A method of treating oligomers in a mother liquor

Abstract

The application discloses a method for treating oligomers in mother liquor, which utilizes a first front mother liquor tank and a second front mother liquor tank, combines with the limited amount of solvent removed in the low-pressure flash evaporation and deep flash evaporation process, realizes effective separation of the oligomers in the mother liquor, can carry out efficient recovery of the solvent twice, solves the problems of the oligomers blocking the container, the heat exchanger, the pump and the pipeline and the like in the solvent recovery system, and achieves good technical application effect; moreover, the method has the advantages of less equipment investment, low production cost, easy implementation, simple operation process, saved manpower, safety and environmental protection, and suitability for the oligomer treatment system of the polyolefin industry, pilot test and small test test device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer separation technology, in particular to a method for treating oligomers in mother liquor. BACKGROUND

[0002] The slurry process high-density polyethylene production process has become the mainstream process for producing high-density polyethylene because of its early industrialization time and mature process technology. The reaction pressure and temperature of the slurry process are relatively mild, the polymerization process is easy to control, the device runs smoothly, and the quality and performance of the produced polyethylene product are good, which is widely used in injection molding, hollow blow molding and film product market and shows good performance.

[0003] The low-pressure slurry process high-density polyethylene process uses straight-chain alkanes as solvents, and the polyethylene powder generated in the reactor is suspended in the solvent to form a slurry. The slurry is separated by centrifugation to separate the mother liquor (containing oligomeric polyethylene wax) and polyethylene powder. The mother liquor then enters the solvent refining system, and after evaporation, rectification and adsorption purification to remove impurities such as oligomers, water and acidic substances in the mother liquor, the refined solvent becomes a refined solvent, and the refined solvent is recycled to the polymerization system. The slurry process polyethylene is limited by the process and operating conditions, and in actual production, in addition to the high molecular weight polyethylene target product, a certain amount of polyethylene oligomers is also produced. The molecular weight of these oligomers is usually less than 10,000, and due to the relatively low molecular weight and small particle size, it is difficult to separate them from the mother liquor (solvent containing oligomers) by centrifugal separation, so the mother liquor usually contains a large amount of oligomers, and these oligomers are also the main by-products generated during the polymerization process. The separation of oligomers is achieved by sending the mother liquor from the mother liquor refining system to the oligomer recovery unit to separate the solvent and oligomers. When the amount of oligomers is large or the block is more, the accumulation of the precipitated oligomers can cause blockage of equipment, heat exchangers and pipelines, etc. Therefore, the normal discharge of oligomers is an important factor in determining the stable production of the device.

[0004] The technical solution for separating and recovering oligomers in industrial production devices is to transport the wax-containing mother liquor in the centrifugal separation system of the mother liquor storage tank to the oligomer separation and solvent recovery system by a slurry pump. The mother liquor is heated to about 80℃ by a preheater and then enters the hot siphon evaporation separation system composed of a hexane mother liquor separation tank and a mother liquor evaporator. In this system, the solvent is evaporated and separated from the polyethylene oligomers, and the separated oligomers are discharged from the bottom of the mother liquor evaporator to the oligomer treatment system. However, when the amount of oligomers is large, it can cause blockage of the discharge pipeline and equipment at the bottom of the mother liquor evaporator, which can further cause the entire device to be unable to operate continuously and stably.

[0005] The journal article "Analysis of operating capacity of hexane recovery system in low pressure polyethylene plant" discloses a process for recovering solvent from low polymer: the stream containing low polymer and hexane enters a low pressure flash tank, the hexane and low polymer are separated by flash evaporation, the gas phase stream containing solvent hexane is obtained at the top of the flash tank after evaporation, which enters the subsequent solvent refining unit; the liquid phase stream is obtained at the bottom of the tank, which mainly contains low polymer and a small amount of hexane. The low pressure flash tank bottom stream is pumped to a low low pressure flash tank for flash evaporation, and the hexane evaporated is condensed by a low low pressure flash tank condenser and then enters a condensate receiving tank. The low polymer and part of the solvent hexane at the bottom of the low low pressure flash tank are pumped into a deactivator, a large amount of hot nitrogen is sent to strip the solvent hexane in the low polymer, and a small amount of low pressure steam can be blown to deactivate the residual catalyst if necessary. The low polymer at the bottom of the deactivator tank directly enters the low polymer treatment unit, and the gas phase at the top of the tank enters the vent gas condenser after alkali washing for further recovery of hexane. The condensate enters the hydrocarbon separation tank for oil-water separation. The oil phase and hexane in the condensate receiving tank are combined and sent to the solvent refining unit, and the water phase is discharged as oily sewage to the sewage treatment unit. This method adds water vapor and a large amount of hot nitrogen, which increases the subsequent treatment section, and has problems such as long process flow, high equipment investment, and complex operating conditions.

