Preparation method of CPVC (Chlorinated Polyvinyl Chloride) through acid phase suspension and nitrogen bubbling deacidification

Abstract

The invention relates to the technical field of chlorinated polyvinyl chloride production, and discloses a preparation method of acid-phase suspension and nitrogen bubbling deacidified CPVC (chlorinated polyvinyl chloride), which comprises the following steps: conveying a special polyvinyl chloride raw material to a high-level weighing bin by air, and automatically and quantitatively feeding; preparing 18 + / -0.5% hydrochloric acid solution through instrument interlocking control, and conveying the hydrochloric acid solution to a storage tank for later use; quantitatively adding hydrochloric acid, a PVC raw material and a special additive system into the batching kettle for mixing; a physical'three-stage deep deacidification technology 'is adopted; treating the precisely centrifuged material, adding nano active calcium carbonate, and drying to obtain a semi-finished product; and blowing the semi-finished product to a mixer, uniformly mixing, and automatically packaging. According to the method, deep deacidification is carried out by adopting a three-stage deep deacidification technology, so that zero wastewater discharge and high quality of the product in the production process are synchronously realized, and key performance indexes such as whiteness, thermal stabilization time and vicat softening point of the CPVC product are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of chlorinated polyvinyl chloride (CPVC) production technology, specifically a method for preparing CPVC using acid-phase suspension and nitrogen bubbling deacidification. Background Technology

[0002] Chlorinated polyvinyl chloride (CPVC), as a key high-performance engineering plastic, has become a core material in high-end applications such as water supply systems, chemical pipelines, power cable protection pipes, and fire sprinkler systems due to its excellent heat resistance, superior chemical corrosion resistance, and inherent flame retardant properties. However, China still mainly relies on imports for high-performance CPVC resin, a situation closely related to the inherent bottlenecks in current mainstream production processes.

[0003] Currently, the commonly used aqueous suspension chlorination process in China generates large amounts of complex wastewater with high chlorine and acid content during production. This wastewater is difficult and costly to treat, and poses environmental risks, severely hindering the industry's sustainable development. Existing technologies mostly focus on end-of-pipe treatment, achieving emission standards through advanced treatment. However, these methods are cumbersome, energy-intensive, and struggle to achieve complete "zero discharge" of wastewater, leaving residual concentrated waste liquid or waste salts with disposal challenges. Furthermore, alkali metal ions introduced to neutralize residual acid in traditional processes remain in the product, leading to decreased thermal stability, reduced whiteness, and a lower Vicat softening point in CPVC, making it prone to decomposition during subsequent thermal processing. Therefore, developing a clean and efficient CPVC production process that can eliminate wastewater generation at the source while improving the overall performance of the product is an urgent technological need with significant industrial value. With increasingly stringent environmental protection requirements and the urgent need for industrial upgrading, developing an innovative CPVC production process that can completely eliminate wastewater generation at the source of production while simultaneously improving the overall performance of the product (such as whiteness, thermal stability, and processing rheological properties) has become a key technical challenge for breaking through industry development bottlenecks and enhancing core competitiveness. Therefore, corresponding technical solutions need to be designed to address this issue. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing CPVC using acid-phase suspension and nitrogen bubbling deacidification. The "acid-phase suspension method" changes the reaction medium from the source, avoiding the wastewater of the aqueous phase method. The "nitrogen bubbling deep physical deacidification" not only achieves efficient deacidification but also improves the product's intrinsic properties (whiteness, thermal stability, and processing performance) through inert protection.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing acid-phase suspension and nitrogen bubbling deacidification CPVC; Includes the following steps: S1. Batching: Special PVC raw materials are pneumatically conveyed to a high-level weighing silo for automatic quantitative feeding. Acidity is monitored using a pH meter, and through interlocking control of a frequency converter and regulating valve, concentrated acid and a 0.5% acidity soaking mother liquor are automatically mixed to prepare a 18±0.5% hydrochloric acid solution, which is then transported to a storage tank for later use. S2. Chlorination: The hydrochloric acid prepared in step S1, along with the PVC raw materials and the acid-phase suspension special additive system (including dispersant, composite additives, and trace initiators), are quantitatively added to the mixing tank and stirred until homogeneous. After heating to 60°C, the mixture is transferred to the chlorination tank. Stirring is started, and the reaction process is automatically controlled according to the preset DCS / PID program: first, nitrogen is introduced to replace the oxygen in the tank, then liquid chlorine is introduced to carry out the substitution reaction. When the chlorine content of the product reaches the standard, the chlorination is stopped, the reaction system is cooled, and transferred to a waiting cooling tank to continue cooling to 60°C.

