SYSTEMS AND METHODS FOR CONVERTING N-BUTANE TO ISO-BUTANE

Abstract

Systems and methods for isomerizing n-butane to form isobutane are disclosed. A segmented reactor system is used to isomerize n-butane. The segmented reactor system comprises a segmented reactor that includes a first catalyst bed and a second catalyst bed separated by a first heat exchanger. The catalyst in the first catalyst bed does not contact the catalyst in the second catalyst bed. During the exothermic process of isomerizing n-butane, the first heat exchanger extracts heat from an intermediate product flowing from the first catalyst bed to the second catalyst bed to improve the conversion rate of n-butane.

Claims

1. A method of isomerizing n-butane to form isobutane, the method comprising: flowing a feed stream comprising n-butane to a reactor, the reactor comprising: a first catalyst bed and a second catalyst bed, wherein the first catalyst bed and the second catalyst bed are separate so that catalyst in the first catalyst bed does not contact catalyst in the second catalyst bed; and a heat exchanger disposed between the first catalyst bed and the second catalyst bed; isomerizing, in the first catalyst bed, at least some of the n-butane in the feed stream to form a first amount of isobutane; flowing an intermediate product comprising the first amount of isobutane from the first catalyst bed to the heat exchanger; cooling, by the heat exchanger, the intermediate product to form cooled intermediate product; flowing the cooled intermediate product to the second catalyst bed; isomerizing, in the second catalyst bed, at least some n-butane, if any, in the cooled intermediate product to form a second amount of isobutane; and flowing a product stream comprising the first amount of isobutane and the second amount of isobutane from the second catalyst bed.

2. The method of claim 1, further comprising: heating the feed stream comprising n-butane with a heat exchange medium before flowing the feed stream to the reactor.

3. The method of claim 2, wherein the feed stream is heated to a temperature in a range of 120 C. to 190 C.

4. The method of claim 1, wherein the feed stream comprises 0.1 to 100 wt. % n-butane, 0 to 4 wt. % isobutane, 0 to 10 wt. % of hydrogen, and 0 to 1 wt. % of C.sub.5+ hydrocarbons.

5. The method of claim 1, wherein the first catalyst bed and the second catalyst bed are fixed beds.

6. The method of claim 1, wherein the heat exchanger in the reactor is a coiled heat exchanger.

7. The method of claim 1, wherein the heat exchanger comprises a tubular-coiled steam heat exchange system.

8. The method of claim 1, wherein the cooling by the heat exchanger reduces the temperature of the intermediate product by between 15 C. and 45 C.

9. The method of claim 1, wherein the catalyst is selected from the group consisting of Zeolite Socony Mobil-5, platinum/SO.sub.4.sup.2ZrO.sub.2, palladium/SO.sub.4.sup.2ZrO.sub.2, H.sub.3PW.sub.12O.sub.40, and combinations thereof.

10. The method of claim 1, wherein the isomerizing in the first catalyst bed and the isomerizing in the second catalyst bed are at a pressure in a range of 25 bar to 32 bar.

11. The method of claim 1, wherein the feed stream has a liquid hourly space velocity in a range of 0.5 h.sup.1 to 2.0 h.sup.1.

12. The method of claim 1, wherein a conversion rate of n-butane from the product stream is in a range of 32% to 67%.

13. A segmented reactor system comprising: a segmented reactor comprising: a first catalyst bed and a second catalyst bed, wherein the first catalyst bed and the second catalyst bed are separate so that catalyst in the first catalyst bed does not contact catalyst in the second catalyst bed; a first heat exchanger disposed between the first catalyst bed and the second catalyst bed; and a reactor housing comprising: a shell configured to enclose the first catalyst bed, the second catalyst bed and the first heat exchanger; a reactor inlet for flowing a feed stream in the segmented reactor; and a reactor outlet for flowing a product stream from the segmented reactor.

14. The segmented reactor system of claim 13, further comprising a second heat exchanger in fluid communication with the reactor inlet, configured to heat a feed stream before flowing the feed stream to the reactor.

