A method for recovering propylene from a propylene oxide plant by-product dichloropropane tail gas and a method for refining dichloropropane

Abstract

The application discloses a recovery method of propylene in a dichloropropane tail gas byproduct of an epoxypropane device and a dichloropropane refining method. The recovery method comprises the following steps: obtaining crude dichloropropane by preparing epoxypropane through a chlorohydrination method; separating the crude dichloropropane through a light component removal process and a rectification process to obtain dichloropropane products and propylene; and returning the propylene to a chlorohydrination reactor for preparing epoxypropane. The propylene recovery can reduce propylene raw material consumption of the epoxypropane device, reduce the amount of dichloropropane tail gas incineration treatment and CO2 emission.

Description

Technical Field

[0001] This invention belongs to the field of chlorohydrin process for preparing propylene oxide, and relates to the purification of the byproduct dichloropropane and the utilization of the tail gas propylene. Specifically, it relates to a method for recovering propylene from the tail gas of dichloropropane produced by a propylene oxide plant and a method for purifying dichloropropane. Background Technology

[0002] Currently, in the chlorohydrin process for propylene oxide production, the byproduct dichloropropane generates tail gas (volume concentration) containing approximately 60% propylene during refining. Existing technologies typically send this tail gas directly to an incineration system, resulting in significant waste of propylene feedstock. Industry statistics indicate that each ton of propylene oxide byproduct tail gas contains approximately 1.37 kg of propylene resources. Direct incineration not only increases carbon emissions but also leads to increased propylene consumption per ton of propylene oxide feedstock. This high-concentration propylene tail gas is generated by a specific process. In the calcium saponification process of chlorohydrin propylene oxide, a certain amount of 1,2-dichloropropane is generated during the chlorohydrinization step. The chlorohydrinization reactor is in a state of excess propylene, and some propylene enters the dichloropropane byproduct along with the dichloropropane.

[0003] The by-product dichloropropane has low purity and high content of impurities (propionaldehyde, chloropropanol, etc.), and cannot be directly used in downstream production facilities. It is generally sold off at a low price, which increases the production cost of downstream facilities. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for recovering propylene from the tail gas of dichloropropane, a byproduct of a propylene oxide plant, comprising the following steps: The crude dichloropropane obtained from the chlorohydrin process for preparing propylene oxide is separated into dichloropropane product and propylene through a light-light product removal process and a distillation process. The propylene is returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide. The crude dichloropropane contains propylene.

[0005] According to an embodiment of the present invention, the crude dichloropropane mainly contains impurities such as propionaldehyde, chloropropanol, dichloroisopropyl ether, and water. By mass percentage, the purity of dichloropropane is ≥80% (e.g., 80~85%), propionaldehyde ≤3.5%, chloropropanol ≤1.7%, water ≤0.28%, dichloroisopropyl ether ≤4%, and 0 < propylene ≤0.8%.

[0006] According to an embodiment of the present invention, the propylene is pressurized and then returned to the chlorohydrin reactor used in the chlorohydrin process for the preparation of propylene oxide. Further, the pressure ratio of the propylene after pressurization to that before pressurization is 5 to 20, for example 7 to 15, with exemplary values ​​of 7, 8, 9, 10, 11, 12, 13, 14, and 15.

[0007] According to an embodiment of the present invention, propylene pressurization is achieved using a gas compressor.

[0008] According to an embodiment of the present invention, the propylene is derived from a light-light removal process and / or a distillation process.

[0009] According to an embodiment of the present invention, the propylene separated in the light-light removal process is obtained by the following method: the crude dichloropropane enters the light-light removal tower and is separated to obtain a first gas phase and a first liquid phase. The first gas phase is condensed to obtain propylene, and the propylene (preferably after pressurization) is returned to the chlorohydrin reactor used in the chlorohydrin process to prepare propylene oxide.

[0010] According to an embodiment of the present invention, the operating parameters of the light-light removal tower include: the light-light removal tower is a sieve plate tower with 50 to 70 (e.g., 60) trays, the kettle temperature is controlled at 100 to 130°C, the top temperature is controlled at 70 to 90°C, and the top pressure is controlled at a slightly positive pressure.

