Indirect CO2 Research Articles

Highly effective hydrogenation of CO2 to methanol over Cu/ZnO/Al2O3 catalyst: A process economy & environmental aspects

The hydrogenation of CO2 to methanol is one of the promising CO2 utilization routes in the industry that can contribute to emissions mitigation. In this work, improved operating conditions were reported for the sustainable catalytic hydrogenation of CO2 to methanol using Cu/ZnO/Al2O3 catalyst operated at 70 bar and 210 °C. The CO2 feedstock used for this process is pure CO2 produced from the cryogenic upgrading process of biogas or hydrocarbon industries and ready-to-use hydrogen purchased at 30 bar and 25 °C. The process was modeled and simulated using the commercial Aspen Plus software to produce methanol with a purity greater than 99% at 1 bar and 25 °C. The simulation results revealed that an adiabatic reactor operated with a CO2/H2 ratio of 1:7 produces methanol with a yield ≥99.84% and a CO2 conversion of 95.66%. Optimizing the heat exchanger network (HEN) achieved energy savings of 63% and reduced total direct and indirect CO2 emissions by 97.8%. The proposed methanol process with an annual production rate of 2.34 kt/yr is economically sound with a payback period of nine years if the maximum H2 price remains below $0.97/kg. Hence, producing or purchasing gray H2 from a steam reforming plant is the most viable economic source for the process.

Tracking the CO2 Emissions of China’s Coal Production via Global Supply Chains

Coal’s green mining and scientific utilization is the key to achieve the national vision of carbon peak by 2030 and carbon neutrality by 2060. Clarifying the CO2 flow of coal production is the core part of decarbonization. This study uses an environmental extended multi-regional input–output (EEMRIO) model to analyze the impact of embodied emissions on the indirect CO2 emission intensity of coal production between China’s coal mining sector and 141 countries/regions. It is found that the CO2 emission intensity of China’s coal production was 34.14 gCO2/MJ in 2014, while the direct and indirect emission intensities were 16.22 gCO2/MJ and 17.92 gCO2/MJ, respectively. From 2007 to 2014, the direct emission intensity of China’s coal production increased by 23%, while the indirect emission intensity decreased by 30%. The key material and service inputs affecting indirect carbon emissions of coal production in China are electricity service, metal manufacturing, chemical products, coal mining, and transport, which accounted for 85.5% of the total indirect emission intensity of coal production in 2014. Globally, a large portion of CO2 from Chinese coal production is emitted to meet foreign direct and indirect demands for material and service inputs. Policy implications related to this outcome are further discussed in the study.

Carbon dioxide limitation of benthic primary production in a boreal lake

Abstract Gross primary production (GPP) by benthic microalgae growing on soft sediments is an important contributor to lake productivity in many lakes world‐wide. As benthic microalgae have access to nutrients in the sediment they have been regarded as primarily controlled by light, while the role of CO2 as a limiting factor for benthic GPP in lake ecosystems is largely unknown. In this study, we experimentally tested for CO2 limitation of benthic GPP by collecting littoral surface sediments, with associated benthic microalgae, from a typical boreal lake. Intact sediment cores were incubated at different depths (light conditions) after addition of dissolved inorganic (bicarbonate) or organic (DOC; glucose) carbon as direct and indirect sources of CO2, respectively. Benthic microalgal GPP was stimulated by both dissolved inorganic carbon and DOC additions at high, but not at low, light levels. This study shows that benthic microalgal GPP can be CO2‐limited when light is not limiting and suggests that both direct (e.g., via groundwater inflow) and indirect (via mineralisation of DOC) CO2 supply can stimulate benthic GPP.

Electrification of Africa through CPV installations in small-scale industrial applications: Energetic, economic, and environmental analysis

