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How does crude oil turn into oil and chemicals

How does crude oil turn into oil and chemicals? Why do different processes produce different products from the same raw materials? Let’s take a look at the specific processes of oil refining and olefin production. There are detailed explanations on raw materials, products and production processes.

The basic ways of refining crude oil are as follows:

  • ① The crude oil is divided into different straight run distillates according to the boiling point requirements of different products, and then the non ideal components in these distillates are removed according to the product quality standards;
  • ② Through chemical reaction conversion, the required components are generated, and then a series of qualified petroleum products are obtained.

The common processes of petroleum refining and petrochemical are atmospheric and vacuum distillation, catalytic cracking, delayed coking, hydrocracking, solvent deasphalting, hydrofining and catalytic reforming.

Atmospheric and vacuum distillation

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1. Raw materials: crude oil, etc.
2. Products: naphtha, crude diesel oil (gas oil), residue, asphalt, vacuum distillation unit.
3. Basic concepts
Atmospheric and vacuum distillation is the combination of atmospheric distillation and vacuum distillation, which is basically a physical process: the feed oil in the distillation tower is divided into oil products (called fractions) with different boiling points according to the evaporation capacity. Some of these oils leave the factory in the form of products after blending and adding additives, and a considerable part is the raw material for subsequent processing units.
Atmospheric and vacuum distillation is the first process of petroleum processing in refinery, which is called primary processing of crude oil. It includes three processes:

  • A. desalination and dehydration of crude oil;
  • B. atmospheric distillation;
  • C. vacuum distillation.

4. Production process
Crude oil usually contains salt and water, which can cause corrosion of equipment. Therefore, before crude oil enters atmospheric and vacuum distillation unit, it is necessary to carry out desalination and dehydration pretreatment, usually adding demulsifier and water.
The crude oil is divided into two parts by flow meter, heat exchange part and brewage tower. One part forms overhead oil, goes through cooler and flow meter, and finally enters tank farm. This part is chemical light oil (so-called naphtha); the other part forms bottom oil, and then goes through heat exchange part to atmospheric furnace and atmospheric tower to form three parts, one part is diesel oil, one part is wax oil and one part is tower The remaining tower bottom oil is further processed in the vacuum furnace and vacuum tower to produce first-line vacuum reducer, wax oil, residual oil and asphalt.
Their respective yields are as follows: naphtha (light gasoline or chemical light oil) accounts for about 1%, diesel oil accounts for about 20%, wax oil accounts for about 30%, residual oil and asphalt account for about 42%, and first-line reduction accounts for about 5%.
The atmospheric and vacuum distillation process does not produce gasoline products, in which the wax oil and residue enter the catalytic cracking process to produce gasoline, diesel oil, kerosene and other refined oil; naphtha is directly sold to other small enterprises to produce solvent oil or enter the next step of deep processing, generally catalytic reforming to produce solvent oil or extract compounds; the first reduction line can directly adjust lubricating oil.

Catalytic cracking

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General crude oil after atmospheric and vacuum distillation can get gasoline, kerosene, diesel and other light oil only 10 ~ 40%, the rest is heavy fraction oil and residual oil. If we want to get more light oil, we must carry out secondary processing of heavy fraction and residual oil. Catalytic cracking is the most commonly used production process of gasoline and diesel, and gasoline and diesel are mainly produced by this process. This is also the most important production link of general petroleum refining and chemical enterprises.
1. Raw materials
About 70% of residuum and gas oil are used as feedstocks for catalytic cracking. However, with the increasing demand for crude oil and light oil, most petrochemical enterprises begin to add vacuum residuum into feedstocks, or even directly use atmospheric residuum as feedstock for refining.
2. Products
Gasoline, diesel oil, slurry (heavy fraction), liquid propylene and liquefied gas; Their respective proportions are 42% for gasoline, 21.5% for diesel, 5.8% for propylene, 8% for LPG and 12% for slurry.
3. Basic concepts
Catalytic cracking is the main process to process heavy oil (such as residue) into light oil (gasoline, kerosene, diesel) in the presence of catalyst. It is the main secondary processing method in the refining process. It belongs to chemical process.
4. Production process
The residue and wax oil pass through the feed oil buffer tank into the riser, settler and regenerator to form oil and gas, and then enter the fractionator.
A part of the oil and gas enters the crude gasoline tower, absorption tower and air compressor, enters the condensing oil tank, passes through the reabsorption tower, stabilization tower, and finally carries out gasoline refining to produce gasoline.
A part of the oil and gas enters the diesel stripper through the fractionator, and then the diesel oil is refined to produce diesel oil. A part of the oil and gas enters the slurry circulation through the fractionator, and finally the slurry is produced.
A part of the oil and gas enters the liquid hydrocarbon buffer tank through the fractionator, passes through the desulfurization adsorption tank, sand filter, water washing tank, desulfurization alcohol stripper, pre alkali washing tank, amine liquid recovery unit, desulfurization stripper and buffer tower, and finally enters the liquid hydrocarbon tank to form liquefied gas.
A part of the oil and gas flows through the liquid hydrocarbon buffer tank into the depropanizer, reflux tower, deethanizer, fine propylene tower and reflux tank, and finally into the spherical tank in the propylene area to form liquid propylene. Liquid propylene is further processed in polypropylene workshop to produce polypropylene.

