Integration of a gaseous olefin stream into a steam cracker

Abstract

A method for producing light olefins includes introducing an olefinic stream into a distillation unit, and distilling the olefinic stream to obtain a distillate and a bottoms. The distillate includes C2 + hydrocarbons, and the bottoms includes C3 + hydrocarbons. The distillate is introduced to a separation unit, and the bottoms and hydrogen are introduced to a hydrogenation unit. The bottoms is hydrogenated, and the hydrogenated stream and a feed stream are introduced into a cracking unit. The feed stream includes propane, butane, naphtha, or combinations thereof. The hydrogenated stream and the feed stream are cracked. The cracked stream includes ethylene, propylene, hydrogen, C4 + hydrocarbons, or combinations thereof. The cracked stream is introduced into the separation unit, and the distillate and the cracked stream are separated to obtain an ethylene stream, a propylene stream, a hydrogen stream, and a C4 + hydrocarbon stream.

Description

INTEGRATION OF A GASEOUS OLEFIN STREAM INTO A STEAM CRACKERCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 665,818 filed June 28, 2024, the entire disclosure of which is hereby incorporated by reference.BACKGROUND

[0002] Light olefin production technology has been dominated by steam cracking of light hydrocarbon feedstocks such as ethane, propane, butane and naphtha. In the steam cracking process, the feedstocks are exposed to high temperatures (> 760 °C), which cracks the feedstocks to a desired product slate of ethylene, propylene, crude C4, pygas, and BTX- streams. The product distribution is dependent on the selected feedstock and operating conditions, such as cracker coil outlet temperature. The two high -volume products produced by a steam cracker, ethylene and propylene, are normally produced at a propylene to ethylene (P / E) ratio < 0.6 for a cracker based on liquid feedstock like naphtha. Crackers based on gaseous feedstock like ethane or propane have lower P / E ratios than crackers based on liquid feedstocks. Ethylene production is typically favored over propylene production and crackers aim to minimize the P / E ratio for a given feedstock, whilst considering the technical and reliability constraints of the cracker.BRIEF SUMMARY

[0003] With a societal drive for steam crackers to become more circular by replacing fossil feedstocks with waste or bio-based feedstocks, alternative means for producing olefins have gained interest. One such route is the production of olefins via syngas conversion. A commercial example of this is the conversion of the CO, H2, and some of the CO2 in synthesis gas to methanol which is subsequently converted to light olefins (C2-C4) in a process known as Methanol-to-Olefins (MTO). Alternative examples are the direct conversion of syngas-to- olefins by means of a bifunctional catalyst comprising a methanol synthesis function and an MTO function. The synthesis gas can be produced from a circular source such as biomass, waste plastics, municipal solid waste or cracker methane off-gas and therefore has a highpotential for producing circular olefins and decarbonizing the chemicals. Embodiments disclosed and described herein address these and other concerns.

[0004] According to one or more embodiments, a method for producing light olefins, the method comprising: introducing an olefinic gas stream into a feed distillation unit; distilling the olefinic gas stream in the feed distillation unit to obtain a distillate stream and a bottoms stream, wherein the distillate stream comprises C2+hydrocarbons and the bottoms stream comprises Cs+hydrocarbons; introducing the distillate stream to a separation unit; introducing the bottoms stream and a hydrogen stream to a feed hydrogenation unit; hydrogenating the bottoms stream in the feed hydrogenation unit to obtain a hydrogenated stream; introducing the hydrogenated stream and a feed stream into a cracking unit, wherein the feed stream comprises, propane, butane, naphtha, or combinations thereof; cracking the hydrogenated stream and the feed stream in the cracking unit to obtain a cracked stream, wherein the cracked stream comprises ethylene, propylene, hydrogen, C4+hydrocarbons, or combinations thereof; introducing the cracked stream into the separation unit; and separating the distillate stream and the cracked stream in the separation unit to obtain an ethylene product stream, a propylene product stream, a hydrogen product stream, and a C4+hydrocarbon product stream.

[0005] Additional features and advantages will be set forth in the detailed description, which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description, which follows, the claims, as well as the appended drawings.

[0006] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0007] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0008] FIG. 1 illustrates a system for integrating a gaseous olefin stream into a cracking system according to embodiments disclosed and described herein; and

[0009] FIG. 2 is a graph showing the effect on P / E ratio for various streams and distillation schemes for the system shown in FIG. 1.DETAILED DESCRIPTION

[0010] One of the key challenges with synthetic olefin streams produced using a syngas route, is that they are typically rich in propylene and leaner in ethylene, with P / E ratios ranging from 0.8 to 2.5, this is in contrast to conventional liquid cracker operation where the P / E ratio is typically < 0.6 or gas-based crackers where P / E is much lower than 0.6. This difference in P / E ratio may limit the ability to integrate the synthetic olefin stream with existing assets for olefin separation, and may negatively impact the capital intensity of synthetic olefins, as additional greenfield olefin separation capacity would be required to obtain polymer-grade monomers. Additionally, ethylene typically commands a higher selling price and therefore there is also a production incentive to lowering the P / E ratio. In the production of circular olefins, lowering the P / E ratio allows for increased circular yield directly to ethylene. Furthermore, it allows for higher amounts of synthetic olefins to be integrated into an existing asset, thereby increasing the proportion of circular product. However, by using the methods and processes disclosed and described herein, olefinic gas streams may be integrated into cracking systems, thereby reducing equipment and operating costs, as well as making olefin processing more circular.

