With the increase of the the global energy consumption has also been increasing, which is about 18 TW nowadays (Dudley, 2018), the anthropogenic CO2 emissions have also been increasing, which is about 410 ppm nowadays (Dudley, 2018; Tans & Keeling, 2019). Numerous evidences have been reported indicating that high atmospheric CO2 concentration can have significant greenhouse effect and thus lead to global warming and climate change (Pachauri et al, 2014; Hansen et al, 2013). Therefore, measures need to be taken to control and reduce the atmospheric CO2 concentration. In such circumstance, carbon capture, utilization and storage (CCUS) technologies have been proposed and developed to close the carbon cycle. Mineral carbonation (MC) is one of the CCUS technologies, which mimics the natural silicate weathering process to react CO2 with silicate materials so that carbon can be stabilized in the form of insoluble carbonates for permanent carbon storage (Seifritz, 1990; Lackner et al, 1995). Both Ca- or Mg-bearing silicate minerals and alkaline silicate industrial wastes can be employed as the feedstock for mineral carbonation (Sanna et al, 2014; Gadikota et al, 2014; Park, 2005; Park & Fan, 2004; Park et al, 2003; Park & Zhou, 2017; Zhou, 2014; Zhao, 2014; Swanson, 2014). While they share similar chemistries and total Mg and Ca contents, different MC feedstock can lead to different challenges for CCUS. As for silicate minerals, although they have large enough capacity to mineralize all the anthropogenic CO2 emissions, their reactivities are generally very low, and measures should be developed to accelerate the carbonation kinetics of the minerals (Sanna et al, 2014). However, the elemental extraction of the silicate minerals is a relatively complicated kinetic process, because silica-rich passivation layer can form on the particle surface during mineral dissolution process and thus the rate-limiting step of the process can change from chemical reaction to mass transfer. Without a clear understanding of the elemental extraction kinetics, the design and evaluation of different acceleration methods aiming at different rate-limiting steps of the process can be challenging. As for alkaline industrial wastes, they are generally more reactive than silicate minerals, but can be more heterogeneous with more complicated compositions. In such cases, the separation and recovery of other elements should also be integrated with the carbonation process so that the overall sustainability of the mineral carbonation technology can be enhanced. In order to address these challenges, this study focused on the fundamental understanding of dissolution and carbonation behaviors of alkaline silicate materials and integration of step-wise separations of rare-earth elements (REEs). Both experimental and modeling studies were carried out to provide insights into how Mg and Ca as well as REEs are leaching into solvents at different conditions, and the fundamental understandings on mineral dissolution kinetics and mechanisms were also put forward. The fate of REEs in different product streams was also identified, and methods were developed and optimized to recover and concentrate REEs, while producing solid carbonates with highest purities. Hopefully, the findings in this study can not only advance the carbon mineralization technology but also contribute to the utilization and extraction of alkaline metals, as well as REEs, from other complex unconventional resources for the sustainable energy and material future.

Carbon Capture and Storage (CCS) technology could help reduce anthropogenic CO2 emissions to the atmosphere. So far, CCS has failed to attract government support in the UK due to high costs of implementation. The broad deployment of CO2-EOR could aid the development of CCS by providing additional revenue streams for investors. The success of the CO2- EOR in the United States has raised the question of whether this success could be replicated in the UKCS. This thesis answers these questions by introducing two distinct models, which analyse the similarities and differences between the two oil provinces from the subsurface and economic perspectives. The first model integrates into the economic framework the behaviour of oil and CO2 in a reservoir. The model is applied to an oil field in the North Sea. It analyses whether the screening criteria developed based on the onshore US experience to screen for oil field candidates for the CO2 would be suitable for the oil fields in the UKCS. The second model is a theoretical CO2-EOR with storage model, which analyses how the inclusion of permanent storage changes the economics of CO2-EOR. The CO2-EOR with storage model allows for an endogenous switching point between the CO2-EOR and the permanent CO2 storage phase depending on the various economic factors, such as oil prices, sequestration subsidies and fees, CO2 price, and oil and gas tax rates. The CO2-EOR with storage model shows different behaviour compared to the case without permanent storage. On the policy level, the main difference between the two countries revealed that the UK strongly focuses on cutting CO2 emissions while the U.S. on boosting domestic oil production. Therefore, the third study in this thesis investigates the net carbon footprint of the CO2-EOR activity in the North Sea.

