Standardization of the Boehm titration. Part I. CO2 expulsion and endpoint determination

The various steps required in the Boehm titration (CO₂ removal, agitation method, endpoint determination, etc.) are carried out in different ways by different research groups, making a comparison of the results between these groups difficult. Herein, the methods of CO₂ expulsion and endpoint determination for the Boehm titration were standardized. Blank samples of the three Boehm reaction bases, NaHCO₃, Na₂CO₃ and NaOH, were examined for complete CO₂ expulsion through sparging with an inert gas (N₂ or Ar), heating, or utilizing a N₂-filled glove box. Boehm titrations using NaOH as the reaction base were studied through direct titration and back-titration. It was found that to minimize errors both the NaOH titrant and HCl should be standardized prior to titration and that a back-titration is preferable for all three reaction bases. Additionally, the titration should be performed immediately after degassing for 2 h with N₂ or Ar, and degassing should continue during the titration. This is found to be particularly true of the NaOH reaction base, where the effects of dissolved CO₂ are the most noticeable and persistent. With sufficient CO₂ removal, there is no significant difference between pH electrode or colour indication endpoint determination, and either is satisfactory.     

Enhanced piezoelectric polarization by subtle structure distortion to trigger efficient photocatalytic CO2RR

Achieving the goal of carbon neutralization using photocatalytic CO₂ reduction has garnered widespread attention. However, rapid bulk-charge recombination seriously impedes the further improvement of photocatalytic properties. In response, we propose a novel strategy to solve this limitation using enhanced piezoelectric polarized electric fields. Co₃O₄ is introduced into NaNbO₃ by straightforward photo-deposition method, which causes the distortion of NbO₆ octahedron to alter the symmetry and boost the piezoelectricity. Meanwhile, the increased Co sites facilitate the adsorption of CO₂, and reduce the reaction energy barrier. As a result, the Co₃O₄-modified NaNbO₃ nanocubes possess outstanding properties of CO₂ reduction under the synergy of ultrasound and visible light with the yield of CO about 4579.71 μmol g⁻¹. Furthermore, the mechanism of piezo-photocatalytic CO₂ reduction is revealed in detail based on DFT, KPFM, and in-suit DRIFTS characterizations, thus providing guidance for the design of high-performance CO₂ photoreduction systems.     

Surface oxide structures on a commercial activated carbon

Direct transmission IR spectra of a commercial activated carbon (Filtrasorb 200, Calgon Corporation) as well as spectra of this carbon after neutralization with 0.25 N solutions of NaOH and HCl are presented. Neutralization capacities for bases of different strengths (NaHCO₃, Na₂C0₃ and NaOH) indicate that the majority of the acidic surface groups (65%) are of weak acidity. This carbon adsorbs acid as well. From the analysis of the spectra it is concluded that the main oxides present on the surface of this particular carbon are lactones, quinones, phenols and carboxylates. The lactonic structures open upon reaction with alkali to give carboxylate structures, and in acid media the carboxylic tautomer is favored. Furthermore upon reaction with acid some of the oxides come off as C0₂. This C0₂ chemisorbs on the carbon surface and generates stable carbonate structures.     

Elution of Gold from Activated Carbon Using Supercritical Carbon Dioxide

Abstract

A novel method for the desorption of gold from activated charcoal is reported. Ion pair solvation of sodium dicyanoaurate (I) (Na⁺ … Au(CN)₂ ^? by tributyl-phosphate facilitates the charge neutralization necessary for the elution of the ionic Au(CN)₂ ^? by the non-polar supercritical carbon dioxide. The method is sensitive to pressure and temperature, and the static (no CO₂ flow) period is more significant than the dynamic (CO² flow) period. The presence of water is necessary to effect extraction.     

