Residual CO2 Research Articles

Residual trapping of carbon dioxide during geological storage—Insight gained through a pore-network modeling approach

To reduce emissions of the greenhouse gas CO2 to the atmosphere, sequestration in deep saline aquifers is a viable strategy. Residual trapping is a key containment process important to the success of CO2 storage operations. While residual trapping affects CO2 migration over large scales, it is inherently a pore-scale process. Pore-network models (PNMs), capturing such processes, are useful for our understanding of residual trapping, and for upscaling trapping parameters for larger scale models. A PNM for simulation of quasi-static two-phase flow; CO2 intrusion (drainage) followed by water flooding (imbibition) was developed. It accounts for pore-scale displacement mechanisms, and was used to investigate residual CO2 trapping. The sensitivity of the residual CO2 saturation to several parameters was studied, to validate a trapping behavior in agreement with earlier studies. Then the PNM was calibrated to core sample data and used to simulate drainage-imbibition scenarios with different turning point saturations. From these the initial-residual saturation curves of CO2 in Heletz sandstone were estimated, essential for future macroscopic-scale simulations. Further, the occurrence of different pore-scale mechanisms were quantified and the size distribution of the residual clusters was shown to exhibit a bimodal appearance. The findings improve the understanding of residual trapping in Heletz sandstone.

Applicability of thermal response tests for assessing in-situ CO2 storage in a saline aquifer

The study aims to evaluate the method of Thermal Response Tests (TRTs) in assessing in-situ residual saturation of CO2 storage in saline aquifers. Similar to TRTs, mathematically the same type of an exact analytical solution presented by Theis is well-established for the transient drawdown in an infinite uniform confined aquifer. With the change of supercritical CO2 and saline water in pore space, the inverse models of temperature change over time either heating or cooling may lead to the detection of a change in thermal properties of fluids and sold matrix. In assessing the overall thermal conductivity using the three inverse models, the Wang model describes the saline aquifer of the interest structurally well among the chosen four conductivity models. The results of the Wang model and the arithmetic model showed almost insensitivity to the residual CO2 saturation up to 50 percents in the estimation of the overall thermal conductivity, while they did a sensitivity to porosity variation of the same range. Accuracy analysis of the three inversion models showed that a developed nonlinear least square inverse model produces the least error in the estimation consistently with the wide range of the residual saturation variation of CO2.

Two-Step Electrodialysis Treatment of Monoethanolamine to Remove Heat Stable Salts

Electrodialysis technology was adapted to removal of heat stable salts from aqueous solutions of alkanolamine absorbents, with monoethanolamine as example. Removal of anions of heat stable salts by electrodialysis from a 30 wt % aqueous solution of monoethanolamine with the degree of carbonation of 0.2 mol of CO2 per mole of monoethanolamine was studied. The two-step removal of heat stable salts by electrodialysis allows the monoethanolamine loss to be reduced and the concentration of residual CO2 in the absorbent solution to be decreased. The suggested two-step electrodialysis treatment scheme allows the concentration of heat stable salts to be maintained on the required level from the viewpoint of their corrosion activity, the total volume of the concentrate to be decreased by 50%, and the monoethanolamine loss to be decreased by 30%. The treatment unit with the circulation volume of the monoethanol absorbent of 100 m3 h–1 was calculated for confirming the efficiency of the two-step electrodialysis treatment scheme. As compared to the one-step electrodialysis treatment scheme, the two-step scheme ensures recovery of 50% of monoethanolamine at the same efficiency of the removal of heat stable salts.

Variations of Residual CO2 and Pressure in Conifer Woody Roots

In continuation of works on the determination of cyclic tree-stem CO2 efflux, vacuum-extracted gas samples of large woody roots of Siberian stone pine and Scots pine are studied. Laser photoacoustic gas analysis was used to obtain chronologies of CO2 and total pressure of gas components in root rings. Spectral and cross-spectral analyses reveal the cyclic character of variations in the chronologies. Such a behavior of the total pressure and CO2 content in large roots can testify to possible cyclic diffusion of CO2 from the roots into soil and then into the atmosphere, which can be considered as a new feature of autotroph respiration. An attempt is made to analyze results of some previous work on a similar subject based on cyclic CO2 efflux from large roots.

