A continuous way to improve chemical manufacturing!

I first walked into a chemistry laboratory in Grade 8, and instantly fell in love with the Round Bottom Flask (RBF) and the varied smells, colours, and textures emerging from it. No matter what you put into the flask you would invariably get a new product each time you placed it on a Bunsen flame. This was pure magic!

Over time, I realized that this ‘multi-talented’ RBF was not that great after all. When extrapolated into a vessel of a larger size – say an Industrial Tank Reactor – the RBF transformed into a dangerous weapon!

Why? When you put a large amount of reagents A and B in a tank reactor, plenty of heat is generated with very cramped space for dissipation. This invariably leads to an explosion. One way to prevent this is to slow down the reaction by adding a large amount of solvent(s). However, this could lead to two problems — decreased yield and excess effluent generation. What is needed is a balance between speed and control, and this is where I am hoping to make a difference.

The IITB-Monash Research Academy, where I have enrolled for a PhD, is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

My project is an earnest attempt to make the current industrial chemical manufacturing better — using a combination of Continuous Flow Chemistry and Heterogeneous Catalysis.

In flow chemistry, a reaction is performed by pumping in the reactive starting materials through tubes or coils as seen in Figure (1) instead of a flask.

In conventional RBFs and industrial tank reactors, the volume that could be held at a time is constant and repeated different batches of reactions are needed to produce a large yield. On the contrary, a reaction could be performed continuously through flow — the process does not stop as long as the starting reagents are pumped in. This not only enables on-demand production but also reduces batch-to-batch variability. Depending on the number of reactions needed to attain the final product, multiple steps could be conveniently performed by simply tailoring the number, nature, type and dimensions of the reactor coils involved. This not only makes the overall process quicker and safer, but also improves the yield, with added advantages like the ability to characterize the reaction progress in-line or during the flow of the reagents and the ability to automate the entire series of reactions no matter how large the process.

To cut a long story short, a reaction that would take 24 hours in a conventional round-bottom reactor in a lab-scale, could be completed within less than 30 minutes in a continuous flow reactor; that too in a safe, efficient and continuous (scalable) fashion.

So how does Heterogeneous catalysis help? This is a type of catalysis where the phase of the catalyst differs from the phase of the reactants or products. In contrast, during homogeneous catalysis, the reactants, products and catalyst exist in the same phase. Heterogeneous catalysis offers many advantages. A reaction that has been uncatalyzed will take hours or even days more to get completed than its catalysed counterpart. So, we see that both these methods are excellent in their own individual ways for making a process faster, easier and more feasible. Imagine what the result would be if the two could be combined?

My project focusses on the concept of process intensification through continuous flow. In simplified terms — a way to make reactions easier, safer and more efficient for both humans and nature.

How well a heterogeneous catalyst can function in a reaction depends on various factors, of which the two most important are morphology (structural shape or size of a material) and yield. It is in these areas that Continuous Flow Chemistry can be employed to simultaneously achieve both – speed on synthesis and control on the process — without the use of any highly technical resources or equipment.

In order to demonstrate this, we synthesized two materials through continuous flow; the morphology of which is depicted in Figure (2). It yielded results which were not just comparable in morphology and quicker (involving less than or equal to half the amount of time needed through the traditional batch techniques), but were scalable as well. For instance, KCC-1 could be produced within 0.5-1 hour through continuous flow when the traditional batch techniques needed 1-4 hours; and PANI, within 5 minutes and a throughput of 17-30 g/h through continuous flow as compared to 24 hours with a maximum throughput of only 3 g/h. These studies prove how continuous flow synthesis can provide a controlled and scalable solution for synthesizing crucial catalytic materials.

Further, polymeric emulsion foams, called PolyHIPEs or PHPs, have been synthesized (morphology included in Figure (2) as well) through conventional batch techniques and can be employed in the demonstration of reaction efficiency in scalable high-throughput dynamically stirred continuous flow reactors, in various industrially important processes like Suzuki coupling, which form the synthetic base of a plethora of pharmaceutical molecules and commercially important products.

Now if I get a chance to go back to school, I will definitely take my Grade 8 chemistry teacher out to lunch!