Dehydrogenation and pyrolysis product recovery using common C3 diverters

Abstract

A process and apparatus integrate the recovery of propylene from a pyrolysis reactor and a paraffin dehydrogenation reactor. A common C3 split column fractionates a propylene product from a propane recycle to a paraffin dehydrogenation reactor. The C3 hydrocarbons may be provided from a pyrolysis reactor and a dehydrogenation reactor.

Description

[0001] Priority Claim

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 384,930, filed on November 23, 2022, the entire content of which is incorporated herein by reference. Technical Field

[0003] This field relates to the recovery of light olefins, ethylene, and propylene, as well as the recovery and separation of light component by-products such as hydrogen, methane, ethane, and propane. Specifically, this field relates to the recovery of ethylene and propylene from pyrolysis effluents and dehydrogenation effluents. Background Art

[0004] The dehydrogenation of propane and the steam cracking of saturated and predominantly paraffinic hydrocarbons such as naphtha, butane, propane, and ethane are important commercial hydrocarbon conversion processes because they produce light olefins, which are building blocks for polyolefins and polymers with growing demand. Specifically, the demand for ethylene and propylene in the petrochemical industry has increased significantly due to their use as precursors in the production of polyethylene and polypropylene for many commercial products. One route for producing propylene is propane dehydrogenation. The main products from a steam cracker are ethylene and propylene; however, other by-products such as hydrogen, methane, and other heavier hydrocarbons can be further processed for other petrochemical processes.

[0005] A method for converting paraffin to olefins via a propane dehydrogenation process involves passing a propane feed stream through a highly selective catalyst to dehydrogenate propane to propylene in the dehydrogenation reactor effluent. The dehydrogenation reactor effluent is cooled and separated into a hydrocarbon-rich fraction and a hydrogen-rich vapor fraction (a portion of which is non-recycled net gas) in a cryogenic separation system, which 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 alone to remove hydrogen from the light hydrocarbons. However, further fractionation is required to separate C2 - materials from the C3 hydrocarbons in the dehydrogenation effluent in a deethanizer tower, which typically also requires refrigeration packages.

[0006] A large amount of the ethylene consumed in the production of plastics and petrochemicals such as polyethylene is produced by the thermal cracking or pyrolysis of hydrocarbons. Pyrolysis also produces a large amount of propylene, which can be used in the plastics industry for the preparation of polypropylene. Steam is typically mixed with the feed stream into the cracking furnace to reduce the hydrocarbon partial pressure and increase the olefin yield, and to reduce the formation and deposition of carbonaceous materials in the cracking reactor. Thus, this process is commonly referred to as steam cracking or pyrolysis.

[0007] Steam cracking produces lower value by-products such as pyrolysis gasoline (cracked gas) and fuel oil (cracked oil). The cracked gas contains a large amount of paraffins and aromatic compounds. The resulting paraffins include normal paraffins and non-normal paraffins that can be recovered or further processed. Aromatic compounds are very stable and difficult to crack in a steam cracker. The paraffin side chains can be removed, but this results in the production of polycyclic aromatic compounds, which increases the yield of low-value fuel oil. Normal paraffins pyrolyze into olefins more selectively than non-normal paraffins.

[0008] There is a need to improve the separation system to recover propylene from the dehydrogenation effluent and the pyrolysis feed effluent. Summary of the Invention

[0009] An improved method and apparatus have been found that use a common C3 splitter tower system to fractionate propylene products from propane recycle to a paraffin dehydrogenation reactor. C3 hydrocarbons can be provided from a pyrolysis reactor and a dehydrogenation reactor.

[0010] These and other features, aspects, and advantages of the present disclosure are further explained by the following detailed description, the drawings, and the appended claims. Brief Description of the Drawings

[0011] Figure 1 is a schematic diagram of the method and apparatus of the present disclosure.

[0012] Figure 2 is Figure 1 a schematic diagram of an alternative embodiment of the method and apparatus.

[0013] Figure 3 is Figure 2 a schematic diagram of an alternative embodiment of the method and apparatus.

[0014] Figure 4 is Figure 3 a schematic diagram of an alternative embodiment of the method and apparatus.

[0015] Definition

[0016] The following detailed description is merely exemplary in nature and is not intended to limit the application and use of the described embodiments. Additionally, there is no intention to be bound by any theory presented in the foregoing background or the following detailed description.

[0017] The term "in communication with" means that material flow is operably permitted between the enumerated components.

[0018] The term "downstream in communication with" means that at least a portion of the material flowing towards the body in the downstream in communication with can flow operably from the object with which it is in communication.

[0019] The term "upstream communication" means that at least a portion of the material flowing out of the body in an upstream communication can operably flow to an object in communication therewith.

[0020] The term "direct communication" means flowing from an upstream component into a downstream component without a compositional change due to physical fractionation or chemical conversion.

[0021] The term "bypass" means that the object loses downstream communication with the bypass body at least within the scope of the bypass.

[0022] As used herein, the term "separator" means a vessel having an inlet and at least one overhead vapor outlet and one bottoms liquid outlet, and may also have an aqueous stream outlet from a boot. A flash drum is a type of separator that can be in downstream communication with a separator that can operate at a higher pressure.

[0023] As used herein, the term "major" or "substantially" means greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0024] The term "C x " is to 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 less than or equal to x, and preferably x and fewer carbon atoms. The term "C x +" refers to a molecule having greater than or equal to x, and preferably x and more carbon atoms.

[0025] The term "column" means one or more distillation columns for separating one or more components having different volatilities. Unless otherwise specified, each column includes a condenser at the top of the column for condensing a portion of the overhead stream and refluxing it back to the top of the column, and a reboiler at the bottom of the column for vaporizing a portion of the bottoms stream and returning it to the bottom of the column. The feed to the column can be preheated. The top pressure is the pressure of the overhead vapor at the column outlet. The bottom temperature is the liquid bottoms outlet temperature. Unless otherwise specified, the overhead line and the bottoms line refer to the net lines from downstream of the column for reflux or reboiling back to the column. Alternatively, a stripping stream can be used for heat input near the bottom of the column.

[0026] As used herein, the term "rich component stream" or "component-rich stream" means that a stream identified as rich coming out of a vessel has a greater component concentration than the feed to the vessel.

[0027] As used herein, the term "lean component stream" or "component-lean stream" means that a stream identified as lean coming out of a vessel has a smaller component concentration than the feed to the vessel. Detailed Description

[0028] The present disclosure is a method and apparatus for integrating the recovery of propylene from a paraffin dehydrogenation reactor and a pyrolysis reactor. It has been found that by utilizing a propane dehydrogenation reactor and a pyrolysis reactor, additional production of propylene can be accompanied by significant production of ethylene by pyrolysis. Additionally, a C3 splitter column is proposed to recover the propylene produced from the pyrolysis reactor and the dehydrogenation reactor.

[0029] Figure 1 The method and apparatus 10 shown include two conversion units, a paraffin dehydrogenation reactor 14 and a pyrolysis reactor 50, and a common recovery system 70. A propane feed stream in a feed line 12 is prepared for loading into the propane dehydrogenation reactor 14. The propane feed stream includes propane and may include other light paraffins such as ethane, n-butane, isobutane, pentane, or isopentane. In some embodiments, the propane feed stream includes at least one other paraffin having from 2 to 30 carbon atoms.

