Process for the photocatalytic continuous chlorination of chlorinated paraffins

Abstract

The present application relates to the field of fine chemical technology, and discloses a kind of photocatalytic continuous chlorination production chlorinated paraffin process, comprising the following steps: S1, premixing feed: after mixing liquid paraffin with photocatalytic additive, with gasification chlorine is continuously sent into static mixer, after dispersion premixing, from bottom to top is sent into the bottom of tubular photocatalytic reactor;S2, axial gradient photo-thermal coupling continuous chlorination: tubular photocatalytic reactor is equipped with jacket cooling circulation system, and its reaction tube is axially from bottom to top equipped with multiple independently controllable ultraviolet light illumination section and cooling section, so that the ultraviolet light wavelength and / or illumination intensity in the reaction tube and reaction temperature form gradient distribution along the material flow direction;Control the turbulent flow state of material in the reaction tube, under the synergistic effect of photocatalytic additive and ultraviolet light, free radical chain chlorination reaction is carried out.The present application has the advantages of short reaction time, high mass transfer efficiency, accurate temperature control, high degree of automation and stable product quality.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, specifically to a process for the continuous photocatalytic chlorination production of chlorinated paraffin. Background Technology

[0002] Chlorinated paraffin is an important fine chemical product, widely used in plasticizers, flame retardants, lubricant additives, and metalworking fluids. Currently, the mainstream industrial process for preparing chlorinated paraffin involves using a multi-stage series glass-lined reactor to introduce chlorine gas into liquid paraffin under thermal or photo-initiated conditions to carry out a free radical substitution reaction.

[0003] However, existing production technologies have several shortcomings in application. First, to ensure the depth of chlorination, the total residence time of materials in the reactor in traditional batch-type processes is often as long as 20 to 38 hours, resulting in low production efficiency. Second, chlorination is a strongly exothermic reaction, and there is a significant temperature gradient within the batch reactor. Local overheating can easily lead to paraffin cracking or dehydrochlorination side reactions, resulting in a darker product color and a higher acid value. Third, the mass transfer efficiency of chlorine in the liquid phase is limited, and insufficient gas-liquid contact can easily lead to localized excessive concentrations of chlorine, causing over-chlorination and coking. Finally, existing processes rely heavily on manual sampling and testing to control the reaction endpoint, lacking online density feedback and automated adjustment methods, resulting in poor batch-to-batch product quality stability.

[0004] Therefore, how to develop a continuous chlorination process with short reaction time, high mass transfer efficiency, precise temperature control, and closed-loop control has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a process for the continuous photocatalytic chlorination of chlorinated paraffins, which has the advantages of short reaction time, high mass transfer efficiency, precise temperature control, high degree of automation and stable product quality, and solves the problems in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A process for the continuous photocatalytic chlorination to produce chlorinated paraffins includes the following steps:

[0008] S1. Premixed feed: Liquid paraffin is mixed with photocatalytic additive and then continuously fed into a static mixer along with gasified chlorine. After dispersion and premixing, it is fed into the bottom of the tubular photocatalytic reactor from bottom to top.

[0009] S2, Axial Gradient Photothermal Coupled Continuous Chlorination: The tubular photocatalytic reactor is equipped with a jacketed cooling circulation system. The reaction tube has multiple independent and controllable ultraviolet irradiation sections and cooling sections from bottom to top, so that the ultraviolet wavelength and / or irradiation intensity and reaction temperature in the reaction tube form a gradient distribution along the material flow direction; the material in the reaction tube is controlled to be in a turbulent flow state, and a free radical chain chlorination reaction is carried out under the synergistic effect of photocatalytic aid and ultraviolet light;

[0010] S3. Density feedback closed-loop regulation: An online density detector is installed in the middle section of the reaction tube to monitor the density of the reactants in real time. When the detected density reaches the preset threshold, the feedback control system automatically adjusts the chlorine feed rate and / or the ultraviolet irradiation power of each section to control the chlorine content of the reaction product within the preset target value.

