Method of dehydrating a small amount of water in liquid organic substances

Membrane separation is the most cost-effective option; please contact me

If the amount of organic material used is not too large, a simple method will suffice; materials with strong adsorption properties such as copper sulfate and calcium oxide can be used. If a large amount of organic material is involved, temperature-controlled adsorption or membrane separation for dehydration is a better approach

What are the specific components of the organic solvent solution? Pressure, temperature, daily processing capacity?

It can be said that all the methods mentioned above can be considered; relatively speaking, azeotropic distillation is a more reasonable approach. It is widely used because the selection of azestic agents, as well as the azeotropic processes, distillation columns, and operating procedures involved are well-established, making it technically simpler. Membrane processes have their advantages, but the main issue is that selecting the appropriate membranes requires a lot of effort; in other words, significant preliminary work is needed, and numerous technical development efforts must be carried out before they can be put into practical use in production. The adsorption method also involves the issue of selecting an adsorbent, and it is necessary to consider whether there will be contamination of the product. Wait.

1. Dehydration and drying of solvents: Water contamination in solvents often occurs during their production or processing, or as a by-product of side reactions; additionally, moisture can enter the solvents during storage due to absorption of humidity. The presence of water has an adverse effect not only on many chemical reactions but also on a series of chemical experimental procedures such as recrystallization, extraction, and washing. Therefore, the dehydration & drying of solvents is an important and frequently performed procedure in chemical experiments. Although water is sometimes added when removing other impurities from the solvent, it is still best to carry out dehydration and drying. Solvents that have been refined and thoroughly dried often still require the addition of appropriate desiccants during storage to prevent them from absorbing moisture. There are several methods for solvent dehydration. (1) Desiccant dehydration: This is the most commonly used method for dehydrating liquid solvents at room temperature. Desiccants come in solid, liquid, and gas forms, and are classified into acidic substances, alkaline substances, neutral substances, as well as metals and metal hydrides. Desiccants have varying properties, and to achieve effective drying, it is necessary to fully consider the characteristics of the desiccant as well as those of the material to be dried. When selecting a desiccant, it is first necessary to ensure that there is no reaction between the substance to be dried and the desiccant ； When the desiccant acts as a catalyst, it should prevent the solvent from decomposing or polymerizing, and no adducts should form between the desiccant and the solvent. In addition, the drying speed, drying efficiency, and water absorption capacity of the desiccant must also be taken into account. In addition, the reverse drying speed, drying efficiency, and water absorption capacity of the desiccant must also be considered. In practical use, acidic substances should be dried using acidic desiccants, alkaline substances should be dried with alkaline desiccants, and neutral substances should be dried with neutral desiccants. When there is a large amount of water in the solvent, it is advisable to avoid using desiccants that catch fire upon contact with water (such as sodium metal) or those that generate intense heat. It is better to first use milder desiccants like calcium chloride to remove moisture, and then apply sodium metal for drying after the water content has been reduced. After adding the desiccant, stir and let it sit overnight. The temperature can be considered in relation to the effect of desiccant properties on the drying speed. The amount of desiccant used should be slightly excessive. When there is excess moisture, the desiccant absorbs water and partially or completely dissolves, turning into a liquid or paste-like substance that separates into two layers; at this point, it should be separated and new desiccant added. The separation of the solvent from the desiccant is generally carried out by decantation, with the residue being filtered; however, if the filtration time is too long or the humidity around is high, moisture may be absorbed again and mixed in. Therefore, sometimes special filtration devices that isolate the process from the atmosphere are used. When handling certain desiccants poses a risk, it can be done inside a safety