Post-treatment method and device for propylene oxide produced by HPPO method

Abstract

The application provides a post-treatment method and device for propylene oxide prepared by HPPO method, and relates to the technical field of chemical synthesis.The method comprises a stripping process, a propylene absorption process, a pre-separation process, a low-temperature recovery process and a propylene oxide absorption process; the stripping process, the propylene absorption process and the low-temperature recovery process are combined to improve the safety of process operation; meanwhile, the pressure energy in the first tail gas is converted into mechanical energy in the low-temperature recovery process, and then the mechanical energy drives a generator to generate electricity; the low-temperature circulating solvent is obtained through the condensation of the first tail gas and the heat coupling of the second tail gas, and the circulating solvent provides the absorbent for the recovery of propylene oxide in the subsequent low-pressure propylene gas phase stream; the pre-separation process, the low-temperature recovery process and the propylene oxide absorption process are combined to realize the effective recovery of propylene oxide and improve the process yield.The post-treatment device for propylene oxide prepared by HPPO method has simple operation process, high energy utilization efficiency, and remarkable environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, specifically to a post-processing method and apparatus for the HPPO process for producing propylene oxide. Background Technology

[0002] Propylene oxide (PO) is the third largest propylene derivative after polypropylene and acrylonitrile. Its main use is in the synthesis of polyether polyols, which are then used to manufacture polyurethane. In addition, propylene oxide is also a major raw material for the preparation of unsaturated polyester resins, nonionic surfactants, oilfield demulsifiers, plasticizers, flame retardants, lubricants and automotive brake fluids. It is widely used in chemical, light industry, pharmaceutical, food and textile fields and is an important organic chemical raw material.

[0003] The industrialized production processes for propylene oxide mainly include the chlorohydrin process, co-oxidation process, and direct hydrogen peroxide oxidation (HPPO). Among them, HPPO has advantages such as simple process, small environmental impact, mild reaction conditions, and high raw material utilization efficiency, and is gradually replacing the traditional propylene oxide production process.

[0004] Patent CN101693703A discloses an energy-saving and emission-reducing process for producing propylene oxide by epoxidation of propylene with hydrogen peroxide. Propylene and hydrogen peroxide undergo an epoxidation reaction under medium pressure and low temperature catalysis by titanium-silicon molecular sieves. The reaction products are separated from unreacted propylene in a propylene distillation column. The tail gas at the top of the propylene distillation column enters an absorption column, where the absorbent is part of the recycled solvent. The rich absorbent is returned to be mixed with the raw material. The gas phase of the absorption column enters a water washing column, from which a mixture of oxygen and water is obtained and discharged from the system.

[0005] Patent US2003109725A1 discloses an olefin epoxidation process in which propylene and hydrogen peroxide undergo an epoxidation reaction in a water-miscible organic solvent catalyzed by titanium-silicon molecular sieves. After the flammable components such as propylene are absorbed by a portion of the reaction tail gas using a recycled solvent, the remaining oxygen and inert gases are discharged together. The product stream is processed to provide a recycled solvent stream, part of which is used for the absorption of the reaction tail gas and part of which is recycled back to the reaction system.

[0006] In patent EP1293505A1, the product stream of the epoxidation reaction is first depressurized in a pressure release device and then enters a pre-evaporator. The stream at the top of the pre-evaporator is condensed and then enters a stripping tower. The gaseous stream at the top of the stripping tower, containing propylene oxide and light components such as propylene, is returned to the reaction system, and the liquid phase at the bottom is subsequently used for propylene oxide product purification.

[0007] In the above technical solutions, the pressure of the reaction tail gas obtained from the propylene oxide post-treatment is relatively high, and direct emission results in energy and material waste. At the same time, the low-pressure propylene gas phase stream containing propylene oxide generated by the product logistics processing unit must be compressed and distilled before being returned to the reaction system. During this process, high-temperature operation will cause the hydrolysis of propylene oxide contained in the low-pressure propylene gas phase stream, thereby increasing the loss of propylene oxide. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention discloses a post-processing method and apparatus for HPPO propylene oxide production, which can solve the problems of energy and material waste caused by high-pressure tail gas emissions in HPPO propylene oxide post-processing and propylene oxide loss during propylene refining.

