Conversion monitoring

Cardiac depressant effects may occur when verapamil or diltiazem is combined with a (p-adrenoceptor antagonoist or a cardiac glycoside. Nifedipine and verapamil are metabolised by cytochrome P-450 3A4. Inhibitors of this enzyme, e.g. HIV-protease inhibitors, cimetidine, fluoxetine, ketoconazole, erythromycin, will increase plasma levels and the dose should be carefully monitored. Conversely, enzyme inducers, e.g. carbamazepine, rifampicin, phenytoin, will decrease their plasma concentrations. 

As already indicated, catalytic titrations are carried out by monitoring conversion of a model reactant while the surface concentration of adsorbed reagent (usually an amine) is increased in measured steps. Conversion of the reactant is determined by means of a pulse reactor or a conventional flow reactor, depending on the needs of the investigator. In order to obtain the most meaningful titration results, we make the following recommendations. 

This work has shown that by monitoring conversion curves by a computer, emulsifier metering can be varied to produce a desired particle size distribution of smalls in a seeded PVC emulsion polymerization. 

Although a lot of information can be obtained with the analysis of diluted polymer lattices samples, as shown previously, the advantages that in situ analysis of the emulsion polymerization processes represent over systems that require dilution are well documented. A dilution step implies sample manipulation and increased measurement dead times. Therefore, regardless the effectiveness of the dilution strategy, there is incentive in continuing the development of in-line and in-situ measurement probes. Of the light based techniques reported only Raman and Near Infrared probes have been used for in situ to monitor conversion." The use of light and specifically fiber optic probes as a particle concentration and particle size detectors is a concept that has become widely accepted. ... 

The cure mechanism for curing triglycidyl -amino phenol with diaminodiphenylsulfone was studied. The concentration of primary and secondary amine and epoxide groups were monitored directly as a function of cure with NIR spectroscopy. In similar fashion, monitoring of the percent conversion of methyl methacrylate to PMMA in situ in a mould used short-wavelength NIR spectroscopy. NIR spectroscopy was also used to monitor conversion during conventional, anionic solution polymerisation of styrene and isoprene to homopolymers and block copolymers (314). 

Near-IR spectroscopy (10000-4000/cm) was successfully used to monitor conversion dining conventional, anionic solution polymerisation of styrene and isoprene to homopolymers and block copolymers. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution polymerisation conditions. In addition to the need for an inert probe, high sampling frequencies were required since polymerisation times ranged from 5s in tetrahydrofuran to 20 minutes in cyclohexane. Preliminary data indicate that near IR is capable of detecting sequence distribution for tapered block copolymers, geometric isomer content, and reactivity ratios for free-radical copolymerisation. 20 refs. USA... 

In these cases, one can monitor conversion versus time and determine the deactivation rate as well as the deactivation rate constant. Figure 19.2 shows an example of conversion varying with reaction time in the ethanol reforming reaction. 

DCM has been used for more than 20 years to produce tibial and acetabular inserts. Historically, the process may have been adopted because the cutting and milling machinery of the day was not numerically controlled and thus less able to accurately produce complicated curves as required to make knee inserts. The physical and mechanical properties of the finished product can be tailored to some degree by varying die DCM cycle, as detailed by Chen, Truss, and others (Han et al. 1981, Truss et al. 1980, Chen, Ellis, and Crugnola 1981). DCM can also be used to produce UHMWPE with properties indistinguishable from stock material produced by closely monitored conversion of compression-molded sheet and extruded rod. 

The application of ultrasonics to the monitoring of emulsion polymerisation reactors is considered. The use of acoustic speed measurements to monitor conversion is demonstrated by its apphcation to the control of the emulsion copolymerisation of styrene and butyl acrylate. The potential of acoustic attenuation for the measurement of particle size is discussed and applied to the determination of the particle size distribution of PVC and PTFE latices. 27 refs. 

For some radionuclides, individual monitoring may not be feasible because of the radiation type(s) emitted and the detection sensitivity of monitoring methods, and reliance must be placed on workplace monitoring. Conversely, for some other... 

Various methods have been used to analyze aliquots from reactions [27, 28], Online measurements by dilatometry have also been reported [29], A significant advance in this field was the adaptation of ACOMP as a means for monitoring conversion and measures of polymer molar mass during the inverse emulsion polymerization of acrylamide, in order to understand both reaction kinetics and mechanisms and, potentially, to control them during the reaction [30],... 

Monitoring conversion in batch and semibatch reactors Multistep polymer reaction processes often move from step to step as preset monomer conversion levels are met for example, in the production of block copolymers or for grafting reactions, such as used in high impact polystyrene. Currently, chemical conversion is... 

Heat-removal systems can be used for monitoring conversion. The record of condensate flow to the reactor in Fig. 10.10 should provide a reliable indication of heat evolution. With a circulating liquid coolant, however, flow must be multiplied by temperature difference from inlet to outlet in order to determine the rate of heat evolution. There are some pitfalls in this system ... 

Fig. 1. Participants are seated around the Conversation Clock table (left). Lapel microphones monitor conversation while the visualization of history is projected in the center. The Conversation Clock provides a visual history of interaction and communication right). Each contribution displays bars colored to indicate the speakers identities. The lengths of these bars indicate the degree of participation, measured by volume. As a conversation progresses, a history is built with concentric rings reminiscent of the rings on a tree.

Spectroscopic techniques can be applied for monitoring conversion. Nuclear-magnetic resonance (NMR) and Fourier-transform infrared (FTIR) can be applied as offline techniques. However, spectroscopic techniques are arguably most attractive if they can be applied online. For example, attenuated total reflectance (ATR) FTIR has been applied to monitor the copolymerization of butyl acrylate and vinylacetate (Jovanovic Dube, 2003). Raman spectroscopy, in combination with a self-modelling curve-resolution technique, has... 

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