Proveniente do processo de pirólise, o biochar é constituído por elevado teor de carbono, em estruturas que são responsáveis pela elevada resistência à degradação. O material vem sendo objeto de estudo por seus diversos usos e benefícios que oferece ao ambiente. Quando aplicado ao solo traz melhorias relacionadas às propriedades químicas, físicas e microbiológicas do mesmo, além de ser ferramenta para o sequestro de carbono, alternativa para disposição de resíduos orgânicos com concomitante produção de energia. Entretanto, as propriedades químicas e físicas dos biochars variam grandemente devido à diversidade de matérias-primas e das condições de produção. O presente estudo visou avaliar a variação das propriedades físicas, químicas e morfológicas do biochar e a influência da matéria-prima e da temperatura de pirólise na caracterização final do produto. Para tanto, foram produzidos biochars oriundos da combinaçao de quatro temperaturas (350, 450, 550 e 650 °C) e de quatro matérias-primas (palha de cana-de-açúcar, casca de arroz, dejeto de galinha e serragem). Em todos os produtos e materiais de origem foram feitas avaliações de pH, condutividade elétrica (C.E.), capacidade de troca catiônica (CTC), teor de carbono (C), nitrogênio (N), hidrogênio (H), material volátil e cinzas, teor de nutrientes, além de avaliação de espectroscopia através de Infravermelho por Transformada de Fourier (FTIR), análise de morfologia por Microscopia Eletrônica de Varredura, análise de termogravimetria e teores de lignina celulose e hemicelulose. Constatou-se variação de algumas proprieades químicas como os teores de C, H, O, materiais voláteis, cinzas, carbono fixo, índice pH, condutividade elétrica e capacidade de troca catiônica com maior influência da temperatura de pirólise. O teor inicial de macro e micronutrientes presentes nas matérias-primas apresentou maior influência na variação das concentrações desses nutrientes nos biochars. De forma geral observou-se aumento da estabilidade química nos diferentes biochars com a elevação da temperatura de pirólise. A recalcitrância dos biochars confere-lhes persitência no solo e é confirmada pelo aumento dos teores de C e diminuição da emissão de CO2 nos tratamentos com adição desses materiais em comparação com adição de suas respectivas matérias-primas. Ademais, a contribuição dos biochars para elevação no pH do solo é de fundamental importância para sua adoção na agricultura sob o ponto de vista de fertilidade do solo. / A product of pyrolysis, biochar is a carbon rich material and its structure is responsible for the high resistance to degradation. Biochar is an interesting object of study due to its diverse applications and amendments to the environment. When applied to the soil, it is able to enhance soil physical, chemical and microbiological properties. It is also pointed as an instrument to sequester carbon and an alternative disposal for organic residues as well as energy source. However, the resultant properties of biochar vary greatly considering the diverse options of feedstocks combined with the contrasting production conditions used to obtain the final product. The present study aimed the evaluation of the different chemical and physical properties within a range of diverse biochars, and the assessment of feedstock or pyrolysis temperature mediated changes. The biochars produced combined pyrolysis temperatures (350, 450, 550 and 650 °C) with four feedstocks (sugar cane straw, rice husk, poultry manure and sawdust). In order to assess biochar properties and the temperature or feedstock mediated changes, several analysis were performed in the feedstock and biochars produced. The analysis included pH, cation exchange capacity, carbon, nitrogen and hydrogen content, proximate analysis, nutrient content, as well as spectroscopy performances such as Fourier Transformed Infrared (FTIR), morphological assessment through Scanning Electron Microscopy (SEM), termogravimetric analysis and lignin, cellulose and hemicellulose contents. The results suggests that temperature influenced greatly some of the chemical properties assessed, such as the contents of C, H, O, volatile matter, ash, fixed C, pH, electrical conductivity, cation exchange capacity. Feedstocks initial macro and micronutrient contents exhibited more influence in the variation of these elements in the biochars. In general, there was an increase in chemical stability in the different biochars with increasing pyrolysis temperature. The high recalcitrance found in biochars enable them to persist within the soil, which was confirmed by the increased levels of C content and decreased CO2 emissions when biochars addition was compared with their feedstocks addition to soils. Moreover, the contribution of biochar in increasing soil pH is very important from a soil fertility standpoint.

