Carbon dioxide
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Carbon dioxide, or CO2, is a very common, naturally occurring molecule that contains two oxygen atoms and one carbon atom.
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Carbon dioxide
- 1. Carbon dioxide, or CO2, is a very common, naturally occurring molecule that contains two oxygen atoms and one carbon atom. Carbon Dioxide
- 2. • It is a naturally occurring gas. • All humans and animals inhale and exhale carbon dioxide when they breathe. • Plants use Carbon Dioxide in a process called Photosynthesis to make their food. • Carbon Dioxide is also called ‘Green House Gas’ • It currently constitutes about 0.041% by volume of the atmosphere
- 3. Physical Properties Smell: Color: Molecular Mass: Shape: Bond-Angle: Melting Point: Boiling Point: Density: It is a non-flammable gas
- 4. Chemical Properties Carbon dioxide is an acidic oxide and reacts with water to give carbonic acid, which is a weak acid. CO2 + H2O ⇌ H2CO3 Carbon dioxide reacts with alkalis to give carbonates and bicarbonates. CO2 + NaOH ==> NaHCO3 NaHCO3 + NaOH ==> Na2CO3 + H2O
- 5. Uses It is used to neutralize alkaline water. It is used for refrigeration and cooling. It is used as an inert gas in chemical processes, in the storage of carbon powder and in fire extinguishers. It is used in metal industry in the formation of casting molds to enhance their hardness Carbon dioxide gas is used to carbonate soft drinks, beers and wine and to prevent fungal and bacterial growth. Large quantities are used as a raw material in the chemical process industry, especially for methanol and urea production. Liquid or solid carbon dioxide is used for quick freezing, surface freezing, chilling and refrigeration in the transport of foods etc. Carbon Dioxide is used as an additive to oxygen for medical use as a respiration stimulant. It is used in oil wells for oil extraction and maintain pressure within a formation. Liquid FrozenCarbon Dioxide (CO2) is a good solvent for many organic compounds.
- 6. Sources of Carbon Dioxide By burning of carbonaceous materials. By the production of H2 by steam water gas. By the Calcination of Calcium Carbonate. By Distillation from air. In the reduction of Iron from its oxides by coke. In the production of cement.
- 7. Manufacturing of Carbon Dioxide on Industrial Scale Recovery as a by-product in the production of SNG:
- 8. • Recovery from the Process of Ammonia:
- 9. • Recovery from the production of Ethanol:
- 10. • Recovery from Flue Gases:
Editor's Notes
- Recovery from the SNG production process: In the recovery of CO2 as a by product in the production of SNG. First the air is allowed to enter in air separation unit(ASU) where the oxygen is separated from the air and is proceeded to Gasifier where the coal is converted into syngas using steam and oxygen at high temp: and pressure. The syngas is filtered by gas cleaning process where particulates are removed. In the next step in water-gas shift reactor the concentration of H2 is increased by water-gas shift reaction where some amount of CO and H2O are converted to CO2 and H2 in a fixed bed catalytic converter. From here the H2, CO, and CO2 are again filtered and CO2 is obtained/recovered, while the CO and H2 are further proceeded for methanation process where SNG is produced.
- Recovery from the process of ammonia production: In the first step the treated natural gas, steam and air are allowed to enter in steam reformer where hydrogen and carbon monoxide are formed. In the next step in gas-water shift reactor carbon monoxide is converted to carbon dioxide and more hydrogen. CO + H2O <===> CO2 + H2 Where the carbon dioxide is then removed for storage or further use. The final step in which any small residual amounts of CO or CO2 from the hydrogen is removed by catalytic methanation. The hydrogen gas obtained is catalytically reacted with nitrogen to form anhydrous ammonia.
- Recovery from the production of ethanol by fermentation: In this process the dextrose(sugar) is entered in the fermenter where the yeast breaks it into alcohol and carbon dioxide in the absence of oxygen the membrane is introduced for filtration and recycling purposes during continuous process. The CO2 is collected from the fermenter as a by product for further use. If 1000 kg of ethanol is produced almost 950 kg of CO2 is obtained.
- Typical chemical absorption unit for CO2 recovery from flue gas: The combustion flue gas coming out of the stack is hot (~ 232°C), and at atmospheric pressure. The flue gas needs to be cooled, before entering the absorber, which usually operates at less than 50°C. This is achieved by spraying cooling water in a direct contact cooler, as shown in bottom left hand side of Figure blower is installed to give the flue gas enough pressure for it to go through the absorption-desorption system. Conventionally, the waste gas to be scrubbed of the CO2 enters the absorber at the bottom, flows up, and leaves at the top, whereas the solvent enters the top of the absorber, flows down (contacting the gas), and emerges at the bottom. Dilution of the circulating amine with water is undertaken to reduce viscosity of the circulating fluid. A higher viscosity fluid would require more power to pump and provide circulation. The liquid amine solution containing the absorbed gas then flows to a regeneration unit (stripper) where it is heated and the acid gases liberated. The solvent regeneration can be carried out at low pressures to enhance desorption of CO2 from the liquid. Some amine solution is typically carried over in the acid gas stream from the regeneration step and the amine solution is recovered using a condenser, in order to avoid excessive solvent losses. The hot lean amine solution then flows through a heat exchanger where it is contacted with the rich amine solution from the contact tower and from there the lean amine solution is returned to the gas contact tower, i.e. absorber.