Replacing conventional generation with renewable generation in power systems is essential for reducing CO2 emissions. It is important to know how effective renewables are in reducing CO2 emissions. Since CO2 reduction cannot be measured directly, different methods have been used to estimate reduction of CO2 emissions. The two most common methods are econometric models and dispatch models. Econometric models apply regression analysis using historical data for CO2 emissions, power production, and electricity demand to estimate CO2 reduction. On the other hand, dispatch models are detailed optimization simulations of power systems where the objective is to calculate the cost-optimal dispatch of the power plants. The dispatch model finds the optimal dispatch for a base case and counterfactual case. In the counterfactual case, the renewable generation in the system is modified. From the difference in CO2 emissions between the two cases, an estimation of CO2 reduction can be made. Recent studies have shown that dispatch models and econometric models can give different estimations of CO2 reduction. However, these studies did not include several factors that can increase CO2 emissions, such as; transmission constraints, security requirements, and non-linear factors. Examples of non-linear factors are; minimum dispatched energy of generating units, start up emissions, minimum up- and downtime for generating units, and energy generated during start-up and shut-down. This thesis examines if there is an agreement between econometric models and dispatch models for estimating CO2 reduction and if the agreement changes when more non-linear factors are considered. To examine these questions a systematic comparison has been done. Two econometric models are constructed, a linear econometric model and a polynomial linear econometric model. The polynomial linear econometric model is constructed to take into account non-linear factors. Eight dispatch models are constructed with increasing modelling complexity. Four model versions do not include any non-linear factors and four include non-linear factors. The results showed that the agreement between econometric and dispatch models is fairly good, except for versions that contain transmission constraints. The simulation is executed in a fictional test system that is not dimensioned for wind power generation at the given buses. Therefore is possible that transmission constraints impacts the reduction of CO2 too heavily. Furthermore, the results show that the non-linear factors contribute to CO2 emission and consequently lower the estimation of CO2 reduction. However, no conclusion can be made if the agreement between econometric and dispatch models divert when more non-linear factors are considered. / Världens utsläpp av CO2 måste minska för att inte jorden ska drabbas av drastiska klimatförändringar som temperaturhöjningar. Idag står elproduktionen för ungefär en fjärdedel av världens utsläpp av CO2. Därmed måste dagens elproduktion och elkraftsystem minska sina utsläpp av CO2 . Ett viktigt verktyg för att kraftsystem ska minska sina utsläpp av CO2 är expansion av förnybar elproduktion. Dock så går det inte att mäta direkt hur mycket CO2-utsläppen minskar vid expansion av förnybar elproduktion. Därför har flera olika estimeringsmetoder utvecklats för att uppskatta CO2-reduktion. De två vanligaste metoderna är ekonometriska modeller och produktionssimuleringsmodeller. Ekonometriska modeller använder sig av regressionsanalys med historiska tidsserier som; CO2 -utsläpp, kraftproduktion och elförbrukning för att uppskata CO2 -minskningen. Produktionssimuleringsmodeller är detaljerade optimeringssimuleringar där avsikten är att beräkna den kostoptimala användningen av kraftverk i ett system. Tidigare studier har visat att ekonometriska modeller och produktionssimuleringsmodeller kan ge olika uppskattningar av CO2 -reduktion. Dock har produktionssimuleringsmodellerna i studierna inte tagit hänsyn till flera faktorer som kan påverka CO2-utsläppen, som t.ex. överföringsbegränsningar, säkerhetsbegräsningar och icke-linjära faktorer. Exempel på icke-linjära faktorer är minimal produktion av energi för varje kraftverk, CO2 -utsläpp vi uppstart, minimal upp- och nertid och produktion vid uppstart och nedstänging för varje generator. Den här uppsatsen undersöker om de två metoderna ekonometriska modeller och produktionssimuleringsmodeller liknade uppskattningar av CO2 -reduktion och hur överrenstämmelsen mellan modellerna påverkas när man beaktar icke-linjära faktorer. För att försöka besvara dessa frågor har en systematisk jämförelse utförts. Två ekonometriska modeller har konstruerats, en linjär och en polynom-linjär ekonometrisk modell. Den polynom-linjära ekonometriska modellen tar i beaktning icke-linjära faktorer. Åtta produktionssimuleringsmodeller har konstruerats och de åtta olika modellerna har formulerats i en ökande ordning av noggrannhet. Fyra av modellerna tar inte hänsyn till några icke-linjära faktorer och fyra av modellerrna tar hänsyn till icke-linjära faktorer.

