Production process of environment-friendly chlorinated paraffin-52

Abstract

This invention relates to the field of chlorinated paraffin production technology and discloses an environmentally friendly production process for chlorinated paraffin-52. Liquid paraffin is sequentially subjected to pre-chlorination with residual chlorine in the tail gas, extraction with concentrated hydrochloric acid to remove water and impurities, and three-stage tail chlorine absorption before being fed into a six-stage series chlorination reactor for continuous photo-initiated chlorination. Chlorine is distributed in decreasing order according to the flow direction of the liquid paraffin, and the feed rate or chlorine flow rate is adjusted online based on the final stage discharge density to stabilize the chlorinated discharge density at 1.23–1.27 g / cm³. The reaction effluent undergoes closed degassing and heavy metal stabilization treatment to obtain the chlorinated paraffin-52 product. The chlorination tail gas is treated with residual chlorine reuse, graphite falling film absorption, packing absorption, and alkaline washing to achieve full utilization of chlorine, recovery of by-product hydrochloric acid, and compliant tail gas emissions.

Description

Technical Field

[0001] This invention relates to the field of chlorinated paraffin production technology, specifically to a production process for an environmentally friendly chlorinated paraffin-52. Background Technology

[0002] Chlorinated paraffin-52 is a commonly used chlorinated plasticizer, flame retardant plasticizer, and additive product, typically produced by a free radical substitution reaction between liquid paraffin and chlorine. Existing production methods for chlorinated paraffin-52 mainly include thermal chlorination, photochlorination, catalytic chlorination, and continuous chlorination. Thermal chlorination is a mature process, but its high reaction temperature and long reaction time can easily lead to a darker product color and quality fluctuations. Photochlorination has a lower reaction temperature and a lighter product color, but the attenuation of the light source and reduced light transmittance can affect reaction stability. Catalytic chlorination has a faster reaction rate, but the peroxide catalytic system presents decomposition stability and safety control issues. While conventional continuous chlorination can improve equipment utilization, insufficient control of residual chlorine in the tail gas, hydrogen chloride absorption, raw material moisture content, and end-chlorination depth can still easily lead to problems such as insufficient chlorine utilization, high tail gas treatment load, high product acid value, darker color, and chlorine content fluctuations.

[0003] In the continuous production of chlorinated paraffin-52, moisture, polar impurities, and trace unsaturated impurities in the liquid paraffin can affect the stability of the chlorination reaction. The hydrogen chloride tail gas produced by the chlorination reaction usually carries a small amount of free chlorine. If it enters the absorption system directly, it will not only increase the alkaline washing load but also affect the quality of the by-product hydrochloric acid. In addition, the chlorine content, density, color, thermal stability, and loss on heating of chlorinated paraffin-52 products require relatively stable ranges. Simply relying on a fixed chlorine flow rate or manual sampling for adjustment is insufficient to adapt to changes in raw material composition, temperature fluctuations, and reaction load.

[0004] Therefore, it is necessary to provide an environmentally friendly production process for chlorinated paraffin-52, which allows the residual chlorine in the chlorination tail gas to be fully utilized before entering the absorption system. At the same time, the impact of raw material impurities is reduced by concentrated hydrochloric acid extraction, and the product quality stability is improved by six-stage continuous chlorination and final-stage density feedback control. This reduces tail gas treatment pressure, increases chlorine utilization, and improves product quality. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide an environmentally friendly production process for chlorinated paraffin-52, which solves the problems of insufficient utilization of residual chlorine in tail gas, high hydrogen chloride absorption load, high product acid value, large fluctuations in chlorine content and density, and unstable color and thermal stability in the existing chlorinated paraffin-52 production process.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a production process for environmentally friendly chlorinated paraffin-52, comprising the following steps: S1. Liquid paraffin is metered and continuously fed into the primary prechlorination reactor and the secondary prechlorination reactor, so that the liquid paraffin comes into contact with the tail gas containing hydrogen chloride and residual chlorine from the subsequent chlorination reaction section. The residual chlorine in the tail gas is used to prechlorinate the liquid paraffin and reduce the free chlorine content in the tail gas. S2. The prechlorinated liquid paraffin is fed into a hydrochloric acid extraction tower and extracted by contact with concentrated hydrochloric acid with a mass fraction of 31% to 38%. After standing and separating into layers, the upper oil phase is taken to obtain liquid paraffin after water and impurity removal. S3. The dehydrated and impurity-removed liquid paraffin is sent to a three-stage tail chlorine absorption vessel to further contact with the tail gas of the subsequent chlorination reaction, so that the residual chlorine in the tail gas is absorbed and reacted by the liquid paraffin to obtain the liquid wax to be chlorinated. S4. The liquid wax to be chlorinated is continuously fed into a six-stage chlorination reactor connected in series. Chlorine gas is introduced into each stage of the chlorination reactor. Under the conditions of photoinitiation and heat maintenance, a free radical substitution chlorination reaction is carried out. The reaction temperature is controlled at 75-95°C and the reaction pressure is not higher than 0.02 MPa. The chlorine flow rate of the six-stage chlorination reactor is distributed in descending order according to the liquid wax flow direction. The sixth-stage chlorination reactor is equipped with online density detection. The feed rate of liquid paraffin and / or the chlorine flow rate of each stage are adjusted according to the discharge density of the sixth stage to control the chlorination discharge density at 1.23 to 1.27 g / cm³. S5. After the material from the sixth-stage chlorination reactor is sent to the crude product temporary storage tank, it enters the closed degassing reactor. Dry air or nitrogen is introduced to remove residual hydrogen chloride. The degassing tail gas enters the degassing absorption tower for absorption and treatment. After degassing, a heavy metal-free stabilizer is added to the chlorinated paraffin to obtain chlorinated paraffin-52 product. S6. The residual chlorine in the tail gas of the chlorination reaction is utilized by passing it through a three-stage tail chlorine absorption vessel, a two-stage prechlorination vessel, and a one-stage prechlorination vessel. Then, it is treated by gas-liquid separation, three-stage graphite falling film absorption, two-stage packing absorption, and alkaline washing absorption to obtain by-product hydrochloric acid and achieve the tail gas emission standard.

