PROCESS FOR PRODUCING BENZENE FROM C5-C12 HYDROCARBON MIXTURE

Abstract

The present invention relates to a process for producing benzene comprising the steps of: a) separating a source feedstream comprising C5-C12 hydrocarbons including benzene and alkylbenzenes into a first feedstream comprising a higher proportion of benzene than the source feedstream and a second feedstream comprising a lower proportion of benzene than the source feedstream and subsequently, b) contacting the first feedstream in the presence of hydrogen with a first hydrocracking catalyst comprising 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 (SiO2) to alumina (Al2O3) molar ratio of 5-200 under first process conditions to produce a first product stream comprising benzene, wherein the first process conditions 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, and c) contacting the second feedstream with hydrogen under second process conditions to produce a second product stream comprising benzene, wherein i) the second process conditions are suitable for hydrocracking and step (c) involves contacting the second feedstream in the presence of hydrogen with a second hydrocracking catalyst comprising 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 (SiO2) to alumina (Al2O3) molar ratio of 5-200 under the second process conditions which include a temperature of 300-600 C., a pressure of 300-5000 kPa gauge and a Weight Hourly space Velocity of 0.1-15 h.sup.1, ii) the second process conditions are suitable for toluene disproportionation and involve contracting the second feedstream with a toluene disproportionation catalyst, or iii) the second process conditions are suitable for hydrodealkylation.

Claims

1. A process for producing benzene comprising the steps of: (a) separating a source feedstream comprising C5-C12 hydrocarbons including benzene and alkylbenzenes into a first feedstream comprising a higher proportion of benzene than the source feedstream and a second feedstream comprising a lower proportion of benzene than the source feedstream and subsequently (b) contacting the first feedstream in the presence of hydrogen with a first hydrocracking catalyst comprising 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 (SiO2) to alumina (Al2O3) molar ratio of 5-200 under first process conditions to produce a first product stream comprising benzene, wherein the first process conditions 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, and (c) contacting the second feedstream with hydrogen under second process conditions to produce a second product stream comprising benzene, wherein i) the second process conditions are suitable for hydrocracking and step (c) involves contacting the second feedstream in the presence of hydrogen with a second hydrocracking catalyst comprising 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 (SiO2) to alumina (Al2O3) molar ratio of 5-200 under the second process conditions which include a temperature of 300-600 C., a pressure of 300-5000 kPa gauge and a Weight Hourly Space Velocity of 0.1-15 h.sup.1, ii) the second process conditions are suitable for toluene disproportionation and involve contacting the second feedstream with a toluene disproportionation catalyst or iii) the second process conditions are suitable for hydrodealkylation.

2. The process according to claim 1, wherein the separation of the source feedstream into the first feedstream and the second feedstream is performed such that the first feedstream comprises C6 hydrocarbons and at least one of non-aromatic C7 hydrocarbons and the second feedstream comprises remaining hydrocarbons including toluene.

3. The process according to claim 1, wherein the first hydrocracking catalyst comprises less than 0.01 parts tin and less than 0.02 parts lead and less than 0.01 parts bismuth on the basis of 100 parts by weight of the total catalyst.

4. The process according to claim 1, wherein BTX is separated from the first product stream and benzene is separated from the BTX.

5. The process according to claim 1, wherein toluene in the first product stream is recycled back to be included in the second feed stream.

6. The process according to claim 1, wherein step c) involves option i) and BTX is separated from the second product stream optionally after the second product stream is combined with the first product stream, and benzene is separated from the BTX.

7. The process according to claim 6, wherein toluene in the second product stream is recycled back to be included in the second feed stream.

8. The process according to claim 1, wherein step c) involves option ii) or iii) and BTX is separated from the second product stream and benzene is separated from the BTX.

9. The process according to claim 8, wherein the benzene from the second product stream is recycled back to be included in the first feed stream.

10. The process according to claim 1, wherein step c) involves option ii) or iii) and the second product stream is recycled back to be included in the source feed stream.

11. The process according to claim 1, wherein the first feedstream is subjected to hydrogenation before step (b) and/or the second feedstream is subjected to hydrogenation before step (c).

12. The process according to claim 1, wherein the source feedstream comprises pyrolysis gasoline, straight run naphtha, light coker naphtha and coke oven light oil or mixtures thereof.

13. The process according to claim 1, wherein the proportion of benzene in the total amount of BTX in the second feed stream is at most 10 wt %.

Description

[0099] FIG. 1 shows a scheme illustrating an example of the process according to the invention. In this example, the source feed stream is separated by a pre-separation means to a first feed stream rich in benzene and a second feed stream poor in benzene. The first feed stream is contacted with hydrogen in the presence of a hydrocracking catalyst in reactor 1. The second feed stream is also contacted with hydrogen in hydrocracking conditions in reactor 2. The hydrocracking product streams comprising LPG and BTX are subjected to gas-liquid separation to be separated into LPG and BTX. BTX is separated into benzene, toluene and xylene. Toluene is recycled back to the second feed stream.

