Carbon dioxide liquefaction

Methods of Liquefaction and Solidification. Carbon dioxide may be Hquefted at any temperature between its triple poiat (216.6 K) and its critical poiat (304 K) by compressing it to the corresponding Hquefaction pressure, and removing the heat of condensation. There are two Hquefaction processes. In the first, the carbon dioxide is Hquefted near the critical temperature water is used for cooling. This process requires compression of the carbon dioxide gas to pressures of about 7600 kPa (75 atm). The gas from the final compression stage is cooled to about 305 K and then filtered to remove water and entrained lubricating oil. The filtered carbon dioxide gas is then Hquefted ia a water-cooled condenser. 

Kohlensaure-messer, m. instrument or apparatus for measuring carbon dioxide, an-thracometer, carbonometer. -saJz, n, carbonate. -schnee, m. carbon dioxide snow, dry ice. -Strom, m. stream or current of carbon dioxide, -verflussigung, /. liquefaction of carbon dioxide, -verlust, m. loss (or escape) of carbon dioxide, -wasche,/, carbon dioxide washer, -wasser, n, carbonated water, soda water. 

During the liquefaction process, usually much of the oxygen, carbon dioxide, sulfur compounds and water are removed so that liquefied natural gas (LNG) IS nearly 100 percent methane. LNG takes up one-six-hundredth the volume of natural gas, with a density less than half that of water. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Fig. 3.1 outlines the liquefaction of air. Air is filtered to remove particulates and then compressed to 77 psi. An oxidation chamber converts traces of hydrocarbons into carbon dioxide and water. The air is then passed through a water separator, which gets some of the water out. A heat exchanger cools the sample down to very low temperatures, causing solid water and carbon dioxide to be separated from the main components. 

In 1839, H- Rose said that the ordinary commercial carbonate liquefied when slowly heated in a retort whereas, in 1870, E. Divers found scarcely any liquefaction. The older carbonate when distilled with anhydrous calcium chloride gave ammonium chloride, calcium carbonate, and carbon dioxide, whereas the newer carbonate gave in addition ammonium carbamate. The solubility of the newer carbonate is about twice as great as the old and the aq. soln. is not charged with carbon dioxide. R. Phillips and E. Divers have also reported as rare the occurrence of the hydrocarbonate in commercial carbonate. In consequence of these differences it is necessary to know whether the old or the new carbonate is in question when discussing the properties of the commercial carbonate. Sometimes the sesquicarbonate is to be understood. 

Preparation of Chlorine by Oxidizing Hydrochloric Acid with Potassium Permanganate. Liquefaction of the Chlorine. Assemble an apparatus as shown in Fig. 54. Spill 10-15 g of potassium permanganate into flask 1. Pour a 37 % hydrochloric acid solution into dropping funnel 2, a saturated sodium chloride solution into cylinder 5, and a little concentrated sulphuric acid into wash bottle 4. Put the end of the gas-discharge tube of the apparatus into test tube 5 cooled outside by solid carbon dioxide (dry ice) wetted with acetone. What is the boiling point of chlorine ... 

In the coal liquefaction process, scales and sludges, formed on the reactor walls, cause severe problems, which limit long operation. The crystal growth of chlorides and carbonates appears to trigger their formation, trapping the other solids. Hence major problems may come from cations, which react with carbon dioxide or chloride ions to form insoluble crystalline solids. The intrinsic solids may not initiate the problem. 

Purification of Air Prior to Liquefaction. Separation of air by cryogenic fractionation processes requires removal of water vapor and carbon dioxide to avoid heat exchanger freeze-up. Many plants today are using a 13X (Na-X) molecular sieve adsorbent to remove both water vapor and carbon dioxide from air in one adsorption step. Since there is no necessity for size selective adsorption, 13X molecular sieves are generally preferred over type A molecular sieves. The 13X molecular sieves have not only higher adsorptive capacities but also faster rates of C02 adsorption than type A molecular sieves. The rate of C02 adsorption in a commercial 13X molecular sieve seems to be controlled by macropore diffusion 37). The optimum operating temperature for C02 removal by 13X molecular sieve is reported as 160-190°K 38). 

In 1732, H, Boerhaave 11 tried without success to condense air to the liquid state by artificial cold and in 1850, J. Natterer likewise failed in an attempted liquefaction of air, although he compressed the gas under nearly 3000 atm. press. but in 1877, L. Cailletet obtained liquid air in the form of a mist by compressing dried air, freed from carbon dioxide, at the temp, of liquid nitrous oxide, and under 200-225 atm. press., and suddenly releasing the press. and in 1884, J. Dewar described a method of liquefying air cooled by means of liquid or solid nitrous oxide —vide 1. 13, 25. Various forms of apparatus have been devised for liquefying air... 