Infrastructure projects are today major contributors to global warming. However, various strategies for reduction of greenhouse gas emission are available, as described in sustainability assessment schemes and performed in infrastructure projects. Beyond the choice of methodology, greenhouse gas reduction represents an important challenge, namely to engage involved actors. The establishment of a common sustainability policy, reflected in procurement requirements could be a solution. However, often in subject of complications such as misunderstandings or increased cost. Impres, a research project aiming to streamline the process of greenhouse gas reduction in the infrastructure sector, conducts case studies around the world in which useful methods and examples are assimilated. In cooperation with Impres, the present report includes the case study of California High-Speed Rail (CHSR). The aim of this report is to compare strategies for greenhouse gas reduction of sustainability assessment schemes for infrastructure projects, and evaluate the feasibility as procurement requirements. Furthermore, to identify corresponding processes of greenhouse gas reduction in the case study of CHSR, as well as revealing important factors towards realization. The course of work involves a study of the schemes Envision, BREEAM Infrastructure, CEEQUAL, IS Rating System as well as the standard PAS 2080. Regarding the case study, the sustainability policy, procurement requirements and project reports are the main used sources. Moreover, qualitative interviews with involved actors have been performed in California. Finally, to create a comparative matrix for greenhouse gas reduction processes, standards ISO and PAS 2080 have been reviewed. The results show that greenhouse gas criteria of the studied schemes not are mandatory to perform in anyone but PAS 2080. Which means that further requisites might be needed in order for the schemes to be useful as procurement requirements. Furthermore, the outlining of processes reveals a weakness in the setting of a greenhouse gas reference point, and while every scheme includes a greenhouse gas quantity assessment, there is a difference in the priority of reduction. Regarding CHSR, an exclaimed policy goal is to perform climate neutral construction. While procurement requirements are limited to quantification of emitted greenhouse gases and the use of effective construction machinery, which is insufficient to meet the goal. Nevertheless, the Authority in charge is performing CO2 compensating measures, such as planting trees. Finally, a variety of driving forces, success factors and challenges for realizing greenhouse gas reduction have been identified. For example, personal motivation and legislation as driving forces. Whereas, sustainability as a core mission, experience and communication are seen as success factors, and resistance to transfer sustainability goals to procurement is an exclaimed challenge. As a conclusion, sustainability assessment schemes do have certain processes for greenhouse gas reduction in common. However, they present criteria with different degrees of obligation, affecting feasibility as procurement requirements. In CHSR, similar processes are found, where further reduction of greenhouse gases can be achieved, especially by an optimized choice of construction materials. In the end, personal motivation seems to be an important factor for introducing and realizing greenhouse gas reduction goals in infrastructure projects. / Impres

[ES] En la actualidad, el elevado consume energético y el aumento de la concentración de CO2 en la atmósfera han hecho necesaria la búsqueda de nuevas opciones para los procesos actuales. Una respuesta ha sido el aprovechamiento de la radiación solar para producir H2 a partir de la ruptura fotocatalítica del agua o la reducción del CO2 emulando a la naturaleza. Para ello, se propone el uso de materiales basados en carbono, de mayor abundancia y accesibilidad que los metales y óxidos metálicos. Además, un punto a tener en cuenta es la morfología, ya que haciendo uso del denominado "efecto de confinamiento" de los materiales 3D mejora notablemente