A method for optimizing process parameters of chlorination of chlorinated paraffin

Abstract

The present application relates to the field of computer-aided optimization of chemical process parameters, and particularly relates to a method for optimizing process parameters of a chlorinated paraffin thermal chlorination reaction. A base paraffin raw material is placed in a reactor, a composite free radical regulating system is injected into the reactor, and chlorine gas is introduced for thermal chlorination reaction. The composite free radical regulating system is composed of an organic peroxide and a nitrogen-containing heterocyclic compound. The organic peroxide is decomposed by heat to form primary free radicals at the initial stage of the reaction. The nitrogen-containing heterocyclic compound is temporarily complexed with free radicals in the system at the chain growth stage, and is released from the complex by heat when the concentration of free radicals in the system decreases. The free radical concentration dynamic balance is maintained throughout the thermal chlorination reaction by the system until the target chlorination degree is reached. The present application suppresses the nonlinear fluctuation of local free radical concentration and reduces the distribution deviation of combined chlorine content in the final product.

Description

Technical Field

[0001] This invention relates to the field of computer-aided optimization of chemical process parameters, and specifically to a method for optimizing process parameters of a thermal chlorination reaction of chlorinated paraffin. Background Technology

[0002] Currently, the production of chlorinated paraffin mainly employs a pure thermal chlorination process. This conventional process involves placing the paraffin raw material in a sealed reaction vessel and continuously heating the reaction system using an external heat source. Once the material temperature reaches a set range, chlorine gas is continuously introduced into the liquid paraffin. Under pure thermal activation conditions, chlorine molecules undergo homolytic cleavage to generate primary free radicals, which initiate a chain substitution reaction. Chlorine atoms gradually replace hydrogen atoms on the carbon chains of the paraffin, and the reaction continues until the bound chlorine content of the liquid phase reaches the target value. The chlorination process is then terminated, and the waste gas is treated to remove acid. This reaction process relies entirely on the system's own absorption of physical heat to activate and maintain the chain reaction of free radicals. Throughout the chain initiation and chain growth stages, no chemical components are added to the system to interfere with the generation or consumption of free radicals.

[0003] The pure thermal chlorination process is highly dependent on the system's thermal activation energy during the initiation stage, resulting in an explosive increase in the initial free radicals. Furthermore, due to the lack of chemical control mechanisms during the subsequent chain growth stage, the free radical concentration within the system exhibits drastic nonlinear fluctuations. The sudden increase in free radical concentration in localized areas leads to random collisions between free radicals, triggering random substitution side reactions. This causes the substitution sites of chlorine atoms on the paraffin backbone to become uncontrollable, resulting in severe microscopic inhomogeneity in the distribution of bound chlorine content in the final product. Summary of the Invention

[0004] To address the shortcomings of existing pure hot chlorination paraffin production processes, such as high dependence of the reaction system on thermal activation energy, drastic nonlinear fluctuations in free radical concentration, easy initiation of random substitution side reactions, and uneven microscopic distribution of bound chlorine content in the final product, this invention provides a method for optimizing the process parameters of the hot chlorination reaction of chlorinated paraffin.

[0005] To address the aforementioned technical problems, this invention provides a method for optimizing the process parameters of a thermal chlorination reaction of chlorinated paraffin, comprising the following technical features: placing a basic paraffin raw material in a reactor, injecting a composite free radical control system into the basic paraffin raw material, and introducing chlorine gas to carry out a thermal chlorination reaction. The composite free radical control system is composed of an organic peroxide and a nitrogen-containing heterocyclic compound. The organic peroxide is thermally decomposed in the initial stage of the thermal chlorination reaction to form primary free radicals. The nitrogen-containing heterocyclic compound undergoes transient complexation with the free radicals in the system during the chain growth stage of the thermal chlorination reaction. When the free radical concentration in the system decreases, the transient complex is thermally decomposed to release free radicals. The composite free radical control system maintains a dynamic balance of free radical concentration throughout the entire thermal chlorination reaction until the target degree of chlorination is reached.

[0006] The thermal chlorination reaction of chlorinated paraffin is a typical free radical chain substitution reaction, consisting of three core stages: chain initiation, chain propagation, and chain termination. In this scheme, the peroxide bond energy of the organic peroxide is much lower than that of the chlorine-chlorine bond in the chlorine molecule. This allows for the generation of primary free radicals at a relatively low temperature during the initial reaction stage, significantly reducing the dependence of the chain initiation step on the system's thermal activation energy and avoiding the explosive generation of primary free radicals caused by high-temperature excitation in purely thermal processes. Nitrogen-containing heterocyclic compounds can form reversible coordination bonds with active free radicals in the system through the lone pair electrons of nitrogen atoms, achieving transient complexation and storage of free radicals during the chain propagation stage. When the free radical concentration in the system decreases, the transient complex decomposes upon heating, releasing the free radicals again. This constructs a dynamic "storage-release" control mechanism, maintaining a stable and controllable free radical concentration throughout the process, suppressing random substitution side reactions caused by sudden local increases in free radicals, and making the substitution sites of chlorine atoms on the paraffin carbon chain more uniform, thus solving the core problem of uneven microscopic distribution of bound chlorine content in the product.

