CN116286084A - Method for dearomatizing straight-run diesel oil fraction - Google Patents
Method for dearomatizing straight-run diesel oil fraction Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G53/00—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes
- C10G53/02—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only
- C10G53/04—Treatment of hydrocarbon oils, in the absence of hydrogen, by two or more refining processes plural serial stages only including at least one extraction step
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
- C10G2300/20—Characteristics of the feedstock or the products
- C10G2300/201—Impurities
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G2400/00—Products obtained by processes covered by groups C10G9/00 - C10G69/14
- C10G2400/04—Diesel oil
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Chemical Kinetics & Catalysis (AREA)
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- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
Abstract
The invention relates to a method for dearomatizing a straight-run diesel fraction, which comprises the following steps: extracting the straight-run diesel fraction by using an aromatic extraction solvent to obtain an extraction rich agent and raffinate oil; washing the raffinate oil with water to obtain a dearomatization straight-run diesel fraction and washing water A; step cooling the extraction rich agent to 40-60 ℃ to obtain separated oil and aromatic semi-lean agent; returning the separated oil to extraction; mixing the aromatic semi-lean agent with water washing water A and then reversely contacting the aromatic semi-lean agent with a back-extraction agent B to obtain an aromatic-rich back-extraction agent and a back-extraction semi-lean agent; washing and distilling the aromatic-rich back extractant to obtain a back extractant B1, washing water B and aromatic-rich oil B; the stripping semi-lean agent is subjected to solvent regeneration treatment to obtain regenerated lean agent, water and a small amount of stripping agent B2; the stripping agent B1 and the stripping agent B2 are used as the stripping agent B for recycling; the water obtained by the solvent regeneration treatment is recycled as water washing water. The method of the invention can effectively reduce the dosage of the stripping agent, greatly reduce the aromatic hydrocarbon index of the raffinate oil, and can be used for steam cracking ethylene raw materials.
Description
Technical Field
The invention relates to the energy-saving and environment-friendly industry, belongs to the field of separation treatment of raw oil, and particularly relates to a method for dearomatizing straight-run diesel oil fractions.
Background
Steam cracking is a main technology for producing ethylene and propylene, the types of raw materials for steam cracking have important influence on the yield of ethylene, mainly comprise light hydrocarbon, naphtha, diesel oil, condensate oil, hydrogenated tail oil and the like, the raw material cost is up to 70% of the ethylene production cost, and the ethylene cost directly influences the downstream product cost, so that the direct-distillation diesel oil is used as a steam cracking raw material to produce chemical products such as ethylene and the like, and is one of important methods for increasing the yield of ethylene and improving the benefit.
Aromatic components in straight-run diesel, particularly polycyclic aromatic hydrocarbons are undesirable components of steam cracking raw materials, the content of aromatic hydrocarbons is high, the triene yield is easy to reduce, the coking possibility of furnace tubes is increased, and the running period of equipment is shortened. Therefore, in order to improve the steam cracking efficiency, a reasonable method is necessary for removing the straight-run diesel aromatic hydrocarbon.
Patent CN108203595a discloses a method for extracting and separating aromatic hydrocarbon and alkane from diesel oil fraction, which adopts a liquid-liquid extraction method, and adopts ion liquid as extractant, and the rich solvent rich in aromatic hydrocarbon after 20-60 ℃ extraction enters a first reduced pressure distillation tower from the bottom of the extraction tower to carry out reduced pressure distillation, the operation temperature of the first reduced pressure distillation tower is 80-150 ℃, light aromatic hydrocarbon with lower boiling point is discharged from the top of the first reduced pressure distillation tower, heavy aromatic hydrocarbon solvent with higher boiling point enters the upper part of a stripping tower, the stripping agent enters the stripping tower from the lower part, the operation temperature is 15-50 ℃, the heavy aromatic hydrocarbon is dissolved in the stripping agent to form a stripping phase after stripping, and lean solvent is discharged from the bottom of the stripping tower. And the back extraction phase enters the lower part of the second reduced pressure distillation tower, the operation temperature is 15-60 ℃, and heavy aromatic hydrocarbon and the back extraction agent are separated through reduced pressure distillation. In the patent, the temperature level layout is arranged in a low-high-low-high mode, the material flow is repeatedly heated and cooled, and the energy cannot be fully and reasonably utilized; in the raw oil with higher heavy aromatic content, the first-stage reduced pressure distillation is difficult, and no distillate oil is likely to be distilled out, so that the consumption uncertainty of the back extractant is caused, and the raw material requirement is higher. .
Disclosure of Invention
The invention aims to solve the problems that the removal of aromatic hydrocarbon in straight-run diesel oil fraction with higher heavy aromatic hydrocarbon content is difficult, the removal process cost is high, and the ethylene production by steam cracking is not facilitated.