[0006] S3. Deacidification: This step is crucial for achieving zero wastewater discharge and improving product quality. It employs a physical "three-stage deep deacidification technology." S3.1 Primary Mechanical Deacidification: The cooled material is conveyed to a fully automatic belt centrifuge for solid-liquid separation. The moisture content of the filter cake after separation is controlled to ≤10%. A hydrochloric acid mother liquor with a concentration of 23~25% is separated. After precision filtration, part of this mother liquor is recycled in step S1 to prepare 18±0.5% hydrochloric acid, and the excess is sold as a by-product hydrochloric acid.

[0007] S3.2 Secondary Hot Soaking and Gas Replacement Deacidification: The filter cake after primary deacidification is transferred to a soaking tank, and secondary centrifugal mother liquor is added at a solid-liquid ratio of 1:2.5. Steam is then introduced to raise the temperature to 85-90℃. The key process is to introduce nitrogen gas from the bottom of the tank for bubbling replacement, continuing for approximately 60-80 minutes, to efficiently replace the residual free chlorine and hydrogen chloride gas in the material, which is then sent to the tail gas treatment system.

[0008] This design specifically uses nitrogen instead of compressed air because oxygen in the air causes oxidative degradation of the CPVC molecular chains at high temperatures, severely affecting the product's whiteness and thermal stability. After this treatment, the hydrogen chloride content in the material can be reduced to ≤0.5%.

[0009] S3.3 Three-stage precision separation + hot water soaking: The material after nitrogen purging is fed into a precision belt centrifuge for precision separation to remove trace amounts of acid trapped inside the material. The moisture content of the filter cake after separation is controlled to ≤8%. The extracted weak acid is filtered and then mixed with concentrated acid to prepare 18±0.5% hydrochloric acid for reuse in the system feed. The excess weak acid is recycled for subsequent soaking processes.

[0010] Subsequently, the material is transferred to a secondary soaking tank, where pure water is added at a solid-liquid ratio of 1:2.5. The temperature is raised to 65-70℃ and soaking continues for 2-3 hours to fully release the residual acid inside the CPVC particles. After soaking, the material is sent again to a precision belt centrifuge for dehydration and separation to further remove trace amounts of acid and water trapped in the material, ultimately ensuring that the material's moisture content is ≤8%. The filtrate is used for primary soaking. When the acid concentration of the filtrate reaches 0.5%, it is precision filtered and mixed with concentrated acid to form 18±0.5% hydrochloric acid, which is then reused in the feed. The wet powder then enters the drying system.

[0011] S4. Drying: The centrifuged material is conveyed to a high-speed mixer via a screw conveyor. 0.8-1.2% nano-activated calcium carbonate is added to the mixer for mixing, ensuring each particle is fully in contact with the nano-activated calcium carbonate. The material then undergoes flash drying and fluidized bed drying sequentially, with the hot air inlet temperature of the drying bed controlled at 65-70℃ to prevent pre-degradation due to localized overheating during the drying stage. Any remaining trace amounts of hydrogen chloride are removed as the moisture evaporates, completely eliminating the hydrogen chloride content in the material until the volatile matter content is ≤0.2%, yielding a semi-finished product. The semi-finished product is then cooled and conveyed out via a pipeline pneumatic system.

