Shortcut Evaluation of Chemical Carbon Dioxide Utilization Processes

Chemical utilization of carbon dioxide seems to be an attractive option for the mitigation of greenhouse gas emissions. However, the respective processes themselves cause substantial greenhouse gas emissions. To achieve a good CO₂ balance, it is necessary not only to fix carbon but also to do this efficiently in terms of reactant supply and energy demand. An evaluation of the CO₂ balance requires detailed process simulation for the utilization reaction and the supply chain. To allow a quick evaluation of the potential to mitigate emissions, a number of estimation methods are presented.     

Co-generation of synthesis gas and C2+ hydrocarbons from methane and carbon dioxide in a hybrid catalytic-plasma reactor: A review

The topics on conversion and utilization of methane and carbon dioxide are important issues in tackling the global warming effects from the two greenhouse gases. Several technologies including catalytic and plasma have been proposed to improve the process involving conversion and utilization of methane and carbon dioxide. In this paper, an overview of the basic principles, and the effects of CH₄/CO₂ feed ratio, total feed flow rate, discharge power, catalyst, applied voltage, wall temperature, and system pressure in dielectric-barrier discharge (DBD) plasma reactor are addressed. The discharge power, discharge gap, applied voltage and CH₄/CO₂ ratio in the feed showed the most significant effects on the reactor performance. Co-feeding carbon dioxide with the methane feed stream reduced coking and increased methane conversion. The H₂/CO ratio in the products was significantly affected by CH₄/CO₂ ratio. The synergism of the catalyst placed in the discharge gap and the plasma affected the products distribution significantly. Methane and carbon dioxide conversions were influenced significantly by discharge power and applied voltage. The drawbacks of DBD plasma application in the CH₄–CO₂ conversion should be taken into consideration before a new plausible reactor system can be implemented.     

Adsorptive cyclic purification process for CO2 mixtures captured from coal power plants

CO₂ capture technology combined with bulk separation and purification processes has become an attractive alternative to reduce capture costs. Furthermore, the required purity in the application for CO₂ conversion and utilization is more stringent than that required from a captured CO₂ mixture for geological storage. In this study, an adsorptive cyclic purification process was developed to upgrade a CO₂/N₂ mixture captured from greenhouse gas emission plants as a feasibility study for a second capture unit or captured CO₂ purifier. To purify 90% CO₂ with balance N₂ as a captured gas mixture, two‐bed pressure swing adsorption and pressure vacuum swing adsorption (PVSA) processes using activated carbon were experimentally and theoretically studied at adsorption pressures of 250–650 kPa and a fixed vacuum pressure of 50 kPa. CO₂ with higher than 95% purity was produced with more than 89% recovery. However, a four‐bed PVSA process could successfully produce CO₂ with greater than 98% purity and 90% recovery. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1051–1063, 2017     

Canadian greenhouse gas mitigation options in agriculture

In 1991, on farm management practices contributed 57.6 Tg CO₂ equivalent in greenhouse gas emissions, that is, about 10% of the anthropogenic GHG emissions in Canada. Approximately 11% of these emissions were in the form of CO₂, 36% in the form of CH₄ and 53% in the form of N₂O. The CO₂ emissions were from soils; CH₄ emissions were from enteric fermentation and manure, and N₂O emissions were primarily a function of cropping practices and manure management. With the emissions from all other agricultural practices included, such as the emissions from fossil fuels used for transportation, manufacturing, food processing etc., the agricultural sector's contributions were about 15% of Canada's emissions. In this publication, several options are examined as to their potential for reducing greenhouse gas emissions. These involve soil and crop management, soil nutrient management, improved feeding strategies, and carbon storage in industrial by-products. The Canadian Economic Emissions Model for Agriculture (CEEMA) was used to predict the greenhouse gas emissions for the year 2010, as well as the impact of mitigation options on greenhouse gas emissions from the agricultural sector. This model incorporates the Canadian Regional Agricultural sub-Model (CRAM), which predicts the activities related to agriculture in Canada up to 2010, as well as a Greenhouse Gas Emissions sub-Model (GGEM), which estimates the greenhouse gas emissions associated with the various agricultural activities. The greenhouse gas emissions from all agricultural sources were 90.5 Tg CO₂ equivalent in 1991. Estimates based on CEEMA for the year 2010 indicate emissions are expected to be 98.0 Tg CO₂ equivalent under a business as usual scenario, which assumes that the present trends in management practices will continue. The agricultural sector will then need to reduce its emissions by about 12.9 Tg CO₂ equivalent below 2010 forecasted emissions, if it is to attain its part of the Canadian government commitment made in Kyoto. Technologies focusing on increasing the soil carbon sink, reducing greenhouse gas emissions and improving the overall farming efficiency, need to be refined and developed as best management practices. The soils carbon sink can be increased through reduced tillage, reduced summer fallowing, increased use of grasslands and forage crops, etc. Key areas for the possible reduction of greenhouse gas emissions are improved soil nutrient management, improved manure storage and handling, better livestock grazing and feeding strategies, etc. The overall impact of these options is dependent on the adoption rate. Agriculture's greenhouse gas reduction commitment could probably be met if soils are recognized as a carbon sink under the Kyoto Accord and if a wide range of management practices are adopted on a large scale. None of these options can currently be recommended as measures because their socio-economic aspects have not been fully evaluated and there are still too many uncertainties in the emission estimates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of Industrial Greenhouse Gas Reduction Strategies Within Consistent System Boundaries

