Prediction of thermal hazards of chemical reactions

A large number of products of the chemical industry are produced using potentially hazardous reactions. The experimental investigation of the hazards of all reactions involved in production processes would be very expensive. The primary reactions—desired reactions which are part of the process—and the secondary reactions—undesired successive or side reactions—should both be considered. In this paper the methods of prediction of thermodynamic and kinetic properties of reactions are discussed.Thermodynamic data are of eminent practical importance because low heats of reaction may indicate that no further experimental investigations are necessary. For primary reactions, e.g. polymerization, diazotization and hydrogenation reactions, reaction enthalpies have been obtained by experimental methods. Typical data can be found in the public literature for the different reaction classes. When compared with theoretical thermodynamic data estimated by the chetah computer program, the agreement is satisfactory. chetah implements Benson's second-order group contribution technique (Benson, 1976).For secondary reactions, especially exothermic decomposition reactions, typical heats of reaction—mostly measured by DSC—have been associated with functional groups. Decompositions and other undesired exothermic reactions that proceed from the same functional group, e.g. a nitro group, have about the same heat of reaction.For the estimation using the chetah program, decomposition reactions have to be assumed which are typical for the functional group. The reaction yielding the maximum exothermic reaction energy was selected. The comparison of experimental heats of reaction with estimated data shows satisfactory agreement.In principle it is also possible to predict kinetic data of secondary reactions, but sufficient experimental data are missing.     

2-氨基-2,3-二甲基丁酰胺氧化合成热危险性研究

为研究2-氨基-23,-二甲基丁酰胺氧化合成的热危险性,采用差示扫描量热仪(DSC)测试2-氨基-2,3-二甲基丁腈和2-氨基-2,3-二甲基丁酰胺的热分解情况,采用反应量热仪(RC1)研究反应温度、双氧水滴加速度和氢氧化钠用量对反应的影响。研究结果显示,2-氨基-2,3-二甲基丁腈吸热热分解温度为149.5℃2,-氨基-2,3-二甲基丁酰胺表现为吸热和放热2段分解过程,吸热和放热分解温度分别为234.4℃和456℃。反应放热速率主要为加料控制,但是,存在一定的热累积。热失控体系最高温度(MTSR)低于2-氨基-23,-二甲基丁腈和2-氨基-23,-二甲基丁酰胺的分解温度,高于体系沸腾温度,在热失控的条件下,反应体系容易导致冲料危险;在优惠的工艺条件范围内,提高反应温度,延长滴加时间,可降低反应的MTSR,提高热转化率和反应安全性。     

化学品反应危险性分级方法研究与应用

针对化学品反应危险性的评价,介绍利用最大分解热,反应放热功率,绝热反应参数等方法对化学品反应危险性进行分级的几种方法及各自特点。通过分析整合不同分级方法,提出一种基于实测反应放热参数的分级方法,此方法以初始放热温度和反应热组成指标体系,同时配合燃爆曲线实现对化学品反应危险性的分级,得到的结果对于化学品的安全评价有较强的参考价值。考察了6种有机过氧化物的放热性质,诠释了有机过氧化物的反应危险性,应用所提出的反应危险性分级方法对其进行分级,并对分级方法进行了验证。该方法结合了实验结果和多种分级方法的优点,使化学品反应危险性分级方法具有更强的实用性。     

混酸中甲苯半间歇硝化过程的危险性研究

为了解甲苯在混酸中硝化的危险性,用差示扫描量热法(DSC)测试甲苯、混酸及一硝基甲苯的热分解情况,用反应量热仪(RC1e)研究搅拌速度、温度及硝酸过用率3因素对目的反应的影响。结果表明,混酸分解温度最低,而当目的反应的3因素出现异常,以及反应过程中发生冷却失效时,均可导致硝化反应体系不稳定,此时若不停止加料,并采取措施,易引起混酸的分解,进一步可引起一硝基甲苯的分解,导致严重后果。     