In order to achieve the above object, the present invention provides the following technical solutions:
a method for dearomatizing a straight-run diesel fraction, comprising the following steps:
1) Performing extraction treatment on the straight-run diesel fraction by using an aromatic extraction solvent at a temperature of not lower than 80 ℃ and a pressure of 0.35-0.65 MPa to obtain an extraction rich agent and raffinate oil; washing raffinate oil to obtain straight-run diesel oil fraction with aromatic hydrocarbon removed and washing water A;
2) Performing step cooling treatment on the extraction rich agent obtained in the step 1) to 40-60 ℃ to repeatedly dissolve and separate out non-aromatic oil in the step cooling treatment, so as to obtain purified separated oil and aromatic semi-lean agent; returning the obtained purified precipitated oil to 1) for reflux, and improving the recovery rate of raffinate oil;
3) Mixing the aromatic semi-lean agent obtained in the step 2) with the stripping agent A obtained in the step 1) to form a stripping mixture A, and reversely contacting the stripping mixture A with the stripping agent B at the temperature of 40-60 ℃ and the pressure of 0.1-0.4 MPa; the back extraction agent A is the water washing water A obtained in the step 1), and the back extraction agent B can be selected from any one of C4-C10 alkane solvents; after the reverse contact, the extracted oil dissolved in the stripping mixture A is dissolved in the stripping agent B to obtain an aromatic-rich stripping agent and a stripping semi-lean agent;
4) Washing and distilling the aromatic-rich back extractant obtained in the step 3) to obtain washing water B, a back extractant B1 and aromatic-rich oil A; the stripping semi-lean agent obtained in the step 3) is subjected to solvent regeneration treatment to obtain regenerated lean agent, water and a small amount of stripping agent B2;
5) Returning the regenerated lean agent obtained in the step 4) to 1) as an aromatic hydrocarbon extraction solvent for recycling; returning the stripping agent B1 and the stripping agent B2 obtained in the step 4) to the step 3) to serve as the stripping agent B for recycling; returning the water obtained by the solvent regeneration treatment of the 4) to 1) and/or 4) as water washing water for recycling; and 3) returning the water washing water B obtained in the step 4) to the step 3) to be used as the stripping agent A for recycling.
In the scheme of the invention, the type of the aromatic hydrocarbon extraction solvent in 1) is not particularly limited, the boiling point difference between the solvent and the raw oil is not required to be considered, and any solvent which can be used for extracting aromatic hydrocarbon in the raw oil in the prior art can be used for extracting the straight-run diesel fraction in the invention.
In a preferred scheme of the invention, the extraction treatment of 1) is carried out in an extraction tower, the temperature of the bottom of the extraction tower is controlled to be 80-150 ℃, and the temperature of the top of the tower is not higher than the thermal degradation temperature of the aromatic hydrocarbon extraction solvent.
In a preferred embodiment of the present invention, in the extraction treatment of 1), the mass ratio of the aromatic hydrocarbon extraction solvent to the straight-run diesel fraction (abbreviated as hydrocarbon mass ratio) is 2 to 10:1, and more preferably 4 to 6:1.
In a preferred scheme of the invention, the water washing of 1) is carried out at 40-60 ℃.
In the preferred scheme of the invention, the step cooling treatment of the 2) is specifically as follows: allowing the extraction rich agent with the temperature not lower than 80 ℃ to flow along a sufficiently long pipeline from top to bottom, allowing a cooling medium with the temperature of 40-60 ℃ to flow from bottom to top at the periphery of the pipeline, and performing countercurrent heat exchange on the two partition walls; the length-diameter ratio of the pipeline is at least 4-10, the flow rate of the extracting rich agent is controlled to be 0.4-2m/s, and the flow rate of the cooling medium is controlled to be 0.2-1 m/s.
In a more preferred embodiment of the present invention, the flow of the extraction rich agent is a film forming flow from top to bottom in the downcomer.
In a further preferred scheme of the invention, the step cooling treatment is completed by adopting a falling film cooling concentration tank with the following structural characteristics: the falling film cooling concentration tank comprises a liquid inlet tank, a downcomer and a liquid storage tank; the liquid inlet tank is used for receiving the extracted rich agent and entering the falling film cooling and concentrating tank; the downcomer is used for enabling the extraction rich agent to flow in a film forming way from top to bottom, and the length-diameter ratio is at least 4-10; the liquid storage tank is used for storing condensed extraction rich agent (or aromatic semi-lean agent); the liquid inlet tank is communicated with the inlet of the downcomer, and after the extraction rich agent enters the downcomer through the liquid inlet tank, the downcomer controls the feeding quantity of the extraction rich agent and the flow rate of the cooling medium to enable the extraction rich agent and the cooling medium to form a temperature gradient respectively. In a more preferred scheme, the liquid storage tank can be provided with coalesced deoiling filler so as to further facilitate oil separation; the liquid storage tank can be further provided with a valve for controlling the boundary position of the aromatic semi-lean agent and the precipitated oil; the tank top and the tank bottom of the falling film cooling concentration tank can be respectively provided with a precipitated oil discharge port and an aromatic semi-lean agent discharge port.
In the scheme of the invention, the purpose of the step cooling treatment of the 2) is to fully separate out the non-aromatic oil in the extraction enriching agent so as to purify the separated oil and concentrate the aromatic oil obtained in the subsequent steps, and the principle of the step cooling treatment is mainly as follows: in the countercurrent heat exchange process of the extraction rich agent and the cooling medium, along with the extension of the countercurrent heat exchange distance, the temperature of the cooling medium gradually rises from bottom to top, and the temperature of the extraction rich agent in the pipeline gradually decreases from top to bottom, so that the temperature of the extraction rich agent in the pipeline with a long enough length can form a gradient from top to bottom. Known in the art are: the lower the temperature, the lower the solubility of the hydrocarbon species in the extractant and conversely the higher the solubility. Therefore, in the continuous flow heat exchange process from top to bottom, as the temperature gradually decreases, the part of the non-aromatic hydrocarbon with low solubility, which is initially dissolved into the extraction rich agent because of large quantity, is selectively separated out when the temperature is relatively low. Because the density of the separated oil is smaller than that of the extraction rich agent, the separated oil separated out in advance can flow upwards in the pipeline and reversely to the extraction rich agent which enters later. In the reverse flow process, the temperature of the extraction rich agent contacted with the precipitated oil which is precipitated at a lower temperature is always relatively high, and the precipitated oil is dissolved into the extraction rich agent again according to the solubility rule. The dissolved part analyzes oil, and the oil can be separated out again after the oil continuously flows downwards along with the extraction of the rich agent in the pipeline and exchanges heat with cold water for cooling. With the downward flow of continuous extraction rich agent and the upward flow of separated oil, the countercurrent contact process of two phases can realize the multistage repeated dissolution and separation of non-aromatic hydrocarbon, and finally reach equilibrium. Because the dissolution capacity of the aromatic hydrocarbon extraction solvent for aromatic hydrocarbon is larger than that for non-aromatic hydrocarbon, the aromatic hydrocarbon is firstly dissolved in the dissolution process, and the non-aromatic hydrocarbon with smaller solubility is firstly separated out when the temperature is reduced, and then the aromatic hydrocarbon with larger solubility is separated out, so that the non-aromatic hydrocarbon is firstly separated out and then the aromatic hydrocarbon is separated out in the separation process. In the multistage repeated dissolution and precipitation process, the aromatic hydrocarbon is fully dissolved in the aromatic hydrocarbon extraction solvent, but not fully precipitated, so that the purposes of purifying the precipitated oil and concentrating the aromatic oil obtained in the subsequent steps are achieved.
