Desiccant, as the name suggests, plays a role of moisture-proof and dehumidifying. It can be widely used in the moisture and dampness of the home, such as the moisture absorption and drying of the wardrobe. The shoe cabinet placed a few packages of desiccant can effectively prevent the shoes from moldy and fade, and so on. In fact, the desiccant is also widely used in the exportation of the goods, such as large quantities of furniture, clothing, shoes, agricultural products and so on in the export container. Tide storage.
The classification of desiccant
1. Silica gel
1. The chemical composition and physical structure of silica gel determine that it has many characteristics that other similar materials are difficult to replace: high adsorption properties, good thermal stability, stable chemical properties, high mechanical strength, etc.
2. The interior of the silica gel desiccant is a very fine pore network structure, which can absorb water and retain water through its physical attraction. As a desiccant, it is widely used as a desiccant in the dry and moisture-proof of aviation components, computer devices, electronic products, leather products, medicine, food and other industries, even if silica gel is used. The desiccant is immersed in the water, and it will not soften or liquefy; 3, it has non-toxic, tasteless, non corrosive and pollution-free characteristics, so it can be directly contact with any item. Silica gel desiccant is the most suitable moisture absorption environment at room temperature (20~32 C) and high temperature (60~90 C). It can reduce the relative humidity to about 40%, so the application range of the desiccant is very wide.
4, silica gel safety performance: silica gel can produce dry effect on human skin, therefore, should wear good work clothes when operating. If silica gel enters the eye, it is necessary to use a lot of water to wash and find a doctor as soon as possible. The silica gel drier is the only desiccant that can be used directly with food and medicine through American FDA certification, and it will not cause harm to the human body, and will not be absorbed by the human body, but it can be discharged naturally with the excrement.
Two. Montmorillonite
1, clay drier, the appearance of the shape of the gray ball, the most suitable for the environment below 50 degrees of humidity, when the temperature is higher than 50 degrees, the clay "water release" degree is greater than the "water absorption" degree, but the advantage of clay is cheap;
2. Montmorillonite desiccant was discovered and used in the field of desiccant from Germany South Chemical Company in 80s of last century. Because of its low price, a good adsorption effect has gradually become one of the main raw materials of mineral desiccant in the world.
3. Montmorillonite desiccant is also called bentonite desiccant and clay drier.
4. The color of montmorillonite desiccant is purple, gray and purplish red.
5. Characteristics:
(1) environmental protection: the natural montmorillonite desiccant of YISHION is a raw material, made by drying, without any additives and soluble substances. It is a non corrosive, non-toxic and pollution-free green environmental protection product. It can be treated as a general waste after use. It can not pollute the environment and can be degraded naturally.
Adaptability: under various temperature conditions, the moisture absorption performance can be kept stable.
Moisture resistance: good moisture absorption performance, saturated moisture absorption rate of more than 50% of its own weight, 1.5 times the traditional desiccant.
Three. Molecular sieve
1. Molecular sieve desiccant. It is a synthetic and highly adsorptive desiccant product of water molecules. Crystalline aluminosilicate compounds have regular and uniform pores in the crystal structure. The pore size is the order of magnitude of the molecular size. It only allows molecules with smaller diameter than the pore size. The son is sieved according to the size, so it is called the molecular sieve;
2, the size of its pore size can be controlled by different processing technology. In addition to adsorbing water gas, it can also adsorb other gases and can still hold water molecules well at high temperatures above 230 degrees C.
3. Characteristics of molecular sieve desiccant:
Under the condition of ultra low humidity, water vapor in the environment can still be absorbed in large quantities to effectively control the humidity of the environment.
Second, the moisture absorption rate is very fast, and absorb a lot of water vapor in a very short time.
Four. Mineral
1, active mineral desiccant, also known as concave soil desiccant, is made of pure natural raw mineral attapulgite and active hygroscopic agent through activation and refining, green environmental protection, non-toxic and tasteless, no harm to the human body;
2, at room temperature and general humidity with good adsorption activity, static dehumidification and odor removal efficiency, because of the chlorine ion, can not be directly contact with food, medicine, metal and so on.
