Process for producing BTX

Abstract

The invention relates to a process for hydrocracking a feedstream comprising hydrocarbons to obtain BTX in a gas phase hydrocracking reactor system which comprises (i) an upstream end and a downstream end, (ii) a plurality of successive reaction zones distributed along the reactor between the upstream end and the downstream end, wherein each of the reaction zones has a bed of a hydrocracking catalyst contained therein and (iii) a plurality of quench zones, the quench zones being distributed along the reactor and each being situated between successive reaction zones, wherein the process comprises: (a) injecting a first portion of a hydrogen gas into the upstream end and a first portion of a hydrocarbon gas into the upstream end and (b) injecting a second portion of the hydrogen gas into at least one of the quench zones and injecting a second portion of the hydrocarbon gas into at least one of the quench zones, wherein the molar ratio between hydrogen and hydrocarbons entering each of the reaction zones is 1:1 to 4:1, wherein the molar ratio between hydrogen and hydrocarbons entering the reaction zones decreases with the distance of the reaction zone from the upstream end of the reactor.

Claims

1. A process for hydrocracking a feedstream comprising hydrocarbons to obtain BTX in a gas phase hydrocracking reactor system which comprises (i) an upstream end and a downstream end, (ii) a plurality of successive reaction zones distributed along the reactor system between the upstream end and the downstream end, wherein each of the reaction zones has a bed of a hydrocracking catalyst contained therein and (iii) a plurality of quench zones, the quench zones being distributed along the reactor system and each being situated between successive reaction zones, wherein the process comprises: (a) injecting a first portion of a hydrogen gas into the upstream end and a first portion of a hydrocarbon gas into the upstream end and (b) injecting a second portion of the hydrogen gas into at least one of the quench zones and injecting a second portion of the hydrocarbon gas into at least one of the quench zones, wherein a molar ratio between hydrogen and hydrocarbons entering each of the reaction zones is 1:1 to 4:1, wherein the molar ratio between hydrogen and hydrocarbons entering the reaction zones decreases with the distance of the reaction zone from the upstream end of the reactor system; and wherein the hydrocracking the feedstock produces the BTX in the reaction zones.

2. The process according to claim 1, wherein either the hydrocarbon gas or the hydrogen gas is injected into each of the quench zones.

3. The process according to claim 2, wherein the hydrocarbon gas and the hydrogen gas are injected into the quench zones in an alternating fashion such that either the hydrocarbon gas or the hydrogen gas is injected in one quench zone and the other gas is injected in a subsequent quench zone.

4. The process according to claim 1, wherein a mixture of the hydrocarbon gas and the hydrogen gas is injected into each of the quench zones.

5. The process according to claim 1, wherein the gas phase hydrocracking reactor system comprises a single reactor comprising the reaction zones and the quench zones.

6. The process according to claim 1, wherein the molar ratio between hydrogen and hydrocarbons entering the reaction zone closest to the downstream end is at least 25% lower than the molar ratio between hydrogen and hydrocarbons entering the reaction zone closest to the upstream end.

7. The process according to claim 1, wherein the molar ratio between hydrogen and hydrocarbons entering the reaction zone closest to the upstream end is 1.5:1 to 4:1 and/or the molar ratio between hydrogen and hydrocarbons entering the reaction zone closest to the downstream end is 1:1 to 3:1.

8. The process according to claim 1, wherein a hydrocracking product stream from the downstream end of the reactor system has a molar ratio between hydrogen and hydrocarbon of at most 2:1.

9. The process according to claim 1, wherein the hydrocarbon gas comprises C5-C12 hydrocarbons.

10. The process according to claim 1, wherein the hydrocarbon gas comprises first stage or multi-stage hydro-treated pyrolysis gasoline, straight run naphtha, hydrocracked gasoline, light coker naphtha and coke oven light oil, FCC gasoline, reformate, FT (Fischer-Tropsch) or synthetic naphtha or mixtures thereof.

