A Top to Bottom Approach for Assessment of Safety, Health and Environmental Aspects In

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A top to bottom approach for assessment of safety, health and environmental aspects in early development stages of a chemical process

Konrad Hungerbühler, Shailesh Shah, Fabio Visentin and Ulrich Fischer*

Safety & Environmental Technology Group,

Institute of Chemical and Bioengineering,

Swiss Federal Institute of Technology (ETH), CH-8093 Zurich, Switzerland
{hungerb,sshah,fvisentin,ufischer}@chem.ethz.ch

*Corresponding Author:

Ulrich Fischer

Institute of Chemical and Bioengineering

Swiss Federal Institute of Technology (ETH)

HCI G138 ETH-Hoenggerberg

CH-8093 Zurich

Switzerland

Tel: +41 1 6325668
Fax: +41 1 6321189
Email:

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Abstract

The concept of integrated process development stresses the importance of considering all economic as well as environmental, health and safety aspects starting from the early stages of developing a new chemical process. The use of this concept in early stages makes chemical processes by itself environmental and health friendlier, safer and by achieving this, at the same time also more economic. This paper presents a methodology that assesses a chemical process in early development phases in a top to bottom approach under environmental, health and safety (EHS) aspects. These aspects are most effectively considered early in chemical process design. The identification of environmental, health and safety hazards is done with the help of EHS method (Koller et al., 2000) in the form of indices. This qualitative hazard identification is based on physical and chemical, environmental, health and safety related properties of the substances. The total chemical hazards are defined with the help of these indices together with the mass of the chemicals considering the context specific process together with safety and end of pipe technologies.

The hazard identification of a chemical process requires data from databases or from laboratory experiments. A super database, called, EHS database is developed to make hazard identification process faster. The lack of safety related data in early development phase makes laboratory experiments an important step. To gather specific safety data, for example, reaction parameters, a new small-scale Combined Reaction Calorimeter (CRC.v4) fitted with an integrated infrared-attenuated total reflection (IR-ATR) probe is presented based on the combination of the principles of power compensation and heat balance calorimetry. This calibration-free calorimeter has a sample volume of about 40 ml, uses a metal block as an intermediate thermostat and is applicable to higher pressure up to 30 bars. The performance of CRC.v4 is demonstrated with the help of a three-phase hydrogenation reaction in Visentin et al. (2004).

Keywords:EHS database, EHS assessment, Pressure reaction calorimeter (CRC)

Introduction

In the development of new chemical processes, integrated assessment of environmental, health, safety and economic aspects leads to better selection of
synthesis routes and optimum process design. Incorporation of these aspects in early process design needs a systematic methodology that, in a stepwise manner, performs assessment of available synthesis routes and arranges them in a scale for making decisions. A lot of research has been done by academia and industries dedicated separately to environmental, health and safety hazards assessment in a chemical process. A large variety of methods exist for identifying and assessing the hazard potential or safety of chemical processes during the design phase (e.g., HAZOP, Dow Fire & Explosion Index (Dow Chemicals, 1994), METRIK (Ruppert, 1999), Rapid Risk Analysis (Khan and Abbasi, 1998)). These methods vary significantly in goal, scope, structure and the exact way of considering safety aspects (Koller et al., 2001). Similarly, various methods exist for evaluation of environmental hazards related with chemical products or chemical processes (Pratt et al., 1993, Hansen et al., 1999, Jia et al., 1996, Mallick et al., 1996). However, only a few publications are available considering integration of environmental, health and safety aspects during the chemical process design. Preston and Hawksley (1997) stressed the importance of using a single framework for assessing safety, health as well as environmental (SHE) effects during process development. The INSIDE project (Turney et al., 1997) led to a toolbox for inherent SHE in process design. Our EHS method (Koller et al., 2000) was developed for integrated assessment of environmental, health and safety aspects in early phases of chemical process design in a top to bottom approach.

Methodology

This methodology assesses safety, health and environmental aspects in a single framework in early development stages of a chemical process. A key characteristic of the early phases of process design is that the knowledge, amount and quality of process information increase continuously but, on the other hand, degree of freedom decreases as shown in Figure 1. The methodological approach of our EHS-tool is divided into qualitative, quantitative and technological assessment as shown in Figure 2 and is performed stepwise as the detail information about quantities and technologies becomes available. In early development phase of process design, only information about presence of chemicals and reaction conditions is available via reaction recipe. Therefore it is a challenge to perform safety, health and environmental assessment at such stages. The EHS method (Koller et al., 2000) handles the limitation of detail information by performing qualitative assessment for each chemical under eleven effect categories based on its physical and chemical, environmental and toxicity properties (see Figure 3). These properties lead to the determination of Dangerous Property (DP) of a substance. In the next step, Dangerous Property is modified with the relevant fate factor to obtain the Effective Dangerous Property (EDP). These fate factors are Mobility, Degradation and Accumulation (e.g., safety and health effects for which damage occurs only after transmission via air (acute or chronic toxicity) are modified with the mobility of the substance). The resulting qualitative indexes on a scale between zero and one identify problems related with handling or release of chemicals.

As the information about flow-sheet, mass-balance, energy-balance and reaction conditions are available, quantitative assessment is done by taking mass and process conditions into account. In EHS method, relevant mass of chemicals is considered for safety, health and environmental assessment. For environmental assessment – total mass of output, for safety assessment - maximum inventory and for health assessment – presence of chemical (standard mass of one kg) is chosen. The consideration of mass together with Effective Dangerous Property (EDP) provides the Potential of Danger (PoD) of a substance.

