A method for improving polyolefin screw devolatilization effect and its application

Abstract

The invention discloses a method and application of using dichloromethane as a stripping agent to improve the devolatilization effect of a polyolefin screw, wherein the method is to inject a dichloromethane solvent into a molten polyolefin in a devolatilization extruder, wherein the dichloromethane is uniformly dispersed under the mixing action of the screw, and liquid-liquid extraction occurs with the residual solvent in the polyolefin to form a low-boiling azeotrope, which is discharged in a vacuum section to achieve the purpose of deep devolatilization of the polyolefin product. The method of the invention has the advantages of simple process, low equipment requirements, low cost, wide applicability, high devolatilization efficiency, safety and stability, etc., and can be widely used in the field of deep devolatilization of polyolefin product screws, and has versatility and high efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of polyolefin material preparation, and particularly relates to a method for improving the devolatilization effect of a polyolefin screw by using dichloromethane as a stripping agent and an application thereof. Background Art

[0002] Polyolefin products are mostly produced by solution polymerization, and organic solvents are used in the production process. The residual organic solvents in the polyolefin products will have various adverse effects on the terminal applications of polyolefin products, especially their applications in high-end fields such as electronics, medical packaging and optical lenses. Therefore, reducing the residual solvents in polyolefin products has become an important link in improving the quality of polyolefin products.

[0003] In the production process of polyolefin products, deep screw devolatilization is the top priority for removing volatiles (solvents, monomers and low molecular weight products, etc.). The main factors affecting the deep devolatilization of screws include screw combination, threaded elements, vacuum, stripping agent and devolatilization process, among which the introduction of stripping agent is extremely important for improving the deep devolatilization effect. Traditional stripping agents are mainly ultrapure water, liquid carbon dioxide and liquid nitrogen. Although ultrapure water can improve the devolatilization effect to a certain extent, it has a high boiling point and poor compatibility with many organic solvents, making it difficult to significantly improve the deep devolatilization effect. Although liquid carbon dioxide and liquid nitrogen have a more obvious improvement in the devolatilization effect, they have high requirements for equipment, high cost and poor process stability. It can be seen that traditional stripping agents have many shortcomings and are difficult to meet the application needs of polyolefin products in high-end fields such as electronic and electrical, medical packaging and optical equipment, making the development of new screw deep stripping devolatilization processes of far-reaching significance. Summary of the invention

[0004] The invention aims at the deficiencies of the prior art and provides a method for improving the devolatilization effect of a polyolefin screw by using dichloromethane as a stripping agent.

[0005] Another object of the present invention is to provide application of this method in deep devolatilization of polyolefins.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for improving the devolatilization effect of a polyolefin screw comprises the steps of injecting dichloromethane as a stripping agent into molten polyolefin in a devolatilization extruder, uniformly dispersing the dichloromethane under the mixing action of the screw, liquid-liquid extraction with residual solvent in the polyolefin to form a low-boiling azeotrope with a boiling point of 40-70°C, and discharging the mixture in a vacuum section.

[0008] In a specific embodiment, the polyolefin is selected from one or more of cyclic olefin copolymer (COC), cyclic olefin polymer (COP), ethylene-α-olefin copolymer elastomer (POE), low density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene propylene diene monomer rubber (EPDM), and styrene-butadiene rubber (SBR); preferably, the α-olefin is selected from at least any one of butene, hexene, and octene.

[0009] In a specific embodiment, the residual solvent is an organic solvent, preferably one or more selected from n-hexane, cyclohexane, methylcyclohexane, toluene, and isoparaffins.

[0010] In a specific embodiment, the method comprises the following steps:

[0011] 1) Turn on the devolatilization extruder, set the host temperature, and after the temperature stabilizes, turn on the external vacuum system, set the system vacuum degree, and adjust the screw speed;

[0012] 2) low-pressure high-purity nitrogen is introduced into the nitrogen inlet of the devolatilization extruder, and the feeder is turned on to feed the polyolefin containing residual solvent into the twin-screw devolatilization extruder through the feed port;

[0013] 3) After the molten polyolefin fills the barrel, the dichloromethane solvent is injected into the molten polyolefin from the extruder additive feed port through a high-pressure plunger pump, and the dichloromethane and the residual solvent undergo liquid-liquid extraction to form a low-boiling azeotrope, which is discharged in the vacuum section.

