OPTIMIZED PROCESS FOR THE HYDROTREATING AND HYDROCONVERSION OF FEEDSTOCKS DERIVED FROM RENEWABLE SOURCES

Abstract

The present invention describes a process for treating a feedstock obtained from a renewable source, comprising a step a) of hydrotreating said feedstock, a step b) of separation into at least a light fraction and at least a hydrocarbon liquid effluent, a step c) of removing at least a portion of the water from the hydrocarbon liquid effluent, a step d) of hydroconversion of at least a portion of the hydrocarbon liquid effluent, said hydroconversion step d) being characterized firstly by the use of a bifunctional catalyst comprising a molybdenum and/or tungsten sulfide phase promoted with nickel and/or cobalt and secondly by a ratio between the partial pressure of hydrogen sulfide and of hydrogen at the inlet of the hydroconversion unit of 10 less than 5?10.sup.?5 and a step e) of fractionation of the effluent obtained from step d) to obtain at least a middle distillate fraction.

Claims

1. A process for treating a feedstock obtained from a renewable source chosen from oils and fats of plant or animal origin, or mixtures of such feedstocks, containing triglycerides and/or free fatty acids and/or esters, comprising at least: a) a step of hydrotreating said feedstock in the presence of a catalyst in a fixed bed, said catalyst comprising a hydrogenating function and an oxide support, at a temperature of between 200 and 450? C., at a pressure of between 1 MPa and 10 MPa, at an hourly space velocity of between 0.1 h.sup.?1 and 10 h.sup.?1 and in the presence of a total amount of hydrogen mixed with the feedstock such that the hydrogen/feedstock ratio is between 70 and 1000 Nm.sup.3 of hydrogen/m.sup.3 of feedstock, b) a step of separating at least a portion of the effluent obtained from step a) into at least a light fraction and at least a hydrocarbon liquid effluent, c) a step of removing at least a portion of the water from the hydrocarbon liquid effluent obtained from step b), d) a step of hydroconversion of at least a portion of the hydrocarbon liquid effluent obtained from step c) in the presence of a bifunctional hydroconversion catalyst in a fixed bed, said catalyst comprising a molybdenum and/or tungsten sulfide phase in combination with at least nickel and/or cobalt, said hydroconversion step being performed at a temperature of between 250? C. and 500? C., at a pressure of between 1 MPa and 10 MPa, at an hourly space velocity of between 0.1 and 10 h.sup.?1 and in the presence of a total amount of hydrogen mixed with the feedstock such that the hydrogen/feedstock ratio is between 70 and 1000 Nm.sup.3/m.sup.3 of feedstock, in the presence of a total amount of sulfur such that the ratio between the partial pressure of hydrogen sulfide and of hydrogen at the inlet of said hydroconversion step is less than 5?10.sup.?5, e) a step of fractionating the effluent obtained from step d) to obtain at least a middle distillate fraction.

2. The process as claimed in claim 1, in which, in step a), the feedstock is placed in contact with a catalyst in a fixed bed at a temperature of between 220 and 350? C., at a pressure of between 1 MPa and 6 MPa, and at an hourly space velocity of between 0.1 h.sup.?1 and 10 h-1, the feedstock being placed in contact with the catalyst in the presence of hydrogen and in the presence of a total amount of hydrogen mixed with the feedstock such that the hydrogen/feedstock ratio is between 150 and 750 Nm.sup.3 of hydrogen/m.sup.3 of feedstock.

3. The process as claimed in claim 1, in which the separation step b) is performed by combining one or more high-pressure and/or low-pressure separators, and/or steps of distillation and/or of high-pressure and/or low-pressure stripping.

4. The process as claimed in claim 1, in which said step c) is performed by drying, by passage over a desiccant, by flash, by decantation or by a combination of at least two of these techniques.

5. The process as claimed in claim 1, in which step d) is performed in the presence of a total amount of sulfur such that the ratio between the partial pressure of hydrogen sulfide and of hydrogen at the inlet of said hydroconversion step is less than 4?10.sup.?5.

6. The process as claimed in claim 5, in which step d) is performed in the presence of a total amount of sulfur such that the ratio between the partial pressure of hydrogen sulfide and of hydrogen at the inlet of said hydroconversion step is less than 3?10.sup.?5.

7. The process as claimed in claim 6, in which step d) is performed in the presence of a total amount of sulfur such that the ratio between the partial pressure of hydrogen sulfide and of hydrogen at the inlet of said hydroconversion step is less than 2?10.sup.?5.

