A PROCESS FOR CONVERTING NATURAL GAS TO HIGHER HYDROCARBON(S)

Abstract

The present invention relates to a process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s) in n reaction zones operated in series, wherein m reaction zones are not participating in the conversion process and only (nm) reaction zones are operated under reaction conditions sufficient to convert at least a portion of said natural gas to an effluent having said higher hydrocarbon(s). An object of the present invention is to provide a process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s) wherein a high reactant, i.e. methane, conversion can be achieved.

Claims

1. A process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s) in n reaction zones operated in series, wherein m reaction zones are not participating in the conversion process and only (nm) reaction zones are operated under reaction conditions sufficient to convert at least a portion of said natural gas to an effluent having said higher hydrocarbon(s), wherein each reaction zone is initially numbered serially with a designator from 1 to n, the process comprising: (a) providing a quantity of catalytic material within each reaction zone; (b) providing to the reaction zone designated as 1 a hydrocarbon feedstock containing natural gas; (c) heating at least a portion of the effluent of the said reaction zone designated as 1 to the inlet temperature of the reaction zone designated as 2, and more generally, heating at least a portion of the effluent of each reaction zone with a designator equal or smaller than (nm1) to the inlet temperature of the reaction zone with a designator larger by one than that of the reaction zone from which said effluent originates; (d) transferring said at least portion of said effluent of the said reaction zone designated as 1 to said reaction zone designated as 2, and more generally, transferring said at least portion of said reaction zone with a designator equal or smaller than (nm1) to the reaction zone with a designator larger by one than that of the reaction zone from which said at least portion of said effluent originates; (e) maintaining said reaction zone designated as 2 at an average temperature higher than or equal as in reaction zone designated as 1, and more generally, maintaining each reaction zone with a designator equal or smaller than (nm) at an average temperature higher or equal as in the reaction zone with designator smaller by one than that of said reaction zone, feeding the effluent from the reaction zone with the designator (nm) to another process unit, and regenerating the reaction zones with a designator larger than (nm), followed by (f) terminating transferring effluent from the reaction zone with the designator (nm1) to the reaction zone with the designator (nm); (g) starting regenerating said reaction zone with the designator (nm) containing deactivated catalytic material; (h) raising the inlet temperature of each reaction zone with a designator equal or smaller than (nm1) to the former inlet temperature of the reaction zones with a designator larger by one than that of said reaction zone, respectively; (i) changing the value of each designator equal or smaller than (n1) to a number larger by one than its initial value, and changing the value of the designator with a value of n to 1, (j) repeating steps (b) to (i).

2. A process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s) in n reaction zones operated in series, wherein m reaction zones are not participating in the conversion process and only (nm) reaction zones are operated under reaction conditions sufficient to convert at least a portion of said natural gas to an effluent having said higher hydrocarbon(s), wherein each reaction zone is initially numbered serially with a designator from 1 to n, the process comprising: (a) providing a quantity of catalytic material within each reaction zone; (b) providing to the reaction zone designated as 1 a hydrocarbon feedstock containing natural gas; (c) heating at least a portion of the effluent of the said reaction zone designated as 1 to the inlet temperature of the reaction zone designated as 2, and more generally, heating at least a portion of the effluent of each reaction zone with a designator equal or smaller than (nm1) to the inlet temperature of the reaction zone with a designator larger by one than that of the reaction zone from which said effluent originates; (d) transferring said at least portion of said effluent of the said reaction zone designated as 1 to said reaction zone designated as 2, and more generally, transferring said at least portion of said reaction zone with a designator equal or smaller than (nm1) to the reaction zone with a designator larger by one than that of the reaction zone from which said at least portion of said effluent originates; (e) maintaining said reaction zone designated as 2 at an average temperature higher than or equal as in reaction zone designated as 1, and more generally, maintaining each reaction zone with a designator equal or smaller than (nm) at an average temperature higher or equal as in the reaction zone with designator smaller by one than that of said reaction zone, feeding the effluent from the reaction zone with the designator (nm) to another process unit, and regenerating the reaction zones with a designator larger than (nm), followed by (f) terminating transferring effluent from the reaction zone designated as 1 to the reaction zone designated as 2; (g) starting regenerating the reaction zone designated as 1 containing deactivated catalytic material; (h) decreasing the inlet temperature of each reaction zone with a designator larger than 1 and equal or smaller than (nm) to the former inlet temperature of the reaction zones with a designator smaller by one than that of said reaction zone, respectively; (i) changing the value of each designator equal and larger than 2 to a number smaller by one than its initial value, and changing the value of the designator with value 1 to n, (j) repeating steps (b) to (i).