[0011] According to an embodiment of the present invention, the pressure of the propylene separated in the light-light removal process does not exceed 15 kPa, for example, 10-15 kPa, and is increased to 170 kPa.

[0012] According to an embodiment of the present invention, the propylene separated in the distillation process is obtained by the following method: the first liquid phase enters a distillation column and is separated to obtain a second gas phase; the second gas phase is condensed to obtain propylene, and the propylene (preferably after pressurization) is returned to the chlorohydrin reactor used in the chlorohydrin process to prepare propylene oxide.

[0013] According to an embodiment of the present invention, the pressure of the propylene separated in the distillation process is no more than 15 kPa, for example 10-15 kPa, and is increased to 170 kPa.

[0014] According to an embodiment of the present invention, the operating parameters of the distillation column include: a top temperature of 80~120℃, a bottom temperature of 100~150℃, a top pressure controlled at a slightly positive pressure, and a bottom liquid level controlled at 20%~80%.

[0015] According to an embodiment of the present invention, the propylene oxide device is equipment used in the chlorohydrin-calcium saponification process for propylene oxide.

[0016] The present invention also provides the application of the above-described propylene recovery method in the purification of dichloropropane.

[0017] The present invention also provides a method for purifying dichloropropane, including the above-mentioned method for recovering propylene.

[0018] According to an embodiment of the present invention, the purification method of dichloropropane includes the following steps: The crude dichloropropane obtained from the chlorohydrin process for preparing propylene oxide is separated into dichloropropane product and propylene through a light-light removal process, a distillation process and a dehydration process. The propylene is returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide. Preferably, the propylene is derived from a light-light product removal process and / or a distillation process; Preferably, the propylene is pressurized and returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide.

[0019] According to an embodiment of the present invention, the crude dichloropropane, the light-light product removal process, the distillation process, the pressurization process, etc., are all as defined above.

[0020] The present invention also provides a method for producing propylene oxide by chlorohydrin reaction, including the above-mentioned method for purifying dichloropropane.

[0021] Beneficial effects After the tail gas from the dichloropropane refining unit is sent to the propylene oxide unit, CO2 emissions and tail gas incineration are reduced. Propylene in the tail gas can be recycled and reused in the main reaction of propylene oxide, which can effectively reduce the propylene feedstock consumption of the propylene oxide unit. The annual propylene recovery is about 250t, which reduces the unit consumption of propylene oxide products from the chlorohydrin method and calcium saponification method by about 1.37kg / tPO. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a dichloropropane purification apparatus. Figure label: 1-Dichloropropane buffer tank, 11-Dichloropropane feed pump; 2-Light weight removal tower, 21-First condenser, 22-First reflux tank, 23-First reflux pump, 24-First bottom pump, 25-First reboiler; 3-Distillation column, 31-Second condenser, 32-Second reflux tank, 33-Second reflux pump, 34-Second bottom pump, 35-Second reboiler; 4-Dehydration tower, 41-Third condenser, 42-Third reflux tank, 43-Third reflux pump, 44-Third bottom pump, 45-Third reboiler; 5-Gas compressor, 6-Chlorohydrin reactor, 7-Heavy component receiving tank, 8-Dichloropropane storage tank. Detailed Implementation

[0023] Methods for purifying dichloropropane The purification method for dichloropropane includes the following steps: The crude dichloropropane obtained from the chlorohydrin process for preparing propylene oxide is separated into dichloropropane product and propylene through a light-light removal process, a distillation process, and a dehydration process. The propylene is then returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide.

[0024] According to an embodiment of the present invention, the light-light removal process includes: crude dichloropropane entering a light-light removal tower, separating to obtain a first gas phase and a first liquid phase, the first liquid phase entering a distillation process, the first gas phase being condensed to obtain propylene and a first condensate, the propylene (preferably after pressurization) being returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide, and the first condensate being refluxed to the light-light removal tower.

