Oxalate as an intermediate in the base-catalysed water-gas shift reaction

The conversion of CO to H₂ and CO₂, in the presence of 1.0 M solutions of sodium carbonate, hydroxide and formate has been studied in the temperature range 200–350 °C. The decomposition of 1.0 M solutions of sodium formate, oxalate and carbonate under argon pressure was investigated using the same reaction conditions. It is shown that carbonate reacts readily with CO to produce oxalate, which decomposes easily to formate and CO₂. The formate is the most stable intermediate under the reaction conditions and only decomposes rapidly to carbonate and H₂ above 300 °C, making the water-gas shift reaction truly catalytic. Sodium hydroxide is not an intermediate in this reaction but first reacts with CO₂, formed during the reaction, to produce carbonate. Based on these results a new mechanism is proposed for the base-catalysed water-gas shift reaction.     

Techno-economic evaluation of advanced IGCC lignite coal fuelled power plants with CO2 capture

The techno-economic evaluation of four novel integrated gasification combined cycle (IGCC) power plants fuelled with low rank lignite coal with CO₂ capture facility has been investigated using ECLIPSE process simulator. The performance of the proposed plants was compared with two conventional IGCC plants with and without CO₂ capture. The proposed plants include an advanced CO₂ capturing process based on the Absorption Enhanced Reforming (AER) reaction and the regeneration of sorbent materials avoiding the need for sulphur removal component, shift reactor and/or a high temperature gas cleaning process. The results show that the proposed CO₂ capture plants efficiencies were 18.5–21% higher than the conventional IGCC CO₂ capture plant. For the proposed plants, the CO₂ capture efficiencies were found to be within 95.8–97%. The CO₂ capture efficiency for the conventional IGCC plant was 87.7%. The specific investment costs for the proposed plants were between 1207 and 1479 €/kW_e and 1620 €/kW_e and 1134 €/kW_e for the conventional plants with and without CO₂ capture respectively. Overall the proposed IGCC plants are cleaner, more efficient and produce electricity at cheaper price than the conventional IGCC process.     

Silica-templated melamine-formaldehyde resin derived adsorbents for CO2 capture

Adsorption on porous solids is an emerging alternative for CO₂ capture that seeks to reduce the costs associated to the capture step. The enhancement of a specific adsorption capacity may be carried out by increasing the affinity of the adsorbent surface to CO₂. Nitrogen enrichment is reported to be effective in introducing basic functionalties that enhances the specific adsorbent-adsorbate interaction for CO₂. In this work a templating technique was used to produce highly porous nitrogen enriched carbons from melamine-formaldehyde resins. Nitrogen incorporated into the polymer matrix results in the greater stability of the adsorbents in terms of volatile and thermal loss of nitrogen. CO₂ capture performances were evaluated between 25 °C and 75 °C in a thermobalance. CO₂ adsorption capacities up to 2.25 mmol g⁻¹ of CO₂ at 25 °C were achieved. Both texture and surface chemistry influence the CO₂ capture performance of the adsorbents. The carbonisation temperature used during the synthesis step controls the nitrogen functional groups present, as determined by XPS, with the loss of triazine nitrogen with increasing carbonisation temperature proposed to account for the decreased CO₂ affinity.     

An economic feasibility study of O2/CO2 recycle combustion technology based on existing coal-fired power plants in China

In order to reduce the CO₂ emission from the coal-fired power plants, O₂/CO₂ recycle combustion (Oxy-combustion) technique has been proposed through combining a conventional combustion process with a cryogenic air separation process. The technique is capable of enriching CO₂ concentration and then allowing CO₂ sequestration in an efficient and energy-saving way. Taking into account the CO₂ taxation and CO₂ sale, the paper evaluates the economic feasibility of Oxy-combustion plants retrofitted from two typical existing conventional coal-fired power plants (with capacities of 2 × 300 MW and 2 × 600 MW, respectively) with Chinese data. The cost of electricity (COE) and the CO₂ avoidance cost (CAC) are also considered in the evaluation. The COE of the retrofitted Oxy-combustion plant is nearly the same as that of the corresponding conventional plant if the unit price of CO₂ sale reaches 17-22 $/t (different cases). The CAC of the retrofitted 2 × 300 MW Oxy-combustion plant is 1-3 $/t bigger than that of the retrofitted 2 × 600 MW Oxy-combustion plant. Supercritical plants are more economical and appropriate for Oxy-combustion retrofit. The result indicates that Oxy-combustion technique is not only feasible for CO₂ emission control based on existing power plants but is also cost-effective.     