11. The process according to claim 1, wherein the hydrocracking catalyst comprises 0.01-1 wt-% hydrogenation metal in relation to the total catalyst weight and a zeolite having a pore size of 5-8 and a silica (SiO.sub.2) to alumina (Al.sub.2O.sub.3) molar ratio of 5-200 and wherein process conditions in each of the reaction zones include a temperature of 425-580 C., a pressure of 300-5000 kPa gauge and a Weight Hourly Space Velocity of 0.1-15 h.sup.1.

12. The process according to claim 11, wherein the zeolite is a ZSM-5 zeolite.

13. The process according to claim 11, wherein the hydrogenation metal is platinum.

14. The process according to claim 11, wherein the hydrocracking catalyst comprises the hydrogenation metal deposited on the zeolite.

Description

(1) The present invention will now be elucidated by the following non-limiting drawings in which:

(2) FIG. 1 shows a scheme illustrating an example of a gas phase hydrocracking reactor system where cooling of the effluents are performed by heat exchangers,

(3) FIGS. 2-3 show schemes illustrating examples of a gas phase hydrocracking reactor system where cooling of the effluents are performed by either a hydrogen gas stream or a hydrocarbon gas stream and

(4) FIGS. 4-5 show schemes illustrating examples of a gas phase hydrocracking reactor system where cooling of the effluents are performed by gas streams, which are according to the invention.

(5) Same components of the system are represented by the same reference numbers throughout the figures wherever possible.

(6) FIG. 1 shows a scheme illustrating an example of a conventional gas phase hydrocracking reactor system. The reactor system comprises, from an upstream end to an downstream end, a first catalyst bed 100, a second catalyst bed 200, a third catalyst bed 300 and a fourth catalyst bed 400. Between the first catalyst bed 100 and the second catalyst bed 200, a first heat exchanger 120 is provided. Similarly, a second heat exchanger 220 and a third heat exchanger 320 are provided between successive catalyst beds. Each catalyst bed represents a reaction zone.

(7) Hydrocarbon gas 10 and hydrogen gas 20 to be fed to the first catalyst bed are at room temperature. The mixture 15 of the hydrocarbon gas 10 and hydrogen gas 20 are fed to a heating means to obtain a heated mixture 31 of hydrocarbon and hydrogen. The ratio between hydrogen and hydrocarbon in the heated mixture 31 is in the range of 1:1 to 4:1. The heated mixture 31 is fed to the first catalyst bed 100 set to a desired temperature. The first effluent 30 from the first catalyst bed 100 enters the first heat exchanger 120 which produces a cooled stream 41. The cooled stream 41 enters the second catalyst bed 200. This is repeated until the hydrocracking product stream 60 is obtained from the fourth catalyst bed 400.

(8) FIGS. 2-5 show schemes illustrating examples of a gas phase hydrocracking reactor system where cooling of the effluents are performed by gas streams instead of heat exchangers. FIGS. 4-5 illustrate examples of a gas phase hydrocracking reactor system according to the invention.

(9) FIG. 5 shows a scheme illustrating an example of the gas phase hydrocracking reactor system according to the invention. The reactor system comprises, from an upstream end to an downstream end, a first catalyst bed 100, a second catalyst bed 200, a third catalyst bed 300 and a fourth catalyst bed 400. Between the first catalyst bed 100 and the second catalyst bed 200, a first quench zone 110 is provided. Similarly, a second quench zone 210 and a third quench zone 310 are provided between successive catalyst beds.

(10) Hydrocarbon gas 10 and hydrogen gas 20 to be fed to the reactor are at room temperature. The hydrocarbon gas 10 is first split into a first portion 11 of the hydrocarbon gas which is to be fed to the upstream end of the reactor and a second portion 12 of the hydrocarbon gas which is to be fed to the quench zones. Similarly, the hydrogen gas 20 is split into a first portion 21 of the hydrogen gas which is to be fed to the upstream end of the reactor and a second portion 22 of the hydrogen gas which is to be fed to the quench zones.

