Green Chemistry Principle #3: Less Hazardous Synthesis

By Kenny Chen, Member-at-Large for the GCI and Laura Reyes, Co-Chair for the GCI

3. Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

The idea of practicing safe chemistry sounds intuitive, but contemporary technology, policy, and knowledge of long-term health and environmental impacts are often limiting factors in determining how safe a process is. In other words, scientists are always working with what they have in terms of technology and knowledge of hazards, and that story may change as we learn more.

In our video, we briefly described the recent history of technologies used to generate chlorine gas, focusing on the transition from mercury cell processes to membrane cell processes.

Chlorine has been produced industrially since the 19th century, when it was widely used in textiles and paper industries. Nowadays, it is essential in many plastics and chemical industries, for example to make the plastic polyvinyl chloride or PVC.

In the past, the mercury cell process was widely used to make chlorine. We now know that resulting contamination from mercury waste has tragic health and environmental effects, but that was not always the case due to previous limitations in technology, knowledge of heavy metal accumulation, and resulting policies. For example, as we talk about in the video, the mercury cell-based chloralkali process caused the infamous case of Minamata disease that struck Ontario in 1970, severely affecting two native communities.

Now, the membrane cell is the preferred choice for the chloralkali process. The increased use of this cellulose-based technology has resulted in decreased use of the mercury cell, which in turn has reduced mercury emissions into the environment.

Despite large improvements, even in 2013 more than 5 tonnes of mercury were released into the environment due to the chloralkali process, which leaves significant room for improvement as we move forward, whether by improved technology or stricter regulation.

Sometimes, we can’t help but learn new information over time about the long-term safety of technologies and chemical processes. Even so, we must use the knowledge that is available at all times so that we can create and modify processes that are less hazardous by design. In this way, we will have inherently safer chemistry by keeping green chemistry principle #3 in mind.

References

Handbook of Chlor-Alkali Technology – History of the Chlor-Alkali Industry (http://link.springer.com/book/10.1007%2Fb113786)

Best Available Techniques (BAT) Reference Document for the Production of Chlor-alkali (http://www.eurochlor.org/chlorine-industry-issues/chlor-alkali-bref.aspx)

Chlorine Industry Review 2013-2014 (http://www.chlorinethings.eu/files/downloads/annual-report-2014-full-final.pdf)