pH-Based Control of the Kinetics and Process Safety of the Highly Exothermic Reaction Between Ammonium Chloride and Sodium Nitrite for Flow-Assurance Applications

Summary The highly exothermic reaction between ammonium chloride (NH4Cl) and sodium nitrite (NaNO2) has an important application in the area of flow assurance. Because of the high heat generation, this reaction has been used as a heat source for the fluidization of low-melting-point deposits formed during oil and gas production. Because this reaction is strongly pH dependent, the incorrect choice of pH can result in an uncontrollable temperature increase caused by the system’s inability to dissipate the large amount of heat generated in a short time, causing accidents such as structural damage and explosions. Thus, the aim of this work was to study a method that involved adjusting the pH over time to ensure controlled heat generation, with high calorimetric conversion, and avoid the development of a thermal-runaway reaction (pH-based control of the kinetics and process safety). The kinetics and thermodynamics of this reaction were studied using heat-flow reaction calorimetry and attenuated total reflection (ATR)-Fourier-transform infrared (FTIR) (ATR-FTIR) spectroscopy. Following a semiempirical approach, calorimetric and spectroscopic data were fitted to a kinetic equation using nitrite, ammonium (NH4+), and hydronium concentrations. The molar enthalpy calculated was –322.92 kJ/mol, and the Arrhenius parameters were determined as the frequency factor [ln(A)] = 22.21 and the apparent activation energy (Ea) = 63.40 kJ/mol. The kinetic model constructed made it possible to properly evaluate the pH profile that should be maintained to control the kinetics (heat-generation rate) and process safety [time to maximum rate under adiabatic conditions (TMRAD)] of the reaction. The strategy of adjusting the pH over time ensured controlled heat generation and high calorimetric conversion, which cannot be achieved by simply adding catalyst at the beginning of the reaction, and minimized the risk of developing a runaway reaction. However, in real applications, the pH control must be made using the balance between the thermal risk (TMRAD) and the performance of the method (qr), because although it is possible to decrease the thermal risk (increase the value of TMRAD) by increasing the pH, this increase is accompanied by a decrease in the heat-generation rate. Thus, from the proper balance of these factors (qr and TMRAD), pH control can ensure adequate levels of heat production within an acceptable thermal risk. Supplementary materials are available in support of this paper and have been published online under Supplementary Data at https://doi.org/10.2118/205389-PA. SPE is not responsible for the content or functionality of supplementary materials supplied by the authors.

Thermal Hazard Characteristics of Unsaturated Polyester Resin Mixed with Hardeners

Unsaturated polyester resin (UP) is a critical polymer material in applications of many fields, such as the chemical industry, military, and architecture. For improving the mechanical properties, some hardeners, such as methyl ethyl ketone peroxide (MEKPO) or tert-butyl peroxy-2-ethylhexanoate (TBPO), can trigger the curing reaction in UP polymerization, which causes that UP changes the structure from monomer to polymer. However, polymerization is a strong exothermic reaction, which can increase the risk of thermal runaway reaction in UP. Therefore, the mechanisms and characteristics in the thermal runaway reaction of UP mixed with hardeners should be studied for preventing and controlling UP explosion. The thermal hazards of UP mixed with hardeners were determined by thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) analysis. According to the results, UP mixed with MEKPO exhibited a more violent mass loss and exothermic reaction than UP mixed with TBPO. Furthermore, the thermal runaway reactions of UP mixed with MEKPO or TBPO with different mixing proportions of 1:1, 3:1, and 5:1 were determined. Irrespective of MEKPO or TBPO, the mixing proportions of 3:1 exhibited a high onset temperature and low enthalpy of curing reaction (ΔHexo). This demonstrated that this proportion was safer during UP polymerization. The results of this study can provide useful information for preventing UP explosion and developing polymerization technology.

Rheological Study of Phenol Formaldehyde Resole Resin Synthesized for Laminate Application

Heat explosions are sometimes observed during the synthesis of phenol formaldehyde (PF) resin. This scenario can be attributed to the high latent heat that was released and not dissipated leading to the occurrence of a runaway reaction. The synthesis temperature and time played important roles in controlling the heat release, hence preventing the resin from hardening during the synthesis process. This study aims to assess the rheological and viscoelasticity behaviors of the PF resin prepared using paraformaldehyde. The prepared PF resin was designed for laminate applications. The rheological behavior of the PF resin was assessed based on the different molar ratios of phenol to paraformaldehyde (P:F) mixed in the formulation. The molar ratios were set at 1.00:1.25, 1.00:1.50 and 1.00:1.75 of P to F, respectively. The rheological study was focused at specific synthesis temperatures, namely 40, 60, 80 and 100 °C. The synthesis time was observed for 240 min; changes in physical structure and viscosity of the PF resins were noted. It was observed that the viscosity values of the PF resins prepared were directly proportional to the synthesis temperature and the formaldehyde content. The PF resin also exhibited shear thickening behavior for all samples synthesized at 60 °C and above. For all PF resin samples synthesized at 60 °C and above, their viscoelasticity results indicated that the storage modulus (G′), loss modulus(G″) and tan δ are proportionally dependent on both the synthesis temperature and the formaldehyde content. Heat explosions were observed during the synthesis of PF resin at the synthesis temperature of 100 °C. This scenario can lead to possible runaway reaction which can also compromise the safety of the operators.