A recuperação e a restauração florestal de ecossistemas degradados podem não acontecer das maneiras desejadas, se houver carência nutricional ou suprimento inadequado de nutrientes às plantas no estádio inicial de desenvolvimento de espécies florestais nativas. O objetivo da presente investigação foi avaliar os efeitos da deficiência de nutrientes nas plantas na fase inicial de desenvolvimento das espécies florestais nativas Schinus terebinthifolius Raddi (aroeira-pimenteira), Cordia superba Cham. (baba-de-boi) e Cariniana estrellensis (Raddi) Kintze (jequitibá-branco). Foram observadas as alterações ultra-estruturais e teciduais das células do mesofilo das folhas, foi descrita a sintomatologia visual de deficiência nutricional, foram feitas as determinações de teores de macro e micronutrientes, das taxas de assimilação de gás carbônico e de transpiração, e as mensurações da altura e da produção de biomassa. O experimento foi conduzido em casa de vegetação, em blocos ao acaso, com três repetições e treze tratamentos para cada espécie, empregando a técnica de diagnose por subtração (-N, -P, -K, -Ca, -Mg, -S, -B, -Cu, -Fe, -Mn, -Mo, -Zn), sendo que em um dos tratamentos, as espécies nativas foram cultivadas em solução nutritiva completa, com todos os macros e micronutrientes. Durante o experimento e em sua análise, foi observada a seqüência de eventos que motivaram os sintomas de deficiência e a diminuição na produção de biomassa. Sabe-se que falta de um nutriente provoca alteração molecular, o que alterou as ultraestruturas celulares das folhas que foram observadas por microscopia. Essas modificações celulares provocaram alterações no tecido vegetal que induziram nas plantas os sintomas visuais específicos de cada nutriente que foram descritos. Como efeito fisiológico da deficiência nutricional, de forma geral, constataram-se diminuições nas taxas de fotossíntese e de transpiração e, por conseguinte, na produção de biomassa. Estes resultados claramente evidenciam o fato de que projetos de implantação de florestas ou de recuperação e restauração de ecossistemas degradados por meio do plantio das três espécies florestais nativas, em solos que necessitem de suplementação nutricional, poderão ter seu sucesso comprometido se não houver complementação nutricional / The recovery and forest restoration of degraded ecosystems may not be occur as desired if there is a nutritional deficiency or an inadequate supply of nutrients in the initial phase development of native forest species. The objective of this research was to evaluate the macronutrient and micronutrient deficiency effects on Brazilian native species young plants: Schinus terebinthifolius Raddi, Cordia superba Cham. and Cariniana estrellensis (Raddi) Kintze. Ultrastructural and tissue of the mesophyll cells of leaves changes were observed by microscopy, the visual symptom of nutritional deficiencies were described, the nutrient contents were analyzed, the carbon assimilation and transpiration rates were measured, the plant heights and the biomass production were measured. The experiment was carried on a greenhouse in a randomized block design with three replications and thirteen treatments for each species, using the technique of diagnosis by subtraction (-N, -P, -K, -Ca, -Mg, -S, -B, - Cu, -Fe, -Mn, -Mo, -Zn) and in one of the treatments the species were grown in a nutrient solution with all macro and micronutrients. It was observed, during the experiment and its analysis, a sequence of events that caused the visual symptoms and decreased the biomass production. It is known that the nutrient deficiency causes molecular alterations, which consequently led the changes in cellular ultrastructure of the leaves and they were observed by microcopy. These cellular changes caused modifications in the foliar tissue, and the plants showed specific visual symptoms of each nutrient, which they were described. As physiological effect of nutritional deficiency, in general decreases the photosynthesis and transpiration taxes, and consequently the biomass production were decreased. These results clearly project that forest implantation or recovery and restoration of damaged ecosystems by planting the three native species in soils that require nutritional supplementation may have its success compromised if there is no a nutritional supplementation

