Promotional effect of transition metal doping on the properties of KF/CaO catalyst for biodiesel synthesis

A series of heterogeneous KF/CaO catalysts modified with transition metals (lanthanum, cerium, and zirconium) were prepared via wet impregnation method and applied to the trsansesterification process of waste cooking oil (WCO) as feedstock with methanol to biodiesel production. The structure, performance of the solid catalysts was characterized by X-ray diffraction (XRD), temperature programmed desorption of CO₂ (CO₂-TPD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The effect of methanol/oil molar ratio, ¹reaction time, reaction temperature, catalyst amount, and stability was investigated. The results showed that 10 wt% of lanthanum, cerium, and zirconium improved the catalytic activity of KF/CaO catalyst. The maximum catalytic activity using the lanthanum doping of 10wt% on KF/CaO catalyst was reached 98.7% under the optimal reaction condition of methanol/oil molar ratio of 12:1, reaction for 1 h at reaction temperature of 65°C, and 4% (wt/wt oil) catalyst amount. In addition, the FAME yield of KF/CaO/La catalyst remained higher than 95% after 10 cycles. The promotional effect of lanthanum doping could be attributed to the enhancement of the basicity strength of KF/CaO catalyst and block the leach of Ca²⁺ in the transesterification reaction.     

Study on the failure mechanism of potassium-based sorbent for CO2 capture and the improving measure

With thermogravimetric apparatus (TGA), X-ray diffraction (XRD) and barium sulfate gravimetric methods, the carbonation reactivities of K₂CO₃ and K₂CO₃/Al₂O₃ in the simulated flue gases with SO₂ are investigated and the reaction equations are inferred. Results show that there are KHCO₃ and K₂SO₃ generated. The generation K₂SO₃ reduces the utilization ratio of the sorbent. H₂O may accelerates the sulfation reaction of AR K₂CO₃ as K₄H₂(CO₃)₃·1.5H₂O is generated in the reaction among K₂CO₃, SO₂ and H₂O. K₂SO₃ is directly generated from sulfation reaction of K₂CO₃/Al₂O₃, because there are K₂CO₃·1.5H₂O and K₂SO₃ generated in the reaction among K₂CO₃/Al₂O₃, SO₂ and H₂O. K₂CO₃·1.5H₂O does not react with SO₂, and K₂CO₃·1.5H₂O/Al₂O₃ reacts with SO₂ slowly. Compare with the reaction process without H₂O pretreatment, the reaction rates of KAl30 increased after H₂O pretreatment and the failure ratio is about a half of that without H₂O pretreatment. So, K₂CO₃/Al₂O₃ shows good carbonation and anti-sulfation characteristic after H₂O pretreatment.     

Model prediction on the rise of pCO2 in uniform flows by leakage of CO2 purposefully stored under the seabed

A numerical study was conducted to predict pCO₂ change in the ocean on a continental shelf by the leakage of CO₂, which is originally stored in the aquifer under the seabed, in the case that a large fault connects the CO₂ reservoir and the seabed by an earthquake or other diastrophism. The leakage rate was set to be 6.025 × 10⁻⁴ kg/m²/sec from 2 m × 100 m fault band, which corresponds to 3800 t-CO₂/year, referring to the monitored seepage rate from an existing EOR field. The target space in this study was limited to the ocean above the seabed, the depth of which was 200 or 500 m. The computational domain was idealistically rectangular with the seabed fault-band perpendicular to the uniform flow. The CO₂ takes a form of bubbles or droplets, depending on the depth of water, and their behaviour and dissolution were numerically simulated during their rise in seawater flow. The advection–diffusion of dissolved CO₂ was also simulated. As a result, it was suggested that the leaked CO₂ droplets/bubbles all dissolve in the seawater before spouting up to the atmosphere, and that the increase in pCO₂ in the seawater was smaller than 500 μ atm.     

