CN111100708B

CN111100708B - Hydrocracking method for producing chemical raw materials

Info

Publication number: CN111100708B
Application number: CN201811270112.3A
Authority: CN
Inventors: 赵阳; 赵广乐; 毛以朝; 龙湘云; 戴立顺
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2018-10-29
Filing date: 2018-10-29
Publication date: 2021-12-17
Anticipated expiration: 2038-10-29
Also published as: CN111100708A

Abstract

A hydrocracking process for the production of a chemical feedstock, the process comprising: raw oil sequentially enters a hydrofining reaction zone and a hydrocracking reaction zone for hydrogenation reaction in the presence of hydrogen, gas-liquid separation and fractionation are carried out on obtained reaction products, so that a light naphtha fraction, a heavy naphtha fraction, a diesel oil fraction and a tail oil fraction are obtained, a hydrofining catalyst is filled in the hydrofining reaction zone, and a hydrocracking catalyst is filled in the hydrocracking reaction zone, wherein the hydrogen partial pressure in the hydrocracking reaction zone is 20-80% of that in the hydrofining reaction zone, and the hydrogen partial pressure range in the hydrofining reaction zone is 12-20 MPa. The method provided by the invention can be used for producing high-quality tail oil fraction while greatly increasing the yield of heavy naphtha.

Description

Hydrocracking method for producing chemical raw materials

Technical Field

The invention relates to the field of hydrocracking, in particular to a hydrocracking method for producing chemical raw materials.

Background

Ethylene is a basic raw material of petrochemical industry, and with the development of national economy, the ethylene production capacity of China is rapidly increased, but the ethylene production capacity cannot meet the demand of domestic markets for ethylene, and about half of ethylene production capacity depends on import. Therefore, the development of petrochemical feedstock olefin production technologies is one direction of development in the petrochemical industry.

Steam cracking of hydrocarbons is the primary means of ethylene production. In the process of preparing ethylene by steam cracking, the raw oil cost accounts for a large proportion of the total cost, and generally the raw oil cost accounts for more than 60 percent of the total cost. Therefore, the optimal selection of raw oil is an important factor influencing the benefit of the ethylene plant. From the world, the sources of raw materials for preparing ethylene by steam cracking are wide, light fraction raw materials comprise light hydrocarbon and naphtha, and heavy fraction raw materials comprise AGO, hydrocracking tail oil and the like. Among them, light hydrocarbons and hydrocracking tail oil are ethylene raw materials with better economical efficiency, followed by naphtha, and AGO is a relatively poor raw material. The light hydrocarbon yield in China is not high, and the proportion of light hydrocarbon in ethylene raw materials in China is very small. In addition, the crude oil in China is mostly heavy crude oil, the extraction rate of straight-run naphtha is low, the straight-run naphtha is also used as a raw material for producing high-octane reformate, and the contradiction between raw materials in oil refining and chemical industry is increasingly prominent. Thus, the production of ethylene feeds by a hydrocracking unit is an advantageous way to expand the source of the ethylene feedstock.

The hydrocracking technology is characterized in that heavy fractions such as Vacuum Gas Oil (VGO) and the like react with hydrogen in the presence of a catalyst, so that the dual purposes of improving the product quality and lightening the heavy oil product are achieved. Hydrocracking yields a wide cut product from the gas, naphtha, middle distillate and unconverted tail oil fraction. The hydrocracking tail oil has high paraffin and naphthene content and low aromatic hydrocarbon content, and is a high-quality ethylene raw material prepared by steam cracking.

As a feedstock for the production of ethylene, the BMCI value is generally used as an important measure of the performance, and the smaller the value, the higher the ethylene yield. Fundamentally, the magnitude of the BMCI value depends on its hydrocarbon composition, with the least alkane BMCI value, the next most cycloalkane, the most aromatic, the more chain branching the higher the BMCI value.

The reformer is an important secondary processing unit in a refinery for producing high octane gasoline blending components or for producing aromatic base stocks. The reformed gasoline has the characteristics of high octane number, no olefin, no sulfur and nitrogen impurities and the like, and is a high-quality gasoline blending component. Benzene, toluene and xylene are basic raw materials in petrochemical industry, and the oil generated by the reforming device is rich in benzene, toluene and xylene, and high-value aromatic hydrocarbon products can be obtained through separation.

