Method and device for removing iron impurities in polypropylene powder

Abstract

The invention provides a method and a device for removing iron impurities in polypropylene powder. The invention discloses a method for removing iron impurities from polypropylene powder. The method comprises the following steps: S1, enabling the polypropylene powder containing the iron impurities to sequentially pass through a feeding section, a purifying section and a discharging section; s2, in the purification section, the polypropylene powder sequentially passes through multiple layers of magnetic frames, and each layer of magnetic frame comprises multiple magnetic rods; s3, controlling the downward moving speed of the polypropylene powder among the multiple layers of magnetic frames; and S4, collecting the polypropylene powder from which the iron impurities are removed through a discharging section. According to the invention, the residual iron impurities in the polypropylene powder can be economically, efficiently and continuously removed, so that the quality of a polypropylene product is improved.

Description

Technical Field

[0001] The invention relates to a method and a device for removing impurities from polypropylene powder, in particular to a method and a device for removing iron impurities from polypropylene powder, and belongs to the technical field of polypropylene resins. Background Art

[0002] The preparation process of polypropylene resin involves high temperature, high pressure, mass transfer and heat transfer. Most of the dynamic and static equipment and pipelines used in these processes such as material storage, fluid transportation, reaction, heat exchange and separation are made of steel. Due to material flushing, stirring, friction or manufacturing, inspection and maintenance, and incomplete cleaning of the internal grinding of pressure vessels due to inspection and supervision, various forms of iron impurities will inevitably remain in the polypropylene powder. Once the polypropylene powder and iron impurities enter the downstream extrusion granulation section for melting, dispersion and pelletizing, the iron impurities are completely wrapped by the polypropylene resin and are extremely difficult to detect and remove. Even trace amounts of iron impurities will have a significant impact on polypropylene used in films, fibers, medical devices, sanitary products and household appliances. Not only will it cause filter blockage and affect production efficiency, but it will also cause product quality to decline or even fail to meet the standards. In particular, with the rapid development of new energy industries such as capacitors and lithium battery separators, the required electrical membrane-grade high-purity polypropylene resin has more stringent requirements on the content of metal impurities.

[0003] There are many methods for removing impurities from polypropylene powder in the prior art. For example, the methods disclosed in Chinese invention patents CN201911264474.6, CN202210727808.4, CN202110952214.9 and CN202211396382.5; or the use of ultra-high activity catalysts to reduce the content of metal impurities such as titanium, magnesium, and silicon in polypropylene resin, but it is impossible to reduce the iron impurities remaining in the production process of polypropylene resin; or the use of supercritical CO2 or high-efficiency solvents to remove metal impurities and oil-like organic matter in polypropylene powder, not only the process is complicated, the required solvent cost is high, but also the iron impurities are basically not removed. Summary of the invention

[0004] Based on the above background, the purpose of the present invention is to provide a method and device for removing iron impurities from polypropylene powder to solve the problems described in the background technology.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A method for removing iron impurities from polypropylene powder, the method comprising the following steps:

[0007] S1, passing the polypropylene powder containing iron impurities through the feeding section, purification section and discharging section in sequence;

[0008] S2. In the purification section, the polypropylene powder is passed through multiple layers of magnetic racks in sequence, each layer of the magnetic racks including multiple magnetic rods;

[0009] S3, controlling the downward movement rate of the polypropylene powder between the multi-layer magnetic racks;

[0010] S4. Collect the polypropylene powder after removing the iron impurities through the discharging section.

[0011] Preferably, in step S2, the center distance between two adjacent magnetic rods on each layer of the magnetic frame is configured to be 2-4 times the outer diameter of a single magnetic rod.

[0012] Preferably, in step S2, the center distance between each two adjacent layers of magnetic racks is configured to be 2-4 times the outer diameter of a single magnetic rod.

[0013] Preferably, in step S2, the magnetic bars of each layer of the magnetic frame are arranged in a staggered manner, and the staggered distance of the magnetic bars of each layer of the magnetic frame from top to bottom is configured to be 1-2 times the outer diameter of a single magnetic bar.

[0014] Preferably, in step S3, the downward movement rate of the polypropylene powder between the multi-layer magnetic frames is controlled to be 10-20 mm / s.