[0007] Furthermore, in S1, the liquid paraffin is C 14 ~C 17 Liquid paraffin is filtered through an 80-120 mesh before feeding, and the water content of the liquid paraffin is controlled below 0.08%.

[0008] Furthermore, in step S2, the mass ratio of concentrated hydrochloric acid to liquid paraffin is 0.03–0.12:1, the extraction temperature is 35–60°C, and the extraction contact time is 10–40 min.

[0009] Furthermore, in S4, the chlorine flow rate of the six-stage chlorination reactor, calculated based on the total chlorine volume, is as follows: Stage 1: 22%–28%, Stage 2: 22%–28%, Stage 3: 17%–23%, Stage 4: 12%–18%, Stage 5: 7%–13%, and Stage 6: 3%–8%.

[0010] Furthermore, in step S4, the liquid paraffin feed rate is 0.50–0.67 t / h, and the total chlorine feed rate is 1.12–1.50 t / h.

[0011] Furthermore, in S4, each chlorination reactor is equipped with a circulating cooler, which is a graphite heat exchanger. The heat of reaction is removed through jacket cooling and external circulating cooling, so that the temperature difference between each reactor is controlled within ±5℃.

[0012] Furthermore, in step S5, the degassing temperature is 45–75°C, the flow rate of dry air or nitrogen is 0.02–0.12 m³ / (m³·min), and the degassing process ends when the pH of the absorbent after the degassing tail gas is absorbed by water is 6.5–7.5.

[0013] Furthermore, in step S5, the amount of heavy metal-free stabilizer added is 0.08% to 0.20% of the mass of chlorinated paraffin, and the heavy metal-free stabilizer is selected from one of epoxidized soybean oil, glycerol ether stabilizers, and epoxidized fatty acid esters.

[0014] Furthermore, in S6, the three-stage graphite falling film absorption and the two-stage filler absorption adopt a countercurrent absorption method, and the absorption temperature is controlled below 40°C. Part of the concentrated hydrochloric acid obtained from absorption is returned to S2 as an extraction acid, and the other part is sent out as a by-product hydrochloric acid after passing through oil removal filtration, activated carbon adsorption and resin adsorption in sequence.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention employs a combined process of "residual chlorine pre-chlorination of tail gas, concentrated hydrochloric acid extraction, three-stage tail chlorine absorption, and six-stage continuous chlorination." This process reuses the residual chlorine in the chlorination reaction tail gas for pre-chlorination of liquid paraffin and tail chlorine absorption before it enters the final absorption system. This reduces the free chlorine content in the tail gas, lowering the processing load on subsequent graphite falling film absorption, packing absorption, and alkali washing systems. It also improves chlorine utilization, reduces ineffective chlorine consumption, and lowers tail gas emission pressure. Simultaneously, the concentrated hydrochloric acid extraction step reduces the content of moisture, polar impurities, and impurities affecting color stability in the liquid paraffin, making the raw materials entering the main chlorination stage more stable. This helps reduce problems such as increased acid value, darker color, and increased side reactions during the reaction process.

