Enzyme Chemistry in Carbon Dioxide

Polymer‐supported pyridinium salts, prepared by quaternarization of crosslinked poly(4‐vinylpyridine) with alkyl halides, effectively catalyze the reaction of carbon dioxide (1 atm) and glycidyl phenyl ether (GPE) to afford the corresponding five‐membered cyclic carbonate (4‐phenoxymethyl‐1,3‐dioxolan‐2‐one). Poly(4‐vinylpyridine) quarternarized with alkyl bromides show high catalytic activities, and the reaction of carbon dioxide (1 atm) and GPE at 100 °C affords 4‐phenoxymethyl‐1,3‐dioxolan‐2‐one quantitatively in 6 h. The rate constant in the reaction of GPE and carbon dioxide in N‐methyl pyrrolidinone using poly(4‐vinylpyridine) quarternarized with n‐butyl bromide (kobs = 102 min−1) is almost comparable with those for homogeneous catalysts with good activities (e.g., LiI), and the rate of the reaction obeys the first‐order kinetics. A used catalyst may be recovered by centrifugation, and the recycled catalyst also promotes the reaction of GPE and carbon dioxide. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5673–5678, 2007

At present, there is no universal method for studying the solubility of substances in supercritical fluid media. The expediency of combining certain methods of solution saturation and composition analysis is determined by the object of study, the range of concentrations. In the case of low solubility of solids in the solvent, a flow-through system or dynamic solubility measurement method is usually used to obtain the required amount of precision weighing material. The dynamic method for measuring the solubility of substances in supercritical carbon dioxide is not without its drawbacks, which primarily include the need to strictly control the mass flow rate of supercritical carbon dioxide in the cell with the substance being measured. With an increase in the consumption of supercritical dioxide from zero (static method) to a certain value, the concentration of the measured substance in supercritical carbon dioxide within the acceptable level of uncertainty for measuring the solubility of 4-6% can be considered unchanged. The plateau of the concentration of the measured substance in supercritical carbon dioxide from the flow rate obtained in the diagram corresponds to the saturation state of the solvent, which is carbon dioxide and the solute, which corresponds to the concept of solubility. However, with a further increase in the consumption of carbon dioxide, the concentration begins to decrease and it can no longer be considered equilibrium. This is due to the fact that at significantly high flow rates of carbon dioxide, which is a solvent, coming into contact with the substance being dissolved, it does not have time to saturate it and, accordingly, weakly dissolves it. This concentration does not correspond to the concept of solubility. Thus, the determination of the range of mass flow rate at which the conditional state of saturation of the solvent and the solute is reached is the most important stage in studies to measure the solubility of substances in supercritical fluids. Based on the results of experimental data measuring the solubility of tannin in supercritical carbon dioxide, the dependences of the concentration of tannin in supercritical carbon dioxide on the mass flow rate are presented. It follows from the results that, in the flow rate range of 0-0.6 g/min, the tannin concentration in supercritical carbon dioxide is practically independent of the solvent flow rate, which is evidence of the equilibrium of this concentration and its compliance with the concept of solubility.

An experimental study on the flow characteristics of electronic expansion valves (EEVs) for heat pump system using carbon dioxide as a refrigerant have been carried out in this study. Many researches and efforts have been made to replace chemical refrigerants like Chloro-Fluoro-Carbon (CFC) and Hydro-Chloro-Fluoro-Carbon (HCFC) with natural refrigerants such as carbon dioxide and apply natural refrigerants to chillers or heat pump systems. In this study, we focused on the development of EEV and 4-way valve among the important components of heat pump system using natural refrigerant. The mass flow rate was measured at various EEV inlet temperature and pressure conditions with respect to several EEV openings operated at a heat pump system which has about 10 kW of cooling capacity. The heat pump system consists of a reciprocating compressor, a gas cooler, an evaporator, an EEV, and a 4-way valve which was developed for this study. The inlet temperature and pressure of an EEV was varied from 5°C to 40°C and from 7 MPa to 10 MPa, respectively. The mass flow rate of carbon dioxide through the EEV ranged from 50 g/s to 120 g/s. The mass flow rate of carbon dioxide around the critical point was affected by the inlet temperature and pressure of EEV, valve opening, and density variation. An empirical mass flow rate correlation of carbon dioxide based on the Buckingham π-theorem was developed in this study, and this correlation predicted experimental data within an average absolute deviation of 4.2%. The correlation can be applied to predict the mass flow rate through EEV used in the heat pump system using carbon dioxide as a refrigerant. And the reliability test of developed 4-way valve was conducted. This 4-way valve showed stable operation in the high pressure condition.

