Process for the hydrogenation of cracked naphtha

Abstract

The application provides a naphtha cracking hydrogenation method, which effectively reduces the temperature difference in the reactor by setting a circulating pump; timely removes the reaction heat by setting a one-stage circulating heat remover, and utilizes the reaction heat to generate low-temperature hot water, thereby reducing the energy consumption of the device; there is no circulating hydrogen compressor in the process, and new hydrogen enters the one-stage hydrogenation reactor and the two-stage hydrogenation reactor through a hydrogen compressor to react with raw oil, so that the energy consumption of the device is greatly reduced; a one-stage separator is arranged downstream of the one-stage hydrogenation reactor, liquid phase of the one-stage separator enters the two-stage hydrogenation reactor, and gas phase is sent to a downstream device for treatment; due to the arrangement of the one-stage separator, the volume of the two-stage hydrogenation reactor is reduced, and the equipment investment and land occupation are reduced.

Description

Technical Field

[0001] This invention relates to hydrorefining technology for pyrolyzed naphtha in the petrochemical field, specifically to a method for hydrorefining pyrolyzed naphtha. Background Technology

[0002] Naphtha is a primary feedstock in both the refining and petrochemical industries. Generally, naphtha refers to petroleum fractions obtained from primary or secondary processing in refineries with a dry point ≤200-250℃. It typically originates from atmospheric and vacuum distillation units, as well as catalytic cracking, hydrocracking, coking, and ethylene steam cracking units in refineries. Naphtha has diverse applications; in petroleum refining, it is a major feedstock for producing clean gasoline; in petrochemicals, it is a feedstock for producing ethylene, aromatics / polyesters, synthetic ammonia / fertilizers, and hydrogen. The feedstock oil involved in this invention patent is primarily cracked naphtha, a byproduct of catalytic cracking, coking, and steam cracking units for ethylene production.

[0003] Patent CN101845322A discloses a method for reducing the sulfur and olefin content in naphtha. The raw material, catalytic cracked naphtha, is first de-olefinized in a pre-hydrogenation reactor, and then enters a fractionation tower to be cut into light and heavy naphtha. The light naphtha undergoes hydroadsorption desulfurization, while the heavy naphtha enters a selective hydrotreating reactor for hydrodesulfurization. The reaction effluent then enters a hydrotreating reactor for hydrotreating to reduce the olefin content.

[0004] Patent CN112745925A discloses a method for processing gasoline, which involves cutting gasoline feedstock into light gasoline fractions and heavy gasoline fractions. The light gasoline fraction is fed into a hydrotreating reactor to undergo a mild hydrodesulfurization reaction with a hydrotreating catalyst, yielding desulfurized light gasoline; the heavy gasoline fraction is fed into a fluidized bed reactor to undergo adsorption desulfurization reactions with an adsorption desulfurization catalyst.

[0005] Patent CN112745924A discloses a method for processing catalytic cracking gasoline, which uses a fluidized bed reactor to perform hydrodealkylation treatment on catalytic cracking gasoline, enabling the catalytic cracking gasoline to be efficiently converted into low-carbon olefins and light aromatics, and improving the yield of low-carbon olefins.

[0006] As can be seen from the technology disclosed in the above patent applications, existing naphtha hydrogenation technologies mostly adopt fixed-bed hydrogenation methods, which are difficult to process low-quality naphtha over long periods. Summary of the Invention

[0007] The purpose of this invention is to provide a method for hydrogenating pyrolyzed naphtha, which, while reducing the temperature difference within the reactor and producing high-quality hydrogenated naphtha products, extends the operating cycle of the unit, reduces energy consumption, investment, and floor space. The method includes the following steps:

[0008] 1) After being pressurized, the cracked naphtha is mixed with hydrogen and then enters a first-stage hydrogenation reactor;

[0009] 2) The top product of the first-stage hydrogenation reactor enters the first-stage separator for flash evaporation, and the bottom circulating oil of the first-stage hydrogenation reactor is returned to the first-stage hydrogenation reactor after being pressurized and heat-exchanged;

[0010] 3) A first-stage product gas is generated at the top of the first-stage separator, and a first-stage reaction oil is generated at the bottom of the first-stage separator; the first-stage reaction oil is first mixed with hydrogen, then heat-exchanged with the reaction product oil, heated in a heater, and then sent to the second-stage hydrogenation reactor;

[0011] 4) The top product of the second-stage hydrogenation reactor enters the second-stage separator for flash evaporation, and the bottom circulating oil of the second-stage hydrogenation reactor is returned to the second-stage hydrogenation reactor after being pressurized.

