METHOD OF HYDROTREATMENT OF FISCHER-TROPSCH SYNTHESIS PRODUCTS

Abstract

A method of hydrotreatment of Fischer-Tropsch synthesis products, the method including: 1) mixing Fischer-Tropsch wax with a sulfur-containing liquid crystal, contacting a resulting mixture with hydrogen, feeding a hydrogen-containing mixture to a first reaction region, feeding an effluent from the first reaction region to a second reaction region, and carrying out hydrocracking reaction; 2) feeding a hydrocracking product from the second reaction region and Fischer-Tropsch naphtha and diesel fuel to a third reaction region, carrying out hydrofining reaction; feeding an effluent from the hydrofining reaction to a fourth reaction region, and carrying out hydroisomerizing pour-point depression reaction; and 3) feeding an effluent from the fourth reaction region to a gas-liquid separation system to yield hydrogen-rich gas and liquid products, recycling the hydrogen-rich gas, and feeding the liquid products to a distilling system.

Claims

1. A method of hydrotreatment of Fischer-Tropsch synthesis products, the method comprising: 1) mixing Fischer-Tropsch wax with a sulfur-containing liquid crystal, contacting a resulting mixture with hydrogen, feeding a hydrogen-containing mixture to a first reaction region comprising a hydrogenation pretreatment catalyst, feeding an effluent from the first reaction region to a second reaction region comprising a hydrocracking catalyst, and carrying out hydrocracking reaction; 2) feeding a hydrocracking product from the second reaction region and Fischer-Tropsch naphtha and diesel fuel to a third reaction region comprising a hydrofining catalyst, carrying out hydrofining reaction; feeding an effluent from the hydrofining reaction to a fourth reaction region comprising a hydroisomerizing pour-point depressant catalyst, and carrying out hydroisomerizing pour-point depression reaction; and 3) feeding an effluent from the fourth reaction region to a gas-liquid separation system C to yield hydrogen-rich gas and liquid products, recycling the hydrogen-rich gas, feeding the liquid products to a distilling system D, to yield naphtha, diesel fuel and tail oil, and returning the tail oil to the second reaction region.

2. The method of claim 1, wherein the sulfur-containing liquid catalyst in 1) is inferior catalytic cracking diesel fuel or coking diesel fuel; and the sulfur-containing liquid catalyst accounts for 20-50 wt. % of a total weight of the sulfur-containing liquid catalyst and the Fischer-Tropsch wax.

3. The method of claim 1, wherein in 1), the hydrogenation pretreatment is carried out under the following conditions: a reaction temperature is at 300-370° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.5-2.0 h.sup.−1; and a volume ratio of hydrogen to oil is 500-1500.

4. The method of claim 2, wherein in 1), the hydrogenation pretreatment is carried out under the following conditions: a reaction temperature is at 300-370° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.5-2.0 h.sup.−1; and a volume ratio of hydrogen to oil is 500-1500.

5. The method of claim 1, wherein in 1), the hydrocracking reaction is carried out under the following conditions: a reaction temperature is at 330-410° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 600-1500.

6. The method of claim 2, wherein in 1), the hydrocracking reaction is carried out under the following conditions: a reaction temperature is at 330-410° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 600-1500.

7. The method of claim 1, wherein in 2), the hydrofining reaction is carried out under the following conditions: a reaction temperature is at 280-340° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 500-1200.

8. The method of claim 2, wherein in 2), the hydrofining reaction is carried out under the following conditions: a reaction temperature is at 280-340° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 500-1200.

9. The method of claim 1, wherein in 2), the hydroisomerizing pour-point depression reaction is carried out under the following conditions: a reaction temperature is at 280-400° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 400-1200.

10. The method of claim 2, wherein in 2), the hydroisomerizing pour-point depression reaction is carried out under the following conditions: a reaction temperature is at 280-400° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 400-1200.

