Researchers assess the best processes for the use of carbon dioxide by the chemical industry
The use of carbon dioxide (CO2) as a raw material for manufacturing chemical products is one of the possibilities being studied for mitigating the effects of the emission of this gas, which makes up more than 70% of the greenhouse gases released into the atmosphere. Besides reducing global warming, the conversion of CO2 into other products can contribute to delaying the depletion of fossil resources and indicate more modern production methods to the chemical industry.
Data from the literature regarding the amount of energy needed for converting carbon dioxide into a chemical product, however, are limited. In order to increment those data, a group of researchers from the Department of Chemical Engineering of the Polytechnic School of the University of São Paulo (USP) published an article in this month’s issue of the Elsevier Energy Conversion and Management magazine, by the Elsevier publishing company, giving the details of a comparative study of the different methods for estimating the thermodynamic properties of these reactions.
“There are processes that demand more, or less, power for using CO2, in order to make chemical products,” states Professor Claudio Augusto Oller do Nascimento, Deputy Director of the Physical Chemistry Program of the Research Center for Gas Innovation (RCGI) and co-author of the article. “The ideal is to use less power. But, on the other hand, at the same time, you have to look for the one that consumes more CO2.”
The idea is to help transform carbon dioxide, which is now considered to be a type of “waste”, into a commodity. The gas is emitted mainly during the production and burning of fossil fuels, in deforestation and in the scorching of pastures, planted fields, and forests.
The researchers used computational chemistry methods, which adopt computer science principles, to calculate the thermodynamic properties of the reagents and of the products of the reactions.
Products based on carbon dioxide were divided into 16 chemical classes and the enthalpy reaction for manufacturing such chemical substances as acetone, methanol, and acrylic acid. According to the researchers, the so-called semi-empirical quantum chemistry, a quantum method that uses empirical approximations, was the most accurate method for making the calculations.
One of the pillars of the study had to do with the new advances in the field of computational approaches, especially regarding computer-aided molecule design, the researchers wrote.
“One of the most fundamental thermodynamic properties is the enthalpy of formation, which is critical to many engineering areas, because the energy balances depend on the accuracy of their figures,” the article’s authors wrote. Enthalpy of formation is the heat released or absorbed during the synthesis of a substance. “In order to increase the accuracy and avoid expensive methods, semi-empirical methods of quantum chemistry, which are a variant of electronic structure theory,” they stated.
Generally speaking, the new processes for manufacturing chemical products based on CO2 are more energy and material-intense than traditional production routes, according to the researchers; thus, the importance of greater precision when estimating thermodynamic properties.
The work assessed the capacity of six different methods for estimating the properties for calculating the enthalpy of the gas phase. The method known as PM7 (parametrization method 7) was considered to be the most adequate for performing the task, proving itself to be accurate and efficient, compared to the other methods.
The researchers stress that the chemical computation methods are promising for modeling chemical properties and for assessing the optimal structure of molecules.