CO2 Utilization Efficiency Research Articles

Precipitation of silica by CO2 bubbles/microbubbles and kinetics research

In China, the production of silica is mainly achieved through its precipitation process. Carbonization of precipitated silica makes full use of carbon-containing flue gases, such as lime kiln gas, thereby reducing the cost of silica production and making it an effective way of CO2 resource utilization. It is an important research field of cleaner production. The research in this study focuses on the production of precipitated silica through carbonation. This study evaluated the impact of Na2O·3.45SiO2 concentration and carbonization temperature during the process. The pH and temperature of the suspension were observed in order to evaluate the proposed process and contrast it with the traditional bubble generator process. The optimization of carbonization mass transfer by microbubbles was preliminarily studied by experiments and computational analysis methods. The results demonstrated that when the Na2O·3.45SiO2 concentration was at 0.2 mol/L and the temperature was 60 °C, the microbubbles could improve the efficiency of CO2 utilization by 1.9 times. The research on the specific surface area (BET) of the prepared silica powder revealed that BET decreased with the increase of Na2O·3.45SiO2 concentration when bubbling was present. Under bubbling/microbubble conditions, when the temperature was 60 °C, with the Na2O·3.45SiO2 concentration increased from 0.1 M to 0.5 M, the BET decreased by 29.2% and 16.8%, respectively. However, when the concentration of Na2O·3.45SiO2 increased to 0.5 M, the introduction of microbubbles made the BET higher than the bubble by 13.3%. Under bubbling/microbubble conditions, when the temperature increased from 25 °C to 60 °C, BET decreased with the increase of temperature, with the BET decreased by 13.5% and 12.8%, respectively. Furthermore, the kinetics of carbonation at room temperature and 0.2 mol/L Na2O·3.45SiO2 with bubbling were calculated. The results showed that carbonation was pseudo second-order reaction process. The process realized the solid waste utilization of CO2, and had important guiding significance for the preparation of high-performance silica.

Integrated Carbonate-Based CO2 Capture—Biofixation through Cyanobacteria

Microalgae, renowned for their high photosynthetic efficiency and minimal competition with land-based crops, hold great promise in the biofixation of CO2 from waste sources, making them valuable for diverse applications, including biofuels, food production, and biomaterials. An innovative technology, the integrated carbonate-based carbon capture and algae biofixation system is emerging as an alternative to traditional carbon capture and sequestration (CCS) methods. This closed-loop system utilizes bicarbonates as inorganic carbon sources, which can directly enter microalgae photosynthesis, subsequently regenerating carbonates for another cycle of carbon capture. This system offers significant advantages, including cost savings in carbon supply, simplified photobioreactor development, and reduced labor and energy requirements. Nevertheless, further research is essential to evaluate the suitability of various microorganisms and search for optimal growth conditions. In this study, we assessed the performance of two strains of Spirulina within the integrated system. Employing a Design of Experiments approach, we simultaneously varied temperature, bicarbonate concentration, and light irradiation while operating within a lab-scale photobioreactor. We achieved remarkable results, with a biomass productivity of 875 mg/L·d and an impressive CO2 utilization efficiency of 58%. These findings indicate a genuine opportunity for further exploration and scaling of this approach in industrial settings.

Enhancement of carbon bio-fixation and lipid accumulation in Coccomyxa subellipsoidea with triethanolamine CO2 absorbent manipulation

The scenario probed carbon bio-fixation and lipid accumulation in Coccomyxa subellipsoidea with triethanolamine (TEA) CO2 absorbent manipulation. The results stated that CO2 bio-fixation (691.9 mg/L/d), CO2 utilization efficiency (57.84%), CO2 bio-fixation amount (3.86 g), biomass (2.58 g/L), and lipid accumulation (232.30 mg/L/d) in C. subellipsoidea with 100 mg/L TEA batch manipulation were separately 1.28-, 1.28-, 1.26-, 1.26-, and 1.72-fold more than that without TEA management. TEA fed-batch manipulation further augmented carbon fixation and the fixed carbon conversion into lipid with the maximum instantaneous CO2 fixation rate (1065.9 mg/L/d) and lipid productivity (538.7 mg/L/d) that were 1.97- and 3.98-fold more than that without TEA manipulation case. TEA manipulation also heightened the proportions of C16-C18 fatty acids (over 89%) and mono-unsaturated C18:1 (approximate 40.85%) which were commendable for high-quality biofuels-making. Such virtues were attributed to that TEA balanced pH fluctuation, converted CO2 into purposive HCO3- species, modulated glycolysis and TCA cycle to discharge appreciable energy, alleviated oxidative stress to block oxidative attack on lipids, and functioned as precursors to collectively boost CO2 sequestration and lipid accumulation in C. subellipsoidea. The outcomes were expected to provide exemplifications in developing win-win strategy for CO2 sequestration and lipid production by microalgae.

