Since its inception in 1995, the Mary Kay O’Connor Process Safety Center (MKOPSC) has researched the chemical behavior of industrial chemical reactions and processes. Reactive chemical hazards are seldom the characteristic of the chemical by itself but are highly dependent on the process conditions and modes of operation. The thermal behavior of a reaction system is analyzed to identify and assess potential hazards for likely scenarios in which process variables are exceeded or reaction components encounter incompatible materials or contaminants.
An Automated Pressure Tracking Adiabatic Calorimeter (APTAC) and a Reactive Systems Screening Tool (RSST) are currently used for the thermal analysis of reactive systems at the MKOPSC Reactive Chemical Laboratory. Reactions are selected for investigation based on their industrial importance and on major incidents involving injuries or large losses. The reactive chemical research ongoing at the Center consists of three major parts: experimental tests, computational analysis, and development of systematic approach to evaluate reactivity hazard.
The exothermic behavior of a substance is influenced by the presence of functional groups, which also forms a basis for reactivity classification. This behavior suggests that there is an inherent structure-property relationship between the observed calorimetric properties and molecular structure. The effects of contaminants (homogeneous catalysis) have been or will be studied experimentally as well (CISNEROS, 2002).
A reactive chemical experimental database is highly desired for reliable process safety information and safe handling of reactive chemicals. The Center proposes to establish a reactive chemical experimental database based on the published reactivity data and the experimental research at the Center. But, reactive chemical hazards are seldom the primary characteristic of the chemical by itself but are highly dependent on the process conditions and modes of operation. Therefore, the design of database structure and taxonomy is challenging. This database must incorporate parameters such as container and operating conditions other than the chemical involved.
Since 1970s hydroxylamine nitrate (HAN) has been involved in several incidents in different locations, such as Hanford and Savannah River Site (SRS). The most recent incident was a major explosion at the Plutonium Reclamation Facility at Hanford in 1997. Following these incidents, extensive research on hydroxylamine nitrate has been conducted at MKOPSC and other institutes. However most of these research efforts only focused on understanding the unstable behavior or combustion behavior of hydroxylamine nitrate. On-line monitoring, safe storage, and handling criteria of HAN are still far from sufficiently studied and developed.In the current research, aging tests and adiabatic calorimetry, analytical techniques, inverse-based fitting methods, and computational chemistry are combined to represent the aging and storage behavior of hydroxylamine nitrate. Thermal decomposition of aqueous solutions of hydroxylamine nitrate have been subjected to aging tests and adiabatic decomposition tests at temperatures in the range of 30oC-160oC, which covers the normal storage operation temperature and the onset temperatures under current experimental conditions. Furthermore the influence of pressure, impurities, and temperature history profile are also examined. The liquid residue will be analyzed at different stages of aging tests using High Performance Liquid Chromatography (HPLC). The experimental data will be used together with molecular modeling techniques for the elucidation and deduction of the primary decomposition mechanisms and reaction network parameters. Based on this experimental and theoretical research, a model for safe storage of HAN will be proposed.
Calorimetric techniques are widely used to characterize materials. Thermal analysis of minute samples will greatly impact the development of high-throughput screening technologies to aid in the rational design of materials with tailored chemical and biochemical properties. This research focuses on developing a nanocalorimeter to characterize energetic materials for chemical process safety, homeland security, and military applications (Liu et al, 2005).
Key tasks are divided among design, fabrication, and characterization phases while we are focusing on the design and testing of the nanacalorimeter prototype currently. The convergence between nanoscale calorimetry hardware and chemical fingerprinting software will be harnessed to produce an inexpensive (< $1 per chip) and field-deployable system offering greatly expanded capabilities to detect and characterize energetic materials in a complete self-contained package.
Calorimetric measurements to determine reactivity can be resource consuming, so computational methods to predict reactivity hazards present an attractive option. None of the available theoretical methods address the issue of chemical kinetics within a system that affects the rate of energy release and consequent hazards posed by the substance. It is well known that the structure of a substance affects its reactivity and this reactive nature of a compound is reflected in the calorimetric data. This dependence on observed behavior and molecular structure has not been satisfactorily quantified. Therefore, our aim is to develop theoretical methods to quantify both kinetics and thermodynamic based on molecular structure.
To predict reactivity of a substance it is intuitive to deduce probable reaction pathways, but it is difficult to predict the reaction pathways for a compound, especially at high temperatures. Our aim here is to correlate and predict DSC calorimetric data. The approach developed is useful as a screening tool for reactivity parameter predictions as a guide to identify the most significant systems that require more accurate values from experiment or computation.
The proposed screening system is based on thermal analysis techniques, which are inherently capable of providing direct measurement of energy release potential. Therefore, this system does not depend upon prior knowledge of familiar compounds, and it will be able to thermally characterize any type of energy releasing from a solid or liquid compound regardless of if it is a pure compound or a mixture. The device will consist on a chip that will contain a heating/sensing module and a sample receptacle; both will be fabricated in the Materials and Characterization Facility using micro-fabrication techniques to take advantage of the multiple benefits that this technique offers. The temperature control, data acquisition and analysis will be performed using commercial software (LabViewTM). Finally, in order to test the operation of the nano-calorimeter it will be used to measure the energy change due to phase transformations of common substances and to measure energy released by high energetic materials such as TNT, which will show the application of the device for detection of explosive materials. It is worth to mention that this research program has the potential to impact the industrial process safety and homeland security areas by providing a rapid and inexpensive screening technology for detection and characterization of hazardous materials. The proposed nanocalorimeter will be capable of perform rapid material characterization studies outside the standard laboratory environment, or as an effective airport and portal screening tool to detect conventional and non-conventional explosive materials. Additionally, the ability to develop more affordable and accessible calorimetric techniques introduces the possibility of greatly enhancing the education in the fields of chemistry, chemical engineering and chemical process safety.