3. The process according to claim 1, wherein said reaction zones are adiabatic catalytic fixed bed reaction zones.

4. The process according to claim 3, wherein said adiabatic catalytic fixed bed reaction zones are adiabatic radial flow fixed bed reactors.

5. The process according to claim 1, wherein said catalytic material comprises a bifunctional catalyst of molybdenum carbide on zeolite.

6. The process according to claim 1, wherein said total number of reaction zones, n, is at least 4, wherein said total number of reaction zones not participating in the conversion process is at most 6, respectively.

7. The process according to claim 1, wherein step (f) further comprises monitoring the temperature drop along said bed of catalytic material and terminating transferring effluent when said temperature drop comes below a threshold value.

8. The process according to claim 1, wherein the inlet temperature of each reaction zone not in regeneration is continuously adjusted in small steps such that the temperature drop along the catalyst bed in said reaction zone deviates not more than 10% from a constant value.

9. The process according to claim 1, wherein a (n+1)th reaction zone exists which is operated at a lower temperature.

10. The process according to claim 1, wherein in said step (g) of regenerating a regeneration gas is chosen from the group of steam, air and hydrogen, or suitable mixtures thereof.

11. The process according to claim 10, wherein said regeneration gas comprises at least two different components, said different components are dosed together.

12. The process according to claim 10, wherein said regeneration gas comprises at least two different components, said different components are dosed in a sequence.

13. The process according to claim 1, wherein the exothermic heat originating from regenerating said bed of catalytic material is used for preheating of fresh feed to the first reactor on stream.

14. The process according to any one of claim 1, wherein regeneration by coke combustion with an oxygen-containing regeneration gas is carried out at a temperature lower than the minimum temperature at which the reaction in reaction zone 1 to (nm) or catalyst regeneration by coke hydrogenolysis with hydrogen-rich gas in the remaining reaction zones takes place.

15. The process according to claim 6, wherein said total number of reaction zones is at least 7.

16. The process according to claim 6, wherein said total number of reaction zones not participating in the conversion process is at most 4.

Description

[0049] The present invention will now be discussed by way of an example.

[0050] FIG. 1a shows an embodiment of a process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s).

[0051] FIG. 1b shows another phase of the same process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s).

[0052] FIG. 1c shows another phase of the same process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s).

[0053] FIGS. 2a-2g show different sequences of another embodiment of a process for converting natural gas to higher hydrocarbon(s) including aromatic hydrocarbon(s).

[0054] FIG. 3 illustrates the temperature profile during the first three sequences shown in FIGS. 2a-2c.

[0055] Natural gas is fed to the first of a series of n adiabatic catalytic fixed bed reactors. The feed is brought to a preset temperature in the preheater of the first reactor. Each reactor contains particulate catalyst, e.g. a bifunctional catalyst of molybdenum carbide on zeolite, which converts methane and lower hydrocarbons into benzene and other higher hydrocarbons. m reactors are being regenerated in order to remove coke from the catalyst while nm reactors are on stream, which means convert natural gas into aromatics.

[0056] The mixture of reactant and nascent products passes through the first adiabatic reactor where it cools down due to the endothermic nature of the reaction. Hence, a decreasing temperature profile along the flow direction is established inside the catalytic fixed bed of the first reactor. After leaving the first reactor, the effluent is heated up again and enters the second reactor. More natural gas is converted into aromatics in the second reactor where the reactant/product mixtures cool down and a declining temperature profile is again established. The outlet temperature of the second reactor is higher than the outlet temperature of the first reactor. The sequence of reheating the reactant/product mixture, the conversion of the reheated mixture inside each reactor accompanied by temperature decrease, and the converted mixture leaving each reactor at a higher temperature than the outlet temperature of the previous reactor is repeated according to the total number (nm) of reactors on stream.

[0057] The detailed discussion of the FIGS. 1a-1b-1c relates to the specific embodiment of the present invention in which the overall temperature profile increases.

EXAMPLE 1

[0058] A first example is given in FIG. 1a with n=8 reactors of which m=2 reactors are regenerated. The effluent of the last (nm).sup.th reactor on stream is quenched and fed to the product separation section of the process. As a result of the increasing profile of the inlet temperatures of each of the (nm) reactors on stream the catalytic fixed bed of the (nm).sup.th reactor has the highest average temperature. This implies that the rate of coke formation, which is an undesired side reaction, is highest and therefore the catalyst deactivates most quickly in the (nm).sup.th reactor.