[0011] S4. Gas-liquid separation and degassing purification: The reaction product is discharged from the top of the reactor into the gas-liquid separator, and the liquid product enters the degassing tower. Nitrogen gas is introduced for gas stripping and deacidification to remove hydrogen chloride and residual chlorine. Then, a stabilizer is added and mixed evenly to obtain the finished chlorinated paraffin.

[0012] Preferably, in step S2, the inner light-transmitting reaction tube of the tubular photocatalytic reactor is a quartz glass tube or a high borosilicate glass tube with a diameter of 50~200mm and an effective length of 3~15m; the ultraviolet irradiation section is divided into 3~6 independent sections along the axial direction, and a light-shielding partition is provided between each section.

[0013] It is worth noting that quartz glass tubes or borosilicate glass tubes have excellent ultraviolet light transmittance and resistance to high-temperature chemical corrosion, ensuring efficient transmission of ultraviolet light into the reaction solution while preventing damage to the tube body due to strong exothermic reactions. The combination of axially segmented independent light zones and light-shielding partitions ensures that the light intensity and wavelength between each light zone do not interfere with each other, providing a structural basis for achieving a gradient distribution of photothermal coupling.

[0014] Preferably, in step S1, the photocatalytic agent is selected from at least one of nano-titanium dioxide, azobenzene, azobisisobutyronitrile, benzophenone, or silica-supported photosensitizer.

[0015] It is worth noting that the aforementioned photocatalytic promoters can efficiently generate free radicals or initiate electron transfer under ultraviolet light irradiation of specific wavelengths, significantly reducing the activation energy of the chlorination reaction through a synergistic effect. Compared to simple thermal chlorination or photochlorination, this combination can excite free radical chain reactions at lower temperatures, thereby significantly reducing the occurrence of high-temperature cracking side reactions.

[0016] Preferably, in step S2, the ultraviolet wavelength of each ultraviolet illumination segment is independently selected from 200~400nm, and the illumination intensity of the lowest segment is greater than that of the highest segment; specifically, the wavelength of the lowest illumination segment is 254nm and the illumination intensity is 15~30mW / cm². 2 The wavelength of the uppermost illuminated section is 365nm, and the illuminance is 3~8mW / cm². 2 .

[0017] It is worth noting that the chlorine content of the material at the bottom of the reaction tube is relatively low, and the use of 254nm short-wave high-intensity ultraviolet light is conducive to initiating homolytic cleavage of Cl-Cl bonds and promoting the formation of free radicals. However, at the top of the reaction tube, the chlorine content of the material has increased significantly, and 365nm long-wave low-intensity ultraviolet light can maintain the continuous progress of the chain reaction and avoid the over-activation and detachment of the bound chlorine caused by high-intensity light, thus solving the problem of overchlorination at the end of the material.

[0018] Preferably, in step S2, the temperature of each section of the reaction tube from bottom to top is controlled by the jacket circulating cooling water as follows: lower section 80~95℃, middle section 70~80℃, upper section 60~70℃; the reaction pressure is 0.02~0.06MPa; and the total residence time of the material in the reaction tube is 2~8 hours.

[0019] It is worth noting that the decreasing temperature gradient from bottom to top perfectly matches the exothermic pattern of the chlorination reaction, which progresses from intense to gradual. The high temperature in the lower section effectively increases the initial initiation rate, and the exothermic reaction is then carried away in a timely and segmented manner by the jacketed circulating water, preventing the material from accumulating overheating in the middle and upper sections and effectively suppressing product cracking and coking.

[0020] Preferably, in step S2, the material flow velocity in the reaction tube is controlled at 0.05~0.5m / s, so that the material is in a turbulent state with a Reynolds number Re≥4000; the inner wall of the reaction tube is provided with spiral or straight turbulence fins in the axial direction to break the near-wall laminar boundary layer and enhance the radial mixing of gas and liquid.