Light-driven CO2 conversion system: construction, optimization and application

The use of light energy to drive carbon dioxide (CO2) reduction for production of chemicals is of great significance for relieving environmental pressure and solving energy crisis. Photocapture, photoelectricity conversion and CO2 fixation are the key factors affecting the efficiency of photosynthesis, and thus also affect the efficiency of CO2 utilization. To solve the above problems, this review systematically summarizes the construction, optimization and application of light-driven hybrid system from the perspective of combining biochemistry and metabolic engineering. We introduce the latest research progress of light-driven CO2 reduction for biosynthesis of chemicals from three aspects: enzyme hybrid system, biological hybrid system and application of these hybrid system. In the aspect of enzyme hybrid system, many strategies were adopted such as improving enzyme catalytic activity and enhancing enzyme stability. In the aspect of biological hybrid system, many methods were used including enhancing biological light harvesting capacity, optimizing reducing power supply and improving energy regeneration. In terms of the applications, hybrid systems have been used in the production of one-carbon compounds, biofuels and biofoods. Finally, the future development direction of artificial photosynthetic system is prospected from the aspects of nanomaterials (including organic and inorganic materials) and biocatalysts (including enzymes and microorganisms).

Step-wise SO2-feeding strategies for microalgae-based CO2 fixation from flue gas and bioenergy production

Aiming at eliminating the negative effect of SO2 on microalgae CO2 fixation caused by inappropriate SO2-feeding strategies, physiology-based step-wise SO2-feeding strategies were proposed to enhance the bioenergy production of microalgae. The step-wise SO2-feeding strategy (four-step gradient increase from 100 to 400 ppm followed by four-step gradient decrease from 400 to 100 ppm) successfully realized the gratifying proliferation of microalgae by maintaining a better activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), total adenosine triphosphatase (Total ATPase), superoxide dismutase (SOD), and catalase (CAT) enzyme. Moreover, the step-wise SO2-feeding strategy, which considered the microalgal tolerance to sulfur at different growth stages, reduced the accumulation rate of toxic S-compounds in the culture medium by 47.2% and ensured a favorable solution pH of around 7 without the addition of alkaline chemical reagents. Sulfur replenishment and utilization were well-matched (SO2 → HSO3-+SO32-→SO42-→intracellular ammonia acid) under a step-wise SO2-feeding strategy, contributing to a maximum microalgal biomass concentration of 3.26 g L-1, a photosynthetic efficiency of 10.89 %, and biomass energy of 18.97 kJ, which was 85.2%, 185%, and 390% higher than the microalgae cells cultivated under 300 ppm SO2, respectively. Moreover, an increment of 81.4% in CO2 utilization efficiency was also achieved. Overall, this study provided an effective method for achieving microalgal carbon capture from industrial flue gas with high SO2 concentrations.

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.

Accelerating electrochemical CO2 reduction to multi-carbon products via asymmetric intermediate binding at confined nanointerfaces