8. The process as claimed in claim 7, in which step d) is performed in the presence of a total amount of sulfur such that the ratio between the partial pressure of hydrogen sulfide and of hydrogen at the inlet of said hydroconversion step is less than 1.5?10.sup.?5.

9. The process as claimed in claim 1, in which said hydrogen stream undergoes a purification step in the case where the atomic oxygen content in said hydrogen stream at the inlet of step d) is greater than 250 ppm by volume.

10. The process as claimed in claim 1, in which said hydrogen stream undergoes a purification step in the case where the atomic oxygen content in said hydrogen stream at the inlet of step d) is greater than 50 ppm by volume.

11. The process as claimed in claim 9, in which said purification step is performed according to the methods of pressure swing adsorption (PSA) or temperature swing adsorption (TSA), amine scrubbing, methanation, preferential oxidation or membrane processes, used alone or in combination.

Description

DESCRIPTION OF THE FIGURES

[0092] FIG. 1 shows the evolution of the cloud point of the liquid effluent as a function of time during the hydroconversion in example 4.

[0093] FIG. 2 shows the evolution of the cloud point of the liquid effluent as a function of time during the hydroconversion in example 7.

[0094] FIG. 3 shows the evolution of the cloud point of the liquid effluent as a function of time during the hydroconversion in example 8.

[0095] FIG. 4 shows the evolution of the cloud point of the liquid effluent as a function of time during the hydroconversion in example 9.

EXAMPLES

Example 1: Preparation of a Hydrotreating Catalyst (C1)

[0096] The catalyst is an industrial catalyst based on nickel, molybdenum and phosphorus on alumina with contents of molybdenum oxide MoO.sub.3 of 22% by weight, of nickel oxide NiO of 4% by weight and of phosphorus oxide P.sub.2O.sub.5 of 5% by weight relative to the total weight of the finished catalyst, sold by the company Axens.

Example 2: Preparation of a Hydroconversion Catalyst in Accordance With the Invention (C2)

[0097] The silica-alumina powder is prepared according to the synthetic protocol described in patent EP 1 415 712 A. The amounts of orthosilicic acid and of aluminum hydrate are chosen so as to have a composition containing 70% by weight of alumina Al.sub.2O.sub.3 and 30% by weight of silica SiO.sub.2 in the final solid.

[0098] This mixture is rapidly homogenized in a commercial colloidal mill in the presence of nitric acid so that the nitric acid content of the suspension leaving the mill is 8% relative to the silica-alumina mixed solid. Next, the suspension is dried conventionally in an atomizer conventionally from 300? C. to 60? C. The powder thus prepared is formed in a Z-shaped arm in the presence of 8% nitric acid relative to the anhydrous product. The extrusion is performed by passing the paste through a die equipped with orifices 1.4 mm in diameter. The extrudates thus obtained are oven-dried at 140? C., then calcined under a stream of dry air at 550? C. and then calcined at 850? C. in the presence of steam.

[0099] The characteristics of the support thus prepared are as follows: [0100] a mean mesopore diameter, measured by mercury porosimetry, of 7.7 nm, [0101] a total pore volume of 0.49 ml/g, [0102] a mesopore volume of 0.47 ml/g, [0103] a volume of macropores, the diameter of which is greater than 50 nm, of less than 0.01 ml/g, [0104] a BET surface area of 240 m.sup.2/g.

[0105] The silica-alumina extrudates are then subjected to a step of dry impregnation with an aqueous solution of ammonium metatungstate and nickel nitrate, left to mature in a water maturator for 24 hours at room temperature and then calcined for 2 hours in dry air in a bed traversed at 450? C. (temperature increase ramp of 5? C./minute). The weight content of tungsten oxide WO.sub.3 of the finished catalyst after calcination is 27%, and the content of nickel oxide NiO is 3.5%. The distribution coefficient of the metals, measured with a Castaing microprobe, is equal to 0.93.

Example 3: Hydrotreating of a Feedstock Obtained From a Renewable Source According to a Process in Accordance With the Invention

[0106] Pre-refined rapeseed oil with a density of 920 kg/m.sup.3, having an oxygen content of 11% by weight, is hydrotreated in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 190 ml of hydrotreating catalyst C1, the catalyst being sulfurized beforehand. The cetane number is 35 and the fatty acid distribution of the rapeseed oil is detailed in table 1. Prior to the hydrotreating step, said feedstock is supplemented with dimethyl disulfide so as to adjust its sulfur content to 50 ppm by weight.