[0015] Preferably, step S3 further comprises: superimposing a pulsed magnetic field on the static magnetic field of the magnetic rod by a pulsed magnetic field generator, controlling the frequency of the pulsed magnetic field within the range of 0.1-10 Hz, the duty cycle within the range of 10%-90%, and the peak magnetic field intensity being 1.2-2 times the static magnetic field intensity.

[0016] A device for removing iron impurities from polypropylene powder, the device comprising a shell, the interior of the shell being divided into a feeding section, a purification section and a discharging section from top to bottom, the feeding section being a conical cylinder structure, the purification section being a straight cylinder structure, the discharging section being an inverted conical cylinder structure, the angle between the conical surface of the side wall of the feeding section and the horizontal plane being 25°-35°, the angle between the conical surface of the side wall of the discharging section and the vertical plane being 25°-35°, the purification section being provided with a multi-layer magnetic frame, each layer of the magnetic frame comprising a plurality of magnetic rods, a filter screen being further provided above the multi-layer magnetic frame, the aperture of the filter screen being 10-15 mm.

[0017] Preferably, the magnetic bars of each layer of the magnetic frame are arranged in a staggered manner.

[0018] Preferably, the outer diameter of the magnetic rod is 20-30 mm, the aspect ratio is 30-60, and the magnetic strength of each magnetic rod is greater than 10,000 Gauss.

[0019] Preferably, the discharging section is provided with a rotary valve driven by a variable frequency motor, and the rotary valve is used to control the downward movement rate of the polypropylene powder between the multi-layer magnetic frames.

[0020] Preferably, the polypropylene powder iron impurity removal device also includes a pulse magnetic field generator, the magnetic bar includes a permanent magnet core and an electromagnetic coil wound around the outside of the permanent magnet core, and the pulse magnetic field generator is electrically connected to the electromagnetic coil.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The present invention discloses a method and device for removing iron impurities from polypropylene powder, which can achieve economical, efficient and continuous removal of residual iron impurities in polypropylene powder, thereby improving the quality of polypropylene products.

[0023] The present invention can achieve a capture efficiency of up to 99.5% of iron impurities in polypropylene powder by optimizing the design of the multi-layer magnetic frame and the arrangement of the magnetic rods, and does not require the use of chemical reagents. The iron impurities are removed only by relying on the physical magnetic field, and no secondary pollution is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 It is a schematic structural diagram of a device for removing iron impurities from polypropylene powder of the present invention;

[0026] Figure 2 It is a sample diagram of the multi-layer magnetic frame in the present invention;

[0027] Figure 3 This is an experimental effect diagram of the multi-layer magnetic frame in the present invention capturing iron impurities;

[0028] Figure 4 This is another experimental effect diagram of the multi-layer magnetic frame in the present invention capturing iron impurities;

[0029] In the figure: 01, feeding section; 02, purification section; 03, drawer-type filter; 04, magnetic frame; 05, magnetic rod; 06, discharge section. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0031] In the present invention, unless otherwise specified, all parts and percentages are weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are universal standard parts or components known to those skilled in the art, and their structures and principles are known to those skilled in the art through technical manuals or conventional experimental methods.

[0032] The invention discloses a method for removing iron impurities from polypropylene powder, which comprises the following steps:

[0033] S1, passing the polypropylene powder containing iron impurities through the feeding section, purification section and discharging section in sequence;

[0034] S2. In the purification section, the polypropylene powder is passed through multiple layers of magnetic racks in sequence, each layer of the magnetic racks including multiple magnetic rods;

[0035] S3, controlling the downward movement rate of the polypropylene powder between the multi-layer magnetic racks;

[0036] S4. Collect the polypropylene powder after removing the iron impurities through the discharging section.

[0037] The present invention also discloses a device for removing iron impurities from polypropylene powder, which comprises a shell, the interior of which is divided into a feeding section, a purification section and a discharging section from top to bottom, the feeding section is a conical cylinder structure, the purification section is a straight cylinder structure, the discharging section is an inverted conical cylinder structure, the angle between the conical surface of the side wall of the feeding section and the horizontal plane is 30°, the angle between the conical surface of the side wall of the discharging section and the vertical plane is 30°, and the purification section is provided with a multi-layer magnetic frame, and each layer of the magnetic frame includes a plurality of magnetic rods.