自反应性化学物质热危险性综合评估

自反应性化学物质热危险性评估的关键在于表征参数的选择和量化,单一的评估参数往往仅表征其热危险性的某一方面。综合考虑自反应性物质发生热分解反应的难易程度及其造成后果的严重程度两个方面,分别选取放热反应初始温度(To)和反应热(-ΔH)作为相应的表征参数,通过半正态分布函数对这两个指标进行标准化处理。在此基础上根据风险的定义提出了一种新的自反应性化学物质的热危险性综合评估指数(THI指数),并建立相应的热危险性分级标准,对自反应性化学物质的热危险性进行综合评估与分级。结果表明,建立的THI指数所确定的热危险性分级结果与基于活化能和最大绝热温度的RHI指数的反应危险性等级基本一致,该指数能够对自反应性化学物质的热危险性进行定量评估。     

基于筛选测试的化工反应危害评估探讨

本文主要讨论了基于筛选测试方法的化工反应危害评价。该方法是利用DSC、TS“等差热分析仪对化学品和混合物进行热稳定性的筛选测试，根据起始温度和反应焓变对化合物危害程度分级进行分级，建立反应风险指数，从而在小试和中试阶段就将反应危害降低或消除，确保大规模生产时的安全性，为真正实现化工工艺本质安全。此外，还比较了DSC、TSU、AFFAC、RSST等热分析仪，认为TSU和RSST是目前较为合适的热筛选分析仪，为建立反应危害实验室相关仪器的选型提供了参考。     

A posteriori hazard analysis and feedback information of an accidental event in the grains storage of an agrochemical product

The present study concerns a hazardous event which occurred in an industrial storage tank of a ground insecticide. A preliminary post-accident approach of the hazard evaluation is performed. The rapid report of the presence of an unstable functional group in the active product and of its potential thermal instability (CHETAH indices) has led to complete this examination by an experimental study of thermal analysis using isotherm exposition measurement (DTA) or with temperature programming by differential scanning calorimetry (DSC) and oxidability tests (BAM). The apparent kinetics of decomposition of the active matter of the ground insecticide has been represented by a global Arrhenius law.

A model designed for the simulation of heterogeneous thermal runaways based on the numerical solution of the transient mass and energy balances has been further applied to define the critical conditions of the storage and simulate its behavior.

The results obtained during this analysis with the experienced feedback allowed us on one side to explain the hazardous event and especially on the other side to modify the operating protocol of the conditions of formulation of the active matter on the inert mineral support.     

Prediction of energy release hazards using a simplified adiabatic temperature rise

A computationally simple method is outlined to calculate the maximum adiabatic temperature rise for the decomposition of a compound. This method, termed the MART method, is shown to be useful to assess the likelihood of a compound being an energy release hazard. Calculations were made for a number of classes of compounds and the results were analyzed for each class. The method was shown to give relatively clear transitions between compounds not being energy release hazards up to a breakpoint value and being energy release hazards at higher values past the breakpoint value. Peroxides were shown to be a class of compounds that the method works less well on. A predictive rule that could be used regardless of compound class is suggested. The MART method was compared to the more computationally intensive CART method and was found to be quite similar in performance. Also discussed is the potential incorporation of the MART method into the CHETAH^TM software.     

Results of a Round-Robin with di-tertiary-butyl peroxide in various adiabatic equipment for assessment of runaway reaction hazards

The results of a Round-Robin test on the decomposition reaction of 15% w/w di-tertiary-butyl peroxide (DTBP) in toluene are described in the present paper. The aim of the Round-Robin test was to compare the results of different (pseudo-)adiabatic reaction calorimeters in terms of accuracy and reliability for practical applications. The experiments were performed in the Accelerating Rate Calorimeter (ARC), Phi-Tec, Pressure Dewar calorimeter (Dewar), temperature controlled reactor (CRVM) and the Automatic Pressure Track Accelerating Calorimeter (APTAC). Although the various types of equipment showed differences in accuracy and reproducibility, in general, no specific type of equipment seems to out-perform the others in the present study.     

