Slurry experiments

When a number of polymorphs are identified in step one they should be characterized by Differential Scanning Calorimetry (DSC) to obtain AHm and Tm data. This information confirms their relative stabilities with respect to temperature. If DSC data cannot be obtained then slurry experiments should be performed. It is always good practice to confirm the relative stability with sluny experiments because DSC traces can be difficult to interpret correctly, and can mask subtle effects. 

Slurry experiments are a common method of determining which of two polymorphs is thermodynamically more stable. Samples of both polymorphs are added to a solvent and maintained at constant temperature, with agitation, for sufficient time for the stable polymorph to grow at the expense of the less stable form. The final solid form is analysed by X-Ray Powder Diffraction (XRPD) or similar. 

Figure 4.5 Cr as a function of the amount of Cr(VI) remaining in a batch slurry experiments with estuarine sediment. Line gives a Rayleigh fractionation model, with s = 3.4%o. Data from Ellis et al. (2002).

Irandoust and Andersson [22] studied hydrogenation of 2-ethyIhexenal in a monolith. Slurry experiments with powdered monolithic catalyst were also performed. The reaction was investigated at 413-433 K and 0.4-0.98 MPa and at velocities of both phases of 0.023-0.085 m sec". The monolithic process proceeded much faster, as is shown in Fig. 3. This large difference might be due to deactivation of the catalyst during grinding. 

The yield of cis- (equatorial) and trans- (axial) l,4-di-/er/-butylcyclohexane was of interest to compare in slurry hydrogenations using ground cross-flow catalyst with the cross-flow reactor hydrogenation. It was found from this comparison that the selectivity of cis to trans at high conversion was equal to about 10 in slurry experiments, but increased to between 28 and 322 in comparing experiments with the cross-flow reactor. 

Other than the coprecipitation of SSR from the point of equilibrium solubility, SSR may also be occluded during crystallization. To evaluate this possibility, slurry and crystallization experiments were conducted side by side. The results are shown in Table 9-1. They suggest that occlusion may occur. For the case with 50% EtOH, cakes from the crystallization experiments gave a higher purity (94.45% and 93.78%) than the cake (91.66%) from the slurry experiment. However, for the case of 40% EtOH, there was no noticeable improvement of cake purity throughout crystallization. Nevertheless, since the specification of SSR in the final cake is below 0.5%, the improvement seen in the case of 50% ethanol simply cannot be ignored. 

The greatest concern with this approach is lack of nucleation of the most stable form. If the starting API does not contain seeds of the stable form, a successful screen will produce nucleation of the stable form within the duration of the slurry experiments in at least one of the solvents. Lack of adequate solubility, or inhibition of nucleation due to solvent-solute interactions, may preclude transformation to the stable polymorph (Gu et al., 2001). Moreover, impurities or additives, even in trace amounts, can dramatically affect the rate of solvent-mediated polymorphic transformation (Gu et al., 2002 Okamata et al., 2004 Mukuta et ah, 2005). Thus, it is important to have starting API with the highest possible purity. Recrystallization prior to starting this or any type of polymorph screen can be used in an attempt to purify the API. While this could reduce an impurity that might stifle solvent-mediated transformation to the most stable polymorph, it should be noted that recrystallization from solution does not... 

If left in solution, crystals of a polymorph can convert into other polymorphs (a solvent-mediated transformation). The products of these transformations might be unpredictable and irreproducible. Through kinetic factors in the crystallization, the so-called slurry experiments might mislead in attempts to estimate the relative stability of polymorphs from observations of their interconversion in the presence of solvents. In slurry experiments not the most stable polymorph is formed, but the polymorph growing best under these particular conditions. Preferential crystallization of a polymorph does not directly depend on its relative stability. 

The sand slurry experiments were important because of the profound difference in the quantity (S - 1) 1.65 compared with 0.05 or 0.06 for polystyrene. Figure 28 illustrates the lateral solids concentration for sand particles of 0.9 mm diameter. Here, the variation of in situ concentration with position was significant even at a solids concentration of 25 vol%. 

Spectrometer and slurry experiment facilities in the reactor structure would be designed by (XINL-... 

A practically very useful method to investigate hydrates is dynamic vapor sorption (DVS) (see Section 8.2.3.2). It provides information on the water sorption behavior of substances, and while it is less suited than slurry experiments to obtain thermodynamic parameters of hydrates, it provides very valuable kinetic information. 

One of the most useful and unambiguous methods to assess the relative stabUity of two or more forms is suspension equilibration or slurry experiments. If a mixture of two forms is slurried in a solvent at a constant temperature for a long enough period of time, only two outcomes are possible ... 

In addition to the semi-batch slurry experiments, 9/MAO was used in solution in a continuous stirred tank reactor (CSTR) to further investigate the influence of [ethylene]/[macromonomer] ratio on LCB. Figure 7 shows a quantitative analysis of the C-NMR-based LCB content in polyethylene as a function of the [ethylene]/ [macromonomer] ratio [85]. The LCB content was the highest at low ratios and rapidly decreased with an increase in the [ethylene]/[macromonomer] ratio. This is in line with LCB formation via the copolymerization reaction. 

As we have seen, the available evidence suggests that incorporation of alkyl phosphoric acid esters alone into the concentrated detergent slurries prepared for spray drying deactivates whatever antifoam action they may possess. It seems likely therefore that a similar fate awaits direct incorporation of mixtures of hydrocarbons and such esters in detergent slurries. Experience is consistent with that view. Therefore, most of the relevant patents describe a preferred option of incorporation of such mixtures directly by spraying onto powders or carriers and subsequently adding the carrier to the powder [30, 31]. 

We have considered to explain the fast initiation of active sites in low yield gas phase polymerization by a very high rate of diffusion of poisons out of the catalyst. Under slurry process conditions, diffusion coefficient is at least three orders of magnitude lower than for low yield gas phase polymerization. The slow initial polymerization in slurry experiments could perhaps be explained by the slower removal of poisons. 

The fluid temperatures during the water and slurry experiments varied from 35 to 39°C, giving the vapor pressure, pvp. The atmospheric pressure, patm, was 101.9 kPa. The measured flow rates and gauge suction pressures, pgs are related to the cavitation inception criterion in Fig. 2. The NPSHR- value in m of slurry at Qc is then calculated as follows ... 

Figure 12 Illustration of the dynamic nature of coordination polymers and open MOFs under mechanochemical milling conditions. Millmg with a suitable liquid phase leads to the formation of different open- and close-packed materials based on zinc terephthalate. Such high level of structural dynamics is not observed in analogous slurry experiments...

Re) crystallization of form II from acetonitrile in humid atmosphere leads to the formation of phase IV, which comprises both tautomers of H3TBA, keto and enol one (Scheme 13.25b). Two tautomers associate through O-H- -O, N-H- -O, and N-H- - -S hydrogen bonds into 2D networks, while employing a greater number of HB donors/acceptors as compared to other phases. It should be noted that phase IV was also established as the thermodynamically stable form of HgTBA at ambient conditions as confirmed by slurry experiments in several solvents (acetonitrile, ethanol, and chloroform) [25]. 

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