EXPERIMENTS

[0100] Feed mixtures comprising different compositions of hydrocarbons were subjected to hydrocracking in order to determine the influence of the feed compositions to the product compositions.

[0101] In experiment 1, a feed stream having a composition typical for pyrolysis gasoline was subjected to hydrocracking. This corresponds to an example of the conventional process where no pre-separation of the feedstream is performed before hydrocracking.

[0102] In experiment 2, a feed stream comprising a high amount of benzene and substantially no amount of alkylbenzene was subjected to hydrocracking. This corresponds to an example of the hydrocracking of the first feed stream of step b) of the process of the present invention.

[0103] In experiment 3, a feed stream comprising no benzene and consisting of toluene was subjected to hydrocracking. This corresponds to an example of the hydrocracking of the second feed stream of step c) i) of the process of the present invention.

[0104] In experiment 4, a feed stream comprising no benzene and large amounts of toluene, xylene and ethylbenzene was subjected to hydrocracking. This corresponds to a further example of the hydrocracking of the second feed stream of step c) i) of the process of the present invention.

Experiment 1

[0105] Two-stage hydrotreated pyrolysis gasoline having the composition shown in Table 1 was fed to a reactor having a hydrocracking catalyst of 0.03 wt % of Pt deposited on ZSM-5, where the ratio of SiO2/Al2O3 is 80. The process conditions were 476 C., 200 psig, H2/HC=3, WHSV=2 hr.sup.1. The composition of the resulting product stream is shown in Table 1.

[0106] Benzene purity of the product stream is extremely high, i.e. there is substantially no co-boilers of benzene.

[0107] However, the amount of benzene in the product stream is not higher than the source feedstream. A substantial amount of alkylbenzene, particularly toluene and xylene is obtained.

TABLE-US-00001 TABLE 1 Source (wt %) Product (wt %) Benzene 48.11 47.75 Cyclohexane 2.87 0.01 Toluene 16.03 19.22 Mixed xylenes 2.83 2.85 Ethylbenzene 5.61 0.11 Trimethylbenzene 0.03 0.03 Benzene purity 71.14% 99.96%

[0108] Benzene purity is defined as [mass of benzene]/[sum of the masses of benzene, 2-methylpentane, 3-methylpentane, hexane, methylcyclopentane and cyclohexane] in Tables 1-4.

Experiment 2: Benzene-Rich Stream

[0109] A feed having the composition shown in Table 2 was fed to a reactor comprising a hydrocracking catalyst having the same composition as the catalyst used in experiment 1. The process conditions were 470 C., 200 psig, H2/HC=1, WHSV=3 hr.sup.1. The composition of the resulting product stream is shown in Table 2.

[0110] This experiment shows that hydrocracking a source feedstream comprising a high amount of benzene results in some loss of benzene, but chemical grade BTX is obtained from which a large amount of chemical grade benzene can be obtained.

TABLE-US-00002 TABLE 2 Source (wt %) Product (wt %) Benzene 75.36 71.57 Cyclohexane 0 0.01 Toluene 0 3.13 Mixed xylenes 0 0.18 Ethylbenzene 0 0.25 Trimethylbenzene 0 0.01 Benzene purity 78.91% 99.83%

Experiment 3: Benzene-Poor Stream

[0111] A feed having the composition shown in Table 3 was fed to a reactor comprising a hydrocracking catalyst having the same composition as the catalyst used in experiment 1. The process conditions were 450 C., 200 psig, H2/HC=1, WHSV=3 hr.sup.1. The composition of the resulting product stream is shown in Table 3.

[0112] This experiment illustrates the effect of hydrocracking a feed stream with a low benzene content. It can be seen that a substantial amount of toluene converted into benzene and toluene by toluene disproportionation.

TABLE-US-00003 TABLE 3 Source (wt %) Product (wt %) Benzene 0 8.88 Cyclohexane 0 0 Toluene 100 78.25 Mixed xylenes 0 11.26 Ethylbenzene 0 0.01 Trimethylbenzene 0 0.05 Benzene purity 99.96%

Experiment 4: Benzene-Poor Stream

[0113] A feed having the composition shown in Table 4 was fed to a reactor comprising a hydrocracking catalyst having the same composition as the catalyst used in experiment 1. The process conditions were 450 C., 200 psig, H2/HC=1, WHSV=3 hr.sup.1. The composition of the resulting product stream is shown in Table 4.

TABLE-US-00004 TABLE 4 Source (wt %) Product (wt %) Benzene 0 20.16 Cyclohexane 0 0.01 Toluene 65.0 56.47 Mixed xylenes 12.2 15.83 Ethylbenzene 22.7 0.04 Trimethylbenzene 0 0.11 Benzene purity 99.96%

[0114] In this experiment, a feed comprising substantially no components other than alkyl aromatics (toluene, xylene and ethylbenzene) was hydrocracked. This experiment clearly demonstrates that the presence of xylenes limits toluene disproportionation/benzene formation. Substantially all ethylbenzene was converted to benzene, which resulted in the difference in the benzene contents between examples 3 and 4.