Process for npentanizing debutanized natural gasoline feedstock to thermal crackers

Abstract

A process for producing natural gasoline. The process includes increasing the n-pentane concentration of debutanized natural gasoline. The process may include a first concentration process that includes distillation and a second concentration process that includes simulated moving bed adsorption.

Claims

1. A method of increasing n-pentane concentration in debutanized natural gasoline, the method comprising: splitting a stream, comprising primarily n-pentane and isopentane collectively, into a first feed stream comprising primarily n-pentane and isopentane collectively and a second feed stream comprising primarily n-pentane and isopentane collectively; subjecting the first feed stream to a first concentrating process, the first concentrating process comprises distilling and produces a first product stream comprising primarily n-pentane and a second product stream comprising methane, ethane, and propane; and subjecting the second feed stream to a second concentrating process, the second concentrating process comprises simulated moving bed adsorbing to produce a third product stream comprising primarily n-pentane and a fourth product stream comprising primarily isopentane; wherein the first feed stream and/or the second feed stream comprises 85 mol. % to 95 mol. % n-pentane and isopentane collectively.

2. The method of claim 1, wherein the first concentrating process comprises: distilling a combined stream that comprises a mixture of the first feed stream and a recycle stream having primarily isopentane to produce a bottoms stream comprising primarily n-hexane, an intermediate stream comprising primarily n-pentane, and an overhead stream comprising primarily isopentane; combining the intermediate stream and the bottoms stream to produce the first product stream; isomerizing the overhead stream in a reactor to convert at least some of the overhead stream's isopentane to n-pentane; and distilling effluent from the reactor to form the recycle stream and the second product stream.

3. The method of claim 2, wherein the isomerizing includes mixing the overhead stream with hydrogen to form a mixture and contacting the mixture with a catalyst under reaction conditions to isomerize at least some of the isopentane to n-pentane.

4. The method of claim 3, wherein the catalyst does not include zeolite and is a selection from the list consisting of: sulfated zirconia, platinum on alumina, platinum on alumina dosed with perchloroethylene or other chlorinating agent, flouridized catalyst, and combinations thereof.

5. The method of claim 3, wherein the reaction conditions include a reaction temperature of 130 to 276° C., a pressure of 15 to 30 bar and GHSV of 4 to 5.5.

6. The method of claim 4, wherein the catalyst is platinum on alumina dosed with perchloroethylene.

7. The method of claim 4, wherein the catalyst is a flouridized catalyst.

8. The method of claim 1, wherein the catalyst does not contain a zeolite.

9. The method of claim 1, wherein the first feed stream and/or the second feed stream further comprises cypentane, cis pentene, and n-hexane.

10. The method of claim 1, wherein the second product stream further comprises n-butane and isobutane.

11. The method of claim 1, wherein the overhead stream comprises 82 mol. % to 92 mol. % isopentane and 6 mol. % to 16 mol. % neopentane.

12. The method of claim 1, wherein the intermediate stream comprises 96 mol. % to 100 mol. % n-pentane.

13. The method of claim 1, wherein the bottoms stream comprises 55 mol. % to 65 mol. % n-hexane and 35 mol. % to 45 mol. % cypentane.

14. A method of increasing n-pentane concentration in debutanized natural gasoline, the method comprising: splitting a stream, comprising primarily n-pentane and isopentane collectively, into a first feed stream comprising primarily n-pentane and isopentane collectively and a second feed stream comprising primarily n-pentane and isopentane collectively; subjecting the first feed stream to a first concentrating process, the first concentrating process comprises distilling and produces a first product stream comprising primarily n-pentane and a second product stream comprising methane, ethane, and propane; and subjecting the second feed stream to a second concentrating process, the second concentrating process comprises simulated moving bed adsorbing to produce a third product stream comprising primarily n-pentane and a fourth product stream comprising primarily isopentane, wherein the second concentrating process comprises: feeding the second feed stream at a first port in a series of adsorbent columns; feeding an eluent at a second port in the series of adsorbent columns; removing raffinate from a third port in the series of adsorbent columns; removing extract from a fourth port in the series of adsorbent columns; and simulating switching location of the first port, second port, third port, and fourth port repeatedly amongst each other.

15. The method of claim 14, wherein the third product stream comprises 70 to 95 mol. % n-pentane.

16. The method of claim 14, wherein the ports are configured in the following order consistent with the direction of liquid flow through the columns: eluent port, extract port, feed port, and raffinate port.