[0009] To achieve the above technical objectives, one aspect of the present invention provides a post-processing method for producing propylene oxide via the HPPO process, the method comprising the following steps: Stripping process: The material after the HPPO process for producing propylene oxide is stripped to obtain the first gas phase and the first liquid phase material; Propylene absorption process: The propylene absorbent is brought into contact with the first gas phase to absorb the propylene in the first gas phase and obtain the first tail gas; Pre-separation process: The first liquid phase material is separated to obtain a low-pressure propylene gas phase stream, a circulating solvent, and crude propylene oxide for input into the subsequent propylene oxide refining process; Low-temperature recovery process: The first tail gas is expanded by an expander and then separated into gas and liquid to obtain the second tail gas and low-temperature solvent; the second tail gas is reheated and discharged after heat exchange with a portion of the circulating solvent in a cold box; Propylene oxide absorption process: The low-temperature solvent and the circulating solvent output from the cold box are used as propylene oxide absorbents to contact the low-pressure propylene gas phase stream to absorb the propylene oxide in the low-pressure propylene gas phase stream, thereby obtaining crude propylene for input into the subsequent propylene distillation and recovery process and a propylene oxide-rich phase for input into the pre-separation process or upstream reaction process.

[0010] To ensure the safety of the post-processing steps in the HPPO process for producing propylene oxide, a stripping step is included in the above technical solution. An inert gas is used as the stripping agent to remove oxygen generated from the decomposition of hydrogen peroxide in the reacted material, resulting in a first gas phase. Subsequently, a propylene absorption step is implemented to recover propylene from the first gas phase, yielding a first tail gas. The first tail gas obtained from the stripping and propylene absorption steps still has a high pressure. A low-temperature recovery step is implemented, allowing the first tail gas to expand and perform work, driving an electric motor to generate electricity, thereby recovering the tail gas energy. Simultaneously, during the expansion and work of the first tail gas, solvent condenses to obtain a low-temperature solvent, thus reducing solvent loss. Furthermore, the second tail gas obtained from the expansion and work can exchange heat with a portion of the circulating solvent in a cold box, and the cooled circulating solvent and low-temperature solvent can be used as propylene oxide absorbents in the subsequent propylene oxide absorption step. In other words, the post-processing method for producing propylene oxide using the HPPO process of this invention improves the safety of process operation by combining the stripping process, the propylene absorption process, and the low-temperature recovery process. At the same time, it converts the pressure energy in the first tail gas into mechanical energy to drive the generator to generate electricity. The low-temperature solvent is obtained through the condensation of the first tail gas and the thermal coupling of the second tail gas with the circulating solvent, providing an absorbent for the recovery of propylene oxide in the subsequent low-pressure propylene gas phase stream.

[0011] Furthermore, the low-pressure propylene gaseous stream still contains a certain amount of propylene oxide. Directly inputting it into the subsequent propylene distillation recovery process would result in propylene oxide loss. In this invention, the low-temperature solvent and the circulating solvent output from the cold box are used as propylene oxide absorbents to selectively absorb the propylene oxide contained in the low-pressure propylene gaseous stream, effectively reducing propylene oxide loss during subsequent separation. Therefore, the post-treatment method for propylene oxide production via the HPPO process of this invention achieves effective propylene oxide recovery and improves process yield by combining a pre-separation process, a low-temperature recovery process, and a propylene oxide absorption process. The embodiments of this invention show that the recovery rate of propylene oxide in the low-pressure propylene gaseous stream reaches over 99.0%.

[0012] In a further example of the present invention, the temperature and pressure of the first tail gas were explored and optimized. Optionally, the temperature of the first tail gas is 5~90°C, and the pressure is 1.2~4.0 MPaG. Controlling the temperature and pressure of the first tail gas is beneficial to improving the absorption and recovery effect of propylene in the first gas phase, and also beneficial to improving the pressure energy recovery efficiency of the subsequent low-temperature recovery process. In an optional example of the present invention, the temperature of the first tail gas is preferably 10~60°C; in an optional example of the present invention, the pressure of the first tail gas is preferably 1.5~3.5 MPaG. In an optional example of the present invention, the first tail gas may optionally include 60~95 ​​vol% nitrogen, 2~15 vol% oxygen, 0~5 vol% methanol, 0~5000 ppm water, and 0~1000 ppm propylene.

