Method for improving yield of Fischer-Tropsch wax hydrocracking middle distillate

Abstract

The invention discloses a method for improving the yield of Fischer-Tropsch wax hydrocracking middle distillate. The method comprises the following steps: (1) feeding Fischer-Tropsch wax and hydrogen as raw materials into a first reactor and a second reactor which are connected in series; wherein the first reactor and the second reactor are respectively filled with a hydrocracking catalyst, and a raw material fed into the second reactor is a first reaction product discharged from the first reactor; (2) heating the first reactor and the second reactor to 315-335 DEG C, and then carrying out heat preservation treatment for 12-30 hours; (3) after the heat preservation treatment is completed, heating the first reactor and the second reactor so as to prepare middle distillate oil by using Fischer-Tropsch wax; wherein the temperature of the first reactor is increased to 345-370 DEG C, and the temperature of the second reactor is 8-15 DEG C lower than that of the first reactor; and (4) fractionating a second reaction product discharged from the second reactor to obtain middle distillate. According to the method, the yield of the middle distillate is improved under the condition that a harmful passivator is not introduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of Fischer-Tropsch synthesis oil processing technology, and particularly relates to a method for improving the yield of middle distillate oil in Fischer-Tropsch wax hydrocracking. BACKGROUND

[0002] With the decreasing of petroleum resources, the development of alternative energy technologies has attracted much attention. Coal indirect liquefaction technology is an advanced clean energy utilization technology, which can convert carbon and hydrogen elements in coal, natural gas or biomass into clean liquid fuel. Fischer-Tropsch synthesis is a key technology of coal indirect liquefaction, and the main product is Fischer-Tropsch wax. The Fischer-Tropsch wax has a high drop melting point and cannot be directly used as a vehicle fuel. Generally, the Fischer-Tropsch wax is converted into small molecular naphtha and diesel through hydrocracking. The naphtha is characterized by being substantially free of sulfur and nitrogen, and more than 90% of the naphtha is chain hydrocarbon, and the octane number is low. The diesel is characterized by a high cetane number and a low density, and is a high-quality vehicle fuel blending component. Because of the high product added value, the diesel is the preferred product of hydrocracking.

[0003] CN200510068182.7 discloses a method for producing more middle distillate oil from Fischer-Tropsch synthesis oil. The whole distillate of Fischer-Tropsch synthesis oil, hydrogen and a hydrofining catalyst are contacted, and the hydrofining reaction product is separated into naphtha, middle distillate oil and heavy oil. The heavy oil is again contacted with hydrogen and a hydrocracking catalyst, and the hydrocracking product is separated into naphtha, middle distillate oil and tail oil. The tail oil can be recycled to the cracking reactor for further cracking reaction. However, the heavy oil has a bed temperature rise in the hydrocracking reactor, resulting in uneven temperature distribution in the reactor, high temperature, and diesel cracking, which reduces the yield.

[0004] CN201410308766.6 discloses a method for improving the yield of middle distillate oil in Fischer-Tropsch wax hydrocracking. The Fischer-Tropsch wax and hydrogen pass through the hydrocracking catalyst bed in a countercurrent flow, ammonia is injected into the hydrogen, and an ammonia concentration gradient distribution is formed in the catalyst bed, which reduces the temperature sensitivity of the hydrocracking catalyst and improves the yield of the middle distillate oil. However, the reaction system introduces ammonia, which is a hazardous chemical and can pollute the environment. In addition, the introduction of ammonia brings impurities to the clean system, affects the product quality, increases the nitrogen content in the tail gas, and corrodes the equipment. SUMMARY

[0005] The present application aims to provide a method for improving the yield of middle distillate oil in Fischer-Tropsch wax hydrocracking, so as to improve the yield of the middle distillate oil without introducing harmful passivation agents.

