Calcium hydroxide system

Following the initial steps of hydration (Reaction 1) and formation of calcium sulfite (Reaction 2), removal of SO2 in the lime or calcium hydroxide system depends on the formation of calcium bisulfite by reaction of suspended calcium sulfite with sulfur dioxide and water (Reaction 3). 

Sulfate scaling is generally more prevalent in the calcium carbonate system than in the calcium hydroxide system because more sulfate is formed. The calcium hydroxide system reaches steady state below the saturation value of calcium sulfate. 

Calcium Hydroxide System. A Ca( OH )a system is undergoing startup testing at Louisville Gas and Electric Co., Paddy s Run No. 6, on a 70 MW pulverized coal-fired boiler. This system uses carbide sludge, a waste calcium hydroxide material, as the additive for reducing SO2 emissions. The utility is obtaining the carbide sludge from a local industrial firm which produces large quantities of it in the manufacture of acetylene. 

Unha.iring, Unhairing can be done either by a hair save or a hair pulp system. The hair pulp system is preferred by most tanners for its speed and labor efficiency. In the hair pulp system the hides are treated with sodium sulfide (sulfhydrate) and lime (calcium hydroxide). The hair is quickly destroyed by the strong alkaline reducing conditions. 

Calcium Peroxide. Pure calcium peroxide [1305-79-9] Ca02, has been prepared, but the commercial product is a mixture made by reaction of calcium hydroxide and hydrogen peroxide. Commercial material contains either 60 or 75% Ca02 the remainder is a poorly defined mixture of calcium oxide, hydroxide, and carbonate. A well-defined octahydrate [60762-59-6] 8H20, can be crysta11i2ed from aqueous systems. 

The second most common alkalinity control agent is lime [1305-78-8] normally in the form of calcium hydroxide [1303-62-0], used in both water and oH muds. In the latter, the lime reacts with added emulsifiers and fatty acids to stabHi2e water-in-oH emulsions. Lime is used in brine systems containing substantial quantities of soluble calcium and in high pH lime muds. Concentrations are ca 6—57 kg/m (2—20 lb /bbl) (see Lime AND LIMESTONE). 

Reactions of the Side Chain. Benzyl chloride is hydrolyzed slowly by boiling water and more rapidly at elevated temperature and pressure in the presence of alkaHes (11). Reaction with aqueous sodium cyanide, preferably in the presence of a quaternary ammonium chloride, produces phenylacetonitrile [140-29-4] in high yield (12). The presence of a lower molecular-weight alcohol gives faster rates and higher yields. In the presence of suitable catalysts benzyl chloride reacts with carbon monoxide to produce phenylacetic acid [103-82-2] (13—15). With different catalyst systems in the presence of calcium hydroxide, double carbonylation to phenylpymvic acid [156-06-9] occurs (16). Benzyl esters are formed by heating benzyl chloride with the sodium salts of acids benzyl ethers by reaction with sodium alkoxides. The ease of ether formation is improved by the use of phase-transfer catalysts (17) (see Catalysis, phase-thansfer). 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

In this system, the least soluble component is sodium bicarbonate, so this crystallizes out. On calcination it yields sodium carbonate and the carbon dioxide is recycled. The ammonia is recovered by adding calcium hydroxide, producing calcium chloride waste and liberating the... 

NRS [New Regeneration System] A process for regenerating the ion-exchange resin used for removing calcium from sugar solution. If sodium chloride were used, the waste calcium chloride solution would have to be disposed of if sodium hydroxide were used, calcium hydroxide would be precipitated in the resin. The NRS process uses sodium hydroxide in the presence of sucrose, which retains the calcium in solution as calcium saccharate. Developed by the IMACTI Division of Duolite International, The Netherlands. 

In the production of caustic soda by the action of calcium hydroxide on sodium carbonate, 1 kg/s of sodium carbonate is treated with the theoretical quantity of lime. The sodium carbonate is made up as a 20 per cent solution. The material from the extractors is fed to a countercurrent washing system where it is treated with 2 kg/s of clean water. The washing thickeners are so arranged that the ratio of the volume of liquid discharged in... 