[0030] The propane feed stream in line 12 may be cooled in a PDH cold box 16, or may bypass the cold box, and may be transported to a depropanizer fractionator 18 after supplementing the propane feed stream recycled in line 127. In the depropanizer fractionator 18, propane is separated from the heavier components and provided in a first depropanizer overhead stream in line 20. The depropanizer overhead stream in line 20 may be slightly heated or cooled in the dehydrogenation cold box 16 at the outlet to reach 35°C to 40°C and loaded into the paraffin dehydrogenation reactor 14 in a dehydrogenation feed line 21.

[0031] In the dehydrogenation reactor, propane is dehydrogenated to produce propylene. A dehydrogenation catalyst is used in the dehydrogenation reaction to catalyze the dehydrogenation of propane. The conditions in the dehydrogenation reactor may include a temperature of 500°C to 800°C, a pressure of 40 kPa to 310 kPa, and a catalyst-to-oil ratio of 5 to 100.

[0032] The dehydrogenation reaction can be carried out in a fluidized manner such that a gas with or without a fluidizing inert gas containing the reactant alkane is distributed to the reactor in a manner that lifts the dehydrogenation catalyst in the reactor vessel while catalyzing the dehydrogenation of the alkane. During the catalytic dehydrogenation reaction, coke deposits on the dehydrogenation catalyst, resulting in a decrease in the activity of the catalyst. Then the dehydrogenation catalyst must be regenerated in a regenerator. The regenerator can burn the coke from the dehydrogenation catalyst and fuel gas to ensure sufficient enthalpy in the dehydrogenation reactor to promote the endothermic reaction.

[0033] The selected dehydrogenation catalyst should minimize the cracking reaction and favor the dehydrogenation reaction. Catalysts suitable for use herein include active metals that can be dispersed in a porous inorganic support material such as silica, alumina, silica-alumina, zirconia, or clay. Exemplary embodiments of the catalyst include alumina or silica-alumina containing gallium, a noble metal, and an alkali metal or alkaline earth metal.

[0034] The catalyst support comprises a support material, a binder, and optionally a filler material to provide physical strength and integrity. The support material may include alumina or silica-alumina. Colloidal silica or alumina sol can be used as the binder. Alumina or silica-alumina typically contains alumina in the γ, θ, and / or δ phases. The nominal diameter of the catalyst support particles can be from 20 micrometers to 200 micrometers, and the average diameter is from 50 micrometers to 150 micrometers. Preferably, the surface area of the catalyst support is 85 m 2 / g to 140 m 2 / g.

[0035] The fluidized dehydrogenation catalyst can include a dehydrogenation metal on the support. The dehydrogenation metal can be one or a combination of transition metals. Noble metals can be the preferred dehydrogenation metals, such as platinum or palladium. Gallium is an effective metal for paraffin dehydrogenation. The metal can be deposited on the catalyst support by impregnation or other suitable methods, or included in the support material or binder during catalyst preparation.

[0036] The acid functionality of the catalyst should be minimized to prevent cracking and favor dehydrogenation. Alkali metals and alkaline earth metals can also be included in the catalyst to weaken the acidity of the catalyst. Rare earth metals can be included in the catalyst to control the activity of the catalyst. Metals can be incorporated into the dehydrogenation catalyst at a concentration of 0.001 wt% to 10 wt%. In the case of noble metals, it is preferred to use noble metals at 10 parts per million (ppm) by weight to 600 ppm by weight. More preferably, noble metals at 10 ppm to 100 ppm by weight are preferably used. The preferred noble metal is platinum. Gallium should be present in the range of 0.3 wt% to 3 wt%, preferably 0.5 wt% to 2 wt%. Alkali metals and alkaline earth metals can be present in the range of 0.05 wt% to 1 wt%.

[0037] The regenerated catalyst can be contacted with a propane feed stream, possibly in contact with a fluidizing gas, to lift the propane feed stream and the dehydrogenation catalyst into a riser when dehydrogenation occurs. Above the riser, the spent dehydrogenation catalyst and the propylene product can be separated by a centripetal separation device. The propylene product gas can be quenched with a cooling fluid to prevent overreaction to form undesirable by-products. The separation of the propylene product can include quench contact and fractionation to produce a propylene product stream in line 22.

[0038] The paraffin dehydrogenation reactor 14 may alternatively employ a catalytic moving bed reactor. The reactor section may include several parallel or series radial flow reactors heated by charge and interstage heaters. The propane feed stream, which may have hydrogen added, flows through each dehydrogenation reactor from a screened central tube through an annular dehydrogenation catalyst bed to an outer effluent ring. The flow may be in the opposite direction. The dehydrogenation catalyst may include noble metals and their mixtures, modifiers selected from the group consisting of alkali metals or alkaline earth metals and their compositions, components selected from the group consisting of tin, germanium, lead, indium, gallium, thallium and their compositions, and a porous support forming catalyst particles. The catalyst support may include oil-drop alumina spheres.

[0039] The dehydrogenation conditions may include a temperature of 400 °C to 900 °C, a pressure of 0.01 absolute atmosphere to 10 absolute atmospheres, and a liquid hourly space velocity (LHSV) of 0.1 hr -1 to 100 hr -1 . The pressure in the dehydrogenation reactor is maintained at the lowest feasible level consistent with equipment limitations to maximize the chemical equilibrium advantage. The spent dehydrogenation catalyst in the annular catalyst bed may be removed from the bottom of the bed and transferred to a regenerator to burn off the coke from the catalyst in air at 450 °C to 600 °C. The noble metal on the catalyst may be redispersed, dried by an oxychlorination method, and returned to the top of the dehydrogenation catalyst bed as a regenerated dehydrogenation catalyst.

[0040] The dehydrogenation feed stream in line 22 will include light hydrocarbons and hydrogen. Propylene must be separated from other light hydrocarbons such as unreacted propane and hydrogen. Propane can be recycled to the dehydrogenation reactor 14 for propylene production. Hydrogen is a valuable byproduct and can be used elsewhere in the refinery or in the dehydrogenation reactor 14 to control the dehydrogenation reaction.

[0041] Before hydrogen separation, the dehydrogenation feed stream in line 22 may be cooled, compressed, and dried. To effectively separate hydrogen from the light hydrocarbons, the dehydrogenation feed stream in line 22 is cryogenically cooled by passing it through a dehydrogenation cold box 16 to condense the hydrocarbons. In the dehydrogenation cold box 16, the dehydrogenation feed stream in line 22 is cooled by heat exchange with other feed streams (including the dehydrogenation refrigerant feed stream passing through a dehydrogenation cold box 24 in line 25) to provide a cooled dehydrogenation feed stream in line 23, which is fed to a dehydrogenation separator 26. The dehydrogenation refrigerant feed stream in line 25 may have passed through a first compression stage and be at a pressure of 1400 kPa to 1700 kPa.