[0006] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0007] A method for improving the yield of middle distillate oil in Fischer-Tropsch wax hydrocracking, the method comprising:

[0008] (1) Fischer-Tropsch wax and hydrogen are fed into a first reactor and a second reactor connected in series as raw materials; wherein the first reactor and the second reactor are respectively filled with hydrocracking catalyst, and the raw material fed into the second reactor is the first reaction product discharged from the first reactor.

[0009] (2) Heat the first reactor and the second reactor to 315-335℃ and then keep them at that temperature for 12-30 hours.

[0010] (3) After the heat preservation treatment is completed, the first reactor and the second reactor are heated to prepare middle distillate oil using Fischer-Tropsch wax; wherein the first reactor is heated to 345-370℃, and the temperature of the second reactor is 8-15℃ lower than that of the first reactor.

[0011] (4) The second reaction product discharged from the second reactor is fractionated to obtain middle distillate oil.

[0012] In step (1) of the present invention, the raw material first enters the first reactor of two reactors connected in series, and then flows through the second reactor. The specific flow method can be known in the art. For example, Fischer-Tropsch wax and hydrogen enter simultaneously from the top of the reactor, pass through the catalyst bed therein and flow out from the bottom of the first reactor, and then enter the top of the second reactor as raw material, pass through the catalyst bed therein and flow out from the bottom of the second reactor.

[0013] In some embodiments, the Fischer-Tropsch wax is a refined tail oil with an initial boiling point of not less than 365°C, obtained by hydrorefining the Fischer-Tropsch synthesis product oil; preferably, the initial boiling point of the Fischer-Tropsch wax is greater than or equal to 365°C, the dropping melting point is not less than 85°C, the sulfur content is less than 2 μg / g, and the oxygen content is less than 1 wt%.

[0014] In step (2) of the present invention, the first reactor and the second reactor are heated to 315-335°C, preferably 320-330°C, and kept at that temperature for 12-30 hours, preferably 16-24 hours, for example 20 hours, so that the Fischer-Tropsch wax reacts slowly at a low conversion rate, such as about 10%-20%, at a lower temperature, thereby inhibiting the initial activity of the catalyst and facilitating the increase of the yield of the middle distillate oil when the reaction is further heated.

[0015] In a preferred embodiment, in step (2), the heating rate is 5-20°C / h, for example, 10 or 15°C / h.

[0016] In step (3) of the present invention, after the heat preservation treatment in step (2) is completed, the initial activity of the catalyst is suppressed, so that the first reactor and the second reactor can be further heated in order to prepare middle distillate oil using Fischer-Tropsch wax while improving the conversion rate and reducing over-fractionation side reactions.

[0017] In a preferred embodiment, the first reactor is heated to 345-370°C, for example, 350, 355, 360, or 365°C, so that the hydrogenation reaction process in the first reactor is mainly the hydrocracking reaction of Fischer-Tropsch wax. The temperature of the second reactor is 8-15°C lower than that of the first reactor, for example, 10 or 12°C, so that the hydrogenation reaction process in the second reactor is mainly the isomerization dewaxing reaction, thereby increasing the yield of the middle distillate. Preferably, to further improve the yield of the middle distillate oil, the cracking conversion rate of the fraction above 365°C in the Fischer-Tropsch wax entering the first reactor can be further controlled to be 30-50%, for example, 40%, and the cracking conversion rate of the fraction above 365°C in the Fischer-Tropsch wax entering the second reactor can be 10-30%, for example, 20%, which can be adjusted, for example, by temperature and / or space velocity.

[0018] In a preferred embodiment, the catalyst volume in the first reactor accounts for 30%-50% of the total volume of the cracking agent in the first and second reactors, for example, 35%, 40% or 45%.

[0019] In a preferred embodiment, the total volumetric space velocity of the first and second reactors is 1-2.0 h⁻¹. -1 For example, 1.2, 1.5 or 1.8h -1 The hydrogen-to-oil volume ratio is 600-1500:1, such as 800:1, 1000:1 or 1200:1, and the hydrogen partial pressure is 6-10 MPa, such as 8 MPa.

