Oxidation state of a peatland

The oxidative ratio [ORterra] is the amount of O2 released relative to the CO2 sequestered by the terrestrial biosphere and can be used to assess the magnitude of the terrestrial carbon [C] sink. The Intergovernmental Panel on Climate Change [IPCC] use a value of 1.10±0.05 for the ORterra; this value is from one study [Severinghaus 1995]. The value of the ORterra is hence imperative in the calculation of carbon flux to land; an overestimation of OR would result in an underestimation of C flux to land. Peatlands represent the most important terrestrial C store and are predicted to be amongst the ecosystems worst affected by climate change; predicted impacts include lowering of water tables and wildfires. Recent research has found the accepted value of the ORterra to be higher than the value measured in several ecosystems [e.g., Worrall et al. 2013]. The accuracy of the use of 1.10±0.05 for peatland ecosystems and the effects of wildfire on peat soils is assessed here. An outline of the current understanding of the ORterra and the C sink nature of peatland ecosystems is given in Chapter 1. Gaseous flux analysis of the OR of a field peatland ecosystem is performed in Chapter 2. Contributions towards overcoming difficulties in measurement of OR by gaseous flux analysis identified in Chapter 2 are made by measuring OR of an artificial peatland regularly by the same method and by elemental analysis in Chapter 3. Variation in OR with depth and location of Austrian peatlands is analysed in Chapter 4. The effects of wildfire on oxidation state and composition of peat soils from Swineshaw moorland, UK is assessed in Chapter 5. This study finds a significant difference in OR measured by gaseous flux analysis and elemental analysis. The method of gaseous flux measurement of OR was limited by the detection limit of the apparatus and this approach would require long measurement times. Measurement of gas fluxes under dark conditions prior to light conditions increases the rate of photosynthesis. OR measurement by gaseous flux analysis would be best focused on times and locations with high photosynthesis. The accepted value of ORterra is found to be at the maximum extent of values measured by this study and is not representative of the range of values measured in peatland ecosystems. Use of the IPCC’s value for ORterra may be resulting in an underestimation of the global terrestrial C sink. Change in OR with depth and location of peatland ecosystems, and burnt status is found to show significant and complex variation in the samples analysed. Increase in the degree of unsaturation [Ω] and decrease in H/C with depth in peat soils is a result of condensation reactions which occur with burial. Changes to these compositional indicators, and others e.g., C/N in peat soils affected by wildfire, are suggested to be more appropriate for assessing the C-sink nature of peatland ecosystems than the oxidation state or OR

Assessment of the CO2 capture potential from irreplaceable industrial sources

The industrial sector represents approximately 20% of total US CO2 emissions.1 These emissions can be further categorized as direct (accountable on-site, e.g., stationary combustion), indirect (assigned to electricity purchased for power) and process (CO2 liberated as a reaction by-product). For example, steel and cement production both involve processes that directly emit CO2 as a by-product (via the oxidation of metallurgical coke and conversion of calcium carbonate to lime, respectively). While climate change mitigation efforts have the potential to reduce direct and indirect emissions through the adoption of best practice technologies and low-carbon energy sources, process emissions will remain largely unaffected in the absence of radical advances in engineering. As materials like glass, iron, cement and ammonia constitute the irreplaceable fabric of society and have few green analogs, CO2 emissions from these, as from other irreplaceable industrial processes, are projected to increase unabated. With capture technologies in place, these emissions can be diverted instead to viable CO2 reuse and sequestration opportunities, such as enhanced oil recovery (EOR), food processing, refrigeration, and fertilizer production.2 To assess the capture potential of irreplaceable industry, we first geo-reference these sources alongside all current and potential future CO2 sinks, with the goal of making economically sound linkages between source and markets of comparable scale.3 This entails a cost analysis of on-site capture plus additional transport (freight versus pipeline, hazmat fees, etc.) and compression costs. Geographic information systems (GIS) mapping is used to define the most cost-effective mechanisms for CO2 delivery. Further, additional sources of revenue offset (CO2 waste valorization and potential allowance trading) are incorporated to develop a more complete assessment of economic viability. As these costs are inventoried, the financial incentive gap necessary to compel the targeted source-sink pairings to move forward is calculated. Capture costs fell under a wide range, from $89 per tonne to a low of approximately$28 per tonne. Using $40 per tonne CO2 resale as a reference, our results indicate that the most viable industries for installing CO2 capture technologies are ammonia, ethanol, glass, and petrochemicals. Not surprisingly, many of these industries all ready take advantage of these low CO2 capture costs and consequently represent a large portion of the US merchant CO2 market. When revenue from CO2 resale is incorporated, larger contributors to the industrial emission profile like cement and iron and steel fall under the viability threshold. Finally, incentive based policy (like the current California cap and trade program) pushes even more industries toward carbon neutrality and some cases (ammonia, iron and steel, and petrochemicals) become carbon-negative. It should be emphasized that this analysis is a “lowest-hanging fruit” assessment, whereby lowest possible costs are reported based on plant character (CO2 purity) and source-sink transport logistics. An overall assessment by industry is less optimistic and reveals that those industries with prohibitive capture costs are not substantially aided by waste revenue and policy offsets; thus, the most important variable to reducing economic barriers to capture is the relative purity of CO2. This effort will develop a current economic assessment of moving irreplaceable industry toward carbon-neutrality. Though these industrial process emissions represent a smaller portion of total annual CO2 emissions, these opportunities may serve as a driver for learning and public acceptance, with future applicability to the assessment of carbon-neutrality in other sectors