[0014] In a specific embodiment, the main engine temperature of the devolatilization extruder in step 1) is 180-300°C, preferably 220-280°C.

[0015] In a specific embodiment, the vacuum degree of the vacuum system in step 1) is 1 mbar-100 mbar, preferably 1-50 mbar; the screw speed is 30-300 rpm, preferably 50-150 rpm.

[0016] In a specific embodiment, the mass content of the residual solvent in the polyolefin in step 2) is 0.1-5wt%, preferably 0.1-2wt%; preferably, the feed rate of the feeder is 0.5-10kg / h, preferably 1-5kg / h.

[0017] In a specific embodiment, the flow rate of the dichloromethane solvent injected by the high-pressure plunger pump in step 3) is 0.5-100 g / h, preferably 5-50 g / h.

[0018] In a specific embodiment, the process further comprises step 4) pulling the molten polyolefin strands after deep devolatilization by the screw to a pelletizer for pelletization to obtain ultra-low VOC polyolefin particles.

[0019] On the other hand, the aforementioned method for improving the polyolefin screw devolatilization effect is applied in the deep devolatilization of polyolefin.

[0020] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0021] (1) The method of using dichloromethane as a stripping agent to improve the devolatilization effect of a polyolefin screw can efficiently remove the residual solvent in the polyolefin, and has the advantages of simple process, low equipment requirements, low cost, wide applicability, high devolatilization efficiency, safety and stability. Among them, dichloromethane can undergo liquid-liquid extraction with the residual solvent in the polyolefin to form a low-boiling azeotrope, thereby achieving the purpose of efficiently removing the residual solvent.

[0022] (2) The present invention uses dichloromethane as the stripping agent. On the one hand, it has excellent compatibility with most organic solvents and a low boiling point, and can undergo liquid-liquid extraction to form a low-boiling azeotrope. On the other hand, dichloromethane is a non-flammable liquid, and the devolatilization process is safe and stable.

[0023] (3) The method of the present invention using dichloromethane as a stripping agent to improve the polyolefin screw devolatilization effect is suitable for removing a variety of polyolefin residual solvents, can be widely used in the field of polyolefin deep devolatilization, and has versatility and high efficiency. DETAILED DESCRIPTION

[0024] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0025] A method for improving the devolatilization effect of a polyolefin screw using dichloromethane as a stripping agent, wherein dichloromethane is used as a stripping agent and injected into the molten polyolefin in a devolatilization extruder, and the dichloromethane is uniformly dispersed under the mixing action of the screw, and liquid-liquid extraction occurs with the residual solvent in the polyolefin to form a low-boiling azeotrope, which is discharged in a vacuum section to achieve the purpose of efficiently removing the residual solvent. In the present invention, the low-boiling azeotrope refers to a low-boiling azeotrope with a boiling point of 40-70°C.

[0026] Wherein, the polyolefin includes but is not limited to one or more of cyclic olefin copolymer (COC), cyclic olefin polymer (COP), ethylene-α-olefin copolymer elastomer (POE), low density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene propylene diene monomer rubber (EPDM), and styrene-butadiene rubber (SBR); preferably, the α-olefin is selected from at least any one of butene, hexene, and octene.

[0027] The residual solvent is mostly an organic solvent, including but not limited to one or more of n-hexane, cyclohexane, methylcyclohexane, toluene, and isoparaffin solvents.

[0028] The devolatilization extruder is a conventional device in the art, usually a twin-screw extruder, including a vacuum section, and the vacuum section is provided with an exhaust port. The key to the present invention lies in process innovation, and there is no special requirement for the equipment.

[0029] Specifically, the aforementioned method of using dichloromethane as a stripping agent to improve the polyolefin screw devolatilization effect comprises the following steps:

[0030] 1) Turn on the devolatilization extruder, set the host temperature, and after the temperature stabilizes, turn on the external vacuum system, set the system vacuum degree, and adjust the screw speed;

[0031] 2) low-pressure high-purity nitrogen is introduced into the nitrogen inlet of the devolatilization extruder, and the feeder is turned on to feed the polyolefin containing residual solvent into the twin-screw extruder through the feed port;

[0032] 3) After the molten polyolefin fills the barrel, the dichloromethane solvent is injected into the molten polyolefin from the extruder additive feed port through a high-pressure plunger pump, and the dichloromethane and the residual solvent undergo liquid-liquid extraction to form a low-boiling azeotrope, which is discharged in the vacuum section;

[0033] 4) The molten polyolefin strands after deep devolatilization by the screw are pulled to a pelletizer for pelletization to obtain ultra-low VOC polyolefin particles.