[0012] 5) Second-stage gas is generated at the top of the two-stage separator, and reaction oil is generated at the bottom of the two-stage separator;

[0013] 6) The second-stage product gas is first mixed with the first-stage product gas, and then heat-exchanged with hydrogen before being sent to the downstream unit for processing; the reaction product oil is heat-exchanged with the first-stage reaction oil before being sent to the fractionation system for processing.

[0014] The present invention discloses a method for hydrogenating pyrolyzed naphtha, which is further characterized in that: the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are fixed-bed reactors, fluidized bed reactors, or slurry bed reactors.

[0015] The present invention discloses a method for hydrogenating pyrolyte naphtha, further characterized in that: a first-stage hydrogenation reactor is provided with a first-stage circulating pump and a first-stage circulating heat exchanger at the bottom, and a second-stage hydrogenation reactor is provided with a second-stage circulating pump at the bottom.

[0016] The present invention discloses a method for hydrogenating cracked naphtha, further characterized in that: the ratio of the volumetric flow rate of the first-stage circulating pump to the liquid phase volumetric flow rate of the mixed feed in the first-stage hydrogenation reactor is 2 to 10, and the ratio of the volumetric flow rate of the second-stage circulating pump to the liquid phase volumetric flow rate of the mixed feed in the second-stage hydrogenation reactor is 1.5 to 7.

[0017] The present invention discloses a method for hydrogenating pyrolyte naphtha, which is further characterized in that: both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with circulation cups, and the top liquid phase of the first-stage hydrogenation reactor and the second-stage hydrogenation reactor flow to the inlet of the first-stage circulation pump and the second-stage circulation pump, respectively, through the circulation cups.

[0018] The present invention discloses a method for hydrogenating cracked naphtha, which is further characterized in that: both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with feed distributors at the bottom, through which circulating oil and mixed feed are uniformly fed into the catalyst zone of the reactor.

[0019] The present invention discloses a method for hydrogenating pyrolyte naphtha, which is further characterized in that: both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with top separators to enhance the gas-liquid two-phase separation at the top of the reactor and reduce the separation space required for the top two-phase separation.

[0020] The present invention discloses a method for hydrogenating cracked naphtha, further characterized in that: the first-stage circulating heat exchanger is a shell-and-tube heat exchanger or a plate heat exchanger, and the cooling medium of the first-stage circulating heat exchanger is low-temperature hot water or circulating cold water from the refinery, with an inlet temperature of 20–90°C.

[0021] The present invention discloses a method for hydrogenating pyrolyzed naphtha, further characterized in that: the reaction temperature of the first-stage hydrogenation reactor is 40-150℃, the reaction pressure is 2.0-6.0 MPaG, and the temperature difference within the first-stage hydrogenation reactor is no greater than 10℃.

[0022] The present invention discloses a method for hydrogenating pyrolyzed naphtha, further characterized in that: the reaction temperature of the two-stage hydrogenation reactor is 200-400℃, the reaction pressure is 2.0-6.0 MPaG, and the temperature difference within the two-stage hydrogenation reactor is ≤15℃.

[0023] The feedstock for this invention is cracked naphtha from refinery catalytic cracking, coking, and ethylene steam cracking units, which is rich in olefins with a content of 5-40% wt. The cracked naphtha is pressurized by a feed pump, mixed with hydrogen, and then fed into a first-stage hydrotreating reactor for reactions involving alkynes, dienes, saturation of styrene to monoolefins, and ethylbenzene. The first-stage product oil mixed with hydrogen is fed into a second-stage hydrotreating reactor for reactions involving monoolefin saturation, desulfurization, and removal of mercaptans and other impurities.

[0024] The beneficial effects of this invention are as follows:

[0025] 1) Both the first-stage and second-stage hydrogenation reactors are equipped with circulating pumps to effectively reduce the temperature difference within the reactors. 2) The first-stage hydrogenation reactor is filled with olefin-saturated catalyst. The cracking of naphtha, hydrogen, and catalyst releases a large amount of heat of reaction within the first-stage hydrogenation reactor. By installing a first-stage circulating heat exchanger, the heat of reaction can be removed in a timely manner, and the heat of reaction can be used to generate low-temperature hot water, reducing the energy consumption of the unit.

[0026] 2) The process does not involve a circulating hydrogen compressor. Fresh hydrogen is fed into the first-stage and second-stage hydrogenation reactors via a hydrogen compressor to react with the feedstock oil. Because there is no circulating hydrogen compressor, the unit's energy consumption is significantly reduced.