[0007] Furthermore, in the above technical solution, the organic peroxide is at least one of dialkyl peroxide, diacyl peroxide, or peroxide ester, the organic peroxide contains two or more peroxy bond structures, the two or more peroxy bond structures are respectively connected to both ends of alkyl backbones of different carbon chain lengths, and the carbon atom distribution range of the alkyl backbone is C8 to C16.

[0008] In practice, two or more peroxide bonds in the organic peroxide molecule serve as active sites for free radical generation. The peroxide bonds located at both ends of the alkyl backbone have different decomposition temperatures due to differences in chemical environment, allowing them to undergo stepwise homolytic cleavage within the reaction cycle, continuously providing primary free radicals and avoiding insufficient free radical supply in the later stages of the reaction caused by the one-time decomposition of a single peroxide bond. The C8 to C16 alkyl backbone has a similar carbon chain structure to the basic paraffin raw material, exhibiting excellent compatibility and enabling uniform dispersion of organic peroxides in the paraffin system. This avoids free radical bursts caused by excessively high local concentrations. At the same time, the steric hindrance of the long carbon chain can regulate the decomposition rate of the peroxide bonds, ensuring a precise match between the free radical generation rate and the reaction process.

[0009] Furthermore, in the above technical solution, the nitrogen-containing heterocyclic compound is a piperidine derivative or an imidazoline derivative, and a sterically hindered group is attached to the ortho position of the nitrogen atom of the piperidine derivative. The sterically hindered group is tert-butyl or tert-pentyl. The nitrogen-containing heterocyclic compound completes the transient complexation by forming a coordinate bond with the free radical in the system through the lone pair electrons on the nitrogen atom.

[0010] In practice, the nitrogen atoms on the heterocyclic skeletons of piperidine and imidazoline derivatives have unpaired lone pairs of electrons, which can form reversible coordination bonds with active free radicals carrying single electrons, achieving transient complexation of free radicals. The sterically hindered groups such as tert-butyl and tert-amyl at the nitrogen atom can prevent the transient complex formed by the complex from being attacked by other active species in the system and undergoing irreversible decomposition, ensuring the cyclic reversibility of the complexation-decomposition process. At the same time, the sterically hindered groups can adjust the bond energy of the coordination bonds, so that the transient complex can be controllably decomposed within the working temperature range of the reaction system, accurately responding to fluctuations in the concentration of free radicals in the system and achieving dynamic regulation.

[0011] Furthermore, in the above technical solution, before injecting into the reactor, the organic peroxide and the nitrogen-containing heterocyclic compound are placed in supercritical carbon dioxide fluid for supramolecular self-assembly treatment to form a core-shell structured microcapsule precursor in which the nitrogen-containing heterocyclic compound encapsulates the organic peroxide. The microcapsule precursor is then separated, dried, and injected into the reactor as the composite free radical regulation system.

[0012] In practice, supercritical carbon dioxide fluid, with its low viscosity and high diffusivity, provides a uniform medium environment for the supramolecular self-assembly of organic peroxides and nitrogen-containing heterocyclic compounds. Through intermolecular van der Waals forces and hydrogen bonding, nitrogen-containing heterocyclic compounds can achieve directional coating of organic peroxides, forming stable core-shell microcapsules. This core-shell structure can slow down the decomposition rate of the core organic peroxide in the high-temperature reaction system, avoiding the free radical burst caused by its complete decomposition at the beginning of the reaction. At the same time, the nitrogen-containing heterocyclic compounds in the shell can directly complex with the free radicals in the system, achieving a synergistic effect of continuous decomposition and release of free radicals from the core organic peroxide and synchronous regulation of free radical concentration by the nitrogen-containing heterocyclic compounds in the shell, thus significantly extending the effective operating period of the regulation system.

[0013] Furthermore, in the above technical solution, the process of injecting the composite free radical control system into the reactor includes a segmented injection step. In the first segment, 70% of the total mass fraction of the composite free radical control system is injected and mixed with the basic paraffin raw material. In the second segment, when the thermal chlorination reaction proceeds to the degree of chlorination reaching 30%, the remaining mass fraction of the composite free radical control system is injected.