In a preferred scheme of the invention, the mass ratio of the aromatic semi-lean agent to the stripping agent A in the stripping mixture A in the step 3) is 1:0.02-0.1; more preferably 1:0.03 to 0.08.
In a preferred embodiment of the present invention, the stripping agent B in 3) is selected from any one of normal paraffins, isoparaffins or naphthenes of C4-C8, or a mixture of two or more of them; further preferred is any of the normal, isoparaffin or cycloalkane of C6-C7; most preferred is cyclohexane or n-heptane.
In the preferred scheme of the invention, the mass ratio of the stripping mixture A to the stripping agent B in the step 3) is 1:0.2-1; further preferably 1:0.3 to 0.8.
In a preferred scheme of the invention, the stripping mixture A and the stripping agent B in 3) are reversely contacted at the temperature of 40-60 ℃ and the pressure of 0.15-0.2 MPa.
In the prior art, the straight-run diesel oil rich in heavy aromatics, especially polycyclic aromatic hydrocarbons, is difficult to realize industrial application in the steam cracking of ethylene, and the existing dearomatization process aiming at the straight-run diesel oil fraction is high in cost and unsatisfactory in removal efficiency. Compared with the prior art, the method for dearomatizing the straight-run diesel oil has the following advantages:
1) Can effectively improve the recovery rate of raffinate oil, thereby obviously improving the removal rate of aromatic hydrocarbon
According to the invention, the law that substances with low solubility are separated out firstly and substances with high solubility are separated out later is fully utilized, and the solubility of non-aromatic components in the extraction rich agent is changed through gradient cooling after high-temperature extraction, so that the part of the non-aromatic components with low solubility, which are dissolved into the extraction rich agent because of large quantity, is separated out selectively. The preferred cooling equipment of the method is a falling film cooling concentration tank, which can provide a gradient cooling environment from top to bottom for extracting the rich agent, realizes the balance of multistage repeated precipitation and dissolution of non-aromatic precipitation oil at gradient temperature, achieves the dual purposes of purifying the precipitation oil and concentrating the aromatic rich oil, and can effectively improve the recovery rate of raffinate oil in the extraction step, namely improve the yield of target products, thereby obviously improving the aromatic removal rate of the straight-run diesel fraction.
2) Can obviously reduce the dosage of alkane back-extraction agent
After the gradient cooling treatment, as part of dissolved hydrocarbon is separated out, the dosage of the stripping agent B required in the subsequent stripping of the extracting rich agent is obviously reduced. In addition, the invention adopts a double-solvent back extraction process, namely, the water washing water of the raffinate oil is firstly used as a back extraction agent A to be added into the extraction rich agent, so that the polarity of the extraction solvent is changed, the solubility of the extraction solvent to the diesel fraction is reduced, the aromatic oil in the extraction rich agent is easier to separate out, and the dosage of the back extraction agent B can be effectively reduced when the back extraction agent B is used for back extraction in the follow-up process.
3) The invention also establishes a water washing water circulation system, and the raffinate oil and the solvent carried and dissolved by the aromatic-rich back extractant are recovered in a water washing mode, so that no solvent loss exists.
4) The temperature of the extraction is close to the temperature of the solvent regeneration, the solvent in the whole process is heated once and cooled once, and the heat is fully utilized, so that the purposes of energy conservation and consumption reduction can be achieved.
5) The method has wide application range of the raw oil fraction section, and does not need to limit the boiling point difference between the raw material and the extraction solvent.
6) The straight-run diesel fraction treated by the method of the invention has flexible and controllable raffinate oil aromatic hydrocarbon index according to different control conditions, can produce steam cracking raw materials with lower aromatic hydrocarbon index, and widens the sources of ethylene raw materials.
Drawings
FIG. 1 is a schematic flow chart of a method for dearomatizing a straight-run diesel fraction according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a falling film cooling and concentrating tank used in the method for dearomatizing a straight-run diesel fraction according to an embodiment of the present invention.
Reference numerals illustrate:
1-an extraction tower; 2-raffinate oil water washing tower; 3-falling film cooling and concentrating tank; 4-back extraction tower; 5-an aromatic-rich back extractant water washing tower; 6-a stripping agent recovery tower; 7-a solvent regeneration column; 8-a liquid inlet groove; 9-down-comer; 10-a liquid storage tank; 11-an aromatic semi-lean agent-containing discharge port valve; 12-an oil precipitation discharge port; 13-coalescing deoiling filler.
