Carbon dioxide reduction pressure

Cold methanol has proven to be an effective solvent for acid gas removal. Cold methanol is nonselective in terms of hydrogen sulfide and carbon dioxide. The carbon dioxide is released from solution easily by reduction in pressure. Steam heating is required to release the hydrogen sulfide. A cold methanol process is Hcensed by Lurgi as Rectisol and by the Institute Francaise du Petrole (IFP) as IFPEXOL. 

Conventional nitrocellulose lacquer finishing leads to the emission of large quantities of solvents into the atmosphere. An ingeneous approach to reducing VOC emissions is the use of supercritical carbon dioxide as a component of the solvent mixture (172). The critical temperature and pressure of CO2 are 31.3°C and 7.4 MPa (72.9 atm), respectively. Below that temperature and above that pressure, CO2 is a supercritical fluid. It has been found that under these conditions, the solvency properties of CO2 ate similar to aromatic hydrocarbons (see Supercritical fluids). The coating is shipped in a concentrated form, then metered with supercritical CO2 into a proportioning airless spray gun system in such a ratio as to reduce the viscosity to the level needed for proper atomization. VOC emission reductions of 50% or more are projected. 

Liquid carbon dioxide is usually stored under 20 bar pressure at — 18°C. Compression and cooling of the gas between the temperature limits at the triple point and the critical point will cause it to liquefy. The triple point is the pressure temperature combination at which carbon dioxide can exist simultaneously as gas, liquid and solid. Above the critical temperature point of 31°C it is impossible to liquefy the gas by increasing the pressure above the critical pressure of 73 bar. Reduction in the temperature and pressure of liquid below the triple point causes the liquid to disappear, leaving only gas and solid. (Solid carbon dioxide is also available for cryogenic work and at —78°C the solid sublimes at atmospheric pressure.)... 

Atmospheric O2 has a partial pressure of 0.20 bar, and atmospheric water vapor is saturated with carbon dioxide. This dissolved CO2 forms carbonic acid, which generates a hydronium ion concentration of about 2.0 X 10 M. The Nemst equation allows calculation of the half-cell potential for the reduction of 02(g) under these... 

Products Obtained by Electrochemical Reduction of Carbon Dioxide under High Pressure of 10 kg/cm2 Gagea... 

In photoelectrochemical reduction of carbon dioxide, organic solvents and their mixtures with water have also been used. The use of organic solvents has the advantages103 that (1) competitive hydrogen formation can be suppressed and (2) the increased solubility of C02 in nonaqueous solutions28 30 has similar effects to the use of higher C02 pressures. 

Kaneco, S., Shimizu, Y., Ohta, K., and Mizuno, T. (1998) Photocatalytic reduction ofhigh pressure carbon dioxide using Ti02 powders with a positive hole scavenger. Journal of Photochemistry and Photobiology A Chemistry, 115 (3), 223-226. 

The photocatalyzed reduction of carbon dioxide at elevated pressure was also investigated. Porous glass beads were used to obtain efficient gas-liquid contact. With isopropanol as the solvent and 2-propyl formate as the reducing agent,the reaction products were carbon monoxide and hydrogen. The catalyst, chloro(tetraphenyl-porphinato)rhodium(III), was irradiated with visible light /21/. 

RESS [Rapid Expansion of Supercritical Solutions] A process for depositing a film of solid material on a surface. The substance is dissolved in supercritical carbon dioxide. When the pressure is suddenly reduced, the fluid reverts to the gaseous state and the solute is deposited on the walls of the vessel. Used for size-reduction, coating, and microencapsulation. First described in 1879. Developed in 1983 by R. D. Smith at the Battelle Pacific Northwest Laboratory. 

During the combustion the rate of flow of bubbles in the counter often increases rather appreciably because the rapid absorption in the sodium hydroxide-asbestos tube of the carbon dioxide produced causes a slight decrease in the pressure. If this happens reduce the rate of dropping of water from the aspirator or even stop it altogether temporarily. No harm is done by this decrease in pressure. Should there be any small leaks at the constricted parts of the tube there would, it is true, be a danger that air might be sucked in. In view of the short duration of the reduction in pressure, however, the errors caused would have no appreciable effect on the determination. Obviously no adjustment of the flow from the aspirator must be made while the reduced pressure prevails. The former rate of dropping is automatically restored. 

Because the organic chemicals are destroyed in the GPCR reactor by reduction reactions, the main products are gases such as methane, carbon monoxide, and carbon dioxide. These gases, plus the excess feed hydrogen, must be removed at a controlled rate to maintain the set system pressure fluctuations in the system pressure are undesirable and may lead to process upsets. To accommodate the fluctuating reactor loading and gas production, the compressor must be controlled to remove gas from the system at a variable rate. This is accomplished with a variable-speed drive on the compressor. 

The first experiments made by Neuberg and Nord with the simplest diketone, diacetyl, showed at once that this substance can be hydrogenated phytochemically with comparitive ease. Acetylmethylcarbinol appears as an intermediate (see below), and the end product of reduction is asymmetric and levorotatory. Reduction was effected by the action of fermenting yeast on diacetyl. The 2,3-butanediol that is formed can be isolated by alcohol-ether extraction of the fermentation mixture after concentration in the Faust-Heim apparatus or by steam distillation in an atmosphere of carbon dioxide under ordinary pressure it is then carefully concentrated with the birectifier and obtained in the pure state by final fractionation. 

Mediated electrochemical oxidation (MEO) is an ex situ treatment technology that uses electricity, acid, and a metal catalyst to destroy organic wastes at low temperatures and pressures. The proprietary CerOx Corporation MEO configuration uses cerium metal as a catalyst to oxidize organic waste into carbon dioxide and water. The process occurs in an acidic solution, typically nitric acid. The first step involves the generation of an oxidant at the anode, followed by the reduction of water or another chemical species at the cathode. This technology serves as a nonthermal alternative to incineration. 

As its name suggests, supercritical fluid extraction (SEE) relies on the solubilizing properties of supercritical fluids. The lower viscosities and higher diffusion rates of supercritical fluids, when compared with those of liquids, make them ideal for the extraction of diffusion-controlled matrices, such as plant tissues. Advantages of the method are lower solvent consumption, controllable selectivity, and less thermal or chemical degradation than methods such as Soxhlet extraction. Numerous applications in the extraction of natural products have been reported, with supercritical carbon dioxide being the most widely used extraction solvent. However, to allow for the extraction of polar compounds such as flavonoids, polar solvents (like methanol) have to be added as modifiers. There is consequently a substantial reduction in selectivity. This explains why there are relatively few applications to polyphenols in the literature. Even with pressures of up to 689 bar and 20% modifier (usually methanol) in the extraction fluid, yields of polyphenolic compounds remain low, as shown for marigold Calendula officinalis, Asteraceae) and chamomile Matricaria recutita, Asteraceae). " ... 

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