box. The safe is equipped with desiccants to keep it fully dry (I know it’s anhydrous phosphorus pentoxide), or dry air or nitrogen is blown into it. When using desiccants such as molecular sieves or activated alumina, they should be placed inside the glass tube; the solvent flows from top to bottom to undergo dehydration, and this method works well as it prevents contact with the outside environment. Most solvents can be dehydrated using this method, and the desiccant can also be reused. Commonly used desiccants include: ① Metals and metal hydrides such as Al, Ca, Mg: often used for drying alcohol-based solvents; Na, K: suitable for drying solvents such as hydrocarbons, ethers, cyclohexylamine, and liquid ammonia. Note: It poses an explosion risk when used with halohydrocarbons and must never be used. It cannot be used to dry methanol, esters, acids, ketones, aldehydes, and certain amines either. Alcohols containing trace amounts of water can be directly distilled by adding a small amount of metallic sodium. CaH: One gram of calcium hydride reacts quantitatively with 0.85 grams of water; therefore, it provides a better drying effect than alkali metals and phosphorus pentoxide. Suitable for the drying of hydrocarbons, halogenated hydrocarbons, alcohols, amines, ethers, etc., especially solvents such as **furan and other cyclic ethers, dimethyl sulfoxide, and hexamethylenephosphamide. Polar aprotic solvents commonly used in organic reactions are also dried using this method. LiAlH4: Used for drying solvents such as ethers. ②Neutral desiccants: CaSO4, NaSO4, MgSO4: Suitable for drying solvents such as hydrocarbons, halogenated hydrocarbons, ethers, esters, nitromethane, amides, and nitriles. CuSO4: Anhydrous copper sulfate is white; it turns blue when it contains 5 molecules of crystal water, and is commonly used to detect trace amounts of moisture in solvents. CuSO4 is suitable for the dehydration of alcohols, ethers, esters, and lower fatty acids. Methanol can form an adduct with CuSO4, so it is not suitable for use. CaC2: Suitable for alcohol drying. Be careful: when using calcium carbide of poor purity, foul-smelling gases such as hydrogen sulfide and phosphine are generated. CaCl2: Suitable for dry hydrocarbons, halogenated hydrocarbons, ethers, nitrocompounds, cyclohexylamine, nitriles, carbon disulfide, etc. CaCl2 can form adducts with primary alcohols, glycerol, phenols, certain types of amines, esters, etc., so it is not suitable. Activated alumina: Suitable for the drying of hydrocarbons, amines, esters, and formamides. Molecular sieves: Molecular sieves exhibit a significant moisture absorption capacity at low water vapor partial pressures and high monosodium glutamate levels; compared to other desiccants, they have a very high moisture absorption ability. Table 3-1 shows a comparison of the moisture absorption capacity of various desiccants (referring to the milligrams of moisture remaining in 1 liter of air dried with an adequate amount of desiccant at room temperature). Among various desiccants, molecular sieves have a moisture absorption capacity second only to phosphorus pentoxide. Since almost all kinds of solvents can be dehydrated using molecular sieves, they are widely used in both laboratory and industrial settings. Desiccant, residual moisture in liters of dry air, mg; Regeneration temperature, °C: Phosphorus pentoxide – 2×10‑5; Potassium hydroxide (molten) – 3×10‑3; Concentrated sulfuric acid – 3×10‑3; Anhydrous calcium sulfate – 4×10‑3 at 230–250 °C; Magnesium oxide – 8×10‑3; Sodium hydroxide (molten) – 1.6×10‑1; Calcium oxide – 2×10‑1 at 300 °C; Anhydrous calcium chloride – 2×10‑1; 95% sulfuric acid – 3×10‑1; Anhydrous copper sulfate – 1.4 at 400 °C; Molecular sieve – 1×10‑4 at 200–400 °C; Activated alumina – 1.8×10‑3 at 180 °C; Silica gel – 6×10‑3 at 150 °C. ③ Basic desiccants: KOH, NaOH: Suitable for drying basic substances such as amines and cyclic ethers like furan. Acids, phenols, aldehydes, ketones, alcohols, esters, amides, etc. are not applicable. K2CO3: Suitable for drying alkaline substances, halogenated hydrocarbons, alcohols, ethers, esters, nitriles, cellulose solvents, and other solvents. Not applicable to acidic substances. BaO, CaO: Suitable for drying alcohols, alkaline substances, nitriles, and amides. Not applicable to acids and esters. Acidic desiccant H2SO4: Suitable for drying saturated hydrocarbons, halogenated hydrocarbons, nitric acid, bromine, etc. Alcohols, phenols, ethers, unsaturated hydrocarbons, etc., are not applicable. P2O5: Suitable for the drying of hydrocarbons, halogenated hydrocarbons, esters, acetic acid, nitriles, carbon disulfide, and liquid sulfur dioxide. Ethers, alcohols, amines, etc., are not applicable. (2) Fractional distillation dehydration: Solvents with a boiling point