A method for thermal safety risk assessment of benzoic acid reduction reaction

Abstract

A method for thermal safety risk assessment of benzoic acid reduction reaction, comprising: performing thermal stability test on benzoic acid, reducing agent and catalyst; mixing the reducing agent with at least two candidate solvents and performing differential scanning calorimetry test to evaluate compatibility and screen target solvents, and then performing thermal analysis on the reaction liquid of the target system; using a full-automatic chemical synthesis reactor to carry out reaction calorimetry and gas release synchronous characterization, obtaining process data of feeding, heat release, temperature, heat conversion rate and gas, and calculating total heat release, specific heat release, adiabatic temperature rise and MTSR; using an adiabatic accelerating calorimeter to perform secondary decomposition test on the reaction completion liquid to determine Td24 and TMR ad ; comprehensively performing decomposition heat, severity, possibility, risk matrix and process hazard degree assessment, outputting acceptability conclusion and control suggestion; and determining and verifying the thermal stability of the product, realizing thermal safety assessment closed loop.

Description

Technical Field

[0001] This invention relates to the field of thermal risk analysis technology, and in particular to a method for assessing the thermal safety risks of benzoic acid reduction reaction. Background Technology

[0002] my country's chemical industry is one of the pillar industries of the national economy, but while bringing convenience to people, it also brings huge safety hazards. The raw materials and products involved in production, storage, transportation, use, and waste disposal often have flammable, explosive, toxic, harmful, or corrosive properties. Misuse, abuse, or improper disposal can easily cause accidents such as combustion, explosion, and poisoning. Therefore, conducting thermal safety risk assessments before scaling up production is becoming increasingly necessary.

[0003] Although reduction processes have been classified as high-risk processes, current methods for assessing the thermal hazards of reduction reactions are somewhat inadequate, posing a risk of material spillage and even explosion in actual production. Due to a lack of analytical research, the reaction may become uncontrollable during production, easily leading to the accumulation or accidental release of heat and gases, which could easily result in major production safety accidents. Therefore, developing and mastering more methods for assessing the thermal safety risks of reduction reactions, and identifying and mitigating the risks of materials and exothermic / gas-emitting processes before production begins, is of paramount importance to the chemical industry. Summary of the Invention

[0004] In organic synthesis and fine chemical production, the reduction of benzoic acid is a common route for obtaining important intermediates such as benzyl alcohol. This type of reduction system typically involves a combination of a strong reducing agent, a catalyst, and an organic solvent, accompanied by steps such as feeding, heating, and holding. Due to the significant differences in the compatibility of the reducing agent in different solvents, the system may experience additional exothermic and gas releases due to side reactions. Furthermore, under scale-up conditions, there is a risk of instantaneous heat release due to material accumulation, temperature runaway, and sudden pressure increases. In addition, the reaction solution may undergo secondary decomposition or continuous gas release under certain temperature conditions, making it difficult to comprehensively and quantitatively identify and evaluate the thermal safety boundaries of this reaction in process development and scale-up production based solely on experience or single thermal analysis methods. Existing methods for assessing the risk of reaction heat often focus on single-dimensional thermal stability testing or local characterization of the reaction process. They lack a systematic process for the typical exothermic and gas-releasing reaction of benzoic acid reduction, which can integrate material compatibility screening, quantitative analysis of reaction heat and gas release, verification of liquid secondary decomposition, and output of risk classification conclusions. As a result, it is difficult to provide a consistent and reproducible basis for determining process parameter windows and formulating safety control measures.

[0005] To address the aforementioned issues, this invention proposes a thermal safety risk assessment method for the benzoic acid reduction reaction. This method involves conducting thermal stability tests on raw materials and key components, screening the compatibility of reducing agents and candidate solvents, characterizing the target system through reaction calorimetry and gas release, and further performing secondary decomposition tests on the reaction product under adiabatic conditions. The method comprehensively forms multi-dimensional evaluation conclusions, including decomposition heat, severity, probability, risk matrix, and process hazard level. By combining product identification and thermal stability verification, a closed-loop assessment is achieved, thus providing quantitative safety boundaries and control recommendations for the scale-up of the benzoic acid reduction reaction.

[0006] To achieve the above objectives, the present invention provides a method for assessing the thermal safety risk of benzoic acid reduction reaction, comprising the following steps: S1. Material thermal stability and compatibility testing: The thermal stability of benzoic acid, reducing agent, and catalyst was tested using differential scanning calorimetry (DSC). The reducing agent was mixed with at least two candidate solvents to form reducing agent-solvent mixtures. DSC was performed on each of the reducing agent-solvent mixtures to evaluate the compatibility between the reducing agent and each candidate solvent and to screen the target solvent for the benzoic acid reduction reaction. A benzoic acid reduction reaction solution was prepared in the presence of the target solvent and subjected to DSC. S2. Reaction calorimetry and outgassing test: The calorimetry of the benzoic acid reduction reaction is tested using a fully automated chemical synthesis reactor and the outgassing is characterized simultaneously. Process data including at least the feeding curve, the released heat curve, the reaction temperature curve, the jacket temperature curve, the thermal conversion rate curve, and the gas curve are obtained. The characterization results of reaction exothermicity and outgassing are obtained based on the process data. S3. Secondary decomposition test of the completed liquid: The secondary decomposition test of the completed liquid of the reduction reaction is carried out using an adiabatic accelerated calorimeter to obtain adiabatic test data including at least time-temperature-pressure curves, pressure-temperature curves and pressure rise rate-temperature curves, and the decomposition and runaway kinetic characterization results of the completed liquid are obtained accordingly. S4. Safety Risk Assessment: Based on the test data from steps S1 to S3, a safety risk assessment is conducted on the benzoic acid reduction reaction. The safety risk assessment includes at least a heat of decomposition assessment, a severity assessment, a probability assessment, a risk matrix assessment, and a reaction process hazard assessment. The conclusion of the thermal safety risk assessment of the benzoic acid reduction reaction is then output. S5. Product Study: Identify the products of the benzoic acid reduction reaction and conduct thermal stability tests on the products to form a closed loop for thermal safety assessment of the benzoic acid reduction reaction.