[0016] This invention employs a six-stage chlorination reactor in series, distributing chlorine flow rate in decreasing order according to the liquid paraffin flow direction. This maintains a high chlorination rate in the initial stage while allowing for supplementary chlorination and fine-tuning in the later stages, thus avoiding localized over-chlorination and fluctuations in reaction depth. Simultaneously, an online density detector is installed in the sixth-stage chlorination reactor. Based on the final discharge density, the liquid paraffin feed rate and / or chlorine flow rate at each stage are adjusted promptly to ensure stable product density control between 1.23 and 1.27 g / cm³, improving batch-to-batch consistency of chlorinated paraffin-52. Combined with closed degassing and heavy metal-free stabilizer treatment, the residual hydrogen chloride and free acid content in the finished product can be reduced, improving odor, thermal stability, and storage stability. This makes the resulting chlorinated paraffin-52 more suitable for applications requiring high environmental friendliness and quality stability, such as plasticizers, flame-retardant plasticizers, and related additives. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 This embodiment provides a production process for environmentally friendly chlorinated paraffin-52, including the following steps: S1, Select C 14 ~C 17 Liquid paraffin, as a raw material, is first filtered through an 80-mesh filter to control the water content of the liquid paraffin to 0.07%. Then, it is continuously fed into the primary prechlorination reactor and the secondary prechlorination reactor at a feed rate of 0.50 t / h. The tail gas containing hydrogen chloride and residual chlorine from the subsequent chlorination reaction section first enters the secondary prechlorination reactor and then enters the primary prechlorination reactor, where it comes into countercurrent contact with the liquid paraffin. The residual chlorine in the tail gas is used to prechlorinate the liquid paraffin, while reducing the free chlorine content in the tail gas. S2. The pre-chlorinated liquid paraffin is fed into a hydrochloric acid extraction tower and extracted by contact with concentrated hydrochloric acid (31% by mass). The mass ratio of concentrated hydrochloric acid to liquid paraffin is 0.03:1. The extraction temperature is controlled at 35℃, and the extraction contact time is 10 min. After extraction, the mixture is allowed to stand and separate into layers. The upper oil phase is taken to obtain the dehydrated and impurity-free liquid paraffin. S3. The dehydrated and impurity-removed liquid paraffin is sent to the three-stage tail chlorine absorption vessel to further contact with the chlorination reaction tail gas, so that the residual free chlorine in the tail gas is absorbed by the liquid paraffin and a pre-chlorination reaction occurs to obtain the liquid paraffin to be chlorinated. S4. The liquid paraffin to be chlorinated is continuously fed into a six-stage chlorination reactor connected in series. The total chlorine feed rate is 1.12 t / h, and the chlorine flow rate is distributed sequentially according to the total chlorine flow rate: Stage 1 25%, Stage 2 24%, Stage 3 21%, Stage 4 16%, Stage 5 9%, and Stage 6 5%. Each stage of the chlorination reactor uses photo-initiation, and the heat of reaction is removed through jacket cooling and external graphite circulation cooling, keeping the reaction temperature at 75–82℃ and the reaction pressure below 0.015 MPa. The temperature difference between each stage of the reactor is controlled within ±5℃. The sixth-stage chlorination reactor is equipped with an online density detection device. When the discharge density of the sixth stage is lower than 1.23 g / cm³, the liquid paraffin feed rate is appropriately reduced or the chlorine flow rate of the sixth stage is increased. When the discharge density is higher than 1.27 g / cm³, the liquid paraffin feed rate is appropriately increased or the chlorine flow rate of the subsequent stage is reduced, so that the discharge density is stabilized at 1.23–1.27 g / cm³. S5. The effluent from the sixth-stage chlorination reactor is sent to a crude product storage tank, and then to a closed degassing reactor. Dry air is introduced at 45°C for degassing at a rate of 0.02 m³ / (m³·min). The degassing tail gas is then absorbed and treated in a degassing absorption tower. Degassing is stopped when the pH of the absorbent solution after water absorption stabilizes at 6.5–7.5. Subsequently, 0.08 wt% of epoxidized soybean oil is added to the degassed chlorinated paraffin as a heavy metal-free stabilizer, and the mixture is stirred evenly to obtain chlorinated paraffin-52 product. S6. The tail gas from the chlorination reaction passes through a three-stage tail chlorine absorption vessel, a two-stage pre-chlorination vessel, and a one-stage pre-chlorination vessel in sequence to utilize residual chlorine. Then, it undergoes gas-liquid separation, three-stage graphite falling film absorption, two-stage packing absorption, and alkaline washing absorption. Both graphite falling film absorption and packing absorption adopt countercurrent absorption. The absorption temperature is controlled below 40℃. Part of the concentrated hydrochloric acid obtained is returned to the hydrochloric acid extraction tower as an extraction acid, and the other part is sent out as by-product hydrochloric acid after oil removal filtration, activated carbon adsorption, and resin adsorption.

