Stubborn Emissions
At this point you hopefully have a decent idea of carbon dioxide’s role in climate change, the latest trends in our energy economy, and the challenges we face in reducing emissions to meet the goals laid out by the Paris Agreement. We can see that the market share of renewable energy is steadily rising, and government and industry are increasingly facing pressure to decarbonize. Yet, at this rate, we are likely to fall severely short of meeting the emission targets required for a chance to keep global temperature rise below 1.5°C. The transition away from fossil fuels is simply too slow.
But even the most die-hard decarbonization advocates among us might agree that going cold turkey on fossil fuels would require unrealistically radical lifestyle changes. For example, let us consider the most optimistic case in which the entire planet’s electricity demands could be sustained by renewable energies. What would the world look like if we were to immediately stop using all hydrocarbon fuels?
For one, global food security would be severely threatened due to the termination of fertilizer production and a shutdown of most freight transportation. Jobs would need to be replaced overnight for everyone working in the manufacturing, agriculture, and transportation sectors, let alone those working directly in the fossil-fuel industry. Commodities that required petroleum products, including many essential chemicals and pharmaceuticals, would be discontinued until new syntheses were discovered. Most of the population, in both high- and low-income countries, would be forced to abandon their gasoline-fueled cars and motorcycles. All commercial air travel would come to a halt. Beyond the social and political barriers described in chapter 3, the speed of the transition to an emission-free world is clearly limited by certain “stubborn” emissions of the industrial and energy sectors. To understand what makes these sources of GHG emissions so stubborn, we need to look in detail at their source.
The Devil Is in the Details
In chapter 1 we briefly described how industrial and chemical processes typically generate GHG emissions in two ways. However, if we are to be specific, they do so in three ways. The first is by the burning of fossil fuels to generate the high temperatures needed by many chemical processes. These emissions are associated with delivering energy to the process. This can be thought of as the energy required to heat your oven when you are baking bread. For example, the production of ammonia, the principal building block in all the world’s fertilizer, requires temperatures as high as 450°C. When considering the scale at which many of these chemical products are made, one can quickly appreciate their planetary impact from heating alone. The chemical industry currently consumes roughly 10 percent of the world’s energy, most of which is derived from burning fossil fuels. Emissions associated with supplying energy (i.e., heat) to industrial processes can be eliminated by using heat that is derived from renewable energy sources. Burning fossil fuel for heat might be convenient and economically favorable but certainly not necessary.
The second way in which chemical manufacturing emits GHG emissions is through the production of the feedstock chemicals. This aspect of chemical manufacturing is not trivial: while energy accounts for roughly 40 percent of the fossil resources used in the chemical industry, the remaining 60 percent are used as chemical feedstock.166 In our baking analogy, feedstock chemicals are equivalent to the ingredients in a recipe. Many of these ingredients may have associated emissions. For example, the flour originates from wheat or other starchy plants and undergoes multiple steps, including washing, drying, grinding, processing, and maturing before it is ready to be used. Most of these steps require some form of energy (e.g., heat for drying, and mechanical energy for grinding) and therefore are likely to have associated GHG emissions. In the world of chemical manufacturing there are certain feedstock chemicals that are widely used for a variety of processes, much like flour is a common ingredient found in most baking recipes. One of the most common “ingredients,” or feedstock chemicals, is hydrogen gas. Unfortunately the most common method of producing hydrogen on an industrial scale, steam methane reforming, is extremely energy intensive. In steam methane reforming, methane (natural gas) and water are brought to extremely high temperatures and pressures to make carbon monoxide and hydrogen. This process itself requires a great deal of energy to reach such high temperatures and requires natural gas, a fossil fuel, as a chemical input. Fortunately this is not the only known way of producing hydrogen gas. Hydrogen can be produced from the electrolysis of water, which involves using an electric current to split water into its components, hydrogen and oxygen gas. Not all chemical feedstocks, however, have an alternative way of being generated, many being fossil-derived hydrocarbons themselves. Therefore, employing electricity generated from renewable sources can potentially address some, though not all, of the emissions associated with producing chemical feedstocks.
Feedstock: a chemical or material used in a manufacturing process.
Steam methane reforming: a chemical process in which syngas, a mixture of carbon monoxide and hydrogen, is produced from hydrocarbon fuels, typically methane (natural gas) and water.
Carbon monoxide: a colorless, odorless, and poisonous gas consisting of one carbon atom and one oxygen atom. It is widely used in chemical manufacturing.
Electrolysis: a process in which direct electric current is used to drive a non-spontaneous chemical reaction. Electrolysis of water involves using electricity to decompose water into hydrogen and oxygen gas.
The third way in which chemical and industrial processes can produce emissions is by the nature of the process itself; that is, carbon dioxide can be a by-product of an industrial reaction. This is equivalent to the release of carbon dioxide that happens when dough is baked. At this point you might be wondering, “What is carbon dioxide doing in my dough?” Without our going into full details of the science of bread making, many bread recipes require that the dough rise before being baked. At the molecular level the rising occurs because yeast in the dough consumes sugars and converts them into carbon dioxide, creating little pockets of gas that cause the dough to expand. The carbon dioxide is then released when the dough is baked. These carbon emissions have nothing to do with the energy required by the process; rather, they are intrinsic to the chemical reaction of baking bread. Similarly certain industrial processes result in carbon emissions that are by-products of the reaction. They result from the chemical nature of the reaction, rather than from the need to produce energy. This third type of GHG emission, common to the industrial sector, cannot simply be eliminated by employing renewably-sourced energy.
