Alkali materials

Semidry Scrubbers The advantage of semidry scrubbers is in that they remove contaminants by way of a solid waste that is easier to dispose of (less expensive). Initially, the scrubbing medium is wet (such as a lime or soda ash slurry). Then a spray dryer is used to atomize the slurry into the gas which evaporates the water in the droplets. As this takes place, the acid in the gas neutralizes the alkali material and forms a fine white solid. Most of the white solids are removed at the bottom of the scrubber while some are carried into the gas stream and have to be removed by a filter or electrostatic precipitator (discussed later). Although semidry systems cost 5-15% more than wet systems, when combined with a fabric filter, they can achieve 90-95% efficiencies. Dry scrubbers are sometimes used in a very similar fashion, but without the help of gas-liquid-solid mass transfer, these systems use much higher amounts of the solid alkali materials. 

Fluoride-free acid cleaners are finding their way into the general pretreatment cleaning of aluminium as an alternative to strong alkali materials. 

Sulphur vulcanisation of rubber is catalysed by the presence of alkali materials. This activation of the vulcanisation system can result in unwanted short scorch times. The addition of weak acids to the rubber compound results in retardation of the crosslinking mechanism. The common materials used for retardation are... 

The need to remove alkali material from the biogas stream depends on the end use for the gas. Problems associated with alkali vapor formation and deposition are critical in systems where the hot biogas is to be used without significant cool-down. Moderate gas cooling followed by removal of bulk particulates provides adequate cleaning for simple boiler systems that can tolerate some ash deposition. Other applications such as gas turbines require cleaner fuel gases. Since turbines operate at high rotational speeds, deposition can... 

Since cyclone filters can operate at elevated temperatures, the sensible heat in the product gas can be retained. Cyclone filters also remove condensed tars and alkali material from the gas stream, although the vaporized forms of those constituents remain in the gas stream. In practice, the separation of significant amounts of tars from the gas stream may be done sequentially by first removing particulates at higher temperatures, where tars remain vaporized. The gas stream is then cooled and condensed tars are removed. The step-wise approach reduces the tendency of particulate material to stick to tar-coated surfaces and contribute to plugging. 

Yong et ah [175] developed an effective omeprazole buccal adhesive tablet with excellent bioadhesive force and good drug stability in human saliva. The omeprazole buccal adhesive tablets were prepared with various bioadhesive polymers, alkali materials, and croscarmellose sodium. Their physicochemical properties, such as bioadhesive force and drug stability in human saliva, were investigated. The release and bioavailability of omeprazole delivered by the buccal adhesive tablets were studied. As bioadhesive additives for omeprazole tablet, a mixture of sodium alginate and hydroxypropylmethyl cellulose was selected. The omeprazole tablets prepared with bioadhesive polymers alone had bioadhesive forces suitable for a buccal adhesive tablet, but the stability of omeprazole in human saliva was not satisfactory. Magnesium oxide is an alkali stabilizer for omeprazole buccal adhesive tablets. Croscarmellose sodium enhanced the release of omeprazole from the tablets but it decreased the bioadhesive forces and stability of omeprazole tablets in human saliva. 

Alkali. Material containing peroxides should not be dried with KOH or NaOH because explosions may occur.5... 

A hydroxide or carbonate of an alkali metal (e.g., lithium, sodium, potassium, etc), the aqueous solution of which is characteristically basic in chemical reactions. The term may be extended to apply to hydroxides and carbonates of barium, calcium, magnesium, and the ammonium ion. The term alkali should be viewed in relation to the terms corrosive, bases and acids. The EPA defines corrosivity in terms of pH (i.e., wastes with pH <2 or 2.5) or in terms of ability to corrode steel (SAE 20) at a rate of > 6.35 mm (0.250 in.) per year at a temperature of 55° C (13° F). This discussion will address corrosivity as it applies to acids and caustics (i.e., alkali materials). Acids are compounds that yield H ions (actually HjO " ions) when dissolved in water. Common industrial acids include acetic, nitric, hydrochloric, and sulfuric acids. The terms concentrated and dilute refer to the concentrations in solution. Mixing a concentrated acid with enough water will produce a dilute acid. For example, a bottle of concentrated HCl direct from the manufacturer is approximately 12N in HCl, while a solution of HCl used in a titration may be only 0.5N. The latter is a dilute acid solution. 

There is thus very little independent production of chlorine and the principal alkalis, NaOH and KOH. The inability of producers to vary the nearly constant ratio of chlorine to alkali is a constant problem to the industry. Market conditions from time to time make it important to separate some of the production. Plants dedicated to chlorine or sodium hydroxide then may appear. The processes involved in these plants also have great historical interest, and therefore most of this chapter is dedicated to them. Section 15.2 covers the production of chlorine, and Section 15.4 covers the production of caustic soda. Section 15.3 recognizes the separate importance of hypochlorites. These require the combination of chlorine with an alkali material and are not examples of the independent manufacture of the two. However, their major use is as latent sources of chlorine, and they are considered members of the active chlorine family [2], Their characteristic use in sanitation or bleaching depends on the fact that the chlorine in the hypochlorite group is in the -1-1 oxidation state and is a strong oxidizer. 

Sailors are at risk of acute chemical burns from direct contact with strong acids and alkalis. Materials used in the construction, repair, and painting of the ships can cause allergic contact dermatitis. The main allergens are oil, fuels, paints, solvents, lacquers, glues, and phenol-formaldehyde resins (Shaposhnikov 1973). 

In a semidry scrnbbing system, the solntion or slurry is dispersed by nozzles or rotary atomization systems into a fine cloud of droplets.These droplets are brought into contact with a hot gas stream (and herein lies a disadvantage to semidry scrubbing systems) that proceeds to evaporate the water in the droplets. As the water evaporates, the acids in the gas stream react with the alkali material in the drying droplets and neutralize them, forming a fine powder. Most of this powder is removed from the bottom of the spray dryer, while the remainder is entrained in the gas stream and carried out to either a fabric filter or an electrostatic precipitator (ESP). 

Munson JR, Bertram BE, CaldweU JD (The Dallas Group of America, Inc.). 1995. Treatment of Cooking Oils and Fats with Magnesium Silicate and Alkali Materials. US Patent 5597600. 

Additions such as silica and quartz are used to make this special hot pressed carbon more alkali resistant. Normally, alkali materials such as sodium and potassium react with normal carbon to form damaging lamellar compounds that swell, causing volume expansion and spalling of the carbon. However, these alkali materials react preferentially with the silica addition in hot pressed carbon and form compounds that do not swell, avoiding damaging volume expansion or spalling. 

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