Concentric separation-layer mixing

The concentric separation-layer micro mixer is constructed as an assembly of stacked plates for feed supply with three tubes, performing lamination for mixing, set into one another (see Figure 1.116) [39, 53, 136-138] (see also [135]). The tubes are inserted into a frit. The three feed lines are each connected to a tube. In this way, a tri-layered concentric fluidic system is achieved. Besides mixing three solutions, a major application for the device is to separate the two fluids to be mixed by a separation layer, usually being the solvent of the two solutions. This is to delay the mixing process in order to avoid unwanted fouling problems at the mixer outlet This is particularly valuable for spontaneous precipitation reactions which are the main field of application of the mixer. 

M 54] [P 48] Separation-layer micro mixers with concentric multi-layered outlets can be operated in a droplet-forming mode [53] If fast precipitating solutions are contacted in this way with a solvent layer for initial separation, the part of the droplet close to the tube outlets remains transparent, which demonstrates that a tri-layered system still exists with the two reacting solutions not being intermixed, as evidenced by calcium carbonate formation in aqueous solutions as described in [39,136], At the droplet end cap the layers collide and circulation flow sets in. As a result, mixing is achieved and precipitation occurs. The circulation patterns are visualized by the particle trajectories. 

Dry air, spiked with required amounts of cyclohexane vapour, was supplied through a glass tube (internal section 20 cm2) filled with the tested carbon and molecular sieve. An initial concentration of cyclohexane was Co = 3.6 0.1 mg dm-3 (0.1% V/V). The experiments were carried out with two bed configurations 1) a separated (layer of molecular sieve type 4A 2 cm in height, and a layer of activated carbon 2 cm) and 2) mechanically mixed activated carbon with molecular sieve in equal volumetric amounts. 

A) Molisch Test for Carbohydrates. Apply the test to small amounts of the following sucrose, starch, and paper fibers. Place in a test tube 2 ml of one per cent carbohydrate solution or dispersion. Add 2 drops of a 10 per cent solution of a-naphthol in alcohol, and mix. Add this carefully down the side of a tube containing 2 ml of concentrated sulfuric acid so that it will form a separate layer. Carbohydrates give a purple color at the junction of the two liquids. 

Even more subtle is the gradient system in which both solvents A and B have different buffer compositions and precipitation or phase separation occurs as the gradient is formed. If any of the mobile phase component concentrations in the mixing chamber or on the column exceed their solubility in the solution, then phase separation or precipitation occurs. Here it is critical to remember that the adsorbed surface layer on the support material is not necessarily identical to the mobile phase. This adsorbed layer is usually enriched with the solvent components most similar to the support. 

Procedure. The sample, mixed with water, is extracted in a micro test tube with a few drops of chloroform. The chloroform layer is separated and mixed with 3 ml of acetic acid and 2 drops of a 10% aqueous solution of potassium ferricyanide. The development of a green color indicates the presence of ferrocene. With a concentrated solution of ferrocene, a deep blue precipitate is formed. 

To 1 ml of the sample, containing 1 to 10 mg of stilboestrol dipropionate per ml, add 10 ml of 95 per cent ethanol containing 2 to 3 drops of concentrated sulphuric acid and boil the mixture under reflux for two hours. Allow to cool, wash the reaction mixture into a separator with about 50 ml of ether and extract the solution three times with 10-ml portions of N sodium hydroxide, care being taken to ensure that an excess of alkali is present during the first shake. Wash the combined alkaline extracts with about 25 ml of ether and, after separating, shake the ethereal layer with 5 ml of N sodium hydroxide. Discard the separated ether, mix the alkaline liquids, acidify with dilute sulphuric acid... 

Prior to about 1920, flotation procedures were rather crude and rested primarily on the observation that copper and lead-zinc ore pulps (crushed ore mixed with water) could be benefacted (improved in mineral content) by treatment with large amounts of fatty and oily materials. The mineral particles collected in the oily layer and thus could be separated from the gangue and the water. Since then, oil flotation has been largely replaced by froth or foam flotation. Here, only minor amounts of oil or surfactant are used and a froth is formed by agitating or bubbling air through the suspension. The oily froth or foam is concentrated in mineral particles and can be skimmed off as shown schematically in Fig. XIII-4. 

Mix 40 g. (51 ml.) of isopropyl alcohol with 460 g. (310 ml.) of constant boiling point hydrobromic acid in a 500 ml. distilling flask, attach a double surface (or long Liebig) condenser and distil slowly (1-2 drops per second) until about half of the liquid has passed over. Separate the lower alkyl bromide layer (70 g.), and redistil the aqueous layer when a further 7 g. of the crude bromide will be obtained (1). Shake the crude bromide in a separatory funnel successively with an equal volume of concentrated hydrochloric acid (2), water, 5 per cent, sodium bicarbonate solution, and water, and dry with anhydrous calcium chloride. Distil from a 100 ml. flask the isopropyl bromide passes over constantly at 59°. The yield is 66 g. 

Into a 750 ml. round-bottomed flask furnished with a reflux condenser place a solution of 34 g. (18-5 ml.) of concentrated sulphuric acid in 100 ml, of water add 33 g. of di-n-butyl cyanamide and a few fragments of porous porcelain. Reflux gently for 6 hours. Cool the resulting homogeneous solution and pour in a cold solution of 52 g. of sodium hydroxide in 95 ml. of water down the side of the flask so that most of it settles at the bottom without mixing with the solution in the flask. Connect the flask with a condenser for downward distillation and shake it to mix the two layers the free amine separates. Heat the flask when the amine with some water distils continue the distillation until no amine separates from a test portion of the distillate. Estimate the weight of water in the distillate anp add about half this amount of potassium hydroxide in the form of sticks, so that it dissolves slowly. 

Ethyl bromoacetate (1). Fit a large modified Dean and Stark apparatus provided with a stopcock at the lower end (a convenient size is shown in Fig. Ill, 126, 1) to the 1-htre flask containing the crude bromoacetic acid of the previous preparation and attach a double surface condenser to the upper end. Mix the acid with 155 ml. of absolute ethyl alcohol, 240 ml. of sodium-dried benzene and 1 ml. of concentrated sulphuric acid. Heat the flask on a water bath water, benzene and alcohol will collect in the special apparatus and separate into two layers, the lower layer consisting of approximately 50 per cent, alcohol. Run ofi the lower layer (ca. 75 ml.), which includes all the water formed in the... 

Mix 31 g. (29-5 ml.) of benzyl alcohol (Section IV, 123 and Section IV,200) and 45 g. (43 ml.) of glacial acetic acid in a 500 ml. round-bottomed flask introduce 1 ml. of concentrated sulphuric acid and a few fragments of porous pot. Attach a reflux condenser to the flask and boil the mixture gently for 9 hours. Pour the reaction mixture into about 200 ml. of water contained in a separatory funnel, add 10 ml. of carbon tetrachloride (to eliminate emulsion formation owing to the slight difference in density of the ester and water, compare Methyl Benzoate, Section IV,176) and shake. Separate the lower layer (solution of benzyl acetate in carbon tetrachloride) and discard the upper aqueous layer. Return the lower layer to the funnel, and wash it successively with water, concentrated sodium bicarbonate solution (until effervescence ceases) and water. Dry over 5 g. of anhydrous magnesium sulphate, and distil under normal pressure (Fig. II, 13, 2) with the aid of an air bath (Fig. II, 5, 3). Collect the benzyl acetate a (colourless liquid) at 213-215°. The yield is 16 g. 

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