Improved Energy Efficiency of Power-to-X Processes Using Heat Pumps Towards Mobility Sector Defossilization

Combining Power-to-X (PtX) processes with high temperature heat pumps (HTHP) can significantly increase their energy efficiency. Evaluating the example of oxymethylene ethers (OME) production from H₂ via H₂O electrolysis and captured CO₂ from air shows that by upgrading waste heat streams using HTHP, a process overall energy efficiency of higher than 61 % can be achieved compared to 30 % in conventional integrated processes. Thereby, the waste heat stream from H₂O electrolysis already covers the low temperature heat demand for CO₂ capture via direct air capture, not only for OME but also for various PtX products. Importantly, a significant lever for the energy efficiency enhancement is the consideration of other low temperature heat-demanding sectors. High overall process energy efficiencies and the electrification of the industry are key aspects towards a sustainable mobility sector.     

Reaction between CO2 and CaO under dry grinding

This study was carried out to investigate the reaction between CO₂ and materials that contain CaO under dry grinding. Chemical reagent CaO was used in this experiment, and waste concrete was also tested to examine the feasibility of CO₂ sorption into it. Samples were ground in a CO₂ atmosphere by a centrifugal ball mill. The reaction was measured with the constant volume method. The effects of amount of sample, the number and diameter of balls, the concentration of CO₂ in the mixture of CO₂ and air and the rotational speed on the CO₂ sorption were examined. The amount of the CO₂ sorption under grinding was larger than that without grinding. The grinding enhanced the reaction between CaO and CO₂. The CO₂ sorption steeply increased with time in the early stage of grinding. After that, it increased gradually. The CO₂ reacted with the CaO at the surface layer of the newly exposed surface of the CaO particles during the grinding. The initial sorption rate of CO₂ was related with the shear force. In the latter stage of grinding, the grinding process caused the CaO particles to agglomerate. As a result, the sorption of CO₂ became slow. It was found that the waste concrete had high potential for sorption of CO₂ by means of dry grinding.     

CO2 separation by carbon molecular sieve monoliths prepared from nitrated coal tar pitch

The objective of the present work is to develop a simple procedure, which avoids the need of a binder, to obtain activated carbon monoliths from a waste precursor (coal tar pitch) suitable for CO₂ capture and/or separation. The main task of this process consists of a nitration process of the coal tar pitch. This nitration step over the coal tar pitch is characterised by different techniques, such as infrared spectroscopy and thermogravimetric analysis. The nitration treatment produces the oxidation of the pitch molecules, leading to hydrogen consumption and generating oxygenated and nitrogenated surface complexes. As a consequence of this oxidation, nitrated coal tar pitch is an infusible material, which allows the carbonization of monolithic pieces avoiding their fusion. Decomposition of these surface complexes during the carbonization of monoliths generates narrow microporosity, which is suitable for CO₂ capture from gas streams at room temperature. The molecular sieving properties of these materials are studied by CH₄ and CO₂ adsorption kinetics.     

Isolation of a phospholipid fraction from inedible egg

During processing of eggs, large amounts of waste material (feed grade or “inedible egg”) are also produced. The amount of “feed grade egg” that the US industry generates from processing operations is estimated to be approximately 2% of the egg production. Researchers are challenged to investigate potential new uses of this by-product. With nearly 80% of the total phospholipids present in egg being phosphatidylcholine (PC), inedible egg constitutes an inexpensive source of an ingredient with high nutritional and functional properties. Our objective was to optimize and improve existing methods to isolate an enriched phospholipid fraction from dry inedible eggs by selective supercritical fluid extraction (SFE). A phospholipid-rich fraction was successfully extracted with a unique two-step process, consisting of a first step with CO₂ and a second step with ethanol as co-eluent. In an effort to optimize the extraction conditions of the first step, pressure, CO₂ flow rate and temperature effects were investigated. Various times of extraction were also employed to obtain the highest concentration of PC in the residual egg powder with the highest elution of unwanted neutral lipids. Optimal conditions to achieve the highest retention of PC in the dried egg were found to be 41.4 MPa pressure, CO₂ flow rate of approximately 5 l/min and 45 °C sample temperature. A second step with a SFE with CO₂-containing ethanol as modifier resulted in elution of a fraction rich in PC. The yield was estimated to be approximately 49 g PC/kg of dried egg. Results presented demonstrate that supercritical fluid extraction can lead to the isolation of a value-added ingredient from a by-product of the egg industry.     