Description of the embodiments
The invention relates to a method for dearomatizing a straight-run diesel fraction, which is shown in figure 1, and mainly comprises the steps of liquid-liquid extraction by using an extraction tower 1, rich agent pretreatment by using a falling film cooling concentration tank 3, double-solvent back extraction by using a back extraction tower 4, back extraction agent regeneration by using a back extraction agent recovery tower 6 and extraction solvent regeneration by using a solvent regeneration tower 7. Wherein, the pretreatment (namely the gradient cooling and concentration of the falling film cooling and concentration tank 3) of the extraction rich agent and the double solvent back extraction are key cores.
As shown in fig. 1, the specific flow is described as follows:
(1) Countercurrent extraction: the aromatic extraction solvent and the straight-run diesel fraction (raw oil) rich in heavy aromatic are in countercurrent contact in an extraction tower 1 to obtain an extraction rich agent and raffinate oil. The operating pressure of the extraction tower 1 is controlled to be 0.35-0.65 MPa, the operating temperature of the bottom of the tower is controlled to be 80-150 ℃, and the temperature of the top of the tower is not higher than the thermal degradation temperature of the aromatic hydrocarbon extraction solvent. The mass ratio of the aromatic hydrocarbon extraction solvent to the straight-run diesel fraction (abbreviated as hydrocarbon mass ratio) is controlled to be 2-10:1, and more preferably 4-6:1. The raffinate oil enters a raffinate oil water scrubber 2 after heat exchange to obtain target product raffinate oil and water washing water A, and the target product raffinate oil is discharged from the top of the raffinate oil water scrubber 2; the water washing water A is discharged from the bottom of the raffinate oil water washing tower 2.
(2) Pretreatment of the enriching agent: the method comprises the steps of treating an extracted rich agent by using a falling film cooling and concentrating tank 3, wherein the falling film cooling and concentrating tank 3 is generally structured as shown in figure 2 and comprises a liquid inlet tank 8, a liquid outlet pipe 9 and a liquid storage tank 10; the liquid inlet tank 8 is used for receiving the extracted rich agent to enter the falling film cooling and concentrating tank; the length-diameter ratio of the downcomer 9 is at least 4-10; the liquid storage tank 10 is used for storing condensed extraction rich agent (or aromatic semi-lean agent); the liquid inlet groove 8 is communicated with the inlet of the downcomer 9. In a more preferred embodiment, the liquid storage tank 10 may be further provided with a coalescing deoiling filler 13 to further facilitate oil separation; the liquid storage tank 10 can be further provided with an aromatic semi-lean agent discharge port valve 11 for controlling the boundary position of the aromatic semi-lean agent and the separated oil; the top of the falling film cooling concentration tank is provided with a precipitated oil discharge port 12.
The extraction rich agent from the bottom of the extraction tower 1 enters a liquid inlet groove 8 of the falling film cooling concentration tank 3 from the upper part to enter a downcomer 9, and flows in the downcomer 9 from top to bottom, and the cooling medium flows in the falling film cooling concentration tank 3 and outside the downcomer 9 from bottom to top to form reverse flow heat exchange with the extraction rich agent partition wall in the downcomer 9. In the reverse flow process, the feeding amount of the extraction rich agent is controlled to be 0.4-2m/s, and the flow rate of the cooling medium is controlled to be 0.2-1 m/s, so that the extraction rich agent in the downcomer 9 and the water outside the downcomer 9 form a temperature gradient. Because of the influence of the gradient temperature on the solubility of the non-aromatic hydrocarbon in the extraction rich agent, the temperature of the extraction rich agent contacted with the precipitated oil which is precipitated at a lower temperature continuously is relatively high, and the precipitated oil can be dissolved into the extraction rich agent again. The dissolved part analyzes oil, and the oil can be separated out again after the oil continuously flows downwards along with the extraction of the rich agent in the pipeline and exchanges heat with cold water for cooling. With the downward flow of continuous extraction rich agent and the upward flow of separated oil due to relatively low density, the countercurrent contact process of two phases can realize the multistage repeated dissolution and separation of non-aromatic hydrocarbon. The extraction rich agent is pretreated by a circulating cooling medium in a falling film cooling concentration tank 3, heat exchange and cooling are carried out until the temperature reaches 40-60 ℃, the balance of dissolution and precipitation is finally achieved, aromatic hydrocarbon is fully dissolved instead of being fully precipitated, the precipitated oil at the upper layer of the falling film cooling concentration tank 3 is discharged through a precipitated oil discharge port 12 and then returned to the middle part of the extraction tower 1, the extraction rich agent is used for improving the recovery rate of raffinate oil, and the aromatic-containing semi-lean agent at the lower layer is discharged from the tank bottom through an aromatic-containing semi-lean agent discharge port 13.
(3) Double solvent back extraction: mixing the aromatic semi-lean agent from the bottom of the falling film cooling concentration tank 3 in the step (2) with water washing water A (stripping agent A) from the bottom of the raffinate oil water washing tower 2 in the step (1) at a mass ratio of 1:0.02-0.1 (marked as stripping ratio A), more preferably at a mass ratio of 1:0.03-0.08 to form a stripping mixture A, wherein the stripping mixture A enters from the upper part of the stripping tower 4, and the stripping agent B enters from the lower part of the stripping tower 4. The back extraction agent B can be selected from any one of C4-C10 alkane solvents, preferably any one of normal alkane, isoparaffin or cycloalkane of C4-C8, or a mixture of more than two of the normal alkane, isoparaffin and cycloalkane; further preferred is any of the normal, isoparaffin or cycloalkane of C6-C7; most preferred is cyclohexane or n-heptane. The stripping mixture A and the stripping agent B are reversely contacted in the stripping tower 4 to finish stripping, the operating temperature of the stripping tower 4 is controlled to be 40-60 ℃, the operating pressure is controlled to be 0.1-0.4 MPa (preferably 0.15-0.2 MPa), and the mass ratio of the stripping mixture A to the stripping agent B (marked as the stripping ratio B) is controlled to be 1:0.2-1, and further preferably 1:0.3-0.8. The extracted oil dissolved in the stripping mixture A is dissolved in the stripping agent B to obtain an aromatic-rich stripping agent and a stripping semi-lean agent, and the aromatic-rich stripping agent flows out from the top of the stripping tower 4; the stripping semi-lean agent containing water and a small amount of stripping agent B flows out from the bottom of the stripping tower 4.
