A method for in-situ synthesizing polyvinyl chloride resin with high thermal stability

Abstract

The present invention provides a method for in-situ synthesizing a polyvinyl chloride resin with high thermal stability, which relates to the technical field of polyvinyl chloride production. The method for in-situ synthesizing a polyvinyl chloride resin with high thermal stability provided by the present invention comprises the following steps: under the condition of a temperature of -10 - 40 °C, mixing an alkaline solution with a strong oxidant to obtain a mixed solution; adding an isobutyryl chloride solution to in-situ synthesize a highly efficient diisobutyryl peroxide initiator; after the initiator is filtered, it is introduced into a polymerization kettle and uniformly dispersed inside the polymerization kettle through a homogenizing distributor to initiate the polymerization of vinyl chloride. After polymerization, the pressure is released, and the product is filtered, stripped, and dried to obtain a PVC resin with high thermal stability. The synthesis process flow of the initiator is simplified, the problems of transportation and storage of the highly efficient initiator are overcome, the initiator is uniformly dispersed inside the polymerization kettle through the homogenizing distributor, and the PVC molecular chain prepared by this method has a long thermal stability time, high whiteness, and low unstable chlorine content.

Description

Technical Field

[0001] The present invention relates to the technical field of polyvinyl chloride production, and particularly relates to a method for in-situ synthesizing a polyvinyl chloride resin with high thermal stability. Background Art

[0002] Polyvinyl chloride (PVC) is the second largest general-purpose polymer resin in terms of global production capacity, with a production capacity of approximately 58 million tons per year. Industrially, PVC is mainly obtained by free radical polymerization of vinyl chloride (VC). The polymerization methods include suspension polymerization, emulsion polymerization, solution polymerization, and bulk polymerization. The PVC resin produced by suspension polymerization accounts for about 80% of the total production capacity. PVC was industrialized in the early 1930s. Since the 1930s, for a long time, the production of polyvinyl chloride has ranked first in the world's plastic consumption. In the late 1960s, polyethylene replaced polyvinyl chloride. Although polyvinyl chloride plastics now rank second, their production still accounts for more than one-fourth of the total plastic production. As one of the five general-purpose plastics, PVC has a wide range of applications in production and life, from hard products such as water pipes and plastic-steel doors and windows to soft products such as floors and films.

[0003] However, PVC has poor thermal stability. Polyvinyl chloride has poor stability to light and heat. Its softening point is 80°C and it starts to decompose at 130°C. Without adding heat stabilizers, polyvinyl chloride starts to decompose at 100°C, and the decomposition is faster above 130°C. When heated, it decomposes to release hydrogen chloride gas (hydrogen chloride gas is a toxic gas), which causes it to change color, from white → light yellow → red → brown → black. Ultraviolet rays and oxygen in sunlight will cause polyvinyl chloride to undergo photo-oxidative decomposition, thus reducing the flexibility of polyvinyl chloride and finally making it brittle. This is the reason why some PVC plastics turn yellow and brittle after a long time. This limits its application in high-end fields.

[0004] The thermal stability of PVC is mainly determined by the content of unstable chlorine in the PVC molecular chain. The PVC polymerization process is an exothermic reaction, and the heat release will cause the PVC molecular chain to dehydrochlorinate, increasing the content of unstable chlorine. To improve the thermal stability of PVC, the reaction heat can be removed by heat transfer to try to control the temperature stability. However, due to the half-life of common initiators used in PVC, the free radical concentration is not constant. Therefore, the heat release is not uniform. Industrially, uniform heat release is generally achieved through initiator compounding, but this problem has not been completely solved.

[0005] Patent CN1254491C discloses a continuous feeding of an extremely fast initiator during polymerization. An extremely fast organic initiator is used in the polymerization process. The half-life of such initiators at the polymerization temperature is 0.0001 - 0.050 hours, more preferably 0.01 - 0.050 hours, and most preferably 0.002 - 0.050 hours. The feeding of such initiators allows for improved polymerization rate control, a faster polymerization rate, resulting in an increased space-time yield of the polymerization reactor, and as a result, a method for preparing polymers with a very low residual initiator content can be obtained.