[0011] Embodiments disclosed herein include a process whereby an olefinic gas stream can be incorporated into an existing cracking unit by implementing a feed preparation system that primarily includes a feed distillation unit and a feed hydrogenation unit. The feed preparation system can be designed and / or operated in such a manner that it allows one to extract a light fraction containing high value components (such as ethylene and the like) to an existingseparation unit within the cracker while routing a heavier cut to a hydrogenation unit and then to one or more cracking furnaces in the cracking unit. By manipulating the bottoms fraction from the feed distillation unit that is sent to the feed hydrogenation unit and that is subsequently sent to the cracking furnaces, the cracker P / E ratio can be tailored to be economically desirable while remaining within a conventional cracker’s operating limits. Hydrogenation of the heavy cut from the distillation unit can be performed with hydrogen from the separation unit with known industrial catalysts. Alternatively, hydrogenation can be performed with external H2 made on-purpose by means known to one skilled in the art or H2 that is available in an integrated petrochemical facility. Hydrogenation of unsaturated components has the benefit of increasing ethylene and propylene yields of the crackers. Additionally, due to the highly exothermic nature of hydrogenation, the heat generated from the feed hydrogenation unit can be used to provide heat needed for the reboiler of the feed distillation column.

[0012] Embodiments of systems that integrate an olefinic gas stream into a conventional liquid or mixed feed (a combination of liquid and gas (such as ethane and propane) or a mixed gas cracker) cracking unit will now be described with reference to FIG. 1. Embodiments of the cracking system 100 depicted in FIG. 1 include a feed distillation unit 110, a feed hydrogenation unit 120, a cracking unit or furnace 130, and a separation unit 150.

[0013] Olefinic gas streams as described herein can be derived from synthesis gas-based processes, including, but not limited to, direct conversion of syngas to olefins and integrated methanol synthesis and methanol-to-olefins. The synthesis gas can be produced from a carbonaceous feedstock, such as biomass, waste plastics, municipal solid waste or methane derived from steam cracking of hydrocarbons (cracker methane).

[0014] An olefinic gas stream originating from an MTO -based process 101 is introduced into the feed distillation unit 110. The olefinic gas stream 101 comprises methane (CH4), C2 to C4 olefins, and C2 to C4 paraffins. The stream may contain trace amounts of CO2, CO, H2, or oxygenates such as methanol or dimethyl ether (DME). The olefinic gas stream 101 may, in embodiments, have a P / E ratio that is greater than 0.6, such as greater than or equal to 0.8, greater than or equal to 1.0, greater than or equal to 1.2, greater than or equal to 1.4, greater than or equal to 1.6, greater than or equal to 1.8, greater than or equal to 2.0, greater than or equal to 2.2, or greater than or equal to 2.4. In embodiments, the olefinic gas stream 101 hasa P / E ratio that is greater than 0.6 and less than 3.0, such as greater than or equal to 0.8 and less than or equal to 2.8, greater than or equal to 1.0 and less than or equal to 2.6, greater than or equal to 1.2 and less than or equal to 2.4, greater than or equal to 0.8 and less than or equal to 2.4, greater than or equal to 1.0 and less than or equal to 2.4, or greater than or equal to 1.0 and less than or equal to 2.2.

[0015] Examples of two such olefinic gas streams 101 (labeled MTO-1 and MTO-2), produced through different process conditions and configurations, are shown in Table 1. The data shown in Table 1 for stream MTO-1 was referenced from Yarulina, I., Engineering Selective and Stable Methanol to Olefins Catalysts, PhD Thesis, TU Delft (2017) and the data shown in Table 1 for stream MTO-2 was referenced from International Publication Number WO 2022 / 182592A1.

[0016] Table 1

[0017] Within the feed distillation unit 110 the olefinic gas stream 101 is distilled into a distillate stream 114 and a bottoms stream 112. The distillate stream 114 comprises ethylene and the bottoms stream 112 comprises Cs+hydrocarbons. In embodiments, the distillatestream 114 comprises greater than 98.0 wt.% of the C2' components that were present in the olefinic gas stream 101, such as greater than or equal to 98.5 wt.% of the Ci components that were present in the olefinic gas stream 101, greater than or equal to 99.0 wt.% of the Ci components that were present in the olefinic gas stream 101, or greater than or equal to 99.5 wt.% of the C2' components that were present in the olefinic gas stream 101. In one or more embodiments, the bottoms stream 112 comprises less than 1.0 wt.% C2 hydrocarbons, such as less than or equal to 0.8 wt.% C2 hydrocarbons, less than or equal to 0.6 wt.% C2' hydrocarbons, less than or equal to 0.4 wt.% C2' hydrocarbons, less than or equal to 0.2 wt.% C2' hydrocarbons, or less than or equal to 0.1 wt.% C2' hydrocarbons. In embodiments, the bottoms stream 112 is free of C2' hydrocarbons.