Behaviour of bone origin hydroxyapatite at elevated temperatures and in O2 and CO2 atmospheres

In the present work the behaviour of HAp extracted from pig bones at elevated temperatures up to 1000 °C in O₂ and CO₂ atmospheres has been studied. It has been found that CO₂ atmosphere arrests HAp decomposition. Chemical analysis and infrared spectroscopy reveal that no free CaO appears and no decrease of CO₃⁻² group concentration occurs in the material calcined in CO₂ atmosphere. In the O₂ atmosphere at elevated temperatures, CaO and CO₂ are emitted from the samples, although the remaining material retains the HAp structure as indicated by the X-ray diffraction.     

Zur Ozeanischen Pufferwirkung auf den atmosphärischen CO2-Gehalt in einem Fließgleichgewicht

The Buffering Effect of the Oceans upon Atmospheric Carbondioxide Content The influence of the oceans upon atmospheric CO₂-content by an irreversible flow equilibrium is studied. Besides the already disclosed influences of pH value and calcium ions concentration in the seawater an essential effect of the total CO₂-passage through the atmosphere steps forth. Respecting the negligible small amount (lesser than 1%) of anthropogenic carbondioxide in comparison to the annual CO₂-flux through the atmosphere any additional greenhouse effect by human activity is excluded.     

Liquid-phase preparation of catalysts used in slurry reactors to synthesize dimethyl ether from syngas: Effect of heat-treatment atmosphere

A CuZnAl slurry catalyst was prepared directly from a solution of metal salts by an entirely liquid-phase method. The influence of heat-treatment atmospheres with different proportions of CO₂ on the single-step synthesis of dimethyl ether (DME) from syngas was investigated and the catalysts were characterized by powder X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD), X-ray photoelectron spectrometry (XPS) and thermogravimetry-mass spectrometry (TG-MS). Results showed that the introduction of CO₂ into the heat-treatment atmosphere made it easier to reduce the catalyst. It also adjusted the Cu⁰/Cu⁺ ratio on the catalyst surface, the CO₂ reacting with the metallic carbide there to form CO, which then reduced part of the Cu₂O to Cu. Moreover, it was concluded that the final phase structure of the catalyst and the Cu/Zn ratio on its surface depended mainly on its composition and the reaction environment and less so on the heat-treatment atmosphere. In the DME synthesis reaction, it was found that the introduction of CO₂ into the heat-treatment atmosphere restrained the water–gas shift reaction and raised the DME selectivity. An optimal amount of CO₂ in the heat-treatment atmosphere favored the increase of the DME space–time yield. The catalysts performed best when the heat-treatment atmosphere contained 50% CO₂.     

CO2 Reduction to Substitute Natural Gas: Toward a Global Low Carbon Energy System

Methane has proven to be an outstanding energy carrier and is the main component of natural gas and substitute natural gas (SNG). SNG may be synthesized from the CO₂ and hydrogen available from various sources and may be introduced into the existing infrastructure used by the natural gas sector for transport and distribution to power plants, industry, and households. Renewable SNG may be generated when H₂ is produced from renewable energy sources, such as solar, wind, and hydro. In parallel, the use of CO₂-containing feed streams from fossil origin or preferably, from biomass, permits the avoidance of CO₂ emissions. In particular, the biomass-to-SNG conversion, combined with the use of renewable H₂ obtained by electrolysis, appears a promising way to reduce CO₂ emissions considerably, while avoiding energy intensive CO₂ separation from the bio feed streams. The existing technologies for the production of SNG are described in this short review, along with the need for renewed research and development efforts to improve the energy efficiency of the renewables-to-SNG conversion chain. Innovative technologies aiming at a more efficient management of the heat delivered in the exothermic methanation process are therefore highly desirable. The production of renewable SNG through the Sabatier process is a key process to the transition towards a global sustainable energy system, and is complementary to other renewable energy carriers such as methanol, dimethyl ether, formic acid, and Fischer-Tropsch fuels.     

