By Mariah Quintanilla
We all know that bagel coated with sesame, poppy, onion, garlic, caraway and salt. Chemical engineer Nick Thornburg considers an ‘everything’ bagel a reasonable metaphor for an inefficient catalyst, or a compound that speeds up a chemical reaction. For those of us non-chemists, a longer explanation is required.
The point of his metaphor is this: understanding the structure of catalysts with less-selective chemistry (the ‘everything’ bagels of catalysts) is key when developing more efficient chemical processes for ‘greener’ industries.
The U.S. Environmental Protection Agency announced the winners of the Presidential Green Chemistry Challenge earlier this year, a competition incentivizing the use of green chemistry techniques. Initiated in 1996, the green chemistry challenge promotes chemical companies, business practices and researchers who have developed sustainable innovation in “chemical design, manufacture, and use.”
One of this year’s five winners Dow AgroSciences LLC, a chemical company based in Indiana, designed a fertilizer meant to reduce the amount of nitrate that leaches into the soil and ground water.
According to the EPA, a large percentage of the nitrate present in surface and ground water is due to leaching from agricultural activities. The environmentally friendly fertilizer also limits the amount of nitrous oxide emitted into the atmosphere.
When released into the air, nitrous oxide reacts with oxygen to form nitric oxide, a greenhouse gas that is around 300 times more impactful on the ozone than carbon dioxide. Green chemistry technologies like this Dow AgroSciences fertilizer are proactive solutions to the problem of pollution and waste.
What is Green Chemistry?
For non-chemists, the words “green chemistry” may evoke an image of flower-crowned hippies in lab coats, pouring herbal concoctions into test tubes. In truth, green chemistry is the fundamental first step in mitigating pollution, global warming, and our overall impact on the environment. Applying the sustainable principles of green chemistry to industrial systems is more or less like facilitating preventative healthcare for the environment.
The EPA defines green chemistry as, “The design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances.” As the Earth’s natural resources dwindle and toxic byproducts of industrial processes contaminate clean water sources and soil, the 12 principles of green chemistry challenge chemists and chemical engineers to rethink traditionally wasteful chemical processes and design less toxic chemicals.
We’ve made a mess
“We’ve been causing all of these unintended problems,” said Paul Anastas, director of the Center for Green Chemistry and Green Engineering at Yale University, in a phone interview. Traditional chemical processes are “wasteful, they’re toxic, and they’re prone to accidents,” he said.
One process prone to accidents is the use and transport of hydrogen cyanide (HCN), a highly toxic and flammable chemical that is a precursor for many common industrial chemical processes. Today, hydrogen cyanide is used to form the compound poly(methyl methacrylate) (PMMA), or the compound used to make shatterproof glass, said Thornburg, a Ph.D. candidate at Northwestern University who will soon begin work at the National Renewable Energy Laboratory in Colorado.
“Hydrogen cyanide is a horrible poison. To manufacture it at that scale, they have to rail car it across the country,” said Thornburg. “It’s so dangerous to handle and transport,” he said.
From 1995 through 2006, there were at least 32 recorded cyanide spills or leaks, according to the Rainforest Information Centre, a non-profit organization based in Australia. One such incident in 2003 led to the hospitalization of more than 100 people in Taichung County, Taiwan, after a truck transporting 35 tons of liquid cyanide overturned.
How can green chemistry help?
The principles of green chemistry, developed by Anastas and John Warner, president of the Warner Babcock Institute for Green Chemistry in Massachusetts, encourage chemists to incorporate sustainability, efficiency, and safety into every step of a commercial chemical process.
That begins at the molecular level and means designing safer chemicals that incorporate as much of materials used in the chemical process into the final product as possible. Green chemistry principles also encourage designing energy-efficient processes so chemicals quickly degrade and do not build up in the environment.
Although HCN spills pose an immediate threat to humans and animals, other chemical processes can create problems for people and the environment over time. In industrial neighborhoods such as on the Southeast Side of Chicago, black petroleum coke dust—a solid carbon by-product of oil refining resembling coal dust— once coated picnic tables and front porches in the areas surrounding KCBX Terminals, a petroleum coke facility owned by the Koch Brothers.
The terminals now serve as a transit point for train cars, trucks and barges, with no on-site storage piles, a victory for community environmental activists. Petroleum coke is still used as a fuel source in many countries and, when burned, it emits five to 10 percent more carbon dioxide than coal.
A 2013 Congressional Research Service report on petroleum coke noted that the refinery byproduct can threaten human health and the environment with the “release of common pollutants, hazardous substances, and high levels of the greenhouse gas, carbon dioxide,” when it is burned. Within the framework of green chemistry, chemical engineers would aim to produce less of a byproduct, Anastas said.
“A big part of green chemistry [also] focuses on using either no solvents, or greener solvents,” said Thornburg. Solvents are specific substances in which a chemical readily dissolves. The fifth principle of green chemistry calls for safer solvents because, more often than not, they contribute to the overall toxicity of a final product or byproduct.
“Chlorine, bromine and iodine are very toxic and very difficult to clean up. Most of their emittance into environment comes from solvents from chemical processes,” he said. They also tend to consume a great deal of energy in a chemical process because they are often heated, cooled, distilled or filtered.
Stopping pollution before it happens
In addition to the high energy costs, about 90 percent of the reactants and solvents that are used in traditional chemical reactions are not incorporated into the final product, said Anastas. That’s where the second principle of green chemistry comes into play, making sure no atom is wasted. “[In theory], every atom that goes into a chemical manufacturing process should be in the product,” he said.
By estimating the combined effects of all 109 of the Presidential Green Chemistry Challenge winners over the years, the EPA estimates sparing the Earth about 7.8 billion pounds of carbon dioxide, equivalent to removing 810,000 cars from the road. In truth, we have a long way to go before large-scale chemical processes will cease to negatively impact the environment.
This September we passed the 400 parts per million (ppm) mark of carbon dioxide in our atmosphere, concentrations that have increased by about 35 percent since the start of the Industrial Age compared to the previous 1 million years.
“People haven’t been trained historically on how to do green chemistry,” said Anastas. Some of the best chemistry, he argues, is developed by scientists who strive for complete sustainability because it forces them to approach problems creatively. That’s when comparing a catalyst to an ‘everything’ bagel begins to make sense.
For Thornburg, however, the logic of green chemistry is even simpler than a bagel metaphor. Most of us likely heard it from our parents when we complained about having to clean our rooms.
“Let’s just not make a mess in the first place,” he said.
