Carbon Utilization Efficiency Research Articles

Backbone Engineering of Polymeric Catalysts for High‐Performance CO2 Reduction in Bipolar Membrane Zero‐Gap Electrolyzer

AbstractBipolar membranes (BPMs) have emerged as a promising solution for mitigating CO2 losses, salt precipitation and high maintenance costs associated with the commonly used anion‐exchange membrane electrode assembly for CO2 reduction reaction (CO2RR). However, the industrial implementation of BPM‐based zero‐gap electrolyzer is hampered by the poor CO2RR performance, largely attributed to the local acidic environment. Here, we report a backbone engineering strategy to improve the CO2RR performance of molecular catalysts in BPM‐based zero‐gap electrolyzers by covalently grafting cobalt tetraaminophthalocyanine onto a positively charged polyfluorene backbone (PF‐CoTAPc). PF‐CoTAPc shows a high acid tolerance in BPM electrode assembly (BPMEA), achieving a high FE of 82.6 % for CO at 100 mA/cm2 and a high CO2 utilization efficiency of 87.8 %. Notably, the CO2RR selectivity, carbon utilization efficiency and long‐term stability of PF‐CoTAPc in BPMEA outperform reported BPM systems. We attribute the enhancement to the stable cationic shield in the double layer and suppression of proton migration, ultimately inhibiting the undesired hydrogen evolution and improving the CO2RR selectivity. Techno‐economic analysis shows the least energy consumption (957 kJ/mol) for the PF‐CoTAPc catalyst in BPMEA. Our findings provide a viable strategy for designing efficient CO2RR catalysts in acidic environments.

Temporal and Spatial Dynamics in Carbon Utilization Efficiency and Driving Mechanisms in Southeast Tibet from 2012 to 2022

Carbon utilization efficiency (CUE) in terrestrial ecosystems stands as a pivotal metric for assessing ecosystem functionality. Investigating the spatiotemporal dynamics of regional CUE within the context of global climate change not only provides a theoretical foundation for understanding terrestrial carbon cycling but also furnishes essential data support for formulating sustainable management strategies at a regional scale. This study focuses on the southeastern region of Tibet. Utilizing monthly and yearly MOD17A2HGF as primary sources, we employ Thiel–Sen estimation and Mann–Kendall trend analysis to scrutinize the spatiotemporal dynamics of CUE. Systematic analysis of the stability of CUE spatiotemporal changes in the Southeast Tibet region is conducted using the coefficient of variation analysis. The Hurst model is then applied to prognosticate future CUE changes in Southeast Tibet. Additionally, a comprehensive analysis of CUE is undertaken by integrating meteorological data and land-use data. The findings reveal the following: (1) At the monthly scale, regional CUE exhibits discernible variations synchronized with the growth season, with different vegetation types displaying diverse fluctuation patterns. The high-altitude forest area manifests the least annual CUE fluctuations, while evergreen needleleaf forests and evergreen broadleaf forests demonstrate larger variations. At the yearly scale, CUE reveals a non-significant upward trend overall, but there is an augmented fluctuation observed from 2019 to 2022. (2) CUE in Southeast Tibet demonstrates sensitivity to temperature and precipitation variations, with temperature exhibiting a more pronounced and strongly correlated impact, especially in Gongjo County and Qamdo Town. Temperature and precipitation exert opposing influences on CUE changes in the Southeast Tibet region. In the southern (below 28° N) and northern (above 31° N) regions of Southeast Tibet, the response of CUE to temperature and precipitation variations differs. Moreover, over 62.3% of the areas show no sustained trend of change. (3) Vegetation type emerges as a principal factor determining the scope and features of vegetation CUE changes. Grassland and sparse grassland areas exhibit markedly higher CUE values than evergreen broadleaf forests, deciduous broadleaf forests, evergreen needleleaf forests, and deciduous needleleaf forests. Notably, the CUE fluctuation in shrublands and areas with embedded farmland vegetation surpasses that of other vegetation types.