[0013] In a further example of the invention, the types of solvents were explored and optimized. Optionally, the solvent includes at least one of methanol, acetone, and tetrahydrofuran. In an optional example of the invention, the solvent is preferably methanol. It will be understood by those skilled in the art that the solvent is the solvent used in the HPPO reaction process, which can be separated from the reaction products in the post-processing steps and recycled.

[0014] In a further example of the invention, the propylene absorbent is a recycled solvent or a newly input solvent. The propylene absorbed by the propylene absorbent after stripping is obtained in the first gas phase, which facilitates the recycling of raw materials and reduces process costs. The propylene-rich phase obtained after propylene absorption can be recycled back to the upstream reaction process or the pre-separation process.

[0015] In a further example of the present invention, the temperature and pressure of the second tail gas after reheating were explored and optimized. Optionally, the temperature of the second tail gas after reheating is 0~25°C, and the pressure is 0~0.5 MPaG. Compared with the temperature and pressure of the first tail gas, it can be seen that the present invention recovers the pressure energy in the first tail gas, reducing process energy consumption. In an optional example of the present invention, the temperature of the second tail gas is preferably 5~15°C; in an optional example of the present invention, the pressure of the second tail gas is preferably 0.001~0.1 MPaG. In an optional example of the present invention, the second tail gas after reheating can be directly discharged into the atmosphere, which is environmentally friendly, or discharged into an incineration unit for incineration treatment.

[0016] In a further example of the invention, the number of expanders is multiple; the exhaust gas obtained after expansion and gas-liquid separation in the previous expander is reheated in a cold box and then fed into the next expander for further expansion. The exhaust gas is then expanded and separated in the final expander to obtain the second exhaust gas. Thus, the pressure energy in the first exhaust gas can be utilized step-by-step through multiple expanders connected in series, fully converting this energy into electrical energy. Furthermore, because the circulating solvent has a low freezing point, the technical solution of the invention uses a circulating solvent for cold energy recovery during the expansion process, avoiding the freezing blockage problem that may occur when using conventional steam reheating.

[0017] It should be noted that when multiple expanders are included, multiple gas-liquid separation components can be set accordingly to separate the material discharged from each expander into gas and liquid components. The low-temperature solvent obtained from multiple gas-liquid separation components can be combined and used as a propylene oxide absorbent for the propylene oxide absorption process, or it can be separately input into subsequent propylene oxide absorption processes, or it can be combined with the circulating solvent cooled in a cold box and then input into subsequent propylene oxide absorption processes. Those skilled in the art can choose according to their needs, and this does not limit the scope of protection of the present invention.

[0018] In a further example of the invention, the temperature of the propylene oxide absorbent was explored and optimized. Optionally, the temperature of the propylene oxide absorbent is 5~30°C. Embodiments of the invention demonstrate that within this temperature range, the propylene oxide absorbent can selectively absorb propylene oxide from the low-pressure propylene gas stream, thereby improving the overall yield of the HPPO process for producing propylene oxide. In an optional example of the invention, the temperature of the propylene oxide absorbent is preferably 10~25°C. Controlling the temperature of the propylene oxide absorbent within this range enhances process operability.

[0019] In a further example of the invention, the pressure of the low-pressure propylene gaseous stream was explored and optimized. Optionally, the pressure of the low-pressure propylene gaseous stream is 0~0.35 MPaG, preferably 0.01~0.1 MPaG. In an optional example of the invention, the low-pressure propylene gaseous stream may comprise 40~95 vol% propylene, 5~40 vol% propylene oxide, 0~20 vol% methanol, and 0~5 vol% water.

[0020] In a further example of the present invention, the control conditions for the propylene oxide absorption process were explored and optimized. Optionally, the operating pressure of the propylene oxide absorption process is 0~0.35 MPaG, preferably 0.01~0.1 MPaG. Further, the propylene oxide absorption process is carried out in a low-pressure propylene absorption tower, wherein the theoretical plate number of the low-pressure propylene absorption tower is 5~50, preferably 10~25.

[0021] It should be noted that the stripping agent in the stripping process can be an inert gas. The inert gas mentioned in this invention refers to a gas that does not chemically interact with the reactants, such as nitrogen, or a gas of a Group 0 element in the periodic table (such as argon).

[0022] It should be noted that the present invention does not limit the specific operation of the pre-separation process. Those skilled in the art can choose a process to preliminarily separate the reaction raw materials, solvent and target product in the first liquid phase as needed.

