Physical dissolution

When performing dissolution testing, there are many ways that the test may generate erroneous results. The testing equipment and its environment, handling of the sample, formulation, in situ reactions, automation and analytical techniques can all be the cause of errors and variability. The physical dissolution of the dosage form should be unencumbered at all times. Certain aspects of the equipment calibration process may show these errors as well as close visual observation of the test. The essentials of the test are accuracy of results and robustness of the method. Aberrant and unexpected results do occur, however, and the analyst should be well trained to examine all aspects of the dissolution test and observe the equipment in operation. 

To determine whether the low temperature physical dissolution could be separated from the processes with higher activation energies, the following experiments were conducted. 

Toluene is a non-donor solvent and as such Its effect on coal Is one primarily of physical dissolution. 

Notice that four of these steps (s2 through s5) are chemical or electrochemical steps, while step Si denotes the physical dissolution of carbon dioxide as it moves from the gas phase into the electrolyte phase. 

As reaction severity approaches zero the Monterey coal conversion is about 70 percent and the Wyodak is about 40 percent. Liquefaction appears to occur very rapidly to these levels and then slower to the maximum conversion. The initial liquefaction may be a physical dissolution while the slower rate represents a reaction in which chemical bonds are broken, although other explanations are possible. (10)... 

CO is extracted by countercurrent absorption in a column operating at about 2.10 Pa absolute, with a feedstock inlet temperature of about 40 C and effluent exit around 65 C. This is accompanied by the physical dissolution of small amounts of other constituents, including hydrogen, which are salted out by cooling and expansion of the extract at 0.5, 10 Pa absolute Thecomple.x obtained is then preheated to 100 to 105 C and sent to a regeneration column. In this column, operating at 0.15.10 Pa absolute, CO is liberated... 

MULTIPLICATION — An operation of the Great Work by means of which the Powder of Projection is multiplied, either in quantity or quality, to infinity, according to the good pleasure of the artist. In consists in recommencing the operation which has been already performed, but with exalted and perfected matters, and not with crude substances as in the previous case. The whole secret, says one Philosopher, is a physical dissolution in Mercury and a reduction into its First Matter. With this end in view the Philosophers take the Matter, as prepared and cocted by Nature, and reduce it into its First Matter, into the Philosophical Mercury from which it has been extracted. In order to attain to a full acquaintance with this operation five points must be observed ... 

Soluble mucus was considered to be the transient physical dissolution product of the visible surface mucin before it undergoes further enzymatic degradation in the stomach (Gll). It precipitates from filter ... 

In these equations sulfur (IV) in the aqueous phase is the sum of SOz H20, HSO3 and SO,-, while [5.11] describes a simple physical dissolution. Considering the foregoing discussion, the problem is to determine the nature and rate of the sulfur (IV)- sulfur (VI) transformation of bisulfite (HSOj) or sulfite (SOf ) ions (unfortunately there is no agreement among different authors as to whether the bisulfite ion, the sulfite ion, or both is the reactive species). It is well documented that the oxidation of sulfur (IV) to form sulfate ions can be proceeded by the following processes ... 

Electrochemical measurements have shown the limiting stage in the reaction of sulphur with liquid ammonia at -40 C to be the physical dissolution of the element. The number of moles of solid S dissolving equalled the number of NHt SCN ion pairs formed in the presence of KSCN. The principal reaction taking place was ... 

The mechanisms of sorption and/or the interaction of the solute with the mobile phase can be summarized as follows u, physical dissolution in the phase b, physical adsorption on the surface of the phase c, chemical reaction in the bulk phase or on its surface (acido-basic equilibrium, formation of coordination complexes or chelates, association of ionic pairs, exchange of ions, precipitation) d, steric exclusion (molecular sieving effect, gel permeation) e, bioaffinity association. 

For the purposes of this description, the reaction mechanism is considered to consist of two steps. The first of these takes place entirely in the liquid phase and is a bulk diffusion step. It is characterized by a mass transfer coefficient k and is a function of the hydrodynamics of the system, i.e. in this case, the agitation conditions. If the process of interest is a simple physical dissolution, then indeed only this bulk diffusion step is important and the reaction rate is the rate of dissolution. In general, however, there is also a reaction step which takes place at the surface of the solid. 

Neutral paint strippers include halogen-free organic solvents (e.g., glycols, glycol ethers, l-methyl-2-pyrrolidinone) which are generally used at 20-40°C. In contrast to the alkaline paint removers, neutral paint strippers result in purely physical dissolution of the paint from the substrate. Their use is therefore restricted to removing physically drying paints. 

Propylene dissolves in two modes, a physical dissolution mode in the matrix and a binding mode resulting from a reversible chemical reaction with metal complexes. Henry s law commonly expresses the physical dissolution mode for small molecules, while the Langmuir model adequately describes the reversible binding mode, as shown in Eq. (9-2). Mathematically, a Langmuir adsorption isotherm for a small molecule in a porous media is identical to the expression of the olefin concentration bound to the metal complex. 

