Solvent absorption rate

Ballard, B. E. and Biles, J. A. (1964). Effect of crystallizing solvent absorption rates of steroid implants. Steroids, 4, 273-8. [246]... 

Noryl is a rigid dimensionally stable material. Dimensional stabiUty results from a combination of low mold shrinkage, low coefficient of thermal expansion (5.9 x 10 per° C), good creep resistance (0.6—0.8% in 300 h at 13.8 MPa (2000 psi)), and the lowest water absorption rate of any of the engineering thermoplastics (0.07% in 24 h at room temperature). Noryl resins are completely stable to hydrolysis. They are not affected by aqueous acids or bases and have good resistance to some organic solvents, but they are attacked by aromatic or chlorinated aUphatic compounds. 

Dmg loading can be accompHshed by dispersion or adsorption. In dispersed systems, a dmg is blended into a polymer by mechanical means, such as a kneader. The viscosity of the polymer, and the size and concentration of the dmg, need to be optimized to minimize aggregates. Dmgs can also be absorbed by equiUbrating a polymer in a dmg solution. The absorption rate can be accelerated by introducing an appropriate solvent to swell the polymer. AH solvents would then have to be removed. 

It should be noted that the highest possible absorption rates will occur under conditions in which the hquid-phase resistance is negligible and the equilibrium back pressure of the gas over the solvent is zero. Such situations would exist, for instance, for NH3 absorption into an acid solution, for SO9 absorption into an alkali solution, for vaporization of water into air, and for H9S absorption from a dilute-gas stream into a strong alkali solution, provided there is a large excess of reagent in solution to consume all the dissolved gas. This is known as the gas-phase mass-transfer limited condition, wrien both the hquid-phase resistance and the back pressure of the gas equal zero. Even when the reaction is sufficiently reversible to allow a small back pres-... 

Gas solubility. A high gas solubility is desired, since this increases the absorption rate and minimizes the quantity of solvent necessary. Generally, solvents of a chemical nature similar to that of the solute to be absorbed will provide good solubility. 

For absorption applications, precoolers (e.g., spray chambers, quenchers) may be needed to saturate the gas stream or to reduce the inlet air temperature to acceptable levels to avoid solvent evaporation or reduced absorption rates. 

Note that H is simply Henry s constant corrected for units. When the solute gas is readily soluble in the liquid solvent, Henry s law constant (H or H ) is small and Kj approximately equals k, and the absorption process is controlled by the gas film resistance. For systems where the solute is relatively insoluble in the liquid, H is large and K( approximately equals k, and the absorption rate is controlled by the liquid phase resistance. In most systems, the solute has a high solubility in the solvent selected, resulting in the system being gas film resistance controlled. 

Absorption rates of carbon dioxide were measured in organic solutions of glycidyl methacrylate at 101.3 kPa to obtain the reaction kinetics between carbon dioxide and glycidyl methacrylate using tricaprylylmethylammonium chloride(Aliquat 336) as catalysts. The reaction rate constants were estimated by the mass transfer mechanism accompanied by the pseudo-first-order fast reaction. An empirical correlation between the reaction rate constants and the solubility parameters of solvents, such as toluene, A-methyl-2-pirrolidinone, and dimethyl sulfoxide was presented. 

In this study, the absorption rates of carbon dioxide into the solution of GMA and Aliquat 336 in such organic solvents as toluene, N-methyl-2-pirrolidinone(NMP), and dimethyl sulfoxide(DMSO) was measured to determine the pseudo-first-order reaction constant, which was used to obtain the elementary reaction rate constants. 

The absorption rates of CO2 were measured in such non-aqueous solvents as toluene, NMP, and DMSO with GMA concentration ranging Ifom 0.5 to 3 kmol/m in a semi-batch flat-stirred agitated vessel constructed of pyrex glass of 0.075 m inside diameter and of 0.13 m in height. The apparatus and the experimental procedure are the same as those described by... 

If polar solvents are used, either protic (e.g. alcohols) or aprotic (e.g. DMF, CH3CN, DMSO etc), the main interaction might occur between MW and polar molecules of the solvent. Energy transfer is from the solvent molecules (present in large excess) to the reaction mixtures and the reactants, and it would be expected that any specific MW effects on the reactants would be masked by solvent absorption of the field. The reaction rates should, therefore, be nearly the same as those observed under the action of conventional heating (A). 