[0007] In some technical solutions, the reducing agent is selected from any one of NaBH4, Na2SO3, LiAlH4, and NaHSO3; the catalyst is I2; and the candidate solvent is selected from any one or any combination of acetonitrile, ethyl acetate, ethanol, water, methanol, methyl tert-butyl ether, and tetrahydrofuran.

[0008] In some technical solutions, the compatibility test in step S1 includes: The reducing agent was added to the candidate solvent at 5 V to form a mixture, and differential scanning calorimetry was performed on each mixture to determine whether the reducing agent and the corresponding candidate solvent underwent an exothermic reaction and / or an outgassing reaction.

[0009] In some technical solutions, the target solvent obtained in step S1 satisfies at least one of the following conditions: (1) The target solvent is tetrahydrofuran; (2) The solvent volume system of the target solvent is 20 V.

[0010] The experiment found that when the reaction volume was reduced to 5 V, 10 V and 15 V, the reaction stirring state was poor, resulting in poor heat dissipation. Therefore, 20 V was selected.

[0011] In some technical solutions, step S2 includes the following test procedure: The target solvent and benzoic acid are added to the reactor for feeding. The system temperature was raised to the preset temperature and stabilized. The reducing agent is added in batches under stirring conditions; The system was then heated to the reaction temperature. After the system reaches the reaction temperature, a catalyst solution is added to the system, wherein the catalyst solution is a catalyst solution prepared with the target solvent; The reaction is carried out at the stated reaction temperature under heat preservation conditions. After the reaction was completed, a stabilization calibration was performed again, and the test data were calculated and analyzed.

[0012] In some technical solutions, step S2 satisfies at least one of the following conditions: (1) The fully automated chemical synthesis reactor mentioned in step S2 is selected from either EasyMax 402 or RC1mx; (2) The characterization results of the reaction exothermic in step S2 include: integrating the released heat curve over time to obtain the total heat exothermic reaction, and calculating the specific heat exothermic reaction in combination with the total mass of the materials participating in the reaction; (3) In step S2, the adiabatic temperature rise ΔTad and the highest temperature MTSR that the system can reach when the material accumulation is at its maximum under adiabatic conditions are calculated based on the results of the reaction calorimetry test.

[0013] In some technical solutions, step S3 uses an ES-ARC adiabatic accelerated calorimeter in HWS mode to test the reduced reaction completed liquid; and / or, In step S3, the Td24 of the finished liquid is determined based on the adiabatic test data, and the time to reach the maximum reaction rate of the runaway reaction, TMRad, is determined under conditions including at least the process temperature Tp and / or the temperature reaching MTSR.

[0014] In some technical solutions, the risk matrix assessment in step S4 includes: combining the severity assessment results with the probability assessment results to obtain the risk matrix level, and outputting the corresponding acceptability conclusions and control recommendations; and / or, The process hazard assessment in step S4 includes: determining the process temperature Tp and the maximum technical temperature MTT, and comparing Tp, MTSR, and MTT with Td24 obtained in step S3 to output the process hazard level; and judging whether a decomposition reaction is triggered after the target reaction runs out of control based on the relationship between Tp, MTSR, MTT and Td24, and including at least one safety barrier measure among evaporative cooling and / or emergency depressurization when outputting control recommendations.

[0015] In some technical solutions, the benzoic acid reduction reaction product determined in step S5 is benzyl alcohol, and differential scanning calorimetry is performed on benzyl alcohol to verify its thermal stability.

[0016] In some technical solutions, the process of the benzoic acid reduction reaction includes: adding tetrahydrofuran and benzoic acid into a reaction vessel and stirring to dissolve them; adding NaBH4 in batches under stirring conditions; raising the system temperature to 50°C after the addition is complete; adding an iodine catalyst solution prepared with tetrahydrofuran after the system temperature reaches 50°C; and keeping the reaction at 50°C for 20 hours.

[0017] The present invention provides a method for assessing the thermal safety risks of benzoic acid reduction reaction. Based on the assessment results, it can provide effective technical support and guarantee for the thermal safety of the reduction process and the prevention of production safety accidents. It is of great significance for the safe production and the prevention of major accidents in the chemical industry.