3, it should be widely used in products that can not be sealed with oil seal and gas phase, such as optical instruments, electronic products, medical care, food packaging and military products and dry air seal for civil products;
4. Characteristics of mineral desiccant:
(1) the ability of moisture absorption at high temperature is good.
(2) the moisture absorption ability of Beamon at high temperature is excellent.
Five. Fiber
1, the fiber desiccant is made of pure natural plant fiber through special technology, especially the film coated fiber desiccant, which is convenient and practical and does not occupy space.
2, its moisture absorption capacity reaches 100% of its own weight, which is unparalleled by the ordinary desiccant. In addition, the product is safe and sanitary and the price is moderate, which is the ideal choice for many biological, health food and drugs.
3, the characteristics of fiber desiccant:
Environmental protection: natural mineral is the main raw material, which can pollute 100% without pollution.
Safety: innocuous and harmless;
High hygroscopicity: the moisture absorption rate is more than 50% higher than that of silica gel desiccant.
4. High performance price ratio: under the premise of ensuring product effectiveness, it provides a very competitive market price for customers.
Personalized service: it can provide products with different properties according to the requirements of service objects.
Besides odor, natural structure can selectively adsorb toxic gases such as formaldehyde and gaseous sulfide.
Six. Static drying
A quantitative adsorbent and a quantitative solution are balanced by a long time full contact (the treated liquid or gas is mixed with an adsorbent, and the treated liquid or gas does not flow up and down from the top to the adsorbent, which is called static adsorption).
Application:
1. Moisture proof packaging: cameras and photographic materials, precision instruments / electrical appliances, food, medicine, shoes, clothing, leather, weapons, telecommunications equipment, etc.
2. Air dehumidification: family closet, cabinet, floor, musical instruments and so on.
Seven. Dynamic drying
The adsorbents of a certain weight are filled in the adsorption column, so that the concentration of the solution flows at constant temperature at constant temperature, and the adsorption capacity and equilibrium adsorption capacity (the adsorption of the treated liquid or gas flowing up and down by the adsorbent) is measured.
Application of desiccant
1. Physical adsorption
Desiccant is applicable to prevent instrument, instrument, electrical equipment, medicine, food, textile and other kinds of packing items to be dampened. The desiccant is also widely used in the way of shipping, because the goods are often dampened by humidity in the course of transportation, and the desiccant can be effectively moistened and moisture-proof, so that the quality of the goods is guaranteed. Barrier.
1, desiccant for bottled drugs, food moisture-proof. Ensure the drying of contents and prevent the growth of all kinds of fungi.
2. Desiccant can be used as a general packing desiccant for damp proofing.
3, the desiccant can be conveniently placed in all kinds of articles (such as instruments, electronic products, leather, shoes, clothing, food, medicine and household appliances, etc.) in order to prevent moisture from being mouldy or rusty.
Two. Chemisorption
1, acid desiccant: concentrated sulfuric acid and phosphorus pentoxide, used for drying acidic or neutral gases, in which concentrated sulfuric acid can not dry the strong reductive acid gas of hydrogen sulfide, hydrogen bromide and hydrogen iodide; phosphorus pentoxide can not dry ammonia;
2, neutral desiccant: anhydrous calcium chloride, general gas can be dry, but anhydrous calcium chloride can not dry ammonia and ethanol;
3, alkaline desiccant: alkali lime (mixture of CaO and NaOH, KOH), quicklime (CaO), NaOH solid, used for drying neutral or alkaline gases.
The harm of desiccant
1. Burn the digestive tract
The general desiccant contains alkaline compounds, including calcium oxide, and calcium oxide will react with the body's water after entering the body and produce a large amount of heat in the process of reaction, which must burn the wall of the esophagus and the stomach wall, and the digestive tract wall is a very fragile organ, once damaged. It is easy to cause lesions. Many esophageal cancers are due to the development of early esophageal burns without care.
2, lead to blindness
The alkaline chemicals in the food desiccant can cause great damage to the eyes. If you are not careful to splash into the eyes, it will react with the liquid in the eyes and burn the eyeball. The serious person can also cause serious necrosis of the cornea conjunctiva. So the small editor should remind the parents not to play the drier to the children, otherwise it will be made. Unnecessary damage.