Delayed coking 

Coking (coking) is a deep thermal cracking process and one of the methods to deal with residue. It is the only process that can produce petroleum coke, which can not be replaced by any other process. Especially, the special demand for high quality petroleum coke in some industries has led to the coking process playing an important role in the refining industry.
1. Raw materials
The delayed coking and catalytic cracking similar decarbonization process can change the hydrocarbon ratio of oil. The raw materials of delayed coking can be heavy oil, residue oil and even asphalt, which requires low quality of raw materials. The main conversion process of residue is delayed coking and hydrocracking.
2. Products
The main products are wax oil, diesel oil, coke carbon, crude gasoline and some gases, respectively, the proportion of which is: wax oil accounts for 23-33%, diesel oil 22-29%, coke 15-25%, crude gasoline 8-16%, gas 7-10%, and oil rejection 1-3%.
3. Basic concepts
Coking is a deep thermal cracking reaction with hydrogen poor heavy residual oil (such as vacuum residue, cracking residue and asphalt) as raw materials at high temperature (400-500 ℃). Through cracking reaction, part of the residue is converted into gas hydrocarbon and light oil; The condensation reaction makes the other part of the residue into coke. On the one hand, due to the heavy raw materials and a considerable amount of aromatics, on the other hand, the coking reaction conditions are more stringent, so the condensation reaction accounts for a large proportion and produces more coke.
4. Production process
The production process of delayed coking unit is divided into coking and coking removal, coking is continuous operation and coking removal is gap operation. Since the industrial plant generally has two or four coke towers, the whole production process is still continuous operation.
Crude oil is preheated, coking raw material (vacuum residue) is first put into the raw material buffer tank, and then pumped into the convection section of the heating furnace to rise to about 340-350 ℃.
The crude oil after preheating enters the bottom of the fractionator and the oil and gas produced by the coke tower are heat exchanged in the fractionator (the temperature at the bottom of the tower is not more than 400 ℃).
Raw oil and circulating oil are extracted from the bottom of the fractionator together, and then pumped into the radiation section of the heating furnace with a hot oil pump, heated to the temperature required for coking reaction (about 500 ℃), and then enters the coke tower from the lower part through the four-way valve for coking reaction.
The raw materials react in the coke tower to generate coke accumulation in the coke tower. Oil and gas come out from the top of the coke tower and enter the fractionation tower. After heat exchange with the raw oil, the gas, gasoline, diesel oil and wax oil are obtained through fractionation. The bottom circulating oil and raw materials are coked together.

