CONTENTS 4 Azeotropes

ISO 4318 1989, Surface active agents and soaps Determination of water content—Azeotropic distillation method. 

Surface active agents and soaps—determination of water content-azeotropic distillation method 309/1998 ISO 4318/1989... 

Water content Karl Fisher (NF T 60-154) or Azeotropic distiilation (NFT 60113)... 

The water content of crude oils is determined by a standardized method whose procedure is to cause the water to form an azeotrope with an aromatic (generally industrial xylene). Brought to ambient temperature, this azeotrope separates into two phases water and xylene. The volume of water is then measured and compared with the total volume of treated crude. 

Hydrocarbons have, for the most part, replaced CFCs as propellants. Most personal products such as hair sprays, deodorants, and antiperspirants, as well as household aerosols, are formulated using hydrocarbons or some form of hydro-carbon—halocarbon blend. Blends provide customized vapor pressures and, if halocarbons are utilized, a decrease in flammabiUty. Some blends form azeotropes which have a constant vapor pressure and do not fractionate as the contents of the container are used. 

Another process employs a pH maintained at 4—7 and a catalyst that combines a divalent metal cation and an acid. Water is removed continuously by azeotropic distillation and xylene is recycled. The low water content increases the reaction rate. The dibenzyl ether groups are decomposed by the acid the yield of 2,2 -methylene can be as high as 97% (34). 

Even though the simple distillation process has no practical use as a method for separating mixtures, simple distillation residue curve maps have extremely usehil appHcations. These maps can be used to test the consistency of experimental azeotropic data (16,17,19) to predict the order and content of the cuts in batch distillation (20—22) and, in continuous distillation, to determine whether a given mixture is separable by distillation, identify feasible entrainers/solvents, predict the attainable product compositions, quaHtatively predict the composition profile shape, and synthesize the corresponding distillation sequences (16,23—30). By identifying the limited separations achievable by distillation, residue curve maps are also usehil in synthesizing separation sequences combining distillation with other methods. 

The latex can be concentrated by different means. One method consists of heating the latex under vacuum conditions to remove excess water and organic solvent by evaporation. In the case of an organic solvent forming azeotrope with water, the final concentration may be higher and the temperature of the treatment can be reduced. Using the concentrating treatment, the polymer content in the latex can be increased to 70% and the water content can be reduced to 2%. 

During the investigation of the principles governing the process of copolymerization of AN with ISP in DMSO at 30 °C in the presence of ammonium persulfate, it was established that the anisotropic type of copolymerization is characteristic for this pair of monomers. The azeotropic point, as it is seen from Fig. 1 corresponds to a content of 60% of monomeric units of ISP in the monomer mixture. 

Phenol-formaldehyde reactions catalyzed by zinc acetate as opposed to strong acids have been investigated, but this results in lower yields and requires longer reaction times. The reported ortho-ortho content yield was as high as 97%. Several divalent metal species such as Ca, Ba, Sr, Mg, Zn, Co, and Pb combined with an organic acid (such as sulfonic and/or fluoroboric acid) improved the reaction efficiencies.14 The importance of an acid catalyst was attributed to facilitated decomposition of any dibenzyl ether groups formed in the process. It was also found that reaction rates could be accelerated with continuous azeotropic removal of water. 

Normally in the production of diesters great effort is spent in obtaining high yields. Catalytic support of the esterification reaction and azeotropic distillation to remove reaction water yields diesters near 100% purity. The amount of unreacted educt material is usually very small. Following sulfation, in the presence of a hydrotrope to reduce viscosity, a 65% active content product with virtually no byproducts is obtained. 

D A solid insoluble in ethanol/ benzene azeotrope 25 Predominantly diaromatic and polynuclear perhaps combined through naphthenic bridges, with negligible aliphatic content. 

The Asahi process for wet-spinning the copolymer involves water dilution at below 0°C of a solution of the copolymer in aqueous 68 wt% nitric acid (the azeotropic composition). The potential for slow self heating and decomposition have been investigated experimentally with variations in several parameters in a Sikarex safety calorimeter. At 20% polymer content, the slow self heating starts even at ambient temperature, and later involves evolution of 30 mol of uncondensable gas per kg of copolymer with comcommittant boiling of the nitric acid. A 2 step mechanism has been proposed. 

Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic distillation with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality fn, calculated from Mjj and the content of OH groupSj determined by using excess phenyl isocyanate and titration of unreacted phenyl isocyanate with dibutylamine, was 2.78 the content of residual water was 0.02 wt.-%. For the Niax LG-56, 1 =2630, fn=2.78, and the content of H2O was 0.02wt.-%. The triols were reacted with recrystallized 4,4"-diphenylmethane diisocyanate in the presence of 0.002 wt.-% dibutyltin dilaurate under exclusion of moisture at 80 C for 7 days. The molar ratio r0H = [OH]/ [NCO] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60 C in nitrogen atmosphere. The relaxation was sufficiently fast and no extrapolation to infinite time was necessary. 

Ethanol balance The rate of change of the total content volume times the rate + rate of removal as azeotrope. 

The ethanol-water azeotrope (95%ethanol-5%water) is an example of a minimum boiling azeotrope. Its boiling point is lower than that of the components (Fig. 143). If you ve ever fermented anything and distilled the results in the hopes of obtaining 200 proof (100%) white lightning, you d have to content yourself with getting the azeotropic 190 proof mixture, instead. Fermentation usually stops when the yeast die in their own 15% ethanol solution. At room temperature, this is point A on our phase diagram. When you heat the... 

The copolymers tested preliminarily were of the statistical, azeotropic, and block type and the separation experiment was carried out by a concentration-gradient development, for which chloroform and ethyl acetate were used as the initial and second solvents, respectively. It was found that the block copolymers could hardly be developed under the condition which allowed the statistical copolymers to migrate, despite the fact that the block copolymers had higher styrene contents, hence, lower affinities to adsorbent, than the statistical copolymers. 

Ethanol (EtOH) [5h] Commercial products are pure enough for most purposes. The impurities are MeOH, PrOH, Ac, water, etc. In order to reduce 2000 ppm of water in absolute EtOH, about 5% of hexane or cyclohexane is added to the EtOH and the mixture is fractionated to remove the aqueous azeotrope. By this step, the water content is reduced to < 500 ppm. The dehydrated EtOH is then slowly passed through a column of dry molecular sieves (4A) to reduce the water content to 7 ppm. 

It is used for detg the DEtPh content by saponifiqation with KOH soln the alcohol liberated in the reaction is separated by azeotropic distillation and measured by means of iodometric analysis afte dichromate oxidation... 

Separation of the aromatics from each other and from other hydrocarbons by distillation is not economical because of the limited boiling-point differences and the formation of azeotropic mixtures. Instead, extractive or azeotropic distillation and liquid-liquid extraction are applied.234,235 The latter process is by far the most often used technique. The three processes are applied according to the aromatic content of the gasoline source. p-Xylene, the most valuable of the isomeric xylenes, is isolated by freezing (crystallization) or solid adsorption. 

Commercial Examples. The small but often undesirable contents of water dissolved in hydrocarbons may be removed by distillation. In drying benzene, for instance, the water is removed overhead in the azeotrope, and the residual benzene becomes dry enough for processing such as chlorination for which the presence of water is harmful. The benzene phase from the condenser is refluxed to the tower. Water can be removed from heavy liquids by addition of some light hydrocarbon which then is cooked out of the liquid as an azeotrope containing the water content of the original heavy liquid. Such a scheme also is applicable to the breaking of aqueous emulsions in crude oils from tar sands. After the water is removed... 

Ordinary rectification for the dehydration of acetic acid requires many trays if the losses of acid overhead are to be restricted, so that azeotropic processes are used exclusively. Among the entrainers that have been found effective are ethylene dichloride, n-propyl acetate, and n-butyl acetate. Water contents of these azeotropes are 8, 14, and 28.7 wt%, respectively. 

Formic acid can be dehydrated with propyl formate as entrainer. Small contents of formic acid and water in acetic acid can be entrained away with chloroform which forms binary azeotropes with water and formic acid but no other azeotropes in this system. 

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