[0018] In embodiments, a condenser within the feed distillation unit 110 may be operated at temperatures greater than 25 °C, such as greater than or equal to 27 °C, greater than or equal to 30 °C, greater than or equal to 32 °C, greater than or equal to 35 °C, greater than or equal to 37 °C, or greater than or equal to 40 °C. In embodiments, the condenser within the feed distillation unit 110 may be operated at a temperature that is greater than 25 °C and less than or equal to 40 °C, such as greater than or equal to 27 °C and less than or equal to 37 °C, or greater than or equal to 30 °C and less than or equal to 35 °C. A reboiler within the feed distillation unit 110 may be operated at a temperature that is greater than or equal to 90 °C and less than or equal to 130 °C, such as greater than or equal to 95 °C and less than or equal to 130 °C, greater than or equal to 100 °C and less than or equal to 130 °C, greater than or equal to 105 °C and less than or equal to 130 °C, greater than or equal to 110 °C and less than or equal to 130 °C, greater than or equal to 115 °C and less than or equal to 130 °C, greater than or equal to 120 °C and less than or equal to 130 °C, greater than or equal to 125 °C and less than or equal to 130 °C. Operating the feed distillation unit 110 at the above temperatures means standard cooling and heating sources like cooling water or low / medium pressure steam can be used. There is thus no need for complex refrigeration systems for cooling in some embodiments.

[0019] After the olefinic gas stream 101 is separated into the distillate stream 114 and the bottoms stream 112 in the feed distillation unit 110, the distillate stream 114 exits the feed distillation unit 110 and is introduced to the separation unit 150, which will be discussed in more detail below. The bottoms stream 112 exits the feed distillation unit 110 and is introduced into the feed hydrogenation unit 120. By manipulating the distillation fractionfrom the feed distillation unit 110 that is sent to the feed hydrogenation unit 120 and the distillation fraction that is sent to the separation unit 150, the P / E ratio can be tailored to be economically desirable while remaining within the operating limits of the cracking unit 130 and separation unit 150.

[0020] At the feed hydrogenation unit 120, the bottoms stream 112 is combined with a hydrogen stream 102. At typical pressure and temperature operating conditions of the feed distillation column, the temperature of the bottoms stream 112 is comparable to temperatures used in known olefinic hydrogenation. Accordingly, known hydrogenation processes and hydrogenation units can be used to hydrogenate the bottoms stream 112. In the feed hydrogenation unit 120 hydrogen (H2) from the hydrogen stream 102 reacts with hydrocarbons in the bottoms stream 112 to hydrogenate the hydrocarbons from the bottoms stream 112, such as by converting olefins to paraffins, to make a hydrogenated stream 122 that exits the feed hydrogenation unit 120.

[0021] The hydrogenation reactions that occur in the feed hydrogenation unit 120 between the hydrogen stream 102 and the hydrocarbons in the bottoms stream 112 are exothermic reactions that generate a considerable amount of heat. Therefore, according to one or more embodiments, heat from the feed hydrogenation unit 120 is captured and sent as heat stream 162 to the feed distillation unit 110 and can be used in the distillation of olefinic gas stream 101. By redirecting the heat stream 162 from the feed hydrogenation unit 120 to the feed distillation unit 110, the cost of operating the feed distillation unit 110 may be decreased and the feed distillation unit 110 can operate with a lower carbon footprint by not requiring heat from combustible sources. In one or more embodiments, the heat generated by the exothermic hydrogenation reactions in the feed hydrogenation unit 120 is sufficient to run the reboiler in the feed distillation unit 110 without requiring an additional heat source. Thus, in embodiments the feed distillation unit 110 and the feed hydrogenation unit 120 can operate together to be energy neutral. In other embodiments, the heat generated by the hydrogenation reactions in the feed hydrogenation unit 120 exceeds the heat required to operate the reboiler in the feed distillation unit 110 and the feed hydrogenation unit 120 can supply heat to operate the feed distillation unit 110 and be a heat source for other operations. In some embodiments heat can be exchanged between the hydrogenation reactor 120 and the reboiler of the distillation column 120 via a heat transfer medium like condensing / evaporating water, or another suitable heat carrier.

[0022] The hydrogenated stream 122 exits the feed hydrogenation unit 120 and is introduced into the cracking unit or furnaces 130. The hydrogenated stream 122 comprises saturated hydrocarbons (Cs+) from the bottoms stream 112. Hydrogenation of unsaturated components in the bottoms stream 112 may increase the ethylene and propylene yields when the hydrogenated stream 122 is fed to the cracking unit or furnaces 130. Accordingly, in embodiments, the amount of the hydrogenated stream 122 that is fed to the cracking unit 130 may be controlled. In the cracking unit 130, the hydrogenated stream 122 and the feed stream 103 are cracked to obtain a cracked stream 132. The cracked gas stream 132 comprises ethylene, methane, propylene, hydrogen, C4+hydrocarbons, or combinations thereof and is ultimately sent to the separation unit 150. As described in more detail below, the cracking unit 130 can be a gas cracking unit, a liquid cracking unit, or a liquid -gas cracking unit. It should be understood that any gas cracking unit, liquid cracking unit, or liquid-gas cracking unit suitable to convert hydrocarbons to olefins may be used. In embodiments, the cracking unit can be a conventional off-gas fired cracking unit, a hydrogen-fired cracking unit, an electrified cracking unit or any combination thereof.

[0023] References for gas cracking units (furnaces), liquid cracking units (furnaces), can be found in Zahra Gholami et al., “A Review on the Production of Light Olefins Using Steam Cracking of Hydrocarbons” 14, no. 23 (n.d.): 8190. and SM Sadrameli, “Thermal / Catalytic Cracking of Hydrocarbons for the Production of Olefins: A State -of-the- Art Review I: Thermal Cracking Review” 140 (n.d.): 102-15.

