Weight mean vapor molecular

Inclusion of the mean vapor molecular weight in Equation 6 recognizes that this represents the environment in which the flash will occur. The mean molecular weight of the vapor at the trial temperature is cal-... 

Vapor density provides a useful means of molecular weight determination for substances which exert a high vapor pressure at or near room temperature. In the simplest case, an evacuated bulb of known volume is tared, filled with a measured pressure of the gas at a known temperature, and is reweighed. These pressure, temperature, and volume data yield the moles of gas (if the ideal gas law is assumed) and the additional weight data permit the calculation of (he number of grams per mole. 

The term gas-phase polymerization is a misnomer in that it refers only to a polymerization reaction initiated on monomer vapors, generally by photochemical means. High-molecular weight polymer particles are not volatile, so a fog of polymer particles containing growing chains quickly form and the major portion of the polymerization reaction occurs in the condensed state. 

Prior to the work of Eaoult, who developed (1882-1885) the cryo-scopic method for determining molecular weights of dissolved substances, and to van t Hoff s formulation (1886-1888) of the solution laws, no method was available for quantitatively determining the molecular weights of substances in solution. The vapor density method obviously could not be applied to any but very low polymers. No means was at hand for determining the state of polymerization even in instances where polymerization was suspected. 

The relative vapor density (RVD) values in Table 18.9 have been calculated as the density of dry air saturated with the compound of interest at 20°C. This represents the weighted mean molecular weight of the compound-saturated air relative to the mean molecular weight of dry air, which is 29 g/mol. The RVD value may be calculated from Equation 18.23 ... 

A West Texas gas oil is cracked in a tubular reactor packed with silica-alumina cracking catalyst. The liquid feed mw = 0.255) is vaporized, heated, enters the reactor at 630°C and 1 atm, and with adequate temperature control stays close to this temperature within the reactor. The cracking reaction follows first-order kinetics and gives a variety of products with mean molecular weight mw = 0.070. Half the feed is cracked for a feed rate of 60 m liquid/m reactor hr. In the industry this measure of feed rate is called the liquid hourly space velocity. Thus LHSV = 60 hr Find the first-order rate constants k and k " for this cracking reaction. 

PEG-200 was a commercial product (Chemische Werke Hiils, A. G.) with mean molecular weight 182 as determined osmometrically in the vapor phase (with an error of 5%) and with water content of 4.42% as determined by K. Fischer s method. (All weights were corrected with respect to this moisture.) CaCl2 was of analytical reagent grade. For the standard solutions, the stock saturated solution was prepared and maintained at the constant temperature of 25°C. The concentration of CaCl2 was tested by the chloride content argento-metrically. 

Certain numerical algorithms can benefit from the equation in a form that has the dependent variable Ft directly in the diffusive terms on the right-hand side. Moreover, for flows that have relatively small mean-molecular-weight gradients, the second term may be negligible. Examples of this situation would be if there is an inert carrier gas that dominates the species composition. It is not unusual in chemical-vapor-deposition processes for... 

The vapor leaving each tray is in equilibrium with the liquid. This means that the vapor leaving each tray is at its dew point and the liquid leaving each tray is at its bubble point. As the top reflux rate is increased, all the trays are cooled. The vapors leaving trays 3, 4, and 5 are cooled. As a vapor at its dew point cools, the heavier components in the vapor condense into a liquid. The remaining vapors have a lower molecular weight because they are lighter. But this is only half the story. Let us continue ... 

This quantity, in nitroglycol for example, reaches 9°. In fact, a combustion reaction is accompanied, as a rule, by an increase in the number of molecules and a decrease in the mean molecular weight, and the diffusion coefficient of the vapors proves smaller than the thermal diffusivity of the mixture. We should consider that the order of magnitude of ATB here does not change. 

MW = mean molecular weight of the vapor and noncondensable, lb/mole N = number of moles diffused, mole/hr pv = partial pressure of the vapor, atm Pt = total pressure, atm S = diffusion surface, ft2... 

The supersaturation in condensers arises for two reasons. First, the condensable vapor is generally of higher molecular weight than the noncondensable gas. This means that the molecular diffusivity of the vapor will be much less than the thermal diffusivity of the gas. Restated, the ratio of NSc/Npr is greater than 1. The result is that a condenser yields more heat-transfer units dTg/(Tg — Tt) than mass-transfer units dYg/(Yg — Yt). Second, both transfer processes derive their driving force from the temperature difference between the gas Tg and the interface Tt. Each incremental decrease in interface temperature... 

Molecular weight determination of carbosilane dendrimers is best accomplished with electrospray or MALDI-TOF mass spectroscopy, but is also possible with vapor pressure osmometry measurements. In many cases, MALDI-TOF data is sufficiently accurate to indicate slight structural imperfections in dendrimers due to incomplete reactions. Gel permeation chromatography is generally not an effective means of measuring molecular weights of carbosilane dendrimers due to the substantial differences in hydrodynamic volume between spherical dendrimers and linear polystyrene standards. 

Bersted BH (1973) Molecular weight determination of high polymers by mean of vapor pressure osmometry and the solute dependence of the constant of calibration J Appl Polym Sci 17 1415-1430... 

By the end of the nineteenth century, molecular weight determinations carried out by means of vapor density measurements proved that phosphorus(V) and phosphorus(III) oxide in the gaseous state consist of molecules of the compositions P406 (3,86) and P4O10 (87), respectively. However, their molecular structures remained uncertain (see, for example, Ref. 88) until adequate techniques for structure determination such as electron and X-ray diffraction became available (6, 7, 72). 

Since (w 2 + u a) = 0, or in other words, since u 2 and u a are not in the basis, we have a solution feasible for the original problem, with x2 — 1, % = 11, and u2 = 6. That is, the vapor pressure is 11 — Ui = 0 and the mean molecular weight is 34 + u2 = 40. This is the feasible solution which we remarked at the beginning was apparent from inspection of the equations. If at some stage of the calculations we had found that all of the coefficients of the function (u 2 + u a) were negative, indicating that no change of basis could reduce (u 2 + u a), and if (u 2 + u a) were not already zero, we would have been able to conclude that no feasible solution existed. 

This basis is optimal, since neither of the nonbasic variables Xi and Ui can be brought into the basis without increasing the unit cost. Hence the optimal composition is xt = 0, x2 = 0.157, and xa = 0.843. The vapor pressure is 11, just at the limit, while the mean molecular weight is 2.86 above the minimum, or 36.86. The minimum unit cost is 2.84 per pound mole. 

Table 3 (constructed from Refs. 21-24) lists various physical properties for a variety of candidate SCF solvents. A cursory inspection of the entries in this table shows that many hydrocarbons have a critical pressure close to 45 bar and the critical temperature of SCF solvents increases as the molecular weight of the solvent increases or as the polarity or intramolecular hydrogen bonding of the solvent increases. This means that the solvent s vapor pressure curve extends to very high temperature. 

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