17. The method of claim 14, wherein the eluent comprises a selection from the list consisting of: n-butane, isobutane, an alkane of different molecular weight than streams being separated, and combinations thereof.

18. The method of claim 14, wherein the raffinate comprises the third product stream and the extract comprises isopentane.

19. The method of claim 2, wherein the effluent from the reactor comprises 58 mol. % to 69 mol. % isopentane and 15 mol. % to 25 mol. % n-pentane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 shows prior art natural gas fractionator system;

(3) FIG. 2 shows equilibrium data for pentane isomers;

(4) FIG. 3 shows a system for increasing n-pentane concentration in debutanized natural gasoline, according to embodiments of the invention;

(5) FIG. 4 shows a method for increasing n-pentane concentration in debutanized natural gasoline, according to embodiments of the invention;

(6) FIG. 5 shows different sequences of a series of simulated bed adsorbent columns, according to embodiments of the invention; and

(7) FIG. 6 shows a distillation column for performing the separation of n-pentane and isopentane, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 2 shows equilibrium data for pentane isomers. As can be seen from FIG. 2, higher temperature favors n-pentane formation over isopentane formation. Thus, for an isomer separation column used to purify a particular throughput of a mixture of n-pentane/pentane isomers, as temperature increases, the size of the isomer separation column required decreases. However, as temperature increases, hydrocracking and formation of light ends increases. Thus, arriving at the ideal operating temperature involves counter balancing these two effects. Some research suggests that the ideal temperature to separate n-pentane and isopentane is about 276° C.

(9) Some commercially available processes utilize shape selectivity of zeolites to increase branched hydrocarbon content as opposed to linear hydrocarbon content. However, for processes in which hydrocarbons are to be cracked, a high linear hydrocarbon/branched hydrocarbon ratio is preferred. Thus, the use of zeolite as a catalyst is undesirable for producing feedstock for these cracking processes.

(10) A method has been discovered that increases the ratio of linear pentane/branched pentane in debutanized natural gasoline. By increasing this ratio, the utilization efficiency of debutanized natural gasoline as feedstock to thermal cracking units can be improved.

(11) FIG. 3 shows system 30 for increasing n-pentane concentration in debutanized natural gasoline, according to embodiments of the invention. FIG. 4 shows method 40 for increasing n-pentane concentration in debutanized natural gasoline, according to embodiments of the invention. Method 40 may be implemented using system 30.

(12) Method 40 as implemented by system 30 may begin at block 400, which involves splitting feedstock 300 into first feed stream 301 and second feed stream 314. In embodiments of the invention, feedstock 300, and consequently first feed stream 301 and second feed stream 314, each may include primarily n-pentane and isopentane collectively. In embodiments of the invention, feedstock 300, first feed stream 301, and second feed stream 314 may each further include n-butane, cypentane, cis pentene, and n-hexane. First feed stream 301 and/or second feed stream 314 may each comprise 85 mol. % to 95 mol. % n-pentane and isopentane collectively. In embodiments of the invention, feedstock 300, first feed stream 301, and second feed stream 314 may each comprise 45 mol. % to 55 mol. % n-pentane and 35 mol. % to 45 mol. % isopentane. In embodiments of the invention, the n-pentane/isopentane mol. ratio in each of feedstock 300, first feed stream 301, and second feed stream 314 is in a range 1.20 to 1.40.

(13) According to embodiments of the invention, at block 401, first feed stream 301 is subjected to a concentrating process, the concentrating process may include distilling and produces first product stream 310, which includes primarily n-pentane and second product stream 309, which may include methane, ethane, propane, isobutane, and n-butane.

(14) At block 402, in embodiments of the invention, second feed stream 314 is also subjected to a concentrating process. Here, however, according to embodiments of the invention, subjecting second feed stream 314 to a concentrating separation process includes simulated moving bed adsorbing to produce third product stream 315, which may include primarily n-pentane and fourth product stream 316, which includes primarily isopentane.

(15) Block 401 may include blocks 401-1 to 401-4. In embodiments of the invention, the concentrating process of block 401 includes, at block 401-1, distilling combined stream 303, which is a combination of first feed stream 301 and recycle stream 302 (comprising primarily isopentane), in distillation unit 311, to produce bottoms stream 307 (comprising primarily n-hexane), intermediate stream 306 (comprising primarily n-pentane), and overhead stream 304 (comprising primarily isopentane). In embodiments of the invention, overhead stream 304 comprises 82 mol. % to 92 mol. % isopentane and 6 mol. % to 16 mol. % neopentane; intermediate stream 306 comprises 96 mol. % to 100 mol. % n-pentane; and bottoms stream 307 comprises 55 mol. % to 65 mol. % n-hexane and 35 mol. % to 45 mol. % cypentane.