[0034] In step 1), the main engine temperature of the devolatilizing extruder is 180-300°C, for example including but not limited to 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, preferably 220-280°C.

[0035] The external vacuum system enables the vacuum degree of the melt section system of the devolatilization extruder to reach 1 mbar-100 mbar, including but not limited to 1 mbar, 10 mbar, 20 mbar, 40 mbar, 60 mbar, 80 mbar, 100 mbar, preferably 1-50 mbar.

[0036] The screw speed of the twin-screw extruder is adjusted to 30-300 rpm, for example including but not limited to 30 rpm, 60 rpm, 80 rpm, 100 rpm, 120 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, preferably 50-150 rpm. At this screw speed, extrusion processing of molten polyolefin can be achieved.

[0037] In step 2), the residual solvent content of the polyolefin containing the residual solvent added to the feed port of the feeder is 0.1-5wt%, for example, including but not limited to 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, preferably 0.1-2wt%. The residual solvent is, for example, n-hexane.

[0038] The feeding rate of polyolefin through the feeding port of the feeder is 0.5-10kg / h, for example including but not limited to 0.5kg / h, 1kg / h, 2kg / h, 3kg / h, 4kg / h, 5kg / h, 6kg / h, 7kg / h, 8kg / h, 9kg / h, 10kg / h, preferably 1-5kg / h.

[0039] In step 3), after the molten polyolefin fills the barrel, a high-pressure plunger pump is used to inject dichloromethane solvent from the extruder auxiliary agent feed port, so that dichloromethane is directly added to the molten polyolefin, wherein the high-pressure plunger pump flow rate is 0.5-100g / h, for example, including but not limited to 0.5g / h, 1.5g / h, 3g / h, 5g / h, 10g / h, 20g / h, 30g / h, 40g / h, 50g / h, 80g / h, 100g / h, preferably 5-50g / h, more preferably 10-50g / h. The high-pressure plunger pump flow rate is the amount of dichloromethane solvent added, which is based on the feed amount of polyolefin, and the addition mass ratio of the two is 0.001-0.2, preferably 0.01-0.1.

[0040] The present invention also provides various applications of the method for improving the screw devolatilization effect of polyolefins by using dichloromethane as a stripping agent as described above. For example, the method for improving the screw devolatilization effect of polyolefin products by using dichloromethane as a stripping agent according to the present invention can be used for the efficient removal of residual solvents in cycloolefin polymers (COP), cycloolefin copolymers (COC), low-density polyethylene (LLDPE), ethylene-α-olefin (butene, hexene, octene) copolymer elastomers (POE), ethylene-vinyl acetate copolymers (EVA), ethylene propylene diene monomer rubber (EPDM), and styrene-butadiene rubber (SBR). The specific application method of the method of using a dichloromethane stripping agent to improve the screw devolatilization effect of a polyolefin product is as follows: the temperature of a devolatilization extruder is set to 180-300°C, the vacuum degree of a four-stage vacuum system is set to 1-100 mbar, the screw speed is set to 30-300 rpm, low-pressure high-purity nitrogen is introduced into the nitrogen inlet of the devolatilization extruder, polyolefin particles with a residual solvent content of 0.1-5wt% are added to the devolatilization extruder at a feed rate of 0.5-10 kg / h, and after the molten polyolefin fills the barrel, the dichloromethane solvent is injected into the molten polyolefin through a high-pressure plunger pump at a feed rate of 0.5-100 g / h, and the dichloromethane and the residual solvent undergo liquid-liquid extraction to form a low-boiling azeotrope with a boiling point of 40-70°C, which is discharged in the vacuum degree section. The molten polyolefin strands after the screw is deeply devolatilized are pulled to a pelletizer for granulation to obtain ultra-low VOC polyolefin particles.

[0041] The present invention is further described below by means of specific examples, but is not intended to be limiting in any way.