[0006] Chinese patent document CN102585284B discloses a method for recovering solvent from low polymer, which condenses most of the evaporated gas solvent after low pressure flash operation and enters the solvent refining unit for refining; the low polymer and residual solvent enter the low pressure deactivation flash evaporator, water vapor is added to deactivate the catalyst in the low polymer and strip the solvent, the obtained low polymer enters the low polymer treatment unit, the oil phase obtained after condensation and oil-water separation of the hydrocarbon separator of the stripped gas phase component is sent to the solvent refining unit, and the water phase is sent to the sewage treatment unit. This method cancels the low low pressure flash tank, condensate receiving tank and alkali injection system at the top of the deactivator in the process flow reported in the journal article, simplifies the process and reduces equipment investment, but the oil phase and water phase containing solvent still need subsequent treatment units, and the method is not ideal for treating and recovering mother liquor containing a large amount of low polymer.

[0007] Chinese patent document CN111494976B discloses a device for removing diluent in a slurry method polyethylene process. The first stripping section inlet A02 is connected to low-pressure steam, and the second stripping section inlet B02 is connected to a mixed gas of inert gas and low-pressure steam. The polyethylene material containing solvent enters the fluidized stripping tank through the feed port. The stripping tank comprises two stripping units. In the first stripping unit, the solvent on the surface and in the gap of the polyethylene particles is stripped by low-pressure steam. In the second stripping unit, the solvent in the micropore channel of the polyethylene particles is removed by using one or any combination of nitrogen, carbon dioxide and carbon monoxide gas. The operation is carried out in a fluidized state, which improves the heat and mass transfer efficiency and improves the stripping quality. However, this method is only suitable for separating high molecular weight polyethylene material and solvent, and cannot separate oligomers present in the solvent. The presence of oligomers reduces the relative molecular mass of the polyethylene product and increases the melt index, which seriously reduces the mechanical properties of the polyethylene product. SUMMARY

[0008] The present application aims to provide a method for treating oligomers in mother liquor. The mother liquor after centrifugal separation (before entering the solvent recovery system) is the object of treatment. By adding a first pre-mother liquor tank and a second pre-mother liquor tank, and controlling the removal rate of solvent in the first pre-mother liquor tank, the oligomers contained in the mother liquor after centrifugal separation can be separated. Even if the amount of oligomers in the mother liquor is large and the block is more, the phenomenon of container, heat exchanger and pipeline blockage in the mother liquor recovery system can be avoided, and multiple low-pressure flash and stripping operations do not need to be added. The process is simplified, the equipment investment is reduced, the energy consumption is low, and it meets the HSE safety and environmental protection requirements. The solvent recovery rate can reach 90% to 99.9%. Under the conditions of reducing cost, safety and environmental protection, the continuous and stable operation of the device is ensured.

[0009] To achieve the above-mentioned purpose, the present application provides a method for treating oligomers in mother liquor. The treatment device used comprises a first pre-mother liquor tank and a second pre-mother liquor tank.

[0010] The body of the first pre-mother liquor tank is provided with a liquid phase inlet, a gas phase outlet and a mother liquor outlet.

[0011] The body of the second pre-mother liquor tank is provided with a solvent inlet, a material inlet, a circulation outlet and an oligomer outlet.

[0012] The circulation outlet of the second pre-mother liquor tank and the untreated mother liquor are respectively communicated with the liquid phase inlet of the first pre-mother liquor tank through a circulation pipeline and a mother liquor feed pipeline. The mother liquor outlet of the first pre-mother liquor tank is communicated with the material inlet of the second pre-mother liquor tank through a connecting pipeline. The gas phase outlet of the first pre-mother liquor tank is communicated with the mother liquor storage tank through a transmission pipeline provided with a cooling device.