[0014] In practice, when the degree of chlorination of chlorinated paraffin reaches about 30%, the viscosity of the system increases significantly with the increase of chlorine content, which leads to a decrease in the mass transfer efficiency of chlorine in the liquid phase. At the same time, the consumption rate of the original free radicals in the system accelerates, which can easily lead to insufficient free radical concentration and a sudden drop in reaction rate. The staged injection method can inject most of the control system in the early stage of the reaction to ensure the smooth progress of chain initiation and early chain growth. At the critical node of 30% chlorination, the remaining control system is added to replenish the free radical concentration in the system in time, which can make up for the decrease in mass transfer and reaction efficiency caused by the increase in system viscosity. This ensures that a stable dynamic balance of free radical concentration can be maintained in the middle and later stages of the reaction, and avoids large fluctuations in the reaction rate.

[0015] Furthermore, in the above technical solution, the cyclic skeleton of the nitrogen-containing heterocyclic compound is grafted with o-phenanthroline derivative side chains, and micron-sized transition metal oxide particles are simultaneously added to the reactor. The metal ions on the surface of the transition metal oxide particles and the o-phenanthroline derivative side chains form a coordination network. The coordination network constitutes a physical trap structure to restrict the spatial migration path of free radicals in the reactor.

[0016] In practice, the o-phenanthroline derivative has a multidentate coordination structure, which can form stable coordination bonds with metal ions on the surface of transition metal oxide particles, thereby constructing a three-dimensional cross-linked coordination network in the reaction system. The physical trap structure formed by this coordination network can restrict the random spatial migration of active free radicals, avoid excessive aggregation of free radicals in local areas, and confine the activity range of free radicals to the vicinity of the gas-liquid mass transfer interface between paraffin raw materials and chlorine gas, thereby increasing the effective collision probability of free radicals with paraffin carbon chains and chlorine molecules, reducing the bimolecular termination side reactions between free radicals, and further improving the site selectivity and product structure uniformity of the chlorination reaction.

[0017] Furthermore, in the above technical solution, during the thermal chlorination reaction, an ultrasonic physical field with a frequency range between 20 kHz and 50 kHz is applied to the reactor. The application time of the ultrasonic physical field is synchronized with the injection time of the composite free radical control system. The cavitation microfluidics generated by the ultrasonic physical field strips away the agglomerates formed by the composite free radical control system in the basic paraffin raw material.

[0018] In practice, when ultrasound waves of 20 kHz to 50 kHz propagate in a liquid paraffin system, they generate a periodic cavitation effect, forming a large number of microbubbles that collapse rapidly, generating high-intensity microfluidics and shear forces. When ultrasound waves are applied simultaneously with the injection of the composite free radical control system, the agglomerates formed by the control system components can be promptly stripped away through the cavitation microfluidics, allowing the control system to be uniformly dispersed in the paraffin raw material. This avoids the problem of excessively high local concentrations of control components and imbalances in free radical generation and complexation caused by agglomeration, ensuring that the free radical concentrations throughout the entire reaction system can achieve a precise dynamic balance.

[0019] Furthermore, in the above technical solution, when the thermal chlorination reaction reaches the target chlorination degree, an aqueous emulsion containing a hindered phenolic structure is injected into the reactor. The aqueous emulsion forms water-in-oil microemulsion droplets in the reactor. The aqueous phase inside the water-in-oil microemulsion droplets contains dissolved potassium iodide. The potassium iodide and the hindered phenolic structure consume the residual free radicals in the system.

[0020] In practice, after reaching the target chlorination degree, the residual active free radicals in the system will continue to trigger side reactions such as random substitution and carbon chain scission, destroying the structural uniformity and stability of the product. Components containing hindered phenolic structures have phenolic hydroxyl groups, which can capture free radicals through hydrogen transfer reactions to form stable phenolic oxygen radicals, thus rapidly terminating the chain reaction. The structure of water-in-oil microemulsion droplets allows the hindered phenolic structures in the oil phase to capture free radicals in the oil phase system first. At the same time, potassium iodide in the aqueous phase can undergo redox reactions with free radicals at the microemulsion droplet interface, achieving complete removal of free radicals in both the oil and aqueous phases, completely terminating the chain reaction, and avoiding the occurrence of subsequent side reactions.

[0021] Furthermore, in the above technical solution, after the thermal chlorination reaction is completed, the liquid phase mixture in the reactor is transported to a cross-flow nano-ceramic membrane separation component. The pore size distribution of the nano-ceramic membrane separation component is set to retain a molecular weight greater than the molecular weight of the microcapsule precursor shell and less than the molecular weight of the chlorinated paraffin product. The liquid phase mixture forms a tangential flow on the surface of the nano-ceramic membrane separation component.

