Decarbonisation Technology August 2022 issue

at a constant temperature. Moreover, the use of highly active soluble catalyst enables the operating of the reactor at a relatively low temperature compared to other available technologies. Thanks to this low and well- controlled temperature, H₂ incorporation in the carrier, toluene, is maximised with negligible side reactions, allowing for enhanced efficiency of the loop (toluene hydrogenation/MCH dehydrogenation). The mild reactor section operating conditions and simplicity of reactor design lead to lower equipment and capital cost as well as lower operating cost compared to vapour phase technologies. In addition, the mild reactor section operating conditions associated with a well-integrated process result in very low carbon intensity. When produced by electrolysis from renewable energy such as sun or wind, low-carbon hydrogen is available on an intermittent basis, and a large variation in flow can be expected. The simplicity of the design offers a solution to this variability as the process is suitable to handle it and produces an organic liquid that can be easily stored. More than 35 cyclohexane units are licensed by Axens, representing more than 50% of the worldwide market share of capacity, demonstrating the readiness of Axens technology. This presence is based on well- demonstrated reliability and performance. The H₂ loading capacity in terms of operation ranges from a few kta to a few dozen kta. Larger capacity units could be designed while minimising the number of parallel equipment. Dehydrogenation: existing asset that can be used for LOHC technologies: Axens reforming unit at ANCAP refinery

quantities. To satisfy the new market, these specialty chemicals would require the scaling up of production multiples with associated CO₂ emissions. Toluene is abundant as it is produced from naphtha for blending into the gasoline pool to boost octane number. As gasoline is expected to be in excess in the coming years to meet climate objectives, no shortfall is expected to support the growing demand for toluene used as a carrier in the LOHC. LOHC loading with H₂ occurs through catalytic hydrogenation at about the same pressures as the H₂ supply pressures from electrolysers and steam methane reformers. The hydrogen release from the LOHC occurs through catalytic dehydrogenation at low hydrogen pressures. These conversion and reconversion steps, namely, ‘toluene hydrogenation’ and ‘MCH dehydrogenation’, are briefly discussed below. Toluene hydrogenation Axens toluene hydrogenation to MCH technology is based on the cyclohexane production technology from benzene. The hydrogenation of toluene is carried out in the liquid phase with a continuous injection of soluble catalyst. The high catalyst activity ensures the complete conversion of toluene. Toluene hydrogenation is highly exothermic; the liquid is maintained at boiling conditions, so the temperature in the reactor is automatically controlled. Any increase in the reaction rate results in the vaporisation of the liquid MCH Hydrogenation: industry’s benchmark for benzene hydrogenation using Axens liquid phase technology