Specific solvents extract 20%-40% of the coal at temperatures below 200°C (390°F) and the nature of the extract is believed to be similar to, or even represent, the original coal. Specific solvents extract coal by a process of physical dissolution and the nature of the coal extract and the parent coal is believed to be similar. Hence, such solvents can be considered nonse-lective in their action on coal and usually contain a nitrogen atom and an oxygen atom with unshared electrons as a lone pair (Dryden, 1951a). Pyridine, N-methylpyrrolidone, dimeth-ylformamide, and dimethylacetamide are examples of this type of solvent. They are mostly nucleophilic in nature due to the presence of a lone pair of electrons on the nitrogen atom. 

In developing an understanding of the likely magnitude of heat release, the influence of reaction can be initially ignored, so that r(c, T) = o, and the processes taking place now simply involve physical dissolution and diffusion of the dissolved gas and the accompanying conduction of the heat of solution into the semi-infinite liquid phase. By manipulation of the two simultaneous unsteady diffusion/conduction equations, which obey the interfacial boundeiry condition... 

In general, the rate of transfer of the solvent from the bulk solution to the solid surface is quite rapid, and the rate of transfer of the solvent into the solid can be somewhat rapid or slow. These are not, in many cases, the rate-limiting steps in the overall leaching process. This solvent transfer usually occurs initially when the particles are first contacted with the solvent. The dissolving of the solute into the solvent inside the solid may be simply a physical dissolution process or an actual chemical reaction that frees the solute for dissolution. Our knowledge of the dissolution process is limited and the mechanism may be different in each solid (Kl). 

The biological impact due to increased acidification of sea and dissolution of coral matter could be detrimental and irreversible. That is because the timescales of physical dissolution and biological recovery are different. Dissolution and precipitation processes of aqueous CaC03 solutions are controlled by acid-base chemistry these processes are thermodynamically driven. 

Finally, calculations (not comparable with experiment) were periormed which better approximate the physical dissolution process. In these calculations, the dissolved uranium is allowed to spread throve the water solution in layers of increasing ra us and decreasii uranium concentration until the condition of total homogenization is reached. It is found that systems are more reactive when the dissolved material is in close proximity to the dissolving sphere. 

Although the anion is the key factor in determining the physical dissolution of CO 2 in ionic liquids, the cation also plays a role. Despite a wide range of cations reported for CO2 capture, many research groups have concentrated on imidazolium cation. This is because of the acidic C2 proton from the imidazolium ring can interact with anion... 

When solid particles dissolve gradually, either by chemical reaction at their surface or by physical dissolution, and retain their original form, modelling of the process is relatively simple. However, in practice solids tend to be broken up and fall apart. This will always enhance the process rate, so a design based on dissolution of particles that remain intact is dways conservative. 

Figure 2.10 illustrates a diagram of schematizing the processes of multiphase reactions on a liquid particle by the resistant model. As shown in the scheme, multiphase reactions include the processes, (1) transport and diffusion of a gaseous molecule to the gas-liquid surface, (2) accommodation at the interface, (3) -gas-liquid equilibrium at the interface, (4) physical dissolution and diffusion into the bulk liquid, and (5) chemical reaction in the bulk liquid. 

Capture processes were developed in the past to remove acid gases such as carbon dioxide and hydrogen sulfide (H2S) from natural gas. They are mainly based on chemical and physical dissolution of the acid gas in aqueous solutions of amines. The technique is considered as mature enough to be adapted in next future to the treatment of post combustion effluents. The new processes should take into account difference from natural gas treatment such as temperature, pressure or composition of the effluent. However one major barrier for the integration into industrial sites in the few coming years is the economical cost of the so called ton of CO2 avoided. Specific researches are then carried out on both the technology and the choice of the absorbent solutions. 

Absorption in alkaline solution is a common principle used in acid gases capture processes operating for decades in natural gas treatment. The reference absorbent is aqueous solution of monoethanolamine (MEA). The mechanism of capture is a combination of chemical and physical dissolution. The chemical dissolution is based on an acido-basic reaction. The reaction must be reversible in order to regenerate the absorbent solution and recover carbon dioxide for storage. The physical dissolution, usually observed fot high partial pressure of CO2, can be improved by addition of specific physical solvent. 

The dissolution of CO2 in aqueous solution of amine is combination of chemical reactions and physical dissolution. The chemical reactions involved depend on the type of the amine. 

The increase of partial pressure of carbon dioxide forces the physical dissolution. This mechanism is purely mechanical and results in the apparition of molecular CO2 in the solution. This physical dissolution is particularly considerate in the treatment of natural gas in which partial pressure of carbon dioxide can reach hundreds of bars. In the case of CO2 capture in industrial effluent, partial pressure of CO2 remains below atmospheric pressure and carbon dioxide is mainly chemically absorbed with formation of carbamate and hydrogen carbonate. 

The solution concentration and the choice of the amine will be adapted to the conditions of temperature, pressure and composition of the gas stream to be treated. It has been shown that amines can also be combined to improve kinetic of absorption and quantity of dissolved gas [12]. In some cases, physical solvents can also be added to the solution in order to increase physical dissolution. 

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