Electrochemical CO2 reduction (CO2R) to ethylene and ethanol enables the long-term storage of renewable electricity in valuable multi-carbon (C2+) chemicals. However, carbon–carbon (C–C) coupling, the rate-determining step in CO2R to C2+ conversion, has low efficiency and poor stability, especially in acid conditions. Here we find that, through alloying strategies, neighbouring binary sites enable asymmetric CO binding energies to promote CO2-to-C2+ electroreduction beyond the scaling-relation-determined activity limits on single-metal surfaces. We fabricate experimentally a series of Zn incorporated Cu catalysts that show increased asymmetric CO* binding and surface CO* coverage for fast C–C coupling and the consequent hydrogenation under electrochemical reduction conditions. Further optimization of the reaction environment at nanointerfaces suppresses hydrogen evolution and improves CO2 utilization under acidic conditions. We achieve, as a result, a high 31 ± 2% single-pass CO2-to-C2+ yield in a mild-acid pH 4 electrolyte with >80% single-pass CO2 utilization efficiency. In a single CO2R flow cell electrolyzer, we realize a combined performance of 91 ± 2% C2+ Faradaic efficiency with notable 73 ± 2% ethylene Faradaic efficiency, 31 ± 2% full-cell C2+ energy efficiency, and 24 ± 1% single-pass CO2 conversion at a commercially relevant current density of 150 mA cm−2 over 150 h.

The Influencing Factors of CO2 Utilization and Storage Efficiency in Gas Reservoir

Carbon Capture, Utilization and Storage (CCUS) technology is one of the most practical means to meet zero greenhouse gas emission goal of the Paris Agreement and to ensure profitability, which could achieve permanent sequestration of CO2. Due to the cost constraints of CCUS implementation, improving recovery and maximizing storage efficiency have become a critical part of ensuring economic efficiency. This research aims to analyze the effects of key factors on enhancing gas recovery and storage efficiency, combined with the validation of CO2 displacement and storage mechanisms. Therefore, long core experiments and different dimensional simulations were established based on R gas reservoir (one of the actual gas reservoirs in Northeast China), which were designed for sensitivity analyses of different influencing parameters and quantitative analyses of different storage mechanisms during CCUS process. When the conditions (temperature and pressure) were closer to the CO2 critical point, when the following parameters (the CO2 purity, the injection rate and the dip angle) became larger, when the reservoir rhythm was reversed and when the irreducible water was is in existence, the final displacement and storage effects became better because of weaker diffusion, stronger gravity segregation and slower CO2 breakthrough. The contributions of different storage mechanisms were quantified: 83.78% CO2 existed as supercritical fluid; 12.67% CO2 was dissolved in brine; and 3.85% CO2 reacted with minerals. Some supercritical and dissolved CO2 would slowly transform to solid precipitation over time. This work could provide theoretical supports for CCUS technology research and references for CCUS field application. At the same time, countries should further improve CCUS subsidy policies and make concerted efforts to promote the globalization and commercialization of CO2 transport.

Ultrafine Cu nanoclusters confined within covalent organic frameworks for efficient electroreduction of CO2 to CH4 by synergistic strategy

Electrocatalytic CO2 reduction (ECR) to high value-added chemicals by using renewable electricity presents a promising strategy to realize “carbon neutrality”. However, the ECR system is still limited by its low current density and poor CO2 utilization efficiency. Herein, by using the confinement effect of covalent organic frameworks (COFs) to confine the in-situ growth of metal nanoclusters (NCs), we develop a series of Cu NCs encapsulated on COF catalysts (Cu-NC@COF) for ECR. Among them, Cu-NC@CuPc-COF as a gas diffusion electrode (GDE) achieves a maximum CO2-to-CH4 Faradaic efficiency of 74 ​± ​3% (at −1.0 ​V vs. Reversible Hydrogen Electrode (RHE)) with a current density of 538 ​± ​31 ​mA ​cm−2 (at −1.2 ​V vs. RHE) in a flow cell, making it one of the best among reported materials. More importantly, the current density is much higher than the relevant industrial current density (200 ​mA ​cm−2), indicating the potential for industrial application. This work opens up new possibilities for the design of ECR catalysts that utilize synergistic strategy.

Atomically Dispersed Ni-Cu Catalysts for pH-Universal CO2 Electroreduction.

