End-point control

The above-mentioned on-line spectroscopic techniques have involved granulation monitoring for particle size assessments and end-point control however there are other concerns involved with wet granulation which include polymorphic transformations or solvate formation that can affect end product quality. ... 

Gieseler et al. utilized tunable diode laser absorption spectroscopy to detect water vapor concentrations, gas velocities and mass flow during freeze-drying of pure water at different pressure and shelf temperature settings and of a 5%w/w mannitol solution. The analyzer was interfaced to the spool that connected the dryer chamber to the condenser. The reported method was advantageous in that primary and secondary drying end-point control based upon mass flow rate was independent of freeze-dryer size and configuration. ... 

In specialty metal processing such as titanium, the metal is milled with a dilute hydrofluoric acid bath. The bath must be purged of the titanium laden waste acid and replenished with fresh acid periodically. As in the stainless steel case, the titanium waste acid can be neutralized with KOH to precipitate out the metals. The fluoride recovery is greatly dependent upon good pH end point control. If pH is monitored carefully, a greater than 90% fluoride recovery can be achieved. 

The hydrocarbon mixture at the furnace outlet is quenched rapidly in the transfer line exchangers (2) (TLE or SLE), generating high-pressure steam. In liquid crackers, cracked gas flows to a primary fractionator (3) after direct quench with oil, where fuel oil is separated from gasoline and lighter components, and then to a quench water tower (4) for water recovery (to be used as dilution steam) and heavy gasoline production (end-point control). 

FIGURE 11.13 Prepolished (solid) and Postpolished (dotted) wafer thickness profiles with end-point control (from Ref. 27). 

What are the most common methods for end-point control in CMP and which of them can be used in CMP for microfabrication ... 

Werani, J. Production experience with end-point control. Acta Pharm. Seuc. 1988, 25, 247-266. 

Laicher, A. Profitlich, T. Schwitzer, K. Ahlert, D. A modified signal analysis system for end-point control during granulation. Eur. J. Pharm. Sci. 1997, 5, 7-14. 

The main problem with a living polymer is maintaining the strict cleanliness that is demanded by the chemistry. This is a particularly severe problem for large-scale batch polymerizations, but it is a problem more of economics than technology. Living polymerizations are usually run to near completion, so that end-point control is not a problem. Most living polymerizations operate at low temperatures, —40 to - -40°C, to avoid chain transfer reactions. Thus temperature control is a significant scaleup problem. The usual approach is to use 85-95 w % solvent and to rely on sensible heat transfer to the vessel walls. 

J. B. Rawlings, N. F. Jerome, J. W. Hamer, and T. M. Bruemmer. End- point control In semi-batch chemical reactors. In Proceedings of the IFAC Symposium on Dynamics and Control of Chemical Reactors,. Distillation Columns, and Batch Processes, pages 323-328,1989. 

Since the process of saturation of double bonds is not usually carried to completion, as already pointed out earlier, the control of the process to produce specific hydrogenated oil stocks is relatively complex. There are three main aspects which require consideration (1) selection of process conditions, (2) hydrogenation end point control, and (3) hydrogenation selectivity and isomer formation during the process. 

The end-point control of granulation by power consumption measurement in a 25 L high-shear mixer was investigated by Holm et al. (42). The effect of impeller design, impeller speed, liquid addition rate, type of binder, and mixing ratios between lactose and starch on the correlation between power consumption and granule... 

While a discussion on end-point control in general might be in order, pH is used far more widely than any other measurement to sense the state of a reaction. So while pH has some peculiarities of its own, principally its logarithmic character, much of the following commentary applies to other end-point measurements. 

End point control of a batch reaction has one outstanding character istic reset must not be used. The bulk of the reaction is conducted away from the set point-reset would try to overcome this offset and ulti mately result in overshoot. The controller should be proportional-plus-derivative, with zero bias, so that the valve is shut when the set point is reached. If the measurement is pH, reagent should be added through an equal percentage valve (without a cascade flow loop), to match the process characteristic. A system employing temperature and end-point control is shown in Fig. 10.20. 

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