Investigation on hydrothermal-pyrolysis process to eliminate S-pollution from corncob residue utilization: Experiment and life cycle assessment

Corncob residue (CR) is characterized by high S and moisture content, which results in large SOx emissions in the thermal process (incineration/pyrolysis). This study investigated a new hydrothermal-pyrolysis method (HT-PY) to obtain high-quality products (phenol-rich and low moisture content bio-oil, S-free char). Compared with S content of CR, the S content of hydrochar obtained from 300 ℃-HT decreased 63.33 %. After pyrolysis, the S and volatile-sulfur (VS) content of char obtained from 300HT-550PY decreased 84.45 % and 95.24 %, only 0.14 % and 0.01 %. Compared with direct pyrolysis of CR, Hydrothermal pre-treatment improved the decomposition of organic-S in solid phase and eliminate the S-emissions of gas phase. Basing on the experimental data and process simulation, life cycle assessment, and economic cost analysis of CR-HT-PY were also provided benefits. The steam of the hydrothermal unit recovered to the heat supply of furfural production (30796.21 MJ). And the HT-PY system exhibited the lowest GWP and AP environmental impact, SO2 emissions of CR-HT-PY was merely emitted during the hydrothermal process (0.32 kg/ton CR), decreased 98.03 % (15.92 kg SO2/ton CR) compared with direct pyrolysis. The carbon utilization efficiency was also increased by 41.37 % due to higher-quality products. In addition, due to the high value of S-free char, the total economic efficiency of CR-HT-PY was more than twice that of other systems.

Effects of mepiquat chloride and plant population density on leaf photosynthesis and carbohydrate metabolism in upland cotton

BackgroundMepiquat chloride (MC) application and plant population density (PPD) increasing are required for modern cotton production. However, their interactive effects on leaf physiology and carbohydrate metabolism remain obscure. This study aimed to examine whether and how MC and PPD affect the leaf morpho-physiological characteristics, and thus final cotton yield. PPD of three levels (D1: 2.25 plants·m−2, D2: 4.5 plants·m−2, and D3: 6.75 plants·m−2) and MC dosage of two levels (MC0: 0 g·ha−2, MC1: 82.5 g·ha−2) were combined to create six treatments. The dynamics of nonstructual carbohydrate concentration, carbon metabolism-related enzyme activity, and photosynthetic attributes in cotton leaves were examined during reproductive growth in 2019 and 2020.ResultsAmong six treatments, the high PPD of 6.75 plants·m−2 combined with MC application (MC1D3) exhibited the greatest seed cotton yield and biological yield. The sucrose, hexose, starch, and total nonstructural carbohydrate (TNC) concentrations peaked at the first flowering (FF) stage and then declined to a minimum at the first boll opening (FBO) stage. Compared with other treatments, MC1D3 improved starch and TNC concentration by 5.4% ~ 88.4%, 7.8% ~ 52.0% in 2019, and by 14.6% ~ 55.9%, 13.5% ~ 39.7% in 2020 at the FF stage, respectively. Additionally, MC1D3 produced higher transformation rates of starch and TNC from the FF to FBO stages, indicating greater carbon production and utilization efficiency. MC1D3 displayed the maximal specific leaf weight (SLW) at the FBO stage, and the highest chlorophyll a (Chl a), Chl b, and Chl a + b concentration at the mid-late growth phase in both years. The Rubisco activity with MC1D3 was 2.6% ~ 53.2% higher at the flowering and boll setting stages in both years, and 2.4% ~ 52.7% higher at the FBO stage in 2020 than those in other treatments. These results provided a explanation of higher leaf senescence-resistant ability in MC1D3.ConclusionIncreasing PPD coupled with MC application improves cotton yield by enhancing leaf carbohydrate production and utilization efficiency and delaying leaf senescence.

Iodine‐Mediated C─C Coupling in Neutral Flow Cell for Electrochemical CO2 Reduction

AbstractCarbon utilization efficiency is of vital importance for electrochemical CO2 reduction systems. Proton exchange membrane (PEM) electrolyzers using nonalkaline electrolytes can prevent CO2 crossover and increase carbon utilization efficiency, yet they suffer from unfavored C─C coupling and severe hydrogen evolution. Herein, an iodine‐mediated approach to facilitate C─C coupling on Cu‐based catalysts toward multi‐carbon products in a neutral PEM electrolyzer is reported. By in situ constructing an I‐modified Cu surface, the hydrogenation of *CO is promoted and the C─C coupling process progresses through the *CO−*COH pathway with a low energy barrier. A high Faradaic efficiency of ≈72% and a high partial current density of 575 mA cm−2 are achieved for multi‐carbon products. The present study demonstrates an efficient approach to developing advanced CO2 electrolyzers for high‐value products with high efficiency.