la capacidad catalítica de los mismos. Es por esto por lo que, en la presente Tesis Doctoral, se ha desarrollado la posibilidad de obtener materiales grafénicos con estructuración tridimensional, presentado microporos en los que tiene lugar dicho efecto de confinamiento. De este modo, estos materiales son capaces de promover tanto la reacción de oxidación de la benzilamina como la reacción fotocatalítica de obtención de H2 a partir de agua y la de reducción de CO2. Concretamente, los materiales se han obtenido, por un lado, mediante el uso de agentes plantilla y la capacidad de recubrimiento de polisacáridos naturales como es el quitosano; y por otro, sin agentes plantilla, aprovechando la estructura de las ciclodextrinas como precursores del grafeno microporoso. Además, estos últimos materiales se han dopado con heteroátomos, en concreto fósforo, para mejorar la actividad fotocatalítica de estos materiales microporosos basados en carbono. / [CA] En l'actualitat, l'elevat consum energètic i l'augment de la concentració de CO2 en l'atmosfera han fet necessària la cerca de noves opcions per als processos actuals. Una resposta ha sigut l'aprofitament de la radiació solar per a produir H2 a partir de la ruptura fotocatalítica de l'aigua o la reducció del CO2 emulant a la naturalesa. Per a això, es proposa l'ús de materials basats en carboni, de major abundància i accessibilitat que els metalls i òxids metàl·lics. A més, un punt a tindre en compte és la morfologia, ja que fent ús del denominat "efecte de confinament" dels materials 3D millora notablement la capacitat catalítica d'aquests. És per això que, en la present Tesi Doctoral, s'ha desenvolupat la possibilitat d'obtindre materials grafénics amb estructuració tridimensional, presentat microporus en els quals té lloc aquest efecte de confinament. D'aquesta manera, aquests materials són capaços de promoure tant la reacció d'oxidació de la benzilamina com la reacció fotocatalítica d'obtenció d'H2 a partir d'aigua i la de reducció de CO2. Concretament, els materials s'han obtingut, d'una banda, mitjançant l'ús d'agents plantilla i la capacitat de recobriment de polisacàrids naturals com és el quitosan; i per un altre, sense agents plantilla, aprofitant l'estructura de les ciclodextrines com a precursors del grafé microporós. A més, aquests últims materials s'han dopat amb heteroàtoms, en concret fòsfor, per a millorar l'activitat fotocatalítica d'aquests materials microporosos basats en carboni. / [EN] Nowadays, the high energy consumption and the increase of the concentration of CO2 in the atmosphere have made it necessary to search for new options for the current processes. One possible answer has been the use of solar radiation to produce H2 from the overall photocatalytic water splitting or the photoreduction of CO2, by emulating nature. In this context, carbon-based materials, which are more abundant and accessible than metals and metal oxides, are proposed as catalysts. In addition, a point to take into account is the morphology, since making use of the so-called "confinement effect" of 3D materials significantly improves their catalytic capacity. This is the reason why, in this Doctoral Thesis, the possibility of obtaining graphene materials with three-dimensional structuring has been developed, presenting micropores in which this confinement effect takes place. In this way, these materials have been able to promote both the oxidation reaction of benzylamine and the photocatalytic reaction of obtaining H2 from water and the reduction of CO2. Specifically, the materials have been obtained, on the one hand, by using template agents and the coating capacity of natural polysaccharides such as chitosan; and on the other hand, without template agents, taking advantage of the structure of cyclodextrins as precursors of microporous graphene. In addition, the latter materials have been doped with heteroatoms, specifically phosphorus, to improve the photocatalytic activity of these carbon-based microporous materials. / El autor agradece el proyecto PID2021-126071OB-C21 financiado por MICINN/AEI /10.13039/501100011033/ a FEDER Una manera de hacer Europa, por la financiación recibida, y al Ministerio por la FPU que me ha permitido desarrollar estos 4 años de trabajo. / García Mulero, A. (2023). 3D Structured Graphenes as (Photo)Catalysts [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/192544