11. The method of claim 1, wherein the hydrogenation pretreatment or hydrofining catalyst comprises a carrier selected from aluminum oxide or silicon-containing aluminum oxide and a hydrogenation active metal loaded on the carrier; the hydrogenation active metal comprises at least two active ingredients of non-noble metals of VIB and/or VIII family; and a content of active metal oxides is 25-40 wt. % of a total weight of the hydrogenation pretreatment or hydrofining catalyst.

12. The method of claim 2, wherein the hydrogenation pretreatment or hydrofining catalyst comprises a carrier selected from aluminum oxide or silicon-containing aluminum oxide and a hydrogenation active metal loaded on the carrier; the hydrogenation active metal comprises at least two active ingredients of non-noble metals of VIB and/or VIII family; and a content of active metal oxides is 25-40 wt. % of a total weight of the hydrogenation pretreatment or hydrofining catalyst.

13. The method of claim 1, wherein the hydrocracking catalyst comprises an acidic material as a carrier selected from amorphous silica-alumina, molecular sieve, or a mixture thereof, and a hydrogenation active metal which is a combination of a VIB-family metal element selected from molybdenum (Mo) and Tungsten (W) and a VIII-family metal element selected from cobalt (Co), Nickle (Ni), platinum (Pt) and palladium (Pd); and a content of active metal oxides is 25-40 wt. % of a total weight of the hydrocracking catalyst.

14. The method of claim 2, wherein the hydrocracking catalyst comprises an acidic material as a carrier selected from amorphous silica-alumina, molecular sieve, or a mixture thereof, and a hydrogenation active metal which is a combination of a VIB-family metal element selected from molybdenum (Mo) and Tungsten (W) and a VIII-family metal element selected from cobalt (Co), Nickle (Ni), platinum (Pt) and palladium (Pd); and a content of active metal oxides is 25-40 wt. % of a total weight of the hydrocracking catalyst.

15. The method of claim 13, wherein the carrier of the hydrocracking catalyst is a combination of amorphous silica-alumina and one or more selected from a Y-type molecular sieve, a β molecular sieve, a ZSM molecular sieve and an SAPO molecular sieve; and the hydrogenation active metal is a combination of W—Ni, Mo—Ni or Mo—Co.

16. The method of claim 14, wherein the carrier of the hydrocracking catalyst is a combination of amorphous silica-alumina and one or more selected from a Y-type molecular sieve, a β molecular sieve, a ZSM molecular sieve and an SAPO molecular sieve; and the hydrogenation active metal is a combination of W—Ni, Mo—Ni or Mo—Co.

17. The method of claim 1, wherein the tail oil separated in 3) is recycled completely or partially to the second reaction region for hydrocracking.

18. The method of claim 2, wherein the tail oil separated in 3) is recycled completely or partially to the second reaction region for hydrocracking.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention is described hereinbelow with reference to accompanying drawings, in which the sole FIGURE is a method of hydrotreatment of low-temperature Fischer-Tropsch synthesis products according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] To further illustrate the invention, experiments detailing a method of hydrotreatment of low-temperature Fischer-Tropsch synthesis products are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

[0022] As shown in the sole FIGURE, a first reactor A comprises a first reaction region A1 and a second reaction region A2 in longitudinal direction; a hydrogenation pretreatment catalyst is placed on a bed of the first reaction region A1, and a hydrocracking catalyst is placed on the bed of the second reaction bed A2; and rich hydrogen is fed inward through a pipe 5 from a top of the first reactor A. 1) Fischer-Tropsch wax and a sulfur-containing liquid catalyst are mixed and then mingled with the rich hydrogen after entering into the first reactor A through a pipe 1; a mixture is subjected to hydrogenation pretreatment in the first reaction region A1 first, and the reaction effluent enters into the second reaction region A2 to carry out hydrocracking.