Methodology for CO2 chain analysis

The paper presents a methodology for CO₂ chain analysis with particular focus on the impact of technology development on the total system economy. The methodology includes the whole CO₂ chain; CO₂ source, CO₂ capture, transport and storage in aquifers or in oil reservoirs for enhanced oil recovery. It aims at supporting the identification of feasible solutions and assisting the selection of the most cost-effective options for carbon capture and storage. To demonstrate the applicability of the methodology a case study has been carried out to illustrate the possible impact of technology improvements and market development. The case study confirms that the CO₂-quota price to a large extent influence the project economy and dominates over potential technology improvements. To be economic feasible, the studied chains injecting the CO₂ in oil reservoirs for increased oil production require a CO₂-quota price in the range of 20–27 €/tonne CO₂, depending on the technology breakthrough. For the chains based on CO₂ storage in saline aquifers, the corresponding CO₂-quota price varies up to about 40 €/tonne CO₂.     

Application of TiO2 nanoparticles for eco-friendly biodiesel production from waste olive oil

An environmentally benign, simple, and efficient process has been developed for biodiesel production from waste olive oil in the presence of a catalytic amount of TiO₂ nanoparticles at 120°C with a conversion of 91.2% within 4 h. The present method affords nontoxic and noncorrosive medium, high yield of biodiesel, clean reaction, and simple experimental and isolation procedures. The catalyst can be recycled by simple filtration and reused without any significant reduction in its activity.     

基于混合生命周期评价模型的我国食物系统水资源消耗及二氧化碳排放核算

食物生产不仅依赖水资源,同时产生大量二氧化碳排放,这种资源环境影响存在于食物系统整个产业链。为促进食物系统节水降碳,本文构建了包含5大类共23种具体食物部门的混合生命周期评价模型,对各类食物系统的完全水资源消耗和二氧化碳排放进行了核算与比较。结果表明：①不同食物的水资源消耗和二氧化碳排放差异明显,动物性食物的平均水资源消耗和二氧化碳排放强度分别为植物性食物的1.9 ～ 15.0倍和1.9 ～ 2.7倍;②食物系统直接和间接水资源消耗占比较为接近,但二氧化碳排放主要源自上游产业链的间接排放,占比高达80.9%;③食物系统间接水资源消耗主要来自农业部门,而间接碳排放主要来自电力生产和供应业、基础化工原料制造业、非金属矿产品行业和交通运输业;④从营养元素供给看,动物性食物提供蛋白质和脂肪的资源环境影响高于植物性食物,蔬菜和主食分别在提供维生素C和碳水化合物上具有最小的环境成本。基于本文结果,食物系统节水应主要提高生产环节用水效率,而降碳则主要依靠上游产业减排,特别是发电和化肥生产等行业的协同节水减碳潜力。同时,本文结果也可为未来基于环境影响制定膳食指南提供数据支撑。     

Intermediate storage of carbon dioxide in geological formations: A technical perspective

Enhanced oil recovery (EOR) through CO₂ flooding has been practiced on a commercial basis for the last 35 years and continues today at several sites, currently injecting in total over 30 million tons of CO₂ annually. This practice is currently exclusively for economic gain, but can potentially contribute to the reduction of emissions of greenhouse gases provided it is implemented on a large scale. Optimal operations in distributing CO₂ to CO₂-EOR or enhanced gas recovery (EGR) projects (referred to here collectively as CO₂-EHR) on a large scale and long time span imply that intermediate storage of CO₂ in geological formations may be a key component. Intermediate storage is defined as the storage of CO₂ in geological media for a limited time span such that the CO₂ can be sufficiently reproduced for later use in CO₂-EHR. This paper investigates the technical aspects, key individual parameters and possibilities of intermediate storage of CO₂ in geological formations aiming at large scale implementation of carbon dioxide capture and storage (CCS) for deep emission reduction. The main parameters are thus the depth of injection and density, CO₂ flow and transport processes, storage mechanisms, reservoir heterogeneity, the presence of impurities, the type of the reservoirs and the duration of intermediate storage. Structural traps with no flow of formation water combined with proper injection planning such as gas-phase injection favour intermediate storage in deep saline aquifers. In depleted oil and gas fields, high permeability, homogeneous reservoirs with structural traps (e.g. anticlinal structures) are good candidates for intermediate CO₂ storage. Intuitively, depleted natural gas reservoirs can be potential candidates for intermediate storage of carbon dioxide due to similarity in storage characteristics.     