[0012] Adding nano-activated calcium carbonate during the drying process can achieve multiple benefits through its neutralization reaction (CaCO3 + 2HCl → CaCl2 +CO2↑ + H2O): it can not only completely eliminate trace amounts of hydrogen chloride produced by material evaporation, improving product purity, but also prevent acidic gases from corroding equipment; at the same time, the carbon dioxide generated by the reaction can form an inert atmosphere in situ, thereby improving process safety.

[0013] S5. Mixing and Packaging: The semi-finished product is pneumatically conveyed to the mixer, and after being fully mixed and evenly mixed, it is automatically packaged.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: Solving the problem of acidic wastewater pollution in CPVC production at its root and improving the intrinsic quality of the products not only has significant environmental benefits, but also has profound strategic significance for ensuring the security of the national key material supply chain and promoting the localization of high-end chemical materials.

[0015] This invention relates to a CPVC resin production process based on "acid-phase suspension method" and "three-stage deep physical deacidification" technology. By integrating the acid-phase suspension method with a three-stage deep physical deacidification technology that combines mechanical separation, enhanced heat and mass transfer, precision separation, and hot water immersion, wastewater generation is avoided at the source of the reaction medium, and the traditional water washing-alkali neutralization process is completely replaced. Specifically, the first-stage deacidification separates the main acid solution through centrifugal separation, and the resulting 23-25% hydrochloric acid can be directly reused or used as a by-product. The second-stage deacidification uses nitrogen bubbling at high temperatures to create intense gas-liquid disturbance, reducing the partial pressure of hydrogen chloride in the gas phase and powerfully removing free chlorine and hydrogen chloride from the resin micropores. Nitrogen protection effectively prevents high-temperature oxidative degradation. The third-stage deacidification, through the synergistic effect of precision separation and hot water immersion, further consolidates the deacidification effect and precisely controls the product moisture content. This process achieves zero wastewater discharge during production while significantly improving product whiteness, thermal stability, and processing performance, realizing a dual breakthrough in resource recycling and product high quality.

[0016] Zero wastewater discharge and water conservation: Through the above combined process, the traditional washing and alkali neutralization steps are eliminated at the source, completely eliminating the generation and discharge of process wastewater. Compared with the traditional aqueous phase method, approximately 20 tons of water can be saved per ton of product, resulting in significant environmental benefits. Significantly improved product quality: Utilizing a deep deacidification process under nitrogen protection, the oxidation and chain breaking of CPVC molecular chains and coloring side reactions during high-temperature treatment are effectively suppressed, leading to a comprehensive improvement in product performance indicators, especially a significantly extended dynamic thermal stability time and a marked increase in whiteness, fundamentally improving the intrinsic quality. Cost reduction and efficiency improvement: The hydrochloric acid separated in the first-stage deacidification process is recycled, reducing production costs. Simultaneously, the short and tightly integrated process flow, employing a fully automated design, significantly reduces labor costs and labor intensity, further improving production efficiency. Attached Figure Description

[0017] Figure 1 This invention relates to a method for preparing CPVC using acid-phase suspension and nitrogen bubbling deacidification. The flowchart. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] See Figure 1 A method for preparing acid-phase suspension and nitrogen bubbling deacidification CPVC includes the following steps: S1. Batching: Special PVC raw materials are pneumatically conveyed to a high-level weighing silo for automatic quantitative feeding. Acidity is monitored using a pH meter, and through interlocking control of a frequency converter and regulating valve, concentrated acid and a 0.5% acidity soaking mother liquor are automatically mixed to prepare a 18±0.5% hydrochloric acid solution, which is then transported to a storage tank for later use. S2. Chlorination: The hydrochloric acid prepared in step S1, along with the PVC raw materials and the acid-phase suspension special additive system (including dispersant, composite additives, and trace initiators), are quantitatively added to the mixing tank and stirred until homogeneous. After heating to 60°C, the mixture is transferred to the chlorination tank. The chlorination tank is started with a single button, and stirring is initiated. The reaction process is automatically controlled according to a preset DCS / PID program: first, nitrogen is introduced to replace the oxygen in the tank, followed by liquid chlorine for the substitution reaction. The chlorine flow rate is calculated based on the PVC feed rate. When the chlorine content of the product reaches the standard, chlorination is stopped, the reaction system is cooled, and transferred to a cooling tank to continue cooling to 60°C.