The Influence of Supercritical Carbon Dioxide (SC‐CO2) on Electrolytes and Hydrogenation of Soybean Oil

The electrochemical hydrogenation of soybean oil with supercritical carbon dioxide (SC‐CO₂) has been studied to seek ways for substantial reduction of the trans fatty acids (TFA). The solubility of CO₂ in electrolytes and the conductivity of electrolytes were investigated using a self‐made electrochemical hydrogenation reactor. The optimum hydrogenation parameters were assessed. Both the solubility of CO₂ in electrolytes and the conductivity of electrolytes increased with increasing CO₂ pressure. When the pressure reached a critical point of CO₂, the solubility of CO₂ expressed as a mole fraction was 0.42 in cathode electrolyte and 0.1 in anode electrolyte. At 8 MPa, the conductivity of electrolytes was 1.5 times higher than that at 2 MPa. When the pressure was higher than the critical point of CO₂, the solubility of CO₂ in electrolytes and the conductivity of electrolytes reached a stable value. The optimum condition for electrochemical hydrogenation of soybean oil in SC‐CO₂ were reaction pressure (8 MPa), reaction temperature (48 °C), current (125 mA), agitation speed (300 rpm), and reaction time (8 h). Fatty acid profile, iodine value, and TFA content were evaluated at the optimum parameters. This investigation showed that the electrochemical hydrogenation of soybean oil in SC‐CO₂ was improved. The reaction time was shortened by 4 h, and TFA content was reduced by 35.8% compared to traditional hydrogenation process.     

Hydrogenation to convert CO2 to C1 chemicals: Technical comparison of different alternatives by process simulation

Carbon dioxide (CO₂) conversion by catalytic reaction with hydrogen to produce different C1 chemicals is a promising strategy in view of the development of a sustainable chemical industry. In this work, two CO₂ hydrogenation routes are investigated in detail, respectively syngas and formic acid syntheses. Starting from published experimental reaction data, simulation models based on a kinetic analysis were developed and implemented in Aspen Plus process simulator. The two processes are analyzed according to a number of selected technological indicators, comprising CO₂ conversion, specific H₂ consumption, product yield, energy duties, and carbon emissions. To extend our study, three additional CO₂ conversion pathways are considered, respectively methanol, methane, and urea syntheses, whose technological performances were retrieved from similar studies available in the scientific literature. Under the assumption that H₂ is available from renewable sources, our results highlight that CO₂ conversion routes towards fuel compounds (ie, syngas and methane) look particularly appealing from the energy balance point of view. If non-renewable energy is used to produce H₂, the actual environmental benefits (in terms of net CO₂ emissions) strongly depend on the country-specific carbon intensity for electricity generation.     

A New Catalytic Transesterification for the Synthesis of Ethyl Methyl Carbonate

The application of a novel Ce_0.5Zr_0.5O₂ mixed oxide prepared by the microemulsion method as a support of Ru catalysts for the reforming of CH₄ with CO₂ originates a high-activity catalytic system with excellent stability under reaction conditions. The support characteristics clearly determine the catalytic stability of Ru catalysts under CH₄ + CO₂ reaction conditions. The introduction of cerium as a promoter in the ZrO₂ structure is shown to improve the catalyst performance by increasing the oxygen mobility in the support and consequently reducing deactivation by carbon deposition during reaction.     

Exploring the Effects of the Interaction of Carbon and MoS2 Catalyst on CO2 Hydrogenation to Methanol

Hydrogenation of CO₂ to form methanol utilizing green hydrogen is a promising route to realizing carbon neutrality. However, the development of catalyst with high activity and selectivity to methanol from the CO₂ hydrogenation is still a challenge due to the chemical inertness of CO₂ and its characteristics of multi-path conversion. Herein, a series of highly active carbon-confining molybdenum sulfide (MoS₂@C) catalysts were prepared by the in-situ pyrolysis method. In comparison with the bulk MoS₂ and MoS₂/C, the stronger interaction between MoS₂ and the carbon layer was clearly generated. Under the optimized reaction conditions, MoS₂@C showed better catalytic performance and long-term stability. The MoS₂@C catalyst could sustain around 32.4% conversion of CO₂ with 94.8% selectivity of MeOH for at least 150 h.     