Viscosities, thermal conductivities and diffusion coefficients of CO2 mixtures: Review of experimental data and theoretical models

Accurate experimental data on the thermo-physical properties of CO₂-mixtures are pre-requisites for development of more accurate models and hence, more precise design of CO₂ capture and storage (CCS) processes. A literature survey was conducted on both the available experimental data and the theoretical models associated with the transport properties of CO₂-mixtures within the operation windows of CCS. Gaps were identified between the available knowledge and requirements of the system design and operation. For the experimental gas-phase measurements, there are no available data about any transport properties of CO₂/H₂S, CO₂/COS and CO₂/NH₃; and except for CO₂/H₂O(/NaCl) and CO₂/amine/H₂O mixtures, there are no available measurements regarding the transport properties of any liquid-phase mixtures. In the prediction of gas-phase viscosities using Chapman–Enskog theory, deviations are typically <2% at atmospheric pressure and moderate temperatures. The deviations increase with increasing temperatures and pressures. Using both the Rigorous Kinetic Theory (RKT) and empirical models in the prediction of gas-phase thermal conductivities, typical deviations are 2.2–9%. Comparison of popular empirical models for estimation of gas-phase diffusion coefficients with newer experimental data for CO₂/H₂O shows deviations of up to 20%. For many mixtures relevant for CCS, the diffusion coefficient models based on the RKT show predictions within the experimental uncertainty. Typical reported deviations of the CO₂/H₂O system using empirical models are below 3% for the viscosity and the thermal conductivity and between 5 and 20% for the diffusion coefficients. The research community knows little about the effect of other impurities in liquid CO₂ than water, and this is an important area to focus in future work.     

Nanocatalyzed biodiesel synthesis from the oily contents of Marine brown alga Dictyota dichotoma

This research article demonstrates biodiesel synthesis through the methanolysis of the oily contents (4.02 ± 0.27% w/w on dried basis) of Dictyota dichotoma collected from the coast of Hawksbay, Pakistan. The metal oxides (CaO, MgO, ZnO, and TiO₂) used as nanocatalysts were refluxed (5% K₂SO₄), calcinated (850 °C) and characterized by Atomic Force Microscopy (AFM) which produced 93.2% w/w FAME (biodiesel) at relatively mild condition (5% catalyst, 65 °C, 3 h, 18:1 molar ratio) using CaO. Whereas, MgO, ZnO, and TiO₂ produced 92.4%, 72.5%, and 31.8% w/w FAME, respectively at elevated condition (225 °C). Thus, CaO was considered to be the best catalyst among the others. This tri-phase reaction require continuous fast mixing and the yield depends on the reaction parameters like catalyst amount, temperature, reaction time and molar ratio (methanol: oil). The reusability of these heterogeneous catalysts simplified the purification step, reduced the waste generation and make the final product technically and economically viable.     

Water/acid gas interfacial tensions and their impact on acid gas geological storage

