1、 Water and non-aqueous solvents
Water: Water is the most important solvent that exists in nature. In industrial cleaning, water is both the solvent for most chemical cleaning agents and the solvent for many dirt.
Non aqueous solvents: Non aqueous solvents dissolve polymers, oil stains, etc., including the process of transforming the dissolved substance into a molecular state, as well as the process of swelling and dispersing the dissolved substance into smaller particle states. It includes hydrocarbons and halogenated hydrocarbons, alcohols, ethers, ketones, esters, phenols, and their mixtures. Mainly used for dissolving organic scale.
2、 Pickling solution (mainly hydrochloric acid)
The basic composition of pickling solution: adding necessary corrosion inhibitors, wetting agents, defoamers, and thickeners.
Corrosion inhibitor: A substance that can prevent or slow down the corrosion of metals in environmental media at low concentrations.
Wetting agent: It is a surfactant that can repel gases adsorbed on solid surfaces and accelerate or evenly contact with liquids. Such as Pingpingjia, OP emulsifier, Tween-80, Triton X-100, etc.
Defoamer: a substance that can reduce the surface tension of liquid, inhibit the formation of foam, or make the original foam disappear or decrease.
Thickening agent: It is an additive that increases the viscosity of the pickling medium to prolong its residence and action time on the cleaned surface.
The basic process of acid washing:
(1) The basic process of acid washing to remove metal oxides
Alkali washing to remove oil stains - hot water rinsing, acid washing, cold water rinsing, neutralization, cold water rinsing, post-treatment (as needed, such as passivation, phosphating, drying, coating, etc.) - waste liquid treatment
(2) The basic process of acid washing to remove inorganic salt scale on the heating surface
Hot alkali cleaning (to loosen inorganic salt scale) - one water rinse, one acid wash, one water rinse, one passivation treatment - waste liquid treatment
3、 Alkali washing solution (mainly used to remove grease, protein, etc.)
Compared with pickling solutions, it has the following advantages and disadvantages:
Advantages: It will not cause metal corrosion, significant changes in workpiece size, or rapid rusting.
Disadvantages: High cost, slow rust removal and scaling speed, etc.
4、 Surfactant
Concept: Also known as surfactant, it is a type of substance that aggregates at the interface between two substances and can significantly change the surface tension of the liquid and the interfacial properties between the two phases. It can change the interface state of the system, resulting in a series of effects such as wetting or anti wetting, emulsification or demulsification, foaming or defoaming, and solubilization. Daily soap, laundry detergent, shampoo, margarine, salad dressing, etc. are all surfactants.
The properties of surfactant aqueous solutions: wetting, emulsifying and dispersing, cleaning, foaming, and foaming
The basic composition of surfactants: Any surfactant is composed of non-polar lipophilic (hydrophobic) hydrocarbon chain groups and polar hydrophilic (oleophobic) groups. Surfactant molecules are amphiphilic molecules with both lipophilic and hydrophilic properties.
The use of surfactants (mainly in chemical engineering): By utilizing the dispersibility and wettability of surfactants, many chemical production processes can be altered. For example, emulsification can increase the reaction rate of mixed systems with insoluble substances, and surfactants can improve the yield of certain extraction processes.
Main surfactants
Anionic surfactant
Main features: Cleanliness improves with increasing temperature: Adding alkali is beneficial for increasing cleaning power: except for sodium alkylbenzene sulfate,
The cleaned fabric has a good hand feel and a relatively low price.
Cationic surfactant
Amphoteric surfactant
Common features: It has good surface activity, strong stain removal, wetting, emulsification, and dispersibility, and also has characteristics such as sterilization, anti-static, and softness. Mild performance, minimal irritation, and moisturizing effect on the skin. Good compatibility with coarse volume and easy degradation. Easy to dissolve in water, resistant to hard water, strong foaming ability. In acidic solutions, it exhibits cationic properties; In alkaline solutions, it exhibits anionic properties.
Non ionic surfactants: polyethylene glycol type, polyol type
Special types of surfactants (including polymer surfactants, biosurfactants, silicon-based and fluorine-containing surfactants, etc.)
Usage and precautions of surfactants
Select and use different surfactants based on their types and characteristics, surface adsorption residue, safety, concentration, solubility, foaming ability, temperature and cloud point, stability to hard water, correct selection of different raw material combinations, and cost-effectiveness.
5、 Metal chelating agent
Concept: Metal chelating agents are an important class of compounds used in the cleaning process. In metal cleaning, it can be used to remove scale and rust on the metal surface. Adding chelating agents to boiler water and circulating cooling water can prevent the formation of scale. Adding chelating agents to already scaled systems can loosen and remove scale through the chelating effect of chelating agents.
Inorganic metal chelating agent
Ammonia: It is a cleaning agent used to clean copper scale
Polyphosphate polymer
Organic metal chelating agent
Citric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, polyacrylic acid, etc.
6、 Dirt adsorbent
Concept: By utilizing the difference in affinity of dirt to different material surfaces, dirt is transferred from the surface of the originally attached object to another material surface in a gas or fluid medium, achieving the purpose of removing dirt. This cleaning process is called adsorption cleaning. The substance suitable for this purpose is called an adsorbent, and the adsorbed substance is called an adsorbate.