TABLE-US-00001 TABLE 1 Characteristics of the rapeseed oil used as feedstock for the hydrotreating Fatty acid composition (%) 14:0 0.1 16:0 5.0 16:1 0.3 17:0 0.1 17:1 0.1 18:0 1.5 18:1 trans <0.1 18:1 cis 60.1 18:2 trans <0.1 18:2 cis 20.4 18:3 trans <0.1 18:3 cis 9.6 20:0 0.5 20:1 1.2 22:0 0.3 22:1 0.2 24:0 0.1 24:1 0.2

[0107] Before hydrotreating the feedstock, the catalyst is sulfurized in situ in the unit, with a distillation gas oil supplemented with 2% by weight of dimethyl disulfide, under a total pressure of 5.1 MPa, a hydrogen/supplemented gas oil ratio of 700 Nm.sup.3 per m.sup.3. The volume of supplemented gas oil per volume of catalyst and per hour is set at 1 h.sup.?1. Sulfurization is performed for 12 hours at 350? C., with a temperature increase ramp of 10? C. per hour.

[0108] After sulfurization, the operating conditions of the unit are adjusted so as to perform the hydrotreating of the feedstock: [0109] HSV (volume of feedstock/volume of catalyst/hour): 1 h.sup.?1. [0110] total working pressure: 5.1 MPa, [0111] hydrogen/feedstock ratio: 700 Nm.sup.3 of hydrogen/m.sup.3 of feedstock, [0112] temperature: 310? C.

[0113] The hydrogen employed is supplied by Air Products and has a purity of greater than 99.999% by volume.

Steps b) and c): Separation of the Effluent Obtained From Step a)

[0114] All of the hydrotreated effluent obtained from step a) is separated using a gas/liquid separator so as to recover a light fraction predominantly containing hydrogen, propane, water in vapor form, carbon oxides (CO and CO.sub.2) and ammonia, and a liquid hydrocarbon effluent predominantly consisting of linear hydrocarbons. The water present in the liquid hydrocarbon effluent is removed by decantation. The liquid hydrocarbon effluent thus obtained has an atomic oxygen content of less than 80 ppm by weight, said atomic oxygen content being measured via the infrared adsorption technique described in patent application US 2009/0018374, and a sulfur content of 2 ppm by weight and a nitrogen content of less than 1 ppm by weight, said nitrogen and sulfur contents being measured, respectively, by chemiluminescence and by UV fluorescence. Said liquid hydrocarbon effluent has a density of 791 kg/m.sup.3. The liquid hydrocarbon effluent is composed of paraffins; its composition, measured by gas chromatography, is given in table 2.

TABLE-US-00002 TABLE 2 composition of the liquid hydrocarbon effluent used as feedstock for the hydroconversion Distribution of the n-paraffins by carbon number (% m/m) nC8 0.01 nC9 0.00 nC10 0.01 nC11 0.01 nC12 0.01 nC13 0.02 nC14 0.06 nC15 0.97 nC16 4.09 nC17 17.70 nC18 72.77 nC19 0.67 nC20 1.56 nC21 0.18 nC22 0.56 nC23 0.09 nC24 0.23 nC25 0.02 nC26 0.02

Example 4: Hydroconversion of the Liquid Hydrocarbon Effluent Obtained From Example 3 According to a Process Not in Accordance With the Invention

[0115] Hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 50 ml of hydroconversion catalyst C2, the catalyst being sulfurized beforehand. Sulfur is introduced beforehand in the form of dimethyl disulfide into said liquid hydrocarbon effluent, so as to obtain a total sulfur content of 500 ppm by weight in said liquid hydrocarbon effluent.

[0116] The catalyst C2 undergoes a step of in situ sulfurization in the unit, with Isane supplemented with 2% by weight of dimethyl disulfide, under a total pressure of 5.1 MPa, a hydrogen/supplemented Isane ratio of 350 Nm.sup.3 per m.sup.3. The volume of supplemented Isane per volume of catalyst and per hour is set at 1 h.sup.?1. Sulfurization is performed for 12 hours at 350? C., with a temperature increase ramp of 10? C. per hour.

[0117] After sulfurization, the operating conditions of the unit are adjusted so as to perform the hydroconversion of the liquid hydrocarbon effluent containing 500 ppm by weight of sulfur: [0118] HSV (volume of feedstock/volume of catalyst/hour)=1 h.sup.?1. [0119] total working pressure: 5.1 MPa, [0120] hydrogen/feedstock ratio: 700 Nm.sup.3 of hydrogen/m.sup.3 of feedstock.