Hydrocracking

The basic principle of heavy oil lightening is to change the relative molecular weight and hydrogen carbon ratio of the oil, and changing the relative molecular weight and hydrogen carbon ratio is often carried out at the same time. There are two ways to change the hydrogen to carbon ratio of oil: decarbonization and hydrogenation.
1. Raw materials: heavy oil, etc
2. Products: light oil (gasoline, kerosene, diesel or feedstock for catalytic cracking and cracking to olefins)
3. Basic concepts
Hydrocracking belongs to the hydrogenation route of petroleum processing, which is to add hydrogen from the outside in the presence of catalyst to improve the hydrogen carbon ratio of oil.
Hydrocracking is essentially an organic combination of hydrocracking and catalytic cracking. On the one hand, it can convert heavy oil products into light oil products such as gasoline, kerosene and diesel oil through cracking reaction. On the other hand, it can prevent the formation of a large amount of coke like catalytic cracking. Moreover, it can remove sulfur, chlorine and oxygen impurities in feedstock by hydrogenation, so as to saturate olefins.
4. Production process
According to the state of catalyst in the reactor, it can be divided into fixed bed, boiling bed and suspended bed.
(1) Fixed bed hydrocracking
Fixed bed is to place granular catalyst in the reactor to form a static catalyst bed. The feed oil and hydrogen enter the reaction system after reaching the reaction conditions through temperature and pressure rise. First, hydrofining is carried out to remove sulfur, nitrogen, oxygen impurities and dienes, and then hydrocracking is carried out. After the reaction product is cooled, separated, depressurized and fractionated, the target product is sent out of the unit, and the gas with high hydrogen content (80%, 90%) is separated and used as circulating hydrogen.
Unconverted oil (called tail oil) can be partially recycled, fully recycled or not recycled once.
(2) Fluidized bed hydrocracking
Boiling bed (also known as expanded bed) process is to drive the movement of catalyst with certain particle size by fluid flow rate to form gas, liquid and solid three-phase bed, so that hydrogen, feed oil and catalyst can fully contact to complete the hydrogenation reaction process.
The fluidized bed process can treat feedstocks with high metal content and carbon residue value (such as vacuum residue) and convert heavy oil deeply; But the reaction temperature is higher, generally in the range of 400 ~ 450 ℃.
This process is complex and has not been industrialized in China.
(3) Slurry bed hydrogenation process
Suspended bed process is a kind of hydrogenation process which has been paid more attention to in order to adapt to the very poor raw materials. Its principle is similar to that of fluidized bed. The basic process is that the fine powder catalyst is premixed with the raw material, and then flows into the reactor from bottom to top with hydrogen. The catalyst is suspended in the liquid phase for hydrocracking reaction, and the catalyst flows out from the top of the reactor with the reaction products.
The unit can process all kinds of heavy crude oil and common crude oil residue, but the investment is large. The process is still in the stage of research and development in China.

Solvent deasphalting

Solvent deasphalting is a pretreatment process of inferior residue. By means of extraction, the gum and pitch are removed from the vacuum residue (sometimes atmospheric residue) obtained from crude oil distillation to produce deasphalting oil, which is a refining process for petroleum products.
1. Raw material: heavy oil such as vacuum residue or atmospheric residue
2. Products: deasphalting oil, etc
3. Basic concepts
Solvent deasphalting is a kind of petroleum refining process for processing heavy oil. The process uses heavy oil such as vacuum residue as raw material, and hydrocarbons such as propane and butane as solvent for extraction. The extract, i.e. deasphalting oil, can be used as heavy lubricating oil raw material or cracking raw material, and the raffinate deasphalting oil can be used as road asphalt or other purposes.
4. Production process
Including extraction and solvent recovery. Generally, one-stage extraction process or two-stage extraction process is adopted in the extraction part.
There is less propane in asphalt and heavy deasphalting oil solution, so one-time evaporation and stripping are used to recover propane. Light deasphalting oil solution contains more propane, so multi effect evaporation and stripping or critical recovery and stripping are used to recover propane to reduce energy consumption.
The critical recovery process is to make light deasphalting oil and a large part of propane settle and separate in the critical tower under the conditions of approaching the critical temperature and slightly higher than the critical pressure (the critical temperature of propane is 96.8 ℃ and the critical pressure is 4.2mpa), so as to avoid the evaporation and condensation process of propane, Therefore, the energy consumption can be greatly reduced.
The domestic solvent deasphalting process mainly includes sedimentation two-stage deasphalting process, critical recovery deasphalting process and supercritical extraction solvent deasphalting process.
(1) Two stage deasphalting process by sedimentation method
Two stage deasphalting by settlement method is developed on the basis of conventional one stage deasphalting. On the basis of studying the special properties of Daqing vacuum residue, it is noticed that conventional propane deasphalting can not make full use of this resource, and a new deasphalting process has been developed
(2) Critical recovery deasphalting process
The solubility of solvent to oil decreases with the increase of temperature. When the temperature and pressure are close to the critical condition, the solubility of solvent to oil is very low. At this time, the propane solvent can be directly recycled after cooling without evaporation.
(3) Deasphalting process with supercritical extraction solvent
Supercritical fluid extraction (SFE) is a technology that uses the abnormal phase equilibrium and thermodynamic properties of the extraction system near the critical region, and changes the temperature, pressure and other parameters to make the solubility of the components in the system change dramatically, so as to achieve the separation of components.