[0023] Another aspect of the present invention provides a post-processing apparatus for the HPPO process for producing propylene oxide, the apparatus comprising: Stripping tower: The feed port of the stripping tower is used to input the material after the reaction of HPPO to produce propylene oxide, the first discharge port is used to output the first gas phase obtained after stripping, and the second discharge port is used to output the first liquid phase material obtained after stripping. Propylene absorption tower: The first inlet of the propylene absorption tower is connected to the first outlet of the stripping tower, the second inlet of the propylene absorption tower is used to input propylene absorbent, and its outlet is used to output the first tail gas; Pre-separation unit: used to separate the first liquid phase material to obtain low-pressure propylene gas phase stream, circulating solvent, and crude propylene oxide product input to the subsequent propylene oxide refining process; The cryogenic recovery unit includes an expander, a gas-liquid separator, and a cold box. The inlet of the expander is used to input the first exhaust gas, and the outlet of the expander is connected to the gas-liquid separator. The gas phase outlet of the gas-liquid separator is connected to a discharge pipeline via a first heat exchange channel in the cold box for reheating, and the liquid phase outlet of the gas-liquid separator is used to output cryogenic solvent. The second heat exchange channel of the cold box is used to input circulating solvent that exchanges heat with the material in the first heat exchange channel. Propylene oxide absorption tower: The first inlet of the propylene oxide absorption tower is used to input the low-pressure propylene gaseous stream, and the second inlet is used to input the low-temperature solvent and the circulating solvent output from the second heat exchange channel of the cold box; the gaseous outlet of the propylene oxide absorption tower is used to output crude propylene, and the liquid outlet is used to output the propylene oxide-rich phase.

[0024] Furthermore, there are multiple expanders and gas-liquid separators; the outlet of the previous stage expander is connected to the gas-liquid separator, the gas phase outlet of the gas-liquid separator is connected to the inlet of the next stage expander via the heat exchange channel of the cold box for reheating, and the gas phase outlet of the last stage gas-liquid separator is connected to the discharge pipeline via the heat exchange channel of the cold box for reheating. It should be noted that the gas phase outlets of multiple gas-liquid separators are connected to different heat exchange channels in the cold box.

[0025] Furthermore, the above technical solution does not limit the structure of the expander. In an optional example of the present invention, the expander is a turbine expander or a screw expander. Optionally, the expander is connected to equipment such as a generator, an oil supply system, and a monitoring and control system, thereby converting pressure energy into mechanical energy, and further into electrical energy, to achieve energy recovery and reuse.

[0026] Furthermore, the above technical solution does not limit the structure of the gas-liquid separator. In optional examples of the present invention, the gas-liquid separator may be a wire mesh type, a high-efficiency separation blade type, or a swirl plate type, and is more preferably a high-efficiency separation blade type.

[0027] Furthermore, the above technical solutions do not limit the structure of the propylene oxide absorption tower. In optional examples of the present invention, the propylene oxide absorption tower is a packed tower or a plate tower; further, the first feed inlet of the propylene oxide absorption tower is located at the bottom and the second feed inlet is located at the top; further, a gas phase distributor is provided at the bottom of the propylene oxide absorption tower; further, a gas phase demister is provided at the top of the propylene oxide absorption tower; further, the theoretical number of plates in the propylene oxide absorption tower is 5~50, preferably 10~25.

[0028] Furthermore, the discharge pipeline is either a pipeline that directly discharges into the atmosphere or a pipeline that connects to the incineration unit, resulting in high environmental benefits for the entire device.

[0029] Furthermore, the liquid phase outlet of the propylene oxide absorption tower is connected to the upstream reaction process or the pre-separation unit, thereby achieving effective recovery of the low-pressure propylene gaseous stream propylene oxide.

[0030] Compared with existing technologies, the beneficial effects of this invention are as follows: The HPPO process for propylene oxide post-treatment improves process safety by combining stripping, propylene absorption, and cryogenic recovery processes. Simultaneously, the cryogenic recovery process converts the pressure energy in the first tail gas into mechanical energy, which drives a generator to produce electricity. A cryogenic circulating solvent is obtained through condensation of the first tail gas and thermal coupling with the second tail gas, providing an absorbent for the subsequent recovery of propylene oxide from the low-pressure propylene gas stream. The combination of pre-separation, cryogenic recovery, and propylene oxide absorption processes achieves effective propylene oxide recovery, improving process yield. The HPPO process propylene oxide post-treatment device of this invention has a simple operation process, high energy utilization efficiency, and significant environmental and economic benefits. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A structural diagram of a post-processing apparatus for producing propylene oxide using the HPPO method of the present invention is shown (for the sake of brevity, only the low-temperature recovery unit and the propylene oxide absorption process are shown in the diagram).

