A continuous preparation method of chlorinated paraffin based on visible light photosensitive slow-release initiation

Abstract

The application provides a continuous chlorinated paraffin preparation method based on visible light photosensitive slow-release initiation, and relates to the technical field of chemical industry. The method comprises the following steps: mixing refined paraffin and an organic photosensitive component to form a reaction precursor; after being heated to a reaction temperature, chlorine is introduced and a chlorination reaction is carried out by continuously irradiating with visible light to obtain crude chlorinated paraffin; and the chlorinated paraffin is obtained by negative pressure degassing and stabilizer treatment. The application indirectly initiates the chlorination reaction in the form that the organic photosensitive component absorbs visible light to form an excited state, replaces the traditional ultraviolet light direct photolysis initiation mechanism of chlorine molecules, makes free radicals generate slowly, effectively inhibits local heat concentration, carbon chain rupture and over-chlorination and other side reactions, and the obtained product has light color, low acid value and excellent thermal stability. The visible light LED light source has low energy consumption, long service life and high safety, and is suitable for industrialized continuous production.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and more specifically, to a continuous preparation method of chlorinated paraffin based on visible light-induced photosensitive slow release. Background Technology

[0002] Chlorinated paraffins are an important class of fine chemical products, obtained from paraffin through a chlorination substitution reaction. They are widely used as plasticizers and flame retardants for plastics such as polyvinyl chloride (PVC). Currently, the main industrial methods for synthesizing chlorinated paraffins include thermal chlorination and photochlorination. Thermal chlorination relies on heat energy to initiate the homolytic cracking of chlorine gas at relatively high temperatures (typically 100-110℃), generating chlorine free radicals, which then undergo a free radical substitution reaction with paraffin. This method involves high reaction temperatures, numerous side reactions, a darker product color, and poor thermal stability. Photochlorination uses an ultraviolet light source (main wavelength approximately 340nm) to irradiate the reaction system, utilizing the high energy of ultraviolet photons to directly homolytically crack chlorine molecules, generating chlorine free radicals to initiate the chlorination reaction. Compared to thermal chlorination, the reaction temperature of photochlorination is lower, but it still needs to be maintained within the range of 80-110℃. Furthermore, the high-energy initiation characteristics of ultraviolet light lead to a rapid and concentrated generation of free radicals and localized heat release, still posing risks of carbon chain breakage and overchlorination side reactions, affecting the product's color and thermal stability.

[0003] In the industrial production of chlorinated paraffins, ultraviolet (UV) photochlorination has long been dominant, and research on the selection of related light sources clearly points to the UV band as the optimal initiation wavelength. Although there have been some technical discussions within the industry regarding other light sources or additives, none have deviated from the technical framework of direct UV initiation or thermal initiation. From the broader perspective of photochemical synthesis, visible light-driven free radical reactions have made some progress in the synthesis of small molecule organic molecules in recent years. However, these research systems differ significantly from the gas-liquid two-phase industrial chlorination system using long-chain paraffins as raw materials and chlorine gas as the chlorinating agent in terms of reaction substrates, chlorine source types, reaction phases, and industrial-scale applicability.

[0004] In summary, current technologies for preparing chlorinated paraffins still primarily rely on ultraviolet light initiation or thermal initiation, with significant room for improvement in initiation mechanisms and process control. Therefore, there is an urgent need to develop a new method for preparing chlorinated paraffins that offers a milder and more controllable reaction process, fewer side reactions, and suitability for continuous industrial production. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous preparation method for chlorinated paraffin based on visible light photosensitive slow release, which solves the technical problems of instantaneous large-scale generation of free radicals, concentrated local exothermic reactions, and frequent carbon chain breaking side reactions in the existing ultraviolet chlorination process.

[0006] Other features and advantages of the invention will become apparent from the following detailed description, or may be learned in part by practice of the invention.

[0007] This invention provides a continuous preparation method of chlorinated paraffin based on visible light photosensitized sustained release, the method comprising: S1, Prepare refined paraffin wax by mixing refined paraffin wax with organic photosensitive components to form a reaction precursor; S2, the reaction precursor is placed in a reaction device, heated to the reaction temperature, chlorine gas is introduced into it and visible light is applied at the same time to carry out the chlorination reaction and obtain crude chlorinated paraffin. S3, the crude chlorinated paraffin is degassed to remove residual chlorine and hydrogen chloride, and then a stabilizer is added to obtain chlorinated paraffin.