This paper aims to evaluate the energetic, economic, and environmental performances of small-scale concentrated photovoltaics (CPV) power systems under 107 African climatic and financial zones with different energy mixes. The proposed concept focuses on small-scale installations for small- or medium-scale industrial premises as such devices are involved in the international strategy about micro-grids. Yearly average electric productions, capacity factors, economic and environmental considerations, and sensitivity were all analysed. The mathematical methodology for calculating the power of a concentrated triple-junction solar cell, the annual energy conversion of a CPV plant, the costs, and the CO2 mitigation were assessed.The parametric study shows that the capacity factor becomes highest for a cell area of 5.5 cm2 or if the concentration ratio reaches the value of 2400. Furthermore, LCOE is lowest for Errachidia in Morocco with 15.88 c$/kWh followed by Fada in Chad with 16.82 c$/kWh, while it is highest in Wad Hajm in Sudan as 5.23 × 1016 c$/kWh. Moreover, South Africa allows the highest reduction of indirect CO2 emissions. Furthermore, energy produced is greatest in Errachidia in Morocco (606.27 GWh), Tiaret in Tunisia (601.11 GWh), and Upington in South Africa (598.11 GWh). Results are shown on innovative GIS maps of Africa.

High-temperature thermal storage-based cement manufacturing for decarbonization

Cost-effective CO2 capture is essential for decarbonized cement production since it is one of the largest CO2 emission sources, where 60% of direct emissions are from CaCO3 decomposition and 40% are from fuel combustion. This work presents a low-carbon cement manufacturing process by integrating it with renewable energy for electric heating and thermal storage to replace the burning of fossil fuels in the conventional calciner. The low-carbon renewable energy reduces the indirect CO2 emissions from electricity consumption. The high-temperature CO2 is employed as the heat transfer fluid between the energy storage system and the calciner. In the proposed basic manufacturing process, the CO2 from the CaCO3 decomposition can be directly collected without energy-consuming separation since no impurities are introduced. Furthermore, the remaining CO2 from fuel combustion in the kiln can be captured through monoethanolamine (MEA) absorption using waste heat. In the two situations, the overall CO2 emissions can be reduced by 69.7% and 83.1%, respectively, including the indirect emissions of electricity consumption. The economic performance of different energy storage materials is investigated for materials selection. The proposed manufacturing process with a few high-temperature energy storage materials (BaCO3/BaO, SrCO3/SrO, Si, etc.) offers a higher CO2 emission reduction and lower cost than alternative carbon capture routes, i.e., oxyfuel. The cost of CO2 avoided as low as 39.27 $/t can be achieved by thermochemical energy storage with BaCO3/BaO at 1300 °C, which is superior to all alternative technologies evaluated in recent studies.

Verification Analysis of Volume Flow Measured by a Direct Method and by Two Indirect CO2 Balance Methods

Ammonia and greenhouse gases have a negative impact on the environment. The most important agricultural sources of ammonia are dairy cattle housing systems, which are mainly naturally ventilated. Estimating emissions for naturally ventilated barns (NVB) is challenging due to the large number of influencing factors. Most notably, the direct coupling of the inside flow regime with ambient and turbulent weather conditions causes difficulties in measuring ventilation rates, gas concentrations and emissions; thus, different methods are available. In this study, we compared the outputs of total volume flow obtained by two indirect methods (CO2 mass balance) to the direct method. The latter we assume in this study as the reference method since it is a fundamental approach that estimates airflow on the inlet. In the context of mass balancing, we compared wind related (sampling method 1) and non-wind related (sampling method 2) approaches for measuring CO2 concentrations. The total volume flow calculations were based on hourly measurements of CO2 concentrations obtained by Fourier transform infrared (FTIR) spectrometer. Data were collected over a period of six months. The values of the total volume flow were filtered for prevailing southern winds (90∘ angle). The wind related method (sampling method 1) in stable cross-inflow conditions produces more accurate and realistic values in terms of the general representation of the values in comparison with direct method and can be considered further for measurements of volume flow in the NVBs.

Controllable biomimetic mineralization and characterization of hydrated magnesium carbonates using sodium carboxymethyl cellulose