[0032] The above figures include the following reference numerals: 11-First-stage expander, 12-First-stage gas-liquid separator, 13-Second-stage expander, 14-Second-stage gas-liquid separator, 2-Cold box, 3-Generator, 4-Propylene oxide absorption tower. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0034] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0035] Example 1

[0036] A post-processing unit for propylene oxide production via the HPPO process. Figure 1 A structural diagram of the device is shown, which includes: Stripping tower: The feed port of the stripping tower is used to input the material after the reaction of HPPO to produce propylene oxide. The first discharge port is used to output the first gas phase obtained after stripping, and the second discharge port is used to output the first liquid phase material obtained after stripping.

[0037] Propylene absorption tower: The first inlet of the propylene absorption tower is connected to the first outlet of the stripping tower. The second inlet of the propylene absorption tower is used to input propylene absorbent, and its outlet is used to output the first tail gas.

[0038] Pre-separation unit: used to separate the first liquid phase material to obtain a low-pressure propylene gas phase stream, a circulating solvent, and crude propylene oxide to be fed into the subsequent propylene oxide refining process.

[0039] The cryogenic recovery unit includes an expander, a gas-liquid separator, and a cold box 2. The inlet of the expander is used to input the first tail gas, and the outlet of the expander is connected to the gas-liquid separator. The gas phase outlet of the gas-liquid separator is connected to the discharge pipeline through the first heat exchange channel in the cold box 2 for reheating, and the liquid phase outlet of the gas-liquid separator is used to output the cryogenic solvent. The second heat exchange channel of the cold box 2 is used to input the circulating solvent that exchanges heat with the material in the first heat exchange channel.

[0040] Propylene oxide absorption tower 4: The first inlet of propylene oxide absorption tower 4 is used to input low-pressure propylene gaseous stream, and the second inlet is used to input low-temperature solvent and circulating solvent output from the second heat exchange channel of cold box 2; the gaseous outlet of propylene oxide absorption tower 4 is used to output crude propylene, and the liquid outlet is used to output propylene oxide-rich phase.

[0041] It should be noted that the number of expanders and gas-liquid separators in the HPPO process propylene oxide post-treatment device of this invention can be multiple; wherein, the outlet of the previous stage expander is connected to the gas-liquid separator, the gas phase outlet of the gas-liquid separator is connected to the inlet of the next stage expander via a heat exchange channel for reheating in the cold box 2, and the gas phase outlet of the last stage gas-liquid separator is connected to the discharge pipeline via a heat exchange channel for reheating in the cold box 2. Figure 1 The diagram shows a structure comprising two expanders. The first exhaust gas is fed into the first-stage expander 11 for expansion and work, and then fed into the first-stage gas-liquid separator 12 for gas-liquid separation. The resulting exhaust gas is fed into the cold box 2 for reheating and then fed into the second-stage expander 13 for expansion and work, and then fed into the second-stage gas-liquid separator 14 for gas-liquid separation. The resulting exhaust gas is reheated in the cold box 2 and then fed into the incineration unit. The low-temperature solvents obtained from the two gas-liquid separations are combined and then combined with the low-temperature circulating solvent output from the cold box, and fed into the subsequent propylene oxide absorption tower as absorbent.

[0042] It should be noted that when multiple expanders are included, multiple gas-liquid separation components can be set accordingly to separate the gas and liquid of the material discharged from each expander; the gas phase outlets of multiple gas-liquid separators are connected to different heat exchange channels in the cold box 2.

[0043] Example 2

[0044] A post-processing method for producing propylene oxide via the HPPO process specifically includes the following steps: Stripping process: The material after the HPPO process for producing propylene oxide is stripped to obtain the first gas phase and the first liquid phase material; Propylene absorption process: The propylene absorbent is contacted with the first gas phase to absorb propylene from the first gas phase and obtain the first tail gas. The propylene absorbent is methanol. The flow rate of the first tail gas is 5915 kg / h, the temperature is 30℃, the pressure is 2.8 MPaG, and the composition is shown in Table 1.

