Method for producing C3 / C4 product from light oil

Abstract

The invention relates to the field of raffinate oil utilization and conversion, and discloses a method for producing a C3 / C4 product from light oil, which comprises the following steps: (1) introducing light oil into a hydrocracking reaction zone filled with a hydrocracking catalyst to carry out a hydrocracking reaction under a low-pressure hydrogen condition to obtain a hydrocracking product; the content of saturated hydrocarbon in the raffinate oil is 90 wt%-100 wt%; and (2) separating the hydrocracking product. According to the method provided by the invention, the liquefied gas rich in C3 and isomeric C4 can be produced by taking the raffinate oil as a raw material under a low-pressure hydrogen condition.

Description

Technical Field

[0001] The present invention relates to the technical field of light oil utilization and conversion, and in particular to a method for producing C3 / C4 products from light oil. Background Art

[0002] At present, the traditional oil refining industry is facing the challenge of transforming from large-scale and clean production to "oil conversion" and energy conservation and carbon reduction. Since the octane number of aromatic raffinate oil itself is not high and the demand for blending gasoline is low, there is an urgent need for a high-value utilization method for aromatic raffinate oil.

[0003] The best raw materials for chemical plants such as ethylene are low-carbon normal alkanes. Therefore, using low-sulfur and low-nitrogen raffinate oil as raw materials to produce propane and butane, while producing a portion of light naphtha mainly composed of low-carbon hydrocarbons, can provide high-quality raw materials for chemical plants and solve the problem of excess low-value-added raffinate oil resources in refineries.

[0004] CN12409121A discloses a method for converting light naphtha into low-carbon olefins and aromatics, wherein light naphtha with a C5 and C6 paraffin content of 99% is separated by normal isomerization, and the isomer components are fed to a hydrocracking unit and separated to obtain refinery dry gas, propane, normal butane and isobutane, and then these components are further converted into ethylene and propylene by steam cracking or propane dehydrogenation. The conditions of the hydrocracking unit in the method include a temperature of 330 to 360°C and a pressure of 6 to 8 MPa gauge pressure. After separation by the hydrocracking unit, the proportions of refinery dry gas, propane, normal butane and isobutane are 6%, 31%, 29% and 34% respectively.

[0005] WO2021236149A1 discloses a method for converting light naphtha fractions into high-value products through two-stage reaction zones. The raw material passes through a first reactor loaded with a bifunctional catalyst, partially reforming the light naphtha into BTEX, and partially cracking the light naphtha into ethane, propane and butane. The effluent from the first reactor is passed through a gas-liquid separation unit to produce liquid and gas products. After removing hydrogen and methane from the gas product, the gas is converted into light olefins under steam cracking conditions through a second reactor.

[0006] CN13307717A discloses a method for producing propane by hydrogenation of light hydrocarbons, wherein the light hydrocarbon raw material, hydrogen-rich gas and circulating light hydrocarbon are heated, and then catalytic cracking reaction is carried out under acidic catalyst conditions, and the reaction product is cooled and fractionated to obtain dry gas, propane and aromatic gasoline components. The raw material of the method is a raw material with an alkane content greater than 50wt% and a carbon number range of C4 to C13, the reaction temperature is 250 to 550°C, the pressure is 0.01 to 5.0MPa, and the mass space velocity is 0.1 to 5.0h -1, the hydrogen-to-oil ratio is 30 to 800:1, and the catalyst is a HZSM-5 molecular sieve.

[0007] At present, technologies that use propane and butane as their main products often have relatively high restrictions on raw materials, such as the carbon number and alkane content of the raw material hydrocarbon composition. In addition, under relatively mild reaction conditions, the yields of the products propane and butane are often relatively low. Summary of the invention

[0008] The purpose of the present invention is to provide a hydrocarbon oil conversion method which takes light oil as raw material and maximizes the yield of propane and isobutane.