[0019] Example 2 This embodiment provides a production process for environmentally friendly chlorinated paraffin-52, including the following steps: S1. Select C14 to C17 liquid paraffin, filter it through a 100-mesh filter, control the water content of the liquid paraffin to be 0.05%, and then continuously feed it into the primary prechlorination reactor and the secondary prechlorination reactor at a feed rate of 0.58 t / h, so that the liquid paraffin can fully contact the tail gas containing hydrogen chloride and residual chlorine from the subsequent chlorination reaction section, and use the residual chlorine in the tail gas to prechlorinate the liquid paraffin.

[0020] S2. The prechlorinated liquid paraffin is fed into a hydrochloric acid extraction tower and extracted by contact with concentrated hydrochloric acid with a mass fraction of 35%. The mass ratio of concentrated hydrochloric acid to liquid paraffin is 0.08:1. The extraction temperature is controlled at 45℃ and the extraction contact time is 25min. After extraction, the mixture is allowed to stand and separate into layers. The upper oil phase is taken to obtain liquid paraffin after water and impurity removal.

[0021] S3. The dehydrated and impurity-removed liquid paraffin is sent to the three-stage tail chlorine absorption vessel to continue to react with the residual chlorine in the chlorination reaction tail gas to obtain the liquid paraffin to be chlorinated. This step not only further utilizes the residual chlorine in the tail gas, but also reduces the free chlorine load of the subsequent absorption system. S4. The liquid paraffin to be chlorinated is continuously fed into a six-stage chlorination reactor connected in series. The total chlorine feed rate is 1.30 t / h, and the chlorine flow rate is distributed sequentially according to the total chlorine volume: Stage 1 27%, Stage 2 25%, Stage 3 20%, Stage 4 15%, Stage 5 9%, and Stage 6 4%. Each stage of the chlorination reactor uses photo-initiated free radical substitution chlorination under conditions of maintained reaction heat and external circulation cooling. The reaction temperature is controlled at 82–88℃, and the reaction pressure is controlled below 0.02 MPa. Each stage of the chlorination reactor is equipped with a graphite circulating cooler. Through the combination of jacket cooling and external circulation cooling, the temperature difference between each stage is controlled within ±4℃. An online density detection device is installed at the outlet of the sixth-stage chlorination reactor. The feed rate of liquid paraffin and the chlorine flow rate of each stage are adjusted in real time according to the density of the sixth-stage output, so that the chlorinated output density is controlled at 1.23–1.27 g / cm³. S5. After the material from the sixth-stage chlorination reactor is transferred to the crude product storage tank, it enters the closed degassing reactor. Dry nitrogen is introduced at 60°C for degassing at a rate of 0.07 m³ / (m³·min). The degassing tail gas is then absorbed in a degassing absorption tower. Degassing is terminated when the pH of the absorbent solution after water absorption stabilizes at approximately 7.0. Subsequently, 0.14 wt% of a glycerol ether stabilizer is added, and the mixture is stirred thoroughly to obtain chlorinated paraffin-52. S6. The chlorination reaction tail gas is sequentially passed through a three-stage tail chlorine absorption vessel, a two-stage pre-chlorination vessel, and a one-stage pre-chlorination vessel to recover residual chlorine. It then undergoes gas-liquid separation, three-stage graphite falling film absorption, two-stage packing absorption, and alkaline washing absorption. The three-stage graphite falling film absorption and the two-stage packing absorption employ countercurrent absorption, with the absorption temperature controlled below 38℃. A portion of the concentrated hydrochloric acid obtained from absorption is returned to the S2 cycle for raw material extraction, while the other portion, after oil removal filtration, activated carbon adsorption, and resin adsorption, is sent off as by-product hydrochloric acid.