[0021] It is worth noting that the combination of the inner wall turbulent fins and the turbulent flow pattern forcibly disrupts the laminar boundary layer at the pipe wall, greatly enhancing the microscopic mixing of the gas and liquid phases. This allows dissolved chlorine gas to be rapidly and uniformly transferred to the area surrounding the paraffin molecules. This dynamic turbulent mass transfer significantly improves the reaction rate and is the core physical guarantee for reducing the residence time from the traditional 20 hours or more to 2-8 hours.

[0022] Preferably, in step S1, the liquid paraffin is a n-alkane with a carbon chain length of C14~C20, the n-alkane content is ≥95%, and the aromatic content is ≤1%; the mass ratio of liquid paraffin to chlorine is 1:0.8~1.35; the chlorine is pressure-stabilized to 0.02~0.08MPa by a buffer tank before entering the static mixer, and the outlet of the buffer tank is equipped with a chlorine flow meter and an automatic regulating valve to receive the regulation command of the feedback control system.

[0023] It is worth noting that the high-purity n-alkane feedstock avoids the problem of photochemical side reactions of aromatic components under ultraviolet light, which would cause the product to darken in color. The pre-pressurized chlorine buffer tank, combined with a high-precision flow meter and regulating valve, enables the subsequent closed-loop control system to respond instantly and precisely adjust the gas intake, thus ensuring the dynamic balance of the reaction.

[0024] Preferably, in step S4, the operating temperature of the degassing tower is 90~110℃, the operating pressure is 0.01~0.05MPa, the nitrogen flow rate is 0.5~2 times the volume of the liquid product per hour, and the acid value of the crude chlorinated paraffin after degassing is reduced to below 0.05mgKOH / g; the stabilizer is one or more combinations of epoxidized soybean oil, ethylene glycol glycidyl ether, or phenolic antioxidants, and the amount added accounts for 0.1~0.5% of the crude product weight.

[0025] It is worth noting that the combination of micro-positive pressure (0.01~0.05MPa) and nitrogen stripping process can effectively remove hydrogen chloride and chlorine dissolved in the crude product, while avoiding excessive volatilization of light components under negative pressure. At the same time, epoxy compound stabilizers can continuously neutralize potential acidic substances during product storage, significantly improving the product's long-term thermal stability and color retention.

[0026] Preferably, the gas phase tail gas separated by the gas-liquid separator in step S4 is cooled to recover the entrained paraffin oil and then sent to the primary falling film absorption tower to absorb hydrogen chloride with water to produce 28-31% by-product hydrochloric acid; the residual gas after primary absorption is sent to the secondary packed absorption tower, where residual chlorine and hydrogen chloride are absorbed by dilute alkaline solution to meet emission standards; the tail gas discharged from the primary falling film absorption tower that is not absorbed by water can be compressed by a compressor and returned to the static mixer in step S1, mixed with fresh chlorine, and then recycled back into the reactor.

[0027] It is worth noting that the exhaust gas treatment system of this invention constructs a closed-loop resource recycling path: recovering raw materials entrained in the reaction through cryogenic recovery, absorbing high-value hydrochloric acid as a byproduct through falling film absorption, and eliminating residual toxic gases through alkaline washing. Among these, the compression and reuse process of residual chlorine gas greatly improves the economy of atom, enabling the comprehensive utilization rate of chlorine gas to reach an industry-leading level, and significantly reducing the burden of environmental exhaust gas treatment.

[0028] Preferably, in step S3, the preset target value is that the chlorine content of the reaction product reaches 50-54%; when the density signal monitored by the online density detector reaches the preset threshold corresponding to the chlorine content, the feedback control system synchronously reduces the output power of the ultraviolet irradiation section located in the middle and upper sections of the reaction tube to prevent the product from undergoing overchlorination side reaction.