[0022] In practice, the tangential flow design of the cross-flow nano-ceramic membrane separation module can prevent solid particles in the liquid mixture from forming a filter cake layer on the membrane surface, ensuring the continuous and stable operation of the separation process. By precisely setting the molecular weight cutoff range of the membrane, the residual microcapsule precursors and their decomposition products in the reaction system can be completely retained, while the target chlorinated paraffin product passes through the membrane module, achieving efficient and continuous separation of the chlorinated paraffin product from the residual components of the control system. This avoids the residual control components affecting the thermal stability and subsequent processing performance of the product, and eliminates the need for additional separation steps such as distillation and extraction, simplifying the process.

[0023] Furthermore, in the above technical solution, the chlorinated paraffin product liquid that has been intercepted and permeated by the nano-ceramic membrane separation component is directly introduced into the melt blending zone of the twin-screw extruder. Polyvinyl chloride resin powder and nano-calcium carbonate filler are added simultaneously in the melt blending zone. The chlorinated paraffin product liquid coats the polyvinyl chloride resin powder and the nano-calcium carbonate filler in the twin-screw extruder to form a blended granule.

[0024] In practice, the chlorinated paraffin product liquid after membrane separation still has high residual heat, which can be directly introduced into the melt blending zone of the twin-screw extruder. This residual heat can reduce the heating energy consumption required for the melt blending of polyvinyl chloride resin. At the same time, the liquid chlorinated paraffin can uniformly coat the surface of polyvinyl chloride resin powder and nano-calcium carbonate filler, realizing in-situ efficient blending of plasticizer, resin and filler. This avoids the repeated energy consumption of reheating and melt blending of chlorinated paraffin product after cooling in traditional processes, while improving the dispersion uniformity of each component and ensuring the processing performance and mechanical properties of the final blended granules.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By injecting a composite free radical regulation system composed of organic peroxides and nitrogen-containing heterocyclic compounds into the basic paraffin raw material, the organic peroxides are used to generate primary free radicals through thermal decomposition in the initial stage, reducing the system's dependence on thermal activation energy. Simultaneously, the nitrogen-containing heterocyclic compounds undergo transient complexation with free radicals in the system during the chain growth stage, and then decompose upon heating when the free radical concentration decreases, releasing the free radicals. This establishes a dynamic equilibrium mechanism for free radical concentration throughout the reaction. This mechanism suppresses sudden increases in local free radical concentration and random collisions between free radicals, constrains the attack paths of free radicals on the paraffin backbone, makes the substitution sites of chlorine atoms on the carbon chain more uniform, reduces the distribution deviation of bound chlorine content in the final product, and solves the problem of uneven microscopic distribution of chlorine content in the product under purely thermal initiation.

[0026] 2. Organic peroxides and nitrogen-containing heterocyclic compounds are self-assembled with supercritical carbon dioxide fluid to form core-shell microcapsule precursors, which delays the release cycle of the regulatory components in the high-temperature system. Side chains of o-phenanthroline derivatives are grafted onto the cyclic framework of the nitrogen-containing heterocyclic compounds and combined with micron-sized transition metal oxide particles to form a coordination network trap, restricting the spatial migration path of free radicals within the reaction system. Combined with cavitation microfluidics generated by ultrasonic physical fields to exfoliate the aggregates, and the injection of water-in-oil microemulsion droplets containing hindered phenolic structures and potassium iodide when the target chlorination degree is reached to consume residual free radicals in the system and terminate side reactions, the unreacted microcapsules are retained by a cross-flow nano-ceramic membrane separation component after the reaction. The obtained chlorinated paraffin product liquid is directly melt-blended and granulated with polyvinyl chloride resin powder and nano-calcium carbonate filler in a twin-screw extruder, forming a closed-loop process from free radical concentration control to in-situ product separation and blending. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0028] Example 1: Raw material formula: Basic paraffin raw material: C12-C14 normal liquid paraffin, number average molecular weight 192, bromine value 0.12gBr / 100g, water content ≤50mg / kg, dosage 1000kg; The complex free radical regulation system consists of an organic peroxide of 1,10-bis(tert-butylperoxide)decane (a dialkyl peroxide with 10 carbon atoms in the alkyl backbone and peroxy bonds at both ends, conforming to the C8-C16 range) and a nitrogen-containing heterocyclic compound of 4-(1,10-o-phenanthroline-5-carboxamido)-2,2,6,6-tetramethylpiperidine (a piperidine derivative with a tetramethyl substituent at the tert-butyl position on the nitrogen atom and an o-phenanthroline derivative side chain grafted onto the cyclic skeleton). The mass ratio of the two is 1:2, and the total amount used is 2.4 kg. Micron-sized transition metal oxide particles: micron-sized zinc oxide, particle size D50=2.5μm, purity ≥99.5%, dosage 0.8kg; Terminating agent: 2,6-di-tert-butyl-p-methylphenol oil-in-water aqueous emulsion, solid content 30%, aqueous phase contains 10% potassium iodide by mass, dosage 8 kg; Separation equipment: Cross-flow alumina nano-ceramic membrane separation module, molecular weight cutoff 1000 Da, membrane channel pore size 2 mm, effective membrane area 0.5 m²; Blending equipment: co-rotating parallel twin-screw extruder, length-to-diameter ratio 40:1, screw diameter 35mm.