[0038] The technical difficulties of the method and device for removing iron impurities from polypropylene powder of the present invention are: first, how to make the iron impurities carried by the polypropylene powder smoothly penetrate the downward flowing powder layer and be captured by the magnetic rods. This requires reasonable control of the spacing of the magnetic rods in each layer of the magnetic frame, the spacing of the staggered arrangement of two adjacent layers of magnetic frames, and the spacing between the multiple layers of magnetic rods, so that the iron impurities carried by the polypropylene powder can be removed economically and efficiently. Second, how to make the polypropylene powder flow out of the discharging section evenly without bias flow and channel flow, give full play to the role of each magnetic rod, and improve the removal rate of iron impurities. Third, how to ensure the processing efficiency while preventing the high-speed moving powder from washing away the iron impurities captured by the magnetic rods.

[0039] The technical solution of the present invention is further described in detail below in conjunction with multiple embodiments.

[0040] Example 1

[0041] Polypropylene powder with an iron impurity content of 10 ppmwt enters Figure 1The device for removing iron impurities from polypropylene powder is shown.

[0042] The polypropylene powder enters the 304 stainless steel feed section 01 with a smooth inner wall from the top, and the angle between the cone surface of the feed section and the horizontal is 30°.

[0043] Afterwards, the powder enters the 304 stainless steel purification section 02 with a smooth inner wall by gravity, and is spread on the drawer-type filter screen 03 made of 304 stainless steel to remove flakes and blocks. The filter screen has an aperture of 10mm.

[0044] The polypropylene powder then enters the 6-layer magnetic rack 04 of the purification section in turn with gravity. Each layer of magnetic rack 04 is composed of multiple permanent magnetic rods 05. The outer diameter of each magnetic rod 05 is 25mm, the aspect ratio is 40, the magnetic strength is 15,000 Gauss, and the center distance between every two magnetic rods 05 is 3 times the outer diameter of a single magnetic rod, that is, 75mm. The center distance between each two adjacent layers of magnetic racks is 2.0 times the outer diameter of a single magnetic rod, that is, 50mm. The offset distance from top to bottom of the magnetic rods 05 of each layer of magnetic rack 04 is 1.0 times the outer diameter of a single magnetic rod 05, that is, 25mm.

[0045] The polypropylene powder with iron impurities removed enters the internally polished smooth 304 stainless steel conical discharge section 06 by gravity, and the angle between the conical surface of the discharge section 06 and the vertical is 30°. This angle is close to the angle of repose (angle of rest) of the polypropylene powder. The structure of the discharge section can make the polypropylene powder realize uniform piston flow discharge in the discharge section, that is, the residence time of the polypropylene powder in the discharge section is uniform, and there will be no bias flow or channel flow, so the contact time between the polypropylene powder and the multi-layer magnetic frame in the purification section is uniform.

[0046] The discharging section 06 is connected to a rotary valve driven by a variable frequency motor to control the downward movement rate of the polypropylene powder between the magnetic racks 05 in the purification section to be 15 mm / s.

[0047] Finally, the flow rate of iron impurities in the polypropylene powder at the outlet of the rotary valve was reduced to 0.5 ppmwt, that is, the capture efficiency of the multi-layer magnetic frame 05 in the purification section for iron impurities was 99.5 wt%.

[0048] Example 2

[0049] The technical solution is the same as that of Example 1, except that the downward movement rate of the polypropylene powder between the magnetic racks in the purification section is controlled to be reduced to 5 mm / s by a rotary valve driven by a variable frequency motor.

[0050] Example 3

[0051] The technical solution is the same as that of Example 1, except that the downward movement rate of the polypropylene powder between the magnetic racks in the purification section is increased to 30 mm / s by controlling the rotary valve driven by a variable frequency motor.

[0052] Example 4

[0053] The technical solution is the same as that of Example 1, except that the downward movement rate of the polypropylene powder between the magnetic racks in the purification section is increased to 45 mm / s by controlling the rotary valve driven by a variable frequency motor.

[0054] The parameter settings of Examples 1-4 and the comparison of the capture efficiency for iron impurities are shown in Table 1.

[0055] Table 1 Effect of powder movement rate in purification section on iron impurity capture efficiency

[0056]

[0057] According to Table 1, the iron impurity capture efficiency of Example 1 and Example 2 is the highest, but the powder movement rate of Example 2 is too slow, and the powder processing capacity is significantly lower than that of Example 1, so the data of Example 1 is the best. Reasonable control of the downward movement rate of the powder between the multi-layer magnetic frames can not only ensure the capture efficiency of iron impurities, but also improve the powder processing capacity and device utilization.

