Benzene-water dehydration

Azeotropic Distillation. The concept of azeotropic distillation is not new. The use of benzene to dehydrate ethyl alcohol and butyl acetate to dehydrate acetic acid has been in commercial operation for many years. However, it was only during World War II that entrainers other than steam were used by the petroleum industry. Two azeotropic processes for the segregation of toluene from refinery streams were developed and placed in operation. One used methyl ethyl ketone and water as the azeo-troping agent (81) the other employed methanol (1). 

Whereas compounds of type 345 are not known, the transient existence of tetraphenylthieno[3,4- ]furan (348) has been demonstrated. Sulfoxide 347 refluxed in acetic anhydride under nitrogen gave a pale violet color which was attributed to 348 in the presence of dimethyl acetylenedicar-boxylate a Diels-Alder adduct (349) was formed in 70% yield. 76-479 dehydration of 347 can also be effected by base treatment with hydroxide ion in benzene/water with a phase-transfer catalyst affords a deep-blue... 

Figure 3 shows the results obtained for the benzene-water system and compares these with the results from the benzene-water-hydrochloric acid system. The acid-free system exhibited the almost linear adsorption isotherm expected at low water concentrations, while the data from the acid system, although somewhat scattered, suggest that the adsorption capacity was increased when some HC1 was present. In any case, the feasibility of using Z200H to dehydrate the benzene-hydrochloric acid system was demonstrated, and justified embarking on regeneration and dynamic equilibrium test studies. 

Chloroform Formic acid Methanol Water Dehydrated alcohol Benzene Ether Freely soluble Freely soluble Freely soluble Freely soluble Sparingly soluble Practically insoluble insoluble... 

The dehydrator is a column with-about 30 trays, designed to separate the water from the phenol by heteroazeotropic distillation in the presence of benzene and feed-and make-up toluene. The benzene/water azeotrope (bplJ>13 69 C, water content 8.8 per cent weight) and toluene/water azeotrope (bpl013 = 84 Q water content 13.5 per cent weight) leaving at the top are cooled rod condensed to yiddjwo phases ... 

Monohydrate, prisms from water. Anhydrous leaflets from hot alcohol + chloroform, mp 152°. Freely sol in water, alcohol, ether insol in chloroform, benzene. Easily dehydrated to the lactone. Aq solns are stable. 

The potassium fluoride is heated for 24 h at 125°, then ground very fine and dried for a further 24 h in a vacuum drying oven at 150°. Larger amounts are dehydrated azeotropically with benzene after removal of the benzene-water mixture by distillation, a higher-boiling solvent (see below) is added and the residual benzene is distilled off. 

This two-tower system can be used to separate a number of binary systems, such as isobutanol-water, aniline-water, or benzene-water. In the last system the solubility of water in benzene is so low that a single-tower system is usually used for the dehydration of benzene,... 

Separation of alcohols, such as ethanol and butanol, from the fermentation broth is traditionally done by distillation. The higher the alcohol concentration in the fermentation broth, the lower the energy required for distillation. For ethanol fermentation, the broth usually contains 10-15% (w/w) ethanol. After distillation, ethanol concentration in the distillate is about 90% (w/w). The distillation process will not yield more than 93% (w/w) ethanol, which is the azeotropic mixture of ethanol-water. Azeotropic mixtures cannot be separated by distillation because the compositions of ethanol in the vapor and liquid phases are the same. Therefore, azeotropic distillation with benzene or dehydration with molecular sieves is usually used to remove the remaining water and produce fuel grade ethanol (99.9 wt-%). 

Place 24 ml. (24 5 g.) of aniline, 13 ml. (15 5 g.) of nitro-benzene,t and 62 ml. (75 g.) of the anhydrous glycerol in the flask and mix thoroughly. (If the glycerol is still warm from the dehydration, cool the mixture in water.) Now add slowly 36 ml. (66 g.) of concentrated sulphuric acid, shaking the mixture thoroughly during the addition. The mixture at first... 

Pinacol (tetramethylethyleneglycol). Pinacol hydrate may be dehydrated in the following manner (compare Section 11,39). Mix 100 g. of pinacol hydrate with 200 ml. of benzene and distil a mixture of water and benzene passes over. Separate the lower layer and return the upper layer... 

Amino-4-nitrophenol. This derivative, 2-hydroxy-5-nitroani1ine (9), forms orange prisms from water. These prisms are hydrated with one water of crystallization, mp 80—90°C, and can be dehydrated over sulfuric acid to the anhydrous form, mp 143 —145°C. The compound is soluble in ethanol, diethyl ether, acetic acid, and warm benzene and slightly soluble in water. 