[0008] Based on this technical solution, step S1 further includes: S1.1, the raw paraffin wax is pumped into a settling tank for oil-water separation, and then the upper layer of paraffin wax is pumped into an adsorption tower containing adsorbent for adsorption and refining to obtain refined paraffin wax. S1.2, the organic photosensitive component and a portion of refined paraffin are pre-mixed in a mixer to obtain a photosensitive component premix, and then the photosensitive component premix is ​​mixed online with the remaining refined paraffin to form a uniform reaction precursor.

[0009] Furthermore, based on this technical solution, the organic photosensitizing component is selected from one or more of naphthol derivatives, coumarins, and phenothiazines.

[0010] Based on this technical solution, step S2 further includes: S2.1. Add the reaction precursor to the chlorination reactor, introduce nitrogen into the reactor to purge the internal air, and heat the material to 80~95℃; S2.2. Maintain the temperature, stop the nitrogen supply, and continuously introduce chlorine gas from the bottom of the reactor in a bubbling manner. At the same time, turn on the visible light source set outside the reactor to continuously irradiate the reactants and carry out the chlorination reaction. S2.3. Continuously monitor the density of the material inside the reactor. When the density value reaches 1.23~1.25 g / cm³, [further monitoring is required]. 3 When the chlorination and light exposure are stopped, crude chlorinated paraffin is obtained.

[0011] Based on this technical solution, the visible light source is further defined as an LED light source with an emission wavelength of 400~700nm, and the fluctuation range of the light intensity is controlled within ±5% by a regulated power supply during the reaction process.

[0012] Based on this technical solution, further step S3 includes: S3.1. Transfer the crude chlorinated paraffin into a blower refining kettle equipped with an external circulation pump. Start the circulation pump to circulate the material in the kettle. At the same time, evacuate the refining kettle to form a negative pressure to remove residual chlorine and hydrogen chloride gas from the material. S3.2. Add heat stabilizer through the feed port of the refining kettle, continue stirring and circulating for 0.5 to 2 hours, then stop the negative pressure and circulation, cool to room temperature, and obtain chlorinated paraffin product.

[0013] Based on this technical solution, further, the reaction equipment mentioned in step S2 is a seven-stage chlorination tower connected in series, with the height of adjacent chlorination towers decreasing sequentially. The material relies on gravity overflow to achieve continuous flow from the first stage to the seventh stage, and the amount of chlorine gas introduced into each chlorination tower decreases step by step along the material flow direction.

[0014] Based on this technical solution, each chlorination tower is further equipped with a self-circulating graphite cooler, and the reaction temperature of each chlorination tower is controlled by adjusting the cooling water flow rate.

[0015] Compared with existing technologies, the continuous preparation method of chlorinated paraffin based on visible light photosensitive sustained release of the present invention has the following technical advantages: By pre-mixing the organic photosensitive component with paraffin raw material, the reaction system is irradiated with visible light, where the photosensitive component absorbs light energy to form an excited state, which then initiates the chlorination reaction. Since the photon energy of visible light is insufficient to directly break the Cl-Cl bonds of chlorine molecules, the reaction process must use the photosensitive component as an energy medium. This indirect initiation pathway makes the generation of free radicals more gradual and controllable. Compared to the ultraviolet chlorination method, which relies on ultraviolet photons to directly homolytically cleave chlorine molecules to generate chlorine free radicals, the high energy of ultraviolet light leads to an instantaneous burst of free radical generation. This method fundamentally suppresses the problem of violent exothermic reactions and localized overheating caused by an instantaneously high concentration of free radicals.

[0016] Secondly, the method of this invention effectively reduces the occurrence of side reactions through process improvements resulting from the gradual generation of free radicals. Because the free radical generation rate is stable and the exothermic reaction is dispersed, the local temperature rise of the system is effectively controlled, and side reactions such as carbon chain breakage and overchlorination are significantly reduced. The chlorinated paraffin product obtained in this way has quality advantages such as lighter color, better thermal stability, and lower acid value. Meanwhile, the visible light LED light source itself generates far less heat than traditional ultraviolet mercury lamps, produces no high-energy ultraviolet radiation or ozone, has a safer operating environment, and the LED light source has a long lifespan and low maintenance costs.

