Carbon dioxide absorption process

As examples of micro-channel process intensification and the respective equipment, in particular gas/liquid micro reactors and their application to toluene and various other fluorinations and also to carbon dioxide absorption can be mentioned [5]. Generally, reactions may be amenable to process intensification, when performed via high-temperature, high-pressure, and high-concentration routes and also when using aggressive reactants [5]. 

CATACARB [Catalyzed removal of carbon dioxide] A process for removing carbon dioxide and hydrogen sulfide from gas streams by absorption in hot potassium carbonate solution containing a proprietary catalyst. Developed and licensed by Eickmeyer and Associates, KS, based on work at the U.S. Bureau of Mines in the 1950s. More than a hundred plants were operating in 1997. See also Benfield, Carsol, Hi-pure, Giammarco-Vetrocoke. 

Using an industrial oxidation reaction and carbon dioxide absorption in aqueous alkaline solutions, it was validated in some sets of process conditions that such pilot reactors show similar performance as their... 

The specimen and reaction mixture are placed in the reaction vessel, which is attached to a reflux condenser. Heat is then applied and the onset of boiling in the reaction mixture is taken as the start of the process. Periodically thereafter, carbon dioxide absorption tubes are removed from the train and replaced by tubes of known weight. Some experiments have been conducted19 in which the reflux mixture was brought to a boil and the test specimen thereafter introduced through a side tube in the reaction flask. This procedure insures that the reaction period... 

The CNG process removes sulfurous compounds, trace contaminants, and carbon dioxide from medium to high pressure gas streams containing substantial amounts of carbon dioxide. Process features include 1) absorption of sulfurous compounds and trace contaminants with pure liquid carbon dioxide, 2) regeneration of pure carbon dioxide with simultaneous concentration of hydrogen sulfide and trace contaminants by triple-point crystallization, and 3) absorption of carbon dioxide with a slurry of organic liquid containing solid carbon dioxide. These process features utilize unique properties of carbon dioxide, and enable small driving forces for heat and mass transfer, small absorbent flows, and relatively small process equipment. 

The CNG acid gas removal process is distinguished from existing AGR processes by three features. The first feature is the use of pure liquid carbon dioxide as absorbent for sulfurous compounds the second feature is the use of triple-point crystallization to separate pure carbon dioxide from sulfurous compounds the third feature is the use of a liquid-solid slurry to absorb carbon dioxide below the triple point temperature of carbon dioxide. Pure liquid carbon dioxide is a uniquely effective absorbent for sulfurous compounds and trace contaminants triple-point crystallization economically produces pure carbon dioxide and concentrated hydrogen sulfide for bulk carbon dioxide absorption the slurry absorbent diminishes absorbent flow and limits the carbon dioxide absorber temperature rise to an acceptable low value. The sequence of gas treatment is shown in Figure 1, an overview of the CNG acid gas removal process. 

The absorption of carbon dioxide with slurry and the regeneration of slurry by flashing carbon dioxide require small temperature and pressure driving forces. The small driving forces derive from the huge surface area of the solid carbon dioxide particles and the low viscosity of the slurry. Compared with other sub-ambient temperature carbon dioxide removal processes, the CNG process requires less refrigeration even though process temperatures are often lower. 

For carbon dioxide absorption, the heat of absorption could provide the heat required to desorb the carbon dioxide. The system would be adiabatic. However, the only effective solvent is the alkaline carbonate to bicarbonate reaction - The Benfield Process. ... 

The Selectoxo process (Engelhard) reduces the hydrogen consumption of the methanation system, as well as the inert gas content of the purified synthesis gas fed to the synthesis loop. After low-temperature shift conversion, the cooled raw gas is mixed with the stoichiometric quantity of air or oxygen needed to convert the carbon monoxide to carbon dioxide. The mixture is then passed through a precious-metal catalyst at 40-135 °C to accomplish this selective oxidation [740]-[743], The carbon dioxide formed by the Selectoxo reaction adds only slightly to the load on the downstream carbon dioxide absorption system. 

It should also be noted that absorption has been used to remove contaminants from natural gas streams during processing. In the early 1930s di-ethanolamine was used as an absorbent for both hydrogen sulfide and carbon dioxide.This process became known as the Gerbitol Process. Other alkanolamines such as mono-ethanolamine and di-isopropanolamine have also found wide application. 

