US-12617740-B2 - Fractionation for polymerized reactor effluent

US12617740B2US 12617740 B2US12617740 B2US 12617740B2US-12617740-B2

Abstract

A method including recovering a polymerization reactor effluent stream from one or more polymerization reactors, flashing the polymerization reactor effluent stream to form a flash gas stream, separating, in a first column, the flash gas stream into a first column overhead stream, a first column side stream, and a first column bottoms stream, separating the first column overhead stream into a gas stream and a liquid stream, and introducing a feed comprising the gas stream and at least a portion of the liquid stream to a second column to produce a second column overhead stream, a second column side stream, and a second column bottoms stream. A second column bottoms stream flow rate can comprise less than or equal to about 25 vol % of a total flow rate and a second column side stream flow rate can comprise greater than or equal to about 75 vol % the total flow rate.

Inventors

Joseph A. CURREN
Wei Qi
Anurag Gupta

Assignees

CHEVRON PHILLIPS CHEMICAL COMPANY LP

Dates

Publication Date: 20260505
Application Date: 20240209

Claims (20)

1 . A method comprising: recovering a polymerization reactor effluent stream from one or more polymerization reactors; flashing the polymerization reactor effluent stream to form a flash gas stream; separating, in a first column operated at a first column pressure, the flash gas stream into a first column overhead stream, a first column side stream, and a first column bottoms stream; separating the first column overhead stream into a gas stream and a liquid stream; and introducing a feed comprising the gas stream and at least a portion of the liquid stream to a second column operated at a second column pressure, to produce a second column overhead stream, a second column side stream, and a second column bottoms stream, wherein the second column bottoms stream has a second column bottoms stream flow rate of isobutane and the second column side stream has a second column side stream flow rate of isobutane, wherein a total flow rate of isobutane comprises the second column bottoms stream flow rate and the second column side stream flow rate, and wherein the method comprises operating such that the second column bottoms stream flow rate comprises less than or equal to about 25 volume percent (vol %) of the total flow rate and the second column side stream flow rate comprises greater than or equal to about 75 vol % of the total flow rate; and wherein the method does not include compressing the first column overhead stream, the gas stream, or the at least the portion of the liquid stream prior to introducing the gas stream and the at least the portion of the liquid stream as the feed to the second column.
2 . The method of claim 1 , further comprising returning at least a portion of the first column side stream to at least one of the one or more polymerization reactors.
3 . The method of claim 1 further comprising recycling at least a portion of the second column side stream to the one or more polymerization reactors.
4 . The method of claim 1 , wherein the second column bottoms stream is a substantially olefin-free isobutane stream comprising greater than or equal to about 95 weight percent (wt %) isobutane, less than or equal to about 50 ppmw olefins, less than or equal to about 0.1 ppmw hydrogen, or a combination thereof.
5 . The method of claim 1 wherein the second column pressure is within 10% of the first column pressure.
6 . The method of claim 1 , wherein a reboiler duty of a reboiler associated with the second column is less than a reboiler duty of a reboiler associated with a second column in a same method except wherein the second column is not operated at a second column pressure that is within about 10% of the first column pressure, and wherein a diameter of the second column is less than a diameter of the second column utilized to provide a same separation in the same method.
7 . The method of claim 1 , comprising no preheating of the feed or components thereof between the second column and the first column.
8 . The method of claim 1 , wherein the second column side stream comprises less than or equal to about 0.1 ppmw hydrogen, less than or equal to about 10 weight percent (wt %) ethylene, greater than or equal to about 80 wt % isobutane, or a combination thereof.
9 . The method of claim 1 further comprising maximizing an amount of ethylene in the second column side stream, while maintaining a concentration of hydrogen in the second column side stream below a tolerance of the one or more polymerization reactors, and recycling at least a portion of the second column side stream to at least one of the one or more polymerization reactors.
10 . The method of claim 1 carried out with a system comprising: the one or more polymerization reactors configured to produce the polymerization reactor effluent stream; a flash apparatus configured for flashing the polymerization reactor effluent stream to form the flash gas stream; the first column configured to separate the flash gas stream into the first column overhead stream, the first column side stream, and the first column bottoms stream; a liquid/vapor separator configured for separating the first column overhead stream into a the gas stream and the liquid stream; and the second column configured to receive the feed comprising the gas stream and at least a portion of the liquid stream and separate the feed to produce the second column overhead stream, the second column side stream, and the second column bottoms stream, wherein a second column bottoms outlet line is configured for the second column bottoms stream flow rate of isobutane and a second column side stream is configured for the second column side stream flow rate of isobutane, and wherein the system does not comprise a compressor between the first column and the second column.
11 . The method of claim 10 , configured for operation of the second column at a pressure within about 10% of a pressure at which the first column is operated.
12 . The method of claim 10 , wherein the second column bottoms stream is a substantially olefin-free isobutane stream comprising greater than or equal to about 85 weight percent (wt %) isobutane, less than or equal to about 1 wt % olefins, less than or equal to about 0.1 ppmw hydrogen, or a combination thereof.
13 . The method of claim 10 , wherein the second column is in operation at a second column pressure and the first column is in operation at a first column pressure, wherein the second column pressure is within about 10% of the first column pressure.
14 . The method of claim 13 wherein a reboiler duty of a reboiler associated with the second column is less than a reboiler duty of a reboiler associated with a second column in a same method except wherein the second column is not operated at a second column pressure that is within about 10% of the first column pressure, and wherein a diameter of the second column is less than a diameter of the second column utilized to provide a same separation in the same system.