[0020] S3, Deacidification: This step is crucial for achieving zero wastewater discharge and improving product quality. It employs a physical "three-stage deep deacidification technology." S3.1 Primary mechanical deacidification: The cooled material is conveyed to a fully automatic belt centrifuge for solid-liquid separation, and the moisture content of the filter cake is controlled at ≤10%; a hydrochloric acid mother liquor with a concentration of up to 23~25% is separated; after filtration, part of the mother liquor is reused in step S1 to prepare 18±0.5% hydrochloric acid, and the excess is sold as by-product hydrochloric acid.

[0021] S3.2 Secondary hot soaking and gas replacement deacidification: The filter cake after primary deacidification is transferred to the primary soaking tank, and secondary soaking mother liquor is added at a solid-liquid ratio of 1:2.5. Steam is introduced to raise the temperature to 85-90℃. During this process, the key is to introduce nitrogen gas from the bottom of the tank for bubbling replacement, which lasts for about 60-80 minutes to efficiently replace the residual free chlorine and hydrogen chloride gas in the material and send it to the tail gas treatment system.

[0022] This design uses nitrogen instead of compressed air because oxygen in the air can cause CPVC molecular chains to oxidize and degrade at high temperatures, severely affecting the whiteness and thermal stability of the product. After this treatment, the hydrogen chloride content in the material can be reduced to ≤0.5%.

[0023] S3.3 Three-stage precision separation + hot water soaking: The material after nitrogen purging is sent to a precision belt centrifuge for precision separation to remove trace amounts of acid encapsulated inside the material. The moisture content of the filter cake after separation is controlled to be ≤8%. The weak acid that is removed is filtered and mixed with concentrated acid to prepare 18±0.5% hydrochloric acid for reuse in the system feed. The excess weak acid is recycled for subsequent soaking processes.

[0024] Subsequently, the material is transferred to a secondary soaking tank, where pure water is added at a solid-liquid ratio of 1:2.5. The temperature is raised to 65-70℃ and the material is soaked for 2-3 hours to fully release the residual acid inside the CPVC particles. After soaking, the material is sent to a precision belt centrifuge for dehydration and separation to further remove trace amounts of acid and water trapped in the material, ultimately ensuring that the material's moisture content is ≤8%. The filtrate is used for primary soaking. When the acid concentration of the filtrate reaches 0.5%, it is precision filtered and mixed with concentrated acid to form 18±0.5% hydrochloric acid, which is then reused for feeding. The wet powder material enters the drying system.

[0025] S4. Drying: The centrifuged material is conveyed to a high-speed mixer via a screw conveyor feeder. 0.8~1.2% nano-activated calcium carbonate is added to the mixer for mixing, ensuring that each particle is fully in contact with the nano-activated calcium carbonate. Then, the material undergoes flash drying and fluidized bed drying in sequence, with the hot air inlet temperature of the drying bed controlled at 65~70℃ to avoid pre-degradation of the material due to local overheating during the drying stage. The trace amounts of residual hydrogen chloride in the material are also removed as the water evaporates, completely eliminating the hydrogen chloride content in the material until the volatile matter content of the material is ≤0.2%, yielding a semi-finished product. The semi-finished product is then cooled and sent out through a pipeline pneumatic conveying system.

