Pour point depressants (anti-gel) are a complex of additives that combine copolymers and surfactants, aimed at improving engine performance in the winter. Antigels prevent waxing and thickening of the fuel when the temperature drops. Depressant additives protect metal components of the fuel system from corrosion and promote complete combustion of the fuel.
Where and why should we use anti-gel?
The chemical structure of the liver shows high levels of alkanes (from normal to slightly branched structure). Paraffins are characterized by elevated pour points, which impair the rheological properties of the liquid, in particular mobility and fluidity. Similarly, saturated hydrocarbons are found in petroleum products. The use of pour point depressants can improve rheology in a variety of applications:
- extraction of “black gold”;
- processing of crude oil and oil products;
- improvement of characteristics of various types of fuel.
For crude oils, pour point depressants improve the transportability and pumpability of waxy grades.
Extraction of fuel raw materials
Saturated hydrocarbons crystallize at relatively high temperatures (about 0°C), that causes a number of negative effects. Large clots form in the liquid, its mobility decreases. The exact crystallization temperature is determined by the number of carbon atoms of the alkane macromolecule and the position of the substituent radical in the main chain.
The heating the oil to 50-60°C allows to prevent the crystallization of paraffin. Today it is an outdated, economically unjustified technique that requires unnecessary costs. Moreover, in some cases, this procedure is technologically impossible. An alternative way to lower the temperature is to mix two grades of oil (with high and low paraffin). The third option to reduce the crystallization temperature is to dilute the crude oil with solvents. All of these technologies require additional time and resources.
The use of pour point depressants is superior in efficiency and economic benefits to all of the above methods. A significant decrease in the pour point and an increase in fluidity can be achieved already after adding 0.05-0.10% anti-gel. Effects of depressant additives during oil transportation are listed below:
- reduction of electricity consumption;
- reducing the wear of pipelines;
- prevention of paraffin deposits.
At the same time anti-gel is in demand when transporting oil by land and water means – tankers, cisterns. For pipelines it is important to improve the rheological properties, for transportation on ships, railways and roads, additives have a positive effect on the physical and mechanical properties of the product.
Like crude oil, diesel fuel contains paraffins. Lowering the temperature leads to crystallization and the formation of “large particles”. Their dimensions exceed the pores of the filter elements. Accordingly, the amount of fuel supply to the engine is reduced, that complicates the work and prevents the engine from starting. Additionally, crystallized paraffin is deposited on the walls of fuel lines and other joints. This reduces the effective section of the lines, increases the wear of the fuel system elements.
How depressant additives work
The anti-gel does not directly affect macromolecules of saturated hydrocarbons. Additives do not dissolve paraffin. The concentration of alkanes in oil or oil products does not change. The action of depressant additives is aimed at the shape, size and structure of hydrocarbon macromolecules in the dispersed phase.
The anti-gel prevents paraffin crystallization. As a result, large-scale aggregates that reduce the fluidity of the liquid are not formed in the fuel. At the same time, clogging of the pores of the filter elements is prevented, the level of hydrocarbon deposits on the walls of the fuel hoses and other system components is significantly reduced.
Depressant additives for diesel fuel
Anti-gel is a special additive used to improve the low-temperature properties of diesel fuel. At the same time, pour point depressants are used in oil production and refineries. There are various types of anti-gel, where the main effect is a decrease in the pour point, pumpability and filterability, complemented by other functions. Combined additives contain dispersants, anti-corrosion and other components.
Fuel brand dependence
The transition to winter operation of the car engine begins with a temperature of 5°C. According to weather conditions there are three types of fuel on the market:
- summer – suitable for positive temperatures;
- winter – applied in the range from 0 to -20°C;
- arctic – the lower limit of operation is -50°С.
Differences between varieties are due to the content of paraffins. As a standard, the deterioration of the rheological and operational properties of the fuel occurs during the crystallization of saturated hydrocarbons. The temperature of the beginning of this process depends on the length of the paraffin and the location of the substituent radical in the main chain of the macromolecule. The use of pour point depressants is recommended when the air temperature exceeds the cloudiness index of the fuel by 10°C.
The main fuel parameters that determine the use of anti-gel
The turbidity of diesel fuel signals that the paraffins in the oil product are turning into a solid state. The need to add depressant additives is tied to this parameter. The cloud point determines the initial stage of the process of saturated hydrocarbons crystallization.
The second indicator is related to freezing. This parameter is more important for oil producing and oil refineries. When the pour point is reached, the crude oil and its products turn into jelly. Such a liquid is no longer possible to pump through the pipeline. Obviously, the jelly-like fuel will also not be able to enter the engine. This is a state to which fuel should not be brought.
