Creating Added Value with a Waste: Methylation of Amines with CO2 and H2

摘要

The transformation and utilization of CO2 is a desirable alternative to CO2 storage for cutting the emissions of this greenhouse gas, while creating added value that can compensate for the energetic and economic costs of its capture. In this respect, the reduction of CO2 to fuels has the potential to mitigate meaningful volumes of anthropogenic CO2 emissions. Nonetheless, the current technologies cannot compete with the low cost of fossil fuels (hydrocarbons, coal, and gas). In fact, CO2 utilization is limited today to applications outside of the fuel sector, such as consumer goods (food preservatives, drinks, etc.), enhanced oil recovery (EOR) technologies, and the production of chemicals. Among them, the conversion of CO2 to chemicals represents about 70 % of the 220 mega-tonnes of CO2 utilized annually. This segment is dominated by a handful of processes, namely the Bosch-Meiser process for the production of urea from CO2 and ammonia, the Kolbe-Schmitt synthesis of salicylic acid (from CO2 and phenol), and the transformation of CO2 to carbonates. Interestingly, these reactions result in the functionalization of CO2 without significantly reducing the carbon oxidation state. Indeed, CO2 reduction, using renewable carbon-free reductants and abundant noble-metal-free catalysts, remains a challenge for the design of novel utilization technologies. CO2 is therefore an attractive carbon feedstock as it is cheap, renewable, and nontoxic and its transformation could contribute to achieving sustainability in the chemical industry. It should be noted, however, that its conversion to chemicals will not reduce significantly CO2 emissions as this application scales to a maximum of 5 % of the 30 gigatonnes of CO2 released every year by human activities. The main advantage of CO2 conversion to chemicals is the concomitant creation of added value which can circumvent the cost associated with CO2 capture and transformation. As an example, the six-electron reduction of CO2 to methanol must compete with the petrochemical production of MeOH, which sets its market value to 410 ? per tonne. In contrast, the market value of methylamines, which are platform chemicals such as MeNH2, Me2NH, and Me3N, exceeds 4000 ? per tonne. The reduction of CO2 to methylamines could therefore offer viable technologies for the transformation of CO2. Yet, this reaction remained unknown ... until 2013!