To alleviate the pressing problem of greenhouse gas emissions, the development and deployment of sustainable energy technologies is necessary. One potentially viable approach for replacing fossil ...fuels is the development of a H
2
economy. Not only can H
2
be used to produce heat and electricity, it is also utilised in ammonia synthesis and hydrocracking. H
2
is traditionally generated from thermochemical processes such as steam reforming of hydrocarbons and the water-gas-shift (WGS) reaction. However, these processes suffer from low H
2
yields owing to their reversible nature. Removing H
2
with membranes and/or extracting CO
2
with solid sorbents
in situ
can overcome these issues by shifting the component equilibrium towards enhanced H
2
production
via
Le Chatelier's principle. This can potentially result in reduced energy consumption, smaller reactor sizes and, therefore, lower capital costs. In light of this, a significant amount of work has been conducted over the past few decades to refine these processes through the development of novel materials and complex models. Here, we critically review the most recent developments in these studies, identify possible research gaps, and offer recommendations for future research.
This paper reviews the advances of enhanced thermo-chemical processes applying H
2
-selective membrane reactors and
in situ
CO
2
capture for selective H
2
production.
To shift the world to a more sustainable future, it is necessary to phase out the use of fossil fuels and focus on the development of low‐carbon alternatives. However, this transition has been slow, ...so there is still a large dependence on fossil‐derived power, and therefore, carbon dioxide is released continuously. Owing to the potential for assimilating and utilizing carbon dioxide to generate carbon‐neutral products, such as biodiesel, the application of microalgae technology to capture CO2 from flue gases has gained significant attention over the past decade. Microalgae offer a more sustainable source of biomass, which can be converted into energy, over conventional fuel crops because they grow more quickly and do not adversely affect the food supply. This review focuses on the technical feasibility of combined carbon fixation and microalgae cultivation for carbon reuse. A range of different carbon metabolisms and the impact of flue gas compounds on microalgae are appraised. Fixation of flue gas carbon dioxide is dependent on the selected microalgae strain and on flue gas compounds/concentrations. Additionally, current pilot‐scale demonstrations of microalgae technology for carbon dioxide capture are assessed and its future prospects are discussed. Practical implementation of this technology at an industrial scale still requires significant research, which necessitates multidisciplinary research and development to demonstrate its viability for carbon dioxide capture from flue gases at the commercial level.
In a fix: Biofixation of CO2 from flue gases with microalgae is a promising way of dealing with greenhouse gas emissions to produce value‐added products. Microalgae fix CO2 faster than terrestrial plants and do not compete with agricultural crops. This review critically assesses the influence of flue gas compounds on microalgae carbon‐partitioning strategies to tune the product composition, large‐scale development, and overall process economics.
•HBr doping technique for improving calcium looping performance has been demonstrated at pilot scale.•Attrition resistance of calcium sorbent at pilot scale has been demonstrated due to HBr ...doping.•Successful production of cement from the residues has been demonstrated at the kg scale.
One of the main challenges for commercialising calcium looping (CaL) as a CO2 capture technology is maintaining a high level of sorbent reactivity during long-term cycling. In order to mitigate the decay in carrying capacity, research has moved towards producing enhanced sorbents. However, this creates potential problems related to ease of scaling up production techniques and production costs, and raises the question as to whether such approaches can be used at large scale. On the other hand, a key advantage of CaL over other carbon capture technologies is synergy with the cement industry, i.e., use of spent sorbent as a feedstock for clinker production. In this work two enhanced materials: (i) limestone doped with HBr through a particle surface impregnation technique; and (ii) pellets prepared from limestone and calcium aluminate cement, were tested in a 25 kWth dual fluidised bed pilot-scale reactor in order to investigate their capture performance and mechanical stability under realistic CaL conditions. Moreover, the spent sorbent was then used as a raw material to make cement, which was characterised for phase and chemical composition as well as compressive strength. The HBr-doped limestone showed better performance in terms of both mechanical strength and stability of the CO2 uptake when compared to that of pellets. Furthermore, it was shown that the cement produced has similar characteristics and performance as those of commercial CEM 1 cement. This indicates the advantages of using the spent sorbent as feedstock for cement manufacture and shows the benefits of synthetic sorbents in CaL and suitability of end-use of spent sorbents for the cement industry, validating their synergy at pilot scale. Finally, this study demonstrates the possibility of using several practical techniques to improve the performance of CaL at the pilot scale, and more importantly demonstrates that commercial-grade cement can be made from the lime product from this technology.