Straight run naphtha is the primary source of reformer feed. For a long time, the yield of crude oil light oil is low in China, the straight-run naphtha is one of the raw materials of an ethylene unit, and the shortage of reforming raw materials becomes one of the main factors limiting the development of the reforming unit. The hydrocracking process is an important means for heavy oil conversion, and the obtained heavy naphtha has the characteristics of high aromatic hydrocarbon content and low sulfur and nitrogen impurity content, can be directly used as a high-quality reforming device for feeding, and makes up for the defects of the straight-run naphtha.

According to the market demand for high-quality tail oil and heavy naphtha, a hydrocracking technology capable of producing both heavy naphtha and high-quality tail oil is urgently needed.

CN1854263A discloses a hydrocracking method for producing chemical raw materials to the maximum, the heated raw oil and hydrogen enter a first reaction zone to contact with a hydrofining catalyst and a hydrocracking catalyst in turn, the reaction material flow is subjected to oil-gas separation, the obtained hydrogen-rich gas is compressed and then recycled with recycle hydrogen, the liquid is fractionated to obtain light naphtha, heavy naphtha, diesel oil fraction and tail oil fraction, wherein the diesel oil fraction is mixed with recycle hydrogen after being pressurized and then contacts with a hydrocracking catalyst in a second reaction zone, and the reaction material flow in the previous step are mixed and enter a separation and fractionation system. The method can produce more than 98% of chemical raw materials including liquefied gas, light naphtha, heavy naphtha and tail oil. This prior art proposes the concept of recycling diesel to the second hydrocracking reaction zone and then converting all to light components.

CN101117596A discloses a hydrogenation method capable of flexibly producing diesel oil and chemical raw materials. Three reactors are set up, namely a hydrotreating 1 reactor, a hydrocracking reactor and a hydrotreating 2 reactor. Wherein, the tail oil is recycled for producing diesel oil in a high yield, and the diesel oil is recycled for producing naphtha in a high yield. Also, the process proposes a concept for recycling the diesel fraction.

CN101173189A discloses a two-stage hydrocracking method for producing chemical raw materials. Characterized in that heavy raw oil and hydrogen are mixed and then enter a first-stage hydrotreating zone, hydrogen-rich gas obtained by separating first-stage effluent directly enters a second-stage hydrocracking reaction zone, and naphtha and tail oil obtained by separation are used as chemical raw materials. The middle distillate oil alone or mixed with other inferior distillate oil enters a second-stage hydrogenation treatment zone for cracking. The method provides a concept of circularly cracking the middle distillate to produce naphtha in more.

In addition, the aromatic hydrocarbon is an important chemical raw material, the heavy naphtha is used as the feed of a reforming device for producing the aromatic hydrocarbon, the market prospect is better, the yield of the heavy naphtha is increased along with the increase of the conversion rate, but the selectivity of the heavy naphtha is reduced along with the increase of the conversion rate, and the light naphtha has higher yield. Tail oil is also an important chemical raw material, and for a hydrocracking device, how to increase the yield of naphtha by reducing the yield of diesel oil while ensuring the same yield of tail oil is one of the problems to be solved urgently.

The current processing technology for producing heavy naphtha and high-quality tail oil mainly comprises the following points: (1) producing heavy naphtha and tail oil by adopting a one-pass process; (2) the diesel or middle distillate is recycled to the second cracking reaction zone to increase the yield of heavy naphtha.

However, for enterprises needing to produce heavy naphtha and high-quality product tail oil at the same time, the scheme has the following defects:

(1) the yield of heavy naphtha under one-time passing process is not enough to meet the product requirements of enterprises;

(2) after the yield of the heavy naphtha meets the enterprise requirements, the yield of the light naphtha or the light hydrocarbon is higher;

(3) after the yield of the heavy naphtha meets the enterprise requirements, the yield of the diesel oil is higher, and the yield of the tail oil is lower;

(4) the diesel oil or the middle distillate oil is recycled to the second cracking reactor, which is equivalent to the addition of a first-stage hydrocracking device, an additional reactor and a hydrogen recycling system are needed, the complexity of the device is increased, and the investment is increased.