Nitrogen-functionalized porous carbons for enhanced CO2 capture

The global consequences of increased anthropogenic carbon dioxide emissions are well documented. To avoid the catastrophic long-term damages associated with climate change, much attention has been devoted to the development of CO2 emission mitigation strategies. A present challenge in the mitigation of anthropogenic CO2 emissions involves the design of less energy- and water-intensive capture technologies. Traditional capture methods, e.g. MEA solvent scrubbing, have prohibitive regeneration costs, and recent concerns in drought-ridden states like California have brought these water-intensive processes under increased scrutiny. Sorbent-based capture represents a promising solution to the aforementioned hurdles, as they do not incur the heavy energy penalties associated with solvent regeneration. However, to be considered competitive with their more mature, solvent-based counter-parts, these sorbents must exhibit i) high CO2 loading capacity and ii) high CO2/N2 selectivity. Ultra-microporous character and surface nitrogen functionality have been reported to be of great importance to the enhancement of CO2 capacity and CO2/N2 ideal selectivity. However, the role of pore size in combination with surface N-functionalities in the enhancement of these properties remains unclear. To investigate these effects, grand canonical Monte Carlo (GCMC) simulations were carried out on pure and functionalized 3-layer graphitic slit pore models. Theoretical isotherms were constructed as the PSD-weighted sum of individual slit-pore models of width varying from 3.5 to 200Å. In addition to pure and monovacancy-graphite, the following functional groups were isolated for testing at ~3% coverage: pyridinic nitrogen, pyrrolic nitrogen, quaternary nitrogen, and oxidized-pyridinic nitrogen. Our results reveal that nitrogen surface-functionalization can enhance CO2 loading by upwards of 90 percent over pure graphite. Increasing surface-coverage of quaternary-nitrogen resulted in enhanced loading, though higher coverage loadings converged at approximately 4 mmol CO2 g-1 sorbent. Charge analysis revealed that enhanced loading was strongly correlated with the oxidation state of surface-bound oxygen and, to a lesser extent, nitrogen at low pressures, with a decreasing effect at higher pressures. Functionally bound hydrogen contributed at higher (ambient) pressures suggesting a secondary mechanism of adsorbate stabilization. Ideal CO2/N2 selectivities were calculated for pure and N-doped models using both HL (low pressure) and IAST (working pressure) methods. Our results show that N-doping can enhance HL but not IAST selectivity. This is attributed to the introduction of a few highly active surface sites through surface N-modification. Additionally, selectivity was found to be greatly enhanced in the ultra-microporous volumes (3.5 - 7Å). These results illustrate that N-functionalization can influence CO2 and N2 adsorption behavior, particularly in narrower pores where opposing wall potentials overlap – an important consideration in the rational design of future carbon-based sorbents

Mineral carbonation opportunities in the western United States

Mineral carbonation—the production of carbonates from carbon dioxide and alkaline earth compounds—is a candidate route for carbon capture and storage because alkali earth carbonates are stable over geologic time. Successful mineral carbonization requires a source of alkalinity near a source of carbon dioxide and a chemical pathway requiring only mild energy input. Please download the file below for full content