(11) The first portion 11 of the hydrocarbon gas and the first portion 21 of the hydrogen gas are mixed to form a mixture 15. The mixture 15 is fed to a heating means to obtain a heated mixture 31 of hydrocarbon and hydrogen. The ratio between hydrogen and hydrocarbon in the heated mixture is in the range of 1:1 to 4:1. The heated mixture 31 is fed to the first catalyst bed 100 set to a desired temperature. The first effluent 30 from the first catalyst bed 100 enters the first quench zone 110.

(12) The second portion 12 of the hydrocarbon gas is further split up into two fractions. One fraction 12a is added to the first quench zone 110 to be mixed with the first effluent 30 from the first catalyst bed 100 to obtain a first quenched mixture 41. By the addition of the hydrocarbon gas 12a having a room temperature, the temperature is lowered and the ratio between hydrogen and hydrocarbon is lowered. The first quenched mixture 41 is fed to the second catalyst bed 200 set to a desired temperature. The second effluent 40 from the second catalyst bed 200 enters the second quench zone 210.

(13) The second portion 22 of the hydrogen gas is added to the second quench zone 210 to be mixed with the second effluent 40 from the second catalyst bed 200 to obtain a second quenched mixture 51. By the addition of the hydrogen gas 22 having a room temperature, the temperature is lowered and the ratio between hydrogen and hydrocarbon is increased. The second quenched mixture 51 is fed to the third catalyst bed 300 set to a desired temperature. The third effluent 50 from the third catalyst bed 300 enters the third quench zone 310. The fraction 12b of the second portion 12 of the hydrocarbon gas is added to the third quench zone 310 to be mixed with the second effluent 50 from the second catalyst bed 300 to obtain a third quenched mixture 61. By the addition of the hydrocarbon gas 12b having a room temperature, the temperature is lowered and the ratio between hydrogen and hydrocarbon is lowered. The quenched mixture 61 is fed to the fourth catalyst bed 400 set to a desired temperature. A hydrocracking product stream 60 is obtained and exits the reactor system from the downstream end.

(14) The addition of the quench gas is performed such that the molar ratio of hydrogen and hydrocarbons in the quenched mixtures entering the catalyst beds is in the range of 1:1 to 4:1.

(15) FIG. 4 shows a scheme illustrating an example of the gas phase hydrocracking reactor system according to the invention. The catalyst beds 100-400 and the quench zones 110-310 in FIG. 4 are the same as the reactor in FIG. 5, but the hydrocarbon gas and hydrogen gas to be fed to the reactor system is first mixed before being split into a first portion 15 which is to be fed to the upstream end of the reactor and a second portion 14 of which is to be fed to the quench zones.

(16) The first portion of the hydrocarbon gas and the first portion of the hydrogen gas are fed as a mixture 15 to a heating means to obtain a heated mixture 31 of hydrocarbon and hydrogen. The ratio between hydrogen and hydrocarbon in the heated mixture 31 is in the range of 1:1 to 4:1. The heated mixture 31 is fed to the first catalyst bed 100 set to a desired temperature. The first effluent 30 from the first catalyst bed 100 enters the first quench zone.

(17) The second portion 14 of the mixture is further split up into three fractions 14a, 14b, 14c. Each of the fractions 14a, 14b, 14c is added to the first quench zone 110, the second quench zone 210 and the third quench zone 310, respectively, to be mixed with the effluent from the previous catalyst bed to decrease the temperature. The third quenched mixture 61 from the third quench zone 310 is fed to the fourth catalyst bed 400 set to a desired temperature. A hydrocracking product stream 60 is obtained and exits the reactor system from the downstream end.

(18) The addition of the quench gas (mixture of hydrocarbon gas and hydrogen gas) is performed such that the molar ratio of hydrogen and hydrocarbons in the quenched mixtures entering the catalyst beds is in the range of 1:1 to 4:1.