[0023] 2) A second reactor B comprises a third reaction region B1 and a fourth reaction region B2 in longitudinal direction; and a hydrofining catalyst is placed on the bed of the third reaction region B1, and the hydrocracking catalyst is placed on the bed of the fourth reaction bed B2.

[0024] 3) A cracked product from the second reaction region A2 is mixed with Fischer-Tropsch light ingredients (Fischer-Tropsch diesel fuel and naphtha) through a pipe 2 and fed into the third reaction region B1 of the second reactor B through a pipe 3 for hydrofining reaction; the product after refining enters the fourth reaction region to carry out a hydroisomerizing pour point depressant reaction. The product after pour point depressant reaction enters into a gas-liquid separator C through a pipe 6, the gas phase ingredients (mainly referring to hydrogen and containing sulfureted hydrogen at the same time) enters into a circulating compressor E through a pipe 7; the hydrogen-rich gas after compression is mixed with the new hydrogen of a pipe 4 and are fed inward from the top of the first reactor A through a pipe 5. Liquid phase ingredients enter into a fractioning system D through a pipe 8 for fractioning to acquire dry gas 9, naphtha 10, diesel fuel 11 and tail oil 12. Furthermore, the tail oil 12 is recycled completely or partially to the second reaction region A2 in the first reactor A for recycle cracking.

[0025] The sulfur-containing liquid catalyst in the step 1) is inferior catalytic cracking diesel fuel and coking diesel fuel; and the sulfur-containing liquid catalyst accounts for 10-65 wt. % of a total weight of the sulfur-containing liquid catalyst and the Fischer-Tropsch wax, particularly, 20-50 wt. %.

[0026] In 1), the hydrogenation pretreatment is carried out under the following conditions: a reaction temperature is at 280-390° C.; a hydrogen partial pressure is 2.0-15 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 300-2000.

[0027] Preferably, the hydrogenation pretreatment is carried out under the following conditions: a reaction temperature is at 300-370° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.5-2.0 h.sup.−1; and a volume ratio of hydrogen to oil is 500-1500.

[0028] In 1), the hydrocracking reaction is carried out under the following conditions: a reaction temperature is at 300-450° C.; a hydrogen partial pressure is 2.0-15 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 300-2000.

[0029] Preferably, in 1), the hydrocracking reaction is carried out under the following conditions: a reaction temperature is at 330-410° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 600-1500.

[0030] In 2), the hydrofining reaction is carried out under the following conditions: a reaction temperature is at 250-380° C.; a hydrogen partial pressure is 2.0-15 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 300-2000. Preferably, the hydrofining reaction is carried out under the following conditions: a reaction temperature is at 280-340° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 500-1200.

[0031] In 2), the hydroisomerizing pour-point depression reaction is carried out under the following conditions: a reaction temperature is at 250-450° C.; a hydrogen partial pressure is 2.0-15 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 300-2000. Preferably, the hydroisomerizing pour-point depression reaction is carried out under the following conditions: a reaction temperature is at 280-400° C.; a hydrogen partial pressure is 4.0-10 MPa; a volume velocity is 0.4-6.0 h.sup.−1; and a volume ratio of hydrogen to oil is 400-1200.

[0032] The hydrogenation pretreatment or hydrofining catalyst comprises a carrier selected from aluminum oxide or silicon-containing aluminum oxide and a hydrogenation active metal loaded on the carrier; the hydrogenation active metal comprises at least two active ingredients of non-noble metals of VIB and/or VIII family; and the content of active metal oxides is 10-50 wt. % of a total weight of the catalyst, preferably, 25-40 wt. %.

[0033] The hydrocracking catalyst comprises an acidic material as a carrier selected from amorphous silica-alumina, molecular sieve, or a mixture thereof, and a hydrogenation active metal which is a combination of a VIB-family metal element selected from molybdenum (Mo) and Tungsten (W) and a VIII-family metal element selected from cobalt (Co), Nickle (Ni), platinum (Pt) and palladium (Pd). The content of active metal oxides is 10-50 wt. % of a total weight of the catalyst, preferably, 25-40 wt. %.