[0009] In order to achieve the above object, the present invention provides a method for producing C3 / C4 products from light oil, the method comprising:

[0010] (1) introducing light oil into a hydrocracking reaction zone filled with a hydrocracking catalyst under low pressure and hydrogen conditions to carry out a hydrocracking reaction to obtain a hydrocracking product; the content of saturated hydrocarbons in the light oil is 90 wt% to 100 wt%;

[0011] (2) separating the hydrocracking products to obtain C3 / C4 products and light naphtha products above C5; the yield of liquefied gas in the C3 / C4 products is not less than 50 wt%;

[0012] The conditions of the hydrocracking reaction are controlled so that the conversion rate of the hydrocracking reaction zone is 42% to 88%; the conversion rate = (1-the mass percentage of C5 or higher hydrocarbons in the C5 or higher light naphtha product * the yield of the C5 or higher light naphtha product / the mass percentage of C5 or higher hydrocarbons in the light oil) * 100%;

[0013] Based on the total weight of the hydrocracking catalyst, the content of active metal elements in the hydrocracking catalyst in terms of oxides is 10wt% to 50wt%, and the remainder is a carrier; based on the total weight of the carrier, the carrier contains 45wt% to 80wt% of an acidic component, and the acidic component is at least one of a Y-type molecular sieve and its modified products.

[0014] The method provided by the present invention can convert light oil raw materials such as aromatic raffinate oil to produce C3 / C4 products.

[0015] The method provided by the invention can produce liquefied gas rich in C3 and isomerized C4 using light oil as a raw material under low-pressure hydrogen conditions.

[0016] The method provided by the present invention realizes the production of C3 and C4 products from raffinate oil under low-pressure hydrocracking conditions for low-nitrogen naphtha raw materials, maximizes the yield of propane and isobutane, and provides high-quality raw materials for chemical plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic flow chart of a method for producing C3 / C4 products from light oil according to a preferred specific embodiment of the present invention.

[0018] Description of Reference Numerals

[0019] 1, 3, 5, 7, 9, 11, 12, 14, 15, 16 are pipelines

[0020] 2: Raw oil pump

[0021] 4: Heating furnace

[0022] 6: Hydrocracking reaction zone

[0023] 8: High pressure separator

[0024] 10: Gas purification unit

[0025] 13: Fractionation unit DETAILED DESCRIPTION

[0026] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0027] As mentioned above, the present invention provides a method for producing C3 / C4 products from light oil, the method comprising:

[0028] (1) introducing light oil into a hydrocracking reaction zone filled with a hydrocracking catalyst under low pressure and hydrogen conditions to carry out a hydrocracking reaction to obtain a hydrocracking product; the content of saturated hydrocarbons in the light oil is 90 wt% to 100 wt%;

[0029] (2) separating the hydrocracking products to obtain C3 / C4 products and light naphtha products above C5; the yield of liquefied gas in the C3 / C4 products is not less than 50 wt%;

[0030] The conditions of the hydrocracking reaction are controlled so that the conversion rate of the hydrocracking reaction zone is 42% to 88%; the conversion rate = (1-the mass percentage of C5 or higher hydrocarbons in the C5 or higher light naphtha product * the yield of the C5 or higher light naphtha product / the mass percentage of C5 or higher hydrocarbons in the light oil) * 100%;

[0031] Based on the total weight of the hydrocracking catalyst, the content of active metal elements in the hydrocracking catalyst in terms of oxides is 10wt% to 50wt%, and the remainder is a carrier; based on the total weight of the carrier, the carrier contains 45wt% to 80wt% of an acidic component, and the acidic component is at least one of a Y-type molecular sieve and its modified products.

[0032] In the present invention, the yield of the C5 or higher light naphtha product = the total mass of the liquid product obtained after the hydrocracking product is fractionated / the mass of the light oil * 100%.

[0033] Preferably, the conditions of the hydrocracking reaction are controlled so that the conversion rate in the hydrocracking reaction zone is 60% to 88%, more preferably 62% to 88%.

[0034] Preferably, in the hydrocracking catalyst, based on the total weight of the carrier, the carrier contains 45 wt% to 60 wt%, more preferably 45 wt% to 55 wt%, particularly preferably 45 wt% to 50 wt% of the acidic component.

[0035] The method of the present invention may also include, before introducing the light oil into the hydrocracking reaction zone for the hydrocracking reaction, preheating the light oil alone or together with hydrogen, for example, introducing the light oil into a heating furnace for preheating treatment; and then introducing the preheated material into the hydrocracking reaction zone for the hydrocracking reaction. The present invention has no special requirements for the preheating temperature, which may be the temperature required for the hydrocracking reaction or slightly lower than the temperature required for the hydrocracking reaction.