[0022] Example 3 This embodiment provides a production process for environmentally friendly chlorinated paraffin-52, including the following steps: S1. Select C14 to C17 liquid paraffin, filter it through a 120-mesh filter, control the water content of the liquid paraffin to be 0.04%, and then continuously feed it into the primary prechlorination reactor and the secondary prechlorination reactor at a feed rate of 0.67t / h. The chlorination tail gas containing hydrogen chloride and residual chlorine comes into full contact with the liquid paraffin, and the free chlorine in the tail gas is absorbed by the liquid paraffin and participates in the prechlorination reaction. S2. The prechlorinated liquid paraffin is fed into a hydrochloric acid extraction tower and extracted by contact with concentrated hydrochloric acid with a mass fraction of 38%. The mass ratio of concentrated hydrochloric acid to liquid paraffin is 0.12:1. The extraction temperature is controlled at 60℃ and the extraction contact time is 40 min. After extraction, the mixture is allowed to stand and separate into layers. The lower acid phase and entrained water are removed, and the upper oil phase is taken to obtain the dehydrated and impurity-free liquid paraffin. S3. The dehydrated and impurity-removed liquid paraffin is fed into a three-stage tail chlorination absorption reactor for further contact with the tail gas from the subsequent chlorination reaction. This allows the residual chlorine in the tail gas to continue to be absorbed and reacted by the liquid paraffin, yielding the liquid wax to be chlorinated. S4. The liquid paraffin to be chlorinated is continuously fed into a six-stage chlorination reactor connected in series. The total chlorine feed rate is 1.50 t / h, and the chlorine flow rate is distributed sequentially according to the total chlorine flow rate: Stage 1 28%, Stage 2 27%, Stage 3 20%, Stage 4 14%, Stage 5 7%, and Stage 6 4%. Each stage of the reactor carries out a free radical substitution chlorination reaction under photo-initiated and heat-maintained conditions. The reaction temperature is controlled at 88–95℃, and the reaction pressure is controlled below 0.02 MPa. During the reaction, heat is removed through jacket cooling and external graphite circulation cooling to keep the temperature difference between each stage of the reactor within ±5℃. The sixth-stage chlorination reactor is equipped with an online density detection device to adjust the liquid paraffin feed rate and chlorine flow rate in conjunction with the discharge density, maintaining the discharge density at 1.23–1.27 g / cm³. S5. The effluent from the sixth-stage chlorination reactor is transferred to a crude product storage tank, and then to a closed degassing reactor. Dry nitrogen is introduced at 75°C for degassing at a rate of 0.12 m³ / (m³·min). The degassing tail gas is then treated in a degassing absorption tower. Degassing is terminated when the pH of the absorbent solution after water absorption reaches 6.5–7.5. Subsequently, 0.20 wt% of epoxy fatty acid ester is added as a heavy metal-free stabilizer, and the mixture is stirred thoroughly to obtain chlorinated paraffin-52. S6. The tail gas from the chlorination reaction is successively passed through a three-stage tail chlorine absorption vessel, a two-stage pre-chlorination vessel, and a one-stage pre-chlorination vessel to recover residual chlorine. Then, it undergoes gas-liquid separation, three-stage graphite falling film absorption, two-stage packing absorption, and alkaline washing absorption. Part of the concentrated hydrochloric acid obtained from the absorption is returned to S2 as an extraction acid, and the other part is successively passed through oil removal filtration, activated carbon adsorption, and resin adsorption before being sent out as by-product hydrochloric acid.

[0023] Comparative Example 1: No extraction with concentrated hydrochloric acid was performed. The difference between this comparative example and Example 3 is that the concentrated hydrochloric acid extraction step in S2 is omitted. That is, the liquid paraffin after secondary prechlorination does not undergo 38% concentrated hydrochloric acid extraction to remove water and impurities, but directly enters the tertiary tail chlorine absorption vessel. The remaining process conditions are the same as in Example 3.

[0024] Specifically, the liquid paraffin was still filtered through a 120-mesh filter, the feed rate was 0.67 t / h, the total chlorine feed rate was 1.50 t / h, and the chlorine flow distribution, reaction temperature, pressure, degassing conditions and stabilizer addition amount of the six-stage chlorination reactor were consistent with those in Example 3.

[0025] Comparative Example 2: No tail chlorine recycling prechlorination was implemented The difference between this comparative example and Example 3 is that the primary and secondary prechlorination reactors in S1 are omitted, and the tertiary tail chlorine absorption reactor in S3 is also omitted. The tail gas of the chlorination reaction does not react with the liquid paraffin in residual chlorine contact, but directly enters the subsequent gas-liquid separation, graphite falling film absorption, packing absorption and alkaline washing absorption system. After filtration and extraction with concentrated hydrochloric acid, the liquid paraffin directly enters the six-stage series chlorination reactor. The remaining process conditions are the same as in Example 3.