Softening removes hardness using chemical precipitation. The two major chemicals used are calcium hydroxide and sodium carbonate, thus no priority pollutants will be introduced into the system. 

Outside this, a zone of perhaps 10 to 30 m thickness, which, in reasonably well-hydrated systems, is largely occupied by relatively massive calcium hydroxide crystals, with occasional interruptions of more porous regions. 

Calcium carbonate is used to buffer acidic soils. In soils that contain sulfuric acid calcium carbonate, it will react with the acid to produce calcium sulfate (CaS04), carbon dioxide, and water H SO., + CaCO.M —> CaSO., + CCU + H.O... The ability ofvari-ous limes to neutralize acid in a soil is given in terms of calcium carbonate equivalents. In this system, limestone has a calcium carbonate equivalent of 100. If a slaked lime (calcium hydroxide) has a calcium carbonate equivalent of 150, then only two-thirds as much of slaked lime would be needed to achieve the same neutralizing effect. Calcium carbonate... 

When this is done, the calcium hydroxide is included in the melting furnace slag, and the unspent calcium carbide is either used or oxidized in the melting furnace. Little testing has been done to determine the actual fate of the sulfur. Most of it may be included in the slag, but it may also be emitted to the air as sulfur dioxide, or, for foundries with wet emission control systems, it may be dissolved in the water. 

Retention characteristics and elution order of carotenoid cis-trans isomers with C30-bonded phases are strikingly similar to those obtained with normal-phase systems using calcium hydroxide columns (190). Different carotenoids exhibit varying retention behavior in response to temperature changes for C30 and C34 polymeric stationary phases as compared with a Cl8 polymeric phase (179). These behaviors are believed to be related to conformational changes in the longer stationary phases with temperature. The slot model proposed for the retention of planar... 

The initial step was to study systems with reverse solubility curves to learn the general pattern of the onset of scaling which would be of value for understanding the sea water system. Calcium sulfate, lithium carbonate, sodium sulfate, and calcium hydroxide have reverse solubility curves in water, are readily available, and are soluble to an extent that neither visual observation of scale nor chemical analysis would be a problem. 

Sax (Ref 10) compares Ca silicide to calcium hydroxide as a skin, eye and respiratory system irritant, and to the silanes as a great fire and explosion hazard. Ingestion of Ca silicide may cause death or permanent injury after very short exposure to small quantities... 

Although the basic processes using lime (calcium hydroxide) and soda ash (sodium carbonate) to soften water by precipitating insoluble hardness salts have been known for 200 years, they are still relevant today. Many large industrial cooling systems around the world use lime-soda-softened makeup water, especially in some newly industrializing countries, where local water supplies may be particularly hard and the economics favor this process rather than, say, ion exchange. 

Von Getler et al. [23] were the first to consider these processes during spray absorption drying when they examined the material system of SO2 and Ca(OH)2. In the opinion of these authors, the absorption of sulfur dioxide is limited either by the dissolution of solid or by the gas-phase mass transfer in the first drying period of the drop. The product of this reaction causes substantial diffusion resistance for the absorbed sulfur dioxide and thus obstructs further reactions as the calcium hydroxide remains in the core. 

Investigations of absorption in liquid-sprayed gas-solid fluidized beds in the context of these investigations are limited to the material system of sulfur dioxide, air, and calcium hydroxide suspension. Here, the calcium hydroxide represents the reactants necessary in the liquid for the shifting of the equilibrium. 

A preliminary design of the hydroxide to hydride regeneration system was analyzed to identify process stream conditions and to allow the major equipment components to be sized such that a capital equipment cost could be developed. One of the major benefits of this system is that hydrogen is produced as part of the process. This hydrogen is then contacted with the lithium metal later in the process to make lithium hydride. The system is shown in Figure 10. The analysis was conducted for both lithium hydroxide and calcium hydroxide regeneration. 

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