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The increasing share of renewable energy sources in the electricity grid causes curtailments, which prevent exploiting the full environmental and economic potential of renewable electricity. Power-to-X processes can utilize this electricity to produce certain products that would have been otherwise produced from fossil-based sources. To benefit the most, these Power-to-X processes need to be optimized for a maximum resource-efficiency. We demonstrate that the sole replacement of raw materials for industrial process concepts is not expedient. We therefore develop optimization-based methods to identify sustainable process concepts and support their optimal design. These methods are applied to the production of dimethoxymethane (referred to as DMM or OME1)—a promising synthetic fuel candidate and intermediate for the production of longer-chain oxymethylene ethers (OME3-5). To analyze DMM and OME3-5 production using established process concepts, we implement process models with detailed thermodynamic models from the open literature. Even by considering their maximum potential for heat integration, these process concepts have been found to be much less efficient than those for the production of other synthetic fuel candidates. Therefore, fundamentally new processes need to be designed. Emerging Power-to-X processes are usually on a very different stage of development. To enable a fair comparison and support process design, we develop a methodology that incorporates optimization-based methods on different hierarchy levels. The methodology allows a systematic way to design and evaluate each candidate regarding three key performance indicators: production costs, exergy efficiency, and global warming impact. Applied to five reaction pathways for DMM production, we identified the direct reduction of CO2 to be the most suitable one for sustainable DMM production at its current state. For a successful implementation, detailed process models are necessary. As the complicated form of such models often cause difficulties for deterministic optimization, we develop a hybrid process model for reductive DMM production incorporating Gaussian processes and artificial neural networks. For solving the resulting nonconvex program, we use a reduced-space formulation and a hybrid between the McCormick and the auxiliaryvariable method implemented in our deterministic global solver MAiNGO. Only with these measures on both the modeling and algorithm level, convergence was possible. As Power-to-X design problems often contain discrete decisions, we analyze different problem formulations regarding their suitability for global superstructure optimization and applied the most suitable one to the design problem for reductive DMM production. For mixed-integer nonlinear programming problems containing nonconvex functions, we identified such formulations as particularly promising that reduce the number of optimizationvariables. Although they introduce nonconvex terms, corresponding relaxations remain comparably tight for our example problems. However, a large library with benchmark problems of different complexity would be necessary to derive generally valid statements. The application of optimization-based methods to DMM production has demonstrated great potential. However, also limitations and further improvement potential was identified—for both the methods and DMM production as a Power-to-X process.

Los gradientes ambientales proporcionan escenarios naturales para abordar la variabilidad en la dinámica de los sistemas boscosos a diferentes escalas espaciales y temporales. Debido a la importancia de los bosques dentro del sistema terrestre y considerando las fluctuaciones en el clima previstas para las próximas décadas, resulta importante explorar las respuestas potenciales de los bosques a los cambios climáticos. En Argentina, las masas forestales templadas de América del Sur, están representadas por los bosques Andino-Patagónicos en una angosta faja paralela a los Andes. Austrocedrus chilensis (D.Don) Pic.Ser. et Bizzarri (ciprés de la cordillera) es una conífera endémica de los bosques templados de Chile y Argentina. Las poblaciones de A. chilensis en Argentina se desarrollan en un abrupto gradiente pluviométrico (2000 a 500 mm totales anuales) desde los Andes hasta el ecotono con la estepa patagónica. El objetivo de esta tesis fue analizar la relación entre el crecimiento radial de A. chilensis y las variaciones climáticas pasadas a lo largo del gradiente de precipitación (oeste-este), empleando patrones de crecimiento y de mortalidad episódica, para explorar las respuestas potenciales de la especie frente a escenarios futuros de Cambio Climático. En este estudio se desarrollaron 28 cronologías de ancho de anillo a lo largo de tres transectas en la Patagonia argentina: Norte (40°S), Centro (41°S) y Sur (42°S). Se utilizaron datos de precipitación de 21 estaciones meteorológicas y 3 grillas de temperatura para las relaciones clima-crecimiento y la construcción de los índices de humedad. Las relaciones entre las variaciones del crecimiento radial y el clima, en general, fueron positivas con la precipitación y negativas con la temperatura. Precipitaciones abundantes desde finales de primavera a verano durante la temporada de crecimiento, favorecieron el crecimiento radial en todo el gradiente oeste-este para las tres latitudes. Temperaturas elevadas para el mismo periodo, afectaron negativamente el crecimiento. Particularmente la intensidad de la respuesta a las variaciones de precipitación y temperatura de verano fue mayor en los bosques