• Energy Research

Abstract The steam reforming of the main biodiesel by-product, glycerol, has been catching up the interest of the scientific community in the last years. The use of glycerol for hydrogen production is an advantageous option not only because glycerol is renewable but also because its use would lead to the decrease of the price of biodiesel, thus making it more competitive. Consequently, the use of biodiesel at large scale would significantly reduce CO2 emissions comparatively to fossil fuels. Moreover, hydrogen itself is seen as a very attractive clean fuel for transportation purposes. Therefore, the industrialization of the glycerol steam reforming (GSR) process would have a tremendous global environmental impact. In the last years, intensive research regarding GSR thermodynamics, catalysts, reaction mechanisms and kinetics, and innovative reactor configurations (sorption enhanced reactors (SERs) and membrane reactors (MRs)) has been done, aiming for improving the process effectiveness. In this review, the main challenges and strategies adopted for optimization of GSR process are addressed, namely the GSR thermodynamic aspects, the last developments on catalysis and kinetics, as well as the last advances on GSR performed in SERs and MRs.

Abstract The steam reforming of the main biodiesel by-product, glycerol, has been catching up the interest of the scientific community in the last years. The use of glycerol for hydrogen production is an advantageous option not only because glycerol is renewable but also because its use would lead to the decrease of the price of biodiesel, thus making it more competitive. Consequently, the use of biodiesel at large scale would significantly reduce CO2 emissions comparatively to fossil fuels. Moreover, hydrogen itself is seen as a very attractive clean fuel for transportation purposes. Therefore, the industrialization of the glycerol steam reforming (GSR) process would have a tremendous global environmental impact. In the last years, intensive research regarding GSR thermodynamics, catalysts, reaction mechanisms and kinetics, and innovative reactor configurations (sorption enhanced reactors (SERs) and membrane reactors (MRs)) has been done, aiming for improving the process effectiveness. In this review, the main challenges and strategies adopted for optimization of GSR process are addressed, namely the GSR thermodynamic aspects, the last developments on catalysis and kinetics, as well as the last advances on GSR performed in SERs and MRs.

Abstract A thermodynamic study was performed aiming to compare the performance of different reactor configurations, namely traditional (TR), sorption-enhanced (SER), chemical looping (CLR) and chemical-looping sorption-enhanced reforming (SE-CLR) for the steam reforming of olive mill wastewater (OMW), a byproduct of olive oil production, to produce green hydrogen. This analysis was accompanied by an energy balance in order to maximize energy efficiency and achieve autothermal operating conditions. The parameters assessed in the thermodynamic study were temperature (250–900 °C) and steam-to-carbon molar ratio (0.15–3.0), but also, for the sorption-enhanced process, the ratio between the CO2 sorbent and the OMW (0–8.0), and for the chemical looping process the ratio between the oxygen carrier and the OMW (0–6.0). The SER showed higher hydrogen yield for the range of conditions tested than both the traditional and chemical looping reformers, with a hydrogen purity above 99%. By combining sorption-enhanced with chemical looping reforming, an H2 purity above 99% and a yield higher than that for chemical looping by itself were observed. For the CLR and SE-CLR configurations, a system in which the energy released is higher than the required was achieved by varying the amount of oxygen carrier, enabling operating under autothermal conditions. A pinch analysis was performed for the CLR and the SE-CLR to quantify the possible heat integration in a realistic system. It was found that CLR can be 71% self-sufficient, whilst SE-CLR can be 55% self-sufficient.

Abstract A thermodynamic study was performed aiming to compare the performance of different reactor configurations, namely traditional (TR), sorption-enhanced (SER), chemical looping (CLR) and chemical-looping sorption-enhanced reforming (SE-CLR) for the steam reforming of olive mill wastewater (OMW), a byproduct of olive oil production, to produce green hydrogen. This analysis was accompanied by an energy balance in order to maximize energy efficiency and achieve autothermal operating conditions. The parameters assessed in the thermodynamic study were temperature (250–900 °C) and steam-to-carbon molar ratio (0.15–3.0), but also, for the sorption-enhanced process, the ratio between the CO2 sorbent and the OMW (0–8.0), and for the chemical looping process the ratio between the oxygen carrier and the OMW (0–6.0). The SER showed higher hydrogen yield for the range of conditions tested than both the traditional and chemical looping reformers, with a hydrogen purity above 99%. By combining sorption-enhanced with chemical looping reforming, an H2 purity above 99% and a yield higher than that for chemical looping by itself were observed. For the CLR and SE-CLR configurations, a system in which the energy released is higher than the required was achieved by varying the amount of oxygen carrier, enabling operating under autothermal conditions. A pinch analysis was performed for the CLR and the SE-CLR to quantify the possible heat integration in a realistic system. It was found that CLR can be 71% self-sufficient, whilst SE-CLR can be 55% self-sufficient.

The steam reforming of ethanol, methanol, and other oxygenates (e.g., bio-oil and olive mill wastewater) using Ni-based catalysts have been studied by the scientific community in the last few years. This process is already well studied over the last years, being the critical point, at this moment, the choice of a suitable catalyst. The utilization of these oxygenates for the production of “green” H2 is an interesting alternative to fuel fossils. For this application, Ni-based catalysts have been extensively studied since they are highly active and cheaper than noble metal-based materials. In this review, a comparison of several Ni-based catalysts reported in the literature for the different above-mentioned reactions is carried out. This study aims to understand if such catalysts demonstrate enough catalytic activity/stability for application in steam reforming of the oxygenated compounds and which preparation methods are most adequate to obtain these materials. In summary, it aims to provide insights into the performances reached and point out the best way to get better and improved catalysts for such applications (which depends on the feedstock used).

The steam reforming of ethanol, methanol, and other oxygenates (e.g., bio-oil and olive mill wastewater) using Ni-based catalysts have been studied by the scientific community in the last few years. This process is already well studied over the last years, being the critical point, at this moment, the choice of a suitable catalyst. The utilization of these oxygenates for the production of “green” H2 is an interesting alternative to fuel fossils. For this application, Ni-based catalysts have been extensively studied since they are highly active and cheaper than noble metal-based materials. In this review, a comparison of several Ni-based catalysts reported in the literature for the different above-mentioned reactions is carried out. This study aims to understand if such catalysts demonstrate enough catalytic activity/stability for application in steam reforming of the oxygenated compounds and which preparation methods are most adequate to obtain these materials. In summary, it aims to provide insights into the performances reached and point out the best way to get better and improved catalysts for such applications (which depends on the feedstock used).