Disclosure of Invention

The inventor of the invention finishes the technical scheme of the invention based on the following invention ideas:

in general, a one-pass process is an effective means for producing heavy naphtha, diesel oil and tail oil, and by improving the conversion depth, the yield of the heavy naphtha is correspondingly increased; correspondingly, the tail oil quality at high conversion depth is also improved. Therefore, the conversion depth is improved under the one-pass process, and the tail oil is properly lightened (the yield and the quality of the tail oil are not reduced), so that the aims of producing heavy naphtha in a large amount and producing the tail oil are fulfilled. However, in practical situations, the above solutions have disadvantages, which mainly appear in the following aspects:

(1) after the conversion rate is improved, the yield of light hydrocarbon and light naphtha is correspondingly greatly increased, and for a fixed hydrocracking device, the light hydrocarbon in a fractionation system of the fixed hydrocracking device often has a bottleneck, so that the improvement range of the conversion depth is limited;

(2) after the conversion rate is improved, the chemical hydrogen consumption is greatly increased; at the same time, the selectivity of the heavy naphtha is reduced (more light naphtha fraction is produced) and the aromatic potential of the heavy naphtha is reduced.

In addition, in the above-mentioned scheme, while the yield of heavy naphtha is increased, in order to keep the yield of tail oil constant, part of middle distillate is inevitably cut into tail oil, which is not favorable for improving the quality of tail oil.

In order to overcome the defects of the prior hydrocracking process technology that the heavy naphtha is produced simultaneously to improve the tail oil quality (a one-time process and the conversion depth is simply improved), some methods are also provided at present, for example, a method for recycling part or all of middle distillate oil (kerosene and diesel oil) to a second cracking reaction zone. This can greatly increase the yield of heavy naphtha, but the process is more complex and increases the investment.

Therefore, the present invention is directed to overcome the above-mentioned drawbacks of the prior art and to provide a new hydrocracking process for producing chemical raw materials to achieve a more economical and efficient production of both heavy naphtha and high quality tail oil.

In order to achieve the above object, the present invention provides a hydrocracking process for producing a chemical raw material, comprising: raw oil sequentially enters a hydrofining reaction zone and a hydrocracking reaction zone for hydrogenation reaction in the presence of hydrogen, gas-liquid separation and fractionation are carried out on obtained reaction products, so that a light naphtha fraction, a heavy naphtha fraction, a diesel oil fraction and a tail oil fraction are obtained, a hydrofining catalyst is filled in the hydrofining reaction zone, and a hydrocracking catalyst is filled in the hydrocracking reaction zone, wherein the hydrogen partial pressure in the hydrocracking reaction zone is 20-80% of that in the hydrofining reaction zone, and the hydrogen partial pressure range in the hydrofining reaction zone is 12-20 MPa.

The method provided by the invention can realize production of heavy naphtha and high-quality tail oil on the premise of reducing equipment investment. Specifically, the invention can greatly increase the yield of heavy naphtha and simultaneously produce high-quality tail oil. Compared with the method in the prior art, the method of the invention has the advantages that the selectivity of heavy naphtha is better, the aromatic hydrocarbon is higher, and the heavy naphtha is a better quality reformer feed; the tail oil has better quality and is a raw material for preparing ethylene by using steam with higher quality; in addition, the hydrogen consumption is low, and the device investment is also small.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

As previously mentioned, the present invention provides a hydrocracking process for producing a chemical feedstock comprising: raw oil sequentially enters a hydrofining reaction zone and a hydrocracking reaction zone for hydrogenation reaction in the presence of hydrogen, gas-liquid separation and fractionation are carried out on obtained reaction products, so that a light naphtha fraction, a heavy naphtha fraction, a diesel oil fraction and a tail oil fraction are obtained, a hydrofining catalyst is filled in the hydrofining reaction zone, and a hydrocracking catalyst is filled in the hydrocracking reaction zone, wherein the hydrogen partial pressure in the hydrocracking reaction zone is 20-80% of that in the hydrofining reaction zone, and the hydrogen partial pressure range in the hydrofining reaction zone is 12-20 MPa.

By adopting the method provided by the invention, the overall selectivity of naphtha fraction can be effectively improved, the yield of diesel oil fraction is reduced, and the yield of tail oil fraction is maintained; and the selectivity of heavy naphtha is emphatically improved, and the aromatic potential of naphtha is favorably improved.