[0029] Preparation method steps: Preparation of composite free radical regulation system Organic peroxides and nitrogen-containing heterocyclic compounds were added to a high-pressure reactor in a predetermined ratio. Supercritical carbon dioxide fluid was introduced into the reactor, and the temperature was controlled at 38°C, the pressure at 7.5 MPa, and the stirring rate at 150 r / min. The reactor was subjected to supramolecular self-assembly for 2.5 h. After the treatment was completed, the pressure was slowly released to atmospheric pressure, the material in the reactor was removed, and the material was placed in a vacuum drying oven at 40°C for 6 h to obtain a core-shell structured microcapsule precursor of organic peroxides encapsulated by nitrogen-containing heterocyclic compounds, i.e., a composite free radical regulation system. The precursor was sealed and stored in the dark for later use.

[0030] Thermal chlorination reaction process: The basic paraffin raw material is added to a closed tower reactor equipped with a jacketed heater, stirring device, ultrasonic generator, and chlorine distributor. Stirring is started and the stirring rate is controlled at 80 r / min. The material in the reactor is heated to 85°C through the jacket heat transfer oil. First stage injection: After mixing 70% (1.68 kg) of the total mass of the composite free radical control system with micron-sized zinc oxide particles, inject it into the reactor and stir it with the basic paraffin raw material for 10 min; at the same time, turn on the ultrasonic generator and apply an ultrasonic physical field with a frequency of 30 kHz and a power density of 0.8 W / cm², and continue to apply it until the reaction is over. Open the chlorine cylinder and continuously introduce chlorine into the reactor through the chlorine distributor. Control the chlorine introduction rate to 12 kg / h, maintain the pressure inside the reactor at 0.15 MPa, and control the reaction temperature at 90 ± 2℃ to carry out the thermal chlorination reaction. The chlorination level of the material in the reactor is monitored online. When the chlorination level reaches 30%, the second stage of injection is performed: the remaining 30% of the complex free radical control system (0.72 kg) is injected into the reactor, and the chlorination rate and reaction conditions are maintained to continue the reaction. The chlorination degree was continuously monitored online. When the chlorination degree of the material reached the target value of 52%, the chlorine gas supply was immediately stopped, the ultrasonic generator was turned off, a terminator was quickly injected into the reactor, and the mixture was stirred for 15 minutes to terminate the chain reaction in the system and obtain crude chlorinated paraffin product.

[0031] Product separation and blending granulation: The crude chlorinated paraffin product in the reactor is conveyed to a cross-flow nano-ceramic membrane separation unit. The feed pressure is controlled at 0.3 MPa and the cross-flow velocity is 2.5 m / s, so that the liquid mixture forms a tangential flow on the membrane surface. The nano-ceramic membrane has a molecular weight cutoff of 1000 Da, which is greater than the molecular weight of the microcapsule precursor shell monomer (about 450 Da) and less than the upper limit of the number average molecular weight range of the target chlorinated paraffin product (about 780 Da). The membrane separates and retains unreacted microcapsule precursors, zinc oxide particles and high molecular weight byproducts, and a purified chlorinated paraffin product liquid is obtained through permeation. The refined chlorinated paraffin product liquid obtained from permeation is directly conveyed to the melt blending zone of a twin-screw extruder while being kept at a constant temperature. At the same time, SG-5 type polyvinyl chloride (PVC) resin powder and nano-calcium carbonate filler are added to the melt blending zone. The mass ratio of chlorinated paraffin product liquid, PVC resin powder, and nano-calcium carbonate is controlled at 25:100:5. The temperature of each section of the twin-screw extruder is controlled at 120℃-165℃, and the main engine speed is 300r / min. The material is melt blended in the extruder, and the chlorinated paraffin product liquid uniformly coats the PVC resin powder and nano-calcium carbonate filler. After extrusion through a die, water cooling, and pelletizing, PVC blend granules are obtained.

[0032] Example 2: The organic peroxide was replaced with 1,12-bis(octanoylperoxide)dodecane (diacyl peroxide, with 12 carbon atoms in the alkyl main chain and peroxy bonds at both ends, conforming to the C8-C16 range), and the remaining raw materials, formulation, process steps and parameters were completely consistent with those in Example 1.

[0033] Example 3: The nitrogen-containing heterocyclic compound was replaced with 2-tert-butyl-4-(1,10-o-phenanthroline-5-yl)imidazoline (an imidazoline derivative with a sterically hindered tert-butyl group attached to the ortho position of the nitrogen atom and an o-phenanthroline derivative side chain grafted onto the cyclic skeleton). All other raw materials, formulations, process steps and parameters were completely consistent with those in Example 1.