[0034] The acidity center of the hydrocracking catalyst has two functions: cracking and isomerization, and its carrier can be one or more selected from a Y-type molecular sieve, a (3 molecular sieve, a ZSM molecular sieve and an SAPO molecular sieve. Furthermore, the hydrocracking catalyst also contains the amorphous silica-alumina.

[0035] The tail oil separated in 3) can be recycled completely or partially to the second reaction region for hydrocracking.

[0036] The hydrocracking catalyst used in the method of the invention can also be existing commercial hydrofining catalysts.

[0037] A hydroisomerizing pour-point depressant catalyst used in 2) can be existing commercial hydroisomerizing pour-point depressant catalysts.

[0038] In the invention, the sulfur-containing liquid catalyst comprises the inferior catalytic cracking diesel fuel or coking diesel fuel.

[0039] To further explain the key points of the invention, the following further explains the invention in connection with the specific embodiment; however, the invention is not limited to the embodiment below.

Example 1

[0040] Low-temperature Fischer-Tropsch wax was mixed with a sulfur-containing liquid catalyst comprising inferior catalytic cracking diesel fuel in accordance with a certain proportion by weight. The inferior catalytic cracking diesel fuel accounted for 25% of the total weight of the mixture. The properties of the low-temperature Fischer-Tropsch wax and the liquid catalyst comprising inferior catalytic cracking diesel fuel are listed in Table 1. The mixed raw material was fed to a first reactor A to mix with the hydrogen-rich gas, and the mixture was subjected to hydrogenation pretreatment in the first reaction region A1 first, and then the hydrocracking reaction was carried out in the second reaction region A2; the products obtained from the hydrocracking reaction were fed to the third reaction region B1 of the second reactor B with the Fischer-Tropsch diesel fuel and naphtha (see Table 1 for properties of Fischer-Tropsch diesel fuel) to carry out hydrofining reaction; the products obtained from the hydrofining reaction were fed to the fourth reaction region B2 for hydroisomerizing pour-point depression reaction; the products obtained from the reaction were fractionated using a fractioning system to yield a diesel fuel fraction No. 1. See Table 2 for properties of the diesel fuel fraction No. 1.

[0041] Reaction conditions of the hydrogenation pretreatment: the reaction temperature was 350° C., the reaction pressure was 6.0 Mpa, liquid hourly space velocity (LHSV) was 1.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1000. The conditions of hydrocracking: the reaction temperature was at 380° C., the reaction pressure was 6.0 Mpa, LHSV was 1.5 h.sup.−1, and the volume ratio of hydrogen to oil was 1000. The conditions of the hydrofining: the reaction temperature was 310° C., the reaction pressure was 6.0 Mpa, LHSV was 3.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1000. The conditions of the hydroisomerizing pour-point depression: the reaction temperature was at 350° C., the reaction pressure was 6.0 Mpa, LHSV was 3.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1000.

Example 2

[0042] The example employs the same mixed raw material as that in Example 1, and the mixed raw material was fed to a first reactor A to mix with the hydrogen-rich gas, and the mixture was subjected to hydrogenation pretreatment in the first reaction region A1 first, and then the hydrocracking reaction was carried out in the second reaction region A2; the products obtained from the hydrocracking reaction were fed to the third reaction region B1 of the second reactor B with the Fischer-Tropsch diesel fuel and naphtha (see Table 1 for properties of Fischer-Tropsch diesel fuel) to carry out hydrofining reaction; the products obtained from the hydrofining reaction were fed to the fourth reaction region B2 for hydroisomerizing pour-point depression reaction; the products obtained from the reaction were fractionated using a fractioning system to yield a diesel fuel fraction No. 2. See Table 2 for properties of the diesel fuel fraction No. 2.