[0042] The dehydrogenated refrigerant stream in line 25 can be a mixture of up to 6 components, which are appropriately selected to meet the requirements of the propane dehydrogenation unit and the pyrolysis unit. The mixed refrigerant composition can contain 0 mol% to 7 mol% inert gas, 11 mol% to 35 mol% methane, 25 mol% to 40 mol% C2 hydrocarbons, 20 mol% to 50 mol% C3 hydrocarbons, and 0 mol% to 15 mol% C5 hydrocarbons. The inert gas can be nitrogen, and the C5 hydrocarbon can be isopentane. The refrigerant stream in line 25 can pass through the dehydrogenation cold box 16 and then expand through the expansion valve 24 to cool the refrigerant stream by the latent heat of evaporation and return through the dehydrogenation cold box 16.

[0043] The cooled dehydrogenated stream in line 23 is separated in the dehydrogenation separator 26 to provide a net gas overhead stream rich in hydrogen in the dehydrogenation separator overhead line 28 extending from the top of the dehydrogenation separator, and a liquid dehydrogenated stream rich in hydrocarbons in the dehydrogenation separator bottom line 30 extending from the bottom of the separator. The dehydrogenation separator 26 can be operated at a temperature between -100 °C (-150 °F) and 66 °C (150 °F) and more typically between -95 °C (-138 °F) and -40 °C (-40 °F), and at a gauge pressure between 690 kPa (100 psig) and 1.4 MPa (200 psig).

[0044] By sufficiently condensing the hydrocarbons in the dehydrogenation separator 26, the net gas overhead stream in the separator overhead line 28 is sufficiently pure hydrogen from one 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. The net gas overhead stream in line 28 can be directed to the dehydrogenation cold box for heating and provide a product hydrogen stream that can be used elsewhere in the refinery or plant. The hydrogen recycle stream can be withdrawn from the net gas overhead stream in the separator overhead line 28 through the control valve thereon in the hydrogen recycle line 27 to the propane overhead stream in line 20 to provide the hydrogen requirement for the dehydrogenation reaction in the dehydrogenation feed line 21. The heated tail gas stream can be provided at a temperature between 32 °C (90 °F) and 60 °C (140 °F) and a gauge pressure between 760 kPa (110 psig) and 1.2 MPa (170 psig).

[0045] The liquid dehydrogenation feed stream in line 30 of the dehydrogenation separator is rich in hydrocarbons that can be refined to obtain valuable products. The liquid dehydrogenation feed stream in line 30 of the dehydrogenation separator can be heated to evaporate the hydrocarbons by passing it through a dehydrogenation cold box. The hydrocarbons evaporated in line 30 are heated by releasing the latent heat of vaporization, and thus assist in cooling the dehydrogenation feed stream passing through the dehydrogenation cold box 16 in line 22. The necessary heat exchange in the dehydrogenation cold box 16 occurs between the cold feed stream and the hot feed stream and the dehydrogenation refrigerant feed stream in line 25. The liquid dehydrogenation feed stream in line 30 is heated by passing it through the dehydrogenation cold box 16 and fed to the dehydrogenation stripper 34.

[0046] The liquid dehydrogenation feed stream in line 30 includes some light residues such as methane and ethane, which must be separated from the larger hydrocarbons such as propylene and propane. Therefore, the liquid dehydrogenation feed stream in line 30 is passed to the dehydrogenation stripper 34 for fractionation after being heated to a temperature of 0 °C (30 °F) to 45 °C (113 °F) in the dehydrogenation cold box 16. The dehydrogenation stripper 34 separates the liquid dehydrogenation feed stream into a stripper top stream rich in C2 - hydrocarbons and some stripped C3 hydrocarbons in a stripper top line 36 extending from the top of the stripper rich in methane and ethane and a stripper bottom stream in a stripper bottom line 38 extending from the bottom of the stripper 34 rich in C3 hydrocarbons. The light residues are stripped off, and these light residues have a limited amount of C3 hydrocarbons in the overhead vapor. However, the C3 hydrocarbons are recovered in the demethanizer 40, and the stripper top stream is directed to the demethanizer. The stripper top stream in line 36 is heat - exchanged with the demethanizer bottom stream in line 72 to cool the stripper top stream in the heat exchanger 37 and fed as a demethanizer feed stream in a demethanizer feed line 39 to the demethanizer 40 to remove methane and lighter gases from the stripper top stream. The stripper bottom stream in line 38 is split into a reboil stream, which is re - boiled and returned to the paraffin dehydrogenation stripper 34, and a net stripper bottom stream is transported in a net stripper bottom line 42 to the C3 splitter 120. The stripper 34 can be operated at a bottom temperature of 30 °C (90 °F) to 60 °C (140 °F) and a top gauge pressure of not more than 1.5 MPa to 1.9 MPa (gauge). The stripper 34 can be in downstream communication with the paraffin dehydrogenation reactor 14.

[0047] The method and apparatus 10 omit the low - temperature cooling equipment associated with the paraffin dehydrogenation deethanizer and required for propylene recovery. Instead, propylene recovery will occur downstream of the pyrolysis reactor 50.

[0048] Feed the refrigerant stream in the preliminary refrigerant line 202 into the first refrigerant compressor 200, where the refrigerant stream is compressed in a first compression stage to a pressure of 1500 kPa to 1750 kPa to provide a first compressed refrigerant stream in line 206. The refrigerant stream can be a mixed refrigerant stream as previously described. Split the first compressed refrigerant stream in line 206 into a reboiling refrigerant stream in line 204 and a dehydrogenated refrigerant stream in line 25. The reboiling refrigerant stream in line 204 undergoes heat exchange with the reboiler bottom stream taken from the deethanizer bottom stream in line 78 on the second side of the deethanizer bottom reboiler exchanger 201 on the first side of the reboiler line 79, so as to boil the deethanizer bottom reboiler stream and cool the first compressed refrigerant stream in line 204, thereby providing a cooled first compressed refrigerant stream in line 205 and a deethanizer bottom reboiler stream that is returned to the deethanizer. The cooled first compressed refrigerant stream in line 205 is further cooled to near ambient temperature in a cooler and separated in a separator 208 to provide a second compressed refrigerant stream in the top line 210, and the liquid in the second compressed liquid stream is removed in the bottom line 211. If necessary, supplementary bottom reboiling in the deethanizer 74 may be necessary, and in addition to the heat provided by the first compressed refrigerant stream in line 204, this supplementary bottom reboiling is also provided by a low-level heat stream.

[0049] Take out the dehydrogenated refrigerant stream from the cooled first compressed refrigerant stream in line 206 in line 25 and transport the dehydrogenated refrigerant stream to the dehydrogenation cold box 16, where the dehydrogenated refrigerant stream is heat-exchanged with the dehydrogenated stream in line 22 to cool the dehydrogenated stream and other streams, thereby heating the dehydrogenated refrigerant stream in line 207. After passing through the dehydrogenation cold box 16, the cooled dehydrogenated refrigerant stream in line 25 passes through an expansion valve 24 to evaporate the dehydrogenated refrigerant stream, thereby cooling it and providing an evaporated dehydrogenated refrigerant stream in line 207. The evaporated dehydrogenated refrigerant stream in line 207 returns through the dehydrogenation cold box 16 to further provide net cooling to the streams passing through it (including the dehydrogenated stream in line 22). The heated evaporated dehydrogenated refrigerant stream in line 207 returns to provide a part of the refrigerant stream in the preliminary refrigerant line 202.