[0034] Example 4: The mass ratio of organic peroxide to nitrogen-containing heterocyclic compound was adjusted to 1:1, and the remaining raw materials, formulation, process steps and parameters were completely consistent with those in Example 1.

[0035] Example 5: The mass ratio of organic peroxide to nitrogen-containing heterocyclic compound was adjusted to 1:3, and the remaining raw materials, formulation, process steps and parameters were completely consistent with those in Example 1.

[0036] Example 6: The supercritical carbon dioxide supramolecular self-assembly step of the complex free radical regulation system is omitted. The organic peroxide and nitrogen-containing heterocyclic compound are directly mixed at a mass ratio of 1:2 and used as the complex free radical regulation system. The other raw materials, formulations, process steps and parameters are completely consistent with those in Example 1.

[0037] Example 7: No micron-sized zinc oxide particles were added; all other raw materials, formulations, process steps, and parameters were completely consistent with Example 1.

[0038] Example 8: The step of applying the ultrasonic physical field is omitted. The remaining raw materials, formula, process steps and parameters are completely consistent with those of Example 1.

[0039] Example 9: The hindered phenol aqueous emulsion used for termination was replaced with 2,6-di-tert-butyl-p-methylphenol aqueous emulsion (30% solid content, water-in-oil type) without potassium iodide. All other raw materials, formulations, process steps and parameters were completely consistent with those in Example 1.

[0040] Example 10: The frequency of the applied ultrasonic physical field was adjusted to 20kHz, and the remaining raw materials, formula, process steps and parameters were completely consistent with those in Example 1.

[0041] Example 11: The frequency of the applied ultrasonic physical field was adjusted to 50kHz, and the remaining raw materials, formula, process steps and parameters were completely consistent with those in Example 1.

[0042] Example 12: The timing of the injection of the second-stage complex free radical control system was adjusted to when the chlorination degree of the reaction system reached 25%. The other raw materials, formulation, process steps and parameters were completely consistent with those in Example 1.

[0043] Comparative Example 1: The complex free radical regulation system uses only organic peroxides and does not add nitrogen-containing heterocyclic compounds. The amount of organic peroxide used is the same as that in Example 1. The supercritical carbon dioxide supramolecular self-assembly step is omitted. All other raw materials, process steps and parameters are completely consistent with Example 1.

[0044] Comparative Example 2: The conventional pure thermal chlorination process described in the background technology was used, without the addition of any complex free radical control system, micron-sized zinc oxide particles, or ultrasonic physical field. All other reaction conditions (basic paraffin raw material dosage, reaction temperature, pressure, chlorine gas introduction rate, and target chlorination degree of 52%) were completely consistent with those in Example 1. After the reaction reached the target chlorination degree, only nitrogen purging and deacidification treatment were used. The reaction was not terminated by adding hindered phenol aqueous emulsion, and membrane separation and twin-screw mixing steps were not performed.

[0045] Comparative Example 3: The frequency of the applied ultrasonic physical field was adjusted to 10kHz, which is outside the 20kHz-50kHz range defined in this invention. The other raw materials, formula, process steps and parameters were completely consistent with those in Example 1.

[0046] Comparative Example 4: The segmented injection step of the complex free radical regulation system was omitted. The entire 2.4 kg complex free radical regulation system was injected into the reactor at the initial stage of the reaction. The remaining raw materials, formulation, process steps and parameters were completely consistent with those of Example 1.

[0047] Test method: Chlorination degree and distribution uniformity test: The oxygen flask combustion method specified in GB / T9872-2026 "Determination of halogen content in rubber and thermoplastic elastomers" was adopted. Ten parallel samples were randomly selected from each product sample for chlorination degree test. The relative standard deviation (RSD) of chlorination degree was calculated. The smaller the RSD, the better the uniformity of chlorine content distribution in the product.

[0048] Reaction time test: Record the total time from the start of chlorine gas introduction to the system reaching the target chlorination degree of 52%, in hours.

[0049] Free radical concentration fluctuation coefficient test: The free radical concentration in the system during the reaction process was monitored online using an electron spin resonance spectrometer (ESR). Data was collected every 30 minutes, and the coefficient of variation of the free radical concentration throughout the reaction process was calculated as the free radical concentration fluctuation coefficient. The smaller the value, the better the dynamic balance of the free radical concentration.

[0050] Byproduct content testing: The total mass fraction of polychlorinated isomers and carbon chain scission byproducts in the product was determined by gas chromatography-mass spectrometry (GC-MS), and the units are %.

[0051] Thermal stability test: The Congo red method specified in GB / T2917.1-2002 "Determination of the release of hydrogen chloride and any other acidic products at high temperature from blends and products mainly composed of vinyl chloride homopolymers and copolymers" was adopted to test the thermal stability time of the product at 180℃. The unit is min. The larger the value, the better the thermal stability of the product.

