Cloud point reduction

Figure 5.9 shows an example of the efficiency of these products. The reductions of CFPP and pour point can easily attain 6 to 12°C for concentrations between 200 and 600 ppm by weight. The treatment cost is relatively low, on the order of a few hundredths of a Franc per liter of diesel fuel. In practice, a diesel fuel containing a flow improver is recognized by the large difference (more than 10°C) between the cloud point and the CFPP. 

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

As the temperature of dilute aqueous solutions containing ethoxylated nonionic surfactants is increased, the solutions may turn cloudy at a certain temperature, called the cloud point. At or above the cloud point, the cloudy solution may separate into two isotropic phases, one concentrated in surfactant (coacervate phase) and the other containing a low concentration of surfactant (dilute phase). As an example of the importance of this phenomena, detergency is sometimes optimum just below the cloud point, but a reduction in the washing effect can occur above the cloud point (95). However, the phase separation can improve acidizing operations in oil reservoirs (96) For surfactant mixtures, of particular interest is the effect of mixture composition on the cloud point and the distribution of components between the two phases above the cloud point. 

The use of kerosene or 1 fuel oil in reducing the cloud point of distillate fuel is common practice. By diluting the fuel with these lighter streams, wax-related problems can be minimized, but not eliminated. As a general rule a reduction in... 

Reduction of fuel viscosity at high temperatures. At temperatures above the cloud point, wax in fuel is not organized into a lattice-like network or into an organized crystalline form. Above the cloud point temperature, fuel viscosity is influenced primarily by the chemical composition and concentration of all fuel components. 

Drug release profiles from the tablets in various dissolution media are shown in Fig. 2. In all cases the release rates decreased initially from the control (distilled water) as electrolyte concentration increased, until a minimum release rate was obtained. As the electrolyte concentration further increased the release rates similarly increased until a burst release occurred. These initial decreases in release rates were probably coincident with a decrease in polymer solubility, in that as the ionic strength of the dissolution medium is increased the cloud point is lowered towards 37°C. It may be seen from Table 5 that minimum release rates occurred when the cloud point was 37°C. At this point the pore tortuosity within the matrix structure should also be at a maximum. It is unlikely to be an increase in viscosity that retards release rates since Ford et al. [1] showed that viscosity has little effect on release rates. Any reduction in hydration, such as that by increasing the concentration of solute in the dissolution media or increasing the temperature of the dissolution media, will start to prevent gelation and therefore the tablet will cease to act as a sustained release matrix. 

At the present time the problems associated with cloud points which are too high are addressed in three ways. These are (a) cold filtration, (b) the use of additives, and (c) the blending with conventional diesel fuel. The recent inclusion of B20, a 20% blend of methyl esters with diesel fuel, as an allowable friel under the US FT ACT program, is not arbitrary. At the 20% level, significant reductions in CFPP of the esters can be achieved. This reduction obviously is related to the individual cloud points of the diesel friel and methyl esters separately. As an example, a beef tallow methyl ester (CFPP = +20), when blended at the 20% level with a petrodiesel having a CP of -3, d a resulting CP of 11. The reduction effect is not linear over the whole range and has the maximum benefit below 20%. 

One method of sulfur removal from refinery streams is by hydrodesulfurization (HDS) in the refineries. This step also directly impacts the characteristics of low sulfur diesel fuels, such as density, aromatics content, cetane number, and cloud point. The magnitude of these changes will depend upon the type and setup of refinery HDS units. However, in the end some refractory compounds in fuel, e.g., 4,6-diraethyl dibenzothiophene, are very resistant to desulfurization, owing to the inaccessibility of the organically bound sulfur atom. Lower pressure HDS units which can work satisfactorily at 350 rag/kg sulfur levels, may have difficulty achieving reduction to 50 or 10 rag/kg sulfur level. 

WI1 Winoto, W., Tan, S.P., Shen, Y., Radosz, M., Hong, K., and Mays, J.W., High-pressure micellar solutions of polystyrene-Z>/ocA -polybutadiene and polystyrene-Z)/ >c -polyisoprene in propane exhibit cloud-pressure reduction and distinct micellization end points. Macromolecules, 42, 3823, 2009. 

Furthermore, addition of hydrophobic ibuprofen resulted in a collapse of all of the gels. The latter is analogous to the findings by Scherlund et al. on the temperature-induced gelation of PEO-PPO-PEO block copolymers on addition of lidocaine and prilocaine in their base forms (see Figure 1.14), as well as to the findings by Carlsson et al. on pH-dependent reductions of the cloud points of poly(A -isopropyl acrylamide) solutions on addition of either lidocaine or prilocaine (215). 

The presence of CO2 in UCST polymer blends has been shown to enhance blend miscibility. Walker et al. [136] observed a depression of the cloud point temperature for low-molecular-weight blends of polystyrene/polyisoprene using a combination of visual inspection, small-angle neutron scattering, and spectrophotometry. In the presence of 13.8 MPa of CO2, a reduction of the cloud point was observed compared to the same system in the absence of SCCO2. This demonstrates the ability of CO2 to promote miscibihty in UCST blends, and consequently an increase in the processing window is available. Walker et al. [137]... 

The following parameters of three different compounds (a polyether-modified silicone, a silicone with mixed substituents and a carbohydrate-modified silicone) were investigated and compared solubility in water, cloud point [4], reduction of surface tension in water (Table 1) and the viscosity as function of the shear rate in bulk (Fig. 1). 

Aqueous solutions of complex soaps (1-3) are drag reducers, as are certain conventional soaps (4-6) and nonionic surfactants (7-11), and they do not have some of these deficiencies. They have the advantage of regaining their drag reducing effectiveness after subjection to high shear fields. The latter two are effective near their coacervation temperature or cloud point (upper consolute temperature). The addition of electrolyte lowers the cloud point and therefore the temperature at which effective drag reduction occurs. Cloud points can be adjusted to convenient temperatures in this manner. 

At 32.0 0, which is above the cloud point, drag reduction levels are... 

Drag reduction measurements on a VL 90/10 Brij 96/92 mixture with 0.5N Na SO showed the highest drag reduction at a temperature above the cloud point where relative viscosity had begun to decrease. No mechanical... 

The other factor that causes reduction in the cloud point is the increase of the alkyl chain length in oxyethylated alcohols. Following the assumed interpretation, one can expect a correlation between the seizure load and the increase in the hydro-phobic properties of oxyethylated alcohols. The dependences can be conveniently analyzed on the basis of the results shown in fig. 17.11b, which clearly point to a significant effect of the increase in hydrophiUcity of the compound. The differences... 

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