(4) And (3) recycling a stripping agent B: the aromatic-rich stripping agent from the top of the stripping tower 4 in the step (3) enters an aromatic-rich stripping agent water washing tower 5, water washing water B and an aromatic-rich stripping agent after water washing are obtained, the aromatic-rich stripping agent after water washing enters a stripping agent recovery tower 6 through heat exchange, and the stripping agent B1 and aromatic-rich oil A are obtained through reduced pressure distillation; the stripping agent B1 is discharged from the top of the stripping agent recovery tower 6 and returned to the lower part of the stripping tower 4 in the step (3) for recycling; aromatic-rich oil A is discharged from the bottom of the stripping agent recovery tower 6. The water washing water B and the water washing water A from the step (1) are jointly used as the stripping agent A for the double solvent stripping of the step (3).
(5) Solvent recovery and water circulation: the stripping semi-lean agent containing water and a small amount of stripping agent B from the bottom of the stripping tower 4 enters a solvent recovery tower 7 through heat exchange, reduced pressure distillation is carried out, water distilled from the tower top and a small amount of stripping agent B2 are subjected to standing separation, and the water returns to the raffinate oil water washing tower 2 in the step (1) and/or the aromatic-rich stripping agent water washing tower 5 in the step (4) to be used as raffinate oil water washing water and aromatic-rich stripping agent water washing water for recycling; and (3) returning the stripping agent B2 to the lower part of the stripping tower 4 in the step (3) for recycling or combining and distilling the stripping agent B with the aromatic-rich stripping agent after washing in the step (4). The regenerated lean agent discharged from the bottom of the solvent recovery tower 7 enters the extraction tower 1 in the step (1) for recycling.
In the above embodiment, the aromatic hydrocarbon extraction solvent in (1) is selected from a single or compound solvent which can meet the dearomatization requirement of the target product, and the boiling point difference between the raw oil and the extraction solvent is not limited. For example, a single solvent such as sulfolane, dimethyl sulfoxide and glycol solvent can be selected as the extraction solvent, or two or more of sulfolane, dimethyl sulfoxide, glycol solvent, N-methylpyrrolidone, propylene carbonate, 2-pyrrolidone, N-dimethylformamide and N, N-dimethylacetamide can be selected as the compound extraction solvent after being compounded. The above solvents are only examples and are not limiting to the scope of the invention.
The method for dearomatizing the straight-run diesel fraction provided by the invention is described in detail below with reference to examples. Based on the procedure of the above detailed description, the following examples were formed using specific solvents and conditions.
Four raw oil materials are selected in the example, and the properties of the raw oil materials are shown in table 1.
TABLE 1 essential properties of raw oil
The dearomatization effect is characterized by the following parameters in the implementation process.
Aromatic hydrocarbon removal rate ρ%, percent: the higher the aromatics removal rate, the lower the aromatics content in the raffinate.
Aromatic index BMCI: according to the correlation index established by the two basic properties of the distillation range and the density of the oil product, the numerical value represents the content of aromatic hydrocarbon in the oil product. The lower the BMCI value, the higher the triene yield after cleavage.
The above aromatic hydrocarbon removal rate ρ is calculated using the following formula:
however, the following examples are merely illustrative, further illustrate the invention, and should not be construed as limiting the scope of the invention.
Example 1
The aromatic hydrocarbon extraction solvent A is a mixture of 70% of sulfolane and 30% of 2-pyrrolidone by weight percentage, and the raw oil is diesel oil fraction I. Liquid extraction and solvent regeneration were performed according to the scheme of fig. 1. Wherein the mass ratio of the extractant hydrocarbon is 4:1, the operating temperature of the extraction tower 1 is 85 ℃, and the operating pressure is 0.3MPa; the extraction of the rich agent is separated by cooling to 40 ℃ through a falling film cooling concentration tank 3; the operation temperature of the back extraction tower 4 is 40 ℃ and the operation pressure is 0.2MPa; the stripping agent A is water, the stripping ratio A is 0.04:1, the stripping agent B is cyclohexane, and the stripping ratio B is 0.6:1; the stripping agent recovery tower 6 is used for separating the stripping agent B from aromatic hydrocarbon by reduced pressure distillation, the tower bottom operation temperature is 40 ℃, and the operation pressure is 20kPa; the solvent regeneration column 7 was used to separate water from the extraction solvent at an operating temperature of 175℃and an operating pressure of 15kPa. The specific conditions and results are shown in Table 2.