[0121] The hydrogen stream used and entering the hydroconversion step is supplied by Air Products: it has a purity of greater than 99.999% and is free of hydrogen sulfide. The ratio between the partial pressure of hydrogen sulfide and the partial pressure of hydrogen is then equal to 4?10.sup.?4.

[0122] Steady temperature stages at 333 and 343? C. are applied so as to vary the severity of the hydroconversion. Measurement (typically daily) of the cloud point (via the method ASTM D5773) of the liquid effluent makes it possible to monitor the change in performance of the catalyst at each steady temperature stage. For each temperature, the test time is prolonged until a stable cloud point is obtained. Once stability of the cloud point is achieved, the liquid effluent is accumulated for 24 hours. Under the chosen operating conditions, no deactivation of the catalyst is observed (see FIG. 1).

[0123] At the unit outlet, inline analysis by gas chromatography and a gas counter makes it possible to calculate the mass of light hydrocarbons produced (essentially hydrocarbons containing 1 to 5 carbon atoms) and present in the hydrogen stream. Said liquid effluent is subsequently weighed and then fractionated by distillation so as to determine the yield of middle distillate (130? C..sup.+ cut, corresponding to hydrocarbons with a boiling point of more than 130? C.).

[0124] The middle distillate yield is calculated as follows:

[00002]$\mathrm{Yield}\left(\mathrm{middle}\mathrm{distillate}\right)=\left[\begin{array}{c}\left(\mathrm{mass}\mathrm{of}\mathrm{liquid}\mathrm{effluent}?{\mathrm{\%130}}^{+}\mathrm{cut}/100\right)/\\ \left(\mathrm{mass}\mathrm{of}\mathrm{liquid}\mathrm{effluent}+\mathrm{mass}\mathrm{of}\mathrm{light}\mathrm{hydrocarbons}\right)\end{array}\right]?100$

[0125] Moreover, the cloud point and the motor cetane number of the middle distillate cut are determined, respectively, via the method ASTM D5773 and via the CFR method ASTM D613.

[0126] The main characteristics of the effluents produced and the associated operating conditions are reported in Table 3.

Example 5: Hydroconversion of the Liquid Hydrocarbon Effluent Obtained From Example 3 According to a Process in Accordance With the Invention

[0127] Hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 50 ml of hydroconversion catalyst C2, the catalyst being sulfurized beforehand. Sulfur is introduced beforehand in the form of dimethyl disulfide into said liquid hydrocarbon effluent, so as to obtain a total sulfur content of 50 ppm by weight in said liquid hydrocarbon effluent.

[0128] The catalyst C2 undergoes a sulfurization step identical to that reported in example 4.

[0129] After sulfurization, the operating conditions of the unit are adjusted so as to perform the hydroconversion of the liquid hydrocarbon effluent containing 50 ppm by weight of sulfur: [0130] HSV (volume of feedstock/volume of catalyst/hour)=1 h.sup.?1. [0131] total working pressure: 5.1 MPa, [0132] hydrogen/feedstock ratio: 700 Nm.sup.3 of hydrogen/m.sup.3 of feedstock.

[0133] The operating conditions are thus the same as those of example 4, only the sulfur content in the liquid hydrocarbon effluent is different.

[0134] The hydrogen stream used and entering the hydroconversion step is supplied by Air Products: it has a purity of greater than 99.999% by volume and is free of hydrogen sulfide. The ratio between the partial pressure of hydrogen sulfide and the partial pressure of hydrogen is then equal to 4? 10.sup.?5.

[0135] The steady temperature stages are adjusted so as to obtain middle distillate cloud points that are comparable to those obtained in example 4. Measurement (typically daily) of the cloud point of the liquid effluent makes it possible to monitor the change in performance of the catalyst at each steady temperature stage. For each temperature, the test time is prolonged until a stable cloud point is obtained. Once stability of the cloud point is achieved, the liquid effluent is accumulated for 24 hours. Under the chosen operating conditions, no deactivation of the catalyst is observed.

[0136] Said liquid effluent is subsequently weighed and then fractionated by distillation so as to determine the yield of middle distillate in the manner reported in example 4.