Biologie der Methan-Bildung

Biology of methane formation. It has long been known that methane is produced in nature where organic compounds are degraded by microorganisms under anaerobic conditions. On an industrial scale, this process has been used for more than 50 years in the stabilization of sewage sludge from municipal waste water treatment plants. Recently it could be demonstrated that at least three different groups of bacteria are involved in the degradation of organic material into methane and CO₂. Hydrolytic and fermentative bacteria first degrade the organic compounds into various alcohols, fatty acids, hydrogen and CO₂. The second group of bacteria convert these metabolites into acetic acid, hydrogen, and CO₂, which are then utilized by the methanogenic bacteria to produce methane and CO₂.     

Gas–liquid–solid reaction system for CO2 electroreduction to formate without using supporting electrolyte

The use of bismuth-based catalysts is promising for formate production by the electroreduction of CO₂ captured from waste streams. However, compared to the extensive research on catalysts, only a few studies have focused on electrochemical reactor performance. Hence, this work studied a continuous-mode gas–liquid–solid reaction system for investigating CO₂ electroreduction to formate using Bi-catalyst-coated membrane electrodes as cathodes. The experimental setup was designed to analyze products obtained in both liquid and gas phases. The influence of relevant variables (e.g., temperature and input water flow) was analyzed, with the thickness of the liquid film formed over the cathode surface being a key parameter affecting system performance. Promising results, including a high formate concentration of 34 g/L with faradaic efficiency for formate of 72%, were achieved.     

Electrochemical CO2 Reduction: Recent Advances and Current Trends

With rising levels of CO₂ in our atmosphere, technologies capable of converting CO₂ into useful products have become more valuable. The field of electrochemical CO₂ reduction is reviewed here, with sections on mechanism, formate (formic acid) production, carbon monoxide production, reduction to higher products (methanol, methane, etc.), use of flow cells, high pressure approaches, molecular catalysts, non-aqueous electrolytes, and solid oxide electrolysis cells. These diverse approaches to electrochemical CO₂ reduction are compared and contrasted, emphasizing potential processes that would be feasible for large-scale use. Although the focus is on recent reports, highlights of older reports are also included due to their important contributions to the field, particularly for high-rate electrolysis.     

Syngas Stoichiometric Adjustment for Methanol Production and Co-Capture of Carbon Dioxide by Pressure Swing Adsorption

Methanol is an important raw material in industry and is commonly produced from syngas. The stoichiometric ratio (H₂–CO₂)/(CO + CO₂) of the methanol synthesis reactor feed stream must be adjusted to approximately 2.1. In this study, the replacement of the solvent unit within a coal to methanol process by a pressure swing adsorption (PSA) unit is proposed. The PSA produces a hydrogen enriched stream, to adjust the stoichiometric ratio of the methanol feed stream, and simultaneously captures the carbon dioxide for future sequestration. The feed flow rate is sub divided into eight 4-bed PSA units, operated with a defined phase lag between them in order to flatten the products (composition and flow rate) oscillations. The results show that the stoichiometric adjustment is possible and that oscillations on the products flow rate and composition are reduced to less than 3%. A carbon dioxide stream of 95.15% is obtained with a recovery of 94.2% and a productivity of 82.7 mol CO₂/kg/day. The power consumption of the global process is 119.7 MW, which includes the requirements for the rinse stream (64.4 MW) and the compression of the CO₂ product to 110 bar for sequestration (55.3 MW).     