Le CO2 et la biomasse sont abondants dans la nature. La conversion de ces deux éléments constitutifs en carburants ou en produits chimiques à valeur ajoutée par des méthodes électrochimiques est essentielle pour atténuer la crise énergétique et réduire la pollution de l'environnement, ainsi que pour atteindre la carbone neutralité. Au cours des dernières décennies, de nombreux efforts ont été consacrés à ce domaine, mais la plupart d'entre eux se concentrent sur la conception de catalyseurs et l'amélioration des performances, et seules quelques recherches se concentrent sur de nouvelles réactions ou sur le mécanisme de ces réactions. Ici, nous développons une série de nouvelles réactions et étudions les mécanismes de ces réactions en utilisant la spectroscopie in situ, les principaux résultats sont les suivants : 1) Les réactions de réduction du furfural ont été menées en utilisant une feuille de Cu électrochimique comme catalyseur, et l'alcool furfural (FA, efficacité faradique, FE : 43,0%) et le 2-méthylfurane (MF, FE : 57,5%) ont été obtenus après électrolyse sous -0,43V (par rapport à l'électrode à hydrogène réversible, RHE). Les effets des différentes facettes du catalyseur sur la sélectivité ont été étudiés, et le Cu (110) produit préférentiellement de l'AF, tandis que les défauts sont les sites actifs pour la formation de MF. La spectroscopie Raman operando a montré que la production de FA et de MF partage le même intermédiaire à l'étape initiale, avec différents sites actifs conduisant aux différentes voies entre les étapes intermédiaires et suivantes et générant différents produits. 2) Des produits de liaison C-N (acétamide et formamide) ont été obtenus par la réaction de réduction du CO2 (CO2RR) avec la combinaison du substrat NH3 et des électrocatalyseurs commerciaux à base de nanoparticules de Cu ou de CuO. Avec l'optimisation, la FE maximale de ces deux produits est de ~10% au total, et la meilleure condition de réaction est 50mg Cu NPs, 1M KOH, avec 0.3M NH3, à -0.78V (vs. RHE) pendant 30 mins. L'IR in situ a montré que la formation de formamide et de formate partage le même intermédiaire, et que la production d'acétamide et d'acétate subit une voie de réaction similaire. 3) L'hydroxyméthanesulfonate (HMS), le sulfoacétate (SA) et le méthanesulfonate (produits de liaison C-S, FE représente 6% au total) ont été obtenus par le couplage CO2RR avec l'ajout de sulfite (SO32-), et des NPs de Cu2O synthétisées par la méthode de chimie humide ont été utilisées comme électrocatalyseurs. Parmi ces trois composés à liaison C-S, le HMS est le principal produit, la FE pouvant atteindre un maximum de 6 %. Le XRD in situ a montré que Cu0 est l'espèce active pour le processus de couplage C-S. Les calculs operando Raman et DFT ont montré que *CHOH est l'intermédiaire clé dans la formation de la liaison C-S, et que le couplage entre *CHOH et SO32- est l'étape qui détermine le taux. / CO2 and biomass are abundant in nature. Conversion of these two building blocks into fuels or value-added chemicals by electrochemical methods is essential for alleviating the energy crisis and reducing environmental pollution, and achieving carbon neutrality. In the past few decades, much effort has been devoted to this field, but most of this focuses on the design of catalysts and improvement of the performances, and only few research thrusts focus on new reactions or the mechanism of these reactions. Herein, we develop a series of new reactions and investigate the mechanisms of these reactions by using in-situ spectroscopy, the main results are shown as follows: 1) Furfural reduction reactions were conducted by using an electrochemical roughed Cu foil as the catalyst, and furfural alcohol (FA, Faradaic efficiency, FE: 43.0%) and 2-methylfuran (MF, FE: 57.5%) were obtained after electrolysis under -0.43V (vs. reversible hydrogen electrode, RHE). The effects of different facets on the selectivity were investigated, and Cu (110) is preferential to produce FA, while defects are the active sites for the formation of MF. Operando Raman spectrum showed that the production of FA and MF share the same intermediate at the initial stage, with different active sites leading to the pathway differential on the intermediate of the following steps and generating different products. 