Qingsheng Wang

Thermal Decomposition Pathways of Hydroxylamine: Theoretical Investigation on the Initial Steps

Hydroxylamine (NH(2)OH) is an unstable compound at room temperature, and it has been involved in two tragic industrial incidents. Although experimental studies have been carried out to study the thermal stability of hydroxylamine, the detailed decomposition mechanism is still in debate. In this work, several density functional and ab initio methods were used in conjunction with several basis sets to investigate the initial thermal decomposition steps of hydroxylamine, including both unimolecular and bimolecular reaction pathways. The theoretical investigation shows that simple bond dissociations and unimolecular reactions are unlikely to occur. The energetically favorable initial step of decomposition pathways was determined as a bimolecular isomerization of hydroxylamine into ammonia oxide with an activation barrier of approximately 25 kcal/mol at the MPW1K level of theory. Because hydroxylamine is available only in aqueous solutions, solvent effects on the initial decomposition pathways were also studied using water cluster methods and the polarizable continuum model (PCM). In water, the activation barrier of the bimolecular isomerization reaction decreases to approximately 16 kcal/mol. The results indicate that the bimolecular isomerization pathway of hydroxylamine is more favorable in aqueous solutions. However, the bimolecular nature of this reaction means that more dilute aqueous solution will be more stable.

Simple relationship for predicting onset temperatures of nitro compounds in thermal explosions

Nitro compounds are capable of rapid chemical decompositions with a large amount of energy releases and hence pose significant thermal explosion hazards. Molecular simulation has been well established and demonstrated as an effective tool to predict physical and/or chemical properties of energetic materials, such as onset temperature, heat of reaction, and shock sensitivity. In this work, a simple relationship for predicting the onset temperature of nitro aromatic compounds containing other functional groups is developed based on their molecular structures. The results have shown that the thermal onset temperature of a specific nitro aromatic compound is strongly related to its excitation energy (a singlet state to triplet state). The predicted onset temperatures show very good agreement with respect to the measured onset temperatures by differential scanning calorimetry. Deviations compared to the experimental values are very small. These correlations can be used to computationally screen new nitro compounds for their thermal explosion hazards. These correlations can also be applied as a preliminary thermal analysis method and expedite the evaluation process of new energetic materials.

Prediction of the self-accelerating decomposition temperature of organic peroxides using QSPR models

Organic peroxides are widely used unstable compounds that have caused many serious industrial incidents. Self-accelerating decomposition temperature (SADT) is one of the most important parameters to describe the thermal instability hazards of organic peroxides. However, it is very difficult to obtain experimental data of SADT due to high cost, the time involved and safety issues of laboratory tests. Quantitative structure–property relationship (QSPR) models have been proposed as an effective tool to predict thermal stability of organic peroxides. In this work, a dataset including 50 SADTs of organic peroxides was built and their molecular descriptors were calculated at B3LYP/6-31G(d) level using Gaussian 09. Two novel predictive models were successfully developed by multiple linear regression (MLR) and support vector machine (SVM). Both models were validated to have an excellent goodness of fit, internal robustness and external predictive ability. The MLR model was a linear equation with the average absolute error of training set and test set being 9.78 and 9.91, while the SVM model was a nonlinear model with the two values being 4.33 and 5.75, respectively. The SVM model has higher accuracy and is much more effective than the MLR model. This research provides general guidelines and methodology of establishing QSPR models to predict SADTs for other organic peroxides and unstable hazardous chemicals.

Thermal decomposition of hydroxylamine: isoperibolic calorimetric measurements at different conditions.

Thermal decomposition of hydroxylamine, NH2OH, was responsible for two serious accidents. However, its reactive behavior and the synergy of factors affecting its decomposition are not being understood. In this work, the global enthalpy of hydroxylamine decomposition has been measured in the temperature range of 130-150 °C employing isoperibolic calorimetry. Measurements were performed in a metal reactor, employing 30-80 ml solutions containing 1.4-20 g of pure hydroxylamine (2.8-40 g of the supplied reagent). The measurements showed that increased concentration or temperature, results in higher global enthalpies of reaction per unit mass of reactant. At 150 °C, specific enthalpies as high as 8 kJ per gram of hydroxylamine were measured, although in general they were in the range of 3-5 kJ g(-1). The accurate measurement of the generated heat was proven to be a cumbersome task as (a) it is difficult to identify the end of decomposition, which after a fast initial stage, proceeds very slowly, especially at lower temperatures and (b) the environment of gases affects the reaction rate.

Molecular simulation studies on chemical reactivity of methylcyclopentadiene.

Molecular simulations are important to predict thermodynamic values for reactive chemicals especially when sufficient experimental data are not available. Methylcyclopentadiene (MCP) is an example of a highly reactive and hazardous compound in the chemical process industry. In this work, chemical reactivity of 2-methylcyclopentadiene, including isomerization, dimerization, and oxidation reactions, is investigated in detail by theoretical computational chemistry methods and empirical thermodynamic-energy correlation. On the basis of molecular simulations, an average value of -15.2 kcal/mol for overall heat of dimerization and -45.6 kcal/mol for overall heat of oxidation were obtained in gaseous phase at 298 K and 1 atm. These molecular simulation studies can provide guidance for the design of safer chemical processes, safer handling of MCP, and also provide useful information for an investigation of the T2 Laboratories explosion on December 19, 2007, in Florida.

