Cost reduction of solvent recovery in pharmaceutical plants – Case Study

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Use of Solvents

The pharmaceutical industry relies on the use of large quantities of organic solvents in a great number of manufacturing steps including chemical synthesis, fermentation, extraction, formulation and finishing of products. Solvents such as acetone, methyl ethyl ketone and tetrahydrofuran are commonly used as reaction media and for extracting products in the pharmaceutical, specialty chemicals and fragrance industries. Other solvents frequently encountered include hexane, dichloromethane, methanol, ethyl acetate, toluene, xylene, triethylamine, butyl acetate and isopropanol.

Solvent Recovery

Solvent disposal costs and VOC emissions control have been primary concerns in the industry for some time. For various reasons, there is an increasing interest in recovering solvents with the direct cost saving being one of the strongest arguments. In some processes with intensive solvent use, the cost of the solvent can be a significant proportion of the overall product cost.

Another compelling reason for recovering solvents is the increasing environmental legislation against emissions; such emissions may be as a result of a process design where solvent recovery was not incorporated at the outset, or where venting has occurred as a result of plant problems. With increasing commercial and regulatory pressures on pharmaceutical industries, the recovery, reconditioning and reuse of solvents is an important aspect of running production facilities efficiently. Further, the FDA initiative 'Pharmaceutical Manufacturing in the 21st Century' - with its goal of optimizing production processes so that quality becomes an integral element of the process - marks a crucial turning point.

Batch distillation

The most popular method of recovering solvents is filtration and distillation. Alternatively, carbon bed absorbers are occasionally used for filtration, and steam is then used to desorb and recapture the solvents. The disadvantage of this technique is that water is introduced into the recovered solvents and this must be removed before they can be reused. A batch distillation process is therefore employed to purify the solvent to an acceptable level for reuse.

Clearly, there is no advantage in purifying the solvent beyond the required level as this would represent wasted resources, so analyzers such as the MAXUM II process gas chromatograph are used to give an accurate, reliable, continuous online measurement of the concentration of solvents.

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