In a groundbreaking exploration at the intersection of chemical engineering and safety science, researchers from Nanjing Tech University have unveiled critical advancements in the diazotization synthesis of 2-aminonaphthalene-1,5-disulfonic acid (2-ANDSA). This pivotal work, published recently in Emergency Management Science and Technology, navigates the treacherous terrain of diazonium salt production, a cornerstone yet perilous reaction in the chemical industry. By integrating rigorous experimental optimization with sophisticated calorimetric assessments and kinetic modeling, the team has traced the intricate reaction pathways and thermal profiles that underpin this volatile synthesis, illuminating pathways to safer industrial scale-up without sacrificing product integrity.
Diazotization reactions have long stood as a chemical double-edged sword—indispensable for generating reactive diazonium salts but fraught with severe thermal risks. The exothermic nature of these transformations, often liberating heat exceeding −150 kJ/mol, combined with the propensity of diazonium salts to decompose violently under slight thermal perturbations, has led to numerous catastrophic incidents worldwide. Historically, industry mitigation strategies have revolved around semi-batch operations under stringent low-temperature conditions. However, such approaches often compromise reaction homogeneity, invite undesirable side reactions, and impair yields, creating a persistent safety and economic bottleneck.
The study spearheaded by Professor Juncheng Jiang’s team breaks new ground through a methodical dissection of process parameters influencing 2-ANDSA diazonium salt synthesis. Focused on experimental control under two distinct temperature regulation modes, the research meticulously varied reaction temperature, feed rates, stoichiometric ratios, and mixing intensities. This meticulous approach aimed to untangle the delicate interplay between reaction efficiency and thermal hazard potential, yielding a refined process blueprint that prioritizes safety without undermining chemical performance.
One of the most compelling revelations relates to the nuanced effect of temperature on reaction outcomes. While operating within a narrow low-temperature band from 0 to 10 °C preserved high purity levels exceeding 95%, elevating temperatures into the 20 to 30 °C range triggered disproportionately large increases in heat release and maximum synthesis reaction temperatures (MTSR). These thermal escalations amplify the risk of runaway decomposition events, underscoring the critical importance of vigilant temperature regulation during scale-up.
The control over feed rate emerged as another pivotal factor. The study demonstrated that maintaining feed rates between 0.10 and 0.15 mL/min is essential for balancing purity and thermal stability. Higher feeding speeds resulted in a precipitous decline in product purity and a doubling of heat release, signifying a precarious shift toward dangerously unstable reaction conditions. This observation highlights the necessity for precision pumping and feed control systems in industrial implementations.
Stoichiometric balance of reactants, particularly hydrochloric acid and sodium nitrite, further dictates both safety and yield. Optimizing the HCl molar ratio near 2.4 optimized purity (up to 96.8%) and moderated heat generation, whereas excessive acid concentrations exacerbated exothermicity. Sodium nitrite levels exceeding a 1.0 molar ratio dramatically elevated maximum heat release rates without appreciably enhancing purity, presenting a clear mandate to tightly regulate this parameter to circumvent runaway risks.
An often-overlooked but crucial factor, mixing intensity, was elucidated through stirring rate investigations. The research identified 400 revolutions per minute (rpm) as the optimal stirring speed, striking a balance between achieving adequate reactant homogenization and preventing overheating-related instabilities. Excessive agitation rates, conversely, were linked to thermal hotspots and reaction volatility, emphasizing the importance of fine-tuned mechanical agitation in large-scale reactors.
Temperature control modes introduced further insights. Comparative analyses between Tr (reactor temperature) and Tj (jacket temperature) control modes revealed superior performance of Tr mode during initial reaction stages, with more effective heat dissipation and lower MTSR values. This finding holds significant implications for industrial reactor design, suggesting that focusing control efforts directly on reactor contents rather than external cooling jackets can mitigate runaway hazard potential more effectively.
Advanced thermal hazard assessments employing differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), and kinetic modeling validated the experimental optimization strategies. The analyses confirmed that 2-ANDSA diazonium salts exhibit decomposition onset at relatively low temperatures, accompanied by rapid gas evolution—factors that compound the hazards associated with uncontrolled thermal excursions. These assessments provided a quantitative risk framework through the application of Risk Matrix and Stoessel Criticality Diagrams, categorizing the optimized process as low-risk under strict operational controls.
Importantly, this comprehensive study goes beyond the academic, offering a pragmatic roadmap for the chemical industry to reconcile the inherent dangers of diazotization with commercial imperatives. The integration of calorimetry data and kinetic models enables process engineers to anticipate and preemptively neutralize thermal runaway scenarios, ensuring safer process intensification and scale-up.
This work resonates profoundly in sectors relying on diazonium chemistry, including dye manufacturing and pharmaceuticals, where consistent product purity and process safety are paramount. The adoption of these refined parameters can substantially diminish the frequency of industrial accidents, reduce economic losses, and protect both personnel and infrastructure.
Moreover, the methodology detailed in this research sets a new standard for investigating hazardous chemical reactions. The coupling of experimental rigor with computational insights fosters a more predictive understanding of reactive systems, empowering safer innovation across a spectrum of chemical production challenges.
In conclusion, the Nanjing Tech University team’s research represents a vital advance in chemical process safety, blending foundational reaction mechanism elucidation with actionable operational guidelines. As the chemical industry continues to grapple with the balancing act between innovation and safety, studies like this redefine best practices and chart a path toward more robust and responsible manufacturing paradigms.
Subject of Research: Not applicable
Article Title: Reaction mechanism and thermal hazard assessment of diazotization for 2-aminonaphthalene-1,5-disulfonic acid (2-ANDSA)
News Publication Date: 30-Jun-2025
References: DOI 10.48130/emst-0025-0010
Keywords: Engineering, Technology, Agriculture