Human error analysis of the Macondo well blowout

The Macondo well blowout resulted in 11 fatalities and caused the largest nonintentional oil spill in history. The situation stemmed from a series of human errors through all stages of the project leading up to the blowout and subsequent explosion. These errors include faulty interpretation of signals indicating problems with well and safety system integrity, inappropriate modifications to safety systems, inadequate design of critical systems, failure to provide redundancy in the design stage, failure to adhere to administrative controls for the safe operation, failure to follow the American Petroleum Institute Recommended Practices 75 on drilling mud circulation, and others. Twenty five specific errors have been identified and classified into eight categories. The results show that the majority of the errors are latent errors and caused by poor leadership in the organization or management. In order to resolve these issues it is necessary to create a safety culture in which safety is paramount in operations and facilities. There are many lessons learned from this incident, but the most important lesson is that safety must be a way of life, beginning in the design stage and carrying through the project life cycle.

Thermal degradation and flammability of nanocomposites composed of silica cross-linked to poly(methyl methacrylate)

The effect of polymer cross-linkages on thermal degradation of silica/poly (methyl methacrylate) (PMMA) nanocomposites is investigated using a single novel nanoparticle. Nanosilica surface treated with KH570, an organic surface treatment capable of free-radical polymerisation, was used to cross-link PMMA via an in situ method. Scanning electron microscopy was used to characterise nanosilica before use, while X-ray diffraction confirmed silica was well dispersed in PMMA. Thermogravimetric analysis (TGA) results showed that thermal degradation of silica cross-linked nanocomposites was significantly stabilised compared to PMMA, with a 30% reduction in the peak mass loss rate. Kinetic studies revealed the degradation of nanocomposites in this work abide by first-order kinetics, with an increase in the degradation activation energy of approximately 100 kJ mol−1. This is nearly double the improvement compared to conventional PMMA-silica nanocomposites in literature, showing dramatic enhancements to thermal stability. Analysis of high-temperature residuals from TGA tests suggest that cross-linked silica have increased char yields when compared with both PMMA and traditional silica nanocomposites. Cone Calorimetry results showed the materials in this work have reduced heat release rates compared to PMMA and traditional silica-PMMA nanocomposites.

Application of incident command system in emergency response

The Incident Command System (ICS) is a standardized approach typically structured into five functional areas: command, operations, planning, logistics, and finance. The system allows for the integration of personnel, facilities, equipment, procedures, and communications within an organizational structure. It is a mature system and has been used by industries for a long time to aid in the proper mitigation of industrial incidents. The course named “Hazardous Materials Incident Management” is taught in the Department of Fire Protection & Safety at Oklahoma State University, which is designed to prepare students to manage hazardous materials emergencies through extensive hands‐on trainings. This article shows three design scenarios and how the ICS procedures are applied by student teams during the field trainings. Emergency response can be safely and effectively accomplished only when procedures are established and standardized through appropriate training. The discussion will help the academia and industry to well prepare/train the next generation of both public and private sector emergencyresponse personnel.

Prediction of lower flammability limits of blended gases based on quantitative structure–property relationship

This work focuses on developing predictive quantitative structure−property relationship (QSPR) models for lower flammability limits (LFLs) of gas mixtures. Experimental LFLs of 86 blended gases were extracted from a single reference, and their mixture descriptors were calculated solely from individual molecular structure by Gaussian 09. Multiple linear regression (MLR) analysis was employed to develop the models, and three different external validation methods were carried out to check the predictive capabilities of the models. The validations have shown that these models possess great predictive power with excellent goodness of fit and internal robustness; hence, they are deemed to be qualified to predict LFLs for other blended gases with no experimental LFL data available. The applicability domains (AD) of the models were defined as well, and all the points were within the AD area. The main advantages of the established models are their simplicity and possibility of extending them for the determination of LFLs of other gas mixtures, while the LFLs of the individuals do not need to be provided.

Evacuation simulation of confined spaces in petrochemical facilities

With the growth of the petrochemical industry, confined space evacuation has been a major safety issue due to the potential fatalities and injuries caused by inadequate emergency response. In this work, two existing software, BuildingEXODUS and FDS+Evac, were used to simulate the required safe egress time (RSET) in different evacuation environments. Vertical and horizontal storage tanks were constructed using these two simulation software. Then, different parameters such as occupant load, with and without internal obstruction, and exit size were studied in different simulation scenarios. The simulation results from the software have shown good agreement with those from field experiments. It was found that the RSET of a vertical storage tank is nearly half of that of a horizontal storage tank. The work has demonstrated that the fire safety software could be used to simulate evacuations from confined spaces in petrochemical facilities.