Start up of a new continuous facility for the hydrothermal reduction of CO2

The high pressure processes of the University of Valladolid have built a continuous pilot plant for studying the scale up of hydrothermal CO2 reduction processes.  The hydrothermal CO2 reduction (in aqueous media at high pressure and temperature) is a promising method for converting the CO2 in chemicals and fuels such as formic acid, methanol or methane using metals or alcohols as reductants. The process have yields over 60% and it is potentially easy to integrate with CO2 producing facilities, nevertheless most of the work done so far is at laboratory scale. The new facility will contribute to the development of solutions for the CO2 emitting industries.


Figure 1. Experimental device for the hydrothermal reduction of CO2

Although the society has now a bad image of CO2, this compound is a renewable resource and  can be used like a reagent and transformed it to fuels and chemical compounds such as formic acid, methane or methanol. In this way, CO2 treatment becomes a business opportunity. This can be made by reducing the CO2 in hydrothermal media using water and high pressure-temperature conditions. A advantage to work in this way is avoid working directly with hydrogen (The water acts as a source of hydrogen ), so that process is safer than others.

This process has the additional advantage of being easily integrated in CO2 producing industries such as power plants by  CO2 capture that use an alkaline sodium hydroxide solution. The connection of a hydrothermal reactor after the  CO2 scrubber can  be implemented in an easy way because the reaction is occurring in aqueous media. Thus, CO2 separation or purification are not necessary and, what it is more the reaction is favoured by alkaline conditions.

Nevertheless, so far this process only has been carried out in batch or semicontinuous  way at laboratory scale.

The objective of AQUA CO2NV process is to develop a continuous hydrothermal reduction process. To do so, a continuous facility has been developed, in order to study technical solutions to contribute the industrial implementation of the process. The advantage of working in this way is a more efficient, less time-consuming and energy-consuming process than batch or semicontinuous one.

Figure 2. Schematic diagram for the continuous CO2 reduction process

Our facility consists of two feed lines, one of them is preheating water, while the other is the aqueous CO2 solution as sodium bicarbonate. The preheating water line circulates through a heating coil, before mixing with the bicarbonate line in the mixing point. After that, the mixture moves inside the reactor, where reducing reagents and catalysts can be placed. The bicarbonate transforms to produce chemical compounds, mainly formic acid. Then, the effluent is despressurized by passing through a needle valve. Afterward the fluid cools down with water in a heat exchanger. Finally the fluid is separated in a liquid stream and a gaseous stream in a flash.

The facilities can work with flows between 0.05 and 10 mL/min, which will allow working with residence times from a few seconds to several hours. The working pressure limit is 250 bar. The range of working temperature is between 275ºC and 600ºC.

This new versatile plant will allow us to study different technical solutions to develop a continuos process such as working at semi-batch regime, mixing streams with different catalyst or reagents at different steps and residence times or measuring kinetics parameters at different residence times and temperature.

This research has been funded by the Spanish Ministry of Economy and Competitiveness through project ENE2014-53459-R, “AQUA-CO2NV”.

Daniel Roman

ENE2014-53459-R, “AQUA-CO2NV”

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