Solvent azeotropic water removal

Total cost = 0.63 for 2.25 lb material = 0.63/2.26 lb = 0.28/lb The above calculations are based on a theoretical molecular weight of 1000 with prices of bulk monomer quantities taken from CMR, February 27, 1978, resulting in a total material cost for the final product of 0.28/lb. (RMC phthalic anhydride, 0.26/lb RMC ethylene glycol, 0.25/lb). Manufacture is by simple fusion cook or solvent azeotropic water removal. 

The polymer can be synthesized from 4,4 -difluorobenzophenone bis-phenol A and 4 -hydroxy phenyl-4-hydroxybenzoate. NMP and toluene are used as a solvent and for azeotropic water removal. The condensation is conducted at 155°C for 8 h using a Dean-Stark trap. In the final stage of condensation, the toluene is drained and the temperature is increased to 190°C. 

Utilizing a new water trap that contains a 4-A molecular sieve, Zhu et al. (2003) synthesized PBS with of 24,800 after polycondensation for 70 h with SnCl as a catalyst and dimethyl benzene as the solvent and water-removing agent. (Ishii et al. (2001) reported one-step synthesis of PBS by distannoxane-catalyzed polymerizafion of succinic acid and butanediol in a two-phase system of solvent (decalin) and molten polymer under azeotropic conditions at atmospheric pressure. When the reaction time was extended to 72 h in the presence of 0.001 mol% of l-chloro-3-hydroxy-l,l,3,3-tetrabutyldistannoxane, PBS with of 117,(XX) and of 277,(XX) was obtained. Sun et al. examined the effect of different catalysts, such as SnCl, Ti(OiPr), Ti(OBu), Sn(Oct)2, Zn(Ac)j, and p- toluenesulfonate (p-TS), on the molecular weight of solution-polymerized PBS. Among these catalysts, SnCl showed the most promising result PBS with the highest of 79,(XX) was observ after reaction for 12 h. 

Dilution of urine with acetonitrile, azeotropic distillation for water removal, evaporation of solvent, redissolution in acetone and derivatization using pentafluorobenzyl bromide. 

The checkers found that the residue after removal of solvent contained water, which they removed azeotropically with toluene. Subsequent incomplete removal of the toluene led to amounts of stannane greater than theoretical. 

A solution of 11.28 g (40 mmol) of (2S,3S,5S)-2,5-diamino-l,6-diphenyl-3-hydroxyhexane and 4.88 g (40 mmol) of phenylboric acid in 1 liter of toluene was refluxed and the water azeotropically removed with the aid of a Dean Stark trap until the distillate was clear. The solvent was then removed in vacuo to provide the crude desired compound which was used immediately without further purification. 

The impact of electron donor ligands in NdX3-systems has already been discussed in Sect. 2.1.1.1. ligands such as alcohols, trialkyl phosphates, alkyl sulfoxides, alkyl amides, THF, N-oxides, pyridine etc. are added in order to facilitate water removal from NdCl3 6H20 by azeotropic distillation and in order to increase solubility and activity of NdCl3-based catalyst systems in organic solvents. 

Water and often fine sand and silt are held in various crude oils in permanent emulsions. Particularly crudes obtained by secondary methods and those from tar sands where water or steam are used contain water and mineral matter emulsified therein by the surface forces on small particles and drops. Azeotropic distillation removes the relatively small amount of water, using the solvent as an entrainer which dilutes the crude. This allows the mineral matter to be separated easily without using centrifuges with their substantial cost and wear, free of organic material, so it may be discarded with-out hazards of fire or odors the bitumen to be recovered for such use or cracked to give volatile fractions and coked to an ash-free coke the water to be obtained as distilled water for reuse. 

In step-growth polymerizations with unfavorable values of K, it is therefore standard practice to operate at high temperatures and reduced pressures to remove the condensation products. This is typical of the manufacture of linear polyesters where the final stages of the polymerization are at pressures near I mm Hg and temperatures near 280 C. Alkyds (Section 5.4.2) are branched polyesters produced by esterification reactions of mixtures of polyhydric alcohols and acids with varying functionalities. They are used primarily in surface coatings. Alkyd syntheses are completed at temperatures near 240°C. It is not necessary to reduce the pressure to pull residual water out of the reaction mixture, because the final products are relatively low-molecular-weight fluids that are diluted with organic solvents before further use. In one process variation, a small amount of a solvent like xylene is added to the reactants to facilitate water removal by azeotropic... 

