Ethane separation with cryogenic heat exchanger

Abstract

The process and apparatus integrate the decarbonizer column with a cryogenic heat exchanger by reboiling the decarbonizer column with a refrigerant stream and / or cooling the decarbonizer overhead line in the cryogenic heat exchanger. While a single-stage separator and a single decarbonizer column can be used to obtain high-purity hydrogen and an ethane-rich off-gas stream from a pure gas stream, conventionally, a double-stage separator and two decarbonizer columns were each required for equivalent purity.

Description

Technology Field

[0001] Priority statement

[0002] This application claims priority from U.S. Provisional Application No. 63 / 169,415 filed April 1, 2021, which is incorporated herein in its entirety.

[0003] Technology field

[0004] The present technical field relates to the separation of hydrogen and light hydrocarbons at cryogenic temperatures. More specifically, the present technical field relates to the recovery of propylene from light hydrocarbons. Background Technology

[0005] The dehydrogenation of hydrocarbons is an important commercial hydrocarbon conversion process due to the existing and increasing demand for dehydrogenated hydrocarbons for the manufacture of various chemical products, such as detergents, high-octane gasoline, oxygenated gasoline blending components, pharmaceutical products, plastics, synthetic rubber, and other products well known to those skilled in the art. In particular, the demand for propylene in the petrochemical industry has increased significantly due to its use as a precursor in the manufacture of polypropylene for packaging materials and other commercial products. Other downstream uses of propylene include the production of acrylonitrile, acrylic acid, acrolein, propylene oxide and glycol, plasticizers, oxo alcohols, cumene, isopropyl alcohol, and acetone. One route for producing propylene is the dehydrogenation of propane.

[0006] The process of converting paraffin to olefin involves passing a paraffin feed stream through a highly selective catalyst, whereby the paraffin is dehydrogenated into the corresponding olefin, producing a dehydrogenation reactor effluent. The step of cooling and separating the dehydrogenation reactor effluent into a hydrocarbon-rich fraction and a hydrogen-rich vapor fraction (of which some are non-recycled net gases) is provided to a cryogenic separation system requiring refrigeration to cool the process stream in order to separate hydrogen from light hydrocarbon liquids. Conventional cryogenic separation systems remove hydrogen from light hydrocarbons by cooling the process stream alone. However, additional fractionation is required to separate C2- materials from C3 hydrocarbons in the dehydrogenation effluent of a dehydrogenator column, which typically requires a refrigeration package.

[0007] Improvements to the cryogenic separation system are necessary to make propylene production and purification more economical.

[0008] The inventors have discovered an improved process and apparatus for integrating a decarbonizer column with a cryogenic heat exchanger by reboiling the decarbonizer column with a refrigerant stream and / or cooling the decarbonizer overhead line in a cryogenic heat exchanger.

[0009] These and other features, aspects, and advantages of the present invention are further explained by the following detailed description, drawings, and appended claims. Brief explanation of the drawing

[0010] The drawing is a schematic diagram of the process and apparatus of the present invention. definition The following detailed description is merely illustrative and is not intended to limit the application and use of the described embodiments. Furthermore, it is not bound by any theory presented in the preceding background art or the following detailed description. The term "communication" means that the flow of matter between the listed components is operationally permitted. The term "downstream connection" means that at least a portion of the material flowing to the subject of the downstream connection can flow operablely from the object to which the subject communicates. The term "upstream connection" means that at least a portion of the material flowing from the subject of the upstream connection can flow operablely to the object to which the subject communicates. The term "direct connection" means that flow from an upstream component enters a downstream component without undergoing a change in composition due to physical separation or chemical conversion. The term "bypass" means that an object moves out of downstream communication with the bypassing entity, at least to the extent of bypassing. As used herein, the term “separator” means a vessel having an inlet and at least an overhead vapor outlet and a bottom liquid outlet, and may also have an aqueous stream outlet from a boot. A flash drum is a type of separator that can be downstream connected to a separator capable of operating at a higher pressure. As used herein, the term “predominant” or “dominant” means more than 50%, suitably more than 75%, preferably more than 90%. Term "C x " should be understood to refer to a molecule having the number of carbon atoms indicated by the subscript "x". Similarly, the term "C x -" refers to a molecule containing carbon atoms less than or equal to x, preferably x or fewer. The term "C x +" refers to a molecule having more than or equal to x carbon atoms, preferably x or more. The term “column” means a distillation column or columns for separating one or more components of different volatility. Unless otherwise indicated, each column comprises a condenser at the overhead of the column for condensing a portion of the overhead stream and recirculating it back to the top of the column, and a reboiling unit at the bottom of the column for vaporizing a portion of the bottom stream and sending it back to the bottom of the column. The feed to the column may be preheated. The top pressure is the pressure of the overhead vapor at the outlet of the column. The bottom temperature is the temperature at the liquid bottom outlet. Unless otherwise indicated, the overhead line and bottom line refer to the net line from the column downstream of the recirculation or reboiling to the column. Alternatively, a stripping stream may be used for heat input near the bottom of the column. As used herein, the term "component-rich stream" means that the component concentration of the rich stream coming out of the container is higher than that of the feed into the container. As used herein, the term “dilute stream” means that the dilute stream exiting the container has a lower concentration of components than the feed into the container. Specific details for implementing the invention