[0042] The main raw material sources of the present invention are as follows:

[0043] Dichloromethane, cyclohexane, methylcyclohexane, and toluene were purchased from Alfa Aesar Chemicals;

[0044] Cyclic olefin polymer (COP), cyclic olefin copolymer (COC), low-density polyethylene (LLDPE), ethylene-octene copolymer elastomer (POE), ethylene-vinyl acetate copolymer (EVA), ethylene propylene diene monomer rubber (EPDM), and styrene-butadiene rubber (SBR) are all purchased on behalf of Beijing Inokai Technology Co., Ltd.

[0045] Nitrogen was purchased from Air Liquide (Shanghai) Compressed Gas Co., Ltd.

[0046] The main equipment involved in the present invention is as follows:

[0047] Devolatilization twin-screw extruder: adopts Ruiya RXT26-58 four-stage vacuum unit.

[0048] High-pressure plunger pump: Use the SP0530 plunger pump produced by Shanghai Sanwei Scientific Instrument Co., Ltd.

[0049] Vacuum pump: VACUU PURE 9M3 / H screw pump from PRAND with a maximum vacuum degree of 0.005mbar.

[0050] The main testing methods involved in the present invention are as follows:

[0051] Solvent content: tested using Agilent 7697A headspace gas chromatograph.

[0052] The present invention relates to a method for preparing polyolefin particles having a solvent content of 0.1-2 wt % as follows:

[0053] (1) Preparation of cycloolefin copolymer (COC) particles: 5 kg of COC particles were uniformly dispersed in a stainless steel tray, and 280 g of cyclohexane solution was uniformly sprayed onto the surface of the COC particles using a spray bottle. The tray was sealed with plastic wrap and allowed to stand for 4 h. After the COC particles completely absorbed the cyclohexane solvent, the headspace analysis test showed that the cyclohexane content was 4.98 wt %, i.e., COC particles with a solvent content of 4.98 wt % were obtained.

[0054] (2) Preparation of cycloolefin polymer (COP) particles: 5 kg of COP particles were uniformly dispersed in a stainless steel tray, and 220 g of methylcyclohexane solution was uniformly sprayed onto the surface of the COP particles using a spray bottle. The tray was sealed with plastic wrap and allowed to stand for 4 h. After the COP particles completely absorbed the methylcyclohexane solvent, the headspace analysis test showed that the methylcyclohexane content was 4.08 wt%, i.e., COP particles with a solvent content of 4.08 wt% were obtained.

[0055] (3) Preparation of low-density polyethylene (LLDPE) particles: 5 kg of LLDPE particles were uniformly dispersed in a stainless steel tray, and 180 g of toluene solution was uniformly sprayed onto the surface of the LLDPE particles using a spray bottle. The tray was sealed with plastic wrap and allowed to stand for 4 h. After the LLDPE particles completely absorbed the toluene solvent, the toluene content was tested by headspace analysis to be 3.17 wt%, i.e., LLDPE particles with a solvent content of 3.17 wt% were obtained.

[0056] (4) Preparation of ethylene-octene copolymer elastomer (POE) particles:

[0057] Take 5kg of POE particles and evenly disperse them in a stainless steel tray. Use a spray bottle to evenly spray 120g of toluene solution onto the surface of the POE particles. Seal the tray with plastic wrap and let it stand for 4 hours. After the POE particles completely absorb the toluene solvent, the headspace analysis test shows that the toluene content is 2.10wt%, i.e., POE particles with a solvent content of 2.10wt% are obtained.

[0058] (5) Preparation of ethylene-vinyl acetate copolymer (EVA) particles:

[0059] 5 kg of EVA particles were evenly dispersed in a stainless steel tray, 80 g of toluene solution was evenly sprayed onto the surface of the EVA particles using a spray bottle, the tray was sealed with plastic wrap, and the mixture was allowed to stand for 4 h. After the EVA particles completely absorbed the toluene solvent, the toluene content was tested by headspace analysis to be 1.14 wt%, i.e., EVA particles with a solvent content of 1.14 wt% were obtained.

