Isomerization process

Abstract

A hydrocarbon isomerization system for an iC4 feed stream removes C3 from an isomerization reactor feed stream by adding a depropanizing column to remove C3 from a reactor effluent stream that has passed through a stabilizer column. This configuration prevents accumulation of C3 in the system and provides significant savings by reducing the size of the chloride handler used to remove chloride from the exhaust gas, increasing chloride recovered into the hydrocarbon feed stream for use in combination with an isomerization catalyst. A significant utility savings are provided as well as a reduction in the amount of total chloroethane (PERC) and adsorbent required.

Description

[0001] Priority declaration

[0002] This application claims priority to U.S. patent application No. 17 / 900,367, filed on August 31, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The presently disclosed subject matter relates generally to methods and apparatus for isomerizing hydrocarbons, and more particularly to minimizing chloride consumption and sorbent dosage reduction in methods and apparatus for isomerizing hydrocarbons. Background Art

[0004] The isomerization catalyst requires continuous injection of chloride to maintain acid site activity at a combined feed rate of 150 wppm to the isomerization reactor, such as in UOP PENEX TM METHODS AND BUTAMER TM The chlorides injected into the isomerization reactor lead to the presence of hydrogen chloride and / or other chlorinated compounds in the gaseous and liquid effluents obtained from the isomerization unit, which inevitably leads to corrosion of the facility, the formation of chlorine-based deposits or salts, or accelerated fouling of the catalysts that may be located downstream of the isomerization unit. It is therefore important to eliminate all traces of hydrogen chloride or other chlorinated compounds from these effluents.

[0005] Typically, such chlorides are scrubbed with a caustic solution in a net gas scrubber (NGS) before the exhaust is sent to a fuel header or an alternate destination. This requires continuous large caustic consumption, and refiners want to reduce the disposal costs of spent caustic. Caustic handling and disposal is environmentally problematic and cost intensive.

[0006] Alternatively, a portion of the chloride in the effluent stream can be recovered and recycled by absorption with the feed stream, as described in US10479741 and US10710943. This reduces the chloride in the reactor effluent, making it feasible to replace caustic with a chloride treater using an adsorbent. This still requires large amounts of adsorbent for chloride removal, and refiners tend to reduce the amount to reduce the cost of fresh adsorbent and landfill after use.

[0007] Therefore, there is a need for improved methods and apparatus for efficiently treating chlorine injected into an isomerization process and reducing net chloride consumption. In addition, it is desirable to reduce the amount of adsorbent required for the chloride treater in the overall process, thereby reducing associated costs. Other desirable features and characteristics of the inventive subject matter will become apparent from the following detailed description of the subject matter and the appended claims, taken in conjunction with the accompanying drawings and this subject background.

[0008] In some current designs, it has been found that under the operating conditions of the isomerization reactor, there is a certain amount of C3 hydrocarbons that eventually enter the stabilizer off-gas stream and then enter the absorber. Almost all of the C3 from the absorber vapor feed stream is absorbed in the liquid feed stream, which causes the C3 to accumulate in the loop formed by the reactor, stabilizer and absorber. This requires a larger proportion of the gas stream stabilizer to bypass the absorber, resulting in more chlorides entering the chloride processor and requiring large multiple chloride processors. Summary of the invention

[0009] Provided are systems and methods for isomerizing a hydrocarbon feed stream containing at least one of C4 to C7 hydrocarbons, wherein the method and method include isomerizing a first portion of the hydrocarbon feed stream under isomerization conditions in an isomerization reactor in the presence of an isomerization catalyst and hydrogen to produce an isomerized stream; stabilizing the isomerized stream in a stabilizer unit to provide a stabilizer off-gas stream containing chlorides and a liquid isomerized stream; and sending the liquid isomerized stream to a depropanizer to produce a C4 product stream and a C3 vapor stream. A first portion of the stabilizer off-gas stream can be sent to an absorber to provide an absorber overhead stream and an absorber bottoms stream. A second portion of the stabilizer off-gas stream can be sent to a chloride processor. A C3 vapor stream from the depropanizer can be sent to a chloride processor. The absorber bottoms stream can be sent to the isomerization reactor.

[0010] The hydrocarbon feed stream may be dried prior to being sent to the absorber and isomerized in the isomerization reactor.

[0011] The C4 product stream may comprise normal C4 hydrocarbons. The hydrocarbon feed stream may comprise 95%-98% isobutane. The stabilizer off-gas stream may also comprise C2-hydrocarbons, hydrogen and chlorides. 97%-98% of the chlorides may be sent from the absorber to the isomerization reactor. The stabilizer unit and the depropanizer may each comprise 30 trays.