Microenvironment Regulation Strategies Facilitating High-Efficiency CO2 Electrolysis in a Zero-Gap Bipolar Membrane Electrolyzer.

In alkaline and neutral zero-gap CO2 electrolyzers, the carbon utilization efficiency of the electrocatalytic CO2 reduction to CO is less than 50% because of inherently homogeneous reactions. Utilization of the bipolar membrane (BPM) electrolyzer can effectively suppress (bi)carbonate formation and parasitic CO2 losses; however, an excessive concentration of H+ in the catalyst layer (CL) significantly hinders the activity and selectivity for CO2 reduction. Here, we report a microenvironment regulation strategy that controls the CL thickness and ionomer content to regulate local CO2 transport and the local pH within the CL. We report 80% faradaic efficiency of CO at a current density of 400 mA/cm2 without the use of a buffering layer, exceeding that of state-of-the-art catalysts with a buffering layer. A carbon utilization efficiency of 63.6% at 400 mA/cm2 is also obtained. This study demonstrates the significance of regulating the microenvironment of the CL in a BPM system.

Modeling and analysis of air combustion and steam regeneration in methanol to olefins processes

Light olefins is the incredibly important materials in chemical industry. Methanol to olefins (MTO), which provides a non-oil route for light olefins production, received considerable attention in the past decades. However, the catalyst deactivation is an inevitable feature in MTO processes, and regeneration, therefore, is one of the key steps in industrial MTO processes. Traditionally the MTO catalyst is regenerated by removing the deposited coke via air combustion, which unavoidably transforms coke into carbon dioxide and reduces the carbon utilization efficiency. Recent study shows that the coke species over MTO catalyst can be regenerated via steam, which can promote the light olefins yield as the deactivated coke species can be essentially transferred to industrially useful synthesis gas, is a promising pathway for further MTO processes development. In this work, we modelled and analyzed these two MTO regeneration methods in terms of carbon utilization efficiency and technology economics. As shown, the steam regeneration could achieve a carbon utilization efficiency of 84.31%, compared to 74.74% for air combustion regeneration. The MTO processes using steam regeneration can essentially achieve the near-zero carbon emission. In addition, light olefins production of the MTO processes using steam regeneration is 12.81% higher than that using air combustion regeneration. In this regard, steam regeneration could be considered as a potential yet promising regeneration method for further MTO processes, showing not only great environmental benefits but also competitive economic performance.

Enrichment Strategies for Efficient CO2 Electroreduction in Acidic Electrolytes.

Electrochemical CO2 reduction reaction (CO2 RR) has been recognized as an appealing route to remarkably accelerate the carbon-neutral cycle and reduce carbon emissions. Notwithstanding great catalytic activity that has been acquired in neutral and alkaline conditions, the carbonates generated from the inevitable reaction of the input CO2 with the hydroxide severely lower carbon utilization and energy efficiency. By contrast, CO2 RR in an acidic condition can effectively circumvent the carbonate issues; however, the activity and selectivity of CO2 RR in acidic electrolytes will be decreased significantly due to the competing hydrogen evolution reaction (HER). Enriching the CO2 and the key intermediates around the catalyst surface can promote the reaction rate and enhance the product selectivity, providing a promising way to boost the performance of CO2 RR. In this review, the catalytic mechanism and key technique challenges of CO2 RR are first introduced. Then, the critical progress of enrichment strategies for promoting the CO2 RR in the acidic electrolyte is summarized with three aspects: catalyst design, electrolyte regulation, and electrolyzer optimization. Finally, some insights and perspectives for further development of enrichment strategies in acidic CO2 RR are expounded.

