Industrial grease is classified in various ways due to its complex formation and composition. Based on the specific chemical characteristics of dirt: grease, scale, rust, microbial sludge, gum and polymer residues, sugar residues, dust residues, and other types of dirt.
Grease is composed of different components such as oils, dust deposited in the environment, salt particles, moisture, and the surface quality change products of the objects being cleaned, forming a viscous oily deposit.
1. Sources of Industrial Grease
Residues of oily raw materials or products: e.g., contamination from oil fields, oil pipelines, storage tanks, refining equipment in direct or indirect contact with petroleum and its processed products; contamination of food industry equipment and utensils by animal and plant fats; contamination by inks, oil-based coatings, pigments, etc., in industries like printing, dyeing, and painting.
Contamination of mechanical products: During metal rolling, processing, storage, transportation, maintenance processes, in hydraulic transmission equipment, oil-containing products used for rust prevention, lubrication, cooling, transmission, etc., can easily lead to grease contamination of machinery, equipment, pipelines, tools, surrounding environment, and related raw materials and products.
2. Types and Properties of Industrial Grease
Biological fats (vegetable and animal fats): Mainly composed of esters formed by various fatty acids and glycerol, known as fatty oils. Apart from fatty oils, they may also contain small amounts of free fatty acids, sterols, pigments, and vitamins. There is no absolute boundary between oil and fat.
Mineral oils: Including petroleum, shale oil, coal tar, etc., mainly composed of a mixture of hydrocarbons.
Coal tar residue is a typical grease formed by the combination of viscous oil and dust particles. The main hydrocarbons in petroleum can be distilled or fractionated to obtain products like gasoline, kerosene, diesel, lubricating oil, paraffin, and asphalt. Gasoline, kerosene, and diesel are light petroleum products. Some greases contain paraffin, such as the grease in oil extraction and pipeline transportation. Asphalt is a complex mixture of organic compounds of different molecular weights and their non-metal derivatives, a black-brown high-viscosity organic liquid that is insoluble in water, ether, acetone, and dilute ethanol, but soluble in low-boiling alkanes, carbon disulfide, carbon tetrachloride, pyridine, etc.
3. Hazards of Industrial Grease
Grease on material surfaces not only affects their appearance but also their processing performance. For example, grease on the surface of steel affects its weldability, conductivity, as well as the adhesion of coatings and platings. Oil stains on surfaces of vehicles, trains, ships, submarines, aircraft, instruments, machinery, etc., not only affect their aesthetics but also their performance and normal operation. Oil stains on the exterior of urban buildings affect the city’s image and environmental hygiene. Oil stains and wax deposits in oil production in oil extraction pipes, pipelines, and tanks affect their production, transportation, and storage capacity, increasing energy consumption.
4. Common Industrial Grease Cleaning Methods
Due to the high viscosity of grease, strong adhesion of solid particles in dirt, and strong hydrophobicity, it is difficult to remove with plain water. Depending on the situation, the following methods are generally used for cleaning:
Alkaline aqueous solution cleaning method: Alkaline aqueous solutions can cause saponification of biological fats, producing water-soluble fatty acid salts and glycerol. Through emulsification, dispersion, dissolution, and with the help of mechanical and thermal physical enhancement methods, grease of biological fat types can be effectively removed.
Surfactant aqueous solution cleaning method: Surfactants can significantly reduce surface tension, increase wetting and penetration, enhance emulsification ability, and quickly and effectively remove most dirt (including but not limited to grease from biological fats and mineral oils). Even coal tar can be removed by selecting appropriate surfactants and using additional heating as a reinforcement method. Wax deposits can also be cleaned using a surfactant and appropriate solvent method.
Organic solvent cleaning method: Organic solvent cleaners have good solubilizing effects on substances insoluble in water (such as fats, waxes, resins, rubber, dyes, etc.) and various organic dirt. They are liquid at room temperature and pressure, have good flowability, low viscosity, high volatility, leave minimal residue on the surface after cleaning, and do not change the properties of solutes and solvents during dissolution. However, organic solvents are costly, flammable, volatile, and should be considered only when other methods are ineffective.
5. Common Anionic Surfactants for Industrial Cleaning
-Anionic surfactants are compounds that can reduce the surface tension of liquids or the interfacial tension between liquid-liquid, liquid-solid phases. They possess properties such as increasing wetting, emulsification, dispersion, solubilization, foaming, defoaming, corrosion inhibition, and antistatic properties, playing a crucial role in the cleaning process. Anionic surfactants can be classified into ion-type surfactants and non-ion-type surfactants based on their composition and structure, with the former further divided into anionic surfactants, cationic surfactants, and amphoteric surfactants.
-The most commonly used in cleaning agents are anionic surfactants, followed by non-ionic surfactants, with amphoteric surfactants being used less frequently. Cationic surfactants are generally not used in cleaning agents, but their addition can provide disinfectant properties to detergents. When selecting surfactants, special requirements should also be considered. For instance, under extreme conditions such as strong alkalis, strong acids, high temperatures, strong oxidants, chemically stable surfactants like alkyl aryl sulfonates, alkyl diphenyl ether disulfonates, and fluorosilicone surfactants can be used.
