Temperature programming flow control

They are suitable for stepless speed variation and can be controlled through speed, torque, temperature or flow of a process. They can also be programmed for any sequence of operation. 

Pyrolysis-Gas Chromatography-Mass Spectrometry. In the experiments, about 2 mg of sample was pyrolyzed at 900°C in flowing helium using a Chemical Data System (CDS) Platinum Coil Pyrolysis Probe controlled by a CDS Model 122 Pyroprobe in normal mode. Products were separated on a 12 meter fused capillary column with a cross-linked poly (dimethylsilicone) stationary phase. The GC column was temperature programmed from -50 to 300°C. Individual compounds were identified with a Hewlett Packard (HP) Model 5995C low resolution quadruple GC/MS System. Data acquisition and reduction were performed on the HP 100 E-series computer running revision E RTE-6/VM software. 

This derivation shows that retention time is dependant on three factors temperature, energies of intermolecular interactions and flow rate. Temperature and flow rate are controlled by the user. Energies of intermolecular interactions are controlled by stationary phase choice. This theory is also the basis for the popular software programs that are available for computer-assisted method development and optimization [4,5,6,7]. More detailed descriptions of the theory behind retention times can be found in the appropriate chapters in the texts listed in the bibliography. 

Differential thermal analysis (DTA) is a technique in which the temperature difference between the sample tested and a reference material is measured while both are subjected to the controlled temperature program. Differential scanning calorimetry (DSC) is a technique in which the heat flow difference between the sample and reference material is monitored while both are subjected to the controlled temperature program. Thermogravimetric analysis (TGA) is a technique in which the weight of a sample is monitored during the controlled temperature program. 

Automatic operation of the metering pump allows repetitive injections with unattended operation. Precise control of the carrier-gas flow ensures stable chromatograms and reproducible timings for collection of samples. Independent column oven and vaporizer temperatures are available up to 300°C and these can be operated with temperature programming or isothermally. The latter option is the most common. 

Similarly, Aga (excerpt 13A) describes the types of columns that she will use to achieve enantiomeric separation (an essential feature of her proposed work), but she does not devote space to a description of GC/MS parameters (e.g., temperature program, carrier gas, flow rates). She describes the general approach that she will use to analyze soil samples in the soil degradation study but provides few details on how soil moisture will be controlled or how the soil samples will be extracted and analyzed (details we would expect to see in a journal article describing this work). 

In DSC the sample is subjected to a controlled temperature program, usually a temperature scan, and the heat flow to or from the sample is monitored in comparison to an inert reference [75,76], The resulting curves — which show the phase transitions in the monitored temperature range, such as crystallization, melting, or polymorphic transitions — can be evaluated with regard to phase transition temperatures and transition enthalpy. DSC is thus a convenient method to confirm the presence of solid lipid particles via the detection of a melting transition. DSC recrystaUization studies give indications of whether the dispersed material of interest is likely to pose recrystallization problems and what kind of thermal procedure may be used to ensure solidification [62-65,68,77]. 

In addition to the high-pressure assembly, the modified system incorporates a new real-time data collection system coupled with a PC based computer. Experimental parameters, such as the valve firing sequence and the reactor temperature-control program, can be set from the computer. Reactants are introduced through two high-spe pulse valves or two continuous feed valves that are fed by mass flow controllers. In high-speed transient response experiments, the QMS is set at a particular mass value and the intensity variation as a function of time is obtained. In steady-flow experiments. 

The feed gas flow rate was monitored and controlled by mass flow controllers. Product gases were fed through heated stainless steel lines to a sample loop in an automated gas chromatograph. The GC analysis was performed using two isothermal columns (80°C) in series, a Porapak T and a Molecular Sieve 5A column. When necessary, a second GC analysis using a temperature programmed Hayesep R column was used to separate and detect small hydnx arbons (such as ethylene and ethane) and H2O. 

Temperature-programmed reaction (TPR) studies of partial oxidation of propylene was carried out by flowing CsHe (Praxair), O2 (Praxair), H2 (Praxair) and Ar (Praxair) through DRIFTS and stainless steel tubular reactor (3/8 OD) loaded with catalyst. Feed gas at 40 mFmin and 1 atm consists of C3H6 (10%), O2 (10%), H2 (10%) and Ar (70%) for temperature program reaction studies. Prior to each experiment, the catalyst was pretreated in H2 (10 vol%) and O2 (10 vol%) simultaneously at 250°C. Temperature was monitored with a K type thermocouple connected to an omega temperature controller. 

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. 

The configuration of the GC system also affects the result. Many factors, such as column type, gas flow control, and temperature programming, if not set up correctly, will affect the performance of the GC. In the authors opinion, the first thing to do in a GC analysis is to choose the right column. One can then elucidate the optimal conditions for other factors (see Critical Parameters). 

All reactors, batch or flow, may be operated in three main ways in regard to temperature. These are isothermal, adiabatic and temperature-programmed. For the last, in a batch reactor the variation of temperature with time may be programmed, or in a fixed bed reactor the variation of temperature along the length of the bed may be controlled. 

Temperature-programmed reduction (TPR) is normally used in the characterization of catalysts [18,91-93], In general, to carry out a TPR experiment, a reducing gas mixture, typically 5% hydrogen in nitrogen, flows continuously over the sample [92], The gas flow rate can be varied precisely using either built-in controls or an optional mass flow controller accessory. 

A dynamic model for on-line estimation and control of a fixed bed catalytic reactor must be based on a thorough experimental program. It must be able to predict the measured experimental effects of the variation of key variables such as jacket temperature, feed flow rate, composition and temperature on the dynamic behaviour of the reactor this, in turn, requires the knowledge of the kinetic and "effective" transport parameters involved in the model. 

C/min) divided by the flow rate (F ml/min). Because of this, it may be hard to reproduce retention data in temperature programmed GC exactly, because whereas it may be possible to accurately control the heating rate, it may be more difficult to reproduce the flow rate F within 0.5%. 

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