[0024] In embodiments, the cracked stream 132 typically has a P / E ratio that is less than 0.60, such as less than or equal to 0.55, less than or equal to 0.50, less than or equal to 0.45, less than or equal to 0.40, less than or equal to 0.35, less than or equal to 0.30, less than or equal to 0.25, less than or equal to 0.20, less than or equal to 0.15, less than or equal to 0.10, or less than or equal to 0.05. In one or more embodiments, the cracked stream 132 has a P / E ratio that is greater than or equal 0.01 and less than or equal to 0.60, such as greater than or equal to 0.05 and less than or equal to 0.60, greater than or equal to 0.10 and less than or equal to 0.60, greater than or equal to 0.15 and less than or equal to 0.60, greater than or equal to 0.20 and less than or equal to 0.60, greater than or equal to 0.25 and less than or equal to 0.60, greater than or equal to 0.30 and less than or equal to 0.60, greater than or equal to 0.35 and less than or equal to 0.60, greater than or equal to 0.40 and less than or equal to 0.60, greater than or equal to 0.45 and less than or equal to 0.60, greater than or equal to 0.50 andless than or equal to 0.60, greater than or equal to 0.55 and less than or equal to 0.60, greater than or equal 0.01 and less than or equal to 0.55, greater than or equal to 0.05 and less than or equal to 0.55, greater than or equal to 0.10 and less than or equal to 0.55, greater than or equal to 0.15 and less than or equal to 0.55, greater than or equal to 0.20 and less than or equal to 0.55, greater than or equal to 0.25 and less than or equal to 0.55, greater than or equal to 0.30 and less than or equal to 0.55, greater than or equal to 0.35 and less than or equal to 0.55, greater than or equal to 0.40 and less than or equal to 0.55, greater than or equal to 0.45 and less than or equal to 0.55, greater than or equal to 0.50 and less than or equal to 0.55, greater than or equal 0.01 and less than or equal to 0.50, greater than or equal to 0.05 and less than or equal to 0.50, greater than or equal to 0.10 and less than or equal to 0.50, greater than or equal to 0.15 and less than or equal to 0.50, greater than or equal to 0.20 and less than or equal to 0.50, greater than or equal to 0.25 and less than or equal to 0.50, greater than or equal to 0.30 and less than or equal to 0.50, greater than or equal to 0.35 and less than or equal to 0.50, greater than or equal to 0.40 and less than or equal to 0.50, greater than or equal to 0.45 and less than or equal to 0.50, greater than or equal 0.01 and less than or equal to 0.45, greater than or equal to 0.05 and less than or equal to 0.45, greater than or equal to 0. 10 and less than or equal to 0.45, greater than or equal to 0.15 and less than or equal to 0.45, greater than or equal to 0.20 and less than or equal to 0.45, greater than or equal to 0.25 and less than or equal to 0.45, greater than or equal to 0.30 and less than or equal to 0.45, greater than or equal to 0.35 and less than or equal to 0.45, greater than or equal to 0.40 and less than or equal to 0.45, greater than or equal 0.01 and less than or equal to 0.40, greater than or equal to 0.05 and less than or equal to 0.40, greater than or equal to 0.10 and less than or equal to 0.40, greater than or equal to 0.15 and less than or equal to 0.40, greater than or equal to 0.20 and less than or equal to 0.40, greater than or equal to 0.25 and less than or equal to 0.40, greater than or equal to 0.30 and less than or equal to 0.40, greater than or equal to 0.35 and less than or equal to 0.40, greater than or equal 0.01 and less than or equal to 0.35, greater than or equal to 0.05 and less than or equal to 0.35, greater than or equal to 0.10 and less than or equal to 0.35, greater than or equal to 0.15 and less than or equal to 0.35, greater than or equal to 0.20 and less than or equal to 0.35, greater than or equal to 0.25 and less than or equal to 0.35, greater than or equal to 0.30 and less than or equal to 0.35, greater than or equal 0.01 and less than or equal to 0.30, greater than or equal to 0.05 and less than or equal to 0.30, greater than or equal to 0.10 and less than or equal to 0.30, greater than or equal to 0.15 and less than or equal to 0.30, greater than or equal to 0.20 and less than or equal to 0.30, greaterthan or equal to 0.25 and less than or equal to 0.30, greater than or equal 0.01 and less than or equal to 0.25, greater than or equal to 0.05 and less than or equal to 0.25, greater than or equal to 0.10 and less than or equal to 0.25, greater than or equal to 0.15 and less than or equal to 0.25, greater than or equal to 0.20 and less than or equal to 0.25, greater than or equal 0.01 and less than or equal to 0.20, greater than or equal to 0.05 and less than or equal to 0.20, greater than or equal to 0.10 and less than or equal to 0.20, greater than or equal to 0.15 and less than or equal to 0.20, greater than or equal 0.01 and less than or equal to 0.15, greater than or equal to 0.05 and less than or equal to 0. 15, greater than or equal to 0. 10 and less than or equal to 0.15, greater than or equal 0.01 and less than or equal to 0.10, greater than or equal to 0.05 and less than or equal to 0.10, or greater than or equal 0.01 and less than or equal to 0.05.