[0026] Specifically, the liquid paraffin feed rate was 0.67 t / h, the concentrated hydrochloric acid mass fraction was 38%, the mass ratio of concentrated hydrochloric acid to liquid paraffin was 0.12:1, the extraction temperature was 60℃, and the extraction time was 40 min; the total chlorine feed rate was 1.50 t / h, and the chlorine distribution and temperature control methods of the six-stage chlorination reactor were the same as in Example 3.

[0027] Comparative Example 3: The six-stage decreasing chlorine distribution method was not used. The difference between this comparative example and Example 3 is that the chlorine gas in the six-stage chlorination reactor is not distributed in descending order according to the flow direction of the liquid wax, but rather in an equal amount of chlorine is introduced in each stage. That is, the chlorine gas flow rate in the first to sixth stage chlorination reactors is approximately 16.7% of the total chlorine gas. The other process conditions are the same as in Example 3.

[0028] Test methods To verify the impact of the process of this invention on the product quality stability, residual chlorine utilization efficiency, and environmental friendliness of chlorinated paraffin-52, the chlorinated paraffin-52 products and production processes obtained in Examples 1-3 and Comparative Examples 1-3 were tested. After each group of processes had been running continuously and stably, the 4th hour of continuous operation was taken as the starting point for stable sampling. Samples were taken every 30 minutes for a total of 8 samplings. The samples from the same group were mixed evenly and used as the test samples for that group. Each indicator was tested in parallel 3 times, and the average value was taken as the final result.

[0029] 1. Chlorine content test Weigh approximately 0.2000 g of the chlorinated paraffin sample to be tested and place it in an oxygen bomb combustion apparatus. Add an appropriate amount of absorbent liquid and allow the sample to completely combust and decompose. The chlorides produced during combustion are absorbed by the absorbent liquid. After combustion, transfer the absorbent liquid to an Erlenmeyer flask and titrate with silver nitrate standard solution, setting up a blank test. Calculate the chlorine content in the sample based on the amount of silver nitrate standard solution consumed, and express the result as a mass percentage. The optimal chlorine content range for chlorinated paraffin-52 is 51.0%–53.0%.

[0030] 2. Density and density fluctuation test The density of the sample at 20℃ was determined using a digital densitometer. Before testing, the instrument was calibrated with distilled water and a standard density solution. The sample was equilibrated in a constant temperature water bath at 20±0.5℃ for 30 minutes before being injected into the densitometer's measuring cell. The results were recorded after the readings stabilized.

[0031] 3. Acid value test Weigh approximately 5.00 g of chlorinated paraffin sample, dissolve it in a neutral ethanol-toluene mixture, add phenolphthalein indicator, and titrate with a 0.01 mol / L potassium hydroxide ethanol standard solution until a faint red color appears and persists for 30 seconds. Simultaneously perform a blank test, calculate the acid value based on the amount of potassium hydroxide standard solution consumed, and express the result as mgKOH / g. A lower acid value indicates less residual hydrogen chloride, free acid, and acidic byproducts in the product.

[0032] 4. Color Test The chlorinated paraffin sample was kept at a constant temperature of 50℃ for 30 minutes to ensure uniform sample flowability. It was then transferred to a colorimetric tube and compared with the platinum-cobalt standard color scale. The color value of the sample was recorded, and the result is expressed as Hazen. A smaller color value indicates a lighter product color and less influence from impurities and side reactions.

[0033] 5. Heating Loss Test Weigh approximately 10.00 g of sample into a pre-weighed glass weighing dish, spread it evenly, and then heat it in a 125±2℃ forced-air drying oven for 2 hours. After removing it, cool it to room temperature in a desiccator and weigh it. Calculate the weight loss during heating based on the difference in mass before and after heating. This indicator is used to evaluate the content of low-boiling matter, residual hydrogen chloride, and volatile impurities in the product.

[0034] 6. Thermal stability test Weigh 20.00g of sample and place it in a heat-resistant glass test tube. Heat at a constant temperature of 175±2℃ in an oil bath for 4 hours. After heating, observe the color change of the sample and determine the acid value and color after heating. The increase in acid value and color after heating is used to evaluate thermal stability; the smaller the increase in acid value and the less the increase in color, the better the thermal stability of the product.

[0035] 7. Residual hydrogen chloride test Weigh 10.00 g of sample, add 100 mL of deionized water, and extract by shaking at 60 °C for 30 min. After standing and separating the layers, take the aqueous phase and titrate the chloride ion content with silver nitrate standard solution. Convert the result to the residual hydrogen chloride content in the sample, and express the result in mg / kg. The lower the residual hydrogen chloride content, the more complete the sealing, degassing, and absorption treatment.