Globally, the forestry sector is the second largest contributor of greenhouse gases, and sustainable forest management is a major target of international environmental policy. However, there is the assumption underlying many policy recommendations that an increase in above-ground carbon stocks correspond to long term increases in ecosystem carbon stocks, the majority of which is stored in soils. We analyzed soil carbon and nitrogen dynamics in forest soils that had undergone twenty years of organic inputs manipulations as part of the Detritus Input and Removal Treatment (DIRT) network. There was no statistically significant effect of the rate of litter or root inputs on the carbon or nitrogen in bulk soil, on respiration rates of soil in laboratory incubations, on the non-hydrolyzed fraction of soil organic matter, or on any organic matter associated with any density. However, there is evidence for positive priming due to increased litter inputs; doubling the rate of litter inputs decreased C and N contents of bulk soil and decreased respiration rates of soil. Furthermore, there is evidence that roots influence soil organic matter dynamics more strongly than above-ground inputs. Both of these results trends match data from other DIRT sites, and are supported by the literature. / Graduation date: 2012

Wälder haben im Bezug zum Klimawandel mehrere Rollen: Sie sind Kohlenstoffspeicher, -senken, sowie Lieferanten von Holz als Rohstoff für die Kohlenstoffspeicher in Produkten und für Substitution fossiler Energieträger. Unter Klimaschutzgesichtspunkten ist es wünschenswert, die Kohlenstoffbindung im Gesamtsystem aus Senken, Speichern und Substitution zu maximieren und zu entscheiden, welche Maßnahme an welchem Ort und unter welchen Rahmenbedingungen den größten positiven Effekt auf die CO2-Bilanz hat. Um die Speicherung in den verschiedenen Kompartimenten erfassen zu können müssen geeignete Inventurverfahren zur Verfügung stehen. Die IPCC – GPG benennen die Speicher und geben zum Teil Anforderungen an die zu erreichende Inventurgenauigkeit. Aus der klassischen Forsteinrichtung stehen genügend Methoden zur Verfügung, um das oberirdische Volumen sehr genau zu erheben. Um den Anforderungen an ein umfassendes Kohlenstoffmonitoring genügen zu können, müssen diese Verfahren in den Bereichen Erfassung von Störungsfolgen, Totholzdynamik, Boden und der Berechnung von Gesamt-Kohlenstoffvorräten aus dem Holzvolumen ergänzt werden. Zusätzlich bietet sich an, Bewirtschaftungsmaßnahmen entsprechend zu erfassen, um ihre Auswirkung auf die Kohlenstoffdynamik ebenfalls feststellen zu können. Dies ist für die Berichterstattung zwischen Inventuren sowie für die Herausrechnung von nicht-menschenverursachter erhöhter Kohlenstoffspeicherung („factoring out“ im Sinne des KP) wünschenswert. Wenn Bewirtschaftungsmaßnahmen unterschieden werden können und ihre Auswirkungen auf C-Vorräte bestimmbar sind, ist eine Verifizierung erhöhter Speicherung auch z. B. für Projekte nach Art. 3.4 des KP durchführbar. Diese Arbeiten stecken jedoch noch in der Anfangsphase. Im Rahmen dieser Arbeit wurde die erste verfügbare qualitative Übersicht zu dieser Thematik erstellt. Die Optimierung der Wald-Holz-Option wird durch die im Kyoto-Protokoll (und den zugehörigen Folgeabkommen) vereinbarten Regelungen erschwert, da einerseits zwischen Wald und Produkten eine Trennung besteht und andererseits die Maßnahmenverantwortlichem im Wald nicht direkt durch das KP angesprochen werden. Eingeschlagenes Holz wird im Wald als Emission betrachtet und dem entsprechenden Sektor zugerechnet, was jedoch keine Auswirkungen auf den Forstbetrieb hat. Dieser profitiert im Gegenteil derzeit von der durch die – auch von KP Regelungen beeinflussten – Holzpreise und erhöht die Nutzungen, was zu Vorratsabsenkungen im Wald führt. Ob diese Absenkungen durch die Substitutionseffekte des geernteten Holzes kompensiert werden ist derzeit noch nicht geklärt. Um die Trennung zwischen Wald und Produktpool aufzuweichen bietet es sich an, die Waldbesitzer am Emissionsrechtehandel teilhaben zu lassen, damit nicht nur die Ernte sondern auch der Ernteverzicht finanziell bewertbar sind. Sozio-ökonomische Szenarien zur künftigen Entwicklung der Landwirtschaft zeigen große Flächenpotentiale, die für die Nahrungs- und Futtermittelproduktion nicht mehr benötigt werden oder nicht mehr rentabel sein werden. Eine mögliche Nutzung in Zukunft sind