[0050] In the second compressor 212, the second stage of compression compresses the second compressed refrigerant stream from the top of the separator 208 in line 210 to a pressure of 4500 kPa to 5500 kPa to provide a second compressed refrigerant stream in line 214. The second compressed refrigerant stream in line 214 exchanges heat with the deethanizer side reboiler stream from the deethanizer 74 in line 75 on the second side of the deethanizer side reboiler exchanger 203 on the first side of the deethanizer side reboiler exchanger, to reboil the side reboiler stream and cool the second compressed refrigerant stream in line 214, to provide a cooled second compressed refrigerant stream in line 215. If desired, the second compressed refrigerant stream in line 214 may also be further cooled in an additional exchanger. The cooled second compressed refrigerant stream in line 215 may be combined with the second compressed liquid stream from the separator 208 in line 211 to provide a total second compressed refrigerant stream in line 220 to the pyrolysis cold box 58. The deethanizer side reboiler exchanger 203 may be in communication downstream of the second compressor on the first refrigerant side of the compressor.

[0051] Then the total second compressed refrigerant stream in line 220 is passed to the pyrolysis cold box 58, where the total second compressed refrigerant stream exchanges heat with the processed pyrolysis stream in line 57 to heat the processed pyrolysis stream and other streams and cool the total second compressed refrigerant stream in line 220. After passing through the pyrolysis cold box 58, the total second compressed refrigerant stream in line 220 is passed through an expansion valve 222 to vaporize the total second compressed refrigerant stream, thereby further cooling the total second compressed refrigerant stream and providing a vaporized second compressed refrigerant stream in line 224. The vaporized second compressed refrigerant stream in line 224 may be returned through the pyrolysis cold box 58 to provide net cooling to the streams passing through it, including the processed pyrolysis stream in line 57. The heated vaporized dehydrogenation refrigerant stream in line 224 is returned to provide a portion of the refrigerant stream in the primary refrigerant line 202.

[0052] The pyrolysis feed stream in the feed line 52 (optionally supplemented with recycled ethane from line 93) is charged to the pyrolysis reactor 50, which may be a steam cracker for cracking hydrocarbons under steam to produce a pyrolysis stream in the pyrolysis line 54. The cracking feed stream may optionally be in the gas phase. The pyrolysis reactor 50 may preferably be operated at a temperature of 750 °C (1382 °F) to 950 °C (1742 °F). The pyrolysis feed stream may be one of a number of feed streams entering at the same or different points in the furnace to maximize product yields. The pyrolysis feed stream may be an ethane stream or a naphtha stream.

[0053] The pyrolysis stream exiting the pyrolysis reactor 50 in the pyrolysis line 54 may be in a superheated state. One or more quench towers or other devices, not shown but preferably an oil quench tower and / or a water quench tower, may be used to quench the pyrolysis stream. The pyrolysis stream may be alkali-washed in the scrubbing tower 56 to remove acidic gases, and the scrubbing gas is compressed to provide a treated pyrolysis stream in line 57, which is then cooled in the pyrolysis cold box 58.

[0054] Although other streams may be recovered from the pyrolysis reactor 50, the treated pyrolysis stream in line 57 is a gaseous hydrocarbon stream. The treated pyrolysis stream in line 57 is cooled in the pyrolysis cold box 58 by heat exchange with the net gas from lines 68 and 70 of the demethanizer 40 and the vaporized secondary compressed refrigerant stream in line 224 after expansion across the valve 222 and fed into the demethanizer 40. The demethanizer 40 may be in downstream communication with the paraffin dehydrogenation reactor 14, the pyrolysis reactor 50, and the stripping column 34.

[0055] In the demethanization fractionation column, the cooled stripping column top stream rich in C2 - hydrocarbons together with some stripped C3 hydrocarbons in line 39 and the cooled pyrolysis stream in the demethanizer feed line 59 are fractionated to provide a demethanizer top stream rich in methane and hydrogen in the demethanizer top line 62, and a demethanized bottom stream rich in C2+ hydrocarbons in the demethanizer bottom line 64. The cooled treated pyrolysis stream in line 57 may be cooled in the demethanizer reboiler heat exchanger 63 by heat exchange with the bottom reboil stream in line 69 to cool the cooled treated pyrolysis stream in line 57 so as to provide a demethanizer feed stream in line 59 and a reboiled bottom stream returning to boil in the column in line 69. The cooled treated pyrolysis stream in line 57 may also be cooled in the demethanizer reboiler heat exchanger 63 by heat exchange with the side reboil stream in line 71 to further cool the cooled treated pyrolysis stream in line 57 so as to provide a demethanizer feed stream in line 59 and a reboiled side stream returning to boil in the column in line 71. The demethanizer feed stream in line 59 may be additionally cooled by expansion across a turbine expander, not shown. Cooling reflux is provided by utilizing a side stream containing very little ethylene from a suitable tray near the top of the demethanizer 40, thereby achieving a demethanizer top stream with very little ethylene loss. The side stream is compressed, cooled, and returned as reflux to the demethanizer 40. Allowing the C1 - stream mainly comprising hydrogen and methane to be stripped as the net top stream of the demethanizer 40 also minimizes ethylene loss. Figure 1 Figure 1 ​The arrangement of the recycle stream is not shown. Hydrogen and methane are further separated by further cooling in the demethanizer cooler and separating in the hydrogen-methane separator 66 to provide a hydrogen-rich net gas stream in the net overhead line 68 and a methane-rich net liquid stream in the net liquid line 70, and both the net gas stream and the net liquid stream are transferred to the pyrolysis cold box 58 to provide cooling for the processed pyrolysis stream in line 57.

[0056] The demethanizer bottoms stream in line 64 is split into a bottoms reboil stream in the bottoms reboil line 69 and a net demethanizer bottoms stream in the net demethanizer bottoms line 72. The bottoms reboil stream is reboiled by heat exchange with the processed pyrolysis stream in line 57 in the demethanizer reboil exchanger 63 and returned to the demethanizer 40. The net demethanizer bottoms stream is heat-exchanged with the stripper overhead stream in line 36 in the heat exchanger 37 to heat the net demethanizer stream in line 72, thereby providing a heated net deethanizer stream in the demethanizer feed line 73. Then, the net demethanizer stream is fed to the deethanizer 74 and cools the stripper overhead stream in line 36.

[0057] The deethanizer 74 fractionates the net demethanizer bottoms stream in the demethanizer feed line 73 into a deethanizer overhead stream rich in C2 hydrocarbons in line 76 and a deethanizer bottoms stream rich in C3+ hydrocarbons in line 78. The demethanizer overhead stream in line 76 is cooled by the C2 splitter side stream taken from one side of the C2 splitter 80 in the C2 splitter side reboiler 81. The condensed overhead stream in line 76 is fed to the deethanizer receiver 77, where the overhead stream is separated into a liquid reflux stream that refluxes back to the deethanizer 74 and a net deethanizer overhead stream in line 83 that is fed to the C2 splitter 80.