Catalysed carbon gasification with Ba13CO3

The interaction of barium carbonate with carbon black was studied to understand catalysed CO₂ gasification of carbon. Temperature-programmed reaction with isotopic labelling of the carbonate and the carbon showed that carbon dramatically accelerated the rate of BaCO₃ decomposition to form BaO and CO₂, which rapidly gasified carbon to form CO. Pure BaCO₃ was observed to exchange carbon dioxide with the gas-phase, and the exchange rate was increased significantly by carbon at higher temperatures, due to formation of a carbon-carbonate complex. The interaction of BaCO₃ and C to form a complex occurred well below gasification temperatures, and BaCO₃ did not decompose until after gasification began and the gas phase CO₂ concentration was low. During catalysed gasification, formation of gaseous CO from a surface oxide is shown directly to be the slow step in the reaction. The active catalyst appears to cycle between BaCO₃ and BaO (both of which interact with carbon). The rates of carbonate decomposition, catalytic gasification, and exchange with gaseous CO₂ are all slower for BaCO₃ than for K₂CO₃, indicating the large differences in carbonate-carbon interaction between alkali carbonates and alkaline earth carbonates. The two carbonates apparently follow different reaction mechanisms.     

Decomposition of methane and its reaction with CO2 over Rh/ZSM-5 catalyst

The decomposition of methane, its conversion into higher hydrocarbons and the reaction between CH₄ and CO₂ have been investigated on Rh/ZSM-5 in a fixed bed continuous-flow reactor. Independently of the temperature at 523–973 K, the decomposition of methane gave hydrogen, surface carbon and a small amount of ethane: ethylene and benzene were not detected. The reactivity of surface carbon formed at different temperatures has been examined toward H₂, O₂ and CO₂. The carbon exhibited less reactivity toward CO₂. The reaction between CH₄ and CO₂ occurred rapidly above 673 K to give CO and H₂ with a ratio of 1.3–1.6. Very little carbon was deposited during the reaction. It is concluded that the facile reactions between CH_x and CO₂ are responsible for the lack of carbon deposition. However, a significant amount of carbon deposition and the deactivation of the catalyst occurred when more than 4–5% of ethane was added to the reacting gas mixture. The extent of deactivation can be decreased by using a large excess of CO₂. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of potassium and sodium carbonate catalysts on the rate of gasification of metallurgical coke

The catalytic effects of potassium and sodium carbonates on the rate of gasification of metallurgical coke with carbon dioxide have been investigated by the thermogravimetric method. The experiments were carried out using metallurgical coke fines mixed with 5 wt% catalyst, the mixture pressed into disc-shaped pellets from which a small specimen (23 mg) was cut and used. The reaction was carried out at temperatures ranging from 725 to 900°C using pure CO₂ at 1 atm.The rates were measured for uncatalyzed coke-CO₂ reaction and with K₂CO₃, Na₂CO₃ and mixed (K, Na)₂CO₃ catalysts. Potassium carbonate exhibited the greatest catalytic activity closely followed by the mixed catalyst and sodium carbonate. For the K₂CO₃-catalyzed reaction, an activation energy of 41.74 (±3.13) kcal/mole was found; and for the Na₂CO₃-catalyzed reaction the figure was 40.27 (± 5.05) kcal/mole.The catalysis is thought to occur by the “vapor cycle” mechanism. It consists of reduction (M₂CO₃→2M) followed by oxidation (2M → M₂CO₃). When CO₂ is present in the system the alkali vapor (M) quickly gets reconverted to the carbonate.     

Determination of kinetics of CO2 absorption in solutions of 2‐amino‐2‐methyl‐1‐propanol using a microfluidic technique

The kinetics for the reactions of carbon dioxide with 2‐amine‐2‐methyl‐1‐propanol (AMP) and carbon dioxide (CO₂) in both aqueous and nonaqueous solutions were measured using a microfluidic method at a temperature range of 298–318 K. The mixtures of AMP‐water and AMP‐ethylene glycol were applied for the working systems. Gas‐liquid bubbly microflows were formed through a microsieve device and used to determine the reaction characteristics by online observation of the volume change of microbubbles at the initial flow stage. In this condition, a mathematical model according to zwitterion mechanism has been developed to predict the reaction kinetics. The predicted kinetics of CO₂ absorption in the AMP aqueous solution verified the reliability of the method by comparing with literatures’ results. Furthermore, the reaction rate parameters for the reaction of CO₂ with AMP in both solutions were determined. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4358–4366, 2015     