Effect of a titania covering on CNTS as support for the Ru catalysed selective CO methanation

One of the major set-backs in the selective CO methanation process, as the final clean-up step in removing residual CO from reformate gas feed, is the reverse water gas shift (RWGS) reaction. This reaction is an undesired reaction because, it runs parallel with the selective CO methanation reaction. This increases the CO outlet concentration. The catalytic performance of ruthenium supported on carbon nanotubes (CNTs), nitrogen doped carbon nanotubes (NCNTs), titania coated carbon nanotubes (NCNT-TiO2 and CNTs-TiO2) and TiO2 anatase (TiO2-A) for selective CO methanation was investigated. The feed composition relevant to reformate gas was used but in the absence of steam. The experiments were conducted within a temperature range of 100 °C and 360 °C. It was observed that carbon dioxide methanation was suppressed until CO methanation attained a maximum conversion for all the catalysts studied. The Ru/NCNT showed higher activity than Ru/CNT at all temperatures examined due to the nitrogen incorporation in the carbon domains. Both Ru/CNT and Ru/NCNT however promoted the RWGS reaction at temperatures above 250 °C. The Ru/CNT-TiO2 catalyst recorded the highest activity for both the CO and selective CO methanation followed by Ru/TiO2-A. The presence of titania on the carbon nanotubes significantly retarded the RWGS reaction from about −120% CO conversion to about 80% CO conversion, while selectivity towards methane increased in all catalysts with increasing temperature.

Early gait abnormalities relate to brainstem and spinal cord pathology in CLN1 disease

Dissolution trapping is one of the most important mechanisms for geological carbon storage (GCS). Recent laboratory and field experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and coupled scCO2 dissolution and water flow, i.e., scCO2 dissolution at local pores/pore throats creating new water-flow paths, which in turn enhance dissolution by increased advection and interfacial area. However, the impacts of pore-scale characteristics on these coupled processes have not been investigated. In this study, imbibition and dissolution experiments were conducted under 40°C and 9 MPa using a homogeneous/isotropic hexagonal micromodel, two homogeneous elliptical micromodels with low or high anisotropy, and a heterogeneous sandstone-analog micromodel. The four micromodels, initially saturated with deionized (DI)-water, were drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at different rates with logCa (the capillary number) ranging from −6.56 to −4.34. Results show that bypass of scCO2 by displacing water is the dominant mechanism contributing to the residual CO2 trapping, triggered by heterogeneity in pore characteristics or pore-scale scCO2-water distribution. Bypass can be enhanced by pore heterogeneity or reduced by increasing transverse permeability, resulting in relatively low (<2% of CO2 solubility) or high (9–13% of CO2 solubility) dissolved CO2 concentration in displacing water. The overall dissolution of residual scCO2 increases with decreasing Ca, and approaches to their solubility at low Ca value with sufficient residence time. This main trend is similar to a capillary desaturation curve that represents the relationship between the residual saturation and Ca. Spatially, dissolution initiates along the boundary of bypassed scCO2 cluster(s) in a non-equilibrium manner, and the coupling of water flow and dissolution occurs which fragments the bypassed scCO2 clusters and enhance scCO2 dissolution.

Characterizing the Dissolution Rate of CO2-Brine in Porous Media under Gaseous and Supercritical Conditions

The CO2-brine dissolution homogenizes the distribution of residual CO2 and reduces the leakage risk in the saline aquifer. As a key parameter to immobilize the free CO2, the dissolution rate of CO2-brine could be accelerated through mechanisms like diffusion and dispersion, which are affected by the subsurface condition, pore structure, and background hydrological flow. This study contributed the calculated dissolution rates of both gaseous and supercritical CO2 during brine imbibition at a pore-scale. The flow development and distribution in porous media during dynamic dissolution were imaged in two-dimensional visualization using X-ray microtomography. The fingerings branching and expansion resulted in greater dissolution rates of supercritical CO2 with high contact between phases, while the brine bypassed the clusters of gaseous CO2 with a slower dissolution and longer duration due to the isolated bubbles. The dissolution rate of supercritical CO2 was about two or three orders of magnitude greater than that of gaseous CO2, while the value distributions both spanned about four orders of magnitude. The dissolution rates of gaseous CO2 increased with porosity, but the relationship was the opposite for supercritical CO2. CO2 saturation and the Reynolds number were analyzed to characterize the different impacts on gaseous and supercritical CO2 at different dissolution periods.