(19) FIG. 2 shows a scheme illustrating an example of the gas phase hydrocracking reactor in which only hydrogen gas is used as a quench gas fed to the quench zones. Hydrogen gas 22a, 22b, 22c are fed to the quench zones 110, 210 and 310, respectively.

(20) FIG. 3 shows a scheme illustrating an example of the gas phase hydrocracking reactor in which only hydrocarbon gas is used as a quench gas fed to the quench zones. Hydrocarbon gas 12a, 12b, 12c are fed to the quench zones 110, 210 and 310, respectively.

EXAMPLES

(21) Simulations were carried out using a naphtha feed, the feed composition is shown in Table 1. The reactor is operated at 450 C., 200 psig, weight hourly space velocity of 2.6 h.sup.1 and H:HC of 3.

(22) TABLE-US-00001 TABLE 1 Naphtha feed composition Components Mass fraction (by wt) Pentane 0.128 Hexane 0.130 Methylcyclopentane 0.083 Benzene 0.007 Heptane 0.127 Methylcyclohexane 0.066 Toluene 0.014 Octane 0.090 Ethylcyclehexane 0.073 Ethylbenzene 0.027 Nonane 0.143 Isopropylbenzene 0.041 Butylbenzene 0 Decane 0.071 Total 1

Example 1 (Comparative): Series of Reactors with Interstage Cooling

(23) The hydrocarbon feed is subjected to hydrocracking by a system as illustrated in FIG. 1. The hydrocarbon feed is pre-mixed with hydrogen and heated to reaction temperature before entering the first reactor. Interstage heat exchangers are used to control the reactor temperature. The temperature and the molar ratio of hydrogen to hydrocarbon (indicated as H:HC) in the streams are summarized in Table 1.

(24) TABLE-US-00002 TABLE 1 Reactors with interstage heat exchanger cooling Reactor 100 200 300 400 Stream 31 30 41 40 51 50 61 60 Temperature ( C.) 430 470 430 470 430 470 430 470 Flowrate (kg/h) 10000 10000 10000 10000 10000 10000 10000 10000 H:HC 3.0 2.1 2.1 1.6 1.6 1.1 1.1 0.9

(25) In this example, the heat exchangers are required for cooling the effluent from the previous catalyst bed.

Example 2 (Comparative): Series of Reactors with Pure H2 Coldshot Cooling

(26) The hydrocarbon feed is subjected to hydrocracking by a system as illustrated in FIG. 2. H2 is introduced at each stage of the reactor to control the temperature. The temperature and the molar ratio of hydrogen to hydrocarbon (indicated as H:HC) in the streams are summarized in Table 2.

(27) TABLE-US-00003 TABLE 2 Reactors with pure H2 coldshot cooling Reactor 100 200 300 400 Stream 31 30 41 40 51 50 61 60 Temperature ( C.) 430 473 430 475 435 473 434 470 Flowrate (kg/h) 10000 10000 10500 10500 11000 11000 11550 11550 H:HC 3.0 2.1 3.0 2.2 2.9 2.4 3.0 2.7

(28) In this example, the heat exchangers are not required for cooling the effluent from the previous catalyst bed. Instead, the effluent from the previous catalyst bed is mixed with a stream of H2 of room temperature (cold shot) in quench zones between catalyst beds. The cold shot decreases the effluent temperature while increasing the ratio between hydrogen and hydrocarbons.

(29) Use of only hydrogen results in a high H2:hydrogen ratio in each of the reaction zones. The large amount of hydrogen leads to a large reactor size which is undesirable.

Example 3 (Comparative): Series of Reactors with Pure Naphtha Coldshot Cooling

(30) The hydrocarbon feed is subjected to hydrocracking by a system as illustrated in FIG. 3. Hydrocarbon is introduced at each stage of the reactor to control the temperature. The temperature and the molar ratio of hydrogen to hydrocarbon (indicated as H:HC) in the streams are summarized in Table 3.