[0058] The net deethanizer overhead stream in line 83 may include acetylene, which needs to be selectively hydrogenated to make it a suitable ethylene feed for the polymerization unit. The deethanizer overhead stream may be at an appropriate pressure for selective hydrogenation. The net deethanizer overhead stream in line 83 may be mixed with a hydrogen stream and processed in the acetylene selective hydrogenation reactor 87 to convert acetylene to ethylene, and then dried to provide a selectively hydrogenated deethanizer overhead stream in line 89.

[0059] In the selective hydrogenation reactor 87, selective hydrogenation of C2 - polyolefins occurs. A broad range of suitable operating pressures in the selective hydrogenation reactor 87 is from 276 kPag (40 psig) to 5516 kPag (800 psig) or from 345 kPag (50 psig) to 2069 kPag (300 psig). Relatively moderate temperatures between 25 °C (77 °F) and 350 °C (662 °F) or between 50 °C (122 °F) and 200 °C (392 °F) are typically employed. The vapor hourly space velocity of the reactants for the selective hydrogenation catalyst can be 30 h−1 or above 300 h−1, or above 15 h−1 up to 600 h−1. To avoid the undesired saturation of a large amount of monoolefins, the molar ratio of hydrogen to polyolefins in the material entering the selective hydrogenation catalyst bed is maintained between 0.75:1 and 1.8:1.

[0060] The selective hydrogenation catalyst can be any suitable catalyst capable of selectively hydrogenating acetylene in a C2 - hydrocarbon stream. Particularly preferred selective hydrogenation catalysts include 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 such as silica and alumina. Preferably, the selective hydrogenation catalyst can comprise copper and nickel metals supported on alumina. The selective hydrogenation effluent can leave the selective hydrogenation reactor 87 and enter the dryer 95. The dryer 95 provides a dry gaseous stream in the overhead line 89 of the selective hydrogenation deethanizer and can feed it to the C2 splitter tower 80.

[0061] The deethanization bottoms stream in line 78 provides a bottoms reboil stream in line 79, which is reboiled by heat exchange with the first compressed refrigerant stream in line 204 in the deethanizer bottom reboiler 201 and fed back to the deethanizer 74. The deethanization bottoms stream in line 78 also provides a net deethanization bottoms stream, which is fed to the depropanizer 18 in line 82. The deethanizer 74 operates at an overhead temperature of - 10 °C (15 °F) to - 32 °C (- 25 °F) and a bottoms gauge pressure of 1.1 MPa (160 psig) to 2.4 MPa (350 psig). The deethanizer bottom reboiler 201 can be in communication downstream of the first compressor on the first refrigerant side of the deethanizer bottom reboiler 201.

[0062] The selectively hydrogenated deethanizer overhead stream in C2 splitter feed line 89 is rich in C2 hydrocarbons and is fed to C2 splitter 80. C2 splitter 80 fractionates the deethanizer overhead stream in line 89 into a C2 splitter overhead stream rich in ethylene in C2 splitter overhead line 84 and a C2 splitter bottoms stream rich in ethane in C2 splitter bottoms line 86. The C2 splitter overhead stream in line 84 is condensed by heat exchange with the expanded and cooled second compressed propylene refrigerant stream in line 130 in C2 splitter condenser 131 to provide a condensed C2 splitter overhead stream in line 96 and a propylene refrigerant stream in line 129. The condensed C2 splitter overhead stream in line 95 is separated in C2 splitter receiver 132 into a liquid stream that refluxes to C2 splitter 80 and a small net vapor C2 splitter overhead stream of offgas in net C2 splitter overhead line 133, which net vapor C2 splitter overhead stream can be separated in demethanizer 40. A side liquid stream can be withdrawn as a product ethylene stream in line 88 from a side near the top of C2 splitter at a height below the reflux feed to the column. The C2 splitter bottoms stream in line 86 provides a reboiled C2 splitter bottoms stream in line 91. The reboiled C2 splitter bottoms stream is reboiled by heat exchange with the first propylene refrigerant from the first propylene refrigerant compressor 136 in line 134 in C2 splitter bottoms reboiler 95 to provide a reboiled C2 splitter bottoms stream that is fed back to C2 splitter 80 and a cooled first compressed propylene refrigerant stream. A knockout drum may be provided upstream of the first propylene refrigerant compressor 136 to remove liquid prior to compression.

[0063] The C2 separator bottoms stream in line 86 provides a net C2 separator bottoms stream rich in ethane that is recycled in line 93 and may be charged via line 52 to pyrolysis reactor 50 to produce more ethylene. The ethane recycle stream in line 93 may be heat exchanged with the processed pyrolysis stream 57 to cool the pyrolysis stream in pyrolysis cold box 58. In this way, the ethane recycle stream 93 can be heated before it is fed to pyrolysis reactor 50 ( Figure 1 not shown). C2 splitter 80 operates at a top temperature of -32 °C (-25 °F) to -60 °C (-75 °F) and a bottom gauge pressure of 690 kPag (100 psig) to 1.8 MPa (260 psig). C2 splitter 80 may alternatively use a heat pump compression scheme in which the operating temperature and pressure of C2 splitter 80 can be much lower, such as 0.55 MPag (80 psig) to 1 MPag (150 psig), and the top temperature is -65 °C (-85 °F) to -40 °C (-40 °F).

[0064] In the second propylene refrigerant compressor 138, the cooled first propylene refrigerant stream in line 134 that is cooled from the bottom stream of the boiling C2 separator is compressed to provide a second compressed propylene refrigerant stream. A knockout drum may be provided upstream of the second propylene refrigerant compressor 138 to remove liquid prior to compression. The second compressed propylene refrigerant stream in line 140 may be heat exchanged with the ethylene product stream in line 88 to heat and vaporize ethylene that may be withdrawn from the column as a liquid stream to provide a heated ethylene product stream and a cooled second compressed propylene refrigerant stream. The cooled and liquefied second propylene refrigerant compressor stream may be expanded in a throttle valve 142 to further cool the propylene refrigerant stream in line 130, thereby providing refrigerant to the C2 splitter condenser 131.

[0065] The depropanizer tower 18 may be in downstream communication with the pyrolysis reactor 50. The depropanizer tower 18 may receive at least two C3 feeds. The first C3 feed stream is the dehydrogenation charge stream in line 12, which is supplemented with a propane recycle stream from the net C3 splitter bottom line 127 in the first depropanizer tower feed line 13. The second C3 feed stream is the net deethanizer bottoms stream, which is fed to the depropanizer tower 18 in the net deethanizer bottom line 82. The dehydrogenation charge stream in line 12 may be fed into the depropanizer tower 18 after passing through the dehydrogenation cold box 16, or may be fed directly bypassing the dehydrogenation cold box. The first C3 feed stream in line 12 and the second C3 feed stream in line 82 are fractionated in the same depropanizer tower 18.