Using electricity derived from renewable sources can eliminate the carbon emissions associated with the heat and the hydrogen required for many chemical and industrial processes. Electricity can replace fossil fuels to generate heat, and electrolysis can provide a sustainable, emissions-free way of producing hydrogen. We should point out that, even though a solution exists, it does not mean that it can be implemented overnight. Practically speaking, we must consider priorities when it comes to implementing low-carbon energy. To start by replacing the most carbon-intensive pathways with low-carbon or zero-carbon solutions would be the most effective means in terms of emission mitigation. Replacing our fossil-based industrial sector will require a reinventing of much of our existing infrastructure: electrolyzers will be needed to generate hydrogen gas, industrial reactors will have to be redesigned and rescaled to accommodate electricity-derived power, and massive amounts of low-carbon electricity will need to be generated and made accessible. The main challenge lies in the latter point – the scale of low-carbon electricity that would be required. This is not to say that electrifying our chemical industries is impossible – it is technically feasible – but it is not yet achievable under current trends in renewable-electricity production. Overcoming this challenge will require large investment by stakeholders and aggressive policy from governments to kick-start its development.
There remain those “stubborn” emissions that are either associated with certain chemical feedstocks or intrinsic to the reactions themselves. These are harder to address from a technological standpoint and require a rethinking of certain industrial processes altogether. The industry’s non-trivial reliance on fossil resources, and its resulting emissions, is the reason that chemical manufacturing is anticipated to be the single largest source of oil consumption by the year 2030. Although we have focused much of this discussion on the industrial sector, the transportation sector also has a stubborn emissions problem, as mentioned earlier. As we saw in chapter 1, electric vehicles are steadily occupying a greater share of the market; however, despite demonstration of electric heavy-transport-vehicle prototypes – and commercial adoption in some instances – they are unlikely to reach the commercial scale required to meet emission targets. It will be difficult to cut completely our usage of hydrocarbon fuels.
The key point we wish to illustrate here is that even with the most aggressive investment in renewable energy, which itself is not without its own set of challenges, it would be next to impossible to render our existing industrial processes and transportation usage completely emissions free. Generating electricity from renewable sources, despite being effective and necessary in the battle against climate change, alone cannot enable a rapid transition to a zero- emission economy. There must be other ways to help us achieve net-zero emissions.
To Remove or to Capture?
The concentration of CO2 in the atmosphere is dictated by the amount going in, as well as that going out. Most of the conversation around climate action tends to focus on stopping further emissions from entering the atmosphere, and rightly so. After all, anthropogenic emissions are something our species should be able to control. However, is it possible that we have reached a point where we need to start seriously considering removing emissions from the atmosphere or capturing stubborn emissions right at their source? If we removed more carbon dioxide from the atmosphere than we put in, could this grant us additional time to transition our economy? And if we were to remove it, where would it go?
The next section will address some of these questions. First, let us clarify some terminology. Removing CO2 versus capturing CO2, although similar, are slightly different concepts. Carbon dioxide removal (CDR) involves removing carbon dioxide from the atmosphere. Carbon capture, by contrast, involves capturing CO2 at a point source, such as a stream of industrial waste gas, before it escapes into the atmosphere. Carbon capture is a way to avoid emissions, whereas CDR is a solution to remove emissions that have already accumulated. Much like the separating of recyclable items from trash at home beats the sifting through garbage in a landfill, one can quickly appreciate how carbon capture is more practical than CDR. In addition, capturing carbon emissions before they escape into the atmosphere is both easier and cheaper than using technology to remove emissions that are already in the atmosphere. According to the IPCC, CDR can help resolve these otherwise “hard-to-decarbonize” sectors. It estimates that 100 to 1,000 Gt of CO2 removal will be necessary during the twenty-first century to ensure that warming goes no higher than 1.5°C.79 To give some perspective, this will likely require us to be removing up to 15 Gt of CO2 per year by 2100 – the equivalent of all of humanity’s CO2 output in 1970.
Before proceeding any further, let us not forget that CDR already exists in nature thanks to photosynthesis. Photosynthetic plants and organisms convert carbon dioxide and water into biomaterials, such as sugars and cellulose, using sunlight. In the grand view of the carbon cycle, afforestation strategies, biomass plantations, or algae farming serve the purpose of enhancing the storage capacity of the terrestrial and oceanic sinks. The natural decomposition of biomass does eventually release carbon dioxide back into the atmosphere, through the earth’s natural carbon cycle, as discussed in chapter 2. One way of holding the carbon captured by plants indefinitely is to convert it into biochar and then bury it deep in the soil to prevent its decomposition back into CO2.167 Biochar is a form of charcoal produced by subjecting biomass to very high temperatures in the absence of oxygen. The oxygen-free nature of the combustion prevents carbon from escaping in the form of carbon dioxide, yielding a black brittle material that has an energy content superior to that of its original biomass. Biochar’s carbon-rich composition renders it an effective soil enhancer, as discovered by the pre-Columbian peoples of the Amazon who used it extensively over centuries to enrich and make productive what was otherwise sterile land. Its long-term stability makes biochar a particularly effective form of carbon sequestration because it can last in the soil for up to thousands of years.