Metallic membranes for N2 separation & post-combustion CO2 capture improvement

Carbon (CO2) capture represents an important role in the reduction greenhouse gas emissions. Among various CO2 capture technologies currently investigated, post-combustion capture allows for the retrofitting of existing plants and industrial units. Today, the amine scrubbing is considered the most competitive method for CO2 removal in the flue gases from power plants in comparison to other technologies. Nevertheless, recent work has shown that the energy requirement for solvent recovery can decrease the overall efficiency of the power plants up to 16%1. Moreover, additional costs may occur in the solvent absorption technology because of solvent disposal and its continuous replacement due to chemical deterioration. In contrast, membrane systems usually do not require additional chemicals or solvents. In addition, membranes offer higher energy efficiencies, greater operational flexibility as well as simplicity of operation and maintenance. Polymeric membrane operations are currently being explored for CO2 capture in power plants. However, some issues still remain regarding the scalability and reliability of the polymeric materials under real operating conditions where the temperature is often too high for polymer stability. Metallic membranes, by contrast, usually require high temperature for operation and may be more beneficial in saving energy under high temperature conditions. In particular, their use for N2 removal from coal-fired flue gases located nearby the boiler exit may result in increased concentrations of CO2 and pollutants with a significant reduced gas volume in the downstream, allowing for traditional emissions controls to perform more efficiently and, consequently, lowering the overall energy consumption and capital and operating costs. Therefore, the aim of this work is to explore the potentiality of N2-selective metallic membranes for post-combustion CO2 capture. In particular, the effect of different temperature and pressure conditions as well as the effect of different gas exposure on membrane performance, in terms of N2 permeating flux and ideal selectivity of N2 with respect to other gas is studied and analyzed. Moreover, scanning electron microscope (SEM), electron microprobe analyzer (EMPA), and X-ray photoelectron spectroscopy (XPS) analyses are used for investigating the effect of the different operating conditions on the membrane surface. Based on a preliminary theoretical investigation using density functional theory, the Group V transition metals (e.g., vanadium (V), niobium (Nb) and tantalum (Ta)) show strong affinity toward N2. Therefore, these metals are chosen as membrane materials in this study. Pure V, Nb, and Ta foils with a thickness of 40 μm are used. Dp [kPa] 200 300 400 500 N2 Permeance [mol/s·m2·kPa] 3.23·10-8 2.85·10-8 2.78·10-8 2.55·10-8 Permeation tests with pure gases (He, N2 and CO2) are performed to characterize the membranes in terms of N2 permeating flux and ideal selectivity at different temperature and pressure, which are varied from 400 to 600 °C and from 2.0 to 6 bar, respectively. Nb test results are only shown as a particular example in this abstract. In Table 1, the N2 permeances as a function of Δp are reported. The Nb membrane showed complete selectivity towards N2 permeation at 400 °C and trans-membrane pressure (Dp) greater than 3.0 bar. At lower pressure, no N2 permeating flux through the membrane is detected. The Nb membrane is completely destroyed when the temperature is increased up to 500 °C. EMPA analysis on this membrane showed the presence of oxygen on the surface, as illustrated in Figure 1. Among the metallic membranes used in this study, V membrane showed better performance in terms of N2 permeating flux and long-term stability. Therefore, the future study will be focused on the synthesis and analysis of V alloys in order to enhance the N2 permeance and improve the resistant of membrane towards oxidation

Opportunities for industrial CO2 capture and utilization in the US

Carbon dioxide capture from flue gases has largely failed to gain traction due to their prohibitively high cost. One strategy to lower capture costs is to target capture from emissions with higher CO2 concentration. This presentation focuses specifically on a sub-section of industrial CO2 emissions, of which there are no carbon-free routes for the formation of products such as cement, glass, iron and other metals. Although these emissions do not represent the majority, unlike the electricity and transportation sectors, they are not replaceable with renewables or bio-energy routes, and in fact, their scale matches well with CO2 utilization opportunities. A low-cost pathway, including separation, compression and transportation to currently available utilization opportunities has been identified. In particular, our cost model corrects for differences in exhaust composition, flow rate, and geo-specific utilization demand. A regional case-study for the US state of Pennsylvania reveals steel and cement manufacturing as the least cost options. Further, we find that transportation via trucks is generally the low-cost alternative compared to pipeline transport for small volumes on the order of 100 kt CO2/a. These results are presented in the context of other complexities such as the relative feasibility of extracting CO2 process emissions from combustion emissions, theoretical maximum commodity outputs by region, and competitive-based commodity trading (regional and international) inspired by localized CCUS efforts