Water is the compound most commonly removed by azeotropic distillation on scale, and some examples are presented in Chapters 5 and 6. Removing water by azeotroping is a convenient operation on scale to reach strictly anhydrous conditions, which may be key for running the reaction or for crystallizing the product. Excellent references are available to describe azeotropes of solvents with water and other compounds [38, 39]. In general, small, unlike molecules form azeotropes, as shown in Table 4.6. 

Reducing distillation pressure can reduce the portion of the minor azeotropic component for some solvents. As shown in Table 4.7, by dropping the distillation pressure from 760 mm to 25 mm the amount of water removed in EtOAc drops by more than 50%. If reducing the pressure results in no azeotrope, these conditions are said to break the azeotrope. Reducing the distillation pressure does not always decrease the proportion of the minor component in the azeotrope, as shown in Table 4.7 for the i-PrOH-11,0 azeotrope. 

Spent solvents nearly always contain some water. Dehydration is an essential step in their recovery, but is difficult because most polar solvents form azeotropes with water. Final water removal by distillation is... 

In an extractive distillation the attraction between the solvent and one or more of the components in the mixture is necessary whereas a repulsion between the entrainer and one or more components in the mixture is required for an azeotropic distillation. For example advantage is taken of the highly repulsive forces that develop between benzene and water, when benzene is used as the entrainer to separate a mixture of ethanol-water. This repulsion results in an immiscible pair. However, when the same mixture is separated by an extractive distillation, ethylene glycol is used as the solvent. Water is attracted to the solvent and is removed with it from the bottom of the tower. 

Water can also be removed from ammonium salts by heating them in high-boiling inert solvents, the water being continuously removed as azeotrope. Nitrobenzene and xylene have been used for this purpose. Formylations occur relatively readily and for formylation of, e.g., jV-methylaniline it suffices to use boiling toluene.691... 

The solvent process uses about 10 per cent of a water-immiscible solvent in the reaction mixture. This solvent promotes better control by reducing the viscosity and provides a good means of water removal by azeotropic distillation. 

Solvent Process. In the solvent process, or solvent cook, water formed from the reaction is removed from the reactor as an azeotropic mixture with an added solvent, typically xylene. Usually between 3 to 10 wt % of the solvent, based on the total charge, is added at the beginning of the esterification step. The mixed vapor passes through a condenser. The condensed water and solvent have low solubiUty in each other and phase separation is allowed to occur in an automatic decanter. The water is removed, usually to a measuring vessel. The amount of water collected can be monitored as one of the indicators of the extent of the reaction. The solvent is continuously returned to the reactor to be recycled. Typical equipment for this process is shown in Figure 2. The reactor temperature is modulated by the amount and type of refluxing solvent. Typical conditions are ... 

This may be offset in economic terms by the fact that almost aU useful azeotropes in solvent recovery are low boiling. As a result, they reduce the temperature difference over the condenser and hence reduce its capacity. Thus, to use perchloroethylene to dehydrate DMF at atmospheric pressitre requires 781 cal/g of water removed at a column top temperature of 83.5 °C whereas ordinary fractionation might need 950 cal/g at 100 °C. With cooling water at 20 °C the load on the condenser would be harder to handle for the lower heat input. 

The azeotrope formed by water and diethyl ether is single phase. Unlike ethanol and several other solvents which have single-phase water azeotropes, it is impracticable to form a low-boiling ternary azeotrope to remove water because the boiling point of diethyl ether is so low that the condensing of any such system would be very difficult. 

Organic solvents are used for a variety of purposes in the chemical industry, e.g. for synthesis of pharmaceuticals, to precipitate materials from aqueous solutions, for cleaning purposes, and for drying of final products. Spent solvents nearly always contain some water. Dehydration is an essential step in their recovery but difficult since most of the more common solvents form azeotropes with water. Final water removal by distillation is then impossible or complicated. Conventional entrainer distillation is not a real option for pharmaceutical or fine-chemical production. The addition and afterwards removal of the entrainer is difficult and the residual concentration will have to be monitored continuously. Furthermore, entrainer distillation systems require a certain minimum capacity to be economical. Quite often this capacity is above the amount of solvent that will have to be treated at a single location. The only solution is then in many cases to ship out the spent solvent and buy fresh one, with all the related problems of logistics and storage. 

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