[0018] The present invention, by employing the above technical solution, has at least the following beneficial effects: 1. This invention incorporates material thermal stability testing and compatibility screening upfront. By comparing the reducing agent with various candidate solvents using differential scanning calorimetry, it can identify potential exothermic and gas release risks between the reducing agent and solvent in the early stages of process development. This allows for the selection of target solvents and solvent volume systems for the benzoic acid reduction reaction from the source, avoiding the accumulation of hidden heat and gas sources caused by selecting solvents based solely on experience. It also reduces the probability of sudden exothermic reactions, local overheating, and pressure fluctuations during subsequent scale-up, and provides a more realistic and comparable consistent system basis for subsequent calorimetric and adiabatic evaluations.

[0019] 2. This invention uses a fully automated chemical synthesis reactor to simultaneously characterize the calorimetry and gas release of the benzoic acid reduction process. It can obtain process curves of the changes in feeding, temperature, and heat and gas release over time. Based on these curves, key indicators such as the total heat release, specific heat release, adiabatic temperature rise ΔTad, and MTSR can be calculated. This transforms the qualitative judgment of heat accumulation and runaway trend during the feeding stage into quantifiable parameters, providing a clear basis for matching cooling capacity, optimizing feeding strategies, and determining the process temperature window. This significantly improves the guidance and operability of the evaluation conclusions for scale-up production.

[0020] 3. This invention conducts secondary decomposition tests on the reduced reaction liquid under adiabatic conditions, obtaining kinetic characterization results such as Td24 and TMRad related to the decomposition triggering and runaway rate. It can effectively identify the risk blind spots where the system may still release heat or continue to release gas after the main reaction ends, avoiding the safety hazards caused by the thermal stability of the endpoint material due to ignoring only the reaction calorimetry results, such as storage, residence or abnormal operating conditions. This improves the full life cycle thermal safety evaluation of this type of exothermic and gas-releasing reaction.

[0021] 4. This invention organically combines decomposition heat assessment, severity assessment, probability assessment, risk matrix assessment, and reaction process hazard assessment. It can output risk matrix levels and acceptability conclusions, and can also determine whether a decomposition reaction may be triggered after runaway based on temperature boundary relationships such as Tp, MTSR, MTT, and Td24. Furthermore, it proposes safety barrier schemes such as evaporative cooling and emergency depressurization in the control recommendations, so that the assessment results can be directly transformed into safety control measures for engineering implementation, thereby improving the feasibility and consistency of the risk assessment report.

[0022] 5. This invention introduces product identification and product thermal stability verification at the end of the risk assessment process, linking the product information at the process endpoint with thermal safety parameters to form a closed-loop verification mechanism from raw material compatibility and thermal behavior of the reaction process to the thermal stability of the finished liquid and product. This helps to improve the reliability and reproducibility of the assessment conclusions, reduce safety uncertainties caused by unclear products or endpoint materials, and is therefore more suitable for process development, process scale-up and production safety management scenarios of benzoic acid reduction reaction. Attached Figure Description

[0023] Figure 1 This is a DSC test curve of benzoic acid; Figure 2 The DSC test curve of NaBH4 is shown below. Figure 3 DSC test curve of NaBH4in 5 V ACN; Figure 4 DSC test curve of NaBH4in 5 V EA; Figure 5 The DSC curve of NaBH4 in 5 V EtOH is shown. Figure 6 The DSC test curve of NaBH4 in 5 V H2O; Figure 7 The DSC curve of NaBH4 in 5 V MeOH is shown. Figure 8 The DSC test curve of NaBH4 in 5 V MTBE is shown. Figure 9 The DSC test curve of NaBH4 in 5 V THF is shown. Figure 10 The image shows the DSC curve of the benzyl alcohol pre-reaction mixture, where the pre-reaction reduction solution includes benzoic acid, reducing agent NaBH4, catalyst I2, and solvent THF. Figure 11 The image shows the DSC curve of the benzyl alcohol post-reaction mixture, where the post-reaction reduction solution includes benzoic acid, reducing agent NaBH4, catalyst I2, and solvent THF. Figure 12 DSC test curve of benzyl alcohol; Figure 13 The feed curve (Mr), heat release curve (qr_hf), reaction temperature curve (Tr), jacket temperature curve (Tj), thermal conversion rate curve (qr_hf Integral Conversion), and gas curve (Gas) for the reduction reaction process are shown. Figure 14 The time-temperature-pressure curve of the ARC solution in HWS mode was tested to complete the reduction reaction. Figure 15 Pressure-temperature profiles of the ARC liquid in HWS mode for the reduction reaction completion test; Figure 16 Pressure rise rate-temperature curve of ARC in HWS mode for complete reduction reaction; Figure 17 This is a standard chart for the acceptable level of runaway reactions. Detailed Implementation

[0024] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of the present invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0025] In the text, V in 5 V and 20 V represents the volume ratio of solvent to the mass ratio of the substrate benzoic acid.

[0026] Example 1: This embodiment provides a method for assessing the thermal safety risks of benzoic acid reduction reaction, including the following steps: Step 1: Material thermal stability test Using a differential scanning calorimeter, the thermal stability of benzoic acid and the reducing agent NaBH4 was first tested. Then, NaBH4 was mixed with one of the following solvents: acetonitrile (ACN), ethyl acetate (EA), ethanol (EtOH), H2O, methanol (MeOH), methyl tert-butyl ether (MTBE), and tetrahydrofuran (THF). The thermal stability of the mixtures was then tested to screen out suitable solvents for the following process. Finally, a suitable solvent volume system was selected, and the thermal stability of the benzoic acid reduction reaction solution was tested. Figure 1 This is a DSC test curve for benzoic acid, from... Figure 1 It can be seen that one endothermic peak and one exothermic peak were detected between (0 - 400)℃. The endothermic peak started at 119.41℃ and ended at 146.82℃; the exothermic peak started at 278.55℃ and ended at 315.03℃, releasing 16.77 J / g of heat.