[0137] The main characteristics of the effluents produced and the associated operating conditions are reported in Table 3. It is observed that, in comparison with the non-compliant example 4, the reduction in the ratio P(H.sub.2S)/P(H.sub.2) makes it possible to improve the activity of the catalyst. Specifically, the temperature required to achieve a comparable cloud point value is 2 to 3? lower. Furthermore, reducing the ratio P(H.sub.2S)/P(H.sub.2) also makes it possible to improve the selectivity of the catalyst since, for a comparable cloud point value, the yield of middle distillate increases by 5 points.

Example 6: Hydroconversion of the Liquid Hydrocarbon Effluent Obtained From Example 3 According to a Process in Accordance With the Invention

[0138] Hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 50 ml of hydroconversion catalyst C2, the catalyst being sulfurized beforehand. Sulfur is introduced beforehand in the form of dimethyl disulfide into said liquid hydrocarbon effluent, so as to obtain a total sulfur content of 15 ppm by weight in said liquid hydrocarbon effluent.

[0139] The catalyst C2 undergoes a sulfurization step identical to that reported in example 4.

[0140] After sulfurization, the operating conditions of the unit are adjusted so as to perform the hydroconversion of the liquid hydrocarbon effluent containing 50 ppm by weight of sulfur: [0141] HSV (volume of feedstock/volume of catalyst/hour)=1 h.sup.?1. [0142] total working pressure: 5.1 MPa, [0143] hydrogen/feedstock ratio: 700 Nm.sup.3 of hydrogen/m.sup.3 of feedstock.

[0144] The operating conditions are thus the same as those of example 4, only the sulfur content in the liquid hydrocarbon effluent is different.

[0145] The hydrogen stream used and entering the hydroconversion step is supplied by Air Products: it has a purity of greater than 99.999% by volume and is free of hydrogen sulfide. The ratio between the partial pressure of hydrogen sulfide and the partial pressure of hydrogen is then equal to 1.2?10.sup.?5.

[0146] The steady temperature stages are adjusted so as to obtain middle distillate cloud points that are comparable to those obtained in example 4. Measurement (typically daily) of the cloud point of the liquid effluent makes it possible to monitor the change in performance of the catalyst at each steady temperature stage. For each temperature, the test time is prolonged until a stable cloud point is obtained. Once stability of the cloud point is achieved, the liquid effluent is accumulated for 24 hours. Under the chosen operating conditions, no deactivation of the catalyst is observed.

[0147] Said liquid effluent is subsequently weighed and then fractionated by distillation so as to determine the yield of middle distillate in the manner reported in example 4.

[0148] The main characteristics of the effluents produced and the associated operating conditions are reported in Table 3. It is observed that, in comparison with the non-compliant example 4, the reduction in the ratio P(H.sub.2S)/P(H.sub.2) makes it possible to improve the activity of the catalyst. Specifically, the temperature required to achieve a comparable cloud point value is 5 to 6? lower. Furthermore, reducing the ratio P(H.sub.2S)/P(H.sub.2) also makes it possible to improve the selectivity of the catalyst since, for a comparable cloud point value, the yield of middle distillate increases by 6 points.

TABLE-US-00003 TABLE 3 Main characteristics of the effluents produced by hydroconversion and associated operating conditions Example 4 (non-compliant) 5 (in accordance) 6 (in accordance) Reaction 333 343 331 340 328 337 temperature (? C.) HSV (h.sup.?1) 1 1 1 1 1 1 Total pressure 5.1 5.1 5.1 5.1 5.1 5.1 (MPa) H.sub.2/feedstock 700 700 700 700 700 700 (Nm.sup.3/m.sup.3) P(H.sub.2S)/P(H.sub.2) 4 ? 10.sup.?4 4 ? 10.sup.?4 4 ? 10.sup.?5 4 ? 10.sup.?5 1.2 ? 10.sup.?5 1.2 ? 10.sup.?5 Yield of middle 83 61 88 66 89 67 distillate (weight %) Cloud point of the ?4 ?35 ?4 ?36 ?5 ?35 middle distillate (? C.) Cetane number of 78 69 78 68 77 69 the middle distillate

Example 7: Hydroconversion of the Liquid Hydrocarbon Effluent Obtained From Example 3 According to a Process Not in Accordance With the Invention

[0149] Hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 50 ml of hydroconversion catalyst C2, the catalyst being sulfurized beforehand. Sulfur is introduced beforehand in the form of dimethyl disulfide into said liquid hydrocarbon effluent, so as to obtain a total sulfur content of 50 ppm by weight in said liquid hydrocarbon effluent.