[0045] Table 1

[0046] Pre-separation process: The first liquid phase material is separated to obtain a low-pressure propylene gaseous stream, a circulating solvent, and crude propylene oxide for subsequent propylene oxide refining processes. The composition of the low-pressure propylene gaseous stream is shown in Table 2.

[0047] Table 2

[0048] Cryogenic Recovery Process: The cryogenic recovery unit includes a two-stage expander. The first-stage exhaust gas enters a two-stage turbine expander system. The outlet temperature of the first-stage expander 11 is -28℃, and the outlet pressure is 0.8 MPaG. After passing through the first-stage gas-liquid separator 12, the cryogenic methanol liquid phase flow rate is 55 kg / h, and the gas phase flow rate is 5861 kg / h. The gas phase enters the cold box 2 for reheating to 10℃ before entering the second-stage expander 13. The outlet temperature of the second-stage expander 13 is -70℃, and the outlet pressure is 0.05 MPaG. After passing through the second-stage gas-liquid separator 14, the cryogenic methanol liquid phase flow rate is 4 kg / h, and the gas phase flow rate is 5857 kg / h. The gas phase enters the cold box 2 for reheating to 10℃ before being discharged into the incineration system. In addition, a portion of the recycled liquid methanol at a temperature of 30℃ and a flow rate of 20000 kg / h enters the cold box 2, and after recovering its cold energy, its temperature is 16℃.

[0049] In the cryogenic recovery unit, the expansion process drives generator 3 to generate electricity, and the total electricity recovered by the two stages is 244kW.

[0050] Propylene oxide absorption process: Liquid methanol after cold recovery, liquid methanol from the outlet of primary gas-liquid separator 12, and liquid methanol from the outlet of secondary gas-liquid separator 14 all enter propylene oxide absorption tower 4 as a low-temperature propylene oxide absorbent. The low-pressure propylene gaseous stream feed temperature is 38℃, pressure is 0.055 MPaG, and flow rate is 13122 kg / h. Propylene oxide absorption tower 4 is a packed tower with a theoretical plate count of 20 and a top pressure of 0.05 MPaG. The low-pressure propylene gaseous stream is fed from the bottom, distributed by a gas phase distributor, and then countercurrently absorbed with the propylene oxide absorbent fed from the top within the tower. The crude propylene output from the top of the tower has a flow rate of 10142 kg / h and a temperature of 50℃, and its composition is shown in Table 3.

[0051] Table 3

[0052] Referring to Tables 2 and 3, the recovery rate of propylene oxide contained in the low-pressure propylene gas stream reached 99.4%. In this embodiment, the crude propylene is sent to the subsequent propylene distillation and recovery process after being defoamed by a gas phase demister, while the bottom liquid stream is sent back to the reaction process or the pre-separation process.

[0053] Example 3 A post-treatment method for producing propylene oxide via the HPPO process is described. The specific process of this embodiment is the same as that of Embodiment 2, except that the flow rate of the first tail gas obtained in the propylene absorption process is 6258 kg / h, the temperature is 30°C, the pressure is 1.2 MPaG, and the composition is shown in Table 4.

[0054] Table 4

[0055] The cryogenic recovery unit in the cryogenic recovery process includes a two-stage expander. The first-stage exhaust gas enters a two-stage turbine expander system. The outlet temperature of the first-stage expander 11 is -13℃, and the outlet pressure is 0.35 MPaG. After passing through the first-stage gas-liquid separator 12, cryogenic methanol is separated into a liquid phase with a flow rate of 102 kg / h and a gas phase with a flow rate of 6156 kg / h. The gas phase enters the cold box 2 for reheating to 10℃ before entering the second-stage expander 13. The outlet temperature of the second-stage expander 13 is -41℃, and the outlet pressure is 0.05 MPaG. After passing through the second-stage gas-liquid separator 14, cryogenic methanol is separated into a liquid phase with a flow rate of 17 kg / h and a gas phase with a flow rate of 6139 kg / h. The gas phase enters the cold box 2 for reheating to 10℃ before being discharged into the incineration system. In addition, a portion of the recycled liquid methanol at a temperature of 30℃ and a flow rate of 20000 kg / h enters the cold box 2, where its temperature is reduced to 21℃ after recovering its cooling capacity.

[0056] In the cryogenic recovery unit, the expansion process drives generator 3 to generate electricity, and the total electricity recovered by the two stages is 204kW.