[0027] Figure 2 The graph shows the DSC test results for the reducing agent NaBH4; from Figure 2 It can be seen that one endothermic peak and two exothermic peaks were detected between (0 - 400)℃. The endothermic peak started at 21.22℃ and ended at 42.16℃; the first exothermic peak started at 208.17℃ and ended at 238.16℃, releasing 13.28 J / g of heat; the second exothermic peak started at 241.39℃ and ended at 292.50℃, releasing 89.65 J / g of heat. Figure 3 The DSC test curve of NaBH4in 5 V ACN; by Figure 3 Three exothermic peaks were detected between 0 and 400 °C. The first exothermic peak started at 123.56 °C and ended at 174.73 °C, releasing 33.97 J / g of heat. The second exothermic peak started at 206.24 °C and ended at 282.61 °C, releasing 1110.74 J / g of heat. The third exothermic peak started at 324.77 °C and ended at 380.49 °C, releasing 93.79 J / g of heat. When NaBH4 was added to ACN at 5 V, exothermic and gas-releasing phenomena occurred, indicating that NaBH4 reacted with the solvent ACN. The DSC spectrum also showed an exothermic peak starting at 123.56 °C, meaning that when NaBH4 acts as a reducing agent and ACN as a solvent, exothermic reactions are introduced, leading to a decrease in the reaction yield.

[0028] Figure 4 The DSC test curve of NaBH4in 5 V EA; by Figure 4 Two exothermic peaks were detected between 0 and 400 °C. The first exothermic peak started at 195.23 °C and ended at 318.77 °C, releasing 1375.72 J / g of heat. The second exothermic peak started at 335.19 °C and ended at 384.34 °C, releasing 35.33 J / g of heat. The DSC spectrum also shows an exothermic peak starting at 195.23 °C. This means that when NaBH4 is used as a reducing agent, EA as a solvent introduces exothermic reactions, which also leads to a decrease in the reaction yield.

[0029] Figure 5 The DSC curve of NaBH4 in 5 V EtOH; by Figure 5 It can be seen that one exothermic peak and one endothermic peak were detected between (0 - 400)℃. The exothermic peak started at 109.09℃ and ended at 206.57℃, releasing 637.99 J / g of heat. The endothermic peak started at 305.33℃ and ended at 365.34℃. When EtOH was added to NaBH4 at 5 V, exothermic and gas release phenomena occurred, indicating that NaBH4 reacted with the solvent EtOH. The DSC spectrum also shows an exothermic peak starting at 109.09℃, which means that when NaBH4 is used as a reducing agent and EtOH is used as a solvent, exothermic reactions are introduced, which also leads to a decrease in the reaction yield.

[0030] Figure 6 The DSC curve of NaBH4 in 5 V H2O; by Figure 6It can be seen that an exothermic peak was detected between (0 - 400)℃, starting from 72.34℃ and ending at 176.16℃, releasing 391.70 J / g of heat. When NaBH4 was added to H2O at 5 V, exothermic and gas-releasing phenomena occurred, indicating that NaBH4 reacted with the solvent H2O. The DSC spectrum also shows an exothermic peak starting from 72.34℃, which means that when NaBH4 is used as a reducing agent and H2O is used as a solvent, exothermic reactions are introduced, which also leads to a decrease in the reaction yield.

[0031] Figure 7 The DSC curve of NaBH4 in 5 V MeOH is shown. Figure 7 It can be seen that two endothermic peaks and one exothermic peak were detected between (0 - 400)℃. The first endothermic peak started at 29.89℃ and ended at 64.64℃, and the second endothermic peak started at 79.74℃ and ended at 111.33℃. The exothermic peak started at 111.33℃ and ended at 193.51℃, releasing 197.09 J / g of heat. When MeOH was added to NaBH4 at 5 V, a violent exothermic and gas-releasing phenomenon occurred, indicating that NaBH4 reacted with the solvent MeOH. The DSC spectrum also shows that endothermic and exothermic peaks were generated starting from 29.89℃, which means that when NaBH4 is used as a reducing agent, MeOH as a solvent will introduce exothermic reaction and also lead to a decrease in the reaction yield.

[0032] Figure 8 The DSC test curve of NaBH4 in 5 V MTBE is shown; Figure 8 It can be seen that an exothermic peak was detected between (0 - 400)℃, starting from 215.07℃ and ending at 295.84℃, releasing 117.02 J / g of heat. When 5 VMTBE was added to NaBH4, an exothermic phenomenon was generated, indicating that NaBH4 reacted with the solvent MTBE. The DSC spectrum also shows an exothermic peak starting from 215.07℃, which means that NaBH4, as a reducing agent, and MTBE, as a solvent, introduce exothermic reactions and also lead to a decrease in the reaction yield.