[0150] The catalyst C2 undergoes a step of in situ sulfurization in the unit, with Isane supplemented with 2% by weight of dimethyl disulfide, under a total pressure of 5.1 MPa, a hydrogen/supplemented gas oil ratio of 700 Nm.sup.3 per m.sup.3. The volume of supplemented Isane per volume of catalyst and per hour is set at 1 h.sup.?1. Sulfurization is performed for 12 hours at 350? C., with a temperature increase ramp of 10? C. per hour.

[0151] After sulfurization, the operating conditions of the unit are adjusted so as to perform the hydroconversion of the liquid hydrocarbon effluent containing 50 ppm by weight of sulfur: [0152] HSV (volume of feedstock/volume of catalyst/hour)=0.6 h.sup.?1. [0153] total working pressure: 2.8 MPa, [0154] hydrogen/feedstock ratio: 470 Nm.sup.3 of hydrogen/m.sup.3 of feedstock.

[0155] The hydrogen stream used in the hydroconversion step is supplied by Air Products: it has a purity of greater than 99.999% by volume and is free of hydrogen sulfide. The ratio between the partial pressure of hydrogen sulfide and the partial pressure of hydrogen is then equal to 6?10.sup.?5.

[0156] In comparison with examples 4 and 5, the operating conditions chosen are more stringent with respect to the stability of the catalyst. Without wishing to be bound by any theory, the Applicant thinks that the reduction in the total working pressure and in the hydrogen/feedstock ratio may promote deactivation by coking of the catalyst.

[0157] Steady temperature stages at 326 and then 336? C. are applied so as to vary the severity of the hydroconversion, and a return point is applied at 326? C. to evaluate the deactivation of the catalyst. Regular measurement (typically daily) of the cloud point of the liquid effluent makes it possible to monitor the change in performance of the catalyst at each steady temperature stage. For each temperature, the test time is prolonged until a stable cloud point is obtained. Once stability of the cloud point is achieved, the liquid effluent is accumulated for 24 hours. Said liquid effluent is subsequently weighed and then fractionated by distillation so as to determine the yield of middle distillate in the manner reported in example 4.

[0158] FIG. 2 represents the change in the daily measurement of the liquid effluent in the course of the test. Under the chosen operating conditions, the catalyst undergoes deactivation at each test temperature, as evidenced by the increase in the cloud point value between the start and the end of each steady temperature stage. For example, at the first point at 326? C., the cloud point increases from ?19? C. (after 36 hours) to ?10? C. at 252 hours, at which value the activity of the catalyst becomes stable. Deactivation is also observed at the second point (steady temperature stage at 336? C.). Finally, the return point applied at 326? C. confirms the deactivation of the catalyst: the cloud point stabilizes at 1? C., as opposed to ?10? C. as the stabilized value at the end of the first point. The increase in the cloud point between the first measured value and the last measured value is employed to evaluate the deactivation of the catalyst:

[00003]$\mathrm{Deactivation}\mathrm{of}\mathrm{the}\mathrm{catalyst}=\mathrm{final}\mathrm{cloud}\mathrm{point}\left(?C.\right)-\mathrm{initial}\mathrm{clod}\mathrm{point}\left(?C.\right)$

[0159] The deactivation of the catalyst and the main characteristics of the effluents produced and the operating conditions associated with point No. 1 and point No. 2 are reported in table 4.

Example 8: Hydroconversion of the Liquid Hydrocarbon Effluent Obtained From Example 3 According to a Process in Accordance With the Invention

[0160] Hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 50 ml of hydroconversion catalyst C2, the catalyst being sulfurized beforehand. Sulfur is introduced beforehand in the form of dimethyl disulfide into said liquid hydrocarbon effluent, so as to obtain a total sulfur content of 10 ppm by weight in said liquid hydrocarbon effluent.

[0161] The catalyst C2 undergoes a sulfurization step identical to that reported in example 6.

[0162] After sulfurization, the operating conditions of the unit are adjusted so as to perform the hydroconversion of the liquid hydrocarbon effluent containing 11 ppm by weight of sulfur: [0163] HSV (volume of feedstock/volume of catalyst/hour)=0.6 h.sup.?1. [0164] total working pressure: 2.8 MPa, [0165] hydrogen/feedstock ratio: 470 Nm.sup.3 of hydrogen/m.sup.3 of feedstock.

[0166] The operating conditions are thus the same as those of example 6, only the sulfur content in the liquid hydrocarbon effluent is different.

[0167] The hydrogen stream used in the hydroconversion step is supplied by Air Products: it has a purity of greater than 99.999% by volume and is free of hydrogen sulfide. The ratio between the partial pressure of hydrogen sulfide and the partial pressure of hydrogen is then equal to 1.2?10.sup.?5.

