Why is separation a key technology in chemical engineering that determines product quality and cost?

In chemical engineering, separation processes are essential for obtaining the desired product and are responsible for efficiently separating the different substances produced after a reaction. Various techniques, such as distillation and membrane separation, can be utilized to increase purity and reduce costs, and they play an important role in many industries beyond chemical processing.

 

This year, rice farming is not doing so well due to the frequent rains. Nevertheless, when harvest time comes, the countryside is full of life. But imagine if, after a bumper harvest, all the threshers in the country are broken and unable to separate the rice grains. Farmers would have to worry about their livelihoods because of unsold rice. This is because what we value is the grain of rice that can be separated from the husk and eaten, not the grain surrounded by the husk.
Something similar is happening in the chemical industry. If the chemical industry is the production of products from raw materials through chemical reactions, the chemical reactions are analogous to farming, and the separation of the desired substances from the resulting products is analogous to the threshing process. Just as the threshing process is essential for rice to be edible, so is the separation of the desired substances. The stream of material exiting a chemical reactor does not contain only the desired product substance, but many other substances. The feedstock has impurities, and when unwanted reactions occur, the resulting products must be removed, and any feedstock that does not react completely is also an impurity.
These impurities can cause unwanted reactions, deteriorate the mechanical properties of the product, or cause various adverse effects on human health and the environment. Therefore, the products produced by chemical reactions must be separated and purified to become valuable products.
The most commonly used device in the separation process is the distillation column. You’ve probably wondered about the tall, towering structure that is the most recognizable feature of a chemical plant. Just like water boils at 100°C, every substance has its own boiling point, and distillation is a way to separate substances by taking advantage of the fact that different substances have different boiling points.
It’s easy to find examples of distillation in everyday life. For example, spirits like whiskey and shochu are alcoholic beverages that have been concentrated through distillation. Alcohol has a boiling point of around 78°C, and maintaining a temperature between 78°C and 100°C allows the alcoholic components to vaporize better. The water component, on the other hand, remains liquid, so collecting the evaporated gases yields a liquid with a high alcohol concentration. In the production of chemicals, this distillation principle is applied on a much more complex and large scale. The distillation columns used in chemical plants usually require a purity of more than 90%, so the size and complexity is a far cry from the devices used to distill alcohol, but the basic principle is the same.
As you can imagine from the size of the distillation column, the cost of the separation process is quite high, sometimes much higher than the chemical reaction. Especially for products where purity is important, it is not uncommon for the separation process to cost more than 50% of the final product price, including raw materials, transportation, storage, etc. For this reason, separation processes occupy a central place in chemical engineering, and in extreme cases, separation alone, without chemical reactions. A prime example is the oil refining process, where the main objective is to separate the various components already contained in the oil. While some chemical reactions are utilized in this process, it is primarily centered around separation.
In recent years, several other separation techniques have been explored in addition to distillation. For example, membrane separation involves the selective separation of gaseous or liquid substances by passing them through a very thin membrane. Compared to distillation, this technology uses less energy and has a lower environmental impact, making it the next generation of separation technology. Adsorption, on the other hand, selectively adsorbs and separates substances on a solid surface and is often used to remove certain contaminants from air or water.
Separation processes are not only an integral part of these chemical processes, but also play an important role in other industries. For example, in food processing, separation is used to remove impurities from beverages or cooking oils, or to concentrate certain ingredients from raw materials. The pharmaceutical industry also relies on separation to increase the purity of compounds for drug development. The need for separation processes in these various industries is vital, as it ensures the quality and safety of the products produced.
In chemical engineering, separation is not just a process, but a critical factor that determines the quality and price of the final product. Without separation, the substances produced by chemical reactions cannot be properly utilized, and improper separation can lead to poor product performance or adverse environmental impacts. Separation processes will continue to be researched and developed as a key area of chemical engineering. The technology of separation processes is essential in order to make the various products we use more efficiently and safely. This will allow us to get better products and maintain a sustainable environment.