With respect to the climate goals of the greenhouse gas (GHG) neutrality in 2050, different GHG reduction strategies are discussed for industrial processes. For a comparison of the strategies carbon direct avoidance (CDA), carbon capture and storage, and carbon capture and utilization (CCU), the method system expansion is applied. Exemplarily, the CO₂ reduction potential and the energy demand are determined. The Carbon2Chem® project is described as an example of CCU for the steel and chemical production. The direct reduction with H₂ represents the CDA strategy for the steel industry.     

Reducing heavy oil carbon footprint and enhancing production through CO2 injection

The world's dependence on heavy oil production is on the rise as the existing conventional oil reservoirs mature and their production decline. Compared to conventional oil, heavy oil is much more viscous and hence its production is much more difficult. Various thermal methods and particularly steam injection are applied in the field to heat up the oil and to help with its flow and production. However, the thermal recovery methods are very energy intensive with significant negative environmental impact including the production of large quantities of CO₂. Alternative non-thermal recovery methods are therefore needed to allow heavy oil production by more environmentally acceptable methods. Injection of CO₂ in heavy oil reservoirs increases oil recovery while eliminating negative impacts of thermal methods.In this paper we present the results of a series of micromodel and coreflood experiments carried out to investigate the performance of CO₂ injection in an extra-heavy crude oil as a method for enhancing heavy oil recovery and at the same time storing CO₂. We reveal the pore-scale interactions of CO₂-heavy oil-water and quantify the volume of CO₂ which can be stored in these reservoirs.The results demonstrate that CO₂ injection can provide an effective and environmentally friendly alternative method for heavy oil recovery. CO₂ injection can be used independently or in conjunction with thermal recovery methods to reduce their carbon footprint by injecting the CO₂ generated during steam generation in the reservoirs rather than releasing it in the atmosphere.     

Increasing carbon utilization in Fischer-Tropsch synthesis using H2-deficient or CO2-rich syngas feeds

Fischer-Tropsch technology has become a topical issue in the energy industry in recent times. The synthesis of linear hydrocarbon that has high cetane number diesel fuel through the Fischer-Tropsch reaction requires syngas with high H₂/CO ratio. Nevertheless, the production of syngas from biomass and coal, which have low H₂/CO ratios or are CO₂ rich may be desirable for environmental and socio-political reasons. Efficient carbon utilization in such H₂-deficient and CO₂-rich syngas feeds has not been given the required attention. It is desirable to improve carbon utilization using such syngas feeds in the Fischer-Tropsch synthesis not only for process economy but also for sustainable development. Previous catalyst and process development efforts were directed toward maximising C₅₊ selectivity; they are not for achieving high carbon utilization with H₂-deficient and CO₂-rich syngas feeds. However, current trends in FTS catalyst design hold the potential of achieving high carbon utilization with wide option of selectivities. Highlights of the current trends in FTS catalyst design are presented and their prospect for achieving high carbon utilization in FTS using H₂-deficient and CO₂-rich syngas feeds is discussed.     