[0006] Although patents US6639037B2 and US8367784B2 disclose that the continuous initiator (CiD) dropping technique can stabilize the free radical concentration, they do not disclose how to achieve rapid dispersion of the initiator in the polymerization kettle. At the same time, the continuously dropped initiators all belong to ultra-high-efficiency initiators, and transportation and storage must be carried out below -20°C, which is not easy for transportation and storage. This increases the cost and difficulty for large-scale production in factories.

[0007] Based on this, the present invention provides a method for in-situ synthesizing a high thermal stability polyvinyl chloride resin. On the one hand, the initiation rate is increased by preparing a highly efficient diisobutyryl peroxide initiator, and at the same time, after the initiator is prepared, it directly participates in the reaction, solving the problem of difficult transportation of ultra-high-efficiency initiators, and realizing the uniform dispersion of the initiator inside the polymerization kettle through a homogenizing distributor. Summary of the Invention

[0008] The object of the present invention is to provide a method for in-situ synthesizing a high thermal stability polyvinyl chloride resin, which simplifies the synthesis process flow of the initiator and overcomes the transportation and storage requirements of high-efficiency initiators; through a homogenizing distributor, the uniform dispersion of the initiator inside the polymerization kettle is realized, so that the unstable chlorine content in the PVC molecular chain prepared is small and the thermal stability is good.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A method for in-situ synthesizing a highly efficient diisobutyryl peroxide initiator, comprising the following steps:

[0011] (1) Under the condition of a temperature of -10 - 40°C, mix an alkaline solution with a strong oxidant to obtain a mixed solution;

[0012] (2) Add an isobutyryl chloride solution to in-situ synthesize a highly efficient diisobutyryl peroxide initiator;

[0013] Preferably, in step (1), the alkaline solution is selected from at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, and lithium hydroxide solutions, and the concentration of the alkaline solution is 10 - 95%;

[0014] Further preferably, the concentration of the sodium hydroxide solution is 25-40%, the concentration of the potassium hydroxide solution is 80-95%, the concentration of the barium hydroxide solution is 20-35%, and the concentration of the lithium hydroxide solution is 10-22%.

[0015] Even more preferably, the concentration of the sodium hydroxide solution is 30-35%, the concentration of the potassium hydroxide solution is 85-90%, the concentration of the barium hydroxide solution is 25-30%, and the concentration of the lithium hydroxide solution is 15-20%.

[0016] Preferably, in step (1), the strong oxidant is selected from at least one of Na 2 O 2 , K 2 O 2 , MgO 2 , CaO 2 , BaO 2 , H 2 O 2 ; the concentration of the strong oxidant solution is 20-100%. Further preferably, the strong oxidant is selected from at least one of Na 2 O 2 , K 2 O 2 , BaO 2 , H 2 O 2 ; the concentration is 20-80%. Even more preferably, the strong oxidant is selected from at least one of Na 2 O 2 , K 2 O 2 , H 2 O 2 ; the concentration is 20-40%.

[0017] Preferably, in step (2), when adding the isobutyryl chloride solution, the specific operation is as follows: the isobutyryl chloride solution is added dropwise into the mixed solution within 1.5-3.5 h, and the dropping temperature is -5-5°C. Further preferably, the specific operation is as follows: isobutyryl chloride is added dropwise into the mixed solution within 1-5 h, and the dropping temperature is -5-0°C.

[0018] Preferably, in step (2), the reaction time for in-situ synthesis is 20-60 min.

[0019] Preferably, in step (2), the dry basis mass ratio of the isobutyryl chloride to the alkaline solution is 1:0.25-1.5, and the mass ratio of the isobutyryl chloride to the strong oxidant is 1:1-2.0. Further preferably, in step (2), the dry basis mass ratio of the isobutyryl chloride to the alkaline solution is 1:0.5-1.5, and the mass ratio of the isobutyryl chloride to the strong oxidant is 1:1.2-1.5.

[0020] A method for in-situ synthesizing polyvinyl chloride resin with high thermal stability, comprising the following steps:

[0021] (1) Prepare an initiator by the above method for in-situ synthesizing an efficient diisobutyryl peroxide initiator.

[0022] (2) After filtering the initiator, introduce it into a polymerization kettle, and uniformly disperse it inside the polymerization kettle through a homogeneous distributor to initiate the polymerization of vinyl chloride. After polymerization, relieve the pressure, filter, strip, and dry to obtain the PVC resin with high thermal stability.