Solution of desiccant food error
1. There is no need for strain of silicon gum
Some desiccant are made of silica gel. These silica gel will not have a chemical reaction after entering the body, and it will not be digested and absorbed, so if there is no need for tension, so long as it is waiting for it to be discharged from the body, but if there is a body discomfort, please go to the doctor immediately, such as dizziness, nausea and vomiting.
2, drink water in time to dilute
Some desiccant contain iron oxide, which will react with the water in the body to produce iron, which causes iron poisoning. If you eat this kind of desiccant, do not panic, drink water immediately or pure milk. It can play the role of dilution, and then go to a professional hospital after taking first aid measures. Treat, do not urge vomiting, because it can cause digestive tract burns, and it will outweigh the gains.
Drying method of desiccant
1. Drying of solids
1, dry: put the dry solid on the surface of the plate or in a Petri dish, as far as possible to lay a thin layer, then cover it with filter paper or culture dish, so as to avoid dirt, and then put it at room temperature until it is dry, it is economical and convenient to remove the low boiling point solvent.
2, infrared light drying: if the solvent is not easy to volatilize in the solid, in order to accelerate drying, the common infrared lamp is often dry, the drying temperature should be lower than the melting point of the crystal, and a thermometer can be placed next to the drying time to control the temperature, and the solid can be turned over at any time to prevent the caking, but it is easy to sublimate or have poor thermal stability under normal pressure. The crystal can not be dry with the infrared light, the infrared lamp can adjust the temperature with adjustable transformer. The temperature should not be adjusted too high in use, and the water droplets are spattered on the bulb.
3, oven drying: in the laboratory, an electrothermal dryness box with automatic temperature control system is commonly used in the laboratory. The temperature is generally 50~300 C, and the temperature should be controlled in the range of 100~200 degrees C. The oven is used to dry the non corrosive, volatile and non decomposing products, and avoid volatile, flammable, explosive. Bake in a oven so as not to be dangerous; 4, dryer dry: ordinary dryer is generally applicable to the preservation of samples with easy moisture solution or sublimation, but the drying efficiency is not high, the time is long, the desiccant is usually placed under the porous porcelain plate, and the dry sample is installed on the porcelain plate or on the porcelain plate and used on the porcelain plate. The desiccant is determined by the nature of the removal of the solvent.
Two. Liquid drying
1, desiccant dehydrating in the choice of drying agent should be the first to pay attention to its scope of application, that is, the selected desiccant can not react with the liquid to be dry, or dissolve, such as anhydrous calcium chloride and alcohol, amines are easy to form a complex, so it can not be used to dry these two types of compounds; secondly, the desiccant should be fully considered. Drying capacity, that is, water absorption capacity, drying efficiency and drying speed, water absorption capacity refers to the amount of water absorbed by the unit mass desiccant, and the drying efficiency refers to the amount of water remaining in the solution when the balance is reached.
2. Azeotropic drying method
Many solvents can form a azeotropic mixture with water, the azeotropic point is lower than the solvent itself, so when the azeotropic mixture is steamed, the rest is the anhydrous solvent. Obviously, these solvents do not need to be dried with a desiccant, such as the industrial ethanol can only get 95.5% ethanol through simple distillation, that is, the best fractionating column can not be obtained. Ethanol, in order to completely remove the water in the ethanol, a proper amount of benzene can be added to the ethanol to be azeotropic distillation, and first steam is steamed with benzene water ethanol azeotropic mixture (boiling point 65 C), then a mixture of benzene and ethanol (boiling point at 68 degrees C), and the residue continues to be steamed as anhydrous ethanol.
Three, the drying of gas
When gas takes part in the reaction, the gas generator or gas in the cylinder is often dried through a desiccant, and the solid desiccant is usually installed in a dry tube, a drying tower or a large U tube. The liquid desiccant is installed in various forms of the flask, depending on the nature, dosage, humidity, and reaction conditions of the dried gas. Choose different desiccant and instruments. Calcium oxide, sodium hydroxide and other basic desiccating agents are often used to dry methylamine, ammonia and other basic gases. Calcium chloride is often used to dry HCl, hydrocarbons, H2, O2, N2, CO2, SO2 and so on. Concentrated sulfuric acid is often used to dry HCl, hydrocarbons, Cl2, N2, H2, CO2, etc.