[0058] Example 5

[0059] The technical solution is the same as that of Example 1, except that the center distance between two adjacent magnetic rods on each layer of the magnetic frame is adjusted to twice the outer diameter of a single magnetic rod, that is, 50 mm.

[0060] Example 6

[0061] The technical solution is the same as that of Example 1, except that the center distance between two adjacent magnetic rods on each layer of the magnetic frame is adjusted to 4 times the outer diameter of a single magnetic rod, that is, 100 mm.

[0062] Example 7

[0063] The technical solution is the same as that of Example 1, except that the center distance between two adjacent magnetic bars on each layer of the magnetic frame is adjusted to 5 times the outer diameter of a single magnetic bar, that is, 125 mm.

[0064] The comparison of parameter settings and capture efficiency of iron impurities between Example 1 and Examples 5-7 is shown in Table 2.

[0065] Table 2 Effect of the center distance between two adjacent magnetic bars on each layer of the magnetic rack on the capture efficiency of iron impurities

[0066]

[0067] According to Table 2, the iron impurity capture efficiency of Example 1 and Example 5 is the highest, but the center distance of the magnetic rods in Example 5 is small, and more magnetic rods are required for each layer of magnetic rack, so the data of Example 1 is the best. Reasonable control of the center distance between two adjacent magnetic rods on each layer of magnetic rack can not only ensure the capture efficiency of iron impurities, but also reduce the cost of the device.

[0068] Example 8

[0069] The technical solution is the same as that of Example 1, except that the center distance between each two adjacent layers of magnetic frames is increased to 4.0 times the outer diameter of a single magnetic rod, that is, 100 mm.

[0070] Example 9

[0071] The technical solution is the same as that of Example 1, except that the center distance between each two adjacent layers of magnetic racks is increased to 6.0 times the outer diameter of a single magnetic rod, that is, 150 mm.

[0072] The comparison of parameter settings and capture efficiency of iron impurities between Example 1 and Examples 8-9 is shown in Table 3.

[0073] Table 3 Effect of the center distance between two adjacent magnetic bars on each layer of the magnetic rack on the capture efficiency of iron impurities

[0074]

[0075] According to Table 3, the data of Example 1 is the best. Reasonable control of the center distance between each two adjacent layers of magnetic racks can make the polypropylene powder always within the capture range of the strong magnetic field when moving downward, which can improve the capture efficiency of the multi-layer magnetic racks in the purification section for iron impurities.

[0076] Example 10

[0077] The technical solution is the same as that of Example 1, except that the offset distance from top to bottom of the magnetic bars of each layer of the magnetic frame is increased to 3.0 times the outer diameter of a single magnetic bar, that is, 75 mm.

[0078] Embodiment 11

[0079] The technical solution is the same as that of Example 1, except that the offset distance from top to bottom of the magnetic bars of each layer of the magnetic frame is increased to 5.0 times the outer diameter of a single magnetic bar, that is, 125 mm.

[0080] The comparison of parameter settings and capture efficiency of iron impurities between Example 1 and Examples 10-11 is shown in Table 4.

[0081] Table 4 Effect of the displacement distance of the magnetic bars from top to bottom on the iron impurity capture efficiency of each layer of the magnetic frame

[0082]

[0083] According to Table 4, the data of Example 1 is the best. If the displacement distance of the magnetic bars of each layer of the magnetic frame from top to bottom is too large, the number of magnetic bars that can be arranged on each layer of the magnetic frame is reduced, and part of the polypropylene powder is not within the capture range of the strong magnetic field when moving downward, which will reduce the capture efficiency of the multi-layer magnetic frame of the purification section for iron impurities.

[0084] Example 12

[0085] The technical solution is the same as that of Example 1, except that the polypropylene powder iron impurity removal device further includes a pulse magnetic field generator, the magnetic bar includes a permanent magnet core and an electromagnetic coil wound around the permanent magnet core, and the pulse magnetic field generator is electrically connected to the electromagnetic coil. The pulse magnetic field generator is used to superimpose a pulse magnetic field on the static magnetic field of the magnetic bar, and the frequency of the pulse magnetic field is controlled to be within the range of 0.1-10 Hz, the duty cycle is within the range of 10%-90%, and the peak magnetic field strength is 1.2-2 times the static magnetic field strength.

