream before heat exchange with the bottom stream of the deethaner.

3. The method of claim 1, further comprising separating the cooled deethaner overhead stream in a deethaner receiver to provide a tail gas stream, and heating the tail gas stream in the cryogenic heat exchanger.

4. The method according to claim 3 further comprises heating the propane-containing feed stream in the cryogenic heat exchanger and loading the propane stream into the dehydrogenation reactor.

5. An apparatus for separating propane from ethane, comprising: An ethane stripper having a top line exiting the top of the ethane stripper and a bottom line exiting the bottom of the ethane stripper; A reboiler line that remains connected to the bottom line of the deethanizer; A compressor used to compress the refrigerant flow; A reboiling heat exchanger having a first side connected to the bottom line of the deethanizer and a second side connected to the compressor; A refrigerant expander that remains in communication with the second side of the reboiling heat exchanger for cooling the refrigerant; The passageway for the cryogenic exchanger and the refrigerant line in the cryogenic exchanger that maintains downstream communication with the refrigerant expander; as well as The reactor effluent passage in the cryogenic exchanger and a single-stage separator that maintains downstream communication with the effluent passage.

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