15. The segmented reactor system of claim 14 wherein the first heat exchanger comprises: a first medium inlet for heat exchange medium in fluid communication with a second medium outlet of the second heat exchanger; and a first medium outlet for heat exchange medium in fluid communication with a second inlet of the second heat exchanger.

16. The segmented reactor system of claim 13, further comprising a charge heater in fluid communication with the second heat exchanger and the reactor inlet of the reactor housing, wherein the charge heater is configured to heat the feed stream until the feed stream is substantially fully vaporized.

17. The segmented reactor system of claim 13, wherein the segmented reactor is an axial flow reactor.

18. The segmented reactor system of claim 13, wherein the first catalyst bed and the second catalyst bed are fixed beds.

19. The segmented reactor system of claim 13, wherein the first heat exchanger comprises a coiled heat exchanger.

20. The segmented reactor system of claim 19, wherein the first heat exchanger includes a tubular-coiled steam heat exchange system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0024] FIG. 1 shows a schematic diagram for a segmented reactor system, according to embodiments of the invention; and

[0025] FIG. 2 shows a schematic flowchart for a method of isomerizing n-butane to form isobutane, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] A method has been discovered for isomerizing n-butane to form isobutane. A segmented reactor comprising a first catalyst bed, a second catalyst bed, and a first heat exchanger is used for the isomerization reaction. In embodiments of the invention, a heat exchanger is disposed between the first catalyst bed and the second catalyst bed. By using this heat exchanger to extract heat from an intermediate product flowing from the first catalyst bed to the second catalyst bed, process control and process optimization can be improved, and the equipment costs can be reduced, compared to conventional methods that require the use of several heat exchange trains at the outlet of each of two serial reactors.

[0027] With reference to FIG. 1, a schematic diagram is shown of segmented reactor system 10. In embodiments of the invention, segmented reactor system 10 may be used for isomerizing n-butane to form isobutane. As shown in FIG. 1, segmented reactor system 10 may comprise segmented reactor 100. In embodiments of the invention, segmented reactor 100 may comprise first catalyst bed 101 and second catalyst bed 102. In embodiments of the invention, both first catalyst bed 101 and second catalyst bed 102 may be fixed beds. First catalyst bed 101 and second catalyst bed 102 may be separate such that catalyst in first catalyst bed 101 does not contact catalyst in second catalyst bed 102. The catalyst in first catalyst bed 101 and second catalyst bed 102 may include any isomerization catalyst that can catalyze isomerization of an alkane. In embodiments of the invention, exemplary catalysts may include, but are not limited to Zeolite Socony Mobil-5, platinum/SO.sub.4.sup.2ZrO.sub.2, palladium/SO.sub.4.sup.2ZrO.sub.2, H.sub.3PW.sub.12O.sub.40, and combinations thereof.

[0028] In some conventional systems for isomerizing n-butane, two fixed bed reactors in series are used to react with n-butane. In embodiments of the invention, a total amount of catalyst in first catalyst bed 101 and second catalyst bed 102 may be less than or equal to the total amount of catalyst in the two fixed bed reactors in the conventional system for isomerizing n-butane to achieve substantially the same productivity of isobutane and n-butane conversion rate. In embodiments of the invention, segmented reactor 100 may further include first heat exchanger 103 disposed between first catalyst bed 101 and second catalyst bed 102. First heat exchanger 103 may be configured to extract heat from or provide heat to an intermediate product flowing from first catalyst bed 101 to second catalyst bed 102. Particularly, for isomerization of n-butane, first heat exchanger 103 may be used to extract heat from an intermediate product flowing from first catalyst bed 101 to second catalyst bed 102 because isomerization of n-butane to form isobutane is an exothermic process.

[0029] In embodiments of the invention, segmented reactor 100 may further comprise reactor housing 104. Reactor housing 104 may comprise a shell configured to enclose first catalyst bed 101, second catalyst bed 102, and first heat exchanger 103. Reactor housing 104 may further comprise reactor inlet 105 for flowing a feed stream in segmented reactor 100, and reactor outlet 106 for flowing a product stream from segmented reactor 100.

