초록 ▼

The invention concerns a process for producing middle distillates from a paraffinic feed produced by Fischer-Tropsch synthesis, using a hydrocracking/hydroisomerization catalyst which comprises: at least one hydrodehydrogenating element selected from the group formed by elements f

The invention concerns a process for producing middle distillates from a paraffinic feed produced by Fischer-Tropsch synthesis, using a hydrocracking/hydroisomerization catalyst which comprises: at least one hydrodehydrogenating element selected from the group formed by elements from group VIB and group VIII of the periodic table; 0.01% to 6% of phosphorus as a doping element; and a non-zeolitic support based on mesoporous alumina-silica.

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The invention claimed is: 1. In a process for producing middle distillates, comprising contacting a paraffinic feed under sufficient catalytic hydrocracking and hydroisomerization conditions so as to produce said middle distillates, said paraffinic feed comprising a cut produced directly or indirec

The invention claimed is: 1. In a process for producing middle distillates, comprising contacting a paraffinic feed under sufficient catalytic hydrocracking and hydroisomerization conditions so as to produce said middle distillates, said paraffinic feed comprising a cut produced directly or indirectly by Fischer-Tropsch synthesis, the catalyst being a hydrocracking/hydroisomerization catalyst comprising: at least one hydrodehydrogenating element selected from elements from group VIB and group VIII of the periodic table; and a non-zeolitic support comprising alumina-silica; said alumina-silica having the following characteristics: a percentage of silica in the range of 5% to 95% by weight; a sodium content of less than 0.03% by weight; a total pore volume, measured by mercury porosimetry, in the range of 0.45 to 1.2 ml/g; a porosity such that: i) the volume of mesopores with a diameter in the range of 40 to 150 Å and a mean pore diameter in the range 80 to 140 Å represents 30-80% of the total pore volume measured by mercury porosimetry; ii) the volume of macropores with a diameter of more than 500 Å represents 20-70% of the total pore volume measured by mercury porosimetry; a BET specific surface area in the range of 100 to 550 m2/g; an X ray diffraction diagram which contains at least the characteristic principal peaks of at least one transition alumina included in the group composed of alpha, rho, khi, eta, gamma, kappa, theta and delta aluminas, the improvement wherein said catalyst comprises 0.01% by weight to 6% by weight of P2O5 as a doping element, and wherein the concentration of P2O5 as a doping element is sufficient to provide an increased yield of middle distillate compared to the same catalysts having a content of P2O5 below 0.01% by weight and above 6% by weight. 2. A process according to claim 1, said catalyst also comprising boron and/or silicon as doping elements. 3. A process according to claim 1, in which the volume of mesopores with a diameter in the range 40 to 150 Å and a mean pore diameter in the range 80 to 120 Å represents in the range 40% to 70% of the total pore volume measured by mercury porosimetry. 4. A process according to claim 1, in which the alumina-silica comprises 30% to 50% of Q2 sites, in which one Si atom is bonded to two Si or Al atoms and to two OH groups, and also comprises 10-30% of Q3 sites in which one Si atom is bonded to three Si or Al atoms or to an OH group. 5. A process according to claim 1, in which the catalyst support is constituted by alumina-silica alone. 6. A process according to claim 1, in which the catalyst support comprises 1% to 40% by weight of binder. 7. A process according to claim 1, in which the support consists essentially of a mixture of alumina-silica and at least one binder selected from silica, alumina, clays, titanium oxide, boron oxide and zirconia. 8. A process according to claim 1, in which the hydrocracking/hydroisomerization catalyst contains a noble group VIII metal. 9. A process according to claim 7, in which the hydrocracking/hydroisomerization catalyst contains 0.05% to 10% of noble group VIII metal. 10. A process according to claim 1, in which the hydrocracking/hydroisomerization catalyst comprises platinum and/or palladium. 11. A process according to claim 9, in which the amount of phosphorus in the catalyst is in the range of 0.01% to 4% by weight of oxide. 12. A process according to claim 10, in which the amount of phosphorus in the catalyst is in the range of 0.01% to 2.5% by weight of oxide. 13. A process according to claim 1, wherein the, catalyst exhibits a proportion of octahedral AlVI, determined by solid 27Al MAS NMR spectral analysis of more than 50%. 14. A process according to claim 1, wherein, the catalyst has a cationic impurities content of less than 0.1% by weight. 15. A process according to claim 1, wherein the catalyst has an anionic impurities content of less than 1% by weight. 16. A process for producing middle distillates from a paraffinic feed produced by Fischer-Tropsch synthesis, according to claim 1, comprising the following successive steps: removing from the paraffinic feed a single fraction, termed the heavy fraction, with an initial boiling point between 120-200° C.; a) hydrotreating at least a portion of said heavy fraction; b) fractionating resultant hydrotreated fractions into at least 3 fractions: at least one intermediate fraction having an initial boiling point T1 in the range 120 to 200° C., and an end point T2 of more than 300° C. and less than 410° C., at least one light fraction boiling below the intermediate fraction, at least one heavy fraction boiling above the intermediate fraction; c) passing at least a portion of said intermediate fraction over said hydroisomerization/hydrocracking catalyst; d) passing at least a portion of said heavy fraction over said hydroisomerization/hydrocracking catalyst; e) distilling the hydrocracked/hydroisomerized fractions to obtain middle distillates, and recycling the residual fraction boiling above said middle distillates in step e) over said catalyst treating the heavy fraction. 