PROCESS FOR PRODUCING LPG AND BTX

Abstract

The invention relates to a process for producing LPG and BTX, comprising a) subjecting a mixed hydrocarbon feedstream to first hydrocracking in the presence of a first hydrocracking catalyst to produce a first hydrocracking product stream; b) separating the first hydrocracking product stream to provide at least a light hydrocarbon stream comprising at least C2 and C3 hydrocarbons, a middle hydrocarbon stream comprising C4 and/or C5 hydrocarbons and a heavy hydrocarbon stream comprising at least C6+ hydrocarbons and c) subjecting the heavy hydrocarbon stream to second hydrocracking to produce a second hydrocracking product stream comprising BTX, wherein the second hydrocracking is more severe than the first hydrocracking, wherein at least part of the middle hydrocarbon stream is recycled back to the first hydrocracking in step a).

Claims

1. A process for producing LPG and BTX, comprising a) subjecting a mixed hydrocarbon feedstream to first hydrocracking in the presence of a first hydrocracking catalyst to produce a first hydrocracking product stream; b) separating the first hydrocracking product stream to provide at least a light hydrocarbon stream comprising at least C2 and C3 hydrocarbons, a middle hydrocarbon stream comprising C4 and/or C5 hydrocarbons and a heavy hydrocarbon stream comprising at least C6.sub.+ hydrocarbons and c) subjecting the heavy hydrocarbon stream to second hydrocracking in the presence of a second hydrocracking catalyst to produce a second hydrocracking product stream comprising BTX, wherein the second hydrocracking is more severe than the first hydrocracking, wherein at least part of the middle hydrocarbon stream is recycled back to the first hydrocracking in step a).

2. The process according to claim 1, wherein the first hydrocracking is a hydrocracking process suitable for converting a hydrocarbon feed that is relatively rich in naphthenic and paraffinic hydrocarbon compounds to a stream rich in LPG and aromatic hydrocarbons.

3. The process according claim 1, wherein the first hydrocracking catalyst is a catalyst containing one metal or two or more metals of group VIII, VI B or VII B of the periodic classification of elements deposited on a carrier.

4. The process according to claim 1, wherein the second hydrocracking product stream is substantially free from non-aromatic C6.sub.+ hydrocarbons.

5. The process according to claim 1, wherein the second hydrocracking is performed using a 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 Å and a silica (SiO.sub.2) to alumina (Al.sub.2O.sub.3) molar ratio of 5-200 under conditions comprising a temperature of 300-580° C., a pressure of 0.3-5 MPa gauge and a Weight Hourly Space Velocity (WHSV) of 0.1-15 h.sup.−1.

6. The process according to claim 1, wherein the first hydrocracking conditions comprise a lower process temperature than the second hydrocracking conditions.

7. The process according to claim 1, wherein the mixed hydrocarbon feedstream comprises a naphtha or a naphtha-like product.

8. The process according to claim 1, wherein H2 or H2 and C1 hydrocarbon is separated from the first hydrocracking product stream before the separation between the light, middle and heavy hydrocarbon streams.

9. The process according to claim 1, wherein the separation between the light hydrocarbon stream and the middle hydrocarbon stream is performed to separate between C3 hydrocarbon and iC4 hydrocarbon, between iC4 hydrocarbon and nC4 hydrocarbon or between nC4 hydrocarbon and C5 hydrocarbon.

10. The process according to claim 1, wherein the separation between the middle hydrocarbon stream and the heavy hydrocarbon stream is performed to separate between iC4 hydrocarbon and nC4 hydrocarbon, between nC4 hydrocarbon and C5 hydrocarbon or between C5 hydrocarbon and C6 hydrocarbon.

11. The process according to claim 1, wherein at least part of non-recycled C4 hydrocarbon from the middle hydrocarbon stream is subjected to a further step selected from the group consisting of isomerization, butane dehydrogenation (non-oxidative and oxidative), reaction with methanol and reaction with ethanol and combinations thereof.