Sludge produced from wastewater treatment has little to no value and is typically treated through volume reduction techniques, such as dewatering, thickening, or digestion. However, these methods ...inherently increase heavy metal concentrations, which makes the sludge unsuitable for land spreading and difficult to dispose of, owing to strict legal requirements/regulations concerning these metals. We addressed this problem, for the first time, by using recyclable low-cost protic ionic liquids to complex these toxic metals through a chemical fractionation process. Sewage sludge samples collected from wastewater plants in the UK were heated with methylimidazolium chloride (HmimCl, triethylammonium hydrogen sulfate (TEAHSO4) and dimethylbutylammonium hydrogen sulfate (DMBAHSO4) under various operating temperatures, times and solids loadings to separate the sludge from its metal contaminants. Analysis of the residual solid product and metal-rich ionic liquid liquor using inductively coupled plasma-emission spectrometry showed that HmimCl extracted >90% of CdII, NiII, ZnII, and PbII without altering the phosphorus content, while other toxic metals such as CrIII, CrVI and AsIII were more readily removed (>80%) with TEAHSO4. We test the recyclability of HmimCl, showing insignificant efficiency losses over 6 cycles and discuss the possibilities of using electrochemical deposition to prevent the buildup of metal in the IL. This approach opens up new avenues for sewage sludge valorization, including potential applications in emulsion fuels or fertilizer development, accessed by techno-economic analysis.
Calcium looping is a high-temperature solid-looping process for CO2 capture, exploiting cyclical carbonation of CaO. Previous work investigating the effects of steam on the carbonation reaction has ...produced conflicting results, with the majority of work conducted using thermogravimetric analyzers (TGA). Here, pressurized carbonation kinetics in the presence of steam in a 3kWe pressurized spout-fluidized bed reactor, gives a rigorous insight into the effects of steam. Pseudo-intrinsic kinetics were determined using an effectiveness factor model along with activation energies and kinetic expressions. The mechanism in which steam promotes CO2 adsorption on the surface of CaO was investigated using density functional theory (DFT). The molecular-scale changes on the CaO surface owing to the presence of steam compared to the base case of CO2 adsorption on a ‘clean’ (without steam) surface were simulated with the Cambridge Serial Total Energy Package (CASTEP) software. The results suggest that steam promotes CO2 adsorption via the formation of surface OH groups on the CaO surface.
•This is the first article on the effects of pressure on the CaO-CO2 reaction in the presence of steam inside a reactor.•The presence of steam improves carbonation kinetics.•This is the first time DFT theory has been applied to the CaO-CO2 reaction in the presence of steam.•How steam improves carbonation rate is explained by a surface model.
Biomass combustion with in situ CO2 capture via the calcium looping cycle is a novel process for the production of low- (or even negative-) carbon heat and power. Both processes can take place in the ...same unit vessel because of their compatible operating temperatures (600–700 °C). Combining the two process steps is beneficial in terms of reduced number of unit operations and process complexity. However, biomass combustion at this lower temperature range can result in the production of tar. In addition to reduced combustion efficiency, the presence of tar can lead to the blockages and fouling of downstream process equipment and loss of sorbent reactivity because of coking. Higher temperatures are known to increase tar conversion; however, this is detrimental to the rate of carbonation. Pressurizing the process allows higher CO2 partial pressures to be achieved and therefore alleviates the thermodynamic limitations on the process. Our work employed a novel high-temperature, pressurized fluidized-bed reactor to investigate the influence of temperature, pressure, and the presence of CaO on biomass combustion and tar yield. Higher operating pressures and temperatures or the addition of CaO were found to significantly reduce the gravimetric tar yield. However, the extent of CO2 capture appeared to have been limited by rapid combustion kinetics at the higher end of the investigated temperature and O2 partial pressure ranges. Size exclusion chromatography and ultraviolet fluorescence analysis of the product tars helped to provide insights into tar production and destruction pathways under different conditions.
