Separation processes crystallisation

The result of any crystallisation process is a crystalline matter with a certain CSD, certain crystal habit and purity. These properties very often are quality requirements and well defined by market demands. Certainly, also the crystallisation process itself requires a minimum CSD, as the resulting suspension still has to be separated. This separation can be effected the more perfectly (purity) as more compact (crystal habit) and coarser (CSD) the crystals are. Quality and economy of the separation process crystallisation are therefore strongly dependent from crystal size, CSD and crystal habit. These properties also take influence to the storage ability, the dust-freeness and also the bulk density of the product. 

A.S. Myerson and K. Toyokura, Crystallisation as a Separation Process, ACS, Washington DC, 1990. ISBN 0841218641. 

All freeze separation processes depend on the formation of pure solvent crystals from solution, as described for eutectic systems in Section 15.2.1. which allows single-stage operation. Solid-solution systems, requiring multistage-operation, are not usually economic. Several types of freeze crystallisation processes may be designated according to the kind of refrigeration system used as follows . 

Thijssen and Spicer1 1191 has given a general review of freeze concentration as an industrial separation process and Bushnell and Eagen(63) have discussed the status of freeze desalination. The potential of freeze crystallisation in the recycling and re-use of wastewater has been reviewed by Heist 120, and the kinetics of ice crystallisation in aqueous sugar solutions and fruit juice are considered by Omran and King(121). 

The concept of process intensification does not need to apply to the whole of an API production process. There is merit in looking at hybrid reaction schemes, which retain the benefits of, or capital investment in, batch equipment but use continuous processes for the generation of hazardous intermediates [17] or for certain unit processes. Of these, hydrogenation [18], filtration [19], phase separation [20], crystallisation [21] and drying [22] are good examples. 

Sodium chlorate is produced by the electrolysis of a sodium chloride solution in an electrolyzer without a diaphragm, having an iron cathode and a magnetite or graphite anode. For the manufacture of potassium chlorate either the sodium chloride solution is used, or a mixed solution of both sodium and potassium chloride. The chlorate solution obtained will finally be converted with potassium chloride into potassium chlorate, which is separated by crystallisation while the mother liquor is returned to the electrolytic process. The potassium chloride solution will not be electrolyzed directly as potassium chlorate is sparingly soluble and the potassium chloride entrained in the chlorate crystals is not easy to remove. 

Mukhopadhyay M, Patel CR. Gas Antisolvent crystallisation at ambient temperature for enrichment of phytochemicals. Proceedings of the National Seminar and Workshop on Advanced Separation Processes, IIT-Kharagpur, India, August 2002. 

SFE must be seen within a group of separation processes which are well known, widely used, and sufficiently well understood. These processes comprise the various forms of distillation (rectification), evaporation, crystallisation, liquid- liquid extraction,... 

The isolation by bipolar electrodialysis was applicable and gave an alkali free product. The precipitation via hydrazones (see later) was conducted directly from the cultivation broth. In this way, the process was remarkably faster and simpler than separation and crystallisation prior to chemical reactions. Some more details are provided in Sect. 19.5.1. 

The separation of the solid phase does not occur readily with some liquid mixtures and supercooling is observed. Instead of an arrest in the cooling curve at /, the cooling continues along a continuation of c/ and then rises suddenly to meet the line f g which it subsequently follows (Fig. 1,13, 1, iii). The correct freezing point may be obtained by extrapolation of the two parts of the curve (as shown by the dotted line). To avoid supercooling, a few small crystals of the substance which should separate may be added (the process is called seeding ) these act as nuclei for crystallisation. 

The high sodium ion concentration results in facile crystallisation of the sodium salt. This process of salting out with common salt may be used for recrystallisation, but sodium benzenesulphonate (and salts of other acids of comparable molecular weight) is so very soluble in water that the solution must be almost saturated with sodium chloride and consequently the product is likely to be contaminated with it. In such a case a pure product may be obtained by crystallisation from, or Soxhlet extraction with, absolute alcohol the sul-phonate is slightly soluble but the inorganic salts are almost insoluble. Very small amounts of sulphones are formed as by-products, but since these are insoluble in water, they separate when the reaction mixture is poured into water ... 