An important purpose of the computational methods is to provide values under conditions when the substances are unstable and cannot be measured accurately or safely, such as the heat of formation of hydroxylamine. Another important need is to supplement experimental data to determine reaction mechanisms for reactive hazard assessment. From these computations and experimental investigations, correlations are developed to extend at lower cost and expertise the detailed results to other systems. At the Mary Kay O’Connor Process Safety Center, we employ a variety of molecular modeling techniques to estimate thermo-physical properties, predict calorimetric data, and assess potential hazards due to chemical reactivity which is summarized in the following paragraphs.
As mentioned earlier, calorimetric studies on aqueous solutions of HA indicate that it is a highly reactive compound, but its properties have been insufficiently characterized. More specifically, a reliable HA heat of formation needed for reaction energy determinations was not available due to its instability. The aim of studying elementary reactions of HA decomposition is to understand the initiation steps leading to HA runaway reactions and explosive behavior. Such an understanding of the behavior of HA at the molecular level can lead to development of better inhibitors to prevent metal catalysis and consequently prevent or reduce thermal runaway reactions.
It is known in the industry that a trace amount of contaminants may have significant effects on the reaction rate. The center has conducted experiments on the effects of trace metals, base, and acid in the HA decomposition (Cisneros, 2002; Saraf, 2003; Wei, 2005). Further efforts are desired to correlate contamination study with homogeneous and heterogeneous catalysis research. None of the steps investigated so far have predicted the initiation phase of HA decomposition, but research continues to determine probable mechanisms for HA catalysis in presence of metals ions at the molecular level.
Current understanding and modeling of runaway reactions are usually inadequate for predictions of system behavior because they are based on overall behavior parameters and do not account for detailed chemical and transport events of branched-chain thermal processes. We plan to model energetic and runaway reaction systems using a synergistic combination of experimental methods to analyze the decomposition species and kinetics and theoretical methods to calculate missing kinetic parameters. Initially, we will focus on hydroxylamine but the techniques and protocols developed will be useful for other energetic and runaway reactions. We will measure the overall runaway reaction behavior using calorimetry, identify reactive intermediates, and measure rate constants using in situ FTIR for the liquid phase reactions and laser spectroscopy for the vapor phase reactions.
These results will be employed to determine rates using microcanonical rate theory. Based on the Reynolds number of the reacting flow, both laminar and turbulent flow will be considered in the macroscopic runaway behavior analysis. An important goal of this research is to enable accurate prediction of runaway reaction behavior, which is needed for designs of safer and more economic industrial processes involving highly energetic and reactive chemicals. Also, this research could contribute to an industrial protocol for analysis of rapid and energetic chemical reactions.
The Center has developed a structured approach for the evaluation of reactive chemical hazards that integrates literature data screening, computational estimations, theoretical modeling, and experimental measurements (Aldeeb, 2003). The main goal of this systematic approach is to focus the research on the most likely and most hazardous reaction stoichiometry and hence reduce the need for detailed experimental analysis for a large number of process reactions. More detailed and advanced experimental analyses may be required for the more complex and reactive systems. The Center employs calorimetric measurements and classical and quantum chemistry models to determine properties of chemicals and to analyze chemical systems.
EO is a very versatile compound, storing considerable energy in its ring structure. Its reactions proceed mainly via ring opening and are highly exothermic. Under appropriate conditions, it is known to undergo a variety of reactions, such as isomerization, polymerization, hydrolysis, combustion and decomposition.
Due to its very reactive characteristic and widely industrial applications, EO has been involved in a number of serious incidents: Doe Run 1962, Freeport 1974, Deer Park 1988, and Union Carbide Corporation’s Seadrift 1991 The impacts may be severe in terms of death and injury to people, damage to physical property, and effects on the environment. For instance, the incident in the Union Carbide in 1991 caused one fatality, extensive damage to the plant with the property damage of up to 80 million dollars.
Effect of contamination is a considerable cause of EO incidents. The presence of trace impurities such as alkalis, acids, oxidizers, iron chlorides, iron oxides and aluminum may reduce the thermal stability of a nominally pure chemical and cause unexpected runaway reactions under normal process conditions. Therefore, it is necessary to investigate the effects on EO of likely acid and base contaminants, such as EDTA, KOH, and ammonia.
His research will be focused on the activity of EO and some contaminants (KOH, aqueous ammonia, EDTA). Experiments will be conducted with the Automatic Pressure Tracking Adiabatic Calorimeter (APTAC). The data that will be measured by the APTAC include:
The data acquired and the shapes of the curves provide information about potential hazards posed by the reactions that occur in the system.
The data will also be used in the kinetic analysis of a runaway reaction and the design of safety relief valves as well.