Process parameters initial temperature

This section is principally devoted to the preparation of thermally sensitive hydrogel particles using the batch polymerization process. The effect of each reactant and parameter (initiator, temperature, cross-linker agent) on the polymerization process (polymerization kinetic, conversion, final particle size, morphology, water-soluble polymer, etc.) is presented and discussed. For the... 

The limitations of early instrumentation were extreme. Engineers were first able to get on-line measurements for only the simplest process parameters - initially only temperature and pressure. As interest in on-line measurements grew, various manufacturers developed instrumentation for chemical process streams. Soon, instrumentation was available for simple infrared measurements, water determination, simple ultraviolet measurements, density, and viscosity. The spectroscopic instruments (1R, UV, etc) of this era were simplistic devices similar to colorimeters that used filters to provide the appropriate frequency or range of frequencies to quantitate one or more components of the process stream. 

The initiator is the most important reactor parameter in the polymer process. The initiator type affects the molecular weight and conversion limits in a reactor of fixed size and the molecular weight distribution of the material at a given conversion level. The initiator type dictates the initiator amount for a given conversion, the operating temperature range and sensitivity of the reactor to an unstable condition. 

Mikroreaktorenfur die chemische Synthese, Nachrichten aus der Chemie, May 2000 Chip technology initiates quest for small structures better temperature control on the small scale fast mixing by diffusion several kg productivity per day no novel, but better chemistry perfect control over process parameters corresponding increase in selectivity basic micro-reactor functions selected examples of use micro reactors as routine tools in the laboratory first start-up companies [113],... 

The desired product is P, while S is an unwanted by-product. The reaction is carried out in a solution for which the physical properties are independent of temperature and composition. Both reactions are of first-order kinetics with the parameters given in Table 5.3-2 the specific heat of the reaction mixture, c, is 4 kJ kg K , and the density, p, is 1000 kg m . The initial concentration of /I is cao = 1 mol litre and the initial temperature is To = 295 K. The coolant temperature is 345 K for the first period of 1 h, and then it is decreased to 295 K for the subsequent period of 0.5 h. Figs. 5.3-13 and 5.3-14 show temperature and conversion curves for the 63 and 6,300 litres batch reactors, which are typical sizes of pilot and full-scale plants. The overall heat-transfer coefficient was assumed to be 500 W m K. The two reactors behaved very different. The yield of P in a large-scale reactor is significantly lower than that in a pilot scale 1.2 mol % and 38.5 mol %, respectively. Because conversions were commensurate in both reactors, the selectivity of the process in the large reactor was also much lower. 

The variation of the unit cell parameters versus temperature is reported in Figure 2. For the as-synthesized sample, at room temperature, the cell parameter are a=7.5675, b=l 8.1187, c=26.0605 A and the cell volume is 3573.2 A3. In the first step of heating (T <120 °C) only small variation of the cell parameters are shown. The volume variation is mostly due to the c parameter shortening, since it is the most subjected to temperature induced modifications. Between 120 and 360 °C a remains almost constant, c decreases of 0.1%, while b slightly increase-up to 215 °C- and subsequently regains its initial value. The combination of these variations leads an inflection in the volume contraction, slowing down its decrease. Above 390 °C the cell volume remains almost constant and only minor variations in the parameters are observed. The final values obtained after the refinement at 715 °C accounted a variation of -0.25, +0.07, -0.77 and -0.95% for a, b, c and V respectively. The minor variation of the cell parameters above 450 °C indicates that at this temperature the dehydration process is almost fulfilled. The TG curve in flowing air shows that the total mass variation of the as-synthesized phase is 15.8%. Dehydration process is almost fulfilled at about 500 °C above this temperature only... 

With the above-described heat transfer model and rapid solidification kinetic model, along with the related process parameters and thermophysical properties of atomization gases (Tables 2.6 and 2.7) and metals/alloys (Tables 2.8,2.9,2.10 and 2.11), the 2-D distributions of transient droplet temperatures, cooling rates, achievable undercoolings, and solid fractions in the spray can be calculated, once the initial droplet sizes, temperatures, and velocities are established by the modeling of the atomization stage, as discussed in the previous subsection. For the implementation of the heat transfer model and the rapid solidification kinetic model, finite difference methods or finite element methods may be used. To characterize the entire size distribution of droplets, some specific droplet sizes (forexample,.D0 16,Z>05, andZ)0 84) are to be considered in the calculations of the 2-D motion, cooling and solidification histories. 