Because the reaction is driven by protonation of the carbonyl functionality, reacting species were expected to be localized on the bed of the acid catalyst subjected to microwave irradiation. Hexane was used as a nonpolar solvent to minimize solvent absorption and superheating. Elimination of catalyst superheating in a continuous-flow reactor was most probably the reason why no significant differences were observed between the reaction rates under the action of microwave and conventional heating. 

In this case it is assumed that a pure gas A is being absorbed in a solvent eontaining a chemically inert component B. Both the solvent and B are not volatile and the fraction of A in the liquid bulk equals zero. The binary mass transfer coefficient Kij between A and the solvent in eq. (4) is given a typical value of 1 X lO" m/s, whereas the total concentration of the liquid Cr is set to 1 x 10 mol/m, also a typical value. Parameters to be chosen are the solubility of A, x i, the fraction of B in the solvent Xg, the mass transfer coefficient between A and B, K/ g and the mass transfer coefficient between B and the solvent, Kg. The results of the calculations are presented in Table 1. Since both the solvent and component B possess a zero flux. Kgs has no influence on the mass transfer process and has therefore been omitted. The computed absorption rate has been compared with the absorption rate obtained from analytical solutions for the following cases. 

The relations of molar extinction coefficients and oxygen absorption rates, plotted vs. time, are illustrated in Figures 3 and 4 (solvents, benzene and butyric acid, respectively). The variation of coefficients was parallel to the rate of oxygen absorption—i.e. the larger the coefficient, the higher the oxygen absorption rate. It is considered therefore that the catalyst at its maximum absorption coefficient is in a desirable form for oxidizing acrolein. 

Liquid-solid HPLC can be used for the separation and analysis of metal chelates of diacetyl bis(thiobenzhydrazone) (DBTH) [61]. The limit of detection of the metals as measured by the absorbance of their chelates is of the order of 1 ng per injection at a signal to noise ratio of 10 1. Absorption maxima are determined by making a wavelength scan of the individual chelates. The DBTH chelates of copper(II), mercury(II), lead(II) and zinc (II) may be analyzed in a system consisting of Merckosorb SI-60 (particle diameter, 40 /um) with benzene as the eluting solvent. Flow-rates range from 0.05 to 1 ml/min. 

The liquid holdup of the packing section decreases, which leads to a lower conversion of the kinetically controlled reactions of C02 and a reduction in the C02 absorption rate. As a consequence, the solvent mole fractions of HC()3 and carbamate decreases whereas the relative fraction of HS increases. The selectivity of the absorption process toward the H2S and HCN reduction is enhanced by minimizing the liquid holdup of the column. At the same time, a larger interfacial area improves the performance of the plant. Therefore, modem industrial sour gas scrubbers should be equipped with structured packings. 

Specification of the separation. A separation is specified by defining column feed flow rate and composition, overhead solute concentration (alternatively, solute recovery), and the concentration of solute (if any) in the lean solvent. If the purpose of absorption is to generate a specific solution, as in acid manufacture, the solution concentration completes the separation specification. For all other purposes, one specifying variable (e.g., rich solvent concentration or solvent flow rate) remains to be specified and is usually set by optimization as outlined below. 

In a majority of instances, particularly with pesticides, combinations of chemicals (e.g., organic solvents, mineral oils) are mixed to enhance the chemical toxicity. Consequently, the toxicity profile is altered. Lipophilicity modulates the absorption rate of the chemical from the site of entry into the system (lung, skin, mucous membrane). Thus, the fat-solubility pattern of a test chemical helps for easy cell membrane transport to reach the active site of intracellular enzymes and trigger possible toxic effects. The toxicity profile of active ingredients of pesticides and those of formulated products of pesticides differ widely. 

In a potassium carbonate system, different additives can be used to increase the C02 absorption rate. In any wet scrubbing system, improved tower packing can be used. A change from random to structured packing can lead to higher solvent circulation rates and improved mass transfer86. 

---