[0023] Preferably, the homogeneous distributor in step (2) is selected from at least one of a single-layer tubular liquid distributor, a double-layer tubular liquid distributor, a jet liquid distributor, and a disc liquid distributor; more preferably, the homogeneous distributor in step (2) is selected from at least one of a double-layer tubular liquid distributor and a jet liquid distributor.

[0024] Preferably, the specific parameters of step (2) are: the feeding rate of the initiator into the polymerization kettle is 0.5 - 1 g / min, the initiation temperature is 15 - 90 °C, and the polymerization time is 1.5 - 40 h; more preferably, the specific parameters of step (2) are: the feeding rate of the initiator into the polymerization kettle is 0.6 g / min, the initiation temperature is 35 - 70 °C, and the polymerization time is 2.0 - 10 h.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The method for preparing polyvinyl chloride resin with high thermal stability provided by the present invention simplifies the synthesis process flow of the initiator and overcomes the transportation and storage requirements of the efficient initiator.

[0027] (2) The uniform dispersion of the initiator inside the polymerization kettle is achieved through a homogeneous distributor. The PVC molecular chains prepared by this method have a small content of unstable chlorine and good thermal stability. Detailed Embodiments

[0028] In order to make the technical means, creative features, achieved purposes, and functions of the present invention easy to understand, the following specific embodiments are used to further clarify the present invention. However, the following embodiments are only the preferred embodiments of the present invention and not all of them. Based on the embodiments in the embodiments, other embodiments obtained by those skilled in the art without creative efforts all belong to the protection scope of the present invention. It should be noted that the raw materials used in the present invention are all ordinary commercially available products, and no specific limitation is made on their sources. The technical and scientific terms used in the embodiments have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0029] Example 1

[0030] (1) 62.5 g of 32% sodium hydroxide solution was cooled to 0 °C to prepare an alkaline solution; the alkaline solution was stirred and mixed with 140 g of 27.5% hydrogen peroxide solution, stirred and reacted for 30 min, and then cooled to 0 °C to obtain a mixed solution;

[0031] (2) 107 g of isobutyryl chloride was slowly and uniformly added dropwise to the mixed solution obtained in step (1) while stirring, and the temperature was controlled at 0 °C. The isobutyryl chloride was added dropwise within 120 min; after the addition of isobutyryl chloride was completed, the mixture was stirred and reacted for another 30 min at 0 °C to obtain a highly efficient diisobutyryl peroxide initiator;

[0032] (3) After the reaction was completed, stirring was stopped, and it was introduced into a vinyl chloride polymerization kettle heated to 57 °C at a rate of 0.6 g / min through a double-layer tubular liquid distributor. After reacting for 5 hours, the pressure was released, and after filtration, stripping, and drying, high heat stability PVC resin was obtained.

[0033] Example 2

[0034] Differing from Example 1, in step (1), 62.5 g of 32% sodium hydroxide solution was replaced with 30 g of 90% potassium hydroxide;

[0035] Under the same other conditions and steps, high heat stability PVC resin was obtained.

[0036] Example 3

[0037] Differing from Example 1, in step (1), 140 g of 27.5% hydrogen peroxide solution was replaced with 385 g of 10% Na 2 O 2 solution;

[0038] Under the same other conditions and steps, high heat stability PVC resin was obtained.

[0039] Example 4

[0040] Differing from Example 1, in step (2), the addition of isobutyryl chloride within 120 min was replaced with the addition of isobutyryl chloride within 60 min;

[0041] Under the same other conditions and steps, high heat stability PVC resin was obtained.

[0042] Example 5

[0043] Differing from Example 1, in step (3), the double-layer tubular liquid distributor was replaced with a jet liquid distributor;

[0044] Under the same other conditions and steps, high heat stability PVC resin was obtained.

[0045] Example 6

[0046] Different from Example 1, in step (3), the speed of 0.6 g / min was replaced with a speed of 1.0 g / min;

[0047] Under the same other conditions and steps, a PVC resin with high thermal stability was obtained.

[0048] Comparative Example 1

[0049] Different from Example 1, in step (3), it was directly dropped into a vinyl chloride polymerization kettle heated to 57°C at a speed of 0.6 g / min. After reacting for 5 hours, the pressure was released, and after filtration, stripping, and drying, a PVC resin with high thermal stability was obtained;

[0050] Under the same other conditions and steps, a PVC resin was obtained.