In order to further improve the quality of tail oil, the hydrogen partial pressure in the hydrocracking reaction zone is preferably 25-75% of the hydrogen partial pressure in the hydrofining reaction zone.

According to a preferred embodiment, the hydrogen partial pressure in the hydrocracking reaction zone is less than 12 MPa.

According to a preferred embodiment, the hydrogenation reaction conditions of the hydrogen refining reaction zone include: the airspeed is 0.6-1.5h^-1The volume ratio of hydrogen to oil at the inlet is 700-1000, and the reaction temperature is 340-425 ℃.

According to a preferred embodiment, the hydrogenation reaction conditions of the hydrocracking reaction zone include: the airspeed is 1.0-2.5 h^-1The reaction temperature is 360-425 ℃.

In the present invention, specific kinds of the hydrorefining catalyst and the hydrocracking catalyst are not particularly limited, and may be catalysts conventionally used in the art for hydrorefining and hydrocracking, respectively.

In order to further improve the quality of tail oil, preferably, the hydrofining catalyst contains a carrier and an active metal element loaded on the carrier, and optionally contains an auxiliary element, wherein the carrier is selected from at least one of silicon oxide, aluminum oxide and silicon oxide-aluminum oxide, the active metal element is selected from at least one of a VIB group metal element and a VIII group metal element, and the auxiliary element is selected from at least one of boron, fluorine and phosphorus.

More preferably, the hydrorefining catalyst contains 1 to 10 wt% of nickel element calculated by oxide, 10 to 50 wt% of molybdenum element and/or tungsten element calculated by oxide, 0.5 to 8 wt% of phosphorus element calculated by oxide, 1 to 10 wt% of fluorine element calculated by element, and the balance of silica-alumina carrier, based on the total amount of the hydrorefining catalyst. Still more preferably, in the hydrorefining catalyst, the content of silica in the silica-alumina is 2 to 45% by weight and the content of alumina is 55 to 98% by weight, based on the total weight of the silica-alumina.

The hydrocarbon composition of the hydrocracking tail oil is closely related to the reaction depth and the performance of the hydrocracking catalyst. The higher the degree of reaction, the higher the paraffin content of the tail oil, the lower the aromatic content, and the lower the BMCI value of the tail oil, but at the same time the amount of tail oil is reduced accordingly. For the same conversion depth, the preferable hydrocracking catalyst of the invention can reduce the BMCI value of the tail oil and improve the quality of the tail oil while ensuring the yield of the tail oil.

In a preferred aspect of the present invention, the hydrocracking catalyst includes a carrier and an active component selected from at least one of nickel, molybdenum, tungsten, and cobalt supported on the carrier.

Further preferably, the hydrocracking catalyst contains nickel in an amount of 1 to 10 wt% calculated on oxide basis, tungsten in an amount of 10 to 50 wt% calculated on oxide basis, and optionally contains molybdenum in an amount of 1 to 15 wt% calculated on oxide basis; the carrier contains alumina and Y-type molecular sieve.

More preferably, the content of the alumina is 30-80 wt%, and the content of the Y-type molecular sieve is 2-70 wt%.

More preferably, the Y-type molecular sieve in the carrier is a phosphorus-containing Y-type molecular sieve, and the phosphorus content of the phosphorus-containing Y-type molecular sieve is 0.3-5% by mass and the pore volume is 0.2-0.95 mL/g.

The hydrocracking method for producing the chemical raw materials provided by the invention also has the following specific advantages:

(1) the reaction activity of the hydrocracking catalyst is improved;

(2) the BMCI value of the tail oil is basically not reduced;

(3) on the premise of the same naphtha yield, the aromatic hydrocarbon of naphtha can be improved;

(4) the yield of the middle distillate oil is reduced, and the selectivity of naphtha is improved;

(5) the selectivity of the heavy naphtha can be improved, and the potential aromatic content of the heavy naphtha can be improved;

(6) and the hydrogen consumption can be saved, and the investment cost of the device can be reduced.

The following examples further illustrate the process of the present invention, but are not intended to limit the invention thereto.

The properties of the reaction raw materials in examples and comparative examples are shown in Table 1.