Sodium bicarbonate precipitates from solution and is recovered by filtration. Ammonium chloride is then crystallised from the filtrate, separated, washed, and dried. The exact proportion of ammonium chloride recovered depends on the relative demands for sodium carbonate and ammonium chloride. If economic conditions requite, part of the ammonia can be recovered and returned to the hrine-ammoniation step by distillation of the ammonium chloride solution ia the presence of lime. The spent calcium chloride Hquor, a final product ia manufacture of sodium carbonate by the ammonia—soda process, can also be used to obtain ammonium chloride. This Hquor is treated with ammonia and carbon dioxide... 

The ammonium sulfate and sodium chloride are simultaneously dissolved, preferably ia a heel of ammonium chloride solution. The sodium chloride is typically ia excess of about 5%. The pasty mixture is kept hot and agitated vigorously. When the mixture is separated by vacuum filtration, the filter and all connections are heated to avoid cmst formation. The crystalline sodium sulfate is washed to remove essentially all of the ammonium chloride and the washings recycled to the process. The ammonium chloride filtrate is transferred to acid resistant crystallising pans, concentrated, and cooled to effect crystallisation. The crystalline NH Cl is washed with water to remove sulfate and dried to yield a product of high purity. No attempt is made to recover ammonium chloride remaining ia solution. The mother Hquor remaining after crystallisation is reused as a heel. 

Tanks are used in innumerable ways in the chemical process iadustry, not only to store every conceivable Hquid, vapor, or soHd, but also ia a number of processiag appHcations. For example, as weU as reactors, tanks have served as the vessels for various unit operations such as settling, mixing, crystallisation (qv), phase separation, and heat exchange. Hereia the main focus is on the use of tanks as Hquid storage vessels. The principles outlined, however, can generally be appHed to tanks ia other appHcations as weU as to other pressure-containing equipment. 

There are essentially four steps or unit operations in the manufacture of fatty acids from natural fats and oils (/) batch alkaline hydrolysis or continuous high pressure hydrolysis (2) separation of the fatty acids usually by a continuous solvent crystallisation process or by the hydrophilisation process (J) hydrogenation, which converts unsaturated fatty acids to saturated fatty acids and (4) distillation, which separates components by their boiling points or vapor pressures. A good review of the production of fatty acids has been given (1). 

Thebaine, CjgHgiOgN. This base, which occurs in opium to the extent of 0-1 to 1 per cent., was first obtained by Pelletier and Thiboumery, who regarded it as isomeric with morphine, and named it paramorphine. It was examined by Kane, who first called it thebaine, and by Anderson, who described a method of isolation and provided the formula given above. It remains in the mother liquor after the removal of morphine and eodeine hydrochlorides in Gregory s process, and in Hesse s method of isolating it from this source is obtained as the acid tartrate. This is crystallised from hot water, and the alkaloid regenerated from it is reerystallised from dilute alcohol, from which it separates in leaflets, or from dry alcohol in prisms, m.p. 193°, — 218-6° (EtOH) or — 229-5°... 

This formula was confirmed hy Haworth and Perkin s synthesis of a-flZZocryptopine from herherine, the first application of a process, of which examples have heen given already in the syntheses of cryptopine (p. 298) and protopine (p. 301) hy the same authors. Anhydrotetrahydromethyl-herherine (I cf. hase (a), p. 346) in dry chloroform was added to a solution of perhenzoic acid in ether cooled helow 5°. The amine oxide, C21H23O5N (II), separated as an oil, which after shaking with sodium hydroxide solution, solidified and was crystallised from water in slender prisms, m.p. 135°. It was dissolved in acetic acid, hydrochloric acid added, the mixture heated in boiling water for an hour and the hase precipitated hy addition of potassium hydroxide. The precipitate was dissolved in methyl alcohol, ether added, the alcohol washed out with water and the ethereal... 

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