Example 2
The aromatic hydrocarbon extraction solvent B is a mixture of 70% of dimethyl sulfoxide and 30% of N-methyl pyrrolidone by weight percentage, and the raw oil is diesel oil fraction I. Liquid extraction and solvent regeneration were performed according to the scheme of fig. 1. Wherein the mass ratio of the extractant hydrocarbon is 4.5:1, the operating temperature of the extraction tower 1 is 90 ℃, and the operating pressure is 0.3MPa; the extraction of the rich agent is separated by cooling to 40 ℃ through a falling film cooling concentration tank 3; the operation temperature of the back extraction tower 4 is 40 ℃ and the operation pressure is 0.2MPa; the stripping agent A is water, the stripping ratio A is 0.05:1, the stripping agent B is cyclohexane, and the stripping ratio B is 0.5:1; the stripping tower recovery tower 6 is used for separating the stripping agent B from aromatic hydrocarbon by reduced pressure distillation, the operating temperature is 40 ℃, and the operating pressure is 20kPa; the solvent regeneration column 7 is used to separate water from the extraction solvent at an operating temperature of 160℃and an operating pressure of 20kPa. The specific conditions and results are shown in Table 2.
Example 3
Liquid extraction and solvent regeneration were carried out according to the procedure of FIG. 1, with the extraction agent hydrocarbon mass ratio of 6:1, and the aromatic extraction solvent, the feed oil and other process conditions were the same as in example 1. The specific conditions and results are shown in Table 2.
Example 4
Liquid extraction and solvent regeneration were carried out according to the procedure of FIG. 1, with reference to example 1, wherein the operating temperature of the extraction column 1 was 130℃and the aromatic hydrocarbon extraction solvent, the feed oil and other process conditions were the same as in example 1. The specific conditions and results are shown in Table 2.
Example 5
Liquid extraction and solvent regeneration were carried out according to the procedure of FIG. 1, with reference to example 1, wherein the stripping column 4 was operated at 60℃and the aromatic hydrocarbon extraction solvent, the feed oil and other process conditions were the same as in example 1. The specific conditions and results are shown in Table 2.
Example 6
Liquid extraction and solvent regeneration were performed according to the procedure of fig. 1 by the method of reference example 1, wherein the stripping agent B was n-heptane, the bottom temperature of the stripping agent recovery column 6 was 50 ℃, and the aromatic hydrocarbon extraction solvent, the raw oil and other process conditions were the same as those of example 1. The specific conditions and results are shown in Table 2.
Example 7
Liquid extraction and solvent regeneration were carried out according to the procedure of FIG. 1, wherein the stripping ratio A was 0.08:1, and the aromatic extraction solvent, the feed oil and other process conditions were the same as in example 1. The specific conditions and results are shown in Table 2.
Example 8
Liquid extraction and solvent regeneration were carried out according to the procedure of FIG. 1, wherein the stripping ratio B was 0.8:1, and the aromatic hydrocarbon extraction solvent, the raw oil and other process conditions were the same as in example 1. The specific conditions and results are shown in Table 2.
Table 2: extraction and regeneration of data under different conditions
Table 2 shows that the process of the present invention has arene eliminating rate over 85% to the straight run diesel oil fraction I, greatly reduced raffinate oil arene index, and the raffinate oil may be used as steam cracking material for producing ethylene and has wide ethylene material source.
Example 9
The aromatic hydrocarbon extraction solvent C is a mixture of 80% of propylene carbonate and 20% of N, N-dimethylacetamide in percentage by weight, and the raw oil is diesel oil fraction II. The liquid-liquid extraction and solvent regeneration were performed according to the procedure of fig. 1, with reference to the method of example 1, and the modification of some of the process parameters included: the hydrocarbon mass ratio of the extractant is 5:1, the operating temperature of the extraction tower 1 is 110 ℃, the back extraction ratio A is 0.05:1, the bottom temperature of the solvent regeneration tower 7 is 170 ℃, the pressure is 20KPa, and other process conditions are the same as those of the embodiment 1. The specific operating conditions are shown in Table 3, and the raffinate results are shown in Table 4.
Example 10
The aromatic hydrocarbon extraction solvent D is a mixture of 60% of sulfolane, 20% of 2-pyrrolidone and 20% of propylene carbonate by weight percentage, and the raw oil is diesel fraction III. The liquid-liquid extraction and solvent regeneration were performed according to the procedure of fig. 1, with reference to the method of example 1, and the modification of some of the process parameters included: the hydrocarbon mass ratio of the extractant is 4:1, the operating temperature of the extraction tower 1 is 100 ℃, the back extraction ratio A is 0.03:1, the back extraction ratio B is 0.5:1, and other process conditions are the same as those of the embodiment 1. The specific operating conditions are shown in Table 3, and the raffinate results are shown in Table 4.
Example 11
The aromatic hydrocarbon extraction solvent E is a mixture of 70% of dimethyl sulfoxide and 30% of N, N-dimethylformamide by weight percentage, and the raw oil is diesel oil fraction IV. Liquid-liquid extraction and solvent regeneration were carried out according to the procedure of FIG. 1, with the extraction agent hydrocarbon mass ratio of 5:1, the extraction column 1 operating temperature of 115℃and the stripping ratio A of 0.05:1, the solvent regeneration column 7 bottom temperature of 160℃and the pressure of 20KPa, and the other process conditions were the same as in example 1. The specific operating conditions are shown in Table 3, and the raffinate results are shown in Table 4.
TABLE 3 different extraction conditions employed for different diesel fractions
TABLE 4 results of raffinate oil after extraction of different distillation ranges of straight-run diesel oil fraction and extractant
Tables 3 and 4 show the extraction conditions and raffinate oil results of the straight-run diesel oil fractions with different distillation ranges as the raw oil, which shows that the process of the invention can realize good aromatic hydrocarbon removal effect on the straight-run diesel oil fractions with various distillation ranges, and can select proper solvents according to different extraction requirements of the raw oil, and can avoid the difference of boiling points of the solvents and the raw oil, thus the application range of the raw material is wide, and the selection range of the extraction solvents is wide.