一种基于层次分析法的危险化学品源安全评价综合模型

危险化学品源的安全评价是安全生产管理中的一项重要内容.目前用于危险化学品源安全评价与分级的常用方法有后果分析法、道指数法、蒙德指数法以及使用临界系数判别重大危险源的方法等.在实际应用中,单独使用某一方法时,由于存在各种片面性问题而得不到满意的评价结果; 几种方法同时使用时,其评价指标、评价结果以及结果的形式又会互相冲突.为解决上述问题,建立了基于层次分析法的综合评价模型.首先,根据安全评价要求构建3层次的评价体系,在各层次中构造判断矩阵,并计算4种常用方法相对综合评价模型的置信度; 其次,对各方法统一危险分级标准,均采用危险分数划定危险级别,并取各危险分数的加权平均值--综合危险分数作为综合评价模型下的危险源分级标准.采用综合评价模型可消除单一方法进行评价时的片面性和偏差,同时,评价结果的一致化使得判断危险化学品源的危险级别以及由此采取相应级别的管理措施成为可能,将更有利于实际安全生产管理指导.     

石化企业危险化工工艺风险等级评估指标分解

伴随石化企业的迅猛发展,危险品越来越多,生产条件越来越苛刻,同时带来的是更为重大的风险隐患以及安全事故,因此对危险工艺的风险评估就显得尤为重要.考虑到目前还没有什么好的方法来判别某种工艺就一定是危险化工工艺,因此本文在国家安监总局划分的15种危险化工工艺的基础上,根据危险化工工艺表征涉及的影响因素,结合化工工艺的实际情况,选择具有典型代表意义的重要性评价指标作为研究对象,建立了由67个具体指标形成的动态指标体系,并运用指标分类分解方法对各个指标进行量化,最后采用模糊数学综合评价对危险化工工艺进行了软件化评估,从而为政府和企业加强安全管理提供了便利,进一步实现石化企业的本质安全化.     

Investigation on the self-decomposition and explosion hazard of azo compounds

Azo compounds are self-reactive chemicals that violently produce flammable gases with heat release (i.e., an exothermic reaction). However, the explosion mechanism and ignition probability of azo compounds have not been clearly defined for storage or transportation. In this study, explosion scene analyses and various pyrolysis tests were performed to evaluate the thermal decomposition characteristics and explosion phenomena of azo compounds in a storage facility. The chemical debris collected from a fire scene was determined to be similar to the pyrolyzate of one of the tested azo compounds used by Py-GCMS. The minimum amounts of azo compounds, which could be ignited by self-decomposition heat, were calculated from the results of differential scanning calorimetrys and the heat transfer equation. The results were used to discuss a safety and response strategy for preventing the propagation of an explosion accident, namely a chemical backdraft.     

Thermal hazard evaluation for γ-valerolactone production by using formic acid as hydrogen donor

Aiming at the green and sustainable energy substitution and supply, biomass valorization has become a potential strategy to face the energy crisis and increasing demand all over the world from long-term perspectives. Among the bio-based chemicals, γ-valerolactone (GVL) production from hydrogenation of levulinic acid (LA) and its esters has attracted great interests due to its wide applications, such as fuel, solvent, and additives. However, the safety evaluation for this hydrogenation reaction has received few attentions. To fill this gap, thermal hazard evaluation for GVL production from LA hydrogenation by using formic acid (FA) as hydrogen donor was first performed. The process conditions were optimized by using orthogonal experimental method for further calorimetry study. Thermal stability of chemicals and thermal risk of reaction process under adiabatic conditions were investigated by applying differential scanning calorimetry and accelerating rate calorimeter Phi-Tec II, respectively. The results revealed that the chemicals were stable in temperature range from 30 to 250 °C except FA due to its evaporation and decomposition with endothermic behaviors. The reaction process under isothermal and adiabatic conditions demonstrates that the decomposition of FA was rapid and followed by the hydrogenation of LA to GVL. Based on kinetic model under adiabatic conditions and risk matrix, the thermal runaway risk was found to be medium, indicating that certain safety measures should be properly designed and taken for loss prevention. This work could benefit the safety design and thermal risk prevention for GVL production by using FA as hydrogen donor.     