[0025] According to an embodiment of the present invention, the operating parameters of the light-light removal tower include: the light-light removal tower is a sieve plate tower with 60 plates, the bottom temperature is controlled at 100~130℃, the top temperature is controlled at 70~90℃, and the top pressure is controlled at a slightly positive pressure.

[0026] According to an embodiment of the present invention, the first gas phase condensation temperature is ≤40℃.

[0027] According to an embodiment of the present invention, the light-weight removal process is carried out in the following apparatus: a light-weight removal tower, a first condenser, a first reflux tank, and a first reflux pump; The material inlet of the first condenser is connected to the top of the light-weight removal tower, the liquid phase outlet of the first condenser is connected to the material inlet of the first reflux tank, the material outlet of the first reflux tank is connected to the material inlet of the first reflux pump, and the material outlet of the first reflux pump is connected to the light-weight removal tower.

[0028] According to an embodiment of the present invention, the pressure of the propylene separated in the light-light removal process does not exceed 15 kPa, and is pressurized to 170 kPa before being returned to the chlorohydrin reactor used in the chlorohydrin process for the preparation of propylene oxide.

[0029] According to an embodiment of the present invention, the distillation process includes: the first liquid phase enters a distillation column and is separated to obtain a second gas phase; the second gas phase is condensed to obtain propylene and a second condensate; the propylene (preferably after pressurization) is returned to the chlorohydrin reactor used in the chlorohydrin process to prepare propylene oxide; a portion of the second condensate enters a dehydration process; and another portion of the second condensate is refluxed back to the distillation column.

[0030] According to an embodiment of the present invention, the first liquid phase enters a distillation column and is further separated to obtain a second liquid phase, which is then collected, for example, into a heavy component receiving tank.

[0031] According to an embodiment of the present invention, the operating parameters of the distillation column include: a top temperature of 80~120℃, a bottom temperature of 100~150℃, a top pressure controlled at a slightly positive pressure, and a bottom liquid level controlled at 20~80%.

[0032] According to an embodiment of the present invention, the second vapor-phase condensation temperature is ≤50°C.

[0033] According to an embodiment of the present invention, the pressure of the propylene separated in the distillation process does not exceed 15 kPa, and is pressurized to 170 kPa before being returned to the chlorohydrin reactor used in the chlorohydrin process for the preparation of propylene oxide.

[0034] According to an embodiment of the present invention, the dehydration process includes: the second condensate enters a dehydration tower, and is separated to obtain a third gas phase and a third liquid phase; the third liquid phase enters a dichloropropane storage tank; the third gas phase is condensed and refluxed, with a portion returned to the dehydration tower and a portion returned to the light-light removal process (e.g., returned to the first reflux tank).

[0035] According to an embodiment of the present invention, the dehydration process is carried out in the following apparatus: a dehydration tower, a third condenser, a third reflux tank, and a third reflux pump; The material inlet of the third condenser is connected to the top of the dehydration tower, the liquid phase outlet of the third condenser is connected to the material inlet of the third reflux tank, the material outlet of the third reflux tank is connected to the material inlet of the third reflux pump, and the material outlet of the third reflux pump is provided with two branches, one branch is connected to the dehydration tower, and the other branch is connected to the light-light removal process (preferably the first reflux tank).

[0036] According to an embodiment of the present invention, the operating parameters of the dehydration tower include: the dehydration tower is a packed tower, the bottom temperature is controlled at 90~130℃, the top temperature is controlled at 80~100℃, and the top pressure is controlled at a slightly positive pressure.

[0037] According to an embodiment of the present invention, the third gas-phase condensation temperature is ≤60℃. According to an embodiment of the present invention, the propylene pressurization is achieved using a gas compressor.

[0038] [Dichloropropane purification equipment] The purification unit for dichloropropane includes: a dichloropropane buffer tank, a light precipitator removal unit, a distillation unit, and a dehydration unit; The dichloropropane buffer tank is used to store crude dichloropropane obtained from the preparation of propylene oxide by the chlorohydrin method. The gas phase outlet of the light-light removal unit and the gas phase outlet of the distillation unit are respectively connected to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide.

