Suspension of Drops

Settling and coalescence are common when the dispersed and continuous phases are of different density and when agitation provides only minimal circulation throughout the vessel. It is therefore important to determine the minimum speed for drop suspension. Most reported work is semiempirical and follows the approach of Zwietering (1958) for the just suspended state of solids in liquids. 

There are analogies between the minimum impeller speed Njs for solids suspension and Nmm for drop suspension. Both depend on density difference, continuous phase viscosity, and impeller diameter. However, Njs depends directly on particle size, while Nmin depends instead on interfacial tension and the other physical properties that determine drop size. Skelland and Seksaria (1978) determined the minimum speed to form a liquid-liquid dispersion from two settled (separated) phases of different density and included the sensitivity to impeller location. The vessels used were fully baffled. They determined Nmin for systems of equal volumes of light and heavy phase. Studies included use of single impellers placed midway in the dense phase (C = H/4), at the o/w interface (C = H/2) and midway in the lighter phase (C = 3H/4). They also examined the use of dual impellers located midway in both phases. Several impeller types were tested, including a propeller (Prop), a 45° pitched blade tmbine (PBT), a flat-blade turbine (FBT), and a curved-blade turbine (CBT). Their results are correlated by the following equation, which is dimensionless  

Ap = pd —Pc. The magnitude of the constants C20 and as, given in the Table 12-5, are a measure of the ease of suspension formation. Low C20 values indicate that dispersions are formed at low speeds. Large C20 values (single impellers) suggest that higher speeds are required for minimum suspension. Turbines at the o/w interface require lower speed than in other locations. Radial flat-blade turbines placed in the light phase appear to be inefficient. 

In an earlier study, Nagata (1975) determined minimum agitation conditions for forming a dispersion using a baffled cylindrical vessel and four-blade turbine impellers of D/T =, placed at C = T/2. The following equation shows his dimensional correlation  

and Nmm (rpm). Off-center locations are seldom used, but the vortex due to eccentricity creates an efficient means to help form dispersions. The lack of dependency on Xd indicates that only low viscosity dispersed phases were considered. 

---

There are two general approaches that one might follow in trying to apply the LBM to flowing suspensions of red cells. One approach is to treat the red cell as a drop. Dupin et al. used this approach. Since one is considering a suspension of drops, a two-fluid version of the LBM mnst be considered. Chen and Doolen described some early work on developing two-flnid versions of the LBM. A drawback of this approach is that it is not clear how snch an approach could correctly describe the equilibrium shape of a red cell. One wonld need to incorporate a membrane with the correct elastic properties into the LBM formulation. 

Agitation plays a controlling role in the liquid-liquid systems considered herein. It controls the breakup of drops, referred to as dispersion, the combining of drops, known as coalescence and the suspension of drops within the... 

The hydrochloride of the amine may be prepared precisely as that of the primary amine. For recrystallisation, boil a suspension of the powdered salt in petroleum (b.p. 60-80°), and then add acetone slowly in small drops until the boiling suspension just becomes clear allow the stirred solution to cool until crystallisation starts, and then chill in ice-water before collecting the colourless plates of the hydrochloride, which after drying in a vacuum desiccator have m.p. 132-134°. 

The residue in the flask is either a solution or a suspension of the potassium salt of the acid derived from the ester in diethylene glycol. Add 10 ml. of water and 10 ml. of ethyl alcohol to the residue and shake until thoroughly mixed. Then add a drop or two of phenolphthalein and dilute sulphuric acid, dropwise, until just acid. Allow the mixture to stand for about 5 minutes and then Alter the potassium sulphate. Use the clear filtrate for the preparation of a sohd derivative or two of the acid (see Section 111,85,4). 

To a vigorously stirred suspension of 4 mol of lithium amide (see II, Exp. II) in 2.5 1 of liquid ammonia were added in 25 min 2 mol of propargyl alcohol (commercially available, purified before use by distillation at 100-120 mm). The suspension became very thin. Subsequently, the dropping funnel was combined with a gas inlet tube reaching about 1 cm beneath the surface of the ammonia. The vent on the splashing tube was removed. Methyl iodide (2 mol) was added to the vigorous-... 

The fourth and most interesting of the polymerization techniques we shall consider is called emulsion polymerization. It is important to distinguish between suspension and emulsion polymerization, since there is a superficial resemblance between the two and their terminology has potential for confusion A suspension of oil drops in water is called an emulsion. Water-insoluble monomers are used in the emulsion process also, and the polymerization is carried out in the presence of water however, the following significant differences also exist ... 

The apparent viscosity, defined as du/dj) drops with increased rate of strain. Dilatant fluids foUow a constitutive relation similar to that for pseudoplastics except that the viscosities increase with increased rate of strain, ie, n > 1 in equation 22. Dilatancy is observed in highly concentrated suspensions of very small particles such as titanium oxide in a sucrose solution. Bingham fluids display a linear stress—strain curve similar to Newtonian fluids, but have a nonzero intercept termed the yield stress (eq. 23) ... 