[0057] In the propylene oxide absorption process, the crude propylene output from the top of the propylene oxide absorption tower has a flow rate of 10346 kg / h and a temperature of 51℃. Its composition is shown in Table 5.

[0058] Table 5

[0059] The recovery rate of propylene oxide contained in the low-pressure propylene gas stream reached 99.35%.

[0060] Example 4 A post-treatment method for producing propylene oxide via the HPPO process is described. The specific process of this embodiment is the same as that of Embodiment 2, except that the flow rate of the first tail gas is 5594 kg / h, the temperature is 30°C, the pressure is 4.0 MPaG, and the composition is shown in Table 6.

[0061] Table 6

[0062] Cryogenic Recovery Process: The cryogenic recovery unit includes a three-stage expander. The first exhaust gas enters the three-stage turbine expander system. The outlet temperature of the first-stage expander 11 is -28℃, and the outlet pressure is 1.25 MPaG. After passing through the first-stage gas-liquid separator 12, the cryogenic methanol liquid phase flow rate is 39 kg / h, and the gas phase flow rate is 5554 kg / h. The gas phase enters the cold box 2 for reheating to 10℃ before entering the second-stage expander 13. The outlet temperature of the second-stage expander 13 is -44℃, and the outlet pressure is 0.35 MPaG. After passing through the second-stage gas-liquid separator 14, the cryogenic methanol liquid phase flow rate is 1 kg / h, and the gas phase flow rate is 5553 kg / h. The gas phase enters the cold box 2 for reheating to 10℃ before entering the third-stage expander 15. The outlet temperature of the third-stage expander 15 is -44℃, and the outlet pressure is 0.05 MPaG. There is no cryogenic methanol liquid phase, and the gas phase flow rate is 5554 kg / h. After entering the cold box 2 for reheating to 10℃, it is discharged into the incineration system. In addition, a portion of the recycled liquid methanol, at a temperature of 30°C and a flow rate of 20,000 kg / h, enters cold box 2, where the temperature is 13°C after the cold energy is recovered.

[0063] In the cryogenic recovery unit, the expansion process drives generator 3 to generate electricity, and the total electricity recovered by the three stages is 268kW.

[0064] The crude propylene output from the top of the propylene oxide absorption tower in the propylene oxide absorption process has a flow rate of 10051 kg / h and a temperature of 50℃. Its composition is shown in Table 7.

[0065] Table 7

[0066] Based on Tables 2 and 7, the recovery rate of propylene oxide contained in the low-pressure propylene gaseous stream reached 99.4%.

[0067] Example 5 A post-processing method for producing propylene oxide using the HPPO process is described in this embodiment. The specific process is the same as in Example 2, except that in the low-temperature recovery step, a portion of the recycled liquid methanol with a flow rate of 20,000 kg / h and a temperature of 21°C is further cooled to 5°C with chilled water. In the propylene oxide absorption step, the crude propylene output from the top of the propylene oxide absorption tower has a flow rate of 9,707 kg / h and a temperature of 48°C, and its composition is shown in Table 8.

[0068] Table 8

[0069] The recovery rate of propylene oxide contained in the low-pressure propylene gas stream reached 99.6%.

[0070] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A post-processing method for producing propylene oxide via the HPPO process, characterized in that, The process includes the following steps: Stripping process: The material after the HPPO process for producing propylene oxide is stripped to obtain the first gas phase and the first liquid phase material; Propylene absorption process: The propylene absorbent is brought into contact with the first gas phase to absorb the propylene in the first gas phase and obtain the first tail gas; Pre-separation process: The first liquid phase material is separated to obtain a low-pressure propylene gas phase stream, a circulating solvent, and crude propylene oxide for input into the subsequent propylene oxide refining process; Low-temperature recovery process: The first tail gas is expanded by an expander and then separated into gas and liquid to obtain the second tail gas and low-temperature solvent; the second tail gas is reheated and discharged after heat exchange with a portion of the circulating solvent in a cold box; Propylene oxide absorption process: The low-temperature solvent and the circulating solvent output from the cold box are used as propylene oxide absorbents to contact the low-pressure propylene gas phase stream to absorb the propylene oxide in the low-pressure propylene gas phase stream, thereby obtaining crude propylene for input into the subsequent propylene distillation and recovery process and a propylene oxide-rich phase for input into the pre-separation process or upstream reaction process.

