Crystallization modifiers

Wax blends Wax cracking Wax crystal modifiers Wax emulsions Waxes... 

Water-soluble crystal modifiers such as yellow pmssiate of soda (YPS) (sodium ferrocyanide decahydrate) or ferric ammonium citrate may also be added to some types of salt as anticaking agents. Both are approved by the U.S. Food and Dmg Administration for use in food-grade salt. YPS and Pmssian Blue (ferric ferrocyanide), are most commonly added to rock salt used for wintertime highway deicing. Concentrations of YPS and Pmssian Blue in deicing salt vary, typically in the range of 20—100 ppm. 

NOTE All-polymer programs employ various types of organic deposit control agents (DCA) such as phosphinocarboxylic acid (PCA) products, which tend to be high temperature-stable sludge dispersants, crystal modifiers, and hardness transporters. 

Cold flow improvers (pour point depressants) These viscosity improvers are often specified in cold climates for unheated gas oil or where existing residual oil heaters are inadequate. The use of these paraffin crystal modifiers permits fuel to continue to flow at temperatures of 30 to 40 °F lower than the point at which wax crystallization would normally occur. 

As a crystallization modifier, it can prevent syrups from forming crystals of sugar. It is used to add body and viscosity to mixtures, and can protect against damage from freezing and drying. 

Figure 3. Intracellular freezing of 8-cell mouse embryos cooled at 20 °C/min in 2 M DMSO. The black "flashing" occurring in cells at -31 °C to -46 °C is characteristic of intracellular ice formation, and is caused by the scattering of light by many small highly branched ice crystals. (Modified from Rail et al., 1983.)...

W e know of many examples of the effect of impurities of crystallization. In many cases impurities will completely inhibit (2-4) nucleus formation. Reading the literature on this subject impresses one with the frequent occurrence of hydrocolloids as crystal modifiers, particularly where sugar or water is the material being crystallized. The use of gelatin, locust bean gum, or sodium alginate in ice cream is just one example of many practical applications of hydrocolloids in crystal modification. 

Unfortunately, we do not know enough to explain the mechanism of action of these crystal modifiers in each case. Instead, let us look at what we know about crystal growth mechanism and propose some ideas regarding the action of hydrocolloids. 

Feliu JM, Herrero E, Orts JM, Rodes A. 1996. CO adsorption and oxidation on Pt(lOO) single crystals modified by irreversibly adsorbed adatoms. Proc Electrochem Soc 96/98 68-82. 

The impurity interacts with the band structure of the host crystal, modifying it, and often introducing new levels. An analysis of the band structure provides information about the electronic states of the system. Charge densities, and spin densities in the case of spin-polarized calculations, provide additional insight into the electronic structure of the defect, bonding mechansims, the degree of localization, etc. Spin densities also provide a direct link with quantities measured in EPR or pSR, which probe the interaction between electronic wavefunctions and nuclear spins. First-principles spin-density-functional calculations have recently been shown to yield reliable values for isotropic and anisotropic hyperfine parameters for hydrogen or muonium in Si (Van de Walle, 1990) results will be discussed in Section IV.2. 

CHDM is a very effective crystallization modifier for PET and as stated earlier low-level modification yields crystalline polyesters (PETGs) that are important... 

The separation of the stereoisomers was done by fractional crystallization modifying the method described in ref. (14). After filtering the catalyst and evaporating the majority of water ethanol was added and pure cis isomer was precipitated. Then the precipitate was filtered and washed with the ethanol. After cooling the mother liquor the cis isomer precipitate was removed again, and the solvent evaporation, precipitation, filtration and washing cycle was repeated twice. 

During winter and under other low-temperature operating conditions, fuel cannot be effectively filtered at temperatures much below its cloud point unless the fuel wax is diluted with kerosene or treated with a wax crystal modifier. 

Operability additives must often be used at high treat rates, 1,000 ppm or higher, to obtain a reduction in LTFT temperature greater than 10°F (5.6°C). Some wax crystal modifiers provide LTFT performance. However, as with operability additives, the performance should always be evaluated before use. 

The addition of a wax crystal modifier to diesel fuel is a common and well-accepted alternative to kerosene dilution. Wax crystal modifiers are typically polymeric compounds which have the ability to co-crystallize with wax to alter the size, shape, and structure of the wax crystal lattice. 

Two possibilities exist to explain how wax crystal modifiers work. They are summarized as follows ... 

This concept deals with the possibility of the wax crystal modifier acting as the seed crystal onto which fuel wax crystallizes. This explanation requires that the modifier crystallize at the same temperature as the fuel wax. Once crystallized, the wax crystal modifier thus controls the conformation and structure of the resultant wax crystal. 