CO2 electroreduction is of great significance to reduce CO2 emissions and complete the carbon cycle. However, the unavoidable carbonate formation and low CO2 utilization efficiency in neutral or alkaline electrolytes hinder its application at commercial scale. The development of CO2 reduction under acidic conditions provides a promising strategy, but the inhibition of the hydrogen evolution reaction is difficult. Herein, the first work to design a Ni-Cu dual atom catalyst supported on hollow nitrogen-doped carbon is reported for pH-universal CO2 electroreduction to CO. The catalyst shows a high CO Faradaic efficiency of ≈99% in acidic, neutral, and alkaline electrolytes, and the partial current densities of CO reach 190 ± 11, 225 ± 10, and 489 ± 14mA cm-2 , respectively. In particular, the CO2 utilization efficiency under acidic conditions reaches 64.3%, which is twice as high as that of alkaline conditions. Detailed study indicates the existence of electronic interaction between Ni and Cu atoms. The Cu atoms push the Ni d-band center further toward the Fermi level, thereby accelerating the formation of *COOH. In addition, operando characterizations and density functional theory calculation are used to elucidate the possible reaction mechanism of CO2 to CO under acidic and alkaline electrolytes.

Nuclear magnetic resonance study on enhanced shale oil recovery by CO2 injection: A case study

ABSTRACT The successful development of shale oil is significant to provide oil steadily. The comparisons of enhanced shale oil recovery by CO2 flooding and huff-n-puff methods for shale cores without and with fractures were investigated by nuclear magnetic resonance (NMR) spectra and physical simulation experiments. The effects of injection pressure and injection amount on enhanced shale oil recovery by CO2 flooding were considered, as well as the displacement mechanism of oil at different sections of the core. With the increases of injection pressure and injected PV, the oil recovery of CO2 flooding increases while the utilization efficiency decreases. The oil recoveries of CO2 with 2PV are 14% and 23% at 9 and 18 MPa, meanwhile, the values of the produced oil amount per mole of CO2 are 7% and 5% at 9 and 18 MPa. The oil content near the inlet of the core decreases greatly with the increasing PV while the oil content near the outlet has a slight decrease. After CO2 injection of 7 PV, the oil content near the outlet is still as high as 80%. Moreover, the factors of pressure, cycles, and soaking time were examined for CO2 huff-n-puff. The oil recovery increases while the utilization efficiency decreases with the increasing pressure and cycles in CO2 huff-n-puff. The total oil recoveries after three cycles are 56% and 69% at 9 and 20 MPa, while the values of the produced oil amount per mole of CO2 are 42% and 20%. With the increase of cycle, the swept area increases and the displacement efficiency of the swept core has a great enhancement. Compared with CO2 flooding, CO2 huff-n-puff method has greater oil recovery and CO2 utilization efficiency because of the sufficient contacting time between oil and CO2 and high swept ability. Therefore, CO2 huff-n-puff is beneficial for shale oil production. This work can provide the optimized method and parameters for the production in Enan Chang 7 zone.

Using a well-to-well interplay during the CO2 huff-n-puff process for enhanced oil recovery in an inclined oil reservoir: Experiments, simulations, and pilot tests

A well-to-well interplay of CO2 huff-n-puff is proposed as a novel gas injection strategy for displacing interwell-remaining oil in a well pair in an inclined oil reservoir. The well-to-well interplay mechanisms for enhanced oil recovery (EOR) are first studied in the laboratory using a three-dimensional (3D) physical model. Different CO2 injection schemes are designed according to different well locations, and the production performance including oil, water, and gas rates is used for the EOR evaluation. A sensitivity analysis of the well-to-well interplay is then studied using a numerical model, and geological, developmental and fluidic factors are considered in the simulations. The experimental results show that, when CO2 is injected into a lower well, a higher well always benefits with an oil increment. Under the effects of gravity segregation and edge-water driving, the injected CO2 at the lower position can move upward to a higher position, where a large proportion of crude oil remains between wells after natural edge-water flooding. Oil recovery from the well-to-well interplay is 2.30% higher than conventional CO2 huff-n-puff in the laboratory. Numerical results show that CO2 injection mass, stratigraphic dip, horizontal permeability, and interwell spacing are the factors that most influence the well-to-well interplay; an application criterion for the well-to-well interplay is then proposed based on the simulations. Pilot tests using the well-to-well interplay of CO2 huff-n-puff have been widely applied in C2-1 Block, Jidong Oilfield, China, since 2010. A total of 2.27 × 104 m3 crude oil was recovered to the end of 2018, and the oil/CO2 exchange ratio was as high as 3.92. The well-to-well interplay not only effectively extracted the interwell-remaining oil but also achieved higher CO2 utilization efficiency. The findings of this study can lead to a better understanding of the EOR mechanisms used in the well-to-well interplay during the CO2 huff-n-puff process in an inclined oil reservoir.

