Caustic purification system

Fig. 38. Caustic purification system a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feed pumps e, ammonia feed preheater f, extractor g, trim heater h, ammonia subcooler i, stripper condenser j, anhydrous ammonia storage tank k, primary flash tank 1, evaporator reboiler m, evaporator n, caustic product transfer pumps o, purified caustic product cooler p, purified caustic storage tank q, ammonia stripper r, purified caustic transfer pumps t, overheads condenser u, evaporator v, evaporator vacuum pump w, aqueous storage ammonia tank x, ammonia scmbber y, scmbber condenser 2, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

Caustic Purification System, OxyTech Systems, Inc., Chardon, Ohio, 1988. 

ELTECH Systems Corporation Caustic Purification System 1985. 

Even though most chemical purification methods are not carried out at low temperatures, they are useful in several cryogenic gas separation systems. Ordinarily water vapor is removed by refrigeration and adsorption methods. However, for small-scale purification, the gas can be passed over a desiccant, which removes the water vapor as water of crystallization. In the krypton-xenon purification system, carbon dioxide is removed by passage of the gas through a caustic, such as sodium hydroxide, to form sodium carbonate. 

Finding an economic method to continuously reuse 90 to 95 percent of an acid will (1) reduce incoming chemical consumption (for the factory), (2) reduce the cost to process parts (fewer rejects), (3) provide better quality control, and (4) reduce the chemicals (for example, caustic soda) required to neutralize the spent acid before discharge. Eliminating the need to handle spent acids will decrease the exposure of hazardous materials to employees and will reduce the wastewater treatment burden. This type of bath purification system may eliminate the need to dump selected concentrated wastes. 

The liquid ammonia absorbs salt, chlorate, carbonate, water, and some cau.stic. It is then stripped, concentrated, and returned to the extraction process. The concentrated caustic leaving the extractor is stripped free of ammonia, which is recovered, concentrated, and recirculated. Typical purities before and after caustic purification are shown in Table 20. This process is offered for license by PPG Industries and OxyTech Systems. 

The purification of the liquid alkylate from the reaction system is done in a conventional fashion (Figure 5). Before feeding the crude ethylbenzene to distillation, the aluminum chloride and the residual HCl must be completely removed. Water washing accomplishes most of this task final traces are removed by a caustic soda treatment. This process is completely reliable, is free from emulsion formation, and there is no downstream fouling or corrosion to worry about. 

Water, after the preliminary treatment methods of Section 12.4.1, can be called purified. Here, we use the term to refer to the higher levels of purification in Table 12.1 or to those processes which remove dissolved contaminants. In the chlor-alkali process, the major uses of purified water are dilution of catholyte, processing of membrane-cell caustic liquor, preparation of ion-exchange system regenerants, manufacture of hydrochloric acid, acidification of brine, and, sometimes, dissolving of salt. It also serves as utility and seal water in the membrane preparation area and in certain parts of the process. 

A commercial installation that uses jet scrubbers in combination with packed columns to remove hydrochloric acid vapors from the exhaust gas of a chemical manufacturing plant is described by Papamarcos (1 0). A schematic diagram of this installation is shown in Figure 6-19. The jet scrubbers are designated Jet Venturis by the manufacturer, Croll-Reynolds Co. Inc. however, they are not venturi scrubbers. The system consists of two jet scrubbers in series which use water to recover 98% of the HCl, followed by two short packed columns in series which use a dilute caustic solution for final purification to about 2... 

The principal source of chlorine-containing gas in caustic-chlorine plants is the liquefaction step where noncondensables are vented from chlorine condensers as sniff gas containing 30 to 40% chlorine by weight. Dilute gas may be collected at other points in the operation this gas also requires purification before it can be vented to the atmosphere. A number of processes have been developed to recover the chlorine from the vent-gas streams, including its use for the manufacture of bleach. Where the demand for bleach does not justify this operation, a regenerative recovery system is neces.sary, and one of the simplest of these involves absorption in water. The absorption of chlorine gas in water is also an important step in the manufacture of certain types of wood pulp. In this application, the process is intended primarily to provide a source of concentrated bleaching solution however, design data which have been obtained for the absorption step are equally applicable to gas-purification or chlorine-recovery operations. 

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