[0025] In embodiments where the cracking unit 130 is a gas cracking unit, the feed stream 103 the feed stream 103 is a gaseous stream that comprises ethane, propane, butane, or combinations thereof. In embodiments, the gaseous feed stream 103 can be a fresh gas feed or the gaseous feed stream can be ethane and propane containing gas generated from naphtha cracking that are recycled to the gas cracking unit 130. In embodiments, unconverted ethane and propane can also be recycled to the gas cracking unit 130. Thus, in one or more embodiments, the gas cracking unit is a propane cracking unit. In embodiments where the cracking unit 130 is a gas cracking unit, the distillation unit 110 may be operated to provide a hydrogenated stream 122 suitable for a gas cracking unit. In such embodiments, the distillation unit 110 is operated at a bottoms to feed ratio that is greater than or equal to 0.25 and less than or equal to 0.75, such as greater than or equal to 0.30 and less than or equal to 0.75, greater than or equal to 0.35 and less than or equal to 0.75, greater than or equal to 0.40 and less than or equal to 0.75, greater than or equal to 0.45 and less than or equal to 0.75, greater than or equal to 0.50 and less than or equal to 0.75, greater than or equal to 0.55 and less than or equal to 0.75, greater than or equal to 0.60 and less than or equal to 0.75, greater than or equal to 0.65 and less than or equal to 0.75, greater than or equal to 0.70 and less than or equal to 0.75, greater than or equal to 0.25 and less than or equal to 0.70, greater than or equal to 0.30 and less than or equal to 0.70, greater than or equal to 0.35 and less than or equal to 0.70, greater than or equal to 0.40 and less than or equal to 0.70, greater than or equal to 0.45 and less than or equal to 0.70, greater than or equal to 0.50 and less than or equal to 0.70, greater than or equal to 0.55 and less than or equal to 0.70, greater than or equal to 0.60and less than or equal to 0.70, greater than or equal to 0.65 and less than or equal to 0.70, greater than or equal to 0.25 and less than or equal to 0.65, greater than or equal to 0.30 and less than or equal to 0.65, greater than or equal to 0.35 and less than or equal to 0.65, greater than or equal to 0.40 and less than or equal to 0.65, greater than or equal to 0.45 and less than or equal to 0.65, greater than or equal to 0.50 and less than or equal to 0.65, greater than or equal to 0.55 and less than or equal to 0.65, greater than or equal to 0.60 and less than or equal to 0.65, greater than or equal to 0.25 and less than or equal to 0.60, greater than or equal to 0.30 and less than or equal to 0.60, greater than or equal to 0.35 and less than or equal to 0.60, greater than or equal to 0.40 and less than or equal to 0.60, greater than or equal to 0.45 and less than or equal to 0.60, greater than or equal to 0.50 and less than or equal to 0.60, greater than or equal to 0.55 and less than or equal to 0.60, greater than or equal to 0.25 and less than or equal to 0.55, greater than or equal to 0.30 and less than or equal to 0.55, greater than or equal to 0.35 and less than or equal to 0.55, greater than or equal to 0.40 and less than or equal to 0.55, greater than or equal to 0.45 and less than or equal to 0.55, greater than or equal to 0.50 and less than or equal to 0.55, greater than or equal to 0.25 and less than or equal to 0.50, greater than or equal to 0.30 and less than or equal to 0.50, greater than or equal to 0.35 and less than or equal to 0.50, greater than or equal to 0.40 and less than or equal to 0.50, greater than or equal to 0.45 and less than or equal to 0.50, greater than or equal to 0.25 and less than or equal to 0.45, greater than or equal to 0.30 and less than or equal to 0.45, greater than or equal to 0.35 and less than or equal to 0.45, greater than or equal to 0.40 and less than or equal to 0.45, greater than or equal to 0.25 and less than or equal to 0.40, greater than or equal to 0.30 and less than or equal to 0.40, greater than or equal to 0.35 and less than or equal to 0.40, greater than or equal to 0.25 and less than or equal to 0.35, greater than or equal to 0.30 and less than or equal to 0.35, or greater than or equal to 0.25 and less than or equal to 0.30.

[0026] In embodiments where the cracking unit 130 is a liquid cracking unit, the feed stream 103 is a liquid feed stream comprising naphtha, natural gas condensate, or generally hydrocarbons at a liquid state at ambient conditions or combinations thereof. Within the cracking unit 130, the liquid feed stream is converted into cracked stream 132, and the cracked stream 132 comprises, ethylene, methane, propylene, hydrogen, C4+hydrocarbons, or combinations thereof. The liquid cracking unit can be any cracker that is suitable to convert liquid hydrocarbons, such as by converting paraffins to olefins and the like. In embodimentswhere the cracking unit 130 is a liquid cracking unit, the distillation unit 110 may be operated to provide a hydrogenated stream 122 suitable for a liquid cracking unit. In such embodiments, the distillation unit 110 is operated at a bottoms to feed ratio that is greater than or equal to 0.25 and less than or equal to 0.65, such as greater than or equal to 0.30 and less than or equal to 0.65, greater than or equal to 0.35 and less than or equal to 0.65, greater than or equal to 0.40 and less than or equal to 0.65, greater than or equal to 0.45 and less than or equal to 0.65, greater than or equal to 0.50 and less than or equal greater than or equal 0.65, greater than or equal to 0.55 and less than or equal to 0.65, greater than or equal to 0.60 and less than or equal to 0.65, greater than or equal to 0.25 and less than or equal to 0.60, greater than or equal to 0.30 and less than or equal to 0.60, greater than or equal to 0.35 and less than or equal to 0.60, greater than or equal to 0.40 and less than or equal to 0.60, greater than or equal to 0.45 and less than or equal to 0.60, greater than or equal to 0.50 and less than or equal greater than or equal 0.60, greater than or equal to 0.55 and less than or equal to 0.60, greater than or equal to 0.25 and less than or equal to 0.55, greater than or equal to 0.30 and less than or equal to 0.55, greater than or equal to 0.35 and less than or equal to 0.55, greater than or equal to 0.40 and less than or equal to 0.55, greater than or equal to 0.45 and less than or equal to 0.55, greater than or equal to 0.50 and less than or equal greater than or equal 0.55, greater than or equal to 0.25 and less than or equal to 0.50, greater than or equal to 0.30 and less than or equal to 0.50, greater than or equal to 0.35 and less than or equal to 0.50, greater than or equal to 0.40 and less than or equal to 0.50, greater than or equal to 0.45 and less than or equal to 0.50, greater than or equal to 0.25 and less than or equal to 0.45, greater than or equal to 0.30 and less than or equal to 0.45, greater than or equal to 0.35 and less than or equal to 0.45, greater than or equal to 0.40 and less than or equal to 0.45, greater than or equal to 0.25 and less than or equal to 0.40, greater than or equal to 0.30 and less than or equal to 0.40, greater than or equal to 0.35 and less than or equal to 0.40, greater than or equal to 0.25 and less than or equal to 0.35, greater than or equal to 0.30 and less than or equal to 0.35, or greater than or equal to 0.25 and less than or equal to 0.30. As an example referring to embodiments, the bottoms to feed ratio may be defined as the mass flow of bottoms stream 112 divided by the mass flow of olefinic gas stream 101.