Carbon-negative valorization of biomass waste into affordable green hydrogen and battery anodes

The global Sustainable Development Goals highlight the necessity for affordable and clean energy, designated as SDG7. A sustainable and feasible biorefinery concept is proposed for the carbon-negative utilization of biomass waste for affordable H2 and battery anode material production. Specifically, an innovative tandem biocarbon + NiAlO + biocarbon catalyst strategy is constructed to realize a complete reforming of biomass pyro-vapors into H2+CO (as a mixture). The solid residues from pyrolysis are upgraded into high-quality hard carbon (HCs), demonstrating potential as sodium ion battery (SIBs) anodes. The product, HC-1600-6h, exhibited great electrochemical performance when employed as (SIBs) anodes (full cell: 263 Wh/kg with ICE of 89%). Ultimately, a comprehensive process is designed, simulated, and evaluated. The process yields 75 kg H2, 169 kg HCs, and 891 kg captured CO2 per ton of biomass achieving approx. 100% carbon and hydrogen utilization efficiencies. A life cycle assessment estimates a biomass valorization process with negative-emissions (−0.81 kg CO2/kg-biomass, reliant on Sweden wind electricity). A techno-economic assessment forecasts a notably profitable process capable of co-producing affordable H2 and hard carbon battery anodes. The payback period of the process is projected to fall within two years, assuming reference prices of 13.7 €/kg for HCs and 5 €/kg for H2. The process contributes to a novel business paradigm for sustainable and commercially viable biorefinery process, achieving carbon-negative valorization of biomass waste into affordable energy and materials.

Soil and foliar Si fertilization alters elemental stoichiometry and increases yield of sugarcane cultivars

Silicon (Si) fertilization is widely recognized to improve the development of crops, especially in tropical soils and cultivation under dryland management. Herein, our working hypothesis was that Si stoichiometry favors the efficient use of carbon (C), nitrogen (N), and phosphorus (P) in sugarcane plants. Therefore, a field experiment was carried out using a 3 × 3 factorial scheme consisting of three cultivars (RB92579, RB021754 and RB036066) and three forms of Si application (control without Si; sodium silicate spray at 40 mmol L−1 in soil during planting; sodium silicate spray at 40 mmol L−1 on leaves at 75 days after emergence). All Si fertilizations altered the elemental C and P stoichiometry and sugarcane yield, but silicon-induced responses varied depending on sugarcane cultivar and application method. The most prominent impacts were found in the leaf Si-sprayed RB92579 cultivar, with a significant increase of 7.0% (11 Mg ha−1) in stalk yield, 9.0% (12 Mg ha−1) in total recoverable sugar, and 20% (4 Mg ha−1) in sugar yield compared to the Si-without control. In conclusion, our findings clearly show that silicon soil and foliar fertilization alter C:N:P stoichiometry by enhancing the efficiency of carbon and phosphorus utilization, leading to improved sugarcane production and industrial quality.

Mechanistic Insights into Formationof Residual Solidin Lignin Depolymerization.

Current techniques of lignin conversion are challenged by the low carbon utilization efficiency resulting from the severer generation of residual solid (char). Therefore, a better understanding of pathway for char formation is significant and highly desired to lignin valorization. In this work, we propose a fundamental mechanistic insight into char formation in the lignin depolymerization, using hydrothermal decomposition as the model reaction. The results demonstrate that the char featuring a multi-layer construction of coke and oligomer contains mainly G units, primarily generated from native G-lignin and demethoxylation of S-lignin. Instead, H-lignin contributes to the formation of volatile monophenols. Furthermore, new methylene bridges form between the benzene ring in lignin, which consequently results in the formation of recalcitrant char. Based on these observations, a plausible mechanism for char formation is proposed and verified by the density functional theory calculation.

Temperature and soil moisture change microbial allocation of pesticide‐derived carbon