Acid gas geological disposal is a promising process to reduce CO₂ atmospheric emissions and an environment-friendly and economic alternative to the transformation of H₂S into sulphur by the Claus process. Acid gas confinement in geological formations is to a large extent controlled by the capillary properties of the water/acid–gas/caprock system, because a significant fraction of the injected gas rises buoyantly and accumulates beneath the caprock. These properties include the water/acid gas interfacial tension (IFT), to which the so-called capillary entry pressure of the gas in the water-saturated caprock is proportional. In this paper we present the first ever systematic water/acid gas IFT measurements carried out by the pendant drop technique under geological storage conditions. We performed IFT measurements for water/H₂S systems over a large range of pressure (up to P = 15 MPa) and temperature (up to T = 120 °C). Water/H₂S IFT decreases with increasing P and levels off at around 9–10 mN/m at high T (≥70 °C) and P (>12 MPa). The latter values are around 30–40% of water/CO₂ IFTs, and around 20% of water/CH₄ IFTs at similar T and P conditions. The IFT between water and a CO₂ + H₂S mixture at T = 77 °C and P > 7.5 MPa is observed to be approximately equal to the molar average IFT of the water/CO₂ and water/H₂S binary mixtures. Thus, when the H₂S content in the stored acid gas increases the capillary entry pressure decreases, together with the maximum height of acid gas column and potential storage capacity of a given geological formation. Hence, considerable attention should be exercised when refilling with a H₂S-rich acid gas a depleted gas reservoir, or a depleted oil reservoir with a gas cap: in the case of hydrocarbon reservoirs that were initially (i.e., at the time of their discovery) close to capillary leakage, acid gas leakage through the caprock will inevitably occur if the refilling pressure approaches the initial reservoir pressure.     

The influence of the precursor and synthesis method on the CO2 capture capacity of carpet waste-based sorbents

Adsorption is one of the most promising technologies for reducing CO₂ emissions and at present several different types of sorbents are being investigated. The use of sorbents obtained from low-cost and abundant precursors (i.e. solid wastes) appears an attractive strategy to adopt because it will contribute to a reduction not only in operational costs but also in the amount of waste that is dumped and burned in landfills every year. Following on from previous studies by the authors, in this work several carbon-based adsorbents were developed from different carpet wastes (pre-consumer and post-consumer wastes) by chemical activation with KOH at various activation temperatures (600–900 °C) and KOH:char impregnation ratios (0.5:1 to 4:1). The prepared materials were characterised by chemical analysis and gas adsorption (N₂, −196 °C; CO₂, 0 °C), and tested for CO₂ adsorption at temperatures of 25 and 100 °C. It was found that both the type of precursor and the conditions of activation (i.e. impregnation ratios, and activation temperatures), had a huge influence on the microporosity of the resultant samples and their CO₂ capture capacities. The carbon-based adsorbent that presented the maximum CO₂ capture capacities at 25 and 100 °C (13.8 wt.% and 3.1 wt.%, respectively), was prepared from a pre-consumer carpet waste and was activated at 700 °C using a KOH:char impregnation ratio of 1:1. This sample showed the highest narrow microporosity volume (0.47 cm³ g⁻¹), thus confirming that only pores of less than 1 nm are effective for CO₂ adsorption at atmospheric pressure.     

Re-establishment of the proper injectivity of the CO2-injection well Ktzi 201 in Ketzin, Germany

The onshore CO₂-storage site Ketzin consists of one CO₂-injection well and two observation wells. Hydraulic tests revealed permeabilities between 50 and 100 mD for the sandstone rock units. The designated injection well Ktzi 201 showed similar production permeability. After installation of the CO₂-injection string, an injection test with water yielded a significantly lower injectivity of 0.002 m³/d kPa, while the observation wells showed an injection permeability in the same range as the productivity. Several possible reasons for the severe decline in injectivity are discussed. Acidification of the reservoir interval, injection at high wellhead pressure, controlled mini-fractures and back-production of the well are discussed to remove the plugging material to re-establish the required injectivity of the well. It has been decided to perform a nitrogen lift and analyse the back-produced fluids. Initially during the lift, the back-produced fluids were dark-black. Chemical and XRD analyses proved that the black solids consisted mainly of iron sulphide. Sulphate-reducing bacteria (SRB) were detected in fluid samples with up to 10⁶ cells/ml by fluorescent in situ hybridisation (FISH) indicating that the formation of iron sulphide was caused by bacterial activity. Organic compounds within the drilling mud and other technical fluids were likely left during the well completion process, thus providing the energy source for strong proliferation of bacteria. During the lift, the fraction of SRB in the whole bacterial community decreased from approximately 32% in downhole samples to less than 5%. The lift of Ktzi 201 succeeded in the full restoration of the well productivity and injectivity. Additionally, the likely energy source of the SRB was largely removed by the lifting, thus ensuring the long-term preservation of the injectivity.     