[0059] When a preset minimum conversion is reached indicated by a minimum temperature drop along the catalytic bed of the (nm).sup.th reactor as result of catalyst deactivation, the (nm).sup.th reactor will be taken off stream and regenerated. For this, the catalytic bed is first cooled down by a purge gas, e.g. cold methane without preheating, and then the catalyst is regenerated by converting coke with a regeneration gas. At the same time, all inlet temperature set points of the first to (nm1).sup.th reactor are raised to the values of the second to (nm).sup.th reactor before the (nm).sup.th reactor was taken off stream for regeneration. The feed stream is not fed to the first reactor anymore but to the n.sup.th reactor which has been regenerated until now. The inlet temperature set point of the n.sup.th reactor is now the same as for the first reactor before the (nm).sup.th reactor was taken off stream for regeneration. According to FIG. 1B the effluent of the n.sup.th reactor is now routed to the first reactor (n=8 and m=2).

[0060] The (nm1).sup.th reactor has the highest average temperature now and will be the next one to be regenerated. Once the temperature drop inside the (nm1).sup.th reaches a preset minimum value the same switching sequence is triggered like described above. After the new switching event, as shown in FIG. 1c, the feed will be routed to the (n1).sup.th reactor, the average temperature level in the (nm2).sup.th reactor will be the highest and the effluent of the (nm2).sup.th reactor is fed to the product separation section (n=8 and n=2).

[0061] The process as discussed above has been disclosed in Table .

TABLE-US-00001 TABLE 1 Schematic overview of status of reaction zones in the process according to the invention Reaction zone (number) 1 2 3 4 5 6 7 8 Cycle 1 R R R R R R X X 2 R R R R R X X R 3 R R R R X X R R 4 R R R X X R R R 5 R R X X R R R R 6 R X X R R R R R 7 X X R R R R R R 8 X R R R R R R X 9 R R R R R R X X

[0062] From Table 1 one can deduce that in the first cycle only reaction zones 1-6 are participating in the conversion process whereas reaction zones 7-8 are not participating in the conversion process. The sequence in the first cycle is thus 1-2-3-4-5-6 (on stream) and 7-8 (off stream). In the second cycle reaction zone 8 is taken off stream and the first reaction zone will now be reaction zone 8. The effluent from reaction zone 8 is fed to the inlet of second reaction zone, now being reaction zone 1. The sequence in the second cycle is thus 8-1-2-3-4-5 (on stream) and 6-7 (off stream), wherein the highest temperature is in reaction zone 5. The sequence in the third cycle is thus 7-8-1-2-3-4 (on stream) and 5-6 (off stream), wherein the highest temperature is in reaction zone 6. This table 1 shows a number of nine cycles wherein the situation of cycle 1 is similar to cycle 9. As mentioned before, the present invention is not restricted to any specific number of reaction zones.

[0063] In the FIGS. 1a-1c the reference numbers used refer to the following:

[0064] 11=Natural gas

[0065] 12=Products

[0066] 13=Effluent from reactor 8=Feed to reactor 1 (ring main)

[0067] 14=Feed header

[0068] 15=Product header

[0069] 16=Preheater

[0070] 17=Reactor

[0071] 18=Regeneration effluent header

[0072] 21=Regeneration gas header

[0073] 22=Regeneration gas

[0074] 23=Decoking products

EXAMPLE 2

[0075] A second example is given in FIG. 2a-2g with n=7 reactors of which m=4 reactors are regenerated with hydrogen-containing gas and k=1 is regenerated with oxygen-containing gas.

[0076] In the FIGS. 2a-2g the reference numbers used refer to the following (please note that these numbers do not refer to the numbers used in Example 1):

[0077] 1 Preheater 1 to n (7)

[0078] 2 Reaction zone 1 to n

[0079] 3 Natural gas feed

[0080] 4 Product mixture

[0081] 5 Hydrogen-rich regeneration gas feed

[0082] 6 Hydrogen-rich regeneration gas effluent

[0083] 7 Oxygen-containing regeneration gas feed

[0084] 8 Oxygen-containing regeneration gas effluent

[0085] 9 Natural gas distribution line

[0086] 10 Product collection line

[0087] 11 Hydrogen-rich regeneration gas distribution line

[0088] 12 Hydrogen-rich regeneration gas collection line

[0089] 13 Ring main

[0090] 14 Oxygen-containing regeneration gas distribution line

[0091] 15 Oxygen-containing regeneration gas collection line

[0092] The effluent of the last (second) reactor on stream is quenched and fed to the product separation section of the process. The catalyst beds of each of the two reactors on stream have the same average temperature. The catalyst in the first reactor has accumulated more coke and is more deactivated than that in the second reactor because it has been on stream for longer.

