Inherently Safer Acids - A Case Study on the Application of Polyelectrolytes

Strong acids, such as aqueous hydrochloric acid, are commonly used in the chemical process industry to purify streams or remove particulates from raw material, product, and waste streams. The benefits of HCl are its' low cost, large dissociation constant, and stability over time. However, the hazards associated with handling and processing HCl must be seriously considered when designing plants and specifying materials of construction and personal protective equipment. This typically results in higher capital, maintenance, and replacement costs to minimize the potential for personnel injury, equipment damage, and associated business interruption. This paper examines one such facility where aqueous hydrochloric acid had been in use for many years. A number of inherently safer design (ISD) principles were evaluated against the existing operation, in order to identify opportunities for risk reduction. As a result, the inherent safety of the process was enhanced by converting an HCl system for dissolving inorganic particulates to a sequestration process utilizing polyelectrolytes. Application of this inherently safer process reduces maintenance costs, capital replacement costs, and most importantly, the potential for employee exposure. A review of the process chemistry and examples of process technologies that ultimately led to this inherently safer design are provided.