[0012] 95%-98% of the C3 hydrocarbons from the stabilizer bottoms stream are removed by the depropanizer. The stabilizer tower can be operated at a pressure of 300 psig-350 psig, a temperature of 90°F-120°F, and a reflux to feed mole ratio of 0.5-1.5. The depropanizer can be operated at a pressure of 150 psig-200 psig, a temperature of 90°F-120°F, and a reflux to feed mole ratio of 0.5-1.5. The C3 vapor stream is sent from the depropanizer to the chloride treater. The chloride treater removes chlorides and produces a net gas.

[0013] By adding a depropanizer, the present invention has been found to have many advantages. These include a significant reduction in the need to introduce chlorides into the process, with perchloroethylene (PERC) consumption reduced by 70%-80%. There is a similar reduction in the need for adsorbents, up to 70%-80%, which includes the advantage of reduced land fill costs and allows the use of 2 chloride treaters in series to remove chlorides, rather than 3 chloride treaters in previous designs. The reduction in equipment has the further advantage of providing a 30%-35% reduction in total utility costs. The accumulation of light ends is significantly reduced as C3 is reduced from 8%-10% to 1%-3%. The addition of a depropanizer allows the operation to have more flexibility to handle higher levels of C3 in the feed, and if desired, a separate C3-rich product stream can also be produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Various embodiments will be described below in conjunction with the following drawings, wherein like numerals represent like elements, and wherein:

[0015] Figure 1 is a schematic diagram of a method and apparatus for isomerizing hydrocarbons according to an exemplary embodiment.

[0016] The skilled person will understand that Figure 1 The elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, Figure 1 The dimensions of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various embodiments of the present disclosure. Also, common and well-known elements that are useful or necessary in commercially feasible embodiments are often not depicted to facilitate less obstruction of viewing of the various embodiments of the present disclosure. DETAILED DESCRIPTION

[0017] The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or their application and uses. In addition, it is not intended to be bound by any theory presented in the preceding background or the following.

[0018] Provided herein is a method and apparatus for isomerizing hydrocarbons. The method includes isomerizing at least a portion of a hydrocarbon feed stream containing at least one of C4 to C7 hydrocarbons under isomerization conditions in the presence of an isomerization catalyst and hydrogen to produce an isomerized stream. The isomerized stream is stabilized in a stabilizer to provide a stabilizer waste gas stream and a liquid isomerized stream. The liquid isomerized stream from the bottom of the stabilizer tower contains C3+ and is sent to a depropanizer to produce a C4+ product stream and a C3 vapor stream. The stabilizer waste gas stream contains C2, hydrogen and chlorides. At least a portion of the stabilizer waste gas stream is contacted with an exchange stream to provide an absorber tower top stream and an absorber tower bottom stream containing chlorides. The absorber tower bottom stream is conveyed to an isomerization reactor. The exchange stream can be a portion of a hydrocarbon feed stream leading to an isomerization reactor or a side draw from a deisobutanizer tower located downstream of the isomerization reactor. The absorber overhead stream, the stabilizer off-gas stream that bypasses the absorber, and the depropanizer vapor stream are combined and passed through a heater to raise the temperature to 120°F–160°F before entering a chloride treater to remove residual chlorides to produce a net gas stream.

[0019] As shown in the figure, Figure 1 The process flow lines in the description may be referred to interchangeably as, for example, lines, conduits, branches, distributors, streams, effluents, feeds, products, portions, catalysts, extracts, recycles, pumps, discharges, and caustics.

[0020] As used herein, the term "unit" may refer to a region comprising one or more equipment items and / or one or more sub-regions. Equipment items may include one or more reactors or reactor vessels, heaters, exchangers, pipelines, pumps, compressors, and controllers. In addition, equipment items such as reactors, dryers, or containers may also include one or more regions or sub-regions.

[0021] As used herein, the term "vapor" may refer to a gas or a dispersion that may include or consist of one or more hydrocarbons.

[0022] As used herein, the term "stream" may include various hydrocarbon molecules and other substances. In addition, the term "stream containing Cx hydrocarbons" may include a stream containing hydrocarbons with "x" carbon atoms, suitably including a stream containing most hydrocarbons with "x" carbon atoms, and preferably having at least 75% by weight of hydrocarbon molecules with "x" carbon atoms, respectively. In addition, the term "stream containing Cx+ hydrocarbons" may include a stream containing most hydrocarbon molecules with more than or equal to "x" carbon atoms, and suitably includes a stream containing less than 10% by weight and preferably less than 1% by weight of hydrocarbon molecules with x-1 carbon atoms. Finally, the term "Cx-stream" may include a stream containing most hydrocarbon molecules with less than or equal to "x" carbon atoms, and suitably includes a stream containing less than 10% by weight and preferably less than 1% by weight of hydrocarbon molecules with x+1 carbon atoms.

