Chloride removal disadvantages

The original Regitz procedure for diazo transfer to a -keto ester (131) used p-toluenesulfonyl azide (132 equation 54). This reagent works well, and is easy to prepare from the corresponding sulfonyl chloride. A disadvantage of this reagent is that the p-toluenesulfonylamide coproduct (134), as well as any excess p-toluenesulfonyl azide, have to be removed from the product diazo ketone (133) before it can be used. 

The condensing steam turbine has a relatively low thermal efficiency because about two-thirds of the steam enthalpy is lost to cooling water in the condenser. Expensive boiler feedwater treatment is required to remove chlorides, salts, and silicates, which can be deposited on the blades causing premature failure. The blades are already under erosion conditions because of water drops present in the condensing steam. Even with these disadvantages, the condensing turbine is still selected, especially in a process that requires very large compressor drivers and relatively low amounts of process steam. 

A major disadvantage of the Wacker chemistry using chloride catalysts is the production of chlorinated byproducts such as chloroethanal. These have to be removed since they are toxic and cannot be allowed in the wastewater. In the small recycle loop the catalyst solution is heated to 160 °C which leads to decomposition of chlorinated aldehydes under the influence of the metal chlorides. The traces going over the top in the gas/liquid separator have to be removed from the wastewater by different means. The toxicity inhibits biodegradation. Chlorine free catalysts have been studied but have not (yet) been commercialised. 

Zinc dust is frequently covered with a thin layer of zinc oxide which deactivates its surface and causes induction periods in reactions with compounds. This disadvantage can be removed by a proper activation of zinc dust immediately prior to use. Such an activation can be achieved by a 3-4-minute contact with very dilute (0.5-2%) hydrochloric acid followed by washing with water, ethanol, acetone and ether [/55]. Similar activation is carried out in situ by a small amount of anhydrous zinc chloride [156 or zinc bromide [157 in alcohol, ether or tetrahydrofuran. Another way of activating zinc dust is by its conversion to a zinc-copper couple by stirring it (180g) with a solution of 1 g of copper sulfate pentahydrate in 35 ml of water [/55]. 

In aqueous acetic acid, the disproportionation of the platinum still occurs quite rapidly, and it can be suppressed further by adding mineral acid. Hydrochloric acid is often used, but this has a disadvantage in that the exchange rate is inversely proportional to the chloride ion concentration. Perchloric acid has been found to be more satisfactory (55). The platinum(II) catalyst most used is sodium or potassium tetrachloropla-tinate(II). An aromatic compound added to the reaction mixture also inhibits disproportionation of the platinum(II) complex—benzene, pyrene, and other aromatics have been used. A comparative study of the effect of various aromatics on the H—D exchange in alkanes has been carried out (55). Even under optimum conditions, the disproportionation [Eq. (4)] still takes place, and the catalytic platinum(II) is slowly removed from the reaction mixture. To get useful rates of exchange in alkanes, temperatures of 100° to 120°C have to be used, and the disproportionation rate increases with temperature. 

The methods using sulfur(IV) species have some disadvantages as pH decreases, such as handling difficulties and high cost. Removal of chlorine residues with ammonia and chloro-aminines have harmful effects on aquatic environments and have other unpleasant properties, such as obnoxious odor, dechlorination odor, etc. Therefore, a method for reduction of chlorine to chloride using metallic iron in chlorine solutions has been studied by Ozdemir and Tufekci (1997). Chlorine solutions were prepared from chlorine obtained either by NaCl electrolysis or commercially. The chlorine solution in water was mixed at 20°C in a temperature-controlled bath. The experi-... 

To minimize hydrolysis of the propylene oxide (b.p. 34.2°C) as it is formed, it is flashed (rapidly removed) from the reactive lime slurry. Yields of propylene oxide are 75% or better based on propylene. The advantage of the chlorohydrin route to propylene oxide over the two hydroperoxidation processes is that it yields essentially a single product to market. The disadvantage is the large quantities of coproduced aqueous calcium chloride that has to be discarded safely. The small amount of by-product 1,2-dichloropropane may be pyrolyzed to allyl chloride, useful for the preparation of allyl monomers, allyl alcohol, and allylamines. Or it may be blended with 1,3-dichloropropene to produce an effective soil fumigant. 

As can be seen from the chromatogram in Fig. 3-55, a baseline separation between fluoride, acetate, and formate is obtained with this eluent. However, this method has only limited applicability for routine analyses. Ions such as chloride, nitrate, and sulfate have much longer retention times under these chromatographic conditions, which may lead to interferences with subsequent analyses. Therefore, the separator column must be flushed occasionally with carbonate solution of the concentration c = 0.1 mol/L to remove ions that are strongly retained at the stationary phase. However, the relatively long time required for the subsequent reconditioning of the separator column with the tetraborate eluent, which takes at least one to two hours, is a disadvantage. 

The main disadvantages of this phosgene process are 1) The high toxicity and corrosiveness of phosgene 2) The use of copious amounts of methylene chloride solvent (10 times the weight of the product) This solvent is water soluble, so it contaminates the wash water and 3) The complex cleanup to remove ionic materials. 

Chlorides are removed from water with a carbon adsorbent. The carbon particle diameter is 0.2 cm, the viscosity and density of water are 0.8 cP and 1 g/cm, respectively, and the diffusion coefficient of the chlorides in water is 2.37 x 10" cm /s. Calculate the mass transfer coefficient and bed diameter to treat 125,000 cm /s water for superficial velocities of 5, 10, 25, 100, 250 cm/s. Explain the disadvantage of increasing the superficial velocity. 

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