[0039] According to an embodiment of the present invention, the dichloropropane refining apparatus further includes a gas compressor disposed on the connecting pipeline between the gas phase outlet of the light-light-removal unit and the chlorohydrin reactor used for the preparation of propylene oxide by the chlorohydrin method, and / or, the gas phase outlet of the distillation unit is respectively connected to the connecting pipeline between the chlorohydrin reactor used for the preparation of propylene oxide by the chlorohydrin method.

[0040] According to an embodiment of the present invention, the liquid phase outlet of the light-light removal unit is connected to the material inlet of the distillation unit, and the vapor phase condensate outlet of the distillation unit is connected to the material inlet of the dehydration unit; further, the vapor phase condensate outlet of the dehydration unit is connected to the light-light removal unit.

[0041] According to an embodiment of the present invention, the light-light removal unit includes: a light-light removal tower, a first condenser, a first reflux tank, and a first reflux pump; The material inlet of the first condenser is connected to the top of the light-weight removal tower, the liquid phase outlet of the first condenser is connected to the material inlet of the first reflux tank, the material outlet of the first reflux tank is connected to the material inlet of the first reflux pump, and the material outlet of the first reflux pump is connected to the light-weight removal tower.

[0042] According to an embodiment of the present invention, the distillation unit includes: a distillation column, a second condenser, a second reflux tank, and a second reflux pump; The material inlet of the second condenser is connected to the top of the distillation column, the liquid outlet of the second condenser is connected to the material inlet of the second reflux tank, the material outlet of the second reflux tank is connected to the material inlet of the second reflux pump, and the material outlet of the second reflux pump is provided with two branches, one branch is connected to the distillation column, and the other branch is connected to the dehydration process (preferably the dehydration tower).

[0043] According to an embodiment of the present invention, the dehydration unit includes: a dehydration tower, a third condenser, a third reflux tank, and a third reflux pump; The material inlet of the third condenser is connected to the top of the dehydration tower, the liquid phase outlet of the third condenser is connected to the material inlet of the third reflux tank, the material outlet of the third reflux tank is connected to the material inlet of the third reflux pump, and the material outlet of the third reflux pump is provided with two branches, one branch is connected to the dehydration tower, and the other branch is connected to the light-light removal process (preferably the first reflux tank).

[0044] According to an embodiment of the present invention, the liquid outlet of the light-light removal tower is connected to the material inlet of the distillation tower, and the vapor condensate outlet of the distillation tower is connected to the material inlet of the dehydration tower; further, the vapor condensate outlet of the dehydration tower is connected to the first reflux tank.

[0045] According to an embodiment of the present invention, the dichloropropane refining apparatus further includes a heavy component receiving tank connected to the liquid phase outlet of a distillation unit (distillation column).

[0046] According to an embodiment of the present invention, the dichloropropane refining apparatus further includes a dichloropropane storage tank connected to the liquid phase outlet of the dehydration unit (dehydration tower).

[0047] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0048] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0049] like Figure 1 The dichloropropane refining apparatus shown includes: a dichloropropane buffer tank 1, a light component removal unit, a distillation unit, a dehydration unit, a gas compressor 5, a chlorohydrin reactor 6, a heavy component receiving tank 7, and a dichloropropane storage tank 8.

[0050] Dichloropropane buffer tank 1 is used to store crude dichloropropane obtained from the preparation of propylene oxide by the chlorohydrin method.

[0051] The light-light ... The dichloropropane buffer tank 1 is connected to the material inlet of the light-light removal tower 2. The material inlet of the first condenser 21 is connected to the top of the light-light removal tower 2. The liquid phase outlet of the first condenser 21 is connected to the material inlet of the first reflux tank 22. The gas phase outlet of the first condenser 21 is connected to the chlorohydrin reactor 6 via the gas compressor 5. The material outlet of the first reflux tank 22 is connected to the material inlet of the first reflux pump 23. The material outlet of the first reflux pump 23 is connected to the light-light removal tower 2. The bottom of the light-light-removal tower 2 is equipped with a first reboiler 25, and the liquid phase outlet of the light-light-removal tower 2 enters the distillation tower 3 of the distillation unit via the first bottom pump 24.

