Integrated stabilizer in deisobutane column for isomerization and product separation of hydrocarbons

Abstract

An isomerization process includes a deisobutanizer receiving a feed comprising n-butane. The deisobutanizer delivers a portion of its bottoms to the reboiler and another portion to the isomerization reactor along with hydrogen, and the reactor effluent is returned to the column. A stabilizer is integrated with the column, the top stream is used as a reflux and the bottom contains an iso-butane rich stream, which is an iso-butane product stream. The overhead effluent is sent to a separator that separates the hydrocarbons and the effluent, where the hydrocarbons are sent to the deisobutanizer, the effluent is recycled to a stabilizer, where the stabilizer separates the reactor effluent into a product stream comprising an isobutane product stream, an n-butane product stream, and a lighter hydrocarbon product stream.

Description

[0001] This application is a divisional application of an invention patent application with a priority date of April 16, 2020, application number 202180027860.2, and name “Integrated stabilizer in a deisobutanizer tower for isomerization and product separation of hydrocarbons”. Technical Field

[0002] This invention relates to the isomerization of hydrocarbons and to the fractionation of a product effluent stream for efficiently separating isoparaffins from a feedstock and more particularly to such an isomerization process including an integrated stabilizer in the fractionation section. Background Art

[0003] About 90% of the total butane consumption in the United States is in gasoline manufacturing, where n-butane is used directly as a blending component and isobutane is used to make high-octane alkylates or to make isobutylene to make methyl tertiary butyl ether. Chemical uses account for another 6-8% of total butane. Due to the recent increase in demand for high-octane gasoline, as well as the federally mandated reduction in gasoline vapor pressure, there is a need for a process that can efficiently convert n-butane to isobutane to ultimately increase the production of high-octane blending components.

[0004] Since the boiling points of n-butane and isobutane are relatively close, and a relatively pure isobutane product is desired, the deisobutanizer is generally operated at a high reflux ratio. Thus, the heat duty of the deisobutanizer is a significant component of the operating cost of the butane isomerization process, and becomes increasingly important as higher purity isobutane product streams are sought. Therefore, an improved n-butane isomerization process having improved capital and operating costs is sought.

[0005] The object of the present invention is a process and an apparatus for the isomerization and fractionation of hydrocarbons with reduced reflux demand and reboiler duty by means of a stabilizer integrated with a deisobutanizer. Summary of the invention

[0006] The isomerization system includes a deisobutanizer receiving a feed containing normal butane. The deisobutanizer delivers a portion of its bottoms to a reboiler, another portion is sent to an isomerization reactor together with hydrogen, and the reactor effluent is returned to the tower. A stabilizer is integrated with the tower, the stabilizer overhead stream is used as reflux, and the bottoms contain an isobutane-rich stream, which is an isobutane product stream. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 - General scheme of an isobutane plant with a stabilizer section; isomerization of n-butane to isobutane by means of a stabilizer integrated with a deisobutanizer;

[0008] Figure 2- a stabilizer section in the bottom of the deisobutanizer; n-butane isomerized to isobutane by a stabilizer integrated in the bottom of the deisobutanizer;

[0009] Figure 3 - General scheme of an isomerization unit with a stabilizer section; hydrocarbons, namely n-butane, n-pentane, n-hexane, n-heptane are isomerized into isomers and heavier isomers by a stabilizer integrated with a catalytic distillation column. DETAILED DESCRIPTION

[0010] The isomerization system includes a deisobutanizer receiving a feed containing normal butane. The deisobutanizer delivers a portion of its bottoms to a reboiler, another portion is sent to an isomerization reactor together with hydrogen, and the reactor effluent is returned to the tower. A stabilizer is integrated with the tower, the stabilizer overhead stream is used as reflux, and the bottoms contain an isobutane-rich stream, which is an isobutane product stream.

[0011] Method and apparatus for isomerization of hydrocarbons and fractionation of product effluent streams. Traditionally, stabilizer towers have been used for isomerization of hydrocarbons. The present invention can provide an isomerization process with lower capital cost and lower utility cost due to integration of the stabilizer section into the distillation or reaction-distillation tower. Reduction in reflux requirements of the distillation tower and reduction in reboiler duty due to heat exchange between the stabilizer and distillation sections are effects of the present invention. Exemplary embodiments are provided below.