2. The post-processing method for producing propylene oxide via the HPPO process according to claim 1, characterized in that, The temperature of the first exhaust gas is 5~90℃, preferably 10~60℃; the pressure of the first exhaust gas is 1.2~4.0MPaG, preferably 1.5~3.5MPaG.

3. The post-processing method for producing propylene oxide via the HPPO process according to claim 1, characterized in that, The solvent includes at least one of methanol, acetone, and tetrahydrofuran, preferably methanol; And / or, the propylene absorbent is a recycled solvent or a newly input solvent.

4. The post-processing method for producing propylene oxide via the HPPO process according to claim 1, characterized in that, The temperature of the second exhaust gas after reheating is 0~25℃, preferably 5~15℃; the pressure is 0~0.5MPaG, preferably 0.001~0.1MPaG.

5. The post-processing method for producing propylene oxide via the HPPO process according to claim 1, characterized in that, The number of expanders is multiple; the exhaust gas obtained after expansion and gas-liquid separation in the previous expander is reheated in a cold box and then fed into the next expander for expansion. After expansion and gas-liquid separation in the last expander, the second exhaust gas is obtained.

6. The post-processing method for producing propylene oxide via the HPPO process according to claim 1, characterized in that, The temperature of the propylene oxide absorbent is 5~30℃, preferably 10~25℃.

7. The post-processing method for producing propylene oxide via the HPPO process according to claim 1, characterized in that, The pressure of the low-pressure propylene gaseous stream is 0~0.35 MPaG, preferably 0.01~0.1 MPaG; And / or, the operating pressure of the propylene oxide absorption process is 0~0.35MPaG, preferably 0.01~0.1MPaG; Preferably, the propylene oxide absorption process is carried out in a low-pressure propylene absorption tower, wherein the theoretical plate number of the low-pressure propylene absorption tower is 5 to 50, preferably 10 to 25.

8. A post-processing apparatus for producing propylene oxide via the HPPO process, characterized in that, include: Stripping tower: The feed port of the stripping tower is used to input the material after the reaction of HPPO to produce propylene oxide, the first discharge port is used to output the first gas phase obtained after stripping, and the second discharge port is used to output the first liquid phase material obtained after stripping. Propylene absorption tower: The first inlet of the propylene absorption tower is connected to the first outlet of the stripping tower, the second inlet of the propylene absorption tower is used to input propylene absorbent, and its outlet is used to output the first tail gas; Pre-separation unit: used to separate the first liquid phase material to obtain low-pressure propylene gas phase stream, circulating solvent, and crude propylene oxide product input to the subsequent propylene oxide refining process; The cryogenic recovery unit includes an expander, a gas-liquid separator, and a cold box. The inlet of the expander is used to input the first exhaust gas, and the outlet of the expander is connected to the gas-liquid separator. The gas phase outlet of the gas-liquid separator is connected to a discharge pipeline via a first heat exchange channel in the cold box for reheating, and the liquid phase outlet of the gas-liquid separator is used to output cryogenic solvent. The second heat exchange channel of the cold box is used to input circulating solvent that exchanges heat with the material in the first heat exchange channel. Propylene oxide absorption tower: The first inlet of the propylene oxide absorption tower is used to input the low-pressure propylene gaseous stream, and the second inlet is used to input the low-temperature solvent and the circulating solvent output from the second heat exchange channel of the cold box; the gaseous outlet of the propylene oxide absorption tower is used to output crude propylene, and the liquid outlet is used to output the propylene oxide-rich phase.

9. The post-processing apparatus for HPPO propylene oxide production according to claim 8, characterized in that, The number of expanders and gas-liquid separators is multiple; the outlet of the previous stage expander is connected to the gas-liquid separator, the gas phase outlet of the gas-liquid separator is connected to the inlet of the next stage expander via the heat exchange channel of the cold box for reheating, and the gas phase outlet of the last stage gas-liquid separator is connected to the discharge pipeline via the heat exchange channel of the cold box for reheating.

10. The post-processing apparatus for producing propylene oxide via the HPPO process according to claim 8, characterized in that, The expander is a turbine expander or a screw expander; And / or, the discharge pipeline is a pipeline that discharges directly to the atmosphere or a pipeline connected to the incineration unit; And / or, the liquid phase outlet of the propylene oxide absorption tower is connected to the upstream reaction process or the pre-separation unit.

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