[0011] The present invention relates to a process and apparatus that integrates the separation of hydrogen, C2- hydrocarbons, and C3+ hydrocarbons into a single system having a single refrigeration package. A single refrigerant system is used to facilitate cooling and condensation over a wide temperature range. The process and apparatus utilize a cryogenic heat exchanger incorporating a decarbonizer column, thereby eliminating the use of steam for reboiling in the cryogenic heat exchanger and substantially reducing fractionation costs by utilizing a refrigeration system. The process and apparatus enable the use of a single decarbonizer column instead of two conventional decarbonizer columns, which reduces capital costs and operational complexity. The process and apparatus enable reduced compressor stages, number of equipment, and utility usage.

[0012] The process and apparatus include the step of passing a reactor feed stream containing hydrocarbons and hydrogen from a reactor feed line (2) through a dehydrogenation reactor (4) to provide a dehydrogenation reactor effluent stream to an effluent line (6). The reactor feed stream of line (2) may be preheated in a high-temperature combination feed exchanger (5) before passing through the dehydrogenation reactor (4).

[0013] The reactor feed stream comprises propane. In some embodiments, the reactor feed stream comprises other light paraffins such as ethane, butane, normal butane, isobutane, pentane, or iso-pentane. In some embodiments, the reactor feed stream comprises at least one paraffin having 2 to 30 carbon atoms. The hydrogen-to-hydrocarbon molar ratio of the feed stream is in the range of 0.005 to 0.6.

[0014] The preheated reactor feed stream comes into contact with a dehydrogenation catalyst in a dehydrogenation reactor (4) maintained under dehydrogenation conditions to produce a dehydrogenation reactor effluent stream containing hydrogen, unconverted paraffin, and olefin in the effluent line (6). The dehydrogenation reactor (4) may be a reaction zone containing multiple stages or multiple reactors often in series.

[0015] The dehydrogenation catalyst may be a highly selective platinum-based catalyst system. An example of a catalyst suitable for a light paraffin dehydrogenation process may be a catalyst composite comprising a Group VIII noble metal component, a Group IA or IIA metal component, and a component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof (all of which are on an alumina support).

[0016] The dehydrogenation conditions are a temperature of 400°C to 900°C, a pressure of 0.01 to 10 atmospheres (absolute pressure), and 0.1 to 100 hr- 1 It includes the liquid space velocity per hour (LHSV). Generally, for normal paraffin, the lower the molecular weight, the higher the temperature required for comparable conversion. The pressure in the dehydrogenation reactor (4) is kept as low as feasible in accordance with equipment limits to maximize chemical equilibrium benefits. Dehydrogenation reactions are typically endothermic.

[0017] The reactor feed stream of the reactor feed line (2) can be heat exchanged with the reactor effluent stream of line (6) in the high-temperature combined feed exchanger (5). The dehydrogenation reactor effluent stream of line (6) is cooled by heat exchange with the reactor feed stream (2) in the high-temperature combined feed exchanger (5) and compressed in the reactor effluent compressor (11) to provide a compressed reactor effluent stream. The compressed reactor effluent stream of the reactor effluent line (6) is passed to the cryogenic separation system (10) to provide an olefin stream and a hydrogen stream.

[0018] The reactor effluent stream may contain light hydrocarbons and hydrogen. In paraffin dehydrogenation, the desired product is often propylene, which must be separated from other light hydrocarbons such as propane and hydrogen. Propane can be recycled in the dehydrogenation reactor (4) for the production of propylene. Hydrogen is a valuable byproduct and can be used elsewhere in the refinery, such as as fuel for combustion heaters in the dihydrogenation process. Some hydrogen can be recycled back into the reactor (4) to control the dehydrogenation reaction.

[0019] To effectively separate hydrogen from light hydrocarbons, the reactor effluent stream is cooled by passing through a cryogenic heat exchanger (16) to condense the hydrocarbons. In the cryogenic heat exchanger (16), the reactor effluent stream of line (6) is routed through an effluent passage (7), which is cooled by heat exchange with another stream passing through the cryogenic heat exchanger to provide a cooled reactor effluent stream to line (8).

