Análise técnico-econômica da produção de hidrogênio via reforma a vapor do etanol para a síntese de amônia

Abstract

The use of fossil fuels as opposed to the use of renewable sources or processes with lower environmental impacts is still guided, in general, by the lack of economically attractive solutions in the market to compete and justify applications with lower carbon emissions. In the context of the commitment to reduce the emission of greenhouse gases signed by the countries participating in the Paris Agreement, which aims to achieve, by the middle of this century, a maximum increase of 1.5°C in global temperature when compared to preindustrial averages, the need to change current energy matrices becomes evident. In this sense, several processes and new materials have been studied and, among them, hydrogen appears as an opportunity, given its importance, its volume produced and its main raw material, which is methane extracted from non-renewable natural gas deposits. In this way, the use of renewable sources to produce H2 allows obtaining an environmentally less aggressive chain of derivatives, such as the so-called “Green Ammonia”. In this work, a simulation was proposed, with the aid of the Aspen Plus® process simulator, of the steam reforming of ethanol from sugarcane to supply hydrogen to an ammonia production plant with the purpose of carrying out a technical analysis of the process, through thermodynamic and process simulations in which the temperature, the molar ratio between water vapor and ethanol and the operating pressure were varied, as well as a preliminary economic evaluation, in order to verify its feasibility when compared to the current methane steam reforming process. In short, it was found that the predominant reaction route in the Ni-Al lamellar double hydroxide catalyst used in this work involved a significant formation of methane in its intermediate reactions and, consequently, the yield of hydrogen formation in the reactions was conditioned to the balance of CH4 with the other species present in the reaction media. For the economic and process evaluation, three operating conditions that contemplated the particularities of H2 production addressed throughout the work were evaluated and the one with the lowest cost, whose value was USD4.55/kg H2, operated with the reformer at 900°C, 20 bar and molar ratio between steam and ethanol equal to 8. This production cost represents a value approximately twice as high as the cost of production via steam reforming of methane and this is mainly due to the cost of ethanol.