17. A process for producing middle distillates from a paraffinic feed produced by the Fischer-Tropsch synthesis, according to claim 1, comprising the following steps: a) separating at least a light fraction from the feed to obtain a single fraction, termed the heavy fraction, with an initial boiling point in the range of 120-200° C.; b) optionally, hydrotreating said heavy fraction, optionally followed by a step c) for removing at least a portion of the water; d) passing at least a portion of said optionally hydrotreated fraction heavy fraction over said hydroisomerization/hydrocracking catalyst so as to convert more than 80% by weight of products with a boiling point of 370° C. or more into products with a boiling point of less than 370° C.; and e) distilling the hydrocracked/hydroisomerized fraction to obtain middle distillates, and recycling the residual fraction boiling above said middle distillates to step d). 18. A process for producing middle distillates from a paraffinic feed produced by the Fischer-Tropsch synthesis, according to claim 1, comprising the following steps in succession: a) fractionating (step a)) the feed into at least 3 fractions: at least one intermediate fraction having an initial boiling point T1 in the range of 120° C. to 200° C., and an end point T2 of more than 300° C. and less than 410° C.; at least one light fraction boiling below the intermediate fraction; at least one heavy fraction boiling above the intermediate fraction; b) hydrotreating (step b)) at least a portion of said intermediate fraction, then passing at least a portion of the hydrotreated fraction over said hydrocracking/hydroisomerization catalyst; f) passing (step f)) at least a portion of said heavy fraction over said hydrocracking/hydrocracking catalyst with a conversion of more than 80% by weight of products with a boiling point of 370° C. or more into products with a boiling point of less than 370° C.; e) and g) distilling (steps e) and g)) at least a portion of the hydrocracked/hydroisomerized fractions to obtain middle distillates. 19. A process for producing middle distillates from a paraffinic feed produced by the Fischer-Tropsch process, comprising the following successive steps: a) optional fractionation of the feed into at least one heavy fraction with an initial boiling point in the range of 120° C. to 200° C. and at least one light fraction boiling below said heavy fraction; b) optional hydrotreatment of at least a portion of the feed or the heavy fraction, optionally followed by a step c); c) for eliminating at least a portion of the water; d) passing at least a portion of the effluent or the optionally hydrotreated fraction over a first hydroisomerization/hydrocracking catalyst containing at least one noble metal from group VIII; e) distilling the hydroisomerized/hydrocracked effluent to obtain middle distillates (kerosene, gas oil) and a residual fraction boiling above the middle distillates; f) over a second hydroisomerization/hydrocracking catalyst containing at least one noble metal from group VIII, passing at least a portion of said residual heavy fraction and/or a portion of said middle distillates, and distilling the resulting effluent to obtain middle distillates with the provision that at least one of steps (d) and (f) is conducted according to claim 1. 20. A process for producing middle distillates from a paraffinic feed produced by the Fischer-Tropsch process according to claim 1, comprising the following successive steps: a) separating the feed into at least one fraction with a low boiling point (B) which is richer in oxygen-containing compounds and at least one fraction with a high boiling point (A) which is less rich in oxygen-containing compounds; b) subjecting said fraction (B) to a hydrogenating treatment under conditions of a nature which avoids any substantial variation in its mean molecular weight, to obtain a hydrogenated substantially non oxygen-containing mixture of hydrocarbons; c) recombining at least a portion of said hydrogenated mixture of step b) with said fraction (A) to form a mixture (C) of straight-chain hydrocarbons with a reduced oxygen-containing hydrocarbon content and subjecting said mixture (C) to a hydrocracking treatment in the presence of said hydroisomerization/hydrocracking catalyst to convert at least 40% of said fraction with a high boiling point into a hydrocarbon fraction which may be distilled at a temperature of less than 370° C.; d) separating at least one hydrocarbon fraction from the product obtained in step c) having the distillation temperature in the middle distillates range. 21. In a process for producing middle distillates, comprising contacting a paraffinic feed under sufficient catalytic hydrocracking and hydroisomerization conditions so as to produce said middle distillates, said paraffinic feed comprising a cut produced directly or indirectly by Fischer-Tropsch synthesis, the catalyst being a hydrocracking/hydroisomerization catalyst comprising: at least one hydrodehydrogenating element selected from elements from group VIB and group VIII of the periodic table; and a non-zeolitic support comprising alumina-silica; said alumina-silica having the following characteristics: a percentage of silica in the range of 5% to 95% by weight; a sodium content of less than 0.03% by weight; a total pore volume, measured by mercury porosimetry, in the range of 0.45 to 1.2 ml/g; a porosity such that: iii) the volume of mesopores with a diameter in the range of 40 to 150 Å and a mean pore diameter in the range 80 to 140 Å represents 30-80% of the total pore volume measured by mercury porosimetry; iv) the volume of macropores with a diameter of more than 500 Å represents 20-70% of the total pore volume measured by mercury porosimetry; a BET specific surface area in the range of 100 to 550 m2/g; an X ray diffraction diagram which contains at least the characteristic principal peaks of at least one transition alumina included in the group composed of alpha, rho, khi, eta, gamma, kappa, theta and delta aluminas, the improvement wherein said catalyst comprises about 1% by weight of P2O5 as a doping element, and wherein the concentration of P2O5 as a doping element is sufficient to provide an increased yield of middle distillate compared to the same catalysts having a content of P2O5 below 0.01% by weight and above 6% by weight.