[0052] The distillation unit includes: a distillation column 3, a second condenser 31, a second reflux tank 32, a second reflux pump 33, a second bottom pump 34, and a second reboiler 35; The material inlet of the second condenser 31 is connected to the top of the distillation column 3, the liquid outlet of the second condenser 31 is connected to the material inlet of the second reflux tank 32, the gas outlet of the second condenser 31 is connected to the chlorohydrin reactor 6 via the gas compressor 5, the material outlet of the second reflux tank 32 is connected to the material inlet of the second reflux pump 33, and the material outlet of the second reflux pump 33 is provided with two branches, one branch is connected to the distillation column 3, and the other branch is connected to the dehydration tower 4 of the dehydration process; The bottom of distillation column 3 is equipped with a second reboiler 35, and the liquid phase outlet of distillation column 3 enters the heavy component receiving tank 7 via the second bottom pump 34.

[0053] The dehydration unit includes: a dehydration tower 4, a third condenser 41, a third reflux tank 42, a third reflux pump 43, and a third bottom pump 44; The material inlet of the third condenser 41 is connected to the top of the dehydration tower 4, the liquid phase outlet of the third condenser 41 is connected to the material inlet of the third reflux tank 42, the material outlet of the third reflux tank 42 is connected to the material inlet of the third reflux pump 43, and the material outlet of the third reflux pump 43 is provided with two branches, one branch is connected to the dehydration tower 4, and the other branch is connected to the first reflux tank 22.

[0054] The liquid phase outlet of the light phase removal tower 4 is connected to the dichloropropane storage tank 8 via the third bottom pump 44.

[0055] Process description: Crude dichloropropane (6 m³ / h, by mass percentage, with dichloropropane purity of 80%-85%, propionaldehyde ≤3.5%, chloropropanol content ≤1.7%, water content ≤0.28%, dichloroisopropyl ether ≤4%, and 0 < propylene ≤0.8%) enters the light component removal tower to remove light components, water, and dichloropropane azeotropes from the feedstock. The gaseous phase separated product is discharged from the top of the tower and condensed (≤40℃) in the top condenser before entering the reflux tank. The dichloropropane in the lower part of the liquid in the reflux tank is returned to the top of the light component removal tower by a reflux pump. The bottom material of the light component removal tower is pumped to the distillation tower for further distillation to remove heavy components, yielding purified dichloropropane (≥99.95%). Refined dichloropropane, after being condensed (≤50℃) at the top of the distillation column, enters the distillation column reflux tank. The refined dichloropropane in the reflux tank is partially returned to the top of the distillation column by the distillation column reflux pump, and partially pumped to the subsequent dehydration column for further water removal. The heavy components from the bottom of the distillation column are transported to the heavy component storage tank. The light component content in the refined dichloropropane obtained from the bottom of the dehydration column is further reduced and sent to the dichloropropane storage tank. The top material is pumped by the dehydration column reflux pump to the light component removal reflux tank for the recovery of some light components. The vapor phase from the top of the light component removal column and the distillation column (pressure controlled at ≤15KPa) is sent to the propylene oxide unit's circulating gas compressor (compressed to 170KPa), and then re-enters the chlorohydrin reactor to react with hypochlorous acid, thereby achieving further recovery of propylene from the tail gas.

[0056] Table 1 Core Control Parameters

[0057] As a distillation tower that further improves the quality of raw materials, the dehydration tower returns the distilled light components to the dehydration tower for material recovery.

[0058] Before the modification, propylene dissolved in dichloropropane left the system along with byproducts and was incinerated, resulting in a waste of raw propylene.

