Application of surfactants in fuel oil

Since combustion is a complex oxidation process, in order to make it fully reactive and prevent coking, many additives are used in fuel oil. Some of them are directly involved in the reaction, and some are not directly involved in the reaction, but are used to improve the stability of the fuel oil and improve the safety of the burner and storage.

Additives directly involved in the reaction

A. Antiknock agent

Antiknock agent is used to reduce the knock of gasoline in the combustion process, the main technical index is to improve the octane number of gasoline. Its principle of action is mainly in the combustion process can produce free radicals quickly, help gasoline fully combustion, the earliest use is tetraethyl lead. With the improvement of air quality requirements, the use of tetraethyl lead and other lead-containing compounds has been restricted, and alternatives to lead-containing compounds have become the object of research and development. Since gasoline is first mixed with air when it is burned, oil-soluble surfactants are also the first to be considered.

Methylcyclopentadiene manganese tricarbonyl has been used as an alternative to lead compounds, which has a tendency to form sediments during use and is still under research and development. In addition, there are alcohols and ethers to improve the octane number also contribute. Organic nitrogen can also be used as a supplement for antiknock agents.

So far, there is no good method to determine the formation of free radicals, and the development of antiknock agents is mainly based on experimental attempts.

B. Cetane number improver

Cetane number improver is an additive to improve the combustion performance of diesel oil. Its mechanism of action is to decompose into free radicals, promote the combustion chain reaction, reduce the activation energy of the combustion reaction, and thus improve the ignition performance of the fuel oil. The main compounds that can improve the cetane number are alkyl nitrates, but peroxides, metallometallic compounds and easily decomposed compounds are also cetane number improvers.

C. Ignition booster

Accelerant is a kind of additive to promote combustion and improve combustion performance of fuel. The use of accelerant can make the equipment clean, reduce sludge deposition, improve combustion efficiency, save energy consumption, and reduce environmental pollution.

The main accelerant used for light oil is the alcohol solution of silicone compounds, such as 0.5% (SiCH2CH2COOH)2C02 methanol solution, which can significantly reduce the black smoke emission of diesel oil. Heavy oil additives mainly include alkali earth metal nitrate and so on. Nitrate can reduce the smoke and dust of heavy oil combustion by more than 50%. In order to improve the combustion performance of heavy oils, alkyl nitrate is also used. In addition, some metal oxides also help with combustion.

Fuel performance stabilizer

A. Antioxidant and anti-gel agent

There are a certain amount of unsaturated hydrocarbons in fuel oil, these compounds will produce oxides under the action of temperature and light, and then polymerize to form gel precipitation, thus affecting the quality of oil and combustion effect. These effects are mainly manifested in blocking the oil circuit, sticking the steam gate, increasing the carbon accumulation and reducing the power. Antioxidant and anti-gel agents mainly inhibit the oxidation chain reaction of hydrocarbons, mainly amines and phenols. Such as N, N monopropyl-p-phenylenediamine, 2,4 monomethyl-6-tert-butylphenol, 2, 6-tert-butyl-p-cresol, etc.

B. Deicing agent

Because there is a certain amount of water in the air, the fuel also contains a certain amount of water. Fuel sometimes goes from room temperature to low temperature. In this process, the dissolved water may turn into suspended water and freeze, forming ice crystals that clog the fuel system and cause oil supply to be interrupted. The main additives to prevent ice crystals are oil-soluble compounds that can form cosolubilies with water, such as ethylene glycol methyl ether, and carbonates and borates.

C. Low temperature flow performance improver

The low temperature flow improver of fuel oil is mainly used to improve the pour point and filterability of oil. The main reason for affecting the flow performance is the precipitation of wax, so the additive should be able to act with the wax to prevent its precipitation. The first additives used were polyethylene and ethylene-vinyl acetate copolymer (EVA), followed by a mixture of EVA and chlorinated paraffin and other polymers, the amount of 0.01% to 0.05%.

