Pressure Swing Distillation for the Recovery of Acetonitrile

BACKGROUND

A leading American pharmaceutical company came to Koch Modular for the design and manufacture of a modular acetonitrile (ACN) distillation system. ACN is often used as a solvent in the production of insulin, antibiotics, and synthetic pharmaceuticals.

Although the client was previously recovering ACN and selling it at the azeotrope concentration, they decided to invest in a system that would recover dry ACN to be reused n their process. However, ACN forms an azeotrope with water, making its separation from an aqueous feed stream unattainable by conventional distillation methods.

Koch Modular engineers are well-versed in a number of distillation methods, including those that break azeotropes. They designed a system that relies on pressure swing distillation (PSD), achieving separation by taking advantage of a shift in composition of an azeotropic mixture with pressure.

CHALLENGE

To provide some background on the process, a complex feed consisting of ACN, water, and trace propionitrile, among a number of components, comes from an existing distillation column that removes all lower boiling impurities. Since the required purity of the recovered ACN could not be achieved in that single distillation column, Koch Modular was to provide a pressure swing distillation system to achieve it. Although the breaking of an azeotrope presents a challenge on its own, there are also challenges unique to modules being installed in places with unconventional climate restrictions in addition to those unique to pharmaceutical clients. For example, because the module installation site is surrounded by salty sea breeze, deliberate thought was required when planning materials of construction to avoid any material corrosion. Additionally, the trace propionitrile in the feed would also be present in the product stream, presenting possible build-up concerns after repeated recycling of the ACN solvent. Not to mention, the FDA regulations that pharmaceutical clients are subject to can limit any modifications to be made to the system after process validation by the FDA

SOLUTION

Koch Modular addressed climate challenges by choosing corrosion-resistant materials and appropriate coatings that can withstand the sea breeze, as well as accounting for any possible galling that may take place with materials such as stainless steel. Also, it was determined that the trace propionitrile in the purified and recycled ACN product would cause any buildup issues, though an additional column was offered to guarantee elimination of even those trace amounts. The inflexibility of the FDA process validation regulations was overcome by thorough process development and maintaining constant communication throughout the project timeline to ensure that no modifications would be necessary later in the schedule.

RESULTS

Koch Modular provided a complete modular pressure swing distillation system designed to process their feed and provide a recovered product containing at least 95 wt% ACN and <0.5 wt% water. Ultimately, with the recovery of purified ACN, this system reduces any waste solvent disposal costs and offers cost-saving and environmental benefits. It also demonstrates the ability of Koch Modular engineers to work with the stringent regulations imposed on the pharmaceutical industry, and optimize construction materials depending on site climate conditions.