[0051] Comparative Example 2

[0052] Different from Example 2, in step (3), it was directly dropped into a vinyl chloride polymerization kettle heated to 57°C at a speed of 0.6 g / min. After reacting for 5 hours, the pressure was released, and after filtration, stripping, and drying, a PVC resin with high thermal stability was obtained;

[0053] Under the same other conditions and steps, a PVC resin with high thermal stability was obtained.

[0054] Comparative Example 3

[0055] Different from Example 3, in step (3), it was directly dropped into a vinyl chloride polymerization kettle heated to 57°C at a speed of 0.6 g / min. After reacting for 5 hours, the pressure was released, and after filtration, stripping, and drying, a PVC resin with high thermal stability was obtained;

[0056] Under the same other conditions and steps, a PVC resin with high thermal stability was obtained.

[0057] Comparative Example 4

[0058] Different from Example 4, in step (3), it was directly dropped into a vinyl chloride polymerization kettle heated to 57°C at a speed of 0.6 g / min. After reacting for 5 hours, the pressure was released, and after filtration, stripping, and drying, a PVC resin with high thermal stability was obtained;

[0059] Under the same other conditions and steps, a PVC resin with high thermal stability was obtained.

[0060] Comparative Example 5

[0061] Different from Example 6, in step (3), it was directly dropped into a vinyl chloride polymerization kettle heated to 57°C at a speed of 1 g / min. After reacting for 5 hours, the pressure was released, and after filtration, stripping, and drying, a PVC resin with high thermal stability was obtained;

[0062] Under the same other conditions and steps, PVC resin with high thermal stability is obtained.

[0063] Comparative Example 6

[0064] Different from Example 1, in step (1), 62.5 g of 32% sodium hydroxide solution was replaced with 560 g of 5% potassium hydroxide;

[0065] Under the same other conditions and steps, PVC resin with high thermal stability is obtained.

[0066] The results of the thermal stability time, whiteness, and unstable chlorine content of the PVC resin products obtained in Examples 1-6 and Comparative Examples 1-6 are shown in Table 1.

[0067] Table 1. Thermal stability time, whiteness, and unstable chlorine content of PVC resin

[0068]

[0069]

[0070] As can be seen from Table 1 above, the PVC resin prepared by the present invention has good thermal stability, high whiteness, and low unstable chlorine content.

[0071] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for in-situ synthesizing polyvinyl chloride resin with high thermal stability, characterized in that, it comprises the following steps: (1) In-situ synthesizing a highly efficient initiator of diisobutyryl peroxide, which comprises the following steps: 1-1. Under the condition of a temperature of -10 - 40 °C, mixing an alkaline solution with a strong oxidant to obtain a mixed solution; the alkaline solution is selected from at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, and lithium hydroxide solutions, and the concentration of the alkaline solution is 10 - 95%; 1-2. Adding an isobutyryl chloride solution to in-situ synthesize a highly efficient initiator of diisobutyryl peroxide; the dry basis mass ratio of the isobutyryl chloride to the alkaline solution is 1:0.25 - 1.5, and the mass ratio of the isobutyryl chloride to the strong oxidant is 1:1 - 2.0; (2) After the reaction in step (1) ends, stop stirring, pass through a homogenizing distributor into a polymerization kettle to initiate the polymerization of vinyl chloride, relieve the pressure after polymerization, and filter, strip, and dry to obtain a PVC resin with high thermal stability; the homogenizing distributor is selected from at least one of a double-layer tube liquid distributor and a jet liquid distributor.

2. The method according to claim 1, characterized in that, The strong oxidant described in Step 1-1 is selected from at least one of Na 2 O 2 , K 2 O 2 , MgO 2 , CaO 2 , BaO 2 , H 2 O 2 , and the concentration of the strong oxidant solution is 20-100%.

3. The method according to claim 1, characterized in that, For the addition of the isobutyryl chloride solution in step 1-2, the specific operation is: the isobutyryl chloride solution is added dropwise into the mixed solution within 1.5 - 3.5 h, and the dropping temperature is -5 - 5 °C.

4. The method according to claim 1, characterized in that, The reaction time for the in-situ synthesis in step 1-2 is 20 - 60 min.

5. The method according to claim 1, characterized in that, The specific parameters of step (2) are: the feeding rate of the initiator into the polymerization kettle is 0.5 - 1 g / min, the initiation temperature is 15 - 90 °C, and the polymerization time is 1.5 - 40 h.

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