[0168] Steady temperature stages at 326 and then 336? C. are applied so as to vary the severity of the hydroconversion, and a return point is applied at 326? C. to evaluate the deactivation of the catalyst. Regular measurement (typically daily) of the cloud point of the liquid effluent makes it possible to monitor the change in performance of the catalyst at each steady temperature stage. For each temperature, the test time is prolonged until a stable cloud point is obtained. Once stability of the cloud point is achieved, the liquid effluent is accumulated for 24 hours.

[0169] Said liquid effluent is subsequently weighed and then fractionated by distillation so as to determine the yield of middle distillate in the manner reported in example 4.

[0170] FIG. 3 represents the change in the daily measurement of the liquid effluent in the course of the test. Under the chosen operating conditions, the catalyst undergoes deactivation at each test temperature, just as is observed in the non-compliant example 7. However, the deactivation is less pronounced than in example 7. For example, at the first point at 326? C., the cloud point increases from ?20? C. (after 24 hours) to ?15? C. at 288 hours, at which value the activity of the catalyst becomes stable. Deactivation is also observed at the second point (steady temperature stage at 336? C.). Lower deactivation of the catalyst makes it possible to achieve lower stabilized cloud point values than in example 6: ?15? C. at the end of point 1 (as opposed to ?10? C. in example 6), ?22? C. at the end of point 2 (as opposed to ?16? C. in example 6). Finally, the stabilized cloud point value at point 3 (return point) confirms the lower deactivation: ?4? C. as opposed to +1? C. in example 6.

[0171] The deactivation of the catalyst and the main characteristics of the effluents produced and the associated operating conditions are reported in Table 4. It is observed that, in comparison with the non-compliant example 6, the reduction in the ratio P(H.sub.2S)/P(H.sub.2) allows, all factors being otherwise equal, multiple gains when the operating conditions bring about deactivation of the catalyst. Firstly, in comparison with the non-compliant example 6, the deactivation is lower. Secondly, for a given reaction temperature, the decrease in the ratio P(H.sub.2S)/P(H.sub.2) makes it possible to improve both the yield of middle distillate and the cold properties of said middle distillate.

TABLE-US-00004 TABLE 4 Main characteristics of the effluents produced by hydroconversion and associated operating conditions Example 7 (non-compliant) 8 (in accordance) Deactivation (? C.) 20 16 Reaction temperature 326 336 326 336 (?C.) HSV (h.sup.?1) 0.6 0.6 0.6 0.6 Total pressure (MPa) 2.8 2.8 2.8 2.8 H.sub.2/feedstock (Nm.sup.3/m.sup.3) 470 470 470 470 P(H.sub.2S)/P(H.sub.2) 6.0 ? 10.sup.?5 6.0 ? 10.sup.?5 1.2 ? 10.sup.?5 1.2 ? 10.sup.?5 Yield of middle distillate 80 72 81 75 (weight %) Cloud point of the ?10 ?17 ?15 ?22 middle distillate (? C.) Cetane number of the 76 74 75 73 middle distillate

Example 9: Hydroconversion of the Liquid Hydrocarbon Effluent Obtained From Example 3 According to a Process in Accordance With the Invention

[0172] During the use of the catalyst in the industrial hydroconversion unit, it may arise that the ratio P(H.sub.2S)/P(H.sub.2) is not in accordance with the invention over certain periods, for example on account of sporadic poor functioning of the tools that may be used for purifying the hydrogen sent into the unit and/or the liquid hydrocarbon effluent obtained from step c). Readjusting the ratio P(H.sub.2S)/P(H.sub.2) to within a range in accordance with the invention, after functioning under non-compliant conditions, also makes it possible to improve the performance of the catalyst, as illustrated below.

[0173] Hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed in a reactor which is temperature-regulated so as to ensure isothermal functioning and with a fixed bed containing 50 ml of hydroconversion catalyst C2, the catalyst being sulfurized beforehand.

[0174] The catalyst C2 undergoes a sulfurization step identical to that reported in example 6.