A numerical study of capillary pressure–saturation relationship for supercritical carbon dioxide (CO2) injection in deep saline aquifer

Carbon capture and sequestration (CCS) is expected to play a major role in reducing greenhouse gas in the atmosphere. It is applied using different methods including geological, oceanic and mineral sequestration. Geological sequestration refers to storing of CO₂ in underground geological formations including deep saline aquifers (DSAs). This process induces multiphase fluid flow and solute transport behaviour besides some geochemical reactions between the fluids and minerals in the geological formation. In this work, a series of numerical simulations are carried out to investigate the injection and transport behaviour of supercritical CO₂ in DSAs as a two-phase flow in porous media in addition to studying the influence of different parameters such as time scale, temperature, pressure, permeability and geochemical condition on the supercritical CO₂ injection in underground domains. In contrast to most works which are focussed on determining mass fraction of CO₂, this paper focuses on determining CO₂ gas saturation (i.e., volume fraction) at various time scales, temperatures and pressure conditions taking into consideration the effects of porosity/permeability, heterogeneity and capillarity for CO₂–water system. A series of numerical simulations is carried out to illustrate how the saturation, capillary pressure and the amount of dissolved CO₂ change with the change of injection process, hydrostatic pressure and geothermal gradient. For example, the obtained results are used to correlate how increase in the mean permeability of the geological formation allows greater injectivity and mobility of CO₂ which should lead to increase in CO₂ dissolution into the resident brine in the subsurface.     

Systematic development of predictive molecular models of high surface area activated carbons for adsorption applications

Adsorption in porous materials is a promising technology for CO₂ capture and storage. Particularly important applications are adsorption separation of streams associated with the coal power plant operation, as well as natural gas sweetening. High surface area activated carbons are a promising family of materials for these applications, especially in the high pressure regimes. As the streams under consideration are generally multi-component mixtures, development and optimization of adsorption processes for their separation would substantially benefit from predictive simulation models. Here, we develop a molecular model of a high surface area carbon material based on a random packing of small fragments of a carbon sheet. In the construction of the model, we introduce a number of constraints, such as the value of the accessible surface area, concentration of the surface groups, and pore volume to bring the properties the model structure close to the reference porous material (Maxsorb carbon with the surface area in excess of 3000 m²/g). We use experimental data for CO₂ and methane adsorption to tune and validate the model. We demonstrate the accuracy and robustness of the model by predicting single component adsorption of CO₂, methane and other relevant components under a range of conditions.     

Extrusion with Carbon Dioxide (CO2) and Characterization of ABS/Mg (OH)2/Nanoclay Composites

In this paper, carbon dioxide (CO₂) is used to form a high-density microcellular thermoplastic foam structure in order to reduce polymer consumption and facilitate dispersion of Mg (OH)₂ and nanoclay fillers. A twin-screw extruder system was used to predistribute inorganic fillers into the ABS polymer, resulting in composite ABS/filler pellets. This is followed by the use of a single-screw extruder wherein supercritical carbon dioxide is introduced into the formulation. Finally, the resulting foam ABS/filler/CO₂ pellets are injection- molded into test samples. The structure and properties of the composites are characterized using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Furthermore, ABS/Mg(OH)₂/nanoclay polymer composite samples are tested to obtain their yield and tensile strengths, elastic moduli, yield and tensile elongations, izod impact strengths, hardness values, heat deflection temperatures (HDT), Vicat softening points, and melt flow indices (MFI). These tests reveal that for the overall reduction in the amount of polymer in the samples, material properties did not generally deteriorate and even showed improvements in some areas. Moreover, resulting injection-molded samples have been shown to possess dimensional integrity due to the continued expansion of CO₂ during the molding operation.     