2) C-N bond products (acetamide and formamide) were obtained by CO2 reduction reaction (CO2RR) with the combination of NH3 reactants and commercial Cu or CuO nanoparticle (NPs) electrocatalysts. The maximum FE of these two products is ~ 10% in total. With optimization, we found a higher pH, thicker catalyst layer, and larger size of cations are beneficial to the production of acetamide. This can be attributed to the higher production of C2 intermediate and further leads to a higher FE of acetamide. In-situ IR showed that the formation of formamide and formate share the same intermediate, and the production of acetamide and acetate undergoes a similar reaction pathway. The mechanism can help to design the new next generation catalyst with a higher efficiency, which is beneficial to the future application of this reaction in chemical industry. Nitrate and nitrite are used instead of ammonia as nitrogen sources to produce C-N bond compounds, which suggests that this reaction provides a new possibility for organic synthesis. In all, this reaction expands the scope of the CO2RR application, and is also good for the development of organic synthesis. 3) Hydroxymethanesulfonate (HMS), sulfoacetate (SA) and methanesulfonate (C-S bond products, FE is 6% in total) were obtained by coupling CO2RR with the addition of sulfite (SO32-), and Cu2O NPs which synthesized by the wet chemistry method were used as electrocatalysts. Among these three C-S bond compounds, HMS is the main product, FE can reach 6% maximum. In-situ XRD showed that Cu0 is the active species for C-S coupling process. Operando Raman and DFT calculation further showed that *CHOH is the key intermediate in the C-S bond formation, and the coupling between *CHOH and SO32- is the rate-determining step. The discovery of reaction intermediates opens up the possibility of designing highly efficient catalysts, which can promote the application of this reaction in real industries. Also, this reaction provides a new possibility to synthesize C-S bond products, which have the potential to partially replace traditional organic synthetic routes with greener and more sustainable procedures.

In dieser Arbeit wurden zwei Messaufbauten für die online Gasanalyse von elektrochemischen Reaktionen entwickelt und im Hinblick auf ihre Unterschiede und Gemeinsamkeiten sowie auf den Designprozess im Allgemeinen verglichen: Differenzielle elektrochemische Massenspektrometrie (DEMS) zur Untersuchung von Nebenreaktionen in Natriumionenbatterien (SIBs). Verschiedene Designansätze aus der Literatur wurden verglichen, um den für die Anwendung in SIBs am besten geeigneten zu finden. Danach wurde ein selbst entwickeltes Design implementiert und validiert. Für die Datenauswertung wird ein neuartiger Ansatz für DEMS in Alkaliionenbatterien vorgestellt, der eine interne Validierung der Ergebnisse ermöglicht. Eine Zusammenfassung der Literatur über bekannte Reaktionen, die zur Gasbildung in Alkali-Ionen-Batterien führen, wird als Referenz die Gasentwicklung in den in dieser Arbeit untersuchten Materialien herangezogen. Das System wird zur Messung der Gasentwicklung verschiedener Elektrodenmaterialien in Halbzellenkonfiguration und zur Bewertung des Zusammenspiels einiger Elektroden in Vollzellenkonfiguration verwendet. Bei den untersuchten Materialien handelt es sich um: Natrium-Mangan-Nickeloxid (NaMNO), Natrium-Vanadium-Phosphat (NVP), Preußisch Weiß (PW), Graphit und Hartkohlenstoff. Als Elektrolyte wurden überwiegend 1M NaPF6 in Diglyme (2G), bzw. Propylencarbonat (PC) verwendet. Das zweite System ist eine rotierende Scheibenelektrode in Verbindung mit Gaschromatographie (RDE-GC). Es wurde entwickelt, um kinetische Effekte bei der elektrokatalytischen CO2-Reduktion an Kupferelektroden zu untersuchen. Die