[0023] As used herein, the term "overhead stream" may mean a stream withdrawn at or near the top of a vessel, such as a column.

[0024] The term "tower" means one or more distillation columns used to separate one or more components with different volatilities. Unless otherwise specified, each tower includes a condenser at the top of the tower to condense the overhead vapor and reflux a portion of the overhead stream to the top of the tower. A reboiler is also included at the bottom of the tower to vaporize and return a portion of the bottom stream to the bottom of the tower to provide fractionation energy. The feed to the tower can be preheated. The top pressure is the pressure of the overhead vapor at the tower outlet. The bottom temperature is the liquid bottom outlet temperature. The top line and the bottom line refer to the net line from the downstream of the tower to reflux or reboil to the tower.

[0025] As used herein, the term "bottoms stream" may mean a stream withdrawn at or near the bottom of a vessel, such as a column.

[0026] As used herein, the term "substantially" may mean that the amount of a compound or class of compounds in a stream is generally at least 90 mole percent, preferably 95 mole percent, and optimally 99 mole percent.

[0027] Reference is shown according to Figure 1 The illustrated embodiment of the method and apparatus 1 presents an exemplary embodiment of a method and apparatus for isomerizing hydrocarbons.

[0028] The hydrocarbon feed stream 70 includes at least one of C4 to C7 hydrocarbons. At least a portion of the hydrocarbon feed stream 70 is sent to the upper region of the absorber vessel 62, and a second portion of the hydrocarbon feed stream is shown entering the lower portion of the absorber vessel. In the absorber vessel 62, the hydrocarbon feed stream 70 absorbs chlorides from the gas stream 60. In the system of the present invention, almost all of the overhead stream 60 from the stabilizer column 14 is sent to the absorber 62, wherein 97%-98% of the stream enters the absorber, and 2%-3% of the stream bypasses the absorber to be combined with the absorber overhead stream 74.

[0029] exist Figure 1 In the isomerization reactor 10, a chloride-rich hydrocarbon feed stream 64 leaves the absorber vessel 62 and is sent to the isomerization reactor 10, which includes one or more reactors. As shown, make-up hydrogen 66 and a chloride compound 68, such as hydrogen chloride or perchloroethylene, can be introduced into the chloride-rich hydrocarbon feed stream 64, and the chloride-rich hydrocarbon feed stream 64 can be heated in one or more heat exchangers (not shown) of the isomerization reactor 10. The reactor 10 includes a suitable isomerization catalyst and is operated under isomerization conditions suitable for isomerizing hydrocarbons from the chloride-rich hydrocarbon feed stream 64 and providing an isomerization effluent 12.

[0030] The isomerization effluent 12 is passed to a stabilizer unit 14. Separation of the isomerization effluent 12 is performed in the stabilizer unit 14 to provide a stabilizer off-gas stream 60 comprising chlorides and a liquid isomerate stream 16 comprising C3+ hydrocarbons.

[0031] Liquid isomerate 16 is passed to depropanizer 22. Depropanizer overhead stream 24 containing C3 and light hydrocarbons is cooled in heat exchanger 26, and stream 28 is passed to vessel 30, where C3 stream 32 is sent to absorber overhead stream 74, first heated to 150F by heat exchanger 75 to increase gas velocity, and then treated by chloride treater 76, where net gas 78 exits from the bottom of chloride treater 76. Heavier stream 34 containing C4 hydrocarbons exits vessel 30 and is pumped by pump 36, where stream 38 is returned to depropanizer 22 as reflux. The depropanizer may have 30 trays, as does stabilizer column 14. A mixed C4+ product stream exits depropanizer 22 as bottoms stream 42, and a portion of the product stream may be heated in heat exchanger 40 and returned to depropanizer 22. In this embodiment, two chloride treaters operated in series have been found to be sufficient to remove chlorides from the net gas stream.The chloride treater may have a smaller capacity than prior art systems.

[0032] Returning to the stabilizer column 14, the stabilizer off-gas stream 60 comprises chlorides which are removed and recycled to the isomerization reactor 10. Thus, the stabilizer column overhead vapor stream 56 is cooled by the heat exchanger 54, and the cooled stream 52 is sent through the vessel 44 along with the vapor stream 60 comprising C2-, H2 and chlorides to the absorber 62. A heavier stream 46 comprising C3-C4 hydrocarbons leaves the vessel 44 and is pumped by the pump 48, with the stream 50 being returned to the stabilizer column 14 as reflux.