The carbon dioxide absorption via nondispersive manbrane contactors has been investigated by many researchers in the past years. Besides the analysis of the effect of different parameters on the efficiency of the process, like operating temperatures and stream flow rates, type and concentration... 

The process requires a large amount of fuel to calcine both the limestone and sodium bicarbonate and to generate steam for ammonia recovery. For the reaction proper, no fuel is required. In fact, large volumes of cooling water are required to remove the heat generated by the absorption and reaction of ammonia and carbon dioxide. The process has an imperfection in that an undesirable solution of calcium chloride also is produced. 

Use of heat downstream of the low temperature shift converter for absorption refrigeration which is used in the ammonia recovery section. In conventional plants this low level heat is used for reboiling in the carbon dioxide removal process. 

Several revamp options are available for modification of the carbon dioxide removal section depending on the type of carbon dioxide removal process. The processes mostly used in ammonia plants are chemical absorption processes based on either hot potassium carbonate (HPC) such as Benfield, or Vetrocoke, or amine solutions such as MEA. The chemical carbon dioxide removal processes may be improved or replaced with a physical process in which the absorbent is regenerated by simply flashing off carbon dioxide. In this way the need for regeneration heat may be reduced or eliminated. A physical carbon dioxide removal system may result in energy savings of 0.01-0.35 Gcal/MT ammonia. 

Chapter 9 deals with developments in the application of MCs and the associated improvements in membrane fabrication to overcome current limitations due to membrane wetting problems, which lower the efficiency of mass transfer and reduce membrane life. There are numerous advantages of MCs over conventional methods for carbon dioxide absorption and stripping technology such as their compacmess and high effective surface area per unit volume. MCs have also been developed for treatment of aqueous systems and they offer a combined membrane separation and absorption process in one physical setting. 

Example 17.3-1 Carbon dioxide absorption with amines In many industrial processes, carbon dioxide must be removed from a gas mixture. This removal is frequently accomplished by scrubbing with aqueous solutions of pH 8 to 10 containing compounds like... 

Anhydrous lithium hydroxide [1310-65-2], LiOH, is obtained by heating the monohydrate above 100°C. The salt melts at 462°C. Anhydrous lithium hydroxide is an extremely efficient absorbent for carbon dioxide (qv). The porous stmcture of the salt allows complete conversion to the carbonate with no efficiency loss in the absorption process. Thus LiOH has an important role in the removal of carbon dioxide from enclosed breathing areas such as on submarines or space vehicles. About 750 g of lithium hydroxide is required to absorb the carbon dioxide produced by an individual in a day. 

Early Synthesis. Reported by Kolbe in 1859, the synthetic route for preparing the acid was by treating phenol with carbon dioxide in the presence of metallic sodium (6). During this early period, the only practical route for large quantities of sahcyhc acid was the saponification of methyl sahcylate obtained from the leaves of wintergreen or the bark of sweet bitch. The first suitable commercial synthetic process was introduced by Kolbe 15 years later in 1874 and is the route most commonly used in the 1990s. In this process, dry sodium phenate reacts with carbon dioxide under pressure at elevated (180—200°C) temperature (7). There were limitations, however not only was the reaction reversible, but the best possible yield of sahcyhc acid was 50%. An improvement by Schmitt was the control of temperature, and the separation of the reaction into two parts. At lower (120—140°C) temperatures and under pressures of 500—700 kPa (5—7 atm), the absorption of carbon dioxide forms the intermediate phenyl carbonate almost quantitatively (8,9). The sodium phenyl carbonate rearranges predominately to the ortho-isomer. sodium sahcylate (eq. 8). 

Conversion Processes. Most of the adsorption and absorption processes remove hydrogen sulfide from sour gas streams thus producing both a sweetened product stream and an enriched hydrogen sulfide stream. In addition to the hydrogen sulfide, this latter stream can contain other co-absorbed species, potentially including carbon dioxide, hydrocarbons, and other sulfur compounds. Conversion processes treat the hydrogen sulfide stream to recover the sulfur as a salable product. 

Lime-Kiln Operation. Gases containing up to 40% carbon dioxide from the lime kiln pass through a cyclone separator, which removes the bulk of entrained dust. The gas is then blown through the two scmbbers, which remove the finer dust, cooled, and passes iato an absorption tower. Here carbon dioxide may be recovered by the sodium carbonate or Girbotol process. 

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