Filtration decantation

Chemical synthesis can include chlorination, alkylation, nitration, and many other substitution reactions. Separation processes include filtration, decantation, extraction, and centrifugation. Recovery and purification are used to reclaim solvents or excess reactants as well as to purify intermediates and final products. Evaporation and distillation are common recovery and purification processes. Product finishing may involve blending, dilution, pelletizing, packaging, and canning. Examples of production facilities for three groups of pesticides foUow. 

Filtration, decanting and centrifuging to separate a solid from a liquid (p. 18). 

Sedimentation, Filtration, Decantation, Evaporation, Loading, Sieving and Distillation. 

II.l INTRODUCTION Before the student attempts to carry out the analytical reactions of the various cations and anions detailed in Chapters III and IV, he should be familiar with the operations commonly employed in qualitative analysis, that is with the laboratory technique involved. It is assumed that the student has had some training in elementary practical chemistry he should be familiar with such operations as solution, evaporation, crystallization, distillation, precipitation, filtration, decantation, bending of glass tubes, preparation of ignition tubes, boring of corks, and construction of a wash bottle. These will therefore be either very briefly discussed or not described at all in the following pages. 

Isolation and purification of substances filtration, decantation, centrifugation, magnetic separation, crystallization, distillation. 

The filtration of a hot, saturated solution to remove solid impurities or charcoal can be done in a number of ways. Processes include gravity filtration, pressure filtration, decantation, or removal of the solvent using a Pasteur pipette. Vacuum filtration is not used because the hot solvent will cool during the process and the product will crystallize in the filter. 

As the most abundant liquid that occurs on Earth, water is very cheap and, more importantly, not toxic, so it can be used in large amounts without any associated hazard. In this medium, reactions can be carried out under mild conditions and yields and selectivities can therefore be largely improved. Furthermore, water-soluble compounds, such as carbohydrates, can be used directly without the need for the tedious protection-deprotection sequences. Finally, water-soluble catalysts can be reused after filtration, decantation, or extraction of the water-insoluble products [lb]. 

To ensure consistency and efficiency, sample handling (filtration, decantation, centrifugation, sample splitting, etc.), preservation, storage, and transportation procedures must be properly and accurately documented, and adhered to by field personnel. 

If the sample (solution or mixture) is known to contain water, then not only should this information be recorded but also extreme care must be taken to ensure that the sampling method is compatible with water being present. Comments are provided in Section 5 regarding the removal of water and other volatile materials that can interfere with an analysis. Also, if a sample is seen to be made up of more than one phase, it is helpful to obtain spectra from each separated phase. Techniques such as filtration, decanting, and centrifuging should be used if practical to ensure representative sampling of a particular phase. Record the nature of the phase being... 

Leaving the refinery, jet fuel has generally no free water and contains only a small quantity of dissolved water. But humidity from the air and tank breathing result in continuous intrusion of water that must be then removed by decanting and filtration. This is why jet fuel needs to be tested for its ability to separate the contained water. 

Into a 1-litre beaker, provided with a mechanical stirrer, place 36 - 8 g. (36 ml.) of aniline, 50 g. of sodium bicarbonate and 350 ml. of water cool to 12-15° by the addition of a little crushed ice. Stir the mixture, and introduce 85 g. of powdered, resublimed iodine in portions of 5-6 g, at intervals of 2-3 minutes so that all the iodine is added during 30 minutes. Continue stirring for 20-30 minutes, by which time the colour of the free iodine in the solution has practically disappeared and the reaction is complete. Filter the crude p-iodoaniline with suction on a Buchner funnel, drain as completely as possible, and dry it in the air. Save the filtrate for the recovery of the iodine (1). Place the crude product in a 750 ml. round-bottomed flask fitted with a reflux double surface condenser add 325 ml. of light petroleum, b.p. 60-80°, and heat in a water bath maintained at 75-80°. Shake the flask frequently and after about 15 minutes, slowly decant the clear hot solution into a beaker set in a freezing mixture of ice and salt, and stir constantly. The p-iodoaniline crystallises almost immediately in almost colourless needles filter and dry the crystals in the air. Return the filtrate to the flask for use in a second extraction as before (2). The yield of p-iodoaniline, m.p. 62-63°, is 60 g. 

The Iodine may be recovered from the aqueous filtrate, containing sodium iodide, in the following manner. Add 33 ml. of concentrated sulphuric acid and a solution of 65 g. of sodium dichromate in 65 ml. of water. Allow the iodine to settle, wash it three times by decantation, filter, and allow to dry on a clock glass. The weight of crude iodine is about 50 g. 

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