ALTERNATIVE GENERATION OF H2, CO AND H2, CO2 MIXTURES FROM STEAM-CARBON DIOXIDE REFORMING OF METHANE AND THE WATER GAS SHIFT WITH PERMEABLE (MEMBRANE) REACTORS

A new process is proposed which converts CO₂ and CH₄ containing gas streams to synthesis gas, a mixture of CO and H₂ via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO₂ and H₂ via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H₂ in permeate by using metal membranes, and H₂ rich mixtures by using ceramic, glass and composite type permselective membranes. H₂ and CO₂ can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration.

CO and H₂ can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO₂ and H₂ in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H₂ from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO₂ and CH₄ gases and related hydrocarbon-CO₂ feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H₂, H₂ mixture products.     

Sustainable clean coal power generation within a European context - The view in 2006

The future use of coal will require strict environmental compliance with an increasing need to minimise emissions of CO₂, particularly from power plants. A pan-European approach is being established to ensure that EU industry can have available, by 2020, fossil fuel power plants that are either capable of capturing almost all their CO₂ emissions in an economically viable manner, or are designed to include CO₂ capture systems (“capture-ready”). The overall aim is to provide a significant impetus to research, development, demonstration and deployment activities such that coal and other fossil fuels can be used in a sustainable manner.     

Wild Soybean Oxalyl-CoA Synthetase Degrades Oxalate and Affects the Tolerance to Cadmium and Aluminum Stresses

Acyl activating enzyme 3 (AAE3) was identified as being involved in the acetylation pathway of oxalate degradation, which regulates the responses to biotic and abiotic stresses in various higher plants. Here, we investigated the role of Glycine soja AAE3 (GsAAE3) in Cadmium (Cd) and Aluminum (Al) tolerances. The recombinant GsAAE3 protein showed high activity toward oxalate, with a K_m of 105.10 ± 12.30 μM and V_max of 12.64 ± 0.34 μmol min⁻¹ mg⁻¹ protein, suggesting that it functions as an oxalyl–CoA synthetase. The expression of a GsAAE3–green fluorescent protein (GFP) fusion protein in tobacco leaves did not reveal a specific subcellular localization pattern of GsAAE3. An analysis of the GsAAE3 expression pattern revealed an increase in GsAAE3 expression in response to Cd and Al stresses, and it is mainly expressed in root tips. Furthermore, oxalate accumulation induced by Cd and Al contributes to the inhibition of root growth in wild soybean. Importantly, GsAAE3 overexpression increases Cd and Al tolerances in A. thaliana and soybean hairy roots, which is associated with a decrease in oxalate accumulation. Taken together, our data provide evidence that the GsAAE3-encoded protein plays an important role in coping with Cd and Al stresses.     

Kinetics of carbon dioxide reaction with diethylaminoethanol in aqueous solutions

Differential rates of CO₂ adsorption into 0.90, 0.47 and 0.24 M aqueous solutions of 2-(diethylamino)ethanol (DEAE) were measured at 323 K over a wide range of carbonation ratios. A rigorous thermodynamic model was used to define species activities which were coupled with Danckwerts' gas-liquid reaction model to deduce the kinetics. The reaction of CO₂ with this highly basic tertiary amine occurs by two pathways: (1) a minor path via the CO₂ reaction with hydroxide ion and (2) a predominant reaction pathway that can be characterized by its first order dependency on the free amine concentration. The second reaction was proposed to involve an internal salt-like intermediate,.     

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     

Intermediates and products formed during fatty acid α-oxidation in cucumber (Cucumis sativus)

Fatty acid α-oxidation is an essential metabolic pathway both in plants and in mammals which is still not completely understood. We previously described and purified an α-oxidation enzyme in cucumber which has been used in the present investigation of the α-oxidation reaction mechanism. Free fatty acids, and not the CoA thioesters, were found to undergo α-oxidation in cucumber. 2-Hydroxy- and 2-oxopalmitic acids were identified as palmitic acid α-oxidation intermediates by high-performance liquid chromatography and gas chromatography—mass spectrometry analysis in cucumber subcellular 150,000×g _max pellets obtained by differential centrifugation. Incubation of purified α-oxidation enzyme with [1-¹⁴C]palmitic acid resulted in the formation of both the above-described intermediates and the C _n−1 product, pentadecanal, and ¹⁴CO₂. Besides ¹⁴CO₂, ¹⁴C-formate was identified as an α-oxidation product from [1-¹⁴C]palmitic acid in cucumber subcellular fractions. Fe²⁺ stimulated the ¹⁴CO₂ and ¹⁴C-formate production, and the addition of ascorbate and 2-oxoglutarate together with Fe²⁺ resulted in optimal α-oxidation activities, suggesting a dioxygenase reaction mechanism, as previously shown in mammals. NADPH and, to a lesser extent, NADH stimulated the total ¹⁴C-formate plus ¹⁴CO₂ production but had only slight or no effects on ¹⁴CO₂ production. H₂O₂ showed concentration-dependent inhibitory effects, while FAD had neither effect on ¹⁴CO₂ nor ¹⁴CO₂ plus ¹⁴C-formate production. The results in the present study demonstrate that an α-oxidation enzyme in cucumber is capable of oxidizing palmitic acid via 2-hydroxy- and 2-oxopalmitic acid to produce pentadecanal and CO₂. In contrast to the subcellular 150,000×g _max fraction, the purified α-oxidation enzyme could neither produce formate nor convert ¹⁴C-formate into ¹⁴CO₂, indicating two possible α-oxidation routes in cucumber.     