15 . The method of claim 10 , comprising no compressor for compressing of the first column overhead stream, the gas stream, or the at least the portion of the liquid stream prior to introduction of the gas stream and the at least the portion of the liquid stream in the feed to the second column.
16 . The method of claim 10 , comprising no preheater for preheating of the feed or components thereof between the second column and the first column.
17 . The method of claim 10 , wherein a liquid side draw stage of the second column is separated from a feed stage of the second column by more than 5 theoretical or actual stages, or by from about 3 to about 20 theoretical or actual stages, wherein the liquid side draw stage is a stage from which or tray from immediately above which the second column side stream is withdrawn, and wherein the feed stage is a stage to which or a tray immediately above which the feed is introduced to the second column.
18 . The method of claim 1 , wherein the bottoms stream flow rate comprises less than or equal to about 15 volume percent (vol. %) of the total flow rate and the side stream flow rate comprises greater than or equal to about 85 vol. % of the total flow rate.
19 . The method of claim 1 , wherein the first column pressure and the second column pressure are in a range of from about 120 to 140 psig.
20 . A method comprising: recovering a polymerization reactor effluent stream from one or more polymerization reactors; flashing the polymerization reactor effluent stream to form a flash gas stream; separating, in a first column operated at a first column pressure, the flash gas stream into a first column overhead stream, a first column side stream, and a first column bottoms stream; separating the first column overhead stream into a gas stream and a liquid stream; introducing a feed comprising the gas stream and at least a portion of the liquid stream to a second column operate at a second column pressure to produce a second column overhead stream, a second column side stream, and a second column bottoms stream; and wherein the second column pressure is within about 10% of the first column pressure, and wherein the first column pressure and the second column pressure are in a range of from about 120 to 140 psig.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS None. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable. TECHNICAL FIELD The present disclosure relates to systems and methods for processing an effluent from a polymerization reaction process. More particularly, the disclosure relates to removing one or more undesired components and recycling one or more reusable components from a polymerization reaction effluent stream. Still more particularly, the current disclosure relates to systems and method for treating a polymerization reactor effluent that operates a deethanizer column at a pressure similar to a pressure of an upstream dehexanizer column, with a majority of the isobutane recovered via the deethanizer removed via a side stream of the deethanizer. BACKGROUND The production of polymers such as polyethylene requires a high purity feedstock of various components, including monomers, diluents, and co-monomers. In order to offset some of the costs and maximize production, it can be useful to reclaim and/or recycle some feedstock components from an effluent stream resulting from the polymerization reaction. To accomplish this, the reclaimed effluent streams have conventionally either been routed through a purification process or redirected through other redundant processing steps. Conventional attempts to industrially produce high purity feedstock components has required the operation of numerous distillation columns, compressors (e.g., to achieve the high pressures needed in such conventional processes), refrigeration units (e.g., to achieve cryogenic temperatures) and various other equipment. As such, the equipment and energy costs associated with feedstock purification represent a significant proportion of the total cost for the production of such polymers. Further, the infrastructure required for producing, maintaining, and recycling high purity feedstock represents a significant portion of the associated cost. Further, such conventional attempts to recover feedstock components have not enabled sufficient control parameters to prevent and/or control deleterious plant conditions. The drawbacks of these designs can lead to process delays, increased costs, and/or other inefficiencies. As such, an improved separation system for polymerization reaction effluent streams is needed. BRIEF DESCRIPTION OF THE DRAWINGS The detailed description will reference the drawings briefly described below, wherein like reference numerals represent like parts, unless otherwise indicated. FIG. 1A is a schematic of a polymerization system or polymer production system (PPS), according to aspects of this disclosure; FIG. 1B is a schematic of a flash gas treatment system (FGTS), according to aspects of this disclosure; FIG. 1C is a schematic of a flash gas production system (FGPS) operable to produce a flash gas, according to aspects of this disclosure; FIG. 1D is a schematic of a polymerization system, according to aspects of this disclosure; FIG. 2 is a schematic of a portion of a flash gas treatment system (FGTS), according to aspects of this disclosure; FIG. 3 shows deethanizer temperature profiles obtained with different amounts of ethylene in a substantially olefins-free isobutane stream (OFIC4) and ethylene and hydrogen in a recycle isobutane stream (RIC4); FIG. 4 shows deethanizer temperature profiles obtained with different amounts of ethylene in the substantially olefins-free isobutane stream (OFIC4) and ethylene in the recycle isobutane stream (RIC4); and FIG. 5 shows deethanizer temperature profiles for 10° F. (colder) deviation on feed at different amounts of ethylene in the substantially olefins-free isobutane stream (OFIC4) and hydrogen in the recycle isobutane stream (RIC4). DETAILED DESCRIPTION Herein disclosed are systems and methods of treating a polymerization reactor(s) effluent stream. In the conventional flash gas treatment processes, a deethanizer column is operated at approximately double the pressure of an upstream dehexanizer column. This change in pressure requires the inclusion of a dehexanizer overhead compressor. This compressor increases the capital cost of such conventional designs, and can present operational difficulties. Furthermore, operating the deethanizer at higher pressures increases the energy consumption of the stripping process occurring therein. Via the system and method of this disclosure, the deethanizer can be operated at a lower pressure, similar to that of the dehexanizer column, such that the dehexanizer compressor can be eliminated. This can also substantially reduce steam/energy consumption and reduce venting of ethylene. Conventional designs can utilize higher pressures in the deethanizer in an effort to limit/reduce isobutane losses from the process in the deethanizer overhead. However, as noted above, a downside of this higher pressure in the deethanizer is the requirement of the dehexanizer overhead compressor and increased steam consumption in the deetha