Heterogeneity, pore pressure, and injectate chemistry: Control measures for geologic carbon storage

Desirable outcomes for geologic carbon storage include maximizing storage efficiency, preserving injectivity, and avoiding unwanted consequences such as caprock or wellbore leakage or induced seismicity during and post injection. To achieve these outcomes, three control measures are evident including pore pressure, injectate chemistry, and knowledge and prudent use of geologic heterogeneity. Field, experimental, and modeling examples are presented that demonstrate controllable GCS via these three measures. Observed changes in reservoir response accompanying CO2 injection at the Cranfield (Mississippi, USA) site, along with lab testing, show potential for use of injectate chemistry as a means to alter fracture permeability (with concomitant improvements for sweep and storage efficiency). Further control of reservoir sweep attends brine extraction from reservoirs, with benefit for pressure control, mitigation of reservoir and wellbore damage, and water use. State-of-the-art validated models predict the extent of damage and deformation associated with pore pressure hazards in reservoirs, timing and location of networks of fractures, and development of localized leakage pathways. Experimentally validated geomechanics models show where wellbore failure is likely to occur during injection, and efficiency of repair methods. Use of heterogeneity as a control measure includes where best to inject, and where to avoid attempts at storage. An example is use of waste zones or leaky seals to both reduce pore pressure hazards and enhance residual CO2 trapping.

Linking the local vertical variability of permeability and porosity to newly-interpreted lithofacies in the lower Mt. Simon CO2 reservoir

A full understanding of the subsurface processes relevant to CO2 geo-sequestration, including CO2 movement and trapping, requires establishing basic relationships between the sedimentary architecture in CO2 reservoirs and the associated variations in petrophysical attributes that can affect plume dynamics and residual CO2 trapping. In this context, the variance and covariance of petrophysical attributes of the lower Mt. Simon Sandstone reservoir (Illinois, USA) are quantitatively decomposed according to sedimentary textures and structures that vary among sedimentary facies. Building on Ritzi et al. (2016), the sedimentary facies of the lower Mt. Simon are re-classified with new interpretations of sedimentary structures. A newly-revised methodology is used in which factor interactions are formally quantified and the magnitude of their contribution to the variance is compared to the main-factor effects. The decomposition results show the main-factor effects contributing to the variance of permeability and porosity are the differences in grain-size and the presence or absence of bleaching textures. The differences in permeability or porosity among the newly defined sedimentary structures make a relatively small contribution to the sample variance, and the 2-way and 3-way factor interactions are negligible. Permeability and porosity increase with coarser grain size, independent of the presence or absence of bleaching and independent of sedimentary structure. The presence of bleaching textures reduces permeability and porosity independent of the grain size or sedimentary structure. The general approach and these specific results aid in developing parsimonious reservoir simulation models.

Modeling the Effect of Modified Atmospheres on Conidial Germination of Fungi from Dairy Foods.

Modified atmosphere packaging (MAP) is commonly applied to extend food shelf-life. Despite growth of a wide variety of fungal contaminants has been previously studied in relation to modified-atmospheres, few studies aimed at quantifying the effects of dioxygen (O2) and carbon dioxide (CO2) partial pressures on conidial germination in solid agar medium. In the present study, an original culture method was developed, allowing microscopic monitoring of conidial germination under modified-atmospheres in static conditions. An asymmetric model was utilized to describe germination kinetics of Paecilomyces niveus, Mucor lanceolatus, Penicillium brevicompactum, Penicillium expansum, and Penicillium roquefoti, using two main parameters, i.e., median germination time (τ) and maximum germination percentage (Pmax). These two parameters were subsequently modeled as a function of O2 partial pressure ranging from 0 to 21% and CO2 partial pressure ranging from 0.03 to 70% (8 tested levels for both O2 and CO2). Modified atmospheres with residual O2 or CO2 partial pressures below 1% and up to 70%, respectively, were not sufficient to totally inhibit conidial germination,. However, O2 levels < 1% or CO2 levels > 20% significantly increased τ and/or reduced Pmax, depending on the fungal species. Overall, the present method and results are of interest for predictive mycology applied to fungal spoilage of MAP food products.

Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

Arctic geoengineering wherein sunlight absorption is reduced only in the Arctic has been suggested as a remedial measure to counteract the on-going rapid climate change in the Arctic. Several modeling studies have shown that Arctic geoengineering can minimize Arctic warming but will shift the Inter-tropical Convergence Zone (ITCZ) southward, unless offset by comparable geoengineering in the Southern Hemisphere. In this study, we investigate and quantify the implications of this ITCZ shift due to Arctic geoengineering for the global monsoon regions using the Community Atmosphere Model version 4 coupled to a slab ocean model. A doubling of CO2 from pre-industrial levels leads to a warming of ~6 K in the Arctic region and precipitation in the monsoon regions increases by up to ~15%. In our Arctic geoengineering simulation which illustrates a plausible latitudinal distribution of the reduction in sunlight, an addition of sulfate aerosols (11 Mt) in the Arctic stratosphere nearly offsets the Arctic warming due to CO2 doubling but this shifts the ITCZ southward by ~1.5° relative to the pre-industrial climate. The combined effect from this shift and the residual CO2-induced climate change in the tropics is a decrease/increase in annual mean precipitation in the Northern Hemisphere/Southern Hemisphere monsoon regions by up to −12/+17%. Polar geoengineering where sulfate aerosols are prescribed in both the Arctic (10 Mt) and Antarctic (8 Mt) nearly offsets the ITCZ shift due to Arctic geoengineering, but there is still a residual precipitation increase (up to 7%) in most monsoon regions associated with the residual CO2 induced warming in the tropics. The ITCZ shift due to our Global geoengineering simulation, where aerosols (20 Mt) are prescribed uniformly around the globe, is much smaller and the precipitation changes in most monsoon regions are within ±2% as the residual CO2-induced warming in the tropics is also much less than in Arctic and Polar geoengineering. Further, global geoengineering nearly offsets the Arctic warming. Based on our results we infer that Arctic geoengineering leads to ITCZ shift and leaves residual CO2 induced warming in the tropics resulting in substantial precipitation decreases (increases) in the Northern (Southern) hemisphere monsoon regions.

A Prospective, Observational Trial Assessing the Efficacy of Abdominal Compression in Reducing Laparoscopic-Induced Shoulder Pain.

Postoperative shoulder pain is a condition associated with laparoscopic surgery and presumably attributed to residual carbon dioxide (CO2) in the abdomen. The intent of the current prospective, observational study was to assess the efficacy of abdominal compression in mitigating this painful complication. We recruited 30 patients who were treated with laparoscopic surgery for the management of gynecologic disease. All study participants underwent abdominal compression to evacuate the CO2 associated with their pneumoperitoneum. Postoperatively, the subjects' pain intensity was measured via the visual analogue scale at 12, 24, and 48 hours. The patients' mean postoperative visual analogue scale pain scores were the highest during the initial 12 hours (1.93), and thereafter, steadily declined at 24 hours (0.73) and 48 hours (0.70) ( P = .045). Furthermore, toxicity was reasonable, with only 20% of subjects who reported grade ≤2 nausea and vomiting. Abdominal compression is a relatively safe procedure that appears to sufficently evacuate residual CO2, thereby reducing the severity of laparoscopic surgery induced shoulder pain.

The Influence of Heterogeneity in Wettability and Pore Structure in CO2 Geological Sequestration: A Pore-scale Study

Owing to the complexity of geological formation, a detailed understanding of all transportation phenomenon of CO2/water in porous media occurring in CGS is not yet gained. Heterogeneity in wettability and pore structure exists in mostly natural geological formation which has been proof that gives strong effects on porous media flow. Since macroscopic transportation phenomenon in porous media are always determined by pore-scale properties, investigation on heterogeneity at pore-scale gives the most fundamental influence mechanisms of heterogeneity in wettability and pore structure. In this study, we reported a pore-scale study on the influence of heterogeneity in wettability and pore structure in vertical CO2/water displacement experiments using a micro-CT machine. Two stratified sand packs, BZ06+BZ02, quarz+dolomite, were employed in displacement experiments. The experiment results indicate that, CO2 saturation pattern shows a big difference between dolomite layer and quartz layer, CO2 enters more pore spaces and owns higher CO2 saturation in dolomite layer than quartz layer in drainage. While in glass beads pack, it is noticeable that the capillary barrier of BZ02 layer significantly affects CO2 percolation process. CO2 occupied little void volume of BZ02 porous matrix. In imbibition, residual CO2 was mainly trapped in more wetting quartz layer in quartz+dolomite pack, and more compact layer in BZ06+BZ02 pack.