[0026] Adding nano-activated calcium carbonate during the drying process allows for more uniform coating of CPVC particles due to its high specific surface area. This not only effectively neutralizes trace amounts of acid but also synergistically improves the product's long-term thermal stability (such as aging whiteness) and mechanical properties (such as elastic modulus).

[0027] S5. Mixing and Packaging: The semi-finished product is pneumatically conveyed to the mixer, and after being fully mixed and evenly mixed, it is automatically packaged.

[0028] Example 1: 1. Ingredient preparation and feeding 3600 kg of special PVC raw material was pneumatically conveyed to the high-level silo; 16 m³ of hydrochloric acid solution with a concentration of 18±0.5% was prepared in the batching system; the 25 m³ batching kettle was turned on for stirring, and hydrochloric acid, PVC raw material and a specified amount of special additive for acid phase suspension method were added in sequence. After mixing evenly, the temperature was raised to 60°C, and then the mixture was pumped into a 25 m³ enamel chlorination kettle.

[0029] 2. Chlorination reaction After the chlorination reactor is sealed, first open the tail gas vent valve and open the vent valve to introduce nitrogen gas from the bottom of the reactor to purge the oxygen inside. The nitrogen gas flow rate is controlled at 65~75 m³. Then close the nitrogen gas and vent valve. Introduce 2400 kg of liquid chlorine into the reactor to carry out the chlorination substitution reaction. This acid phase method has a high reaction rate and good effect. The reaction temperature is controlled at 60~102℃, the reaction pressure is about 0.25 MPa, the instantaneous chlorine flow rate is (900 kg / h at 60~80℃, 750 kg / h at 80~102℃), and the reaction time is about 3.15 h. After the reaction is completed, cool the system to 60℃.

[0030] 3. Three-stage deep deacidification treatment S3.1 Primary mechanical deacidification: After the reaction, the material is separated into solid and liquid by a fully automatic belt centrifuge to obtain approximately 16.5 m³ of concentrated hydrochloric acid with a mass fraction of 23-25%, and approximately 5350 kg of wet CPVC material with a water content of approximately 10%.

[0031] S3.2 Secondary hot soaking and gas replacement deacidification: The wet CPVC material treated in the first stage is transferred to the first-stage soaking tank, and about 14 m³ of soaking centrifugal mother liquor is added. The temperature is raised to 85~90℃. Subsequently, nitrogen gas is introduced from the bottom of the tank to perform a bubbling and gas stripping operation to efficiently replace and drive out the hydrogen chloride dissolved in the material. In a preferred embodiment, the nitrogen gas flow rate is 80~90 m³ / h, and the gas stripping time is 60~80 minutes. This process reduces the hydrogen chloride content in the material to below 0.5%, and the replaced hydrogen chloride-containing gas is sent to the tail gas treatment system. S3.3 Three-stage precision separation and hot water soaking: The material is fed into a precision belt centrifuge for separation to remove the trace amounts of acid encapsulated inside, so that the moisture content of the resulting filter cake is no more than 8%; the removed weak acid is precision filtered and then mixed with concentrated acid to prepare hydrochloric acid with a concentration of 18%±0.5%, which is reused in the feeding process; the excess weak acid is recycled for the soaking process.

[0032] Subsequently, the material is transferred to a secondary soaking tank, and pure water is added at a mass ratio of 1:(2.5-3) between the wet CPVC material and pure water. The mixture is then soaked at 70°C for 2-3 hours to fully release the residual acid inside the CPVC particles. After soaking, the material is subjected to precision centrifugation to dehydrate it again, ensuring that its water content is not higher than 8%. The filtrate is recycled for the primary soaking process. When the acid concentration of the filtrate reaches 0.5%, it is drawn out and, after precision filtration, prepared into hydrochloric acid for reuse.