[0029] It is worth noting that the online density detection is linked with the mid-to-upper stage illumination power to construct a dynamic "end-stage overchlorination defense mechanism". When the product density (chlorine content) is detected to be about to reach the target value, the subsequent stage light intensity is actively reduced to avoid excessive chlorine addition, thereby ensuring that the chlorination depth of the product is uniform and consistent, and preventing large-scale overchlorination accidents that are most likely to occur during process scale-up.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. This invention, through the axial gradient photothermal coupling design of the tubular photocatalytic reactor and combined with turbulent enhanced mass transfer, shortens the residence time of the chlorination reaction from 20-38 hours in the traditional batch reactor to 2-8 hours, greatly improving the production efficiency of chlorinated paraffin.

[0032] 2. This invention effectively overcomes the problems of local overheating and material coking caused by the strong exothermic reaction of chlorination through the synergistic effect of multi-segment independent temperature control and gradient reduction of light intensity, significantly reducing the acid value of the product and improving the color of the product.

[0033] 3. By adding an online density detector and a feedback control system, this invention achieves adaptive adjustment of chlorine gas feed and ultraviolet light power, thereby improving the batch stability of products in continuous production.

[0034] 4. This invention improves the effective utilization rate of chlorine gas through the cascade recovery and recycling of tail gas, and achieves efficient collection of by-product hydrochloric acid, which meets the requirements of green chemical development. Attached Figure Description

[0035] Figure 1 The flowchart shown is a flowchart of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] To address the problems of long reaction times, difficulty in temperature control, susceptibility to localized overchlorination and coking, low chlorine utilization, and large fluctuations in product quality in existing technologies, the following technical solution is proposed. Please refer to [link / reference needed]. Figure 1 .

[0038] A process for the continuous photocatalytic chlorination to produce chlorinated paraffins includes the following steps:

[0039] S1. Premixed feed: Liquid paraffin is mixed with photocatalytic additive and then continuously fed into a static mixer along with gasified chlorine. After dispersion and premixing, it is fed into the bottom of the tubular photocatalytic reactor from bottom to top.

[0040] S2, Axial Gradient Photothermal Coupled Continuous Chlorination: The tubular photocatalytic reactor is equipped with a jacketed cooling circulation system. The reaction tube has multiple independent and controllable ultraviolet irradiation sections and cooling sections from bottom to top, so that the ultraviolet wavelength and / or irradiation intensity and reaction temperature in the reaction tube form a gradient distribution along the material flow direction; the material in the reaction tube is controlled to be in a turbulent flow state, and a free radical chain chlorination reaction is carried out under the synergistic effect of photocatalytic aid and ultraviolet light;

[0041] S3. Density feedback closed-loop regulation: An online density detector is installed in the middle section of the reaction tube to monitor the density of the reactants in real time. When the detected density reaches the preset threshold, the feedback control system automatically adjusts the chlorine feed rate and / or the ultraviolet irradiation power of each section to control the chlorine content of the reaction product within the preset target value.

[0042] S4. Gas-liquid separation and degassing purification: The reaction product is discharged from the top of the reactor into the gas-liquid separator, and the liquid product enters the degassing tower. Nitrogen gas is introduced for gas stripping and deacidification to remove hydrogen chloride and residual chlorine. Then, a stabilizer is added and mixed evenly to obtain the finished chlorinated paraffin.

[0043] In this embodiment, specifically, in step S2, the inner light-transmitting reaction tube of the tubular photocatalytic reactor is a quartz glass tube or a high borosilicate glass tube with a diameter of 50~200mm and an effective length of 3~15m; the ultraviolet irradiation section is divided into 3~6 independent sections along the axial direction, and a light-shielding partition is provided between each section.

[0044] In this embodiment, specifically, in step S1, the photocatalytic aid is selected from at least one of nano-titanium dioxide, azobenzene, azobisisobutyronitrile, benzophenone, or silica-supported photosensitizer.

[0045] In this embodiment, specifically, in step S2, the ultraviolet wavelength of each ultraviolet illumination segment is independently selected from 200~400nm, and the illumination intensity of the lowest segment is greater than that of the highest segment; specifically, the wavelength of the lowest illumination segment is 254nm and the illumination intensity is 15~30mW / cm². 2The wavelength of the uppermost illuminated section is 365nm, and the illuminance is 3~8mW / cm². 2 .