Thermal decomposition kinetic of liquid organic peroxides

This study demonstrates the application of isothermal calorimeter for investigating the thermal decomposition of several liquid organic peroxides, such as t-Butyl peroxy acetate (TBPA), Di-tert butyl peroxide (DTBP), and Cumene hydroperoxide (CHP). The decomposition mechanism and kinetic can be identified from case to case. TBPA and DTBP undergo first order reaction, whereas CHP occurs autocatalysis. Accurate kinetic can be assessed on the basis of discerning these various schemes of given samples. Consequently, the thermal runaway or reactive hazards potential of organic peroxides can be determined, for instance as a self accelerating decomposition temperature (SADT).     

Inclusion of pressure hazards into NFPA 704 instability rating system

The lack of awareness in identifying potential hazardous reactions is commonly cited as a cause of accidents. One major problem is the lack of consensus to assign appropriate reactivity hazards ratings. NFPA 704 instability rating system is widely used throughout the chemical industry. However, this system does not take into account pressure hazards. Inclusion of pressure hazards into the NFPA 704 instability rating will provide a more comprehensive rating system, which will characterize hazards that may arise not only from exothermic reactions, but also from endothermic decompositions with gas evolution. In this work we present a proposed method for developing a simple methodology to include pressure and pressure rates into the assignment of instability ratings. The current NFPA 704 instability rating number for the systems studied does not show a trend between the pressures and pressure rates generated with the assigned rating. Therefore, arbitrary threshold values were chosen to rank the substances according to the pressure and pressure rate generated. Results obtained from a variety of systems with endothermic decompositions show that their pressure and pressure rates have magnitudes comparable to systems that decompose exothermically. So far, this method has been applied only to a limited set of data. However, assignment of arbitrary values for normalized maximum pressures generated and pressure rates, taking as reference the values obtained for the thermal decomposition of cumene hydroperoxide and di-terbutyl peroxide appears to give reasonable limits for the rating chemicals based on their relative pressure hazards.     

Flammability estimation of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Ionic liquids (ILs) are known as room temperature molten salts, which are considered green replacement to traditional organic solvents. The fire hazards of traditional organic solvents mainly depend on the combustibility of their vapors, thus ILs are generally regarded as nonflammable owing to their low volatility. However, recent studies show that ILs may combust due to the potential hazards of thermal decomposition, indicating the issue of fire and explosion of ILs are eager to be evaluated during the applications. In this study, the fire and explosion hazards of IL 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₆mim][NTf₂]) are explored in different aspects. The traditional definition of the flammability for the common organic solvent is not thoroughly applicable to [C₆mim][NTf₂] due to the low volatility. Furthermore, the common definition of reactivity for traditional organic solvents also fails to apply, because the decomposition reaction is indeed an endothermic reaction. However, the auto-ignition of some decomposition products will result in fire and explosion hazards for [C₆mim][NTf₂]. Therefore the application of such data in safety purposes should be very careful.     

Mixing hazard evaluation of organic peroxides with other chemicals

Organic peroxides (POs) have been widely used in chemical industries as initiators of polymerization, hardening or bridge formation agents, and they are known for its self-reactive and also mixing hazard characteristics when mixed with other chemicals such as acids and alkalis. It is the purpose of this investigation to propose a simple but useful evaluation flow of mixing hazards of POs with other chemicals using conventional experimental techniques such as a glass test tube test, Dewar vessel test and DSC is proposed. 7 kinds of POs (DEPD, THP, TBEH, TBTC, MEKPO, DTBP, THHP) were mixed with sulfuric acids with various concentration, sodium hydroxide solutions, -iron(III) oxide and acrylonitrile (AN).