Recently, fixing CO2 within minerals is an environmentally friendly way of CO2 sequestration and utilization strategy. Inspired by cyanobacteria mediated carbonation of hydrated magnesium carbonates (HMCs), the indirect CO2 biomimetic mineralization process involving NH4HCO3-MgCl2 using NaCMC was investigated to obtain HMCs with complex superstructures. The crystal phase, morphology, structure, thermal stability and surface of HMCs were characterized by XRD, SEM, TG and XPS methods. The HMCs products are composed of urchin-like particles assembled by nesquehonite rods at a low NaCMC concentration. At a higher NaCMC concentration, Dypingite flowers assembled by nanosheets generate in situ at the dissolution defects of nesquehonite rod by increasing the NaCMC concentration. The irregular dypingite agglomerates assembled by adjacent flower-like structures and the well-developed dypingite spheres composed of intensive plate-like crystallites are synthesized at temperature above 65 °C. By adjusting the molar ratio of Mg2+/HCO3−, dypingite flakes grow on the top of nesquehonite rods. The superstructure of HMCs was destroyed when increasing the solution pH from 8 to 10. The decomposition of HMCs is characterized by dehydration (or dehydroxylation) and decarbonation stages. XPS confirms that the surface properties for nesquehonite and dypingite are quite different. This study provides insights into the preparation of HMCs with complex hierarchical structures based on biomimetic carbonation.

Advances in synthetic biology of CO2 fixation by heterotrophic microorganisms

Human activities increase the concentration of atmospheric carbon dioxide (CO2), which leads to global climate warming. Microbial CO2 fixation is a promising green approach for carbon neutral. In contrast to autotrophic microorganisms, heterotrophic microorganisms are characterized by fast growth and ease of genetic modification, but the efficiency of CO2 fixation is still limited. In the past decade, synthetic biology-based enhancement of heterotrophic CO2 fixation has drawn wide attention, including the optimization of energy supply, modification of carboxylation pathway, and heterotrophic microorganisms-based indirect CO2 fixation. This review focuses on the research progress in CO2 fixation by heterotrophic microorganisms, which is expected to serve as a reference for peaking CO2 emission and achieving carbon neutral by microbial CO2 fixation.

5-HT7 receptors expressed in the mouse parafacial region are not required for respiratory chemosensitivity.

A brainstem homeostatic system senses CO2/H+ to regulate ventilation, blood gases and acid–base balance. Neurons of the retrotrapezoid nucleus (RTN) and medullary raphe are both implicated in this mechanism as respiratory chemosensors, but recent pharmacological work suggested that the CO2/H+ sensitivity of RTN neurons is mediated indirectly, by raphe‐derived serotonin acting on 5‐HT7 receptors. To investigate this further, we characterized Htr7 transcript expression in phenotypically identified RTN neurons using multiplex single cell qRT‐PCR and RNAscope. Although present in multiple neurons in the parafacial region of the ventrolateral medulla, Htr7 expression was undetectable in most RTN neurons (Nmb +/Phox2b+) concentrated in the densely packed cell group ventrolateral to the facial nucleus. Where detected, Htr7 expression was modest and often associated with RTN neurons that extend dorsolaterally to partially encircle the facial nucleus. These dorsolateral Nmb +/Htr7 + neurons tended to express Nmb at high levels and the intrinsic RTN proton detectors Gpr4 and Kcnk5 at low levels. In mouse brainstem slices, CO2‐stimulated firing in RTN neurons was mostly unaffected by a 5‐HT7 receptor antagonist, SB269970 (n = 11/13). At the whole animal level, microinjection of SB269970 into the RTN of conscious mice blocked respiratory stimulation by co‐injected LP‐44, a 5‐HT7 receptor agonist, but had no effect on CO2‐stimulated breathing in those same mice. We conclude that Htr7 is expressed by a minor subset of RTN neurons with a molecular profile distinct from the established chemoreceptors and that 5‐HT7 receptors have negligible effects on CO2‐evoked firing activity in RTN neurons or on CO2‐stimulated breathing in mice.Key points Neurons of the retrotrapezoid nucleus (RTN) are intrinsic CO2/H+ chemosensors and serve as an integrative excitatory hub for control of breathing.Serotonin can activate RTN neurons, in part via 5‐HT7 receptors, and those effects have been implicated in conferring an indirect CO2 sensitivity.Multiple single cell molecular approaches revealed low levels of 5‐HT7 receptor transcript expression restricted to a limited population of RTN neurons.Pharmacological experiments showed that 5‐HT7 receptors in RTN are not required for CO2/H+‐stimulation of RTN neuronal activity or CO2‐stimulated breathing.These data do not support a role for 5‐HT7 receptors in respiratory chemosensitivity mediated by RTN neurons.

