Activated carbon is used to eliminate the coloured impurities produced in the reactor during the synthesis of active pharmaceutical ingredients. Composed of porous carbonaceous material that retains undesirable molecules by adsorption, it is used to purify and decolourise the products synthesised. Activated carbon can be added directly to the reactor before being filtered, or better still, as the media in a filtering device.
Free carbon filtration
The classic technique involves pouring free activated carbon directly into the reactor, once API synthesis is complete, and then filtering off the carbon saturated with impurities. Depending on the quantity and particle size of the carbon used, this second stage can be carried out using a series of standard filter bags and cartridges or high-performance filter bags, which are essential for black fines. The latter are made up of several layers of non-woven polymers, up to 8. To optimise the distribution of the granulometric load and therefore ultimately the life of these bags, the different layers that make them up have increasing densities in the direction of fluid flow. Elimination efficiency is 99.98%.
Choose the right filter bag geometry for free carbon filtration
Pay attention to the geometry of the filter bags used to recover the free carbon in the reactor. They should be conical rather than cylindrical to facilitate their extraction at the end of the purification-decolourisation process. The carbon particles, of the order of a few microns, tend to settle to the bottom of the bag, carried along by the fluid during filtration. This effect, combined with the differential pressure that presses the bag against its support basket, makes extraction difficult at the end of the process, sometimes even tearing cylindrical bags apart. This results in tedious cleaning steps and an additional risk of exposure for operators. With a conical bag, the coal is more evenly distributed and it is much easier to remove it from its support without tearing it.
Use filter elements integrated with activated carbon
Instead of using free carbon, filter cartridges or lenticular modules with activated carbon media can be used. These alternatives eliminate the need to handle powdered carbon and the subsequent filtration required to recover it from the reactor. More compact, cleaner and easier to handle, these devices are also more economical. They are made from high-purity activated carbons, such as Norit grade SX Ultra. This pharmaceutical-grade carbon also meets the requirements of the Food Chemical Codex. Particular attention must be paid to the speed at which the fluid passes through these elements, to optimise filtration quality without excessively slowing down the API production process.
