The H2 potential of the Colombian coals in natural conditions

Coal gasification to manufacture dihydrogen (H2) has long been known as a surface process. Recent works have also highlighted the H2 generating potential of the Organic Matter (OM). The evolution of OM generates H2 all along the process but this gas is only expected to remain as free H2 after the maturation and expulsion of the hydrocarbons (HC) which means at a high temperature of above 200 °C. In this paper we studied the potential of three different tertiary coals from Amaga, La Jagua de Ibirico and Barrancas, all located in Colombia. Their H2 yields were studied using a pyrolyser and the kinetic of the H2 generation were quantified. All the studied coals are immature to early mature as source rock (SR) with large TOC content, between 66 and 83%, and good H2 potential. The highest values were found for the Barrancas area where the potential reached 25 mg H2/g TOC. The temperature corresponding to the peak of H2 generation is between 740 and 800 °C depending of the heating rate. This corresponds to the 200–300 °C for the H2 kitchen, even if the H2 generation starts before as already observed for continental organic rich source rock. Comparison with the other coals shows that H2 potential is linear with TOC. In the Colombian coals, the H2 yield in mg H2/g of rock is around 1/4 of the TOC content. In average, these coals have so a H2 yield about 10 000 mmol H2/kg of rock, two orders of magnitude above the "best" olivines. It should nevertheless be kept in mind that the extrapolation of these laboratory data to sedimentary basins remains unconstrained and will need to be refined when well data and modelling tools are available.