[0033] The iC4 feed 70 is dried by dryer 71 and divided into streams 72 and 73 which enter absorber vessel 62. As described above, within absorber vessel 62, chloride compounds from stabilizer off-gas stream 60 comprising a mixture of C2-, H2 and HCl are absorbed by contact with the dried hydrocarbon feed stream 70 and returned to isomerization reactor 10 in chloride-rich hydrocarbon feed stream 64. Table 1 below shows summary data from a process simulation based on the principles of the present invention which indicates some significant advantages of adding a depropanizer to the system as described below.

[0034] The present invention and the addition of a depropanizer have been found to have a number of advantages. These include a significant reduction in the need to introduce chlorides into the process, with perchloroethylene (PERC) consumption reduced by approximately 70%-80%. There is a similar reduction in the need for chloride removal adsorbents, up to 70%-80%, which includes the advantage of reduced land fill costs in addition to the cost of fresh adsorbents, and allows the use of 2 chloride treaters in series to remove chlorides, rather than 3 chloride treaters in series in previous designs. The reduction in equipment has the further advantage of providing a 30%-35% reduction in total utility cost. As C3 is reduced from 8%-10% to 1%-3%, the accumulation of light ends is significantly reduced. The addition of a depropanizer allows the operation to have greater flexibility to handle higher levels of C3 in the feed, and also to produce a separate C3-rich product stream if desired.

[0035] Example

[0036] A comparison was made between a prior art system with 88% of the stabilizer off-gas stream passing through the absorber and a new system with 97% of the stabilizer off-gas stream passing through the absorber and a stabilizer tower with fewer trays. The depropanizer prevents buildup of C3's in the process.

[0037] surface

[0038] parameter Previous Construction New Construction HCl recovery rate weight % 88.0 97.06 PERC injection MT / year 3.52 0.86 Stabilizer Pressure psig 290 320 Stabilizer tray 50 30 Stabilizer reboiler duty MW 2.51 0.87 Depropanizer Pressure psig not applicable 175 Depropanizer tray not applicable 30 Depropanizer reboiler load MW not applicable 0.96 Number of Chloride Processors 3 2 Chloride Treater Dimensions mm x mm 1300x 10500 900x 9500

Claims

1. A process for isomerizing a hydrocarbon feed stream comprising at least one of a C4 to C7 hydrocarbon, wherein the process comprises: isomerizing a chloride-rich hydrocarbon feed stream under isomerization conditions in an isomerization reactor in the presence of an isomerization catalyst and hydrogen to produce an isomerized stream; stabilizing the isomerize stream in a stabilizer unit to provide a stabilizer off-gas stream comprising C2-hydrocarbons, H2, and chlorides and a liquid isomerize stream; as well as The liquid isomerate stream is sent to a depropanizer to produce a C4+ product stream and a C3 vapor stream.

2. The method of claim 1 further comprising absorbing chlorides from the gas stream with a dry hydrocarbon feed stream in an absorption column to provide a chloride-rich hydrocarbon feed stream and a chloride-depleted vapor.

3. The process of claim 2, wherein a first portion of the stabilizer off-gas stream is sent to an absorber to provide an absorber overhead stream and an absorber bottoms stream.

4. The process of claim 2, wherein a second portion of the stabilizer off-gas stream bypasses the absorber and is sent to a chloride treater.

5. The process of claim 2, wherein the absorber bottoms stream is sent to the isomerization reactor.

6. The process of claim 2, wherein the hydrocarbon feed stream is dried before being sent to the absorber and isomerized in the isomerization reactor.

7. The process of claim 1 wherein the hydrocarbon feed stream comprises 95% to 98% isobutane.

8. The process of claim 1, wherein the stabilizer off-gas stream further comprises C2-hydrocarbons, hydrogen, and chlorides.

9. The process of claim 1, wherein 97% to 99.9% of the chloride is sent from the absorber to the isomerization reactor.

10. The process of claim 1 wherein the stabilizer is operated at a pressure of 300 psig to 350 psig, a temperature of about 32°C to 49°C (90°F to 120°F), and a reflux to feed ratio of 0.5 to 1.5, and the depropanizer is operated at a pressure of 150 psig to 200 psig, a temperature of 32°C to 49°C (90°F to 120°F), and a reflux to feed ratio of 0.5 to 1.5.

Images