Biochar: a carbon-rich solid residue (charcoal) that remains stable for up to thousands of years; it is often used as a soil enhancer.
Alternatively, biomass can be processed in biorefineries, facilities that convert biomass into a wide array of products, most notably biofuels. Many different types of biorefineries exist at various stages of technological and commercial development, but all are based on the same general concept, that is, breaking down plant matter into its component sugars, starches, oils, and cellulose, using some combination of heat or chemical treatments. Common examples of biomass feedstocks include corn, wheat, cassava, sugarcane, sugar beet, and wood. The versatility of feedstock allows biorefineries to produce a wide range of products, including oil, dietary fibers, pulp and paper, glycerin, and cattle feed. For example, ethanol can be made from corn, biodiesel from palm oil, and aviation fuel from sugarcane.* Many important chemicals used in industry can be obtained from lignin, a polymer compound found in the walls of plant cells alongside cellulose that is often a waste by-product of biorefining operations. Recovered lignin can be used for a range of applications, including glues, plastics, and carbon fibers, or broken down further to create a feedstock that can be used to manufacture a wider range of chemicals.
Biorefinery: a facility, process, or plant that con¬verts biomass into a range of products.
Biofuel: a fuel produced through biological, rather than fossil, sources; biofuels include ethanol, biodiesel, and green diesel.
Unlike biochar, the biofuels created from biomass do not offer long-term carbon sequestration: burning biofuels, after all, releases carbon back into the atmosphere. While proponents of biofuels might argue that making fuels from biomass can help to keep fossil carbon in the ground, the climate impact of biofuels is not so simple. Wood and plants are more renewable sources of carbon when compared to fossil reserves; however, this rests on the assumption that the rate of plant regrowth is adequate to offset biofuel’s carbon emissions. Dynamic lifecycle analysis of biofuels from wood estimates that it would take between 44 and 104 years for biofuel emissions to be recaptured by the terrestrial sink.169 So, although it could potentially play a role in managing carbon emissions over the long term, the time scale of biofuel’s carbon payback does not align with our short-term mitigation goals. It becomes even harder to justify the use of biofuels when solar energy is undisputedly scalable to any future demand, is already used on a large scale to produce heat and electricity, and poses little or no competition with agricultural land. This said, biofuels could make sense in some specific contexts. For example, a sawmill could be powered by its own wood scrapes, where biomass waste is generated regardless, and jet fuel could be made from biomass instead of exclusively from refined petroleum sources.
Today, however, carbon capture technologies are certainly not limited to natural sequestration mechanisms in the form of biomass. Chemical separation technologies can filter out carbon dioxide from highly concentrated streams of industrial waste emanating from smokestacks. Steel mills, refineries, and power, cement, and fertilizer plants all are suitable carbon capture sites because they offer point sources of carbon. Currently, there are twenty large-scale carbon capture projects worldwide, most of which are integrated with industrial operations. According to Julio Friedmann, senior research scholar at Columbia University’s Center for Global Energy Policy, these facilities currently capture 40 million tonnes of CO2 per year – the equivalent of taking eight or nine million cars off the road.170 Unsurprisingly, sectors possessing stubborn emissions, namely chemical, iron, steel, aluminum, and cement manufacturing, are the most common to employ carbon capture technologies.
When carbon dioxide is sequestered via biomass, the plant’s natural photosynthetic mechanism takes care of the hard work. Capturing carbon dioxide without the help of photosynthesis, it turns out, is not trivial. Several strategies for capturing CO2 from both concentrated and diluted sources are currently under investigation. These include physical and chemical absorption into solutions, adsorption by different classes of solid materials, and cryogenic and membrane separation technologies.
Absorption: a process in which a fluid is dissolved by a liquid or a solid.
Adsorption: a process by which atoms or molecules adhere to a surface.
Cryogenic: occurring at very low temperatures, typically less than −150°C.
The most common method for capturing carbon dioxide at atmospheric pressure from large-scale industrial emitters is by using amine solutions in a chemical absorption process. Amines are renowned for their ability to react reversibly with carbon dioxide, meaning that while they can easily react to form chemical bonds with CO2, under the right conditions, the reverse is also possible. The direction of the reaction is controlled by temperature, allowing CO2 molecules to be “picked up” and subsequently “released” as needed. In practice, this involves flowing a flue gas, typically composed of 10–15 percent CO2, through two chambers connected by a recirculation system. Both chambers contain an amine solution; however, the first chamber is held at a lower temperature of roughly 40°C, and the second sits at a higher temperature of 100°C. Upon passing through the first chamber, CO2 molecules in the flue gas react with the amine solution to form carbamates and bicarbonates. The flow then continues to the second chamber, where the higher temperature causes the release of relatively pure CO2 from the carbamate-bicarbonate solution. In practice, the process takes place in two towers, referred as the absorber and the stripper. The gaseous waste stream rises up the absorber tower, where it contacts a downward flow of CO2-catching amine solution. The CO2-rich amine solution is then sent to the stripper tower, where heat from rising steam releases, or strips, the CO2 from the amine, which is returned to the absorber.
Amines: chemical compounds that contain a nitrogen atom and a pair of lone electrons.