Tendenzen der Energieversorgung im Hinblick auf die CO2-Diskussion

Energy supply trends with regard to carbon dioxide (CO₂). Carbon dioxide (CO₂) is regarded as the main cause of the ?greenhouse effect”? in the atmosphere. Although this problem is well known, the chances for a reduction of CO₂ emissions are limited. On the one hand there is no immediate need for action because for the time being the catastrophes are taking place on the computer only. On the other hand population figures and thirst for energy are steadily increasing. Moreover, the possible measures for a reduction of CO₂ are limited. Considering the FRG's share of the carbon dioxide concentration, the targeted 25% reduction of CO₂ emissions by the year 2005 could be achieved. A large potential of energy saving and CO₂ reduction are realized by industrial cogeneration. No further technical development in order to open up this potential is needed because the technically and economically optimal solution is already available with the combined gas turbine process. In order to make use of this potential, the hurdle in the licensing procedure for industrial power plants with an output of more than 10 MW must be removed. In addition, cooperation between the energy supply corporations and industry has to be improved.     

Carbon nano-layer coated TiO2 nanoparticles for efficient photocatalytic CO2 reduction into CH4 and CO

Solar-driven photocatalytic reduction of CO₂ into value-added fuel is an exciting concept that can address serious global challenges such as greenhouse effect and energy crisis. However, the low sunlight utilization by the photocatalysts and their high production costs have greatly hindered their mass adoption. Herein, we proposed a facile and efficient approach to prepare the carbon nano-layer coated TiO₂ as an efficient photocatalyst for the photocatalytic reduction of CO₂ into CH₄ and CO. By pyrolyzing linear low-density polyethylene, a carbon nano-layer was formed on the surface of TiO₂. The obtained carbon nano-layer coated TiO₂ was able to exhibit superior photocatalytic CO₂ reduction activity as compared to its unmodified counterpart, whereby, a CH₄ production rate of ~2.30 μmol · g⁻¹ h⁻¹ was achieved (prepared at a dwelling temperature of 600 °C). Meanwhile, a CO production rate of ~16.76 μmol · g⁻¹ h⁻¹ was recorded for the materials prepared at a dwelling temperature of 500 °C. The enhanced CH₄ and CO production can be attributed to the elevated absorbance in the visible-light region, decreased band gap and effective restriction of photogenerated electron-hole pair recombination. Thus, based on the results, carbon nano-layer coated TiO₂ can be a promising alternative for the photocatalytic reduction of CO₂ into valuable fuel for large-scale application.     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

High Temperature Co-Electrolysis as a Key Technology for CO2 Emission Mitigation – A Model-Based Assessment of CDA and CCU

The mitigation of CO₂ emissions is a major challenge for modern society. While the mitigation of energy-related emissions can be achieved comparatively easy by switching to renewable energy sources, reduction of process-related industrial emissions is considerably more challenging. To reduce industrial CO₂ emissions, two basic routes are available: carbon direct avoidance (CDA) and carbon capture and utilization (CCU). It is shown that in terms of efficiency, CDA is to be favored when applicable. However, for applications where emissions cannot be avoided, CCU can be a viable approach allowing for emission mitigation.     

A Single Stage Membrane Process for CO2 Capture from Flue Gas by a Facilitated Transport Membrane

Carbon dioxide is the most important anthropogenic greenhouse gas and it accounts for about 80% of all greenhouse gases (GHG). The global atmospheric CO₂ concentrations have been increased significantly and have become the major source responsible for global warming; the greatest environmental challenge the world is facing now. The efforts to control the GHG emissions include the recovery of CO₂ from flue gas. In this work, feasibility analysis, based on a single stage membrane process, has been carried out with an in-house membrane program interfaced within process simulation program (AspenHysys) to investigate the influence of process parameters on the energy demand and flue gas processing cost. A novel CO₂-selective membrane with the facilitated transport mechanism has been employed to capture CO₂ from the flue gas mixtures. The results show that a membrane process using the facilitated transport membrane can also be considered as an alternative CO₂ capture process and it is possible to achieve more than 90% CO₂ recovery and 90% CO₂ purity in the permeate with reasonable energy consumption compared to amine absorption and other capture techniques.     

Application of a Waste Carbon Material as the Carbonaceous Reductant During Silicon Production

It is important to study the application of alternative carbon reductants for industrial silicon smelting to reduce consumption of carbonaceous reducing agents, electricity, and CO₂ emissions during silicon production. In this study, an industrial experiment was carried out in an 8 MVA submerged arc furnace using waste carbon material in place of approximately 20% partial reducing agents. The system was analyzed for silicon yield, power consumption, overall energy efficiency, CO₂ emissions, and the utilization rate of carbonaceous materials. The system improved the efficiency of carbonaceous materials and decreased power consumption using alternative carbon reductants. The results have showed that use of waste carbon materials reduced carbon emissions per ton silicon by more than 19.14% and specific CO₂ emissions decreased to 0.865 t.     