Hydrofining

Hydrofining generally refers to reprocessing some petroleum products that cannot meet the requirements of use through hydrogenation process to achieve the specified performance index.
1. Refined raw materials: gasoline, diesel oil, kerosene, lubricating oil, petroleum wax, etc. with more harmful impurities such as sulfur, oxygen and nitrogen.
2. Refined products: refined modified gasoline, diesel oil, kerosene, lubricating oil, petroleum wax and other products.
3. Basic concepts
Hydrofining process is a general term for catalytic modification of various oil products under hydrogen pressure. It refers to the hydrolysis reaction of various non hydrocarbon compounds in oil under certain temperature and pressure, catalyst and hydrogen, and then remove from oil products to achieve the purpose of refining oil products.
Hydrofining is mainly used for refining oil products, and its main purpose is to improve the performance of oil products by refining.
4. Production process
The process flow of hydrofining generally includes reaction system, oil heat exchange, cooling, separation system and circulating hydrogen system.

Reaction system

After the feed oil is mixed with new hydrogen and circulating hydrogen, and heat exchange with the reaction product, it enters the heating furnace in the gas-liquid mixed state (in this way, the hydrogen mixing in front of the furnace) and then enters the reactor at the reaction temperature.
The reactor feed can be either gas phase (when refining gasoline), or gas-liquid mixed phase (when refining diesel oil or heavier oil than diesel). The catalyst in the reactor is usually filled in layers to control the reaction temperature by injecting cold hydrogen. The mixture of circulating hydrogen and oil is hydrogenated through each catalyst bed.

Generating oil heat exchange, cooling and separation system

The reaction product comes out from the bottom of the reactor, and enters the high-pressure separator after heat exchange and cooling.
Before cooler, high pressure washing water should be injected into the product to dissolve ammonia and partial hydrogen sulfide produced by reaction.
The reaction products are separated from oil and gas in high pressure separator. The separated gas is circulating hydrogen, in which, in addition to the main component hydrogen, there are a small amount of gaseous hydrocarbons (non condensable gas) and hydrogen sulfide not soluble in water; the separated liquid products are hydrogenated to generate oil, and a small amount of gaseous hydrocarbon and hydrogen sulfide are dissolved.
The generated oil is reduced pressure and then enters the low-pressure separator to further separate the gaseous hydrocarbons and other components, and the products are separated into qualified products in the fractionation system.

Circulating hydrogen system

After the circulating hydrogen separated from the high-pressure separator passes through the storage tank and the circulating hydrogen compressor, a small part (about 30%) directly enters the reactor for cold hydrogen, and the rest is sent to mix with the raw oil for recycling in the device. In order to ensure the purity of circulating hydrogen and avoid hydrogen sulfide accumulation in the system, hydrogen sulfide recovery system is commonly used. Generally, hydrogen sulfide is absorbed and removed by ethanolamine, and recycled with rich liquid (absorption liquid). The desorption hydrogen sulfide is sent to sulfur making device for sulfur recovery and purified hydrogen is recycled.

Catalytic reforming 

1. Main raw materials
Naphtha (light gasoline, chemical light oil, stable light oil), which is generally produced in refineries, can also be produced in stable stations of oil production plants. Naphtha with good quality has low sulfur content and is nearly colorless in color.
2. Main products
High octane gasoline, benzene, toluene, xylene and other products (these products are the main raw materials for the production of synthetic plastics, synthetic rubber, synthetic fiber, etc.), and a large number of by-products hydrogen.
3. Basic concepts
Reforming: hydrocarbon molecules rearrange into new molecular structures.
Catalytic reforming unit: the direct run gasoline (i.e. naphtha) or the mixed oil of secondary processing gasoline is used as raw material. Under the action of catalyst (platinum or polymetallic), the hydrocarbon molecules are rearranged into new molecular structures through dehydrogenation, hydrocracking and isomerization, and the main purpose is to produce C6-C9 aromatic hydrocarbon products or high octane gasoline, The by-product hydrogen is used for the secondary processing of thermal cracking, delayed coking gasoline or diesel oil hydrofining.
4. Production process
According to the basic principle of catalytic reforming, a complete reforming industrial unit mainly includes raw material pretreatment and catalytic reforming. The reforming unit for the purpose of producing aromatics also includes aromatics extraction and aromatics distillation.