[0017] Furthermore, the method of this invention has good adaptability to continuous industrial production. When implemented in conjunction with a multi-stage chlorination reactor, the visible light photoinitiator system can maintain a gradual generation of free radicals in each reaction stage. Combined with the process strategy of gradually decreasing the chlorine flow rate along the material flow direction, the degree of chlorination reaction at each stage is more uniform, and the overall temperature control accuracy and product quality consistency are significantly improved, showing good prospects for industrial application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the continuous preparation method of chlorinated paraffin based on visible light photosensitive sustained release according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the preparation process of the reaction precursor described in step S1 of the present invention; Figure 3 This is a schematic diagram of the preparation process of crude chlorinated paraffin described in step S2 of the present invention. Figure 4 This is a schematic diagram of the preparation process of chlorinated paraffin described in step S3 of an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a continuous preparation method for chlorinated paraffin based on visible light photosensitive slow release. The method first premixes refined paraffin with organic photosensitive components to form a reaction precursor. Then, visible light irradiation is used in conjunction with the organic photosensitive components to achieve the gradual generation of free radicals and the mild and controllable chlorination reaction. Finally, the product is refined by negative pressure degassing and the addition of stabilizers. This method not only ensures the product quality of chlorinated paraffin but also reduces the occurrence of side reactions and significantly improves the safety of the process and its adaptability to industrial continuous production.

[0022] In one implementation, such as Figure 1 As shown, a continuous preparation method of chlorinated paraffin based on visible light photosensitized sustained release includes the following steps: S1, Prepare refined paraffin wax by mixing refined paraffin wax with organic photosensitive components to form a reaction precursor.

[0023] like Figure 2 As shown in S1.1, the raw paraffin wax is pumped into a settling tank for oil-water separation, and then the upper layer of paraffin wax is pumped into an adsorption tower containing adsorbent for adsorption and refining to obtain refined paraffin wax. S1.2, the organic photosensitive component and a portion of refined paraffin are pre-mixed in a mixer to obtain a photosensitive component premix, and then the photosensitive component premix is ​​mixed online with the remaining refined paraffin to form a uniform reaction precursor.

[0024] Residual moisture and impurities in paraffin raw materials can affect the uniformity of the dispersion of photosensitive components. Furthermore, moisture reacts with chlorine gas in the subsequent chlorination reaction to generate hypochlorous acid, accelerating equipment corrosion and reducing chlorine utilization. Therefore, the core of raw material refining lies in removing free water and polar impurities from the raw materials through sedimentation and adsorption, creating favorable conditions for the uniform dispersion of photosensitive components. Simultaneously, the uniformity of the dispersion of photosensitive components directly determines the uniformity of free radical generation induced by visible light. Therefore, this invention premixes the photosensitive components with a portion of refined paraffin to obtain a premix, which is then mixed online with the remaining refined paraffin. This staged mixing method avoids localized excessively high or low concentrations of the photosensitive components caused by adding them all at once to a large amount of paraffin, ensuring a uniform distribution of the photosensitive components in the reaction precursor.

[0025] S2, the reaction precursor is placed in a reaction device, heated to the reaction temperature, chlorine gas is introduced into it and visible light is applied at the same time to carry out the chlorination reaction, and crude chlorinated paraffin is obtained.

[0026] like Figure 3 As shown, S2.1. Add the reaction precursor to the chlorination reactor, introduce nitrogen into the reactor to purge the internal air, and heat the material to 80~95℃; S2.2. Maintain the temperature, stop the nitrogen supply, and continuously introduce chlorine gas from the bottom of the reactor in a bubbling manner. At the same time, turn on the visible light source set outside the reactor to continuously irradiate the reactants and carry out the chlorination reaction. S2.3. Continuously monitor the density of the material inside the reactor. When the density value reaches 1.23~1.25 g / cm³, [further monitoring is required]. 3 When the chlorination and light exposure are stopped, crude chlorinated paraffin is obtained.

[0027] Visible light photoinitiation, as a technical approach distinct from traditional direct ultraviolet light initiation, relies heavily on the selection of photosensitive components and the setting of reaction process parameters to determine the chlorination reaction effect and product quality. This invention selects one or more of naphthol derivatives, coumarins, and phenothiazines as organic photosensitive components. These components exhibit good absorption in the visible light band, absorbing light energy to form an excited state. Through energy transfer or electron transfer, they activate chlorine molecules, achieving a gradual generation of free radicals. This effectively avoids the problems of instantaneous explosive generation of free radicals and concentrated localized exothermic reactions caused by direct photolysis of chlorine molecules under traditional ultraviolet light.