[0012] More specifically, if Figure 1 As shown, n-C4 isomerization; the stabilizer part is integrated into the top of the deisobutanizer. An exemplary embodiment can be a method for isomerizing a feed stream containing normal butane. The feed stream containing normal butane is sent to a deisobutanizer. The deisobutanizer delivers a portion of its bottoms to a reboiler, and another portion from its bottoms or from a tray located above the bottoms is sent to the isomerization reactor together after mixing with hydrogen, and the reactor effluent is returned to the tower. A portion of the overhead stream of the deisobutanizer is used as a reflux liquid, and a portion is sent to a stabilizing section integrated into the top of the deisobutanizer. C1-C3 hydrocarbons are removed in this section, and the bottom product contains at least 93% by weight of isobutane. Compared with the traditional scheme in which the reactor effluent is first sent to a stabilizing tower, this scheme has reduced the specific overall reflux demand and reboiler load.

[0013] Another embodiment of the present invention is as Figure 2As shown, normal C4 isomerization; the stabilizer section is integrated into the bottom of the deisobutanizer. Another exemplary embodiment can be a method for normal butane isomerization. The stabilizer section is integrated into the bottom section of the deisobutanizer. The feed stream containing normal butane is sent to the deisobutanizer. The deisobutanizer delivers a portion of its bottoms to the reboiler, and another portion from its bottoms or from the tray above the bottoms is sent to the isomerization reactor after mixing with hydrogen. The output stream of the reactor is sent to the stabilizer section, where C1-C3 hydrocarbons are removed. A portion of the bottoms stream of the stabilizer section is reboiled and a portion is sent to the deisobutanizer. Commercial iC4 products are taken from the overhead stream of the deisobutanizer. The heat integration between the stabilizer section and the bottom section of the deisobutanizer allows the reboiler load on the deisobutanizer to be reduced.

[0014] Another embodiment of the present invention is as Figure 3 As shown, an isomerization technology with an integrated stabilizer section. Another exemplary embodiment is a method for isomerizing C5-C6 and / or C6-C7 fractions. The method includes providing a hydrocarbon stream to a reaction-rectifying tower. The top product from the high-pressure separator is returned to the tower as a reflux, and another part is sent to a stabilization section integrated into the top of the reaction-rectifying tower. C1-C3 hydrocarbons are removed in this section, and the bottom product containing mainly branched C5+ hydrocarbons is mixed with the isomer product leaving the tower. Due to the heat integration of the stabilizer section and the distillation section of the tower, the present invention provides a reduced reflux demand.

[0015] A catalytic distillation column receives a feed, wherein some portion of the feed descends through the catalytic distillation column to a reboiler and leaves the column as heavy isomers. The light portion of the feed then passes upward through the catalytic distillation column. A stabilizer is integrated with the column, the overhead stream is used as reflux after separation of lighter hydrocarbons by a low-pressure separator, and the bottoms of the stabilizer contain an isomer-rich product stream, a portion of which is recycled to the stabilizer after reboiled by a reboiler. The overhead effluent is sent to a high-pressure separator, which separates hydrocarbons from effluent hydrogen, wherein the hydrocarbons are sent to a stabilizer in the column, which is integrated with the top of the catalytic distillation column; and the effluent hydrogen is recycled to the column through a compressor and a dryer. The column contains a side draw product that is isomers. The isomer-rich stream is taken from a point selected from the side draw of the catalytic distillation column and / or the bottom portion of the stabilizer. The side draw isomer-rich stream is a vapor, a liquid, or a combination thereof.

[0016] The stabilizer includes a top cooler configured to condense vapor from the column and the stabilizer. A reflux stream from the top condenser is fed to the top tray of the stabilizer.

[0017] In some embodiments of the present invention, an intermediate reboiler in the bottom portion of the reboiler is also included. In some embodiments of the present invention, the isomerate product stream is the heating medium in the intermediate reboiler. In some embodiments of the present invention, an intermediate reboiler in the bottom portion of the deisobutanizer is also included.