[0020] The single-stage separator (20) is in downstream communication with the effluent passage (7). The cooled reactor effluent stream of line (8) is separated in the single-stage separator (20) to provide a hydrogen-rich pure gas overhead stream of the separator overhead line (22) extending from the overhead of the single-stage separator and a hydrocarbon-rich separator bottom stream of the separator bottom line (24) extending from the bottom of the single-stage separator. The single-stage separator (20) can operate at temperatures of -150°C (-101°F) to 66°C (150°F), more generally -95°C (-138°F) to -40°C (-40°F) and gauge pressures of 690 kPa (100 psig) to 1.4 MPa (200 psig).

[0021] The pure gas overhead stream of the separator overhead line (22) is sufficiently pure hydrogen from a single separation stage by thorough condensation of hydrocarbons in a single-stage separator (20). The pure gas overhead stream may 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. The hydrogen recycling line (25) may provide the hydrogen requirements for the reaction by recycling a portion of the pure gas of the separator overhead line (22) through a control valve into the reactor feed stream of line (6). The pure gas overhead stream may be routed to a cryogenic heat exchanger (16) to be heated by passing through the separator overhead passage (23) and may provide a product hydrogen stream that can be used at a refinery or elsewhere in the plant. The separator overhead passage (23) may be in direct downstream communication with the separator overhead line (22) of the single-stage separator (20). The heated off-gas stream can be provided at a temperature of 32°C (90°F) to 60°C (140°F) and a gauge pressure of 760 kPa (110 psig) to 1.2 MPa (170 psig).

[0022] The separator bottom stream is rich in hydrocarbons that can be purified for high-value products. The separator bottom stream of the separator bottom line (24) is pumped and expanded over the expander (26) to vaporize the hydrocarbons and pass through the cryogenic exchanger (16). The vaporized hydrocarbons are cooled by providing heat of vaporization, thus helping to cool the reactor effluent stream passing through the cryogenic exchanger in the effluent passage (7) from line (6). The separator bottom stream is heated by passing through the decarbonizer feed passage (27) of the cryogenic heat exchanger (16) to provide a decarbonizer feed stream to the decarbonizer feed line (28).

[0023] The decarbonizer feed stream of line (28) contains ethane and propane, which must be separated from each other. Accordingly, at a temperature of -31°C (-25°F) to -3°C (25°F), the decarbonizer feed stream of line (28) is passed to a decarbonizer column (30) for fractionation. An optional polypropylene plant recycling stream of line (29) containing a hard end may be added to the decarbonizer feed stream of line (28). The decarbonizer column (30) separates the decarbonizer feed stream of decarbonizer feed line (28) into a decarbonizer overhead stream of a decarbonizer overhead line (32) extending from the overhead of an ethane-rich decarbonizer column and a decarbonizer bottom stream of a decarbonizer bottom line (34) extending from the bottom of a propane-rich decarbonizer column. The decarbonization overhead stream of line (32) is transferred to a cryogenic heat exchanger (16), passes through a decarbonization overhead passage (33) in the cryogenic heat exchanger to be cooled to further condense C3+ hydrocarbons, and provides a cooled decarbonization overhead stream in a cooled decarbonization overhead line (35). The decarbonization overhead passage (33) can be downstream connected to the decarbonization overhead line (32) of the decarbonization column (30).

[0024] The cooled decarbonizer overhead stream of line (35) is returned to the decarbonizer receiver (36). The decarbonizer receiver (36) is a separator that separates gas from the condensate. The decarbonizer receiver (36) may be in downstream communication with the decarbonizer overhead passage (33) in the cryogenic heat exchanger (16). The decarbonizer receiver operates at a temperature of -32°C (-25°F) to -60°C (-75°F) and a gauge pressure of 690 kPa (100 psig) to 1.1 MPa (160 psig). The decarbonizer off-gas stream of the decarbonizer receiver overhead line (38) extending from the overhead of the decarbonizer receiver (36) carries a C2- hydrocarbon-rich off-gas stream to the cryogenic heat exchanger (16). The off-gas stream of line (38) is heated by heat exchange in the off-gas passage (39) through the cryogenic heat exchanger (16) to provide a heated off-gas stream. The heated off-gas stream can be provided at a temperature of -32°C (90°F) to 60°C (140°F) and a gauge pressure of 690 kPa (100 psig) to 1.1 MPa (160 psig).