[0020] In this invention, the hydrocracking catalyst used can be a commonly used hydrocracking catalyst in the art; in some embodiments, the hydrocracking catalyst loaded in the first and second reactors is an amorphous silica-alumina supported non-precious metal catalyst (the support is amorphous silica-alumina and alumina as a binder), the metal component of the non-precious metal catalyst is Group VIB and Group VIII non-precious metals, wherein the Group VIB metal is Mo and / or W, and the Group VIII metal is Ni metal, and the content of Group VIII metal is 2-12% and the content of Group VIB metal is 10-30% based on the total weight of the catalyst; or, the hydrocracking catalyst loaded in the first and second reactors is an amorphous silica-alumina supported precious metal catalyst, the precious metal is Pt or Pd, and the precious metal content is 0.3-1% of the total weight of the catalyst.

[0021] To further improve the yield of middle distillate oil, in a preferred embodiment, the hydrocracking catalyst packed in the first reactor is an amorphous silica-alumina supported non-precious metal catalyst. The metal components of the non-precious metal catalyst are Group VIB and Group VIII non-precious metals, wherein the Group VIB metal is Mo and / or W, and the Group VIII metal is Ni. Based on the total weight of the catalyst, the content of Group VIII metal is 2-12%, such as 4%, 6%, 8% or 10%, the content of Group VIB metal is 10-30%, such as 13%, 15%, 17%, 20% or 25%, and the content of amorphous silica-alumina is 45-60%, such as 50% or 55% (the catalyst support does not contain molecular sieves and consists of amorphous silica-alumina and alumina as a binder).

[0022] The first reactor is filled with a hydrocracking catalyst that is an amorphous silica-alumina supported non-precious metal catalyst. The metal components of the non-precious metal catalyst are group VIB and group VIII non-precious metals, wherein the group VIB metal is Mo and / or W, and the group VIII metal is Ni. Based on the total weight of the catalyst, the content of group VIII metal is 2-12%, such as 4%, 6%, 8% or 10%, the content of group VIB metal is 10-30%, such as 13%, 15%, 17%, 20% or 25%, and the content of amorphous silica-alumina is 30-40%, such as 35% (the catalyst support does not contain molecular sieves and consists of amorphous silica-alumina and alumina as a binder).

[0023] In step (4) of the present invention, the second reaction product discharged from the second reactor is fractionated to obtain middle distillate oil; the distillation range of the middle distillate oil can be 160-365℃; preferably, the flash point of the middle distillate oil is not lower than 60℃ and the pour point is not higher than -20℃.

[0024] Unless otherwise specified, all percentages or percentages mentioned in this invention refer to mass percentages or mass percentages.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] This invention introduces Fischer-Tropsch wax as a reactant to react slowly at low conversion rates, suppressing the initial activity of the catalyst. Then, under the action of the catalyst, the two reactors are raised to different temperatures to carry out hydrocracking reactions. The first reactor is dominated by cracking reactions, while the second reactor is dominated by isomerization and pour point depletion reactions, thereby increasing the yield of middle distillate. The method of this invention increases the yield of middle distillate oil without introducing harmful passivating agents. The resulting middle distillate oil has a flash point of not less than 60°C and a pour point of not more than -20°C, resulting in high-quality products. Detailed Implementation

[0027] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" as used herein may include any and all combinations of one or more of the associated listed items. The terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0031] In this invention, the conversion rate of fractions above 365°C = the content of fractions above 365°C in the feed - the content of fractions above 365°C in the discharge;

[0032] 160-365℃ middle distillate oil yield = mass of 160-365℃ distillate oil in the product / feed rate;

[0033] Selectivity of middle distillate oil at 160-365℃ = Yield of middle distillate oil at 160-365℃ / Conversion rate of fractions above 365℃

[0034] Example 1

[0035] (1) The first reactor and the second reactor (both fixed-bed hydrogenation reactors) are connected in series, and 50 ml of hydrocracking catalyst (prepared according to the steps of Example 1 in CN202010652196.8, the specific composition is shown in Table 1, wherein the first reactor is filled with catalyst 1 and the second reactor is filled with catalyst 3) is injected from the top of the first reactor, flows through the catalyst bed and flows out from the bottom, and then directly enters the top of the second reactor, flows through the catalyst bed and flows out from the bottom of the reactor;

[0036] (2) Heat preservation treatment: The first reactor and the second reactor are heated to 330℃ at a rate of 10℃ / h and kept at a constant temperature for 24h.