[0018] It will be understood that the systems and methods described herein are not limited to any particular temperature range, pressure range, flow rate, stream composition, etc. It is contemplated that the systems and methods described herein can be modified by one of ordinary skill in the art to accommodate a variety of reactor effluent compositions and other necessary conditions and parameters.

[0019] It will also be appreciated that the systems and methods described herein will have numerous technical and commercial advantages. Technical advantages include, but are not necessarily limited to:

[0020] ● Improve fractionation efficiency;

[0021] ● Reduce facility requirements;

[0022] ● Reduce overall energy requirements;

[0023] ● Reduce the need for reflow;

[0024] ● Reducing reboiler duty; and

[0025] ● Reduce isobutane losses in the system.

[0026] Business advantages include, but are not necessarily limited to:

[0027] ● 20-30% reduction in capital requirements compared to conventional tower solutions;

[0028] ● Improvement in fractionation economics;

[0029] ● Less layout space (equipment footprint) requirements;

[0030] ● Advantages of factory upgrades / de-bottlenecking;

[0031] ● improve the overall value of the product; and

[0032] ● Alternative uses of existing assets to improve the overall economic performance of the plant.

[0033] In the foregoing description, the invention has been described with reference to specific embodiments thereof. However, this description should be viewed as illustrative rather than restrictive. For example, apparatus, towers, stabilizers, processes, reactants, normal paraffins, isoparaffins, products, isomers, and operating conditions that fall within the claimed or disclosed parameter ranges but are not specifically noted or tried in a specific example are all contemplated to be within the scope of the invention.

[0034] The present invention can be implemented in the absence of undisclosed elements. In addition, the present invention can suitably include, consist of or consist essentially of disclosed elements. The isomerization system includes a deisobutanizer or catalytic distillation tower receiving a feed containing normal butane. The deisobutanizer delivers a portion of its bottoms to a reboiler, another portion is sent to an isomerization reactor together with hydrogen, and the reactor effluent is returned to the tower. A stabilizer is integrated with the tower, the top stream of the stabilizer is used as a reflux liquid, the lighter hydrocarbons are C1-C3 hydrocarbons, and the bottoms contain a stream rich in isobutane, which is an isobutane product stream.

[0035] As used throughout the claims, the words “comprising” and “comprises” should be interpreted to mean “including but not limited to” and “includes but not limited to”, respectively.

[0036] As used herein, the word "substantially" shall mean "to a large extent but not entirely as specified."

[0037] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0038] As used herein, the term "about" in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (eg, it includes the degree of error associated with measurement of the given parameter).

[0039] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

Claims

1. A system for isomerization of normal paraffins, comprising: a deisobutanizer having a feed of a feedstock containing normal paraffins, and a deisobutanizer bottoms; a reboiler configured to receive a first portion of the deisobutanizer bottoms; an isomerization reactor configured to receive a second portion of the deisobutanizer bottoms after mixing with hydrogen or a deisobutanizer effluent from a tray located above the deisobutanizer bottoms, wherein the isomerization reactor has a reactor effluent that is returned to the column; a stabilizer integrated with the deisobutanizer, the stabilizer having an overhead stream serving as stabilizer reflux and a bottoms stream containing an isomer-rich stream, the isomer-rich stream being an isomer product stream; as well as A separator is configured to receive the deisobutanizer overhead stream and is configured to separate the hydrocarbons into at least two streams, wherein the first stream is sent to the deisobutanizer as deisobutanizer reflux liquid and the remaining stream is sent to the stabilizer.

2. The isomerization of normal paraffins according to claim 1, wherein: At least a portion of the isomerate product stream is recycled to the stabilizer in a recycle stream.

3. The isomerization of normal paraffins according to claim 1, wherein: The stabilizer separates the isomerized effluent into branched C4+ hydrocarbons and a lighter hydrocarbon product stream and hydrogen.

4. The isomerization of normal paraffins according to claim 1, further comprising an intermediate reboiler in the bottom portion of the reboiler, and wherein the isomerate product stream is the heating medium in the intermediate reboiler.