Example 1

The raw materials in the table 1 are adopted as feeding materials, raw oil sequentially enters a hydrofining reaction zone and a hydrocracking reaction zone in the presence of hydrogen for hydrogenation reaction, gas-liquid separation and fractionation are carried out on obtained reaction products, so that a light naphtha fraction, a heavy naphtha fraction, a diesel oil fraction and a tail oil fraction are obtained, a hydrofining catalyst RN-32V is filled in the hydrofining reaction zone, and a hydrocracking catalyst RHC-5 is filled in the hydrocracking reaction zone. The process conditions, product distribution and key product properties are listed in tables 2 and 3.

As shown in tables 2 and 3, when the hydrogen partial pressure in the hydrotreating reaction zone was 15MPa, and the hydrocracking reaction temperature was 375 ℃ under a medium pressure of 11MPa in the hydrocracking reaction zone, the middle east wax oil was treated by the method in example 1, the total yield of naphtha + tail oil in the product reached 63.9%, the selectivity for naphtha was 47.1%, the selectivity for heavy naphtha fraction reached 84.8%, the yield was 27.3%, and the aromatic hydrocarbon reached 57.2, and the product was a good-quality reformer feed, and the yield of tail oil fraction was 31.7%, and the BMCI value was 10.6, and it was a good-quality ethylene production feedstock by steam cracking.

Compared with the comparative example 1, the hydrogen partial pressure of the hydrocracking reaction zone in the embodiment is lower by about 3.5MPa, and under the condition of similar yield of the tail oil, the yield of the chemical raw materials (naphtha + tail oil) is about 1.9 percent, the yield of the heavy naphtha is about 2.4 percent points, the aromatic hydrocarbon is 3.1 percent, and the BMCI value of the tail oil is basically equivalent. The method can give consideration to both heavy naphtha and tail oil, and the tail oil has excellent quality while producing more heavy naphtha.

Example 2

As shown in tables 2 and 3, when the hydrocracking reaction zone hydrogen partial pressure was 8MPa and the hydrocracking reaction temperature was 375 ℃, the middle east wax oil was treated by the method of example 2, and the total yield of naphtha + tail oil in the product was 65.5%, the selectivity of naphtha was 50.4%, the selectivity of heavy naphtha fraction was 84.9%, the yield was 29.7%, the aromatic hydrocarbon was 58.5, and the product was a good-quality reformer feed, and the yield of tail oil fraction was 30.5%, and the BMCI value was 10.1, and thus the product was a good-quality ethylene production feedstock by steam cracking.

Compared with the comparative example 1, in the embodiment, the hydrogen partial pressure of the hydrocracking reaction zone is lower by about 6.5MPa, the yield of chemical raw materials (naphtha + tail oil) is higher by about 3.5%, the yield of heavy naphtha is higher by about 4.8 percentage points, the heavy aromatics potential is higher by 4.4%, and the BMCI value of the tail oil is lower by 0.5 unit. The method can give consideration to both heavy naphtha and tail oil, and the heavy naphtha and chemical raw materials are produced more, and the quality of the heavy naphtha and the tail oil is also excellent.

Example 3

As shown in tables 2 and 3, when the middle east wax oil was treated by the method in example 3 under the conditions of low pressure of 4MPa hydrogen partial pressure in the hydrocracking reaction zone and a cracking reaction temperature of 375 ℃, the total yield of naphtha + tail oil reached 67.6%, the selectivity of naphtha was 54.8%, the selectivity of heavy naphtha fraction was 85.0%, the yield was 33.4%, the aromatics were 60.7, and the product was a good-quality reformer feed, and the yield of tail oil fraction was 28.3% and the BMCI value was 9.8, and thus it was a good-quality ethylene production feedstock by steam cracking.

Compared with the comparative example 1, the hydrogen partial pressure of the hydrocracking reaction zone in the embodiment is lower by about 10.5MPa, the yield of chemical raw materials (naphtha + tail oil) is higher by about 5.6%, the yield of heavy naphtha is higher by about 8.5 percentage points, the heavy aromatics potential is higher by 6.6%, and the BMCI value of the tail oil is lower by 0.8 unit. The method can give consideration to both heavy naphtha and tail oil, and the heavy naphtha and chemical raw materials are produced more, and the quality of the heavy naphtha and the tail oil is also excellent.

