When extracted from the wells, oil is accompanied by a mixture of carbon dioxide (CO2) and gaseous hydrocarbons, particularly methane (CH4), both atmospheric pollutants, which are normally re-injected into the wells today, which makes the process more expensive. Ideally, these two main gaseous components would be collected and separated so that methane could be used as a fuel and carbon dioxide stored properly.

Professor José Roberto Nunhez (second on the right) with Lucídio Cristóvão Farderlone, Daniela da Silva Damaceno and Nayla Xiomara lozada Gardia (first on the left): ANP Award for Technological Innovation in 2019

This is the scope of the studies that have been carried out by a group of researchers from Unicamp and USP. In this case, the idea involves the formation of gas hydrates, in which the solidified water retains the gases in question in its interstices. The crystalline structure formed, which resembles ice, has a large gas storage capacity: one liter of methane hydrate, for example, can contain approximately 168 liters of this gas.

Then, from these crystalline structures - obtained under conditions of adequate pressure and temperature - it is possible to separate methane for use as a fuel and keep carbon dioxide trapped. There would then remain two possibilities for disposal of carbon dioxide hydrates: they would be deposited either in the wells or on the seabed, in which the low temperature (4 degrees Celsius) and high pressure would definitely keep them stable.

The project, which aimed to capture and store carbon dioxide (CO2) and methane (CH4), through the gas hydrates production process, was coordinated by Professor Song Won Park, from the Department of Chemical Engineering at Escola Politécnica da USP and had the technical coordination of Professor José Roberto Nunhez, from the Department of Process Engineering at the Faculty of Chemical Engineering (FEQ) of Unicamp. The study had the collaboration of supervisors from the two teachers: by the Polytechnic School, by Adriano Ferreira de Mattos Silvares (post-doctoral student), João Pedro Ferreira del Pintor and Vitor Hideyo Isume (master's students); by Unicamp, postdoctoral students Lucídio Cristóvão Farderlone and Daniela da Silva Damaceno, doctoral student Nayla Xiomara lozada Gardia and master student Aglaer Nasia Cabral Leocádio.

This study, developed within the scope of the special participation clause of the National Agency of Petroleum, Natural Gas and Biofuels (ANP), is sponsored by Petrogal Brasil, which actively participates in technical coordination through Carlos Augusto and Marcella Mathias, who work on the projects.

For the initial experimental studies a bench system was used for the production of gas hydrates, built in Portugal, based on technology patented by the Laboratory of Separation and Reaction Engineering, Faculty of Engineering of Porto (FEUP) and produced by the company Paralab .

In the NETmix ® minireactor, a component of the equipment, both water and gases come into contact with each other and produce gas hydrates at the appropriate pressure and temperature. The auspicious initial results led to the construction, by the same company, of a pilot equipment with a capacity ten times greater, already tested by FEUP, and which is coming to Unicamp. These two equipments were the first to be built in the world specifically for the production of hydrates, although NETmix has been used in Europe for several other processes in a long time.

The differentials

Professor Nunhez explains that the use of hydrates is old. The project aimed to propose a real, concrete and fast solution for the capture of CO2 and purification of CH4, using industrial installations of small dimensions on marine platforms. Hydrates are formed at low temperatures, but during processing there is a large release of heat that requires the quickest possible removal for the process to continue and accelerate. In mixing tanks, which would be an option for the production of hydrates, heat removal is slow and can take hours, unlike the proposed process in which the formation of the hydrate takes place in seconds.

Indeed, in the tanks as their quantities increase, the capacity for thermal exchange decreases. One of the biggest problems in obtaining hydrates is the high energy released in their formation. It is abundantly mentioned in the specific literature that, with the increase in scale in the mixing tanks, energy is not released with the same efficiency that occurs in smaller tanks since the scaling reduces the relationship between the heat exchange area and the volume in transformation takes place. In contrast, the new process uses a technology that guarantees the same level of heat exchange even with an increase in scale.

The great advantage of the proposed equipment, whose reactor consists of a network of static mixers, is that they have structures that allow the flow of water and gases introduced to be divided several times, allowing greater contact between them. In this technology, the equipment, in the heat exchange, has characteristics of micro mixers. Depending on the production schedule, it is enough to increase the number of mixers, a process that facilitates the heat dissipation necessary for the formation of hydrates. That is, mixers are gradually added so that the production of hydrates occurs according to the flow of the gases to be processed.

Another advantage of the system is its compact installation when compared to mixing tanks. In other words, the occupied area becomes smaller and the process is continuous. Naturally, the hydrates of carbon dioxide and methane need to be removed as they are formed for later separation of the gases in order to have only the hydrates of carbon dioxide.

In fact, explains Nunhez, the idea is to remove the hydrocarbon first, in this case methane, and keep the carbonate gas hydrate: “As the hydrates of these gases have different stability, methane can be preferentially released. This separation is still being studied and, although not trivial, it involves a problem that can be solved by chemical engineering using what is called thermodynamic equilibrium ”.

This, in summary, is the idea of the ongoing project. In the tests already carried out, hydrates were obtained with the mixture of CO2 and CH4 - used in the same proportion as they are found in oil wells - and, separately, of CO2 hydrates. Similar results were obtained with the use of sea water, with saline composition, which could inhibit the formation of hydrates.

The professor credits the awarding of the prize to the very encouraging results achieved and to the worldwide potential of the developed technology. In conclusion, he concludes: “We show that technology works and brings a great advance in terms of technological innovation because it enables a continuous process at an incomparable speed in relation to what occurs in a battery process in which hydrates are formed over time ”.

In 2019, the worked won the ANP Technological Innovation Award, granted in five categories in its sixth edition. It aims to recognize the results achieved by research, development and innovation (RD&I) projects that represent technological innovation for the oil, natural gas and biofuels sector developed in Brazil by research institutions accredited by the Agency, with resources from exploration contracts and production. The award received by researchers from Unicamp and USP falls under category I: “Exploration and Production of Oil and Gas”.