[0036] Preferably, in step (1), the carbon number of the light oil is C5-C12, the paraffin content is 30wt%-100wt%, the cycloparaffin content is 0wt%-70wt%, and the aromatic content is 0wt%-10wt%.

[0037] More preferably, the paraffin content of the light oil is 45 wt % to 90 wt %.

[0038] More preferably, the cycloparaffin content of the light oil is 10 wt% to 50 wt%.

[0039] More preferably, the light oil has an aromatic content of 0.1 wt% to 8 wt%.

[0040] Preferably, the density of the light oil at 20°C is 0.68-0.75 g / cm 3 .

[0041] Preferably, the light oil is selected from one or more of refinery light oil from an aromatics extraction unit, reforming raffinate oil, and DCC gasoline hydrogenation unit raffinate oil.

[0042] Preferably, the nitrogen content in the light oil is ≯20 μg / g, the sulfur content is ≯300 μg / g, and the arsenic content is ≯0.2 μg / g.

[0043] Preferably, the pressure of the hydrocracking reaction is ≯8.0 MPa.

[0044] According to a preferred embodiment, the hydrocracking reaction temperature is 280-420°C, the pressure is 0.2-8.0 MPa, and the light oil volume space velocity is 0.5-20.0 h -1 , the volume ratio of hydrogen to oil is 100~2000.

[0045] Preferably, the carrier of the hydrocracking catalyst further contains at least one heat-resistant inorganic oxide selected from silicon oxide and aluminum oxide.

[0046] Particularly preferably, based on the total weight of the carrier, the content of the heat-resistant inorganic oxide is 20 wt % to 55 wt %.

[0047] Preferably, in the hydrocracking catalyst, the active metal elements are selected from at least two of Group VIB metal elements and Group VIII metal elements.

[0048] According to a particularly preferred embodiment, in the hydrocracking catalyst, the active metal element includes at least one selected from the metal elements of Group VIB and at least one selected from the metal elements of Group VIII; based on the total weight of the hydrocracking catalyst, the content of the metal element of Group VIB is 5wt% to 35wt%, and the content of the metal element of Group VIII is 1wt% to 8wt%, calculated as oxide.

[0049] Preferably, in step (1), a protective catalyst is also loaded upstream of the hydrocracking catalyst; based on the total volume of the catalyst in the hydrocracking reaction zone as 100%, the loading volume of the protective catalyst is 1% to 50%, and the loading volume of the hydrocracking catalyst is 50% to 99%.

[0050] Preferably, in step (1), the protective catalyst is selected from at least one of a hydrotreating catalyst, a hydroarsenication catalyst and a hydrodemetallization catalyst.

[0051] According to a particularly preferred embodiment, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; and the protected catalyst is a hydrorefining catalyst and / or a hydrodemetallization catalyst.

[0052] Preferably, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; the protected catalyst contains a protectant carrier and a protectant active metal component, the protectant carrier is alumina, and the protectant active metal component contains at least one element selected from Group VIII metal elements and at least one element selected from Group VIB metal elements.

[0053] More preferably, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; in the protected catalyst, based on the total weight of the protective agent, the content of the metal element of Group VIII is 0.3 wt% to 5 wt%, and the content of the metal element of Group VIB is 1 wt% to 30 wt%, calculated as oxide.

[0054] According to a preferred specific embodiment, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; in the protected catalyst, the active metal component of the protective agent contains at least one of nickel and cobalt elements, and contains at least one of molybdenum and tungsten elements.

[0055] According to another preferred embodiment, in step (1), the arsenic content of the light oil is 1 μg / g to 30 μg / g, and the protected catalyst comprises a hydro-dearsenification catalyst.

[0056] More preferably, the hydrodearsenicating catalyst carrier is alumina, and the active metal component contains at least one of nickel and cobalt, and at least one of molybdenum and tungsten. Calculated as oxides, the total content of the nickel and the cobalt is 0.1wt% to 6wt%, and the total content of the molybdenum and the tungsten is 1wt% to 20wt%.

[0057] According to another preferred embodiment, in step (1), the total metal content of the light oil is 0.1 wt% to 2 wt%, and the protected catalyst is a hydrodemetallization catalyst.

