Streams, Process titration

The above system of directly sensing a process stream without more is often not sufficiently accurate for process control so, robot titration is preferred in that case by means of for instance the microcomputerized (64K) Titro-Analyzer ADI 2015 (see Fig. 5.28) or its more flexible type ADI 2020 (handling even four sample streams) recently developed by Applikon Dependable Instruments20. These analyzers take a sample directly from process line(s), size it, run the complete analysis and transmit the calculated result(s) to process operation (or control) they allow for a wide range of analyses (potentiometric, amperometric and colorimetric) by means of titrations to a fixed end-point or to a full curve with either single or multiple equivalent points direct measurements with or without (standard) addition of auxiliary reagents can be presented in any units (pH, mV, temperature, etc.) required. 

Titrations in non-aqueous solvents have been traditionally an important tool for the accurate determination of various pharmaceuticals, some acids in foods, use of some acids or bases in detergents, cosmetics and textile auxiharies, in the analysis of industrial process streams, the analysis of polymers [1-7]. The determination of the pK or pK values of organic compoimds with acidity or basicity constant less than 10 can only be reahsed in non-aqueous media. Although water has excellent solvent properties, it is not suitable for such organic compotmds since the pH jump at the equivalence point in aqueous solution carmot be evalrrated with reasonable accuracy, with this resrrlt, the end point carmot be found. Moreover, most of this compotmds ate not soluble in water. For these reasons, titration in non-aqueous media has recently acqttired great importance. It is now well known that non-aqueous titrations greatly depend on the solvents used [4, 8-13]. 

In addition to the analysis of the thermal stability of the perchloric acid organic reaction media mixtures, a procedure was worked out to determine the fate of the perchloric acid by chlorine analysis of the batch, effluent streams, etc. Preliminary analyses on selected process samples showed no tendency for perchloric acid to concentrate in recycle material and therefore build up in the reactor. A total of less than 1% of the initial charge of perchloric acid (total chlorides calculated as perchloric acid) was found in the combined recovered acid-ester and olefin fractions. Less than 1 % of the initial charge of perchloric acid was found in the finished ester. The analytical method used was an oxygen bomb decomposition, followed by titration of chlorides with 0.0liV silver nitrate, using a recording automatic titrator. The eventual fate of the perchloric acid catalyst was... 

Sulfide (S=) and the polysulfides S > Sf> S and S were determined (11,17,18) by titrating coal conversion process stream specimens into 25 to 30 ml of 0.01 M orthohydroxymercurybenzoate (HMB). This is a Lewis acid which reacts as follows with the Lewis bases S= through S= ... 

Other process characteristics that affect control performance are both steady-state and dynamic nonlinear behavior. Steady-state nonlinear behavior refers to the steady-state gain varying, dependent on operating point or time. For example, the pH of a process stream is highly nonlinear, dependent on the operating point on the titration curve. Further, depending on the stream component composition, the titration curve itself may vary over time. 

Studies of the acidic properties of the surfaces of samples by the TPDA method were carried out as follows. Samples (0.2 g) with 1-2 mm grain size were placed in a flow reactor (c(=0.6 cm) and were conditioned in a stream of helium (F= 60 ml/min) for 1 h at 550 °C. After decreasing the temperature to 100 °C the sample was saturated with ammonia. Completion of saturation was monitored by titration of the ammonia at the exit of the reactor. The saturated sample was treated with helium at 100 °C to remove the physically adsorbed ammonia (30 min). The sample was then subjected to programmed heating in a stream of helium at a rate of 26°/min. The thermodesorption process was monitored with a catharometer and the amount of ammonia desorbed was determined by titration with HCl. 

H. du Plessis, J.F. van Staden, Determination of sulphuric acid in process effluent streams using sequential injection titration, Talanta 52 (2000) 83. 

Another broad field of applications involves continuous coulometric titrators which are employed in process stream analyzers. In these the generating current is continuously adjusted to maintain a small excess of electrogenerated titrant to react with material in the incoming liquid or gaseous sample stream. The level of generating current is a measure of the instantaneous concentration of the titrated substance (29, 30), Coulometric titration methods have also been used in chromatographic detectors and for determination of homogeneous reaction rates (31). 

Nicholson proposed a differential potentiometric tltrator involving two indicator electrodes for the automatic control of processes in industrial plants [35]. As can be seen from Fig. 7.20, the sample and reagent streams are split and led to two half-cells via capillary tubes adjusted to provide slightly different titrated fractions. The potential difference (AE) between the two indicator electrodes Is transmitted to a control and detection system (D) which regulates the flow of titrant in an automatic fashion by means of valve V, thereby maintaining the preselected AE between the two ends of the cell. The speed of titrant addition, reflected by the flow meter (M), is a measure of the sample composition. An evaluation of the instrument carried out by the titration of dichromate with iron(II) revealed that the conditions to be used must be carefully selected. Thus, stable electrode responses are only obtained in the zone where Fe(II) prevails, and not in that where dichromate prevails over the former as the process determining the potential obtained in such a zone is irreversible. This method therefore has limited application in the control of slow reactions. 

Several papers have appeared within the last several years describing the application of thermometric titrations for silicate analysis (11). The instrumentation is less expensive than spectrometers but has not yet received widespread use in the U.S. silicate industry. However, somewhat analogous procedures are commonplace for analysis of caustic and alumina in the Bayer process streams of the aluminum industry (12). 

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