[0037] (3) After the heat preservation treatment is completed, the temperature is raised to carry out the hydrocracking reaction: the average reaction temperature of the first reactor is 360℃, the average reaction temperature of the second reactor is 350℃, the hydrogen partial pressure is 7MPa, the Fischer-Tropsch wax injection rate is 140g / h, and the hydrogen flow rate is 157NL / h; the specific reaction conditions are shown in Table 3.

[0038] (4) The second reaction product was fractionated to obtain the middle distillate oil. The results are shown in Table 4.

[0039] Example 2

[0040] The difference from Example 1 is that the first reactor is filled with catalyst 2 and the second reactor is filled with catalyst 4; the specific reaction conditions are shown in Table 3.

[0041] The results are shown in Table 4.

[0042] Table 1. Composition of each catalyst (balance is alumina used as catalyst support)

[0043]

[0044] Table 2 Properties of Fischer-Tropsch Wax

[0045]

[0046] Example 3

[0047] The difference from Example 1 is that both the first and second reactors are filled with catalyst 1; the remaining reaction conditions are the same as in Example 1.

[0048] The results are shown in Table 4.

[0049] Table 3 Reaction conditions

[0050] First hydrocracking reactor: Example 1 Example 2 Hydrogen partial pressure, MPa 7 7 Average reaction temperature, °C 360 363 Cracking conversion, % 40.6 48.1 Second hydrocracking reactor: Hydrogen partial pressure, MPa 7 7 Average reaction temperature, °C 350 353 Cracking conversion, % 20.5 28.3 Total volumetric space velocity, h -1 ]] 1.6 1.6 Total hydrogen to oil volume ratio, v% / v% 800：1 800：1

[0051] Table 4 Reaction Results

[0052]

[0053] Comparative Example 1

[0054] The difference from Example 1 is that the heat preservation treatment in step (2) is omitted, while the rest is the same as in Example 1. The results are shown in Table 4.

[0055] Comparative Example 2

[0056] The difference from Example 3 is that the heat preservation treatment in step (2) is omitted, the second reactor is omitted, and 100 ml of hydrocracking catalyst is loaded into the first reactor. The rest is the same as in Example 3. The results are shown in Table 4.

[0057] Comparative Example 3

[0058] The difference from Example 3 is that the heat preservation treatment in step (2) is omitted, the first reactor is omitted, and 100 ml of hydrocracking catalyst is loaded into the second reactor. The rest is the same as in Example 3. The results are shown in Table 4.

[0059] A comparison between Example 1 and Example 3 shows that Example 1, by using a different preferred catalyst, is more conducive to increasing the yield of the middle fraction and lowering the product pour point.

[0060] As can be seen from the comparison between Example 1 and Comparative Example 1, without heat preservation treatment, the yield of the middle fraction decreases and the product pour point increases.

[0061] As can be seen from the comparison between Example 3 and Comparative Example 2, without heat preservation treatment and with only the first reactor, the yield of middle distillate oil further decreases;

[0062] A comparison of Example 3 and Comparative Example 3 shows that without heat preservation treatment and with only a second reactor, the yield of middle distillate oil further decreases.