AbstractTemperature and soil moisture are known to control pesticide mineralization. Half‐life times () derived from pesticide mineralization curves generally indicate longer residence times at low soil temperature and moisture but do not consider potential changes in the microbial allocation of pesticide‐derived carbon (C). We aimed to determine carbon use efficiency (, formation of new biomass relative to total C uptake) to better understand microbial utilization of pesticide‐derived C under different environmental conditions and to support the conventional description of degradation dynamics based on mineralization. We performed a microcosm experiment at two MCPA (2‐methyl‐4‐chlorophenoxyacetic acid) concentrations (1 and 20 mg kg−1) and defined 20°C/pF 1.8 as optimal and 10°C/pF 3.5 as limiting environmental conditions. After 4 weeks, 70% of the initially applied MCPA was mineralized under optimal conditions but MCPA mineralization reached less than 25% under limiting conditions. However, under limiting conditions, an increase in was observed, indicating a shift towards anabolic utilization of MCPA‐derived C. In this case, increased C assimilation implied C storage or the formation of precursor compounds to support resistance mechanisms, rather than actual growth since we did not find an increase in the tfdA gene relevant to MCPA degradation. We were able to confirm the assumption that under limiting conditions, C assimilation increases relative to mineralization and that C redistribution, may serve as an explanation for the difference between mineralization and MCPA dissipation‐derived degradation dynamics. In addition, by introducing to the temperature‐ and moisture‐dependent degradation of pesticides, we can capture the underlying microbial constraints and adaptive mechanisms to changing environmental conditions.

Analysis of the spatial-temporal evolution of Green and low carbon utilization efficiency of agricultural land in China and its influencing factors under the goal of carbon neutralization

Agricultural land is the most basic input factor for agricultural production and an essential component of terrestrial ecosystems, which plays a vital role in achieving carbon neutrality. Giving full play to the carbon-neutral contribution of agricultural land is a crucial part of China's economic transformation and green development. It incorporates carbon and pollution emissions from agricultural land use into the unexpected outputs of the Green and Low-carbon Utilization Efficiency of Agricultural Land (GLUEAL) evaluation system. The study utilized several advanced analytical tools, including the super-efficient Slacks-Based Measure (SBM) model, Exploratory Spatial-Temporal Data Analysis (ESTDA) method, Geodetector, and Geographically and Temporally Weighted Regression (GTWR) model. The objective was to examine the spatial-temporal evolution of GLUEAL and identify the factors that influenced it in all 31 provinces of China from 2005 to 2020. The results show that: (1) The overall spatial-temporal evolution of GLUEAL showed an increasing trend, but the disparity between provinces and regions became wider. (2) Most provinces have not yet made significant spatial and temporal jumps. They have high spatial cohesion with specific "path-dependent" characteristics. (3) The Geodetector results reveal that the Number of Rural Labor Force with Higher Education (NRLFHE) and Technology Support for Agriculture (TSA) have insufficient explanatory power on average for GLUEAL. Agricultural Economic Development Level (AEDL), Urbanization Level (UL), Multiple Crop Index (MCI), Planting Structure (PS), Degree of Crop Damage (DCD), Financial support for agriculture (FSA), and Agricultural mechanization level (AML) had stronger explanatory power on average for GLUEAL and were important factors influencing GLUEAL levels. (4) The average influence of AEDL, UL, FSA, and AML on GLUEAL changed from negative to positive. The average influence of MCI and DCD on GLUEAL was negative, and the average influence of PS on GLUEAL changed from positive to negative. This study provides a comprehensive description of the spatial and temporal evolution of GLUEAL in China. It reveals the key factors influencing GLUEAL and analyzes their spatial variations and impact patterns. These findings offer robust evidence for government policymakers to formulate policy measures for sustainable agricultural development and optimized resource allocation, promoting the transformation of agricultural land towards green and low-carbon practices and advancing the achievement of sustainable development goals.

Acidic CO2 electrolysis addressing the "alkalinity issue" and achieving high CO2 utilization.

Electrochemical CO2 reduction reaction (CO2RR) provides a promising approach for sustainable chemical fuel production of carbon neutrality. Neutral and alkaline electrolytes are predominantly employed in the current electrolysis system, but with striking drawbacks of (bi)carbonate (CO32-/HCO3-) formation and crossover due to the rapid and thermodynamically favorable reaction between hydroxide (OH-) with CO2, resulting in low carbon utilization efficiency and short-lived catalysis. Very recently, CO2RR in acidic media can effectively address the (bi)carbonate issue; however, the competing hydrogen evolution reaction (HER) is more kinetically favorable in acidic electrolytes, which dramatically reduces CO2 conversion efficiency. Thus, it is a big challenge to effectively suppress HER and accelerate acidic CO2RR. In this review, we begin by summarizing the recent progress of acidic CO2 electrolysis, discussing the key factors limiting the application of acidic electrolytes. We then systematically discuss addressing strategies for acidic CO2 electrolysis, including electrolyte microenvironment modulation, alkali cations adjusting, surface/interface functionalization, nanoconfinement structural design, and novel electrolyzer exploitation. Finally, the new challenges and perspectives of acidic CO2 electrolysis are suggested. We believe this timely review can arouse researchers' attention to CO2 crossover, inspire new insights to solve the "alkalinity problem" and enable CO2RR as a more sustainable technology.