[0046] In this embodiment, specifically, in step S2, the temperature of each section of the reaction tube from bottom to top is controlled by the jacket circulating cooling water as follows: lower section 80~95℃, middle section 70~80℃, upper section 60~70℃; the reaction pressure is 0.02~0.06MPa; and the total residence time of the material in the reaction tube is 2~8 hours.

[0047] In this embodiment, specifically, in step S2, the material flow velocity in the reaction tube is controlled at 0.05~0.5m / s, so that the material is in a turbulent state with a Reynolds number Re≥4000; the inner wall of the reaction tube is provided with spiral or straight turbulence fins in the axial direction, which are used to break the near-wall laminar boundary layer and enhance the radial mixing of gas and liquid.

[0048] In this embodiment, specifically, in step S1, the liquid paraffin is a n-alkane with a carbon chain length of C14~C20, the n-alkane content is ≥95%, and the aromatic content is ≤1%; the mass ratio of liquid paraffin to chlorine is 1:0.8~1.35; before entering the static mixer, the chlorine is pressure-stabilized to 0.02~0.08MPa by a buffer tank, and the outlet of the buffer tank is equipped with a chlorine flow meter and an automatic regulating valve to receive the regulation command of the feedback control system.

[0049] In this embodiment, specifically, in step S4, the operating temperature of the degassing tower is 90~110℃, the operating pressure is 0.01~0.05MPa, the nitrogen flow rate is 0.5~2 times the volume of the liquid phase product per hour, and the acid value of the crude chlorinated paraffin after degassing is reduced to below 0.05mgKOH / g; the stabilizer is one or more combinations of epoxidized soybean oil, ethylene glycol glycidyl ether, or phenolic antioxidants, and the amount added accounts for 0.1~0.5% of the crude product weight.

[0050] In this embodiment, specifically, the gas phase tail gas separated by the gas-liquid separator in step S4 is cooled to recover the entrained paraffin oil and then sent to the first-stage falling film absorption tower to absorb hydrogen chloride with water to produce 28-31% by-product hydrochloric acid; the residual gas after the first-stage absorption is sent to the second-stage packed absorption tower, where residual chlorine and hydrogen chloride are absorbed by dilute alkaline solution to meet emission standards; the tail gas discharged from the first-stage falling film absorption tower that is not absorbed by water can be compressed by a compressor and returned to the static mixer in step S1, where it is mixed with fresh chlorine and then recycled back into the reactor.

[0051] In this embodiment, specifically, in step S3, the preset target value is that the chlorine content of the reaction product reaches 50~54%; when the density signal monitored by the online density detector reaches the preset threshold corresponding to the chlorine content, the feedback control system synchronously reduces the output power of the ultraviolet irradiation section located in the middle and upper sections of the reaction tube to prevent the product from undergoing overchlorination side reaction.

[0052] Example 1 (Preparation of Chlorinated Paraffin-52)

[0053] This embodiment uses the process of the present invention to prepare chlorinated paraffin-52, and the specific parameters are as follows:

[0054] In step S1, the liquid paraffin is selected from n-alkanes with a carbon chain length of C16~C18 (n-alkanes content 98%, aromatics content 0.5%), and the photocatalytic aid is selected from azobisisobutyronitrile, with an addition amount accounting for 0.3% of the mass of the liquid paraffin.

[0055] In step S2, the tubular photocatalytic reactor uses a borosilicate glass tube with a diameter of 100 mm and an effective length of 8 m. The ultraviolet irradiation section is divided into three segments along the axial direction. The lower segment has an ultraviolet wavelength of 254 nm and an irradiation intensity of 20 mW / cm². 2 The upper ultraviolet wavelength is 365nm and the light intensity is 5mW / cm². 2 The inner wall of the reaction tube is equipped with spiral turbulence fins, the material flow velocity is controlled at 0.25 m / s, and the material is in a turbulent state with a Reynolds number Re≥4500. The reaction temperature is controlled from bottom to top by the jacket circulating water: 85℃ in the lower section, 75℃ in the middle section, and 65℃ in the upper section. The reaction pressure is 0.03 MPa, and the total material residence time is 5 hours.

