Dow Process

Dow process The process for the extraction of magnesium from sea-water by precipitation of Mg(OH)2 by Ca(OH)2 followed by solution of the hydroxide in hydrochloric acid. 

Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

The Huron-Dow Process. The Huron-Dow (H-D) process is a refinement of the cathodic reduction of oxygen in an alkaline electrolyte yielding low strength hydrogen peroxide directiy. Earlier attempts reHed on neutralizing the excess caustic or forming insoluble metal peroxides (92). The two reactions involved are... 

The main benefit of the Dow process was control of the polymer architecture. The polymer from the self-condensation process possessed a linear stmcture, but there were other difficulties. The monomer was cosdy and removal of the cuprous bromide by-product was difficult (17) ultimately, scale-up difficulties terrninated the Dow PPS development. However, there was a growing recognition that PPS was an attractive polymer with an excellent combination of properties. 

Figure 5 illustrates a typical distillation train in a styrene plant. Benzene and toluene by-products are recovered in the overhead of the benzene—toluene column. The bottoms from the benzene—toluene column are distilled in the ethylbenzene recycle column, where the separation of ethylbenzene and styrene is effected. The ethylbenzene, containing up to 3% styrene, is taken overhead and recycled to the dehydrogenation section. The bottoms, which contain styrene, by-products heavier than styrene, polymers, inhibitor, and up to 1000 ppm ethylbenzene, are pumped to the styrene finishing column. The overhead product from this column is purified styrene. The bottoms are further processed in a residue-finishing system to recover additional styrene from the residue, which consists of heavy by-products, polymers, and inhibitor. The residue is used as fuel. The residue-finishing system can be a flash evaporator or a small distillation column. This distillation sequence is used in the Fina-Badger process and the Dow process. 

More recent process research aimed at anionic PS is that of BASF AG. Unlike the Dow Process, the BASF process utilizes continuous linear-flow reactors (LFR) with no back-mixing to make narrow polydispersity resins. This process consists of a series alternating reactors and heat exchangers (Fig. 22). Inside the reactors, the polymerization exotherm carries the temperature from 30°C at the inlet to 90°C at the outlet. The heat exchangers then take the temperature back down to 30°C. This process, which requires no solvent, results in the formation of narrow polydispersity PS. 

Cesium Halides. Cesium bromide, [7787-69-1], CsBr, mol wt 212.82, theoretical cesium content 62.45%, is a colorless crystalline soUd, having a melting point of 636°C, a specific gravity of 4433 kg/m, and a solubUity of 1.23 kg/L of water at 25°C. It is usuaUy prepared by neutrali2ing the carbonate or hydroxide with HBr, but it is also the primary product of the Dow process (25) for poUucite processing. 

The bulk of commercial styrene is prepared by the Dow process or some similar system. The method involves the reaction of benzene and ethylene to ethylbenzene, its dehydrogenation to styrene and a final finishing stage. It is therefore useful to consider this process in each of the three stages. 

Other routes for the preparation of phenol are under development and include the Dow process based on toluene. In this process a mixture of toluene, air and catalyst are reacted at moderate temperature and pressure to give benzoic acid. This is then purified and decarboxylated, in the presence of air, to phenol (Figure 23.5). 

Phenol was manufactured for many years by the Dow process, in which chlorobenzene reacts with NaOH at high temperature and pressure (Section 16.S). Now, however, an alternative synthesis from isopropylbenzene, commonly called... 

FIGURE 12.12 A schematic representation of the electrolytic cell used in the Dow process for magnesium. The electrolyte is molten magnesium chloride. As the current generated by the external source passes through the cell, magnesium ions are reduced to magnesium metal at the cathode and chloride ions are oxidized to chlorine gas at the anode. 

Dow Process Developments. The Dow technology is taught in a large number of U.S. patents. Those by McDonald et al (26), Ruffing (27), and Finch ( ) are good illustrations of this series of developments as is the summary by Amos 2). ... 

The Dow process consists of the formation of an acid-terminated soft segment, first by the esterification of polyoxyalkylene or other glycol, followed by the reaction of a diisocyanate and additional diacid to form PESA. 

Huntsman solvent-based collection and refining system, 15 506 Huron-Dow process, 14 42, 53 Huygens principle, 17 424 H values, 23 284 Hyaluronan, 20 577 Hyaluronic acid, 4 706 20 456 classification by structure, 4 723t function as ingredient in cosmetics, 7 829t... 

As a result, the second-generation processes used rhodium as the metal. The first rhodium-catalysed, ligand-modified process came on stream in 1974 (Celanese) and more were to follow in 1976 (Union Carbide Corporation) and in 1978 (Mitsubishi Chemical Corporation), all using triphenylphosphine (tpp). The UCC (now Dow) process has been licensed to many other users and it is... 

Similarly, Dow has entered into a joint venture agreement with Dom-tar of Canada to operate what the companies hope will be by 1990 a self-sustaining PET and HDPE recycling business. The North American company is expected to take postconsumer plastics and, using a proprietary Dow process, convert them into resins for use in Domtar s manufacturing or to be sold by Dow. 

The Dow Process utilizes an elimination/addition reaction to convert chlorobenzene to phenol. The proposed mechanism for this reaction is shown in Figure 8-3. The high-temperature reaction begins with chlorobenzene and aqueous sodium hydroxide. Note that this mechanism starts with the hydroxide attacking as a base, beginning dehydrohalogenation to form benzyne. The second hydroxide ion attacks as a nucleophile to form a carbanion intermediate, which behaves as a base in the last step to yield the final product. 

Liquid-phase oxidation of toluene to benzoic acid (Dow process,980,985,986 Mid-Century process987) may be carried out in acetic acid or without solvent. Cobalt(II) naphthenate or cobalt(II) 2-ethylhexanoate promoted by bromine is used as the catalyst at 140-190°C, at about 8-10 atm pressure. The highly exothermic oxidation is... 

Figure 12.18 shows the layout of an electrolytic cell used for the commercial production of magnesium metal from molten magnesium chloride (the Dow process). As in a galvanic cell, oxidation occurs at the anode and reduction occurs at the cathode, electrons travel through the external wire from anode to cathode, cations move through the electrolyte toward the cathode, and anions move toward the anode. But unlike the spontaneous current in a galvanic cell, a current must be supplied by an external electrical power source. This current drives electrons through the wire in a predetermined direction (Fig. 12.19). The result is...

Dow process The electrolytic production of magnesium from molten magnesium chloride. 

In time of war the industries of a country strive to produce as much toluene as possible. The effort results in the production also of increased quantities of other aromatic hydrocarbons, particularly of benzene, and these become cheaper and more abundant. Every effort is made to utilize them profitably for military purposes. As far as benzene is concerned, the problem has been solved through chlorobenzene, which yields aniline and phenol by the Dow process, and hence picric acid, and which gives dinitro-chlorobenzene on nitration which is readily convertible, as will be described later, into picric acid and tetryl and several other... 

Steam and silica gel to produce phenol from chlorobenzene, the Dow process with steam and a copper salt catalyst, etc. 

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