[0025] The decarbonization bottom stream of the decarbonizer bottom line (34), which is rich in C3+ hydrocarbons, can be extended from the bottom of the decarbonizer column and can be split into two or three streams. The net decarbonization bottom stream can be taken from the decarbonization bottom stream of line (34) to the splitter feed stream of the net decarbonizer bottom line (40). The splitter feed stream containing propylene and propane can be transferred from the net decarbonizer bottom line (40) to the propylene-propane splitter column (50). The propylene-propane splitter column (50) can be downstream connected to the decarbonizer bottom line (34). The first reboiling decarbonization bottom stream is taken from the first reboiling decarbonization bottom line (42) from the decarbonization bottom stream of line (34), passes through the first side of the first decarbonizer reboiling heat exchanger (44), boils by heat exchange with a high-temperature refrigerant on the second side of the first decarbonizer reboiling heat exchanger, and can be returned to the bottom of the decarbonizer column (30). The first side of the first decarbonizer reboiling heat exchanger (44) can be downstream connected to the decarbonizer bottom line (34). A second side of the first decarbonizer reboiling heat exchanger may be in downstream communication with a second refrigerant passage (63) passing through a refrigerant separator overhead line (102) and / or a first refrigerant compressor (66) and possibly a second compressor (68) and / or a cryogenic heat exchanger (16) (all of which will be described later).

[0026] In one embodiment, the second reboiling decarbonization bottom stream is taken from the second reboiling decarbonization bottom line (46) from the decarbonization bottom stream of line (34), passes through the first side of the second decarbonizer reboiling heat exchanger (48), boils by heat exchange with the second compression splitter overhead stream of the second splitter overhead line (58) to be described later at the second side of the second decarbonizer reboiling heat exchanger, and can be returned to the bottom of the decarbonizer column (30). The first side of the second decarbonizer reboiling exchanger (48) can be in downstream communication with the decarbonizer bottom line (34), and the second side of the decarbonizer reboiling exchanger can be in downstream communication with the splitter compressor (53). The bottom of the decarbonizer can be operated at a temperature of 16°C (50°F) to 43°C (120°F) and a gauge pressure of 1.7 MPa (250 psig) or less, preferably 690 kPa (100 psig) to 1.4 MPa (200 psig).

[0027] A refrigerant stream transferred from the second side of the first decarbonizer reboiling heat exchanger (44) to the refrigerant line (70) may be mixed with a liquid refrigerant stream in line (72) and cooled in the cryogenic heat exchanger (16). The cryogenic heat exchanger (16) operates with a mixed refrigerant stream containing nitrogen and a refrigerant stream that may contain some or all of C1 to C5 hydrocarbons. The refrigerant stream is passed through a combined refrigerant line (60) passing through the first refrigerant passage (61) of the cryogenic heat exchanger (16). In the line (60) prior to the first refrigerant passage, the refrigerant may be at a temperature of 16°C (60°F) to 43°C (110°F) 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 the cryogenic heat exchanger (16) and exits the cryogenic heat exchanger. The first refrigerant passage (61) of the combination refrigerant line (60) of the cryogenic heat exchanger (16) may be in downstream communication with the second side of the first decarbonizer reboiling exchanger (44). The cooled refrigerant stream is expanded and vaporized in a refrigerant expander (62) that cools it, providing a low-temperature refrigerant stream at a temperature of -67°C (-90°F) to -101°C (-150°F) and a gauge pressure of 310 kPa (45 psig) to 1 MPa (140 psig). The low-temperature refrigerant stream passes through the second refrigerant passage (63) in the cryogenic heat exchanger (16) to heat the low-temperature refrigerant stream while cooling all other streams passing through the cryogenic heat exchanger. The second refrigerant passage (63) of the combined refrigerant line (60) of the cryogenic heat exchanger (16) may be in downstream communication with the refrigerant expander (62). The heated refrigerant stream may be at a temperature of 10°C (50°F) to 54°C (130°F) and a gauge pressure of 276 kPa (40 psig) to 931 kPa (135 psig) when exiting the cryogenic heat exchanger after the second refrigerant passage (63) in the heated refrigerant line (64).

[0028] The heated refrigerant stream exiting the cryogenic heat exchanger (16) from the second refrigerant passage (63) to line (64) is at low pressure and in a vapor state. Therefore, it undergoes compression to boost 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 the compressed refrigerant stream in the compressed refrigerant line (74). An air cooler (67) may be installed to cool the compressed refrigerant between the first refrigerant compressor (66) and the second refrigerant compressor (68). A knockout drum, not shown, may be provided upstream of each compressor to remove liquid from the compressor inlet. The compressed refrigerant stream of line (74) may be at a temperature of 107°C (225°F) to 152°C (275°F) and a gauge pressure of 4.5 MPa (650 psig) to 5.2 MPa (750 psig).