The most common type of wax crystal modifier used to reduce the pour point and filtration temperature of distillate fuel is based on ethylene vinylacetate (EVA) copolymer chemistry. These compounds are quite common throughout the fuel additive industry. The differences, however, are found in the variation in the molecular weight and the acetate ratio of the copolymer. 

On occasion, the performance of an EVA copolymer can be enhanced by blending with a wax crystal modifier of a different chemical type. Wax crystal modifiers used to modify the crystal structure of lubricant, residual fuel, and crude oil waxes can be blended at low concentrations with EVA copolymers to improve their performance. However, the performance enhancement is usually fuel specific and not broad ranged. Also, the low-temperature handling properties of the EVA may be impaired when blended with other wax crystal modifiers. 

Problems associated with the use of wax crystal modifiers do not pertain so much to the ability of the modifier to perform, but to the proper application technique. These copolymers are quite viscous in nature and must be diluted in solvent in order to be handleable. Even after dilution, they are still quite viscous and have relatively high pour points. 

Whenever a wax crystal modifier does not perform as expected, there are several possible explanations. Some of the possibilities are as follows ... 

In order for a wax crystal modifier to function properly, it must be present to cocrystallize with fuel wax. This requires that the modifier be added to fuel well before wax crystal formation begins. 

It is known that wax can begin the process of organization into a crystal structure above the actual, observable cloud point temperature. Because of this fact, the wax crystal modifier should be added at a temperature at least 20°F (11.1°C) above the cloud point of the fuel. Addition at this higher temperature helps to ensure that the modifier is completely solubilized in the fuel prior to the formation of the wax crystals. 

Wax crystal modifiers added after wax crystals begin to form will have only minimal affect at modifying the size, shape, and structure of wax crystals. Consequently, little improvement in the low temperature handling characteristics of the fuel will be obtained. 

When wax crystal modifiers are added to cold fuel, even to fuel well above its cloud point, modifiers may not dissolve properly. The polymeric nature of wax crystal modifiers makes them quite viscous at low temperatures. Additive suppliers will often provide modifiers in a highly dilute form (i.e., 10% or 20% solution), so they will remain fluid at low temperatures. 

However, if a typical, nondiluted wax crystal modifier is added to fuel which is at a cold temperature of+10°F to +20°F (-12.2°C to -6.7°C), it may not dissolve completely in this fuel. The result will be additive accumulation as a viscous layer at the bottom of a fuel or storage tank. Ultimately, the additive will be trapped by a filter as it flows from the tank. 

A second, and even worse possibility, would be the addition of cold additive to cold fuel. In this case, the additive would not dissolve at all and would set as a gelled mass at the bottom of the fuel tank. When the gelled wax crystal modifier does move from the tank, it may plug a cold fuel line or filter. If allowed to reach a pump, the gelled additive could cause sticking of pistons or other pump parts. 

FUEL WAS PREVIOUSLY TREATED WITH A WAX CRYSTAL MODIFIER... 

Occasionally, wax crystal modifiers will not provide the performance anticipated. Either the response to additive treatment was much less than expected or no response was obtained. When this occurs, it is quite possible that the fuel was previously treated with a wax crystal modifier. Under these circumstances, the expected performance of secondary treatment with wax crystal modifier is minimal. 

It is quite time consuming and expensive to analyze for the presence of a wax crystal modifier in fuel. However, it is possible to determine whether a fuel already contains a wax crystal modifier by analyzing the following test information ... 

Fuel which does not contain a wax crystal modifier will have temperature differences between the cloud and pour points typically from 15°F to 20°F (8.3°C to 11.1°C). If the difference between the cloud and pour point values is greater than 25°F (13.9°C), it is quite reasonable to believe that the fuel contains a wax crystal modifier. 

The cloud point and the cold filter plugging point temperatures for fuel which does not contain a wax crystal modifier can often be the same. Typically, untreated cloud point and CFPP values will be within 2°F to 4°F (about 1°C to 2°C) of each other. If the temperature difference between an untreated fuel s cloud point and CFPP differ by 10°F (5.6°C) or more, the fuel probably contains a wax crystal modifier. 

Some chemical additives such as corrosion inhibitors, wax crystal modifiers, detergents, and demulsifiers provide performance which is difficult to duplicate through refining without adversely affecting some other fuel property. Other additives such as metal chelators, fuel sweeteners, biocides, lubricity improvers, foam control agents and combustion enhancers can also be used to solve fuel performance problems. 

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