12. The process according to claim 1, wherein the separation between the light hydrocarbon stream and the middle hydrocarbon stream is performed to separate between C3 hydrocarbon and iC4 hydrocarbon; the separation between the middle hydrocarbon stream and the heavy hydrocarbon stream is performed to separate C5 hydrocarbon and C6 hydrocarbon; step b) involves separating between the C4 hydrocarbon of the middle hydrocarbon stream and the C5 hydrocarbon of the middle hydrocarbon stream; at least part of the C5 hydrocarbon in the middle hydrocarbon stream is recycled back to the first hydrocracking in step a); and at least part of the C4 hydrocarbon in the middle hydrocarbon stream is subjected to a further step selected from the group consisting of isomerization, butane dehydrogenation (non-oxidative and oxidative), reaction with methanol and reaction with ethanol and combinations thereof.

13. The process according to claim 1, wherein C4.sub.− hydrocarbon in the second hydrocracking product stream is separated from the second hydrocracking product stream to be recycled back to the separation of step b) or combined with the light hydrocarbon stream.

14. The process according to claim 1, wherein the amount of methane in the first hydrocracking product stream is at most 5 wt %.

15. The process according to claim 1, wherein the amount of the C4 and C5 hydrocarbons in the at least part of the middle hydrocarbon stream is at least 70 wt %.

16. The process according to claim 5, wherein the temperature is 425-580° C.

17. The process according to claim 7, wherein the mixed hydrocarbon feed stream has a boiling point range of 20-200° C.

Description

EXAMPLES

Example 1

[0104] A feed consisting of n-pentane was subjected to hydrocracking in order to determine the influence of hydrocracking conditions to the product compositions. The experiments were carried out in a 12 mm reactor, wherein the catalyst bed was located in the isothermal zone of the reactor heater. The catalyst used was a mixture of 2 grams of Pt on alumina (Pt-loading of 0.75 wt %) and H-ZSM-5 (SiO.sub.2/Al.sub.2O.sub.3=80).

[0105] The feed stream was fed to the reactor. The feed stream enters a vaporizer section prior to the reactor where it is vaporized at 280° C. and mixed with hydrogen gas. The conditions used throughout these experiments were: WHSV=1/hr, pressure was 1379 kPa (200 psig) and the molar ratio H.sub.2/hydrocarbons was 3. The temperature of the isothermal zone of the reactor was varied between 375 and 450° C. The effluent of the reactor was sampled in the gas phase to an online gas chromatograph. Product analyses were carried out once per hour.

TABLE-US-00001 TABLE 1 Compositions of hydrocracking product effluent Component 375° C. 400° C. 425° C. 450° C. Methane (wt %) 0.5 1.1 2.2 3.9 Ethane (wt %) 3.3 7.2 12.7 19.4 Propane (wt %) 16.3 24.4 32.8 39.7 Butanes (wt %) 16.9 19.8 20.8 19.0 i-Pentane (wt %) 11.9 13.8 13.4 9.6 n-Pentane (wt %) 49.0 32.3 17.3 7.2 C6+ (wt %) 2.1 1.4 0.8 1.2 Selectivity (—) 98.7 98 96.8 95.3

[0106] The compositions of the product effluent at different reactor temperatures are provided in Table 1. The selectivity was defined as (100%−(amount of methane formed/amount of C5 converted)). The amount of C5 converted is defined as (total amount−(i-pentane and n-pentane)). By comparing the results in Table 1, it was observed that when the reactor temperature is decreased, the overall selectivity is increased during hydrocracking. It is anticipated that a similar trend will be observed when a feed consisting of butanes is subjected to hydrocracking (based on experiments using different carbon number paraffin feeds and conversions and production rates obtained using naphtha type feeds).

[0107] It can therefore be concluded that a higher selectivity can be achieved by operating at a lower temperature. A higher selectivity can be achieved by recycling the unconverted paraffins as in the process of the invention, instead of operating the hydrocracking unit at increased temperatures.