Classification: (divided into physical and chemical adsorption based on the nature of the applied force)
Physical adsorption: If all the chemical binding forces of particles on the solid surface have been saturated by adjacent particles, the particles on the solid surface and the adsorbate can only be attracted to each other by intermolecular forces (van der Waals forces).
Chemical adsorption: If the chemical bonding of atoms on the solid surface is not fully saturated by adjacent atoms and there is still the ability to form chemical bonds, electron transfer can occur between the adsorbent and the adsorbate, forming chemical bonds.
Common dirt adsorbents: activated carbon, zeolite, diatomaceous earth (silicate after diatom death), bentonite
For example, the formula for car cleaning brightener is: 240g of triethanolamine, 600g of oleic acid, 450g of diatomaceous earth, 6.15g of white oil, and 22.51g of water. First, dissolve triethanolamine in water, add a mixture of white oil and oleic acid to water, stir, add diatomaceous earth, and mix completely. When using, dip a cotton cloth in this solution and apply it to the surface of the car body. After it dries, wipe it to remove the oil stains on the surface of the car body.
7、 Biocides and sludge stripping agents
Premise: In an open circulating cooling water system, the temperature of the cooling water is usually between 32-42 ℃. The cooling water is in full contact with the air in the cooling tower, and the microorganisms in the air and the supplementary water continuously enter the circulating cooling water system. These conditions are very suitable for the reproduction of microorganisms.
Inorganic biocides
Common inorganic biocides include compounds of chlorine, sodium hypochlorite, chlorine dioxide, ozone, and bromine (new types of biocides)
Organic biocides
Chlorophenols (easily polluting the environment, not easily biodegradable, rarely used)
Quaternary ammonium salts such as Neomethoxam. It is sometimes used as a defoamer.
Also: organotin compounds, organosulfur compounds, organobromine compounds, organochlorine compounds
The commonly used organic chlorine biocide is sodium dichloroisocyanurate, with the trade name of Youchuangjing. It has the characteristics of high efficacy, long efficacy, low toxicity, stable storage, relatively low harm, and easy administration.
Microbial sludge stripping agent
Some killing agents, such as Jie Er Mie and Xin Jie Er Mie, have a stripping effect themselves.
8、 Enzyme preparation (enzyme structure is amino acid)
Concept: Enzymes are organic compounds that exist within organic bodies and are biocatalysts that can accelerate reactions. Enzymes, as biocatalysts, possess the characteristics of general chemical catalysts as well as their own properties.
The enzyme preparations used for cleaning include lipase, protease, amylase, and cellulase
The application of enzymes in water
Cleaning of dirt (vegetable oils, proteins, cellulose), desizing of textiles, degumming of raw silk (alkaline protein degumming), dredging of pipelines, cleaning and recycling of photosensitive waste film (alkaline protein washing), cleaning of agricultural products and food machinery, cleaning of contact lenses
Nine Corrosion and Inhibitors of Metals in Metal Processes
During the cleaning process, cleaning agents may cause corrosion to various metal materials. When cleaning metal materials and their products, such as components, machinery, equipment, buildings, etc., it is necessary to fully consider the damage that corrosion may cause and take necessary technical measures.
Common metal corrosion during cleaning process
Corrosion in acidic cleaning media, corrosion in alkaline cleaning media, corrosion in neutral cleaning media, and corrosion in the atmosphere
Classification of corrosion inhibitors
Definition: The characteristic that can prevent and slow down the corrosion of metals in environmental media at low concentrations is called a corrosion inhibitor.
Classification: Classified by electrode process inhibition: cathode type, anode type, mixed type
Common corrosion inhibitors
(1) Acidic medium corrosion inhibitors: Urotropin, Ruodun, Shen 1-D, Blue-5, Blue-826
(2) Corrosion inhibitors for alkaline media: sodium nitrite, sodium butyrate, potassium dichromate, etc
(3) Oil soluble corrosion inhibitor
(4) Gas-phase corrosion inhibitor
10、 Foaming and defoaming during the cleaning process
Production and function of foam
Conditions for foam generation:
A: There are bubbles in continuous and full contact with the liquid, which is necessary for the gas to form foam in the liquid dispersion system
B: Foam has a certain life, that is, the foam breaking speed is lower than the foaming speed.
C: The gas does not dissolve in the liquid of the dispersed system.
The beneficial role of foam in cleaning
A: Foam can absorb and carry oil drops and solid dirt
B: Foam can indicate the effectiveness of cleaning operation
C: Foam can also indicate the rinsing process of workpiece
Harm of foam to cleaning operation
The existence of foam sometimes brings trouble to the cleaning operation, especially in the strong mechanical mixing, spraying and ultrasonic cleaning. Due to the formation of a large number of foam, the working solution overflows out of the tank, causing loss of raw materials, delayed cleaning operations, and also polluting the environment, so defoaming treatment should be carried out.
Defoaming method
(1) Prepare cleaning solution using low foaming raw materials
(2) Foam can be reduced by changing the temperature
(3) Spray cold water on foam
(4) Prevent air from entering
(5) Avoid collisions with cleaning liquids
(6) Add appropriate defoamers or inhibitors
Common foam regulators: foaming agent, foam stabilizer, defoamer