Gasification of Inferior Coal with High Ash Content under CO2 and O2/H2O Atmospheres

The gasification reaction of Nantong inferior coal was investigated in a laboratory fixed-bed reactor under CO₂ and O₂/H₂O atmospheres. The effects of the bed temperature and inlet-gas concentration on the yields of CO, H₂, and CH₄ were studied. The effects of coal ash and particle size on the fixed-carbon conversion were also investigated, and kinetic analysis was conducted with a homogeneous model. The product-gas-heating value and fixed-carbon conversion increased when the temperature was increased from 950 °C to 1100 °C under CO₂ atmosphere. When the inlet-CO₂ concentration was increased from 50 to 100 vol.%, the low heating value of the product gas and carbon conversion ratio slightly increased. During the gasification of inferior coal under the O₂/H₂O atmosphere, the CO concentration increased rapidly with increasing temperature. The H₂ and CH₄ concentrations increased initially and then decreased. The maximum gas heating value of 7934 kJ/m³ was obtained under the O₂ concentration of 70 vol.% at a bed temperature of 1050 °C. The cold-gas efficiency increased with increasing temperature and became 40.6% and 86.4% at 1100 °C under the CO₂ and O₂/H₂O atmospheres, respectively. The gasification reaction of the Nantong inferior coal strongly depended on the content of inherent inorganic matter. The gasification rates for both the CO₂ and O₂/H₂O atmospheres were independent of the particle size. The activation energy for the CO₂ and O₂/H₂O gasification reactions were 137 and 81 kJ/mol, respectively. The gasification reactions of the Nantong coal, which was performed under two different atmospheres, were compared and the reaction activity of the gasification reaction under CO₂ atmosphere was found to be much lower than that under the O₂/H₂O atmosphere.     

Monitoring of the microbial community composition in saline aquifers during CO2 storage by fluorescence in situ hybridisation

This study reveals the first analyses of the composition and activity of the microbial community of a saline CO₂ storage aquifer. Microbial monitoring during CO₂ injection has been reported. By using fluorescence in situ hybridisation (FISH), we have shown that the microbial community was strongly influenced by the CO₂ injection. Before CO₂ arrival, up to 6 × 10⁶ cells ml⁻¹ were detected by DAPI staining at a depth of 647 m below the surface. The microbial community was dominated by the domain Bacteria that represented approximately 60% to 90% of the total cell number, with Proteobacteria and Firmicutes as the most abundant phyla comprising up to 47% and 45% of the entire population, respectively. Both the total cell counts as well as the counts of the specific physiological groups revealed quantitative and qualitative changes after CO₂ arrival. Our study revealed temporal outcompetition of sulphate-reducing bacteria by methanogenic archaea. In addition, an enhanced activity of the microbial population after five months CO₂ storage indicated that the bacterial community was able to adapt to the extreme conditions of the deep biosphere and to the extreme changes of these atypical conditions.     

CO2SINK—From site characterisation and risk assessment to monitoring and verification: One year of operational experience with the field laboratory for CO2 storage at Ketzin, Germany

The CO₂SINK pilot project at Ketzin is aimed at a better understanding of geological CO₂ storage operation in a saline aquifer. The reservoir consists of fluvial deposits with average permeability ranging between 50 and 100 mDarcy. The main focus of CO₂SINK is developing and testing of monitoring and verification technologies. All wells, one for injection and two for observation, are equipped with smart casings (sensors behind casing, facing the rocks) containing a Distributed Temperature Sensing (DTS) and electrodes for Electrical Resistivity Tomography (ERT). The in-hole Gas Membrane Sensors (GMS) observed the arrival of tracers and CO₂ with high temporal resolution. Geophysical monitoring includes Moving Source Profiling (MSP), Vertical Seismic Profiling (VSP), crosshole, star and 4-D seismic experiments. Numerical models are benchmarked via the monitoring results indicating a sufficient match between observation and prediction, at least for the arrival of CO₂ at the first observation well. Downhole samples of brine showed changes in the fluid composition and biocenosis. First monitoring results indicate anisotropic flow of CO₂ coinciding with the “on-time” arrival of CO₂ at observation well one (Ktzi 200) and the later arrival at observation well two (Ktzi 202). A risk assessment was performed prior to the start of injection. After one year of operations about 18,000 t of CO₂ were injected safely.     

