Deep desulphurization of low sulphur content feedstock

Abstract

The invention pertains to a process for deep desulphurization of low sulphur content feedstock comprising the steps of providing a low sulphur content hydrocarbon feedstock and contacting said hydrocarbon feedstock with a cobalt-molybdenum desulphurizing system or a nickel-molybdenum desulphurizing system in an oxide form in order to obtain a very low sulphur product comprising less than 5 ppm by weight sulphur.

Claims

1. Process for deep desulphurization of low sulphur content hydrocarbon feedstock comprising the steps of: a) providing a low sulphur content hydrocarbon feedstock comprising less than 50 ppm by weight sulphur, b) providing a desulphurizing system comprising a Group VI element selected from cobalt and nickel and a Group VIII element being molybdenum, the Group VI and Group VIII elements being in oxide form, c) optionally drying the desulphurizing system by submitting it to a hydrogen flow at a temperature lower than 250° C., d) desulphurizing the low sulphur content hydrocarbon feedstock by contacting said hydrocarbon feedstock with the optionally dried desulphurizing system in the presence of hydrogen, at a temperature ranging from 220 to 420° C. and at a pressure of less than or equal to 80 bar, to obtain a hydrocarbon fluid comprising less than 5 ppm by weight sulphur, wherein the process further comprises a step of: e) hydrodearomatizing the obtained hydrocarbon fluid comprising less than 5 ppm by weight sulphur.

2. The process of claim 1, wherein the Group VI/Group VIII desulphurizing system is a cobalt-molybdenum desulphurizing system in oxide form.

3. The process of claim 2, wherein the cobalt-molybdenum desulphurizing system in oxide form comprises cobalt oxide and molybdenum trioxide.

4. The process of claim 1, wherein the Group VI/Group VIII desulphurizing system is supported on alumina or silica-alumina.

5. The process of claim 1, wherein the hydrogen flow ranges from 60 to 100 NL/h for 30 minutes to 2 hours.

6. The process of claim 1, wherein the pressure is less than or equal to 70 bar.

7. The process of claim 1, wherein the temperature ranges from 240 to 400° C.

8. The process of claim 1, wherein said hydrocarbon feedstock is contacted with the optionally dried desulphurizing system with a hydrogen to hydrocarbon ratio H.sub.2/HC ranging from 250 to 350 NL/L.

9. The process of claim 1, wherein the Liquid Hourly Space Velocity ranges from 0.1 to 5 h.sup.−1.

10. The process of claim 1, wherein the low sulphur content hydrocarbon feedstock comprises less than 30 ppm by weight sulphur.

11. The process of claim 1, wherein the low sulphur content hydrocarbon feedstock contains less than 5 ppm by weight of dissolved hydrogen sulphide, based on the total weight of the low sulphur content hydrocarbon feedstock.

12. The process of claim 1, wherein the low sulphur content hydrocarbon feedstock has an initial boiling point and a final boiling point between 100° C. and 400° C.

13. The process of claim 1, wherein the low sulphur content hydrocarbon feedstock has a distillation range defined by the difference between the final boiling point and the initial boiling point, not exceeding 80° C.

14. The process of claim 1, wherein the obtained hydrocarbon fluid comprises less than 3 ppm by weight sulphur.

15. The process of claim 5, wherein the hydrogen flow ranges from 60 to 100 NL/h at a temperature ranging from 100° C. to 200° C.

16. The process of claim 1, wherein the Liquid Hourly Space Velocity ranges from 0.3 h.sup.−1 to 2 h.sup.−1.

17. The process of claim 1, wherein the Group VI/Group VIII desulphurizing system is a cobalt-molybdenum desulphurizing system in oxide form supported on alumina or silica-alumina.

18. The process of claim 1, wherein said hydrocarbon feedstock is contacted with the optionally dried desulphurizing system with a hydrogen to hydrocarbon ratio H.sub.2/HC ranging from 250 to 350 NL/L and with a Liquid Hourly Space Velocity ranging from 0.3 h.sup.−1 to 2 h.sup.−1.

19. The process of claim 1, wherein the contacting temperature ranges from 250 to 380° C.

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) FIG. 1 represents a curve illustrating the amount of sulphur in function of reaction conditions and the time on stream, with ( - - ) representing the amount of sulphur in the hydrocarbon feedstock and () representing the amount of sulphur in the desulphurized hydrocarbon fluid.