[0013] The method for treating oligomers in mother liquor comprises the following steps:

[0014] (1) The untreated mother liquor enters the first pre-mother liquor tank through the liquid inlet for low pressure flash evaporation, the obtained gas phase enters the mother liquor storage tank after being cooled by the cooling device, and the residual liquid phase enters the second pre-mother liquor tank through the mother liquor outlet and the material inlet, and the oligomers are precipitated by cooling, and the solvent removal rate of the low pressure flash evaporation is controlled to be 95% to 97% (based on the total amount of the solvent in the first pre-mother liquor tank);

[0015] (2) The liquid in the second pre-mother liquor tank enters the first pre-mother liquor tank through the circulation outlet and the liquid inlet for deep flash evaporation, the obtained gas phase enters the mother liquor storage tank after being cooled by the cooling device, and the residual liquid phase enters the second pre-mother liquor tank through the mother liquor outlet and the material inlet, and the oligomers are precipitated by cooling, and the solvent removal rate of the deep flash evaporation is controlled to be 99% to 99.9% (based on the total amount of the solvent in the first pre-mother liquor tank);

[0016] (3) Hexane is added through the solvent inlet to dissolve the oligomers precipitated in the second pre-mother liquor tank, and then the oligomers are discharged through the oligomer outlet;

[0017] Wherein, the steps in the whole treatment process are continuously carried out without interruption.

[0018] The untreated mother liquor refers to the remaining liquid (mother liquor) after the slurry obtained after the polymerization reaction in any existing process for preparing high molecular weight polyethylene by the slurry method is centrifuged to separate the polyethylene powder.

[0019] Optionally, in the method for treating oligomers in mother liquor provided by the application, the positions of the outlets and inlets in the first pre-mother liquor tank are not limited, as long as the implementation of the above scheme can be met. The liquid inlet and the gas outlet are both arranged at the top of the first pre-mother liquor tank, and the mother liquor outlet is arranged at the bottom of the first pre-mother liquor tank.

[0020] Optionally, in the method for treating oligomers in mother liquor provided by the application, the positions of the outlets and inlets in the second pre-mother liquor tank are not limited, as long as the implementation of the above scheme can be met. The solvent inlet and the material inlet are both arranged at the top of the second pre-mother liquor tank, the circulation outlet is arranged on the side wall of the second pre-mother liquor tank, and the oligomer outlet is arranged at the bottom of the second pre-mother liquor tank.

[0021] Optionally, in the method for treating oligomers in mother liquor provided by the present application, the temperature and pressure of the low-pressure flash evaporation in the first pre-mother liquor tank are not particularly limited, and can be adjusted according to the components in the mother liquor, and the solvent removal rate of the low-pressure flash evaporation is controlled to be 95% to 97%.

[0022] Optionally, in the method for treating oligomers in mother liquor provided by the present application, in step (2), the temperature for precipitating oligomers is not particularly limited, and more than 99.5% of the oligomers can be precipitated, and the temperature for precipitating oligomers is recommended to be 0 to 20°C, preferably 5 to 10°C.

[0023] Optionally, in the method for treating oligomers in mother liquor provided by the present application, the temperature and pressure of the deep flash evaporation in the first pre-mother liquor tank are not particularly limited, and can be adjusted according to the components in the mother liquor and the temperature and pressure of the low-pressure flash evaporation, and the solvent removal rate of the deep flash evaporation is controlled to be 99% to 99.9%.

[0024] Optionally, in the method for treating oligomers in mother liquor provided by the present application, in order to more conveniently control the nodes of each step and ensure the safety of the whole process, a liquid level meter and a safety valve are respectively arranged on the first pre-mother liquor tank, the second pre-mother liquor tank and the mother liquor storage tank; preferably, in step (1), the liquid level of the first pre-mother liquor tank during the low-pressure flash evaporation is controlled to be 20% to 80%, more preferably 30% to 50%.

[0025] Optionally, in the method for treating oligomers in mother liquor provided by the present application, in step (2), when the liquid level of the second pre-mother liquor tank is 10% to 50%, preferably 20% to 30%, the liquid in the second pre-mother liquor tank is circulated to the first pre-mother liquor tank for deep flash evaporation.

[0026] Optionally, in the method for treating oligomers in mother liquor provided by the present application, the liquid level of the mother liquor storage tank is controlled to be 40% to 80%, preferably 50% to 70%.

[0027] Optionally, in the method for treating oligomers in mother liquor provided by the present application, the temperature of the mother liquor storage tank is 25 to 60°C, preferably 30 to 50°C.

[0028] Optionally, in the method for treating oligomers in mother liquor provided by the application, the temperature in the first pre-mother liquor tank, the second pre-mother liquor tank and the mother liquor storage tank can be controlled in a conventional manner in the industry, such as a jacketed temperature control layer can be arranged on the outer wall of the first pre-mother liquor tank, the second pre-mother liquor tank and the mother liquor storage tank, the jacketed temperature control layer is filled with temperature control water flow, and the jacketed temperature control layer is circularly connected with an external water source through a pipeline.

