Solvent exchange methods

Table 5 lists the results of a-pinene conversion obtained over niobium or titanium grafted MCM-41 and MCM-48 samples where the template was first removed by solvent exchange method followed by calcination. The catalytic activities are comparatively higher than ones obtained over niobium or titanium grafted MCM-41 and MCM-48 samples where template was removed using a conventional thermal method (direct calcination). A similar trend for the H202 efficiency was noticed. 

Epoxidation over niobium or titanium grafted mesoporous molecular sieves where template was removed by solvent exchange method prior to calcination ... 

A variety of vinyl monomers, such as methyl methacrylate and styrene, may be used. Complete filling of the cell lumens and other voids (the full-cell process ) is easily accomplished by first subjecting the wood to a partial vacuum (about 0.3 in. of Hg) and then covering it with the monomer and soaking it for 2-6 hr, depending upon the species of wood and its dimensions. Some penetration of the monomer into the cell walls also may be obtained by using a diffusion process, such as a solvent-exchange method. 

Yeo, Y. Chen, A.U. Basaran, O.A. Park, K. Solvent exchange method a novel microencapsulation technique using dual microdispensers. Pharm. Res. 2004, 21 (8), 1419-1427. 

The wet cellulose acetate membranes prepared in the foregoing step for re verse osmosis should be dried to be used for gas separation. The water in the membrane cannot be evaporated in air the asymmeuic porous structure of the membrane is destroyed during the evaporation step. Instead, the following multiple-stage solvent exchange method can be applied. 

The above calculation steps were applied to the experimental data obtained using a cellulose acetate reverse osmosis membrane dried by the solvent exchange method. The details of the condition of the membrane preparation are reported in the literature [236]. The transport parameters obtained from the above experimental data were A = 0.1277 x 10 m", Aj = 0.1500 x 10 kmoI/m sPa, K = 4.0 x 10 m, and (7 = 1.3 x 10" m for CO2 gas. Note that an average pore size R as low as 4 x 10" m was obtained. Furthermore. flux components, Qsh and Qs were calculated and the contribution of the component flux to the total flux was determined for different gases under different operating pressures. The results are illustrated in Figure 6.20. 

GC method was used that separates the 20 most common API solvents for the identification of unknown solvent residues in samples. Then a second shorter analysis time method was used for fast throughput and quantitation of samples. An example of a generic GC process solvents exchange method is illustrated in Figure 7, with a mixture of 26 common process solvents listed in the ICH guideline diluted in N,N-dimethylacetamide. Figure 8 shows an example of actual process solvent-exchange analysis. 

FIGURE 7 Generic solvent-exchange method, direct injection GC/FID. From bottom to top blank injection and GC volatiles test solution. Peaks I, methanol 2, n-pentane 3, ethanol 4, acetone 5 isopropyl alcohol 6, acetonitrile 7, methyl acetate 8, methylene chloride 9 methyl tertiary butyl ether 10, n-hexane 11, propanol 12, methyl ethyl ketone 13, ethyl acetate 14, sec-butanol 15, tetrahydrofuran 16, cyclohexane 17, hexamethyidisiloxane 18, benzene 19, n-heptane 20, butyl alcohol 21, 1,4-dioxane 22, methyl isobutyl ketone 23, pyridine 24, toluene 25, isobutyl acetate 26, n-butyl acetate 27, p-xylene 28, dimethylacetamide 29, solvent impurities. 

Nanofiltration can become a strong alternative for traditional solvent exchange methods, without the drawbacks of elevated temperatures or azeotropic mixtures (Livingston et al., 2003). The principle requires a membrane that shows high permeation rates for the (first) solvent, whereas the component should be rejected. The feed stream is then filtered until nearly 10-30% of the volume is retained (and thus severely concentrated). Afterwards,... 

Sample preparation Cement pastes should be mixed, cast and dried according to the recommendations given in Chapter 1 describing the best way to prepare the sample. For MIP, the solvent exchange method is best suited to preserve the pores. The sample should be cut at the required dimension and mass in the bulk of the paste (i.e. the edges of the sample should be discarded). 

As illustration, Figure 9.9a shows MIP cumulative pore volumes for a white cement paste mixed at w/c = 0.40 after 28 days of sealed hydration using different sample drying methods. Figure 9.9b shows the first derivatives of these results. Taking the solvent exchange method as an example, there are two main intrusion steps which correspond to two main peaks on the derivative. The peak centred at 25 nm pore radius is part of the capillary pore volume. The degree to which the peak located at small pore radii... 

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