Energieholzplantagen. Informationen zu möglichen Erträgen sind zur Zeit noch unzureichend und Analysen zur Nachhaltigkeit dieser Erträge unter Klimawandel sind nicht vorhanden. In dieser Arbeit wurde mit dem ökophysiologischen Waldwachstumsmodell 4C an Beispielsstandorten in Brandenburg das Wachstum von Energieholzplantagen unter derzeitigem Klima und unter verschiedenen regionalisierten Klimawandelszenarien bis 2055 simuliert. Ertragspotentiale liegen derzeit auf der Mehrzahl der Standorte im positiven Bereich, auf einigen Standorten ist jedoch nur begrenzt mit positiven Deckungsbeiträgen zu rechnen. Bis 2055 ist in allen Szenarien mit einem leichten Rückgang der Erträge und einer deutlicheren Verringerung der Grundwasserneubildung unter Energieholzplantagen zu rechnen. Die Unterschiede zwischen Standorten sind jedoch derzeit und unter zukünftig möglichem Klima stärker als klimabedingte Änderungen. Bei der großflächigen Anlage von Energieholzplantagen können negative Auswirkungen auf die Biodiversität und andere Naturschutzbelange eintreten. Eine diese Effekte abmildernde Flächengestaltung, die trotzdem Erträge auf dem Niveau heutiger Vollerwerbslandwirtschaft erreicht, ist möglich. Insgesamt lässt sich für die Optimierung der Wald-Holz-Option feststellen, dass eine Nicht-Nutzung bestehender Waldflächen unter Klimaschutzgesichtspunkten negativ ist. Der Substitutionseffekt geernteten Holzes beträgt zusätzliche ca. 70 Prozent Kohlenstoff, die in dieser Form in nicht bewirtschafteten mitteleuropäischen Wäldern nicht zusätzlich gespeichert werden. Es ist davon auszugehen, dass sich durch die Berücksichtigung von Substitutionseffekten andere – wahrscheinlich kürzere – als die heute üblichen Produktionszeiten ergeben. Auf bisher waldfreien Flächen ist die Anlage von Energieholzplantagen positiver zu werten als eine normale Aufforstung. / Forests are important for climate protection: They sequester and store carbon, and provide timber for wood products and fossil fuel substitution. These functions interact in a complex way. From a climate protection point of view it is desirable to optimize these interactions, i.e. to maximize the amount of carbon stored in the whole system (called „forest-timber-option“) and to analyse what impact a management decision at the local level has with regard to the amount of carbon in the atmosphere. Inventory methods to estimate the total amount of carbon in a forest are needed. Classical forest inventories assess above-ground tree volume. To estimate total car-bon in accordance with the requirements of the Kyoto-Protocol, these inventories need to be expanded with regard to the assessment of disturbances, dead wood de-composition, soil carbon, and the estimation of carbon from volume. Methods in-vented here can also be used to assess local-level management activities, or to “fac-tor out” non-human-induced changes in carbon pools. The optimization of the „forest-timber-option“ is restricted due to regulations of the Kyoto-Protocol, because forest-related measures are accounted for under other sec-tors than wood and timber use. Harvested timber is estimated as an “emission” from the forest, and forest owners have no benefit from the use of wood for industrial pur-poses. Here, an inclusion of forestry in emission trading schemes can be advanta-geous. Alternative ways to produce wood are short-rotation coppice plantations on agricul-tural soils. Information about growth and yield potentials are scarce for the regions where land availability is high. Aspen (P. tremula, P. tremuloides) was parameterized in an eco-physiological forest growth model (“4C”) to assess these potentials on sites in Eastern Germany under current and under changing climatic conditions. The re-sults indicate that growth potentials are more sensitive to soil quality than to climatic conditions. Potential yields allow for incomes comparable to standard agriculture, but biodiversity and groundwater recharge may be negatively affected by large-scale plantations. An optimization of the „forest-timber-option“ requests the use of timber from forests. Harvested timber substitutes additional 70 % of carbon from fossil fuels. Forests un-der total protection do store more carbon than managed forest, but not equivalent to the substitution effects. Total protection of forests is thus no viable means for climate protection under Central European conditions.