Example 4

As shown in tables 2 and 3, when the hydrocracking reaction zone had a hydrogen partial pressure of 8MPa and a cracking reaction temperature of 380 ℃, the middle east wax oil was treated by the method in example 4, and the total yield of naphtha + tail oil was 69.7%, the selectivity of naphtha was 61.8%, the selectivity of heavy naphtha fraction was 83.5%, the yield was 20.7%, the aromatic hydrocarbon was 56.3, and the product was a good-quality reformer feed, and the yield of tail oil fraction was 20.7%, and the BMCI value was 8.3, and the product was used as a good-quality ethylene production feedstock by steam cracking.

Compared with the comparative example 2, the hydrogen partial pressure of the hydrocracking reaction zone of the embodiment is lower by about 6.5MPa, the cracking reaction temperature is lower by about 3 ℃, and the yield of the tail oil is basically equivalent, but the yield of the chemical raw materials (naphtha + tail oil) is higher by about 5.9%, the yield of the heavy naphtha is higher by about 5.7 percentage points, the heavy aromatics potential is higher by 4.0%, and the BMCI value of the tail oil is basically equivalent. The method can give consideration to both heavy naphtha and tail oil, and the heavy naphtha and chemical raw materials are produced more, and the quality of the heavy naphtha and the tail oil is also excellent.

Comparative example 1

As shown in tables 2 and 3, when the middle east wax oil was treated by the method of comparative example 1 under the conditions that the hydrogen partial pressure in the hydrotreating reaction zone was 15MPa, the hydrogen partial pressure in the hydrocracking reaction zone was 14.5MPa, and the hydrocracking reaction temperature was 375 ℃, the total yield of naphtha + tail oil was 62.0%, the selectivity of naphtha was 44.1%, the selectivity of heavy naphtha fraction was 83.0%, the yield was 24.9%, the aromatic hydrocarbon was 54.1, and it was possible to feed a reformer, and the yield of tail oil fraction was 32.0%, and the BMCI value was 10.6.

Compared with examples 1, 2 and 3, the hydrogen partial pressure of the hydrocracking reaction zone of the comparative example is higher, but the yield of chemical raw materials (naphtha + tail oil) is lower, the naphtha selectivity is lower, the heavy naphtha selectivity is slightly lower, and the heavy naphtha aromatic potential is smaller.

Comparative example 2

As shown in tables 2 and 3, when the middle east wax oil was treated by the method of comparative example 2 under the conditions of a hydrogen partial pressure of 15MPa in the hydrotreating reaction zone, a hydrogen partial pressure of 14.5MPa in the hydrocracking reaction zone, and a hydrocracking reaction temperature of 383 ℃, the total yield of naphtha + tail oil was 63.8%, the selectivity of naphtha was 54.5%, the selectivity of heavy naphtha fraction was 81.3%, the yield was 35.2%, and the number of aromatics was 52.3, and the naphtha fraction was fed to the reformer, and the tail oil fraction yield was 20.5%, and the BMCI value was 8.3, and the high-quality ethylene cracking feedstock was obtained.

Compared with example 4, in the case of substantially equivalent yield of tail oil, the hydrocracking reaction zone in comparative example 2 requires higher hydrogen partial pressure and higher hydrocracking reaction temperature, but the chemical raw material (naphtha + tail oil) yield is lower, the naphtha selectivity is lower, the heavy naphtha selectivity is slightly lower, and the heavy naphtha aromatic potential is smaller.

TABLE 1 Properties of the raw materials

Table 2 examples process conditions and product distribution

1) Naphtha selectivity: mass fraction of naphtha fraction yield to (naphtha + diesel) yield 2) heavy naphtha selectivity: mass fraction of heavy naphtha yield to total naphtha yield