Engineering Solutions for Limiting the Increase of Atmospheric Carbon Dioxide

The article describes possible engineering solutions that can reduce the carbon dioxide (CO₂) content of the air. To demonstrate the point fossil fuel power plants will be taken as a model for the source of CO₂. The global mass balance shows that the oceans play a major role in storing CO₂. The hypothesis presented states that the real problem is not the absolute CO₂ content, rather its change. Consequently, present emissions should be stored for future release. Under the current worldwide measures to reduce power consumption CO₂ emissions are unlikely to decrease. A number of strategies for the maritime sequestration of CO₂ are reported in the contribution. One proposal for sequestration is the use of shallow waters which form a thermohaline current: the dissolved gas will travel for hundreds of years in deep sea currents. In the latter case, CO₂ injection is easily achieved. Several scenarios are considered for the fate of this CO₂‐enriched current. The environmental impact is briefly reported. The article will describe current research requirements, demonstrating that similar research in the US and Japan is presently more advanced in comparison to that in Europe. The sequestration of carbon dioxide on land will be the subject of a second publication. It is obvious that the sequestration of CO₂ is the method after all rational chances to save energy.     

Effects of carbon dioxide and acidic carbon compounds on the analysis of Boehm titration curves

In the characterization of the surface functionality of acid-oxidized carbon nanotubes (CNTs) using the Boehm titration method, dissolution of acidic carbon compounds (ACCs) fragmented from the acid-oxidized CNTs and atmospheric carbon dioxide (CO₂) in the reaction base results in a somewhat over-estimation of the surface functionality of the CNTs. We developed a modified Henderson–Hasselbalch equation to show that the influence of the carboxylic and phenolic groups of ACCs and atmospheric CO₂ on the resultant titration curve can be identified and quantitatively measured, which makes it possible to determine the true surface functionality of acid-oxidized CNTs and ACCs.     

High-pressure phase equilibrium for the hydroformylation of 1-octene to nonanal in compressed CO2

The hydroformylation reaction in supercritical carbon dioxide or CO₂-expanded liquids (CXLs) has many advantageous properties. However, accurate phase behavior and equilibrium must be known to properly understand and engineer these systems. In this investigation, the vapor-liquid equilibrium and mixture critical points of CO₂ systems with 1-octene, nonanal, 1-octene and nonanal mixtures, and mixtures of 1-octene, nonanal and syngas (CO/H₂) were measured at 60 °C up to 120 bar of pressure. The Peng-Robinson equation of state with van der Waals two-parameter mixing rule was employed successfully to correlate the binary mixture data and predict the ternary mixture data. The presence of CO/H₂ pressure increased the mixture critical points and decreased the volume expansion at any given pressure. In an actual reaction, the mixture critical point would increase throughout the reaction, while the volume of the liquid phase would decrease. These data will aid the understanding and reaction engineering for the hydroformylation reaction in CO₂-expanded liquids and supercritical fluids.     

Kinetics of the reaction of oxygen with carbon monoxide adsorbed on palladium

A study of the kinetics of the reaction of adsorbed carbon monoxide with oxygen on polycrystalline palladium is reported in which a pressure jump method was used to induce transients in the carbon dioxide production. Through an analysis of these transients under a variety of conditions of temperature and oxygen pressure, some details of the kinetics have been delineated. At relatively low temperatures and under a significant O₂ pressure, CO(a) is desorbed more readily as CO₂, via the reaction CO(a) + O(a) → CO₂, than as CO. The reaction is first order in oxygen and the rate is limited by the rate of adsorption of oxygen onto sites which are in close proximity to CO(a). Oxygen adsorption at sites which are further than a critical distance from CO(a) are unreactive. The critical distance increases with temperature reflecting increased mobility. Under conditions where both CO(a) and O(a) are significant and both CO(g) and O₂(g) are small the rate is limited by the mobility of CO(a) and/or O(a). The amount of CO(a) during the course of the steady-state oxidation reaction can be determined by analyzing the transient CO₂ production which occurs following a pressure jump in carbon monoxide.     