Flue gas: gas exiting a pipe into the atmosphere.
Carbamate: an organic compound derived from carbamic acid.
Although the amine CO2-capture systems are well developed, they have several drawbacks including the energy consumption needed for the second chamber, as well as corrosion and degradation limitations of the CO2-capture absorbents. Research in this area is therefore mainly focused on increasing the rate at which the amines react with CO2 and decreasing the temperature required for the release step. Improvements can be made through slight modifications to the chemical structure of the amine molecule. The difficulties experienced with amine solutions can alternatively be circumvented by using solid sorbents – typically, amines chemically tethered to silica particles or porous materials – such as zeolites and metal organic frameworks (MOFs), which have high and selective absorption capacities for CO2.
Sorbent: a molecule used to absorb liquid or gases.
Zeolite: aluminosilicate minerals characterized by their microporous structure.
Metal organic framework (MOF): a class of compounds composed of metal atoms attached to organic molecules that form a characteristically porous structure.
According to the laws of thermodynamics, the higher the concentration of CO2, the less energy is required to capture it. Simply put, it is easier to collect CO2 from concentrated sources, such as flue-gas streams, than from thin air. For this reason, carbon capture is most effective, in terms of both energy and cost, when applied at point sources, such as cement manufacturing, chemical refineries, and power plants.171 Capturing CO2 from more concentrated sources, however, is not without its challenges. The high rates and variable compositions of flue-gas streams can make efficient extraction of pure CO2 tricky. Anyone who has used a water- filtration system knows that the process is certainly not instantaneous. Similarly, filtering CO2 out of industrial flue-gas streams involves a trade-off between the speed of the process and the quality of the product. Separating carbon dioxide from a stream of industrial waste gas can therefore be made easier by ensuring that the stream is as concentrated as possible. Power plants that employ carbon capture technologies can take one of three different approaches to purifying their waste carbon emissions so that they might be more readily captured. These approaches are known as post-combustion, oxy-fuel combustion, and pre-combustion.
Post-combustion is the simplest approach from a process standpoint. It involves sending the untreated stream of flue gas directly through a carbon-dioxide-capture unit, such as the one based on amine-solution technology described previously. No special tweaks are needed to the process: fossil fuel is combusted in air, and carbon dioxide is separated from the waste stream. Post-combustion carbon capture is used at the Boundary Dam Carbon Capture Project in Saskatchewan, Canada, which sequesters nearly one million tonnes of CO2 per year at the site of a coal- fired power plant.
Oxy-fuel combustion and pre-combustion employ further steps to produce more concentrated CO2 streams. In oxy-fuel combustion, oxygen is first separated from air and then mixed with recycled flue gas. The fuel in question is then combusted by this mixture of oxygen and flue gas, rather than by air. This produces a stream of flue gas mostly composed of CO2, which can be readily captured. Although oxy-fuel combustion is practiced in some industries, such as welding and metal cutting, in which a heat source is readily available, it has yet to be adopted for power generation due to the high cost associated with separating oxygen from air. Several pilot-scale projects currently exist, seeking to develop oxy-fuel combustion to sequester carbon emissions from power plants.
Finally, pre-combustion involves taking the fuel in question and exposing it to air at extremely high temperatures and pressures to make synthesis gas (a mixture of hydrogen, carbon monoxide, and CO2; also known as syngas), in a process known as gasification. The syngas then undergoes a chemical reaction to yield a rich mixture of hydrogen and CO2 (the concentration of CO2 in this mixture can be as high as 50 percent), making it much easier to subsequently capture the CO2. This is the capture method employed by the Great Plains Synfuels Plant in North Dakota, which produces methane (natural gas) from coal. Since it began integrating carbon capture into its process in 2000, the facility has captured three million tonnes of carbon dioxide that would otherwise have been released into the atmosphere. In all these approaches the separated stream of CO2 can be further purified and compressed for transportation.
Synthesis gas (or syngas): a mixture of hydrogen and carbon monoxide (and often small amounts of carbon dioxide). Its name derives from its use as a precursor to making synthetic natural gas.
Up until now, our discussion of non-photosynthetic means of capturing carbon dioxide has focused exclusively on capture from industrial waste streams. As mentioned earlier, capturing from concentrated sources is much easier, energetically speaking, than capturing from dilute sources. It should therefore come as no surprise that 90 percent of the existing non-photosynthetic CO2-capture capacity currently in operation is integrated with industrial processes to capture from highly concentrated waste streams.172 However, we cannot neglect that a significant portion of emissions derive from small distributed sources, such as transportation and buildings. It is therefore also important to develop methods that are suited to smaller applications, such as tailpipes and chimneys.
Aside from natural sequestration via biomass, chemical technologies are emerging that can enable direct air capture of carbon dioxide. Interestingly, the chemistry is reminiscent of a high-speed version of that which occurs in the oceans in the earth’s carbon cycle. The approach involves bringing large quantities of air into contact with hydroxide-rich solutions, which can react with CO2 to form carbonates. Unfortunately the high solubility of these carbonate products makes it difficult to separate and collect them from the solution. A second step is therefore required in which a reaction between the carbonate and calcium hydroxide forms solid calcium carbonate (CaCO3). The CO2 can be released from this solid carbonate upon exposure to extremely high temperatures (roughly 700°C).