[0030] In embodiments of the invention, segmented reactor system 10 may further include second heat exchanger 107 in fluid communication with reactor inlet 105. Second heat exchanger 107 may be installed upstream of reactor inlet 105, configured to heat a feed stream before flowing the feed stream into segmented reactor 100. The catalytic process of the isomerization of n-butane occurs in vapor phase. Hence, according to embodiments of the invention, second heat exchanger 107 may heat the feed stream until it vaporizes. In embodiments of the invention, segmented reactor system 10 may further comprise charge heater 108 configured to heat feed stream until the feed is fully vaporized. Charge heater 108 may be installed after second heat exchanger 107 and before reactor inlet 105. Charge heater 108 may be used to heat the feed stream when at least part of the feed stream from heat exchanger 107 is not vaporized.

[0031] In embodiments of the invention, first heat exchanger 103 may comprise first medium inlet 109 for flowing exchange medium in first heat exchanger 103, and first medium outlet 110 for flowing exchange medium out from first heat exchanger 103. Second heat exchanger 107 may include second medium inlet 111 for flowing exchange medium in second heat exchanger 107, and second medium outlet 112 for flowing exchange medium out of second heat exchanger 107. In embodiments of the invention, first medium inlet 109 of first heat exchanger 103 is in fluid communication with second medium outlet 112 of second heat exchanger 107. Further, in embodiments of the invention, first medium outlet 110 of first heat exchanger 103 is in fluid communication with second medium inlet 111 of second heat exchanger 107. Thus, heat extracted from an intermediate product flowing from first catalyst bed 101 to second catalyst bed 102 by first heat exchanger 103 may be transferred to heat the feed stream via exchange medium flowing in second heat exchanger 107. In embodiments of the invention, first heat exchanger 103 may be a coiled heat exchanger or any other heat exchanger based on convective and conductive heat exchange mechanism. According to embodiments of the invention, first heat exchanger 103 may include a tubular-coiled steam heat exchange system.

[0032] According to embodiments of the invention, segmented reactor 100 may be an axial flow reactor. Although FIG. 1 shows segmented reactor 100 with two catalyst beds, in embodiments of the invention, segmented reactor 100 may comprise two or more catalyst beds. A heat exchanger may be disposed between each of two adjacent catalyst beds of a plurality of catalyst beds.

[0033] FIG. 2 shows method 20 for isomerizing n-butane to form isobutane. Method 20 may be implemented by segmented reactor system 10 as shown in FIG. 1. According to embodiments of the invention, method 20 may start with heating a feed stream before flowing the feed stream to a reactor, as shown in block 201. The reactor may be segmented reactor 100. The feed stream may be heated by heat transfer carried out by second heat exchanger 107 and/or charge heater 108. In embodiments of the invention, charge heater 108 may heat the feed stream when the feed stream is not fully vaporized by second heat exchanger 107. In embodiments of the invention, the feed stream is heated to a temperature in a range of 120 C. to 190 C. and all ranges and values therebetween, including ranges of 120 C. to 125 C., 125 C. to 130 C., 130 C. to 135 C., 135 C. to 140 C., 140 C. to 145 C., 145 C. to 150 C., 150 C. to 155 C., 155 C. to 160 C., 160 C. to 165 C., 165 C. to 170 C., 170 C. to 175 C., 175 C. to 180 C., 180 C. to 185 C., or 185 C. to 190 C.