Korrelation von Massentransporteigenschaften und der Gasproduktanalyse kann Aufschluss über die Massentransportabhängigkeit von Selektivität und Aktivität der Reaktion geben. Hier wird die Gasanalyse genutzt, um die elektrochemischen Daten in Teilstromdichten zu dekonvolutieren, die unter definierten Stofftransportbedingungen zur Bildung verschiedener Produkte führen. / In this thesis two independent measurement setups for online gas analysis, in electrochemical reactions are developed and compared in terms of their differences and similarities and on the design: Differential electrochemical mass spectrometry (DEMS) for the investigation of side reactions in sodium-ion batteries (SIBs). Different design approaches from literature are evaluated to find the most suitable for the application in SIBs. After that a custom design is implemented and validated. A novel approach to DEMS in alkali-ion batteries for the data evaluation is presented, that enables internal verification of the results. Known reactions that lead to gas formation in alkali-ion batteries are reviewed form the literature, as a reference to discuss the gas evolution found in materials investigated. The system is used to measure the gas evolution of different electrode materials in half-cell configuration, and to evaluate the interplay of some of the electrodes in full-cell configuration. Materials that are studied are: sodium manganese nickel oxide (NaMNO), sodium vanadium phosphate (NVP), prussian white (PW), graphite and hard carbon. To do that two model electrolytes were selected 1M NaPF6 in diglyme (2G) and propylene carbonate (PC). The second system is a rotating disc electrode coupled with gas chromatography (RDE-GC). It is designed to study kinetic effects on the electrocatalytic CO2 reduction (CO2RR) on copper electrodes. The correlation of defined mass transport properties and gas product analysis can give insight into the mass transport dependencies on the selectivity and activity of the reaction. Here the gas analysis is used to deconvolute the electrochemical data into partial current densities, that lead to the formation of different products, under defined mass transport conditions. While some challenges remain, preliminary data that underlines the capability of such system as well as the findings on how to design such a system are presented.

Cette thèse de doctorat s’inscrit dans le cadre d’analyse du processus d'achat de transport. Plusieurs dispositifs gouvernementaux français ont été introduits pour sensibiliser les entreprises (chargeurs et transporteurs) vis-à-vis des émissions CO2 induites par le transport de marchandises. Le travail réalisé pendant cette thèse se sert de ces dispositifs comme « terrain d’études » pour comprendre quels leviers peuvent être mobilisés pour conduire les chargeurs (entreprises clientes) à mieux prendre en compte les contraintes environnementales. / This doctoral thesis forms part of the transportation purchasing process analysis. Several French government schemes have been introduced to raise companies’ awareness (shippers and carriers) regarding the CO2 emissions inducedby the transport of goods. The work achieved during this thesis uses these schemes as a "field study" to explore the impact of public policies and identifies levers that encourage shippers (client companies) to take the environmental footprint of products being transported into greater account. / Esta tesis doctoral se inscribe en el proceso de compra de transporte de mercancías y productos. El análisis se centra en el caso francés, ya que, durante los últimos años, el gobierno de dicha nación implantó y propulsó varios programas parasensibilizar a las empresas (cargadores y transportistas) con respecto a las emisiones de gases efecto invernadero y otros perjuicios medioambientales derivados del transporte de mercancías. A lo largo de la tesis doctoral, se realizan varios estudios de caso para explorar el impacto de las políticas públicas de contratación sostenible e identificar las medidas que podrían motivar a los cargadores (empresas clientes) a tener más en cuenta la huella medioambiental de los productos transportados.