Ferric-manganese doped sulphated zirconia nanoparticles catalyst for single-step biodiesel production from waste cooking oil: Characterization and optimization

Biodiesel of waste cooking oil origin is gaining attention as a replacement for current fossil fuels, as its low-priced, recycled feedstock shall prevent food source competition, which is estimated to happen with current biodiesel production processes. As a result, waste cooking oil has been claimed to be a highly potential feedstock for biodiesel production. In the present research work, Fe-Mn doped sulphated zirconia catalyst was synthesized and used in simultaneous esterification and transesterification of waste cooking oil to biodiesel synthesis. The catalyst was prepared through the impregnation method and characterized by using XRD, TPD-NH_3, FT-IR, BET, and TEM. Response surface methodology (RSM) in conjunction with the central composite design (CCD) was applied to statistically evaluate and optimize the biodiesel preparation process. It was found that the synthesis of biodiesel achieved an optimum level of 97.2% waste cooking oil methyl ester’s (WCOME’s) yield at the following reaction conditions: methanol/oil molar ratio: 10:1, catalyst concentration: 3.0 wt %, and reaction temperature: 160 °C. The extremely high WCOME’s yield of 97.2% was proved to be due to high acidity, surface area, and large pore diameter; reactants can easily diffuse into the interior pore of the catalyst and allow them to be in contact with active sites that enhance catalytic activity.     

Environmental policy stringency,renewable energy consumption and CO2 emissions: Panel cointegration analysis for BRIICTS countries

ABSTRACT

The aim of this paper is to investigate the relationship between environmental policy stringency and CO₂ emissions in BRIICTS (Brazil, Russia, India, Indonesia, China, Turkey and South Africa) for the period 1993–2014 after controlling for renewable energy, fossil energy, oil prices and income. We believe that this is the first attempt to use the recently OECD-developed environmental policy stringency index to test the effectiveness of environmental stringency policy in reducing CO₂ emission in these countries. Applying the Panel Pooled Mean Group Autoregressive Distributive Lag (PMG-ARDL) estimator, we found an inverted U–shaped relationship between environmental policy stringency and CO₂ emissions. This suggests that initially strict stringent environmental policy does not lead to improvements in the environment but after a certain level or a threshold point, environmental stringency policy leads to improvement in environmental quality. Renewable energy consumption was negatively related to CO₂ emissions while fossil energy consumption and real oil prices and income were positively and significantly related to CO₂. Our findings suggest that strengthening the stringency of environmental policies and promoting renewable energy are effective ways of preventing environmental degradation in BRIICTS countries.     

A model for the CO2 capture potential

Global warming is a result of increasing anthropogenic CO₂ emissions, and the consequences will be dramatic climate changes if no action is taken. One of the main global challenges in the years to come is therefore to reduce the CO₂ emissions.Increasing energy efficiency and a transition to renewable energy as the major energy source can reduce CO₂ emissions, but such measures can only lead to significant emission reductions in the long-term. Carbon capture and storage (CCS) is a promising technological option for reducing CO₂ emissions on a shorter time scale.A model to calculate the CO₂ capture potential has been developed, and it is estimated that 25 billion tonnes CO₂ can be captured and stored within the EU by 2050. Globally, 236 billion tonnes CO₂ can be captured and stored by 2050. The calculations indicate that wide implementation of CCS can reduce CO₂ emissions by 54% in the EU and 33% globally in 2050 compared to emission levels today.Such a reduction in emissions is not sufficient to stabilize the climate. Therefore, the strategy to achieve the necessary CO₂ emissions reductions must be a combination of (1) increasing energy efficiency, (2) switching from fossil fuel to renewable energy sources, and (3) wide implementation of CCS.     