[0086] The parameter settings of Example 1 and Example 12 and the comparison of the capture efficiency of iron impurities are shown in Table 5.

[0087] Table 5 Effects of static magnetic field and static magnetic field superimposed on pulse magnetic field on iron impurity capture efficiency

[0088]

[0089] According to Table 5, Example 12 adopts a method of superimposing a static magnetic field with a pulsed magnetic field, so that the capture efficiency of the multi-layer magnetic frame in the purification section for iron impurities is further slightly improved compared with Example 1. This is because the periodic additional magnetic force generated by the pulsed magnetic field enhances the adsorption of tiny iron impurities and iron impurities wrapped by polypropylene powder.

[0090] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for removing iron impurities from polypropylene powder, characterized in that: The method comprises the following steps: S1, passing the polypropylene powder containing iron impurities through the feeding section, purification section and discharging section in sequence; S2. In the purification section, the polypropylene powder is passed through multiple layers of magnetic racks in sequence, each layer of the magnetic racks including multiple magnetic rods; S3, controlling the downward movement rate of the polypropylene powder between the multi-layer magnetic racks; S4. Collect the polypropylene powder after removing the iron impurities through the discharging section.

2. The method for removing iron impurities from polypropylene powder according to claim 1, characterized in that: In step S2, the center distance between two adjacent magnetic rods on each layer of the magnetic frame is configured to be 2-4 times the outer diameter of a single magnetic rod.

3. The method for removing iron impurities from polypropylene powder according to claim 1, characterized in that: In the step S2, the center distance between each two adjacent layers of magnetic racks is configured to be 2-4 times the outer diameter of a single magnetic rod.

4. The method for removing iron impurities from polypropylene powder according to claim 1, characterized in that: In the step S2, the magnetic bars of each layer of the magnetic frame are arranged in a staggered manner, and the staggered distance of the magnetic bars of each layer of the magnetic frame from top to bottom is configured to be 1-2 times the outer diameter of a single magnetic bar.

5. The method for removing iron impurities from polypropylene powder according to claim 1, characterized in that: In the step S3, the downward movement rate of the polypropylene powder between the multi-layer magnetic frames is controlled to be 10-20 mm / s.

6. The method for removing iron impurities from polypropylene powder according to claim 1, characterized in that: The step S3 also includes: superimposing a pulse magnetic field on the static magnetic field of the magnetic rod by a pulse magnetic field generator, controlling the frequency of the pulse magnetic field to be in the range of 0.1-10 Hz, the duty cycle to be in the range of 10%-90%, and the peak magnetic field intensity to be 1.2-2 times the static magnetic field intensity.

7. A device for removing iron impurities from polypropylene powder, characterized in that: The device comprises a shell, the interior of the shell is divided into a feeding section, a purification section and a discharging section from top to bottom, the feeding section is a conical cylinder structure, the purification section is a straight cylinder structure, the discharging section is an inverted conical cylinder structure, the angle between the conical surface of the side wall of the feeding section and the horizontal plane is 25°-35°, the angle between the conical surface of the side wall of the discharging section and the vertical plane is 25°-35°, the purification section is provided with a multi-layer magnetic frame, each layer of the magnetic frame includes a plurality of magnetic rods, and a filter screen is also provided above the multi-layer magnetic frame, and the aperture of the filter screen is 10-15mm.

8. The device for removing iron impurities from polypropylene powder according to claim 7, characterized in that: The magnetic bars on each layer of the magnetic rack are arranged in a staggered manner.

9. The device for removing iron impurities from polypropylene powder according to claim 7, characterized in that: The discharging section is provided with a rotary valve driven by a variable frequency motor, and the rotary valve is used to control the downward movement rate of the polypropylene powder between the multi-layer magnetic frames.

10. The device for removing iron impurities from polypropylene powder according to claim 7, characterized in that: The polypropylene powder iron impurity removal device also includes a pulse magnetic field generator. The magnetic rod includes a permanent magnet core and an electromagnetic coil wound around the permanent magnet core. The pulse magnetic field generator is electrically connected to the electromagnetic coil.

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