Experimental study of possibility to increase the efficiency of CO2 utilization on iron-containing fillers with green energy carriers generation

Results of additional laboratory studies are presented for carbon dioxide utilization method with green generation of hydrogen and hydrocarbons. The method consists in interaction of water with dissolved CO2 on the surface of iron-containing fillers. The process proceeds at temperatures starting from ambient conditions and does not require creation of high pressures or electric current in the system. The interaction is accompanied by intense evolution of gas phase with high content of hydrogen. Carbon is transformed into carbonates and small quantities of generated hydrocarbons. Influence of temperature and process parameters is studied for steel turnings used as a prototype of cheap fillers produced from metalworking wastes. The possibility to optimize the degree of CO2 utilization is shown by controlling the carbonized water saturation pressure. According to the results of considered and previous series of experiments, the achieved degree of CO2 utilization is up to 76-83%, with hydrogen content in the output gas of 63-82%. Keywords: carbon dioxide utilization; hydrogen; hydrocarbons; iron-containing filler; carbonated water; iron turnings; green energy carriers.

Feasibility evaluation of CO[formula omitted] EOR and storage in tight oil reservoirs: A demonstration project in the Ordos Basin

Among the techniques to mitigate CO2 emissions into atmosphere, CO2 geological storage is the only option for gigaton removal of CO2. This study performs a pilot test of CO2-EOR and storage in a tight reservoir of Baibao oilfield, located at the Ordos Basin of China. Two scenarios: CO2 injection through two newly drilled wells and total nine wells, with two CO2 injection schemes: continuous injection (CI) and water alternative gas (WAG) injection, are considered. Simulation results show that both CO2 injection schemes can substantially increase oil production, compared to the current waterflooding. To be more specific, WAG, in contrast to CI, increases oil production by 7.9% and 16.2% for the two- and nine-injection well scenarios, respectively. Yet, as for CO2 storage, WAG, compared with CI, finally leads to a decrease of stored CO2 by 9.6% and 15%, for the two- and nine-CO2 injection well scenarios, respectively. From the aspect of CO2 utilization efficiency, net CO2 utilization ratio of WAG is smaller than the one from CI regardless of the number of CO2 injection well. Besides, for the two- and nine-injection well scenarios, maximum net utilization ratios are achieved after 7–8 years’ and 4–5 years’ injections, respectively. The sensitive analyses reveal that the impact of CO2 injection rate of WAG on total oil production is more significant than the water injection in WAG. Water injection rate in WAG negatively affects the total CO2 storage and CO2 net utilization ratio whereas the higher CO2 injection rate dramatically increases the total CO2 storage. Overall, this study not only sheds light on achieving double-win goal via CO2 injection, but also can be a valuable reference for other CO2-EOR and storage pilot tests in tight reservoirs.

The potential impact of replacing nitrate with ammonium hydroxide in microalgae production on the biomass productivity and CO2 utilization efficiency