[0029] To cool the compressed refrigerant stream of line (74), it may be heat-exchanged with the deferred refrigerant side stream at the deferred refrigerant side line (76) of the deferred refrigerant upper reboiling heat exchanger (78) to provide the cooled compressed refrigerant stream of the cooled compressed refrigerant line (80) and the heated deferred refrigerant side stream of the deferred refrigerant return line (82). The deferred refrigerant upper reboiling heat exchanger (78) has a first side communicating with the deferred refrigerant side line (76) from the deferred refrigerant column (90) and a second side communicating with the compressed refrigerant line (74). The second side of the deferred refrigerant upper reboiling heat exchanger communicates downstream with the first refrigerant compressor (66) and / or the second refrigerant compressor (68). A valve-type bypass is provided from the compressed refrigerant line (74) to the cooling compressed refrigerant line (80) to regulate the amount of heat passing through the upper depropaneizer reboiling heat exchanger (78).

[0030] The cooled compressed refrigerant stream of the cooling compressed refrigerant line (80) may be further cooled in an air cooler and separated by passing through a refrigerant separator (100) into a vapor refrigerant stream of the overhead refrigerant line (102) extending from the overhead of the refrigerant separator and a liquid refrigerant stream of the bottom refrigerant line (104) extending from the bottom of the refrigerant separator. The refrigerant separator (100) may be in downstream communication with the second side of the upper reboiling heat exchanger (78) of the depropaneizer. The vapor refrigerant stream of the overhead refrigerant line (102) may be further cooled by passing through the second side of the first depropaneizer reboiling heat exchanger (44) for heat exchange with the first reboiling depropaneizer bottom stream in the line (42) passing through the first side of the first depropaneizer reboiling heat exchanger (44). A second side of the first decarbonizer reboiling heat exchanger (44) may be in downstream communication with the refrigerant separator overhead line (102). The condensed refrigerant stream is transferred back from the first decarbonizer reboiling heat exchanger (44) to the condensed refrigerant line (70) to reconfigure the combined refrigerant stream of the combined refrigerant line (60) to resume the cycle. A valved bypass is provided in the overhead refrigerant line (102) to control the amount of heat exchange across the first decarbonizer reboiling heat exchanger (44). The refrigerant stream is compressed in the compressor (66) and possibly the compressor (68) before the heat exchange in the first decarbonizer reboiling heat exchanger (44) with the decarbonizer bottom stream in line (42) to provide sufficient heat for reboiling.

[0031] The liquid refrigerant stream of the lower refrigerant line (104) also has heat that can be recovered. The liquid refrigerant stream of line (104) can heat exchange with the lower stream of the combined net splitter to heat the lower stream of the combined net splitter of the selective hydrogenation feed exchanger (108) at the lower line (124) of the combined net splitter. A first side of the selective hydrogenation feed exchanger (108) can be in downstream communication with the lower line of the net splitter (106), and a second side can be in downstream communication with the lower line of the refrigerant separator (104). A valved bypass is provided in the lower refrigerant line (104) to regulate the amount of heat exchange across the selective hydrogenation feed exchanger (108). The cooled liquid refrigerant stream of the liquid refrigerant line (72) is transferred back from the optional hydrogenation feed exchanger (108) to reconfigure the combined refrigerant stream of line (60) into the condensed refrigerant stream of line (70) to resume the refrigeration cycle. Cooling of the refrigerant stream of the combined refrigerant line (60) is performed in the cryogenic heat exchanger (16) after heat exchange with the first decarbonized reboiling bottom stream in the first decarbonized reboiling heat exchanger (44).

[0032] The splitter feed stream of line (40) contains propane and propylene that must be separated to obtain a propylene product and to recycle propane to the reactor (4). The propylene-propane splitter column (50) splits the splitter feed stream into a propylene-rich splitter overhead stream in a splitter overhead line (52) extending from the overhead of the splitter column and a propane-rich splitter bottom stream in a splitter bottom line (54) extending from the bottom of the splitter column. The splitter overhead stream is compressed in a splitter compressor (53) which serves to condense the splitter overhead stream and provide the compressed splitter overhead stream to the compressed splitter line (55). The splitter compressor (53) may be in downstream communication with the splitter overhead line (52). The compressed splitter overhead stream of line (55) may be further cooled by a cooling water heat exchanger. The compression splitter overhead stream of line (55) may have a temperature of 48°C (80°F) to 71°C (160°F) and a gauge pressure of 1.2 MPa (175 psig) to 1.9 MPa (275 psig). After heat exchange, the temperature of the compression splitter overhead stream may be reduced to 3°C (5°F) to 6°C (10°F).