5. A system for isomerization of n-butane, comprising: an n-butane-rich fraction fed to a deisobutanizer including a stabilizer; a reactor effluent fed to a deisobutanizer including a stabilizer; a deisobutanizer configured to deliver a portion of its bottoms to the reboiler, another portion to the isomerization reactor after mixing with hydrogen, and the reactor effluent to be returned to the stabilizer; The stabilizer is integrated with the deisobutanizer; The stabilizer has light hydrocarbons and hydrogen at the top of the tower, and the light hydrocarbons at the top of the tower are C1-C3 hydrocarbons; The column has an overhead product extracted from the column and / or stabilizer, the overhead product being an isomerate stream, the isomerate stream being an isobutane product stream.

6. The system according to claim 5, wherein: The overhead isobutane-rich stream is the recycle stream to the deisobutanizer.

7. The system of claim 5, further comprising an intermediate reboiler in the bottom portion of the deisobutanizer column.

8. A method for isomerizing normal paraffins, comprising: a catalytic distillation column receiving a feed comprising normal paraffins, the catalytic distillation column delivering a portion of its bottoms to a reboiler and another portion being heavy isomers; A stabilizer is integrated with the column, the top stream is used as reflux after separation of lighter hydrocarbons by a low-pressure separator, and the stabilizer bottoms contain an isomer-rich product stream, a portion of which is recycled to the stabilizer after reboiled by a reboiler; The overhead effluent is sent to a high-pressure separator, which separates hydrocarbons from effluent hydrogen, wherein the hydrocarbons are sent to a stabilizer in the tower, which is integrated with the top of the deisobutanizer; The column has a side draw product which is an isomerate.

9. The isomerization method according to claim 8, wherein: The feeds are C5-C6, C6-C7, C5-C7 fractions.

10. The isomerization method according to claim 8, wherein: The lighter hydrocarbon product stream comprises C1 to C3 hydrocarbons.

11. The isomerization method according to claim 8, wherein: The isomerate product stream is branched C4+ hydrocarbons.

12. The isomerization process of claim 8, further comprising an intermediate reboiler in the bottom portion of the reboiler, and wherein the isomerate product stream is the heating medium in the intermediate reboiler.

13. The isomerization method according to claim 8, wherein: The stabilizer is at or near the top of the tower or near the bottom of the tower.

14. The isomerization method according to claim 8, wherein The isomer-enriched stream is taken from a point selected from the side draw of the catalytic distillation column and / or the bottom portion of the stabilizer.

15. The isomerization method according to claim 8, wherein: The side draw which is an isomer-enriched stream is selected from vapor, liquid or a combination thereof.

16. The isomerization method according to claim 8, wherein: The isomerate-rich stream is branched C4+ hydrocarbons.

17. A method for isomerizing normal paraffins, comprising: feeding a feedstock containing normal paraffins to a deisobutanizer having a deisobutanizer bottoms; receiving a first portion of the deisobutanizer bottoms in a reboiler; receiving a second portion of the deisobutanizer bottoms or a deisobutanizer effluent from a tray above the deisobutanizer bottoms after mixing with hydrogen in an isomerization reactor, wherein the isomerization reactor has a reactor effluent returned to the column; and wherein the stabilizer integrated with the deisobutanizer has an overhead stream used as stabilizer reflux liquid, and a bottoms stream containing an isomer-rich stream, the isomer-rich stream being an isomer product stream; and The separator receives the top stream of the deisobutanizer and divides the hydrocarbon into at least two streams, wherein the first stream is sent to the deisobutanizer as the deisobutanizer reflux liquid, and the remaining stream is sent to the stabilizer.

18. The method for isomerizing normal paraffins according to claim 17, wherein: At least a portion of the isomerate product stream is recycled to the stabilizer in a recycle stream.

19. The method for isomerizing normal paraffins according to claim 17, wherein: The stabilizer separates the isomerized effluent into branched C4+ hydrocarbons and a lighter hydrocarbon product stream and hydrogen.

20. The process for isomerizing normal paraffins according to claim 17, further comprising an intermediate reboiler in the bottom portion of the reboiler, and wherein the isomerate product stream is used as a heating medium in the intermediate reboiler.

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