DETAILED DESCRIPTION OF THE INVENTION

(2) According to a first aspect, the process of the Invention comprises deep desulphurization of low sulphur content hydrocarbon feedstock. Appropriate feedstocks are e.g. gasoil, kerosene, Ultra Low Sulphur Diesel, gasoline . . . . Preferred feedstocks for Implementing the process of the invention are hydrocarbon fluids having a boiling range ranging from 60 to 350° C., in particular from 100 to 300° C. According to an embodiment, feedstocks have a boiling point in the range from 100° C. to 400° C., preferably from 150° C. to 350° C. Typically, the Initial boiling point and the final boiling point of the feedstock can be measured according to well-known methods for the skilled person, such as according to the ASTM D-86 standard. According to an embodiment, the low sulphur content hydrocarbon feedstock has a distillation range defined by the difference between the final boiling point and the initial boiling point, not exceeding 80° C., preferably not exceeding 60° C.

(3) The low sulphur content hydrocarbon feedstock comprises less than 50 ppm sulphur, preferably less than 30 ppm sulphur, more preferably less than 20 ppm sulphur and even more preferably less than 10 ppm sulphur, based on the total weight of the low sulphur content hydrocarbon feedstock. According to an embodiment, the low sulphur content hydrocarbon feedstock comprises from 2 to 30 ppm by weight sulphur, from 3 to 20 ppm by weight sulphur or from 3 to 10 ppm by weight sulphur. The sulfur content can be measured according to well-known methods for the skilled person, such as ISO 20846 method.

(4) According to a preferred embodiment, the low sulphur content hydrocarbon feedstock comprises less than 5 ppm by weight of dissolved hydrogen sulphide, preferably less than 3 ppm by weight of dissolved hydrogen sulphide, more preferably less than 1 ppm by weight of dissolved hydrogen sulphide and even more preferably less than 0.5 ppm by weight of dissolved hydrogen sulphide, based on the total weight of the low sulphur content hydrocarbon feedstock. The dissolved hydrogen sulphide content can be measured according to well-known methods for the skilled person, such as by UV fluorescence. The detection limit of this method is typically of 0.5 ppm of dissolved hydrogen sulphide.

(5) In a preferred embodiment, desuiphurizing system of the present invention comprises cobalt oxide CoO or nickel oxide NiO and molybdenum trioxide MoO.sub.3. According to a preferred embodiment, the Group VI element is cobalt and the weight ratio of Co/(Co+Mo) ranges from 0.1 to 0.5, preferably from 0.2 to 0.4. According to another preferred embodiment, the Group VI element is nickel and the weight ratio of Ni/(Ni+Mo) ranges from 0.1 to 0.5, preferably from 0.2 to 0.4.

(6) In a preferred embodiment, cobalt and molybdenum or nickel and molybdenum are supported on alumina or silica-alumina.

(7) The desulphurizing system is prepared in the conventional manner in the form of, for example, spheres or extrudates. Examples of suitable types of extrudates have been disclosed in the literature (see, int. al., U.S. Pat. No. 4,028,227). Highly suitable for use are cylindrical particles (which may be hollow or not) as well as symmetrical and asymmetrical polylobed particles (2, 3 or 4 lobes). The alumina or silica-alumina support is prepared by extrusion in the form of spheres or extrudates, dried, and further calcined (in the presence or absence of steam) in a temperature range of 475-900° C. The pore volume of the support should generally be in the range of 0.5-2 ml/g, preferably between 0.75-1 mL/g. The specific surface area will generally be in the range of 30-400 m.sup.2/g (measured using the BET method).

(8) According to an embodiment of the invention, the desulphurizing system is prepared by impregnating the alumina or silica-alumina support with an aqueous solution of each metal. For example, the cobalt-molybdenum desuiphurizing system is prepared by impregnating the alumina or silica-alumina support with an aqueous solution of cobalt nitrate and ammonium molybdate. The obtained mixture is washed, dried and calcined according to usual well-known methods.

(9) According to an optional embodiment of the invention, the Group VI/Group VIII desulphurizing system in oxide form is submitted to a hydrogen flow in order to dry the desulphurizing system.

(10) According to a particular embodiment, the desulphurizing system is submitted to a hydrogen flow from 60 to 100 NL/h, preferably of 80 NL/h during 30 minutes to 2 hours, preferably during 1 hour. The temperature for the drying step of the catalyst is lower than 250° C., preferably lower than 220° C., more preferably ranging from 100° C. to 200° C.

(11) Typically, the drying step allows to remove residual water but does not allow to reduce the Group VI and Group VIII elements of the catalyst. Indeed, the drying step is not a reduction step leading to a catalyst wherein the totality of the Group VI and Group VIII elements are in a metallic form. In the process of the invention, the desulphurizing system totally or partially in an oxide form is contacted with the hydrocarbon feedstock. Typically, there is no step of reduction of the desulphurizing system before the contact with the hydrocarbon feedstock.