[0059] After the upgrade, the addition of a dichloropropane refining process allows for the separation of the byproduct dichloropropane from propylene. This results in two advantages: firstly, refined dichloropropane with a purity of ≥99.95%, increasing the product's added value; and secondly, the propylene in the dichloropropane can be distilled off and recovered (20 Nm³ of propylene recovered per hour), then reintroduced into the propylene oxide unit's circulating gas compressor, pressurized, and fed into the chlorohydrin reactor, improving propylene utilization. Propylene recovery reduces propylene feedstock consumption in the propylene oxide unit and decreases incineration. After the upgrade, the annual propylene recovery is approximately 250 tons, and the propylene consumption per ton of propylene oxide is reduced by approximately 1.37 kg / tPO.

[0060] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering propylene from dichloropropane tail gas, a byproduct of a propylene oxide plant, characterized in that, The recycling method includes the following steps: The crude dichloropropane obtained from the chlorohydrin process for preparing propylene oxide is separated into dichloropropane product and propylene through a light-light product removal process and a distillation process. The propylene is returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide. The crude dichloropropane contains propylene.

2. The recycling method according to claim 1, characterized in that, By mass percentage, the crude dichloropropane contains ≥80% (e.g., 80-85%) dichloropropane, ≤3.5% propionaldehyde, ≤1.7% chloropropanol, ≤0.28% water, ≤4% dichloroisopropyl ether, and 0 < propylene ≤0.8%.

3. The recycling method according to claim 1, characterized in that, The propylene is pressurized and returned to the chlorohydrin reactor used in the chlorohydrin process to prepare propylene oxide. Preferably, the pressure ratio of propylene after pressurization to that before pressurization is 5 to 20.

4. The recycling method according to claim 1, characterized in that, The propylene is derived from a light-light removal process and / or a distillation process.

5. The recycling method according to claim 1, characterized in that, The propylene separated in the light-light removal process is obtained by the following method: the crude dichloropropane enters the light-light removal tower and is separated into a first gas phase and a first liquid phase. The first gas phase is condensed to obtain propylene, and the propylene (preferably after pressurization) is returned to the chlorohydrin reactor used in the chlorohydrin process to prepare propylene oxide. Preferably, the operating parameters of the light-light removal tower include: the light-light removal tower is a sieve tray tower with 50 to 70 trays, the bottom temperature is controlled at 100 to 130°C, the top temperature is controlled at 70 to 90°C, and the top pressure is controlled at a slightly positive pressure; Preferably, the pressure of the propylene separated in the light propylene removal process does not exceed 15 kPa, and is increased to 170 kPa.

6. The recycling method according to claim 1, characterized in that, The propylene separated in the distillation process is obtained by the following method: the first liquid phase enters the distillation column and is separated to obtain the second gas phase; the second gas phase is condensed to obtain propylene, and the propylene (preferably after pressurization) is returned to the chlorohydrin reactor used in the chlorohydrin process to produce propylene oxide; Preferably, the pressure of the propylene separated in the distillation process is no more than 15 kPa, and is increased to 170 kPa. Preferably, the operating parameters of the distillation column include: a top temperature of 80~120℃, a bottom temperature of 100~150℃, a top pressure controlled at a slightly positive pressure, and a bottom liquid level controlled at 20%~80%.

7. The application of the propylene recovery method according to any one of claims 1 to 6 in the purification of dichloropropane.

8. A method for purifying dichloropropane, characterized in that, The refining method includes the propylene recovery method according to any one of claims 1 to 6.

9. The refining method according to claim 8, characterized in that, The purification method for dichloropropane includes the following steps: The crude dichloropropane obtained from the chlorohydrin process for preparing propylene oxide is separated into dichloropropane product and propylene through a light-light removal process, a distillation process and a dehydration process. The propylene is returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide. Preferably, the propylene is derived from a light-light product removal process and / or a distillation process; Preferably, the propylene is pressurized and returned to the chlorohydrin reactor used in the chlorohydrin process for preparing propylene oxide.

10. A method for producing propylene oxide by chlorohydrin reaction, comprising the purification method of dichloropropane as described in claim 8 or 9.

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