Between a Rock and a Hard Place
We have mainly focused on the capture part of carbon capture and storage, but the storage aspect is just as critical. Carbon dioxide can be stored in many ways. No matter the approach, it is key that the storage remains reliably stable over long periods of time to minimize the risk of carbon escaping back into the atmosphere.
Geological storage is one of the most common approaches to storing carbon dioxide beyond sequestering it in the form of biomass. As the name suggests, it involves compressing gaseous CO2 until it reaches a supercritical state, then injecting it into deep underground reservoirs of porous rock, where it should remain indefinitely.
Supercritical state: a phase a of matter in which a substance possesses properties in between those of a gas and those of a liquid.
Maintaining CO2 in a supercritical state is key to geological sequestration. Although CO2 is a gas under ambient conditions, it transforms into a supercritical fluid – a state that endows it with properties that are intermediate between those of a gas and those of a liquid – under extremely high pressure.* Most important, supercritical CO2 is roughly three hundred times more dense than gaseous CO2 (600 kg/m3 compared to 1.98 kg/m3), meaning that significantly larger quantities can be sequestered in a given volume of rock. The supercritical state is also desirable for geological storage because, in this form, the CO2 still expands, much like a gas, to fill the porous structure of the rock. In other words, supercritical CO2 exhibits the low viscosity reminiscent of a gas, while retaining the high density of a liquid. To remain in its supercritical state, the CO2 must be subject to extremely high-pressure conditions, which is why it must be stored very deep (typically ~1 km) underground.
Not all rock can securely store CO2, and storage locations are therefore carefully selected by expert geologists and geological engineers. Gaseous carbon dioxide is injected into a region of underground porous rock that is covered by a layer of impermeable rock. The impermeable layer acts as a seal to contain the carbon dioxide and prevent it from leaking back into the atmosphere. The physical properties of CO2 also need to be considered. Once stored, it can react with the minerals in the rock to produce carbonate compounds. This process effectively turns carbon dioxide into part of the rock in a process known as mineral trapping. Understanding the chemistry of these processes is critical to ensuring that geological storage remains safe and effective over the long term.
The worldwide capacity for storing CO2 in underground sedimentary formations is estimated to range from 6,000 to 25,000 Gt.175 This means that, even with the most conservative estimates, there is more than enough underground storage available to address all the excess CO2 in the atmosphere.* This is only true, however, if, once stored, the carbon remains stable in the rock formations and does not leak out. So, how long can carbon dioxide be safely stored in geological formations? One study determined the CO2 retention in reservoirs to be 98 percent over a period of ten thousand years for well-managed reservoirs, and 78 percent for poorly regulated ones.176 Another way of seeing it is that the risk of leakage from geological reservoirs is considered to be comparable to that of natural gas storage, which is also very low. Still, management of geological storage sites is critical to ensuring their long-term viability, and continuous monitoring is needed to help detect any problems as early as possible.
Another storage option for CO2 is in the oceanic sink, which has an estimated storage potential of roughly 1,000 Gt. However, this is unlikely to be a wise choice given the potential effects of released CO2 on marine organisms. Chemical species in solution or liquid pools on the ocean floor risk changing the acidity and ionic constituents of the local environment, which in turn have adverse effects on ocean ecosystems. Large-scale storage of CO2 in the oceans is also riskier, with the release of carbon dioxide expected to occur over hundreds, rather than thousands, of years. Given the large capacity of geological storage and the already ongoing ocean-acidification problem, it would be wise to leave our oceanic sink alone.
Carbon capture and storage can not only help to meet our short-term emission targets but also allow us to manage the atmospheric CO2 level and global temperature in the long term. And it is, to some degree, technologically possible. However, if this is all sounds too good to be true, you are right. The fact remains that carbon capture and storage are not considered economically viable at present. Capturing CO2 directly from air, or even from a smokestack, though possible, remains expensive and energy intensive. Profit is usually the overriding consideration when it comes to commercializing a process. Ultimately, large-scale deployment of carbon capture and storage facilities is required for the industry to fulfill its full emission-reduction potential.* The International Energy Agency estimates that over two thousand large-scale facilities would need to be built, requiring hundreds of billions of dollars in investment. However, current policies are insufficient to ensure that industry scales up at the rate required. The main challenge lies in the fact that carbon capture and storage technology is relatively new and therefore deemed riskier by investors. This could be alleviated by putting forth aggressive policy measures that place greater value on reducing carbon emissions. Government can help incentivize the development of carbon capture and storage technology through carbon taxes and grants; some have proved successful in the past.
One of the world’s largest demonstrations of carbon capture and storage to date is the Sleipner and Snøhvit project in Norway. Located offshore in the North Sea, near the Norway–United Kingdom border, it captures and stores roughly 0.85 million tonnes of CO2 every year from a natural-gas power plant and stores it geologically in an offshore deep saline formation. The project came about in response to Norway’s 1991 carbon tax, which placed a high penalty on offshore petroleum production that vented carbon dioxide into the atmosphere. Starting at USD 35 per tonne of CO2 in 1996, it was raised to USD 65 per tonne in 2016.178 The policy was successful by ensuring that the price on carbon was much higher than the USD 17 per tonne cost of capture and storage.
