Back in 2014, humans emitted 35.9 metric gigatons of carbon dioxide into the atmosphere, mostly from burning coal and natural gas in power plants, and other industrial processes. Chemical engineer, Lynden Archer has an idea if chemists could capture carbon dioxide and turn it into chemical building blocks for other product, the way plants do, carbon dioxide would not be a nuisance anymore, but a gift.
By injecting carbon dioxide deep underground, scientists have been trying to store it from exhaust flues at power plants and other emitters. Without large subsidies, however, this expensive carbon sequestration process may not be economically viable. Injecting carbon dioxide into old oil wells to drive out more oil is one application, but it’s not enough, and it’s not clear it even pays, given current low oil prices. Proponents of utilizing carbon rather than storing it hope they will profit by creating something of value from this waste product. The most likely applications use the gas as a raw material for making chemical products, which could also pay off by replacing petrochemicals with something greener.
Carbon dioxide is a stable molecule and doesn’t store much energy in its chemical bonds. To use it, chemists have to add energy, often through heating, which usually requires electricity. Much of that comes from power plants that burn coal or natural gas—emitting more carbon dioxide into the atmosphere, even more than was captured.
Carbon Dioxide (CO2) Crystal Structure
Paul Bunje, senior scientist in the Energy and Environment group at the XPrize Foundation, hopes that awarding a big prize for a solution will stimulate a diverse group of technologists. Next Wednesday, the foundation will announce that more than 40 teams are competing to win a $20 million prize. The winner of the Carbon XPrize, to be announced in spring 2020, will sequester the most carbon dioxide into a product of greatest net value. Some teams aim to make polymers or fuels to replace gasoline or industrial chemicals.
Archer is well aware of the pitfalls of trying to do environmentally friendly chemistry with carbon dioxide. “Usually, you consume so much energy that it’s cost prohibitive—but we get energy back,” he says. “That surprised us.”
The cell runs on aluminum and air. Inside, oxygen reacts with an electrode made of aluminum to form a highly reactive aluminum superoxide capable of reacting with otherwise reluctant carbon dioxide. The two react to generate aluminum oxalate. The fuel cell captures some energy from these chemical reactions, and although it requires a voltage to drive the reaction, the process appears to generate more electricity than it consumes, Archer says. Because the metal is consumed, choosing the right one is key. He settled on aluminum because it’s abundant and inexpensive. And even though aluminum production emits carbon dioxide, Archer hopes his system will capture enough carbon within oxalates to offset that.
The Cornell group cautions that it doesn’t fully understand the chemical reactions involved. The early version of the fuel cell uses an expensive material called an ionic liquid as the electrolyte, for example. If it plays a critical role and can’t be replaced, the technology may not be viable, says Archer.
Without pointing fingers at any project, in particular, Howard Herzog says many of those that promise to use captured carbon look a little too good to be true. Herzog is a senior research engineer at the MIT Energy Initiative and a proponent of carbon sequestration. “Carbon dioxide is spent energy,” he says. Getting value out of carbon dioxide in the form of commodity chemicals or energy, without putting more energy in somewhere in the life cycle of the product, is extremely difficult. “You can’t win in terms of energy. Thermodynamics tells us that,” Herzog says.
Although Herzog admits that some of the companies may be profitable, he’s skeptical about the potential for carbon utilization to have a significant environmental impact. He was a lead author of the 2005 IPCC Special Report on Carbon Dioxide Capture and Storage and says the report’s conclusions about carbon utilization still hold: The potential to make a dent in global emissions is small. Even if the chemical industry used carbon dioxide to make all its products—something no one thinks is likely—they couldn’t sop up all the emissions.
source - http://www.scientificamerican.com/