[0033] The first compression splitter overhead stream of the first compression splitter overhead line (56) is taken from the compression splitter overhead stream of line (55). The second compression splitter overhead stream of the second compression splitter overhead line (58) is taken from the compression splitter overhead stream of line (55). The second decarbonization bottom stream of the second decarbonization bottom line (46) is reboiled by heat exchange with the second compression splitter overhead stream of line (58) in the second decarbonization reboiling heat exchanger (48). The first side of the second decarbonization reboiling heat exchanger (48) can be in downstream communication with the decarbonization bottom line (34), and the second side of the second decarbonization reboiling heat exchanger (48) can be in downstream communication with the splitter compressor (53). Heat exchange in the second decarbonizer reboiling heat exchanger (48) serves to cool the second compression splitter overhead stream in line (58). The propylene product stream in line (59) can be taken from the cooled second compression splitter overhead stream, and the second reflux splitter overhead stream in the second reflux splitter line (110) can be refluxed as a second reflux stream to the propylene splitter column (50) at compression pressure.

[0034] The reboiling splitter bottom stream is taken from the splitter bottom stream of the splitter bottom line (54) to the reboiling splitter bottom line (112) and is reboiled by heat exchange with the first compression splitter overhead stream of the first compression splitter bottom line (56) in the splitter reboiling heat exchanger (114). The splitter reboiling heat exchanger (114) has a first side downstream communicating with the splitter bottom line (54) and a second side downstream communicating with the splitter compressor (53). The first compression splitter overhead stream of the first compression splitter bottom line (56), cooled by heat exchange with the reboiling splitter bottom stream of line (112) in the splitter reboiling heat exchanger (114), is returned to the splitter column (50) as a first reflux stream at compression pressure. The splitter bottom stream of line (54) can have a temperature of 21°C (70°F) to 32°C (90°F) and a gauge pressure of 62 kPa (90 psig) to 1034 kPa (150 psig).

[0035] The net splitter bottom stream is taken from the splitter bottom stream at the net splitter bottom line (106). The net splitter bottom stream is propane-rich and can be recycled to the reactor (4). However, diolefins and acetylenes can damage the dehydrogenation catalyst and must be converted to monoolefins in the selective hydrogenation reactor (120). Thus, hydrogen from the hydrogen stream (122) is added to the net splitter bottom stream to provide a combined net splitter bottom stream of line (124) that is heated in the selective hydrogenation feed heat exchanger (108). The combined net splitter bottom stream of the combined net splitter bottom line (124) can be heat exchanged with the liquid refrigerant stream of the bottom refrigerant line (104) at the selective hydrogenation feed heat exchanger (108) and can be charged into the selective hydrogenation reactor (120).

[0036] The bottom stream of the combined net splitter is selectively hydrogenated in a selective hydrogenation reactor (120) in the presence of hydrogen and a selective hydrogenation catalyst. The selective hydrogenation reactor (120) is typically operated under relatively mild hydrogenation conditions. Since these conditions typically cause the hydrocarbon to exist as a liquid phase substance, the reactants will usually be maintained under a minimum pressure sufficient to keep the reactants as liquid phase hydrocarbons. Thus, 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 mild temperatures of 25°C (77°F) to 350°C (662°F), or 50°C (122°F) to 200°C (392°F), are typically used. The liquid space velocity of the reactants through the selective hydrogenation catalyst is 1.0 hr -1 Exceeding and 35.0 hr -1 To prevent undesirable saturation of a significant amount of monoolefin hydrocarbons, the molar ratio of hydrogen to diolefin hydrocarbons in the bottom stream of the combination net splitter entering the layer of the selective hydrogenation catalyst is maintained at 0.75:1 to 1.8:1. Any suitable catalyst capable of selectively hydrogenating diolefins may be used. Suitable catalysts include, but are not limited to, catalysts comprising copper and at least one other metal such as titanium, vanadium, chromium, manganese, cobalt, nickel, zinc, molybdenum, and cadmium or mixtures thereof. The metal is preferably supported on an inorganic oxide support, for example, silica and alumina.

[0037] The optionally hydrogenated net splitter bottom stream containing propane is transferred to the hydrogenation effluent line (126) after gas separation and added to the new propane feed stream in line (128), and both are fed to the depropination column (90). The depropination column (90) may be in downstream communication with the splitter bottom line (54). The depropination column (90) separates the optionally hydrogenated net splitter bottom stream and the new propane feed stream to provide a propane-rich depropination overhead stream in the overhead line (92) extending from the overhead of the depropination column and a C4+ hydrocarbon-rich depropination bottom stream in the depropination bottom line (94) extending from the bottom of the depropination column.

[0038] The depropinator overhead stream of the depropinator overhead line (92) can be cooled and completely condensed and supplied to the depropinator receiver (93). The receiver bottom stream exits the bottom of the depropinator receiver at the depropinator receiver bottom line (95). The depropinator reflux stream taken from the depropinator receiver bottom line (95) refluxes the condensed propane back to the depropinator column (90). The depropinator receiver (93) operates at a temperature of 20°C (68°F) to 70°C (158°F) and a gauge pressure of 1.4 MPa (200 psig) to 1.8 MPa (261 psig).

