Chemical manufacturing is a delicate process involving numerous stages. Each stage requires the utmost care to avoid contamination and maintain product quality. Distillation is a critical process that separates components in a mixture through heating and cooling processes.
Distillation methods fall into either batch or continuous distillation. Generally, batch distillation is useful when processing small volumes of special chemicals, solvent recycling and recovery, and pharmaceutical intermediates. Moreover, batch distillation occurs when input components change routinely, like new materials every batch. As a result, it promises flexibility, allowing seamless change across different chemicals.
On the other hand, continuous distillation is more common in fractional distillation columns for petroleum and bulk petrochemicals. In addition, the process is ideal where the material composition does not change frequently. The ceaseless nature of continuous distillation capitalises on bulk distillation and efficiency.
The right distillation method is crucial in chemical manufacturing. Therefore, the choice between batch or continuous distillation depends on the chemical and reactant materials’ volume. In addition, each distillation process has its unique features and limitations. Therefore, understanding the method that best suits the manufacturing needs requires an in-depth look into batch and continuous systems.
Batch distillation repeatedly separates components in a mixture batch-wise. The process is easy and yields high purity levels of the separated chemical.
Batch distillation is possible in a single column with multiple components separating into different receiver tanks. The application of batches optimises flexibility as a single process can manage several chemicals. Therefore, after distilling one batch, the column is open for a different component mixture, especially with automation. However, batch distillation is prone to contamination. Intermediate material between distillation processes should go to a slops receiver for recycling into the pot on the next batch. When switching to a new batch, trace amounts of the previous batch remain in the system and easily infiltrate the next lot. Fortunately, installing the Clean In Place (CIP) technology ensures there is no residue from the previous batch.
Advantages of batch distillation
- Batch distillation allows the separation of multiple chemicals with varying compositions into separate tanks and is, therefore, flexible. For example, running a single batch for a few days is possible and then changing to a new mixture after that.
- Batch processes can be fully automated using advanced control using ChemCad.
- The system often requires a single column with a still pot and two or three receiver tanks and is therefore cost-effective.
- When switching from one receiver to another, mistakes are rectifiable by recycling impurities into the still pot for the next batch.
Disadvantages of batch distillation
- Contamination is the greatest risk.
- The batch size depends on the still pot. Therefore, smaller pots can only accommodate small volumes of chemicals at a time.
Continuous distillation separates components without interruptions until the distillation process ends. The method accelerates the system’s efficiency as there are no limits to the mixture size for separation. However, the process requires more infrastructure, including more columns to accommodate the different chemical mixtures. The number of columns is expressed as N-1, where N is the number of separated components after distillation.
Advantages of continuous distillation
- The size of the pot does not limit the volume possible for distillation. Rather, the process quantity depends on the amount of upstream feed storage.
- Greater efficiency as the system does not need continuous cleaning and adjustment.
- Requires more infrastructure, including columns and resulting space requirements. Therefore, a multi-component system will need multiple columns, each with a reboiler, condenser, and reflux system.
- The need for more infrastructure has a cost implication, and the system is, therefore, more costly.
Batch and continuous distillation of chemicals are useful across multiple manufacturing industries, including fabrication engineering. However, remember that the best choice ultimately depends on the volume and nature of mixtures for separation. Finally, the choice must consider the cost implications, including repairs and maintenance.