Carbon capture and utilization via chemical looping dry reforming

Chemical looping combustion (CLC) is a clean energy technology for CO₂ capture that uses periodic oxidation and reduction of an oxygen carrier with air and a fuel, respectively, to achieve flameless combustion and yield sequestration-ready CO₂ streams. While CLC allows for highly efficient CO₂ capture, it does not, however, provide a solution for CO₂ sequestration.Here, we propose chemical looping dry reforming (CLDR) as an alternative to CLC by replacing air with CO₂ as the oxidant. CLDR extends the chemical looping principle to achieve CO₂ reduction to CO, which opens a pathway to CO₂ utilization as an alternative to sequestration. The feasibility of CLDR is studied through thermodynamic screening calculations for oxygen carrier selection, synthesis and kinetic experiments of nanostructured carriers using cyclic thermogravimetric analysis (TGA) and fixed-bed reactor studies, and a brief model-based analysis of the thermal aspects of a fixed-bed CLDR process.Overall, our results indicate that it is indeed possible to reduce CO₂ to CO with high reaction rates through the use of appropriately designed nanostructured carriers, and to integrate this reaction into a cyclic redox (“looping”) process.     

Dissolution of olivine in the presence of oxalate, citrate, and CO2 at 90 °C and 120 °C

In this article, we report the results from a study of olivine dissolution kinetics under operating conditions suitable for ex situ aqueous mineral carbonation for CO₂ storage. We studied the effect of oxalate and citrate ions on the dissolution of gem-quality San Carlos olivine (Mg_1.82Fe_0.18SiO₄). Flow-through experiments were performed at 90 °C and 120 °C, at f_CO2 between 4 and 81 bar, with a solution containing either sodium oxalate or sodium citrate in a molality range between 10⁻³ and 10⁻¹. The pH was varied between 2 and 7 by adding HCl, LiOH, and adjusting f_CO2. At all investigated temperatures and for pH values in a broad range, both sodium oxalate and sodium citrate increased dissolution rate with the strongest effect up to one order of magnitude in presence of 0.1 m of oxalate, at 120 °C, and above pH 5. The enhancement effect was primarily ascribed to the oxalate or citrate ions that are the dominant species in this pH range. The overall dissolution process was described using the population balance equation (PBE) coupled with a mass balance equation to account for the evolution of the particle size distribution (PSD) of olivine. Far from equilibrium conditions for dissolution were established in all the experiments in order to achieve a surface-reaction controlled mechanism. We described the reaction with a surface complexation model, which assumes adsorption of a proton and of an oxalate (citrate) ions (proton and oxalate) on adjacent sites in order to enhance dissolution, and we derived a dissolution rate equation in presence of oxalate:where r^? is the specific dissolution rate commonly used in absence of organic compounds, and K_H, K_X, and β are thermodynamic and kinetic parameters. The values of these parameters have been estimated from the experimental data and the agreement between the model results and the experiments is very good.     

Thermal decomposition of zinc zirconyl oxalate pentahydrate

Thermal decomposition of zinc zirconyl oxalate (ZZO) has been investigated employing thermogravimetric, differential thermal analysis and differential thermogravimetric techniques and chemical analysis. The decomposition proceeds through three steps. The first step is the dehydration of the zinc zirconyl oxalate pentahydrate in the temperature range 303–473 K. The second stage is the decomposition of the oxalate giving an intermediate residue containing both oxalate and carbonate between 473–613 K. The third and final stage is the decomposition of the intermediate between 613–833 K to give zinc zirconate. The infrared spectral and X-ray data confirm the formation of ZnZrO₃.     