[0029] Optionally, in the method for treating oligomers in mother liquor provided by the application, the jacketed temperature control layer on the outer wall of the first pre-mother liquor tank and the second pre-mother liquor tank is a conical shell structure with an upper inlet and a lower outlet.

[0030] The jacketed temperature control cavity on the outer wall of the mother liquor storage tank is a cylindrical shell structure with a lower inlet and an upper outlet.

[0031] Optionally, in the method for treating oligomers in mother liquor provided by the application, a corresponding control valve group and related accessories can be arranged on each pipeline and equipment in the treatment device in a conventional manner, such as a flow controller and a delivery pump are arranged on the mother liquor feeding pipeline.

[0032] A pneumatic regulating valve is arranged on the connecting pipeline.

[0033] A pressure regulating valve is arranged on the transmission pipeline between the gas phase outlet and the cooling device.

[0034] A circulating delivery pump is arranged on the circulating pipeline.

[0035] A delivery pump is arranged on the outlet pipeline at the bottom of the mother liquor storage tank, and the like.

[0036] The delivery pump and the circulating delivery pump can be one or a combination of centrifugal pumps, diaphragm pumps, gear pumps and shield pumps, which can be adjusted according to actual conditions.

[0037] Optionally, in the method for treating oligomers in mother liquor provided by the application, in a general existing slurry method for preparing high molecular weight polyethylene, the untreated mother liquor obtained includes a gas phase component (a solvent), monomer ethylene, a comonomer, hydrogen and oligomers, and other unavoidable impurities, etc., wherein the comonomer includes at least one of propylene, 1-butene and 1-hexene, and the solvent is any one of propane, isobutane, isopentane and hexane.

[0038] Optionally, in the method for treating oligomers in mother liquor provided by the present application, the cooling device on the transmission pipeline can be any conventional device that can cool the gaseous phase material discharged from the gas phase outlet of the first pre-mother liquor tank into liquid, and is not specifically limited, such as a cooler with a circulating water inlet at the lower part of the shell and a circulating water outlet at the upper part, and a temperature control valve arranged on the pipeline between the circulating water inlet and the circulating water outlet.

[0039] Optionally, in the method for treating oligomers in mother liquor provided by the present application, the entire oligomer treatment process can be controlled by a DCS distributed control system, including temperature, liquid level, and pressure, etc.

[0040] In the method for treating oligomers in mother liquor provided by the present application, the untreated mother liquor after centrifugal separation is pumped into the first pre-mother liquor tank, and then the solvent, monomer, comonomer, and hydrogen in the mother liquor are flashed by heating, and most of the gaseous phase components after cooling by the cooling device enter the mother liquor storage tank. The liquid phase components remaining in the first pre-mother liquor tank enter the second pre-mother liquor tank, and the oligomers in the mother liquor are precipitated by reducing the temperature of the second pre-mother liquor tank. The mother liquor with oligomer content below 2wt% is cooled and stored in the second pre-mother liquor tank after being separated from the precipitated oligomers. When the mother liquor in the second pre-mother liquor tank accumulates to a certain liquid level, the upper liquid in the second pre-mother liquor tank is pumped and recycled into the first pre-mother liquor tank for deep flashing. After continuous treatment of the mother liquor by this process, when the oligomer content in the second pre-mother liquor tank accumulates to a certain level, hexane is added to the second pre-mother liquor tank and the temperature is raised to dissolve the oligomers in hexane, and then the oligomers are discharged from the second pre-mother liquor tank and enter the oligomer treatment system. The flashed solvent is cooled and enters the mother liquor storage tank, and is treated in the subsequent solvent refining unit and then recycled.

[0041] The oligomers are treated by the oligomer treatment method of the application before the mother liquor after centrifugal separation enters the solvent recovery system, compared with the existing oligomer separation technology, without adding multi-stage low-pressure flash evaporation and stripping operation, the process is simplified, the equipment investment is reduced, the energy consumption is low, and the HSE safety environmental protection requirements are met. The oligomers contained in the mother liquor after centrifugal separation are separated out, the phenomenon of container, heat exchanger and pipeline blockage in the mother liquor recovery system is avoided, the production cost is reduced, the manpower and material resources are saved, the device is ensured to run continuously and stably in the state of safety and environmental protection. In addition, the flash evaporated solvent contains uncooled gas phase components such as ethylene, hydrogen, propylene and 1-butene, which are separated by subsequent sections and then recycled into the polymerization reactor. Moreover, a small amount of catalyst remaining in the mother liquor does not need to be inactivated, because the slurry material after the reaction is first flashed into the flash tank, most of the solvent is removed after flashing, and the remaining material enters the polymer centrifugal separator to separate the target product, and the remaining material is the mother liquor to be treated. In the flash tank, most of the polymerization monomers ethylene, molecular weight regulator hydrogen, comonomer propylene and 1-butene are removed, which will not promote further polymerization, and the system after flashing does not have the conditions for polymerization.

