Hydrothermal preparation of carbonaceous material from biomass. Study of applicatiions as porous materials and energy carriers.

During 2009, the world oil production achieved 4,4 billons tons [1]. The current fossil fuel compsumption rate and the limitation of fossil fuel reserves are causes of energy dependence and geopolitical conflicts among countries. Moreover, the atmospheric CO2 concentration continues rising, with the known implications on the environment. It is clear that renewable sources of energy have a major role on the future energy scheme.

Among these alternatives, biomass is a promising energy source, with known advantages. Nowardays, the energy exploitation of biomass has been accomplished via different processes; among thermochemical routes, pyrolysis, gasification and combustion are the most important. These processes require the use of high temperatures appart from previous drying or densifying processes, which increase the economic and energy input. In this line, the search of  efficient ways to turn biomass into carbon rich materials involves a very interesting threat.

 The hydrothermal carbonization process can be an option for this task since it does not requires such harsh conditions. In this process the precursors are subjected to realtively low pressure and mild temperature conditions in water where coalification takes place. As a result, an insoluble char-like product with a high energy content is obtained.

This method enjoys the significant advantages of being an exothermic process, avoid previous drying, and has proved to be highly effficient since practically all the starting carbon stays bound to the final carbon material. Therefore, it allows to efficiently bind the CO2 taken by the plants during their growing.

Moreover, the carbonaceous material (often referred to as hydrochar) can present very interesting characteristics with respect to their use in adsorption process, soil ammendement, etc. Also the processes can be directed toward the production of activated carbons, carbon nanomaterials, microspheres, etc. These materials show a very important role in current society in the field of the removal of pollutants by adsorption processes, gas separation, catalysis, electrode materials, etc.   

Due to these reasons the hydrothermal carbonization (HTC) of cellulosic materials has recently arisen the interests of many researchers [2-7], although the mechanisms which influence the final characteristics of the hidrochar and their relation to experimental conditions are not yet fully understood. It is therefore very interesting to carry out studies on the hydrothermal carbonization processes of biomass, optimizing the process variables (temperature, time, use of catalysts...)  in order to obtain high value  products within an economical and environmental sustainable scheme.

1. 1.     Most of the research on HTC of carbon-rich precursors have been made with simple products as glucose, starch, sacarose  [12] while

 glucose has been used as only reference  product for a mechanisctic study. [13]

Other authors have used carbohydrates it in combination with metals to create different carbon/metal nanostructures such a as Te@carbon-rich composite nanocables [8], Cu@carbon submicrocables [9]. The behaviour of starch has been investigated by non-catalytic [10] and catalytic HTC with metal ions as iron [11].

This project aims to study the HTC of different lignocellulosic residues from two points of view:

a) The increase in their energy density, and their CO2 binding efficiency of the whole process for each species.

b) The preparation of porous materials to be used in adsorption applications. The understanding of the processes taking place and how the change in experimental conditions can change the chemical, porosity, morphological and adsorptive characteristics of the materials.

This study offers therefore an added value to the residues generated as a result of agroindustrial activities, by means of sustainable and environmental friendly processes.