[0034] In embodiments of the invention, the feed stream may comprise n-butane at a concentration of 0.1 to 100 wt. %. According to embodiments of the invention, the feed stream may comprise primarily n-butane. The feed stream may further comprise isobutane at a concentration of 0 to 4 wt. % and all ranges and values therebetween, including ranges of 0 to 0.2 wt. %, 0.2 to 0.4 wt. %, 0.4 to 0.6 wt. %, 0.6 to 0.8 wt. %, 0.8 to 1.0 wt. %, 1.0 to 1.2 wt. %, 1.2 to 1.4 wt. %, 1.4 to 1.6 wt. %, 1.6 to 1.8 wt. %, 1.8 to 2.0 wt. %, 2.0 to 2.2 wt. %, 2.2 to 2.4 wt. %, 2.4 to 2.6 wt. %, 2.6 to 2.8 wt. %, 2.8 to 3.0 wt. %, 3.0 to 3.2 wt. %, 3.2 to 3.4 wt. %, 3.4 to 3.6 wt. %, 3.6 to 3.8 wt. %, or 3.8 to 4.0 wt. %. In embodiments of the invention, the feed stream may further include hydrogen at a concentration of 0 to 10 wt. % and all ranges and values therebetween, including 1 wt. %, 2 wt. %, 3 wt. %, 4 wt. %, 5 wt. %, 6 wt. %. 7 wt. %, 8 wt. %, 9 wt. %, or 10 wt. %. A small amount of C.sub.5+ hydrocarbons may be included in the feed stream. A concentration of the C.sub.5+ hydrocarbons may be in a range of 0 to 1 wt. % and all ranges and values therebetween, including 0 wt. %, 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %, 0.6 wt. %, 0.7 wt. %, 0.8 wt. %, 0.9 wt. %, or 1.0 wt. %.

[0035] Block 202 shows that the feed stream may be flowed to segmented reactor 100. The feed stream may be fully vaporized as shown in block 201 before entering segmented reactor 100. In embodiments of the invention, the feed stream has a liquid hourly space velocity (LHSV) in a range of 0.5 h.sup.1 to 2.0 h.sup.1 and all ranges and values therebetween, including ranges of 0.5 h.sup.1 to 0.6 h.sup.1, 0.6 h.sup.1 to 0.7 h.sup.1, 0.7 h.sup.1 to 0.8 h.sup.1, 0.8 h.sup.1 to 0.9 h.sup.1, 0.9 h.sup.1 to 1.0 h.sup.1, 1.0 h.sup.1 to 1.1 h.sup.1, 1.1 h.sup.1 to 1.2 h.sup.1, 1.2 h.sup.1 to 1.3 h.sup.1, 1.3 h.sup.1 to 1.4 h.sup.1, 1.4 h.sup.1 to 1.5 h.sup.1, 1.5 h.sup.1 to 1.6 h.sup.1, 1.6 h.sup.1 to 1.7 h.sup.1, 1.7 h.sup.1 to 1.8 h.sup.1, 1.8 h.sup.1 to 1.9 h.sup., or 1.9 h.sup.1 to 2.0 h.sup.1.

[0036] As shown in block 203, method 20 may further include isomerizing, in first catalyst bed 101, at least some of the n-butane in the feed stream to form a first amount of isobutane. The isomerizing may be at a pressure in a range of 25 bar to 32 bar and all ranges and values therebetween including ranges of 25 bar to 26 bar, 26 bar to 27 bar, 27 bar to 28 bar, 28 bar to 29 bar, 29 bar to 30 bar, 30 bar to 31 bar, or 31 bar to 32 bar. As described above, according to embodiments of the invention, first catalyst bed 101 may be any isomerizing catalyst that can catalyze isomerization of an alkane. Exemplary catalysts may include, but are not limited to Zeolite Socony Mobil-5, platinum//SO.sub.4.sup.2ZrO.sub.2, palladium/SO.sub.4.sup.2ZrO.sub.2, H.sub.3PW.sub.12O.sub.40, and combinations thereof. A conversion rate of n-butane from first catalyst bed 101 may be in a range of 1 to 67% and all ranges and values therebetween, including ranges of 1 to 5%, 5 to 10%, 10 to 15%, 15 to 20%, 20 to 25%, 25 to 30%, 30 to 35%, 25 to 40%, 40 to 45%, 45 to 50%, 50 to 55%, 55 to 60%, and 60 to 67%.