The final step is to consider process and safety technologies to handle hazardous chemicals and pollutants. A list of process and safety technologies is given to user to select on the basis of availability in the chemical plant. Potential of Danger (PoD) of a chemical is reduced if suitable technology is present to prevent and protect the dangerous conditions. The resulting remaining potential of danger helps in making decisions about taking steps to increase inherent safety, for example, selection of synthesis routes, selection of chemicals, solvents, cooling/heating media etc. for a particular process and selection of the better process conditions.

Collection of property data via EHS super-database

The automated collection of chemical property data from different database sources is important because there is lack of property data and time to perform assessment in early stages of design. The EHS method handles the data problem by assigning a number of priorities for each effect category (e.g., volatility of chemicals can be identified by Mobility effect category which can be indexed qualitatively with the help of chemical class or vapour pressure or boiling point or melting point, the availability of only one property out of these four can determine the volatility of a chemical) and by calculating missing property data. The methodology uses EHS super-database in combination with a specific method coded in a tool (Koller et al., 1999 and Shah et al., 2003) for collection, combination and calculation of property data that is shown in Figure 4. This super-database imports property data from several database sources (e.g., IUCLID (European Chemicals Bureau, 1998), IGS (Nationale Alarmzentrale, 1997), CHRIS (US Coastal Guard, 1986), EPIWIN (EPI Suite, 1998)). It combines imported data with the help of statistical methods (e.g., arithmetic or geometric mean) and calculates missing properties by QSARs. The tool with EHS super-database carries out assessment of processes or synthesis routes with the help of imported data and the above described EHS method.

Collection of reaction data via small-scale reaction calorimeter

Reaction calorimetry is used to identify thermodynamic and kinetic parameters, which are crucial for design, optimization and safety of chemical processes. In the early development stages of speciality chemicals, pharmaceutical and pesticide processes, it is often not possible to perform large volume experiments in the laboratory because of limited availability of test substances, for example, reactants and intermediates. For such a case, the gain of reaction data implies the application of a small-scale reaction calorimeter. To improve the information content of a single measurement of a reaction, calorimeter needs to be combined with further analytical sensors such as an IR-ATR probe.A new pressure resistant small-scale reaction calorimeter CRC.v4 (Visentin et al., 2004, see Figure 5) that combines the principles of power compensation and heat balance (Zogg et al., 2003) is used in this methodology to collect thermodynamic and kinetic data for thermal process safety assessment. This new small-scale reaction calorimeter has a volume of 20-50 ml and is equipped with an integrated infrared-attenuated total reflection FTIR ATR probe. Moreover the new reaction calorimeter is pressure-proof up to 30 bars and in-situ on-line corrections for the overall heat transfer coefficient avoids the need of any calibration.

A key aspect of the reaction calorimetry is the isothermal control of the reaction temperature. This is required for three reasons: (1) IR spectra can change as a function of temperature; (2) Kinetic evaluation of the non-isothermal reaction runs implies more unknown parameters than isothermal evaluation; (3) Calorimetric evaluation of non-isothermal data requires the knowledge of the dynamic behavior of the calorimeter. In the new calorimeter, isothermal conditions are maintained using the power compensation principle. Peltier elements are implemented to compensate the change of the heat transfer coefficient and the heat transfer area during the measurement making time-consuming calibrations unnecessary.The Hastelloy reactor vessel is easily exchangeable and is available with and without the IR-ATR probe.

The new calorimeter has been tested using three chemical reactions: the neutralization of sodium hydroxide with sulfuric acid, the hydrolysis of acetic anhydride and the acetylation of a substituted benzopyranol (the substrate is not specified because of industry cooperation). The comparison of the results with those of a previous devices demonstrate the increased precision of the new calorimeter and highlights the fact that the equipment can easily deal with fast and highly exothermic reactions under strictly isothermal conditions (Zogg et al., 2003 and Visentin et al., 2004).

The procedure to obtain reaction kinetics and thermodynamic data (e.g., heat of reaction, activation energy and rate constants) is shown in Figure 6 and presented in Zogg et al. (2003). These data can be used in Reaction/Decomposition effect category in EHS method to identify reaction hazards. Furthermore these data are useful in making detail thermal process safety assessment (Shah et al., 2004).

Conclusion

A top to bottom approach is presented in this paper to perform safety, health and environmental assessment at early development stages of a chemical process design. The methodology gives a systematic approach to carry out the assessment while EHS super-database and small-scale reaction calorimeter in laboratory provide property and reaction data for the assessment. The combined use of EHS assessment methodology, EHS super-database and small-scale reaction calorimeter should contribute to make assessment procedure faster, more systematic and less test substance demanding. This approach should be used in the screening phase of synthesis and process research. In such a preliminary development stage, the top to bottom approach can help to widen the critical bottleneck, i.e. the systematic capacity building to reach in minimum “time to market”, an outstanding industrial process with highest inherent EHS performance and thus with a maximum of overall efficiency.

Nomenclature

CHRISchemical hazard response information system

CRC.v4combined reaction calorimeter version 4

DPdangerous property

EDPeffective dangerous property

EHSenvironment, health and safety

EPIWINestimations programs interface for windows

FTIR-ATRFourier transforms infrared - attenuated total reflection

HAZOPhazard and operability study

IGSInformationssystem für gefährliche und umweltrelevante Stoffe

IR-ATRinfrared - attenuated total reflection

IUCLIDinternational uniform chemical information database

METRIKmethod for risk classification

PoDpotential of danger

QSARquantitative structure activity relationship

SHEsafety, health and environment

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