“Selling” CO2 removed from the atmosphere in the form of other fuels or of chemical products for industry could change our view regarding carbon and help reduce emissions
One of the current technology trends for carbon abatement is to convert the CO2 into reusable products, which is called Carbon Capture and Utilization (CCU). Several projects of the FAPESP Shell Research Centre for Gas Innovation (RCGI) focus on this objective. For example, they look to obtain value-added products from the hydrogenation of CO2; or remove CO2 from the atmosphere by means of a photocatalytic cell and transform it into a useful organic product for industry; or integrate thermoelectric power plants with CO2 conversion technologies to mitigate greenhouse gas (GHG) emissions. RCGI researchers have already listed more than 140 products that can be obtained based on CO2.
Chemist Pedro Vidinha, who is one of the scientists on the RCGI team involved in a CCU project, holds that there are many advantages for initiatives of this type and the success of those technologies has the potential for changing the course of our environmental policies.
“In my opinion, if we are able to obtain products from CO2 with a positive economic and energy balance, it will be possible to make money with this and, then, environmental policies related to CO2 could change. With the existence of practical carbon abatement technology, anyone who has these technologies will force those who do not have them to pay CO2 emissions quotas. But I imagine that the horizon for these changes is about 20 years down the road from today,” he stated.
According to him, there are two paths to the utilization of CO2: generate either fuels or chemicals. In the case of fuels, the carbon cycle is a closed one, because they will be burned again and the CO2 will be recaptured, over and over again). In the case of chemicals, it is necessary to arrive at substances for which there is an industry demand, such as urea. “The world already produces 150 million tons of urea per year. Today, it is the biggest product, in terms of quantity, obtained from CO2. If there was an increase in the consumption of urea, and if we began to produce more, the volume of CO2 abatement achieved would be colossal.” Urea is a product used in making nitrogen fertilizers and plastic, among others.
In conjunction with his team of eight researchers, Vidinha is attempting to reduce CO2 and obtain alcohols, like methanol, ethanol, and even butanol, with the use of hydrogen as a reagent and highly effective catalysts, composed of metal compounds and organic binders.
“We have been able to produce butanol, which is fantastic, because, in this case, we changed a substance with one carbon atom (CO2) to one with four carbon atoms (C4H10O). We increased the energy density of the molecule, because the more carbon there is, the more energy is accumulated.”
According to him, butanol has many applications: it is a so-called building block for other molecules. “For example, it is possible to obtain butane from it by way of an established industrial process. Once we have butanol from CO2, we can think about a polymer industry based on CO2,” he added.
Differential – Vidinha explains that most of the processes for making use of CO2 imply the use of high temperatures, but he and his team are able to produce methanol, ethanol, and butanol practically at room temperature.
“I have found the current state of the art process to have its lowest temperature between 150oC and 180oC. That is very good, because those temperatures can be reached by using the heat resulting from other industrial processes. That is: this CO2 conversion plant could be placed in another industry, reusing the heat caused by the first. In our processes, we established that we would work with a temperature of 40oC. We then developed catalysts that allow us to react CO2 with H2 to obtain methanol, ethanol, and butanol at 40oC.”
However, the metals used by the team to make the catalysts are expensive, or they are rare. “We use Iridium and Rhodium. With Iridium, we are able to obtain butanol and, with Rhodium, methanol and ethanol. With these catalysts, we obtained a selectivity rate for butanol of more than 90%.”
Another condition of the process is pressure, which, at first, is not a problem. “We work at 40oC with a pressure of 280 bars. But pressure is not a problem for industry, at least for Shell, with which we have close contact through the RCGI. Temperature is a problem, because it comes at a high cost, among other things. But, pressure, in this case, is no problem.”
Products and processes – According to Vidinha, there are dozens of composites that can be obtained only from CO2.
“But, if we think of starting with another molecule and incorporating CO2, there could be hundreds of different reactions. We can have carbon storage initiatives, when CO2 is introduced to another molecule, but there is also carbon utilization, when that molecule is used for something.”
He mentions isopropanol, butanol, hexanol, formic acid, acetic acid, and other products that have market value and can be obtained from CO2. “The most valuable products would be butanol, or other long-chain alcohols… The greater the number of carbon atoms, the better. Or we could think about performing a Fischer Tropsch reaction directly from CO2 (with CO2 and H2), and produce an ecologically favorable grade of gasoline.” In the Fischer Tropsch process, a catalyst is used to convert synthesized gas (CO and H2) into liquid hydrocarbons.
The chemist says that this “ecologically favorable gasoline” would be much more environmentally important if the H2 came from a renewable source, like water, for example, despite the fact that the hydrogen obtained from the electrolysis of water is expensive. “Now, if H2 comes from fossil sources, like natural gas, maybe this wouldn’t make much sense. We need to look at the process in an integrated manner. But it is not enough to obtain the product or perform the reaction. The sustainability of the entire supply chain must by verified. I think that version 2.0 of the CO2 abatement should be the integration of processes.”