Environmental Responsibility: An Emerging Paradigm of Indian Public Sector -A Case Study

Corporate Environmental Responsibility is relatively a new concept which includes different ideas, actions, strategies and ideologies. The concept clearly identifies and explains the role played by the corporations in the current environmental crisis. Its basic premise is that a corporation engages in environmentally beneficial actions to reduce society’s burden on our ecosystem and promote environmental sustainability. Corporate Environmental Responsibility is about managing the use of natural resources in the most effective and efficient manner in order to reduce environmental impacts and financial costs. This study is pertaining to the corporate Environmental responsibilities as a part of corporate social responsibilities of Indian Oil Corporations. It discusses on the amount of direct and indirect energy consumption and CO2 emission created and its responsibilities towards the society are analyzed.The study found that, total Environmental Expenditure is increasing: for Corporate Social Responsibility Expenditure was Rupees 460.37 crore in that Rs.252.48 was spent for Covid 19 (2% of average Net Profit as per Section 135(5)), health and sanitation was Rupees 29.54 crores and for Swatch Bharat was Rs.16.38 crores, It is a welcoming feature and environmental concern of Indian Oil Corporation, otherwise Corporate Social Responsibility.

Life cycle assessment shows that retrofitting coal-fired power plants with fuel cells will substantially reduce greenhouse gas emissions

Life cycle assessment shows that retrofitting coal-fired power plants with fuel cells will substantially reduce greenhouse gas emissions

Success and failure of the voluntary action plan: Disaggregated sector decomposition analysis of energy-related CO2 emissions in Japan

To accomplish the goal of reducing greenhouse gas (GHG) emissions, the Japanese Business Federation (JBF) has implemented the voluntary action plan (VAP), which includes the unique feature of not penalizing industrial organizations for failing to meet the CO2 emissions or energy consumption reduction targets. This study evaluates the role of the VAP in emission reduction by analyzing highly disaggregated data of 197 sectors from 1980 to 2015 using the logarithmic mean Divisia index (LMDI) method. The results indicate that the increase in CO2 emissions among Japanese industries is mainly caused by the increase in indirect CO2 emissions. Moreover, the energy consumption structure has progressively shifted from fossil fuels to electricity. The decomposition analysis highlights two key points. (1) The VAP is ineffective in reducing emissions in sectors with low market concentration. (2) Energy intensity targets of the VAP does not lead to a significant reduction in CO2 emissions. Thus, this study concludes that the contribution of the VAP in reducing CO2 emissions is limited. Evidence from our research suggests four directions for future policy design and implications.

Economic accounting and high-tech strategy for sustainable production: A case study of methanol production from CO2 hydrogenation

The global proposal of ‘carbon neutrality’ puts forward higher innovation demand for the cleaner energy production. The potential for employing “green” methanol produced from hydrogen obtained by water electrolysis and collected CO2 from a gas-fired power station is examined in this study.The consumption of electricity for renewable methanol production is 1.045 times as much as that for traditional methanol production, the traditional method consumes 2.5 times as much thermal energy as the renewable methanol process. In addition, the total direct and indirect CO2 emissions from renewable methanol production are almost one-third of the emissions from the traditional method. The total cost of setting up the units of a renewable and a traditional methanol production plant with an annual capacity of 100,000 tons is $50.1 million and $46.806 million in this study case, respectively. If the methanol price hits $310 per ton, renewable methanol production will be highly economically viable. But if electricity and gas prices rise or CO2 emission tax is imposed, renewable and conventional methanol production plants will lose their economic feasibility. Therefore, in order to deal with this risk, the establishment of special high-tech parks is of great significance to reduce costs and stabilize the sustainable development of relevant industries.

Indirect CO2 emissions caused by the fuel demand switch in international shipping

In 2020 the fuel sulphur limit in international shipping was reduced from 3.5 to 0.5 wt%. Three adaptive measures dominate: (i) increased exhaust gas cleaning in the maritime industry enabling continued use of high-sulphur fuel oil, (ii) increased refining output ratio of low-sulphur fuels, and iii) increased use of blended fuels. As (i) and (ii) are insufficient to comply with the new demand, refiners will resort to (iii), which requires increased crude oil throughput. Extracted crude oil will typically oxidize completely over longer time periods, so increased crude oil throughput is synonymous with increased CO 2 emissions of up to 323 Mton in 2020, corresponding to ∼1% of the total global CO 2 emissions from fossil fuels. Transferring demand from low-value to high-value oil products cause indirect CO 2 emissions, and vice versa. CO 2 emissions can be mitigated by prioritizing demand reduction according to oil product value starting with the most valuable products.