Ammonium hydroxide has many advantages as a CO 2 absorbent compared with other amine solutions in Carbon Capture, Utilization and Storage. In this work, the use of ammonium hydroxide was suggested to replace the nitrate as an alternative nitrogen source and to enhance the CO 2 utilization and biomass production during microalgae cultivation. Abiotic absorption experiments showed that the CO 2 absorption capacity of culture medium increased with the increase of ammonium hydroxide concentration, and it kept consistent with different kind of CO 2 absorbents. Consumption curves for sodium nitrate and ammonium hydroxide were built from batch cultivation experimental data and it was found that the microalgal cells had faster growth rates when these nutrients concentrations were kept at low levels (2 mmol/L and 4 mmol/L, respectively). In the fed-batch cultures under both indoor and outdoor operations, the maximum biomass concentration and carbon utilization efficiency using ammonium hydroxide as a nitrogen source was much higher than that of using sodium nitrate as a nitrogen source. By using pH-regulated CO 2 supplementation, the pH of the microalgae culture medium was maintained within the neutral or slightly alkaline range. Thus, the volatilization of ammonium hydroxide was negligible. These results indicated that replacing nitrate with ammonium hydroxide could be a promising approach to increase CO 2 utilization efficiency and to reduce production costs in microalgae cultivation. • Replacing sodium nitrate with ammonium hydroxide as the nitrogen source was first proposed in microalgal cultivation. • Biomass concentration and carbon utilization efficiency using ammonium hydroxide as nitrogen sources were achieved by 2.35 g/L, and 114.93%. • A 32.8 % increase in the biomass productivity using ammonium hydroxide compared to that of sodium nitrate under outdoor conditions. • Ammonium hydroxide could be a cheaper source of nitrogen that can enhance CO 2 utilization by microalgae.

Conversion of Reactive Carbon Solutions into CO at Low Voltage and High Carbon Efficiency.

Electrolyzers are now capable of reducing carbon dioxide (CO2) into products at high reaction rates but are often characterized by low energy efficiencies and low CO2 utilization efficiencies. We report here an electrolyzer that reduces 3.0 M KHCO3(aq) into CO(g) at a high rate (partial current density for CO of 220 mA cm–2) and a CO2 utilization efficiency of 40%, at a voltage of merely 2.3 V. These results were made possible by using: (i) a reactive carbon solution enriched in KHCO3 as the feedstock instead of gaseous CO2; (ii) a cation exchange membrane instead of an anion exchange membrane, which is common to the field; and (iii) the hydrogen oxidation reaction (HOR) at the anode instead of the oxygen evolution reaction (OER). The voltage reported here is the lowest reported for any CO2 to CO electrolyzer that operates at high current densities (i.e., a partial current density for CO greater than 200 mA cm–2) with a CO2 utilization efficiency of greater than 20%. This study highlights how the choice of feedstock, membrane, and anode chemistries affects the rate and efficiency at which CO2 is converted into products.

Supplementation with rac-GR24 Facilitates the Accumulation of Biomass and Astaxanthin in Two Successive Stages of Haematococcus pluvialis Cultivation.

The unicellular freshwater green alga Haematococcus pluvialis has attracted much research attention due to its biosynthetic ability for large amounts of astaxanthin, a blood-red ketocarotenoid that is used in cosmetics, nutraceuticals, and pharmaceuticals. Recently, numerous studies have investigated the functions of natural astaxanthin; however, the high cost of the production of astaxanthin from H. pluvialis cultures restricts its commercial viability. There is an urgent need to fulfill commercial demands by increasing astaxanthin accumulation from H. pluvialis cultures. In this study, we discovered that treatment of H. pluvialis cultures at the beginning of the macrozooid stage (day 0) with 1 μM rac-GR24, a synthetic analogue of strigolactones (a class of phytohormones), led to significant increases in biomass [up to a maximum dry cell weight (DCW) of 0.53 g/L] during the macrozooid stage and astaxanthin (from 0.63 to 5.32% of DCW) during the hematocyst stage. We elucidated that this enhancement of biomass accumulation during the macrozooid stage by rac-GR24 is due to its increasing CO2 utilization efficiency in photosynthesis and carbohydrate biosynthesis. We also found that rac-GR24 stimulated the overproduction of nicotinamide adenine dinucleotide phosphate (NADPH) and antioxidant enzymes in H. pluvialis cultures, which alleviated the oxidative damage caused by reactive oxygen species generated during the hematocyst stage due to the exhaustion of nitrogen supplies. Moreover, rac-GR24 treatment of H. pluvialis synergistically altered the activity of the pathways of fatty acid biosynthesis and astaxanthin esterification, which resulted in larger amounts of astaxanthin being generated by rac-GR24-treated cultures than by controls. In summary, we have developed a feasible and economic rac-GR24-assisted strategy that increases the amounts of biomass and astaxanthin generated by H. pluvialis cultures, and have provided novel insights into the mechanistic roles of rac-GR24 to achieve these effects.