Still, not all countries have a stringent enough policy on carbon to justify the economics of carbon capture and storage. If capturing from point sources is already non-trivial for companies to justify financially, the situation for direct air capture is worse because the technology is even more expensive. The situation is forcing companies to find alternative ways of ensuring that their carbon capture projects are economically viable, yielding business outcomes that often appear controversial from the point of view of climate action. The business model that has allowed most large-scale capture and storage projects to survive to date has meant working with oil companies to offer their captured CO2 for enhanced oil recovery (EOR). Of the twenty large-scale carbon capture projects in operation worldwide, thirteen currently sell their captured CO2 for EOR.
Enhanced oil recovery (EOR): methods used to increase the quantity of crude oil that can be recovered from a reservoir. The most common method involves injecting gaseous CO2 into the reservoir to reduce the interfacial tension and the viscosity of the oil such that it might be brought to the surface more efficiently.
Enhanced oil recovery involves injecting supercritical CO2 into oil reserves to help extract more oil from a well. The CO2 blends with the oil and increases the overall pressure in the reservoir, forcing the oil toward the production wells. The relatively low viscosity of supercritical CO2 compared to that of other reservoir fluids also allows the oil to flow more easily. These mechanisms allow CO2 EOR to help recover 60 percent of oil in a reservoir, which is substantial when one considers that standard extraction methods recover no more than 10–40 percent of a reservoir’s oil content.179
Proponents of EOR justify its environmental benefits by pointing out that it effectively lowers the carbon footprint of oil. After all, roughly 90–95 percent of the injected CO2 remains trapped in underground rock formation in the space previously occupied by oil. Still, we must not forget the fate of the extracted oil, which releases CO2 emissions back into the atmosphere upon combustion. If the amount of carbon being trapped underground is greater than that being released by the combustion fuel, can CO2 EOR be considered a carbon-negative technology?
Estimating the net carbon emission associated with CO2 EOR projects is unfortunately not straightforward. It depends on several factors, including the source of the CO2 used, the amount of CO2 sequestered, and the additional emissions associated with a CO2 EOR operation – not to mention the emissions that come from the production, refining, and consumption of the resulting petroleum product. This is not helped by the fact that estimating the carbon emissions associated with conventional oil production alone has proved to be non-trivial. The exact emissions are highly dependent on the nature of the individual oil project and may vary greatly between locations. Interestingly, when it comes to CO2 EOR, studies have shown the potential for decarbonization to be highly time dependent: more CO2 tends to be released as oil production declines. Specifically, EOR projects tend to yield negative emissions during the first six to eighteen years of operation and then become carbon positive.180 The timing is therefore critical when one considers the role and impact of CO2 EOR in the greater climate-action strategy.
One thing, however, is clear: a CO2 EOR scheme can only offer emission-mitigation benefits if the CO2 used is captured from an anthropogenic emissions source, such as an industrial waste stream, or is removed directly from the atmosphere. Unfortunately this is not the case at present. Most EOR projects use CO2 drawn from geological resources in the ground because of the lack of CO2 located close to oil fields. In the United States there exists over 6,000 km of CO2 pipeline infrastructure to simply transport CO2 to the site of EOR operations. Using carbon dioxide from geological sources essentially uses more fossil resources to extract fossil fuels. At best, drawing CO2 from the ground for CO2 EOR projects simply displaces geologically stored carbon from one location to another; however, this is challenging given the inevitability of leaks, and some is guaranteed to be lost to the atmosphere along the way. A sobering 70 percent of the CO2 injected in oil wells today for EOR in the United States comes from geological sources.172
Optimists might argue that a lower carbon version of oil-and-gas production is still better than nothing. Integrating carbon capture with CO2 EOR has the potential to reduce significantly the oil industry’s carbon footprint if the carbon used is drawn only from anthropogenic sources. Although the oil industry’s current model counts CO2 as a cost to be minimized, strong policy could compel operations to maximize the CO2 sequestered in the process. Moreover, CO2 EOR is currently the only large-scale permanent carbon-sequestration operation that is profitable. Under the right policy measures, it could help jump-start large-scale carbon capture and storage projects by creating a financial incentive to capture and sequester carbon geologically.
At the same time it is not surprising that carbon capture and storage as a mitigation strategy remains controversial among environmentalists who see it as a Band-Aid solution or even an excuse to prolong the era of fossil-based power generation. Carbon capture and storage technologies indeed do fall in a gray area in our current political climate. As Howard Herzog writes in his book Carbon Capture, “today the right hates anything to do with climate change, even if it could benefit fossil fuels. Similarly, the left hates anything to do with fossil fuels, even if they can help mitigate climate change. One can say that carbon capture has become an orphan technology.”181
Whichever perspective you take, it is important to remember some key facts. First, EOR technology can really only be justified if the CO2 being injected is captured from air or an industrial waste stream; even in this case, it will only offer net negative emissions in the first decade or so of operation. Second, although existing large-scale carbon capture projects tend to have CO2 EOR operations as their clients for economic reasons, they are not technologically constrained to the oil industry. As we saw earlier, there is no shortage of geological sequestration capacity; storing CO2 in oil wells is by no means the only option. Carbon capture and storage technologies can exist and operate sans fossil industries and therefore should not be seen as strictly synonymous with the fossil economy. Finally, we cannot turn a blind eye to the evidence suggesting that fossil-fuel companies have been aware of the risk of rising CO2 emissions for decades, while fostering doubt about the climate crisis.182 Is it reasonable that these same companies should control large-scale carbon capture and sequestration? Ultimately one must ask whether a decarbonization pathway based on the financial incentive of CO2 EOR coheres with public interest in the context of a climate emergency.