Carbon-neutral light olefins production for energy decarbonization: Process development and techno-econo-environmental analysis

Low-carbon olefins, as important platform molecules, are generally produced by limited fossil energy, resulting in massive carbon emissions and intensive energy consumption inevitably. Therefore, it is necessary to develop clean and sustainable alternatives. With this in mind, three low-carbon olefin production processes using waste CO2 and green H2 were proposed, including the methanol-mediated (Option A) and Fischer-Tropsch synthesis (FTS)-based CO2-to-olefin (CTO) processes. Herein, the FTS-based CTO processes are classified into the direct (Option B) and indirect routes (Option C) without/with the reverse water–gas-shift unit. Meanwhile, rigorous process models were established, and detailed mass and energy balances of three processes were obtained with the aid of the process simulator. Moreover, in order to evaluate the feasibility and compare the differences in process performances of three proposed processes quantitatively, comprehensive techno-econo-environmental assessments of three processes were conducted at the system level. The results indicate that, firstly, from a technical perspective, the FTS-based processes are more competitive than the methanol-mediated process due to their higher energy efficiency (67.93%) and carbon utilization efficiency (84.22%). Secondly, from an economic perspective, the methanol-mediated process has a better economic prospect in the minimum olefin selling price (2527.08 $/tonne C2–C4 olefins). Lastly, from an environmental perspective, the methanol-mediated process is more environmentally friendly owing to its lower CO2-eq emissions (61.13 kg CO2-eq/tonne C2–C4). Moreover, for two FTS-based processes, the direct route is favorable in energy efficiency and minimum olefin selling price, whereas the indirect route is preferable in the carbon utilization efficiency and environmental impacts. Overall, the study provides novel approaches for the production of low-carbon olefins, and is of significant importance for reducing carbon footprint and achieving carbon neutrality.

Energy-oriented utilization from organic wastewater: Directional photoelectrocatalytic conversion of phenol to C1 fuels

To solve the problems of energy consumption, carbon emissions and pollution simultaneously, the directional conversion of phenol to hydrocarbon fuels through a pathway of “phenol → CO2 → HCO3–→HCOOH” was explored, with self-supplied CO2 as both carbon-based transition carrier and electron acceptor. In this economic approach, photoelectrocatalytic (PEC) deep mineralization of phenol was realized on the photoanode to provide CO2, together with the waste electrons from mineralization, was PEC converted into formate as the major liquid product on photocathode under an applied potential of 3 V and simulated sunlight. The total carbon utilization efficiency of phenol to hydrocarbons is 6.76%, and the conversion efficiency of formic acid is as high as 94.8% within 8 h PEC reaction. The integrated cell achieved the recovery of 2.75% waste electrons from phenol oxidation to produce liquid fuel. This work provides a promising “carbon neutral” strategy, which is important for realizing pollutant resource utilization and alleviating energy shortage.

A coal-based polygeneration system of synthetic natural gas, methanol and ethylene glycol: Process modeling and techno-economic evaluation

Coal to synthetic natural gas(CtSNG) industry is an effective way to alleviate the contradiction between supply and demand of natural gas in China. However, the product structure of the traditional CtSNG process is single and the carbon utilization rate is low, so there may be potential risks of product and coal price fluctuations. In order to address these issues, a coal-based polygeneration process of SNG, methanol and ethylene glycol(CtSMEG) was proposed in this study and compared with the CtSNG process. The entire CtSMEG system was first modelled and simulated by Aspen Plus, then the detailed techno-economic analysis was performed and the carbon balance and exergy balance were established. In addition, its carbon utilization efficiency, exergy efficiency and CO2 emissions were compared to that of the traditional CtSNG process. The results showed that the carbon utilization efficiency and exergy efficiency of the CtSMEG system were increased by 35.3 % and 27.3 % respectively, and the CO2 emissions and wastewater discharge were reduced by 0.613 kg/kg-production and 1719.3 kg/h. Although the total capital investment of the CtSMEG system was higher than that of the CtSNG process, the net present value was better than that of the CtSNG process. According to these findings, the CtSMEG system would be an effective way to overcome the problems of the current CtSNG process.