CO2 capture from the industry sector

It is widely accepted that greenhouse gas emissions, especially CO2, must be significantly reduced to prevent catastrophic global warming. Carbon capture and reliable storage (CCS) is one path towards controlling emissions, and serves as a key component to climate change mitigation and will serve as a bridge between the fossil fuel energy of today and the renewable energy of tomorrow. Although fossil-fueled power plants emit the vast majority of stationary CO2, there are many industries that emit purer streams of CO2, which result in reduced cost for separation. Moreover, many industries outside of electricity generation do not have ready alternatives for becoming low-carbon and CCS may be their only option. The thermodynamic minimum work for separation was calculated for a variety of CO2 emissions streams from various industries, followed by a Sherwood analysis of capture cost. The Sherwood plot correlates the relationship between concentrations of a target substance with the cost to separate it from the remaining components. As the target concentration increases, the cost to separate decreases on a molar basis. Further, a spatial analysis of CO2 point sources revealed that as the purity of CO2 emissions increases, the quantity at a single source tends to decrease. Furthermore, the lowest cost opportunities for deploying first-of-a-kind CCS technology were found to be in the Midwest and along the Gulf Coast. Many high purity industries, such as ethanol production, ammonia production and natural gas processing, are located in these regions. The southern Midwest and Gulf Coast are also co-located with potential geologic sequestration sites and enhanced oil recovery opportunities. As a starting point, these sites may provide the demonstration and knowledge necessary for reducing carbon capture technology costs across all industries, therefore improving the economic viability for CCS and climate change mitigation. The various industries considered in this review were examined from a dilution and impact perspective to determine the best path forward in terms of prioritizing for carbon capture. A possible implementation pathway is presented that initially focuses on CO2 capture from ethanol production, followed by the cement industry, ammonia, and then natural gas processing and ethylene oxide production. While natural gas processing and ethylene oxide production produce high purity streams, they only account for relatively small portions of industrial process CO2. Finally, petroleum refineries account for almost a fifth of industrial process CO2, but are comprised of numerous low-purity CO2 streams. These qualities make the latter three industries less attractive for initial carbon capture implementation, and better suited for consideration towards the end of the industrial carbon capture pathway

H2 production in Palladium-based Membrane Reactor

One possible use for hydrogen, without direct greenhouse gas emissions, is as feed for a fuel cell (FC), with the most readily available technology being a proton exchange membrane FC (PEMFC). In order to avoid the poison of PEMFC’s Pt-based catalyst due to the presence of ppm levels of CO, the hydrogen feed needs to be ultra-pure. The industrial process for hydrogen production, which is a multi-step energy intensive process followed by further separation/purification, can be a potential source [1]. However, as an alternative method a Pd-based membrane reactor (MR) can be used owing to its ability to provide the pure hydrogen without any further purification. Moreover, the MR works at milder operating conditions compared to the traditional system. In the last years, Pd-based composite membranes, i.e. thin metallic layer supported on such porous materials as ceramics or stainless steel, have been considered owing to their lower cost (thin Pd layer) and higher mechanical resistant (porous support) than dense Pd-based ones [2]. Therefore, the aim of this study is to analyze the potentialities of a Pd membrane supported on porous stainless steel (PSS) with the intent to produce pure hydrogen from methane steam reforming. The initial characterization of the membrane by way of ideal selectivity took place at 400°C with H2, He and N2 and P in the range of 1.5 - 3.0 bar. After ideal selectivity characterization of the Pd/PSS membrane, methane steam reforming reaction is carried out in MR by varying reaction pressure and sweep gas flow rate. The best performance of the Pd-based MR is obtained at 400 °C, 3.0 bar and 100 mL/min of sweep-gas, yielding a methane conversion of 84%, hydrogen recovery of 82%, and obtaining a pure hydrogen stream at the permeate side. REFERENCES [1] Rostrup-Nielsen, J.R., Catalytic steam reforming. 1984: Springer. [2] Liguori, S., et al., Performance of a Pd/PSS membrane reactor to produce high purity hydrogen via WGS reaction. Catalysis Today, 2012. 193(1): p. 87-94