[0058] More preferably, the hydrodemetallization catalyst carrier is alumina, and the active metal component contains at least one of nickel and cobalt, and at least one of molybdenum and tungsten, and the total content of the nickel and cobalt is 0.5wt% to 3wt% and the total content of the molybdenum and tungsten is 1wt% to 30wt% in terms of oxides. More preferably, the total content of the nickel and cobalt is 1wt% to 3wt% and the total content of the molybdenum and tungsten is 1wt% to 30wt% in terms of oxides.

[0059] The present invention has no particular requirements on the source of the aforementioned catalyst, which can be prepared by methods known in the art, or a catalyst with corresponding characteristics can be purchased commercially. The present invention will not be described in detail herein, and those skilled in the art should not interpret this as a limitation of the present invention.

[0060] The present invention has no particular requirements for the specific separation method described in step (2). Those skilled in the art may adopt separation methods known in the art, such as gas-liquid separation, fractionation, etc. The examples of the present invention provide a specific separation method by way of example, and those skilled in the art should not interpret this as limiting the scope of protection of the present invention.

[0061] The separation of the present invention can be performed in a separator (e.g., a high-pressure separator) for gas-liquid separation. The gas product obtained after the gas-liquid separation can be recycled back to the device for the hydrocracking reaction after purification. The liquid product obtained after the gas-liquid separation is preferably further fractionated to obtain the C3 / C4 product and the light naphtha product.

[0062] The light naphtha product obtained in the present invention can be mixed with the raw oil as unconverted oil according to production needs, and then circulated to the reaction system for full conversion, or it can be led out of the device. The present invention has no special requirements for this.

[0063] The following combination Figure 1 The process flow diagram shown provides a preferred specific embodiment of a method for producing C3 / C4 products from light oil according to the present invention. Specifically, the method comprises:

[0064] (1) Under low-pressure hydrogen conditions, light oil is introduced into a heating furnace 4 through pipeline 1, a feed oil pump 2 and a pipeline 3 in sequence for preheating, and hydrogen is introduced into the heating furnace 4 through pipeline 16 to obtain a preheated material; the preheated material is introduced into a hydrocracking reaction zone 6 in sequence filled with a hydrocracking catalyst through pipeline 5 for a hydrocracking reaction to obtain a hydrocracking product;

[0065] (2) The hydrocracking product is introduced into a high-pressure separator 8 via pipeline 7 for gas-liquid phase separation; the gas phase flowing out of the high-pressure separator 8 enters a gas purification unit 10 via pipeline 9, and the purified gas can be circulated back to the reaction system as circulating hydrogen via pipeline 11; the liquid phase flowing out of the high-pressure separator 8 enters a fractionation unit 13 via pipeline 12, and the propane-rich gas phase exits the device via pipeline 14; after fractionation in the fractionation unit, light naphtha containing components above C5 is drawn out from pipeline 15, and this part of light naphtha can also be used as unconverted oil according to production needs and mixed with the feedstock oil from the pipeline via pipeline, and then circulated to the reaction system for full conversion.

[0066] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the raw materials used are all common commercially available products.

[0067] Unless otherwise specified, the following examples use Figure 1 The process flow shown is carried out.

[0068] The properties of the light oil used below are listed in Table 1; the properties of the catalyst used are listed in Table 2.

[0069] The catalysts used in the following examples are prepared by methods known in the art, for example, they can be prepared by the method provided in CN112742440A or purchased commercially.

[0070] Table 1: Properties of light oil

[0071]

[0072] Table 2: Catalyst conditions

[0073]

[0074] Example 1

[0075] use Figure 1 The process flow shown is carried out, and no protective catalyst is set in the hydrocracking reaction zone. The process parameters and other information involved are listed in Table 3.

[0076] The distribution and properties of the obtained products are listed in Table 4.

[0077] Comparative Example 1

[0078] use Figure 1 The process flow shown is carried out, and no protective catalyst is set in the hydrocracking reaction zone. The process parameters and other information involved are listed in Table 3.

[0079] The distribution and properties of the obtained products are listed in Table 4.

[0080] Example 2

[0081] use Figure 1 The process flow shown is carried out, and a protective catalyst is set in the hydrocracking reaction zone, and the protective catalyst is located upstream of the hydrocracking catalyst. The process parameters and other information involved are listed in Table 3.

[0082] The distribution and properties of the obtained products are listed in Table 4.