[0027] In embodiments where the cracking unit 130 is a liquid-gas cracking unit, the feed stream 103 is split into a liquid feed stream and a gas feed stream, and the liquid feed stream is fed to a liquid cracking unit and the gas feed stream is sent to a gas cracking unit. The gasfeed stream, the liquid feed stream, the gas cracking unit, and the liquid cracking unit used in the embodiments comprising a liquid-gas cracking unit can, in embodiments, be a combination of the gas feed stream, the liquid feed stream, the gas cracking unit, and the liquid cracking unit described above. Within the cracking unit 130, the liquid -gas feed stream is converted into cracked stream 132, and the cracked stream 132 comprises, ethylene, methane, propylene, hydrogen, C4+hydrocarbons, or combinations thereof. The liquid-gas cracking unit can be any cracker that is suitable to convert liquid and gas hydrocarbons, such as by converting paraffins to olefins and the like. In embodiments where the cracking unit 130 is a liquid-gas cracking unit, the distillation unit 110 may be operated to provide a hydrogenated stream 122 suitable for a liquid-gas cracking unit. In such embodiments, the distillation unit 110 is operated at a bottoms to feed ratio that is greater than or equal to 0.25 and less than or equal to 0.75, such as greater than or equal to 0.30 and less than or equal to 0.75, greater than or equal to 0.35 and less than or equal to 0.75, greater than or equal to 0.40 and less than or equal to 0.75, greater than or equal to 0.45 and less than or equal to 0.75, greater than or equal to 0.50 and less than or equal to 0.75, greater than or equal to 0.55 and less than or equal to 0.75, greater than or equal to 0.60 and less than or equal to 0.75, greater than or equal to 0.65 and less than or equal to 0.75, greater than or equal to 0.70 and less than or equal to 0.75, greater than or equal to 0.25 and less than or equal to 0.70, greater than or equal to 0.30 and less than or equal to 0.70, greater than or equal to 0.35 and less than or equal to 0.70, greater than or equal to 0.40 and less than or equal to 0.70, greater than or equal to 0.45 and less than or equal to 0.70, greater than or equal to 0.50 and less than or equal to 0.70, greater than or equal to 0.55 and less than or equal to 0.70, greater than or equal to 0.60 and less than or equal to 0.70, greater than or equal to 0.65 and less than or equal to 0.70, greater than or equal to 0.25 and less than or equal to 0.65, greater than or equal to 0.30 and less than or equal to 0.65, greater than or equal to 0.35 and less than or equal to 0.65, greater than or equal to 0.40 and less than or equal to 0.65, greater than or equal to 0.45 and less than or equal to 0.65, greater than or equal to 0.50 and less than or equal to 0.65, greater than or equal to 0.55 and less than or equal to 0.65, greater than or equal to 0.60 and less than or equal to 0.65, greater than or equal to 0.25 and less than or equal to 0.60, greater than or equal to 0.30 and less than or equal to 0.60, greater than or equal to 0.35 and less than or equal to 0.60, greater than or equal to 0.40 and less than or equal to 0.60, greater than or equal to 0.45 and less than or equal to 0.60, greater than or equal to 0.50 and less than or equal to 0.60, greater than or equal to 0.55 and less than or equal to 0.60, greater than or equal to 0.25 andless than or equal to 0.55, greater than or equal to 0.30 and less than or equal to 0.55, greater than or equal to 0.35 and less than or equal to 0.55, greater than or equal to 0.40 and less than or equal to 0.55, greater than or equal to 0.45 and less than or equal to 0.55, greater than or equal to 0.50 and less than or equal to 0.55, greater than or equal to 0.25 and less than or equal to 0.50, greater than or equal to 0.30 and less than or equal to 0.50, greater than or equal to 0.35 and less than or equal to 0.50, greater than or equal to 0.40 and less than or equal to 0.50, greater than or equal to 0.45 and less than or equal to 0.50, greater than or equal to 0.25 and less than or equal to 0.45, greater than or equal to 0.30 and less than or equal to 0.45, greater than or equal to 0.35 and less than or equal to 0.45, greater than or equal to 0.40 and less than or equal to 0.45, greater than or equal to 0.25 and less than or equal to 0.40, greater than or equal to 0.30 and less than or equal to 0.40, greater than or equal to 0.35 and less than or equal to 0.40, greater than or equal to 0.25 and less than or equal to 0.35, greater than or equal to 0.30 and less than or equal to 0.35, or greater than or equal to 0.25 and less than or equal to 0.30. It should be understood that in embodiments, the liquid-gas cracking unit may be one or more liquid cracking units and gas cracking units operating in parallel.