[0066] The first C3 feed is rich in propane. The second C3 feed will typically be rich in propylene and heavier hydrocarbons since the second C3 feed contains the pyrolysis effluent. Thus, the first C3 feed stream containing propane in line 12 can be supplemented with a recycle propane stream from the C3 splitter 120 in the bottoms line 127 of the net C3 separator to provide a first depropanizer feed stream in the depropanizer line 13 and fed to the first side 181 of the depropanizer 18. A second C3 feed stream including the deethanized pyrolysis stream in the bottoms line 82 of the net deethanizer is fed to the second side 182 of the depropanizer 18. The depropanizer 18 includes a dividing wall 90 and feeds the first depropanizer feed stream in the first depropanizer feed line 13 to the first side 181 and feeds the second depropanizer feed stream in the bottoms line 82 of the net deethanizer to the second side 182 of the dividing wall 90 of the same depropanizer 18. The dividing wall can be vertical and divides the top 18t of the depropanizer 18 into a first side 181 and a second side 182 and prevents the horizontal flow of the two feeds, thus preventing cross-contamination between the two feeds. The dividing wall 90 extends to the top 18t of the depropanizer 18 but is spaced from the bottom 18b of the depropanizer. The depropanizer 18 fractionates the first C3 feed stream in line 13 into a propane charge stream and a C4+ hydrocarbon stream and fractionates the second C3 stream in line 82 into a C3 pyrolysis stream and a C4+ hydrocarbon stream. A C3 stream from another source (such as from a condensate stripper) in line 19 can be fed to the second side 182 of the depropanizer 18.

[0067] The first depropanizer overhead stream is withdrawn in line 92 from the top 18t of the first side 181 of the depropanizer, condensed and a portion is refluxed back to the first side 181 of the column, while the net first depropanizer overhead stream in line 20 is withdrawn as a propane charge stream to the paraffin dehydrogenation reactor 14. The paraffin dehydrogenation reactor 14 can be in downstream communication with the depropanizer 18 and specifically with the first side 181 of the depropanizer. The second depropanizer overhead stream is withdrawn in line 94 from the top 18t of the second side 182 of the depropanizer, condensed, and a portion is refluxed back to the second side of the column, while the net second depropanizer overhead stream is withdrawn in line 96 as a C3 pyrolysis stream for feeding to the C3 splitter 120. The C3 splitter 120 can be in downstream communication with the depropanizer 18 and specifically with the second side 182 of the depropanizer 18. The C3 splitter 120 can also be in downstream communication with the dehydrogenation reactor 14 and the pyrolysis reactor 58. The dehydrogenation reactor 14 can also be in downstream communication with the C3 splitter 120. The overhead streams in lines 20 and 96 can be withdrawn at a temperature of 35°C to 65°C and a pressure of 1.5 MPa(g) to 1.9 MPa(g), which are the conditions in the overhead of the depropanizer 18.

[0068] The debutanizer 18 may also include an inner wall 100, which may be horizontal for separating the top 18t of the column from the bottom 18b. The inner wall 100 may be located below the dividing wall 90. The bottom edge of the dividing wall 90 may be sealed to the top of the inner wall 100 to further minimize the cross-mixing of the components of the two C3 feeds. The inner wall 100 prevents vertical flow in the column, but does not need to be a pressure-retaining wall. The peripheral well 102 collects liquid from above the inner wall 100 and transports the liquid to below the wall by guiding the liquid from above the inner wall to a location where it may leave the column 18 and return below the inner wall through a valved liquid line 104. Vapor from below the inner wall 100 may be transported through a vapor line 106, which has a control valve for controlling the vapor flow rate to above the inner wall. 25% to 40% of the trays in the debutanizer may be below the inner wall 100. The control valve on the vapor line 106 allows control of the vapor flow rate from below the inner wall 100 to above the inner wall on the first side 181 and the vapor flow rate from below the inner wall 100 to above the inner wall on the second side 182 of the dividing wall. The vapor line 106 is shown transporting vapor out of the column 18, but the transport may occur within the column.

[0069] Below the inner wall 100, a single C4+ stream is produced in the debutanizer bottoms line 108. A reboil stream is taken from the bottoms line 108, boiled, and returned to the column. The net debutanizer bottoms stream is taken in line 109 below the inner wall 100 and may be fed to a deisobutanizer 110. The bottom temperature of the column may be between 70 °C and 130 °C.

[0070] The debutanizer bottoms stream rich in C4+ hydrocarbons in line 109 may be fractionated in the deisobutanizer 110 to provide an overhead stream including butanes in line 112 and a bottoms stream including a pyrolysis oil stream containing C5+ hydrocarbons in the bottoms line 114. The deisobutanizer 110 may be in downstream communication with the bottoms line 108 of the debutanizer 18. The deisobutanizer overhead stream may be withdrawn from the deisobutanizer 110 in the deisobutanizer overhead line 112. The deisobutanizer overhead stream including mixed butanes in line 112 may be recovered and further sent for butadiene extraction (not shown) in a petrochemical facility or otherwise valorized through further processing.

[0071] The deisobutanizer bottoms stream taken from the bottom of the deisobutanizer 110 in line 114 is a pyrolysis oil rich in C5+ hydrocarbons, which may be suitable for downstream processing in a hydrotreating unit. The deisobutanizer 110 operates in a bottom temperature range of 140 °C (284 °F) to 190 °C (374 °F), preferably 140 °C (284 °F) to 170 °C (338 °F), and a top pressure range of 450 kPag (65 psig) to 700 kPag (100 psig).

[0072] The C3 splitter column 120 fractionates the C3 pyrolysis feed stream in line 96 and the C3 pyrolysis feed stream from the second side 182 of the depropanizer 18 in the net stripped dehydrogenation feed stream in line 42 into an acrylonitrile product stream in the C3 splitter overhead line 122 and a propane recycle stream in the C3 splitter bottoms line 124.

[0073] In a first embodiment, the C3 pyrolysis feed stream in line 96 and the net stripped dehydrogenation feed stream in line 42 are fed to the same C3 splitter fractionation column 120. The C3 pyrolysis feed stream in line 96 is fed to the C3 splitter fractionation column 120 at a height above the feed of the net stripped dehydrogenation feed stream in line 42 to the C3 splitter fractionation column. The acrylonitrile overhead stream is withdrawn from the top of the column in the overhead line 122 extending from the top of the C3 splitter column, condensed and part of it is refluxed back to the column as reflux, while the net acrylonitrile product stream in line 123 is withdrawn as the acrylonitrile product stream. In this embodiment, the overhead pressure is between 1.5 MPa (gauge) and 1.9 MPa. The condenser can be cooled by cooling water. A propane-rich propane recycle stream can be withdrawn in the C3 splitter bottoms line 124 and split into three streams. The first stream is the first bottoms reboil stream in line 125, which can be boiled by heat exchange with a low-pressure stream. The second stream is the second bottoms reboil stream in line 126, which can be boiled by heat exchange with the quench water stream in the quench water line 128, which is a waste heat stream obtainable from the circulating hot water in the pyrolysis unit and is used to quench the pyrolysis reactor effluent and / or other warm streams. The second reboil stream in line 126 can be boiled by the entire pyrolysis quench water stream in line 128. The quench water stream in line 128 can provide sufficient or almost sufficient heating requirements for the C3 splitter column 120. The remaining heat load can be provided by low-pressure steam or a heat pump compressor.