Power generation with CO2 capture: Technology for CO2 purification

The goal of this paper is to find methodologies for removing a selection of impurities (H₂O, O₂, Ar, N₂, SO_x and NO_x) from CO₂ present in the flue gas of two oxy-combustion power plants fired with either natural gas (467 MW) or pulverized fuel (596 MW). The resulting purified stream, containing mainly CO₂, is assumed to be stored in an aquifer or utilized for enhanced oil recovery (EOR) purposes. Focus has been given to power cycle efficiency i.e.: work and heat requirements for the purification process, CO₂ purity and recovery factor (kg of CO₂ that is sent to storage per kg of CO₂ in the flue gas). Two different methodologies (here called Case I and Case II) for flue gas purification have been developed, both based on phase separation using simple flash units (Case I) or a distillation column (Case II). In both cases purified flue gas is liquefied and its pressure brought to 110 atm prior to storage.Case I: A simple flue gas separation takes place by means of two flash units integrated in the CO₂ compression process. Heat in the process is removed by evaporating the purified liquid CO₂ streams coming out from both flashes. Case I shows a good performance when dealing with flue gases with low concentration of impurities. CO₂ fraction after purification is over 96% with a CO₂ recovery factor of 96.2% for the NG-fired flue gas and 88.1% for the PF-fired flue gas. Impurities removal together with flue gas compression and liquefaction reduces power plant output of 4.8% for the NG-fired flue gas and 11.6% for the PF-fired flue gas. The total amount of work requirement per kg stored CO₂ is 453 kJ for the NG-fired flue gas and 586 kJ for the PF-fired flue gas.Case II: Impurities are removed from the flue gas in a distillation column. Two refrigeration loops (ethane and propane) have been used in order to partially liquefy the flue gas and for heat removal from a partial condenser. Case II can remove higher amounts of impurities than Case I. CO₂ purity prior to storage is over 99%; CO₂ recovery factor is somewhat lower than in Case I: 95.4% for the NG-fired flue gas and 86.9% for the PF-fired flue gas, reduction in the power plant output is similar to Case I.Due to the lower CO₂ recovery factor the total amount of work per kg stored CO₂ is somewhat higher for Case II: 457 kJ for the NG-fired flue gas and 603 kJ for the PF-fired flue gas.     

Predicting δCDIC dynamics in CCS: A scheme based on a review of inorganic carbon chemistry under elevated pressures and temperatures

Stable carbon isotopes are important tools to assess potential storage sites for CO₂, as they allow the quantification of ionic trapping via isotope mass balances. In deep geological formations high p/T conditions need to be considered, because CO₂ dissolution, equilibrium constants and isotope fractionation of dissolved inorganic carbon (DIC) depend on temperature, pressure and solute composition. After reviewing different approaches to account for these dependencies, an expanded scheme is presented for speciation and carbon isotope fractionation of DIC and dissolution of CaCO₃ for pCO₂ up to 100 bar, pH down to 3 and temperatures of up to 200 °C. The scheme evaluates the influence of respective parameters on isotope ratios during CO₂ sequestration. The pCO₂ and pH are the dominant controlling factors in the DIC/δ¹³C/pH system. The fugacity of CO₂ has major impact on DIC concentrations at temperatures below 100 °C at high pCO₂. Temperature dependency of activities and equilibrium dominates at temperatures above 100 °C. Isotope ratios of DIC are expected to be about 1–2‰ more depleted in ¹³C compared to the free CO₂ at pCO₂ values above 10 bar. This depletion is controlled by carbon isotope fractionation between CO₂ and H₂CO₃* which is the dominant species of DIC at the resulting pH below 5.