[0093] When a preset minimum conversion is reached indicated by a minimum temperature drop along the catalytic bed of the first reactor as result of catalyst deactivation, the second reactor will be taken off stream and regenerated. For this, the catalyst is regenerated by converting coke with a hydrogen-rich regeneration gas. At the same time, the inlet temperature set point of the second reactor is adjusted to the value of the first reactor before it was taken off stream for regeneration. The feed stream is not fed to the first reactor anymore but to the second reactor. The inlet temperature set point of the second reactor is now the same as for the first reactor before it was taken off stream for regeneration. According to FIG. 2b the effluent of the second reactor is now routed to the third reactor.

[0094] The catalyst bed of the second reactor has been on stream for the longest time now and will be the next one to be regenerated. Once the temperature drop inside the second reactor reaches a preset minimum value the same switching sequence is triggered like described above. After the new switching event, as shown in FIG. 2c, the feed will be routed to the third reactor, the catalyst bed in the third reactor will have been on stream for the longest time and the effluent of the fourth reactor is fed to the product separation section.

[0095] FIGS. 2d, 2e and 2f show how the feed and effluent streams are routed during the next three sequences. After the sixth (nk)th switching event, the first sequence (FIG. 2a) is repeated.

[0096] The seventh (n)th reactor is regenerated with oxygen-containing regeneration gas, e.g. diluted air, at a lower temperature and does not participate in each switching sequence. When regeneration by oxygen is completed, the catalyst bed of the seventh reactor is carburized and reheated with a hydrocarbon-rich gas, e.g. natural gas feed, and put back into the series of reactors participating in the switching sequence, i.e. on stream or regenerated by hydrogen-rich gas. At the same time, the first reactor is put out of the series of reactors participating in the switching sequence, cooled down, e.g. with cold natural gas feed, and regenerated with oxygen-containing gas, e.g. diluted air. FIG. 2f shows that feed of oxygen-containing regeneration gas to the seventh reactor has stopped and feed of natural gas to the seventh reactor for catalyst carburization has started. FIG. 2g shows how feed and effluent streams are routed after putting the seventh reactor out of and the first reactor into the switching sequence after the previous cycle of six (nk) switching sequences has finished.

[0097] Table 2 gives an overview of a complete cycle of switching events (sequence #1 to 6), and the start of a second cycle with the second to seventh reactor participating in the switching sequences (sequences #7 and later). After the first complete cycle (sequences #1 to 6), the seventh reactor is put into and the first reactor out of the series of reactors participating in the switching sequences (sequence #7).

TABLE-US-00002 TABLE 2 Schematic overview of status of reaction zones in the process according to the invention according to another embodiment Reactor Sequence # # 1 2 3 4 5 6 7 FIG. 1 Reaction Reaction H2 H2 H2 H2 O2 2a Regen Regen Regen Regen Regen 2 H2 Reaction Reaction H2 H2 H2 O2 2b Regen Regen Regen Regen Regen 3 H2 H2 Reaction Reaction H2 H2 O2 2c Regen Regen Regen Regen Regen 4 H2 H2 H2 Reaction Reaction H2 O2 2d Regen Regen Regen Regen Regen 5 H2 H2 H2 H2 Reaction Reaction O2 2e Regen Regen Regen Regen Regen 6 H2 Reaction H2 H2 H2 Reaction Carbu- 2f Regen Regen Regen Regen rization 7 O2 Reaction Reaction H2 H2 H2 H2 2g Regen Regen Regen Regen Regen 8 O2 H2 Reaction Reaction H2 H2 H2 Regen Regen Regen Regen Regen 9 O2 H2 H2 Reaction Reaction H2 H2 Regen Regen Regen Regen Regen . . . . . . . . . . . . . . . . . . . . . . . .

[0098] In Table 2the term Regen means regeneration, the term H2 means hydrogen, the term O2 means oxygen.

[0099] FIG. 3 illustrates the temperature profile during the first three sequences shown in FIGS. 2a -2c, and in table 2.