[0060] (6) Preparation of EPDM particles:

[0061] Take 5kg of EPDM particles and evenly disperse them in a stainless steel tray. Use a spray bottle to evenly spray 40g of toluene solution onto the surface of the EPDM particles. Seal the tray with plastic wrap and let it stand for 4 hours. After the EPDM particles completely absorb the toluene solvent, the headspace analysis test shows that the toluene content is 0.58wt%, i.e., EPDM particles with a solvent content of 0.58wt% are obtained.

[0062] (7) Preparation of styrene-butadiene rubber (SBR) particles:

[0063] 5 kg of SBR particles were evenly dispersed in a stainless steel tray, 10 g of toluene solution was evenly sprayed onto the surface of the SBR particles using a spray bottle, the tray was sealed with plastic wrap, and the mixture was allowed to stand for 4 h. After the SBR particles completely absorbed the toluene solvent, the toluene content was tested by headspace analysis to be 0.12 wt%, i.e., SBR particles with a solvent content of 0.12 wt% were obtained.

[0064] Example 1 COC screw deep devolatilization

[0065] The devolatilization extruder was turned on, the main engine temperature was set to 300°C, the vacuum degree of the four-stage vacuum system was set to 1 mbar, the screw speed was set to 30 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, and COC particles with a cyclohexane content of 4.98 wt% were added to the devolatilization extruder at a feed rate of 0.5 kg / h. After the molten COC filled the barrel, dichloromethane was injected into the molten COC through a high-pressure plunger pump at a feed rate of 0.5 g / h, and liquid-liquid extraction occurred with the residual cyclohexane solvent to form a low-boiling azeotrope, which was discharged in the vacuum section. Finally, the devolatilized COC was cut into strands to obtain COC particles after deep devolatilization. The cyclohexane and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0066] Example 2 COC screw deep devolatilization

[0067] The devolatilization extruder was turned on, the main engine temperature was set to 300°C, the vacuum degree of the four-stage vacuum system was set to 1 mbar, the screw speed was set to 30 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, and COC particles with a cyclohexane content of 4.98 wt% were added to the devolatilization extruder at a feed rate of 0.5 kg / h. After the molten COC filled the barrel, dichloromethane was injected into the molten COC through a high-pressure plunger pump at a feed rate of 50 g / h, and liquid-liquid extraction occurred with the residual cyclohexane solvent to form a low-boiling azeotrope, which was discharged in the vacuum section. Finally, the devolatilized COC was cut into strands to obtain COC particles after deep devolatilization. The cyclohexane and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0068] Example 3 COC screw deep devolatilization

[0069] The devolatilization extruder was turned on, the main engine temperature was set to 300°C, the vacuum degree of the four-stage vacuum system was set to 1 mbar, the screw speed was set to 30 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, and COC particles with a cyclohexane content of 4.98 wt% were added to the devolatilization extruder at a feed rate of 0.5 kg / h. After the molten COC filled the barrel, dichloromethane was injected into the molten COC through a high-pressure plunger pump at a feed rate of 100 g / h, and liquid-liquid extraction occurred with the residual cyclohexane solvent to form a low-boiling azeotrope, which was discharged in the vacuum section. Finally, the devolatilized COC was cut into strands to obtain COC particles after deep devolatilization. The cyclohexane and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0070] Example 4 COP screw deep devolatilization

[0071] The devolatilization extruder was turned on, the main engine temperature was set to 280°C, the vacuum degree of the four-stage vacuum system was set to 10 mbar, the screw speed was set to 80 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, COP particles with a methylcyclohexane content of 4.08 wt% were added to the devolatilization extruder at a feed rate of 1.5 kg / h, and after the molten COP filled the barrel, dichloromethane was injected into the molten COP through a high-pressure plunger pump at a feed rate of 20 g / h, and liquid-liquid extraction occurred with the residual methylcyclohexane solvent to form a low-boiling azeotrope, which was discharged in the vacuum section, and finally the devolatilized COP was cut into strips and pelletized to obtain COP particles after deep devolatilization, and the methylcyclohexane and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0072] Example 5 LLDPE screw deep devolatilization