[0028] Before the chlorination reaction, the air inside the reaction equipment is replaced with an inert gas to effectively prevent side reactions between oxygen and chlorine or free radicals under light conditions, ensuring the chlorination reaction is focused. The reaction temperature is maintained at 80-95℃, and with the visible light photosensitive initiation system, this temperature range ensures that the chlorination reaction proceeds at an appropriate rate, preventing thermal carbon chain breakage due to excessive temperature and insufficient production efficiency due to excessively low temperature. Chlorine is introduced from the bottom of the reaction equipment via bubbling, which allows for full dispersion of chlorine in the paraffin system, increases the gas-liquid contact area, and improves chlorine utilization. The bubbling also promotes mixing of the reactants, and the self-circulating cooler achieves a high reflux ratio and fully mixed state. The visible light source is located outside the reaction equipment, using an LED light source with a wavelength of 400-700nm. The light intensity fluctuation is controlled within ±5% by a regulated power supply. Continuous and stable visible light irradiation is an important physical condition for maintaining the gradual generation of free radicals. During the reaction, the density of the material inside the reactor was continuously monitored. When the density value reached 1.23~1.25 g / cm³, the density was recorded. 3 The process involves stopping chlorination and light exposure, using density as the endpoint control indicator. It is simple to operate and suitable for continuous industrial production.

[0029] S3, the crude chlorinated paraffin is degassed to remove residual chlorine and hydrogen chloride, and then a stabilizer is added to obtain chlorinated paraffin.

[0030] like Figure 4 As shown, S3.1. The crude chlorinated paraffin is transferred into a blower refining kettle equipped with an external circulation pump. The circulation pump is started to circulate the material in the kettle. At the same time, the refining kettle is evacuated to form a negative pressure to remove residual chlorine and hydrogen chloride gas from the material. S3.2. Add heat stabilizer through the feed port of the refining kettle, continue stirring and circulating for 0.5 to 2 hours, then stop the negative pressure and circulation, cool to room temperature, and obtain chlorinated paraffin product.

[0031] After the chlorination reaction is completed, residual unreacted chlorine gas and hydrogen chloride gas (a byproduct of the reaction) remain dissolved in the crude chlorinated paraffin. If not removed, this will lead to a high acid value, decreased storage stability, and a risk of corrosion for downstream applications. This invention employs a negative pressure combined with material circulation for degassing. The crude chlorinated paraffin circulates within a blower-driven refining vessel equipped with an external circulation pump. The negative pressure environment created by vacuum extraction draws residual chlorine and hydrogen chloride gas out of the material. Circulation continuously refreshes the gas-liquid interface, improving degassing efficiency. After degassing, a heat stabilizer is added, and stirring and circulation continue for 0.5–2 hours to ensure complete mixing of the stabilizer and material. The heat stabilizer effectively complexes residual trace amounts of unstable chlorine in the product, inhibiting thermal decomposition during storage and processing, and improving the product's thermal and storage stability.

[0032] In one embodiment, the reaction equipment described in step S2 is a seven-stage chlorination tower connected in series, with the height of adjacent chlorination towers decreasing sequentially. The material flows continuously from the first stage to the seventh stage by gravity overflow, and the amount of chlorine gas introduced into each chlorination tower decreases progressively along the material flow direction. The seven-stage series design disperses the exothermic reaction heat across multiple reaction zones, avoiding localized overheating caused by concentrated exothermic heat in a single-stage reactor. Material flows by gravity overflow, eliminating the need for interstage transfer pumps, simplifying equipment configuration and reducing energy consumption. The progressively decreasing chlorine flow rate distribution strategy matches the reaction process characteristics of the gradually decreasing chlorination sites of paraffin in each chlorination tower, avoiding excessive tail gas treatment burden caused by excessive chlorine in later stages, while simultaneously improving the overall chlorine utilization rate.

[0033] Furthermore, each chlorination tower is equipped with a self-circulating graphite cooler, and the reaction temperature of each chlorination tower is controlled by adjusting the cooling water flow rate. The self-circulating graphite cooler utilizes the thermosiphon effect of the material in the reactor to achieve natural circulation, requiring no external power. The material reaches a fully mixed state under a high reflux ratio, which can efficiently remove the heat of reaction and ensure uniform material concentration and temperature distribution within the tower. Combined with the smooth free radical generation state brought about by the visible light photoinitiation system, the temperature control of each chlorination tower is more precise, effectively suppressing the adverse effects of local temperature rise on the quality of chlorinated paraffin products.

[0034] Example 1

[0035] Raw paraffin wax was pumped into a settling tank and allowed to settle for 5 hours for oil-water separation. The upper layer of paraffin wax was then pumped into an adsorption tower containing activated clay adsorbent for adsorption and purification to obtain refined paraffin wax. Coumarin was selected as the organic photosensitizing component. The organic photosensitizing component and a portion of the refined paraffin wax were pre-mixed in a mixer for 0.5 hours to obtain a photosensitizing component premix. The photosensitizing component premix was then mixed online with the remaining refined paraffin wax to form a homogeneous reaction precursor. The amount of organic photosensitizing component added was 0.1% of the mass of the refined paraffin wax.