Reactions of carbon dioxide on pyrophoric nickel-on-silica surfaces

: The electron rich polyhydride complex molybdenum Mo(dmpe)2H4, formed by reduction of Mo(dmpe)2Cl2 under H2, reacts with CO2 to give a complex manifold of products containing formate, carbon dioxide and carbonate ligands. The final product of the reaction is Mo(dmpe)2(CO3)H2, in which reductive disproportionation of CO2 has led to a formation of a carbonate ligand. Two other products have been identified in which only two of the initial hydrides have been retained, one of which is the crystallographically characterized bis-formate Mo(dmpe)2(OCHO)2. The complex crystallizes in the monoclinic space group P and has an octahedral geometry with trans Eta 1-formate ligands. A precursor to 3 containing an Eta 2-CO2 ligand has been spectroscopically characterized as MKo(dmpe)2(CO2)(OCHO)H. Two complexes formed early in the reaction sequence, before elimination of H2, have been spectroscopically identified as Mo(dmpe)2(CO2)(OCHO)H3 and Mo(dmpe)2(OCHO)2H2. The characteristic absorptions between 1600 and 2800 cm-1 of the formate, carbonate, hydride, and carbon dioxide ligands in these molecules have been assigned on the basis of Carbon 13 and deuterium labelling studies.

The reaction of carbon dioxide with a mixture of a superbase and alcohol affords a superbase alkylcarbonate salt via a process that can be reversed at elevated temperatures. To utilize the unique chemistry of superbases for carbon capture technology, it is essential to facilitate carbonation and decarbonation at desired temperatures in an easily controllable manner. Here, we demonstrate that the thermal stabilities of the alkylcarbonate salts of superbases in organic solutions can be tuned by adjusting the compositions of hydroxylic solvent and polar aprotic solvent mixtures, thereby enabling the best possible performances to be obtained from the various carbon dioxide capture agents based on these materials. The findings provides valuable insights into the design and optimization of organic carbon dioxide absorbents.

Cyanidation effluents are treated in order to reduce the cyanide level down to regularity limits. Cyanide recovery is the most desired route for treatment of effluents of high cyanide consuming ores, in particular, due to economic and environmental incentives. In this study, carbon dioxide (CO2) was utilised as an alternative for acidification of cyanide solutions prior to absorption/recovery of hydrogen cyanide (HCN(g)) in alkaline solutions. Kinetic tests have indicated that reaction time is an important parameter for the recovery of cyanide, which reached 89.1% over a period of 90 min. Effects of concentration of cyanide (0.5-1.5 g/L NaCN), flow rate of carbon dioxide (0.38-1.15 L/min. CO2) and time (30-90 min.) on the recovery of cyanide (%) were investigated in detail by a two-level full factorial design (23). The statistical evaluation of the data showed that flow rate of carbon dioxide and time were statistically significant parameters. Efficiency of the process was not affected by the concentration of cyanide. The results demonstrated that high recoveries of cyanide up to 93.1% could be achieved under suitable conditions. Introduction of air (1.15 L/min.) as a carbon dioxide source was found to be inefficient and require longer reaction periods for high recoveries i.e. no recovery at 90 min. vs. 95.4% at 24 h. A separate test performed using a real pregnant leaching solution (PLS) yielded a cyanide recovery of 49.7%. These finding demonstrated that using carbon dioxide can be used for acidification of cyanide solutions for cyanide recovery.

Stringent environmental regulations and higher costs of effluent treatments in oil and gas process industries have necessitated research into ways to improve the operating procedures in effluent treatment plant. In Gas-to-liquid (GTL) plant, a significant quantity of reaction water is produced and various chemicals are used as intermediate treatment chemicals. The reaction water is contaminated by these chemicals which impair the pH and the related properties of the water. The pH has to be controlled before the water is re-used or released to the environment. A laboratory-scale effluent neutralization unit for pH control was designed and built to demonstrate the feasibility of utilising produced carbon dioxide (CO2) from reforming reactions in both the synthesis and hydrogen production units in GTL plant for insitu effluent treatment. At the end of the reaction, the total volume of carbon dioxide used was recorded. This paper presents experimental neutralisation characteristics for different operating conditions. The prime advantage of this process can be thought to be less expensive than other published carbon capture and storage (CCS) processes. Moreover the carbon dioxide does not require further compression, dehydration and storage facilities before usage. Pipeline transportation is also drastically reduced since the captured carbon dioxide is utilised within the plant. This study demonstrated that, the neutralisation time increased by 3.15 minutes with increase in effluent volume from 40 to 60 litres and by 10.4 minutes as the temperature increased from 20oC to 50oC. The increase in the flow rate of carbon dioxide from 15 litres/min to 35 litres/min decreased the neutralization time from 19.15 minutes to 13.32 minutes. Finally it was estimated that about 64% of the daily carbon dioxide production which would have otherwise been emitted to the atmosphere was used in the treatment process. Introduction The fact that the concentrations of carbon dioxide in the atmosphere are increasing is known to environmentalists, researchers and government agencies. The causes of global change lie in the industrial activities of human society and ultimately in the population growth and increase in resource use by man. Human activities have increased carbon dioxide concentrations from approximately 280 to 355ppm since 1800 (Vitousek, 1994). This increase is likely to have climatic consequences on biota in all earth's terrestrial ecosystems. The need to reduce global climate change due to emission of carbon dioxide (CO2) and other greenhouse gases has led to research in carbon capture and sequestration (CCS). Several relatively small-scale carbon capture and sequestration approaches are currently in development and demonstration stages as highlighted by Hoekman, 2010. Direct injection into the oceans has also been suggested but there are a number of uncertainties over the ecological impact and equilibrium of the gas with the atmosphere. In the medium term, depleted oil and gas reserves, unmineable coal seams, and deep saline formations are the best options for carbon dioxide storage. Deep saline formations appear to offer the potential to store several hundreds of years' worth of carbon dioxide emissions. This must be validated, and site selection criteria must be developed and shared internationally to identify the most appropriate storage sites. Wider international collaboration and consensus are critically needed to ensure the viability, availability and permanence of carbon dioxide storage. However carbon capture and sequestration faces both technical and economic challenges. Therefore, there is the need to explore other methods to deal with carbon dioxide emissions. Transformation to chemical feedstock like methanol is a commercially proven technology, however carbon dioxide captured from flue gas from furnaces will not be economical for this purpose because of its low pressure. Recompression is required before the carbon dioxide could be processed to methanol (Ritter et al, 2007). Another well-known process - the Sabatier reaction, converts carbon dioxide to methane as shown in Eq. (1).

Arylcarbamic esters were synthesized directly from carbon dioxide and an aromatic amine via a zinc carbamate. The alkylation of the reaction mixture of carbon dioxide, an aromatic amine, and diethylzinc with dialkyl sulfate formed alkyl arylcarbamate in a high yield. Also, 2-hydroxycyclohexyl diphenylcarbamate was obtained selectively in a good yield by the reaction of carbon dioxide, epoxycyclohexane, and ethylzinc diphenylamide. Other arylcarbamates of 1,2-cyclohexanediol were obtained by the reactions of carbon dioxide, an aromatic amine, diethylzinc, and epoxycyclohexane.