[0042] Compared with the prior art, the application has the following advantages:

[0043] Beneficial effect 1: The method for treating oligomers in mother liquor provided by the application uses the first and second front mother liquor tanks, and limits the amount of solvent removed in the low-pressure flash evaporation and deep flash evaporation process, to achieve effective separation of oligomers in the mother liquor, while enabling efficient recovery of the solvent twice, solving the problem of oligomer blockage of containers, heat exchangers, pumps and pipelines in the solvent recovery system, and achieving good technical application effect; moreover, the device investment is small, the production cost is low, the method is easy to implement, the operation process is simple, manpower is saved, and it is safe and environmentally friendly, and is suitable for oligomer treatment systems of polyolefin industry, pilot and small-scale test devices.

[0044] Beneficial effect 2: The method for treating oligomers in mother liquor provided by the application avoids blocking the hot siphon type evaporation separation system composed of the mother liquor preheater and the mother liquor separation tank and the mother liquor evaporator by treating the oligomers in the mother liquor after centrifugal separation, which enables the oligomer separation and the solvent recovery system to run stably for a long time.

[0045] Beneficial effect 3: The method for treating oligomers in mother liquor provided by the application, the flash evaporated solvent is cooled and then enters the mother liquor storage tank, and is treated by the subsequent solvent refining unit and then recycled, which has the advantages of simple process, convenient operation, low energy and material consumption, and high solvent recovery rate (the solvent recovery rate can reach 90% to 99.9%). BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The structure diagram of a treatment device used in the method for treating oligomers in mother liquor provided by the present application is shown. DETAILED DESCRIPTION

[0047] The present application will be described in detail below by examples. It is necessary to point out here that the following examples are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above content of the present application.

[0048] In the description of the present application, it is necessary to point out that the orientation or positional relationship indicated by the terms "top", "bottom" and "side wall" and the like is based on the orientation or positional relationship shown in the drawings and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0049] In the description of the present application, it is necessary to point out that, unless otherwise explicitly specified and limited, the terms "communication" and "connection" should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0050] In view of the problems in the prior art that when the slurry is centrifugally separated into mother liquor (containing oligomer polyethylene) and polyethylene powder, the solvent in the mother liquor is recovered, when the oligomer therein is relatively large, it will be accumulated and precipitated, thereby causing the blockage of equipment, heat exchangers and pipelines and the like, and the problems of unstable normal production and the like. The method for treating oligomers in mother liquor provided by the present application digests, absorbs and innovates the existing slurry method oligomer treatment device and method, and on this basis, the present application adds a first front mother liquor tank and a second front mother liquor tank between the existing centrifugal separation device and the solvent refining system, combines the connection relationship of the two front mother liquor tanks to control the amount of solvent removed in the low-pressure flash evaporation and deep flash evaporation process, and designs a continuous and stable high-availability method for treating oligomers in mother liquor. In continuous high-load production, the running cycle of the hexane refining system is improved, the blockage frequency of the wax refining system heat exchanger is effectively reduced, the device running stability is improved, the number of shutdowns caused by the blockage of the solvent refining system is reduced, the long-term stable high-load operation of the device is ensured, a huge economic effect is brought to the enterprise, and important technical support is provided for the slurry method polyolefin production device.

[0051] To better illustrate the present invention, specific embodiments are described below, but these embodiments do not constitute a limitation of the present invention.

[0052] Example 1

[0053] This embodiment provides a method for treating oligomers in mother liquor, using a treatment device such as... Figure 1 As shown, the processing device includes a first pre-processing mother liquor tank, a second pre-processing mother liquor tank, a mother liquor cooler, and a mother liquor storage tank;

[0054] The first pre-treatment mother liquor tank has a liquid inlet and a gas outlet at the top and a mother liquor outlet at the bottom.

[0055] The second pre-treatment mother liquor tank has a solvent inlet and a material inlet at the top, a circulation outlet on the side wall, and an oligomer outlet at the bottom.