Ways to reduce carbon dioxide emissions from arable machinery and tractor units

The article is devoted to the search for ways to reduce carbon dioxide emissions in the technological operation of plowing. Ways to reduce CO2 emissions were determined on the basis of computational experiments conducted using a mathematical model of an arable unit compiled according to the efficiency criterion - the minimum integral emission of carbon dioxide. Integral CO2 emission, in addition to direct and indirect CO2 emissions over the life cycle of the arable unit, includes CO2, which could be absorbed from the atmosphere by the crop lost due to the influence of the parameters of the unit. The influence of the parameters of the tractor and the unit on the emission of carbon dioxide during its manufacture, technical and production operation is analyzed. Computational experiments were conducted to identify the influence of some external factors (field area, seasonal load volume, etc.) on the efficiency of the arable unit.

Sustainable process for enhanced CO2 mineralization of calcium silicates using a recyclable chelating agent under alkaline conditions

This study explored a key challenge of aqueous indirect CO2 mineralization: the consumption of chemicals for a large pH swing between acidic and alkaline conditions and the production of waste fluid. Herein, we proposed and experimentally examined the technical feasibility of a sustainable process for enhanced CO2 mineralization using a new potentially recyclable alkaline solution of chelating agent [N,N-dicarboxymethyl glutamic acid (GLDA)] at near-room temperatures. This process comprising the following: enhanced Ca extraction from silicates with suppressed formation of silica-rich passivation layer via the combined actions of proton and chelating agent attacks at weakly alkaline conditions; Ca carbonation using sodium carbonate at high pH and temperature; and regeneration of the extraction solution (i.e., a decrease in pH and silicon removal) via CO2 gas dissolution. Ca extraction experiments using representative calcium silicate (CaSiO3) at various GLDA concentrations and initial pHs under 50 °C demonstrated the possibility of enhanced Ca extraction with almost all GLDA molecules combining with Ca (Ca/GLDA≈1) at an optimum condition (0.1 M GLDA and pH 8 in this study). This type of extraction is desirable as it contributes to an efficient Ca carbonation in addition to a decreased stability of the Ca-GLDA complex; indeed, most of the extracted Ca were carbonated to aragonite at 80 °C. Moreover, such extraction with the relatively low pH of 8 was found to be desirable for solution regeneration that involves pH adjustment (reduction) because of low silica solubility at lower pH. It was demonstrated that room-temperature CO2 bubbling removed almost all Si as amorphous SiO2, during which CO2 captured as NaHCO3 was also occurring. The recyclability of extraction solution was also demonstrated in this paper. This study encourages further extensive studies to optimize reaction conditions, particularly for using alkaline solid wastes, to make the process both technically and economically feasible.

Biomimetic mineralization and characterization of hierarchically structured hydrated magnesium carbonates: The effects of sodium alginate

Recently, CO2 mineralization involving magnesium salt provides a feasible way for carbon sequestration. The produced hydrated magnesium carbonates (HMCs) can be used as functional materials and will bring huge economic benefits. Inspired by the mineralization in biological organisms, the indirect CO2 mineralization process involving NH4HCO3-MgCl2 in the presence of sodium alginate (SA) was systematically investigated. XRD, SEM, FTIR, TG and XPS were used to characterize the crystal phase, morphology, structure and surface of HMCs. By the regulation of temperature, HMCs with a complex hierarchical structure were successfully synthesized, i.e., sea urchin-like nesquehonite assembled by nanorods and 3D spiderweb-like hydromagnesite assembled by nanosheets. The presence of SA inhibits the phase transition from nesquehonite to hydromagnesite, and the inhibitory effect increases as the concentration of SA increases. By decreasing the molar ratio of Mg2+/HCO3−, the shape of nesquehonite particle changes from a sphere to an ellipsoid or a gourd. The spherical structure of nesquehonite is destroyed in a weak alkaline solution and the crystalline product is flower-like hydromagnesite in a strong alkaline solution. The decomposition process of HMCs is composed of dehydration (or dehydration and dehydroxylation) stage and decarbonation stage. XPS results for nesquehonite and hydromagnesite are quite different due to their different surface structure. This study will provide insights into the preparation of hierarchically structured HMCs by indirect CO2 mineralization and promote added values of HMCs by biomimetic mineralization method.