A. Ester condensation. A suspension of 9.40 g. (0.41 gram atom) of powdered sodium in 100 ml. of absolute ether is placed in a 1-1. three-necked flask (Note 1) fitted with a reflux condenser, dropping funnel, and a calcium chloride tube. A solution of 23.8 ml. (0.41 mole) of absolute alcohol (Note 2) in 50 ml. of abso-... 

A solution of 3jS-hydroxy-5a-androstan-17-one tosylate (193, 60 mg) in tetrahydrofuran (10 ml, freshly distilled from lithium aluminum hydride) is added dropwise to a boiling suspension of lithium aluminum deuteride (60 mg) in tetrahydrofuran (10 ml). The resulting suspension is heated under reflux for 30 min and after cooling the excess reagent is decomposed by the careful addition of a few drops of water. The heating is continued for a few minutes to coagulate the inorganic salts which are removed by filtration... 

Cyano-3 -hydroxy-5a-pregnan-20-one A suspension of 5a-pregnane-3, 20-dione (2 g) in ethanol (90 ml) is treated with acetone cyanohydrin (4 ml) and three drops of triethylamine and stirred at room temperature until complete dissolution. After 3 hr, the solution is diluted with 200 ml of water, acidified with acetic acid and the crystalline precipitate is thoroughly washed with water and dried under vacuum to give 2.1 g (97%) of product mp 172-178° (dec). A sample recrystallized from ethyl acetate melts at 176-179° (dec) [a]p 86° (ethyl acetate). 

A solution of sodium methoxide, prepared from sodium (23 g) and dry methanol (500 mL), was added drop-wise at 0 °C to a stirred suspension of aminoacetonitrile hydrochloride (18, 100 g, 1.08 mol) in dry methanol (100 rnL). After stirring for 2 h at rt the precipitated sodium chloride was filtered off and the filtrate concentrated in vacuo. EtOAc (20 mL) was added and evaporated under reduced pressure to remove all traces of methanol. The oily residue was dissolved in dry EtOAc (100 mL) and anhydrous sodium sulfate added. After cooling, the precipitate was filtered off. The solution of crude aminoacetonitrile was used without further purification. This solution was added drop-wise during a period of 1 h to a vigorously stirred, ice-cooled solution of carbon disulphide (100 mL, 1.66 mol) in dry EtOAc (100 mL) under an N2 atmosphere. Continued mechanical stirring and water-free conditions were essential. The mixture was stirred at 0 °C for 1 h. The resultant precipitate was filtered off, washed with EtaO and dried, giving the product 50 as yellow crystals (99 g, 75 % on amount of sodium), m.p. 131 °C dec. IR (KBr) v max 1630, 1500 cm. ... 

Preparation of 7-(D-0t-phenyigiycyiamido)-3-chioro-3-cephem-4-carboxyiic acid To a suspension of 280 mg (1.2 mmol) of 7-amino-3-chloro-3-cephem-4-carboxylic acid in 14 ml of acetonitrile was added with stirring at room temperature 0.5 ml of N, 0-bis-(trimethylsilyl)acetamide to form the soluble disilylmethyl derivative thereof. The solution was cooled to 0°C and was slowly added to a solution of the mixed anhydride formed by reacting 408 mg (1.5 mmol) of methyl-3-a-carboxybenzylaminocrotonate sodium salt with 161 mg (1.7 mmol) of methyl chloroformate in the presence to 2 drops of N, N-dimethylbenzyl amine in 7 ml of acetonitrile. 

The temperature is again lowered to 20°C to 25°C and maintained at this value by cooling with ice while 500 ml methanol are added drop by drop. The resulting solution is admixed drop by drop to a suspension of 240 g powdered caustic soda in 800 ml methanol at 20°C to 25°C. After mixing is completed, stirring is continued for 30 minutes at room temperature. The solution now contains inorganic salts and /3-dlmethylamino-a-methoxyethoxyacroleln. 

The purified intermediate melted at 210°C. 70.9 g (0.10 mol) of the intermediate was dissolved in 150 ml dimethyl acetamide, and 15 g (0.08 mol) tributylamine was added. The mixture was heated to 50°C, and 56.6 g (0.62 mol) 1,3-dihydroxyisopropylamine (2-amino-1,3-pro-panediol) dissolved in 80 ml dimethylacetamide was added drop by drop. The reaction went to completion within a few hours, and the reaction mixture was evaporated to dryness in a vacuum. The oily residue was added to 350 ml methylene chloride with vigorous agitation, and the resuiting precipitate was filtered off and purified by repeated suspension of warm methyiene chioride. 

A) Preparation of dt-N-(y-Chloromercuri-li-Methoxy)-Propylcamphoramic Acid A suspension of 31.9 g (= 0.10 M) of mercuric acetate in 25 ml of methanol is stirred for 30 minutes at room temperature in a 4-necked flask equipped with stirrer, dropping funnel, drying tube and thermometer. To this suspension is added dropwise and with stirring, a solution of 23.9 g (= 0.10 M) of dl-N-allyl-camphoramic acid... 

---