Anionic surfactants in aqueous solutions can decompose into lipophilic anions and hydrophilic metal ions. In terms of molecular structure, the lipophilic group mainly consists of alkyl groups such as alkyl, isoalkyl, and alkylbenzene; the hydrophilic group mainly consists of water-soluble salts such as sodium salts, potassium salts, and ethanolamine salts. Anionic surfactants are the most widely used in cleaning agents, with fatty acid alkali metal salts (soaps), alkyl sulfate salts, and alkyl sulfonate salts being the most common. Their advantages include: low cost, improved washing power when used with alkalis, better solubility with increasing temperature, wide range of applications, etc.
①Fatty acid alkali metal salts: Produced by saponification of fats and alkalis under heating conditions. Depending on the carbon atom number of fatty acids in fats and the type of alkali used, soaps with significantly different properties can be produced. For example, with longer carbon chains in fatty acids, the solidification point and hardness increase; the pH value of the aqueous solution of sodium and potassium salts of fatty acids is about 10, while that of ammonium salts of fatty acids is about 8, allowing for selection based on the alkalinity requirements of the cleaning agent. Sodium stearate is soluble in hot water and alcohol, dissolves slowly in cold water and cold alcohol. It is resistant to hard water but not to acidity, has poor foaming properties, good washing power at high temperatures, and weak washing power at medium and low temperatures. It can be used as an emulsifier, providing mild and gentle cleaning effects. Potassium laurate has good solubility in cold water, strong resistance to hard water, high foaming power, produces abundant foam, and has good cleaning power in warm water. It can act as an emulsifier and is a major component of liquid soaps and shampoos.
②Alkyl sulfate salts: Can be divided into alkyl sulfate salts (AS), alkyl ether sulfate salts (AES), and alkyl phenol ether sulfate salts (less commonly used due to poor biodegradability). These surfactants have excellent cleaning and foaming properties, are stable in hard water, and their aqueous solutions are neutral or slightly alkaline. Sodium lauryl sulfate, a white powder, is easily soluble in water, has strong foaming power, produces rich, white, fine foam, and exhibits excellent emulsifying and cleaning properties. It is used as a raw material for detergents, leveling agents in the printing and dyeing industry, and flotation agents for minerals. Sodium lauryl ether sulfate can adjust the hydrophilicity by adding polyethylene oxide substances. Therefore, the aqueous solution of sodium lauryl ether sulfate is better than sodium lauryl sulfate, remaining transparent even at low temperatures, suitable for producing transparent aqueous detergent solutions. It has particularly strong cleaning power and high viscosity, which can also act as a solubilizing agent in formulations.
③Alkyl sulfonate salts: This is the most important category of anionic surfactants. They exhibit better chemical stability and stronger surface activity compared to alkyl sulfate salts. Additionally, sulfonate salts
Additionally, sulfonate salts have better surface activity. Different alkyl chain lengths or different alkyl structures in sulfonate salts exhibit different surface activities, serving as emulsifiers, wetting agents, penetrating agents, foaming agents, and defoaming agents.
④Sodium alkylbenzene sulfonate: Odorless, soluble in water, resistant to acid and alkali, good thermal stability, non-toxic, non-irritating to the skin, can be mixed with non-ionic surfactants without affecting their original properties. It has good cleaning and emulsifying abilities, good stability with metal salts and oxides, especially effective in cold water and at very low concentrations. Its drawback is its poor ability to prevent dirt redeposition, suitable for washing wool and fabrics.
⑤Sodium alpha-olefin sulfonate: Properties change with increasing carbon atom number. It has optimal solubility with 12 carbon atoms, optimal cleaning power with 15-17 carbon atoms, and optimal foaming power with 14-16 carbon atoms. Sodium alpha-olefin sulfonate has good synergy with enzymes and exhibits good compatibility with other anionic and non-ionic surfactants, reducing the amount of surfactants in formulations.
⑥Sodium dodecylbenzene sulfonate: A white powder, easily soluble in water, strong foaming power, rich, white, fine foam, excellent emulsifying and cleaning properties, used as a raw material for detergents, leveling agent in the printing and dyeing industry, and flotation agent for minerals. The product becomes cloudy when stored below 10°C but returns to its original state upon warming, with no change in quality.
⑦Alkyl phosphate ester salts: A high-foaming and extremely mild anionic surfactant, with excellent wetting, emulsifying, antistatic, and thickening effects.
⑧Polyethylene glycol dodecyl ether phosphate ester salt: An anionic surfactant derived from non-ionic surfactants, with high viscosity and strong degreasing power. Due to its high viscosity and ability to linger on surfaces for a long time, it enhances cleaning effectiveness, making it suitable for cleaning vertical hard surfaces.