[0052] The test results are shown in Table 1: Table 1. Performance test results of each embodiment and comparative example:

[0053] Results analysis: Examples 1-12 all employ the composite free radical regulation system and supporting process of the present invention. Compared with the conventional pure thermal chlorination process of Comparative Example 2, the reaction time is shortened by more than 30%, the relative standard deviation of chlorination degree is reduced by more than 85%, the free radical concentration fluctuation coefficient is reduced by more than 80%, the total content of by-products is reduced by more than 85%, and the thermal stability time at 180°C is increased by more than 100%. This fully demonstrates that the technical solution of the present invention can effectively solve the core defects of the prior art, such as high reaction activation energy requirements, drastic fluctuations in free radical concentration, uncontrollable chlorine substitution sites, uneven microscopic distribution of chlorine content in products, numerous by-products, and poor thermal stability, and fully achieves the expected technical effects.

[0054] Comparative Example 1 used only organic peroxides, lacking the free radical transient complexation regulation function of nitrogen-containing heterocyclic compounds. Compared with Example 1, the reaction time was extended by 23.2%, the chlorination degree RSD increased by 290.6%, the free radical concentration fluctuation coefficient increased by 212.6%, the total by-product content increased by 323.8%, and the thermal stability time decreased by 34.9%. These results demonstrate that organic peroxides and nitrogen-containing heterocyclic compounds are indispensable core components for achieving the effects of this invention. Only through the synergistic effect of "controllable generation of primary free radicals + dynamic storage and release of free radicals" can the dynamic balance of free radical concentration be achieved throughout the reaction process. Using organic peroxides alone can only reduce the activation energy of the chain initiation stage, but cannot suppress the drastic fluctuations in free radical concentration during the chain growth stage, and cannot significantly improve the uniformity of the product chlorine content.

[0055] Example 6 omits the supercritical self-assembled core-shell structure preparation step. Compared with Example 1, the reaction time is extended by 11.6% and the chlorination degree RSD is increased by 112.5%, which proves that the core-shell structure can delay the decomposition rate of organic peroxides, achieve long-term release of the controlled components, and significantly improve the stability of the reaction process and the uniformity of the products. In Example 7, no micron-sized transition metal oxide particles were added, so a coordination network trap structure could not be formed. Compared with Example 1, the degree of chlorination RSD increased by 78.1% and the free radical fluctuation coefficient increased by 50.7%, proving that the coordination network can restrict the random spatial migration of free radicals, improve the site selectivity of chlorination reaction, and reduce side reactions. In Example 8, no ultrasonic physical field was applied. Compared with Example 1, the chlorination degree RSD increased by 93.75%, proving that the cavitation microfluidics generated by ultrasound can effectively strip away the aggregates in the control system, achieve uniform dispersion of them in the paraffin raw material, and avoid the increase of side reactions caused by local concentration imbalance. In Example 9, potassium iodide was not added as the terminator. Compared with Example 1, the thermal stability time decreased by 11.9%, demonstrating that the biphasic free radical scavenging system of hindered phenol and potassium iodide can more thoroughly terminate the chain reaction and eliminate the negative impact of residual free radicals on the thermal stability of the product.

[0056] In Examples 10 and 11, the ultrasonic frequencies were within the 20kHz-50kHz range specified in this invention, and all performance indicators were close to those of Example 1, maintaining excellent levels. However, in Comparative Example 3, the ultrasonic frequency was 10kHz, exceeding the specified range. Compared to Example 1, the chlorination degree RSD increased by 134.4%, and the total by-product content increased by 128.6%. These results demonstrate that the process parameter range specified in this invention is a necessary condition for achieving excellent technical effects. When parameters exceed the specified range, the expected dispersion and control effects cannot be achieved, and product performance significantly declines.

[0057] Comparative Example 4 omitted the segmented injection step and injected the entire control system at once. Compared with Example 1, the reaction time was extended by 17.9%, the chlorination degree RSD increased by 237.5%, and the free radical fluctuation coefficient increased by 174.0%. These results demonstrate that segmented injection can accurately match the changes in system viscosity and free radical demand during the reaction process, avoiding the problems of free radical bursts in the early stage of the reaction and insufficient free radical supply in the later stage. It is a key step in maintaining the dynamic balance of free radical concentration throughout the reaction process.

[0058] In summary, the technical solution of this invention, through the synergistic effect of the composite free radical regulation system and the corresponding process optimization steps, achieves dynamic and precise control of free radical concentration throughout the entire thermal chlorination reaction of chlorinated paraffin, improves the uniformity of chlorine content distribution in the product, reduces the probability of side reactions, shortens the reaction cycle, and enhances the thermal stability of the product. The comparison results of each embodiment and comparative example fully demonstrate the inventiveness and unexpected technical effects of the technical solution of this invention.