[0056] The circulation outlet of the second pre-processing mother liquor tank and the untreated mother liquor are connected to the liquid phase inlet of the first pre-processing mother liquor tank via circulation pipeline and mother liquor feed pipeline, respectively; the mother liquor outlet of the first pre-processing mother liquor tank is connected to the 100,000-ton material inlet of the second pre-processing mother liquor tank via connecting pipeline; the 100,000-ton gas phase outlet of the first pre-processing mother liquor tank is connected to the mother liquor storage tank via a transmission pipeline equipped with a cooling device (a mother liquor cooler is used in this embodiment).

[0057] Each of the first pre-treatment mother liquor tank, the second pre-treatment mother liquor tank, and the mother liquor storage tank is equipped with a level gauge and a safety valve. Each of these tanks has a jacketed temperature control layer on its outer wall for temperature control. The jacketed temperature control layer contains temperature-controlled water and is connected to an external water source via pipelines for circulation. Furthermore, the jacketed temperature control layers on the outer walls of the first and second pre-treatment mother liquor tanks are conical shell structures with an upper inlet and a lower outlet; the jacketed temperature control cavity on the outer wall of the mother liquor storage tank is a cylindrical shell structure with a lower inlet and an upper outlet.

[0058] Each piece of equipment is equipped with corresponding accessories on the connecting pipelines. Specifically, the mother liquor feed pipeline is equipped with a flow controller and a transfer pump; the connecting pipeline is equipped with a pneumatic regulating valve; the transmission pipeline between the gas phase outlet and the cooling device is equipped with a pressure regulating valve; the circulation pipeline is equipped with a circulation transfer pump; and the outlet pipeline at the bottom of the mother liquor storage tank is equipped with a transfer pump, etc.

[0059] The aforementioned transfer pumps and circulating transfer pumps can be one or a combination of centrifugal pumps, diaphragm pumps, gear pumps, canned motor pumps, etc., and the specific type can be adjusted according to the actual situation.

[0060] The entire oligomer processing device provided by this invention can be controlled by a DCS distributed control system during use, including the liquid level and pressure in each device.

[0061] The mother liquor obtained from the production of single-peak high-density polyethylene pipe material (density 0.965 g / cm 3 , melt index 0.8 g / 10 min) is used as the treatment object. Specifically, the polymerization monomer used in the process is ethylene, the comonomer is propylene, the molecular weight regulator is hydrogen, the catalyst is a Z-N titanium-based catalyst, and the solvent is hexane. The reactor outlet slurry is flashed into a flash tank, and the flashed slurry is pumped into a polymer centrifugal separator through the bottom of the flash tank. The remaining liquid phase components (i.e., the mother liquor) after separation of the target product are treated in the oligomer treatment device of the present application, which includes the following steps:

[0062] (1) The mother liquor after centrifugal separation without any treatment is metered by a flow meter and enters the first pre-mother liquor tank through the liquid phase inlet. The flow rate is set to 150 L / h. When the liquid level of the first pre-mother liquor tank is 10%, the temperature of the first pre-mother liquor tank is raised to about 85°C by the temperature control water system in the jacketed temperature control layer, and the liquid level of the first pre-mother liquor tank is controlled at 40%. The flash pressure of the pressure regulating valve is set to 0.1 MPa, and then low-pressure flashing is performed to control the solvent removal rate to be 95%-97%.

[0063] (2) The gas phase components obtained by low-pressure flashing are discharged through the gas phase outlet, cooled in the mother liquor cooler, and then stored in the mother liquor storage tank. After continuous flashing for 3 h, the discharge control valve between the mother liquor outlet at the bottom of the first pre-mother liquor tank and the material inlet of the second pre-mother liquor tank is opened, and the opening degree is set to 10%. The residual liquid phase after flashing is input into the second pre-mother liquor tank, and the temperature of the second pre-mother liquor tank is controlled at 5-10°C by the temperature control water system in the jacketed temperature control layer for oligomer precipitation treatment.

[0064] (3) When the liquid level of the second pre-mother liquor tank accumulates to 20%-30%, the circulating pump in the circulating pipeline is started to transport the liquid phase in the upper layer of the second pre-mother liquor tank to the first pre-mother liquor tank through the circulating outlet and the liquid phase inlet. Then, the temperature of the first pre-mother liquor tank is raised to 110°C by the temperature control water system in the jacketed temperature control layer, the pressure is reduced to 0.05 MPa for deep flashing, and the solvent removal rate is controlled to be 99%-99.9%.

[0065] (4) The gas phase components after deep flashing and cooling in the mother liquor cooler are stored in the mother liquor storage tank (the temperature of the mother liquor storage tank is controlled at about 30°C). When the liquid level of the mother liquor storage tank is 50%, it is pumped to the solvent recovery and refining unit for treatment. Hexane is added through the solvent inlet, and the temperature of the second pre-mother liquor tank is controlled at 80°C to dissolve the oligomers precipitated in the second pre-mother liquor tank, which is then discharged through the oligomer outlet and enters the oligomer recovery and treatment unit.