[0033] 4. Drying and post-treatment After centrifugation, the material is conveyed to a high-speed mixer via a screw feeder, and 0.8-1.2% nano-activated calcium carbonate is added and mixed evenly to ensure that the particles are in full contact with the stabilizer. Subsequently, it undergoes flash drying and fluidized bed drying in sequence, with the temperature of the hot air inlet controlled at 65-70℃ to avoid local overheating and pre-degradation of the material. During this process, residual trace amounts of hydrogen chloride are removed with the evaporation of water, ensuring that the volatile content of the material is ≤0.2%, yielding approximately 4350 kg of finished product. The resulting chlorinated polyvinyl chloride resin has a chlorine content of approximately 67.9%, a whiteness of 96, an aging whiteness (165℃ / 10s) of 90, a Vicat softening point of 121℃, a tensile strength of 58 MPa, and an elastic modulus of 2727 MPa.

[0034] Comparative Example 1 (Traditional Aqueous Suspension Method) In the traditional aqueous suspension process for producing chlorinated polyvinyl chloride (CPVC), process water is first added to the reactor, along with dispersants, emulsifiers, and initiators. Then, 3600 kg of PVC raw material is added, the agitator is turned on, the manhole is sealed, and the temperature is raised to 70°C. Nitrogen gas is then introduced from the bottom of the reactor through the vent valve to purge oxygen, with the nitrogen flow rate controlled at 50 m³. 2400 kg of liquid chlorine is then introduced through the vent valve to carry out the chlorination substitution reaction. The reaction temperature is controlled at 70~109°C, and the reaction pressure is controlled at 0.45 MPa. After the reaction, the material is transferred to a water washing tank for hot water washing to remove the hydrochloric acid generated in the reaction. This process consumes a large amount of water, with an average of about 20 m³ of process water consumed per ton of CPVC product.

[0035] Subsequently, when the pH of the slurry is below 2, it is heated and sodium carbonate is added for neutralization. This process takes about 8 hours and is subject to manual control, making it prone to over- or under-addition of alkali, which can lead to localized gelatinization of the material or incomplete neutralization of residual acid. Residual acid or alkali can affect the thermal stability of the product, resulting in lower whiteness, a lower Vicat softening point, and promoting decomposition during thermal processing.

[0036] After neutralization, the material needs to be washed again to remove residual alkali. The slurry is then centrifuged and dried to obtain the finished product. The entire washing and neutralization process generates a large amount of wastewater with high salt, high chloride ion, and high COD, resulting in high treatment costs and significant environmental impact.

[0037] The chlorinated polyvinyl chloride resin obtained had a chlorine content of 67.6%. The tested properties of the obtained product were: whiteness 84, aging whiteness (165℃ / 10s) 78, Vicat softening point temperature 103℃, tensile strength 52MPa, and elastic modulus 2221MPa.

[0038] Comparative Example 2 (using compressed air for displacement) The process steps are basically the same as those in Example 1 of this invention, except that nitrogen is replaced with compressed air. The other process parameters (temperature, time, solid-liquid ratio, centrifugation conditions, etc.) are the same as those in Example 1. The only difference is that in the secondary hot soaking and gas replacement deacidification step (S3.2), compressed air of the same flow rate is used instead of nitrogen for bubbling replacement.

[0039] By employing a three-stage deep deacidification process combining acid-phase suspension and nitrogen bubbling, the traditional high-water-consumption and high-pollution neutralization washing process is completely eliminated, while comprehensively improving product performance. The resulting CPVC resin exhibits significantly better thermal stability (whiteness 96, aging whiteness 90) and heat resistance (Vicat softening point 121℃) than the traditional aqueous phase method (Comparative Example 1) and the compressed air replacement process (Comparative Example 2). This is attributed to the effective prevention of high-temperature oxidative degradation by nitrogen protection. This process achieves efficient hydrochloric acid recovery and closed-loop recycling of waste liquid, eliminating high-salt wastewater at the source. The reaction is completed at a lower reaction pressure (0.2 MPa) and in a shorter time (3.15 h), achieving clean, efficient, and safe industrial production while ensuring high product performance and consistency.