[0043] Reaction conditions of the hydrogenation pretreatment: the reaction temperature was 360° C., the reaction pressure was 8.0 Mpa, liquid hourly space velocity (LHSV) was 1.5 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of hydrocracking: the reaction temperature was at 390° C., the reaction pressure was 8.0 Mpa, LHSV was 2.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of the hydrofining: the reaction temperature was 330° C., the reaction pressure was 8.0 Mpa, LHSV was 4.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of the hydroisomerizing pour-point depression: the reaction temperature was at 360° C., the reaction pressure was 8.0 Mpa, LHSV was 3.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200.

Example 3

[0044] Low-temperature Fischer-Tropsch wax was mixed with a sulfur-containing liquid catalyst comprising inferior catalytic cracking diesel fuel in accordance with a certain proportion by weight. The inferior catalytic cracking diesel fuel accounted for 40% of the total weight of the mixture. The mixed raw material was fed to a first reactor A to mix with the hydrogen-rich gas, and the mixture was subjected to hydrogenation pretreatment in the first reaction region A1 first, and then the hydrocracking reaction was carried out in the second reaction region A2; the products obtained from the hydrocracking reaction were fed to the third reaction region B1 of the second reactor B with the Fischer-Tropsch diesel fuel and naphtha (see Table 1 for properties of Fischer-Tropsch diesel fuel) to carry out hydrofining reaction; the products obtained from the hydrofining reaction were fed to the fourth reaction region B2 for hydroisomerizing pour-point depression reaction; the products obtained from the reaction were fractionated using a fractioning system to yield a diesel fuel fraction No. 3. See Table 2 for properties of the diesel fuel fraction No. 3.

[0045] Reaction conditions of the hydrogenation pretreatment: the reaction temperature was 365° C., the reaction pressure was 8.0 Mpa, liquid hourly space velocity (LHSV) was 1.5 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of hydrocracking: the reaction temperature was at 380° C., the reaction pressure was 8.0 Mpa, LHSV was 2.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of the hydrofining: the reaction temperature was 330° C., the reaction pressure was 8.0 Mpa, LHSV was 4.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of the hydroisomerizing pour-point depression: the reaction temperature was at 360° C., the reaction pressure was 8.0 Mpa, LHSV was 4.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200.

Example 4

[0046] Low-temperature Fischer-Tropsch wax was mixed with a sulfur-containing liquid catalyst comprising inferior coking diesel fuel in accordance with a certain proportion by weight. The inferior coking diesel fuel accounted for 40% of the total weight of the mixture. The properties of the liquid catalyst comprising inferior coking diesel fuel are listed in Table 1. The mixed raw material was fed to a first reactor A to mix with the hydrogen-rich gas, and the mixture was subjected to hydrogenation pretreatment in the first reaction region A1 first, and then the hydrocracking reaction was carried out in the second reaction region A2; the products obtained from the hydrocracking reaction were fed to the third reaction region B1 of the second reactor B with the Fischer-Tropsch diesel fuel and naphtha (see Table 1 for properties of Fischer-Tropsch diesel fuel) to carry out hydrofining reaction; the products obtained from the hydrofining reaction were fed to the fourth reaction region B2 for hydroisomerizing pour-point depression reaction; the products obtained from the reaction were fractionated using a fractioning system to yield a diesel fuel fraction No. 4. See Table 2 for properties of the diesel fuel fraction No. 4.

[0047] Reaction conditions of the hydrogenation pretreatment: the reaction temperature was 365° C., the reaction pressure was 8.0 Mpa, liquid hourly space velocity (LHSV) was 1.5 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of hydrocracking: the reaction temperature was at 380° C., the reaction pressure was 8.0 Mpa, LHSV was 2.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of the hydrofining: the reaction temperature was 330° C., the reaction pressure was 8.0 Mpa, LHSV was 4.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200. The conditions of the hydroisomerizing pour-point depression: the reaction temperature was at 360° C., the reaction pressure was 8.0 Mpa, LHSV was 4.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1200.

