Carbon dioxide removal from atmosphere

It is estimated that photosynthesis is a sink for around 60 billion tons of carbon every year, by far the strongest mechanism for carbon dioxide removal from the atmosphere. (This removal is almost exactly balanced by the respiration of animals, which combines oxygen with hydrocarbons to produce carbon dioxide and water vapor.)... 

The vast majority of current power plants use coal or natural gas as the fuel source and air as the source of oxygen. In these plants, the stack gas is at essentially atmospheric pressure and contains a large concentration of nitrogen (76 mol%). A small amount of excess air is used, which gives a stack composition of 4.8 mol% O2. The carbon dioxide concentration is only 13.2 mol%. The principal proven method for carbon dioxide removal from a low-concentration, low-pressme gas uses amine absorption, which involves chemical reaction of carbon dioxide with an amine, such as monoethanolamine (MEA). 

However, the ability of these and other forms of plant life to absorb carbon dioxide is not keeping up with the increase in carbon dioxide. Most scientists agree that the primary source of the increase of carbon dioxide is the burning of fossil fuels such as gasoline, coal, and natural gas. The cutting and burning of trees in the rain forests (deforestation) also reduces the amount of carbon dioxide removed from the atmosphere. 

Another concept arising from the carbon footprint is that of offsetting. A carbon footprint can be offset by doing something that will remove the carbon dioxide produced from the atmosphere. Such actions include planting trees, or promoting some... 

Carbon dioxide removal by slurry absorption is attractive down to about -75°C, a temperature easily achieved by slurry regeneration to slightly above one atmosphere carbon dioxide pressure. For example, with a -75°C exit gas temperature, slurry absorption reduces the carbon dioxide content of a 1000 psia synthesis gas from about 13 to about 4 mole percent, a 70% reduction in carbon dioxide content. The exact level to which carbon dioxide can be removed from a treated gas by slurry absorption also depends on the solubility of solid carbon dioxide in the treated gas the solubility of solid carbon dioxide in synthesis gas (3H2 CO) is illustrated in Figure 10 for several synthesis gas pressures. Fine removal of carbon dioxide to lower levels is accomplished by conventional absorption into a slip stream of the slurry solvent which is regenerated to meet particular product gas carbon dioxide specifications. 

Estimation of Atmospheric Carbon Dioxide.—A convenient method is that of Pettenkofer,4 which consists in introducing a standard solution of barium hydroxide into a large bottle containing several litres of the air to be examined. The bottle is shaken from time to time to keep the sides moistened wit-h the solution, and after 5 or 6 hours the absorption of carbon dioxide may be regarded as complete. The baryta solution is decanted into a small stoppered bottle and allowed to stand until any suspended barium carbonate has settled. A portion of the clear liquid is then removed and titrated with dilute sulphuric acid, using phenol-phthalein as indicator. The diminution in alkalinity due to combination with carbonic acid is thus measured, and from the data obtained the percentage of carbon dioxide m the atmosphere may easily be calculated. 

Another approach is to increase carbon dioxide uptake by forests to reverse the effects of severe deforestation of the last 150 years. It has been estimated that a rapidly growing rainforest can remove 4-7kg/m year of carbon dioxide from the atmosphere, as compared to a typical crop uptake of 0.8-1.6kg/m year. Thus, vigorous reforestation could assist in increasing the photosynthetic removal of carbon dioxide from the atmosphere [59]. Annual crops also perform photosynthetic uptake of carbon dioxide, but consumption and metabolism of the product(s) and prompt decomposition of the plant wastes promptly return the fixed carbon dioxide to the atmosphere [60]. 

In laboratory surroundings, some plants respond to increased carbon dioxide by growing faster. There has been speculation this effect, operating on a worldwide basis, will limit or reduce the amount of carbon dioxide in the atmosphere. The amount of carbon removed from the atmosphere by this process will probably be small. In most natural environments plant growth is limited by the soil... 

A typical carbon dioxide removal system consists of an absorber where the feed gas is introduced at the bottom and the lean propylene carbonate solution is contacted with the rising gas in a countercurrent manner. The carbon dioxide content of the treated gas depends upon the initial content of C02 in the lean gas. The rich gas (containing the removed C02 and other compounds) is passed through an intermediate flash tank from where some of the low molecular hydrocarbons are recycled to the absorber. The stripped solvent is then passed through a low pressure flash tank where the carbon dioxide is flashed to the atmosphere and the lean gas is pumped back to the absorber. This process can be modified further to achieve lower C02 exit concentrations in the treated natural gas by adding strippers operating at atmospheric pressure followed by vacuum strippers. Power requirements for any of these units are very low, thus keeping the process very efficient and economical. 