[0036] 8. Exhaust gas free chlorine and alkaline scrubbing load test A sampling port is set up before the tail gas enters the terminal alkaline scrubbing tower. Free chlorine in the tail gas is absorbed using potassium iodide absorbent, and the concentration is calculated by titration with sodium thiosulfate standard solution. The amount of sodium hydroxide solution added to the alkaline scrubbing tower is recorded during 8 hours of continuous operation and converted into alkali consumption per unit product, expressed as kgNaOH / t product. This indicator is used to evaluate the impact of tail chlorine reuse pre-chlorination and tertiary tail chlorine absorption on the end-of-pipe environmental treatment load.

[0037] Table 1: Quality Test Results of Chlorinated Paraffin-52 Table 2: Continuous Production Stability and Exhaust Gas Treatment Indicators As shown in Tables 1 and 2, after eliminating the concentrated hydrochloric acid extraction step in Comparative Example 1, although the chlorine content and density remained within the target range for chlorinated paraffin-52, the acid value increased to 0.168 mg KOH / g, significantly higher than the 0.049 mg KOH / g in Example 3. The color increased from 39 Hazen in Example 3 to 92 Hazen, the weight loss upon heating increased from 0.11% to 0.25%, the residual HCl increased from 29 mg / kg to 96 mg / kg, and the increase in acid value after 175℃ for 4 hours also increased to 0.118 mg KOH / g. This indicates that when liquid paraffin is not extracted with concentrated hydrochloric acid, residual moisture, polar impurities, and impurities that easily cause coloration will enter the main chlorination stage. During the chlorination reaction and subsequent degassing, these impurities are more likely to form acidic byproducts and unstable components, leading to a higher acid value, darker color, increased volatile residues, and decreased thermal stability. Therefore, concentrated hydrochloric acid extraction is not a simple pretreatment step, but a key measure to improve the acid value, color, and thermal stability of the product.

[0038] After eliminating the primary and secondary pre-chlorination reactors and the tertiary tail chlorine absorption reactor in Comparative Example 2, although the acid value, color, and residual HCl of the product were lower than those in Comparative Example 1, its tail gas treatment indicators deteriorated significantly. Table 2 shows that the free chlorine in the tail gas before terminal absorption in Comparative Example 2 increased to 386 mg / m³, far higher than the 43 mg / m³ in Example 3; the alkali consumption per unit product increased to 18.6 kg NaOH / t of product, and the chlorine utilization rate decreased to 94.3%. This indicates that after eliminating tail chlorine reuse, the free chlorine in the chlorination reaction tail gas failed to re-contact with the liquid paraffin and participate in the pre-chlorination reaction, but instead directly entered the terminal absorption system, resulting in a significant increase in alkali washing load and increased ineffective chlorine loss. This proves that the present invention, by setting up tail gas residual chlorine pre-chlorination and tertiary tail chlorine absorption steps, can reuse the free chlorine in the tail gas for the liquid paraffin chlorination reaction, thereby reducing tail gas treatment pressure, improving chlorine utilization rate, and reducing alkali consumption.

[0039] Comparative Example 3 did not use a six-stage decreasing chlorination distribution method, but instead used equal amounts of chlorination at each stage. The product chlorine content was 52.18%, and the density at 20℃ was 1.253 g / cm³. While the single sampling results were still close to the target range, the continuous stability significantly deteriorated. The density fluctuation range of the sixth-stage output expanded to 1.229-1.276 g / cm³ over 8 hours, with the maximum fluctuation reaching 0.047 g / cm³, significantly higher than the 0.012 g / cm³ in Example 3. Simultaneously, the acid value of Comparative Example 3 increased to 0.083 mg KOH / g, the color increased to 108 Hazen, the weight loss upon heating increased to 0.20%, the residual HCl increased to 64 mg / kg, and the increase in acid value after 175℃ for 4 hours increased to 0.091 mg KOH / g. This indicates that the equal-volume chlorination method cannot adequately match the reaction requirements of liquid paraffin at different chlorination stages. It easily leads to localized excessive chlorine in the initial stages, insufficient chlorine replenishment in the later stages, or fluctuations in reaction depth, resulting in localized overchlorination, increased side reactions, and a darker product color. Therefore, a six-stage decreasing chlorination distribution combined with final-stage density feedback control is beneficial for maintaining a high reaction rate in the initial stages and allowing for precise chlorine replenishment in the later stages, thereby improving density stability and product consistency in continuous production.