Based on the proposed evaluation flow the testing results were classified into 4 ranks due to the hazard criteria. Futhermore DEPD/acrylonitrile mixtures were investigated in more detail and the influences of the mixing ratio and the stirring speed were discussed.     

Using thermal analysis with kinetic calculation method to assess the thermal stability of 2-cyanopropan-2-yliminourea

Azo compounds, which are commonly used as initiators and blowing agents, are also typical self-reactive materials capable of undergoing runaway reaction during storage and transportation, which can cause severe fires and accidents. To ensure the thermal safety of azo compounds in the process, transportation, and applications, this study investigated 2-cyanopropan-2-yliminourea, which can also be called V-30. First, thermal decomposition characteristics under the non-isothermal conditions were obtained using differential scanning calorimetry. Second, the collected data were combined with a mathematical model to evaluate the primary thermal hazard during the process for V-30. Then, based on a heat-transfer model, the self-accelerating decomposition temperature (SADT) was extrapolated for consideration and non-consideration of consumption of chemicals. The results showed that SADT of V-30 was less than 80 °C. Therefore, it is essential to avoid a temperature beyond SADT or the cooling system will fail. The influence of consumption was also considered for SADT in this study.     

2-Methylpyridine-N-oxidation runaway studies

Calorimetry has been used in order to identify the runaway behavior of 2-methylpyridine-N-oxidation (2-picoline-N-oxidation). Experiments were performed in an Automatic Pressure Tracking Adiabatic Calorimeter (APTAC), employing 2-methylpyridine-N-oxide (2-picoline-N-oxide) with or without catalyst, 2-methylpyridine-N-oxide, hydrogen peroxide, 2-methylpyridine (2-picoline) and catalyst, and 2-methylpyridine, hydrogen peroxide and catalyst. Approximately 16.5 g of aqueous solutions were used in 100 ml closed glass cells in all but one measurement. Measurements were performed isothermally or employing the Heat-Wait-Search (HWS) technique. During reaction runaway, any excess of hydrogen peroxide and the produced 2-methylpyridine-N-oxide decompose releasing non-condensable gases and raising the pressure. It was found that the reaction runaway is condition-sensitive. Catalyst, the presence of 2-picoline and/or its N-oxide, affect hydrogen peroxide and/or 2-picoline-N-oxide decomposition rates. Further research accompanied by analytical measurements of the gas and liquid phase would provide indications in regard to the decomposition mechanisms followed in those cases.     

A quantitative risk management framework for dust and hybrid mixture explosions

Dust and hybrid-mixture explosions continue to occur in industrial processes that handle fine powders and flammable gases. Considerable research is therefore conducted throughout the world with the objective of both preventing the occurrence and mitigating the consequences of such events. In the current work, research has been undertaken to help move the field of dust explosion prevention and mitigation from its current emphasis on hazards (with an accompanying reliance on primarily engineered safety features) to a focus on risk (with an accompanying reliance on hierarchical, risk-based, decision-making tools). Employing the principles of quantitative risk assessment (QRA) of dust and hybrid-mixture explosions, a methodological framework for the management of these risks has been developed.The QRA framework is based on hazard identification via credible accident scenarios for dust explosions, followed by probabilistic fault-tree analysis (using Relex – Reliability Excellence – software) and consequence severity analysis (using DESC – Dust Explosion Simulation Code – software). Identification of risk reduction measures in the framework is accomplished in a hierarchical manner by considering inherent safety measures, passive and active engineered devices, and procedural measures (in that order). An industrial case study is presented to show how inherent safety measures such as dust minimization and dust/process moderation can be helpful in reducing dust and hybrid-mixture explosion consequences in a 400-m³ polyethylene storage silo.