RU2099389C1 - Method of producing lower olefins from vacuum gas oil - Google Patents

Abstract

FIELD: petroleum processing and petrochemistry. SUBSTANCE: vacuum gas oil is processed in two steps. In the first one, vacuum gas oil is subjected to heat cracking at 495-505 C, products being separated into light fraction with content of dark components not higher than 8% and heavy fraction. In the second step, light fraction (gas, gasoline, and, if necessary, kerosene-diesel fractions) is pyrolyzed at temperatures above 750 C. As a result, heavy part of heat cracking products (fraction above 500 C), which is low-grade raw material for pyrolysis, is withdrawn as component of furnace oil or raw material for coking process. EFFECT: increased yield of target product (lower olefins) and reduced coking process. 1 dwg , 2 tbl

Description

 The invention relates to processes for producing lower olefins by processing petroleum residual raw materials using the pyrolysis process and can be used in the petrochemical and chemical industries.

A method for producing lower olefins from vacuum gas oil is known. Gas oil is preheated to 170 ^o C in a primary separation heat exchanger, then mixed with steam and sent to a pyrolysis furnace, where the process is carried out at a temperature of 750-775 ^o C.

 The disadvantage of this method is the accelerated deposition of coke in furnaces, the installation is annually stopped for preventive maintenance. Very high consumption of low-quality liquid pyrolysis products (see Thematic review "Current State and Prospects of the Technological Progress of the Oil Refining and Petrochemical Industry" M. TsNIITENeftekhim, 1976, p. 75).

A known method of producing lower olefins by processing vacuum gas oil, described in the book "Pyrolysis of hydrocarbons". M. "Chemistry", 1987, p. 52-58. According to this method, lower olefins are obtained by pyrolysis of vacuum gas oil with its preliminary preparation. The specificity of the composition of the heavier oil fractions predetermines the development of special technology. Crude vacuum gas oil has a low ethylene yield potential and causes increased coke formation. Vacuum gas oil is characterized by sulfur and nitrogen compounds. Special methods of preliminary preparation include hydrodesulfurization, hydrodearomatization, hydrocracking and extractive dearomatization. Removal of sulfur and nitrogen compounds reduces the corrosion activity of raw materials, which lengthens the life of tubular pyrolysis furnaces. However, such preliminary preparation does not significantly increase the ethylene yield, the ethylene yield, the yield of heavy fractions, boiling ≥ 200 ^o C, remains high, the degree of coke formation remains high (see Mukhina T.N. et al. Pyrolysis of hydrocarbon raw materials M. Chemistry, 1987 .).

Closest to the proposed method is a method of processing petroleum residual raw materials by thermal cracking followed by pyrolysis of liquid distillation thermocracking, while the thermal cracking process is carried out due to the heat of the pyrolysis products (see ed. Certificate. USSR N 977477, class C 10 G 51 / 02)
The disadvantages of this method include.

 1. Poor quality of the residue due to the unstable heavy liquid pyrolysis products entering it.

 2. The inability to combine the production of lower olefins with the production of middle distillates due to the ingress of low-quality pyrolysis products into the latter (naphthalene compounds, phenanthrene, anthracene, etc.).

 3. The increase in energy consumption for rectification of gases due to the displacement of thermocracking gases having a low percentage of lower olefins with pyrolysis gases.

 4. An increase in coking and a decrease in the mileage of the pyrolysis furnaces due to the unstable secondary pyrolysis products entering the distillate fractions for pyrolysis.

 5. The low yield of lower olefins.

 6. The accumulation in raw materials of pyrolysis of practically non-subjected to pyrolysis of the ballast fraction of pyrobenzene, and primarily benzene.

 The aim of the proposed method is to eliminate the above disadvantages.

This goal is achieved in that the heavy residual fractions are processed in 2 stages. At the first stage, they are subjected to thermocracking at a temperature of 460-510 ^o C. Thermocracking products are divided into a light gas-vapor part in the boiling range of C ₁ 360 ^o C with dark oil products (fractions with a boiling point above 360 ^o C) up to 8% weight and heavy fraction . In the second stage, the gas-vapor part is subjected to pyrolysis at a temperature of 750-830 ^o C. Since, in comparison with the known method, the raw material base of pyrolysis increases due to the involvement of hydrocarbons in C ₄ inclusive, and also because light hydrocarbons (hydrogen, methane, ethane ) have an initiating effect on the pyrolysis process of the heavy part, the total yield of lower olefins increases. At the same time, energy consumption for the process is reduced, coke formation is reduced, and the travel time of pyrolysis furnaces is significantly increased, heavy residues used as boiler fuel are obtained with improved quality. The limitation of the content of such petroleum products boiling at temperatures above 360 ^o C in the gas-vapor fraction sent for pyrolysis is 8% due to the fact that dark petroleum products contain a significant amount of resins, asphaltenes and unsaturated hydrocarbons, which leads to a sharp increase in coke formation and a decrease in the mileage of pyrolysis furnaces and increases the output of the heavy liquid fraction of pyrolysis, impairs its quality. With an increase in the amount of dark petroleum products in the pyrolysis feed, the overlapping of fractions significantly increases, i.e. heavier fractions with a boiling end of 400-450 ^o C. appear in the pyrolysis feedstock

When increasing the clarity of rectification (reducing the fraction content ≥ 360 ^o C below 8%) of the pyrolysis feedstock, a significant increase in energy costs occurs due to an increase in the irrigation ratio.