significantly different from that of water can be dehydrated using a distillation column with high fractional distillation efficiency (rectifier), which is a commonly used method for dehydration. (3) Azeotropic distillation dehydration: Solvents that form an azeotrope with water cannot be dehydrated by fractional distillation. If a solvent containing trace amounts of water is subjected to azeotropic distillation, although there is some loss of the solvent, most of the water can be removed. Most solvents can form azeotropic mixtures with water. (4) Evaporation, distillation drying: For solvents that are difficult to volatilize and cannot form an azeotrope with water, the water can be removed preferentially by heating or vacuum distillation. For example, solvents such as ethylene glycol, ethylene glycol-butyl ether, diglyme-ethyl ether, polyethylene glycol, polypropylene glycol, and glycerol are all suitable. (5) Drying with dry gas: When drying poorly volatile solvents, reflux is generally carried out slowly while blowing in thoroughly dried air or nitrogen; the gas removes the moisture from the solvent, which is then released through the drying tube at the end of the condenser. This method is applicable to the drying of solvents such as ethylene glycol and glycerin. 6) Others: Under special circumstances, acetic anhydride can be used to dry acetic acid by adding anhydride in an equimolar amount to the water present in it, or by directly adding anhydride for drying purposes. The dehydration of formic acid can be achieved by using anhydrous boric acid, which is obtained by heating boric acid to high temperatures until it melts, followed by cooling and crushing. There is also a cooling and drying method. For example, hydrocarbons are cooled using a refrigerant, where the water turns into ice to achieve dehydration. 2 Methods for purifying solvents: Solvents that are nearly pure are generally obtained through fractional distillation using methods such as distillation or rectification. However, for some solvents in which impurities are difficult to separate using distillation columns, these impurities must be removed in advance, and one method for this is molecular sieve treatment. Molecular sieves are classified according to their effective diameter; for example, those with an effective diameter of 3 angstroms are called 3A molecular sieves, those with 4 angstroms are called 4A molecular sieves, those with 5 angstroms are called 5A molecular sieves, those with 9 angstroms are called 10X molecular sieves, and those with 10 angstroms are called 13X molecular sieves. Table 3-2 shows the types of molecular sieves used for various molecules. For example, 5A molecular sieve can be used to adsorb and separate butanol from a mixture of butanol isomers, while 4A molecular sieve can be used to separate methylamine and dimethylamine. The applicable method is the same as that for desiccant dehydration; a packing layer device is preferable. When purifying solvents, the choice of materials for equipment and vessels has an impact on the purity of the solvent; glass instruments are generally preferred. Table 3-2: Main molecules adsorbed by various molecular sieves 3A 4A 5A 10X 13X H2 CH4 C3H8 CHCl3 1,3,5-Trimethylbenzene O2 C2H6 C4H10 CHBr3 CO CH3OH C2H5Cl (CH3)2CHOH CO2 CH3CN C2H5Br (CH3)2CHCl NH3 CH3NH2 C2H5OH iso-C4H10 H2O CH3Cl C2H5OH (CH3)3N CH3Br C2H5NH2 (C2H5)3N C2H2 CH2Cl2 C(CH3)4 CS2 CH2Br2 C(CH3)3Cl (CH3)2NH C(CH3)3OH CH3I CCl4 C6H6 C6H5CH3 C6H4(CH3)2 Cyclohexane Thiophene Furan Pyridine Dioxane Naphthalene Quinoline (Excerpted from Wanke Chemical Online Community, sz22033, 2007-3-9 18:14)

How can I get in touch with you? I need to dehydrate organic substances; please contact hzjdlsw@126.com

:victory::victory: How can I get in touch? Contact hzjdlsw@126.com

Where are you from? What water needs to be removed? How much? What is the moisture content? Perhaps I can serve you

I can handle alcohol dehydration with ease

Molecular sieves are used for deep dehydration; water with added salts is suitable for high water content cases, while pervaporation is a better option for you

Considering the issue of re-contamination, it is recommended to use inorganic membrane pervaporation technology. You can check out Wuhan Zhihong Sibo Chemical Technology Co., Ltd.; they are leaders in this field in China. www.zhsbtec.com

First, check for immiscibility; if they are immiscible, extraction will suffice. For mutually soluble substances, distillation (for non-azeotropic systems), membrane separation, and adsorption methods.

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How to handle the dehydration of phenolic products? That is, the moisture in p-cresol and dimethylphenol. Currently, the moisture level is kept at 0.1%-0.2%, and it is hoped to reduce it further below 0.1%