Fabrication of Y-junction carbon nanotubes by reduction of carbon dioxide with sodium borohydride

Y-junction carbon nanotubes with a bamboo-shaped structure have been synthesized by reduction of CO₂ with NaBH₄ at 700 °C. The X-ray power diffraction pattern indicates that the products are hexagonal graphite, and transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images reveal the morphology and structure of carbon nanotubes. The effects of reaction temperature on the growth of the Y-junction carbon nanotubes were also discussed in the paper. Reduction of supercritical CO₂ with sodium borohydride is a promising green chemical method for economically producing Y-junction carbon nanotubes.     

Influence of porosity and surface groups on the catalytic activity of carbon materials for the microwave-assisted CO2 reforming of CH4

In this work, various carbon materials were studied as catalysts/microwave receptors for the CO₂ reforming of the CH₄ reaction. Carbon materials with a different textural development (metallurgical coke, activated carbons, re-activated carbon) were selected as catalysts in order to determine the role of porosity and pore size in dry reforming. Microporosity was found to be necessary for a good performance of the carbon catalysts. An activated carbon and an oxidized activated carbon were compared in order to evaluate the influence of oxygen surface groups on the catalytic activity of carbons for the dry reforming reaction. Oxidized carbons were found to be bad catalysts, especially under microwave heating. The importance of CO₂ reactivity for carbon materials to be able to act as acceptable catalysts was also established.     

Biodegradation of Poly(butylene succinate) Powder in a Controlled Compost at 58 ��C Evaluated by Naturally-Occurring Carbon 14 Amounts in Evolved CO2 Based on the ISO 14855-2 Method

The biodegradabilities of poly(butylene succinate) (PBS) powders in a controlled compost at 58 °C have been studied using a Microbial Oxidative Degradation Analyzer (MODA) based on the ISO 14855-2 method, entitled “Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions—Method by analysis of evolved carbon dioxide—Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test”. The evolved CO₂ was trapped by an additional aqueous Ba(OH)₂ solution. The trapped BaCO₃ was transformed into graphite via a serial vaporization and reduction reaction using a gas-tight tube and vacuum manifold system. This graphite was analyzed by accelerated mass spectrometry (AMS) to determine the percent modern carbon [pMC (sample)] based on the ¹⁴C radiocarbon concentration. By using the theory that pMC (sample) was the sum of the pMC (compost) (109.87%) and pMC (PBS) (0%) as the respective ratio in the determined period, the CO₂ (respiration) was calculated from only one reaction vessel. It was found that the biodegradabilities determined by the CO₂ amount from PBS in the sample vessel were about 30% lower than those based on the ISO method. These differences between the ISO and AMS methods are caused by the fact that part of the carbons from PBS are changed into metabolites by the microorganisms in the compost, and not changed into CO₂.     

A composite equation of state for the modeling of sonic carbon dioxide jets in carbon capture and storage scenarios

The development of a novel composite two‐phase method to predict the thermodynamic physical properties of carbon dioxide (CO₂) above and below the triple point, applied herein in the context of Reynolds‐Averaged Navier–Stokes computational modeling has been detailed here. A number of approaches have been combined to make accurate predictions in all three phases (solid, liquid, and gas) and at all phase changes for application in the modeling of releases of CO₂ at high pressure into the atmosphere. Predictions of a free release of CO₂ into the atmosphere from a reservoir at a pressure of 10 MPa and a temperature of 283 K, typical of transport conditions in carbon capture and storage scenarios, is examined. A comparison of the results shows that the sonic CO₂ jet that forms requires a three‐phase equation of state including the latent heat of fusion to realistically simulate its characteristics. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3928–3942, 2013