[0037] As shown in block 204, method 20 may further include flowing an intermediate product comprising the first amount of isobutane from first catalyst bed 101 to first heat exchanger 103. According to embodiments of the invention, the intermediate product may comprise 1 to 65 wt. % isobutane, 35 to 99 wt. % n-butane, 0.0002 to 0.5 wt. % hydrogen and 0.001 to 20 wt. % C.sub.5+ compounds. In embodiments of the invention, the intermediate product from first catalyst bed 101 may be at a temperature of 110 to 250 C. and all ranges and values therebetween including ranges of 110 to 120 C., 120 to 130 C., 130 to 140 C., 140 to 150 C., 150 to 160 C., 160 to 170 C., 170 to 180 C., 180 to 190 C., 190 to 200 C., 200 to 210 C., 210 to 220 C., 220 to 230 C., 230 to 240 C., and 240 to 250 C. Block 205 shows that the first intermediate product from first catalyst bed 101 may be cooled by first heat exchanger 103 to form a cooled intermediate product. In embodiments of the invention, cooling by first heat exchanger 103 may reduce the temperature of the intermediate product by between 15 C. to 45 C., and all ranges and values therebetween, including 15 C. to 18 C., 18 C. to 21 C., 21 C. to 24 C., 24 C. to 27 C., 27 C. to 30 C., 30 C. to 33 C., 33 C. to 36 C., 36 C. to 39 C., 39 C. to 42 C., or 42 C. to 45 C.

[0038] Block 206 shows that method 20 may further include flowing the cooled intermediate product to second catalyst bed 102. As shown in block 207, at least some n-butane, if any, may be isomerized in second catalyst bed 102 to form a second amount of isobutane. Second catalyst bed may comprise any isomerization catalyst for alkane isomerization. Exemplary catalysts may include, but are not limited to Zeolite Socony Mobil-5, platinum/SO.sub.4.sup.2ZrO.sub.2, palladium/SO.sub.4.sup.2ZrO.sub.2, H.sub.3PW.sub.12O.sub.40, and combinations thereof. Similar to isomerization in first catalyst bed 101, a reaction pressure in second catalyst bed may be in a range of 25 bar to 32 bar and all ranges and values therebetween.

[0039] As shown in block 208, a first product stream comprising the first amount of isobutane and the second amount of isobutane may be flowed from second catalyst bed 102. In embodiments of the invention, a final conversion rate of n-butane in the first product stream from second catalyst bed 102 may be in a range of 32% to 67% and all ranges and values therebetween, including ranges of 32% to 35%, 35% to 38%, 38% to 41%, 41% to 44%, 44% to 47%, 47% to 50%, 50% to 53%, 53% to 56%, 56% to 59%, 59% to 62%, 62% to 65%, or 65% to 67%. In embodiments of the invention, the first product stream from second catalyst bed 102 may be at a temperature of 100 to 250 C. and all ranges and values therebetween, including ranges of 100 to 110 C., 110 to 120 C., 120 to 130 C., 130 to 140 C., 140 to 150 C., 150 to 160 C., 160 to 170 C., 170 to 180 C., 180 to 190 C., 190 to 200 C., 200 to 210 C., 210 to 220 C., 220 to 230 C., 230 to 240 C., and 240 to 250 C. The isobutane from the first product stream may be used to produce methyl-tertiary-butyl-ether.

[0040] In summary, embodiments of the invention involve systems and methods for isomerizing n-butane to form isobutane. The methods may include using systems that comprise a segmented reactor including a first catalyst bed and a second catalyst bed. The first catalyst bed and the second catalyst bed may be separated by a first heat exchanger configured to extract heat from an intermediate product flowing from the first catalyst bed to the second catalyst bed. By using the system, the operating process and the process control can both be simplified compared to a conventional system that comprises two separated reactors in series and several heat exchange trains for each of the reactors. Therefore, the systems and the methods of using the system to isomerize n-butane, according to embodiments of the invention, may reduce the costs for equipment, operating, and process control.

[0041] Although embodiments of the present invention have been described with reference to blocks of FIG. 2, it should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIG. 2. Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 2.

[0042] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.