Discovery was published in an article in the Journal of CO2 Utilization
A catalyst made with titanium oxide and rhenium oxide produced excellent results in converting carbon dioxide (CO2) into methanol, according to a study published in September in the Journal of CO2 Utilization. Developed within the scope of a project of the FAPESP Shell Research Centre for Gas Innovation (RCGI), the study recorded a selectivity of 98% for methanol and a conversion rate of nearly 20% of the CO2. That is, 20% of the carbon dioxide used in the process were transformed into (CH3OH), through a chemical reaction with hydrogen (H2) called hydrogenation, without the use of any other additive.
“This is considered to be one of the best results found in the literature,” stated Pedro Vidinha, Professor in the Fundamental Chemistry Department of the Institute of Chemistry of the University of São Paulo (IQ-USP), who was a coauthor of the article. The researcher is involved with an RCGI group that is attempting to generate products of value from carbon dioxide, which is an important greenhouse gas. The catalyst was developed in a laboratory within the scope of the studies of Doctoral candidate Maitê Lippel Gothe, under Professor Vidinha’s guidance.
“This combination of titanium and rhenium was highly fortunate, because it generated a surface that is capable of linking with CO2 and hydrogen and, thus, bringing about the reaction that produces methanol,” Prof. Vidinha said. CO2 is a very stable molecule and, in order to break the connections between carbon and oxygen, energy must be used. “The energy level for this reaction is normally very high. We used a catalyst to lower the amount of energy required to make this break,” he explains.
In this process, it was essential to take the reaction to a pressure level much higher than atmospheric pressure. Otherwise, the mixture of CO2 and hydrogen, when heated, would not produce methanol, but merely carbon monoxide (CO). After experimenting, the researchers came to the conclusion that the best behavior of the catalyst for the desired purpose (producing methanol) occurred at a pressure of 100 bar and a temperature of 200°C, at a proportion of one molecule of CO2 for every four molecules of hydrogen. “The temperature and pressure conditions used seem to be high, but they can easily be obtained in industrial processes,” Prof. Vidinha states.
Another product that customarily results from the mixture of CO2 and hydrogen is methanol, which is also a greenhouse gas and, therefore, is an undesirable consequence. And, for that reason, the researchers were elated about the high 90% selectivity rate for methanol, which was obtained with the catalyst that had been developed. This high rate of selectivity demonstrates that, due to the flow process developed, the chemical reaction went practically in only one direction, resulting in methanol.
As a colorless liquid, methanol can be used as a fuel or as an additive for gasoline, but its main use, at the present time, is as a solvent or as a raw material for other industrial products. “We are attempting to evolve our project into developing increasingly better products, so that the CO2 emitted into the atmosphere is able to have a cycle that is different from the natural one, that is, a cycle essentially industrial,” Vidinha states. “As though it were an anthropogenic CO2 regeneration cycle.”
Now, according to him, the group is in the phase of attempting to understand how and why, at the molecular level, they achieved such a good result. “We accomplished a good thing, but now we have to explain how we got there. It is a long process, and the techniques are exceptionally sophisticated.”
The next step within the RCGI group will be to attempt to produce ethanol from carbon dioxide. “If we have already been able to arrive at methanol, which has only one carbon [in its chemical structure], might we be able to use a similar strategy to arrive at ethanol, which has two carbons, and for that reason is of greater value?” According to him, it would be third-generation ethanol, which would benefit from an energy platform already set up, for a product that is also well-known to Brazilians.
One idea is that the same mills that make ethanol from sugarcane could make use of the carbon dioxide emitted in the production process, transforming it into composites of commercial interest, like methanol and ethanol – thus obtaining another product to sell, and with environmental benefits, because CO2 would no longer be emitted into the atmosphere.
More than developing processes for transforming CO2, the big challenge of these technologies is in obtaining the hydrogen used for causing the chemical reactions of hydrogenation, because a good share of that gas also comes from fossil fuels, the researcher explained. “Brazil has exceptional conditions for producing hydrogen from water, which uses electricity from renewable sources, with a clean energy source, like wind, water or solar, so that this process is, in fact, viable. There is enormous potential in this area.”
The summary of the article, “Selective CO2 hydrogenation into methanol in a supercritical flow process” can be read at https://www.sciencedirect.com/science/article/abs/pii/S2212982019311631#!