They give OLED TV screens their color and protect rubber from being eaten away by oxygen. They’re a key molecular building block for everything from pharmaceuticals to fertilizers and herbicides. This important family of industrial chemicals — called hindered amines — is a silent ingredient in thousands of ordinary products we take for granted.
But there’s a problem: hindered amines, which are manufactured from petroleum, are difficult to make. “[A]ll of the existing techniques for producing these amines are complicated and expensive,” says engineer Milad Abolhasani, an associate professor at NC State University. That led Abolhasani and Malek Ibrahim, who was a postdoc in his lab, to begin searching for a better method for synthesizing the valuable industrial chemical.
“We were successful,” Abolhasani says. Their method, which incorporates a second catalyst and a continuous flow reactor, works up to 70 times faster than the most commonly used production process, the authors say. It’s described in a paper published Wednesday in the peer-reviewed journal Nature Communications.
An improvement to HAM
The new method builds on a process called hydroaminomethylation (HAM). It’s plenty going for it — it makes amines from cheaper inputs and in fewer steps, producing only water as a byproduct — but the chemical industry hasn’t widely adopted HAM because it’s too unpredictable. For instance, HAM can yield the wrong products. Researchers have figured out how to do HAM better, but putting those improvements into practice extends the manufacturing process for hours. What’s more, the catalyst, rhodium, is expensive.
Abolhasani and Ibrahim reimagined the process by making use of a continuous flow reactor. “ “Our HAM process takes less than 30 minutes in most cases,” Abolhasani says. “The only products are hindered amines and water. And we are able to recycle the primary catalyst, rhodium/N-Xantphos, which further drives down costs.”
A co-catalyst and continuous flow reactor make the difference
The researchers made two major improvements to the process. First, they figured out that using a second catalyst — fluorinated benzoic acid — would improve efficiency and bring down the cost of materials. “By designing a cooperative catalyst system, we’ve demonstrated that the rate of the HAM reactions in our system can be 70 times higher than the existing state-of-the-art processes,” Ibrahim says.
They also designed the process to take place in a continuous flow reactor. This change from conventional HAM offers several improvements. Continuously pumping gaseous and liquid inputs through the system makes it possible for engineers to speed up some of the reactions that happen during the manufacturing process, dramatically increasing efficiency.
“This process is also a good example for how flow chemistry platforms can improve catalyst turnover frequency, which is increasingly important as the price of rhodium catalysts goes up," Ibrahim says.
If the chemical industry embraces the new technique, this research will have ripple effecst that will touch consumers across the world — though few of them will ever know it.