Precipitation crystallization

Phthalonitrile. In a 1 litre round-bottomed flask, provided with a reflux condenser, place 100 g. of phthalamide and 350 ml. of acetic anhydride. Reflux for 5-6 hours. Add the reaction product whilst still hot cautiously to 700 ml. of boiling water this decomposes the excess of acetic anhydride. Cool in ice, and then render the reaction mixture alkaline with sodium hydroxide solution. Filter ofiF the precipitated crystals at the pump, wash with water, and dry at 100°. The yield of the crude nitrile is 70 g. After one or two recrystallisations from benzene, the m.p. should be 141°—that of pure phthalonitrile. It is usually best to distil the crude nitrile under reduced pressure (Figs. II, 19, 3-4) the distillate has m.p. 137-138°, and the m.p. is raised to 141° after one recrystallisation from benzene. 

Precipitation. The precipitation of aluminum tribydroxide ia the recovery step of the Bayer process is achieved either by loweting the temperature or by diluting the pregnant Hquor and reduciag its pH. Both methods reverse the direction of equation 35, but seeding with previously precipitated crystals is required ia order to initiate nucleation. 

In the United States and some European countries, beet-sugar-waste molasses, or Stefen s waste, has been used as raw material for MSG production. The 2-pyrrohdinone-5-carboxyhc acid [98-79-3] contained ia beet sugar as by-product, is hydrolyzed at weakly alkaline pH, and moderate temperature (eg, pH 10.5—11.5, at 85°C for 2 h) to avoid racemization (14). The pH of the hydrolyzate is adjusted to 3.2 with a mineral acid to precipitate crystals of L-glutamic acid. The L-glutamic acid crystals obtained are transformed to MSG as described above. 

The color obtained is a function of both the composition and the particle size of the precipitated crystals. A redder color results from both increased selenium to sulfur ratio and from larger crystals, caused by a more severe heat treatment. Hence, it is possible to make, from the same glass, a series of color filter types, by controlled reheating. 

Figure 8.26 Monte Carlo simulation of MSMPR precipitated crystal agglomerate specific surface area Hostomsky and Jones, 1993a)...

Jones, A.G. and Teodossiev, N.M., 1988. Microcomputer programming of dosage rate during batch precipitation. Crystal Research and Technology, 23, 957-966. 

To a solution of 2.5 g of 3-ethoxy-16/3-ethylestra-3,5-diene-17/3-ol dissolved in 50 ml of methanol is added 1.2 ml of concentrated hydrochloric acid, followed by stirring for 10 minutes. The reaction solution is poured into 250 ml of water. The precipitated crystals are collected by filtration and recrystallized from ether to give 2.3 g of 16/3-ethyl-17/3-hydroxy-estra-4-en-one melting at 152°Cto 153°C. 

Additional purification of the product and improvement of particle size and shape can be achieved by re-ciystallization. The process consists of sequential dissolutions of potassium heptafluorotantalate in appropriate solutions at increased temperatures, filtration of the solution to separate possible insoluble parts of the product and cooling of the filtrated solution at a certain rate. The precipitated crystals are filtrated, washed and dried to obtain the final product. Re-crystallization can be performed both after filtration of the preliminary precipitated salt or after drying if the quality of the product is not sufficient. HF solutions of low concentrations are usually used for re-ciystallization. In general, even water can be used as a solvent if the process is performed fast enough. Nevertheless, practical experience suggested the use of a 30—40% HF solution within the temperature interval of 80-25°C, and a cooling rate of about 8-10°C per hour. The above conditions enable to achieve an acceptable process yield and good performance of the product. 

Precipitation/Crystallization to Produce Nano- and Microparticles Because fluids such as C02are weak solvents for many solutes, they are often effective antisolvents in fractionation and precipitation. In general, a fluid antisolvent may be a compressed gas, a gas-expanded liquid, or a SCF. Typically a liquid solution is sprayed through a nozzle into CO2 to precipitate a solute. As CO2 mixes with the liquid phase, it... 

The formation of the solid phase (nucleation, precipitation, crystal growth, biomineralization) ... 

Due to the great similarity of the chemical properties of the rare earth elements, their separation represented, especially in the past, one of the most difficult problems in metallic chemistry. Two principal types of process are available for the extraction of rare earth elements (i) solid-liquid systems using fractional precipitation, crystallization or ion exchange (ii) liquid-liquid systems using solvent extraction. The rare earth metals are produced by metallothermic reduction (high purity metals are obtained) and by molten electrolysis. 