[0027] 3) A separator is installed downstream of the first-stage hydrogenation reactor. The liquid phase from the first-stage separator enters the second-stage hydrogenation reactor, while the gas phase is sent to the downstream unit for processing. Due to the installation of the first-stage separator, the volume of the second-stage hydrogenation reactor is reduced, thus reducing equipment investment and land occupation. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings:

[0029] Figure 1 This is a schematic diagram of the process of the present invention;

[0030] 1. Hydrogen compressor; 2. Feed pump; 3. First-stage circulating heat exchanger; 4. First-stage hydrogenation reactor; 5. First-stage circulating pump; 6. First-stage separator; 7. Feed furnace; 8. Second-stage hydrogenation reactor; 9. Second-stage circulating pump; 10. Second-stage separator; 11. Hydrogen heat exchanger; 12. Reactant oil heat exchanger; 13. Feed distributor; 14. Top separator; 15. Circulation cup. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings:

[0032] Reference Figure 1 The process involves pressurizing cracked naphtha via feed pump 2, mixing it with a portion of hydrogen pressurized by hydrogen compressor 1, and sending it to the bottom of the first-stage hydrotreating reactor 4. Together with circulating oil, it is evenly distributed into the catalyst zone of the first-stage hydrotreating reactor 4 via the bottom feed distributor 13. The first-stage hydrotreating reactor 4 is primarily filled with saturated catalysts such as alkynes and dienes. Under the action of the catalysts, the olefins in the cracked naphtha undergo a saturated reaction with hydrogen to produce monoolefins, ethylbenzene, etc. To prevent catalyst coking and degradation within the first-stage hydrotreating reactor 4, a first-stage circulating pump 5 is installed at the bottom of the reactor. The volumetric flow rate of the first-stage circulating pump 5 is 2 to 10 times the liquid phase volumetric flow rate of the first-stage mixed feed. Through oil circulation and the first-stage circulating heat exchanger 3, the heat of reaction can be removed in a timely manner, and the bottom inlet temperature of the first-stage hydrotreating reactor 4 can be controlled. In the first-stage hydrogenation reactor 4, a top separator 14 and a circulation cup 15 are installed at the top. The liquid phase at the top outlet flows through the circulation cup 15 to the inlet of the first-stage circulation pump 5, while the gas phase at the top outlet carries some liquid product to the first-stage separator 6 for gas-liquid flash separation. The gas phase in the first-stage separator 6 is mixed with the gas phase in the second-stage separator 10 and sent to the downstream unit for processing. The liquid phase in the first-stage separator 6 is mixed with hydrogen that has been pressurized by the hydrogen compressor 1 and heated by the hydrogen heat exchanger 11, and then sequentially passes through the reaction product oil heat exchanger 12 and the feed furnace 7 to be heated to the reaction temperature before entering the bottom of the second-stage hydrogenation reactor 8.

[0033] The two-stage hydrotreating reactor 8 is equipped with a feed distributor 13, a circulation cup 15, and a top separator 14. The bottom feed and circulating oil of the two-stage hydrotreating reactor 8 are mixed and uniformly fed into the catalyst zone through the feed distributor 13. The two-stage hydrotreating reactor 8 is mainly filled with mono-olefin saturation and hydrorefining catalysts. A two-stage circulation pump 9 is located at the bottom of the two-stage hydrotreating reactor 8, and its volumetric flow rate is 1.5 to 7 times the liquid phase volumetric flow rate of the mixed feed. Inside the two-stage hydrotreating reactor 8, under the action of bottom hydrogen and oil circulation, the feed oil-circulating oil-hydrogen-catalyst are uniformly distributed in the catalyst zone. The cracked naphtha undergoes a mono-olefin saturation reaction with hydrogen, and impurities are removed. The liquid phase at the top of the second-stage hydrogenation reactor 8 flows through the circulation cup 15 to the inlet of the second-stage circulation pump 9. The gas phase at the top of the second-stage hydrogenation reactor 8 carries some liquid product to the second-stage separator 10 to complete gas-liquid flash separation. The gas phase at the top of the second-stage separator 10 is mixed with the gas phase of the first-stage separator and sent to the downstream unit for processing. The liquid phase at the bottom of the second-stage separator is sent to the fractionation unit for processing.