[0033] Figure 9 The DSC test curve of NaBH4 in 5 V THF is shown; Figure 9 It can be seen that no obvious endothermic and exothermic phenomena were observed between (0 - 400)℃, indicating that NaBH4 does not react with the solvent THF.

[0034] Figure 10 This is a DSC curve of the benzyl alcohol pre-reaction mixture; from Figure 10It can be seen that three exothermic peaks were detected between (0-400)℃. The first exothermic peak started at 192.67℃ and ended at 238.86℃, releasing 24.61 J / g of heat; the second exothermic peak started at 285.71℃ and ended at 358.49℃, releasing 33.93 J / g of heat; and the third exothermic peak started at 378.14℃ and ended at 399.59℃, releasing 12.24 J / g of heat. Figure 11 This is a DSC curve of the benzyl alcohol post-reaction mixture; from Figure 11 It can be seen that two exothermic peaks were detected between (0-400)℃. The first exothermic peak started at 280.68℃ and ended at 358.22℃, releasing 15.77 J / g of heat. The second exothermic peak started at 372.26℃ and ended at 399.53℃, releasing 15.31 J / g of heat.

[0035] Step 2: Calorimetry test of the reduction reaction The calorific value of the reaction was tested using the fully automated chemical synthesis reactor EasyMax 402 according to the following procedure: 10 g benzoic acid, 123.14 g tetrahydrofuran, 53.37 g I₂ in THF solution, and 7.83 g NaBH₄.

[0036] This yields the following curves during the benzoic acid reduction reaction: feed curve (Mr), heat release curve (qr_hf), reaction temperature curve (Tr), jacket temperature curve (Tj), thermal conversion rate curve (qr_hf Integral Conversion), and gas curve (Gas). Figure 13 As shown in the figure, the qr_hf curve is the heat effect curve of the exothermic process. After integrating it over time, the total heat released by the reaction is obtained. It can be calculated that during the feeding process, the temperature inside the reactor rises, and during the heat preservation process, the temperature inside the reactor stabilizes. The total heat released is 23.20 kJ, and the total mass of the material participating in the reaction is 194.34 g. Therefore, the specific heat release of this reaction is 119 J / g. ΔTad is the adiabatic temperature rise, which is the total heat released in the synthesis reaction or material decomposition. It is the temperature at which the system can rise under adiabatic conditions. In this reaction, ΔTad is 87 K. MTSR is the highest temperature that the system can reach under adiabatic conditions when the material accumulation is at its maximum. The highest temperature MTSR corresponding to the runaway reaction in the reduction process is calculated to be 56℃. Since the reduction reaction of benzoic acid is a normal pressure reaction, the highest technical temperature (MTT) is the boiling point of the largest material in the reaction system under normal pressure, namely the boiling point of tetrahydrofuran: 66℃.

[0037] During the batch addition of sodium borohydride, 1551 mL of gas was released; when I2 was added in 5 V THF solution, 1014 mL of gas was released; the maximum gas release rate was 1.31 L / min / mol.

[0038] Step 3: Secondary decomposition test of the reduction reaction completed solution The time-temperature-pressure curve of the ARC solution in HWS mode after the reduction reaction was completed ( Figure 14 The curves represent temperature and pressure, respectively, and the pressure-temperature curve of the ARC solution after the reduction reaction is complete, measured in HWS mode. Figure 15 The curve represents the pressure), and the pressure rise rate-temperature curve of the ARC liquid after the reduction reaction is completed, measured in HWS mode. Figure 16 The curve represents the pressure rise rate.

[0039] Depend on Figure 14 , 15 As shown in Figure 16, no significant exothermic phenomenon was detected in the reduction reaction solution from 30-300℃; when the process temperature is 50℃, the time to reach the maximum runaway reaction rate (TMR) is... ad > 24 h, when the temperature reaches the system's maximum temperature (MTSR), the time to reach the maximum runaway reaction rate (TMR) ad > 24 h.

[0040] At room temperature, slow gas release can be observed, with the maximum gas release rate occurring at 279°C.

[0041] Step 4: Safety Risk Assessment of Reduction Reaction The safety risk assessment for reduction reactions includes the following: The process includes assessment of the heat of decomposition of substances, severity assessment, probability assessment, risk matrix assessment, and hazard assessment of the reaction process. The explosion hazard of the material is assessed based on the heat of decomposition, the severity of the runaway reaction is assessed based on the adiabatic temperature rise, the probability of the reaction is assessed based on the time to reach the maximum reaction rate, and the process hazard assessment is conducted in combination with relevant temperature parameters to determine the hazard level of the reaction process.

[0042] (1) Assessment of the heat of decomposition of substances: through the heat of decomposition Q d To evaluate the potential explosion hazard of materials, the heat of decomposition Q of the raw materials and the reactants is determined. d The heat of decomposition of raw materials and reactants, Q d The larger the value, the greater the potential explosion hazard. The heat of decomposition is assessed using the heat of decomposition of the substance; the standards are shown in Table 1.

[0043]

[0044] Based on the adiabatic thermal test results of the liquid after the reduction reaction, the decomposition exothermic reaction of the liquid after the reduction reaction is 15.77 J / g < 400 J / g, which is assessed as Level 1, indicating a potential explosion hazard.