Pyrrohdinone (2-pyrrohdone, butyrolactam or 2-Pyrol) (27) was first reported in 1889 as a product of the dehydration of 4-aminobutanoic acid (49). The synthesis used for commercial manufacture, ie, condensation of butyrolactone with ammonia at high temperatures, was first described in 1936 (50). Other synthetic routes include carbon monoxide insertion into allylamine (51,52), hydrolytic hydrogenation of succinonitnle (53,54), and hydrogenation of ammoniacal solutions of maleic or succinic acids (55—57). Properties of 2-pyrrohdinone are Hsted in Table 2. 2-Pyrrohdinone is completely miscible with water, lower alcohols, lower ketones, ether, ethyl acetate, chloroform, and benzene. It is soluble to ca 1 wt % in aUphatic hydrocarbons. 

Consider azeotropic distillation to dehydrate ethanol with benzene. Initial steady-state conditions are as shown in Fig. 13-108. The overhead vapor is condensed and cooled to 298 K to form two hquid phases that are separated in the decanter. The organic-rich phase is returned to the top tray as reflux together with a portion of the water-rich phase and makeup benzene. The other portion of the water-rich phase is sent to a stripper to recover organic compounds. Ordinarily, vapor from that stripper is condensed and recycled to the decanter, but that coupling is ignored here. 

Ethanol [64-17-5] M 46.1, b 78.3 , d 0.79360, d 0.78506, n 1.36139, pK 15.93. Usual impurities of fermentation alcohol are fusel oils (mainly higher alcohols, especially pentanols), aldehydes, esters, ketones and water. With synthetic alcohol, likely impurities are water, aldehydes, aliphatic esters, acetone and diethyl ether. Traces of benzene are present in ethanol that has been dehydrated by azeotropic distillation with benzene. Anhydrous ethanol is very hygroscopic. Water (down to 0.05%) can be detected by formation of a voluminous ppte when aluminium ethoxide in benzene is added to a test portion. Rectified... 

Merck and Maeder have patented the manufacture of arecaidine by loss of water from l-methyl-4-hydroxypiperidine-3-carboxylic acid. A method of producing the latter has been describd by Mannich and Veit and has been developed by Ugriumov for the production of arecaidine and arecoline. With the same objective, Dankova, Sidorova and Preobrachenski use what is substantially McElvain s process,but start by converting ethylene oxide, via the chlorohydrin and the cyanohydrin, into -chloropropionic acid. The ethyl ester of this with methylamine in benzene at 140° furnishes methylbis(2-carbethoxyethyl) amine (I) which on refluxing with sodium or sodium Moamyloxide in xylene yields l-methyl-3-carbethoxy-4-piperidone (II). The latter is reduced by sodium amalgam in dilute hydrochloric acid at 0° to l-methyl-3-carbethoxy-4-hydroxypiperidine (III) which on dehydration, and hydrolysis, yields arecaidine (IV R = H), convertible by methylation into arecoline (IV R = CH3). 

The water-insoluble salts such as Cs2,5Ho., iPWi204o efficiently catalyse dehydration of 2-propanol in the gas phase and alkylation of m-xylene and trimethyl benzene with cyclohexene this catalyst is much more active than Nafion-H, HY-zeolite, H-ZSM-5, and sulphated zirconia (Okuhara et al., 1992). 

Volkov (1994) has given a state-of-the-art review on pervaporation. A number of industrial plants exist for dehydration of ethanol-water and (.vwpropanol-water azeotropes, dehydration of ethyl acetate, etc. There is considerable potential in removing dissolved water from benzene by pervaporation. The recovery of dis.solved organics like CH2CI2, CHCI3, CCI4, etc. from aqueous waste streams also lends itself for pervaporation and pilot plants already exist. 

This procedure is a modification of preparations of 3-phen)d, sydnone described earlier. The dehydration of N-nitroso-N phenylglycine has also been effected by the use of thionyl chloride and pyridine in dioxane, thionyl chloride in ethertrifluoroacetic anhydride in etherand diisopropylcarbodiimide in water or by reaction of the alkali metal salts of N-nitroso-N-phenylglycine with phosgene or benzenesulfonyl chloride in water or with acetyl chloride in benzene. ... 

The shape-selectivity of ZSM-5 is particularly remarkable. Active centres at the inner walls of the catalyst readily release protons to organic reactant molecules forming carbonium ions, which in turn, through loss of water and a succession of C—C forming steps, yield a mixture of hydrocarbons that is similar to gasoline. The feedstock can be methanol, ethanol, corn oil or jojoba oil. The shape-selectivity of this catalyst is particularly striking, as can be seen from the product distribution obtained for the dehydration of three different alcohols (Table 8.2). The product distribution can be understood in terms of the intermediate pore size of ZSM-5, which can accommodate linear alkanes and isoalkanes as well as monocyclic aromatic hydrocarbons smaller than 1, 3, 5-trimethyl benzene. In Table 8.3, we list some of the recent innovations in catalysis, to highlight the important place occupied by molecular-sieve catalysts. 

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