[0083] Comparative Example 2

[0084] use Figure 1 The process flow shown is carried out, and no protective catalyst is set in the hydrocracking reaction zone. The process parameters and other information involved are listed in Table 3.

[0085] The distribution and properties of the obtained products are listed in Table 4.

[0086] Example 3

[0087] use Figure 1 The process flow shown is carried out, and a protective catalyst is set in the hydrocracking reaction zone, and the protective catalyst is located upstream of the hydrocracking catalyst. The process parameters and other information involved are listed in Table 3.

[0088] The distribution and properties of the obtained products are listed in Table 4.

[0089] Comparative Example 3

[0090] use Figure 1 The process flow shown is carried out, and a protective catalyst is set in the hydrocracking reaction zone, and the protective catalyst is located upstream of the hydrocracking catalyst. The process parameters and other information involved are listed in Table 3.

[0091] The distribution and properties of the obtained products are listed in Table 4.

[0092] Example 4

[0093] use Figure 1 The process flow shown is carried out, and no protective catalyst is set in the hydrocracking reaction zone. The process parameters and other information involved are listed in Table 3.

[0094] The distribution and properties of the obtained products are listed in Table 4.

[0095] Comparative Example 4

[0096] use Figure 1 The process flow shown is carried out, and no protective catalyst is set in the hydrocracking reaction zone. The process parameters and other information involved are listed in Table 3.

[0097] The distribution and properties of the obtained products are listed in Table 4.

[0098] Example 5

[0099] use Figure 1 The process flow shown in the figure is carried out, the types of feedstock oil in the hydrocracking reaction zone are different, and the types of protected catalysts are different. The information such as the process parameters involved are listed in Table 3.

[0100] The distribution and properties of the obtained products are listed in Table 4.

[0101] Table 3

[0102]

[0103]

[0104] The catalyst loading volume percentages in Table 3 are calculated based on the total catalyst loading volume for the hydrocracking reaction.

[0105] Table 3 (Continued)

[0106]

[0107] The catalyst loading volume percentages in Table 3 are calculated based on the total catalyst loading volume for the hydrocracking reaction.

[0108] Table 4

[0109]

[0110] From the above results, it can be seen that the method provided by the present invention can convert naphtha raw material into liquefied gas products under milder conditions, wherein the yield of propane and isobutane are relatively close. However, the method provided in the comparative example obviously requires a higher temperature and a lower space velocity to convert the raw oil into liquefied gas, etc.

[0111] In addition, it can be seen from the above results that the hydrocracking technology of the present invention has an excellent effect of producing more C3\C4 liquefied gas.

[0112] In addition, the results of Example 5 also show that by using a suitable hydrofining or hydrodemetallizing agent to treat the metal-containing raw materials and satisfying the feed requirements of the cracking stage, high-quality cracking products can be obtained, and the yield of the product C3\C4 liquefied gas is high.

[0113] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for producing C3 / C4 products from light oil, characterized in that: The method includes: (1) introducing light oil into a hydrocracking reaction zone filled with a hydrocracking catalyst under low pressure and hydrogen conditions to carry out a hydrocracking reaction to obtain a hydrocracking product; the content of saturated hydrocarbons in the light oil is 90 wt% to 100 wt%; (2) separating the hydrocracking products to obtain C3 / C4 products and light naphtha products above C5; the yield of liquefied gas in the C3 / C4 products is not less than 50 wt%; The conditions of the hydrocracking reaction are controlled so that the conversion rate of the hydrocracking reaction zone is 42% to 88%; the conversion rate = (1-the mass percentage of C5 or higher hydrocarbons in the C5 or higher light naphtha product * the yield of the C5 or higher light naphtha product / the mass percentage of C5 or higher hydrocarbons in the light oil) * 100%; Based on the total weight of the hydrocracking catalyst, the content of active metal elements in the hydrocracking catalyst in terms of oxides is 10wt% to 50wt%, and the remainder is a carrier; based on the total weight of the carrier, the carrier contains 45wt% to 80wt% of an acidic component, and the acidic component is at least one of a Y-type molecular sieve and its modified products.

2. The method according to claim 1, wherein: The conditions of the hydrocracking reaction are controlled so that the conversion rate of the hydrocracking reaction zone is 60% to 88%, preferably 62% to 88%.