Liquefied natural gas (LNG) is a very clean fuel in that the few impurities present in natural gas (water vapor, hydrogen sulfide, carbon dioxide, particulates and foreign matter, etc.) are removed almost completely when the natural gas is liquefied. Liquefaction also removes most of the hydrocarbons heavier than propane so that the resulting fuel is 95-99% methane with the remainder being primarily ethane with a smaller amount of propane. The liquefaction process is so efficient at removing contaminants that it removes the odorant placed in natural gas for transmission over pipelines (natural gas odorants are primarily mer-captans which contain sulfur and are relatively large molecules). 

LNG is simple to re-gasify in order to deliver almost pure methane at the end users. In contrast to natural gas that contains typically around 90% methane, and some ethane, propane and heavier hydrocarbons, the liquefaction process involves pre-treatment of the gas in order to remove carbon dioxide, sulphur compounds, water, and petroleum gases with carbon number higher than one (butane, propane etc.). This is done in order to avoid formation of solids in the cold heat exchangers. The presence of nitrogen is usually limited at about 1% (refer Table 2 on page 81). 

Carbon forms two oxides - carbon monoxide (CO) and carbon dioxide (C02). Carbon dioxide is the more important of the two, and in industry large amounts of carbon dioxide are obtained from the liquefaction of air. Air contains approximately 0.03% by volume of carbon dioxide. This value has remained almost constant for a long period of time and is maintained via the carbon cycle (Figure 13.13). However, scientists have recentiy detected an increase in the amount of carbon dioxide in the atmosphere to approximately 0.04%. 

Low-temperature adsorption systems continue to find an increasing number of applications. For example, systems are used to remove the last traces of carbon dioxide and hydrocarbons in many air-separation plants. Adsorbents are also used in hydrogen liquefaction to remove oxygen, nitrogen, methane, and other trace impurities. They are also used in the purification of helium suitable for liquefaction (grade A) and for ultrapure helium (grade AAA, 99.999% purity). Adsorption at 35 K will, in fact, yield a helium with less than 2 ppb of neon, which is the only detectible impurity in helium after this treatment. 

Carbon dioxide produced from ethanol fermentation plants or landfill gas may be recovered with similar processes. Unique to the fermentation plant is the ability to recover the carbon dioxide directly from the ethanol distillation tower, followed by a secondary water wash. Final purification and liquefaction stages then follow the normal process flow. Landfill gas recovery is unique in requiring essentially the removal of the methane and trace impurities.7,17 Several processes exist to... 

The P-V Isotherms of Carbon Dioxide The importance of critical temperature of a gas was first discovered by T. Andrews in his experiments on pressure-volume relationships (isotherms) of carbon dioxide gas at a series of temperatures. The isotherms of carbon dioxide determined by him at different temperatures is shown in the figure given above. Consider first the isothermal at the lowest temperature, viz., 13.1 C. The point A represents carbon dioxide in gaseous state occupying a certain volume under a certain pressure. On increasing the pressure, its volume diminishes as is indicated by the curve AB. At B which represents a pressure of 49.8 atm, liquefaction of the gas commences and thereafter a rapid decrease in volume takes place at the same pressure, as more and more of the gas is converted into the liquid state. At C, the gas has been completely liquefied. Now, as the liquid is only slightly compressible, further increase of pressure produces only a very small decrease in volume. A steep line CD that is almost vertical shows this. 

The isotherm EFGH at 21.5 C shows a similar behaviour except that now the liquefication commences at a higher pressure and the horizontal portion FG, representing decrease in volume, becomes smaller. At still higher temperatures, the horizontal portion of the curve becomes shorter and shorter until at 31.1 C it reduces just to a point (represented by X). At this temperature, therefore, the gas passes into liquid state imperceptibly. Above 31.1 C, the isotherm is continuous. There is no evidence of liquefaction at all. Andrews concluded that if the temperature of carbon dioxide is above 31.1 C, it cannot be- liquefied, no matter how high the pressure may be. He called 31.1 C as the critical temperature of carbon dioxide. Since then, other gases have been... 

As has already been explained, it is necessary to cool a gas below its critical temperature before it can be liquefied. In the case of a gas like ammonia, chlorine, sulphur dioxide or carbon dioxide, which has a fairly high critical temperature the application of a suitable pressure alone is sufficient to cause liquefaction. Gases... 

At the temperatures plotted in figure 4.2, carbon dioxide does not liquefy. Only at temperatures below about 32°C will a C02-rich liquid form. This is in contrast to the isotherms that will be shown for hydrogen sulfide, which show a distinct break at the liquefaction point. 

Absorption of carbon dioxide in a suspension of lime and thermal coal liquefaction are examples of Type I reactions. In the first example, calcium carbonate is produced by carbonation of suspensions of lime, whereas, in the second example, coal is liquified in the presence of hydrogen and oil to produce a host of products. These and several other examples of this type of reaction are summarized in Table 1-1. 

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