Experimental demonstration of 80 kWth chemical looping combustion of biogenic feedstock coupled with direct CO2 utilization by exhaust gas methanation

Chemical looping combustion is a highly efficient CO2 separation technology without direct contact between combustion air and fuel. A metal oxide is used as an oxygen carrier in dual fluidized beds to generate clean CO2. The use of biomass is the focus of current research because of the possibility of negative CO2 emissions and the utilization of biogenic carbon. The most commonly proposed OC are natural ores and residues, but complete combustion has not yet been achieved. In this work, the direct utilization of CLC exhaust gas for methane synthesis as an alternative route was investigated, where the gas components CO, CH4 and H2 are not disadvantageous but benefit the reactions in a methanation step. The whole process chain, the coupling of an 80 kWth pilot plant with gas cleaning and a 10 kW fluidized bed methanation unit were for this purpose established. As OC, ilmenite enhanced with limestone was used, combusting bark pellets in autothermal operation at over 1000 °C reaching high combustion efficiencies of up to 91.7%. The fuel reactor exhaust gas was mixed with hydrogen in the methanation reactor at 360 °C and converted with a methane yield of up to 97.3%. The study showed especially high carbon utilization efficiencies of 97% compared to competitor technologies. Based on the experimental results, a scale-up concept study showed the high potential of the combination of the technologies concerning the total efficiency and the adaptability to grid injection.Graphical

Carbonation in Low-Temperature CO2 Electrolyzers: Causes, Consequences, and Solutions

Electrochemical reduction of carbon dioxide (CO2) to useful products is an emerging power-to-X concept, which aims to produce chemicals and fuels with renewable electricity instead of fossil fuels. Depending on the catalyst, a range of chemicals can be produced from CO2 electrolysis at industrial-scale current densities, high Faraday efficiencies, and relatively low cell voltages. One of the main challenges for up-scaling the process is related to (bi)carbonate formation (carbonation), which is a consequence of performing the reaction in alkaline media to suppress the competing hydrogen evolution reaction. The parasitic reactions of CO2 with the alkaline electrolytes result in (bi)carbonate precipitation and flooding in gas diffusion electrodes, CO2 crossover to the anode, low carbon utilization efficiencies, electrolyte carbonation, pH-drift in time, and additional cost for CO2 and electrolyte recycling. We present a critical review of the causes, consequences, and possible solutions for the carbonation effect in CO2 electrolyzers. The mechanism of (bi)carbonate crossover in different cell configurations, its effect on the overall process design, and the economics of CO2 and electrolyte recovery are presented. The aim is to provide a better understanding of the (bi)carbonate problem and guide research directions to overcome the challenges related to low-temperature CO2 electrolysis in alkaline media.

Highly efficient electrocatalytic CO2 reduction over pyrolysis–free conjugated metallophthalocyanine networks in full pH range

Herein, we report the first work on pyrolysis–free synthesis of robust conjugated metallophthalocyanine–based covalent triazine frameworks (MPc–CTF, M= Co, Ni) for pH-universal electrocatalytic CO2 reduction reaction (CO2RR). CoPc–CTF shows high CO Faradaic efficiency over 94%, and long-term stability over 10 h in full pH range, and industry level CO partial current densities of 378.8 mA cm−2, 165.9 mA cm−2, 172.5 mA cm−2 in alkaline, neutral and acidic electrolytes, respectively. Particularly, the CO2 utilization efficiency reaches 51.3% in acidic electrolytes. Moreover, operando characterizations and density functional theory calculations indicate the promoting effect of triazine moiety in CoPc–CTF to accelerate the formation of *COOH intermediates during CO2RR. This work provides an encouraging direction for designing robust conjugated network supported single site catalysts to access high product selectivity and high carbon utilization efficiency in electrocatalytic CO2 reduction reaction.