[0040] Product Performance Comparison The product obtained in Example 1 and the comparative product were tested, and the results are shown in the table below: As shown in the table, the data indicates that the CPVC resin produced using the three-stage deacidification process based on acid-phase suspension and nitrogen bubbling of this invention is comprehensively superior to the traditional aqueous phase method (Comparative Example 1) and the compressed air replacement process (Comparative Example 2) in key properties such as whiteness, thermal stability, heat resistance, mechanical strength, and impact toughness. In particular, the improvements in the two core heat resistance indicators—thermal stability time (+64.2%) and Vicat softening point (increased by approximately 18°C)—are extremely significant. Simultaneously, excellent low-temperature impact resistance and resistance to hydrostatic brittle fracture are achieved, comprehensively demonstrating the significant effect of this invention's process in improving the high-end performance of CPVC products. The CPVC resin produced using the method of this invention (Example 1) comprehensively surpasses the traditional aqueous phase method products (Comparative Example 1) and (Comparative Example 2) in core application performance. The significant improvement in whiteness and heat-aged whiteness directly proves that nitrogen protection effectively inhibits oxidative discoloration; the thermal stability time is extended by more than double, and the Vicat softening point is increased by nearly 20°C, fully verifying the fundamental improvement of the product's intrinsic thermal properties by eliminating sodium ion residue. At the same time, this invention completely eliminates process wastewater, resulting in significant environmental benefits.

[0041] It should be noted that the above embodiments are only used to illustrate the technical concept and core advantages of the present invention, and are not intended to limit the scope of protection of the present invention. For those skilled in the art, any adjustments, modifications, and equivalent substitutions made to the process flow, equipment selection, and parameter ranges without departing from the principles of the present invention should be considered to fall within the scope of protection defined by the claims of the present invention. For example, the centrifuge equipment can be other types of precision solid-liquid separators; the nitrogen source can be air separation nitrogen production or liquid nitrogen vaporization; the drying system can be other forms of low-temperature high-efficiency dryers, etc.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the invention is defined by the appended technical solutions rather than the foregoing description, and thus all changes falling within the meaning and scope of equivalent elements of the technical solutions are intended to be included within the present invention.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification, characterized in that, The method and steps include the following: S1. Batching: Special PVC raw materials are pneumatically conveyed to the high-level weighing silo to achieve automatic quantitative feeding; acidity meter is used for monitoring, and through the interlocking control of frequency conversion pump and regulating valve, concentrated acid and 0.5% acidity soaking mother liquor are automatically prepared into hydrochloric acid solution with a concentration of 18±0.5%, and transported to storage tank for later use. S2, Chlorination: The hydrochloric acid prepared in step S1, along with the PVC raw materials and the special additive system for acid phase suspension method, are quantitatively added into the mixing tank, and the stirrer is turned on to mix evenly. S3. Deacidification: Deacidification is carried out using physical "three-stage deep deacidification technology"; first, mechanical deacidification, then heating and bubbling replacement, and finally precision separation and hot water purification; S4. Drying: After precision centrifugation, the material is conveyed to a high-speed mixer via a screw conveyor feeder. 0.8~1.2% nano-activated calcium carbonate is added to the mixer for mixing, so that each particle can fully contact the nano-activated calcium carbonate. Then, it goes through flash drying and fluidized bed drying in sequence, and the temperature of the hot air inlet of the drying bed is controlled at 65~70℃ to completely evaporate and remove the residual trace amounts of hydrogen chloride until the volatile content of the material is ≤0.2%, and a semi-finished product is obtained. The semi-finished product is cooled and then sent out through a pipeline air conveying system; S5. Mixing and Packaging: The semi-finished product is pneumatically conveyed to the mixer, and after being fully mixed and evenly mixed, it is automatically packaged.

2. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 1, characterized in that: In step S3, primary mechanical deacidification is first performed, and the method includes the following steps: The cooled material is conveyed to the Chenhala fully automatic belt centrifuge for solid-liquid separation. The moisture content of the filter cake after separation is controlled to be ≤10%. 23-25% hydrochloric acid was separated from the chlorination mother liquor; After precision filtration, part of the mother liquor is reused in step S1 to prepare 18±0.5% hydrochloric acid, and the excess is sold as by-product hydrochloric acid.

3. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 2, characterized in that: The next step involves secondary hot soaking and gas replacement deacidification, with the following steps: The filter cake after primary deacidification is transferred to a primary soaking tank. The filter cake contains 10% water and dissolved hydrogen chloride. Secondary soaking mother liquor is added at a solid-liquid mass ratio of 1:2.

5. At this time, the hydrogen chloride content of the material in the tank is 1.3~1.6%. The temperature is raised to 85℃~90℃ by steam. Nitrogen gas is introduced from the bottom of the reactor for bubbling replacement. The nitrogen flow rate is 80~90 m³ / h and the gas stripping time is 60~80 minutes. This efficiently replaces the residual free chlorine and hydrogen chloride gas in the material and sends it to the tail gas treatment system. After this treatment, the hydrogen chloride content in the material can be reduced to 0.3-0.6%.

4. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 3, characterized in that: Finally, a three-stage precision separation is performed, and the steps include the following: The material after nitrogen purging is fed into a precision belt centrifuge for precise separation to remove trace amounts of acid trapped inside the material. The moisture content of the filter cake after separation is controlled to be ≤8%. The extracted weak acid is filtered and then mixed with concentrated acid to prepare 18±0.5% hydrochloric acid, which is then reused in the system feed. The excess weak acid is recycled for subsequent soaking processes.

5. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 4, characterized in that: Continue adding hot water for soaking, following these steps: The material is transferred to a secondary soaking tank, pure water is added at a solid-liquid ratio of 1:2.5, the temperature is raised to 65~70℃ and soaked for 2~3 hours to fully release the residual acid inside the CPVC particles; After soaking, the material is sent back to a precision belt centrifuge for dehydration and separation to further remove trace amounts of acid and water trapped in the material, ultimately ensuring that the material's moisture content is ≤8%. The filtrate is used for primary soaking. When the acid concentration of the filtrate reaches 0.5%, it is finely filtered and mixed with concentrated acid to form 18±0.5% hydrochloric acid, which is then reused for feeding. The wet powder enters the drying system.

6. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 1, characterized in that: In step S2, the auxiliary agent system includes a dispersant and a composite auxiliary agent; The dispersant is hydrophobic silica; The composite additive is composed of fatty alcohol polyoxyethylene ether, polyvinylpyrrolidone and benzoyl peroxide, with a mass percentage of 35%:55%:10%.

7. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 6, characterized in that: The dispersant and composite additive are added at amounts of 0.28% and 0.22% of the mass of the PVC raw material, respectively. The mixture is heated to 60°C and then transported to the chlorination reactor. The chlorination reactor is started with one button, and the stirring is activated. Liquid chlorine is automatically introduced according to the preset DCS / PID program to carry out the substitution reaction. When the chlorine content of the material reaches 67±1%, the chlorine supply is stopped, the reaction system is cooled down and transferred to the waiting cooling reactor to continue cooling to 60℃.

8. The method for preparing CPVC by acid-phase suspension and nitrogen bubbling deacidification according to claim 1, characterized in that: In step S4, nano-activated calcium carbonate is added to neutralize the trace amounts of hydrogen chloride evaporated from the material, thereby neutralizing the residual trace amounts of hydrogen chloride and generating carbon dioxide to form an inert atmosphere.

9. A chlorinated polyvinyl chloride resin prepared by the method according to any one of claims 1 to 8, characterized in that: The resin has a whiteness ≥95, a thermal stability time ≥150 min, and a Vicat softening point of 120℃.

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