[0040] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A production process for an environmentally friendly chlorinated paraffin-52, characterized in that, Includes the following steps: S1. Liquid paraffin is metered and continuously fed into the primary prechlorination reactor and the secondary prechlorination reactor, so that the liquid paraffin comes into contact with the tail gas containing hydrogen chloride and residual chlorine from the subsequent chlorination reaction section. The residual chlorine in the tail gas is used to prechlorinate the liquid paraffin and reduce the free chlorine content in the tail gas. S2. The prechlorinated liquid paraffin is fed into a hydrochloric acid extraction tower and extracted by contact with concentrated hydrochloric acid with a mass fraction of 31% to 38%. After standing and separating into layers, the upper oil phase is taken to obtain liquid paraffin after water and impurity removal. S3. The dehydrated and impurity-removed liquid paraffin is sent to a three-stage tail chlorine absorption vessel to further contact with the tail gas of the subsequent chlorination reaction, so that the residual chlorine in the tail gas is absorbed and reacted by the liquid paraffin to obtain the liquid wax to be chlorinated. S4. The liquid wax to be chlorinated is continuously fed into a six-stage chlorination reactor connected in series. Chlorine gas is introduced into each stage of the chlorination reactor. Under the conditions of photoinitiation and heat maintenance, a free radical substitution chlorination reaction is carried out. The reaction temperature is controlled at 75-95°C and the reaction pressure is not higher than 0.02 MPa. The chlorine flow rate of the six-stage chlorination reactor is distributed in descending order according to the liquid wax flow direction. The sixth-stage chlorination reactor is equipped with online density detection. The feed rate of liquid paraffin and / or the chlorine flow rate of each stage are adjusted according to the discharge density of the sixth stage to control the chlorination discharge density at 1.23 to 1.27 g / cm³. S5. After the material from the sixth-stage chlorination reactor is sent to the crude product temporary storage tank, it enters the closed degassing reactor. Dry air or nitrogen is introduced to remove residual hydrogen chloride. The degassing tail gas enters the degassing absorption tower for absorption and treatment. After degassing, a heavy metal-free stabilizer is added to the chlorinated paraffin to obtain chlorinated paraffin-52 product. S6. The residual chlorine in the tail gas of the chlorination reaction is utilized by passing it through a three-stage tail chlorine absorption vessel, a two-stage prechlorination vessel, and a one-stage prechlorination vessel. Then, it is treated by gas-liquid separation, three-stage graphite falling film absorption, two-stage packing absorption, and alkaline washing absorption to obtain by-product hydrochloric acid and achieve the tail gas emission standard.

2. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In S1, the liquid paraffin is C 14 ~C 17 Liquid paraffin is filtered through an 80-120 mesh before feeding, and the water content of the liquid paraffin is controlled below 0.08%.

3. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In step S2, the mass ratio of concentrated hydrochloric acid to liquid paraffin is 0.03–0.12:1, the extraction temperature is 35–60°C, and the extraction contact time is 10–40 min.

4. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In S4, the chlorine flow rate of the six-stage chlorination reactor, calculated based on the total chlorine volume, is as follows: Stage 1: 22%–28%, Stage 2: 22%–28%, Stage 3: 17%–23%, Stage 4: 12%–18%, Stage 5: 7%–13%, and Stage 6: 3%–8%.

5. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In step S4, the liquid paraffin feed rate is 0.50–0.67 t / h, and the total chlorine feed rate is 1.12–1.50 t / h.

6. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In S4, each chlorination reactor is equipped with a circulating cooler, which is a graphite heat exchanger. The heat of reaction is removed through jacket cooling and external circulation cooling, so that the temperature difference between each reactor is controlled within ±5℃.

7. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In step S5, the degassing temperature is 45–75°C, the flow rate of dry air or nitrogen is 0.02–0.12 m³ / (m³·min), and the degassing process ends when the pH of the absorbent after the degassing tail gas is absorbed by water is 6.5–7.

5.

8. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In step S5, the amount of heavy metal-free stabilizer added is 0.08% to 0.20% of the mass of chlorinated paraffin, and the heavy metal-free stabilizer is selected from one of epoxidized soybean oil, glycerol ether stabilizers, and epoxidized fatty acid esters.

9. The production process of environmentally friendly chlorinated paraffin-52 according to claim 1, characterized in that, In S6, the three-stage graphite falling film absorption and the two-stage packing absorption adopt a countercurrent absorption method, and the absorption temperature is controlled below 40°C. Part of the concentrated hydrochloric acid obtained from absorption is returned to S2 as an extraction acid, and the other part is sent out as a by-product hydrochloric acid after passing through oil removal filtration, activated carbon adsorption and resin adsorption in sequence.

Images