[0036] The precursor was added to the chlorination reactor, and nitrogen gas was introduced into the reactor to purge the internal air. The material was then heated to 85°C. The temperature was maintained, and the nitrogen supply was stopped. Chlorine gas was continuously introduced into the reactor from the bottom using a bubbling method at a rate of 0.8 mol / h·kg paraffin. Simultaneously, a visible light LED light source located outside the reactor was turned on, with a wavelength of 450 nm and an illuminance of 20 mW / cm². 2 The light intensity fluctuation was controlled within ±5% by a regulated power supply to continuously irradiate the reactants and carry out the chlorination reaction. The density of the material in the reactor was continuously monitored, and when the density reached 1.24 g / cm³... 3 When the chlorination and light exposure are stopped, crude chlorinated paraffin is obtained.

[0037] The crude chlorinated paraffin was transferred to a blower-type refining reactor equipped with an external circulation pump. The circulation pump was started to circulate the material within the reactor, while the reactor was evacuated to -0.08 MPa and maintained under negative pressure for 1 hour to remove residual chlorine and hydrogen chloride gases. Epoxidized soybean oil was added as a heat stabilizer through the feed port of the refining reactor at a rate of 0.5% of the mass of the crude chlorinated paraffin. Stirring and circulation continued for another hour, after which the negative pressure and circulation were stopped, and the mixture was cooled to room temperature to obtain the chlorinated paraffin product.

[0038] In this embodiment, the chlorination reaction equipment employs a seven-stage chlorination tower series, with the height decreasing sequentially between adjacent towers. The material flows continuously from the first to the seventh stage via gravity overflow. The amount of chlorine gas introduced into each tower decreases progressively along the material flow direction, with the chlorine flow rates for each stage being 0.8 mol / h·kg, 0.7 mol / h·kg, 0.6 mol / h·kg, 0.5 mol / h·kg, 0.4 mol / h·kg, 0.3 mol / h·kg, and 0.2 mol / h·kg, respectively. Each chlorination tower is equipped with a self-circulating graphite cooler, and the reaction temperature of each tower is controlled within the range of 80–95°C by adjusting the cooling water flow rate.

[0039] Example 2

[0040] Raw paraffin wax was pumped into a settling tank and allowed to settle for 6 hours for oil-water separation. The upper layer of paraffin wax was then pumped into an adsorption tower containing activated carbon adsorbent for adsorption and purification to obtain refined paraffin wax. 1-Naphthol was selected as the organic photosensitizing component. The organic photosensitizing component and a portion of the refined paraffin wax were pre-mixed in a mixer for 0.5 hours to obtain a photosensitizing component premix. The photosensitizing component premix was then mixed online with the remaining refined paraffin wax to form a homogeneous reaction precursor. The amount of organic photosensitizing component added was 0.2% of the mass of the refined paraffin wax.

[0041] The reaction precursor was added to the chlorination reactor, and nitrogen gas was introduced into the reactor to purge the internal air. The material was then heated to 90°C. The temperature was maintained, and the nitrogen supply was stopped. Chlorine gas was continuously introduced into the reactor from the bottom using a bubbling method at a rate of 1.0 mol / h·kg paraffin. Simultaneously, a visible light LED light source located outside the reactor was turned on, with an emission wavelength of 520 nm and a light intensity of 30 mW / cm². 2 The light intensity fluctuation was controlled within ±5% by a regulated power supply to continuously irradiate the reactants and carry out the chlorination reaction. The density of the material in the reactor was continuously monitored, and when the density reached 1.25 g / cm³, the reaction was initiated. 3 When the chlorination and light exposure are stopped, crude chlorinated paraffin is obtained.

[0042] In this embodiment, a staged cooling and temperature control strategy is adopted for the chlorination reaction. In the initial stage of the chlorination reaction, no cooling water is introduced into the self-circulating graphite cooler. The heat released by the photosensitive reaction itself gradually raises the material temperature from room temperature to the target reaction temperature range. When the material temperature reaches the preset upper limit of 95°C, cooling circulating water is introduced into the self-circulating graphite cooler to remove the heat of reaction and control the material temperature within the range of 90~95°C. In the later stage of the reaction, as the chlorination reaction rate gradually decreases and the heat release decreases, the cooling water flow rate is gradually reduced to maintain the reaction temperature at 90°C until the reaction is completed. This staged cooling and temperature control strategy fully utilizes the self-heating effect in the early stage of the photosensitive reaction, reducing the energy consumption of the external heating source. Simultaneously, by precisely controlling the timing of cooling water intervention, it avoids temperature fluctuations and energy waste caused by forced cooling throughout the reaction.