[0028] The cracked stream 132 is introduced into the separation unit 150 with the distillate stream 114, where these streams are separated to obtain an ethylene product stream 152, a propylene product stream 154, a methane produce stream 155, a hydrogen product stream 156, and a C4+product stream 158. The separation unit 150 may be any separator suitable for separating mixed hydrocarbon streams into an ethylene product stream 152, a propylene product stream 154, a methane produce stream, a hydrogen product stream 156, and a C4+product stream 158. Exemplary separation units are described, for example, in Edgar L. Mohundro. Overview on C2 and C3 selective hydrogenation in ethylene plants. In 15th Ethylene Produces Conference, volume 15. AIChE, 2003. Session 64: Ethylene Plant Technology C2 and C3 Hydrogenation Technology Review. In addition, a gas recycling stream 104 includes any combination of hydrocarbons considered to be in a gaseous state at atmospheric conditions, such as ethane, propane, butane, etc. In embodiments, the gas recycling stream may be directed from the separation unit 150 and combined with feed stream 103.

[0029] The hydrogen product stream 156 may exit the separation unit 150 and be partially redirected to the feed hydrogenation unit 120 where the hydrogen product stream 156 may be used as or integrated into the hydrogen stream 102 that is used to hydrogenate hydrocarbonsfrom the bottoms stream 112 that exit the feed distillation unit 110. In embodiments, the hydrogen stream 102 may be generated by any suitable means of H2 generation, including but not limited to H2O electrolysis, methane reforming or partial oxidation. By incorporating the hydrogen product stream 156 into the feed hydrogenation unit 120, a limited amount of hydrogen needs to be used in the process. The hydrogen product stream 156 may, in embodiments, be separated from the steam cracker off-gas stream comprising, for example, methane and hydrogen, and the hydrogen may be separated by methods to known one in the art such as pressure swing adsorption (PSA) or membrane separation, or the like and combinations thereof.

[0030] In addition, according to embodiments, the C4+product stream 158 that exits the separation unit 150 may be redirected to the liquid or gas cracking unit 130 or 140 where it may be combined with the feed streams 103 or 104 where the C4+hydrocarbons in the C4+ product stream 158 may be cracked and integrated into the gaseous cracked stream 132.

[0031] As noted above, embodiments disclosed and described herein provide a process whereby a synthetic olefin stream can be incorporated into an existing liquid cracking system by running the synthetic olefin stream through a feed preparation system consisting of the feed distillation unit and the feed hydrogenation unit, as shown in FIG. 1. The feed distillation unit and the feed hydrogenation unit can be designed or operated in such a manner that they allow the extraction of valuable components, such as propylene and ethylene, to be directed to the separation unit while routing a heavier bottoms stream to the cracking unit. By manipulating the distillation fraction from the feed distillation unit that is sent as a bottoms stream to the feed hydrogenation unit and the distillation fraction that is sent as a distillate stream to the separation unit, a P / E ratio can be tailored to be economically desirable while remaining within the cracking unit's operating limits. Hydrogenation of unsaturated components in the bottoms stream has the benefit of increasing ethylene and propylene yields when fed to the cracking unit.

[0032] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided suchmodification and variations come within the scope of the appended claims and their equivalents.EXAMPLES

[0033] The following Examples are offered by way of illustration and are presented in a manner such that one skilled in the art should recognize are not meant to be limiting to the present disclosure as a whole or to the appended claims.

[0034] Table 2 : Yields of Steam Cracker for Various Feedstocks

[0035] Data in Table 2 referenced from U.S. Patent No. 11,220,469.

[0036] The above data shows olefin production for previously disclosed steam cracking processes (Table 2). As shown in the examples below, by integrating a methanol to olefins (MTO) stream into the separation unit of the steam cracking processes, even better olefin production may be achieved.

[0037] For the integrated processes, various integrated mass and energy balances were developed using Aspen Plus Process Simulator flowsheets for processes as shown in FIG. 1.

[0038] For this example, the ultimate P / E ratio of the cracking unit when no MTO stream is introduced is 0.45. By ultimate P / E, the effect of recycle gases to cracking furnaces are included. In this example, and as referenced in FIG. 2, a de-ethanizer refers to operation of the feed distillation unit such that most of Ci components (> 99 wt.%) are present in thedistillate stream with the bottoms stream consisting of > 99 wt.% Cs+components. Analogously, a de-propanizer refers to operation of > 99 wt.% recovery of Cs’ in the distillate stream and > 99 wt.% C4+components in the bottoms stream.