[0175] After sulfurization, the step of hydroconversion of the liquid hydrocarbon effluent obtained from example 3 is performed under various operating conditions, some of which simulate temporary functioning of the unit not in accordance with the invention over certain periods. Table 5 reports the various operating conditions applied. Throughout the test, the temperature, the total pressure, the hydrogen/feedstock ratio and the HSV are kept constant. Points 1 and 4 are not in accordance with the invention on account of their excessively high ratio P(H.sub.2S)/P(H.sub.2) (supplementation of the feedstock with dimethyl disulfide), whereas points 2 and 3 are compliant. For points 2 and 4, oxygenated impurities are also present in the hydrogen stream. This is performed by using a calibration mixture containing hydrogen, carbon monoxide and carbon dioxide supplied by Air Products. The content of atomic O contained in the hydrogen stream is then 4200 ppm by volume. Regular measurement (typically daily) of the cloud point of the liquid effluent makes it possible to monitor the change in performance of the catalyst at each steady temperature stage. For each temperature, the test time is prolonged until a stable cloud point is obtained. Once stability of the cloud point is achieved, the liquid effluent is accumulated for 24 hours. Said liquid effluent is subsequently weighed and then fractionated by distillation so as to determine the yield of middle distillate in the manner reported in example 4.

[0176] FIG. 4 represents the change in the daily measurement of the liquid effluent in the course of the test. Under the chosen operating conditions, the catalyst undergoes deactivation at the first test point (non-compliant), just as is observed in examples 7 and 8. It is observed that the cloud point stabilizes at a value of ?6? C. All factors being otherwise equal, adjusting the ratio P(H.sub.2S)/P(H.sub.2) to a value in accordance with the invention, at point 2, enables the catalyst to regain activity. At point 2, the cloud point stabilizes at ?8? C. At point 3, the addition of oxygenated compounds to the hydrogen induces a loss of activity of the catalyst, the cloud point then stabilizing at ?5? C. At point 4, all factors being otherwise equal, adjusting the ratio P(H.sub.2S)/P(H.sub.2) to a value not in accordance with the invention also induces a loss of activity of the catalyst, the cloud point then stabilizing at a 0? C. Whether in the presence or in the absence of oxygenated compounds, it thus appears advantageous to work within a P(H.sub.2S)/P(H.sub.2) ratio range in accordance with the invention.

[0177] Finally, table 5 reports the main characteristics of the effluents produced at each operating point, when the unit is stabilized. Here also, the operating mode in accordance with the invention is advantageous. All factors being otherwise equal, adjusting the ratio P(H.sub.2S)/P(H.sub.2) to values in accordance with the invention makes it possible both to gain in yield of middle distillate and also to improve the cold properties of said middle distillate (comparison of point 1 and point 2 and comparison of point 3 and point 4).

TABLE-US-00005 TABLE 5 Main characteristics of the effluents produced by hydroconversion and associated operating conditions for example 9 Point No. 1 Point No. 2 Point No. 3 Point No. 4 Operating Not in accordance In accordance In accordance Not in accordance mode with the invention with the invention with the invention with the invention Comment Supplementation Supplementation Supplementation Supplementation of the liquid of the liquid of the liquid of the liquid hydrocarbon hydrocarbon hydrocarbon hydrocarbon effluent obtained effluent obtained effluent obtained effluent obtained from example 3 from example 3 from example 3 from example 3 with dimethyl with dimethyl with dimethyl with dimethyl disulfide to obtain disulfide to obtain disulfide to obtain disulfide to obtain 50 ppm by weight 10 ppm by weight 10 ppm by weight 50 ppm by weight of sulfur in said of sulfur in said of sulfur in said of sulfur in said effluent effluent effluent effluent Use of hydrogen Use of hydrogen with oxygenated with oxygenated impurities impurities (CO and CO.sub.2) (CO and CO.sub.2) Reaction 333 333 333 333 temperature (? C.) HSV (h.sup.?1) 1.0 1.0 1.0 1.0 Total pressure 2.8 2.8 2.8 2.8 (MPa) H.sub.2/feedstock 470 470 470 470 (Nm.sup.3/m.sup.3) Composition >99.999% >99.999% 99.66% volume 99.66% volume of the volume H.sub.2 volume H.sub.2 H.sub.2 H.sub.2 hydrogen 0.26% volume CO 0.26% volume CO stream 0.08% volume 0.08% volume CO.sub.2 CO.sub.2 4200 ppm O 4200 ppm O P(H.sub.2S)/P(H.sub.2) 6.0 ? 10.sup.?5 1.2 ? 10.sup.?5 1.2 ? 10.sup.?5 6.0 ? 10.sup.?5 Yield of middle 81 84 88 85 distillate (weight %) Cloud point of ?5 ?7 ?3 3 the middle distillate (? C.) Cetane 77 77 78 80 number of the middle distillate