Electroreduction of CO2/CO to C2 Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis.

Direct electrochemical reduction of CO2 to C2 products such as ethylene is more efficient in alkaline media, but it suffers from parasitic loss of reactants due to (bi)carbonate formation. A two-step process where the CO2 is first electrochemically reduced to CO and subsequently converted to desired C2 products has the potential to overcome the limitations posed by direct CO2 electroreduction. In this study, we investigated the technical and economic feasibility of the direct and indirect CO2 conversion routes to C2 products. For the indirect route, CO2 to CO conversion in a high temperature solid oxide electrolysis cell (SOEC) or a low temperature electrolyzer has been considered. The product distribution, conversion, selectivities, current densities, and cell potentials are different for both CO2 conversion routes, which affects the downstream processing and the economics. A detailed process design and techno-economic analysis of both CO2 conversion pathways are presented, which includes CO2 capture, CO2 (and CO) conversion, CO2 (and CO) recycling, and product separation. Our economic analysis shows that both conversion routes are not profitable under the base case scenario, but the economics can be improved significantly by reducing the cell voltage, the capital cost of the electrolyzers, and the electricity price. For both routes, a cell voltage of 2.5 V, a capital cost of $10,000/m2, and an electricity price of <$20/MWh will yield a positive net present value and payback times of less than 15 years. Overall, the high temperature (SOEC-based) two-step conversion process has a greater potential for scale-up than the direct electrochemical conversion route. Strategies for integrating the electrochemical CO2/CO conversion process into the existing gas and oil infrastructure are outlined. Current barriers for industrialization of CO2 electrolyzers and possible solutions are discussed as well.

Analysis of China's urban household indirect carbon emissions drivers under the background of population aging

Population aging is an important concern not only in China but also to many developed countries, and it will be a more serious issue throughout the world in the future. From this point, understanding the impact of population aging on CO2 emissions is important for achieving carbon neutral in the future. To analyze this impact, this study quantifies lifestyle and urban household's consumption impacts upon carbon emissions from the indirect CO2 emissions aspect and uses the structural decomposition method to analyze the factors influencing the growth of indirect CO2 emissions from 2007 to 2012. The analysis results indicate that the indirect CO2 emissions peak at 20 s age group and gradually decline as age increases. Since elderly households have relatively lower indirect CO2 emissions, population aging in the future will reduce indirect CO2 emissions. The decomposition analysis for indirect CO2 emissions shows that the effects of changes in consumption pattern and production technology progress reduced indirect CO2 emissions to a large extent. The main factors leading to the increase in indirect CO2 emissions are the increase in the number of households and consumption volume. The corresponding policy implications are proposed based on our findings: improving energy efficiency in older households, promoting energy conservation promotion among younger households, and cultivating consumers’ green-consumption awareness.

An innovative environmental parameter: Expanded Total Equivalent Warming Impact

The greenhouse gas emissions caused by human activities determined an increase of global mean temperature during last decade. The growing heating, cooling, ventilation and refrigeration demands for residential, commercial and industrial sectors represent the major contributor to environmental emissions. The environmental analysis represents a good strategy for evaluation, comparison and selection of energy supply system on the basis of users’ demands. The global warming potential of energy conversion devices is usually analysed by considering energy consumption, indirect and direct greenhouse gas emissions caused by refrigerants leakages through the well-known Total Equivalent Warming Impact index, TEWI. In this paper a detailed and extended version of TEWI index, Expanded Total Equivalent Warming Impact (ETEWI) parameter is proposed to calculate CO2 equivalent emissions from direct and indirect contributions in the HVAC&R sectors. The standard TEWI index contributes are revisited to determine the emissions by an accurate evaluation of direct refrigerant leakages and by detailing the indirect emissions caused by electric energy consumption . In addition, new emissions’ contributions are investigated. The novelty of this approach can be summarised in two key-points: the possibility of analysing the environmental impact of both electric and gas driven devices and the definition of an innovative environmental parameter to take into account the direct/indirect contributions of the Urban Heat Island effect and the indirect CO2 emissions due to losses in distribution and transportation pipelines that supply natural-gas to energy conversion systems.