Amine-functionalized polycarbosilane hybrids for CO2-selective membranes

Commercially available polycarbosilane has been chemically modified with primary and secondary amino silane derivatives in order to provide amine-functionalized polycarbosilane as hydrophobic solid sorbent capable of reversibly capturing CO₂ from flue gas streams. CO₂ uptake by the samples was investigated at the molecular level using thermogravimetric analysis under CO₂ atmosphere, in situ DRIFTS analysis, and CO₂ sorption isotherm. The reaction paths and sorption mechanisms were examined by comparing with the CO₂ adsorbing behaviors previously studied for amine-functionalized SiO₂, and proven to be related to the presence of adsorbed water, as well as the nature of the grafted amino silanes. With effective CO₂ adsorption rate, regeneration capacity at 40–50 °C, and lesser sensitivity to moist due to its hydrophobic Si-C backbone, secondary amine-functionalized polycarbosilane hybrids have potential applications in membrane gas separation through facilitated transport of CO₂.     

THE EFFECT OF VARIOUS SODIUM SILICATES AND OTHER ELECTROLYTES ON CLAY SLIPS1

Attention is drawn to the fact that different brands of sodium silicate vary 250 % in their soda to silica ratio. Four silicates with ratios from 1:1.8 to 1:4 were added on a basis of per cent Na₂O to slips of six clays commonly used in the whiteware industry. Rate of flow, hydrogen-ion concentration, and settling behavior were studied. Maximum rate of flow was produced in each case while the slip was acid. Those silicates high in silica were the most potent in their effect on rate of flow for a given amount of Na₂O. The effect was also more pronounced than that of NaOH, Na₂CO₃, or silica sol which were used as comparisons. Possible explanations of the mechanism of deflocculation are discussed to explain the results.     

Adsorption and separation of CO2/N2 and CO2/CH4 by 13X zeolite

Accumulation of greenhouse gases in the atmosphere is responsible for increased global warming of our planet. The increasing concentration of carbon dioxide mainly from flue gas, automobile and landfill gas (LFG) emissions are major contributors to this problem. In this work, CO₂, CH₄ and N₂ adsorption was studied on Ceca 13X zeolite by determining pure and binary mixture isotherms using a constant volume method and a concentration pulse chromatographic technique at 40 and 100°C. The experimental data were then compared to the predicted binary behaviour by extended Langmuir model. Results showed that the extended Langmuir theoretical adsorption model can only be applied as an approximation to predict the experimental binary behaviour for the systems studied. Equilibrium phase diagrams were obtained from the experimental binary isotherms. For these systems, the integral thermodynamic consistency tests were also conducted. It was found that Ceca 13X exhibits large CO₂/CH₄ and CO₂/N₂ selectivity and could find application in landfill gas purification, CO₂ removal from natural gas and CO₂ removal from ambient air or flue gas streams. © 2011 Canadian Society for Chemical Engineering     

Decarburisation behaviour of high-carbon MgO-C refractories in O2-CO2 oxidising atmospheres

High-carbon MgO-C refractories have been widely used in oxygen bottom blowing converters due to their excellent thermal shock resistance property. However, decarburisation is unavoidable in MgO-C refractory materials applied around oxygen bottom blowing tuyeres. To alleviate the decarburisation rate of MgO-C refractories and prolong the furnace life of oxygen bottom blowing converters, a new method consisting of mixing CO₂ in the bottom blowing oxygen was proposed by the authors. The decarburisation behaviour of MgO-C refractories in O₂-CO₂ oxidising atmosphere has not been studied before. Herein, the effects of the CO₂ ratio in the O₂-CO₂ oxidising atmosphere on the decarburisation amount and the microstructure of the decarburisation zone were investigated experimentally. The results show that as the CO₂ ratio increases, the weight loss of the MgO-C refractory decreases with a parabolic trend and the decarburisation zone depth decreases with a linear trend. Micrographs show that pores form in the decarburisation zone, and the amount of pores decreases as the CO₂ ratio increases. The results confirm that mixing CO₂ in the bottom blowing oxygen can effectively alleviate the decarburisation of MgO-C refractories.