Greening Chemistry is a series of opinion columns, written by a rotating group of contributors.
I have a confession to make. When planning syntheses, I of course consider many factors that are key to general conservation and green chemistry principles: my starting materials, solvents, and auxiliary chemicals; their sources, risks, and disposal. But I routinely forget about the hidden ingredient—electricity. Fortunately, there are a multitude of ways we chemists can reduce the amount of electricity we use. It just requires thoughtfulness, creativity, or a bit of both.
Too often, I will tell a student to reflux their reaction overnight (Sorry, Isaiah!), or even over the weekend, in the sure knowledge that their reaction will have completed in that time. I will tell them how efficient this is with regards to their time, because the reaction will be bubbling away in their fume hood while they are doing something else. However, if I am sure that the reaction will be finished on their return, what I am really saying is that I know that it will be heated longer than is necessary.
This happens even though I am well aware that the greatest environmental impact of the work that we do often comes from the energy that we use. My research group recently conducted cradle-to-gate life cycle assessments of three different routes to one of our most commonly made ionic liquids (1-ethyl-3-methylimidazolium acetate). Sure, the study did what we had originally wanted and pointed to which route was best to use, but perhaps the bigger message was that electricity use was a major contributor to the impacts for all three routes.
“The greatest energy demand in chemistry laboratories comes from heating and cooling, especially when doing both at the same time.”
This has led me to think about simple ways in which we can reduce our energy demand. I am lucky to be in a modern building with things like energy-saving fume hoods built in. But few of us have any control over this level of investment.
Of course, one option is to buy a whole lot of the latest energy-saving equipment to replace what’s in use. Not only is this expensive, it will also lead to the disposal of plenty of perfectly serviceable kit, which itself is usually environmentally negative. However, it is important that when the time to replace old kit does come, we make low energy demand one of our key criteria.
The greatest energy demand in chemistry laboratories comes from heating and cooling, especially when doing both at the same time (for example, heating under reflux and solvent removal by rotary evaporator, or rotavap).
For those who have access to the appropriate equipment, microwave heating of reactions is now frequently used, with claims of better reaction outcomes as well as energy savings. But there is plenty that those restricted to conventional heating can do.
To return to my original example of heating under reflux, buying a simple power-socket timer has allowed us to continue to run our reactions when we are not there but to stop them in good time. Coupling this timer with an air condenser has allowed us to massively reduce our use of an energy-intensive recirculating cooler. Well-fitted metal heating blocks lose much less heat than oil baths do, and they avoid the messy problems associated with the oil. Finally, insulating the flask has enabled us to turn down the power of the heater, which it turns out is possible to set lower than 10!
My second example is isolating products by using a rotavap to remove solvents. There are similar solutions, such as covering the surface of a water bath with hollow insulating balls to prevent heat loss and so reduce electricity demand. Admittedly, these balls are plastic, but they can be used over again. But I would first ask whether you can design your reaction to avoid solvent removal completely. It is well known that having more steps in a series of reactions to get to a product leads to an increase in the amount of waste. Closer inspection shows that this waste is mostly associated with the isolations of intermediate products, usually in the form of discarded solvent. Each of these isolations will generally also require the use of a rotavap, with its associated heating and cooling. Designing the reaction so that these isolations are unnecessary prevents both chemical waste and energy costs. If the isolation of the product is necessary, is it possible to select a solvent in which the starting materials are soluble but the product is not, so that the product will precipitate and can be isolated by filtration?
Credit:
Courtesy of Tom Welton
My examples are by no means comprehensive, but I hope that they do offer food for thought when it comes to electricity use in the laboratory. By thinking about how we might adapt either our reactions or our equipment, or both, we can make great savings in our energy use, and with that our laboratory’s carbon footprint, while at the same time saving on those bills (even if it seems that someone else is paying them). What’s not to like?
Professor Tom Welton, OBE, is an emeritus professor of sustainable chemistry at Imperial College London and past president of the Royal Society of Chemistry. In 2004, he became the world’s first (at least as far as he knows) professor of sustainable chemistry.
Views expressed are those of the authors and not necessarily those of C&EN or ACS.