mixtos (oeste) que en los bosques ecotonales (este). El 68% de los eventos de sequías hidrológicas extremas provocó reducciones en el crecimiento de individuos vivos hasta un 80% en relación al crecimiento previo (cinco años), independientemente de la ubicación en el gradiente pluviométrico. Sólo la sequía de 1998-99 evidenció mayor reducción en los bosques compactos (mésico) y menor en los ecotonales. A su vez, el 49,5% de la mortalidad se relacionó con eventos de sequías. Por otro lado, la edad de los individuos y la capacidad de recuperación pos-sequía (eventos previos a la muerte) fueron factores determinantes en la mortalidad de árboles en pie. La evaluación del crecimiento a escala regional mediante un análisis de componentes principales, mostró que la señal común dominante de los 28 sitios explica en un 67% de la variabilidad total (61%, CP1 y 6%, CP2) en el crecimiento, mostrando el CP2 una asociación con la latitud. La cronología regional con altos valores de confiabilidad se extendió desde el año 1640 al año 2014. La comparación entre el clima actual (1967-2011) y los escenarios futuros de cambio global, moderado: RCP4.5 y severo: RCP8.5 en diferentes ventanas temporales, muestra para finales del siglo XXI una reducción de las precipitaciones de primavera-verano entre un 25% y 41%. La temperatura para el mismo periodo aumentaría entre 0,9°C y 2,7°C con respecto al clima actual (RCP4.5 y RCP8.5, respectivamente). Considerando las relaciones medias con el clima, el crecimiento de A. chilensis podría verse afectado negativamente bajo los futuros escenarios climáticos. Teniendo en cuenta la influencia de las sequías en el crecimiento y la mortalidad, la intensificación o aumento en la frecuencia de estos eventos, podrían afectar severamente la dinámica de los bosques de A. chilensis y en consecuencia su conservación en el tiempo. Environmental gradients provide natural scenarios to address the variability and dynamics of forest systems at different spatial and temporal scales. Due to the importance of forests within the Earth system and considering the expected fluctuations in the climate of the next decades, it is important to analize the potential responses of the forests to climate change. In Argentina, the temperate forest of South America are represented by the Patagonian Andean forests in a narrow belt parallel to the Andes. Austrocedrus chilensis (D.Don) Pic.Ser. et Bizzarri (cypress of the Cordillera) is a conifer endemic to Chile and Argentina. The populations of A. chilensis develop in Argentina across an abrupt precipitation gradient (2000 to 500 annual total mm) from the Andean Cordillera to the ecotone with the Patagonian steppe. The objective of this thesis was to analyze the relationship between the radial growth of A. chilensis and the past climatic variations along the precipitation gradient (west-east), using growth patterns and episodic mortality, to explore the potential responses of this species to future scenarios of climate change. In this study, 28 ringwidth chronologies were developed along three transects in the Argentine Patagonia: North (40° S), Center (41° S) and South (42° S). Precipitation data from 21 meteorological stations and 3 temperature grids were used to climate-tree growth relationships and construct humidity indices for each transect. In general, the relationships between the variations of radial growth and climate were positive with precipitation and negative with temperature. The radial growth of A. chilensis along the gradient is favored by above-average precipitation in late spring –summer during the growing season. Temperatures above the long-term mean during the same period are unfavorable to tree growth. Particularly, the intensity of the response to variations in summer precipitation and temperature was greater in mixed forests (west) than in ecotonal forests (east). Sixty eight percent of extreme hydrological droughts resulted in growth reductions to 80% in living trees, regardless of the location in the rainfall gradient. Only the 1998-99 drought showed a greater reduction in compact forests (mesic) than in ecotones. In turn, 49.5% of mortality was related to drought events. On the other hand, the age of the individuals and the post-drought recovery capacity (events prior to death) were determining factors in the death of standing trees. The PC analysis of the residual tree-ring chronologies shows the high similarity of tree-growth response to climatic variation. The first two factors accounted for 61% and 6% (PC1 and PC2, respectively) of the total variance. The PC2 was related with latitude. The highest quality period of the tree-ring regional chronology covered from 1640 to 2014. The comparison between the current climate (1967-2011) and moderate future scenarios: RCP4.5 and severe: RCP8.5, in different windows from 2016 to 2100, showed toward the end century XXI, precipitation reduction for spring and summer between 25% and 41%. The temperature at the same period would increase between 0.9° C and 2.7° C (RCP4.5 and RCP8.5, respectively). The growth of A. chilensis could be negatively affected by rising temperatures and drier conditions under future climate scenarios. Taking into account the influence of droughts on growth and mortality, the intensification or increase in the frequency of these events could severely affect the dynamics of the A. chilensis forests, and consequently their conservation in time. Fil: Marcotti, Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. CCT- Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina; Argentina. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina