ACOMP

Wavelength (nm) Compound (Acomp AIs.) Mancha (Acranj/Al.S.) Rio (Acomp AIs.) Sierra (Acomp/Aps.) Commercial sample (Acoin/Aps.)... 

The entropic effects of the creation of a cavity in the water to accommodate the ion (similar to ASn in (Abraham et al. 1982)) and of the compression from the gas to the solution (similar to Acomp in (Marcus 1986)) are taken care of together in a neutral term, A5nt. It is calculated from the entropies of hydration of small neutral molecules or rare gas atoms, interpolated for a radius n the same as that of the ion A5 t = -3 - 600(n/nm) J K mol In the electrostricted hydration shell the permittivity and its temperature derivative are assumed to have the infinitely large field values. Using for this purpose d, the relfactive index of water at the sodium D line, e = = 1-776 and (de /dT)p = 2(dni)/dT)p = -1 x 10-"K (at... 

Determination of [p] hence requires that of the sample solvent and the total viscosity of the fluid containing the macromolecules 7] be measured. In some analytical techniques, such as SEC and ACOMP, the concentration is usually low enough that to a good approximation [p] = where is measured by combining viscometer and concentration detector data. Importantly, [ )] is a direct measure of the ratio of a polymer s hydrodynamic volume to its molar mass M. 

Because the reaction medium is normally quite concentrated, however, rheological and other measurements often only indirectly measure molecular mass and other single chain properties, because the interactions between polymer chains often dominate signals from undiluted reactor contents. Automatic continuous online monitoring of polymerization reactions (ACOMP) provides a solution for this. ACOMP is covered in Chapters 11-13. 

It is important to emphasize that the development of fiber optics technology is a fundamental cornerstone that allowed for the development of real in-line and in-situ monitoring spectroscopic techniques, as the sampling device can be placed at very harmful environments, while the spectrometer still sits in a process control room. Without the support of fiber optics technology, samples have to be prepared and placed inside the illuminated chambers (as performed in the lab since the nineteenth century) or pumped through sampling windows (as performed in advanced systems intended for process and product development, such as automatic continuous online monitoring of polymerization reactions (ACOMP) [37- 1] in order for spectral data to be obtained. 

Alb AM. Automatic Continuous Online Monitoring of Polymerization Reactors (ACOMP) Progress in Characterization of Polymers and Polymerization Reactions. PhD Thesis, Tulane University, New Orleans. 

Alb AM, Reed WF. Recent advances in Automatic Continuous Online, Monitoring of Polymerization reactors (ACOMP). Macromol Symp 2008 271 15-25. 

Alb AM, Reed WF. Fundamental measurements in online polymerization reaction monitoring and control with a focus on ACOMP. Macromol React Eng 2010 4 470-485. 

AUTOMATIC CONTINUOUS ONLINE MONITORING OF POLYMERIZATION REACTIONS (ACOMP)... 

The ACOMP front end is the ensemble of pumps, mixing chambers, filters, and conditioning steps that prepare the continuous highly dilute and conditioned stream and deliver it to the detector train. Lag times between withdrawal and detection are typically from 10s to 100s of seconds, with... 

Advantages of ACOMP include its versatility as a generalized approach, its ability to make fundamental measurements without recourse to empirical models and calibration, its capacity for providing a data-rich stream of complementary information from multiple independent detectors, yielding multifaceted characteristics of polymerization reactions, and its use of the front end to extract, dilute, and condition a sample stream that allows sensitive detectors to provide reliable data without exposing them to harsh reactor or sample conditions. Disadvantages include the mechanical complexity of the front end, the delay time between a continuous fluid element s extraction from the reactor and downstream measurement by the detector train, and a small but continuous waste stream. ACOMP is more invasive than probes that can be placed at an outside reactor window, but are no more invasive than in situ probes, in that in either case access to the reactor contents is required. 

Some guiding principles of ACOMP are listed in the following ... 

Obtaining high-quality data with model-free primary quantities allows the richness of the ACOMP results to be used for building chemical, physical, and mechanistic models to any degree of elaboration desired, and for potential full feedback control of reactions. 

Comparing ACOMP with In Situ Methods Such As Near Infrared and Raman... 

While ACOMP gives the comonomer conversions, which those techniques also do, ACOMP additionally and simultaneously evolution of weight average molecular weight and [p], average polymer properties of critical importance in the nltimate characterization, and utilization of the polymers. Additionally, ACOMP can provide immediate detection of nnforeseen or unwanted phenomena such as microgelation, runaway reaction, dead end reaction, onset of tnrbidity, and so on. 

There are no inherent limitations on which detectors can be used in ACOMP, and detector selection is made according to the needs of each monitoring situation. A standard configuration involves MATS, a differential R1 detector, a UVWIS detector, and a single capillary viscometer. Infrared, fluorescence, and conductivity detectors are other examples of instruments that can be incorporated. 

FIGURE 11.1 A simplified schematic of an ACOMP system, showing the front end used for extraction, dilntion, and conditioning of reactor content, and a typical series of detectors through which the dilute, conditioned sample continuously flows. 

The Tulane group developed a MATS instrument specifically to meet the demanding environment of ACOMP, and Brookhaven Instruments Corporation (BIC, Holtsville, NY) took a license from Tulane for this design and currently produces the Bl-MWA (Molecular Weight Analyzer) for ACOMP, size exclusion chromatography (SEC), and batch applications (http //www.bic.com/BI-MwAmw.html). 

ACOMP Delay Time and Response Time Because ACOMP involves continuous withdrawal, dilution, and conditioning of reactor liquid, there is inevitably both (i) a delay time between when a fluid element is withdrawn and when a measurement of its properties is made by the detector train, and (ii) a system response time associated with the various mixing processes involved. 

Delay times in ACOMP typically run from 10s to 100s of seconds, and depend on the flow rates, degree of dilution, the type of reaction, and the tubing and mixing chambers employed. In some cases, where flow rate from the reactor is variable, the detector signals can be used to continuously compute changing delay times [1],... 

The signal measured by a detector D(t) is related to the actual physical signal in the reactor, S(t), such as monomer concentration, via the ACOMP system response function R(t) according to ... 

The inset to Figure 11.2b shows the ACOMP system response function Rit), which was determined experimentally by rapidly injecting a small volume of acrylamide (Am) into the reactor to cause a step function in concentration, shown in Figure 11.2a (measured by the UV absorbance in this case) ... 

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