[0043] The crude chlorinated paraffin was transferred to a blower-type refining reactor equipped with an external circulation pump. The circulation pump was started to circulate the material within the reactor, while the reactor was evacuated to -0.09 MPa and maintained under negative pressure for 1.5 hours to remove residual chlorine and hydrogen chloride gases. Epoxidized soybean oil was added as a heat stabilizer through the feed port of the refining reactor at a rate of 0.8% of the crude chlorinated paraffin mass. Stirring and circulation continued for another 1.5 hours, after which the negative pressure and circulation were stopped, and the mixture was cooled to room temperature to obtain the chlorinated paraffin product.

[0044] In this embodiment, the chlorination reaction equipment adopts a seven-stage chlorination tower series, with the height of adjacent chlorination towers decreasing sequentially. The material relies on gravity overflow to achieve continuous flow from the first stage to the seventh stage. The amount of chlorine gas introduced into each chlorination tower decreases progressively along the material flow direction, with the chlorine flow rates for each stage being 1.0 mol / h·kg, 0.85 mol / h·kg, 0.7 mol / h·kg, 0.55 mol / h·kg, 0.4 mol / h·kg, 0.3 mol / h·kg, and 0.2 mol / h·kg, respectively. Each chlorination tower is equipped with a self-circulating graphite cooler.

[0045] Example 3

[0046] Raw paraffin wax was pumped into a settling tank and allowed to settle for 8 hours for oil-water separation. The upper layer of paraffin wax was then pumped into an adsorption tower containing activated clay adsorbent for adsorption and purification to obtain refined paraffin wax. 10-Methylphenothiazine was selected as the organic photosensitizing component. The organic photosensitizing component and a portion of the refined paraffin wax were pre-mixed in a mixer for 0.5 hours to obtain a photosensitizing component premix. The photosensitizing component premix was then mixed online with the remaining refined paraffin wax to form a homogeneous reaction precursor. The amount of organic photosensitizing component added was 0.05% of the mass of the refined paraffin wax.

[0047] The reaction precursor was added to the chlorination reactor, and nitrogen gas was introduced into the reactor to purge the internal air. The material was then heated to 80°C. The temperature was maintained, and the nitrogen supply was stopped. Chlorine gas was continuously introduced into the reactor from the bottom using a bubbling method at a rate of 0.5 mol / h·kg paraffin. Simultaneously, a visible light LED light source located outside the reactor was turned on, with a wavelength of 600 nm and an illuminance of 15 mW / cm². 2 The light intensity fluctuation was controlled within ±5% by a regulated power supply to continuously irradiate the reactants and carry out the chlorination reaction. The density of the material in the reactor was continuously monitored, and when the density value reached 1.23 g / cm³... 3 When the chlorination and light exposure are stopped, crude chlorinated paraffin is obtained.

[0048] The crude chlorinated paraffin was transferred to a blower-type refining reactor equipped with an external circulation pump. The circulation pump was started to circulate the material within the reactor, while the reactor was evacuated to -0.07 MPa and maintained under negative pressure for 2 hours to remove residual chlorine and hydrogen chloride gases. A calcium-zinc composite stabilizer was added as a heat stabilizer through the feed port of the refining reactor at a rate of 0.3% of the mass of the crude chlorinated paraffin. Stirring and circulation continued for 0.5 hours, after which the negative pressure and circulation were stopped, and the mixture was cooled to room temperature to obtain the chlorinated paraffin product.

[0049] In this embodiment, the chlorination reaction equipment employs a seven-stage chlorination tower series, with the height decreasing sequentially between adjacent towers. The material flows continuously from the first to the seventh stage via gravity overflow. The amount of chlorine gas introduced into each tower decreases progressively along the material flow direction, with the following chlorine flow rates: 0.5 mol / h·kg, 0.45 mol / h·kg, 0.4 mol / h·kg, 0.35 mol / h·kg, 0.3 mol / h·kg, 0.25 mol / h·kg, and 0.2 mol / h·kg, respectively. Each chlorination tower is equipped with a self-circulating graphite cooler, and the reaction temperature of each tower is controlled within the range of 80–95°C by adjusting the cooling water flow rate.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 2 is that no organic photosensitive component is added, and only visible light LED light source is used for chlorination reaction. The remaining operation steps and process parameters are completely consistent with Example 2.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 2 is that the visible light LED light source is replaced with an ultraviolet mercury lamp light source, while the other operating steps and process parameters are completely the same as in Example 2.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 2 is that the reaction equipment in step S2 is a single-stage reactor, not a seven-stage chlorination tower, and the chlorine flow rate is the total chlorine flow rate of the seven-stage chlorination tower in Example 2. The remaining operating steps and process parameters are completely consistent with Example 2.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 2 is that a self-circulating graphite cooler is not used; the reaction temperature is controlled only by jacket cooling water. The remaining operating steps and process parameters are completely consistent with those of Example 2.