The role of the ammonium salt anion is not the loading of the amphipathic weak base per se, but rather to control the stability of loading and the profile and rate of release of the amphipathic weak base from the liposome to the external aqueous phase. Two major factors that differentiate the different anions are, firstly, their ability to induce precipitation/crystallization/ gelation in the intraliposome aqueous phase (1,12), and secondly, their effect on the membrane/buffer and octanol/buffer partition coefficient of the amphipathic weak base (1). Regarding the precipitation, the higher the amount of precipitated amphipathic weak base, the more stable is the loading and the slower is its release rate (10-12,18,33,35) and (Wasserman et al.). There are also some risks involved in the precipitation which in some cases reduce the mechanical stability of the liposomes and change liposome shape (36). 

Generation of products —evaporation, electrowinning, precipitation, crystallization... 

Controlled crystallization preferred over precipitation Crystallizations used to upgrade key intermediates Minimal dilution, to minimize Vniax and increase productivity Exotherms and gas evolution liability worse with scale-up Cryogenic or very high temperatures require specialized equipment... 

Nitro-pentammino-chromic Chloride, [Cr(NH8)5X02]Cl2, is prepared from ehloro-pentammino-chromic chloride by heating it for a short time with water acidified with nitric acid, allowing the mixture to cool slowly, and filtering off the undissolved ehloro-pentammino-salt. The filtrate, which contains aquo-pentammino-ehromic salt, is decomposed with sodium nitrite and a 12 per cent, solution of hydrochloric acid after a few minutes the precipitate formed is collected, washed with water, dissolved in water, and filtered into a strong solution of ammonium chloride. The precipitated crystals are collected, washed with water and alcohol, and obtained as yellow octahedral prisms.-The salt, which is soluble in water, decomposes on heating with hydrochloric acid, giving chloro-pentammino-salt.3... 

Why does the intensity of the solution s colour change Filter off the precipitated crystals through a Buchner funnel. What is contained in the mother solution ... 

Transfer the contents of the bowl into a beaker and cool it in a bath with ice. Filter out the precipitated crystals in a Buchner... 

When the reaction has terminated, filter off the precipitate and evaporate the solution in a bowl on a water bath until a film forms. What is the composition of the precipitated crystals Cool the solution to 0 °C, filter oH the crystals on a Buchner funnel, and dry them in a drying cabinet. Transfer the dry crystals into a previously weighed weighing bottle, weigh it, and calculate the yield in per cent. Write the equations of all the reactions. 

Pour 2-3 ml of hydrazine on a watch glass and ignite it. The hydrazine should burn with a violet flame. If the sample of the obtained preparation does not ignite, freeze out the anhydrous hydrazine. To do this, put the receiver into a bath with ice. Pour the liquid off the precipitated crystals (what is the composition of the liquid and the crystals ), melt the crystals again, and repeat the operation. 

Filter off the precipitated crystals, collect them (carefully, hydro-xylamine is poisonous ), weigh them, and calculate the yield in per cent. Examine the shape of the crystals under a microscope. Write the equations of the reactions. 

Cool the small amount of the phosphorus iodide solution remaining in the flask with ice. Separate the precipitated crystals using a filter No. 2 in a stream of an inert gas (see Fig. 645) and wash them with dry carbon tetrachloride. Put the crystals into a weighed weighing bottle. Calculate the yield in per cent. 

Rapidly transfer the solution into a bowl and cool it to room temperature. Filter off the precipitated crystals using a glass filter No. 3 (about 400 mesh). 

Prepare hot saturated solutions of aluminium and potassium sulphates. To do this, dissolve 6.66 g of aluminium sulphate crystallohydrate in 5 ml of hot (/ 70 °C) water. Calculate what amount of potassium sulphate is equimolecular to 6.66 g of the aluminium sulphate crystallohydrate. Weigh this amount of potassium sulphate and dissolve it in 10 ml of hot water. Pour the potassium sulphate solution into that of aluminium sulphate. Cool the solution, filter off the precipitated crystals, dry them between sheets of filter paper, weigh them, and determine the yield of the substance in per cent. Examine the shape of the crystals under a microscope and draw them. 

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