Gas scrubber design in pharmaceutical R & D

Kevin Hettenbach, University of Rhode Island


Pharmaceutical processes involving difficult to control off-gases are often transferred from the laboratory to the pilot plant without development and implementation of efficient gas scrubber operations. Two case studies are presented which involve effective scrubber design for mitigation of low boiling point volatile organic compounds (VOCs) based on scale-up from a laboratory bubble column to a pilot plant packed column, including: (1) a toluene/methanesulfonic acid (MSA) scrubber system to mitigate isobutylene emissions from tert-butoxycarbonyl (BOC) deprotection reactions, and (2) an aqueous ethanolamine scrubber system specifically to remove methyl bromide liberated during a demethylation process. On-line vapor phase mass spectrometry (MS) was used as a tool to aid in scrubber development, monitor reaction off-gas generation, and quantify scrubber efficiency on both laboratory and pilot plant scales to ensure safe and environmentally benign processes. The scale-up methodology involved determining the required pilot plant packed column superficial liquid velocity based on an equivalent physical liquid phase mass transfer coefficient (kL) for the laboratory bubble column. Utilizing an equivalent kL value upon scale-up resulted in essentially the same scrubber efficiency for both the isobutylene and methyl bromide scrubber systems. The acceptable isobutylene and methyl bromide loading rates for the pilot plant scrubber were determined based on the respective laboratory scale gas absorption rates for a fast, irreversible first order reaction of isobutylene in toluene and methyl bromide in ethanolamine. The scrubber design methodology was applied to a third case study involving an aqueous oxone scrubber system for mitigating dimethyl sulfide vapors/odors, such that pilot plant hydrodynamic factors and potential processing scale were determined based on laboratory results. Utilization of the scrubber design methodology eliminated the need for pilot plant experiments prior to scale-up. ^

Subject Area

Engineering, Chemical|Engineering, Environmental

Recommended Citation

Kevin Hettenbach, "Gas scrubber design in pharmaceutical R & D" (2009). Dissertations and Master's Theses (Campus Access). Paper AAI3401122.