Comparison Example 1

[0048] Low-temperature Fischer-Tropsch wax was fed to a first reactor A to mix with the hydrogen-rich gas, and the mixture was subjected to hydrogenation pretreatment in the first reaction region A1 first, and then the hydrocracking reaction was carried out in the second reaction region A2; the products obtained from the hydrocracking reaction were fed to the third reaction region B1 of the second reactor B with the Fischer-Tropsch diesel fuel and naphtha (see Table 1 for properties of Fischer-Tropsch diesel fuel) to carry out hydrofining reaction; the products obtained from the hydrofining reaction were fed to the fourth reaction region B2 for hydroisomerizing pour-point depression reaction; the products obtained from the reaction were fractionated using a fractioning system to yield a diesel fuel fraction No. 5. See Table 2 for properties of the diesel fuel fraction No. 5.

[0049] Reaction conditions of the hydrogenation pretreatment: the reaction temperature was 330° C., the reaction pressure was 8.0 Mpa, liquid hourly space velocity (LHSV) was 1.5 h.sup.−1, and the volume ratio of hydrogen to oil was 1000. The conditions of hydrocracking: the reaction temperature was at 400° C., the reaction pressure was 8.0 Mpa, LHSV was 1.5 h.sup.−1, and the volume ratio of hydrogen to oil was 1000. The conditions of the hydrofining: the reaction temperature was 330° C., the reaction pressure was 8.0 Mpa, LHSV was 3.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1000. The conditions of the hydroisomerizing pour-point depression: the reaction temperature was at 360° C., the reaction pressure was 8.0 Mpa, LHSV was 3.0 h.sup.−1, and the volume ratio of hydrogen to oil was 1000.

TABLE-US-00001 TABLE 1 Properties of Fischer-Tropsch wax, diesel fuel, and liquid catalysts Inferior Fischer- catalytic Inferior Fischer- Tropsch cracking coking Properties Tropsch wax diesel fuel diesel fuel diesel fuel Density (20° C.)/g/cm.sup.3 0.7967 0.7621 0.8962 0.8373 distillation range/° C. 217-740 138-328 184-360 203-345 Sulphur/μg/g — — 7000 5000 Nitrogen/μg/g — — 882 1212 Pour point/° C. — 25 −8 −11 Cetane number — 69.8 33.9 49

TABLE-US-00002 TABLE 2 Properties of products Com- Example Example Example Example parison Properties 1 2 3 4 example 1 of Diesel Diesel Diesel Diesel Diesel products fuel No. 1 fuel No. 2 fuel No. 3 fuel No. 4 fuel No. 5 Density 0.8243 0.8211 0.8325 0.8200 0.7413 (20° C.)/ g/cm.sup.3 Sulphur/μg/g <10.0 <10.0 <10.0 <10.0 <1.0 Pour −25 −31 −35 −36 2 point/° C. Cetane 55 54 53 58 61 number

[0050] From Table 2, when the liquid catalyst is doped at certain proportion through the method of the invention, the density of the diesel fuel fraction acquired through transformation from the low-temperature Fischer-Tropsch synthesis product is greater than 0.82 g/cm.sup.3, its sulfur content is less than 10.0 μg/g, and its cetane number is greater than 51, thereby meeting the indexes of Euro V standard. Further, through the method of the invention, the pour point of the acquired diesel fuel is below 0° C. which can meet the requirements of low-temperature flow property of diesel fuel in a low-temperature area. However, if the Fischer-Tropsch wax is subjected to hydrocracking independently, for example at proportion 1, the density of the acquired diesel fuel is 0.7413 g/cm.sup.3 only, the density thereof cannot achieve the indexes of diesel fuel for vehicle, and the pour point thereof is at 2° C. only which cannot meet the requirements of low-temperature diesel fuel in the low-temperature area.

[0051] While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.