Minimizing Methane: Cow Version

One piece of advice I give to my students every semester in G-Chem is to be wary of lighting a cigarette in a field of cows. Especially if all their butts are facing you. My students are unlikely to face such a scenario in this day and age, but the trope always elicits laughter every time I’ve used it.

The oxidation of methane (CH₄) via combustion is a standard example in G-Chem. I use it in the first semester when students learn stoichiometry and how to balance chemical equations, but it also gives them practice drawing out the Lewis structures of all reactants and products. They can track which bonds are being made and broken in the chemical reaction, and given average bond energies make an estimate of the energy released in the reaction. The energy released is substantial per unit mass, and this makes methane (the main component of natural gas) an excellent fuel. In the second semester, we examine fuel efficiency in detail when we cover thermodynamics and kinetics, and methane combustion is compared to other fuels.

The classroom I teach in has a demonstration bench with a sink and a gas line. Students in G-Chem lecture are also co-enrolled in the laboratory, and they have covered lab safety issues and what to do when you smell ‘gas’. (Methane has no odor, but an additive is added so that human noses can quickly detect a gas leak.) There are enough cow fart jokes around that students typically know that cows release methane, and I probably discuss ‘natural’ gas in a humorous light (all puns intended). In class, I mimic turning on the gas line to prepare the students for the scenario; they should prepare to run away! (We also discuss why there is no explosion when gas leaks into a room full of oxygen until a spark lights things up! I've mentioned this in a previous blog post that discussed the possible origin of dragon fire.)

In any case, this week I was happy to read the following short article in Chemical & Engineering News (C&EN) on minimizing methane from cattle. It gives me some new factoids to add to my cow fart advice, but allows me to introduce more chemistry! Here’s what I learned: The annual methane release from a cow is typically 70-120 kg but the majority is released by burping, not farting. I’ll have to change the story I tell my students so they are aware that cows facing you are potentially more problematic. Also, about 7.5% of global greenhouse emissions comes from cows. That’s a big number! The hero of the story however is a cattle-feed additive with the active ingredient 3-nitrooxypropanol (3-NOP, but I will call it NOP for short). The picture below comes from the C&EN article where I have overlaid the line structure of NOP. The cow’s mouth is appropriately wide open!

The claim made by DSM, the company trying to add NOP to cattle feed, is that “a quarter teaspoon per cow per day is enough to inhibit the formation for methyl-coenzyme M reductase, an enzyme used by methane-generating microbes in a cow’s digestive system.” Tests on 48 cows over 12 weeks saw a 30% reduction in methane emissions. As a bonus, NOP also reduces the cost of feed (by 3-5%) because cows use less energy when they generate less methane, thus the cows don’t consume as much feed. Sounds pretty good, doesn’t it? It will be interesting to see how NOP competes with other ‘natural’ methane-minimizing additives (flax seed, linseed, garlic and citrus extracts), assuming its use is approved by regulators.

I might also be able to bring up this example when discussing climate change. Who knew that cow emissions could be so interesting!