Claims

1. A method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin, characterized in that, A basic paraffin raw material is placed in a reactor, and a composite free radical control system is injected into the basic paraffin raw material and chlorine gas is introduced to carry out a thermal chlorination reaction. The composite free radical control system is composed of organic peroxides and nitrogen-containing heterocyclic compounds. The organic peroxides are thermally decomposed in the initial stage of the thermal chlorination reaction to form primary free radicals. The nitrogen-containing heterocyclic compounds undergo transient complexation with the free radicals in the system during the chain growth stage of the thermal chlorination reaction. When the free radical concentration in the system decreases, the transient complexes are thermally decomposed to release free radicals. The composite free radical control system maintains the dynamic balance of free radical concentration throughout the thermal chlorination reaction until the target degree of chlorination is reached.

2. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 1, characterized in that, The organic peroxide is at least one of dialkyl peroxide, diacyl peroxide, or peroxide ester, and the organic peroxide contains two or more peroxy bond structures, which are respectively connected to both ends of an alkyl backbone with different carbon chain lengths, and the carbon number distribution range of the alkyl backbone is C8 to C16.

3. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 1, characterized in that, The nitrogen-containing heterocyclic compound is a piperidine derivative or an imidazoline derivative. The nitrogen atom of the piperidine derivative is attached to a sterically hindered group at the ortho position. The sterically hindered group is tert-butyl or tert-pentyl. The nitrogen-containing heterocyclic compound completes the transient complexation by forming a coordinate bond with the free radical in the system through the lone pair electrons on the nitrogen atom.

4. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 1, characterized in that, Before being injected into the reactor, the organic peroxide and the nitrogen-containing heterocyclic compound are subjected to supramolecular self-assembly in supercritical carbon dioxide fluid to form a core-shell structured microcapsule precursor in which the nitrogen-containing heterocyclic compound encapsulates the organic peroxide. The microcapsule precursor is then separated, dried, and injected into the reactor as the composite free radical regulation system.

5. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 1, characterized in that, The process of injecting the composite free radical control system into the reactor includes a staged injection step. In the first stage, 70% of the total mass fraction of the composite free radical control system is injected and mixed with the base paraffin raw material. In the second stage, when the thermal chlorination reaction proceeds to the degree of chlorination reaching 30%, the remaining mass fraction of the composite free radical control system is injected.

6. The method for optimizing process parameters of the thermal chlorination reaction of chlorinated paraffin according to claim 3, characterized in that, The nitrogen-containing heterocyclic compound has a phenanthroline derivative side chain grafted onto its cyclic skeleton. Micron-sized transition metal oxide particles are simultaneously added to the reactor. The metal ions on the surface of the transition metal oxide particles form a coordination network with the phenanthroline derivative side chain. The coordination network constitutes a physical trap structure that restricts the spatial migration path of free radicals within the reactor.

7. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 1, characterized in that, During the thermal chlorination reaction, an ultrasonic physical field with a frequency range between 20 kHz and 50 kHz is applied into the reactor. The application time of the ultrasonic physical field is synchronized with the injection time of the composite free radical control system. The cavitation microfluidics generated by the ultrasonic physical field strips away the agglomerates formed by the composite free radical control system in the base paraffin raw material.

8. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 1, characterized in that, When the thermal chlorination reaction reaches the target chlorination degree, an aqueous emulsion containing a hindered phenolic structure is injected into the reactor. The aqueous emulsion forms water-in-oil microemulsion droplets in the reactor. Potassium iodide is dissolved in the aqueous phase inside the water-in-oil microemulsion droplets. The potassium iodide and the hindered phenolic structure consume the free radicals remaining in the system.

9. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 4, characterized in that, After the thermal chlorination reaction is completed, the liquid mixture in the reactor is transported to a cross-flow nano-ceramic membrane separation component. The pore size distribution of the nano-ceramic membrane separation component is set to retain a molecular weight greater than the molecular weight of the microcapsule precursor shell and less than the molecular weight of the chlorinated paraffin product. The liquid mixture forms a tangential flow on the surface of the nano-ceramic membrane separation component.

10. The method for optimizing process parameters of thermal chlorination reaction of chlorinated paraffin according to claim 9, characterized in that, The chlorinated paraffin product liquid, which is intercepted and permeated by the nano-ceramic membrane separation component, is directly introduced into the melt blending zone of a twin-screw extruder. Polyvinyl chloride resin powder and nano-calcium carbonate filler are added simultaneously in the melt blending zone. The chlorinated paraffin product liquid coats the polyvinyl chloride resin powder and the nano-calcium carbonate filler in the twin-screw extruder to form a blended granule.

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