[0066] Example 2

[0067] The processing device used in this example is the same as that used in Example 1, and the processing object is the mother liquor obtained from the production of bimodal high-density polyethylene film products (density 0.945 g / cm 3 , melt index 2.8 g / 10 min). Specifically, the polymerization monomer used in the process is ethylene, the comonomer is 1-butene, the molecular weight regulator is hydrogen, the catalyst is a Z-N titanium-based catalyst, and the solvent is hexane. The slurry material at the reactor outlet is flashed into a flash tank, and the flashed slurry material is pumped into a polymer centrifugal separator through the bottom of the flash tank. The remaining liquid phase components (i.e., the mother liquor) after the separation of the target product are processed in the oligomer processing device of the present application. The specific steps are similar to those of Example 1, except that the control of some parameters in each step is different. See Table 1 for details.

[0068] Example 3

[0069] The processing device used in this example is the same as that used in Example 1, and the processing object is the same as that used in Example 1. The specific processing method is similar to that of Example 1, except that the control of some parameters in each step is different. See Table 1 for details.

[0070] Example 4

[0071] The processing device used in this example is the same as that used in Example 1, and the processing object is the same as that used in Example 2. The specific processing method is similar to that of Example 1, except that the control of some parameters in each step is different. See Table 1 for details.

[0072] Table 1

[0073]

[0074] The processing object (mother liquor after centrifugal separation without any treatment) and the cooling liquid in the mother liquor storage tank in each example were sampled, and then the oligomer content in each was detected using high-temperature gel permeation chromatography (GPC). The oligomer separated from the second pre-mother liquor tank was sampled, and the content of VOC (volatile organic compounds), hexane, ethylene, and comonomer in it was tested using gas chromatography. The specific results are shown in Table 2 below.

[0075] Table 2

[0076]

[0077]

[0078] From the data in the above table, by using the first pre-liquor tank and the second pre-liquor tank, combining with the amount of removing solvent in the limited low-pressure flash evaporation and deep flash evaporation process, the effective separation of oligomers in the mother liquor is realized, and at the same time, two times of efficient recovery of the solvent can be carried out, and the problems of oligomer blocking vessels, heat exchangers, pumps and pipelines in the solvent recovery system are solved. Moreover, the improvement of the operation cycle of the solvent recovery and refining system ensures the stability of the device operation, reduces the number of shutdowns of the device due to the blockage of the solvent recovery and refining system, and ensures the long-term stable high-load operation of the device.

[0079] Of course, the present application can also have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims of the present application.

Claims

1. A method for treating oligomers in mother liquor, characterized in that, The processing equipment used includes a first pre-treatment mother liquor tank and a second pre-treatment mother liquor tank; The first pre-treatment mother liquor tank is provided with a liquid phase inlet, a gas phase outlet and a mother liquor outlet on its main body; The second pre-treatment mother liquor tank is equipped with a solvent inlet, a material inlet, a circulation outlet, and an oligomer outlet. The circulation outlet and the untreated mother liquor are connected to the liquid phase inlet via circulation pipeline and mother liquor feed pipeline, respectively; the mother liquor outlet is connected to the material inlet via connecting pipeline; and the gas phase outlet is connected to the mother liquor storage tank via a transmission pipeline equipped with a cooling device. The method for treating oligomers in the mother liquor includes the following steps: (1) The untreated mother liquor enters the first pre-processing mother liquor tank through the liquid phase inlet and is subjected to low-pressure flash evaporation. The resulting gas phase is cooled by the cooling device and then enters the mother liquor storage tank. The residual liquid phase enters the second pre-processing mother liquor tank through the mother liquor outlet and the material inlet. The oligomers are precipitated by cooling, and the solvent removal rate of the low-pressure flash evaporation is controlled to be 95% to 97%. (2) The liquid in the second pre-processing mother liquor tank is introduced into the first pre-processing mother liquor tank through the circulation outlet and the liquid phase inlet for deep flash evaporation. The resulting gas phase is cooled by the cooling device and then enters the mother liquor storage tank. The remaining liquid phase is introduced into the second pre-processing mother liquor tank through the mother liquor outlet and the material inlet. The oligomers are precipitated by cooling, and the solvent removal rate of the deep flash evaporation is controlled to be 99% to 99.9%. (3) Hexane is added through the solvent inlet to dissolve the oligomers precipitated in the second pretreatment mother liquor tank, and then discharged through the oligomer outlet; The entire processing procedure is carried out continuously without interruption.