[0058] Effect test

[0059] The chlorinated paraffin products prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance testing according to industry standard testing methods. The test indicators included product color (platinum-cobalt color number), acid value, and thermal decomposition temperature. The results are shown in Table 1.

[0060] Table 1: Performance tests of chlorinated paraffins prepared in the examples and comparative examples.

[0061]

[0062] As shown in Table 1, the chlorinated paraffins prepared in Examples 1-3 of this invention have a color (platinum-cobalt color number) ≤90, an acid value ≤0.03mgKOH / g, and a thermal decomposition temperature ≥150℃. All performance indicators meet or exceed the quality requirements of industry standards, demonstrating excellent overall quality. Among them, Example 2 exhibits the best performance indicators, with a thermal decomposition temperature of 165℃, significantly higher than other examples. This may be because it not only uses 1-naphthol as the organic photosensitive component with a suitable ratio, but also employs a 520nm visible light wavelength and a seven-stage cascaded chlorination tower with a decreasing chlorination rate strategy to achieve the gradual generation of free radicals. Furthermore, it adopts a staged cooling and temperature control strategy. In the initial stage of the chlorination reaction, the photosensitive reaction itself releases heat to achieve natural temperature rise, avoiding the problems of low initial reaction temperature and uneven reaction rate caused by forced cooling throughout the process. After reaching the upper temperature limit, cooling water is precisely introduced, making the temperature control more stable throughout the reaction, further improving the uniformity of the free radical generation rate, and more thoroughly suppressing carbon chain breakage and overchlorination side reactions.

[0063] In contrast, Comparative Example 1, lacking the addition of organic photosensitive components, could not effectively initiate the chlorination reaction by using only visible light irradiation. The amount of free radicals generated in the system was extremely small. In order to achieve the target density, the reaction time had to be significantly extended. The prolonged heating caused the product color to darken to 350, the acid value to increase, and the thermal decomposition temperature to decrease, resulting in a serious deterioration in product quality.

[0064] Although Comparative Example 2 uses an ultraviolet mercury lamp as the light source, it belongs to the traditional direct initiation path of ultraviolet light. Free radicals are generated instantly in large quantities, local heat release is concentrated, and there are more carbon chain breakage and overchlorination side reactions. Although the product color, acid value and thermal decomposition temperature are better than Comparative Example 1, they are still significantly worse than Examples 1-3. This also shows that under the visible light photosensitive initiation system, the gradual generation of free radicals is beneficial to improving the quality of chlorinated paraffin.

[0065] Comparative Example 3 uses a single-stage reactor, where the exothermic reaction of chlorination is concentrated in a single reaction zone, significantly increasing the difficulty of temperature control and causing frequent local overheating. The product color is No. 200 and the thermal decomposition temperature is 135℃, indicating that the seven-stage chlorination tower in series can improve the product quality of chlorinated paraffin by dispersing the heat of reaction to multiple zones.

[0066] Comparative Example 4 employed a forced cooling method throughout the reaction, without implementing a phased cooling temperature control strategy. Cooling water was introduced to remove heat at the initial stage of the reaction, resulting in a slow temperature rise and a low reaction rate in the early stages. Furthermore, the cooling intensity was not adjusted in time when heat release decreased in the later stages of the reaction, leading to an unsteady temperature distribution throughout the reaction, characterized by "low at the beginning and high at the end." The free radical generation rate fluctuated, and the product color (150) and thermal decomposition temperature (146℃) were significantly inferior to those of Example 2 (60 and 165℃). This comparative result demonstrates that the phased cooling temperature control strategy of this invention, through its sequential control of initial heat storage and self-heating, precise temperature control in the middle stage, and gradient cooling in the later stage, results in a smoother temperature change throughout the reaction. This, combined with the gradual generation characteristics of free radicals induced by visible light photosensitivity, significantly contributes to improving product quality.

[0067] In Examples 1-3 above, the organic photosensitizing components are selected from naphthol derivatives, coumarins, and phenothiazine compounds, which have good light absorption capabilities in the visible light band. They transfer energy to chlorine molecules by forming excited states or activate chlorine molecules via single-electron transfer pathways, achieving a gradual generation of free radicals and effectively suppressing the explosive generation of free radicals and localized heat concentration problems caused by traditional direct initiation with ultraviolet light. The seven-stage cascade chlorination tower, combined with a progressively decreasing chlorine flow rate and a self-circulating graphite cooler, leverages the advantages of visible light photosensitivity and slow-release initiation throughout the entire chlorination reaction process. Free radicals are generated gradually in each reaction stage, the chlorine flow rate between stages matches the decreasing reaction progress, temperature control is precise, and the incidence of side reactions is significantly reduced. The product undergoes negative pressure circulation degassing and stabilizer treatment, resulting in thorough removal of free chlorine and hydrogen chloride, and excellent storage stability.