[0056] In step S3, the preset target value is set to a chlorine content of 52%. When the online density detector reaches the threshold, the feedback control system reduces the output power of the middle and upper ultraviolet lamps to 65% of the initial power.

[0057] In step S4, the temperature of the degassing tower is 100℃, the pressure is 0.02MPa, the nitrogen flow rate is 1.5 times the liquid phase volume per hour, and the stabilizer is epoxidized soybean oil, with an addition amount of 0.3% of the crude product weight.

[0058] Example 2 (Preparation of Chlorinated Paraffin-42)

[0059] This embodiment uses the process of the present invention to prepare chlorinated paraffin-42, and the difference from Example 1 is:

[0060] In step S2, the total residence time of the material is controlled at 3.5 hours, the reaction temperature in the middle section is controlled at 80℃, the reaction temperature in the upper section is controlled at 72℃, and the reaction pressure is 0.04MPa; in step S3, the preset target value is set at a chlorine content of 42%.

[0061] Comparative Example 1 (Traditional autoclave process)

[0062] This comparative example uses a traditional four-stage series-connected batch photochlorination reactor. No axial photothermal gradient is provided in the reactor; all stages of the reactor are illuminated with 254nm wavelength ultraviolet light (illuminance of 15mW / cm²).2 The reaction temperature was uniformly controlled at 95℃. No forced turbulent flow was applied to the materials, and the inner wall of the reactor had no turbulence fins. No online density feedback control system was used during the reaction; instead, manual, timed sampling was used to control the endpoint. All other raw material specifications, photocatalyst dosage, and post-treatment processes remained consistent with Example 1, with the target chlorine content set at 52%.

[0063] Test Example (Product Performance Test)

[0064] The chlorinated paraffin products prepared in Examples 1, 2, and Comparative Example 1 were subjected to performance tests, and the test results are shown in the table below:

[0065] Test item Example 1 (chlorinated paraffin-52) Example 2 (chlorinated paraffin-42) Comparative Example 1 (traditional kettle comparison) Chlorine content found 52.1% 42.3% 51.8% (reaction to 24h) Acid value (mg KOH / g) 0.02 0.03 0.45 Color (APHA) 25 20 310 (dark brown) Total reaction residence time 5 hours 3.5 hours 28 hours Chlorine gas utilization 92.5% 93.8% 78.2%

[0066] The data from the above experimental examples show that:

[0067] Using the process of this invention (Examples 1 and 2), the reaction residence time is significantly shortened from 28 hours in the traditional process to 3.5-5 hours, and the chlorine utilization rate is significantly improved to over 92%. In contrast, the traditional batch process (Comparative Example 1), lacking turbulent mass transfer enhancement and axial gradient temperature control, results in coking and carbonization of the material in the later stages of the reaction, leading to a product color exceeding 310 and an acid value exceeding the standard. This invention achieves unexpected technical effects through the synergistic effect of "tubular turbulent mass transfer + gradient photothermal coupling + density closed-loop feedback".

[0068] Working principle: During production, high-purity liquid paraffin (C14~C20 n-alkanes) is first premixed with the selected photocatalytic additive according to the specified ratio. Then, it is continuously pumped into a static mixer along with the vaporized chlorine gas. In the static mixer, the material and gas are fully dispersed and atomized premixed to form a stable gas-liquid two-phase flow, which is then fed into the bottom of the tubular photocatalytic reactor from bottom to top.