(16) In embodiments of the invention, at block 401-2, intermediate stream 306 is combined with bottoms stream 307 to produce first product stream 310. In embodiments of the invention, first product stream 310 comprises 85 mol. % to 95 mol. % n-pentane. In embodiments of the invention, the composition of stream 310 is about 93 mol. % n-pentane, about 3 mol. % cyclopentane and about 4 mol. % n-hexane. First product stream 310 may also include n-hexane, cypentane, n-butane, isobutane, methane, ethane, and propane.

(17) Method 40 may further include, at block 401-3, isomerizing overhead stream 304, in reactor 312, to convert at least some of overhead stream 304's isopentane to n-pentane. In embodiments of the invention, the isomerizing includes mixing overhead stream 304 with hydrogen 305 and contacting this mixture with a catalyst under reaction conditions sufficient to isomerize at least some of the isopentane to n-pentane. According to embodiments of the invention, the catalyst used in isomerizing the isopentane may include a selection from the list consisting of: sulfated zirconia, platinum on alumina, platinum on alumina dosed with perchloroethylene or other chlorinating agent, flouridized catalyst, and combinations thereof. However, in embodiments of the invention, the catalyst used does not contain zeolite because zeolite favors formation of branched hydrocarbons. The reaction conditions for the isomerization process in reactor 312 may include a reaction temperature of 130 to 276° C., a pressure of 15 to 30 bar and GHSV of 4 to 5.5. In embodiments of the invention, effluent 308 from reactor 312 comprises 58 mol. % to 68 mol. % isopentane and 15 mol. % to 25 mol. % n-pentane.

(18) Method 40 may also include, at block 401-4, distilling effluent 308 from reactor 312, in distillation column 313, to form recycle stream 302 and second product stream 309. According to embodiments of the invention, recycle stream 302 may comprise 62 mol. % to 72 mol. % isopentane and 15 mol. % to 25 mol. % n-pentane. According to embodiments of the invention, second product stream 309 may comprise 20 mol. % to 30 mol. % methane, 20 mol. % to 30 mol. % ethane, 20 mol. % to 30 mol. % propane, 10 mol. % to 20 mol. % n-butane, and 5 mol. % to 15 mol. % isobutane.

(19) In embodiments of the invention, a supplemental process for separating n-pentane from isopentane is provided. For example, in embodiments of the invention, the concentrating process of block 402 is provided. Block 402 may include a concentrating process using a simulated moving bed (SMB) of a typical adsorbent molecular sieve such as type 5A. Embodiments of the invention may utilize further enhanced capacity molecular sieves. Typical SMB operation involves moving eluant, extract, feed, and raffinate ports in a timed sequence. This movement of ports simulates movement of the solid bed without actually moving the solid bed. A programmable logic controller or a digital sequencer operates a number of solenoid valves that redirect the flows in a predetermined sequence. A digital sequencer has the advantage of having no moving parts. It is therefore more reliable than any other technique to implement a simulated moving bed.

(20) Block 402 may include blocks 402-1 to 402-4. Block 402-1 may include feeding second feed stream 314 at first port P1 in a series of adsorbent columns 318 to 321. In embodiments of the invention, block 402-2 involves feeding eluent 317 at second port P2 in the series of adsorbent columns 318 to 321. The eluent may include n-butane or isobutane, an alkane of different molecular weight than the streams being isomerized. At block 402-3, raffinate is removed from third port P3 in the series of adsorbent columns 318 to 321. In embodiments of the invention, method 40 further includes, removing extract from a fourth port in the series of adsorbent columns 318 to 321. According to embodiments of the invention, the raffinate comprises third product stream 315 and the extract comprises fourth product stream 316. In embodiments of the invention, third product stream 315 comprises 70 to 95 mol. % n-pentante and fourth product stream 316 comprises 80 to 95 mol. % isopentante.

(21) According to embodiments of the invention, block 402-4 involves simulating location switching of first port P1, second port P2, third port P3, and fourth port P4 repeatedly amongst each other, while maintaining the following order consistent with the direction of liquid flow through the columns: eluent port, extract port, feed port, and raffinate port.

(22) FIG. 5 shows different sequences of the series of simulated bed adsorbent columns 318 to 321, according to embodiments of the invention. The different sequences are a result of the simulated switching and show ports P1 to P4 are located in different positions consistent with the simulated moving bed.

