There is presently an urgent demand for efficient and/or renewable energy technologies to correct global warming. However, these energy technologies are limited mainly by political and economic constraints of high costs and the lack of subsidy. Carbon-pricing strategies, such as carbon-emission taxes and carbon-emission trading schemes, may reduce this gap between sustainable and unsustainable energy technologies. Therefore, this paper seeks to analyze both of these carbon-pricing instruments in the Mexican energy sector to promote upgrading biogas investment and to substitute liquified petroleum gas consumption using an optimization approach. Furthermore, we propose a multi-objective optimization approach to encourage investment in the biogas supply chain supported by an effective use of carbon-pricing schemes. A case study of the central western region of Mexico was made to analyze the performance of the proposed methodologies. The results show that carbon-emission taxes and carbon-emission trading systems stimulate, with some limitations, the investment in biogas projects for fossil fuel substitution. Nevertheless, using the proposed multi-objective optimization formulation leads the discovery of a more efficient use of the above-mentioned carbon-pricing schemes, thus reaching higher economic and environmental benefits than traditional carbon-pricing policies, with a lower cost/price per ton of carbon dioxide equivalent.
The main goal of this paper is to critically review current microkinetics available for Fischer-Tropsch synthesis (FTS) modelling, in order to propose the best way to follow this set of complex reactions; therefore a microkinetic model was developed for FTS, accomplishing surface chemistry, heterogeneous kinetics, and single-event previous development for Co-based catalysts. Model starts simulating CO activation on catalyst surface, and then formation of methane, ethane and subsequent chain growth. Reaction rates were derived following the formalism of Langmuir-Hinshelwood-Hougen-Watson (LHHW); surface steps were proposed in consequence of feasibility. Chain growth was modelled by single-event steps, taking into account geometrical conformation explicitly. Number of growth steps of 1-olefins was rectified as requiring one more active site than mechanisms proposed previously; it was found that formation of these olefins exhibits a fast drop in chain growth; this phenomenon is explained in terms of probable geometrical conformations that lead to the number of single events. Experimental results in literature about isothermal synthesis of hydrocarbons in the gasoline range were simulated in a fixed-bed laboratory reactor; thermodynamic consistency was derived from chemical equilibrium over all reactions occurring during FTS. Equilibrium constants were evaluated as function of Gibbs free energy, and partial pressures of reactants and products.
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