3. The method according to claim 1 or 2, wherein: The carbon number of the light oil is C5-C12, the paraffin content is 30wt%-100wt%, the cycloparaffin content is 0wt%-70wt%, and the aromatic content is 0wt%-10wt%.

4. The method according to any one of claims 1 to 3, wherein: The light oil is selected from one or more of the refinery light oil of the aromatic extraction unit, the reforming raffinate oil, and the DCC gasoline hydrogenation unit raffinate oil.

5. The method according to any one of claims 1 to 4, wherein: The nitrogen content in the light oil is ≯20 μg / g, the sulfur content is ≯300 μg / g, and the arsenic content is ≯0.2 μg / g.

6. The method according to any one of claims 1 to 5, wherein: The pressure of the hydrocracking reaction is ≯8.0MPa; Preferably, the temperature of the hydrocracking reaction is 280-420°C, the pressure is 0.2-8.0 MPa, and the light oil volume space velocity is 0.5-20.0 h -1 , the volume ratio of hydrogen to oil is 100~2000.

7. The method according to any one of claims 1 to 6, wherein: The carrier of the hydrocracking catalyst further contains at least one heat-resistant inorganic oxide selected from silicon oxide and aluminum oxide; Preferably, based on the total weight of the carrier, the content of the heat-resistant inorganic oxide is 20 wt% to 55 wt%.

8. The method according to any one of claims 1 to 7, wherein: In the hydrocracking catalyst, the active metal elements are selected from at least two of Group VIB metal elements and Group VIII metal elements.

9. The method according to claim 8, wherein: In the hydrocracking catalyst, the active metal elements include at least one selected from the VIB group metal elements and at least one selected from the VIII group metal elements; based on the total weight of the hydrocracking catalyst, the content of the VIB group metal element is 5wt% to 35wt%, and the content of the VIII group metal element is 1wt% to 8wt% in terms of oxide.

10. The method according to any one of claims 1 to 9, wherein: In step (1), a protective catalyst is also loaded upstream of the hydrocracking catalyst; based on the total volume of the catalyst in the hydrocracking reaction zone as 100%, the loading volume of the protective catalyst is 1% to 50%, and the loading volume of the hydrocracking catalyst is 50% to 99%.

11. The method according to claim 10, wherein: In step (1), the protective catalyst is selected from at least one of a hydrotreating catalyst, a hydroarsenic removal catalyst and a hydrodemetallization catalyst.

12. The method according to claim 11, wherein: In step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; the protected catalyst is a hydrorefining catalyst and / or a hydrodemetallization catalyst; Preferably, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; the protected catalyst contains a protectant carrier and a protectant active metal component, the protectant carrier is alumina, and the protectant active metal component contains at least one element selected from Group VIII metal elements and at least one element selected from Group VIB metal elements; Preferably, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; in the protected catalyst, based on the total weight of the protective agent, the content of the metal element of Group VIII is 0.3 wt% to 5 wt%, and the content of the metal element of Group VIB is 1 wt% to 30 wt% in terms of oxide; Preferably, in step (1), the nitrogen content in the light oil is greater than 20 μg / g, or the sulfur content is greater than 300 μg / g, or the arsenic content is greater than 0.2 μg / g, or the mercury content is greater than 0.2 μg / g; in the protected catalyst, the active metal component of the protective agent contains at least one of nickel and cobalt elements, and contains at least one of molybdenum and tungsten elements.

13. The method according to claim 11, wherein: In step (1), the arsenic content of the light oil is 1 μg / g to 30 μg / g, and the protected catalyst comprises a hydrodearsenification catalyst; Preferably, the hydrodearsenicating catalyst carrier is alumina, and the active metal component contains at least one of nickel and cobalt, and at least one of molybdenum and tungsten. Calculated as oxides, the total content of the nickel and the cobalt is 0.1wt% to 6wt%, and the total content of the molybdenum and the tungsten is 1wt% to 20wt%.

14. The method according to claim 11, wherein: In step (1), the total metal content of the light oil is 0.1 wt% to 2 wt%, and the protected catalyst is a hydrodemetallization catalyst; Preferably, the hydrodemetallization catalyst carrier is alumina, and the active metal component contains at least one of nickel and cobalt, and at least one of molybdenum and tungsten. Calculated as oxides, the total content of the nickel and the cobalt is 0.5wt% to 3wt%, and the total content of the molybdenum and the tungsten is 1wt% to 30wt%.

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