Comparative example 1
In the method of example 1, the same aromatic hydrocarbon extraction solvent and raw oil were used for liquid-liquid extraction and solvent regeneration, but the extraction rich agent was discharged from the bottom of the extraction column 1, and then was directly fed into the stripping column 4 for double solvent stripping after being mixed with the stripping agent A, without being fed into the falling film cooling and concentrating tank 3 shown in FIG. 1, and the other conditions were the same as in example 1. The specific conditions and results are shown in Table 5.
Comparative example 2
Referring to the method of example 1, the same aromatic extraction solvent and raw oil were used for liquid-liquid extraction and solvent regeneration, but the extraction rich agent was discharged from the bottom of the extraction column 1, and then was directly fed into the stripping column 4 for double-solvent stripping after being mixed with the stripping agent A, without being fed into the falling film cooling and concentrating tank 3 shown in FIG. 1, and the amount of the stripping agent B was increased, and the other conditions were the same as those of example 1. The specific conditions and results are shown in Table 5.
Comparative example 3
In the method of reference example 1, the same aromatic hydrocarbon extraction solvent and raw oil are used for liquid-liquid extraction and solvent regeneration, but the semi-lean agent rich in aromatic hydrocarbon obtained by gradient cooling of the extraction rich agent through the falling film cooling concentration tank 3 is directly fed into the solvent regeneration tower 7 for reduced pressure distillation without being treated by the stripping tower 4, the aromatic rich stripping agent water washing tower 5 and the stripping agent recovery tower 6, and other conditions are the same as those of example 1. The specific conditions and results are shown in Table 5.
Comparative example 4
Referring to the method of example 1, the same aromatic hydrocarbon extraction solvent and raw oil were used for liquid-liquid extraction and solvent regeneration, except that the aromatic semi-lean agent discharged from the bottom of the falling film cooling concentration tank 3 was not mixed with the stripping agent a, and was fed separately into the upper part of the stripping column 4, i.e., the double solvent stripping in example 1 was changed to single solvent (stripping agent B) stripping, and the other conditions were the same as in example 1. The specific conditions and results are shown in Table 5.
Comparative example 5
With reference to the method of example 1, the same aromatic hydrocarbon extraction solvent and raw oil were used for liquid-liquid extraction and solvent regeneration, except that the double-agent extraction was not used and the amount of the stripping agent B was increased so that the quality of the lean regeneration reached the same as in example 1. The specific conditions and results are shown in Table 5.
Table 5: changing the influence of process conditions on extraction results
As can be seen from Table 5, in example 1, the recovery rate of raffinate oil can be increased and the aromatic oil-rich purity (aromatic hydrocarbon content of extract oil) can be improved by pretreating the extract rich agent through stepwise cooling and returning the separated oil in the rich agent to the extraction tower. In addition, the use amount of the stripping agent B can be effectively reduced after the stripping rich agent in the embodiment 1 is subjected to step cooling pretreatment and is mixed with the stripping agent A. Compared with comparative example 1, in example 1, the recovery rate of raffinate oil is improved from 70.25% to 78.85% due to the rich agent subjected to step cooling pretreatment and the reflux of separated oil, and the aromatic hydrocarbon removal rate is obviously improved; the amount of stripping agent B used in example 1 was significantly reduced when a similar dearomatization effect was achieved compared to comparative example 2; compared with comparative example 3, the regenerated lean agent in example 1 has better quality through double solvent back extraction, and the regenerated lean agent is used for extraction, so that the aromatics removal rate of raffinate oil after extraction is improved by about 20%; compared with comparative example 4, in example 1, the quality of the regenerated lean agent is improved after the double solvent back extraction despite the lower extraction temperature, and the regenerated lean agent is used for extraction, so that the significantly improved aromatic hydrocarbon removal rate is still obtained. In the prior art, the single stripping agent is generally adopted, and if the regeneration effect of the double stripping agent is to be achieved, the usage amount of the stripping agent B is greatly improved, and just like comparative example 5, 5 times of the stripping agent B in the embodiment 1 is needed to obtain the dearomatization effect and the solvent regeneration effect equivalent to those in the embodiment 1.
Comparative example 6
The method of example 1 was referred to as liquid-liquid extraction and solvent regeneration using the same aromatic extraction solvent and raw oil, except that the falling film cooling and concentration tank 3 was replaced with a direct cooling tank, i.e., the temperature gradient change of the extracted rich agent in example 1 by countercurrent heat exchange with the cooling medium in the downcomer was replaced with heat exchange with the cooling medium at a constant temperature in the cooling tower without flow rate (/ or in a stationary state), and no gradient temperature was formed, so that the extracted rich agent in the cooling tower was simultaneously cooled to 40 ℃, and the other conditions were the same as in example 1. The results of the aromatic content in the oil are shown in Table 6.
TABLE 6
As can be seen from the comparison of Table 6, compared with the method of directly cooling the extraction rich agent to the same temperature, the method can fully separate out the non-aromatic separation oil in the extraction rich agent by pretreatment cooling at gradient temperature, the recovery rate of raffinate oil can be obviously improved by the backflow of separation oil, the aromatic hydrocarbon content in the separation oil is obviously reduced, and finally the aromatic hydrocarbon content of the extraction oil is obviously improved.