Simulation of CO2 Migration for the Planning of Well Test Configurations at the South West Hub Project, Western Australia

Containment of injected CO2 at the South West Hub project in Western Australia is dependent on non-structural trapping mechanisms in the 1500 m thick Wonnerup Member of the Lesueur Sandstone due to uncertainties regarding the sealing character of the ∼600 m thick overlying Yalgorup Member. Therefore, vertical migration distance and sweep efficiency and their impact on residual saturation and CO2 dissolution need to be properly assessed through reservoir simulations. We find that conventional Darcy-flow reservoir simulations result in significantly different predictions of plume migration compared to invasion percolation modelling when injecting at the base of the Wonnerup Member. If numerical predictions of the fate of injected CO2 are sensitive to the choice of model, care must be taken when selecting the methodology. One way to validate simulation predictions at a scale appropriate to the modelling is the use of well tests. In the Wonnerup Member a vertical migration test is recommended for consideration to confirm whether conventional reservoir simulations or percolation invasion modelling accurately predict the CO2 migration processes at the site. This test would involve a small injection of CO2 that is allowed to migrate upwards. The migration would be monitored with repeat pulsed neutron logging. This represents a new kind of test unique to the situation for the South West Hub site.

Prediction of CO2 Saturation by Using Well Logging Data, in the Process of CO2-EOR and Geological Storage of CO2

CO2 saturation monitoring is one of the key parameters to determine the geological storage of CO2. Because of the CO2-EOR or CO2 injection, the CO2-brine-rock interactions in reservoirs will lead to a series of complex changes in the mineral composition of rocks, porosity, pore structure, properties of formation water and residual oil saturation. At the same time, the difference of the CO2 spread range in reservoirs will cause the different CO2 saturation in different regions; in the same region, the reservoir CO2 saturation will also be different at the different time. To predict the complex variation of CO2 saturation in reservoirs, the processing and interpretation of the time-lapse logging data and the comparative analysis are needed. The steps for determining the CO2 saturation are as follows. Before CO2 injection, the background values of the formation water, rock mineral composition, porosity, pore structure and oil saturation are determined by the implementation of well logging. Firstly, the formation water parameters were monitored and determined at a specified time in the process of CO2 injection or CO2-EOR. Secondly, the time-lapse well logging was carried out to determine the rock mineral composition, porosity, pore structure, oil saturation and saturation CO2. The case-hole formation resistivity, pulsed neutron logging series and C/O logging series are often used to process and interpret the results of well logging data and to predict the residual oil and CO2 saturation. In addition, if the variety of porosity would be ignored, CO2 saturation is based on the prediction. CO2 saturation is equal to the parameter such as: ((the background value of the acoustic logging porosity) – (the time-lapse neutron logging porosity))/ (the background value of the acoustic logging porosity).

Development of Synthetic Ca-based CO2 Sorbents for Sorption Enhanced Reforming Coupled to Ca/Cu Chemical Loop

Sorption Enhanced Reforming (SER) is a very promising option that allows H2 production coupled with capturing CO2 by sorption. The present research work focus in the sorbent point of view and several synthetic materials with a high CO2 absorption capacity and chemically and mechanically stable during multi-cyclic operation (at least 40 calcination-carbonation cycles and 100 cycles in some cases) under the typical SER process conditions have been developed. Two different synthesis routes (co-precipitation and mechanical mixing) have been followed trying to evaluate the effect of two different inert supports (magnesium oxide and mayenite) on the evolution of the CO2 carrying capacity of the materials. Also, sorbents have been synthesized with different morphologies (powder and particles) and sizes (from 100 microns up to 2mm) in order to test their reactivity and mechanical suitability for large scale reactor system operation. Synthetic dolomite with a molar CaO/MgO ratio of 2:1 synthesized by co-precipitation method exhibited very stable performance for 100 consecutive carbonation/calcination cycles and a residual CO2 carrying capacity of 0.29 grCO2/grcalcinedsorbent. Also a very promising result has been obtained for this sorbent mixed with a commercial catalyst in a preliminary SER experiment that yield a H2 production of 92% vol. (d.b.).

Residual Trapping of Supercritical CO2: Direct Pore-scale Observation Using a Low Cost Pressure Cell for Micro Computer Tomography

We describe the design and fabrication steps of a low-cost, modular experimental cell for flooding and X-ray tomography visualization of the rock samples at reservoir conditions (confining pressure up to 45 MPa, pore fluid pressure up to 20 MPa, and temperature up to 80°C). The main body of the cell is made from Polyether ether ketone (PEEK) tube. The cell can be easily machined and assembled in house from off-the-shelf components at a low cost. Modular design allows adopting the cell to a wide range of X-ray visualization experiments. To demonstrate the capabilities of the equipment we are presenting how the residual CO2 phase spreads in the rock as a function of thermo-physical conditions, namely, for ambient condition CO2 gas, near-critical CO2 gas, liquid CO2, and supercritical CO2.

