Inherently safer design of solvent processes at the conceptual stage: Practical application for substitution

Abstract

The implementation of inherently safer design concepts is considered beneficial to avoid hazards during early stages of design. The application of existing process design and modeling techniques that aid ‘substitution’, ‘intensification’ and ‘attenuation’ has been shown in this work. The techniques have been applied to solvent processes because of the inherent hazards associated with them, such as large inventories, and presence of highly toxic and flammable materials. For ‘substitution’, computer aided molecular design technique has been applied to select inherently safer solvents for a solvent operation. For ‘intensification’ and ‘attenuation’, consequence models and regulatory guidance from EPA RMP have been integrated into process simulation. Combining existing techniques provides a design team with a higher level of information to make decisions based on process safety. A case study has been shown for liquid extraction of acetic acid–water mixture. Suitable solvents were identified using ICAS 11.0-ProCAMD, and consequence models were integrated into Aspen plus simulator using a calculator sheet. Solvents such as 5-nonanone, 2-nonanone and 5-methyl-2-hexanone provide inherently safer options, but conventionally-used solvent, ethyl acetate, provides higher degree of separation capability. A conclusive decision regarding feasible solvents and operating conditions would depend on design requirements, regulatory guidance, and safety criteria specified for the process. Inherent safety has always been an important consideration to be implemented during early design steps, and this paper presents a methodology to incorporate the principles and to obtain inherently safer alternatives.