Claims

1. A method for improving the yield of Fischer-Tropsch wax hydrocracking middle distillate, the method comprising: (1) Fischer-Tropsch wax and hydrogen are fed into a first reactor and a second reactor connected in series as raw materials; wherein the first reactor and the second reactor are respectively filled with hydrocracking catalyst, and the raw material fed into the second reactor is the first reaction product discharged from the first reactor. (2) Heat the first reactor and the second reactor to 315-335℃ and then keep them at that temperature for 12-30 hours. (3) After the heat preservation treatment is completed, the first reactor and the second reactor are heated to prepare middle distillate oil using Fischer-Tropsch wax; wherein the first reactor is heated to 345-370℃, and the temperature of the second reactor is 8-15℃ lower than that of the first reactor. (4) The second reaction product discharged from the second reactor is fractionated to obtain middle distillate oil.

2. The method according to claim 1, characterized in that, In step (2), the first reactor and the second reactor are heated to 320-330℃ and then kept at that temperature for 16-24 hours.

3. The method according to claim 1 or 2, characterized in that, In step (2), the heating rate is 5-20℃ / h.

4. The method according to any one of claims 1-3, characterized in that, In step (3), the cracking conversion rate of the fraction above 365°C in the Fischer-Tropsch wax entering the first reactor is 30-50%; and the cracking conversion rate of the fraction above 365°C in the Fischer-Tropsch wax entering the second reactor is 10-30%.

5. The method according to any one of claims 1-4, characterized in that, The catalyst volume of the first hydrocracking reactor accounts for 30%-50% of the total catalyst volume of the first and second cracking reactors.

6. The method according to claim 5, characterized in that, The total volumetric space velocity of the first and second reactors is 1-2.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 600-1500:1, and the hydrogen partial pressure is 6-10 MPa.

7. The method according to any one of claims 1-6, characterized in that, The first and second reactors are filled with hydrocracking catalysts that are amorphous silica-alumina supported non-precious metal catalysts. The metal components of the non-precious metal catalysts are Group VIB and Group VIII non-precious metals, wherein the Group VIB metals are Mo and / or W, and the Group VIII metals are Ni metals. Based on the total weight of the catalysts, the content of Group VIII metals is 2-12%, and the content of Group VIB metals is 10-30%. Alternatively, the first and second reactors are filled with hydrocracking catalysts that are amorphous silica-alumina supported precious metal catalysts, wherein the precious metals are Pt or Pd, and the content of the precious metals is 0.3-1% of the total weight of the catalysts.

8. The method according to claim 7, characterized in that, The first reactor is filled with a hydrocracking catalyst that is an amorphous silica-alumina supported non-precious metal catalyst. The metal components of the non-precious metal catalyst are group VIB and group VIII non-precious metals, wherein the group VIB metal is Mo and / or W, and the group VIII metal is Ni. Based on the total weight of the catalyst, the content of group VIII metal is 2-12%, and the content of group VIB metal is 10-30%. The catalyst support contains amorphous silica-alumina and alumina as a binder, and the content of amorphous silica-alumina is 45-60%. The second reactor is filled with a hydrocracking catalyst that is an amorphous silica-alumina supported non-precious metal catalyst. The metal components of the non-precious metal catalyst are group VIB and group VIII non-precious metals, wherein the group VIB metal is Mo and / or W, and the group VIII metal is Ni. Based on the total weight of the catalyst, the content of group VIII metal is 2-12%, and the content of group VIB metal is 10-30%. The catalyst support contains amorphous silica-alumina and alumina as a binder, and the content of amorphous silica-alumina is 30-40%.

9. The method according to any one of claims 1-8, characterized in that, The Fischer-Tropsch wax is a refined tail oil with an initial boiling point of not less than 365°C, obtained by hydrorefining the Fischer-Tropsch synthesis product oil. Preferably, the Fischer-Tropsch wax has an initial boiling point of ≥365°C, a dropping melting point of ≥85°C, a sulfur content of ≤2μg / g, and an oxygen content of ≤1% by weight.

10. The method according to any one of claims 1-9, characterized in that, The distillation range of the middle distillate oil is 160-365℃; Preferably, the flash point of the middle distillate oil is not lower than 60°C and the pour point is not higher than -20°C.

Images