[0039] In this example, “MTO-1 : no feed pretreatment” is a comparative example where a stream according to MTO-1 in Table 1 is fed into the separation unit of a steam cracker without any treatment (z.e., no feed distillation and no feed hydrogenation); “MTO-2: no treatment” is a comparative example where a stream according to MTO-2 from Table 1 is fed into the separation unit of a steam cracker without any treatment (z.e., no feed distillation and no feed hydrogenation); “Standard PE” is known cracking system without the introduction of any MTO stream; “MTO-1 : feed depropanizer” is a comparative example where a stream according to MTO-1 in Table 1 is treated according to FIG. 1 and the feed distillation unit is operated as a de-propanizer; “MTO-2: feed depropanizer” is a comparative example where a stream according to MTO-2 in Table 1 is treated according to FIG. 1 and the feed distillation unit is operated as a de-propanizer; “MTO-1 : feed deethanizer” is an example where a stream according to MTO-1 in Table 1 is treated according to FIG. 1 and the feed distillation unit is operated as a de-ethanizer; “MTO-2: feed deethanizer” is an example where a stream according to MTO-2 in Table 1 is treated according to FIG. 1 and the feed distillation unit is operated as a de-ethanizer;

[0040] As shown in FIG. 2, by operating a feed de-ethanizer system, the cracker ultimate P / E can in fact be reduced while allowing displacement of fossil -based feedstock for circular based feedstock converted to light olefins via synthesis gas. Therefore, circularity goals and cracker profitability and operation can be simultaneously accomplished.

[0041] Using methods disclosed and described herein, the P / E ratio of fluids (either gas or liquid) in the cracker complex may be controlled by using a distillation unit and a hydrogenation unit to treat olefinic gas streams prior to introducing those streams into the cracking units. For instance, in embodiments a significant proportion of C2 hydrocarbons from the olefinic gas stream may be removed as a distillate stream from the distillation unit to increase the P / E ratio of the bottoms stream exiting the bottom of the distillation unit. Likewise, in embodiments C2 hydrocarbons and a portion of C3 hydrocarbons may be removed as a distillate stream exiting the top of the distillation unit to provide a targeted P / E ratio of the bottoms stream from the distillation unit. In this way, after the bottoms streamhas undergone hydrogenation, the P / E ratio of the fluids in the cracking unit may be controlled.

[0042] The introduction of the MTO stream has the additional benefit of olefin, especially ethylene, production without the production of hydrogen as a byproduct typically encountered in liquid and gas cracking furnaces. This presents an additional energy saving in the so-called cracked gas compressor system (part of unit 150 in Figure 1), where gas is compressed to achieve separation of components. Due to the high relative volume of the hydrogen, it is a significant contributor to shaft power of the gas compression. Integration of the MTO stream therefore has the benefit of reducing the shaft work requirement of unit 150 in Figure 1, while maintaining olefin production.

Claims

CLAIMS1. A method for producing light olefins, the method comprising: introducing an olefinic gas stream into a feed distillation unit; distilling the olefinic gas stream in the feed distillation unit to obtain a distillate stream and a bottoms stream, wherein the distillate stream comprises C2+hydrocarbons and the bottoms stream comprises Cs+hydrocarbons; introducing the distillate stream to a separation unit; introducing the bottoms stream and a hydrogen stream to a feed hydrogenation unit; hydrogenating the bottoms stream in the feed hydrogenation unit to obtain a hydrogenated stream; introducing the hydrogenated stream and a feed stream into a cracking unit, wherein the feed stream comprises, propane, butane, naphtha, or combinations thereof; cracking the hydrogenated stream and the feed stream in the cracking unit to obtain a cracked stream, wherein the cracked stream comprises ethylene, propylene, hydrogen, C4+hydrocarbons, or combinations thereof; introducing the cracked stream into the separation unit; and separating the distillate stream and the cracked stream in the separation unit to obtain an ethylene product stream, a propylene product stream, a hydrogen product stream, and a C4+hydrocarbon product stream.

2. The method of claim 1, wherein the olefinic gas stream is obtained from a methanol-to-olefins process or a direct syngas to olefins process.

3. The method of claim 2, wherein the olefinic gas stream is derived from a carbonaceous feedstock through a syngas intermediate.

4. The method of any one of claims 1 to 3, wherein the olefinic gas stream comprises a propylene to ethylene (P / E) ratio that is greater than 0.6.

5. The method of any one of claims 1 to 4, wherein the olefinic gas stream comprises a P / E ratio that is greater than 0.6 and less than 3.0.

6. The method of any one of claims 1 to 5, wherein a PZE ratio of the cracked stream is less than 0.60.

7. The method of any one of claims 1 to 6 wherein a P / E ratio of the cracked stream is less than 0.4.

8. The method of any one of claims 1 to 7, wherein the cracking unit is a liquid steam cracking unit, and the distillation unit is operated at a bottoms to feed ratio of greater than or equal to 0.25 and less than or equal to 0.65.

9. The method of any one of claims 1 to 7, wherein the cracking unit is a gas steam cracking unit, and the distillation unit is operated at a bottoms to feed ratio of greater than or equal to 0.25 and less than or equal to 0.75.

10. The method of claim 9, wherein the cracking unit is a propane cracking unit.

11. The method of any one of claims 1 to 7, wherein the cracking unit is a mixed liquid-gas steam cracking unit, and the distillation unit is operated at a bottoms to feed ratio of greater than or equal to 0.25 and less than or equal to 0.75.

12. The method of any one of claims 1 to 11, wherein heat generated at the feed hydrogenation unit is integrated to the feed distillation unit.

13. The method of any one of claims 1 to 12, wherein a condenser in the feed distillation unit is operated at a temperature that is greater than 25 °C, and a reboiler in the feed distillation unit is operated at a temperature that is from 90 °C to 130 °C.

14. The method of any one of claims 1 to 13, wherein a part of the hydrogen product stream is introduced into the feed hydrogenation unit.

15. The method of any one of claims 1 to 14, wherein the hydrogenated stream and the feed stream are introduced into the cracking unit such that a total feed into the cracking unit comprises less than 99.9 wt.% of the feed stream.

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