Issue link: https://www.e-digitaleditions.com/i/666166
Tablets & Capsules April 2016 23 Process background Today, most tablet coatings are aqueous, but many pharmaceutical manufacturing operations still use VOCs such as ethanol and isopropyl alcohol (IPA). This includes the manufacture of active pharmaceutical ingredients (APIs) that are dissolved in VOCs and then spray-dried to create an amorphous solid or granules. Most of these processes are batch operations, and that leads to signifi- cant and nonlinear VOC concentrations in their exhaust. In fact, the VOC concentration often exceeds the lower explosive limit (LEL) by 100 percent. In the presence of an ignition source and sufficient oxygen, these process exhausts—if not mitigated—will lead to an explosion. Figure 1 tracks the emissions and LEL concentration of the exhaust from a fully loaded tray dryer that were mea- sured after heat was applied to drive off the VOCs. Approximately 30 seconds after heat was applied, the IPA concentration peaked at approximately 250 percent of LEL. If this stream were delivered straight to an oxidizer operating at high temperature, there would be an explo- sion. About 8 minutes after spiking, the VOC concentra- tion decreased to approximately 25 percent of LEL, which is the acceptance limit of most standard equipment that treat VOCs using catalytic or thermal oxidation. Fluid-bed processors can generate the same peaks, as Figure 2 shows. In this case, the processor's inlet air tem- perature is 40°C for 20 minutes and then remains at 45°C until the end of the production run. Following the initial product transfer into the fluid-bed dryer, the exhaust con- centration reached an initial peak concentration of Figure 1 Emissions from a tray dryer that include IPA LEL (%) and flowrate (kg/h) LEL % kg/h Time (m) 300 250 200 150 100 50 0 14.35 14.45 14.55 15.05 15.15 15.25 15.35 15.45 15.55 16.05 16.15 16.25 16.35 16.45 Figure 2 Emissions from a fluid-bed processor that include IPA LEL (%) and flowrate (kg/h) LEL % kg/h Time (m) 800 700 600 500 400 300 200 100 0 9.00 9.05 9.10 9.15 9.20 9.25 9.30 9.35 9.40 9.45 9.50 9.55 10.00 10.05 10.10