Air pollutants from poultry production, such as ammonia (NH3) and particulate matter (PM), have raised concerns due to their potential negative impacts on human health and the environment. Vegetative ...environmental buffers (VEBs), consisting of trees and/or grasses planted around poultry houses, have been investigated as a mitigation strategy for these emissions. Although previous research demonstrated that VEBs can reduce NH3 and PM emissions, these studies used a limited number of samplers and did not examine concentration profiles. Moreover, the differences between daytime and nighttime emissions have not been investigated. In this study, we characterized emission profiles from a commercial poultry house using an array with multiple sampling heights and explored the differences between daytime and nighttime NH3 and PM profiles. We conducted three sampling campaigns, each with ten sampling events (five daytime and five nighttime), at a VEB-equipped poultry production facility. NH3 and PM samples were collected downwind from the ventilation tunnel fans before, within, and after the VEB. Results showed that ground-level concentrations beyond the VEB decreased to 8.0% ± 2.7% for NH3, 13% ± 4% for TSP, 13% ± 4% for PM10, and 2.4% ± 2.8% for PM2.5 of the original concentrations from the exhaust tunnel fan, with greater reduction efficiency during daytime than nighttime. Furthermore, pollutant concentrations were positively intercorrelated. These findings will be valuable for developing more effective pollutant remediation strategies in poultry house emissions.
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•Three field campaigns were conducted at a typical poultry house equipped with VEBs.•Pollutant concentrations (NH3, TSP, PM10, and PM2.5) were positively intercorrelated.•Ground-level concentrations decreased to 2.4%–13% of the original value with VEBs.•Reduction of pollutants was more effective during the daytime than nighttime.
The transition to a low-carbon economy is an enormous challenge. With increasing deployment of intermittent renewable energy, there is a recognised need for scalable options for grid-scale, ...long-term, high energy density, energy storage. Grid-scale energy storage combined with carbon capture and utilisation (CCU) potentially provides a high level of flexibility and reliability. However, previous power-to-gas (P2G) studies have only examined the use of synthetic natural gas (SNG) derived from electrolytic hydrogen and either biomass- or industrially-derived CO
2
for this application; making the whole power-to-power (P2P) value chain low carbon at best. Instead, our work assesses the techno-economic feasibility of using direct air capture to develop truly carbon-neutral P2P pathways. After assessing nine net-zero emission configurations using existing technologies, we found that using SNG as an energy storage carrier may be the least expensive route despite being more complex than power-to-hydrogen (P2H). P2H is currently held back by the high cost of H
2
storage and the low volumetric density of H
2
relative to SNG. Thus, bringing down the cost of H
2
storage and building more salt caverns will be imperative for P2H, whereas reducing the cost of carbon capture should be a key priority for accelerating the deployment of power-to-methane (P2M) technologies.
Carbon-neutral energy storage will be an essential technology in delivering a decarbonised, resilient energy system.
Biochemical combinatorial techniques such as phage display, RNA display and oligonucleotide aptamers have proven to be reliable methods for generation of ligands to protein targets. Adapting these ...techniques to small synthetic molecules has been a long-sought goal. We report the synthesis and interrogation of an 800-million-member DNA-encoded library in which small molecules are covalently attached to an encoding oligonucleotide. The library was assembled by a combination of chemical and enzymatic synthesis, and interrogated by affinity selection. We describe methods for the selection and deconvolution of the chemical display library, and the discovery of inhibitors for two enzymes: Aurora A kinase and p38 MAP kinase.
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