Combined effect of increasing the post‐reformer temperature and adding red mud as a secondary catalyst in the thermocatalytic reforming of digestate

This work studies the combined effect of increasing the post‐reformer temperature and introducing red mud as a support catalyst in the thermocatalytic reforming (TCR®) of digestate. The TCR® method, developed by the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT (abbreviated as Fraunhofer UMSICHT), is an extension and improvement of pyrolysis. In other words, the products of the TCR®, especially the biooil, have been shown to be more thermally stable and, therefore, more applicable than the products of pyrolysis. However, optimization of the process is necessary for achieving commercialization of the process. The crux of the optimization process is the investigation of factors influencing the product yield and quality. Two factors that essentially differentiate the TCR® from pyrolysis are the post‐reformer temperature and the nature of the catalyst. It is expected that changes in these would lead to significant changes in the outcome of the process. Normally, the biochar from the feedstock acts as the catalyst but in this study a support catalyst, red mud, a solid waste from the processing of bauxite, has been added. The post‐reformer temperatures used are 600 and 750 °C. The results show that increase in the post‐reformer temperature increases the gas yield as well as the hydrogen fraction of the gas and reduces the yields of the other products. Meanwhile, addition of red mud as a support catalyst also increases the hydrogen fraction of the gas, even when the gas yield does not increase. Overall, the addition of red mud increases the yields of the liquid and gaseous products and reduces the yield of the solid product, although it has little or no influence on specifically the yield of the biooil. Nevertheless, both factors (increasing post‐reformer temperature and addition of red mud) improve the quality of the oil. Finally, the quality of the product water tends to improve in both cases. Finally, it is observed that the influence of red mud is more pronounced at the lower post‐reformer temperature (600 °C). This implies that the introduction of red mud in the TCR® of digestate at the industrial level can help lower the energy and, thus, cost of the process.