Construction of zwitterionic porous organic frameworks with multiple active sites for highly efficient CO2 adsorption and synergistic conversion

Porous organic frameworks fabricated by well-defined monomeric compounds with different active sites have been regarded as the promising nano-materials for improving the efficiency of CO2 capture and utilization. In this study, novel zwitterionic porous organic frameworks (ZPOFs) alternately connected by benzimidazole, triazine and imidazolium modules were prepared facilely via ZnCl2-catalyzed bi-component polymerization. The influences of different monomer concentration and polymerization temperature on structural properties of the ZPOFs were discussed in detail. It indicates that the ZPOFs present attractive structure characteristics of high specific surface area and hierarchical pore structure, and have abundant hydrogen bond donors, Lewis bases and nucleophilic groups, respectively. The ZPOFs as-obtained were applied to CO2 adsorption and conversion into cyclic carbonate by coupling with epoxide. The experiment results showed that the ZPOFs could afford the highest CO2 adsorption capacity of 2505 μmol/g at 273 K and 1.0 bar CO2 pressure. The effects of ZPOFs structures and reactions conditions on the catalytic performance were investigated. Under the optimized conditions of 70 °C, 2.0 MPa CO2 for 2.0 h, and cooperating with tetrabutylammonium iodide (TBAI) cocatalyst, the ZPOF-450–30 could efficiently and selectively catalyze the CO2/epoxides cycloaddition reaction to yield corresponding cyclic carbonates. Moreover, the ZPOF-450–30 catalyst could be simply separated with durable high stability and activity. Finally, we compared the catalytic behaviors with reported similar heterogeneous catalysts and proposed a feasible ZPOFs-catalyzed mechanism.

Maximize microalgal carbon dioxide utilization and lipid productivity by using toxic flue gas compounds as nutrient source

NOx and SOx present in flue gas inhibit microalgal based CO2 mitigation process. In this work, 13 microalgal strains were screened to evaluate their gradual acclimation capacity to toxic flue gas compounds, by testing their growth capability and photosynthetic ability in dissolved flue gas compounds. Six strains out of them were evaluated for their acclimation to bicarbonate and 15% CO2 as sole carbon sources. Two strains, Micractinium pusillum KMC8 and Scenedesmus acutus NCIM5584 were found to accumulate nitrite as fixed nitrogen and showed improved growth performance in photobioreactor upon stepwise acclimation to bisulphite/sulphite. Notably, the strain KMC8 showed a high tolerance and rapidly acclimated dissolved flue gas compounds with higher biomass yield (1.32 g L−1) and neutral lipid accumulation (32%), enhanced CO2 utilization efficiency (3.07%) and CO2 fixation rate (136.79 mg L−1 d−1) post acclimation. KMC8 sustained its stability in biomass and lipid productivity while simultaneously bio-mitigated CO2 under semi-continuous mode.

Valorization of CO2 to DME using a membrane reactor: A theoretical comparative assessment from the equipment to flowsheet level

Carbon utilization plays a pivotal role in the circular carbon economy approach. However, CO2 conversion technologies, including thermocatalytic hydrogenation approaches, entail several challenges such as thermodynamic limits and low kinetic rates. In the pursuit of eliminating these two hurdles, this study aims to highlight the unique synergy and high potential of the combination of two emerging technologies: catalytic zeolite membrane reactor and direct dimethyl ether synthesis over hybrid catalysts of Cu/ZnO/Al2O3/HZSM-5. To this end, an equation-based pseudo homogenous model for a plug flow membrane reactor, previously developed in Aspen Custom Modeler, will be verified using experimental data in the literature and then coupled with the appropriately selected kinetic models, which describe this particular reaction system accurately. This enables us to confidently identify the impact of several membrane reactor's characteristics and process parameters on the conversion and selectivity. We also analyze a membrane-reactor-based dimethyl ether synthesis process and compare it with the conventional counterpart. According to our results, at 7.5 MPa pressure, a membrane-based process design offers 1.5%, 44.5% and 69.4% savings in power, heating and refrigerant utilities, respectively. These reductions correspond to 7.3% improvement in CO2 utilization efficiency as a metric to compare the environmental performance of emerging green fuel/chemicals.