According to the above considerations if the optimization is performed under fixed process parameters the initial step in library design is finished, i.e. the catalysts of the initial library can be introduced into the experimental hologram. However, it is strongly recommended to include one or two process parameters into the library design procedure. Reaction temperature and hydrogen pressure is the two most important process parameters influencing both the activity and the reactivity. 

Novozhilov (Ref 9) noted other instances where the instability criterion of Zel dovich is not satisfied. He also noted ZeTdovich s assertion that the form of the stability criterion may change if the variation in the surface temperature and the inertia of the reaction layer of the condensed phase are taken into account, and stability criteria obtained under the assumption that the chemical reaction zone in the condensed phase and all of the processes in the gas phase are without inertia. Novozhilov used a more general consideration of the problem to show that the stability region is determined by only two parameters Zel dovich s k and the partial derivative r of the surface temperature with respect to the initial temperature at constant pressure t=(dTi/(fro)p. Combustion is always stable if k 1, combustion is stable only when r >(k — l) /(k +1)... 

Let us introduce a characteristic temperature T, which is typical for the specific process being discussed (it might be the wall temperature, the initial temperature of the reactive medium, and so on). The introduction of this characteristic temperature allows us to obtain partial derivatives 5. These are as follows ... 

This type of process is much less sensitive to process parameter than the isoperi-bolic or polytropic reactors. By increasing the heating rate from 10 to 20 °C IT1, the temperature departs from its set point by some degrees. At 30 °C h"1 the set temperature is significantly surpassed and at 40 °C h 1 there is a significant overshoot of the maximum temperature of 100 °C. The disadvantage of this policy is that the initiation of the reaction is difficult to detect. Nevertheless, it may be detected by observing the temperature difference between jacket and reaction medium. 

The dynamic behavior of the reactor can be simulated by solving Eqs. (1)—(6). The differential-algebraic solver DASSL [14] is used to give the solution of these equations. The initial conditions for MA, MB, Me, Mo used in all simulation studies are 12, 12, 0, and Okmol, respectively. The initial values of both reactor and jacket temperature are set to 20 °C. Other process parameter values used in the reactor models are listed in Table 1. 

Drug release may be affected by a number of process parameters such as drug loading, polymer molecular weight, polymer composition, initial concentration of the polymer in the organic phase of the emulsion, amount of emulsifier, stirring speed, vacuum pressure, solvent evaporation time and temperature. These parameters were kept constant and only the amount of NaOH was varied. Therefore, changes in the in vitro release curves should reflect only the effect of NaOH in various concentrations. ... 

In the present work the decomposition of hydrocarbons was carried out at presence of intermetallide hydride Mg2NiHx as high-dispersed powder which was received by hydride dispergation of an initial alloy. The work is aimed at finding correlation between process parameters (temperature, composition of gas phase) varied in a wide range and the contents of carbonaceous products. 

Heterogeneous catalysts are not just chemicals in the ordinary sense of the word they are performance chemicals or surface-active materials. Naturally, the performance of the catalyst will depend not so much on the initial composition or surface of it as on the real surface, which is formed and stabilized and then changing dynamically under the prevailing process conditions. Here one has to take into account known and controlled process parameters such as temperature, pressure, reactant concentration, and space velocity, as well as variable factors such as feed composition, and unpredictable or unsuspected factors such as impurities and poisons in the feed [65, 66]. 

Methane-coupling reaction conversions and yields less than 25 percent initially were—and still are—below those acceptable for commercial fuel and chemical feedstock production. But worldwide research and development in more recent years continue to suggest that variations in process parameters, reactor design, and catalyst composition and structure may bridge this gap. Lower reaction temperatures—in the 300-400°C range may... 

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