When this additive is added to the fuel oil, it will be immersed in the wax crystal nucleus near the cloud point and precipitate together with the wax. The presence of the additive makes the wax crystal precipitate with small particles, because it adsorbed on the surface of the wax crystal, through the action of the polar group, maintain the fine dispersion effect, prevent the formation of the mesh crystal, thereby improving the flow performance of the fuel.

The additives developed and used in China are mainly ethylene-vinyl acetate copolymer compounds, and alkyl aryl compounds are used abroad. Compounds that can prevent the formation of network structure during wax crystallization are likely to become flow performance improvers. There are more than 30 varieties of commonly used commercial additives, most of which are ethylene-vinyl acetate copolymers and long chain dicarboxylic acid amide compounds.

D. Antistatic additive

Static electricity will cause great harm to the safety performance of fuel oil, antistatic additives are generally ionic surfactants that can improve the conductivity of fuel. The cause of static electricity in oil is the movement of small particles or the friction between solid and liquid interface, and its mechanism can be explained by the double electric layer theory. In order to prevent the accumulation of static electricity, it is usually necessary to increase the electrical conductivity of the oil, because the lower the electrical conductivity, the longer the charge dissipation time.

The antistatic additive used in the early days was magnesium soap, but its dosage was large and it was not suitable for most petroleum products. At present, magnesium oleate and chromium naphthenate are used more, and alkylsalicylate and butanone chromium dioleate ferrocene are also used in research. The following are some additives: tetrisopentylamine picrate, calcium diisopropyl salicylate, magnesium oleate, monoalkyl and dialkyl chromium salicylate, chromium naphthenate, chromium oleate, chromium dioleate butadione ferrocene, polyamine salt, etc. Since these additives are different types of surfactants, the synthesis route has a great influence on the performance.

Chromium alkyl salicylate is generally used for the complex decomposition of sodium alkyl salicylate with chromium acetate or chromium chloride. Calcium succinate sulfonate is in the presence of catalyst, benzene is oxidized to butenediic anhydride, esterified with alcohol, and then sulfonated with sodium bisulfite, and then react with calcium, magnesium, barium salt and so on to obtain the required compound.

In use, the compound additive effect is better than a single additive, usually calcium salt and chromium salt mixed action, and add an appropriate amount of nitrogen-containing compounds.

Mechanical protective agent

During the combustion process, the oil must interact with the burner. In transit and pipeline interaction, polar substances in the oil will cause harm. In order to reduce and mitigate these hazards, many surface-active additives are used in oil products.

A, metal passivator

During the pumping process, the fuel will come into contact with the metal and accelerate the oxidation of the fuel. This oxidation refers to the oxidation and polymerization of olefin in the fuel oil to form a gum, which is deposited on the fuel components, thereby reducing the operating performance.

At present, the main use of metal passivator is N, N '1,2 methylene salicylidene 1, 2-propylene diamine, its mechanism of action is to react with metal, generate chelate, make metal inactive, to achieve the purpose of stabilizing oil. As a commercial product, different manufacturers have different names, but the main ingredients are the same, and there is also a small amount of alkylphenol salts of complex organic amines.

B, anti-wear and anti-rust agent

The anti-wear additive is an organic matter containing organic polar groups, which can be adsorbed on the surface of the friction parts to avoid dry friction between metals and improve the lubrication performance of the fuel. There are phosphorus and non-phosphorus compounds used abroad, and the main ones used in China are naphthenic acid and dimeric acid. Several commonly used are: dimeric acid, phosphate ester, naphthenic acid, phosphorus containing organic matter, amino alkyl phosphate ester and so on.

The action mechanism of these additives is mainly adsorption on the metal surface to form a protective layer. Because it is used in oil products, it should be an oil-soluble surfactant, and the stronger the effect with the metal, the better the effect.

One of the characteristics of fuel additives is that they are in the oil, so that the oil can be fully mixed with the air during combustion, or interact with impurities and metals in the oil, which determines that they have the characteristics of surface/interface activity. With the emergence and increasing of synthetic surfactants, it is very promising to systematically study surfactants to promote the performance of oil products. Its research should also develop from experience to theory.