[0073] The devolatilization extruder was turned on, the main engine temperature was set to 260°C, the vacuum degree of the four-stage vacuum system was set to 20 mbar, the screw speed was set to 120 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, and LLDPE particles with a toluene content of 3.17 wt% were added to the devolatilization extruder at a feed rate of 3 kg / h. After the molten LLDPE filled the barrel, dichloromethane was injected into the molten LLDPE through a high-pressure plunger pump at a feed rate of 30 g / h, and liquid-liquid extraction occurred with the residual toluene solvent to form a low-boiling azeotrope, which was discharged in the vacuum section. Finally, the devolatilized LLDPE was strip-cut and pelletized to obtain LLDPE particles after deep devolatilization. The toluene and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0074] Example 6 POE screw deep devolatilization

[0075] The devolatilization extruder was turned on, the main engine temperature was set to 240°C, the vacuum degree of the four-stage vacuum system was set to 40 mbar, the screw speed was set to 160 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, POE particles with a toluene content of 2.10 wt% were added to the devolatilization extruder at a feed rate of 5 kg / h, and after the molten POE filled the barrel, dichloromethane was injected into the molten POE through a high-pressure plunger pump at a feed rate of 50 g / h, and liquid-liquid extraction occurred with the residual toluene solvent to form a low-boiling azeotrope, which was discharged in the vacuum section, and finally the devolatilized POE strands were pelletized to obtain POE particles after deep devolatilization, and the toluene and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0076] Example 7 EVA screw deep devolatilization

[0077] The devolatilization extruder was turned on, the main engine temperature was set to 220°C, the vacuum degree of the four-stage vacuum system was set to 60 mbar, the screw speed was set to 200 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, EVA particles with a toluene content of 1.14 wt% were added to the devolatilization extruder at a feed rate of 6 kg / h, and after the molten EVA filled the barrel, dichloromethane was injected into the molten EVA through a high-pressure plunger pump at a feed rate of 70 g / h, and liquid-liquid extraction occurred with the residual toluene solvent to form a low-boiling azeotrope, which was discharged in the vacuum section, and finally the devolatilized EVA was cut into strips to obtain EVA particles after deep devolatilization, and the toluene and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0078] Example 8 EPDM screw deep devolatilization

[0079] The devolatilization extruder was turned on, the main engine temperature was set to 200°C, the vacuum degree of the four-stage vacuum system was set to 80 mbar, the screw speed was set to 250 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, EPDM particles with a toluene content of 0.58 wt% were added to the devolatilization extruder at a feed rate of 8 kg / h, and after the molten EPDM filled the barrel, dichloromethane was injected into the molten EPDM through a high-pressure plunger pump at a feed rate of 90 g / h, and liquid-liquid extraction occurred with the residual toluene solvent to form a low-boiling azeotrope, which was discharged in the vacuum section, and finally the devolatilized EPDM was cut into strips and pelletized to obtain deeply devolatilized EPDM particles, and the toluene and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0080] Example 9 SBR screw deep devolatilization

[0081] The devolatilization extruder was turned on, the main engine temperature was set to 180°C, the vacuum degree of the four-stage vacuum system was set to 100 mbar, the screw speed was set to 300 rpm, low-pressure high-purity nitrogen was introduced into the nitrogen inlet of the devolatilization extruder, SBR particles with a toluene content of 0.12 wt% were added to the devolatilization extruder at a feed rate of 10 kg / h, and after the molten SBR filled the barrel, dichloromethane was injected into the molten SBR through a high-pressure plunger pump at a feed rate of 100 g / h, and liquid-liquid extraction occurred with the residual toluene solvent to form a low-boiling azeotrope, which was discharged in the vacuum section, and finally the devolatilized SBR was cut into strands and pelletized to obtain SBR particles after deep devolatilization, and the toluene and dichloromethane solvent contents were tested by headspace analysis. The test results are shown in Table 1.

[0082] In addition, the screw deep devolatilization process was performed without adding dichloromethane, and the screw deep devolatilization operation of COC, COP, LLDPE, POE, EVA, EPDM and SBR was repeated, which were Comparative Examples 1, 2, 3, 4, 5, 6 and 7. Ultrapure water and liquid carbon dioxide were added during the screw deep devolatilization process, and the screw deep devolatilization operation of COC was repeated, which were Comparative Examples 8 and 9, respectively. The test results are shown in Table 1.

