Desulphurizing a hydrocarbons-containing feed

Abstract

 Method of desulphurizing a hydrocarbons-containing feed (1) in the presence of hydrogen (5, 8) in a catalytic reactor (3) at a desulphurization pressure and temperature, which method comprises the steps supplying the feed (1) to the catalytic reactor (3) and allowing the feed to react with hydrogen; removing from the catalytic reactor (3) a desulphurized stream (10); and separating the desulphurized stream (10) into a gaseous overhead (15) and a liquid product stream (17), wherein the process further comprises supplying a hydrogen-containing gas (5, 8) to the inlet (15, 42) of a membrane unit (19, 45) which includes a membrane (20, 47) that is selective for methane, removing from the retentate outlet (23, 53) of the membrane unit (19, 45) a gas enriched in hydrogen (26, 56), and supplying the gas enriched in hydrogen (26, 56) at desulphurization pressure to the catalytic reactor (3).

Description

[0001] The present invention relates to a method of desulphurizing a hydrocarbons-containing feed in the presence of hydrogen in a catalytic reactor at a desulphurization pressure and temperature. Such a method is referred to as hydrotreating or hydrodesulphurization.

[0002] Two basic processes are applied, a liquid phase or trickle flow process for a heavier hydrocarbons-containing feed, for example kerosene and heavier hydrocarbons and a vapour phase process for a lighter hydrocarbons-containing feed, for example light straight-run and cracked fractions.

[0003] In both methods the hydrocarbons-containing feed is desulphurized in the presence of hydrogen in a catalytic reactor at a desulphurization pressure and temperature. The desulphurizing pressure is typically in the range of from 2 to 6 MPa and the desulphurizing temperature is typically in the range of from 300 to 380 °C. The catalyst employed in hydrodesulphurization can be any suitable catalyst.

[0004] The hydrogen required for hydrodesulphurization is delivered by a hydrogen-containing refinery stream. Such a stream is for example obtained from a reforming process, such as platforming. Such a stream contains hydrogen and hydrocarbons, in particular hydrocarbons in the range of C₁ through C₅.

[0005] From the catalytic reactor is removed a desulphurized stream, which is cooled to a temperature in the range of from 40 to 50 °C and separated in a separator into a gaseous overhead and a liquid product stream. The hydrogen-containing gaseous overhead is recycled to the catalytic reactor, and the liquid product stream is further treated.

[0006] In hydrodesulphurization, it is desirable to have a relatively high partial pressure of hydrogen in the catalytic reactor. This requires treating the hydrogen-containing refinery stream and/or the hydrogen-containing gaseous overhead from the separator.

[0007] It is an object of the present invention to treat the hydrogen-containing streams with a membrane unit so as to increase the hydrogen-content of these streams. It is a further object of the present invention to carry out the membrane treatment so as to avoid pressure losses in the membrane unit.

[0008] To this end the method of desulphurizing a hydrocarbons-containing feed in the presence of hydrogen in a catalytic reactor at a desulphurization pressure and temperature according to the present invention comprises the steps supplying the feed to the catalytic reactor and allowing the feed to react with hydrogen; removing from the catalytic reactor a desulphurized stream; and separating the desulphurized stream into a gaseous overhead and a liquid product stream, wherein the process further comprises supplying a hydrogen-containing gas to the inlet of a membrane unit which includes a membrane that is selective for methane, removing from the retentate outlet of the membrane unit a gas enriched in hydrogen, and supplying the gas enriched in hydrogen at desulphurization pressure to the catalytic reactor.

[0009] The membrane that is selective for methane is a membrane which preferentially permeates methane to hydrogen, suitably, the selectivity of methane to hydrogen (αCH₄/H₂) of greater than 1.6. The selectivity αA/B is defined as the quotient of the permeability of the substances A over the permeability of substance B.

[0010] Suitable membranes are comprise a layer of rubbery polydimethylsiloxane (PDMS).

[0011] The invention will now be described by way of example in more detail with reference to the accompanying drawing which shows schematically a flow scheme of the process according to the present invention.

[0012] In the desulphurization method of the present invention a hydrocarbons-containing feed is supplied through a conduit 1 to a catalytic reactor 3 at a pressure and a temperature which are suitable to desulphurize the hydrocarbons-containing feed in the presence of hydrogen which is supplied through conduits 5 and 8.

[0013] The feed is allowed to react with the hydrogen so as to obtain desulphurized hydrocarbons and hydrogen sulphide. From the catalytic reactor 3 a desulphurized stream is removed through a conduit 10. The desulphurized stream is separated in separator 11 into a gaseous overhead removed through conduit 15 and a liquid product stream removed through conduit 17. The liquid product stream is passed away through conduit 17 for further treatment, which further treatment is not relevant to the present invention and will therefore not be discussed.

[0014] The gaseous overhead contains unreacted hydrogen, gaseous hydrocarbons and hydrogen sulphide. At least part of the gaseous overhead stream is recycled to the catalytic reactor 3.

[0015] To do this, the process of the present invention further comprises supplying a hydrogen-containing gas in the form of the gaseous overhead 15 to the inlet 18 of a membrane unit 19. The membrane unit 19 includes a membrane 20 that is selective for methane, which membrane separates the membrane unit 19 into a retentate side 21 and a permeate side 22 having outlets 23 and 24, respectively, wherein the inlet 18 of the membrane unit 19 opens into the retentate side 21. The pressure in the permeate side 22 is lower than that in the retentate side 21.

[0016] From the retentate outlet 23 of the membrane unit 19 is removed a gas enriched in hydrogen through conduit 26 which is in fluid communication with the conduit 8 so as to supply the gas enriched in hydrogen at desulphurization pressure to the catalytic reactor 3.

[0017] From the outlet 24 of the permeate side 22 of the membrane unit 19, a permeate stream is removed through conduit 30. The permeate stream can be further treated (not shown).

[0018] It is advantageous to use a membrane that is selective for methane, because the pressure drop experienced by the gas enriched in hydrogen is much lower than in the case that a membrane was used that was selective for hydrogen, wherein at least a greater part of the hydrogen passes to the permeate side.

[0019] If the pressure of the gas enriched in hydrogen passing through the conduit 26 is below the pressure which prevails in the catalytic reactor 3, the gas is compressed by compressor 33.

[0020] Optionally a bleed stream is removed through conduit 35.

[0021] The hydrogen required for hydrodesulphurization is delivered by a hydrogen-containing refinery stream 40. Such a stream is for example obtained from a reforming process, such as platforming. Such a stream contains hydrogen and hydrocarbons, in particular hydrocarbons in the range of C₁ through C₅.

[0022] The hydrogen-containing refinery stream 40 can be supplied directly to the catalytic reactor 3, however, suitably, the stream is treated so as to remove at least part of the hydrocarbons therefrom. Which is advantageous because in this way the partial pressure of hydrogen in the catalytic reactor can be increased.

[0023] To do this, the process of the present invention further comprises supplying a hydrogen-containing gas in the form of the hydrogen-containing refinery stream 40 to the inlet 42 of a second membrane unit 45. The second membrane unit 45 includes a membrane 47 that is selective for methane, which membrane separates the second membrane unit 45 into a retentate side 49 and a permeate side 50 having outlets 53 and 54, respectively, wherein the inlet 42 of the second membrane unit 45 opens into the retentate side 49. The pressure in the permeate side 50 is lower than that in the retentate side 49.

[0024] From the retentate outlet 53 of the second membrane unit 45 is removed a gas enriched in hydrogen through conduit 56 which is in fluid communication with the conduit 5 so as to supply the gas enriched in hydrogen at desulphurization pressure to the catalytic reactor 3.

[0025] From the outlet 54 of the permeate side 50 of the second membrane unit 45, a permeate stream is removed through conduit 60. The permeate stream can be further treated (not shown).

[0026] For the reasons given above, it is here as well advantageous to use a membrane that is selective for methane.

[0027] If the pressure of the gas enriched in hydrogen passing through the conduit 56 is below the pressure which prevails in the catalytic reactor 3, the gas can be compressed by compressor 63.

[0028] Suitably, the desulphurized stream passing through the conduit 10 is cooled before it enters into the separator 11.

[0029] In order to enhance the membrane selectivity the hydrogen-containing gas which is supplied to the inlet of the membrane unit is suitably cooled to a temperature in the range of from 0 to 40 °C. This is suitably done by indirect heat exchange (not shown).

Claims

1. Method of desulphurizing a hydrocarbons-containing feed in the presence of hydrogen in a catalytic reactor at a desulphurization pressure and temperature, which method comprises the steps supplying the feed to the catalytic reactor and allowing the feed to react with hydrogen; removing from the catalytic reactor a desulphurized stream; and separating the desulphurized stream into a gaseous overhead and a liquid product stream, wherein the process further comprises supplying a hydrogen-containing gas to the inlet of a membrane unit which includes a membrane that is selective for methane, removing from the retentate outlet of the membrane unit a gas enriched in hydrogen, and supplying the gas enriched in hydrogen at desulphurization pressure to the catalytic reactor.

2. Method according to claim 1, wherein the hydrogen-containing gas which is supplied to the inlet of the membrane unit is the gaseous overhead from the desulphurized stream.

3. Method according to claim 1 or 2, wherein the hydrogen-containing gas which is supplied to the inlet of the membrane unit is a hydrogen-containing refinery stream.

4. Method according to claim 2 or 3, wherein hydrogen-containing refinery stream is supplied to a first membrane unit and wherein the hydrogen-containing refinery stream is supplied to a second membrane unit.

5. Method according to any one of the claims 1-4, wherein the hydrogen-containing gas which is supplied to the inlet of the membrane unit is cooled to a temperature in the range of from 0 to 40 °C.

Drawing