Table 3 key product properties primary product properties

Item	Example 1	Example 2	Example 3	Example 4	Comparative example 1	Comparative example 2
							Heavy naphtha fraction
Density at 20 deg.C/(g/mL)	0.7492	0.7506	0.7521	0.7487	0.7457	0.7421
							Length of ar	57.2	58.5	60.7	56.3	54.1	52.3
Distillation Range (D-86)/. deg.C
							IBP	80	81	82	77	82	74
10％	106	108	107	100	109	105
							50％	129	130	128	123	129	127
90％	163	162	163	156	161	156
							FBP	181	182	178	177	180	179
Tail oil fraction
							Density at 20 deg.C/(g/mL)	0.8321	0.8303	0.8307	0.8264	0.8313	0.8256
Distillation range (D-1160)/. deg.C
							IBP	245	257	249	240	257	240
10％	346	345	346	346	345	342
							50％	410	409	412	409	409	406
90％	476	466	477	466	466	462
							95％	494	492	490	480	488	477
BMCI value	10.6	10.1	9.8	8.3	10.6	8.3

Claims

1. A hydrocracking process for producing a chemical feedstock comprising: raw oil sequentially enters a hydrofining reaction zone and a hydrocracking reaction zone for hydrogenation reaction in the presence of hydrogen, gas-liquid separation and fractionation are carried out on obtained reaction products, so that a light naphtha fraction, a heavy naphtha fraction, a diesel oil fraction and a tail oil fraction are obtained, a hydrofining catalyst is filled in the hydrofining reaction zone, and a hydrocracking catalyst is filled in the hydrocracking reaction zone, wherein the hydrogen partial pressure in the hydrocracking reaction zone is 20-80% of that in the hydrofining reaction zone, and the hydrogen partial pressure range in the hydrofining reaction zone is 12-20 MPa.

2. The process of claim 1, wherein the hydrogen partial pressure in the hydrocracking reaction zone is 25 to 75% of the hydrogen partial pressure in the hydrofinishing reaction zone.

3. The process of claim 1 or 2, wherein the hydrogen partial pressure in the hydrocracking reaction zone is less than 12 MPa.

4. The process of claim 1, wherein the hydrofinishing catalyst comprises a carrier and an active metal element loaded on the carrier, and optionally an auxiliary element, wherein the carrier is selected from at least one of silica, alumina and silica-alumina, the active metal element is selected from at least one of a group VIB metal element and a group VIII metal element, and the auxiliary element is selected from at least one of boron, fluorine and phosphorus.

5. The method according to claim 4, wherein the hydrorefining catalyst comprises 1 to 10 wt% of nickel element in terms of oxide, 10 to 50 wt% of molybdenum element and/or tungsten element in terms of oxide, 0.5 to 8 wt% of phosphorus element in terms of oxide, 1 to 10 wt% of fluorine element in terms of element, and the balance of silica-alumina carrier, based on the total amount of the hydrorefining catalyst.

6. The method according to claim 5, wherein the content of silica in the silica-alumina is 2 to 45% by weight and the content of alumina in the hydrofinishing catalyst is 55 to 98% by weight, based on the total weight of the silica-alumina.

7. The process of claim 1, wherein the hydrocracking catalyst comprises a carrier and an active component supported on the carrier, the active component being selected from at least one of nickel, molybdenum, tungsten and cobalt.

8. The process of claim 7, wherein the hydrocracking catalyst contains nickel in an amount of 1 to 10 wt.% as an oxide, tungsten in an amount of 10 to 50 wt.% as an oxide, and optionally molybdenum in an amount of 1 to 15 wt.% as an oxide; the carrier contains alumina and Y-type molecular sieve.

9. The method of claim 8, wherein the alumina is present in an amount of 30 to 80 wt% and the Y-type molecular sieve is present in an amount of 2 to 70 wt%.

10. The method according to claim 8, wherein the Y-type molecular sieve in the carrier is a phosphorus-containing Y-type molecular sieve, and the phosphorus-containing Y-type molecular sieve has a phosphorus mass fraction of 0.3-5% and a pore volume of 0.2-0.95 mL/g calculated on oxide basis.

11. The process of claim 1, wherein the hydrogenation reaction conditions of the hydrofinishing reaction zone comprise: the airspeed is 0.6-1.5 h^-1The volume ratio of hydrogen to oil at the inlet is 700-1000, and the reaction temperature is 340-425 ℃.

12. The process of claim 1, wherein the hydrogenation reaction conditions of the hydrocracking reaction zone comprise: the airspeed is 1.0-2.5 h^-1The reaction temperature is 360-425 ℃.