[0074] The third stream withdrawn from the bottoms stream 124 is the net propane recycle stream in line 127, which can be recycled to the first side 181 of the depropanizer 18 to remove C4+ hydrocarbons from the propane feed stream in line 12, which is charged to the paraffin dehydrogenation reactor 14 for dehydrogenation in the first depropanizer overhead stream in line 20 after fractionation. The acrylonitrile recovery from the propane-acrylonitrile splitter column 120 can be at least 99 wt% or at least 99.5 wt% purity.

[0075] Figure 2 An alternative embodiment of the C3 splitter column 120' using a heat pump compressor but operating at a lower pressure is shown. The elements having the same configuration as Figure 1 will have the same as Figure 2 in Figure 1the same reference numerals. Elements having different configurations from the corresponding elements in Figure 1 are denoted with the same reference numerals but with an apostrophe (') in Figure 2 . The configuration and operation of the embodiments of Figure 2 are substantially the same as those in Figure 1 .

[0076] The propylene top product stream is withdrawn in line 122' and fed to compressor drum 130. In compressor drum 130, a vapor top product stream extending from the top of the drum in drum top line 132 is separated from a top liquid product stream extending from the bottom of the drum in drum bottom line 134. The top vapor product stream in drum top line 132 is compressed in compressor 136 to provide a compressed vapor product stream in line 138. A return portion of the compressed vapor product stream is cooled, condensed (possibly by process heating), and returned to compressor drum 130 in line 139, while a reboil portion in line 140 is heat exchanged with a first boiling stream in first reboil line 125' in first reboiler 142 and refluxed to the column in line 144. A propylene product stream may be withdrawn in line 123'.

[0077] The top pressure in C3 splitter tower 120' is between 650 kPa and 1.3 MPa (g). The bottom temperature may be between 20 °C and 60 °C.

[0078] Figure 3 An alternative embodiment of C3 splitter tower 120" is shown which utilizes a pre-fractionation C3 splitter tower 150 in addition to the main C3 separator fractionation tower 120". Elements having the same configuration as those in Figure 2 will have the same reference numerals as those in Figure 3 . Elements having different configurations from the corresponding elements in Figure 2 will have the same reference numerals but with a double apostrophe (") in Figure 2 . The configuration and operation of the embodiments of Figure 3 are substantially the same as those in Figure 3 are substantially the same as those in Figure 2 .

[0079] First, in the debutanizer C3 splitter tower 150, the net stripped dehydrogenation feed stream in the debutanizer stripper bottom line 42" provides a propylene-rich debutanizer feed stream in the debutanizer top line 152 and a debutanizer bottom feed stream 154 rich in propane. The debutanizer 150 can be in communication downstream of the dehydrogenation reactor 14. The debutanizer feed stream in the top line 152 is condensed, and a portion is refluxed back to the tower as reflux, while the propylene-rich net debutanizer feed stream in the net top line 153 is fed to the main C3 splitter tower 120". The reboiler feed stream in the line 155 of the debutanizer C3 splitter tower 150 is boiled by using the waste heat feed stream available in the quench water feed stream, so as to maximize the purity of the propylene-rich feed stream in the line 153. In this embodiment, the top pressure in the debutanizer C3 splitter tower 150 is between 1.5 MPa (gauge) and 1.9 MPa. The condenser can be cooled by cooling water. The debutanizer bottom feed stream rich in propane can be withdrawn in the line 154 and split into two feed streams. The first feed stream is the first bottom reboiler feed stream in the line 155, which can be boiled by heat exchange with the quench water stream and / or other warm feed streams in the line 128". The second feed stream withdrawn from the debutanizer bottom feed stream 154 is the net propane recycle feed stream in the line 127", which can be recycled to the propane feed stream in the line 12. The propane feed stream is charged to the paraffin dehydrogenation reactor 14 for dehydrogenation after fractionation on the first side 181 of the depropanizer 18 to remove C4+ hydrocarbons. The net propane recycle feed stream in the line 127" can have no more than 1 mol% of propylene. The bottom temperature of the debutanizer can be between 50 °C and 60 °C.

[0080] Both the propylene-rich debutanizer stream in line 153 and the C3 pyrolysis stream in the net second depropanizer overhead line 96 are fractionated in the main C3 splitter tower 120". The main C3 splitter tower 120" can be connected downstream of the debutanizer tower 150. The C3 pyrolysis stream in the net second depropanizer overhead line 96 can be fed to the main C3 splitter tower 120" at a higher elevation than the feed of the debutanizer stream in line 153. The propylene overhead stream is withdrawn in line 122 and fed to the compressor drum 130. In the compressor drum 130, the vapor overhead stream extending from the top of the drum in the drum overhead line 132 is separated from the overhead liquid stream extending from the bottom of the drum in the drum bottom line 134. The overhead vapor stream in the drum overhead line 132 is compressed in the compressor 136 to provide a compressed vapor stream in line 138. The return stream of the compressed vapor stream is cooled and returned to the compressor drum 130 in line 139, while the reboil stream in line 140 is heat-exchanged with the C3 splitter bottoms reboil stream in the reboil line 125' in the reboiler exchanger 142 and refluxed to the tower in line 144. The propylene product stream is withdrawn in line 123'. The main C3 splitter tower 120" uses the waste heat in the quench water stream to reboil the boiling stream in line 155 to perform residual purification on the propylene product stream, which is required after maximizing purification in the debutanizer C3 splitter tower 150.

[0081] The main bottoms stream in line 124" is withdrawn from the bottom of the main C3 splitter tower 120" and split into two streams. The first stream is the bottoms reboil stream in the reboil line 125', which can be boiled by heat-exchanging with the reboil stream of the compressed vapor stream in line 140. The second stream is the net main C3 splitter bottoms stream in line 141, which can have no more than 2 mol% propylene or even less, depending on the degree of purification achieved in the debutanizer C3 splitter tower 150. The net main C3 separator stream can be recycled to the debutanizer C3 splitter tower 150 for debutanization together with the net stripper dehydrogenation stream in the net stripper bottoms line 42". The net main C3 stream in line 141 can be fed to the debutanizer tower 150 at a lower elevation than the net stripper dehydrogenation stream in the net stripper bottoms line 42".

[0082] The overhead pressure in the main C3 splitter tower 120" can be between 650 kPa(g) and 1.3 MPa(g). The bottom temperature can be between 20 °C and 60 °C.

[0083] Figure 4Shows an alternative embodiment of the C3 splitter tower 120", which in addition to the main C3 splitter fractionator also utilizes a debutanizer C3 splitter tower 150#, and in addition to debutanizing both the C3 pyrolysis feed stream in the net second depropanizer overhead line 96# and the net stripped dehydrogenation feed stream in the stripped bottoms line 42" together in the debutanizer C3 splitter tower 150#. Having the same configuration as Figure 3 in Figure 4 the components will have the same reference numerals as Figure 3 in Figure 3 Components having a different configuration from the corresponding components in Figure 4 will have the same reference numerals but will be denoted with a hash symbol (#). Figure 4 The configuration and operation of the embodiment of Figure 3 are substantially the same as those in

[0084] except for these exceptions.

