The importance of ammonia in the fertilizer industry has been widely acknowledged over the past decades. In view of the upcoming increase of world population and, in turn, food demand, its production rate is likely to increase exponentially. However, considering the high dependence on natural resources and the intensive emission profile of the contemporary ammonia synthesis route, as well as the rigid environmental laws being enforced at a global level, the need to develop a sustainable alternative production route becomes quite imperative. A novel approach toward the synthesis of ammonia has been realized by means of non-thermal plasma technology under ambient operating conditions. Because the given technology is still under development, carrying out a life cycle assessment (LCA) is highly recommended as a means of identifying areas of the chemical process that could be potentially improved for an enhanced environmental performance. For that purpose, in the given research study, a process design for a small-scale plasma-assisted ammonia plant is being proposed and evaluated environmentally for specific design scenarios against the conventional ammonia synthesis employing steam reforming and water electrolysis for hydrogen generation. On the basis of the LCA results, the most contributory factor to the majority of the examined life cycle impact categories for the plasma-assisted process, considering an energy efficiency of 1.9 g NH 3 /kWh, is the impact of the power consumption of the plasma reactor with its share ranging from 15% to 73%. On a comparative basis, the plasma process powered by hydropower has demonstrated a better overall environmental profile over the two benchmark cases for the scenarios of a 5% and 15% NH 3 yield and an energy recovery of 5% applicable to all examined plasma power consumption values.

An eco-efficiency analysis has been conducted, as a sustainability performance indicator, by combining the life cycle costs (LCC) and the environmental impacts of diverse plasma-assisted ammonia and nitric acid synthesis routes, for which a detailed process design for small-scale production has been previously reported. The proposed design of the specific plasma processes involves new upstream and downstream activities, which are independent of conventional natural resources and comprise less equipment. In the context of this study, the impact of the product yield and plasma power consumption on the eco-efficiency profiles of the selected plasma processes is evaluated and benchmarked against that of the established synthesis pathways. Results show a relatively improved environmental profile of the plasma-assisted NH3 (5% NH3 yield), considering a power consumption of 17.2 g NH3 kWh−1 and energy recovery of 5%, against that of the contemporary production route. In the case of the plasma-assisted HNO3 (6% NO yield) synthesis, incorporating a power consumption of 7.77 kWh kg−1 NO and a 20% energy recovery, a better ecological footprint is displayed as compared to the conventional chemical process. Both plasma processes are characterized by higher LCC than the conventional ones, with the plasma-assisted nitric acid displaying a more competitive LCC profile. A clear contribution of the utilities (upstream and downstream equipment) to both the environmental and cost benefits is shown, and the plasma plant is the enabler of such integration. The contribution is related to both the number reduction of equipment (process simplification) and improved operation (process intensification). Given the outcomes of this study, the concept of developing modular plants incorporating the plasma technology and renewable energy sources—e.g. wind power—for synthesizing ammonia and nitric acid demonstrates promising potential and promotes a new window of opportunities for future sustainable decentralized fertilizer production; such as distributed production at the farm site, with the opportunity to react immediately to weather changes and to local conditions (soil, climate, crops, farming business model).

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This work studies the variational quantum eigensolver (VQE) algorithm, which is designed to determine the ground state of a quantum mechanical system by combining classical and quantum hardware. Two methods of reducing the number of required qubit manipulations, prone to induce errors, for the variational quantum eigensolver are studied. First, we formally justify the multiple [Formula: see text] symmetry qubit reduction scheme first sketched by Bravyi et al. [arXiv:1701.08213 (2017)]. Second, we show that even in small, but non-trivial systems such as H2, LiH, and H2O, the choice of entangling methods (gate based or native) gives rise to varying rates of convergence to the ground state of the system. Through both the removal of qubits and the choice of entangler, the demands on the quantum hardware can be reduced. We find that in general, analyzing the VQE problem is complex, where the number of qubits, the method of entangling, and the depth of the search space all interact. In specific cases however, concrete results can be shown, and an entangling method can be recommended over others as it outperforms in terms of difference from the ground state energy.