Raw material pretreatment

The raw material is cut into the range of distillation range suitable for reforming and impurities harmful to catalyst are removed.
Pretreatment includes: pre arsenic removal, pre fractionation and pre hydrogenation.

Catalytic reforming process

Catalytic reforming is to rearrange the raw oil molecules to produce naphthenic dehydrogenation, aromatization and isomerization of the refined oil after pretreatment by using polymetallic (Platinum rhenium, platinum iridium, platinum tin) catalyst at certain temperature and pressure, so as to increase aromatics or increase octane number of gasoline.
The reaction system flow widely used in industrial reformer can be divided into two categories: fixed bed reactor semi regeneration process and mobile bed reactor continuous regeneration process.

Summary of olefin production technology

Olefin industry is the foundation of petrochemical industry in the world. With olefin as raw material, petrochemical industry has derived many products. In particular, the “ethylene, propylene and butadiene” as the representative of the triene, is the cornerstone of the petrochemical industry. The following is a summary of the process technology used in olefin production.

MTO technology

The mainstream MTO production technologies in the world mainly include UOP, MTO technology of hydro company, DMTO technology of Dalian Institute of Chemical Physics, Chinese Academy of Sciences (hereinafter referred to as Dalian Institute of Chemical Physics) and SMTO technology of Sinopec. The three technologies are relatively mature and have achieved success in industrial application. DMTO and SMTO technologies of SINOPEC are widely used in domestic plants. At present, both technologies are in process optimization and catalyst improvement to improve catalytic efficiency and overall economy.

Methanol to propylene technology

Methanol to propylene (MTP) technology is mainly developed by Lurgi company and Tsinghua University. MTP of Lurgi company has successfully transferred Shenhua Ningxia Coal Industry Group Co., Ltd. and Datang Group of China to build 520000 T / A and 460000 T / a methanol to propylene plants respectively.
Tsinghua University has developed the MTP technology of fluidized bed process, and its reactor type is very similar to MTO process. It passed the achievement appraisal organized by China Petroleum and Chemical Industry Association on November 27, 2009.

Propane Dehydrogenation Technology

The main industrial processes for propane dehydrogenation to propylene in the world are as follows:

  • Oleflex process of UOP company in USA;
  • Catofin process of ABB Lummus company in USA;
  • Wood star technology.

The three technologies are relatively mature, and the oleflex process of propane dehydrogenation of UOP company is the most transferred one. The process uses platinum based catalyst, with propylene selectivity of 84% and propane one-way conversion of 35% ~ 40%.

Olefin disproportionation technology

The main reaction of olefin disproportionation technology is the disproportionation of ethylene and 2-butene to propylene. At present, meta-4 process of IFP company, Oct process of ABB Lummus company and processes of Sasol, BASF, equistar, Lyondell company are relatively mature. Dalian Institute of chemical materials and Sinopec Shanghai Research Institute of petrochemical industry also conducted relevant research.

Light hydrocarbon catalytic cracking to olefins

Propylene production from C4-C8 olefins by catalytic cracking of olefins is based on the conversion of C4-C8 olefins into propylene and ethylene by fixed bed or fluidized bed process.
The typical selective catalytic cracking processes of C4 olefins to produce propylene are as follows:

  • ExxonMobil’s MOI process;
  • The OCP process of atofina and UOP;
  • Superflex process of Arco chemical company;
  • Propylur process of Lurgi company (FBCC process of Linde company);
  • Omega process of Asahi chemical company;
  • Sasol’s olefin catalytic cracking process, etc;
  • Sinopec Beijing Research Institute of chemical industry and Shanghai Research Institute of petrochemical industry have also developed related processes.

Catalytic dehydrogenation of butene

At present, the domestic technology of butadiene production by oxidative dehydrogenation of butene is at the leading level in the world. The main technical suppliers include Qilu Petrochemical Company of Sinopec and Jinzhou Petrochemical Company of PetroChina, mainly including fluidized bed process and fixed bed process.
The most representative fluidized bed process is the butene oxidative dehydrogenation unit of PetroChina Jinzhou Petrochemical Company.
The rubber plant of Qilu Petrochemical Company, Sinopec, is the most representative of the fixed bed process. Both processes have been industrialized.

Source: Network Arrangement – China Flanges Supplier: www.epowermetals.com

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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