When the pour point depressant is added at an early stage, before the air temperature drops to cloudiness, the engine continues to run properly. Therefore, a temperature difference of 10°C was chosen. With a larger difference, the use of anti-gel does not create any effects.
Depressant additives for petroleum, oils and fuels
Depressant additives are available in a variety of formulations. There are additives obtained on the basis of copolymerization products and non-polymer additives. Additionally, polymeric depressants are divided into three groups according to their composition. The first contains copolymers of ethylene and polar monomers. The second category includes olefin copolymers, the third – polymethyl methacrylate (PMA). Often, the composition of the additive determines the application of the depressant – crude oil, diesel fuel or oils.
Depressants for fuel
It is necessary to use reagents for diesel fuel carefully, following certain rules (which can be found in the instructions):
- apply only to the specified grades of fuel;
- observe the established concentrations (proportions);
- pour liquid into the fuel tank slowly;
- before adding the depressant, keep the car for several hours in a “warm” place.
It should also be borne in mind that additives are produced directly for diesel fuel. Therefore, they should not be poured into gasoline. But even in the case of diesel fuel, it is important to consider the brand of fuel.
Excessive concentration of the additive in the fuel has the opposite effect. The low-temperature properties of diesel fuel do not improve, but deteriorate – the pour point and ultimate filtration increase.
In this direction, depressants produced with the participation of alkylnaphthalenes and alkylphenol compounds are of priority. In particular, additives based on calcium alkylphenolate with an admixture of alkylphenol are used. Such a composition lowers the pour point. But this additive is especially effective when used in the residual components of base oils. Alternatively, PMA depressants are used.
Improvement of depressants for crude oil, various fuels and oils is ongoing, as the mechanism of action has not yet been clearly established. It is assumed that the reason for the improvement in low-temperature rheological properties is due to the electrostatic nature of the effect. According to the hypothesis, pour point depressants form an energy barrier on the surface of particles of the dispersed phase in their suspensions. This leads to repulsion of crystallites and prevents their aggregation. In fact, stable colloidal complexes are formed. But obtaining information about the exact mechanisms of crystallization of solid hydrocarbons significantly complicates the multicomponent composition of oil raffinates.
Synthetic rubbers: effectiveness of pour point depressants
Synthetic rubbers are polymers with elastic and electrical insulating properties. Derived from byproducts of petroleum, rubbers exhibit water resistance and find applications in a variety of industries. One example of the use of synthetic polymer products is viscosity and depressant additives for fuels and oils. Synthetic rubbers based on copolymers of olefins, as well as acrylic (PA) or methacrylic (PMA) acid esters, are most widely used.
Most synthetic rubber additives produce a number of effects that improve the properties of the fuel. Therefore, depressants based on copolymers often have a thickening effect and increase the antiwear properties of the oil product. Another important aspect is related to the dependence of the attachment efficiency on the chemical composition of oil products. The content of n-paraffins plays a key role. Therefore, the effectiveness of depressants for different brands of oils and diesel or other fuels will be different.
This is a class of additives produced on the basis of ethylene propylene rubbers. The additives got their name due to the ability to change the viscosity of the oil product with temperature variation. The fluidity of a liquid is affected by the structure of the rubber macromolecule. At low temperatures, the polymer is in a twisted state, without directly affecting the viscosity of the medium. The heating of the oil product during engine operation leads to straightening of the polymer chains. This leads to an increase in viscosity at high temperatures, when the fluidity of the fuel or oil, on the contrary, decreases. In fact, synthetic rubber as an additive compensates for the decrease in viscosity.
At the same time, synthetic rubber molecules create stable colloidal complexes in a finely dispersed medium. This significantly reduces the intensity of crystallization and subsequent coagulation. In this way, the stratification of the oil product is prevented, key parameters are reduced – the pour point and ultimate filtration.
The depressant effect for various additives based on synthetic rubbers works in a similar way. The n-paraffins in the oil crystallize when the temperature drops. The first demonstration of this process is the turbidity of the liquid. Next, coagulation occurs. Crystals grow and aggregate, which leads to the formation of large-scale spatial structures. In this case, the fuel actually loses its mobility and is unable to even be pumped.
The addition of a depressant to the oil product prevents the second stage of the process. Prevents coagulation. Synthetic rubbers, interacting with n-paraffin crystallites, form their own stable complexes, excluding further growth of macromolecules.