[0083] Table 1 Polyolefin screw deep devolatilization conditions and results

[0084]

[0085]

[0086] It can be seen from the above test results that the deep screw devolatilization of the polyolefin product using dichloromethane as the stripping agent in each embodiment of the present invention has a significant effect on the removal of residual solvents, and the lowest removal can be below 10ppm. The schemes without adding dichloromethane in Comparative Examples 1-7 have a poor effect on the removal of residual solvents. The scheme of adding ultrapure water as a stripping agent in Comparative Example 8 also has a limited effect on the removal of residual solvents. The scheme of adding liquid CO2 as a stripping agent in Comparative Example 9 has a better effect on the removal of residual solvents, but it is also difficult to reach below 10ppm. At the same time, the cost of liquid CO2 is high and the equipment requirements are relatively high.

[0087] Although the above embodiments have described the technical solutions of the present invention in detail, the technical solutions of the present invention are not limited to the above embodiments. Without departing from the idea and purpose of the present invention, any changes made to the technical solutions of the present invention will fall within the scope defined by the claims of the present invention.

Claims

1. A method for improving the devolatilization effect of a polyolefin screw, characterized in that: The invention comprises the steps of injecting dichloromethane as a stripping agent into the molten polyolefin in the devolatilization extruder, uniformly dispersing the dichloromethane under the mixing action of the screw, liquid-liquid extraction with the residual solvent in the polyolefin to form a low-boiling azeotrope, and discharging the mixture in the vacuum section.

2. The method according to claim 1, characterized in that The polyolefin is selected from one or more of cyclic olefin copolymer (COC), cyclic olefin polymer (COP), ethylene-α-olefin copolymer elastomer (POE), low density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene propylene diene monomer rubber (EPDM), and styrene butadiene rubber (SBR).

3. The method according to claim 2, characterized in that The α-olefin is selected from at least any one of butene, hexene and octene.

4. The method according to claim 1 or 2, characterized in that: The residual solvent is an organic solvent.

5. The method according to claim 4, characterized in that The organic solvent is selected from one or more of n-hexane, cyclohexane, methylcyclohexane, toluene and isoparaffin.

6. The method according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Turn on the devolatilization extruder, set the host temperature, and after the temperature stabilizes, turn on the external vacuum system, set the system vacuum degree, and adjust the screw speed; 2) low-pressure high-purity nitrogen is introduced into the nitrogen inlet of the devolatilization extruder, and the feeder is turned on to feed the polyolefin containing residual solvent into the twin-screw devolatilization extruder through the feed port; 3) After the molten polyolefin fills the barrel, the dichloromethane solvent is injected into the molten polyolefin from the extruder additive feed port through a high-pressure plunger pump, and the dichloromethane and the residual solvent undergo liquid-liquid extraction to form a low-boiling azeotrope, which is discharged in the vacuum section.

7. The method according to claim 6, characterized in that The main engine temperature of the devolatilization extruder in step 1) is 180-300°C.

8. The method according to claim 7, characterized in that The main engine temperature of the devolatilization extruder in step 1) is 220-280°C.

9. The method according to claim 6, characterized in that The vacuum degree of the vacuum system in step 1) is 1 mbar-100 mbar; the screw speed is 30-300 rpm.

10. The method according to claim 6, characterized in that The vacuum degree of the vacuum system in step 1) is 1-50 mbar; the screw speed is 50-150 rpm.

11. The method according to claim 6, characterized in that In step 2), the mass content of the residual solvent in the polyolefin is 0.1-5wt%.

12. The method according to claim 11, characterized in that In step 2), the mass content of the residual solvent in the polyolefin is 0.1-2 wt%.

13. The method according to claim 11, characterized in that The feeding speed of the feeder in step 2) is 0.5-10 kg / h.

14. The method according to claim 13, characterized in that The feeding speed of the feeder in step 2) is 1-5 kg / h.

15. The method according to claim 6, characterized in that In step 3), the flow rate of the dichloromethane solvent injected by the high-pressure plunger pump is 0.5-100 g / h.

16. The method according to claim 15, characterized in that In step 3), the flow rate of the dichloromethane solvent injected by the high-pressure plunger pump is 10-50 g / h.

17. The method according to claim 15, characterized in that The method also includes step 4) pulling the molten polyolefin strands after deep devolatilization by the screw to a pelletizer for pelletization to obtain ultra-low VOC polyolefin particles.

18. Use of the method for improving the polyolefin screw devolatilization effect according to any one of claims 1 to 17 in the deep devolatilization of polyolefin.

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