This work examines the impact of a viscosity force parameter, fluid velocity, and a capillary force parameter, interfacial tension, on the saturation, morphology, and topology of NW fluid in Bentheimer sandstone after primary imbibition, drainage, and secondary imbibition. Brine and air (used as a proxy for supercritical CO₂) flow experiments were performed on 6 mm diameter Bentheimer cores and were quantified via imaging with x-ray computed microtomography (x-ray CMT), which allows for three dimensional, non-destructive, pore-scale analysis of the amount and distribution of NW phase fluid within the sandstone cores. It was found that trapped NW phase saturation decreases with increases in capillary number, average blob size decreases with increases in capillary number, and the number of NW blobs increases with increases in capillary number. In addition, it was found that NW phase trapping is dependent on initial NW phase connectivity within the porous medium; with more negative values of initial NW phase Euler number resulting in less trapping. We suggest that the Euler number-saturation and the capillary number-saturation relationships for a given medium should be taken into consideration when designing a CO₂ sequestration scenario. / Graduation date: 2013

Understanding the physics of multiphase plumes and their simulation through numerical modeling has been an important area of research in recent times in the area of environmental fluid mechanics. The two renowned numerical modeling types that are commonly used by researchers today to simulate multiphase plumes in nature are the mixed-fluid and the two-fluid integral models. In the present study, a detailed review was performed to study and analyze the two modeling approaches for the case of a double plume (upward moving inner plume with downward moving annular outer plume) with the objective of ascertaining which of these models represent the prototype physics in the integral plume model equations with a higher degree of completeness and accuracy. A graphical user interface was designed to facilitate running the models. By comparison to laboratory scale experimental data and through sensitivity analyses, a rigorous effort was made to determine the most appropriate choice of initial conditions needed at the start of the model computation and at the peeling locations and to obtain the most consistent values of the different model parameters that are necessary for calibration of the two models. Consequently, with these selected sets of initial conditions and model parameters, the models were run and their outputs compared against each other for three different case studies with ambient conditions typical of real environmental data. The dispersed phases considered were air bubbles in two cases and liquid CO2 droplets for the third case, with water as the continuous phase in all cases. The entrainment coefficient was found to be the most important parameter that affected the model results. In all the three case studies conducted, the mixed-fluid model was found to predict about 30% higher values for the peel heights and the DMPR (Depth of Maximum Plume Rise) than the two-fluid model.

Mineralization has the potential to capture CO₂. In nature, mineralization is the chemical weathering of alkaline-earth minerals in which stable carbonate minerals are formed, which leads to the removal of CO₂ from the atmosphere. The adsorptive carbonation reaction of olivine ((Mg,Fe)₂SiO₄)), consisting mainly of pure magnesium silicate (Mg₂SiO₄), a main constituent of the Earth’s crust, was carried out to estimate its potential application to the separation of CO₂ in the presence of water vapor in combustion plumes. Based on the thermodynamics for a basis of the reaction mechanism, the olivine carbonation reaction is thermodynamically favorable. Water vapor was found to play an important role in improving the carbonation rate, and experimental results revealed that carbon dioxide carbon dioxide can bind into olivine minerals to form highly stable surface carbonates. The reaction activity of olivine and pure Mg₂SiO₄ in the presence/absence of water vapor was carried out by varying the temperature, reactant concentrations, and space time. Based on changes in CO₂ concentration with time, the reaction kinetic model of pure Mg₂SiO₄carbonation was developed. The reaction order was found to be approximately 1 for CO₂. The activation energy derived for the Arrhenius equation of Mg₂SiO₄-based carbonation is 76.2 ± 4.8 kJ/mol based on the changes in the reaction rates with temperature in the range of 150-200°C. To investigate the molecular reaction mechanism of CO₂ adsorption on the metal oxide surface, forming carbonates, we performed the quantum mechanical calculation of CO₂ adsorption on a CaO (100) surface. It shows that CO₂ molecules strongly react with the CaO surface due to its high reactivity and high basicity. Consequently, this study will basically lay the groundwork for the chemical mechanism of mineral carbonation of olivine with carbon dioxide in the presence of water vapor and as provide relevant information for the practical application of CO₂ sequestration by stable adsorption on mineral silicates.

Polymers rich in primary amine groups are proposed to be effective adsorbents for the reversible adsorption of CO2 from moderately dilute gas streams (10% CO2) and ultra-dilute gas streams (e.g. ambient air, 400 ppm CO2), with their performance under ultra-dilute conditions being competitive with or exceeding the state-of-the-art adsorbents based on supported poly(ethyleneimine) (PEI). The CO2 adsorption capacity (mmol CO2/g sorbent) and amine efficiency (mmol CO2/mmol amine) of linear poly(allylamine) (PAA), cross-linked poly(allylamine) prepared by post-polymerization crosslinking with epichlorohydrin (PAAEPI), and branched poly(allylamine) prepared by branching of poly(allylamine) with divinylbenzene (PAADVB) are presented here and compared with state-of-the-art adsorbents based on supported PEI, specifically branched and linear, low molecular weight PEI. Silica mesocellular foam, MCF, serves as the support material for impregnation of the amine polymers. In general, branched polymers are found to yield more effective adsorbents materials. Overall, the results of this work show that linear PAA, cross-linked PAAEPI, and branched PAADVB are promising candidates for solid adsorbents with high capacity for CO2.