Claims (9)
1. A method for dearomatizing a straight-run diesel fraction, which is characterized by comprising the following steps:
1) Performing extraction treatment on the straight-run diesel fraction by using an aromatic extraction solvent at a temperature of not lower than 80 ℃ and a pressure of 0.35-0.65 MPa to obtain an extraction rich agent and raffinate oil; washing raffinate oil to obtain straight-run diesel oil fraction with aromatic hydrocarbon removed and washing water A;
2) Performing step cooling treatment on the extract rich agent obtained in the step 1) to 40-60 ℃, wherein the step cooling treatment comprises the following steps: allowing the extracting rich agent with the temperature not lower than 80 ℃ to flow along a long pipeline from top to bottom, allowing a cooling medium with the temperature of 40-60 ℃ to flow from bottom to top at the periphery of the pipeline, and performing countercurrent heat exchange on the two partition walls; the length-diameter ratio of the pipeline is at least 4, the flow rate of the extracting rich agent is controlled to be 0.4-2m/s, and the flow rate of the cooling medium is controlled to be 0.2-1 m/s; the refined separated oil and the aromatic semi-lean agent are obtained through step cooling treatment; returning the obtained purified precipitated oil to 1) for reflux, and improving the recovery rate of raffinate oil;
3) Mixing the aromatic semi-lean agent obtained in the step 2) with the stripping agent A obtained in the step 1) to form a stripping mixture A, and reversely contacting the stripping mixture A with the stripping agent B at the temperature of 40-60 ℃ and the pressure of 0.1-0.4 MPa; the back extraction agent A is the water washing water A obtained in the step 1), and the back extraction agent B can be selected from any one of C4-C10 alkane solvents; after the reverse contact, the extracted oil dissolved in the stripping mixture A is dissolved in the stripping agent B to obtain an aromatic-rich stripping agent and a stripping semi-lean agent;
4) Washing and distilling the aromatic-rich back extractant obtained in the step 3) to obtain washing water B, a back extractant B1 and aromatic-rich oil A; the stripping semi-lean agent obtained in the step 3) is subjected to solvent regeneration treatment to obtain regenerated lean agent, water and a small amount of stripping agent B2;
5) Returning the regenerated lean agent obtained in the step 4) to 1) as an aromatic hydrocarbon extraction solvent for recycling; returning the stripping agent B1 and the stripping agent B2 obtained in the step 4) to the step 3) to serve as the stripping agent B for recycling; returning the water obtained by the solvent regeneration treatment of the 4) to 1) and/or 4) as water washing water for recycling; and 3) returning the water washing water B obtained in the step 4) to the step 3) to be used as the stripping agent A for recycling.
2. The method of claim 1, wherein: 1) The extraction treatment is carried out in an extraction tower, the temperature of the bottom of the extraction tower is controlled to be 80-150 ℃, and meanwhile, the temperature of the top of the tower is not higher than the thermal degradation temperature of the aromatic hydrocarbon extraction solvent.
3. The method of claim 1, wherein: 1) In the extraction treatment, the mass ratio of the aromatic hydrocarbon extraction solvent to the straight-run diesel oil fraction is 2-10:1.
4. The method of claim 1, wherein: 1) The water washing is carried out at 40-60 ℃.
5. The method of claim 1, wherein: 2) The step cooling treatment is completed by adopting a falling film cooling concentration tank with the following structural characteristics: the falling film cooling concentration tank comprises a liquid inlet tank, a downcomer and a liquid storage tank; the liquid inlet tank is used for receiving the extracted rich agent and entering the falling film cooling and concentrating tank; the downcomer is used for enabling the extraction rich agent to flow in a film forming way from top to bottom, and the length-diameter ratio is 4-10; the liquid storage tank is used for storing the condensed extraction rich agent; the liquid inlet tank is communicated with the inlet of the downcomer, and after the extraction rich agent enters the downcomer through the liquid inlet tank, the downcomer controls the feeding quantity of the extraction rich agent and the flow rate of the cooling medium to enable the extraction rich agent and the cooling medium to form a temperature gradient respectively.
6. The method of claim 1, wherein: 3) The mass ratio of the aromatic semi-lean agent to the stripping agent A in the stripping mixture A is 1:0.02-0.1.
7. The method of claim 1, wherein: 3) The back extractant B is selected from any one of normal alkane, isoparaffin or cycloparaffin of C4-C8 or the mixture of more than two of the normal alkane, isoparaffin and cycloparaffin.
8. The method of claim 1, wherein: 3) The mass ratio of the stripping mixture A to the stripping agent B is 1:0.2-1.
9. The method of claim 1, wherein: 3) The stripping mixture A and the stripping agent B are reversely contacted at the temperature of 40-60 ℃ and the pressure of 0.15-0.2 MPa.
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| CN103361118A (en) * | 2012-04-01 | 2013-10-23 | 中国石油化工股份有限公司 | Method for recovering aromatic hydrocarbons from gasoline containing olefin and sulfide |
| CN108203595A (en) * | 2016-12-20 | 2018-06-26 | 中国石油化工股份有限公司 | A kind of method of aromatic hydrocarbons and alkane in extracting separation diesel oil distillate |
| CN108690658A (en) * | 2017-04-07 | 2018-10-23 | 中国石油天然气股份有限公司 | A method of aromatic hydrocarbons in recycling low arene content oil |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103361118A (en) * | 2012-04-01 | 2013-10-23 | 中国石油化工股份有限公司 | Method for recovering aromatic hydrocarbons from gasoline containing olefin and sulfide |
| CN108203595A (en) * | 2016-12-20 | 2018-06-26 | 中国石油化工股份有限公司 | A kind of method of aromatic hydrocarbons and alkane in extracting separation diesel oil distillate |
| CN108690658A (en) * | 2017-04-07 | 2018-10-23 | 中国石油天然气股份有限公司 | A method of aromatic hydrocarbons in recycling low arene content oil |
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