(31) TABLE-US-00004 TABLE 3 Reactors with pure naphtha coldshot cooling Reactor 100 200 300 400 Stream 31 30 41 40 51 50 61 60 Temperature ( C.) 430 473 436 472 433 475 442 487 Flowrate (kg/h) 7500 7500 8300 8300 9200 9200 10000 10000 H:HC 3.0 2.1 1.9 1.4 1.3 0.9 0.9 0.6

(32) In this example, the heat exchangers are not required for cooling the effluent from the previous catalyst bed. Instead, the effluent from the previous catalyst bed is mixed with a stream of hydrocarbon of room temperature (cold shot) in quench zones between catalyst beds. The cold shot decreases the effluent temperature while decreasing the ratio between hydrogen and hydrocarbons.

(33) Use of only hydrocarbon eventually results in a H2:hydrocarbon ratio which is too low. Although a low H2:hydrocarbon ratio is advantageous for achieving a small reactor size, the H2:hydrocarbon ratio is too low in the last reaction zone to avoid a high risk of catalyst deactivation in the last reaction zone in this example.

Example 4: Series of Reactors with HCH2 Mixture Coldshot Cooling

(34) The hydrocarbon feed is subjected to hydrocracking by a system as illustrated in FIG. 4. A mixture of hydrogen and hydrocarbon is introduced at each stage of the reactor to control the temperature. The temperature and the molar ratio of hydrogen to hydrocarbon (indicated as H:HC) in the streams are summarized in Table 4.

(35) TABLE-US-00005 TABLE 4 Reactors with hydrogen_naphtha mixture coldshot cooling Reactor 100 200 300 400 Stream 31 30 41 40 51 50 61 60 Temperature ( C.) 430 474 433 480 435 485 435 488 Flowrate (kg/h) 6000 6000 7000 7000 8300 8300 10000 10000 H:HC 3.0 2.1 2.2 1.5 1.6 1.1 1.3 0.9

(36) In this example, the heat exchangers are not required for cooling the effluent from the previous catalyst bed. Instead, the effluent from the previous catalyst bed is mixed with a mixture of H2 and hydrocarbon of room temperature (cold shot) in quench zones between catalyst beds. The cold shot decreases the effluent temperature while slightly increasing the ratio between hydrogen and hydrocarbons.

Example 5: Series of Reactors with Alternate HC and Hydrogen Coldshot Cooling

(37) The hydrocarbon feed is subjected to hydrocracking by a system as illustrated in FIG. 5. A stream of hydrogen or a stream of hydrocarbon is introduced at each stage of the reactor to control the temperature. The temperature and the molar ratio of hydrogen to hydrocarbon (indicated as H:HC) in the streams are summarized in Table 5.

(38) TABLE-US-00006 TABLE 5 Reactors with hydrogen and naphtha coldshot cooling Reactor 100 200 300 400 Stream 31 30 41 40 51 50 61 60 Temperature ( C.) 430 474 433 470 431 474 435 472 Flowrate (kg/h) 7800 7800 8700 8700 8950 8950 10000 10000 H:HC 3.0 2.1 1.9 1.4 2.3 1.7 1.6 1.3

(39) In this example, the heat exchangers are not required for cooling the effluent from the previous catalyst bed. Instead, the effluent from the previous catalyst bed is mixed with a stream of H2 or hydrocarbon of room temperature (cold shot) in quench zones between catalyst beds. The cold shot decreases the effluent temperature while changing the ratio between hydrogen and hydrocarbons.

(40) A hydrocarbon stream is fed as cold shot to the effluent from the first bed. This leads to a decrease in H:HC ratio. A hydrogen stream is fed as cold shot to the effluent from the second bed, leading to an increase in the H:HC ratio. Subsequently, a hydrocarbon stream is fed as cold shot to the effluent from the third bed. This leads to a decrease in H:HC ratio.

(41) By injecting the hydrocarbon stream and the hydrogen stream alternately, the ratio between hydrogen and hydrocarbons is adjusted to be relatively stable. The H2:hydrocarbon ratio can be controlled such that it is sufficiently low for achieving a small reactor size while being maintained within the desired range.