Distillative purification

Hydrogenation of the nitrobenzene Separation of the reactor products by condensation Recovery of crude aniline by distillation Purification of the crude nitrobenzene Recovery of aniline from waste water streams... 

Most of the terephthalic acid is produced with a catalyst system developed by Scientific Design. It was purchased by Amoco and Mitsui and is referred to as the Amoco Oxidation. The solvent is acetic acid. Compressed air is used as the source for oxygen. The catalyst dissolved in acetic acid and the two reactants are continuously fed into the reactor. The temperature is around 200 °C and the pressure is approximately 25 bar. The reaction is very exothermic (1280 klrnoT1, calculation from data in Stull et al [16] often a much higher, erroneous value is cited). This heat of reaction is removed by evaporation/condensation of acetic acid and can be used in the solvent distillation/purification part of the plant. A scrubber washes the vent gases... 

General Procedure for Preparation of Triazones 5a-f. 264 mg (3 mmol) /V,/V-di-metliylurea, 1 g paraformaldehyde, 3 mmol primary amine 4a-f and 2 g montmorillonite K-10 were irradiated by microwave in a Teflon vessel. The reaction mixture was filtered and washed with water. The organic phase was separated and dried with Na2S04 and concentrated by vacuum distillation. Purification of the... 

A solution of 4-formyloxy-3-hydroxy-l-butene (1.06 g, 10 mmol) and propionic acid (1 drop) in triethylorthoacetate (6 g, 40 mmol) was heated at 140°C under conditions for distillative removal of ethanol. After 2 hours, the excess of ethylorthoacetate was removed by distillation in vacuo. The residue was hydrolysed with water and extracted with AcOEt. The product was purified by flash chromatography on Si02 (eluant AcOEtihexane, 2 8) (1 g, 60%) but distillative purification is preferred when larger quantities are involved. 

Task Distillation Purification Separation Recovery Distillation... 

Attempted catalytic hydrogenation of oxime E,Z-25 ended up with significant amounts of ring-opened compounds hampering distillative purification of the desired compound rac-26. 

N 13.72% ndls, mp 112° sol in ale eth. It was prepd by reacting ethylene diamine with ethyl chloroformate and vacuum distillation purification. Its heat of combstn is 1066kcal/mol heat of formation 231kcal/nol at const vol. 

The RO process was implemented at the Institute of Atomic Energy, Swierk. The wastes collected there, from all users of nuclear materials in Poland, have to be processed before safe disposal. Until 1990 the wastes were treated by chemical methods that sometimes did not ensure sufficient decontamination. To reach the discharge standards the system of radioactive waste treatment was modernized. A new evaporator integrated with membrane installation replaced old technology based on chemical precipitation with sorption on inorganic sorbents. Two installations, EV and 3RO, can operate simultaneously or separately. The membrane plant is applied for initial concentration of the waste before the evaporator. It may be also used for final cleaning of the distillate, depending on actual needs. The need for additional distillate purification is necessitated due to entrainment of radionuclides with droplets or with the volatile radioactive compounds, which are carried over. 

In the dry process, introduced by Allied Chemical Corp., the uranium concentrate is pelletized and directly reduced with hydrogen to uranium(IV) oxide at temperatures between 540 and 650°C in a fluidized bed reactor. Hydrofluorination to uranium(IV) fluoride proceeds in two fluidized bed reactors connected in series. After fluorinating the uranium(IV) fluoride formed in a production unit consisting of a flame-reactor and a fluidized bed reactor, the uranium(Vl) fluoride produced is purified in a two stage pressure distillation process. This distillative purification process is necessary, because, in contrast with the wet process, no purification is carried out in earlier stages. 

While the nonvolatile character of IL is a major advantage over conventional solvents, it is a limitation due to the impossibility of purifying ILs by distillation. Purification can be thus a significant challenge. 

Acid-catalyzed reaction of lb with acetone and simultaneous azeotropic removal of water provides diethyl (27 ,3i )-2,3-0-isopropylidenetartrate 3 in 82—83% yield after distillative purification [3]. However, it has been reported that upon application of this method in petroleum ether as solvent, significant racemate formation was observed [4]. The preferred method for the preparation of 3 involves a transketalization reaction of lb with 2,2-dimeth-oxypropane under acidic catalysis. The yield is nearly quantitative with no loss of optical integrity [5]. 

Tetrahydrofuran forms explosive mixtnres with air within the range 2.0-11.8% by volume in air. It is susceptible to form organic peroxides when exposed to air or light. Severe explosion can occur during distillation, purification, or use of impure tetrahydrofuran. Solvent containing peroxide can explode when dried with caustic soda or caustic potash, or when evaporated and may catch Are in contact with lithium aluminum hydride or other metal hydrides. Violent reactions can occur when combined with strong oxidizers. 

A crude lactide stream produced in the lactide synthesis reactors contains lactic acid, lactic acid oligomers, water, meso-lactide, and further impurities. Two main separation methods, distillation and crystallization, are currently employed for lactide purification. Crystallization may be carried out either by solvent crystallization or melt crystallization. The most used method for production of ultra-pure lactide in laboratory is by repeated recrystallization of a saturated lactide solution in mixtures of toluene and ethyl acetate [15, 23, 24]. Lactide purification using C4-12 ethers [25], and an organic solvent that is immiscible with water to extract the solution with water [26] are also reported. Melt crystallization is more practical in industry for lactide purification. Several types of equipment are described in the literature for melt crystallization [17, 27-30]. This method uses the differences in the melting points of L-, D-, and meso-lactide for separating the different lactides from each other. In a distillation process, the crude lactide is first distilled to remove the acids and water, and then meso-lactide is separated from lactide [11, 31]. Different methods are reported in the literature for distillation purification of lactide [32, 33]. In... 

In general, aldehydes are more volatile, toxic, or unstable than their corresponding alcohols. And if these are used without previous distillation/purification, the presence of other byproducts could affect not only the real concentration of the active aldehyde in the reaction, but the impurities could also interfere in the course of the reactions reacting with other species present in the process. For this reason, the use of alcohols, with their subsequent oxidation, instead of the corresponding aldehydes is an interesting improvement in this and in other MCRs, and it would widen significantly the versatility and scope of the aldehyde-based MCRs [57]. 

Pyran di- and monoethyl esters 4 and 26 presented their own particular challenges because they are liquids. Purification by distillation is an obvious yet challenging solution, but was made workable by carefully controlling the impurities arising from the reaction of 2-chloroethyl ether with diethyl malonate. Eventually, direct production of the monoester 26 without isolation of 4 or distillative purification was achieved (figure 12). 

Preparative Methods acetic anhydride is prepared industrially by the acylation oi Acetic Acid with Jfetene. A laboratory preparation of acetic anhydride involves the reaction of sodium acetate and Acetyl Chloride followed by fractional distillation. Purification adequate purification is readily achieved by fractional distillation. Acetic acid, if present, can be removed by refluxing with CaC2 or with coarse magnesium filings at 80-90 °C for 5 days. Drying and acid removal can be achieved by azeotropic distillation with toluene. ... 

Patel N. R., V. E. Lewis, and M. D. Enderson, Method for removal of aldehydes fiom chenucal manufacturing production streams during distillative purification, U.S. Patent 6,074,532 (2000). 

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