Pore-scale Analysis of In Situ Contact Angle Measurements in Mixed-wet Rocks: Applications to Carbon Utilization in Oil Fields

Carbon utilization in depleting oil reservoirs is considered as an important component in achieving the widespread commercial deployment of carbon capture and storage (CCS) technology. With absent strong climate policy, CO2 enhanced oil recovery (EOR) process adds a significant revenue stream and makes the subsequent carbon storage process economically feasible. This is reflected in the great majority of CO2 storage projects in oil fields utilizing CO2 for EOR. Therefore, early deployment of subsurface carbon dioxide storage is likely to focus on injection into depleted or producing oil fields. Observations and modelling have shown that capillary trapping of CO2 through capillary forces within the pore space of the water-wet rocks, typical of subsurface saline aquifers, is one of the most significant mechanisms for storage capacity. This important storage process is also a factor determining the ultimate extent of CO2 plume migration within the reservoir, enhancing the security of the storage process. In contrast, carbonate oil reservoirs are characterized by a mixed-wet state in which the capillary trapping of nonpolar fluids have been observed to be significantly reduced relative to trapping in water-wet rocks typical of saline aquifers unaltered by the presence of hydrocarbons. This study discuss the first observations of supercritical CO2 in a mixed-wet carbonate rock. Here we show that residual CO2 trapping of supercritical CO2 in a limestone altered to a mixed-wet state with crude oil is significantly less than trapping in water-wet systems characteristic of saline aquifers. The initial-residual CO2 saturations characteristic curve are reported for each system from core scale observations. While pore scale observations provided the first in situ contact angle measurements of supercritical CO2 in a mixed-wet rock and pore to pore arrangements of CO2 droplets. The measurements were compared with trapping of N2 and was similar in the water-wet rock. After altering the sample's wettability to a mixed-wet, however, trapping of CO2 was much less than N2. Here we provide a theoretical explanation of the different response in trapping between CO2 and N2 in the mixed-wet rock.

CO2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO2 purification in H2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H2-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the CO2 concentration to less than 100 ppm via the aforementioned process. The CO2 adsorption capacity of potassium-promoted hydrotalcite at elevated temperatures under different adsorption (mole fraction, working pressure) and desorption (flow rate, desorption time, steam effects) conditions was systematically investigated using a fixed bed reactor. It was found that the CO2 residual concentration before the breakthrough of CO2 mainly depended on the total amount of purge gas and the CO2 mole fraction in the inlet syngas. The residual CO2 concentration and uptake achieved for the inlet gas comprising CO2(9.7 mL/min) and He (277.6 mL/min) at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and 0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual CO2 concentration compared to purging with an inert gas. The residual CO2 concentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/CO2 purification.

Lipid content and fatty acid composition of Porosira glacialis and Attheya longicornis in response to carbon dioxide (CO2) aeration.

In the current study two novel psychrophilic diatoms Porosira glacialis and Attheya longicornis were tested for suitability to CO2 mitigation coupled with production of the physiologically requisite omega– 3 fatty acids. This study is in line with the worldwide conducted research aimed at applying biorefinery concept to heavy polluting industries. Since the production of algal high value compounds, i.e. essential fatty acids, relies on utilization of residual CO2 emissions coming from industry, the costs of such production maybe substantially reduced. Besides, the ecological benefits of the biorefinery concept being implemented are obvious, since CO2 is one of the major greenhouse gases. The current research has shown that one of the tested microalgal species, the diatom P. glacialis showed good tolerance to high (20–25%) levels of CO2 and maintained growth rates comparable to controls. The total lipid content in the CO2 aerated culture increased from 8.91 to 10.57% in cell dry mass. Additionally, the content of docosahexaenoic acid (DHA) increased from 3.90 to 5.75%, while the concentration of eicosapentaenoic acid (EPA) decreased from 26.59 to 23.66%. In contrast, A. longicornis did not demonstrate any significant increase in total lipid content. Besides, its growth was hampered by high levels of CO2 aeration.