The intense pressure to reduce emissions drastically in the little time we have left can warrant more Band-Aid-style solutions. In May 2019 Germany, in a struggle to cut its industrial emissions, announced plans to revive a carbon capture and storage project that had been previously halted in 2017 due to mounting pressure from local residents.183 Although it may not be the ideal choice, challenges in addressing these stubborn emissions can leave leaders with little choice. At the end of the day, some degree of sequestration remains a necessary component to a global carbon-mitigation strategy despite the economic and deployment challenges it faces. Most important, it should be considered a supplemental tool in the climate-action toolbox, rather than a substitute for conventional mitigation approaches. Just because we have ways of removing some atmospheric carbon dioxide does not justify prolonging emission-intensive industrial practices.
A New Way of Thinking
Richard Buckminster Fuller, author, architect, engineer, inventor, entrepreneur, polymath, and humanitarian, famously wrote: “Pollution is nothing but resources we’re not harvesting. We allow them to disperse because we have been ignorant of their value. But if we got into a planning basis, the government could trap pollutants in the stacks and spillages and get back more money than this would cost out of the stockpiled chemistries they’d be collecting.” Buckminster Fuller’s observation captures the essence of a major paradigm shift that is already underway.
Nobody likes Band-Aid-style solutions, but with stubborn emissions from the industrial sector it might seem like we have no choice. As mentioned earlier, fossil fuels can be replaced by renewable sources for generating heat and energy, but industries like chemical manufacturing use fossil fuels not only for energy but also as feedstock materials. Does a non-fossil feedstock that would fulfill the needs of our chemical manufacturing industry even exist?
Buckminster Fuller’s statement was incredibly prescient. As it turns out, the chemistry of the CO2 molecule lends it to being a key ally in the plight to address industry’s stubborn reliance on fossil fuels. Carbon dioxide, the product of burning hydrocarbon fuels, is itself a carrier of carbon and can therefore replace the fossil-derived feedstocks that are conventionally used in industry. Why not use our excess CO2 to manufacture chemicals and fuels, instead of merely treating it as an inconvenient waste product?
This concept of capturing, recycling, and repurposing CO2, better known as CO2 utilization,* is being increasingly endorsed by researchers and policymakers. According to University of Sheffield professor Peter Styring, if 100 percent of urea (which is used as a fertilizer), 30 percent of minerals, 20 percent of chemicals and polymers, 10 percent of methane, and 5 percent of diesel and aviation fuels were made using CO2, this could consume up to 1.34 Gt every year.184,185 It is estimated that using CO2 to manufacture minerals, chemicals, and fuels has the potential to reduce carbon emissions between 10 and 20 percent by 2030.186 While these numbers are not insignificant, one can see that carbon utilization is certainly not a silver bullet for climate change. Switching our fossil-based energy infrastructure to one that is based on renewable energy and addressing emissions related to land use are still the dominant components of any serious emissions-reduction strategy. Carbon utilization’s secret weapon, however, is its potential to eliminate fossil fuels from the supply chain by offering a fossil-free solution to industry’s need for a carbon-based feedstock. So, although its emissions-mitigation potential may appear relatively small, carbon dioxide utilization is revelatory because it discredits the view that, even with all the renewable energy in the world, our society cannot survive without fossil fuels.
Urea: an organic compound commonly used as a nitrogen source in fertilizers.
Carbon dioxide utilization, however, is not simply a scheme to monetize CO2. The sustainable economy of the future would ideally see the resource-to-product-to-market sequence replaced by a circular system, in which all “waste” product would instead be recycled, and resources would no longer be viewed as finite. The world’s current manufacturing economy, in the simplest terms, involves the extraction of natural resources (fossil fuels, minerals, lumber, water, etc.), which are then refined and processed by industry to produce valuable commodities (fuels, chemicals, materials, pharmaceuticals, electronics, etc.). The CO2 emissions that are generated at every step in the process are left to the atmospheric and oceanic reservoirs, where they contribute further to the greenhouse effect and ocean acidification. If, however, we were to treat CO2 as a useful resource instead of a liability, we could finally get a handle on climate change by closing the carbon loop, as shown in figure 12. It is, however, crucial that in the process of building a future green economy,187 the commodification of atmospheric carbon not be exploited by growth-oriented, free-market thinking for short-term gains.
Green economy: defined by the UN Environment Programme as an economy “that results in improved human well-being and social equity, while significantly reducing environmental risks and ecological scarcities. It is low carbon, resource efficient, and socially inclusive.”
Figure 12. The circular CO2 economy, in which fossil resources are eliminated, and CO2 is continuously recycled to produce valuable commodities.
The conversion of excess CO2 into value-added products will play a critical and important role in moving both the transportation sector and the industrial sector into the fossil-free-energy economy over the short and near term. The chemical industry’s current supply chain comprises about forty thousand chemicals made from oil, gas, and biomass, granting it enormous potential to adopt CO2-utilization technologies. Similarly, the conversion of CO2 to liquid hydrocarbons could hold the key to decarbonizing the transport sector’s stubborn emissions associated with large transport vehicles.188,189
A global carbon-dioxide initiative is already underway with strategies in place to harness market demand for products that capture and reuse CO2.* We already have the technical know-how to incorporate CO2 into the industrial supply chain for the production of key chemicals, such as carbon monoxide, olefins, aromatics, ammonia, and methanol.