(23) Although embodiments of the present invention have been described with reference to blocks of FIG. 4, 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. 40. For example, embodiments of the invention may include the concentration process described in block 401, without the concentration process described in block 402. Likewise, embodiments of the invention may include the concentration process described in block 402, without the concentration process described in block 401. Further, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 4.

(24) As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLES

Example 1

Material Balance of the First Concentration Process

(25) Table 1 below shows a simulated material balance for the first concentration process as described with respect to block 401 above.

(26) TABLE-US-00001 TABLE 1 DIP Colum NGL Feed + Scrub H2 Feed Rec Ovhd Side draw Bottom Rx exit ovhd Recycle nPentane Stream # 305 301 303 304 306 307 308 309 302 309 + 310 mol % mol % mol % mol % mol % mol % mol % mol % mol % wt % H.sub.2 100.00% 0.00% CH.sub.4 1.30% 24.75% 0.53% C.sub.2H.sub.6 1.33% 25.31% 1.02% C.sub.3H.sub.8 1.33% 25.31% 1.50% isobutane 0.50% 9.53% 0.74% nButane 0.08% 0.03% 0.04% 0.00% 0.00% 0.79% 15.11% 1.18% Isopentane 40.91% 57.70% 88.09% 0.00% 0.00% 63.69% 0.00% 67.21% 0.00% nPentane 50.18% 32.19% 0.00% 100.00% 0.00% 19.53% 0.00% 20.61% 88.07% neopentane 7.78% 11.87% 0.00% 0.00% 11.54% 0.00% 12.18% 0.00% CyPentane 2.48% 0.90% 0.00% 0.00% 38.99% 0.00% 0.00% 0.00% 2.38% Cis2Pentene 2.48% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% nHexane 3.88% 1.40% 0.00% 0.00% 61.01% 0.00% 0.00% 0.00% 4.58% Total 100.01% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% MW 72.58 72.32 72.14 72.15 79.92 70.31 37.06 72.15 69.36 Kg/Kgmol t/hr 0.45 184.00 507.19 331.42 162.88 12.88 332.24 9.19 323.06 184.95 Mass Balance −0.49 Error t/h

Example 2

Distillation Column

(27) FIG. 6 shows distillation column 60 for performing the separation of n-pentane and isopentane, according to embodiments of the invention. Distillation column 60 may be used to function as distillation unit 311 in system 30 to carry out the distillation described in block 401-1 of method 40. Table 2 below shows a simulation of the separation duty for distillation column 60 in implementing the distillation described in block 401-1 of method 40.

(28) TABLE-US-00002 TABLE 2 Stream Name Stream Description S1 S2 S3 S4 Phase Liquid Liquid Liquid Liquid Temperature C. 45.000 82.573 83.829 70.661 Pressure KG/CM2 4.100 4.022 4.024 4.000 Total Mass Rate KG/NR 507119.000 0.000 175468.284 331650.716 Total Weight Comp. Percent H.sub.2 0.0000 0.0000 0.0000 0.0000 METHANE 0.0000 0.0000 0.0000 0.0000 ETHANE 0.0000 0.0000 0.0000 0.0000 PROPANE 0.0000 0.0000 0.0000 0.0000 ISOBUTANE 0.0000 0.0000 0.0000 0.0000 BUTANE 0.0241 0.0000 0.0000 0.0369 NEOPENTANE 7.7613 0.0000 0.0000 11.8675 IPENTANE 57.5612 0.0000 0.0014 88.0146 PENTANE 32.1125 99.2818 92.6552 0.0809 CP 0.8727 0.4542 2.5223 0.0000 HEXANE 1.6682 0.2557 4.8211 0.0000

Example 3

Design of Simulated Moving Bed

(29) Table 3 shows an example of a typical design for a simulated moving bed, which may be used to implement the concentrating described above in block 402.

(30) TABLE-US-00003 TABLE 3 nPentaniser Separation Design using SMB Typical design Number of columns 60.00 Column length meter 2.21 Column diameter meter 9.50 Adsorbent volume m.sup.3 9381.97 particle size m10.sup.−3 meter 0.30 aspect ratio D/L 4.31 productivity kg/(hr m.sup.3 adsorbent) 54.00 adsorbent capacity kg/m.sup.3 adsorbent 90.00 Adsorbed adsorbate in all 844376.93 beds at a time switches per minute 3.63 Switches per hr 218.00

(31) 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.