Residence time and concentration

The aim of the present study was to apply steam pretreatment to corn stover and investigate the influence of different pretreatment conditions— temperature, residence time, and concentration of H2S04—on sugar yield and the effect of inhibitors on subsequent ethanol yield. 

These are all devices which reduce both the product concentration and residence time in the gas phase and so minimize product losses through subsequent reactions. Methods (1), (2), and (3) are means of controlling selectively the residence time and concentrations of certain specific products in the discharge and a choice can only be made between them in the light of the physical properties of the various constituents of the gas phase. The fourth method, which does not discriminate between the concentrations or residence times of reactants and products, can only be evaluated when the relative rates of the competing reactions are known. Of the various techniques available, simultaneous reaction and absorption in a heterogeneous reactor (Method 2) opens up interesting... 

The factors which govern the efficiency of waste destmction iaclude atomi2ation, ie, mean drop si2e, and si2e distribution temperature residence time O2 concentration and flow patterns. 

The classical experiment tracks the off-gas composition as a function of temperature at fixed residence time and oxidant level. Treating feed disappearance as first order, the pre-exponential factor and activation energy, E, in the Arrhenius expression (eq. 35) can be obtained. These studies tend to confirm large activation energies typical of the bond mpture mechanism assumed earlier. However, an accelerating effect of the oxidant is also evident in some results, so that the thermal mpture mechanism probably overestimates the time requirement by as much as several orders of magnitude (39). Measurements at several levels of oxidant concentration are useful for determining how important it is to maintain spatial uniformity of oxidant concentration in the incinerator. 

The equiHbrium approach should not be used for species that are highly sensitive to variations in residence time, oxidant concentration, or temperature, or for species which clearly do not reach equiHbrium. There are at least three classes of compounds that cannot be estimated weU by assuming equiHbrium CO, products of incomplete combustion (PlCs), and NO. Under most incineration conditions, chemical equiHbrium results in virtually no CO or PlCs, as required by regulations. Thus success depends on achieving a nearly complete approach to equiHbrium. Calculations depend on detailed knowledge of the reaction network, its kinetics, the mixing patterns, and the temperature, oxidant, and velocity profiles. 

Since about 1965, efficient vacuum evaporators have been used in most plants. Second stage evaporators, where the ammonium nitrate is concentrated to more than 99%, are designed to retain only a small volume of melt, have short residence times, and are protected from overheating and contamination by sensitizers. Falling film units are especially suited for this appHcation. 

Plugflow reactor (PER), in which all portions of the charge have the same residence time. The concentration varies with time and position, according to the equation,... 

Fig. 30. Conversions of two reactors with the same kinetics, residence times, and inlet concentrations.

Glaser and Lichtenstein (G3) measured the liquid residence-time distribution for cocurrent downward flow of gas and liquid in columns of -in., 2-in., and 1-ft diameter packed with porous or nonporous -pg-in. or -in. cylindrical packings. The fluid media were an aqueous calcium chloride solution and air in one series of experiments and kerosene and hydrogen in another. Pulses of radioactive tracer (carbon-12, phosphorous-32, or rubi-dium-86) were injected outside the column, and the effluent concentration measured by Geiger counter. Axial dispersion was characterized by variability (defined as the standard deviation of residence time divided by the average residence time), and corrections for end effects were included in the analysis. The experiments indicate no effect of bed diameter upon variability. For a packed bed of porous particles, variability was found to consist of three components (1) Variability due to bulk flow through the bed... 

Chemically reactive elements should have a short residence time in seawater and a low concentration. A positive correlation exists between the mean ocean residence time and the mean oceanic concentration however, the scatter is too great for the plot to be used for predictive purposes. Whitfield and Turner (1979) and Whitfield (1979) have shown that a more important correlation exists between residence time and a measure of the partitioning of the elements between the ocean and crustal rocks. The rationale behind this approach is that the oceanic concentrations have been roughly constant, while the elements in crustal rocks have cycled through the oceans. This partitioning of the elements may reflect the long-term chemical controls. The relationship can be summarized by an equation of the form... 

The ratio of monomer to initiator ranges from 1 1 to 10 1, and preferentially is set to 9 1 [126]. By setting initiator concentration, initiator type, residence time and temperature, the polymer molecular weight, conversion and solution viscosity are determined. The monomer is, e.g. acrylate-based with or without styrene. The pressure is regulated to be 2 x 10 -5 x 10 Pa in order to avoid solvent and monomer boiling. 

P 62] The acid cleavage was carried out at 45-75 °C at a pressure of 1-5 bar. Water may be added at levels of 0.3-1 wt.-% [64]. This addition was made upstream of the micro reactor or directly inside. The residence time was set in the range 0.5-5 min. Sulfuric acid was used as catalyst. By changing residence time and acid addition, the residual cumene hydroperoxide content was favorably reduced to 0.1-0.3 wt.-%. For this, an acid concentration of 50-500 ppm is typically required. Part of the so cleaved product stream may be recycled. 

The quantity of unoxidised NO in the gases leaving the cooler-condenser will depend on the residence time and the concentration of NO and N02 in the inlet stream. For simplicity in this preliminary balance the quantity of NO in the outlet gas will be taken as equal to the quantity formed from the absorption of N02 in the condensate to form nitric acid ... 

However, the laboratory data seem to indicate that maintaining a constant concentration in the reactor to maintain 63% sulfuric acid in the reactor would be beneficial. Careful temperature control is also important. These two factors would suggest that a mixed-flow reactor is appropriate. There is a conflict. How can a well-defined residence time and a constant concentration of sulfuric acid be simultaneously maintained ... 

MAFRAM divides the agricultural environment into two main zones, which are the on- and off-farm zones. Six compartments (air, water, soil, sediment, aboveground plants, and roots) are included in on- and off-farm zones. The MAFRAM output includes the intercompartmental transport and transfer rates, the primary loss mechanisms, chemical concentration, amount, residence time, and the rank of risk in each compartment. 

The bulk of this chapter is devoted to a discussion of optimization with regard to selectivity considerations. In the sections that follow we will take 3 = 0 in order to concentrate on the primary effects and to simplify the discussion. Consequently, in this chapter, the terms space time, mean residence time, and holding time may be used interchangeably. 

Thermal plasma-assisted decomposition (cracking) of heavy hydrocarbons is reported in Ref. 141. Decomposition of paraffinic hydrocarbons including C16H34 by Ar-H2 plasma was carried out by continuous injection of the hydrocarbon in the spouted-bed reactor. Controlling temperature, residence time, and H2 concentration allows reaching the... 

Recently, such a temperature oscillation was also observed by Zhang et al (27,28) with nickel foils. Furthermore, Basile et al (29) used IR thermography to monitor the surface temperature of the nickel foil during the methane partial oxidation reaction by following its changes with the residence time and reactant concentration. Their results demonstrate that the surface temperature profile was strongly dependent on the catalyst composition and the tendency of nickel to be oxidized. Simulations of the kinetics (30) indicated that the effective thermal conductivity of the catalyst bed influences the hot-spot temperature. 

The example shows that residence time and pipe diameter affect the sulfide concentration in the wastewater of a pressure pipe. Although this impact has opposite directions, the fast transport results in the lowest sulfide concentration. 

A reversible reaction, A B, is conducted in a two stage CSTR with cooling between stages to 25 C which is also the fresh feed temperature. Inlet concentration Aq = 10, Other data follow. Compare residence times and other operating conditions for 80% conversion with and without intercooling. 

Find the temperatures, residence time and the first stage concentration when the overall conversion is to be 90%,... 

---