[0069] After the material enters the tubular reactor, it is irradiated by high-intensity ultraviolet light (254 nm) at the bottom. This excites the photocatalytic agent, generating a large number of free radicals, which trigger a vigorous free radical substitution reaction between chlorine and paraffin. As the material continues to rise along the tube wall, the high-temperature environment in the lower section (80-95°C) ensures efficient initiation. Subsequently, the temperature in the middle section gradually decreases to 70-80°C, and in the upper section to 60-70°C. The jacketed circulating cooling water continuously removes the large amount of heat released by the chlorination reaction, coupled with an axially decreasing ultraviolet light intensity (365 nm in the upper section, 3-8 mW / cm²). 2This effectively suppresses the excessive chlorination and deHCl side reactions in the middle and late stages. The flow rate of the material in the reaction tube is precisely controlled in a turbulent state (Re≥4000). Combined with the turbulence fins on the inner wall of the tube, the near-wall laminar boundary layer is continuously destroyed, which greatly enhances the mass transfer efficiency of chlorine and paraffin, enabling the material to complete the conversion process that takes more than 20 hours in traditional processes within 2 to 8 hours.

[0070] When the reactants pass through the middle section of the reactor, the online density detector installed here monitors the change in material density in real time and transmits the data to the feedback control system in real time. The system automatically adjusts the chlorine feed rate and the ultraviolet irradiation power of each section according to the preset density and chlorine content threshold (corresponding to a final chlorine content of 50~54%). Once the density is detected to be close to the target value, the controller will prioritize reducing the output power of the ultraviolet lamps in the middle and upper sections to provide flexible protection and prevent the product from being overchlorinated.

[0071] Finally, the reaction product that reaches the target chlorine content is discharged from the top of the reactor and enters the gas-liquid separator, where most of the gas phase tail gas (containing HCl and unreacted Cl2) is separated from the liquid phase product. The liquid phase product enters the degassing tower, where nitrogen is introduced at 90~110℃ and 0.01~0.05MPa for stripping, which powerfully removes the HCl and trace amounts of chlorine remaining in the oil phase, reducing the acid value to below 0.05mgKOH / g. Then, 0.1~0.5% of epoxidized soybean oil and other stabilizers are added by weight of the crude product and mixed to obtain a high-quality chlorinated paraffin product.

[0072] The separated gaseous tail gas undergoes a cascade treatment process: first, the high-boiling-point paraffin oil entrained in the gas is condensed and recovered by a cooler and returned to the static mixer; then, the tail gas is sent to a first-stage falling film absorption tower, where HCl gas is absorbed countercurrently with water to efficiently produce 28-31% concentration of by-product hydrochloric acid; the residual gas, which still contains a small amount of chlorine after the first-stage absorption, is sent to a second-stage packed absorption tower, where the residual acidic gas is completely neutralized and absorbed with dilute alkali solution, and then discharged after meeting the standards. The chlorine gas discharged from the top of the first-stage falling film absorption tower that has not been absorbed by water is compressed and pressurized by a compressor, and then returned to the inlet of the static mixer in step S1 through a pipeline, where it is mixed with fresh chlorine gas and reintroduced into the reaction, realizing the closed-loop recycling of chlorine gas.

[0073] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, 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 process, method, article, or apparatus.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A process for the continuous photocatalytic chlorination production of chlorinated paraffins, characterized in that, Includes the following steps: S1. Premixed feed: Liquid paraffin is mixed with photocatalytic additive and then continuously fed into a static mixer along with gasified chlorine. After dispersion and premixing, it is fed into the bottom of the tubular photocatalytic reactor from bottom to top. S2, Axial Gradient Photothermal Coupled Continuous Chlorination: The tubular photocatalytic reactor is equipped with a jacketed cooling circulation system. The reaction tube has multiple independent and controllable ultraviolet irradiation sections and cooling sections from bottom to top, so that the ultraviolet wavelength and / or irradiation intensity and reaction temperature in the reaction tube form a gradient distribution along the material flow direction; the material in the reaction tube is controlled to be in a turbulent flow state, and a free radical chain chlorination reaction is carried out under the synergistic effect of photocatalytic aid and ultraviolet light; S3. Density feedback closed-loop regulation: An online density detector is installed in the middle section of the reaction tube to monitor the density of the reactants in real time. When the detected density reaches the preset threshold, the feedback control system automatically adjusts the chlorine feed rate and / or the ultraviolet irradiation power of each section to control the chlorine content of the reaction product within the preset target value. S4. Gas-liquid separation and degassing purification: The reaction product is discharged from the top of the reactor into the gas-liquid separator, and the liquid product enters the degassing tower. Nitrogen gas is introduced for gas stripping and deacidification to remove hydrogen chloride and residual chlorine. Then, a stabilizer is added and mixed evenly to obtain the finished chlorinated paraffin.

2. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S2, the inner light-transmitting reaction tube of the tubular photocatalytic reactor is a quartz glass tube or a high borosilicate glass tube with a diameter of 50~200mm and an effective length of 3~15m; the ultraviolet irradiation section is divided into 3~6 independent sections along the axial direction, and a light-shielding partition is provided between each section.

3. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S1, the photocatalytic agent is selected from at least one of nano-titanium dioxide, azobenzene, azobisisobutyronitrile, benzophenone, or silica-supported photosensitizer.

4. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 3, characterized in that, In step S2, the ultraviolet wavelength of each ultraviolet illumination segment is independently selected from 200~400nm, and the illumination intensity of the lowest segment is greater than that of the highest segment; specifically, the wavelength of the lowest illumination segment is 254nm and the illumination intensity is 15~30mW / cm². 2 The wavelength of the uppermost illuminated section is 365nm, and the illuminance is 3~8mW / cm². 2 .

5. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S2, the temperature of each section of the reaction tube from bottom to top is controlled by the jacket circulating cooling water as follows: lower section 80~95℃, middle section 70~80℃, upper section 60~70℃; the reaction pressure is 0.02~0.06MPa; and the total residence time of the material in the reaction tube is 2~8 hours.

6. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S2, the material flow velocity in the reaction tube is controlled at 0.05~0.5m / s, so that the material is in a turbulent state with a Reynolds number Re≥4000; the inner wall of the reaction tube is provided with spiral or straight turbulence fins in the axial direction to break the near-wall laminar boundary layer and enhance the radial mixing of gas and liquid.

7. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S1, the liquid paraffin is a n-alkanes with a carbon chain length of C14~C20, the n-alkanes content is ≥95%, and the aromatics content is ≤1%; the mass ratio of liquid paraffin to chlorine is 1:0.8~1.35; before entering the static mixer, the chlorine is pressure-stabilized to 0.02~0.08MPa by a buffer tank, and the outlet of the buffer tank is equipped with a chlorine flow meter and an automatic regulating valve to receive the regulation commands from the feedback control system.

8. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S4, the degassing tower operates at a temperature of 90-110℃ and a pressure of 0.01-0.05MPa. The nitrogen flow rate is 0.5-2 times the volume of the liquid product per hour. After degassing, the acid value of the crude chlorinated paraffin drops below 0.05mgKOH / g. The stabilizer is one or more combinations of epoxidized soybean oil, ethylene glycol glycidyl ether, or phenolic antioxidants, and the amount added accounts for 0.1-0.5% of the crude product weight.

9. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S4, the gas phase tail gas separated by the gas-liquid separator is cooled to recover the entrained paraffin oil and then sent to the first-stage falling film absorption tower to absorb hydrogen chloride with water to produce 28-31% by-product hydrochloric acid; the residual gas after the first-stage absorption is sent to the second-stage packed absorption tower to absorb the residual chlorine and hydrogen chloride with dilute alkaline solution to meet the emission standards. The exhaust gas discharged from the first-stage falling film absorber that is not absorbed by water can be compressed by a compressor and returned to the static mixer in step S1. After being mixed with fresh chlorine gas, it can be recycled back into the reactor.

10. The process for continuous photocatalytic chlorination to produce chlorinated paraffin according to claim 1, characterized in that, In step S3, the preset target value is that the chlorine content of the reaction product reaches 50~54%. When the density signal monitored by the online density detector reaches the preset threshold corresponding to the chlorine content, the feedback control system synchronously reduces the output power of the ultraviolet irradiation section located in the middle and upper sections of the reaction tube to prevent the product from undergoing overchlorination side reaction.

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