[0068] This invention provides a continuous preparation method for chlorinated paraffin based on visible light photosensitive slow-release initiation. It combines visible light photosensitive initiation with a multi-stage series continuous chlorination process, along with precise control of raw material refining, reaction temperature control, and product post-processing. This method solves the technical problems of instantaneous explosive generation of free radicals, concentrated local exothermic reactions, carbon chain breakage, and frequent overchlorination side reactions in traditional ultraviolet chlorination processes. The method is simple to operate, highly controllable, and suitable for industrial continuous production. The prepared chlorinated paraffin product has a light color, low acid value, and excellent thermal stability, which can directly meet the application requirements of plasticizers and flame retardants, and has good prospects for industrial application.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A continuous preparation method of chlorinated paraffin based on visible light-induced photosensitive sustained release, characterized in that, The method includes: S1, Prepare refined paraffin wax by mixing refined paraffin wax with organic photosensitive components to form a reaction precursor; S2, the reaction precursor is placed in a reaction device, heated to the reaction temperature, chlorine gas is introduced into it and visible light is applied at the same time to carry out the chlorination reaction and obtain crude chlorinated paraffin. S3, the crude chlorinated paraffin is degassed to remove residual chlorine and hydrogen chloride, and then a stabilizer is added to obtain chlorinated paraffin. Step S1 includes: S1.1, the raw paraffin wax is pumped into a settling tank for oil-water separation, and then the upper layer of paraffin wax is pumped into an adsorption tower containing adsorbent for adsorption and refining to obtain refined paraffin wax. S1.2, the organic photosensitive component and a portion of refined paraffin are pre-mixed in a mixer to obtain a photosensitive component premix, and then the photosensitive component premix is ​​mixed online with the remaining refined paraffin to form a uniform reaction precursor; the organic photosensitive component is selected from one or more of naphthol derivatives, coumarins, and phenothiazines. Step S2 includes: S2.

1. Add the reaction precursor to the chlorination reactor, introduce nitrogen into the reactor to purge the internal air, and heat the material to 80~95℃; S2.

2. Maintain the temperature, stop the nitrogen supply, and continuously introduce chlorine gas from the bottom of the reactor in a bubbling manner. At the same time, turn on the visible light source set outside the reactor to continuously irradiate the reactants and carry out the chlorination reaction. S2.

3. Continuously monitor the density of the material inside the reactor. When the density value reaches 1.23~1.25 g / cm³... 3 When the chlorination and light exposure are stopped, crude chlorinated paraffin is obtained.

2. The continuous preparation method of chlorinated paraffin based on visible light photosensitive sustained release as described in claim 1, characterized in that, The visible light source is an LED light source with an emission wavelength of 400~700nm, and the fluctuation range of the light intensity is controlled within ±5% by a regulated power supply during the reaction process.

3. The continuous preparation method of chlorinated paraffin based on visible light photosensitive sustained release as described in claim 1, characterized in that, Step S3 includes: S3.

1. Transfer the crude chlorinated paraffin into a blower refining kettle equipped with an external circulation pump. Start the circulation pump to circulate the material in the kettle. At the same time, evacuate the refining kettle to form a negative pressure to remove residual chlorine and hydrogen chloride gas from the material. S3.

2. Add heat stabilizer through the feed port of the refining kettle, continue stirring and circulating for 0.5 to 2 hours, then stop the negative pressure and circulation, cool to room temperature, and obtain chlorinated paraffin product.

4. The continuous preparation method of chlorinated paraffin based on visible light photosensitive sustained release as described in claim 1, characterized in that, The reaction equipment described in step S2 is a seven-stage chlorination tower connected in series. The height of adjacent chlorination towers decreases sequentially. The material relies on gravity overflow to achieve continuous flow from the first stage to the seventh stage. The amount of chlorine gas introduced into each chlorination tower decreases step by step along the material flow direction.

5. The continuous preparation method of chlorinated paraffin based on visible light photosensitive sustained release as described in claim 4, characterized in that, Each chlorination tower is equipped with a self-circulating graphite cooler, and the reaction temperature of each chlorination tower is controlled by adjusting the cooling water flow rate.

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