2. The method as described in claim 1, characterized in that, The liquid phase inlet and the gas phase outlet are both located at the top of the first pre-treatment mother liquor tank, and the mother liquor outlet is located at the bottom of the first pre-treatment mother liquor tank.

3. The method as described in claim 1, characterized in that, The solvent inlet and the material inlet are both located at the top of the second pre-treatment mother liquor tank, the circulation outlet is located on the side wall of the second pre-treatment mother liquor tank, and the oligomer outlet is located at the bottom of the second pre-treatment mother liquor tank.

4. The method as described in claim 1, characterized in that, The temperature of the low-pressure flash evaporation is 70~120℃.

5. The method as described in claim 1, characterized in that, The pressure of the low-pressure flash evaporation is 0.05~0.15MPa.

6. The method as described in claim 1, characterized in that, In step (2), the temperature at which oligomers precipitate is 0~20℃.

7. The method as described in claim 1, characterized in that, The temperature of the deep flash evaporation is 90~130℃.

8. The method as described in claim 1, characterized in that, The pressure of the deep flash evaporation is 0.01~0.1MPa.

9. The method as described in claim 1, characterized in that, The first pre-treatment mother liquor tank, the second pre-treatment mother liquor tank, and the mother liquor storage tank are respectively equipped with level gauges and safety valves.

10. The method as described in claim 9, characterized in that, In step (2), when the liquid level of the second pre-prepared mother liquor tank is 10%~50%, the liquid in the second pre-prepared mother liquor tank is circulated to the first pre-prepared mother liquor tank for deep flash evaporation.

11. The method as described in claim 9, characterized in that, The liquid level in the mother liquor storage tank is controlled between 40% and 80%.

12. The method as described in claim 1, characterized in that, The temperature of the mother liquor storage tank is 25~60℃.

13. The method as described in claim 1, characterized in that, The first pre-treatment mother liquor tank, the second pre-treatment mother liquor tank, and the mother liquor storage tank are all provided with a jacketed temperature control layer on their outer walls. The jacketed temperature control layer contains temperature-controlled water, and the jacketed temperature control layer is circulated to an external water source through pipelines.

14. The method as described in claim 13, characterized in that, The jacketed temperature control layer on the outer wall of the first pre-prepared mother liquor tank and the second pre-prepared mother liquor tank is a conical shell structure with an upper inlet and a lower outlet.

15. The method as described in claim 1, characterized in that, A flow controller is installed on the mother liquor feed pipeline.

16. The method as described in claim 4, characterized in that, The temperature of the low-pressure flash evaporation is 80~100℃.

17. The method as described in claim 5, characterized in that, The pressure of the low-pressure flash evaporation is 0.1 MPa.

18. The method as described in claim 6, characterized in that, In step (2), the temperature at which oligomers precipitate is 5~10℃.

19. The method as described in claim 7, characterized in that, The temperature of the deep flash evaporation is 100~120℃.

20. The method as described in claim 8, characterized in that, The pressure for deep flash evaporation is 0.05 MPa.

21. The method as described in claim 9, characterized in that, In step (1), the liquid level of the first pre-prepared mother liquor tank is controlled at 20%~80% during the low-pressure flash evaporation.

22. The method as described in claim 21, characterized in that, In step (1), the liquid level of the first pre-prepared mother liquor tank is controlled at 30%~50% during the low-pressure flash evaporation.

23. The method as described in claim 10, characterized in that, In step (2), when the liquid level of the second pre-prepared mother liquor tank is 20%~30%, the liquid in the second pre-prepared mother liquor tank is circulated to the first pre-prepared mother liquor tank for deep flash evaporation.

24. The method as described in claim 11, characterized in that, The liquid level in the mother liquor storage tank is controlled at 50%~70%.

25. The method as described in claim 12, characterized in that, The temperature of the mother liquor storage tank is 30~50℃.

26. The method as described in claim 13 or 14, characterized in that, The jacketed temperature control layer on the outer wall of the mother liquor storage tank is a cylindrical shell structure with a lower inlet and an upper outlet.

27. The method as described in claim 1 or 15, characterized in that, A pneumatic regulating valve is installed on the connecting pipeline.

28. The method as described in claim 1 or 15, characterized in that, A pressure regulating valve is installed on the transmission pipeline between the gas phase outlet and the cooling device.

29. The method as described in claim 1 or 15, characterized in that, The circulation pipeline is equipped with a circulation pump.

Images