[0039] The net overhead stream of the net defronitrifier overhead line (96) is extended across the defronitrifier overhead expander (86) to vaporize and cool it, is supplemented with hydrogen from the hydrogen recycling line (25), and is further cooled in the reactor feed passage (88) of the cryogenic heat exchanger (16) to provide the reactor feed stream of the reactor feed line (2). The hydrogen-to-hydrocarbon molar ratio of the reactor feed stream in the range of 0.005 to 0.6 is controlled by the control valve of the hydrogen recycling line (25).

[0040] The reactor feed stream of the reactor feed line (2) exiting the reactor feed passage (88) can be provided at a temperature of 32°C (90°F) to 60°C (140°F) and a gauge pressure of 69 kPa (10 psig) to 0.5 MPa (80 psig).

[0041] The deferred refrigerant side stream taken from the deferred refrigerant side line (76) of the deferred refrigerant (90) is reboiled in the deferred refrigerant upper reboiling heat exchanger (78) by heat exchange with the compressed refrigerant stream of line (74), which can provide the cooled compressed refrigerant stream of line (80) and the heated deferred refrigerant side stream of line (82), which are returned to the deferred refrigerant column (90) as a steam stream through its side. The deferred refrigerant side stream taken from line (76) is suitably a liquid stream taken from the liquid trap of the deferred refrigerant column (90).

[0042] The defrosting bottom stream of the defrosting bottom line (94) is rich in C4+ hydrocarbons. The defrosting reboiling stream taken from line (97) from the defrosting bottom stream of line (94) can be heated in the defrosting reboiling heat exchanger (99) and returned to the bottom of the defrosting column (90). The net defrosting bottom stream containing C4+ hydrocarbons can be taken as a product in the net defrosting bottom line (98). The defrosting bottom (93) operates at a temperature of 80°C (176°F) to 130°C (195°F) and a gauge pressure of 1.5 MPa (217 psig) to 2 MPa (290 psig).

[0043] The process and apparatus make it possible to obtain high-purity hydrogen from the pure gas stream of line (23) and high-purity ethane from the off-gas stream of line (38) using a single-stage separator (20) and a single decarbonizer column (30), whereas conventionally, a double-stage separator and two decarbonizer columns were required for equivalent purity.

[0044] concrete Implementation example

[0045] The following is described with specific embodiments, but it will be understood that this description is intended to illustrate the scope of the foregoing description and the appended claims, and is not intended to limit them.

[0046] A first embodiment of the present invention is a process for separating ethane from propane, comprising the steps of: passing a decarbonizer feed stream containing ethane and propane through a decarbonizer column to provide an ethane-rich decarbonizer overhead stream and a propane-rich decarbonizer bottom stream; and reboiling the decarbonizer bottom stream by heat exchange with a refrigerant stream. An embodiment of the present invention is one, any, or all of the prior embodiments of the present paragraph up to the first embodiment of the present paragraph, further comprising the step of cooling the decarbonizer overhead stream by a heat exchanger in a cryogenic heat exchanger to provide a cooled decarbonizer overhead stream. An embodiment of the present invention is one, any, or all of the prior embodiments of the present paragraph up to the first embodiment of the present paragraph, further comprising the step of cooling the reactor effluent stream in a cryogenic heat exchanger to provide a cooled reactor effluent stream. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the first embodiment of this paragraph, further comprising the step of separating a reactor effluent stream cooled in a single-stage separator to provide a net gas overhead stream and heating the net gas overhead stream in a cryogenic heat exchanger. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the first embodiment of this paragraph, further comprising the step of compressing a refrigerant stream before heat exchange with a decarbonization bottom stream. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the first embodiment of this paragraph, further comprising the step of cooling the refrigerant stream in a cryogenic heat exchanger after heat exchange with a decarbonization bottom stream, expanding the cooled refrigerant stream to provide a low-temperature refrigerant stream, and heating the low-temperature refrigerant stream in a cryogenic heat exchanger.One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the first embodiment of this paragraph, further comprising the step of separating a cooled decarbonizer overhead stream in a decarbonizer receiver to provide an off-gas stream and heating the off-gas stream in a cryogenic heat exchanger. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the first embodiment of this paragraph, further comprising the step of heating a feed stream containing propane in a cryogenic heat exchanger and charging the propane stream into a dehydrogenation reactor. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the first embodiment of this paragraph, further comprising the step of reboiling a portion of the decarbonizer bottom stream and transferring the net ethaneizer bottom stream for further fractionation. One embodiment of the present invention is an embodiment of any or all of the prior embodiments of the present paragraph up to the first embodiment of the present paragraph, which further comprises the step of operating a decarbonizer column at an overhead pressure of 250 psig or less.