IPCC SR15 rapporterade att alla framtida scenarier för att begränsa klimatförändringen till 1,5°C är starkt beroende av negativa utsläppstekniker, såsom geografisk CO2-lagring som används av Stockholm Exergi’s Värtaverket. Men kan man uppnå starkare klimatvinster genom en cirkulär koldioxidekonomi? Bildandet av en cirkulär koldioxidekonomi är absolut nödvändigt för att uppnå global koldioxidneutralitet, men hur kommer vi dit? Elektrolys av CO2 erbjuder en ekonomiskt och miljömässigt attraktiv väg för att uppgradera CO2-utsläpp till värdefulla bränslen och råvaror, vilket minskar användningen av fossila resurser och CO2-utsläpp till atmosfären. Detta examensarbete undersöker möjligheten att ta bort 720 000 ton-CO2-utsläpp från det avfallseldade kraftvärmeverket i Högdalen som fallstudie, via elektrokemisk reduktion av CO2 till eten, med målet att producera polymera konstruktionsmaterial, för att fungera som en kolsänka. Dessa polymerer har utvärderats utifrån kriterier som kapacitet som kolsänka, marknadsstorlek och LCA. Eten är den mest användbara råvarukemikalien för polymerproduktion och har ett betydande koldioxidavtryck på 1,73 ton CO2 per producerade eten. Att använda eCO2RR skulle minska betydande CO2-utsläpp och överbrygga luckan mellan fossila och förnybara resurser. Detta examensarbete föreslår en preliminär processdesign, komplett med en teknoekonomisk modell för att beräkna ekonomin, mass- och energibalanser för ett flertal scenarier. Över hundra elektrokatalysatorer har studerats i en litteraturgenomgång, där 5 st elektrokatalysator har valts ut baserat på olika styrkor i särskilda meritvärden, för att fastställa prestationsmål för lönsamhet. Den teknoekonomiska modellen drog slutsatsen att vid nuvarande prisläge på 700 SEK/MWh kunde ingen av elektrokatalysatorerna uppnå lönsamhet. Att sänka elpriset till LCOE för vindkraft till 335 SEK/MWh, blev resultaten mycket lönsamma, inklusive IRR upp till 41,3%. Modellparametrar ändrades för att fastställa de viktigaste variablerna i en omfattande känslighetsanalys. Vi kan dra slutsatsen att strömtätheter på 400-600 mA/cm2 är gynnsamma och med så låg bibehållen cellspänning som möjligt (<2,4V). Om man specifikt inriktar sig på eten som produkt kan det vara fördelaktigt att ytterligare öka lönsamheten genom att producera myr- eller ättiksyra som ett nästa steg, vilket har fördelen av enklare vätskegasseparering och för att undvika produktion av metan och etanol. För lönsamhet krävs en livstid på minst 2-4 år för elektrokatalysatorn (CCM), 10 år för stacken och 20 år för elektrolyssystemet. I miljöanalysen studerades massbalans-lagringen av CO2. Detta uppnåddes genom att ta bort de direkta utsläppen från Högdalenverket. De indirekta utsläppen förhindrades genom att ersätta konventionella processer av elkällans kolintensitet. Baserat på genomsnittet av elektrokatalysatorerna skulle värdlandet behöva kräva en kolintensitet för elproduktionen under 101 och 153 tCO₂/GWh för NET-direkt respektive indirekt CO2-avlägsnande. Följaktligen kan högre CO2-besparingar uppnås genom handel med koldioxidsnål svensk el till grannländer med mycket högre koldioxidintensitet. Totalt sett var den direkta koldioxidminskningen mellan 487 300 till 575 000 ton CO₂ och en indirekt minskning på mellan 1 065 000 till 1 219 000 ton CO₂, beroende på energieffektivitet och produkter. Den största utmaningen för kommersiell framgång för alla eCO2RR-projekt bortsett från de tekniska prestandaaspekterna är att nödvändiga förändringar i skatteregelverket behövs, så att el från elektrolysprojekt till gröna kemikalier blir skattebefriade, som jämförbart med förbränning av förnybar biomassa är befriad från CO2-skatter. / The IPCC SR15 reported that all future scenarios to limit climate change to 1.5°C are heavily reliant on negative emission technologies, such as geographical CO2 storage employed by Stockholm Exergi’s Värtaverket. But can stronger climate benefits be achieved through a circular carbon economy? The formation of a carbon circular economy is imperative towards achieving global carbon neutrality, but how do we get there? Electrolysis of CO2 offers an economically and environmentally attractive route to upgrade CO2 emissions to valuable fuels and feedstocks, thus reducing the use of fossil resources and CO2 emissions to the atmosphere, hence closing the cycle.  