[0045] (2) Severity assessment: based on adiabatic temperature rise ΔT ad To assess the severity of the runaway reaction, ΔT ad The larger the value, the greater the severity of the runaway reaction; using adiabatic temperature rise (ΔT) ad The severity of the runaway reaction was assessed, and the assessment criteria are shown in Table 2.

[0046] Δ T ad It is calculated using the following formula: Δ T ad =Q r / (m1C p1 +m2C p2 +m3C p3 ) In the formula, Q r —The heat released by the reaction, kJ; m1—Total mass of reactants, kg; m2—Total mass of catalyst, kg; m3—Total mass of packing, kg; C p1 —Specific heat capacity of the material after reaction, kJ / kg / ℃; C p2 —Specific heat capacity of the catalyst, kJ / kg / ℃; C p3 —Specific heat capacity of the filler material, kJ / kg / ℃.

[0047]

[0048] Based on the calorimetric test results of the reduction reaction, the adiabatic temperature rise ΔT ad At <50 K, the severity of the runaway reduction reaction is assessed as Grade 1.

[0049] (3) Probability assessment: If the feed can be immediately cut off when the cooling of the runaway system fails after the reaction runs out of control, the time to reach the maximum reaction rate of the runaway system (TMR) will be used. ad To assess the likelihood of an uncontrolled reaction, TMR ad The smaller the value, the greater the likelihood of an uncontrolled reaction.

[0050] Data were obtained using an adiabatic accelerated calorimeter, differential scanning calorimetry, and microcalorimetry. (TMR) ad It can be calculated using a formula =

[0051] During the test, in addition to being absorbed by the material, the test system also absorbs some heat. (TMR) ad The correction value is calculated using a formula.

[0052] =

[0053] Note:

[0054] In the formula: The R-gas constant is 8.314, with units of joules per mole Kelvin [J / (mol·K)]. T m - The temperature at which the reaction rate reaches its maximum value, in Kelvin (K). q T0 - The rate of exothermic reaction at temperature T0, expressed in watts per kilogram (W / kg). - Thermal inertia factor.

[0055] m s - The mass of the test material is measured in kilograms (kg). C ps - The specific heat capacity at constant pressure of the test material is expressed in kilojoules per kilogram of Kelvin [kJ / (kg·k)]. m b - The mass of the test container is measured in kilograms (kg). C pb - The specific heat capacity at constant pressure of the test container is expressed in kilojoules per kilogram of Kelvin [kJ / (kg.k)].

[0056] Using TMR ad The probability of runaway reactions is assessed on a time scale, and the assessment criteria are shown in Table 3.

[0057]

[0058] Based on the adiabatic thermal test results of the completed reduction reaction solution, the Td24 of the completed reaction solution is 270℃. When the system process temperature is 50℃, the time to reach the maximum runaway reaction rate (TMR) is... ad >24 h, when the temperature reaches the system's maximum temperature (MTSR), the time to reach the maximum runaway reaction rate (TMR) ad>24 h, the probability of runaway reaction is assessed as level 1, with a low probability of runaway reaction; where Td24 is the temperature at which the maximum reaction rate is reached in 24 h under adiabatic conditions.

[0059] (4) Risk Matrix Assessment: Acceptability of Out-of-Control Response = Severity of Out-of-Control Response × Probability of Out-of-Control Response. The higher the severity and probability of an out-of-control response, the lower the acceptability of the out-of-control response; conversely, the lower the severity and probability of an out-of-control response, the higher the acceptability of the out-of-control response. An assessment of the acceptability of the out-of-control response is conducted using a matrix based on the probability and severity of the out-of-control response. The assessment criteria are detailed in [link to assessment criteria]. Figure 17 In the diagram, Level I represents the control measures taken during the production process in accordance with design and specification requirements.

[0060] Level II involves taking control measures in accordance with design and specification requirements during the production process to ensure the effectiveness of these measures. It is advisable to reduce the risk level through process optimization.

[0061] Level III projects should prioritize reducing risk through process optimization. For high-risk projects that require industrialization, control measures should be implemented in accordance with design and specification requirements during production, necessary regional isolation should be adopted, and full automation should be achieved.

[0062] The acceptable level of runaway reactions, from highest to lowest, is: Grade I > Grade II > Grade III.

[0063] Based on the severity assessment and probability assessment results, the risk matrix is ​​assessed as Level I, which is an acceptable risk: control measures should be taken in accordance with design requirements during the production process, and the level of safety management should be improved.

[0064] (5) Hazard assessment of the reaction process: The parameters involved include: The exothermic enthalpy generated during the reaction; Heat Conversion; Qrmax - the maximum exothermic rate of the reaction; The highest temperature that the MTSR-runaway system can reach; MTT (Medium Temperature Tolerance) is the highest temperature achieved by a reaction system. Under normal pressure, it represents the boiling point of the solvent or mixture in the reaction system. Under closed system conditions, it represents the temperature corresponding to the maximum permissible pressure of the reaction vessel.

[0065] The process hazard level is assessed using four temperature parameters: Tp, maximum technical temperature (MTT), MTSR, and Td24. The assessment criteria are shown in Table 4.

[0066] Table 4. Hazard Assessment Criteria for Reaction Processes grade Temperature parameter relationship Consequences and Explanations 1 Tp < MTSR < MTT < Td24 The reaction hazard is low. When MTSR is less than MTT and Td24, the system will not trigger secondary decomposition reactions of the materials, nor will it cause violent boiling and overflow of the reactants. However, it is still necessary to avoid prolonged heating of the reactants to prevent reaching the MTT. 2 Tp < MTSR < Td24 < MTT The potential decomposition risk MTSR is lower than MTT and Td24, and will not trigger secondary decomposition reactions of the materials, nor will it cause violent boiling and material surge. However, since MTT is higher than Td24, if the system remains in an uncontrolled state, it may trigger secondary decomposition reactions. These secondary decomposition reactions continue to release heat, eventually causing the reaction system to reach the MTT, which can lead to dangerous accidents such as material surge. 3 Tp < MTT < MTSR < Td24 There is a risk of material overflow and decomposition. If the median surcharge (MTSR) is greater than the median time (MTT), the reactants are more likely to boil, leading to a dangerous overflow and potentially causing a sudden increase in system pressure. However, if the MTSR is less than the median time (Td24), the likelihood of a secondary decomposition reaction is low, and evaporative cooling of the system materials can serve as a heat exchange measure, acting as a safety barrier. At level 3 hazard, the rate of exothermic reaction at the MTT significantly impacts system safety. Therefore, risk control measures such as emergency pressure reduction at the upper limit and emergency cooling should be fully considered and implemented to prevent material overflow and secondary decomposition reactions that could lead to an explosion. 4 Tp < MTT < Td24 < MTSR The risk of material overflow and decomposition is high, with a potential explosion risk. The MTSR is greater than the MTT and Td24, and the system temperature may exceed the MTT, causing the reactants to boil and leading to a material overflow hazard, and triggering a secondary decomposition reaction. In this situation, the exothermic rates of various reactions in the reaction system at the MTT have a significant impact on the overall safety of the process. Evaporation cooling, emergency depressurization, and emergency cooling measures provide some safety assurance; however, they cannot completely prevent secondary decomposition reactions. For Level 4 hazard, a reliable and effective technical and engineering design measure should be established. 5 City <Td24<MTSR<MTTTp<Td24<MTT<MTSR The risk of explosion is high. With a median mitral stress (MTSR) greater than a median dt (Td24), the runaway system is highly susceptible to secondary decomposition reactions. These reactions are exothermic, and the system temperature could easily exceed the median mitral stress (MTT), leading to an even more dangerous situation. In this case, simply relying on evaporative cooling and reducing system pressure is insufficient for ensuring system safety. Therefore, Level 5 hazard is an extremely dangerous situation, and conventional techniques are inadequate. Process optimization and area isolation measures should be implemented instead.

[0067] According to the reaction calorimetry test results of the reduction reaction, the process temperature Tp = 50 °C, the maximum temperature MTSR that the synthesis reaction may reach under adiabatic conditions at the actual feeding rate is 56 °C, the technical maximum temperature MTT = 66 °C, and according to the secondary decomposition test Td24 of the completed liquid of the reduction reaction is 270 °C, it is obtained that Tp < MTSR < MTT < Td24 (50 °C < 56 °C < 66 °C < 270 °C), that is, the reaction process risk assessment at the actual feeding rate is level 1.

[0068] The process of the reduction reaction of benzoic acid is as follows: Add tetrahydrofuran and benzoic acid into the reaction kettle, stir and dissolve, then add NaBH4 in batches. After the feeding is completed, heat up to 50 °C and wait for 20 h.

[0069] The chemical reaction formula is as follows:

[0070] After the target reaction gets out of control, if the temperature does not reach the technical limit (MTSR < MTT), and since MTSR is lower than Td24, then the decomposition reaction will not be triggered. Only when the reaction material stays for a long time under the condition of heat accumulation can MTT be reached. At this time, evaporation cooling can serve as an auxiliary safety barrier. Such a process has low thermal risk.

[0071] Therefore, for the situation of level 1 risk, no special measures are required, but the reaction material should not stay in the heat accumulation state for a long time. As long as it is properly designed, evaporation cooling or emergency pressure relief can serve as a safety barrier.

[0072] Step Five: Research on the reduction reaction product of benzoic acid For the research on the reduction reaction product of benzoic acid, its product was determined and the corresponding thermal stability test was carried out to ensure its safety.

[0073] Figure 12 It is the DSC test curve of the compound benzyl alcohol; from Figure 12 it can be seen that 1 exothermic peak was detected between (0 - 400) °C. The exothermic peak started from 169.84 °C and ended at 227.32 °C, and the heat released was 186.84 °C.

[0074] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for assessing the thermal safety risks of benzoic acid reduction reaction, characterized in that, Includes the following steps: S1. Material thermal stability and compatibility testing: The thermal stability of benzoic acid, reducing agent, and catalyst was tested using a differential scanning calorimeter (DSC). The reducing agent was mixed with at least two candidate solvents to form reducing agent-solvent mixtures. DSC was then performed on each of the reducing agent-solvent mixtures to evaluate the compatibility between the reducing agent and each candidate solvent, and to screen for target solvents for the benzoic acid reduction reaction. A benzoic acid reduction reaction solution was prepared in the presence of the target solvent and subjected to DSC. S2. Reaction calorimetry and outgassing test: The calorimetry of the benzoic acid reduction reaction is tested using a fully automated chemical synthesis reactor and the outgassing is characterized simultaneously. Process data including at least the feeding curve, the released heat curve, the reaction temperature curve, the jacket temperature curve, the thermal conversion rate curve, and the gas curve are obtained. The characterization results of reaction exothermicity and outgassing are obtained based on the process data. S3. Secondary decomposition test of the completed liquid: The secondary decomposition test of the completed liquid of the reduction reaction is carried out using an adiabatic accelerated calorimeter to obtain adiabatic test data including at least time-temperature-pressure curves, pressure-temperature curves and pressure rise rate-temperature curves, and the decomposition and runaway kinetic characterization results of the completed liquid are obtained accordingly. S4. Safety Risk Assessment: Based on the test data from steps S1 to S3, a safety risk assessment is conducted on the benzoic acid reduction reaction. The safety risk assessment includes at least a heat of decomposition assessment, a severity assessment, a probability assessment, a risk matrix assessment, and a reaction process hazard assessment. The conclusion of the thermal safety risk assessment of the benzoic acid reduction reaction is then output. S5. Product Study: Identify the products of the benzoic acid reduction reaction and conduct thermal stability tests on the products to form a closed loop for thermal safety assessment of the benzoic acid reduction reaction.

2. The thermal safety risk assessment method according to claim 1, characterized in that, The reducing agent is selected from any one of NaBH4, Na2SO3, LiAlH4, and NaHSO3; the catalyst is I2; and the candidate solvent is selected from any one or any combination of acetonitrile, ethyl acetate, ethanol, water, methanol, methyl tert-butyl ether, and tetrahydrofuran.

3. The thermal safety risk assessment method according to claim 1, characterized in that, The compatibility test in step S1 includes: The reducing agent was added to the candidate solvent at 5 V to form a mixture, and differential scanning calorimetry was performed on each mixture to determine whether the reducing agent and the corresponding candidate solvent underwent an exothermic reaction and / or an outgassing reaction.

4. The thermal safety risk assessment method according to claim 1 or 3, characterized in that, The target solvent obtained in step S1 meets at least one of the following conditions: (1) The target solvent is tetrahydrofuran; (2) The solvent volume system of the target solvent is 20 V.

5. The thermal safety risk assessment method according to claim 1, characterized in that, Step S2 includes the following test procedure: The target solvent and benzoic acid are added to the reactor for feeding. The system temperature was raised to the preset temperature and stabilized. The reducing agent is added in batches under stirring conditions; The system was then heated to the reaction temperature. After the system reaches the reaction temperature, a catalyst solution is added to the system, wherein the catalyst solution is a catalyst solution prepared with the target solvent; The reaction is carried out at the stated reaction temperature under heat preservation conditions. After the reaction was completed, a stabilization calibration was performed again, and the test data were calculated and analyzed.

6. The thermal safety risk assessment method according to claim 1, characterized in that, Step S2 satisfies at least one of the following conditions: (1) The fully automated chemical synthesis reactor mentioned in step S2 is selected from either EasyMax 402 or RC1mx; (2) The characterization results of the reaction exothermic in step S2 include: integrating the released heat curve over time to obtain the total heat exothermic reaction, and calculating the specific heat exothermic reaction in combination with the total mass of the materials participating in the reaction; (3) In step S2, the adiabatic temperature rise ΔTad and the highest temperature MTSR that the system can reach when the material accumulation is at its maximum under adiabatic conditions are calculated based on the results of the reaction calorimetry test.

7. The thermal safety risk assessment method according to claim 1, characterized in that, In step S3, the reduced reaction solution is tested using an ES-ARC adiabatic accelerated calorimeter in HWS mode; and / or, In step S3, the Td24 of the finished liquid is determined based on the adiabatic test data, and the time to reach the maximum reaction rate of the runaway reaction (TMR) is determined under conditions including at least the process temperature Tp and / or the temperature reaching the MTSR. ad .

8. The thermal safety risk assessment method according to claim 1, characterized in that, Step S4, the risk matrix assessment, includes: combining the severity assessment results with the probability assessment results to obtain the risk matrix level, and outputting the corresponding acceptability conclusions and control recommendations; and / or, The process hazard assessment in step S4 includes: determining the process temperature Tp and the maximum technical temperature MTT, and comparing Tp, MTSR, and MTT with Td24 obtained in step S3 to output the process hazard level; and judging whether a decomposition reaction is triggered after the target reaction runs out of control based on the relationship between Tp, MTSR, MTT and Td24, and including at least one safety barrier measure among evaporative cooling and / or emergency depressurization when outputting control recommendations.

9. The thermal safety risk assessment method according to claim 1, characterized in that, The benzoic acid reduction product identified in step S5 is benzyl alcohol, and differential scanning calorimetry is performed on benzyl alcohol to verify its thermal stability.

10. The thermal safety risk assessment method according to claim 1, characterized in that, The process of the benzoic acid reduction reaction includes: adding tetrahydrofuran and benzoic acid into a reaction vessel and stirring to dissolve them; adding NaBH4 in batches under stirring conditions; raising the system temperature to 50°C after the addition is complete; adding an iodine catalyst solution prepared with tetrahydrofuran after the system temperature reaches 50°C; and keeping the reaction at 50°C for 20 hours.

Images