[0047] A second embodiment of the present invention is a decarbonizing column having a decarbonizing overhead line exiting the overhead of the decarbonizing column and a decarbonizing bottom line exiting the bottom of the decarbonizing column; a reboiling line communicating with the decarbonizing bottom line; a compressor compressing a refrigerant stream; and a reboiling heat exchanger comprising a first side communicating with the decarbonizing bottom line and a second side communicating with the compressor. An embodiment of the present invention is an embodiment of any or all of the prior embodiments of the present paragraph up to the second embodiment of the present paragraph, further comprising a refrigerant expander communicating with the second side of the reboiling heat exchanger for cooling the refrigerant. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the second embodiment of this paragraph, further comprising a cryogenic exchanger and a passage of a refrigerant line within the cryogenic exchanger communicating downstream with a refrigerant expander. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the second embodiment of this paragraph, and the passage of a refrigerant line in the cryogenic exchanger communicating downstream with a refrigerant expander is a second passage of a refrigerant line and further comprises a first passage of a refrigerant line within the cryogenic exchanger communicating downstream with a second side of a reboiling exchanger. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the second embodiment of this paragraph, further comprising a effluent passage of a reactor effluent in the cryogenic exchanger and a single-stage separator communicating downstream with the effluent passage. One embodiment of the present invention is an embodiment of any or any of the prior embodiments of this paragraph up to the second embodiment of this paragraph, wherein the cryogenic exchanger further comprises a separator overhead passage, and the separator overhead passage is in direct downstream communication with the overhead line of a single-stage separator.One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the second embodiment of this paragraph, wherein the decarbonizer overhead path is further included in a cryogenic exchanger, and the decarbonizer overhead path is in downstream communication with the overhead line of the decarbonizer column. One embodiment of the present invention is one, any, or all of the prior embodiments of this paragraph up to the second embodiment of this paragraph, wherein the decarbonizer receiver is further included in downstream communication with the decarbonizer overhead path.

[0048] A third embodiment of the present invention is a decarbonizing column having a decarbonizing overhead line exiting the overhead of the decarbonizing column and a decarbonizing bottom line exiting the bottom of the decarbonizing column; a cryogenic exchanger having a refrigerant passage in downstream communication with an expander; and a decarbonizing overhead passage of the cryogenic exchanger, wherein the decarbonizing overhead passage is in downstream communication with the overhead line of the decarbonizing column. An embodiment of the present invention is an embodiment of any or all of the prior embodiments of the present paragraph up to the third embodiment of the present paragraph, further comprising a reboiling heat exchanger having a first side in communication with the decarbonizing bottom line and a second side in communication with the refrigerant passage of the cryogenic exchanger.

[0049] A fourth embodiment of the present invention is a process for separating hydrogen from ethane, comprising the steps of: cooling a reactor effluent stream of a cryogenic heat exchanger containing hydrogen and ethane 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 a downstream rich in 94 mol% or more of hydrogen and ethane.

[0050] It is understood that those skilled in the art, using the foregoing description without further elaboration, can make full use of the invention and easily identify the essential features of the invention, and make various changes and modifications to the invention and adapt them to various uses and conditions without departing from the spirit and scope of the invention. Accordingly, the foregoing preferred specific embodiments should be interpreted merely as illustrative and not as limiting the remainder of the invention in any way, and are intended to include various modifications and equivalent arrangements that fall within the scope of the appended claims.

[0051] In the above, unless otherwise indicated, all temperatures are given in Celsius, and all parts and percentages are by weight.

Claims

Claim 1 A process for separating ethane from propane, comprising the steps of: passing a decarbonizer feed stream containing ethane and propane through a decarbonizer column to provide an ethane-rich decarbonizer overhead stream and a propane-rich decarbonizer bottom stream; reboiling the decarbonizer bottom stream by heat exchange with a refrigerant stream; cooling the reactor effluent stream 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 and heating the net gas overhead stream in a cryogenic heat exchanger. Claim 2 A process according to claim 1, further comprising the step of cooling the decarbonizer overhead stream by heat exchange in a cryogenic heat exchanger to provide a cooled decarbonizer overhead stream. Claim 3 An apparatus for separating ethane from propane, comprising: a decarbonizer column having a decarbonizer overhead line exiting the overhead of the decarbonizer column and a decarbonizer bottom line exiting the bottom of the decarbonizer column; a reboiling line communicating with the decarbonizer bottom line; a compressor for compressing a refrigerant stream; a reboiling heat exchanger having a first side communicating with the decarbonizer bottom line and a second side communicating with the compressor; a reactor effluent effluent passage in a cryogenic exchanger and a single-stage separator communicating downstream with the effluent passage; and a separator overhead passage in a cryogenic exchanger, which is directly downstream communicating with the overhead line of the single-stage separator. Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 delete

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