Tillage-induced CO2 emission from soil

The influence of agricultural production systems on greenhouse gas generation and emission is of interest as it may affect potential global climate change. Agricultural ecosystems can play a significant role in production and consumption of greenhouse gases, specifically, carbon dioxide. Information is needed on the mechanism and magnitude of gas generation and emission from agricultural soils with specific emphasis on tillage mechanisms. This work evaluated four different tillage methods on the short-term CO₂ and water vapor flux from a clay loam soil in the Northern Cornbelt of the USA. The four tillage methods were moldboard plow only, moldboard plow plus disk harrow twice, disk harrow and chisel plow using standard tillage equipment following a wheat (Triticum aestivum L.) crop compared with no tillage. The CO₂ flux was measured with a large portable chamber commonly used to measure crop canopy gas exchange initiated within 5 minutes after tillage and continued intermittently for 19 days. The moldboard plow treatment buried nearly all of the residue and left the soil in a rough, loose, open condition and resulted in maximum CO₂ loss. The carbon released as CO₂ during the 19 days following the moldboard plow, moldboard plow plus disk harrow, disk harrow, chisel plow and not tilled treatments would account for 134%, 70%, 58%, 54% and 27% respectively of the carbon in the current year's crop residue. The short-term carbon dioxide losses 5 hours after four conservation tillage tools was only 31% of that of the moldboard plow. The moldboard plow lost 13.8 times as much CO₂ as the soil area not tilled while different conservation tillage tools lost only 4.3 times. The smaller CO₂ loss following conservation tillage tools is significant and suggests progress in developing conservation tillage tools that can enhance soil carbon management. Conservation tillage reduces the extent, frequency and magnitude of mechanical disturbance caused by the moldboard plow and reduces the air-filled macropores and slows the rate of carbon oxidation. Any effort to decrease tillage intensity and maximize residue return should result in carbon sequestration for enhanced environmental quality. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimal European cooperative supply chains for carbon capture,transport, and sequestration with costs share policies

In the past decades, CO₂ constituted nearly the 80% of anthropogenic greenhouse gases emissions therefore, global actions are needed to tackle the increase of carbon concentration in the atmosphere. CO₂ (carbon) capture and storage has been highlighted among the most promising options to decarbonize the energy and industry sectors. Considering a large-scale infrastructure at European level, economic cooperation has been highlighted as a key requirement to relieve single countries from too high risk and commitment. This article proposes an economic optimization for cooperative supply chains for CO₂ capture and storage, by adopting policies that balance the spread of costs among countries, according to local characteristics in terms of population, CO₂ emissions, and macroeconomic outcome. Results show that the additional European investment for cooperation (max. +2.6% with respect to a noncooperative network) should not constitute a barrier toward the installation and operation of such more effective network designs.     

Thermodynamic analysis of glycerol dry reforming for hydrogen and synthesis gas production

A thermodynamic analysis of glycerol dry reforming has been performed by the Gibbs free energy minimization method as a function of CO₂ to glycerol ratio, temperature, and pressure. Hydrogen and synthesis gas can be produced by the glycerol dry reforming. The carbon neutral glycerol reforming with greenhouse gas CO₂ could convert CO₂ into synthesis gas or high value-added inner carbon. Atmospheric pressure is preferable for this system and glycerol conversion keeps 100%. Various of H₂/CO ratios can be generated from a flexible operational range. Optimized conditions for hydrogen production are temperatures over 975 K and CO₂ to glycerol ratios of 0-1. With a temperature of 1000 K and CO₂ to glycerol ratio of 1, the production of synthesis gas reaches a maximum, e.g., 6.4 mol of synthesis gas (H₂/CO = 1:1) can be produced per mole of glycerol with CO₂ conversion of 33%.     

