In-Situ Monitoring of Chemical Reactions

One of the most important developments in pharmacentical process research of the past several decades has been the introdnction of bench-scale experimental tools for efficient and accnrate in situ monitoring of chemical reactions. Snch tools inclnde reaction calorimetry, which measnres a property directly proportional to reaction rate (a differentiaf method), and spectroscopic methods snch as Eonrier transform infrared (ETIR) spectroscopy, which measnres a property proportional... 

There are already several excellent reviews and multiauthored books that describe various designs for high pressure spectroscopic vessels [10,12-16]. This chapter demonstrates the use of vibrational spectroscopy for in situ monitoring of chemical reactions in SCFs. 

LTP Real-time in-situ monitoring of chemical reactions Ma et al. [151]... 

In situ Monitoring of Chemical Reaction Using Raman Microscopy... 

Instead of relying on the volatility of the halide, as in the direct combination and two-bulb approaches, the solubility of halides may be exploited to intercalate from solutions of nonaqueous solvents . Although this technique allows reaction at relatively low temperatures, for which in situ monitoring of reaction progress is easy, the solvent may participate in the reaction through both co-intercalation and direct chemical reaction. 

In recent years, real-time monitoring of chemical reactions and product streams has become more and more important in the polymer and plasties industry. This is due to the growing economic and legislative demands on product quality and the environmental protection. The industry needs rapid, reliable, non-invasive and cost effective analytical methods for process control. Conventional process analysis techniques are physical measurements such as temperature, flow, pressure and others. The obtained In Situ Spectroscopy of Monomer and Polymer Synthesis... 

Laser-induced Raman microscopy can be used to monitor a chemical reaction in a microfluidic channel. In situ monitoring of imine formation reaction in a glass microfluidic chip was previously performed. In order to moni-... 

With the introduction of LT and VT STM, it is now possible to monitor the fundamental steps of chemical reactions, that is, reactant chemisorption, diffusion, and catalytic transformation. A detailed review covering this subject was published by Wintterlin in 2000 [24]. Since then, in situ STM studies have flourished and expanded to the visualization of the reaction pathway and kinetics of surface processes. In the following section, we highlight selected examples of recent progress in using in situ STM for studying fundamental catalytic processes. 

The plan of this chapter is as follows. In Section 11 the basics of high-pressure technology and equipment are covered with particular reference to (a) the types of equipment that have actually been used to smdy chemical reactions and (b) the techniques in use for in situ and on-the-fly monitoring of chemical equilibria, products structure, reaction kinetics, and mechanism. Section III deals with fundamental concepts to treat the effect of high pressure on chemical reactions with several examples of applications, but with no claim of extensive covering of the available hterature. In Section IV the results obtained in the study of molecular systems at very high pressures will be discussed, and some conclusive remarks will be presented in Section V. 

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been proven to be an excellent means of characterizing coals and related materials. This report is devoted to the evaluation of the technique as a method for situ monitoring of the chemical structural changes wrought in reactions of coal with fluid phases. This technique does not require a supporting medium (matrix) which can contain chemical artifacts which inherently serve as a barrier for access to the solid coal. The rapid response of the Fourier transform infrared technique is further beneficial for kinetic studies related to combustion, liquefaction, gasification, pyrolyses, etc. Experimental equipment and techniques are described for studies over wide ranges of pressure (10 5 Pa to ca 1.5 x 10 kPa) and temperature (298 K to 800 K). 

The ability to monitor the chemical composition of a reaction mixture in situ in real time allows both sensing and control of the process variables in order to provide more consistent product, improved efficiency and reduced costs. In situ monitoring also allows analysis of processes not amenable to sampling such as extremes of temperature and/or pressure, and toxic or air-sensitive reagents. Instmments designed for in situ measurement of IR and Raman spectra are available commercially. IR instruments typically use an ATR element at the end of a metal immersion probe (usually stainless steel or hastelloy to give good chemical compatibility). The probe is linked to the spectrometer... 

In this chapter the interrelation between mechanical properties, molecular mobility and chemical reactivity is discussed. Examples of how the changes in charge recombination luminescence, heat capacity and rate constants of chemical reactions can be related to the evolution of viscoelastic properties and the transitions encountered during isothermal cure of thermosetting materials are given. The possible application of the experimental techniques involved to in-situ cure process monitoring is also reviewed. 

This is not the case of real-time infrared (RTIR) spectroscopy, " a technique that permits one to look at the chemical processes by monitoring in situ the disappearance of the monomer reactive group upon UV exposure. By this technique conversion versus time curves have been directly recorded for polymerizations occurring within a fraction of a second. RTIR spectroscopy proved also well suited to study the photopolymerization of monomer mixtures, which leads to the formation of copolymers or interpenetrating polymer networks, as it allows the disappearance of each type of monomer to be accurately followed in the course of the reaction. The performance of the three analytical techniques most commonly used to follow in real time high-speed photopolymerizations are summarized in Table 1. 

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