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Oxalic Acid often exists as dihydrate - basic info., process and application
Basic information
English name: Oxalic Acid (dihydrate)
Chinese name: 草酸（Cao Suan）
CAS number: 6153-56-6
Molecular formula: C₂H6O6
Molecular weight: 90.03 g/mol
Structural formula: HOOC-COOH
Melting point: 101-102℃ (anhydrous oxalic acid)
Solubility: Easily soluble in water, ethanol and other polar solvents
Appearance: White crystal or powder
Odor: Odorless or slightly acidic odor
Density: 1.65 g/cm³
Acidic: Strongly acidic, easily reacts with base to form oxalate
Why Oxalic Acid is dihydrate?
Oxalic acid is often found in the form of oxalic acid dihydrate (oxalic acid dihydrate, C₂H₂O₄·2H₂O) for reasons closely related to its chemical properties and physical stability:
1. Strong hygroscopic properties of oxalic acid
Oxalic acid is a strongly polar organic acid with a strongly polar carboxyl group (-COOH), which can bind to water molecules through hydrogen bonds. This intermolecular hydrogen bond makes oxalic acid easily absorb water from air at room temperature and pressure to form dihydrate.
2. Thermodynamic stability
The crystal structure of oxalic acid dihydrate is very stable, and the water molecules in its lattice are firmly bound to oxalic acid molecules through hydrogen bonds, thus reducing the free energy of the system. This low energy state makes dihydrate easier to form and more stable at room temperature.
3. The influence of environmental humidity
Under natural conditions, there is usually some humidity in the environment. When oxalic acid is exposed to air, the molecule rapidly absorbs water and converts it into dihydrate. Therefore, it is difficult for pure anhydrous oxalic acid to remain anhydrous for a long time in an open environment.
4. Easy to store and handle
Oxalic acid dihydrate can effectively avoid moisture absorption and agglomeration of oxalic acid powder due to its stable crystal structure, and reduce the volatility and corrosion of oxalic acid. This makes it more convenient and secure during storage, transportation and use.
5. Advantages of physical properties
Melting point change: the melting point of oxalic acid dihydrate is 101-102℃, which will lose crystalline water and be converted into anhydrous oxalic acid when heated. Compared with anhydrous oxalic acid, it is easier to control the melting and decomposition process of dihydrate, which is suitable for industrial operation.
Solubility: Oxalic acid dihydrate has good solubility, easy to dissolve in water and the dissolution process is more stable.
Riel Chemical Oxalic Acid
Riel Chemical has a long history in the production of solid Oxalic Acid dihydrate(C₂H₂O₄·2H₂O). As a leading chemical enterprise, Riel Chemical introduced modern oxalic acid production process as early as the 2006, and continuously optimized production process and improved product quality through independent research and development and international technical cooperation. At present, oxalic acid produced by Riel Chemical is known for its high purity and stability, and is widely used in industrial and civil fields.
Key attributes
Chemical formula: C2H2O4·2H2O
CAS: 6153-56-6
Purity: 99.6%
Production standard
COA need meets GB/T1626-2008：
| No. | Items for detecting and analyzing | Standard value |
| 1 |
Oxalic acid content (C2H2O4) ％≥ |
99.6 |
| 2 | Sulfide (as SO4) ％≤ | 0.07 |
| 3 | Combustion residue ％≤ | 0.01 |
| 4 | heavy metal (as Pb) ％≤ | 0.0005 |
| 5 | Fluoride (as Fe) ％≤ | 0.0005 |
| 6 | Chlorine (as Cl) ％≤ | 0.0005 |
| 7 | Calcium (as Ca) ％≤ | 0.0005 |
| 8 | Water insoluble content ％≤ | 0.02 |
Oxalic acid production process
Riel Chemical uses a green and efficient synthesis process to achieve large-scale industrial production of oxalic acid through optimized catalytic reaction and refined management.
1. Selection of raw materials
Main raw materials:
A sugar compound, such as sucrose or starch
Carbon monoxide (CO)
Sodium hydroxide (NaOH) or potassium hydroxide (KOH)
Raw materials are strictly screened and pretreated to ensure the stability of reaction conditions and product quality.
2. Production process
The production of solid oxalic acid mainly adopts the following two processes: chemical synthesis and catalytic oxidation. Riel Chemical combines the advantages of both processes to achieve efficient production.
Sugar oxidation reaction:
Under alkaline conditions, oxalic acid is formed by the oxidation reaction of carbohydrate raw materials with oxidants such as sodium chlorate or hydrogen peroxide.
2. Catalytic method:
With carbon monoxide and sodium hydroxide as raw materials, sodium oxalate was produced under the action of catalyst, and then oxalate was produced by acidification.
Crystallization and drying:
The oxalic acid solution was concentrated, cooled, crystallized, and finally separated by centrifugation and vacuum drying to obtain solid oxalic acid.
Technology and equipment used
Riel Chemical's oxalic acid production line uses world-leading equipment and technology to ensure high efficiency, low energy consumption and environmental protection standards.
1. Technology
Continuous reaction technology:
Fully automated production from raw material reaction to product separation improves productivity and stability.
Green chemical technology:
Through the recovery of waste gas (such as carbon monoxide) and waste liquid treatment, to achieve green production process.
2: Equipment
Reactor: corrosion-resistant autoclave for carbon monoxide catalytic reaction.
Separation equipment: multi-stage centrifuge and cyclone separator to ensure the purity of oxalic acid crystal.
Drying equipment: vacuum drying system to prevent the decomposition of oxalic acid by heat.
Exhaust gas treatment system: absorption tower and catalytic unit for the recovery of carbon monoxide and other exhaust gas.
Production capacity and output
Annual output:
Riel Chemical's annual output of solid oxalic acid reaches 50,000 tons, providing sufficient supply for domestic and foreign markets.
Product features and application areas
1. Product features
High purity: ≥99.6%
Strong stability: no impurity interference, stable chemical properties.
A variety of packaging specifications: 25kg/ bag or customized packaging to meet different market needs.
2. Application area
Metal surface treatment:
Oxalic acid can be used to remove rust and oxides from metal surfaces and is the core component of metal surface cleaners.
Often used for stainless steel, aluminum and copper cleaning.
3.Textile and dye industry:
Used as a bleaching agent to enhance the brightness and whiteness of textiles.
Used as a dye neutralizer to adjust the pH of dye solution.
4.Pharmaceutical and Chemical Industry:
Used as an intermediate in pharmaceutical production.
It is an important raw material for the production of oxalate (such as diethyl oxalate).
5.Paper and printing:
Oxalic acid can be used to bleach pulp and improve the finish and quality of paper.
6.Electronics Industry:
Oxalic acid is used in electronic cleaners that clean the surfaces of circuit boards and semiconductor components.
（Quartz sand washed with oxalic acid）
Author: Real Chemicals. Edited: June 2023