Carbon dioxide removal in ammonia plants is usually accomplished by organic or inorganic solvents with suitable activators and corrosion inhibitors. In a few circumstances, C02 is removed by pressure swing adsorption (PSA) (see Chapter 3). The removed C02 is sometimes vented to the atmosphere, but in many instances it is recovered for the production of urea and dry ice. Urea is the primary use of carbon dioxide and, in case of a natural gas feed, all of the C02 is consumed by the urea plant. This practice is especially significant since C02 is a proven greenhouse gas. Typically, 1.3 tons of C02/ton of NH3 is produced in a natural gas-based ammonia plant. The C02 vented to the atmosphere usually contains water vapor, dissolved gases from the absorber (e.g., H2, N2, CH4, CO, Ar), traces of hydrocarbons, and traces of solvent. Water wash trays in the top of the stripper and double condensation of the overhead help to minimize the amount of entrained solvent. The solvent reclaimer contents are neutralized with caustic before disposal. Waste may be burned in an incinerator with an afterburner and a scrubber to control NOx emissions. 

Carbonated beverages are bottled at high pressures of carbon dioxide. When the cap is removed, the fizzing results from the fact that the partial pressure of carbon dioxide in the atmosphere is much less than that used in the bottling process. As a result, the equilibrium quickly shifts to one of lower gas solubility. 

Hot potassium carbonate is usually used as the absorption solvent for carbon dioxide removal. A small purge stream is vented from the suction side of the compressor to remove inerts before the gas enters the carbon dioxide absorber. Carbon dioxide is vented to the atmosphere and the ethylene-rich offgas from the absorber is recycled to the acetic acid vaporizer. 

As pollutants go, carbon dioxide might be considered a relatively innocuous component of our atmosphere. After all, every breath we exhale contains about 4% carbon dioxide even though the inhaled air is only about 0.04% carbon dioxide. Fossil fuel combustion and natural decay processes combined with forest and grassland fires release billions of metric tons of carbon dioxide into the atmosphere annually. At the same time, trees, grasses, and other plants remove equivalent quantities of carbon dioxide from our atmosphere each year. Carbon dioxide is constantly being dissolved in and released from the ocean and other bodies of water as their temperature fluctuates. In other words, carbon dioxide is constantly being added to and removed from our atmosphere by a variety of processes, some natural and some of human origin. 

It is estimated that natural mechanisms remove 10 hillion tons of carbon dioxide per year from our atmosphere. Thus, at present levels of fossil fuel comhustion, we put about 25 billion tons of carbon dioxide into the atmosphere each year. Natural mechanisms remove only 10 hillion tons, so we are producing a net increase of about 15 billion tons of carbon dioxide in our atmosphere each year That explains the trend in carbon dioxide concentrations. The carbon dioxide concentration is increasing and we are almost certainly responsible for that increase. 

Carbon Dioxide Removal (CDR) Geoengineering techniques and technologies that remove carbon dioxide from the atmosphere in an attempt to combat climate change and global warming. 

Iron Fertilization of the Oceans. The intentional introduction of iron into the upper layers of certain areas of the ocean to encourage phytoplankton blooms is a form of CDR. The concept rehes on the fact that increasing certain nutrients—such as iron— in nutrient-poor areas stimulates phytoplankton growth. Carbon dioxide is absorbed from the surface of the ocean during the processes of photosynthesis when the phytoplankton, marine animals, and plankton die and sink in the natural cycle, that carbon is removed from the atmosphere and sequestered in the ocean s depths. 

The combustion of fossil fuels must produce carbon dioxide as a product, but does the carbon dioxide have to go into the atmosphere The U.S. Department of Energy (DOE) does not think so it has started a dialogue and research program that unites the government with academia and industry to develop technologies to "sequester" or trap carbon dioxide. In the simplest case, carbon dioxide is removed from the exhaust gas before the gas is emitted into the atmosphere. In more complex scenarios, carbon is removed from hydrocarbon fuels before combustion, producing hydrogen, which then becomes the primary fuel for the plant. 

Carbon capture refers to measures that at least temporarily remove carbon dioxide from the atmosphere or prevent its release to the atmosphere. One way in which net release of carbon dioxide to the atmosphere is prevented is the use of biomass for fuel and raw material in place of petroleum. When biomass is burned, carbon dioxide is released, but exactly the same amount of carbon dioxide was removed from the atmosphere for the photosynthetic production of the biomass. Therefore, on balance, using biomass as fuel does not add carbon dioxide to the atmosphere. If biomass is not burned or does not decay, its production amounts to a net loss of atmospheric carbon dioxide. 

Chill the concentrated solution of the amine hydrochloride in ice-water, and then cautiously with stirring add an excess of 20% aqueous sodium hydroxide solution to liberate the amine. Pour the mixture into a separating-funnel, and rinse out the flask or basin with ether into the funnel. Extract the mixture twice with ether (2 X25 ml.). Dry the united ether extracts over flake or powdered sodium hydroxide, preferably overnight. Distil the dry filtered extract from an apparatus similar to that used for the oxime when the ether has been removed, distil the amine slowly under water-pump pressure, using a capillary tube having a soda-lime guard - tube to ensure that only dry air free from carbon dioxide passes through the liquid. Collect the amine, b.p. 59-61°/12 mm. at atmospheric pressure it has b.p. 163-164°. Yield, 18 g. 

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