Pressure-programmed controlled-flow

In the first section, the mechanisms involved in size exclusion chromatography are discussed this is an area where additional understanding and clarification still are needed. Data treatment with respect to statistical reliability of the data along with corrections for instrumental broadening is still a valid concern. Instrumental advances in the automation of multiple detectors and the developm.ent of a pressure-programmed, controlled-flow supercritical fluid chromatograph are presented. 

Pressure-Programmed Controlled-Flow Supercritical Fluid Chromatograph... 

In this paper, an instrument is described in which the inlet liquid flow rate is held constant and the pressure regulated by a pneumatically actuated flow control valve at the exit of the column. This approach permits the use of a wide-range pressure program with a controlled flow. Also, by selecting mobile phases that are liquids at ambient laboratory conditions, several types of conventional liquid chromatographic detectors may be utilized. 

If you have measured resolution of a few key components of a mixture under a small number of conditions, commercial software is available to optimize conditions (such as temperature and pressure programming) for the best separation.19 Just over the horizon, greatly improved separations will be possible by coupling two different columns in series with programmable control of the flow rates (pressure) in each column during the separation.20... 

Flow controllers should maintain a constant carrier gas flow-rate during temperature programming. In order to function properly, the carrier gas pressure to the flow controller usually must be 15-20 psig greater than the desired pressure at the column at the maximum temperature. If this is not done, or if the controller is defective, flow rates will decrease as the column temperature rises. 

To maintain the production rate, product quahty, and plant safety requires a data acquisition and control system. This system consists of tenperature, pressure, liquid level, flow rate, and conposition sensors. Computers record data and may control the process. Modem chemical plants use program logic controllers (PLC) extensively. According to Valle-Riestra [20], instrumentation cost is about 15% of pinchased equipment cost for little automatic control, 30% for full automatic control, and 40% for computer control. 

Two separate models based on Dow Advanced Continuous Simulation Language (DACSL) were used in these studies. The first model used laboratory data and parameter estimation to determine the Arrhenius constants for two desired and eight undesired reactions in a process. The second model used the Arrhenius constants, heats of reaction, different physical properties, and reactor parameters (volume, heat transfer properties, jacket control parameters, jacket inlet temperature) to simulate the effect of reaction conditions (concentration, set temperature, addition rate) on the temperature of the reaction mixture, pressure and gas flow rates in the reactor, yield, and assay of the product. The program has been successfully used in two scale-ups where the optimum safe operating conditions, effect of various possible failures, and control of possible abnormal conditions were evaluated. 

Zone 2A active damper Ap control system (Provides active Ap adjustment for control of contamination from Zone 2A to Zone 2 and HEPA input air filtration.) Fail closed causes increased Ap to from Zone2A Zone 2 Mechanical failure of active damper, loss of air pressure for damper pneumatic actuator, programmed control system failure, or plugged filter Control and monitoring system indications and periodic maintenance inspections Leak rate through airlock doors and Room 109 shielded door may increase to reduce Ap somewhat No effect to positive effect since reduced flow may extend residence time in Zone 2A HEPA and charcoal exhaust filters... 

Janssen, H.-G., Rijks, J. A. and Cramers, C. A. (1990) Flow rate control in pressure-programmed capillary supercritical fluid chromatography. J. Microcol Sep., 2, 26-32. 

Flow programming offers advantages such as reduced separation lime, less column bleed, and lower eluting temperature for labile compounds but has not been widely used in gas chromatography because temperature programming is experimentally easier to perform. In 1990, electronic pressure control (EPC) [30J was developed, which allows operation in the constant-pressure, constant-flow, and pressure-programming modes. Whether temperature programming will be re-... 

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