This thesis explores the possibility of removing the 720,000 tCO2 emissions of the case study waste-fired CHP plant, Stockholm Exergi’s Högdalenverket, via the electrochemical reduction of CO2 (eCO2RR) towards ethylene, with the goal of producing polymeric construction materials, to act as a carbon sink. These polymers were evaluated on criteria such as, capacity as a carbon sink, market size and LCA. Ethylene is the prevailing commodity chemical for polymer production and has a significant carbon footprint of 1.73 tonCO2 per tonne of ethylene produced. Displacement via the eCO2RR would prevent substantial CO2 emissions and bridge the gap between fossil and renewable resources.  This thesis describes a preliminary process design, complete with technoeconomic model to calculate the economics, mass and energy balances of numerous scenarios. Electrocatalyst data from an in-depth literature review comprising of over 100 catalysts was drawn, with 5 electrocatalyst candidates selected based on strengths in particular figures of merit, to determine performance targets for profitability. The technoeconomic model concluded that at the current price point of 700 SEK/MWh, none of the electrocatalysts could achieve profitability. Lowering the electricity price to the levelized-cost of electricity (LCOE) for wind, 335 SEK/MWh, yielded highly profitable results, including IRR up-to 41.3%. Model parameters were changed to determine the most important variables in an extensive sensitivity analysis. Concluding that performance targets require current densities of 400-600 mA/cm2 whilst maintaining as low cell voltage as possible (<2.4 V). When specifically targeting ethylene, it is beneficial to increase profitability through targeting more valuable, formic, or acetic acid, which has the advantage of easier liquid-gas separation and to avoid production of methane and ethanol. For stability, 2-4 years minimum is required for the catalyst-coated membrane (CCM), 10 years for the stack and 20 years for the electrolyser systems.    In the environmental analysis, capabilities for carbon storage were studied via CO2 balance. This was achieved by taking the direct emissions removed from Högdalenverket, the indirect emissions prevented by replacing conventional processes and by the carbon intensity of the electricity source. Based on the average energy efficiency and performance of the electrocatalysts, the host country would require a carbon intensity of electricity production below 101 and 153 tCO₂/GWh for NET direct and indirect CO2 removal, respectively. Consequently, higher CO2 savings were achieved by trading low-carbon Swedish electricity to neighbouring countries with much higher carbon intensities. Overall, the direct carbon reduction was between 487,300 to 575,000 tCO₂ and indirect reduction of between 1,065,000 to 1,219,000 tCO₂, subject to energy efficiency and targeted products.  It remains that aside from the technical performance aspects of the eCO2RR catalysts, the major roadblock towards the commercial success of all eCO2RR projects is the required adjustments to regulatory framework, such that electricity for electrolysis projects towards green chemicals exempt from taxes in a similar way to renewable biomass combustion exempt from CO2 taxes.

科学研究費補助金 研究種目:一般研究(A) 課題番号:03402043 研究代表者:中原 信生 研究期間:1991-1994年度