(12) According to the invention, the deep desulphurization step comprises contacting the hydrocarbon feedstock with the optionally dried desulphurizing system wherein a fraction of the Group VI and Group VIII elements can be in metallic state, typically at least a fraction of the Group VI and Group VIII elements are in an oxide form during the deep desulphurization step. Typically, the deep desulphurization step does not comprise a step of sulphurization of the desulphurizing system before contacting it with the hydrocarbon feedstock.

(13) According to a particular embodiment, the desulphurizing system used in the process of the present invention is not fluorinated before being implemented in said process.

(14) According to a particular embodiment, the process for deep desulphurization comprises contacting the hydrocarbon feedstock with only one desulphurizing system comprising Group VI and Group VIII elements.

(15) According to a particular embodiment, the process for deep desulphurization comprises contacting the hydrocarbon feedstock with only one desulphurizing system comprising cobalt and molybdenum, in other words the process preferably does not comprise contacting the hydrocarbon feedstock with any additional desulphurizing system comprising elements different from cobalt and molybdenum.

(16) According to a particular embodiment, the process for deep desulphurization comprises contacting the hydrocarbon feedstock with only one desuiphurizing system comprising nickel and molybdenum, in other words the process preferably does not comprise contacting the hydrocarbon feedstock with any additional desulphurizing system comprising elements different from nickel and molybdenum.

(17) According to the present invention, the deep desulphurization step is implemented at a pressure of less than or equal to 80 bar, preferably less than or equal to 70 bar, preferably ranging from 20 to 60 bar, more preferably from 30 to 50 bar and preferentially at about 40 bar and at a temperature ranging from 220 to 420° C., preferably from 240 to 400° C., preferably from 250 to 380° C., more preferably from 260 to 360° C., more preferably from 270 to 340° C. even more preferably from 280 to 320° C. and preferentially at about 300*C.

(18) It is quite advantageous to implement the deep desulphurization step at a relatively low pressure below 80 bar since the process can thus be easily Integrated in existing hydrotreating units that work at this (or similar) pressure, without the need of major modification to existing production plants.

(19) In a particular embodiment, the hydrocarbon feedstock is contacted with the optionally dried desulphurizing system with a hydrogen to hydrocarbon ratio H.sub.2/HC ranging from 250 to 350 NL/L of hydrocarbon feedstock, preferably from 270 to 330 NL/L and preferentially of 300 NL/L. According to the invention, the deep desulphurization step is implemented at a Liquid Hourly Space Velocity ranging from 0.1 to 5 h.sup.−1, preferably from 0.3 to 2 h.sup.−1, more preferably from 0.5 to 1 h.sup.−1 and preferentially of 0.7 h.sup.−1.

(20) According to the invention, the deep desulphurization step may be carried out in one single reactor or in several successive reactors, preferably in two successive reactors.

(21) The low-sulphur hydrocarbon fluid obtained after the deep desulphurization step and comprising less than 5 ppm, preferably less than 3 ppm, more preferably less than 2 ppm by weight sulphur, may be used in applications where a very low sulphur content is required. In particular, such low-sulphur hydrocarbon fluids may be used as fuel base.

(22) The low-sulphur hydrocarbon fluids obtained after the deep desulphurization step may also be used as feedstock for units, e.g. hydrogenation units, running with catalysts that are particularly susceptible to sulphur poisoning. This is for example the case of hydrodearomatization catalysts. According to a second aspect, the process of the invention further comprises a step of hydrodearomatization of the obtained very low sulphur hydrocarbon fluid comprising less than 5 ppm, preferably less than 3 ppm, more preferably less than 2 ppm by weight sulphur. According to one embodiment, the very low sulphur hydrocarbon fluid contains more than 20% aromatics, preferably more than 30%. According to another embodiment, the very low sulphur hydrocarbon fluid contains less than 100% aromatics, preferably less than 70%.

(23) Typically, the obtained dearomatized hydrocarbon fluids comprise less than 100 ppm, preferably less than 50 ppm, and more preferably less than 30 ppm aromatics.

(24) In a preferred embodiment, the hydrodearomatization step is carried out in the presence of a nickel containing catalyst. More preferably the nickel containing catalyst is a supported catalyst. In a preferred embodiment, the hydrodearomatization step comprises two hydrogenation stages. The amount of catalyst in the desulphurization reactor and the two hydrodearomatization reactors, expressed in wt %, can be according to the scheme 0.05-0.5/0.10-0.70/0.25-0.85, for example 0.07.0.25/0.15-0.35/0.4-0.78 and most preferably 0.10-0.20/0.20-0.32/0.48-0.70. In other terms, according to this scheme, the desulphurization reactor comprises from 5 to 50 wt %, the first hydrodearomatization reactor comprises from 10 to 70 wt % and the second hydrodearomatization reactor comprises from 25 to 85 wt % of the total mass of desulphurization catalyst and hydrodearomatization catalyst.

(25) In a preferred embodiment, the hydrodearomatization step further comprises a separation stage, whereby unreacted hydrogen is recovered and a stream of hydrogenated product is recovered. The unreacted hydrogen can be recycled at least in part, to the inlet of the hydrodearomatization process. The stream of hydrogenated product can be recycled at least in part, to the inlet of the hydrodearomatization step. The separation stage can comprise up to three separators staged with decreasing pressure. The pressure in the last separator can be about atmospheric pressure. In one embodiment, the process of the present invention comprises a step of hydrodearomatization of the low-sulphur fluid followed by a step of fractionation. The hydrocarbon fractions obtained by fractionation have defined boiling ranges, e.g. of less than 90° C., the boiling range being defined as the difference between the final boiling point and the initial boiling point.

(26) The fluids obtained by the process of desulphurization and hydrodearomatization, and optionally fractionation, of the invention may be used in drilling fluids, as Industrial solvents, in coating fluids, in explosives, in concrete demoulding formulations, in adhesives, in printing inks, in metal working fluids, as cutting fluids, as rolling oils, as Electrical Discharge Machining fluids, rust preventive in industrial lubricants, as extender oils, in sealants or polymers formulation with silicone, as viscosity depressants in plasticised polyvinyl chloride formulations, in resins, as crop protection fluids, in pharmaceutical products, in paint compositions, in polymers used in water treatment, paper manufacturing or printing pastes and cleaning solvents.

Example

(27) 1. Supported CoMo System and Pilot Unit

(28) The test was performed in a pilot unit comprising two reactors, using a commercial supported CoMo system (CoO, MoO.sub.3 on Al.sub.2O.sub.3) in oxidic form. In each reactor, 56 ml of supported CoMo system were loaded mixed with 50% vol of SIC 0.1 mm. A total of 112 ml of supported CoMo system were loaded in the two reactors.

(29) 2. Feed Characterization

(30) A gasoil (GO) with a sulphur content of 8.9 ppmw was used, as represented by the dashed line on FIG. 1. The GO has a dissolved hydrogen sulphide content of less than 0.5 ppm by weight (i.e. the detection limit of the method used), as measured by UV fluorescence.

(31) 3. Supported CoMo System Drying

(32) The supported CoMo system was dried in situ by submitting it to a H.sub.2 flow (80 NL/h) for 1 hour at 150° C. (with a heating rate of 20° C./h) in order to remove residual water.

(33) 4. Testing Conditions

(34) Phase I: Stabilization

(35) The same GO was used as stabilization feed (T=150° C., LHSV=0.7 h.sup.−1, P=40 bar). After about 60 hours on stream, a stable sulphur content of 7.5 ppmw was reached (see FIG. 1).

(36) Phase II: Test in the Conditions of the Invention

(37) After stabilization, temperature was increased to 350° C. (ramp, 20° C./h). This condition (350° C., LHSV 0.7 h.sup.−1, P=40 bar) was maintained for 480 hours. A very low sulphur content of about 0.6 ppmw in the hydrocarbon fluid was obtained at the end of Phase II.

(38) Phase III: End of Test

(39) In order to evaluate the desulphurization activity at lower temperature, after 480 hours of test, the temperature was lowered to 200° C. and maintained for about 80 more hours. A sulphur content of about 6.9 ppmw sulphur remained in the liquid effluent.

(40) A summary of the reaction conditions is reported in Table 1 below.

(41) TABLE-US-00001 TABLE 1 reaction conditions during Phases I to III Phase II Test (According Phase I to the Phase III Stabilization invention) End of test Pressure (barg) 40 40 40 LHSV (h.sup.−1) 0.7 0.7 0.7 Feed rate (mL/h) 78.4 78.4 78.4 H.sub.2/HC (NL/L) 300 300 300 Hydrogen flow (NL/h) 23.5 23.5 23.5 WABT* (° C.) (REACTOR 1) 150 350 200 WABT* (° C.) (REACTOR 2) 150 350 200 Duration of condition (h) 60 480 80 *WABT: Weight Average Bed Temperature

(42) During all the experiment, the mass balance was >99%, calculated according to the following formula:

(43) $\mathrm{mass}\mathrm{balance}=1-\left(\frac{\mathrm{IN}-\mathrm{OUT}}{\mathrm{IN}}\right)$

(44) wherein IN represents the total mass of liquid and gas at the inlet of the reactor and OUT represents the total mass of liquid and gas at the outlet of the reactor.