[0084] The C3 pyrolysis feed stream in the net second depropanizer overhead line 96# and the net stripped dehydrogenation feed stream in the stripped bottoms line 42" are debutanized together in the debutanizer C3 splitter tower 150#. In an embodiment, the net second depropanizer overhead line 96# can be fed to the debutanizer tower at a height above the feed of the net stripped dehydrogenation feed stream in the stripped bottoms line 42" to the tower. Instead of fractionating the net main C3 feed stream in line 141#, the net main C3 feed stream can be added to the net propane recycle stream in line 127# to provide a common net propane recycle stream to be dehydrogenated in the paraffin dehydrogenation reactor 14. Both towers 150# and 120" produce a net bottoms stream with very little propylene, so the common net propane recycle stream formed by adding the net main C3 feed stream in line 141# to the net propane recycle stream in line 127# consists essentially of propane.

[0085] Embodiment

[0086] A cost analysis was performed on the disclosed integrated method, in which a common C3 splitter tower system is used to fractionate propylene from propane in the feeds of a stripped dehydrogenated C3 stream and a pyrolyzed C3 stream. This analysis was performed for 500 thousand tons of propylene per year for the dehydrogenation unit and 500 thousand tons of propylene and 1500 thousand tons of ethylene per year for the pyrolysis unit.

[0087] It was found that the energy usage of using two C3 splitter tower systems (one for the dehydrogenation unit and one for the pyrolysis unit) is the same as the energy usage of using one C3 splitter tower system. However, it was found that the integrated method saves 25% to 30% in tray count and tower height, resulting in a significant 15% reduction in capital costs, which is equivalent to a savings of $5M.

[0088] Specific implementation

[0089] While the following is described in connection 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.

[0090] A first embodiment of the present disclosure is a method for separating propylene from propane, the method comprising: fractionating a C3 pyrolysis feed stream and a dehydrogenation feed stream into a propylene product stream and a propane recycle stream; and dehydrogenating the propane recycle stream. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: feeding the C3 pyrolysis feed stream to a fractionation column above the dehydrogenation feed stream. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: stripping the dehydrogenation feed stream of light gases and then fractionating with the C3 pyrolysis feed stream. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: withdrawing a propane stream from the bottom of the fractionation column and reboiling a first portion by heat exchange with LP steam and a second portion by heat exchange with hot quench water. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: condensing the propylene product stream by heat exchange with cooling water. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, wherein the overhead stream from the fractionation column is separated into an overhead vapor stream and an overhead liquid stream; compressing the overhead vapor stream to provide a compressed vapor stream and reboiling the bottom stream from the fractionation column by heat exchange with the compressed vapor stream. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: fractionating the dehydrogenation feed stream in a debutanizer to provide a debutanized stream and the propane recycle stream, and fractionating the debutanized stream in a main column. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: fractionating the C3 pyrolysis feed stream in the main column to provide a propylene product stream and a main bottom stream. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: fractionating the main column bottoms stream in the debutanizer. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further comprise: fractionating the debutanized stream in the main column to provide a propylene product stream and a main bottom stream. Embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, wherein the debutanizer is operated at a higher overhead pressure than the main fractionation column.The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, wherein the overhead stream from the main fractionation column is separated into a main vapor stream and a main overhead liquid stream; the main vapor stream is compressed to provide a compressed main vapor stream, and the main fractionation bottoms stream from the main fractionation column is reboiled by heat exchange with the compressed vapor stream. The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further include: fractionating the C3 pyrolysis stream in the prefractionation column. The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the first embodiment in this paragraph, and the embodiments further include: recovering the main fractionation bottoms stream as the propane recycle stream.

[0091] A second embodiment of the present disclosure is a method for separating propylene from propane, the method comprising: fractionating a dehydrogenation stream into a propylene stream and a propane recycle stream in a fractionation column; fractionating a C3 pyrolysis stream into a propylene stream and a propane recycle stream; and dehydrogenating the propane recycle stream. The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the second embodiment in this paragraph, wherein the fractionation column is a prefractionation column, and fractionating the propylene stream from the overhead of the prefractionation column in a main fractionation column to provide the propylene product stream. The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the second embodiment in this paragraph, and the embodiments further include: fractionating the C3 pyrolysis stream in the prefractionation column. The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the second embodiment in this paragraph, and the embodiments further include: fractionating the C3 pyrolysis stream in the main fractionation column.

[0092] A third embodiment of the present disclosure is an apparatus for separating propylene from propane, the apparatus comprising: a fractionation column in downstream communication with a dehydrogenation reactor and a pyrolysis reactor; the dehydrogenation reactor in downstream communication with the fractionation column. The embodiments of the present disclosure are one, any, or all of the foregoing embodiments in this paragraph to the third embodiment in this paragraph, and the embodiments further include: a prefractionation column in downstream communication with the dehydrogenation reactor; and the main fractionation column in downstream communication with the prefractionation column.

[0093] Although no further elaboration is provided, it is believed that those skilled in the art can make the most of the present disclosure by using the foregoing description and can easily determine the basic features of the present disclosure without departing from the spirit and scope of the invention, and various changes and modifications can be made to the present disclosure and adapted to various uses and conditions. Therefore, the foregoing preferred specific embodiments should be understood as being merely illustrative and not limiting the remainder of the present disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0094] In the foregoing, all temperatures are shown in degrees Celsius and all parts and percentages are by weight, unless otherwise indicated.

Claims

1. A method for separating propylene from propane, the method comprising: fractionating a C3 pyrolysis stream and a dehydrogenation stream into a propylene product stream and a propane recycle stream; and dehydrogenating the propane recycle stream.

2. The method according to claim 1, wherein the method further comprises: Feeding the C3 pyrolysis stream to a fractionation tower above the dehydrogenation stream.

3. The method according to claim 1, the method further comprising: Stripping the dehydrogenation stream of light gases and then fractionating with the C3 pyrolysis stream.

4. The method according to claim 1, wherein the method further comprises: Removing a propane stream from the bottom of the fractionation tower, and reboiling a first portion by heat exchange with LP steam and a second portion by heat exchange with water.

5. The method according to claim 4, the method further comprising: Condensing the propylene product stream by heat exchange with cooling water.

6. The method according to claim 1, wherein a top stream from the fractionation tower is separated into a top vapor stream and a top liquid stream; compressing the top vapor stream to provide a compressed vapor stream, and reboiling a bottom stream from the fractionation tower by heat exchange with the compressed vapor stream.

7. The method according to claim 1, the method further comprising: Fractionating the dehydrogenation stream in a prefractionation tower to provide a prefractionated stream and the propane recycle stream, and fractionating the prefractionated stream in a main tower.

8. The method according to claim 7, wherein the method further comprises: Fractionating the C3 pyrolysis stream in the main tower to provide a propylene product stream and a main bottom stream.

9. An apparatus for separating propylene from propane, the apparatus comprising: a fractionation tower in downstream communication with a dehydrogenation reactor and a pyrolysis reactor; the dehydrogenation reactor in downstream communication with the fractionation tower.

10. The device according to claim 9, the device further comprising: a prefractionation tower in downstream communication with the dehydrogenation reactor; and the fractionation tower in downstream communication with the prefractionation tower.

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