Environmental considerations: treatment of exhaust gases from film-coating processes Graham SUMMARY Solvents such as acetone, methylene chloride, chloroform, ethanol and methanol must be prevented from entering the environment. Two options are available: convert all the processes to aqueous-based formulations or recover all the solvent by the use of an appropriate system. Recovery is expensive and is generally the reason for pharmaceutical companies to convert coating formulations to aqueous systems or formulate aqueous coating for all new products. Where this is not possible, a solvent recovery system must be used. Some options are discussed in this chapter together with. | Page 240 9 Environmental considerations treatment of exhaust gases from film-coating processes Graham SUMMARY Solvents such as acetone methylene chloride chloroform ethanol and methanol must be prevented from entering the environment. Two options are available convert all the processes to aqueous-based formulations or recover all the solvent by the use of an appropriate system. Recovery is expensive and is generally the reason for pharmaceutical companies to convert coating formulations to aqueous systems or formulate aqueous coating for all new products. Where this is not possible a solvent recovery system must be used. Some options are discussed in this chapter together with systems for removing particulates from the exhaust gases. INTRODUCTION No coating process is 100 efficient in terms of the amount of solids incorporated into the coating and the amount actually deposited on the tablets. Some losses will always occur. The efficiency of the process is very difficult to measure as the tablets themselves may lose weight by abrasion and by loss of moisture from the core during the coating process. Weighing the tablets before and after coating will not therefore give an absolute measure of the weight of coating deposited. Various workers have devised methods of measuring the amount of coating applied and have claimed efficiencies of 85-95 and even higher. Some of the coating material will be deposited on the pan and some will escape with the drying air in the exhaust system. Page 241 Material can be lost from the tablets in several ways. If the tablets are not dedusted before they are loaded into the pan the dust on them will be removed by the tumbling action intertablet friction and the exhaust air. If tablets are left rolling in the pan for any length of time without application of sufficient coating then the frictional effects of the tablets being in contact with each other and the pan will result in some weight loss. This material will be removed .