Table 1 shows the performance of the method depending on the content of the fraction ≥ 360 ^o C in the pyrolysis feedstock (the fraction C ₁ 360 ^o C enters the pyrolysis).

From table 1 it follows that in the range of fractions ≥ 360 ^o C in the pyrolysis feedstock of 2-8%, an increase in the content of TFA for each percent increase in fractions ≥ 360 ^o C is 0.1 0.16 wt. in the range of 8-20%, the increase in the content of TFA is 0.3-0.4% wt.

Distinctive features of the proposed method is that the thermal cracking products of oil residual raw materials are divided into heavy fractions and a light gas-vapor fraction within the boiling range of C ₁ 360 ^o C with the content of fractions boiling at a temperature above 360 ^o C in an amount of not more than 8% wt. which is sent to pyrolysis.

 The proposed method increases the yield of target products, including lower olefins, reduces the degree of coking and increases the mileage of pyrolysis furnaces, reduces the energy consumption for distillation, allows you to combine the production of lower olefins with medium distillers, improves the quality of the residue, eliminates the accumulation of pyrobenzene in the pyrolysis feedstock ( primarily benzene).

The drawing shows a schematic diagram of the implementation of the proposed method. Heavy residual raw materials at a pressure of 20-30 atm come through pipeline 1 to a thermocracking furnace 2. Thermocracking takes place at a temperature of 460-510 ^o C. Thermocracking products enter through a pipeline 3 to a separation unit 4. Separation unit 4 may consist of one complex or several distillation units columns. Heavy products of thermal cracking - diesel fuel and boiler fuel are discharged through pipelines 5 and 6 as target products, or the fraction of diesel fuel is also sent to pyrolysis. Light thermocracking products in the first phase are sent through pipeline 7 to the block of pyrolysis furnaces 8, where they are subjected to high-temperature pyrolysis at temperatures above 800 ^o C.

Pyrogas after quenching (not shown in the diagram) enters the pyrogas preparation unit 9, from where the heavy pyrolysis fractions are discharged through pipelines 10 and 11. The light part of the pyrogas is sent to compressor 12 and is gas-separated at block 13, from where the target products (ethylene, propylene, fractions C ₄ ) are discharged through pipelines 14, 15, 16.

Example 1 (known method). Take the residue of direct distillation of oil and contact it with a mixture of vaporous products of pyrolysis and thermocracking, while the raw material is heated, and the products of thermocracking and pyrolysis are cooled. The dehydrated and partially condensed mixture of thermocracking and pyrolysis products is sent to distillation, where gaseous products are isolated, and the liquid fraction C ₅ 300 ^o C, which is sent to pyrolysis. The pyrolysis products are sent to a thermocracking reactor, where they are directly contacted with the residue of direct distillation of oil heated in a heat exchanger (see AS 977477).

 Yields of the main products: ethylene 11.2% propylene 8.5% boiler fuel 61.7% The furnace run time is not more than 5 days, since poor-quality unstable liquid pyrolysis products (naphthalene compounds, phenanthrene, anthracene) get into the pyrolysis feed.

Example 2. The residual fuel oil of West Siberian oil in the first stage is subjected to thermocracking at a pressure of 20-30 at and a temperature of 460-510 ^o C. Yields of products: gas 4% gasoline 12.7% diesel fraction 34.5% boiler fuel 48 , 8% A gas-vapor fraction containing gas, gasoline, a diesel fraction with a boiling range of C ₁ 360 ^o C, containing up to 8% of fractions 360-390 ^o C, is sent to pyrolysis at a temperature of 820 ^o C. The total product yields (per fuel oil): ethylene 12.8% dry gas (H ₂ + CH ₄₎ 7.1% propylene, 8.3% C ₄ fraction pyrolysis pirobenzin 6.5% 8.6% TZHP and fuel oil 56.7% run time echey 30 days.

Example 3. Under the conditions of example 2, a gasoline fraction is subjected to pyrolysis with a boiling range of NK-180 ^o C. In this case, simultaneously with the production of lower olefins, high-quality diesel fractions are obtained, which, after hydrofining, are used as target products.

Total product yields (per fuel oil): dry gas (H ₂ + CH ₄ ) 2.7% ethylene 6.1% propylene 2.8% C ₄ fraction 1.7% pyrobenzene - 2.5% diesel fraction 180-360 ^o C 34.5% of solid fuel and boiler fuel - 49.7%. Ovens travel time of 40-50 days. Comparative data on the known and proposed method are shown in table 2.

 From the above examples it is seen that the inventive method leads to an increase in the yield of the target product and a decrease in the yield of residual products in comparison with the known method, the run time of the furnaces increases (coke formation decreases). In view of the withdrawal of pyrobenzene as the target product, the aromatic benzene fraction, which is the ballast for the pyrolysis process, does not accumulate in the pyrolysis feed.

 The withdrawal of pyrobenzene in the known method will lead to the simultaneous withdrawal of thermocracking from the gasoline process, which will reduce the amount of pyrolyzable raw materials and the yield of lower olefins.

Claims (1)

A method of producing lower olefins by thermal processing of oil residual feedstock, including its preliminary thermal cracking with further separation of the thermal cracking products into fractions and subsequent pyrolysis of the light fraction, characterized in that the thermal cracking products are separated into a heavy fraction and a light gas-vapor fraction within the boiling range from C ₁ to 360 ^o With the content of fractions boiling at a temperature above 360 ^o With not more than 8 wt. sent to pyrolysis.

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