Chemical reactions involving carbon dioxide are prominent in a variety of environments and, therefore, important for modeling reaction pathways and quantifying molecular abundances. In atmospheres and in outer solar system ices, for example, radiation induced degradation of abundant chemical species like ozone, oxygen, carbon dioxide, or molecular nitrogen can liberate high energy oxygen or nitrogen atoms that may react with carbon dioxide. This work presents a study of these reactions where in the carbon dioxide — oxygen atom reaction, two carbon trioxide isomers (C2v and D3h symmetry) were found to form. In the carbon dioxide — nitrogen atom system, the bent OCNO radical was formed. Rate constants have been derived for these reaction pathways and the dynamics of the reactions are investigated.

CO2 Emission Reduction and CO2 Fixation on the Ground by Using Supercritical Carbon Dioxide as an Alternative to Organic Solvents

An in-house set-up was developed for determining the permeability of, paint films towards carbon dioxide. The system implemented the so-called Wicke-Kallenback method, described in EN 1062-6. This method consists of a two-chamber permeation cell divided by a supported paint film. A carbon dioxide/nitrogen mixture stream (15% CO2/85% N2) is fed to the retentate chamber and a nitrogen carrier stream is fed to the permeate chamber. Carbon dioxide permeates from the retentate to the permeate chamber. The carbon dioxide flow rate is obtained from the permeate concentration and flow rate. From the carbon dioxide flow rate it is possible to calculate the paint film permeability towards this gas. The coating system is applied on a Kraft paper support sheet; the Kraft paper by itself shows negligible permeation, resistance. Coatings to be considered as “surface protection systems for concrete” must comply with EN 1504-2. This standard requires that the paint film permeability have an equivalent air thickness of SD≥50 m. The unit developed was able to quickly determine permeabilities as low as an equivalent air thickness of SD=1500 m.

For the purpose of examining the possibility of performing reduction of carbon dioxide, and concurrently producing more value-added products from hydrocarbon, as a reducing agent, a reaction of carbon dioxide and propane on HZSM-5 catalysts containing Ga, Zn and Pt was conducted by using a continuous flow reaction apparatus. The catalytic test demonnstrated the possibility of conducting the reduction of carbon dioxide with simultaneous aromatization of propane on metal-loaded HZSM-5. Thus, carbon dioxide was reduced to carbon monoxide, and propane was converted into aromatics, mainly composed of benzene, toluene and xylene isomers, and lower alkenes generating by-products, such as methane and ethane. Among the catalysts examined in the present study, Zn-loaded HZSM-5 was most effective for the reduction of carbon dioxide by propane. It was also found that the introduction of carbon dioxide had some favorable effects on the aromatization of propane. Carbon dioxide suppressed catalyst deactivation caused by coke deposition and formation of by-product, ethane, to improve the selectivity of lower alkenes, such as ethene and propene.

PHOTOSYNTHESIS, PHOTOREDUCTION AND DARK REDUCTION OF CARBON DIOXIDE IN CERTAIN ALGAE

Carbon dioxide and N-phenylethylenimine were allowed to copolymerize using a Bronsted acid such as phenol or acetic acid to give a white powder, melting at 160–270°C, with a carbon dioxide content of 2.90–20.5 mol %. The content of carbon dioxide in the copolymer increased with carbon dioxide in the feed, while the melting point decreased. The infrared spectrum of the copolymer showed the characteristic peak of urethane linkage. 3-Phenyl-oxazolidone-2, which might be produced by the reaction of carbon dioxide and N-phenylethylenimine, did not react with carbon dioxide or N-phenylethylenimine and was not contained in the copolymer. Carbon dioxide did not react with poly(N-phenylethylenimine) or phenol. From the facts mentioned above, it was concluded that the formation of urethane linkage was due to the copolymerization of carbon dioxide and N-phenylethylenimine. From ultraviolet spectroscopic analysis of the mixture of carbon dioxide and N-phenylethylenimine, an appreciable interaction between two monomers was observed. From the experimental data on the monomer composition in the feed and copolymer, the apparent monomer reactivity ratios were evaluated. On the basis of these results, the probable mechanism of the copolymerization via a complex of carbon dioxide and N-phenylethylenimine was proposed.