NO and SO2 removal in non-thermal plasma reactor packed with glass beads-TiO2 thin film coated by PCVD process

We analyzed the NO and SO₂ removal in the non-thermal plasma discharge process combined with TiO₂ photocatalyst. The non-thermal plasmas were generated by dielectric barrier discharge with glass beads as dielectric materials. The TiO₂ thin films were coated on the glass beads uniformly without crack by a rotating cylindrical plasma chemical vapor deposition reactor. The NO and SO₂ removal efficiencies obtained in non-thermal plasma–TiO₂ photocatalysts hybrid system were higher than those in plasma process only, because of the additional removal of NO and SO₂ by photocatalysts. The NO and SO₂ removal efficiencies become higher, as applied peak voltage, pulse frequency and gas residence time increase, or as the initial NO and SO₂ concentrations decrease. The hybrid system of non-thermal plasma and photocatalyst thin film on glass beads prepared by PCVD process is quite efficient method to remove NO and SO₂.     

Reduction of Greenhouse Gas Emissions from Gas,Oil, and Coal Power Plants in Pakistan by Carbon Capture and Storage (CCS): A Review

The production of energy in Pakistan as a developing country mainly depends on consumption of fossil fuels, which are the main sources of greenhouse gas (GHG) emissions. These emissions can be mitigated by implementing carbon capture and storage (CCS) in running plants. An overview of the current and future potentials of Pakistan for CCS is provided, indicating a great potential for this technology to capture CO₂ emissions. The amine CO₂ capture process as the most mature procedure is currently applied in many oil and gas companies in Pakistan, which can be employed to capture CO₂ from other industries as well. Pakistan has a great CO₂ storage potential in oil, gas, and coal fields and in saline aquifer as well as significant resources of Mg and Ca silicates suitable as feedstock in the carbon mineralization process. For further development and implementation of CCS technologies in Pakistan, economic and policy barriers as the main obstacles should be alleviated.     

Ni single-atom arrays as self-supported electrocatalysts for CO2RR

Developing highly active, selective, and stable electrocatalysts for the CO₂ reduction reaction (CO₂RR) is essential to relieve the greenhouse effect and the energy crisis. Traditional catalytic electrodes require ionomer binders, which inevitably impose undesired high CO₂ transport resistance and block the active sites. Herein, Ni single atoms anchored on nitrogen-doped carbon nanoarrays (denoted as Ni-SAC-NA) were developed as the electrode without additional ionomers for efficient CO₂RR. The unique nanoarray structure provided a higher specific surface area, more exposed active sites, and enhanced electron/mass transport due to its short diffusion pathway and ionomer-free nature. As a result, the Ni-SAC-NA electrode exhibited enhanced activity of CO₂RR and selectivity towards CO with Faradaic efficiency of 96.7%, turnover frequency of 27,504 h⁻¹, and cathodic energy efficiencies of 54.9% at −0.88 V (vs. RHE). Our findings provide a rational design strategy for CO₂RR electrocatalysts by constructing ionomer-free electrodes.     

Potential of agroforestry for carbon sequestration and mitigation of greenhouse gas emissions from soils in the tropics

Losses of carbon (C) stocks in terrestrial ecosystems and increasing concentrations of greenhouse gases in the atmosphere are challenges that scientists and policy makers have been facing in the recent past. Intensified agricultural practices lead to a reduction in ecosystem carbon stocks, mainly due to removal of aboveground biomass as harvest and loss of carbon as CO₂ through burning and/or decomposition. Evidence is emerging that agroforestry systems are promising management practices to increase aboveground and soil C stocks and reduce soil degradation, as well as to mitigate greenhouse gas emissions. In the humid tropics, the potential of agroforestry (tree-based) systems to sequester C in vegetation can be over 70 Mg C ha^–1, and up to 25 Mg ha^–1 in the top 20 cm of soil. In degraded soils of the sub-humid tropics, improved fallow agroforestry practices have been found to increase top soil C stocks up to 1.6 Mg C ha^–1 y^–1 above continuous maize cropping. Soil C accretion is linked to the structural development of the soil, in particular to increasing C in water stable aggregates (WSA). A review of agroforestry practices in the humid tropics showed that these systems were able to mitigate N₂O and CO₂ emissions from soils and increase the CH₄ sink strength compared to cropping systems. The increase in N₂O and CO₂ emissions after addition of legume residues in improved fallow systems in the sub-humid tropics indicates the importance of using lower quality organic inputs and increasing nutrient use efficiency to derive more direct and indirect benefits from the system. In summary, these examples provide evidence of several pathways by which agroforestry systems can increase C sequestration and reduce greenhouse gas emissions.