Olefin: a class of hydrocarbon molecules that contain one or more pairs of carbon atoms linked by a double bond. They are important in the manufacturing of chemicals, plastics, and synthetic rubber.
Aromatic: a class of hydrocarbon molecules with characteristic planar ring structures. They are used in the manufacturing of a variety of chemicals, including dyes, as well as polymers and synthetic fibers.
Methanol: a volatile and colorless liquid consisting of a methyl group bonded to a hydroxyl group. It is widely used in chemical manufacturing.
Ammonia: a compound containing three hydrogen atoms bonded to a nitrogen atom. Its uses include fertilizer, cleaning products, refrigeration, and pharmaceuticals.
The utilization of CO2 is not an entirely new concept. A number of large-scale industrial processes that consume CO2 were developed during the period from 1880 to 1893. These processes include the synthesis of urea from ammonia; the Solvay process for making glass, soap, and paper and for bleaching fabric; the synthesis of sodium hydrogen carbonates, the most common use being baking powder; and the production of salicylic acid, a feedstock for many chemicals, the best known of which is Aspirin.
Solvay process: an industrial process for making sodium carbonate from calcium carbonate (aka limestone), ammonia, and brine
One need not search far to find ways in which CO2 already enables many modern technologies. Its applications include soft drinks, dry-ice solid refrigerants, ingredients in frozen foods, enhancers for plant growth and greenhouses, the cooling of bunches of grapes in winemaking, reactive atmospheres for welding, capsules for air guns, extinguishers for electrical and oil fires not put out by water, a supercritical solvent for the removal of caffeine from coffee, polymer processing, chromatography separations, near-infrared gas lasers, ingredients for construction materials such as cement and concrete, fumigants to increase shelf life and remove infestations, and even euthanasia for laboratory research animals.
The modern chemical manufacturing industry, however, still relies predominantly on fossil-derived feedstock, and until very recently CO2 has been viewed as a waste product rather than a valuable commodity.* The situation today is changing. Mounting pressures to address our rising emissions and the growing demand for energy, food, medicine, and consumer goods around the world are requiring us to seriously rethink our industries. It is rather ironic that the world’s most maligned molecule might just help transition away from a fossil fuel–based economy.
KEY TAKEAWAYS
• Aspects of the chemical manufacturing and transportation sectors possess “stubborn” emissions that cannot be resolved by switching to renewable energy.
• It is easier to capture carbon dioxide from concentrated, rather than dilute sources, such as industrial waste streams.
• Carbon storage is only effective if it can ensure safe, long-term storage, with minimal leaking of carbon dioxide into the atmosphere.
• Carbon dioxide can be safely stored in geological reservoirs without the risk of leakage, provided the sites are well selected and carefully monitored.
• Carbon capture and storage, although technologically feasible, remains costly, and large-scale deployment is not feasible under current policy.
• Enhanced oil recovery (EOR) can help reduce the carbon footprint of oil in some cases, but only if the carbon dioxide used is sourced from the atmosphere or captured from anthropogenic point sources and stored underground post-EOR.
• Carbon capture and storage should be considered a supplemental strategy rather than a substitute for conventional mitigation approaches.
• Fossil-derived feedstocks conventionally used in industry can be replaced with captured carbon dioxide.
• The sustainable economy of the future would ideally see the resource-to-product-to-market sequence replaced by a circular system, in which all “waste” products would instead be recycled, and resources would no longer be viewed as finite.
• Carbon-dioxide removal, capture, storage, and utilization are just some of many key components forming the larger climate-change action strategy to achieve net-zero emissions.
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* A 2019 report found that replacing all conventional aviation fuel with sustainable aviation fuels, though theoretically possible, would require some 170 new biorefineries to be built per year from 2020 to 2050.168
* CO2 becomes a supercritical fluid at 31.1°C and 72.9 atmospheres.
* To put this in perspective, recall that we currently emit roughly 33 Gt of CO2 globally every year.
* Although large-scale deployment of CDR and carbon-capture infrastructure is ideal for maximizing their mitigation potential, it is not required to render them relevant to climate policy or eligible for investment. In this regard, they differ strongly from geoengineering strategies, which demand an all-or-nothing approach and comprehensive global coordination to be effective. When it comes to CDR and carbon capture, the question of scale need not pose a barrier, because these technologies can be implemented from the bottom up through local initiative, on a case-by-case basis.177
* Although the word utilization has become more or less synonymous with use, it holds the specific meaning of using something in a manner for which it was not originally intended. Carbon dioxide utilization implies putting CO2 to use in unconventional ways, outside its natural role in the earth’s carbon cycle, by transforming it into chemicals, fuels, and minerals.
* See https://www.globalco2initiative.org/ for full details on the Global CO2 Initiative.
* A slight interest in CO2 emerged in the 1970s when it was found to be a beneficial additive in the production of methanol, as well as useful for creating improved solvents for lithium-ion battery electrolytes, like propylene carbonate.