Cost of energy analysis of integrated gasification combined cycle (IGCC) power plant with respect to CO2 capture ratio under climate change scenarios

This paper presents the results of the cost of energy (COE) analysis of an integrated gasification combined cycle (IGCC) power plant with respect to CO₂ capture ratio under the climate change scenarios. To obtain process data for a COE analysis, simulation models of IGCC power plants and an IGCC with carbon capture and sequestration (CCS) power plant, developed by the United States Department of Energy (DOE) and National Energy Technology Laboratory (NETL), have been adopted and simulated using Aspen Plus. The concept of 20-year levelized cost of energy (LCOE), and the climate change scenarios suggested by International Energy Agency (IEA) are also adopted to compare the COE of IGCC power plants with respect to CO₂ capture ratio more realistically. Since previous studies did not consider fuel price and CO₂ price changes, the reliability of previous results of LCOE is not good enough to be accepted for an economic comparison of IGCC power plants with respect to CO₂ capture ratio. In this study, LCOEs which consider price changes of fuel and CO₂ with respect to the climate change scenarios are proposed in order to increase the reliability of an economic comparison. And the results of proposed LCOEs of an IGCC without CCS power plant and IGCC with CCS (30%, 50%, 70% and 90% capture-mole basis- of CO₂ in syngas stream) power plants are presented.     

Aprotic phosphonium-based ionic liquid as electrolyte for high CO2 electroreduction to oxalate

In this study, a new CO₂ electroreduction electrolyte system consisting of tetrabutylphosphonium 4-(methoxycarbonyl) phenol ([P₄₄₄₄][4-MF-PhO]) ionic liquid (IL) and acetonitrile (AcN) was designed to produce oxalate, and the electroreduction mechanism was studied. The results show that using the new IL-based electrolyte, the electroreduction system exhibits 93.8% Faradaic efficiency and 12.6 mA cm⁻² partial current density of oxalate at −2.6 V. The formation rate of oxalate is 234.4 μmol cm⁻² h⁻¹, which is better than those reported in the literature. The mechanism study using density functional theory (DFT) calculations reveals that [P₄₄₄₄][4-MF-PhO] can effectively activate CO₂ molecule through ester and phenoxy double active sites. In addition, in the phosphonium-based ionic environment, the potential barriers of the key intermediates *CO₂⁻ and *C₂O₄²⁻ are reduced by the induced electric field, which greatly facilitates the activation and conversion of CO₂ molecule to oxalate.     

The Catalytic Mechanism of Pdx2 Glutaminase Driven by a Cys-His-Glu Triad: A Computational Study

The catalytic mechanism of Pdx2 was studied with atomic detail employing the computational ONIOM hybrid QM/MM methodology. Pdx2 employs a Cys-His-Glu catalytic triad to deaminate glutamine to glutamate and ammonia – the source of the nitrogen of pyridoxal 5’-phosphate (PLP). This enzyme is, therefore, a rate-limiting step in the PLP biosynthetic pathway of Malaria and Tuberculosis pathogens that rely on this mechanism to obtain PLP. For this reason, Pdx2 is considered a novel and promising drug target to treat these diseases. The results obtained show that the catalytic mechanism of Pdx2 occurs in six steps that can be divided into four stages: (i) activation of Cys₈₇, (ii) deamination of glutamine with the formation of the glutamyl-thioester intermediate, (iii) hydrolysis of the formed intermediate, and (iv) enzymatic turnover. The kinetic data available in the literature (19.1–19.5 kcal mol⁻¹) agree very well with the calculated free energy barrier of the hydrolytic step (18.2 kcal.mol⁻¹¹), which is the rate-limiting step of the catalytic process when substrate is readily available in the active site. This catalytic mechanism differs from other known amidases in three main points: i) it requires the activation of the nucleophile Cys₈₇ to a thiolate; ii) the hydrolysis occurs in a single step and therefore does not require the formation of a second tetrahedral reaction intermediate, as it is proposed, and iii) Glu₁₉₈ does not have a direct role in the catalytic process. Together, these results can be used for the synthesis of new transition state analogue inhibitors capable of inhibiting Pdx2 and impair diseases like Malaria and Tuberculosis.     

Partial O2-fired coal power plant with post-combustion CO2 capture: A retrofitting option for CO2 capture ready plants

In the work presented in this paper, an alternative process concept that can be applied as retrofitting option in coal-fired power plants for CO₂ capture is examined. The proposed concept is based on the combination of two fundamental CO₂ capture technologies, the partial oxyfuel mode in the furnace and the post-combustion solvent scrubbing. A 330 MW_el Greek lignite-fired power plant and a typical 600 MW_el hard coal plant have been examined for the process simulations. In a retrofit application of the ECO-Scrub technology, the existing power plant modifications are dominated by techno-economic restrictions regarding the boiler and the steam turbine islands. Heat integration from processes (air separation, CO₂ compression and purification and the flue gas treatment) can result in reduced energy and efficiency penalties. In the context of this work, heat integration options are illustrated and main results from thermodynamic simulations dealing with the most important features of the power plant with CO₂ capture are presented for both reference and retrofit case, providing a comparative view on the power plant net efficiency and energy consumptions for CO₂ capture. The operational characteristics as well as the main figures and diagrams of the plant’s heat balances are included.