Solvent removal Viscosity

Rerunning is a second distillation step applied to distillate stocks in order to remove undesirable higher boiling materials from the product. These materials may be present because of poor fractionation in the primary distillation step more frequently they are heavy polymers formed in treating operations. Rerunning may be combined with solvent removal, as in the case of heavy lube distillates which are diluted with naphtha to lower their viscosity before being chemically treated. 

B. (3-Bromo-3,3-difluoropropyl)trimethylsilane. A 1-L, four-necked flask is equipped with a mechanical stirrer, thermometer, Claisen adapter, septum inlet, reflux condenser (the top of which is connected to a calcium chloride drying tube), and a solid addition funnel. The flask is charged with (1,3-dibromo-3,3-difluoropropyl)trimethylsilane (78.3 g, 0.25 mol), and anhydrous dimethyl sulfoxide (200 mL), and the solid addition funnel is charged with sodium borohydride (11.5 g, 0.30 mol) (Notes 7 and 8). The stirred solution is warmed to 80°C, and sodium borohydride is added at a rate sufficient to maintain a reaction temperature of 80-90°C (Note 9). Toward the end of the addition, an additional portion of dimethyl sulfoxide (200 mL) is added via syringe to lower the viscosity of the reaction mixture. After the addition is complete, the mixture is cooled in an ice-water bath, diluted with 100 mL of pentane, and cautiously quenched with 12 M hydrochloric acid until no further gas evolution occurs. The mixture is transferred to a separatory funnel and washed with three, 100-mL portions of 5% brine. The pentane extract is dried over calcium chloride and the solvent removed through a 15-cm Vigreux column. Further fractionation yields 41.5 g (72%) of 3-bromo-3,3-difluoropropyltrimethylsilane, bp 139-141 °C (Note 10). 

The most critical factor in this process is temperature control in the second reactor. The viscosity of the mixture top to bottom changes with temperature, but also with PS concentration. If hot spots develop because of the exothermic reaction, a runaway can occur. In that event, the batch must be immediately quenched, ruining it. Several process improvements (not shown in Figure 23—12) include using agitators, solvents, and solvent removers. 

Functionalization can, of course, also be carried out in solution, e.g., in te-trahydrofuran. In this case, temperature control is much easier and the problem of undesired condensation in the functionalization step is reduced. The viscosity increase due to the stronger hydrogen bondings of the formed carboxylic acid end groups is not of importance in the modification step in solution as viscosity can be adjusted through the amount of solvent. Nevertheless, complete solvent removal afterwards sometimes turns out to be laborious. 

Viscosity of Polymer Solutions. Polymer solutions are very common. Glues, pastes, and paints are just a few examples of commercially available aqueous suspensions of organic macromolecules. Also, recall from Chapter 3 that certain types of polymerization reactions are carried out in solution to assist in heat removal. The resulting polymers are also in solution, and their behavior must be fully understand in order to properly transport them and effect solvent removal, if necessary. 

The evaporating flask should be less than one-half full for efficient solvent removal. Prolonged evaporation time should be avoided to minimize pigment degradation. A marked reduction in the rate of evaporation as well as an apparent increase in viscosity in indicative that the residual liquid, is mostly water. 

Because of solvent removal, the concentration and apparent viscosity rise considerably with increasing length of the processing zone. Within the limits of 90-95% polymer, the influence exerted by the great increase... 

After solvent removal the aerosols produced from slurries deliver solid particles, the diameters of which are those of the powder particles. In slurry nebulization used for flame work or plasma spectrometry, they are injected with a velocity that is less than or equal to the nebulizer gas atom velocities, as viscosity drag forces are responsible for their entrainment into the ICP. The velocity of the gas atoms (vG) can be calculated from the gas temperature at the location considered (TG), the injection velocity (vi) and the temperature at the point of injection (T), as vG = Vi x TG/Ti and the acceleration of particles (d2z/dt2) as a result of the viscosity drag forces is ... 

Viscosity of the dispersed phase Polymer concentration Volume fraction of dispersed phase to continuous phase Quantity of drug in the dispersed phase Concentration of porosigen Increase of agitation rate Increase of temperature Solvent removal rate... 

As with other techniques, the material requirements for rotogravure printing depend on the curing process. For drying (solvent removal), a viscosity of between 0.01 and 0.2 mPa s is appropriate, resulting in a film about 1 p,m thick [23], which is more than sufficient for many printed electronics applications. UV curing the film allows for thicker films, up to about 8 p,m thick. 

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