[0034] In this embodiment, the first-stage circulating heat exchanger uses a shell-and-tube heat exchanger, and the cooling medium is low-temperature hot water from the refinery, with an inlet temperature of 20–90°C. The ratio of the volumetric flow rate of the first-stage circulating pump to the liquid phase volume in the mixed feed is 2–10, and the ratio of the volumetric flow rate of the second-stage circulating pump to the liquid phase volume in the mixed feed is 1.5–7. Due to the circulating pumps, the temperature difference within the first-stage hydrogenation reactor is no greater than 10°C, and the temperature difference within the second-stage hydrogenation reactor is no greater than 15°C. The reaction temperature in the first-stage hydrogenation reactor is 40–150°C, and the reaction pressure is 2.0–6.0 MPaG. The reaction temperature in the second-stage hydrogenation reactor is 200–400°C, and the reaction pressure is 2.0–6.0 MPaG.

[0035] The above are merely typical embodiments of the present invention. Those skilled in the art can make appropriate modifications and improvements based on them, but they are substantially the same as the present invention and also fall within the protection scope of the present invention.

Claims

1. A method for hydrogenating pyrolyzed naphtha, characterized in that... Includes the following steps: 1) After being pressurized, the cracked naphtha is mixed with hydrogen and then enters a first-stage hydrogenation reactor; 2) The top product of the first-stage hydrogenation reactor enters the first-stage separator for flash evaporation, and the bottom circulating oil of the first-stage hydrogenation reactor is returned to the first-stage hydrogenation reactor after being pressurized and heat-exchanged; 3) A first-stage product gas is generated at the top of the first-stage separator, and a first-stage reaction oil is generated at the bottom of the first-stage separator; the first-stage reaction oil is first mixed with hydrogen, then heated by heat exchange with the reaction product oil and then sent to the second-stage hydrogenation reactor. 4) The top product of the second-stage hydrogenation reactor enters the second-stage separator for flash evaporation, and the bottom circulating oil of the second-stage hydrogenation reactor is returned to the second-stage hydrogenation reactor after being pressurized. 5) Second-stage gas is generated at the top of the two-stage separator, and reaction oil is generated at the bottom of the two-stage separator; 6) The secondary product gas is first mixed with the primary product gas, then heat-exchanged with hydrogen before being sent to the downstream unit for processing; the reaction product oil is heat-exchanged with the primary reaction oil before being sent to the fractionation system for processing. The first-stage hydrogenation reactor is equipped with a circulating pump and a circulating heat exchanger at the bottom, and the second-stage hydrogenation reactor is equipped with two circulating pumps at the bottom. The ratio of the volumetric flow rate of the first-stage circulating pump to the liquid phase volumetric flow rate of the mixed feed in the first-stage hydrogenation reactor is 2 to 10, and the ratio of the volumetric flow rate of the second-stage circulating pump to the liquid phase volumetric flow rate of the mixed feed in the second-stage hydrogenation reactor is 1.5 to 7. The reaction temperature of the first-stage hydrogenation reactor is 40–150°C, the reaction pressure is 2.0–6.0 MPaG, and the temperature difference within the first-stage hydrogenation reactor is no greater than 10°C. The reaction temperature of the two-stage hydrogenation reactor is 200–400℃, the reaction pressure is 2.0–6.0 MPaG, and the temperature difference inside the two-stage hydrogenation reactor is no greater than 15℃. No circulating hydrogen compressor is installed in the process. Fresh hydrogen is pressurized by the hydrogen compressor and then supplied to the first-stage hydrogenation reactor and the second-stage hydrogenation reactor respectively.

2. The method for hydrogenating pyrolyzed naphtha according to claim 1, characterized in that: The first-stage hydrogenation reactor and the second-stage hydrogenation reactor are either fixed-bed reactors, fluidized-bed reactors, or slurry-bed reactors.

3. The method for hydrogenating pyrolyzed naphtha according to claim 1, characterized in that: Both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with top separators.

4. The method for hydrogenating pyrolyzed naphtha according to claim 1, characterized in that: Both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with feed distributors at the bottom.

5. The method for hydrogenating pyrolyzed naphtha according to claim 1, characterized in that: Both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with circulation cups. The liquid phase at the top of the first-stage hydrogenation reactor and the second-stage hydrogenation reactor flows to the inlet of the first-stage circulation pump and the second-stage circulation pump, respectively, through the circulation cups.

6. The method for hydrogenating pyrolyzed naphtha according to claim 1, characterized in that: The first-stage circulating heat exchanger is a shell-and-tube heat exchanger or a plate heat exchanger. The cooling medium for the first-stage circulating heat exchanger is low-temperature hot water or circulating cold water from the refinery, and the inlet temperature of the cooling medium is 20-90℃.

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